How to improve the NPSH of the slurry pump?
There are both external and internal causes for cavitation in the slurry pump, and the external cause acts through the internal cause. The external factor is the NPSH of the device, which is the energy provided by the device that exceeds the vaporization pressure at the inlet of the slurry pump, and the internal factor is the NPSH of the slurry pump, which is provided by the slurry pump itself at the pump inlet. Energy beyond vaporization pressure. The NPSH of the pump indicates the quality of the anti-cavitation performance of the pump itself. Under certain flow conditions, if the NPSH of the device is less than that of the pump, the pump will generate cavitation. Therefore, improving the cavitation performance of the pump is mainly considered from two aspects: improving the NPSH of the device and reducing the NPSH of the pump. Because the internal factors play a decisive role, the main consideration is to reduce the NPSH of the pump itself and improve the cavitation performance of the pump itself.
The method to improve the NPSH of the device is:
(1) Using a vertical pump, press the first-stage impeller at the bottom.
(2) Lower the installation elevation of the pump. When using on land, the pump can be installed below the ground. On ships, a caisson can be installed at the bottom of the ship and the pump can be installed in the caisson.
(3) Raise the height of the suction container or increase the pressure of the suction liquid level.
(4) Strengthen the cold insulation of the suction container and the suction pipeline to prevent the introduction of surrounding heat, increase the temperature of the liquefied gas, increase the vapor pressure of the liquefied gas, and reduce the NPSH of the device.
It is often uneconomical to increase the NPSH of the device, so the fundamental measure is to improve the cavitation performance of the pump to reduce the NPSH of the vegetable. The main methods used in cryogenic pumps are:
(1) Specially designed impellers are used according to the required cavitation performance. In order to improve the flow situation at the pump inlet 1:1, even the impeller with this low speed (less than 20) adopts the inlet twisted blade.
(2) Install the inducer in front of the first stage impeller. The inducer is an axial flow impeller. The inducer is cloud-like in the case of cavitation at the beginning. The cavitation performance of the inducer itself can be designed to be very high, and the liquid of the inducer increases the energy to ensure that the liquid flow will not cavitate in the pump impeller, because liquefied gas has less influence on cavitation than water, and it is not easy to cause flooding. corrosion damage, so the use of an inducer on a cryopump is appropriate.
(3) The first-stage impeller with super-cavitation is adopted. Practice has proved that the use of supercavitation impeller can widely adapt to different liquid flow conditions, it is a new technology developed recently.