http://www.interacademycouncil.net/Object.File/Master/10/335/Clean%20Coal%20Technology_%20Coal%20Liquefaction.pdf

We recently made report of an article that had been written for the "Kirk-Othmer Encyclopedia of Chemical Technology", which presented a rather comprehensive overview of Coal conversion science, including it's history and descriptions of several variations.

 

As seen in: WVU Explains Coal Conversion Technology | Research & Development, that article was composed by WVU Professor of Chemical Engineering, Dr. Dady B. Dadyburjor, in collaboration with a representative from China's official "State Key Laboratory of Coal Conversion", one Zhenyu Liu.

First, we realize that the "Kirk-Othmer Encyclopedia" is likely unfamiliar to the majority of our readers. It is, by reports, a highly-regarded chemical technology reference work, composed of many volumes and published, we believe, in multiple languages.

 

It is relied upon for technical information by chemical industry professionals around the world.

 

More about it can be learned via: Kirk-Othmer Encyclopedia of Chemical Technology [Review]; by Cory Craig, Physical Sciences and Engineering Library, University of California; a link which we should have included in that prior report.

 

In any case, we submit herein, via the initial link in this dispatch, an example of Zhenyu Liu's individual work, which, we think, provides some further information concerning the technology of Coal liquefaction, information supplemental and complementary to that presented with Dadyburjor in the Kirk-Othmer entry.

 

Comment is inserted within, and follows, excerpts from:

 

"Clean Coal Technology: Direct and Indirect Coal-to-Liquid Technologies

 

2005


Zhenyu Liu; State Key Laboratory of Coal Conversion; Chinese Academy of Science

 

Introduction: Coal-to-liquid technology refers to chemical processes which convert solid coal into liquid fuels and chemicals. ... (The) the main functions of the coal-to-liquid processes are breakage of the coal’s
molecular size and addition of hydrogen into coal, or, in other words, destructive hydrogenation of coal.

 

These processes are generally termed coal liquefaction.


There are two types of coal liquefaction schemes in principle. One is direct coal liquefaction, which refers to decomposition of coal and addition of hydrogen directly to coal ... . Another one is indirect coal liquefaction, which refers to destruction of all the coal into gaseous carbon monoxide and hydrogen through gasification, and then hydrogenation of carbon monoxide to liquid fuels and chemicals.

 

For both schemes, coal is usually ground into fine particles for better reaction, and the reactions have to be carried out at elevated temperatures and pressures, in the presence of catalysts. Destructive fractionation of
coal commonly called pyrolysis of coal can also be categorized into direct coal liquefaction where solvent and catalyst are not used, and in many cases no hydrogenation is involved.


Since coal always contains, besides carbon and hydrogen, inorganic materials, ... mineral matter or “ash”, and sulfur, nitrogen and oxygen, etc. commonly called “heteroatoms”, coal liquefaction processes involve also rejection and/or capture and/or conversion of those materials.


To meet the market standards and specifications for transportation fuels the liquefaction processes contain always various types of product upgrading steps after the formation of the primary liquefaction products.

 

In 1913, Friedrich Bergius invented the direct coal liquefaction process and was awarded the Nobel Prize for chemistry in 1931 for this pioneering work.

 

In 1923, Franz Fischer and Hans Tropsch discovered the indirect liquefaction process, which is addressed today as the FT synthesis.

 

Since then both of the coal liquefaction schemes experienced fast developments and went to commercial application in Germany and England in World II.

 

In the same period of time ... Japan and France also built coal liquefaction plants.

 

The greatest successes in indirect coal liquefaction were made in South Africa since 1950s due to its limited petroleum reserves and abundant coal reserves, and political circumstances.

 

The South Africa Coal Oil and Gas Corporation Ltd. (SASOL) had its first FT synthesis plant, Sasol I, in operation in 1955, the second and the third plants, Sasol II and Sasol III, in operation in 1982. During this period, the FT technology advanced significantly ... .

 

The products of Sasol I includes diesel, gasoline, light and heavy naphtha, liquid petroleum gases, fuel oil, cracking stock, paraffin, various types of waxes, various types of ketones and alcohols ... .

 

The chemicals produced in Sasol II and III include ethylene (560 t/d), alcohols (250 t/d), LPG (640 m3/d), sulfur (270 t/d), tar products (540 t/d) and ammonia (360 t/d).

 

In 2000, Sasol’s annual profit was more than 1.3 billion U.S. dollars without government subsidy.

 

Methanol synthesis from carbon monoxide and hydrogen is also considered as a route of indirect coal liquefaction, which was patented by Bayer in 1923. Methanol can be used as a fuel, an octane extender for gasoline, feed stock for the production of polymers and other chemicals.

 

Indirect coal liquefaction processes also include methanol-to-oil and methanol-to-olefin processes. An example of the methanol-to-oil process is Mobil’s Methanol-to-Gasoline, which uses ZMS-5 zeolite catalyst and was commercialized in New Zealand in 1986 with an annual oil production of 570,000 tons.

 

Co-production of direct coal liquefaction fuels and electricity with advanced gasification systems (IGCC) are expected to reduce the cost of the liquid fuel. The estimated cost reduction is significant and likely to be in the range of $5/bbl.


Co-processing of coal with other hydrocarbon streams ... such as post-consumer plastic material and tire rubber, is also to be effective in cost reduction of direct coal liquefaction fuels, because it may reduce the severity of the liquefaction conditions compared to a stand-alone coal hydrogenation process, recycle to extinction the low value and heavy fractions, take advantage of synergies of operation, and the favorable economics and/or politics.

 

(In indirect Coal liquefaction, "FT synthesis", the reactions) between carbon monoxide and hydrogen for paraffinic hydrocarbons and oxygenates are all exothermic, and the heat evolved is approximately 20 percent of the heat of combustion of the product. Therefore, control of reaction temperature is a major engineering challenge.

 

(We have earlier documented that such exothermic heat energy arising from synthesis gas catalytic condensation, to form liquid hydrocarbons, can be recovered and either used as process heat for other steps within the total system; or, used to produce steam and then generate electricity as a commercial by-product of the Coal liquefaction process.)

 

FT synthesis produces a wide range of products, including light hydrocarbon gases, paraffinic waxes, and oxygenates. A great current interest is in the production of high-molecular-weight material for premium diesel and jet fuels, which can be adjusted by choice of catalyst and operating conditions.

 

Much of the research and process development on indirect coal liquefaction ... is aimed at matching the synthesis conditions with modern, efficient coal gasifiers such as those developed by Texaco, Dow, and Shell.

 

(It has been) recognized that integration of FT synthesis with electricity generation offers opportunities for significant overall efficiency increase and cost reduction such as those proposed in Vision 21 of U.S. DOE.

 

Although tremendous progresses have been made in past decades on advancement of coal liquefaction processes and the technologies are competitive or near competitive with petroleum-derived fuels depending upon the oil price, the coal liquefaction processes by nature are characterized by complexity and large scale operations ... and are energy and investment intensive (and) these (factors) have led to doubt and misconceptions on the processes, and exaggeration of the problems in general public, even in scientific communities not directly dealing with coal conversion.

 

It is important to note that some of these questions are not technical, but have had crucial influence on policy making and on long-term planning on the development of clean coal technology. To overcome these problems some key facts need to be addressed and made known to the public, policy makers, government
officials and to the general scientific community.

 

Since (alternative, i.e., solar, etc., energy development) is not expected to have revolutionary changes in the means of motor vehicles, and the use of motor vehicles are expected to increase in the coming decades,
especially to the countries deficient with oil, the supply of liquid hydrocarbon fuels based on coal conversion inevitably becomes the only logical choice ... .

 

One of the obstacles in development and commercialization of coal liquefaction processes is the misconception in public and decision-makers that coal liquefaction is by nature “wasting of energy” because that production of one ton of oil will generally consume about 3.5 tons coal in direct coal liquefaction and close to 5 tons coal in indirect coal liquefaction. These alarming weight ratios, while being true by number, are improper and misleading descriptions for energy processes, since the energies contained in one ton of coal are much lesser than the energies contained in one ton of oil, and any types of coal contains significant amounts of ash which has no heating value.


Theoretical calculation and actual practices have shown 50-55% overall thermal efficiencies for indirect coal liquefactions and about 60% for direct coal liquefaction. The current state of art of coal-fired power generation, in contrast, has thermal efficiencies of 45%.

 

Compared to current chemical industries especially oil refineries the coal liquefaction processes are significantly more complex and more investment intensive. (Based on specified assumptions, it has been estimated that)  the overall investment per unit product of a direct coal liquefaction plant is about 4.72 times that of an oil refinery. The utility consumption of the direct coal liquefaction is also higher ... .

 

However, the overall profit of the direct coal liquefaction is 3.96 times the oil refinery, indicating better economy for coal liquefaction.


It is important to note that the above economic comparison is influenced by the prices of oil and coal, but the price of coal plays a less important role compared to that of oil, because the major parts of the direct coal liquefaction cost is the processing.

 

It is also important to note that coal liquefaction plants are more likely to be located at the vicinity of coal mines, where the price of coal is low and stable, and not influenced by fluctuations in transportation/shipping cost. But the oil price is expected to increase in general ... due to cost increases in exploration, extraction and transportation.

 

These would further make coal liquefaction more economical in the future.

 

Coal liquefaction processes, direct and indirect, involve hydrogen making, i.e. conversion of a portion of carbon in coal into hydrogen through gasification and/or water-gas-shift reaction. In principle about 1/3 of the carbon in coal needs to be used for hydrogen making, which suggests a conversion of 1/3 of the carbon in coal to carbon dioxide, a greenhouse gas which is mainly released from the use of coal. This carbon
dioxide is in a much pure state in comparison to that in flue gases from combustion of coal ... and can be easily recovered.

 

Conclusions:

 

Coal liquefaction is a realistic choice for countries deficient with oil but abundant with coal reserves.

 

Coal liquefaction processes are ... economically competitive at oil price of $25/bbl and at cost of coal at (the)coal mines (without cost of shipping and handling).

 

Liquefaction of coal significantly reduces shipping and handling cost of coal, a reduction of 75-80% on thermal energy equivalent bases.


Liquefaction of coal produces ultra-clean fuels and converting the polluting elements such as sulfur and nitrogen into marketable products at low cost.


(Highly concentrated) carbon dioxide rejected from coal liquefaction plants provides a good platform for carbon dioxide (recovery) at low cost.


Integration of direct and indirect coal liquefaction processes and blending of the fuels produced in these two processes will result in fuels that meet the increasing stringent specification requirement at high thermal efficiency.


Integration of coal liquefaction plants with modern electricity generation via gasification of coal will result in about 15% reduction in fuel cost.


Environmental beneficiations from coal liquefaction, including reduced cost for carbon dioxide (recovery) should be fully considered in assessment of coal liquefaction."

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Note that beneficial environmental effects can be realized from Coal conversion processes, including a much "reduced cost" for recovering concentrated Carbon Dioxide.

 

We submit that the effective cost of Coal liquefaction, which is already "economically competitive at oil price of $25/bbl", along with the beneficial environmental effects "from coal liquefaction", could be improved even further if the "reduced cost" CO2, so conveniently recovered from Coal liquefaction processes, were then directed into a secondary processor, such as described in:

 

Penn State Solar CO2 + H2O = Methane | Research & Development | News; concerning: "High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels; The Pennsylvania State University; Efficient solar conversion of carbon dioxide and water vapor to methane;

 

and, be thereby converted, by means of environmental energy, into Methane, which could then, as in:

 

More Standard Oil 1944 CO2 + CH4 = Hydrocarbons | Research & Development; concerning: "United States Patent 2.347.682 - Hydrocarbon Synthesis; 1944; Assignee: Standard Oil Company of Indiana; Abstract: In practicing my invention I ... prefer to employ... methane (which is) mixed with such proportion of carbon dioxide and steam as to give a gas mixture ... hereinafter referred to as ... 'synthesis' gas' (which can then be catalytically reacted and made to form) C3 and C4 hydrocarbons (that) are rich in olefins and may be converted ... into high quality motor fuels or heavier oils";

 

be reacted with even more Carbon Dioxide, and made thereby to form the raw material from which we could synthesize even more "motor fuels", similar to and compatible with, we would guess, the "liquid fuels and chemicals" produced by the various Coal liquefaction technologies described herein by WVU collaborator Zhenyu Liu; which technologies are "economically competitive" and, thus, a "realistic choice for countries deficient with oil but abundant with coal reserves".

 


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