FR3047299A1 - METHOD AND DEVICES EMPLOYING IT TO PERFORM HOMOGENEOUS PARTIAL OR TOTAL COMBUSTION - Google Patents

Abstract

The invention relates to a method and the main characteristics of the devices making it possible to implement it to obtain combustion at temperatures as homogeneous as possible (which is one of the conditions to be fulfilled to produce little NOx) and to have stable combustion. even when one tries to partially or totally oxidize poor or very poor gases. According to the invention, the combustion is carried out in a chamber in which the gases are rapidly rotated so that the hot gases heat the oxidant and fuel to a temperature such that they can burn, and this advantageously in less than one turn made by the gases in the room.

Description

The invention is part of the total or partial combustion processes and techniques and in particular of the methods and materials for homogeneously burning (that is to say without a particularly hot zone, as can be in a flame). fuel can be quite poor (as are for example blast furnace gas or air gasification gas). The application of the invention to a homogeneous combustion developed throughout the following text is not the only interesting industrial application of the process which can also be used more generally for gas-gas reactions, reactions of suspended matter in one or more gases and even for reactions between liquids in which it is desired to homogenize the media.

In the following, we will use (to facilitate comprehension) the terms "homogeneous combustion" to speak of a reaction which is made in a medium as homogeneous as possible at the macroscopic level in terms of temperatures and concentrations of various components.

To obtain a stable combustion of a rich as well as poor fuel, it is often used so-called pre-mix burners or burners making mixtures between more or less rotating jets generally turbulent: in the premix burners, the fuel is mixed as homogeneously as possible with the oxidant (for example air) and the mixture is ignited in a combustion chamber. It then develops a flame by the usual process of flame front propagation. But if the gas to be burned is a poor or very poor gas, given the low content of combustible components of this gas, the speed of propagation of the flame may be low or very low, which may lead to unstable flames .

The problems posed by the flame stability of combustion increase when one has to deal with poor or particularly poor gases, which leads to burn these poor gases to particular solutions often unsatisfactory. For combustion, for example blast furnace gases, reheating air in a free flame can stabilize it. But this has the disadvantage, regardless of an additional cost due to the price of the heat exchanger, to increase at least all the local high temperatures and thus to increase the NOx products.

The desire to produce as little NOx as possible and to reduce the local extreme temperatures that occur in the flames of burners has led to "low NOx" burners (methane for example or various hydrocarbons). In low NOx burners, combustion fumes are partially recycled in the flame. The innovation object of this patent meets various needs and in particular the following: achieve a partial or total combustion of gas (which can be poor because of its composition, particularly because of a nitrogen content and vapor of very important water) without producing too much NOx and having a stable combustion. This is important when one wants to burn poor gases whose flame is difficult to stabilize properly.

On a general level, the burning in flame leads to the existence of particularly hot zones (flames) in which the production of NOx is activated. In order to limit this production of NOx, a technique usually used consists of mixing in the flame fumes from the combustion zone. Mixing fumes with burning gas and oxidant depletes the fuel-oxidant mixture and leads to the same flame-stabilization difficulties that are encountered in burning poor gases.

Faced with these difficulties, a technique currently extensively studied in order to reduce the amounts of NOx formed during a combustion is the homogeneous combustion without flame. The invention described here allows a homogeneous combustion which has the advantage of being without flame and therefore without a particularly hot point. In addition, it makes it possible to stably achieve total or partial combustion of even poor gases.

According to this invention, the fuel and the oxidant introduced into the combustion space in a distributed manner along its length are vigorously and rapidly mixed with large volumes of very hot fumes as a result of combustion which are very rapidly re-circulated in the combustion chamber. reaction space essentially by a rotary motion of all the gases in this space. The important mixture achieved by the rotation of the gases, in addition to favoring the mixing of the fuel and the oxidant, warms them up rapidly allowing to reach a sufficient temperature so that the oxidation takes place in spite of the high dilution, and that without reaching locally the very high temperatures that would reach a flame in this mixture. The temperatures reached must only be those which provide the activation energy necessary for the homogeneous combustion by contact of the diluted oxidant with the fuel (also diluted) by the mixture.

The present patent discloses a method and devices for implementing it to achieve the intended homogeneous combustion. This process and the devices making it possible to use it advantageously apply, for example, to the total or partial oxidation of a lean gas gasification gas to which, of course, it is not limited.

The method consists in introducing the fuel and the oxidant into the mass of high temperature gas rotating in a combustion chamber in which a circular flow takes place whose axis of rotation has the same direction as the length of the chamber, maintained motion. by a judicious means, possibly by a fan resistant to the temperatures that prevail in the chamber, and / or advantageously by the exchange of momentum between the gas that rotates in the chamber and the fuel and / or the oxidant injected at speeds sufficient by orifices arranged so that the direction of the fluids injected is, instead of injection, in the direction and direction of the flow of gas in this place. It is necessary for the momentum transmitted to the rotating gases to overcome the pressure losses associated with the resistances due to the rotation of the gases that the amount of movement added by the injected gases is sufficiently high, which is obtained by high speeds of injected gas. It should also be ensured that the device for feeding the injected gases to the injection orifices disturbs the flow of the gases as little as possible.

The method also provides that the injection is made through orifices sufficiently small so that the mixing takes place advantageously in much less than one turn of the gas in the combustion chamber.

The products of the reaction exit through the ends of the chamber or by a strip oriented in the direction of the length of the chamber.

Devices for applying this method may be various. In particular, three devices are used which implement the method of the invention: a high temperature elevation device (up to 1000 to 1200 ° C.) of intermediate gases of a biomass air gasifier. This device may be a closed reactor, the shape of the surface which limits the chamber is not necessarily cylindrical. This surface may be of square or polyhedral section or other, although being advantageously quasi-cylindrical of revolution. The flow inside the chamber is generally of revolution around the axis of the chamber.

The device may also be an open reactor in which the reactor shape is that of a reversed half-cylindrical bottom channel extended by parallel flat faces, which corresponds to a reactor whose combustion zone is open to another zone. of the apparatus and can supply very hot gas, through the periphery of the rotating flow, this other zone. Note that in this device, the main flow remains of revolution about the axis of the half-cylinder of the partially surrounding surface.

The third device may be called a lean gas burner that can be introduced into the central chamber of a boiler designed to put a conventional burner oil or gas for example. Instead of the conventional burner, the fuel is introduced around a cylindrical cane. The cane is extended inside the central combustion chamber and is equipped with a set of small flat ducts that wisely inject the air into the chamber by providing a quantity of motion that vigorously turns the gases in the chamber. The device ensures homogeneous combustion and produces a very hot cylinder of gas where the conventional burner flame would be installed. The combustion space is, in all three cases, advantageously delimited by a cylindrical wall of revolution.

The wall of the chamber may consist of several layers: for example, on the outside there will be a layer of metal (for example sheet metal) which provides the seal and is sufficiently resistant to mechanical stresses and corrosion of cold walls (due to condensation which may occur at times although the temperature of this layer is usually advantageously maintained such that there is no condensation on this outer layer tight). Then, for example, there will be a thermal insulation layer, advantageously made of refractory wool, fixed inside the preceding layer. Finally, it will advantageously a more or less thin metal sheet of a metal resistant to both temperature and possible corrosion (due to a particular component of the gases when they are at high temperature). This sheet metal layer covers the inside of the thermal insulation layer. The wall of the chamber, in the case where it is the inner wall of a boiler, is simply the steel wall of the chamber of said boiler.

Injections of combustible and oxidant gases for example (being noted that the fuel or the oxidant are not necessarily gases) which take place within the framework of the devices developed in the following text (remember that these are cases non-limiting particular) can advantageously be made by orifices (optionally slots) disposed on or at the end of conduits which bring the injected gases to the injection orifices. These injections, to ensure the persistence of the overall rotation of the gases, must be advantageously in the direction that the surrounding flow instead of the injection.

In the reaction space, or elevation at high temperature, cylindrical of revolution in which the hot gases rotate, the injected gases must have approximately a direction perpendicular to both the radius and the axis of revolution of the space of reaction.

In the version in which the injections of oxidant fill, as the fuel injections, this condition, the fuel and the oxidant can be brought to the orifices each in two different ways: - by flattened conduits, located approximately in planes perpendicular to the the axis of the chamber, conduits whose shape is advantageously aerodynamic vis-à-vis the flow which surrounds them and which are fed either through the outer wall or by a central pipe advantageously located in the axis of the chamber of combustion - by a pipe, or several pipe sections, flattened and aerodynamic shape vis-à-vis the flow that surrounds them, longitudinal parallel to the axis of revolution of the combustion chamber, fed from the wall or from a pipe located advantageously in the axis of the chamber by radial sections of pipe (flattened and aerodynamic shape vis-à-vis the flow around them) - bent pipe sections connected to a pipe or box outside the chamber or pipe located in the center of the chamber.

It will be noted that, despite the dominance of the tangential component of the velocity in the chamber, the flow of gas leaving the chamber induces an axial component of velocity. It is the composition of these two components that defines the speed in the various points. The speeds are therefore not precisely in a plane perpendicular to the axis of the chamber but more precisely, in the case of a gas outlet at one end of the combustion chamber, on a helix with increasing pitch towards the outlet of which the axis is the axis of the chamber. This can cause the flattened pipes carrying oxidizer and fuel to be not exactly on disks but rather on propellers.

FIG. 1 represents a circular combustion chamber corresponding to the first case above, seen in section along a plane perpendicular to the axis of the chamber, in which the injection of the oxidant and the fuel are made through the outer wall by two slots having a wall in common. It shows the outer wall (1), the insulation layer (2) and the inner wall (3) thin sheet. It also shows the flattened lines (4) which bring the gases and the air in parallel plane layers and having a common face. It shows the leading edge (5) of the aerodynamic profile of these flattened pipes and the trailing edge (6) through which the fuel in the center and the oxidant in thin layer out on both sides. We see baffles (7) which guide the air space so that it is well perpendicular to the radius and thus in the direction of the general flow when it leaves. It shows, grouped together in one space the fuel supply boxes (8) and air (9) feeding the various flattened pipes. It shows the pipe (10) which brings air to the supply box (9) which concerns it. Finally, there is a flange (11) which makes it easier to assemble and connect the boxes. It shows the plates (12) for fixing the ignition burners and the gas starting line (13).

FIG. 2 represents the same chamber as FIG. 1, seen in section along a particular axial plane. The fact that the pitch of the speed propeller is increasing leads to the gradual increase of the angle with respect to the axis of the fuel and air injection pipes when approaching the exit.

FIG. 3 is a perspective view of a combustion chamber integrated into a device corresponding to the second case above and to a configuration in which the fuel enters through flattened ducts located in planes perpendicular to the axis of the chamber. (One of the formulas mentioned in the description) while the air enters by an aerodynamic conduit parallel to the axis of the chamber and fed at one end. It will be noted the outer wall (1), the thermal insulation (2), the inner wall (3) which is here of polyhedral section, more closed than a half-cylinder, and completed by flat walls (14) of each side. Here, the flattened lines (4) are located in planes perpendicular to the axis and bring the fuel gas from the box (8). Here, the oxidant is not distributed around the pipes bringing the fuel as in the previous case but it is distributed along the trailing edge of the sheet metal (15) by a slot. It is brought into this sheet metal (15) whose aerodynamic shape will be noted, by an air duct (16) immersed in the insulation of the bottom of the chamber. Note the inlet (17) of the flame of the ignition burner in the chamber.

FIG. 4 represents a section of the chamber seen in perspective in FIG.

Figures 5, 6 and 7 relate to the third case described above.

Figure 5 shows a lean gas burner (20) in the inner chamber (21) of a commercial boiler. The central air supply pipe (18), the aerodynamically flattened ducts (19), which transport and inject air into the flow from the pipe (18), will be noted. The line (22) brings the fuel C rotating around the central air supply line (18).

Figure 6 shows an enlargement of the flattened and curved aerodynamic ducts (19).

FIG. 7 represents a section of one of the flattened ducts (19) which inject the air into the chamber represented in FIG. 5. It will be noted the thin slot (23) through which the air is injected and the aerodynamic shape of the air. the cup.

The first described version of the invention can advantageously be used in gasification plants of various materials and in particular more or less wet biomass in which it will advantageously achieve a high temperature elevation chamber of the intermediate gases of the oxidation gasifier. partial of these gases by air.

The second version of the invention described above can advantageously be used in compact and monobloc biomass gasification plants where it will advantageously make it possible to produce a high temperature elevation chamber for the intermediate gases of the gasifier by partial oxidation of these gases by air.

The third version has a large number of industrial applications insofar as it advantageously makes it possible to post-burn lean gas both by using cold air and heated air, and in particular to make this post-combustion by Instead of a burner that would supply a boiler, making existing boilers likely to be supplied with lean gas, including gas gasification air biomass or coal.

The industrial applications of the process and the devices making it possible to implement it objects of the present patent are not limited to the cases cited above.

Claims (12)

Claims 1) A process for carrying out an exothermic reaction between a plurality of reactants, wherein the place in which the process takes place is called a chamber, characterized in that: a) in the chamber, the reagents and the products of the reaction are in motion. rotation about an axis that will be called axis of the chamber, driven in this movement by mixing the amount of movement of the reagents entering the chamber and reaction products and reagents therein or by the use of a mechanical means of rotating, the dimension of the chamber in the direction of the axis of rotation being called the length of the chamber and the faces of the chamber limiting it in length b) the reactants are injected into the flow in a distributed manner along the length of the chamber and mixed with the reaction products present in the chamber the speed of rotation of the mixture in the chamber and the characteristics of the injection of r active in the chamber are such that the reactants are mixed with the reaction products in less than one revolution around the axis of the chamber 2) Process according to claim 1 characterized in that the reactants are a fuel and an oxidizer, the process then being called a combustion process and the combustion chamber reactor. 3) Process according to any one of the preceding claims characterized in that the reaction products exit through the ends of the chamber or by a strip oriented in the direction of the length of the chamber. 4) Device for implementing the method according to any one of the preceding claims, characterized in that the injection into the flow of at least one of the reactants is made by at least one aerodynamically shaped pipe vis- with respect to the flow, which will be called introduction pipe. 5) Device according to claim 4 characterized in that the fluid which passes through said at least one introduction conduit out of this conduit to the flow by at least one orifice or slot located on the trailing edge of this pipe. 6) Device according to any one of claims 4 and 5 characterized in that at least one of the introduction pipes injecting a reagent into the flow has a common wall with at least one pipe injecting another reagent into the flow . 7) Device according to any one of claims 4 to 6 characterized in that at least one section of an introduction pipe is either parallel to the axis of the chamber, or approximately perpendicular to the axis of the chamber . 8) Device according to any one of claims 4 to 7 characterized in that one or more introduction lines are fed either directly or via at least one aerodynamically shaped pipe vis-à-vis the 'flow. 9) Device according to claim 8 characterized in that at least one supply line is located approximately in the axis of the chamber. 10) Device according to any one of claims 8 to 9 characterized in that at least some introduction pipes are bent to facilitate the passage of reagents from the pipe which feeds these introduction lines to these introduction lines. 11) Device according to any one of claims 4 to 10 characterized in that said at least one introduction pipe and, in the case where there is, the pipes feeding this introduction pipe, form an assembly that it can be passed into the combustion chamber of a boiler through the orifice reserved for the installation of a conventional burner, so that this assembly can be easily substituted for a burner. 12) Gasification device characterized in that it comprises a device according to one of claims 4 to 10.