WO2006037952A1

WO2006037952A1 - Catalyst delivery system

Info

Publication number: WO2006037952A1
Application number: PCT/GB2005/003717
Authority: WO
Inventors: Trevor R. Griffiths; B. M. Gibbs; S. K. Roy; R. C. Lundin
Original assignee: Lgr Llc
Priority date: 2004-10-01
Filing date: 2005-09-27
Publication date: 2006-04-13
Also published as: AU2005291124A1; CA2582965A1; BRPI0516757A; KR20070102992A; AU2005291124B2; RU2386078C2; JP2008514898A; MX2007003918A; EP1800057A1; RU2007116040A; CN101107476A; US20080264047A1; GB0421837D0

Abstract

The present invention provides a catalytic aerosol delivery system for generating an aerosol containing chemical catalyst pre-cursors for delivery either directly into the flame zone of a combustion reaction system, or directly into the inlet air or inlet fuel or the fuel/ air mixture, or directly into the hot exhaust gases of a combustion reaction, or any combination of these three. The system and the composition of the invention enables a reduction in pollution emitted from the combustion chambers and ensures more efficient and clean combustion. In most applications, the combustion system and composition of the invention results in improved fuel economy.

Description

Catalyst Delivery System

Delivery systems for generating sparging gases containing catalyst particles and delivering them into a flame zone of combustion systems are known in the art.

Searles and Bertelsen (In Business Briefing: "Global Truck and Commercial Vehicle Technology"; London' World Marketing Research Centre; 2000; p. 97-102; EU Directive 1999/99 EC) have reviewed the existing technologies that are able to meet the EU and US exhaust emission regulations for diesel-powered trucks and other commercial vehicles, or heavy-duty vehicles. These technologies include diesel oxidation catalysts, DeNOx catalysts and nitrogen oxide (NOx) adsorbers, selective catalytic reduction (SCR) and diesel particulate filters (DPFs), as well as filter technology for particulate matter crankcase emission control.

The catalytic converter was first introduced in the US in 1974 in passenger cars and currently more than 275 million of the world's 500 million cars and nearly 90% of all new cars produced worldwide are equipped with catalytic converters. However, exhaust emission control technology for diesel powered heavy-duty engines has not yet experienced a similar, widespread application.

Another area of concern is the sulphur content of diesel fuel. Sulphur has a major negative impact on the catalyst performance due to the strong adsorption of sulphur on to the catalyst surface. Therefore the surface area of the catalyst is reduced and as a result the amount of nitrogen dioxide formed on the oxidizing catalyst is reduced. This presents a problem for some DPFs and NOx adsorbers as they rely on nitrogen dioxide for their regeneration. Further, sulphur reacts with chemical NOx traps more strongly than NOx, thereby decreasing NOx storage capacity and requiring more vigorous and frequent regeneration, and hence increasing fuel consumption.

It should be noted that a diesel oxidation catalyst converts carbon monoxide and hydrocarbons to carbon dioxide and water. Therefore these systems decrease the mass of particulate matter emissions but it has been found that these systems have little effect on NOx emissions.

Diesel oxidation catalysts may also be used in conjunction with NOx adsorbers, DeNOx catalysts, DPFs or SCR to decrease nitrogen dioxide levels or to clean up any bypass of injected hydrocarbons, urea or ammonia.

The conventional automotive catalytic converter consists essentially of a ceramic honeycomb, through which the exhaust gases pass. The insides of the catalytic converter are coated with a fine layer of platinum or palladium, rhodium and cerium catalyst. The platinum component of the catalyst oxidizes CO to CO₂ and UHCs to CO₂ and steam, and the rhodium reduces the levels of NOx formed.

It is known that catalytic converters degrade with time and use. Since 1984 catalytic converters have been fitted to all vehicles in Germany. As a result of this, trace amounts of platinum and rhodium have been detected alongside autobahns.

WO 02/083281 discloses a sparging gas catalyst delivery system wherein a catalyst mixture receptacle comprises an air inlet to an inlet tube, a secondary splash chamber and a gas outlet. Gas is sparged through the liquid in the receptacle via a tube having an outlet near the bottom of the liquid and the resulting combination of gas, vapour from the liquid, liquid splashes and catalyst is directed towards the combustion zone. However, according to this document it is important that the liquid vapour and liquid catalyst splashes are not transported to the combustion zone and WO 02/083281 thus discloses that a secondary splash chamber is necessary. This chamber serves to reduce the effects of liquid catalyst splashing into or condensing within the connecting duct between the receptacle and the combustion zone as this reduces the performance of the system. It is also stated in WO 02/083281 that such splashing is undesirable as it results in an uncontrollable rate of consumption of the catalyst mixture. This can lead to unpredictable combustion and/or too high a rate of catalyst consumption.

US Patent No. 6776606 also discloses a catalytic delivery system comprising a sparging tube connected to a gas inlet through which a gas, usually air, is bubbled through the catalytic mixture via a tube having an outlet near the bottom of the liquid. In this way, it is stated, catalyst particles may be non-evaporatively fluidised and carried into the oxidation flame zone by a gas stream through the popping of the bubbles at the liquid-gas interface. The catalyst particles are then carried via a transport line into a flame zone by the gas stream

One problem which is associated with the use of sparging gas to introduce catalysts or catalyst precursors into combustion systems is that some of the catalysts or catalyst precursors can adhere to surfaces with which the gas stream comes into contact. Therefore, some of the catalyst precursors used in the prior art will adhere to the surfaces of any feed lines into which the sparging gas leaving the catalyst solution receptacle flows before reaching the combustion chamber. This reduces the efficiency of the system and represents a waste of expensive catalyst material.

An aerosol is defined as a fine dispersion of solid or liquid particles in a gas. The aerosol delivery system used in the present invention works in a similar manner to that used in the spraying of a dilute solution into a flame as employed in atomic absorption spectroscopy. The process of generating aerosols as fine sprays may be referred to as nebulization or atomization. Aerosols are generated by sucking up or pumping a liquid and mixing it under turbulent flow with a gas, usually air, and ejecting it through one or more small orifices. The loading of the air depends on a variety of parameters, including gas flow and liquid flow rates. Aerosols can also be generated by ejecting a liquid alone under high pressure through one or more small orifices. Ultrasound devices can also be used to generate finely dispersed aerosols. In the context of the present invention the terms atomization and nebulization can be used interchangeably as indicating the provision of an aerosol: this aerosol consists of a fine spray of catalytic material that is delivered into a pre-combustion zone and/or a combustion zone and/or to a post-combustion zone. Aerosol delivery systems are known in the art. However, to date systems of this type have not been employed in the delivery of catalytic materials to combustion zones.

The production of an aerosol in accordance with the invention is to be distinguished from the principle of sparging which involves the process of bubbling a chemically inert gas through a liquid. In the case of the present invention, an aerosol is formed by turbulent mixing of liquid containing catalyst in solution with the gas, under pressure, immediately prior to ejecting it through a fine nozzle. Mixing and nebulizing in this way provides a steady and continuous supply of aerosol which contains catalyst at trace levels.

It is an aim of the present invention to overcome various disadvantages of or improve on the properties of the prior art systems. Thus it is an aim of the invention to provide an aerosol delivery system that can be introduced directly into one or more of the inlet air or the combustion zone or into the hot exhaust gases of a combustion system.

It is a further aim of the invention to provide an aerosol delivery system that provides a significant improvement in the reduction of CO, Nox, UHCs and sulphur oxide emissions from combustion systems relative to the prior art systems.

It is a further aim of the present invention to provide an aerosol delivery system that reduces the corrosion that occurs within combustion systems employing low-NOx burners and thereby increases the lifetime of such combustion systems relative to the systems of the prior art.

It is a further aim of the present invention to provide an aerosol delivery system that increases the combustion efficiency of a combustion system relative to the systems of the prior art. It is therefore an aim of the present invention to maintain the flame temperature of the combustion system and reduce the excess air levels so as to improve the thermal efficiency of the combustion system.

It is also desirable that the aerosol delivery system of the present invention reduces the amount of carbon and char that is deposited on the interior of the combustion system.

Furthermore it would be desirable that the aerosol delivery system of the present invention reduces the noise and vibration associated with combustion systems relative to prior art systems.

It is a further aim of the present invention to provide an aerosol delivery system that can be used to revive inefficient converters, such as those which have been in service for a period of time.

It is a further aim of the present invention to provide an aerosol delivery system wherein the catalyst is retained within the combustion system.

It is a further aim of the present invention to provide an aerosol delivery system that interacts with the mercury found in coal, and other combustible materials and high temperature gas streams, and prevents or reduces the amount emitted in the exhaust gas.

The applicant has surprisingly found that these and other problems can be addressed by delivering the catalysts or catalyst precursors directly into and around the combustion site by use of an aerosol delivery system. Thus, the present invention satisfies some or all of the above aims.

According to one aspect of the present invention there is provided an aerosol delivery system for use in conjunction with a combustion apparatus, the system comprising: a chamber including a first inlet for supplying a source of gas to the chamber, a second inlet for supplying a catalyst solution containing one or more inorganic metal salts in a solvent to the chamber, and an atomising nozzle for releasing fluid from the chamber in the form of an aerosol; wherein the first inlet and the second inlet and atomising nozzle are arranged so that the gas and fluid in the chamber mix and combine to form an aerosol when released through the nozzle; and wherein the nozzle is in fluid communication with one or more of: a pre- combustion zone, a combustion zone and a post-combustion zone.

In an embodiment, the nozzle is present in the combustion zone. In another embodiment, the nozzle is present in a pre-combustion region where air and fuel are mixed prior to combustion. In another embodiment, the nozzle can be in a pre-combustion region where there is only fuel and/or the nozzle can be in a pre-combustion region where there is only air i.e. before they two components are mixed. In another embodiment, the nozzle can be in a post-combustion region. The nozzle thus provides aerosol to the combustion products in an exhaust region. The nozzle includes one or more discharge orifices to allow the fluid mixture to exit in the form of an aerosol. The shape of the aerosol discharge exiting the nozzle depends on the size, number and arrangement of the discharge orifices in the nozzle. The aerosol shape can thus be produced as required. A substantially conical shape for the nozzle is preferred as this leads to a conical aerosol.

In another embodiment, more than one nozzle can be present. Thus, nozzles can independently supply aerosol to one or more of trie above regions. The catalytic solution may be the same or different in each case. The nozzle shape and arrangement of discharge orifices can be the same or different in each case xvhere more than one nozzle is present.

In an embodiment of the present invention, the supply of gas and catalytic solution to the chamber is continuous so that the aerosol may be sprayed continuously from the nozzle. Alternatively, the supply of the gas or the solution to the chamber may be interrupted so that the aerosol is sprayed intermittently from the nozzle.

Aerosols can also be generated without the use of air. If the catalyst precursor solution is subjected to high pressure and allowed to exit through a very fine nozzle it exits as an aerosol. Thus in an alternative embodiment of the above applications, where an aerosol is described as being generated using a gas, for example air, in combination with a solution of catalyst then such a generation system can be replaced by a high pressure gasless system; there is no need for a supply of pressurised gas. It is sufficient simply to supply a solution of the catalyst under pressure to the nozzle. This embodiment has applications in all of the cases for which the aerosol is produced by mixing gas and solution, such as industrial burners, boilers and SI and diesel engines (i.e., both open and closed flame systems).

The combustion may take place in open flame or closed flame applications. Open flame applications include coal, gas and oil fired boilers and furnaces. Closed flame applications include petrol and diesel internal combustion engines. In an embodiment of the present invention, the aerosol is used in vehicles that have been fitted with a catalytic converter.

As used herein, a combustion zone means and includes an area where oxidation of a fuel occurs and the area immediately surrounding that area, for example, a combustion chamber.

The one or more metal salt in the catalyst solution is a catalyst for the combustion of the fuel being consumed or for the oxidation or reduction of th.e combustion products (exhaust) to harmless or cleaner products. The catalyst may be a simple or binary compound, a complex metal salt, or an organometallic compound.

Preferably the catalytic solution of the present invention comprises one or more inorganic salts or organometallic compounds of platinum, palladium, rhodium, rhenium, ruthenium, osmium, cerium, iridium, indium, magnesium, aluminium, titanium, copper, zinc, lithium, potassium, sodium, iron, molybdenum, manganese;, gold or silver. Preferably the solution of the present invention comprises one or more compounds of a Group VIII element (i.e. Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt), magnesium or aluminium. More preferably the compound is a compound of platinum, rhodium, rhenium, magnesium or aluminium. If only one compound is used the solution must contain either a platinum or a rhodium salt. In an embodiment, the compound is present in solution in a concentration of from 0.1 to 2.0 mg/ml. More preferably the concentration is from 0.2 to 1.0 mg/ml. The molecular weight of the compounds may be from 200 to 2000, and more preferably is in the range 200 to 750.

It is especially preferred that the inorganic metal salts are present as HaPtCl₆, RhCb, HReO₄, MgCl₂ and AICI3. The complex ions that are formed in water from such inorganic metal salts include [PtCl₆]^2", [Rh(H₂O)₆J³⁺ and [ReO₄]^".

In a preferred embodiment of the invention the catalyst precursor solution concentrate comprises one or more metal salts wherein the metal is selected from platinum, rhodium, rhenium or aluminium. The concentration of platinum as H₂PtCU₁OH₂O in the catalyst precursor solution concentrate is in the range of 0.2 to 1.0 mg/ml; more preferably in the range of 0.5 to 0.7 mg/ml; especially preferably at a concentration of 0.6 mg/ml. The concentration of rhodium in the catalyst precursor solution concentrate as RJ1CI3 is preferably in the range of 0.04 to 1.2 mg/ml; more preferably in the range of 0.06 to 0.09; especially preferably at 0.07 mg/ml. The concentration of rhenium in the catalyst precursor solution concentrate as HReO₄ is preferably in the range of 0.05 to 1.5 mg/ml; more preferably in the range of 0.08 to 1.2 mg/ml; especially preferably in the range of 1.0 mg/ml. The concentration of aluminium as AICI3 in the catalyst precursor solution concentrate is preferably in the range of 0.05 to 1.0 mg/ml; more preferably at a concentration of 0.07 mg/ml.

In a further preferred embodiment of the invention aluminium in the solution of the present invention is substituted by magnesium such as MgCl₂ at a concentration in the range of from 0.05 to 1.0 mg/ml; more preferably at a concentration of 0.07 mg/ml.

In a still further preferred embodiment of the invention only a proportion of the aluminium is replaced by magnesium so that the catalyst precursor solution comprises both aluminium and magnesium. In a still further preferred embodiment of the invention, where both platinum and rhodium are present in the catalytic solution, the ratio of platinum to rhodium is about 8.6: 1 ; the ratio of platinum to aluminium is about 8.6:1; the ratio of platinum to rhenium is about 6:1 and where aluminium is substituted by magnesium the ratio of platinum to magnesium is about 8.6:1.

However, the ratios of components of the invention may vary above and below these limits. Therefore, the ratio of platinum to rhenium is preferably in the range of from 30:1 to 1:1; more preferably in the range of 15:1 to 2:1. The ratio of platinum to aluminium or magnesium is preferably in the range of 30: 1 to 1 : 1 ; more preferably in the range of 15:1 to 2:1. The ratio of platinum to rhodium is preferably in the range of from 30:1 to 4:1; more preferably from 15:1 to 4:1.

In a further embodiment of the invention the catalyst precursor solution comprises only platinum and one other inorganic metal salt of rhodium, rhenium, magnesium or aluminium.

The solvent may be any solvent which is capable of dissolving the one or more metal salt (catalyst) and which is capable of forming a stable aerosol. Ideally, the solvent has a significant vapour pressure at normal temperature and pressure though the solvent must not be too volatile otherwise the catalyst could be deposited prematurely in the feed line and/or consumed too quickly. The most effective solvents have boiling points in the range 8O⁰C to 14O⁰C at normal temperatures and pressure. The solvent is preferably water. Alcohol (such as methanol or ethanol) or a hydrocarbon solvent may also be used as a solvent. The solvent may also be a mixture of suitable solvents. Water is the preferred solvent due to its ability to dissolve a number of inorganic metal salts and its ability to form a stable aerosol.

The solvent may additionally include an antifreeze such as, for example, ethylene glycol. Other additives can also be included as necessary. In a further aspect, the present invention provides a method for catalysing the combustion of a fuel, the method comprising the steps of: a) providing a supply of a solution of catalyst and a supply of a pressurised gas to a chamber, wherein the chamber includes a nozzle in fluid communication with one or more of: a pre-combustion zone, a combustion zone and a post-combustion zone, b) mixing the solution and the gas in the chamber, c) forcing the mixture of solution and gas through the nozzle to form an aerosol in the pre-combustion zone, combustion zone or post-combustion zone of fuel combustion apparatus.

The aerosol of the present invention and the fuel may be introduced into the combustion zone of a fuel injection diesel or petrol engine either simultaneously or separately.

In an embodiment of the present invention the, aerosol may be introduced into the combustion zone of an engine with the air from the carburettor. In order to minimize the distance between the point at which the inorganic metal salts are introduced to the combustion system and the required point of use (i.e. the combustion zone) the aerosol is introduced into the air stream of spark ignition engines just before it enters the carburettor so that it is mixed with the vaporized fuel and the mixture then enters the engine. For diesel engines, the aerosol is introduced into the air stream after it has passed through the air filter.

Combustion requires the presence of radicals in and around the flame, and the catalytic material, such as platinum and/or rhodium, that the system of the present invention introduces into the combustion process improves the process significantly. This is achieved by enabling a greater amount of radicals to be generated, and thus reducing the amount of excess oxygen normally required, and hence saving fuel. This also improves emissions. In an embodiment, the present invention provides a method for reducing the harmful emissions of a combustion system, particularly NOx, by introducing an aerosol containing one or more inorganic metal salts into the final hot exhaust gas streams of combustion systems exiting a combustion system. These systems may or may not employ emission reduction systems or technologies in, before or just after the combustion zone. Preferably the aerosol of the present invention is introduced into the hot exhaust gas streams of an internal combustion engine (using diesel, petrol, bio-diesel and alternative fuels etc) or power or process station boilers, burners and dryers.

Coal is one fuel that benefits from the combustion technology of the present invention. One major application of the invention is thus to the various NOx reduction techniques used in coal combustion. In particular the process can be applied to coal combustion in furnaces and boilers employing various NOx reduction devices and procedures for reducing carbon in ash, etc.

The two major mechanisms of NOx formation in combustion processes are thermal-NOx and fuel-NOx. The former is dominant when the fuel contains no inherent nitrogen (e.g., natural gas) and the latter dominant when the fuel is coal or heavy fuel oil or similar. Combustion modification techniques aim to limit NOx formation in the early stages of the combustion process. Our process is compatible with and applicable to these methods.

Preferably the aerosol of the present invention is introduced into the hot exhaust gas streams of combustion systems in combination, directly or indirectly, with ammonia or urea and, as required, in conjunction with added hydrocarbons and air to attain the required reaction temperature. The aerosol of the present invention may be introduced simultaneously or separately into the hot exhaust gas stream, or other appropriate site, of the combustion system employing the ammonia/urea/hydrocarbon/air system for NOx, CO and carbon reduction, particularly in coal-fired and similar oil or solid fuel-fired plant employing SNCR (Selective Non-Catalytic Reduction) strategies to reduce emissions. In the air staging method to reduce NOx, the combustion air is staged so that the primary combustion zone operates with an overall fuel-rich stoichiometry and the remaining air is injected downstream. Applying our process to this method involves injecting the catalyst at suitable point(s) in both stages. Low-NOx burners are designed to achieve the staging effect through partitioning the air and fuel flow inside the burner in such a manner so as to delay combustion, reduce the availability of oxygen and reduce peak flame temperature. All of these factors help reduce NOx. Applying our process to this method involves the aerosol catalyst being introduced at all points so that it can additionally enhance the radical reactions that reduce the NOx that is still formed, thereby improving their efficiency and the overall efficiency of NOx reduction as well as that of the combustion process as a whole.

NOx levels can also be reduced by the technique of flue gas recirculation, which introduces a diluent into the combustion chamber. Applying our process to this method involves introducing the aerosol catalyst and intimately mixing it with the diluent. Another way of lowering NOx is by lowering excess air levels. This reduces NOx but can cause unwanted problems such as unstable combustion, reduced burnout, slagging, fouling and corrosion. However, using the aerosol catalyst of the present invention minimises these problems since it enables the combustion process to proceed normally. This is due to the extra radicals it generates in the flame.

There are also a number of post-combustion NOx control techniques. These are generally termed flue gas treatments, and can be subdivided into: (a) Selective Catalytic Reduction (SCR), (b) Selective Non-catalytic Reduction (SNCR), and (c) Non-selective Catalytic Reduction (NSCR).

Method (b) employs the injection of ammonia gas or aqueous ammonia or aqueous urea into the flue gas. The radical reaction that takes place essentially converts the NOx into oxygen and nitrogen, but the reaction only takes place within limited reaction conditions. The introduction of aerosol catalyst in accordance with another aspect of the present invention into flue gases (in the same manner as the aerosol catalyst is introduced into the combustion region or the pre-combustion region) will enhance these reactions, and extend the operation temperature window. In accordance with the process of the present invention, the catalyst is injected into or with the ammonia gas or aqueous ammonia or urea and ammonium and/or other salts are added as necessary into the flue gas.

The catalyst supplied to the flue gas in accordance with the method of the present invention can also be used to maintain the efficiency and extend the lifetime of SCR catalysts, be they platinum-based or comprising other recognised catalytic agents. The platinum and rhodium homogeneous catalyst in the gas stream entering the catalyst grid system will aid the catalysis taking place on the catalyst, and the platinum and rhodium that attach and remain on the catalyst, platinum-based or otherwise, will help prevent carbon and char build-up on the SCR catalyst by participating catalytically in their oxidation to carbon dioxide gas.

One example concerns combustors employing SCR, SNCR or NSCR techniques to reduce NOx. It is possible, and common, that some NOx still remains and exits the plant through the final stack into the atmosphere. A technique used to reduce final stack NOx is to employ final stack injection of ammonia or urea. If the temperature is not high enough then a pilot flame, burning a suitable hydrocarbon gas, is also employed to bring the exiting gases within the temperature window and thus enable the ammonia or urea to react with the NOx. The nebulized catalyst can be injected into the pilot flame prior to entering the radical reaction region. This will create the platinum and rhodium catalyst species and also lower the temperature window so that the radical reaction will be more efficient and the quantity of gas required for the pilot flame will be reduced, leading to a fuel saving.

The process of the present invention has a number of applications. The aerosol or nebulizing spray that is generated is injected into an air stream that mixes with fuel and enters a combustion zone. This concept can be extended to all high temperature reactions that involve chemical and radical mechanisms. Thus the present invention also includes the concept of the introduction of an aerosol catalyst into all situations where it is known or supposed that vapour phase radical reactions are taking place (since the catalyst generated at the elevated temperature involved will increase the number of radicals present): the applications of the process are thus not limited to those involving combustion but can include high temperature chemical reactions involving radicals, particularly those also involving homogeneous and heterogeneous catalysts in the oil refining industry. The oil- refining industry and certain related industries use platinum catalysts at high temperatures. These deteriorate with time and usage and have to be cleaned or replaced. The present invention has the potential to extend the life and efficiency of such catalysts.

The technology of the present invention as described herein will also have applications in the oil refining industry because the catalytic combustion process of the invention provides increased performance and output, and also reduced maintenance. One particular problem in this area is unwanted soot deposition in the furnaces that supply thermal energy to, for example, oil distillation plant, and the soot has to be removed periodically. The present invention provides a solution to this problem.

The process of the present invention can also be used for CO clean-up as well as soot and char burn-off. All of these processes can be enhanced by the injection of the catalyst aerosol, since radical reactions are involved in each of these processes. Applications include catalytic crackers, reformers and other refining processes, and fluidised bed combustion processes.

In a further embodiment of the invention, spray injection of an aerosol is used to achieve sulfur capture using one or more additives based on compounds of elements in Group II of the Periodic Table. There are various chemicals and procedures employed to remove oxides of sulfur from exhaust and flue gases. It is believed that the co-injection of noble metal catalyst with these chemicals, or upstream if the gas temperatures are too low to generate the elemental metals, will improve their sulfur removal efficiency and extend the lower temperature limit of the reactions involved.

This process also enables trace amounts of mercury be captured in a similar way. Currently the technology for removing mercury from coal during combustion is desired but unproven or not fully proven. Mercury readily forms amalgams with most metals (but not iron) but including the noble metals and it is believed that it will attach to the platinum and rhodium coated surfaces formed within coal-fired boilers and under the conditions pertaining therein. Of the mercury removal technology currently under test none of the techniques employs the property of mercury to form amalgams.

In one embodiment the metal (catalyst) derived from the solution used in the present invention is either retained in the combustion chamber or adheres to the surface through which exhaust gases pass or it is trapped within the honeycomb structure of the catalytic converter. This is advantageous as the adhered metal (catalyst) then participates in heterogeneous catalyst reactions and therefore provides a continuously renewed catalytic surface upon which continuous reactions occur.

In another aspect of the present invention there is provided a method of pre-treating fuel, the method comprising the steps of: a) providing a supply of a solution of catalyst and a supply of a pressurised gas to a chamber, wherein the chamber includes a nozzle in fluid communication with one or more of: a pre-combustion zone, a combustion zone and a post- combustion zone, b) mixing the solution and the gas in the chamber, forcing the mixture of solution and gas through the nozzle to form an aerosol, wherein the aerosol is applied to solid fuel so as to pre-treat the fuel prior to combustion.

The fuel is preferably solid fuel.

Embodiments of the invention may include the use of an aerosol catalyst composition and delivery system in either open or closed flame applications such as boilers, power or process station boilers, burners and dryers, furnaces, turbine engines, reciprocating engines, incinerator engines, open flames, spark ignition engines, natural gas engines, gasoline engines, rotary engines, internal combustion engines using diesel, petrol, bio-diesel and diesel or petrol engines and other alternative fuel, etc., or systems wherein fuel is oxidised. Usually oxidation of the fuel involves combustion in air or an oxygen rich medium. Oxidation may be affected by supplying other sources of oxygen that liberate oxygen under combustion conditions. The aerosol delivery system of the present invention comprises a rigid container that is impervious to the solution that it contains. The container may be made from any material that is suitable for the desired use of the aerosol. In a preferred embodiment of the invention the container of the aerosol is made from ceramics, metals or plastic or combinations thereof.

The pressurized gas of the aerosol delivery system may be any gas that is suitable for the desired use of the aerosol such as a positively or negatively ionized or neutral gas, for example selected from air, steam, nitrogen, argon, helium, carbon monoxide, carbon dioxide and combinations thereof. Preferably the pressurized gas is air. Under certain circumstances the pressurized gas comprises air and an additional oxygen component or ammonia gas.

The gas of the aerosol delivery system is preferably subjected to a pressure in the range of from 30 to 90 psi. More preferably a pressure in the range of from 50 to 70 psi is required.

The solution of the aerosol delivery system is subjected to pressure. Preferably the solution is subjected to a pressure in the range of from 20 to 70 psi. More preferably the solution is subjected to a pressure in the range of from 30 to 50 psi.

There is a wide range of ways for generating aerosols. Any system that generates an aerosol can in principle be used to generate the catalyst aerosol, and the choice will depend upon the intended application of the catalyst aerosol.

The pH of the catalyst pre-cursor solution used in the aerosol delivery system of the present invention should be such as to prevent deterioration or decomposition with subsequent formation of a colloid or fine precipitate and is preferably less than 5. More preferably the pH of the catalyst precursor solution is in the range of from 4 to 1; even more preferably in the range of 3.0 to 1.4; especially preferably in the range of from 1.6 to 2.2. In a preferred embodiment the present invention generates several catalysts in the flame, or in the exhaust gases, having introduced their precursors directly or by means of the inlet air, into the flame or the exhaust gases. This leads to increased oxygen atom concentration and free radical generation to improve combustion rates and thus efficiency during residence time.

It is believed that certain of the inorganic metal salts and organometallic compounds decompose into elemental form within the hot flame or within the hot exhaust gases creating the traditional combustion elements which catalyse reactions with oxygen and the molecules and radicals formed as intermediates in the combustion process. In the present invention the elemental form of at least one of platinum, palladium, rhodium, rhenium, ruthenium, osmium, cerium, iridium, indium, magnesium, aluminium, titanium, copper, zinc, lithium, potassium, sodium, iron, molybdenum, manganese, gold or silver are present in the flame or within the hot exhaust gases at a level in the region of ppm to ppb. Preferably platinum and rhodium are present in the flame or within the hot exhaust gases at a level in the region of ppm to ppb. The concentration of the inorganic metal salts or organometallic compounds in the aerosol introduced into the combustion system or hot exhaust gases is dependent upon the size and characteristics of each combustion system.

The aerosol delivery systems of the present invention contain inorganic metal salts or organometallic compounds in an amount in the ppm to ppb level that is dependent upon the thermal output and size of the combustion system. Preferably one or more inorganic metal salts are present in the solution at a concentration in the range of from 1 to 1000 ppb. More preferably the one or more inorganic metal salts are present in the solution at a concentration in the range of from 50 to 100 ppb. It has been advantageously found that only low levels of the inorganic metal salts are required to act as catalysts. This enables ppb to ppm levels of these catalyst precursors to be carried into the combustion chambers such, as the combustion chambers of coal or gas-fired industrial boilers or spark ignition and diesel engines. Therefore, the aerosol of the present invention effectively places the inorganic metal salts or organometallic compounds in the region where combustion takes place. The dose rate of the diluted catalyst pre-cursor solution in the form of an aerosol of the present invention is dependent upon the desired use. However, the dose rate is preferably in the range of from 0.1 to 1 US gallons per hour. More preferably the dose rate is 0.5 US gallons per hour. The extent of dilution is dependent upon the rate at which the fuel is consumed or the thermal energy supplied by the boiler.

In a further embodiment of the invention the aerosol is used in connection with combustion chambers using fuel such as diesel fuel, gasoline, number 2 fuel oil, bunker oil, fuel oils refined from crude oil, compressed natural gas, liquefied natural gas, gasohol, hydrocarbons, corn oil, vegetable oil, mineral oil, coal, coal gas, asphalt vapours, oxidisable vapours, wood, paper, straw, biofuels, combustible waste and combinations thereof.

The operating temperature of the combustion system suitable for use in connection with the aerosol of^" the present invention is preferably in the regions of 500 to 2000⁰C; preferably 900 to 1600⁰C; more preferably 1000 to 1500⁰C.

Viewed from a still further aspect the present invention provides a miniature aerosol delivery system for use with diesel or petrol engines. The dimensions of the aerosol delivery system depend on the intended use of the aerosol. Since the system can be arranged not to experience the high temperatures pertaining to, for example, coal-fired plant, a miniature system employing an ultrasonic generator (see above) to produce the fine aerosol can be employed.

Preferably the width of the miniature aerosol delivery system of the present invention can be from between 10 cm to 2 m depending on the intended use.

It is a further advantage of the invention that vibrations of the engine to which the aerosol delivery device and method of the present invention is applied ensures thorough mixing of the catalyst precursor solution. A further benefit of the invention is that the elemental form of the catalyst salts or organometallic compounds, e.g., platinum and rhodium, adheres to the interior of the furnace and to other compounds adhering to the furnace interior that are derived from the components of the catalyst aerosol and therefore catalytic activity continues beyond the period over which the catalytic mixture is sprayed into the system.

The aerosol delivery system may advantageously reduce the noise and vibration associated with combustion engines. For example, the presence of platinum is thought to cause the flame to burn in diesel engines at a lower temperature and thus it does not go out before the piston has reached the end of its travel. A feature of diesel engines is their "rattle," better termed harmonics. This arises when the energy of the expanding gases has decreased beyond a certain point, partly due to the drop in temperature arising from adiabatic expansion and when the flame goes out. When this occurs the piston still has approximately one quarter of its travel still to go. The piston movement at this point changes from a push to a pull action, creating rattle. When the aerosol delivery system of the present invention is installed, the harmonics are much reduced and the engine is much quieter and smoother. Under normal circumstances, when combustion is initiated the resulting expansion pushes the cylinder down. It is believed that the platinum containing aerosol system of the present invention is involved in producing oxygen atoms and thus keeps the flame and expansion going longer. Furthermore, it is believed that the platinum makes for a faster burn, thereby sustaining the flame and contributing to the increased power levels experienced.

The optimum conditions for operating a spark ignition engine for minimum CO and NOx emissions are somewhat opposed. The higher the temperature in the combustion chamber the lower the amount of CO formed and therefore by operating the engine at as high a temperature as possible will minimize CO emissions. However, the reverse is true for the formation of NOx, and for minimum emissions the temperature in the combustion chamber should be as low as possible. Currently, engines are tuned to be close to the crossover in the plots of CO and NOx formation as a function of temperature and in conjunction with the efficiency of the catalytic converter. The unique advantage of the aerosol delivery system of the present invention is that combustion temperatures no longer have to be designed to range around the above crossover temperature for minimizing CO, NOx: and unburned hydrocarbon levels in the exhaust gases from the combustion chamber. The lower temperature regime consequently means that the amount of NOx formed is less, and this quantity is further reduced by the presence of rhodium in the combustion chamber. Another consequence and advantage is that the workload on the catalytic converter is now much reduced and so its efficiency and lifetime is extended.

The inclusion of rhenium in the catalyst concentrate of the present invention is believed to contribute to smoother and quieter engine running and hence its role is considered to be that of making for a smoother flame burn and a smooth front to the flame.

The applicants have surprisingly found that the aerosol delivery system of the present invention improves the burn characteristics of a fuel and therefore less carbon deposited in the combustion system. Furthermore, the amount of catalyst may be later or subsequently reduced. In some circumstances the aerosol delivery system of the present invention results in the production of bright blue flames, which are indicative of particularly efficient fuel combustion. The advantage of this technique is that the combustion system has a cleaner interior, cleaner fly ash, and a small but steady injection of catalyst so that catalyst erosion or poisoning does not take place. Therefore, the present invention provides an increase in the lifetime of the combustion system.

The present invention will now be illustrated by the following figures in which:

Figure 1 is a schematic diagram showing an open flame application according to one aspect of the present invention,

Figure 2 is a side view of an aerosol delivery system according to the present invention,

Figure 3 is a top view of the aerosol delivery system of Figure 2, and Figure 4 is a side view of another aerosol delivery system according to another embodiment of the present invention.

In Figure 1, a supply of air 1 is fed to blower 2 and into mixer 3 where it is combined with fuel from fuel source 4. Oxygen could be used to supplement or instead of the air. The mixture 5 of air and fuel are fed into combustion chamber 6 where combustion takes place. The combustion products 7 i.e. the exhaust gases then exit the combustion chamber and pass through an exhaust region 8 which includes a heat exchanger 9.

The reference letters a to i indicate suitable injection sites for placement of the aerosol delivery system of the present invention. Thus, aerosol spray containing the catalytic solution may be delivered at any of the sites indicated by the letters a to i. More than one such site may be present in the apparatus. Where more than one site is present the catalytic solution delivered may be the same or different as another aerosol delivery site in the same application. The preferred sites are at one or more of a., c and d since this improves combustion and reduces fuel consumption. For reducing NOx levels, aerosol delivery sites in the post-combustion zones are preferred. Thus, delivery at g, h or i are preferred. Injection can also take place with or without the addition of ammonia or urea (not shown) to these regions.

Figure 2 shows a simple injector in which a tangential entry duct 10 supplies catalyst solution to swirl chamber 11 in aerosol delivery head 12. Pressurised gas is delivered by duct 13 to swirl chamber 11. An atomising nozzle 14 includes orifices 15 which are sized and arranged to provide a fine aerosol mist 16. In the example shown, the atomising nozzle 14 is generally conical in shape leading to a conical shape aerosol mist 16. Intimate mixing of the gas and catalysis solution takes place in the swirl chamber 11 prior to ejection through orifices 15 in nozzle 14 due to the positioning of gas duct 13 and duct 10 in swirl chamber 11.

Figure 3 shows a simplified top view of the aerosol delivery device of figure 2. Discharge orifices 15 can be seen disposed in a regular pattern around atomising nozzle 14. The pattern of the orifices is governed by the shape of atomised spray that is desired. Figure 3 shows a conical atomising nozzle 14 since this leads to a conical spray of aerosol 15 which gives rise to the most advantageous effects in terms of reducing fuel consumption and improving NOx levels.

Figure 4 shows a water-cooled atomiser 17 which passes through furnace wall 18 and the inner insulating ceramic brick lining 19 of the furnace. The atomiser 17 is made of metal and includes a water jacket 20 which is formed by providing a source of cooling water 21 through channel 22 within the body of the atomiser 17. Catalyst solution 23 is fed via channel 24 to swirl chamber 25. Pressurised gas 26, in this case air, is fed to the swirl chamber 25 by channel 27. The catalyst solution and air mix in swirl chamber 25 and pass through atomising nozzle 28 and form a spray cone of aerosol 29.

The following examples demonstrate the effectiveness of the invention.

Example 1

A boiler (Johnston 800 hp rated at 33 million BTU's per hour)) was becoming less efficient at producing steam and to offset this the amount of gas supplied was increased. The boiler was examined and found to have a defective air supply resulting in incomplete combustion and carbon deposits within the furnace. The air supply system of the boiler was repaired and theaerosol delivery system of the present invention was installed . Subsequent measurements showed that after installation of the aerosol of the present invention the noise level had decreased from 107 to 97 decibels. The boiler -was run for a month at close to maximum load in operation with the aerosol delivery system of the present invention. After a month it was found that the interior of the furnace was much cleaner and that the fuel savings were around 4%. Further measurements showed that the NOx levels were reduced by 26.8% after 6.5 weeks, from 149 ppm to 109 ppm. After 13 weeks of operation with the aerosol delivery system it was found that the NOx levels had been reduced by 33% overall to 100 ppm and the overall fuel saving was aroαind 4%.

Example 2 Another boiler (Johnston 800 hp rated at 33 million BTU's per hour)) was run at around 25% load. After determining the baseline NOx level and the percentage excess of oxygen the aerosol delivery system of the present invention was installed and in operation for three weeks. The results showed that the boiler could be maintained at 25% load with excess oxygen reduced by 45% and hence a fuel reduction of about 4%. The NOx level of this boiler was reduced by 36% from 136 ppm to 87 ppm. The flame was described by the company boiler engineer as the bluest flame he had seen closest to a pure hydrogen flame.

Claims

1. An aerosol delivery system for use in conjunction with a combustion apparatus, the system comprising: a chamber including a first inlet for supplying a source of gas to the chamber, a second inlet for supplying a catalyst solution containing one or more inorganic metal salts in a solvent to the chamber, and an atomising nozzle for releasing fluid from the chamber in the form of an aerosol; wherein the first inlet and the second inlet and atomising nozzle are arranged so that the gas and fluid in the chamber mix and combine to form an aerosol when released through the nozzle; and wherein the nozzle is in fluid communication with one or more of: a pre- combustion zone, a combustion zone and a post-combustion zone.

2. An aerosol delivery system as claimed in claim 1, wherein the nozzle is present in the combustion zone.

3. An aerosol delivery system as claimed in claim 1 or 2, wherein the nozzle is present in a pre-combustion region where air and fuel are mixed prior to combustion.

4. An aerosol delivery system as claimed in claim 1 or2, wherein the nozzle is in a pre- combustion region where there is only fuel and/or the nozzle is in a pre-combustion region where there is only air i.e. before they two components are mixed.

5. An aerosol delivery system as claimed in claim 1, 2, 3 or 4 wherein the nozzle is in a post-combustion region.

6. An aerosol delivery system as claimed in any preceding claim, wherein the nozzle is a conical shape.

7. An aerosol delivery system as claimed in any preceding claim, wherein more than one nozzle can be present.

8. An aerosol delivery system as claimed in any preceding claim, wherein the supply of gas and catalytic solution to the chamber is continuous so aerosol is sprayed continuously from the nozzle.

9. An aerosol delivery system as claimed in any preceding claim, wherein the catalytic solution of the present invention comprises one or more compounds including a metal selected from: platinum, palladium, rhodium, rhenium, ruthenium, osmium, cerium, iridium, indium, magnesium, aluminium, titanium, copper, zinc, lithium, potassium, sodium, iron, molybdenum, manganese, gold and silver.

10. An aerosol delivery system as claimed in any preceding claim, wherein the compound is present in solution in a concentration of from 0.1 to 2.0 mg/ml.

11. A method for catalysing the combustion of a fuel, the method comprising the steps of: a) providing a supply of a solution of catalyst and a supply of a pressurised gas to a chamber, wherein the chamber includes a nozzle in fluid communication with one or more of: a pre-combustion zone, a combustion zone and a post- combustion zone, b) mixing the solution and the gas in the chamber, c) forcing the mixture of solution and gas through the nozzle to form an aerosol in the pre-combustion zone, combustion zone or post-combustion zone of fuel combustion apparatus.

12. A method for catalysing the combustion of a fuel as claimed in claim 11, wherein the aerosol the fuel may be introduced into the combustion zone of a fuel injection diesel or petrol engine either simultaneously or separately.

13. A method for catalysing the combustion of a fuel as claimed in claim 11 or 12, wherein the aerosol is introduced into the hot exhaust gas streams of a combustion system.

14. A method for catalysing the combustion of a fuel as claimed in claim 11, 12, or 13, wherein the pressurized gas is selected from: air, steam, nitrogen, argon, helium, carbon monoxide, carbon dioxide and combinations thereof.

15. A method for catalysing the combustion of a fuel as claimed in claim 11, 12, 13 or 14, wherein the gas is subjected to a pressure in the range of from 30 to 90 psi.

16. A method for catalysing the combustion of a fuel as claimed in any of claims 11 to 15, wherein the solution is subjected to a pressure in the range of from 20 to 70 psi.

17. A method of pre-treating fuel, the method comprising the steps of: a) providing a supply of a solution of catalyst and a supply of a pressurised gas to a chamber, wherein the chamber includes a nozzle in fluid communication with one or more of: a pre-combustion zone, a combustion zone and a post- combustion zone, b) mixing the solution and the gas in the chamber, forcing the mixture of solution and gas through the nozzle to form an aerosol, wherein the aerosol is applied to solid fuel so as to pre-treat the fuel prior to combustion.

18. A method as claimed in claim 17, wherein the fuel is solid fuel.