Study and economic evaluation of calorific value adjustment process in the LNG terminal

A certain typical liquefied natural gas (LNG) receiving terminal in China as an example, for the exchange and economic problems caused by high C₂⁺ components in the feed-in liquefied natural gas, the calorific value of natural gas products is adjusted by extracting C₂ and C₃⁺ components from rich LNG and injecting nitrogen/liquid nitrogen. In order to evaluate incomes of the four kinds of technologies, ethane and C₂⁺ recovery and nitrogen gas injection (plan A & B) and liquid nitrogen injection (plan C) with their refrigeration cycle have been simulated by using the Aspen HYSYS to prepare the energy consumption analysis. In addition, economic benefits of four calorific value adjustment systems are analyzed based on energy measurement. The results show that the after-tax net income of the receiving terminal which adds liquid nitrogen to adjust calorific value is 36.83% higher than which extracts C₂⁺ components in the volume measurement system. Under the system of energy measurement, the income of C₂⁺ recovery and plan A, B and C is increased by 8.67%, 12.15%, 12.16% and 7.09% respectively compared to the original measurement mode, and the liquid nitrogen injection (plan C) has the highest after-tax net income. Therefore, considered in terms of product's sales and the operation and capital costs under the current situation of heat value adjustment technology, the liquid nitrogen injection process which inject liquid nitrogen in the exit of high pressure external transport pump is feasible, effective, and economical.