Coal combustor and slag-exhausting device therein

Abstract: In order to stably maintain a combustion capability in a combustion furnace for coal gassification purpose, it is necessary to stably exhaust molten slag produced within the furnace so as not to be stagnated. The present invention provides a combustion furnace for coal gassification purpose, which is constructed in such manner that cooling of molten slag exhausted from a combustion furnace for coal gassification purpose may be minimized and thereby the molten slag produced in the combustion furnace may be stably exhausted. A slag exhausting device (1) is disposed at the center of a bottom portion (5) of a combustor (4), this slag exhausting device (1) has an upper bank (2) opened upwards with a flare angle (ϑ) of 30° - 45° and a cylindrical lower portion (3), and among a height (H) of the upper bank (2), a height (L) and a diameter (ds) of the cylindrical lower portion (3) and a diameter (D) of the combustor (4) are maintained the relations of ds/D = 0.2 - 0.4, L/ds = 0.2 - 0.6 and H/D = 0.05 - 0.15.

Description: BACKGROUND OF THE INVENTION: 1. Field of the Invention: The present invention relates to a coal combustor applicable to a coal gassification apparatus, a boiler or the like for business use and industrial use and a slag exhausting device therein. 2. Description of the Prior Art: At first, as one example of the prior art, description will be made on a construction of a coal combustor in an entrained bed coal gassification furnace and a slag exhausting device provided at the bottom portion of the coal combustor with reference to Fig. 5. Such coal combustors are disclosed e.g. in documents DE-A-1 040 734 ; DE-A-1 287 724 ; DE-A-2 552 077 and EP-A-0 241 866. A slag exhausting device 11 is disposed at the center of the bottom portion of a coal combustor 12, coal and char charged by burners 13 equipped along the circumferential direction of the combustor 12 at first produce combustion gas as a result of combustion, then produce combustible gas as a result of gassification, at the same time an ash content in the coal and char becomes molten slag, it is centrifugally separated from the gas by a swirl flow formed by burner jet flows 15, then adheres to a cylindrical wall surface of the combustor 12, flows down due to the gravity and accumulates at the bottom portion 16 of the combustor, and it is exhausted via this slag exhausting device 11 into a slag chamber 17 and towards a slag hopper 18 disposed thereunder. During this process, in order to facilitate exhaust of the molten slag 14 from the slag exhausting device 11, it is necessary to maintain the molten slag 14 flowing out at a temperature as high as possible. Although the molten slag 14 is held at a sufficiently high temperature and has a good fluidity (a low viscosity) at the bottom portion 16 of the combustor where the slag is subjected to strong radiation within the combustor 12, on the vertical surface of the slag exhausting device 11 the radiation becomes weak, hence the temperature of the molten slag 14 lowers, and a fluidity is degraded (a viscosity becomes high). Therefore, as a contrivance for preventing lowering of a temperature of the molten slag in the slag exhausting device, a structure for accumulating molten slag 14 and then making it flow down by providing a bank 19 and a gate 20 around a slag hole as shown in Fig. 5, was adopted. However, in the case where a circular hole (slag hole) is opened at the center (the center axis of a cylinder) of the bottom portion 16 of the combustor 12 in which a swirl flow is formed and thereby the combustor is connected with a slag chamber 17 thereunder, due to a pressure distribution along the radial direction within the combustor shown in Fig. 3 a descending flow flowing from the combustor 12 towards the slag chamber 17 is generated at the circumferential wall portion of the hole (region A) while an ascending flow flowing from the slag chamber 17 towards the combustor 12 is generated at the central portion of the hole (region B) as shown in Fig. 4. Consequently, high-temperature gas within the combustor 12 flows as a descending flow along the lower surface of a slag flow in the slag hole portion, and the molten slag is heated by the high-temperature gas. The prior art as described above involves the following problems: (1) At the bottom portion of the combustor 12, it becomes necessary to make molten slag flow out through the gate 20 only, and necessarily the bank 19 around the slag hole becomes high. Consequently the height of a vertical surface of the slag hole becomes high, hence radiation heat arriving at the vertical surface from the combustion region decreases, heat dissipated from the slag increases, and due to lowering of a slag temperature, a fluidity of the slag is degraded. (2) Furthermore, since increase of the height of the vertical surface of the slag hole would intercept the gas flow in the slag hole portion described in the preceding section, a flow rate of high-temperature gas flowing from the combustor towards the slag chamber 17 in the circumferential wall portion of the slag hole decreases, hence heating of the slag by the high-temperature gas is reduced, and so, a fluidity of the slag is deteriorated. (3) In the event that the above-described deterioration of a fluidity of slag is remarkable, solidification (coagulation) of molten slag would occur in the slag hole portion, thereby a slag hole is blocked and operation of the furnace becomes impossible. SUMMARY OF THE INVENTION: It is therefore one object of the present invention to provide an improved coal combustor which is free from the above-described disadvantages in the prior art. A more specific object of the present invention is to provide an improved slag exhausting device to be equipped in a coal combustor, in which the above-described various problems in the prior art have been resolved. According to a principal feature of the present invention, as shown in Fig. 1, while a height H of an upper bank 2 rising from the bottom portion 5 of a coal combustor is maintained at a necessary value, the tip end portion of the upper bank is flared appropriately (with a flare angle ) in an inverse conical shape, a height of a vertical surface of a slag hole is shortened, and thereby an amount of radiation arriving at the slag hole from a combustion region is increased. According to an additional feature of the present invention, a flow rate of high-temperature gas flowing from a combustor through a circumferential wall portion of a slag hole to the outside of the combustor is set at a proper value by adjusting configurations (a height H of an upper bank 2, a flare angle  of the same upper bank 2, a diameter ds of a cylindrical lower portion 3 in a slag exhausting device and a height L of the same cylindrical lower portion 3 as shown in Fig. 1) in the following manner: (i) The range of the flare angle  of the upper bank 2 in the slag exhausting device is adjusted at 30° - 45°; (ii) The ratio ds/D of the diameter ds of the cylindrical lower portion 3 in the slag exhausting device to the diameter D of the combustor is set at 0.2 - 0.4; (iii) The ratio L/ds of the height L of the vertical surface of the cylindrical lower portion 3 to the diameter ds of the cylindrical lower portion is set at 0.2 - 0.6; and (iv) The ratio H/D of the height H of the upper bank 2 to the diameter D of the combustor is set at 0.05 - 0.15. According to the present invention, owing to the above-described structural feature, the following advantages can be obtained: (1) Molten slag accumulated at the bottom of a combustor is forcibly collected in the slag exhausting device provided at the center axis of the cylinder of the combustor as an influence of a swirl flow (an influence of flows within a boundary layer at the bottom of the combustor) and smoothly flows into a gate of the upper bank. (2) Since the flare angle of the upper bank is properly chosen, within the slag hole an amount of radiation heat arriving from the combustion increases, and therefore, dissipation heat of molten slag (the slag flowed out of the gate and the slag centrifugally separated by the swirl flow and adhered to the inner wall of the slag hole) decreases, and lowering of a temperature can be suppressed. (3) Since the height of the upper bank and the height and diameter of the cylindrical lower portion are properly chosen, a part of the high-temperature gas within the combustor flows into the slag hole jointly with the molten slag and flows out of the combustor, and therefore, the molten slag is heated and lowering of a slag temperature can be suppressed. In addition, as a result of the above-mentioned advantages of the slag exhausting device, improvements in reliability of operations of a coal combustor can be achieved. The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following detailed description of the operation principle and one preferred embodiment of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a schematic view of a slag exhausting device in a coal combustor according to one preferred embodiment of the present invention; Fig. 2 is diagrams showing relations among a radiation heat amount Q, a high-temperature gas flow rate W and various parameters in the slag exhausting device according to the present invention; Fig. 3 is diagrams showing a swirl velocity distribution and a static pressure distribution; Fig. 4 is schematic views showing gas flows occurring at the bottom portion of a combustor and in the slag hole portion; and Fig. 5 is schematic views showing one example of an entrained bed coal gassification furnace in the prior art. GENERAL DESCRIPTION OF THE INVENTION: At first, description will be made on an operation principle of the present invention. As shown in Fig. 2, an amount of radiation Q arriving at the inside of the slag hole increases as the flare angle  of the upper bank 2 in the slag exhausting device becomes large. In addition, a flow rate W of the high-temperature gas flowing out of the combustor through the slag hole to a slag chamber outside of the combustor becomes larger as the flare angle of the upper bank 2 in the slag exhausting device is larger, as the height L of the cylindrical lower portion 3 is lower, and further as the diameter ds of the cylindrical lower portion 3 is larger. Expressing these relations by mathematical formulae, the following formulae are established: Q ∝  W ∝ ds/D W ∝ ds/L However, if the flare angle  is excessively enlarged, the amount of radiation heat arriving at the bottom portion of the combustor decreases, and so, a fluidity of the molten slag is deteriorated at the bottom portion of the combustor. Also, if a flow rate of the high-temperature gas is excessively increased, a burning condition is deteriorated as an influence of low-temperature gas flowing into the combustor from a slag chamber outside of the combustor. Furthermore, dispersion of molten slag occurs at the outlet portion of the slag hole, and so, harmful effects such that slag adheres to the wall surface of an outer vessel of the combustor and solidifies there, would occur. In addition, with regard to the ratio H/D of the height H of the upper bank 2 to the diameter D of the combustor, in the case where H/D is 0.05 or less, since a slag dam-up volume of the bank becomes small, slag would become to flow out along the entire slag hole over the bank not only through the gate, and so, dispersion of molten slag would occur at the outlet of the slag hole. If the ratio H/D becomes 0.15 or more, at the bottom portion of the furnace an area of a shadow of the inclined portion of the upper bank of the slag hole would increase, hence radiation heat within the furnace becomes to arrive hardly at this portion, and solidification of molten slag would occur, and harmful effects such that a fluidity of slag at the bottom portion of the furnace is deteriorated, would arise. Therefore, the flare angle  of the upper bank 2, the diameter ds of the cylindrical lower portion 3 and the height L of a vertical surface of the cylindrical lower portion 3 are set at proper values. According to the present invention, by determining proper regions with respect to the angle , the ratio L/ds and the ratio ds/D as indicated in the diagrams in Fig. 2, a slag fluidity in the slag exhausting device is enhanced without adversely affecting a coal combustor, and thereby slag can be smoothly exhausted from the slag exhausting device. DESCRIPTION OF THE PREFERRED EMBODIMENT: One preferred embodiment of the present invention as applied to a pressurized entrained bed coal gassification furnace is disclosed in the following. A general configuration of the slag exhausting device is similar to that shown in Fig. 1, and when the following conditions were employed, slag could be exhausted smoothly from the slag exhausting device: i) a flare angle of the tip end portion of the slag hole  = 30° ii) a ratio of a slag hole diameter to a combustor diameter ds/D = 0.25 iii) a ratio of a slag hole vertical surface height to a slag hole diameter L/ds = 0.5 iv) a ratio of a slag hole portion bank height to a combustor diameter H/D = 0.15 While a principle of the present invention has been described above in connection to one preferred embodiment of the invention, it is intended that all matter contained in the above description and illustrated in the accompanying drawings shall be interpreted to be illustrative and not as limitation to the scope of the invention.

Claims: A coal combustor of the type that coal is burnt while swirling, thereby an ash content is caught at a furnace wall due to centrifugal forces to be dropped to the bottom of a combustion chamber, and it is exhausted to the outside of the combustion furnace through a slag exhausting device at the bottom of the combustion chamber; characterized in that said slag exhausting device has an upper bank (2) rising from the bottom of the furnace and opened upwards in an inverse conical shape with a flare angle , and a cylindrical lower portion (3), the flare angle () of said upper bank (2) is 30° - 45°, a ratio of a diameter (ds) of the cylindrical lower portion to a diameter (D) of the combustion furnace is 0.2 - 0.4, a ratio of a height (L) to the diameter (ds) of said cylindrical lower portion (3) is 0.2 - 0.6 and a ratio of a height (H) of the upper bank (2) to the diameter (D) of the combustion furnace is 0.05 - 0.15. A slag exhausting device disposed at the center of the bottom of a coal combustion furnace; characterized in that said device has an upper bank (2) rising from the bottom of the furnace and opened upwards in an inverse conical shape with a flare angle , and a cylindrical lower portion (3), a gate (6) is cut in said bank (2) extending downwards from its top edge, a flare angle (8) of said upper bank is 30° - 45°, a ratio of a diameter (ds) of the cylindrical lower portion (3) to a diameter (D) of the combustion furnace is 0.2 - 0.4, a ratio of a height (L) to the diameter (ds) of said cylindrical lower portion (3) is 0.2 - 0.6 and a ratio of a height (H) of the upper bank (2) to the diameter (D) of the combustion furnace is 0.05 - 0.15.

Inventors: KOBAYASHI YOSHINORI, NAKASHIMA FUMIYA, SONODA KEISUKE, TOKUDA KIMISHIRO, KOBAYASHI, YOSHINORI, NAKASHIMA, FUMIYA, SONODA, KEISUKE, TOKUDA, KIMISHIRO, Kobayashi, Yoshinori, c/o Nagasaki Shipyard &amp; Mach, Nakashima, Fumiya, c/o Mitsubishi Jukogyo, Sonoda, Keisuke, c/o Nagasaki Research &amp; Dev., Tokuda, Kimishiro, c/o Nagasaki Research &amp; Dev.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1993
Main classification: C10J3
IPC codes: F23J1, C10J3