Impacts of reusing treated blowdown water on circulating water and corresponding control measures

In order to improve the water utilization efficiency, a natural gas purification plant used the treated water from electrodialysis(ED) and multiple-effect evaporation(MEV) processes as make-up water in the recirculating system. However, the field coupon tests showed the corrosion rate reached 0.15 mm/a, beyond the requirements set by GB 50050-2007. The water quality analysis indicated that Ca²⁺ and Mg²⁺ concentration in the treated water from ED and MEV was comparatively low. When the volume of make-up water was significant, it would lead to low Cycles of Concentration(CoC), increase of water stability index and corrosivity. Bench-scale tests investigated the impacts of reusing treated blowdown water on circulating cooling water and subsequently, organophosphate complex was prepared to formulate the water treatment chemical b to inhibit the corrosion. The tests showed that when the sum of Ca²⁺ concentration and the total alkalinity was in the range of 200-600 mg/L, both corrosion inhibition rate and scale inhibition rate could be higher than 90%, which guaranteed the steady operation of the natural gas purification plant.