H2 MIXING WITH FUEL REDUCES CO2 EMISSION? 4

[RED007]

Dear Friends,
i just entered into industry. we had problem with amount of co2 emission in power plants, where some generators are running with diesel,some with gas and some with duel fuel. i read a short description about the addition of H2 to fuel gas reduces the amount of co2 emission.does anyone knows about this process. our primary aim is to reduce the amount of co2 releasing to atmosphere, as it is costing the company a lot. your advise and references are much appreciated.

thanks and regards

 

[TD2K]

How is the emission of CO2 costing your company money? Do you have a carbon tax?

The principle how H2 reduces your CO2 emissions is quite easy. Combustion of H2 produces only water. Therefore, you have to burn less additional hydrocarbon fuel (which produces the CO2) to release the same total heat as with 100% hydrocarbon fuel.

The trick is getting the H2. If you aren't already producing it or have it available, the main method of H2 production is steam reforming of hydrocarbon. That takes fuel, typically hydrocarbon based fuels which sort of defeats the whole purpose of making the H2 to reduce your CO2 emissions.

 

[Flareman]

If you can't get Hydrogen, work on using lighter fuels.
Methane generates about 1.28 lb CO2 per Million Btu output
Propane about 1.5 lb/MMBtu
Hexane about 1.58 lb/MMBtu
Cetane (Diesel) approx 1.62 lb/MMBtu

If you can get hydrogen, you will need to speak with burner equipment manufacturers to see how the hydrogen will affect the operating conditions.


David

 

[RED007]

Dear TD2K,

i'm actually looking for your reply, as i have been observing your answers to many of the questions posted in eng-tips. actually, as you expected we have a carbon tax. one more thing is we have duel fuel system, and the back pressure of exhaust gases should not effect the engine performance by any means.as i have just joined into industry as a chemical engineer graduate i need every help of you all experts inorder to stand in my field.so would be able to suggest any methods by which you can reduce the emission of Co2 by large amount? is it not a good idea to mix H2 with fuel feed? what about the conversion of CO2 to methane as: CO2 + 4H2 = CH4+ 2H2O, which is an exothermic reaction. please advise me.

 

[RED007]

dear Flareman,

thanks for your kind reply.we don't have hydrogen ailability at plant site. do you think replacing the existing generators with lighter fuels is economical than any other process, if our criteria is only reducing the emission of CO2?is it enough to change the burners in the generator system or anything else should be replaced inorder to use lighter fuels as a replacement. your reply is much appreciated.
thanks for everything.
red007

 

[Flareman]

RED007
It depends on the type of burners you have. In many cases, when the fuel is directly injected into the flame, you can easily switch the fuels and simply make a small adjustment to the operating pressure to give the same heat release. You may also have to "tweak" the air settings to reshape the flame but generally, switching gaseous hydrocarbon fuels is not a big deal. You do have to speak with the burner supplier to be sure.
This is probably the easiest change you can make as far as the burners are concerned so it seems like a good plan.
You need to look at the stoichiometry of the fuels you have available and their costs relative to the carbon output saving. If you are handling diesel fuel at the moment, there are bunkering and loading costs attached to that whereas natural gas may be readily available as a piped supply with no attendant costs so the saving may be more than the carbon tax alone.

Good luck

David

 

[RED007]

Dear David,
thanks for your reply.As u said the natural gas could have been a good idea. but we have off-shore oil/gas plant, but as i said before they have been using oil in some plants and gas or both in some plants as a duel fuel option. how one can avoid back pressure of co2 emitted inorder to not to effect the performance of generator engine. do you think replacing the fuel with methane or propane will be a good idea.what other alternatives would you be able to suggest? your reply is much appreciated.

With best regards,

RED007.

 

[RED007]

HI DAVID,
there is one more thing that i would like to let you know. we are currently using fuel gas as maximum fuel to generate power, but still we are facing the co2 emission problems. only when you are not having the fuel gas in stock, we are choosing diesel as an replacement. as u said we are planing to replace the small amount of diesel, which we are currently using will also be replaced with methane, but i need to more practical way of doing it, as the compressed methane or propane storage and handling is difficult? how do deal with this situation practically? what is best means of reducing CO2 emission in case of natural gas as fuel on offshore? please reply soon.

With best regards,
RED007.

 

[TD2K]

RED007, you need to stand back and think about this. Use the engineering principles you've just finished taking in University.

For example, you say you are looking at replacing your diesel generators and associated storage tanks with gas fired generators and storage tanks. I assume these are backup generators as you say "replace the small amount of diesel".

How much diesel do you use in a year? How much CO2 does that release? If you were to convert these to gas, how much CO2 would you 'save'(for a first pass assume equal heat inputs)? That gives you a dollar value.

Now, if you were to installed compressed gas backup versus diesel, how much gas would you need to have to give you the same backup capacity as your existing diesel tanks? That will set the size of the storage vessels you need.

You would need to consider the costs to change your existing diesel generators over to gas fired, the costs of the storage pressure vessels to store the compressed gas as backup fuel and any other equipment needed (compressors to refill the tanks after use?) against the savings in CO2 emissions. Then there are some softer issues to consider such as are you going to have as reliable a backup system as you do now?

Frankly, this sounds like a knee jerk reaction someone has had with little/no thought put into it.

 

[MariusChE]

Red

The gas-water shift reaction is one of the most studied thermodynamic reactions that is out there. It is overall endothermic and not so easy to do as you may think. The methane will react with air to produce CO2. The shift needs high pressure and temperature. Keep digging...

remove.marius_che@yahoo.com

 

[RED007]

DEAR TD2K,

thanks for your reply. as you said i have a data about the amount of diesel and the co2 emitted per ton of diesel consumed. but as david(flareman)said methane generates 1.28lb Co2 per millionBtu out out, but what should be the efficiency of the engine/turbine to generate this amount? please suggest how can i calculate the volume of a storagetank/bunker required to store compressed methane? and does the compressed gas can be directly pumped/unloaded from a tanker?how could you maintain the internalpressure of storage tank/bunker above the vapour pressure of methane with the varying fluid volume of the storage tank?please forgive my ignorance.please sugest any references if atall you think useful
best regards,
RED007.

 

[oxilume]

TD2K,

Calculate the amount of CO2 you need to sequester (remove) to be within your permit limit.

Take a slipstream based upon your above calculation from the flue gas and scrub the CO2 with a glycol-amine process which uses a mix of DEG or TEG, MEA or DEA.

Todd

 

[butlen]

Red

I agree with TD2k that you need to start at first principles. Look at your energy needs and your entire process. Is your current process (for which the electrical energy is required) efficient, or could you reduce your energy demand. Does your process have byproducts, or waste heat, which could be re-cycled or utilised. If you have several generators working together do you use the exhaust heat? If you have reasonable power outputs its relatively cheap to recover jacket and exhaust heat in a waste heat recovery boiler, then you could expand the steam across a steam turbine generator to improve cycle efficiency (with 7MWe output from engines you could get another say 2.5MWe extra from an STG)

Only after looking at this should you look at the final option of scrubbing the CO2.

After you have looked at the worst case scenario of scrubbing, then you should consider that it may be cheaper to buy CO2 reduction credits from someone else (who can more cheaply reduce their emmissions) and use these to offset your emmissions.


Neil

 

[RED007]

Dear friends,
please note that according to our data 10MW lectric current producing 88750 tonnes of CO2 from both gas(max.usage)and diesel fuel. but according to flareman(david) for example if you use methane as fuel it produces 1.614 E+11MW of power for 88750 tonns of CO2(on the basis of 1.28 lb of CO2 per million Btu out put) millon. but according to our data it should be equal to 10MW. so approximately we have to remove 90000 tonnes of CO2 has to be removed from the process. so now i want to find out what concentration and amount of amine is needed? i want to know in what ratio the fuel and hydrogen has to be injected and in what form in to the engine combustion chamber inorder to reduce the emission of CO2? your help will be appreciated.
thanks
RED007.

 

[butlen]

Red

Please give the following for clarity
1) How much electricity does your site use?
2) How much electricity does your site generate?
3) What type of generators do you have?
4) How much CO2 do you emit?
5) How much do you need to reduce your CO2 reduction by?
6) What does the tax cost per tonne CO2?

Neil

 

[Montemayor]

RED007 (Chemical):

I just got back from vacation and found this thread which takes me back to a time when I had to confront this some years back. I mixed H2 and various fuel gases for firing steam boilers - and also mutually fired the H2 with fuel oils. I can share my hands-on experience in case it helps. However, there are a lot of words, information, ideas, and opinions being batted back and forth on this issue and very little basic data is offered by you. butlen is making this point in his list of questions.

Basically, you've said you are generating power by "burning" various fuels - including diesel. Then you mention the use of "generator engine". You probably mean a diesel engine generator. But then, how do you intend to have us believe that you can switch fuels in a Diesel engine? You really should state your basic data very clearly; otherwise, you'll have an endless thread. In order to cut things to the quick allow me to state that you're going to find that it is economically not feasible to burn H2 to generate steam and power a turbine for electric energy. TD2K is stating this basic, practical fact. You cannot logically expect to purchase (or produce) H2 for fuel purposes within a boiler in order to back out CO2-producing fuels. Even if you had so-called "free", local produced H2 it would still not be economically possible. For one thing, not only the burners but also the combustion chamber and boiler tubes would have to be re-evaluated and possibly modified. Hydrogen does not produce CO2 - this is basic chemistry. What is more important for the combustion and heat recovery is that the lack of CO2 reduces the flames'luminosity and radiation qualities. The combustion chamber design is different and more challenging.

Additionally, you will find that the quantity of H2 required to replace (on a net, effective Btu per Btu basis) the fuel oil or natural gas will be priced out of a competitive range. It is just too damn expensive.

The idea of removing the CO2 from the flue gas as an answer is nonsense. Absorbing the CO2 and recovering it is no challenge. But what are you going to do with 90,000 tonnes of the stuff? I presume this is per day? You don't state the rate, but the issue is still DISPOSAL! You can't put it into the atmosphere (otherwise, you'd leave it in the flue!), so the only answer would be to sell it or use it as secondary or tertiary recovery for re-pressuring oil reservoirs. Great! Now you're in the CO2 business, competing with Praxair and Air Liquide. I don't think this is where you want to head with your scope unless your company has deep, deep pockets of cash.

The idea of Methanating the CO2 with H2 to produce Methane fuel is again not much of a process challenge. As you know, it is an exotherm; however, you have to carry it out at a relative high temperature and invest in process equipment. You will soon discover that the cost of the purchased H2 will outstrip the value of the produced CH4.

My comments are not meant to be negative nor contradictory; I've been there and back and it just doesn't work economically. The frank and naked truth is that some junk-science freaks in your government bodies have gotten it in their heads that they will dictate engineering to the engineers - whether we like it or not. The facts are that they are failing to comply with basic, logical truths and science. Fossil fuels are here because of a reason - not because we like to generate so-called "green house" gases. The answer is still fossil fuels (diesel, nat. gas, LPG, etc.) - that is, unless you accept nuclear energy (ugh!)
TD2K says it well when he states "Frankly, this sounds like a knee jerk reaction someone has had with little/no thought put into it." My experience, exactly.

The bottom line is: Forget about so-called Hydrogen power for now. The technology is not here yet to produce cost-effective H2. Better and more practical answers are:

1) approve nuclear power;
2) Hydroelectric;
3) geothermal; and
4) fire the stupid politicians who dreamed up the CO2 tax (this is the best solution).

Sorry I can't offer a miracle.


Art Montemayor
Spring, TX

 

[RED007]

Hi Montemayer,

please note that we are trying to reduce 90000 tonns of Co2 /anum out of 750000 tonnes of over all CO2 emission and are ready to invest 4.5 millon pounds/anum to achieve this. In an year approximately 84MW of power will be generated. what hapens if you add 15% by volume of H2 with fuel? do you think the alteration of burners or fuel ratio wouldn't help much? we have currently Avon turbine generators and facing atleast 70% losses in the production. i can provide you with more info in near future. what about the diffusion of CO2 into sea water? producing CH4 from CO2+H2 may initially needs a lot of energy but once the reaction starts the heat generated by the reaction will be enough to proceed further as the reaction is highly exhothermic. please advise with all your sugestions.

With best regards,

Red007

 

[RED007]

HI,
here is the data for one plant:

1)diesel consumption=1158 tonns/yr
2)fuel gas consumption=30 million cubic meter/yr
3)over all CO2 emission =120040 tonnes/yr
4)we have 3 SOLAR MARS type turbines fueled by gas/diesel with each of nominal out put=10MW
5)power required =18 to 21MW
6)CO2 credits cost=£5/tonne
5)Required amount of CO2 reduction from this plant=30000 to 40000 tonnes/yr
6) the diesel efficiency will be 30% when 2 turbines are in operation but falls from 30% to 27% when 3 turbines are in operation.
7). please also note that one turbine among three is like a backup if any one the other two fails or the required load exceeds 20MW.

i request all of you give valuable suggestions after all.

With best regards,

Red007

 

[TD2K]

RED007,

Don't take this wrong as it's not aimed at you but your company is not serious about this project. You are new to this field and you do not have anyway near the experience depth needed to look at the various possibilities even for a screening level review. You should be working on much simplier projects to learn engineering.

In my opinion, it seems to be that 'someone' at the top has asked/demanded/directed that your company look at ways of reducing their CO2 credit cost and your company, as a sop to this 'request', has assigned it to you. That way, they can say they are working on it when in reality, the directed 'reductions' of at least 25% are ridiculous.

There is no magic way of significantly reducing CO2 emissions from fired equipment other than reducing the power demand once you primarily run on fuel gas. Adding H2 to the mixture does not reduce CO2 other than by its contribution to the amount of heat released (on a kJ for kJ basis).

My first approach would be to involve Solar and ask them how to maximize the efficiency of the existing units and what overall efficiency improvements are possible. You could significantly improve the overall efficiency by adding in heat recovery to the existing units but that adds another wrinkle of complexity to the entire question. This typically means producing steam to generate additional electricity but then you have a steam plant to build, water treatment issues, cooling requirements, etc. The first question that springs to mind though is if this heat recovery is economical now, why wasn't it part of the original design (it's a rhetorical question: likely because it wasn't economical then and therefore is unlikely to be economical now).

My suggestion would be to hire a consulting company that can do a screening study for you and come up with options and order of magnitude costs to hand to upper management or whoever came up with this idea as to why it's not feasible. You are in a tough position and your supervisor/manager are not doing their jobs by dumping something as vague as this on you with the lack of support you appear to be getting.

While I give you credit for diving in headfirst into this assignment, you have bitten off way too much to chew.

 

[Montemayor]

To TD2K (Chemical):

AMEN, brother!

To RED007 (Chemical):

I strongly recommmend you read very carefully and take good notes of what TD2K has expressed. This is as good, practical, engineering advice as you can get on this specific problem. What is being detailed out for you is a logical, comprehensive engineering manner of solving a complex problem like yours. It is complex not because of the chemistry and the math; rather, it is complex because of the many alternatives, lack of definitive scope, the politics involved, and the diversified disciplines that it involves. Additionally, it impacts (or will be decided by) top management business and political decisions which are totally out of your control.

But don't dispair and start thinking that the handling of the problem at your level is not "engineering"! This is EXACTLY what engineering is all about - the resolution of problems. I really like TD2K's advice because it stresses the basic, fundamental rule that should be every young engineer's: Never go to your boss(es) with problems or quandries; go to them with ANSWERS or RECOMMENDATIONS. If your bosses or company are worth their salt, they will be eternally grateful for that kind of response and action on your part.

I would hope other young engineers out there are reading this thread and taking note.

Good Luck.

Art Montemayor
Spring, TX