Gas valves interstage pressure between SRV and GCV high-SEP10.pdf

7/28/2019 Gas valves interstage pressure between SRV and GCV high-SEP10.pdf

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15 SEPTEMBER 2010 TS TIDINGS

TECHNICAL SERVICES / PSSR

FEED BACK NO. 2

PROJECT: SILK ROAD SUGARS, KAKINADA, 1X35MW,FRAME 6B GTG

PROBLEM: GAS VALVES INTERSTAGE PRESSURE BETWEEN SRV (STOP RATIOVALVE) AND GCV (GAS CONTROL VALVE) HIGH CAUSING CONTINUOUS

VENTING OF GAS AND START PERMISSIVE NOT AVAILABLE.

Problem details and analysis:

The gas turbine supplied to Silk road sugars, Kakinada is originally for gas

fuel only. Due to non availability of gas, GT was commissioned in October 2009 with

liquid fuel after carrying out necessary modifications. Customer received gas and GT

was commissioned with natural gas in the first week of September 2010.

While commissioning the Gas fuel system for the GT, it was observed that

while charging the Gas fuel upto Gas valve compartment from the customer Gas filter

skid, heavy noise was observed from the Gas skid vent line and confirmed that the

gas was coming out from the vent line which is gas valves interstage vent point.

Interstage lies between Stop speed ratio valve and Gas control valve and it was

suspected that the SRV was passing. It was also noticed that the interstage pressure

was showing almost that of the Gas supply pressure but it was building up very slowly.

Gas turbine start permissive was also lost due to interstage fuel pressure high.

Matter was referred to BHEL, hyderabad and upon their instructions itwas decided to carry out air blowing of the line up to the exit point from the Gas fuel

skid. This was done to eliminate the foreign particles that might have stuck in the

SRV valve seat. The entry point to the Gas fuel skid was dummied and the pipe

leading to the GT was disconnected. Instrument air line was connected to one of the

pressure gauge point of the system. Air blowing was done by pressurising the line and

opening both the valves (SRV and GCV) one by one for depressurisation through the

exit point. Air blowing was carried out 10-15 times and observed that rust was

coming out of the pipeline.

After normalisation once again Gas was charged upto gas fuel skid andsame condition which had prevailed earlier was once again observed.

It was decided to service the valve. Valve was dismantled, serviced and

lapped after getting the valve drawings from BHEL Hyderabad. It was observed that

high amount of Rust was accumulated in the valve and casing and was cleaned

thoroughly using Diesel. Blue matching was done after lapping and found to be

perfect.


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After assembling back the valve, Gas was once again charged and it was

observed that still heavy noise was observed through the vent. Subsequently the

impulse pipeline connections and vent connection which was done at BHEL Hyderabad,was verified using the valve drawings. On inspection it was found that the vent line

connection was taken from SRV top which is same as that of the supply point and was

not matching with the valve drawings. As per the valve vent line has to be taken from

the bottom as shown in the figure below which is encircled.


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After correcting the same, Gas was charged and found everything to be

normal. Interstage pressure was also reading zero. Gas Turbine was started with gas

firing mode.

MIXED FUEL OPERATION OF GTG.

As both the fuels are available and as per customer need, mixed Fuel

firing operation was also established for the GTG, firing with both NAPTHA and GAS.

Fuel sroke reference (FSR) for both the fuels will be different. Ie for Liquid fuel,

FSR will be termed as FSR1 and for gas fuel it will be FSR2. Mixed fuel operation

has been carried out by following steps.

1.Gas turbine was kept under a load of 16 MW which is the minimum load requiredfor the mixed fuel operation.

2.Minimum FSR1 required for mixed fuel operation is 8.5% and Minimum FSR2required is 17.36%.

3.At 16 MW load, FSR (Combined value of FSR1 and FSR2) with any of the fuelalone was observed to be around 30%.

4.Machine was kept running with Gas, and Distillate selection was made ON fromthe Graphics page. On selection, Liquid fuel stop valve got opened, Bypass Servo

valve current became active, Warren fuel pump clutch got engaged, and FSR2started reducing after one minute and FSR1 started increasing. When the FSR

conditions as said in point no.2 got satisfied, the MIX fuel selection was

executed and both the FSRs stayed at that value itself with the mix value

percentage.

5.Mix fuel selection was also carried out by keeping the machine running withNaptha and Gas selection was executed. Gas Stop solenoid valve got energized,

SRV got opened and FSR1 started decreasing and FSR 2 started increasing.

When the FSR conditions were met, the MIX fuel selection was executed.Conclusion:

After modifying the tap off point for the interstage impulse and vent line from the

valves block assembly to the correct location GT gas firing was successfully carried

out.

Gas valves interstage pressure between SRV and GCV high-SEP10.pdf

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