Coal Gasification History

In the 1850s, the gas producer was invented, and the water-gas process was discovered in Europe. In the gas producer, coal and coke were completely converted to gas by reacting coal with air and steam continuously in a downward moving bed at atmospheric pressure. The gas obtained in this method, called producer gas, had a low heating value (3500-6000kJ/m3). 

To enhance the heating value of the gas product, a cyclic steam-air process was developed in 1873. This process produced water gas, composed chiefly of carbon monoxide and hydrogen, which had a higher heat value (12,000-13,000 kJ/m3) compared with the producer gas. Furthermore, by adding oil to the reactor, the heating value was enhanced (to 19,000-20,500kJ/m3). This type of fuel gas, carbureted water gas, became the standard for gas distributed to residences and industry in the U.S. until the 1940s. 

Composition (mol %) Oven Gas Producer Gas Water Gas Carbureted Water Gas Synthetic Coal Gas 

Composition (mol %) BGL (Fixed Dry) Shell (Dry Feeding) Texaco (Slurry) 

The composition of the syngas generated through different gasification methods can be totally different. Also, the gas products depend on the coal used, the oxygen purity, and the gasification conditions (e.g., temperature, pressure, reactants, and coal/oxygen ratio). Compositions of some typical coal gas products from different processes are listed in Tables 4.1 and 4.2. 

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Building large commercial coal gasification combined cycle units could be difficult based on the history traditional power generators have had with simpler chemical processes. Sequesting the C02 can be another technological challenge. 

Finally, it is of interest, not only to the student of industrial archelogical history, but also to the modern technologist, to refer to coal gasification. A few decades ago the gasification of coal provided a means of supplying communities with coal gas, a mixture of hydrogen, methane and carbon monoxide, which could be ignited in burners and used as a domestic or industrial source of heat. With the discovery of natural gas... 

A computer model has been developed to provide numerical simulations of fluidized bed coal gasification reactors and to yield detailed descriptions, in space and time, of the coupled chemistry, particle dynamics and gas flows within the reactor vessels. Time histories and spatial distributions of the important process variables are explicitly described by the model. With this simulation one is able to predict the formation and rise of gas bubbles, the transient and quasi-steady temperature and gas composition, and the conversion of carbon throughout the reactor. 

Acid Gas Components. The oil and gas industries have a long history of effectively removing and processing carbon dioxide, hydrogen sulfide, and carbonyl sulfide, (collectively termed acid gases because they are acidic) from fuel gas streams. It is common to remove H2S and CO2 from raw natural gas before the gas enters the natural gas pipeline system. In coal gasification, a portion of the feed coal converts to CO2. 

History. Public Service of Indiana (PSI) is a major electric utility located in the state of Indiana. PSI is severely impacted by the SO2 reduction provisions of the Clean Air Act Amendment (CAAA) of 1990 due to it s large use of local high sulfur Indiana coals in older coal-fired units with no existing SO controls. However, there are special provisions in the CAAA for coal gasification repowerin. These provisions are discussed in detail in the Environmental Aspects, Section 4, of this report. Briefly, coal gasification repowering extends the Phase I SO2 emission allowances to the end of 1999 for the specific units repowered. The much lower Phase II allowances do not become effective until the end of 2003 for the specific units repowered. 

Commercial coal gasification processes are those that have a long history of commercial operation and are currently available to an electric utility for the routine production of fuel gas without further commercial-scale testing or demonstration except when testing specific coals. This category includes four gasification processes or technologies ... 

Mineral impurities in coal are known to be primary contributors to the slagging and fouling of utility boilers, fly ash and bottom ash production as well as atmospheric pollution. They also produce undesirable effects in some parts of hydrogenation processes such as liquifaction and gasification (1,2,3). Despite a long history of investigation prompted by these observations, many questions remain unanswered. 

After the devolatilization and rapid-rate methane formation stages are completed, char gasification occurs at a relatively slow rate various models to describe the gasification kinetics of this material for various limited ranges of conditions have been proposed. The differential rates of reaction of devolatilized coal chars are a function of temperature, pressure, gas composition, carbon conversion, and prior history. 

If coal is intended to serve as fuel for industrial gasification processes, it is smart to borrow know-how for coal characterization from combustion research because of its long and comprehensive history. Hence, well-known analysis methods and classification schemes will appear, which must be always reviewed in the light of gasification conditions that differ from combustion in terms of oxidant (oxygen and steam instead of air), operation pressure (20-100 bar), and overall reducing atmospheres (products are CO and H2 instead of CO2, H2O). 

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