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long term effects of using lower than design pressure at turbine inlet

long term effects of using lower than design pressure at turbine inlet

(OP)
We've got a case where due to less than ideal function of our steam drier, we've got steam coming to a turbine with a higher moisture content than is desired.

To compensate for this, they're currently running the machine with lower inlet pressure (higher steam consumption) to drop the moisture level.

They are unclear, however, on what long-term effects there may be because of this. In my research online and in the Sanders text, I haven't been able to find anything that speaks directly to that issue.

I DO understand the effects of higher moisture content, but... can somebody help me understand what, if any, problems might arise from lowering the inlet pressure?

RE: long term effects of using lower than design pressure at turbine inlet

The lower pressure itself will not hurt anything.
On the other hand the wet steam will eat your turbine alive.
What is the temp/pressure/quality of the steam at the exhaust?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: long term effects of using lower than design pressure at turbine inlet

I will try to help if you can supply some additional information. Please provide information on the turbine as follows:
Type of turbine: Single or multi-stage, backpressure or condensing
Original rating, or operating point, power output in kW or hp
Original inlet steam conditions: flow, pressure, temperature, moisture content
Original exhaust conditions: pressure, temperature, and if available, moisture content
New inlet steam conditions: flow, pressure, temperature, moisture content
New exhaust conditions: pressure, temperature, and if available, moisture content
Power output with new inlet and exhaust conditions

Best regards!

RE: long term effects of using lower than design pressure at turbine inlet

(OP)
Yeah, right after asking this question, I realized I don't have enough information yet to do a real investigation.

The question was asked to me as a theoretical question in general, not specifically applied (as of yet) to a specific turbine.

However, in going back to ask for more information (which I'm still waiting on a full answer for), I did get at least a bit more info.

It seems I mis-heard or mis-understood the real question/problem. It seems the reality is that the steam field in question has actually reduced pressure, so that we now have a lower enthalpy source in general. They then had to bump up the flow rate to produce the same power output. So, the real question then was what would the general effect of that change be. Also, upon asking them a second time, they SAY that the separators are working well, such that the steam quality entering the system should be the same.

The short answer to my very general question then seems to be... if the steam enters at lower enthalpy than design, I would expect to see a higher moisture content in later stages. Based on that higher moisture content, I should expect lower efficiency in general from the entrained fluid, as well as increased corrosion and erosion from the higher volume of fluid condensing within the machine (on both blades and casing alike).

If that sounds correct, in general, I'll go ahead and close this question out here, and open a new thread with more specific details once I get more info on the actual case at hand.

Thank you very much for the suggestions of what information is relevant in answering this question!!

I don't currently have access to any turbine analysis software (I have a proposal in for AxSTREAM that's at least getting looked at, but no real movement yet).

Thanks for the help so far.

RE: long term effects of using lower than design pressure at turbine inlet

Keep digging. My instinct tells me YOU have not been given the full picture yet.

I see nothing yet to show me (you) that anybody is trying to "hide something" or "justify a bad economics decision" about the field by getting you to analyze bad or incorrect data and write up a justification, but you don't have the full story yet. And what you have been asked to analyze has changed twice, with the actual data (guesses ?) changing three times.

RE: long term effects of using lower than design pressure at turbine inlet

(OP)
Yeah, what's changing is me repeating the question to get them to explain the problem to me completely. Unfortunately, at this point, my only sources of information are my boss (who asked me the question in the hallway a month ago, shortly before I had an unpredicted 3 week absence), and an electrical engineer who's working on a different project at the same site, who happened to hear the original question (and who has worked on efficiency tests previously).

Also, I'm fairly new in this field, so I am myself not yet fully tuned-in enough to ask the right questions right off the bat.

It remains for me, now, to find myself a better information source, more directly connected to the problem.

RE: long term effects of using lower than design pressure at turbine inlet

I have seen plant run similar to case you propose.

The steam field is running down so open the production wells fully and open the turbine inlet valves fully. The steam pressure drops to match the output of wells. Assuming the two phase separators are stilling operating in design range, there should be no change to the steam wetness, It will still be saturated but at a lower pressure.

Within the turbine the blades will not be seeing the conditions they were designed for. They will not be as efficient. There will be a change in the location wetness and condensate drop out along the turbine flow path. The turbine designer/supplier should be able to advise the effect on the turbine.

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