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Researchers Propose Dual-Bed Configuration to Increase Efficiency and Reduce Emissions from Coal Gasification

Scheme of the gasification process with air using two reactors. Click to enlarge. Credit: ACS

Researchers in Italy are proposing a new dual-bed configuration for coal gasification that, in laboratory simulations of Coal-to-Liquids production, is 71.1% more energy efficient; increases the mass yield of synthetic fuel by 39.4%; and releases 31.9% less CO2 than conventional gasification.

Applied for power generation, the dual bed configuration increases plant efficiency by 27.9% and decreases CO2 emissions decrease by 21.8%, compared to a conventional IGCC process. A paper on their work is scheduled for the 19 November issue of the ACS journal Energy & Fuels.

The dual fluidized bed reactor scheme thermally couples a combustor, in which coal is burnt with air, and a gasifier, which is fed with coal and steam, via the circulation of an inert solid. The required heat for the gasifier is transferred by using the inert solid as the carrier.

Pressures in the two reactors are kept different (19.5 bar for the combustor, 20 bar for the gasifier) both to avoid the contamination of syngas, and to keep the two environments apart from each other. The fluidization agent in the combustor is the same air used for pneumatic transport of the inert solid,; in the gasifier, it is the steam.

In our process, coal and saturated steam at 20 bar are fed to the gasifier. The heat carrying the mixture of inerts and ash from the combustor enters the gasifier from the top of the reactor. The syngas produced exits from the top whereas unreacted char and inerts exit from the bottom by gravity and are carried back to the combustor by means of compressed air. In the combustor, coal is burnt to supply the heat needed to take the inert back to the temperature of combustion. Syngas is routed to a cyclone to remove dust and inerts for which, because of unavoidable losses, a makeup is needed. A gas expander is fed by combustion gases and operates between the combustor pressure and near-atmospheric conditions. Power from the expander is recovered to run the air compressor.

—Sudiro et al. (2008)

For the analysis of the Fischer-Tropsch CTL application, the researchers coupled the gasifier-combustor configuration with a conventional CTL process. The syngas is rich in methane, which needs to be removed before entering the FT process in order to avoid reducing the yield. The methane removal, achieved using a pressure-swing-adsorption (PSA) unit with activated carbon, results in a synthetic natural gas (SNG) co-product stream.


  • M. Sudiro, A. Bertucco, F. Ruggeri, and M. Fontana (2008) Improving Process Performances in Coal Gasification for Power and Synfuel Production. ASAP Energy Fuels, doi: 10.1021/ef800293h


Henry Gibson

Absolutely delightful. I invented a different system operating on similar heat transfer principals. I am glad to see that it works without having to build it myself.

This device eliminates the need for large steam boilers and turbines, and coal fired power plants can be built with multiple large but not huge gas engines or combined cycle turbines. The use of relatively small gas engines allows quick load following and voltage control and redundantcy. UTC makes heat recovery devices for exhaust to produce electricity for more efficiency if desired. This device can also be fitted to the exiting exhaust after the expander and also to the syngas exit if the gas needs to be cooled for processing. Such devices are used for geothermal energy and can also be had from Ormat and others.

It is possible that more energy can be had from the expander than is used by the compressor and those combined systems become a gas turbine fueled by coal. MITI can make air bearing compressors and turbines for low maintenance long life small systems.

Depending on the price of methane, it can be sold or burnt or even liquified for later use or sale. Such a unit should also produce methanol and store it for sale or direct conversion to gasoline which is a simple patented process. FT synthesis is not as good as methanol production.


Great! With 300 years of reserves the US is the Saudi Arabia of coal. We may get out of this con scheme the oil producers have yet! Dig baby, dig!

Dan A

Coal gasification's efficiency has been pushing 50%, so a 27.9% increase in efficiency would push it to ~63%, which is higher than that of natural gas combined cycle. Is that really possible? Either way, great news.

jv - "With 300 years of reserves the US is the Saudi Arabia of coal."

First of all there is not actually that much coal as this figure was calculated as if coal use does not increase and that all the coal is recoverable which it is not.

Second like Peak Oil if you start trying to replace oil with CTL you just get Peak Coal in about 50 years or less.

Third we really do not want this amount of carbon in the atmosphere.


Nice process indeed

It is time to stop this illusion that america has 300 years of coal, this was based on very unriable estimate done in the 70s. Recent studies have pointed out that the reserves a much less than that. In fact the production of coal in terme of energy has already peaked in US about 10 years ago because the quality is getting worse and worse. So CTL can help but it is not a desirable solution not only because it release too much CO2 in the atmosphere but also because it is highly capital intensive and also expensive to run. Mining all the coal in US has very detrimental effect on the environment as well.

Henry Gibson

Al Gore did not have the courage to show how France reduced its green house gases by converting to nuclear. Nor did he show how Germany has increased its greenhouse gas by turning off nuclear and replacing it with coal.

Every second there are 25 nuclear explosions in each pound of your body. This is about half what it was two billion years ago. The same trite comment about no nuclear reactors being built(in the US) since the 1970s is false, but was part of the recent presidential debate.

The CO2 cost of imported oil is not known, so there may be many advantages to using coal. The coal to natural gas facility in North Dakota ships its CO2 more than a hundred miles in a pipe to a Canadian oil company that pumps it down wells to get twice the production of oil.

Everything seems to be related to the first three laws of thermodynamics. You cannot win. You cannot even break even. You cannot get out of the game alive. ..HG..


Since there is a lot of surplus energy (at night), the efficiency could be increased easily by (additional) electrical heating of the gasifier.
Secondly, every powerplant has a lot of 'waste steam' that could be fed into the gasifier.

I meant : 'a lot of surplus electricity (at night),...


The claimed efficiency improvements are relative to existing IGCC despite having two coal input points not one. Unfortunately coal gasification without exhaust CO2 capture is not going to cut it if carbon limits apply. Same goes for coal fired supercritical steam or air dried lignite; the CO2 reduction is still not enough. Note carbon limits will apply in Europe, Australia, Scandinavia and the US whichever candidate becomes president.

I think further evidence that coal is not going to last 200 years is the huge price increases in the 18 months prior to the Wall St meltdown. In any form coal is a loser and so are we if we stick with it.

Alex Kovnat

We Americans (and by the way this is probably true in China as well) could cut our carbon dioxide gas-puffing by a significant amount, if only we could put out underground coal mine fires which are not only polluting the atmosphere but also wasting coal as well.

There is plenty of lignite coal in North Dakota and out west, and who knows how much is out there if we were to decide to look, just as we've found a lot of oil.

But I am not enthralled with turning full-tilt to coal or shale. For one thing, there is the matter of global warming. And another issue is mercury. Right now the Chinese are pouring heaven knows how many tons of mercury into the atmosphere every year from coal-burning, and not all of that mercury stays in China. It drifts, like radioactive fallout from atmospheric nuclear weapon tests, across the sea and reaches us here in the USA.

Of course we Americans are hardly innocent in this regard. We've polluted the great lakes and our environment generally, with mercury over the course of more than a century of massive coal-burning.

If nuclear power plants were found to have been surreptitiously polluting our environment with strontium-90, there would be howls of protest.

If we are to use coal gasification, my suggestion is to co-gasify coal along with natural gas. That way, coal's surplus of carbon and natural gas's surplus of hydrogen would even out one another. In addition, if we are to continue to utilize coal, we must remove and sequester (or, utilize as a resource in their own right) mercury, other mineral elements, and finally also URANIUM and THORIUM which are known to occur in small amounts in coal.


China has roughly the same installed electricity base as the U.S. though 90% is coal fired compared to ~50% here. China is rapidly experiencing their own domestic "peak coal" and are having to import from Australia hand over fist.

If we (the U.S.) were smart, we would phase out all of our coal fired electricity domestically so we would be positioned 30 years from now to export to China. Got to get those $s back somehow!

Seriously, the U.S. is just like the Saudi Arabia of coal. We have the largest and most easily extracted reserves. 300 years worth? No. Probably more like 100 years worth assuming no demand increase. Still, that's a lot of coal we could sell to the Chinese.

Kit P


Again, where do you live?

I live in coal country and get my electricity almost entirely from coal. My air is clean, my environment is beautiful. Levels of mercury are at natural levels and our children do not have levels above a threshold of harm.

It gets old having folks who live in a cesspool explain what is wrong with how we do things? Tell treehugger how the German coal industry doing?


The exports of US coal are increasing since China has stopped exporting. This is creating jobs but also causing the price of coal to US users to increase. This is a reason so many new nuke plants are in the planning stage. My utility and a neighboring utility were adamant about not building new nukes. Each has two nuke plants that run very well but were old guard coal operators at heart.

Many of the large US utilities own coal reserves, operate coal mines, and coal transportation systems. They are submitting COLs to the NRC for new nukes because they make more money sell coal to treehugger.

Since I am not in the coal industry, I find some of the trends odd. High BTU, high sulfur coal is in demand overseas. Do the users of this coal meet US standards for emissions.

Alton Fingaster

Yesterday, Barak Obama pledged to treat CO2 as a dangerous pollutant, if elected. Any plans you might have had to use coal, oil sands, oil shale, heavy oils, etc. may as well be thrown away, if the US elects The One.

Earth's terrestrial and aquatic plants will be dismayed to learn how they have been poisoned by CO2 all these epochs of time. Many of our plants evolved when CO2 levels were much higher, and are currently "starved" for CO2. How sad they will be to learn of the new carbon regime.

stas peterson

As a good little Socialists it is appropriate to reserve all the energy for the socialist bretheren states.

The US does not need any energy, the proletariat would be much happier becoming landless, ignorant, serfs and wards of the Messiah's state. And much easier to control too.


Heavy oils are in Alberta Canada, not in the US, so Alton is wrong on that. Why are there such anti-business opinions existing around people in the West? I ve never met an Asian who says such things. Don't be jealous when they become richer than you are.

AAEG-life member

The US is more than the Saudi of coal, using UCG technologies the USA has 1.6 TRILLON tons of coal accessible with current technologies at a margin price of >$2.5 mmbtu for the syngas at the well heads. I should know I'm a Exploration Geologist by trade so statement is professional fact not the blog rubbish people post here. UCG technology is mature as Kazakhstan has been using it successfully for 40 yes 40 years to run gas turbine and boiler fired power plants in a region of the world where the coal seams are to deep to mine. don't take my word for it look up UGC and Kazakhstan on any academic search engine please do real research not internet googling. 85% of US coal is too deep for traditional column and pier mining but the depth is perfect for hydrogasification or O2 fired UGC the over burden contains the cavity and provides the pressure needed to speed the kinetics of the reaction. the syngas can be FT at the well heads or converted cataliticaly to CH4 using the reverse water gas shift for the make up H2 and sent via pipeline. symilarly a methanol catalyst can be used to turn the hot reactive syngas to MtOH from pipeline to a central plant and used in the Exxon MtOH to Octane process over zeolites.

AAEG-life member

English is not my first language apologies for any errors

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