WATERLESS SYSTEM AND METHOD FOR COOLING A METALLURGICAL PROCESSING FURNACE

Abstract

The present invention relates to a waterless system and method for cooling a metallurgical processing furnace. Supercritical carbon dioxide (sCO.sub.2) is used as a coolant, as opposed to water, which provides several advantages. For example, sCO.sub.2 can be used at higher temperatures, the risk of an explosion (with use of water) is eliminated, there are no problems with regard to reverse solubility of water at higher temperatures that can foul passageways, and smaller cooling passages can be used thus reducing the cost of cooling panels. A system is disclosed which uses a reservoir to store the sCO.sub.2, a compressor or pump to cause the delivery of the sCO.sub.2 to cooling passages in the furnace, a pressure reducing valve or a turbine to decrease the pressure of the sCO.sub.2, and a heat exchanger to cool the sCO.sub.2 to a liquid state as the sCO.sub.2 travels back to the reservoir.

Claims

1. A waterless system for using sCO.sub.2 to cool a metallurgical processing furnace, the system comprising: a reservoir configured to store the sCO.sub.2; at least one of a compressor or a pump connected to the reservoir and configured to pull the sCO.sub.2 from the reservoir and deliver the sCO.sub.2 to cooling passages in one or more panels comprising the metallurgical processing furnace; at least one of a pressure reducing valve or a turbine connected to the furnace and configured to decrease the pressure of the sCO.sub.2; and a gas to air heat exchanger connected to the reservoir as well as to the at least one pressure reducing valve or turbine, wherein the gas to air heat exchanger is configured to receive the sCO.sub.2 from the at least one pressure reducing valve or turbine, and wherein the gas to air heat exchanger is configured to cool the sCO.sub.2 such that the sCO.sub.2 is in a liquid state as it leaves the air to gas heat exchanger and travels back to the reservoir.

2. The waterless system as recited in claim 1, wherein the at least one pressure reducing valve or turbine comprises the turbine, the turbine is coupled to a generator which recovers heat energy in the sCO.sub.2 taken from the metallurgical processing furnace and turns the heat energy into electricity.

3. The waterless system as recited in claim 1, further comprising a chiller that is connected to the gas to air heat exchanger and the reservoir, wherein the chiller is configured to reduce the temperature of the sCO.sub.2 and turn the sCO.sub.2 into a liquid state before proceeding to the reservoir.

4. A method for using sCO.sub.2 to cool a metallurgical processing furnace, the method comprising: using a reservoir to store the sCO.sub.2; using at least one of a compressor or a pump connected to the reservoir to pull the sCO.sub.2 from the reservoir and deliver the sCO.sub.2 to cooling passages in one or more panels comprising the metallurgical processing furnace; using at least one of a pressure reducing valve or a turbine connected to the furnace to decrease the pressure of the sCO.sub.2; and using a gas to air heat exchanger connected to the reservoir as well as to the at least one pressure reducing valve or turbine to receive the sCO.sub.2 from the at least one pressure reducing valve or turbine and to cool the sCO.sub.2 such that the sCO.sub.2 is in a liquid state as the sCO.sub.2 leaves the air to gas heat exchanger and travels back to the reservoir.

5. The method as recited in claim 4, wherein the step of using the at least one of a pressure reducing valve or a turbine comprises using the turbine which is coupled to a generator, and wherein the step further comprises using the generator to recover heat energy in the sCO.sub.2 taken from the metallurgical processing furnace and turning the heat energy into electricity.

6. The method as recited in claim 4, further comprising using a chiller connected to the gas to air heat exchanger and the reservoir to reduce the temperature of the sCO.sub.2 into a liquid state before the sCO.sub.2 proceeds to the reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference numerals identify like elements in which:

[0033] FIG. 1 is a schematic diagram of a system which in in accordance with an embodiment of the present invention; and

[0034] FIG. 2 is a block diagram of a method using the system shown in FIG. 1, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] While this invention may be susceptible to embodiment in different forms, there are shown in the drawings and will be described herein in detail, specific embodiments with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated.

[0036] FIG. 1 is a schematic diagram of a system 10 provided in accordance with a preferred embodiment of the present invention. As shown, the system 10 is employed in connection with a metallurgical processing furnace 12, such as an electric-arc furnace (EAF), blast furnace, basic oxygen furnace (BOF), etc. for the production of steel, iron, nickel, copper, etc. The furnace 12 incorporates cooling panels 28 or some other type of cooling system. In FIG. 1, only half the furnace 12 is shown in section. As shown, the furnace 12 contains a molten metal bath 13.

[0037] The system 10 in accordance with an embodiment of the present invention uses supercritical carbon dioxide (sCO.sub.2) to cool the furnace 12. The properties of sCO.sub.2 change significantly near the pseudo-critical line, which exists above the critical pressure and critical temperature of the sCO.sub.2. At supercritical pressure, there is no liquid-vapor phase transition so the sCO.sub.2 does not expand suddenly, in high contrast to how water quickly expands to steam. As such, using sCO.sub.2 eliminates the risks of explosion associated with using water as a coolant. Furthermore, the heat capacity of sCO.sub.2 increases significantly near the pseudo-critical line, which gives it beneficial thermal capabilities.

[0038] As shown in FIG. 1, the system 10 comprises a reservoir 14 which is configured to store carbon dioxide (CO.sub.2). The CO.sub.2 is under high pressure in the reservoir 14, which maintains a large portion of the CO.sub.2 in a liquid state with a smaller portion of gas above in the reservoir 14.

[0039] The system 10 also includes a pump or compressor 16 that is configured to pull the CO.sub.2 from the reservoir 14, causing an increase in pressure. The cooling fluid (sCO.sub.2) is then sent into panel cooling passages 18 in walls 20, roof/dome 22, basin 24, exhaust gas evacuation duct 26 and/or an auxiliary apparatus such as burner boxes, injector boxes, and tubular instrumentation panels protruding into the metallurgical processing furnace 12. The schematic shown in FIG. 1 only shows the protruding wall cooling panels 28 for clarity. The passages of these panels 28 can be pipes or tubes in contact with the hot face of the panels 28 (nearest the molten metal), passageways cast into the walls 20, or passages formed by welding or brazing combinations of plate, pipe or tube together to provide the fluid a thermal conduction path to the hot face. These passages are generally serpentine in nature so as to provide complete thermal coverage of the hot face of the panel 28. The panels 28 of the metallurgic furnace 12 are generally limited in size to be smaller than the whole of the walls 20, roof/dome 22, exhaust gas evacuation duct 26, or basin 24 to minimize thermal stress. As multiple panels 28 comprise a section, these panels 28 can be cooled in parallel or series in the cooling circuit by connecting them with hoses, tubes, or piping. Preferably, multiple separate circuits of passageways are built into each panel 28. These separate circuits preferably have individual leak detection units that are tied into automatic shutdown systems that allow a leaking circuit to be closed while still maintaining cooling flow to the remainder of the cooling panel 28.

[0040] As discussed previously hereinabove, water-cooled systems must keep the water below a certain temperature so to mitigate the risk of fouling the water passages. In contrast to water, sCO.sub.2 does not contain dissolved minerals and therefore will not cause fouling of the passages. The operating temperature of the sCO.sub.2 can be raised substantially, thereby reducing the differential temperature between the furnace and the cooled wall, which reduces the heat removed from the furnace 12 and results in the saving of energy.

[0041] Furthermore, the sCO.sub.2 has a much lower viscosity than water, thereby allowing for a much smaller passage for the same pressure drop. The smaller passage allows the panel to be thinner which reduces the amount of material used to manufacture the panel and therefore the cost of the panel 28.

[0042] As shown in FIG. 1, the system 10 preferably includes a pressure reducing mechanism 30 that is configured to reduce the pressure of the sCO.sub.2 as the sCO.sub.2 passes therethrough. Once the sCO.sub.2 is through the furnace 12 portion of the cooling circuit, the sCO.sub.2 passes through the pressure reducing mechanism 30. Preferably, the pressure reducing mechanism 30 is configured to drop the pressure of the sCO.sub.2 slightly above the tank storage pressure of the reservoir 14. This expansion drops the temperature slightly due to the Joule-Thomson effect.

[0043] The pressure reducing mechanism 30 can take many forms. For example, a pressure limiting valve can be used, or a turbine 32 can be used. If a turbine 32 is used, preferably the turbine 32 is coupled with a generator 34 which recovers the waste heat energy taken from the metallurgical processing furnace 12 and turns it into electricity for running the turbine 32.

[0044] As shown in FIG. 1, preferably the system 10 also includes a gas to air heat exchanger 36. After the sCO.sub.2 fluid passes through the pressure reducing mechanism 30 (such as a pressure reducing valve or expansion turbine), the sCO.sub.2 is further cooled in the air to gas heat exchanger 36 preferably with the use of cooling fans 38. Preferably, the sCO.sub.2 is kept at a high enough pressure that it is in a liquid state as it leaves the air to gas heat exchanger 36.

[0045] As shown in FIG. 1, an optional chiller system 40 using a refrigerant cycle can be used for extremely hot ambient temperatures where additional cooling is required to turn the sCO.sub.2 into a liquid state. Regardless of whether a chiller 40 is used, the system 10 is configured such that the sCO.sub.2 fluid recycles back to the reservoir 14 for subsequent use as a coolant in the system 10, as described previously.

[0046] FIG. 2 is a block diagram of a method 42 using the system 10 shown in FIG. 1, in accordance with an embodiment of the present invention. The method 42 is a method for using sCO.sub.2 to cool a metallurgical processing furnace 12. As shown, the method 42 comprises using a reservoir 14 (see FIG. 1) to store the CO.sub.2, using at least one of a compressor and a pump 16 (see FIG. 1) to pull the sCO.sub.2 from the reservoir 14 and deliver the sCO.sub.2 along cooling passages associated with the metallurgical processing furnace 12, using at least one of a pressure reducing valve and turbine 32 (i.e., a pressure reducing mechanism 30 as indicated in FIG. 1) to decrease the pressure of the sCO.sub.2, and using a gas to air heat exchanger 36 (see FIG. 1) to cool the sCO.sub.2 such that the sCO.sub.2 is in a liquid state as the sCO.sub.2 leaves the air to gas heat exchanger 36 and travels back to the reservoir 14. As shown, a chiller 40 (see FIG. 1) can also be used reduce the temperature of the sCO.sub.2, into a liquid state before the sCO.sub.2 proceeds to the reservoir 14.

[0047] Using sCO.sub.2 as a coolant for metallurgical processing furnace 12 provides several advantages over using water, such as: (i) eliminating the need to keep the coolant below a certain temperature in order to preserve the integrity of cooling passages; (ii) eliminating the risk of explosions in case the coolant leaks through a crack or fusion into the furnace; (iii) providing for planned maintenance interventions without requiring the furnace itself to be suddenly halted for a long time, without affecting the productivity of the furnace; (iv) requiring fewer and less expensive maintenance and repair interventions with respect to those generally required by panels and cooling systems for metallurgical processing furnaces. Additionally, sCO.sub.2 does not contain dissolved minerals like water does and therefore does not have an issue with inverse solubility fouling out the cooling passages. The sCO.sub.2 cooling fluid can be operated at much higher temperatures than water, which reduces the heat loss from the furnace to the cooling fluid. Finally, the fact that sCO.sub.2 has a lower viscosity compared to water allows for cooling passages to be smaller, which enables the thickness of the panels to be reduced thus reducing the costs of the panels.

[0048] While specific embodiments of the invention have been shown and described, it is envisioned that those skilled in the art may devise various modifications without departing from the spirit and scope of the present invention.