GE Frame 9E MS9001E Air Processing Unit

A

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Avworhiare

Sir,

I want to understand the working of the APU on the air inlet system/filter house and

2. The bird grid vent pipe on the gas turbine compartment end. what roles it plays? I noticed recently when there was a sudden grid loss fumes started coming out. this even scared some people around.

Thanks
 
Sir,

1. The purpose of the APU is to cool and dry the air which is extracted from the axial compressor discharge. The only time this happens, though, is when there is flow through the APU--and that's only when the device(s) fed by the extraction line are in use. The most common usage for extraction air is for self-cleaning inlet air filter systems, and since they don't run continuously (usually) there is no flow through the APU. Or, said another way, the only time there's flow through the APU is when the self-cleaning inlet air pulsing system is in use.

This causes some issues with the drain used on many of the APUs. It is usually made of cast iron, and moisture which collects in the drain can--and does--cause rust, which then causes problems with the operation of the drain.

Some APUs are very simple (a large "loop" of fined pipe to cool the air as it flows through, and a drain to remove the moisture which condenses as the air is cooled. Some APUs have two cylinders with moisture removing materials inside and there is a small control panel which operates a few small solenoids to cycle between the two cylinders. The effectiveness of this is extremely questionable as even when the pulsing system is in use there isn't too much flow through the APU.

Some APUs also hace large electric fans used to increase the cooling as the air passes through the finned tube loop, but in my experience the temperature switch which drives the fan cycles it on and off during the day even when there's no air flowing through the APU--which is most of the time. So, it's just a waste of electricity driving the fan if there's no air flowing through the APU. (The "control system" used on the APU is NOT very sophisticated.)

Some APUs also have small solenoids on the drain outlet which cycle periodically (on an adjustable basis) which blow moisture out of the drain--again, when there is air flowing through the APU to cool. Otherwise, it's just puffing periodically.

Some sites run their pulsing systems much more frequently--either on a manual basis, or because the ambient climate is dirtier (dusty roads; dust from nearby factories or process plants; etc.).

2. The purpose of the "bird grid" over the ends of pipes open to atmosphere is to prevent birds from building nests in the ends of open pipes. It's not clear where the other end of the pipe you are describing is located. There is usually a gooseneck (180 degree bend of pipe) vent on the gas fuel piping system that is pressurized momentarily when the turbine is shut down or trips as gas trapped between valves is vented. But, without knowing what the pipe is connected to, that's about all I can think of.

I want to point out the existence--and the <b>importance</b>--of the unit P&IDs (GE has typically called them Piping Schematic Diagrams in the past). They are crucial to understanding the operation of a GE-design heavy duty gas turbine, and, compared to some P&IDs I've seen they are actually pretty easy to read and interpret. They are located in the Operations & Maintenance Manuals provided with the unit, and also somewhere in the same manual should be a document called the 'Piping Symbols' "drawing" which is a legend (description of the symbols used on the P&IDs). Every control room should have available a full set of P&IDs for the operators. The operators should be encouraged to study and understand the P&IDs, and they should also be required to go out to the unit and find every item on the P&IDs (check valves; manual valves; control valves; instruments (transmitters; gauges; switches; etc.). Maintenance technicians and plant engineers should have their own worn, dog-eared and marked-up copy of the P&IDs, with notes about devices and calibrations and adjustments and locations.

There is no better way for people to get familiar with the systems and control devices in use on the turbine. NONE. Period. Full stop. A lot of questions can easily be answered by referring to the P&IDs. A LOT of operational "problems"--especially those beginning immediately after a maintenance outage--can be solved by using the P&IDs to go out and ensure that all manual valves are in the proper positions after a maintenance outage.

P&IDs are the best place to start understanding systems and operations. There are also some very useful notes on every P&ID which can be used to enhance understanding and operation. The answer to the second question is best derived by using the P&IDs to understand where the other end of the pipe is located and what flows out of the pipe--and when there should be flow (as well as when there shouldn't be flow). The P&ID won't have ALL of that detail, but you can see what valve(s) are in the pipe and from there it's possible to determine when the valves are open and when they're closed (from the programming in the turbine control system)--but the P&ID is always the best place to start.

I hear all the time, "The P&IDs are so difficult to read!" To which I respond, "Yes; at first, they seem difficult. But keep working with them and they <b>quickly</b> get easier--and they value becomes very clear, also."

Hope this helps!
 
This sounds like the bearing 2 breather pipe. You are seeing oil mist. When you had a grid loss the mist oil eliminator motors also stopped. Provided you ran down on the emergency dc lop there should be no permanent damage done.

> 2. The bird grid vent pipe on the gas turbine compartment
> end. what roles it plays? I noticed recently when there was
> a sudden grid loss fumes started coming out. this even
> scared some people around.
 
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