Yeah, it is devastating to larger compressors. I have seen pictures where 12 out of 16 stages of blades that have corn cobbed. The forces in those machines are significantly higher than in turbo compressors. But the RPM of turbocharger compressors is so very much higher. Mind boggling really.

So many times I have read discussions about turbocharger surge and stall and so many times the I had thought that the writer just does not really get it. I am sure 600MW and RJ have done the same. Lots of bad information out there. No way I really understand very much of it either. In fact, I was not aware of rotational type stall that was explained on Wikepedia. I was only aware of the axial types.

The best anology, for most cases, that I can think of relating the surge and stall is sort of like the common cold. The cause is the virus the effect is the runny nose where a stall is the cause and the surge is the effect.

Jim

 

FWIW for those still looking at the BD surge protection valves I believe that they are set up to open and prevent barking. From what I can gather they have an electronic controller is able to do this effectively. I you believe their hype. I would find a person that has one and talk to them.

From my point of view they are a bit spendy and it was easier to tune my waste gate / driving style around the barking.

Jim

 

We have a 2,500 HP, 4 stage, 325 Psi cetrifugal compressor at the power station. 1st and 2nd stages are driven at around 17,000 RPM and the 3rd and 4th at over 27,000 RPM. The 1st stage compressor wheel is over 16" in diameter. You would not believe the amount of care that goes into the control system design to specifically avoid surge and stall at all costs. The computer which runs tha machine uses a combination of inlet valves, outlet valves, interstage bypass valves, a final blowoff valve and pressure and flow inputs for each stage, that all work in harmony to keep the machine in a mode far removed from any stage stalling/surging. If all else fails, the machine will trip if it cannot move far enough away from a surge zone. Pretty neat really. Operation with severe surge destroyed a stage within minutes, then that stage debris made it through the intercooler and into the next stage... etc .etc. etc. Happened about 10 years ago, when some of the safeguards were jumpered out by a moron field service rep. Machine was a total loss except for the motor....


Kp

 

I also work with many large centrifical compresors. On our 13,000hp electric refrigeration unit we use an antisurge controller. It is basicly a recycle from discharge to suction. The conrtoller looks at the differental pressure between suction and dischage vrs flow. It then does a calculation on the amount of flow required for the delta pressure accross the unit and sets the recycle setpoint acordingly.

Most of out other 1200hp gas tubine driven compressors use a single setpoint on the recycle valve.



To break "surge" down to easy to understand terms:

On one side of the compressor (intercooler) you have say 30psi on the other side (air filter) you have a suction or negitive pressure. The presurized air wants to flow to the easiest place, from the 30psi side of the wheel down to the -0 side of the wheel...but... it can't under normal operation due to the FLOW traveling through the compresor.. However.. There is situation where the dicharge pressure can actualy overcome the flow. This is called surge. The higer the differnce in pressure across the compresor the more flow that is required to keep the pressure from going backwards.

That is why my stock turbo "barks" at 30 psi when I let off the throttle quickly. At 30psi it takes a LOT of flow to keep the pressure from going backwards. When you let off the throttle quick the turbo slows down (flow decreases) but the dicharge pipeing (intercooler and hoses) is still at 30psi. The 30psi then then trys to push back to the -0psi side, stops the flow, and you get the "bark".


If you want some entertainment you should listen to a 13,000hp compressor suge. It ain't pretty

 

We got a couple of turbines around here that can do around 220,000 Hp on a nice cold day. They are 3600 RPM frame types.

We also have four more turbines that are aeroderivitives that can do about 32,000 Hp each. The aeroderivitives have 2 rotors. The high pressure rotor shaft is hollow. The low pressure rotor shaft runs right down the middle of the high pressure rotor shaft and uses the same inside bearing. The high pressure shaft runs about 13,500 RPM and the low pressure shaft runs about half of that.

Jim

 

The aeroderivitives turbines you are taking about, are they are what is commonly refered to as a split shaft? The "low presure" wheel running the application and the "high pressure" wheel running the engine/compressor?

We use Solar split shaft turbines. Had an "Orenda" single shaft unit quite a few years ago but as load increased on the motor the engine/compressor slowed down to much resulting in high EGT.

Not that anyone here would know anything about high EGT.....

 

well if this is the case then the electronicly controlled blow-off valve that BD sells should work. i mean if its watching the throttle and vents when you let up then that would keep the compressor from surging no?

 

If it barks much just check the air filter frequently..lol
thats what I got out of all that...oh and barking alot could be a hazard to your turbo.

 

Well, while were on the subject of upping the ante on who works with the highest power turbines.. We 'got a 975,000 HP steam turbine at my plant!!! lol

Now, I'm just waiting for someone else to chime in who works at Gavin, Mountainer, Zimmer, Rockport or Amos with their 1,750,000 HP steam turbines !!!!! lol


220,000 HP ....sounds like a 7FA, eh Jim ??? What plant you work at ??


Kp

 

They are a 501FD's. Its a 2 on 1 co-gen so the steamer does a bit more.

Where I used to work long ago we had a couple of steamers that did in the neighborhood of 1,500,000 Hp.

Jim

 

Not sure of their exact designated name. But no, the low and high pressure turbines only drive the low and high pressure compressors. In the application, they are called gas generators and only produce thrust just like on a 727. The exhaust gases then pass through another turbine placed directly in the exhaust stream. The turbine is called a power turbine. Thats how you get the work out of them. But in some applications I believe you are right though, the low pressure rotor is shaft coupled via a reduction gear and does the real work.

And yes...

EGT is as much of a concern for turbine engines as it is for diesel engines.

Jim

 

Yeah, I really got off the subject sorry. I think for the most part barking a little the turbo can tolerate fairly well. But like RJ said, it can cause problems.

Surge is kind of another thing concerning turbo charged engines. The compressor will stall for various reasons and some people will talk about surge from only the compressors point of view.

But many people will often refer to surge as it is what the truck does. It surges. Keep in mind that the compressor is supplying air to the engine and what drives the compressor is the exhaust supplied by the engine via the turbine. So now chop the air to the engine and you chop the exhaust to the turbine. Then restore air to the engine and you restore exhaust to the turbine. Its an oscillating surge of engine power as things get de-synchronized.

During those times I am told, that along with some barking of the turbo, you get bucking of the whole truck and a noticeable change in RPM sound from the turbo. I am not completely sure of the all reasons, but I think one is a turbo too large for the engine. Those applications would be more prone to doing going into surge. But it could be referred to by the engine / turbo interaction / reaction and surging change in engine power as much as it only refers only to strictly compressor surge.

This is only what I have read on internet sites, various boards and talked about with a few people. So consider the above only a regurgitation of information than anything from my own personal experience.

Looking at most of the compressor maps I have seen, the surge line is fairly vertical. Maybe most of the maps would angle at near a 85 to 70 degree angle. So that indicates a pretty good tolerance to surge. I dont't believe that is any accident on the part of the turbo designer. Other maps I have seen the surge line might angle much more sharply, like 45 degrees or more. Those types of compressors would be much more sensitive to surge. The flow rate and inlet / outlet pressure conditions would have to be tightly maintained within controlled tolerances.

Only to make it more complicated after all this talk about compressor stall and surge is that the compressor has to connected to a turbine that provides the power to make it turn. And I believe the balance between the two is really out my ability to comprehend. Mind boggling really.

Jim

 

I just traded an 01 3500 6 speed that had a straight pipe, it barked like crazy. other than that it was pretty much stock, but i never had a problem and you know i made it bark whenever i could, sounded too cool!

 

incidently i just put a straight pipe on and removed the silencer ring on my 07 today and can't get it to bark no matter how hard i try. Talk about disapointed...

 

I can swing it with this crowd. I was a Shift Engineer in a power plant up here for a couple of years, 545000 hp, 400 mW. The little cogen where I'm at now is 40 mW and it isn't egt that is our problem, it's combustion chamber temp and first stage blade temp. The thing is, does anyone have a way to fix Turbo Bark??? I think I might have found a way. But I'm not tellin. hehe