Gasification, coal types

For the gasification process no usable quantitative relations were established between the petrographical coal properties and the gasification behaviour. It is possible without any material problems to convert nearly all the Rhenish brown coal types into gaseous hydrocarbons or synthesis gas. 

However, actual high-temperature gasification reaction rates are not known, and the residence time at a given reactor temperature is usually determined empirically based on small-scale gasifier experiments. It is also generally accepted that reaction rates vary with coal type. 

The work on catalysis reviewed thus far does not include either gasification at elevated pressures or the use of volatile coals. The bench-scale work now reported compares the catalytic activity of various additives in the gasification of volatile coals with steam under pressure and studies other process parameters of interest such as gasification temperature, type of contact with the catalyst, degree of gasification, and repeated use of catalyst. Results of pilot plant gasification tests using additives are also reported. 

As with other processes, the characteristics of the coal feedstock (e.g., heating value and ash, moisture, and sulfur content) have a substantial impact on plant efficiency and emissions. As a result, the cost of producing hydrogen from coal gasification can vary substantially depending on the proximity to appropriate coal types. 

While there has been some discussion (Chapters 13 and 16) on the influence of physical process parameters and the effect of coal type on coal conversion, a note is warranted here regarding the influence of these various parameters on the gasification of coal. Most notable effects are those due to coal character, and often due to the maceral content... 

Produced from Co l. Estimates of the cost of producing methanol from coal have been made by the U.S. Department of Energy (DOE) (12,17) and they are more uncertain than those using natural gas. Experience in coal-to-methanol faciUties of the type and size that would offer the most competitive product is limited. The projected costs of coal-derived methanol are considerably higher than those of methanol produced from natural gas. The cost of the production faciUty accounts for most of the increase (11). Coal-derived methanol is not expected to compete with gasoline unless oil prices exceed 0.31/L ( 50/bbl). Successful development of lower cost entrained gasification technologies could reduce the cost so as to make coal-derived methanol competitive at oil prices as low as 0.25/L ( 40/bbl) (17) (see Coal conversion processes). 

Ammonia from coal gasification has been used for fertilizer production at Sasol since the beginning of operations in 1955. In 1964 a dedicated coal-based ammonia synthesis plant was brought on stream. This plant has now been deactivated, and is being replaced with a new faciUty with three times the production capacity. Nitric acid is produced by oxidation and is converted with additional ammonia into ammonium nitrate fertilizers. The products are marketed either as a Hquid or in a soHd form known as Limestone Ammonium Nitrate. Also, two types of explosives are produced from ammonium nitrate. The first is a mixture of fuel oil and porous ammonium nitrate granules. The second type is produced by emulsifying small droplets of ammonium nitrate solution in oil. 

Hydrocarbons from Synthesis Gas and Methanol. Two very important catalytic processes in which hydrocarbons are formed from synthesis gas are the Sasol Eischer-Tropsch process, in which carbon monoxide and hydrogen obtained from coal gasification are converted to gasoline and other products over an iron catalyst, and the Mobil MTG process, which converts methanol to gasoline range hydrocarbons using ZSM-5-type 2eohte catalysts. 

Natural gas requires no fuel treatment however, low-Btu gas, espeeially if derived from various coal gasification processes, requires various types of cleaners for use in a gas turbine. These cycles can get very complex as indicated by a typical system, which utilizes a steam bottoming cycle to achieve high efficiency. Vaporized fuel oil gas is already cleansed of its impurities in the vaporization process. 

Data boundary The equipment types for whieh data are presented in the resource (such as pipelines, valves or instruments) plant type (coal gasification facility, nuclear or ammonia plant, for example). 

The Texaco gasification process, currently owned by GE, is also of the EF type. A main difference with the aforementioned technologies is that the fuel is fed as a water slurry, whereas Koppers-Totzek- and Shell-based coal gasifiers use some steam. 

The types of reactions involving fluids and solids include combustion of solid fuel, coal gasification and liquefaction, calcination in a lime kiln, ore processing, iron production in a blast furnace, and regeneration of spent catalysts. Some examples are given in Sections 8.6.5 and 9.1.1. 

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