Case Study: On the pulse
The benefits of Pulse-Chlorination at Qatargas, Ras Laffan
To maintain a reliable and efficient operation of seawater cooling water systems, the typical industry practice is chlorination, in general by continuous dosing and periodic shock dosing. Due to concerns about potential environmental effects on the local marine environment, the Qatar Ministry of the Environment (MoE) has set the residual chlorine limit in cooling seawater discharges at 0.05 mg/L. To comply with regulatory requirements and ensure the highest standards of environmental practice in line with the Qatargas Direction Statement, Qatargas implemented Pulse-Chlorination® (P-C) as its antifouling strategy.
P-C is a cost-effective intermittent dosing regime, which is recognized as the European Union (EU) Best Available Technology (BAT) for biofouling mitigation of once-through cooling seawater systems. It combines optimal fouling control with minimal chlorine discharge, while retaining safe and reliable plant operations and has successfully been implemented worldwide through on-site field tests at industries ranging from oil and gas, nuclear and conventional power plants.
P-C has been in operation at Qatargas since 2008. To date, no fouling issues of concern and no associated problems in production have occurred, as confirmed by multiple inspections. The implementation of Pulse-Chlorination at Qatargas has been successful, with significant improvements in both fouling mitigation and significant reductions in the discharge of total residual oxidants (TRO). With the implementation of P-C, the objectives set for achieving “chlorine” discharges of as low as reasonably practical have been met.
The Qatar Ministry of Environment has concurred with Qatargas to acknowledge the technology as a method to control biological fouling in its seawater cooling system and satisfying regulatory concerns over the use of hypochlorite in once through seawater cooling water systems. The environmental benefits of P-C have been awarded with the ‘Excellence in Environmental Technology’ category at the RESCO Offshore Arabia 2009 Conference.
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Authors: Harry J. G. Polman, Maarten M.C. Bruijs (DNV KEMA Nederland B.V., Energy & Sustainability); Farhan Khan, James Baldwin (Qatargas Operating Company Limited).