DAP尾气循环联产MAP过程分析与现场实验

分析了引进60万吨/年磷酸二铵（DAP）装置尾气排放产生“磷铵雨”污染的热力学机理，主要是尾气湿度过高在烟囱内局部位置产生凝雾.提出尾气脱湿消减质量能量的过程同时成为磷酸一铵（MAP）产品加工过程的循环工艺.计算表明该工艺使尾气湿含量减少至0.065 kg H₂O•（kg air)^-1，所获能量可以替代24万吨/年MAP生产装置热能消耗的45%.尾气部分冷凝-磷酸降膜蒸发过程耦合技术是实现该工艺高效率利用二次能源的关键.现场实验表明耦合过程总的传热系数达500～600 W•m^-2•K^-1，同时具有磷酸浓缩低温、低循环量和扩展蒸发表面的优势，证明了DAP尾气循环联产MAP清洁生产技术的前景.

PROCESS ANALYSIS AND PILOT EXPERIMENT FOR MONOAMMONIUM PHOSPHATE PRODUCTION COMBINING WITH DIAMMONIUM PHOSPHATE EXHAUST GAS RECYCLING

Process thermodynamics analysis was made of the mechanism of P-NH₃ polluted droplets formation in the exhaust gas discharged from a 600 kt•a^-1 diammonium phosphate (DAP) production line.The key factor was the overly high humidity of tail gas, which caused condensation taking place locally in the stack.A recirculation technique was proposed to combine the tail gas dehumidification into the process of monoammonium phosphate (MAP) production in which the heat energy, released from reducing water content in the tail gas below 0.065 kg H₂O•(kg air)^-1, could be used to substitute as much as 45% of the heat energy consumption for a 240 kt•a^-1 MAP production line.To obtain the high efficiency of secondary energy utilization for this process,an unique technique was developed to integrate the processes of partial condensation of tail gas with falling film evaporation of raw phosphoric acid.The feasibility was demonstrated by the pilot experiments in which the total heat transfer coefficient reached 500—600 W•m^-2•K^-1.Some other advantages were also found significant for phosphoric acid concentration compared with the traditional technique, such as lower evaporation temperature，lower recycling rate and especially expansion of evaporation surface areas. The experimental results displayed a very promising future application for the cleaner process of MAP production combined with recirculation of DAP exhaust gases.