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7 comments
Active Contributor

Join Date: Sep 2009
Posts: 14

Turbine Low Load Operation - Below 50% MCR

05/18/2013 2:40 AM

Our power plant turbines are rated for 142 MW. They are condensing, hp/lp, extraction type turbines. Due to poor performance of condenser, our load is restricted to less than 50% of the rated capacity. The main steam at the admission point is 80 barg , 525 deg celcius. We are restricting the load so that the condenser vacuum is not below -- 0.8 barg ( 0.2 barg absolute). I would like know whether this low load operation will affect the Lp turbine blades. if so, what are the measures to reduce the damage. we are working on condenser problem, which may take a year to solve the probelm.

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Associate

Join Date: May 2011
Posts: 54
Good Answers: 1
#1

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 12:52 AM

Pl provide some more details like tempetature of cooling water at condensor inlet / outlet at different loads.

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Active Contributor

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Posts: 14
#3
In reply to #1

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 4:27 AM

At the present weather conditions, the condenser inlet & outet temperatures are 27 & 29 deg celcius. Also i would like to mention here that, our turbines are extraction type in which in the HP exhaust, most of the steam is sent to desalination units and the rest is sent to the condenser (40% ). Since we are operating at low load almots 90% steam at the HP exhaust is going to the desalination units and minimum flow to condenser. Almost the turbine is working like a back pressure turbine. steam pressure to the Lp turbine is almost 1 bar absolute and the temperature is 178 deg celcius. the condenser pressure is 0.2 ( - 0.8 ) barg absolute and condenser exhaust temperature is 61 deg celcius.

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Member

Join Date: Aug 2009
Posts: 7
Good Answers: 1
#2

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 4:18 AM

What is the reason for the poor condenser performance? If its fouling or scaling, you can obtain some improvement by dosing a dispersant/antiscalant combination at the condenser CCW inlet. Failing that you can perform an off load clean to remove any blockages & scale. This would be a combination of HP jetting & chemical cleaning. It should take 4 - 7 days, depending on your condenser set up. As for plant damage, one would think that the LP blade tip and hood temperatures will be elevated. In addition to that, steam flow to your condensate heaters will be lower than optimal, as will your distillate return system efficiency. Furthermore, your deaerator efficiency will be markedly lower than normal. A potentially greater risk is that your condensate dissolved oxygen concentration will be significantly greater than it should be. Dependant on the regime you follow, this will firstly significantly increase copper dissolution in your condenser, and general corrosion & hence metal transport, within the rest of the steam/water cycle, resulting in reduced feed heater & boiler efficiency, accelerated under deposit corrosion, increased solid particle carryover into the steam & hence increased SPE in the HP turbine, a significantly greater risk of FAC, especially if you're on an AVT(R) regime.

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Active Contributor

Join Date: Sep 2009
Posts: 14
#4
In reply to #2

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 4:42 AM

The reason for the poor condenser performance is total failure of Intake sea water cleaning station ( bar/band sceens ) and the chlorine injection. The combined effect is sea shell barnicle growth in the sea water inlet and ingress of sand/mud to the condenser. both problems are being rectified,but it may take some time. The condenser is fouled with barnicles, mud and sand. We did hydro ject cleaning but no use , with in days again condenser is choked. So we are forced to run at low load. we do regular cleaning of condenser. There is a concern in the department about the damage to the Lp turbine at this load on continuous operation. Could you kindly explain the combination HP jetting and chemical cleaning. Also the terms " SPE, FAC, AVT(R). What is your suggestion for our condition.

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#5
In reply to #4

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 5:09 AM

Your cooling system is once through, so scaling shouldn't be an issue except for possibly the top tubes of the outlet pass. In this case, traditional chemical cleaning shouldn't be required. I would consider introducing a chlorine dosing station in your inlet duct to try to control the bivalves and a dispersant dosing station at the condenser inlet to control the biofilm/mud. You need to do something about the sand because it is going to erode your condenser tubes. Solid particle erosion (SPE) will affect any high velocity areas - blade tips, diaphragm vanes, valve seats, etc. Flow accelerated corrosion (FAC), previously known as erosion corrosion is a continual process where loosely adherent iron oxides, particularly magnetite, is removed in highly turbulent areas of feed water piping, 2 phase flow areas & the like, and are subsequently replenished, leading to wall thinning. All volatile treatment - reducing (AVT(R)) is a steam/water cycle treatment regime where a reducing agent like hydarazine or carbohydrazide is dosed to reduce the dissolved oxygen concentration & promote the generation of magnetite. It was thought that the magnetite would protect the piping from corrosion, but subsequent research has shown that haematite provides more protection, so AVT(O) (oxidising) was introduced, where the oxygen is controlled by mechanical means & the pH adjusted with ammonia so as to minimise corrosion of ferrous alloys.

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Guru
Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2008
Location: CHENNAI, TAMIL NADU, INDIA.
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#6

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 6:20 AM

Dear Mr.swccramas,

Pl. furnish the details as found in the HMBD and for what load conditions the condenser is designed, and what are the extraction quantity and parameters, so that we can understand and suggest some remedy.

What about the Ejector for condenser, Is it OK, as it also has to be looked into.? What about air-ingress in to the condenser.

DHAYANANDHAN.S

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Commentator

Join Date: Nov 2008
Posts: 98
Good Answers: 4
#7

Re: Turbine Low Load Operation - Below 50% MCR

05/19/2013 11:57 PM

Instead of extracting work from steam, last stage blades will be working on steam, churning it and raising temperature. If your last stage blades disc is not shrink fitted, it will not cause appreciable harm during long run. Exhaust temperature to condenser, i.e. 61 degree C is high due to this churning effect. Stellite coating on the last stage blades tips, if provided, may be affected due to higher temperature. Vibration might have increased a bit as compared to previous condition. In this condition, I doubt your condenser vacuum might have also reduced resulting in reduced efficiency.

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Users who posted comments:

dhayanandhan (1); IRSHAD (1); marcus43 (2); satendrakumart (1); swccramas (2)

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