Generators running on oil and gas

[etgbccc2003]

Hi guys,

How easy is it for power generators to switch between different feed? Example. Can a generator running on oil today be running on natural gas tomorrow? If yes, is it true that most large power plants have such generators that can switch fuel easily?

Thanks.

 

[ScottyUK]

It can certainly be done - our gas turbines are dual fuel machines, primarily running on natural gas but being able to run on naphtha too. Theoretically we have a third fuel in the form of propane but that hasn't been successfully run more than a couple of times.

There is significantly increased risk of tripping the turbine during fuel transfer because of the number of interacting factors, but it can be done. 'Easy' isn't a word I would use, other than it is a fairly simple sequence to initiate from the operator's perspective. It is challenging for the control system and engine.


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Sometimes I only open my mouth to swap feet...

 

[catserveng]

I have seen a number of gas fired turbine powered generators that used diesel fuel as a backup fuel source, mostly units in the 2 to 10 MW size range. If the control and fuel systems are well designed and maintained we have had no problems with them going between fuels.

On IC or recip engines there are a number of differences between the internal engine parts and accessory items. We rebuild engines from diesel to gas or gas to diesel, but these are farily extensive exercises.

There are some dual fuel or as some are called pilot fueled engines that use a smaller amount of liquid fuel as an ignition source and run natural gas to provide most of the power.

 

[sslobodan]

I am working For GE Jenbacher Distributor in Russia.
We don't have Engines that run on Diesel And Gas, but I'v just finished project where we have Engines running on Natural Gas and Propane. Difference between power output between Natural Gas/ Propane mode is 3/1. The reason for it is that with gas you have butane number (like octane number at oil based fuels) and higher he is the more power you get. Technically speaking it is not impossible to get engine running on oil derivates also as on gas because it is the same principle, but due to a different process it is very expensive, and I don't know any engine running on both (at least on this market). We use a standard diesel engine for backup plant power supply if anything goes wrong with gas engines, and it is only to maintain PLC online and critical controlling systems. It is not for power distribution.

 

[GTstartup]

Most Gas turbines can run also on oil as Catserveeng stated but they are not limited to the 2 to 10MW size stated, there are hundreds that can switch over on line and even many that can run on a mixture of #2 fuel oila dn natural gas. As scotty stated even natural gas and propane is not that rare. As fas as how "easy" is, obviously it has to engineered and commissioned this way. After that, assuming it is commissioned correctly, it's basically a push of a button (or click of a mouse)

 

[TurbineGen]

GTstartup is correct. We have several units in the 70-100 MW range that run on natural gas as well as fuel oil. As ScottyUK said, switching fuels isn't necessarily easy, but assuming the system was designed properly, switching fuels shouldn't be a complicated task. The process can be time consuming on some units. None of ours can switch fuels readily while generating.

Maybe if I try, I can get both feet in my mouth.

 

[Hoxton]

Well it all depends on the size of the power plant!

Conventional stem plants (boiler + steam turbine) can have dual fuel burners in their boilers.

I used to be involved with small (1 to 5MW) gas turbines. They were usually natural gas fuelled, but in UK were usually specified as diesel / natural gas fuel. They would change over under load, and were often started on diesel (to excercise the pumps etc) then change over to gas. This was because gas contracts can be interuptible at the whim of the gas supplier.

For reciprocating engines, the gas fuelled engine came first, invented by Otto (often forgotten - Dr Diesel came later).

Nowadays as catserveng says, we have several variations:

Direct Injection Diesel Engine - liquid fuel only.
Larger (5+ MW) engines can be configured to run on Heavy Fuel Oil (HFO. They usually start / stop on standard diesel fuel to flush out the HFO, which can be solid at 35C. They could run on straigt diesel, but this often costs twice as much as HFO.

Dual fuel engine - This basically a diesel engine, with fuel gas admitted into the inlet manifold, uasing about 10% of the engergy as diesel fuel as a "pilot" to ignite the gas. Not used much in smaller engines now, I think, because of the cost of the diesel fuel, and I understand that they are difficult to get to meet modern exhaust emission limits. Typical application used to be in a sewage works, where the engine was fueled with the methane from the sewage digester. The advantage being, if the gas was not available, the engine could continue to run as a straight diesel engine.

Spark ignition gas engine. This is basically musch like a car's pertrol engine. With a gas mixer in place of the carburettor. Advnmtage: very efficient, relatively low emissions. They can have a gas fuel changeover system (again at a sewage works), but these are fairly uncommon in UK, at least. Modern gas engines are quite hi-tech and have computer management systems - very much like the modern car engines.

Finally - there is what I call a "bi - fuel" engine, which is a standard diesel engine with an add - on kit to enable it to run on gas as well. These seem to take higher levels of liquid fuel as a pilot fuel - about 20% say. Again, may have difficulty in meeting emissions limits and efficiency may be poor.

So as we say, its horses for courses!

Its possible to convert an engine from one type to another (say with the bi-fuel kit) but otherwise it is a major rebuild (pistons, liners, cylinder heads etc etc).

 

[etgbccc2003]

Thanks guys. I've learnt a lot.

 

[alehman]

Can you state the type of prime mover?

Diesel engines can be made dual fuel and can run on a range of oil to gas ratios from 100% oil down to a few %. Some oil is required to maintain ignition. You get less power on gas than oil however.