Modelling and Evaluation of a Waste Incineration Flue Gas Treatment Process
Abstract: As environmental awareness is raised, flue gas treatment is gaining more interest and stricter legislation on emissions pushes technological development. Sysav has a waste incineration plant with a flue gas cleaning process which includes removal of acid gases. This is performed by two subsequent scrubbers and following each scrubber a droplet separator is located to prevent transfer of liquid to the next unit. The objective of the report was to study sources to scaling on droplet separators. A literature study reviewed key parameters connected to absorption and scaling, which were compared to Sysav’s operating conditions. It was found that scaling typically consists of calcium sulfite hemihydrate (CaSO3' ½ H2O) and calcium sulfate dihydrate (CaSO4'2H2O). Aspen Plus was used to develop a model to represent Sysav’s process and qualitatively assess key parameter influence on absorption of HCl and SO2, and formation of CaSO3' ½ H2O and CaSO4'2H2O. Operational data from the process was implemented from specific time periods. Sensitivity analyses were carried out in which key parameters such as pH, liquid flow, gas flow, temperature and oxygen content were varied. The model successfully modeled absorption of HCl and SO2 with dependance on key parameters as expected for all key parameters except liquid-to-gas ratio. Calcium sulfite formation was influenced by key parameters according to theory for most parameters but deviating results occurred. Calcium sulfate formation was troubled with unexpected results from the sensitivity analyses. The chemistry for the solid formation in Aspen should be improved in future studies. Actions for scale control in Sysav’s process were proposed such as stabilizing pH, investigating limestone utilization, modifying demister washing procedures and adding particles for seeding.
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