Low outlet pressure of the blast furnace circulating water pump – seeking assistance
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Ferrosilicon furnace circulating water pump. The height difference from the liquid surface to the end of the pipeline is 15 meters; there are 9 elbows, and 3 gate valves and check valves. The export pipeline and valves are DN600. The length of the steel pipe export pipeline is approximately 300 meters. It is required that the pressure at the end of the pipeline be above 0.3 MPa. Select a double-suction pump with an inlet diameter of DN500, an outlet diameter of DN400, a flow rate of 2200 cubic meters, and a head of 68 meters. Equipped with a 6/560kw/380v variable-frequency motor, with a rated current of 1040A. Currently, the operating frequency is 43 Hz, the current is 774 A. The outlet pressure gauge shows 0.3 Mpa, while the pressure at the end of the pipeline is 0.18 Mpa. After adjusting the frequency to 50 Hz, the current reached 920 A. The noise and vibration levels during the pump’s operation increased significantly; however, there was hardly any change in the end pressure or the pressure at the outlet. Even when adjusting the opening degree of the outlet valve, there was no noticeable change in the pressure gauge. The suction height at the pump inlet meets the requirements; there is no cavitation. Dear experts, why doesn’t the outlet pressure value change after adjusting the valve and frequency? How can the terminal pressure be increased?
Try to reduce the outlet valve until the pressure reaches the specified value; then, as the system pressure rises, increase the speed to its maximum level. Gradually open the outlet valve thereafter, but ensure that the current does not exceed the rated value and that the pressure remains above the specified level. The key problem is caused by the failure to build up system pressure. For reference.
I also believe it’s because the pipeline resistance is too low, preventing system pressure from building up. Additionally, the pressure values were not observed after gradually changing the valve opening and frequency. Thank you for the guidance!
Let’s talk about the suction conditions; the cavitation in double-suction pumps is different from that in small end-suction pumps
The altitude is 1160 meters. The pump’s NPSHr value is 3.7 meters; the diameter of the suction pipeline is DN600. There are no bottom valves on the elbows. The temperature of the fluid is below approximately 45°C, and the distance from the liquid surface to the centerline of the impeller is about 2 meters.
In cases like this, if the system pressure does not meet the required levels, it is necessary to adjust the main return valve in order to ensure that the pressure and flow rates are within the specified ranges; this is for reference only.
Your answers are always spot-on; I learn a lot from them!
Is the suction port of the suction type, with the liquid level lower than that of the pump? With your conditions, by setting it to 50Hz, the pipeline resistance is low, so the flow rate could exceed 3000. The net positive suction head value is no longer that of the rated point, and moreover, the values specified for the rated point are often exaggerated. Essentially, the low pipeline resistance combined with an excessively high flow rate leads to cavitation. Even if severe cavitation does not occur, such a high flow rate still results in significant noise and increased vibration
This pump is not suitable for this blast furnace; the top pressure can be increased by designing a new impeller.:handshake
We specialize in dampers for pumps; we can discuss this together. Contact number: 13773488901