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APETT Engineering

Magazine December

2016

June 2016 Edition

December 2016

Edition

The Association of

Professional Engineers of

Trinidad and Tobago

APETT’s Mission:

The Association of

Professional Engi-

neers of Trinidad and

Tobago is a learned

society of profession-

al engineers dedicat-

ed to the develop-

ment of engineers

and the engineering

profession. The asso-

ciation promotes the

highest standards of

professional practice

and stimulates

awareness of tech-

nology and the role

of the engineer in

society.

ISSUE 2

December 2016 Edition

APETT Engineering Magazine December 2016

TABLE OF CONTENTS

Chemical Engineering: Importance of selecting the right Specific Gravity for Page 10

Differential Pressure Level Transmitters

By: Eng. Dillon Nancoo

Leadership: Leadership in the Workplace Page 6

By: Eng. Imtiaz Easahak

Mechanical Engineering: The Battle against Corrosion Under Insulation (CUI) Page 16

By: Eng. Amanda Hunte-Balgobin and Eng. Donald Ramdass

Mechanical Engineering: The Art of Bolt Torquing Page 18

By: Eng. Faheema Baksh

Electrical Engineering/Chemical Engineering: Multiple Model Page 21

Predictive Control Bridging the Information Gap to Regulate

Highly Non-Linear Processes Part II: Controlling a CSTR

By: Eng. Dr. Brian Aufderheide, Eng. Adrian Lutchman and Eng. Makeda Wilkes

Civil Engineering: Short Slabs Technology for Concrete Pavements Page 26

By: Eng. Avaleen Mooloo

Civil Engineering: The New Procurement Legislation: Implications of Major Page 29

Shifts from the Past

By: Eng. Winston Riley

DISCLAIMER: Statements made and information presented by contributors to this Magazine do not necessarily reflect the

views of APETT, and no responsibility can be assumed for them by APETT or its Executive Members and Editors.

Chemical Engineering: Amine System Foaming in the Natural Gas Processing Page 13

Industry

By: Eng. Terry Mungal

Editor’s Message

Eng. Julio Bissessar

Eng. Julio Bissessar is currently

a Graduate Trainee Process

Engineer at Atlantic LNG. Julio

has over one and a half years-

work experience between

Atlantic LNG and Petrotrin. He

holds a Masters of Engineering

(M.Eng) in Process Engineering

from the University of Trinidad

and Tobago (UTT) and has

topped his year in Engineering.

Julio has also participated in a

number of engineering related

competitions. These include

winning with his group (Eng.

Laura Lewis and Eng. Shameal

Ali) the BP's Ultimate Field Trip

(UFT) International Engineering

Competition of 2014 , winning

a special prize for the senior category of the NIHERST's

Prime Minister's Awards for

Scientific Ingenuity of 2015 and

a runner up for the IET's Pre-

sent Around The World

(PATW) Engineering Competi-

tion of 2014/2015. Julio has also

won the best design project at

the Bachelor's level (2013) and

the M.Eng level (2015) at UTT.

He has also presented at the

Oil and Gas Technical Confer-

ence of Trinidad and Tobago

2014.

Merry Christmas 2016 and have a Bright and Prosperous New Year 2017!

Cheers!

Season’s greetings and welcome to the

second edition of APETT’s Engineering

Magazine, December 2016 Edition. This is

APETT’s first year publishing the bi-annual

Engineering Magazine, which incorporates

articles from all Engineering Disciplines.

We are all aware of the current econom-

ic situation that we as well as many other

countries face. Given that the energy sec-

tor contributes largely towards Trinidad

and Tobago’s GDP, we evidently suffer a

great deal as a result of lower oil and gas

prices. Eng. Imtiaz Easahak discusses lead-

ership in the workplace and Kotter’s eight

-step approach to leading change, quite

applicable and appropriate given today’s

economy.

Process Engineer Dillon Nancoo goes on

to discuss the importance of effective lev-

el measurement and explains how specific

gravity of a fluid impacts level readings.

Process Engineer Terry Mungal discusses

the causes of foaming in absorption col-

umns, and identifies what can be done to

reduce the likelihood of this incident oc-

curring.

Eng. Amanda Hunte-Balgobin and Eng.

Donald Ramdass collaborated to share

with us the impact of Corrosion Under

Insulation (CUI) at processing facilities

and how this can certainly be a risk that

we need to look out for in our daily func-

tions as engineers. Eng. Faheema Baksh

also shared the importance of bolt

torqueing while reducing the buildup of

stresses. Great reads!

Under Electrical Engineering/ Process En-

gineering, we have the second part of the

multiple model predictive control article

written by Eng. Dr. Brian Aufderheide,

Eng. Adrian Lutchman and Eng. Makeda

Wilkes. This article continues along the

lines of the first, going in depth with utiliz-

ing this advanced controls technique on a

Continuous Stirred Tank Reactor (CSTR).

Our civil engineers, Eng. Avaleen Mooloo

and Eng. Winston Riley wrap up our engi-

neering magazine for this year. Eng. Avaleen

Mooloo discusses the economic benefits of

utilizing concrete roads and pavements

while Eng. Winston Riley discusses the new

procurement legislation when compared to

the past.

Finally, I would like to thank each and every

one of our Readers for your continued sup-

port; I hope you enjoyed it as much as I did

compiling it. I would like to extend special

thanks to those who contributed articles

during 2016 and would also like to recog-

nize Eng. Anna Warner (Chemical Division

Chair), Eng. Suzette Baptiste (Public Rela-

tions Officer), Eng. Farah Hyatali (Chemical

Division Treasurer) for their assistance in

sourcing articles as well as editing, and our

tech savvy Eng. Jonathan Chang

(Webmaster). I do wish each and every one

of you and your families a very Merry

Christmas 2016 and a bright and prosper-

ous New Year 2017. Cheers!

APETT graciously welcomes its regular

readers as well as its new readers. To con-

tribute in discussions, join our LinkedIn

group or keep updated with activities by

visiting our website at www.apett.org. Engi-

neers across all Disciplines, both within the

Industry and Academia, are invited to con-

tribute to our Magazine. To submit articles

or for further queries, please contact us at:

[email protected] or chemical-

[email protected]

Message from APETT’s President

Eng. Fazir Khan

Eng. Fazir Khan is a Registered

Engineer with the Board of

Engineering of Trinidad and

Tobago (BOETT) and has

been a member of the Associ-

ation of Professional Engineers

of Trinidad and Tobago since

1991. He is also a member of

the British Hydrological Socie-

ty (ICE). He has worked at

Alpha Engineering and Design,

a registered professional con-

sulting engineering and project

management firm for the last

25 years and is now the Man-

aging Director. Fazir has also

served on the Board of Direc-

tors of Trinidad Contractors

Limited for the last five years.

Eng. Khan has over 30 years of experience as a practicing

professional Civil Engineer and

Project Manager, working

throughout the Caribbean.

Fazir graduated from The

University of the West Indies

(UWI), Trinidad with a BSc.

(Hons) in Civil Engineering

and has a diploma in Manage-

ment from the Henley Univer-

sity (UK). He has previously

held positions in APETT as

Assistant Secretary, Vice Pres-

ident Strategy and President-

Elect.

Dear APETT Members,

First I want to congratulate and thank Eng. Julio Bissessar, Eng. Anna Warner and the

rest of the new editorial committee for their perseverance in making this bi-annual

APETT Engineering Magazine a success. To see contributions from all our Divisions is

heartening.

I can also report that we have completely switched over from our old website provider

to a much better state of the art platform that is internally managed at a lower cost.

For that we are grateful to the IT Committee, headed by Eng Roger Chan Soo (APETT

Vice President), Jonathan Chang and Jason Gordon. You are therefore encouraged to

go to our Website and look at the new content and features. One of the things that

you will see is our formalized advertising policy (Ref: http://www.apett.org/home/

images/slideshow1/APETT-Advertising-Policy-Document-161018.pdf). This effort was

spearheaded by our very hard working PRO Eng. Suzette Baptiste with input from the

rest of the 2016/2017 Council. Again we encourage feedback and participation from

you our membership.

The end of the year is usually also a time for reflection. I urge us all to do some intro-

spection, both as the APETT organization and as individual engineers. It is especially

critical for us engineers to recognize the economic challenges that we face as a country

concomitant with the need to diversify our economy and increase our efficiency and

effectiveness in all facets of our involvement in society. We are reminded on page one

of this magazine that this is actually our mission. Are our academics changing the cur-

ricula to keep pace with the changing needs of industry? Are our engineering students

also understanding the need to embrace entrepreneurial spirit in times of little job op-

portunities? Can our engineers in private enterprise take on board the need to partner

with UWI and UTT to carry out relevant research and development and to invest in

young engineers, through employment, even in these lean times? I am talking about

financial commitment here. With dismal forecasts for oil and gas prices and produc-

tion rates, we have to seek out what gives us as a country new or enhanced competi-

tive advantage through the discipline of engineering.

Apart from the above there is need for us to set an example to the rest of the country

with respect to our ethical conduct. We can do very little about high labor costs or

government bureaucracy. But we certainly can conduct ourselves and our business in

an ethical manner that is one of the cornerstones of our profession. This is why it is

important for all of us to read Eng. Riley’s Article on page 29 that addresses the enact-

ment of the procurement legislation bill. As a country we can no longer afford the

wastage and pilferage that is par for the course.

As engineers we have a duty to use our education, training and intellect to innovate,

influence where possible, while acting in the best interest of the public and the country.

Seasons Greetings and best wishes to you your families for the new year.

Fazir Khan

http://www.apett.org/home/images/slideshow1/APETT-Advertising-Policy-Document-161018.pdf

http://www.apett.org/home/images/slideshow1/APETT-Advertising-Policy-Document-161018.pdf


Leadership in the Workplace

By Imtiaz Easahak, Eng. BSc., M.Sc. MBA, REng., MAPETT

Kotter’s eight-step approach to leading change

Trinidad and Tobago has been impacted by Gas shortfall as well as low oil prices over the past couple years. Our ability

to respond to these economic changes depend to a large extent on our willingness to change our approach to work in

order to improve efficiency and productivity. Organizational change has been a much studied topic and many manage-

ment articles can be found on it. The following is a step-wise approach that was proposed by leadership and change

management guru, John Kotter- a professor at Harvard Business School and world-renowned change expert, Kotter

introduced his eight-step change process in his 1995 book, "Leading Change."

Step One: Create Urgency

For change to happen, it helps if the whole company re-

ally wants it. Develop a sense of urgency around the

need for change. This may help you spark the initial moti-

vation to get things moving.

This isn't simply a matter of showing people poor sales

statistics or talking about increased competition. Open

an honest and convincing dialogue about what's happen-

ing in the marketplace and with your competition. If

many people start talking about the change you propose,

the urgency can build and feed on itself.

What you can do:

Identify potential threats, and develop scenarios

showing what could happen in the future.

Examine opportunities that should be, or could be,

exploited.

Start honest discussions, and give dynamic and con-

vincing reasons to get people talking and thinking.

Request support from customers, outside stakehold-

ers and industry people to strengthen your argument.

Step Two: Form a Powerful Coalition

Convince people that change is necessary. This often

takes strong leadership and visible support from key peo-

ple within your organization. Managing change isn't

enough - you have to lead it.

You can find effective change leaders throughout your

organization - they don't necessarily follow the tradition-

al company hierarchy. To lead change, you need to bring

together a coalition, or team, of influential people whose

power comes from a variety of sources, including job

title, status, expertise, and political importance.

Once formed, your "change coalition" needs to work as a

team, continuing to build urgency and momentum around

the need for change.

What you can do:

Identify the true leaders in your organization.

Ask for an emotional commitment from these key

people.

Work on team building within your change coalition.

Check your team for weak areas, and ensure that you

have a good mix of people from different departments and

different levels within your company.

Step Three: Create a Vision for Change

When you first start thinking about change, there will

probably be many great ideas and solutions floating

around. Link these concepts to an overall vision that peo-

ple can grasp easily and remember.

A clear vision can help everyone understand why you're

asking them to do something. When people see for them-

selves what you're trying to achieve, then the directives

they're given tend to make more sense.

What you can do:

Determine the values that are central to the change.

Develop a short summary (one or two sentences)

that captures what you "see" as the future of your organ-

ization.

Create a strategy to execute that vision.

Ensure that your change coalition can describe the

vision in five minutes or less.

Practice your "vision speech" often.

Step Four: Communicate the Vision

What you do with your vision after you create it will

determine your success. Your message will probably

have strong competition from other day-to-day commu-

nications within the company, so you need to communi-

cate it frequently and powerfully, and embed it within

everything that you do.

Don't just call special meetings to communicate your

vision. Instead, talk about it every chance you get. Use

the vision daily to make decisions and solve problems.

When you keep it fresh on everyone's minds, they'll re-

member it and respond to it.

It's also important to "walk the talk." What you do is far

more important - and believable - than what you say.

Demonstrate the kind of behavior that you want from

others.

What you can do:

Talk often about your change vision.

Openly and honestly address peoples' concerns and

anxieties.

Apply your vision to all aspects of operations - from

training to performance reviews. Tie everything back to

the vision.

Lead by example.

Step Five: Remove Obstacles

If you follow these steps and reach this point in the

change process, you've been talking about your vision and

building buy-in from all levels of the organization. Hopeful-

ly, your staff wants to get busy and achieve the benefits

that you've been promoting.

But is anyone resisting the change? And are there process-

es or structures that are getting in its way?

Put in place the structure for change, and continually

check for barriers to it. Removing obstacles can empower

the people you need to execute your vision, and it can

help the change move forward.

What you can do:

Identify, or hire, change leaders whose main roles are

to deliver the change.

Look at your organizational structure, job descrip-

tions, and performance and compensation systems to en-

sure they're in line with your vision.

Recognize and reward people for making change hap-

pen.

Identify people who are resisting the change, and help

them see what's needed.

Take action to quickly remove barriers (human or

otherwise).

Step Six: Create Short-term Wins

Nothing motivates more than success. Give your company

a taste of victory early in the change process. Within a

short time frame (this could be a month or a year, de-

pending on the type of change), you'll want to have results

that your staff can see. Without this, critics and negative

thinkers might hurt your progress.

Create short-term targets - not just one long-term goal.

You want each smaller target to be achievable, with little

room for failure. Your change team may have to work

very hard to come up with these targets, but each "win"

that you produce can further motivate the entire staff.

What you can do:

Look for sure-fire projects that you can implement

without help from any strong critics of the change.

Don't choose early targets that are expensive. You

want to be able to justify the investment in each project.

Thoroughly analyze the potential pros and cons of

your targets. If you don't succeed with an early goal, it can

hurt your entire change initiative.

Reward the people who help you meet the targets.


Eng. Imtiaz Easahak has over 19 years’ experience in the chemical

and gas processing industries. He has a B.Sc. Degree in Chemical

and Process Engineering, Masters in Production Management and an

MBA from Heriot- Watt University. He is currently the President-

Elect of APETT and a Registered Engineer (BOETT) in Trinidad and

Tobago. Prior to joining Atlantic, he worked at Nu Iron, Interna-

tional Steel Group, Cliffs and Associates Limited, IPSL and Mittal

Steel in Engineering and Managerial positions. Imtiaz joined Atlantic

LNG in 2007 and is currently functioning as the Process Engineering

Manager .

Step Seven: Build on the Change

Kotter argues that many change projects fail because

victory is declared too early. Real change runs deep.

Quick wins are only the beginning of what needs to be

done to achieve long-term change.

Launching one new product using a new system is great.

But if you can launch 10 products, that means the new

system is working. To reach that 10th success, you need

to keep looking for improvements.

Each success provides an opportunity to build on what

went right and identify what you can improve.

What you can do:

After every win, analyze what went right and what

needs improving.

Set goals to continue building on the momentum

you've achieved.

Learn about kaizen, the idea of continuous improve-

ment.

Keep ideas fresh by bringing in new change agents

and leaders for your change coalition.

Step Eight: Anchor the Changes in Corporate

Culture

Finally, to make any change stick, it should become part

of the core of your organization. Your corporate culture

often determines what gets done, so the values behind

your vision must show in day-to-day work.

Make continuous efforts to ensure that the change is

seen in every aspect of your organization. This will help

give that change a solid place in your organization's cul-

ture.

It's also important that your company's leaders continue

to support the change. This includes existing staff and new

leaders who are brought in. If you lose the support of

these people, you might end up back where you started.

What you can do:

Talk about progress every chance you get. Tell suc-

cess stories about the change process, and repeat other

stories that you hear.

Include the change ideals and values when hiring and

training new staff.

Publicly recognize key members of your original

change coalition, and make sure the rest of the staff - new

and old - remembers their contributions.

Create plans to replace key leaders of change as they

move on. This will help ensure that their legacy is not lost

or forgotten.

Key Points

You have to work hard to change an organization suc-

cessfully. When you plan carefully and build the proper

foundation, implementing change can be much easier, and

you'll improve the chances of success. If you're too impa-

tient, and if you expect too many results too soon, your

plans for change are more likely to fail.

Create a sense of urgency, recruit powerful change lead-

ers, build a vision and effectively communicate it, remove

obstacles, create quick wins, and build on your momen-

tum. If you do these things, you can help make the change

part of your organizational culture. That's when you can

declare a true victory. Then sit back and enjoy the change

that you envisioned so long ago.

By Dillon Nancoo, Eng. B.Sc. , AMIChemE “If the specific gravity of the process fluid in a vessel decreases the level observed on the differential

pressure transmitter will show a lower than it actually is and vice versa”

Importance of selecting the right

Specific Gravity for Differential

Pressure Level Transmitters


P1 = ρ x g x L1 0

P2 = ρ x g x L2 0

Effective level measurement in the Chemical Processing

Industry is critical to safe and efficient operation. There

have been many process safety incidents that have result-

ed from either malfunctions in vessel level measurement

or poor understanding of how these critical devices op-

erate. Two common examples include the overfilling of a

petrol tank at an the Buncefield Oil Transfer and Storage

Facility located at Hemel Hempstead, Hertfordshire, Eng-

land and the overfilling of a Raffinate splitter at the Brit-

ish Petroleum(BP), Texas City Oil Refinery.

At the Buncefield Depot the malfunction of level meas-

urement devices resulted in the overflow of an unleaded

petrol storage tank. The ensuing release of hydrocarbons

resulted in a major fire that lasted for five days, causing

significant environmental damage and injury to over forty

persons.

One of the root causes of the BP Texas City hinges on

the technical subject of this article. Overfilling of the raf-

finate splitter at the BP refinery occurred due to false

readings on the equipment level gauges as a result of a

change in the specific gravity of the liquid being invento-

ried into the process vessel. This incident resulted in the

death of 15 employees and injury to over 180 persons.

These incidents emphasize the importance of the reliabil-

ity and validity of the level readings being measured on

chemical storage vessels in chemical processing indus-

tries. Various technologies exist for the measurement of

liquids contained within process vessels. The most com-

mon technologies include Differential Pressure Transmit-

ters, Displacement Type Transmitters, Ultrasonic Trans-

mitters and Radar Type Transmitters. The focus of this

article is on the Differential Pressure type transmitters.

We shall focus firstly on how these types of transmitters

work followed by a case study which will aid in the un-

derstanding of the impact of the fluid specific gravity on

the measured vessel level.

Level transmitters operating on the philosophy of differen-

tial pressure typically measure the pressure at two distinct

points along the vertical axis of a vessel filled with the pro-

cess fluid. The difference in the pressure at these two

point is proportional to the height of fluid in the vessel.

Take for example the vessel shown in figure 1 below. At

reference point L1 and L2 the pressure of the fluid can be

estimated as follows:

The differential pressure between P1 and P2 is thus given

by

∆P = P2 - P1 = ρg(L2 - L1)

When differential pressure is measured in the units

mmH20 the equation becomes

∆P = sg x (L2 - L1)

Again looking at the figure above if the liquid level con-

tained in the vessel is at reference point L1 the differen-

tial pressure of the Lower Range Value is given by the

following relationship:

Pressure at Low Pressure Leg is the sum of the Pressure

due to liquid at L1 and the Pressure due to seal liquid in

the High pressure leg (L1 ρ D0 ρL).

Pressure at High Pressure Leg is equal to the Pressure

due to seal liquid in the High pressure leg (D+D0) x ρH).

The Lower Range Value is thus given by,

Rl = (L1 ρ D0 ρL) - [(D+D0) x ρH)]

If the liquid level is at reference point L2 the differential

pressure of the Upper Range Value is given by the fol-

lowing relationship:

Pressure at Low Pressure Leg is the sum of the pressure

due to liquid at L2 and Pressure due to seal liquid in the

High pressure leg (L2 ρ + D0 ρL). Pressure at High Pres-

sure Leg is equal to the Pressure due to seal liquid in the

High pressure leg (D+D0) x ρH). The Upper Range Value

is thus given by,

Ru =(L2 ρ + D0 ρL) - [(D+D0) x ρH)]

The range of the level Transmitter is thus equal to the

difference between the lower range value and the upper

range value. Given the range of the differential pressure

between the upper and lower reference points the level

at a point, L, between L1 and L2 is given by the following

relationship

L = 100% x DPL/( Ru - Rl)

Where DPL is the measured differential pressure at the

level L. Given this understanding a case study showing

the implications of the specific gravity of the operating

fluid in the above relationships.

Case Study:

The waste storage tank D-01, typically stores waste wa-

ter from the process plant. When the level in the tank is

high a vacuum truck is used to pump the liquid out of the

tank. The level transmitter, LI-01, on the tank is calibrat-

ed for the storage of water with a specific gravity of 0.99.

On 23rd March 2015 operators on the plant decided to

send hydrocarbon liquid to the waste water tank due to

some operational constraints. The on field operator lined

up the process valves to allow the hydrocarbon liquid to

be sent to the storage tank. The operations control

room was informed so that they could monitor the level

and let the field operator know when to stop the liquid

flow to D-01. At 2110hrs the control room operator

was informed that there was an overflow of hydrocarbon

liquids from the tank D01. On review of the level trans-

mitter he observed that the level was relatively constant

at 75%. A sample of the contents of the tank revealed

that the specific gravity of the liquid was 0.74.

The change in the specific gravity of the liquid will affect

the differential pressure being observed on the level

transmitter. As a rule of thumb if the specific gravity of

the process fluid in a vessel decreases the level observed

on the differential pressure transmitter will show a lower

than it actually is and vice versa.

The importance of choosing the correct specific gravity

for calibration of the differential pressure transmitter as

well as choosing the correct method of liquid level de-

tection cannot be exaggerated enough. False readings can

have severe implication on both the process, equipment

and the environment.

Typically the instrument tubing connecting the upper tap

to the lower tap of the Transmitter L-01 is filled with a

seal fluid which can be the process fluid or a seal liquid

e.g. glycol. The lower impulse tubing shall be referred to

as the low pressure leg while the upper tubing shall be

referred to as the high pressure leg. The upper and low-

er tubing may contain different seal fluids or may be the

same fluid type.

Higher levels can influence carryover creating operation-

al issues with process units and increasing operating

costs due to loss of raw material. Lower levels can im-

pact operation of process pumps and lead to loss of liq-

uid seals at the base of knock out drums.

Based on the calibration range for the transmitter the

range calculated using the process fluid as water (s.g.

0.99) is 0 to 52.37kPa. Any liquid level between the two

level transmitter tapping points L1 and L2 will produce a

differential pressure in the range 0 to 52.37kPa the same

range a mentioned previously. However changing the

fluid specific gravity will impact the differential pressure

value and hence the range of the transmitter. The table

below shows how the range varies as the specific gravity

of the process fluid is changed.

It can be observed from the table above that as the specific gravity of the measured fluid decreases, should the trans-

mitter calibration remain unchanged the level in the tank will show a level lower than the actual fluid level. This phe-

nomenon is particularly important when process safety risk exists with having a high level in a storage vessel. In the

example mentioned above the fluid’s specific gravity changed from approximately 0.99 to 0.74. This change in specific

gravity resulted in a shrinkage of the differential pressure measured across the range of the transmitter. As a result

when the physical level in the tank level rose to 100% the displayed level on the Transmitter LI-01 was 75%. As a re-

sult of this discrepancy the alarm high level alarm on tank D-01 did not sound to indicate to the operations personnel

that the level was increasing. It was only when the on field operator noticed that liquid was overflowing from the tank

into a bunded area around the tank that the operation of pump fluid to the waste was halted.

Incidents such as the one mentioned in the example above as well as the numerous process safety incidents highlight

the importance of the accuracy of level instrumentation and why proper selection is key. Despite the issue mentioned

above differential pressure level measurement is undoubtedly one of the most reliable and accurate forms of level indi-

cation. However for services where varying degrees of specific gravity is expected for the liquid being measured, alter-

native methods should be considered. Magnetic or float type devices have been used as a magnetic float contained in a

chamber will move as the fluid level rises and decreases. This type of gauge works well in a clean service but can prove

a nightmare for process operators when in a dirty service. Impurities from the process tend to accumulate along the

walls of the chamber and cause the float to become lodged, resulting in improper readings. Guided wave technology

(GWR) is becoming increasing popular as this technology boasts its ability to be unaffected by changes in the process

conditions including fluid specific gravity.

GWR is based on the principle of time domain reflectometry (TDR). With TDR, a low-energy electromagnetic pulse is

guided along a probe. When the pulse reaches the surface of the medium being measured, the pulse energy is reflected

up the probe to circuitry that then calculates the fluid level based on the time difference between the pulse being sent

and the reflected pulse received. Use of this technology will obviously come at an additional cost. However the cost to

people, environment and assets far outweighs the cost for having proper level instrumentation for the correct applica-

tion.

Using the correct method of liquid level determination will undoubtedly reduce the risk of a process safety incident

from occurring and make for a more stable process operation. Understanding the limitations of certain type of trans-

mitters when performing selection for specific applications is critical for successful plant operation. Despite the engi-

neer selecting the best transmitter for a particular application the on field users of the technology must be made aware

of their limitations to prevent a significant process safety incident.

Table 1: Variation in Transmitter Level Reading with changes in

Specific Gravity

Fluid S.G. Transmitter Range (kPa) Level observed when liquid is at upper tapping point (%)

0.999 52.37 100.0%

0.9 47.18 90.1%

0.7 36.69 70.1%

0.5 26.21 50.1%

0.3 15.73 30.0%


Eng. Dillon Nancoo Graduated from the University of the West Indies with a Bachelor of

Science Degree in Chemical and Process Engineering in 2009 and is currently pursuing a

Master’s in Business Administration at the School of Business and Computer Science. He

is currently employed at Atlantic LNG Company of Trinidad and Tobago as a Process Op-

timization Engineer for the last six years, and is an Associate member of the Institution of

Chemical Engineers (IChemE) .


Amine System Foaming in the Natural

Gas Processing Industry

By Terry Mungal, Eng., B.Sc. Chemical Engineering

In the natural gas processing industry amines are used to

remove acidic gases such as CO2 and H2S from the inlet

feed (natural gas) before the gas is further processed. A

persistent operational problem in the gas sweetening

industry is amine system foaming. Foaming has contribut-

ed to high capital/production losses annually in the indus-

try and as a result increased operating expenditure and

reduced process efficiency.

Foam is the result of a mechanical incorporation of a gas

into a liquid where the liquid surrounds a volume of gas

creating a bubble. The free liquid captured between the

gas bubbles begins to drain as the bubbles rise past the

bulk gas/liquid interface. The free liquid will drain from

around the gas bubble until the gas pressure inside the

gas bubble is greater than the liquid wall’s surface. If bub-

bles are being formed at a quicker rate than the existing

ones are breaking they will accumulate as foam.

Characteristics needed to present a foam concern are:

Foaming tendency – the ease at which a solution

forms a foam bubble

Foam stability – foam resistance to break into con-

tinuous liquid phase

Surface tension is an indication of foaming tendency. The

lower the surface tension the more susceptible the solu-

tion is to foam (for e.g. liquid hydrocarbons have a low

surface tension and tend to foam).

The formation and stability of the bubble depends on

physical conditions and surface characteristics. Stabilized

foams are the result of contaminants that promote the

formation of a gelatinous layer, increase the surface vis-

cosity and inhibit drainage.

Contaminants in Amine System

Contaminants that cause amine system foaming originates

primarily from three (3) sources: make-up water, feed gas

and generated contaminants formed by the reactions of

amine and contaminants.

Below is a list of the typical contaminants that promote

amine system foaming:

Liquid hydrocarbons - They are soluble in aqueous amine

solution and therefore reduces its surface tension.

Water soluble surfactants – corrosion inhibitors, well treat-

ing compounds, antifoams

Solid particulates – iron sulphide (formed by reaction be-

tween H2S in feed gas and carbon steel piping)

Amine degradation products – BHEEU and BHEETU (bis

hydroxyethyl ethoxy urea and bis hydroxyethyl ethoxy

thiourea). Formed by reaction between Diglycolamine and

CO2/COS.

Heat Stable Salts (HSS) – If impure make-up water is used

contaminants such as sodium, potassium, calcium, magne-

sium, chloride, sulfate and bicarbonate ions can react with

the amine cation forming heat stable salts.

Antifoam agent – Excessive addition can aggravate foaming

issue.

Foaming is usually the first sign of contamination issues in

the amine system which can occur with a small concentra-

tion of heavy hydrocarbons, solid particulates or injection

chemicals. Frequently, foaming occurs not as a result of

one single contaminant in the system but multiple.

Symptoms of Amine System Foaming

The following are typical symptoms to indicate foaming in

the amine system.

Sudden increase in column differential pressure (DP)

High solution carryover to downstream equipment

Erratic/drastic drop in liquid levels

Sharp increase in flash gas flow

Abnormal column temperature profile (higher tem-

peratures on the higher trays)

Off-specification unit results (high acid gas loadings

and low CO2 removal efficiency)

Antifoams

Typically, the first response to a foaming episode is the

addition of an antifoaming agent to the system. Antifoam

addition should only be seen as a temporary measure and

not a permanent or long term fix.

Antifoams are intended to facilitate gas and liquid disen-

gagement by weakening the cell structure of the bubbles.

While this may bring the foaming event under control and

reduce the severity of foaming it does not eliminate it.

The foam inducing contaminants are still present in the

recirculating amine system. Over time addition of anti-

foam can appear to become less effective. This is because

antifoams are surface active and are therefore removed by

the activated carbon bed. Also when antifoam droplets

coalesce into larger droplets they are incorporated into

the foaming structure less efficiently; hence, less effective

in breaking the foam. Antifoams are also known to be-

come inactive when they agglomerate with suspended

solids.

In order to reduce foaming events focus should be placed

on removing the contaminants from the system. Technol-

ogies have been developed by different companies to re-

move contaminants. One such technology is as ‘Sigma

Pure’ by MPR Services Inc. This involves using a slip stream

from the recirculating amine stream and sending it

through a foaming column where the amine is made to

foam. The foam is then separated from the solution and

the contaminants that caused or promoted the foaming

are also removed.

Trouble Shooting Guide / Recommendations for

Amine System Foaming

The following are recommendations to assist in reducing

amine system foaming caused by typical contaminants:

Reclaimer Operation: Ensuring the reclaimer is in service

could prevent amine degradation and decomposition

products such as BHEEU and BHEETU and also Heat Sta-

ble Salts from accumulating in the amine system. The reac-

tions between amine and CO2 and COS are reversible at

temperatures of 171.1 to 182.2 degC. HSS will be re-

moved when the reclaimer comes offline for cleaning

Mechanical and Carbon Filtration in Circulating Slip

Stream: Approximately 10-12% of the recirculating amine

stream should be flowed through a slip stream with me-

chanical filters. Iron sulphide particles will be removed

from the amine solution by mechanical filtration. Antifoam

and other dissolved organics would be removed by the

activated carbon bed. Ensure mechanical filter and activat-

ed carbon bed are replaced when decline in performance

is observed.

Inlet Separation: If hydrocarbon carryover is suspected as

the cause of foaming check vessel for any mechanical dam-

age (such as demister failure).

Flash Tank Operation: If hydrocarbons are suspected to

be the cause of foaming the tanks should be operated at

minimum pressure to flash out excessive hydrocarbon and

skim off this layer. A schedule should be developed to

skim the Flash tank and also Reflux Drum to remove as

much hydrocarbons from the system to prevent accumu-

lation.

Lean Amine/Feed Gas Approach Temperature: If hydro-

carbons are suspected to be the cause of foaming in the

Absorber ensure the lean amine temperature entering the

top of the tower is 5.6 to 8.3 degC higher than the inlet

feed gas to prevent hydrocarbon condensation. If the ap-

proach temperature is less than 5.6 degC increase lean

amine temperature to reduce the hydrocarbon condensa-

tion potential.

Analytical Testing of Amine: Samples of the plant’s amine

concentration and acid gas loadings (rich and lean) should

be taken daily along with monitoring of process conditions

to determine if operating parameters are within the speci-

fied ranges and threshold values. Samples of lean amine

should be sent to amine supplier every 3 months to per-

form a comprehensive analysis to determine the health of

the plant’s amine solution.

Amine System Foaming will continue to be a major opera-

tional problem until the respective amine system is care-

fully analyzed due to the many different causes of foaming.

Permanent measures should be pursued such as contami-

nant removal and/or detection rather than dependence on

temporary control measures (use of antifoam agents) to

reduce the instances of foaming.

Eng. Terry Mungal, Process Engi-

neer 1 (Atlantic LNG) graduated

from UWI St. Agustine with a BSc.

in Chemical and Process Engineer-

ing in 2009. He has been working

at Atlantic as a Process Engineer

for the past 6 years. Eng. Mungal

currently is attached to the Pro-

cess Optimization Team.


By Amanda Hunte-Balgobin, Eng., REng, B.Sc., MSc. and

Donald Ramdass, Eng., REng, BSc.

The Battle against Corrosion Under

Insulation (CUI)

This process led to a greater understanding of the design, operation, constructability and maintenance data relevant

to CUI. It involved the revalidation of the Risk Based Inspection (RBI) Model, bearing in mind the importance of accu-

rate and up-to-date process safety information in the identification of risk to the facility. The assessment sought to

identify all credible damage mechanisms across the facility and validate current operating conditions that would have

varied from what was previously recorded in the Inspection and Corrosion database. Lines that were labeled as un-

insulated were found to be insulated on-site, and missing or inaccurate process design data were updated.

Insulation removal, inspection and repair

A temperature range of 30oC - 120oC was utilized for prioritization of CUI inspections, based on typical corrosion

rates within the standard CUI criteria, and all locations of concern were investigated. The total number of locations

inspected almost doubled by the end of the project underlining the extensive scope that was covered by the project

team. The field interventions included insulation removal/repairs and design/fabrication/installation of perforated alu-

minum cages which were executed by a local Fabric Maintenance contractor. Figure 1 shows one of the areas of sig-

nificant corrosion inspected and subsequently repaired.

Review, selection and execution of Advanced Non-Destructive Examination (NDE) Techniques for de-

tection of CUI Research was conducted across the industry on each of the techniques focusing on the advantages and disadvantages

for application at the facility. Long Range Ultrasonics (LRUT) was selected for extensive runs of piping, and Short

Range Ultrasonics (SRUT) for support locations. Considering that these techniques were not available locally, the

service was awarded to a reputable international inspection agency. This was the first time in the company’s history

that such advanced techniques were utilized for CUI Inspection.

Evaluation and use of alternative methods to insulation for Personnel Protection –

One of the major successes of the project was the elimination of risk for quite a few areas across the facility. Mineral

wool was used as the insulating material for Personal Protection (PP). It is now recognized that this material increases

the risk of CUI since it retains water and can leach salts that contribute to coating breakdown and accelerate corro-

sion. The replacement of PP insulation with cages will not only extend the coating life and reduce the preparation

cost for inspection in the future, but also eliminates the risk of CUI since without insulation there can be no CUI.

The Acoustic Insulation specification was also revised preventing direct contact with the pipe, thus reducing the risk

of CUI.

Figure 1 Corrosion Under Insulation

Corrosion is a natural process; it is the gradual degradation of materials (usually

metals) by chemical reaction with their environment. With Corrosion Under

Insulation (CUI) the insulation that surrounds the steel creates a closed system

trapping water which leads to accelerated corrosion. CUI has been described as

the silent killer in many industries due to its unpredictable and disguised nature.

If not highlighted as a threat to a facility, it can go undisturbed for many years

and could lead to significant Process Safety incidents.

In order to mitigate the risk of CUI, several initiatives were undertaken by the

company including:

Review of the Corrosion Model (Corrosion Threat Assessment)

and validation of the operating conditions

Figure 2 Results of Inspection Findings

The inspection findings are shown in the chart displayed and have been categorized as:

Significant required immediate attention (repairs / replacement).

Gross required a wrap or most cases re-coating.

Moderate required re-coating.

Good no further work needed before re-insulation.

The findings highlighted the fact that over 50% of the insulated piping had

experienced coating failure as a minimum. Coatings generally provide

adequate protection up to 10-15 years once the surface preparation and

application were properly done according to the manufacturer’s recom-

mendation. These statistics are in line with this rule of thumb and high-

lights the need for further insulation removal, inspection and recoating of

all assets within this age range.

Another major facet in the battle against CUI was the need to raise awareness of the CUI risk to the facility among the

wider employee base. The annual Process Safety Week events, which are aimed at sensitizing all employees on the im-

portance of process safety and asset integrity, facilitated informative sessions on the issue. Various interactive presenta-

tions were conducted with Maintenance, Operations, Engineering and contractors which served to educate persons about

the severity of CUI and which encouraged them to assume greater accountability in the prevention and mitigation of CUI.

Their support was also solicited in strengthening their efforts in protecting insulation jacketing, reporting damaged insula-

tion and informing the Inspection and Corrosion Management Team when actual operating conditions may differ from

design. Turnaround safety stand-downs were also used as another opportunity to engage contractors on the cause and

effect of CUI, and to encourage them to support the CUI efforts on the frontline.

This project highlighted the challenges related to the inspection of all areas affected by CUI, as full insulation removal is

impractical and very costly. This project has also created sustainable value as it has facilitated the updates to the RBI and

Corrosion Model, deepened the company’s understanding of vulnerable locations on other Trains and allowed for re-

design in an effort to eliminate CUI in the future. It has shown, most importantly, that CUI, if left unchecked can have a

significant impact on the facility, compromising the safety and reliability of its operations.

Eng. Donald Ramdass has served the Oil and Gas industry for

the past twelve (12) years. Graduating with a B.Sc. in Mechanical

Engineering, he has worked in the construction, exploration/

production and refining sectors of the industry. He currently

works in the LNG sector and holds the position of Inspection

Engineer at Atlantic for the past six (6) years.

Eng. Amanda Hunte-Balgobin has served the Oil and Gas indus-

try for the last eight (8) years. Graduating with a B.Sc. in Chemical

and Process Engineering, she made a shift in her career and has

served as Corrosion Engineer at Atlantic for the past five (5) years.

Throughout that time she has attained her M.Sc. Engineering Manage-

ment (Distinction) and is currently working on the final thesis for her M.Sc. in Corrosion Control Engineering, with Manchester University,

England.

The Art of Bolt Torqueing

By Faheema Baksh, Eng., B.Sc. Mechanical Engineering, MASME

Figure 1. Types of stresses associated with bolts.


Overview

Threaded fasteners are by far the most commonly used joints in mechanics. They are used in a wide range of applica-

tions from household appliances, to cars, and even children’s toys. In the industry, nuts and bolts are simple mechanical

devices which work together to provide the clamping force that will hold two parts together, whether those parts are

steel beams or sections of a pipeline. Typically, poorly bolted joints can lead to leaks and high vibration. Among the pos-

sible causes of failure for bolted assemblies, the most frequent is poor assembly. This is where bolt torqueing or ten-

sioning come into play and will be discussed further in this article.

What is the Clamping Force? \

When a bolt is tightened, tension is created in the bolt

which stretches the bolt (similar to a spring). Provided

the bolt is not stretched beyond the elastic limit of the

bolt material, it will want to return to its original size

and length. This tension acts as the clamping force. Ten-

sion combined with friction between the bolt and the

nut is what prevents the bolt from loosening. It also

ensures the rigidity of the whole assembly (that is, mini-

mizes vibration), prevents leakage at seals, avoids shear

stresses on the bolts, and reduces the influence of dy-

namic loads on the fatigue life of the bolts. Therefore it

is important to achieve the desired tension for bolted

joints.

Effects of Overtightening

Within the elastic limit, a metal part such as a bolt follows Hooke’s law, i.e. the strain is proportional to the stress

(load). The stress in the bolt never exceeds the elastic limit or yield point. Otherwise, this can lead to bolt failure.

What is Bolt Torque? Torque is one of the most common methods of installing bolts, where the objective is to stretch the bolt to a predeter-

mined load. The stretching is accomplished by turning the nut, which pulls the bolt due to the angle of the threads.

There are standard torque values for specific bolt sizes and grades. With the use of a calibrated torque wrench, these

standard torque values can be obtained.

Figure 2. Tensile Stress-Strain Diagram with respect to Bolts.

Table 1: Tensioning and Torqueing Main Attributes.

It is important to note that torque does not equate to tension, but rather the torque reading is an indirect indication of

the desired tension. During torqueing, input energy is lost overcoming the mating friction under the head, nut, and

mating threads. Only a portion of input energy is converted into bolt stretch. Standard torque values are based on the

following formula:

T = Torque (ft-lbs) D = Nominal Diameter (inches)

P = Desired Clamp Load Tension (lbs) K = Torque Coefficient also known as the “Nut Factor” (dimensionless)

The nut factor can be thought of as anything that increases or decreases the friction within the threads of the nut. This

takes into account the geometry of the threads, the thread friction factor between the bolt and nut, and also the un-

derhead friction factor between the nut face and the surface it rolls over. There is no standard value for K. Further-

more, no two bolts respond exactly the same to a given torque. There are numerous real-world complications, for

instance: dirt/rust/debris on the threads, damaged threads, hole misalignment, etc. Many factors can decrease the

amount of energy that actually converts to bolt stretch. To counter this, the bolts and nut must be properly lubricated.

Lubrication reduces the friction during tightening resulting in more energy conversion of torque to bolt stretch. Lubri-

cant should be applied to both the nut surface and the bolt threads.

Torqueing vs. Tensioning Tensioning is another method of tightening bolts, the objective of which is to stretch the bolt to a predetermined load

by using force to elongate the bolt. This is accomplished using hydraulics. The nut can then be seated manually using a

wrench.

Conclusion In conclusion, bolts have a wide range of applications, both in the house hold and in the industry. When a bolt is tight-

ened, it acts like a spring and elongates. The tension created acts as the clamping force holding the bolted pieces to-

gether. Tension combined with friction prevents the bolt from loosening, thus preventing leaks and ensuring the rigidity

of the assembly. Therefore for any bolted assembly, there is a minimum desired bolt tension. However, care must be

taken not to overtighten a bolt either, since overtightening can also result in bolt failure if the material’s yield point is

exceeded.

Bolt torqueing is a common method for tightening bolts. With standard torque values and torque tables, it is very sim-

ple to use and implement. Its main downfall, however, is that the torque values are calculated using a nut factor, K,

which in reality can be affected by a host of things including rust, damaged threads, and hole alignment. As such, torque

is not necessarily a direct representation of the desired tension in the bolt. Conversely, there is also bolt tensioning

which is more accurate, albeit generally more costly than bolt torqueing. One way to counter the unknown nature of

the nut factor is to use lubrication on the bolt threads and nut face. This reduces the friction during tightening resulting

in more energy conversion of torque to bolt stretch. Overall, neither method is wrong. The method chosen would

depend on the specifics of the joint such as the physical space available or the size of the bolt.

Tensioning Main Attributes

Stability and ease of control

Highly accurate

Generally more expensive

than other systems Most often used on large

bolts

Torqueing Main Attributes

Less accurate than hydraulic

tensioning

Less expensive to purchase

More versatile Usually used on smaller fasteners

Simple to use

Eng. Baksh holds a B.Sc. (Hons.) Mechanical Engineering (2014) and is currently pursuing a Masters

Production Engineering at The University of the West Indies. Since graduating she has worked at Me-thanex Trinidad Limited, currently functioning as part of the Mechanical Projects Team. Eng. Baksh was elected as the Engineering Student Speaker for the Engineering Awards at the University of the West

Indies in 2014. Her drive and ambition took her through the various stages of the IET PATW competi-tion to the Finals in London in 2014. Grateful for all that she has accomplished thus far, Eng. Baksh is also a regular volunteer for Methanex’s Mentoring Our Children program, believing that with a little

encouragement and the right example, anyone can achieve great things.


Multiple Model Predictive Control

Bridging the Information Gap

to Regulate Highly Non-Linear Processes

Part II: Controlling a CSTR

By Dr. Brian Aufderheide1 , Eng., PhD.,

Makeda Wilkes, Eng., B.Sc., M.Eng., and Adrian Lutchman, Eng., B.Sc.

1 Correspondence to [email protected]

Figure 1: Model predictive control (Rao et al, 2001)

Introduction

There are several difficulties in regulating chemical indus-

trial processes: the interactions between control pairs,

systems can be highly nonlinear, load disturbances can

occur, and number of online measurements are often

limited especially when it comes to compositions and

concentrations. Model Predictive Control (MPC) han-

dles interactions of control loops readily and can operate

with limited output measurements. However, handling

different operating regions and disturbances are typically

done using an Extended Kalman Filter (EKF) to estimate

parameters or disturbances. Another approach is to use

multiple models to cover different disturbances and/or

operating regions. Multiple Model Predictive Control

(MMPC) was discussed in detail in Part I of this article

(Aufderheide et al, 2016).

Here we will be covering more details on how MMPC

works comparing the advanced control strategy using actual

step responses for the model bank and first order plus

dead time (FOPDT) models versus using a first principles

based EKF that is the traditional approach for nonlinear

MPC.

The in silico study was done with the Van de Vusse reaction

system which has input multiplicity, gain sign changes, and

inverse responses.

Model Predictive Control (MPC)

MPC is a control algorithm that is analogous to playing a

computer in a game of chess (Fig. 1). At the top of Figure

1, the current sampling instance k, a model is used to pre-

dict the output behavior of the system, P sample intervals

into the future, based on the past states and M future con-

trol moves. The future control moves are optimally esti-

mated to minimize predicted error from the set point.

Feedback is achieved by implementing only the first of the

M moves. At the bottom of Figure 1, based on the actual

measurements of the output at the (k+1)th instance, the

model predictions are corrected as an additive disturbance

to account for model mismatch and unmeasured disturb-

ances. The optimization procedure is repeated in a receding

horizon framework to compute a new set of moves (Rao et

al, 2001). The equations for MPC were outlined in the pre-

vious Part I article in Aufderheide et al 2016.

Figure 2: Multiple Model Predictive Control (MMPC)

Differential Equations:

NONLINEAR MPC: EXTENDED

KALMAN FILTER (EKF)

The strength and weakness of MPC is having an accurate

model to handle the nonlinear process under different

operating conditions. Most research done on MPC is in

various types of model development and update strate-

gies. The typical approach when a first principles set of

differential equations are available is to apply a Kalman

Filter to estimate the process’ state variables. The Ex-

tended Kalman Filter (EKF) is when parameter(s) are

appended to the differential equations as additional states

to be estimated.

The optimization is similar to that for MPC but instead of

minimizing future predicted error here you are minimiz-

ing past differences in model/plant. For complete equa-

tions see Aufderheide and Bequette, 2003.

Multiple Model Predictive Control

The serious limitation to an EKF is that the number of

parameters estimated cannot exceed the number of

measured outputs (Kozub, MacGregor 1992).To get

around the information limitation, a multiple model adap-

tive estimator is used to obtain a prediction model for

MPC (see fig. 2). Model bank can be varied by feed con-

centration, dilution rate, kinetic parameters etc. The

bank of models can be step response models, as used in

Dynamic Matrix Control (DMC) or state space models

(linearized models from fundamental ordinary differential

equations). The key here is that you are providing addi-

tional information for the final prediction model. If the

system responses lie within the existing model bank, then

it will work well. Information requirement is similar to

fitting only one parameter since we are requiring the

algorithm to choose one model out of the bank.The final

prediction model can be a weighted average (blended)

model or be a winner takes all highest weight model as

prediction to MPC.

The algorithm is computationally inexpensive and insures

that probabilities are bounded from 0 to 1. An additional

benefit is that poor models are rejected exponentially

fast so having a very large number of models does not

necessarily lead to a very large drop in controller perfor-

mance. The equations for the Recursive Bayesian theo-

rem were discussed in the previous Part I article in Auf-

derheide et al 2016.

Control of Van de Vusse Reaction:

Comparison of Multiple Model

Methods to Extended Kalman Filter

To better understand the success of MMPC using a bank of

First Order Plus Dead Time models regulating the cardio-

vascular system of dogs and pig see Part I (Aufderheide et

al, 2016), work was done in silico with a simple but difficult

system to regulate, the Van de Vusse reaction (Aufderheide

and Bequette, 2003).

The Van de Vusse system has input multiplicity (Fig. 3)

where two dilution rates can lead to the same product con-

centration of B, Cb. To the left of the optimum concentra-

tion of B, the process gain is positive and there is an inverse

response making it very challenging to control (Fig. 3). At

the optimum, the process gain is zero and is uncontrollable.

To the right of the optimum the process has a second or-

der response with a negative gain and control is readily at-

tained (Fig. 4). Disturbances to the processes are changes

in the feed concentration, Ca,in , and in the kinetic parame-

ters that shift the overall gains and location of the optimum

values possible (Fig. 3).

VDV Equations:

Figure 3: Steady state curves for

two feed concentrations of Cain

and for both sets of kinetic

parameters

Figure 4: Sample step responses for the nominal case starting at

steady state dilution rates (Uss).


Figure 5: Start up problem with sudden change in kinetic parameters at 15 minutes

Figure 6: Actual

plant output vs.

predicted output

The control objective is to operate closely to the opti-

mum point to maximize the concentration of B. Here

we are comparing three different models for MPC; the

first principles Extended Kalman Filter, the actual step

responses for different operating conditions and different

disturbances, and the minimal bank of First Order Plus

Dead Time models that span both positive gains with

dead times to represent the inverse responses and First

Order Models with negative gains to represent the Se-

cond Order responses found at dilution rates higher than

the optimum. MPC tuning was adjusted appropriately

for all three model types.

Figure 5 shows the control results for all three model

types on a cold start up problem to reaching a desired

set point of 1.25 moles B/L. At 15 minutes, a second set

of kinetic parameters occurs as a disturbance.

The EKF with a small deviation after the disturbance

takes almost 4 minutes to return to the set point. Most

impressive is how quickly the step response (SR) model

bank rejects the disturbance taking less than one minute

to return to the set point. Compared to the EKF-based

MPC this is less than a quarter of the time. SR also out-

performs the EKF-based MPC taking less than 2 minutes

to reach the set point from startup. FOPDT takes 12

minutes to reject the disturbance. The actual SR model

bank controller is detuned to have the best performance

for this case and can even be quicker than that shown

here.

The actual step response model bank has by far the best

performance selecting models closest to the actual process

quickly and efficiently.

Figure 6 compares the one step ahead predictions of the

two different model banks and the single model EKF. All

three provide very good estimates here with EKF having

slightly worse mismatch from the actual process after the

disturbance occurs.

Conclusions

If you have a detailed model of differential equations for

your process and only a few key parameters to estimate

with sufficient information (number of measured outputs

equals or exceeds number parameters to fit), then an EKF

is the approach to take for your MPC model. If you can

run different step responses mimicking possible process

disturbances prior to them actually occurring then develop

a model bank that contains these different operating condi-

tions and use them for MMPC. This can handle any num-

ber of parameter changes and different process conditions,

and work exceedingly well.

But the reality often is that you cannot develop a detailed

model be it the complication in the system itself and/or a

lack of data to fit all the parameters needed for the system.

Nor is it possible to run the actual process over a set of

different operating conditions and disturbances. So what

can be done? Develop a First Order Plus Dead Time mod-

el bank and use it as a Gray Box System Identification tool

and as long as good control is sufficient this will work and

handle a myriad of different disturbances and process con-

ditions.

Current Work

Right now we are working on different multiple input

multiple output processes using a bank of state space

models covering various operating conditions and param-

eterizations. A state space model is a linearized form of

the non-linear differential equations. These systems are

the non-isothermal VDV regulating both reactor temper-

ature and product concentration, a waste system and an

industrial pH neutralization pit. The industrial pH neu-

tralization pit stemmed from an industrial design project

and was modeled from first principles.

A feasibility study using the waste system was done lev-

eraging a first principle model of a process into a bank of

state space models that span parameterization and oper-

ating conditions to handle large set point changes and

various load disturbances with a Multiple Model Predic-

tive Controller. Automated tuning is done by using

Skogestad (2003) Method of FOPDT approximation for

each input/output combination then applied to Shridhar

& Cooper (1998) MIMO MPC tuning rules (Wilkes and

Aufderheide, 2017).

Future Work: Putting MMPC into

Current MPC Commercial Software The implementation of MMPC strategies on an industrial

scale could be done in one of two ways, by using a sys-

tem that supports MPC and continually updating the sys-

tem models or by performing all model identification and

MPC functionality externally and sending the manipulated

variable outputs only. In both cases the calculations that

require multi-dimensional linear algebra should be exe-

cuted by a computational math package, such as Matlab

or Aspen Custom Modeler and the plant control imple-

mented by a Distributed Control Systems (DCS) soft-

ware application, such as the Emerson DeltaV application

framework.

MPC is supported through the fully configurable MPCPro

and MPCPlus function blocks that are shipped with the

DeltaV system. Emerson provides system identification

tools (DeltaV Predict) that use plant data to create a

prediction model. It does not provide for online model

update. Emerson has provided and interface called Event

Monitor that can call a procedure from an external appli-

cation such as Matlab, and read and write data to this

application through an Open Process Connectivity

(OPC) connection. In principle this should allow the ex-

port of plant data to Matlab, and import of updated mod-

el bank including the Bayesian Recursive algorithm.

The second option could also be implemented using the

Event Monitor interface, in this instance plant data is

sampled periodically and sent to Matlab where all com-

putations are carried out, including MPC linear algebra.

DeltaV would send the external calculated control move

via the Analog Output port. Aspen Custom Modeler

(ACM) can work in conjunction with the Aspen DMC

Plus module. The model bank and update will be very

straight forward to implement in the ACM.

It really comes down to the module for the multiple model

bank to be able to receive information in parallel with the

built in MPC modules of Aspen and DeltaV while also al-

lowing it to pass prediction models and tuning parameters

to them. We will be investigating the Aspen products in

silico using dynamic process plants in Aspen HYSYS/Plus

including ACM working with DMC Plus. DeltaV software is

used in our chemical engineering laboratory and any modifi-

cations to multiple model banks can be done there on pilot

absorption and distillation columns.

Eng. Dr. Brian Aufderheide completed his

PhD in Chemical Engineering at Rensselaer

Polytechnic Institute. His areas of expertise

are in advanced control and modeling of

biomedical, chemical, and biological processes.

He has consulted for both medical device and

biotechnology companies. He was sole engi-

neer and QC supervisor of a 40MM lb/yr

custom extrusion company. He has over

12years experience in education developing

over 25 new courses. He is a returned Peace

Corps Volunteer. He is dedicated in helping

his students to succeed. Currently he is an

Associate Professor in Process Engineering at

the University of Trinidad and Tobago.

Eng. Makeda Wilkes obtained her M. Eng in Process

Engineering at the University of Trinidad and Tobago.

She is a Research Assistant at the University currently

working towards publications in Process Control

Education and Advanced Process Control. Makeda

teaches Matlab, assists with developing material and

teaching Process Design to the BaSc final year students.

She co-supervises both BaSc and M. Eng design pro-

jects. Her current research interest are model predic-

tive control in chemical and industrial engineering

applications.

Eng. Adrian Lutchman is an Instructor at the

University of Trinidad and Tobago. He worked

as a Process Engineer for nearly a decade

before joining the University. Adrian has

worked in Process Design (NMWG) and

Ammonia production (IPSL, YARA). At present

Adrian is a member of the Process Engineering

team at UTT, he teaches in the areas of Pro-

cess Design and Simulation, Process Control .


Short Slabs Technology for Concrete

Pavements

By Avaleen Mooloo Eng., B.Sc., M.Sc., MAPETT

Introduction

Concrete roads in the Caribbean have been an excellent

solution for countries that do not have the financial re-

sources for the continuous maintenance required for flex-

ible roads. The chronology of conventional reinforced and

plain concrete roads can be seen in many Caribbean is-

lands, and even in Trinidad there is a very good history of

concrete roads such as the Paramin road, the residential

suburb of Valsayn, Port of Spain port and Piarco airport.

Some of these roads were constructed well over 40 years

ago and are still in good condition and serviceability.

In the last couple of years, engineering technology has

evolved to become more “sustainable”. This means that

great consideration is taken into account for design, mate-

rials used for construction, the method of construction

and maintenance of the completed structure so that there

are no negative impacts to the environment and the pub-

lic. This approach has caused Concrete Pavements to be-

come very popular though very costly. There has been

significant growth in concrete solutions for rigid pave-

ments and one of these is the Short Slabs Thin Concrete

Pavement (TCP) technology.

Short Slabs Thin Concrete Pavements

There are basically four types of concrete pavements: plain,

plain doweled, reinforced and continuously reinforced, of

which short slabs are either plain or plain doweled.

Plain pavements are constructed without reinforcing steel

or doweled joints. Load transfer at the joints is obtained by

the interlocking of the aggregates between the cracked faces

below the joint saw cut or groove. For load transfer to be

effective, it is necessary that short joint spacing be used.

Plain doweled pavements are built without reinforcing steel;

however, smooth steel dowel bars are installed as load

transfer devices at each contraction joint and relatively

short joint spacings are used to control cracking.

So, what is the difference between conventional concrete

pavements and short slab pavements? Both are designed

using the AASHTO method. Once the thickness design is

given for the conventional pavement, an alternative design is

done using the short slab methodology.

The American Concrete Institute (ACI 360 & ACI 302) nor-

mally recommends joint spacing criteria of 24 times the slab

thickness for unreinforced slabs. The short slabs is based on

the methodology of reduction of the tensile stress originat-

ed by the front and rear axles loaded simultaneously at the

edges of the slab when it is curled upward. The slab is opti-

mized by reducing the joint spacing near to 10 times the slab

thickness and reducing the concrete pavement thickness on

condition that the tensile stress is equal to or lower than

the conventional design.

Fig 1: Example of

Concrete Road.

Fig 2: Comparison of Conventional pavement to Short slabs.

Before After

Figure 3: Comparison of thickness of concrete pavements

Traditional vs. Short Slab pavements

The design variables that the method takes into account

for pavement design includes:

Transit (in terms of Equivalent Single Axle Loads,

ESAL’s)

Reliability (Statistical parameter)

Overall deviation (Statistical parameter)

Modulus of Rupture (Flexural strength of the con-

crete)

Load transfer (J)

Drainage Coefficient

Modulus of subgrade Reaction (K)

Initial Serviceability

Final Serviceability

The traffic information is also analyzed using the AASH-

TO method in order to determine the critical axle load

that most severely damages the pavement structure. In

any given traffic data, the Tridem Axles are the most

critical axle load that will cause the most damage to the

pavement structure, therefore the maximum tensile

stress analysis is performed using the Tridem Axle in 3D

finite element software (EVER FE 2.4).

When comparing both structures it is clear that the deteri-

oration will be different due to the fact that they bear loads

and stresses differently.

Short Slabs in the Caribbean:

GUYANA:

PROJECT– REHABILITATION OF GNSC INTERNAL

ROAD- GEORGETOWN (0.11KM)

GTP SOLUTION: Cement treated base (CTB) & TCP

CUSTOMER: GNSC

PROJECT’S DESCRIPTION: LENGTH OF PAVING: 0.11

KM, LAYING THICKNESS: 13 CM. PAVING WIDTH of

5m; 1 shoulder: 1 m, curb & slipper drainage and pedestrian

sidewalk. It includes supply of Cement and Design & Engi-

neering.

STATUS: COMPLETED

TRINIDAD:

PROJECT– REHABILITATION OF TCL PLANT INTER-

NAL ROAD – CLAXTON BAY (0.5KM)

GTP SOLUTION: Cement Treated Base (CTB) & TCP

CUSTOMER: TCL CLAXTON BAY PROJECT’S DESCRIPTION: LENGTH OF PAVING: 0.5

KM, LAYING THICKNESS: 12 CM. PAVING WIDTH of 6

m (min); curb & slipper drainage. It includes supply of Ce-

ment, Concrete and Design & Engineering.

STATUS: IN PROGRESS

Area of Concrete 580m2

Volume of concrete 80m3

Weight of cement 49 ton

Project Total Cost US $35K

Area of Concrete 3100m2

Volume of concrete 370m3

Weight of cement 184 ton

Project Total Cost US $150K

CONCLUSION

Concrete pavements are without a doubt superior to asphalt pavements and this is highlighted below:`

ADVANTAGES OF CONCRETE ROADS

ECONOMIC ENVIRONMENTAL SOCIAL & FUNCTIONAL

Low maintenance Less GHG emissions Performance

Predictable material prices Reduced UHI effect Durability

Life cycle cost Storm water management Safety (friction, reflects at night)

Fuel economy Material recyclability Noise reduction

Energy savings Aesthetics & versatility

Fires in tunnels can ignite asphalt

which adds to the heat, smoke and

difficulty in firefighting and evacua-

tion due to molten asphalt.

Concrete does not burn or emit

toxic gases and countries such as

Austria mandates all pavements in

tunnels be made of concrete.

CONCRETE VS ASPHALT DURABILITY LIFE CYCLE COST

FUEL CONSUMPTION URBAN HEAT ISLAND EFFECT

CONCRETE ROADS – THE SAFER OPTION

LIGHT REFLECTION HIGHER SKID RESISTANCE

TUNNEL CONSTRUCTION LESS NOISY

Superior strength of

Concrete over Asphalt

ensures low & predicta-

ble maintenance costs.

Design life of concrete

≤ 50 yrs. with road last-

ing 3X longer than as-

phalt before major re-

hab required

Concrete pavement will

reduce de f l ec t ion -

induced fuel consump-

tion by 50-60% compared

to asphalt of same thick-

ness. 3% improvement

on vehicle consumption

which saves around

46.5MMt of CO2 annually

Light coloured surfaces

e.g. concrete reduce this

urban heat island effect.

Converting LA from as-

phalt to concrete would

reduce temp by around

0.6°C (1°F) resulting in

saving of USD 90M for air

conditioning

Concrete is naturally

brighter and more reflec-

tive than other pavement

surfaces. Concrete reflect

3x more light than asphalt

& lighting intensity can be

reduced up to 30% with-

out compromising night

vision

Higher skid resistance of

concrete reduces braking

distances by 12-15% in

both wet & dry condi-

tions, compared to As-

phalt. Concrete surfaces

do not RUT & the risk of

hydroplaning is effective-

ly eliminated

Noise level of con-

crete roads can be

greatly reduced

without sacrificing

durability or safety

by choosing an ap-

propriate surface

texture e.g. broom

f inish, diamond

ground surface or

exposed aggregates

Eng. Mooloo has worked for the past 12 years with the TCL Group in our cement

companies in Trinidad, Barbados, Jamaica and Guyana on multi-million upgrades for

optimization of efficiencies of the cement plants. For the last six years she has been

working on establishing markets for the alternative uses of cement primarily through

sustainable pavement solutions and eco-housing. Eng. Mooloo is currently pursuing an

M.Phil. Civil Engineering, holds an M.Sc. Construction Engineering and Management

and a B.Sc. (hons) Civil Engineering all at UWI. She has been awarded a Certificate of

Achievement from IEEE for special investigative project - 2004 and the PSC Nitrogen

Trinidad Ltd Scholarship—2000. Eng. Mooloo is a Member of APETT and a Member

of the Powerful Ladies Of Trinidad and Tobago (PLOTT).


The New Procurement Legislation:

Implications of Major Shifts from

the Past

By Winston Riley, Eng., B.Sc., FAPETT

The Implications under Act #1 of 2015

The new procurement legislation Act #1 of 2015 and Act #5 of 2016 “provide for public procurement, and for the retention

and disposal of public property, in accordance with the principles of good governance, namely accountability, transparency, integri-

ty and value for money, the establishment of the Office of Procurement Regulation, the repeal of the Central Tenders Board Act.”

The past is represented by the CTB Act which through amendments ushered in the proliferation of Government to

Government arrangement (GtoG) and State Owned Enterprises (SOEs). Accountability under the CTB is modeled on

procedural compliance.

The present legislation initiates sustainable procurement and brings into play Local Content Requirements (LCR), Value

for Money (VM), Risk Management (RM) and a modern results-oriented management approach.

The new procurement legislation sets up a legal framework through which LCR sustainability and VM can be linked and

operationalized in a transparent manner. Act #1 of 2015 (the Act) makes three important shifts from the past by:

1. Giving a procuring entity the power to prioritize LCR in procurement proceedings. The Act defines local content as “the local

value added to goods, works or services measured as the amount of money or percentage of each dollar of expenditure re-

maining in Trinidad and Tobago after the production of the good or the performance of the work or service;”

Sub-Section 28 (1) states: “A procuring entity may limit participation in procurement proceedings to promote local industry deve l-

opment, local participation, and local content.”

2. Subjecting to the Act all G to G arrangements, all treaty arrangements and arrangements with all financial institutions. This

shift allows for the determination and transparent disclosure of LCR in procurement proceedings related to treaty arrange-

ments with foreign Governments and financial institutions. Sub-Section 7 (2) of the Act states: “To the extent that this Act

conflicts with an obligation of the State under or arising out of the following:

a) A treaty or other form of agreement to which Trinidad and Tobago is a party with one or more States or entity within a State;

…..

b) an agreement entered by the Government of Trinidad and Tobago with an international financing institution; or

c) an agreement for technical or other cooperation between the Government of Trinidad and Tobago and the Government of a

foreign State,

The requirements of the treaty or agreement shall prevail except that the procurement of goods, works or services shall be gov-

erned by this Act and shall promote the socio-economic policies of Trinidad and Tobago and shall adhere to the objects of this Act.

Sub-Section 7 (3) states: “A procuring entity engaged in procurement proceedings relating to a treaty or agreement referred to in

Sub-Section 2(a) shall comply with Section 29 and submit a report on such compliance to the Office (Office of Procurement Regu-

lations) (OPR).

Sub-Section 7 (4) states: “The Office shall, within twenty-one days of receiving a report under Sub-Section (3) forward a copy of

the report to the Speaker of the House of Representatives who shall cause the report to be laid before Parliament at the earl iest

opportunity.”

Section 29 sets out the pre-and post-qualification requirement as outlined in the procuring entities regulations and hand-

books approved by the OPR for the procurement of goods, works, and services.

3. By (a) defining “sustainable procurement as a process whereby public bodies meet their needs for goods, works or

services in a way that achieves value for money on a long-term basis in terms of generating benefits not only to the public

body, but also to the economy and the wider society, whilst minimizing damage to the environment;” (b) outlining under

subsection 5(1) (c) that “The objects of this Act are to promote local industry development, sustainable procurement,

and sustainable development, in public procurement and the disposal of public property.” (c) defining value for money in

sustainable terms.

Engineers in Trinidad and Tobago, because of their sheer numbers relative to any other profession, occupy crucial deci-

sion-making positions in almost all SOEs and Ministries responsible for the procurement of goods, works and services

under the Public-Sector Investment Programme.

The OPR oversees the procurement process through regulations, guidelines, handbooks and special handbooks. The spe-

cial handbooks are drafted by each procuring agency for approval by the OPR. It is through the special handbooks that

engineers can act as a collective and have influence on LCR - a prerogative mainly of an economist.

In procurement, LCR is mainly represented by Performance Metrics. LCR affects VM sustainability and trade and thus

demands research for the development of national policy positions with variations relative to sectors such as manufactur-

ing, petrochemical, construction, IT, Communications, etc. thus raising the politics of procurement to international levels.

A Simple Guide: the Measurement of Local Content in Public Procurement

A procurement system requires a standardized approach for measuring and validating the local content of goods, works,

and services required by a solicitation document. The solicitation document should include a stipulated minimum thresh-

old for tender validity. Stipulated minimum threshold, although designed to improve local content in the future, can have

negative effects on efficiency and effectiveness at a given time and thus has “Value for Money implications in the context

of preferential treatment. Stipulated minimum thresholds is thus a function of Government policy. The guide allows for

the calculation of LCR and the foreign Component Requirements of EXIM Banks of countries under G to G and other

Treaty Arrangements.

LCR shall be expressed as a percentage of the “submission” price exclusive of VAT, and shall be calculated as follows:

LCR = (1 - x/y) x 100 wherein

(x) is the imported component in Trinidad and Tobago Dollars and

(y) the tender price in Trinidad and Tobago Dollars.

Eng. Riley holds a B.Sc. Civil Engineering (1967) and was awarded the Chaconia Gold

Medal in 2016 for his distinguished and outstanding service to Trinidad and Tobago at

the National Awards Ceremony. He has received awards for excellence from the Facul-

ty of Engineering, UWI in 1986, APETT in 1987 and 2010, and in 2015 Eng. Riley re-

ceived APETT’s highest award (Career of Excellence Award). Eng. Riley is a Fellow and

Past President (1983-1984) of APETT, Past President of the Contractors Association of

Trinidad and Tobago, Past President of Joint Consultative Council (JCC) for ten years

and served on several Cabinet Appointed Committees in the Industry. As President of

APETT, he initiated and managed the first Caribbean Housing Conference. As President

of the JCC for the Construction Industry (1998-2010), he successfully lobbied for the

establishment of a Master’s Degree Programme in Project Management at UWI and the

standardization of construction contracts. He also initiated and managed a training ar-

rangement for professionals in the Caribbean on the FIDIC forms on Construction

Contracts. He has over the last 15 years, been a passionate advocate for Public Pro-

curement Reform in Trinidad and Tobago and now chairs the Private Sector Civil Socie-

ty Group on Public Procurement.


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The Art of Bolt Torqueing

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Part II: Controlling a CSTR

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