WO2020044065A1

WO2020044065A1 - Wood-burning stove

Info

Publication number: WO2020044065A1
Application number: PCT/HR2019/000020
Authority: WO
Inventors: Mladen Stupnišek
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-08-31
Filing date: 2019-07-24
Publication date: 2020-03-05
Anticipated expiration: 2021-02-28
Also published as: HRPK20181405B3; HRP20181405A2

Abstract

A wood-burning stove with an upright combustion chamber (4) enables a more complete wood burning by the method of top down burning with an embedded system of sheet metal ducts (3), enabling pre-heating and distribution of additional air through holes for secondary combustion in the upper part of the combustion chamber, which contributes to a more complete wood burning. By doing so, the emission of hazardous gases (carbon monoxide CO and unburned hydrocarbons CxHy), soot and fine particles in flue gases is reduced. A fine particle separator, comprising a centrifugal gravity cyclone (22) and an electrostatic filter (23), contributing to the reduction in the emission of fine particles in flue gases, is added to an outlet flue pipe (19). An added heat exchanger (25) heats fresh outside air, whereby the additional thermal efficiency of flue gases is achieved as well as natural room ventilation by outside air, which is heated without the need for a fan. A spiral turbulator (27) embedded in a flue pipe (26) and serpentine baffles (30) embedded in an air tube (29) increase heat transfer to supplied outside air, increasing thus the thermal efficiency. The fine particle separator (22 and 23) and the heat exchanger (25) can also be located in an adjacent room by means of a short intermediate pipe through a partition wall.

Description

WOOD-BURNING STOVE

DESCRIPTION OF THE INVENTION

Field of the invention

The present invention relates to a new design of a stove for ecoffiendly and energy efficient heating with logs. According to the international patent classification, the invention falls within field F24B: Domestic stoves or ranges for solid fuels; implements for use in connection with stoves or ranges.

Technical problem

Classic wood stoves have low fuel efficiency and due to incomplete combustion emit in the environment large amounts of environmentally harmful components in flue gases: carbon monoxide CO, unbumed hydrocarbons C_xH_y and fine particles. The standards for such types of stoves prescribe acceptable limits for these hazardous components in flue gases, in particular fine particles (PM 10 = Particle Meter 10 Microns) and recently also PM2.5. The existing stoves can hardly meet those requirements, whereas on the other hand, the use of wood, the cheapest renewable energy source of biomass, is promoted. This encourages solutions for enhancing the wood-burning methods with complete combustion. Wood stoves have glazed doors to create a visual impression. However, incomplete combustion causes soot and condensed resin to be deposited on glass, which undermines a visual impression and is thus sought to be prevented. To increase the thermal efficiency, systems of enhanced convection heat transfer to supplied outside air are being developed.

State of the art

To reduce hazardous gas components (CO and C_xH_y) in flue gases and to prevent soot and unbumed deposits in flues, different stove designs and wood-burning methods for reducing the portion of incomplete combustion are applied. In stoves of greater power, pyrolytic combustion in an additional chamber or with the application of catalyst is used. In stoves of relatively small heating power for room heating, so-called secondary combustion on top of a combustion chamber is applied, before entering a flue pipe, whereby depositing of unbumed particles in flue pipes and a chimney is reduced. This is achieved by supplying additional air, so-called“secondary air” to the combustion chamber through a holed tube on top of the combustion chamber (US2016/0186989 Al). To prevent depositing on door glass, so-called“tertiary air”, separated from“primary” one, is supplied directly before glass, without special pre-heating (GB2533040) and (DE202015105434 Ul). To reduce the emission of fine particles, in stoves of small heating power, their separation by applying electrostatic filters embedded in the flue pipe or in the chimney is also starting to be introduced. To increase the wood energy efficiency, enhanced convection heating of“internal” room air by applying heat exchangers is used, which exchangers are located in the stove (AT516353 A2) or are separated within the framework of the flue pipe (ES2435615 A2) and (FR1553014). The separated heat exchanger is applied also for heating supplied outside air, whereby room ventilation is also achieved. This is achieved by forced air circulation by means of a fan (GR20120100571) since there is great resistance to the flow in transverse tubular heat exchangers and it cannot be overcome by natural chimney buoyance.

Disclosure of the invention

The essence of the invention is a design of a wood-burning stove and additional fittings that significantly improve wood burning and thereby reduce the emission of hazardous gaseous components and fine particles in flue gases, but also increase the thermal efficiency of flue gases before entering a chimney. A more complete combustion is achieved by the method of top down wood burning in an upright rectangular combustion chamber. Therein, a duct made of heat-resistant steel sheet is installed along the entire width of the back side, in the continuation of a steep roof and the front side around glazed doors in one piece for supplying additional air. Additional air is thus pre heated in those ducts and secondary combustion is achieved in the entire upper part of the combustion chamber by such air outflowing through the holes, and simultaneously the depositing of soot on door glass is prevented. To separate fine particles from flue gases, a fine particle separator, comprising a centrifugal gravity cyclone (for coarser particles) and an electrostatic filter (for finer particles), is added directly to an outlet combustion chamber pipe. The separation of fine particles is more efficient immediately after flue gases leave the combustion chamber since the difference in density for gravitational separation and ionization for electrostatic separation are higher at higher temperatures. This is especially important since the standards always reduce the limit for fine particles (PM 10). In the US, for the year 2020, a new limit (PM2.5) was adopted. Adding the fine particle separator directly to the outlet flue pipe enables the stove to empty very easily fine particles from the separator, which is a huge difference in relation to the state of the art, whereby electrostatic filters are installed in flue pipes before the chimney or in chimneys, where the emptying of fine particles is made difficult. Beside the stove, a parallel heat exchanger is added, in which the heat of flue gases is transferred to fresh air supplied from the outside, whereby both better thermal efficiency and room ventilation by heated fresh outside air is achieved. A spiral turbulator in the flue pipe and serpentine baffles in the air tube significantly increase heat transfer from flue gases to fresh outside air since turbulence is achieved in both media, flue gases and heated air. Since this is achieved by parallel natural heat buoyance of flue gases and air upwards, there is no need for forcible pushing by means of a fan. Fittings for separating flying particles from flue gases (centrifugal gravity cyclone and electrostatic filter) and parallel heat exchanger can be placed in an adjacent room through a partition wall by means of a short intermediate pipe, spreading thus heat to another room as well.

Brief description of the drawings

The enclosed drawing presents a vertical cross-section of a wood-burning stove with an added fme particle separator, comprising a centrifugal gravity cyclone with an electrostatic filter and an added heat exchanger (recuperator) for heating fresh outside air. The stove comprises a steel sheet mantle (1), lined with ceramic plates (2) with a combustion chamber (4) being in an upright position and rectangular. There are two glazed doors (13 and 15) on the front side of the stove and there are two openings for primary air (1 1 and 14) on the lower glazed door (13). On the back side of the combustion chamber, there is a heat resistant-steel sheet duct (3), in which, through an opening (6), additional air from the room enters, is pre-heated in the combustion chamber and through holes enters from the duct in the upper part of the combustion chamber for secondary combustion and to glazed doors as tertiary air. Outside the combustion chamber mantle, there is an external convection mantle (17), which can be rectangular, round or oval, in which room air is heated by natural heat buoyance. A separator of fine particles from flue gases, comprising a centrifugal gravity cyclone (22) and an electrostatic filter (23), as well as a heat exchanger (25) for heating fresh outside air supplied through a tube (28), is added to a combustion chamber outlet flue pipe (19).

Detailed description of at least one embodiment of the invention

Dry wood is placed through lower glazed door (13) on the bottom of a combustion chamber (4) and then through upper glazed door (15) until the middle of the height of the upper glazed door. A damper of the outlet flue pipe (20) of the combustion chamber, primary air supply (11 and 14) on the bottom glazed door (13), additional air opening (6) for secondary combustion as well as outside air supply (28) to a heat exchanger (25) are opened. Wood on top of the combustion chamber are lit by a firelighter and thereafter both glazed doors are closed. Wood bums top down in the combustion chamber, stimulated by primaiy air and by means of additional air by secondary combustion before flue gases leave the combustion chamber through an outlet flue pipe (19). By the method of top down wood burning, a more complete combustion with the lower emission of hazardous gases, soot and fme particles in flue gases is achieved since burning is performed continuously on top of unbumed layer of wood at a steady speed and heating power. In a centrifugal gravity cyclone (22) and an electrostatic filter (23), fine particles are separated from flue gases, which thereafter enter the heat exchanger (25), in which outside air supplied through a tube (28) is heated. Heated outside air leaves through an opening (32) and flue gases flow through a flue elbow (33) into a chimney. By doing so, in the heat exchanger (25), heat of flue gases is transferred by convection to supplied fresh outside air, whereby the thermal efficiency of flue gases is increased and spontaneous room ventilation is also achieved by pre-heated air without the need for a fan. At the same time, between stove mantle made of sheet metal (1) and external convection mantle (17), stove heat is transferred to room air. A spiral turbulator (27) is embedded in a flue pipe of the heat exchanger (26) and serpentine baffles (30) are embedded in an external air tube (29), which contributes to the better thermal efficiency of flue gases and at the same time to simultaneous heating of fresh outside air, which serves the purpose of room ventilation and wood burning in the stove.

Manner of the invention applicability

A wood-buming stove falls within the type of“domestic stoves” and is intended for heating detached buildings, apartments and weekend cottages by using logs, the cheapest renewable energy source of biomass. Wood burning by applying the top down burning method with additional secondary combustion by pre-heated air contributes to a more complete combustion and thereby also to the lower emission of hazardous gases and flying particles. Additional pre-heated air prevents also the depositing of soot on door glass. The steady slow-burning of wood is achieved by controlled primary and additional air supply, which for one feeding with logs lasts several hours and in continuation, embers and accumulated heat in a ceramic lining prolong the heating for several hours. To prolong the heating, a smaller amount of wood may be added to the existing embers. An added centrifugal gravity cyclone and an electrostatic filter reduce the emission of fine particles in flue gases and a heat exchanger increases the thermal efficiency of flue gases and at the same time contributes to spontaneous room ventilation by outside air, which is heated. Two parts of the entire installation (the stove and a fine particle separator with the heat exchanger) can be installed together or separately in two adjacent rooms by applying a short intermediate flue pipe. The reduction in the emission of hazardous components in flue gases (ecology) and the increase in the fuel efficiency (energy efficiency), as well as spontaneous room ventilation by pre-heated outside air are the main technical and economic advantages of this invention in relation to the state of the art. Table: Comparison of basic characteristics of wood-burning stoves

List of used reference signs

1. Stove mantle made of sheet metal

2. Ceramic lining of the combustion chamber

3. Additional air duct made of sheet metal

4. Combustion chamber

5. Stove ceramic bottom

6. Opening for additional air supply

7. Heat insulation

8. Ash pan made of sheet metal

9. Ash pan guides

10. Stove feet

11. Lower opening for primary air supply

12. Handle of the lower glazed door

13. Lower glazed door

14. Upper opening for primary air supply

15. Upper glazed door

16. Handle of the upper glazed door

17. Convection mantle

18. Upper stove plate

19. Outlet flue pipe

20. Damper of the outlet flue pipe

21. Intermediate flue pipe

22. Centrifugal gravity cyclone

23. Electrostatic filter

24. Flue pipe extension

25. Heat exchanger

26. Flue pipe of the heat exchanger

27. Spiral turbulator

28. Tube for supplying outside air to the heat exchanger

29. Air tube of the heat exchanger

30. Serpentine baffles in the air tube

31. Flue pipe reduction

32. Tube for heated outside air outflow into the room

33. Flue elbow

34. Control opening of the flue elbow

Claims

1. A wood-burning stove for heating with logs by the method of top down burning, with a

combustion chamber lined with ceramic material, with glazed doors, with openings for air supply for primary and secondary combustion, and a heat exchanger, characterized in that the combustion chamber (4) is in an upright position and rectangular, with two glazed doors (13 and 15), with an added external convection mantle (17), a system of ducts made of sheet metal (3) for additional air supply for secondary combustion is installed on the back side of the combustion chamber, a fine particle separator (22 and 23) and a parallel heat exchanger (25) for heating supplied outside air are added to an outlet flue pipe (19).

2. The wood-burning stove according to claim 1, characterized in that two glazed doors (13) and (15) are embedded upright on the front side of the combustion chamber.

3. The wood-burning stove according to claim 1, characterized in that two air openings for primary combustion (11 and 14) are on the lower glazed door.

4. The wood-burning stove according to claim 1, characterized in that an additional air duct (3), made of heat-resistant steel sheet, is installed on the back side of the combustion chamber, along the entire combustion chamber width, it is folded into a steep holed roof from an opening (6) and continued with vertical holed ducts before glazed doors, for secondary combustion and prevention of soot deposits on the door glass.

5. The wood-burning stove according to claim 1, characterized in that the external convection mantle (17) made of sheet metal can be rectangular, round or oval.

6. The wood-burning stove according to claim 1, characterized in that the separator of fine particles from flue gases, comprising a centrifugal gravity cyclone (22) and an electrostatic filter (23), is added to the outlet flue pipe (19).

7. The wood-burning stove according to claim 1, characterized in that the parallel heat

exchanger (25) for heating fresh outside air supplied through an inlet tube (28) is added to the fine particle separator (22 and 23).

8. The wood-burning stove according to claim 7, characterized in that a spiral turbulator (27) is embedded in a flue pipe of the heat exchanger (26) and serpentine baffles (30) are embedded in an air tube (29) to increase turbulence of flue gases and air, thereby increasing heat transfer.

9. The wood-burning stove according to claims 6, 7 and 8, characterized in that the fine particle separator (22 and 23) and the heat exchanger (25) can be located also separately from the stove, in an adjacent room, and connected with a short intermediate flue pipe through a partition wall.