EP0315250A2 - Device for combustion of non-burnt substances - Google Patents

Abstract

Device for combustion of non-burnt substances in smoke released by the combustion of a fuel such as, for example, but not exclusively, wood, the abovementioned combustion device being formed, inter alia, by a pipe comprising at one of its ends an entrance opening for the smoke. Said pipe (1) comprises, moreover, at least one catalyser (3) downstream of the entrance opening for the smoke (2) and an admission tube for oxidant (4) external to the pipe (1) so that the oxidant projected from the admission tube (4) forms a mixture with the smoke, this mixture passing all the way through the catalyser (3) and being directed towards the other end of the pipe (1), and at least one supplementary oxidant admission tube (7) is provided. <IMAGE>

Description

The present invention relates to a device for combustion of unburnt substances contained in fumes given off by the combustion of a fuel such as, for example but not exclusively, wood, said aforementioned combustion device being formed, inter alia, by a duct comprising a smoke inlet orifice.

In this regard, it is known that the fumes given off by the combustion of wood contain creosote, that is to say wood tar in the gaseous stage.

It is also known that this creosote forms a non-negligible part of the total capacity for releasing calories, in other words, combustibility, in particular of wood.

It is no less known that, mixed in smoke with water vapor and other gaseous compounds, creosote leaves, generally, intact from the heating body to follow its path in the chimney and deposit there in the form of tar vegetable or to, by escaping from the chimney, cause pollution of the environment.

To remedy the harmful effects of creosote, it is known to use a process known per se, in particular catalysis, this process making it possible to burn, to a certain extent, this creosote and thus to reduce its effects, by the stimulating action. that the catalyst exerts on the combustion of the smoke with which it is in contact. The disadvantage of this process is that it achieves a satisfactory yield only in a temperature range, characteristic of the catalyst, namely at relatively low temperature, corresponding to a combustion fire, in this case wood, soft. Furthermore, even in good conditions of temperatures where the yield is good, the combustion of creosote obtained by catalysis is not total, which, at the same time, has the consequence that there has been no total removal of the calories contained in the fumes, that these have emerged.

The object of the invention is precisely to remedy the aforementioned drawback of the catalysis process and to provide an entirely satisfactory solution to the problems caused by the incomplete combustion of creosotes by causing the combustion of smoke by the oxidant contained in the burnt gases.

To achieve this objective in accordance with the invention, the phenomena of catalysis and afterburning have been combined in a surprising manner, as will be described below. To this end, the combustion device according to the invention is produced in the form of a duct comprising, in addition to the smoke inlet orifice at one of its ends, at least one catalyst downstream from the orifice inlet of the fumes and an oxidizer inlet tube external to the main duct that the oxidant sprayed from the inlet tube forms a mixture with the fumes, this mixture passing through the catalyst, from side to side, and heading towards the other end of the conduit and in that at least one additional oxidizer inlet tube is provided.

According to an alternative embodiment of the invention, the oxidizer is formed by air, in particular by oxygen.

According to a remarkable characteristic of the invention, the above-mentioned conduit comprises, downstream of the catalyst, at least one baffle acting as a heat shield at the height of the additional air intake so as to leave a passage for the mixture of oxidant and fumes leaving the catalyst between said baffle and the supply of additional air.

According to a preferred embodiment of the invention, the baffle is formed by a plate, the surface of which occupies substantially half of a cross section of the duct, said plate being located on the opposite side with respect to the inlet tube of additional air.

According to an additional embodiment of the invention, downstream of the baffle, means for cooling the flue gas are provided allowing the condensation of said fumes and in that means for collecting the fumes condensed by said cooling means are provided , comprising a means of controlled extraction thereof.

Other details and advantages of the invention will emerge from the description which will be given below, of a device for combustion of unburnt substances contained in fumes.

• La figure 1 représente une vue en perspec­tive avec brisure partielle du dispositif de combustion suivant l'invention.
• La figure 2 est un graphique représentant les courbes de rendement en fonction de la température pour la catalyse et la postcombustion.

This description is given by way of example only and does not limit the invention in any way. The reference notations refer to the appended figures.

• Figure 1 shows a perspective view with partial breakage of the combustion device according to the invention.
• Figure 2 is a graph showing the yield curves as a function of temperature for catalysis and afterburning.

The device illustrated in FIG. 1, and purely by way of example, comprises a duct 1, in the present case of square section, in which an orifice 2 is provided to allow the entry of the fumes coming from the combustion of a fuel, in particular wood in a heating body, not shown in FIG. 1. Port 2 also allows the entry of oxidizer, in this case secondary air, the primary air having been used for the combustion of wood in this case in the heating body not shown. The secondary air is supplied via an air inlet tube 4 oriented towards the orifice 2, so as to allow the injection of air into the orifice 2.

In an embodiment which is formally claimed, the air inlet is made by several nozzles 5, all connected to the main air inlet tube 4. Advantageously, provision may be made for an equidistant arrangement of the nozzles 5 along the tube 4 in order to obtain a premix as homogeneous as possible of the fumes and air as soon as they penetrate into the orifice 2.

Downstream of the orifice 2, a catalyst 3 is provided. Concerning the expression "downstream", it is of course necessary to be situated in relation to the direction of flow of the smoke and air mixture. According to a particularly advantageous form of the invention, the catalyst 3 is formed by a skeleton structure, more particularly a grid, of which only the upper surface has been shown in the figure, the thickness thereof being indicated by the symbol "h", as can be seen in Figure 1.

The substrate making up the grid is advantageously formed by an extruded ceramic material. This substrate is lined with an intermediate coating of inert material and a catalytic material, such as, for example, palladium or platinum.

Downstream of the catalyst 3, a baffle 6 can also be distinguished, formed by a refractory material. According to a preferred embodiment of the invention, au provides, approximately at the same height as this baffle and outside the duct 1, an additional secondary air inlet tube 7 advantageously provided, in a similar manner to the tube 4, d 'nozzles 8. The arrows indicate the direction of the supply air. The baffle 6 is located on the side opposite to that bordered by the air intake tube 7.

According to Figure 1, the smoke intake orifice 2 is disposed on a lateral side of the duct 1, which makes it possible to avoid fouling of the grid forming the catalyst 3, fouling due to wood combustion residues.

FIG. 2 clearly shows the complementarity of catalysis and post-combustion, each process giving rise to an optimal yield in complementary temperature ranges. The temperature ranges corresponding to the zones in columns A, B and C in FIG. 2 represent respectively low, medium and bright lights. The ascending curve indicates the relationship between efficiency and temperature for catalysis. It shows that the efficiency of catalysis decreases with temperature. Maximum efficiency is reached for low intensity fires. On the other hand, the downward yield curve representing the post-combustion situation indicates, that the yield of the latter increases with temperature, full performance being reached at high heat.

It will be observed that the yield curves are symmetrical with respect to their common point representing a well-determined temperature. It follows from the above that from this well-determined temperature, the efficiency of the catalysis is equaled by that of the post-combustion allowing higher temperatures to be obtained, necessary for the strongest possible elimination of the unburned substances still included in the fumes.

The fumes given off by the combustion of wood in the heating body penetrate into the lateral orifice 2, after having been premixed with the secondary air projected from the tube 4. The premix thus formed having penetrated into the duct 1 passes through the catalyst 3 undergoing the effects of catalysis. Catalysis starting at 260 ° C, the temperature in the heating body will preferably be low and correspondingly the fire will therefore be mild to obtain maximum catalysis efficiency.

Under these conditions, the gas mixture passing through the catalyst 3 comes out at a temperature varying between 960 ° C. (low heat and maximum yield) and possibly 600 ° C. (high heat and minimum yield). In the outlet zone, downstream of the catalyst, the gas mixture comes into contact with hot secondary air blown from the tube 4 into the gas mixture flow partially discharged from creosote and capable, to a certain extent, of re-ignite according to the flow temperature at the inlet 2. The minimum temperature necessary for combustion starting around 600 ° C. is therefore reached downstream of the catalyst 3 in combination with the addition, according to the invention, of secondary air blown in. downstream of the catalyst 3 up to the baffle 6. There therefore follows an afterburner downstream of the arrival of the additional secondary air 7, which allows the almost complete elimination of the last creosote residues or combustible materials still present in the gas flow containing the treated fumes, by the significant rise in temperature. This temperature can reach a range from 1200 to 1400 ° C. Indeed, when the fire is bright, as shown in the Figure 2, the afterburner gives its full performance. It follows that at the outlet of the duct 1 all the tars are burned and that, consequently, all the calories that the treated fumes were able to release have been, which, undoubtedly, constitutes an essential objective of the invention.

Note that if the fire is very low and burns without burning, there is a risk that the catalyst 3 will go out. This can be prevented by passing the supply of secondary air from the tube 4 through an area located downstream of the catalyst 3, and more particularly, downstream of the baffle 6, for example by means of a bimetallic strip. , not shown in the figure, causing the supply of secondary air when the fumes fall below 250 ° C, which the superheated secondary air can then reactivate the catalyst 3. The temperature of the heating body and its fumes exceeding again 260 ° C., the flow of superheated air can then be stopped, and replaced by a fresh flow, because, as described above, the catalysis must take place at a sufficiently low temperature to obtain a good yield.

As for the afterburner, it will occur independently of the temperature of the incoming fumes at the level of the orifice 2 since the fumes feeding the afterburner reach at least 600 ° C., the natural starting temperature of the afterburner. Consequently, as soon as there is catalysis, the temperatures of the gas flow containing the fumes at the outlet of the device according to the invention, combining the phenomena of catalysis and post-combustion, will always be between 1200 and 1400 ° C., and whatever the state of the fire in the heating body, provided that there is fire and emission of smoke.

This results in the very important advantage of the invention according to which, the optimum yield being always reached, since a maximum of calories are taken from the fumes, which then also results in a lower consumption of wood.

Example:

As fuel, dead wood is used. The duct, of square section according to the example described has a side of 8 cm. The catalyst has a thickness of 5 cm.

The dimensions of the baffle, of rectangular section, are 8 cm by 4 cm. The distance between the downstream end of the catalyst and the baffle is 10 cm.

The smoke flow is of the order of 1 to 3 m³ per hour, producing 3500 to 4500 kcal / h maximum from dead wood. The ratio of the smoke and air flow rates is respectively 3: 1, the part of air comprising all of the air added from the two air supply tubes.

As indicated above, the above description is given only by way of example and in no way limits the invention. Consequently, several modifications can be envisaged without departing from the scope of the present application.

This is how the section of the duct could be round, which, in certain applications, may be preferable for purely practical reasons.

Secondary air can just as easily be replaced by pure oxygen, thereby activating combustion.

The smoke inlet orifice, instead of being lateral, could be frontal, which in applications other than those of burning wood, in heating bodies such as wood stoves, may be required. This is so, for example, when the device is applied to exhaust pipes.

Claims (7)

1. Device for combustion of unburnt substances contained in fumes given off by combustion of a fuel such as, for example but not exclusively, wood, the aforementioned combustion device being formed, inter alia, by a duct comprising at one from its ends a smoke inlet orifice, characterized in that said duct (1) further comprises at least one catalyst (3) downstream of the smoke inlet orifice (2) and a tube d oxidizer inlet (4) external to the duct (1) so that the oxidizer sprayed from the inlet tube (4) forms a mixture with the fumes, this mixture passing through the catalyst (3), right through, and moving towards the other end of the duct (1) and in that at least one additional oxidizer inlet tube (7) is provided. 2. Device according to claim 1, characterized in that the aforementioned conduit (1) comprises, downstream of the catalyst (3), at least one baffle (6) acting as heat shield and arranged at the height of the arrival of additional air (7) so as to leave a passage (9) to the mixture of oxidant and fumes leaving the catalysis (3) between said baffle (6) and the supply of additional air (7). 3. Device according to claim 2, characterized in that the baffle (6) is formed by a plate, the surface of which occupies substantially half of a cross section of the duct (1), said plate being located on the opposite side with respect to to the additional air intake tube (7). 4. Device according to any one of claims 1 to 3, characterized in that the catalyst (3) is formed by a grid, the substrate of which is composed of an extruded ceramic, provided with an intermediate coating of inert material and d '' a surface coating of catalytic material. 5. Device according to any one of claims 1 to 4, characterized in that the oxidizer inlet tubes (4, 7) are provided with nozzles (5, 8), preferably mutually arranged at substantially equal distance, said nozzles (5, 8) pointing towards this duct (1) so as to allow a substantially uniform distribution of the oxidant inlet. 6. Device according to any one of claims 1 to 5, characterized in that the oxidant is formed by air, more particularly by oxygen. 7. Device according to any one of claims 2 to 6, characterized in that, downstream of the baffle (6), means for cooling the flue pipe (1) are provided allowing the condensation of said fumes and in that means for collecting the fumes condensed by said cooling means are provided, comprising means for controlled extraction thereof.

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