Determination of a Suitable Biocide Program for Microbial Control in Liquefied Natural Gas (LNG) Cooling Water Trains

Abstract

Determination of a Suitable Biocide Program for Microbial Control in Liquefied Natural Gas (LNG) Cooling Water Trains

Microorganisms can cause numerous issues in oil and gas systems, including microbiologically influenced corrosion (MIC), generation of hydrogen sulphide (H2S), and biofouling. They are often controlled using biocides, however the complicated nature of many processes and their microbial communities means that rigorous biocide selection must be carried out to ensure that the treatment chemicals are effective from both a technical and cost point of view.

To protect two fresh cooling water trains from issues caused by microbial growth at a liquefied natural gas (LNG) plant, we carried out an extensive biocide evaluation study. The efficacy of 18 biocides (from 9 vendors) was tested against representative groups of microorganisms known to be present in the fresh cooling water; sulphate-reducing bacteria (SRB), nitrate-reducing bacteria (NRB), Pseudomonas spp. (MGB), iron-reducing bacteria (IRB) and Legionella. In addition to time kill tests, the performance of each biocide was assessed in minimum inhibitory concentration tests for SRB, NRB, MGB and IRB.

Data obtained from sessile (SRB, NRB, MGB, IRB) planktonic (SRB, NRB, MGB, IRB) and dedicated Legionella biocide tests was used to rank the biocides, as individual products. From this ranking, the biocides from one vendor were the best performing. Both these products demonstrated a quick kill action, but also preservative, longer lasting biocidal effects, which are important for a closed water system. In addition, no incompatibility was observed between the two most effective products either between each product or with either system water.