EP2003395A2 - Method for gasification of waste in a rotary hearth furnace and furnace for gasification of waste - Google Patents

Abstract

The method involves treating wastes (1) introduced in a furnace with rotating hearth at a temperature between 400 and 600 degree centigrade to produce condensable gas, non-condensable gas and coke resting on a rotating hearth (14) of the furnace. The condensable and non-condensable gases and the coke are treated at a temperature between 800 and 1100 degree centigrade and are set in presence of water vapor to produce synthesis gas. An independent claim is also included for a furnace with rotating hearth for gasification of organic wastes.

Description

The present invention relates generally to the field of waste gasification.

More specifically, the invention relates, according to a first aspect, a gasification process of organic waste.

The known waste gasification techniques are based on fluid bed or percolation technologies through a fixed bed.

These techniques are effective in terms of gasification efficiency but require, prior to gasification, a precise calibration of the waste. Indeed, the waste must be of the order of a millimeter and have a homogeneous distribution and constant size.

In this context, the present invention aims to provide a waste gasification process satisfactory in terms of gasification efficiency, simplified implementation, and faster realization.

• une première étape pendant laquelle les déchets introduits dans le four sont traités à une température comprise entre 400 et 600°C, et produisent ainsi des gaz condensables, des gaz incondensables, et du coke reposant sur la sole du four, et
• une deuxième étape pendant laquelle les gaz condensables et incondensables et le coke sont traités à une température comprise entre 800 et 1100°C, et sont mis en présence de vapeur d'eau, et produisent des gaz de synthèse.

To this end, the process according to the invention for gasification of organic waste is essentially characterized in that the waste is introduced into a rotary hearth furnace in which they are successively treated in at least two concomitant steps, including:

• a first step during which the waste introduced into the furnace is treated at a temperature between 400 and 600 ° C, and thus produce condensable gases, incondensable gases, and coke resting on the hearth of the oven, and
• a second step during which the condensable and incondensable gases and the coke are treated at a temperature between 800 and 1100 ° C, and are brought into the presence of water vapor, and produce syngas.

The invention therefore has the advantage of providing waste gasification free of heavy preparation upstream, which simplifies the process as a whole and saves time and a reduced cost of implementation.

In a preferred embodiment of the invention, the method further includes a third step of burning the coke residues of the second step by raising them to a temperature of between 1000 and 1300 ° C.

Advantageously, at least a portion of the synthesis gases obtained in the second stage are extracted and recovered energetically.

Preferably, the heat generated by the third step is used for the heat treatments of at least the first and second stages.

Part of the synthesis gases obtained in the second stage are advantageously burned in the third stage.

According to a particular version of the invention, the furnace hearth stores heat during the third step and restores it at least during the first and second steps.

The waste, before being introduced into the oven, can be subjected to grinding and / or screening.

The waste introduced into the furnace preferably has a larger dimension at most equal to 100 millimeters.

In the second step, the water vapor is for example injected into the coke resting on the sole, preferably through the sole.

Preferably, in the third step, oxygen, and in particular air, is supplied to the oven.

According to a preferred version of the invention, the materials resting on the hearth of the furnace, such as waste or coke, are mixed, in particular with the aid of saddles present above the hearth, such as rakes or rakes. plowshares, for example of steel.

The term "materials" refers to waste products and all their products obtained from the reactions of the first, second and third stages. In particular, "floor-based materials" are termed waste and their products which are based on the hearth of the oven.

In particular, the waste is a mixture of solid, pulverulent and / or liquid waste.

In a particular embodiment of the invention, the waste introduced into the furnace is deposited on the hearth, at the periphery thereof, and then, during the rotation of the hearth, punctually pushed towards the center of the furnace. sole, materials resting on the oven floor, such as waste or coke, following a spiral-shaped path.

Materials resting on the hearth of the oven can be pushed and mixed by the saddles.

Advantageously, each step takes place respectively in a defined volume inside the oven.

According to a preferred version, at least a portion of the gases and / or fumes present in the third step are burned at this stage and circulate above the volumes defined in the furnace to indirectly heat the contents of said volumes.

Oxygen, and in particular air, can be injected above the defined volumes in the furnace.

The waste is preferably introduced as a continuous flow into the oven.

For example, the waste is selected from alternative fuels made from household and industrial waste, grinding scrap, sludge from water treatment plants, contaminated wood, industrial organic waste, and / or agricultural waste.

According to a second aspect, the invention relates to a rotary hearth furnace for the gasification of organic waste, comprising an oven enclosure delimited by a bottom, a peripheral wall and an upper wall, and a rotating hearth, above the bottom of the enclosure, capable of rotation about an axis, and intended to receive the waste. Said oven is characterized in that it further comprises an internal set of walls above the rotating hearth, defining three chambers inside the enclosure, around the axis of rotation of the hearth.

The oven according to the invention may advantageously further comprise mixing means in the oven chamber above the hearth, said mixing means being at least intended to return and mix materials resting on the hearth, such as the waste or coke.

The mixing means are particularly rables, such as rakes or plowshares, for example steel.

Preferably, the mixing means are arranged radially relative to the axis of rotation of the sole.

• la figure 1 représente un diagramme d'un mode de réalisation du procédé selon l'invention ; et
• la figure 2 représente schématiquement un four à sole tournante selon l'invention, adapté à la mise en oeuvre du procédé selon l'invention.

Other characteristics and advantages of the invention will emerge clearly from the detailed description which is given hereinafter, by way of indication and in no way limiting, with reference to the appended drawings in which:

• the figure 1 represents a diagram of an embodiment of the method according to the invention; and
• the figure 2 schematically represents a rotary hearth furnace according to the invention, adapted to the implementation of the method according to the invention.

In the figure 1 waste 1 is introduced into the furnace (not shown) and undergoes the first step 2 therein.

This first step 2 consists of drying and at least partly producing the thermolysis of the waste. It produces coke which rests on the hearth of the furnace and is thus directed, by the rotation of the sole, towards the second stage 3.

Gases are also obtained during this first step 2. They contain incondensable gases, such as methane CH ₄ , ethane C ₂ H ₆ , carbon monoxide CO, and hydrogen H ₂ , and condensable gases, such as tar and phenol.

These gases are also directed to the second step 3.

The second step 3 is successive to the first step 2 for the same batch of waste. These two steps 2, 3 are concomitant in the oven.

The second step 3 is carried out at a temperature higher than that of the first step 2 and possibly makes it possible to terminate the thermolysis of the waste and of their reaction products resulting from the first step 2.

This second step 3 is the gasification step. This is done through the introduction of 4 steam.

The water vapor is injected in particular into the coke resting on the sole, and preferably through the sole.

This water vapor allows the cracking of coke and condensable gases from the first stage 2.

The gases obtained in the second stage 3, called synthesis gas, are preferably extracted, at the outlet 5, from this stage 3.

The extracted synthesis gas is for example washed, dusted, and filtered, before being recovered energy in a gas turbine or boiler.

According to a particularly advantageous version of the invention, the process includes a third combustion step 6, at a temperature of between 1000 and 1300 ° C.

This third step 6 is successive to the second step 3 for the same batch of waste. The three steps 2, 3, 6 are carried out concomitantly in the oven.

An oxidant, in this case the oxygen of the air, is brought to the inlet 7.

In this third step 6, the coke residues from the second step 3 are treated.

In addition, part of the synthesis gases obtained in the second step 3 can also be burned in the third step 6.

The third step 6 generates a lot of heat, by the combustion of coke residues, which are for example in the state of smoke at this stage, as well as by that of a part of the gases coming from the second stage 3. This heat is advantageously used, as shown by the arrows 8, for the heat treatments of the first and second stages 2, 3.

The heat generated in the third step 6 is sufficient to heat the oven, and in particular for the heat input required respectively for the unfolding of the first, second and third steps 2, 3, 6.

The heat generated in the third step 6 is for example stored by the oven floor, which is made of refractory material. The sole then restores this stored heat to the materials in the furnace, and in particular to the materials resting on the sole.

Particularly advantageously, each step 2, 3, 6 of the process according to the invention takes place respectively in a defined volume inside the furnace. Each volume is for example a chamber as described below.

At least a portion of the gases and / or fumes present in the third step 6, in other words obtained directly at this step 6 and possibly from the second step 3, can advantageously circulate above the volumes defined in the oven to indirectly heat up the content of said volumes.

For example, they circulate at the roof of the oven, i.e. the upper part of the furnace chamber, under the upper wall thereof.

Oxygen, and in particular air, is preferably injected above the volumes defined in the furnace to promote the combustion of gases and / or fumes circulating therein.

To the figure 2 is shown a rotary hearth furnace, adapted to the implementation of the method according to the invention, gasification of organic waste.

This oven comprises a furnace enclosure 10 delimited by a bottom 11, a peripheral wall 12 and an upper wall 13.

Above the bottom of the enclosure, the rotating hearth 14 is rotatable about an axis 15. It is intended to receive the waste introduced by the inlet 16.

The oven further comprises an internal assembly 17 of walls above the rotating hearth 14. The assembly 17 of walls defines at least two, and preferably three, chambers 18a, 18b, 18c within the enclosure 10, around the axis 15 of rotation of the sole.

The set 17 of walls has one or more planes preferably perpendicular to that of the hearth 14. It spares one or more passage spaces above the hearth 14, so that the materials resting on the hearth can circulate under the set of 17 walls.

Thus, the rooms defined by the set of walls are not quite closed by the wall or walls.

• Les déchets introduits par l'entrée 16 sont soumis au traitement de la première étape dans la chambre 18a. Les gaz et le coke obtenus passent sous l'ensemble 17 de parois et entrent dans la chambre 18b pour la gazéification. Le coke est en rotation avec la sole 14.
• De la vapeur d'eau est amené en entrée 19 pour la gazéification. Cette entrée est de préférence au niveau de la sole 14, et tout préférentiellement à travers la sole 14.
• Une partie des gaz de synthèse de la deuxième étape sont extraits par la sortie 20.
• La rotation continue de la sole 14 transporte les résidus de coke dans la chambre 18c, par passage sous l'ensemble 17 de parois.
• Dans la chambre 18c a lieu la troisième étape de combustion. De l'air est amené par l'entrée 21.
• Les cendres restant sur la sole 14 en fin de troisième étape sont extraites par la sortie 22.

By way of example, here is an embodiment of the process according to the invention used in the furnace shown in FIG. figure 2 :

• The waste introduced by the inlet 16 is subjected to the treatment of the first step in the chamber 18a. The gases and coke obtained pass under the set of walls 17 and enter the chamber 18b for gasification. The coke is in rotation with the sole 14.
• Water vapor is fed to inlet 19 for gasification. This inlet is preferably at the sole 14, and most preferably through the hearth 14.
• Some of the synthesis gases of the second stage are extracted through the outlet 20.
• The continuous rotation of the hearth 14 carries the coke residues in the chamber 18c, passing under the set 17 of walls.
• In the chamber 18c takes place the third stage of combustion. Air is brought through the entrance 21.
• The ashes remaining on the hearth 14 at the end of the third stage are extracted by the exit 22.

The method according to the invention can advantageously operate continuously. The waste is then introduced in continuous flow into the oven.

The oven hearth rotates advantageously continuously and at a constant speed. The speed of the sole is adjustable.

The oven can operate in piston mode, or in spiral mode.

In piston mode, the waste is preferably deposited on a radius of the hearth and the ashes obtained at the end of the process are extracted from the oven using for example an extraction screw.

In spiral mode, the waste introduced into the furnace is deposited on the sole, on the periphery thereof, then, during the rotation of the hearth, punctually pushed towards the center of the hearth, the materials resting on the oven floor, such as waste or coke, following a spiral path.

For example, on a sole 5 meters wide, the waste is deposited on 50 centimeters on this width.

The spiral mode offers the advantage of greater waste processing speed compared to the piston mode. The rotation speed of the hearth is generally greater in spiral mode than in piston mode.

The oven may include mixing means in the oven enclosure above the hearth. These mixing means are at least intended to return and mix the materials (waste, coke, etc.) resting on the sole.

These mixing means are, for example, saddles, such as rakes or sets of plowshares. They are preferably made of steel.

Materials resting on the hearth of the furnace, such as waste or coke, can thus be mixed during the process. This mixture prevents the formation of a top layer of ash on the pile of materials, which layer has the disadvantage of isolating the rest of the cluster.

The mixing means are for example arranged radially relative to the axis of rotation of the sole.

The materials resting on the hearth of the oven can be not only mixed by the mixing means, but also pushed by these means, particularly in the context of operation of the spiral oven.

The organic waste concerned by the invention may be of a heterogeneous nature, and in particular be mixtures of solid, pulverulent and / or liquid waste.

For example, the waste is selected from alternative fuels made from household and industrial waste, grinding scrap, sludge from water treatment plants, contaminated wood, industrial organic waste, and / or agricultural waste.

Preferably, the waste, before being introduced into the oven, is subjected to grinding and / or screening, to advantageously select waste having a larger dimension at most equal to 100 millimeters.

One of the advantages of the process of the invention is to possibly require only a grinding and / or a summary screening, and to accept waste of heterogeneous size, such as between about 1 millimeter and about 100 millimeters.

In addition, compared to a waste incineration process, the method according to the invention makes it possible to limit importantly the emission of carbon dioxide CO ₂ , for the same amount of treated waste.

Claims (15)

Process for gasification of organic waste, characterized in that the waste (1) is introduced into a rotary hearth furnace in which they are successively treated in at least two concomitant steps (2, 3, 6), including: - a first step (2) during which the waste (1) introduced into the furnace is treated at a temperature between 400 and 600 ° C, and thus produce condensable gases, incondensable gases, and coke resting on the sole of the oven, and - A second step (3) during which the condensable and incondensable gases and coke are treated at a temperature between 800 and 1100 ° C, and are brought into the presence of water vapor, and produce synthesis gas. The process of claim 1, further including a third step (6) of burning the coke residues of the second step (3) at a temperature of between 1000 and 1300 ° C. Process according to Claim 1 or 2, in which at least part of the synthesis gases obtained in the second step (3) are extracted and recovered energetically, and / or in which part of the synthesis gases obtained in the second stage (3 ) are burned in the third step (6). A process according to any one of claims 2 and 3, wherein the heat generated by the third step (6) is used for heat treatments of at least the first and second steps (2, 3). A method according to any one of claims 2 to 4, wherein the furnace hearth stores heat during the third step (6) and restores it at least during the first and second steps (2, 3). Process according to any one of claims 1 to 5, wherein the waste (1), before being introduced into the oven, are subjected to grinding and / or screening. Process according to any one of claims 1 to 6, wherein the waste (1) introduced into the oven has a larger dimension at most equal to 100 millimeters. A process as claimed in any one of claims 1 to 7, wherein in the second step (3) the water vapor is injected into the coke on the hearth, preferably through the hearth. A process as claimed in any one of claims 2 to 8 wherein in the third step (6) oxygen, and in particular air, is supplied to the oven. Process according to any one of Claims 1 to 9, in which the materials resting on the hearth of the furnace, such as waste or coke, are mixed, in particular with the aid of rakes present above the hearth, such as rakes or plowshares, for example of steel. Process according to any one of Claims 1 to 10, in which the waste (1) is a mixture of solid, pulverulent and / or liquid waste. Process according to any one of claims 1 to 11, wherein each step (2, 3, 6) takes place respectively in a defined volume inside the furnace. A process according to claim 12, wherein at least a portion of the gases and / or fumes present in the third step (6) are burned at this step (6) and circulate over the defined volumes in the furnace to indirectly heat the content of said volumes. Process according to any one of Claims 1 to 13, in which the waste (1) is chosen from substitute fuels made from household and industrial waste, grinding scrap, sludge from water treatment plants. , the contaminated wood, industrial organic waste, and / or agricultural waste. Rotary hearth furnace for the gasification of organic waste, comprising: an oven enclosure (10) delimited by a bottom (11), a peripheral wall (12) and an upper wall (13), - a rotating hearth (14), above the bottom (11) of the enclosure, rotatable about an axis (15), and intended to receive the waste, said furnace being characterized in that it further comprises an inner wall assembly (17) above the rotary hearth (14), defining three chambers (18a, 18b, 18c) within the enclosure ( 10), around the axis (15) of rotation of the sole.

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