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TECHNICAL FIELD

The present invention relates to a process for the thermal-chemical treatment of organic and/or inorganic sludge and of solid waste containing organic substances, present in varying concentrations .

In particular, the sludge and/or solid waste treated are as follows:

biological sludge from domestic and industrial wastewater treatment plant;

inorganic sludge polluted by organic sludge including solvents, hydrocarbons and biological and organic chemical process residues;

digestate from the production of biogas from domestic, animal and vegetable waste;

aggregates such as sand, clay and drainage sludge from excavations during the reclamation of water courses, lake and sea water;

aggregates polluted by hydrocarbons, solvents and residues from biological and organic chemical processes (e.g. railway sleepers) ;

bilge sludge;

- solid urban refuse from separate refuse collection schemes, and in particular the wet, organic waste from this;

filter pressed sludge from the cleaning of septic tanks ;

- filter pressed sludge or slurry from livestock sewage ;

filter pressed sludge or slurry from tanning;

filter pressed sludge or slurry from textile industry wastewater treatment;

organic residues (biomass) from food processing facilities such as sugar refineries, fruit juice production plant and canneries.

The process according to the present invention comprises two successive steps of drying and carbonization which can be conducted in a continuous cycle in two reactors operating in cascade, under vacuum, with a residual pressure of less than 0.2 bar (absolute) .

Alternatively, the steps of drying and carbonization can be conducted in a single reactor only which performs the two operations under vacuum with a residual pressure of less than 0.2 bar (absolute) and operates in the intermittent batch mode .

The products of the process are as follows:

a) a carbon biochar;

b) an organic phase, obtained from separation by evaporation and distillation of the condensate fluid, containing all the volatilized molecules;

c) water.

The present invention applies to the sector for waste treatment processes and in particular to the sector for the thermal treatment of organic and inorganic wastes designed to produce secondary raw materials.

BACKGROUND ART

It is known that the masses of organic and/or inorganic sludges and solid waste containing organic substances, in varying concentrations, are processed in treatment plant employing drying, pyrolysis and incineration to recover the energy content of this waste and to reduce the mass for waste disposal. Examples of these organic and inorganic sludges and solid wastes are biological sludge from domestic and industrial wastewater treatment plant, inorganic sludge polluted by organic sludge including solvents, hydrocarbons and biological and organic chemical process residues, digestate from the production of biogas from domestic, animal and vegetable waste, aggregates such as sand and clay and drainage sludge from excavations from the reclamation of water courses, lake and sea water.

All the treatment processes cited above inevitably involve the emission into the atmosphere of the products deriving from the related combustion processes.

The traditional methods used for this purpose and for these types of waste matter are based on drying processes which use hot air, combustion gases from heat generation and drying with superheated steam. The thermal energy produced by burning the dried product can provide sufficient energy for drying operations or for other operations where additional energy is required.

These methods have been described in numerous publications and patents such as MUJU DAR A S ED

MUJUMDAR A S: "Chapter 19: Superheated steam drying" 1 January 2007 (2007-01-01), HANDBOOK OF INDUSTRIAL DRYING, CRC PRESS, US LNKD-DOI: 10.1201/9781420017618. CH19.

These processes are usually performed in large treatment facilities because of the problems related to control of the environmental impact especially with respect to atmospheric emissions .

DESCRIPTION OF THE INVENTION

The present invention provides a process for the thermal-chemical treatment of organic and/or inorganic sludge and of solid waste containing organic substances where the process is able to eliminate or at least reduce the shortcomings described above and where the thermal- chemical treatment process does not cause any harmful emissions into the atmosphere.

The invention also provides a suitable treatment for various types of waste, both organic and inorganic, which is able to remove various types of organic and inorganic pollutant .

From certain types of waste the process can also produce substantial amounts of surplus energy and also secondary raw materials with a calorific value.

For other types of waste the process enables the reuse of the treated material in the environment rather than its disposal in a dump, with evident environmental and economic advantages .

The process is practically without atmospheric emissions if one excludes the combustion fumes produced by the heat generator.

The process returns significant amounts of purified, recycled water to the environment. This is an advantage given that water is an increasingly precious resource.

All that can be recovered from inside the waste is in fact recovered. The only the fraction that needs to be sent for disposal is the fraction derived from the combustion of the steam generator.

1. Removal of polluting substances from any type of organic and inorganic waste

2. Production at the end of the process of one or more types of secondary raw material ready for re-use

3. Production at the end of the process of a watery fraction whose contaminant concentration levels do not prevent it from being returned to the environment .

4. A substantial reduction, at the end of the process, in the amount of waste to be sent for disposal as unrecyclable process waste

Elimination of any type of gaseous emission into the environment, excluding such emissions from the thermal energy generator.

Reduction in the amount of energy needed for the treatment process.

DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become clear on reading the description given below of one embodiment, provided as a non-binding example, with the help of the accompanying drawings, in which:

Figure 1 is a block diagram of the procedure according to the present invention;

Figure 2 is a diagram showing a complete view of the plant according to the present invention;

Figures 3 to 8 show various perspective and detailed views of the plant according to the present inventions .

DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

The annexed figures and in particular to Figure 1, 1 show the plant according to the present invention, indicated in its entirety by the numeral 10, and comprising a storage section 11 for the waste to be treated, a volumetric adaptation section 12, a dosing section 13, a dehydration and first treatment reactor 14 and an over-extraction and molecular recombination reactor 15.

The plant also comprises a cooling hopper 16, a section for the storage of treated waste 17, a section for the generation of thermal energy 18, a section for the generation of vacuum 19, a section for the condensation of transport and reaction steam 20, a section for the treatment of condensate 21 and a section for the treatment of condensation water 22.

The process starts in the storage section 11 for the waste to be treated, where the material to be treated is accumulated and stored prior to treatment in a controlled and contained manner so that it can be classified for the treatment downstream.

The material passes to the volumetric adaptation section 12 where mechanical cutters reduce the material to be treated to pieces of a suitable size for treatment; this operation is not always necessary.

In the next step the material passes to the dosing section 13 where it weighed ready for batching to the reactor. The dosed material is transported to the reactor by conveyor belts .

Next, the material passes into the first treatment and dehydration reactor 14, that is, into the first reactor used for dehydration.

For this part of the process the reactor is closed and kept under vacuum. Inside the reactor there is a system of horizontal, twin-shaft blades which agitate the material being treated keeping it in continuous movement .

The reactor 14 is kept at a controlled temperature by a jacket through which eutectic salts pass. The internal temperature is controlled by a system of probes and is kept above the equilibrium temperature of the water vapour system at approximately 120 - 140 °C in order to enable the evaporation of all the water and low boiling-point substances present inside the waste to be treated.

A countercurrent of water vapour is fed into the reactor in order to transport and extract the volatile substances and the water contained in the material being treated and the volatile substances also where no water is present. The temperature controller indicates when the water in the waste being treated has been completely- evaporated and the material is ready for transfer to the second reactor.

The material now passes through the over-extraction and molecular recombination reactor 15. After the dehydration step, the material is transferred to a second reactor. Inside this reactor there is a system of horizontal, twin-shaft blades which agitate the material being treated keeping it in continuous movement . The reactor is kept at a controlled temperature by a jacket through which eutectic salts pass. The temperature inside is controlled by a system of probes. The temperature inside the reactor is kept at approximately 350 - 420 °C in order to enable the extraction of the decomposed and volatile substances present inside the waste to be treated. A countercurrent of water vapour is fed into the reactor in order to transport and extract the volatile substances and the water contained in the material being treated and the volatile substances also where no water is present. During this step at a higher temperature, stripping of the substances which pass to the gaseous phase takes place. At the same time molecular recombination also takes place as a function of the type of pollutant and the type of waste present. Molecular combination changes the chemical speciation of many of the elements contained in the waste being treated.

In the block diagram in Figure 1, the numeral 16 indicates the cooling hopper. At the end of the extraction and molecular recombination step the treated material is unloaded into a cooling hopper. Cooling at this stage is necessary in order to enable the transport and storage of the material treated under safe conditions. A vacuum is also maintained in this hopper to prevent the possible ignition of uncontrolled combustion.

The numeral 17 in the block diagram in Figure 1 indicates the storage section for the treated material . The material, treated and cooled, is transported on conveyor belts or screw feeders to suitable storage zones or similar ready for re-use. The treated material does not contain pollutants. It can be re-used as a fuel if it has the necessary calorific power. It can be used as building material if it has the necessary mechanical properties. It can also be used as repair material in environmental and reclamation projects.

The numeral 18 indicates the section generating the thermal energy needed for the process, for heating the eutectic sales and for generating the steam; the thermal energy is produced by a burner. It should be noted that if a thermal energy unit is not present it will be possible to used mains electrical power for these functions. This will of course worsen the energy balance.

The burner can be fed with fossil fuels from outside the process or with secondary raw material originating from this process. This latter solution clearly improves the energy balance of the process. The combustion fumes from the burner can be used to heat the eutectic salts needed to heat the two reactors 14 and 15 and to produce the countercurrent of transfer water vapour which is fed to both reactors. The combustion fumes, once they have performed their function are discharged into the atmosphere in a controlled manner. The ash produced by the combustion process is the only waste produced by the treatment process which requires disposal.

The vacuum generation section 19 generates the vacuum inside the reactors and inside the cooling and unloading hopper; the vacuum is provided by liquid ring pumps .

The numeral 20 indicates the section for the condensation of transport and reaction steam, where the steam current used by the reactors 14 and 15 is fed to the treatment process. Initially the steam is passed through a cyclone in order to separate the heavier particles present in the flow. After this the steam is condensed, under vacuum. This is done without any emissions into the atmosphere.

In the condensate treatment section 21 the condensate obtained is treated in a evaporation and enrichment cell where it is separated, under vacuum, into two flows. One flow contains organic acids, nitrogenous components and other substances . This is known as the organic flow or oil and is destined for re-use and recycling. The second flow consists of water which will be treated afterwards before being discharged.

Lastly, in the section for the treatment of condensation water 22, the water from the previous section is treated in chemical-physical and biological purification equipment to eliminate any pollutants present before being discharged. Any sludge produced can be returned to the treatment process that produced it in the first place. This process step does not produce waste but returns controlled water to the environment.

In Figure 2, the numeral 13 indicates the hopper where the material to be treated is weighed, dosed and then batched onto the conveyor belt 23 which transfers it to the dehydration reactor 14. After the reactor has been loaded, the system is closed and placed under vacuum by the high-vacuum unit 19. The material in the reactor (14) is kept at a controlled temperature by means of a jacket that allows the passage of eutectic salts which are heat-controlled by appropriate probes, in order to permit evaporation of the water and thus perform the first dehydration step. At the end of this step, the material is transferred, under vacuum, to the second reactor 15 where molecular recombination takes place. Both reactors are equipped with a twin- shaft mixing blade system which homogenizes the material in the reactors. In the second reactor too, the temperature is controlled by a probe system that controls the eutectic salt heating system.

The substances which pass to to the gaseous phase are sent to the stripping column 24. The material treated in this way is then discharged into the cooling hopper 16, still under vacuum, to prevent the risk of uncontrolled combustion, and on reaching a safe temperature the material is transferred by screw feeders, conveyor belts, elevators or pneumatic transport systems to the storage section 17.

In Figure 3 , the numeral 18 indicates the heat generator that heats the molten salts for the two reactors and generates the steam used to transport the volatile elements to the damping system.

On the most fully equipped system, the heat generator can also be fitted with heat regenerators 25. The currents of steam pass through the cyclones 26 to the condensate treatment section 21 where they are divided into two flows: the organic flow or oil destined for reuse or recycling and the flow of water which is transferred to the water treatment section 22 which consists of chemical-physical and biological treatment tanks 27 from which water-purified sludge is obtained which is then further compacted by means of a filter- press 28 and returned to the initial treatment cycle.

The plant is managed by a supervision system installed in the control cabin 29, while the electrical controls are installed in the local electrical cabinets 30.

The invention is described above with reference to a preferred embodiment. It is nevertheless clear that the invention is susceptible to numerous variations which lie within the scope of its disclosure, in the framework of technical equivalents .