PCDD/PCDF reduction by the co-combustion process

Abstract

A novel process, termed the co-combustion process, has been developed and designed to utilise the thermal treatment of municipal solid waste (MSW) in cement clinker production and reduce PCDD/PCDF emissions. To test the conceptual design; detailed engineering design of the process and equipment was performed and a pilot plant was constructed to treat up to 40 tonnes MSW per day. The novel process features included several units external to the main traditional cement rotary kiln: • an external rotary kiln and secondary combustion unit capable of producing a hot gas at 1200 °C; • an external calcinations unit in which the hot gas calcined the limestone thus making significant energy savings for this chemical reaction; • the lime generated was used in a second chamber to act as a giant acid gas scrubber to remove SO x and particularly HCl (a source of chloride); • a gas cooler to simulate a boiler turbogenerator set for electricity generation; • the incorporation of some of the bottom ash, calcined lime and dust collector solids into the cement clinker. A PCDD/PCDF inventory has been completed for the entire process and measured PCDD/PCDF emissions were 0.001 ng I-TEQ/Nm 3 on average which is 1% of the best practical means [Hong Kong Environmental Protection Department, 2001. A guidance note on the best practicable means for incinerators (municipal waste incineration), BPM12/1] MSW incineration emission limit values.