RIASSUNTO
Abstract
Abu Dhabi Gas Liquefaction Company Ltd (ADGAS) owns and operates three LNG trains at DAS island. Trains 1 and 2 have common utilities while train 3 has a separate utilities system. The three LNG trains have a once-through sea cooling water (SCW) system which includes a series of heat-exchangers. The integrity and operational availability of these heat-exchangers is is vital for LNG facilities, and they operate most efficiently at an optimised water flow conditions which are required to prevent internal fouling, scaling, erosion corrosion and/or microbially induced corrosion (MIC).
To maintain the flow of seawater cooling system at the optimum parameters and to prevent blockage and corrosion due to micro and macro fouling (bivalves (oysters, mussels) and other marine organisms) the procedure at ADGAS is continuous injection of hypochlorite at the seawater intake of the trains. During the previous years, marine growth was however observed together with an increased fouling rate within the SCW system. Hence ADGAS initiated a review of the chlorination system and its efficiency. Sweco Nederland BV (SWNL) was contracted to perform a scouting survey for the seawater species at DAS island and a review on the existing chlorination system. For optimal control of biofouling, it was concluded the Pulse-Chlorination® technology (Bruijs, 2015) was feasible and recommended. During the second phase of this work, SWNL mobilised a laboratory on site at DAS Island for an optimization study on site. During this study, procedures are followed to monitor the target species behavioural response to a variety of hypochlorite dosing settings. Through a period of 6 weeks of experimentation the optimal Pulse-Chlorination dosage procedure was assessed. This Pulse-Chlorination procedure is an optimized intermittent dosing method that enhances a repetitive mode (on /off) of hypochlorite dosing, typically varying between 10 – 20 minutes. This procedure forces bivalves to continuous switch between metabolic mode (aerobic vs. anaerobic), whereby a physiological exhaustion of the bivalve is reached, resulting in a highly effective biofouling control. Through application of the Pulse-Chlorination dosing procedure an environment is created inside the SCW system in which larvae of fouling species will not settle and thus will not develop large fouling communities. Hereby settlement and growth of biofouling is prevented. In general, the advantages of Pulse-Chlorination are numerous. For ADGAS, the optimised chlorine dosing results in increased production due to the improved cooling water hydraulics, reduced operational risks, less consumption / production of hypochlorite (hence less ECP operation and maintenance expenditures) and more importantly less chlorine levels in the outfall, which is the largest benefit from an environmental point of view.