Effects of hydrogen content on nitrogen expansion liquefaction process of coke oven gas

Abstract

Coke oven gas (COG) is a by-product when producing coke from coal. Producing liquefied natural gas (LNG) is an efficient way of utilizing COG. The amount of hydrogen in COG 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, a series of liquefaction processes of COG containing different amount of hydrogen are simulated in this paper. It turns out that the hydrogen content exerts a great influence on the unit power consumption and the liquefaction rate of the processes. In order to ensure very low concentration of hydrogen in LNG product, distillation is added to the process. The processes with or without distillation are compared. Furthermore, for the processes with distillation, the liquefaction process is integrated with distillation separation of hydrogen to upgrade the quality of LNG. Simulations indicate that LNG can be produced by improved nitrogen expansion processes with acceptable energy consumption. The unit power consumption increases with the increase of hydrogen content of COG and the increase of the methane recovery rate. And the unit power consumption of the process with distillation is about 10% lower than that of process without distillation, when the methane recovery rate is fixed.