Simulation And Optimization Of Preparation Of Synthetic Gas From Lean Natural Gas

Phase â…¡ plant of a fertilizer company with a designed annual capacity of450,000tonnes of ammonia, uses lean natural gas with LHV and a high content ofCO₂and N2as raw material. And utilizes ammonia synthesis processes combinationof Kellogg Brown&Root（KBR）, in which the core technology is cryogenicpurification process. The paper selected the preparation of synthetic gas from lean gasusing steam reforming process and aMDEA CO₂removal system as the researchobject. Due to the high energy consumption of CO₂removal system, which in generalaccounts for10%¹5%of total energy consumption of ammonia synthesis, there are alot of energy-saving potential. This paper aimed at exploring the ways to reduce theenergy consumption of CO₂removal system, using chemical process simulation andoptimization method.First of all, simulated calculation was made on lean gas steam reforming processbased on Aspen HYSYS software. The property calculation model which was chosewere SRK and PR equation of state. Simulation values were well consistent withdesign values. However, after a further comparison of composition of reformed gas,the results showed that a better calculation effect was obtained when using PR. Thesimulation calculation also applied to aMDEA CO₂removal process, choosing DBRAmine Package as property calculation model, calculation values also were wellcoincided with design values. According to the above simulated calculation, theestablished model for the process were suitable. Therefore, the consequence couldprovide a further optimization research with a reliable basis.In view of the existing process, an improved process that lean natural gas waspre-decarbonized was put forward and simulated calculation was made on twodifferent solutions of the improved process. Then sensitivity analysis was performedon the operating parameters of the pre-decarbonized process, optimized operatingparameters were obtained. Design and operation of the devices were achieved on thebasis of these parameters. Besides, how the degree of pre-decarburization influencedon energy consumption was taken into consideration. The results showed that whenlean gas was decarburized to5%（mole fraction）, a better energy-saving effect wasacquired. By comparing the energy consumption of decarburization of two differentsolutions of the improved process, the fact proved that the pressurization prior to decarburization process was better than the decarburization prior to pressurizationprocess.Finally, a comprehensive contrast between the original process and the improvedprocess was carried out. The conclusion was as follow, in the aspects of energyconsumption of decarburization and steam reforming process, production capacity, theimproved process showed clear advantages. But a set of decarburization equipmentwas added. Overall, the improved process had a very good application prospect.