GB2071141A - Solid fuel/oil dispensions containing metallo-porphyrins as stabilisers - Google Patents

Abstract

A uniformly dispersed fuel composition contains (a) 15 to 55% by weight of particles of a solid friable fuel, e.g. coal, (b) a fraction consisting of or containing a high concentration of metallo-porphyrins and (c) a fuel oil medium. The size of the majority of the solid particles is in the range 1 to 15 micron. The metallo-porphyrins are preferably derived from a petroleum fraction and act to enhance the stability of the composition. The composition may be prepared by grinding (a) in (c), air being excluded during the grinding operation, and adding (b) before, during or after grinding. The composition is suitable for use as a fuel for industrial burners.

Description

SPECIFICATION Dispersions of solid fuel in oil This invention relates to dispersions of solid fuel in oil and to a method for their preparation.

Coal oil-slurries have previously been disclosed, see for example, British Patent Specification No.

975687. Whilst these have behaved as near Newtonian non-settling fluids in pipelines, they separate on standing. Thus such slurries are suitable for use immediately after preparation or pipelining hut are not suitable for transportation by tanker nor for storage.

Our British Patent Specification No. 1523193 describes and claims a method for the preparation of a uniform coal oil dispersion which method comprises grinding coal in a medium consisting essentially of gas oil and/or a heavier petroleum fraction until the particle size is reduced to a value below 10 micron and the dispersion contains 1 5 to 55% by weight coal, expressed as a percentage by weight of the total dispersion, and until a stable dispersion results on ceasing grinding.

Japanese Patent Application No. 5318604 discloses coal oil mixtures which are stabilised by the addition of (a) a non-ionic surfactant, (b) a metalloporphyrin compound and (c) water in amount at least 5% by weight of the total weight of the mixture.

It is stated that all three components are essential.

We have now discovered that under the special conditions hereinafter set forth, the stability of dispersions of solid fuel in oil can be increased by the addition of metallo-porphyrins without additional surfactants or water being necessary.

Alternatively, the grinding time required to produce a dispersion of desired stability may be reduced.

Thus, according to the present invention, there is provided a uniformly dispersed fuel composition containing (a) 15 to 55% by weight, preferably 30 to 45%, of particles of a friable solid fuel, the size of the majority of the particles being in the range 1 to 15 micron, preferably 2 to 8 micron, (b) a fraction consisting of or containing a high concentration of metallo-porphyrins and (c) a fuel oil medium, the percentage being expressed as percentage by weight of the total weight of the dispersion.

Petroleum is a convenient source of fractions containing a high concentration of metallo-porphyrins.

By a high concentration of metallo-porphyrins, with respect to petroleum we mean a concentration which is higher that the average concentration of metallo-porphyrins in crude petroleum generally or corresponding petroleum fractions; a concentration which is high within a particularfraction of any given crude petroleum because of a natural concentration of porphyrins within it, e.g. in a particular boiling range; or a high concentration which is achieved because a crude petroleum fraction has been specially treated to concentrate porphyrins within it.

Such fractions are preferably present in the fuel composition in amount 0.1 to 25% by weight, most preferably 1 to 10% by weight, of the total weight of the dispersion.

In general heavy crude oils tend to contain more porphyrins than lighter crudes. Such crudes have API gravities of about 30O and below. Examples of such crudes include Venezuelan crudes, e.g. Boscan, and heavy Arabian and Iranian crudes.

A method for isolating vanadyl porphyrins from a mixture with other compounds is described in our pending British Patent Application Serial No.

2030564A.

This discloses a method for the isolation of van adyl porphyrins from a mixture thereof with hydrocarbons and/or hetero hydrocarbons which method comprises the stages of (1) passing the mix turethrough a column packed with silica to effect a ch romatographic concentration of the porphyrins, (2) passing the concentrate through a column packed with alumina to effect a further chromatographic concentration of the porphyrins, and (3) passing the second concentrate through a column packed with a product, derived from an inorganic oxide containing surface hydroxyl groups, containing groups of general formulae (I) and/or (11).

wherein R is a divalent radical containing up to 20 carbon atoms, R' and R2 are halogen atoms, organic radicais containing up to 20 carbon atoms, or hydrolysis products thereof, M is a metallic or hydrogen ion and (a) is an integer corresponding to the valency of M, to effect a third chromatographic concentration.

Suitable friable solid fuels include coals of various ranks, solvent refined coal, coal coke and petroleum coke. A very suitable coal is bituminous coal.

The fuel oil may be a fuel oil having a viscosity of not more than 6000 seconds, preferably not more than 3500 seconds, Redwood No. 1 at 1 00'F (38"C).

The required viscosity may be achieved by "cutting back" if necessary with, for example, gas oil.

In the case of certain heavier fuel oil fractions it may be necessary to heat them in orderto render them sufficiently mobile to permit dispersal of the solid fuel particles therein.

The compositions may be prepared by grinding the solid friable fuel in the fuel oil with the exclusion of air. The porphyrin rich fraction may be added before, during or after grinding.

Thus, according to another aspect of this invention, there is provided a method for the preparation of a uniform dispersion of a friable solid fuel, a fraction containing a high concentration of metallo 'Dorphyrins and a fuel oil medium which method comprises grinding the solid fuel in the fuel oil medium until the particle size of the majority of the particles of the solid fuel is reduced to a value in the range 1 to 15 micron, and the dispersion contains 15 to 55 Ó by weight solid fuel particles, air being excluding during the grinding operation and, before, during or after grinding, adding a fraction consisting of or containing a high proportion of metallo orphyrins, all percentages being expressed as a percentage by weight of the total dispersion.

Preferably the solid fuel supplied to the grinding process is pre-ground to a particle size not greater than 250 micron.

When the porphyrin rich fraction is added after grinding it is necessary to mix it thoroughly with the dispersion. This operation may be achieved by homogenising in a high speed vortex mixer.

Grinding can be carried out in vibratory, agitatory or tumbling ball mills.

When using an agitatory or vibratory ball mill, the pre-ground solid fuel is preferably pre-mixed with the fuel oil before grinding, e.g. in a high speed vortex mixer.

The grinding time will depend on the nature of the mill.

It is necessary to exclude air during the grinding operation. This can easily be achieved in the case of vibratory and agitatory ball mills by filling the mill completely.

In the case of a tumbling ball mill, the contents will take up a kidney shaped configuration as the mill rotates. This cascades smoothly with little splashing or surging. Grinding takes place in the interior of the kidney shaped mass and few, if any, freshly ground surfaces are exposed to the gaseous atmosphere in the mill. The gaseous atmosphere is thus excluded from the grinding operation.

If no special precautions are taken, this atmosphere will normally be air. However, in order to reduce the risk of free oxygen contamination still further, in view of the adverse effect which this has on product stability, it is preferred to operate the tumbling ball mill with the contents under an inert blanket, e.g. of nitrogen. This has the further advantage of eiiminating the risk of forming hazardous vapour mixtures. Inert gas blanketing is particularly advantageous when grinding at relatively high temperatures, e.g. close to or above the flash point of the liquid.

When using a ball mill, it is, of course, desirable to use balls made of a material which does not react with the solid and which does not wear unduly either itself or the interior surface of the mill during the grinding. Ball mills usually contain steel or glass bails and these are suitable for the present purpose.

The stability of the solid fuel dispersion is a function ofthreevariables-the method of grinding, the final particle size and the final concentration of solid n oil - enhanced by a fourth - the porphyrinic frac t on. If all four are chosen correctly, then the result ing dispersion at ambient temperature is in the form of a gel in which a physical network is formed by uleophilic solid particles in oil. It is a uniform struc ture from which the solid particles cannot settle out because they form part of it. This is unlike coal bil dispersions prior to those disclosed in 1523193 which were merely siurries in which the coal parti cles were suspended in the oil from which they would eventually settle out At elevated temperature, although the gel-like.

structure is less apparent, the same interactions occurto confer enhanced stability.

If the solid is not ground in the oil in the absence of air, the ground particles will not be oleophilic and the gel will not form. If the solid particle size is too great, then the gel will not form. The concentration of the solid particles is also critical. If It is too low, the gel will not form. If it is too high the gel will be too solid-likefor pumping.

Such solid fuel oil dispersions are suitable for use in blast furnaces, cement kilns, industrial boilers, marine boilers and utility boilers.

The invention is illustrated with reference to the following examples.

Example I The fuel oil was a mixed-source fuel oil with a viscosity of 950 Redwood 1 seconds at 1 00"F (38"C). It had the following properties.

Sulphur content %wt : 3.5 Water content %wt : 0.05 Specific gravity 15.6"C/15.6"C : 0.964 Kinematic viscosity at 60 C cSt : 72.0 80 C cSt : 29.7 100"CcSt : 17.0 The coal was a bituminous coal ex Durham coal field of Rank 501 with thefollowing ultimate and initial particle size analyses (air-dried basis): Carbon content % wt : 78.1 Hydrogen content % wt : 4.87 Nitrogen content % wt : 1.7 Total sulphur content %wt : 1.74 Chlorine content %wt : 0.25 Water content % wt : 2.3 Ashcontentat8l5"C %wt : 5.1 + 500 micron %wt : 0.1 - 500 + 212 micron %wt : 1.6 -212+75micron %wt : 21.0 75 + SS micron %wt : 14.2 < 53 micron %wt : 63.1 The fuel oil (1300 g) was warmed to 30"C and the pulverised coal (700 g) was added slowly with continuous stirring with a high-speed vortex mixer. The resulting slurry containing 35% wt coal in fuel oil was pumped at a rate of 260 ml/min to a stirred-ball mill sold under the name of Dyno mill Type KDL by Willy Bachofen Maschinefabrik, Basle, Switzerland.

The mill grinding chamber, a horizontally mounted cylinder of volume 600 ml contained 1 mm steel balls (500 ml).

The balls were stirred by agitator discs mounted on a horizontal shaft which ran parallel with the axis of the cylinder. The shaft speed was set at 4500 rpm to give a disc peripheral speed of 15 mlsec. The product was collected as it emerged from the mill. The average size of the coal particles was 4.4 micron.

After standing for 24 hours at 1 OO"C this coal/fuel oil dispersion showed considerable signs of instability forming a layer of sludge.

Example 2 To a sample of this coal/fuel oil dispersion (147 g) was added 4.5 g of a sample of Boscan crude distillate, (the fraction boiling between 500 -650 C under a pressure in the range 2 - 10 micron Hg) with continuous stirring using a high speed vortex mixer. Stirring was continuous for 8 minutes. The dispersion of final composition 34% wt coal, 3% wt Boscan crude distillate and 63% wt fuel oil showed only the slightest signs of instability after 24 hours at 1 OO"C, the sample becoming slightly thicker towards the bottom but with no layer of sludge deposit.

The distillate contained 570 ppm V, 45 ppm Ni and 5.0% S.

Claims (17)

1. A uniformly dispersed fuel composition containing (a) 15 to 55% by weight of particles of a solid friable fuel, the size of the majority of the particles being in the range 1 to 15 micron, (b) a fraction consisting of or containing a high concentration of metallo-porphyrins and (c) a fuel oil medium, the percentage being expressed as percentage by weight of the total weight of the dispersion.

2. A composition according to claim 1 wherein the concentration of solid fuel particles is in the range 30 to 45% by weight.

3. A composition according to either of the preceding claims wherein the size of the majority of the fuel particles is in the range 2 to 8 micron.

4. A composition according to any of the preceding claims wherein the fraction containing a high concentration of metallo-porphyrins is a petroleum fraction.

5. A composition according to claim 4 wherein the concentration of the petroleum fraction containing metallo-porphyrins is in the range 0.1 to 25% by weight of the total weight of the dispersion.

6. A composition according to claim 5 wherein the concentration of the petroleum fraction containing metallo-porphyrins is in the range 1 to 10% by weight.

7. A composition according to any of the preceding claims wherein the friable solid fuel is a coal, solvent refined coal, coal coke or petroleum coke.

8. A composition according to claim 7 wherein the friable solid fuel is bituminous coal.

9. A composition according to any of the preceding claims wherein the fuel oil medium is a petroleum fuel oil fraction having a viscosity of not more than 6000 seconds Redwood No. 1 at 38"C.

10. A composition according to claim 9 wherein the fuel oil medium is a petroleum fuel oil fraction having a viscosity of not more than 3500 seconds Redwood No. 1 at 38"C.

11. A method for the preparation of a uniform dispersion of a friable solid fuel, a fraction containing a high concentration of metallo-porphyrins and a fuel oil medium, which method comprises grinding the solid fuel in the fuel oil medium until the particle size of the majority of the particles of the solid fuel is reduced to a value in the range 1 to 15 micron and the dispersion contains 15 to 55% by weight solid fuel particles, air being excluded during the grinding operation and, before, during or after the grinding operation, adding a fraction consisting of or containing a high concentration of metallo-porphyrins, all percentages being expressed as a percentage by weight of the total dispersion.

12. A method according to claim 11 wherein the solid fuel supplied to the grinding process is preground to a particle size not greater than 250 micron.

13. A method according to either of claims 11 or 12 wherein grinding is carried out in a vibratory or agitatory ball mill.

14. A method according to claim 13 wherein the solid fuel is dispersed in the fuel oil medium prior to grinding.

15. A method according to either of claims 11 or 12 wherein grinding is carried out in a tumbling ball mill.

16. A composition as hereinbefore described with reference to Example 2.

17. A method as hereinbefore described with reference to Example 2.