Morning Sun HVAC design mini program
First, the working principle of centrifugal refrigeration compressor
Centrifugal refrigeration compressors are available in single-stage, two-stage and multi-stage structures. Single-stage compressors are mainly composed of suction chambers, impellers, diffusers, volutes and so on. For multistage compressors, components such as corners and returners are also available. A working impeller and a fixed element (such as an aspirator, diffuser, corner, reflux or volute, etc.) make up one stage of the compressor.
Working principle:
When the impeller of a single-stage centrifugal refrigeration compression compressor rotates, the refrigerant gas enters the impeller channel through the inlet adjustable flow guide vane through the suction chamber, and the gas rotates with the impeller under the impetus of the impeller blade. Due to the action of centrifugal force, the gas flows radially along the impeller path and leaves the impeller, at the same time, a low pressure is formed at the inlet of the impeller, and the gas is continuously sucked in by the suction pipe. In this process, the impeller works on the gas, so that its kinetic energy and pressure can be increased, and the pressure and flow rate of the gas are increased. Then, the gas enters the expander and volute with a gradually expanded cross-section at a high speed, the flow rate gradually decreases, most of the gas kinetic energy is converted into pressure energy, the pressure is further increased, and then it is drawn out of the compressor.
For multistage centrifugal refrigeration compressors, in order to continue to increase the refrigerant gas pressure, the gas is introduced into the next stage impeller for compression using a bend and a returner.
Second, centrifugal refrigeration compressor surge causes and judgments
Centrifuge surge is the killer of centrifuges, high-speed refrigerated centrifuges and ultra-high-speed refrigerated centrifuges the probability of surge is relatively large, serious will damage the centrifuge rotor and other accessories, the following we will analyze the causes and solutions of centrifuge surge:
Centrifuge surge causes
1. Condenser fouling: condenser heat exchange tube surface water quality scale (open circulation cooling water system is the most prone to scale), resulting in increased heat transfer heat resistance, heat exchange effect decreased, so that the condensation temperature increased or evaporation temperature decreased, in addition, due to water quality untreated and poor maintenance, also caused by the heat exchange tube inside the surface deposition of sand, impurities, algae and other substances, resulting in an increase in condensation pressure and lead to centrifuge wheezing.
2. The refrigeration system has air: when the centrifugal unit is running, because the evaporator and the low-pressure pipeline are in a vacuum state, the connection is very easy to penetrate the air, and the air is a non-condensable gas, the insulation index is very high, when the air condenses in the upper part of the condenser, causing the condensation pressure and condensation temperature to increase, resulting in the centrifuge wheezing.
3. The cooling water circulation of the cooling tower is insufficient, and the inlet water temperature is too high. Due to the poor cooling effect of the cooling tower, the condensation pressure is too high, resulting in surge.
4. Evaporator evaporation temperature is too low: due to insufficient system refrigerant, reduced cooling load, the ball valve opening is too small, resulting in evaporation pressure is too low and wheezing.
5. When shutting down, the small guide vane angle and the pressure of the centrifuge exhaust port are not turned off. When the centrifuge is stopped, due to the sudden disappearance of the pressurization, the high-pressure refrigerant vapor in the volute and condenser is poured backwards, which is easy to wheezing.
6. Impeller friction shell, bearing unbalanced.
Centrifuge surge removal
1. Condenser scaling: remove dirt from the heat transfer surface and clean the cooling tower.
2. Air exclusion in the system: start the extraction recovery device, the non-condensable gas is discharged, and the refrigerant pressure is generally pumped to a saturation pressure slightly lower than the saturation pressure corresponding to the temperature of the refrigeration jing liquid.
3. Surge occurs after start-up: anti-surge adjustment is carried out. When the energy regulation is greatly reduced, the suction volume is insufficient, that is, the vapor cannot flow evenly into the impeller, resulting in a sharp drop in the exhaust pressure, the compressor is in an unstable working area, and wheezing occurs. In order to prevent surge, a part of the compressed steam can be bypassed to the evaporator by the exhaust pipe, which can not only prevent surge. It is also beneficial for centrifuge start-up: reducing the vapor density and pressure at start-up can reduce the starting power.
4. Evaporation pressure is too low: check the reason why the evaporation pressure is too low, the refrigerant is insufficient to add refrigerant, the refrigeration load is small, and the energy adjustment blade is closed.
5. Surge during shutdown: When stopping the centrifuge, attention should be paid to whether the main motor is reversed, and the angle of the guide vane is closed as much as possible to reduce the pressure of the centrifuge exhaust port.
During the operation of the centrifuge, the stability of the condensation pressure and evaporation pressure should be maintained, so that the cooling amount of the centrifugal mechanism is higher than the surge point corresponding to the cooling capacity to prevent surge.
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