Analysis Of Influence Of Chlorine On Boiler Equipment In Desulfurization Wastewater Treatment Process

The wet flue gas desulfurization technology makes the chlorine in the flue gas continuously enriched in the absorption tower slurry.The high concentration of chloride ion affects the normal and safe operation of the desulfurization system.The timely discharge of desulfurization wastewater is the main measure to maintain the chloride ion concentration at a low level.Coal yard spraying and flue jet treatment have low cost and simple process,which are hot technologies in wastewater treatment.However,chloride ion has a strong corrosive effect on metals,which may affect boiler equipment during processing.Studying the migration and transformation law of Cl-in the treatment of desulfurization wastewater is of great significance to ensure the safety performance of equipments.In this paper,the amount of desulfurization wastewater is calculated based on the balance of desulfurization materials.The chloride ion enrichment model of desulfurization system is established.Besides,the influencing factors of desulfurization wastewater volume and enrichment time are studied.Taking a 660 MW unit as an example,when calculation based on the chlorine content in the coal,the amount of desulfurization wastewater is 1.81 t/h,and the amount of desulfurization wastewater is 5.1 t/h when calculated according to the HCl design concentration in the flue gas before desulfurization system.The calculation of the chloride ion enrichment time of the desulfurization system can provide a theoretical guidance for the actual discharge of the desulfurization wastewater.Secondly,combustion results in the furnace under the coal yard spraying process was simulated by thermodynamic equilibrium,and the influencing factors of chlorine precipitation characteristics during coal combustion were studied.The results showed that chlorine was mainly precipitated in the form of HCl(g)during coal combustion,and a small amount of NaCl(g),KCl(g)and C1(g)were generated at high temperature.The ash melting point experiment showed that the ash melting point of coal ash was reduced after added with desulfurization wastewater.DT was reduced by 18℃after added with a mass of 0.735%(calculated as Cl)desulfurization wastewater.The calculation of the corrosion rate of chlorine on the high-temperature heating surface showed that the more the desulfurization wastewater was treated,the more severe the corrosion was.When wastewater treatment capacity was 7.5 t/h,the corrosion rate of T91 was 0.019 mm/a,while the corrosion rate of 15CrMoG was 0.418 mm/a;the higher the temperature,the more severe the corrosion.The corrosion rate of T91 at 500℃ was 0.13mm/a,while the corrosion rate at 650℃ was 1.05 mm/a.Under this treatment method,83.7%of the chlorine in the coal eventually returned to the desulfurization system,which disrupted the system’s chlorine balance,so coal yard spraying was not suitable for long-term stable operation.Finally,the flue gas evaporation results of the flue jet treatment process was also simulated by thermodynamic equilibrium,and the precipitation characteristics of chlorine during evaporation process were studied.The results showed that when the flue gas evaporated the desulfurization wastewater,most of the chlorine was precipitated as a solid,and the rest was precipitated as a gas.When the pretreated desulfurization wastewater was evaporated in the flue gas,the chlorine was basically precipitated as NaCl(s),which then could be removed by electrostatic precipitator.The calculation of hydrochloric acid dew point and dew point corrosion rate in the tail flue showed that the flue jet increased the risk of dew point corrosion and the low temperature corrosion rate of the tail flue.While this has little effect when the amount of wastewater treatment was small.Flue jet can effectively achieve the solidification of chlorine in desulfurization wastewater.In this paper,the migration and transformation of chlorine in two desulfurization wastewater treatment methods,that was coal field spraying and flue spraying,were studied through thermodynamic equilibrium calculation.A chloride ion enrichment model for the desulfurization system was established.The high-temperature and low-temperature corrosion rate of chlorine were calculated.The chlorine balance of the two circulating treatment methods provided a certain theoretical guidance for the desulfurization wastewater treatment of power plants.