摘要： 随着我国能源结构优化，液化天然气(Liquefied Natural Gas，LNG)作为清洁能源的消费量与进口量持续增长，但其含有的乙烷及以上轻烃不仅影响热值与计量，还制约资源综合利用效率。在梳理美国专利US0188996A1、US7069743B2及中国专利CN1318543C等传统工艺的基础上，提出一种基于直接换热(Direct Heat Exchange，DHX)的LNG轻烃回收新工艺，该工艺引入重接触塔实现甲烷与轻烃的二次精细分离，取消传统工艺中的闪蒸塔，通过富液温度梯级利用、脱乙烷塔能量回收等设计，优化换热网络与能耗分布，基于PR(Peng Robinson)状态方程和HYSYS软件进行了工艺模拟，从能耗、产品质量、㶲、换热网络等方面进行了综合比对，并结合响应曲面实验设计和NSGA-II(Non-dominated Sorting Genetic Algorithms-II)算法实现了目标函数优化。结果表明，如仅实现从LNG富液中提取甲烷，本文工艺的能耗较美国专利US0188996A1、美国专利US7069743B2和中国专利CN1318543C分别下降了35.9%、46.4%和44.9%；本文工艺高位发热量可降至34.16 MJ/m³，满足一类天然气质量要求，总㶲损为7171 kW，系统㶲效率57.4%；换热网络分析显示，其最小换热温差与对数平均温差更小，热集成度更高；经NSGA-II算法优化后，在乙烷收率变化不大的前提下，总能耗可从16 863 kW降至16 701 kW，在总能耗变化不大的前提下，乙烷收率可从93.52%升高至97.85%。本文工艺在降低能耗、提升产品质量与资源回收率方面具有显著优势，可为LNG轻烃回收的工程设计与现场运行提供重要理论支撑。

关键词: 液化天然气, 轻烃回收, 重接触塔, 乙烷收率, 直接换热工艺(DHX), NSGA-II算法

Abstract:

With the optimization of China ‘s energy structure, the consumption and import volume of Liquefied Natural Gas (LNG) as a clean energy have continued to increase. However, the light hydrocarbons containing ethane and above not only affect calorific value and metering, but also restrict the comprehensive utilization efficiency of resources. Based on the review of traditional processes such as US patent US0188996A1, US7069743B2 and Chinese patent CN1318543C, a new process for LNG light hydrocarbon recovery based on Direct Heat Exchange (DHX) is proposed. This process introduces a heavy contact tower to achieve secondary fine separation of methane and light hydrocarbons, eliminates the flash tower in the traditional process, and optimizes the heat exchange network and energy consumption distribution through designs such as stepwise utilization of rich liquid thermal energy and energy recuperation within the deethanizer. Process simulations were conducted based on the PR (Peng Robinson) state equation and HYSYS software. Comparative analyses covered energy consumption, product quality, exergy, heat exchange network, etc. The objective function optimization was achieved by combining the response surface experimental design and the NSGA-II (Non-dominated Sorting Genetic Algorithms-II) algorithm. The results show that if only methane is extracted from LNG rich liquid, the energy consumption of the process proposed in this paper is reduced by 35.9%, 46.4% and 44.9% respectively compared with the US patent US0188996A1, the US patent US7069743B2 and the Chinese patent CN1318543C. The high calorific value of the process in this paper can be reduced to 34.16 MJ/m³, meeting the quality requirements of Class I natural gas. The total exergy loss is 7171 kW, and the exergy efficiency of the system is 57.4%. Heat exchange network analysis shows that its minimum heat exchange temperature difference and logarithmic mean temperature difference are smaller, and the heat integration degree is higher. After optimization by the NSGA-II algorithm, with little change in ethane yield, the total energy consumption can be reduced from 16,863 kW to 16,701 kW. With little change in total energy consumption, the ethane yield can increase from 93.52% to 97.85%. The process proposed in this paper has significant advantages in reducing energy consumption, improving product quality and resource recovery rate, and can provide important theoretical support for the engineering design and on-site operation of LNG light hydrocarbon recovery.

Key words: LNG, light hydrocarbon recovery, heavy contact tower, ethane yield, Direct Heat Exchange (DHX), NSGA-II algorithm

中图分类号: 

• TE64

• TQ221