Catalytic combustion system and combustion control method

Details Catalytic combustion system and combustion control method Catalytic combustion system and combustion control method

1999-06-04

2001-08-07

Lazarus, Ira S. (Department: 3743)

Combustion

Process of combustion or burner operation

Starting or shutdown procedure

C431S007000, C431S011000, C431S268000, C431S328000, C431S161000, C060S723000

Reexamination Certificate

active

06270336

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns technical means especially capable of improvement in high-temperature durability and expansion of the turn down ratio (TDR) in catalytic combustion systems which are used mainly in heat sources and heating applications for catalytic combustion of gaseous fuels or liquid fuels.
2. Related Art of the Invention
Various types of catalytic combustion systems, which use a catalyst body exhibiting an oxidation activity against the fuel to cause catalytic reactions to take place at a surface of the catalytic body, have been known in the art, and their typical combustion method is a premix type structure as shown in FIG.
1
.
Referring first to
FIG. 1
, there is shown a commonly-used premix type structure, in which a fuel gas supplied from a fuel supply valve
1
is mixed with air supplied from an air supply valve
2
in a premix chamber
3
, and is delivered to a preheat burner
5
through a premix gas inlet port
4
. This premix gas is ignited by an ignition unit
6
, thereby forming a flame at the preheat burner
5
. High-temperature exhaust gases as a result of such flame formation pass through a catalyst body
8
disposed in a combustion chamber
7
while heating the catalyst body
8
, and are discharged from an exhaust port
9
. When the catalyst body
8
is heated up to reach its catalyst activity temperature, fuel supply is temporarily stopped by the fuel supply valve
1
to put out the flame formed at the preheat burner
5
. Thereafter, by an immediate resupply of fuel, catalytic combustion is started again. The catalyst body
8
enters a high-temperature state. Through a glass
10
located upstream of and in a face-to-face arrangement with the catalyst body
8
, the catalyst body
8
radiates heat while releasing heat in the form of exhaust gas for application of heat, heating, and drying. In the foregoing premix type structure, premix gases, whose excess air ratio (i.e., the ratio of an actual amount of air to the air amount theoretically required for fuel complete oxidation) is not less than 1, are constantly supplied to the catalyst body
8
, in other words, the catalyst body
8
is operated in an atmosphere excessively abounding with oxygen.
In the above-described conventional catalytic combustion system, a high-temperature atmosphere is produced which is accompanied by the constant coexistence of oxygen at a reaction center position of the catalyst body. As a consequence, constituents of a catalyst are inevitably subject to deterioration by heat. Generally, metals of the platinum group, such as Pt, Pd, and Rh, are frequently used as catalysts for combustion in view of their heat resistance and reaction activity. However, the problem of using such metals is that at high temperatures (from 800 to 900 degrees centigrade), it is difficult to attain steady combustion performance for a long time because of reduction of the active spot count due to aggregation and transpiration of precious metal particles. In premix-type catalytic combustion systems, owing to the drop in activity, the reaction center position is shifted toward the downstream side of the catalyst body, therefore resulting in failing to maintain complete combustion. In addition to such a drawback, in the system making utilization of radiation heat from a catalyst upstream-side surface, the quantity of radiation heat decreases as the service time increases.
SUMMARY OF THE INVENTION
Bearing in mind the above-described problems with the conventional catalytic combustion system such as high-temperature durability and TDR limitation ones, the present invention was made with a view to providing catalytic combustion systems capable of improvement in high-temperature durability and expansion of the turn down ratio (TDR).
A catalytic combustion system of the present invention comprises:
(a) a gaseous mixture inlet port, located at the upstream side of said catalytic combustion system, for the entrance of a fuel-air mixture;
(b) an exhaust gas outlet port, located at the downstream side of said catalytic combustion system, for the exit of an exhaust gas;
(c) a primary combustion chamber in which a first catalyst body is disposed, said catalyst body having a porous base material with numerous communicating holes that supports thereon an oxidation catalyst;
(d) a secondary supply port, located downstream of said primary combustion chamber, for the supply of a gaseous mixture or air; and
(e) a secondary combustion chamber located downstream of said secondary supply port;
wherein at the time of combustion, if a given condition is satisfied, it is arranged such that said combustion takes place, with an excess air ratio in said primary combustion chamber set below 1.
A combustion control method of the present invention for use in a catalytic combustion system having
(a) a gaseous mixture inlet port, located at the upstream side of said catalytic combustion system, for the entrance of a fuel-air mixture;
(b) an exhaust gas outlet port, located at the downstream side of said catalytic combustion system, for the exit of an exhaust gas;
(c) a primary combustion chamber in which a catalyst body is disposed, said catalyst body being formed of a porous base material with numerous communicating holes that supports thereon an oxidation catalyst;
(d) a secondary supply port, located downstream of said primary combustion chamber, for the supply of a gaseous mixture or air; and
(e) a secondary combustion chamber located downstream of said secondary supply port; comprises such process that
the excess air ratio of said primary combustion chamber is initially set above 1 and after the rate of combustion of said secondary combustion chamber exceeds a given level, combustion is made to take place, with the excess air ratio of said primary combustion chamber set below 1.


REFERENCES:
patent: 4230443 (1980-10-01), Berg et al.
patent: 4321233 (1982-03-01), Tsuhi et al.
patent: 4354821 (1982-10-01), Kesselring et al.
patent: 4459126 (1984-07-01), Krill et al.
patent: 5019546 (1991-05-01), Murakami et al.
patent: 5022226 (1991-06-01), Bell
patent: 5190453 (1993-03-01), Le et al.
patent: 5207053 (1993-05-01), Spadaccini et al.
patent: 5235804 (1993-08-01), Colket, III et al.
patent: 5258349 (1993-11-01), Dalla Betta et al.
patent: 5588298 (1996-12-01), Kalina et al.
patent: 44 38 356 (1996-05-01), None
patent: 0 807 786 (1997-11-01), None
patent: 61-272509 (1986-12-01), None
patent: 03056138 (1991-03-01), None
patent: 4-084009 (1992-03-01), None
patent: 4-80505 (1992-03-01), None
patent: 04174201 (1992-06-01), None
patent: 4-198618 (1992-07-01), None
patent: 5-157211 (1993-06-01), None
patent: 05157211 (1993-06-01), None

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