EP0932798B1 - Method and device for heat treatment of waste products - Google Patents

Abstract

An apparatus and method are for the pyrolysis of waste. The aparatus has a rotating cell formed of a cylinder in combination with a truncated cone rotating on the same axis. The apparatus also has a hopper for charging the waste at one end of the cylinder, an ash box at the other end of the cylinder, a gas recuperator, and a retaining threshold between the cylinder and the truncated cone. A region of intimate contact of the waste with itself is created, whereby the waste is converted into coke which is used as fuel in the pyrolysis of the waste.

Description

The subject of the present invention is a method of heat treatment of waste, especially waste household and industrial, but not exclusively, and installation for its implementation of the kind including a rotating combustion cell in which are introduced waste by a loading end, while at the other end are collected the slag, while the gases are recovered upstream or downstream of the cell, as described in document-WO-A-8 802 284.

Currently, in this kind of rotary kiln, the waste is put into exothermic combustion by air supply oxidizer which has the effect of carrying out the combustion of all the hydrocarbons contained in the wastes including brewing, during their movement to the ashtray, is ensured by the rotation of the cylindrical hearth and / or conical.

At this stage of combustion, the gases are burned at 99% and bottom ash has a content of unburnt from 2 to 10% under form of carbon.

The reduction by oxidation of almost all of the hydrocarbons results in high temperatures of over 1200 ° C for waste with calorific value lower (PCI) average of 2000 Kcal / kg, temperatures which can reach over 1400 ° C with PCI waste from 3500 Kcal and more.

1- Les poussières, mises en suspension par l'aération forcée des déchets se trouvant dans les fumées, fondent et se déposent sur les parois du four et de la chaudière.

2- Les mâchefers sont aussi en fusion et s'agglomèrent aux parois.

These high temperatures cause the following phenomena:

1- The dust, suspended by the forced ventilation of the waste in the smoke, melts and settles on the walls of the oven and the boiler.

2- The bottom clinkers are also in fusion and agglomerate on the walls.

To avoid these phenomena, there is only one solution, introduce excess air, air which does not participate not combustion, but whose role is to temper the combustion temperatures around 850-900 ° C.

1- Il réclame de l'énergie pour être produit et extrait.

2- Le volume de fumées généré est plus important et nécessite des circuits de gaz de plus grandes sections et volumes.

3- Les éléments toxiques et polluants, se trouvant dans les déchets, sont entraínés dans presque leur totalité dans les fumées et nécessitent un dispositif plus volumineux et plus complexe pour les capter.

4- La réglementation internationale étant de plus en plus contraignante, elle impose des températures des combustions des fumées supérieures à 1150°C et des teneurs en polluants et poussières très basses, lesquels sont plus particulièrement générés par la combustion avec excès d'air.

5- Les fumées produites à 900°C permettent seulement un rendement de 60 à 65% en récupération de chaleur, alors qu'il est souhaitable d'atteindre 80 à 85%.

6- Dans un foyer travaillant avec de l'air en excès, il est très difficile, sinon impossible, de maítriser l'apport énergétique fourni par des déchets de PCI supérieur à 3500 Kcal/kg.

However, this excess air has the following drawbacks:

1- It requires energy to be produced and extracted.

2- The volume of smoke generated is greater and requires gas circuits with larger sections and volumes.

3- The toxic and polluting elements, found in the waste, are entrained almost in their entirety in the fumes and require a larger and more complex device to capture them.

4- International regulations are becoming more and more restrictive, it imposes smoke combustion temperatures above 1150 ° C and very low levels of pollutants and dust, which are more particularly generated by combustion with excess air.

5- The fumes produced at 900 ° C only allow a yield of 60 to 65% in heat recovery, while it is desirable to reach 80 to 85%.

6- In a home working with excess air, it is very difficult, if not impossible, to control the energy supply provided by PCI waste higher than 3500 Kcal / kg.

To overcome these drawbacks, we imagined a new heat treatment process using the pyrolysis which allows, in the absence of oxygen, to distill all low temperature waste in the range of 600 to 700 ° C whatever their PCI.

This new process also aims to produce gases fuels rich in CO, CH4, various tars which are burnt at 1200 ° C in self-combustion in a room specific. These weakly charged gases pollutants due to low temperatures, require treatment whose complexity and dimensions are significantly lower than incineration.

To implement this process, the installation includes a rotating cell composed of a cylinder and of a truncated cone rotating on the same axis.

Pyrolysis takes place in the cylindrical part of the cell and, as it is greedy in energy, this is supplied by the coke produced by itself and whose combustion takes place in the truncated cone defined as being the pyrolysis heat generator. The reduction thermal, pyrolysis / combustion of coke, takes place at countercurrent, the gases produced circulating against the current solids.

To allow pyrolysis, it is necessary to have in the cell an area in which the waste during distillation is heated by energy thermal from the aforementioned generator. Has a certain stage of their heating, the waste needs to be intimately brought into prolonged contact to be processed into coke.

The fundamental characteristic of the installation of heat treatment of the waste in question, resides basically in the fact that it has this area of intimate contact with waste determined by a threshold of reserved retainer between the cylindrical part and the part frustoconical of the rotating cell.

Indeed, crossing this threshold obliges the waste, during coking, to form a volume of which the constituents are brought into close contact with each other, while receiving some oxygen. At this time, the waste reaction temperature is approximately 700 ° C. This restraint, artificially created by the threshold, allows obtaining a coke which serves, in the cone generator, to fuel to provide the hot gas flow needed to pyrolysis.

In this cone, in the known manner, the combustion air is distributed under ignition coke by a network of nozzles fed by channels.

The invention is described below using an example and references to the attached drawing in which:

The single figure is a schematic view of the waste heat treatment installation according to the invention.

In the drawing, the reference 1 designates the rotating cell rotated by schematic mechanical means under references 2.

Upstream of cell 1, arrow 3 indicates the waste loading hopper fitted with a flap 4 and a push button 5.

The pyrolysis gas recovery chimney is designated by the reference 6.

Downstream of cell 1 is arranged an ashtray 7 for the evacuation of slag or coke symbolized by the arrow 8.

It goes without saying that the accessories and others devices such as the loading hopper, the recovery or even the ashtray, are known elements which are chosen according to the results to be obtained.

The rotating cell 1 is constituted, according to the invention, of a cylindrical part 9, constituting the pyrolyzer, associated with a frustoconical part 10 forming the generator. Between cylinder 9 and truncated cone 10 is reserved a zone 11 connecting the end 12 of the cylinder 9 and the large base 13 of the truncated cone 10. This zone 11 constitutes a waste retention threshold affecting a significant taper resulting from the difference in diameter between the cylinder 9 and the truncated cone 10.

In the frusto-conical part 10, a network of nozzles supplied by air distribution channels of combustion. Arrows 14 symbolize this air supply.

• La production d'un gaz de pyrolyse au PCI de 900 à 1100 Kcal/Nm3, faiblement pollué et à haut taux de valorisation s'opérant dans les meilleures conditions.
• Un respect des normes antipollution les plus exigeantes avec des moyens réduits.
• Une réduction sensible du volume et des coûts des équipements.

We can see that thanks to this solid waste treatment installation at PCI ranging from 1500 to 10,000 Kcal / kg, we obtain:

• The production of a pyrolysis gas at PCI from 900 to 1100 Kcal / Nm3, slightly polluted and with a high recovery rate, operating under the best conditions.
• Compliance with the most demanding anti-pollution standards with limited resources.
• A significant reduction in the volume and costs of equipment.

Claims (4)

1. Waste heat treatment method in which pyrolysis is carried out to distil at a low temperature (600 to 700°C) with no oxygen present all the combustible waste regardless of their lower calorific power (LCP) and to produce coke and combustible gases rich in CO, CH4 and miscellaneous tars able to be then burnt at 1200°C on self-combustion in a specific chamber, characterised in that the hot gas flow required for pyrolysis of the waste during distillation is provided by combustion in the absence of air of the coke in a contact zone close to the waste, the gases produced circulating counter to the solids.
2. Waste heat treatment installation for implementing the method according to claim 1 and including a rotating cell (1) formed of a cylinder (9) associated with a truncated cone (10) rotating on the same axis and comprising a waste loading hopper (3) at one extremity, an ash pan (7) at the other extremity and a gas recuperator (6), characterised by the fact that a retention threshold (11) is reserved between the cylindrical chamber (9) and the truncated chamber (10) creating the contact zone close to the waste during coking where the latter receives a small amount of oxygen in a sub-stoichiometric quantity to transform it into coke acting as a fuel on pyrolysis of the waste.
3. Installation according to claim 2, characterised by the fact that the threshold (11) for retaining the waste embodying the link of the cylinder (9) and the truncated cone (10) is constituted by the difference of diameter (12) between the cylinder (9) and the diameter (13) of the large base of the truncated cone (10).
4. Installation according to claim 2, characterised by the fact that the truncated cone (10) of the cell (1) comprises a network of nozzles fed by channels distributing the combustion air (14) in a sub-stoichiometric quantity under the coke on ignition so as to provide the heat flow required for pyrolysis.

Images