required. The analyser can also differentiate between soft deposits (organic and microbiological fouling) and hard deposits (scaling). The early detection capability of the analyser allows corrective actions to be taken before biofilm can cause heat transfer loss or equipment damage. The advanced chlorine stabiliser chemistry employed as part of the biofilm detection and control programme is used in combination with sodium hypochlorite to produce a pat- ented, in situ stabilised active chlorine solution. The resulting solution is not consumed when reacting with the EPS’s pro- tective slime matrix, thereby allowing the solution to pene- trate the biofilm, where it reacts only with the hydro-sulphur and sulphur-sulphur bonds of the biological proteins on the cell membrane and within the microorganisms. The in situ stabilised active chlorine solution not only controls both planktonic and sessile microorganisms but also removes existing biofilm and inhibits biofilm regrowth. The solution also effectively controls biofilms that harbour legionella. The in situ stabilised active chlorine solution does not increase the corrosion of metal substrate because of its lower oxidation reduction potential (ORP). For the same reasons, the solution does not degrade cooling water inor- ganic deposit inhibitors or react with other organics poten- tially present in the water. Thus, adsorbable organic halogen (AOX) and trihalomethane (THM) production does not occur. The lack of these reactions provides desirable environmental and health advantages over strong oxidising biocides. Unlike strong oxidising biocides, ammonia and amine contamination in cooling water does not increase the demand for the in situ stabilised active chlorine solution. Additionally, the patented solution results in lower chloride levels and reduced overall corrosivity of the cooling water. Stainless steel, in particular, has a reduced risk of chloride- induced stress cracking. As a complement to the biofilm detection and control programme, the Solenis HexEval performance monitoring programme is available. Using advanced monitoring and predictive modelling capabilities, this programme enables decision-makers to identify which heat exchangers pose the greatest threat to reliable operation because of biofoul- ing, scale or both. As a result, plant personnel can develop appropriate action plans. Solenis experts work directly with plant engineers to assign a critical rating score to each exchanger based on its impact on production if taken offline for cleaning or repair. The algorithm, developed from more than five million hours of study time on thousands of heat exchangers, then anal- yses the flow study data of each exchanger, within the context of its design, to calculate a hydrothermal stress coefficient (HSC) – a discrete value used to assess the relia - bility of the heat exchanger and identify factors threatening its performance. Case history: Marathon refinery Marathon Petroleum Corporation operates the Garyville oil refinery on the banks of the Mississippi River in south - eastern Louisiana between Baton Rouge and New Orleans. The facility has a crude oil refining capacity of 596,000 barrels per calendar day. Crude refining takes place in 19
processing units using 10 cooling towers and more than 400 individual heat exchangers. Heat exchanger reliability and efficiency have a dramatic impact on the profitability of the operation. The facility and its water treatment supplier, Solenis, monitor the conditions of the water chemistry and the individual heat exchangers to ensure smooth operation. Hidden biofilm cost Despite maintaining corrosion coupon rates of less than two mils per year (mpy) and controlling water treatment parameters within key operating indicators (KOIs) for min- eral saturation and corrosion inhibitor residuals, the refinery struggled with heat exchanger bundle failures and effi - ciency losses between turnarounds. Even with corrosion coupon results well within indus- try standards, heat exchanger bundle lifespans averaged seven years, lower than predicted. Corrosion coupon data suggested that the exchanger longevity should have been 50-80% longer. Agar dip slides, used to measure aerobic planktonic bacteria growth, routinely yielded results well within the Cooling Technology Institute (CTI) guidelines of 10 1 –10 2 cfu/ml. Halogen residuals, used to control plank- tonic microorganisms, conformed to recommended values. The programme used a non-oxidising biocide, selected by laboratory kill studies, fed to the system two to three times per week. Still, summer conditions resulted in constrained refinery capacity, with exchangers being taken offline for cleaning because of water side fouling and requiring Underappreciated and underestimated aspects of industrial cooling water treatment include the effect of biofilm on heat transfer unscheduled shutdowns for cleaning, repair, and replace- ment. The negative impact on plant production and profita - bility ran into the millions of dollars annually. Because the heat exchangers were typically removed from service for decontamination, deposit analysis did not show the true cause of the corrosion, which was ultimately determined to be biofilm. The steaming required to decon - taminate the process side dehydrated the biofilm. Despite deposit analysis that predicted a different corrosion mecha- nism, closer inspections of failed bundles revealed UDC and pitting resulting from biofilm. In addition, corrosion coupon visual examination and laboratory testing confirmed that biofilm was the root cause of the problem. A million-dollar problem Marathon and Solenis set about defining the problem and developing a plan to address the root cause. Before changes to the existing treatment programme could be rec- ommended, the hypothesis that biofilm was the root cause of the exchanger problems required additional validation. To do this, Solenis, working with the local Marathon team,
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PTQ Q1 2024
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