Cooling of process solutions in metal industry
Cooling of process solutions
Many processes need to be maintained within a temperature range for optimum efficiency of quality of treatment and minimizing breakdown of process chemicals. They may require heat input before starting to process (such as after a shutdown period overnight), but current passed during the electrochemical reactions or some chemical reactions may heat the solution beyond the range required. There are three common systems used in surface treatment:
- the simplest cooling system is once-through with water running once through cooling coils in the vats and discharging the water to foul sewer or surface water: water may come from the town supply, a nearby river or a borehole extracting groundwater. Water may also be recycled from other uses in the installation (such as used rinse-water or treated effluent) before discharge. The water used may require treatment before use, such as filtration of river or groundwater. These systems have the highest water usage and will be one of the biggest uses of water in an installation
- in recirculating cooling tower systems, the cooling water is recycled constantly through a cooling tower. However, running the water over the cooling tower maintains a high dissolved oxygen level which can cause corrosion within the system and evaporation of water at the tower can cause the build-up of suspended solids. The recirculating water may therefore require treatment to prevent corrosion and some of the water must be discharged periodically to prevent build-up of excess dissolved solids
- in closed systems, where the coolant is not in contact with the outside air. This minimises corrosion and there is no build-up of dissolved solids. The cooling system may be refrigerated or pass through fan-cooled radiators.
Electricity is also consumed in cooling systems for pumping and for chilling in refrigerated systems.
Source: BAT Surface Treatment of Metals and Plastic, Aug. 2006.