Numerical Simulation Of Thermal Environment And Optimization OfAirflow In Urea Prilling Tower

The urea prilling tower is a key equipment of cooling the molten urea into the particles.The urea prilling tower of natural ventilation type is a circular or rectangular tall concretestructure. Its advantages are stable, convenient management, low operating cost. Its one ofdisadvantages is greatly influenced by environmental conditions. Daqing petrochemicalcorporation fertilizer plant of urea prilling tower was built in the1970s, belongs to the typicalnatural ventilation type. In recent years, the urea prilling tower is always in overloadoperation, lead to the urea prilling tower of urea product temperature too high, so the productsdifficult to bag and ensure the quality. It shows that the existing prilling tower internalenvironment can not meet the demand of the new workload. Thus it can be seen that it isurgent to improve the urea prilling tower and internal environment to ensure the quality of theproducts, and reasonable renovation scheme is the precondition to transform its thermalenvironment.The research target of this paper is mainly to improve the prilling tower internalenvironment to reduce the temperature of the urea products. The current situation and theinfluencing factors of urea prilling tower are simulated, and the simulation results arecompared with the measuring results. The urea products temperature is predicted by thermalenvironment simulation of transformed urea prilling tower, and then transformation scheme isanalyzed on whether meet the requirements.The main research content includes the following several parts:1. The main purpose is to study the relationship function of drop distance and landingtime. Considering atmospheric temperature, and the production yield, the mathematical modelof the urea prilling tower prilling process is analyzed on the motion of particle landing time,particle, ventilation, heat transfer and mass transfer process of mutual influence, and theresearch drop distance and landing time of urea prilling tower internal environmental impact.2. In the convective heat transfer between air and particles, the urea heat resistance isneglected in the convection equation. On the basis of the measurement in the urea prillingtower, we build the three-dimensional simulation model and mesh grids by structured andunstructured grids. Thus the coupling model between particles and air is solved by Fluentsoftware. In the calculation of particles orbit, we need to consider the integrating continuousand discrete methods, and solve the discrete and continuous phase equation alternately untilboth convergences. The calculation is completed by two-way coupling. This part is mainly from two aspects to analysis the internal thermal environment in prilling tower. On the onehand, the air velocity field and temperature field are analyzed according to influence by thelanding particles. On the other hand, the particles movement is analyzed by Reynolds numberand velocity.3. Based on the measured data, the air temperature field and velocity field in internalthermal environment is analyzed by Fluent software, considering the temperature at theentrance, urea workload and urea particle diameter, and influenced by inlet air temperature,humidity, unilateral outside the wind tower, nozzle temperature molten urea, urea particle sizeand the overflowing.4. According to the urea prilling tower thermal environment impact factor analysisresults and the principle of "chimney effect", air distribution in prilling tower is optimized andretrofit scheme is put out. In the scheme thermal environment and urea product temperatureare simulated by Fluent software.Combined with chemical fertilizer plant of Daqing petrochemical company urea prillingtower operation characteristics in this topic, the present situation and after transformation ofthe urea prilling tower are simulated with urea prilling tower internal environment factors byFluent software. Then air distribution is optimized to reduce the temperature of urea product.Research conclusion of urea prilling tower transform work has a certain theoretical guidancerole.