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(11) | EP 1 072 671 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Process for combustion of a sulphur-containing liquid fuel with reduced emission of sulphur oxides, and corresponding combustion plant |
| (57) Process for combustion of a sulphur-containing liquid fuel with reduced emission
of sulphur oxides (SOx) and corresponding combustion plant, in which combustion is
performed of an emulsion comprising a continuous phase consisting of the liquid fuel
and an aqueous phase, dispersed in the said continuous phase, in which a sorbent capable
of reducing the emission of SOx is introduced. The amount of sulphur sorbent is determined
as a function of the quantity of sulphur present in the fuel and of the maximum permissible
concentration of SOx in the gaseous effluents, and in the emulsion the aqueous solution
of the sorbent is dispersed in the liquid fuel in the form of particles having a mean
diameter such as to obtain an SOx reduction efficiency of at least 90%. |
[0001] The present invention relates to a process for combustion of a sulphur-containing liquid fuel with reduced emission of sulphur oxides and to the corresponding combustion plant. More particularly, the present invention relates to a process for combustion of a sulphur-containing liquid fuel with reduced emission of sulphur oxides and to the corresponding combustion plant, wherein an emulsion comprising a continuous phase consisting of the liquid fuel and an aqueous phase, dispersed in the said continuous phase, wherein a sorbent capable of reducing the emission of sulphur oxides is introduced.
[0002] The need to reduce emission of polluting agents into the atmosphere during the combustion of hydrocarbons, for example for the production of heat in thermal or thermoelectric plants, is nowadays strongly felt. In particular, strict standards have been introduced concerning concentration of sulphur oxides (SOx) in the gaseous effluents produced by the combustion of combustible oils. The generic formula SOx is commonly used to indicate sulphur oxides produced during the combustion of sulphur-containing fuels, without referring to a particular oxidation level of sulphur.
[0003] To comply with such standards, operators of thermal or thermoelectric plants turned to the use of combustible oils with low sulphur content, i.e. containing a quantity of sulphur such as to produce SOx at a concentration lower than the limits imposed by the law. This solution involved an increase in operating costs, since it severely limited the choice of supply sources for the fuel, directing it towards the most valuable petroleum reserves, characterized by low sulphur content, whose availability is limited to a few geographical areas.
[0004] An alternative to the use of fuels with low sulphur content is represented by the processes for desulphurization of the gaseous effluents produced by combustion. Such processes require the use of complex plants for after-treatment of gaseous effluents, commonly known as DESOX, in which SOx are converted by reaction with a desulphurizing agent, for example calcium carbonate, into salts of alkaline earth metals, for example calcium sulphate. In this way, huge quantities of ash are produced, which can be disposed of in the preduction of cements and the like. However, DESOX plants, while being very efficient in decreasing SOx, require an immense initial investment for their construction and constitute a substantial increase in plant maintenance costs.
[0005] Another possible method for reducing emissions of SOx is represented by the use of an agent capable of blocking sulphur (sulphur sorbent) during combustion.
[0006] For example, in patent US-3,948,617, a process is described for combustion of a sulphur-containing fuel wherein the emission of SOx is reduced by injection of an alkaline substance, for example an aqueous solution of a hydroxide, in particular sodium hydroxide or potassium hydroxide, into the fuel feed line at a point immediately before entry into the burner.
[0007] In the article by Cioni et al, published in the Proceedings of the 49th Congress of "Associazione Termotecnica Italiana" (Italian Thermotechnical Engineering Association) (Perugia, 26-30 September 1994, Chap.8, Part 12, pp. 1407 ff), a method is described for reducing SOx emissions by injection of a sorbent, in particular lime or calcium carbonate, directly into the combustion chamber. The authors indicate a rather low efficiency for the desulphurization, with a percentage desulphurization ranging from 30 to 40% using a molar ratio of sorbent to sulphur of 2.
[0008] Also known are attempts to reduce SOx emissions by introducing the sorbent into the fuel emulsified with water. For example, patent application EP-512,721 describes a liquid fuel in the form of an oil-in-water emulsion in which a sulphur sorbent is dispersed in the form of solid particles. The sorbent may be, for example, calcium hydroxide, magnesium carbonate or magnesium oxide. The particles of the sorbent have dimensions similar to those of combustible oil droplets dispersed in water, namely between 2 and 50 microns, preferably between 5 and 30 microns. In the working examples reported in EP-512,721, with a mole ratio of sorbent to sulphur of 1, an SOx removal efficiency of about 50 %, at most 65 %, is indicated.
[0009] In patent application WO 91/04310, a method is described for reducing SOx emission from sulphur-containing fuels, wherein a mixture consisting of two sulphur sorbents, a first sorbent insoluble in water and a second sorbent soluble in water, is introduced into the fuel. The water-insoluble sorbent may be, for example, calcium or magnesium carbonate, while the soluble sorbent can be selected from calcium, sodium and magnesium carboxylates. The fuel may consist of, inter alia, an oil-in-water hydrocarbon emulsion, obtained using suitable mixtures of surfactants. According to what is reported in WO 91/04310, the use of a mixture of sorbents as described above increases the SOx removal efficiency, bringing it for example, in the case where a mixture of 90% of CaCO3 and 10% of calcium acetate is used, up to values ranging from 31 to 44 %.
[0010] In patent US-4,804,495, a multiple emulsion between a high density hydrocarbon and water is described, wherein a water-in-oil (W/O) primary emulsion, consisting of droplets of water dispersed in a continuous phase of hydrocarbon, is in turn dispersed in a continuous aqueous phase (W'), giving rise to formation of a multiple emulsion (W/O/W'). The particles of water in the primary emulsion have a diameter lower than 10 µm, preferably ranging from 0.1 to 5 µm, while the particles of primary emulsion in the aqueous phase have a diameter of about 10-100 µm. In that patent, the possibility is indicated of providing, by means of the external aqueous phase, an agent capable of reacting with the sulphur present in the hydrocarbon, for example a hydroxide or a carbonate of an alkali or alkaline earth metal. No working examples demonstrating feasibility of this SOx reduction method are provided.
[0011] In Japanese patent application JP 56-159291, a method is described for reducing formation of SOx and of nitrogen oxides (NOx), wherein a sulphur sorbent and water are mixed with a combustible oil to produce an emulsion, which is then fed into a furnace. As sorbents, CaO, Ca(OH)2, MgO, Mg(OH)2, NaOH, dolomite, calcium formate and fatty acid calcium salts can be used. No indications are provided about the type and characteristics of the produced emulsion. In the examples, a percentage addition of the sorbent (equivalent ratio) corresponding to the efficiency of SOx reduction as defined hereinbelow, of around 80%, at most 87.2%, is reported.
[0012] On the basis of the Applicant's experience, the processes for reducing SOx emissions known in the art which require using a sulphur sorbent dispersed in the fuel do not make it possible to obtain satisfactory results. In particular, the Applicant has found that the known processes display a low SOx removal efficiency, so that to abate a predetermined quantity of sulphur it is necessary to use a quantity of sorbent in considerable excess compared to the stoichiometric quantity calculable as difference between the quantity of sulphur present in the fuel and the maximum quantity of SOx permissible in the gaseous effluents produced by the combustion. The necessity of operating with excess sorbent has many disadvantages. First of all, it is necessary to carry out many trials on the combustion plant, in order to establish, given a certain type of sulphur-containing fuel, the optimal excess quantity of sorbent for maintaining the SOx level below the maximum permissible quantity. The use of excess quantities of sorbent also involves an appreciable increase in the running costs of the plant. But the most important point is that the excess sorbent which does not react with sulphur increases the quantity of particulate present in the gaseous combustion effluents, causing problems of clogging along the smoke path, particularly in heat exchangers present in the plant. Furthermore, as the excess sorbent generally consists of alkaline substances, it can trigger corrosion processes in the plant and, by causing an increase in pH value in the ash produced, makes disposal of the ash and its re-use in other production processes more complex.
[0013] The Applicant has now found that, in a process for combustion of a sulphur-containing liquid fuel, it is possible to reduce the emission of SOx, maintaining its concentration in the gaseous effluents below the maximum permissible quantity, by using a water-in-oil emulsion of the liquid fuel with an aqueous phase, wherein the aqueous phase contains a predetermined quantity of a water-soluble sorbent and is dispersed in the fuel in the form of particles with a mean diameter such as to obtain an SOx removal efficiency of at least 90%, preferably at least 95%. In other words, the Applicant has found that the efficiency of the SOx removal depends on the mean diameter of the particles of aqueous phase containing the sorbent dispersed in the liquid fuel. In particular, it is possible to obtain an efficiency of at least 90% by using a water-in-oil emulsion wherein the dispersed aqueous phase containing the sorbent has a mean particle diameter (numerical mean) of less than 5 µm, preferably between 0.01 and 2 µm, more preferably between 0.05 and 1 µm (numerical mean). The Applicant has further found that the implementation of the process according to the present invention makes it possible to obtain a considerable reduction in the concentration of nitrogen oxides (NOx) in the gaseous effluents, with a reduction, compared to the fuel as such, generally between 15 and 35%.
[0014] In a first aspect, the present invention thus relates to a process for combustion of a sulphur-containing liquid fuel with reduced emission of sulphur oxides (SOx), the said process comprising:
preparing an aqueous solution of a sulphur sorbent;
forming a water-in-oil emulsion between the said aqueous solution and the sulphur-containing liquid fuel so as to obtain a predetermined quantity of sulphur sorbent in the emulsion;
feeding the said emulsion into a combustion device;
characterized in that in the emulsion the aqueous solution of the sorbent is dispersed in the liquid fuel in the form of particles having a mean diameter such as to obtain an SOx reduction efficiency of at least 90%, preferably at least 95%.[0015] In a preferred embodiment, the aqueous solution of the sorbent is dispersed in the liquid fuel in the form of particles having a mean diameter of less than 5 µm, preferably between 0.01 and 2 µm, more preferably between 0.05 and 1 µm (numerical mean).
[0016] In a second aspect, the present invention relates to a plant for combustion of a sulphur-containing liquid fuel, the said plant comprising a combustion chamber, at least one burner inserted into the said combustion chamber, a device for producing an emulsion of the liquid fuel with an aqueous solution of a sulphur sorbent, a tank for accumulating the said emulsion connected to the said device for producing the emulsion, and a system for feeding the emulsion from the accumulation tank to the burner, characterized in that the said emulsion production device is capable of dispersing the aqueous solution of the sorbent in the liquid fuel in the form of particles having a mean diameter of less than 5 µm, preferably between 0.01 and 2 µm, more preferably between 0.05 and 1 µm (numerical mean).
[0017] According to a preferred aspect, the combustion plant further comprises a tank for storage of the sulphur sorbent, containing the sorbent in concentrated form, a dilution tank equipped with an inlet connected to the said storage tank and with an outlet connected to the emulsion production device, and a line for feeding the water into the said dilution tank.
[0018] Within the scope of the present description and of the claims, with "SOx reduction efficiency" it is meant the percentage ratio of sulphur moles actually abated to sulphur moles corresponding stoichiometrically to the quantity of sorbent introduced into the combustion. In other words, the greater the efficiency of the process of SOx reduction in the gaseous effluents, the lower the quantity of sorbent to be used to abate a predetermined quantity of sulphur. A quantity of abated sulphur stoichiometrically equal to the quantity of sorbent used corresponds to an efficiency of 100%.
[0019] Within the scope of the present invention and of the claims, "sulphur sorbent" means a chemical agent, generally of inorganic nature, which is capable of converting, during the combustion process, the sulphur and the SOx into compounds, generally sulphur salts (for example sulphates, sulphides or sulphites), in the form of solid particles that can be removed from the gaseous effluents by appropriate means for removal and collection of powders, for example by means of electrostatic precipitators, bag filters, cyclones and the like.
[0020] According to the present invention, particularly preferred are sulphur sorbents that are at least partially soluble in water, having a solubility (at 25°C) generally greater than 2% by weight, preferably greater than 15% by weight, as the Applicant in fact considers that injecting into the combustion device a sulphur sorbent that is substantially insoluble in the aqueous phase and hence in the form of a solid presents many disadvantages, and in particular premature wear of the injection nozzles because of abrasion by the solid particles.
[0021] The sulphur sorbent according to the present invention can be selected, for example, from oxides, hydroxides, chlorides, carbonates and acetates of alkali or alkaline earth metals, or mixtures thereof, such as: sodium hydroxide, potassium hydroxide, barium hydroxide, magnesium hydroxide, calcium hydroxide, barium chloride, barium acetate, or mixtures thereof. Particularly preferred among these are: sodium hydroxide and potassium hydroxide.
[0022] As indicated above, given the high efficiency of SOx reduction obtainable with the process according to the present invention, the quantity of sorbent present in the water-in-oil emulsion is predetermined on the basis of the stoichiometric quantity necessary to eliminate a predefined quantity of SOx, the latter being calculated as the difference between the quantity of sulphur present in the fuel and the maximum permissible concentration of SOx in the gaseous effluents.
[0023] The quantity of water to be used to form the emulsion is predefined in such a way as to dissolve the sorbent in the desired quantity without however adversely affecting the quality of the combustion. In general, the quantity of water present in the emulsion ranges from 5 to 40% by weight, preferably from 10 to 30% by weight.
[0024] As liquid fuels, hydrocarbons deriving from petroleum commonly used in thermal or thermoelectric plants, in particular fluid, semi-fluid or heavy combustible oils having a sulphur content generally greater than 0.2% by weight, generally ranging from 0.25% to 2% by weight, can be used.
[0025] The water-in-oil emulsion between the aqueous solution of the sorbent and the liquid fuel can be produced by known techniques provided that these are capable of securing dispersion of the aqueous phase in the liquid fuel with controllable particle dimensions, and in particular make it possible to transfer to the system of fluids to be emulsified a quantity of energy sufficient to divide the dispersed aqueous phase into particles with a mean diameter between the values indicated above.
[0026] For this purpose, the equipment described in patent EP-124,061 can advantageously be used. That equipment consists of a turbo transducer comprising an emulsification chamber wherein the liquid fuel and the aqueous phase are subjected to a combined mechanical and electromagnetic action. The entry of the fluids into the emulsification chamber takes place via an injector which imparts to the fluids a turbulent motion of mainly axial direction.
[0027] Another type of equipment and corresponding process advantageously usable to produce an emulsion according to the present invention are described in European patent application No. 98109242.2, filed on 20.05.98. This process involves the use of an emulsification chamber wherein the fluids to be emulsified are injected via an injection system which imparts to the fluids a motion having substantially orthogonal direction with respect to the overall direction of movement of the fluids across the emulsification chamber. This injection system can in particular be created by means of a diffuser equipped with an inlet through which a flow of liquid is fed in an essentially axial direction and at least one outlet which leads to the interior of the chamber with its axis lying on a plane substantially orthogonal to the direction of flow on entry. In this way, an efficient dispersion of one fluid into the other is effected, with formation of particles of the dispersed phase of mean diameter of the order of one micron, or even lower. Preferably, the liquid fuel and the aqueous phase are mixed together before being fed into the emulsification chamber. In a preferred embodiment, the diffuser comprises a hollow cylindrical body having in its side wall through holes with radial axis, the said cylindrical body having one end connected to the inlet of the emulsification chamber and another end closed. At the outlet of the emulsification chamber, there is preferably a conveyor for the emulsion comprising a hollow cylindrical body having through holes with radial axis in its wall side, the said cylindrical body having one end connected to the outlet from the emulsification chamber and another end closed.
[0028] The emulsions thus produced are stable in time even without addition of surfactants, and in any case have sufficient stability for their use in thermal or thermoelectric plants, where long periods of fuel storage are generally not required.
[0029] The present invention will now be further illustrated with reference to the attached drawings, in which:
Figure 1 is a schematic representation of a thermal plant in which the process according to the present invention can be implemented;
Figure 2 is a schematic representation of a device for producing and storing an emulsion of a combustible oil with water containing a sulphur sorbent for use in the process according to the present invention.
[0030] With reference to Figure 1, the thermal plant comprises a combustion chamber (1), generally prism-shaped, into which are inserted the burners (2), generally arranged in a ring at one or more levels. To the burners is connected a device (not shown in Figure 1) for feeding the fuel to the burners themselves. Typically, on the walls of the chamber (1) and along the path of the gaseous effluents there are tube linings and/or heat exchangers (not shown in Figure 1), by means of which the heat produced from the combustion is transferred to a fluid (for example water/steam, diathermic oil, and the like) which makes it possible to utilize this heat, for example in a plant for the generation of electric current. Inserted at the base of the combustion chamber (1) is the duct (3) for the entry of hot air (to support the combustion), while at the top is the duct (4) for the removal of the gaseous effluents produced by the combustion. Along this duct (4), further heat exchangers (5), for example of Ljungstroem type, which allow to recover at least in part the residual heat transported by the gaseous effluents and to utilize it to preheat the air entering the combustion chamber, can be inserted. Via a duct (6), the gaseous effluents are conveyed through a device (7) for removal of the solid particles transported by the effluents themselves, for example an electrostatic precipitator, with formation of ash which is collected in a collector (8). The gaseous effluents are then passed through the duct (9) to the chimney stack (10).
[0031] Figure (2) represents a possible embodiment of a plant for producing or storing the emulsion of combustible oil with water containing a sulphur sorbent, which is fed to the burners of the thermoelectric plant described above.
[0032] This plant comprises a system for producing the aqueous solution of sorbent comprising a storage tank (11) for the sulphur sorbent, containing the sorbent in concentrated form (that is in the form of a solid or a concentrated solution), connected to a dilution tank (12) via a metering pump (13). In the dilution tank (12), the aqueous solution of sorbent is prepared at the desired concentration, for example by introducing mains water via a duct (14). In the dilution tank (12), there is preferably a mechanical stirrer (not shown in Figure 2), to facilitate dissolution of the sorbent in the water. From the dilution tank (12), the solution of sorbent is introduced, via a metering pump (15), into an emulsification device (16), consisting of an emulsifier, or several emulsifiers arranged in series, into which is fed, via the metering pump (17), the combustible oil coming from a service tank (18), in its turn connected to a storage tank (19) via a feed pump (20). The emulsion produced by the emulsifier is then passed to an accumulation tank (21), and then, via one or more thrust pumps (22), to the burners (2) of the boiler. The ducts which connect the emulsion production zone with the rest of the plant are equipped with a system of valves (23) which make it possible to cut off the emulsifier (16) from the feed to the burners (2) and hence to feed the burners (2) with the fuel alone.
EXAMPLE 1
[0034] Combustion trials were performed using an industrial diathermic oil tube bundle boiler from the firm U. Girola, model HT/O 12 (nominal thermal power: 1395 kW; furnace thermal power: 1660 kW), equipped with a monobloc combustible oil burner from the firm Riello, model Press 200 T/N Eco, with three flame-jump stages with mechanical atomization.
[0035] In a first trial, the furnace was fed with a combustible oil (C.O.) alone, of the type Denso BTZ, produced by Cam Tecnologie, having a viscosity greater than 13°E and a sulphur content of 0.75 % by weight. The SOx concentration in the gaseous effluents (anhydrous smoke) was measured in accordance with the standard UNI 10246.1, and that of NOx in accordance with the standard UNI 9970, using an analyser from the firm Eurotron, model Greenline. The theoretical concentration of SOx calculated on the basis of the stoichiometric ratios was 1233 mg/Nm3 @ 3% O2.
[0036] The same boiler was then fed with a water-in-oil emulsion of the same combustible oil containing 20% by weight of mains water. The emulsion was prepared using an emulsifier from the firm Mec System, model SS, equipped with a GA/AB adapter.
[0037] Next, emulsions obtained with the same equipment indicated above, wherein the mains water had been replaced by an aqueous solution of NaOH with increasing concentrations of NaOH corresponding to a theoretical SOx reduction, calculated on the basis of the stoichiometric ratios, of 200, 400, 600, 800, 1000, 1200 and 1233 mg/Nm3 @ 3% O2 respectively, were fed into the boiler. In all cases in the emulsion produced a mean size of about 0.1 µm for the particles of aqueous phase dispersed in the fuel was found by Scanning Electron Microscope (SEM) analysis. The SEM analysis was performed on samples obtained by freezing the emulsion at -80°C followed by sectioning.
[0038] For every test, the actual concentration of SOx in the gaseous effluents was measured, and from this the actual SOx reduction and hence the SOx reduction efficiency were obtained.
[0039] The results of the tests are given in Table 1. As can be seen, the process according to the present invention makes it possible to obtain a high efficiency of SOx reduction, close to 100% and in any case not less than 90% (mean value: 92.4%), and a considerable reduction in NOx (about 20-30% compared to the corresponding emulsion without NaOH).
EXAMPLE 2
[0040] The combustion process according to the present invention was implemented on a thermo-electric power plant characterized by an electrical output power of 30 MW.
[0041] The power plant, the design of which (as regards the thermal part) corresponds to that reproduced in Figure 1, was made up of a boiler having eight tangential burners, each with a thermal power of 14 MW, arranged on two levels, which produced up to a maximum of 135,000 kg/hr of steam at the pressure of 92 kg/cm2 and at the temperature of 512°C.
[0042] To perform the tests, a plant for the production of the water-in-oil emulsion, the design of which corresponds to that reproduced in Figure 2, was inserted into the original plant, between the service tank and the feed system to the burners, using a concentrated solution of NaOH at 30% by weight as the sulphur sorbent, diluted in the dilution tank to obtain the desired concentration by introduction of mains water.
[0043] In a first test, the boiler was fed with a combustible oil alone having a sulphur content of 0.47% by weight. The theoretical concentration of SOx in the gaseous effluents calculated on the basis of the stoichiometric ratios was 752 mg/Nm3 @3% O2. The concentration of SOx actually measured, in accordance with the method described above, was between 716 and 765 mg/Nm3 @3% O2, with a mean value of 740 mg/Nm3 @3% O2.
[0044] The same boiler was then fed with a water-in-oil emulsion of the same combustible oil containing 18% of mains water. The flow rate of the fuel to the burners was suitably adjusted to maintain the electric power output at 30 MW. The SOx concentration in the gaseous effluents was between 704 and 759 mg/Nm3 @3% O2, with a mean value of 731 mg/Nm3 @3% O2.
[0045] Next, the boiler was fed with an emulsion of the same type in which the mains water had been replaced with an NaOH aqueous solution having a concentration such as to obtain a quantity of NaOH of 0.51% by weight relative to the total weight of the emulsion, corresponding to a theoretical SOx reduction, calculated on the basis of the stoichiometric ratios, of 352 mg/Nm3 @3% O2. The flow rate of the fuel to the burners was suitably adjusted to maintain the electric power output at 30 MW. The SOx concentration in the gaseous effluents was between 343 and 419 mg/Nm3 @3% O2, with a mean value of 381 mg/Nm3 @3% O2. Hence the mean SOx reduction measured was 350 mg/Nm3 @3% O2, corresponding to an efficiency of 99.43%.
[0046] An elemental analysis was performed by the SEM-EDX technique (SEM analysis with back-scattered electron detector) on the ash collected from the electrostatic precipitator, from which it was found that the ash consisted essentially of particles of sodium sulphate, with the presence of particles of unburnt material covered with sodium sulphate. To check for the possible presence of unreacted NaOH, a titration curve with a 1 N HCl solution was determined on the ash. The initial pH value of the ash was about 10, while the titration curve demonstrated the presence of sodium carbonate in a quantity of about 2-3% by weight. These results demonstrate the substantial absence of unreacted NaOH in the ash, since the presence of NaOH even in small quantities would have resulted in a much higher initial pH value (around 14) and a titration curve typical of a strong base.
1. Process for combustion of a sulphur-containing liquid fuel with reduced emission of
sulphur oxides (SOx), the said process comprising:
preparing an aqueous solution of a sulphur sorbent;
forming a water-in-oil emulsion of the said aqueous solution with the sulphur-containing liquid fuel so as to obtain a predetermined quantity of the sulphur sorbent in the emulsion;
feeding the said emulsion into a combustion device;
characterized in that in the emulsion the aqueous solution of the sulphur sorbent is dispersed in the liquid fuel in the form of particles having a mean diameter such as to obtain an SOx reduction efficiency of at least 90%.2. Process according to Claim 1, wherein the SOx reduction efficiency is at least 95%.
3. Process according to Claim 1 or 2, wherein the aqueous solution of the sorbent is
dispersed in the liquid fuel in the form of particles having a mean diameter of less
than 5 µm.
4. Process according to Claim 3, wherein the aqueous solution of the sorbent is dispersed
in the liquid fuel in the form of particles having a mean diameter of between 0.01
and 2 µm.
5. Process according to Claim 4, wherein the aqueous solution of the sorbent is dispersed
in the liquid fuel in the form of particles having a mean diameter of between 0.05
and 1 µm.
6. Process according to any one of the preceding claims, wherein the sulphur sorbent
is at least partially soluble in water.
7. Process according to Claim 6, wherein the sulphur sorbent has a solubility (at 25°C)
greater than 2% by weight.
8. Process according to Claim 7, wherein the sulphur sorbent has a solubility (at 25°C)
greater than 15% by weight.
9. Process according to any one of the preceding claims, wherein the sulphur sorbent
is selected from oxides, hydroxides, chlorides, carbonates and acetates of alkali
or alkaline earth metals, or mixtures thereof.
10. Process according to Claim 9, wherein the sulphur sorbent is selected from sodium
hydroxide, potassium hydroxide, or mixtures thereof.
11. Process according to any one of the preceding claims, wherein the quantity of water
present in the emulsion ranges from 5 to 40% by weight.
12. Process according to Claim 11, wherein the quantity of water present in the emulsion
ranges from 10 to 30% by weight.
13. Process according to any one of the preceding claims, wherein the liquid fuel has
a sulphur content greater than 0.2% by weight.
14. Process according to Claim 13, wherein the liquid fuel has a sulphur content ranging
from 0.25% to 2% by weight.
15. Plant for the combustion of a sulphur-containing liquid fuel, the said plant comprising
a combustion chamber, at least one burner inserted into the said combustion chamber,
a device for producing an emulsion of the liquid fuel with an aqueous solution of
a sulphur sorbent, a tank for accumulating the said emulsion connected to the said
device for producing the emulsion, and a system for feeding the emulsion from the
accumulation tank to the burner, characterized in that the said emulsion production
device is capable of dispersing the aqueous solution of the sorbent in the liquid
fuel in the form of particles having a mean diameter of less than 5 µm.
16. Plant according to Claim 15, wherein the emulsion production device is capable of
dispersing the aqueous solution of the sorbent in the liquid fuel in the form of particles
having a mean diameter ranging from 0.01 to 2 µm.
17. Plant according to Claim 16, wherein the emulsion production device is capable of
dispersing the aqueous solution of the sorbent in the liquid fuel in the form of particles
having a mean diameter ranging from 0.05 to 1 µm.
18. Plant according to any one of Claims 15 to 17, further comprising a tank for storing
the sulphur sorbent, containing the sorbent in a concentrated form, a dilution tank
equipped with an inlet connected to the said storage tank and with an outlet connected
to the emulsion production device, and a duct for feeding the water into the said
dilution tank.
19. Plant according to any one of Claims 16 to 18, further comprising a duct for entering
hot air into the combustion chamber and a duct for removing the gaseous effluents
produced by the combustion from the combustion chamber.
20. Plant according to Claim 19, wherein along the duct for removing the gaseous effluents
a device for the elimination of the solid particles transported by the gaseous effluents
is present.