In the zero-discharge treatment project of industrial wastewater, the main pumps involved are water inlet pumps, high-pressure pumps, booster pumps, circulation pumps, and chemical dosing pumps. These pumps are mainly centrifugal pumps/plunger pumps, screw pumps/slurry pumps, metering pumps, axial flow pumps, and sometimes shielded pumps. The uses of these pumps are:
1. Centrifugal pumps: generally used for conditions with large flow rates and not particularly high lifts. For example, feed pumps and high-pressure pumps in the process section before high-pressure reverse osmosis have large flow rates and low lifts, and generally horizontal centrifugal pumps are selected; for example, booster pumps have high inlet pressures and high outlet pressures, and high-quality centrifugal pumps with high component requirements are selected.
2. Plunger pumps: generally used for conditions with small flow rates, particularly high lifts, and normal inlet pressures (<1.5bar). The efficiency of centrifugal pumps is very low under low flow and high head conditions. For example, the efficiency of centrifugal pumps is less than 35% under conditions where the flow is less than 15m and the head is higher than 230m. Under such conditions, plunger pumps are generally selected; if the head is above 500m and the flow is below 10m3/h, plunger pumps should be selected.
3. Shielded pumps: Generally used for conditions with high inlet pressure, small flow, and particularly high outlet pressure. For example, the booster pump in the (ultra) high-pressure reverse osmosis process section, even with a flow of less than 10m and an inlet pressure of more than 80bar, the efficiency of centrifugal pumps is very low and the cost is high. At this time, shielded pumps should be selected.
4. Sludge pumps generally use special plunger pumps, slurry pumps and screw pumps. Special plunger pumps/slurry pumps are selected under conditions with large flow, and screw pumps are selected under conditions with small flow and high head.
5. Metering pumps are generally selected for reagent addition, especially under conditions with small flow.
