LNG与NGL联产工艺优化及改进

Optimization and improvement of LNG and NGL co-production process

关键词:  优化  联产工艺  NGL  LNG  冷干气回流  遗传算法  混合冷剂  火用分析

Key words:  optimization  co-production process  NGL  LNG  cold residue reflux  genetic algorithm  mixed refrigerant  exergy analysis

摘要:

为了降低LNG与NGL联产工艺能耗以及进一步提高乙烷回收率,采用Aspen HYSYS软件进行仿真模拟,其中凝液回收工艺采用冷干气回流工艺,制冷循环采用混合冷剂制冷工艺,在保持乙烷回收工艺各参数不变、保证乙烷回收率在95%以上的前提下,以压缩机总能耗与LNG产品质量流量的比值为目标函数,以换热器夹点温差为约束条件,使用遗传算法进行优化。并针对基础流程优化后换热器HX-2中对数平均温差大、冷热组合曲线温差波动范围大的问题提出了改进方案。然后通过火用分析方法定量对比优化改进前后主要设备的火用损失。研究结果表明:①对基础流程优化后单位能耗由0.55 kW·h/kg降低到0.41 kW·h/kg,换热器HX-1对数平均温差由10.6 ℃降低到5.6 ℃,换热器HX-2对数平均温差由7.6 ℃降低到6.7 ℃；②采用遗传算法优化后,改进流程单位能耗由基础流程的0.41 kW·h/kg 降低到0.36 kW·h/kg,换热器HX-1对数平均温差无明显变化,换热器HX-2对数平均温差由6.7 ℃降低到4.9 ℃；③改进流程优化后与基础流程相比,火用损失减少43.92%。其中换热器HX-2火用损失减少最多,占总火用损失减少量的32.14%。 

Abstract:

In order to reduce the energy consumption of LNG and NGL co-production process and further improve ethane recovery rate, a process simulation model using the Aspen HYSYS is established. In the co-production process, cold residue recycle process for NGL recovery and single mixed refrigerant cycle for the refrigeration process are used. Under the premise of maintaining the parameters of the ethane recovery process unchanged and ensuring the ethane recovery above 95%, taking ratio of the compressor general energy consumption and mass flow of LNG products as the objective function and using the minimum temperature approaches of the heat exchanger as the constraint, the genetic algorithm is used to optimize the co-production process.According to the optimization results of the basic process, an improved scheme is proposed for large logarithmic mean temperature difference in the heat exchanger HX-2 and large temperature difference between the hot and cold composite curves. Exergy destructions of main facilities before and after optimization by exergy analysis are compared quantitatively. Research results were obtained. First, after optimizing the basic process, the unit energy consumption reduced from 0.55 kW·h/kg to 0.41 kW·h/kg. The logarithmic mean temperature difference of heat exchanger HX-1 decreased from 10.6 ℃ to 5.6 ℃ and that of heat exchanger HX-2 decreased from 7.6 ℃ to 6.7 ℃. Second, after genetic algorithm optimization, by comparing of the basic process and the modified process, unit energy consumption reduced from 0.41 kW·h/kg to 0.36 kW·h/kg, and the logarithmic mean temperature difference of heat exchanger HX-2 reduced from 6.7 ℃ to 4.9 ℃, but heat exchanger HX-1 didn't change significantly. Third, compared with the basic process, the optimized modified process reduced the exergy destruction by 43.92%, and the heat exchanger HX-2 exergy destruction decreased the most, accounting for 32.14% of the total exergy destruction reduction.