AU2006203646B2 - Dry slag discharge device for coal-fired boiler - Google Patents

Description

P/00/0l Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL TO BE COMPLETED BY APPLICANT Name of Applicant: BEIJING GUODIAN FUTONG SCIENCE AND TECHNOLOGY DEVELOPMENT CO. LTD Actual Inventors: ZHENQIANG LIU XIANGYANG LI YUWEI WANG Address for Service: CALLINAN LAWRIE, 711 High Street, Kew, Victoria 3101, Australia Invention Title: DRY SLAG DISCHARGE DEVICE FOR COAL-FIRED BOILER The following statement is a full description of this invention, including the best method of performing it known to us:- -2 DRY SLAG DISCHARGE DEVICE FOR COAL-FIRED BOILER BACKGROUND OF THE INVENTION Field of Invention The present invention relates to an output apparatus for the ash slag at the 5 bottom of the coal-fired boiler of power plant, and more particularly, to a dry slag discharge device for the coal-fired boiler operated under negative pressure. Related Art Presently, the coal-fired boiler of power plant mainly utilizes the hydraulic slag discharge system and equipment with the disadvantages as follows : (1) The slag is 1o directly dropped into the cooling water from the bottom of the boiler, so that the combustible material in the ash slag and the heat thereof are lost, and the devices at the bottom of the boiler are corroded by the steam generated. (2) The water resource is consumed a lot, the environment is polluted by the discharged ash slag water, and the disposal cost is high. (3) Said system is complicated and requires high 15 maintenance and repair cost. Some apparatus employing dry slag discharge system and equipment have occurred recently, such as the steel belt slag discharger manufactured by Magaldi Indusfrie Srl and the dry slag discharge system composed of such a slag discharger, i.e. MAGALDI ASH COOLER (MAC) system. 20 A method for discharging coal dust from the bottom of the boiler in a dry condition is disclosed in Japanese Patent JP-A-63-6319, in which a ventilating conveyor belt is disposed under the combustion chamber, a conveyor belt cover is covered around the conveyor, and the conveyor belt cover is connected with the combustion chamber, so as to form an enclosed system; an air suction port is 25 arranged on the conveyor belt cover for importing air to cool the slag. The slag fallen down from the combustion chamber is received and outputted by the conveyor belt, meanwhile the air entering from the air suction port is passed through the slag layer, to cool down the slag, and the air is heated up by absorbing the sensible heat 22/08/06,15885 speci,2 -3 contained in the slag. The heated air is returned by the suction fan to the combustion room for further heating up after being sent into the air pre-heater, so that the sensible heat contained in the slag can be recycled, thereby improving the boiler efficiency. On the other hand, the cooled slag after heat release is discharged out of 5 the boiler by the conveyor belt in a dry condition, no cooling water is required and slag disposal is easier. However, the coal-fired boiler disclosed in said patent is operated under micro-negative pressure i.e., vacuum condition. Furthermore, said patent has the following disadvantages: (1) When the bottom of the combustion chamber is opened to discharge the bottom slag down onto the conveyor belt, due to 10 vacuum condition of the interior of the combustion chamber, the ambient air will enter into to the boiler hearth with an uncontrollable amount. (2) The supporting board of the conveyor belt is designed as a lattice-like shape, the function of which is to make the air pass through the slag layer. However, when a large amount of slag is to be disposed, the slag layer is accumulated thickly on the supporting board, so that 15 the air is difficult to pass through the slag layer for cooling, thereby decreasing cooling efficiency. Moreover, it will increase the production cost if the width of the conveyor belt is enlarged in order to make the slag layer thinner. A process and apparatus for continuous dry removal of bottom ash is disclosed in W087/0423 1. Similarly to the above-mentioned Japanese Patent, an enclosed high 20 temperature resistant conveyor belt is disposed at the bottom of the boiler, which is driven by friction. The conveyor belt is constructed of a plurality of overlapping steel plates and a high strength steel wired belt. The steel plates are folded into a continuous slot and fixed by bolts and crosspieces inserted into the steel wired belt. The steel plates can expand in every direction. In vacuum operated boilers, the air 25 used to cool the slag is entered through a controllable operating valve, passing the ash against the direction of the ash delivery and entered into the boiler hearth after absorbing heat. Said patent has the following disadvantages: (1) The bottom slag will be agglomerated due to coal quality and/or combustion condition. If large slag lumps with hundreds of kilos weight are generated, then the conveyor belt will be directly 30 impacted by the slag from the combustion chamber, causing some parts of the conveyor belt damaged. (2) If a large amount of slag is to be discharged, as the slag can not be cooled sufficiently, the temperature of the housing and the box of the 22/08/06,15885 speci,3 -4 conveyor belt will exceed a specified value, thereby impairing the production safety. (3) If a large amount of slag is to be discharged, the amount of the entering cooling air will need to be increased to improve the cooling efficiency. However, because the cooling air is totally entered into the boiler hearth after absorbing heat, if the amount 5 of air entering into the bottom of the boiler (i.e., theoretically defined as amount of air leaked), exceeds a predetermined value (i.e., excess coefficient of boiler air), then the boiler can not be operated normally, thereby impairing the boiler efficiency.(4) if a large amount of slag is to be discharged, in order to satisfy the cooling efficiency of the slag, the length of the high temperature conveyor belt will be prolonged or the 10 number of the conveyor belts will be increased, thereby increasing the cost. A steam boiler ash discharger is disclosed in Chinese patent CN1050178. in which a secondary conveyor belt for further cooling connected to the main conveyor belt is provided. The air imported through the air inlet of the container is directly entered into the boiler against the delivery direction of the two conveyor belts after 15 absorbing heat. A bi-parting door is utilized which can work in full opening, half opening and closing states. The bi-parting door generally works in half opening state to block large slag lumps. When large slag lumps occur, the bi-parting door is operated in full opening state to drop the large slag lumps down onto the conveyor belt gently. Said patent has the following disadvantages: (1) The production cost is 20 increased by use of two conveyor belts for cooling. (2) When a great amount of bottom slag appears or the slag is agglomerated in the boiler due to coal quality varying, the amount of the cooling air as required will be increased. However, the cooling air is totally entered into the boiler hearth after absorbing heat, inducing output loss due to excessive cooling air which is beyond the permission of the boiler 25 hearth, hence impairs normal operation of the boiler. (3) The bi-parting door is difficult to withstand great impact of the large slag lumps, and the size of the slag lumps intercepted can not be efficiently controlled. An air and water transporting/cooling device for high temperature and loose materials is disclosed in Chinese patent CN1646860A, in which atomizing water is 30 sprayed onto the slag layer to assist cooling, so as to improve the cooling efficiency and reduce the size of the conveyor belt. Although the temperature of the slag can be 22/08/06, 15885 speci,4 -5 decreased and controlled by using said device, there are still some problems as follows: (1) Since the atomizing water is directly sprayed onto the slag layer, the activity of the slag will be impaired after hydrolysis, and the steam generated as the water contacts with the high temperature slag will corrode the parts at the bottom of 5 the boiler. (2) The water is carried away by the slag or directly lost due to evaporation, causing huge water consumption. (3) The remaining carbon contained in the high temperature slag can not be further burnt, negatively influencing utilization of the dry slag. A separating/cooling device for loose materials for the fluidized bed boiler is 10 disclosed in Chinese patent CN1636121A which employs a conveyor belt equipped with wing plates with holes. According to said separating/cooling device, in order to improve the cooling efficiency of the slag, an appropriate slot is manufactured in the plates of the conveyor belt and an extension device is provided perpendicular to the plates. The top cover and side plates of the conveyor belt box form a water chamber 15 for the cooling water. However, the fuels to be burned in the boiler are ground before entering into the boiler. A large number of particles of Imm are contained in the bottom slag. On the other hand, it is difficult and expensive to make a slot smaller than 1mm on the plates of the conveyor belt. Therefore, if fine particles enter into the interior of the conveyor belt, the wear between the meshed belt and the supporting 20 rollers as well as the rollers will be increased which will shorten the life of the conveyor belt. Furthermore, a conveyor belt for carrying loose material at high temperatures is disclosed in British patent GB1357276. The conveyor has the features as follows : (1) the conveyor belt has a driving drum 111 and a tensioning drum 110. 25 The upper branch of the conveyor has supporting rollers 103, and the lower branch thereof has supporting wheels 104. (2)the conveyor belt includes tank-type supporting plates and high intensity steel belts. The high intensity steel belts are contacted with the rollers to function as driving by way of friction. The tank-type supporting plates are used to support high temperature materials. (3) each tank-type 30 supporting plate is connected to the steel belt 101 by way of the pins 105 and the cross plate 106 inserted into the steel belt 101. Several steel belts 101 are connected 22108/06.15885 speci,5 -6 in series through the connecting pins 107. Therefore, the tank-type supporting plates and the steel belts can expand in any direction, so as to carry loose material at high temperatures. A dry conveying device for high temperature ash slag of coal-fired boiler is 5 disclosed in Chinese patent CN2459550Y. Said device has a steel belt conveyor 3 above which a hydraulic slag crusher 1 and grills 2 are arranged. The grills 2 are mounted under the hydraulic slag crusher 1. The hydraulic slag crusher I and the grills 2 are supported by the case 13. The upper portion of case 13 is connected with the cold ash hopper 15 set at the lower part of the boiler, and the lower portion of 10 case 13 is connected with the upper part of the steel belt conveyor 3. Big agglomerated slag lumps blocked by the grills 2 are periodically extruded and crushed by the hydraulic slag crusher 1 moving along the grills 2, then the crushed slag lumps drop on the steel belt before delivered away. Also, the crushed slag lumps are easy to cool down. 15 SUMMARY OF THE INVENTION In order to overcome the disadvantages of the prior art, the present invention provides a dry slag discharge device for the coal-fired boiler matched with the conventional coal-fired boiler of power plant which considerably improves the 20 cooling efficiency of the boiler slag. The dry slag discharge device for the coal-fired boiler according to the invention has a sealed box joined in seal manner to the boiler slag storage hopper. A high temperature resistant conveyor belt passing through the slag hole of the boiler slag storage hopper is provided inside said sealed box for receiving and transporting the 25 slag. An air inlet is set downstream of the joint of the sealed box and the boiler slag storage hopper in the transmission direction of the high temperature resistant conveyor belt. The sealed box includes inside it a transportation cavity for containing said high temperature conveyor belt and a separate cooling cavity above said 22/08/06.15885 speci.6 -7 transportation cavity. A spraying mechanism is arranged in said separate cooling cavity. The transportation cavity is separated from the separate cooling cavity by a water stop sheet. Said spraying mechanism sprays cooling water to the water stop 5 sheet. Said spraying mechanism includes a plurality of atomizing nozzles mounted on the sealed box. Said water stop sheet and said atomizing nozzles are longitudinally arranged in continuous or discontinuous manner along the transmission direction of the high temperature resistant conveyor belt. Said water shop sheet is connected in seal manner with side plates of the sealed box, forming a 10 separate cooling cavity with the top cover and the sidewalls of the sealed box. The dry slag discharge device for the coal-fired boiler according to the invention further includes a water chamber communicated with the separate cooling cavity which is formed by welding the sidewalls and the side plates together. A water inlet is set on the side plate which also lies at the portion of the separate cooling cavity for 15 introducing the cooling water to the water chamber from the water stop sheet. The dry slag discharge device for the coal-fired boiler according to the invention further includes a slag crusher and an intermediate slag hopper, the former locating under the discharge end of the high temperature resistant conveyor belt in the sealed box and connecting in seal manner with the sealed box, the latter locating under the 20 former and connecting in seal manner with the former. The intermediate slag hopper has a spiral shaped chamber for secondary cooling. A screen plate is mounted in the intermediate slag hopper for blocking large slag lumps. The screen apertures of said screen plate are 5-30mm in size. The technical effects generated by the dry slag discharge device for the coal 25 fired boiler of the invention are described as follows: (1) A separate cooling cavity and a transportation cavity are provided inside the sealed box of the dry slag discharge device for the coal-fired boiler of the invention. The cooling water is sprayed by the spraying mechanism in the separate cooling cavity. On one hand, the slag in the transportation cavity is cooled, on the other hand, the cooling water does 30 not contact with the slag in the transportation cavity, so that the activity of the slag 22/08/06,15885 speci,7 -8 will not be impaired after hydrolysis. (2) The separate cooling cavity is formed of the top cover and sidewalls of the sealed box, two side plates in the sealed box and a water stop sheet. In addition, two water inlets are set respectively on the two side plates which also lie at portion of the separate cooling cavity. After absorbing heat, 5 the cooling water is collected into the water chamber from the water stop sheet through the water inlet on the side plates for cycling use, the water chamber thereof being communicated with the separate cooling cavity, so as to avoid waste of water resource. (3) A plurality of atomizing nozzles are mounted on the top cover of the sealed box. The atomizing water sprayed by the atomizing nozzles forms a layer of 10 water fog curtain in the separate cooling cavity, which absorbs the heat of the cooling air from the air inlet to reduce the temperature of the cooling air entering the sealed box. The coagulated water is collected into the water chambers from the water stop sheet through the water inlet on the side plates. The cooling air flowing within the sealed box absorbs the heat released by burning of the slag and the sensible heat 15 contained in the slag, and releases heat to the atomizing water at the same time. Therefore, the temperature difference between the cooling air and the slag layer is obvious all the time, which improves the cooling effect. (4) The cooling water circulated within the water chambers absorbs the heat released by the high temperature slag layer, further improving the cooling efficiency. (5) The intermediate 20 slag hopper of the dry slag discharge device for the coal-fired boiler of the invention has a spiral shaped chamber constructed of an inner wall, an outer wall and spacer plates. The chamber can be connected with the water supply system for importing the cycling cooling water. Furthermore, the chamber can also be connected with the air inlet on the sealed box, so that the cooling air is entered into the chamber by action 25 of the suction fan or negative pressure of the boiler. The cooling water or the cooling air flowing within the chamber absorbs the heat released by the bottom slag in the intermediate slag hopper, further improving the cooling efficiency. (6) A screen plate is mounted in the intermediate slag hopper, of which the screen apertures thereof having a size of 5-30mm. This way, the slag under 30mm can pass through the 30 screen plate, and then transported to the subsequent systems by the air-lock feeder 21; while the slag larger than 30mm keep on cooling on the screen plate for 0.5-2 hours, and then transported to the subsequent systems by the air-lock feeder. 22108/06,15885 speci,8 -9 Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various 5 changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed 10 description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: FIG. 1 is a schematic view of the dry slag discharge device for the coal-fired boiler according to the invention; FIG. 2 is a sectional view taken along the line A-A of Fig. 1; 15 FIG. 3 is a sectional view taken along the line B-B of Fig. 1; FIG. 4 is a sectional view of the intermediate slag hopper; FIG. 5 is a sectional view of the intermediate slag hopper equipped with a screen plate; FIG.6 is a schematic view of the screen plate; 20 FIG. 7 is a sectional view taken along the line C-C of Fig.1; and FIG.8 is schematic view of the structure of the throttle. DETAILED DESCRIPTION OF THE INVENTION 22/08/06,15885 speci,9 - 10 Referring to Figs. 1-8, the boiler slag storage hopper I of the dry slag discharge device of the invention is connected to the boiler combustion chamber through the water-sealed troughs 27 (or high temperature resistant metal expander) which are used to absorb the high temperature heat expansion at X, Y and Z directions (three 5 dimensions) of the boiler body. The boiler slag storage hopper 1 is supported by a steel structure. A plurality of grills 2 made of the shockproof and high temperature resistant material are evenly distributed under the boiler slag storage hopper 1. The plurality of grills 2 are also supported by the steel structure of the boiler slag storage hopper 1. 10 The interval space of the grills 2 is sized as 300-1000 mm according to the agglomerating conditions of the boiler. The high temperature bottom slag freely fallen from the boiler combustion chamber is as hot as about 8500C in a loose state and sometimes is agglomerated into large lumps. If the bottom slag is fallen from the top of the boiler as high as 40 meters, a great impact force will be generated. The 15 bottom slag falls through the boiler hearth and the boiler slag storage hopper 1, with large slag lumps intercepted by the grills 2 and small slag lumps falling onto the conveyor belt 4. The large slag lumps intercepted by the grills 2 are monitored by the camera 32. The monitoring signals are transmitted to the control room. After the large slag lumps are cooled sufficiently, they are crushed into small lumps at the 20 inspection window 33 with special de-agglomeration tool by operators, and then fall on the conveyor belt 4. The structure disclosed in Chinese patent CN2459550Y is an alternative here, in which a hydraulic slag crusher is arranged on the grills 2 for automatically crushing the large slag lumps. A plurality of pairs of shutting doors 3 made of high temperature resistant 25 materials are mounted at the exit of the boiler slag storage hopper 1, which are driven by the hydraulic cylinder 28. Each pair of shutting doors 3 are operated in close state or open state. If the shutting door 3 are operated in close state, the bottom slag will be temporarily accumulated in the boiler slag storage hopper 1, so as to provide convenience for the equipment maintenance. If the shutting door 3 are operated in 30 open state, the bottom slag will freely fall down onto the conveyor belt 4. 22/08/06,15885 speci, 10 - 11 The sealed box 7 is joined in seal manner to the boiler slag storage hopper I by elastic sealing members 36. The sealed box 7, the slag crusher 5, the intermediate slag hopper 6 and the air-lock feeder 21 are joined in seal manner together by flanges into a sealed system. A high temperature resistant conveyor belt 4 is set within the 5 sealed box 7 to transport the small slag lumps fallen from the grills 2 to the slag crusher 5. The high temperature resistant conveyor belt 4 is constructed of a flat spiral shaped high temperature resistant metal wired belt and a plurality of high temperature resistant metal plates. The metal wired belt takes the function of driving, and the metal plates take the function of supporting, wherein the connection way of 10 the two is same as that disclosed in GB1357276. The high temperature resistant conveyor belt 4 is driven by the driving drum 34 by way of friction. The tensioning drum 35 provides sufficient tension to the high temperature resistant conveyor belt 4 and moves automatically with elongation or shortening of the conveyor belt 4 to keep the tensioning force constant. A plurality of supporting rollers 29 are arranged under 15 the high temperature resistant conveyor belts 4 to support the upper branch of the conveyor belt 4 for loading. Due to the structure limitation, the plurality of supporting rollers 29 generally have small size diameter, of which the axle journal thereof being smaller than 50mm in diameter. Once the fallen large slag lumps directly impact on the high temperature resistant conveyor belt 4, the plurality of 20 supporting rollers 29 will be damaged and the high temperature resistant conveyor belt 4 will be partly deformed or locked, inducing the device close down. Therefore, the grilles 2 are disposed in this invention in order to prevent such an accident. Two side plates 8 are respectively welded to the sidewalls 13 of the sealed box 7 to form two water chambers 9. In other embodiments of this invention, the number of 25 water chambers 9 can also be 1, 3 or other. The side plates 8 are continuously and longitudinally arranged along the high temperature resistant conveyor belt. A drainpipe 16 is positioned near the upper part of each water chamber 9. Drainpipe 16 connects the two water chambers and discharges water into the reclaiming pool or tank. A plurality of atomizing nozzles II are mounted on the top cover 14 of the 30 sealed box 7, which are supplied with pressure water by a water supply system. The plurality of atomizing nozzles 1 1 share the water supply system with water-sealed troughs 27. A water stop sheet 10 is provided above the high temperature slag layer 22/08/06,15885 speci,1 I - 12 12, each end of which is connected in seal manner with the corresponding side plate 8 with no leakage at the joint thereof. A separate cooling cavity is formed by the water stop sheet, the corresponding side plates 8, the top cover and sidewalls of the sealed box 7. A water inlet 15 is set on the side plate 8 which also lies on the portion 5 of the separate cooling cavity. The two ends of the water stop sheet 10 employ an edgefold configuration to prevent the atomizing stream falling onto the high temperature slag layer 12 due to negative pressure. The atomizing nozzles 11 and the water stop sheet 10 are longitudinally arranged in continuous or discontinuous manner along the high temperature resistant conveyor belt 4. There is a slit of 5 10 25mm between the top surface of the high temperature resistant conveyor belt 4 and both of the upright edges of the side plates 8. The slits are sealed by the accumulated high temperature slag layer 12 during operation of the conveyor belt. The atomizing water sprayed by the atomizing nozzles 11 forms a layer of water fog curtain in the separate cooling cavity, which absorbs the heat of the cooling air to 15 reduce the temperature of the cooling air entering the sealed box 7. The coagulated water is collected into the water chambers 9 from water stop sheet 10 through the water inlet 15 on the side plates 8. The cooling water circulated within the water chambers 9 absorbs the heat released by the high temperature slag layer 12. The cooling air flowing within the sealed box 7 absorbs the heat released by remaining 20 burning of the slag and the sensible heat contained in the slag, and releases the heat to the atomizing water at the same time. Therefore, the temperature difference between the cooling air and the slag layer 12 is obvious all the time, which improves the cooling effect. In addition, the cooling water collected in the water chambers 9 continuously flows through the drainpipe 16 for carrying off a portion of heat. The 25 cooling water in the water chambers 9 can also be provided by the water supply system. The water chambers 9 can directly absorb the heat of the bottom slag, further improving the cooling efficiency. An air inlet 30 and an air outlet 37 are provided on the sealed box 7. The air outlet 37 is connected with the suction fan 25 made of wear-resistant structures 30 through the air duct 23. The air inlet 30 is set downstream of the joint of the sealed box 7 and the boiler slag storage hopper 1 in the transmission direction of the high 22/08/06,15885 speci,12 - 13 temperature resistant conveyor belt 4. The air outlet 37 is set on the top cover 14 of the sealed box where less dust exists, so that there will be less dust entering into the suction fan 25. The air outlet 37 is adequately spaced from the air inlet 30, so that the cooling air entering from the air inlet 30 exchanges heat with the top of the high 5 temperature boiler slag layer 12 within the sealed box 7. In order to further improve the cooling effect, an air inlet 30a is arranged upstream of the joint of the sealed box 7 and the boiler slag storage hopper 1 in the transmission direction of the high temperature resistant conveyor belt 4. Two throttles 22 and 22a are arranged on the sealed box 7 for restricting the 10 cooling air entering into the boiler hearth, respectively positioned downstream and upstream of the joint of the sealed box 7 and the boiler slag storage hopper I in the transmission direction of the high temperature resistant conveyor belt. Throttles 22a keep in close state during operation for prohibiting the cooling air entering into bottom of the boiler, it can be opened only for maintenance. Both throttles 22 and 15 22a include a bar 22b, a sheet 22c, two guard boards 22d and a driving cylinder 22e. The sheet 22c is driven by the cylinder 22e to move up and down. The guard boards 22d are connected in seal manner with the top cover 14 of the sealed box 7 to form a sliding chute. The sheet 22c moves within the sliding chute as a lock gate. Two pressure sensors 31 and 31a are set at both sides of the throttle 22. The discharge 20 amount of the suction fan 25 is controlled via detecting the vacuum pressures at both sides of the throttle 22 by the pressure sensors 31 and 31 a, and the air at the bottom of the boiler is not sucked out. When the high temperature bottom slag is transferred on the high temperature resistant conveyor belt 4, the ambient air is entered into the sealed box 7 through the 25 air inlets 30 and 30a by the combination of the negative pressure of the boiler and the suction fan 25 according to the quantity of the bottom slag. The amount of the entering air is not restricted by the operation of the boiler, but just controlled according to the requirements for cooling the bottom slag. The cooling air entering via the adjustable air inlet 30 flows above the slag layer 12 and exchanges heat with 30 the top of the slag. Therefore, the bottom slag is cooled by releasing heat, and the cold air is warmed up by absorbing heat. The cooling air entering via the adjustable 22/08/06,15885 speci, 13 -14 air inlet 30a flows under the high temperature resistant conveyor belt 4 and exchanges heat with the bottom of the slag layer. Then, the heated cooling air comes up from head of the high temperature resistant conveyor belt 4 and turns back to flow above the slag on the high temperature resistant conveyor belt 4 against the 5 transmission direction of the high temperature resistant conveyor belt 4, thereby continuously exchanging heat with the slag. The amount of the air entering the boiler hearth which has completed heat exchange with the slag is controlled within the allowable air leakage ratio of the boiler by adjusting the sheet 22c of the throttle 22 and the spacing (extent of opening) between the top surface of the high temperature 10 resistant conveyor belt 4 and the side plates 8. The remaining air is entered into the air duct 23 via the air outlet 20 adjacent to the top cover 14 and discharged by the suction fan 25, then reloaded into the boiler or discharged to the ambient air. According to the above-mentioned structure, the amount of the entered cooling air is controlled according to the requirements for cooling the bottom slag, 15 meanwhile the amount of the leakage air entering the boiler hearth is controlled within the allowable air leakage ratio, so that the requirements of boiler's normal operation can be satisfied. The high temperature bottom slag falls onto the high temperature resistant conveyor belt 4 which moves slowly with changeable speed, forming a continuous 20 high temperature slag layer 12. The thickness of the high temperature slag layer 12 can be adjusted by varying the speed of the high temperature resistant conveyor belt 4. The high temperature slag layer 12 is transported to the discharge end at the head of the high temperature resistant conveyor belt 4, and then falls into the slag crusher 5. As large slag lumps are pre-crushed, the particle size of the slag discharged from 25 the slag crusher 5 is 10-50mm. Smaller particle size of the crushed slag tends easier to cool down. After processed through the slag crusher 5, 50% of the bottom slag becomes smaller than 10 mm in particle size which is easier to cool down. Then the bottom slag enters the intermediate slag hopper 6 from the slag crusher 5. An air-lock feeder 21 is provided at the exit of the intermediate slag hopper 6. 30 The air-lock feeder 21 operates in a continuous or discontinuous state, the output force of which can be controlled via variable frequency. The time of the accumulated 22/08/06,15885 speci, 14 - 15 slag layer retained in the intermediate slag hopper 6 is controlled by the air-lock feeder 21 via varying the output force or selecting different operation state. The time ranges generally 0-2 hours. The air-lock feeder 21 takes the functions of feeding and air locking, so as to prevent the air from subsequent systems entering the sealed 5 system. The intermediate hopper 6 includes an upper flange 6f, a lower flange 6g, an inner wall 6a, an outer wall 6b, spacer plates 6c, an exit 6d and an entrance 6e. A spiral shaped chamber 17 is constructed of the inner wall 6a, the outer wall 6b and the spacer plates 6c. The chamber 17 can be connected with the water supply system for importing the cycling cooling water. Also, the exit 6d can be connected with the 10 air inlet 30 of the sealed box 7 to introducing the cooling air into the chamber 17 by action of the negative pressure of the suction fan 25 or the boiler. The cooling water or the cooling air flows within the chamber 17 absorbs the heat released by the bottom slag in the intermediate slag hopper 6, further improving the cooling efficiency. The air-lock feeder 21 connected with the lower flange 6g is 15 discontinuously operated to transport the slag to the subsequent systems. The time of the accumulated slag layer 18 retained in the intermediate slag hopper 6 is 0.5-2 hours. The accumulated slag layer 18 keeps on releasing heat which is carried away by the cooling water or the cooling air. A screen plate 19 can be mounted within the intermediate slag hopper 6, which 20 is mounted on the wall of the intermediate slag hopper 6 by an oscillating axle head 20a. The oscillating axle 20 is electrically or pneumatically driven, and the amplitude thereof is controlled by the control system. A plurality of screen apertures 19a of 5 30mm in diameter size are fabricated on the screen plate 19. The slag of smaller size passing through the screen apertures is transported to the subsequent systems by the 25 air-lock feeder 21 which is continuously operated. The slag of larger size keeps staying on the screen plate 19 for 0.5-2 hours for further cooling. Then the amplitude of the screen plate 19 is increased, so that the slag of larger size is transported to the subsequent systems by the air-lock feeder 21. The high temperature bottom slag is transported to the subsequent conveyor 30 belts or pneumatic pipelines by the air-lock feeder 21, finally collected into slag storage tank 26 and periodically delivered away by a carrier vehicle 24. 22/08/06, 15885 speci,15 -16 The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following 5 claims. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group 10 of integers or steps. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form or suggestion that the prior art forms part of the common general knowledge in Australia. 22108/06,15885 speci, 16 - 17 LIST OF REFERENCE NUMERALS 1: boiler slag storage hopper 2: grill 3: shutting door 5 4: high temperature resistant conveyor belt 5: slag crusher 6: intermediate slag hopper 6a: inner wall 6b: outer wall 10 6c: spacer plate 6d: exit 6e: entrance 6f: upper flange 6g: lower flange 15 7: sealed box 8: side plate 9: water chamber 10: water stop sheet 11: atomizing nozzle 20 12: high temperature slag layer 22/08/06,15885 speci,17 - 18 13: side wall of sealed box 14: top cover of sealed box 15: water inlet 16: drain line 5 17: chamber 18: accumulated slag layer 19: screen plate 19a: screen aperture 20: oscillating axle 10 20a: oscillating axle head 21: air-lock feeder 22,22a:throttle 22b: bar 22c: sheet 15 22d: guard board 22e: cylinder 23: air duct 24: carrier vehicle 25: suction fan 20 26: slag storage tank 27: water-sealed trough 22/08/06,15885 speci,18 - 19 28: hydraulic cylinder 29: supporting roller 30,30a:air inlet 31,3 1a:pressure sensor 5 32: camera 33: inspection window 34: driving drum 35: tensioning drum 36: elastic sealing member 10 37: air outlet 22/08106,15885 speci, 19

Claims (10)

1. A dry slag discharge device for a coal-fired boiler, including a sealed box joined in seal manner to the boiler slag storage hopper, wherein a high temperature resistant conveyor belt passing through the slag hole of the boiler slag 5 storage hopper is provided inside said sealed box for receiving and transporting the slag, and an air inlet is set downstream of the joint of the sealed box and the boiler slag storage hopper in the transmission direction of the high temperature resistant conveyor belt, wherein a transportation cavity for containing said high temperature conveyor belt and a separate cooling cavity set on upper part of said transportation 10 cavity are further arranged within the sealed box, and a spraying mechanism is arranged in said separate cooling cavity.

2. The dry slag discharge device according to Claim 1, wherein the transportation cavity is separated from the separate cooling cavity by a water stop sheet, said spraying mechanism spraying cooling water to the water stop sheet. 15

3. The dry slag discharge device according to Claim I or Claim 2, wherein said spraying mechanism includes a plurality of atomizing nozzles mounted on the sealed box.

4. The dry slag discharge device according to Claim 2 or Claim 3, wherein said water stop sheet and said atomizing nozzles are longitudinally arranged in 20 continuous or discontinuous manner along the transmission direction of the high temperature resistant conveyor belt.

5. The dry slag discharge device according to any one of Claims 2 to 4, wherein said water shop sheet is connected in seal manner with the side plates in the sealed box, and forms the separate cooling cavity with the top cover of the sealed 25 box and the sidewalls thereof. 06/04/]Ojm I 5885apr6.claims.doc,20 -21

6. The dry slag discharge device according to Claim 5, further including: at least one water chamber communicated with the separate cooling cavity, said water chamber being formed by welding the side walls and the side plates together; 5 a water inlet set on the side plate which also lies at the portion of the separate cooling cavity for introducing the cooling water to the water chamber from the water stop sheet.

7. The dry slag discharge device according to any one of the preceding Claims, further including: 10 a slag crusher under the discharge end of the high temperature resistant conveyor belt in the sealed box and connecting in seal manner with the sealed box; and an intermediate slag hopper under said slag crusher and connecting in seal manner with the slag crusher, said intermediate slag hopper including a chamber 15 for secondary cooling.

8. The dry slag discharge device according to Claim 7, wherein said chamber is a spiral shaped chamber.

9. The dry slag discharge device according to Claim 7 or Claim 8, wherein a screen plate is mounted in the intermediate slag hopper for blocking large slag 20 lumps.

10. The dry slag discharge device according to Claim 9, wherein said screen plate has screen apertures of 5-30mm in diameter size. I. A dry slag discharge device for a coal-fired boiler, substantially as hereinbefore described with reference to the accompanying drawings. 25 06/ 0 4/1OjmI5885apr6.claims.doc,21