5 replies to this topic

[sheiko]

Hi,

In my refinery, we mix 45% jet + 55% medium gasoil (320-350°C) to fabricate what we call "combustion gasoil" for the cogenerations.

The mains constraints are:
- maximum viscosity at combustion chamber entrance:6 cst @ 40°C.
- Maximum water content: 0.1% vol.
- Maximum sulfur: 0.8 % wt.

Now I want to propose the following: to use Light Naphta (light gasoline leaving the gasoline splitter) instead of Jet, because light naphta is less valuable than Jet. I don't know why Jet is actually used instead of Light Naphta.

I would like to know if you have ever tried this? And what it your opinion? Do you think it is "thermodynamically" feasible?...

Thanks in advance

Edited by sheiko, 01 August 2011 - 07:28 PM.

[breizh]

Hi Sheiko ,

Did you try in your lab? What do you mean by thermodynamically feasible ?
I've no experience about your products .

Breizh

[sheiko]

Hi Sheiko ,

Did you try in your lab? What do you mean by thermodynamically feasible ?
I've no experience about your products .

Breizh

1/ Not yet. I am asking for feedback in case some of you would already have dealt with this question.

2/ I meant, even though light naphta and gasoil are hydrocarbons, have you ever experienced problems when mixing them?

[Profe]

Hi Sheiko
About your question, the ligth Naptha is more volatile and his flash point is lower than than Kero/Jet cut, also the SG and IBP of Naptha is lower than Jet, the naptha has a lower calorific power.

I Think that helps you.

Good luck.

Fausto

[Technical Bard]

2/ I meant, even though light naphta and gasoil are hydrocarbons, have you ever experienced problems when mixing them?

Light naphtha is often simply pentane and hexane, as these are fractionated for use as chemical feeds or to be feed to a isomerization unit to improve octane number for gasoline. Depending on the properties (aromaticity) of your heavy gas oil and how cleanly it was fractionated from residue (CCR / C5 insolubles) could mean that there are instabilities between these streams; the result could be precipitated asphaltenes.


I would recommend you do significant lab testing of such a mixture for both stability, physical and combustion properties before attempting this at any kind of scale.

[kkala]

“Combustion gas oil” is assumed to be burnt in gas turbines (GTs) to produce electricity and steam (cogeneration). Mentioned GT “constraints” for viscosity, moisture, sulphur, could be kept when jet fuel is replaced with light naphtha (this can be verified in the lab, yet no problem is generally anticipated). Having no operating experience and limited theoretical knowledge, I can only share thoughts as below:

1. GTs met in earlier studies were able to burn following fuels , without change in efficiency.
-Natural gas, as well as diesel as backup (32 MW)
- Diesel or commercial propane (not butane or LPG, 18 MW).
-Natural gas, as well as diesel as backup (380 MW). Supplier had placed diesel specifications (concerning its chemical compounds) stricter than commercial diesel (due to risk of plugged injection into burning chambers), but these were alleviated by pointing out that diesel was for backup (1-2 days/year).
2. Consequently a single gas turbine can be flexible enough to burn a variety of fuels from natural gas to diesel. GTs are not like internal combustion engines, where a change in fuel composition causes change in its cetane (or octane, or methane) number, thus risk of knocking. In this sense, substituting jet fuel with naphtha in their feeding fuel does not anticipate a problem, at least at first look.
Jet fuel specifications require not to solidify in -50 or -60 oC ; this is not of concern for GTs operating at grade at ambient temperatures.
However possibility for any precipitate, resulting from mixing gas oil with naphtha, should be excluded (as pointed out by Technical Bard) by laboratory tests. Contrary to gasoline blender, naphtha added to diesel blender is of unknown consequences to me, concerning potential precipitates (that would plug the GT injection).
3. Some reserve is indicated, since some points of gas turbine operation have not been understood (e.g. why mentioned 18 MW turbine could not burn butane?). I would first check fuel specification in GT manual; then ask advice from GT supplier”. Efficiency may be retained, but some other factor could create need of more frequent maintenance, thus reducing operational availability. It is probable that even supplier does not know potential problems in detail, you will know them (if any) by long term operation. A trial may be worth while, unless warned about a specific problem related to naphtha.