I am aware of the fact that compressor surge is a phenomenon that happens when forward flow through compressor can no longer be maintained due to an increase in pressure across compressor and a momentary flow reversal occurs. But I want to know all and the most important internal as well as external conditions where the chances of surge are high.. so if anybody can point a link or explain how does the following effect axial compressor surge.

We have experienced compressor surges at one of our GTs with a loud bang few times. My general understanding is that a compressor surge is highly likely when the following conditions exist.

1. compressor is heavily fouled & hence compressor efficiency is low and so is CDP.

2. high delta P across inlet air filters and thus higher inlet vacuum, hence less flow.

3. High humidity and low ambient temperature.

4. IGVs are partially closed (modulated)

5. Low Turbine speed (due to low system frequency)

6. Very high CDP when ambient temperature is extremely low.

7. Low value of inlet scroll differential pressure.

I think all above conditions (isolated or concurrent) increase the chances of compressor surge. I want to know which parameter has the highest, lowest or no impact and how to prevent surge.

We don't have a surge control valve, so whenever our machines surged, it was observed that compressor inlet section was found very dirty, so we did an offline wash and restarted the machine without any problem.

James

 

You say that this has happened on one turbine out of several on site, and multiple times to the same turbine.

And that each time you have found a very dirty compressor.

You haven't told us if the compressor has ever been refurbished or repaired, just that the same unit has experienced multiple surges and has been washed, off-line, and then put back in service.

You also haven't told us if the compressor discharge pressure of the affected unit is significantly different at the same ambient and power output as the other units at the site, or if it is lower or even significantly lower.

It's always been my impression that a surge or stall on a rotating axial compressor can cause permanent damage to either or both rotating and stationary blades, sometimes resulting in catastrophic failure. It would seem the affected unit has avoided catastrophic failure, but that repeated surges has possibly increased the propensity for the unit to experience successive surge conditions because of the damaged airfoils.

Very low ambients can result in very high flows through the compressor exceeding the compressor operating limit.

High filter differential pressures usually result in ruptured filter elements, causing ingestion of dirt and filter components into the compressor. Many units have implosion doors that will open on high inlet "suction" to prevent rupture of the filters. Most of the time when the implosion doors open the turbine is either tripped or shutdown to prevent continued operation with unfiltered air.

High humidity at low ambients is usually cause for installation of inlet air heating systems to prevent ice formation on the inlet guide vanes, which might be drawn into the compressor inlet damaging the compressor blades (rotating and stationary).

I would have to think that when a turbine is purchased for installation in a particular location that it is designed, configured and equipped to withstand the expected operating conditions (not including extreme fouling). This might include programming of the turbine control system to limit output to protect the compressor.

So, based on the information provided it would seem that something is amiss with one unit at your site. Either the control system isn't working correctly or the system is being operated outside design conditions. Sometimes, on sites with multiple units, one or more units can experience compressor fouling faster than the other units because of roads being closer or some dust and/or humidity being ingested because the inlet is downstream of some source that doesn't so directly affect the other units.

There are lots of reference sources on axial compressor surge and -stall on the World Wide Web; use your preferred search engine to further your research. Unfortunately, most of the information seems to be related to aircraft engines, but then GTs are very closely related to aircraft engines.

 

you are right, this machine's compressor fouling is faster since it is located near a smoke producing factory, and close to our cooling tower. The other machine is also not far off, yet is in better zone with lot of trees around. We have two identical GTs, and the output of the one which has compressor problem is nearly 6% less than the other.

 

There's also on-line water washing, but in cases like this, it's probably not as effective as in many other cases.

In cases like this, it's best just to bite the bullet and shut down more frequently to perform off-line water washes.

Your comment about the decreased performance is unclear. Do you mean it's down 6% when it's clean compared to the other machine in relatively clean condition, or that it's down 6% while running and likely fouled?

If it's the former, then it's likely that there is already some kind of damage to the axial compressor. If it's the latter, then there's still the likelihood that catastrophic damage could occur if the condition continues without some kind of abatement or more frequent washes. And this still doesn't mean that some mechanical damage hasn't already occurred from the prior events.

 

We are facing the same problem on our 50MW gas turbine.In 12 years of its operation our machine surged 3-times.

conditions were the same all time
Fouled compressor+ambient temperature high so CDP low+ low frequency

so we keep critical watch on efficiency of the compressor and do offline washing when efficiency becomes low.

one thing is very important we do have 2-gas turbines of same output but now the machine which surged now has 2~3 MW lesser output then the 2nd one which never surged. although CDP remains same and CDT 10F higher than other which is not surged in Summer season

 

Hi friends;

I think also fuel system also produce the surge on compressor. The reason i think is that if amount of fuel is excessive due to any component failure the combustion back pressure is increase which may be produce the surge. am i right?

Thanks