EP3765792B1

EP3765792B1 - Solid fuel heater with three-zone combustion air supply

Info

Publication number: EP3765792B1
Application number: EP19766636.5A
Authority: EP
Inventors: Michal HALADA
Original assignee: Bh Property SRO
Current assignee: Bh Property SRO
Priority date: 2018-03-12
Filing date: 2019-03-11
Publication date: 2024-06-12
Anticipated expiration: 2039-03-11
Also published as: CZ307859B6; CZ2018122A3; EP3765792C0; EP3765792A1; UA124798C2; EP3765792A4; WO2019174655A1; RU2754480C1

Description

Field of the Invention

The invention relates to a solid fuel heater with three-zone combustion air supply, in particular firewood gasification boilers.

Background of the Invention

The most advanced solid fuel heaters, in particular firewood gasification boilers, are equipped with a three-zone (or three-stage) combustion air supply - i.e., secondary air, lower primary air, and upper primary air. Secondary air is admitted to the flame in the nozzle (an orifice, connecting upper fuel area, and bottom overfire area). Secondary air accomplishes combustion of inflammable gaseous elements of the flame - i.e., secondary combustion. Lower primary air is supplied to the glowing fuel layer situated at the lower part of the fuel area. Lower primary air accomplishes transformation of solid fuel into gaseous elements - i.e., primary combustion (or gasification) in the lower fuel layer. Lower primary air defines output of the heater. Upper primary air is supplied above the fuel layer in the upper part of the fuel area. Upper primary air increases intensity of primary combustion - by growth of the glowing layer. Upper primary air facilitates combustion of fuels with low mass burning rate (large pieces, soft or wet wood). Accelerates heating-up. Sometimes is also referred to as the pre-drying air.
Secondary air is usually drawn through an independent vent (represented by the system of piping lines, ducts, and cavities) with a controlling element (damper) at the inlet, which is manually controlled; more sophisticated appliances include a boiler regulator controlled by an electric drive on the basis of the signal sent by a lambda sensor.
Upper primary air and lower primary air are usually introduced through one common vent (of the primary air), at the inlet of which is also mounted the controlling element (damper), controlled either manually or by the electrically-driven boiler regulator depending on the output requirements (a signal emitted by flue gas sensors and water temperature sensors). Subsequently, said common vent is divided into upper primary air vent and lower primary air vent. Usually applied design is as follows: said common vent (of the primary air) ends behind refractory metal sheet lining, installed on the side walls of the fuel area. Subsequently, a part of the primary air behind the lining flows upwards as the upper primary air, another part of the primary air behind the lining flows downwards as the lower primary air. Orifices are made in the lower part of the mentioned refractory lining, through which the lower primary air is delivered into the fuel area, and orifices in the upper part, through which the upper primary air is delivered into the fuel area. Surface ratio between upper and lower orifices defines relative proportions of upper and lower primary air supplies. Said ratio is chosen to satisfy the most commonly used fuels. As the standard, the value is approximately 2:1 in favor of the lower primary air. Constant value of this ratio is disadvantageous for burning of fuels with different parameters. For instance, standard quantity of the upper primary air results in an undesirable mass burning rate in the overall fuel area volume in case of fuels characterized by high mass burning rate (dry and small pieces such as wooden chips, branches, and cuttings). Thus, quality of combustion, controllability and efficiency are reduced. The opposite situation is faced as to the fuel with low mass burning rate (moistened wood or large pieces). In such a case, there is a lack of upper primary air, combustion takes place with a lot of excess air, lower output, lower efficiency, and combustion quality.
The equipment burning pellets is known from the Chinese document CN 204005952 U , containing combustion air supply, inlet and outlet orifices of primary, secondary and tertiary air, whereas said primary air, as well as secondary and tertiary air supplies, run in the separate piping lines i.e., vents.
Therefore, existing heaters, in particular gasification boilers, do not allow an efficient adjustment to fuels with various properties, namely moistened fuel and larger pieces on one hand, and smaller and dry fuel (chips) on the other.
A method approximately according to the preamble of claim 1 is known from EP 2 085 694 A2 disclosing a method for controlling a woodburning stove and an electronic control (38) for a woodburning stove (2) of the type including a combustion chamber (6) which is downwards separated from an ash chamber (18) by means of a grate bottom (12) and having a walling (8) at the rear and at both sides, which upwards has an inclining forwards/upwards extending wall part (22), the combustion chamber (6) upwards, preferably via a reversing plate (24), being connected with a chimney (28) via a flue gas exhaust (28), the control including a thermal sensor (46) and a A-probe (48) provided in the flue gas exhaust (26), wherein the control (38) is incorporated in a cabinet (36) which is adapted to be disposed below the ash chamber (18) and which includes a common air intake (48) and one or more regulating valves (34, 40, 42) with a damper plate, each drivingly connected with an electric motor (50, 52, 54) arranged in the cabinet, the motor being control connected with the electronic control (38), the regulating valve or valves (34, 40, 42) interacting with air ducts for supplying primary and secondary combustion air (19, 33, 45), the air ducts being disposed side by side at a rear side of the woodburning stove (2).

Object of the Invention

The solid fuel heater with three-stage combustion air supply according to the invention eliminates deficiencies in known equipment, containing a lower outlet orifice of the lower primary air, upper outlet orifice of the upper primary air, secondary outlet orifice and secondary inlet orifice of the secondary air, whereas said secondary air between the secondary inlet orifice and secondary outlet orifice runs in the independent vent (line). In addition, the heater comprises two independent vents (lines) from the inlet to the outlet of the lower and upper primary air, entering the combustion area. Mentioned independent vents are designed to contain the first inlet orifice of the lower primary air and second inlet orifice of the upper primary air, whereas the lower primary air between the first inlet orifice and lower outlet orifice runs in the independent vent of the lower primary air and upper primary air between the second inlet orifice and upper outlet orifice runs in the independent vent of the upper primary air. The summary of the technical design is that the damper, mounted on the arm, is assigned to each inlet orifice of supplies of primary air and secondary air, whereas the arm is attached to the shaft, whereas inlet orifices are equipped with their common moving orifice.
According to the first advantageous embodiment of the invention, inlet orifices for supplies of primary air and secondary air are located on the distributor, fixed to the external side of the heater, whereas the shaft, to which the arms are attached, is located outside said distributor.
It is preferable to control quantities of supplies of primary air and secondary air, entering the inlet orifices, by the moving orifice with two controlling orifices.
The preference of the invention is that it enables, in a simple manner, by movement of the orifice 5, to achieve any required ratio of all three types of air (secondary, upper primary, and lower primary) and, consequently, to optimally adjust the heater to effective combustion of various fuels as well as immediate combustion condition. One electric drive is sufficient to control air supply ratios, whereas design of existing boilers demands two electric drives. I.e., another preference includes simplicity, and the consequent lower price, and higher reliability.

Summary of Figures in Drawings

FIG. 1 Schematic representation of the heater - front view
FIG. 2 Cross-section "A-A" of the heater, shown in Fig. 1
FIG. 3 Schematic axonometric (3D) projection view on air distributor; controlling orifice not shown for clarity.
FIG. 4 Schematic front view on the air distributor with the orifice in the position with a balanced supply of secondary air and lower primary air, burning normal fuel with standard mass burning rate (e.g., dry logs).
FIG. 5 Schematic front view on the air distributor with the orifice in the position with a maximum supply of secondary air, burning fuel with high mass burning rage (e.g., dry wooden chips).
FIG. 6 Front view on the air distributor with the orifice in the position with a maximum supply of upper primary air, burning fuel with low mass burning rate (e.g., wet or large logs).

Description of Embodiments

The example of embodiment of the invention, shown in Fig. 1, illustrates the heater 100 - a gasification boiler for manual loading of wood, with the fuel area 1 in the upper and overfire area 17 in the lower part. The combustion air distributor 4 shaped as a cuboid, containing three mutually separated chambers, is located on the frontal face of the heater 100. Each of these chambers has circular inlet orifices in the front wall to supply combustion air; the first inlet orifice 14.1 is intended for lower primary air supply, second inlet orifice 14.2 is intended for upper primary air supply, and the inlet orifice 14.3 is intended for secondary air supply. Inner faces of inlet orifices 14.1, 14.2 and 14.3 are equipped with round dampers 13, each of them is attached to the curved arm 7; all three arms 7 are tightly connected to the shaft 8, located outside of the distributor 4. Both ends of the shaft 8 are positioned in the couple of revolving fitments 6. Arm geometry 7 is designed in a manner that common center of gravity of arms 7 and dampers 13 in all operating positions, i.e., from closed to fully opened, is located on the right side from the axis of rotation of the shaft 8, so as the dampers 13, when closed, are in their rest position by effects of gravity. Rectangular, in horizontal direction moving, orifice 5 with the couple of rectangular controlling orifices 15, is located on the front surface of the distributor 4 (moving orifice 5 highlighted as a shaded surface). In addition, the orifice 5 contains an elongated central slot 18, located horizontally in the middle of the orifice 5, facilitating entry of arms 7 and defining the minimum size of restriction of surface of the inlet orifices 14.1, 14.2, 14.3. The orifice 5 provides achievement of the requested ratio of individual types of the air for all existing operating conditions (heating-up, combustion, burning-out) and all possible fuels (high mass burning rate, standard, low mass burning rate). Lower vent piping 10 of the lower primary air, supplied to the lower outlet orifice 16, is attached to the lower wall of the left chamber of the distributor 4. Secondary vent piping 9 of the secondary air, supplied to the outlet orifice 12, consisting of the secondary air outlet nozzle, is attached to the lower wall of the central chamber of the distributor 4. Upper vent piping 3 of the primary air, supplied to the upper outlet orifice 11 of the outlet primary air, is attached to the upper wall of the right chamber of the distributor 4.
Other alternative embodiments of the invention are possible; the distributor 4 need not to be an independent body, may be integrated into the boiler body, for example the boiler body will form a rear wall of the distributor 4 etc. Individual chambers of the distributor 4 may be sequenced differently compared to the example of embodiment. The orifice 5 need not to be sliding but, for instance, revolving. Shape and quantity of controlling orifices 15 of the orifice 5 may be different etc.
The function of the heater 100 is as follows: combustion air flows into the inlet orifices 14.1, 14.2 and 14.3 of the distributor 4, using for example an FD fan. A blow of air swings out the dampers 13 with the arms 7 inside the distributor 4. The relative proportion of quantity of the air flowing through the individual inlet orifices 14.1, 14.2 and 14.3 is defined by position of the orifice 5 through its controlling orifices 15. The shaft 8, connecting the arms 7, identically slightly turns said arms 7 and all three dampers 13 are opened identically. Position of the orifice 5, shown in Fig. 1 , identically uncovers the first inlet orifice 14.1 of the lower primary air and the inlet orifice 14.3 of the secondary air (of the left and central chamber of the distributor 4), whereas the second inlet orifice 14.2 of the upper primary air (right chamber) is uncovered only minimally, through the central slot 18 of the orifice 5. Consequently, both secondary and lower primary air flow into the boiler in an approximately identical rate whereas flow of the primary air is only minimal. For example, the orifice 5 is in such a position in case of already flaming up boiler, burning common fuel with standard mass burning rate (such as dry logs). Share of flows of the individual types of air for this specific position of the orifice 5 see Fig. 4, i.e., ca. 45% of the lower primary air, ca. 45% of the secondary air, and ca. 10% of the upper primary air.
Another alternative position of the orifice 5, shown in Fig. 5, defines flows of individual types of air as follows: secondary air reaches the maximum flow of ca. 85% at the inlet orifice 14.3, whereas flows of lower and upper primary types of air at the inlet orifices 14.1 and 14.2 are only minimal, defined by the surface of the central slot 18 of the orifice 5, i.e., ca. from 5 to 10%. For example, the orifice 5 is in such a position in case of already flaming up boiler, burning fuel with high mass burning rate (such as dry wooden chips).
Another alternative position of the orifice 5, shown in Fig. 6, defines flows of individual types of air in a way that the upper primary air reaches the maximum flow of ca. 60% at the second inlet orifice 14.2. Flow of the lower primary air at the first inlet orifice 14.1 is partly limited, reaching ca. 30%, and flow of the secondary air at the inlet orifice 14.3 is minimal as the flow is defined by the surface of the central slot 18 of the orifice 5, reaching ca. 10%. For example, the orifice 5 is in such a position in case of heated up or already flaming up boiler, burning fuel with low mass burning rate (such as wet or large logs).

List of Reference Signs

100: heater
1: fuel area
2: fuel
3: upper vent (primary air)
4: distributor
5: orifice
6: fitment
7: damper arm
8: shaft
9: secondary vent (secondary air)
10: lower vent (primary air)
11: upper outlet orifice (primary air)
12: outlet orifice (secondary air)
13: damper
14.1: first inlet orifice (lower primary air)
14.2: second inlet orifice (upper primary air)
14.3: inlet orifice (secondary air)
15: controlling orifice
16: lower outlet orifice (primary air)
17: overfire area
18: central slot (of the orifice)

Claims

Solid fuel heater with three-zone combustion air supply, comprising a lower outlet orifice (16) and a first inlet orifice (14.1) of a lower primary air, wherein the lower primary air between the first inlet orifice (14.1) and the lower outlet orifice (16) runs in a first independent vent (10), and an upper outlet orifice (11) and a second inlet orifice (14.2) of an upper primary air between the second inlet orifice (14.2) and the upper outlet orifice (11) runs in a second independent vent (3), and, an outlet orifice (12) and an inlet orifice (14.3) of a secondary air, wherein the secondary air between the inlet orifice (14.3) and the outlet orifice (12) runs in a third independent vent (9); wherein three dampers (13) are attached to three respective arms (7) assigned to three respective inlet orifices (14.1, 14.2 and 14.3),
characterized in that the arms (7) are connected to a shaft (8), and in that the inlet orifices (14.1, 14.2 and 14.3) are equipped with a common moving orifice (5).
Heater according to claim 1 characterized in that the inlet orifices (14.1, 14.2 and 14.3) are located on a distributor (4), fixed to an external side of the heater (100), whereas the shaft (8) is located outside said distributor (4).
Heater according to claim 1 characterized in that the moving orifice (5) contains two controlling orifices (15).