Removal of carbon dioxide in closed loop off‐gas treatment systems

Abstract

A combustor with a closed loop off‐gas recirculation system has been constructed to demonstrate a gas treatment and purification system that can be installed on hazardous and mixed‐waste incineration and vitrification equipment to virtually eliminate the potential for release of hazardous or radioactive materials to the environment. In initial tests, a 250,000 BTU/h (75 kW thermal) combustor was operated in an open loop to demonstrate the removal of combustion product CO₂ in a fluidized bed of CaO (lime), and particulates were removed with hot gas candle filters. An absorbent solution treatment (AST) process is now being developed for removal of CO₂ from a side loop. High CO2 concentrations can be maintained in the recirculating gases, and this improves the performance of commercially available processes used to purify gases and produce CO₂. Incineration systems with closed loop off‐gas treatment can have a high throughput and accommodate more hazardous and more radioactive waste streams than what would be possible with a conventional incinerator. With the AST process, CO₂ and water vapor go through two changes of state before release, effectively separating these combustion products from contaminants released during incineration or vitrification. Oxygen is added to support combustion, and solids are separated by precipitation and filtration.