Steady State Modeling of Urea Synthesis Loop

Urea, which is known to be an important petrochemical product, is mainly used as fertilizer. Urea (NH2CONH2) is produced commercially by reaction of ammonia (NH3) and carbon dioxide (C02), under conditions depending on each particular plant technology. There are a lot of urea synthesis technologies available such as Snamprogetti process, Stamicarbon process and etc. In most operating process the synthesis reaction is carried out in the liquid phase, at pressure from 13 to 25 MPa and at temperature between 170°C and 200°C. In this study, a simulation is developed specifically for the high pressure urea synthesis section of the ABFPlant; which adopt Stamicarbon process. In this study, the formation of ammonium carbamate is considered to occur through the heterogeneous reaction of carbon dioxide and ammonia. In present study, the urea reactor is divided into three reactors namely the equilibrium reactor where the ammonium carbamate formation take place, and two continuous stirred tank reactors in which the urea formation and biuret formation are taking place respectively. The validity of the proposed simulation was demonstrated using the actual plant data from ABF Plant. From the Aspen HYSYS simulation result, it shows that the simulation could predict the behavior of the urea reactor as well as the urea synthesis section as per literature but could not give the accurate value. The CO2 conversion in the first equilibrium reactor is calculated by Aspen HYSYS to be approximately similar as found in the ABF Plant; that is 60% (with 5.2% error) while Polymath 5.1 calculates the C02 conversion in the equilibrium reactor to be approximately 60% which also agrees with the Aspen HYSYS and the ABF Plant data. For the second CSTR reactor, HYSYS and Polymath 5.1 calculate the conversion of ammonium carbamate to urea to be 92.75%) and 94% respectively which agreed with each other. The overall conversion of CO2 to urea in the high pressure urea synthesis loop with the recycle stream is calculated by HYSYS to be approximately 89.73%) which is 10% higher than is found in the ABF Plant. The urea yield formed in the high pressure urea synthesis loop is calculated by HYSYS to be 90.86%) which is 5.5%) higher than is found in the ABF Plant. From the study conducted, it is found that this simulation could be used to predict the CO2conversion as well as urea yield obtained while the throughput is varied within 10%o error