US3371189A - Apparatus for establishing and maintaining an atmosphere controlled as to pressure, temperature, gas content and rate of gas flow, and closed and semi-closed arc heater loop apparatus for use therein - Google Patents

Description

2 1968 G. A. KEMENY ETAL 3,371,189

APPARATUS FOR ESTABLISHING AND MAINTAINING AN ATMOSPHERE CONTROLLED AS TO PRESSURE, TEMPERATURE, GAS CONTENT AND RATE OF GAS FLOW, AND CLOSED AND SEMI-CLOSED ARC HEATER LOOP APPARATUS FOR USE THEREIN Filed Aug. 20. 1964 4| A POWER 2 43 SUPPLY 4 7 FlG.l.

ARC 23 HEATER TEMPERATURE 28 SENSING 30 3| p 18 GAS DEVICE v SOURCE ll 38 34 |9 24 l4 l5 F|G'3 SOURCE -26 3s v J V? 42 DUST F IG-Z- s SE A T R 53 P 0 ARC? POWER 43 37 J PRE-COOLER 5| 33 HEATER SUPPLY TEMPERATURE Ly l8 26 SENSING DEVICE 6|. 6 34 29/ GAS T SOURCE u 38 V 2 1 v 31 30 mm PRE-COOLER 34 -|3 52%] I7 2% Elm DUST I I5 SEPARATOR V 66 WITNESSES Georg f Kl rsgn y MJW 8. Peter E Kienosf United States Patent APPARATUS FOR ESTABLISHING AND MAIN- TAINING AN ATMOSPHERE CONTROLLED AS TO PRESSURE, TEMPERATURE, GAS (IONTENT AND RATE OF GAS FLOW, AND CLOSED AND SEMI-CLOSED ARC HEATER LOOP APPARATUS FOR USE THEREIN George A. Kemeny, Franklin Township, and Peter F. Kienast, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Aug. 20, 1964, Ser. No. 390,898 8 Claims. (Cl. 219-383) ABSTRACT OF THE DISQLOSURE Loop apparatus for providing a controlled atmosphere controlled as to pressure, temperature, gas content and rate of gas flow, especially suitable for metal working in gases at high temperatures, includes an arc heater having an energizing circuit and having compressed gas at a predetermined pressure and rate of flow supplied thereto to be heated to a desired temperature, and a furnace operatively connected to the arc heater for utilizing the gas for metal working, and including means forming a closed loop for recycling gas through the furnace. Additionally, means is provided for removing a predetermined minor portion of gas from the closed loop at a predetermined pressure and rate of flow to maintain the pressure and rate of gas flow in the furnace substantially constant. Some embodiments employ a preheater, heated by the removed gas, to preheat gas supplied to the'arc heater; others employ in addition to a preheater a dust separator circuit for cleaning removed gas, and after it is used in the preheater, feeding it back into the arc heater to thereby reduce the total quantity of gas required for operation of the furnace.

This invention relates to improvements in methods and apparatus for providing controlled atmospheres in closed and semi-closed loop systems, especially suitable for metal working in gases at high temperatures, and particularly to such loops using arc heaters for heating the gases.

As will be readily understood by those skilled in the art, in metal working it is necessary to raise metals to tempering, annealing, melting or reducing temperatures, and in some processes it is further necessary or desirable to control the specific atmosphere in which the metal is heated.

Apparatus suitable for practicing the methods of our invention employs an arc heater which passesthe gas to be heated through an are which rotates between water cooled electrodes. The high speed of rotation of the arc provides uniform enthalpy and temperature at the gas injector. The are heater transforms electric energy to heat energy directly without the need for conventional heating elements or consumable electrodes. This makes it possible to achieve very. high gas temperature Without contamination. Since the arc heater is especially suited for high temperature operation, only a small quantity of gas flow is required to raise the operating temperature in the furnace to the required value thereby increasing the efiiciency of the method and apparatus.

The apparatus is also especially suitable for use in systems or any application requiring high temperature gas flows, and is characterized by high efficiency of operation, continuous operation, temperature control in the furnace, pressure control in the furnace and throughout the systern, the ability to produce temperatures required for a wide range of particular applications, and control of the specific atmosphere in the system.

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To this end, the apparatus embodying our invention and suitable for practicing the method of our invention includes an arc heater the gas input to which is or may be supplied through a heat exchanger. The heated gas from the arc heater is supplied to means forming a closed path, the path forming means including a furnace portion of enlarged diameter for containing the metal or other substance to be heated, having a door for placing the metal inside the furnace. A tempearture sensing device connected inside the furnace near the substance to be heated is connected to a control which automatically regulates the power into the arc heater and accordingly regulates the temperature of gas in the arc heater. Gas from the arc heater, after passing around the closed path and around the metal to be heated returns to a point in the closed channel or closed path near the point of injection, from whence a portion of it passes through the heat exchanger and is exhausted. The fraction of gas discharged from the main loop may be bled from any part of the main loop but for efficiency reasons it is desirable that this gas be ejected from a location downstream of the furnace portion of the loop. A large portion of the gas is recycled.

In another embodiment of the inveniton, the portion of the gas removed from or allowed to escape from the closed path, after passing through the heat exchanger, is precooled and then passed through a dust separator or other filter and supplied back into the arc heater. This type of configuration is particularly attractive if the heated gas is sufliciently expensive to make it economically unattractive to waste a portion of the gas flow.

In both embodiments, an additional input or inputs are provided to the means forming the closed path for supplying another gas or other gases in addition to that heated by the arc heater, to provide an atmosphere having any desired ratio of gas content. Heat is transferred from the heated gas to the unheated gas by convection.

An object of our invention is to provide a new and im proved method of establishing and maintaining an atmosphere controllable as to pressure, temperature, gas content, and rate of gas flow.

Another object is to provide new and improved apparatus for controlling an atmosphere, and offering advantages over any now existing in the art.

A further object of our invention is to provide new and improved closed and semi-closed loop apparatus employing an arc heater for heating metals in a controlled atmosphere.

An additional object is to provide a new and improved closed loop system in which gas, after passing around the metal or other surfaces to be heated in the furnace, is filtered and channeled back through an arc heater and thence recycled'through the heating furnace.

Another object of our invention is to provide a heat treating apparatus wherein an arc heater is used to heat all these gases presently contemplated for this application.

S ill a further object is to provide a new and improved heating furnace in which the atmosphere may be easily controlled.

These and other objects will become more clearly ap parent after a study of the following specification, when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a view partially in cross-section of semiclosed loop arc heater apparatus according to our invention;

FIG. 2 is a view partially in cross-section of the preferred embodiment of a closed loop system embodying our invention; and

FIG. 3 is a view of a simplified embodiment of our in vention.

Referring now to the drawings, in which like reference numerals are used throughout to designate like parts, for a more detailed understanding of the invention, and in particular in FIG. 1 thereof, reference numeral generally designates a heating furnace having a portion 11 of enlarged diameter with a door 12 therein; the substance to be treated, for example a metal, is indicated at 13, mounted upon a suitable saucer or other support 14. In the illustrative drawing of FIG. 1, gas flows from left to right and exits from the furnace 10 into a conduit 15 which, as shown, loops back and is connected with the entrance end of the furnace, providing a closed loop or closed path for the flow of gases. There is a chamber 16 of substantially enlarged diameter at the entrance end of the closed furnace loop, having a throat of substantially reduced diameter 17, having a gas inlet pipe 18 with a nozzle 1d closely adjacent the throat 17. Gas entering the furnace area from the nozzle 19 is the gas which has been heated by the arc heater generally designated 23. Are

heater 23 has been shown externally located with respect to the loop. Actually the arc heater is relatively small and can also be located in chamber 16. The gas from nozzle 19 passes up a relatively long portion 24 into the portion of enlarged diameter 11. It is seen that closely adjacent the nozzle 17 on the furnace side thereof is an additional gas inlet pipe 25 connected to a gas source 26 shown in block form for convenience of illustration. It will be understood that the inlet pipe 25 may contain suitable valve means, and that the inlet itself may consist of separate holes or nozzles suitably directed, not shown for convenience of illustration; gas entering from the pipe 25 enters obliquely or tangentially to gas entering 24 at the nozzle 19, which assists in providing good mixing of the gases.

The aforementioned chamber 16 has a gas outlet conduit or pipe 28 communicating with a heat exchanger generally designated 29. Gas from conduit 28 after passing through the heat exchanger 2h is exhausted through the outlet pipe 30 which contains a suitable valve 31. The valve 31 is preferably a pressure-actuated valve for maintaining a substantially constant pressure in the furnace generally designated 10. It is seen that in the heat exchanger 29, heat from the gas passing through conduit 28 is transferred to a pipe or conduit 33 which supplies the input to the arc heater 23, conduit 33 being connected to receive the output of the compressor 34 connected to inlet pipe 35. Inlet pipe 35 may be used if air is to be drawn into the system or if a desired gas has to be pressurized by means of compressor 34. Alternately, if compressed gas available in cylinders or from other sources is to be heated in the arc heater, compressor 34 may be eliminated.

It is seen that the furnace generally designated 10 has a temperature sensing device 37 with a temperature responsive element 38 disposed in the furnace 10. The temperature sensing device 37 supplies an output by Way of leads 41 and 42 to the power supply 43 which controls the power input to the arc heater. The temperature sensing device 37 accordingly is connected to automatically control the power input to the arc heater 23 to thereby maintain a constant predetermined gas temperature in the furnace 10. It will be readily understood that, in accordance with the rate of flow of gas or gases through the furnace, the temperature sensing device may be readjusted or reset to maintaina predetermined temperature, and the temperature sensing device and power supply 43 are understood to include means, not shown for convenience of illustration, for varying the temperautre which is tobe maintained within the furnace 10.

In the operation of the apparatus of FIG. 1, gas enteringinlet pipe 35, after compression at 34 and being preheatedby passing through the heat exchanger 29 is further heated in the arc heater 23. The operation of gas are heaters is well known and need not be described herein in detail. For a fuller understanding of the manner in which electrical energy is directly converted to heat energy in an arc heater, reference may be had to Patent No. 3,048,736 entitled Arc Chamber by W. S. Emmerich, issued August 7, 1962 and assigned to the assignee of the instant invention. The heated gas from are heater 23 passes through the nozzle 19 into the injection or aspirator system where it mixes with the colder gas, which may include gas supplied from source 26, and induces the required flow velocity in the main heating loop including the furnace having the chamber 11. Proportional mixing of the high temperature gas from the arc heater and the other gas in the system will determine the furnace temperature. Material to be heated, illustrated generally at 13, is located in the furnace. The major portion of the gas will recycle due to the aspiration effect and will again be mixed with and heated by the gas from nozzle 19, the arc heater output. A pressure actuated valve 31 regulates the system by enabling some, or a small portion, of the gas to escape or be exhausted through a heat exchanger, thus preheating the gas being compressed into the arc heater. Due to the presence of the heat exchanger, less electrical input will be required to raise the gas to the required temperature, thus increasing the system efficiency. The temperature sensing device 37 including temperature sensing element 38 controls the input power to the are heater 23 to achieve proper operating conditions. Preferably the furnace and if desired the entire recycling system has either brick lining, not shown for convenience of illustration, or Water cooling, not shown for convenience of illustration, depending upon the operating temperature, any convenient arrangement being suitable.

It is seen, then, that the apparatus of FIG. 1 provides an integrated system for heating metals for tempering, annealing, melting or reducing, and provides an integrated system for any process requiring heated gas flow. The apparatus and system of FIG. 1 provide complete control of the atmosphere of the heating process, and in the semi-closed loop system of FIG. 1, the arc heater provides suificient action to maintain the gas flow. The need for blowers and compressors in the high temperature loop is thereby eliminated.

The apparatus of FIG. 1 is suitable for practicing the method of our invention, defined and claimed hereinafter, for establishing and maintaining an atmosphere controlled as to pressure, temperature, gas composition, and rate of gas flow.

Particular reference is made now to FIG. 2, which shows closed loop apparatus according to our invention. The apparatus of FIG. 2 differs from that of FIG. 1 in that outlet pipe 30', corresponding to outlet pipe 30 of FIG. 1, supplies an input to a precooler 51, of any convenient design, which supplies an output by way of conduit 52 to a dust separator or other filter 53, the output of the dust separator or filter 53 being connected to the aforementioned input pipe, in this case pipe 35', supplying an input to the compressor 34.

In the apparatus of FIG. 2, gas discharge from the heat exchanger 29 is recycled through the compressor. Otherwise the operation of the apparatus of FIG. 2 is similar to the aforedescribed operation of the apparatus of FIG. 1.

In the apparatus of FIG. 2, where gas is supplied from source 26 to provide a mixture in furnace 10, a small portion of gas may be bled from the closed loop by bleeder 61 controlled by valve 62 to assist in maintaining constant pressure in the closed path and furnace. The system may be initially charged with gas or gases through valve 66.

Pressure level in the furnace in either embodiment can be of any desired level, including atmospheric pressure, which facilitates the charging operation.

Where air, or only one gas, is to constitute the atmosphere, inlet pipe 25 and source 26 may be omitted. Also, a gas mixture containing gases in desired ratio of composition, may be admitted to inlet pipes 35 and 35'. Particular reference is made now to FIG. 3. A simplified configuration utilizing an arc heater may consist of a chamber 70 into which the discharge from the nozzle 75 of the arc heater 71 is suitably directed to mix the gas volume in this chamber so as to obtain the desired pressure, temperature uniformity, and gas composition in that part of the chamber where heating or heat treatment is to occur. Material to be treated is symbolized at 74. Temperature sensing can be as shown in FIG. 1. Excess gas removal from this chamber and pressure control can be accomplished by a vent 72 located at any convenient location. Gas inside the chamber follows the path indicated at 73.

Whereas we have shown and described three new and novel embodiments of apparatus suitable for practicing the methods of our invention, it will be understood that changes may be made and equivalents substituted without departing from the spirit and scope of the invention.

We claim as our invention:

1. Arc heater loop apparatus suitable for heating of metals in tempering, annealing, melting or reducing processes or processes requiring heated gas flows comprising, in combination, an arc heater having a gas input and a gas output, electrical circuit means connected to the arc heater for bringing a potential thereto to form the arc and including means for regulating the power of the arc heater, furnace means including means forming a closed path, means including nozzle means for bringing the heated gas from the gas output of the arc heater and injecting the heated gas into the closed path, the means forming a closed path including chamber means adapted to have the metal to be heated placed therein, a temperature sensing device operatively connected to the chamber means for sensing the temperature therein, the temperature sensing device being operably connected to the means for controlling the power to the arc heater, exhaust conduit means connected to the furance means at a predetermined position for exhausting gas from the furnace means at a predetermined pressure and at a predetermined rate of flow to maintain the pressure and the rate of gas flow in the furnace means substantially constant, and means including compressor means and heat exchanger means connected to the input of the arc heater to supply gas thereto, the heat exchanger means being connected to the exhaust conduit means whereby the heat of gas exhausted from the furnace means preheats gas supplied as an input to the arc heater.

2. Arc heater loop apparatus for providing an atmosphere controlled as to pressure, temperature, gas content and rate of gas flow and suitable for use in metal treating apparatus comprising, in combination, an arc heater,

' circuit means including power regulating means connected to the arc heater for providing an arc of variable intensity therein, means including compressor means for supplying a compressed gas input to the arc heater, the

arc heater heating gas passing therethrough to a predetermined temperature in accordance with the power supplied thereto, furnace means including means forming a closed path and having a throat portion and having a chamber therein, a nozzle disposed in the closed path forming means near the throat portion thereof and connected to the arc heater to receive the heated gas therefrom, means for bringing an additional gas into the furnace means obliquely to the gas from the nozzle means to provide a well-mixed gas mixture in the furnace, the chamber being adapted to have the metal to be heated placed therein, means for sensing temperature variations in the gas in the chamber, the means for sensing temperature variations being connected to the power regulating means and automatically regulating the power to the arc heater in accordance with the temperature of the gas in the chamber, a major portion of gases passing through the chamber being recycled therethrough, and means for exhausting a predetermined minor portion of gas from the path forming means at a predetermined Cir pressure and at predetermined rate of flow to maintain the pressure and the rate of gas flow in the furnace means substantially constant.

3. Are heater loop apparatus according to claim 2 including in addition heat exchanger means having the gas which is exhausted from the closed path supplied thereto, the compressed gas passing through the heat exchanger prior to entry into the arc heater, precooler means connected to the heat exchanger to receive the exhausted gas after passing through the heat exchanger, and dust separator means connected to the precooler means to receive the output therefrom, said compressor means being connected to the dust separator means to receive the output therefrom.

4. Arc heater loop apparatus comprising, in combination, an arc heater having an energizing circuit, means for supplying compressed gas at a predetermined pres sure and rate of flow to the arc heater, furnace means including means forming a closed loop for the recycling of gas through the furnace means, means for supplying the heated gas output of the arc heater to the closed loop, the major portion of the gas in the closed loop being recycled through the furnace means, means for admitting an additional gas into the closed loop at a predetermined rate of flow to provide a gas mixture having substantially constant proportions, and means for removing a predetermined minor portion of gas from the closed loop at a predetermined pressure and rate of flow to maintain the pressure and rate of gas flow in the furance means substantially constant.

5. Arc heater loop apparatus comprising, in combination, an arc heater having an energizing circuit, means for supplying compressed gas at a predetermined pressure and rate of flow to the arc heater, furnace means including means forming a closed loop for the recycling of gas through the furnace means, means for supplying the heated gas output of the arc heater to the closed loop, the major portion of the gas in the closed loop being recycled through the furnace means, means for removing a predetermined minor portion of gas from the closed loop at a predetermined pressure and rate of flow to maintain the pressure and rate of gas flow in the furance means substantially constant, and heat exchanger means connected in the means for removing gas from the closed loop, the heat exchanger means being connected to the means for supplying compressed gas to the arc heater whereby the heat from gas removed from the closed loop preheats the compressed gas prior to its admission to the arc heater.

6. Arc heater loop apparatus comprising, in combination, an arc heater having an energizing circuit, means for supplying compressed gas at a predetermined pressure and rate of flow to the arc heater, furnace means including means forming a closed loop for the recycling of gas through the furnace means, means for supplying the heated gas output of the arc heater to the closed loop, a temperature sensing device disposed in the furnace means, controllable means in the energizing circuit for the arc heater for adjusting the power to the arc heater to thereby regulate the temperature of the gas heated in the arc heater, means connecting the controllable means to the temperature sensing device whereby variations in temperature in the furnace means automatically regulate the power to the arc heater and there- -by regulate the temperature to which the gas is heated therein, the major portion of the gas in the closed loop being recycled through the furnace means, and means for removing a predetermined minor portion of gas from the closed loop at a predetermined pressure and rate of flow to maintain the pressure and rate of gas flow in the furnace means substantially constant.

7. Arc heater loop apparatus comprising, in combination, an arc heater having an energizing circuit, means for supplying compressed gas at a predetermined pressure and rate of flow to the arc heater, furnace means including means forming a closed loop for the recycling of gas through the furnace means, means for supplying the heated gas output of the arc heater to the closed loop, the major portion of the gas in the closed loop being recycled through the furnace means, means for removing a predetermined minor portion of gas from the closed loop at a predetermined pressure and rate of flow to maintain the pressure and rate of gas flow in the furnace means substantially constant, means for precooling and filtering that portion of gas removed from the closed loop, means for compressing the filtered gas, and means for applying the filtered gas to the arc heater as a portion of the compressed gas supplied thereto.

8. Are heater loop apparatus comprising, in combination, an arc heater having an energizing circuit, means for supplying compressed gas at a predetermined pressure and rate of flow to the arc heater, furnace means including means forming a closed loop for the recycling of gas through the furnace means, means for supplying the heated gas output of the arc heater to the closed loop, the major portion of the gas in the closed loop being recycled through the furnace means, means for admitting at least a second gas to the closed loop at a predetermined rate of flow, the second gas being admitted at an angle oblique to the flow of gas from the arc heater to thereby provide a well-mixed gas mixture having a predetermined substantially constant ratio of composition, and means for removing a predetermined minor portion of gas from the closed loop at a predetermined pressure and rate of flow to maintain the pressure and rate of gas flow in the furnace means substantially constant.

References Cited UNITED STATES PATENTS 1,896,910 2/1933 Merkt -1 -l. l58--1 2,252,319 8/1941 Holden 263'-14 2,504,320 4/ 1950 Gamble 263-43 2,639,910 5/1953 Cone et al. 263l5 3,010,009 11/1961 Ducati 2l9112 3,029,635 4/1962 Fetz 219-121 RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner.

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