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Anonymous Poster #1

Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/07/2011 2:07 AM

hi all,

i am a young engg. fresher in power plant working on the project of low vacuum problem in the condenser of the coal based thermal power unit of 120MW. condenser vacuum is maitained by ejector. the problem is that after the commissioning of unit the condeser vacuum is consistantly low then the design vacuum of condenser. so for maitaining the vacuum we are using two ejector. there is no major leak detected in helium leak test. so what may be the probable cause for the low vacuum?

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#1

Re: low vacuum problem in condenser of coal based thermal power plant

12/07/2011 2:16 AM

I'm not a boiler/turbine guy, but I wonder about the presence of noncondensable gases in the steam. (Not sure how this pertains to steam systems, but it is an issue in refrigeration systems.)

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#2

Re: low vacuum problem in condenser of coal based thermal power plant

12/07/2011 5:50 AM
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#3

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/07/2011 2:37 PM

The condenser has a vacuum release valve, this valve is water sealed, check that this seal is working correctly.

Regards JD.

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#4

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/07/2011 10:37 PM

Things that need to be checked include:

· Condensate for traces of cooling water contamination.

· Gland sealing steam must be at greater than the internal turbine pressure.

· Condenser casing gasket must be sealing.

· Hotwell flanges and valves must be sealing.

· Are the air ejectors functioning correctly

Remember boilers are hot and turbines are noisy but condensers really suck.

BAB

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#5

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/07/2011 11:09 PM

If you have checked the tube leakage and other factors already mentioned like gland sealing, valve leaking and non-condensable gases, then the other most common cause is condenser tube fouling.

Estimate the current condenser tube cleanliness factor and see how it compares to the design. If low, then tube cleaning is required.

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#6

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/08/2011 12:31 AM

You may want to check for leaks around the crossover from the IP Turbine to the LP turbines. This is generally not a factor at higher loads, but can be at lower loads.

Another place to check for leaks is under insulation on thermal drain lines between drain traps and the condenser. If the power plant is very old, the moisture in these lines can corrode lines in runs of several feet. Being under insulation, they are hard to detect sometimes as they can act as a delay line between the time of helium admittance. They may also be very small but if enough exist, they are accumulative.

Check the exhaust line from your boiler feed pump(s) as well. High vibration in these areas tend to cause cracking or tears that get longer with use.

Of course you have extraction drain lines, and heater drain lines as well which can develop leaks especially closer to the source of vacuum (the condenser or hotwell).

There is a large rubber expansion joint generally found around the condenser on your mezzanine which from time to time can develop leaks. It may be hard to pinpoint leaks with helium here as well. These are not easy to access either.

Drains below the hotwell will not drain when under vacuum, but will admit a lot of air into the condenser. You would think that it would be easy to locate because of draining liquid. This is not the case unless you happen to check it after the vacuum has been bled off.

The earlier posts have some good suggestions as well.

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#10
In reply to #6

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/10/2011 5:22 AM

thanks a lot..... pls suggest some leak test other thn helium test.

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#11
In reply to #10

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/10/2011 2:34 PM

Look for a good sonic or infrasonic detector and listen for leaks. Did you find your problem? We at CR4 would like to know how we did.

Another thing to check for vacuum leak is the rupture diaphragm on the turbine and/or boiler feed pump(s).

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#7

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/08/2011 12:38 AM

Are you having fun yet? "....the problem is that after the commissioning of unit the condeser vacuum is consistantly low then the design vacuum of condenser..."

After commissioning implies that commissioning has occurred. I can't see how it was ever deemed to be commissioned if it didn't meet the design parameters.

Find the commissioning records, see whose signature is on the acceptance certificate and ask them to sweat it out.

On the other hand, if you are the one who is trying to commission it than talk to the designer. Was the design ever peer reviewed?

There are 5 things that I can think of that may cause your lower than expected vacuum:

A vacuum leak

Inadequate ejector capacity

Excessive incoming

Obstructed outgoing

Inadequate cooling

Or none of the above and something else that others might suggest.

You may well have already "fixed" a design (or capacity) error by introducing the second ejector.

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#8

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/08/2011 2:49 AM

there are many cozes tht may affect the condenser vacuum.we had the same probl on one of our 220mw units. the following are factors to consider

  • TTD (terminal temperature difference) i.e exhaust steam tmp - CW outlet temp (ths shld be about 6 deg)
  • cleaniliness of the condenser tubes (do u have an on-line cleaning mechanism)
  • hot drains to the condenser (increases work load of the condenser)
  • CW flow rate, inlet and outlet temperature
  • ambient temperatures
  • efficiency of the air ejectors
  • any condenser leakages
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#9

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

12/09/2011 8:28 AM

Hi,

If you have any leakage into your condenser or any incondensable gases coming into the condenser, find out by checking the tail pipe of your ejectors. Measuring the outflow at this point (by orifice plate or other instrument) gives you a good indication of any existing leakages. You may have a measuring device at that point. Good systems have.

If the flow is normal then take a good look at the ejectors themselves. Particularly where their condenser drains are connected. Take a good look at the design of the layout especially if they never worked properly from commissioning. Normally primary ejector condenser drains into turbine condenser hotwell via U waterseal. Secondary to a drains tank.

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#12

Re: Low Vacuum Problem In Condenser of Coal Based Thermal Power Plant

06/22/2012 8:00 PM

 Hi young use smoke test generator to identify the air ingress into the condenser. Operations to co-ordinate with the possible areas to check for the air ingress and witness the test.   Operations may provide operation parameters such as   Steam Inlet properties into Steam Turbine - Pressure & Temp and Flow Power loading on the TG Blead Steam Properties - Pressure, Temp & Flow Condenser Vacuum, Hotwell Level, Cooling Water Temp, Cooling water Pressure.  Ejector Operation Parameters - Steam Pressure and Temp. Gland Steam Operation parameters - Steam Pressure.   Compare these parameters with the other turbine.   Air Ingress test & study of the operation parameters may identify the reasons for low vacuum.   NOTE Check the cooling The casing and diaphragm design shall permit the diaphragm position to be readily adjusted within the casing to maintain concentricity with the rotor position. 2.3.5 Stages designed for normal operation on wet steam (0.5% and greater moisture level) shall be provided with protection against moisture erosion.  This shall include rotating as well as stationary components and the casing itself.  The Vendor shall state in his proposal, all protective measures taken to limit moisture erosion, including the use of any non-standard materials. 2.3.6 Turbines with normal steam temperatures of 455°C or greater shall be furnished with temperature probe pairs at the following locations for monitoring inner and outer wall temperatures: a) steam chest flange inner and outer surfaces; b) main pressure casing flange inner and outer wall on right and left sides of the casing approximately inline with the first stage exit. The temperature monitoring system shall be provided by the purchaser.

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