9 replies to this topic

[sheiko]

Hi,
NFPA (National Fire Protection Association) distinguishes flammable liquids from combustible liquids with the flash point:
- combustibles have flash point > 37.8 deg C
- flammables have flash point < 37.8 deg C
Is it acceptable to use a flammable mixture as a combustible in gas turbine burners for example?
I am asking because I have noticed this practice in an oil refinery.
Any normative reference, litterature will be welcome!

Edited by sheiko, 25 March 2012 - 09:45 PM.

[ankur2061]

Sheiko,

Crude Oil, Naphtha and Motor Gasoline are the only commercial liquid fuels that have a flash point below 37.8°C. Is your fuel one of these? Kerosene, Heavy Fuel Oils (e.g. #6) and Diesel are all considered combustibles since their flash point is above 37.8°C.

The table in the link below provides a list of flammables and combustibles as well as their flash points.

http://books.google....stibles&f=false

Additionally, GE does supply gas turbines fired using liquid Naphtha which falls in the flammable category. References provided in the link below may help:

http://www.eng-tips.....cfm?qid=221401

Regards,
Ankur.

[sheiko]

Thanks Ankur,
The refinery plan to burn light naphtha in gas turbines.

Edited by sheiko, 03 April 2012 - 07:38 PM.

[sheiko]

The danger I see with the practice of burning flammable liquids (such as gasoline) in industrial gas turbine, is that flash point is well below ambiant temperature (around -40°c for gasoline).
Is it recommendable to burn it as if it was a combustible (that is a liquid that needs to be heated to start releasing its flammable vapors)?

[kkala]

1. Once we explored the possibility of an existing gas turbine (few MW) to change its fuel from diesel to LPG (1997). The supplier clarified that the turbine could burn gaseous propane at practically same efficiency and without modification, but not gaseous butane.
This might be related to higher antiknocking ability of propane (commercial market has internal combustion engines - with spark plug - burning natural gas or propane, but not butane). However no evidence was found.
2. A heavy basic load gas turbine burns natural gas, and backup fuel is diesel. This diesel has specifications stricter than automotive diesel.
3. Above actual observations, along with http://www.eng-tips...cfm?qid=194171 seem to create some evidence for the following.
α. A gas turbine should burn the fuel specified for it, otherwise there may be loss of efficiency or even some damage. If a change of fuel feed is planned, ask the Supplier well in advance, usually being very willing to advise consequences.
β. Gas turbines can burn a wide range of fuels, as indicated in Fig 1 of http://www.ge-energ...te%20Paper.pdf . But a specific gas turbine cannot burn all fuels of Fig 1.
γ. Some parts of gas turbine are delicate. It is not easy to predict suitability of a new fuel to it, at least by inexperienced (like me). Heating value, Wobbe index, composition, other parameters, seem to play a role.
4. Comments or different experiences welcomed, for a better view of the topic.

Edited by kkala, 05 April 2012 - 04:43 PM.

[S.AHMAD]

1. Only vendor can confirm the suitability of naphtha in place of diesel.
2. The concern with naphtha/gasoline is for storage and handling not for combustion in a turbine since the combustion is taking place in the combustion chamber and the one that drives the turbine blade is the hot exhaust gas.
3. Combustion of diesel requires the diesel to be atomized but it is not necessary for naphtha/gasoline this may require different type of burner. Only vendor can confirm the burner suitability.
4. Theoretically, if the turbine is designed to burn diesel and gas, the turbine should be able to take any fuel in between these two.

[Sadananda Konchady]

Here is an example where ethanol has been used in a gas turbine. Please see the weblink at:
http://www.ecomagina...ed-for-ethanol/

[kkala]

S.AHMAD, concerning point 4 of post No 6, I could not understand why the specific gas turbine of point 1 (post No 5) was able to burn propane but not butane. Contrary to propane, butane has a poor methane number (characterizing antiknocking quality for the gas, as octane number for petrol). This excludes butane from commercial internal combustion engines (with spark plug). No evidence was found that butane was excluded from the specific turbine for the same reason. Yet other gas turbines can burn butane, as indicated in Fig 1 of the last link, post No 5 ( http://www.ge-energ...te%20Paper.pdf ). Same Fig 1 indicates gas turbines to burn ethanol, as also mentioned in post No 7. But a specific gas turbine can burn a limited range of fuels reported in Fig 1.
As General Electric says in the mentioned link, "Gas turbines have demonstrated distinctive capabilities to accept a wide variety of fuels" and "The success has been possible by introducing incremental enhancements", apparently not to all turbine models. So advice from Supplier had better be requested, if a fuel out of specs (for the specific turbine) has to be used.
Note: Probably every "circle" on Fig 1 represents a specific gas turbine, only colleagues from General Electric could give clarifications.

Edited by kkala, 06 April 2012 - 07:23 AM.

[S.AHMAD]

Kkala
1. I am in the same boat as you that I do not understand why the turbine cannot use C4 but can burn C3 since the main different between the two is the molecular weight and of course the specific heat of combustion. However, for gas turbine, octane number does not play an important role. It is only significant in reciprocating engine.
2. This is probably due to different burner design. For a specific burner, there is specific range of fuel that can burn efficiently.
3. The best person to clarify would be the manufacturer/vendor.

Edited by S.AHMAD, 08 April 2012 - 07:57 PM.

[kkala]

Yes, we have to ask supplier for a fuel not specified for a specific turbine. Probably "Gas turbine combustion: alternative fuels and emissions" by A. H. Lefebure can give some insight, http://www.cheresour...-starting-point '> http://www.cheresour...-starting-point , if we had available time.
Siemens report on gas turbine fuels can be seen at http://www.energy.si...Flexibility.pdf '> http://www.energy.si...Flexibility.pdf .
Note: "knocking" index concerning internal combustion engines is
methane number for gaseous fuels
octane number for petrol
cetane number for diesel.