EP3561382A1

EP3561382A1 - Pellet burner afterburner

Info

Publication number: EP3561382A1
Application number: EP19460022.7A
Authority: EP
Inventors: Michal Brzeski
Original assignee: Pellasx Sp zoo SK
Current assignee: Pellasx Sp zoo SK
Priority date: 2018-04-25
Filing date: 2019-04-25
Publication date: 2019-10-30
Also published as: PL236104B1; PL425361A1

Abstract

The pellet burner afterburner according to the present invention is installed in the burner at the border of a combustion chamber (2) and a fuel inlet (3) being the terminal section of an internal feeding pipe (4), seated on the feeding pipe (4).

Furthermore, the afterburner according to the present invention is characterized in that it contains a guiding pull rod (5), which makes a reciprocating movement and is connected by means of an articulated joint (6) and guides (7) to a movable ring (8), which has cut-outs (9) on its perimeter, adapted to both the number and the shape of the profiled guiding vanes (10), which are fitted at equal intervals to the mounting plate (11), whereby the ring (8) is slide-mounted on to the guiding vanes (10).

Description

The subject of the invention is an afterburner designed to burn pellets and agro pellets, mounted in the door of any heating boiler, fired with oil, gas or solid fuel (central heating boiler, stove, fireplace or another heating device designed to heat buildings and interiors).
There are known examples of pellet and agro-pellet burners made of heat-resistant, acid-resistant and non-corrosive materials, operating as automatic devices, fitted with a fuel chute with a dispenser in the form of a feeding pipe that feeds pellets to the inside of the burner by means of a worm (screw) feeder, driven by a motor and a reduction gear, supplying a certain amount of fuel in the form of granulate or pellets to a thick-walled, heat-resistant combustion chamber (firebox), optionally immovable or rotary. Inside each combustion chamber there is a cast iron grate, with a multipoint blower delivering air which penetrates through holes and/or nozzles or, by way of example, through a series of longitudinal shutters in the form of blinds, mounted by means of articulated joints to the external surface of the combustion chamber, on its different sides, covering air inlets (such a mechanism of combustion chamber aeration in a pellet burner is known from the patent description PL226498 ) .
Furthermore, previously known burners enabling combustion of solid fuels such as pellets and agro pellets are fitted with a fan, usually located in the rear chamber of the burner or outside that chamber. The fan, driven by a separate motor, blows the air necessary for the combustion process into the combustion chamber.
Most of the previously known modern solutions do not require daily maintenance - firing-up, combustion, shut-down and cleaning are controlled automatically.
By way of example, as in the solution known from the utility model PL 63 683 (Y1 ), the grate is fitted with an in-built heating element - an igniter, which initiates the burner operation. The igniter is located at the end of the worm feeder. The worm (screw) feeder supplies a small amount of fuel to start the burner. The initiation process involves a cycle of heating the fuel and igniting the resulting brand by means of a precisely working fan located in the rear chamber of the burner. This burner is fitted with an electronic control unit. The unit, after analyzing the signal from a photocell built into the burner body, starts dosing air in order to ignite a portion of pellets on the burner grate. After firing up the first portion and re-analyzing the photocell signal, the control unit begins precise fuel and air dosing to achieve a continuous fuel gasification process. Burner automation, by analyzing photocell signals and checking the combustion chamber pressure, maintains the optimal composition of the fuel-air mixture.
As generally known, fuel supplied to the grate remains immobile for a long time. During the process of its combustion, ash and slag are generated and subsequently adhere and stick to the surface of the grate, forming a scale that clogs the openings and makes it difficult for ash to fall into the ash chamber and obstructs the flow of air to the burner. In a longer period of time it blocks the air flow, which may result in extinguishing the combustion process. Burner designers constantly search for new solutions to eliminate problems associated with scale build-up and accumulation in the combustion chamber and to afterburn the residual material.
The most commonly used burners are those in which - in order to eliminate this problem - the furnace is regularly being moved by rotating the chamber where the processes of scaling, sintering and ash formation take place. As a result, combustion products are continuously being removed from the combustion chamber, without causing burner power loss and at the same time preventing clogging of the chamber typically occurring in standard burners.
A much more effective solution seems to be a solid fuel boiler burner known from the utility model description PL69175 (Y1 ), fitted with a rotating grate in the form of two drums, an outer drum and an inner drum placed inside it, with openings all over its surface, where the inner drum serves as a grate. On one side of the inner drum a gear wheel is attached, which meshes with a smaller driving gear attached to a driving shaft. The inside of the outer drum and the outside of the inner drum are ribbed. A rotary grate with such a design causes fuel to tumble, thus preventing the slag shell formation on the surface of the grate, which, as its volume increases, obstructs the combustion process. The ribs mounted on the drums act as reinforcement and heat sink protecting the grate from overheating.
A similar solution featuring the use of two chambers in a burner (known as pipe-in-pipe) is taught by the patent descriptions PL.221002 (B1 ) and PL.223794 (B1 ). According to the latter solution, the burner is fitted with a seamless rotating combustion chamber made of drawn pipe without any welds (which undoubtedly affects its strength and stress resistance). The cylindrical surface of the said combustion chamber is fitted with openings through which the air needed to burn the fuel bed is forced. It is also equipped with a second pipe with a larger diameter, which is a rotating blowing chamber, located around the combustion chamber. In addition, the openings in the combustion chamber have axes at an alpha angle, preferably 45° to 50°, to the cylinder radius of the combustion chamber, and are located on the surface of the combustion chamber along a spiral line and may have different cross-sectional shapes, preferably elliptical or bean-shaped.
During the operation of the burner according to the present invention, air is supplied from the blower system to the blower chamber where an air channel is formed between the two chambers and air pressure is created. The air necessary to sustain the combustion process enters the burner through openings located on the cylindrical surface of the furnace pipe. The movement of burning fuel particles in relation to one another, enabling the creation of gaps for air flow, is forced by a motor which rotates the burner around its axis in either one or two directions. The burnt fuel, in the form of ash, is pushed away by the masses of new fuel and moves towards the outlet, taking out the volatile parts of the ash, depositing them in the ash chamber (ash burner), from where they pass through the boiler and are evacuated to the smoke stack. At the same time, such a construction of the burner causes the flame feather to swirl in the feeder, which minimizes the risk of flash back. Such a burner design ensures additional air supply to the burnt fuel mass, which increases overall combustion efficiency.
The purpose of the invention was to develop a system that would control the air flow in the burner even more effectively, fully controlling the amount of air supplied to the burner combustion chamber, minimizing slag formation, and effectively afterburning fuel as well as organic and inorganic gases resulting from the combustion process, such as carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), sulfur oxides (SOx), as well as chemical gases present in the pellets as a result of their production process. In fact, although pellets are by definition an environmentally friendly fuel, pellet manufacturers offer various grades of this fuel, differing in terms of raw materials used for production, and thus in terms of end product parameters and quality. One of the pellet categories are pellets with quality guarantee, i.e. actual biofuel, burned mainly in modern boilers in single-family houses (the raw material used in the production of such pellets is wood waste from sawmills, wood processing plants and forests, mainly sawdust and shavings, less often bark, wood chips, energy crops, straw and biomass subjected to three successive production processes (drying, grinding and high pressure pressing in a rotary press); biomass is produced without an adhesive as the hot mass of the lignin and cellulose molecules present in the wood exhibits adhesive properties). Another category of pellets are the so-called industrial pellets, intended for large power companies such as power plants and combined heat and power plants. Industrial pellets are produced from a great variety of raw materials, such as wood, bark, straw, dried apple pulp, sunflower husks, energy crops, etc., which are often contaminated and additionally contain environmentally unfriendly harmful chemicals such as glues and varnishes.
The pellet burner afterburner according to the present invention, which is mounted at the border of the combustion chamber and the fuel inlet which is the terminal section of the internal feeding pipe, through which fuel is delivered to the combustion chamber, is mounted on the feeding pipe and is fitted with a guiding pull rod, performing a reciprocating motion, connected by means of an articulated joint and guides with a movable ring with cut-outs on its perimeter, adjusted to both the number and the shape of the profiled guiding vanes, mounted at equal intervals on the mounting plate, whereby the ring is slide-fitted on the guiding vanes.
The outer diameter of the inner feeding pipe and the inner diameter of the movable ring are loose-fitting.
The principle of operation of the pellet burner afterburner according to the present invention is that the guiding pull rod connected to the articulated joint makes a reciprocal movement, which in turn causes the movable ring to move along the system of guiding vanes and the inner pipe, while the guiding vanes manipulate the width of the gap through which air is supplied to the combustion chamber, collect air flowing around them and swirl the stream of air entering the combustion chamber so as to form the flame and exhaust gases into an appropriate vortex. At the same time, due to the sliding movement of the ring on the guiding vanes and the inner pipe, the afterburner works alternately in two positions, i.e.:

in the closed position - the movable ring, moving along the vanes, approaches the front wall of the combustion chamber as closely as possible, thus closing the access of air to the combustion chamber,
in the open position - in this case the movable ring is moved backwards as far as possible in relation to the combustion chamber and finds itself near the mounting plate, thus opening additional air supply to the combustion chamber.

The adjustment of the afterburner position and thus its closure or opening is controlled by an actuator (pneumatic or hydraulic), a motor or a mechanical pull rod manually controlled by a human operator.
Thanks to the solution according to the present invention, a simple solution has been obtained to improve pellet burner operation. The afterburner controls the flow of air supplied during the fuel combustion process, through additional turbulence increasing thrust and enabling oxidation (afterburning) of combustible exhaust gas components, reducing the toxicity of these exhaust gases, or even reducing emissions of pollutants. As a result, the applied solution of air division into primary and afterburning increases combustion efficiency. Thanks to the afterburner, the combustion chamber is self-cleaned from ash and slag. Consequently, the burner is efficient, maintenance-free and ensures a constant power level. The use of the afterburner additionally makes it possible to burn fuels of inferior quality, which, when burned in conventional burners, cause them to clog up.
The object of the present invention is shown in an embodiment illustrated in a schematic drawing, whose Fig. 1 presents the side view of the afterburner in the fully closed position, Fig. 2 - the side view of the afterburner in the fully open position Fig. 3 - the perspective view of the afterburner in the fully open position, Fig. 4. - the perspective view of the afterburner in the fully closed position, Fig. 5 - the front view of the afterburner, i.e. as seen from the combustion chamber, and Fig. 6 - the vertical cross-section of the burner passing through the rotation axis of the burner with the afterburner placed inside it.
The afterburner 1 is installed in the pellet burner at the border of combustion chamber 2 and inlet 3, which is the terminal section of the internal feeding pipe 4, through which fuel is supplied into combustion chamber 2; it is seated on the feeding pipe 4 and contains a guiding pull rod 5, effecting a reciprocating motion, connected by means of an articulated joint 6 and guide rails 7 to a movable ring 8 with cut-outs 9 on its perimeter, adapted to both the number and the shape of the profiled guiding vanes 10, fixed at equal intervals on the mounting plate 11, where the ring 8 is slide-fitted on the guiding vanes 10.
The outer diameter of the inner feeding pipe 4 and the inner diameter of the movable ring 8 are loose-fitting.
The afterburner 1 operates in such a way that the guiding pull rod 5 connected to the articulated joint 6, having its axis of rotation on the bolt, makes a reciprocating movement, which in turn causes the movable ring 8 to move over the guiding vane system 10 and over the inner pipe 4, while the guiding vanes 10 manipulate the width of the gap (not shown in the figure) through which air is supplied to the combustion chamber 2, collect the air flowing around them and swirl the stream of air entering the combustion chamber 2 in such a way that the flame and combustion gases form an appropriate vortex, whereby due to the sliding movement of the ring 8 along the guiding vanes 10 and the inner pipe 4, the afterburner 1 alternately operates in two positions, i.e.:

in the closed position - the movable ring 8, moving along the vanes 10, approaches the front wall of the combustion chamber 2 as closely as possible, thus closing the access of air to the combustion chamber 2,
in the open position - in this case the movable ring 8 is moved backwards as far as possible in relation to the combustion chamber 2 and finds itself near the mounting plate 11, thus opening additional air supply to the combustion chamber 2.

The adjustment of the appropriate position of the afterburner and thus its closure or opening is controlled by an actuator (either pneumatic or hydraulic, not shown in the figure), a motor, mechanical pull rod manually controlled by a human operator.

Claims

The pellet burner afterburner, containing a feeding pipe that delivers a certain amount of fuel by means of a worm feeder to the combustion chamber, inside which there is a grate with a multipoint air blower, characterized in that an afterburner (1) is mounted at the border of a combustion chamber (2) and a fuel inlet (3), which is the terminal section of an internal feeding pipe (4), is seated on a feeding pipe (4) and contains a guiding pull rod (5) which effects a reciprocating motion, connected by means of an articulated joint (6) and guides (7) with a movable ring (8), having cut-outs (9) on its perimeter, appropriately adjusted to both the number and the shape of profiled guiding vanes (10), mounted at equal intervals on a mounting plate (11), whereby the ring (8) is slide-fitted on the guiding vanes (10).
The pellet burner afterburner according to claim 1 characterized in that its internal diameter of the movable ring (8) and the external diameter of the internal feeding pipe (4) are loosely fitted.
The pellet burner afterburner according to claim 1 characterized in that its settings are controlled by an actuator.
The pellet burner afterburner according to claim 1 characterized in that its settings are controlled manually.