Catalytic insert for NO.sub.x reduction

The fuel in the fuel rich inner cone of the flame is catalyzed by a partial oxidation catalyst into carbon monoxide and hydrogen which have a lower peak flame temperature thereby reducing thermal NO.sub.x. The insert is heated and radiates heat with a further reduction of peak flame temperature.

BACKGROUND OF THE INVENTION 
In the complete combustion of common gaseous fuels, the fuel combines with 
oxygen to produce carbon dioxide, water and heat. There can be 
intermediate reactions producing carbon monoxide and hydrogen. The heat, 
however, can also cause other chemical reactions such as causing 
atmospheric oxygen and nitrogen to combine to form oxides of nitrogen or 
NO.sub.x. While NO.sub.x may be produced in several ways, thermal NO.sub.x 
is associated with high temperatures, i.e. over 2000.degree. K. The flame 
is zoned so that different parts of the flame are at different 
temperatures. NO.sub.x production can be reduced with the lowering of the 
peak flame temperature. The reduction in NO.sub.x is required because it 
is a prime component in the generation of photochemical smog and reduction 
can be achieved through turbulence of the gases being combusted and/or by 
heat transfer from the high temperature portion of the flame. Providing a 
catalytic coating on combustion apparatus is known as exemplified by U.S. 
Pat. No. 5,437,099 which discloses the use of a catalyst in the first 
stage of a multiple-stage combustion device which is specifically 
disclosed as a gas turbine. In general, a catalyst permits a reaction to 
take place or speeds up or changes the conditions under which a reaction 
takes place. 
SUMMARY OF THE INVENTION 
The present invention takes into consideration the partial premixed 
structure of an inshot burner flame which has two cones. The inner cone 
has a fuel rich mixture of natural gas, or the like, and oxygen which can 
be readily catalyzed by a partial oxidation catalyst into carbon monoxide 
and hydrogen. The outer cone is where combustion is completed and is the 
hottest part of the flame. Catalytic partial oxidation involves the use of 
a catalyst to alter the natural gas fuel input to produce a new fuel 
stream which is enriched with carbon monoxide and hydrogen. When the new 
fuel stream is combusted, the peak flame temperatures are lowered which 
reduces thermal NO.sub.x. 
The basic premise of the present invention is that for catalysis to be 
initiated the catalyst must first be heated to a certain activation 
temperature on the order to 600.degree. F. Rather than using an additional 
energy source, such as electricity, the present invention uses the flame 
itself Either the inner or outer flame is used to supply the necessary 
energy to "light off" the catalyst which then allows the unburnt methane 
and oxygen inside the inner cone to be catalyzed into hydrogen and carbon 
monoxide. Additionally, the catalytic insert in using the flame to provide 
the necessary energy to "light off" the catalyst acts as a heat transfer 
media thereby tending to reduce the peak flame temperature and further 
reducing the production of thermal NO.sub.x. 
It is an object of this invention to provide a radiative heat sink for the 
flame. 
It is another object of this invention to convert methane and oxygen into 
carbon monoxide and hydrogen through a catalytic reaction. 
It is a further object of this invention to reduce the production of 
thermal NO.sub.x. These objects, and others as will become apparent 
hereinafter, are accomplished by the present invention. 
Basically, a catalytic insert is located in or inside the flame of an 
inshot burner. The catalyst is heated by the flame such that catalysis is 
initiated thereby allowing unburnt fuel and oxygen inside the inner cone 
to be catalyzed into hydrogen and carbon monoxide and the heated catalyst 
provides radiative heat transfer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIGS. 1-3 the numeral 10 generally designates the catalytic insert of 
the present invention. The catalyst can typically be: 1) transition metal 
oxides such as those of chromium, manganese, or vanadium; 2) noble metals 
such as platinum, palladium, rhodium, or iridium; 3) materials such as 
magnesium oxide and pure nickel. In the case of the transition metal 
oxides and noble metals, they may be a coating on a ceramic matrix such as 
alumina or a metal matrix such as fecraly, an alloy of iron, chromium and 
yttrium. In the case of magnesium oxide and pure nickel, the entire insert 
10 may be made of catalytic material. Insert 10 is of generally 
cylindrical shape with a plurality of axially extending, spaced bores 10-1 
providing a flow path therethrough. Bores 10-1 have a length to width or 
diameter ratio of at least two such that the bores 10-1 have much larger 
surface areas than the cross sections of the flow paths. The surface area 
is increased by providing rectangular cross sectioned bores 10-1 rather 
than cylindrical bores. 
Turning now to FIG. 3, insert 10 is located in the bell orifice inlet 21 of 
heat exchanger 20 by any suitable means. Inshot burner 30 is spaced from 
and faces insert 10 such that insert 10 is in the flame 50 when burner 30 
is operating. The location of insert 10 relative to the flame 50 requires 
that at least a portion is located in inner cone 50-1 to produce 
catalysis. The heating of the insert to achieve catalysis can be achieved 
in inner cone 50-1 and/or outer cone 50-2. 
In operation, gaseous fuel, such as natural gas, is supplied under pressure 
to port 31 of inshot burner 30 of a furnace. The gas supplied to port 31 
passes annular opening 32 aspirating atmospheric air which is drawn into 
burner 30. The fuel-air mixture exits burner 30 in flame 50. Flame 50 
impinges on insert 10 and passes through bores 10-1 into heat exchanger 
20. As illustrated, inner cone 50-1 impinges upon insert 10 and, within 
bores 10-1, outer cone 50-2 starts to develop such that both inner cone 
50-1 and outer cone 50-2 emerge from insert 10. The heat from flame 50 
coupled with heat transfer within insert 10 causes the insert to act as a 
radiative heat sink for flame 50. When the material/catalyst heats up, a 
portion of the flame's energy will be converted into radiation lowering 
the flame temperature and reducing NO.sub.x. Additionally, through 
catalysis upon heating the catalyst, the fuel gases and atmospheric air in 
the fuel rich inner cone 50-1 are changed to hydrogen and carbon monoxide 
which burn at a lower temperature and further help to reduce thermal 
NO.sub.x. 
Referring to FIG. 4, the insert 110 is suitably secured to inshot burner 30 
rather than being located in the heat exchanger as in the FIG. 3 device. 
Additionally, insert 110 is within the inner core 50-1 of flame 50. As in 
the FIG. 3 device, the flame heats insert 110 which radiates energy and 
produces catalysis of the fuel rich gases in the inner cone 50-1. 
Insert 210 which is illustrated in FIG. 5 and insert 310 which is 
illustrated in FIG. 6 each has a plurality of radially extending surfaces 
210-1 to 210-n and 310-1 to 310-n, respectively. Insert 210 and 310 would 
function like inserts 10 and 110. 
Although preferred embodiments of the present invention have been described 
and illustrated, other changes will occur to those skilled in the art. It 
is therefore intended that the scope of the present invention is to be 
limited only by the scope of the appended claims.