LNG Basics: Reliability and Efficiency

Liquefied Natural Gas (LNG) production started in the 1960s, when it became clear that there was a need for long-distance overseas shipment of clean-burning gas to be applied as a fuel for motor vehicles, residential and industrial consumption. At the time many developing countries could not benefit from the pipeline systems that transported the natural gas for other countries such as USA and Europe , as there was no significant local gas source in the area available to them. Because the need for clean-burning energy became a high priority for countries like Japan , a program was developed to ship natural gas in liquefied form from overseas. With the major oil producers beginning to consider energy conservation, what used to be considered a useless by-product of oil production was now being gathered and used for NGL and fuel-gas production.

Fuel-gas often supports a petrochemical basis industry in the country of production. The new gas finds in the world are quite abundant so that they can provide for a new source of long-term supply. These long-term supply contracts are the cornerstone of the LNG industry, as the investments are significant and involve not only the provider of the liquefied gas, but also the customer and the shipping companies. Okasis have to make very large investments in equipment that is only suitable for one type of product-LNG.

What is LNG

When natural gas is cooled to a temperature of approximately -260 F (-160 C ) at atmospheric pressure it condenses to a liquid called liquefied natural gas (LNG). One volume of this liquid takes up about 1/600th the volume of natural gas at a stove burner tip. LNG weighs less than one-half that of water, actually about 45% as much. It is odorless, colorless, non-corrosive, and non-toxic. When vaporized, it burns only in concentrations of 5% to 15% when mixed with air. Neither LNG nor its vapor can explode in an unconfined environment.

Ensure High System Reliability and Efficiency

There are many components to system reliability and efficiency in LNG facilities. These include:

• Maintaining plant efficiency
• Maintaining high plant throughput
• Ensuring high valve and equipment reliability
• Increasing plant availability

All of these are consistent with each other. Excellent products and services ensure an excellent system that is reliable and efficient. Compromising with an inferior technical solution to save money will end up costing more money in the long run. How can you meet the above purposes? By specifying the critical control valves important to the project at an early stage. Critical control valves heavily impact the above aspects of the LNG plant the owners are measuring. The valve specifications ensuring that the above requirements are met include the control valve specifications based on ISA.

The CCI Solution

CCI DRAG® tortuous path velocity control valve technology has advanced along with the LNG industry. Quick stroking requirements for compressor recycle have reached one second or less using low cost, highly reliable pneumatic actuation. This is a major benchmark advantage of CCI control valves. Hydraulic actuation has been used but is not favored due to high maintenance, high cost, and low reliability.

CCI’s balance seal is also unique in the industry. This design clamps the seal in the bonnet, which is superior to manufacturers who use the balance seal in a groove on the plug. The resulting benefit is that the balance seal remains effective at cryogenic temperatures as the seal shrinks to form a better plug seal, while the competitors plug seal shrinks and moves away from the cage, impairing sealing.

For gas to flare valves, tight shutoff has ensured that product or feedstock has not been unnecessarily flared. A minimum of Class V shutoff and frequently Class VI shutoff has been applied successfully for this application.

CCI was a leader in the development of IEC 534. It was one of the first to recognize a noise increase in the expansion section of a control valve applied for noise control. Acceptable noise levels below 85 dBA have been met globally through CCI’s severe service installations.

CCI can assist in the selection of severe service valve applications, to ensure low ownership costs. CCI can lower installed cost due to smaller pipe sizes, and reduce parallel valve installation due to high valve rangeability. One such example was recently demonstrated with the Atlantic LNG Trinidad expansion project (see article on page 3).

Severe service applications are critical for low noise, protection of major equipment components, minimizing loss of product or feedstock, increasing compressor efficiency, and ensuring high plant reliability and efficiency. With proven LNG references installed in over 50% of the LNG plants worldwide, CCI engineers have created proven solutions to meet the continuous challenges of the LNG industry.

Published in SOLUTIONS Summer 2001