Avaliação do efeito de aditivos na dessulfuração de gases de combustão (FGD) em unidade piloto de SDA

• Ano de defesa: 2019
• Autor(a) principal: França, Ítalo Waldimiro Lima de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Engenharia química; Cal - Aditivos; Gases - Combustão; Additives; Lime dissolution
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/40160

Air pollution is a serious environmental concern through the world. SO2, mainly emitted from fossil fuel combustion, is a major and quite harmful air pollutant. On coal fired power plants, flue gas desulphurization (FGD) is a highlight procedure, due to its high SO2 removal efficiency, low utility consumption and valuable byproducts. Semi-dry FGD systems are mainly represented by Spray Dryer Absorbers (SDA), and hydrated lime slurry (Ca(OH)2) is commonly applied as SO2 sorbent. In general, the lime slurry is atomized into small drops, then it reacts with SO2, so removing it from flue gas. The overall efficiency for SO2 removal (rSO2) is usually limited by the sorbent dissolution. In the present work, initially the dissolution of calcium hydroxide was studied by pH-Stat method. Then, it was also evaluated its applicability on flue gas desulphurization on a SDA pilot scale. Temperature, pH and stirring presented significant effect to lime dissolution. Stirring present no effect above 1320 rpm, indicating a possible mass transfer limitation at lower stirring rates. Nevertheless, as temperature increases, the dissolution reaction rate increased considerable (200%, from 20 to 80 °C). Activation energy was about 25.52 kJ.mol-1. Some additives showed some enhancement in quicklime dissolution rate: ammonium chloride (25%), ammonium acetate (25%), ammonium nitrate (50%) and adipic acid (50%). Ammonium nitrate seemed to overcome a mass transfer limitation on lime dissolution. For desulphurization assays, hydrated lime slurries (10 and 20 wt %) supplied with additives were investigated. Magnesium hydroxide, ammonium nitrate, ammonium acetate, ammonium phosphate, citric acid, urea, and sodium hydroxide were evaluated as additives for SO2 removal. Additives containing ammonium ions (NH4+) improved SO2 removal from the flue gas and increased the sorbent utilization (XCa(OH)2). The lime slurry formulation with 10% of Ca(OH)2 and 2% of NH4NO3 reduced the SO2 content by approximately 60% and improved sorbent utilization by 45%. A Design of Experiments (DOE) was carried out to optimize lime slurry composition (Ca(OH)2 and NH4NO3 concentrations) and showed that for 1000 ppm (SO2 inlet concentration), slurry containing 20 wt% Ca(OH)2 and 10% NH4NO3 presented SO2 removal about 80%. For 2000 ppm, the same lime slurry formulation removed 60% of sulfur dioxide from flue gas. Recycle assays have showed that fly ash still contains considerable amount of reactants that were not converted, and could be reused on the process.