PCDDs, PCDFs emission control by dry scrubbing system

Abstract

Presently, in Japan there are no limitations on the emission of PCDDs or PCDFs, but in order to study the feasibility of dry type air pollution control, a pilot plant was constructed in 1988 and the removal efficiencies for PCDDs, acid gas and heavy metals were measured. At the same time PCDDs concentration was compared with that of a previously installed electrostatic precipitator (ESP) plus wet scrubber line. In this paper, the following two items are reported. 1. (1) The difference in the amounts of PCDDs and PCDFs produced due to differences in gas temperature and retention time in ESP and fabric filter (FF). 2. (2) Removal efficiencies of PCDDs and PCDFs of fabric filter. PCDDs concentration, generally 100–200 ng/Nm 3 at the boiler outlet (ESP inlet and/or Quench Reactor (QR) inlet), increased several times at the ESP outlet, but it showed almost no increase at the QR outlet due to a sudden temperature drop. The temperature was 280–310°C, and the gas retention time was 12 sec. during passage through ESP so that it is thought that PCDD was formed under these conditions. On the other hand, a removal efficiency of approx. 90% was obtained with the fabric filter, and the PCDD at the bag outlet was at a sufficiently low level.