Flue gas purification within energy intense sectors and process industries is a crucial measure to ensure reduced emissions. Industrial processes change over time according to emission requirements and for the improvement of internal profitability. To increase the internal use of chemicals, paper mills have constructed a chemical recycling process where also internal energy for the plant is conducted. Non-condensable gases are ventilated from the recycling process and consist of volatile sulfur compounds which are highly corrosive and obtain a very unpleasant odor. The gases are combusted in a Low-nox-burner to be destroyed. Flue gas genererated from the burner is purified together with the flue gases from the recovery boiler, and represent 4% of total. The work aims to investigate a separate purification process for desulfurization in the flue gases from the burner, in order to achieve reduced emission levels of sulfur dioxide. Multicriteria analysis is used as a structured approach to identifying alternatives within flue gas purification of sulfur oxides and adaptation to the area of use. Together with theoretical calculations of flows in the system and relation to implementation aspects, the work has compiled proposals and information on how the flue gas treatment process after the burner can be carried out. Concentration levels of sulfur dioxide found in the flue gas have been determined by indentifying two operating cases. The concentration of sulfur dioxide reaches ~30000 mg/Nm3 which represents 1-1.4wt% and 362-493 kg SO2/h. A reduction rate of 98% should be achieved to keep emissions below the permissible emission limit of 25 mg/Nm3, where the flue gases must leave the plant together with the flue gases from the recovery boiler. Three flue gas desulphurization systems are analyzed in the work, two adsorption systems with sorbent activated carbon and sodium bicarbonate and one absorption system. The absorption system by wet flue gas purification with neutralizing sodium hydroxide as sorbent should be used where recycling of secondary products to other processes are easily performed. For the separation of sulfur, used liquid should undergo regeneration according to the Wellman Lord process. The flow of liquid to ensure solubility of SO2 and mass transport in the system reaches 167-249 m3/h where additional 50 m3/h should be added to achieve profitability across the system with absorption factor 1.47. How the liquid can be circulated in the system is regulated by the input concentration of NaOH where 0.4% is the lowest concentration for one circulation with 98% of reduction. Identified precipitation of Na2SO4 in the liquid is expected to reach ~0.4 kg/m3 which needs to be compensated by increased supply of NaOH in the liquid. During regeneration, 60 kW of energy per cubic meter of liquid is expected to be added to the system where concentrated gas of SO2 is released and can be condensed to sulfuric acid for further use within the plant. Released amount of SO2 is represented by the relationship of circulation and regeneration, and need to be kept within the critical level of profitability. Emission levels of sulfur dioxide are expected to be reduced by a separate purification system as higher concentrations indicate better reduction conditions. The exact amount of emissions varies with the sulfidity of the plant and the amount of non-condensable gases added to the burner. Based on identified operating cases, emission amounts of 16-22 mg/Nm3 can be expected.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-85387 |
| Date | January 2021 |
| Creators | Pettersson, Mikaela |
| Publisher | Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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