離心壓縮機優(yōu)缺點（Centrifugal compressor; advantages and disadvantages）

1、離心壓縮機優(yōu)缺點（Centrifugal compressor; advantages and disadvantages）The concept of surge1) the concept of surge surge is characteristic of centrifugal compressor itself, only caused by the surge of air intake is reduced to a certain value. We already know from the front, when the volume is reduced to a ce

2、rtain extent, will appear as the rotating detachment, further reduce traffic, will form a large area of the vortex in the back of the blade, the flow separation layer is extended to the entire channel, and filled the entire leaf, and the air flow can not flow blockage, smooth flow, then the flow det

3、eriorated seriously. The outlet pressure of the compressor will suddenly decrease, because the compressor always and joint working system, then the pressure in the pipe network will not be reduced, so the outlet gas pressure in the pipeline will be greater than the pressure of the compressor, and th

4、e pipe network in the gas to the compressor back, until the gas pressure drops below the outlet of the compressor when the back pressure so far, stop, the compressor starts to flow through the compressor gas supply, and increase, The compressor and return to normal work. But when the pressure in the

5、 pipe network to restore the original pressure, compressor flow and reduced air flow system of the back, so the cycle, the flow oscillation periodically in the whole system, this phenomenon is called surge. The surge is not only related to rotation from severe compressor, and is related to network s

6、ystem. Network capacity is bigger, the greater the surge amplitude, lower frequency. The frequency of surge and network capacity with approximately inversely proportional to the square.2) surge surge phenomenon and judging unit, the pressure fluctuation in a low frequency and high amplitude generate

7、d between the compressor and the pipeline system, the unit has strong vibration, a serious noise control system, also the large fluctuations. According to the following method to determine whether general in surge condition. (1) monitoring of compressor outlet pipe flow noise. Under normal condition

8、 of export is continuous and low voice. But close to the surge, the oscillating flow of the whole system generates periodic, thus in the outlet pipeline is sound change, periodic surge, noise intensified, and even appeared in a sonic boom. (2) observed flow and outlet pressure of compressor. The sta

9、ble operation of the centrifugal compressor when the outlet pressure and flow rate change is not big, is fluctuating, when approaching or entering surge condition, the changes of the two large, large amplitude periodic pulsation occurs. (3) the body and shaft vibration observation. When approaching

10、or entering surge condition, the body and the shaft vibration occurred strong vibration change, its amplitude is greatly increased compared with normal operation.3) harm surge surge is the performance of centrifugal compressor abnormal an unstable running state. When surge occurs, the form of oscill

11、atory network system of the whole unit of the air cycle. It will not only make the compressor performance deteriorated significantly, the flow parameters (pressure, flow) greatly pulsation, vibration of the whole compressor greatly intensifies, will make the compressor rotor and stator components su

12、bjected to dynamic stress, inter stage pressure disorders caused by strong vibration, the sealing and bearing damage, even occurrence of rotor and stator components collide, compress air leakage, explosion and other serious incidents,So we must avoid running in the surge conditions in operation.4) m

13、any reasons for compressor surge surge caused by the basic reason in the actual operation, but the basic reason is nothing more than the following two types: the first one: the flow of the actual operation is less than the surging flow, such as reduction of production, insufficient gas supply, exces

14、sive inhalation of entrance filter clogging, Guan Daozu force, impeller channel or flow channel blockage. Second: the compressor outlet pressure is lower than the pipe pressure. Such as the pipe resistance increases, the inlet pressure is too low, the compressor speed change. The compressor outlet p

15、ressure is lower than the pressure of the pipe network, will cause the operating point of the compressor moves to small flow area to enter the surge condition. The front and the surge caused only is the direct cause of the intake decreases to a certain value is not a contradiction.5) surge curve and

16、 anti surge curve for each speed, the compressor has the corresponding flow surge, surge flow is less than that of compressor surge, we connect the surge occurred under various speeds (point connected to the surge point, namely the characteristic curve) can get a curve, which is surging the curve of

17、 the compressor, as shown in figure 16. So, dont let the compressor run in the surge area shown in. This will be through the anti surge control system is implemented. The surge curve is usually a parabola while considering the surge margin, you can create a curve with a similar surge in the right pi

18、cture, this is to protect the curve. There is no need to protect the curve with this surge curve completely similar, or by the surge curve to get the translation, and as long as they can ensure the compressor with margin can be appropriate in the normal operating range. This makes the configuration

19、and selection of anti surge control system of the instrument is very simple, and is more reasonable. At a certain speed, the actual flow rate and the speed of the compressor under surge flow ratio called surge margin. The margin is too large, then the power consumption increases, and poor economy, i

20、s too small, too close from the surge point, poor security. The general anti surge margin in 110% to about 125%, in determining the margin size, but also to adjust the instruments error factors into considerationCentrifugal compressor has the following four advantages:1. in the same cold conditions,

21、 especially in large capacity when compared with the reciprocating compressor, saves the massive oil device, weight and size of smaller units, small occupied area;2. centrifugal compressor has simple and compact structure, fewer moving parts, reliable, durable, low operation cost;3. easy to realize

22、multi-stage compression and multiple evaporation temperature, easy to achieve low power consumption of intermediate cooling;4. centrifugal unit lubricating oil mixed with a little smaller, affect the heat transfer performance of the heat exchanger, the unit has a high efficiency.The centrifugal comp

23、ressor also has the following four disadvantages:1. rotor speed is high, in order to ensure the width of impeller of centrifugal compressor must be used for large and medium flow situations, not suitable for small flow applications;2. single stage pressure ratio is low, in order to get a high pressu

24、re ratio should be used in multistage impeller, usually with gear;3. centrifugal compressor surge is a disadvantage to add anti surge system unit;FourThere is no big change in the working condition of the same unit of centrifugal compressor, and the scope of application is relatively narrow1, you ca

25、n use the plants heat recovery devices, reasonable comprehensive utilization of heat energy, improve the total thermal efficiency of production process, thereby saving power investment, reduce product costs.2. The utility model has the advantages of simple structure, less wearing parts, convenient m

26、aintenance, reliable operation, and no need to prepare a machine.3, high speed, gas supply even, small footprint, less investment.4, the elimination of gas with oil shortcomings.5, scope of application: large and medium flow, low pressure occasions.Shortcoming:1, the efficiency of the centrifugal co

27、mpressor piston compressor low efficiency will be 5-10%.2, centrifugal compressor can only work in the design conditions to achieve maximum efficiency, easy to surge.3, centrifugal compressor can not get small flow at high pressure ratio. Single level rarely exceeds 3.4, poor operation adaptability,

28、 large gas flow rate, large friction resistance, low efficiency, surge phenomenon.5, medium and large well-designed piston compressor efficiency of more than 75%, while the centrifugal compressor is usually less than 70%;6, the exhaust pressure changes with the flow rate.7, intolerance magazines and

29、 drops.8, because of technical and processing equipment factors, higher cost, long delivery time.9, the compression outlet temperature is higher, the heat exchange area is big.10, single-stage pressure ratio is lowAdvantages of centrifugal compressor:(1) small footprint, simple structure, small qual

30、ity, large gas transmission, no standby machine, low cost of equipment investment;(2) the centrifugal compressor is driven by steam, which is beneficial to the comprehensive and reasonable application of the by-product steam, and reduces the energy consumption;(3) the vulnerable parts of centrifugal

31、 compressor are few, the operation is stable, and the operation cost is low;(4) the centrifugal compressor has uniform gas supply and easy adjustment, and can realize automatic control;(5) there is no need to inject lubricating oil into the cylinder;Disadvantages of centrifugal compressor:(1) the ef

32、ficiency of centrifugal compression is lower than that of reciprocating flow due to the flow loss of the high velocity air flow;(2) it uses occasions with atmospheric quantity;(3) the requirement of compressed medium is high;(4) susceptible to changes in compression medium, temperature, pressure, an

33、d composition;The main working parts of a centrifugal compressor for compressing gases are the high speed impeller and a diffuser with a gradually increasing flow. In short, the working principle of centrifugal compressor impeller is by doing work on the gas flow in the impeller and diffuser, and lo

34、wering speed diffuser using centrifugal boost function, the mechanical energy is converted into gas pressure energy.More generally, the gas in the impeller flow of centrifugal compressor, high speed rotation of the impeller to make the gas under the action of centrifugal force, a pressure increase,

35、on the other hand also greatly increase the speed, the centrifugal compressor impeller through the first static motive of the mechanical energy is transformed into kinetic energy and gas. Since then, the gas flows through the diffuser channel, the channel section gradually increased, in front of the

36、 lower velocity of gas molecules, gas molecules behind continue to surge forward, most of the gas kinetic energy into static pressure energy, which is further play the role of booster.Obviously, the impeller work on the gas is the root cause of the increase in gas pressure,The impeller in unit time

37、for unit mass gas work is related to the impeller edge of the circle speed U2 is closely related: the greater the value of U2, the impeller of the gas on the work done more. The relationship between U2 and impeller speed and impeller outer diameter size is as follows:Outer diameter of D2- impeller i

38、n type m;N- impeller speed, r/min.Therefore, the centrifugal compressor must have a high speed, because:1) for the size of the impeller, the higher the speed of N, the more energy the gas gets, the greater the pressure;2) for the same circumferential speed (also can be described as the same impeller

39、 work ability), the higher the speed n, the impeller diameter can be smaller, so that the volume and weight of the compressor is smaller;3) because the centrifugal compressor can raise the pressure of the gas through an impeller, the single stage pressure ratio (the ratio of the outlet pressure to t