Treatment And Renovation Of Exhaust Dust In Mono-ammonium Phosphate Production

Monoammonium phosphate?MAP?,also known as ammonium dihydrogen phosphate,is a white crystal with a chemical formula of NH₄H₂PO₄,which is a phosphorus-nitrogen fertilizer.In industrial production,phosphate rock?pulp?is reacted with sulfuric acid,and the reaction slurry is subjected to liquid-solid separation to obtain wet dilute phosphoric acid?effective P₂O₅ content 28%³2%?,and then neutralized by gas ammonia and phosphoric acid to obtain The monoammonium phosphate slurry,the reaction slurry is concentrated by multiple effects?three or two times?,and then sprayed on the return material for granulation,and then sieved to obtain granular monoammonium phosphate.Or use a high pressure pump to spray into the drying tower to produce powdered monoammonium phosphate.At present,the domestic mature phosphoric acid and ammonium phosphate production process is a multi-paddle multi-tank flash cooling,a fluorine-containing absorption treatment with dry absorption gypsum,and a low-concentration phosphoric acid in aerobic ammonia.And the slurry is multi-effect?three or two times?countercurrent evaporative concentration,rotary kiln spray granulation and high pressure spray powder monoammonium phosphate production process.In 2009²012,Fuyang Zedong Chemical Group Co.,Ltd.built three sets of production equipment with an annual output of 500,000 tons of monoammonium phosphate.?The first phase of granular monoammonium phosphate design scale is 150,000tons/year,Phase II and III The project is designed to be powdered monoammonium phosphate?180,000 tons/year?.The original design can reach the national standard exhaust particulate matter?120mg/m3?.As the country pays more and more attention to environmental protection,the monitoring and management of chemical production enterprises“exhaust gas,waste water,solid waste”is becoming more and more strict,and the environmental protection pressure faced by chemical production enterprises is also greater.“Exhaust gas,waste water,solid The disposal of waste determines the living space and development direction of the enterprise.The three times of random sampling of the tail gas of the granular monoammonium phosphate production unit after the design was put into operation were:110 mg/m3,105mg/m3,and 90.8 mg/m3.The test results show that the particulate matter content in the granular monoammonium phosphate tail gas does not exceed the particulate matter content?120mg/m3 specified in the standard GB16297-2012.However,with the severe environmental protection situation,the emission index is increasingly strict,and the company carries out rectification of exhaust gas as required.Through the inspection of the brother units in the country,it is better to treat the powdered and granular monoammonium phosphate tail gas in a unit in Guizhou.The granular monoammonium phosphate tail gas treatment process is the granulation tail gas by the cyclone dust collector,venturi The washing and the three-stage washing tower are washed into the wet electric demisters and emptied,and combined with the actual and external unit inspection results of the company,it is proposed to carry out technical transformation of the dust removal system from the following aspects;?1?Add cyclone dust collector;the original design device is a single cyclone dust collector,and the dust removal effect is limited.Now the quality of phosphate rock in our unit is gradually decreasing,and the content of phosphate magazine is often high,and the granulation effect in the kiln granulation process Poor,resulting in increased content of monoammonium phosphate dust in the rotary kiln,consider adding a cyclone.?2?Renovation of the washing section;after investigation of other brother units and analysis of its current device,it is considered that the washing effect of the original washing device is insufficient?formerly a primary washing tower?,except for retaining the existing pipeline washing system.In addition,another stage of the washing tower is added in series,and in the aspect of defoaming,the swirling plate is still used for defoaming.Aiming at the long-term use of the washing water,the water temperature is increased,the washing effect is lowered,the fresh water replenishing amount of the washing tower is increased,and a part of the high-temperature water is flowed to the cooling tower,and the washing water is cooled by the cooling tower.?3?Increasing the electric defogger;by investigating the fraternal unit,the good work in the treatment of monoammonium phosphate dust is carried out by the electric demister at the last stage of the exhaust gas treatment,and on the one hand,the monoammonium phosphate carried in the exhaust gas can be removed.Dust and dust can also remove the atomized water droplets brought by the high-temperature washing,and comprehensively reduce the pollutant content of the particulate matter?PM10?and fine particulate matter?PM2.5?.?4?The closed form of the ash outlet under the original cyclone is controlled by the counterweight type ash discharge valve.Since the monoammonium phosphate dust will be fouled on the ash discharge valve plate after the damp,the cyclone dust collector system is not tightly sealed and leaks.Reduce the dust removal efficiency,and at the same time,the dust leaks and scatters during the ash discharge,resulting in poor environmental sanitation on the site.Now consider changing the lower ash port weight unloading ash valve to a closed screw conveyor to solve the air leakage problem of the cyclone system.It not only improves the efficiency of the cyclone,but also solves the problem of dust leakage during the ash,and improves the environmental sanitation at the operating site.?5?Process optimization;1 Due to the large difference in temperature of the granulator exhaust gas,the dust on the pipe wall is damp,resulting in more and more pipe wall bonding,which eventually causes blockage of the pipe.In addition,in the production,the temperature of the exhaust gas is increased to reduce the moisture on the wall surface,but the more the temperature is increased,the more the dust is generated,and the more fouling occurs on the pipeline,forming a vicious circle.The temperature of the granulation needs to be reasonably controlled.2 Because the temperature of the inlet kiln will increase the amount of system dust,the moisture content of the I effect slurry can be increased?currently the water content in production is generally 23%,and the moisture index can now be adjusted to 24-26%?.When the moisture is increased,the viscosity of the slurry is reduced,which is favorable for spray granulation and at the same time reduces the generation of dust;3 The control of the fan,the exhaust fan and the hot fan are not well coordinated.In the abnormal situation where the speed is unstable or the adjustment range is large,some of the powder that can be gravity-sedimented by itself is sucked into the exhaust gas treatment device,and the exhaust gas treatment is increased.The pressure of the device can reasonably control the coordinated operation of the two fans,which not only avoids the heat loss caused by the exhaust of the exhaust fan,but also maintains the micro-negative pressure in the system,which is beneficial to increase the self-settlement of the particles.