Question

Enlist the names of different types of processes available for production Urea and select a particular production process with proper Justification. Draw a neat sketch of Process flow diagram with major equipments.

Answer 1

The industrial synthesis of urea is carried out by the reaction between ammonia and carbon dioxide at high pressure. Industrially CO2 and NH3 used from the different processes Such as:

1. Steam Reforming

2.Biomass Gasification

3. Water Electrolysis

4. From the Naptha and Natural gases.

Among these, Naptha and the natural gas-based process is most often used in industries since it is abundantly available at a lower cost compared to other processes. From the Naptha combustion easily CO2 will be produced and it is utilized as the feed stocks after separating water vapors. Hence most of the industries are based on the Naptha feed stocks for production of Urea.

From the reaction of CO2 and NH3, ammonium carbamate is generated which is further dehydrated by the application of heat to form urea and water.

The reaction scheme involves as showbn below:

1.) NH3 + CO2- NH2COONH4

2.) NH2COONH4- CO(NH2)2 + H2O

Reaction 1 is fast and exothermic and it achieves 100% conversion under synthesis conditions while the Reaction 2 is slower and endothermic and does not go to completion. The overall conversion on a co2 basis is achieved by 70-80%. According to Le Chatelier's principle conversion increases with increasing temperature and NH3/CO2 ratio and decreases with increasing H2O/CO2 ratio. The decomposition of carbamate to CO2 and NH3 achieved by the reactor effluent to be depressurized and heated. Initially, the urea plants are operated on a once-through principle where the off-gases were utilized as feedstocks for other products. Later Partial Recycle techniques were developed to recover and recycle some of the NH3 and CO2 to the process. It was essential to recovering all of the gases for recycling to the synthesis to optimize raw material utilization and since recompression was too expensive an alternative method was developed.

Based on the CO2 and Ammonia reaction and optimized recyle strem of effluent gases, types of majorly used industrial processes are as below:

1). Carbon dioxide stripping process

2.) Ammonia stripping process

3.) Advanced cost & energy saving process

4.) Isobaric double recycle process

The simple blockdiagram for urea synthesis is as shown in fig.