EQUIPMENT - 5-INCH-DIAMETER THERMAL SCREW
Hazen has a five-inch-diameter thermal screw for bench- and pilot-scale studies to simulate plug flow processing typical of commercial rotary-kiln, multiple-hearth, and thermal-screw furnaces. A four-inch-diameter screw is contained within a housing 5 inches in diameter and 10 feet long. The screw and housing are constructed of stainless steel alloy, allowing for operating temperatures of 1000ºC (1850ºF) in either oxidizing, reducing, or mixed gas atmospheres. The test unit is indirectly heated over a 45-inch length of hot zone using propane burners positioned beneath the five-inch pipe. Adjusting the individual burners provides a controlled temperature profile across the hot zone. Process gases can be directed countercurrently or cocurrently to the solids flow. Exhaust gases leaving the system pass through a cyclone and a baghouse for dust removal. The gases leaving the dust collection device pass through a wet scrubber for final cleaning before being exhausted to the atmosphere. If necessary, an afterburner can be installed for final high-temperature oxidation of the process gases. Material is fed continuously to the thermal screw using a variable-speed screw feeder, after which it is conveyed through the hot zone with the four-inch screw. Retention times in the hot zone can be as long as five hours. Product leaving the hot zone is carried through a water-cooled zone before being discharged to a collection canister. The thermal screw 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. 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.
