| China is a major yellow phosphorus production country, and yellow phosphorus production accounts for80%of world production. According to statistics:In2010, Chinese yellow phosphorous production is899000tons. When1t of yellow phosphorous is produced using the electric furnace method, about2500-3000Nm3(standard cubic meter at0℃and1.013bar) of tail gas is released. Yellow phosphorus tail gas contain CO87-92%, total sulfur0.8-8g/m3, phosphorus0.5-1.5g/m3and other impurities.Some enterprises try to using yellow phosphorus tail gas which has high calorific value(10.5-11MJ/m3) burning steam boiler, but P2O5and SO2that generate after yellow phosphorus tail gas combustion corrosion furnace heat exchanger and heat exchanger tube wall, and finally lead to the boiler shutdown in7-90days. At present, yellow phosphorus tail gas utilization is less than30%, the majority of factories emission it directly after combustion not only resulting waste of energy, but also causing pollution on the atmospheric environment.In order to improve the level of resource utilization of yellow phosphorus tail gas. In this paper, the premixed combustion method was examined combustion of yellow phosphorus tail gas in fluidized bed, and calcium sorbent was tested for removing of phosphoric pentoxide and sulfur dioxide during combustion. The purpose is to explore an efficient using of yellow phosphorus tail gas heat technology which can prevent corrosion and reduce environmental pollution.The results are listed as follows:(1) The commercial computer software package FactSage6.2was used to predict theory of yellow phosphorus tail gas combustion temperature, combustion gas composition, reaction products of the reaction with Ca(OH)2, and the influence of combustion temperature on reaction products.(2) Using diffusion combustion way burning off yellow phosphorus tail gas, the combustion temperature was500-620℃. Ca(OH)2of sulfur and phosphorus fixation was reduced, because Ca(OH)2reacted with CO2in this temperature.(3) A suitable for gas combustion fluidized bed boiler was set up on the basis of the gas combustion theory and particle flow theory. The effect of temperature on the retention of phosphoric pentoxide in hydrated lime was examined by changing air fuel ratio. The results show that the highest temperature of yellow phosphorus tail gas premixed combustion in fluidized bed is1060℃and the temperature can be stabilized above870℃in air fuel ratio between1.7-4.2. The sorbent can react with phosphoric pentoxide and removal efficiencies increasing with temperature. For instance, phosphoric pentoxide removal by hydrated lime, which was86%at1060℃,47%at920℃, and30%at870℃in fluidized bed. XRD analysis results showed that the sorbent react with phosphoric pentoxide first formed into basic calcium phosphate, after changing into calcium phosphate. Calcium phosphate is changed into calcium pyrophosphate at high temperature.(4) In order to investigate the absorbent surface area on phosphorus and sulfur fixing effect. In this paper, Ca(OH)2sorbent was prepared with clay as additives, The result show that the addition of clays can promote internal Ca(OH)2of sorbent particle decomposition, improve SO2removal efficiency and sorbent utilization, however, furnace temperature rise slower which is not conductive to the removal of P2O5. In120min reaction time, SO2removal efficiency increase about10%, P2O5removal efficiency decrease about5%, and sorbent utilization increase about8.5%, when the content of clays is25%in sorbent. The study also found that CaO with SiO2and Al2O3reaction to form a glassy substance, which can inhibit heat release to raise the temperature, finally lead to Ca(OH)2/clays sorbent sintered.(5) The effect of ZnO, Fe2O3and MgO on the retention of P2O5and SO2in Ca(OH)2was examined at960-980℃.The results show that ZnO additive can induce Ca19Zn2(PO4)14cover sorbent surface which is not conducive retention of P2O5and SO2result in sorbent inactivation within a short reaction time. Fe2O3additive can react with CaO to from Ca2Fe2O5, which reduce removal rate of SO2, at the same time improve removal rate of P2O5. MgO additive can promote SO2and P2O5gas spread in sorbent, accelerate phosphorus crystal particle formation, thereby improving the absorbent on SO2and P2O5removal rate. In120min reaction time, SO2removal efficiency increase about7.5%, P2O5removal efficiency increase about19.5%,when the content of MgO is25%in sorbent.(6) In order to understand the distribution of sulphur and phosphous compound in different particle size combustion ashes, combustion ashes were collected from circulating fluidized bed boiler which is mixed burning of yellow phosphorus tail gas.The results show that circulating fluidized bed boiler which main use coal as the fuel, and mixed burning off yellow phosphorus tail gas furnace temperature is between795-950℃. Because of alternating atmosphere in furnace, large particles which fluidized degree is lower long time stay in dense phase bed area of high temperature and low oxygen, so the rate and degree of sulfur capture are lower. Small particles rate and degree of sulfur capture are higher, because small particles are reactive and stay in oxygen content enough regional. CaO on P2O5fixed quantity independent of particle size, the rate and degree of phosphorus capture are higher, when the temperature increase, and CaO and P2O5contact more fully. |
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