Intervening when feed gas is too lean: Heavies removal challenges for LNG projects
Pipeline-quality feed gas for US LNG projects poses a unique challenge: heavy hydrocarbon removal. Most of the feed gas from a pipeline network has been preprocessed to extract valuable NGLs, so it is typically lean.
When actual natural gas compositions to liquefaction plants are even leaner than previously estimated and designed for, these treatment units are further stressed to meet the target specifications. Consequently, increased pressure drop/freezing in cryogenic exchangers has been observed in multiple North American LNG projects. For North American LNG projects early in the development cycle, most attention is placed on the liquefaction unit and familiar choices are made for gas treatment that are common for large-scale LNG trains that have been built over the last several decades. Conventional heavies removal designs are often considered for North American projects due to their perceived process simplicity and low capital cost (CAPEX).
This paper reviews proven technologies that show benefits for heavy hydrocarbon removal systems for lean feed compositions. The discussion includes an analysis among heavy hydrocarbon removal technologies using a case study approach which considers different ranges of feed gas compositions and delineates an optimal selection for each composition. The paper also highlights relative capital and operating expenditure estimations among different technologies and the significant impacts to liquefaction process efficiency.