基于变压吸附制氮系统的BOG再冷凝工艺

为了解决LNG接收站在低输量工况下闪蒸气(Boil-Off Gas,以下简称BOG)回收不完全的问题,在不增加冷凝工艺复杂性的前提下,基于现有设备的实际工况及工艺流程,以热力学原理、静态仿真计算结果为依据,在传统的蓄冷式BOG冷凝方案的基础上,结合LNG冷能利用方式,提出了一种基于LNG接收站制氮系统的蓄冷回收BOG新工艺,并进行了BOG温度、冷凝器入口压力、LNG组分等参数的敏感性分析,明确了新工艺的适用条件。运用效果表明:(1)新工艺充分利用了LNG接收站的现有设备,每年可为LNG接收站节能创收近160万元;(2)新工艺可实现高负荷下的BOG冷凝,其冷凝外输工艺可作为辅助冷凝工艺,冷凝回罐工艺可作为应急工艺——液氮用于蓄冷、气氮用于吹扫,可满足接收站的多种需求;(3)较之于前人提出的4种BOG处理工艺(多级压缩、级间冷却、预冷和透平回收轴功),新工艺在对外输量的依赖性、流程安全性及操作性等方面均有优势。结论认为:新工艺在设备投资、能耗、工艺安全性及经济效益上都具有明显的优势,值得推广应用。

A BOG recondensation process based on a PSA nitrogen system

The boil-off gas (BOG) cannot be recovered completely in the operational mode of low flow rate at LNG receiving terminals. In view of this, a new cold-storage BOG recovery process based on the nitrogen system of an LNG receiving terminal was proposed without increasing the complexity of a condensation process. This new process was developed bases on the actual behavior and technological process of existing equipments, the thermodynamic principles and the static simulation calculation results. Its development is on the basis of the traditional cold-storage BOG condensation program, combined with an LNG cold energy utilization mode. Then, sensitivity analysis was conducted on BOG temperature, inlet pressure of the condenser and LNG composition, and the applicable conditions of this new process were determined. And the following operation results were obtained. First, this new process makes full use of the existing equipments at an LNG receiving terminal and provides the terminal with annual revenue of CNY 1 600 thousand owing to energy saving. Second, by virtue of this new technology, the BOG condensation under high loads can be realized. And various requirements of an LNG receiving terminal can be satisfied with the condensation transportation process as an auxiliary condensation process and the condensation backflow as an emergency process (liquid nitrogen used for cold storage and gas nitrogen for purging). Third, compared with the four previously proposed BOG treatment processes (compound compression, interstate cooling, precooling and turbine recovery shaft work), this new process is more advantageous in terms of transportation dependency, process security and operability. It is concluded that this new process is remarkably advantageous in equipment investment, energy consumption, technological safety and economic benefit, so its application is worth popularizing.