FR2641056A1 - Improved postcombustion method with rapid triggering for solid fuels and means intended for implementing it - Google Patents

Abstract

Improved postcombustion method for solid fuels. Method characterised in that a flow of new air is injected into a postcombustion chamber 4 close to the hearth, in order rapidly to trigger and sustain the postcombustion, which air has been preheated by an exchange with the hearth or the smoke, then brought up to a temperature of at least 400 DEG C by at least one independent heating means outside the hearth. This invention is of interest to the constructors of heating appliances, boilers and incinerators, and more particularly of stoves and closed hearths for fireplaces.

Description

 The present invention relates to an improved rapid release afterburner for solid fuel heaters and for incinerators.

 It also relates to the means intended to implement it.

 More particularly, the invention relates to a process for rapidly triggering and maintaining the afterburning of volatile materials and unburnt gases from combustion in boilers, heating appliances and devices & solid fuels and in incinerators burning domestic waste. and industrial.

 The purpose of this deposit is to complete and describe the improvements made since the basic deposit made a year ago by the same depositor.

 The state of atmospheric pollution is critical in our cities, especially in winter, when heaters with solid fuels but also liquids operate almost permanently.

 The present invention aims to further improve afterburning and describes general and specific means of simple and economical construction to achieve this in the case of heating appliances and boilers using solid fuels as well as in the case of incinerators.

 This improved afterburning technique makes it possible to burn practically all volatile materials as well as the unburnt gases from combustion from the start of combustion in order to reduce the emission rate of these materials and gases to a very low value, while recovering the heat energy from their combustion.

 In particular, it enables post-combustion to be started as quickly as possible after the start of the fire in a solid fuel hearth and in an incinerator.

 In addition, the present invention overcomes all the drawbacks of the methods and devices known in this field.

 To this end, the invention relates to an improved afterburner process & rapid triggering, characterized in that a lton injects, at least at one level, into a postburner chamber near the outlet of the hearth, a flow of fresh air. preheated or not, enriched or not with oxygen, brought quickly to a temperature of at least 400 C, preferably 500 e Ct at the start of combustion and each time the fire is activated or reactivated.

 The heating apparatus, boiler or incinerator and the like intended to implement the above process is characterized in that it has an afterburner chamber located beyond the hearth, as close as possible to the smoke outlet and a circuit for the supply of fresh air, preheated or not, injected into the afterburner chamber as well as at least one heating means independent of the energy of the hearth, in the form of an electric heating element for rapidly carrying this air & a minimum value temperature equal to 4000c and means for detecting the rise in temperature of the hearth supplemented by a circuit for controlling the means for heating the fresh air.

The numerous specific advantages of the invention are as follows: no device through the evacuation pipe for
fumes maximum thermal efficiency particularly low pollution rate; reasonable added value removal of any demanding manipulation; decrease in corrosion; compact set. energy recovery with simple and reliable means
wheat; no deterioration: lifetime equal to that of
hearth rapid initiation of afterburning.

The invention will be clearly understood on reading the description which follows, given by way of nonlimiting example on an embodiment with reference to the accompanying drawings in which FIG. 1 is a schematic view in vertical section
a closed fireplace hearth with postcom chamber
bustion adjoining the hearth according to the invention; Figure 2 is a schematic view in vertical section
a closed fireplace hearth with postcom chamber
bustion and injection of a preheated air stream in
rich in active oxygen or ozone ;; Figure 3 is a vertical section of a closed hearth
fitted with an integrated afterburner chamber
ralement au foyer figure 4 is a vertical section of a closed hearth
equipped with an afterburner superior to the
focus Figures 5a and 5b are sectional views, respecti
vertical and horizontal, of a modu
area & concentric circuits constituting a module
afterburner with exchanger to be mounted on a hearth
closed chimney Figures 6, 7, 8 are the characteristic diagrams
fresh air ventilation circuits, in dot lines
tilled, and smoke, in thick lines, between the hearth,
the afterburner and the smoke outlet
In the chimney
- Figure 6 is a schematic sectional view of
fresh air supply circuit in a version known as
stepped afterburner, using channels
separated
- Figure 7 is a schematic sectional view of
fresh air supply circuit in a version called F
post-combustion using a double channel
- Figure 8 is a schematic view in hori section
zontale of an afterburner in the
flue outlet with representation of
adjoining fresh air supply circuit.

 For reasons of clarity and better general understanding, the two illustrative figures of the previous filing have been included here.

 The general inventive idea consists in injecting, at at least one level, into a post-combustion chamber located as close as possible to the outlet of the hearth, a stream of fresh air, that is to say of combustion air preheated by the heat given off by the hearth or the fumes and carried simultaneously and quickly, by at least one independent heating means external to the hearth, for example electric, disposed near the afterburner chamber, & at least 400ex, preferably 500 "C , heating means associated by an exchanger with the heat coming directly from the hearth, or by the fumes from the start of combustion until the self-maintenance of afterburning, to continue to inject this flow of fresh air at a lower temperature, at least equal to 2000C then to bring its temperature to at least 400 C, for example 500 C, at least at each activation or reactivation of the fire until the self-maintenance regime of the afterburner then to con keep injecting this fresh air stream at a lower temperature, for example by removing the independent heating means.

 According to a variant, air eprichi is injected in simple oxygen, active or activated or enriched with a gas or a gaseous, catalytic or oxidizing complex, promoting combustion.

 According to another variant, the afterburner chamber is adjacent to the hearth or integrated into the hearth.

 According to yet another variant of this process, the enrichment of the air is carried out using ozone produced by a generator at the injection opening in the afterburner chamber.

 Fluctuations in the temperature of the hearth are thus avoided by an independent heating means outside the hearth.

 The post-combustion process according to the invention will be described more particularly below, then in a second part the various means intended to implement it and some of their variants on an example of closed fireplace hearth and stove using as solid fuel wood.

 Of course, appliances using other solid fuels are also suitable. This is the case for coal, household and industrial waste and household waste in incinerators.

 More particularly, the method consists in initiating the post-combustion as quickly as possible after the start of the combustion of the solid fuel, by injecting, as close as possible to the after-combustion chamber located near the hearth, in particular near from the smoke outlet from the hearth, a new oxidizing air, that is to say containing a sufficient quantity of oxygen, enriched or not, activated or not, previously brought to a triggering temperature of at least 400-C , for example 500 "C.

 This air is brought to the trigger temperature of at least 400ex, for example 500 "C, totally or at least partially by means of heating independent of the hearth, for example by heating by electricity by means of low thermal inertia. , so as to initiate afterburning in the shortest possible time after the start of wood combustion.

 For reasons of energy saving, provision is made to preheat the air up to, for example, a temperature between 200 "C and 400" C by a circuit for supplying fresh air in direct contact or indirect with at least one wall of the hearth.

 This preheating is only useful and effective in the phase immediately after the initial phase, when the heat of combustion has been transmitted to the aeraulic preheating circuit and makes it possible to heat the fresh air.

 During the initial phase, independent electric heating plays the main role. It is therefore advisable to reinforce its action while reducing its inertia.

 To do this, the fresh air intake is partially closed off, since it comes from outside the home, during the heat rise of the electric heating element. This avoids bringing & this element of the outside air at a temperature too low compared to that to be reached.

 As the new air supply circuit is heated by the heating of the fireplace, the air inlet can be opened completely or gradually.

 We will now describe below several basic means and some variants intended to put.

implement the above process in various heating devices but also in industrial or household waste incinerators.

 The term "hearth" will be used below to designate the place of combustion. It must be understood as a combustion chamber, that is to say as a heating enclosure where the main combustion takes place, namely that of solid fuel, or as an incineration hearth in the case of an incinerator.

 To facilitate understanding of the improvement, the basic schematic embodiment will first be described, as shown in FIGS. 1 and 2.

 In a wood stove or a closed hearth with a metal hearth 1 of the box type constituting a combustion chamber 2 above an ash grate 3, provision is made, downstream of the hearth, outside the hearth or combustion chamber, in the direction of the fumes, an afterburner chamber 4, adjacent to the hearth, for example of the smoke outlet, chamber arranged near the hearth, for example adjoining the hearth, at the rear thereof, on a path 5 of the fumes, for example curved downwards.

 This afterburning chamber is separated from the hearth by a metal plate or wall 6.

 As will be seen below, many other locations of the room are possible. It should simply be placed as close as possible to the smoke outlet but outside the fireplace.

 The afterburner chamber 2 has an opening, for example a side opening, which serves as an inlet 7 through which an air duct 8 for supplying fresh air or secondary air from the room or from the outside opens. This channel is occupied over a whole cross section by an electric heating block 9 crossed by the flow of fresh air, preheated or not, advantageously produced in the form of a heating cartridge fitted with electric heating resistors.

 As will be seen below, a variant with several channels is provided, either independent or as a double channel, one of the channels of which is occupied by an electrical block allowing electric heating of lower power.

 The combustion chamber also has a smoke inlet and outlet.

 Advantageously, the air is taken from the room and preheated in contact with the walls of the hearth or in contact with the fumes, by means of an exchanger, after they leave the hearth to the afterburner chamber, then heated by a electric heating means at the desired temperature.

 Thus, in terms of means, according to an interesting variant, the circuit for preheating the fresh air is adjacent to the smoke evacuation circuit from its outlet from the hearth to the afterburner chamber.

 Of course, the electric heating element is located downstream in the vicinity of the entrance to the afterburner chamber.

 This is the triggering temperature, that is to say the temperature triggering the post-combustion in the initial phase and then the self-maintenance temperature.

 The air flow is natural or forced by a fan or a turbine 10 from a completely or partially closable air inlet.

 The electrical energy control and regulation assembly of the means for heating the injected air flow consists, for example, in the basic version, of two temperature sensors 11 and 12 mounted respectively in the combustion chamber 2 and in the afterburner chamber 4. These sensors are connected to an electronic control circuit 13 acting on the supply of electrical energy to the means for heating the secondary air and, optionally on its flow, by means of the fan or the turbine 10.

 The sensor 11 of the combustion chamber 2 detects the rise in temperature to control the means for heating the secondary air. The second sensor 12, mounted in the post-combustion chamber is a safety sensor which transmits to the control circuit the signal for the start and end of auto-combustion, making it possible to check at all times the proper functioning and to control the shutdown or the decrease in electric heating energy. Another safety sensor 14 may exist on the air injection circuit which provides information on the operation of the heating cartridge.

 This is achieved by using surface circuits or resistive deposits. Simple wirewound electrical resistors are also suitable.

 According to a particular embodiment, in addition to the heating cartridge or in isolation, an ozone generator 15 is provided at the outlet of the duct or air duct 8 for supplying preheated fresh air, as shown in FIG. 2.

 The air inlet of the fresh air supply circuit can be partially or totally blocked by a shutter 16 or other device controlled from the sensors 12 and 14.

 The method implemented by the means described above is distinguished by the following characteristics.

 Is injected laterally into the afterburner chamber 4 located beyond the hearth a flow of fresh air brought quickly, during the start of combustion phase, at a temperature of at least 400ex until triggering of the autocombustion in the afterburner. This secondary air flow is heated by electrical heating means, for example by a heating cartridge disposed in the aeraulic channel 8 for injecting secondary air taken from outside, cartridge equipped with a series of electrical resistances according to the power required. It is, for example, traversed entirely by the flow of fresh air.

 This secondary air is preferably preheated beforehand along the walls of the hearth or by the heat of the fumes.

 It contains a minimum percentage of oxygen of 6% but preferably between 12% and 16%.

 The rise in temperature of the hearth 2 is detected by the sensor 11 to automatically control the electrical means for heating the flow of injected fresh air.

 Self-combustion is detected to bring the temperature of the air flow to a minimum value between 200-C and 400-C.

 Each time the combustion chamber rises in temperature, a new heating phase of the air flow is heated to a temperature of at least 400 "C, for example 500 C, until auto-combustion is that is to say the self-maintenance of the afterburner, corresponding to each reactivation of the fire detected by the temperature sensor 12 in the afterburner chamber 4.

 We will now examine, with reference to FIGS. 3 to 8, particular embodiments implementing the method according to the invention.

 According to the variant shown in Figure 3, the afterburner 4 of the closed hearth 1 is integrated into the hearth at its rear part. It has an inlet 17 for the smoke outlet passage.

 It is shaped as a baffle by a partition 18 and constitutes the smoke outlet path in permanent operation of the hearth.

 Conventionally, a direct smoke evacuation valve allows emergency or safety evacuation for example.

 The secondary air supply circuit is formed, for example, of a duct 19 connected at its outer end to a fan 20 and opening at its other end at the inlet 17 of the afterburner chamber 4.

 The conduit contains the electric heating block 9 shown in the form of an electric coil.

 The duct comes from outside the hearth under the afterburner chamber and goes up along the rear wall of the hearth.

 To ensure preheating, at least one surface of the duct is in contact with the wall of the hearth.

 According to the variant shown in Figure 3, the afterburner 4 of the closed hearth 1 is integrated in the upper part of the hearth.

 This chamber communicates with an upper exchanger 21 towards an evacuation duct 22.

 The secondary air supply circuit is a channel 23 which passes behind the rear wall of the hearth, this constituting, for example, one of its lateral faces.

 The secondary air enters the channel, * its base, by natural aspiration in the channel occupied over a part of its length by the heating block 9 and opens at 24 in the upper part into the afterburner chamber 4.

 Likewise, the hearth opens out at the top in the afterburner chamber 4.

 A modular variant will now be described with reference to FIGS. 5a and 5b in which the secondary air is heated in an exchanger in contact with the fumes.

 The assembly forms a modular bloo 26 to be mounted above a heating appliance, in particular a closed fireplace hearth.

 This module constitutes a simple upper part above the closed hearth on which it is mounted. It is sufficient to solder it or to fix it mechanically and to connect it aeraulically to the smoke evacuation pipe leaving the appliance.

 In addition to its general module configuration, it has the particularity of constituting a concentric exchanger between the fumes and the secondary air.

 More specifically. the post-combustion module shown consists of an external circuit 27 surrounding an internal circuit 28 as shown in FIGS. 5a and 5b.

 The two circuits are arranged side by side. The external circuit 26 brings the secondary air to the afterburner chamber. It includes the heating block 9. LB internal circuit 28 is that of smoke evacuation from the fireplace. The latter begins at an outlet 29 of a collecting box 30. The outlet opens into the afterburner chamber 4 having another inlet 31 near the heating block 9 constituting the end of the external circuit 27.

 The internal smoke circuit expands upwards to reach an outlet chamber 32 communicating with an exhaust duct 33.

 A valve 34 for direct smoke evacuation is also provided between the grouping box and the outlet chamber 32.

 This variant uses the heat contained in the fumes to preheat the secondary air.

 It constitutes one - of the most efficient and best adapted exchangers.

 We will now describe two variants using staged afterburning, that is to say the splitting of the supply circuit of secondary air or fresh air into two separate circuits, one called heating 35 comprising the heating block 9 and the other says preheating 36.

 These are the variants shown in FIGS. 6 and 7.

 The variant shown in Figure 6 has two separate channels offset in height so as to achieve the injection of secondary air & different levels.

 There is thus formed in the afterburner a first lower injection zone 37 for secondary air at high temperature and a second injection zone 38 greater than the first at lower temperature.

 In the first zone opens a heating duct 39 provided with the heating block 9 bringing the fresh air at high temperature, for example 500 C.

In the second injection zone 38 opens another conduit, distinct from the first, for example along the wall of the hearth in order to preheat the air.

 The variant shown in FIG. 7 is of the double channel type 40 running along the hearth. The double channel 40 is divided into two parallel channels 41 and 42 arranged side by side, respectively a heating channel and a preheating channel.

 The heating channel 41 is equipped at its outlet from the heating block 9. It opens into the afterburner chamber 4 at a lower level. The temperature of the fresh air ejected is established at that determined for the initiation of afterburning, for example 500 C.

 The preheating channel 42 is free. It opens into the afterburner on a higher level. The temperature of the fresh air ejects is lower than the threshold for triggering the afterburning located between 200 "C and 400 C.

 A last variant shown in Figure 8 is said to evacuation.

 This variant applies to a fireplace with a smoke duct 43 having a birth 44 opening out from a smoke box 45.

 According to the particular characteristic of this variant, the afterburning chamber 4 is formed by or integrated at the start 44 of the flue pipe 43. An air duct 46 opens laterally into the flue pipe 43 at the base thereof. This duct transports fresh air, for example blown through a fan 47.

 The heating channel 46 can be single or doubled with a preheating channel as in certain variants described above.

 Of course, this embodiment requires a birth 44 of smoke flue of suitable constitution. In fact, the heat released by the afterburner is large enough to have to be removed more quickly than by simple radiation.

 Thus, the metal constituting the opening of the flue pipe will be resistant to high temperatures and the opening 44 will preferably be used as the central element of a heat exchanger or it will be thermally insulated by a thick coating 48.

 Various other possibilities exist such as for example a fin tip on which is blown air.

Claims (22)

 1. Post-combustion process with rapid triggering of volatile materials and unburned gases resulting from the combustion of solid fuels in heating appliances, boilers, incinerators and the like, by injecting fresh air previously heated, characterized in that one injects , at at least one level, by at least one air duct in a post-combustion chamber (4) located as close as possible to the outlet of the hearth (2), a flow of preheated oxidizing fresh air, which is carried rapidly this flow of fresh air preheated by at least one electrical heating means provided in at least one air channel disposed near the afterburner, means associated by an exchanger with preheating by the heat energy coming from the hearth to a temperature of at least 400 "C, for example 500 ° C, in the initial phase of combustion in the hearth until the initiation and self-maintenance of the afterburner in the post chamber combustion (4) and in that it detects that the self-maintenance of the afterburner is maintained, that the temperature of the fresh air injected is then reduced to a minimum value and that again brings the temperature of the fresh air flow injected to a temperature of at least 4000C on each reactivation of the fire detected by the rise in temperature of the combustion chamber (2) or hearth, transmitted by a sensor and that the the temperature is again reduced.  2. Method according to claim 1, characterized in that the flow of fresh air is preheated by the heat of the hearth (2) or fumes.  3. Method according to the preceding claims, characterized in that the minimum value of the temperature of the fresh air is reached by eliminating the heating by the independent heating means.  4. Method according to the preceding claims, characterized in that the fresh air is injected at two different levels into the afterburner chamber, including the lower level, for the fresh air circuit from the heating circuit containing the means of independent heating.  5. Method according to the preceding claims, characterized in that the electrical heating means is produced in the form of a heating block (9) according to a cartridge provided with electrical resistors occupying the entire cross section of the channel or an air channel injection (8).  6. Method according to the preceding claims, characterized in that the injected fresh air flow is enriched with active oxygen.  7. Method according to claims 1 to 6, characterized in that the fresh air flow is enriched by a gas or a gaseous catalytic or oxidizing complex promoting combustion.  8. Method according to the preceding claims, characterized in that the flow of fresh air is forced by a fan or a turbine with interposition on the inlet of the fresh air of a movable shutter element (16) completely closing or partially, during the initial phase preceding afterburning, the entry of the air duct into the fresh air.  9. Heating apparatus, boiler, incinerator and the like, intended to implement the improved post-combustion process with rapid triggering, as claimed above, characterized in that it has an after-combustion chamber (4) located beyond the hearth (2), as close as possible to the smoke outlet and a new air intake circuit injected into the afterburner (4) as well as at least one external, electric and independent heating means energy of the hearth in the form of a heating element associated with an exchanger with the hearth or the fumes, to bring this air quickly to a temperature of minimum value equal to 400in and means for detecting the rise in temperature of the hearth (2 ) as well as a control circuit (13) of the means for heating the fresh air.  10. Apparatus according to claim 9, characterized in that the fresh air intake circuit comprises a means of preheating from the heat of the hearth.  11. Apparatus according to claim 9, charac curly in that the fresh air is preheated in an exchanger from the heat contained in the fumes before their arrival in the afterburner.  12. Apparatus according to claim 11, charac frieze in that the intake circuit and preheating of the fresh air is adjacent to the smoke evacuation circuit leaving the home to the post-combustion chamber, the heating element being located downstream.  13. Apparatus according to claim 9, charac terse in that the afterburner chamber (4) is adjacent to the hearth (2) separated therefrom by a metal wall (6) and divided by a baffle.  14. Apparatus according to claims 9 and 13, characterized in that the afterburner chamber (4) is disposed in the upper part of the hearth (2) as close as possible to the outlet of the hearth.  15. Apparatus according to claims 9 to 12, characterized in that the afterburner chamber is the outlet of the hearth.  16. Apparatus according to claims 9 & 13 characterized in that the afterburner chamber is integrated into the hearth.  17. Apparatus according to claim 9, charac curly in that the electric heating means is a cartridge (9) provided with electric heating resistors, cartridge placed in the inlet air duct and heating of the fresh air in the vicinity of the entry of said channel into the afterburner.  18. Apparatus according to claims 9 to 15, characterized in that the fresh air supply circuit is divided into a heating circuit containing the cartridge (9) of electric heating and a preheating circuit.  19. Apparatus according to claim 18, charac terse in that the inputs of the circuits in the afterburner are made at different levels and in that the input of the heating circuit is located at the lower level.  20. Apparatus according to claims 18 and 19, characterized in that the heating and preheating circuits are contained in the same channel of a heat exchanger with the heat of the hearth or fumes.  21. Apparatus according to claim 9, charac terized in that the exchanger is formed by an external circuit (27) for the fresh air and an internal circuit (28) for the fumes, the two circuits being juxtaposed and concentric .  22. Apparatus according to claims 9 and 21, characterized in that the exchanger, the afterburner (4) and the arrival and departure of the fumes before and after the afterburner constitute a modular unitary assembly to be mounted on a closed fireplace.