CA1147624A - Catalytic combustion system with fiber matrix burner - Google Patents
Catalytic combustion system with fiber matrix burnerInfo
- Publication number
- CA1147624A CA1147624A CA000379977A CA379977A CA1147624A CA 1147624 A CA1147624 A CA 1147624A CA 000379977 A CA000379977 A CA 000379977A CA 379977 A CA379977 A CA 379977A CA 1147624 A CA1147624 A CA 1147624A
- Authority
- CA
- Canada
- Prior art keywords
- matrix
- mixture
- temperature
- reaction zone
- fibers
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
- F23D14/12—Radiant burners
- F23D14/18—Radiant burners using catalysis for flameless combustion
Abstract
ABSTRACT OF THE DISCLOSURE
A combustion system which includes a catalytic burner of a fiber matrix com-position for combusting an air-fuel mixture with high efficiency and low NOX
emissions. The burner matrix is comprised of high temperature resistant fibers randomly oriented and packed together to form interstitial spaces for the mixture flow path. The thickness of the matrix and density of the fibers are within an optimum range for maintaining combustion in a shallow heterogeneous reaction zone at a temperature below the use temperature of the fiber by radiating heat transfer from the zone. The matrix forms a heat insulation barrier to maintain the matrix temperature at the inlet side below the ignition temperature of the mixture for preventing flashback. Strands of a catalytic material can be interspersed through the matrix. The matrix can be in the form of a hollow cylindrical shell for use within the combustion chamber of a firetube boiler system.
A combustion system which includes a catalytic burner of a fiber matrix com-position for combusting an air-fuel mixture with high efficiency and low NOX
emissions. The burner matrix is comprised of high temperature resistant fibers randomly oriented and packed together to form interstitial spaces for the mixture flow path. The thickness of the matrix and density of the fibers are within an optimum range for maintaining combustion in a shallow heterogeneous reaction zone at a temperature below the use temperature of the fiber by radiating heat transfer from the zone. The matrix forms a heat insulation barrier to maintain the matrix temperature at the inlet side below the ignition temperature of the mixture for preventing flashback. Strands of a catalytic material can be interspersed through the matrix. The matrix can be in the form of a hollow cylindrical shell for use within the combustion chamber of a firetube boiler system.
Description
A-3566 ~ 7~
CATALYTIC COMBU~TION SYSTEM WITH FIBER MATRIX BURNER
The invention described herein was made in the course oft or under, a contract with the Environmental Protection Agency.
This invention relates in general to catalytic combustion technology, and in particular relates to catalytic combustion systems such as firetube boilers and burners for use therein.
Conventional firetube boiler systems incorporating diffusion flame burners achieve high combustion efficiency (low CO and HC) but produce relatively high nitrogen oxide emissions (NOx). Typically, conventional diffusion flame burners cannot achieve NOx emissions below 100 ppm (volume basis at 0%
excess oxygen for gaseous and liquid fuels without significant nitrogen content). In view of the widespread use of firetube boiler systems of this type the adverse consequences of atmospheric pollution and photochemical smog are significant.
Radiant burners have previously been developed which employ discrete fuel-air jets to heat up a ceramic block which in turn radiates energy. Burners of this type are not applicable to catalytic combustion in a firetube boiler system as in the present invention.
It is a general object of the invention to provide a new and improved fuel-air combustion system and method operating at high combustion efficiency (low CO and HC), high overall system efficiency, and low thermal NOx emissions.
Another object is to provide a combustion system and method suitable for use in firetube boilers with high overall boiler effieiency and reduced atmospheric pollutants and photochemical smog.
Another object is to provide a combustion system and method of the type described which is capable of operating at near-stoichiometric mixtures with catalytic bed temperatures below the adiabatic flame temperature of the mixture and within the temperature limitations of the bed material.
... ~
7~
Another object is to provide a catalytic combustion system and method o~ the type described which operates at low excess air levels to limit stack gas energy losses for maintaining high o~,erall efficlency while slso maintaining the combustion bed temperature at acceptably low levels to minimize thermal NOx emissions.
The invention in summary comprises a catalytic combustion system incorporat-ing a burner formed by a matrix of high temperature resistant fibers with interstitial spaces in the matrix forming a flowpath for the fuel-air mixture.
The density of the fibers and thickness of the burner are within an optimum range so that the mixture combusts at a heterogeneous reaction zone along a shallow layer on one side of the burner. Heat is transferred primarily by radiation from the reaction zone so that the temperature of the body is maintained below its use temperature and below the adiabatic flame temperature of the mixture.
Figure 1 is a fragmentary cross-section of a burner matrix according to the invention.
Figure 2 is a chart depicting the approximate temperature profile within the matrix as a function of depth through the thickness of the burner of Figure 1.
Figure 3 is a schematic diagram of a firetube boiler system incorporating the burner matrix of Figure 1.
Figure 4 is a perspective view, partially broken away and exploded, of the firetube boiler system of Figure 3.
Figure 5 i5 a chart depicting cornbustion surface temperature for a burner matrix of the invention as a function OI theoretical air for different face velocities of the fuel-air mixture.
Figure 6 is a chart depicting NO~ emissions for the burner matrix used in Figure 5 as a function of theoretical air for different face velocities of the fuel-air mixture.
The catalytic burner system of the invention incorporates a burner 10 of porous matrix composition as illustrated in the cross-section of Figure 1. The material of the matrix is comprised of randomly oriented fibers 12 of a high temperature resistant material such as alumina silieate. The fibers are pacl;ed to an optimum density in tha range of substantially 12 to 16 lb/ft3 to form the desired shape and thickness, e.g. a flat pad as in Figure lo With this range of densities the interstitial spaces between the fibers provides a flow path for the fuel-air mixture over the entire extent of the matrix pad. In ~igure 1 the inlet side 14 is shown on the left of the pad with the mixture moving through the pad for combustion at a heterogeneous reaction zone 16 on the right hand side.
The fiber matrix composition of the burner pad has relatively poor internal heat conductivity so that the upstream portion 18 of the matrix forms a heat insulation barrier such that reaction zone 16 is established along a shallow layer ~7~
at a depth of only a few millimeters on the outlet side of the pad. The shallow depth of the reaction zone produces significant heat transfer away from the zone primarily by radiation with some transfer by convection. The rate of this radiative transfer is such that the surface temperatlire of the fiber material in the reaction zone is maintained below the adiabatic flame temperature of the fuel-air mixture and also below the "use" temperature of the fiber material. In comparison, many conventional combustors with relatively thick cores, e.g.
honeycomb bed combustors, result in a deep combustion zone with high peak temperatures within the core. The substantially lower surface temperature of the matrix materials in the present invention thereby permits operation at near-stoichiometric mixtures with relatively low NOx emissions and high combustion efficiencies as compared to combustors of conventional design.
An important feature of the invention is that the problem of flashback into the incoming fuel-air mixture is minimized. The poor internal heat conduction of the fiber matrix and the shallow depth at the reaction zone prevents temperature rise on the surface at the inlet side which could otherwise lead to detonations and destruction of the flame. The approximate temperature profile for the burner pad of Figure 1 is illustrated in the graph of Figure 2. The temperature at $he surface on the inlet side and through the major depth lB of the pad is substantially ambient or close to the temperature of the incoming mixture.
Approaching the heterogeneous reaction zone 16 the temperature rises sharply.
Rapid transfer of heat by radiation from the downstream surface is represented by the downturn at the tail of the temperature curve.
.
The thickness of the burner pad is selected in accordance with the particular fiber matrix density. With a fiber matrix density oî 12 lb/ft3 a pad thickness of substantially one inch is optimum; a thicker pad would result in increased pumping requirements and reduce system efficiency while a thinner pad would increase the risk of flashback. Similarly, a matrix with a density of higher than the optimum would undesirably increase pumping requirements while a density below the optimum range would not contain the reaction zone to the shaUow layer which produces the desired radiative heat transfer for maintaining the low temperatures of the matrix in the reaction zone.
A burner pad suitable for use in the invention can comprise a pad of Cerablanket fibers (alumina silicate) sold by the Johns-Manville Company with a density of approximately 12 lb/ft3. This material has a use temperature in the range of 1600 F to 2500 F with an optimum heat release rate per unit area of 80,00û -150,000 Btu/hr-ft2. A fiber material of this character can be formed into the desired matrix shape, e.g. a cylindrical shell, by forming a wet slurry of the fibers by means of conventional vacuum-forming techniguesO
The catalytic activity of the burner pad can be improved by the addition of materials having a higher degree of catalytic activity, e.g. strands of a catalytic metal such as chrome wire can be interspersed through the matrix. In addition, the matrix can be formed in two or more separate layers, each having different densities or different compositions. Thus, for controlling flashback the layer on the upstream side could be of a composition which is less catalytic than the downstream layer, and the strands of catalytic metal could be contained in only ~7~
the downstream layer.
Figures 3 and 4 illustrate the burner system of the invention incorporated into a firetube boiler 20. In the system catalytic burner 22 is comprised of a fiber matrix formed into a cylindrieal shell configuration. The matrix material comprises Cerablanket fibers sold by the Johns-Manville Company with a density oE approximately 12 lb/ft3, and the radial thickness of the cylinder wall 24 is approximately one inch. The downstream end of the cylinder is capped by a circular fiber matrix pad 26 of a composition, density and thickness similiar to that of the cylindrieal wall of the burner. The upstream end of the cylinder is sealed by a flange 28 of the iretube boiler combustion chamber 30.
The fuel-air rnixture is directed into the burner through Q per~orated manifold tube 32 extending concentrically within the burner. The wall of the matrix iS
rigidly supported by radial spokes 34 extending from the maniEold tube.
Burner 22 is mounted coaxially within firetube combustion chamber 30 with the radial spacing between the outer surface of the matrix and the combustion chamber surface 36 in the range of 1 to 5 inches. Typically the inner diameter of the combustion chamber is in the range of 14 to 25 inches and the chamber length is in the range of 3 to 15 feet.
1'he fuel for the firetube boiler system may be gaseous, e.g. natural gas, or vaporized liquid. The fuel is premixed with air and forced under pressure into the manifold tubes of the burners. The burner may operate on diesel fuel in which case the fuel is partially vaporized by preheating the air stream to 42S F
prior to mixing with the fuel.
The premixed air-fuel mixture is directed under a positive pressure through manifold tube 32 and the interior volume 3B of the burner. The mixture is forced outwardly through the interstitial spaces in the rnatrix and emerges from the outer surfac2 where it is artificially ignited. Heterogeneous combustion is uniformly established in reaction ~one 16 over the entire outer surface of the cylinder and end cap 26 to a depth of a few millirneters of the matrix. Heat is transferred outwardly from the reaction zone primarily by radiation with some contribution by convective transfer. This heat transfer limits the matrix surface temperature to less than 2500, the use temperature of the fiber material, while the adiabatic flame temperature of the reactive mixture exceeds 3500 F. The heat radiation is absorbed by the surrounding metal wall 36 of the firetube combustion chamber, and the wall conducts heat to the boiler water 40 to heat the water or to raise steam. Flue ~ases are forced to the end of the firetube and out through the flue passage 42 or into additional firetube passes.
In another example of the invention the operating results demonstrate the low emission characteristics and the ability to radiatively transfer heat to surround-ing surfaces. In this example, the burner element is comprised of the previously-deseribed Cerablanket fiber material at a density of 12 lb/ft3. The element is in the shape of a flat circular disc of 6 inch diameter and 1 inch thickness. The disc i5 mounted within a conduit perpendicular to the flow of premixed air-fuel reactants. The mixture is forced under positive pressure through the disc and is - ~ :
, 7~
ignited at the downstream îace to establ;sh the heterogeneous reaction zone to a depth of a few millimeters.
The operating results of the flat circular disc burner configuration using natural gas fuel and varied inlet flow velocity conditions are depicted in Figures 5 and 6.
Figure S depicts the matrix surface ternperature of the heterogeneous reaction zone as a function of theoretical air for three different ~ace velocities. Curve 44 depicts the results at a face velocity of 2 ft/sec, curve 46 at a face velocity of 1 ft/sec, and curve 48 at a face velocity of 1/2 ft!sec. The graph dennonstrates that lower velocities result in lower surfaee temperatures at the lower excess air levels (100 to 130% theoretical air) where firetube boilers normally operate. The graph of Figure 6 demonstrates that this lower surface temperature is advantageous in reducing NOX emissions (ppm) as a function of percent theoretical air, with curve 50 depicting the results at a face velocity of 2 ft/sec, curve 52 at a velocity of 1 ft/sec, and curve 54 at a velocity Oe 1/2 ft/sec. As demonstrated by the curve 54 in Figure 6, NOX emissions oE less than 10 ppm at 115% theoretical air are possible. Additionally, high combustion efficiency (low CO and HC) can be achieved simultaneously with low NOX emissions.
The low surface temperatures represented in Figure 5 also demonstrate the effectiveness of radiative heat transfer away from the heterog~eneous reaction zone. The indicated temperatures of 2200 F to 2500 F at 100% theoretical air are within the use temperature capabilities of the alumina silicate fibers which comprise the matrix, and these temperatures are also far below the mixture's adiabatic flame temperature of 3500 F. These results demonstrate that the optimum flow velocity for the particular matrix material which was employed is in the range of l/3 to 1/~ ft/sec.
The foregoing demonstrates that the invention provides a eatalytic burner with important operating advantages, particularly for firetube boilers. Comb~lstion in the fiber matrix of the burner takes plaee at relatively low temperatures with active heat transfer to achieve low emissions of nitrogen oxides. The matrix can be fabricated in a variety of configurations, such as a cylindrical shell compatible with the combustion chamber of a firetube boiler. Good combustion efficiency is achieved and high overall boiler efficien(!y realized in that the burner can operate at near-stoichiometric conditions. The burner CM be operated on a variety of gaseous ~ld liquid ~with pre-vaporization~ fuels.
While the foregoing embodiments are at present considered to be preferred it is understood that numerous variations and modifications may be made therein by those skilled in the art Md it is intended to cover in the appended claims all such variations and modifications as fall within the true spirit and scope of the invention.
.
'~
' ,: , ' ' ' ~ . ,:
CATALYTIC COMBU~TION SYSTEM WITH FIBER MATRIX BURNER
The invention described herein was made in the course oft or under, a contract with the Environmental Protection Agency.
This invention relates in general to catalytic combustion technology, and in particular relates to catalytic combustion systems such as firetube boilers and burners for use therein.
Conventional firetube boiler systems incorporating diffusion flame burners achieve high combustion efficiency (low CO and HC) but produce relatively high nitrogen oxide emissions (NOx). Typically, conventional diffusion flame burners cannot achieve NOx emissions below 100 ppm (volume basis at 0%
excess oxygen for gaseous and liquid fuels without significant nitrogen content). In view of the widespread use of firetube boiler systems of this type the adverse consequences of atmospheric pollution and photochemical smog are significant.
Radiant burners have previously been developed which employ discrete fuel-air jets to heat up a ceramic block which in turn radiates energy. Burners of this type are not applicable to catalytic combustion in a firetube boiler system as in the present invention.
It is a general object of the invention to provide a new and improved fuel-air combustion system and method operating at high combustion efficiency (low CO and HC), high overall system efficiency, and low thermal NOx emissions.
Another object is to provide a combustion system and method suitable for use in firetube boilers with high overall boiler effieiency and reduced atmospheric pollutants and photochemical smog.
Another object is to provide a combustion system and method of the type described which is capable of operating at near-stoichiometric mixtures with catalytic bed temperatures below the adiabatic flame temperature of the mixture and within the temperature limitations of the bed material.
... ~
7~
Another object is to provide a catalytic combustion system and method o~ the type described which operates at low excess air levels to limit stack gas energy losses for maintaining high o~,erall efficlency while slso maintaining the combustion bed temperature at acceptably low levels to minimize thermal NOx emissions.
The invention in summary comprises a catalytic combustion system incorporat-ing a burner formed by a matrix of high temperature resistant fibers with interstitial spaces in the matrix forming a flowpath for the fuel-air mixture.
The density of the fibers and thickness of the burner are within an optimum range so that the mixture combusts at a heterogeneous reaction zone along a shallow layer on one side of the burner. Heat is transferred primarily by radiation from the reaction zone so that the temperature of the body is maintained below its use temperature and below the adiabatic flame temperature of the mixture.
Figure 1 is a fragmentary cross-section of a burner matrix according to the invention.
Figure 2 is a chart depicting the approximate temperature profile within the matrix as a function of depth through the thickness of the burner of Figure 1.
Figure 3 is a schematic diagram of a firetube boiler system incorporating the burner matrix of Figure 1.
Figure 4 is a perspective view, partially broken away and exploded, of the firetube boiler system of Figure 3.
Figure 5 i5 a chart depicting cornbustion surface temperature for a burner matrix of the invention as a function OI theoretical air for different face velocities of the fuel-air mixture.
Figure 6 is a chart depicting NO~ emissions for the burner matrix used in Figure 5 as a function of theoretical air for different face velocities of the fuel-air mixture.
The catalytic burner system of the invention incorporates a burner 10 of porous matrix composition as illustrated in the cross-section of Figure 1. The material of the matrix is comprised of randomly oriented fibers 12 of a high temperature resistant material such as alumina silieate. The fibers are pacl;ed to an optimum density in tha range of substantially 12 to 16 lb/ft3 to form the desired shape and thickness, e.g. a flat pad as in Figure lo With this range of densities the interstitial spaces between the fibers provides a flow path for the fuel-air mixture over the entire extent of the matrix pad. In ~igure 1 the inlet side 14 is shown on the left of the pad with the mixture moving through the pad for combustion at a heterogeneous reaction zone 16 on the right hand side.
The fiber matrix composition of the burner pad has relatively poor internal heat conductivity so that the upstream portion 18 of the matrix forms a heat insulation barrier such that reaction zone 16 is established along a shallow layer ~7~
at a depth of only a few millimeters on the outlet side of the pad. The shallow depth of the reaction zone produces significant heat transfer away from the zone primarily by radiation with some transfer by convection. The rate of this radiative transfer is such that the surface temperatlire of the fiber material in the reaction zone is maintained below the adiabatic flame temperature of the fuel-air mixture and also below the "use" temperature of the fiber material. In comparison, many conventional combustors with relatively thick cores, e.g.
honeycomb bed combustors, result in a deep combustion zone with high peak temperatures within the core. The substantially lower surface temperature of the matrix materials in the present invention thereby permits operation at near-stoichiometric mixtures with relatively low NOx emissions and high combustion efficiencies as compared to combustors of conventional design.
An important feature of the invention is that the problem of flashback into the incoming fuel-air mixture is minimized. The poor internal heat conduction of the fiber matrix and the shallow depth at the reaction zone prevents temperature rise on the surface at the inlet side which could otherwise lead to detonations and destruction of the flame. The approximate temperature profile for the burner pad of Figure 1 is illustrated in the graph of Figure 2. The temperature at $he surface on the inlet side and through the major depth lB of the pad is substantially ambient or close to the temperature of the incoming mixture.
Approaching the heterogeneous reaction zone 16 the temperature rises sharply.
Rapid transfer of heat by radiation from the downstream surface is represented by the downturn at the tail of the temperature curve.
.
The thickness of the burner pad is selected in accordance with the particular fiber matrix density. With a fiber matrix density oî 12 lb/ft3 a pad thickness of substantially one inch is optimum; a thicker pad would result in increased pumping requirements and reduce system efficiency while a thinner pad would increase the risk of flashback. Similarly, a matrix with a density of higher than the optimum would undesirably increase pumping requirements while a density below the optimum range would not contain the reaction zone to the shaUow layer which produces the desired radiative heat transfer for maintaining the low temperatures of the matrix in the reaction zone.
A burner pad suitable for use in the invention can comprise a pad of Cerablanket fibers (alumina silicate) sold by the Johns-Manville Company with a density of approximately 12 lb/ft3. This material has a use temperature in the range of 1600 F to 2500 F with an optimum heat release rate per unit area of 80,00û -150,000 Btu/hr-ft2. A fiber material of this character can be formed into the desired matrix shape, e.g. a cylindrical shell, by forming a wet slurry of the fibers by means of conventional vacuum-forming techniguesO
The catalytic activity of the burner pad can be improved by the addition of materials having a higher degree of catalytic activity, e.g. strands of a catalytic metal such as chrome wire can be interspersed through the matrix. In addition, the matrix can be formed in two or more separate layers, each having different densities or different compositions. Thus, for controlling flashback the layer on the upstream side could be of a composition which is less catalytic than the downstream layer, and the strands of catalytic metal could be contained in only ~7~
the downstream layer.
Figures 3 and 4 illustrate the burner system of the invention incorporated into a firetube boiler 20. In the system catalytic burner 22 is comprised of a fiber matrix formed into a cylindrieal shell configuration. The matrix material comprises Cerablanket fibers sold by the Johns-Manville Company with a density oE approximately 12 lb/ft3, and the radial thickness of the cylinder wall 24 is approximately one inch. The downstream end of the cylinder is capped by a circular fiber matrix pad 26 of a composition, density and thickness similiar to that of the cylindrieal wall of the burner. The upstream end of the cylinder is sealed by a flange 28 of the iretube boiler combustion chamber 30.
The fuel-air rnixture is directed into the burner through Q per~orated manifold tube 32 extending concentrically within the burner. The wall of the matrix iS
rigidly supported by radial spokes 34 extending from the maniEold tube.
Burner 22 is mounted coaxially within firetube combustion chamber 30 with the radial spacing between the outer surface of the matrix and the combustion chamber surface 36 in the range of 1 to 5 inches. Typically the inner diameter of the combustion chamber is in the range of 14 to 25 inches and the chamber length is in the range of 3 to 15 feet.
1'he fuel for the firetube boiler system may be gaseous, e.g. natural gas, or vaporized liquid. The fuel is premixed with air and forced under pressure into the manifold tubes of the burners. The burner may operate on diesel fuel in which case the fuel is partially vaporized by preheating the air stream to 42S F
prior to mixing with the fuel.
The premixed air-fuel mixture is directed under a positive pressure through manifold tube 32 and the interior volume 3B of the burner. The mixture is forced outwardly through the interstitial spaces in the rnatrix and emerges from the outer surfac2 where it is artificially ignited. Heterogeneous combustion is uniformly established in reaction ~one 16 over the entire outer surface of the cylinder and end cap 26 to a depth of a few millirneters of the matrix. Heat is transferred outwardly from the reaction zone primarily by radiation with some contribution by convective transfer. This heat transfer limits the matrix surface temperature to less than 2500, the use temperature of the fiber material, while the adiabatic flame temperature of the reactive mixture exceeds 3500 F. The heat radiation is absorbed by the surrounding metal wall 36 of the firetube combustion chamber, and the wall conducts heat to the boiler water 40 to heat the water or to raise steam. Flue ~ases are forced to the end of the firetube and out through the flue passage 42 or into additional firetube passes.
In another example of the invention the operating results demonstrate the low emission characteristics and the ability to radiatively transfer heat to surround-ing surfaces. In this example, the burner element is comprised of the previously-deseribed Cerablanket fiber material at a density of 12 lb/ft3. The element is in the shape of a flat circular disc of 6 inch diameter and 1 inch thickness. The disc i5 mounted within a conduit perpendicular to the flow of premixed air-fuel reactants. The mixture is forced under positive pressure through the disc and is - ~ :
, 7~
ignited at the downstream îace to establ;sh the heterogeneous reaction zone to a depth of a few millimeters.
The operating results of the flat circular disc burner configuration using natural gas fuel and varied inlet flow velocity conditions are depicted in Figures 5 and 6.
Figure S depicts the matrix surface ternperature of the heterogeneous reaction zone as a function of theoretical air for three different ~ace velocities. Curve 44 depicts the results at a face velocity of 2 ft/sec, curve 46 at a face velocity of 1 ft/sec, and curve 48 at a face velocity of 1/2 ft!sec. The graph dennonstrates that lower velocities result in lower surfaee temperatures at the lower excess air levels (100 to 130% theoretical air) where firetube boilers normally operate. The graph of Figure 6 demonstrates that this lower surface temperature is advantageous in reducing NOX emissions (ppm) as a function of percent theoretical air, with curve 50 depicting the results at a face velocity of 2 ft/sec, curve 52 at a velocity of 1 ft/sec, and curve 54 at a velocity Oe 1/2 ft/sec. As demonstrated by the curve 54 in Figure 6, NOX emissions oE less than 10 ppm at 115% theoretical air are possible. Additionally, high combustion efficiency (low CO and HC) can be achieved simultaneously with low NOX emissions.
The low surface temperatures represented in Figure 5 also demonstrate the effectiveness of radiative heat transfer away from the heterog~eneous reaction zone. The indicated temperatures of 2200 F to 2500 F at 100% theoretical air are within the use temperature capabilities of the alumina silicate fibers which comprise the matrix, and these temperatures are also far below the mixture's adiabatic flame temperature of 3500 F. These results demonstrate that the optimum flow velocity for the particular matrix material which was employed is in the range of l/3 to 1/~ ft/sec.
The foregoing demonstrates that the invention provides a eatalytic burner with important operating advantages, particularly for firetube boilers. Comb~lstion in the fiber matrix of the burner takes plaee at relatively low temperatures with active heat transfer to achieve low emissions of nitrogen oxides. The matrix can be fabricated in a variety of configurations, such as a cylindrical shell compatible with the combustion chamber of a firetube boiler. Good combustion efficiency is achieved and high overall boiler efficien(!y realized in that the burner can operate at near-stoichiometric conditions. The burner CM be operated on a variety of gaseous ~ld liquid ~with pre-vaporization~ fuels.
While the foregoing embodiments are at present considered to be preferred it is understood that numerous variations and modifications may be made therein by those skilled in the art Md it is intended to cover in the appended claims all such variations and modifications as fall within the true spirit and scope of the invention.
.
'~
' ,: , ' ' ' ~ . ,:
Claims (6)
1. A combustor for burning an air-fuel mixture with high combustion efficiency and low NOx emissions comprising the combination of a burner body in a hollow cylindrical shell configuration and comprised of a matrix of high temperature resistant fibers with interstitial spaces between the fibers forming R
flow path for the mixture, with the fibers packed to a density in the range of 12 to 16 lb/ft3 so that combustion of the mixture is sustained at a heterogeneous reaction zone along an outer layer of the shell whereby heat transfers outwardly by radiation from the reaction zone to maintain the temperature of the matrix in the zone below the adiabatic flame temperature of the mixture and also below the use temperature of the fibers.
flow path for the mixture, with the fibers packed to a density in the range of 12 to 16 lb/ft3 so that combustion of the mixture is sustained at a heterogeneous reaction zone along an outer layer of the shell whereby heat transfers outwardly by radiation from the reaction zone to maintain the temperature of the matrix in the zone below the adiabatic flame temperature of the mixture and also below the use temperature of the fibers.
2. A combustor as in claim 1 which includes inlet manifold means for injecting the mixture within the shell for flow outwardly through the interstitial spaces of the matrix.
3. A combustor as in claim 2 including a cylindrical combustion chamber having a wall radially spaced about the outer surface of the shell for absorbing radiant energy transferred from the reaction zone of the matrix.
4. A method of combusting a fuel-air mixture with high combustion efficiency and low thermal NOx emissions, comprising the steps of directing a flow of the mixture through interstitial spaces in a matrix of high temperature resistant fibers packed to a density in the range of 12 to 16 lb/ft3, combusting the mixture at a heterogeneous reaction zone along a layer of the matrix on the side downstream of the flow, and radiating heat from the reaction zone at a rate which maintains the temperature of the matrix in the zone below the adiabatic flame temperature of the mixture and also below the use temperature of the fibers.
5. A method as in claim 4 in which heat conduction from the reaction zone through the matrix in a direction upstream of the flow is at a rate so that the temperature of the upstream side of the matrix is below the ignition temperature of the mixture for preventing flashback into the upstream flow of gases.
6. A method as in claim 4 in which the stoichiometry of the mixture is in the range of 100 to 130% theoretical air.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16483180A | 1980-06-30 | 1980-06-30 | |
| US164,831 | 1980-06-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1147624A true CA1147624A (en) | 1983-06-07 |
Family
ID=22596279
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000379977A Expired CA1147624A (en) | 1980-06-30 | 1981-06-17 | Catalytic combustion system with fiber matrix burner |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS5747120A (en) |
| CA (1) | CA1147624A (en) |
| GB (1) | GB2080700B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9599336B1 (en) | 2012-03-01 | 2017-03-21 | Midco International, Inc. | Burner assembly and system for heating drying air |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4784599A (en) * | 1982-05-14 | 1988-11-15 | Garbo Paul W | Liquid fuel combustion with porous fiber burner |
| EP0389652A1 (en) * | 1989-03-28 | 1990-10-03 | Siemens Aktiengesellschaft | Catalytic heating panel |
| US5593299A (en) * | 1991-01-09 | 1997-01-14 | Pfefferle; William C. | Catalytic method |
| WO1992016792A1 (en) * | 1991-03-15 | 1992-10-01 | Radian Corporation | Apparatus and method for combustion within porous matrix elements |
| WO1992016795A1 (en) * | 1991-03-15 | 1992-10-01 | Radian Corporation | Apparatus and method for combustion within porous matrix elements |
| JP2953237B2 (en) * | 1993-01-11 | 1999-09-27 | 日本鋼管株式会社 | boiler |
| AT402660B (en) * | 1994-07-25 | 1997-07-25 | Vaillant Gmbh | Heating appliance |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5190036A (en) * | 1975-02-05 | 1976-08-06 |
-
1981
- 1981-06-09 GB GB8117628A patent/GB2080700B/en not_active Expired
- 1981-06-17 CA CA000379977A patent/CA1147624A/en not_active Expired
- 1981-06-26 JP JP56099540A patent/JPS5747120A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9599336B1 (en) | 2012-03-01 | 2017-03-21 | Midco International, Inc. | Burner assembly and system for heating drying air |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2080700A (en) | 1982-02-10 |
| JPS5747120A (en) | 1982-03-17 |
| GB2080700B (en) | 1984-12-19 |
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