Simulation and Optimization of an Air Pollution Control System Dealing with Flue Gases from Combustion of Syngas Produced through a Municipal Solid Waste Plasma Gasification and Melting Process.

Abstract: The aim of this report is to study a proposed air pollution control (APC) system designed to treat flue gases produced during the combustion of waste derived syngas. In order to achieve this objective, a literature study was done to gain insight into the pollution formation during gasification and combustion of syngas, and a model of the APC system was built using the Aspen Plus software. This model was used in four different case studies aimed at optimizing the water and chemical requirements throughout the system. Several different types of wastes were considered; municipal solid waste (MSW) representing that which is normally generated in developed countries, MSW representing that which is normally generated in developing countries, a waste composition representing that of the plastic fraction of MSW, and a waste composition representing that of the biomass fraction of MSW.   Based on the results of the literature study, a few conclusions could be drawn. Sulfur compounds could be expected to be found in the form of H2S in the syngas and SO2 in the flue gases. Chlorine compounds could be expected to be found in the form of HCl and the nitrogen compounds in the form of NH3, HCN and N2 after gasification and NO after combustion. The amount of research done in the area of MSW gasification, and combustion of MSW based syngas, is, however, small, and more research is needed.   Based on the results of the case studies, the amount of NaOH varied greatly depending on flue gas composition and negligibly depending on recirculation setup. The total amount of water required varied notably between the different cases studied and no case stood out clearly as the optimal case for all four waste compositions. The case studies seemed to indicate a trend towards an increased total water requirement with an increase in the amount recirculation. The four best cases where cases 2,3,4 and 10, out of which case three has been recommended as a good initial estimate from which to depart when finding the optimal setup for a specific system under study. In case 3, 40 wt% of the fresh water from the first splitter was sent to the direct contact scrubber, 50 wt% of the remaining fresh water was sent to the absorption tower, 40 wt% of the liquid leaving the absorption tower was recycled back to the direct contact scrubber, and 40 wt% of the remaining water leaving the absorption tower was recycled back to the absorption tower.