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INTRODUCTION

Water is an effective heat transfer agent. It is also an excellent solvent and therefore contains amounts of almost every substance with which it has been in contact since it fell from the sky, yesterday or 1,000 years ago. In addition, water facilitates the dissolution of the components of mechanical systems that it contacts. Water is also a desirable biological media. Water will shelter and transport a wide range of microbes, the nutrients needed for growth. Effectively utilizing water in recirculating cooling water systems without experiencing unacceptable rates of equipment degradation and performance deterioration requires understanding and control of system water chemistry. This also involves proper equipment design to minimize the potential for water related problems. In addition, water source selection, water pretreatment before use and internal water treatment are necessary.

The water chemistry, treatments and operational control methods discussed in this chapter apply specifically to open recirculating cooling water systems containing either cooling towers or evaporative condensers. Heat rejection in open recirculating systems is accomplished primarily by evaporation of water in the cooling tower. The air-water contact in the cooling tower affects, both directly and indirectly, the system water chemistry Direct contact of water with air results in near saturation with dissolved oxygen and carbon dioxide in the air. Airborne dust is scrubbed from the air, increasing the suspended solids concentration of the cooling water, and the water is continuously inoculated with airborne microorganisms. Evaporation of water in the cooling tower causes the dissolved and suspended matter in the makeup water to be concentrated in the recirculating water. These processes all influence the corrosion, scaling, deposition and microbiological fouling potential of the system.

The objective of this chapter is to provide a general overview of open recirculating cooling water operations, problems and chemical treatment, as a technical resource and reference aid for process engineers and management personnel with no previous experience in cooling water systems. After studying this chapter, workers who need more detailed technical information will find many good textbooks and reference papers available. At the other end of the spectrum, operating personnel should refer to specific process manuals for detailed operating information.