The calculation of the head of a circulation pump
Thread Content
A water pump is now needed to send the water from the tank to a higher point, from where it then flows back into the cooling tower (the higher point is much above the cooling tower). The question is whether the friction losses in the circuit (that is, from the high point back to the cooling tower) should be taken into account when calculating the head required for the water pump Because, in theory, this amount of loss should be completely compensable by the potential energy of the water at its highest point.
It’s fine to include it; even if you don’t account for your pump’s head, you still need to leave some margin.
There is a question regarding pump head: http://bbs.hcbbs.com/thread-1400529-1-1.html (Source: Haichuan Chemical Forum). This post can help answer your question~~
Loop losses need not be considered; water flows downhill, after all.
We are engaged in energy-saving technological upgrades, so we hope to be as accurate as possible in our calculations.
Thank you. I read that post, but the best answer doesn’t fit my specific situation. Firstly, in the actual operation of alumina plants, the highest point in the evaporation workshop is around 28 meters, while the height of the cooling tower is about 6 meters; these values are normal, but there is a significant difference between the two heights. Secondly, the amount of cooling water required in the evaporation workshop is generally quite high, around 3,000 tons per hour; in other words, a flow rate of 3,000 tons must be ensured at a height of 28 meters. Therefore, when selecting the head based on the vertical height, 28 meters should definitely be used as the reference. Since we are engaged in energy-saving upgrades, it is necessary to achieve a high degree of precision regarding pressure losses; that’s why this question was raised. After all, the circuits involve large flow rates and numerous bends, resulting in significant pressure losses.
Check if you have any requirements regarding the backflow pressure; if not, it can be ignored – as long as the fluid can reach the higher points. However, it’s best to include a margin in the engineering calculations, otherwise you’ll regret it!
The head of the circulation pump represents the energy loss in the entire circulation pipeline; to carry out a detailed calculation, this factor must be taken into account
This post was last edited by arpcd on 2015-9-18 at 12:25. Is the height of the workshop more than 20 meters higher than that of the cooling tower? Was the factory built in a mountainous area? ? The height of 28 meters is determined by the geographical elevation and cannot be changed, but the head capacity of your pump is not necessarily 28 meters; with careful calculation, it is possible for it to be as low as a few dozen meters. Obviously, if instead of pipes, open channels are used at the outlet of the circulating water in a workshop that is 28 meters high, allowing the water to flow freely into the atmosphere, it can then be directed to a cooling tower or tank located more than 20 meters below that level. This is similar to ordinary water conveyance channels, like the famous Hongqi Canal in Henan. In this case, one only needs to calculate the elevation of 28 meters plus the resistance losses caused by the water-using equipment in the workshop; once the total of these losses is taken into account, as long as the circulating water at the workshop outlet remains at atmospheric pressure (with a slight positive pressure to ensure water flow), it will be fine. . The water equipment throughout the workshop can be considered as a branch pipeline, and the pressure loss can be calculated based on the water equipment that generates the greatest resistance. Assuming the resistance loss of the plant equipment is 5 meters, then the head required for your pump should be 28 + 5 = 33 meters. This 33 meters is a bit excessive; in other words, the energy consumption is too high. The 28-meter height difference in the return water is wasted. The reason is simple: starting from Yibin in Sichuan, where the Three Rivers converge (at an elevation of about 400 meters), up to Shanghai (at an elevation of 0 meters), there is only a slight 400-meter height difference over thousands of kilometers. The reason so many hydropower stations are built in Sichuan is due to the large height differences along those thousands of kilometers of river course – going from 4,000 or 5,000 meters down to 400 meters. With a 28-meter height difference, it’s entirely possible to generate power over a distance of more than 200 kilometers. To put it exaggeratively, one could even install a small turbine to generate electricity and compensate for the energy consumed by the circulation pumps. The logic is clear: if the water simply falls back into your pool, a height difference of 28 meters is clearly too much – it’s excessive. Using a pump with a head of 28 meters would be a waste! If it is an energy-saving renovation, it is recommended that you create a sealed system, such as the condensate chamber in large power plants. By utilizing the principle of siphoning, the operating pressure can be set to vacuum, which reduces the head required by the circulation pump and thus lowers its power consumption. In other words, to ensure proper circulation (it is necessary to account for the resistance losses in the return water flow), the water-using equipment in your facility can operate under vacuum conditions, with atmospheric pressure being used to push the water upward. In areas with high altitudes, 10 meters may not be sufficient; 8 meters should suffice, right? So, your original head of 33 meters will be reduced to 33-8=25 meters, which will save 25% in energy consumption. . . Ask the water supply and drainage technician at your factory what siphon drawing is, what a siphon well is, and when to break the siphon. . . . If it is truly an energy-saving renovation, supplying water via siphon is the most energy-efficient method. .
It must be taken into account that the resistance of the pipes and equipment from the inlet to the outlet affects the water flow rate.
It’s just my personal opinion; I’m not sure if it’s reasonable or not. Please share your thoughts! When selecting a pump, people take the pump’s performance curve into consideration. After choosing the appropriate pump, it’s also necessary to check whether its head at zero flow rate is greater than 28 meters. If it is, then that pump will meet the requirements.