The Technology To Suppress The Formation Of Dioxins By Dechlorination During PVC Heat Treatment

With economic growth and social development,solid waste is increasing,and thermal treatment is currently the main method of solid waste treatment.These wastes contain chlorinated organic substances such as PVC,which will generate toxic and harmful substances such as dioxins during thermal treatment.Excessive dioxins can affect human health,so it is particularly important to suppress the generation of dioxins during thermal treatment.Studies have shown that chlorides such as HCl in the flue gas are the key to the generation of dioxins.Therefore,the chlorine in the flue gas can be removed to achieve the purpose of inhibiting the generation of dioxins.At present,dechlorination experiments are mainly carried out at low temperature in a single atmosphere.However,the formation temperature of dioxin is mainly between 250-500℃,so it should be dechlorinated in the middle and high temperature stage to avoid the re-synthesis of dioxin after cooling down.With reference to the stable properties of chlorinated salts such as calcium chloride and sodium chloride at high temperatures,calcium carbonate and sodium carbonate were selected as dechlorination agents in the experiment to study their dechlorination mechanism and performance at medium and high temperatures.The specific research content is as follows:（1）From the perspective of thermal analysis kinetics,the thermal weight loss characteristics and kinetic processes of PVC and PVC covered with dechlorination agent under air and nitrogen atmosphere are analyzed.The experimental results show that the thermal weight loss of PVC has 2 stages,and the thermal weight loss of PVC covered by dechlorination agent has 3-4 stages.In an air atmosphere,an exothermic reaction occurs in the second stage of the thermal weight loss of PVC covered by the dechlorinating agent,it is different from pure PVC or thermal decomposition of the dechlorinating agent,and mainly nucleation and nuclear growth reactions or diffusion reactions occur.Other endothermic and exothermic reactions occurred in the third and fourth stages of the dechlorination agent,mainly phase-interface reactions.Under a nitrogen atmosphere,other exothermic reactions occur in the third stage of the thermal weight loss of PVC covered by the two dechlorination agents,mainly phase interface reactions.The reaction process of dechlorinating agent dechlorination mainly occurs from the late stage of the second stage to the third stage and the fourth stage,which is400-1050℃.It mainly occurs diffusion reaction and phase interface reaction.（2）Through the establishment of a tube furnace thermal treatment dechlorination system,to study the influence of temperature,dechlorination agent type and addition ratio on the dechlorination performance of the dechlorination agent under different atmospheres,and select the best dechlorination technology conditions.The experimental results show that the dechlorination effect of sodium carbonate is better than that of calcium carbonate.The best technical condition under air atmosphere is900℃,n（Na₂CO₃）:n（Cl）=1.5,and the fixed rate of chlorine element is 73.55%,the inorganic chlorine content in the liquid is 14.97%.The best technical conditions under nitrogen atmosphere are 700℃,n（Na₂CO₃）:n（Cl）=0.5,the fixed rate of chlorine element is 70.20%,and the content of inorganic chlorine in the absorption solution is16.74%.At the same time,the product analysis results show that the chlorine element mainly exists in the solid product in the form of inorganic chloride after the action of the dechlorination agent.（3）Simulate the flow field and temperature field of the dry spray dechlorination agent on both sides of the flue.The results show that spraying sodium carbonate on both sides of the flue at 1000°C can make the sodium carbonate fill the flue section and fully mix with the flue gas.,and the dechlorination agent is in the optimal temperature range of 700-900°C.