TABLE OF CONTENTS There are a number of gasification processes that, for various reasons, fall outside the categories that have been discussed here. These are in situ gasification of coal, also known as underground gasification, gasification in a molten metal or slag bath, plasma gasification and hydrogasification.
Gasification of coal in situ has a number of obvious attractions. Such a process has the potential to tap resources not otherwise readily or economically accessible. It would also eliminate the safety hazards and costs associated with underground mining. The ash would be left underground.
The first recorded proposal for underground coal gasification (UCG) was by Siemens in 1868, followed by Mendeleyev 20 years later. Initial experiments in the United Kingdom were broken off by the advent of World War I. No further work was done until the 1930s, when an experimental station was started in the Donetsk coalfield in the then Soviet Union, to be followed by commercial installations in 1940 (Weil and Lane, 1949). Underground gasification continued at a number of locations in the Soviet Union until the late 1970s, with production of some 25,000 million Nm 3 of gas from around 6.6 million tons of coal ( kten, 1994). This production came from seams of 50 to 300 m in depth.
In the 1980s, a number of small experimental units were operated in the United States. In Europe, tests have been conducted in Belgium (1986 1987), and then in Spain. The Spanish trial was...
