The KBR Transport Gasifier
Fluid-bed gasification is also being developed in the high-velocity regime. Such a gasifier is the Kellogg Brown and Root (KBR) transport gasifier, for which a gas velocity in the riser of 11-18m/s is reported (Smith etal. 2002). The objective of this development is to demonstrate higher circulation rates, velocities, and riser
Figure 5-10. Lurgi Circulating Fluid-Bed Gasifier (Source: Greil and Hirschfelder 1998)
densities than in conventional circulating beds, resulting in higher throughput and better mixing and heat transfer rates.
The fuel and sorbent (limestone for sulfur removal) are fed to the reactor through separate lock hoppers. They are mixed in the mixing zone with oxidant and steam, and with recirculated solids from the standpipe. The gas with entrained solids moves up from the mixing zone into the riser. The riser outlet makes two turns before entering the disengager, where larger particles are removed by gravity separation. Smaller particles are largely removed from the gas in the cyclone. The solids collected by the disengager and cyclone are recycled to the mixing zone via the standpipe and J-leg.
The gas is cooled in a syngas cooler prior to fine particulate removal in a candle filter. In the demonstration facility, both ceramic and sintered metal candles have
Figure 5-11. KBR Transport Gasifier (Source: Smith etal. 2002)
been tested. The temperature of the test filter can be varied between 370 and 870°C by bypassing the syngas cooler.
The sorbent added to the fuel reacts with the sulfur present to form CaS. Together with a char-ash mixture, this leaves the reactor from the standpipe via a screw cooler. These solids and the fines from the candle filter are combusted in an atmospheric fluid-bed combustor.
The transport reactor was operated in combustion mode from 1997 to 1999. Between September 1999 and 2002 the plant was operated over 3000 hours in gasification mode, most of this with air as oxidant. Average carbon conversion rates are about 95%, and values of up to 98% have been achieved.
Gasification takes place at 900-1000°C and pressures between 11 and 18 bar. There has been little oxygen-blown operation to date. All oxygen data has been taken at lower pressures.