Experimental evaluation of free chlorine adsorption from circulating water in cooling towers by activated carbon in a fixed bed column

Abstract

One of the most important absorbents used in the water and sewage industry and oil and gas industry is the activated carbon, which can be used to remove free chlorine from water and wastewater. If the important parameters of the process affecting the adsorption efficiency are not recognized and controlled, it can cause irreparable damage to downstream equipment and the environment. In the cooling towers system, excessive amounts of chlorine are often injected into the system, which can cause severe corrosion of the equipment and stop production. In this study, the removal of free chlorine from the circulating water of the cooling tower was examined by adsorption and in order to evaluate the effect of pH and water flow containing free chlorine and concentration in the inlet water, experiments were performed on a pilot scale. The adsorbent used in this research was PICA's Industrial Carbon Active. For this purpose, a tower with a fixed bed was first designed and built. The tower used 4,500 grams of activated carbon as an adsorbent. Experimental results showed that by passing 51549 liters of chlorinated water with free chlorine (at different concentrations and pH), 4058 g of chlorine was absorbed by activated carbon. Experimental results also showed that the lower the pH of the solution and the higher the flow rate of the solution, the higher the amount of chlorine adsorption by activated carbon. Also in this study, kinetic reaction of chlorine adsorption by activated carbon was investigated with Thomas, Adams – Bohart, and Yoon-Nelson Models, and the reaction rate constant K for the Thomas and Adams – Bohart models was Kb = KTh = 0.02037037 min-1 (R2=0.915), and for the kinetic models of Wang and Yoon – Nelson, KW=KYN = 0.022 min-1 was obtained and the time required to consume 50% of the adsorption bed was t1/2=258.09 min. The Wolburska kinetic model did not match well with the experimental data (R2=0.769).