Field of the invention

The present invention relates to a plant for combustion or incineration of various materials, in particular waste, with abatement and destruction of the pollutant fumes resulting from combustion.

It is emphasized that in the present description by "combustion" is meant a process in the presence of air, whether in excess or in defect, with consequent exclusion of the processes based upon the phenomenon of pyrolysis, i.e., in the absence of air.

In greater detail, the plant according to the invention is conceived for thermodestruction of any combustible material with or without recovery of the thermal energy produced by combustion, but in any case with drastic reduction of the percentages of pollutants in the resulting fumes. It is a system for incineration of waste and thermodestruction of the incondensable gases and dioxins resulting from incineration of any type of waste, including second-degree raw materials that after combustion are discharged into the atmosphere. The present plant finds particular application in the sector of incineration of waste - such as urban solid waste (USW), special waste, industrial waste, and all the solid-fossil and liquid-fossil toxic-noxious derivatives, waste and second-degree raw materials that comprise all the fossil residues, exhausted mineral and vegetable oils, all the residuals of petroleum and fossils of any kind, and tyres for motor vehicles - and of thermodestruction of the pollutant atoms contained in the fumes and incondensables.

In the various possible applications, the plant can be adapted to operate in combination with combustion furnaces of a different type, both ones with variable temperature and ones with controlled and constant temperature, or again rotary furnaces with variable geometry and the like. The plant can moreover be adapted according to the materials that are to undergo destruction and the type of energy that it is desired, if possible, to recover, on the basis of the requirements of small and medium-sized industries up to large plants for the systematic destruction of waste, with a recovery of up to 95% of the potential energy contained in the waste. State of the art

In the current state of the art, incineration systems are known comprising a furnace for combustion of the material by thermodestruction and a postcombustion device designed for bringing the resulting fumes of combustion to very high temperatures in order to abate the percentage of pollutants, for example dioxins and sulphates, but are totally devoid of separators of CO ₂ and condensers for condensing the water contained in the incondensables that are to be destroyed.

In greater detail, in the fumes that are to reach the atmosphere numerous pollutants are generally present, such as CO, SO, SO ₂ , HCI, HF, NO, NOx, particulates present in larger amounts, and other noxious components in low concentrations but of high toxicity such as polycyclic aromatic hydrocarbons (PAHs), compounds of heavy metals (mercury, cadmium), organo- chlorinated compounds (polychlorobiphenyls, dioxins, furans). At the current state of the art, for incineration of waste also known are furnaces referred to as "gasification furnaces", constituted by a combustion chamber thermally insulated from the outside world and coated on the inside with a refractory material, in which the fuel is burnt using an amount of oxygen that is insufficient for complete oxidation of the material present in order to produce a combustible gas (syngas), which may then be burnt to produce thermal energy to be recovered, for example, via a steam turbine or an explosion engine. Moreover known are incineration plants based upon alternating-charging rocking furnaces, in which adjustment of the air for the combustion is carried out on the basis of the stoichiometric scale, i.e., by pressure. Known from the Italian patent No. IT1316578 is a system for thermodestruction of waste, in which a succession of separator modules is used for pre-treatment of the fumes that leave the combustion chamber and that are to go to a postcombustor once they have been deprived of the condensable components, such as water, dust, and carbon dioxide. This solution has not, however, solved the problem of a complete cleaning and separation of the incondensable gases introduced into the postcombustor and of the temperature necessary to obtain thermodestruction thereof. Incineration plants of a known type present numerous drawbacks.

A first drawback is represented by the fact that the abatement of pollutant fumes does not prove satisfactory unless the postcombustion process is brought up to very high temperatures, this both in energy-recovery plants and in thermodestruction plants for the abatement alone of pollutants. In particular, in traditional incineration systems regulation of the air for combustion is performed on the basis of the stoichiometric scale, and hence cannot be performed automatically at any moment, as would be necessary when there is a continuous variation of the characteristics of the waste. A further drawback of incineration systems of a known type is that they present a high energy consumption.

A further drawback is that incineration systems of a conventional type are unable to burn toxic-noxious waste.

Known postcombustion systems are in fact characterized by a high energy consumption due to the presence in the fumes of carbon dioxide and condensate, which knocks down the temperature necessary for destruction of the noxious fumes. Summary of the invention

The purpose of the present invention is to overcome the drawbacks of known incineration systems, and to propose a plant that is able to destroy thermally combustible materials of any type and in particular waste of any kind, at the time same obtaining a level of abatement of the pollutant fumes that is much higher than in known systems, to reach values of concentration of pollutants that are lower than the values required by the relevant standards. According to the invention, the above purpose is achieved with a plant according to Claims 1- 14. According to a further aspect of the invention, the plant comprises an assembly for recovery of the energy produced by combustion.

According to the invention, the above purpose is achieved with a plant according to Claims 15-23.

Further purposes are achieved according to the attached dependent claims. The advantages obtained basically consist in the possibility of destroying any type of material completely, in particular also toxic-noxious waste, with a drastic abatement by thermodestruction of the resulting pollutant fumes.

A second advantage lies in the energy efficiency of the process of thermodestruction of the incondensables. A third advantage consists in the adaptability of the plant to different requirements in terms of material to be destroyed, size of the plant, and energy requirements.

A fourth advantage consists in the possibility of recovering the energy produced by combustion. A fifth advantage consists in the possibility of thermodestruction in a continuous process of material that is non-uniform in terms of volume and quality, maintaining the pollutant values of the fumes at output below fixed and pre-set values.

List of the drawings The technical characteristics of the invention, according to the aforesaid purposes, emerge clearly from the contents of the annexed claims, and advantages that it affords will become even more evident from the ensuing detailed description and the annexed plates of drawings, wherein:

- Figure 1A shows an example of thermodestruction plant of a traditional type;

- Figure 1 is a schematic representation of a first embodiment of the plant;

- Figure 2 is a schematic representation of a second embodiment of the plant equipped with an energy-recovery assembly;

- Figure 3 shows a preferred embodiment of a module for separation of carbon dioxide according to the invention.

Detailed description

With reference to the attached figures, described herein is a plant according to the invention, comprising a combustion chamber 1 for combustion of a mass of fuel supplied from a supply mouth 26.

By way of example, and as will be specified more fully in the course of the description, the chamber 1 can be constituted by an incinerator furnace, a boiler supplied, for example, with coal or with tyres for motor vehicles, or other device operating by combustion in the presence of oxygen, hence excluding devices which operate by pyrolysis.

The chamber 1 is connected via a pipe 9 to a postcombustion device 2 for thermodestruction of the incondensable gases generated by combustion, which is also connected, via a pipe 27, to a supply 21 of air rich in oxygen, preferably for separation of the nitrogen component, in order to maintain optimal carburation of the postcombustor, which is regulated by a control unit 23 and by a regulation valve 24 for modulating the air. Preferably, the postcombustor 2 is constituted by three cylinders and a base, which may also present different shapes, and is equipped with three manifolds: a first one for inlet of gases 43, which leads to a modulating burner 16 with the function of bringing the postcombustor up to temperature; a second one, i.e., the pipe 9, which conveys the incondensable gases; and a third one, designated by 19, for discharge. All the components are preferably made of stainless steel coated on the inside with refractory material 18 having the function of maintaining the internal temperature of the postcombustor itself constant.

It is understood that the postcombustor 2 may have shapes and characteristics optimized in relation to the constructional design of the plant. According to the invention, set along the pipe 9, in an intermediate position between the chamber 1 and the postcombustor 2 is at least one module 4 for abatement, by difference in specific weight, of carbon dioxide and/or carbon monoxide present in the combustion fumes, as also of any other component having a specific weight higher than that of the incondensables, such as LPG, methane, propane, butane, or the like.

In a preferred embodiment, the modules 4 are constituted by a conveyor 8 traversed from top down by the combustion fumes and by a current of water, which is introduced into the cylinder by a piping 12 and laps the flow of fumes, englobing and drawing along with it the carbon dioxide and possible dust, which is conveyed via a drainage pipe 11 into an underlying tank 10 for deposit of waste water. The circulation of the water can moreover be assisted by a recirculating pump 17, which draws from the tank 10, which is preferably made of stainless steel and is connected to the sewage network, and delivers into the piping 12. With reference in particular to Figure 4, described hereinafter is a preferred embodiment of the module 4 for the abatement of CO ₂ , CO, dust, and other components of relatively high specific weight.

The module 4 has inside it a series of pilot tubes or ducts 44, which may have different cross sections and shapes according to the requirements and have the function of directing the residue of combustion coming from the chamber 1 through the pipe 9 at inlet to the module 4. According to the invention, the pilot ducts are distributed in at least two diffusers 45, 47, which are set in the internal section 46 of the module 4 and are separated by an empty portion 48 of the section 46. With this solution, the fumes coming from the chamber 9 are distributed and traverse the ducts 44 of the first diffuser 45, invade the empty portion 48, and are distributed again and traverse the ducts 44 of the second diffuser 47.

During transit through the module 4, the fumes are impinged upon by the water coming from the line 12 and sent into the module 4 preferably through sprayers 49. Thanks to the thermal jump that occurs in the combustion chamber, the incondensable gases increase in volume and enter the module 4 with a specific weight lower than the carbon dioxide, dust, carbon monoxide, and other components, which are impinged upon by the flow of water and precipitated by difference of specific weight through the drainage pipe 11. Advantageously, the presence in succession of a number of diffusers separated by an empty portion enables improvement of the surface of exchange between the fumes to be precipitated and the water, drastically reducing the residual content thereof in the pipe 9 downstream of the module 4.

In addition, according to the invention, in steady running conditions the module 4 is traversed by the "dirty" waste water, pushed by the pump 17, with the advantage of favouring englobing of carbon dioxide, CO, and dust and their precipitation into the tank 10, as compared to the use of clear water or mains water.

Moreover provided downstream of the module 4 along the piping 9 is a separator module 5 for abatement of the water vapour present in the fumes, which preferably comprises a tube-nest exchanger traversed by the fumes and by the recirculating water pushed by the pump 17, which causes condensation of the steam and falling thereof into a tank 10 preferably made of stainless steel and connected to the sewage network. In greater detail, the separator 5 is an air/water separator constituted by two cylinders made of stainless steel or by other suitable material, inside which two nests of pipes are connected, sized so as to be self-cleaning and isolated in a fluid-tight way so as to be traversed by the exhaust fumes without coming into contact with the cooling water that laps the outer surface of the pipes themselves. Advantageously, the treatment of separation of carbon dioxide, dust, and water vapour (and possibly nitrogen) from the fumes coming from the combustion chamber 1 makes it possible to limit or eliminate in the postcombustion step the cooling effect otherwise caused by the fumes, and to obtain resulting gases that can be used for a further recovery of heat and of electrical energy and that after postcombustion are rendered altogether harmless.

In this connection, it is emphasized that any incineration furnace produces dioxins in the combustion chamber already at the temperature of 300 ⁰ C; then, as the temperature rises in the combustion chamber, the dioxins previously produced burn but other more resistant ones are produced, and so on until dioxins are produced that to undergo destruction require in known systems the use of postcombustors operating at above 1100 ⁰ C. Thanks to the invention the pollutant atoms undergo previously a treatment of separation of carbon dioxide and dust and condensation of the water vapours, whilst the incondensables are pushed into the postcombustor and can be burnt at a relatively low temperature indicatively comprised between 600-700 ⁰ C or lower, with evident energetic advantage of the thermodestruction process.

In the example described, set downstream of the module for separation of the condensate 5 a negative-pressure device 6 is provided set along the piping 9 with inlet of the fumes at the bottom and outlet at the top. The negative-pressure device 6 is preferably a extractor with variable r.p.m., or flow regulator, which determines vacuum supply of the plant, i.e., of the combustion chamber 1 , inducing a negative pressure in the upstream pipes, and a positive pressure downstream, with the further effect of aspirating the condensation gases contained in the fumes through the modules 4 and 5, and pushing the residual incondensable gases into the subsequent stretch of the piping 9.

Moreover provided further downstream, along the piping 9, is a module 7 for abatement of the hydrochloric acid contained in the combustion fumes that are by now deprived of the condensation component and are to go on to the postcombustor. Preferably, the module 7 is constituted by a cylindrical container 7, inside which a mixture of water and bicarbonate, soda or the like is present, preferably supplied automatically for neutralizing the acids contained in the incondensables. The cylinder 7 is traversed from bottom to top by the fumes coming from the piping 9 and comprises a pump 20 for circulation of the bicarbonate mixture taken from a deposit 19, which draws in from the tank 10, the bicarbonate mixture being introduced via a piping 30 into the pipe 9 at inlet to the cylinder 7. In addition, also the module 7 is traversed by the recirculating water coming from the piping 30 and poured back into the tank 10 via the drainage pipe 11. It is understood that the number and sizing of the modules 4, 5, 6, 7 is variable and can be optimized on the basis of the type of waste or fuel to be burnt and of the dimensions of the plant, as likewise of the desired application.

In operation, the fumes introduced by the pipe 9 traverse the bicarbonate mixture present in the cylinder 7 and undergo abatement of the acids, which are poured, by now neutralized, into the tank 10 through the stretch of drainage pipe 11 , reaching the top stretch of the pipe 9 without any acid content.

At the same time the pump 20 carries out circulation of the bicarbonate mixture by drawing from the deposit 29 and from the tank 10 via a piping 49. Advantageously, according to the invention, the devices for abatement of the carbon dioxide 4, water vapour 5, and hydrochloric acid 7 can be assembled in a replaceable and modular way along said pipe 9 on the basis of the application and size of the plant and the type of fuel introduced into the chamber 1. At outlet from the module 7, the pipe 9 conveys the residual incondensable gases into the postcombustor 2, to carry out thermodestruction thereof, already at temperatures that range from 600 to 700 ⁰ C. Once thermodestruction of the fumes has been carried out, the postcombustor 2 finally discharges, via a pipe 19, the residual fumes, which are by now free from any pollutant content. Advantageously, the connection pipe 9, before conveying the component of incondensable gases coming from the combustion chamber 1 into the postcombustor, passes through all the separator devices 4, 5, 7, which consequently form a closed circuit of the system. Once again with reference to the figures, a plant according to the invention can comprise a control unit 23 for governing a valve 24 for regulation of the volume of oxygen-enriched air that is to reach the postcombustor 2 on the basis of the values of oxygen content detected by a probe 25 set in the proximity of the outlet of the combustion fumes from the chamber 1. With this solution it is advantageously possible to adapt automatically the temperature reached in the postcombustor, and hence the level necessary for thermodestruction of the pollutants, on the basis of the type of fuel introduced, even if the latter varies over time as occurs in the case of urban solid waste. In this context, it is specified that the combustion chamber 1 may consequently be constituted by a furnace for incineration of solid and/or liquid toxic-noxious waste, for example, chemical/pharmaceutical waste, or else again by a boiler for combustion of coal or tyres, or else a converter furnace supplied with liquid fossils, or a furnace for incineration and gasification of urban solid waste (USW).

With reference to Figure 2, described hereinafter is an embodiment of the invention comprising an energy-recovery assembly 31 set between said combustion chamber 1 and the module for abatement of carbon dioxide 4. In this case, the combustion chamber 1 is preferably constituted by a combustion chamber of a gasification furnace 41 for the production of syngases, which does not require supply of air for the combustion because it works in defect of air, but uses only a limited amount of carbon dioxide that serves for transfer of the gases obtained from the furnace 1 to the assembly 31 , without, however, burning the gas produced.

In the preferred embodiment illustrated, the assembly 31 comprises a postcombustor 13, which comprises a modular burner 16 and is supplied via a pipe 50 by the combustion fumes of the chamber 1 and which, in turn, supplies a steam generator 3 provided with an outlet 32 for the steam produced that is to be sent on to a turbine 15, preferably through a valve 38, and with an outlet 40 for the residual fumes that are to be sent on to the device for abatement of carbon dioxide 4.

In this embodiment a second control unit 33 may moreover be provided for governing a valve 34 for regulation of the volume of oxygen-enriched air that comes from the supply 21 and that is to be sent to the postcombustor 2 and/or 13, which can be modified on the basis of the values of oxygen content detected by the probe 25 set at the outlet from the chamber 1 and by a probe 35 set, instead, in the proximity of the outlet 40 of the combustion fumes from the steam generator 3. Preferably, a second steam generator 14 can moreover be provided, supplied by the postcombustor 2 and provided with an outlet 36 for the steam produced that is to be sent on to a turbine 15, preferably through a valve 38, and moreover connected to the outlet 19 of the pollutant-free exhaust fumes. According to the invention moreover envisaged is the use of a probe 37 for measuring the contents of the fumes at the exhaust 19, which is connected to the control unit 23. Advantageously, reading of the characteristics of the gases emitted by the plant through the exhaust 19 enables optimization of the combustion temperature that can be obtained in the chamber 1 , in the postcombustor 2, and in the postcombustor 13 .

By way of example provided hereinafter are the results of two different tests conducted by means of sampling of the fumes produced by a plant made in compliance with the plant of Figure 1 , by measuring the contents of the fumes detected at the outlet 19.

Example of Analysis 1 The samplings carried out comprised: - determination of the parameters of the combustion fumes using a MADUR "GA-40 PLUS" analyser;

- sampling for determination of dust and recovery of the condensate with subsequent determination of T.O.C. (total organic carbon) in the condensate recovered in the tank 10 and of some metals once again in the condensate and on a filter after it was treated with nitric acid; the determination of the metals was carried out by means of atomic-absorption spectrophotometry;

- sampling for determination of the incondensable volatile organic substances after prior absorption of the flow sampled on a vial of activated carbon, extraction with CS ₂ , and subsequent gaschromatographic determination;

- sampling for determination of acids (HCI and HF) after prior bubbling of the flow drawn into a basic solution; the subsequent determination of the chloride and fluoride ions was performed by means of ion chromatography. The samples were taken at the outlet 19 of the combustion fumes from the postbumer 13.

During sampling the plant was supplied with offcuts of finished leather, shearings and bags for containing raw leather, shredded plastic drums, urban solid waste (USW), empty containers of chemical products, PVC, chrome-leather shavings, and drums made of rubber.

COMBUSTION-FUME PARAMETERS

In the following tables the values of concentration given in the second column are normalized at the temperature of 273 K and at the pressure of 101.3 kPa, whilst in the third column the same values of concentration are given referred, however, to an oxygen content of 11% (as indicated in the attachments of the Ministerial Decree dated February 05, 1998 "Determination of the limit values and prescriptions for the emissions into the atmosphere of the activities of recovery of energy from non-dangerous waste" - "Determinazione dei valori limite e prescrizioni per Ie emissioni in atmosfera delle attivita di recupero energia dai rifiuti non pericolosi" and in the attachment of the Italian Ministerial Decree No.124 dated February 25, 2000.

DUST, T.O.C., AND METALS Condensate recovered = 32 ml

* = 0.5 mg/Nm ³ as average value of the sum of the concentrations of ten metals (Sb, As, Pb, Cr, Co, Cu, Mn, Ni, V, Sn).

HYDROFLUORIC ACID. HYDROCHLORIC ACID, AND INCONDENSABLES

The following volatile organic substances were identified, all with concentrations of much lower than 1 mg/Nm ³ :

Example of Analysis 2

A series of analyses were conducted for sampling the combustion fumes for determination of polychlorodibenzodioxins (PCDDs), polychlorodibenzofurans (PCDFs), and polycyclic aromatic hydrocarbons

(PAHs).

The samples were taken at outlet of the combustion fumes from the postcombustor.

The samplings carried out comprised:

- determination of the parameters of the combustion fumes with MADUR

"GA - 40 PLUS" analyser; - determination of PCDDs, PCDFs, and PAHs according to the method UNICHIM No. 825/1988 and subsequent modifications as indicated in the attachments of the Italian Ministerial Decree dated February 25, 2000;

- in particular a sample was taken of the aeriform in isokinetic conditions (method UNICHIM 494), by inserting downstream of the sampling and dust- collection probe a coolant for recovery of the condensate and at outlet from the condenser two absorption cartridges containing synthetic resins;

- at the end of sampling both the probe and the condenser were accurately washed with acetone; the washings were then added to the solvent used for extraction of the micropollutants from the condensate;

- the determination of the micropollutants was carried out on the particulate material, on the condensate, and on the adsorbent material after prior "extraction" with toluene;

- all the extracts combined were divided into two aliquots, one for determination of the PAHs and one for determination of the PCDDs and of the PCDFs, after prior purification and separation from the PCBs by means of mass-spectrometry gaschromatography;

- the results of the analyses conducted were normalized at the temperature of 273 K, at the pressure of 101.3 kPa, and referred to a volume of dry gas. CONDITIONS OF OPERATION OF THE PLANT

During sampling, the plant was supplied with urban solid waste (USW), offcuts of "finished" leather, shearings and bags for containing raw leather, shredded plastic drums, other empty containers of chemical products, chrome-leather shavings, and other waste of plastic material coming from various processing operations.

In addition, the postcombustor 13 was programmed in such a way that the gases produced by incineration of the waste were brought, after the last introduction of combustion air and before expulsion into the atmosphere, at a temperature of at least 95O ⁰ C. RESULTS OF ANALYSES

Given in the tables below are the concentrations of the pollutants found and referred to an oxygen content of 11%. PARAMETERS OF THE COMBUSTION FUMES

PCDDs - PCDFs - PAHs

Start of sampling End of sampling Effective duration of sampling

Time: 16.30 Time: 04.30 720 min

Suction flow Volume sampled (I) Volume sampled (273 K 101.3 kPa)

11.1 l/min 8340.5 7906.1

( ^* ) as mean value detected for a sampling period of 8 hours and referred to 11% of O ₂ in the gaseous effluent.

The invention achieves important advantages. The system is pre-arranged for modular solutions, i.e., for providing both in medium-sized and in large-size plants a series of modular and conversion furnaces that can be used also in alternating phases. With the system in question syngas is produced with any waste, for example through a coaxial furnace with programmed and continuous supply through which a high level of functionality and safety is achieved. This result is possible not only because the combustion furnace is a variable-geometry furnace but also because it is supplied with oxygen-enriched air, produced by the device 21 , for example, a device that separates nitrogen from the supply air of the burners, furnaces, heat accelerators, and postcombustors. With this solution it is hence possible to provide progressively smaller and more compact plants, but ones having a functionality and efficiency of thermodestruction of pollutants that is increasingly high. In fact, if it is considered that the nitrogen contained in the air is approximately 70% and if 40% is extracted, in proportion to the size it is possible to build systems of dimension that are 30% - 40% smaller.

In addition, since the amount of nitrogen that is introduced into the chambers for combustion of the waste and into the heat accelerators is normally 30%-40% higher, thanks to the invention the extinguishing effect is prevented and hence there is obtained a saving for ignition of the furnaces and of the heat accelerators, which require an amount of energy that is 30- 40% less to reach steady running conditions.

Thanks to the possibility of adjusting the supply of the oxygen-enriched air and to the use of the adjustable aspirator 6, the plant constitutes a true means of thermal destruction of waste and fumes with continuos variable adjustment at a controlled temperature.

In addition, the plant is suited for obtaining easily the conversion of electric power stations into fossil-carbon power stations. Furthermore, with the gases that are produced it is possible to supply cogeneration or produce LPG, along with abatement of the pollutants into the atmosphere.

In addition, thanks to the invention destruction of the incondensables produced by combustion and recovery of the potential energy contained therein in order to produce electrical energy are obtained. The system forming the subject of the present invention enables in fact recovery both of the potential energy of the waste introduced into the combustion chamber and of the resulting incondensables, which form an excellent syngas with a calorific power higher than 516 000 kcal. At the same time, said incondensables, by passing through the postcombustor already at temperatures of 600-700 ⁰ C are destroyed, as likewise the pollutants contained in the carbon atoms, etc., in such a way that, once freed into the environment, they are altogether harmless and breathable.

The system thus conceived is suitable for evident industrial application; it may likewise undergo numerous modifications and variations, all of which fall within the scope of the inventive idea; all the items may moreover be replaced by technically equivalent elements.