Chemical cleaning of aluminium alloy heat exchanger tube in low temperature multi-effect seawater desalination system

The work aims to investigate the chemical cleaning technology of aluminum alloy heat exchanger tube in low temperature multi-effect desalination system and put the technology into field use. The chemical composition of scale on the aluminum alloy heat exchanger tube was analyzed by X-ray fluorescence spectroscopy (XRF). The corrosion rate of 5052 aluminum alloy in different cleaning agents was tested and the corrosion inhibition efficiency at different concentrations of corrosion inhibitors was evaluated in rotary coupon corrosion simulation test. During the field application, pH, Ca2+, Mg2+ concentra-tion of the system and corrosion rate of aluminum alloy were monitored to control the cleaning process and evaluate the cleaning effect. Main components of heat exchange tube scale were CaCO3 and CaSO4. In the selected cleaning agents, aluminum alloy corrosion rate was the highest in hydrochloric acid and the minimal in citric acid. Sulfamic acid was selected as the aluminum alloy heat exchanger tube cleaning agent because of corrosion and scale removal ability. At 40 °CS the corrosion rate of aluminum alloy in 4% sulfamic acid without and with 2 g/LHSD103 inhibitor was 1.434 mm/a and 0.084 mm/a respectively, which indicated that the corrosion inhibition efficiency was 94.14%. After that, increasing the corrosion inhibitor concentration did not obviously improve the corrosion inhibition efficiency. In the field, the average corrosion rate of aluminum alloy coupons was 0.146 mm/a and the corrosion inhibition efficiency was 90%. The acid cleaning process ended up after 21 h. After acid cleaning, the pH was stable around 2, the concentration of Ca2+ and Mg24 did not increase significantly and the scale on aluminum alloy heat exchanger tube was cleaned out. CaCO3 and CaSO4 scale on the aluminum alloy heat exchanger tubes can be effectively removed by sulfamic acid as cleaning agent, and the corrosion inhibitor has obvious protective effect on aluminum alloy so that good cleaning effect is obtained by field application. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.