EP0194261A1

EP0194261A1 - Burner for burning solid fuels

Info

Publication number: EP0194261A1
Application number: EP19850900112
Authority: EP
Inventors: Matti RÄTY; Juhani PITKÄKANGAS
Original assignee: Maamiehen Sahko Oy
Current assignee: Maamiehen Sahko Oy
Priority date: 1984-09-18
Filing date: 1984-11-26
Publication date: 1986-09-17
Also published as: FI843656A0; FI75922C; FI850808L; FI850808A0; WO1986001873A1; FI75922B

Abstract

Le terme "brûleur" qualifie ici un appareil d'alimentation et de combustion de combustibles qui peut être installé de façon à servir d'équipement auxiliaire associé à un fourneau. Le brûleur (1) comprend la chambre de combustion (7), la grille (8) placée au fond de la chambre de combustion et le cendrier (9) situé sous la grille. La chambre de combustion est pourvue d'un dispositif automatique d'alimentation du combustible (4) qui lui est connecté par un puits d'admission du combustible ou autre structure similaire. Le but de l'invention est d'obtenir une amélioration des brûleurs de combustibles solides et de leurs dispositifs d'alimentation et de réaliser un brûleur dont la sortie peut être ajustée assez rapidement dans une plage étendue, avec des périodes d'entretien plus longues que celles des brûleurs conventionnels de combustibles solides. Le brûleur(1) forme une unité séparée qui peut être extérieurement installée en association avec un fourneau ou avec un agencement de fourneau. Le dispositif d'alimentation du combustible (4) est connecté au brûleur (1) par un puits incliné (6) d'admission du combustible. Le dispositif d'admission (4) est pourvu d'un dispositif régulateur qui règle la dispersion du combustible en un écoulement continu ayant le volume voulu dans la chambre de combustion (7). Le puits incliné (6) d'admission du combustible (6) est connecté à la grille (8), qui a de préférence la même largeur que le puits d'admission du combustible. La chambre de combustion (7) est pourvue d'un souffleur (11) employé pour insuffler dans la chambre de combustion un courant d'air de combustion ayant le volume voulu.The term "burner" here qualifies a fuel supply and combustion apparatus which can be installed so as to serve as auxiliary equipment associated with a stove. The burner (1) comprises the combustion chamber (7), the grate (8) placed at the bottom of the combustion chamber and the ashtray (9) located under the grate. The combustion chamber is provided with an automatic fuel supply device (4) which is connected to it by a fuel intake well or other similar structure. The object of the invention is to obtain an improvement of the solid fuel burners and their supply devices and to produce a burner whose output can be adjusted fairly quickly over a wide range, with longer maintenance periods. than conventional solid fuel burners. The burner (1) forms a separate unit which can be installed externally in association with a stove or with a stove arrangement. The fuel supply device (4) is connected to the burner (1) by an inclined fuel intake well (6). The intake device (4) is provided with a regulating device which regulates the dispersion of the fuel in a continuous flow having the desired volume in the combustion chamber (7). The inclined fuel intake well (6) (6) is connected to the grid (8), which preferably has the same width as the fuel intake well. The combustion chamber (7) is provided with a blower (11) used to inject into the combustion chamber a stream of combustion air having the desired volume.

Description

BURNER FOR BURNING SOLID FUELS

The present invention relates to a burner for burning solid, i.e. pulverous or granular fuels, the said burner comprising a combustion chamber, a grate located at the bottom of the combustion chamber and an ash pit below the grate; to the combustion chamber there is connected an automatic fuel feeder by means of an inlet shaft or the like. The term 'burner' is here employed to refer to a fuel feeding and burning device which is installed in connection to a furnace.

In the prior art there are known separate front extension furnaces which can be connected to standard central heating furnaces. The front extension furnace comprises a combustion chamber, a grate and an ash pit. The front furnace is connectable to the furnace proper by means of a fire shaft. A fuel storage hopper is located above the front extension furnace so that between the hopper and the combustion chamber there are arranged locking means which are used for dosing fuel into the combustion chamber. For primary air supply and ash removal, the combustion chamber is provided with a hatch. For secondary air supply, an air inlet pipe is connected to the fire shaft. The fuel is gasified in the front extension furnace, and the resulting gases are burned by means of secondary air in the furnace proper .

The front extension furnaces are devices of the same size as the main furnace, and their purpose is to readjust for example an old oil furnace so that it is suitable for burning sawdust or wood chips. The readjustment operation are cumbersome and the front extension furnace requires a lot of space. This kind of a front extension furnace and main furnace combination has a high draft resistance, and

O P1 the output regulation of the combustion process in the said combination becomes difficult. The combination is not easily adapted to quick changes in the fuel charge, and it does not function with small charges. Damp wood chips or damp sawdust cannot be used as fuel because the combustion temperature is relatively low, and the fuel supply into the front extension chamber is carried out in comparative y large and uneven batches by means of opening the locking members.

The German Patent Publications No. 62 043, 917 741 and 917 742 introduce various furnace contructions resembling the front extension furnace and main furnace combinations; in these furnace constructions, the combustion chamber provided for the solid fuel and the afterburning chamber for the gases form a uniform furnace assembly. The combustion chamb.er is. large and it is provided with vertical and/or inclined grate arrangements. The use of these arrangements aims at achieving a high total output, which again requires that large amounts of fuel are treated at a time. The furnace output cannot be substan ially regul ated .

The installation of an automatic solid fuel feeder in connection to the aforementioned types of furnace and/or front extension furnace and main furnace combinations is difficult, sometimes outright impossible. If the feeder is managed to be connected to the furnace, the burning efficiency often remains poor becauce these furnaces and/or front extension furnaces generally have a large grate and a combustion chamber which is too small with respect to the grate. The flame temperature remains too low because the flames get into immediate contact with the cold fire surfaces and are cooled off so that complete combustion is not possible. The feeder input height also tends to rise

OMPI high, particularly in bottom-heated furnaces where the fuel is fed in through the fuel supply hatch. In conventional furnaces the burning of sod peat, milled peat, peat pellets and straw pellets is also difficult owing to the large amount of created ashes and the fact that the ashes are sintered .

Within the class of regular burners which are suited for solid fuels can be included for instance stokers that are primarily meant for burning wood chips, and incineration dishes or shafts which are provided with various fuel feeding means located on the top or on the same l e vel as the dish or shaft itself. The stokers, incineration dishes and shafts are installed within the furnace combustion chamber so that they take up part of the chamber volume. The feeding means are often spiral feeders.

The drawbacks in the aforementioned burners are connected with ash removal, fuel supply and power regulation. Ashes are removed for instance from the combustion chamber of the stoker or from the fire shaft of the burner so that they are pushed off by the fresh fuel fed in by the feeder spiral. The ashes are sintered, i.e. the ashes, while first melting and subsequently cooling off, form a solid substance which sticks onto the walls of the combustion chamber or onto the shaft or the grate. The sintered ashes diminish the combustion space and block the air inlets in the shaft or in the grate. While the operation of the feeder is continued, part of the unburned fuel drops over the edges of the stoker or of the fire shaft down onto the bottom of the furnace, and thus the air supply is obstructed, which causes the combustion process to slow down. This causes the maintenance periods to become fairly short, particularly at times when the fuel charge is at its largest. The output regulation is also difficult with these

kind of burners; it is particularly difficult to arrange the apparatus to idle, i.e. to function with minimum output. Moreover, the spiral feeding system is sensitive to disturbances and expensive to manufacture.

In the prior art there are known several different feeders, such as spiral feeders and spiral conveyors, piston feeders and flake feeders, which may be suited for feeding solid fuels into furnaces or burners. These prior art conveyors and feeders are, however, sensitive to sand and pebbles as well as to the nonhomogenous composition of the fuel in question. In addition to this, they require an amount of driving power which is incommensurate to their conveying or feeding power. Consequently their running expences often are high, and moreover their purchase price tends to be high , too .

The object of the present invention is to achieve an improvement in solid fuel burners and feeders and to realize a burner, the output whereof can be regulated within a wide range and fairly quickly, and which burner needs regular maintenance at remarkably longer intervals than conventional solid fuel burners. The invention is characterized by the novel features enlisted in the appended patent claims.

The aforementioned drawbacks are eliminated in the solid fuel burner of the present invention. The burner forms a separate unit which can be combined to any existing furnace, particularly externally. By means of this burner, all existing types of furnaces can be provided with a feeder, and more specifically with an automatic feeder of a certain type. The burner is installed for instance in the bottom hatch of the furnace so that the feeder input height remains low, preferably between 30-60 cm. In the burner,

O PI the fuel is burned directly and immediately. There is always a relatively small amount of fuel located on the grate, whereas a plentiful amount of air needed for the combustion is fed into the fuel by means of a blower. The temperature of the flame is remarkably high. This leads to a high burning efficiency. Inside the furnace there is left additional space for proper afterburning brickworks, for instance, so that the combustion process proceeds in a high temperature to the very end. The fuel supply into the combustion chamber is regulated by means of the automatic feeder connected to the inclined fuel inlet shaft, and the amount of combustion air is regulated by means of a blower; consequently the ratio between the fuel and the combustion air is accurately adjusted. All furnaces can be turned into top-heated furnaces operated on the so-called scattering principle. All of the fire surfaces of the furnace are put into practical use, so that the outlet temperature of the ■ combustion gases is decreased and the total ef iciency of the furnace is increased. Idling losses are accordingly diminished, because the amount of fuel scattered each time into the combustion chamber of the burner is only the amount needed for keeping up the fire.

In the burner of the invention, solid fuel is burned in a process which is in complete control; the total efficiency of the furnace whereto the burner is connected can be adjusted within a very wide range by regulating the fuel supply and the air flow. In conventional furnaces or in furnaces provided with a front extension furnace, this kind of process-sca e control is not possible.

In the combustion chamber of the burner there can also be burned materials which have a low ash melting point and a high ash content, because the combustion chamber can, if required, be provided with an automatic ash removal system. In the burner of the invention, the ash remover installed in connection with the combustion chamber has a twofold task: first, it drops the ashes from the grate into the ash pit, and second, it moves the burning fuel forward and thus makes space for the fresh fuel supplied from the fuel inlet shaft.

The principle of the fuel feeder employed in connection with the burner of the invention is the idea that two or more toothed or flaked support members, such as planes, rods or rails move back and forth so that the adjacent support members always move to opposite directions and that the toothing or flaking is made asymmetrical in the forward direction of the support members so that the solid fuel is to be conveyed or fed, is more easily moved in one direction, i.e. the transport direction, than in the opposite direction.

This type of feeder can be employed for conveying and/or feeding even exceptionall nonhomogenous and/or extremely light materials. A slight toothing or flaking of the support members with respect to the lump size and lump distribution of the transported material leads to a surprisingly high material transfer efficiency. By regulating the length of the back and forth movement of the supporting member, the transport properties of the apparatus can be adjusted so that they are optimal while the weight, porosity etc. of the treated material are changed. Power demand, compared to the conveying and/or feeding power, is extremely modest. The apparatus has a simple structure. By employing this apparatus, for instance the feeding of wood chips into a burner is carried out evently so that among others the total efficiency of the heating apparatus is improved. Moreover, the feeder is not easily blocked, and it is well suited for example for very large burners up to 1000 kW. In the following the invention is described in more detail with reference to the appended drawings, where

Figure 1 is an illustration of a preferred embodiment of the burner of the invention, seen in side-view cross-section; Figure 2 is an illustration of the burner of figure 1, shown along the section A-A; Figure 3 is an illustration of another preferred embodiment of the burner of the invention; Figure 4 is a cross-sectional view of a feeder used in connection with the burner of the invention; Figure 5 is an illustration of the structure of the feeder of figure 4 seen from the top, and Figure 6 is an illustration of the structure of the same feeder seen from below.

In figures 1 and 2, the burner 1 according to the invention is connected to the furnace 2, preferably to its bottom hatch 3. The fuel bin is connected to the burner 1 by means of the feeder 4. The burner 1 comprises the inclined fuel inlet shaft 6, at the top end whereof the feeder is connected. The height h of the fuel inlet shaft 6 is profitably between 30...70 cm and the inclination angle °c is profitably between 45°-80°. The fuel inlet shaft 6 extends as far as the combustion chamber 7. At the bottom part of the combustion chamber, at the end of the fuel inlet shaft 6, there is located the grate 8 with a width s preferably equal to that of the fuel inlet shaft 6 and also to the width of the feeder 4, or at least roughly equal . Below the grate 8 there is located the ash pit 9. The rear part of the fuel inlet shaft forms a closed air space 10 provived with the blower 11. The ash pit 9 and the air space 10 can be either separate or interconnected. The ash disposal hatch 12 is located at the back of the ash pit 9.

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. Λ, The fuel feeder 4 is provided with a regulation means (not illustrated in the drawings) which regulates the scattering of the fuel; the fuel is scattered in a continuous flow of a desired volume into the combustion chamber. The fuel entering through the feeder 4 is subsequently dropped onto the grate 8 through the fuel inlet shaft 6. The blower 11 is employed for blowing the air required for the burning into the combustion chamber in a flow of a desired volume. The electric motor of the blower is controlled by means of a suitable regulating device. The grate 8 is formed of several step-like members 81, 82, 83, which members descend parallel to the inclined fuel inlet shaft 6. Through the openings between the members of the grate 8, the combustion air generated by the blower 11 is mainly directed into the combustion chamber 7. The combustion chamber 7 is made of refractory material and it is not directly connected to the fire surfaces of the furnace, i.e. it can be insulated from them. Because of the possible afterburning brickworks provided in the furnace 2 itself, and because of the combustion chamber, the temperature of the flames rises so high that the solid fuel burns as completely as possible. The area of the grate 8 and of the bottom of the combustion chamber likewise is roughly the same as the cross-sectional area of the fuel inlet shaft. The area of the grate is relatively small, and consequently the burner as a whole can be easily installed for example in the bottom hatch of some conventional furnaces or the like. The fuel is dropped in small batches defined by the regulation means from the feeder 4 onto the grate 8 according to the power demand. The amount of combustion air is regulated by means of the blower 11. When the regulating adjustments are carried out correctly, the combustion process takes place in a remarkably even fashion because the amount of fuel added each time is small and the interval between fuel additions is short.

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, WΪPO _ In the preferred embodiment of figure 3, the grate 8 is replaced by only one air opening 15, and the bottom of the combustion chamber 7 now forms the grate 16.

Fuels such as milled peat, sod peat, peat pellets and straw pellets have a high ash content and a low ash melting point. While burning these fuels, the separate and sintered ashes are removed from the combustion chamber 7 by means of a special ash remover 13, which ash remover is illustrated in figure 3. It is programmed to be operated by means of a timer and for instance a linear motor 14 so that at defined intervals it enters through the air opening 15 and shifts the ashes a defined length forward until the ashes fall from the grate 16 into the ash pit of the furnace. After this operation, the ash remover 13 always returns to its back postion, wherefore it stays in the hot space only an •instant at a time. The second task of the ash remover 13 is to spread the fuel : it spreads the burning fuel and ashes forward on the grate, and thus makes room for the fresh fuel which is continuously being fed through the fuel inlet shaft .

If only wood chips are burned, the grate 16 can be replaced by the stepped grate according to figure 1 , and the ash removal system can be left out. The chips are scattered in small batches and at short intervals onto the stepped grate 8, and simultaneously the blower 11 blows combustion air in through the openings of the said grate. The combustion process takes place evenly and completely, particularly if afterburning brickworks are provided in the furnace comustion chamber. The formation of ashes is extremely slight (0,5 % ) , and consequently the deashing periods are 1 ong.

Figures 4-6 illustrate the fuel feeder 4. The said feeder is installed between the fuel bin 5 and the fuel inlet shaft 6. The fuel inlet shaft 6 is profitably provided with a closing trap 17 and a controlling member thereof, such as the electromagnet 18.

The feeder 4 is formed of two or more elongated adjacent support member 41 , which support members are arranged on the same level and are moved in turns back and forth in the fuel conveying or shifting direction B. At the top part of these support members 41, there are arranged the proper conveyor member 42, which are asymmetrical in the shifting direction B so that while the member 41 moves towards the fuel inlet shaft, the conveyor member 42 grips the fuel to be shifted, but while the member 41 moves to the opposite direction, the conveyor member 42 allows the fuel to slide over .

In the preferred feeder embodiment illustrated in the drawings, the support member 41 and the conveyor members 42 form the rod 41 provided with teeth 42, i.e. the toothed rod. Each support member 41 is placed so that it rests on at least one sliding rail 19, which sliding rail is connected to a power source such as the electric motor 20 by means of the articulated rod 21 and the reduction gear 22.

On the border area between the walls of the bin 5 and the moving support members 41 , there are arranged asymmetrical jags, dents, brackets or equivalent obstructing members 23. They are for instance bent form the wall edges so that they allow the fuel to be shifted forward towards the inlet shaft 6 but prevent it from moving bakcwards. The obstructing members 23 can be for example - f1 ake-1 ike or triangular. The bottom part of the bin wall , as well as the walls of the channel wherein the moving support members are 1 1

located, can have a structure similar to that of the support members 41 and the conveyor members 42, but they are stationary so that they function as obstructing members .

The feeder is operated so that the electric motor 20 runs the reduction gear 22, onto the outlet axes 24 whereof there are eccentrically attached the articulated rods 21, which rods are employed for moving the two dented rods 41, 42 installed at the bottom 51 of the bin 5 by means of the sliding rails 19. Power is transmitted to the dented rods 41, 42 via the fastening members 25 fixed in the apertures 52 made in the bottom 51 of the bin 5. There can be several dented rods 41 , 42 placed side by side. The adjacent dented rods 41, 42 move on the same l evel back and forth in opposite directions,, so that the solid fuel is shifted from the bin 5 into the fuel inlet shaft 6 because of the triangular side profile of the conveyor members 42 and because of the continuous back-and-forth movement of the support members 41 in the opposite direction. Particularly while shifting ight fuels or the like, the obstructing members 23 efficiently prevent the material from shifting back in the return direction. The closing trap 17 is open while the feeder is in operation and closed while the feeder is in stand-by position. The closing trap 17 is controlled by means of the electromagnet 18.

The bin 5 and the fuel inlet shaft 6 have a welded airtight structure, so that air is not let into the burner through the feeder 4. The purpose of the sliding rails located at the bottom of the bin 5 is to prevent the support members 41 from moving sideways or vertically, as well as to prevent the fuel from gettin below the support members 41. The purpose of the closing trap 17 is to make sure that the fire does not extend to the bin 5 while the feeder is not in operation. The closing trap 17 is not needed if the fuel inlet shaft 6 has a sufficient height, for instance 50 cm.

The rods and the support members 41 , and the dents 42 or equivalent conveyor members must be designed so that they, while moving away from the fuel inlet shaft 6, draw along as little fuel as possible. In the exemplary case, on the side of the fuel inlet shaft 6, the dents 42 were roughly vertical and on the other side they were slightly inclined, the angle of inclination being for instance between 10...30°. In the exemplary embodiment explained above, the width of the support members 41 and the conveyor members 42 can vary for example within the range 5...100 cm.

The conveying power of the feeder can be adjusted or changed by changing the number of the support members 41 and the length of their movement, by adjusting the rotating speed of the electric motor, by changing the transmission ratio of the reduction gear 22, by changing the width of the bin bottom 51 and of the support members 41, either by narrowing or widening them, as well as by making the electric motor 20 to run periodically.

The length of the movement of the support member 41 is always adjusted with respect to the properties of the material to be shifted. The more porous, the more flexible and the lighter the material is, the longer is the back-and-forth movement required. Heavy materials are shifted by short movements.

The power of the electric motor 20 is defined according to the size of the bin 5, the transmission ratio of the gear 22 and the feeding rate. In practical experiments the employed values have been: bin volume 500 1, transmission ratio 60:1, in which case the outlet rotation speed of the gear 22 is 25 rotations per minute and the frequency of the back-and-forth movements of the adjacent support members 41 is about 25/min. In that case the feeding rate with a 0,25 kW eletric motor is 600 1 wood chips per hour, which corresponds to the caloric capacity of about 600 kW.

The feeder of the above description can be employed for shifting wood chips or equivalent for^'long distances, i.e. at least tens of meters, for instance from the storage into the burner. In that case the feeder is installed for example in an open chute, in a closed pipe or a closed channel , wherein the conveyor or pair of conveyors proper are located. It is profitable to provide the inner surface of the channel or the walls of the chute with the asymmetrical obstruction members 23 illustrated above in connection with figure 2. This secures a successful shifting particularly for light and porous fuel .

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Claims

14PATENT CLAIMS

1. A burner for burning solid, pulverous or granular, fuels, the said burner comprising a combustion chamber, a grate connected thereto and an ash pit located below the grate, the said combustion chamber being provided with an automatic fuel feeder connected thereto by means of an inlet shaft, c h a r a c t e r i z e d in that

- the burner (1) is a separate unit which can be externally installed in a furnace or in a furnace assembly;

- the fuel feeder (4) is connected to the burner (1) by means of an inclined fuel inlet shaft (6) and the feeder (4) is provided with regulation means which regulates the fuel to be scattered in a continuous flow of a desired volume into the combustion chamber;

- the inclined fuel inlet shaft (6) is connected to the grate. (8; 16) which is profitably of the same width as the fuel inlet shaft;

- the combustion chamber^' (7) is provided with a blower (11) which is employed for blowing the necessary combustion air as a flow of a desired volume into the combustion chamber.

2. The burner of claim 1, c h a r a c t e r i z e d in that the area of the grate (8; 16) is equal in size to the cross-sectional area of the fuel inlet shaft.

3. The burner of claim 1 or 2, c h a r a c t e r i z e d in that within the combustion chamber (7), above the grate (16) there is at least one air opening (15) through which the combustion air brought in by the blower (11) is at least partly conducted into the combustion chamber.

4. The burner of claim 1 or 2, c h a r a c t e r i z e d in that the grate (8) is formed of several step-like members (81, 82, 83) which are located parallel to the inclined fuel inlet shaft (6).

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5. The burner of claim 1, 2 or 3, c h a r a c t e r i ¬ z e d in that in connection to the grate (16) there is installed a combined fuel spreading device and remover (13) which is arranged to move in an automated fashion back and forth on the grate surface.

6. The burner of claim 1 or 2, c h a r a c t e r i z e d in that it is directly installed in the bottom hatch or equivalent opening of a conventional furnace so that the combustion chamber of the burner is directly connected to the combustion chamber of the furnace.

7. The burner of claim 1, 2 or 3, c h a r a c t e r i ¬ z e d in that the feeder (4) consists of at least two elongated adjacent support members (41) which move back and forth in turns on the same level and in the fuel shifting direction, at the upper part of which support members (41) there are arranged the conveyor members (42) which are asymmetrical in the transport direction in such a fashion that as the support member (41 ) moves towards the fuel inlet shaft (6), the conveyor member (42) grips the fuel to be shifted, but as the support member (41) moves to the opposite direction, the conveyor member (42) allows the fuel to slide over (figures 4, 5 and 6).

8. The burner of claim 7, c h a r a c t e r i z e d in that the support members (41) of the feeder are planes which are shifted along sliding rails (19) or the like grooves (figures 4 and 5).

9. The burner of claim 7 or 8, c h a r a c t e r i z e d in that the conveyor members (42) of the feeder have a side profile which bears at least a rough similarity to a triangle, so that the front surface of the conveyor members (42) is substantially steeper than the rear surface (figure 4).

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