Liquefied Natural Gas (LNG) Analysis

Application Summary

Natural gas production has surged over the last decade with the discovery of large new gas wells and gas plant expansions. The abundance of natural gas reserves has led to low domestic trading prices and a need to export for all major natural gas producing countries. Natural gas is also viewed as a placeholder as political agendas are pushing for less reliance on coal and development of renewable energy technologies. U.S. News forecasts a “20% increase in demand for U.S. natural gas by 2020”. The U.S. is expected to be the third largest exporter of LNG by the end of the decade only behind Australia and Qatar.

For transportation and storage, natural gas is cooled and compressed into a liquid called liquefied natural gas (LNG). There is about a 600:1 volume change from gas phase to liquid phase which equates to more efficient use of storage and transportation resources for exporters. Contaminants in natural gas which need to be removed prior to liquefaction include Total sulfur and BTEX.

Increasingly strict reporting regulations and tariffs on the sulfur content of sales quality natural gas has boosted the need for analyzers with a fast response time and multi-component measurement capabilities. In addition, natural gas process producers often need to comply with contractual pipeline agreements and are interested in corrosion prevention on their liquefaction equipment.

Benzene, toluene and xylenes (BTEX) in pre-liquefied natural gas readily freezes at the cold temperatures required in the liquefaction process. The liquefaction equipment can become blocked or coated by these solids which requires shut down for maintenance. As a preemptive measure, LNG producers remove BTEX from the natural gas before liquefaction. Validation of the BTEX concentration in pre-liquefied natural gas ensures efficient BTEX removal to protect downstream equipment.

Analysis Point Analyte Typ. Range Suitable Analyzer
Pre-liquefaction Total Sulfur H2S 0-5 ppm OMA Process Analyzer
with AAI natural gas sampling system
200 psig gas pressure
COS 0-5 ppm
Methyl Mercaptan 0-5 ppm
Ethyl Mercaptan 0-5 ppm
BTEX Benzene 0-30 ppm

Measuring Total Sulfur in LNG

The ASTM method for total sulfur analysis calls for oxidation of all present sulfur compounds to sulfur dioxide for straightforward measurement. When a stream contains many different sulfur species, or unknown exotic sulfur compounds, this method is usually the only option.

The OMA-300 Total Sulfur Direct Analyzer takes a different approach, measuring up to 5 sulfur compounds directly in the unaltered sample using powerful multi-component analysis software and a high-resolution UV-Vis spectrophotometer.

The OMA-300 Total Sulfur Direct has compelling benefits for the process operator:

  • Richer data through individual concentration measurement of each constituent sulfur species
  • Decades of proven reliability measuring multiple sulfur compounds simultaneously
  • Highly suitable for natural gas applications (e.g. pipeline gas)

Measuring BTEX in LNG

The OMA-300 also provides a reliable BTEX measurement to help verify BTEX concentrations and avoid costly shutdowns for maintenance.

With a relatively high freezing point to methane, BTEX compounds readily solidify at the cold temperatures required for liquefaction of natural gas. Frozen BTEX compounds have widely deleterious effects on liquefaction machinery and storage tanks, obliging serious maintenance. To prevent this situation, LNG producers remove BTEX from the natural gas prior to liquefaction.

The expense of BTEX removal can be all for naught without a reliable method of validating the BTEX level in the cleaned natural gas and ensuring that removal is successful.

The OMA BTEX Analyzer continuously monitors BTEX concentration in the natural gas after the BTEX removal stage. This provides constant verification that the cleaning process is functioning properly and that there will be no freezing issues in the liquefaction stage. When BTEX levels above threshold are detected, the stream can automatically be diverted from the liquefaction process.

Incorporating OMA BTEX analysis into a natural gas liquefaction operation reduces costs in various ways. Maintenance events due to frozen BTEX are virtually obliterated by diverting high-BTEX streams from liquefaction. Additionally, the assurance of clean feed gas allows the LNG plant to run at much colder temperatures and much greater efficiency. Savings on power costs from running the BTEX removal system at the minimum power required, as regulated by the OMA feedback loop, are proven to be significant.