FI104345B - Oven heat exchanger design and method for recovering combustion heat - Google Patents

Description

104345

Furnace Heat Exchanger Structure and Method for Recovery of Combustion Heat in a Furnace Furnace Förbränningsvärme

The invention relates in particular to an integrated heat exchanger arrangement for a furnace structure for burning wood or the like, in particular a furnace core cassette, wherein the furnace structure furnace is led by a a wall of which is limited to the hearth, and a heat exchange chamber acting as a passage for the combustion gases, respectively, with at least one substantially thin common wall portion between the channels. The invention also relates to a method for recovering heat from the hot combustion gases exiting the upper end of the furnace structure fire furnace, which are first conducted downwardly in a first passage, i.e. a downpipe, and then in a second passage and ·· to balance the temperature conditions in the gutter.

Conventionally, the wood burning furnace structure has consisted of a fire chamber with a lower grate through which a substantial portion of the oxygen-containing air required for the combustion process is fed to the furnace. Above the furnace, a flue duct begins, which in the most advanced furnace structures comprises a smoky salt, in which the flue gases and any residual air are mixed to permit the subsequent combustion of combustible charcoal gas which has not yet been burned, after which the resulting flue gases are discharged into the flue. Between the fire chamber and the upper combustion chamber associated with the smokestack, the most modern furnace structures have a narrower drainage structure than the rest of the flue, which is intended to cause turbulence in the flue gases and thereby improve the combustion of the flue gases.

In old-fashioned tile stoves, hot flue gases are led from the top of the furnace, which is arranged in a substantially open space, down each side of the furnace to a manifold underneath the furnace, from where the gases rise from the rear to the flue. The purpose of such a structure is that the hot flue gases release their heat to a substantially large mass of stone, which is formed by the furnace structure itself. However, the operation is slow due to the slow warming of the aggregate and in all cases the heat transfer is ineffective. The traditional oven is first cold and only hot after a long period of heating. In the case of very efficient heating, there is still a risk that the stone structure will be heated unevenly and even excessively and thus be prone to breakage.

Increasing environmental awareness has also set increasingly stringent emission requirements for wood burning furnace structures. Similarly, it has been found that there is still room for improvement in the known furnace structures, whereby a significant amount of the components still combustible per se are removed by the flue gases. Similarly, some of the heat contained in the flue gases still passes through the flue as waste heat. However, despite extensive experiments, no means has been found to significantly increase the efficiency of conventional wood-burning furnace structures while ensuring that the emissions to the climate of harmful substances such as some hydrocarbons, particulates and the like are minimized. Thus far known furnace structures can still be considered to be quite unsatisfactory. This is regrettable, given that 3 104345 wood is a renewable energy in its own right, which should also be made more efficient in small households, without causing any additional environmental problems.

Another Finnish patent application FI-980045 of the same applicant provides a solution for improving the efficiency of the furnace combustion process and reducing harmful emissions. Such patent application is hereby deemed to be included in this application. At the same time, the need to improve heat recovery in this furnace arrangement as well as in conventional furnaces has emerged and this application is directed to improving the utilization of heat from combustion gases.

The features of the invention will be apparent from the appended claims. Thus, the furnace construction arrangement according to the invention is particularly known in that the drainage channel is surrounded by a rising heat exchange chamber forming a riser channel with separate heat exchanger arrangements having heat-dissipating separate heat exchanger arrangements. Thus, the flue duct is formed as a heat exchanger having a downflow duct for hot combustion gases and a surrounding flue gas riser between which there is at least a substantially thin common wall portion.

The method of the invention is further characterized in that heat is removed from the furnace structure by holding the drain duct externally at least substantially the interior and exterior surfaces of the heat exchange chamber surrounding the drain duct and heat exchange utilized through heat exchanger arrangements. Thus, the hot combustion gases exiting the furnace structure are first conducted downwardly and upstream thereof, whereby the temperature of the outer surface of the outer channel remains substantially constant with said heat transfer from one channel to another.

4, 104345

Preferably, the above-described recovery structure is substantially directly associated with the furnace structure, wherein the combustion gas afterburner and the furnace smoke chamber provide a composite channel substantially dimensioned for the internal mixing of the combustion gases with at least 75 ° thin controls so that the gases escape from the furnace structure in a substantially horizontal direction. However, the arrangement of the invention is also applicable to other furnace structures known per se.

The solution according to the invention differs substantially from the arrangements known to date for furnace structures, in particular in that the combustion gases are directly conveyed through a counter-current efficient heat exchanger, the outer surfaces of which, by means of the arrangement, achieve a uniform high temperature.

The invention will now be described in more detail with reference to an advantageous embodiment thereof and with reference to the accompanying drawings, in which Fig. 1 is a schematic drawing of a prior art furnace structure, Fig. 2 schematically shows a basic arrangement of the heat exchanger arrangement according to the invention. Figure 3 shows a vertical section along line B-B of Figure 4 of a furnace structure according to a preferred embodiment of the invention, and Figure 4 correspondingly shows a horizontal sectional view of the furnace structure of Figure 3 at line A-A.

According to Fig. 1, a conventional efficient wood burning furnace has a furnace 1 with a bottom formed by a grate 2 with an ash space 3 underneath. The furnace 1 is provided with a combustible wood batch 4 which is lit in a manner known per se. The oxygen-containing primary air 5 required for combustion of the wood flows primarily through the grate 2 and generally also through the air vents 7 arranged in the lower half of the furnace door 6, mainly to the upper part of the furnace 1. After ignition, the wood charge 4 burns oxygen in the air so that the heat generated in the furnace 1 causes the combustible gases to evaporate from the wood charge 4. The gases ignite and burn, particularly above the charge 4, whereby the radiant heat of the combustion flame 8 The heat generated by the combustion process is recovered either by the heat exchange directly associated with the cooker structure, e.g., by the heat of the stove, by the heat of the furnace mass or by separate heat exchange arrangements. In this way, wood has traditionally been burned for ages.

In the most recent furnace structures, the space above the above-mentioned fire chamber 1 is further separated into a separate afterburner space 9, i.e. a secondary fire chamber. The combustion gases 10, still containing combustible gases such as carbon monoxide, are then introduced into the afterburner 8 via a separate narrow drain 11, whereby the secondary air from the combustion gases 10, in particular the hatch 6, is efficiently vented by the increased flow velocity and the desired turbulence. In combustion chamber 9, the flammable gases are sought to be burned as closely as possible so that the flue gases 13 leaving the combustion chamber 9 should mainly contain only non-combustible components, in particular carbon dioxide and water vapor, which are generally introduced directly into the smoke flue 32.

6 104345

Finnish patent application no. The furnace solution according to FI-980045 differs in principle from the conventional technique described above. Reference is first made to Figure 2, which shows that the furnace structure in question does not have any narrow drain between the furnace 1 and the afterburner, and thus the combustion gases are not accelerated to produce turbulence mixing the combustion gases and air. Instead, a gas channel dimensioned according to the laminar flow, generally designated 14, continues above the furnace.

Advantageously, according to the invention, the hot gas duct 25, which is part of the heat exchanger arrangement according to the invention, is suitably connected directly to said combustion gas duct 14 as a substantially vertical downward extension of the gas duct 14. According to the invention, the ascending duct 30 at least partially surrounds this ascending duct 25 so that preferably a relatively thin structure wall 29, which facilitates heat transfer, is common to both ducts.

The functional cross-section of the gas duct 14 serving as the afterburning space, i.e. the minimum distance between the combustion gas control members 16, 17 and the minimum distance between the other wall surfaces delimiting the duct, is substantially uniform.

The hot combustion gases pass through and substantially burn off through this afterburner conduit 14 so that they no longer contain significant amounts of combustible constituents. In accordance with a particularly preferred embodiment of the invention, the hot gases 15 flow downwardly along a triangular downwardly extending conduit 25, practically to the bottom 35 of the furnace structure. At the base 35, the gutter 25 terminates to form a gas passageway 36 opening into the gutter 30, where the direction of the gas flow is reversed. The flue gases, which have now partially released their heat, are preferably distributed into a riser channel 30, which is substantially rectangular in cross section and surrounds 7 104345 triangular downpipe 25 where it rises upwards. Thus, the hotter gases passing through the gutter 25 throughout the distance release heat in the gutter 30 behind the thin wall to the upstream relatively cooler gases.

The gases in the riser channel 30, on the other hand, release heat through the exterior surfaces 34, 34a, 34b of the riser channel, and especially through the heat exchanger tubes 31 preferably arranged in the riser channel to the open air, a separate heat transfer system such as liquid and / or brick. At the same time, the gases are also in continuous contact with the relatively hotter surface 29 of the duct 25 and thus the heat transfer from the duct 25 to the environment is as efficient as possible. Partial heat is also transferred away from the riser channel end surfaces, i.e. the bottom 35 and the upper portion of the channel 30, preferably through the surfaces of the collecting chamber 37.

In contrast to the prior art, the solution of the invention is characterized in that the heat-releasing surfaces of the structure have a substantially uniform and uniformly high temperature, which facilitates the use of the furnace and its application for various applications without low temperature inefficient surfaces or danger. With the arrangement according to the invention, these properties are also achieved with a very high degree of load on the furnace.

Thus, in accordance with a preferred embodiment of the invention, the furnace structure is comprised of a tin cassette, which itself can be bricked into a fireplace of the desired material or such furnace. Figures 3 and 4 show an example of such a cassette. Therein, the guide members 16 and 17 and the channel walls 19, 26, 29 and 34, 34a, 34b preferably consist of relatively thin metal plates or sheets having a low thermal capacity and efficiently transferring heat from the gases to and from the furnace structure.

Figures 2 to 4 further show a secondary air arrangement wherein secondary air 22 is led into the furnace 1 through a narrow slot 23 or a row of holes in its rear wall 19 into a flame zone 8 above the wood bundle 4. Particularly preferably, behind the furnace structure, between the down wall 26 of the downwardly draining duct 25, which ensures effective pre-heating of the secondary air 22.

As will appear from the foregoing, the downflow duct 25, which serves as an extension of the afterburner combustion duct 14, is preferably downwardly behind the furnace 1 and immediately adjacent to the narrow but preferably furnace-wide secondary air supply duct 24. 4 is preferably triangular in cross section so that one side is formed by the rear wall 19 of the furnace 1 and lower by the wall 26 of the secondary air supply duct, and its other two sides 29 are bordered directly from the lower part 35 of the furnace structure to the ascending According to one embodiment of the invention, the one or more heat exchanger surfaces 26, 29, 34 further comprise heat transfer facilitating shapes such as ribs, ridges or similar effective surface extending shapes. Preferably, the ascending duct further comprises heat exchange tubes 31 for heating room air or, for example, heat transfer fluid. For heating the room air, the tubes 31 preferably extend at their ends open throughout the length of the riser channel 30, i.e. they open into the space outside the channel 30.

When the duct 25 extending the combustion duct is disposed between the hot furnace 1 on the one hand and the hot smoke ducts 30 on the other hand, the temperature of the combustible gases remains high enough for as long as possible allowing efficient exhaustion of the gases before discharge through flue 32. At the same time, the hot surface 26 conducts heat to the secondary air duct 26 for preheating the secondary air, which in turn contributes to improved combustion at the beginning of the process. Surprisingly, it has been found that this arrangement, by virtue of the particularly high efficiency of the heat exchange, allows combustion at very high power without the temperature of the flue gases 13 leaving the flue 32 rising too high. Thus, in contrast to the prior art, the structure according to the invention in most cases allows burning with a full firebox and with full draft without causing danger or inconvenience.

The furnace structure according to the invention achieves a much smoother and more complete combustion and thus more efficient utilization of the energy of wood compared to the previously known solutions. The proportion of harmful compounds contained in the flue gases, such as carbon monoxide, harmful hydrocarbons and particles, is significantly lower than previously known. At the same time, the temperature of the flue gases is significantly lower compared to known solutions and thus the utilization of the amount of heat contained in the wood is more efficient. Figure 2 further shows that the solution according to the invention achieves a much more compact furnace construction than the prior art.

Certain advantageous features of the invention have been exemplified above with reference to one embodiment, but it will be apparent to one skilled in the art that the structure can be modified in many other ways within the scope of the appended claims without departing from the spirit of the invention. It is clear, for example, that the heat exchanger arrangement of the invention can also be used in connection with furnace structures other than those shown.

Claims (10)

10 104345 An integrated heat exchanger arrangement of a furnace structure, in particular for burning wood or the like, in particular a furnace core cassette, wherein the furnace furnace furnace (1) is led by a flue duct having a second end (32) associated with a flue or such flue gas outlet (15) a downstream conduit (25) for combustion gases (15) extending substantially vertically downwardly, one wall of which is adjacent to the fireplace (1) and a heat exchange chamber (30) acting as a passage for the combustion gases (15), at least one substantially thin common wall portion (29), characterized in that the drainage duct (25), on its sides other than those bordering the furnace (1), is substantially surrounded by a heat exchange chamber (30) forming an ascending duct with separate heat-dissipating heat exchanger arrangements (31). 2. Arrangemang enligt patentkravet 1, anchoring tongue, att den nedätgäende kanale (25) som utformats som en förlängning av en förbränningskanal (14) anordnad siltpligen. för efterförbränning av Heta förbränningsgaser (15) account here tvärsnitt är väsentligen triangulär, Medan tvärsnittet hos den coloringxlingskammare (30) som ätminstone delvis omger densamma årventligen rectangle, varvid en väg (19) i den nedg. 1) och / eller en secondaryärluftkanal (24) i anslutning account. v densamma bildar en bakvägg (26) eller en del av en hiss. • < Arrangement according to Claim 1, characterized in that the drainage channel (25) formed as an extension of a combustion duct (14) suitably adapted for post-combustion of the hot combustion gases (15) has a substantially triangular cross-section whereas the heat exchange chamber (30) has a substantially rectangular cross-section. wherein one wall (19) of the drainage duct (25) simultaneously forms the rear wall (26) of the furnace furnace structure (1) and / or the associated secondary air duct (24) or a portion thereof. 3. Arrangemang enligt patentkravet 1 eller 2, kännetecknad därav, att ätminstone coloringxlingsväggen (29) mellan den nedätgäende kanalen (25) and coloringxlingskammaren (30) and transforming the material into the material of the material. 14 104345 Arrangement according to Claim 1 or 2, characterized in that at least the heat exchange wall (29) between the downflow channel (25) and the heat exchange chamber (30) is made of sheet or similar heat-conducting material which is very thin. "104345 11 4. Arrangemang enligt face av patentkraven 1 ... 3, turn-tecknad därav, att colorful-lingsarrangemangen vid colorful-växlingskammaren (30) omfattar en eller warmth flera i vardera änden high-flooding channel (31) för friskluft i den som stigarkanal verkande colorful xlingskammaren (30) och utsträcker sig i dess längs- eller allmänt lodräta riktning och warmpligen frän ände account ände i construktionen. Arrangement according to one of the preceding claims 1 to 3, characterized in that the heat exchanger arrangements of the heat exchange chamber (30) comprise one or more plurality of substantially ascending heat exchange chambers (30) at each end thereof extending generally longitudinally and suitably from end to end. an open duct for heating fresh air or the like (31). 5. Arrangemang enligt face av patentkraven 1 ... 4, ankle -tecknad därav, att ätminstone den gemensamma väggen (29) mellan den nedätgäende kanalen (25) och coloringxlingskammaren (30) uppvisar i sig stump Lister, chamber eller liknande ut-spräng som förbättra överföringen av colorful. Arrangement according to one of the preceding claims 1 to 4, characterized in that at least the common wall (29) between the drain channel (25) and the heat exchange chamber (30) has ribs, ridges or similar projections known per se to facilitate heat transfer. 6. Arrangemang enligt face av patentkraven 1 ... 5, tele-t e c k n d davav, att coloringxlingskammarens (30) yttre väggar är utformade som coloringxlare i förhällande account det utrymme och / eller den construction som omger construktionen. Arrangement according to any one of claims 1 to 5, characterized in that the outer walls of the heat exchange chamber (30) are formed as a heat exchanger with respect to the space and / or structure surrounding the structure. 7. Förfarande för ätervinning av Värme ur Heta förbrännings-gaser (15) som avlägsnar sig vid Övre änden av eldstaden (1) i en firskonstruktion och vilka account att börja med leds i en: första kanal, dvs. en nedätgäende kanal (25) väsentligen nedät och därefter leds uppät i motsatt riktning i en annan kanal, dvs. i en Värmeväxlingskammare (30) som stär i contact med den nedätgäende kanalen (25), colors in the color att förflytta sig mellan den nedätgäende kanalen (25) 1) för att utjämna de inbördes temperatureurförhällanden som räder i eldstaden (1) och i den nedätgäende canalen (25), bosom-tecknat därav, att man avlägsnar color ur fire-construction genome att hrla det inre utrymmet och ytterytorna ( ) som utifrän ätminstone väsentligen omger den nedätgäende kanalen (25) kallare än väggarna (29) mellan den nedätgäende kanalen (25) och coloring xlings- • kammaren (30), varvid en väsentl ig color games genome en eller 1S 104345 flere väsentligen feel väggar (29) gemensamma för channelen (25) och coloringxlingskammaren (30) förflyttas frän kanalen (25) till kammaren (30) och därifrän via där belägna värtne-nytx. A method of recovering heat from the hot combustion gases (15) exiting the upper end of the furnace body fire lance (1), which are conducted first in a first conduit, i.e. a downflow channel (25), and subsequently in a second conduit contacting the downflow channel (25) in the heat exchange chamber (30) in the opposite direction upwards, whereby heat is passed between the downpipe (25) and the furnace (1) to balance the temperature conditions in the furnace (1) and downpipe (25), characterized in that heat is removed from the furnace structure externally at least substantially the interior and exterior surfaces of the heat exchange chamber (30), which is colder than the walls (29) between the drain channel (25) and the heat exchange chamber (30), substantially as the heat flows through one or more common thin walls (29) from the duct (25) to the chamber (30) and from there through heat exchanger arrangements (31) in the heat exchange chamber (30) 12 104345. 8. Förfarande enligt patentkravet 7, kännetecknat därav, att man med hjälp av coloringxlingsarrangemang (31) inne i coloringxlingskammaren (30) häller Temperuren hos Värme-växlingskammarens (30) ytteryta väsentligen jämn. Method according to Claim 7, characterized in that the temperature of the outer surface of the heat exchange chamber (30) is kept substantially constant in the vertical direction by means of the internal heat exchanger arrangements (31) of the heat exchange chamber (30). 9. Förfarande enligt patentkravet 7 eller 8, kännetecknat därav, att man bringar de Heta gaserna (15) nedd i den account tvärsnittet väsentligen triangulära nedät-gäende kanal (25) som anordnats i närheten av 1 (1) bakvägg ungefärän. botten (35), dérifrän de i quorumxlingskammaren (30) leds uppät i närheten av yttre sidan av den triangulära nedätgäende kanalens (25) ytterväggar (29) warmpligen förbi en förbränningskanal (14) som anordnats för de heta föränn frän eldstaden (1). Method according to Claim 7 or 8, characterized in that the hot gases (15) are brought downwardly in a substantially triangular drainage channel (25) arranged close to the rear wall of the furnace (1) until approximately flush with the bottom (35) of the furnace structure. over matched 25) of the outer wall (29) outside of the area: the heat exchange chamber (30) up to a suitably from the furnace (1) for leading hot combustion gases (15) in the combustion passage (14). Method according to one of Claims 7 to 9, characterized in that the medium to be heated, suitably air, is passed through separate heat exchange tubes (31) in the heat exchange chamber (30), preferably in the substantial flow direction of the hot gases in the chamber (30). 13 104345 • 1. Ett integrerat Värmeväxlingsarrangemang för en ugns- construction avsedd för förbränning av veder ellnande, särskilt för en inbyggnadskassett för en fire, colors frän Ugens eldstad (1) leder en bust channel vars ena ände (32) the channel canopy (13), the canopy canopy (13), the canopy omfattar canopy (25) the canopy (15), the canopy canopy (15), the canopy canopy (15) en gränsar till eldstaden (1), och en Värmeväxlingskammare (30) som main motvarvar vis visar som stigarkanal för rökgaserna (15), colors det mellan kanerna (25, 30) finns ätminstone et väsentligen known gemensamt väggavsnitt (29) nne -tecknat därav, att den nedätgäende kanalen (25) vid de av you sidor som inte angränsar account eldstaden (1) väsentligen omges av en Värmeväxlingskammare (30) som bil Dar en med roach shakesxlingsarrangemang (31) för avledande av Värme försedd stigarkanal. 10. Förfarande enligt face av patentkraven 1 ... 9, turn -tecknat därav, att ett upvvärmbart medium, soapigen • luft bringas att söre sigskilda coloringxlingsrör (31) som befinner sig i coloringxlingskammaren (30), med fördel i kammaren (30) befintliga Heta gasernas strak-ningsriktning. «• ·