FUEL-CONVEYING INCINERATION GRATE FOR INCINERATING PLANTS, ESPECIALLY FOR WASTE MATERIALS

Abstract: In a fuel-conveying grate for incinerating plants, consisting of sections having a number of grate beams (1) extending obliquely downward in the direction of movement of the fuel, said beams having a grate top (4) stepped downwardly and being placed with lateral surfaces (3) closely adjacent to each other across the width of the grate, adjacent beams being reciprocable in the longitudinal direction, each beam being adapted for the passage therethrough of a heat-transmission medium, the main novel features are that immediately below the grate surface and in heat-transmitting contact with said surface and the lateral surfaces, longitudinally extending ducts (6, 7) for heat-transmission medium are provided. When heat-transmission medium is circulated through the ducts, temperature differences along the length of the beam are balanced, so that the difference in width between its two ends caused by temperature differences is minimized. In this manner, unwanted interspaces between adjacent beams are avoided.

Description: FUEL-CONVEYING INCINERATION GRATE FOR INCINERATING PLANTS. ESPECIALLY FOR WASTE MATERIALS TECHNICAL FIELD The present invention relates to a fuel-conveying in¬ cineration grate for incinerating plants, especially for waste materials, of the kind set forth in the preamble of claim 1. BACKGROUND ART In principle, incineration grates of the kind referred to above are well-known and are normally used with two or more sections mutually overlapping, the uppermost section functioning as an infeed grate apportioning the fuel into the incinerating plant from a fuel shaft above the upper part of the grate, whilst the function of com¬ bustion per se is served by the lower section or sections, the lowermost section also discharging the solid products of combustion, such as ashes and slags, to suitable re¬ moval devices. In a grate of this kind disclosed in US patent publication No. 4,471,704 and having two sections, adjacent grate beams are reciprocated longitudinally in opposite phase, and the stepped grate surface is formed by a number of grate elements placed edge-to-edge. In another grate of the kind referred to, disclosed in US patent specification No. 4,494,469, every other grate beam is reciprocable longitudinally, while the remaining grate beams are stationary. In this grate, the grate surface is formed by a number of grate blocks composed of grate rods, each block comprising two steps of the stepped surface. In these previously known grates, it is not possible for a heat-transmission medium to flow through the grate beams. In incinerating plants for waste material, especially the infeed grate, i.e. the uppermost grate section in the plant, is subject to extremely inhomogeneous heat influences; this is due to its function and position in the plant as well as variations in the calorific value of the waste material being fed in by this grate, because the processes taking place on the infeed grate comprise both a drying of the waste material and an initial gasi¬ fication and ignition of the latter, and the manner, in which all this proceeds and hence the heating of the grate, depends to a high degree of the (net) calorific value of the waste material, i.e. especially its moisture content. In previously known incineration grates, such as those disclosed in the above-mentioned US patent specifications, these conditions have made it difficult to achieve an effective seal between the adjacent, relatively recipro¬ cable grate beams, more particularly between their lateral surfaces; this is caused by the temperature differences along the grate beams creating differences in their de¬ grees of thermal expansion. An insufficient seal between adjacent lateral surfaces partly results in a greater guantity of ashes and uncombusted waste falling through the grate, this obviously being highly undesirable in consideration of the desire to achieve a sterilization and combustion of the waste material, partly an unintended distribution of the primary air, passing in an uncon¬ trolled fashion up through the gaps between adjacent lateral surfaces. In order to achieve a better sealing function, incinera¬ tion grates of the kind referred to initially normally comprise facilities for pressing the grate beams in each section together in the lateral direction, this also making it possible to accommodate attrition on the lateral surfaces of the grate beams. This attrition, being - of course - due to the relative movements of the grate beams, will, because of their material properties, be a minimum at a relatively low temperature. DISCLOSURE OF THE INVENTION It is the object of the present invention to allieviate the disadvantages referred to above, partly by providing a homogeneous temperature and thermal expansion along the length of the grate beams, partly a lower temperature of the latter and, as far as infeed grates are concerned, a possibility of accelerating the drying of waste material with a high moisture content on these grates. According to the present invention, this object is achiev¬ ed by means of the features set forth in the character- izing clause of claim 1. By circulating the heat-transmission medium in the ducts, variations in temperature along the length of the grate beam are eliminated or reduced, and it is also possible to cool or heat the grate beam depending on the tempera¬ ture of the heat-transmission medium. Even though the grate surface, as in the grate disclosed in US patent specification No. 4,471,704, could consist of a number of separate grate elements, each in heat- conducting contact with the longitudinal ducts, the em¬ bodiment set forth in claim 2 is preferred, as it simpli¬ fies the construction and facilitates assembly and main- tenance. In a further preferred embodiment, set forth in claim 5, the heat-transmission medium flows downwardly along one side of the grate beam and upwardly along its opposite side, thus contributing further to reducing any temperature differences along the length of the grate surface. The embodiment set forth in claim 6 is preferred if the temperature, at which the heat-transmission medium is supplied to the grate beam in the incineration grate, is lower than the average temperature of the grate surfaces. In addition to the primary effect of the circulating heat-transmission medium, viz. an equalization of tempe¬ rature along the length of the grate surface, this will result in a cooling of the latter and of the lateral surfaces and hence a reduction of the attrition on the relatively moving lateral surfaces on adjacent grate beams. Alternatively, the embodiment set forth in claim 7 may be preferred, when the supply temperature of the heat- transmission medium is higher than the average temperature of the grate surfaces. This can be advantageous in infeed grates, when waste material with a high moisture content is to be incinerated, as this material will be receiving heat from the heated grate surfaces for the evaporation of the moisture already when being delivered from the shaft. At the same time, also in this case an equalization of temperature along the length of the grate surface is achieved. This heating medium may then be a heat-trans¬ mission medium having circulated in a succeeding grate section in the incinerating plant. In principle, the heat-transmission medium may be any suitable fluid, such as a gas, a liquid or a two-phase medium, but in practice it is preferred, as indicated in claim 8, to use water as the heat-transmission medium, preferably alone in the liquid phase. Since this water should preferably have been treated in the same manner as feed water for boilers so as to avoid scale being deposited in the ducts and in the inlet and outlet con¬ duits, it may advantageously after having circulated in the incineration grate be supplied to the economizer of the incinerating plant. Alternatively, it may be made to flow through a heat exchanger for cooling and supplying useful heat. Further advantageous embodiments of the incineration grate according to the invention, the effects of which will be evident from the detailed portion of the present description, are set forth in claims 3 and 4. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present descrip¬ tion, the invention will be explained in more detail with reference to the drawings, in which Figure 1 is a diagrammatic side view, partly in longitu- dinal section, of a combustion grate according to the invention, Figure 2 likewise diagrammatically and at a larger scale shows a part-sectional view through a section of an in- cineration grate according to the invention, Figure 3 is a longitudinal sectional view along the line III-III in Figure 4 through a grate beam in an incinera¬ tion grate according to the invention, Figure 4 is a plan view of the grate beam of Figure 3, and Figure 5 is a sectional view of the grate beam shown in Figures 3 and 4 taken along the line V-V in Figure 3, at an enlarged scale. DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 is a side view showing an incineration grate according to the invention consisting of four sections I, II, III and IV, in which the grates in each section consist of a number of grate beams generally designated 1, the side surfaces of which are closely adjacent to each other across the width of the grate. A stationary grate beam 1 is shown in section I, while a reciprocable grate beam 1 is shown in section II. As far as the present invention is concerned, these grates are of similar con¬ struction. As shown, the grate beams 1 have a stepped grate surface and extend obliquely downward in the direc¬ tion of movement of the fuel, the grate beams 1 in a preceding section overlapping grate beams 1 in a succeed- ing section. Below the grate beams 1 in each section there is a primary-air space P, and the combustion space F of the incinerator plant extends across and along the entire incineration grate. The grate section I is an infeed grate feeding-in refuse to be incinerated from a chute or shaft (not shown) into the incinerating plant. From the grate section IV, un-combusted material, i.e. slags and ashes, fall into a slag pit S, from which it may be removed e.g. by means of a conveyor (not shown) . Figure 2 is a part-sectional view at a larger scale through a grate section in an incineration grate according to the invention, in which reciprocable grate beams 1 are placed between stationary grate beams 1 as shown and described in the previously mentioned US patent publica¬ tion No. 4,494,469. Figures 3, 4 and 5 show a grate beam 1 in longitudinal section, in plan view and in cross-section, respectively. The grate beam 1 comprises two main sideboards 2, each having affixed thereto an upper sideboard 3, of which the latter may be in slidable abutment against corres¬ ponding upper sideboards on adjacent grate beams in the grate. The top edges of the upper sideboards 3 are step¬ ped, and an equally stepped, unitary grate plate 4 is secured to these top edges. A primary-air opening 5 ex¬ tending in the longitudinal direction of the grate plate 4 is formed in the centre of each of the latter's steps. The primary-air openings may be omitted in some of these steps, thus in the uppermost steps in infeed grates, i.e. the steps to the left in Figures 3 and 4, on which no combustion is taking place. Two ducts 6 and 7 extend below, along the full length of and in heat-transferring contact with the grate plate 4 and the upper sideboards 3, the top sides of these ducts thus being stepped in the same manner as the grate plate 4. At the lower end of the grate beam 1, i.e. in Figures 3 and 4 the right- hand end, the ducts 6 and 7 are connected to each other through a tubular duct 10, the ducts 6 and 7 being sepa¬ rated by an interspace 11 extending below the primary- air openings 5 in the grate plate 4 and thus connecting the primary-air openings 5 with the primary-air space P below the incineration grate and the grate beam 1. At the upper end of the grate beam l, i.e. the left-hand end in Figure 3 and 4, each of the ducts 6 and 7 have connecting points 13 and 12, respectively - in Figures 3 and 4 shown purely diagrammatically - for supplying a heat-transmission medium to the ducts 6 and 7 and removing said medium from them. Now, if water at room temperature is made to flow through the connecting point 13 and the duct 6, via the tubular duct 10 to the duct 7 and upwardly through the latter towards the connecting point 12, a general cooling of the lower, heated part (the right-hand part in Figures 3 and 4) of the grate beam 1, more particularly of the latter's grate plate 4 and upper sideboards 3, takes place. This causes a thermal contraction of this part of the grate beam 1 to take place, this especially causing a reduction of its width between the outside surfaces of the upper sideboards 3. The water thus having been heated will, when flowing upwardly through the duct 1 , cause the upper part of the adjacent upper sideboards 3 and the overlying part on the grate plate 4 to be heated, thus causing a thermal expansion of the grate beam 1 in this region, especially an increase of its width between the outside surfaces of the upper sideboards 3. Depending on the flow velocity of the water, this makes it possible to achieve an equalization of the width of the grate beam between the outside surfaces of the upper sideboards 3 along the length of the beam, thus making it possible to overcome or at least reduce the disadvantage of lack of sealing between adjacent grate beams 1. At the same time, a cooling of the hottest parts of the upper sideboards 3 and hence a reduced wear on the latter is achieved. Further, when burning waste with an especially high net calorific value, and when not only drying, initial gasi¬ fication and ignition of the waste material occur on the infeed grate, but also an undesired combustion of this waste, a cooling of the grate beams 1 of the infeed grate will be able to cause cooling of the waste material on the latter, thus delaying these processes to such an extent that the undesired combustion on the infeed grate is avoided. If, instead of water at room temperature, heated water is made to flow through the ducts 6 and 7 in the grate beams l of the infeed grate, e.g. water having been heated by circulating through grate beams 1 in a succeeding grate section in the incinerating plant, it is also in this manner possible to achieve the desired equalization of the outside width of each grate beam 1 along its length and hence the desired sealing between adjacent grate beams 1 in the infeed grate. When burning very humid waste with a low net calorific value, the heated grate beams 1 will then also be able to accelerate the evapora¬ tion of moisture from the waste material, thus ensuring a normal process of drying, gasification and ignition of the waste material on the infeed grate. LIST OF PARTS F combustion space P primary-air space S slag pit I grate section/infeed grate II grate section III grate section IV grate section 1 grate beam 2 main sideboard 3 upper sideboard 4 grate plate 5 primary-air opening 6 duct 7 duct 10 tubular duct 11 interspace 12 connecting point 13 connecting point

Claims: CLAIMS: 1. Fuel-conveying incineration grate for incinerating plants, especially refuse-incinerating plants, and consis- ting of sections having a number of grate beams 1 extend¬ ing obliquely downward in the direction of movement of the fuel, said grate beams (1) having a grate top (4) stepped downwardly in said direction and being placed with lateral surfaces (3) closely adjacent to each other across the width of the incineration grate, mutually adjacent grate beams (1) being relatively reciprocable in the longitudinal direction, each grate beam being adapted for the passage therethrough of a heat-transmis¬ sion medium, c h a r a c t e r i z e d i n that i - mediately below the grate surface (4) of each grate beam (1) and in heat-transmitting contact with said surface (4) and the wear-resistant lateral surfaces (3) of the grate beam (1), longitudinally extending ducts (6,7) for said heat-transmission medium are provided, as well as connecting points (12,13) at one end of the grate beam (1) for the flow of heat-transmission medium towards and away from said ducts (6,7). 2. Incineration grate according to claim 1, c h a r- a c t e r i z e d i n that the grate top (4) of each grate beam (1) is a unitary member extending along the full length of the grate beam (1) . 3. Incineration grate according to claim 1 or 2, c h a r a c t e r i z e d by two ducts (6,7) extending below the grate top (4) along the full length of the latter. 4. Incineration grate according to claim 3, c h a r- a c t e r i z e d by longitudinally extending primary- air openings (5) in the middle of at least some of the steps of the stepped grate top (4) , said openings (5) communicating with a primary-air space (P) below the grate through a longitudinally extending interspace (11) between the two ducts (6,7) . 5. Incineration grate according to claim 3 or 4, c h a r a c t e r i z e d i n that the inflow and out- flow (12,13) of the heat-transmission medium are provided at the upper ends of the ducts (6,7), the latter being interconnected (at 10) with each other at their lower ends. 6. Incineration grate according to any one or any of the claims 1-5, c h a r a c t e r i z e d i n that the heat-transmission medium is a cooling medium. 7. Incineration grate according to any one or any of the claims 1-5, c h a r a c t e r i z e d i n that the heat-transmission medium is a heating medium. 8. Incineration grate according to any one or any of the claims 1-7, c h a r a c t e r i z e d i n that the heat-transmission medium is water. AMENDED CLAIMS [received by the International Bureau on 24 Oune 1996 (24.06.96); original claims 1 and 4 amended; remaining claims unchanged (2 pages)] 1. Fuel-conveying incineration grate for incinerating plants, especially refuse-incinerating plants, and consis- ting of sections having a number of grate beams (1) ex¬ tending obliquely downward in the direction of movement of the fuel, said grate beams (1) having a grate top (4) stepped downwardly in said direction and being placed with lateral surfaces (3) closely adjacent to each other across the width of the incineration grate, mutually adjacent grate beams (1) being relatively reciprocable in the longitudinal direction, each grate beam being adapted for the passage therethrough of a heat-transmis¬ sion medium, c h a r a c t e r i z e d in that i - mediately below the grate surface (4) of each grate beam (1) and in heat-transmitting contact with said surface (4) and the wear-resistant lateral surfaces (3) of the grate beam (1) , at least two longitudinally extending ducts (6,7) for said heat-transmission medium are pro- vided, as well as connecting points (12,13) at one end of the grate beam (1) for the flow of heat-transmission medium towards and away from said ducts (6,7), said late¬ ral surfaces (3) being capable of being placed sealingly close to each other over the full length of the beams (1) , primary-air openings (5) for the supply from beneath of primary air for the combustion on the grate being provided in the grate beams (1) spaced from said lateral surfaces (3) . 2. Incineration grate according to claim l, c h a r¬ a c t e r i z e d in that the grate top (4) of each grate beam (1) is a unitary member extending along the full length of the grate beam (1) . 3. Incineration grate according to claim 1 or 2, c h a r a c t e r i z e d by two ducts (6,7) extending below the grate top (4) along the full length of the latter. 4. Incineration grate according to claim 3, c h r¬ a c t e r i z e d by the primary-air openings (5) being provided as longitudinally extending primary-air openings (5) in the middle of at least some of the steps of the stepped grate top (4) , said openings (5) communicating with a primary-air space (P) below the grate through a longitudinally extending interspace (11) between the two ducts (6,7) . 5. Incineration grate according to claim 3 or 4, c h a r a c t e r i z e d in that the inflow and out¬ flow (12,13) of the heat-transmission medium are provided at the upper ends of the ducts (6,7) , the latter being interconnected (at 10) with each other at their lower ends. 6. Incineration grate according to any one or any of the claims 1-5, c h a r a c t e r i z e d in that the heat-transmission medium is a cooling medium. 7. Incineration grate according to any one or any of the claims 1-5, c h a r a c t e r i z e d in that the heat-transmission medium is a heating medium. 8. Incineration grate according to any one or any of the claims 1-7, c h a r a c t e r i z e d in that the heat-transmission medium is water.

Inventors: BINNER SIEGFRIED, JENSEN RASMUS STIG, BINNER, SIEGFRIED, JENSEN, RASMUS, STIG
Applicants: BINNER SIEGFRIED, JENSEN RASMUS STIG, VOELUND ECOLOGY SYSTEMS AS, BINNER, SIEGFRIED, JENSEN, RASMUS, STIG, VOELUND ECOLOGY SYSTEMS A/S
Application year: 1995
Main classification: F23H3
IPC codes: F23G5, F23H3, F23H7