Computer Simulation And Analysis Of Solvent Recovery Process In Rectisol Technology

The 200,000 T/Y large-sized low-pressure methanol plant in Shanghai Coking and Chemical Corporation was the largest methanol production plant in China in the past years. The low temperature methanol wash unit (Rectisol Unit) of the plant is situated in the position of critical importance in methanol production.This article is to describe set-up of a reasonable simulation model for the Rectisol recovery process according to the practical design / production conditions of the 200,000 T/Y methanol plant in Shanghai Coking by using Aspen Plus as software tool to obtain the instructive information for the production process management, thus achieving the goal of raising productivity, reducing energy consumption, stabilizing production and then gaining more economic benefit.The main tasks fulfilled and the relative successes achieved are as follows:To set up the simulation model of the Rectisol recovery by using Aspen Plus software and to adjust the parameters of the model according to the field data. This model can be used for analog calculation of Rectisol recovery process.On the basis of the set up model, utilizing the sensitivity analysis tool in the Aspen Plus software to analyze the influences of various mainoperating parameters on the Rectisol recovery process. The results showed that the trend of the influence of variable parameters could better reflect the real situation of the Rectisol recovery process:To analyze the operating conditions of each unit in different operation cases and provide relevant measures for adjustment and control.To make recalculation for the capacity of a number of critical towers and columns by utilizing the capacity calculation function of RadFrac module and indicate their maximum production capacity. The results showed that compare with the design capacity of each tower / column, the real capacity was increased in varying degrees.The following important conclusion was come to through all kinds of analysis:The operating conditions after optimization of the flash unit are as follows: The temperature is possibly low, normally at -36 to -34℃ and the pressure is 1000 to 1100Kpa. At that moment CO₂ content in the flash gas is controlled at between 50% and 60%.The sulfide content in the vent gas from H2S enriching tower T102 is affected by two factors: One is the split fraction of T102 desulfurizing section. The more the split fraction value is, the less sulfide the vent gas contains. The other is the amount of stripping nitrogen to be used. It was found that the sulfide content in the vent gas is basically in direct proportion to the amount of stripping nitrogen to be used. The spritfraction of T102 desulfurizing section is between 0.5 % and 0.65%.As for the amount of steam for hot-regeneration tower T103, the temperature of the tower should be held at 95℃. The maximum liquid flow can be increase by additional 20%.The proper ratio of reflux to feed material of the dehydration tower T104 is 1.70 to 1.93 and suggested as 1.81. Keeping the temperature of the tower at 135.7℃ ensures satisfying the discharge requirements of the tower bottoms.The task described in this article was fulfilled by means of the tools for process simulation, sensitivity analysis, operation case analysis and optimization analysis provided by Aspen Plus software. The results worked out have great significance to the practical production.