Glass manufacturing – Processes – Forming product or preform from molten glass
Patent
1988-01-07
1989-01-10
Lindsay, Robert L.
Glass manufacturing
Processes
Forming product or preform from molten glass
65 5, 65 19, 65 27, 65134, 75 42, 110341, 501 36, 501 44, 432 95, 432195, C03B 3701, C03B 3706, C03B 512, F27B 109
Patent
active
047971428
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of preparing a melt for the production of mineral wool wherein a raw material having a composition suitable for the preparation of the melt and a carbonaceous material are fed into a preheating zone in the upper portion of a shaft furnace and oxygen-containing gas is introduced into an oxidation zone in the lower portion of the shaft furnace to effect a combustion of the carbonaceous material and to heat the raw material and wherein a melt is discharged from the bottom of the shaft furnace.
In the prior art methods of the above mentioned type the carbonaceous material used typically consists of coke and the oxygen-containing gas is normally oxygen-enriched air which is suitably preheated to a temperature of at least 450.degree. C. and preferably about 500.degree. C. A known shaft furnace type for the preparation of a melt for the production of mineral wool is a cupola furnace. Such furnace normally comprises four temperature zones, i.e. a melting bath, an oxidation zone, a reduction zone, and a preheating zone.
The lower portion of the cupola furnace constitutes the melting bath and comprises the melt formed in the cupola which melt is located in the space between the pieces of coke which are resting on the bottom of the cupola and which support the material laying thereabove. The temperature in the melting bath is typically in the range of 1500.degree.-1550.degree. C.
The oxidation zone is located above the melting bath and the lower portion of said zone is provided with a gas inlet nozzles, the so-called tuyeres, through which the preheated gas is introduced into the furnace. The actual combustion of the coke takes place during the movement of the preheated air up through the oxidation zone, and the gas temperature rises from about 500.degree. C. to about 2000.degree. C. thus causing the material which moves down through the oxidation zone to be heated to its melting point as a result of the melting of the raw material. The melt formed flows down into the melting bath where the temperature, as mentioned, typically is 1500.degree.-1550.degree. C. The vertical extension of the oxidation zone is determined by the amount of oxygen introduced as the reduction zone starts at the level where the oxygen introduced through the tuyeres is consumed for combustion of the coke.
In the reduction zone where the temperature range is between 1000.degree. and 1500.degree. C., coke reacts with the CO.sub.2 formed in the oxidation zone in connection with the combustion of coke so as to form CO in an amount which is double the amount of consumed CO.sub.2 based on volume.
This reaction is heat consuming and causes 20-25% of the energy released by the combustion in the oxidation zone to be lost as latent heat in the smoke gas when the CO content of the latter is 6-10%. Even though this amount of heat may be recovered by a secondary combustion, it will be desirable to avoid the formation of CO i.e. because a secondary combustion requires relatively high plant investments and the efficiency of such secondary combustion is relatively low.
The reduction i.e. the CO formation is strongly dependent on temperature in the temperature range above 1000.degree. C. as it e.g. is increased with a factor of 10 when the temperature rises from 1000.degree. to 1200.degree. C. On the other hand, the reaction speed for the conversion of CO.sub.2 into CO is so low at temperatures below 1000.degree. C. that no appreciable reduction takes place in the preheating zone located above the reduction zone wherein the materials introduced at the top of the cupola are preheated from the ambient temperature to about 1000.degree. C.
The object of the present invention is to eliminate or limit the conversion of the CO.sub.2 formed during combustion into CO by a method of the type defined above.
This object is obtained with the method according to the invention, which method is characterized in that the combustion in the oxidation zone is controlled in such a manner that the temperature in the transition between the ox
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Lindsay Robert L.
Rockwool International A/S
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