Here again, the Fadec can sense the abnormal amount of fuel flow for the power setting and take preventive action to prevent any engine instability.Neither of these examples would be applicable to IGTs but they serve to illustrate that given enough time for the Fadec to sense an unusual mode of operation, it is possible to prevent stall/surge. If an anti-choke valve is present, start the compressor with that valve initially closed, then slowly ramp it open • Perform a choke test in addition to a surge test to determine the choke line and establish a choke control line. However, during startup/emergency shutdown, the operating point will move towards the surge line because flow is …
The hope is that detection of such waves will allow the Fadec to prevent stall and surge.The fundamental problem is the nominal time period required for the actuation of a variable stator or a bleed is about 200 msec. And nowhere is this more true than in temperature rate and molecular weight.As per …Quench control is used in closed loop refrigerant applications where cooling of the hot recycle gas stream is achieved by …
This compressor blade is Stall immediately increases stage aerodynamic loss: The blade lift goes down and the desired pressure increase is not achieved. A compressor surge is flow through a compressor that is against the direction of flow during normal operation or an oscillating flow in both directions. Surge line. For example, shutting off downstream processes or changing the production rate imply a load change for the compressor that can cause the system to enter surge. | Published by PSI Media, Inc | 7628 Belmondo Lane | Las Vegas, NV 89128 This is termed a The gas path in a typical single-spool six-stage axial compressor is shown in Fig 1. Recycle Trip Line. Given that the average gas-path velocity in an axial direction is relatively constant for a GT compressor, as pressure and air density increase in the direction of flow the blades and stators become shorter. Air enters IGVs (inlet guide vanes, which are not present on all gas turbines) and passes through each of the stages, on its way to the combustor section. The useable section of the map relating to centrifugal compressors is limited by the surge and choke lines and the maximum permissible compressor speed. Even for a compressor operating relatively far from the surge curve, unexpected events can occur that can cause the compressor operating point to cross the surge line. Such compression ratios translate to gas-turbine thermal efficiencies in the 35% to 45% range. With this as an enjoinder, let’s look at how an axial compressor operates.To efficiently compress a gas over a range of operating conditions is not an easy task. During stalled operation, the average air flow through the compressor is steady, but during surge, the flow rate will rapidly (milliseconds, msec) pulse—sometimes so violently that reverse flow is induced, often accompanied by a loud “bang.”In extreme cases, a sudden combustor-induced flame may shoot out the back end of the machine (Fig 5) and possibly out of the compressor inlet as well. This now puts the operating point on the surge line as shown in the figure-2.
Typically the PI (Proportional Integral) control algorithm will active and start to modulate the anti surge control valve if the compressor operates between the control line and the surge line. The time required for the low spool to increase its rpm is now sufficiently long for the Fadec to sense the unusual relationship between low- and high-spool speeds and be able to activate a bleed to prevent the occurrence of surge.Another example: Aircraft gas turbines operating in severe rain or hail storms where extra fuel is required to process and evaporate the water being swallowed by the engine. Then engine control systems, such as Fadec (Full-Authority Digital Electric Control), are programmed to keep the operating point of the compressor well away from the so-called stall or surge lines.
Pressure ratios of the latest frame engines go as high as 30:1; those for aeroderivative machines, up to about 40:1.
Over the last 75 years these compressors have been improved continuously, today achieving component efficiencies of more than 90%. Independent voice of the gas-turbine-based generation sector© 2014 CCJ Online, Inc. All rights reserved.
As soon as the system pressure in the discharge line reaches 10 bar the compressor begins to surge.
The compressor operating behavior is defined by a map displaying the association between pressure ratio and volume or mass flow rate. To illustrate: In the early 1950s, an axial compressor with 15 stages might have had an overall pressure ratio of 4:1.