The EERC's pilot-scale fluid-bed gasifier (FBG) has been used to gasify a range of fuels including lignite, subbituminous coal, petcoke, both untreated and treated biomass, and various mixes thereof. Syngas has been generated for use in Fischer–Tropsch synthesis , material corrosion testing, examination of coal pretreatment, and more. Building from the EERC's many years of experience with bench-scale fluid-bed gasification, the FBG promises to reliably generate clean, high-pressure syngas directly from a variety of solid feeds for any number of potential applications.

The FBG is capable of feeding up to 9.0 kg/hr (20 lb/hr) of pulverized coal or biomass at pressures up to 70 bar absolute (1000 psig). The externally heated bed is initially charged from an independent hopper with silica sand or, in the case of high-alkali fuels, an appropriate fluidization media. Independent mass flow controllers meter the flow of nitrogen, oxygen, steam, and recycled syngas into the bottom of the fluid bed. Various safety interlocks prevent the inadvertent flow of pure oxygen into the bed or of reverse flow into the coal feeder. Recycled syngas is injected several inches above the bottom distributor plate, which prevents direct combustion of syngas with oxygen entering at the bottom of the bed.

After a review of available alloys, Haynes 556® was selected as the material most suitable for fabrication of the high-temperature, high-pressure system as well as for all of the reactor nozzles and the cyclone. The reactor was designed with the capability to operate at the following maximum operating pressures:

• 70 bar (1000 psig) at operational temperatures of 843°C (1550°F)
• 45.8 bar (650 psig) at an operational temperature of 917°C (1650°F)
• 21.7 bar (300 psig) at an operational temperature of 1018°C (1800°F)

The 2500-pound 316H stainless steel flanged connections at the top and bottom of the reactor are limited to somewhat lower maximum operating temperatures but do not greatly impact the operation of the gasifier, as they are generally cooler than the reactor bed itself. Sixteen thermocouple ports are spaced every 10 to13 cm (4 to 5 inches) up the bed to monitor for loss of fluidization, solids agglomeration, and localized combustion zones.

Coal is fed from a pressurized K-Tron® loss-in-weight feeder that provides online measurement of coal feed rate at pressures up to 70 bar (1000 psig). This system allows instantaneous measurement of the fuel feed rate to the gasification system. The feed system electronic controls are interfaced to a data acquisition system that allows for local or remote computer control of the fuel feed rate. Above the main feed hopper is the fuel charge hopper. The fuel charge hopper is manually charged with fuel through the top valve while at atmospheric pressure. It is then sealed and pressurized. Finally, the fuel feed material is transferred by gravity feed to the weigh hopper inside through the lower dual-valve system. The entire feed system pressure vessel is on a movable platform to allow easy transition from the FBG to the EERC’s entrained-flow gasifier.

Coal feed from the K-Tron system drops through a long section of vertical tubing and is then pushed quickly into the fluid bed through a downward-angled feed auger. Syngas exiting the fluid bed passes through a cyclone before flowing into a transport reactor that uses regenerable sorbent to remove sulfur from the syngas stream. The syngas then passes through a hot candle filter to remove fine particulate before entering a series of fixed beds. One bed is a polishing bed of ZnO that removes all remaining traces of sulfur from the syngas. Other beds can be loaded with water–gas shift catalyst, heavy metal sorbent, a chlorine guard, or other sorbents and catalysts. The clean, shifted syngas, still hot and pressurized, is then routed through a series of water-cooled condensers to remove volatile organics and moisture. The clean, dry syngas exiting the condensers is then recycled through a compressor to the bottom of the FBG, and a portion is vented through a control valve to maintain system pressure. The syngas exiting the system passes through a Coriolis meter and a dry gas meter for mass balance. A slipstream of this depressurized, dry gas is also fed to a laser gas analyzer and a gas chromatograph for online analysis of major gas components and for low-level (ppb) analysis of sulfur species. In addition, operators can periodically sample syngas from various points throughout the system using Dräger® tubes for H2S and other trace gases to verify low-level chromatograph data.