Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D9/00—Cooling of furnaces or of charges therein
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B7/00—Blast furnaces
  • C21B7/10—Cooling; Devices therefor

Definitions

• This invention relates to the use of polyorgano­siloxane fluids as cooling media for processes which include handling of molten salts, metals, metalloids, or alloys. More specifically, this invention relates to improved safety of these processes by eliminating the hazard of a steam explosion when water is used as a cooling medium.
• Water is the most common liquid heat transfer medium because of its availability and low cost.
• water poses the significant safety hazard of a steam explosion if water is allowed to contact molten salt or molten metal, metalloids, or alloys thereof at elevated temperatures.
• Steam explosions are characterized by extremely rapid increase in pressure resulting in subsequent rupture of a containing vessel. The release of this explosive force could cause risk to life and property. While the mechanism of steam explosions is not completely under­stood, this occurrence is a phenomenon which is more than a pressure build-up due to rapid vaporization of liquid water.
• Electric smelting furnaces to produce metals, metalloids, and alloys thereof are examples of processes which handle molten materials.
• Submerged electric arc furnaces are used extensively in the reduction of oxygen-­containing compounds to produce metals, metalloids, and alloys thereof. More recently, plasma technology is being applied to the above-noted oxide reductions. Examples of such metals, metalloids, and alloys are iron, aluminum, silicon, steel, ferrosilicon, and other ferroalloys.
• Nelson and Duda "Steam Explosion Experiments with Single Drops of Iron Oxide Melted with a CO2 Laser. Part II. Parametric Studies," Sandia National Laboratories, Albuquerque, New Mexico, NUREG/CR-2718, SAND82-1105, R3, printed April, 1985, discuss laboratory studies on the phenomenon of steam or vapor explosions using molten iron oxide and water.
• Nelson and Duda disclose the testing of n-pentadecane with molten iron oxide. Nelson and Duda were not able to create a vapor explosion with n-pentadecane as had been created with water.
• Polydiorganosiloxanes provide a safer alternative to water as a liquid heat transfer fluid.
• the significantly higher boiling point and subsequent lower vapor pressure of polydiorganosiloxanes lessens the hazard caused by a coolant leak into the furnace due to the rate of pressure rise and level of ultimate pressure, particularly in the case of a closed furnace.
• polydimethylsiloxanes do not exhibit an explosive reaction, similar to a steam explosion, when exposed to a molten medium at elevated temperatures.
• the term "elevated temperatures” means temperatures greater than 500°C. This unexpected finding is discussed in an example, infra. This unexpected finding is a marked improvement in the operation of processes handling molten materials at elevated temperatures, since it greatly reduces the hazard to life and property.
• polydimethylsiloxane fluids afford an improved heat transfer fluid as compared to conventional organic heat transfer fluids such as mineral oils, higher boiling aliphatic materials such as n-pentadecane, and high phenyl-containing materials such as the Dowtherm® J. Dow Corning Corporation technical bulletins, "Information about Syltherm® 800 Heat Transfer Liquid,” Form No. 22-761G-86, and "A Guide to Specifying Syltherm® 800 Heat Transfer Liquid,” Form No. 24-183A-86, outline the advantages of polydimethyl­siloxanes fluids as compared to conventional organic heat transfer fluids.
• an improvement to processes in which molten materials are handled at elevated temperatures under conditions that will be delineated herein comprising (a) providing a molten medium, the molten medium being at a temperature greater than about 500°C.; (b) providing means for containing the molten medium; (c) using a heat transfer fluid for cooling the means for containing the molten medium; (d) providing means for removing heat from the heat transfer fluid; and (e) providing means for conveying the heat transfer fluid between the means for containing the molten medium and the means for removing heat from the heat transfer fluid, the improvement comprising using a poly­organosiloxane fluid as the heat transfer fluid.
• the molten medium may be a molten salt; a molten metalloid; a molten metal; a mixture of a molten metalloid and a molten metal; a mixture of molten metals; a molten metalloid oxide; a molten metal oxide; a mixture of a molten metalloid oxide and a molten metal oxide; a mixture of metal oxides; a mixture of a molten metalloid oxide and a corresponding molten metalloid; a mixture of a molten metal oxide and a corresponding molten metal; a mixture of a molten metalloid oxide, a molten metal oxide, and a corresponding molten alloy; and a mixture of molten metal oxides and a corresponding molten alloy.
• Many of these combinations of molten materials describe conditions that exist within metallurgical furnaces.
• a steam explosion or a vapor explosion is characterized by extremely rapid increase in pressure which occurs when liquid water contacts a molten material. While the mechanism of steam explosions is not completely understood, this occurrence is a phenomenon which is more than a pressure build-up due to rapid vaporization of liquid water.
• a steam explosion usually results in the rupture of the vessel containing the molten material with the associated hazards to life and property.
• a temperature of a molten medium of greater than about 500°C. is believed by the inventors to be a lower temperature limit at which a steam or vapor explosion becomes a significant safety hazard.
• smelting furnaces to produce materials such as silicon and steel operate at temperatures in excess of 1500°C.
• the metalloid produced may be silicon and the like.
• the metals produced may be iron, aluminum, and the like.
• the alloys produced may be steel, ferrosilicon, and the like.
• “Means for containing the molten medium” for the purposes of the instant invention can be structures such as bath bodies for containing molten salts for heat transfer purposes. These structures may also be furnaces used in smelting metalloid oxides, metal oxides, or mixtures thereof to produce metalloids, metals, or alloys thereof.
• the heat transfer fluid used for cooling the means for containing the heat source is a polyorganosiloxane fluid.
• the polyorganosiloxane fluid should be low enough in viscosity to facilitate ease of circulation through the zones of a furnace requiring cooling. The viscosity can be in the range of 1 to 50 centistokes.
• the polyorganosiloxane fluid may be a polydiorganosiloxane fluid.
• the polydiorgano­siloxane fluid may be a polydimethylsiloxane fluid. Further, the polydimethylsiloxane fluid may be a trimethylsiloxy-­endblocked fluid containing heat-stabilizing additives.
• “Means for removing heat from the heat transfer fluid” for the purposes of the instant invention can be any conventional means of transferring heat from a hot liquid. These means can include use of the hot fluid to vaporize water to generate steam and to recover heating value, cooling by conventional heat exchange with cooling water or ambient air, and the like.
• a preferred molten medium temperature for using the polyorganosiloxane fluid is a temperature greater than about 500°C.
• a more preferred molten medium temperature for using the polyorganosiloxane fluid is a temperature greater than about 750°C.
• the most preferred molten medium temperature for using the polyorganosiloxane fluid is a temperature greater than about 1000°C.
• a preferred polyorganosiloxane fluid is a polydi­methylsiloxane fluid.
• a more preferred polyorganosiloxane fluid is a trimethylsiloxy-endblocked polydimethylsiloxane fluid.
• the most preferred polyorganosiloxane fluid is a trimethylsiloxy-endblocked polydimethylsiloxane fluid containing heat-stabilizing agents.
• the composition and method for preparing the trimethylsiloxy-endblocked polydimethylsiloxane fluid containing heat-stabilizing agents are disclosed by Halm in U.S. 4,122,109, issued October 24, 1978; and in U.S. 4,193,885, issued May 18, 1980.
• the preferred viscosity of the polydimethylsiloxane fluid is in the range of about 5 to 20 centipoise.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• General Engineering & Computer Science (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Silicon Polymers (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
• Furnace Details (AREA)

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Publications (3)

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• 1987
  • 1987-10-06 CA CA000548662A patent/CA1310049C/en not_active Expired - Lifetime
  • 1987-11-02 EP EP19870309663 patent/EP0283622B1/de not_active Expired
  • 1987-11-02 DE DE8787309663T patent/DE3772971D1/de not_active Expired - Fee Related
  • 1987-12-16 NO NO875251A patent/NO875251L/no unknown
  • 1987-12-24 AU AU83066/87A patent/AU596483B2/en not_active Ceased
  • 1987-12-28 BR BR8707074A patent/BR8707074A/pt unknown
  • 1987-12-28 JP JP33039887A patent/JPS63172886A/ja active Pending

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