Cooling Water Systems

Types of Cooling Water Systems

There are three different types of cooling water systems: Once-through Cooling Systems, Closed Recirculating Systems, and Open Recirculating Systems.

In once-through cooling systems, water is taken from a body of water for cooling before returning to the source. Once-through cooling systems have a chief characteristic of using large quantities of water for cooling.

In closed recirculating systems, water circulates in a closed loop with negligible evaporation or interaction with an open environment. Critical cooling applications use closed systems to avoid disruptions resulting from equipment failure, which are highly sensitive to deposition occurring on heat transfer surfaces. The use of high-quality makeup water strives to provide optimal operational conditions. 

The design requirements of an open recirculating system involve the need to dissipate the generated heat using a cooling tower or evaporation pond. The system draws water from a pond or cooling tower basin for cooling and returns the used water to the designated evaporation unit for cooling. The open recirculating system repeats the reuse process, topping up freshwater to make up for water loss to evaporation. 

Different problems of cooling water systems

The problems encountered in cooling water systems originate from corrosion, scale formation, and fouling.

Corrosion is a correlative function between water characteristics and the type of metals present in the system. The presence of corrosion can lead to metal failures and damage to essential equipment of the operating systems. Deposition of corrosion products can also effectively reduce heat transfer rates in heat exchangers and affect the low rates, lowering the productivity and output of a cooling water system.

Scale formation happens when the concentration of scale-forming ionic species in the feedwater exceeds its solubility limits, facilitating the process of precipitation to occur. Precipitation is affected by increasing temperature, operation in high-pressure environments, and pH of the feedwater and system. With depositions on heat transfer surfaces, heat transfer efficiencies reduce, and productivity and output are greatly affected. 

The accumulation and settling of corrosion products, suspended solids, and unwanted microbial growth results in the process of fouling. On top of the build-up on surfaces, fouling also exacerbates the issue of under-deposit corrosion. 

Treatment solutions for associated problems

Temperature, pressure, pH, and flow velocity of cooling water systems influence scaling. In regions of the plant where the skin temperature of the heat exchanger surface exceeds 200°F (93°C), scale formation is most likely to occur. The deposition of suspended solids exacerbating scale formation happens when there is a reduction in water velocity of the heat exchanger tubes. Poor or non-ideal water velocities can result from issues like poor distribution of water flow and plugging. 

Open recirculating systems use evaporative cooling towers to dissipate heat before reusing the cooling water. This water reuse increases the concentration of scale-forming species (concentration factor) under high heat environments, increasing precipitation when solubility limits exceed. The cycle of concentration of scale-forming species also leads to an increase in pH of the system, enabling the formation of more high pH-sensitive scales like calcium carbonate. Systems incorporating sulfuric acid to lower pH face the potential formation of gypsum (calcium sulfate), calcium phosphate, or magnesium silicates. 

CrestoGuard 464 serves as a versatile solution to the different scaling problems as it effectively inhibits the formation of the scale species across a broad pH spectrum. Polymeric in nature, the added dispersancy of CrestoGuard 464 improves suspensibility, discouraging the settling of suspended solids in low-velocity waters. In waters with high levels of silica and iron, the supplementation of CrestoGuard 459 addresses the problem of silica scale and fouling. 

Corrosion in cooling water systems can result from deposition, increased concentrations of dissolved solids, and microbiological growth altogether. As an electrochemical reaction, the increased conductivity from increased concentrations of dissolved solids increases corrosion rates. Deposition promotes under-deposit corrosion, and microbiological growth can accelerate corrosion by introducing corrosive metabolic byproducts into the cooling water.

A holistic and comprehensive treatment program that addresses corrosion and deposition is the most effective and efficient method to tackle the problem. CrestoGuard 402 inhibits both corrosion and scale formation at the same time with an improved environmental profile. 

For cooling systems with exposure to an external environment, the introduction of oxygen facilitates bacteria, algae, and fungal growth. CrestoGuard 168 serves a broad spectrum biocide with bio-dispersant properties, allowing for biofouling and biofilm control. For targeted algae growth, CrestoPro C140 is highly effective for treatment.