Gas Burning Gas Turbines
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Gas Burning Gas Turbines
How does one inject enough gaseous fuel into a ground based gas turbine to make it run at high power? Would one have regular aeroengine liquid fuel igniters to fire it up.?
Down Under we are seeing many installations having gas burning gas turbines powering medium sized electrical power generators with some fuelled by diesel and most by gaseous natural gas or coal seam gas or even methane. Some run at only 3000 RPM to facilitate direct drive to alternators.
Just can't get my head around how huge volumes of gas find their way into the burners. Perhaps the gas is liquified first.
Down Under we are seeing many installations having gas burning gas turbines powering medium sized electrical power generators with some fuelled by diesel and most by gaseous natural gas or coal seam gas or even methane. Some run at only 3000 RPM to facilitate direct drive to alternators.
Just can't get my head around how huge volumes of gas find their way into the burners. Perhaps the gas is liquified first.
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I think you'll find those gas generators are operating at a considerably higher RPM than 3,000. A reduction drive may be used for the generator, but 3,000 rpm is a little low for a turbine engine. Typically a turbine engine will be turning 18,000 to 30,000 rpm.
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Whilst I cannot offer any thoughts on the turbine speed, are you sure the turbine is being turned directly by the burned gas? I have understood that in a gas powered electricity generating unit (which is what I assume you're talking about) the gas is used to heat water or some other liquid which is then used to drive the turbine. I'm not an engineer so I bow to the far greater knowledge that others have and may offer you but I believe this is more efficient that driving the turbine by heated gas because of the energy that can be transported by a liquid for any given volume.
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A bit more info here guys, plus more from the links at the bottom of the page.
General Electric LM6000 - Wikipedia, the free encyclopedia
General Electric LM6000 - Wikipedia, the free encyclopedia
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Hello
Let's take as example a gas fired turbine used for electricity. In the turbine enter air and fuel (gas) . the turbine + the generator reach 3000 rpm (3600 valid for Canada and USA) and the extra energy obtained from fuel burning will not increase the number of rotations over 3000 (3600) but will increase the MW produced. On the other side, the energy of burnt gases after they have been used in the gas turbine it can be used entering in HRSG ( heat recovery steam generator) where it is produced steam ( used for producing electric/thermal energy).
I hope I was clear enough.
I hope I was clear enough.
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A gas turbine engine will run on anything that is combustible, e.g., coal dust.
However the length of time it will run for is dependent on the lubrication that is provided to the bearings of the engine.
However the length of time it will run for is dependent on the lubrication that is provided to the bearings of the engine.
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Milt, I know you are more than familiar with the Avon and thats what used in our gas plant to run things - off gas. Even an industrialised version of the Olympus does similar work, and RB211. No liquidifcation, straight gas.
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Brian
Thanks for the comments. Didn't know you had an Avon doing its thing at Sale, presumably linked to a generator via some extra stages of turbine at the tail pipe.
But how do you get the gas fuel into an Avon? The avtur fuel nozzles would be useless. What gas feed pressure do you need and what is its operating RPM and EGT.
A few years ago I found a couple of Avons, one ex Canberra and one ex Sabre, back of a workshop at Richmond NSW. Both less auxilliary gearboxes so no starters. Ethusiasm had one running using a truck starter motor attached to the gearbox drive shaft and a burning oxy torch poked into a hole where an igniter had been removed. Wish I had had a camera handy.
Perhaps I once flew your Avon.
Thanks for the comments. Didn't know you had an Avon doing its thing at Sale, presumably linked to a generator via some extra stages of turbine at the tail pipe.
But how do you get the gas fuel into an Avon? The avtur fuel nozzles would be useless. What gas feed pressure do you need and what is its operating RPM and EGT.
A few years ago I found a couple of Avons, one ex Canberra and one ex Sabre, back of a workshop at Richmond NSW. Both less auxilliary gearboxes so no starters. Ethusiasm had one running using a truck starter motor attached to the gearbox drive shaft and a burning oxy torch poked into a hole where an igniter had been removed. Wish I had had a camera handy.
Perhaps I once flew your Avon.
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Industrial Gas Turbines
The majority of Industrial gas turbines today are based on Aviation gas turbines but with heavy duty auxilliaries and where practical Waste Heat Recovery to increase efficiency
A large number of these engines RUN yes RUN for thousands of hours at a stretch
Typical Machines being PW & GE in various guises, RR Olympus and Avon - in past have used Orenda (Canadian Avon? derivative, were they on the CF-100) and Natco-Viking Norwegian derivative of older PW types
In smaller engines the Solar Range (Centaur & Saturn) are industrial turbines built on "aviation lines"
Then there are the RUSTON (now EGT?) turbines - to put it simply they were "CLYDE built"
There are undoubtedly other manufacturers
Fuels for industrial use range from Town Gas to various Hydrocarbon Gas Streams (sweet & sour), Kerosine ((Avtur if affordable), Diesel, Marine Diesel, Crude Oil (sweet & Sour) and as previously mentioned some form of fluidised coal (Dust) - in many cases machines can be set to run dual fuel normally Gas/Diesel or Diesel/Crude Oil
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A large number of these engines RUN yes RUN for thousands of hours at a stretch
Typical Machines being PW & GE in various guises, RR Olympus and Avon - in past have used Orenda (Canadian Avon? derivative, were they on the CF-100) and Natco-Viking Norwegian derivative of older PW types
In smaller engines the Solar Range (Centaur & Saturn) are industrial turbines built on "aviation lines"
Then there are the RUSTON (now EGT?) turbines - to put it simply they were "CLYDE built"
There are undoubtedly other manufacturers
Fuels for industrial use range from Town Gas to various Hydrocarbon Gas Streams (sweet & sour), Kerosine ((Avtur if affordable), Diesel, Marine Diesel, Crude Oil (sweet & Sour) and as previously mentioned some form of fluidised coal (Dust) - in many cases machines can be set to run dual fuel normally Gas/Diesel or Diesel/Crude Oil
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The power turbine RPM depends on the frequency of your electrical grid.
50 hz grid = 3000 rpm
60 hz grid = 3600 rpm
I once heard of a unit powered by methane recovered from a landfill. As long as a pump is available to boost the gas up to a pressure higher than the engine's compressor discharge pressure, and enough BTU's can be had, and you keep it lubricated, it will run nearly forever.
50 hz grid = 3000 rpm
60 hz grid = 3600 rpm
I once heard of a unit powered by methane recovered from a landfill. As long as a pump is available to boost the gas up to a pressure higher than the engine's compressor discharge pressure, and enough BTU's can be had, and you keep it lubricated, it will run nearly forever.
i stripped out some ex 707 jt4s a few years ago, they where off to the states to be converted for installation in isocontainers for use on oil rigs, its a good way to use the burnoff gas
gs
gs
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I have seen (and heard) the installations at a couple of UK power station, used for "peak lopping" and as emergency generators
Fiddlers Ferry Warrington - 4x 2 pairs of RR Avons powering uncoupled turbine/generator sets. The two exhausts are combined to power the turbine
Heysham A/B - 4 RR Olympus each with it's own turbine/generator again uncoupled.
As related, many years ago, on a training course the engines could be swapped between aircraft and this use!
Fiddlers Ferry Warrington - 4x 2 pairs of RR Avons powering uncoupled turbine/generator sets. The two exhausts are combined to power the turbine
Heysham A/B - 4 RR Olympus each with it's own turbine/generator again uncoupled.
As related, many years ago, on a training course the engines could be swapped between aircraft and this use!
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Norwich U.K. used to have some gas turbine powered generators (RR Avons?) in its power station. They were only used for short term high demand requirements IIRC. And one of the companies at a local North Sea Gas installation get their AC supply from an Avon powered 3.75 MW set, fuelled off the incoming gas. This runs 24/7 all year, and is only shut down when the entire plant is closed for maintenance during the summer low demand period.
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Should I conclude that the gas fired Avon engines being used for electrical power generation using additional turbine stages at the tail pipe are able to have enough high pressure gas pushed through their existing burner nozzles to run them at medium RPM?
Otherwise there would need to be extensive design changes made to the combustion cans.
Can someone please describe the modifications necessary to an Avon turbo jet to convert it to burn gaseous fuel?
Otherwise there would need to be extensive design changes made to the combustion cans.
Can someone please describe the modifications necessary to an Avon turbo jet to convert it to burn gaseous fuel?
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The basic process is this - I assume it applies to Avon or any other engine:
The jet engine in its normal aeronautical usage is a gas turbine designed to deliver hot gas at about 25 psig (1.8-1.9 bars) to an exhaust nozzle, where it is accelerated to produce thrust.
For power generation use, the exhaust nozzle is cut off and replaced with a power recovery turbine, designed to crank a lot of torque into a generator at 3000 or 3600 rpm. It's mechanically independent of the Avon.
When a high-bypass turbofan is so employed, the job is a little easier: The existing low pressure turbine can do the job, once the fan is removed.
The jet engine in its normal aeronautical usage is a gas turbine designed to deliver hot gas at about 25 psig (1.8-1.9 bars) to an exhaust nozzle, where it is accelerated to produce thrust.
For power generation use, the exhaust nozzle is cut off and replaced with a power recovery turbine, designed to crank a lot of torque into a generator at 3000 or 3600 rpm. It's mechanically independent of the Avon.
When a high-bypass turbofan is so employed, the job is a little easier: The existing low pressure turbine can do the job, once the fan is removed.
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high pressure gas pushed through their existing burner nozzles
I've been following this thread and hoping someone could answer your question. I'm unfamiliar with the oil/gas/electricity generation industries, so I wonder how much energy must be spent to compress the natural gas enough to make this work. Don't really know what pressures the NG comes out of the ground at, is processed at, or normally transported in industrial scales at.
At 1 bar, a liter of gas contains about two orders of magnitude less energy than a liter of Jet A, so I suspect to achieve similar power output a) the fuel nozzles are quite a bit larger and b) the delivery pressures are on the order of 10-100bar.
It would be wonderful if someone in the know could comment on how this dramatic change in fuel is achieved and perhaps what the energy economics from well to turbine are compared to liquid fuels. They must be favorable: these things are hugely popular.
I've been following this thread and hoping someone could answer your question. I'm unfamiliar with the oil/gas/electricity generation industries, so I wonder how much energy must be spent to compress the natural gas enough to make this work. Don't really know what pressures the NG comes out of the ground at, is processed at, or normally transported in industrial scales at.
At 1 bar, a liter of gas contains about two orders of magnitude less energy than a liter of Jet A, so I suspect to achieve similar power output a) the fuel nozzles are quite a bit larger and b) the delivery pressures are on the order of 10-100bar.
It would be wonderful if someone in the know could comment on how this dramatic change in fuel is achieved and perhaps what the energy economics from well to turbine are compared to liquid fuels. They must be favorable: these things are hugely popular.
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This thing isn't rocket science. The Turbine will run if sufficient hot gas is generated. The fuel control units vary fuel flow, either gas of liquid, rdepending on throttle or governer unit. The critical thing is airflow, as the turbine blades and pressure levels are RPM dependent. As long as it is in the operating range, it'll run fine.
The liquid original fuel will be sprayed in a fine mist, so mixes well with the incoming air into the combustor and maintain the flame front. The Gas should do the same and though you would logically expect nozzles to be altered, like you'd change jets on a boiler to change fuel types, it ain't necessarily so.
The Hastle of converting aero gas turbines by gearing shafts is not worth it. Free turbines or power recovery(free) turbines coupled to a variable constant speed output gearbox is straight forward, used frequently on AC generators for years anyway.
The Avon, olympus or whatever is simply being used as a gas generator. Even taking a High Bypass turbofan, you'd either unbolt the fan and add an adaptor so the bypass acted as a turboshaft, which would be more elegant as the throttle would work as a governor to maintain constant RPM of the N1.
Whatever solution is used, it's certainly man-sized engineering, and proper noisy, just like it should be!
The liquid original fuel will be sprayed in a fine mist, so mixes well with the incoming air into the combustor and maintain the flame front. The Gas should do the same and though you would logically expect nozzles to be altered, like you'd change jets on a boiler to change fuel types, it ain't necessarily so.
The Hastle of converting aero gas turbines by gearing shafts is not worth it. Free turbines or power recovery(free) turbines coupled to a variable constant speed output gearbox is straight forward, used frequently on AC generators for years anyway.
The Avon, olympus or whatever is simply being used as a gas generator. Even taking a High Bypass turbofan, you'd either unbolt the fan and add an adaptor so the bypass acted as a turboshaft, which would be more elegant as the throttle would work as a governor to maintain constant RPM of the N1.
Whatever solution is used, it's certainly man-sized engineering, and proper noisy, just like it should be!
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The power generating stations usually have natural gas piped in at 800 psi (50 bar IIRC) so further compression is unnecessary. The metering valve is rather large compared to a Jet-A unit, as is the plumbing and the fuel nozzles - but otherwise it operates about the same.
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Aeroderivative gas turbines have been used in industrial power generation and offshore / onshore pipeline gas compression for decades. They use diesel (DF2) or natural gas. Some of the more common gas turbine (or more accurately, as someone mentioned above, gas generator) equivalents are:
Aircraft Model = Industrial Model and MW output
Allison T56 = Allison 501/517/601 3-10MW
GE CF6-6 = GELM2500/+ 25-30MW
GE CF6-50 = GE LM5000 38MW
GE CF6-80 = GE LM6000 45MW
Pratt & Whitney J75/JT4 = FT/GG 4 15MW
Pratt & Whitney JT8 = FT/GG 8 30MW
Rolls Royce Avon = RR Avon 10MW
Rolls Royce Olympus = RR Olympus 20MW
Rolls Royce RB21 = RR RB211 25-30MW
Rolls Royce Trent = RR Trent 50MW
Roughly speaking, 1MW is enough to power a city of 1000 people. 40MW, 40,000 people, etc.
Aeroderivatives have many advantages, such as high efficiency, high power v. weight/footprint which is important for offshore and marine applications, and quick start/stop with no maintenance penalty for power grid peak shaving applications.
Disadvantages over more conventional "heavy frame" type turbines are relatively expensive capital costs (offset by lower fuel burn), stricter fuel quality (contrary to previous post, they can't just burn "anything", and the specs are pretty tight due to the cooling hole technology in the hot section).
Aeroderivatives consist of essentially the "core" gas generator, without the high bypass fan. For example, a GE LM2500 is about 90% common with its aircraft cousin.
In the late 1970's, the UK oil & gas offshore sector tended to use the Rolls Royce technology, while the Norwegian sector chose mostly the GE LM2500. Today more than 100 GE gas turbines are used offshore Norway for power production and gas compression.
Aircraft Model = Industrial Model and MW output
Allison T56 = Allison 501/517/601 3-10MW
GE CF6-6 = GELM2500/+ 25-30MW
GE CF6-50 = GE LM5000 38MW
GE CF6-80 = GE LM6000 45MW
Pratt & Whitney J75/JT4 = FT/GG 4 15MW
Pratt & Whitney JT8 = FT/GG 8 30MW
Rolls Royce Avon = RR Avon 10MW
Rolls Royce Olympus = RR Olympus 20MW
Rolls Royce RB21 = RR RB211 25-30MW
Rolls Royce Trent = RR Trent 50MW
Roughly speaking, 1MW is enough to power a city of 1000 people. 40MW, 40,000 people, etc.
Aeroderivatives have many advantages, such as high efficiency, high power v. weight/footprint which is important for offshore and marine applications, and quick start/stop with no maintenance penalty for power grid peak shaving applications.
Disadvantages over more conventional "heavy frame" type turbines are relatively expensive capital costs (offset by lower fuel burn), stricter fuel quality (contrary to previous post, they can't just burn "anything", and the specs are pretty tight due to the cooling hole technology in the hot section).
Aeroderivatives consist of essentially the "core" gas generator, without the high bypass fan. For example, a GE LM2500 is about 90% common with its aircraft cousin.
In the late 1970's, the UK oil & gas offshore sector tended to use the Rolls Royce technology, while the Norwegian sector chose mostly the GE LM2500. Today more than 100 GE gas turbines are used offshore Norway for power production and gas compression.