High-Temperature Furnace with a Graphite Heating Tube
Abstract Generated abstract
This article describes the design and testing of a laboratory high-temperature furnace using a graphite tubular heater. Its main focus is the heater fastening assembly, which uses spring-loaded conical cast-iron bushings in brass current-carrying electrodes to provide reliable electrical contact, water-cooled contact zones, and easy heater replacement. The furnace incorporates two-zone thermal insulation, nitrogen protection against oxidation, optional vacuum operation, temperature observation by thermocouple or optical pyrometer, and a transformer-based power circuit for smooth regulation. Test data are reported for several power levels, indicating controllable heating rates and operation at specified temperature regimes within narrow limits.
Full Text
P. G. Usov, A. S. Bogma
HIGH-TEMPERATURE FURNACE WITH A GRAPHITE HEATING TUBE
(Presented by the scientific seminar of the Department of General Chemical Technology)
The developed design of a laboratory furnace with a graphite heating tube (Fig. 1) is in principle analogous to furnaces described in the technical literature [1, 2]. The main difficulty in designing this type of furnace is fastening the heater, a matter that is not entirely clearly reflected in the literature sources. This article is devoted to the development and description of the fastening assembly for the heating tube, and to the design and testing of the furnace.
The ends of the graphite tubular heater 1 are fastened in current-carrying brass disk-shaped electrodes 2 by means of conical spring-loaded (with a slit in one place) cast-iron bushings 3. Good contact is thereby ensured by pressing the bushings into the conical holes of the electrodes with clamping nuts 4 through rings 5 made of refractory material. To avoid overheating of the tube at the points of contact with the electrodes, water cooling is provided in the cover 6 and in the bottom 7 of the furnace.
The entire space between the heater 1 and the metal furnace body 8 is filled with thermal insulation, divided by a magnesite tube 9 into two zones. The inner zone 10 consists of charcoal in the form of granules (2–3 mm) and, as it burns out, is replaced when the heating tube is changed. The outer stationary insulation 11 is made of foam-fireclay brick.
To create a protective atmosphere against intensive oxidation of the heater, technical nitrogen is used; it is supplied to the working space of the furnace through branch pipe 12 and discharged in the lower part through branch pipe 13. The furnace is hermetically sealed and can operate under vacuum; for ease of operation it is made rotatable.
The temperature in the furnace can be measured with a high-temperature thermocouple or with an optical pyrometer through the sighting heat-resistant glass 14.
The electrical circuit for supplying power to the furnace (Fig. 2) provides smooth temperature control. In the power circuit of the resistance furnace 3, supply is provided by a regulating autotransformer 1 of the AOMK—100/0.5 type and an internal transformer 2 of the OSU 80/0.5 type.
Principal dimensions of the furnace
Height of the furnace — 500 mm.
Diameter of the furnace body — 330 mm.
Height of the heating tube — 250 mm.
Fig. 1. Schematic of a high-temperature furnace:
1—graphite tubular heater; 2—brass electrodes; 3—cast-iron bushings; 4—clamping nuts; 5—rings of refractory material; 6—furnace cover; 7—furnace bottom; 8—metal furnace shell; 9—magnesite tube; 10—charcoal zone; 11—foam-fireclay brick zone; 12—branch pipe for nitrogen inlet; 13—branch pipe for gas outlet; 14—sight glass.
Fig. 2. Electrical circuit for powering the furnace: 1—autotransformer of type AOMK—100/0.5; 2—internal transformer of type OSU—80/0.5; 3—resistance furnace.
The rate of temperature rise can be set arbitrarily. Some data from furnace tests are given in Table 1 and in Fig. 3.
Table 1
| No. | Power, kW | Voltage at the heater terminals, V | Current in the transformer secondary circuit, A | Cooling-water consumption, l/h |
|---|---|---|---|---|
| 1 | 1.8 | 3.0 | 600 | 300 |
| 2 | 3.4 | 4.0 | 850 | 320 |
| 3 | 5.25 | 5.0 | 1050 | 320 |
| 4 | 7.5 | 6.0 | 1250 | 370 |
| 5 | 12.8 | 8.0 | 1600 | 390 |
Fig. 3. Temperature-rise curves versus time as a function of the power consumed:
\(N_1\)—1.8 kW; \(N_2\)—3.4 kW; \(N_3\)—5.25 kW; \(N_4\)—7.5 kW; \(N_5\)—12.8 kW.
The described fastening of the heating tube is comparatively simple and reliable, provides good electrical contact, and allows the heater to be replaced easily. The electrical circuit makes it possible to operate at any specified temperature regime within very narrow limits.
REFERENCES
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V. S. Veselovskii, I. V. Shmanenkov, E. V. Nosachev. Heating Devices in Laboratory Practice. 5th ed., Goskhimizdat, 1951.
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S. G. Tresvyatskii, V. V. Gribkov, P. L. Volodin, K. M. Serov. High-temperature vacuum furnaces for firing highly refractory materials. Ogneupory, No. 7, 1960.