after opening the valve's VA13, VA19 in air purge system, why there is a lot of water around it?

I think it should be the air compressor condensate after turbine shut down.
am i true?

would you please suggest a way to remove this water because it can cause corrosion in the regulator valves and VA13, VA19.

best regards

 

david,

There should be some "low-point drains" in the piping systems. They are usually just small pipe "nipples" (1/4-inch, Schedule 80 pipe) with pipe plugs on one end mounted vertically each with a very tiny hole (orifice) drilled in them. They are intended be "draining" all the time, which means there is a very small flow of high-pressure air at all times through the orifice hole. M ANY people think these are "leaks" and so they remove the pipe nipple from the air purge piping and put a pipe plug in its place. And if they are (incorrectly) deemed leaks and removed, they usually get plugged with rust or other contaminants and so don't work.

Finally, it's VERY common for the Atomizing Air Pre-cooler temperature regulating valve to be adjusted incorrectly. It should be set for 275 deg F (135 deg C). But, since the Robertshaw mechanism typically used for the temperature regulating valve is SLOW, there is a tendency for 'Atomizing Air Temperature High' Process Alarms to be annunciated during turbine start-up--and people go and misadjust the regulator in a misguided attempt to resolve the short-lived Process Alarm (the handle on the side is NOT for adjusting the temperature setpoint!!!) and then forget about it. So, moisture condenses in the Pre-Cooler and there is no automatic drain on the Pre-Cooler shell. (It should have a Pre-Cooler shell drain valve which can be used to see if there is moisture in the shell--which there should NOT be if the regulator is working properly).

An improperly adjusted Atomizing Air Temperature Regulating Valve is the most common cause of water (condensate) in Atomizing Air and Purge Air Piping. The second most common cause is plugged or removed low-point drains. Low-point drains are shown schematically on the respective P&ID (Atomizing Air; Fuel Purge; Liquid Fuel; etc., depending on the vintage and packager of the GE-design heavy duty gas turbine).

If a "slug" of water reaches the Main (Accessory Gear-driven) Atomizing Air Compressor it will damage or destroy the compressor. Most Main AA Compressors cannot tolerate inlet air temperatures in excess of approx. 300 deg F (150 deg C) and if the air is too cold then moisture will condense, so it's pretty important for the Atomizing Air Pre-Cooler Temperature Regulating Valve (VTR2-1, I believe) to be adjusted and maintained correctly.

Hope this helps!

Please write back to let us know what you find.

 

hi,

I should mention that water collects inside the control air pipe line to the actuator of the valves VA13 (GAS system purge) & VA19 (Liquid fuel system purge).

This piping has a filer (FA4-1 : ATOMIZING AIR ACTUATION AIR FILTER) at the beginning of the line that is seemed to be the only drain place.

The Regulator Valves VPR54-1 & VPR44-1-4 that regulates the control air to the actuator of the purge Valves have also been damaged and have a high amount of corrosion. It seems that there should be a drain mounted near to these purge valves for this purpose to drain the water condensate collected on the valve actuator. What's your idea about removing this water condense?

May be use the instrument air for all of time operation or NOT?

Thank you.

 

david,

A proper design would have had low-point drains in the actuator air supply as well, as mentioned before.

If your plant has a reliable source of clean, dry instrument air that is available during unit starting and shut down, that is always a better choice.

The concept behind using axial compressor discharge air for pneumatic actuators on GE-design heavy duty gas turbines is so that the packager of the turbine or the designer of the plant or the EPC doesn't have to procure and provide a source of instrument air for the turbine pneumatic actuators.

Some turbines are installed so that they can be started without AC (called "black start" units), so there may not be a source of AC for the instrument air compressor until after the unit is started.

But, when a plant has a reliable source of dry, instrument air for actuating the gas turbine's and its auxiliary pneumatic actuators it's usually a better choice--just for the reasons you cited.

 

Hi,

This machine has instrument air during start up and shutdown.

I didn't find the low-point drains in the actuator air supply. The VTR2-1 don't working properly because the sensor is very sensitive and all of time is destroyed. the handle on the side is used for adjusting the temperature set point (100 DC). this sensor must change every time. This a PROBLEM for this valves (VTR2-1, VTR1-1). It is better to solve it by GE COMPANY.

I ask from you about can use instrument air for all of time during startup, operation, shutdown. It's possible or not for normal operation?

 

david,

Yes, it is possible (better) to use instrument air at all times--if it's available at all times.

I only mentioned startup and shutdown because some times plants don't have air available then.

But if there is a reliable supply of dry instrument air at all times then it's better to use instrument air.

There is supposed to be a low-point drain on the bottom of the porostone filter vessel (FA-nn).

 

I am a big fan of installing a coalescing and self draining type air filter at each point of use.

Keeps the dirt, oil, and water out of your instruments.

The self draining part is important since it is likely no one will bother to go out and drain them. I have seen them full of water and oil way too many times.

 

When did you get water from drain points?

what is frequency of moisture being collected?

Some times during off-line water wash water+detergent get accumulated in the piping of purge air, detergent lead to corrosion and Regulators(VPR) gaskets damage.

Other possibility is that Atomizing air cooler may leak, in shutdown state CCW will pass to the atomizing air circuit and one may assume that condensation formation there

Just a little sharing.

Further experts are requested to comment

 

david,

The temperature regulating valves and actuators typically provided with most GE-design heavy duty gas turbines are NOT installed with the proper protection required for a device with a capillary tube. People climb around piping and piping components without a care--as if any component is designed to withstand the weight of person standing on it or jumping up and down on it.

And, maintenance and operations personnel don't observe much--if any--care when working around capillary tubes (if they even know what one is, looks like, or does).

There are literally thousands of Robertshaw actuators for all kinds of regulating valves in service around the world--and when installed properly, and adjusted properly they work for decades without a single problem. Once properly adjusted, they require almost no future adjustment (presuming heat exchangers are properly maintained, and cooling water supply temperatures don't vary much). That makes them an ideal actuator (when properly installed!) for most GE-design heavy duty gas turbines, where the people operating and maintaining them are nearly oblivious to how things work and take very little care during operation and maintenance activities. Most operations and maintenance personnel never take the time to read any of the manuals provided with the equipment--until long after it's broken or not functioning properly.

Sure, one could install an electrically-operated actuator, or a pneumatically-operated actuator, or an electrohydraulically-operated actuator--but at what cost? People already complain about the cost of GE turbines and auxiliaries enough as it is. Increasing the cost--and needlessly increasing the complexity at the same time--by providing equipment that requires more care and maintenance (calibration; instrument air; electric power; hydraulics; etc.) is not the answer.

However, the owner and operator of any GE-design heavy duty gas turbine--once it's out of warranty--is free to make any changes they want to any auxiliary. There are many suitable actuators for the same valve that can be purchased, engineered and installed (at a <b>MUCH HIGHER COST</b> than a similar Robertshaw) to effect the same control that a very simple and effective Robertshaw actuator has done for decades.

As long as it's properly installed, adjusted, and appropriate care is used during maintenance activities.

The problem is that most sites don't find out they or the maintenance personnel they contracted with to perform their outage even know the actuator has a capillary until it's broken and not working. (And, that's difficult to understand because when the capillary is broken and the fluid inside leaks out it has a very distinctive smell and leaking fluid is hard not to see, also.) And, they want to blame GE--instead of the installer or the maintenance personnel.

And, SB is correct. When performing an off-line water wash it's intended for manual isolation valves for the air supply through FA-14 to various actuators to be closed before beginning the wash, and then opened once completed.