Combustion – Process of combustion or burner operation – Heating feed
Patent
1987-11-25
1990-02-06
Price, Carl D.
Combustion
Process of combustion or burner operation
Heating feed
431 12, 431 4, 431215, 432181, 423237, F23L 1504
Patent
active
048985309
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the combustion of fuel using regenerative burners. A regenerative burner has a heat store used to cool products of combustion and, subsequently, to impart heat to air which is to be used for combustion. Regenerative burners are normally used in pairs, the burners of the pair being operated alternately. In a first part of a cycle of operation, air flows through the heat store of one burner and is discharged from the burner with fuel into a combustion space which is common to the pair of burners. Hot products of combustion pass from the combustion space through the heat store associated with the other burner and transfer heat to that heat store. In the second part of the cycle, the direction of the air flow is reversed and air flows through the hot heat store to the combustion space, being heated by heat exchange with the heat store so that heat recovered from the products of combustion during the first part of the cycle is returned to the combustion space. This results in efficient operation, by which we mean that the products of combustion carry to the atmosphere a relatively small proportion of the heat released by combustion of the fuel. A disadvantageous consequence is that the temperature attained in the combustion space is relatively high. This promotes the formation of oxides of nitrogen.
The combustion space may comprise distinct parts, for example a furnace chamber where workpieces are heated and two smaller spaces, adjacent to respective ones of the burners, where much of the combustion takes place.
It is an object of the present invention to avoid emission to the atmosphere of exhaust gases containing significant proportion of lower oxides of nitrogen.
According to a first aspect of the invention, there is provided a method of operating a burner wherein combustion air is passed through heat storage means to the burner, fuel is discharged from the burner with the combustion air and burns in a combustion space, hot products of combustion are passed from the combustion space through the heat storage means separately from the combustion air passing to the burner, heat is transferred from the products of combustion to the heat storage means and that heat is subsequently transferred to combustion air which is passed through the heat storage means, characterised in that a reducing agent is introduced into the products of combustion before said products leave the heat storage means and in that, before the products of combustion leave the heat storage means, the reducing agent reduces oxides of nitrogen present in the products of combustion.
The temperature in the heat storage means will vary with time and/or with the position at which the temperature is measured. In a case where, during a part of a cycle of operation, the products of combustion are directed along a path which extends through the heat storage means, the temperature at a selected position along that path will increase during that part of the cycle. At any instant, there will be a temperature gradient along that path. If, during a subsequent part of the cycle, cool combustion air is directed along that path through the heat storage means, the temperature at the selected position along the path will fall and there will be a different temperature gradient along the path at a selected moment during the subsequent part of the cycle.
The position at which the reducing agent is introduced into the products of combustion may be selected according to the temperature conditions to ensure that the mixture comprising reducing agent and oxides of nitrogen is at an appropriate temperature for the required reduction to occur before the gases leave the heat store.
A proportion of the products of combustion may be re-cycled to the combustion space to dilute the air and fuel discharged into the combustion space.
Reduction of the oxides of nitrogen preferably occurs whilst said oxides are in contact with surfaces of refractory elements in the heat store or with surfaces defining the flowpath between the combustion space and t
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patent: 4216060 (1980-08-01), Murata et al.
patent: 4328020 (1982-05-01), Hughes
patent: 4372770 (1983-02-01), Krumwiede et al.
patent: 4427362 (1984-01-01), Dykema
patent: 4521389 (1985-06-01), Blanton, Jr. et al.
patent: 4540361 (1985-09-01), Gagne
patent: 4599100 (1986-07-01), Demarest, Jr.
Johns Gary
Wills Brian
Price Carl D.
Stordy Combustion Engineering Limited
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