Gas Turbine Controls

Hello, I am doing a report on Gas Turbine combustion controls
I am just wondering
-what does the gas turbine compressor discharge pressure control?
-what does the Exhaust gas temperature control
-what does the speed feedback control?
-what does the temperature on the inlet of the compressor control?

Any response would be greatly appreciated
 
Zorif,

I can only speak to GE heavy duty gas turbine control philosophies and practices, and I'm only going to answer with regards to conventional (diffusion flame) combustors.

Axial compressor discharge pressure is used primarily in the calculation of maximum allowable exhaust temperature, in conjunction with the exhaust gas temperature. Together the two can be used to make a very good approximation of firing temperature--which, in GE gas turbines refers to the temperature of the exhaust gases leaving the first stage turbine nozzle. It is this temperature which determines the hot gas path parts life, and since everyone wants to maximize power output AND parts life "controlling" this temperature (which at present for most GE-design heavy duty gas turbines can't be measured directly) in order to achieve optimal power output and parts life.

Speed feedback, in a GE-design heavy duty gas turbine, primarily control the fuel gas pressure between the Stop/Ratio Valve and the Gas Control Valve. This is primarily done so that flow through the Gas Control Valve is proportional to stroke, and by measuring the stroke (travel; opening) of the Gas Control Valve one can make a very good approximation of fuel gas flow-rate. If the turbine burns liquid fuel, speed feedback is also used in the control of the liquid fuel flow-rate.

In general, the inlet temperature of the axial compressor inlet isn't used by the turbine control system to control anything. HOWEVER, the temperature of the inlet air directly affects the power produced by the gas turbine (cooler air is more dense; since the the shaft of a turbine driving a synchronous generator is relatively constant as air density increases air flow through the axial compressor increases (for the same IGV (Inlet Guide Vane Angle) and this increase in mass flow through the unit results in increased power output). Gas turbines are rated (on the nameplate) for a certain power output at a certain ambient (axial compressor inlet) temperature; cooler air allows the turbine to produce slightly more power, while hotter air results in decreased power output--all a result of changes in ambient (axial compressor inlet) temperature and density.

Hope this helps!
 
I also
Zorif,

I can only speak to GE heavy duty gas turbine control philosophies and practices, and I'm only going to answer with regards to conventional (diffusion flame) combustors.

Axial compressor discharge pressure is used primarily in the calculation of maximum allowable exhaust temperature, in conjunction with the exhaust gas temperature. Together the two can be used to make a very good approximation of firing temperature--which, in GE gas turbines refers to the temperature of the exhaust gases leaving the first stage turbine nozzle. It is this temperature which determines the hot gas path parts life, and since everyone wants to maximize power output AND parts life "controlling" this temperature (which at present for most GE-design heavy duty gas turbines can't be measured directly) in order to achieve optimal power output and parts life.

Speed feedback, in a GE-design heavy duty gas turbine, primarily control the fuel gas pressure between the Stop/Ratio Valve and the Gas Control Valve. This is primarily done so that flow through the Gas Control Valve is proportional to stroke, and by measuring the stroke (travel; opening) of the Gas Control Valve one can make a very good approximation of fuel gas flow-rate. If the turbine burns liquid fuel, speed feedback is also used in the control of the liquid fuel flow-rate.

In general, the inlet temperature of the axial compressor inlet isn't used by the turbine control system to control anything. HOWEVER, the temperature of the inlet air directly affects the power produced by the gas turbine (cooler air is more dense; since the the shaft of a turbine driving a synchronous generator is relatively constant as air density increases air flow through the axial compressor increases (for the same IGV (Inlet Guide Vane Angle) and this increase in mass flow through the unit results in increased power output). Gas turbines are rated (on the nameplate) for a certain power output at a certain ambient (axial compressor inlet) temperature; cooler air allows the turbine to produce slightly more power, while hotter air results in decreased power output--all a result of changes in ambient (axial compressor inlet) temperature and density.

Hope this helps!
Thank you very much for your detailed response, I hope i had signed up and asked questions about in earlier stages of my report.
Can you please elaborate Air-fuel Ratio control and how it ties to Exhaust gas temp montoring
My report is due tomorrow and i am still looking for few key bits of information. My report is basically focusing on the Combustion Control of a gas turbine. In the report i speak of Temperature control parameters that tie into the fuel intake line( i may be wrong) , rotational speed feedback for IGV's as well as fuel intake line
I have rough sketch up of my personal P&ID from my understandings of the information i gathered

Can I please get some feed back on it?
as well as any sources that would be great help with the addition of the material for my report
 

Attachments

Zorif,

You have the basics covered in your P&ID--just that in my experience, axial compressor inlet temperature isn't actually used for all that much. (Having said that, newer machines with multiple stages of variable stationary axial compressor blades (vanes) might be using that parameter; I just haven't encountered one yet that I can really observe and analyze.)

Most people are very surprised to learn that the air/fuel control computer in the 4-cylinder car they drive is more sophisticated than the turbine control system is. For existing ("legacy") GE-design heavy duty gas turbines, the air/fuel ratio is NOT monitored nor controlled. Not at all. All of that is done by sizing fuel nozzles and extensive knowledge of the characteristics of the machine (axial compressor; turbine section; exhaust), along with the expected fuel characteristics (Btu; methane; etc.). Exact stoichimetrics is all that important (thought it would make things a little more efficient.) And, in my personal opinion, it is extremely difficult to monitor air flow at the flow-rates experienced by some of these machines. There is a lot of "stratification" of air flows, and so it's very difficult to measure exactly. I know of some machine that have oxygen analyzers in the exhaust, but I'm told they are difficult to situate for any kind of precision measurement, and because the air flow can vary so much depending on ambient temperature and IGV angle and fuel flows and exhaust flows and exhaust back-pressure and inlet air filter cleanliness, they are deemed not accurate enough for air/fuel control. (They are used primarily to measure the lack of combustible vapors in the exhaust after the unit is shut down, so that it can be started sooner/faster without worry of explosion or fire due to combustible vapors not being properly purged prior to starting.)

There are some good reference books on combustion (gas) turbines available these days, but many of them are more than USD150.00. There are some good used book sellers on the World Wide Web that ship anywhere in the world, and sometimes the book quality is very good (if not, it's usually well documented in the sale listing). Please don't download pirated copies of these books; people make their living from the sale of these books and just because they can be scanned and uploaded to the Ether doesn't mean it's legal to do so nor is it ethical to do so. And that includes downloading pirated books being unethical.

Temperature control (exhaust temperature control--to control firing temperature) does play a part in the fuel control valve opening. But it does so through the turbine control system, not directly to the fuel control valve.

Hope this helps!
 
Thank you very much for a prompt response CSA. It definitely helped :)
This is very Informative. I imagine you have had a fair share of dealing with the controls and automation aspects of gas turbines throughout your career.
I am just looking for guidance as a student who is about to graduate from the Instrumentation Engineering Technologist program. What are some career opportunities that I can explore? Whats lucrative? Where is the industry headed?
 
Zorif,

Yes; I've seen a few turbine controls in my almost 40 years in the business. It's been very satisfying, and as a GE employee for most of those years performing start-ups (commissioning) around the world I was very fortunate, and back then, they paid very well and we had top-notch accommodations and travel. But, that's all changed now, for many reasons--the biggest being that some Managers believe that multi-million dollar machines can be commissioned by non-engineers with little or no training or experience--and Customers will pay top dollar for that kind of service. All the while they are paying these technicians less and less, expecting them to be away from home more and more, and travel and live in less desirable conditions.

The power generation industry is changing--almost daily. Renewables are driving the change, and as ”green hydrogen” becomes a bigger and bigger possibility the opportunities in gas turbine operation and controls are going to be growing as well. There's almost no way (without huge battery installations or pumped hydro storage) that immediate requirements for power can be met when renewables are not producing (lack of sunshine; lack of wind; transmission issues; etc) without gas turbines. So, it's not going away any time soon.

My recommendation is to get hired by a plant with at least one experienced technician who is willing to train you to become his peer. You have to be industrious, motivated and willing to get dirty, as well as work nights and weekends. You have to also be fully conscious of the fact that while some people are very smart and have a lot of experience they could share that not everyone is a good teacher.

You want to work at a site where they have a ”library” of manuals and drawings that are available to you (and others). And you have to be willing to go through those manuals and drawings one by one, make copies for yourself of drawings you deem informative and helpful, and then make notes on those drawings to help improve your understanding and ability to troubleshoot with them--and even to help explain to others and help train them as your knowledge and experience improves. (WARNING: I have been to far too many sites which do not allow, under any circumstances, access to manuals and drawings. Why? That's a subject for another thread, but suffice it to say that some people don't want anyone else to know more or discover more than they know--which hurts everyone on the site. Including the site's ability to make power, and money.)

You need to learn to read P&IDs from different vendors (they're not all alike--some are better than others; some are much worse than most). You need to be able to find time to read and study manuals (I used to do it at night in hotel rooms when I was traveling and not at home). And, you need to recognize and understand that most technical manuals are either written in large part by engineers or by technical writers. Engineers DO NOT make good technical writers, because what is intuitively obvious to them should be intuitively obvious to everyone else so they very often forget to include those choice bits of information. Also, when they are writing a procedure they very often say do this (Step 1), then this (Step 2), then this (Step 3), then this (Step 4), but don't forget to do this (Step 5) before you do Step 3. Yes; that's right. So, you want to read them carefully, and write your own procedure based on this kind of (inexcusable) documentation. And, of course, there are the "intuitively obvious" steps that just don't get written down, because, well, they're so obvious to the author--and therefore to everyone else!--that they don't need to be written down.

Technical writers rarely have any experience with the equipment they are tasked with writing about. They get snippets of information from engineers--the same engineers who often write manuals...--and try to make something useful out of them. Often, they can create nice graphics and beautiful formatting, but the information just isn't all that useful.

You will learn to spot both these types of documents and manuals the more you read and study them. In the absence of any formal training on the equipment, they are all that's available. While you may find some very useful information on the World Wide Web, most of it is tribal knowledge and there are a lot of myths and falsehoods which are propagated for years, decades even, without being challenged.

And that's where you're most important skill is most useful: Critical thinking. You need to have the ability to read something, think it over in your mind, and decide if it passes the "smell test." (If food isn't quite fresh, or worse, it usually smells--bad. Documentation can be the same.) If it doesn't seem complete, or doesn't seem correct, then try to do some more investigation and analysis. Many manufacturers have websites and technical support options that can be extremely helpful but only if you use them.

Power plants are made up of components and devices and sensors from MANY different manufacturers and sources. There's no such thing as a power plant built using equipment from one manufacturer. You will be required to work on equipment from many different manufacturers. You need to understand how the process works in order to be able to troubleshoot and/or repair equipment and restore the operation to normal.

It can be very difficult work, but it can also be very satisfying--and you can earn a good wage as well, especially as your experience and knowledge grows.

Finally, as you mature and gain more knowledge and experience you will be asked more and more to make important decisions about whether or not to shut down a plant to replace or repair a failed or failing equipment. This is risk management, and it pays well but can be very stressful. But it's the natural progression if you continue to rise through the ranks of your peers.

There will always be a need for electricity, the way it's produced is changing, and will continue to change. Gas turbines, because of their ability to start ”quickly” and because of their efficiency are almost guaranteed to be around for decades--only the fuel will change. Some say eventually (some form of) nuclear will replace everything else, but in my personal opinion gas turbines will be the backup to nuclear plants. Always.

It's even possible you will find another area that interests you more. Or, a manufacturer's representative company will hire you to be a salesman/technician, which can also be rewarding and lucrative. You may end up with your own such company. Remember: ”Nothing ventured, nothing gained.” Advancement is not really possible without risk. Not just in the technical world, but also in personal life.

Go forth and prosper!
 
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