Refuse melting furnace

Abstract: A rectangular type of refuse melting furnace (11) comprises a furnace body (12) with a rectangular horizontal cross section, a furnace cover (13) fixed on the top of the furnace body, and refuse heating elements (21) disposed vertically through the furnace cover, and characterized by having a hearth (12a) shaped into a reversed arch as viewed from the shorter sides of said furnace body. Arc discharging electrodes (21), electric resistance heating electrodes, or plasma torches, for example, may be used as refuse heating elements. The heating elements (21) are arranged along a longitudinal centerline of the furnace cover at predetermined intervals. Also, refuse inlets (22) are made through the furnace cover, and are located between the heating elements. One of the longer sides of the furnace body is provided with discharge ports (41) of molten slag (B), while one of the shorter sides of the furnace body is provided with a discharge port (42) of molten metal (A) which is located at a lower position than the discharge ports of molten slag.

Description: This invention relates to a refuse melting furnace, and more particularly to a rectangular type of refuse melting furnace. A refuse melting furnace with a heat source such as arc discharging electrodes, electric resistance heating electrodes, or plasma torches is used to melt ashes of burnt refuse or industrial wastes containing combustible and incombustible substances and metals. There are two major types of such furnaces, namely a circular furnace and a rectangular furnace. To be more exact, one has a circular horizontal cross section, and the other has a rectangular horizontal cross section. Recently rectangular furnaces have been more widely used than circular ones because the former are easier to increase in volume and to maintain, and have a higher melting efficiency as well. The present invention accordingly relates to an improvement in a rectangular refuse melting furnace. A conventional rectangular refuse melting furnace is disclosed in Japanese Patent Publication Tokkai 61-213510 where a melting furnace comprises a rectangular box-shaped body, a cover fixed on the top of the body, and plural arc discharging electrodes extending vertically through the cover. With the convention furnace, however, the hearth, which is formed of firebricks, is of a flat construction. In other words, the firebricks to form the hearth are so arranged as to make up a horizontal plane. Thus, the hearth is apt to be damaged. Also much molten metal is apt to remain on the hearth. In addition, with the conventional furnace, both molten slag and molten metal are discharged from one and the same discharge port and, hence, the two must be separated magnetically or otherwise in order to be able to reutilize the discharged substances as effective materials. With the flat hearth, molten metal produced as the refuse is melted passes into the small openings between the firebricks which form the hearth, and then solidifies. Thereupon, the solidified metal more or less lifts those firebricks out of place, with the result that the surface of the hearth becomes uneven. Also, due to the unevenness of the hearth, much molten metal may remain on the hearth. Repairing such a hearth is very difficult, because the metal exists on it or between the firebricks in solidified state. Attention is also drawn to the disclosures of US-A-4773630 and US-A-4697532. The present invention aims to provide a rectangular type of refuse melting furnace which overcomes the difficulties associated with the prior art. The present invention provides a rectangular type of refuse melting furnace, which comprises a furnace body with a rectangular horizontal cross section having two longer sides and two shorter sides, a furnace cover fixed on the top of said furnace body, and refuse heating elements (such as are discharging electrodes, electric resistance heating electrodes, or plasma torches) disposed vertically through said furnace cover, and a hearth having a downwardly-curved transverse cross section as viewed from shorter sides of said furnace body; wherein said refuse heating elements are arranged along a longitudinal centreline of said furnace cover at predetermined intervals, and refuse inlets are located through said furnace cover between said refuse heating elements; and wherein one of the longer sides of said furnace body is provided with discharge ports for molten slag, and one of the shorter sides of said furnace body is provided with a discharge port for molten metal which is located in close proximity to the downwardly curved hearth and being substantially centralised with respect to the transverse direction of said furnace body, characterised in that said discharge port for molten metal is defined by an upper end portion of a stream barrier by overflow and a discharge opening for molten metal is located in the stream barrier, and in that said upper end portion of said stream barrier is located at a lower position than said discharge ports for molten slag and said discharge opening is located adjacent the lowest position of the hearth. The refuse heating elements are preferably electrodes or plasma torches, and in particular the said electrodes may be arc discharging electrodes for electric resistance heating electrodes. With the invention, molten slag and molten metal are not discharged from one and the same discharge port, but discharge ports for the two different molten substances are provided separately. Refuse inlets and an exhaust gas vent are made through the furnace cover. The refuse heating elements are arranged at predetermined intervals along a longitudinal centreline of the furnace cover. The refuse inlets are located between the heating elements, because by so doing the refuse put into the furnace can be effectively heated from opposed sides. As for the discharge ports for molten slag, more than one are provided on one of the longer sides of the furnace body at a predetermined interval, so that one of the discharge ports can be used when the other is repaired. As for the discharge port for molten metal, it should be provided on one of the shorter sides of the furnace body at a position lower than the discharge ports for molten slag. Moreover, it is required that the discharge port for molten metal be located in close proximity to the downwardly-curved hearth and be substantially centralised with respect to the transverse direction of the furnace body, in order to smoothly let the molten metal out from the furnace. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a refuse melting furnace which embodies the invention in one preferred form; Fig. 2 is a vertical, transverse cross section of the furnace; and Fig. 3 is a vertical, longitudinal cross section of one end portion of the furnace. A refuse melting furnace 11 which embodies the invention in one preferred form will now be described in detail with reference to the drawing. The furnace 11 includes a furnace body 12 and a cover 13 fixed on the top of the furnace body 12. As may be appreciated from Fig. 1, the furnace body 12 has a rectangular horizontal cross section. As shown in Fig. 1, a total of six arc discharging electrodes 21 are arranged at regular intervals along a longitudinal centreline of the cover 13. It will be appreciated, however, that electric resistance heating electrodes or plasma torches may be used instead of the arc discharging electrodes. As clearly shown in Figs. 2 and 3, the electrodes 21 are disposed vertically through the cover 13. Between the electrodes 21 are located refuse inlets 22 which are made through the cover 13 (Fig. 1). In addition, an exhaust gas vent 23 is made through the cover 13 (Fig. 1). As clearly shown in Figs. 2 and 3, the furnace body 12 includes a furnace shell 31 lined with firebricks 33. Refractories 32 are provided between the furnace shell 31 and the firebricks 33. Reference numeral 33a designates those of the firebricks 33 that form a hearth 12a. As clearly illustrated in Fig. 2, the hearth 12a has a downwardly - curved transverse cross section as viewed from the shorter sides of the furnace body 12. Two discharge ports 41 for molten slag are connected to one of the longer sides of the furnace body 12, and are spaced apart from each other by a predetermined distance (Figs. 1 and 2). On the other hand, one of the shorter sides of the furnace body 12 is provided with a discharge port 42 for molten metal (Figs. 1 and 3). This port 42 is located at a lower position than the discharge ports 41 for molten slag. Also, as shown in Fig. 3, the port 42 is located on an extension to the lowest portion of the hearth 12a. In addition, the discharge port 42 for molten metal is defined by a stream barrier 42a projecting upwardly from the end of the foregoing extension and by a counter barrier 12b extending transversely for a certain distance along one of the shorter sides of the furnace body 12 so as to separate molten slag and molten metal. Thus, the molten metal A comes out from the furnace 11 by overflowing from the discharge port 42. Also, the stream barrier 42a is provided with a discharge opening 42b from which the molten metal A can be discharged deliberately when necessary. As described above and as clearly illustrated in the drawing, the hearth 12a has a downwardly-curved transverse cross section. Of the firebricks 33a (to form the hearth 12a), therefore, the higher ones (those firebricks that are in higher positions) act to press against the lower ones, with the result that openings between the firebricks 33a, if any, are very small, compared with the openings between the firebricks to make up the flat hearth of the conventional rectangular type of melting furnace. In addition, with the curved hearth 12a, should the molten metal pass into the openings between the firebricks 33a and solidify, there would be little possibility that the firebricks 33a may be lifted out of place. For this reason, there is little danger of the surface of the hearth 12a becoming uneven and, hence, little danger of that surface being damaged. Also, for the same reason, there is little possibility that much molten metal may remain on the hearth 12a. Moreover, with the invention, since molten slag and molten metal are discharged from different ports, a subsequent separation of them is not required for reutilizing them as effective materials. They can be reutilized as such as they are.

Claims: A rectangular type of refuse melting furnace (11), which comprises a furnace body (12) with a rectangular horizontal cross section having two longer sides and two shorter sides, a furnace cover (13) fixed on the top of said furnace body, and refuse heating elements (21) disposed vertically through said furnace cover, and a hearth (12a) having a downwardly-curved transverse cross section as viewed from shorter sides of said furnace body; wherein said refuse heating elements are arranged along a longitudinal centerline of said furnace cover at predetermined intervals, and refuse inlets (22) are located through said furnace cover between said refuse heating elements; and wherein one of the longer sides of said furnace body is provided with discharge ports (41) for molten slag (B), and one of the shorter sides of said furnace body is provided with a discharge port (42) for molten metal (A) which is located in close proximity to the downwardly curved hearth and being substantially centralized with respect to the transverse direction of said furnace body, characterised in that said discharge port (42) for molten metal (A) is defined by an upper end portion of a stream barrier (42a) by overflow and a discharge opening (42b) for molten metal (A) is located in the stream barrier (42a), and in that said upper end portion of said stream barrier (42a) is located at a lower position than said discharge ports (41) for molten slag (B) and said discharge opening (42b) is located adjacent the lowest position of the hearth (12a). A rectangular type of refuse melting furnace as claimed in claim 1, characterized in that the said refuse heating elements are electrodes or plasma torches. A rectangular type of refuse melting furnace as claimed in claim 2, characterized in that said electrodes are arc discharging electrodes (21) for electric resistance heating electrodes.

Inventors: KINTO KOUICHIRO, KINTO, KOUICHIRO
Applicants: DAIDO STEEL CO LTD, DAIDO TOKUSHUKO KABUSHIKI KAISHA
Application year: 1993
Main classification: F23G5
IPC codes: F23J1, C03B5, F23G5, B09B3, F27B3