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US-12623943-B2 - Method of preparing a melt for the production of man-made mineral fibres

US12623943B2US 12623943 B2US12623943 B2US 12623943B2US-12623943-B2

Abstract

The invention relates to a method of preparing a mineral melt in a cupola furnace that uses at least one plasma torch to provide heat energy to the furnace. The plasma torch uses nitrogen, carbon monoxide, carbon dioxide, or a mixture thereof as the carrier gas. The invention also relates to a cupola furnace for the preparation of the mineral melt, and the use of a plasma torch in a cupola furnace to reduce the amount of NO x and/or hydrogen in the furnace off-gas.

Inventors

  • Lars Elmekilde Hansen
  • Haosheng Zhou

Assignees

  • ROCKWOOL A/S

Dates

Publication Date
20260512
Application Date
20211119
Priority Date
20201119

Claims (18)

  1. 1 . A process for preparing a mineral melt in a cupola furnace, said process comprising supplying mineral material to the cupola furnace, and providing heating energy to the cupola furnace, said cupola furnace having a base, such that said mineral material is melted to form a mineral melt that collects in the base of the cupola furnace, and wherein the process produces off-gas, wherein: the cupola furnace comprises at least two temperature zones, including a hot zone at the base of the cupola furnace and an oxidation zone above the hot zone; (i) the cupola furnace is equipped with at least one tuyere providing a source of oxygen in the oxidation zone; (ii) the cupola furnace comprises at least one plasma torch that uses as carrier gas nitrogen, carbon monoxide, carbon dioxide, or a mixture thereof, and provides plasma heating in the hot zone; (iii) greater than 50% of the heating energy provided to the cupola furnace is provided by the at least one plasma torch; (iv) the temperature in the oxidation zone is below 1,400° C.; (v) the temperature in the hot zone is greater than the temperature in the oxidation zone; (vi) water is substantially excluded from any zone of the cupola furnace where the temperature is above 750° C.
  2. 2 . The process as claimed in claim 1 , wherein greater than 60% of the heating energy provided to the cupola furnace is provided by the at least one plasma torch.
  3. 3 . The process as claimed in claim 1 , wherein the temperature in the oxidation zone is below 1,300° C.
  4. 4 . The process as claimed in claim 1 , wherein heating is provided in the hot zone solely by the at least one plasma torch.
  5. 5 . The process as claimed claim 1 , wherein the temperature in the hot zone is above 800° C.
  6. 6 . The process as claimed in claim 1 , wherein the carrier gas enthalpy is from 2.0 to 6.0 kWh/Nm 3 .
  7. 7 . The process as claimed in claim 1 , wherein the melt has the following composition expressed as oxides, by weight %: SiO 2 35-50 Al 2 O 3 12-30 TiO 2 up to 2 Fe 2 O 3 2-12 CaO 5-30 MgO 0-15 Na 2 O 0-15 K 2 O 0-15 P 2 O 5 0-3 MnO 0-3 B 2 O 3 0-3.
  8. 8 . The process as claimed in claim 1 , wherein the cupola furnace produces off-gas comprising NO x in an amount of less than 400 ppm.
  9. 9 . The process as claimed in claim 1 , wherein the carrier gas is nitrogen.
  10. 10 . The process as claimed in claim 1 , wherein the carrier gas comprises at least one component of the off-gas.
  11. 11 . The process as claimed in claim 10 , wherein the at least one component of the off-gas undergoes off-gas cleaning prior to its use as carrier gas.
  12. 12 . The process as claimed in claim 10 , wherein the carrier gas consists of the at least one component of the off-gas.
  13. 13 . The process as claimed in claim 1 , wherein greater than 70% the heating energy provided to the cupola furnace is provided by the at least one plasma torch.
  14. 14 . The process as claimed in claim 1 , wherein the temperature in the oxidation zone is below 1,200° C.
  15. 15 . The process as claimed claim 1 , wherein the temperature in the hot zone is above 900° C.
  16. 16 . The process as claimed in claim 1 , wherein the carrier gas enthalpy is from 3.0 to 5.0 kWh/Nm 3 .
  17. 17 . The process as claimed in claim 1 , wherein the cupola furnace produces off-gas comprising hydrogen in an amount of less than 20,000 ppm.
  18. 18 . A process for manufacturing man-made vitreous fibre (MMVF) comprising the steps of: (i) forming a melt using a process as defined in claim 1 ; (ii) fiberizing the melt by means of an internal or external spinning process; and (iii) collecting the formed fibres.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national stage application of International Patent Application No. PCT/EP2021/082247, filed Nov. 19, 2021, which claims priority to European Application No. 20208659.1, filed Nov. 19, 2020, the disclosures of each of which are incorporated herein by reference in their entirety, including any figures, tables, and drawings. FIELD OF INVENTION The invention relates to a method of preparing a mineral melt in a cupola furnace that uses at least one plasma torch to provide heat energy to the furnace. The plasma torch uses nitrogen, carbon monoxide, carbon dioxide, or a mixture thereof as the carrier gas. BACKGROUND Methods of preparing a mineral melt for the production of man-made mineral fibres (MMVF) are known to be carried out in shaft furnaces, such as cupola furnaces. They involve heating mineral material in the presence of coke and an oxygen-containing gas to form the mineral melt. It is challenging to produce mineral melts in a process that reduces harmful emissions in the off-gas of a cupola furnace. Cupola furnaces typically comprise a range of temperature zones, including a hot zone, an oxidation zone, a reduction zone, and a preheating zone. The lower portion of the cupola furnace constitutes the hot zone. The hot zone comprises the mineral melt formed in the cupola, which mineral 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 above. In typical cupola furnaces, the melt temperature in the hot zone is in the range of 1450° C. to 1550° C., and it takes a relatively long time to change the temperature of a mineral melt at this location. Further, the distance between the top and bottom of the hot zone is relatively large. This is needed to ensure that the correct oxidation zone temperature is maintained in traditional cupola furnaces. The oxidation zone (also known as the combustion zone) is located above the hot zone. The lower portion of the oxidation zone is usually provided with gas inlet nozzles, known as tuyeres, through which preheated air or another oxidation gas is introduced into the furnace. Heating is usually generated by combustion of coke. The combustion of the coke takes place during the movement of the preheated air up through the oxidation zone, and the gas temperature may rise from about 500° C. to about 2,000° C., thus causing raw material that moves down through the oxidation zone to be heated to its melting point. This melted mineral material flows down into the hot zone at the base of the cupola furnace. The vertical extension of the oxidation zone is determined by the amount of oxygen introduced into the furnace. The reduction zone is above the oxidation zone, and starts at the level where the oxygen introduced through the tuyeres is consumed by combustion of the coke. In the reduction zone, where the temperature is typically between 1,000° C. and 1,500° C., coke reacts with the CO 2 formed in the oxidation zone to form CO in an amount which is double the amount of consumed CO 2 based on volume. This reaction is endothermic causing about 20-25% of the energy released by the combustion in the oxidation zone to be lost as latent heat in the off-gas. As is typical, the off-gas may be used to heat the raw materials due to be melted in the cupola furnace in the preheating zone. The preheating zone is above the reduction zone. WO 87/06926 relates to a process of producing a mineral melt, in which some of the heating can be provided by use of a plasma torch. In the method, CO in the off-gas is reduced. This may be achieved by using coke to provide at least two thirds of the furnace heating energy. The remainder may be provided by a plasma torch amongst other methods. There is no distinction made between the carrier gases suitable for use with the plasma torch. Whilst there are advantages to the use of a plasma torch to provide some of the heat energy to the furnace, we find that when plasma torches that use air as the carrier gas are used to form mineral melts, off-gases are formed that comprise a relatively high amount of NOx, such as up to 7,000 to 10,000 ppm. NOx is deleterious to both the environment and animals, including humans. This is normally mitigated by adding a reducing agent, such as hydro-carbon gases. Off-gas from such cupola furnaces may still contain over 3,100 ppm of NOx, which is many times higher than many national limits. Accordingly, it would be necessary to provide clean-up systems to minimise release of NOx into the atmosphere. Further, hydrogen may account for up to 20% of the off-gas produced by cupola furnaces heated by plasma torches that use air as the carrier gas. This would present an explosion risk to the furnace. It is desirable to provide a method for the production of a mineral melt suitable for use in the formation of MMV fibres, such as glass fibre or stone fibre, which process minimises the amount of