Why does a centrifugal refrigeration compressor wheeze? How to deal with it?

        Surge is a centrifugal refrigeration compressor (i.e., speed type refrigeration compressor) is a unique feature. It is manifested in when the single-stage centrifugal refrigeration compressor in the low load (rated load of 25% or less) operation, easy to occur “wheezing”, resulting in periodic increase in noise and vibration, and even damage to the compressor in serious cases.

       This may be by the single-stage centrifugal refrigeration compressor special structure and operation mode decision, because it is a kind of speed type refrigeration compressor, rather than volume type refrigeration compressor (such as reciprocating and rotary).　

       Centrifugal unit wheezing is one of the characteristics of the single-stage centrifugal unit, it is due to the compressor discharge pressure is less than the condenser pressure, resulting in the compressor can not realize the discharge, but the compressor is constantly suction, and thus the unit appears to be violent vibration and noise. Generally speaking, the load of the unit is lower than 30% of the total load of the unit, that is, there will be “wheezing”.　

        Mainly due to the unit running load is too low, generally speaking, one is the entire system load is too low, and the use of centrifugal units must be run may occur, you can take measures, if the centrifugal units have been used, you can set up in the computer system to ensure that the minimum operating load of the unit in the more than 30% (this is the most stupid way), the best solution is to use the system with the size of the unit, that is, to ensure that the minimum load of the entire system is greater than the minimum load of the unit used. The best solution is to match the size of the unit used in the system, that is, to ensure that the minimum load of the entire system is greater than the smallest one centrifugal unit used 30% of the load. Or the use of centrifugal units and screw units with the program, it is the inherent characteristics of the centrifugal compressor, but with the speed change and the wheezing point after the shift. Generated due to the compressor discharge pressure is less than the condenser pressure, resulting in pressure back-up and thus impact on the impeller. High-speed centrifuges are particularly susceptible to surge (e.g., Carrier, York single-stage centrifuges), which is generally overcome by means of hot-gas bypass, or by limiting the degree of opening of the guide impeller, thereby limiting the increase in condensing pressure.

        Due to the low-speed multi-stage centrifuges due to the lower speed is generally 2900 rpm, the point of surge away from the point of operation, this type of model can be in operation at a low load of 10% (such as Trane's multi-stage centrifuges) Surging is unique to centrifuges, but not only single-stage, multi-stage centrifuges will be wheezing, as usual, Trane three-stage centrifuges will not wheeze? The reason for this is that at low loads the suction volume is low, so the exhaust pressure may be lower than the condensing pressure, so the condenser gas backflow is repeated. It is characterized by loud sound and current fluctuation.

        Generally wheezing because the unit is easy to produce low load operation or cooling water inlet temperature is too high or suction pressure is too low caused by the elimination method is to eliminate the causes of the above three problems, or to do hot gas bypass wheezing control can be achieved by opening the compressor's bypass valve or directly venting a portion of the gas in order to maintain the compressor's minimum flow rate. However, since passing gas through the bypass or venting means wasting energy, it is usually desirable to determine the surge flow rate as accurately as possible so that, in practice, unnecessary waste can be avoided. However, determining the surge flow rate is not an easy task. Because it is not a fixed value, but with other parameters, so for other parameters also have an impact, but also to take into account the surge system. This results in a variety of control schemes with different measurement methods. The selection of a suitable surge control system for a particular application depends on a number of factors, including: the type of compressor, the variation of the load, the simplicity and reliability of the measuring elements and the accuracy required by the surge control system.

Why is there a wheezing phenomenon?

1, first of all, you can be sure that this project is certainly used centrifugal machine, then we know centrifugal machine, in fact, is a speed type model. Compressor is mainly through the inlet refrigerant gas into the compressor after being impeller speed and get kinetic energy, high speed gas from the impeller out into the expansion tube, the refrigerant speed is reduced, the pressure is enhanced, so as to complete the process of compression of refrigerant.　

2、The reason for generating wheezing. Mainly with the impeller outlet of the refrigerant speed (can be divided into radial speed and tangential speed, which are related to the impeller,) when the unit is running in part load, radial speed with the load decreases and correspondingly decreases, which results in tangential speed and the impeller angle decreases, when the angle is small to a certain value, the compressor gas can not be compressed out of the vortex in the impeller, at this time, the high-pressure gas in the condenser will flow backwards into the impeller, so that the compressed gas in a short period of time, the compressor gas can not be compressed out of the vortex in the impeller, at this point the high pressure gas condenser. Impeller, so that the compressed gas in a short period of time to increase the gas discharge, and then backflow back, and so on and so forth, at this time, the compressor has entered the wheezing state.　

3、Methods for solving the surge.

A, improve the design of the impeller and expansion tube. (mainly product development department to do)　

B, the use of frequency conversion technology, expensive.

C, the use of hot gas bypass method, part of the load operation of energy consumption, uneconomical.

D. Adopt multi-stage centrifugal technology.

There are several ways to prevent the wheezing:　　

1, product design: imported guide vane + adjustable diffuser linkage control (Meitong has this patent), can prevent the centrifuge low load due to refrigerant flow reduction and exhaust pressure is less than or equal to the condensing pressure;

2, the system program: according to the actual operating habits, select the appropriate size of the centrifugal unit + screw unit with; fundamentally avoid the centrifugal unit is in low load operation! Centrifugal compressor belongs to the speed compression type, can not directly improve the pressure of the inhaled refrigerant gas, but the speed of the inhaled refrigerant gas. The high speed refrigerant from the compressor exhaust port passes through a diffuser before entering the condenser, which converts the kinetic energy of the refrigerant gas speed into potential energy of pressure (speed reduction, pressure increase). This is the compression principle of the centrifugal compressor.　

         When the load is reduced to less than 30%, the refrigerant flow is reduced; if the shape of the compressor outlet diffuser is not adjustable (relatively large), the refrigerant gas can not be raised above the condensing pressure pressure value, the refrigerant circulating pressure difference is insufficient, resulting in the compressor outlet refrigerant turbulence, vibration increased, serious damage to the compressor! The simple way, similar to the faucet outlet blocked part of the same, the water pressure will be suddenly raised, the water can also shoot farther.

Shanghai KUB Refrigeration Equipment Co., Ltd.

Free Call Video Chat