The high-pressure ash water pump experiences significant vibration, and there are numerous black spots on the surface of the guide vanes

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The high-pressure ash water pump experienced significant vibration. Upon disassembly, black spots were found on the surfaces of all guide vanes, and there were signs suggestive of cavitation on those surfaces as well; the impellers had turned black and could not be restored to their original color Let’s analyze how this came about! Appendix: 3. Equipment Overview 3.1 Process Flow Brief description of the process: Grey water from 3 deaeration tanks (704V109-309), with a pressure of 0.3–0.4 Mpa and a temperature of 110°C, is collected in the main pipe at the inlet of the carbon scrubbing tower feed pumps. From there, it is distributed to each carbon scrubbing tower feed pump (704P106-606); after being pressurized by the pumps to around 10 Mpa, it is gathered in the high-pressure grey water main pipe. From this main pipe, the flow is divided into seven branches; six of these branches pass through grey water heaters (704E103-603) to reach a temperature of 135°C, after which they are used to maintain the liquid level in the carbon scrubbing towers (703T101-601) as well as to supply coolant to the degasifier (703F10-601) in emergency situations ； The other main pipe goes directly to the lock chamber as water for flushing the lock chamber ； 3.2 Technical parameters of the equipment: Pump model: ZDF250-135A×8. Flow rate: 131.89–316.54 m3/h. Head: 1024 m. Inlet pressure of the pump: 0.3 MPa. Outlet pressure of the pump: 9.667 MPa. Medium transported: 99.95% water, 0.05% ash. Viscosity: 0.25 MPa·s; density: 950 kg/m3. Rotational speed: 2980 r/min. Power of the accompanying motor: 1250 kW. 3.3 Structure of the equipment: This pump is a vertically split 8-stage centrifugal pump. The main components of this pump include the pump base, pump frame, pump cover, pump body, oil station, inlet and outlet pipes, intermediate short pipes, volute, guide vanes, impeller, throttle bushing, counter-rotating seal ring, shaft, modular mechanical seal, and sliding bearing components. This pump is a high-pressure self-balancing multi-stage centrifugal pump, with the rotor impellers arranged symmetrically; the axial forces generated by each stage of impellers cancel each other out, allowing for the balance of axial forces on the rotor components without the need for a balance disk or balance drum. In addition, a thrust bearing is installed at the end of the pump to handle instantaneous and residual axial forces; during the start-up and shutdown of the pump, as well as when there are sudden changes in system conditions, this thrust bearing can withstand sufficient axial forces to prevent damage to the pump.