EQUIPMENT - 2-INCH-DIAMETER BATCH FLUID BED
Hazen’s two-inch-diameter fluidized-bed furnace allows for quick and inexpensive evaluation of fluidized-bed processing parameters, such as temperature, residence time, and process gas composition. The system is used for the evaluation of limestone decomposition and attrition characteristics in a fluid bed, for combustion and pyrolysis testing of waste materials, and for preoxidation treatment of refractory gold ores prior to cyanidation.
The two-inch-diameter fluid-bed assembly includes a fluidization gas preheater and a four-inch-diameter expanded freeboard. The furnace is externally heated throughout its length by electrical resistance heaters providing capability for operating at temperatures as high as 900°C (1,650°F).
Primary fluidizing gas enters the unit through the preheating zone at the bottom and is distributed uniformly across the diameter of the bed zone through a perforated metal distribution plate positioned at the bottom of the fluid bed. Process gases pass to an external cyclone for disengaging dusts from the process gas stream, then to a scrubbing circuit and either a condenser or afterburner for final cleaning of gases before they are exhausted to the atmosphere. An external baghouse or electrostatic precipitator can be used as required to capture fine particulates that may escape the cyclone. Alternatively, the furnace lid can be equipped with an internal sintered metal filter that will retain particulates larger than five microns within the fluid bed. This application is commonly used for testing the physical decrepitation characteristics of limestones and other materials, or to separate volatile metals from nonvolatile metals.
Feed is introduced continuously or batchwise to the furnace. Process batches from 0.75 to 1.25 pounds can be added through the lid, depending on the bulk density of the material being tested. Continuous feed rates of one to two pounds per hour can be metered from a screw through a water-cooled nozzle at the top of the fluid bed, or through a side port located just above the fluid-bed zone. Air, nitrogen, or other process gases are used to transport the material from the feeder to the fluid bed.
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 constitutents, 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.