EP2679658A1 - Vitrification of inerts and purification of the gas from the pyrogasification of waste - Google Patents

Abstract

The method involves introducing a bubbling tub (2) containing melted mineral compounds, into a chamber (1), where the mineral compounds is maintained at temperature of about 1100/1400 degree Celsius. The tub is in contact with fuel gas flow and solid particles in suspension. The solid particles are collected and melted in the tub. The mineral compounds are continually removed from the tub having integrated solid particles, and vitrified by contact with a cold liquid such that purified fuel gas is recovered at an outlet of the chamber. An independent claim is also included for a fuel gas purifying plant.

Description

The present invention is in the context of the thermal treatment of waste by pyrogasification and more particularly relates to the vitrification of the mineral fractions of said waste and the purification of the gas produced.

It is already known from the patent document FR 2763341 to treat waste by pyrogasification to recover its energy. In a first step the waste undergoes in a gasification reactor equipped at its base with an atmospheric fluidized bed, at a temperature of the order of 600 ° C, a transformation into lean gas type fuel gases. This gas also causes the mineral fraction of waste whose particle size gradually decreases due to attrition to which they are subjected in the fluidized bed. In a second step, combustion of the gases produced previously, carried out with a small excess of air, takes place in a combustion chamber downstream of the gasification reactor. The adiabatic temperature reached during this combustion, exceeding 1250 ° C, melts the solid residues which are removed by flow and cooled by quenching. This produces vitrified granules which can be used eg. in the construction of roads.

Simultaneously effecting the combustion of the gas and the melting of the inerts it contains requires having a combustion chamber whose volume is large enough to have a residence time necessary for the heating and the melting of the particles. whose size is determined by the fluidization rate of the gasification reactor.

This chamber must also have a refractory coating resistant to the erosion of molten minerals brought to a very high temperature. These constraints have a not insignificant impact not only on the cost of the equipment but also on that of their maintenance.

In addition the range of waste treated is limited by the technical possibilities of the gasification reactor, in particular a high rate of inert is penalizing and some materials such as reinforcements tires are not allowed.

Finally, the two process steps are closely related, making the possibility of independent operation relatively complex.

Moreover, it is also known from the patent document EP 2265697 , to produce a combustible gas directly from solid waste that may contain biomass, which may also contain metals, including iron such as used tire reinforcements, automotive grinding residues (ABR), sludge, combustible materials substitution (MCS). For this purpose, the waste is brought into contact with a bath of molten silicates in the presence of a gas containing water vapor, oxygen or CO2, which makes it possible, thanks to this addition of oxidant, to gasify a portion garbage. The optimum temperature of the silicate bath is maintained in particular by means of burners immersed in said bath. The iron of the waste dissolves in the molten silicate without precipitating to the extent that said silicate is renewed continuously before reaching its saturation Fe.

But this process remains economically unsuitable for waste low inert content, especially those containing a lot of biomass or plastics.

The present invention aims at the possibility of treating various wastes, in particular that can contain a lot of inerts, in order to be able to recover a maximum of energy by acting on the lean gas before combustion to separate the interes and then vitrify them and this at a temperature regime adapted to the needs of vitrification. This treatment thus concerns a flow rate of gas which does not represent more than 15% of the flow rate of fumes used for vitrification in the case of the integrated prior art pyrogasification / combustion / vitrification process in which the inerts are only eliminated completely. end of operation. In this way the combustion of the clean gas can then be carried out under optimum conditions, further facilitating the final treatment of the fumes.

It also aims to produce vitrified granules that can have characteristics adapted to the particular uses that can be envisaged.

It also aims flexible operating systems, able to adapt to different types of waste, each of the elements can work alone for particular categories of waste, said various elements being also able to combine their operation as needed.

The present invention also makes it possible to widen the range of usable gasification means.

To this end, it proposes a process for purifying a combustible gas resulting from a pyrogasification of waste operations melting the solid particles suspended in said gas and then eliminating them by vitrification, characterized in that it constitutes a separate treatment step. a subsequent step of operating the combustible gas and comprising the introduction into a chamber containing a bath of molten inorganic compounds, the flow of combustible gas laden with residues comprising heavy organic compounds or tars and solid particles in suspension, the melting of the solid particles and the cracking of the tars under the effect of the temperature in the enclosure, the bath capture of the molten residues, the continuous elimination of the compounds of the bath having integrated the residues then the recovery in outlet of the purified fuel gas chamber.

It proposes to introduce the flow of charged combustible gas into its residues in an orientation substantially perpendicular to the surface of the bath of molten inorganic compounds.

The bath can be kept bubbling at a temperature of the order of 1100/1400 ° C. under the effect of burners immersed in the bath.

The invention also proposes to be able to introduce additional waste directly into the chamber, to put it in contact with the bath in which they abandon their inert materials and metals, and under the effect of heat undergo gasification, partial or total , thus generating additional fuel gases that help maintain the bath temperature. This possibility of introducing additional waste is, however, only optional.

Additions of oxidizing gases can be made through the hearth of the enclosure.

The partial oxidation of the additional waste introduced into the enclosure can contribute to the maintenance of the temperature of the bath.

The invention further proposes to take advantage of the residues captured in the bath to produce exploitable vitrified granules as by-product recyclable by adapting the composition of the bath to achieve the composition required by the intended use. The composition of the molten bath can therefore be adapted to produce, by vitrification, exploitable vitrifiats.

The invention also proposes an installation allowing both this purification of the fuel gas manufactured and the production of exploitable vitrifiats, separated and upstream from the operating means of the fuel gas.

Thus, the invention also relates to an installation for purifying a combustible gas laden with solid particles in suspension and tars, produced by pyrogasification of waste, characterized in that it is separate and upstream from the means for exploiting the gas. fuel and comprising an enclosure containing a bath of molten inorganic compounds maintained at a temperature of about 1100/1400 ° C, a feed line for the flow of combustible gas and residues in suspension, a device for introduction of solids to renew the mineral compounds of the bath, an overflow to maintain constant the level of said bath and an evacuation of the purified combustible gases out of the enclosure.

The flow supply line of the combustible gas and suspended residues may be oriented substantially perpendicular to the surface of the bath.

The overflow can drain into a vitrification tank containing water to form granules vitrifiats by sudden cooling.

The invention will now be described in more detail with reference to the attached figure which represents an installation according to the invention.

The installation according to the invention shown in the attached figure comprises an enclosure 1 enclosing a whirlpool 2 of molten inorganic compounds, supplied at its upper part by a supply pipe 3 directed substantially perpendicularly to the surface of the molten bath 2 which transports the output stream of a pyrogasification previously not shown, fixed bed or fluidized, or tank reactor, or other. The distance between the upper part of the chamber and the surface of the bath 2 is generally of the order of 1 m but can also be larger and be of the order of 3 m. Advantageously, this pipe 3 passes through a preheating chamber 4. The output stream of a pyrogasification can comprise combustible gases, residues containing solid particles which constitute the mineral fraction of the initial waste, tars which depending on the temperature are in gas phase or in the form of particles in suspension. The bath 2 of inorganic compounds is at a temperature of the order of 1100/1400 ° C .; it is continuously renewed and maintained at a constant level thanks firstly to a solids introduction device 5, in particular an endless screw or a piston device, opening into or on the bath 2 and also on the other hand to a means of evacuation such as an overflow 6. The mineral compounds of the bath 2 may be mainly silicates, cullet, ashes. The bath 2 is maintained at the required temperature by burners 7 immersed in the bath 2, passing through the hearth of the chamber 1, supplied with fuel gas and oxidizing gas necessary for their operation. Additional feeds 8 of oxidizing gas passing through the hearth of the enclosure 1 may also be added. A gas evacuation 9 is provided through the roof of the enclosure 1, preferably in a zone opposite the arrival of the feed pipe 3 of products from the prior pyrogasification. The overflow 6 is connected hermetically to a cylinder 10 which is immersed in a vitrification tank 11 filled with coolant, in particular water, intended to cool and vitrify the molten solids extracted from the enclosure 1 and a extraction device 12, of the conveyor or worm type, spring of this tray 11 vitrifiats so produced. This cylinder 10 prevents the introduction of air into the system or gas leaks. The device 5 for introducing the solids allowing the initial filling of the bath 2 with mineral compounds also makes it possible to renew said compounds, the correction of the composition of this bath 2, in particular to modify if desired the composition of the vitrifiats, also serves, if desired, to introduce in the enclosure 1 other waste, in particular biomass, RBA, tires with their metal carcass, by-products of combustion and incineration etc ... which are not compatible with pyrogasification preliminary and / or used to introduce combustible waste which by combustion supplement or provide thermal inputs to the bath 2. It is to take advantage of this possibility of introducing additional waste that additions of oxidizing gas, in addition to that who is necessary for the operation of the submerged burners for their thermal input to the bath 2, are provided through the feeds 8 so as to achieve the gasification / combustion of this waste. The device 5 can also gather the products from several pyrogasification reactors or other facilities, for introduction into the plant according to the invention. The evacuation 9 of the gas supplies one or more devices for exploiting extracted gases such as direct heating installations (combustion chamber, baking oven, dryers, heat exchanger, etc.). Given the high degree of purification in solid residues operated by the bath 2, the gas can, by means of a possible simplified complementary purification treatment, directly supplying heat engines or gas turbines in particular for the production of electricity, in which the extracted gases constitute the fuel. These extracted gas operating devices are not shown separately or in detail but referenced 13 whatever they are.

This installation according to the invention operates from the flow of products from one or more pyrogasification reactors whatever they are and to this freedom of choice as for the previous gasification step, the invention adds its own independence and its own flexibility of operation.

The installation described above works as explained below.

Waste, in general the non-recyclable fraction of industrial and urban waste, including those containing or consisting of biomass, subjected to pyrogasification, generate combustible gases and solid residues in suspension at a relatively low temperature of the order of 600 ° C which are introduced into the installation of the invention by the supply line 3 in a direction substantially perpendicular to the surface of the liquid 2 composed of molten minerals. which forces the solid residues introduced or what remains after their melting during their journey in the chamber 1 to impact said bed 2 and interact with it. During the passage of the preheating chamber 4, a thermal contribution can be made to raise the temperature of the gases charged with residues. Thanks to the submerged burners and possibly additional injections of oxidizing gas, preferably oxygen or enriched air, through the sole of the chamber 1 which produce a stirring of molten minerals, this bed 2 is bubbling, which further enhances its interaction with the solid residues introduced. This bed 2 is maintained at the temperature required by the composition of the products to be treated (of the order of 1100/1400 ° C) by the submerged burners; it captures the melts of the solid particles carried by the gas, generated by the upstream pyrogasification and the bottom or melts them in case they are not or not completely melted during their impact with it. If the heat input into the preheating chamber 4 has not been sufficient to crack all the tars, the heat of the chamber 1 and the bath 2 completes this action. Complementary waste, either incompatible with the preceding pyrogasification, or necessary to constitute or complete the bed 2 of mineral compounds, or again to modify the composition of the bed 2 are also possibly introduced directly into this chamber 1 by the device 5 for introducing the solid. This waste can be waste whose characteristics do not justify or are not suitable for the pyrogasification practiced previously (rate of inertness too high, presence of certain mineral fibers, etc ...). These can be biomass, complementary urban waste, RBA, MCS, used tire waste including metal carcasses, smoke treatment residues, waste electrical and electronic equipment (WEEE), etc. This waste contributes, by their total or partial oxidation, to the maintenance of the temperature of the bath 2 and of the enclosure 1, so that the operation of the submerged burners can, depending on the energy released, be reduced or even interrupted. bubbling state of the bed 2 remaining then maintained by the injection of oxidizing gas through the feeds 8. If this reaction generates gas they are added to the gases initially introduced into the chamber 1 by the supply line 3. The solid residues from the preceding pyrogasification and introduced into the chamber 1 in suspension in the gas stream, to which are added the solid residues from newly introduced complementary waste produced by the device 5, are melted or destroyed by the heat of the enclosure 1 and end up being captured by the bubbling melt bed 2 of inorganic compounds. The bath 2 being continuously renewed, it can dissolve the metal compounds, especially iron, without there being any precipitation of metal, the renewal being done at a rate such that the dissolution limit is not reached. Metal precipitation is avoided by adjusting the flow of oxidizing gas injected by the gas feeds 8. This liquid bath 2 also picks up all the dust so that the gas that escapes through the evacuation 9 is purified to such a point that it can by means of a simplified complementary purification treatment feed a heat engine, alone or in mixture with a supplement of natural gas.

As and when the installation operates, the initial molten bath 2 is replaced by ashes and inert whose composition depends on the type of waste introduced. The level of the bath 2 is kept constant by the flow through the overflow 6 to the devitrification tank 11 which ensures by quenching with water the vitrification and the recovery of all the inerts which passed through the installation, under pellet form of vitrifiats, those from the prior pyrogasification, those from the complementary introduction of waste by the device 5 and possibly those from other facilities also introduced by the device 5. As already mentioned the installation according to the The invention also has the advantage of absorbing different inerts and also of accepting suitable additives in the composition of its melt 2 so that it can be simultaneously a vitrifying production unit of selected and exploitable compositions.

The fact that in the chamber 1 the gas is brought to a temperature close to that of the molten compounds of the bath 2 and that it eventually reaches this temperature when it impacts the bath 2 also results in the inevitable cracking of the tars from waste in light elements such as CO, H ₂ , CH ₄ , ..., which permanently eliminates any fouling by condensation and deposition of said tars and thus allows the gas to be cooled and transported without risk of fouling.

Due to the high temperature prevailing in the chamber 1 because of the significant radiative effect of the bath 2 of melted mineral compounds, also thanks to the temperature at which the gases from the prior pyrogasification are introduced, thanks to the possible contribution additional heat during the crossing of the chamber of preheating 4, thanks to the distance between the arrival of the gases from the pyrogasification through the upper part of the chamber 1, also thanks to the possible heat gains due to the combustion of additional waste that can be introduced in the chamber 1 by the device 5, the solid particles suspended in the incoming gas stream are rapidly melted and the tars quickly cracked during their journey to the bath 2 inside the chamber 1. The orientation of the flow of the gas loaded in residues in a direction substantially perpendicular to the surface of the bath 2, ensures the capture by said bath molten products and also ensures that solid particles even not or incompletely melted during their journey can not survive and will necessarily be captured at approach or at the moment of their impact with the surface of the bath and that the tars will also be cracked.

The resulting gas can be used for integrated gasification for heat production or heat and power cogeneration. In this case, the quality of the gas produced makes it possible to overcome most of the constraints specific to thermal generators using fumes from the combustion of waste or biomass in substitution for natural and industrial gases, in direct heating installations ( dryers, baking ovens, ...) or, with the simplified complementary treatments, as purified synthesis gas for the supply of thermal engines or gas turbines in the optimized production of electricity. In particular the purified clean fuel gas extracted from the enclosure can be used directly to supply the submerged burners 7 or the preheating zone 4.

The method according to the invention makes it possible to dissociate the combustion function of the gas resulting from the pyrogasification of the waste from that of melting / vitrification of the inert gases.

• la mise en oeuvre de générateurs de vapeur d'une conception plus économique, proche de celle utilisant les combustibles commerciaux gazeux et liquides
• la conversion à la biomasse des installations de combustion existantes limitées au remplacement des équipements de combustion conventionnels par un ensemble de gazéification/combustion du gaz, sans changement de chaudières et des équipements en aval
• la réduction du volume des inertes des déchets par vitrification et leur valorisation de façon économiquement intéressante.

The capture and vitrification of almost all of the mineral fraction of waste or biomass upstream and separately from the combustion of gas allows:

• the implementation of steam generators of a more economical design, close to that using commercial gaseous and liquid fuels
• the conversion to biomass of existing combustion plants limited to the replacement of conventional combustion equipment by a gasification / gas combustion system, without change of boilers and downstream equipment
• the reduction of the volume of inert waste by vitrification and their recovery in a economically interesting way.

Claims (10)

Process for the purification of a combustible gas resulting from a pyrogasification of waste effecting a melting of the solid particles suspended in said gas and then their elimination by vitrification, characterized in that it constitutes a treatment step separated from the subsequent step of operation of the combustible gas and in that it comprises introducing into a chamber (1) containing a bath (2) of molten inorganic compounds, a flow of combustible gas laden with residues comprising heavy organic compounds or tars and particles suspended solids, melting of solid particles and cracking of tars by temperature in chamber (1), bathing of molten residues by continuous removal of bath compounds (2) having integrated the residues, then the recovery at the outlet of the enclosure (1) clean fuel gas. Process according to Claim 1, characterized in that the flow of combustible gas charged with residues is introduced into the enclosure (1) in an orientation substantially perpendicular to the surface of the bath of molten inorganic compounds. Method according to one of the preceding claims characterized in that the bath (2) is kept bubbling at a temperature of about 1100/1400 ° C under the effect of burners (7) immersed in the bath (2). Method according to one of the preceding claims, characterized in that complementary waste is introduced directly into the enclosure (1) and brought into contact with the bath (2) in which they give up their inert materials and metals and under the effect of heat undergo gasification releasing additional combustible gases. Process according to Claim 4, characterized in that oxidative gas inputs are made through the bottom of the enclosure (1). Process according to the preceding claim, characterized in that the partial oxidation of the additional waste introduced into the enclosure (1) contributes to maintaining the temperature of the bath (2). Process according to one of the preceding claims, characterized in that the composition of the molten bath (2) is adapted so as to produce, by vitrification, exploitable vitrifiats. Apparatus for purifying a combustible gas laden with suspended solids and tars, produced by pyrogasification of waste, characterized in that it is separated and upstream from the operating means for the fuel gas and in that it comprises an enclosure (1) containing a bath (2) of molten inorganic compounds maintained at a temperature of about 1100/1400 ° C, a conduit (3) for supplying the flow of fuel gas and residues in suspension, a device ( 5) introduction of solids to renew the mineral compounds of the bath (2), an overflow (6) to maintain constant the level of said bath (2) and an evacuation (9) of the purified fuel gases out of the enclosure ( 1). Installation according to claim 8 characterized in that the pipe (3) for supply of flow of combustible gas and residues in suspension is oriented substantially perpendicular to the surface of the bath (2). Installation according to claim 9 characterized in that the overflow (6) is evacuated in a vat (11) of vitrification containing water to form granules of vitrifiats by sudden cooling.

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