JP2000240907A - Device and method for hybrid catalyst combustion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a higher excess air combustion possible, and reduce NOx further by providing a heat transmitting-converting body having air permeability, which converts the sensible heat of a gas into a radiation, and emits to the upstream side, at the outlet of an vapor phase combustion section. SOLUTION: This device is equipped with a combustion chamber 3 comprising a catalyst combustion section 1 and a combustion catalyst of a combustor 100, and a vapor phase combustion section 2 on the downstream side of the catalyst combustion section 1. A hybrid catalyst combustion wherein one part of a fuel is combusted in the catalyst combustion section 1, and the remaining part of the fuel is combusted in the vapor phase combustion section 2, is realized. In addition, in the vapor phase combustion section 2, an obstructive member 5 which induces a re-circulation to the stream of a combustion gas is provided on the wall surface in a manner to be projected. Also, the combustor 100 is equipped with a heat transmitting-converting body 4 which has air permeability, and converts the sensible heat of a waste gas into a radiation, and emits to the upstream side, at the outlet section of the combustion chamber 3, and the waste gas is discharged from the vapor phase combustion section 2 through the heat transmitting-converting body 4. The heat transmitting-converting body 4 takes away the sensible heat of the waste gas, and radiates to the combustion chamber 3 side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber having a combustion passage formed therein, a catalytic combustion section comprising a combustion catalyst provided in the combustion passage, and a gas phase combustion section provided downstream of the catalytic combustion section. The present invention relates to an application of a hybrid catalytic combustion technique in which a part of fuel is burned in a catalytic combustion part and a remaining fuel is burned in the gaseous phase combustion part.

[0002]

2. Description of the Related Art In appliances operated at a high air ratio, such as a household indoor open-type warm air heater, a cogeneration system, and a gas turbine combustion device for power generation, an improvement in combustion stability at a high air ratio is required. Significant NOx reduction may be achieved. On the other hand, these devices have lower NO
There is a demand for x conversion. Above all, a household indoor open-air type warm air heater emits exhaust gas directly to the living space, so NOx
It has been desired to reduce NOx to the limit of 1 ppm (0% oxygen) or less.

As shown in FIG. 7, a catalytic combustion section 1 filled with a combustion catalyst and a subsequent gas phase combustion section 2 are provided in a combustion chamber 3 and have an adiabatic theoretical combustion temperature of 1500 ° C. or less (air ratio of about 1. (6) or more, in which a mixed gas of fuel and air is partially catalytically oxidized and combusted in a catalytic combustion section, and gas phase oxidation is induced in a downstream gas phase combustion section to complete combustion (referred to as a hybrid catalytic combustion method). Is proposed as a means for achieving ultra-low NOx (Japanese Patent Publication No. 6-506290).

[0004] In such a hybrid catalytic combustion, as a means for partially burning in the catalytic combustion section, palladium having the highest activity at a low temperature with respect to methane as a fuel and a self-reaction suppressing action at a high temperature is used as a catalytically active substance. With a metal honeycomb as a catalyst substrate, a catalyst coat layer (cell) and an uncoated layer (cell) are adjacent to each other, and the heat generated by catalytic oxidation is mixed with the premixed gas and heat passing through the connected non-catalyst layer. By taking measures such as exchanging and physically preventing excessive temperature rise, the catalyst layer in the catalytic combustion section has 2
0 to 70% is catalytically oxidized, and the catalyst temperature is 700 to 950
° C.

[0005]

In such a hybrid catalytic combustion, it is necessary to perform combustion under a higher air ratio condition in order to realize ultra-low NOx.
However, when combustion is performed at a high air ratio, incomplete combustion tends to occur, and it is difficult to perform stable combustion.
It is necessary to suppress the generation of incomplete combustion components such as O.
Also, in a combustor used for a home heater, unlike the one used for a gas turbine, it is difficult to preheat air introduced into the combustor, and the gas temperature discharged from the combustor is About 100 ° C. is sufficient. On the other hand, in order to perform hybrid catalytic combustion, the temperature of a mixed gas of fuel and air introduced into the catalyst depends on the type of fuel.
It must be preheated to ~ 600 ° C.

Further, a conventional hybrid catalytic combustion apparatus aimed at application to a home heater is intended for a kerosene-based liquid fuel in which catalytic oxidation is relatively easy. There is a problem that such a combustor is difficult to apply to a city gas or a natural gas based fuel containing methane having the lowest catalytic oxidation activity as a main component.
In other words, when applied to city gas and natural gas fuel,
It is necessary to set the preheating temperature of the mixed gas introduced into the catalyst 100 to 200 ° C. higher than that of the kerosene-based liquid fuel. For this reason, when a large heat exchanger is installed to increase the preheating of the mixed gas, problems such as pressure loss and increase in the combustor themselves arise. For this reason, the catalyst and the gas-phase combustion section are designed to be more compact. It is necessary to perform heat transfer with only the heat exchanger on the mixed gas side described above.
The required preheating cannot be achieved. Therefore, for a combustor mainly applied to city gas and natural gas-based fuel, it was necessary to develop a further improved combustor structure.

Accordingly, in view of such circumstances, an object of the present invention is to realize ultra-low NOx combustion and to realize hybrid catalytic combustion excellent in combustion stability.

[0008]

In a hybrid catalytic combustion device, it is important to suppress a sensible heat loss carried away by exhaust gas from the combustion device. A combustion chamber comprising a catalytic combustion unit comprising a combustion catalyst in the combustion flow path, a gas phase combustion unit downstream of the catalytic combustion unit, and a part of a mixed gas of fuel and air in the catalytic combustion unit. To configure a hybrid catalytic combustion device that burns the remainder of the mixed gas in the gas-phase combustion section, as described in claim 1, the outlet of the gas-phase combustion section has air permeability, A heat transfer converter that converts sensible heat of gas into radiation and discharges it to the upstream side is provided. That is,
The hybrid catalytic combustion device according to the present invention converts the sensible heat of exhaust gas into radiation at the outlet of a combustion chamber comprising a catalytic combustion section comprising a combustion catalyst and a gas phase combustion section downstream thereof, and discharges the sensible heat to the upstream side thereof. A configuration in which a heat transfer converter is arranged, a portion of the mixed gas is burned in the catalytic combustion section, and the remaining portion of the mixed gas is burned in the gas phase combustion section, and exhaust gas is discharged from the gas phase combustion section through the heat transfer converter. And Since the heat transfer converter heated by the sensible heat of the exhaust gas is radiatively transferred to the upstream combustion chamber preferentially, convective heat loss from the combustion chamber can be suppressed, and the heat can be suitably fed back to the upstream side. Even if the operation is performed at a higher air ratio, the combustion is stabilized, and a lower NOx can be achieved by lowering the peak temperature of the combustion reaction.

Such a hybrid catalytic combustion device is
As described in claim 2, the heat transfer converter,
It is preferable to be formed of a ceramic foam having a three-dimensional skeletal structure or a ceramic having a honeycomb structure. As described above, since the heat transfer converter is formed of ceramic foam or ceramic honeycomb, the heat transfer converter has a large skeletal surface area, and the sensible heat of the exhaust gas is efficiently transferred to the heat transfer converter, and the heat transfer is performed. Most is radiated to the upstream side, sensible heat loss of exhaust gas is greatly suppressed, and combustion can be completed at a higher air ratio side.
The combustion amount range that can achieve the above can be expanded. Further, as a ceramic foam, a mesh diameter of 0.3 to 10 mm, a porosity of 6
0 to 95% is preferable, and the material is cordierite,
Alumina-cordelite, alumina titania, mullite and silicon carbide are preferred. The ceramic honeycomb preferably has an opening diameter of 0.3 to 10 mm and a porosity of 60 to 95%, and the material is preferably cordierite, alumina-cordelite, alumina titania, mullite, or silicon carbide. Further, the thickness of the heat transfer converter is 5 to 25 mm.
The degree is preferable, and the sensible heat of the gas can be suitably radiated to the upstream side.

In general, when combustion is performed under a high air ratio condition to realize low NOx, incomplete combustion is likely to occur. However, the hybrid catalytic combustion device according to the present invention can be configured so that incomplete combustion components such as CO that are likely to be generated during operation at a high air ratio can be removed. That is, as described in claim 3, the heat transfer converter can be provided by applying a catalytic substance having an oxidizing activity to a combustible gas. That is, the heat transfer converter is coated with a carrier having a high specific surface area such as alumina, silica, zirconia, and the like, and a transition metal such as palladium, platinum, manganese, chromium, cobalt, nickel or the like having catalytic oxidation activity, or its oxidation. The precursor compound of the product is impregnated and supported, and is activated, or at the time of producing the heat transfer converter, by mixing and molding the above-mentioned transition metal having catalytic oxidation activity or the precursor compound of the oxide thereof, A combustible gas can be coated with a catalytic substance having an oxidizing activity on the heat transfer converter. As a result, harmful combustion intermediate products such as CO and aldehyde contained in the exhaust gas are not released to the downstream side of the heat transfer converter, and the emission from the combustion device can be suppressed.

Alternatively, as described in claim 4,
The heat transfer converter may be a catalytic substance having an oxidizing activity for a combustible gas. In this way, by using the heat transfer converter as the catalytic substance itself, the incomplete combustion component is not discharged to the downstream side, and the structure is simpler and more economical. In this case, a honeycomb or ceramic foam molded directly from a manganese-substituted hexaaluminate as a high-temperature oxidation catalyst can also be effectively used as a heat transfer converter.

In the conventional hybrid catalytic combustion apparatus, the mixed gas before being supplied to the catalytic combustion section is provided between the heat transfer converter and the catalytic combustion section, as described in claim 5. May be provided with a heat absorbing portion of a preheating mechanism for preheating the heat. With this configuration, the mixed gas supplied to the catalytic combustion unit can be preheated,
For example, even when city gas containing methane as a main component having low catalytic activity is used as fuel, stable hybrid catalytic combustion with extremely low NOx can be realized. Such a preheating mechanism can be configured to perform heat exchange between the combustion gas discharged from the gas-phase combustion section and the mixed gas before being supplied to the catalytic combustion section. It can be configured that the mixed gas is preheated by using radiant heat radiated from the converter.

According to a sixth aspect of the present invention, there is provided a combustion method in a hybrid catalytic combustion apparatus including a combustion chamber having a combustion flow path formed therein, wherein the combustion flow path comprises a catalyst comprising a combustion catalyst. A hybrid that includes a gas-phase combustion unit downstream of the catalytic combustion unit, and burns a part of the mixed gas of fuel and air in the catalytic combustion unit and the remainder of the mixed gas in the gas-phase combustion unit. A catalytic combustion method, wherein a heat transfer converter that has air permeability, converts sensible heat of gas into radiation, and discharges the gas upstream is provided at an outlet of the gas-phase combustion unit, By flowing the exhaust gas after combustion inside the heat transfer converter, converting the sensible heat of the exhaust gas into radiation and releasing it to the upstream side, suppressing convective heat loss from the combustion chamber. I do. By performing such a hybrid catalytic combustion method, ultra low NO
x can realize stable hybrid catalytic combustion.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 The basic structure of a hybrid catalytic combustion device according to the present invention will be described with reference to FIG. The combustor 100 is provided with a catalytic combustion section 1 composed of a combustion catalyst and a combustion chamber 3 composed of a gas phase combustion section 2 on the downstream side. This makes it possible to realize hybrid catalytic combustion in which part of the fuel is burned in the catalytic combustion part 1 and the remainder of the fuel is burned in the gas phase combustion part 2. Further, the gas-phase combustion unit 2 is provided with a baffle member 5 for inducing recirculation in the flow of the combustion gas, protruding from the wall surface. Further, the combustor 100 according to the present invention includes, at the outlet of the combustion chamber 3, a heat transfer converter 4 having air permeability, converting sensible heat of exhaust gas into radiation, and discharging the radiation to the upstream side, The exhaust gas is discharged from the gas phase combustion section 2 through the heat transfer converter 4. As will be described later, the heat transfer converter 4 is made of alumina-cordierite ceramic foam having a three-dimensional skeletal structure. When the exhaust gas flows through the gaps between the ceramic foams, the sensible heat of the exhaust gas is reduced. It is configured to rob and radiate to the combustion chamber 3 side. As a result, the upstream side of the heat transfer converter 4 is heated by the radiation of the heat transfer converter 4, the sensible heat loss of the exhaust gas is suppressed, the operation at a higher air ratio becomes possible, and the ultra-low NOx hybrid catalyst is used. A combustion device can be realized.

Next, FIG. 2 shows the temperature distribution of the heat transfer converter 4 when the exhaust gas flows. The heat transfer converter 4 is made of a ceramic foam made of alumina-cordierite having a three-dimensional skeleton structure, and has a large skeleton surface area, so that the sensible heat of the exhaust gas is transferred to the heat transfer converter 4 with high efficiency, and Radiated as radiant energy. At this time, the heat transfer converter 4
On the upstream side, the heat rays are radiated to the upstream side without being interrupted, but most of the heat rays going to the downstream side are shielded, and the exhaust gas lowers the temperature by the radiated heat quantity and moves to the downstream side. Thus, the heat rays radiated in the heat transfer converter 4 are attenuated according to the optical thickness before and after the point, and the amount of radiated heat is synergistic in proportion to the fourth power of the absolute temperature. The temperature drops rapidly upstream of 4, and most of the sensible heat of the exhaust gas is radiated upstream. Therefore, the sensible heat loss of the exhaust gas is greatly suppressed, the combustion can be completed at a higher air ratio, and the combustion amount range in which ultra-low NOx can be achieved can be expanded.

[Embodiment 2] Next, as an embodiment of the present invention, an outline of a hybrid catalytic combustion apparatus according to the present invention, which is intended to be applied to a hot air heater using city gas or natural gas as fuel, is shown. 3 to 6. 3 is an overall perspective view of the hybrid catalytic combustion device according to the present invention, FIG. 4 is an elevational sectional view of the hybrid catalytic combustion device of FIG. 3, and FIG. 5 is a heat exchange for preheating the mixed gas of the hybrid catalytic combustion device of FIG. FIG. 6 is a plan sectional view of the combustion section of the hybrid catalytic combustion device of FIG.

Referring to FIGS. 4 and 5, air from air inlet 16 and fuel from fuel introduction pipe 17 are first introduced into heat exchange section 18 for preheating the mixed gas. A dispersion nozzle is attached to the tip of the fuel introduction pipe 17 so as to sufficiently mix the fuel and air (not shown). The heat exchange section 18 is formed so that heat from the top plate heated by the combustion gas is transmitted to the mixed gas by conduction.
Various structures for this purpose are conceivable, but here, the diameter 4 is welded to the top plate, extends downward, and is attached in a staggered manner.
mm SUS heat transfer rod type heat exchanger 19 is used. The mixed gas is preheated while circumventing the periphery of the partition plate 13, and is guided to the inside of the catalyst holder 20 from the opening on the opposite side of the inlet as shown in FIG. 3. At the inlet of the combustion chamber, a dispersion plate for improving the dispersion of the mixed gas was used (not shown).

Referring to FIGS. 3 and 4, the outlet of the catalyst holder 20 has a width of 85 mm, a depth of 20 mm, and a layer height of 20 mm.
And the outside of the catalyst holder 20 is covered with a heat insulating material. The combustion catalyst unit 11 forms a carrier layer having a high specific surface area on one side of a support made of a corrugated metal sheet, and applies and activates a palladium-based catalytic material of a transition metal having catalytic activity on the carrier layer. The support is spirally wound and formed into a honeycomb shape. In the combustion catalyst portion 11 thus formed, heat generated is dispersed by heat conduction to the wall surface having a catalyst and the wall surface having no catalyst and through which only the mixed gas flows, and the re-high temperature of the catalyst is reduced by 9%.
The temperature can be suppressed to 50 ° C. or less, deterioration of the catalyst can be suppressed, and stable catalytic combustion can be maintained. The combustion catalyst section 11 includes a thermocouple 21 for detecting a catalytic reaction and controlling combustion.

Referring to FIGS.
Is a space for securing a residence time necessary for the unburned fuel partially burned by the catalytic combustion and heated to be completely burned by the gas-phase radical reaction. A heat insulating member 22 is installed inside the gas phase combustion unit 12,
Has a folded structure. An igniter 23 for starting the combustion by spark ignition of the mixed gas and a thermocouple 24 for observing the state of the gas phase reaction are provided at the folded portion of the gas phase combustion unit 12. In the gas-phase combustion part 12, an outlet is provided on one side in the longitudinal direction. The outlet portion is made of alumina-cordierite ceramic foam having 6 cells / 25mm, an apparent specific gravity of 0.43, and a thickness of 12mm. The heat transfer converter 14 is provided. Further, the heat transfer converter 14 is coated with a high specific surface area material such as alumina as a carrier having a high specific surface area,
Oxidation active substances such as palladium and platinum having catalytic activity are impregnated and supported on the intermediate products of combustion of CO or hydrocarbons to be activated.

A low-pressure fan (not shown) having a blade diameter of 60 mm was set upstream of the air inlet 16 of the hybrid catalytic combustion device, and a performance test was performed using natural gas-based city gas. The combustion was started as follows.
First, the igniter 23 is turned on with the fan voltage set to a voltage value at which an air flow rate corresponding to an air ratio of 1.4 is obtained at a combustion rate of about 2500 kcal / h.
Next, when a gas corresponding to 2500 kcal / h is introduced with a flow rate adjustment by a mass flow controller (not shown), the fan voltage is increased by the thermocouple 21 set in the combustion catalyst unit 11 while observing the temperature rising state. Then, the state shifts from catalyst ignition to a steady state. At this time, the temperature of the combustion catalyst section 11 can be controlled so as not to exceed 950 ° C. After reaching the steady state, a stable combustion amount range for achieving low NOx while controlling the fan voltage was determined.
As a result, the combustion amount from 3500 kcal / h to 700 kc
NOx emission concentration 2ppm in the range up to al / h
Below (converted to oxygen 0%), the complete oxidation rate is 99.9% or more,
An ultra-low NOx stable combustion with a CO / CO ₂ ratio of 0.0005 or less is achieved.

[Another Embodiment] In the hybrid catalytic combustion apparatus according to the present invention shown in FIG. 1, the Mn-substituted hexaaluminate is used as a heat transfer converter.

Embedded image Was extruded at a rate of 300 cells per square inch, formed into a honeycomb, and fired at 1200 ° C. to have a thickness of 10 mm. As a result, the pressure loss in the combustion chamber increased, so that the maximum combustion amount was limited to 3200 kcal / h, but the minimum combustion amount was up to 700 kcal / h, and stable combustion was achieved. The fan voltage control range in which good combustion is performed without incomplete combustion is widened, and NOx1pp
m (0% oxygen conversion) was achieved.

The catalyst used in the catalytic combustion section is mainly composed of palladium or platinum, which is a transition metal having catalytic activity, or palladium or platinum.
Catalysts can be used that include one or more cocatalysts selected from palladium, ruthenium, iridium or rhodium.

Further, in the above embodiment, a heat transfer rod or a punching metal for promoting heat transfer is inserted into the catalyst holder 20 shown in FIG. Radiated heat from the catalyst holder 20 can be transferred to the mixed gas.

As a carrier for coating the heat transfer converter 14 shown in FIG. 3, a substance having a high surface area such as alumina, silica, or zirconia can be coated.
Further, as a catalyst to be impregnated and supported on the carrier, a transition metal such as palladium, platinum, manganese, chromium, and cobalt, or an oxide thereof can be used. Further, as a high-temperature oxidation catalyst, one formed directly from a manganese-substituted hexaaluminate into a honeycomb or formed into a ceramic foam can be used as a heat transfer converter.

In the above embodiment, the natural gas-based city gas is used as the fuel. However, the fuel is not limited to the natural gas and the city gas, and the fuel can be freely selected from LPG, kerosene vaporized gas and the like. Further, the hybrid catalytic combustion device according to the present invention can be applied to a low-pressure to high-pressure combustion device.

[0026]

According to the present invention, the sensible heat carried away from the combustion device is largely suppressed, so that excess air combustion can be achieved and the NOx can be further reduced. NO below the reference level
The control range of the air ratio that achieves the x value can be expanded, and control with high safety can be performed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a hybrid catalytic combustion device according to the present invention.

FIG. 2 is a diagram showing a temperature distribution of the heat transfer converter during combustion gas flow.

FIG. 3 is an overall perspective view of a hybrid catalytic combustion device according to the present invention.

FIG. 4 is an elevational sectional view of the hybrid catalytic combustion device of FIG. 3;

5 is a plan sectional view of a heat exchange unit for preheating a mixed gas of the hybrid catalytic combustion device of FIG. 3;

FIG. 6 is a plan sectional view of a combustion section of the hybrid catalytic combustion device of FIG. 3;

FIG. 7 is a cross-sectional view illustrating a basic configuration of a conventional hybrid catalytic combustion device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalytic combustion part 2 Gas-phase combustion part 3 Combustion chamber 4 Heat transfer converter 100 Combustor

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F23C 11/00 312 F23C 11/00 312 F term (reference) 3K017 BA03 BA06 BB04 BB07 BC07 BC09 BC10 BD01 BE05 BF01 3K065 TA01 TA11 TB09 TC05 TC08 TD05 TE04 TF03 TH01 TK02 TK04 TL04 TM02 TP09 4G069 AA01 AA11 AA15 BA01B BA02B BA05B BA13A BC32B BC33B BC58B BC62B BC67B BC70B BC71B BC72A BC72B BC74B BC75A BC75B CD01 DA05 EA24 EB24

Claims (6)

[Claims] A combustion chamber having a combustion flow path formed therein; a catalytic combustion section comprising a combustion catalyst in the combustion flow path; and a gas phase combustion section downstream of the catalytic combustion section. A hybrid catalytic combustion device that burns a part of a mixed gas of fuel and air in a catalytic combustion part, and burns the remainder of the mixed gas in the vapor-phase combustion part. A hybrid catalytic combustion device including a heat transfer converter that converts sensible heat of gas into radiation and discharges the gas upstream. 2. The hybrid catalytic combustion device according to claim 1, wherein the heat transfer converter is made of a ceramic foam having a three-dimensional skeletal structure or a ceramic having a honeycomb structure. 3. The hybrid catalytic combustion apparatus according to claim 1, wherein the combustible gas is coated with a catalytic substance having an oxidizing activity on the heat transfer converter. 4. The hybrid catalytic combustion device according to claim 1, wherein the heat transfer converter is a catalytic substance having an oxidizing activity for a combustible gas. 5. A heat absorbing portion of a preheating mechanism for preheating the mixed gas before being supplied to the catalytic combustion portion, between the heat transfer converter and the catalytic combustion portion. The hybrid catalytic combustion device according to claim 1. 6. A combustion chamber having a combustion passage formed therein, a combustion chamber comprising a catalytic combustion section comprising a combustion catalyst, and a gas phase combustion section provided downstream of the catalytic combustion section. A hybrid catalytic combustion method in which a part of a mixed gas of fuel and air is burned in a catalytic combustion part, and the remaining part of the mixed gas is burned in the gaseous phase combustion part. A heat transfer converter that converts sensible heat of gas into radiation and discharges the gas upstream is provided, and the exhaust gas after combustion in the gas-phase combustion section is allowed to flow inside the heat transfer converter, and A hybrid catalytic combustion method for converting sensible heat into radiation and releasing it to the upstream side to suppress convective heat loss from the combustion chamber.