GASIFICATION OF GREEK LIGNITE IN AN INDIRECT HEAT (ALLOTHERMAL) ROTARY KILN GASIFIER

This work reports the performance results of a pilot-size lignite gasification plant. The feed material was Greek lignite (Megalopolis), currently being employed for electricity generation in pulverized lignite-fired thermoelectric stations. Low energy conversion efficiency, low station availability, and environmental issues call for developing improved processes, e.g., an IGCC (Integrated Gasification Combined Cycle). An indirect heat (allothermal) rotary kiln was selected as the lignite gasification reactor for developing an overall gasification process of improved efficiency. Weeklong gasification runs, at near atmospheric pressure and maximum temperature in the range 900-950°C, validated high DAF lignite conversions, i.e., 90-95%, and the production of a medium heating value synthesis gas (i.e., 11-13 MJ/Nm 3 dry basis), despite the use of air for burning recycled product gas for process heating. Gas composition is equivalent to that of autothermal gasifiers (e.g., Lurgi, Winkler, Koppers-Totzek), which operate on oxygen, under pressure and strict moisture and particle size specifications. Similarly, the kiln gas is comparable to that of an allothermal, high-pressure, fluidized bed gasifier running with a high rank coal feed. The data indicate satisfactory gasification efficiency and a good thermal efficiency that should be improved further through heat integration of a scaled-up process based on an indirect heat rotary kiln gasifier.