A run through the different stages in the LNG Plant life cycle and applications
19 May 2017
First the natural gas has to be extracted, then it usually goes into a pipeline from the resource to a LNG plant. Once the gas arrives at the plant, the liquefaction process begins: the gas is cooled to 259.6°F, which reduces its volume by 620 times. Then the LNG is transported from an LNG terminal to market areas. Once it arrives, it is stored, then re-gasified and connected to the local distribution.
From the construction phase of the project, followed by the pre-commissioning and commissioning phases and finally the operation, temporary air and nitrogen are present throughout:
Now let’s go into more detail regarding key rental air applications at a LNG facility.
Pneumatic tests are conducted to check the structural integrity of the vessel or piping when a hydrostatic test is not possible for various reasons. Generally it requires high quality air to be used for testing critical systems. Pneumatic testing is gaining popularity as systems are becoming more and more advanced and cannot tolerate water.
Nitrogen, being an inert gas, is used to create an inert atmosphere for a LNG tank. The oxygen content in LNG tanks needs to be limited before commissioning and start-up, so that it does not react with the hydrocarbons and create explosive mixtures. To purge the LNG tank, the required acceptance criteria is of 8 percent or less oxygen content in all tank spaces: There is an option of using either liquid nitrogen or an on-site Nitrogen Generation system. The logistics of liquid nitrogen and managing huge quantities of it to a remote project site is always challenging, hence it is preferable to have on-site nitrogen using Membrane technology. A state of the art specialty rental air company can offer the complete Nitrogen Spread with the feed air compressors along with the Nitrogen Membrane Unit to produce nitrogen up to a purity of 99%. The key strengths of Nitrogen units vs. Liquid Nitrogen are:
It is generally used to test vessels during pre-commissioning of any LNG facility. Typically systems are pressurized with a mixture of 1% Helium and 99% Nitrogen. The pressurization takes place in several steps up to normal operating pressure or up to 95% of the relief valve setting. The system is then tested and any leaks are reported using Helium as a tracer gas. Any leak is detected using a mass spectrometer device. As Helium has the smallest molecular size, even a very small leak can be detected.
A few final words, always remember to ask your compressed air and nitrogen rental supplier if they had experience with an LNG project: a world renowned company is always preferable and will avoid surprises and headaches.