closed cooling tower or closed loop cooling tower, is a cooling device that is designed to remove the heat of the process fluid, thereby cooling the process fluid. With coil exchangers placed in the tower, the whole cooling process is achieved through heat transfer among the air, spray water & circulating water via coil exchanger inside.
Closed circuit cooling tower is an upgrade and replacement of open circuit cooling towers. The process fluid circulates in the coil, thereby eliminating the efficiency reduction and system failures caused by floaters, dirt and other matters entering the cooling water system. As a result, it is generally used for cooling projects that require high cleanness of process fluid
A closed loop system protects the quality of the process fluid, reduces system maintenance, and provides operational flexibility at a slightly higher initial cost. If an application must produce full capacity throughout the year, maintaining a clean, reliable system loop is critical.
To further save energy, closed circuit cooling systems allow for pump speed changes. Lowering the pump speed can conserve energy when cooling needs decrease. The flexibility to adjust to cooling and energy needs makes closed loop systems more energy efficient.
Let us see what closed-circuit cooling towers are and how they work. Basically speaking, they exploit the same evaporation principle of open-type coolers: the forced evaporation of a minimal quantity of water lowers temperature of the main water mass.
Closed-loop cooler has two separate fluid circuits:
- one in which the fluid is recirculated inside smooth tube coils (primary circuit),
- one where recirculating water (secondary circuit) is sprayed on top of the coils.
The contact between air (drawn by the fans) and sprayed water provides evaporative cooling similar to an open circuit cooling tower, except that process fluid is never in direct contact with the air (hydraulic separation).
Three reasons why to choose closed-circuit cooling towers
Now we know the basic elements and we can better understand the 3 advantages of closed-circuit cooling towers.
No contamination of the primary circuit. Many civil and industrial processes require to maintain the process fluid uncontaminated by the external environment: for instance, this is true for most of food production processes. Closed-circuit cooling towers, grant this need: in effect, coils separate process fluid from ambient air drawn in by the fans, keeping it clean and uncontaminated in a closed loop.
Reduction of freezing risk. Since the process water circulates in heat exchange coils and never gets in contact with air, glycol can be added to it to lower the fluid freezing point. This can be a big advantage especially in cold countries where temperature frequently goes below zero.
A simpler system. A closed-circuit cooling tower can be an alternative to a system composed by an open circuit cooling tower and a heat exchanger. This leads to some advantage:
Easier plant layout
Reduced footprint
Higher thermal efficiency