EP2373926A1

EP2373926A1 - Method and apparatus for cascaded biomass oxidation with thermal feedback

Info

Publication number: EP2373926A1
Application number: EP09764435A
Authority: EP
Inventors: Richard Matthias Knopf; Georg Knopf
Original assignee: Knopf Privatstiftung
Current assignee: Knopf Privatstiftung
Priority date: 2008-12-02
Filing date: 2009-11-24
Publication date: 2011-10-12
Also published as: US20110303132A1; CA2746826A1; AT507098B1; WO2010063046A1; AT507098A4; WO2010063046A4

Abstract

The invention relates to a method for cascaded biomass oxidation in a dish burner with ejection firing. The fuel (18), together with oxygen-containing primary air, is fed to a gasifier dish (8) having high thermal conductivity, in which the fuel is gasified by pyrolysis in a first combustion step, the resulting gas is conducted through guiding devices (6, 9) over the dish edge (11) of the gasifier dish, or over recesses on the upper dish edge, to the outside wall of the dish (8), and is enriched with oxygen-containing secondary air in the intermediate chamber (10) and converted into a cyclone flow around the outer shell dish during a second combustion step, through the convection of which strong thermal feedback is created, together with the high reflection of the thermal radiation on the guiding devices.

Description

Method and apparatus for cascading biomass oxidation with thermal

feedback

The present invention relates to a method for cascade biomass oxidation in a cup burner with ejection firing and an apparatus for carrying out the method. It relates to the field of heating technology, in particular furnace technology, for solid fuels, with a focus on biomass combustion plants, preferably those for pellets and wood chips.

Use finds this method and the device preferably for hot water, for heating and to a lesser extent for power supply by cogeneration in single and multi-family homes. The method is used for optimum combustion of fuels in a shell burner with discharge control, preferably in firing systems for pellets and wood chips. The device is the central device of a boiler and allows compact, efficient and low-residue combustion for heat recovery.

State of the art

Modern firing systems mainly differ in case systems with and without rust as well as shear firing and retort firing.

In the former, the fuel (pellets, wood chips, shavings, grain and the like) after being fed via a screw conveyor through a chute falls onto a grate or a burner bowl with the ember bed. The initial ignition takes place via a hot blower or electric heaters. The flames lick upwards and the hot flue gases are released upwards via flues to the heat exchangers. The suitability for Halmgüter is not given. Level monitoring is difficult (optically or by lambda probe). With horizontal arrangement of the combustion chamber one speaks of tunnel burners, which also get along without rust. In the combustion zone, the pellets gas with primary air. The secondary air is introduced in an attached combustion cylinder or through laterally arranged nozzle bores. In general, a smaller supply air flow is introduced via the chute to the To reduce the risk of burnback. In tilting and Rüttelrostanlagen the amount of ash is automatically dropped from time to time in the underlying ash collector.

In general, however, a pellet stove - not least due to the high level of fuel homogeneity - occupies a top position in terms of low emission and high efficiency; Carbon monoxide output is well below the values of other single fireplaces and efficiency reaches more than 90%.

Burner firing systems are subdivided into side insertion (cross recess) or underfeed systems, where the feed is from the side or from below onto a grate (rigid, possibly with a tilt function or moved as a feed grate) or a steel plate (as a moving bottom with or without water cooling). In transverse insert firing, part of the combustion air is blown in as primary air through the possibly present grate, air nozzles in the side area of the firing trough or - in the case of advancing grate firing - via end-side air ducts in the grate elements. The primary air also fulfills the function of grate cooling. The secondary air is supplied above the grate or the ember bed or before entering the afterburner.

In retort furnaces, the fuel is fed from below to the retort (fuel pit) with a Stocker screw. In the retort, the drying, pyrolytic decomposition and gasification of the fuel and the combustion of the charcoal is carried out by means of injected primary air. The secondary air is mixed with the combustible gases before entering the hot afterburning zone. It is advantageous to see the low inertia and the residual heat, however, high steel parts wear, unhomogenous ember bed and fuel compression, high residual fuel content in the ash and high pollutant formation during shutdown are disadvantageous. In combustion principles, a distinction is made between burn-through, upper burn-up and lower burn-up. When burning through combustion air is passed through a grate and the fuel stratification. The disadvantage here is the difficult adaptation to the amount of combustion air to the different combustion gas release.

In the upper combustion, the combustion air reaches the side of the ember bed zone. At the bottom burning takes only the lowest layer of the fuel at the

Combustion part. The fuel gases released in the area of the primary air supply are directed via a fan train into the combustion chamber, where they are post-combusted with secondary air supply. If the combustion chamber below, it is called the fall fire, is the Combustion chamber laterally, it is a lateral underburner. In general, the manipulated variable for controlling the different combustion phases (start-up phase, stationary phase with constant power, partial load phase and burn-out phase) is the air. When there is a separation between primary air flow and secondary air flow, there are two control variables. With the primary air, the firing capacity of about 50% to 100% can be influenced. The secondary air controls the complete combustion of combustible gases. In the case of power-controlled boilers, an induced draft or pressure blower is used for power control. At the same time the fuel supply is regulated. Lambda probes are used to measure the excess air in the exhaust gas flow. From DE 10 2005 033 320 of 15.2.2007 is a method for burning solid

Fuels and a device disclosed by this method. Here, a cup-like grate is shown with at least one air chamber, wherein primary air is introduced into this air chamber and secondary air is supplied to this chamber. WO 99/15833 from 1.4.1999 shows a "Self-Stoking Wood Pellets Stove" with the features feed screw, downpipe, brazier and control valves for primary and Sekundärluftzuftihr and an upwardly extending flue.

A disadvantage of the above systems are due to the asymmetrical arrangement of. Elements of difficult to reach state of optimal combustion even under partial load, the complex design or cleaning of the grate and the high space required for the combustion device.

Each of the mentioned systems has advantages and disadvantages, with none of the systems combining the majority of the advantages

Object of the invention

Based on this prior art, a method and a device for optimal combustion of biomass was sought, which combines the advantages of all possible existing systems in itself and also provides good results in partial load conditions. The structure should be compact, the material requirement low and the design minimal compared to the achievable power output. In addition, the number of wear components should be reduced to a reasonable minimum, or else the useful life of the wearing parts should be as large as possible. In addition, a very low-noise combustion plant was desired, with as homogeneous as possible combustion and low turbulence in the heater. Uncontrolled convection of heat should be avoided as much as possible. Likewise, sooting or burn-back should be excluded. Also for the maintenance of the easiest possible accessibility to the surfaces to be cleaned and the easy way to exchange parts should be given.

The protection request

To solve this problem is provided that fuel is supplied together with oxygen-containing primary air of a carburetor shell with high thermal conductivity, wherein the fuel is gasified in the first combustion step by pyrolysis, the resulting gas by conduction devices on the shell edge of the carburetor shell or recesses on the upper shell edge of the Outside wall of the shell is passed and enriched in the space with oxygen-containing secondary air and transferred into a cyclone flow around the shell outer wall during a second combustion step, the high convection takes place together with the high reflection of the heat radiation at the baffles a strong thermal feedback.

In this case, fuel is supplied together with oxygen-containing primary air of a carburetor shell in a shell burner with ejection firing with high thermal conductivity, wherein the fuel is gasified in the first combustion step by pyrolysis. The resulting gas is passed through special baffles above the shell and around the shell. For example, due to the suction due to a suction fan or the pressure of a pressure blower, the gases pass over the shell edge of the carburetor shell or via recesses on the upper edge of the shell directly to the outer wall of the shell. In engwandigen intermediate space, the enrichment me oxygen-containing secondary air and at the same time enforcing a cyclone flow around the shell outer wall is done by suitable devices. In this case, there is a strong mixing and uniform distribution of the exothermic reacting gases in the second combustion step. Reflections of the heat radiation at the guide devices and high convection of the gas flow serve a strong thermal feedback of the materials to each other and thus to a very good burnout of the flue gases. The pyrolysis is improved or can take place in a smaller space. The dense and efficient gas flow causes a flue gas with extremely low pollutant concentration even under partial load. Ascheteilchen be through the Cyclone flow pressed to the burner wall and fall out of the main gas flow. Rus particles and fine particles burn out at the hot diffusers due to their catalytic action.

It is particularly advantageous if the main flow direction of the cyclone flow points downwards and the gas flow at the lowest point below the shell is transferred directly into the diffuser space. As a result, the hot gases are deliberately and homogeneously directed downwards, contrary to the usual chimney direction upwards.

For refinement, the flow can be forced into further cascades with the aid of further alternating shell and funnel-type guide devices. Then, an upward flow again connects to the downward flow and vice versa.

The cascades thus formed represent flow layers with respect to the diffuser space, which can deliver the heat optimized to the environment or heat exchanger.

It is advantageous if the flow rate of the primary air into the carburetor shell and the flow rate of the secondary air into the zones outside the carburetor shell is different or can be controlled independently of one another.

In a device according to the invention guide means are provided above and below a carburetor shell to guide the gas flow after pyrolysis in close contact with the outside of the carburetor shell, wherein at least one Sekundärluftdüse is provided between the carburetor shell and the guide means, the axial flow exit direction has a horizontal component and at least approximately tangent to the carburetor shell wall.

, Essentially, this is an upper area boundary with

Exception of the filling tube and a laterally arranged around the carburetor shell

Limit. The guide means serve to bring the gas flow after the pyrolysis in close contact with the outside of the carburetor shell and to reflect the combustion heat alternately depending on the operating state. With at least one

Secondary air nozzle between the carburetor shell and the guide is a

Forced cyclone flow. For this purpose, the axial flow exit direction of the nozzle is advantageously such that it has a horizontal component. The nozzle axis extends at least approximately tangentially to the carburetor shell wall.

A simple design of the upper guide is the shape of a double-shell cavity cover. This cavity should have at least one air intake opening. The lower limit of coverage may be at least be connected to a nozzle whose air inlet opening is connected to the cavity of the cover. A filling opening with filling tube for the fuel is recessed. This filling tube is also almost gas-tight at the top, so that the flue can only escape downwards. The guide is made by the lower guide, which is designed as a funnel, with the exception of a lower recess, a second shell around the outer wall of the carburetor, with parallel spacing or with downwardly changing distance. In this case, the lower guide is connected to the upper guide.

The lower baffle, like the carburetor shell, may have pyramidal, spherical, conical, paraboloidal or hyperboloidal surface portions.

The carburetor shell and its surrounding guide can advantageously be arranged coaxially and concentrically around a burner axis. They can be rotationally symmetrical. It is advantageous if at least one air outlet opening of a primary air nozzle is positioned just above the shell low point within the shell close to the combustion position of the biomass, whereby the optimum volume of air can be supplied to the pyrolysis. The position of at least one air outlet, u.zw. at least one secondary air nozzle, should be expediently provided on the outside of the shell. At least one of the air supply nozzles can advantageously as an annular gap around a

Be formed filling tube. Alternatively or additionally, a plurality of primary air nozzles or a plurality of secondary air nozzles may be arranged at the same angular distance around the burner axis.

The flow rate through the air supply nozzles is suitably controlled and regulated by at least one intake fan as an exhaust fan. In addition, it can be controlled by a rotary valve around the air intake openings.

Bimetal in the air supply nozzles can be advantageously provided for the temperature-dependent control of the flow rate.

The air supply nozzles can be formed by deep drawing, but also from welded metal pipe pieces or ceramic parts.

The upper guide is expedient spherically shaped to avoid stress distortion or cracks, or has individual separate buckles as expansion reserve. The radial distance between the carburetor shell and the lower guide can be made adjustable against each other. This distance is the same in the axial direction or tapers in the flow direction.

To avoid heat loss up, a thermal insulation layer, preferably made of mineral wool or ceramic fiber is provided above the upper guide.

The carburetor shell can be provided with a spring-loaded impact cone or rust-like components for residual ash application.

The invention will be described in detail with reference to the accompanying drawings. 1 shows a vertical section through the invention.

2 shows the horizontal section A-A 'of Figure 1.

In Fig. 1, the method and the device is illustrated by the vertical section. Shown is the burner 1 with his here clearly recognizable bivalve structure. Above the central filling tube 2, the fuel 18, preferably pellets, wood chips or wood shavings, is introduced onto the carburetor shell 8 by means of a screw conveyor (not shown here). The fuel falls down through the filling tube due to the propulsion of the auger at a time interval due to gravity. He passes the filling opening 20 in the burner cover. The filling tube has a flow resistance at the top, which is carried out by suitable check valves, by seals or by a slight primary air flow due to a pressure surplus, which is not shown here by a pressure fan or a suction fan in the exhaust duct. In the course of combustion, the fuel sinks and the spent fuel is replaced by fresh fuel. Since the optimal operating condition is achieved even with different performances at constant shell level and the fuel from above is rather cold, can be achieved by a detection with a sensor 23, the level for an exact fuel metering even with inaccurate conveyor systems. The fuel 18 from biomass is heated during a cold start via electric heating rods or hot air. This initial heat can be supplied via the primary air nozzles 3 from above with integrated glow wires or via a possible rust from below to start the pyrolysis process. In Figure 1, four primary air nozzles 3 are shown (three visible), which are arranged around the burner axis 19 at an angle of 90 ° and obliquely extend into the carburetor shell 8. The biomass fuel 18 may also be the primary air nozzles 3 cover. The primary air can also be supplied by a possibly attached to the ground or near the bottom of the carburetor grate. Due to the pyrolysis of the fuel is brought into gasification due to the initial heat, while more heat is released, whereby the hot air or electric heating is no longer needed. Gasification produces flammable gases from hydrocarbon compounds, resulting in temperatures of up to 1000 ° C at the bottom of the carburetor shell. By the blower, the gases are led up to the inner wall of the shell, up to the shell edge 11, where the transition takes place in the gap 10. If the shell is suspended at several points or separated by spacers from the lower guide 9, then the flow will slide directly over the edge of the shell. It is also conceivable, however, a direct connection of the shell edge with the upper guide 6, in particular with its lower boundary 22. Then recesses, such as holes must be provided in the upper edge of the shell to the flow in the gap 10 between the carburetor shell and the lower guide 9 to allow. Here, the carburetor shell is a truncated cone shell, which is formed from a 2 mm thick steel sheet with a flat bottom. The opening angle is about 90 ° and the lower guide 9 forms a conical funnel at a radial distance 12 and is axially concentric with it. This creates a double wall with the same distance in the axial direction. Between these walls, the main combustion of pyrolysis gases takes place with the supply of secondary air via secondary air nozzles 13. The shape of the shell does not have to be cone-shaped, any trough-forming shell shape is possible, even the shape of the guide 9 are imposed only minor restrictions. Here are the decisive elements of the shape of the formation of thermal stresses, the desired flow profiles for the combustion gas flow and the aspects of aging wear and maintenance. Thus, spherical, conical, paraboloidal, hyperbolic or even multi-sided pyramidal forms or molding compositions are conceivable. When selecting a downwardly decreasing distance, the rotational speed of the gas flow increases downward. Also, a helical guide groove may be provided on the outer wall of the shell and the inner wall of the guide 9 to achieve dimensional stability paired with a laminar-flow cyclone flow. This cyclone flow is also achieved by the shape of the secondary air nozzles 13. Here six nozzles are distributed in the inlet region of the combustion gases from the carburetor shell in the flow gap 10 evenly around the shell circumference. The angular distance is 60 ° here. The Nozzle mouth 15 is not directed vertically downwards but inclined obliquely to the burner axis 19. The angle is expediently chosen so that the residence time of the flow around the carburetor shell causes good feedback or interaction with the first stage of the combustion. By the feed rate of the fuel 18 via the screw conveyor together with the blower power and the heat extraction, the load is determined. Independently of this, the carburetor shell 8 should be kept at the optimum temperature level as the activation energy for the pyrolysis. The close management of the secondary combustion air to the carburetor shell 8 paired with the high reflection of heat radiation by the guide 9 on the one hand and by the carburetor shell 8 on the other hand cause a self-regulating effect, whereby the gases completely oxidize Lastunahhängig before it comes to hitting the cold diffuser surfaces, and Harmful gases such as carbon monoxide left the fireplace incompletely burned.

The number and shape of the secondary air nozzles is chosen here arbitrarily. Here, the imagination knows no bounds Thus, a split ring nozzle can open into the gap 10, which is formed from the lower boundary 22 of the upper guide 6. Additional baffles can then cause the defined cyclone flow.

Here, the primary air and the secondary air come directly from the cavity 6 of the double-headed upper guide (burner cover). The air is supplied from the outside via the air intake opening (shown here as a circulation gap). The heat conduction of the sheets used and the heat radiation of the combustion gases cause the burner cover reaches high temperatures and thus have high preheating for the primary and secondary air result. The primary air nozzles 3 and the secondary air nozzles 13 are connected via the air inlet openings 4 and 14 directly to the cavity 5 of the burner cover 6 in combination. Heat losses are avoided by the insulating layer 17 above the burner cover 6.

Fig. 2 shows the section along line AA 'of Fig. 1 from above and makes the symmetrical structure of the embodiment clearly. You can see the air inlet openings of the nozzles 3,13 in section, and the carburetor shell. LIST OF REFERENCE NUMBERS

I cup burner 2 filling tube

3 primary air nozzle

4 Air inlet opening in the primary air nozzle

5 Cavity of a bivalve covering

6 upper guide (cover) 7 Air outlet opening from the primary air nozzle

8 carburetor shell

9 lower guide (walling, cyclone nozzle, funnel)

10 gap (2_ combustion stage)

I 1 Shell edge of the carburetor shell 12 Distance between shell and lower guide

13 secondary air nozzle

14 air inlet opening in the secondary air nozzle

15 air outlet opening from the secondary air nozzle

16 air intake opening 17 insulating layer

18 fuel with ashes from biomass

19 burner axis

20 filling opening for the fuel

21 Mouth of the lower guide (nozzle, funnel) into the diffuser space 22 lower limit of the upper guide (cover)

23 Fuel quantity determination sensor

Claims

claims

1. A method for cascading biomass oxidation in a dish burner with ejection firing, characterized in that fuel (18) together with oxygen-containing primary air of a gasifier shell (8) is supplied with high thermal conductivity, wherein the fuel is gasified in the first combustion step by pyrolysis, the resulting Gas through guide means (6,9) over the shell edge (11) of the carburetor shell or recesses on the upper shell edge to the outer wall of the shell (8) is passed and enriched in the space (10) with oxygen-containing secondary air and in a cyclone flow around the shell outer wall during a second combustion step is performed, by the high convection takes place together with the high reflection of the heat radiation at the guide means a strong thermal feedback.

2. The method according to claim 1, characterized in that the

Main flow direction of the cyclone flow pointing down and the gas flow is transferred at the lowest point below the shell (8) in the diffuser space.

3. The method according to claim 1, characterized in that the flow is forced by means of further alternating shell and funnel-like baffles in further cascades, wherein to a downward flow again an upward flow and vice versa to an upward flow again followed by a downward and represent the cascades thus formed flow layer with respect to the subsequent diffuser space.

4. The method according to any one of claims 1 to 3, characterized in that the flow rate of the primary air into the carburetor shell (8) and the

Secondary air in the zones outside the carburetor shell is different or independently controllable.

5. Device (1) for cascade biomass oxidation in a dish burner with ejection firing characterized in that guide means (6.9) above (6) and below (9) of a carburetor shell (8) are provided, the gas stream after pyrolysis in tight Contact with the outside of the carburetor shell (8) to lead and at least one secondary air nozzle (13) between the carburetor shell (8) and the guide means (6.9) is provided, the axial flow exit direction (15) a Has horizontal component and extends at least approximately tangentially to the carburetor shell wall.

6. Device (1) according to claim 5, characterized in that the upper guide (6) constructed as a double-shell cover with cavity (5) and at least one air intake (16), at least one with the lower boundary of the cover (22 ) and the cavity connected nozzle (3,13) with air inlet opening (4,14) and has a filling opening (20) with filling tube (2) for the fuel (18).

7. Device (1) according to claim 5 or 6, characterized in that the lower guide device (9) except for a lower recess (21) is designed as a second shell to the outer wall of the carburetor shell (8) with parallel spacing (12) or with itself after downwardly decreasing distance, and the lower guide (9) is connected to the upper guide (6).

8. Device (1) according to claim 7, characterized in that the lower guide (9) and the carburetor shell (8) have pyramidal, spherical, conical, paraboloidal or hyperboloidal surface portions.

9. Device (1) according to one of claims 5 to 8, characterized in that the carburetor shell and its surrounding guide are arranged coaxially and concentrically about a burner axis (19) and are preferably rotationally symmetrical.

10. Device (1) according to one of claims 5 to 9, characterized in that at least one air outlet opening (7) has at least one Primärluftdüse (3) just above the shell deepest point within the shell (8) close to the combustion position of the biomass (18) and / or at least one air outlet opening (15) has at least one secondary air nozzle (13) on the outside of the shell (8).

11. Device (1) according to one of claims 5 to 10, characterized in that at least one of the air supply nozzles (3, 13) is designed as an annular gap nozzle around the filling tube (2).

12. Device (1) according to one of claims 5 to 10, characterized in that a plurality of primary air nozzles (3) and / or a plurality of secondary air nozzles (13) in the same

Angular distance around the burner axis (19) are arranged.

13. Device (1) according to any one of claims 5 to 12, characterized in that the flow velocity through the air supply nozzles (3,13) by at least one Ansauggebläse as exhaust fan and / or a rotary valve about at least one air intake opening (16) is controllable.

14. Device (1) according to any one of claims 5 to 13, characterized in that regulating means in the air supply nozzles (3,13) are provided.

15. Device (1) according to any one of claims 5 to 14, characterized in that the air supply nozzles (3,13) are formed by deep drawing or welded metal or ceramic pipe pieces.

16. Device (1) according to one of claims 5 to 15, characterized in that the upper guide (6) is spherically shaped, or has individual separate curvatures.

17. Device (1) according to any one of claims 5 to 16, characterized in that the carburetor shell and the lower guide (9) are arranged with a small, constant, or tapering in the flow direction radial distance, wherein the distance is optionally adjustable via the lifting spindle.

18. Device (1) according to any one of claims 5 to 17, characterized in that a thermal insulating layer (17) made of mineral wool or ceramic fiber above the upper guide (6) is provided.

19. Device (1) according to one of claims 5 to 18, characterized in that the carburetor shell has a grate or a spring-loaded impact cone for the ash application

20. Device (1) according to claim 1, characterized in that the fuel mass flow through the level of the fuel at its Einwurfseitiger surface in the carburetor shell by means of a sensor (23) is adjustable.