Measuring Benzene in Pre-Liquefied Natural Gas in Peak Shaving Facilities

Introduction

At peak shaving facilities, natural gas is liquefied and stored on-site, ready to be gasified and delivered to the grid when peak demand occurs. One major concern is incident benzene, which readily freezes in liquefaction and destroys storage equipment. The contaminant poses additional environmental dangers: benzene is carcinogenic. Online monitoring of benzene is required.

With a freezing point of 5.5 °C, benzene readily solidifies at the cold temperatures required for liquefaction of natural gas. Frozen benzene has widely deleterious effects on liquefaction machinery and storage tanks, obliging serious maintenance. To prevent this situation, LNG producers remove benzene from the natural gas prior to liquefaction. The expense of benzene removal can be all for naught without a reliable method of validating the benzene level in the cleaned natural gas and ensuring that removal is successful.

The OMA system continuously monitors benzene concentration in the natural gas after the benzene 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 benzene levels above threshold are detected, the stream can automatically be diverted from the liquefaction process.

Incorporating OMA benzene analysis into a natural gas liquefaction operation reduces costs in various ways. Maintenance events due to frozen benzene are virtually obliterated by diverting high-benzene 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 benzene removal system at the minimum power required, as regulated by the OMA feedback loop, are proven to be significant.

Absorbance Spectra of Benzene

The OMA system is calibrated on standard samples (known concentrations) of benzene in order to learn the distinctive absorbance curve of benzene and produce an excellent correlation between curve height and chemical concentration.

System Benefits

• Continuously measures benzene concentration using dispersive UV-Vis absorbance spectroscopy
• Totally solid state build with no moving parts — modern design for low maintenance
• Ultra-safe fiber optic design with dedicated sample flow cell — no toxic/corrosive sample fluid in analyzer enclosure

Installation and Product Photos

Further Reading