IE904129A1

IE904129A1 - Process for the valorization of solid wastes, in particular¹household refuse, and device for its implementation

Info

Publication number: IE904129A1
Application number: IE412990A
Authority: IE
Original assignee: Gomacris Sa
Priority date: 1989-11-16
Filing date: 1990-11-15
Publication date: 1991-05-22
Also published as: MC2177A1; DK135191A; HU912373D0; PT95907A; HUT69461A; KR920701065A; BR9007027A; YU47234B; CA2045406A1; EP0427899A1; CS566290A3; YU218390A; FI913406A0; AU6757290A; RO106556B1; DK135191D0; WO1991007361A1; MW2591A1

Abstract

A method for upgrading solid waste, especially household garbage, comprising at least 30 % cellulose matter. The method includes the preliminary steps of crushing and sorting the waste to remove metal elements. The method involves heat treating, in a tubular reaction vessel (13) provided with an Archimedean screw and heated by hot flue gases injected through its inlet, said reaction vessel containing a partial vacuum, mineral products and a mixture of a homogeneous mass containing the shredded waste. The mixture particularly contains quick lime, calcium carbonate and caustic soda. In the first part of the reaction vessel, the heat treatment and the addition of said minerals cause a rise in the temperature of the mixture and lead to the production of intense luminous radiation. A device for implementing the method is also disclosed.

Description

The present invention relates to a process for the valorization of solid wastes, comprising at least 30% by weight of cellulosic materials, in particular household refuse; the said process including the preliminary steps of grinding and sorting the said wastes in order to remove metallic elements from them.

The said process consists of thermally treating - in a tubular reactor (13) equipped with an Archimedean screw (24) and heated by the injection of hot combustion gases at its entrance, the said reactor being maintained under a slight partial vacuum - a mixture of a homogeneous mass containing the said shredded wastes and mineral products, the said mixture containing in particular quick lime, calcium carbonate, and caustic soda; the said thermal treatment and the introduction of the said minerals ensuring a rise in temperature of the said mixture in the first part of the reactor sufficient to produce an intense luminous radiation.

The invention also relates to a device for the implementation of the said process.

Fig. 2 gc/c Sheets Sheet 2 TRUE COPY CONVENTION : ! i c PATENTS ACT, 1964 COMPLETE SPECIFICATION {<{ j PROCESS FOR THE VALORIZATION OF SOLID WASTES, IN PARTICULAR HOUSEHOLD REFUSE, AND DEVICE FOR'ITS IMPLEMENTATION i * /65(^- ' ,7,7 -5 7/ ΑΓΓ ι ς f,r GOMACRIS S.A., a body corporate organised according to the laws of Switzerland, of Rue des Etangs 16-18, CH-1920 Martigny, Switzerland Process for the valorization of solid wastes, in particular household refuse, and device for its implementation.

The object of the present invention is a process for the valorization of solid wastes, comprising at least 30% by weight of cellulosic materials.

The said process is advantageously implemented for the valorization of household refuse. Generally speaking, it may be implemented for any type of waste, household, industrial, agricultural..., containing a minimal amount of cellulose.

This process enables the harmful effects and pollution caused by the said wastes to be eliminated by generating an inert material.

This material - a fine or medium type of sand - may be used in particular in construction, for sanding roads, as a filler... It is safe and bacterial development is not observed within it even after a lapse of time.

At present, two main systems are known for the treatment of such wastes. They may be stored in so-called controlled dumps, even deposited unofficially at rural sites. They may also be incinerated. Neither of these systems permits an actual valorization of these wastes and both cause pollution. The pyrolysis of these wastes, which contain chlorinated or fiuorinated plastic materials, generate toxic gases, such as chlorine and dioxine... Their accumulation, without treatment, also leads, in time, to the generation of biogases (especially methane) which are dangerous as result of their odour and/or their fire hazard. Furthermore, the mineralization of these wastes in the soil leads to the appearance of dangerous caverns.

According to the invention, a process is proposed for the disposal of the said wastes without creating pollution, the said process leading to the manufacture of a useful material.

The process of the invention is implemented, as indicated above, with solid wastes, comprising at least 30% by weight of cellulosic materials. It includes the preliminary steps of grinding the said wastes and then of sorting the latter in order to remove metallic elements from them. It consists of thermally treating - in a tubular reactor fitted with a Archimedean screw and heated by injection of hot combustion gases at its inlet, the said reactor being maintained under a slight partial vacuum - a mixture of a homogeneous mass containing the said shredded wastes and mineral products, the said mixture containing in particular quick lime, calcium carbonate, and caustic soda; the said thermal treatment and the introduction of the said minerals ensuring a rise in temperature of the said mixture in the first part of the reactor sufficient to produce an intense luminous radiation.

According to the invention, the wastes are thus subjected to a specific thermal treatment which generates a radiant reaction.

The said wastes were first ground and freed of the metallic elements which they contained. They are used shredded in the form of a homogeneous mass in a mixture with mineral products. They are shreddded in order to be available in the form of fine particles from which a homogeneous mass is easily produced.

The said wastes contain at least 30% by weight of cellulosic materials. As indicated above, they are advantageously household refuse which usually contains about 60% by weight of cellulosic materials, 3% of plastic materials, 7% of metallic products, 4% of glass and 20% of various materials...

The wastes are thermally treated according to the invention in a mixture with minerals, and in particular quick lime, calcium carbonate and caustic soda. These minerals are intended to react exothermically during the process. Advantageously, they are selected so as to develop a maximal activity within the mass while being used in reasonable quantities. Hence, a very reactive quick lime is advantageously selected. As for the calcium carbonate, natural calcium carbonates which, if necessary, are enriched in calcium by the addition to them of calcium chloride are advantageously used for economic reasons in particular...

The mixture - homogeneous mass containing the shredded wastes and minerals - is heated directly at the entrance of the reactor by the injection into it of hot combustion gases. Such hot gases may result, for example, from the combustion of gas or fuel oil.

The reactor used is a reactor equipped with an Archimedean screw or endless screw. Such a screw enables the mass of the reactants to be conveyed to the interior of the reactor and ensures that they undergo a certain degree of mixing.

The reactor is maintained under a slight partial vacuum for the evacuation of the gases. In fact, in the main,water vapour is drawn off.

In the type of reactor described above, it has been shown according to the invention that it is possible to fossilize wastes containing at least 30% of cellulosic materials without generating pollutants. This accelerated fossilization probably takes place at the moment when the intense luminous emission appears in the reactor.

It is the result of the action of heat - in fact, a thermal shock, since hot gases are injected directly at the entrance of the reactor - on a mixture containing certain reactants.

The process of the invention only leads to the expected result - elimination of pollutants and production of an inert product (in the form of brittle fragments) - if the said luminous emission or aura is observed in the reactor.

The composition of the mixture to be introduced into the said reactor and the temperature to which it is appropriate to heat the said mixture on its entry into the said reactor are parameters to be specified for the purpose of producing the said aura.

Their determination and optimization are operations within the capacity of the person skilled in the art.

The homogeneous mass containing the shredded wastes is advantageously produced by mixing the said wastes upstream from the reactor with calcium carbonate and, preferably, natural calcium carbonates in which calcium chloride has optionally been incorporated. The mixing only occurs satisfactorily if the wastes have a certain degree of humidity and this is usually the case. The degree of humidity must not, however, adversely effect the subsequent reaction. It is advantageously comprised between 20 and 40%. In order to exhibit such a degree of humidity, the wastes may be dried (partially) beforehand - if necessary - or, on the other hand moistened. 30 - 40% by weight of natural calcium carbonates are incorporated into the said wastes exhibiting such a degree of humidity. As indicated above, this mass of calcium carbonates may be first enriched in calcium by the addition of calcium chloride to it.

To the said homogeneous mass - shredded wastes + calcium carbonates - other minerals and,in particular, as specified above, quick lime and caustic soda are added according to the invention in order to produce the desired result under the effect of heat.

It is also advantageous to add carbonated silicates (Na2Ca2Mg^H4Si02(C03)3 type).

The introduction of these minerals - quick lime, calcium carbonate (in particular natural calcium carbonates optionally enriched in calcium chloride), caustic soda, and advantageously carbonated silicates - enable the desired result to be obtained : the appearance of an aura by direct heating of the mixture and the production of an inert mass in the form of brittle fragments.

The said minerals, other than calcium carbonate (optionally containing calcium chloride) are introduced for the purposes of the invention (for the generation of the aura'^) in a proportion of about 5 to 35% by weight of the said homogeneous mass. The minimal quantity used obviously depends on the constitution of the said homogeneous mass and in particular on the content of cellulosic matter present in the wastes to be treated. They are advantageously used in approximately equivalent amounts (1/3, 1/3, 1/3): - quick lime between 10 and 45% - caustic soda between 5 and 35% - silicate carbonates between 10 and 45% by weight of the ternary mixture (quick lime + caustic soda + silicate carbonates).

The reactive mass thus constituted - homogeneous mass + minerals - is subjected to a thermal shock on entering the reactor by the injection into it of hot gases.

The aura necessary for fossilization is observed according to the invention when the said reactive mass is at a temperature of 250 to 300°C. This temperature may be obtained within the mass according to the invention by the injection of gases combusted at 500-600°C.

It has previously been pointed out that on being discharged from the reactor the mass exists in the form of brittle fragments.

These recovered fragments are advantageously pulverized. A sand is thus obtained with a density of the order of 0.3 to 0.5. Such a sand cannot easily be used and fillers are advantageously introduced into the process of the invention in order to increase its density. These fillers may be introduced at at least two stages of the process of the invention. They may be incorporated into the sand resulting from passage of the solids discharged from the reactor into a disintegrator and/or incorporated during the manufacture of the homogeneous mass - shredded wastes + calcium carbonate - before its introduction into the reactor.

Downstream from the reactor any type of filler may be used.

Upstream from it, only neutral fillers may be used. By neutral fillers are meant, in the present context, fillers compatible with the thermal reaction (heating + aura). Such neutral fillers may be selected from calcium carbonate, carbonate of lime, powered baryta, the carbonated silicates, powdered clay, powdered sugary-grained gypsum, powdered bauxite..., or their mixtures. Hence it should be noted that calcium carbonate and the carbonated silicates may be used in the process of the invention in greater amounts than those already mentioned above.

By way of illustration, it should be made clear that the calcium carbonate, carbonate of lime mixture may thus represent up to 50% by weight of the said homogeneous mass (calcium carbonate is thus employed both as reactant and as neutral filler).

The baryta (with its sediment) may be used in a proportion of 0 to 30% by weight; clay in a proportion of 0 to 15%, gypsum in a proportion of 0 to 20% and bauxite in a proportion of 0 to 20%. The carbonated silicates taken as a whole may be employed up to a maximum of 30% by weight of the total mass at the entrance of the reactor.

The said fillers make it possible to produce a sand of defined density .

If it is desired to adjust its granulometry - more precisely to increase it - a further step is added to the process of the invention.

The mass issuing from the reactor, after being pulverized and optionally having neutral fillers incorporated within it, is available in the form of a very fine, even impalpable, powder.

Such a powder is advantageously conditioned with pelletizing binders in order to increase its granulometry for the production, in particular, of a medium sand, which can be used in construction.

The binder is advantageously mixed with the powder in a 10 vertical pelletizer of the Flexomix type; the mixture is then dried, which leads to the crystallization of the said binder.

The said binder must be selected so as to comply with the inert, stable character of the product obtained by the process of the invention. It must not introduce bacteria. It is possible to use in particular sodium silicate which will react with the calcium present in the grains of the product.

It is also possible to use a binder based on quick lime, cement slurries, blast-furnace slags and carboxymethyl cellulose (or equivalent). Another binder which can be used is a binder based on water-soluble pitch.

This step involving the treatment of a powdery material in order to increase its granulometry is perfectly well-known to the person skilled in the art.

In this way, waste products are valorized according to the 25 invention without causing pollution in as much as it did not appear necessary to heat the reactive mass in the reactor to a temperature higher than 300°C (pyrolysis of plastic materials). The combustion gases, introduced at the entrance of the reactor to heat the said reactive mass directly, seem either to be trapped in the said mass or to decompose in particular at the time when the said aura is produced.

Another object of the invention is a device for the implementation of the procedure as explained above.

The said device comprises essentially: - a tubular reactor equipped with an Archimedean screw, - a combustion chamber with its outlet at the entrance to the said reactor for the direct supply of calories, - means for feeding the said reactor, - means for maintaining a slight partial vacuum in the said reactor.

The reactor is fed at one end with the reactive mass homogeneous mass containing the shredded waste products and, optionally, neutral fillers + various minerals - by virtue of at least one pressure lock. There may be one pressure lock for the said homogeneous mass and another for the mineral mixture. This (or these) pressure lock(s) will be airtight, fed by a low pressure screw lock, so that under no circumstances is the partial vacuum at the interior of the reactor - necessary for the evacuation of the gases - impaired by an inflow of external air.

The displacement of the said mass to the interior of the reactor is carried out by means of the Archimedean screw (or endless screw). It also ensures the continuous homogenization of the said mass.

The combustion chamber is located upstream from the reactor.

It may be an oil burner or a gas burner.

The hot gases which are generated there, are conveyed to the entrance of the reactor. It has already been pointed out that the expected result is obtained in particular with a temperature at the entrance of the reactor of the order of 500 to 600°C.

The reactants are themselves introduced at room temperature and undergo a thermal shock.

Advantageously, the homogeneous mass containing the shredded waste products, calcium carbonate and possibly other minerals, is produced upstream from the reactor in a ribbon mixer.

At the exit from the said reactor, the mass has already been subjected to a certain degree of cooling. The discharge of the said mass is advantageously carried out in a decompression lock which allows the separation of the gases, on the one hand, and the solids, on the other.

The said solids are discharged by means of gravity.

Advantageously, the fines are recovered by passing the vapours through at least one cyclone separator. The said vapours - mainly constituted of water vapour - are evacuated, for example, by means of a natural stack.

As indicated above, the solids exist in the form of brittle fragments. These fragments can be pulverized in a disintegrator, connected to the device of the invention (downstream from the reactor).

The powder obtained may then be treated in a mixer/crystallizer assembly in order to control its granulometry. In the said mixer, it is mixed with at least one pelletizing binder. The device of the invention may thus advantageously be connected to its essential elements - reactor and the means for heating, feeding, partial vacuum maintenance - upstream from the said reactor a ribbon mixer and in succession downstream from the said reactor a disintegrator and a mixer/drier-crystallizer assembly.

The appended figures 1 and 2 illustrate the implementation of the process of the invention.

More precisely, figure 1 shows schematically a waste treatment plant, in which the said process is implemented and figure 2 shows the elements (of the device of the invention) essential to the implementation of the said procedure.

The numbers in these figures represent : 1, a hopper with sliding bottom and a sliding door, 2, a screw-thread grinder, - 3, an overband scrap metal remover, 4, an escalating conveyer with magnetic drum, - 5, shredder feed conveyer, - 6, a magnetic cage, At this stage of the device, the wastes have been ground and the metallic elements which they contain have been removed. - 7, a screw-thread thredder, 8, a mixer feed conveyer, - 9, a powder silo with lock screw, containing in particular natural calcium carbonates, - 10, a band mixer, - 11, feed conveyer for the reactor, - 12, a powder silo with lock screw, - 13, the reactor for accelerated fossilization, The elements (11) and (12) are the means by which the reactor is fed. - 14 and 15, two cyclones (for the recovery of the fines), - 16, the feed conveyer for the disintegrator, - 17, the said disintegrator (vertical), - 18, the feed conveyer for the pelletizer, - 19, the said Flexomix vertical pelletizer, - 20, the feed conveyer for the drying vat, - 21, the said drying vat, - 22, the stockpile conveyer, - 23, the combustion chamber, - 24, the Archimedean screw in the interior of the reactor, - 25 view ports for observing the interior of the said reactor , - 26, the discharge chute of the said reactor.

In such a plant, 11 869.2 tons of waste are treated per hour.

The time taken for the mass to pass to the interior of the reactor is about 30 min.

The luminous emission or aura was observed in the vicinity of the first third of the reactor whereas the temperature at the interior of the mass conveyed into the said reactor is 250°C; the temperature at the entrance to the reactor varying between 500 and 600°C.

Claims

1. Process for the valorization of solid wastes, comprising at least 30% by weight of cellulosic materials, in particular household 5 refuse; the said process including the preliminary steps of grinding and sorting of the said wastes in order to remove from them metallic elements, characterized in that it consists of thermally treating in a tubular reactor (13) equipped with a Archimedean screw (24) and heated by injection of hot combustion gases at its entrance, the said 10 reactor being maintained under a slight partial vacuum - a mixture of a homogeneous mass containing the said shredded wastes and mineral products, the said mixture containing in particular quick lime, calcium carbonate and caustic soda; the said thermal treatment and the introduction of the said minerals ensuring a rise in temperature of 15 the said mixture in the first part of the reactor such as to produce an intense luminous radiation.

2. Process according to Claim 1, characterized in that the said homogeneous mass includes the said shredded wastes, exhibiting a degree of humidity between 20 and 40%, and 30 to 40% by weight of natural 20 calcium carbonates.

3. Process according to one of the Claims 1 or 2, characterized in that the said mixture also contains carbonated silicates.

4. Process according to any one of the Claims 1 to 3, characterized in that the mineral products employed - other than the 25 calcium carbonate intimately mixed beforehand with the shredded wastes represent from 5 to 35% by weight of the said homogeneous mass.

5. Process according to any one of the Claims 1 to 4, characterized in that the mixture introduced into the reactor also contains neutral fillers - selected from calcium carbonate, carbonate 30 of lime, powdered baryta, carbonated silicates, powdered clay, powdered sugary-grained gypsum, powdered bauxite or their mixtures - in order to regulate the density of the products discharged from the said reactor.

6. Process according to any one of the Claims 1 to 5, 35 characterized in that the mass discharged from the said reactor is treated, after pulverization and the optional intimate mixing with it of neutral fillers, with at least one pelletizing binder in order to produce a product - of the sand type - of defined granulometry.

7. Device for the implementation of the process according to any one of the preceding claims, characterized in that it comprises: - a tubular reactor (13) equipped with an Archimedean screw (24); - a combustion chamber (23) with its outlet at the entrance of the said reactor for the direct supply of calories; - means (11, 12) for feeding the said reactor; - means for maintaining a slight partial vacuum in the said reactor .

8. Device according to Claim 7, characterized in that it comprises, upstream from the said reactor a ribbon mixer (10) for the production of the said homogeneous mass from the shredded wastes.

9. Device according to one of the Claims 7 or 8, characterized in that it comprises downstream from the reactor a pulverizer (17) which converts the mass discharged from the said reactor into a very fine powder.

10. Device according to Claim 9, characterized in that it comprises downstream from the said pulverizer (17) a mixer (19) for the pelletization of the said powder into particles and means (21) for drying/crystallization of the said particles obtained.

11. A process for the valorization of solid wastes according to any preceding claim, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings .

12. A device according to any preceding claim, substantially as hereinbefore described with reference to anf as illustrated in the accompanying drawings.