Prize-winning Quiz on Coal Chemical Engineering Knowledge 18

1.A. 2.D. 3. Cause of vibration: pump cavitation or gas entrapment ； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged. 4. The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5. Characteristics of electrostatic dust removal: large gas handling capacity ； High dust removal efficiency.

1.A. 2.D. 3. Cause of vibration: pump cavitation or gas entrapment ； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged ； Not aligned. 4. The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5. Characteristics of electrostatic dust removal: large gas handling capacity ； It has a high dust removal efficiency, reaching 99%.

1.A. 2.D. 3. Cause of vibration: pump cavitation or gas entrapment ； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged ； Not aligned. 4. The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5. Characteristics of electrostatic dust removal: large gas handling capacity ； It has a high dust removal efficiency, reaching 99%.

1\.A 2\.D 3\Four reasons for vibration and excessive noise: 1. Electrical issues – The motor is the main component of the unit; imbalances in the magnetic fields within the motor and problems with other electrical systems often lead to vibration and noise. For example, in an asynchronous motor during operation, the radial alternating magnetic pulling force between the stator and rotor generated by the interaction of the harmonic fluxes from the stator and rotor teeth, or in a large synchronous motor during operation, situations such as misalignment of the magnetic centers of the stator and rotor or air-gap differences in various directions exceeding the allowable limits, can all cause periodic vibration of the motor and the generation of noise. 2. On the mechanical side, issues such as uneven mass in the rotating parts of motors and pumps, poor manufacturing quality, inadequate installation, asymmetry in the axis of the unit, deflection exceeding allowable limits, low mechanical strength and stiffness of components, wear and damage to bearings and sealing elements, as well as resonance caused by the critical speed of the pump coinciding with the natural frequency of the unit, can all lead to severe vibration and noise. 3. In terms of hydraulics, uneven flow velocity and pressure distribution at the pump inlet, pressure fluctuations of the fluid flowing in and out of the pump, fluid swirling, deviation from the normal flow path, and fluid separation from the pump surface, as well as operating conditions that are not within the specified parameters and pump cavitation caused by various factors, are all common causes of vibration in pump units. Dynamic transition processes such as the start-up and shutdown of water pumps, the opening and closing of valves, changes in operating conditions, and emergency shutdowns in case of accidents, which cause sudden pressure changes in the water conveyance pipes and water hammer effects, often also lead to vibration in the pump house and the machinery. 4. Hydraulic and other aspects: An improperly designed water inlet channel for the unit, or one that is not compatible with the unit; an inappropriate submersion depth of the pumps; as well as improper sequences for starting and stopping the unit – all these can deteriorate the water inlet conditions, create vortices, induce cavitation, or increase the vibration of the unit and the pump house. In units that use destructive siphon vacuum interruption for shutdown, during startup, if it is difficult for air to be entrained in the hump section, the siphon formation time becomes excessively long ； The valve design of the units with door-type flow shutdown is unreasonable; it opens and closes repeatedly, constantly impacting the valve seat ； Reasons such as uneven settlement of the foundation supporting the water pump and motor, or poor rigidity of the foundation, can also cause vibration in the unit. 4\ The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5\ The dust removal efficiency of the electrostatic precipitator is as high as around 99% ； Large amount of gas to be processed ； The flue gas flow rate is low, the resistance is small, and the operating costs are also low. The downside is its complex structure ； Large in size and occupies a lot of space ； Expensive ； Maintenance is also relatively complex ； There are certain requirements regarding the resistance of dust.

1.A. 2.D. 3. Cause of vibration: pump cavitation or gas entrapment ； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged ； Not aligned. 4. The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5. Characteristics of electrostatic dust removal: large gas handling capacity ； It has a high dust removal efficiency of up to 99%, but it is expensive ； Repair is also relatively complex. This post was last edited by sdtclfg on 2009-4-17 15:53]

1. D 2. D 3. The pump is operating under overload conditions; bearings are damaged, anchor bolts are loose, there are faults with the motor and coupling, foreign objects are present, alignment is incorrect, and the outlet is blocked. 4. The ambient temperature rise is less than 65 degrees. 5. High dust removal efficiency and good performance

1. When a centrifugal pump is operating normally, the relationship between its head and the lift height is ( A ). A. Head > Lift height B. Head = Lift height C. Head

1. A 2. D 3. (1) The pump shaft is not aligned with the motor; (2) The bearings are severely worn; (3) The rotor’s dynamic balance is compromised; (4) The foundation bolts are loose, and there are issues with the foundation； (5) Pump evacuation; (6) The pipeline connected to the pump outlet is affected by the system. 4. (1) For sliding bearings, the temperature shall not exceed 80°C. (2) For rolling bearings, the temperature shall not exceed 100°C (85°C when the quality of the grease is poor). 5. It features low energy consumption and low air flow resistance

1. When a centrifugal pump is operating normally, the relationship between its head and the lift height is (A: Head > Lift height). 2. The centrifugal pump is under vacuum with no flow; the possible causes include: (D, all of them). 3. What are the reasons for excessive vibration in a centrifugal pump? (1) Loose foundation bolts; (2) Loose bolts connecting the motor’s foundation to the pump; (3) Misalignment between the motor and the pump; (4) Worn bearings; (5) Vacuum condition inside the pump body. 4. The allowable temperature for bearings is: less than 65 degrees for sliding bearings under normal conditions ； The normal value for rolling bearings is less than 95 degrees. 5. The characteristics of electrostatic dust removal are: a dust removal efficiency of around 99% ； Large amount of gas to be processed ； The flue gas flow velocity is low, resulting in low resistance

1.A. 2.D. 3. Cause of vibration: pump cavitation or gas entrapment ； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged. 4. The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5. Characteristics of electrostatic dust removal: large gas handling capacity ； High dust removal efficiency.

1.A 2.D 3Reason for vibration: pump cavitation or air entrapment； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged ； Not aligned. 4. Sliding bearing

1.A. 2.D. 3. Cause of vibration: pump cavitation or gas entrapment ； Mechanical failure of the pump itself ； Foundation bolts are loose ； The bearing of the motor or pump is damaged ； Not aligned. 4. The normal value for sliding bearings is less than 65 degrees ； The normal value for rolling bearings is less than 95 degrees. 5. Characteristics of electrostatic dust removal: large gas handling capacity ； It has a high dust removal efficiency, reaching 99%.