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Package cooling tower operational description
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1. Package cooling tower operational description (counter flow cooling towers).
Warm water goes inside the cooling tower water distribution system. The distribution system is located at the upper part of the tower, it is build of pipes where are installed nozzles. The nozzles spray the water in small drops inside the tower onto packings (cooling fill). The packings are responsible for the temperature exchange surface of the water and induced air which flows through the cooling tower.
The main factor of the water temperature drop is the water fragmentary transition into the vapour, this process of cooling is based on carrying away the water heat of vaporisation. Water flow down through the packings where is also partially cooled by air. The propulsive effort of this process is the air physical feature of full saturation at the operational temperature. The higher ambient temperature is, the more water is required to saturate the air.
The cooled water flow down to the cooling tower basin and can be reused in the technological process. The airflow is induced through inlet windows located at the lower part of the tower. The air temperature and saturation at the cooling tower fan outlet (fan stack) is higher in comparison to the ambient air. Some parts of the cooling water in the form of very small drops is collected by airflow. To reduce the water drift, above the water distribution system there is located an inertial water drift eliminator.
The cooling effect of the wet cooling tower depends on wet bulb ambient temperature, air volume (fan airflow) and the tower design.
Every cooling tower operational features are calculated for the most demanding conditions (high temperature and high air humidity, at the operating point of the full heat load on the cooling tower). For such conditions there are also selected fans and its motor outputs. In the situation of lower ambient temperatures or lower heat load transmitted to the cooling tower, the installed hardware outputs are useless.
To lower the fan operational costs and to improve operational fan safety, it can be optionally equipped with two speed motors. The fan speed and its power consumption is controlled in the function of the cooled water temperature.
1.1. Water requirements
Because of constant water evaporation while the cooling tower is in operation, the mechanical and chemical impurities concentrate in the cooling water system. To protect the cooling tower from damage and assure its long life time without any failure, the cooling water quality should be checked. Its impurities concentration should not be higher than in the table below. Cooling water demineralization, desludging and water refill is the main factor which has an effect on lifetime of the whole cooling tower construction, its parts and every other equipment of the cooling system.
Water evaporation can be estimated with the use of equation as follows:
Mp = (Mw*T)/600 [m3/h]
Where:
MP - evaporation [m3/h]
MW - cooling tower hydraulic load [m3/h]
T - cold and warm water temperature difference.
In the case of drinking water with low or medium carbonate hardness, the constant amount of demineralisation is about 50% of the vapour.
If constant demineralisation applied (ie. the cooling tower water is constantly refilled), the water amount to refill should be about 150% of the vapour.
The deposit collected at the tower basin should be periodically removed (by the drain valve opening). Check also the filter grid at the water outlet pipe. It is good to stop the water circulation, if possible, and wash the tower basin walls and bottom with pressure equipment.
Before package cooling tower temporary shutdown, it should be disinfected with the use of an appropriate biocide, (i.e. solution Cl02).
Recommended maximal boundary value of the cooling water analysis:
| pH | | 7,0 - 8,5 |
| Carbonate hardness without stabilisation | 0dH | 7 |
| Carbonate hardness with stabilisation | 0dH | 16 |
| Chloride | mg/l | 250 |
| Ferrous | mg/l | 0,5 |
| Ammonia | mg/l | 8 |
| Suspended solids | mg/l | 40 |
2. Optional equipment
Every package cooling tower can be optionally equipped with the following:
- electrical switchboard with frequency converter to control the fan revolutions in the water temperature function,
- two speed electrical motors,
- noise silencer above the fan,
- noise silences of the water rain drop going to the basin,
- higher steel frame construction under the tower basin,
- water treatment equipment.
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