EJECTOR APPARATUS OF FLUIDIZED BED HEAT-TREATING FURNACE

Abstract: Ejector appts. for a fluidised bed heat-treating furnace for heat-treatment of a work A put into a fluidised bed (2) by circulating an exhaust gas at the upper layer portion of a retort (1) driven by a compressed gas and enclosing therein the fluidised bed (2) from the bottom of the retort (1) to its inside to fluidise the fluidised bed. The main body of the ejector consists of at least three members and at least two systems of compressed gases are supplied to contracting portions from compressed gas inlets defined between the ejector members through gaps formed between the ejector members. The gap of each ejector member can be adjusted. The absorption efficiency of the ejector can be freely adjusted over a wide range.

Description: This invention relates to an ejector apparatus for a fluidized bed type heat treatment furnace. Hitherto, various kinds of fluidized bed type heat treatment furnaces in which steel or the like metallic material workpieces are subjected to heat treatment using a fluidized bed including a number of fluidizing particles of alumina or the like material have been proposed (for example, refer to official gazettes of Japanese Patent Application NO. 53434/1984 and Japanese Utility Model Application No. 12604/1985). Figure 4 of the accompanying drawings schematically illustrates one example of the conventional fluidized bed type heat treatment furnaces. Workpieces c to be heat treated are put in a fluidized bed a accommodated in a retort b, and the fluidized bed a is heated up to a heat treatment temperature under the effect of heat generated in a heating chamber d which surrounds the outer periphery of the retort b. The upper part of the retort b is connected to the bottom thereof via piping f extending therebetween. An ejector e is disposed in the piping f. Exhaust gas generated in the upper part of the retort b is introduced into the interior of the retort b from the bottom thereof via the ejector e to activate the fluidized bed a whereby the workpieces c are heat treated. In a case where workpieces c are subjected to carbonizing treatment using alcohol in the fluidized bed type heat treatment furnace as described above, alcohol is delivered to the piping f downstream of the ejector e from an alcohol tank g and it is then introduced into the interior of the retort b along with exhaust gas so as to allow the fluidized bed a to be activated. To this end there has been heretofore used for the ejector e an ejector apparatus as shown in Figure 5 of the accompanying drawings which is a sectional view illustrating important components. Specifically, a tapered centre rod g is disposed along the centre axis of an ejector body e' to form a throttle portion h between the ejector body e' and the centre rod g. The ejector e has an inlet port k at a position located upstream of the throttle portion h so as to permit compressed gas or air (hereinafter referred to simply as compressed gas) to be introduced into the throttle portion h via the inlet port k. As the compressed gas is introduced into the throttle portion h through the inlet port k, flow of the exhaust gas into the ejector e via an exhaust gas inlet port i is accelerated so that the exhaust gas leaving an exhaust gas outlet port j is introduced into the interior of the retort b to repeatedly circulate through the retort. The flow rate of the exhaust gas can be adjusted by varying the pressure of the compressed gas flowing via the inlet port k. When the workpieces c are subjected to carbonizing treatment in the presence of alcohol using the conventional ejector e as constructed in the above-described manner, carbon present in alcohol tends to be adhesively deposited on the inner wall surface of the piping f and the inner wall surface of the ejector e thereby to hinder the flow of the exhaust gas. As a result, there arise problems that activating of the fluidized bed a is degraded and absorptive efficiency is reduced. As the piping f having the ejector e therein is expanded or contracted under the influence of differential temperature appearing across the ejector e, a large magnitude of force is exerted on a nut m that is provided for the adjustment of the width of a gap at the compressed gas inlet port k. This causes the gap to be varied, resulting in the absorptive efficiency being adversely affected. Another problem is that since compressed gas to be introduced into the ejector e flows through a single system line, the result is that the adjustment range is narrow and thereby effective suction over a wide flow rate range cannot be achieved. Additionally, a further problem is that since the centre rod g is disposed along the centre line of the ejector body e', the ejector e itself has to be designed in large dimensions and constituted by many components, and hence is expensive to manufacture. In Chemical Engineers Handbook, Fifth Edition, R.H. Perry, McGraw-Hill Book Company with reference to Fig. 6-31 on page 6-16 there is described an ejector apparatus including an ejector body divided into three members of which two internal members are screwed to the third external member and which define a plurality of throttle portions in the interior of the ejector body, and gas introducing means comprising gaps between respective adjacent said members and compressed gas inlet ports communicating one with each gap, for introducing into said throttle portions compressed gases flowing through two system lines. According to the present invention there is provided an ejector apparatus for a fluidized bed type heat teatment furnace, including an ejector body divided into at least three members defining a plurality of throttle portions in the interior of the ejector body, and gas introducing means comprising gaps between respective adjacent said members and compressed gas inlet ports communicating one with each gap, for introducing into said throttle portions compressed gases flowing through at least two system lines wherein the ejector apparatus further includes, at each gap, threaded portions formed on respective outer peripheral surfaces of the adjacent ejector body members, one of these portions being threaded in the opposite direction to the other, and a nut threadably engaged with these adjacent threaded portions, whereby the gaps can be adjusted. In the accompanying drawings Figures 4 and 5 which have already been referred to are respectively a schematic view of fluidized bed type heat treatment furnace having a conventional ejector apparatus, and a sectional view of this conventional ejector apparatus. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to Figures 1 to 3 of the accompanying drawings, in which: Figure 1 is a circuit diagram for a fluidized bed type heat treatment furnace having an ejector apparatus in accordance with the present invention, Figure 2 is a sectional view of the ejector apparatus in accordance with the present invention, and Figure 3 is a front view of the ejector apparatus taken on line III- III in Figure 2. Referring now to Figure 1, reference numeral 1 designates a retort having a fluidized bed 2 accommodated therein which includes a heating chamber 3 round the periphery thereof. The upper part of the retort 1 is closed by a furnace cover 4 and workpieces A to be quenched are accommodated in the interior of the retort 1 by opening the furnace cover 4. The upper part of the retort 1 is connected to the bottom of the retort 1 via piping 6 extending therebetween which has an ejector 5 disposed in it so that exhaust gas generated in the upper part of the retort 1 is blown into the interior of the retort 1 from the lower part of the retort 1 in order to assure that the exhaust gas is repeatedly circulated through the retort 1. As shown in Figures 2 and 3, the ejector 5 includes an ejector body 5a which is divided into three separate members 7, 8 and 9. The ejector member 7 located on the upstream side as viewed in the direction of flow of exhaust gas has an exhaust gas inlet port 7a which is tapered inwardly in the direction from the upstream end of the ejector body 5a towards the interior of the body 5a, a threaded part 7b formed round the periphery of the inner downstream end of the member 7 and an annular recess 7c in the interior thereof and open in the direction towards the interior of the ejector body 5a. A nozzle 7d protrudes from the interior of the annular recess 7c to provide that the upstream inlet port 7a is open at the downstream end part of this nozzle 7d. The nozzle 7d is entered in a smaller diameter portion 8a formed on the upstream end of the middle ejector member 8 and removably inserted into the downstream end part of the member 7a. O-rings 10 adapted to come into tight contact with the inner peripheral surface of the annular recess 7c are fitted onto the outer peripheral surface of the smaller diameter portion 8a of the ejector member 8 to ensure gastightness between the ejector member 7 and the middle ejector member 8. In addition, a tapered portion 8b is formed on the inner peripheral surface of the smaller diameter portion 8a for adjustably forming a gap between the outer peripheral surface of the nozzle 7d and the inner peripheral surface of the smaller diameter portion 8a. The threaded portion 7b formed on the ejector member 7 is threaded in the opposite direction to a threaded portion 8c formed on the peripheral surface at the upstream end of the middle ejector member 8. A nozzle adjusting nut 11 is threadably engaged with both the threaded portions 7b and 8c so that the gap between the nozzle 7d and the tapered portion 8b is adjusted by rotating the nozzle adjusting nut 11 to adjust freely the quantity of compressed gas (or air) to be introduced from a compressed gas inlet port 12 into a throttle portion 8d of the ejector member 8. Thus, adjusting means F for adjusting the gap between the ejector members 7 and 8 is constituted by the threaded portions 7b and 8c and the nozzle adjusting nut 11 threadably engaged with these portions. The downstream side of the throttle portion 8d at the central part of the ejector member 8 is divergently formed so as to have a gradually increasing diameter in the direction away from the ejector member 7. The open end of the throttle portion 8d having an increased diameter communicates with the upstream end of a nozzle 8e at the downstream end of the ejector member 8. The nozzle 8e protrudes from the central part of an annular recess 8f which is open at the downstream end surface of the ejector member 8. The inner peripheral surface of a smaller diameter portion 9a on the upstream end of the ejector member 9 located downstream of the ejector member 8 is fitted onto the outer peripheral surface of the nozzle 8e. O-rings 13 are fitted onto the outer peripheral surface of the smaller diameter portion 9a to ensure gastightness between the middle ejector member 8 and the ejector member 9 located downstream of the member 8. A tapered portion 9a is formed to provide a freely adjustable gap between the inner peripheral surface of the smaller diameter portion 9a and the outer peripheral surface of the nozzle 8e. A threaded portion 8g on the outer peripheral surface of the downstream end of the ejector member 8 is threaded in the opposite direction to a threaded portion 9c on the outer peripheral surface of the upstream end of the ejector member 9. A nozzle adjusting nut 14 is threadably engaged with both the threaded portions 8g and 9c. The gap between the nozzle 8e and the tapered portion 9b can be adjusted by rotating the nozzle adjusting nut 14 whereby a quantity of compressed gas to be introduced from a compressed gas inlet port 15 into a throttle portion 9d of the nozzle member 9 can be adjusted as required. Thus, adjusting means G for adjusting the gap between the ejector members 8 and 9 is constituted by the thread portions 8g and 9c and the nozzle adjusting nut 14 threadably engaged with these threaded portions. A throttle portion 9d at the central part of the ejector member 9 has a diameter larger than that of the throttle portion 8d of the middle ejector member 8. The downstream side of the throttle portion 9d communicates with a gas outlet port 9f which is divergently formed to have a gradually increased diameter. To compensate the thermal contraction of the piping 6, the gas outlet port 9f is connected to the bottom of the retort 1 via a flexible tube 35, as shown in Figure 1. In Figure 2, reference numerals 16 designate guide pins fitted into the respective ejector members 7, 8 and 9 for preventing relative rotation between adjacent ejector members during rotation of each of the nozzle adjusting nuts 11 and 14. Further, in Figure 1, reference numerals 20 and 24 designate gas supply sources for gas to be processed. N₂ gas is supplied from the supply source 20, air is supplied from the supply source 21, CO₂ gas is supplied from the supply source 22, propane gas is supplied from the supply source 23 and ammonia gas is supplied from the supply source 24. Of these gases, N₂ gas and air are supplied to the two compressed gas inlet ports 12 and 15 on the ejector 5 (see Figure 2), in dependence upon the setting of a switching valve 37, via a flow meter 26 and flow rate adjusting valves 27₂ and 27₃ so that they are then supplied to the throttle portions 8d and 9d from the compressed gas inlet ports 12 and 15. A part of the gases is supplied to the upstream side of the ejector 5 via a solenoid valve 28. In addition, CO₂ gas is supplied to a location on the piping 6 situated downstream of the ejector 5 via a switching valve 38 and a flow meter 26; propane and ammonia gas are supplied to locations on the piping 6 downstream of the ejector 5 via flow meters 26 and solenoid valves 29 and 30; a part of air is supplied into the interior of the upper chamber in the retort 1 via a flow meter 26, a solenoid valve 44 and piping 31; and another part of air is supplied into the interior of an exhaust gas duct 33 via piping 32 including a sluice valve 46. The part of air which has been supplied to the exhaust gas duct 33 is used as combustion air when exhaust gas to be discharged from the retort 1 into the atmosphere is burnt by means of an afterburner 34 (to which propane gas can be supplied via a sluice valve 45) in order to reduce the amount of smelly ammonia in the exhaust gas to be discharged into the atmosphere. Operation of the fluidized bed type heat treatment furnace with the above-described ejector apparatus, and the structure thereof, will now be described in more detail. The fluidized bed 2 in the retort 1 receives heat generated in the heating chamber 3 so that it is heated up to a highest temperature of 1200°C. In a case where the atmosphere in the retort 1 is an environmental atmosphere, air of which the flow rate is adjusted by the flow rate adjusting valve 27₃ is supplied into the interior of the ejector body 5a through the compressed gas inlet port 15 on the ejector body 5a (see Figure 2) so that the ejector 5 is driven to repeatedly circulate the exhaust gas therethrough. Next, when the furnace cover 4 is opened and workpieces A to be heat treated are put in the retort 1, the solenoid valve 28 is opened in response to a signal transmitted from a limit switch 40 for detecting opening and closing of the furnace cover 4 and N₂ gas is then introduced into the upstream side of the ejector 5 by a quantity equal to or more than an amount of air to be sucked by the ejector 5. This prevents air from being sucked by the ejector 5. The workpieces A in the retort 1 are heated up to a heat treatment temperature by causing the fluidized bed 2 to be activated but the required amount of fluidized gas to be introduced into the interior of the retort 1 differs in dependence on the current temperature of the fluidized bed 2. Specifically, a large amount of fluidized gas is required when the fluidized bed 2 has a lower temperature. On the contrary, a small amount of fluidized gas is required when the fluidized bed 2 has a higher temperature. As long as the fluidized bed 2 is operated at a normal working temperature, the amount of compressed gas to be fed to the compression gas inlet port 12 on the ejector body 5a is adjusted by the flow rate adjusting valve 27₂ to maintain the predetermined working temperature. When the interior of the retort 2 is cooled, the flow rate adjusting valve 27₃ is additionally opened to increase the amount of fluidized gas. While the workpieces A are heat treated in the fluidized bed 2, the pressure of fluidizing gas is monitored by means of a pressure switch 41 disposed in the piping 6. If the value of detected pressure is increased higher than or decreased lower than a preset pressure for some reason, an emergency circuit which is not shown in the drawing is activated to interrupt feeding of combustible gas such as ammonia or the like and at the same time stop heating under the effect of heat generated in the heating chamber 3 whereby safety of the whole system is ensured. As shown in Figure 2, the ejector 5 is constituted by the three members 7, 8 and 9 and the gaps between the nozzles 7d and 8e and the tapered portions 8b and 9b can be freely adjusted by rotating the nozzle adjusting nut 11 between the members 7 and 8 and the nozzle adjusting nut 14 between the members 8 and 9. The gap on the nozzle 7d side is previously adjusted by means of the nozzle adjusting nut 11 in order to ensure that the ejector 5 is operated at a normal temperature while the fluidizing pressure is maintained, for example, in the range of 4 to 8 Kg/cm². Additionally, the gap on the nozzle 8e side is previously adjusted by means of the nozzle adjusting nut 14 in order to assure that the ejector 5 is properly operated when the fluidizing pressure is maintained, for example, in the range of 4 to 8 Kg/cm² and the temperature in the furnace is cooled down to a level of about 50°C. In a case where the workpieces A are subjected to carbonizing, N₂ gas is introduced into the ejector 5 and the piping 6 by actuating the switching valve 37 and air is introduced by activating the solenoid valve 29 so that the resultant gas mixture is caused to flow in the interior of the retort 1. Air is introduced into the upper chamber above the fluidized bed 2 by opening the solenoid valve 44. It should be noted that air introduced into the upper chamber in the retort 1 is intended to burn carbonizing gas to prevent carbon from being adhesively deposited on a filter 43. Next, to prevent exhaust gas from being sucked by the ejector 5 while the above operative state is maintained, N₂ gas is supplied to the ejector 5 by opening the solenoid valve 28. This causes the interior of the ejector 5 to be gas sealed in the presence of N₂ gas whereby undesirable reduction of the absorptive efficiency, due to adhesion of carbon or the like present in exhaust gas to the interior of the ejector 5, can be prevented reliably. In a case where the workpieces A are subject to nitriding, N₂ gas is supplied to the piping 6 from the supply source 20 by opening the switching valve 37, CO₂ gas is supplied to it from the supply source 22 by opening the switching valve 38 and ammonia is supplied to it from the supply source 24 by opening the solenoid valve 30, whereby the resultant gas mixture is caused to flow into the interior of the retort 1 so as to allow the fluidized bed 2 to be activated to perform nitriding treatment. At this moment, sluice valves 45 and 46 are opened so that propane and air are introduced into the exhaust duct 33 in order to remove smelly ammonia by burning the exhaust gas to be discharged in the atmosphere from the exhaust duct 33, by operating the afterburner 34. When ammonia reacts with CO₂ gas at a temperature in the range of 80 to 100°C, ammonium carbonate salt is produced in the form of powder. Since production of such salt could cause the piping 6 to be clogged with it, there is a need to take proper measures for ensuring that the temperature of the gas mixture is not maintained within this range. In view of the fact, as mentioned above, that the present invention is carried out in accordance with the illustrated embodiment in which CO₂ gas and ammonia are separately introduced into the piping 6, this embodiment ensures that an occurrence of malfunction such as clogging of the piping 6 with ammonia carbonate salt produced therein is prevented. As described above, the present invention provides an ejector apparatus wherein an ejector body is divided into three members and gaps between adjacent members are adjusted as required by means such as nozzle adjusting nuts which serve to joint the adjacent members together. This arrangement makes it possible to adjust quantities of compressed gases flowing through two system lines by actuating the nozzle adjusting nuts or the like means and thereby adjust over a wide range quantities of compressed gases to be introduced into the ejector apparatus, resulting in suction of the compressed gases being achieved at a high efficiency. Further, according to the present invention, there is no need to place a centre rod along the centre axis of the ejector body as is the case with a conventional ejector apparatus. This enables the ejector body to be designed and constructed in small dimensions in a simple manner whereby the ejector apparatus can be easily manufactured and produced at an inexpensive cost. When N₂ gas or the like is introduced into the ejector during heat treatment to gas seal the interior of the ejector, carbon or the like foreign material involved in exhaust gas is not adhesively deposited on the inner wall surface of the ejector body and thereby reduction of the absorptive efficiency does not occur. In addition, owing to the interposition of a flexible tube between the retort and the ejector, a large magnitude of outer force is not exerted on the ejector under the influence of thermal expansion of the piping connected thereto. This ensures that an occurrence of such a malfunction that the absorptive efficiency is adversely affected by variation of the gaps which have been previously adjusted can be prevented reliably. It should of course be understood that the present invention should not be limited only to the embodiment which has been described above with reference to the accompanying drawings but various changes or modifications may be suitably made within the scope of the present invention as defined by the appended claims.

Claims: An ejector apparatus for a fluidized bed type heat treatment furnace, including an ejector body (5a) divided into at least three members (7,8,9) defining a plurality of throttle portions in the interior of the ejector body, and gas introducing means comprising gaps between respective adjacent said members (7,8,9) and compressed gas inlet ports (12,15) communicating one with each gap, for introducing into said throttle portions compressed gases flowing through at least two system lines wherein the ejector apparatus further includes, at each gap, threaded portions (7b,8c, or 8g,9c) formed on respective outer peripheral surfaces of the adjacent ejector body members (7,8,9), one of these portions (7b or 8g) being threaded in the opposite direction to the other (8c,9c), and a nut (11 or 14) threadably engaged with these adjacent threaded portions (7b,8c, or 8g,9c), whereby the gaps can be adjusted.

Inventors: HANADA YOICHIRO, HATTORI HISASHI, TAKENOSHITA HIDEMITSU, HANADA, YOICHIRO, HATTORI, HISASHI, TAKENOSHITA, HIDEMITSU
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1988
Main classification: C21D1
IPC codes: C21D1, F27B15, F04F5