Heating – Processes of heating or heater operation – Treating an article – container – batch or body as a unit
Reexamination Certificate
1999-09-20
2001-09-04
Wilson, Gregory (Department: 3749)
Heating
Processes of heating or heater operation
Treating an article, container, batch or body as a unit
C432S018000, C431S010000
Reexamination Certificate
active
06283747
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to 98 11798 filed in France on Sep. 22, 1998; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for heating a furnace comprising at least one burner capable of operating on an oxidant the oxygen content of which can vary. Such burners, described, for example, in documents EP-192,682 and EP-432,153, are designed for various situations.
2. Description of Related Art
Most industrial furnaces, such as (s)melting furnaces or annealing furnaces, are equipped with burners which operate on air as the oxidant.
In each application of these burners, a specific oxidant, for example consisting of oxygen-enriched air, is chosen, the oxygen content of the oxidant being kept constant during operation.
Document GB-A-1,514,842 describes a method in which oxygen is periodically added to the oxidizing air to smelt successive charges of scrap in a furnace; after this the oxygen supply is interrupted and the charge is refined using only air as the oxidant. This therefore is a conventional burner “doped” with oxygen in the flame, this document not envisaging the use of pure oxygen.
Document U.S. Pat. No. 4,931,013 teaches the use of a burner which is “doped” with a pure oxygen lance, the injection of which pure oxygen into the combustion air enriches its oxygen content to as much as 35%. Thus, in a first phase, hydrocarbons are completely burnt by virtue of this oxygen “doping”, then the injection of pure oxygen is interrupted and the process continues using only oxygen-enriched air.
Patent abstracts of Japan Vol. 098 No 003 of 27.02.1998 (JP-09-30728) relates to a cremation method in which, in a first phase, a conventional burner is used; in a second phase, in order to be able to cremate items which are difficult to burn, use is also made of a lance which injects a mixture of air and oxygen onto these items on the outside of the burner.
In all these known methods, the air supply is never interrupted, and the oxygen content of the oxidant never exceeds 35%.
Now, depending on the furnaces and particular envisaged applications thereof, and on considerations relating to the thermal performance and running cost, it may prove advantageous to be able to alter the oxygen content in a range which is far wider than 21 to 35%. An oxygen content of 21% is that of air, an inexpensive oxidant but one whose thermal performance is modest. Conversely, an oxidant consisting of almost pure oxygen is very powerful, but expensive. Now, the known burners of the state of the art do not allow such relative optimization of performance with respect to economic cost.
The invention therefore sets out to propose an optimized and economic heating method for all applications of the burners in question.
SUMMARY OF THE INVENTION
To this end, the subject of the invention is a method for heating a furnace comprising at least one burner capable of operating on an oxidant the oxygen content of which can vary, characterized in that:
a) in a first period (P
1
) the burner is supplied with practically pure oxygen so as to provide a large amount of energy for heating,
b) in a second period (P
2
) the burner is supplied with an oxidant, the oxygen content of which can vary between about 100% and 21% according to considerations relating to the desired heat performance and cost of operation of this oxidant,
c) in a third period (P
3
), the burner is supplied with an oxidant, the oxygen content of which is minimal, and which corresponds to a pilot period which requires only a small amount of heating energy.
According to other features of the invention:
during the second period, pure oxygen and air are injected separately into the burner,
during the third period it is predominantly air which is injected into the burner,
the said first period which requires a great deal of heating energy, corresponds to intense heating including the case of a (s)melting period,
for a furnace which is charged in batches, the said first period, corresponds to the raising of the temperature of the product. For a continuous furnace, this first period, corresponds to a high rate of production, that is to say to a high demand for heat.
the flow rates of fuel and air are set to a level such that the heating power of the said at least one burner is more or less 50 to 60% of the nominal power of the burner during the first period.
REFERENCES:
patent: 4547150 (1985-10-01), Vereecke
patent: 4931013 (1990-06-01), Brahmbhatt et al.
patent: 5871343 (1999-02-01), Baukal, Jr. et al.
patent: 5904475 (1999-05-01), Ding
patent: 1 514 842 A (1978-06-01), None
patent: 2 046 415 A (1980-11-01), None
English abstract of JP 09 303728, Patent Abstracts of Japan, vol. 098, No. 3, Feb. 27, 1998.
English abstract of JP 08 277406, Patent Abstracts of Japan, vol. 097, No. 2, Feb. 28, 1997.
English abstract of JP 04 293740, Patent Abstracts of Japan, vol. 017, No. 108, Mar. 5, 1993.
Borissoff Thierry
Charon Olivier
Le Gouefflec Gérard
Legiret Thierry
Burns Doane Swecker & Mathis L.L.P.
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Wilson Gregory
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