EP0564365B1 - Process and apparatus for thermal treatment of wastes, especially solid wastes containing organic materials - Google Patents

Abstract

The invention relates to the thermal treatment of waste containing organic materials. The waste is gasified in a chamber (1) where the waste passes in succession through a drying zone (1A), a gasifying zone (1B) and an oxidant combustion zone (1C), the total quantity of oxidant gas injected into the chamber being substantially less than the stoichiometric quantity, the gases produced in the three zones are mixed, they are extracted and they are subjected to additional oxidation in several phases, between which several cooling processes by heat exchange are interposed. The invention applies in particular to the treatment of solid waste. <IMAGE>

Description

The invention relates to the thermal treatment of waste, in particular solid, containing organic matter.

It is known (publication FR-A-2 234 521) to carry out a combustion of the waste by using an excess of oxidizing gas relative to the quantity of oxidizing gas which would theoretically be necessary to transform all the carbon of the organic materials of the waste into carbon dioxide ("stoichiometric quantity"), this excess of oxidizing gas serving both for combustion and for controlling temperatures, but the quantities of oxidizing gas required lead to significant gas flow rates, which has the effect of requiring significant gas processing facilities and decrease thermal efficiency due to the calories consumed for heating the oxidant gas.

• 1) qui minimise le volume de gaz produits,
• 2) qui maximise le rendement thermique,
• 3) qui fournit l'énergie nécessaire pour traiter éventuellement les résidus minéraux du traitement thermique.

The object of the present invention is to provide a method for performing a thermal treatment of waste:

• 1) which minimizes the volume of gas produced,
• 2) which maximizes thermal efficiency,
• 3) which provides the energy necessary to possibly treat the mineral residues from the heat treatment.

• on réalise la combustion dans une chambre de gazéification oscillante ou tournante où les déchets traversent successivement une première zone ou l'eau contenue dans les déchets s'évapore sous l'action du rayonnement des parois de la chambre et de la chaleur des gaz ambiants, une deuxième zone où l'on gazéifie la majeure partie du carbone contenu dans les déchets tout en injectant sous les déchets un gaz comburant en quantité très inférieure à la quantité stoéchiométrique, de façon à produire des gaz riches en imbrûlés (oxyde de carbone) à une température de 550° C à 700° C, et une troisième zone dans laquelle on injecte un gaz comburant en excès par rapport à la quantité qui serait théoriquement nécessaire pour transformer la totalité du carbone encore contenu dans les déchets solides à l'entrée de cette zone et de façon à produire des gaz à une température de 800 à 1 200°C, la quantité totale de gaz comburant injectée dans la chambre étant sensiblement inférieure à la quantité stoechiométrique ;
• on mélange les gaz produits dans les trois zones, on les extrait de la chambre, on les soumet à une oxydation complémentaire en plusieurs phases entre lesquelles on intercale plusieurs refroidissements par échanges thermiques.

According to the invention:

• combustion is carried out in an oscillating or rotating gasification chamber where the waste successively passes through a first zone or the water contained in the waste evaporates under the action of the radiation from the walls of the chamber and the heat of the ambient gases, a second zone where most of the carbon contained in the waste is gasified while injecting an oxidizing gas under the waste in an amount much lower than the stoichiometric amount, so as to produce gases rich in unburnt (carbon monoxide) at a temperature of 550 ° C. to 700 ° C., and a third zone into which an oxidizing gas is injected in excess in relation to the quantity which would theoretically be necessary to transform all of the carbon still contained in the solid waste at the entry of this area and in order to produce gases at a temperature of 800 to 1,200 ° C, the total amount of gas oxidizer injected into the chamber being substantially less than the stoichiometric amount;
• the gases produced in the three zones are mixed, they are extracted from the chamber, they are subjected to an additional oxidation in several phases between which several cooling by heat exchanges are interposed.

The gases which are extracted from the chamber are in fact rich in combustible components and in particular in carbon monoxide, since overall the chamber operates under sub-stoichiometric conditions.

In a preferred embodiment, the gases leaving the gasification chamber are subjected, in a first phase to partial oxidation, which raises their temperature, and calories are extracted from the gases thus reheated in a bottom ash and / or liquefier. fly ash and / or in a radiation heat exchanger. A final oxidation is then carried out to remove the residual combustible components, and these gases are cooled in exchangers making it possible to produce steam or superheated water.

An example of implementation of the method of the invention will be described below, with reference to FIGS. 1 to 3 of the attached drawing which are diagrams of various waste treatment installations in accordance with the invention.

• une chambre 1 de gazéification ;
• une première chambre 2 d'oxydation de gaz ;
• un échangeur de chaleur 3 destiné à liquéfier puis vitrifier des résidus (mâchefers et/ou des cendres volantes) ;
• le cas échéant un récupérateur de chaleur en complément ou substitution du liquéfacteur 3,
• une chambre 4 d'oxydation finale des gaz ;
• un échangeur de chaleur 5 par radiation avec des tubes d'eau situés sur les parois ;
• un échangeur 10 à faisceau ;
• un système de neutralisation/filtration des gaz 11 et 12.

The installations each include, in series:

• a gasification chamber 1;
• a first gas oxidation chamber 2;
• a heat exchanger 3 intended to liquefy and then vitrify residues (bottom ash and / or fly ash);
• where appropriate, a heat recovery unit in addition to or substitution of the liquefier 3,
• a chamber 4 for final gas oxidation;
• a heat exchanger 5 by radiation with water tubes located on the walls;
• a beam exchanger 10;
• a gas neutralization / filtration system 11 and 12.

The gasification chamber 1 consists of a boiled assembly animated by an oscillating or rotating movement which comprises, in series on the waste path, a first drying zone 1A, a second gasification zone 1B and a third combustion zone oxidant 1C. In the first zone 1A, the water contained in the waste is evaporated by means of radiative transfers (walls + gas). In zone 1B, most of the carbon contained in the waste is gasified (70 to 80%) while injecting air or other oxidizing agent under the waste in an amount much lower than the stoichiometry. This produces gases rich in unburnt at a temperature of 550 ° C to 700 ° C; this reducing zone benefits from the radiative and convective heat inputs from zone 1C and from those produced by the oxidation in the vault of part of the unburnt products produced in 1B by the excess of oxygen or other oxidizing agent originating from zone 1C .

In zone 1C, the carbon still contained in the solid materials at the entrance to this zone is oxidized to carbon dioxide by sending into this zone an amount of air or other oxidizing agent in excess of that which would theoretically be sufficient to carry out this oxidation; gas is thus produced at a temperature of 800 to 1,200 ° C. This total oxidation makes it possible to obtain clinkers having a very low carbon content and having undergone a significant rise in temperature during this third phase.

The clinkers are extracted at the downstream end of the gasification chamber and are recovered by an extractor 6 and then sent to a liquefier / glazing unit 3 where they are brought to high temperature by the gases coming from the oxidation chamber 2.
A part of the combustible fractions of zone B is oxidized by the excess of oxygen coming from zone C, an overall quantity of oxygen is used sufficient to ensure gasification but lower than stoichiometry so that the temperature of the gases at the output is of the order of 650-1000 ° C, significantly lower than the stoichiometric combustion temperature (1300 ° C-1500 ° C). A good sealing of the joints between the fixed and rotating parts allows control of the average leak rate.

The oxygen required in zones C and B is sent by means of two pressurization systems (14) and (15) to two distribution chambers located around the cell, making it possible to send air and / or l oxygen through distribution channels, in different quantities in the two zones.

The slightly inclined gasification chamber in this example is supplied at the upper end of the chamber with the waste coming from a hopper 7 and the gases are evacuated from the gasification chamber by a gas collection chamber 8 which, in the example of FIG. 1 surrounds the gasification chamber. In variants, this gas collection chamber is situated upstream (FIG. 2) or downstream (FIG. 3) from the gasification chamber and it can then be much less bulky since it does not have to surround the gasification. This collection chamber leads to a first oxidation chamber 2 supplied with oxygen and / or air so as to carry out oxidation of all or part of the combustible fractions contained in the gases while maintaining the temperature at a level of 1100 ° C. at 1300 ° C. This temperature control in the first gas oxidation chamber is carried out by measuring the quantity of oxygen injected into this chamber. The hot gases coming from this oxidation chamber 2 are sent to a liquefaction device 3. This liquefaction is caused by heat exchanges (convection and / or radiation), which decreases the temperature of the gases which are then evacuated through a conduit to the second oxidation chamber 4. The solid products to be liquefied are at a temperature lower than that of the gases, which decreases the temperature of the latter. If desired, there is a heat recuperator intended to lower the temperature of the gases to a sufficient level before the final oxidation phase. in addition to or in substitution for the liquefier.

The bottom ash 6 and / or fly ash 15 introduced into the liquefaction chamber are liquefied under the action of heat transfers (convection + radiation) and flow through the bottom of the room to be evacuated and vitrified. These particles can come from origins outside the installation.

This liquefaction / vitrification device can be followed or replaced by a radiation chamber thus making it possible, in all cases, to lower the temperature of the gases to 800-900 ° C. before carrying out the second oxidation, a process which makes it possible to avoid excessive temperature spikes.

The gases coming from the first oxidation chamber and from the heat exchanges (liquefaction and / or radiation chamber) are generally incompletely burnt since the temperature is limited by limiting the injection of air and / or oxygen. A second oxidation zone is therefore produced in which the necessary supplement of oxygen and / or air is introduced to complete the complete oxidation of the residual unburnt products. Heat recovery is then carried out in chamber 5 by radiation in order to cool the gases to a temperature of 600 to 700 ° C.

The gases are finally sent through heat exchange tubes 10 to produce, for example steam, then in the purification and filtration installations 11, 12 in a manner known per se.

The invention is not limited to these exemplary embodiments.

It is in particular provided, in variants, to use several oxidation chambers before the final oxidation chamber.

The technique of the present invention has significant advantages over prior combustion techniques involving total oxidation in the combustion chamber, since the present invention notably makes it possible to reduce the volume of gases in the stack up to 40% less.

The invention also has advantages over a technique which would only involve pyrolysis in the gasification chamber.

In fact, the pyrolysis conditions in zone 1B benefit from the calories released by the exothermic reaction coming from zone 1C with the lean gases from zone 1B and also benefit from the heating of the gases from zone 1B by radiation from the vault and reheating the gases of zone 1B by radiation from the roof and by mixing these gases with the hot gases coming from zone 1C, which would not be the case in the absence of zone 1C.

In addition, zone 1C makes it possible to complete the transformation of carbon into gas and, unlike pyrolysis systems, allows to have a very small amount of carbon in the bottom ash.

Finally, unlike pyrolysis, the present process makes it possible to obtain much lower temperatures in the final zone, thus avoiding the formation of slag which makes pyrolysis installations difficult to control.

Claims (14)

1. A method of thermal treatment for waste, in particular solid waste, containing organic matter, in which method: the waste is gasified in an oscillating or rotary chamber inside which the waste successively passes through a first zone in which the water contained in the waste evaporates under the action of radiation from the walls of the chamber, and of heat from the ambient gases, and a second zone in which a large portion of the carbon contained in the waste is gasified while an oxidizing gas is being injected under the waste, said method being characterized in that the oxidizing gas is in a quantity that is much lower than the stoichiometric quantity, so as to produce gases that are rich in unburnt components (carbon monoxide) at a temperature lying in the range 550°C to 700°C, the waste further passing through a third zone into which an oxidizing gas is injected in excess of the quantity that would theoretically be necessary to transform all of the carbon still contained in the solid waste at the input of the zone, and so as to produce gases at a temperature lying in the range 800°C to 1,200°C, the total quantity of oxidizing gas injected into the chamber being substantially lower than the stoichiometric quantity; and
      the gases produced in the three zones are mixed together, they are extracted from the chamber, and they are subjected to complementary oxidation in a plurality of stages interspersed with cooling stages during which they are cooled by heat exchange.
2. A method according to claim 1, characterized in that the quantity of oxidizing gas sent to said second zone of the gasification chamber lies in the range 40% to 60% of said stoichiometric quantity.
3. A method according to claim 1 or 2, characterized in that in the range 70% to 80% of the carbon contained in the waste is gasified in said second zone.
4. A method according to any one of claims 1 to 3, characterized in that the quantity of oxidizing gas sent to said third zone exceeds by in the range 25% to 40% the quantity required to transform all of the carbon contained in the solid waste at the input of the zone into carbon dioxide.
5. A method according to any one of claims 1 to 4, characterized in that the operating conditions in the gasification chamber are set so that the gases extracted from the chamber are at a temperature lying in the range 650°C to 1,000°C.
6. A method according to any one of claims 1 to 5, characterized in that air is used as the oxidizing gas.
7. A method according to any one of claims 1 to 6, characterized in that the gases output by the gasification chamber are oxidized in part during a first stage, thereby increasing their temperature, heat is extracted from the heated gases, final oxidation is performed so as to eliminate the residual combustible components, and the gases are cooled in heat exchangers enabling steam or super-heated water to be produced.
8. A method according to claim 7, characterized in that the oxidation conditions during the first oxidation stage are set so as to maintain the temperature of the gases in the range 1,100°C to 1,300°C.
9. A method according to claim 7 or 8, characterized in that the temperature of the gases is lowered to in the range 800°C to 900°C before a second oxidation stage is performed.
10. A method according to any one of claims 7 to 9, characterized in that heat is extracted from the gases from the first oxidation stage in a radiation heat exchanger.
11. A method according to any one of claims 7 to 10, characterized in that the gases from said first oxidation are used for liquefying clinker and/or fly ash.
12. An installation for implementing a method according to any one of claims 1 to 11, the installation including an oscillating or rotary gasification chamber (1) fed with waste and inside which the following zones are constituted in series along the path of the waste: a drying first zone (1A), a gasification second zone (1B), and an oxidizing combustion third zone (1C), means (14, 15) for injecting an oxidizing gas under the waste in the second and third zones (1B and 1C), means (8) for collecting the gases from the chamber, a first oxidation chamber (2) fed with oxidizing gas, receiving the collected gases, and oxidizing them in part, means (3) for performing heat exchange with the oxidized gases, and a final oxidation chamber (4) fed with as much extra oxidizing gas as is necessary to complete the oxidation of the residual unburnt components.
13. An installation according to claim 12, characterized in that the means (8) for collecting the gases from the gasification chamber comprise a collecting chamber (8) placed upstream from, downstream from, or around the gasification chamber.
14. An installation according to claim 12 or 13, characterized in that said final oxidation chamber (4) is followed by a radiation heat-recovery chamber (5).

Images