CO2 recovery

[stanlsimon]

I am looking for a device which will separate CO2 from the exhaust stream of an internal combustion engine fueled with gassified wood.

Reclaimed CO2 should be pure enough to be used in a greenhouse for enhanced plant growth.

I am thinking that the device will utilize MEA or Carbonate to strip the CO2.

I would like to buy a package unit pre engineered, size of unit is for a 25 kw generator, (small).

 

[djack77494]

stan,
I do not believe you will find such a system, and if you do, I suspect that the economics would favor letting the engine's CO2 escape and purchasing CO2 for your greenhouse use. There are some commercial processes available for CO2 absorption from flue gases (e.g. Benfield), but they are practical only on a much larger scale than that which you imply.
Doug

 

[stanlsimon]

Economics are going to be against this but never mind that because this is a research project funded by deep pockets.

So, I should plan on hiring someone with experience in this field to design such a device. Whoever can do it could potentially plan on making lots of money.

 

[zdas04]

I looked at doing something similar on a large scale (I wanted pure CO2 to inject into a gas field to enhance methane production) and found that it was much less expensive to separate oxygen from the air in a membrane skid and make the engine oxy-fueled. Then you can take a portion of your stack gas to mix with the oxygen (to get to 80% CO2 and 20% oxygen) and the rest is pretty pure CO2. Techniques to capture the CO2 from an air-fired engine were just too complex to be believed (both temperature and pressure are against you).

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[dcasto]

In the early 70's they tried to capture the CO2 from engine exhaust for reinjection. One of the big Engineering firms designed the system. The enigens were driving compressors and they just took one of the throws on the compressor to compress the exhaust. They used a bank on the gas coolers to cool the exhaust. They removed the CO2 with MEA. The System ran well untill all the piping from the exhaust cooler to the compressor dissolved along with the cooler.

By the time you buy the 304SS and compress the exhaust, you could buy the CO2.

 

[epoisses]

I think as soon as you oxidize any remaining CO to CO2, there are only traces of other components to take out. I'd tend to think that removal with MEA would not be very effective versus a couple of steps to get rid of the trace contaminants.

What else is in the stream?

Re economics, dunno but I know that Shell Pernis refinery in the Netherlands sends CO2 from their steam reformer to nearby greenhouses and I have also heard of refineries selling it to soft drink bottling companies (although that may be tricky on a legal level, I wouldn't want a slug of MEA in my Coke).

 

[stanlsimon]

MEA is quite corrosive, it needs corrosion inhibitors, unless more exotic steel can be found .

So responding to Mr. Simpson's comments, the 80/20 mix is what you use to inject back into the ground? Or do you use that to feed into the engine intake? It seems like running an engine on 100% O2 would require a special engine.

It seems like this would help get rid of the NOx and SOx, depending on what type of fuel is used.

The O2 concentrator that you mentioned sould like an industrial version of what they use in nursing homes for onsite oxygen generation.

 

[Montemayor]

Stanlsimon;

From what I can deduce of your basic data, you are trying to do a complete, natural energy cycle where you harvest organic growth (wood), “gasify” the wood to a methane-rich fuel (by some unknown process), burn the resultant fuel gas in an internal combustion engine that drives an electric generator and emits a CO₂-rich exhaust. The resultant exhaust would be processed to remove the CO₂ and return it to a green house to supply the needed carbon to produce an organic growth (trees?). Although you don’t state as such, this sounds like an agricultural perpetual motion machine. Organic growth produces energy, CO₂, and more organic growth – with some fertilizer, water, and a lot of labor.

I’m not into agriculture, but I’ve been into a lot of CO₂ – generated from combustion products, recovered from chemical processes, and recovered from natural CO₂ wells. I’ve spent a lot of years in design and operation of CO2 recovery plants. I don’t believe your proposed process has a practical chance of succeeding but I think it’s only fair to give you the benefit of the doubt. However, my years of experience confirms what both Dave Simpson and dcasto are stating and alerting you to: beware of the exhaust gas process conditions and prepare for an expensive piping and handling installation just to transport and handle exhaust gas. The MEA purification system should be a piece of cake. The MEA process has been around since Mr. R. R. Bottoms patented it in 1935 for the Girdler Corporation. Since then, quite a lot of Lessons Learned and other improvements have made it a pretty easy application to employ. The main tradeoff is the same as it was in 1935: the reboiler duty requirements are high for regenerating the rich MEA into lean MEA. This feature alone has scuttled many countless other CO2 recovery projects in the past – many of them based on flue gas from electric generating stations.

Contrary to what you state, Monoethanolamine (MEA) is NOT CORROSIVE. In fact, for many years it was known and employed as a corrosion deterrent and inhibitor. Please don’t interpret my factual statement as a criticism against your proposal or statements. My purpose here is merely to state factual information that is backed up by historical field experience and findings. While MEA is not a corrosive chemical, its oxidation products and other side chemicals produced by its degradation through excess heating and combinations with other chemicals do, indeed, produce bad corrosion. An MEA solution with strength of up to 20% MEA can be controlled and maintained in a non-corrosive state by filtering with activated carbon and applying a re-distillation still to the MEA circuit. This is commonly done in almost all successful MEA process units operating today. I have operated plants with up to 18% MEA with only the hot Rich MEA tubes in the MEA exchangers and the tubes in the steam-heated reboiler being constructed of stainless steel. All the remainder of the process was fabricated of mild carbon steel – mainly A-212 or A-516. And I experienced no detectable corrosion – as long as the activated carbon filter and the redistillation still were operating normally. You certainly do not need “exotic steel” to handle MEA solutions up to 18% strength. However, if you don’t know any better or don’t want to maintain a clean and pure MEA solution, you are certainly free to use any expensive exotic alloy if you so desire.

I hope this experience is of some help.

 

[kenvlach]

I agree with Montemayor. Also, I think perhaps that the most practical way to utilize the exhaust CO₂ would be to locate the engine next to the greenhouse, sort of a co-generation process. Use the engine coolant heat & exhaust heat for greenhouse heating, and pipe the cooled exhaust gas (N₂ + H₂O + CO₂) directly into the greenhouse. Need an oxygen monitor to protect humans.

zdas04, wouldn't an oxygen-gas IC engine have to be about 4 times stronger while running hotter? Maybe a dragster engine?

A number of metal finishers tried cogeneration set-ups in the 1990's after natural gas prices shot up. Problem was, the heat demand was greatest during startup, while electricity was needed throughout the day.

 

[stanlsimon]

Thanks for that extensive reply, the gasifier feeds into a IC engine, turbine or perhaps fuel cell CPC is one proposed manufacturer, I have not been able to get a list of exhaust gas constituents as of yet.

Some greenhouses simply divert flue gas from a propane or methane fired boiler, cool it and distribute throughout the greenhouse. A CO detector should be included. Gasified wood fumes after being compressed and ignited in an engine may not be nearly so pure.

What about a simple scrubber / deflegmator using other aqueous solutions, collection efficiency of CO2 does not need to be very high. We are only trying to get up to 1200 ppm of CO2 in the greenhouse atmosphere.

I'm told that unslaked lime absorbs CO2 but would that be selective enough?

Another idea is desublimination using low temperature cascaded refrigeration.

A metal oxide reaction system sounds promising as no NOx would be introduced.

At this point I am investigating feasibility. We will have to find a pre-engineered system or hire a Rasputin to design something.

I did find some installations that were sized down to 6 tonnes/day using MEA type processes but I think we are talking millions of dollars.

 

[zdas04]

I guess I didn't describe the Oxy-Fuel scenario very well.

The mix of gases going into the (unmodified) engine are 80% CO2 (recycled from the stack) and 20% oxygen. By getting the nitrogen out of the combustion process you eliminate the NOx and end up with flue gas that usable CO2 as soon as you cool it. You have to be really careful with your Air-Fuel ratio to make darn sure you don't generate much CO, but the technology to do that is pretty mature.

The point was that it is much less expensive to extract oxygen from air than it is to extract CO2 from flue gas.

David

 

[stanlsimon]

Thanks Dave for the clarification, I thought that is what you were saying. I am not sure how the controls for this will work out because the manufacturer of the downdraft gasifier has some sort of control package that (hopefully) automates the process. In the gasifier they are making CO, H2 and feeding it into the carburator of the engine.

 

[moltenmetal]

Montemayor: it's not really a perpetual motion machine- it's just a solar energy concentrator/storage device. Except of course the idea isn't to use the CO2 emitted from the gasification and power generation directly to help the trees grow- rather he's after growing some higher value plants which have a hope of making the enclosed space of the greenhouse worthwhile. Putting legality aside, there are some very high value plants which this kind of set-up might be very beneficial for...and for which being off the grid would be a big help!

Co-locating fossil-fueled power plants with greenhouses does have some merit. At least you'd get some benefit out of the concentrated CO2, as well as a great deal of benefit out of the waste heat. But of course that only works for about half the year, even in a fairly cold climate.

 

[stanlsimon]

Don't even think about growing the wrong kind of tobacco in this greenhouse. Let's get serious, why can't I just use a simple water column scrubber to capture CO2? The biogas people seem to think it works for them.

 

[dcasto]

You can circulate enough water and regenerate it to get whatever CO2 you want, its not the most cost effective way except for very small amounts.