FR2722271A1 - METHOD AND DEVICE FOR IMPROVING COMBUSTION FOR A POT BURNER AND CORRESPONDING HEATING APPARATUS - Google Patents

Abstract

The invention provides a simple and effective technique for improving combustion for a burner (8) with vaporization of liquid fuel of the pot type. The gas retaining device (9) made in one piece of ceramic material of low inertia thermal, has a plurality of cells (10) and orifices (11) distributed between the cells. The retaining device is placed above the burner so as to create in the alveoli a post-combustion of the gases coming from the burner, to increase the thermal efficiency, to decrease the CO emissions and to stabilize the flames in the burner.

Description

I Method and device for improving combustion for a

  pot burner and corresponding heater.

  The present invention relates to a combustion improvement method for a burner with a liquid fuel vaporization of the pot type, a gas retaining device allowing the implementation of the method, as well as an individual heating device equipped with a such device. There are many types of individual space heaters that consume either electricity or fuels such as wood, coal, fuel oil or gas. The invention relates more particularly to the technique of heating with liquid fuel, such as fuel oil or

fuel oil.

  Heating devices or heat convectors using liquid fuel are intended to meet the heat requirements of a room or, exceptionally, two or three rooms; their power does not exceed 10 KW, they are therefore equipped with vaporization burners whose pace can be adjusted by the user. These burners operate by vaporization of the fuel under the effect of the heat maintained by combustion in the burner. The oil vapors are mixed with the combustion air in the burner enclosure thanks to convection

  resulting from the thermal draft of the chimney.

  There are at present two types of burners with vaporization of liquid fuel: pot burners with a single casing and pot burners with a double casing. French patent 2289846 discloses an example of a burner with a double jacket pot. The burner is fitted with a catalytic converter which reduces unnecessary consumption of liquid fuel and

  increase the heat output of the burner.

  Heaters with a liquid fuel vaporizer burner have lower thermal efficiencies than the liquid fuel atomiser. These devices are connected to a chimney for the evacuation of combustion gases by natural draft. Their operation is therefore very sensitive to variations in the chimney draft linked to the effects of outdoor weather conditions. Combustion in the vaporization burner is generally not complete and carbon monoxide (CO) emissions may be significant in the fumes discharged from the chimney. There is also a risk of fouling by the formation of soot in the smoke evacuation ducts. In addition, during a strong draft from the chimney, by gusts of wind, the flame in the burner pot is not stable and risks being detached from the pot, thus causing the flame to go out, such a situation can be dangerous, because the burner pot continues to give off vapor from the liquid fuel and if the burner is subsequently ignited, the high rate of fuel vapor may cause an explosion in the enclosure of the heating appliance . The object of the present invention is to remedy the drawbacks of burners with vaporization of liquid fuel of the pot type, by

  offering a simple, effective and economical technique.

  The object of the invention is also to improve the combustion of the vapor of the liquid fuel in the burner, in order to increase the thermal efficiency of the heating appliance and to reduce the

  carbon monoxide (CO) emissions in the exhaust fumes.

  The object of the invention is also to increase the safety of use of burners with vaporization of liquid fuel of the pot type by minimizing the risks of the flame stalling in the

  burner in the event of a strong draft from the exhaust chimney.

  Another object of the invention is to achieve energy savings by minimizing the consumption of liquid fuel for a given heating power and reducing the temperature

smoke evacuated.

  The object of the invention is also to produce more compact heating devices in height, comprising a burner with

  vaporization of pot type liquid fuel.

  Yet another object of the invention is to create an imitation appearance of wood or charcoal modifying the classic appearance of the

  pot type liquid fuel vaporization medium.

  The invention firstly proposes a method of improving combustion for a burner with vaporization of liquid fuel of the pot type. The process essentially consists in controlling the excess air from the burner, to define using a piece of refractory material of low thermal inertia immediately above the pot, a space where the excess air ensures a post -combustion making it possible to complete the combustion of at least 50% of the gases coming from the pot, and to evacuate through the orifices of the part a part of the gases directly coming from the pot and the

post-combustion gas.

  The post-combustion space is preferably in the form of a plurality of cells in communication with each other to allow the circulation of the combustion gases. The orifices of the part are preferably distributed between the cells and located at a level lower than the lowest apex of the cells immediately adjacent, so that the post-combustion gases contained in the cells make a detour downward before d '' be evacuated through the orifices of the room. Thus, the residence time of the gases in the post-combustion space is sufficient to allow combustion

  full of gases from the burner pot.

  The invention secondly proposes a gas retaining device intended to improve combustion for a burner with vaporization of liquid fuel of the pot type. The retaining device is constituted by a single piece comprising a plurality of cells and orifices distributed between the cells, so that during use, the part completely covers the top of the burner pot with the cells open towards the low and communicating with each other and with the orifices located below the lowest apex of the alveoli

immediately neighboring.

  Advantageously, the retention device made of ceramic material has a small thickness and a low thermal inertia so as to allow the temperature of the part to rise rapidly when the burner is ignited in order to create conditions of temperature sufficient to ensure the post-combustion of gases from the burner pot. The choice of material to make the retaining device is also important in order to impart an aesthetic appearance of imitation wood or charcoal. For this purpose, the retaining device provides a sensation of heat visually, for example in

  turning red if its temperature exceeds 700.

  The structure of the retaining device, in particular the shapes and dimensions of the cells and the orifices relative to the burner pot, are very important. Take, for example, the depth of the alveoli of the retentor, if it is too great, there is a risk of there being a rapid deterioration of the combustion by saturation of the fumes in the alveoli which cannot be evacuated quickly. On the other hand, if the depth is too shallow, the residence time of the gases

  in the alveoli is too short to ensure good post-

  combustion. According to the invention, a ratio is chosen between the total area of the orifices of the retaining device and the section of the burner pot of between 10 and 25%, for example around 15%. The section of the individual ports can vary between 1.5 and 15% of the total section of the ports. One can for example choose about twenty orifices which are distributed between the cells, which corresponds to an average section of individual orifices of approximately 5% of the total section of the orifices. The depth of the individual cells can vary between 5 and 20% of the diameter of the burner pot, the average ratio being

locate around 10%.

  The invention thirdly proposes an individual heating device or heat convector comprising a burner with vaporization of liquid fuel of the pot type equipped with a gas retaining device which, on the one hand, improves the combustion for the burner and , on the other hand, provides an aesthetic appearance of imitation of

charcoal or wood.

  The invention will be better understood on studying the description

  detailed of some embodiments taken without any limitation being and illustrated by the appended drawings, in which: FIG. 1 is a perspective view of an individual heating appliance equipped with a burner with vaporization of liquid fuel of the pot type ; Figure 2 is a schematic horizontal sectional view of the apparatus of Figure 1 with a retaining device; Figure 3 is a schematic sectional view along a vertical plane parallel to the front face of the apparatus of Figure 1 with a retaining device; Figure 4 is a schematic view in axial section of the pot burner, according to a first embodiment of the invention; Figures 5 and 6 are partial views in axial section of the retaining device according to a second and a third modes of

realization of the invention.

  As illustrated in FIGS. 1 to 3, the individual heating appliance comprises an outer envelope of substantially parallelepiped shape with a front face 1 provided with a glass door 2 actuable by a handle 2a, two lateral faces 3, a rear face 4 , a top face 5 and a base 6. The outer casing is separated into two compartments by a horizontal partition 7. A cylindrical section burner 8 is disposed in the lower compartment in a manner known per se, with its upper opening facing

  to a circular opening 7a of the horizontal partition 7.

  A gas retaining device 9 is placed above the horizontal partition 7 completely covering the circular opening 7a. The retention device 9 is made of ceramic material in a single

  part provided with cells 10 and orifices 11 distributed between the cells.

  The cells 10 are open downwards so as to receive the combustion gases coming from the burner 8. The orifices 11 allow the gases from the burner 8 and the cells 10 to escape towards the outlet duct 12 fixed on the rear face 4 of the outer envelope and connected to a chimney not shown. The discharge conduit 12 is in communication with the upper compartment of the device. An air intake duct 13 also located on the rear face 4 of

  the device, communicates with the bottom compartment of the device.

  The pressure difference between the outlet end of the chimney, not shown, and the interior of the appliance, creates a draft effect forcing the circulation of air from the air intake duct 13 towards the duct. exhaust air 12 after passing through the lower compartment, the burner 8, the orifices 11 of the retention device 9 and the

upper compartment.

  The burner 8 is supplied with a liquid fuel such as fuel oil, via a supply line 14 connected to a liquid fuel supply system, not shown. The liquid fuel at the bottom of the burner 8 evaporates by the heat of the flames in the burner 8 and entrained in forced convection by the supply air passing through the burner. Liquid fuel vapor mixed with excess air introduced through the air intake duct

  13, burns in the burner 8 to provide heat.

  The glass door 2 on the front face 1 of the appliance, allows the user to observe through the glass of the door the upper compartment of the appliance with the retention device 9 masking the burner 8. The retention device 9 in the form of a single thin piece of ceramic material, is preferably chosen with low thermal inertia and reddening as soon as the temperature exceeds 700 C. Thus, by lightly painting the upper face of the retention device 9, it is possible to obtain an imitation wood look or

  burning coal, to increase the aesthetics of the device.

  FIG. 4 shows a burner 8 with vaporization of liquid fuel of the pot and double wall type equipped with a retaining device 9. The burner of the pot type is already the subject of French patent 2289846. The burner 8 comprises a pot exterior 15 substantially cylindrical and open at the top. The cylindrical wall of the pot 15 is provided with a plurality of small openings 1Sa allowing the air introduced into the lower compartment to penetrate inside the pot 15. An inner tubular wall 16 concentric with the outer cylindrical wall of the pot 15 has circular openings

  16a facing radially to the small openings lSa of the outer wall.

  The inner wall 16 is welded on its upper edge to a separation ring 17 secured to the upper part of the cylindrical wall of the pot 15. A skirt 18 of conical interior shape flared upwards is pierced with holes 18a and delimits an annular chute air intake 19. The holes 18a distributed circumferentially make it possible to blow the air towards the center of the opening of the burner 8,

so as to center the flame.

  The pot 15 of the burner 8 has a bottom 20 slightly curved towards the outside. The liquid fuel supply pipe 14 supplies the bottom 20 of the pot 15. A catalyst assembly 21 comprises a catalytic drum 22 with a perforated double metal wall, a metal cover 23 for the drum 22 slightly curved upwards, and a crown 24 formed of a horizontal metal ring 25 on which are welded a number of radially oriented arches 26. The catalyst assembly 21 is placed on the bottom 20 of the burner pot inside the wall 16. An inner fixing ring 27 is welded to the inner wall 16 of the burner 8 in order to support the horizontal ring 25 of crown 24 of the set

catalyst 21.

  To start the burner 8, an ignited metaldehyde pellet can be thrown at the bottom 20 of the pot 15 which ignites the liquid fuel at the bottom 20 of the burner 8. As the liquid fuel introduced through the pipe inlet 14 flows on the bottom 20 of the burner 8, the heating of the liquid fuel causes its vaporization largely at the level of the double metal wall of the catalytic drum 22. The vapor of liquid fuel ignites with the air entering the burner 8 through the openings 15a and 16a. Depending on the flow of liquid fuel introduced to the bottom 20 of the pot 15, the combustion flame hangs at a height more or less distant from the bottom of the pot 15 on the whole

catalyst 21.

  In the absence of the retention device 9 of the invention, the combustion gases from the burner 8 are directly sucked into the duct

  12 of the appliance thanks to the natural draft of the chimney.

  Thus, the combustion gases do not have enough time to release their heat inside the appliance before being evacuated. This results in a low thermal efficiency of the device and a significant risk of fouling. In addition, the combustion of the liquid fuel inside the burner 8 may not be complete, which results in significant emissions of carbon monoxide (CO) which is a toxic product. Finally, in the event of a strong draft from the chimney, the flame risks being detached from the burner 8, thus causing the burner to go out, while the evaporation of the liquid fuel continues inside the pot 15. Thus, the concentration of liquid fuel vapor in the air may be too high, which could lead to general combustion in the upper compartment of the appliance, or even an explosion, during an ignition attempt

subsequent by the user.

  The extremely simple and surprising solution to all of these problems, according to the present invention, consists in placing above the burner 8, the gas retaining device 9 making it possible to retain for a limited time a large part of the combustion gases from of the burner 8, thus ensuring more complete combustion of the gases and improving the heat exchanges between the combustion gases and the appliance. The retaining device 9 in one piece of a ceramic material of low thermal inertia allows a very rapid rise in temperature. The part is preferably made with a fairly small thickness, for example between 2 and 4 mm, which allows a uniform rise in temperature over the entire surface of the part. The part 9 which is simply placed on the horizontal partition 7 completely covers the circular opening 7a. The plurality of cells 10 which are distributed over the part 9, are open downwards and have a depth varying between 5 and 20% of the diameter of the burner 8 or more exactly of the circular opening 7a delimiting the outlet of the burner 8. The orifices 11 distributed between the cells 10 are delimited by the walls of the cells and located at a level substantially

  horizontal below the tops of neighboring cells.

  In operation, when the burner 8 is lit, the flame concentrated on the catalyst assembly 21 very quickly brings the part 9 to a high temperature, so that the internal walls of the cells 10 do not cool the combustion gases from the burner 8. The air entering the burner 8 generally has a 50 to 100% excess relative to the quantity necessary for combustion in the burner. The excess air mixes with the incomplete combustion gases from the burner 8 in the cells 10 of the retention device 9. The temperature in the cells 10 is sufficient

  high to cause additional or post-combustion

  combustion of these incompletely burned gases in the burner. The post office-

  combustion oxidizes toxic carbon monoxide (CO) gas to provide non-toxic carbon dioxide (CO2). Likewise, post-combustion makes it possible to produce more heat which is partly reflected by the internal walls of the cells 10 towards the burner 8, partly absorbed by the retaining device 9 to increase its temperature and partly transmitted by the retaining device 9 to the upper compartment of the appliance. The more complete combustion of the gases implies that the fumes given off and discharged to the chimney have a lower temperature by

  compared to gases which are not completely burnt and directly discharged.

  The following table shows the results of the comparative tests for different flow rates (in liters per hour) of fuel oil between the conventional burner without retaining device and the same burner provided with the retaining device of the invention. There is a significant increase in the temperature of the radiating walls (front face 1 or glass, side faces 3 and rear face 4), a decrease in the temperature of the fumes

  at the outlet of the exhaust duct 12.

Board

  Glass T flow - ambient T (C) T smoke (C) combustible (1 / h) without with A T without with A T retentive retentive retentive retentive

0.34 214 229 + 15 C 178 166 -12 C

  0.37 228.5 258.5 + 30 C 198 176 -22 C

0.45 259 291 + 32 C 228 186 -42 C

0.52 283 328 +45 C 248 194 -58 C

  The retaining device used to carry out the tests has twenty orifices distributed between cells with a depth of between 5 and 20% (and on average 11%) of the diameter of the opening 7a of the horizontal partition 7 separating the upper and lower compartments of the device. The total section of the orifices by

  ratio to the section of the opening 7a of the partition 7 is equal to 15%.

  It is also observed for a flow rate of 0.16 1 / h of liquid fuel that the flame remains attached to the burner with a draft of up to 0.3 mbar (3 mm of water column) with the retaining device, then that the flame is released with a draft of 0.15 mbar (1.5 mmn of water column) without the retaining device. With the retaining device, the thermal efficiency of the device is increased by about 5 points compared to the device without the retaining device. In addition, the presence of the retaining device above the burner makes it possible to make the flame more collected and consequently to reduce the height of the upper compartment of the appliance. So we can make

  the more compact device, saving material.

  In the embodiment illustrated in FIG. 4, the burner 8 comprises a catalyst assembly 21 to improve the combustion in the burner. This set is not essential in the context of

the present invention.

  FIG. 5 shows an embodiment of the retaining device 9 which comprises a peripheral skirt 9a extending downwards by raising the assembly formed by the cells 10 and the orifices 11. On the peripheral skirt 9a, one or several openings 9b making it possible to evacuate part of the burnt gases. The exhaust openings 9b complementary to the orifices 11 of the retention device 9 are sometimes necessary, in particular when the flow of liquid fuel is high for a high thermal power.

  of the individual heater.

  FIG. 6 shows another alternative embodiment of the invention, for which the retention device 9 is identical to that shown in FIG. 4. Around the circular opening 7a, the horizontal partition 7 has on its upper face several studs 7b on which the retaining device 9 is placed. The retaining device 9 is then raised relative to the horizontal partition 7 by the studs 7b, thus leaving interstices 27. The interstices 27 allow the discharge of part of the burnt gases so similar to

  openings 9b in the peripheral skirt 9a in FIG. 5.

he

Claims (12)

  1. A method of improving combustion for a burner (8) with vaporization of liquid fuel of the pot type, characterized in that it consists in: - controlling the excess air in the pot (15) of the burner, - delimit, using a piece (9) of refractory material of low thermal inertia, immediately above the pot, a space (10) where the excess air provides post-combustion for perfect combustion at least 50% of the gases from the burner pot, and - evacuate through orifices (11) from the part a part of the gases   directly from the burner pot and the post-combustion gases.   2. Method according to claim 1, characterized in that it consists in creating the post-combustion space in the form of a plurality of cells (10) in communication with one another, the orifices (11) of the piece (9) being distributed between the cells and located at a level below the lowest peak of the immediately adjacent cells. 3. gas retaining device (9) intended to improve combustion for a burner (8) with vaporization of liquid fuel of the pot type, characterized in that it is constituted by a single part comprising a plurality of cells (10 ) and orifices (11) distributed between the cells, so that during use, the part completely covers the top of the burner pot (15) with the cells open at the bottom and communicating with each other, and with the orifices located below the lowest apex of the immediately adjacent cells, the part being made of material   ceramic with low thermal inertia.   4. Retention device according to claim 3, characterized in that   that the orifices (11) open out substantially at the same level.   5. Retentive device according to claim 3 or 4, characterized in that the part has a uniform thickness between 2 and 4mm.   6. Retention device according to one of claims 3 to 5,   characterized in that the piece blushes from 700 and the outside surface of the piece is painted to give an appearance imitation wood or charcoal.   7. Retention device according to one of claims 3 to 6,   characterized in that the total section of the orifices (11) represents 10 to   % of the burner outlet section (7a).   8. Retention device according to one of claims 3 to 7,   characterized in that the section of the individual orifices (11) varies   between 1.5 and 15% of the total section of the orifices.   9. retention device according to one of claims 3 to 8,   characterized in that the depth of the individual cells (10)   varies between 5 and 20% of the diameter of the burner outlet (7a).   10. Retention device according to one of claims 3 to 9,   characterized in that the part (9) comprises a peripheral skirt (9a)   extending downwards and provided with at least one opening (9b).   11. Individual heating appliance comprising an external envelope, a horizontal partition (7) defining an upper compartment and a lower compartment, a burner (8) with vaporization of liquid fuel of the pot type arranged in the lower compartment and open upwards through a circular opening (7a) of the horizontal partition, characterized in that it comprises a   gas retaining device according to one of claims 3 to 10, the   retaining device being disposed on the horizontal partition covering   fully the circular opening (7a).   12. Heating device according to claim 11, characterized in that the horizontal partition (7) comprises several studs (7b) distributed around the circular opening (7a), so as to raise the retention device (9) leaving interstices (27) between the lower edge of the   retaining device and the upper surface of the horizontal partition.