The Research Of Urea Production By Complete Cycle Method In Aqueous Solution

The technologies in urea production vary a lot and they all have their own features. In Sichuan Meifeng Company, Mianyang Branch, the pre-separation and pre-distillation technology is used. It has a lot of advantages, such as large capacity, thermal energy utilization, carbamate decomposing rate, total ammonia boil-up rate, water balanced amount. After the summarization of technical renovation in our company, the characteristic and chemical equilibrium in urea synthesis were analyzed. According to all the effect in the process, it concluded that proper technology parameters are as following: pressure between 19.6～20.0MPa, temperature 188±2℃, NH₃/CO₂ =4.0(molar ratio), H₂O/CO₂=0.65(molar ratio), the content of CO₂ is 98.5%(dry basis, volume), the resident time is 40min. In this condition, the production process is perfect and the conversion of CO₂ reaches the highest. Furthermore, the best way to improve conversion of carbon dioxide is determined on the base of the previous discussion.With the increase in capacity, the quondam technology which adopted decomposition in middle pressure and pre-distillation limited the production. To solve the bottleneck, we use the pre-separation and pre-distillation technology. Combined the improvement in technology, three technologies which were pre-separation in middle pressure, pre-distillation, pre-separation and pre-distillation were analyzed. Compared three flows of technology, the indexes in material, thermal energy, water balance, carbamate decomposing rate, total ammonia boil-up rate were all discussed. The potential difference of equipment and the effect of pipeline were researched separately. In the meantime, the problems such as potential difference, pipeline, valve and erosion which should be given attention to, are summarized. Using pre-separation and pre-distillation technology instead of pre-distillation technology in urea plant, the results show that the steam consume per ton of urea can be decreased 100kg, the capacity of the first desorbing heater increases about 10%, water vaporized increases 28kg and it's of advantage to water balance in the system. The carbamate decomposing rate and total ammonia boil-up rate increase 7% and 8%, respectively. It shows the initial purpose is obtained and the bottleneck in production is solved too.