production of acrolein

IN THE NAME OF ALMIGHTY ALLAH,

WHO IS THE MOST BENEFICENT AND THE

MOST MERCIFUL

Production of Acrolein by partial

oxidation of Propylene

Project Advisors

Madam Saira Bano

Sir Abdul Rehman

Project Members

Sweeba Zafar 2008-CPE-14

Aleem Naeem 2008- CPE-82

Muhammad Naeem 2008- CPE-38

Muddasar Safdar 2008- CPE-02

DEPARTMENT OF CHEMICAL AND POLYMER ENGINEERING

UNIVERSITY OF ENGINEERING & TECHNOLOGY

LAHORE

Production of Acrolein by partial

oxidation of Propylene

This project is submitted to department of Chemical Engineering, University of

Engineering & Technology

Lahore-Pakistan for the partial fulfillment of the

Requirements for the

Bachelor‟s Degree

In

CHEMICAL ENGINEERING

Internal Examiner: Sign: _______________

Name: _______________

Sign: _______________

Name: _______________

External Examiner: Sign: ________________

Name: ________________

DEPARTMENT OF CHEMICAL AND POLYMER ENGINEERING

UNIVERSITY OF ENGINEERING AND TECHNOLOGY

LAHORE

i

All praises to Almighty

Allah, Whose uniqueness,

oneness & wholeness is

beyond any comparison. All

respects are for His Holy

Prophet, Muhammad (peace

be upon him) who enabled

us to recognize our Creator.

ii

Dedicated to

Our loving Parents, their

resolute patience and guidance

to bring us to this position.

iii

Abstract

This report presents the final year project design of a chemical plant producing

3500 kg/day of Acrolein by partial oxidation of propylene using mixed catalyst.

The mixed catalyst is the bismuth molybdate-based catalyst having an average

particle size of 3.5mm.We selected this catalyst because it is highly active and

selective than other catalysts used for the production of Acrolein. We selected the

capacity on the basis of demand and supply of Acrolein worldwide and with

respect to Pakistan. The process that we selected for the production of Acrolein is

an optimum one because of low cost of propylene. Also propylene is easily

available and the yield of Acrolein obtained is maximum by this process than any

other process. After selecting the capacity and process for production of Acrolein

we did material and energy balance of whole plant and determined the flow rates

and fractions of components across each equipment being used in the plant and

also the heat load for each unit. We designed the four major units of the plant that

are heat exchanger, reactor, absorber and distillation column. Also we did the

mechanical design of reactor. After that we applied control scheme to heat-

exchanger, PFR and distillation column. We did the HAZOP analysis of absorber.

We studied the environmental impacts of Acrolein and the also the steps of

minimizing these impacts. Finally, we determined the cost of all designed

equipments.

iv

Acknowledgement

All praise to ALMIGHTY ALLAH, who provided us with the strength to

accomplish this main project. All respects are for His HOLY PROPHET (PBUH),

whose teachings are true source of knowledge & guidance for whole mankind.

Before anybody else we thank our Parents who have always been a source of

moral support, driving force behind whatever we do. We are indebted to our

project advisors Madam Saira Bano and Sir Abdul Rehman for their worthy

discussions, encouragement, technical discussions, inspiring guidance, remarkable

suggestions, keen interest, constructive criticism & friendly discussions which

enabled us to complete this report. They spared a lot of precious time in advising

& helping us in writing this report.

We are sincerely grateful to Dr. Mahmood Ahmad & Dr. Shaukat Rasool for their

profound gratitude and superb guidance in connection with the project.

Authors

v

Preface

It is a design project and purpose is to present the production of Acrolein by

partial oxidation of propylene using mixed catalyst.

Chapter 1 provides basic knowledge of Acrolein, methods of manufacturing,

physical and chemical properties, applications and other uses of Acrolein.

Chapter 2 deals with capacity selection and different processes for the

manufacturing of Acrolein and the selection of optimum one.

Chapter 3 deals with process description.

Chapter 4 consists of material and energy balance calculations across all

equipments in the plant.

Chapter 5 includes detailed design of shell and tube heat exchanger, reactor,

absorber and distillation column. It also consists of basic knowledge of these

equipments and the specification sheets of all these equipments are also given.

Chapter 6 includes mechanical design of reactor.

Chapter 7 Instrumentation and control for the process is being discussed in this

chapter.

Chapter 8 deals with hazard and operability analysis. Why and how HAZOP

analysis is done.

Chapter 9 includes environmental impacts of Acrolein and what steps are under

taken to minimize these impacts.

Chapter 10 includes cost estimation of all the designed equipments.

vi

Table of Contents

Page #

Chapter # 1

Introduction of Acrolein --------------------1

1.1 Acrolein -------------------------------------------------------1

1.2 History and Origin --------------------------------------------1

1.3 Methods of manufacturing------------------------------------1

1.4 Properties of Acrolein ----------------------------------------2

1.4.1 Physical properties of Acrolein--------------------------2

1.4.2 Chemical properties of Acrolein-------------------------3

1.5 Uses and applications of Acrolein----------------------------3

Chapter # 2

Process and Capacity selection ----------------6

2.1 Process Selection-------------------------------------------------6

2.1.1Vapor phase condensation----------------------------------6

2.1.2 Vapor phase oxidation--------------------------------------6

2.1.3 Partial oxidation of propylene------------------------------6

2.2 Capacity Selection-------------------------------------------------7

Chapter # 3

Process Description-----------------------------11

3.1 Process Description -----------------------------------------------11

vii

Chapter # 4

Material and Energy Balance -----------------14

4.1 Material Balance --------------------------------------------------14

4.1.1 Material Balance across reactor------------------------------14

4.1.2 Material Balance across quench cooler---------------------15

4.1.3 Material Balance across absorption column----------------16

4.1.4 Material Balance across water distillation column---------17

4.1.5 Material Balance across propylene distillation column----18

4.1.6 Material Balance across acrolein distillation column------19

4.2 Energy Balance-----------------------------------------------------19

4.2.1 Energy Balance across mixing point-------------------------19

4.2.2 Energy Balance across preheater-----------------------------20

4.2.3 Energy balance across reactor--------------------------------21

4.2.4 Energy balance across quench cooler------------------------22

4.2.5 Energy Balance across absorption column------------------23

4.2.6 Energy Balance across water distillation column-----------24

4.2.7 Energy Balance across propylene distillation column------25

4.2.8 Energy Balance across acrolein distillation column--------26

Chapter # 5

Designing of Equipments ------------------------27

5.1 Design of Shell and Tube Heat Exchanger ---------------------27

5.1.1Heat Exchanger--------------------------------------------------27

5.1.2 Main Categories of Heat Exchangers------------------------27

5.1.3 Heat exchangers are used--------------------------------------27

5.1.4 Selection of Heat Exchanger----------------------------------28

5.1.5Shell and Tube Heat Exchanger-------------------------------29

5.1.6 Types of Shell and Tube Heat Exchanger-------------------29

viii

5.1.7 Design Calculations--------------------------------------------30

5.1.8 Specification Sheet of heat exchanger-----------------------41

5.2 Design of Reactor--------------------------------------------------42

5.2.1 Selection of Reactor Type-------------------------------------42

5.2.2 Design Calculations--------------------------------------------44

5.2.3 Specification Sheet of reactor--------------------------------54

5.3Design of Absorber-------------------------------------------------55

5.3.1 Packed Columns------------------------------------------------55

5.3.2 Choice of plates or packing-----------------------------------55

5.3.3 Types of packing-----------------------------------------------57

5.3.4 Column Internals-----------------------------------------------60

5.3.5 Packing support----------------------------------------------61

5.3.6 Liquid distributors--------------------------------------------62

5.3.7 Liquid redistributors--------------------------------------------65

5.3.8 Hold-down plates-----------------------------------------------66

5.3.9 Liquid hold-up--------------------------------------------------67

5.3.10Wetting rate-----------------------------------------------------68

5.3.11Column Auxiliaries--------------------------------------------68

5.3.12 Design Calculations-------------------------------------------70

5.3.13 Specification Sheet of absorber------------------------------83

5.4 Design of Distillation Column ----------------------------------84

5.4.1Distillation-------------------------------------------------------84

5.4.2 Types of Distillation Columns-------------------------------85

5.4.3 Choice between plate and packed columns----------------85

5.4.4 Plate Contractors-----------------------------------------------86

5.4.5 Selection of Tray----------------------------------------------86

5.4.6 Factors affecting Distillation Column operation----------87

5.4.7 Design Calculations-------------------------------------------89

5.4.8 Specification Sheet --------------------------------------------103

ix

Chapter # 6

Mechanical design of Reactor------------------104

6.1 Mechanical Design-------------------------------------------------104

Chapter # 7

Instrumentation and Control ------------------106

7.1 Instrumentation and Process Control---------------------------106

7.2 Process instrument-----------------------------------------------107

7.3 Control------------------------------------------------------------107

7.3.1Temperature measurement and control----------------------107

7.3.2Pressure measurement and control---------------------------107

7.3.3 Flow measurement and control------------------------------108

7.4 Control scheme of distillation column--------------------------108

7.5 Heat exchanger control-------------------------------------------111

7.6 Control Scheme of PFR------------------------------------------111

Chapter # 8

HAZOP Study ------------------------------------ 114

8.1 Introduction ---------------------------------------------------------114

8.2 Background ---------------------------------------------------------114

8.3 Types of HAZOP---------------------------------------------------115

8.4 HAZOP guide words and meanings------------------------------116

8.5 HAZOP study of an absorber--------------------------------------116

x

Chapter # 9

Environmental Impact analysis of acrolein -118

9.1Hazards Identification-----------------------------------------------118

9.1.1Potential Acute Health Effects---------------------------------118

9.1.2 Potential Chronic Health Effects------------------------------118

9.2Fire and Explosion Data---------------------------------------------119

9.3Accidental Release Measures---------------------------------------119

9.4 Handling and Storage------------------------------------------------120

9.5Exposure Controls/Personal Protection----------------------------120

9.6First Aid Measures----------------------------------------------------121

Chapter # 10

Cost Estimation -----------------------------------123

10.1 Cost Indexes---------------------------------------------------------123

10.2 Cost Estimation of designed equipments-------------------------124

APPENDICES-------------------------------------129

REFERENCES -----------------------------------155

1

CHAPTER NO: 1

INTRODUCTION OF ACROLEIN

1.1 Acrolein

Acrolein is the basic compound in the series of unsaturated aldehydes. Its

chemical formula is C3H4O and chemical name is 2-propanol. Acrolein is

colorless and highly volatile liquid and soluble in many organic liquids.

1.2 History and origin

Acrolein is highly toxic and flammable material with extreme lachrymatory

properties. Degussa has produced Acrolein commercially since 1938.The process

was based on vapors phase condensation of acetaldehyde and formaldehyde. By

following the Degussa method of acrolein production the first plant to

manufacture acrolein first started in 1942. In 1945 shell started the production of

acrolein by pyrolysis of diallyl ether, a byproduct of synthesis of allyl alcohol by

saponification of allyl chloride. In 1959 shell began producing acrolein by partial

oxidation of propylene.

Acrolein, low mole weight aldehyde containing a C=C solid bond, is a clear to

yellow, flammable, poisonous liquid with a disagreeable odor; boiling at 52.7 0C;

soluble in water, alcohol, and ether; causing tears. Commercial acrolein is

produced by gas-phase oxidation of propylene in the presence of bismuth or

molybdenum oxide. It is also produced as a by-product during the production of

acrylic acid or acrylonitrile.

1.3 Methods of Manufacturing

It was produced commercially starting in 1938 by the vapor-phase

condensation of acetaldehyde & formaldehyde. In 1959, the direct oxidation

of propylene in presence of a catalyst became the preferred commercial

2

process, & variations of this process are the only methods currently used

commercially. The acetaldehyde-formaldehyde route was last used in the

USA in 1970

Manufactured: By oxidation method I-e (A) by oxidation of acetaldehyde;

(B) by oxidation of propylene in liquid phase; (C) by oxidation of propylene

in vapor phase; (D) by oxidation of allyl alcohol;

By heating glycerol with magnesium sulfate.

Prepared industrially by passing glycerol vapors over magnesium sulfate

heated to 330-340 0C.

1.4 properties of acrolein

1.4.1 Physical properties of acrolein

Molecular weight 56.06 kg/kg mole

Odor Extreme sharp, pungent and disagreeable

Color Colorless or yellowish

Boiling point 52.50C at 760 mmHg

Melting point -880C

Density 0.8389 g/cm3 at 20

0C, 0.8621 g/cm

3 at 0

0C

Heat capacity 2139 kJ/kg.K (17 to 440C, liquid)

1200 kJ/kg.K (3000C, vapor)

Standard heat of

formation

-74.483 kJ/mol

Heat of combustion -29098 kJ/kg

Heat of vaporization 542.191 kJ/kg

Heat of

polymerization

-80.4 kJ/mol

PH 6 in 10% solution in water at 250C

Surface tension 0.024N/m at 200C

3

Vapor density 1.94 (Air =1)

Viscosity 0.35 cp at 200C

1.4.2 Chemical properties

CH2=CH-CHO the carbonyl group in the conjugate with the C=C bond is present

in molecule of acrolein because of its two functional group; acrolein is highly

reactive, easily polymerized compound. Its reactive centre can be reacted

selectively and simultaneously. The reaction of acrolein can be understood as

typical of olefin activated for nucleofilic attack by influence of electron attracting

carbonyl group or as a reaction of aldehyde that is unsaturated.

The tendency of acrolein to polymerize is very great; the acrolein can only be

stored in the presence of considerable amounts of stabilizers. In spite of the

presence of stabilizer, small amounts of polymerization catalysts which are able to

initial radical, anionic or cationic propagating polymerization are sufficient to

cause highly polymerization reaction.

1.5 Uses and applications of acrolein

Some of direct and indirect uses of acrolein are

Manufacturing of Acrylic Acid

The largest single use for acrolein is as an isolated intermediate in the

manufacturing of acrylic acid, most of which is converted to its lower alkyl esters.

Preparation of Polyester Resin

Acrolein is used in the preparation of polyester resin, polyurethane, propylene

glycol, acrylic acid, acrylonitrile and glycerol.

Production of Methionione

Acrolein is basic raw material for the production of essential amino acid

methionine because of lack of methionine in many nutrient protein compounds

http://en.wikipedia.org/wiki/Polyester_resin

http://en.wikipedia.org/wiki/Polyurethane

http://en.wikipedia.org/wiki/Propylene_glycol



http://en.wikipedia.org/wiki/Acrylic_acid

http://en.wikipedia.org/wiki/Acrylonitrile

http://en.wikipedia.org/wiki/Glycerol

4

with the average biological demand, it is necessary to add methionine to the

natural food materials for boilers to improve their biological efficiency which is a

protein supplement used in animal feed.

Manufacturing of Glycerol

The chemical reduction of acrolein via alkyl alcohol is the technical process for

the manufacturing of synthetic glycerol.

Microbiological Activity of Acrolein

In biological systems one may expect rapid reactions with any reactive N-H, S-H,

O-H or C-H bond which would lead to molecular modification. In the subsurface

injection of waste waters the addition of 6-10 ppm acrolein controls the growth of

microbes in the food lines thereby preventing plugging and corrosion.

The microbiological activity is further utilized in protecting the liquid fuel against

microorganism. About <500 is in jet fuels or distillate feed tank bottoms. The

dialkyl acetyls of acrolein are also effective in such cases; as a biocide in oil wells

and liquid petrochemical fuels. The growth of algae, aquatic weeds and mollusks

in recirculation process water is controlled by acrolein.

Slime Formation

Slime formation is a serious problem in paper manufacturer: acrolein at 0.4 to 0.6

ppm is effective slimicide in this application.

Acrolein as Tissue Fixative

Acrolein has received quite a bit of attention as a tissue fixative. This property of

acrolein has been utilized for preservation of red blood cells. Acrolein may be

used to cross link invertase at PH 7 to give a water insoluble product which

possesses constant activity for inversion of sucrose for the period of 12 weeks.

Acrolein is sometimes used as a fixative in preparation of biological specimens

for electron microscopy.

http://en.wikipedia.org/wiki/Electron_microscopy

5

Immobilization of Enzymes

Conversion of acrolein into polymers or copolymers processing pendant aldehyde

groups provides polymers which have been utilized for Immobilization of

enzymes.

Other uses

Acrolein has been used to make modified food starch.

In the cross-linking of protein collagen in leather tanning.

In the manufacture of colloidal forms of metals.

In the production of perfumes.

6

CHAPTER NO: 2

PROCESS AND CAPACITY SELECTION

2.1 Process Selection

Acrolein can be produced by different methods.

2.1.1 Vapor phase condensation

Acrolein was first produced commercially in the 1930s through vapor phase

condensation of formaldehyde and acetaldehyde.

2.1.2 Vapor phase oxidation

Acrolein was then produced in 1940s by vapor phase oxidation of propylene using

cuprous oxide catalyst; however, this method was not used at first due to the poor

performance of cuprous oxide catalysts.

2.1.3 Partial oxidation of propylene

Acrolein is being produced by partial oxidation of propylene using mixed catalyst

now a days from 1960s and to produce acrolein by this method using bismuth-

molybdate based catalyst is important one. This is most favored and most

economical method. By the critical study of the processes, catalytic oxidation of

propylene has proved to be the most attractive in terms of raw material and high

yield of acrolein than any other process. This process is attractive because of the

availability of highly active and selective catalysts and the relatively low cost of

propylene.

The process that we have chosen for the production of acrolein is by the “Partial

oxidation of propylene”.

7

2.2 Capacity Selection

Market trends/Demands

Acrolein as a chemical product is rarely sold in large amounts on open market.

Whilst there are producers that sell certain amounts of it, the chemical is

immediately used in the production of other chemicals due to its instability and

safety hazards.

In the case of this project, we will be designing a plant that will produce Acrolein,

which will be piped out directly to the neighboring plant that uses Acrolein to

produce other chemicals. This allows a small scale plant to be designed whilst

avoiding the problem of transporting Acrolein.

Whilst our plant will be producing Acrolein, the price and market of chemical is

fully dependent on products it is used to create and as such market analysis must

be extended to these chemicals. There are six main products that are produced

using Acrolein. These are polyurethane, methonine , Polyester resins, acrylonitrile

and acrylic acid. In the section of the report we will analyze the market for these

products alongside the Acrolein product.

It is possible to collect the information on the global market for the chemicals in

this report but finding exact figures and market percentages is difficult due to

commercial selling of such information. We have tried to obtain as many figures

as possible but they are mostly based on US imports. Whilst this does not show

the global market but it is a reasonable indicator of global market.

Acrolein is not a staple import/export product and due to its overall lack of value

unless further processed, the market is centre around countries and areas with

facilities that process the chemical further.

This can be seen when trying to source prices for Acrolein alone. The majority of

the manufacturers selling Acrolein are doing so from mainland China. Our

product buying websites, the manufacturers are usually nearly all Chinese based.

Looking at the change in market share and Acrolein exports, being imported into

the USA, over the past year, this viewpoint is only reinforced.

8

Figure 2.1. Dominant exporters of acrolein in the world with respect

to number of shipments

Figure 2.2. Dominant exporters of acrolein in the world with respect

to market share changes

9

This data in the tables clearly indicates the Chinese dominance of the Acrolein

export business. Few other countries even more close to affecting the market

share, with hundreds of countries having no noticeable effect at all.

It also shows the same scale of Acrolein import/export market. While other

chemicals having high market share changes, they are only in the single figures in

the most cases. Due to the small scale of Acrolein market however, the market

share changes are far higher as small individual shipment have far greater affect.

This leads to market share changes such as China gaining 27% more market share

from the year before while the Germany loses over 1/3rd

of the market share.

General Acrolein involved market

The current market for Acrolein and its subsequent products has a downward

outlook in the short-term. Asian markets prices dropping has a knock on effect

throughout the global market as potential buyers demand lower prices in the

European and USA markets. Profits are likely to be lower than normal in the

fourth quarter due to this.

The long term outlook for the market is mixed. Prices will rise again due to the

cost of raw materials and increased demand. This should in turn buoy profits

again. However, the dependence on the propene, and thus Acrolein for the

products previously mentioned may soon be threatened due to the rise of new

technologies.

Capacity in

Kg(Demand)

Capacity in Kg (Supply) Years

2523981 1913681 2006-2007

2945678 2283406 2007-2008

3515630 2697086 2008-2009

3940560 3080172 2009-2010

4512567 3673672 2010-2011

10

In the Scenario of Pakistan industry, there is no special attention towards the

generation of acrolein. The Desired chemical is totally exported from different

countries e.g. China, Germany, Malaysia, Iran etc.

So by keeping in view the importance of the above described chemical, special

attention is given to the manufacturing of the acrolein by the Engineers of

University of Engineering and Technology, Lahore.

The suggested pilot plant has the capacity of 3500 kg/day with the annual amount

1277500 kg with the increasing demand and importance of chemical with the

passage of time.

Selected Capacity: 3500kg /day

0500000

100000015000002000000250000030000003500000400000045000005000000

Am

ou

nt

in K

g

Years

Comparison of Demand Vs Supply

Supply

Demand

11

CHAPTER NO: 3

PROCESS DESCRIPTION

3.1 Process Description

Propylene (Stream 2), steam (Stream 4) and compressed air (Stream 6) are mixed

and heated to 250°C. The resultant stream (Stream 8) is sent to a catalytic packed

bed reactor where propylene and oxygen react to form acrolein. The reactor

effluent is quickly quenched to 50°C with deionized water (Stream 10) to avoid

further homogeneous oxidation reactions. Stream 12 is then sent to an absorber,

T-101, where it is scrubbed with water and acrolein is recovered in the bottoms

(Stream 15). The off gas, Stream 14, is sent to an incinerator for combustion.

Stream 15 is then distilled in T-102 to separate acrolein and propylene from water

and acrylic acid. The bottoms (Stream16) consisting of wastewater and acrylic

acid are sent to waste treatment. The distillate (Stream 17) is sent to T-103 where

propylene is separated from acrolein and the remaining water in the system. The

distillate from T-103 contains 98.4% propylene. The bottoms (Stream 19) are then

sent to T-104 where acrolein is separated from water. Stream 21 is sent to waste

treatment, and the distillate (Stream 20) consists of 98% pure acrolein.

12

Figure 3.1. Process flow diagram

13

Table 3.1. Equipment Description

Equipment No. Equipment Name Equipment No. Equipment Name

C-101 Feed air

compressor

P-103A/B Reflux pump

E-101 Reactor preheater P-104A/B Reflux pump

E-102 Condenser R-101 Packed bed

reactor

E-103 Reboiler T-101 Acrolein absorber

E-104 Condenser T-102 Water distillation

tower

E-105 Reboiler T-103 Propylene

distillation tower

E-106 Condenser T-104 Acrolein

distillation tower

E-107 Reboiler V-101 Reflux vessel

P-101A/B Water pump V-102 Reflux vessel

P-102A/B Reflux pump V-103 Reflux vessel

14

CHAPTER NO: 4

MATERIAL AND ENERGY BALANCE

4.1Material Balance

Our plant has capcity of 3500 kg/day.

From capacity selection data,we have to produce acrolein based on above

mentioned capacity so here is materail balace acording to our capacity.

4.1.1Material balance across Reactor

Stream No. /Name 8 9

Mass Flow Rate (kg/hr) 2730 2730

15

4.1.2Material balance across Quench cooler

Stream No./Name 9 10/11 12

Mass Flow Rate(kg/hr) 2730 40527 43257

16

4.1.3 Material balance across Absorption column

Stream No./Name 12 13 14 15

Mass Flow Rate(kg/hr) 43257 1800 1725.9 43332

17

4.1.4 Material balance across Water distillation column

Stream No./Name 15 16 17

Mass Flow Rate (kg/hr) 43332 43086 246.61

18

4.1.5 Material balance across Propylene distillation column


Mass Flow Rate (kg/hr) 246.61 17.91 228.7

19

4.1.6 Material balance across Acrolein distillation column


Mass Flow Rate (kg/hr) 228.7 147.57 81.21

4.2 Energy Balance

Reference Conditions:

Temperature = 298.15K

Pressure = 101.325kN/m2

4.2.1 Energy balance across the Mixing Point

20

Q = n CpT2

T1 dT

Stream

No./Name

1 2 3 4 5 6

Temperature

(k)

477.15 470.15 432.15 417.15 298.15 384.15

Heat load

(KJ/hr)

-24111.6 -29491.3 203333.8

4.2.2 Energy balance across the Preheater

dTCnQiPi

2

1

T

T

Stream No. /Name 7

8

Temperature (k) 413.15

523.15

Heat load (kJ/hr) 432427.1

21

4.2.3 Energy balance across the Reactor

Q reactor= ∆H reactants+∆H reaction+∆H products

Stream No./ Name 8

9

Temperature (k) 523.15

600.15

Heat load ( kJ/hr) 867393.3

1889203.93

∆H reaction = ∆H reaction 1 + ∆H reaction 2 + ∆H reaction 3+ ∆H reaction 4

∆H reaction = -1273275.84 + -140565.6 +-91359.52+-1103420.9

∆H reaction=-2608621.903 kJ/hr

Q reactor =867393.3+ (-2608621.903) +1889203.93

Q reactor=147975.327 kJ/hr

22

4.2.4 Energy balance across the Quench Cooler

dTCnQiPi

2

1

T

T

Stream No./Name 9 10/11

12

Temperature(k) 600.15 298.15

310.15

Heat load (kJ/hr) 1889203.93 0

957166.1

23

4.2.5 Energy balance across the Absorber

dTCnQiPi

2

1

T

T

Stream No. /Name 12 13 14 15


299.15 310.15

Heat load(kJ/hr) 957166.1 0 1914.5 991745.6

24

4.2.6 Energy balance across the Water Distillation Tower

dTCnQiPi

2

1

T

T

Stream No./Name 15 16

17


302.15

Heat load (kJ/hr) 991745.6 4480530.449

2768.57

Q condenser = 308.2kJ/hr

Q reboiler = -97272kJ/hr

25

4.2.7Energy balance across the Propylene Distillation Tower

dTCnQiPi

2

1

T

T

Stream No./Name 17

18 19

Temperature(k) 302.15

299.15 338.15


162.825 66807.52

Q condenser = 12.82 kJ/hr

Q reboiler = -292.18kJ/hr

26

4.2.8 Energy balance across the Acrolein Distillation Tower:

dTCnQiPi

2

1

T

T

Stream No./Name 19

20 21

Temperature 338.15

325.15 378.15


40959.95 12662.4

Q condenser = 113.04 kJ/hr

Q reboiler = -181.8kJ/hr

27

CHAPTER NO: 5

DESIGNING OF EQUIPMENTS

5.1 Design of Shell and Tube Heat Exchanger

5.1.1Heat Exchanger

A heat exchanger is a piece of equipment built for efficient heat transfer from

one medium to another. The media may be separated by a solid wall, so that they

never mix, or they may be in direct contact.

5.1.2 Main Categories of Heat Exchangers

5.1.3 Heat Exchangers are used:

• To get fluid streams to the right temperature for the next process

• Reactions often require feeds at high temperature

• To condense vapours

Heat Exchangers

Recuperaters

Wall Separating Streams

Direct Contact

Regenerators

28

• To evaporate liquids

• To recover heat to use elsewhere

• Chemical processing etc.

5.1.4 Selection of Heat Exchanger

Exchanger

type

Maximum

pressure

range (Bar)

Temperature

approximate

range oC

Normal

area (m2)

Key features

Shell and tube 350 -200 to 700 1 to 1000 Very

adaptable and

can suitable

for gaseous

feeds

Double pipe

heat

exchanger

350

-200 to 700

.25 to 200

Suited for

small

capacities,

Pipe Coils 3 >400 1 to 2500 Pressure drop

between

fluids is

<3Mpa

Spiral tube 10 -300 to 600 2 to 600 Cannot deal

with cursive

fluids

29

5.1.5 Shell and Tube Heat Exchanger

The shell and tube exchanger is by far the most commonly used type of heat-

transfer equipment used in the chemical and allied industries.

Essentially, a shell and tube exchanger consists of a bundle of tubes enclosed in a

cylindrical shell. The ends of the tubes are fitted into tube sheets, which separate

the shell-side and tube-side fluids. Baffles are provided in the shell to direct the

fluid flow and support the tubes. The assembly of baffles and tubes is held

together by support rods and spacers.

Advantages:

1. The configuration gives a large surface area in a small volume.

2. Good mechanical layout: a good shape for pressure operation.

3. Uses well-established fabrication techniques.

4. Can be constructed from a wide range of materials.

5. Easily cleaned.

6. Well-established design procedures.

5.1.6 Types of Shell and Tube Heat Exchanger

Types of shell and tube heat exchangers are given below.

• Fixed tube heat exchanger

• U tube heat exchanger

• Floating tube heat exchanger

It may have different shell and tube passes for flow arrangements.

30

5.1.7 Design Calculations

Design/Problem Statement

Design a shell and tube heat exchanger to heat a feed mixture of,

• Propylene = 4.665kmol/hr = .0545Kg/s

• Steam = 39.77kmol/hr = .1988Kg/s

• Air = .6305kmol/hr = .0051Kg/s

From 413K (140oC) to 523K (250

oC) at pressure 203KN/m

2 (KPa). And heated

by Dowtherm oil from 673K (400oC) to 530K (257

oC).

Design Steps of Shell and Tube Heat Exchanger

The design steps of shell and tube heat exchanger are given below:

• General Design Steps. Part(A)

• Thermal Design. Part(B)

• Hydraulic Design. Part(C)

General Design Steps Part (A)

Step 1

Specification

Step 2

Obtain the necessary thermo Physical properties at mean temperature and perform

energy balance to calculate heat duties and flow rates.

Step 3

Assume suitable value of Overall coefficient.

Step 4

Decide number of shell and tube passes Calculate ΔTlm, correction factor, F, and

ΔTm.

31

Step 5

Determine heat transfer area required:

A= Q/U ΔTm

Step 6

Decide type, tube size, material layout and assign fluids to shell or tube side.

Step 7

Calculate number of tubes.

Step 8

Calculate shell diameter.

Step 9

Estimate tube-side heat transfer coefficient.

Step 10

Decide baffle spacing and estimate shell-side heat transfer coefficient.

Step 11

Calculate overall heat transfer coefficient including fouling factors, Uo.

Step 12

Estimate tube-side and shell-side pressure drops.

Thermal design of Shell & Tube Heat Exchanger Part (B)

Step 1: Specification

32

Hot Fluid[Dowtherm A]

Inlet temperature = 673k(400oC)

Outlet temperature = 530k(257oC)

Cold Fluid[Feed Mixture]

Inlet temperature = 413k(140oC)

Outlet temperature = 523k(250oC)

Step 2: Physical Properties

Mean Temperature of feed mixture:

= (523+413)/2

= 468K(195oC)

Heat Capacity (Cp):

Cp of Propylene at mean temperature = 12.25kJ/Kg.oC

Cp of Steam at mean temperature = 2.01543kJ/Kg.oC

Cp of Air at mean temperature = 1.02202kJ/Kg.oC

Density:

Density of Propylene at mean temperature = 2.21Kg/m3

Density of Steam at mean temperature = 7.106Kg/m3

Density of Air at mean temperature = .754Kg/m3

Viscosity:

Viscosity of Propylene at mean temperature =.004003Kg/m.S

Viscosity of Steam at mean temperature = .1.59x10-5

Kg/m.S

Viscosity of Air at mean temperature = .008637Kg/m.S

Thermal Conductivity (K):

“K” of Propylene at mean temperature = 3.82x10-5

KJ/m.S.oC

“K” of Steam at mean temperature =3.33x10-5

KJ/m.S.oC

“K” of Air at mean temperature =3.825x10-5

KJ/m.S.oC

Physical Properties of Dowtherm “A”:

Mean temperature = (673+530)/2 = 601.5k (328.5oC)

33

Density of Dowtherm at mean temperature = 15.60Kg/m3

Cp of Dowtherm at mean temperature = 2.049KJ/Kg.oC

“K” of Dowtherm at mean temperature = 2.99x10-5

KJ/m.S.oC

Viscosity of Dowtherm at mean temperature=1.16x10-5

Kg/m.S

Heat Duties

Heat duty of cold fluid

Heat duty can be calculated by formula given below.

Q = (m1Cp1+m2Cp2+m3Cp3)ΔT

So using the values of m1, m2,m3 and Cp1,Cp2,Cp3 & ΔT

Q = 118.08KJ/s

Mass flow rate of hot fluid

m = Q/CpΔT

Where

Q = 118.08KJ/s

Cp = 2.049KJ/Kg.oC

ΔT = 143oC m = .4031Kg/s

Step 3: Overall Heat Transfer Coefficient

As our feed is Air and Gas mixture at low pressure. So let us assume overall heat

transfer coefficient ,

U = 6W/m2.oC

OR

= .006KJ/m2S

oC

Value taken from Appendix (B), figure 3

34

Step 4: Calculation of ΔTavg

Our Heat exchanger is 1-2 pass shell and tube heat exchanger

T1= 400oC T2=257

oC

t2=250oC t1=140

oC

As (ΔT1/ ΔT1) = 1.28 which is less than 2 so we will calculate here just ΔTavg

rather than ΔTlm & ΔTm for calculation heat transfer area.

ΔTavg = (ΔT1 + ΔT2)/2 =[(T1–t2)+(T2-t1)]/2

After calculation ΔTavg = 133.5oC

Step 5: Calculation of Heat Transfer Area

Heat transfer area can be calculated by formula given below

Q = UA ΔTavg

A = Q/U ΔTavg

A = 147.4m2

Step 6: Layout, Tube Sizing & Allocation

Heat exchange fluid is allocated toward the shell & feed stream toward

tube sides due to corrosive nature.

Floating head shell and tube heat exchanger with split rings & 1-2 pass

Tubes are “Cupro-Nickel”.

Using Triangular Pitch as shell side fluid is clean.

A Iterative Selection is

(3/4inch

x14 BWG)

35

Suppose

L = 4m

O.D =di= 20mm

I.D = do=16mm

Values taken from Appendix (A), table 1

Step 7: Calculation of Number of tubes

As, Area of Single Tube = π do L

=.2512m2

No. of tubes required Nt = Total Heat Transfer Area/Area of single tube

= 604

According to TEMA standard Values taken from Appendix (A), table 2

Calculation of tube side velocity ut :

Tube cross section Area = (π/4) .di2

= 2.01x10-4

m2

Tubes per pass = Total tubes/2 = 302

Area per pass = (Tubes per pass) x (cross sectional area)

= .061m2

Volumetric flow rate = mass flow rate/density

Where,

ρ = 3.675Kg/m3

Mass flow rate= .2581Kg/s

So after adding values

Volumetric flow rate = .0704m3/S

Tube side velocity = Volumetric flow rate/Area per pass

= 1.153m/s acceptable.

36

Deduction:

According to rule of thumbs and conventions it is well known that the velocity in

the tubes should be between (.92-3.02) m/sec. So our 1-2 pass selection is

acceptable.

Step 8: Calculation of Shell Diameter

As shell side fluid id clean so we will use Triangular pitch 1.25do . So

Pt = 1.25d0

n1 = 2.207

K1 = .249


Bundle diameter Db = do(Nt/K1)1/n1

= .683m

By using split ring floating head Heat.Exchanger

Values taken from Appendix (B), figure 4

Clearance diameter = 65mm = .065m

Shell side Diameter = Bundle diameter + clearance diameter

= .748m

Step 9: Tube side heat transfer coefficient

It can be calculated from the given below formula.

hidi/Kf = jh.Re.Pr..33

.(µ/µw).14

Neglecting .(µ/µw).14

or .(µ/µw).14

=1

Where,

Kf (of mixture) Cp(of mixture) µ(of mixture) L di

3.314x10-5

KJ/m.S.oC

1.9178Kg/Kg.

0C .002881Kg/m.S 4m .016m

Re =(ρ.ut.di)/µ = 24

37

For (L/di) = 250 and Re = 24 from graph, tube side heat transfer factor is,

Jh = 3.4x10-2


Pr = (Cp.µ)/Kf = 166.723

So after putting all these values into above formula gives the Tube side Heat

transfer coefficient is,

hi = .0507KJ/m2.S.

oC or 50.7W/m

2.oC

Step 10: Shell side heat transfer coefficient

Shell side heat transfer coefficient can be calculated by formula given below

hsde/kf = jh.Re.Pr1/3

(µ/µw).14

Neglecting (µ/µw).14 or = 1

Selecting Baffles

25%Cut Segmental Baffles.

Calculating Baffle spacing

According to the TEMA standards the allowed baffle spacing is 0.2Ds

we consider

Baffle Spacing lg= Ds/5 = .1496m

Selecting tube pitch

Tube pitch Pt = 1.25x20 = 25mm = .025m

Calculating cross flow area As

As = (Pt – d0)xDsxlg/Pt

= .0224m2

Calculating mass velocity Gs

Gs = mass of hot fluid/As

= 18.02Kg/s.m

Calculating Equivalent diameter De

De = 1.10/do(Pt2 - .917do

2)

= .014201m

38

Calculating Reynolds's Number Re

Re = Gsde/µ

=22050.09

Calculating Prandtl Number Pr

Pr = Cpµ/Kf

= .7949

Calculating Jh factor

As baffle cut is 25 so from Appendix (B), figure 6

Jh = 4x10-3

Calculating shell side heat transfer coefficient

As,

hsde/kf = jh.Re.Pr1/3

(µ/µw).14

Neglecting (µ/µw).14

and after putting values we have shell side heat transfer

coefficient.

hs = .172KJ/m2.S.

oC or 172.1W/m

2.oC

Step 11: Calculation of overall heat transfer coefficient Uo

Overall heat transfer heat transfer coefficient can be calculated from following

formula.

Where,

Uo = the overall coefficient based on the outside area of the tube,

W/m2 0

C

ho = Outside fluid film coefficient, W/m2 o

C =172.1 W/m2 o

C

hi = Inside fluid film coefficient, W/m2 oC = 50.7 W/m

2 oC

do = Tube outside diameter, m = .02m

39

di = Tube inside diameter, m = .016m

Kw =Thermal conductivity of the tube wall material, W/moC, = 50 W/m

2 oC

hid = Inside dirt coefficient, W/m2 o

C = 5000 W/m2 o

C

hod = Outside dirt coefficient (fouling factor), W/m2 oC =5000 W/m

2 oC


So after adding values into formula we have Uo = 8.2 W/m2 o

C

We will use this Corrected heat transfer coefficient in further calculations.

Corrected Heat Transfer Area

Corrected heat transfer area is given below

A = 107.86m2

Part C: Hydraulic Design

Step 12: Calculation of Pressure Drops

Tube Side Pressure Drop

Pressure drop on tube side is calculated from given formula,

Again Neglecting (µ/µw)-m

or .(µ/µw)-m

=1

Where,

Jf =Friction factor = 3.1x10-1

Values taken from Appendix (B), figure1

Np = No.of tube passes =2

After putting values to above formula, tube side pressure drop is calculated as,

ΔPt= 3.06kpascal or .443PSi

Shell Side Pressure Drop:

Pressure drop on tube side is calculated from given formula,

40

Again Neglecting (µ/µw)-m

or .(µ/µw)-m

=1

Where,

us = Gs/ρ = 1.49m/s

lB =baffle spacing

From graph for 25% Baffle cut,

Jf = 4.8x10-2


After putting values to above formula, shell side pressure drop is calculated as,

ΔPs= 5.43kpascal or .787PSi

41

5.1.8 Specification Sheet of shell and tube heat exchanger

Unit Shell & tube heat exchanger

No. of shell passes 1

No. of tube passes 2

Heat Transfer area 147.4m2

Diameter of shell .748m

Pitch 25mm

No. of tubes 604

Type of tube used 14BWG

No of baffles &type 12(25%cut baffle)

OD & ID of tube 20mm & 16mm

ΔPt on shell side 3.06Kpascal or .443Psi

ΔPs on tube side 5.43kpascal or .787Psi

42

5.2 Design of Reactor

Heterogeneous catalytic reactors are the most important single class of reactors

utilized by chemical industry. Whether their importance is measured by the

wholesale value of goods produced, the processing capacity or the overall

investment in the reactors and associated peripheral equipment. Our process is

continuous process so we only consider reactors for continuous and

heterogeneous processes as gas and solid phases are present.

Classification is in terms of relative motion of the catalyst particles and reactants.

Reactors in which the solid catalyst particles remain in a fixed position

relative to one another (fixed bed, trickle bed and moving bed reactors).

Reactors in which the particles are suspended in a fluid and are constantly

moving about (fluidized bed and slurry reactors).

5.2.1 Selection of Reactor Type

43

Advantages of fixed bed reactor

A fixed bed reactor has many unique and valuable advantages relative to other

reactor types.

One of its prime attributes is its simplicity.

Costs for construction, operation and maintenance relative to moving bed.

It requires a minimum of auxiliary equipment.

For economical production of large amounts of product, fixed bed reactors

are usually the first choice, particularly for gas-phase reactions.

I have selected continuous flow, adiabatic, fixed bed reactor.

i) Continuous reactor

This reaction has low residence time.

Its operating cost is low.

Production variation is not desired.

ii) Adiabatic reactor

The reaction is slightly exothermic.

Equilibrium constant remains constant with that small change in

temperature.

(iii) Fixed bed reactor

Gas vapor catalyzed reaction.

High conversion is desired.

Relatively low operating and fixed

After analyzing different configuration of fixed bed reactors we have concluded

that for our system the most suitable reactor is multi tube fixed bed reactor.

Because of the necessity of removing or adding heat, it may not be possible to use

a single large-diameter tube packed with catalyst. In this event the reactor may be

built up of a number of tubes.

44


Preliminary Data for Reactor Design Calculations

Reactor In Reactor

Out

Temperature 2500C 327

0C

Pressure 203kpa After calculation

Mass flow rate kg/hr

Propylene 195.93 3.921

Nitrogen 1395.1 1395.1

Oxygen 423.68 180.9

Water 716.0 844.76

Acrolein ---- 187.4

Acrylic acid ---- 24.0

Carbon dioxide ---- 94.28

Total flow 2730 2730

45

Reactions

The following reactions and side reactions lead to the production of Acrolein.

C3H6 + O2 C3H4O + H2O (1)

C3H4O + 7/2O2 3CO2 + 2H2O (2)

C3H4O + 1/2O2 C3H4O2 (3)

C3H6 + 9/2O2 3CO2 + 3H2O (4)

Design steps for Reactor

Volume of reactor

Volume & weight of catalyst

Geometry of reactor

Calculation of no. of tubes required

Pressure drop along tube and shell side

Heat transfer coefficient

Heat transfer area

Available area

Specification sheet of reactor

46

Reaction Kinetics

K1=2, K2=4, K3=2

T=623 k R=1.987 kcal/kmol PC3H6 =28.1 kpa

PO2 =13.1 kpa Prexponent term= 0.108 coml./ft3hr

T0 =6230C

P.p of 02 and C3H6 are

PO2 = (5.653/108.32)×203=10.594 kpa

PC3H6= (0.0933108.32) ×203=0.1748 kpa

So rate of reaction is

ri =0.1077 kmol/ft3hr

Volume of Reactor

Design equation is

FAo=4.665 kgmol/hr

XA=0.98

VR=42.429 ft3=1.2014 m

3

Type and volume of Catalyst

A mixture of bismuth molybdate- based catalyst having average particle size of

3.5mm is used as catalyst in the process

Bulk density of catalyst, ρc = 2500 Kg/m3

Bed void fraction, = 0.4

Volume of catalyst = Vr = Vcat (1 +)

47

= 30.306ft3=0.8582 m

3

Weight of catalyst

It can be calculated as:

Weight of catalyst = ρp Volume of catalyst

= 2500 x 0.85817=2145.42 kg

Space Time

𝜏 = V/V0

V=volume of reactor

V0=initial volumetric flow rate

V=1.1808 m3

V0=initial mass/density

So for total inlet initial volumetric flow rate is 2519.10 m3/hr

Space time =1.72sec

Reactor Geometry

Assuming tube length of 12 ft or 3.6576 m and taking the diameter of tube to

prevent deviation from plug flow assumption. Dt/Dp > 10

Where,

Dt = diameter of tube

Dp = diameter of particle

Tube Dimensions: (Selected from Appendix A table 1)

Tube outside diameter do = 1.5 inch or 38.1 mm

Tube inside diameter di =1.37 inch or 34.798 mm

Plug flow test = 38.1/3.5=11 (satisfactory)

Total number of tubes Nt

48

So,

= 0.8582 / (/4 x 0.03482 x 3.6576)

= 246 tubes

(From Appendix A table 2)

Tubes available according to TEMA standards for triangular pitch=246 tubes

P = 1.25do

Where

P = tube pitch

do = outside tube diameter

P = 0.04762 m

Shell Inside Diameter

Numbers of tubes at bundle diameter are gives as:

Where, ND = number of tubes at bundle diameter

So, ND = 18.10

Shell inside diameter= Di=P [ND+1]

Di = 0.908 m

Shell Height

Length of tube=3.66 m

Leaving 20 % spacing above and below

So height of shell = 2 (0.2 3.66) + 3.66

= 5.12064 m

Pressure Drop Calculations

Tube side pressure drop

G

DDg

G

L

P

ppc

75.111501

3

49

Mass velocity G = Mass flow rate /flow area

Flow area = 1.47 inch2/tubes (kern Table 10)

Flow area = 361.62 inch2 = 0.2333 m2

G= 2730/0.2333 = 11716.73kg/hrm2

Particle diameter = DP =3.5mm =0.0035m

Average density of fluid =ρav =PM/RT= 1.6339 kg/m3

μav = 0.088 kg/m. hr

gc = 12.8 x 10 7 m.Kgm/hr2.

Kgf

Now putting all these values in equation we get

∆p = 3478.6 kgf/m2=34 kpa

Shell side pressure drop

Heat duty Q = 147975.32 kJ/hr

Water is used as cooling media having inlet temp. 25 oC and outlet 55

oC

Specific heat capacity of water = 4.318kJ/kg-C

Temperature difference, ΔT = 30K

Q = m.Cp.ΔT

147975.32=m x 4.318 x (55-25)

m=1142.31 kg/hr

Shell side flow area

Ac= π/4 [Di2 – Ntdo

2]

Di = shell inside diameter = 0.889 m

Nt = total number of tubes = 246

do = tube outside diameter = 0.0381 m

Ac = 0.340 m2

50

Equivalent Diameter:

Putting values in above formula

= 0.0510m

Shell side mass velocity = water flow rate / shell side flow area

= 1142.31 / 0.340

= 3357.2 kg/m2

- hr

Viscosity of water = 2.345 kg/m-hr

Reynolds Number Re= G De/µ

= 73

Friction factor for shell side fs = 0.0075 (from Appendix B figure7)

fs = 0.0075 x 144= 1.08

Specific gravity G=1.2

Where

ΔPS = pressure drop

Gs = shell side mass velocity= 686.34 lb/ft2/hr

L = length of tube = 12 ft

Nc = number of passes = 1

De‟= Equivalent diameter = 0.1672 ft

S = specific gravity = 1.2

= 1

Putting above values

ΔPS = 0.000906 psi (negligible)

51

Calculations of Heat Transfer Coefficient

Shell Side

For Shell side heat transfer coefficient

Where,

k = Thermal conductivity of cooling water

= 0.6315 W/m-K

De„= Shell side equivalent dia. = 0.0150 m

For Reynolds Number 73, JH = 4.2 (from Appendix B figure 8)

Shell side heat transfer coefficient, ho = 85.56 W/m2-K

Tube Side

An equation proposed by LEVA to find heat transfer co-efficient inside the tubes

filled with catalyst particles.

G = tube side mass velocity = 11716 Kg/m2-hr

= viscosity of tube side fluid = 0.08 Kg/m-hr

k = 0.04323 W/m-K

Dp = diameter of particle = 3.5 mm

di = Inside diameter of tube = 34.798 mm

Putting values in above equation

hi = 212.95 W/m2-K

Inside & outside dirt coefficient: (from Appendix A table 3)

hid = 5000W/m2-K for organic vapors

hod = 3000W/m2-K for cooling water

D

Dpe

μ

DpG3.5

k

h4.6

0.7

p

D

52

Wall Resistance

Kw = Thermal conductivity of wall = 36 W/m-K

Rw= 4x 10-4

m2-K/W

Over all Heat Transfer Coefficient

do = tube outside diameter = 38.1 mm

di = tube inside diameter = 34.798 mm

Ui = overall heat transfer

By putting the values

Ui = 4.01 W/m2-K

Area required for Heat Transfer

∆T1 = 250-55=195 oC

∆T2 =327-25=302 o

C

∆T =∆T2 +∆T1 /2=248.5 oC

So,

Ui = 4.01W/m2-K

Q = 83506.25 W

Average Temperature = 248.5 oC

Area required for Heat Transfer= 84 m2

53

Area Available for Heat Transfer

Length of tube, Lt = 3.6576 m

Inside Diameter of tube, di = 0.034798m

Hence,

Area available = 246 x π x 0.034798 x 3.6576

= 90 m2

So, sufficient area is available for heat transfer.

54

5.2.3 Specification Sheet of reactor

Reactor

Item: Fixed Bed Multi-Tubular Reactor

Identification: Item No: PFR-101

Function: To convert gaseous mixture of propylene and air to acrolein by catalytic

oxidation.

Tube side:

Material Handled:

1) Reaction mixture consisting of

propylene and air

2) Bismith molybdate based

catalyst

Flow Rate = 2730 Kg/hr

Pressure = 203 kPa

Temperature = 250 oC

Reactor volume = 1.2014 m3

Catalyst weight = 2145.5Kg

Pellet Size = 3.5mm

Porosity = 0.4

Tubes:

Outside diameter = 38.1mm

Inside diameter = 34.80mm

Schedule No. = 40

Tube length = 3.65 m

246 tubes with triangular pitch are

aligned vertically in the shell

Shell Side:

Fluid Handled = water

Heat Duty = 147975.32 kJ/hr

Flow Rate = 1142.31 Kg/sec

Inlet Temperature = 25 oC

Temperature Change = 30 oC

Pressure = 101 kPa

Shell:

Shell Inside diameter = 0.89 m

Shell Height = 5.12m

Shell Thickness = 3.87 mm

Construction Material = Carbon Steel

55

5.3Design of Absorber

5.3.1 Packed Columns

Packed columns are used for distillation, gas absorption, and liquid-liquid

extraction; only distillation and absorption will be considered here. Stripping

(desorption) is the reverse of absorption and the same design methods will apply.

The gas liquid contact in a packed bed column is continuous, not stage-wise, as in

a plate column. The liquid flows down the column over the packing surface and

the gas or vapor, counter-currently, up the column. In some gas-absorption

columns co-current flow is used. The performance of a packed column is very

dependent on the maintenance of good liquid and gas distribution throughout the

packed bed, and this is an important consideration in packed-column design.

A schematic diagram, showing the main features of a packed absorption column,

is given in Figure 5.1

Figure 5. 1.

5.3.2 Choice of plates or packing

The choice between a plate or packed column for a particular application can only

be made with complete assurance by costing each design.

By assuring advantages and disadvantages of each type; which are listed below:

56

Plate columns can be designed to handle a wider range of liquid and gas

flow-rates than packed columns.

Packed columns are not suitable for very low liquid rates.

The efficiency of a plate can be predicted with more certainty than the

equivalent term for packing (HETP or HTU).

Plate columns can be designed with more assurance than packed columns.

There is always some doubt that good liquid distribution can be

maintained throughout a packed column under all operating conditions,

particularly in large columns.

It is easier to make provision for cooling in a plate column; coils can be

installed on the plates.

It is easier to make provision for the withdrawal of side-streams from plate

columns.

If the liquid causes fouling, or contains solids, it is easier to make

provision for cleaning in a plate column; man-ways can be installed on the

plates. With small diameter columns it may be cheaper to use packing and

replace the packing when it becomes fouled.

For corrosive liquids a packed column will usually be cheaper than the

equivalent plate column.

The liquid hold-up is appreciably lower in a packed column than a plate

column. This can be important when the inventory of toxic or flammable

liquids needs to be kept as small as possible for safety reasons.

Packed columns are more suitable for handling foaming systems.

The pressure drop per equilibrium stage (HETP) can be lower for packing

than plates; and packing should be considered for vacuum columns.

Packing should always be considered for small diameter columns, say less

than 0.6 m, where plates would be difficult to install, and expensive.

57

5.3.3 Types of packing

The principal requirements of a packing are that it should:

Provide a large surface area: a high interfacial area between the gas

and liquid.

Have an open structure: low resistance to gas flow.

Promote uniform liquid distribution on the packing surface.

Promote uniform vapor gas flow across the column cross-section.

Many diverse types and shapes of packing have been developed to satisfy these

requirements. They can be divided into two broad classes:

Packing‟s with a regular geometry: such as stacked rings, grids and

proprietary structured packing‟s.

Random packing‟s: rings, saddles and proprietary shapes, which are

dumped into the column and take up a random arrangement.

Grids have an open structure and are used for high gas rates, where low pressure

drop is essential; for example, in cooling towers. Random packings and structured

packing elements are more commonly used in the process industries.

1. Random packing

Raschig rings, are one of the oldest specially manufactured types of random

packing, and are still in general use.

Pall rings, are essentially Raschig rings in which openings have been made

by folding strips of the surface into the ring. This increases the free area and

improves the liquid distribution characteristics.

Berlsaddles, were developed to give improved liquid distribution compared

to Raschig rings,

58

Intalox saddles can be considered to be an improved type of Berl saddle;

their shape makes them easier to manufacture than Berl saddles.

The Hypac and Super Intalox packings can be considered improved types of

Pall ring and Intalox saddle, respectively.

Random Packing is Shown in Figure 5.2.

Figure 5.2.

Ring and saddle packings are available in a variety of materials: ceramics, metals,

plastics and carbon. Metal and plastics (polypropylene) rings are more efficient

than ceramic rings, as it is possible to make the walls thinner .Raschig rings are

cheaper per unit volume than Pall rings or saddles but are less efficient, and the

total cost of the column will usually be higher if Raschig rings are specified. For

new columns, the choice will normally be between Pall rings and Berl or Intalox

saddles. The choice of material will depend on the nature of the fluids and the

operating temperature. Ceramic packing will be the first choice for corrosive

59

liquids; but ceramics are unsuitable for use with strong alkalies. Plastic packings

are attacked by some organic solvents, and can only be used up to moderate

temperatures; so are unsuitable for distillation columns. Where the column

operation is likely to be unstable metal rings should be specified, as ceramic

packing is easily broken.

Packing size

In general, the largest size of packing that is suitable for the size of column should

be used, up to 50 mm. Small sizes are appreciably more expensive than the larger

sizes. Above 50 mm the lower cost per cubic-meter does not normally

compensate for the lower mass transfer efficiency. Use of too large a size in a

small column can cause poor liquid distribution.

Recommended size ranges are:Column diameter Use packing size

<0.3 m (1 ft) <25 mm (1 in.)

0.3 to 0.9 m (1 to 3 ft) 25 to 38 mm (1 to 1.5 in.)

>0.9 m 50 to 75 mm (2 to 3 in.)

2. Structured packing

The term structured packing refers to packing elements made up from wire mesh

or perforated metal sheets. The material is folded and arranged with a regular

geometry, to give a high surface area with a high void fraction as Shown in Figure

5.3

Figure5. 3. (a)

60

Figure 5.3. (b) Make-up of structured packing

The advantage of structured packings over random packing is their low HETP

(typically less than 0.5 m) and low pressure drop (around 100 Pa/m).

They are increasingly being used in the following applications:

For difficult separations, requiring many stages: such as the separation of

isotopes.

High vacuum distillation.

For column revamps: to increase capacity and reduce reflux ratio

requirements.

The applications have mainly been in distillation, but structured packings can also

be used in absorption; in applications where high efficiency and low pressure drop

are needed.

The cost of structured packings per cubic meter will be significantly higher than

that of random packings, but this is offset by their higher efficiency.

5.3.4 Column Internals

The internal fittings in a packed column are simpler than those in a plate column

but must be carefully designed to ensure good performance. As a general rule, the

standard fittings developed by the packing manufacturers should be specified.

Figure 5.4 shows the column internal structure.

61

Figure 5. 4 .Stacked packing used to support random packing

5.3.5 Packing support

The function of the support plate is to carry the weight of the wet packing, whilst

allowing free passage of the gas and liquid. These requirements conflict; a poorly

designed support will give a high pressure drop and can cause local flooding.

Simple grid and perforated plate supports are used, but in these designs the liquid

and gas have to vie for the same openings. Wide-spaced grids are used to increase

the flow area; with layers of larger size packing stacked on the grid to support the

small size random packing as shown in Figure 5.5

The best design of packing support is one in which gas inlets are provided above

the level where the liquid flows from the bed; such as the gas-injection type.

These designs have a low pressure drop and no tendency to flooding. They are

available in a wide range of sizes and materials: metals, ceramics and plastics.

62

Figure 5.5. (a) The principle of the gas-injection packing support

Figure 5.5 .(b) Typical designs of gas-injection supports (Norton Co.). (a) Small

diameter columns (b) Large diameter columns

5.3.6 Liquid distributors

The satisfactory performance of a plate column is dependent on maintaining a

uniform flow of liquid throughout the column, and good initial liquid distribution

is essential.

Various designs of distributors are used. For small-diameter columns a central

open feed pipe, or one fitted with a spray nozzle, may well be adequate; but for

larger columns more elaborate designs are needed to ensure good distribution at

63

all liquid flow-rates. The two most commonly used designs are the orifice type,

shown in Figure5. 6 (a), and the weir type, shown in Figure 5.6 (b). In the orifice

type the liquid flows through holes in the plate and the gas through short stand

pipes. The gas pipes should be sized to give sufficient area for gas flow without

creating a significant pressure drop; the holes should be small enough to ensure

that there is a level of liquid on the plate at the lowest liquid rate, but large enough

to prevent the distributor overflowing at the highest rate.

Figure 5. 6. (a) Orifice-type distributor (Norton Co.)

Figure5. 6. (b) Weir-type distributor (Norton Co.)

64

For large-diameter columns, the trough-type distributor shown in Figure 5.7 can

be used, and will give good liquid distribution with a large free area for gas flow.

All distributors which rely on the gravity flow of liquid must be installed in the

column level, or mal-distribution of liquid will occur.

Figure 5.7. Weir-trough distributors (Norton Co.)

A pipe manifold distributor, Figure 5.8 can be used when die liquid is fed to the

column under pressure and the flow-rate is reasonably constant. The distribution

pipes and orifices should be sized to give an even flow from each element.

Figure 5.8. Pipe distributor (Norton Co.)

65

5.3.7 Liquid redistributors

Redistributors are used to collect liquid that has migrated to the column walls and

redistribute it evenly over the packing. They will also even out any

maldistribution that has occurred within the packing. A full redistributor combines

the functions of a packing support and a liquid distributor; a typical design is

shown in Figure 5.9

Figure 5.9. Full redistributor

The "wal-wiper" type of re-distributor, in which a ring collects liquid from the

column wall and redirects it into the centre packing, is occasionally used in small-

diameter columns, less than 0.6 m. Care should be taken when specifying this

type to select a design that does not unduly restrict the gas flow and cause local

flooding is shown in figure 5.10

66

Figure 5.10. "Wall wiper" redistributor (Norton Co.)

The maximum bed height that should be used without liquid redistribution

depends on the type of packing and the process. Distillation is less susceptible to

maldistribution than absorption and stripping. As a general guide, the maximum

bed height should not exceed3 column diameters for Raschig rings, and 8 to 10

for Pall rings and saddles. In a large diameter column the bed height will also be

limited by the maximum weight of packing that can be supported by the packing

support and column walls; this will be around 8 m.

5.3.8 Hold-down plates

At high gas rates, or if surging occurs through mis-operation, the top layers of

packing can be fluidized. Under these conditions ceramic packing can break up

and the pieces filter down the column and plug the packing; metal and plastic

packing can be blown out of the column. Hold-down plates are used with ceramic

packing to weigh down the top layers and prevent fluidization; a typical design is

shown in Figure 5.11. Bed-limiters are sometimes used with plastics and metal

packing‟s to prevent expansion of the bed when operating at a high-pressure drop.

They are similar to hold-down plates but are of lighter construction and are fixed

67

to the column walls. The openings in hold-down plates and bed-limiters should be

small enough to retain the packing, but should not restrict the gas and liquid flow.

Figure5. 11. Hold-down plate design (Norton Co.)

If the columns must be packed dry, for instance to avoid contamination of process

fluids with water, the packing can be lowered into the column in buckets or other

containers. Ceramic packing‟s should not be dropped from a height of more than

half a meter.

5.3.9 Liquid hold-up

An estimate of the amount of liquid held up in the packing under operating

conditions is needed to calculate the total load carried by the packing support. The

liquid hold-up will depend on the liquid rate and, to some extent, on the gas flow-

rate.

The packing manufacturers' design literature should be consulted to obtain

accurate estimates. As a rough guide, a value of about 25 per cent of the packing

weight can be taken for ceramic packing‟s.

68

5.3.10Wetting rate

Wetting rate is defined as:

wetting rate = volumetric liquid rate per unit cross-sectional area

packing surface area per unit volume

LW = L

AcρLa

Where

L=Liquid Flowrate Kg/hr

Ac=Cross-Sectional area

ρL =Liquid Density Kg/m3

a=Area (m3/m

2)

5.3.11Column Auxiliaries

Operation Time, Minutes

Feed to a train of columns 10 to 20

Between columns 5 to 10

Feed to a column from storage 2 to 5

Reflux drum 5 to 15

69

Figure 5. 12. Illustrative cutaway of a packed tower, depicting an upper bed

of structured packing and a lower bed of random packing.

(Courtesy of Sulzer Chemtech.)

70


Inlet Composition of Gases (Yb) Amounts in Kg-mole

Acrolein 187.4

Propylene 3.921

Acrylic acid 24

Nitrogen 1395.1

Carbon di-oxide 94.28

Oxygen 180.9

Water 41371.26

The Total Flow rate Of gases From reactor is 43256.86 Kg-mole/hr.

Liquid Inlet (Xa) Amounts in Kg-mole

Water 1800

The Total Flow rate of water From De-ionized water source is 1800 Kg-mole/hr.

Top Product Composition (Ya ) Amounts in Kg-mole

Nitrogen 1395.1

Oxygen 180.9

Carbon Di-oxide 94.28

Acrolein 15.3

Propylene 2.33

Water 38.6

The Total Flow rate of top Products from Absorber is 1726.51 Kg-mole/hr.

Bottom Product Compositions (Xb) Amounts in Kg-mole

Acrolein 172.1

Propylene 1.591

Acrylic acid 24

Water 43133.2

The Total Flow rate of bottom Products From Absorber is 43330.89 Kg-mole/hr.

71

Design Conditions

Basis : One Hour Operation

Iso-thermal operation (200 C and 1atm )

Its only Physical Absorption Process

92% Acrolein is absorbed

Absorbent is De-ionized Water

All Other gases are Inert Except Acrolein

Some Specified quantity of Propylene is also Absorbed

Packed-column design procedure

The design of a packed column will involve the following steps:

Select the type and size of packing.

Determine the column height required for the specified separation.

Determine the column diameter (capacity), to handle the liquid and vapor

flow rates.

Select and design the column internal features: packing support, liquid

distributor, redistributors.

The Henry Law Coefficient For Acrolein in water at 200

C

is 8.2025× 10-5

atm-

m3/mole can be converted to the slope of Equilibrium line in mole fraction units

as

P =1atm

1 m3 weights 10

6g

m = 8.2025× 10-5

atm-m3/mole × 1/atm × 10

6 mole H2O /18 m

m =4.55

And

Tan θ = 4.55

72

θ= tan-1

( 4.55)

=77.604

Height of Mass –Transfer Zone

Z= Height of mass transfer zone

Hoy =Height of transfer units ,m

Noy=Number of transfer units

As

Z= Hoy × Noy ----------------------------------------(1)

Calculation of Noy

Here Acrolein is Key Component and design will Be Based on this ,Entering De-

ionized water is free of solute Ya =0

Now

Noy =A/A-1 [ℓn (Yb/Ya)(A-1)+1/A]-------------(2)

As

A=L/mV

Here

Ya= mole Fraction of solute At Top in Gases

Yb= mole Fraction of solute At botom in Gases

m= Slope

L=Liquid Flow rate

V=Vapor Flow rate

Ya =15.3

Yb =187.4

L=1800 Kg-mole/hr

V=43205.94 Kg-mole/hr

A=L/mV=2.298

L/V= 10.459=Slope of Operating line

73

m =10.459

Tan θ =10.459

θ = Tan-1

(10.459)

θ =2.382

By Putting the values in Equation No. 2

Noy =A/A-1 [ℓn (Yb/Ya)(A-1)+1/A]-------------(2)

Noy =3.55

Calculation of Hoy

By using the Gas Film Basis

Hy=[V/S]/Kya------------------------------------------------------------(3)

Here

Kya =Overall Mass-transfer Co-efficient Based on Gas Phase (Kg-mole/m3-sec)

V=Flow rate

S=Cross-Sectional area

By Rule Of Thumb

Kya(Unknown) =Kya (Known)×( Dv Unknown/Dv Known) 0.56

...............(4)

At 200 C

Dv (unknown Acrolein)=0.4069 ft2/hr

Dv (known SO2)=0.448 ft2/hr

Kya (known SO2)=2 Kg-mole/ft3-hr-moles

By Putting the Values in above equation (4)

Kya(Unknown) =Kya (Known)×( Dv Unknown/Dv Known) 0.56

...............(4)

Kya(Unknown) =1.823 Kg-mole/ft3-hr-sec

Kya(Unknown) =0.0180 Kg-mole/m3-sec

74

Calculation of Cross-Sectional Area

As Flow Factor

Flv=Lw/Vw √ρv/ρl------------------------------------------------(5)

L=1800Kgmole/hr

V=172.1kgmole/hr

By using Formula( For Gas)

ρv =PM/RT-------------------(6)

ρv =0.775 Kg/m3

By using Formula( For Liquid)

ρl (water)= AB-(1-T/Tc)n

………………......(7)

Where

ρl (water)=998.20 Kg/m3

By Putting the values in Equation No.5

Flv=Lw/Vw √ρv/ρl------------------------------------------------(5)

Flv=0.291

For Absorber /Stripper

For Ramdom Packing ,Pressure Drop will not normally exceed 80mm of

water/m of Packing.

For Absorber and stripper Range (15------50mm)

We consider flooding velocity as 80 %

We Consider 21mm and Flv=0. 0.291

By Using Appendix B figure 9

As can be calculated by using the formula

Percentage Flooding = [K4 at Design Pressure Drop/K4 at

Flooding]×100----------(8)

Percentage Flooding = [ 0.5/ 0.8]×100

75

=62.5 %

Percentage flooding is satisfied

Type of Packing

Design data for various packings

By using Equation

K4= [13.1(Vw2) Fp (μl/ρl)0.1]/ρv(ρl-ρv)----------(9)

where

Vw, = gas mass flow-rate per unit column cross-sectional area, kg/nrs

Fp= packing factor, characteristic of the size and type of packing,

μl = liquid viscosity, Ns/m2

pL, pv = liquid and vapour densities, kg/m3

By Appendix A table 5

Selecting the Packing

CMR (Ceramic-Mini Rings ) Metal Rings

Dp=#5

a = 50 m2/m

3

Fp=26 m-1

By re-arranging equation as

Vw2 =K4 ρv (ρl-ρv) /13.1 Fp (μl/ρl )

Viscosity of Liquid ( water) at 200

C

ℓog 10 n liq = A+ B/T +CT+ DT2-----------------------------(10)

T=K

n liq =Viscosity Of Liquid (Centipose)

A,B,C=Constant

n liq =1.028 CP

76

n liq =0.00103 N.sec/m2

By putting the values in the following equation


Vw= 2.122 Kg/m2.sec

Gas Flow rate =43256.86 Kgmole/hr

Gas Flow rate =223.05 Kgs/sec

So

Cross-Sectional Area=223.05/2.122 Kg/sec×m2.sec/Kg

=105.11 m2

Diameter of Column

D=[4A/Π]1/2

D=11.57 m


Gas Flow rate =12.001 Kgmole/sec

By using the Gas Film Basis ,Equation No. 3

Hoy=[V/S]/Kya

V/S = 0.114 Kg-mole/Sec.m2

Now Putting all values in equation No. 3

Hoy=[0.114]/0.0180

Hoy=6.34 m

By putting the values in the Equation 1

Z= Hoy × Noy

Z= 6.34×3.55

Z= 22.488 m

Wetting Rate

LW = L

AcρLa

77

Where

L=Liquid Flowrate Kg/hr



a=Area (m3/m

2)

=1.7×10-6

m3/m.sec

Selecting the Packing type

Metal Pall Rings( Density for Mild steel)

Dp=3.5 in (76 mm)

a = 65 m2/m

3

Fp=16 m-1




C

ℓog 10 n liq = A+ B/T +CT+ DT2

T=K

n liq =Viscosity of Liquid (Centipose)

A,B,C=Constant

n liq =1.028 CP

n liq =0.00103 N.sec/m2



Vw= 2.70 Kg/m2.sec



So


=82.68 m2

78

Diameter of Column

D=[4A/Π]1/2

D=10.26 m




Hoy=[V/S]/Kya



Hoy=[0.145]/0.0180

Hoy=8.06 m


Z= Hoy × Noy

Z= 8.06×3.55

Z= 28.62 m

Wetting Rate

LW = L

AcρLa

Where

L=Liquid Flow rate Kg/hr



a=Area (m3/m

2)

=1.6×10-6

m3/m.sec

Metal Pall Rings( Density for Mild steel)

Dp=2 in (50 mm)

a = 102m2/m

3

79

Fp=20 m-1

Satisfied


Plastic Pall Rings

Dp=3.5 in (88 mm)

a = 85 m2/m

3

Fp=16 m-1




C


Here

T=K


A,B,C=Constant

n liq =1.028 CP

n liq =0.00103 N.sec/m2



Vw= 2.70 Kg/m2.sec




=82.51 m2

Diameter of Column

D=[4A/Π]1/2

D=10.25 m



80


Hoy=[V/S]/Kya



Hoy=[0.114]/0.0180

Hoy=6.34 m


Z= Hoy × Noy

Z= 6.34×3.55

Z= 22.48 m

Wetting Rate

LW = L

AcρLa

Where




a=Area (m3/m

2)

=1.2×10-6

m3/m.sec


Plastic Super Intalox Rings

Dp=# 3

a = 88 m2/m

3

Fp=16 m-1




C


81

T=K


A,B,C=Constant

n liq =1.028 CP

n liq =0.00103 N.sec/m2



Vw= 2.70 Kg/m2.sec



So


=82.687 m2

Diameter of Column

D=[4A/Π]1/2

D=10.26 m




Hoy=[V/S]/Kya



Hoy=[0.113]/0.0180

Hoy=6.33 m


Z= Hoy × Noy

Z= 6.33×3.55

Z= 22.48 m

82

Wetting Rate

LW = L

AcρLa

Where




a=Area (m3/m

2

=1.2×10-6

m3/m.sec

83

5.3.13Specification Sheet of absorber

Operation Continuous

Item No.

Packed Absorption Column (T-101)

No. required 1

Function

To absorb Acrolein in Deionized water

No. of transfer units

3.55

Height of transfer units

8.06 m

Size and type of packing

Metal Pall Rings

Total height of column

28.62 m

Packing arrangement

Random

Method of packing

Float into tower filled with water

Type of packing support Gas injection support

Temperature

200

C

Pressure

1 atm

Surface area of the packing material (a) 65 m2/m

3

Absorbent fluid ( Utility) De-ionized water

84

5.4 Design of Distillation Column

In industry it is common practice to separate a liquid mixture by distillation of the

components, which have lower boiling points when they are in pure condition

from those having higher boiling points. This process is accomplished by partial

vaporization and subsequent condensation.

5.4.1Distillation

“Process in which a liquid or vapor mixture of two or more substances is

separated into its component fractions of desired purity, by the application and

removal of heat”.

.

Molecular weight water 18 Kg/Kgmole

Packing factor Fp =16 m-1

85

5.4.2 Types of Distillation Columns

There are many types of distillation columns, each designed to perform specific

types of separations, and each design differs in terms of complexity.

Batch columns

Continuous columns

Batch Columns

In batch operation, the feed to the column is introduced batch-wise. That is, the

column is charged with a 'batch' and then the distillation process is carried out.

When the desired task is achieved, a next batch of feed is introduced.

Continuous Columns

In contrast, continuous columns process a continuous feed stream. No

interruptions occur unless there is a problem with the column or surrounding

process units. They are capable of handling high throughputs and are the more

common of the two types. We shall concentrate only on this class of columns.

5.4.3 Choice between plate and packed columns

The choice between use of tray column or a packed column for a given mass

transfer operation should, theoretically, be based on a detailed cost analysis for

the two types of contactors. However, the decision can be made on the basis of a

qualitative analysis of relative advantages and disadvantages, eliminating the need

for a detailed cost comparison.

The relative merits of plate over packed column are as follows:

i) Plate columns are designed to handle wide range of liquid flow rates

without flooding.

ii) Dispersion difficulties are handled in plate column when flow rate of

liquid are low as compared to gases.

iii) For large column heights, weight of the packed column is more than

plate column.

86

iv) If periodic cleaning is required, man holes will be provided for

cleaning. In packed columns packing must be removed before

cleaning.

v) For non-foaming systems the plate column is preferred.

vi) Design information for plate column is more readily available and

more reliable than that for packed column.

vii) Inter stage cooling can be provided to remove heat of reaction or

solution in plate column.

viii) When temperature change is involved, packing may be damaged.

ix) Random packed columns are not designed with diameter greater than

1.5 m and diameter of tray column is seldom less than 0.67m.

For this particular process, I have selected plate column because:

i) System is non-foaming.

ii) Temperature change is involved.

iii) Diameter is 0.96 meter.

5.4.4 Plate Contractors

Cross flow plates are the most commonly used plate contactors in distillation. In

which liquid flows downward and vapours flow upward. The liquid move from

plate to plate via down comer. A certain level of liquid is maintained on the plates

by weir.

Three basic types of cross flow trays used are

Sieve Plate (Perforated Plate)

Bubble Cap Plates

Valve plates (floating cap plates)

5.4.5 Selection of Trays

I have selected sieve tray because:

i) They are lighter in weight and less expensive. It is easier and cheaper

to install.

87

ii) Pressure drop is low as compared to bubble cap trays.

iii) Peak efficiency is generally high.

iv) Maintenance cost is reduced due to the ease of cleaning.

5.4.6 Factors affecting Distillation Column operation

Vapour flow conditions

• Foaming

• Entrainment

• Weeping/dumping

• Flooding

Foaming

Foaming refers to the expansion of liquid due to passage of vapour or gas.

Although it provides high interfacial liquid-vapour contact, excessive foaming

often leads to liquid build-up on trays. In some cases, foaming may be so bad that

the foam mixes with liquid on the tray above. Whether foaming will occur

depends primarily on physical properties of the liquid mixtures, but is sometimes

due to tray designs and condition. Whatever the cause, separation efficiency is

always reduced.

Entrainment

Entrainment refers to the liquid carried by vapour up to the tray above and is

again caused by high vapour flow rates. It is detrimental because tray efficiency is

reduced: lower volatile material is carried to a plate holding liquid of higher

volatility. It could also contaminate high purity distillate. Excessive entrainment

can lead to flooding.

Weeping/Dumping

This phenomenon is caused by low vapour flow. The pressure exerted by the

vapour is insufficient to hold up the liquid on the tray. Therefore, liquid starts to

88

leak through perforations. Excessive weeping will lead to dumping. That is the

liquid on all trays will crash (dump) through to the base of the column (via a

domino effect) and the column will have to be re-started. Weeping is indicated by

a sharp pressure drop in the column and reduced separation efficiency.

Flooding

Flooding is brought about by excessive vapour flow, causing liquid to be

entrained in the vapour up the column. The increased pressure from excessive

vapour also backs up the liquid in the down comer, causing an increase in liquid

hold-up on the plate above. Depending on the degree of flooding, the maximum

capacity of the column may be severely reduced. Flooding is detected by sharp

increases in column differential pressure and significant decrease in separation

efficiency.

Reflux Conditions

Minimum trays are required under total reflux conditions, i.e. there is no

withdrawal of distillate. On the other hand, as reflux is decreased, more and more

trays are required.

Feed Conditions

The state of the feed mixture and feed composition affects the operating lines and

hence the number of stages required for separation. It also affects the location of

feed tray.

State of Trays and Packing

Remember that the actual number of trays required for a particular separation duty

is determined by the efficiency of the plate. Thus, any factors that cause a

decrease in tray efficiency will also change the performance of the column. Tray

efficiencies are affected by fouling, wear and tear and corrosion, and the rates at

which these occur depends on the properties of the liquids being processed. Thus

appropriate materials should be specified for tray construction.

http://lorien.ncl.ac.uk/ming/distil/distildes.htm#trays

89

Column Diameter

Vapor flow velocity is dependent on column diameter. Weeping determines the

minimum vapor flow required while flooding determines the maximum vapor

flow allowed, hence column capacity. Thus, if the column diameter is not sized

properly, the column will not perform well.

5.4.7 Design Calculations of Distillation Column

Design Steps of Distillation Column

Calculation of Minimum Reflux Ratio Rm.

Calculation of optimum reflux ratio.

Calculation of theoretical number of stages.

Calculation of actual number of stages.

Calculation of diameter of the column.

Calculation of weeping point, entrainment etc.

Calculation of pressure drop.

Calculation of thickness of the shell.

Calculation of the height of the column.

90

Design Calculations of Distillation Column (T-104)

D=147.57 kg/hr

Acrolein = 0.98816

Propylene=0.000206

Water =0.01103

TOP PRODUCT

B= 81.21kg/hr

Acrolein = 0.009389

Water = 0.990610

BOTTOM PRODUCT

P=106KPa

T=650C

T =520C

P=101.325

KPa

T=105 0C

P=130kPa

Feed

F=228.78kg/hr

Acrolein = 0.64100

Propylene=0.0001332

Water = 0.35886

91

From material balance

Feed Composition & Flow Rates (F)

Component Mass Flow Rate

(Kg/hr)

Molar Flow Rate

(Kgmol/hr)

Mass Fraction

Acrolein 146.64 2.618 0.64100

Propylene 0.0304 0.0007 0.0001332

Water 82.09 4.561 0.35886

Top Product Composition and Flow Rates (D)

Component Mass Flow

Rate

(Kg/hr)

Molar Flow

Rate(Kgmol/hr)

Mass Fraction

Acrolein 145.83 2.604 0.98816

Propylene 0.0304 0.0007 0.000206

Water 1.62 0.09 0.01103

Bottom Product Composition & Flow Rates (B)

Component Mass Flow

Rate

(Kg/hr)

Molar Flow

Rate(Kgmol/hr)

Mass Fraction

Acrolein 0.762 0.013 0.009389

Propylene 0 0 0

Water 80.449 4.46 0.990610

Bottom Temperature (TB)

Bubble point calculations

PT = 130 kpa

T=105 oC (Assume)

92

Components Xb=Xi Ki Yi= KiXi

Acrolein 0.009389 3.5475 0.0333

Water 0.990610 1.0094 0.9999

Total 1.03

Top Temperature (TD)

Dew point calculations

PT = 101.325kpa

T=52 oC (Assume)

Components XD=Yi Ki Xi =Yi/ Ki

Acrolein 0.98816 0.9698 1.01

Propylene 0.000206 30.68 0.000006

Water 0.01103 0.1727 0.0638

Total 1.07

Feed Temperature (TF)

Bubble point calculations

PT = 106kpa

T =65 oC

93

Components XF=Xi Ki Yi= KiXi

Acrolein 0.64100 1.4103 0.9040

Propylene 0.0001332 37.6202 0.0050

Water 0.35886 0.2852 0.1023

Total 1.0

Since the bubble point calculations are being satisfied at feed temperature so feed

is saturated liquid.

Selection of key components

Light key Acrolein

Heavy key Water

Calculation of Relative Volatility

Component Top Bottom Average

α Ki αDi=Ki/KHK Ki αBi=Ki/KHK

Acrolein 0.9698 5.615 3.5475 3.514 4.442

Propylene 30.68 177.6 59.818 59.216 102.5

Water

0.1727 1 1.0094 1 1

94

Calculation of minimum reflux ratio (Rm)

Using Underwood equation

q1θα

α

θα

α

θα

α

C

fCC

B

fBB

A

fAA

xxx

As feed is at its bubble point so q = 1

By trial = 1.4

Using equation of min. reflux ratio,

Where,

α = Relative volatility of component with respect to some reference usually

heavy key

xd = Concentration of component in top product

xf= Concentration of component in feed

= Root of equation at Rm

R m = .1414

Actual reflux ratio (R)

R =(1.2 -- 1.5) R m

R = 1.5 R m

R= 0.621

1Rθα

α

θα

α

θα

αm

C

dCC

B

dBB

A

dAA

xxx

95

Minimum Number of Plates (Nm)

By Fenske Equation

Nm = avAB

sA

B

dB

A

αln

x

x

x

xln

(AB)av = Average relative volatility of light key with respect to heavy key= 4.442

A = Light key

B = Heavy key

Nm = 6.41

Theoretical no. of Plates

Gilliland related the number of equilibrium stages and the minimum reflux ratio

and the no. of equilibrium stages with a plot that was transformed by Eduljee into

the relation;

From “Kirk bride” relation

566.0

1175.0

1 R

RR mm

N= 14

Calculation of actual number of stages

Using O‟ Connell‟s Correlation for overall tray efficiency

Average temperature of column = 351.65k

Feed viscosity at average temperature = avg = 0.267 mNs/m2

So,

Eo = 49%

avgavgoE .log5.3251

96

So,

No. of actual trays = Nact = 14-1/0.49= 27

Location of feed Plate

log [ND/NB] = 0.206 log

2

HK

LK

LK

HK

x

x

D

B

DF

ND = No. of stages above the feed plate

NB = No. of stages below the feed plate

B = molar flow rates of bottom

D = molar flow rate of distillate

XLK=mole fraction of light key component

XHK=mole fraction of heavy key component

From which,

NB=16 ND=11

Determination of Column Diameter

Top Conditions Bottom Conditions

Ln = 91.641 kg/hr Lm= Ln +F=320.421 kg/hr

Vn=239.211 kg/hr Vm= Vn =239.211 kg/hr

TD=325.15 k TB=378.15 k

Mavg = 55.5 Mavg =18.35

Liquid density = L = 808.4 kg/m3 Liquid density = L = 953.7kg/m

3

Vapor density = V =1.8 kg/m3 Vapor density = V =0.60 kg/m

3

Surface Tension = σ = 19.88 Dynes/cm

or

0.01988 N/m

Surface Tension=σ= 57.98 Dynes/cm

or

0.05798N/m

97

Flow Parameter

Ln = liquid flow rate in kg/sec

Vn= Vapor flow rate in kg/sec

FLV = Liquid Vapor Factor (Top) = 0.018

FLV = Liquid Vapor Factor (Bottoms) = 0.033

Calculation of flooding velocity

Assumed tray spacing = 0.45

Uf = k1(L -V/V)0.5

Where,

Uf = flooding velocity in m/sec

K1= constant

From Appendix B figure 10

Top K1=0.08

Bottom K1=0.082

Correction for surface tension K1 × [σ/0.02]0.2

Where σ in N/m

Top K1=0.0801

Bottom K1=0.1

Top Uf = 1.695 m/sec

Bottom Uf = 3.985 m/sec

Assuming 90% flooding

So actual vapor velocity (U)

At Top U = 1.525 m/sec

At Bottom U = 3.586 m/sec

0.5

L

v

n

nLV

ρ

ρ

V

LF

98

Maximum volumetric flow rate of vapors = mv = mass vapor flow rate

(3600) × vapor density)

= 0.78 m3

/ s (Top)

mv = 2.226 m3

/ s (Bottom)

Net area required = An = mv/ U

=0.511 m2 (Top)

An= 0.621 m2 ( Bottom)

Assume that downcommers occupies 15% of cross sectional Area (Ac) of column.

Ac = An + Ad

Where, Ad = downcommer area

Ac = An + 0.15(Ac)

Ac = An / 0.85

Ac=0.601m2

(Top)

Ac=0.730m2

(Bottom)

Ac =π/4D2

D = (4Ac/π)

D = 0.87meter (Top)

D = 0.96meter (Bottom)

Since bottom diameter is larger so calculations will be based on bottom conditions.

Liquid flow arrangement

Maximum liquid flow rate = (Liquid mass rate)/ (3600) × (Liquid density)

Max Liquid Rate is at the bottom of column

So, Maximum liquid flow rate = 0.0030m3/sec

From Appendix B figure 11, cross flow single pass plate is selected.

Provisional Plate Design

Column Diameter Dc= 0.96 m

99

Column Cross-sectional Area (Ac)= 0.730 m2

Down comer area Ad = 0.15Ac = 0.109 m2

Net Area (An) = Ac - Ad =0.621 m2

Active area Aa=Ac-2Ad = 0.512 m2

Hole area Ah take 6% Aa = 0.06 × 0.512 = 0.0307 m2

Weir length

Ad / Ac = 0.109 / 0.730 = 0.149

From Appendix B figure 13 ,

Lw / dc = 0.80

Lw = 0.96*0.80= 0.768 m

Weir length should be 60 to 85% of column diameter which is satisfactory.

Take weir height, hw = 50 mm

Hole diameter, dh = 5 mm

Plate thickness = 5 mm (Carbon Steel)

Check Weeping

Uh(min) = [K2-0.9(25.4-dh)]/ v 0.5

Where Uh(min) is the minimum design vapor velocity.

The vapor velocity at weeping point is the minimum velocity for the stable operation.

In order to have K2 value we have to 1st find how (depth of the crest of liquid over

the weir)

Where how is calculated by following formula:

how(max) = 750 (Lm/LLw)2/3

Taking minimum liquid rate at 70% turn down ratio of maximum liquid rate

At Maximum rate (how) = 16.170 mm Liquid

At Minimum rate (how) = 12.73mm Liquid

hw + how = 50 + 12.73 = 62.73 mm Liquid

100


K2 = 30.2

So,

U (min) = 15.66 m/sec

Now taking maximum volumetric flow rate (vapors) at 70% turn down ratio

Actual minimum vapor velocity =minimum vapor rate / Ah

= 21.8 m/sec

So minimum vapor rate will be well above the weep point.

Plate Pressure Drop (P.D)

Consist of

Dry plate P.D (orifice loss)

P.D due to static head of liquid and

Residual P.D (bubbles formation result in energy loss + froth formed in

operating plates)

Dry Plate Drop

Max. Vapor velocity through holes (Uh) = 29.7 m/sec

Active Area = Aa = 0.512 m2

Ah/Aa = Ah/Ap = 0.059

Where Ap is the perforated area.

From Appendix B figure 14, C0 = 0.82

hd = 51(Uh / Co)2 (v / L)

= 42.09 mm liquid

Reisdual Drop

hr = 12.5 × 1000 / L

= 13.1 mm liquid

Total Plate Pressure Drop

ht = hd + hr + (hw +how)

= 117.92 mm liquid

101

Total pressure drop ∆Pt = 9.81 × 10-3

×(ht) ×L× Nact

= 29787.36 Pa = 29.78 KPa

Assumed and calculated pressure drop are almost equal.

Downcomer Liquid backup/ Liquid height in downcomer

Caused by P.D over the plate and resistance to flow in the downcomer itself.

hdc = 166 ×(Lw /L × Aap)2

Take hap = hw-10 = 40 mm = 0.04

Area under apron = hap×Lw

= 0.031 m

2

As Aap is less than Ad = 0.109 m2 so use this value of Aap in the following equation:

hdc = 166 ×(Lw /L × Aap)2

= 1.041 mm

hb = (hw+ how) + ht + hdc = 241mm = 0.241m

hb < ½ (Tray spacing + weir height)

0.241 m < 0.25 m

So tray spacing of 0.45m is acceptable

Residence time

tr =Ad hbc ρL/L(max)

tr = 8.00 sec

It should be > 3 sec.

so, result is satisfactory.

Entrainment

(un) actual velocity (based on net area) = Maximum volumetric flow rate/ Net area

(un) actual velocity = 2.871 m/sec

Velocity at flooding condition uf = 3.586 m/sec

So Percent flooding =un/ uf = 0.80 = 80%

102

Liquid flow factor = FLv =0.033


Fractional entrainment (ψ) = 0.05

Well below the upper limit of (ψ) which is 0.1.

Below this effect of entrainment on efficiency is small.

Number of holes

Area of 1 Hole = (π/4) Dhole2

= 0.0000196 m2

Area of N Holes = 0.0307 m2

Number of Holes = 1566.3

Height of Distillation Column

Height of column Hc = (Nact -1)Hs+ ∆H+ plates thickness

No. of plates = 27

Tray spacing Hs = 0.45 m

∆H= liquid hold up and vapor disengagement

∆H=0.55+0.55=1.1 m

Total thickness of trays = 0.005× 27 = 0.135 m

Height of column = (26 ×0.45) + 1.1+0.135

= 12.9 meters

103

5.4.8 Specification Sheet of Distillation Column

Identification:

Item Distillation column

Equipment-Code T-104

Tray type Sieve tray

Function: Separation of Acrolein from propylene and water

Operation: Continuous

Design Data

No. of trays 27 Weir height 50mm

Pressure drop per

tray

1.1kPa Weir length 0.7688 m

No of Holes 1566.3 Minimum Reflux

Ratio

0.414

Height of column 12.9m Reflux ratio 0.621

Column-Diameter 0.96m Hole size 5mm

Tray spacing 0.45m Entrainment 0.05

Tray thickness 5mm Hole area 0.0307 m2

Flooding 80 % Active area 0.512m2

104

CHAPTER NO: 6

MECHANICAL DESIGN OF REACTOR

6.1Mechanical Design

Shell Thickness

Shell thickness can be calculated by following relationship

𝑒 = 𝑃 𝐷

2𝑓𝐽 − 𝑃+ 𝐶

Where,

e = Design thickness of shell in mm

f = Design stress = 137895 k Pa for carbon steel

J = 1

D = Shell diameter = 0.908 m=908mm

P = Maximum allowable pressure = 205 k Pa

C = Corrosion allowance = 3.2 mm under sever conditions

Shell thickness = 3.87 mm

Material of construction

For the reactor shell, carbon steel is proposed as material of construction as it is

both cheap and also compatible with water. The reactor tubes are suggested to be

of stainless steel so that any contamination of maleic anhydride due to corrosion

products is avoided.

Heads for reactor shell

Standard torispherical heads are most commonly used for pressure up to 15bar.

Thus as ASME standard torispherical heads have been designed for the reactor.

The proposed material of construction is plain carbon steel.

105

Thickness of the head

Cs = Stress concentration factor torispherical head

Rc = Crown radius

Rc = 2.15 m

Rk= Knuckle radius

= 0.06 x Rc= 0.129 m

Cs = 1.77

Thickness = 6.2 mm

Reactor Support

The types of support used for vessels are:

Saddle support

Skirt support

Bracket support

Saddle supports are used for horizontal vessels while other two types are used for

vertical vessels. For the reactor in this case, a skirt support is proposed as it is

safer than bracket support and can more efficiently bear the weight of the reactor

and water as a cooling media circulating through the reactor.

)2.0(2

sCiPJf

sCcRiPe

kRcR /34

1

106

CHAPTER NO: 7

INSTRUMENTATION AND CONTROL

7.1 Instrumentation and Process Control

Measurement is a fundamental requisite to process control. Either the control can

be affected automatically, semi automatically or manually. The quality of control

obtainable also bears a relationship to accuracy, reproducibility and reliability of

measurement methods, which are employed. Therefore, selection of the most

effective means of measurements is an important first step in design and

formulation of any process control system.

Design of control system involves large number of theoretical and practical

consideration such as quality of controlled response, stability, the safety of

operating plant, the reliability of control system, the range of control, easy of start

up, shutdown or changeover, the ease of the operation and cost of control system.

Traditionally one under takes the design of control system for chemical plant only

after the process flow sheet has been synthesized and designed. This allows the

control designer to know

What units are in plant and their sizes

How they are interconnected

The range of the operating conditions

Possible disturbance, available measurements and manipulations

What problem may arise during shutdown and start up

7.2 Process instrument

Process instrument is a device used directly or indirectly to perform one or more

of the following three functions

Measurement

Control

107

Manipulation

The primary purpose of control in process industry is to aid in the economics of

industrial operations by improving quality of product and efficiency of

production.

7.3 Control

Control means methods to force parameters in environment to have specific value.

There is some control on different parameters as follows

7.3.1Temperature measurement and control

Temperature measurement is used to control the temperature of outlet

and inlet streams in heat exchangers, reactors, etc.

Most temperature measurements in the industry are made by means of

thermocouple to facilitate bringing the measurements to centralized location. For

local measurements at the equipment bimetallic or filled system thermometers are

used to a lesser extent. Usually, for high measurement accuracy, resistance

thermometers are used.

All these measurements are installed with thermo wells when used locally. This

provides protection against atmosphere and other physical elements.

7.3.2 Pressure measurement and control

Like temperature, pressure is a valuable indication of material state and

composition.

In fact, these two measurements considered together are the primary evaluating

devices of industrial materials.

Pumps, compressors and other process equipments associated with pressure

changes in the process material are furnished with pressure measuring devices.

Thus pressure measurement becomes an indication of an energy decrease or

increase.

108

Most pressure measuring devices in industry are elastic element devices, either

directly connected for local use or transmission type to centralized location. Most

extensively used industrial pressure measuring device is the Bourdon Tube or a

Diaphragm or Bellow gauges.

7.3.3 Flow measurement and control

Flow indicator is used to control the amount of liquid. Also all manually

set streams require some flow indication or some easy means for occasional

sample measurement.

For accounting purposes, feed and product streams are metered. In addition

utilities to individual and grouped equipments are also metered.

Most flow measuring devices in the industry are Variable Head devices. To a

lesser extent variable area is used as many types are available as special metering

situation arise.

7.4 Control scheme of distillation column

Objectives

In distillation column any of following may be the goals to achieve.

1. Overhead composition

2. Bottom composition

3. Constant over head product rate

4. Constant bottom product rate

Manipulated variables

Any one or any combination of following may be the manipulated variables.

1. Steam flow rate to reboiler

2. Reflux rate

3. Overhead product with drawn rate

4. Bottom product withdrawn rate

109

5. Water flow rate to condenser

Loads or disturbances

Following are typical disturbances.

1. Flow rate of feed.

2. Composition of feed.

3. Temperature of feed.

4. Pressure drop of steam across reboiler.

5. Inlet temperature of water for condenser.

Control scheme

Here is control scheme on acrolein distillation column. Consider the feed to this

column as binary mixture composed of acorlein and water. We can specify four

control variable for this distillation column are

Acrolein product quality

Fractional recovery of acroelin in overhead product (distillate rate)

Liquid level in overhead accumulator

Liquid level at bottom of column

Overall product rate is fixed and any change in feed must be absorbed by

changing bottom product rate. The change in product rate is accomplished by

direct level control of reboiler if the stream rate is fixed, feed rate increases then

vapor rate is approximately constant and the internal reflux flow must increase.

Trying to control the liquid level at the bottom of column with reflux flow or

distillate flow rate involves very long time response because action of

manipulated variable must travel the whole length of distillation column before it

is felt by the controller variable so it cannot be done.

A long time response is involved when we try to control the level in the overhead

accumulator by manipulating the bottoms flow rate & stream flow rate. It is quite

complicated to control the distillate composition or flow rate with bottom flow

110

rate. Since an increase in feed rate increases reflux rate with vapor rate being

approximately constant, then purity of top product increases.

Explanation

First on the cold day or in rainstorm the temperature of cold water in overhead

condenser drops and overhead vapors passing through condenser produces sub

cooled liquid. When sub cooled liquid returns back from reflux to the top tray of

distillation column it causes less vapors to go overhead. Low vapors in overhead

causes less liquid level in accumulators. If the accumulator level is controlled by

reflux flow the latter will decrease thus the disturbance causes by the cooling

water temperature drop does not propagate down the column in terms of increased

liquid level overflow. The acrolein product composition is controlled by distillate

flow. The scheme shown is cascade scheme for distillation column.

Figure 7.1. Control scheme of distillation column

111

7.5 Heat exchanger control

Figure 7.2. Control scheme of heat exchanger

The control objective is to maintain the temperature at desired value and to allow

particulate heat exchange. The manipulated variable is flow rate of utility stream.

The external disturbance that will affect the operation of heat exchanger is

surrounding temperature, inlet temperature and steam pressure and steam

temperature or its flow rate in case when utility is steam. The output variable is

the temperature of outlet process stream and temperature of outlet utility stream.

The above is feedback control scheme for heat exchanger.

The control system of complete plant must permit smooth, safe and relatively fast

startup and shutdown of plant operation.

7.6 Control Scheme of PFR

Objectives

In PFR control any of following may be the goals to achieve

1. Constant Temperature inside the reactor

2. High quality of Product

112

Reactor Variable

The independent variables for the PFR may be divided into following categories

1. Uncontrolled variables

2. Manipulated variables

3. Controlled Variables

Uncontrolled Variables

The variables, which cannot be controlled by controller, are called uncontrolled

variables. The Uncontrolled variables include

1.Vent gases rate

2.Temperature of feed, etc

Manipulated Variables

The independent manipulated inputs are variables, which are adjusted to control

the chemical reaction. Any one or any combination of following may be the

manipulated variables

1.Flow rate of cooling water

2.Flow rate of Feed

3.Flow rate of Product stream

Controlled Variables

Any process variable that is selected to be maintained by a control system is

called a controlled variable. Following are the controlled variables

1.Inside reactor Temperature

2.Inside reactor Pressure

Temperature Control Scheme

The simplest method of cooling a PFR is shown in diagram. Here we measure the

reactor temperature and manipulated variable the flow of cooling water to the

shell side in shell and tube type reactor. Using a shell side for cooling has two

advantages. First, it minimizes the risk of leaks and thereby cross contamination

between the cooling system and the process. Second, heat transfer rate is

increased by using baffles.

113

A temperature sensor measures the inside reactor temperature and transfer signal

to temperature transducer, transducer converts these signals in other form and the

output of transducer is accepted by controller and controller transfer its signal to

final control element. Final control element takes step to overcome these

disturbances.

PFR Control Configuration

Figure 7.3. Control Scheme of PFR

114

CHAPTER NO: 8

HAZOP STUDY

8.1Introduction

A HAZOP survey is one of the most common and widely accepted methods of

systematic qualitative hazard analysis. It is used for both new or existing facilities

and can be applied to a whole plant, a production unit, or a piece of equipment It

uses as its database the usual sort of plant and process information and relies on

the judgment of engineering and safety experts in the areas with which they are

most familiar. The end result is, therefore reliable in terms of engineering and

operational expectations, but it is not quantitative and may not consider the

consequences of complex sequences of human errors.

8.2 Background

The technique originated in the Heavy Organic Chemicals Division of ICI, which

was then a major British and international chemical company. The history has

been described by Trevor Kletz .

In 1963 a team of 3 people met for 3 days a week for 4 months to study the design

of a new phenol plant. They started with a technique called critical

examination which asked for alternatives, but changed this to look for deviations.

The method was further refined within the company, under the name operability

studies, and became the third stage of its hazard analysis procedure (the first two

being done at the conceptual and specification stages) when the first detailed

design was produced.

In 1974 a one-week safety course including this procedure was offered by

the Institution of Chemical Engineers (IChemE) at Teesside Polytechnic.Coming

http://en.wikipedia.org/wiki/Imperial_Chemical_Industries

http://en.wikipedia.org/wiki/Trevor_Kletz

http://en.wikipedia.org/wiki/Phenol

http://en.wikipedia.org/wiki/Hazard_analysis

http://en.wikipedia.org/wiki/Institution_of_Chemical_Engineers

http://en.wikipedia.org/wiki/Teesside_Polytechnic

115

shortly after the Flixborough disaster, the course was fully booked, as were ones

in the next few years.

In the same year the first paper in the open literature was also published. In 1977

the Chemical Industries Association published a guide .Up to this time the

term HAZOP had not been used in formal publications. The first to do this was

Kletz in 1983, with what were essentially the course notes (revised and updated)

from the IChemE courses. By this time, hazard and operability studies had

become an expected part of chemical engineering degree courses in the UK.

8.3Types of HAZOP

1. Process HAZOP

The HAZOP technique which was originally developed to assess plants and

process systems

2. Human HAZOP

It is a family of specialized HAZOPs that are more focused on human errors

rather than technical failures.

3. Procedure HAZOP

It is a review of procedures or operational sequences, sometimes

also denoted as SAFOP, SAFE Operation Study.

4. Software HAZOP

It deals with the identification of possible errors in the

development of software.

Advantages

1. Systematic examination

2. Multidisciplinary study

3. Utilizes operational experience

http://en.wikipedia.org/wiki/Flixborough_disaster

http://en.wikipedia.org/wiki/Chemical_Industries_Association

http://en.wikipedia.org/wiki/Chemical_engineering

116

4. Solutions to the problems identified may be indicated

5. Reduces risks

6. Better contingency

7. More efficient operations

8. Considers operational procedures

8.4 HAZOP guide words and meanings

Guide Words Meaning

No

Less

More

Part of

As well as

Reverse

Other than

Negation of design intent

Quantitative decrease

Quantitative increase

Qualitative decrease

Qualitative Increase

Logical opposite of the intent

Complete substitution

8.5 HAZOP study of an Absorber

Item

No.

Deviation

Causes Consequences Safeguards Actions

AB1

Low pressure Unsuitable

packing

High liquid

loading

Low flooding

efficiency

Flood can

occur

Use pressure

controller at

above stream

of absorber

Use blower

upstream

and also use

suitable

packing for

absorber

High

pressure

Low

pressure

Good

absorption

Use pressure

controller

Use blower

working

117

drop

Low

temperature

Chocking

can occur in

the packing

Efficiency of

absorber

reduces also

pressure drop

increases

Use

temperature

controller for

the

measurement

of

temperature

of inlet gases

and stream

Use control

valve and

controller at

upstream of

absorber

High

temperature

Quencher is

not working

properly

Low

absorption

Damage to the

packing

Use

temperature

controller for

temperature

measuring of

inlet gases

and stream

Use control

valve and

controller at

upstream of

absorber

High

concentration

of CO2

Change in

wood

composition

Increase in

CO2

More water is

required to

remove CO2

Increase in

operating cost

and vice versa

Check CO2

concentration

after cracker,

use wood of

constant

composition

Use

controller

for

controlling

composition

of CO2

Low

concentration

of CO2

Less

conversion

in cracker,

more carbon

remains as it

is

118

CHAPTER NO: 9

ENVIRONMENTAL IMPACT ANALYSIS

OF ACROLEIN

9.1Hazards Identification

9.1.1Potential Acute Health Effects

Acrolein is very hazardous in case of skin contact (irritant), of eye contact

(irritant), of ingestion, of inhalation. Liquid or spray mist may produce tissue

damage particularly on mucous membranes of eyes, mouth and respiratory tract.

Skin contact may produce burns. Inhalation of the spray mist may produce severe

irritation of respiratory tract, characterized by coughing, choking, or shortness of

breath. Severe over-exposure can result in death. Inflammation of the eye is

characterized by redness, watering, and itching. Skin inflammation is

characterized by itching, scaling, reddening, or, occasionally, blistering.

9.1.2 Potential Chronic Health Effects

Acrolein is mutagenic for mammalian somatic cells and for bacteria and/or yeast.

The substance is toxic to lungs, upper respiratory tract. The substance may be

toxic to skin, eyes. Repeated or prolonged exposure to the substance can produce

target organs damage. Repeated or prolonged contact with spray mist may

produce chronic eye irritation and severe skin irritation. Repeated or prolonged

exposure to spray mist may produce respiratory tract irritation leading to frequent

attacks of bronchial infection. Repeated exposure to a highly toxic material may

produce general deterioration of health by an accumulation in one or many human

organs.

119

9.2Fire and Explosion Data

Flammability of the Product: Flammable.

Auto-Ignition Temperature: 220°C (428°F)

Flammable Limits: LOWER: 2.8% UPPER: 31%

Products of Combustion: These products are carbon oxides (CO, CO2).

Fire Hazards in Presence of Various Substances:

Acrolein is highly flammable in presence of open flames and sparks, of heat also

in presence of oxidizing materials.

Explosion Hazards in Presence of Various Substances:

There is a risk of explosion of the product in presence of mechanical impact and

slightly explosive in presence of heat.

Fire Fighting Media and Instructions:

Flammable liquid, soluble or dispersed in water. In case of small fire use dry

chemical powder while for large fire alcohol foam, water spray or fog may be

used.

Special Remarks on Fire Hazards:

Vapors may form explosive mixtures with air. Vapor may travel considerable

distance to source of ignition and flash back. When heated to decomposition it

emits toxic fumes of carbon monoxide, peroxides.

Special Remarks on Explosion Hazards:

Vapors may form explosive mixtures with air.

9.3Accidental Release Measures

Small Spill:

Dilute with water and mop up, or absorb with an inert dry material and place in an

appropriate waste disposal container.

120

Large Spill:

Acrolein is flammable, corrosive and Poisonous liquid. Keep it away from heat

also from sources of ignition. Absorb with dry earth, sand or other non-

combustible material. Do not get water inside container. Do not touch spilled

material. Use water spray curtain to divert vapor drift. Use water spray to reduce

vapors. Prevent entry into sewers, basements or confined areas; dike if needed.

Call for assistance on disposal.

9.4 Handling and Storage

Precautions:

Acrolein should be kept away from sources of ignition. Ground all equipment

containing material. Do not ingest. Do not breathe gas/fumes/ vapor/spray. Never

add water to this product. In case of insufficient ventilation, wear suitable

respiratory equipment. If ingested, seek medical advice immediately and show the

container or the label. Avoid contact with skin and eyes. Keep away from

incompatibles such as oxidizing agents, acids, alkalis.

Storage:

It should be stored in a segregated and approved area. Keep container in a cool,

well-ventilated area also keep it tightly closed and sealed until ready for use.

Avoid all possible sources of ignition (spark or flame). Do not store above 8°C

(46.4°F).

9.5Exposure Controls/Personal Protection

Engineering Controls:

Provide exhaust ventilation or other engineering controls to keep the airborne

concentrations of vapors below their respective threshold limit value. Ensure that

eyewash stations and safety showers are proximal to the work-station location.

121

Personal Protection:

Face shield, full suit and vapor respirator should be used. Be sure to use an

approved/certified respirator with gloves and boots.

Personal Protection in Case of a Large Spill:

A self contained breathing apparatus should be used to avoid inhalation of the

product. Suggested protective clothing might not be sufficient; consult a specialist

before handling this product.

9.6First Aid Measures

Eye Contact:

Check for and remove any contact lenses. Immediately flush eyes with running

water for at least 15 minutes, keeping eyelids open. Cold water may be used. Get

medical attention immediately.

Skin Contact:

In case of contact, immediately flush skin with plenty of water for at least 15

minutes while removing contaminated clothing and shoes. Cover the irritated skin

with an emollient. Cold water may be used. Wash clothing before reuse.

Thoroughly clean shoes before reuse. Get medical attention immediately.

Serious Skin Contact:

Wash with a disinfectant soap and cover the contaminated skin with an anti-

bacterial cream. Seek immediate medical attention.

Inhalation:

If inhaled, remove to fresh air. If no breathing is possible, give artificial

respiration. If breathing is difficult, give oxygen. Get medical attention

immediately.

Serious Inhalation:

Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such

as a collar, tie, belt or waistband. If breathing is difficult, administer oxygen. If

the victim is not breathing, perform mouth-to-mouth resuscitation.

122

WARNING: It may be hazardous to the person providing aid to give mouth-to-

mouth resuscitation when the inhaled material is toxic, infectious or corrosive.

Seek immediate medical attention.

Ingestion:

If swallowed, do not induce vomiting unless directed to do so by medical

personnel. Never give anything by mouth to an unconscious person. Loosen tight

clothing such as a collar, tie, belt or waistband. Get medical attention

immediately.

123

CHAPTER NO: 10

COST ESTIMATION

A plant design must present a process as capable of operating under conditions

which will yield a profit and net profit equals total income minus all expenses.

It is essential that chemical engineer be aware of the many different types of cost

involved in manufacturing processes. Capital must be allocated for direct plant

expenses; such as those for raw materials, labor, and equipment. Besides direct

expenses, many other indirect expenses are incurred, and these must be included

if a complete analysis of the total cost is to be obtained. Some examples of these

indirect expenses are administrative salaries, product distribution costs and cost

for interplant communication.

10.1Cost Indexes

All cost-estimating methods use historical data and are themselves forecasts of

future costs. The prices of the materials of construction and the costs of labor

considerably increase with time due to changes in economic conditions .Therefore

the cost index is used to update the historical cost data available .A cost index is

merely an index value for a given point in time showing the cost at that time

relative to a certain base time. If the cost at some time in the past is known, the

equivalent cost at the present time can be determined by use of cost indexes.

Cost in year A = Cost in year B × (Cost Index in year A/Cost Index in year B)

The common indexes permit fairly accurate estimates if the time period involved

is less than 10 years. Many different types of cost indexes are published regularly

in Chemical Engineering Journal .The most common of these indexes are the

Marshall and Swift all-industry and process-industry equipment indexes, the

Engineering News-Record construction index, the Nelson-Farrar refinery

construction index, and the Chemical Engineering plant cost index.

124

10.2Cost of designed equipments

Cost is being calculated by using following formula

Cost of equipment in year A=Cost of equipment in year B × Cost index in year A

Cost index in year B

Using Marshall and Swift Equipment Cost Index (MS)

Heat Exchanger

From appendix B figure 16,

For carbon steel shell, stainless steel tubes and floating head,

Material adjustment factor = 1

Pressure adjustment factor = 1

Bare cost = $ 140,000

Purchased cost of shell & tube Condenser (Mid 2004) = 140000 × 1 × 1

= $ 140,000

From appendix B figure 17, using Marshall & Swift equipment cost index

Cost index in year 2004 = 1200


Cost in 2012=140000 × 1700/1200

= $ 198,333

125

Reactor

From appendix B figure 16,

For carbon steel shell, stainless steel tubes and fixed head,

Material adjustment factor for fixed tube sheet= 0.8

Pressure adjustment factor for 2.05 bar = 1

Bare cost = $ 31,000

Purchased cost of muti tubular reactor (Mid 2004) = 31000 × 0.8 × 1

= $ 24,800

From appendix B figure 17, using Marshall & Swift equipment cost index



𝐶𝑜𝑠𝑡 𝑖𝑛 2012 = 1700

1200 × 24800

= $ 35,133

126

Absorber

The purchased cost of packed column can be divided into the

following components;

Cost for column shell, including heads, skirts,

manholes and nozzles.

Cost for internals including packing, support and

distribution plates.

Diameter = D = 10.26 m

Height = H = 28.62 m

From Appendix B figure 18,

Material of Construction =C.S(Carbon Steel)

Material Adjustment factor =1

Pressure Adjustment factor =0.5

Bare cost of Absorber = 3×105× 0.5×1

= $150000

From Appendix B figure 19,

Material of Construction =C.S (Carbon Steel)

Packing Material Adjustment factor =1.2

Packed Height =28.26 m

Cost of Absorber (Includes column internal support and distribution) = 5×105× 1.2

= $600000

127

Total Cost of Absorber Column =$150000+$600000

=$210000

Distillation Column

Diameter of column = D = 0.96 m

Height of column = H = 12.9m

Plate type = Sieve plate

Total pressure drop =29787.36pa

Number of plates = 27

Material of construction = Carbon steel

Cost of distillation column= cost of vertical column+ cost of sieve plates


Cost of column in 1998 = (bare cost from fig) ×material factor ×pressure factor

Cost of column in 1998 = (7×1000) ×1×1

Cost of column in 1998 = $7000


Cost of plate in 1998 = (bare cost from fig) ×material factor

Cost of plate in 1998 = (320) ×1

Cost of plate in 1998= $320

128

Cost of plate in 1998 = 320×27 = $8640

Cost of distillation column in 1998 = 8640+7000

=$15640

Marshall and Swift Equipment Cost Index using Appendix B figure 17,

Cost index in 1998 = 1092

Cost index in 2012=1500

Cost of column in 2012=Cost of column in 1998× Cost index in 2012

Cost index in 1998

=15640× (1500/1092)

=$21483.

129

APPENDICES

APPENDIX A

Table 1. Heat exchanger and condenser tube data

130

Table 2. Tube sheet layouts.(Tube counts)

Triangular Pitch

131

Table 3.Fouling factor (Coefficients) typical values

132

Table 4.Fouling factor (Coefficients) typical values

Table 5.Data for different packings

133

Table 5. Continued

134

APPENDIX B

Figure 1. Relation between Reynolds number and

friction factor

135

Figure 2. Relation between Reynolds number and friction factor

with respect to baffle cut

136

Figure 3. Overall Coefficients

137

Figure 4. Tube patterns

138

Figure 5. Tube side heat transfer factor

139

Figure 6. Shell side heat transfer factor, segmental baffles

140

Figure 7. Shell side friction factor

141

Figure 8. Shell side heat transfer curve

142

Figure 9. Generalized pressure drop correlation, adapted from a

figure by the Norton Co. with permission

143

Figure 10. Flooding velocity, sieve plates

144

Figure 11. Selection of liquid flow arrangement

145

Figure 12. Weep point correlation (Eduljee, 1959)

146

Figure 13. Relation between downcomer area and weir length

147

Figure 14.Discharge coefficients, sieve plates

148

Figure 15. Entrainment correlation for sieve plates

149

Figure 16. Purchased cost of shell and tube heat exchanger

150

Figure 17. Variation of cost indices

151

Figure 18. Purchased cost of absorber column

152

Figure 19. Purchased cost of packing

153

Figure 20. Purchaesd cost of distillation column

154

Figure 21.Purchaesd cost of column plates

155

REFERENCES

1. McCabe, W.L, Smith, J.C., & Harriot, P., “Unit Operation of Chemical

Engineering”, McGraw Hill, 5th

ed., Inc, 1993.

2. Sinnot R.K., “Coulson and Richardson‟s Chemical Engineering”, 3rd

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Vol. 6, Butterword Heminann, 1999.

3. Coulson J.M. and Richardson J.F.,“Chemical Engineering”, 5th

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Butterword Heminann, 2002.

4. Branan C.R., “Rules of Thumbs For Chemical Engineers”, Gulf

Publishing Company, 1994.

5. Yaw‟s C.L., “Handbook of Thermodynamics and Physical Properties of

Chemical Compounds”, Knovel Publishing Company, 2003.

6. R.H.Perry, Don W.Green, “Perry„s Chemical Engineer„s Handbook”,

McGrawHill, 7th

ed.

7. Max S.Peters, Klaus D.Timmerhaus, Ronald E.West,” Plant Design And

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ed.

8. O. Levenspiel, “Chemical Reaction Engineering”, 2nd

and 3rd

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Wiley and Sons, 1972, 1999.

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ed., John Wiley, 1982.

11. http://www.google.com.pk/patents?hl=en&lr=&vid=USPAT2270705&id=

QxJEAAAAEBAJ&oi=fnd&dq=production+of+acrolein&printsec=abstra

ct#v=onepage&q=production%20of%20acrolein&f=false

12. http://www.atsdr.cdc.gov/toxprofiles/tp124-c5.pdf - United States

13. http://www.che.cemr.wvu.edu/publications/projects/large_proj/Acrolein.P

DF

http://www.google.com.pk/patents?hl=en&lr=&vid=USPAT2270705&id=QxJEAAAAEBAJ&oi=fnd&dq=production+of+acrolein&printsec=abstract#v=onepage&q=production%20of%20acrolein&f=false



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