In natural gas power plant, we have cooling tower 13 cells, 2 gas turbines, and 1 steam turbine (full load). I would like to know if we start 1 gas turbine and 1 steam turbine (half load), but the cooling towers still work by 13 cells. Will this affect to effectiveness of cooling tower? Because the effectiveness of cooling tower did not change too much during switch from full load to half load.
Yours sincerely,
Once a cooling tower is designed and built, its performance are influenced mainly by wet bulb temperature of the moist air enterrng the tower and the ratio of water and air mass flow rate (L/G ratio).
The question is what happens at water flow rate at part load since the tower is more efficient if the water flow rate reduces. Some calculations (WBT_AIR_IN = 24 °C, air flow rate = 10 kg/s)
full load T_W_IN = 36 °C, T_W_OUT = 27.62 °C eff = 69.83%
half load (L/G = 1) T_W_IN = 30.30 °C, T_W_OUT = 26.11 °C eff = 66.50%
half load (L/G = 0.8) T_W_IN = 30.90 °C, T_W_OUT = 25.68 °C eff = 75.65%
Running a plant at half-load conditions definitely could affect its performance. Normally, the highest performance can be achieved only at full-load conditions, however, in cooling tower, because the heat transferred from CC is reduced, its performance would increase. But, how long do you want to run the plant at this condition? what's your goal?
I think we need to be careful between the performance and the amount of energy that is released in the cooling tower. of course, at full-load the amount of energy will be bigger, but the performance will not be affected considerably because the performance of the cooling tower depends mainly on: the ambient temperature, the humidity, the design.
yes,,the performance of cooling tower mainly depends upon temperature, humidity ratio of environment and type of cooling system used in the tower. you can monitor the operation temperatures, flows and energy used by cooling tower for each load of turbines.normally cooling towers operates with constant speed motor and under half load conditions its performance will be satisfactory.
Yups Performance of the cooling tower will directly affected as the required flow of cooling medium ( which has to be cooled) will also reduced. During 50% TMCR or VWO condition flow always changes which directly affects the performance. Better you should control the fan speed of CT by using VFD, this will ultimately reduces the power consumption and increases the effectiveness.
Generally the efficiency is around 70% and it is depend on , inlet and outlet temperature of air (db & wb), inlet and outlet temperature of the water. Forced draught towers are efficient than the natural draught tower but it is important to select proper fan and fan control to maximise the total efficiency.
Cooling tower designers and manufacturers often use the term Number of Transfer Units (NTU) to refer to the performance of cooling tower. This value mainly depends on the internal conduction of heat in the cooling tower. interior of the droplet has a higher temperature than that of the surface,and heat flows by conduction to the surface where the heat and mass transfer process occurs. Higher the value of the NTU, the closer the temperature of the water leaving the cooling tower will become to the WBT of the entering air.
The thing that most affect the cooling tower are as follows:-
1) it is following natural convection or forced convection.
2) whether it is following counter flow or parallel flow.
Probably the thermal behavior of the filler, is not good, because the water distribution is not good, diffussors not working good and drop size too bog or even a jet. The other possibility is that the filler, is dirty and the thermal iinterchage is not good so the cooling efficiency is not good and will not depend on the load. The recommendation is to make a performance test with some standard line some ASME PTC, or BRitish rule, after that and with the data some conclusions and corrective action could be done.
Once a cooling tower is designed and built, its performance are influenced mainly by wet bulb temperature of the moist air enterrng the tower and the ratio of water and air mass flow rate (L/G ratio).
The question is what happens at water flow rate at part load since the tower is more efficient if the water flow rate reduces. Some calculations (WBT_AIR_IN = 24 °C, air flow rate = 10 kg/s)
full load T_W_IN = 36 °C, T_W_OUT = 27.62 °C eff = 69.83%
half load (L/G = 1) T_W_IN = 30.30 °C, T_W_OUT = 26.11 °C eff = 66.50%
half load (L/G = 0.8) T_W_IN = 30.90 °C, T_W_OUT = 25.68 °C eff = 75.65%
It depends upon
inlet and outlet temperature,Humidity Ratio
Generally cooling tower effectiveness is 70%.
If you are system on half load condition, it means that the time is of winter or less gas supply to turbine and that particular time if you have 2 or 3 cooling tower running. You can switch off one of them and save power consumption. But all this considerations depends upon system requirements.
i) “Range” is the difference between the cooling tower water inlet and outlet temperature.
ii) “Approach” is the difference between the cooling tower outlet cold water temperature and ambient wet bulb temperature. Although, both range and approach should be monitored, the `Approach’ is a better indicator of cooling tower performance.
Cooling tower effectiveness (in percentage) is the ratio of range, to the ideal range, i.e., difference between cooling water inlet temperature and ambient wet bulb temperature, or in other words it is = Range / (Range + Approach).
there are many factor effect on the water temperature outlet of cooling tower one 0f them the packing fill.
When you reduce plant load try to off load some cells. This will definitely reduce your power consumption.
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