EP0198948A2 - Catalytic combustor for combustion of lower hydrocarbon fuel - Google Patents
Catalytic combustor for combustion of lower hydrocarbon fuel Download PDFInfo
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- EP0198948A2 EP0198948A2 EP85111839A EP85111839A EP0198948A2 EP 0198948 A2 EP0198948 A2 EP 0198948A2 EP 85111839 A EP85111839 A EP 85111839A EP 85111839 A EP85111839 A EP 85111839A EP 0198948 A2 EP0198948 A2 EP 0198948A2
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- Prior art keywords
- catalyst
- active component
- platinum
- palladium
- combustion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C13/00—Apparatus in which combustion takes place in the presence of catalytic material
Definitions
- This invention relates to a method for the combustion of lower hydrocarbon fuel. More particularly this invention relates to a catalytic system for generating catalytic combustion of a lower hydrocarbon fuel having 1 to 4 carbon atoms such as methane, ethane, propane, and butane, particularly sparingly flammable methane or natural gas containing methane as a principal component, thereby obtaining a combustion gas substantially free from such noxious components as nitrogen oxides (hereinafter referred to as "NO x "), carbon monoxide (hereinafter referred to as "CO”), and unburned hydrocarbon (hereinafter referred to as "UHC”), and utilizing the heat of the combustion gas as an energy source for various applications and to a method for the combustion by the use of the catalyst system.
- NO x nitrogen oxides
- CO carbon monoxide
- UHC unburned hydrocarbon
- the catalytic combustion system designed to obtain a combustion gas of high temperature by introducing into a catalyst bed a dilute mixed gas having a fuel mixd with air in a concentration not to fall in the range of combustion thereby inducing catalytic combustion of the dilute mixed gas on the catalyst bed has been known to the art.
- the combustion gas is generally caused to reach a high temperature of 1,000° to 1,300°C under 6 to 15 atmospheres.
- the combustion gas is tending toward still higher temperature and pressure.
- the combustion in the catalyst bed has for its object the elevation of the temperature of the gas to the level enough to induce the secondary combustion.
- the combustion in the catalyst bed is not required to be perfect. Once the temperature of the gas rises above the level capable of inducing secondary combustion, the gas in the catalyst bed is no longer required to be heated to a higher temperature and the amount of the residual unburned gas is rather desired to be larger than otherwise.
- the fuel may be introduced into the catalyst bed in the entire amount necessary for attaining the desired temperature, part of the fuel subjected to combustion in the catalyst bed, and the residual unburned fuel used for secondary combustion. Otherwise, part of the fuel may be reserved and then introduced as secondary fuel from behind the catalyst bed and subjected to secondary combustion in combination with the residual unburned fuel.
- the latter procedure proves more desirable because it precludes the possibility of the temperature of the catalyst bed being elevated more than is necessary and the possibility of the catalyst being deteriorated and damaged.
- the temperature necessary for inducing secondary combustion is determined by the kind of fuel, the concentration of the residual unburned fuel (theoretical adiabatic combustion gas temperature), and the linear velocity of fuel. At any rate, this temperature is widely varied by the kind of fuel.
- a temperature of about 700°C is sufficient under ordinary workig conditions.
- a sparingly flammable fuel such as methane or natural gas containing methane as its principal component, a higher temperature in the range of 750° to 1,000°C is necessary, although this level is variable by the working conditions.
- An object of this invention is to provide a novel method for the combustion of a lower hydrocarbon fuel.
- Another object of this invention is to provide a catalytic system for generating catalytic combustion of a lower hydrocarbon fuel, particularly sparingly flammable methane or natural gas containing methane as a principal component thereby producing a combustion gas containing substantially no noxious component and using the heat of the combustion gas as an energy source for various applications and a method for combustion by the use of the catalytic system.
- a further object of this invention is to provide a catalytic system usable advantageously for a combustion system for enabling methane, a hydrocarbon widely recognized as sparingly flammable among other hydrocarbons, or natural gas containing methane as a principal component, introduced at a high linear velocity under a pressure falling in a wide range from normal atmospheric pressure to a highly increased pressure to be ignited at a low temperature by means of a catalyst, elevating the temperature of the combustion gas to a temperature enough to induce secondary combustion, optionally introducing a secondary fuel and allowing the residual unburned fuel to undergo combustion in combination with the introduced secondary fuel, thereby enabling the temperature of the combustion gas to rise to or even beyond the temperature aimed at and a method for combustion by the use of the catalytic system.
- Yet another object of this invention is to provide a catalytic system which enables methane or some other sparingly flammable fuel introduced at a high linear velocity under application of pressure to be ignited at as low a temperature as permissible and allows the temperature of the combustion gas to be elevated to a level in the range of 750° to 1,000°C and which suffers from only small pressure drop and enjoys high durability and a method for combustion by the use of the catalytic system.
- a method for the combustion of a lower hydrocarbon fuel having 1 to 4 carbon atoms by the steps of feeding a flammable mixed gas containing the lower hydrocarbon and molecular oxygen to a catalytic system for combustion which, relative to the flow of the flammable mixed, is provided on the gas inlet side with a front-stage catalyst bed packed with a catalyst containing one member selected from the group consisting of an active component formed of palladium and platinum and an active component formed of palladium, platinum and nickel oxides and on the gas outlet side with a rear-stage catalyst bed packed with a catalyst containing one member selected from the group consisting of an active component formed of platinum and an active component formed of platinum and palladium, causing at least part of the lower hydrocarbon in the mixed gas to undergo catalytic combustion in the catalytic system and enabling the temperature of the combustion gas to be elevated to a level enough to induce secondary combustion.
- the catalytic system of the present invention essentially comprises of two separate catalyst beds, with the catalyst for the front-stage bed and that for the rear-stage bed optically designed respectively to fulfil the function of igniting the flammable mixed gas at a relatively low temperature and the function of elevating the temperature of the combustion gas to a level in the range of 750° to 1,000°C.
- the catalyst to be used in the front-stage bed has an active component formed of palladium and platinum or of palladium, platinum and nickel oxides
- the catalyst for the rear-stage bed has an active component formed of platinum or of platinum and palladium.
- the latter catalyst specifically is adapted so that the temperature of the combustion gas in this catalyst bed will not exceed 1,000°C.
- a catalyst using palladium as an active component therefor is known to excel in the property of igniting methane, in particular, at a low temperature and also excel in the heat-resisting property at elevated t-emperatures of about 1,000°C.
- This invention has originated in the discovery that the catalyst in the front-stage bed near the entrance to the catalytic system, owing to the inclusion therein of a small amount of platinum, is prevented from degradation of the methane-igniting performance due to the oxidation of palladium and is allowed to retain the low-temperature igniting performance intact for a long time and, as the result, the temperature of the combustion gas is enabled to rise stably to a level in the range of 600° to 750°C at a high linear velocity under application of pressure and further in the discovery that the catalyst in the rear-stage bed near the exit from the catalytic system, owing to the inclusion therein of platinum, promotes the combustion and enables the temperature of the combustion gas to reach a level in the range of 750° to 1,000°C.
- the catalytic system as a whole enables methane or natural gas fuel containing methane as a principal component introduced at a high linear velocity under application of pressure to be ignited at a low temperature and allows the temperature of the combustion gas to rise to a level in the range of 750° to 1,000°C and permits its own quality to be retained intact for a long time.
- the catalyst for the front-stage bed is desired to contain therein nickel oxides additionally.
- nickel oxide the low-temperature igniting property exhibited on methane, a particularly sparingly flammable fuel, at a low temperature is improved and, at the same time, owing to the presence of nickel in the form of an oxide and the consequent stable supply of oxygen to palladium, the temperature of the combustion gas is enabled to be elevated to a level in the range of 650° to 900°C even under the conditions of a high linear velocity and application of pressure.
- the catalyst for the rear-stage bed is also desired to incorporate therein palladium as an active component.
- the .synergistic effect produced between platinum and palladium further promotes the combustion.
- this synergistic effect is found to prevent platinum from being oxided into Pt 02 and consequently sublimated.
- a three-stage system obtained by interposing between the front-stage catalyst bed and the rear-stage catalyst bed an intermediate-stage catalyst bed packed with a catalyst containing an active component formed of palladium and nickel oxides, an active component formed of platinum, or an active component formed of palladium, platinum and nickel oxides constitutes itself a catalyst system excellent in%the activity of combustion.
- the front-stage catalyst bed shows improvement in the activity of combustion even under the conditions of a high linear velocity and application of pressure when the catalyst bed is designed in a two-half structure, with the first half of the bed made of a catalyst containing an active component formed of palladium and platinum or of palladium, platinum and nickel oxides and the last half of the bed made of a catalyst containing an active component formed of palladium and nickel oxides, of platinum, or of palladium, platinumm and nickel oxides.
- this front-stage catalyst bed enables the rear-stage catalyst bed which contains an active component made of platinum or of platinum and palladium to manifest the function of combustion smoothly.
- the activity of combustion of the catalytic system as a whole can be maintained at a high level by allowing the temperature of the combustion gas to rise to a level in the range of 500° to 800°C in the first half of the front-stage catalyst bed, to a level in the range of 650° to 900°C in the last half of the front-stage catalyst (intermediate-stage catalyst bed), and finally to a level in the range of 750° to 1,000°C in the rear-stage catalyst bed.
- the catalytic system of the prevent invention is characterized by being designed in a two-stage structure or a three-stage structure by utilizing or combining the characteristic properties owned by noble metals used therein.
- the catalyst system is required to possess the activity of combustion enough to cause ignition of the fuel at a low temperature in the range of 300° to 400°C and permit elevation of the temperature of the combustion gas to a level in the range of 750° to 1,000°C and, at the same time, exhibit the heat-resisting property at temperatures exceeding 1,000°C.
- the catalyst In the case of the catalyst which contains palladium as a sole active component, the catalyst has its fuel-igniting property deteriorated with the progress of combustion as described previously and, owing to what is considered ascribable to change in the oxidized state of palladium, the temperature of the combustion gas fails to reach a high temperature substantially above 750°C.
- the catalyst containing the palladium and nickel oxides as active components has its fuel-igniting property deteriorated in much the same way.
- the catalyst which contains platinum as a sole active component fails to ignite the fuel at a temperature in the range of 300° to 400°C when the fuel happens to be methane or LNG. It requires an ignition temperature substantially exceeding 500°C.
- the catalyst which contains the palladium, platinum, and nickel oxides or the catalyst which contains palladium and platinum possesses a sufficient fuel-igniting property but is incapable of elevating the temperature of the combustion gas to a temperature exceeding the level enough to induce secondary combustion under the conditions of a high linear velocity and application of pressure.
- the catalysts for the front-stage bed and the rear-stage bed are prepared separately of each other and the two catalyst beds may be disposed as juxtaposed to each other or separated from each other by an intervening empty space.
- the two catalyst beds may be obtained in the form of a whole catalyst by preparing a one-piece carrier extending throughout the entire length of the catalytic system, depositing the catalyst for the front-stage bed on the inlet part of the carrier, and depositing the catalyst for the rear-stage bed on the outlet part of the carrier.
- the first half part and the last half part (intermediate stage) of the front-stage catalyst bed and the rear-stage catalyst bed can be prepared.
- the catalyst may be in the form of pellets.
- any of the monolithic carriers in common use in the art can be adopted.
- the monolithic carriers include carriers made of such refractory ceramic substances as cordierite, mullite, a- alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, aluminosilicate, magnesium silicate, zirconia-spinel, zirconmullite, silicon carbide, and silicon nitride and carriers made of such metallic substances as Kanthal alloy and Fecralloy.
- the cell size of the monolithic carriers is desired to be as large as possible on condition that the efficiency of combustion is not impaired.
- Each of the catalyst beds may be formed of catalyst monoliths of one fixed cell size or of two or more different cell sizes. Generally, the cell size. is selected so that the number of cells falls in the range of 40 to 400 per square inch.
- the total length of the catalyst beds is variable particularly with the inlet linear velocity to be used. Under the necessity for decreasing pressure drop, it is generally selected in the range of 50 to 500 mm.
- the lengths of the front-stage catalyst bed and the rear-stage catalyst bed are optimally selected in accordance with such working conditions as inlet linear velocity and inlet temperature. Generally, they are selected both in the range of 20 to 250 mm.
- the catalyst for use in the front-stage catalyst bed is generally produced by coating the monolithic carrier with an active refractory metal oxide such as alumina, silica-alumina, magnesia, titania, zirconia, or silica-magnesia.
- an active refractory metal oxide such as alumina, silica-alumina, magnesia, titania, zirconia, or silica-magnesia.
- alumina, titania, and zirconia prove particularly desirable and alumina is the best selection.
- the amount of the metal oxide to be used for the coating is required to fall in the range of 5 to 50% by weight, preferably 10 to 30% by weight, based on the amount of the completed catalyst.
- the catalyst prepared as described above can be used more advantageously when it is stabilized by addition thereto of the oxide of such an alkaline earth metal as barium or strontium, the oxide of such a rare earth metal as lanthanum, cerium, neodymium, or praseodymium, or silicon, preferably the oxide of rare earth metal.
- the amount of this stabilizing additive is desired to fall in the range of 2 to 20% by weight, preferably 5 to 15% by weight, based on the amount of the aforementioned oxide.
- the catalyst is completed by impregnating the resultant composite with the active components, i.e. palladium, platinum, and nickel, in the form of a water-soluble salt or an alcohol-soluble compound. Otherwise, the catalyst may be obtained by depositing the active components on the active refractory metal oxide and then coating the resultant substance on monolithic carriers.
- Platinum as one of the active components, can be deposited in the form of platinum black particles of an average particle diameter of 0.01 to 5 microns in combination with the active refractory metal oxide.
- water-soluble salt examples include nitrate, sulfate, phosphate, halides, and dinitrodiammine salt.
- Specific examples are palladium nitrate, palladium chloride, dinitrodiammineplatinum, chloroplatinic acid, nickel nitrate, and nickel chloride.
- the catalyst is obtained by impregnating the carrier with the aqueous solution of the salt and calcining the resultant composite at a temperature in the range of 400° to 1,000°C, preferably 600° to 900°C, for 1 to 24 hours, preferably 2 to 6 hours.
- the amounts of the active components to be used in the catalyst for the front-stage catalyst bed are 0.5 to 15% by weight, preferably 2 to 10% by weight, of palladium, 0.1 to 10% by weight, preferably 0.2 to 5% by weight, of platinum and where nickel is additionally incorporated, 0.1 to 20% by weight, 1 to 10% by weight, as NiO.
- the amount of platinum is 0.01 to 1, preferably 0.1 to 0.6 part by weight, based on 1 part by weight of palladium. Even when the catalystic system is formed of three catalyst beds, the catalyst for the front-stage catalyst bed is prepared in the same manner as described above.
- the ratio of palladium/nickel as calculated in Pd/NiO weight ratio is desired to fall in the range of 0.001 to 20, preferably 0.1 to 5.
- the catalyst for use in the rear-stage catalyst bed can be produced by depositing platinum alone or platinum and palladium in the same manner as described above.
- the amount of the active component to be deposited is in the range of 0.1 to 15% by weight, preferably 0.2 to 10% by weight, based on the amount of the completed catalyst.
- the catalyst also contains palladium
- the amount of palladium so added desirably falls in the range of 0.1 to 15% by weight, preferably 0.2 to 10% by weight, as palladium.
- this catalyst contains both palladium and platinum, the amount of platinum is desired to be in the range of 0.01 to 20 parts by weight, preferably 0.2 to 10 parts by weight, based on 1 part by weight of palladium.
- the catalyst is so active that when the temperature in the catalyst bed rises to a level exceeding 1,000°C, there is the possibility of the platinum being sublimated and deprived of activity.
- a desire to avoid this possibility and keep the temperature of the catalyst bed below the level of 1,000°C is advantageously effected by using coarsened platinum particles such as platinum black. It may otherwise be attained by decreasing the amount of platinum deposited, by calcining the completed catalyst at an elevated temperature exceeding 1,000°C before it is put to use, or by optimally selecting the cell size of catalyst and the length of catalyst beds.
- the coexistence of platinum and palladium prevents platinum from sublimation and, at the same time, controls the activity of combustion of platinum.
- the active components can be optimally selected in due accordance with the conditions of use of the catalyst, namely, the kind of fuel, temperature (theoretical adiabatic combustion gas temperature), linear velocity, and application of pressure.
- the pressure can be used in the range of from normal atmospheric pressure to 25 ata. Preferably the pressure is in the range of 6 to 15 ata.
- concentration of the fuel when the lower hydrocarbon fuel is methane, the concentration is in the range of 1.51 to 4.75 volume%, preferably 2.37 to 4.31 volume%, of primary fuel, though it is variable with the temperature of the mixed gas introduced into the catalyst system.
- the concentration is in the range of 0 to 3.24 volume%, preferably 0.44 to 2.38 volume%.
- the linear velocity is in the range of 7 to 40 m/sec, preferably 10 to 30 m/sec. If the linear velocity is less than 7 m/sec, there is the possibility of the combustion entailing the phenomenon of backfire. If it exceeds 40 m/sec, the fuel blows through the catalytic system excessively and the combustion fails to occur sufficiently.
- the fuel to be used in the combustion system operating with the catalyst system of the present invention is either methane or a fuel containing methane as a principal component.
- it is natural gas.
- the natural gas has somewhat variable composition dependeing on the place of its production. It nevertheless contains more than about 80% of methane.
- the fermented methane arising from the disposal of sewage through treatment with activated sludge and the low-calorie methane gas produced by gasification of coal are other fuels usable for this invention.
- more flammable fuels such as ethane, propane, and butane can be used. Light oil is also usable.
- the catalyst system of this invention or the combustion system using this catalyst system is most advantageously incorporated in the gas turbine system for power generation as previously described. It may be otherwise utilized efficiently for the recovery of heat by aftertreatment of gases emanating from the power-generation boiler, heat-recovering boiler, and gas engine or for the recovery of heat and motive power from space heaters using city gas, for example.
- Honeycomb carriers of cordierite measuring 25.4 mm in diameter and 50 mm in length and containing 200 open cells per square inch were coated with a slurry of alumina powder containing 5% by weight of lanthanum oxide and then calcined in the air at 700°C to have lanthanum oxide-containing alumina deposited on the honeycomb carriers at a rate of 20% by weight based on completed catalyst.
- the coated honeycomb carriers were immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid, then dried, and calcined in the air at 700°C for 5 hours to give rise to a complete catalyst having 4.0% by weight of palladium and 0.8% by weight of platinum deposited thereof based on the completed catalyst.
- Honeycomb carriers were coated with lanthanum oxide-containing alumina at a rate of 20% by weight based on completed catalyst by following the procedure of Example 1. Then, the coated honeycomb carriers were immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid, dried, and calcined in the air at 700°C to give rise to a complete carrier having 1.0% by weight of palladium and 0.2% by weight of platinum deposited thereof based on the completed catalyst.
- Honeycomb carriers of aluminum titanate measuring 25.4 mm in diameter and containing 200 open cells per square inch were coated with a thorough mixture of a slurry of alumina powder containing 8% by weight of lanthanum oxide and 2% by weight of silica with platinum black particles having an average particle diameter of 2 microns, dried, and then calcined in the air at 900°C for 2 hours to give rise to a completed catalyst having 18% by weight of lanthanum oxide- and silicon dioxide-containing alumina powder and 2.2% by weight of platinum deposited thereon based on the completed catalyst.
- a completed catalyst having 18% by weight of lanthanum oxide- and silicon dioxide-containing alumina powder and 0.4% by weight of platinum deposited thereon based on the completed catalyst was obtained by following the procedure of Example 3.
- honeycomb carriers as used in Example 1 were coated with a slurry mixture of alumina powder containing 5% by weight of lanthanum oxide with nickel oxide powder, dried, and then calcined in the air at 700°C to have the lanthanum oxide-containing alumina powder deposited on the honeycomb carriers at a rate of 19% by weight and nickel oxide at a rate of 6% by weight based on the completed catalyst.
- the coated honeycomb carriers were then treated by following the procedure of Example 1, to give rise to a completed catalyst having 4% by weight of palladium and 0.8% by weight of platinum deposited thereon based on the completed catalyst.
- honeycomb carriers as used in Example 1 were coated with a slurry of alumina powder containing 7% by weight of lanthanum oxide and 3% by weight of neodymium oxide and then calcined in the air at 1,000°C to have lanthanum oxide- and neodymium oxide-containing alumina deposited on the honeycomb carriers at a rate of 30% by weight based on completed catalyst.
- the carriers were immersed in an aqueous solution containing palladium nitrate and dinitrodiammine-platinum, dried, and then calcined in the air at 700°C for 5 hours to give rise to a completed catalyst having 4.7% by weightt of palladium and 2.3% by weight of platinum deposited thereon based on the completed catalyst.
- honeycomb carriers as used in Example 3 were coated with a slurry of alumina powder containing 3% by weight of silicon dioxide and 2% by weight of praseodymium oxide by following the procedure of Example 6 to have silicon dioxide- and praseodymium oxide-containing alumina deposited on the carrier at a rate of 14% by weight based on completed catalyst. Then, the coated honeycomb carriers were immersed in an aqueous solution containing nitric acid and dinitrodiammineplatinum, dried, and calcined in the air at 900°C for 3 hours to give rise to a completed catalyst having 0.2% by weight of palladium and 1.8% by weight of platinum deposited thereon based on the completed catalyst.
- Honeycomb carriers of mullite measuring 25.4 mm in diameter and 50 mm in length and containing 100 open cells per square inch were coated with a slurry of alumina powder containing 2% by weight of lanthanum oxide and 5% by weight of cerium oxide and calcined in the air at 900°C to have lanthenum oxide- and cerium oxide-containing alumina deposited on the carriers at a rate of 15% by weight based on completed catalyst.
- the coated honeycomb carriers were immersed in an aqueous solution containing palladium nitrate and nickel nitrate, dried, and calcined in the air at 800°C for 4 hours to give rise to a completed catalyst having 2.5% by weight of palladium and 3.7% by weight of nickel oxide deposited thereon based on the completed catalyst.
- honeycomb carriers as used in Example 1 were coated with a slurry of alumina containing 7% by weight of neodymium oxide by following the procedure of Example 1 to have neodymium oxide-containing alumina deposited on the honeycomb carriers at a rate of 20% by weight based on completed catalyst. Then, the coated honeycomb carriers were immersed in an aqueous solution containing chloroplatinic acid, dried, and calcined in the air at 900°C for 3 hours to give rise to a completed catalyst having 2.8% by weight of platinum deposited thereon based on the completed catalyst.
- Example 2 The procedure of Example 1 was repeated, except that the aqueous solution used for the immersion of coated honeycomb carriers contained no platinum. Consequently, there was obtained a completed catalyst having 20% by weight of lanthanum oxide-containing alumina power and 4.0% by weight of palladium deposited thereon based on the completed catalyst.
- Example 8 The procedure of Example 8 was followed, except that honeycomb carriers of mullite containing 200 open cells per squre inch were used instead. Consequently, ther was obtained a completed catalyst having 15% by weight of lanthanum oxide- and cerium oxide-containing alumina powder, 2.5% by weignt of palladium, and 9.4% by weight of nickel oxide deposited thereon based on the completed catalyst. Control 3
- Example 5 The procedure of Example 5 was repeated, except that the aqueous solution for the immersion of coated honeycomb carriers contained no palladium. Consequently, there was obtained a completed catalyst having 1.5% by weight of platinum deposited thereon based on the completed catalyst.
- a front-stage catalyst bed was packed with the catalyst obtained in Example 1 and a rear-stage catalyst bed was packed with the catalyst obtained in Example 2.
- a methane-air mixed gas containing 3% by volume of methane was introduced under application of 10 atmospheres at a flow rate of 167 Nm 3 (STP) per hour at an inlet temperature of 350°C to test for efficiency of combustion and oulet temperature of catalyst bed.
- STP 167 Nm 3
- the linear velocity at the inlet of the catalyst bed was about 30 m/sec.
- the efficiency of combustion was found to be about 71% and the outlet temperature of the catalyst bed to be about 850°C.
- the combustion test was continued by introducing the same mixed gas at a flow rate equivalent to 3% by volume of methane in a downward flow to the catalyst bed and at a flow rate equivalent to 1.1% by volume of methane at a point 30 mm backward from the outlet of the catalyst bed.
- the outlet temperature of the catalyst bed was about 830°C and there was obtained a clean combustion gas at a temperature of about 1,300°C. This performance of the combustion system was maintained continuously over a period of 1,000 hours.
- the outlet temperature of the rear-stage bed was 720°C and no secondary combustion was induced.
- a combustion test was performed by following the procedure of Example 10, using catalyst indicated in Table 2 introducing a liquefied natural gas composed of 88% of methane, 6% of ethane, 4% of propane, and 2% of butane at a flow rate equivalent to 3% by volume in a downward flow to the catalyst bed and at a flow rate equivalent to 1.1% by volume from the outlet of the catalyst bed.
Abstract
Description
- This invention relates to a method for the combustion of lower hydrocarbon fuel. More particularly this invention relates to a catalytic system for generating catalytic combustion of a lower hydrocarbon fuel having 1 to 4 carbon atoms such as methane, ethane, propane, and butane, particularly sparingly flammable methane or natural gas containing methane as a principal component, thereby obtaining a combustion gas substantially free from such noxious components as nitrogen oxides (hereinafter referred to as "NOx"), carbon monoxide (hereinafter referred to as "CO"), and unburned hydrocarbon (hereinafter referred to as "UHC"), and utilizing the heat of the combustion gas as an energy source for various applications and to a method for the combustion by the use of the catalyst system. Description of Prior Art:
- The catalytic combustion system designed to obtain a combustion gas of high temperature by introducing into a catalyst bed a dilute mixed gas having a fuel mixd with air in a concentration not to fall in the range of combustion thereby inducing catalytic combustion of the dilute mixed gas on the catalyst bed has been known to the art.
- Further, it is well known that in the production of a combustion gas at a temperature of 600° to 1,500°C, for example, by the use of the catalytic combustion system of the nature described above, the combustion gives rise to substantially no or absolutely no NO even when air is used as an oxygen source and the combustion gas contains substantially no CO or UHC.
- Various system have been proposed for deriving heat or motive power from this clean hot combustion gas. Systems for disposing of industrial waste gases and recovering heat and motive power from the waste gases have already found utility in practical applications.
- In recent years, with a view to coping with the increasingly tightened restrictions on the release of NOX into the air, increasing studies have come to be directed to utilization of this hot combustion gas as a source for primary motive power such as in the gas turbine for power generation.
- To be used for purposes of this sort, the combustion gas is generally caused to reach a high temperature of 1,000° to 1,300°C under 6 to 15 atmospheres. For improvement of the efficiency of the gas turbine, the combustion gas is tending toward still higher temperature and pressure.
- If an ordinary catalyst is used under such conditions as just described, it is rapidly deteriorated because of elevated temperatures. In the worst case, there ensues the possibility that the catalyst carrier will be melted down and scattered to inflict damage on blades of the turbine.
- As one way of combustion directed to attaining the same purpose without entailing the deterioration and damage of the catalyst, there has been developed the method which obtains a clean combustion gas of the temperature aimed at or of a still higher temperature by first causing combustion of the fuel in the catalyst bed, elevating the temperature of the gas to a level enough to induce secondary combustion and then causing secondary combustion of the residual unburned fuel behind the catalyst bed, or optionally introducing secondary fuel and combining it with the residual unburned fuel thereby preparing secondary fuel and causing combustion of the secondary fuel.
- In this case, the combustion in the catalyst bed has for its object the elevation of the temperature of the gas to the level enough to induce the secondary combustion. Thus, the combustion in the catalyst bed is not required to be perfect. Once the temperature of the gas rises above the level capable of inducing secondary combustion, the gas in the catalyst bed is no longer required to be heated to a higher temperature and the amount of the residual unburned gas is rather desired to be larger than otherwise.
- The fuel may be introduced into the catalyst bed in the entire amount necessary for attaining the desired temperature, part of the fuel subjected to combustion in the catalyst bed, and the residual unburned fuel used for secondary combustion. Otherwise, part of the fuel may be reserved and then introduced as secondary fuel from behind the catalyst bed and subjected to secondary combustion in combination with the residual unburned fuel. The latter procedure proves more desirable because it precludes the possibility of the temperature of the catalyst bed being elevated more than is necessary and the possibility of the catalyst being deteriorated and damaged.
- Here, the temperature necessary for inducing secondary combustion is determined by the kind of fuel, the concentration of the residual unburned fuel (theoretical adiabatic combustion gas temperature), and the linear velocity of fuel. At any rate, this temperature is widely varied by the kind of fuel.
- In the case of such a readily flammable fuel such as propane or light oil, for example, a temperature of about 700°C is sufficient under ordinary workig conditions. In the case of such a sparingly flammable fuel such as methane or natural gas containing methane as its principal component, a higher temperature in the range of 750° to 1,000°C is necessary, although this level is variable by the working conditions.
- An object of this invention, therefore, is to provide a novel method for the combustion of a lower hydrocarbon fuel.
- Another object of this invention is to provide a catalytic system for generating catalytic combustion of a lower hydrocarbon fuel, particularly sparingly flammable methane or natural gas containing methane as a principal component thereby producing a combustion gas containing substantially no noxious component and using the heat of the combustion gas as an energy source for various applications and a method for combustion by the use of the catalytic system.
- A further object of this invention is to provide a catalytic system usable advantageously for a combustion system for enabling methane, a hydrocarbon widely recognized as sparingly flammable among other hydrocarbons, or natural gas containing methane as a principal component, introduced at a high linear velocity under a pressure falling in a wide range from normal atmospheric pressure to a highly increased pressure to be ignited at a low temperature by means of a catalyst, elevating the temperature of the combustion gas to a temperature enough to induce secondary combustion, optionally introducing a secondary fuel and allowing the residual unburned fuel to undergo combustion in combination with the introduced secondary fuel, thereby enabling the temperature of the combustion gas to rise to or even beyond the temperature aimed at and a method for combustion by the use of the catalytic system.
- Yet another object of this invention is to provide a catalytic system which enables methane or some other sparingly flammable fuel introduced at a high linear velocity under application of pressure to be ignited at as low a temperature as permissible and allows the temperature of the combustion gas to be elevated to a level in the range of 750° to 1,000°C and which suffers from only small pressure drop and enjoys high durability and a method for combustion by the use of the catalytic system.
- The objects described above are accomplished by a method for the combustion of a lower hydrocarbon fuel having 1 to 4 carbon atoms by the steps of feeding a flammable mixed gas containing the lower hydrocarbon and molecular oxygen to a catalytic system for combustion which, relative to the flow of the flammable mixed, is provided on the gas inlet side with a front-stage catalyst bed packed with a catalyst containing one member selected from the group consisting of an active component formed of palladium and platinum and an active component formed of palladium, platinum and nickel oxides and on the gas outlet side with a rear-stage catalyst bed packed with a catalyst containing one member selected from the group consisting of an active component formed of platinum and an active component formed of platinum and palladium, causing at least part of the lower hydrocarbon in the mixed gas to undergo catalytic combustion in the catalytic system and enabling the temperature of the combustion gas to be elevated to a level enough to induce secondary combustion.
- The catalytic system of the present invention essentially comprises of two separate catalyst beds, with the catalyst for the front-stage bed and that for the rear-stage bed optically designed respectively to fulfil the function of igniting the flammable mixed gas at a relatively low temperature and the function of elevating the temperature of the combustion gas to a level in the range of 750° to 1,000°C. Thus, the catalyst to be used in the front-stage bed has an active component formed of palladium and platinum or of palladium, platinum and nickel oxides and the catalyst for the rear-stage bed has an active component formed of platinum or of platinum and palladium. The latter catalyst specifically is adapted so that the temperature of the combustion gas in this catalyst bed will not exceed 1,000°C.
- A catalyst using palladium as an active component therefor is known to excel in the property of igniting methane, in particular, at a low temperature and also excel in the heat-resisting property at elevated t-emperatures of about 1,000°C.
- When the conventional catalyst using palladium as an active component is adopted for the purpose of this invention, however, since it is exposed to highly concentrated oxygen at a temperature not exceeding 500°C near the entrance to the catalyst bed, the palladium therein is oxidized and consequently deprived of the ability to ignite methane. In the high temperature zone near the exit of the catalyst bed, the reaction of combustion by the catalyst is curbed owing to what is considered ascribable to change in the oxidized state of palladium and, as the result, the temperature of the combustion gas is not allowed to rise substantially to a high temperature exceeding 750°C.
- This invention has originated in the discovery that the catalyst in the front-stage bed near the entrance to the catalytic system, owing to the inclusion therein of a small amount of platinum, is prevented from degradation of the methane-igniting performance due to the oxidation of palladium and is allowed to retain the low-temperature igniting performance intact for a long time and, as the result, the temperature of the combustion gas is enabled to rise stably to a level in the range of 600° to 750°C at a high linear velocity under application of pressure and further in the discovery that the catalyst in the rear-stage bed near the exit from the catalytic system, owing to the inclusion therein of platinum, promotes the combustion and enables the temperature of the combustion gas to reach a level in the range of 750° to 1,000°C.
- As the result, the catalytic system as a whole enables methane or natural gas fuel containing methane as a principal component introduced at a high linear velocity under application of pressure to be ignited at a low temperature and allows the temperature of the combustion gas to rise to a level in the range of 750° to 1,000°C and permits its own quality to be retained intact for a long time.
- In this invention, the catalyst for the front-stage bed is desired to contain therein nickel oxides additionally. In this case, owing to the presence of nickel oxide, the low-temperature igniting property exhibited on methane, a particularly sparingly flammable fuel, at a low temperature is improved and, at the same time, owing to the presence of nickel in the form of an oxide and the consequent stable supply of oxygen to palladium, the temperature of the combustion gas is enabled to be elevated to a level in the range of 650° to 900°C even under the conditions of a high linear velocity and application of pressure.
- The catalyst for the rear-stage bed is also desired to incorporate therein palladium as an active component. In this case, the .synergistic effect produced between platinum and palladium further promotes the combustion. In a high temperature zone of 1,000°C, this synergistic effect is found to prevent platinum from being oxided into Pt02 and consequently sublimated.
- Further in this invention, it has been found that a three-stage system obtained by interposing between the front-stage catalyst bed and the rear-stage catalyst bed an intermediate-stage catalyst bed packed with a catalyst containing an active component formed of palladium and nickel oxides, an active component formed of platinum, or an active component formed of palladium, platinum and nickel oxides constitutes itself a catalyst system excellent in%the activity of combustion.
- To be specific, the front-stage catalyst bed shows improvement in the activity of combustion even under the conditions of a high linear velocity and application of pressure when the catalyst bed is designed in a two-half structure, with the first half of the bed made of a catalyst containing an active component formed of palladium and platinum or of palladium, platinum and nickel oxides and the last half of the bed made of a catalyst containing an active component formed of palladium and nickel oxides, of platinum, or of palladium, platinumm and nickel oxides. As the result, this front-stage catalyst bed enables the rear-stage catalyst bed which contains an active component made of platinum or of platinum and palladium to manifest the function of combustion smoothly.
- In this case, the activity of combustion of the catalytic system as a whole can be maintained at a high level by allowing the temperature of the combustion gas to rise to a level in the range of 500° to 800°C in the first half of the front-stage catalyst bed, to a level in the range of 650° to 900°C in the last half of the front-stage catalyst (intermediate-stage catalyst bed), and finally to a level in the range of 750° to 1,000°C in the rear-stage catalyst bed.
- The catalytic system of the prevent invention is characterized by being designed in a two-stage structure or a three-stage structure by utilizing or combining the characteristic properties owned by noble metals used therein. For the purpose of this invention, the catalyst system is required to possess the activity of combustion enough to cause ignition of the fuel at a low temperature in the range of 300° to 400°C and permit elevation of the temperature of the combustion gas to a level in the range of 750° to 1,000°C and, at the same time, exhibit the heat-resisting property at temperatures exceeding 1,000°C.
- In the case of the catalyst which contains palladium as a sole active component, the catalyst has its fuel-igniting property deteriorated with the progress of combustion as described previously and, owing to what is considered ascribable to change in the oxidized state of palladium, the temperature of the combustion gas fails to reach a high temperature substantially above 750°C. The catalyst containing the palladium and nickel oxides as active components has its fuel-igniting property deteriorated in much the same way. The catalyst which contains platinum as a sole active component fails to ignite the fuel at a temperature in the range of 300° to 400°C when the fuel happens to be methane or LNG. It requires an ignition temperature substantially exceeding 500°C. It nevertheless excels in the activity of combustion and possesses an ample activity of combustion particularly under the conditions of a high linear velocity and application of pressure. The catalyst which contains the palladium, platinum, and nickel oxides or the catalyst which contains palladium and platinum possesses a sufficient fuel-igniting property but is incapable of elevating the temperature of the combustion gas to a temperature exceeding the level enough to induce secondary combustion under the conditions of a high linear velocity and application of pressure.
- As described above, all the catalysts of one-stage structure have demerits of their own and fail to constitute practicable catalysts under the conditions of combustion under application of pressure in particular.
- In this invention, the catalysts for the front-stage bed and the rear-stage bed are prepared separately of each other and the two catalyst beds may be disposed as juxtaposed to each other or separated from each other by an intervening empty space. Alternatively, the two catalyst beds may be obtained in the form of a whole catalyst by preparing a one-piece carrier extending throughout the entire length of the catalytic system, depositing the catalyst for the front-stage bed on the inlet part of the carrier, and depositing the catalyst for the rear-stage bed on the outlet part of the carrier. In the same manner as described above, the first half part and the last half part (intermediate stage) of the front-stage catalyst bed and the rear-stage catalyst bed can be prepared.
- The catalyst may be in the form of pellets. For the purpose of decreasing pressure drop, however, it is desired to be used in the form of monoliths. For the preparation of this monolithic catalyst, any of the monolithic carriers in common use in the art can be adopted. Typical examples of the monolithic carriers include carriers made of such refractory ceramic substances as cordierite, mullite, a- alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, aluminosilicate, magnesium silicate, zirconia-spinel, zirconmullite, silicon carbide, and silicon nitride and carriers made of such metallic substances as Kanthal alloy and Fecralloy.
- The cell size of the monolithic carriers is desired to be as large as possible on condition that the efficiency of combustion is not impaired. Each of the catalyst beds may be formed of catalyst monoliths of one fixed cell size or of two or more different cell sizes. Generally, the cell size. is selected so that the number of cells falls in the range of 40 to 400 per square inch.
- The total length of the catalyst beds is variable particularly with the inlet linear velocity to be used. Under the necessity for decreasing pressure drop, it is generally selected in the range of 50 to 500 mm. The lengths of the front-stage catalyst bed and the rear-stage catalyst bed are optimally selected in accordance with such working conditions as inlet linear velocity and inlet temperature. Generally, they are selected both in the range of 20 to 250 mm.
- The catalyst for use in the front-stage catalyst bed is generally produced by coating the monolithic carrier with an active refractory metal oxide such as alumina, silica-alumina, magnesia, titania, zirconia, or silica-magnesia. Among these metal oxides cited above, alumina, titania, and zirconia prove particularly desirable and alumina is the best selection. The amount of the metal oxide to be used for the coating is required to fall in the range of 5 to 50% by weight, preferably 10 to 30% by weight, based on the amount of the completed catalyst. The catalyst prepared as described above can be used more advantageously when it is stabilized by addition thereto of the oxide of such an alkaline earth metal as barium or strontium, the oxide of such a rare earth metal as lanthanum, cerium, neodymium, or praseodymium, or silicon, preferably the oxide of rare earth metal. The amount of this stabilizing additive is desired to fall in the range of 2 to 20% by weight, preferably 5 to 15% by weight, based on the amount of the aforementioned oxide. Then, the catalyst is completed by impregnating the resultant composite with the active components, i.e. palladium, platinum, and nickel, in the form of a water-soluble salt or an alcohol-soluble compound. Otherwise, the catalyst may be obtained by depositing the active components on the active refractory metal oxide and then coating the resultant substance on monolithic carriers.
- Platinum, as one of the active components, can be deposited in the form of platinum black particles of an average particle diameter of 0.01 to 5 microns in combination with the active refractory metal oxide.
- Examples of the water-soluble salt are nitrate, sulfate, phosphate, halides, and dinitrodiammine salt. Specific examples are palladium nitrate, palladium chloride, dinitrodiammineplatinum, chloroplatinic acid, nickel nitrate, and nickel chloride. The catalyst is obtained by impregnating the carrier with the aqueous solution of the salt and calcining the resultant composite at a temperature in the range of 400° to 1,000°C, preferably 600° to 900°C, for 1 to 24 hours, preferably 2 to 6 hours.
- The amounts of the active components to be used in the catalyst for the front-stage catalyst bed are 0.5 to 15% by weight, preferably 2 to 10% by weight, of palladium, 0.1 to 10% by weight, preferably 0.2 to 5% by weight, of platinum and where nickel is additionally incorporated, 0.1 to 20% by weight, 1 to 10% by weight, as NiO. The amount of platinum is 0.01 to 1, preferably 0.1 to 0.6 part by weight, based on 1 part by weight of palladium. Even when the catalystic system is formed of three catalyst beds, the catalyst for the front-stage catalyst bed is prepared in the same manner as described above. Particularly, in the catalyst for the first half part of the front-stage catalyst 11 bed which has an active component formed of palladium, platinum, and nickel oxides and in the catalyst for the last half part of the front-stage catalyst bed which has an active component formed of palladium and nickel oxides, the ratio of palladium/nickel as calculated in Pd/NiO weight ratio is desired to fall in the range of 0.001 to 20, preferably 0.1 to 5.
- The catalyst for use in the rear-stage catalyst bed can be produced by depositing platinum alone or platinum and palladium in the same manner as described above. The amount of the active component to be deposited is in the range of 0.1 to 15% by weight, preferably 0.2 to 10% by weight, based on the amount of the completed catalyst. Where the catalyst also contains palladium, the amount of palladium so added desirably falls in the range of 0.1 to 15% by weight, preferably 0.2 to 10% by weight, as palladium. When this catalyst contains both palladium and platinum, the amount of platinum is desired to be in the range of 0.01 to 20 parts by weight, preferably 0.2 to 10 parts by weight, based on 1 part by weight of palladium.
- If platinum is used as a sole active component for the catalyst, then the catalyst is so active that when the temperature in the catalyst bed rises to a level exceeding 1,000°C, there is the possibility of the platinum being sublimated and deprived of activity. A desire to avoid this possibility and keep the temperature of the catalyst bed below the level of 1,000°C is advantageously effected by using coarsened platinum particles such as platinum black. It may otherwise be attained by decreasing the amount of platinum deposited, by calcining the completed catalyst at an elevated temperature exceeding 1,000°C before it is put to use, or by optimally selecting the cell size of catalyst and the length of catalyst beds. The coexistence of platinum and palladium prevents platinum from sublimation and, at the same time, controls the activity of combustion of platinum.
- The active components can be optimally selected in due accordance with the conditions of use of the catalyst, namely, the kind of fuel, temperature (theoretical adiabatic combustion gas temperature), linear velocity, and application of pressure. The pressure can be used in the range of from normal atmospheric pressure to 25 ata. Preferably the pressure is in the range of 6 to 15 ata. As regards the concentration of the fuel, when the lower hydrocarbon fuel is methane, the concentration is in the range of 1.51 to 4.75 volume%, preferably 2.37 to 4.31 volume%, of primary fuel, though it is variable with the temperature of the mixed gas introduced into the catalyst system. When the secondary fuel is additionally supplied to the combustion gas whose temperature has been elevated to a level enough to induce secondary combustion of the aforementioned primary fuel, the concentration is in the range of 0 to 3.24 volume%, preferably 0.44 to 2.38 volume%. The linear velocity is in the range of 7 to 40 m/sec, preferably 10 to 30 m/sec. If the linear velocity is less than 7 m/sec, there is the possibility of the combustion entailing the phenomenon of backfire. If it exceeds 40 m/sec, the fuel blows through the catalytic system excessively and the combustion fails to occur sufficiently.
- The fuel to be used in the combustion system operating with the catalyst system of the present invention is either methane or a fuel containing methane as a principal component. Typically, it is natural gas. The natural gas has somewhat variable composition dependeing on the place of its production. It nevertheless contains more than about 80% of methane. The fermented methane arising from the disposal of sewage through treatment with activated sludge and the low-calorie methane gas produced by gasification of coal are other fuels usable for this invention. Naturally, more flammable fuels such as ethane, propane, and butane can be used. Light oil is also usable.
- The catalyst system of this invention or the combustion system using this catalyst system is most advantageously incorporated in the gas turbine system for power generation as previously described. It may be otherwise utilized efficiently for the recovery of heat by aftertreatment of gases emanating from the power-generation boiler, heat-recovering boiler, and gas engine or for the recovery of heat and motive power from space heaters using city gas, for example.
- Now, the present invention will be described more specifically below with reference to working examples. This invention is not limited to these examples.
- Honeycomb carriers of cordierite measuring 25.4 mm in diameter and 50 mm in length and containing 200 open cells per square inch were coated with a slurry of alumina powder containing 5% by weight of lanthanum oxide and then calcined in the air at 700°C to have lanthanum oxide-containing alumina deposited on the honeycomb carriers at a rate of 20% by weight based on completed catalyst.
- Then, the coated honeycomb carriers were immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid, then dried, and calcined in the air at 700°C for 5 hours to give rise to a complete catalyst having 4.0% by weight of palladium and 0.8% by weight of platinum deposited thereof based on the completed catalyst.
- Honeycomb carriers were coated with lanthanum oxide-containing alumina at a rate of 20% by weight based on completed catalyst by following the procedure of Example 1. Then, the coated honeycomb carriers were immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid, dried, and calcined in the air at 700°C to give rise to a complete carrier having 1.0% by weight of palladium and 0.2% by weight of platinum deposited thereof based on the completed catalyst.
- Honeycomb carriers of aluminum titanate measuring 25.4 mm in diameter and containing 200 open cells per square inch were coated with a thorough mixture of a slurry of alumina powder containing 8% by weight of lanthanum oxide and 2% by weight of silica with platinum black particles having an average particle diameter of 2 microns, dried, and then calcined in the air at 900°C for 2 hours to give rise to a completed catalyst having 18% by weight of lanthanum oxide- and silicon dioxide-containing alumina powder and 2.2% by weight of platinum deposited thereon based on the completed catalyst.
- A completed catalyst having 18% by weight of lanthanum oxide- and silicon dioxide-containing alumina powder and 0.4% by weight of platinum deposited thereon based on the completed catalyst was obtained by following the procedure of Example 3.
- The same honeycomb carriers as used in Example 1 were coated with a slurry mixture of alumina powder containing 5% by weight of lanthanum oxide with nickel oxide powder, dried, and then calcined in the air at 700°C to have the lanthanum oxide-containing alumina powder deposited on the honeycomb carriers at a rate of 19% by weight and nickel oxide at a rate of 6% by weight based on the completed catalyst. The coated honeycomb carriers were then treated by following the procedure of Example 1, to give rise to a completed catalyst having 4% by weight of palladium and 0.8% by weight of platinum deposited thereon based on the completed catalyst.
- The same honeycomb carriers as used in Example 1 were coated with a slurry of alumina powder containing 7% by weight of lanthanum oxide and 3% by weight of neodymium oxide and then calcined in the air at 1,000°C to have lanthanum oxide- and neodymium oxide-containing alumina deposited on the honeycomb carriers at a rate of 30% by weight based on completed catalyst. Then, the carriers were immersed in an aqueous solution containing palladium nitrate and dinitrodiammine-platinum, dried, and then calcined in the air at 700°C for 5 hours to give rise to a completed catalyst having 4.7% by weightt of palladium and 2.3% by weight of platinum deposited thereon based on the completed catalyst.
- The same honeycomb carriers as used in Example 3 were coated with a slurry of alumina powder containing 3% by weight of silicon dioxide and 2% by weight of praseodymium oxide by following the procedure of Example 6 to have silicon dioxide- and praseodymium oxide-containing alumina deposited on the carrier at a rate of 14% by weight based on completed catalyst. Then, the coated honeycomb carriers were immersed in an aqueous solution containing nitric acid and dinitrodiammineplatinum, dried, and calcined in the air at 900°C for 3 hours to give rise to a completed catalyst having 0.2% by weight of palladium and 1.8% by weight of platinum deposited thereon based on the completed catalyst.
- Honeycomb carriers of mullite measuring 25.4 mm in diameter and 50 mm in length and containing 100 open cells per square inch were coated with a slurry of alumina powder containing 2% by weight of lanthanum oxide and 5% by weight of cerium oxide and calcined in the air at 900°C to have lanthenum oxide- and cerium oxide-containing alumina deposited on the carriers at a rate of 15% by weight based on completed catalyst. Then, the coated honeycomb carriers were immersed in an aqueous solution containing palladium nitrate and nickel nitrate, dried, and calcined in the air at 800°C for 4 hours to give rise to a completed catalyst having 2.5% by weight of palladium and 3.7% by weight of nickel oxide deposited thereon based on the completed catalyst.
- The same honeycomb carriers as used in Example 1 were coated with a slurry of alumina containing 7% by weight of neodymium oxide by following the procedure of Example 1 to have neodymium oxide-containing alumina deposited on the honeycomb carriers at a rate of 20% by weight based on completed catalyst. Then, the coated honeycomb carriers were immersed in an aqueous solution containing chloroplatinic acid, dried, and calcined in the air at 900°C for 3 hours to give rise to a completed catalyst having 2.8% by weight of platinum deposited thereon based on the completed catalyst.
- The procedure of Example 1 was repeated, except that the aqueous solution used for the immersion of coated honeycomb carriers contained no platinum. Consequently, there was obtained a completed catalyst having 20% by weight of lanthanum oxide-containing alumina power and 4.0% by weight of palladium deposited thereon based on the completed catalyst.
- The procedure of Example 8 was followed, except that honeycomb carriers of mullite containing 200 open cells per squre inch were used instead. Consequently, ther was obtained a completed catalyst having 15% by weight of lanthanum oxide- and cerium oxide-containing alumina powder, 2.5% by weignt of palladium, and 9.4% by weight of nickel oxide deposited thereon based on the completed catalyst. Control 3
- The procedure of Example 5 was repeated, except that the aqueous solution for the immersion of coated honeycomb carriers contained no palladium. Consequently, there was obtained a completed catalyst having 1.5% by weight of platinum deposited thereon based on the completed catalyst.
- In a sufficiently warmed cylindrical combuster, a front-stage catalyst bed was packed with the catalyst obtained in Example 1 and a rear-stage catalyst bed was packed with the catalyst obtained in Example 2. Into this cylindrical burner, a methane-air mixed gas containing 3% by volume of methane was introduced under application of 10 atmospheres at a flow rate of 167 Nm3 (STP) per hour at an inlet temperature of 350°C to test for efficiency of combustion and oulet temperature of catalyst bed. In this case, the linear velocity at the inlet of the catalyst bed was about 30 m/sec.
- Consequently, the efficiency of combustion was found to be about 71% and the outlet temperature of the catalyst bed to be about 850°C.
- When the methane concentration in the mixed gas 'was changed to 4.1% by volume, the efficiency of combustion reached 100% and there was obtained a clean combustion gas containing substantially no UHC, CO, or NOx. In this case, while the temperature at a point 100 mm behind the catalyst bed rose to 1,300°C, the outlet temperature of the catalyst bed was about 900°C.
- Subsequently, the combustion test was continued by introducing the same mixed gas at a flow rate equivalent to 3% by volume of methane in a downward flow to the catalyst bed and at a flow rate equivalent to 1.1% by volume of methane at a point 30 mm backward from the outlet of the catalyst bed.
- As the result, the outlet temperature of the catalyst bed was about 830°C and there was obtained a clean combustion gas at a temperature of about 1,300°C. This performance of the combustion system was maintained continuously over a period of 1,000 hours.
- A combustion test by the procedure of Example 10 using the catalyst indicated in Table 1 was carried out, with the mixed gas introduced at a flow rate equivalent to '3% by volume of methane in a downward flow to the catalyst bed and at a flow rate equivalent to 1.1% by volume of methane at a point 30 mm backward from the outlet of the catalyst bed. The results are shown in Table 1. It is noted from the results that the catalyst system according with this invention producd a clean combustion gas at about 1,300°C while maintaining the temperature of the catalyst bed below 1,000°C. the level incapable of inducing degradation of activity, whereas the combustion system using the catalyst of Control 1 in the front-stage bed quickly lost ability to ignite the fuel. The catalyst system using the catalyst of Control 2 in the front-stage bed and the catalyst of Example 3 in the rear-stage became unable to ignite the fuel after about 24 hours' combsution.
- In the catalyst system using the catalyst of Control 3 in the front-stage bed and the catalyst of Example 6 in the rear-stage bed, the front-stage bed failed to ignite the fuel and the rear-stage bed ignited it. Although the outlet temperature reached 620°C, no secondary combustion was induced behind the catalyst bed.
-
- A combustion test was performed by following the procedure of Example 10, using catalyst indicated in Table 2 introducing a liquefied natural gas composed of 88% of methane, 6% of ethane, 4% of propane, and 2% of butane at a flow rate equivalent to 3% by volume in a downward flow to the catalyst bed and at a flow rate equivalent to 1.1% by volume from the outlet of the catalyst bed.
- The results were as shown in_Table 2. It is noted from the results that the catalyst system according with this invention produced a clean combustion gas at about 1,300°C containing substantially no UHC, CO, or NO while maintaining the temperature of the catalyst bed below 1,000°C, a level incapable of inducing degradation of activity. This performance was retained intact continuously over a period of 1,000 hours.
Claims (28)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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JP75441/85 | 1985-04-11 | ||
JP60075441A JPS61235609A (en) | 1985-04-11 | 1985-04-11 | Combustion method for methane fuel in catalyst system |
JP60078441A JPH0663627B2 (en) | 1985-04-15 | 1985-04-15 | Combustion method of methane fuel by catalytic combustion catalyst system |
JP78441/85 | 1985-04-15 |
Publications (2)
Publication Number | Publication Date |
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EP0198948A2 true EP0198948A2 (en) | 1986-10-29 |
EP0198948A3 EP0198948A3 (en) | 1988-09-21 |
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EP85111839A Withdrawn EP0198948A3 (en) | 1985-04-11 | 1985-09-19 | Catalytic combustor for combustion of lower hydrocarbon fuel |
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