1 July 2022
WTP

Cooling Tower Types | Components | Principal | Operation and Maintenance

Cooling Tower

1.) Cooling Tower:-

2.) Types of Cooling Tower:-

 

3.) Components of Cooling Tower:-

4.) Principal of Cooling Tower:-

  • Evaporation
  • Heat Transfer Surface
  • Air Flow
  • Air Water Contact Time

Evaporation as means of cooling water is utilized to its fullest extent in cooling towers, which are designed to expose the maximum transient water surface to the maximum air flow for the longest possible time.

Design inlet wet bulb temperature decides the lowest temperature to which water can be cooled

Rate of heat transfer in a cooling tower depends on the following factors:

  1. Surface area of water in contact with air
  2. Relative velocity of air and water during the contact
  3. Duration of air-water contact
  4. Difference between the inlet wet bulb temperature and the required cooled water temperature and the datum level of the cwt and the wet bulb temperature.

Factors Affecting Cooling Towers Performance:

  • Wet Bulb Temperature: Design inlet wet bulb temperature decides the lowest temperature to which water can be cooled.
  • Heat Load.
  • Water Flow Rate, Range and Approach.
  • Interference.
  • Recirculation.
  • Tower Orientation.

5.) Operation & Maintenance of Cooling Tower:-

The cold water temperature obtained from an operating cooling tower will vary with the following influences:-

Heat load: With the fan in full operation, if the heat load increases, the cold water temperature will rise. If the heat load reduces, the cold water temperature will reduce.  Note that the number of degrees (“range”) through which the tower cools the water is established by the system heat load and the amount of water being circulated, in accordance with the following formula:

Range in °C =      Heat Load (KCal/hr)/(LPH x Density of Water )

Range in °C = Heat Load (kilowatts) / Liters/sec x 4.187                  (in SI units)

The cooling tower establishes only the cold water temperature attainable under any operating circumstance.

Air wet-bulb temperature: Cold water temperature will also vary with the wet-bulb temperature of the air entering the louvered faces of the tower. Reduced wet-bulb temperatures will result in colder water temperatures. However, the cold water temperature will not vary to the same extent as the wet-bulb. For example, a 10°C reduction in wet bulb may result in only a 7.5°C-8°C reduction in cold water temperature.

Water flow rate: Increasing the water flow rate (lps) will cause a elevation in cold water temperature, while reducing the water flow rate will cause the cold water temperature to decrease slightly. However, at a given heat load (see formula above), water flow reductions also cause an increase in the incoming hot water temperature.

Air flow rate: Reducing air flow through the tower causes the cold water temperature to rise. This is the approved method by which to control leaving water temperature. If your tower is equipped with a single-speed motor, the motor may be shut off when the water temperature becomes too cold. This will cause the water temperature to rise. When the water temperature becomes too warm for your process, the motor can be restarted. Considering the normal fan and motor sizes utilized cooling towers, approximately 4 to 5 starts per hour are allowable.

Cooling Tower Water Chemistry & Water Treatment :- Maintaining Water Quality:

  1. Circulating water with a pH between 6.5 and 8;
  2. Chloride content (as NaCl) below 500 mg/L;
  3. Sulfate content (SO4) below 250 mg/L;
  4. Total alkalinity (as CaCO3) below 500 mg/L;
  5. Calcium hardness (as CaCO3) not above 50 mg/L;
  6. Maximum inlet water exceed 51.7°C;
  7. No significant contamination with unusual chemicals or foreign substances;

Colling Tower Blowdown:

A cooling tower cools water by continuously causing a portion of it to evaporate. Although the water lost by evaporation is replenished by the makeup system, it exits the tower as pure water leaving behind its burden of dissolved solids to concentrate in the remaining water. Given no means of control, this increasing concentration of contaminants can reach a very high level.

In order to achieve water quality which is acceptable to the cooling tower (as well as the remainder of your circulating water system), the selected water treatment company must work from a relatively constant level of concentrations. This stabilization of contaminant concentrations is usually accomplished by blow down, which is the constant discharge of a portion of the circulating water to waste. As a rule, acceptable levels on which to base a treatment schedule will be in the range of 2-4 concentrations.

Cooling Tower Cleaning:

Operators of water cooling towers, should follow maintenance programs which will reduce to an absolute minimum the opportunity for bacteriological contamination. Public Health Service officials have recommended that “good housekeeping” procedures be followed, such as: regular inspections for concentrations of dirt, scale, and algae; periodic flushing and cleaning; and the following of a complete water treatment program including biocide treatment.

Cooling Tower visual inspection:

The visual inspection should take place at least once a week during the operating season. The periodic flushing and cleaning should be done before and after each cooling season, but in any event at least twice a year.

The louvers (If there), drift eliminators, and easily accessible fill surfaces should be flushed by use of a moderate-pressure water nozzle, being careful not to cause physical damage. A reliable water treatment program should be installed and maintained. Filtration devices may be employed to reduce the suspended solids concentrations, thus increasing the effectiveness of the water treatment program.

6.) Check List of Cooling Tower:-

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