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DESIGN OF SHELL AND TUBE HEAT
EXCHANGER UTILIZING FLUE GASESFROM CALCINERS (Second review)
VISHNU.R
REG No: ETAKCCT016
M-TECH(ICTM)
ROLL NO: 16
GEC THRISSUR
Internal Guide :Prof. Sunil .A.SAPME , Govt Engg College, Thrissur
External Guide: M.K PrabhakaranDeputy Chief Engineer (Mechanical), TTPL ,
Trivandrum
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Production Layout
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Concentration
Concentrator
Lute
Condenser
Vapor
Separator
Drum
Preheater
Overhead
Tank
Conc.
MeasuringTank
Steam
from
boiler
Steam
out
Vapor in
Vapor + Liquid
Liquor From Concentration
feed tank
140 gpl Ti02
190 gpl Ti02
Cooling Water
Vapor in
Precipitation
VaporRecycled
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GENERAL DESIGN CONSIDERATIONS
The general design considerations are categorized as
Selection of flow path
Construction codes
Tube bundle vibration
Testing / Performance Testing
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Selection of Flow Path
Tube side fluid :
More corrosive
Dirtier at higher pressures.
Shell Side Fluid :
Fluid of high viscosity
Gas.
Construction :
Least expensive is alloysteel with the tube side andcarbon steel on the shellside
Cleaning of inside of tubesis readily done than theexterior surfaces.
For gauge pressures inexcess of 2068 kPa for oneof the fluids, the lessexpensive construction hasthe high-pressure fluid inthe tubes.
Heat-exchanger shutdownsare most often caused byfouling, corrosion , anderosion.
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Construction Codes
Shelland Tube Heat Exchangers for General Refinery Services, API
Standard 660, 4th ed., 1982, is published by the American Petroleum
Institute to supplement both the TEMA Standards and the ASME
Code.
Standards of Tubular Exchanger Manufacturers Association, 6th ed.,1978 (commonly referred to as the TEMA Standards), serve tosupplement and define the ASME Code for all shell-and-tube-type heat-exchanger applications.
TEMA Class R design is for the generally severe requirements ofpetroleum and related processing applications. Equipment fabricated inaccordance with these standards is designed for safety and durabilityunder the rigorous service and maintenance conditions in suchapplications.
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TEMA Class C design is for the generally moderate
requirements of commercial and general process applications,
while TEMA Class B is for chemical process service.
Design pressures and temperatures for exchangers usually are
specified with a margin of safety beyond the conditions expectedin service. Design pressure is generally about 172 kPa (25
lbf/in2) greater than the maximum expected during operation or
at pump shutoff.
Design temperature is commonly 14C (25F) greater than the
maximum temperature in service.
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Tube Bundle Vibration
When plate baffled heat exchangers are designed for higher
flow rates and pressure drops , tube vibrations are found and
cause considerable damage to the equipment in service.
The most effective method of dealing with this problem is
the avoidance of cross flow by use of tube support baffles
which promote only longitudinal flow.
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Mechanism of Tube Vibration
Vortex SheddingThe vortex-shedding frequency ofthe fluid in cross-flow over thetubes may coincide with anatural frequency of the tubes
and excite large resonantvibration amplitudes.
FluidElastic CouplingFluid flowing over tubes causesthem to vibrate with a whirlingmotion. The mechanism of fluid-
elastic coupling occurs when acritical velocity is exceededand the vibration then becomesself-excited and grows inamplitude. This mechanismfrequently occurs in process heat
exchangers which suffervibration damage.
Pressure FluctuationsTurbulent pressure fluctuationswhich develop in the wake of acylinder or are carried to thecylinder from upstream may providea potential mechanism for tube
vibration. The tubes respond to theportion of the energy spectrum thatis close to their natural frequency.
Acoustic CouplingWhen the shell-side fluid is a low-density gas, acoustic resonance or
coupling develops when thestanding waves in the shell are inphase with vortex shedding from thetubes. The standing waves areperpendicular to the axis of thetubes and to the direction of cross-flow. Damage to the tubes is rare.However, the noise can be
extremely painful.
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Testing / Performance testing
Hydrostatic testing for emphasizing visual examination of tube
ends.
Leaking tubes.
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Internal-floating-head exchanger
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Constructional Details
FixedTube Sheet Heat Exchangers
Often used than any other type.
This construction requires tube sheet materials welded with
the shell. Any number of tube passes.
Shell side passes can be one to more. Shells with more than
two shell passes are very rare.
Clearance between baffles and shell.
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Expansion joints
Various types of expansion joints
are used to eliminate excessive
stresses caused by expansion. The
need for an expansion joint is afunction of both the amount of
differential expansion and the
cycling conditions to be expected
during operation.
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Tube Side Construction
Tube side header
The bonnet
Channel
Special high pressureclosures
Tube side passes
Tubes
Manufacturing tolerances
Tube joints
Rolled tube joints
Welded tube joints
Double tube sheet joints
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Shell side Construction
Shell sizes
Heat-exchanger shells are generally made from standard-
wall steel pipe in sizes up to 305-mm (12-in) diameter.
Shell Side arrangements One shell pass
Split flow
Double Split flow
Divided flow
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Pitch
It is the shortest distance between two adjacent tubes fora pattern.
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Design Approach
The design approach of a shell and tube heat exchanger for this
thesis work has been subdivided into two as follows :
Service design
Mechanical designService design involves
Calculation of heat duty
Estimation of U
LMTD Estimation of Total heat transfer area
Decide Exchanger layout
Mechanical design involves the design of individual components
of a STHE.
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Service Design
Calculation of Mass flow rates of flue gases:
From the data collected such as manometer reading ,
temperatures , cd , area and further using temperature
relations and chemical properties of flue gases(eg: Specific
heat) in Perrys CEHB ,
The mass flow rate for exhaust gases was found to be 3.729
kg/s
Heat duty of flue gas : 575.64kW
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Mass flow rate of titanium di oxide:
From the calculated heat duty the mass flow rate of the
titanium di oxide was found to be 1.64 kg/s.
To check the design feasibility :
The aim is to evaporate the water from the titanium di
oxide mixture hence increase the specific gravity from
1.64 to 1.75
Analytically it was estimated that 0.14467 liters of water is
to be evaporated from 1 liter of Ti02 to reach the aim.
Also the heat required to vaporize the water content was
around 351.12kW , which is way lower than the actual
heat duty of the flue gas(575.64) . Hence the design was
confirmed feasible.
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Log Mean Temperature Difference
LMTD= 156.33oC
Total number of tubes needed : From the above collected data , and selecting OD 12
BWG tubes and selecting one inch triangular pitch( from
TEMA hand book) , the total number of tubes required is
1503. The tube side heat transfer coefficient is 68.592 W/m2 K
The shell side heat transfer coefficient is 10.366 W/m2 K
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The overall heat transfer coefficient (Uo) = 8.65 Wm2K
Heat transfer area requires : 459.7m2
The length of tubes : 6.096m
Actual heat transfer area : 548.06m2
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Mechanical Design (MS)
Shell side
Diameter= 1.067 m
Design pressure =
1.05atm
Design Temperature =
97oC
Shell thickness = 5mm
Nozzle thickness = 5mm Nozzle diameter =
125mm
Segmental baffles
25% cut transverse
baffles are used
Spacing = 400mm
Thickness = 6mm
Tube side design
Thickness of tubes =
3.404mm
Tube length : 6.09mm
Tube sheet thickness =
11.04mm
Channel(CS) = 10.55mm
Channel cover= 2mm
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Designed Heat Exchanger Specifications
Shell Side Tube Side
Material : Mild Steel Service fluid : Ti02 pulp
Corrosion allowance : 2mm No. of passes : 1
Service fluid : Flue gas Outside diameter : 19.05mm
No. of passes : 1 Inside diameter : 15.64
Shell diameter : 1067mm Wall thickness : 3.404mm
Inlet temperature : 300oC Tube length : 6.096m
Outlet temperature : 160oC Pitch (equilateral triangle) : 76mm
Segmental baffles : 25 % cut Number of tubes : 1503
Shell thickness : 5mm Inlet temperature : 30oC
Nozzle diameter : 125mm Outlet temperature : 30oC
Nozzle thickness : 5mm Nozzle thickness : 5mm
Baffle spacing : 400mm
Thickness of baffles : 6mm
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Possible flaws associated with analytical
calculations
Due to the large effect from other parameters such as designpressure/corrosion allowance, baffle cuts, seal strips, and soon, tube counts , tube passes etc. are to be used as estimatesonly. Exact tube counts are part of the design package of most
reputable exchanger design software and are normally used forthe final design.
Some of the prominent STHE design softwares are
Aspen One (Aspen Engineering Suite)
Aspen HYSYS/HTFS/HTFS+ (Aspen Engineering Suite),used mostly in Petrochemical Industries.
Chemcad 6/CC-Therm from Chemstations Inc.
Comsol multi-physics from Comsol Inc.
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ChemCad 6 / CC Therm Interface
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Chemcad CC-Therm Design Window
Flow sheet Heat Curve
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Proposed Block Diagrams For New
Concentration Unit
RotaryCalciner
Secondary blower
Primary blower
Combustion Chamber
Atomizing Blower
Concen
trator
Flue gas in
Flue gas out
TiO2 In
TiO2 Out
Cooling Tower
Electro Static Precipitator
Fume StackDraught Fan
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Proposed Block Diagram of New Concentration
Unit
Overhead Tank
ShellandTubeHe
at
Exchanger
(Concentrator)
VaporSeparator
Concentration
Measuring
tank
Condenser
Flue Gas in
Flue Gas Out
Aqueous TiO2
Conc. TiO2
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What else to be calculated ?
Final design using Chemcad CC-therm including rating of
HE.
Cost of proposed concentrator(STHE).
Cost of replaced equipment in concentration process.
New layout area.
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REFERENCES
Perrys Chemical Engineers Handbook , 1999 , The McGraw
Hills Companies Inc.
Standards of The Tubular Exchanger Manufacturers
Association , 1999 , ninth edition.
Design and Rating of Shell and Tube Heat Exchangers using
Chemcad , John Edwards , MNL 032A Issued 29 August 08,
Prepared by J.E. Edwards of P & I Design Ltd, Teesside, UK.
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THANK YOU
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