GB2109405A - Fuel oil compositions and use - Google Patents

Abstract

A water-in-fuel oil emulsion, suitable for use as a fuel, contains from 5 to 35% by weight of water, based on the total weight of oil and water; the water containing, as emulsifying aid, from 0.05 to 5 ppm, based on the weight of water, of a mixture of a nonionic or anionic surface active agent and a protective colloid such as sodium alginate or carboxymethylcellulose. A preferred anionic surface active agent is a hydrolysed polyacrylamide. The water also preferably contains a water-softening agent (such as sodium gluconate, ethylenediamine tetraacetic acid and an alkali metal polyphosphate). The invention also consists in a method of generating heat by burning such an emulsion.

Description

SPECIFICATION Fuel oil compositions and use This invention is concerned with improvements in and relating to fuel oil compositions and methods for the generation of heat employing such compositions. More particularly the invention is concerned with fuel oil compositions containing a minor amount of water and taking the form of water-in-oil emulsions.

When conventional fuel oils are burned in a boiler or furnace, even at maximum load, the combustion usuallytakes placewith an insufficient supply of oxygen, and the utilization efficiency commonly ranges from 28% to 65%. Even domestic and central heating boilers give only up to 82% utilization efficiency. However any attempt to supply excess air to the furnace leads to an increased heat energy loss carried by excess air as flue gas. Any unburned liquid fuel remaining at the end of the short energyreleasing or combustion phase not only constitutes a net loss of fuel, but also contributes to the total hydrocarbon emission from the system.

Usually, fuel oils contain high proportions of sulphur and some ash (salts or oxides of sodium and vanadium) so that, after burning, the sulphur and ash discharged into the atmosphere produce complicated flue gases. The flue gases in turn can cause corrosion to the equipment and pollute the atmosphere.

At high temperatures, sodium sulphate and oxides of sodium orvanadium may form deposits on the inner walls of the combustion chamber or flue pipe, thereby leading to corrosion and damage of the equipment and to cleaning problems which can interrupt continuous operation of the equipment.

Other corrosive deposits are formed by the condensation of liquids from the flue at temperatures below the dewpoint of the flue gases and containing, for example, sulphites, sulphates, hydrogen chloride and oxides of nitrogen.

The efficiency of the burning process, the amount of sensible heat extractable from the flue gas within the boiler or furnace and the extent of complete combustion (to reduce the content of hydrocarbons, carbon black and aldehydes in the flue gas) may be improved by emulsifying water in the fuel oil. Heavy oil essentially consists of high molecular weight hydrocarbons. The combustion of such hydrocarbons involves a chain reaction passing through intermediate products with the formation of "chain carrier" which carry the reaction to completion. The chain reaction or"aldehyde degradation mechanism" can be improved by the addition of suitable amounts of water. Further, a large amount of heat will be absorbed by evaporation of the water, which heat then be transferred to the surroundings by means of heat convention and conduction.Accordingly, the presence of water causes a delay in the cracking process and has a diluting effect on the combustion process so that the heat loss is reduced.

Emulsifying the fuel oil with water results in an improvment of the thermal efficiency of a liquid fired combustion plant.

During combustion of a water- containing high boiling point liquid fuel, the water microdroplets can be easily heated beyond their boiling point and may even approach the limits of superheat. At such temperatures, for a given pressure, water homogeneously nucleates and subsequently boils disruptively. The disintegration of the parent droplet essentially forms a secondary atomization process, producing droplets of very fine size.

Moreover, due to the presence of water the severity of the liquid phase coking process is reduced. Most investigations have concentrated on the measurement of the overall effects on parameters such as the pollution emission, heat transfer rates and overall thermal efficiencies of specific combustion appliances fired on both emulsified and conventional fuel oils. It has been shown that a fuel containing 5 - 15% water fired in steam boiler will produce a gas mixture with a 75% reduction in smoke, a 4 - 17% decrease in carbon monoxide, and a 15 - 40% decrease in nitrogen oxides.

The addition of water not only helps the atomization of fuel oil, promotes combustion and heat absorption but also substantially reduces the amount of heat absorbed by the liquid phase cracking occurring with the oil droplets.

Water may be decomposed to hydrogen and oxygen by a micro-explosion. Such an explosive even results in fragmentation of the droplets and thus may lead to more efficient burning of the emulsified fuels. It is believed that this reduction results in a decrease in carbonaceous residues, and offers a plausible explanation for the large observed reductions in a solid emissions from combustion systems utilising emulsified fuels oils. At high flame temperatures, diffusional burning is a major source of nitrogen oxide production. The aqueous emulsion fuel also leads to elevation of the melting point of sodium and vanadium salts thus reduces formation of deposits on on the inner walls of the boiler or furnace.

Solid emissions are substantially reduced, as is discussed in detail in Helion, R, and Boussicand, M., Chauff. Vent. Condit. 47, 13 - 26 (1971); Pariet, J.M; Helion, R; and Robic, G; Rev. General de Thermique 130,979-991(1972); Barrett et al., PB 189075 Battelle Memorial Institute (1968).

The water droplets are assumed to vaporize instantaneously. First a vapour layer is formed between the surface oil film and the central droplet of the emulsion. The bubble then expands until the force exerted by the internal water vapour pressure exceeds the surface tension forces of the film. The saturation temperature of the water droplets is assumed to be dependent upon internal pressure, which in turn depends upon the surface tension forces of the water-oil interface and the water droplet radius. When the emulsion has reached the saturation temperature of the water droplets to rupture the film, the microexplosion occurs.

It has not been found, in accordance with the present invention, that a water-in-oil emulsion suitable for use as a fuel may be produced by emulsifying water in a fuel oil with the aid of a nonionic or anionic surface active agent and a protective colloid.

According to one embodiment of the invention, therefore, there is provided a water-in-oil emulsion, suitable for use as a fuel, comprising a water-in-oil emulsion of water in a fuel oil (such as heavy oil, fuel oil or diesel oil) containing from 5 to 35% by weight, preferably from 5 to 30% by weight, of water based on the total weight of oil and water; the water containing, as emulsifying aid, from 0.05 to 5 ppm, based on the weight of water, of a mixture of a nonionic or anionic surface active agent and a protective colloid.

Suitable nonionic surfactants for use in accordance with the invention include (1) partial long chain fatty acid esters of polyhydroxyl compounds containing from 3 to 6 carbon atoms per molecule; (2) polyalkyleneoxy ethers of partial long chain fatty acid esters of polyhydroxyl compounds containing from 3 to 6 carbon atoms per molecule, wherein the alkyleneoxy groups each contain 2 or 3 carbon atoms; (3) polyalkyleneoxy esters of long chain fatty acids wherein the alkyleneoxy groups each contain 2 or 3 carbon atoms; and (4) long chain fatty acid esters of polyalkyleneoxy esters of polyhydroxyl compounds containing from 3 to 6 carbon atoms per molecule wherein the alkyleneoxy groups each contain 2 or 3 carbon atoms. (The term "long chain fatty acid" as used herein is intended to refer to fatty acids containing from 12 to 18 carbon atoms per molecule).

Examples of nonionic surfactants of class (1) identified above are those derived from compounds containing from 3 to 6 carbon atoms including the polyhydric alcohols and cyclic inner ethers of polydric alcohols, and are, for example, glycerol monooleate, pentaerythritol monolaurate, sorbitan monopalmitate and glucose monstearate. Nonionic surfactants of class (2) identified above include polyethyleneoxy (10) glycerol monopalmitate, polyethyleneoxy (15) pentaerythritol monomyristate, poiyethyleneoxy (1 0)-polypropyleneoxy (10) sorbitan monostearate, polyethyleneoxy (20) sorbitan monostearate, polyethyleneoxy (40) mannitol distearate, polypropyleneoxy (20) sorbitan monostearate, polyethyleneoxy (10) sorbide monolaurate, and polyethyleneoxy (30) glucose monostearate. (The number in brackets indicate the average number of alkylenoxy units per molecule).

Nonionic surfactants of type (31 above include polyethyleneoxy (8) monostearate, polyethyleneoxs (15) distearate polyethyleneoxy (20) monooleate, polyethyleneoxy (20) stearate oleate, polyethyleneoxy (6) monolaurate monolaurate, polypropyleneoxy (10) monooleate and polyethyleneoxy (5) - polypropyleneoxy (5) monolaurate.

Nonionic surfactants of type (4) indicated above include hydroxyethyl glycerol monolaurate, the monopalmitate of polyethyleneoxy (10) pentaerythritol, the dioleate of polyethyleneoxy (6) mannitol. the dioleate of polypropyleneoxy (6) mannitol, the hexaoleate of polyethyleneoxy (20) sorbitol, the pentastearate of polyethyleneoxy (40) sorbital and the monostearate of polyethyleneoxy (6) glucose.

Preferred nonionic surfactants for use in accordance with the invention are polyethyleneoxy compounds of types (2), (3) and (4) which contain at least 6 ethyleneoxy groups for each fatty acid radical.

Water-soluble anionic surfactants suitable for use in the invention include alkali metal (especially sodium) sulphonate, sulphates or carboxylates selected from (1) long chain fatty aliphatic or paraffinic sulphonates; (2) long chain fatty primary alkyl sulphates; (3) long chain sulphor fatty esters; and (4) salts of polymers of alkylene carboxylic acids containing not more than 4 carbon atoms such as poly(methacrylic acid) or poly(acrylic acid).

A preferred class of anionic surfactants of class (4) comprises the hydrolysed poly(meth)acrylamides which may be represented as containing repeating units of the formula:

(In which R is a hydrogen atom or a methyl group and Xis a hydrogen atom or an anion such as a sodium, potassium or ammonium anion).

The concentration of surfactant in the final emulsion is suitably from 0.01 to 5 ppm, based on the weight of water. In case of the hydrolysed polyacrylates discussed above, a concentration of from 0.05 to 0.5 ppm has proved effective.

The concentration of the protective colloid in the final emulsion is suitably from 0.01 to 4 ppm, based on the weight of water.

The most suitable protective colloid for use in the invention is sodium alginate. Other protective colloids include sodium carragheenate and cellulose ethers such as sodium carboxymethylcellulose (CMC).

The emulsifying agents may alterthe superheat limit by changing the fuel : water interfacial characteristics and may also suppress vaporization of water by preventing contact of water micro-droplets with the oil phase.

The aqueous phase of the fuel emulsions of the invention also suitably contains a water softening agent such as an alkali metal (typically sodium) gluconate, ethylenediamine tetraacetate or polyphosphate (such as sodium hexametaphosphate).

A particular class of preferred emulsion for use in accordance with the invention is one in which the water phase contains a mixture of hydrolysed polyacrylamide (as anionic surfactant), sodium alginate or sodium carboxymethyl cellulose (as protective colloid) and sodium gluconate or ethylenedianine tetraacetate and (as water softening agent). Such a mixture preferably contains, based on the total weight of the mixture, from 5 to 90% by weight of hydrolysed polyacrylamide, from 5 to 80% by weight of protective colloid and from 5 to 25% by weight of water softening agent and may, additionally, contain from 10 to 72% by weight of an alkali metal polyphosphate water softening agent.

The emulsions of the invention are conveniently prepared by preparing an aqueous solution of the appropriate emulsifying acid (optionally also con taining any water-softening agent) at a relatively high concentration (a stock solution) and then diluting this with tap water to give the desired final concentration of emulsifying aids. The resultant solvent is then emulisified with the fuel oil by mixing it with the fuel oil (e.g. using a mechanical stirrer rotating at 50 to 1500 rpm) for an adequate period (e.g. 1.5 to 40 minutes) to give the desired emulsion in which the water droplets suitably have a particle size of from 0.5 to 5 microns.

The emulsifying aids of the invention make it possible to produce stable water-in-oil emulsion fuels using varying amounts of water.

In order that the invention may be well understood the following example is given by way of illustration only.

EXAMPLE The following ingredients were mixed in the amounts shown.

Ingredient Amount (O/o by weight) Hydrolysed Polyacrylamide 10 Ethylenediaminetetraacetic acid ................... 5 Sodium alginate ........................................ 10 Sodium gluconate............................... 5 Sodium hexametaphosphate 70 A stock solution was prepared from the mixture by adding the mixture to tap water at a rate of 1 gram of mixture per litre of water.

The mixture was slowly added to the water with stirring and stirring was continued for another 20 minutes until the mixture was completely dissolved.

The stock solution was further diluted with tap water to a concentration of 0.05 to 5 ppm.

The diluted solution was slowly added to fuel oil with mixing, the rotation of velocity of mechanical mixer having from 300 to 1500 rpm and having carried out for 1.5 to 40 minutes.

Fuel oil emulsions thus prepared and containing various amounts of emulsified water were tested in a small experimental boiler. In the tests the flue gas was maintained colourless by opening both oil and air valves as much as possible and then adjusting them continuously. The time required to warm up 20 litres of water to 93"C was recorded. The average value of the time recorded for several experiments is listed in the following table.

Fuel Combustion Initial Volume Highest Time (min.) Water of combustion Temp. fuel Temp. C ( C) used (litres) Heavy 28 28 5.60 1250 oil Fuel contain 28 28 5.35 1320 10% of water Fuel contain 15% of water 26 32 5.00 1344 Fuel contain 20% of water 30 29 5.35 1308 Fuel contain 25% of water 28 28 5.10 1222 Fuel contain 30% of water 28 29 5.90 1236 From the data presented, it is clear that the fuel in accordance with the invention provides economic advantages and an improvement in combustion efficiency. The aqueous emulsion fuel lasts much longer but takes shorter time to reach the required steam vapour pressure, compared to the general fuel used. Moreover, the combustion temperature is higher. (It should be noted that the original water contained of the oil was not included in the calculation).

The fuel emulsion was also tested in a small factory, in an Ku re-boiler, as follows: Model: KMHO40 Max. Pre = 10 kg/cm2 Steam output: 4000 kg/cm2 Capacity: 2 Tons Double Reverberator Made by: Heavy Industries Co. Ltd., The combustion efficiency of the emulsion fuel of the invention was compared with that of Thailand C fuel oil, the experiment being conducted at a rather elevated room temperature of 65"C.

A batch of 474 litres of aqueous oil emulsion fuel w3S prepared by the mixing process described above. Thus, in a one ton capacity steel tank, 379 litres of fuel oil were first placed and when the mixer had reached a speed of 680 rpm, 95 litres of an aqueous solution of emulsifying agent (concentration of 0.3 rpm) were slowly added. After mixing for 6 minutes, the mixer was stopped and the entire 474 litres of homogeneous aqueous emulsion fuel was pumped into the oil tank of the boiler.

The combustion efficiency of this emulsion fuel was tested under the following conditions.

Stsaras vapour pressure, 6.5 kg/cm2; steam exhausted at a constant rate of 6.5 kg/cm2-sec.

Both oil and air valves were continuously adjusted.

The results are shown in the following table.

Type of fuel Records Thailand C Water in Oil Fuel Oil Emulsion Fuel Combustion time 91'5" 99'6" Steam Vapour Pressure Produced 35522.4 kg2 38610 kg2 Time to reach the 6.5 kg/cm2 15' 8' Vapour Pressure Combustion 1 1.0034 Efficiency After consideration of the water content (20%) of the emulsion fuel, the efficiency can be calculated as follows: : 21.73% =38610 - 3Ei522.sl x 20% As indicated in the above calculation, the efficiency of the fuei of the invention is better than that of Thailand C fuel oil.

Claims (8)

1. Awater-in-oil emulsion, suitable for use as a fuel, comprising a water-in-oil emulsion of water in a fuel oil and containing from 5 to 35% by weight of water, based on the total weight of oil and water; the water containing as emulsifying aid, from 0.05 to 5 ppm, based on the weight of water, of a mixture of a nonionic or anionic surface active agent and a protective colloid.

2. An emulsion as claimed in claim 1 in which the anionic surface active agent is hydrolysed polyacrylamide.

3. An emulsion as claimed in claim 1 in which the protective colloid is sodium alginate or a cellulose ether.

4. An emulsion as claimed in claim 1 in which the aqueous phase also contains a water-softening agent.

5. An emulsion as claimed in claim 4 in which the aqueous phase contains a mixture of hydrolysed polyacrylamide (as anionic surface active agent), sodium alginate or carboxymethyl cellulose (as protective colloid), and sodium gluconate or ethylene diamine tetraacetic acid (as water softening agent).

6. An emulsion as claimed in claim 5 in which the said mixture contains, based on the total weight of the mixture, from 5 to 90% by weight of hydro based polyacrylamide, from 5 to 80% by weight of protective colloid, and from 5 to 25% by weight of water-softening agent.

7. An emulsion as claimed in claim 6 in which the said mixture also contains from 40 to 72% by weight of an alkali metal polyphosphate water softening agent.

8. An emulsion as claimed in claim 1 in which the water droplets of the emulsion have a particle size of from 0.5 to 5 microns.