Effects of Hydrogen Content on Nitrogen Expansion Liquefaction Process of Coke Oven Gas

Coke oven gas (COG) is a by-product when producing coke from coal. It is not always easy to make use of COG, causing waste of energy. Producing liquefied natural gas (LNG) is an efficient way of utilizing COG. The amount of hydrogen affects liquefaction process significantly, because its thermal properties are quite different from the other compositions (methane, carbon monoxide, etc.) of COG. Based on nitrogen expansion liquefaction process, this paper simulates a series of liquefaction processes of COG containing different amount of hydrogen. After optimizing these processes and comparing their parameters, it turns out that the hydrogen content exerts a great influence on the unit power consumption and the liquefaction rate of the processes; however its effect on the product purity is not distinct. Furthermore, the liquefaction process is integrated with distillation separation of hydrogen to upgrade the quality of LNG. The ways of achieving energy integration between liquefaction and distillation are suggested, and the influences of some important parameters, such as pressure in the distillation column, are analyzed.