CA1045925A - Wood and oil burning furnace - Google Patents

Abstract

Abstract of the Disclosure A wood and oil burning furnace having a combustion chamber in which logs are laid for burning, a baffle plate across a substantial portion of the top of the combustion chamber, a combustion gas outlet at the top of the chamber, a plurality of secondary air inlet tubes in the upper portion of the combustion chamber, a fan and secondary air preheating chamber in one wall of the combustion chamber and supplying preheated air to such tubes, and oil or gas burner, an auxiliary chamber connected through a port into the combustion chamber and directing the fluid fueled fire into the combustion chamber through the port which is located midway of the length of the sidewall of the combustion chamber.

Description

iO~59;:5 1 Back round o the Invention __ g In numerous localities, substantial quantities of wood and wood scraps are available w~lich may provide an inexpensive source of ~uel. A problem has always existed concerning the burning of wood efficiently for heating purposes, and particularly in burning green wood or wood which has not properly dried or been seasoned.
One of the most importan~ problems in regard to burning of wood for space heating purposes relates to the fact that substantially all wood and especially green wood contains a very substantial amount of creosote and moisture along with some volatile gases such as methane. In the burning of wood, the creosote and moisture is driven off the wood by the heat, and in most wood burning devices, oxygen and moisture cause the creosote to solidify on the interior surfaces of the heat exchanger and stack or flue.
As time goes by, the quantity of solidified creosote builds up on the interior of the heat exchanger or stack so that less and less heat is transmitted to the space being heated, and a greater and greater risk of chimney fires is created.
The woods which are readily available and inexpensive for use in heating are those which are high in creosote content, and such woods include poplar or aspen, willow, pine, tamarack, cedar, balsam, hemlock and birch.
In some locations sawmill slabs or scrap is readily available and inexpensively obtained, but such material is primarily the outer parts of logs including bark, which is the particular part where a substantial amount of creosotes are found.
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l In -the past, there have been some furnaces or burners which have attempted -to burn wood or alternately burn oil in the same irebox or combustion chamber. However, it does not produce eficient burning of the wood or green wood by simply burning oil in the same combustion chamber.
Su~ o the Invention The present invention produces efficient and complete burning o the combustion gases and volatile -~
materials in the fire chamber of the burner or urnace before such combustion gases are allowed to escape into the heat exchanger and flue. This complete combustion is obtained by injecting secondary combustion air, preerably preheated, above the burning logs in the urnace and causing and using such air to produce a cyclonic action in the combustion chamber so that all o the methane gas ~ ;
and creosote is eficiently burned before the combustion gases are allowed to escape. Such secondary combustion air is injected in an array or curtain of jets directed ~ `
trans~ersely across the exit port for the combustion gases 20 prior to the entrance of such combustion gases into the ~;
heat exchanger and flue. An aspirator tube extends the full length of the combustion chamber to create such jets of air and the aspirator tube is supplied with heated fresh air from a preheating chamber in the front wall o the furnace which also keeps the front wall of the urnace at an acceptably low temperature as to avoid any danger to people in the vicinity of the furnace. The heating chamber - in the front wall also substantially surrounds the access door through which logs are supplied into the burner so that the front door is also kept at an acceptably minimal ~ -2-.~ , i~5925 1 temperature, -thus permitti~c~ it to be opened ~or feeding the fire. ~dditional aspirator tubes adjacent the longitudinal sidewalls o~ the combustion chamber direct additional jets o heated secondary air above the log fire on the grates to a~d to the cyclonic turbulence and contribute to the complete combustion of gases and creosote before the combustion gases are allowed to escape from the combustion chamber.
The combustion chamber is provided with an elongate shape to accommodate logs which are in fireplace lengths rather than in stove wood lengths as has been commonly known.
In one particular embodiment, logs of 18 to 23 inches in length are easily accommodated.
The flame from an oil burner is directed into the combustion chamber through the sidewall at a location approximately midway along the length of the sidewall.
As a result of this location of the port through which the oil fired flame is injected into the fire chamber, the oil or gas fueled flame is directed approximately midway along the length of the logs lying in the combustion chamber.
The oil fired flame directed into the combustion chamber creates a double cyclonic action in both ends of the elongate combustion chamber so that substantially identical combustion occurs throughout the entire combustion chamber, ~ `
thus causing the entire logs to be ignited and burned simultaneously. ;
It should be recognized that, whereas it is not ;~-essential that the oil or gas fueled flame be used to supplement the heat provided frGm the wood fire in the burner, at all times, it may be desirable to supplement ~ .

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~, ' , ~04S925 1 the h~at provided Erom the wood fixe by the oil or gas fueled fire when the demands for heat are more than can be supplied from the wood fueled fire. When the wood fueled fire is used in conjunction with the oil or gas fueled flame, combustion of the wood ueled fire is assisted, both as to intensity, and as to assuring that maximum burning of the logs in the burner or furnace is accomplished. In many instances, the heat provided from the wood fueled ~ire will be adequate.
Description of the Drawings Figure 1 is a perspective view of the furnace with `
portions of the paneling broken away for some clarity of detail.
Figure 2 is a transverse section view taken at 2-2 in Figure 1.
Figure 3 is a longitudinal section view taken approximately at 3-3 in Figure 2.
Figure 4 is a horizontal view taken at 4-4 in Figure 3.
~ Detailed Description of the Invention One form of the invention is illustrated in the drawings and is described therein. The combined wood and oil hurning furnace is illustrated in Figure 1 and is indicated in general by numeral 10.
The furnace includes an outer shell or shroud 11 I through which air is circulated to be heated and then I directed back to the heating ducts of the building or space to be heated. Furnace 10 also includes an inner housing 12 ~ which defines the combustion chamber 3. The furnace also ; 30 includes a heat exchanger 14 which conducts the hot , ~ .
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1 combustion ~ases from the housing 12 and through the interior spaces of the outer shell 11 and to a manifold 15 which collects all the combustion gases and discharges such gases to an outlet flue 16 for connection to a stack.
It will be recognized that the heat exchanger 14 comprises a plurality of rectangular metal ducts 14.1 which are generally rectangular in configuration and are spaced apart so -that air may circulate all around the ducts 14.1 for maximum heat exchange. The outer shell or shroud 11 has an interior divider wall 17 which divides the interior of the outer shell 11 into an intake or preheating compartment 11.1 and a second heating compartment 11.2 which completely surrounds the inner housing 12.
The shell or shroud 11 has an air intake opening 11.3, adapted for connection to the air return ducts of a building heating system for delivering air to the furnace to be heated. The air traverses a portion of the heat exchanger 14 which is in the chamber 11.1, and proceeds to a fan 18 which propels the air through the wall 17 and into the heating chamber 11.2. The air in the heating chamber 11.2 circulates around the outer periphery of the inner housing 12 and also through the heat exchanger 14 in the chamber 11.2 and thence is moved outwardly through the air discharge opening 11.4 which is adapted for connection to the hot air delivery ducts in the heating system of a building.
The combustion chamber 13 of the inner housing 12 has a lower portion 13.1 defining a fire pit and an upper portion 13.2 in which combustible gases and particles are ~04~2S

1 substantially consumed beEore being allowed ko exit from the combus-tion chamber.
The upper portion of the housing 12 has a large discharge opening 19 through which combustion gases are directed into a manifold or discharge plenum 20 which is connected to the heat exchanger 14.
The lower portion 13.1 of the combustion chamber ~
is lined with fire brick 21 at tne two longitudinal sides -and across the rear or back side. This lower portion or :.::. - . .
10 fire pit of the combustion chamber confines the logs L ~ ;
which are placed in tha fire chamber for burning. The lower portion of the housing has horizontal grates 22 forming the bottom of the fire pit. The grates are laid on shoulder portions of the housing structure and are spaced apart to allow ashes to fall between the grates.
A removable ash drawer 23 is V-shaped and rests upon a V-shaped panel 24 forming a part of the housing, The drawer 23 has a front panel 23.1 with a handle 23~2 afixed thereon. The front panel of the drawer and the handle lies substantially flush with the outer panel 25 of the hollow or chambered front wall 26 of the housing 12.
As appears in Figure 1, the front panel 25 lies substantially flush with the adjacent portions of the outer shell 11 of the furnace.
The hollow or chambered front wall 26 of the housing 12 has a charging or access opening 27 formed ; therethrough and which is normally closed by an access or fire door 28, which is mounted on hinges 29. An inner panel 30 of the chambered wall 26 cooperates with the outer panel 25 in defining a preheating chamber 26.1 which extends ~l04~2~i 1 all across the width of the housing 12 above the access opening 27, and extends downwardly along hoth sides of the access opening 27 approximately to -the bottom of the access opening 27 and door 28. The metal plate 30 transmits heat from the combustion chamber 13 to the air in the preheating chamber 26.1 so tllat the air therein is heated.
The front wall 26 also defines a passage 26.2 for draft air which enters through a draft opening 25.1 in the outer panel 25 and which may be controlled by a regulator valve. The draft passage 26.2 is defined by a lower portion 30.1 of the inner panel which defines a draft air opening 30.2 through which the draft air is directed into the fire pit adjacent the grates 22.
In the upper portion 13.2 of the combustion ;
chamber, the sidewalls 12.1 and back wall 12.2 are protected from intense heat by auxiliary panels 12.3 which are spaced inwardly.
A generally horizontal baffle plate 31 traverses ;~
a substantial portion of the upper interior of the combustion chamber and i5 secured to one of the longitudinal sidewalls 12.1 adjacent the outlet opening 19. The baffle 31 is also affixed to the rear wall 12.2 of the housing and to the inner panel 30 of the chambered front wall 26. The free edge 31.1 of the baf1e 31 is spaced from the adjacent sidewall of the housing to define a combustion gases discharye passage 32 through which all of the combustion gases, moisture and air must pass as they travel from the upper portion 13.2 of the combustion chamber to the outlet 19.

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1 An array or curtain of adjacent jets or streams of preheated secondary air are directed across the passage 32 from an aix supply or aspirator tube 33 which extends along the free edge 31.1 of the bafle throughout substantially ~ .
the entire length oE the elongate fire chamber 11. ~he air : ;
tube 33 has its front end communicating with the preheating : .
air chamber 26.1 through an opening 33.1 in the inner panel 30 of the chambered wall 26 to receive air under pressure. The tube 33 has a plurality of discharge openings or apertures 33.2 which direct streams or jets of the air from the tube 33 transversely across the discharge passage 32 through which all of the combustion gases must flow.
The streams or jets of air are directed obli~uely downwardly ;
and toward the adjacent lon~itudinal sidewall of the inner housing 12 so as to thoroughly expose all o the combustion gases passing through the passage 32 to fresh heated air ~ :
for completing combustion and also ~or creating a cyclonic turbulence.
Air is supplied into the preheating chamber 26.1 by a fan 34 mounted on the front panel 25 of the chambered wall 26. Air from the an is moved through the preheating chamber 26.1 and into the tube 33. .
A pair o additional air supply or aspirator tubes 35 and 36 are respectively located along the opposite ~:
longitudinal sidewalls of the combustion chamber and :~
immediately above the ire brick 21 which defines the fire pit 13.1. The tubes 35 and 36 have discharge apertures 35.1 and 36.1, respectively, which are oriented to direct air horizontally outwardly away from the adjacent sidewall and substantially horizontally into the central .

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1 area of the combustion chamber. S~cond~ry air is thereby provided which sweeps across ~he top of the fire pit and of the logs and burning material ther~in. Air supply tubes 35 and 36 are both connected to the air preheating chamber 26.1 in the manner illustrated in relation to tube 35 in Figure 3. The portions of the preheating chamber 26.1 which extend downwardly along the side edges of the access opening 27 have openings 26.2 through the inner panel so as to direct air into the two tubes 35 and 36.
One of the longitudinal sidewalls 12.1 of the combustion chamber has a large burner port 12.11 therein.
A fire brick liner 37 is provided for the port, and an .
auxiliary burner chamber 38 is mounted at an exterior location with respect to the housing 12, but within the shell 11 to surround the fire brick lined opening.
The auxiliary chamber 38 is lined with fire brick 37.1.
An oil burner 39 is mounted on a front panel 40 which lies flush with the outer panel 25 of the chambered front wall 26 and flush with the remainder of the outer shell 11. The oil burner 39 is connected into the auxiliary chamber 38 through a duct 39.1. A guard bar 37.2 traverses the opening in the housing sidewall to prevent aebris from being accidentally inserted into the auxiliary chamber 38.
The usual type of thermostats are provided or controlling the functions of the furnace 10. A thermostat may be provided within the outer shell 11, and in the vicinity of outlet 11.4 for assuring that when the ~:
temperature within the shell 11 drops to a irst level :
such as 180, the fan 34 will always be turned back on, .~ -:
30 and if the room thermostat is calling for heat, the oil `

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1 burner 39 will also be turned on; and such thermostat being also for the purpose of turniny both the fan 34 .
and oil burner 39 ofE when temperatures in the shell 11 reach another temperature level, such as 200; and an additional theremostat in the furnace will turn the furnace fan 18 to full speed whenever the temperature in the shell 11 rises to a third temperature level such~ ~
as 140; and as to reduce the speed of an 18 to half ~.
speed when the temperature in the shell reaches a fourth lQ temperature level such as 100. These are conventional and well known theremostatic controls and, except or the control of the fan 34, comprise no portion of the present invention.
In normal operation o the furnace 10, the furnace : may he operated almost entirely on wood fuel, or may be operated only minimally on wood fuel, according to the desires and plans of the person utilizing the furnace. :~
Green or seasoned logs L will be placed in the fire pit on the grates for ~urning and as to increase the heating . ~:
effect of the furnace. In practically all circumstances, when a wood fire is burning in the fire pit, the fan 34 will be turned on, and preheated air from chamber 26.1 is being blown through tubes 33, 35 and 36. In the combustion of logs L in the fire pit, a substantial quantity of comhustion gases including methane gas, moisture in the orm o vapor, and creosote in small particles or vapor form are driven of the logs by the heat of the fire and .-exist in the upper portion of the combustion chamber.
: The preheated secondary air ~hich.is directed out of the ; 30 tuhes 33, 35 and 36 produces a substantial cyclonic -~
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1 turbulence in the upper portion of the combustion chamber and over the logs L in the fire pit so that air and oxygen is adequate to promptly burn all of the volatiles and combustibles which are carried in the combustion gases. .
Air is supplied under the logs to prov.ide primary combustion air, but the swirling turbulence in the upper portion of the : :
combustion chamber produces the thorough burning of the various combustibles, both in gaseour form and in particlized form. When the combustibles are ultimately driven toward the outlet 19 and the heat exchanger 14, the combustion gases must pass through the rather elongate and narrow passage 32, and at this time the combustion gases are subjected to the array or curtain of incoming heated secondary combustion air so that an adequate supply of oxygen is provided for completing the final combustion of any gases that move upwardly toward the outlet 19.
This array of air streams or jets in a curtainlike :
arrangement is directed obliquely downwardly so that the entire ~uantity of combustion gases in the upper portion 13.2 of the combustion chamber revolves downwardly and then upwardly across the port 12.11. As a result of the ::
substantially complete combustion of all the combustibles from the log fueled :Eire, there will be no discernible `.
collection of creosote or other solid materials in the . ~.
ducts of the heat exchanger or in the flue or stack. `
It may be desirable when burning green waod or wood that is freshly cut and is likely to contain a ~:
substantial amount of creosote and moisture, to add supplementary heat from the oil burner 39. When the oil burner is turned on or energized, the burning fluid ~s9~
1 particles ar~ injected into the combustion chamber ~rom the auxiliary chamber 38 at a location approximately midway along the length of the combustion chamber and midway along the length of the logs lying in the fire pit.
This injection oE the burning fluid Eueled fire in-to the combustion chamber produces a double cyclonic action throughout the entire combustion chamber so that the heat of combustion from the fluid fueled fire is applied to :
substantially all portions of the length o~ the logs L
contained in the fire pit. As a result, the entire logs L
will be burning subs-tantially simultaneously. As the stream o fluid fueled fire is injected from the auxiliary chamber 38 and through the port 12.11 in the sidewall, the streams or jets..of air from the air or aspirator tube 33 cause the stream of fluid fueled fire from the oil burner ~:
to be tipped or inclined downwardly so that this stream of fire is directed downwardly into the Eire pit. This downward inclination by reason of the air jets or streams from the tube 33 contributes materially to the turbulence of the combustion gases in the ire pit and contributes materially to the complete combustion of all o the combustible gases in the chamber 13.
It will be recognized that when the combustion gases pass through the heat exchanger 14, the air in the furnace is circulated from the intake opening 11.3 downwardly through the cooler portion of the heat exchanger 14 and thence through fan 18 and chamber 11.2 to and through the .. ~-portion of heat exchanger which is closest to the inner .
housing 12, and therefore the hottest portion. From ~here the circulating air is discharged from the opening 11.4 1 for circulation back to the space -that is beiny hea-ted.
It will be seen that I have provided a new and improved wood and oil burning furnace providing for efEicient combustion of all of -the combustibles in the wood fueled fire.
Preheated secondary air is injected into the upper portion of the combustion chamber in an array of jets or air streams in a curtainlike arrangement across the outlet passage so that all of the combustion gases are subjected to sufficient oxygen to complete their combustion. Three separate air tubes in the combustion chamber produce a swirling and turbulence in a cyclonic action with all of the combustible gases so that such combustibles are entirely consumed in the furnace. An auxiliary oil burner supplies additional fluid fueled fire into the combustion chamber at a location midway along the longitudinal sides of the combustion chamber so that heat of combustion is directed, in a cyclonic turbulence, to all portions of the logs ~-~
lying in the fire pik and particularly to the opposite 20 ends wherein oppositely directed cyclonic turbulence is~ `
produced. It should be understood that the fluid ~ueled fire is produced in this illustrated form by an oil burner, but the auxiliary heat could as well be supplied by other fluid fuels such as natural gas, bottle gas, or the like.

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 . A furnace for burning both wood logs and fluid fuel, comprising:
enclosure means defining an elongate combustion chamber including a lower portion defining a fire pit to confine fuel logs during burning thereof, and also including an upper portion in which gas-carried combustibles may be burned, there being a combustion gases outlet adjacent the top of the chamber;
the enclosure means also having an elongate sidewall extending along the elongate combustion chamber, there being an entrance port through said sidewall and located midway between the ends of the combustion chamber and adjacent the upper portion of the combustion chamber;
a baffle plate extending the full length of the combustion chamber and generally horizontally outwardly from said wall and across a significant portion of the combustion chamber at a location well above the entrance port, said baffle plate having an edge cooperating with the enclosure means to define an elongate combustion gases discharge passage across from and above the entrance port;
a fluid fuel fired burner and a mounting therefor and directing a fluid fueled flame through said entrance port and in a direction transversely across the upper portion of said combustion chamber and intermediate the ends thereof;
an elongate and linear air supply and distributing tube in the upper portion of the combustion chamber and above said entrance port, said tube extending along and closely adjacent the edge of the baffle plate and extending longitudinally of the combustion chamber and substantially from front to back thereof, said tube having a plurality of air discharge ports along its length and oriented and directing air downwardly and away from said entrance port and transversely across said discharge passage to supply combustion air to all of the gases traversing the discharge passage and to cooperate with said fluid fueled flame from the burner in producing cyclonic turbulence at both ends of the combustion chamber and downwardly into the fire pit for inducing accelerated burning of the logs in the fire pit and complete combustion of the gas-carried combustibles in the upper portion of the combustion chamber; and means inducing flow of air in the supply tube.

2. The invention according to claim 1 and including means of preheating the air supplied to said supply tube and utilizing heat from combustion in the combustion chamber for preheating such air.

3. The invention according to claim 1 and also including two additional elongate air supply tubes respectively disposed at opposite sides of the combustion chamber and extending longitudinally thereof throughout substantially the entire length of the elongate combustion chamber and adjacent the upper edge of the fire pit, said additional tubes directing air transversely across the combustion chamber and contributing secondary air and turbulence within the combustion chamber.