Large reductions in the emission of pollutants have been reported in the operation of a novel type of municipal solid-waste treatment plant. A group from the Hong Kong University of Science and Technology’s Dept. of Chemical Engineering (edlinks.chemengonline.com/6518-535) has reported test results recently conducted on a municipal-solid-waste (MSW), co-combustion pilot plant — a novel design combining cement manufacturing, MSW processing and electricity generation (Co-Co process).
The group, led by Gordon McKay, reported that the levels of dioxins in the stack emissions and fly ash were well below those of traditional MSW thermal treatment processes, and well below government and international limits. The emissions of other gases, such as CO, NOx, SOx and HCl, were also well below government limits.
According to the group, the combination of the Co-Co process’ thermal treatment of wastes with cement manufacturing benefits from the synergies of the two processes:
- The energy from the thermal oxidation of the waste material is used to supplement the pre-calcination of the cement raw material, and the residual energy can be used for electricity generation
- The alkaline raw-material feedstocks of the cement making process are used to neutralize the acidic gaseous pollutants generated from the oxidation of waste in a dry-scrubbing process, ensuring optimal fluegas cleaning without the need for additional reagents
- The high temperatures and long residence times needed for cement making will ensure destruction of organic pollutants
- Most average emissions are less than 20% of the best-practical-means (BPM) emission-limit values, and emission levels of dioxins are about 1% of the BPM dioxin emission levels