LNG冷却过程中优化控制的仿真研究

Simulation Research on Optimal Control in LNG Cooling Process

为了保证天然气在液化过程中具有高转化率,同时减少液化过程中的能源消耗,针对天然气的液化过程设计了一种以节能为目标的基于机理的动态优化模型,并对丙烷预冷混合制冷过程(C3MR)中稳态行为进行分析。在该模型中,首先确定高效节能的优化目标,其次分析控制优化中的潜在变量,然后研究稳态情形下的最优行为并寻找该稳态情形下控制变量和受控变量的搭配组合,最后通过关联分析和动态相应评估,探索LNG固定情形下性能最高的控制变量和受控变量的搭配组合。建立模型后使用HYSYS软件开展仿真试验,结果表明,在稳态下,热端入口和出口混合制冷剂流的温差是C3MR液化过程节能效率的重要受控变量;在LNG生产量固定的情形下,(t-fMRV,Δt-fMRL)组合在迅速回到稳态的同时可以使温差损失最小化。因此,在天然气液化过程中,基于机理的动态优化模型既可保证高转化效率,又可减少能源消耗。

In order to improve the energy conversion efficiency and reduce the energy consumption in the process of natural gas liquefaction,established is dynamic optimization model for energy saving based on mechanism according to natural gas liquefaction process and analyzed is the steady stale behavior of the C3 MR process.Determined is the optimization objective of high efficiency and energy saving in natural gas liquefaction process,explored are the auxiliary variables in optimization control,studied is the optimal behavior in steady state situation,searched are collocation and combination of control variables and controlled variables in the steady state situation and explore is the optimal collocation and combination of these variables with the optimal performance in such situation.The software HYSYS is applied for simulation test and the results show that temperature difference(TD) of MR streams between inlet and outlet of warm end is an important controlled variable for controlling energy saving efficiency in natural gas liquefaction process under steady state condition and the combination(T-MRV.TD-MRL) can make temperature difference(TD) loss become the least if LNG production is fixed at the same time of rapid return to steady state.Therefore,in natural gas liquefaction process,the proposed model can not only assure high energy conversion efficiency and can also reduce the energy consumption.