Dynamics of the Change in the Thermal Parameters of the Heat Exchanger and Bio-deposits in the Water-Circulation System of a Metallurgical Unit

Abstract

A new design is proposed for a heat exchanger used in water-circulation systems to cool metallurgical equipment, and the design and operating parameters of the heat exchanger are determined. The exchanger's main parameter - unit thermal resistance - is evaluated for normal operating conditions and the dynamics of its change is examined. Bio-deposits that form on the surface of the exchanger's internal tube are the reason for the sharp increases seen in its thermal resistance. It is found that the surface exhibits a self- cleaning effect, and measures are proposed to make the operation of the heat exchanger more efficient. During the operation of water-circulation and water-cooling systems, various problems arise in connection with the formation of scale on the walls of the heat exchangers, the formation of bio-deposits accompanied by the corrosion of metallic elements of such systems, etc. (1, 2). These deposits result in different complications in the operation of the systems. In par- ticular, they lead to a deterioration in the heat-transfer conditions inside them. That in turn leads to a decrease in cooling effi- ciency and disturbs the operation of the heat exchangers and the cooling systems as a whole. Cooling-system operation is stabilized by having the heat exchangers undergo different types of cleaning, but these measures fail to ensure normal operation of the equipment between cleanings. Particularly difficult problems develop when the heat exchangers in the system are of the plate type. These problems are resolved by using various methods to clean the coolant water in order to prevent the formation of scale and bio-deposits and corrosion of the metallic elements. Certain features of the operation of cooling systems can create bio-deposits. Under certain temperature conditions, these deposits are formed because the water contains organic matter. Slimy deposits (bio-agents) are formed on the walls of the equipment and the tubes, and different types of inorganic suspensions can accumulate on top of the deposited material. The biological deposits in cooling systems are most often combated by treating the water with chlorine and copper sulfate. Of course, the use of these substances leads to additional expense, requires the construction of a chlorination unit and a chlorine-dispensing system, necessitates the introduction of special measures to protect the environment, etc. In light of the above difficulties encountered in using contaminated water in water-circulation systems that employ complex heat-exchange equipment - especially in the metallurgical industry - specialists at the Research Center for Problems of Energy Conservation and Automation at the Ural Federal University have collaborated with the Gaz-Engineering Scientific and Production Enterprise to test a new tube-in-tube heat exchanger for cooling existing equipment at a pipe plant. The design of the heat exchanger maximizes protection of its surfaces from the growth of deposits and facilitates the surfaces' gas-pneu-