Investigating the source of high TRS emissions from a dissolving tank vent

摘要

This research investigates the source of total reduced sulphur (TRS) compounds in a recovery boiler dissolving tank vent stack. Emission tests were carried out with weak wash as the scrubbing medium in the dissolving tank vent scrubber, as well as the dissolving agent in the dissolving tank itself. The tests were repeated with water as both the dissolving agent and the scrubbing medium. At the time of the emission tests the condensate from the evaporators and the foul condensate stripper (contaminated hot water), which is used to make up the weak wash, and the weak wash itself were tested for methanol, sulphur and turpentine (turps) compounds. The results seem to suggest that the presence of sulphur, turpentine compounds and/or methanol in the weak wash could be the source of TRS compounds in dissolving tank vent emissions, in particular methyl mercaptan (MeSH). Most of the MeSH emissions were found to be generated in the scrubber itself. As the weak wash is sprayed through high pressure nozzles into the scrubber, it is atomised and releases low boiling point organic compounds to form gaseous emissions.rnA process of elimination was also used to identify whether the source of MeSH in the weak wash was from the evaporator condensate or the condensate from the foul condensate stripper. The results of this investigation show that the MeSH in the weak wash comes mainly from the evaporator's condensate. A proposal has now been put forward to implement condensate segregation by creating condensate streams with different concentrations of impurities, namely sulphur, turps and methanol. The low concentration condensate would then be used to generate weak wash for emission scrubbing, thereby eliminating the emissions at the source. The regular monitoring of weak wash quality has also been implemented.