In coal mine production, water pump drainage is widely used. The performance of the water pump directly affects the safety of coal mine production. It is of great significance to ensure the integrity and performance of coal mine drainage equipment, especially the main drainage pump. The impeller of a mine pump is a key component that converts the mechanical energy of the prime mover into the pressure energy and kinetic energy of the water. For mine pumps, as long as the impeller performance is good, the normal operation of the pump can be guaranteed. However, for a long time, a major problem that has plagued the normal operation of water pumps is the damage to the impeller blades of the water pump. The main reason for this damage is often the cavitation phenomenon of the impeller during the conversion and transfer of energy. All research pumps produce cavitation. The reason and prevention are very important issues. This is also the key consideration for designers in the selection and installation of coal mine drainage equipment. The main reason for the destruction of the impeller of the coal mine’s main drainage pump during actual use is the existence of solid particles in the water. Increase the severity of mineral water, thereby increasing the possibility and scope of cavitation. For this reason, this article focuses on the specific conditions of the main drainage pump in coal mines and studies the impact of the presence of solid particles on the damage of the impeller.
1. The mechanism of the cavitation phenomenon of mine water pumps
When the absolute pressure at the pump inlet is reduced to the cavitation pressure at the current water temperature, the water vaporizes. The gas dissolved in the water escapes from the water, thus forming many small bubbles that mix the steam and the escaping gas. When these small bubbles flow into the high-pressure zone with water, the bubble bursts, and the surrounding liquid quickly fills the cavities of the original bubble. Due to the short bursting time of the bubble, a hydraulic shock of up to several hundred megabytes is formed. Vapor bubbles continue to form and rupture, and huge hydraulic shocks repeatedly act on the impeller at a frequency of tens of thousands of times per second. For a long time, the surface of the impeller will gradually peel off due to fatigue; at the same time, there are also inclusions in the vapor bubbles. There are some active gases (such as oxygen), and the smooth layer of the metal gradually becomes rough due to electrolysis. After the metal surface roughness is destroyed, the mechanical erosion is accelerated. Under the combined action of mechanical erosion, chemical corrosion and electrochemistry, honeycomb pits quickly appear on the metal surface, and gradually form cavities and damage. This phenomenon is called cavitation.
2. Solutions to cavitation of mine water pumps
The pressure drop is the condition for cavitation. The existence of a large number of bubble bursts in the water is the internal cause of cavitation. The bubbles will burst only when the pressure is reduced. Therefore, in order to improve and reduce the cavitation damage of the impeller of the main drainage pump of the coal mine, two aspects should be improved.
1) Design and manufacturing. ①Change the design of the impeller shape, optimize the structural parameters of the impeller, and improve the external conditions caused by cavitation; ②The blades and other flow parts that are susceptible to cavitation damage should use materials with good cavitation resistance. ③Reduce the pressure head loss of the suction pipe system ∑h. The suction piping system includes the bottom net, the water filter cover, the pipeline, the elbow, the shortening pipe, etc., so that the installation design of these parts is reasonable, the loss is minimized, and it is also an important way to reduce the cavitation phenomenon of the pump. The pump itself must have more than years of cavitation. For this reason, the diameter of the suction port of the hand-stage impeller can be appropriately increased, or the installation angle of the blade inlet of the hand-stage impeller can be appropriately larger, and a double-suction impeller can also be used.
2) Use aspect. ① When mine safety permits, minimize the suction height of the pump and implement high water level drainage. This makes the effective cavitation allowance in pump operation larger. Generally, when the installation height is 2~3.5m, the effect of reducing the damage of the pump due to cavitation is more significant. ②Reduce the density of mine water being discharged. The density of mine water containing pulverized coal and silt is higher than that of pure water. In order to reduce the density of mineral water to reduce pump cavitation, sedimentation treatment should be done before the mine drainage. Reduce the average flow of water into the pump suction pocket
