Big and Clean - A Novel Design for LNG Plants

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper IPTC 11637, "Big and Clean - A Novel Design for LNG Plants," by Barend Johan Jan Pek, Kaart Sander, and Elion Wiveka, Shell, prepared for the 2007 International Petroleum Technology Conference, Dubai, 4-6 December. The paper has not been peer reviewed. The demand for clean and afford-able energy translates into a large demand for liquefied-natural-gas (LNG) production capacity. To meet this increase in production capacity, increasingly larger processing-train sizes have become the trend. A mega-train design is presented for production of more than 10 Mt/a. Much of the LNG expansion is taking place in the Middle East. A typical feed-gas composition from this region was selected as the basis for integration of gas conditioning (treating), natural-gas-liquid (NGL) extraction, liquefaction process, and utility facilities. Introduction The demand for natural gas is forecast to grow by 3%/yr over the next 15 years, with demand for LNG growing by 8–10%/yr. For several years, many projects have been under way, resulting in a constrained contractor market, a worldwide heavy demand for raw materials, and issues regarding logistics of work force and products. These challenges lead to large trains, particularly where large resources are involved, as in the Middle East, Russia, and Australia. An increasingly important challenge is the need to minimize CO2-emission rates. High efficiency is a crucial enabler. Higher efficiency increases the amount of LNG that can be produced for the selected power turbines and compressors that make up a large part of the capital costs. Therefore, the focus is extended to the use of exhaust heat. The full-length paper presents a train design for LNG production at a rate of 11 Mt/a. The design is based on Shell's Parallel Mixed Refrigerant (PMR) Process, which uses propane refrigerant in the precool cycle. Depending on project-specific conditions, such as climate and market opportunities, other designs may be more suitable. The double-mixed-refrigerant process was selected for the Sakhalin LNG project currently under construction (Fig. 1). The PMR concept is scalable from 11 to 6 Mt/a by changing helper-motor size or changing to smaller gas turbines. Improved fuel efficiency by use of waste-heat recovery is applicable to several designs, thus minimizing CO2 emissions. Design Premises Plantwide integration of heat generation and demand is provided by steam. The full use of waste heat from the gas-turbine exhausts enables a step change in plant efficiency with respect to conventional LNG-plant designs and can help to reduce the specific CO2 emissions. This design uses air cooling. Dedicated attention to hot-air recirculation and plot-plan optimization provides a robust design. Should cooling water be available for a once-through or recirculating cooling system, this can be incorporated and will further improve fuel efficiency and, depending on cooling-water-supply complexity, also the specific cost.