Research On The Technical Simulative Optimization Of Nature Gas Cryogenic Unit

As the increasing demand of the C2+ light dydrocarbon in petrochemical engineering, the optimization of the cryogenic system for light dydrocarbon recycling has attracted much attentions. The simulation calculation of the cryogenic system can help to analyze the existential problems, to find out the influence of the operating parameters on the product yield, which has significant instruction to decrease the running cost of the cryogenic system, to improve the yield of the light dydrocarbon.Here, we simulated and optimized the nature gas cryogenic system using the HYSYS simulation software. Based on the material balance principle, the operation situations of the demethanizer, mechanical equipments and heat-exchangers were calculated. The existential problems were analyzed and the corresponding improvement suggestions were further proposed. The results show that:(1) Under the processing capacity of 24145.85 Nm3/h(the designed processing capacity of 25000 Nm3/h), all of the operating parameters were stable, and the recycle rate of the light dydrocarbon was 28.1%, which was 33.3% lower than the designed value. While the recycle rate of dry gas was 62.6%, which was 60.5% higher than the designed value. The recycle rate of ethane and the C1/C2 mole ratio in the light dydrocarbon was matched to the design results.(2) If the heat extracted from the tower bottom was increased, the bottom temperature increased linearly.(3) As the decreasing of the top temperature, the yield of light dydrocarbon in Wanfang gas was also increased. When the top temperature decreased from-70 ℃ to-72℃, the light dydrocarbon yield increased from 6802.35 kg/h to 6965.37 kg/h, and the recycle amount of light dydrocarbon in Wanfang gas was increased from 2.82 t to 2.88 t. If the daily processing capacity was 58×104 m3, 3.48 t more light dydrocarbon can be produced everyday, which provides a considerable economic benefit.(4) The light dydrocarbon yield was significantly influenced by the refrigeration depth, the relationship between which was linear. Every 10 ℃ the refrigeration temperature decreased, the light dydrocarbon yield increased 0.4108 t/104 m3 feed gas. If the daily processing capacity was 58×104 m3, 24.65 t more light dydrocarbon can be produced everyday, which provides a considerable economic benefit.(5) The top and bottom temperature of the demethanizer influenced each other. The bottom temperature changed at different top temperature. In order to fine control these two parameters to get the optimized operation situation, the simulation calculation results showed that when the difference between the top and bottom temperature was ~ 103℃, the C1/C2 mole ratio in the light dydrocarbon from the bottom can be limited to lower than 0.03.