The present invention relates to a means in a heating boiler hav¬ ing a grate onto which fuel material is suppl ed in particle form from a supply pipe, a vibrating means being arranged to cause the grate to vibrate in order to give the fuel particles a toss move- -' ent up from the grate depending on the oscillation effect pro¬ duced by the vibrating means.

In recent years the use of biomass for energy purposes has in¬ creased considerably. The biomass is converted to a fuel in suit¬ able solid form, such as pellets or bric ettes. Fuel pellets are produced from waste-paper, raw timber products, peat, straw and mixtures of these materials, etc. and, due to thei low moisture content (usually below 15%) and high density, they are intended to enable high hearth temperatures when burnt in a heating boiler. However, it has been found that slag is formed due to too high a combustion temperature, in turn caused by too great and rapid sup¬ ply of air. Thus, when wood pellets were burnt intermittently on a grate, this had to be cleared from slag at regular intervals as it became more and more difficult for the primary air to reach the hearth and partially combusted, charcoal pellets had collected on the inner part of the grate.

Fuel pellets have many advantages and valuable properties and there is therefore a great need to solve the problems mentioned above in a satisfactory manner.

EP-A20048089 describes a heating boiler for the combustion of solid fuel on a grate which is not freely suspended in the combus¬ tion chamber but instead rests on a pipe-connection at the bottom of the combustion chamber. A vibrator means is arranged to give the grate a vertical vibratory movement and the grate must therefore be inclined downwards so that the fuel can be spread, while special

measures must be taken to retard spreading of the fuel on the in¬ cl ined grate. The supply means is not connected with the grate or with the vibrator either.

EP-A2 0 041 860 describes a heating boiler at least as compl icated in its design as that according to the specification discussed above. The grate is horizontal and the vibrator arranged so that the fuel particl es resting on the grate are not tossed up but moved forwards without leaving the grate. The forward movement of the fuel particl es is caused by the particl es themselves pushing against each other at the fill ing point, and thus being forced forward. This is facil itated by the vibratory grate.

Swedish patent specification 136 214 describes a vibratory grate for a combustion install ation, which may have a supply funnel with incl ined bottom plate connected to the grate. The fuel supply is regul ated by adjusting an appropriate inclination on the bottom plate. The fuel supply cannot therefore be regul ated simply by al ¬ tering the oscill ation frequency of the vibrator. Neither is the grate freely suspended in the combustion chamber. The vibrator is arranged in the combustion chamber and is connected to the grate, not to the bottom plate of the supply funnel . Neither is the vi¬ brator in any of the described embodiments arranged to impart a tossing movement to the fuel particles. Instead these will only sl ide al ong the bottom pl ate as a coherent bed. The vibrator is not arranged to function as drive source to supply fuel particles to the grate via a supply pipe. First of all , there is no such supply pipe in the known means, secondly the vibrator does not cause the fuel particl es to be tossed obl iquely upwards-forwards, thirdly the bottom plate is incl ined to enabl e the supply of fuel due to a fall ing effect, and fourthly the bottom pl ate is so ar- ranged that, due to vibration, it infl uences the fuel particl es in the funnel so that they fal l down and sl ide along the incl ined bottom plate.

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OMPI

Swedish patent specification 168 460 relates to a method of feed¬ ing fuel along on a vibratory grate with inclined grate surface, while the amplitude is kept constant. No statement is given about free suspension of the grate.

US Patent specification 4,250,818 describes a vibrating combustion bed which is'not freely suspended in a combustion chamber.

A primary object of the present invention is to solve the problems mentioned above in particular in the burning of pellets and simi¬ lar fuel material in a heating boiler and thus considerably i - prove the efficiency of the heating boiler by creating conditions in order to obtain good and uniform combustion and high hearth temperature without the pellets and the combusted material becom¬ ing bonded together to a slag which in turn gradually throttles the supply of primary air to the hearth.

This is achieved according to the present invention which is sub¬ stantially characterised in that the supply pipe is mechanically connected to the grate and arranged to freely support the grate, which is thus freely, suspended in the combustion chamber without contact with the bottom or walls of the combustion chamber, and that the vibrating means is mechanically connected to the supply pipe and arranged to produce a rectilinear reciprocal movement as well as functioning as drive source to feed the fuel particles to the grate via the supply pipe, the vibrating means also being ar¬ ranged to continuously give the fuel particles a toss movement ob- liquely upwards and forwards in the supply pipe and on the grate, whereby the fuel particles move onto the grate and towards the end of the grate opposite the supply pipe.

Preferred embodiments of the invention appear from the following claims.

By having grate and supply pipe buil t together, and journall ed in the manner described, and influenced by a common vibrating means which is mechanically connected to the supply pipe, i .e. located outside the hearth, a simple additional unit is obtained for simple re- building of conventional heating boilers and an improved efficien¬ cy. The rectil inear movement described by the vibrating means i s transmitted directly to the supply pipe and the grate so that the- fuel particl es are constantly hit and will form a toss movement obl iqeuely upwards- forwards in an irregul ar pattern. Since the fuel particles are in motion the whole time they will hit against each other and against the grate so that combusted material on the surfaces of the particl es is removed therefrom and new material is exposed for continued combustion. Neither do the fuel particles have any chance of becoming sintered together or forming slag since they are in constant movement on the grate. They do not, therefore, form a compact bed. In experiments using pell ets in the means according to the invention the heating boiler has been found to be considerably more efficient in that a satisfactory and uni¬ form combustion and high hearth temperature can be maintained in a surprising manner, without pel l ets and the combusted material be¬ ing bound together to sl ag. A very smal l amount of ash is obtained as the only waste product.

The invention will be described further with reference to the ac¬ companying drawings.

Figure 1 shows schematically a heating boiler in section which is provi ded with a means according to the present invention.

Figure 2 shows the heating boiler according to Figure 1 seen from the front with certain parts removed.

The drawings show schematical ly a heating boiler 1 which may be of conventional type. The heating boil er has a combustion chamber 2

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into which the fuel material is introduced and combusted. The flue gases are withdrawn through a flue-gas pipe in known manner.

The heating boiler is equipped with a means according to the pre¬ sent invention which, in the embodiment shown, comprises a grate 3 located in the combustion chamber, said grate having a bottom 4 and surrounding side walls ^{" '} 5. The grate bottom is provided.with through-holes or openings permitting air to flow through the grate in direction from below. The grate is arranged horizontally but may in certain cases be upwardly inclined in order to reduce the speed at which the particles move.

The grate 3 ^" is supported by supporting means permitting it to be brought into oscillation at a suitable frequency by means of a vi¬ brating means so that the fuel material, which is in piece or par¬ ticle form, is brought into a toss movement obliquely up from the bottom 4 of the grate in forward direction.

The fuel material is supplied into the combustion chamber 2 through a supply pipe 6 which in the embodiment shown simultane¬ ously serves as a part of the supporting means for supporting the grate which is thereby freely suspended in the combustion chamber without having any contact with the bottom or walls of the com¬ bustion chamber. A horizontal portion of the supply pipe 6 is passed through an aperture in a vertical door 7 which is detacha- bly mounted to the front of the heating boiler. The supply pipe terminates in the combustion chamber with a vertical portion hav- ing an inclined guide plate 8 which ends above the bottom of the grate so that the fuel material can fall freely onto the grate.

Two brackets 9 are secured to the front door 7 which, via springs 10, support two cross-stays 11 attached to the supply pipe 6. The brackets 9, springs 10 and cross-stays 11, together with the sup- ply pipe 6, form said supporting means for supporting the grate 3 such that this can be brought into rectilinear oscillation as will be described below. In other words, the grate 3 and supply pipe 6

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are springingly or resiliency suspended at the front door 7 via the cross-stays 11 and brackets 9, and the springs 10 connecting the cross-stays 11 and brackets 9.

The supply pipe 6 has a hopper 12 suppl ied with fuel materi al from a store 13 which may consist of a separately suspended funnel im¬ mediately above the hopper 12 as shown in the drawings , or a silo or the l ike having suitable feeding means connected to the supply pipe 6. The funnel 13 has a mouth pipe 14, vertically adjustabl e to cooperate with an incl ined pl ate 15 below, which is arranged in the hopper 12 to regul ate the feeding rate of the fuel material .

The rearwardly inclined pl ate 15 defines a gap 16 with the oppo¬ site wall of the hopper. The size of thi s gap 16 may be adjustabl e if desired, to offer an additional possibil ity of adjusting the correct feeding rate of the fuel material . Sai d control means in the form of the mouth pipe 14 and gap 16, can suitably be control¬ led and adjusted by one or more other functions of the heating boil er and possibly by external factors.

In the shown embodiment, a pipe 17 for the supply of air is passed through the front door 7, paral lel to the supply pipe 6, the air- -supply pipe 17 being connected to a fan motor 18 which can be started when desired to forcedly blow in primary air, for instance for continuous operation or when the heating boiler starts and for a suitable period thereafter. The ai r-supply pipe extends below the grate 3 and ends at the inner end portion of the grate and be- low the bottom 4 of the grate, whereby air for the combustion flows in a favourable manner in direction to the place for the supplying of the fuel material .

A vibrating means 19 is arranged below the supply pipe 6 and in direct mechanical connection therewith. The vibrating means is ar- ranged to bring the supply pipe 6 and thus al so the grate 3 which is rigidly connected to the supply pipe by means of welding or ri v-

et or screw joints, for instance, into oscillation or reciprocal movement with a suitable frequency and amplitude, whereby the os¬ cillating movement is transmitted from the outer end of the supply pipe comprising the hopper 12, to the inner end of the grate. The fuel material in particle form entering the hopper 12 will thus be

#_ fed forward through the supply pipe 6 and further out onto and across the grate where it is graduall -combusted. The fuel parti¬ cl es thus acquire a toss movement such that they the whole time are moved up from the support, i .e. the bottom of the supply pipe and the bottom 4 of the grate, and forwards in rel ation to the support, in a manner particul arly conducive to the combustion. Since the fuel particles are constantly in motion, they will hit against each other and against the grate so that combusted material is removed from the particl es and new material exposed for the conti nued com- bustion. Furthermore, the particl es have no chance of sintering to¬ gether or of forming sl ag si nce they are in constant movement on the grate.

The flow of the fuel material is determined by the frequency and osci ll atory effect of the vibrating means. The oscil l ation a pl i- tude can be regul ated steplessly. Increased oscil l ation ampl itude thus means that the fuel particl es are tossed up in a higher path in rel ation to the grate.

If desi red, the movement course of the fuel particl es can be im¬ proved still further by di recting the air for the combustion in be- low the grate such that the ai - flows up through the apertures in the grate as in the embodiment shown schematically. An excess of air normal for the combustion is thus util ized. If desired, the air flow through the grate can be further increased by feeding back some of the flue-gas leaving, whereby this portion of fl ue-gas is mixed with a quantity of air suitably adjusted for the combustion

( incl uding said excess) . By directing the air-flow in the manner described, both ashes and small pieces of the fuel particl es are prevented from fal l ing down through the grate. Such smal l particl es remain when most of the fuel particl es have been combusted and have

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a size that is smaller than the appertures or openings in the grate.

Any known vibrating means which provides a rectilinear oscillatory movement can be used to effect vibration of the grate and supply pipe and may comprise magnet vibrator, unbalanced motors or me- chanical means such as crank and excenter. According to a prefer¬ red embodiment of the invention a magnet vibrator is used, the os¬ cillations being produced by an electro-magnet supplied with al¬ ternating current. One half-period of the supply voltage is nor¬ mally cut off by means of a uni-directional rectifier in order to obtain a lower periodicity, e.g. 3000 oscillations per minute. An advantage of the magnet vibrator is that it functions extremely reliably. Furthermore, the flow of material can be controlled and regulated steplessly during operation since an alteration in the control signal results practically instantaneously in a corre- sponding alteration in the flow of material. The magnet vibrator is mounted so that its centre line forms an acute angle with the direction of transport of the fuel material, as can be seen from the drawings, thus setting the conveyor, i.e. the supply pipe 6 and grate 3, in rectilinear oscillation, provided the grate supply, pipe and magnet vibrator are correctly balanced in relation to each other and the journal!ing points. Said acute angle between the centre line (the direction of vibration) of the vibrating means and the direction of transport of the fuel material may be varied depending on the desired toss angle (corresponding to said acute angle) of the fuel material. A suitable range of the acute angle is about 25°-40°, the preferred range being 30°-35°. The vibrating means is suitably adjustable so that the direction of vibration and thereby the acute angle and toss angle may be amended to values desired.

In accordance with the invention the magnet vibrator or other vi¬ brating means has the double function to serve as drive source to feed the fuel particles to the grate and also to set the grate in oscillations which result in that the fuel particles are brought in a toss movement obliquely upwards so that they move into the grate

towards its far end at the same time as they are relieved from burnt material by hitting against each other and against the grate, thus essentially improving the combustion and increasing the efficiency of the heating boiler. The supply of the primary air is preferably carried out by forced blowing by means of the fan motor 18, ensuring an uniform and complete combustion at the same time as the. fuel par¬ ticles will be carried and further tossed around by -the air flowing through the grate when they are hit by the air jets. The ash will accompany the flue-gas upwards and then be collected at the bottom of the combustion chamber. Secondary air may be added at a point above the grate, particularly if the fuel particles contain volatile material which would otherwise disappear without being burnt. An ig¬ nition device 20 is preferably arranged in the vicinity of the grate in order to ignite the fuel material when the heating boiler is started. When the correct boiler temperature has been reached the supply of fuel particles is reduced by control means to zero or to such a low level that maintenance combustion can be maintained in the grate until the boiler temperature has fallen and a signal is again given for full combustion.

If considered suitable, a net or the like may be arranged on the roof of the grate to prevent fuel particles from being carried out¬ side the grate.

The means according to the invention has been developed with the problem of burning pellets particularly in mind. However, it offers valuable advantages when burning other fuel materials in particle form and should not therefore be considered to be limited to pel¬ lets.

The means according to the invention comprising grate and vibrating means and supply pipe,. .e. grate and supply pipe built together and journalled in the manner described and actuated by a comπon vi¬ brator, forms a simple additional unit for easy rebuilding of con¬ ventional heating boilers to which feeding means are connected from an adjacent stock of pellets.