Compressors stall

It appears that the large combustion turbines based on new designs have ample air compressor stall margin to avoid derating (33). 

This type of stall occurs when all the blades around the compressor annulus stall simultaneously without the occurrence of a stall propagation mechanism. The circumstances under which individual blade stall is established are unknown at present. It appears that the stalling of a blade row generally manifests itself in some type of propagating stall and that individual blade stall is an exception. 

Blade stall causes Karman vortices in the airfoil wake. Whenever the frequency of these vortices coincides with the natural frequency of the airfoil, flutter will occur. Stall flutter is a major cause of compressor blade failure. 

Blade flutter and rotating stall are problems encountered in the compressor due to poor design or contamination of the blades. Changing blade angles can usually solve the problem however, this adjustment is very... 

For positive displacement compressors, discharge PR valves are nearly always required. Reliance on stalling of a reciprocating compressor is generally not economically attractive, since driver stalling pressures are usually quite high in comparison to operating pressure. 

While all these factors affect the good running of positive-displacement compressors, the effect is far worse with centrifugal machines, which can approach stall condition and so give a much reduced cooling duty... 

Surge is quite similar to aerodynamic stall. Of course, when a compressor surges, its rotor does not stop spinning. The rotor is spun by the motor. But when the flow of gas through the rotor falls below a certain rate, the forward velocity of the gas stops. With no flow, there is no velocity to convert to feet of head. Then, the AP developed by the compressor falls to zero. 

Low voltage motors used in the oil industry usually have modest starting times, since the majority of their driven machines are pumps. Reciprocating compressors and ventilation fans can have reasonably long starting times. It is therefore not normally necessary to provide special relays to detect the stalling condition. 

Hence, the increase in absorber pressure results in forcing the compressor to operate closer to its surge point shown in Figure 25-1. If we raise the absorber pressure too much, the centrifugal compressor will stall or surge in the following manner ... 

Let s assume w e have a constant-speed, motor-driven compressor. The compressor is starting to surge, or stall, or slip, or become unstable. The... 

Surge is an instability of flow through compressor which appears as a periodical sweep. This phenomena causes a lot of noise, a sudden increase in temperature, an increase in blades stress and mechanical damages. The phenomena is due to a decrease in flow rate at specific speed and as a result of inability of fluid to pass over from current pressure ratio. In this situation return flow is appeared also. It usually starts with period stall and with further reduction in flow rate which leads to surge. Necessary condition for occurrence of surge is to be at positive... 

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