EP0084852A2

EP0084852A2 - Solid fuel steel construction boiler for domestic heating applications

Info

Publication number: EP0084852A2
Application number: EP83100440A
Authority: EP
Inventors: Giovanni Jahier
Original assignee: Unical SpA
Current assignee: Unical SpA
Priority date: 1982-01-26
Filing date: 1983-01-19
Publication date: 1983-08-03
Also published as: EP0084852A3

Abstract

The involved technical field is that of boilers, and the invention concerns a solid fuel steel construction boiler for domestic heating applications.

The technical problem was that of providing a boiler wherein the combustion process could be controlled through an automatic control system.

The solution provides for the interior space of the boiler, which is enclosed in a water curtain interspace, to be elongated vertically and divided into an upper zone (1 a) and lower zone (1 b) by a cradle (9) having an aperture (9a) above which a burner is located which comprises a tube (10a) perforated over its lower surface, air being delivered by an electric fan (17) controlled by an automatic control circuit into a chamber (19) whence primary air flows out toward the top portion of the upper zone (1 a) and secondary air is flown into the burner (10), the lower zone (1 b) being connected to a smoke box (12) in communication with the chimney flue.

Description

This invention relates to a solid fuel steel construction boiler for domestic heating applications.
It is a known fact that domestic heating boilers burning such solid fuels as firewood, coal, and industrial waste products, regarded as satisfactory substitutes for petroleum-based fuels, the cost of which has raised excessively, are gaining increasing acceptance.
Among the various types of boilers proposed heretofore, there is one design, which has yet to receive a specific designation in official technical nomenclature, and wherein combustion takes place by naturally induced draft with the flame being directed downwards and out of a fuel supporting grate.
This type of boiler, along with some undoubted advantages, has several disadvantageous features, which it shares with other prior types of boilers. The first being that the'combustion process conditions can only be coarsely controlled, which requires constant attention by an operator, while only poor outputs can be obtained.
Another disadvantage resides in starting difficulties, since starting can only be effected after the chimney flue has been heated by lighting an additional fire at the base thereof. This brings about obvious operating complications.
Moreover, that prior boiler can only be operated with large cross-sectional area chimneys, which are not always available, and this represents a serious limitation to a widespread utilization thereof.
Thus, the task of this invention is to provide a solid fuel steel construction boiler for domestic heating applications, wherein the flame is directed downwards and it is possible to control, by means of an automatic control system, the conditions of the combustion process and adjust the generation of heat to meet the requirements of the system incorporating such a boiler, thereby high outputs and prolonged self-supporting combustion can be achieved, such as are of special import in a family operation environment.
Within this task it is an object of the invention to provide a boiler as indicated, whereby the starting step is made extremely simple and operation with small cross-section area chimneys.
It is a further object of the invention to provide a boiler as indicated, on the inner walls whereof, with the boiler in operation, there can form no heavy deposits of bituminous substances to hinder the transferring of heat from the combustion gases to the water, with attendant output loss and continued maintenance requirements, and which fully accessible for extraordinary maintenance operations.
According to one aspect of the invention the above task and objects are achieved by a solid fuel steel construction boiler for domestic heating applications, characterised in that it comprises a space or volume with vertically elongated shape and being delimited by longitudinal sidewalls, a bottom, and a cover, enclosed by an interspace containing water to be heated and complete with delivery and return connections, and by a front plate and rear plate, also provided at least in part with a similar interspace, subdivided into an upper zone and lower zone by a sheet metal cradle having substantially horizontal generatrices extending longitudinally, and being formed at a middle area thereof with a longitudinally elongated aperture, at an overlying position relatively to said aperture there being arranged a burner comprising a tube which extends from the front plate to the rear plate and is perforated at the lower region of the lateral surface included between means adapted to delimit a space portion in communication with said longitudinally elongated aperture, an air metering unit located on said front plate and including an electric fan controlled by an automatic control circuit and a distribution chamber having its outlet for the primary air facing the top portion of the upper zone of said space portion and its outlet for the secondary air located at the axis of the tube comprising said burner, a smoke box provided at the top with a chimney flue connection and being located at the rear plate and in communication with the lower zone of said space portion, a loading door located on the front plate at the upper zone of said space portion, an inspection door also located on the front plate at the lower zone of said space portion, and a port communicating the upper zone of said space portion to the smoke box and located close to the top thereof and adapted to be shut by means of a manually operated gate.
It will be apparent how with a boiler of this type it becomes possible, thanks to the provision of the air metering unit comprising an electric fan controlled by an automatic control circuit, to achieve optimum operating conditions, with a high output rate and prolonged selfsupporting operation features, as will be explained more clearly hereinafter.
Further features and advantages will be apparent from the following description of two preferred, but not limitative embodiments thereof, illustrated by way of example only in the accompanying drawings, where:

Figure 1 is a perspective view, with some components in ghost lines, of this invention as incorporating the burner according to a first embodiment thereof;
Figure 2 is a sectional view of the invention shown in Figure 1, taken on a longitudinal centerplane through the front plate, with the boiler in steady state operating conditions, the burner being shown in elevation, instead of in section, for clarity of illustration;
Figure 3 is a sectional view of the invention taken on the cross-plane III-III of Figure 1;
Figure 4 is an enlarged scale detail view of the burner of Figure 3;
Figure 5 is a detail view of the port shutting gate for the port which communicates the smoke box to the space portion intended to accommodate the fuel, the gate shut position being shown in full lines, and the gate open position in dash lines;
Figure 6 is a perspective view of a first embodiment of the burner; and
Figure 7 is a front view of that boiler area where the burner shown in Figure 6 is located.

Making reference to the drawing Figures 1 to 5, indicated respectively at 1a and 1b are the upper zone and lower zone of the space portion delimited by the longitudinal sidewalls 2, bottom 3, and cover 4, all of which are enclosed by the interspace 5 containing the water to be heated, complete with delivery 6a and return 6b connections. The boundary of the zones 1a and 1b is completed by the front plate 7 and rear plate 8; the front plate 7 comprises apparataswhich will be explained hereinafter, additionally to the interspace band 7a containing water to be heated, in communication with the interspace 5 through holes such as 7b; the rear plate 8 is enclosed by the interspace 8a, also containing water to be heated and in communication with the interspace 5.
Separation of the upper zone 1a intended to contain the fuel, which in the drawings is represented by firewood but could just as well be coal or any other solid fuel, from the lower zone 1b is accomplished by means of the sheet metal cradle 9 having horizontal generatrices which extend longitudinally and being formed at the center with the aperture 9a, elongated in the longitudinal direction.
At a location overlying said aperture, a burner generally indicated at 10 is provided which comprises the tube 10a with a perforated wall at the lower portion thereof included between two perforated fins 10b and 10c extending substantially vertically; said burner extends longitudinally from the front plate to the rear plate with provisions for thermal expansion, it simply resting with one end with the fins on the bracket 8b, and with the other end, through the tube 10a, onto the stub pipe 19b, which will be described more clearly hereinafter.
The surface area of thermal exchange between the combustion products and water to be heated is increased at the lower zone 1b by anticorrosion dry pipes 11 which open with the end 11a to said zone 1b and communicate at the other end 11b with the smoke box 12 provided with the fitting 12a for connection to a chimney flue and of a chest 12b for ash collection.
There also exists the possibility of communicating the smoke box 12 directly to the upper zone 1a, for the purpose of allowing the effectuation of certain operative steps which will be explained in describing the boiler operation, by moving, through manual operation of the rod 13, the gate 13a from the position where it shuts the port 14, shown in full lines in Figures 1 and 5, to the open one, shown in dash lines in Figure 5.
Provided on the front plate 7 are the loading door 15 which opens to the zone 1a, and the inspection door 16, including a telltale 16a, at the zone 1b, as well as the air metering unit which comprises the electric fan 17 connected, through the fitting 18, to the distribution chamber 19 whence primary combustion air flows out through holes such as 19a, so arranged as to direct the flow of said air toward the top portion of the upper zone 1a, and secondary combustion air flows out through the stub pipe 19b toward the interior of the tube 10a of the burner 10.
Provided inside the fitting 18 is a check valve 20 which is raised by rotation around the pin 21 as the electric fan 17 is started, overcoming its own weight and the action of the weight 22 provided at that end of the rod 23 which is connected to the pin 21 for the purpose of holding the valve 20 steadily in the shut position when the electric fan is inoperative; contact of the rod 21 with the detent 24 secured at an adjustable position along the rod 25 located close to one wall of the fitting 18 affords a limiter for the opening stroke of the valve 20.
Throttling of the secondary air is accomplished by means of the small disk 25a being attached to the end of the threaded shank 26 projecting from the front plate and being provided with the knob 26a, positioned with its axis substantially coinciding with that of the stub pipe 19b; by moving the small disk 25a to and from the mouth of the stub pipe 19b, the intake flow of secondary air to the burner can be controlled.
The electric fan 17 is controlled, as will be explained in describing the boiler operation, by an automatic control circuit comprising the control 27i and safety 27a thermostats installed within the interspace 5, and the combustion gas high temperature 28 and low temperature 28a thermostats, mounted at the top of the smoke box 12.
During the steady state operation of the boiler, the doors 15 and 16 and gate 13a are closed and the electric fan is in operation: a part of the air supplied by the latter to the interior of the distribution chamber 19, constituting the primary combustion air, flows out of the holes 19a, and in following the path indicated by the arrows in Figures 2 and 3, flows through the mass or body of fuel accommodated in the zone 1a and resting on the cradle 9, it meeting, from top to bottom, first the topmost layers comprising firewood being dried and then, in flowing down, the firewood layers undergoing distillation of the volatile substances, and lastly the coal layers at the area adjoining the cradle 9, where combustion proper takes place; the arrows which have been drawn through the perforations in the fins 10b and 10c of the burner and under them in Figures 3 and 4 represent accordingly products of the combustion between the solid and volatile combustible substances of firewood and primary air.
Admixed to these combustion products are also normally present, however, substances which are still combustible, and completion of the combustion is ensured by the secondary air which is supplied from the distribution chamber 19, it entering, through the stub pipe 19b, the tube 10a of the burner to emerge through the holes therein and follow the path indicated by the arrows in Figure 3 and 4.
The flow of combustion products, namely the flame, which is directed downwardly, emerges from the aperture 9a formed at the bottom of the cradle 9 to enter the zone 1b and penetrates, following the path'_. indicated by the arrows in Figures 2 and 3, the end 11a of the dry pipes 11, thus flowing through them and actively exchanging heat with the water contained in the interspace 5, whence it emerges to reach the smoke box 12 and hence the chimney through the fitting 12a.
Through the aperture 9a, ashes are also let out,. but in minimal amount owing to the high degree of efficiency of the process, which will pass between the fins 10b and 10c and the cradle 9.
The combustion process just described is controlled, according to a peculiar aspect of the invention, by the control circuit comprising the cited thermostats, thereby an optimum combustion state can be achieved in a quite comparable manner to oil-fired boilers.
Thus, the control thermostat 27 will stop the electric fan 17, which results in the burner flame being extinguished and a very slow continuation of the combustion, upon reaching a preset temperature for the water to be heated, turning said electric fan on again and consequently reactivating the flame as the water temperature drops below a certain level.
Utilizing the direct proportionality between the flue gas temperature and delivered power, the combustion gas high temperature thermostat 28 also serves, again by acting on the electric fan 17, the highly important function of keeping the combustion state constant as the type of firewood, for example, changes which is gradually affected by the process, to prevent such heat delivery peaks as would occur in a spontaneous process, or an uncontrolled one, following a sudden and concurrent distillation of most of the volatile substances contained in the fuel; it is, therefore, possible to obtain a gradual and sufficiently slow process, such as can ensure a long duration of the same, following adequate loading of fuel in its respective zone extending in a vertical direction to form a storage of sort in the topmost layers not affected by the combustion, even over a time period of twenty four hours, which is the optimum for family operation of the boiler.
The combustion gas low temperature thermostat 28a finally stops the electric fan 17 upon exhaustion of the firewood in the boiler.
Another feature to be emphatized here is that the provision of the air metering unit enables the boiler operation to be rendered independent of the natural draft variations through the chimney flue as weather conditions change, since it is the electric fan 17 which meters the amount of air admitted, it even functioning as a holdback in the event of too powerful a draft.
With the inventive boiler, the starting phase is made particularly easy. This on account of the steady state operation contemplating the provision of an amount of ambers in contact with the cradle 9 which can keep the combustion alive up to a certain level in the fuel pile, notwithstanding the downward direction imparted to the flame, which amount of ambers is created by operating for a certain time period, e.g. a quarter of an hour, in natural upwardly directed draft conditions; for this purpose, the door 16 and gate 13a are opened, thus producing an airflow in the desired direction which is effective to keep the combustion on regardless of how it has been triggered.
At the end of the time period required to form the ambers, the electric fan 17 is started and the door 16 and gate 13a are closed for steady state operation.
The gate 13a is also operated to open prior to opening the door 15 for loading fuel, with the electric fan in operation, in order to avoid being swept by a blast of smoke, and is closed again on completion of the loading operation.
The operation just described results in an almost total absence of bituminous deposits on the boiler walls; the construction of the boiler provides, however, full acessibility in all cases.
Figures 6 and 7 illustrate a first variation of the burner 10; the tube 10a therein, which is supported at the front end by the stub pipe 19b supplying secondary air, and at the rear end by resting the bent flange 29 onto the bracket 30 rigid with the rear plate, has a round cross-section and formed along the bottom generatrix of the lateral surface with the holes 31 for letting out the secondary air.
Aligned along substantially symmetrical generatrices with respect to the vertical diametral plane are two rows of holes, only one whereof is shown in Figure 6, through which are passed the turns of a coil generally indicated at 32 and being made up of the three consecutive sections 32a, 32b, 32c, which define a plurality of rings in the space underlying the tube 10a.
The combustion gases from the fuel which still contain combustible substances will flow between the coil turns into the zone underlying the tube 10a, following the paths indicated by the arrows in Figure 7, being prevented from escaping directly through the aperture 9a in the cradle because the turns of the coil 32 barely skim the edges thereof, thereby the blending thereof with the secondary air from the holes 31 is optimized thanks to the turbulence encouraged by the presence of coil turn sections in the outlet section.
The ashes are then removed, without any risks of occlusion, by gravity through the coil turns.
Another important feature of the boiler shown in Figures 6 and 7 is that the connection of the coil by mere insertion into the holes of the tube lateral surface holes ensures that the tube, by being cooled by the secondary air, can be kept during the operation at a relatively low temperature, although the coil may become red hot; thus, the tube can last longer and it becomes possible to just replace the coil, wherein the deteriorating effects induced in the material by the high temperatures concentrate, even in sections, at the end of the useful cycle life, for a very low cost.
The invention described is susceptible to many modifications and variations, without departing from the scope of the instant inventive concept; thus, for example, the automatic control circuit may include, in addition to the cited thermostats, such other members as a programming clock; the check valve and secondary air throttle may also have any suitable construction.
The cross-section of the burner tube may have any configurations, such as an elliptical one, and the rings provided by the first variation of said burner, instead of being formed by the turns of a coil, may be separated from one another.
In practicing the invention, all of the details may be replaced with other technically equivalent elements; moreover, the materials used, as well as the shapes and dimensions, may be any suitable ones to meet individual requirements.

Claims

1. A solid fuel steel construction boiler for domestic heating applications, characterised in that it comprises a space or volume with vertically elongated shape and being delimited by longitudinal sidewalls (2), a bottom (3), and a cover (4), enclosed by an interspace (5) containing water to be heated and complete with delivery (6a) and return (6b) connections, and by a front plate (7) and rear plate (8), also provided at least in part with a similar interspace, subdivided into an upper zone (1a) and lower zone (1b) by a sheet metal cradle (9) having substantially horizontal generatrices extending longitudinally, and being formed at a middle area thereof with a longitudinally elongated aperture (9a), at an overlying position relatively to said aperture (9a) there being arranged a burner (10) comprising a tube (10a) which extends from the front plate (7) to the rear plate (8) and is perforated at the lower region of the lateral surface included between means adapted to delimit a space portion in communication with said longitudinally elongated aperture (9a), an air metering unit located on said front plate (7) and including an electric fan (17) controlled by an automatic control circuit (27,27a,28,28a) and a distribution chamber (19) having its outlet (19a) for the primary air facing the top portion of the upper zone (1a) of said space portion and its outlet (19b) for the secondary air located at the axis of the tube comprising said burner (10), a smoke box (12) provided at the top with a chimney flue connection and being located at the rear plate (8) and in communication with the lower zone (1b) of said space portion, a loading door (15) located on the front plate (7) at the upper zone (1a) of said space portion, and an inspection door (16) also located on the front plate (7) at the lower zone (1b) of said space portion; a port communicating the upper zone (1a) of said space portion to the smoke box (12) and located close to the top thereof and adapted to be shut by means of a manually operated gate (13a).

2. A boiler according to Claim 1, characterised in that the interspace (5) containing water to be heated on the front plate (7) extends at the distribution chamber (19) of the air metering unit.

3. A boiler according to one or both of the preceding claims, characterised by the provision, in contact relationship with the wall in the bottom portion (3) of the lower zone (1b) of said space portion, of anticorrosion dry pipes (11) adapted to increase at said zone the surface area of thermal exchange by conveying the combustion products toward the smoke box (12).

4. A boiler according to one or more of the preceding claims, characterised in that the burner (10) is arranged to just rest with its rear end onto a bracket (8b) extending from the rear plate (8), and with the other end onto a stub pipe (19b) extending from the air distribution chamber (19), and is inserted into the tube (10a) comprising said burner (10) for directing secondary air thereinto.

5. A boiler according to one or more of the preceding claims, characterised in that the means adapted to delimit a space portion underlying the burner tube (10a) and in communication with the longitudinal aperture (9a) provided in the cradle (9) comprises two perforated fins (10b,10c) which extend vertically downwards from the lateral surface of said tube (10a) in a substantially symmetrical position with respect to the vertical midplane.

6. A boiler according to one or more of the preceding claims, characterised in that the means adapted to delimit a space portion underlying the burner tube (10a) and in communication with the longitudinal aperture (9a) provided in the cradle (9) comprises a plurality of rings (32a,32b, 32c) associated with said tube (10a) by insertion into holes (31) aligned along two generatrices of the lateral surface thereof and located in a substantially symmetrical position with respect to the vertical midplane.

7. A boiler according to one or more of the preceding claims, characterised in that the rings (32a,32b,32c) comprise turns of a coil (32).

8. A boiler according to one or more of the preceding claims, characterised in that the coil (32) is divided into a number of sections.

9. A boiler according to one or more of the preceding claims, characterised in that the rings (32a,32b,32c) are separated from one another.

10. A boiler according to one or more of the preceding claims, characterised in that the rings (32a,32b,32c) are located at a very small distance away from the longitudinal aperture (9a) provided in the cradle (9).

11. A boiler according to one or more of the preceding claims, characterised in that the burner tube (10a) has a substantially square cross-sectional configuration.

12. A boiler according to one or more of the preceding claims, characterised in that the burner tube (10a) has a circular cross-sectional configuration.

13. A boiler according to one or more of the preceding claims, characterised in that the burner tube (10a) has an elliptical cross-sectional configuration.

14. A boiler according to one or more of the preceding claims, characterised in that the air metering unit is provided, on the delivery side of the electric fan (17), with an automatic check valve (20) with the electric fan (17) inoperative.

15. A boiler according to one or more of the preceding claims, characterised in that said check valve (20) has an adjustable opening stroke limiter formed by contacting a rod (23) connected to the pivot pin (21) of said valve (20) with a detent (24) adapted to be secured at an adjustable position close to the wall of the conduit enclosing said valve(20).

16. A boiler according to one or more of the preceding claims, characterised by the provision of a weight (22) at the rod end connected to the pivot pin (21) of said check valve (20), adapted to hold said valve (20) steadily in the closed position with the electric fan (17) inoperative.

17. A boiler according to one or more of the preceding claims, characterised by the provision of a secondary air throttle control (25a).

18. A boiler according to one or more of the preceding claims, characterised in that the secondary air throttle control comprises a small disk (25a) carried at the end of a threaded shank (26) protruding with the other end from the front plate (7) and being positioned on the axis of the stub pipe (19a) which extends from the air distribution chamber (19) for conveying said secondary air.

19. A boiler according to one or more of the preceding claims, characterised in that the automatic control circuit controlling the electric fan (17) of the air metering unit comprises at least one control thermostat (27) and a safety thermostat (27a) inserted into the interspace (5) containing water to be heated, a combustion gas high temperature thermostat (28) and combustion gas low temperature thermostat (28a).