5 replies to this topic

[Laurence]

Hello all,

I am investigating amine based CO2 capture plants for coal combustion. We have several designs and equipment sizes, I have been asked to do a quick check to see which components are particularly large so we can identify where any scale up issues may occur.

The component I am struggling with is a Flash drum which is specified with a diameter of 6m and a height of 17.2m operating at about 1 bar and 120 C. I can’t find any examples of flash drums of this size, it does seem quite large.

Do any of you know of flash drums of similar size or bigger? If so what is their purpose and if possible who constructed/installed them?

Thanks for your time, if would like any more info, I would be happy to give it if I can.

Laurence

[Art Montemayor]

Laurance:

You must be specific in your descriptions and explanations. I have over 25 years of personal design, fabrication, and operational experience in the CO2 industry and I can't understand what it is that you are trying to describe. In order for me to help you, you must furnish details such as your P&ID, vessel datasheet, and backup calculations. I (&others on this Forum) can't be expected to know in detail what it is that is confronting you without you taking the time and effort to explain and furnish us with all the basic data and details you have.

I personally doubt the need for a flash drum in a CO2 capturing process. But I can't make a specific and realistic comment without having all the data and facts. I don't even know the process you are using - much less the P&ID and mass balance!

Await your reply.

[Laurence]

Hello Art,

Thanks for your interest, and that is an impressive amount of experience. I would like to give more detailed information, unfortunately we have very limited information that I can provide, and this was not designed by us but externally so we don’t have significant detailed information.

I suppose in many ways this is not a specific question, it is more a general question. I am more interested to know the sizes of ANY large flash drums in your experience that are used for any purpose. Simply to get a feel for the relative size of this piece of kit. I have struggled to find any reference to flash drums/ KO drums of this kind of size (6m Dia 17m high). Which currently leads me to believe it is very large for a drum.

Would you be able to give any thoughts on the largest flash drums in your experience? Or do you think detailed information is essential for you to come to any conclusion about the relative size of this drum to others?

Lastly to explain the general process and the purpose of the flash drum, just for your interest.

This is for a standard absorber/stripper based system with MEA as the amine solvent. Flue gas enters the absorber where it contacts with the amine and CO2 is absorbed, the CO2 rich solution is pumped to a stripper where it is heated and the CO2 liberated, CO2 lean amine solution is returned to the top of absorber. This is a standard system for CO2/H2S (with MDEA) removal of natural gas and I assume you will have plenty of experience with it.

The flash drum is to be placed on the bottoms outlet of the stripper, where the pressure is dropped to flash off steam which is then recompressed and input into the bottom of the stripper. The aim is to reduce the heating load on the reboiler, obviously there will be an electrical requirement for the compressor, but this is more efficient due to by-passing the heat of evaporation.

I look forward to your reply

Regards

Laurence

[Art Montemayor]

Laurence:

The MEA CO2 removal process is an old one – even older than me. It was applied for patent in about 1930 by a fellow named R.R. Bottoms for the Girdler Corporation. For many years it was called the Girbotol process. A more complete and detailed description of this process can be found in U.S. Pat. No. Re. 18,985, issued Sept. 26, 1933. The first applications involved TEA and DEA, until MEA was applied successfully for CO2 removal. It was also meant for H2S removal – which it did, very efficiently. However, it was discovered that the H2S degraded the MEA into bad and corrosive by-products. The first solutions used for CO2 removal were upwards of 30% wt. and I operated a couple of Girdler plants that used a direct-fired reboiler and 20% wt. MEA solution. We were forced to dispose of the spent and degraded MEA solution after approximately 2,000 – 2,500 hours of operation. The 20% concentration of MEA and the direct-fired conditions were just too much torture for the process. The amine degraded into corrosive acids. We converted to steam-heated BKU reboilers. The hours of service increased, but the degradation of MEA persisted. I was forced to apply continuous, side-stream re-distillation methods to keep the 20% solution clean. In later years I also applied activated carbon adsorption, although I never stopped the re-distillation method because it is the most efficient and thorough of the clean-up methods.

The USA armed forces used skid-mounted Girdler CO2 plants to generate CO2 via combustion and a direct-fired reboiler during World War II, as I have described above. Some of these were installed on air craft carriers to keep all on-board CO2 fire extinguishers supplied around-the-clock.

The corrosive nature of degraded CO2 has been the stuff of nightmares for MEA plant operators. The stories, tales, and failed attempts at controlling the corrosion have filled many books and journals in my lifetime. Stainless steel was one means; others were Inconel, hastelloy, and even titanium – all very expensive solutions. I evolved some of the processes I worked on, to a 10% wt MEA solution and used only carbon steel with stainless steel tubes only in the reboiler steam bundle and the Rich-Lean heat exchanger. One combustion-based CO2 plant that I designed, built, and operated in Lima, Peru in this manner lasted for over 30 years before it was dismantled because the local market had over-grown its capacity. There was no corrosion ever reported with that unit over its entire life.

There isn’t much I haven’t seen or done with CO2 processes. I patented an automatic Dry Ice production machine. I am very familiar with the use of MDEA for sour gas removal from natural gas. However, that process has little or nothing to add to your proposed CO2 capture scheme.

I believe I know exactly what you (or someone else) are trying to accomplish. First and foremost, I suspect you are coming into this proposal assuming you can use high MEA concentrations. I believe that is a grave mistake for a large investment like CO2 capture. Everybody and his brother knows – by now – the rather high reboiler loads required to regenerate the rich MEA. The reboiler heat load dominates the cost figures of running an MEA acid gas process. You obviously don’t want to pay the price of lowering the MEA solution% because this increases the solution flow rate, which increases the reboiler load.

I also suspect you intend to operate the reboiler at a design pressure well over 5 psig – possibly as high as 35 – 50 psig. I would consider this a grave mistake and a misjudgement of the MEA degradation this will cause because of the higher reboiler temperatures. We in industry have for many years found how wise it is to always run the CO2 reboiler-stripper as close to atmospheric pressure as possible, with only the pressure drop caused by the CO2 cooler-condenser being the significant contributor to the reboiler pressure (& temperature). The resultant reboiler pressure has been approximately 5-7 psig. To go higher is to risk increased degradation and corrosion.

Of course, the reason for increasing the reboiler pressure is to allow you to flash the lean solution, recompress it, and inject it back into the reboiler (not into the main steam bundle). If my memory serves me right, I believe this method has already been tried on more than one occasion and it was abandoned because of impracticality.

I don’t see anything wrong with a flash drum that is 6 m dia by 17 m high. Everything is proportional to its related equipment. This size means that your reboiler size is relatively “huge”. But then, you haven’t even furnished us with any reboiler heat loads or flow rates, have you? Therefore, I wouldn’t reflect for much time on the size of the flash drum. I would concentrate on the viability of the process and the quantification of the expected trade-offs that will surely be involved in this process modification. Without specific information, I’m afraid I can’t add more than what I have already.

Good luck.

[SSWBoy]

Hello all,

I am investigating amine based CO2 capture plants for coal combustion. We have several designs and equipment sizes, I have been asked to do a quick check to see which components are particularly large so we can identify where any scale up issues may occur.

The component I am struggling with is a Flash drum which is specified with a diameter of 6m and a height of 17.2m operating at about 1 bar and 120 C. I can’t find any examples of flash drums of this size, it does seem quite large.

Do any of you know of flash drums of similar size or bigger? If so what is their purpose and if possible who constructed/installed them?

Thanks for your time, if would like any more info, I would be happy to give it if I can.

Laurence

Ethylene plant; 1st Stage suction for the Cracked Gas Compressor and 1st Stage Suction for Propylene Refrigeration. Both of these are probably bigger than your example for world scale (1000+ kTa) crackers. I'll have a look tomorrow and see if I can find a rough size for you.

[Laurence]

Art,

Thanks, that’s an interesting bit of background into the amine process. As you say the corrosion/degradation issue is one of significant concern, I understand it becomes a bit of a pickle as the suppliers find that corrosion inhibitors cause increased degradation and degradation inhibitors cause increased corrosion. Also amines have the tendency to foam, so anti foaming additives are required and you end up with an extremely finely balanced mixture…

The supplier we are working with has some small plants with this process working I believe, and although operating at higher pressure is bad for desorption, the CO2 will need to be recompressed once produced, so a complex balance will be require there to reduce overall cost.

I do not believe MEA is not long term future solution for CO2 capture, however at this early stage of development it is a difficult balance as novel solvents for lower regeneration require exceedingly large residence times requiring excessively large absorbers (or several) plus the cost of these solvents is orders higher than that of MEA counteracting there relatively low degradation. With this in mind MEA becomes an interesting first generation solvent, hence the investigation into engineering solutions to reduce heat load.

Thanks for your insight the practicality of such a system is a significant concern, and as you say the size of the vessel alone is not that significant.

SSW Boy

Any approximate examples you can find would be excellent just for my general knowledge.

Thank you both
Laurence