Fluid-Bed Processes
Lurgi Circulating Fluid-Bed Process
The Lurgi CFB process is described in Section 5.2. Plants operating on biomass and or waste include those in Riidersdorf in Germany (500 t/d waste) and Geertruiden - berg in The Netherlands (400 t/d waste wood). In the latter plant the hot gas leaving the cyclone at a temperature of about 500°C is directly со-fired in a 600 MWe coal boiler. In Riidersdorf, the gas is fired in a cement kiln (Greil etal. 2002).
Foster Wheeler Circulating Fluid-Bed Process
The Foster Wheeler (originally Ahlstrom) CFB process was developed to process waste biomass from the pulp and paper industry. The first unit was built in 1983, and the gas was used to replace oil firing of a lime kiln at a paper mill. Three further units were built in Sweden and Portugal for similar applications. The size range is between 17 and 35 MWth.
The largest unit to date has a capacity of 40-70 MWth (depending on fuel) and operates со-firing the gas as a supplement fuel in an existing coal-fired boiler in Lahti, Finland (Anttikoski 2002). The feed is primarily biomass, but various refuse derived fuels are also used.
All these units operate at atmospheric pressure. In a different development, Foster Wheeler has also developed a pressurized version that formed the basis for the 6MWe biomass IGCC at Varnamo in Sweden (see Figure 5-36). The gasifier operates at 20 bar and has a capacity of 18 MWth.
The gasifier feed is pressurized in lock hoppers and a screw feeder is used for the transport from the high-pressure charge bin. Gasification takes place at 950-1000°C. Primary ash removal is via lock hoppers at the bottom of the gasifier. Fine particulate removal takes place in a hot gas filter with ceramic candles (later replaced by metal candles) at 35(MK)0°C, at which temperature the gas enters the combustion chamber of the gas turbine. Tar production from the gasifier is reported to be less than 5 g/Nm3 dry gas. The demonstration program was completed in 1999 after over 8500 hours operation. Technically, it has been a success. The economics are competitive vis-a-vis other biomass systems, but are still dependant on a general biomass-to-power support. (Sydkraft 1998).
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GASIFIER |
The TPS process of TPS Termiska Processer AB is an atmospheric CFB that was, like the Foster Wheeler process described above, developed in the mid-1980s to
provide energy from waste biomass in the pulp and paper industry. The first commercial application was at Greve-in-Chianti in Italy, where two 15MWth units to process refuse-derived fuel went on stream in 1992 (Morris and Waldheim 2002). The process was selected and built for the 8MWe ARB RE IGCC project in the United Kingdom (Morris and Waldheim 2002). A notable feature of the TPS process is the tar cracker, which uses a dolomite catalyst in a second CFB.
Pressurized Fluid-Bed Processes
In addition to the Foster Wheeler process applied in Varnamo and the HTW process described in Section 5.2, there are some other processes operating in a pressurized fluid bed. Of note are two processes both developed out of the IGT U-gas process and tailored for biomass application. One is the RENUGAS process that was applied in a lOOt/d bagasse fuelled unit in Hawaii, but which is no longer in operation (Ciferno and Marano 2002). Another is the Carbona process in Finland. A 20MWth pilot plant has been operated on various biomasses.
