Gas Burning Gas Turbines

[Milt]

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.

[SNS3Guppy]

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.

[Spitoon]

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.

[rmm]

A bit more info here guys, plus more from the links at the bottom of the page.

General Electric LM6000 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/General_Electric_LM6000)

[thewatcher]

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.:)

[Iwasoneonce]

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.

[Brian Abraham]

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.

[Milt]

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.

[pzu]

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

PZU - Out of Africa (Retired)

[barit1]

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. :)

[good spark]

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

[west lakes]

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!

[The Flying Pram]

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.

[Milt]

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?

[barit1]

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.

[skiingman]

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.

[RVF750]

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!:ok:

[barit1]

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.

[skiingman]

barit1: Thank you for that helpful reply.

[Matari]

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.

[Solar]

Milt

Most of your questions have been answered by previous posters and in general they are correct.

As has been pointed out our (Solar) units are industrial gas turbines but built along aviation lines as opposed to the heavy industrial units built by the likes of GE, Westinghouse and many others.

I have never heard of a gas turbine of useable power output running at 3000rpm, as has been pointed out they tend to run at very high (relative to recip engines) rpms which is reduced to the correct speed for the frequency required. This is one of the drawbacks with turbines when applied to say an automotive use, they tend to be happier at high rpm and they have a fairly narrow throttle control band.
Our units as used for power generation tend to be of the duel fuel type which is gas (natural) or diesel. They are usually set up to run primarily on gas but in the event of a loss of gas fuel pressure due to a process fault for example they will transfer automatically to liquid to ensure uninterupted power supply.
The duel fuel injectors are designed to accept both fuels.

Solar

[Matari]

Solar:

I have never heard of a gas turbine of useable power output running at 3000rpm, Many of the industrial aeroderivatives operate at either 3000 rpm output shaft speed (for 50hz) or 3600 rpm (for 60hz). They do this through the use of Low Pressure (power) Turbines which are aerodynamically coupled to the High Pressure Turbine.

In many cases, these LPT (power) turbines alleviate the need for large, heavy reduction gearboxes. The GE LM2500's offshore Norway, for example, do not need reduction gearboxes. However, many other aeroderivatives still need a reduction gearbox to get to the generator's required 3000 or 3600 rpm.

[Solar]

Matari

I suppose thats the same princible as turboprops operate under.
In our units we generally use single shaft units for power generation through gearboxes and split shaft trubines (aerodynamic coupling) for other applications like gas compression or water injection pumps.
With the advance of electronic control technology we now also use the split shaft configuration for the larger turbines 10MW plus but even on these units the generator is driven through a gearbox as the power turbine rpm is well in excess of the normal frequencys.

[west lakes]

Whatever solution is used, it's certainly man-sized engineering, and proper noisy, just like it should be


On a visit to Heysham many years ago, they had all 4 of theirs running. Noisy is only part of it, the office block which is about 50m from the gas turbine house was ever so gently vibrating!

[Oilandgasman]

These are very common offshore and burn fuel gas (85% methane,10%ethane, 5% propane/butane mix) or marine diesel when the gas is not available. The diesel is pumped in through separate burners and some of the better machines can run on both fuels at once, and change from one fuel to the other without losing load.The fuel gas delivery pressure is 15.0 barg and is in the gaseous phase. I am unaware of any liquid gas driven turbines, and those who have accidently done this usually end up with a turbine write off. The burners are pepper pots. Once you get them started they run 24/7. Some of these engines, including 24 month overhauls, have been running for 30 years. Avons, RB 211, Olympus, and GE engines are commonly used. Highest power outputs I have seen are of the order of 24 MW. Power is delivered at 3.3KV and transformed down to 440, 240 and 110V.Turbine speed is as mentioned earlier controlled to give 50 or 60Hz. Most Platforms have up to 3 main generators. As well as driving alternators turbines are used offshore to drive centrifugal compressors, high pressure water injection pumps and crude oil pipeline dispatch pumps. Just like the APU on an aircraft we also have 1-2MW turbines for startup, though diesel driven alternators are also used for this purpose.
In the early days the engines were all American and thus 60 HZ. The British shipyards building the infrastructure were initially unaware of this so we had many clocks in the early days which seemed to make the day pass quickly!!

[Milt]

Now to Co-generation and Overflights.

Fascinating to learn of the ways aircraft gas turbines have been adapted to become reliable quick start electrical power generators and that some apparently run 24/7 non stop for yonks.

Am still intrigued with the methods of injecting high pressure gaseous fuel into the burners and how much the engines have to be derated. Didn't the Avons run at 7600 rpm full chat?

Heartell that some installations get maximum efficiency using co-generation. That is the high temperature exhaust gases are passed through heat exchangers to make steam to drive auxilliary turbines. What a masterpiece of gubbinry that must be. Anyone have a diagram?

Then as a TP I have to be concerned about the effects of the final exhaust plumes on a low flying lighty? Navies must have a problem also overflying funnelled exhaust plumes from a ship's gas turbines.

[Turbines]

Fascinating discussion! I stumbled across this forum when I was doing a search for information on the industrial versions of Rolls Royce's Olympus jets..... called an "industrial gas generator" . It's probably well known that they are used for propulsion in some of the British navy ships, and these are installations wherein the hot gas stream from the engine is piped directly into a separate (and big and heavy!) power turbine. The torque from the PT can drive whatever is coupled to it. In my home town, Dresser Rand had a manufacturing plant where they built huge industrial turbines and gas pipeline compressors. They did a lot of work with the Rolls RB211's, which drove a power turbine coupled to a gearbox and thence to a huge gas pipeline compressor. The engine itself was powered from the same natural gas that was in the pipeline. I could hear them running from my house... beautiful noise! I worked with Pratt & Whitney Canada building our little PT6 turbines for fifteen years ..... marvellously simple, rugged and reliable little wonders.... sewing machine motors compared to the big stuff, of course. Some of those were the ST6 version, which were the industrial version, used for (small) applications much like the big units in these discussions.
So here's my question:
I was asked by a friend to take a look at some turbine parts near my home town, which turned out to be leftovers from a stillborn electrical power generation project. A bit of research showed it to be a Rolls Royce Olympus installation, driving a Rolls Royce SK20 power turbine, which was coupled to a 26 MW 50 cycle electrical generator. (origin was out of North America.... we run all 60 HZ here) There is a generous stock of new spare bearings, combustors, fuel nozzles, temperature probes, etc. with it, but the parts manuals and technical drawings, etc. all went astray when the project ground to a halt. I noted posts from a number of individuals in this thread who seemed well experienced with these aeroderivative installations, and am hoping that one of them might be able to refer me to someone working with an Olympus installation who could help me locate the parts breakdowns I need to identify and sort these items. Any leads would be much appreciated.... maybe I can get this stuff to someone who needs it!
As a side note to the turbines, the concept of aeroderivative power sources existed well before the advent of turbines of course...... In the eighties, the town of Foremost, down near our Alberta/Montana border, was a hotbed of tractor-pulling activity, and one group had an Allison V1710 in about a '39 Chev 1 or 2 ton truck chassis for the pulls. (there are truck as well as tractor classes).
I owned an automotive speed shop at the time, and I built several engines for the participants, and wanted to build a pulling tractor myself, so I began hunting for a suitable powerplant. As our area was home to part of the Commonwealth Forces air training program during WWII, there was still a considerable amount of surplus aviation materiel around, and it wasn't long before I found a Rolls Royce Merlin engine, then another.
Then I hit the jackpot!
It seems that a gentleman who had been a flight engineer with the RAF during WWII had gone to work for Dresser Industries after the war, in the oilfield servicing industry. At the time, the huge triplex pumps used for pumping drilling mud down into the oil bearing rock formations (to fracture the rock and open up passages for the oil flow) required a powerplant the size (and unfortunately the weight! ) of a locomotive engine. Bringing equipment of that weight into some of the oilfields over muskeg areas was a tricky business. The gent I am referring to had a better idea...."why don't we buy up some of these war surplus Merlin engines...... they're up in the 1600 horsepower range like a locomotive diesel...... and use them to run the pumps???" And they did, with resounding success. After that when Dresser was on wellsites with their fracturing rigs, it sounded like Bomber Command was flying over the site! As time went on, they accumulated a lot of used equipment at their storage site south of Edmonton, and I was given a bunch of the Merlin engines... what a find! Alas, my project was not to be....... I ended up selling the engines to one of the unlimited hydroplane teams, where they doubtless provided lots of thrills and noise.
Ahh..... the love of machinery! Anyways, if anyone out there has a clue where I can get my hands on some of the paperwork I need, drop me a reply or a line...... thanks!!

[barit1]

One of my early jobs (late 60s) involved an LM1500 aeroderivative of the J79, upwards of 15K shp and light enough to be airlifted (in modules) to a remote natural gas pipeline pumping station. It ran on NG of course. :ok:

[pzu]

Check your PM's

PZU - Out of Africa (Retired)

[airfoilmod]

Years ago I did some work for Cal-Pine, a small Power generating firm located in Antioch, California. Having seen the powerplants before at MOC UAL in SFO, I recognized them right off. JT8-D's. What a treat working in that sound and smell. I can't recall if they had 4 GU's or cascaded the engines, but I have a possible suggestion for mobile HP.

You are of course familiar with the Chev. 454 RAT. There is a new engine available for Street driving based on that architecture. It is all Aluminum, burns pump Fuel, weighs five Hundred Pounds, and develops 2200 HP.

821 CID, 3 HP per CI. Impressive.

AF

[ChristiaanJ]

I have never heard of a gas turbine of useable power output running at 3000rpm...Matari already more or less answered that.

The GE LM6000 quoted earlier produces over 40MW, which is a lot of useable power in my book. The LP turbine section of that one runs at 3600 rpm, so a 3000 rpm turbine is perfectctly feasible also.

When I tried to read up on the subject some time ago, I got the impression you have:
- twin-spools like the LM6000 with the LP section already running at 3600 rpm, so you can take power directly off the shaft (front or back), without a gearbox,
- nearly-original jet engines such as the Olympus, with a large box with a free turbine bolted on the back, which then drives a generator at 3600 or 3000 rpm directly, or something like a ship's propellor shaft through a gear box,
- smaller single-shaft engines with added turbine stages (cf. turboprop engines) that normally will need a gearbox.

CJ

[Turbines]

Sorry, pzu....... what do you mean by PM's ?

Thanks, Turbines

[pzu]

Check top right of this page and you'll see a box which lists amongst other things Private Messages

Double click & you should have a PM from me

PZU - Out of Africa (Retired)

[Matari]

Airfoilmod:

Having seen the powerplants before at MOC UAL in SFO, I recognized them right off.Did you happen to see the LM2500 at UAL SFO? As I said earlier, that machine is a derivative of the CF-6/TF39 gas turbine that powered the C-5A.

I believe UAL's LM2500 is used in a "cogeneration" application where heat from the exhaust is routed to a heat recovery steam generator, which produces steam for heating or other processes.

It is a remarkably reliable, and thermally-efficienct system.

[ChristiaanJ]

It is a remarkably reliable, and thermally-efficient system.Interesting remark, in a way.

Run them at the optimum rpm, optimum air flow, optimum fuel flow and EGT, maintain them properly, and gas turbines will last nearly forever.

Just keep them away from bird strikes, TOGA "slams" and all those other things pilots will subject them to....

CJ

[Matari]

ChristiaanJ:

Run them at the optimum rpm, optimum air flow, optimum fuel flow and EGT, maintain them properly, and gas turbines will last nearly forever.You're right. Typical (modern generation) natural gas fired powerplants run 25,000 hours between hot section inspections, and 50,000 hours between major overhauls. Regular maintenance of air inlet filtration systems keeps the threat of compressor damage low.

The biggest killer of land or marine gas turbines is fuel quality. Industrial gas turbine operators rarely have the strict fuel specifications and handling procedures of airlines...and no oversight from a regulator authority like the JAA/CAA/FAA. Therefore poor fuel often gets downstream into the turbine.

This is true with diesel (DF2) but also with natural gas fuel. Slugs of condensate, traces of vanadium, sodium, etc. can destroy a hot section very quickly. Operators who fail to invest up front in good fuel sourcing, maintenance practices and fuel filtration systems regret it not long after the units are commissioned.

[barit1]

I believe UAL's LM2500 is used in a "cogeneration" application where heat from the exhaust is routed to a heat recovery steam generator, which produces steam for heating or other processes.

Correct, and the excess electrical power generated is sold back the the utility grid at a nice profit.

BTW, the LM2500 burns Jet-A from the test cell ("bench") fuel farm - I once had to plan my engine tests around the fuel burn rate of the LM2500 so we avoided running on fumes! :eek:

[barit1]

Another variant:

GE Energy lands $200M UAE deal - The Business Review (Albany): (http://albany.bizjournals.com/albany/stories/2009/04/06/daily7.html?ana=yfcpc)

[ChristiaanJ]

barit1,
Stupid question, really, but in the context I presume Abu Dabi has large bauxite deposits?

CJ

[pzu]

"barit1,
Stupid question, really, but in the context I presume Abu DHabi has large bauxite deposits?

CJ"

NO, but it has access to cheap gas and this plus GE Turbines = CHEAP Electricity & thus reasonably priced Aluminium

PZU - Out of Africa (Retired)

[barit1]

PZU has it right.

UAE has trillions of BTUs of natural gas, which is expensive to liquify and transport - thus a limited market.

So their strategy is:

1) Buy bauxite on the open market

2) Generate lots of cheap electricity using otherwise-wasted gas

3) Refine bauxite to high-purity ingots (an energy-intensive process)

4) Sell ingots on the open market

Dubal, just up the coast from Abu Dhabi, has been doing this for 30+ years.

Remember this next time you buy aluminum window frames, or a Cessna. :}