At Amsterdam municipal waste incinerator flue gases are treated by a combination of ‘semi-dry’ and wet scrubbing. During construction of the incinerator Dutch air emission standards were unfortunately tightened: the semi-dry processing originally planned proved inadequate and a scrubber therefore had to be added. This combination means that a lot of chemicals have to be used, creating large volumes of hazardous waste that must be sent to land-fill.
To tackle this problem the incinerator operator has drawn up a design for a back-end process in which the residue from the semi-dry scrubber would be mixed with the scrubber outflow. This would reduce the amount of chemicals that have to be used and yield a CaCl2 solution that can, in principle, be sold as a raw material. It would also cut back the volume of waste sent to landfill and would, moreover, vastly improve the environmental profile of that waste. The energy requirements of the process are substantial, however.
To weigh up the gains of the envisaged treatment process against this additional energy demand a Life Cycle Assessment as well as a first-pass economic analysis were carried out. The results show that the new treatment process would clearly reduce environmental impacts if the CaCl2 solution can indeed be marketed. But even if that proves unfeasible – implying that the chloride salt would have to be discharged – there would still be a small improvement in overall environmental burden. The process also has economic benefits.