An Study On The Mechanism Of Biuret Formation And Its Controlling In A SNAMPROGETTI Stripping Process

Biuret impurity is one of the important quality indexes for fertilizer urea. As a polymer of urea, it is harmful not only to crops, but also to operation of urea production. It is meaningful to study forming mechanism and controlling measures of Biuret in a commercial urea plant.Snamprogetti urea process includes high pressure synthesis, purification (middle and low pressure hydrolysis), vacuum pre-concentration and evaporation, and granulation sections. Biuret is formed in almost all steps throughout the process. The data of a commercial operation show that biuret formation depends on the operation parameters, such as temperature, pressure, N/C and H/C ratio, etc. The formation of biuret is slow below 100C, however, it accelerated obviously when the temperature rises up to 130C. Longer reaction time will increase the content of biuret in urea product. A method to decrease biuret is increasing ammonium partial pressure in synthesis circle because it will be faverite for the reverse reaction of biuret formation.The amount of biuret formed in different sections of SNAM Process was investigated and its effects on both device operation and product quality were discussed in this work. On the bases of analyzing the influence of parameters, such as urea concentration, residential time, temperature, pressure, N/C ratio and production flunctuation, etc., a serials of controlling measures were developed to reducing biuret formation, especially in the situation of low production duty orlow ammonia/carbon ratio. The problem of chock by the crystal from the second vacuum evaporator was well solved by adding screen filtration, increasing flushing water (in V08) and relatively improving device and operation.The operation experience of Jianfeng commercial device shows that the proposed measures are effective for the reduction of biuret and improvement of fertilizer quality, even though under low N/C, low duty period and operation flunctuation. The reduction of biuret formation also benefit to the long term operation of device.