答：風機喘振，顧名思義就象人哮喘一樣，風機出現周期性的出風與倒流，相對來講，軸流式風機更容易發生喘振，嚴重的喘振會導致風機葉片疲勞損壞。
風機出現喘振的現象：
1、風機聲音異常噪聲大、振動大、機殼溫度升高、引送風機喘振使爐膛負壓波動燃燒不穩。
2、電流減小且頻繁擺動、出口風壓下降擺動。

原因：
1、兩風機并列運行時導葉開度偏差過大使開度小的風機落入喘振區運行。
2、煙風道積灰堵塞或煙風道擋板開度不足引起系統阻力過大。
3、風機長期在低負荷運轉。
處理方法:
一般的處理原則是調整負荷、并列運行風機負荷應相近，再根據上面所說的可能原因進行查找，再作相應處理。

1、現象：電流減小且頻繁擺動、出口風壓下降擺動。風機聲音異常噪聲大、振動大、機殼溫度升高、引送風機喘振動使爐膛負壓波動燃燒不穩。

2、原因：煙風道積灰堵塞或煙風道擋板開度不足引起系統阻力過大。；兩風機并列運行時導葉開度偏差過大使開度小的風機落入喘振區運行（我們常碰到的情況是風機導葉執行機構連桿在升降負荷時脫出，使兩風機導葉調節不同步引起大的偏差）；風機長期在低出力下運轉。

3、處理方法：調整負荷、關小高出力風機的導葉開度使風機出力相近，減小負荷量的變化率，加強進風段和出風段的風壓探測和信息反饋控制，再根據上面所說的可能原因進行查找再作相應處理。

預防措施：

1、使泵或風機的流量恒大于QK。如果系統中所需要的流量小于QK時，可裝設再循環管或自動排出閥門，使風機的排出流量恒大于QK. ;

2、如果管路性能曲線不經過坐標原點時，改變風機的轉速，也可能得到穩定的運行工況。

3、對軸流式風機采用可調葉片調節。當系統需要的流量減小時，則減小其安裝角，性能曲線下移，臨界點向左下方移動，輸出流量也相應減小。

4、*根本的措施是盡量避免采用具有駝峰形性能曲線的風機，而采用性能曲線平直向下傾斜的風機。

　　風機喘振的判斷方法

　　1. 聽

　　通風機在穩定運轉的正常工況下，其噪聲較低，而且是連續性的。當接近喘振工況時，由于整個系統產生氣流周期性振蕩，因而在出氣管道中氣流發出的噪聲也時高時低，并產生周期性的變化。進入喘振工況時，噪聲立即大大增加，甚至有爆音出現。

　　2. 看

　　觀測通風機出口的壓力和流量。通風機在穩定工況下運行時，其出口壓力和進口流量的變化不大，也有規律，且所測的數據在平均值附近擺動，變動的幅度很小;當接近進入喘振工況時，二者變化都很大 。

　　觀測機體和軸承的振動情況。當接近進入喘振工況時，風機軸承座將發生強烈的振動，出口管道也會出現強烈的振動 。

　　2、防止喘振的方法

　　1. 風機選型時，其性能要在高效區內。

　　不要人為地隨意增加選型系數，而使風機在實際運行中的實際流量遠遠高于設計流量，若采用大量節流，就很容易把風機調節到喘振區域工作。

　　為此，在風機設計和選型中，要避免工況范圍接近進入喘振區。例如 , 在循環流化床風機的選型中，一般設計院給出兩個參數點TB、BMCR。TB是鍋爐大負荷點，BMCR點為設計運行點，TB點的性能取BMCR點的15%～30%。在選型中二者必須都要考慮，使風機既能在BMCR點進入穩定工況區運行，又可達到TB點。

　　掌握了這些，就可以使BMCR點在高效區運行，要把TB點定位到低效區內，因為風機一般情況下不在此點運行。所以，掌握和了解喘振的特性尤為重要。

　　2. 風機在系統運行中一旦發生喘振，還可以通過改變風機轉速的方法來調整工況范圍。

　　離心通風機可以改變葉輪直徑，軸流通風機可以改變動葉安裝角，這些方法都可以使通風機的性能曲線向小流量區域移動 , 這時喘振臨界線也就相應地向小流量區域移動，這同樣也可以擴大通風機的穩定工況范圍 。

　　3. 由于某些工作場合均不具備上述調節條件，也不能停車而影響生產，所以還有一種簡單快捷的調節方法也可消除喘振，這就是加設放氣閥。

　　以使Q=Q放 +Q喘振 >Qmin，就馬上可以消除喘振。但必須得指出放入大氣的氣體應是無害氣體，若是有害氣體就必須得由小管道引入通風機進口管道中。這種方法的缺點是，會將經過葉輪獲得的動量白白放掉一部分，從而使風機整體效率下降。但因其方法簡單且*，在通風機調節中被廣泛地應用 。

　　4. 兩閥操作法。

　　在通風機的排氣管道上設兩個閥，把兩個閥之間的容積固定為某一值，兩個閥之間的容積相當于一個儲氣罐，*閥直接裝在離風機出口較近的位置上，相當于一個節流閥，稍微節流就可以防喘振;而第二個閥僅作為一個阻力。實踐證明，這種裝置不僅可以達到系統的穩定運行，對減小噪聲也很有利。

　　5. 防喘振環。

　　目前在地鐵或隧道用風機設備中，在主風筒加設防振環已成為普遍趨勢。這種導流片可在氣流出現旋轉脫離時，不是經過葉道產生非穩定氣流團，而是沿著導流片逆向流回葉片。缺點是在此情況下部分氣流做了無用功，但它可以使風機的穩定工況范圍擴大，喘振區域縮小！

　　喘振是指風機出現周期性的出風與倒流，相對來講，軸流風機更容易發生喘振，嚴重的喘振會導致風機葉片疲勞損壞。

      風機出現喘振的現象：

　　(1)風機聲音異常，噪聲大、振動大、機殼溫度升高，引、送風機喘振使爐膛負壓波動燃燒不穩。

　　(2)電流減小且頻繁擺動、出口風壓下降擺動。

　　常見的原因：

　　(1)兩風機并列運行時導葉開度偏差過大使開度小的風機落人喘振區運行。

　　(2)煙風道積灰堵塞或煙風道擋板開度不足引起系統阻力過大。

　　(3)風機長期在低負荷運轉。處理原則：一般是調整負荷、并列運行風機負荷應相近，再根據上面所說的可能原因進行查找，再做相應處理。

　　A: Fan surge, just as the name suggests, is like human asthma. The fan has periodic air outlet and backflow. Relatively speaking, axial flow fans are more prone to surge. Serious surge will lead to fatigue damage of fan blades.

　　Surge of fan:

　　1. Abnormal fan sound, high noise and vibration, increased casing temperature and surge of induced draft fan make furnace negative pressure fluctuate and combustion unstable.

　　2. The current decreases and swings frequently, and the outlet wind pressure drops and swings.

　　reason:

　　1. When the two fans operate in parallel, the guide vane opening deviation is too large, which means that the fan with small opening falls into the surge zone for operation.

　　2. The system resistance is too large due to dust accumulation in the flue and air duct or insufficient opening of the flue and air duct baffle.

　　3. The fan operates at low load for a long time.

　　Treatment method:

　　The general treatment principle is to adjust the load, and the load of parallel running fans should be similar, and then find out the possible causes according to the above, and then deal with them accordingly.

　　1. Phenomenon: the current decreases and swings frequently, and the outlet wind pressure drops and swings. Abnormal fan sound, high noise and vibration, increased casing temperature and surge vibration of induced draft fan make furnace negative pressure fluctuate and combustion unstable.

　　2. Cause: the system resistance is too large due to dust accumulation in the flue and air duct or insufficient opening of the flue and air duct baffle.; When the two fans are running in parallel, the guide vane opening deviation is too large, which means that the fan with small opening falls into the surge zone for operation (we often encounter the situation that the connecting rod of the fan guide vane actuator disengages when lifting and lowering the load, which causes large deviation due to the asynchronous adjustment of the two fan guide vanes); The fan operates under low output for a long time.

　　3. Treatment method: adjust the load, turn down the guide vane opening of the high output fan to make the fan output similar, reduce the change rate of the load, strengthen the wind pressure detection and information feedback control of the air inlet section and the air outlet section, and then find out the possible causes mentioned above before making corresponding treatment.

　　Phenomenon, cause and treatment of fan surge?

　　Precautions:

　　1. Make the flow of pump or fan constant greater than QK. If the required flow in the system is less than QK, a recirculation pipe or an automatic discharge valve can be installed to make the discharge flow of the fan constant greater than qk;

　　2. If the pipeline performance curve does not pass through the coordinate origin, changing the fan speed may also obtain a stable operating condition.

　　3. The axial flow fan is adjusted by adjustable blades. When the flow required by the system decreases, the installation angle will be reduced, the performance curve will move down, the critical point will move to the left and down, and the output flow will decrease accordingly.

　　4. The most fundamental measure is to try to avoid using the fan with hump shaped performance curve, and use the fan with straight and downward inclined performance curve.

　　Judgment method of fan surge

　　1. listen

　　Under the normal working condition of stable operation, the noise of the ventilator is low and continuous. When approaching the surge condition, because the whole system produces periodic oscillation of the air flow, the noise emitted by the air flow in the outlet pipe is also high and low, and has periodic changes. When entering the surge condition, the noise immediately increases greatly, and even there is a popping sound.

　　2. look

　　Observe the pressure and flow at the fan outlet. When the fan operates under stable working conditions, its outlet pressure and inlet flow change little and regularly, and the measured data swing around the average value, with a small range of change; When approaching the surge condition, both of them change greatly.

　　Observe the vibration of engine block and bearing. When approaching the surge condition, the fan bearing pedestal will have strong vibration, and the outlet pipe will also have strong vibration.

　　2. Methods to prevent surge

　　1. when selecting the fan, its performance shall be within the high efficiency zone.

　　Do not artificially increase the type selection coefficient, so that the actual flow of the fan in actual operation is much higher than the design flow. If a large amount of throttling is adopted, it is easy to adjust the fan to the surge area.

　　Therefore, in the fan design and type selection, it is necessary to avoid the operating range approaching the surge area. For example, in the selection of circulating fluidized bed fan, the general design institute gives two parameter points TB and BMCR. TB is the boiler high load point, BMCR point is the design operation point, and the performance of TB point is 15% ~ 30% of BMCR point. Both of them must be considered in model selection, so that the fan can not only enter the stable working condition area at BMCR point, but also reach TB point.

　　After mastering these, we can make the BMCR point operate in the high-efficiency area. We should locate the TB point in the low-efficiency area, because the fan generally does not operate at this point. Therefore, it is particularly important to master and understand the characteristics of surge.

　　2. in case of surge of the fan during system operation, the working condition range can be adjusted by changing the fan speed.

　　The centrifugal fan can change the impeller diameter, and the axial fan can change the installation angle of the moving blade. These methods can make the performance curve of the fan move to the small flow area. At this time, the critical boundary of surge will move to the small flow area accordingly, which can also expand the range of stable working conditions of the fan.

　　3. since some workplaces do not have the above adjustment conditions, and the production can not be affected by shutdown, there is another simple and fast adjustment method to eliminate surge, which is to add a vent valve.

　　So that q=q release +q surge >qmin, surge can be eliminated immediately. However, it must be pointed out that the gas put into the atmosphere should be harmless. If it is harmful, it must be introduced into the fan inlet pipe through a small pipe. The disadvantage of this method is that a part of the momentum obtained through the impeller will be released for nothing, thus reducing the overall efficiency of the fan. However, because of its simple and convenient method, it is widely used in fan regulation.

　　4. two valve operation method.

　　Two valves are set on the exhaust pipe of the fan, and the volume between the two valves is fixed to a certain value. The volume between the two valves is equivalent to an air tank. The * valve is directly installed near the fan outlet, which is equivalent to a throttle valve. A little throttling can prevent surge; The second valve acts only as a resistance. Practice has proved that this device can not only achieve the stable operation of the system, but also be very beneficial to reducing noise.

　　5. anti surge ring.

　　At present, it has become a general trend to add anti vibration ring to the main air duct in the fan equipment for subway or tunnel. This kind of guide vane can flow back to the blade in reverse direction along the guide vane instead of generating unstable airflow mass through the blade passage when the airflow is rotated and separated. The disadvantage is that in this case, part of the air flow has done useless work, but it can expand the stable working condition range of the fan and narrow the surge area!

　　Surge refers to periodic air outlet and backflow of the fan. Relatively speaking, axial flow fans are more prone to surge, and serious surge will lead to fatigue damage of fan blades.

　　Surge of fan:

　　(1) The fan has abnormal sound, high noise and vibration, the casing temperature rises, and the surge of induced draft fan and forced draft fan makes the furnace negative pressure fluctuate and combustion unstable.

　　(2) The current decreases and swings frequently, and the outlet wind pressure drops and swings.

　　Common causes:

　　(1) When the two fans operate in parallel, the guide vane opening deviation is too large, which means that the fan with small opening falls into the surge zone for operation.

　　(2) The system resistance is too large due to dust accumulation in the flue and air duct or insufficient opening of the flue and air duct baffle.

　　(3) The fan operates at low load for a long time. Treatment principle: generally, the load of the fans for load adjustment and parallel operation shall be similar, and then the possible causes mentioned above shall be found out, and then the corresponding treatment shall be carried out.