GB2036072A

GB2036072A - Treatment of Fuel Oil

Info

Publication number: GB2036072A
Application number: GB7940052A
Authority: GB
Original assignee: KING CHEMICALS Ltd C
Current assignee: KING CHEMICALS Ltd C
Priority date: 1978-11-29
Filing date: 1979-11-20
Publication date: 1980-06-25
Also published as: GB2036072B

Abstract

A method of increasing the melting point of ash or slag residues produced during combustion of fuel oil is provided by the addition of either an aqueous silica sol or an emulsion of an aqueous silica sol in an oil phase to the fuel oil prior to combustion. Silica particle size ranges from 10 to 200 millimicrons and preferred oil phases include diesel and similar fuel oils. The invention reduces build up of fused slag deposits on internal components of gas turbines and Diesel engines.

Description

SPECIFICATION Treatment of Fuel Oil The fuel oils used for steam raising and for operating stationary gas turbines and diesel engines, although composed mainly of hydrocarbons, frequently contain substantial amounts of compounds of metals and other elements. Of these impurities, some, such as Sodium, Vanadium and Sulphur, are particularly harmful as they can cause fouling and corrosion.

This is largely due to the fact that the ash from the burnt oil can have a melting point below the temperature of the combustion gases if these elements are present in appreciable quantities.

It is known to add Magnesium and/or Silicon compounds to the oil to raise the melting point of the ash so that it will not fuse and adhere to turbine blades, heat exchanger tubes etc. These additives currently consist of either particulate inorganic compounds dispersed in a hydrocarbon vehicle or of hydrocarbon solutions of organic derivatives such as Magnesium Naphthenate or Siiicones. The former are difficult to apply by virtue of grease-type consistency and unpleasant handling characteristics, and the latter either have an inconveniently low metal content or are expensive.

It is also known that the presence of minor amounts of water in a finely dispersed state in the fuel oil can reduce ash deposits by improving combustion efficiency.

This invention seeks to utilize the advantages of Silicon and water addition without the disadvantages of known methods by dispersing in the fuel oil a controlled amount of an aqueous silica sol.

According to one aspect of this invention there is provided a method of increasing the melting point of ash or slag residues produced during combustion of fuel oil by the addition of an aqueous silica sol to said fuel oil prior to combustion thereof.

In accordance with a second aspect, the invention provides a method of increasing the melting point of ash or slag residues produced during combustion of fuel oil by the addition of an emulsion comprising an aqueous silica sol dispersed in a hydrocarbon vehicle to said fuel oil prior to combustion thereof.

The invention further provides an emulsion for addition to fuel oil prior to combustion comprising a dispersion of an aqueous silica sol in a hydrocarbon vehicle.

The aqueous silica sol or 'aquasol' preferably contains initially 20 to 60% w/w of silica and may be diluted further to lower concentrations before application to the fuel oil or emulsification with the hydrocarbon vehicle. The preferred particle size of the silica lies within the range 10 to 200 millimicrons.

The emulsionof aquasol and hydrocarbon vehicle preferably contains between 10 to 70% by volume of silica aquasol.

Preferred hydrocarbon vehicles are oil phases selected from light or heavy grade Diesel oils, crude fuel oils and refined fuel oils. They may also contain suspended coal or other solid fuel particles but must be substantially free from cationic surfactants or inorganic electrolytes that would cause coagulation of the silica particles.

The aquasol or aquasol emulsion may be dispersed directly into fuel oil immediately prior to injection into the respective burners by using a homogeniser. Alternatively the aquasol may be pre-mixed with an emulsifier and dispersed into the oil feed line. Dispersion in either case may be via a proportioning pump. An aquasol or emulsion concentrate may be produced for addition to an oil storage tank or feeding into the oil feed line.

The silica aquasol is immiscible with oil without added emulsifiers and was found to increase ash and slag residue friability in the burnt fuel oil and hence reduce slag deposits on internal components. An advantage of the invention is that whereas a 10% dispersion of silica in oil can have a consistency similar to grease, a 50% aquasol is quite fluid and this advantage is retained when the sol is subsequently dispersed in oil to form a water-in-oil type emulsion, wherein the silica particles remain virtually totally dispersed in the aqueous phase.

Embodiments of the invention will now be described in the following examples.

Example 1 0.1 part of an ethoxylated wool fat with HLB value about 3 is dissolved in a high-boiling hydrocarbon solvent 5 parts. To this is added, with energetic stirring, 1 part of a silica sol containing 30% of silica and a negligible alkali metal content. The dispersion is passed through a homogeniser to stabilise it. This concentrate is effective for the treatment of up to 10,000 parts of fuel oil, depending on the vanadium and sodium contents.

Other, complementary, fuel oil modifiers such as Magnesium and Manganese compounds and surfactants to control sludge formation may be added to the silica sol dispersion so long as these are chosen with low ionic activities so as not to cause the sol to change to a gel.

Example 2 To an aqueous dispersion containing 50% silica of particle size about 100 millimicrons is added 4% of a propoxylated tallow and 1.5% of an ethoxylated nonylphenol. This mixture, when stirred into a hydrocarbon oil of viscosity 500 centistokes, forms a temporary emulsion for direct injection into the burners.

Example 3 To 100 parts fuel oil of viscosity about 1000 centistokes is added 5 parts magnesium oleate.

Into this solution is stirred 20 parts of a 30% silica aquasol containing 1 part of an ethoxylated nonyl phenol. The resulting emulsion shows no separation after 10 minutes.

Example 4 Two solutions are made up. The first contains 10% magnesium oleate in fuel oil of viscosity 100 centistokes, the other has 0. 1% of an ethoxylated nonyl phenol and 100% of a 30% silica aquasol in water. These solutions are fed simultaneously by means of a metering pump into a fuel oil feed line in a ratio of 1 part of each feed to 1,000 parts oil which gives an emulsion stabie for some minutes.

Example 5 To 10 parts fuel oil of viscosity 1,000 centistokes containing 1% iecithin is added 4 parts of powdered coal and the mixture is ground to give a homogeneous dispersion. To this is now added 0.4 parts of wool wax and 3.5 parts of an aquasol containing 30% silica of particle size about 50 millimicrons and the whole is passed through a homogeniser to give a dispersion of viscosity about 100,000 centistokes which showed no separation or gelling after standing for a week.

In examples 3 and 4, the magnesium oleate serves both as an emulsifier and as a source of magnesium to neutralise sulphuric acid derived from sulphur in the fuel.

Normal treatment will consist of one to two parts of silica (SiO2) to one part of sodium or vanadium or their admixture expressed as their elemental monoatomic form (i.e. Na and V).

Claims

1. A method of increasing the melting point of ash or slag residues produced during combustion of fuel oil by the addition of an aqueous silica sol to said fuel oil prior to castion thereof.

2. A method of increasing the melting point of ash or slag residues produced during combustion of fuel oil by the addition of an emulsion comprising an aqueous silica sol dispersed in a hydrocarbon vehicle to said fuel oil prior to combustion thereof.

3. A method in accordance with either preceding claim wherein the silica particle size ranges from about 10 to 200 millimicrons.

4. A method in accordance with any preceding claim wherein the aqueous silica sol contains between 20 to 60% w/w silica, or is diluted before addition to the fuel oil to contain less than 20% w/w silica.

5. A method in accordance with any one of claims 2 to 4 wherein the emulsion of aqueous silica sol dispersed in a hydrocarbon vehicle contains between 10 to 70% by volume of aqueous silica sol.

6. A method in accordance with any one of Claims 2 to 5 wherein the hydrocarbon vehicle is an oil phase substantially free of cationic surfactants and inorganic electrolytes selected from light Diesel oil, heavy Diesel oil, crude fuel oil and refined fuel oil.

7. A method in accordance with any one of Claims 2 to 6 wherein the hydrocarbon vehicle contains suspended coal or other solid fuel particles.

8. A method in accordance with any preceding claim wherein the aqueous silica sol or emulsion thereof is dispersed directly into fuel oil prior to injection into any burner.

9. A method in accordance with any one of Claims 1 to 7 wherein the aqueous silica sol is pre-mixed with an emulsifier and dispersed into an oil feed line.

10. A method in accordance with any one of Claims 1 to 7 wherein the aqueous silica sol or emulsion thereof is added as a concentrate to an oil storage tank or fed into an oil feed line.

11. An emulsion for addition to fuel oil prior to combustion thereof comprising a dispersion of an aqueous silica sol in a hydrocarbon vehicle.

12. An emulsion in accordance with Claim 11 wherein the silica particle size ranges from about 10 to 200 millimicrons.

13. An emulsion in accordance with Claim 11 or 12 wherein the aqueous silica sol contains between 10 to 60% w/w silica, or is diluted before emulsification with the hydrocarbon vehicle to contain less than 10% w/w silica.

14. An emulsion in accordance with any one of Claims 11 to 1 3 which contains between 10 and 70% by volume of aqueous silica sol.

1 5. An emulsion in accordance with any one of Claims 11 to 14 wherein the hydrocarbon vehicle is an oil phase substantially free of cationic surfactants and inorganic electrolytes selected from light Diesel oil, heavy Diesel oil, crude fuel oil and refined fuel oil.

1 6. An emulsion in accordance with any one of Claims 11 to 1 5 wherein the hydrocarbon vehicle contains suspended coal or other solid fuel particles.

1 7. An emulsion as defined in any of examples 1 to 5.

18. An emulsion for addition to fuel oil prior to combustion thereof substantially as herein described and with reference to any of examples 1 to 5.

1 9. A method of increasing the melting point of ash or slag residues produced during combustion of fuel oil substantially as herein described and with reference to any one of examples 1 to 5.