Amine Acid and Sour Gas Plant Experiences

8/13/2019 Amine Acid and Sour Gas Plant Experiences

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Fire Tube Boiler


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MEA Solutio

Saturated Steam


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MEA Reboiler

MEA Stripper

n

Vapor


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LeanMEA Solution

This is the conventional, industrial manner of generating food-grade CO2 in a continuous,controlled scheme.

Note that the 15% MEA (wt.) solution is kept indirectly away from the very hot reboil hea by the use of a direct-fired reboiler. Although this method involves the cost of a conventi

boiler, it eliminates a lot of the degradation products that are formed when MEA comes in

temperatures in excess of 300 oF. It also allows for easy and convenient means to ensure

the fuel combustion to produce as near a stoichiometric quantity of CO2 without worryingreboiler heat is affected. The amount of steam produced by this method is well in excess

required in the MEA Reboiler and this fact enables the process to have sufficient steam avonly introduce an excess of steam into the reboiler (which ensures that acid gas loadingsreduced in the Stripper with ease), but it also provides steam for an MEA Reclaimer (whi

ensures the non-corrosive state of the circulating solution and the efficient operation of the

The application of a cheaper ("low capital investment") direct-fired reboiler in order to sa

cost of the MEA reboiler reduces the Capital Investment of the plant, but it introduces ma

and expensive maintenance and operating problems for the operator ("owner") of the plant

fired reboiler can accelerate the degradation of MEA into a very corrosive state and causecorrosion problems in the reboiler as well as in all the rest of the equipment. This is a clas

of getting exactly what you paid for. If the eventual owner is not interested in reducing hi

and maintenance costs and other problems, then he/she doesn't pay attention to such impothat will return to threaten his operating profit margin in the end.


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Nitrogen to

Flue Gas

Lean MEA Solution


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Atm.

Condensate from LP Cooler-Condenser

H1

H2

This height should be sufficiently high to

allow effient condensate over flow from the

bottom of the exhaust scrubber and allow

for taking a solution sample for analysis.

LP C

CW Supply

CW Return

LP CO2 + Steam from CO2 Stripper

This height, together with H2 should be

related to the available pressure in the LP

Cooler Separator and give sufficient packing

height for efficent scrubbing.


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ooler-Condenser

LP CO2 to Purification & Compression

LC


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Some background on MEA use in CO2 removal processes:

During the 1950 and 1960's the Liquid Carbonic Corporation (Chicago, Illinois) was the World's largest producer and distributor of

Carbon Dioxide - as a liquefied product ("LiquiFlow") and as a solid ("Dry Ice"). During the 50's, it started to expand itsmarkets in Latin America and decided to install proven, state-of-the-art production plants there. It chose to enter into a purchase/supply

arrangement with a company in Dallas, Texas named International Process Equipment Corporation ("IPEC"). IPEC was majority-owned

by Mr. Robert Graff who had a recognized and respected reputation for designing and building CO2 removal plants mounted on

skids and capable of being easily transported and installed in under-developed locations.

During the early 50's Liquid Carbonic engineers bought some surplus, skid-mounted Girdler CO2 generating plants that had been recovered

from US Naval ships such as World War II air-craft carriers and they learned about the benefits of the skid-mounted design. The

Girdler corporation had specifically designed these units during WWII to function on-board ships to produce CO2 for vital and

important fire extinguishers applications on board. These Girdler plants used a direct-fired heater that burned fuel oil directly

through a stainless steel helical coil inside the furnace. A 20% wt. MEA solution was circulated within the coil by stainless steel

Peerless centrifugal pump. The hot, MEA solution was flashed into bottom of a generator tower packed with Rashig Rings. The

generator tower stripped out the absorbed CO2 from the Rich MEA introduced at the top of the Rashig Ring bed. The generator tower

operated at 40 psig and this was sufficient pressure to send the Lean MEA in the generator sump to the top of the CO 2 absorber.

This design worked very well, but it had notorious amine degradation problems caused by the direct-fired reboiler. This was not a problemfor the Navy; they merely dumped the degraded solution at sea and put in fresh MEA on a timed schedule.

Liquid Carbonic had two Girdler plants with the above design: One at Maracaibo, Venezuela and another at Lima, Peru.

The application of amines for CO2 removal was brought about by the discovery of helium containing carbon dioxide in Thatcher, Colorado,

in 1922. Rodger R. Bottoms, a chemist and lieutenant commander in the Navy, developed a process to exploit this helium deposit

economically by removing the carbon dioxide. In 1929 he synthesized an amine that removed the carbon dioxide from the helium in laboratory

experiments. In 1930 he patented the amine process for the Girdler Corporation for the removal of CO2. In 1935, Robert A. Graff, was

working for Mr. Bottoms as his laboratory assistant. They both were employed by the Girdler Corporation. Mr. Graff went on to form the

Graff Engineering Company in Dallas, Texas employing all the know-how and experience he had accumulated in his association with

R. R. Bottoms and Girdler. Bob Graf actively designed and fabricated amine skid-mounted plants for the Texas-Oklahoma-Louisiana-

Typical Stripper 5/16" Plate, seal welded

35 psig Steam

Condensate

Rich MEA, 200 oF

Water-CO2, 5 psig & 228oF

Lean MEALean MEA Drain & to Reclaimer


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New Mexico Oil Patch, removing CO2 and H2S. His plants employed both direct-fired reboilers and steam-heated reboilers.

Some unique and innovative features that the IPEC skid-mounted MEA plants incorporated were:

• The use of a conventional, fire tube boiler to generate the CO2 gas as well as low pressure steam (35-40 psig).

All the steam generated was sent to a U-tube bundle in a kettle Reboiler that formed part of the Stripper (as shown

in the illustration above) and all the produced condensate returned to the boiler BY GRAVITY. There was no condensate

pump(s), condensate controls, deaerators, or condensate instrumentation. Since Bob Graff needed an MEA heat exchanger

and an MEA cooler, he placed these directly below the kettle Reboiler and in doing so, had to raise the reboiler and its

steam tube bundle to a height that was normally above the top of the steam boiler. This made the application of condensate

gravity return practical and efficient.

• The CO2 stripper used no "fancy" trays or packing. There were approximately 10 trays used in the IPEC Stripper and

each was nothing more than a circular, 5/16" carbon steel plate with a segment cut out. The segment was approximately

15 to 20% of the diameter - depending on the size of the stripper and the CO 2 capacity. These Strippers worked well and

never needed, inspection or maintenance. The design could not be more simplified.

• All the condensate produced in the LP Cooler-Condenser down stream of the Stripper was collected a Vapor-Liquid

Separator and the condensate was returned to the solution system via the sump of absorber. THERE WAS NO

CONDENSATE RETURNED TO THE TOP OF THE STRIPPER AS SO-CALLED "REFLUX" . This not only

worked very simply and trouble-free, it required no reflux pump, flow meter, vales, controls, and instrumentation.

• IPEC incorporated an Amine Reclaimer - a means to re-distill a portion of the Lean Amine in order to precipitate out

any heavy, polimerized amine products or degradation by-products. This device kept the solution working for very long

periods without suffering corrosion in the basic carbon steel material that the plant was constructed out of. Corrosion

was effectively kept under control to the degree that the Reclaimer was kept operating. This feature worked very well

and practically due to the availability of steam from the boiler. With a direct-fired Reboiler, the use of a Reclaimer is not

possible.

Addition notes and background:

When I took over the Lima, Peru operation in 1963, I made some major modifications to the existing 150 kg/hr CO2 plant. I converted

the two-pass CO2 absorber into a one-pass tower and mounted a scrubber on top to use the LP condensate from the Cooler-Condenser

to scrub the exhaust gas exiting the absorber. MEA consumption dropped immediately to 1.0 kg/tonne CO2 produced.

I undertook the design and fabrication of a 400 kg/hr CO2 combustion plant using a steam generator and a Chicago-Pneumatic, 3-stage,

oil-lubricated reciprocating compressor. I fabricated all the rest of the equipment locally in Peru. I patterned my design using a lotof the IPEC design that I had seen and studied while running the Jamaica Carbonics IPEC plant in Kingston, Jamaica previously before

arriving in Peru. I followed Bob Graff's basic concepts with some slight modifications. I employed plain solid Stripper plates, like IPEC.

I tried 6 plates and then 10 and found no difference. I also used tunnel caps on six trays and found no difference. I used all the LP condensate

to scrub absorber exhaust gas and this plant went on to achieve an MEA consumption of 0.5 kg/tonne CO2 produced - a record in Liquid

Carbonic for a pure MEA CO2 plant. I also employed a 12-15% wt. MEA solution instead of 20%wt. and reduced all corrosion within the MEA

circulation system. This plant went on to produce efficiently for approximately 24 years before being de-commissioned because it

was no longer needed. The only exotic material of construction used in its fabrication was a 304 SS Reboiler tube bundle.

After confronting some field practical problems with kettle Reboiler U-tube bundles in Jamaica, I redesigned the Lima Reboiler tube bundle.

In Jamaica we discovered that it was practically impossible to obtain a U-Tube bundle perfectly aligned horizontally. Because of fabrication

tolerances and measurements as well as bundle deformations and heat distortions, the U-shape ("hair pin") did not maintain itself

perfectly while installed. This mean that the top tubes were either sometimes sloped upwards or downwards. This is an important anomaly

that is not discussed nor contemplated in heat transfer texts or classrooms when dealing with steam being condensed in a horizontal hair pin.

Note that should the hair pin be sloped UPWARDS, formed condensate in the top of the hair pin will have a tendency to drain BACK towards

the tube entrance and block the entry of fresh steam. And should the hair pin slope DOWNWARDS, the condensate will simply collect at the

bottom of the tube's return and form a liquid blockage there. Either of these effects will hinder and ultimately cause reduced heat transfer and/or

haphazard operation of the Reboiler. And this was exactly what was detected in the Jamaican plant operation. It was cured with the substitution

of the conventional "U" tube bundle with a "V" type of fabrication - as shown in the illustration below.

With this modification, the Jamaican and Lima Reboilers worked exactly as calculated and predicted, with no fluctuation in heat transfer.

It will be noted by those engineers with some amine plant experience that the above designed operations are in distinct difference

with designs and fabrications of such illustrious engineering firms like Fluor, Brown & Root, and many others who always propose and build

Amine absorbers and Strippers with at least 20+ very sophisticated trays or packings. They also insist on employing a so-called "Reflux" of

condensate on the CO2 Stripper. What none of the design or process engineers with these firms have ever been able to explain, prove, or

calculate to me is the factual and engineering REASONS for doing what they do. They just do it that way because they have always done it.

Yet, they cannot explain the logical and engineering need to have a so-called "Reflux" in what is nothing more than a stripping operation of a

non-condensable gas from a liquid solution. What, if any, purpose there is in such a futile attempt is left unspoken. No one has yet to explain

why the Reflux is needed at the top of a CO2 (or an H2S) stripper. The real truth is: IT ISN'T - AND NEVER WAS - REQUIRED . The


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many IPEC and Girdler plants that were built and operated have proven this throughout the last 70+ years. And I have followed this principle

and proved it in all the plants I designed, built, and operated as well.

What is really embarrassing is that practically all major text books on gas purification - as well as most authors of journal articles - fail to see

or recognize this false and useless engineering design in amine plant design. All that a "Reflux" of condensate can accomplish in the CO2 stripper

is a "scrubbing" of the ascending vapors in the top section of the tower in order to avoid entrainment of MEA in the overheads. But if that is a

necessity, then why not design the stripper and its diameter such that there is no entrainment in the first place? The Strippers I operated and

designed never produced any entrainment - inspite of the inherent excess steam (water vapor) in the overheads due to using all of the boiler's steam

production in the Reboiler tube bundle. Authors such as Kohl, Reisenfeld, Neilsen, Campbell, and Maddox - all intelligent and learned engineers - have

failed to detect what is an obvious mistaken design that is useless and does absolutely nothing to improve an amine plant's operation. However,

a guy like Bob Graff did spot this in 1950 and incorporated a much simpler and fool-proof method.

If one goes to the trouble of using a McCabe-Thiele method of designing a CO2 Stripper, it will be quickly noted that building a CO2 Stripper with

20 trays - whether bubble cap, sieve type, or valve type - is an IGNORANT ENGINEERING OVERKILL. There is definitely no need for so many

trays in an MEA Stripper. And thank goodness for that! There are enough troubles and problems to worry about in an MEA process without having

to put up with investment, care, and maintenance of so many engineered trays.

The latest actors in Amine Plants - such as DEA, MDEA, and even aMDEA - have the characteristic of being selective in absorbing H2S with

preference over CO2 and are actively used in Sour Gas applications. These solutions also demonstrate a propensity for easily having H2S stripped

out of solution in the Stripper. Therefore, they should require less trays than even an MEA Stripper.

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Amine Acid and Sour Gas Plant Experiences

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