EQUIPMENT - 6-INCH-DIAMETER CIRCULATING FLUID BED
This system features a six-inch-diameter by 23-foot-high, fluidized-bed vessel constructed of stainless steel, which is designed to operate either as a circulating or bubbling fluid-bed furnace. It is capable of operating at temperatures of 1,000°C (1,850°F). Gas velocities can be as high as 20 feet per second for circulating fluid-bed tests, and as low as 0.5 foot per second for bubbling-bed applications. Under bubbling fluid-bed operations, the unit’s length provides gas retention times that are comparable to commercial applications.
Process temperatures are maintained using independent combustion gas to indirectly heat the outer shell of the unit to desired temperatures. Fluidization process gases enter the unit through a windbox and perforated distribution plate at the bottom of the fluid bed. The composition of the fluidizing gas can be oxidizing, inert, or mixed as required. Thermocouples are located at 16 positions to monitor the temperature profile of the system; eight are located in the body of the fluid bed.
Process gases and entrained solids escaping the fluid bed enter a cyclone, where a major portion of the solids are separated from the gas to be recycled to the fluid bed or collected as required. The remaining entrained solids are exhausted from the cyclone and collected in a baghouse. The exhaust gas is conveyed to a venturi scrubber for final treatment, thereby serving to close the mass balance around the test system. When operating in a circulating fluid-bed mode, the distribution of the recycled solids and fly ash can be regulated as required.
Solid, liquid, or gaseous feeds can be introduced directly into the vessel at various elevations. Feed rates of dry solid materials range from 5 to 80 pounds per hour, while sludges can be fed at rates of 5 to 30 pounds per hour. Products collected from the system include bed, cyclone, and baghouse solids. The fluidized-bed depth can range from 6 inches to as much as 5 feet, depending on the test application.
The system is equipped with online instrumentation to obtain operating data. Process temperatures, pressures, and gas compositions, including O2, CO2, CO, SO2, NOx, and total hydrocarbons (THC), are monitored and recorded continuously. A gas chromatograph and mass spectrometer are available for measuring other gaseous constituents, such as water, hydrogen, nitrogen, and methane. Differential pressure is measured between the bed and freeboard to monitor and control the fluidization characteristics of the bed medium. A data-acquisition system is used to monitor and record selected process data. Emission sampling for organic compounds, metals, and other inorganic species can be performed as required, using EPA-approved methods.