The present invention relates to a burner head for burning of solid fuels, such as straw, peat, wood chips, coal, etc., comprising an opening for lead-in of the fuel and an opening for discharge of flue gases, and whereby the burner head comprises two tubes having sub¬ stantially parallel axes, whereby one of the tubes is positioned coaxially or with eccentrically positioned axis in relation to the other tube axis.and inside the other tube.

Such a burner head belongs to the state of the Art and is described in Danish patent application no. 2828/83 and is shown in longitudinal cross sections in the Figuresi and 2. This burner head has the drawback, that the materials being used within the combustion area are exposed to large thermal contractions and expansions resulting in either very expensive materials havingto be used as raw materials for the burner head and which materials are able to tole¬ rate the building of high thermal stresses but which mate- rials also are more expensive to handle during the manu- facting process, or the life time for such a burner head comparatively is very short as compared to the advantages being obtained by employing this type of burner head.

The present invention has the purpose to provide a burner head of the aforementioned kind which it is possible tqmanufacturewith lowcosts and of more cheap mate¬ rials, and by which the life time is not limited due to the occurence of thermal stresses in the materials during their use. This is achieved according to the invention by. means of the features mentioned in claim 1. Generally, it is thus sufficient if only the innermost tube is divided into sections. By this means no possibility is present for the occurence of tensions between the two tubes. It is remar-

ked, that in case of using the burner head for large boilers the diameter differences between cold and hot conditions may amount up to some centimeters. Therefore, rather considerable thermal stresses may occur within the materials. By means ^' of the invention these tensions may thus be considerabl reduced.

According to claim 2 clamping means are provided, whereby for instance clamping ribbons may be used which readily may present a certain spring force cooperating to hold the clamping ribbons in gripping position around the positions where the sections meet. If furhtermore, the means according to claim 3 are used in.steadof e".g. suppor¬ ting means which protrude outwardly from the tube sections for " guiding of the clamping ribbons, tube sec- tions with a smooth surface may be used, which though have to be provided with a suitable amount of"holes forthe provi¬ sion of loose rivet connecting elements for the clamping ribbons. It may be an advantage either;to form longishholes, and particularly longish holes in crosswise.direction, ... i.e. perpendicular to the longitudinal direction of the tube sections, in the clamping ribbons or in the tube sections, resepctively. It has been found advantageous to shape the lengths of the sections so that these lengths coorespond approximately to the size of the diameter.

Contrary to the state of the Art, it is advantageous toprovid .a sli±jat .the.^erid of the air passage formed be¬ tweenthe two tubes in themannerdescribed in.claim ^" :4. Here- through it is attained that the mutual operational move- ments of the two tubes due. to the thermal expansions will be more favourable as compared to the slit being shaped invertedly of the specified manner.

Practice has shown, when using embodiments ac¬ cording to the present invention it is advantageous to

arrange vanes as described in claim 5 and/or in claim 9. In this manner the dividing into sections is made more favourable.

A favourable distribution of the heat in the tubes is achieved by means of the features according to claim 6. To achieve a fastening and anchoring for the two tubes, . favourable for the distribution of heat embo¬ diments according to σlaim'7 ars:advantageouslyemployed, op¬ tionally also together with the features described in claim 8.

Embodiments according to the invention, just as embo¬ diments according to the state of the Art, are described in more details as follows with reference to the drawing, wherein: Fig. 1 and 2 illustrate embodiments of the burner head as according to the technique of the state of the Art. A longitudinal cross section is shown in Figure 1, while"the ^" "illustration in Figure 2 is more schematique and serves to indicate the tube directions.

Fig. 3 illustrates a longitudinal cross section through a burner head shaped according to the invention and being substantially straight. Fig. 4 shows cross section IV - IV according to Fi- gure 3,

Fig. 5 illustrates an approximately corresponding em¬ bodiment as the one shown in Figure 3, but with fastening attained.bywelding, and Fig. 6 illustrates schematically a clamping ribbon closure.

Within the single Figures of the drawing the same sign of reference refers to the same means or to means having the same or a corresponding function.

A vertical boiler shell or boiler door carrying..a burner head having a double tube is illustrated in Figure 2.

of the drawing. Dependent on the kind of fuel and on theshape of the combustion chamber the tubes of the burner head may equally well be substantially straight or exhibit an angled shape as indicated in the Figures 1 and 2 inclu- sive of being possibly oblique positioned pointing side¬ ways. The position drawn in dot-and-dash lines in Figure 2 including the angles alpha and beta indicate such possi¬ bilities.

According to Figure 1 two tubes 6 and 7 are arranged coaxially in each other and are fastened to a flange 10 abutting against or being fastened to a boiler shell or boiler door 5. The innermost of the tubes continues into tube 21 in which a feed screw 20 for a solid fuel 2 is arranged. The holes 12, 13, 14, 16, 17 in the innermost tube 7 serve as air supply holes for the supply of fresh air to the combustion, for instance as from a supply tube 9 leading into the intermediary space 8 between the tubes 7 and 6. A ringshaped slit 19 guides a portion of the air supply from the holes 16, 17 into the tube 7 which serves as a flame tube in which the fuel arriving from the feed screw is burning.

In Figure 3 of the drawing a substantially straight shaped burner head as the one illustrated in Figure 1 is shown, butas being an embodiment according to the invention. The difference is mainly that the innermost tube 7 is di¬ vided into sections 7A, 7B, 7C which are kept in position by means of clamping-ribbon-like means 77AB, 77BC. The clamping ribbons which may be loosely tightened around the ends of the sections may be U-shaped with inwardly turned cavity so that the branches of the U-shape are gripping around outwards protruding edges of the ends of the tube sections or around other outwards protruding portions or means upon the tube sections, so that thesemutually and free¬ ly may move due to a large "back-lash", i.e. having so large a "back-lash" that thermal expansion phenomena do"not

lead to squeezings incorporating larger internal heat stresses in the materials. In Figure 6 a clamping ribbon closure is shown which may be employed at the single clamping ribbons 77AB, 77BC, as for instance springlike shaped clamping ribbons havinga rivet or similar means, positioned at one end of the clamping ribbon, and this rivet is gripping into a longish hole in the other end of the clamping ribbon. In this manner the clamping ribbons are kept suitably closed around the section joints as well in cold as in heated conditions.

In the air duct 8 between tube 6 and the internal tube sections 77B and 77Cvanes 118B and 118C, which guide in longitudinal direction, are positioned. These may be positioned there only for air guiding purposes, but they may also serve as mechanical supports to achieve a better holding in position of the tube sections 77B and 77C cen¬ trally in .the tube 6. As illustrated in the Figures 3, 4 and 5 such vanes may be arranged only in the lower half of the burner head. The vanes may be thus positioned that they only stretch along a portion of the longitudi¬ nal lengths of the tube sections 7B and 7C, but as shown in connection with the illustrated embodiment, not stret¬ ching past the single joints between the tube sections 7A, 7B and 7C. This may be anvantageous due to the purpose of air guiding, but it may also be advantageous in that, due hereto, it is easier to pull the inner tube sec¬ tions 77B and 77C out from the central part of the tube 6 as well as to have the clamping ribbons better kept inposition relatively to the external tube 6, particularly at heated condition, as the vanes then serve as position holding means for the clamping ribbons in. relation to the tube 6 by occurrence of longitudinal movements of the clamping ribbons in" relation to the tube 6. It is the most advan¬ tageous that the vanes are positioned internally in the tube 6 not only for the mentioned reason but also because

the tube sections 77B and 77C are most liable to suffer most damage from the burning fuel or in some other way are the first to be worn out, but these are also, .due to their simple shape, in such case the least expensive to exchange with new ones. Furthermore, according to the in¬ vention it is easy to perform such an exchange. Such ex- change may be due to the wish of changing to another type of fuel together with which it is wanted to employ another combination or size of the holes 12, 13 and 14, which holes in the Figures 3 and 5 are designated with 112A and 112B. It may be advantageous that these holes are not. oblique arranged in relation to the longitudinal direction of the tubes, as it usually is the case, but to arrange the holes radially oriented, and possibly backwards poin- ting .in"relation to" the direction of the air flow through the holes, as small particles from the fuel in this waymore easily are prevented from passing unburned through the holes. As indicated by means of the Figures 3 and 4 it may be advantageous to arrange the holes in rows in direction of the peripheral circumference of the tubes whereby .the holes of the single rows are displaced in relation to those of the neighbouring rows. Respec¬ tively, such a displacement might be provided alone or in combination with a mutual rotational displacing of the tube sections when these are connected to each other by means of the clamping ribbon means 77AB and 77BC. The single sections 77B and 77C may hereby be equally shaped, which from the point of view of manufacturing is an advan¬ tage. The fuel supply tube 21 comprises a flange 10 being bolted to a connecting wall between the nearest tube sec¬ tion 7A to the tube 21 and the tube 6. Here two air supply tubes 9 are present. A further flange 100 is arranged on the tube 6. Through a sealing 111 the flange 100 is abut- ting against a boiler shell or a boiler door 5. The tube 6

is prolonged with a tube portion 66 being open at its downwards end and serving to attain a better distribution of the heat from the flame in the tube sections 7B and 7C of the burner head. The tube portion 66 serves to secure a sufficiently long thermal time of reaction for the gases and to secure occurence of turbulence of possible laminar flows of gas arriving into the tube portion 66.

At the end being farthest away from the end of fuel supply the tube 6 has an inwardly turned edge 6D which to- gether with the external side of the tube section 7C forms an air slit 19 from which the air is led out.into the. tube portion 66 and not through holes into the tube sec-;... tion 7C as according to Figure 1. A better stabilizing of the positions of the tube 6 in relation to the tube sec- tions 7B and 7C during the thermal movements is here- through attained. In Figure 4, which illustrates the cross section IV-IV, vanes 118C and also the downwards opening in the tube 66 are shown.

An embodiment of somewhat corresponding kind as the one shown in Figure 3 is illustrated in Figure 5 of the drawing. An.other fastening of the tube 6 and the tube section 7A to the flange 10 is shown, namely a fastening by welding, of which it can be seen that it is the tube section 7A which is welded to the flange 10 whereas a separate connecting element is provided between the tube section 7A and the tube 6 which has a much smaller mate¬ rial thickness than the tube sections 7A, 7B and 7C. .. . _- It is remarked,. that the inwardly turned edge 6D on the, . tube 6 is rather obliquely positioned. Furthermore, in Figure 5 the advantageous embodiment is shown whereby the fuel feed screw 20 comprises a helical portion with a diameter approximately equal to the internal diameter of the tube section 7A. It is possible, that this portion of the feed screwhelix in direction of rotation.may be displaced in tube 21 relative to the preceeding portion.Less materialheat-stressandbetter--heafcTdistributiαrϊandfuel-d istribution'in the tube .sections result hereof.