ITFE970004A1 - PROCESS OF THERMOCHEMICAL CONVERSION OF MUNICIPAL AND SPECIAL WASTE INTO BASIC CHEMICAL PRODUCTS AND PLANT TO CARRY OUT THE PROCESS. - Google Patents

Description

DESCRIPTION

of the invention entitled:

"Process of thermochemical conversion of municipal and special waste into basic chemicals and plant to carry out the process"

The present invention relates to a thermochemical conversion process of urban and special waste into basic chemical products and a plant for carrying out the process.

Thermal processes of pyrolysis, gasification and thermal inertization of waste are known, to obtain marketable organic and inorganic compounds.

A well-known pyrolysis process, called THERMOSELECT (P Pollesel, "Energy recovery from waste - the application of gassification technologies" in "Chemistry and industry" no. 5M996, page 603; E! De Fraja, M Giugliano "Incineration - Energy recovery ", chapter III" Innovative plant design proposals ", in: Politecnico di Milano (Department of Hydraulic, Environmental and Survey Engineering - Environmental Section), ANDIS National Association of Environmental Health Engineering" Urban solid waste engineering - XLIII Refresher course in environmental sanitary engineering - Milan, 5-9 June 1995) provides for this to take place indirectly, that is, not by combustion of a part of the material, but simply by heating it; that gasification takes place at 2000 ° C separately from pyrolysis, and that inertization occurs due to the temperature (between 1200 and 2000 ° C); therefore eg decomposition of organic compounds and by vitrification of inorganic compost.

The drawback of this known process consists in the high heat losses due to the heat exchange, in the high plant costs due to the need to use materials capable of withstanding high temperatures, in the high crushing costs of the solid product as well as in the formation of vitreous crusts and in the consequent erosion of the plants.

Another well-known pyrolysis process, called KWU (E. De Fraja - M. Giugliano) provides that this takes place indirectly as in the previous case, but that there is no gasification and that inertisation occurs due to the temperature, as in the previous case, at about 1300 ° C.

A drawback of this known process consists in the fact that it operates at high temperatures and with low yields.

Another known pyrolysis process is described in the European patent n.

0292987. In it, pyrolysis occurs indirectly as in the Thermoselect process, gasification occurs separately from pyrolysis and with the addition of combustible material extraneous to the waste, and inertization occurs by temperature as in the Thermoselect process.

A drawback of this known process is that it requires the addition of combustible material.

Another well-known process, called PUROX, of Union Carbide Co. (C. Casci, L. Cassitto "Energy from urban and industrial waste", CLUP, Milan, 1984; P. Pollesel) only carries out a high temperature gasification with the use of pure oxygen and produces only solid gas and waste.

A drawback of this known process consists in the fact that it allows to obtain only solid and non-liquid gases and slags, neither oils nor tars.

Another well-known process, called FLASCH PYROLYSIS SYSTEM "GARRETT (C. Casci, L. Cassitto - A. Paratella, A. Buso," Waste disposal "Veneto Region - Regional Council, 1983) provides for an indirect pyrolysis at 500 ° C obtaining only highly viscous and corrosive fuel oils with a marked tendency to polymerize.

Another well-known pyrolysis process, called MONSANTO ENVIRO-CHEM SYSTEM “LANDGUARD” (C. Casci, L. Cassitto; P. Pollesel) involves carrying out soy gasification, by sending air. It poses serious problems in the control of emissions from gas combustion.

Another well-known pyrolysis process, called ANDCO-TORRAX, by Carborundum Co. (C. Casci, L. Cassitto - P. Pollesel) is similar to the PUROX process, but uses a mixture of oxygen and pre-heated air.

Another well-known pyrolysis process developed by the University of Hamburg (A. Paratella, A. Buso) performs the pyrolysis of plastics and rubber only, to obtain carbon black, oil, gas, in a fluidized bed reactor. A drawback of this known process consists in the fact that it operates only with a very specific type of waste.

Another well-known process, called PROCEDINE CORPORATION (A. Paratella, A. Buso) carries out only direct pyrolysis, as in the Thermoselect process, under pressure of 3.4-7 atm., Of molten plastic materials, in a fluid bed. In addition to the drawbacks indicated for the Thermoselect process, this has the further inconvenience of operating under pressure and therefore with very expensive technologies, which among other things are not suitable for the production of liquids and tars.

Another well-known pyrolysis process, called HERBOLD by Oscar Herbold of Mackeshein Germany (A. Paratella, A. Buso) carries out only the pyrolysis of tires and other plastics, working in depression equal to 40 mm of mercury.

Another well-known process, called HERKO-KIENER, involves carrying out only indirect pyrolysis, as in the Thermoselect process, of waste and sewage sludge.

Another well-known process, called INCINERATING FURNACES, involves carrying out a partial combustion of the waste with partial gasification in the absence of air; the gaseous products (fumes) are then separately inerted by thermal decomposition in excess of air and discharged into the atmosphere; solid products (ashes) are discharged without being inerted.

The drawback of this known process is that it discharges solid and gaseous products into the environment and does not produce marketable substances.

Another well-known process, called WRS (Waste Reclaim Loterios - "L'Indipendente" of 13 March 1996 page 28), provides that pyrolysis takes place indirectly at a temperature of about 500 ° C, that there is no gasification and that inerting is carried out separately from pyrolysis.

Drawbacks of this process consist in a lower efficiency of the heat exchange offered by indirect pyrolysis compared to direct pyrolysis; in the impossibility of recovering the carbon dioxide developed by combustion; in the need to use a large quantity of pyrolysis products as fuels to obtain the heat for the pyrolysis itself; in the impossibility, given the low process temperature, to convert any aromatic, chlorinated and oxine compounds that may be present in the waste; and in the possibility that the pyrolysis is not homogeneous, due to the size of the objects that make up the waste, which are not shredded.

Another well-known process used for the treatment of Art waste in Oregon - USA ("INF-INN", n. 4, November 1996; "Energy, Environment, and Innovation 1995, 8-9, 57) provides for the pyrolysis of waste at 310 ÷ 480 ° C, not to carry out the gasification, and to make the inertization take place separately from the pyrolysis.

The drawbacks of this process consist in. problems of lead and mercury emissions into the atmosphere and the impossibility, given the low pyrolysis temperature, to convert any aromatic, chlorinated and oxine compounds that may be present in the waste.

Another well-known process, called DISMO I process (EP-A2-0536468) foresees to operate at high temperature (2200 ° C) and high pressure (100 bar), with the drawbacks of a short duration and high costs of refractory materials. employees.

The purpose of the invention is to eliminate all the drawbacks jointly or severally encountered in the known chemical conversion processes of waste, and to obtain marketable organic and inorganic compounds from urban and special, hazardous and non-hazardous waste.

This object and others that will result from the following description are achieved according to the invention with a process of thermochemical conversion of urban and special waste into basic chemical compounds, characterized in that, within several thermodynamic environments physically interconnected, it is carried out on the wastes previously with additives of inerting substances:

- a pyrolysis operation at a slowly increasing temperature starting from 100 ° C until reaching at least 700 ° C approximately,

- a gasification operation on the carbon residues deriving from the previous pyrolysis treatment at a temperature between 700 ° and 1100 ° C, by means of oxygen mixed with water vapor and carbon dioxide, obtaining hydrogen, carbon monoxide and carbon dioxide, which are used to condition the pyrolysis process,

- an inertization operation of heavy metal compounds, halogenated compounds and aromatic compounds obtained with the previous pyrolysis and gasification treatments, exploiting the heat developed by these treatments, the additive inerting substances and the substances themselves produced by the process.

The present invention is further clarified hereinafter in two of its preferred embodiments and in an executive variant reported for purely illustrative and non-limiting purposes, with reference to the attached drawing tables, in which:

Figure 1 schematically shows a plant for carrying out the process according to the invention in a first embodiment,

Figure 2 shows it according to the horizontal section of fig. 1,

figure 3 shows it according to the same view of fig. 1 in an executive variant,

figure 4 shows it according to the horizontal section IV> -IV of fig. 3, and

Figure 5 schematically shows it in a different embodiment.

As mentioned, the process according to the invention carries out the pyrolysis, gasification and inertization treatments of urban and special, hazardous and non-hazardous waste, preceded, as regards solid waste, by a pre-treatment suitable for:

- eliminate metal and glass parts from waste,

- reduce the size of the waste to about 1-3 cm,

- reduce the amount of water present in the waste through evaporation, and - add inerting substances to the waste.

This pre-treatment is not carried out on liquid waste, which is directly introduced into the process.

Pyrolysis is carried out according to the criteria of dry distillation of wood: slowly and in temperature progression, i.e. gradually increasing the temperature of the material being treated.

In this way, several mixtures of volatile pyrolysis products can be taken, each sampling corresponding to a precise temperature range.

The pyrolysis temperature varies from about 100 ° C (with first the evaporation of moisture and then the release of the water of composition) to about 700-800 ° C, in which practically only a carbon residue remains.

The methods of gasification, occurring in the same physical environment in which the pyrolysis takes place, allow to accentuate the natural reducing characteristics of the pyrolysis environment. Furthermore, “flash” effects are absolutely avoided, ie very fast reactions with rapid contact times between the reactants and the reaction products.

In this way all the reactions can take place, even the one with very slow kinetics compared to the average of the other pyrolysis reactions, such as the saturation of the double bonds, the reduction of oxine bonds and the decomposition of oxygenated products with the evolution of water and carbon dioxide. . Therefore, especially as regards oils and tars, products poor in bonding oxygen and poorly unsaturated are obtained.

Pyrolysis control is then exercised through the following parameters:

- the temperature,

- the kinetics of pyrolysis,

- the partial pressures of the reaction products.

The temperature is regulated by acting on the temperatures of the gases produced in the gasification zone; the pyrolysis kinetics is regulated by the permanence time of the material to be treated and by the regulation of the conditions; temperature and partial pressure of the compounds obtained from pyrolysis; the partial pressures are regulated by controlling the flows for the removal of the volatile reaction products.

The gasification of the carbonaceous residues from the previous pyrolysis treatment takes place at a temperature above 700 ° C, but below 1100 ° C by gaseous oxygen mixed with saturated water vapor and gaseous carbon dioxide. ;

This gaseous oxygen can be constituted by pure technical oxygen or by preferably enriched air.

The main reactions that intervene are the following:

where C must be understood as "carbon residue".

Reactions (1) and (2) are normal combustion reactions; however, reaction (2) is favored over reaction (1) with an appropriate temperature control through the regulation of reactions (3) and (4), to contribute, together with the reaction products of the same, to accentuate the natural reducing environment of pyrolysis.

The heat produced by reactions (1) and (2) allows to develop the necessary temperature for reactions (3) (Boudouard reaction) and (4) to take place.

The regime is therefore autothermal, because a part of the waste is exploited for its characteristics as a fuel, capable of producing the necessary and more than sufficient heat to carry out the process.

Reactions (3) and (4) are strongly endothermic; thanks to them it is therefore possible

- control the gasification temperature (i.e. reactions (1) and (2)),

- control the pyrolysis environment more or less reducing,

- check the temperatures of the pyrolysis process.

The control of reactions (3) and (4) takes place through the regulation of the partial pressures of carbon dioxide and superheated water vapor. This regulation is implemented by controlling the flows of carbon dioxide and superheated water vapor, flows that can also be set to zero, for one of the two gases or for both.

The control of the thermal equilibrium between reactions (1) and (2) and reactions (3) and (4) therefore allows the control of the gasification temperature, and therefore, through the gases produced by this, also the control of the pressures. parts of the pyrolysis products.

Other important gasification reactions are methane formation reactions:

These reactions do not disturb the pyrolysis environment, since methane is a reducing gas, but are favored by too low temperatures (400-600 ° C), that is, such as to counteract reactions (3) and (4) and to cool the last stage of pyrolysis. They are therefore mostly avoided during the process.

Gasification takes place in the presence of pure technical oxygen or enriched air and not air for the following reasons:

- the air is composed of 4/5 nitrogen, which would not intervene in any of the process reactions, instead removing most of the heat produced by the gasification and pyrolysis reaction, without converting thermal energy into chemical energy. This purpose of converting thermal energy into chemical energy is instead scrupulously observed in the process according to the invention. The heat removed from the nitrogen, being at a low temperature, would also be difficult to recover as thermal energy. Furthermore, it should be compensated for by burning larger quantities of material, with consequent reductions in efficiency. Finally, the size of the industrial plants suitable for carrying out the process according to the invention should be increased in proportion to the amount of inert gases introduced into it. Nitrogen should also be separated from volatile gasification and pyrolysis products, leading to additional processing costs;

- the partial pressure of gasification oxygen is regulated by the presence of carbon dioxide and saturated water vapor that participate in reactions (3) and (4). The use of air would therefore exclude, due to the high concentration of nitrogen, the use of carbon dioxide and saturated water vapor (one of the foundations of the process according to the invention), since the partial pressure of the oxygen with consequent inhibition of gasification reactions;

- pure technical oxygen, before intervening in gasification, completes the elimination of carbon residues that may be present in the solid pyrolysis products, according to reaction 1. This procedure is also made possible by the low speed of all the reactions, and by a precise plant peculiarity.

Liquid waste is preferably injected directly into the gasification area or in any case in a high temperature area, in order to evaporate the water present and undergo pyrolysis at that temperature.

All the pyrolysis and gasification reactions take place in slight overpressure, which is sufficient only to compensate for the pressure drops of the gases and therefore to allow their removal. In fact, any increase in pressure inhibits, in accordance with the laws on chemical equilibrium, reactions (3) and (4) and decreases the volatility of heavy compounds (oils), which therefore tend to remain in the reaction environment, undergoing a further cracking.

The inertness treatment concerns the compounds deriving from the previous pyrolysis and gasification treatments, namely the heavy metal compounds, the halogenated compounds and the aromatic compounds.

The inertization of heavy metals is carried out by adding powder to the waste materials rich in pure or combined silica, such as calcium silicate, silica, clay, etc.

The characteristic of silicates of having low melting points is exploited, and therefore of being able to form in the liquid phase at the gasification temperature. This applies with the exception of aluminum silicate, which melts above 1800 ° C. However, aluminum oxides are in no way soluble in water and are therefore not subject to dispersion by leaching, nor to dispersion in the atmosphere, since the plants, with which the process according to the invention is carried out, do not discharge no gas or dust.

Vitrification of the mineral residue is avoided.

The inertization of halogenated compounds is achieved by adding calcium carbonate or similar compounds, such as sodium carbonate, or the solid products obtained from the process, to the waste, as these are rich in free oxides.

At the initial temperature of the process, calcium carbonate reacts with the halogendric acids released in the higher temperature stages, according to the reaction:

The excess of calcium carbonate allows this reaction to take place at all temperature levels of the pyrolysis, until the end of this, when at about 800 ° C the calcium carbonate is completely decomposed into calcium oxide according to the reaction:

At this level, the calcium oxide reacts with the halogendric acids to salify them according to the reaction:

There are no calcium, magnesium, sodium and potassium halides harmful to the environment.

The inertization of alkyl and aromatic halides with higher molecular weight is carried out by calcium oxide, as they are formed at temperatures comparable to that in which the reaction takes place (8). The schematic inertization reaction is therefore the following:

In turn, the halogenated compounds that are formed in this way tend to be found as radicals rather than as stable compounds, and to be inerted as such.

The inertization of aromatic compounds occurs in a different way, depending on the nature of these. It is known that aromatic compounds are formed up to temperatures of about 700-800 ° C, equal to the maximum pyrolysis temperatures of the process according to the invention. Furthermore, these temperatures correspond to the formation of aromatic compounds of greater molecular weight (arenes with condensed nuclei and polynuclear arenes) by condensation of the lighter aromatic compounds.

However, this is also the formation temperature of the heaviest fraction of pyrolysis, corresponding to the formation of tars and heavy oils: this fraction is not further pyrolyzed, but taken as such (as is the case for all the other fractions).

It is therefore evident that the aromatic compounds are partly removed as such together with the heavy oils and tars, and are partly bound to them.

In the first case the inertization occurs by incorporation: the high viscosity of the oils and tars, the low vapor pressure of the aromatic compounds similar to that of the oils and tars which incorporate them, the mutual solvent effect due to the chemical compatibility of the oils and tars with aromatic compounds, prevents these from escaping from the mass. In the second case, the inertization occurs through the formation of molecular bonds.

From what has been said it is clear that the process according to the invention is not a succession of three groups of reactions (pyrolysis, gasification, inertization), but a combination of these groups of reactions. It is in fact based on the interaction of each of these groups of reactions with the other two, interactions that take place as follows.

By their nature, pyrolysis reactions take place in a reducing environment, since gases with these characteristics develop from pyrolysis: carbon monoxide up to about 300 ° C (together with an abundant quantity of carbon dioxide); hydrogen, methane, ethylene and still carbon monoxide (albeit to a lesser extent) above 300 ° C up to about 700 ° C.

In the process according to the invention, the reducing environment is accentuated by the presence of reducing gases produced by gasification to control the reducing capacity of the pyrolysis environment as well as to favor the production of hydrogen as it is and of poorly oxygenated and poorly unsaturated products.

Furthermore, through the gasification reactions (3) and (4), as endothermic, the exothermic pyrolysis reactions are controlled, which take place at temperatures higher than 270 ° C: reactions (3) and (4) in fact, being endothermic, they use the heat of the gasification reactions (1) and (2) and the heat of the exothermic pyrolysis reactions to progress.

The process therefore includes the following enthalpic zones:

- up to about 270 ° C: endothermic pyrolysis reactions;

- from about 270 ° C to about 700-800 ° C: exothermic pyrolysis reactions;

- over about 700-800 ° C: endothermic and exothermic gasification reactions.

Reactions (3) and (4) therefore regulate reactions (1) and (2) and pyrolysis reactions.

By controlling the thermal equilibrium between gasification reactions (1), (2), (3) and (4), it is therefore also possible to control the temperature of the exothermic pyrolysis reactions. The regulation of these temperatures takes place through the inlet modulation of the partial pressures of the three gases pure technical oxygen, carbon dioxide and saturated water vapor.

This temperature control is essential to direct the process towards the production of certain compounds.

It is also possible to control the entire process also by controlling the partial pressures of all the volatile fractions. This control is carried out above all by favoring, or preventing, the removal of certain fractions from others; it is also implemented by regulating the partial pressures of the reducing gasification gases (carbon monoxide and hydrogen) through the gasification reactions (3) and (4).

The regulation of gasification reactions (3) and (4) and exothermic pyrolysis reactions, through the gasification reactions (1) and (2), is essential to regulate the inertization trend. In fact, the gasification temperature must generally not go beyond 1100 ° C, to avoid the vitrification of the solid residue of the process, made up entirely of inorganic materials; moreover, the inertization reactions can only take place at the temperatures in which the pyrolysis and gasification reactions take place.

The reactions of pyrolysis, gasification, inertization are then combined in the process according to the invention in a precise system that has its own characteristics with respect to pyrolysis, gasification and inertization, each considered regardless of the others.

From what has been said it is clear that compared to the prior art the process according to the invention introduces numerous advantages, and in particular:

- the speed of pyrolysis, and therefore of all gasification and inertization reactions, is kept low by means of the progressive and controlled increase in temperature. This happens in contrast to the processes developed so far, which operate at a constant temperature and with high thermal gradients. In the process according to the invention, "flash" processes are therefore avoided, which cause the presence of too oxygenated and unsaturated compounds in the pyrolysis products;

- pyrolysis is carried out in temperature progression, in order to obtain multiple product mixtures (i.e. a mixture for each temperature range), not a single mixture or a single pyrolysis product, as in the processes developed so far;

- the following products are obtained: hydrogen, carbon monoxide, carbon dioxide (which is partly reused in the process to carry out the gasification reaction (3)), methane, ethene and traces of other light gaseous hydrocarbons; pyroligneous acid, i.e. an aqueous mixture of acetic acid, acetone, methanol and other light oxygenated compounds; tar oils; tars; mineralized solids;

- inertization takes place by addition of silicates, inorganic carbonates and incorporation of aromatic compounds in tars and heavy oils, is carried out at the corresponding pyrolysis temperatures and by removing the aromatic compounds together with tars and heavy oils, bound or incorporated in them . Heavy metals combine with silicates in the gasification phase, without vitrifying. All this allows to obtain, unlike the known processes, products without polluting characteristics;

- the carbonaceous residue is completely gasified, and the residue from this operation is subsequently washed at a high temperature (i.e. such as to allow combustion reactions) with pure technical oxygen not mixed. Unlike the other processes, there is therefore no carbon residue, which due to its polluting nature;

a gasifying mixture is used consisting of carbon dioxide, saturated water vapor, pure technical oxygen; by varying the partial pressures of the three gases, it is possible to control the gasification temperature and therefore the temperatures of the pyrolysis reactions (ie the thermal gradient of the entire process). Unlike the other processes, the interplay of the partial pressures of the three gases therefore allows both temperature control and control of the reducing component of the pyrolysis environment;

pure technical oxygen is used instead of air, replacing inert gases, such as nitrogen, with carbon dioxide. Unlike the other processes, therefore, a gas (carbon dioxide) with a double function is thus available: as an inert for the dilution of oxygen (and therefore to control the partial pressure of the latter) and to participate in the reactions gasification (Boudouard reaction);

vitrification of the solid residue is avoided, as it operates at temperatures below 1100 ° C. In this way, unlike other processes, thanks to the type of inertization, the residue does not in any case contain polluting compounds and does not undergo hardening that hinders the crushing operations. Problems related to fouling and erosion of the equipment by the molten glass mass are also avoided;

unlike the other processes, it operates at temperatures below 1100 ° C; the surplus of thermal energy is transformed into chemical energy (producing mainly hydrogen and carbon monoxide). It is therefore possible to achieve considerable savings in plant costs, being able to use low-cost refractory materials. Furthermore, it is possible to have chemical products such as hydrogen and carbon monoxide, instead of thermal energy, which is the form of energy at the highest entropic level;

- the absence of nitrogen due to the use of oxygen instead of air, avoids the dilution of pyrolysis products in this gas; this involves, unlike other processes, a reduction in the size of the plant and operating costs, as well as a significant simplification of the gas separation systems;

- unlike the other processes there is production flexibility, that is, it is possible to direct the production itself towards those pyrolysis and gasification products of greatest interest, by controlling the respective temperatures;

- unlike the other processes, the process according to the invention offers two systems for using the gases obtained: the use of these gases as basic chemical products; or the combustion of these gases, after separation of carbon dioxide, for the production of energy (for example electricity);

- unlike other processes, all products obtained with the process according to the invention are marketable; that is, none of the products must be disposed of or landfilled;

- the process regime is autothermal.

The products obtained from the process may require, depending on the use for which they are intended, further chemical, physical, and / or chemical-physical processing, such as the following.

- Gaseous products: desulphurization, compression, separation, mixing, storage, combustion, entry into gas pipelines.

- Liquid products: desulphurization, distillation, cracking, reforming, reduction, oxidation, mixing, storage, combustion, introduction into oil pipelines.

- Solid products: washing with or without recovery of leached substances, grinding, sintering, separation, mixing, storage, transport.

- All or part of the products: separation and mixing between the gaseous, liquid and solid products obtained from the process or subsequent processing, with each other or with other products extraneous to the process.

To implement the process described above, the invention provides three different plant solutions, and in particular two relating to a single-stage reactor (see figs. 1-4) and one relating to a multistage fluidized bed reactor (see fig. 5) .

With reference to figs. 1 and 2, the plant comprises a single-stage reactor consisting of a vertical cylinder 1 that is four to six times its width high. It is made of metallic material with an internal refractory lining.

At the top of the reactor 1 there is a feed duct 2 for the pre-treated solid waste, equipped with a loading hopper 3.

An injector 7 for the liquid waste to be treated leads to the lower part of the reactor 1.

Inside the reactor 1 suitable diaphragms 4 and grids 5 in steel are provided, having a semicircular shape, superimposed on each other and inclined downwards with an angle equal to the friction angle of the material being treated.

The diaphragms 4 prevent compaction of the material caused by its own weight; they favor its mixing, consequently favoring the contact between the material and the hot gases; allow the withdrawal of pyrolysis products through side inlets 6 suitably distributed along the height of the reactor 1, under the grids 5 and the diaphragms 4.

The grids 5 perform the same function as the diaphragms 4, supporting the material being treated, preventing its compaction and favoring its mixing. They also redistribute hot gases in the mass, including non-condensable gases re-injected into the furnace.

Labyrinth systems or other separators are provided in correspondence with the side outlets 6 for collecting the gases and pyrolysis products, which prevent the entrainment of dust and particles of material.

From the bottom 8 of the reactor 1 the mineralized solid products are withdrawn through the ordinary extraction systems.

At the base of reactor 1 three collectors 9 for oxygen, 10 for carbon dioxide and 11 for water vapor are inserted in an appropriate manner. A fourth manifold 12 is also provided for nitrogen, used as a purge gas during the shutdown of the reactor. It is also possible to use one of the three collectors 9, 10 or 11 as a nitrogen collector.

The gases injected from the bottom of the reactor operate and control the gasification of the completely pyrolyzed material; the hot gases coming from the gasification zone and the superheated non-condensable products re-injected into the reactor support the pyrolysis phase.

The gases ascend along the reactor, inside which a variable temperature is maintained from about 100 ° C in the upper part, up to 1100 ° C at the base, while the mass of waste being treated descends along the reactor itself, meeting the gases in countercurrent.

The reactor 1 is equipped with a coaxial shaft 13, to which arms 14 are fixed which, by rotating, prevent the possible formation of material bridges and facilitate the fall of the material itself.

The reactor illustrated in Figures 3 and 4 constitutes an executive variant of the reactor already described and bears the same numerical references for the equivalent parts. It differs from this in having, instead of the grids and semicircular diaphragms, horizontal circular plates 15 alternately open in correspondence with the central area and the peripheral area to allow the material being treated, pushed by fins 16 applied to the arms 14, to descend towards the bass following a substantially labyrinthine path.

The multistage reactor (see fig. 5) is made up of a system of cylindrical bodies 21, equilateral or elongated, constructively similar to each other but not necessarily the same, preferably in number between four and eight, called "stages".

Each stage 21 is loaded from the top, by means of a suitable device 22, with solid material coming from the previous stage (the first stage is loaded with the waste through an inlet hopper 23; the solid material exiting from each stage passes into the next stage; in the last stage the ashes come out, in a similar way to how it happens in the bottom of the single-stage reactor of the previous examples.

Liquid waste is loaded into a high temperature stage 21, through an injector 29.

the loaded material is kept fluidized inside each stage by the injection of the superheated non-condensable gases produced by a stage 21 or through the gasifying mixture of oxygen 24, carbon dioxide 25 and water vapor 26. The non-condensable gases support pyrolysis , the gasifying gas mixture supports gasification, as occurs in the single-stage reactor.

Each stage 21 of the multistage reactor operates at uniform temperature throughout its volume, given the high turbulence of the fluidized mass, but at a temperature higher than that of the previous stage and lower than that of the next stage.

The pyrolysis and gasification gases are taken from each stage through a suitable device according to the usual technologies of fluidized bed systems (for example a cyclone 27 or another separator located inside the cylindrical body 21). The solid fractions are also withdrawn from each stage through traditional separator devices 28. The technology is therefore similar to that of ordinary fluidized bed reactors.

In the last stage, the gasifying mixture of oxygen, carbon dioxide and water vapor is injected. Furthermore, an injector 30 for nitrogen is provided in at least one stage but preferably in all stages.

In order to completely remove the traces of organic substance and carbon from the ashes and to recover the residual heat contained in them, the solid material leaving the main gasification stage is passed into a further stage 21 ', where it is placed in contact with the pure technical oxygen.

While from a plant engineering point of view the solution illustrated in fig. 5 differs from the solutions illustrated in figs. 1-4, from the point of view of the process the three solutions are equivalent: the zones of different and increasing temperature, collected in the single-stage reactor in a single device, are separated in a sequence of distinct devices in the multistage reactor. There is a precise correspondence between each section of the single stage reactor and each stage of the multistage fluidized bed reactor.

The present invention has been illustrated and described in two of its preferred embodiments and in an executive variant, but it is understood that other variants may in practice apply to them, without however departing from the scope of protection of this patent for industrial invention.

Claims (39)

R I V E N D I C A Z I O N I 1. Process of thermochemical conversion of urban and special waste into basic chemical products characterized by the fact that within several thermodynamic environments physically interconnected, it is carried out on the waste previously added with inerting substances: - a pyrolysis treatment at a slowly rising temperature starting from 100 ° C up to at least 700 ° C, - a gasification treatment on the carbon residues coming from the previous pyrolysis treatment at a temperature between 700 and 1100 ° C, by means of oxygen mixed with water vapor and carbon dioxide, obtaining hydrogen, carbon monoxide and carbon dioxide , which are used to condition the pyrolysis treatment, e - an inertization treatment of the heavy metal compounds, of the halogenated compounds and of the aromatic compounds obtained with the previous pyrolysis and gasification treatments, exploiting the heat developed by these treatments, the additive inerting substances and the substances themselves produced by the process. 2. Process according to claim 1 characterized in that different mixtures of volatile products, corresponding to different temperature intervals, are removed during the pyrolysis treatment. 3. Process according to claim 1 characterized in that the pyrolysis process is controlled by regulating the amount of heat that develops from the gasification reactions. 4. Process according to claim 3 characterized in that the quantity of heat that develops from the gasification reactions is controlled by adjusting the ratio between exothermic gasification reactions and endothermic gasification reactions based on the value of the partial pressures of oxygen, water vapor and carbon dioxide regulated in turn by the flows of these compounds entering the process. 5. Process according to claim 1 characterized in that the kinetics of pyrolysis is controlled by acting on the times of. permanence of the materials to be treated in their respective thermodynamic environments. 6. Process according to claim 1 characterized in that the pyrolysis treatment is controlled by acting on the partial pressures of the reaction products. 7. Process according to claim 6, characterized in that the partial pressures of the reaction products are regulated by acting on the removal flows of the volatile reaction products. 8. Process according to claim 1 characterized in that the inertization treatment of heavy metals is carried out by adding silica-rich substances to the waste to be treated. 9. Process according to claim 8 characterized in that silicates are added to the waste to be treated. 10. Process according to claim 9 characterized in that calcium silicate is added to the waste to be treated. 11. Process according to claim 8 characterized in that silica is added to the waste to be treated. 12. Process according to claim 8 characterized in that glass is added to the waste to be treated. 13. Process according to claim 8 characterized in that clay is added to the waste to be treated. 14. Process according to claim 1 characterized in that the inertization treatment of the halogenated compounds is carried out by adding carbonates of alkaline and / or alkaline-earth metals to the waste to be treated. 15. Process according to claim 14. characterized in that calcium carbonate is added to the waste to be treated. 16. Process according to claim 14 characterized in that sodium carbonate is added to the waste to be treated. 17. Process according to claim 1 characterized in that the inertization of the halogenated compounds is carried out by adding solid products obtained from the process itself to the waste to be treated. 18. Process according to claim 17 characterized in that the inertization of the halogenated compounds is carried out by adding to the waste from. treat products rich in free oxides. 19. Process according to claim 17 characterized in that free oxides are added to the waste to be treated. 20. Process according to claim 1 characterized in that the inertization treatment of the alkyl and aromatic halides is carried out by calcium oxide. 21. Process according to claim 1 characterized in that i) inertization treatment of the alkyl and aromatic halides is carried out by calcium carbonate. 22. Process according to claim 1 characterized in that one or more of the treatments are carried out under slight overpressure substantially corresponding to the pressure drops of the gases during the process itself. 23. Process according to claim 1 to be carried out in a fluidized bed reactor, characterized in that the bed is kept fludified by the gases coming from the process itself. 24. Process according to claim 1 to be carried out in a fluidized bed reactor, characterized in that the bed is kept fluidized by injection of oxygen and / or water vapor and / or carbon dioxide of external origin. 25. Plant for carrying out the process according to one or more of claims 1 to 24 comprising a reactor (1,21), means (2,7,23,29) for loading the waste to be treated into the reactor, and means (6 , 8,27,28) for removing the reactor from the solid and gaseous products obtained, characterized in that they are provided in the reactor (1.21). - different thermodynamic environments physically interconnected with each other, - solid waste loading means (2.23) distinct from liquid waste loading means (7.29), injectors (9,10,11) for oxygen, carbon dioxide and water vapor. 26. Plant according to claim 25 characterized in that it comprises a reactor (1) consisting of a cylindrical body, inside which steel diaphragms (4) and / or grids (5) are arranged, inclined downwards with a angle substantially equal to the angle of friction of the waste to be treated and with the injectors (9,10,11) arranged in the lower part of said cylindrical body. 27. plant according to claim 26 characterized by the fact of comprising in the lower part of the cylindrical body (1) an injector (12) for nitrogen. 28. Plant according to claim 26 characterized by the fact that the cylindrical body is affected on the side wall, in a position below the grids (5) and / or the diaphragms (4), by lateral inlets (6) for the withdrawal of gaseous, condensable products and incondensable. 29. Plant according to claim 26 characterized in that the cylindrical body (1) is equipped with a coaxial shaft (13), rotating, to which arms (14) are fixed. 30. Plant according to claim 26 characterized in that separator members are provided in correspondence with the lateral outlets for sampling the gases and pyrolysis products. 31. Plant according to claim 30 characterized in that the separators are of the labyrinth type. 32. Plant according to claim 23 characterized by the fact of comprising a reactor (1) consisting of a cylindrical body, inside which overlapping circular plates (15) are arranged alternately open at the central area and the peripheral area. 33. Plant according to claims 27 and 30 characterized in that each arm (14) is provided at the bottom with fins (16) acting on the underlying plate (15). 34. Plant according to claim 25 characterized in that it consists of a reactor comprising several fluid bed stages (21), each of which operating at a temperature higher than that of the previous stage and lower than that of the subsequent stage. 35. Plant according to claim 34 characterized in that it comprises, in at least one stage, an injector (30) for nitrogen. 36. Plant according to claim 34 characterized in that each stage (21) is involved in at least one outlet for drawing the condensable and non-condensable gaseous products. 37. Plant according to claim 34 characterized in that separator members (27,28) are provided in correspondence with the lateral outlets for sampling the gases and pyrolysis products. 38. Plant according to claim 37 characterized in that the separators (27,28) are of the cyclone type. 39. Process for converting urban and special waste into base compounds according to claims 1 to 24, plant for carrying out the process according to claims 25 to 38 and substantially as illustrated and described.