Abstract: The 30 000 t/a potassium dihydrogen phosphate production plant of Yunnan Yuntianhua Honglin Chemical Co.，Ltd. adopts organic solvent extraction method to produce potassium dihydrogen phosphate.Ammonium chloride is a by product of the production of potassium dihydrogen phosphate and is mainly used as fertilizer and additive.According to the operation of the ammonium chloride crystal plant，it is necessary to stop the plant every 10 d or so to conduct oil water separation，heating and dissolution and filtration treatment of the mother liquor in the system，and each treatment time needs 4~6 d，which results in low operation rate of the plant and becomes a constraint factor for the longterm stable operation of the potassium dihydrogen phosphate plant.In order to prolong the stable operation period of ammonium chloride crystal system，the optimization and improvement measures were put forward from the aspects of the quality of ammonium chloride stock solution，the clearance between the filter screen and the pushing plate of the centrifuge，the filter screen specification，the high overflow pipe of the ammonium chloride crystallizer and the elimination of fine crystal of ammonium chloride mother liquor.Through improvement，the ammonium chloride crystal system can run stably，and the monthly operation rate of potassium dihydrogen phosphate production plant increases from 40%~50% to over 75%.

Key words: potassium dihydrogen phosphate；ammonium chloride；solvent extraction method