Background Art Generally, the boilers can be classified by their fuel, for instance, oil, gas or coal. Of those boilers, a coal boiler is proper for heating larger space, e. g., big-sized vinyl green house, for its high thermal efficiency and economic advantage for cheap fuel.

A coal boiler is described in the Korean Patent Publication No. 93-8819.

As shown in Fig. 1 and 2, the published boiler comprises; a water path (12) wherein water circulates, a duct portion (20) where heat exhanging occurs in contact with the water path (12), a heating unit (30) to provide heat into the duct portion (20), a coal feeding unit (40) to feed coal to the heating unit (30) from a coal storage (1), an ash crushing unit (50) to crush the ash produced in the heating unit and a ash discharging unit (60) to discharge the crushed ash from the boiler.

The coal feeding unit (40) comprises a piston (42) which slidingly moves at

the outlet of the coal storage (1), a first link (43) driven by a motor (41) for reciprocally moving the piston (42), a switching panel (44) to open and close the outlet of the coal storage (1) according to the reciprocal movement of the piston (42) and a second link (45) powered by the motor (41) to operate the switching panel (44).

Therefore, in the above-described boiler, the coal is automatically fed and the coal ash is automatically discharged in much lessened volume.

The boiler has, however, some defects as below.

Firstly, the thermal efficiency of the boiler is limited by area of the duct portion (20) since the heat exchanging occurs only at the surface of the duct portion (20) no matter how the duct portion (20) is arranged.

Secondly, it pollutes air with powder ash which is emitted out along with the discharged heated air through the duct portion (20).

Thirdly, the life of the crusher is shortened because the edges of the crusher are damaged in crushing the coal ash which usually contains some unburned coal.

Forthly, since the swiching panel is operated by the link, the construction of the boiler is complicated consuming more power.

Disclosure of Invention The present invention is made for solving the above problems of the prior art.

It is, therefore, an object of the present invention to provide a boiler

of high heat-exchanging efficiency by improving the structure of the duct portion.

It is a particular object of the invention to provide an environmental protective boiler by restraining discharge of powdered dust like ash into air.

It is a further object of the present invention to provide a boiler which lengthens ash-crushers life by lessening the damage of the edge of the crusher.

It is also an object the present invention to provide a boiler producing little noise and vibration.

It is still another object of the present invention to provide a boiler having switch panel with simplified structure using less power in operating the outlet of the coal storage.

In accomplishing the foregoing objects, there is provided in accordance with the present invention a boiler comprising a heat exchanging portion having an water path wherein water circulates and a duct portion installed in contact the water path with a plurality of water tubes penetrating the duct portion in which the water moves, a heating unit to provide heat by burning solid fuel into the duct port ion where heat-exchange occurs, a fuel feeding unit having fuel storage to feed fuel to the heating unit, an ash crushing unit to crush the ash produced from the heating unit into a certain size, and an ash discharging unit to discharge the crushed ash.

The duct portion comprises a first duct section which extends upwardly from

the heating unit, a second duct section which extend downwardly from the first duct section and a third duct section which extends upwardly again from the second duct section. A plurality of impeding plates are installed in a certain interval on the inner surface of the duct portion.

The fuel feeding unit comprises a piston slidingly moves at the outlet of the fuel storage, a plurality of links to operate the piston in reciprocating motion powered by a motor, a switching panel to rotate to open and shut the outlet corresponding to the motion of the piston, and a chain to connect a sprocket of the switching panel with the sprocket of the motor.

The heating unit comprises a fire grate on which fuel is placed, a fan under the fire grate to provide air to the fire grate, a subhousing having a guiding panel attached to the fire grate to guide air provided by the fan to the duct portion.

The ash crushing unit comprises a supporting member rotatably supported by the boiler body, a shaft extended from the supporting member having a polygonal setting part; a movable axle slidingly movable along the setting part; and a plurality of blades with plural edges installed on the movable axle in a certain interval. Here, the point angle of the edges is formed to be acute angle so that the coal ash is easily crushed with less impact force.

The ash discharging unit, where coal ash stacks dropping from the ash crushing unit, comprises an ash collecting bucket having an outlet on its side wall, a screw conveyer rotatably supported by the ash collecting bucket, a fixing plate fixed on one side wall of the ash collecting bucket having

a hole corresponding to the outlet, a supporter one end of which is fixed at one side wall of the fixing plate, the other end of which supports the screw conveyer to rotate, and a bearing installed inbetween the supporter and the screw conveyer.

Therefore, according to the present invention, thermal efficiency increases a lot by installing a plurality of water tubes to pass through the duct portion and emission of ash powder is restrained to prevent air pollution by a plurality of impeding plates installed on the inner surface of the duct portion. The blades are combined to the movable axle to decrease impact shock in crushing coal ash so that the edge's life is lengthened.

Brief Description of Drawings Fig. 1 and Fig 2 are cross sectional view and a perspective view partly broken away of a conventional coal burning boiler.

Fig. 3 is a cross sectional view of a coal burning boiler according to the present invention.

Fig. 4a and 4b illustrate the operation of the fuel feeding unit of the boiler according to the present invention.

Fig. 5 is a perspective view of the ash crushing unit and ash discharging unit of the boiler according to the present invention.

Fig 6 is an assembling view showing how the ash crushing unit of the boi ler according to the present invention is assembled.

Fig. 7 is a sectional view of the ash crushing unit and ash discharging unit of the boiler according to the present invention.

Fig. 8 is a perspective view showing the ash discharging unit of the boiler according to the present invention.

Best Mode for Carrying Out the Invention As shown in the Fig. 3, the boiler according to the present invention comprises a heat exchanging portion (110) having a water path (111) where water circulates and a duct portion (120) in contact with the water path (111) accomodating a plurality of water tubes installed in a certain interval to penetrate the duct portion (120) so that heat-exchanging occurs; a heating unit (130) to provide heat to the duct portion (120); a fuel feeding unit (160) to provide coal to the heating unit (130); an ash crushing unit to crush the coal ash produced from the heating unit (130); and an ash discharging unit (150) to discharge the crushed coal ash.

The duct portion (120) has a first duct portion (121) upwardly extended from the heating unit (130), a second duct portion (122) downwardly extended from the first duct portion (121), and a third duct portion (123) upwardly extended from the second duct portion (122). The second duct portion (122) comprises a plurality of impeding plates (125) installed in a certain interval to prevent the powdered ash traveling along with combustion gas.

Each impeding plate (125) has a hole (125a) through which the combustion gas passes. The neighbouring holes (125a) are arranged in zigzag.

The fuel feeding unit (160) comprises a piston (161) slidingly moving at the outlet of the fuel storage (170), a plurality of links (162) powered by a motor (200) to operate the piston (161) to reciprocate, and a switching panel (171) to open or shut the outlet of the fuel storage (170) simultaneously to the reciprocating motion of the piston (161).

A sprocket of the axle (171a) of the switching panel (171) is connected with a sprocket (201) of the motor (200) by a chain (202) so that the switching

panel (171) is rotated by the motor (200). As illustrated in Fig. 4a, the switching panel (171) shut the outlet of the fuel storage (170) when the piston (161) moves back from the heating unit (130). Fig. 4b shows that the switching panel (171) opens the outlet when the piston (161) moves toward the heating unit (130) and then a certain amount of the coal moves down onto the piston (161). When the piston (161) moves back as shown in Fig. 4a, the coal on the piston (161) falls down ahead of the piston (161).

The heating unit (130) comprises a fire grate (131) whereon the coal provided from the fuel feeding unit (160), a fan (135) installed below the fire grate (131) to provide air to the fire grate (131), and a subhousing (133) to support the fire grate (131). A guiding panel (132) is further installed in the subhousing (133) to lead air to the duct portion (120) via the fire grate (131).

The ash crushing unit (140), as shown in the Fig. 4 and 5, comprises a supporting member (141a) rotatably supported by the body of the boiler, a shaft (141) having a setting part (141b) of polygonal shape, a movable axle (142) connected with the setting part (141b) to be slidable along the axle, and blades (143) combined with the movable axle (142) in a certain interval having a plurality of edges (143a). Each of the blades (143) could be directly connected with the setting part (141b). Preferably, the hem of the edges is formed to make an acute angle so that crushing the ash is easily performed with less impact shock.

The ash discharging unit (150), referring to the Figs. 6 and 7, comprises an ash collecting bucket (151) to receive the coal ash falling from the ash crushing unit (140), a screw conveyer (153) rotatably installed in the ash collecting bucket (151), a fixing plate (152) fixed at a side wall of the ash collecting bucket (151) having a ash discharging hole (152a), a

supporter (154) one end of which is fixed to the fixing plate (152) and the other end of which supports the middle part of the screw conveyer (153) rotatable, and a bearings (155) positioned between the supporter (154) and the screw conveyer (153).

The boiler of the present invention having the above structure works as below.

A certain amount of the coal dropped from the fuel storage (170) is provided to the fire grate (131) by the fuel feeding unit (160). As illustrated in the Fig. 4a, the switching panel (171) shuts the outlet of the fuel storage (170) when the piston (161) moves back from the heating unit (130) and, as shown in the Fig. 4b, the switching panel (171) opens the outlet when the piston (161) moves toward the heating unit (130) so that a certain amount of coal is provided to the upper plate of the piston (161). The coal provided to the upper plate of the piston (161) drops ahead of the piston (161) when the piston (161) moves back, as shown in the Fig. 4a. The coal dropped ahead of the piston (161) is carried to the heating unit (130) as the piston (161) moves forward.

The coal provided as above is burned on the fire grate (131) and the heat generated from the burning coal is provided to the duct portion (120). The air from the fan (135) helps the coal burnt and facilitates the circulation of the heat in the duct portion (120). The air is guided to the burning coal by the guiding panel (132).

The thermal transfer occurs between the heat guided along the duct portion (120) and the water circulating through the water tubes (124) and the heat exchanging portion (110).

The powdered dust like coal ash included in the combustion gas is restrained from being emitted by the impeding plate (125) in the duct portion (120). In particular, the efficiency of thermal exchange in the duct portion (120) is improved since the impeding plate (125) having the hole (125a) makes turbulence of the hot air moving along the duct portion (120).

Meantime, the fuel feeding unit (160) provides coal in a certain interval of time and the newly provided coal pushes the burnt coal toward the ash crushing unit (140). At the ash crushing unit (140) the burnt or partially-burnt coal ash is crushed by the rotating blades (143). The acute angled edges (143a) of the blades (143) easily crushes the coal ash. When the edges (143a) impact partially-burnt coal ashes, the impact shock is reduced as the movable axle (142) slides along the shaft (141) so that the damage to the edges (143a) is consequently reduced to improve the durability of the edges (143a).

The crushed coal ash falls down to the ash collecting bucket (151) and then is discharged through the ash discharging hole (152a) by the rotating screw conveyer (153). At this moment, the operation of the screw conveyer (153) is stabilized as the screw conveyer (153) is supported by the supporter (154) at the middle of the screw conveyer to produce less noise and vibration.

The boiler of the present invention has the following advantages.

Firstly, the boiler of the present invention highly improves the thermal efficiency for a plurality of water tubes are placed to pass the duct portion.

Consequently the boiler is more economical than the conventional one.

Secondly, the boiler improves environmental protection for the impeding

plate having hole to restrain the emission of the powdered ash.

Thirdly, the life of the edges of the blades is lengthened for the blades combined to the movable axle which is movable along the shaft diminishing direct impact shock in crushing the coal ash.

Fourthly, the operation of the boiler is performed with much less noise and vibration for the screw conveyer of the ash discharging unit is supported by the supporter.

Fifthly, the structure of the boiler is simple and requires less power for the switching panel is linked by chain with the motor which operates the piston.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all the changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.