Design Considerations for Liquefied Natural Gas Plants in South East Asia
Authors: Myers C. 
Published: December 2007

Liquefied natural gas (LNG) is now a significant part of the world energy trade. Plant design depends on feed gas composition and product pattern. Investment costs are high. Energy use in plants is high and design decisions, particularly in selecting steam or gas turbine drivers, influence operation costs. Regional factors do not impose special limitations on plant design.

The LNG Industry Now

The international trade in LNG is a relatively new one. It started in 1963 when the Compagnie Algerienne du Methane Liquide (CAMEL) plant in Arzew, Algeria, began to make regular shipments to France and the U.K. Since then it has grown rapidly, as can be seen from Fig. 1. Now, total installed capacity is about 8 billion scf/D [227 × 10 6 std m3 /d], which is equivalent to about 1.5 Mbbl/D [0.24 × 10 6 m3] of crude oil in energy content, so that LNG is a significant factor in internationally traded energy supplies. All these plants now ship LNG to either Japan or Europe. Given that the production from one large plant will produce thermal energy at a rate of some 12,000 MW, it is evident that if it is to be delivered to a single terminal, then the terminal must be in an area of high energy consumption. It is characteristic of LNG plants that each is built to meet a specific supply contract, and planned as part of a chain of investments all dedicated to that contract. Investment in LNG carriers and the receiving and regasifying plant will be on a similar scale to that in the LNG plant itself. Without the security of long-term contracts it is doubtful that the very large investments needed to complete the chain--from production of gas, through the LNG plant, shipping, and reception, to regasification and sale to consumers--could be justified or financed. South East Asia is well represented in the LNG industry today. Nearly half of the world's baseload LNG capacity is in the four plants in the region. Table 1 presents some information about the plants commissioned since 1970. In the left column, all such plants, worldwide, are shown; on the right the four plants in the region. In writing this paper, we were seeking some characteristic of the plants in Brunei, Sarawak, and Indonesia that might distinguish them as a group from others. We were not able to find one. Table 1 suggests they are rather typical. They do include two unique features, neither of which can be ascribed to any regional factor. The Brunei plant is the only one to use a cooling tower system, with freshwater makeup, rather than a once through seawater cooling system; that is because of very localized experience in an older adjacent installation. The Arun LNG plant differs from all the others by using gas turbines to drive compressors and power generators, rather than steam turbines. Again that cannot be ascribed to its being in the region; rather, the converse is true, since the relatively high ambient temperature tends to favor steam rather than gas turbines.

Determinants of Plant Design

Two external factors appear significant in fixing the basic design parameters for LNG plants:the composition of the feed gas andthe parameters for LNG plants:the composition of the feed gas andthe nature of the markets accessible for its products.

Table 2 lists the components commonly found in the feed gas to an LNG plant and possible products from them. plant and possible products from them. Methane is the essential constituent of natural gas, and LNG is liquefied methane with some secondary constituents. However, any natural gas will contain other gases to a greater or lesser degree. Some hydrocarbons of higher molecular weight than methane will be included. Although it may be necessary to remove them to meet product specifications, all existing plants benefit from ethane and propane in feed gas, by making use of them as refrigerants. Depending on the quantities available in the feed gas, and on accessible markets, it may be viable to sell propane and butane as liquefied petroleum gas (LPG) products. Associated gas may contain significant quantities of pentanes or heavier components, which may be sold as products. As shown later, an LNG plant is a heavy consumer of energy, and any hydrocarbon constituent in the feed gas may be used as fuel in the plant itself, and that fact gives a degree of flexibility in designing the process plant. Generally, natural gas will contain some acid gas-CO2 or H2S. They are bad news for the plant designer and must be reduced to very low levels. Both will solidify at the low temperatures of LNG and neither is acceptable in the product at any but low concentrations. The processes used to eliminate them from the feed gas are conventional to the gas processing industries-absorption in aqueous solutions of amines or potassium carbonate, or solution in nonaqueous solvents. For feed gases with high concentrations of acid gas, these treatments can be costly, both in capital costs and in energy consumption. Any water content in the feed gas must be reduced to very low levels to avoid ice formation at low temperatures.

JPT

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