Optimization of Energy Consumption of a Synthetic Ammonia Process

Abstract

Ammonia can be produced from a wide range of raw materials such as coal, natural gas, coke and oil. Coal gasification is a process that converts biomass or fossil fuel-based carbonaceous materials into CO, H2 and CO2. A cryogenic air separation process was used to obtain oxygen from air because of high purity and high amount of oxygen, which will be used for coal gasification. For an ammonia synthesis process using pure oxygen gasification, the energy consumption of cryogenic air separation occupies a large proportion. The aim is to reduce energy consumed in the ammonia plant. The models of the process were developed with the aid of Aspen Plus. The energy consumption of the different processes was obtained through energy analysis, economic analysis and sensitivity analysis. From the three simulations, it can be seen that Simulation 3 produced oxygen with the highest purity of 0.979. From the energy analysis, the energy consumed on the total utilities in Simulation 1 was 5.626×1010 BTU/h with an energy savings of 1.55%, the energy consumed in Simulation 2 was 5.286×1010 BTU/h with an energy savings of 1.53% while the energy consumed on the total utilities in Simulation 3 was 1.425×109 BTU/h with an energy savings of 74.90%. Simulation 3 consumed the least energy. The economic analysis showed the total cost of each plant for a 10-year duration. Simulation 1 had a total operating cost of 42.083 billion USD/year, Simulation 2 had a total operating cost of 41.9615 billion USD/year and Simulation 3 had a total operating cost of 918.841 million USD/year. Therefore, Simulation 3 consumed the least cost of total operation. It can also be seen that the higher the energy consumption in a plant, the higher the total cost of the plant as Simulation 3 consumed the least energy, which justified that. Simulation 3 is the air separation plant that optimises the energy consumption, thereby reducing the energy consumed in the whole ammonia plant.