U.S. patent number 3,907,134 [Application Number 05/446,302] was granted by the patent office on 1975-09-23 for water-free liquid fuel slurry and method of producing same.
This patent grant is currently assigned to Carbonoyl Company. Invention is credited to Grant W. Metzger.
United States Patent |
3,907,134 |
Metzger |
September 23, 1975 |
Water-free liquid fuel slurry and method of producing same
Abstract
A substantially water-free, high solid content, stable and
combustible fuel slurry and the method for producing the same are
disclosed. The slurry includes about 5 to about 50 weight percent
of solid particulate carbonaceous material, such as powdered coal,
with substantially the entire balance of the slurry being comprised
of liquid hydrocarbon fuel, such as Bunker C (No. 6) fuel oil, a
slurry suspension stabilizing agent and a slurry viscosity reducing
agent. The slurry viscosity reducing agent is preferably a
detergent, which is added in an amount to reduce the viscosity of
the slurry to a pumpable and flowable level without the addition of
substantial quantities of water. In the process, the addition of
detergent as the slurry viscosity reducing agent prevents formation
of a gel during storage of the slurry.
Inventors: |
Metzger; Grant W. (San Andreas,
CA) |
Assignee: |
Carbonoyl Company (San
Francisco, CA)
|
Family
ID: |
23772087 |
Appl.
No.: |
05/446,302 |
Filed: |
February 27, 1974 |
Current U.S.
Class: |
44/281;
406/49 |
Current CPC
Class: |
C10L
1/322 (20130101) |
Current International
Class: |
C10L
1/32 (20060101); C10L 001/32 () |
Field of
Search: |
;44/51
;302/14,15,16,66 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Vaughn; I.
Claims
What is claimed is:
1. A substantially water-free, high solids content, stable and
combustible fuel slurry comprising:
about 5 to about 50 weight percent of a solid particulate
carbonaceous material of a size below about 200 mesh, about 94 to
about 49 weight percent of a liquid hydrocarbon fuel, a minor
slurry suspension stabilizing amount of starch, and a minor
non-aqueous slurry viscosity reducing amount of soap and being
present in an amount sufficient to maintain said slurry at a
viscosity below about 300 seconds Saybolt Universal when said
slurry is at a temperature of about 175.degree.F, said liquid
hydrocarbon fuel containing said starch and said slurry viscosity
reducing agent and being thoroughly admixed with the particles of
said carbonaceous material.
2. A slurry as defined in claim 1 wherein,
said slurry viscosity reducing agent is present in an amount of
about 0.10 to about 0.50 weight percent, and said starch is present
in an amount of at least about 0.05 weight percent.
3. A slurry as defined in claim 2 wherein,
said liquid hydrocarbon fuel is a fuel oil having a viscosity in
the range of about 50 to about 300 seconds Saybolt universal at
175.degree.F, and said slurry viscosity reducing agent is present
in an amount of about 0.20 to about 0.40 weight percent.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to combustible fuel
slurries containing liquid hydrocarbon fuel and particulate
carbonaceous material, and more particularly, relates to the
control of the viscosity of, the settling of particles from, and
the prevention of the formation of gels in such slurries.
2. Description of the Prior Art
The possibility of adding a solid particulate carbonaceous
material, such as coal, to a liquid hydrocarbon fuel, such as fuel
oil, has been studied for many years. In the last three years, and
particularly during the last year, the importance of reducing the
dependency of the world upon natural gas and liquid hydrocarbon
fuels for its energy has been dramatically demonstrated.
While not constituting a complete solution to this problem,
attempts have been made to add solid particulate carbonaceous
material, such as coal, to liquid hydrocarbon fuels, because such
particulate carbonaceous materials are known to be far more
plentiful than liquid fuels. Accordingly, there is considerable
renewed interest in the possibility of extending and/or
supplementing liquid fuels with solid fuels.
Most heavy industrial fuel users have equipment which is designed
and constructed for the transportation, storage and combustion of
liquid fuels, and yet prior solid-liquid slurries, suspensions or
emulsions have not been accepted for regular use in conventional
equipment. In some instances such equipment has been converted from
its original design for burning solid fuels, a trend which many now
believe may need to be reversed.
Numerous approaches have been taken to the problem of combining a
solid particulate carbonaceous material with a liquid hydrocarbon
fuel. One approach is simply to grind the carbonaceous material to
colloidal size before introducing it into an oil. This is
successful, but the grinding cost involved is prohibitive. It was
also soon discovered that oil-coal slurries tended to form gels
when heated to usable temperatures upon storage, usually
thixotropic gels, which were undesirable as such gels interfered
with pumping and burning of the slurries.
Attempts were made, however, to use the gelling phenomenon to hold
larger than colloidal size particles colloidal suspension. In U.S.
Pat. No. 2,423,913, a gel is formed by holding the heated material
for over 90 hours. The gel is then broken down with more oil, with
the resulting slurry assertedly being pumpable without the
particulate material settling out. This is inherently a very
expensive batch process. In U.S. Pat. No. 1,684,125 a soap is added
to the oil component in sufficient quantities to form a gel, and
the particulate material is then added to the gel, with the gel
reportedly being used to prevent settling of the particulate
material.
Various materials have also been added to attempt to stabilize the
slurry against the settling of the larger than colloidal size
particles. In U.S. Pat. No. 2,118,477 starch was employed in an
attempt to stabilize the slurry, and in U.S. Pat. No. 1,447,008
coal distillates and lime-rosin are used to prevent settling of the
larger slurry particles. Casein, gelatin and rubber have also been
employed as suspension stabilizing agents to prevent slurry
settling. It has been found, however, that such suspension
stabilizing agents must be employed in quantities which undesirably
thicken and increase the viscosity of the slurry in order to
maintain substantial quantities of particulate material from
settling from the slurry. Increasing the slurry viscosity does
reduce the settling problem, but it also undesirably decreases the
number of uses to which the slurry may be put.
Other attempts to stabilize oil-coal slurries have included the use
of cracked fuel oils (U.S. Pat. No. 1,939,587) and the use of a
substantial percentage of colloidal size particles to stabilize the
noncolloidal size particles (U.S. Pat. No. 2,590,733).
Finally, aqueous stabilized oil-coal slurries have been evolved for
pipeline transportation purposes such as is shown in U.S. Pat. No.
3,210,168. Such slurries, however, achieve a desired low slurry
viscosity by the addition of substantial amounts of water which
undesirably reduces the BTU value of the slurry. Furthermore, the
water content of the slurry can be corrosive to the equipment
employed in connection with handling and burning the same.
Accordingly, it is an object of the present invention to provide a
combustible fuel slurry in which liquid hydrocarbon fuels are
extended by solid carbonaceous particles with the resulting slurry
being usable in conventional fuel oil transportation, storage and
burning equipment.
It is a further object of the present invention to provide a method
for controlling the formation of gels in slurries of liquid
hydrocarbons and solid particulate carbonaceous materials and to
further control, without the use of water, the viscosity of such
slurries.
It is still a further object of the present invention to provide a
method for stabilizing the settling of larger particles from the
slurry without undesirably increasing the viscosity of the same or
creating a gel in the slurry or its components.
Another object of the present invention is to create a new, stable,
combustible fuel slurry which will provide energy at a cost
competitive with or lower than the cost of energy provided by
liquid hydrocarbon fuels.
Still a further object of the present invention is to provide a
stable, combustible fuel slurry in which the method of forming the
same and constituents are relatively easy and inexpensive.
The present invention has other objects and features of advantage,
some of which will become more apparent from and are set forth in
detail in the accompanying description hereinafter.
SUMMARY OF THE INVENTION
The substantially water-free, high solid content, stable and
combustible fuel slurry of the present invention is comprised,
briefly, of about 5 to about 50 weight percent of a solid
particulate carbonaceous material with the balance of the slurry
including a liquid hydrocarbon fuel, a slurry suspension
stabilizing agent and a water-free slurry viscosity reducing agent.
The viscosity reducing agent is present in an amount sufficient to
maintain the slurry at a viscosity below about 300 seconds Saybolt
Universal when the slurry is at a temperature of 175.degree.F. The
viscosity reducing agent is preferably a detergent, and the
suspension stabilizing agent is preferably starch.
The process for preventing formation of a gel in and controlling
the settling and viscosity of the above slurry is briefly comprised
of the step of adding to a slurry containing a suspension
stabilizing agent, a detergent in an amount sufficient to maintain
the viscosity of the slurry below 300 seconds Saybolt Universal
when the slurry is at 175.degree.F.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The combustible fuel slurry of the present invention is principally
comprised of a solid particulate carbonaceous material and a liquid
hydrocarbon fuel. As used herein, "solid particulate carbonaceous
material" shall include such materials as bituminous and anthracite
coals, coke, petroleum coke, lignite, charcoal, peat, etc., and
combinations thereof. The expression "liquid hydrocarbon fuel" as
used herein shall include crude and refined hydrocarbon based oils,
including without limitation by enumeration petroleum fuel oils,
heavy residual oils and crude oils, and the like. More
particularly, liquid hydrocarbon fuel oils having a viscosity in
the range of about 50 to about 300 seconds Saybolt Universal at
175.degree.F are preferred. Bunker C (No. 6) residual fuel oil is
particularly useful in the slurry of the present invention.
I prefer that the particulate carbonaceous material be powdered or
pulverized to a size which will enable substantially the entire
quantity employed in the slurry to pass through a 200 mesh sieve or
screen. While such screening results in relatively small particle
sizes, the particles are considerably larger than colloidal size,
and some particles larger than a 200 mesh screen but less than 100
mesh can be tolerated. The cost of pulverizing or grinding coal or
the like to a size appreciably below 200 mesh, particularly
colloidal size, begins to increase dramatically, which could
eliminate the economic advantages of the present slurry. I have
found that such additional grinding does not produce any material
advantage in the practice of the present invention.
The fuel oil and particulate carbonaceous material are preferably
mixed in metered amounts in a homogenizing unit, such as a tube
mill or the like, with enough residence time that the fuel oil is
thoroughly mixed with the particles of the carbonaceous material.
For most users about 5 weight percent of coal or less is not
normally economically interesting, and above 50 weight percent of
pulverized coal begins to cause undesirable flow characteristics in
the slurry. The range which is most interesting for many users
appears to be between about 20 to about 40 weight percent of the
particulate carbonaceous material. The fuel oil comprises
substantially the balance of the slurry, except for the addition of
a small quantity of a suspension stabilizing agent and a small
quantity of a slurry viscosity reducing agent. Thus, the oil will
normally comprise about 94 to about 49 weight percent of the
slurry.
Since the preponderance of the particles contained in the slurry
will be above colloidal size, a slurry suspension stabilizing agent
is added. One of the most readily available and economical
suspension stabilizing agents is starch, and I have found that a
small quantity, for example, about 0.05 weight percent, to be
adequate for use in the slurry of the present invention. Other
suspension stabilizing agents may be employed; however, starch is
the most economical and readily available. It should be noted that
the small percentage of suspension stabilizing agent added does
cause a thickening or increase in the viscosity of the slurry. This
thickening is undesirable from the handling viewpoint, even if it
is desirable as a method of minimizing the settling of
particles.
Thus, the high viscosity of the fuel oils normally employed, the
presence of the suspension stabilizing agent, and the high solid
content of the slurry have a combined effect of increasing the
slurry viscosity substantially to the point at which the slurry
does not have the necessary flow characteristics for transportation
and burning in existing oil burning equipment. Moreover, and very
importantly, I have found that such oil-coal slurries will
precipitously begin congealing into a gel when heated to a usable
temperature after a short period of storage, for example, about 100
hours. This gel makes the slurry very difficult to handle with
ordinary oil handling equipment, and accordingly is very
undesirable.
I have found that selected non-aqueous slurry viscosity reducing
agents can be introduced in small quantities into the coal-oil
slurry to reduce and maintain the viscosity of the slurry at
desired levels, without causing settling of the slurry. The slurry
viscosity reducing agents which can be advantageously used in the
slurry of the present invention include detergents (including
soaps), lignin liquors and amino acids. These viscosity reducing
agents are usually introduced into the slurry or into the liquid
hydrocarbon fuel before the slurry is formed by dissolving the same
in a very small quantity of water. The water, however, is acting
solely as a carrier of the viscosity reducing agent and not to any
significant degree acting as a viscosity reducing agent itself.
Usually the water introduced into the slurry is substantially less
than 1 weight percent of the overall slurry.
The viscosity reducing agent should be present in the slurry in an
amount of at least about 0.05 weight percent and an amount
sufficient to maintain the slurry at a viscosity below about 300
seconds Saybolt Universal when the slurry is at a temperature of
about 175.degree.F. Preferably, the slurry viscosity will be
between about 50 to about 300 seconds Saybolt Universal. I have
found that about 0.10 to about 0.50 weight percent, not including
the water carrier, of viscosity reducing agent will be sufficient
to control and maintain the slurry viscosity below about 300
seconds for slurries formed from fuel oils as viscous as Bunker C
(No. 6). My tests indicate that about 0.20 to about 0.40 weight
percent is desirable for most slurries.
When some viscosity reducing agents, such as lignin liquors, are
employed, the slurry viscosity is controlled and reduced to the
desired level for pumping and burning, but upon storage of such
slurries at an elevated temperature, a gel, which is believed to be
a thixotropic gel, will form. In applications in which the slurry
is to be transported and completely used in less than 90 hours, the
use of non-aqueous viscosity reducing agents such as lignin liquors
or amino acids are entirely adequate for controlling the slurry
viscosity. In other applications, however, the formation of a gel
will occur and is not tolerable.
I have additionally found that certain non-aqueous viscosity
reducing agents have the further advantage of preventing the
formation of gels. More specifically, detergents, which as used
herein shall include salts of higher fatty acids or soaps, effect
the desired reduction of the slurry viscosity and further prevent
the slurry from gelling.
The effectiveness of detergents in preventing the formation of gels
in the slurry is unexpected in light of the prior use of soaps with
fuel oil to form gels. Moreover, the use of detergents as a
viscosity reducing agent is also unexpected in light of prior
teachings that soaps produce thickening of oil-coal slurries when
attempted to be employed as suspension stabilizing agents. I have
found, however, That a low viscosity, readily pumpable and flowable
oil-coal slurry which is stabilized against settling by a
suspension stabilizing agent can be produced when a detergent is
employed as a viscosity reducing agent, and that the slurry will
not gel upon extended heated storage. The slurry is substantially
water-free, can be readily burned and can be economically
produced.
EXAMPLES
The following examples are given by way of illustration of the
combustible fuel slurry of the present invention and the process
for controlling the viscosity and formation of gels therein.
EXAMPLE 1
An average western bituminous coal was pulverized to 100 percent
passing through a 200 mesh screen. No. 6 (Bunker C) fuel oil was
employed as the liquid hydrocarbon fuel. About 60 parts by weight
of fuel oil were heated to 175.degree.F, and the pulverized coal
and a saturated aqueous solution of starch and a saturated aqueous
solution of soap were substantially simultaneously added to the
fuel oil. The aqueous solution of starch contained starch in the
amount of 0.05 weight percent of the resulting slurry, and the
aqueous solution of soap included soap in the amount of 0.28 weight
percent of the slurry. About 40 parts by weight of the coal was
introduced into the fuel oil, and the slurry was mixed thoroughly.
The resulting slurry had a viscosity of about 150 seconds Saybolt
Universal at 175.degree.F and could be readily pumped and atomized
for burning. Additionally, the slurry was stored at 175.degree.F
for 30 days and there was no formation of gel or settling of coal
particles.
EXAMPLE 2
The procedure of Example 1 was repeated with the solid carbonaceous
material being provided by residual petroleum (delayed) coke which
was ground to 100 percent passing a 200 mesh sieve. No. 6 fuel oil
was again employed with 0.05 weight percent starch and 0.25 weight
percent soap being added in saturated aqueous solutions. The
resulting slurry had a viscosity of about 145 seconds Saybolt
Universal at 175.degree.F, and it could be readily pumped and
atomized. The slurry was stored for 30 days and there was no
formation of a gel.
EXAMPLE 3
The procedure of Example 1 was again employed with No. 6 fuel oil
and pulverized coal. The fuel oil had 0.05 weight percent of starch
added thereto and 0.20 weight percent of soap. About 80 parts by
weight of the fuel oil were added to about 20 parts by weight of
pulverized coal. The resulting slurry had a viscosity of about 110
seconds Saybolt Universal at 175.degree.F and was stored for 30
days without the formation of a gel.
EXAMPLE 4
The slurry of Example 1 was reformulated with 0.28 weight percent
of lignin liquor being employed in place of the soap. The resulting
slurry had a viscosity of about 168 seconds Saybolt Universal at
175.degree.F and could be readily pumped and atomized. After about
4 days of storage at 175.degree.F, however, the slurry became a
firm gel.
EXAMPLE 5
The procedure of Example 1 was again repeated with 0.28 percent of
a commercially available detergent used in place of soap as the
viscosity reducing agent. The resulting slurry had a viscosity of
142 seconds Saybolt Universal at 175.degree.F and was stored for 30
days at that temperature without the formation of a gel.
EXAMPLE 6
The procedure of Example 1 was again repeated with the starch
suspension stabilizing agent omitted. The resulting slurry had a
viscosity of about 130 seconds Saybolt Universal at 175.degree.F,
but after storage at that temperature for about 3 hours, settling
of coal particles was observed.
EXAMPLE 7
The procedure of Example 6 was again repeated with about 2.0 weight
percent soap employed instead of 0.28 weight percent. The resulting
slurry had a viscosity of about 350 seconds Saybolt Universal at
175.degree.F and upon storage for 8 hours the viscosity increased
to about 400 seconds Saybolt Universal at 175.degree.F. Settling of
the slurry was also noted.
* * * * *