The present invention relates to a solid fuel stoker and comprising a tunnel shaped combustion chamber or hearth of which the bottom part consists of a water cooled, double walled steel construction with a plane lower part and up¬ wards/outwards inclined side walls, and of which an upper curved part consists of cheramic elements, by said stoker fuel is supplied by means of a worm conveyor through a sto¬ ker opening and carried forward in the hearth by a recipro- eating scraper conveyor arranged along said bottom part, said side walls - between mutual parallel water filled coo¬ ling pipes - are provided with inlet openings for combus¬ tion air.

Known stokers of this type do not exploit the fuel quite optimum, which gives an insufficient fuel economy and may result in environmental problems, because the stoker emits unburnt and/or poisonous gasses to the surroundings.

Furthermore the scraper conveyor of the stoker requires constantly maintenance, as the scraper elements simply are damaged by burning or destroyed by clinkering.

The invention has for its purpose to provide a stoker of the type described in the introductory part, and by which said problems by simple provisions may be solved.

The stoker according to the invention is distinctive in that the scraper conveyor is provided with transverse main- ly triangular, hollow scraper elements being connected with a central beam which in the longitudinal direction is made from sections in such a way that the cooling water may be supplied to the scraper elements via one pipe section and may be discharged from the scraper elements via another pi- pe section, and that the scraper conveyor moreover compri-

ses inlet openings through which primary combustion air may be admitted along the lower part of the heart.

By simple provisions a stoker is hereby obtained, by which the scraper elements by means of water cooling in a simple manner are protected against overheating and destruction. Furthermore a more uniform combustion is obtained by the fact that via the scraper conveyor extra primary combustion air at the same time may be admitted a lower center area of the fuel.

Appropriately the stoker is such provided that the air in¬ let openings for admittance of primary combustion air along the bottom part of the heart is provided in the central beam and is positioned between the scraper elements in out¬ wardly opened, angular recesses along opposite sides of an underside of the beam. Hereby it is obtained in a simple manner, that the air inlet openings by reciprocating of the beam are kept free from ashes constantly.

In order to more optimum to control the admittance of com¬ bustion air in dependence on the actual type of fuel the stoker according to the invention furthermore may be provi¬ ded so that said inlet openings for combustion air in the side walls of the heart are devided into three groups each being connected with separate air inlet channels, namely so that a lowermost group is connected with an air inlet chan¬ nel for primary combustion air, while middle and upper groups are connected with air inlet channels for secundary combustion air, and that - in connection with said air in¬ let channels - air valve means are present for controlling of the air admittance to the respective groups of inlet openings.

In the following the invention is described in more detail with reference to the drawing, in which:-

Fig. 1 is a perspective view - partly in section - of an embodiment for a stoker according to the invention.

Fig. 2 is a perspective view - partly in section - of the heart of the stoker cf. Fig. l.

Fig. 3 is a side view of an embodiment for a scraper con¬ veyor of the stoker according to the invention,

Fig. 4 is a top view of the scraper conveyor cf. Fig. 3,

Fig. 5 is a view - partly in section - of the scraper con¬ veyor cf. Fig. 3 and 4, and

Fig. 6 is a cross sectional view through the heart of the stoker according to the invention.

The stoker 2 shown In Fig. 1, as stoker unit for a not shown heating boiler system, includes a tunnel shaped fuel chamber or heart 4 (Fig. 2) , into which fuel from a fuel silo 6 is stoked by means of a worm conveyor 8 through a stoker opening 10, and by which the combustion air is sup¬ plied by two blowers 12. The longitudinal heart 4 has a plane bottom part 14 and lower side wall parts 16 stretch- ing slightly inclined (approx. 15° from vertical) upwards/ outwards to an upper curved part 18 consisting of cheramic material. The bottom part 14 and the side wall parts 16 consist of steel plate and are water cooled (Fig. 6) . Be¬ tween mutual parallel cooling elements 20 having triangular cross section and formed by welding free edge flanges of angle iron to the outsides of the side wall parts 16, there are in the side wall parts 16 provided rows of air inlet openings 22, which outside the fuel chamber/the heart 4 are connected with air dispersion chambers I, II, or III, as the air inlet openings of each row are divided into three groups, of which the lowermost group of the respective rows

are connected with air dispersion chamber I (primary com¬ bustion air) , while the middle and uppermost groups are connected with the air dispersion chambers II and III (se- cundary combustion air) . The cooling elements 20 are con- nected with a water jacket 24 surrounding the cheramic sus¬ pended arch 18.

On the plane bottom part 14 of the heart 4 a reciprocating scraper conveyor 26 is arranged, which is driven by a not shown driving mechanism from which a central beam 28 stretching along the bottom part 14 of the heart 4 under the stoker opening 10. The beam 28 is provided with side¬ wards projecting hollow scraper elements 30 having such triangular cross section, that a front side 32 of the scra- per element 30 by moving forward is pushing fuel, ashes, or clinker forward in the heart 4, and that a sharp rear edge 34 of the scraper element 30 during the return stroke bring along a minimum of material.

The hollow scraper elements 30 are connected by welding to opposite sides of the beam 28, which in a longitudinal di¬ rection include several parallel pipe sections, namely a lower central air supply pipe 36 with a mainly quadratic cross section, an upper broader discharge pipe 38, and two narrow water supply pipes 40 being placed at the outside of the pipe 36, and which are mutually connected, so that the assembled beam 28 as a whole has a mainly quadratic cross section.

By means of lower side openings 42 in the narrow water sup¬ ply pipes 40 the scraper elements 30 may be supplied with cooling water, which again may be discharged via upper side openings 44 in the broader discharge pipes 38. In the lower part of the beam 28 - between the scraper elements 30 out- wardly open angular recesses 46 are provided, which via air nozzle openings 48 are connected with the air supply pipe

36, so that primary combustion air may be admitted along both sides of the beam 28, when this is reciprocated along the bottom part of the heart, that is under the fuel. When the scraper conveyor 26 is reciprocated in the fuel/ashes the angular recesses 46 along opposite under sides of the beam 28 will automatically keep the air nozzle openings 48 free from fuel/ashes, so that the supplied primary combus¬ tion air unhindered may be admitted along the bottom part 14 of the heart 4.

The scraper conveyor 26 provides for continously to trans¬ port fuel, ashes, and clinker forwards on the bottom part 16 of the heart until ashes and clinker via a brake plate 50 drop into a transverse clinker crushing worm 52 and further out of the stoker by means of a ashes disharging worm 54.

Finally it shall be emphasized, that the stoker according to the invention enables a really effective combustion of almost all solid fuel, including relative humid and possib¬ ly comminuted fuel with a little heating value, which just is possible because there is made use of a closed bottom surface and extra supply of primary combustion air via the scraper conveyor.