Perma-Fix Northwest has recently completed a pilot test with two additional mixed waste processes at their Richland, Washington waste treatment facility. These processes are thermal desorption of organic-contaminated solids and plasma gasification of organic liquids. These processes will greatly enhance mixed waste processing at Perma-Fix Northwest, allowing Perma-Fix Northwest to treat nearly all types of mixed waste. The ability of Perma-Fix Northwest to innovatively combine proven technologies to develop effective waste treatment processes, as was done for mixed waste, make it the leader in waste management.

The Thermal Desorber is a high temperature process that is used to separate solvents, oils, and all types of organic liquids from solids. The process can also be used to recover mercury from sludge, soil, and other waste streams for further treatment, such as by amalgamation. The unit will feed at a nominal rate of 200 lbs/hr and is designed to easily adjust process parameters, depending on waste type and regulatory requirements. The desorber is an indirectly heated retort that tumbles the solids to provide thorough mixing and uniform heating. As the waste is heated, organic materials are evaporated from the waste and drawn out of the desorber into a condenser where they are collected in a liquid form. Non-condensable gases are passed through a pollution control system to remove pollutants. Solids are discharged at the end of the desorber where they are cooled and then treated via stabilization or macroencapsulation to meet Land Disposal Restriction requirements.

Organic liquids recovered from the thermal desorber and organic liquids received in bulk form are processed in a Plasma Gasification System. This system operates at below atmospheric pressure over a range of operating temperatures of approximately 1,650 °F up to over 2,000 °F. Liquid feed is continuously fed to the Plasma Furnace which utilizes a 200-kW transferred arc torch to gasify and partially oxidize the waste feed into primarily carbon monoxide and hydrogen. The offgas is then oxidized in the downstream Secondary Reaction Chamber. The offgas exiting the Secondary Reaction Chamber is cooled to approximately 800 °F or less using ambient room air that is injected directly into the offgas.

Acid compounds, such as hydrogen chloride (HCl), are removed from the resulting offgas using a Dry Acid Gas Removal Unit, which injects sodium bicarbonate into the offgas duct. At the offgas temperature, the sodium bicarbonate reacts to form sodium carbonate that reacts with acid gases to form sodium salt (e.g., NaCl) which is collected in the baghouse filter. The salt product and unreacted sodium carbonate collected in the baghouse are continuously recycled back into the offgas. Periodically, spent solids are purged from the system and fresh sodium bicarbonate is added. The removed spent solids are packaged for disposal. The offgas exiting the Dry Acid Gas Removal Unit is cooled to approximately 400 °F using ambient room air that is injected directly into the offgas. The gas is then cleaned further with HEPA filtration prior to entering the building air pollution control system (building ventilation) and final release.

These technologies are very powerful processes that, when combined with Perma-Fix Northwest existing processes, position Perma-Fix Northwest at the forefront of mixed waste treatment. Currently, Perma-Fix Northwest is testing processes in a series of treatability tests on different types of waste streams. These tests are being used to define optimum processing conditions and level of performances for each type of waste.