Closed Water Circuit Cooling Tower

What is a closed water circuit cooling tower?

In the closed cooling tower, the tubular heat exchanger is placed in the tower, and the cooling effect is ensured by the heat exchange between the circulating air, the spray water outside the tube and the circulating water in the tube. Because the circulating water is a closed loop in the tube, it can ensure that the water quality is not polluted, which can well protect the efficient operation of the main equipment and improve the service life. When the outside temperature is low, the sprinkler system can be stopped to save water.

In the open cooling tower, the cooling water is in direct contact with the air, so after a period of time, the cooling water will be fouled, which is not easy to clean, and then the pipeline is blocked, and the heat transfer effect of the equipment is reduced. The closed cold water tower can avoid this situation and ensure that the circulating medium has no contact with the external environment, thereby ensuring that the composition of the circulating medium does not change, does not evaporate, consumes, and has no impurities, keeping the working fluid clean.

Working principle of closed circuit cooling tower

The working principle of the closed cooling tower is simply closed circulation cooling, which consists of the following systems:

1. Internal circulation: The cooled circulating medium flows and cools through the closed tube bundle, and is completely isolated, closed and non-contact with the outside world.

2. External circulation: also known as spray water, water is pumped from the top of the tower, and sprayed evenly to the outside of the heat exchange tube bundle by a low-lift high-flow spray pump, covered with a thin water film, heated by the high-temperature medium in the tube, and the water film absorbs thermal energy, It is converted into latent heat of vaporization, evaporated into water vapor, and takes away heat energy.

3. Air exchange system: The dry and cold air enters from the lower part of the heat exchange tube bundle, passes over the tube bundle at a high speed, conducts convective heat exchange with the tube wall, and at the same time entrains water vapor and turns into a high-enthalpy gas, which is exhausted by an axial flow fan and sent out of the tower. The purpose of transferring heat energy to outside the tower is realized.

4. Auxiliary systems: air inlet grille, water collector, water distribution system, control system, etc., to ensure the normal operation of the closed cooling tower. In particular, the control system automatically switches between air cooling and air cooling + spray mode according to the temperature of the outlet water and whether it meets the process requirements, completely realizing automatic operation without manual intervention, and realizing efficient operation of water and electricity saving.

Advantages and disadvantages of closed cooling tower

Compared with the open cooling tower, the closed cooling tower has obvious advantages, so the current cooling system basically adopts the closed cooling tower.

1. Closed loop

The circulating medium is completely closed and completely isolated from the outside world. It can not only cool water, but also cool all other flowable media, such as oil cooling, alcohols, refrigerants, salts and other fluids. For example, hydraulic oil cannot penetrate into water. The intermediate links of shell and tube heat exchangers or plate heat exchangers can now be fed directly into the tube bundle of the closed cooling tower.

2. Reduce the footprint

No need to excavate ponds to store fluids due to the complete closed loop within the piping or equipment. In the overall layout of the factory in the early stage of construction, land resources can be more fully utilized, and production equipment, processes and buildings can be arranged. If the closed cooling tower is arranged on the roof of the building, it will further reduce land use and save huge land costs.

3. Reduce operating costs

During operation, air cooling and air cooling + spraying, the two modes are automatically switched, without manual intervention, saving labor, power consumption and water consumption costs, and unlike the open tower operation process, adding a large amount of chemicals to ensure scaling And the problems caused by algae, save the cost of chemicals.

4. Improve production efficiency and reduce failures

Since the temperature and composition of the circulating water are guaranteed, the process production equipment is guaranteed to cool down, reduce failures and maintenance, and fully guarantee the working time, which indirectly improves the production efficiency.

5. Extend the life of production equipment

The stable composition and quality of the circulating water can discharge the heat energy of the production equipment in time, and the internal cooling system is not blocked or corroded, which prolongs the service life of the equipment.

6. No change in ingredients

Due to isolation from the outside world, the composition of the medium is stable, only cooling and cooling, if it does not change due to cooling, the composition will not change.

7. No evaporation

There is no contact with the atmosphere, only the temperature changes, and no water vapor is produced. The total fluid capacity will not be reduced, and there is no need to add new fluid into it.

8. No scaling

Calcium and magnesium ions dissolved in it, because there is neither evaporation nor replenishment of new liquid, the total number of ions remains unchanged, and the total volume of the solution remains unchanged. According to the definition of concentration, the ratio of quantity to volume will never change. Even if there is a certain amount of calcium and magnesium ions, it will not scale because it does not exceed its saturation. For the sake of safety, the general circulating medium still adopts pure water circulation, which can better ensure that the whole system does not scale.

9. No impurities

Whether it is production equipment, system pipelines and closed cooling towers, they are all isolated from the outside world, and all external impurities cannot enter. In this regard, pay attention to 2 points. First, do not store in a pool to prevent impurities from entering and evaporating. Second, add chemicals such as corrosion inhibitors to prevent metal corrosion on the inner wall of the equipment or pipelines passing through, resulting in impurities and blocking pipelines or accessories.

Here let's see the 400T closed water circuit cooling tower specs:

Other points need to be focus on:

1. Antifreeze measures for occasions that are basically not used in winter

If the closed cooling tower does not need to be operated in winter, the spray water and internal circulating water must be drained when it is shut down. The cooling tower adopts a three-dimensional inclined structure in the design of the heat exchanger to ensure smooth flow of water and clean emptying. The top of the heat exchanger is provided with an air valve structure, and compressed air can be introduced to assist in emptying if necessary.

2. Antifreeze problem in occasions running in some time periods

The antifreeze of the closed cooling tower has two parts: the spray water system and the internal circulating water system (softened water).

For the antifreeze problem of the spray water system, an electric heater is usually added in the water sump, which is generally turned on when the spray water is lower than 5 ℃, and stopped when the temperature is above 8 ℃. The temperature probe transmits the signal to the control cabinet to automatically control the start and stop of the electric heater. The power selection of the electric heater is determined according to the circulating water volume and the outside air temperature.

For the antifreeze of the internal circulating water system, ethylene glycol solution can be added or electric heating equipment can be added. The formula of ethylene glycol solution can be consulted by our company.

For larger cooling systems, it is possible to consider digging a pool to pour the spray water into it, which can save electricity costs due to electric heating operation, and can also put medicines in the pool to improve the quality of the spray water.

3. The problem of anti-freezing in the occasion of year-round operation

For a closed cooling tower that operates all year round, if it is equipped with an electronic control system, the number of cooling towers may change due to the load change of the main system, so the problem of antifreeze should also be considered.

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