液化天然气冷能发电复合流程的构建及能效分析

Structure and energy efficiency analysis of combined research on liquefied natural gas cold energy generation

为了探究液化天然气(LNG)冷能发电和NG(天然气)烟气的余热回收,提出由级联朗肯循环与LNG直接膨胀构成的一体化工艺流程.根据LNG气化过程中物理释放特性,结合NG烟气余热特点,确定工艺流程中各个节点的热工参数,开展工艺流程的热力学分析,以论证工艺流程的理论可行性.对LNG气化压力对系统热力学性能的影响进行分析.研究结果表明,LNG直接膨胀与朗肯循环一体化工艺符合热力学基本定律,具有理论可行性,是LNG冷能发电的有效途径之一.在一体化系统中,LNG冷能发电量为55.52kW·h/t,烟气余热回收效率为41.17%,冷能利用的效率为16.25%.主要的损失集中于各个换热器上,占系统总损失的87.86%.随着LNG气化压力的增大(0.2~2.0 MPa),系统的损失降低,系统的效率升高.

An integration process of cascade Rankine cycle and direct expansion of liquefied natural gas（LNG）was constructed for LNG cold energy power generation and natural gas（NG）flue gas waste heat recovery.The thermal parameters of every node in the process were calculated according to the physical exergy release characteristics of LNG regasification process and features of NG waste heat utilization process.Then the thermal analysis of integration process was conducted for comprehending the feasibility of the integration process.The influence of the LNG regasification pressure on the thermal performance of integration process was analyzed.Results show that the integration process of LNG cold energy generation is basically feasible from thermodynamic laws.The output power of the whole process is 55.52kWh/tLNG,and the efficiency of the waste heat recovery in the integration process is 41.17%.The exergy efficiency of LNG cold energy generation in the integration process is 16.25%.The main devices of exergy loss are the heat exchangers,and the exergy loss in the heat exchangers accounts for 87.86 % of the total exergy loss in the process.The exergy loss of the whole process continuously decreases and the exergy efficiency continuously increases along with the increase of the LNG regasification pressure（0.2-2.0 MPa）.