Patent Description:
The solution according to the invention is well suited for use in the types of burners using solid fuel, wherein the solid fuel is fed into the burner continuously as an essentially even infeed, e.g. on a screw conveyor. In such a case, the fuel is preferably mainly wood pellets or wood chips. The burner in which the wood pellets or wood chips are used can also be called a bioburner.

In these types of solid-fuel burner solutions, controlling the heat of the combustion chamber has generally been a problem, in particular conducting excess heat away from the surface of the grate. Excessive heat causes various problems, among them wear of the grate structures that can reduce the service life of the grate.

Efforts have been made to solve the problem in solutions known in the art, mainly with the circulation of flue gases, but this has produced new problems. In such a case, e.g. ash can enter the circulation of flue gases, in which case the ash can block the air space below the grate structure. In that case the air needed in the combustion process, and the oxygen flow therein, is obstructed, in which case the combustion is not able to occur cleanly and efficiently enough. Consequently, the impure combustion also causes environmental problems and emission problems.

Cooling solutions with water circulation have also been used for cooling a grate. One such solution is disclosed in European patent no. <CIT>, which does not, however, relate to the grate of a conventional bioburner, but instead to the grate of a large refuse incineration boiler. The solution according to the patent comprises a downward-staggered grate of large size, in which a number of different grate plates are used. In the top part of the grate are movable grate plates and stationary grate plates disposed in alternate rows one above the other. Both are cooled with water. Since there is a large number of grate plates, the water cooling of all the grate plates with a water pipe leads to a complex and cramped structure in the space below the grate. The vulnerability to faults and the maintenance requirement are high and, at the same time, maintenance and repair measures are difficult to carry out owing to the cramped space.

Document <CIT> presents a solution which has a module cooling system formed of lower walls that are associated under combustion walls to form chambers in which cooling liquid e.g. water, circulates. Each chamber is formed between the corresponding lower wall and combustion wall. A movable part pushing household waste is displaced in translation along an upper side of a component between retracted and deployed positions.

Document <CIT> presents a solution where a sliding fire grate module consists of a plurality of reciprocally moved grating steps, a primary air supply and an ash collector, and the entire grate with all its drive, feed and control elements forms a modular unit suitable for road transport. To this end the grate is laterally delimited by two outwardly open planks through which a coolant can flow, and which bear all the overlapping grating steps on steel tubes which connect them or on steel rollers which are directly or indirectly attached to them. Each grating step consists of hollow grating panel which is fitted with connections for coolant. These grating panels extend over the entire clear width between the planks. Every second grating panel or grating step is driven by its own hydraulic cylinder-piston unit, which is built in directly beneath it and attached with its stationary end to a steel tube connecting the planks. The movable grating panels or grating steps run on steel rollers which are directly or indirectly attached to the planks.

The purpose of this invention is to eliminate the aforementioned drawbacks and to provide a dependable, operationally reliable liquid-cooled grate for a solid-fuel burner, which grate has a long service life and is as maintenance-free as possible. The liquid-cooled grate according to the invention is characterized by what is disclosed in the characterization part of claim <NUM>. Other embodiments of the invention are characterized by what is disclosed in the other claims.

The invention relates to a liquid-cooled grate for a solid-fuel burner, the grate comprising an input aperture for fuel, a fan, and a circulation system for the cooling fluid, and which grate comprises one or more stationary grate levels formed by a stationary grate plate and one or more movable grate levels formed by a movable grate plate, which grate levels are disposed to overlap one above another. Each liquid-cooled stationary grate plate is adapted to cool the movable grate plates that are below it and/or above it that do not have liquid cooling.

One advantage, among others, of the solution according to the invention is that by means of liquid cooling, for example by means of water cooling, the grate elements withstand use better, in which case their service life lengthens. One advantage is also that the cooling does not require the circulation of flue gases, so there is no risk of ash getting into the circulation of the flue gases, in which case the ash could clog the air space below the grate structure and thus prevent the flow of oxygen, whereby the impure combustion would also have environmental problems and emission problems. A further advantage, especially with respect to the aforementioned European patent, is that the grate solution according to the invention is considerably simpler and more maintenance-free. In addition, a smaller space requirement makes better cooling of the movable grate plates possible, because larger cooling liquid pipes can be placed under the grate, in which case the cooling efficiency improves, and therefore also the movable grate plates can be cooled better by means of the stationary grate plates that are above and below the movable grate plates.

In the following the invention will be described in more detail by the aid of one example of its embodiment with reference to the attached simplified drawings, wherein.

<FIG> present a side view of one solid-fuel burner <NUM> according to the invention, more concisely burner <NUM>, partly sectioned at its rim in such a way that the combustion chamber is visible at the point of the grate 1a of the burner <NUM>.

The burner <NUM> according to the invention comprises a boiler 1b, an input aperture <NUM> for the solid fuel, a screw conveyor 4a for fuel with a drive motor 4b, one or more igniters 4c and a fan <NUM> blowing air into the combustion chamber. The solid fuel can be e.g. wood-based chips or pellets. In addition, the combustion chamber of the burner <NUM> comprises a plurality of stationary, liquid-cooled grate plates <NUM> and a plurality of moving grate plates <NUM> as well as a moving mechanism <NUM> for the moving grate plates <NUM>, the drive device <NUM> of which moving mechanism is preferably outside the burner <NUM> at the front end of the burner, i.e. at the first end. The liquid cooling can be e.g. water cooling and the cooling liquid used can be water. The grate plates <NUM> and <NUM> form the part of the grate 1a supporting and moving the fuel and ash.

Furthermore, the burner <NUM> comprises an input pipe <NUM> and an output pipe <NUM> for the circulation of the cooling liquid of the liquid-cooled grate plates <NUM>. The circulation piping of the cooling liquid, e.g. water, is connected to each liquid-cooled grate plate <NUM> in such a way that the cooling liquid circulates in essentially all the stationary grate plates <NUM>. The input pipe <NUM> and output pipe <NUM> for cooling liquid are preferably connected to the liquid cooling system of the burner <NUM>, which system is not presented in the drawings for the sake of clarity. What is essential is that the cooling liquid is arranged to be directed from the cooling system of the burner <NUM> to the input pipe <NUM> for the cooling liquid, and from the input pipe <NUM> into the cooling ducts <NUM> of the stationary grate plates <NUM>, cooling the stationary grate plates <NUM>, and that the cooling liquid is arranged to exit back to the cooling system of the burner <NUM> via the output pipe <NUM> of the cooling system.

The grate plates <NUM> and <NUM> can be of different widths, but suitably they are of equal height, i.e. they are equally thick in the vertical direction. Preferably at least the stationary grate plates <NUM> are of equal height relative to each other and, correspondingly, the movable grate plates <NUM> are of equal height in relation to each other.

The grate plates <NUM> and <NUM> are placed in the grate 1a row by row in such a way that closest to the fuel input end is the topmost row of grate plates situated side by side, which grate plates are preferably fixed, i.e. stationary, grate plates <NUM>. In an overlapping position below the topmost row, up against the bottom surface of the topmost row, is the next row of grate plates situated side by side, which are now preferably movable grate plates <NUM>, which are not provided with liquid cooling ducts or a liquid cooling space, so that there is no circulation of the cooling liquid inside them or in connection with them. This means that the movable grate plates <NUM> themselves do not have liquid cooling of their own. The third row, below and overlapping the second row, is again a row of liquid-cooled fixed grate plates <NUM>, and so on, always with the next row below and overlapping the previous row and farther away from it going towards the second end of the burner <NUM>.

Preferably each row comprised of grate plates <NUM>, <NUM> forms its own grate level. Thus, a grate 1a is formed that is overlapping and staggered downwards in the direction of travel of the fuel, wherein the stationary grate plates <NUM> of every second row are provided with liquid cooling implemented with liquid cooling ducts <NUM>, i.e. with a circulation of cooling liquid, and the moving grate plates <NUM> between them of every other row do not contain liquid cooling ducts <NUM>, nor therefore a circulation of cooling liquid. Each grate row forming a grate level is disposed in the grate 1a transverse to the longitudinal axis of the boiler 1b, i.e. at the same time in the transverse direction of the grate 1a, and the lower row always closer to the second end of the burner <NUM>.

The solid fuel of the burner <NUM> is fed via the fuel input aperture <NUM> to a screw conveyor 4a, which conveys the solid fuel to the combustion chamber of the burner <NUM> for burning, in which combustion chamber the fuel is first guided to the topmost stationary grate plates <NUM> of the burner <NUM>. The burnt solid fuel is transferred in the combustion chamber of the burner <NUM> preferably by means of the movable grate plates <NUM>, which move between the stationary grate plates <NUM> in the direction of the stationary grate plates <NUM>, i.e. towards the second end of the burner <NUM>. The reciprocating movement of the movable grate plates <NUM> is arranged by means of a moving mechanism <NUM>, the first ends of which are connected to the end parts of the movable grate plates <NUM> and the second end of which to the drive device <NUM> of the moving mechanism <NUM>, which drive device is preferably e.g. a spindle motor or a hydraulic cylinder or pneumatic cylinder. The movable grate plates <NUM> are positioned between the stationary grate plates <NUM>, whereby the cooling liquid flowing in the cooling ducts <NUM> of the stationary grate plates <NUM> also preferably cools the movable grate plates <NUM> via their upper and lower surfaces.

<FIG> presents the positioning of the stationary grate plates <NUM> and the movable grate plates <NUM> of the burner <NUM> according to the invention in the second extreme position of the movable grate plates <NUM>, in which the moving mechanism <NUM> of the movable grate plates <NUM> is also in its second extreme position. Thus, the ash produced by the burner <NUM> can be guided away from the grate 1a and the burner <NUM> via the second end of the burner.

<FIG> present one stationary grate plate <NUM> of a burner <NUM> according to the invention. <FIG> presents the frame part 2a of a grate plate <NUM> with its cooling liquid ducts <NUM>, <FIG> presents the cover plate <NUM> to be placed onto the ducts <NUM>, and <FIG> the grate plate <NUM> assembled as a package with the cover <NUM> attached to the frame part 2a.

<FIG> shows one stationary grate plate <NUM> of the burner <NUM> according to the invention and its cooling duct <NUM>, which is arranged to run along a tortuous path inside the frame part <NUM> and to cover as large a surface area as possible of the second planar surface of the grate plate <NUM>, preferably of the top surface. The shape of the route, including the bends, of the duct <NUM> is implemented with mutually parallel, preferably straight, support elements 2b, which have a plurality of holes 2c extending through the entire grate plate <NUM> in the thickness direction for the passage of air and ash. Every second support element 2b is attached to the inner surface of the first end wall of the frame part 2a, extending towards the second end wall in such a way that the free end of the support element 2b is approximately the width of the duct <NUM> away from the inner surface of the second end wall. Correspondingly, every other support element 2b is attached to the inner surface of the second end wall of the frame part 2a, extending towards the first end wall in such a way that the free end of the support element 2b is approximately the width of the duct <NUM> away from the inner surface of the first end wall. Thus, a continuous cooling liquid duct <NUM> circulates inside the frame part 2a from the input aperture 6a to the output aperture 7a.

<FIG> presents the cover plate <NUM> of one stationary grate plate <NUM> of the burner <NUM> according to the invention, which cover plate imitates the shape of the cooling duct <NUM> of a stationary grate plate <NUM> of the burner <NUM> and, when installed into position, seals the cooling duct <NUM> to the end and side edges of the frame part 2a and to the edges of the support elements 2b.

<FIG> presents one stationary grate plate <NUM> of the burner <NUM> according to the invention, with the cover plate <NUM> installed on the frame part 2a to cover the duct <NUM>. The cover plate <NUM> tightly closes the cooling duct <NUM> of the stationary grate plate <NUM> and forms a uniform, tight and essentially coplanar structure with the frame part 2a of a stationary grate plate <NUM>. Preferably, the cover plate <NUM> together with the support elements 2b function as an essentially even bottom surface of a grate plate <NUM> placed into position.

Essentially cool cooling liquid, for example water, is arranged as an essentially continuous flow from the liquid cooling system of the burner <NUM> by means of an input pipe <NUM> into the cooling ducts <NUM> of the stationary grate plates <NUM> via the input aperture 6a. The warmed cooling liquid exits from the cooling duct <NUM> of the grate plate <NUM> in an essentially continuous flow via the output aperture 7a and onwards via the cooling liquid output pipe <NUM> back to the liquid cooling system of the solid-fuel burner <NUM>, where the warmed cooling liquid is cooled again.

Preferably there is a separate connection from the input aperture 6a of each cooled and stationary grate plate <NUM> to the input pipe <NUM> and, correspondingly, there is a separate connection from the output aperture 7a of a grate plate <NUM> to the output pipe <NUM>. Most suitably, the input apertures 6a and the output apertures 7a of the stationary grate plates <NUM> are located at the end adjacent to the fuel input end, i.e. at the end adjacent to the first end of the burner <NUM>. In such a case, the liquid hoses or liquid pipes connected to said apertures 6a and 7a are isolated from fire and ash and are protected under the stationary and movable grate plates.

It is obvious to the person skilled in the art that the different embodiments of the invention are not limited only to the example described above, but that they may be varied within the scope of the claims presented below. What is essential is that the stationary grate plates are preferably cooled by means of essentially cool cooling liquid circulating in the cooling ducts. Thus, for example, the shapes, dimensions, amounts, size and proportions of the main components may differ from those described above.

It is also obvious to the person skilled in the art that the cooling liquid used in the cooling system may also be other than water. What is essential is that the stationary grate plates in the solution according to the invention are preferably cooled by means of the liquid flowing in the cooling duct system of a stationary grate plate, and that the cooling liquid is supplied to the cooling duct system by means of a cooling system.

It is also obvious to the person skilled in the art that the cooling ducts of grate plates can be only in stationary grate plates or only in some of them, or only in movable grate plates or only in some of them, or in both stationary and movable grate plates or only in some of them.

It is also obvious to the person skilled in the art that a number of grate plate assemblies can be installed below the first grate plate assembly. What is essential is that a liquid-cooled stationary grate plate cools down the movable grate plates below and above it.

It is also obvious to the person skilled in the art that the number of stationary and movable grate plates need not be the same, so that e.g. there can be more stationary grate plates than movable grate plates or vice versa.

Claim 1:
Liquid-cooled grate (1a) for a solid-fuel burner (<NUM>), the grate comprising an input aperture (<NUM>) for fuel, a fan (<NUM>) and a circulation system for the cooling fluid, and which grate (1a) comprises one or more stationary grate levels formed by a stationary grate plate (<NUM>) and one or more movable grate levels formed by a movable grate plate (<NUM>), which grate levels are disposed to overlap one above another, in which case the stationary grate plate (<NUM>) comprises a cooling duct (<NUM>), which cooling duct (<NUM>) has an input aperture (6a) at its first end and an output aperture (7a) at its second end, and each liquid-cooled stationary grate plate (<NUM>) is adapted to cool the movable grate plate (<NUM>) below it and/or above it in which there is no liquid cooling, wherein the shape of the route, including bends, of the cooling duct (<NUM>) is implemented with mutually parallel, preferably straight, support elements (2b), characterized in that each of the support elements (2b) has a plurality of holes (2c) extending through the entire grate plate (<NUM>) in the thickness direction for the passage of air and ash.