Improving natural gas liquefaction plant performance with process analyzers – Case Study

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Courtesy of Siemens Industry, Inc. - Process Analytics

LNG is natural gas in its liquid state with high energy density, which makes it useful for storage and transportation over long distances from the gas fields to the consumers. LNG is recovered from natural gas in large-scale liquefaction plants. Process automation is a key issue in LNG plants to ensure cost efficient plant operation and high product quality. Process analyzer deliver important data therefore.

Siemens, a leader in process analytical instrumentation, has proven over decades its capability to plan, engineer, manufacture, implement and service analyzer systems for NG liquefaction plants. This Case Study provides an overview of the processes and describes how Siemens with its analyzer and application know-how meets best the process requirements.

Liquefaction of natural gas to LNG

Natural Gas (NG) is a vital component of the world’s supply of energy. It is one of the cleanest, safest, and most useful of all energy sources. NG is colorless and odorless in its pure form. While it is formed primarily of methane, it can also include ethane, propane, butane, pentane and certain impurities.

Liquified Natural Gas (LNG) is natural gas in its liquid form. It is an odorless, non-toxic and non-corrosive liquid. Natural gas is converted to LNG by cooling it to about -180 °C, at which point it becomes a liquid. This process reduces its volume by a factor of more than 600. This allows natural gas to be transported economically by sea. At its destination, LNG is stored as a liquid until it is warmed to convert it back to gas, blended to comply with local composition and BTU requirements and then sent through pipelines for distribution to consumers and industries. The first LNG liquefaction unit came into operation in 1964 at Arzew, Algeria.

Typical natural gas includes additional components like sulfur, CO2, water and heavier hydrocarbons which have to be removed from the natural gas before cooling. If not, some of them would become solid during refrigeration and interrupt the cooling process. Consequently, a LNG liquefaction unit produces also other chemicals like solid sulfur, NGL (Natural Gas Liquids) and LPG (Liquified Petroleum Gas).

Today LNG accounts for about 4% of natural gas consumption worldwide, and is produced in dozens of large-scale liquefaction plants.

LNG supply chain from gas fields to consumers

The LNG supply chain from gas fields to consumers comprises a number of process and logistic (storage and transportation) steps as shown in fig.1.

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