Steam Turbine Efficiency

[dh328]

Hi,
Recently we have faced a problem in operation of our ethylene refrigerant compressor. Although the compressor is working below full capacity, turbine governor valve is fully opened but steam flow is 18 ton/hr compared to full load steam consumption of 30 ton/hr. we have washed the blades and they are clean. Turbine after first stage pressure is 2.2 kg/cm2G (pretty less than max. allowable). main steam pressure is 15 kg/cm2G and it is surprising that steam pressure after throttling valve is 7.5 kg/cm2G. I think that throttling valve parts are loosen or damaged. some colleagues say that strainer in throttle valve may be chocked. what do you think?
what is solution?

 

[byrdj]

need to open throttle valve and see. a failed valve or screen will send foriegn material into nozzle and blades.

 

[byrdj]

have you verify the actuator or stem is still fully open. is it possible the throttle is partially closed? throttle (stop valves) stems normally hav a back seat that will have a tell tell drain line blowing if not fully open.

a drift or change in the controls could be mispositioning actuator less than full open

 

[JJPellin]

I originally misunderstood the terms you use. If the pressure drop is occurring in the trip and throttle valve (T&T valve), then most of the issues I mentioned originally are not relevant. This valve is supposed to be fully open during normal operation. Most of the T&T valves on our large turbines have inlet screens. Since this valve is usually the final element in all of the automatic turbine trip protection systems, including the overspeed trip system, it is critical that it is working properly. Does your T&T valve have a manual exercising lever? If so, exercise the valve and verify that the stem moves smoothly and is not bound up. If not, move the valve in the closed direction so that the stem moves at 1/4 inch or more and then re-open it. These actions should not affect the speed of the turbine.

Johnny Pellin

 

[dh328]

The index of valve shows that it is open but we are not sure. How to verify? If the screen is covered with debris how to clean it without stopping the turbine?

 

[JJPellin]

Turn the handle in the direction of opening as indicated by the arrow on the handle. If it feels like it is fully open, turn it the other way and observe the valve stem move 1/4" or so as I noted above. Then turn the valve back to the fully open position. This exercised the valve which is a good practice. We do this monthly on all of our large turbines. If the screen in the valve is obstructed, the only possible option would be to perform an on-line wash. If the obstruction is mineral build-up, you might wash it away. If you choose to do an on line wash, you will need to get a detailed procedure from the turbine manufacturer. We have done this on our largest turbine a few times over the years.

Johnny Pellin