Deoxygenation of furnaces with hydrogen-containing atmoshperes
A method of removing oxygen molecules present in a furnace atmosphere having the step of: reacting the oxygen molecules from the furnace atmosphere on one or more catalytic reactors. A furnace having an atmosphere and at least one catalytic reactor for removing oxygen molecules present in said atmosphere
This invention claims the benefit of U.S. Provisional Application 60/737,276, filed Nov. 16, 2005 titled, “in Situ Catalytic Deoxygenation of Heat Treating Furnaces Containing H2 Atmosphere. The disclosure of this provisional application is hereby incorporated by reference.
BACKGROUND OF THE INVENTION100% hydrogen atmospheres and hydrogen containing atmospheres have been routinely used by the heat treating industry both in batch and in continuous furnaces for metal powder reduction, bright annealing of ferrous and non-ferrous metals and other materials requiring thermal processing. During the operation of the furnaces containing 100% hydrogen atmosphere, the ingression of external air into the furnace is a safety concern, especially in the case where the furnace temperature is lower than the auto-ignition temperature of hydrogen, such as in the exit end or cooling zone of the furnace where the furnace temperature is low. In this case the ingressed air will not react with the furnace hydrogen atmosphere to form moisture, and it can consequently accumulate inside the furnace. When the accumulated air or oxygen level inside the furnace reaches an unsafe level, the furnace will have to be shut down and purged with nitrogen (inert) gas. High oxygen levels can also result in the oxidation of materials being treated inside the furnace. This furnace shut-down and purging will decrease productivity and increase production cost.
BRIEF SUMMARY OF THE INVENTIONThe present invention is a method of removing oxygen molecules present in a furnace atmosphere comprising the step of: reacting the oxygen molecules from the furnace atmosphere on one or more catalytic reactors.
The present invention is a method for using a catalytic deoxygenation reactor having a furnace atmosphere comprising hydrogen gas (up to 100%) in order to avoid oxygen build-up in the furnace. The reactor may be placed inside the furnace and may be located along the pathway of ingressing gas whereby the oxygen in the ingressing gas will be catalytically converted with hydrogen from the furnace's atmosphere to water vapor (H20). The reactor comes into contact with the oxygen molecules in the atmosphere by the movement of the gases in the furnace atmosphere. Alternatively, atmosphere moving equipment, for example, fans, pumps, or vacuums, can be provided to move the gases in the furnace atmosphere to foster the contact between the oxygen and hydrogen molecules and the reactor. Alternatively, fan(s), pump(s) or vacuum(s) could be used to draw the atmosphere into a reactor that is located external to the furnace, and the atmosphere gases with the reduced molecular oxygen content could be reintroduced into the furnace downstream of the reactor. The reactor may be located adjacent to or mounted onto the furnace and the gases having the reduced molecular oxygen content could be immediately returned to the furnace atmosphere after passing through the reactor. The invention can lower oxygen levels in the furnace and may prevent oxidation of materials that are being processed in and by the furnace.
Additionally, this invention provides a furnace comprising an atmosphere and at least one catalytic reactor for removing oxygen molecules present in the atmosphere.
These inventions may provide one or more of the following benefits: furnaces and methods for safe operation of furnaces (avoiding the accumulation of oxygen to an unsafe level in the furnace) having a hydrogen-containing atmosphere; furnaces and methods that may avoid or reduce the number of shut-downs and/or nitrogen purgings of furnaces due to air ingression; furnaces and methods that eliminate or reduce the amount of unwanted oxidation of the materials processed in furnaces; furnaces and methods that increase the productivity of furnaces; and furnaces and methods that decrease the production costs of the materials treated in furnaces.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
This invention is directed to a method of using a catalytic reactor typically inside a furnace, for example at the exit end curtain area of a furnace or kiln. The furnace comprises hydrogen gas in its atmosphere (up to 100%). The reactor catalytically converts to water any oxygen leaking-in from the outside of the furnace or internal sources within the furnace.
The term furnace will be used to mean any piece of thermal process equipment with protective or reactive atmosphere capability. Examples of furnaces may include heat-treating furnaces, continuous belt furnaces, rotary furnaces, box furnaces, strand furnaces, strip furnaces, roller-hearth furnaces, float glass furnaces, ceramic kilns, and others that would be known to the art. These furnaces can be used in processing metal, composites or ceramic materials, including sintering, annealing, carburizing, decarburizing, hardening, brazing, nitriding, melting, glass-making and the like.
The atmosphere in the furnace is typically a hydrogen-containing atmosphere. The desired hydrogen-containing atmosphere can contain any amount of hydrogen, typically between 5 and 100%. The balance of the hydrogen-containing atmosphere can be made up of inert gases and/or reactive gases depending upon the process requirements. Examples of inert gases can be nitrogen, argon and helium. Examples of reactive gases may include CO, CO2, propane, methane, ethane, and other alkanes, natural gas, silane, ammonia, and the like. This invention is used to maintain a desired atmosphere within the furnace. In some embodiments, the reactor and method of this invention may be used in conjunction with separate atmosphere generating equipment that may be located inside or outside the furnace. The atmosphere generating equipment will have one or more sources outside the furnace for the gases to be fed, or to be generated and then fed, into the furnace atmosphere.
The term ingressing gas will be used to describe an undesired source of oxygen into the furnace atmosphere. The present invention is a method to prevent undesired ingressing gas from causing a build up of oxygen in a furnace having a hydrogen-containing atmosphere. The ingressing gas can be air that enters the furnace, or it can be a gas that is present as an impurity or impurities in a source for the atmosphere of the furnace (for example, oxygen in a hydrogen gas supply or unreacted oxygen from atmosphere generating equipment). Ingress of air can be from leaking flanges, pipe connections, ports, the entrance and exit for the materials to be processed in the furnace or other openings into the furnace. Ingressing gas, particularly air may result from furnace design, furnace wear, or from changing the size or shape of a material to be processed in a furnace. Further, the source of the ingressing gas may be from the material being processed in the furnace.
The catalytic reactor comprises catalytic materials, such as platinum, palladium, nickel, noble-metals, rhodium, ruthenium, or other materials that promote the reaction of hydrogen and/or reactive gases/hydrocarbons (if present in the furnace atmosphere) with oxygen. The reactor may comprise catalyst alone or a support to hold the catalyst or onto which the catalyst may be coated or adhered. Examples of support materials include alumina, or other ceramic or metallic powders, strips, honeycombs, screens, semi-conductive materials, porous silicon, other porous materials and designs or other support forms.
The reactor may be located anywhere in the furnace. Typically the reactor is located near a source of the ingressing gas which is often at the entrance or exit of the furnace. The reactor is near the source of the ingressing gas so that a majority of the ingressing gas contacts the reactor before it has dispersed within the atmosphere as a whole. The reactor is considered near the source for the ingressing gas if it is less than ten feet away from the source of the ingressing gas. The reactor is particularly useful in furnaces or in sections of furnaces having a hydrogen-containing atmosphere and/or in sections of the hydrogen-containing atmosphere where the temperature of the atmosphere is lower than the auto-ignition temperature of the gases in the atmosphere, such as in the exit end or cooling zone of a furnace. For a hydrogen-containing atmosphere containing mostly hydrogen, the temperature of the furnace may be below 579° C. at atmospheric pressure (auto-ignition temperature for hydrogen). The auto-ignition temperature for the atmosphere will depend on the composition of gases in the atmosphere and the pressure in the furnace. At temperatures below the auto-ignition temperature for the composition of the atmosphere, if the reactor of this invention were not present, the oxygen in the ingressing gas (for example, air) would not react with the hydrogen (and hydrocarbons) in the furnace atmosphere to form water vapor (and CO or CO2), and would consequently accumulate inside the furnace.
The catalytic reactor could also take the form of a furnace curtain material or coating on a curtain material, for example a fiberglass curtain material, or other air ingress blocking means, such as a flap or flexible or inflexible physical barrier being constructed out of catalytically active material. Alternatively, the catalyst could be powders or beads or catalytic coatings on beads or powders that are used to block the furnace exit, which would ensure that oxygen is reacted at the point of entering the furnace or upon initially mixing with the furnace atmosphere with the hydrogen or hydrocarbon to form water vapor or carbon dioxide or carbon monoxide, which is less reactive than oxygen to the materials being processed and safer if present in a hydrogen-containing atmosphere.
In one embodiment, as shown in
In one embodiment, the operation of the catalytic reactor inside the furnace can be monitored by placing a thermocouple inside the catalytic reactor, and another thermocouple outside the catalytic reactor inside the furnace, for example, facing the furnace exit end as shown in
Alternatively, oxygen monitors, other gas analyzers, and/or dew point monitors can be used to measure (directly or indirectly) the oxygen concentration or dew point inside the furnace at the appropriate location(s), which can be used to indicate if deoxygenation reactions due to the presence of the reactor are occurring.
The ingression of air is also a safety and process concern when recapturing and recycling the hydrogen containing atmosphere from the furnace. Since recycling systems must draw the hydrogen containing atmosphere from the furnace into the recycling equipment, there may be a tendency for air to be drawn into the furnace and into the recycling system as well. Furnaces that operate at atmospheric pressure—or close to it are especially prone to air ingression. The use of an in situ catalytic deoxygenation reactor inside the supply piping or across or over the opening to the supply piping from the furnace to a recycle system will improve safety of the furnace from a flammability perspective and also eliminate the need to remove oxygen in the subsequent purification process. Additionally, it may be beneficial to use additional reactors near places of ingressing gas near the opening to the supply piping, for example, near the entrance or exit of the furnace depending upon where the supply piping to the recycling system is located. The reactor of this invention can be used for removing oxygen from the gases in the atmosphere that pass through the reactor at low pressures, for example, less than 1 psig or less than 0.5 psig. The pressures in or near the inlet piping to the recycling system from the furnace may be less than 1 psig or less than 0.5 psig.
EXAMPLES
The operation of the catalytic reactor 17 is monitored by the differential thermocouple 18 based on the exothermic characteristic of the chemical reaction between oxygen and hydrogen.
Alternatively, although not shown, the reactor could comprise catalytic material coated on the physical curtain 14 alone or in addition to the reactor 17 as shown. If desired, catalyst could be provided on one or more other fixtures or structures within the furnace and/or on the internal surfaces of the furnace walls if desired.
One or more reactors can be used in a furnace to remove the oxygen from the atmosphere. If multiple reactors are used they can be located in various locations and have different designs. For example, the reactor shown in
The inventions have been described with reference to particular embodiments. The inventions shall not be limited to the particular embodiments, and shall only be limited by the scope of the claims.
Claims
1. A method of removing oxygen molecules present in a furnace atmosphere comprising the step of: reacting said oxygen molecules from said furnace atmosphere on one or more catalytic reactors.
2. The method of claim 1 wherein said furnace comprises a hydrogen-containing atmosphere.
3. The method of claim 1 wherein said reactor comprises catalyst and a support.
4. The method of claim 1 wherein said catalytic reactor comprises platinum, palladium, nickel, noble metals, rhodium, or ruthenium.
5. The method of claim 1 wherein said reactor comprises: platinum, palladium, nickel, noble metals, rhodium, or ruthenium. supported on metallic, semiconductive or ceramicsubstrate or structure.
6. The method of claim 1 wherein said furnace is a batch furnace or a continuous furnace.
7. The method of claim 1 further comprising the step of monitoring if the reactor is removing said oxygen molecules from the furnace atmosphere.
8. The method of claim 7 wherein said monitoring step is performed by measuring a temperature inside and outside the reactor within the furnace.
9. The method of claim 7 wherein said monitoring step is performed by measuring the composition of the atmosphere within the furnace.
10. The method of claim 1 wherein said reactor is used in furnaces for a process selected from the group consisting of: bright annealing ferrous or non-ferrous parts, heat-treating, hardening, carburizing, brazing parts, sintering metal or ceramic powders, sealing glass to metals and float glass production.
11. The method of claim 1 further comprising the step of locating said at least one reactor near a source of ingressing gas.
12. The method of claim 1 further comprising the step of locating said at least one reactor near the exit of the furnace or at the entrance of the furnace.
13. The method of claim 1 further comprising the step of incorporating said one or more reactors into one or more furnace structures.
14. The method of claim 13 wherein said one or more furnace structures are selected from the group consisting of: curtain, flap, powder lock, bead lock, and exit door.
15. The method of claim 1 further comprising the step of locating said reactor in an in-take pipe to an atmosphere recycle system.
16. The method of claim 1 further comprising the step of locating said reactor near an opening to the in-take pipe to an atmosphere recycle system.
17. The method of claim 1 further comprising the step of locating said reactor in a portion of said furnace where the atmosphere temperature is less than 579° C.
18. A furnace comprising an atmosphere and at least one catalytic reactor for removing oxygen molecules present in said atmosphere.
19. The furnace of claim 18 further comprising monitoring means for said one or more reactors.
20. The furnace of claim 18 wherein said atmosphere is less than 579° C.
Type: Application
Filed: Nov 8, 2006
Publication Date: May 17, 2007
Inventors: Donald Bowe (Zionsville, PA), Minfa Lin (Macungie, PA), Robert Edwards (Macungie, PA)
Application Number: 11/594,477
International Classification: C21D 1/76 (20060101);