EP0685550A1 - Process and plant having a preheating unit for the pyrolysis of waste - Google Patents

Abstract

In a pyrolysis installation with a rotary pyrolysis furnace (1), the furnace (1) is connected by a sealed connection (10) to an upstream solids preheating arrangement (2) having at least two zones (2a,b) in which the solids are preheated to different temps., and a gas extraction device (12), into which pyrolysis gas passes after passage through at least one of the zones (2a,b). Also claimed is a solids pyrolysis process involving preheating the solids to different temps. and self-cleaning of the pyrolysis gas by percolation relative to the preheating stage. <IMAGE>

Description

The present invention relates to the field of heat treatment of solid materials, and more particularly pyrolysis (or thermolysis) furnaces intended to treat solids such as industrial and / or household waste.

Most known ovens or installations consist of an oven, fixed or rotating, equipped with heating means mostly located outside the oven.

French patent application FR 2 668 774 describes a cylindrical oven which rotates around a horizontal axis and which is heated by burners located in an annular space around the oven.

This type of installation proves to be a major energy consumer since it is necessary to bring to temperatures up to 800 ° C a very large mass of solids.

The present invention aims to improve in particular but not exclusively this type of rotary kiln, by essentially reducing energy needs, costs, and by simplifying the general design of the installation.

Specifically, the present invention allows self-purification of the pyrolysis gases, as will be explained below.

The present invention advantageously makes it possible to treat waste of very variable nature and humidity.

Flexibility and modularity in operation are also obtained according to the invention.

To achieve the aims and advantages set out above, the present invention relates to an installation intended for the pyrolysis of solids comprising a rotary kiln inside which the pyrolysis is carried out and a means for heating the rotary kiln.

According to the invention, the installation further comprises a means for preheating the solids disposed upstream of said furnace, said means comprises at least two zones in which the solids are preheated to different temperatures, and a device for extracting the gases in which the pyrolysis gases are brought after having passed through at least one of said zones of preheating, a sealed connection being also provided between said rotary kiln and said preheating means

Advantageously, the installation further comprises means intended to individually regulate the temperature in each preheating zone and in said rotary oven.

Preferably, the temperature inside said preheating means is adjusted so as to always be lower than a given temperature T₀.

Without departing from the scope of the invention, the device for extracting the pyrolysis gases is disposed between two preheating zones, relative to the direction of propagation of the solids in the installation.

According to one embodiment of the invention, the extraction device also allows the separation and / or the evacuation of certain solids.

More specifically, the preheating means can be tubular, of substantially horizontal axis and include at its end associated with the connection with the furnace, a narrowing.

The installation according to the invention may also comprise means placed upstream of said rotary kiln, intended for injecting a basic element into the solids.

According to the invention, a device intended to evacuate the pyrolysis gases in the event of an emergency can also be provided.

The present invention further relates to the pyrolysis process associated with the installation.

The application to the pyrolysis of industrial and / or household waste is more particularly targeted by the invention.

Other characteristics, advantages and improvements will appear on reading the description which follows, given by way of illustration and in no way limiting, of an embodiment of the invention, with reference to the single appended figure.

This figure indeed shows schematically, by a longitudinal section, an installation according to the invention.

The installation comprises a rotating part 1, preceded by a means of preheating the waste, of elongated shape and substantially cylindrical 2, said means 2 being supplied with waste from a hopper 3 via a transfer line 4.

The waste from the hopper 3 is dosed, compacted and then pushed into the transfer line 4 by a pusher 5 or any other device known to those skilled in the art which can perform the same function.

The waste enters a first zone 2a of the preheating means 2. The waste can be heated there indirectly by a heating jacket 6a swept by a hot fluid supplied by a line 7a or by the combustion of a fuel suitable for inside said envelope.

The first zone 2a of the preheating means is used to remove a good part of the moisture contained in the waste, and to preheat it to a temperature between 50 and 150 ° C, and preferably between 60 and 90 ° C.

Preferably, the temperature of the waste leaving the zone 2a is measured using a probe 8a, and the information obtained serves to regulate the heat input to the heating jacket 6a.

The heating of the waste then continues in a second zone 2b of the preheating means 2 according to a process substantially equivalent to that of the first zone 2a, that is to say with a heating jacket 6b supplied with hot fluid by a line 7b . In the second zone 2b, the moisture remaining after the first zone 2a is eliminated, and the waste is brought to a temperature of between 100 and 500 ° C., preferably between 140 and 200 ° C.

The temperature at the outlet of the second zone 2b is advantageously controlled by means of a probe 8b and the information obtained is used to regulate the heating means 6b.

The end 9 of the second preheating zone 2b is connected to the rotating part 1 by means of a seal 10. The end 9 may be provided with a narrowing 11, intended to maintain a flow of waste compact inside the transfer line 4 and in the preheating pipe 2.

Between zones 2a and 2b, at the level of a zone referenced 2c is a gas extraction device 12, a priori unheated, but thermally insulated.

This extraction device 12 receives the water vapor produced by the waste in parts 2a and 2b and the pyrolysis gases produced in the rotating cylinder 1, after they have passed against the current bed of waste in zone 2b.

To perform this function, the extraction device 12 includes means 13 such as porous surfaces, orifices, grids, or any other equivalent means, allowing the passage of gases from part 2c of the preheating pipe to said device. extraction, without entailing significant quantities of solid matter.

The pyrolysis gases and the water vapor are then evacuated from the device 12, by means of a line 14, while the possible solids accompanying the gases, can be separated from the gases by sedimentation in the device 12 or by any other means. known to those skilled in the art, then evacuated by a line 15.

After leaving the preheating means 2, the waste falls by gravity into the rotating cylinder 1 to form a bed 20. The rotating cylinder 1 is more or less inclined, depending on the inventory and the desired solids flow rate.

This rotating cylinder 1 can be heated by means placed outside such as burners using for example pyrolysis gases, or by means 21 placed directly inside the rotating cylinder as illustrated in the single appended figure. In this case, the heating means 21, mounted on a fixed part 22 can be constituted for example, by a tubular bundle in which combustion of a fuel such as natural gas or pyrolysis gases is freed of the essentials. tars and particles. The tube bundle can also be supplied with a hot fluid obtained for example by heating air in the boiler which burns the pyrolysis gases. The fixed part 22 is connected to the rotating part 1 by means of a seal 23 which ensures perfect gas tightness between the atmosphere prevailing in said cylinder 1 and the outside.

Advantageously, the fixed part 22 can be equipped with a device 24 intended for the emergency evacuation of the pyrolysis gases, in the event that the flow of the pyrolysis gases is severely braked or can no longer take place in the tubing. 2b or else in the extraction device 12.

In the rotating cylinder 1, the waste is treated at temperatures between 150 and 900 ° C, and preferably between 400 and 600 ° C. The waste progresses from the entrance to the fixed part 22. The resulting solid phase is concentrated in the part 22a, then evacuated by a line 25.

A hopper 26 intended for injecting a basic (absorbent) element into the waste can also be mounted on the preheating means 2, preferably in the zone 2a.

It will be understood that the advantage of the preheating tubing (or means) is to dry the waste, then to heat it to a temperature close to but below the temperature T₀ from which the waste emits toxic substances such as chlorinated products, substances that absolutely must be trapped in the solid phase present in the rotating part.

It is important that the gas phase in the rotary kiln 1 is homogeneous, and it could be advantageous to employ means known to those skilled in the art to intensify the circulation of gases in said rotary part and to improve the mixing of the gases and solids.

Furthermore, it is important to note that when the pyrolysis gases percolate through waste in part 2b of the preheating pipe, they participate in the heating of the waste. The lowering of the temperature of the pyrolysis gases in this part leads to the condensation of the tars and the trapping of certain acidic compounds such as hydrochloric acid by basic substances added voluntarily to waste or which, more generally, accompany most industrial and household waste. There is also a retention of the finest particles in the waste bed. The result of this phase of "filtration" by the bed of waste, is a gas, freed from its polluting elements, tar and dust, a gas which can for example be reused immediately in the heating device 21.

The originality of the device according to the invention can be illustrated by the following example:

Household waste is treated with a device identical to that of the appended figure. The waste is 30% moisture. The settings of the three heating zones are such that the temperatures are respectively 100, 150 and 500 ° C at the outlet of parts 2a, 2b and 1. When the waste is in part 2c, they have lost approximately 50% of their humidity . Excluding thermal losses, the energy inputs at the devices 6a, 6b and 21 are respectively 0.523, 0.268 and 0.368MJ / kg of treated waste.

In the case of a conventional rotary kiln without preheating pipe, the energy requirements would be 1.52 MJ / kg of waste. It is therefore noted, still excluding thermal losses, that the proposed system allows an overall energy gain of 25%, and that the energy consumption at the rotating part no longer represents more than 25% of what it is with the oven. traditional turning point.

• une auto-épuration des gaz de pyrolyse par percolation de ceux-ci au travers du lit de déchets 2b présent dans le moyen de préchauffage avec notamment une élimination des goudrons par condensation (ceux-ci peuvent faire quelques aller et retour entre la partie tournante et la tubulure de préchauffage, mais ils finissent par être craqués thermiquement), avec fixation des composés acides résiduels non piégés au niveau de la partie tournante et avec élimination de l'essentiel des fines particules entrainées par le gaz, par filtration au travers du lit de déchets dans la tubulure de préchauffage;
• un abaissement des besoins énergétiques de l'opération grâce à l'utilisation d'une bonne partie de la chaleur sensible des gaz de pyrolyse pour le chauffage des déchets d'une part, et grâce à une diminution sensible de la taille de la partie tournante du dispositif, principale source de pertes thermiques, d'autre part;
• une diminution des coûts et une simplification des problèmes de construction réalisées notamment grâce à une diminution sensible des dimensions du cylindre tournant par rapport aux systèmes traditionnels;
• une possibilité de traiter des déchets de nature et d'humidité très variables grâce à la présence de plusieurs zones de chauffage (2a, 2b, 1) réglées indépendamment les unes des autres.

From the above it appears that the most significant advantages of the device according to the invention are the following;

• self-purification of the pyrolysis gases by percolating them through the waste bed 2b present in the preheating means with in particular elimination of the tars by condensation (these can go back and forth between the rotating part and the preheating tubing, but they end up being cracked thermally), with fixing of the non-trapped residual acid compounds at the level of the rotating part and with elimination of most of the fine particles entrained by the gas, by filtration through the waste bed in the preheating pipe;
• a reduction in the energy needs of the operation thanks to the use of a good part of the sensible heat of the pyrolysis gases for the heating of the waste on the one hand, and thanks to a significant reduction in the size of the rotating part the device, the main source of heat loss, on the other hand;
• a reduction in costs and a simplification of the construction problems achieved in particular thanks to a significant reduction in the dimensions of the rotating cylinder compared to traditional systems;
• a possibility of treating waste of very variable nature and humidity thanks to the presence of several heating zones (2a, 2b, 1) regulated independently of each other.

Claims (11)

1) Installation intended for the pyrolysis of solids comprising a rotary kiln (1) inside which the pyrolysis is carried out, a means (21) for heating the rotary kiln, characterized in that it further comprises a means (2 ) for preheating solids disposed upstream of said furnace, in that said means (2) comprises at least two zones (2a, 2b) in which the solids are preheated to different temperatures and a device (12) for extracting gases in which the pyrolysis gases are supplied after having passed through at least one of said preheating zones (2a, 2b), and in that a sealed connection (10) is provided between said rotary oven (1) and said means of preheating (2). 2) Installation according to claim 1, characterized in that it further comprises means (8a, 8b) for individually adjusting the temperature in each preheating zone (2a, 2b) and in said rotary oven (1). 3) Installation according to claim 2, characterized in that the temperature inside said preheating means is adjusted so as to always be below a given temperature T₀. 4) Installation according to any one of the preceding claims, characterized in that the device (12) for extracting the pyrolysis gases is disposed between two preheating zones (2a, 2b) relative to the direction of propagation of the solids in the installation. 5) Installation according to claim 4, characterized in that the extraction device (12) also allows the separation and / or the evacuation of certain solids. 6) Installation according to any one of the preceding claims, characterized in that the means (21) for heating the rotary kiln is arranged inside said oven (1). 7) Installation according to any one of the preceding claims, characterized in that the preheating means (2) is tubular, of substantially horizontal axis and comprises at its end (9) associated with the connection (10) with the furnace ( 1), a narrowing (11). 8) Installation according to any one of the preceding claims, characterized in that it further comprises a means (26) placed upstream of said rotary kiln, intended to inject a basic element in the solids. 9) Installation according to any one of the preceding claims, characterized in that it further comprises a device (24) intended to evacuate the pyrolysis gases in the event of an emergency. 10) Process for the pyrolysis of solids comprising a pyrolysis step obtained by heating said solids, characterized in that it further comprises a preliminary preheating step carried out at several different temperatures, and a self-purification of the pyrolysis gases carried out by percolation said gases relative to the preheating step. 11) Application of the method according to claim 10 and of the installation according to any one of claims 1 to 9 to the pyrolysis of industrial and / or household waste.

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