Desulfurization Technology And Engineering Practice By Sodium-calcium Dual-alkali Scrubbing Method

Coal is the main energy source in China, a large number of coal-fired and the higher sulfur content in the coal results in a large number of SO2emissions. Presently, SO2has become the key restraint factor for the sustainable development of the economy and society. So it is imperative under the situation to control its pollution. This paper determined the optimum process parameters by analyzing the factors influencing the desulfurization efficiency for Lanzhou Petrochemical fertilizer plant desulfurization device by sodium-calcium dual-alkali scrubbing method. In addition, this study proposed the solutions for scaling and corrosion problems of desulfurization device by investigating the reasons. The main results are as follows:1. For the desulfurization device by sodium-calcium dual-alkali scrubbing method, the desulfurization efficiency can be improved by changing the operation conditions, such as SO2concentration in the absorption tower entrance, the ratio of liquid and gas, pH, Na+concentration, and temperature of flue gas. By investigating the effect of these factors on desulfurization efficiency, the optimum process parameters can be determined as follows:The SO2concentration in the absorption tower entrance was less than1200mg/Nm3and was prohibited more than1555mg/Nm3. The pH should be controlled in the10.0～11.9and5.0-7.0for in the sedimentation tank and the absorption tower export, respectively. By selecting above operation parameters, it can not only guarantee high desulfurization efficiency, but also can control scaling to the maximum.2. The analysis for the cause of scaling in the process of desulfurization devices running indicated that the scaling of desulfurization devices is mainly because calcium sulfite and calcium sulfate did completely precipitate. In the regeneration process, excess Ca(OH)2entered the desulfurization tower with circulating fluid and produced scaling. In addition, due to the high ash content in the flue gas, SiO2, Al2O3, Fe2O3, CaO, MgO compounds in the ash and CO2, SO2, HCl, etc. in the flue gas can generate various scaling factors, such as bicarbonate, sulfate, chloride, silicate. In the case of continuously concentrated, the scaling factors exceeded their limit of saturation values. Finally, they precipitated and adhered to the desulfurization tower and the pipeline. By analyzing various measures for scale inhibition, the scale inhibitor KLW-408was selected finally and the scale inhibition efficiency and the corrosivity were estimated. The results indicated that the scale inhibitor KLW-408 displayed the high scale inhibition efficiency and the corrosion for pipelines was below the state standards, which fully meet the requirements of desulfurization devices running.3. Due to source of corrosion, such as ash, SO2, NOx, HF, HCl etc. existing in the flue gas, some antisepsis material were used to preventing corrosion to desulfurization equipment, such as carbon steel and high alloy clad steel plate for absorber inlet flue, alloy C-276for wet and dry interface of absorber inlet, glass flake resin for absorption tower, area from absorber export to the chimney, SPUA-102polyurea, glass fiber reinforced epoxy and acid-resistant porcelain for buffer tank, settling tank, reaction tank.