Newsgroups: sci.chem,sci.environment
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: Vanadium & nickel in crude oil
Date: Sun, 13 Oct 1996 14:57:46 GMT

The original article hasn't arrived here, so i'm responding
to a followup....

charliew@hal-pc.org (charliew) wrote:
>In article <...>,  "Roger W. Faulkner" <rfaulkner@interramp.com> wrote:
>>I read some time ago that some venezuelan crudes have relatively high
>>concentrations of vanadium & nickel. It is more than 100 ppm in the
>>crude, and can be as high as 1% by weigt in residual asphalts.

Almost all crudes have levels of a range of elements, including nickel,
vanadium, sulfur, phosphorus, nitrogen etc. There may be "asphalts"
but they are unlikely to have the same specifications as residual fuel
oils for use in gas turbines, or even residual fuel oils for other
combustion uses.

>>I wonder if these concentrations should be a matter of concern? In
>>particular, some gas turbines use residual oil as fuel (especially in
>>the winter when natural gas is in short supply), and these turbines
>>are often in urban areas.

Well, the presence of vanadium, calcium, lead, sodium
and potassium are of *huge* concern to the owners of gas
turbines, and thus are usually limited by specification. If you are
interested, I suggest you obtain a copy of ASTM D2880-92
"Standard Specification for Gas Turbine Fuel Oils" as it
includes several appendices that discuss the need to control
trace elements.

In it, you will find that the levels of these elements are very
closely controlled because they form compounds that are
extremely corrosive to the turbine blades. The most commonly
used grades for gas turbines are the distillate grades
( 0-GT, 1-GT, 2-GT ) . 3-GT can be either a heavy distillate or
a light residual, and 4-GT is a heavy residual grade, both 3-4
would be used cautiously, probably with additional
specifications, and both would require heating.

For all grades the following recommended maximum limits
apply, however some purchasers can choose to exceed them,
and others may apply more stringent limits - depending on
their turbines.

Sodium + Potassium	 0.5 ppm mass
Calcium    		0.5 ppm mass
Lead			0.5 ppm mass
Vanadium		0.5 ppm mass

The total amount of inorganic material is controlled
by the maximum ash content. Grades 0 - 2 = 0.01%, and
3 = 0.03% mass. Grade 4 has no limit, as it is assumed
the purchaser and supplier will negotiate the important
quality criteria.

In general, the heavier the fraction, the cheaper the energy,
and the higher the concentrations of undesirable elements
( such as S,Na,K,Ca,V). That trend is usually counterbalanced
by the increasing costs of emissions cleanup and turbine
maintenance when moving to heavier fuels, however those
problems reduce if the gas turbine operates in the low
temperature ( below 650C inlet gas temperature ) range.

There are complex interactions between the elements that
make them very undesirable in fuels for gas turbine use.

The sodium and potassium can combine with vanadium to
form corrosive eutectics which melt at temperatures as low
as 566C, and can combine with sulfur in the fuel to yield
sulfates with melting points in the operating temperature
range of many gas turbines. Corrosion is severe in turbines
with inlet gas tempertures above 650C. Some purchasers
may additionally water wash the fuel to reduce these elements.

Calcium can even inhibit the corrosive effects of vanadium, but
it unfortunately forms hardbonded deposits that are not
self-spalling when the turbine is shut down, and which aren't
removed by water washing.

Vanadium can form  low melting compounds ( such as vanadium
pentoxide that melts at 691C ) that induce severe corrosive
attacks on all the high temperature alloys used for gas turbine
blades. If there is sufficient magnesium in the fuel, it will combine
with the vanadium to form higher melting point compounds which
reduce the corrosion rate to an acceptable level. The resulting ash,
however, requires additional cleaning procedures. The ratio of
Mg to V is usually controlled at 3-3.5 by the addition of magnesium
to any fuels with high V. Turbines with inlet gas temperatures below
650C have less corossion problems caused by vanadium.

Sulfur is not usually controlled, as the Na and K are instead.
However, for turbine with waste heat recovery systems, the sulfur
levels may be controlled to prevent cold-end corrosion.

Lead also causes corrosion, and also inhibits the beneficial
effect of magnesium  additives on vanadium, and so is also
controlled.

Nickel can be indirectly controlled by the ash requirement for
the lighter grades, but as nickel is a known human carcinogen,
and nickel carbonyl is extremely toxic, there are strict emissions
limits for all installations burning fuels which contain significant
concentrations of nickel compounds.

Most purchasers will include the acceptable levels of regulated
elements in their fuel specification, often based on recommendations
from turbine manufacturers, and so you need to discuss
your concerns with the owners of the turbines to ascertain what
fuels are being used, and their elemental levels. Your local
environmental regulatory agency may well have an inventory
of emissions for the sites of concern.

                   Bruce Hamilton