Glass manufacturing – Processes – Operating under inert or reducing conditions
Patent
1998-06-03
2000-04-11
Vincent, Sean
Glass manufacturing
Processes
Operating under inert or reducing conditions
651344, 651346, 432159, 432195, 432196, C03B 5435
Patent
active
06047565&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to glassmaking furnaces, in particular the furnaces used in the manufacture of flat glass of the "float" type, and it relates more specifically to a method and a device intended to reduce the emission of NO.sub.x in the gaseous effluents discharged from the furnace.
2. Discussion of the Background
It is a concern of glassmaking furnace manufacturers to limit as much as possible the emissions of NO.sub.x in the combustion smoke, especially because of the fact that the standards are becoming increasingly demanding in this regard. These emissions should therefore be limited to 500 mg/M.sup.3 of NO.sub.x, a limit which the known methods do not allow to be obtained, or do allow, but to the detriment of their profitability.
The factors which influence the formation of NO.sub.x gases are known. These are essentially the temperature, since their emission increases exponentially above 1300.degree. C., or the excess air, since the NO.sub.x gases depend on the square root of the oxygen concentration, or else the N.sub.2 concentration.
A known method consists in causing a reducing agent to act on the gases emitted so that the NO.sub.x gases are converted into nitrogen. This agent may be ammonia, but the drawbacks of storing and handling such a substance are known. It is also possible to use a natural gas as reducing agent, but to the detriment of the consumption of the furnace.
It therefore turns out to be preferable to avoid these methods, and it has already been considered to adopt so-called primary measures, for example by preventing the formation of NO.sub.x within the flame itself, by reducing the excess combustion air. To do this, it was sought to limit the hot air which passes into the regenerator and to eliminate or decrease the inducted-cold-air intakes around the injectors in the unsealed furnace. It is thus possible to decrease the sprayed primary air by increasing the fuel-spraying pressure. For this purpose, it is necessary to provide a continuous control of the excess oxygen in the regenerator chambers and to use suitable fuel injectors. However, the results obtained remain insufficient and do not enable the percentage indicated above to be readily achieved.
Another primary measure consists in acting on the temperature. Thus, attempts may be made to modify the distribution of the fuel in order to reduce the maximum thermal level of the furnace, or to install suitable injectors in order to decrease the momentum of the fuel right to the limit of the appearance of unburnt gases in the discharge flue. It is also possible to use a spraying agent other than air, for example steam, when this is available.
SUMMARY OF THE INVENTION
As these primary measures do not enable the fixed objectives to be achieved, a method and a device have been conceived, according to the present invention, by means of which the resulting effects obtained by each of the known primary methods are combined, that is to say that the invention succeeds in first of all limiting the temperature peaks, while maintaining the length of flame, and in increasing the volume of the flame front in order to reduce the temperatures. Furthermore, staging of the combustion by the fuel and by the oxidizer are provided. Finally, it is advantageous to move towards the use of a flame containing 100% oxygen at the hottest level in the furnace.
SUMMARY OF THE INVENTION
One subject of the present invention therefore consists of a method of combustion for melting glass, in which the fuel and the oxidizer are both fed so as to spread the fuel/oxidizer contact over time and/or to increase the volume of this contact for the purpose, in particular, of limiting the temperature peaks and of reducing the emission of NO.sub.x gases.
The subject of the invention is also a glass-making furnace of the furnace type for manufacturing flat glass, operating, in particular, in reversal mode, which furnace implements the process according to claim 1 and is provided on at least one of its sides wit
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Database WPIDS, week 9413, Derwent Information LTD, AN 94-102665, DE 4244068 C1 (RUHRGLAS GMBH), abstract, Apr. 1994.
Saint Gobain Vitrage
Vincent Sean
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