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Field of application of the invention

This invention concerns the treatment and disposal of waste organic material such as, but not exclusively, solid urban waste, and refers in particular to a gasification plant of such materials with the production of a fuel deriving from the waste, that is to say synthesis gas-SynGas-which is then usable in systems for the production of electric and/or thermal energy. State of the technique

As is known gasification is a process without combustion that enables a fuel to be obtained from the thermal treatment of urban and non urban organic waste.

The document US-6 938 562 is indicative of such a gasification process, carried out however in a discontinuous way, in the sense that each reaction cell, or reactor, must be cooled and open after the treatment of each load in order to remove the residue and to load the new material to be processed. This also involves and requires the need each time to heat the material and once again to restore the gasification conditions with a loss in time and evident waste of energy.

In the present practice, the gasification that takes advantage of a molecular disassociation process, called pyrolysis, represents a valid alternative to all the incineration combustion plant, that above all cause problems of oxidation and production of dioxins and other pollutants.

The materials that can be treated in a pyrolysis process are typically

- the dry fractions of the urban waste, separated by mechanical systems and collected in an undifferentiated way and/or bio dried waste;

- the scrap coming from the selection of waste from differentiated collecting, that is the part not intended for salvage; and furthermore, up to 50% in weight, of declared assimilated waste such as: non chloride plastics; polycouplings (cartons for milk, wine, fruit juices...); the non chloride synthetic rubbers; resins and synthetic and artificial fibres with a content of Cl< at 0, 5% in mass; worn out tyres.

The CDR obtained, however, must correspond to precise requirements and parameters regulated by rules, such as those in the following table:

Pci CDR mm

Humidity in mass max

Chlorine in mass min

Sulphur in mass min

Ashes on dry in mass min

Pb (volatile) on dry in mass max

Cr on dry in mass max

Cu (solub. comp.) on dry in max mass

The gasification process is carried out in plants starting from various materials obtaining combustion gasses from it according to a general scheme

CH ₃

The organic material, regardless of its vegetable, animal or synthetic origin, contains solar energy that the photosynthesis process has imprisoned between the carbon and hydrogen molecules. Consequently, in a closed ambient with temperatures below 500 ⁰ C and in the almost total absence of oxygen these waste products, that contain carbon, become completely modified by splitting the molecules, generally long carbonaceous chains, into more simple carbon monoxide, hydrogen and methane molecules that form a "synthesis gas " -SynGas- which is sufficiently pure to be used as it is.

The gas that develops in a length of time from between 8 and 24 hours, so as to come close to the natural degradation time of the molecules, represented by 15% to 30% in weight of the original organic material, depending on the process temperature which is normally made up of: hydrogen (H ₂ ), carbon monoxide (CO) and carbon dioxide (CO ₂ ); methane (CH ₄ ) and light hydrocarbons; traces of hydrocarbons with more molecular weight; various contaminants among which stands out TAR, that is bituminous oil produced following the reactions of pyrolysis and present in a vapour state inside the gas. The inferior calorific capacity developed by the gas in the combustion in a boiler, for the production of superheated steam to be used in a turbine of a generator, is usually between 3,000 kcal/m ³ and 4,500 kcal/m ³ .

All with an average efficiency of 70% compared to the energy introduced, variously distributed in electricity and heat, and with a quantity of ashes remaining at the end of the process equal to about 3% of the starting mass.

Due to the effect of the kinetics of the gasification reaction and other particular conditions such as the relatively low treatment temperature, it reduces: to over a hundred times the emission of fine dust, in particular the production of nano-powders; to at least half of the production of hydrochloric acid, sulphur dioxide and carbon monoxide; to a third of the nitrogen oxides; from 20 to 50 times the heavy metals; the concentration of dioxins and furans to a level so low that it cannot be measured. Object of the Invention

The object of the invention is however to propose an innovative plant to optimise the conditions and improve the efficiency, modular structure and safety of a gasification process of waste organic materials to be carried out advantageously in a continuous system which enables parity of performance with a discontinuous gasification system, to reduce both the down time and dimensions of the treatment cells and to ensure operating continuity of the equipment downstream.

The result, as sought-after, is a production of SynGas usable then as an energetic vector for the operating of a generator group and/or the production of thermal energy, principally with a completely negligible if not inexistent environmental and pollution impact. Such an object is achieved in compliance with the invention using a system according to the preamble in claim 1 and where principally each primary reaction cell has a steel body with a special internal refractory covering, closed by depression, and associated with means for supplying it continuously with material to be processed and provided with means for evacuation, also continuous, of residual non-gasifiable material.

In fact, the gasification process involves all the organic parts present in each reaction cell, inside which there can be found non organic and inert materials such as glass, metals, etc. In this case, on conclusion of the primary process, these materials are extracted and transported to be selected. After the primary process, followed by the use of SynGas, a maximum residue estimable in 2 - 3% of ashes and aggregates can be found.

As regards to emissions in the atmosphere, as already pointed out, the destruction of an organic compound is the function of the temperature to cause the chemical bonds to break. In the proposed system, in one chamber or secondary cell like an after-burner, constant temperatures are reached which are by far higher than those necessary for breaking the more stable bonds. In this way, thanks to the non combustion in the primary cell and to the use of steam turbines, there are no emissions of fumes from the process, but only steam and the mere emissions of hot air and CO ₂ .

The energy recovery happens through the production of superheated steam and at high pressure for the feeding of turbines of a generator, both with the direct use of the heat not used in this way, for example for district heating, and for the delivery of electric energy. The combination of these ways of recuperating thermal energy from waste makes this discharge process economically more favourable compared to all past and present solutions.

The energy recuperation system also plays an important role in the depuration of fumes. In fact, a rapid cooling of the fumes reduces the possibility of secondary reaction of the formation of pollutants, for example the formation ex novo of dioxins, furthermore the lowering of temperature causes a contraction of the levels of the fumes in the following depuration plants.

Brief Description of the Drawings The invention will however be from here on described in greater detail making reference to the enclosed indicative and not restrictive drawings, in which:

Fig. 1 shows a general lay-out of a treatment location for the gasification of waste; Fig. 2 shows a general lay-out of the plant according to the invention; Figs. 3, 3a and 3b show, respectively, an end view, a view from above and an internal view of a primary reaction cell;

Fig. 4 shows a cross-section of a primary cell; Fig. 5 shows a cross-section view of the detail X circled in Fig. 3; Fig. 6 shows a cross-section view of the detail Y circled in Fig. 3;

Fig.7 shows a cross-section view of the detail Z circled in Fig. 6. Detailed Description of the Invention

The one represented is however a preferred solution of a plant for the gasification of organic waste for the production of SynGas and for a successive use of the latter.

The plant is made up mainly of: a primary group (A) of gasification cells 10; a secondary molecular dissociation group (B) of the SynGas in a post- combustion chamber 11 ; a thermal energy production system (C), in particular steam, coming from the thermal exchange with gas exiting from the post combustion chamber 11 ; an electric current generator unit (D); a suppression and refrigeration device of the discharges in the atmosphere (E); an electronic control system (F); a weighing machine for weighing the conferred waste (G); an administration and technical control office (H). The dimensioning and capacity of the plant will depend on the daily quality and quantity of the material to be processed and, obviously, on the available space.

In particular, every primary gasification cell 10 consists in an external steel container 12 and an internal refractory structure to guarantee the thermal stability at the process temperatures (350°-500°C). As regards to an internal refractory structure, the most appropriate was found to be one with a ceramic fibre panel 13 adhering to the internal surface of the steel container and one with a dense refractory concrete coat 14 superimposed on said panel. This coat of concrete is basically made of alumina and kaolin, even though from time to time in different ratios, and is spread directly inside the cell 10 and kept in place by gripper elements 15 projecting from the wall of the container and through the ceramic fibre panel 13.

As regards to the temperature process, it is reached and maintained by heating, for example by methane gas, the internal ambient of each primary cell, avoiding, thanks to a lack of oxygen, every combustion flame reaction that directly invests the treated waste and, consequently, every oxidation reaction.

For this reason, all the primary cells are permanently closed and are placed in depression regime (-0, 5 bar), which also ensures that possible thermal and untreated gas loss are avoided. The external temperature of the cells during the process reaches about 30-35°C, thanks to the excellent thermal isolation. The primary cells 10 can be of various sizes both in height and in width and depth - Figs 3, 3a and 3b, respecting however an intransgressible ratio and which is determinant for the thermal performance of the process. The optimal ratio between the length and width of each primary cell will be between 1.50 and 3.20, usually between 1.70 and 1.80, depending on the material to be processed, and the bed, that is the volume, of material inside the cell that can be adjusted conveniently through the loading of material. Once the material in each primary cell has reached the optimal quantity to start the process, a computerized control system will make the temperature increase to the required degree, as stated previously, with a slight depression (-0,5 Bar) and with oxygen present that will be reduced to a lower percentage or to a limit equal to 6%. For the running of the process, inside each single primary cell are provided some control sensors in order to detect the exact temperature, pressure and percentage of oxygen; the information collected will be sent, in real time, to a central elaborator and should there be faults or malfunctions, a safety mechanism will immediately intervene by modifying the clashing parameters or if at a limit, by stopping the whole system.

The material to be processed is fed to the primary cells 10 continuously, even if in variable quantities depending on the treatment speed that is the gasification of the material in said cells. For this purpose the plant comprises a transportation group 16 that extends from a stocking pit 17 of the material up to the primary cells and is set up to download the material into each individual cell using a summit stellar valve system 29 conceived both for avoiding both thermal and gas loss from the cells and the entrance of air, thus of oxygen, in the same, so as not to modify the conditions of the reaction in action. To control the loading of the material into the primary cells, each one is mounted on loading cells 18, which enables the material to be measured which is progressively gasified and to adjust the loading of the new material to be processed in an equivalent quantity as the gasified one, maintaining in this way the volume of the material in each cell constant and the continuous function of the plant. Each primary cell 10 is also provided with means for an evacuation from its bottom of the dry and clean ashes and non gasified residue and which are possibly recyclable in various ways. Evacuation is carried out by means of a pliable conveyor 19, for example made of iron, which moves to the storage containers 20 and is carried out by an automated process. In particular at the bottom of each cell is provided a grating 21 , and below this a double closing system at two different levels 22 and 23. Each closing system is made up of doors 22 that open when the others doors 23 are closed. In this way the ashes and the non gasified waste are downloaded first through the opening of a door, the one at the top level, whereas the other remains closed, and then through the opening of the other door, the one on the bottom level, towards the conveyor 19 after the first closes, so as not to modify the depression state inside the cell caused by loss of heat and the entrance of air from outside. In other words, each primary cell operates in a slight depression and this remains unchanged both on the continuous load side of the material to be processed, and on the download side of the ashes and waste from the bottom.

If necessary, at the end of the gasification process on the bottom of each primary cell, that is on its grating 21 , only the inert will remain which can be collected either manually or automatically, representing a high recyclable value. With the gasification in the primary cells, all the organic material inserted is transformed in gas that springs from the summit 28 of the cells and is canalised, through safety valves 30 towards the secondary group B that is to say to the pos-combustion cell or chamber 11. The gas gushes out due to the fact that it has been treated at a temperature, that of pyrolysis, not sufficiently high enough to purify it and it may still contain noxious substances, but on passing from the primary cells 10 to the secondary cell or chamber 11 it is not by any means dispersed into the surrounding atmosphere as it is immediately collected in a manifold 24 and then transmitted in a conduit 25 through a safety valve -non shown.

In this phase the gas is made to pass into a chamber to mix with air 26 where it becomes enriched with oxygen (O2 > 22%) and the pressure from negative becomes slightly positive. On entering the secondary cell 11 , the gas is burnt by means of small burners at a temperature of between 900° and 1800 ⁰ C, at an average of about 1500 ⁰ C. In this way the exposure time and the high temperatures enable the gasses to be purified if certain minimum threshold levels are respected: 1000 ⁰ C for 1 sec. (EEC Directive 2000/76); over 1000 ⁰ C the shortening of the exposition time follows a logarithmic trend and so for 1500 ⁰ C a fraction of a second would be more than enough. However, to reach the maximum efficiency and optimum results for environmental reasons, the system proposed is adjusted for an exposition of the gas for 3 sees, at a temperature of 1500 ⁰ C.

The secondary cell 11 is constructed like a steel container and with ceramic refractory and filter systems for the high temperatures. As already applies for each primary cell 10, and here for all the more reason, also the secondary cell or chamber 11 has on its inside a high number of sensors which have the task of monitoring and calibrating each process phase also in relation to the effluent fumes content from a fumes purification plant and from a terminal chimney stack 27. In other words the composition of the emissions is checked continuously and, in feedback, the temperature in the secondary cell is adjusted by conveniently varying the fuel/combustion supporter ratio in order to obtain the "cracking" of the non gasified noxious substances so as to avoid discharging the latter into the atmosphere.

After flowing through the passage in the secondary chamber 11 , the gas obtained is basically without pollutants or noxious substances of importance, exiting as fumes at a temperature close to 1000 ⁰ C. For technical reasons connected with the successive use of the feeding of a turbine, a drop in this temperature level is carried out by means of appropriate cooling towers and a water circulating heat exchanger group preferably in the immediate vicinity of the output of the secondary cell in order to avoid additional canalization for the fumes at over 1000 ⁰ C. Water vapour is obtained in this way and a minimum part of which is dispersed into the atmosphere, in reality in the form of a flow of humid air at about 35°C and 0,5 Bar of pressure. Once the vapour has reached the required working temperature, it is piped to a turbine for the successive production of electric energy by means of an alternator.

Both the turbine and the alternator can be conventional.

The cooling system provided to lower the high temperatures of the fumes exiting from the cell or secondary chamber can also be used to cool various parts of the system. Rapid cooling of the fumes reduces the possibility of secondary reactions and the formation of pollutants, for example dioxin. Furthermore the lowering of the temperature of the fumes upstream of the damping systems establishes various advantages among which are: a contraction in the flow of the fumes in purification plants; the size of the conveyors; a considerable reduction in the quantity of evaporated water from the damping systems in the case of humid treatment of fumes; a reduction in the percentage of vapour in the fumes discharged and consequent lowering of the dew-point of the same.

The cooling takes place in a closed circuit with water with certain chemical-physical characteristics which are constantly controlled to avoid scale on the surfaces of the heat exchanger. The system will be basically made up of a well, circulation pumps and exchangers or cooling towers.

The control system foresees, through a network of sensors such as thermometers, pressure switches, oxymeters and cabled chromatographs in various units, that the data is grouped in one single control panel and control of the system on three safety levels: FIRST, human control: a team of technicians monitor, from an internal control room, the whole gasification cycle, 24 hours a day, guaranteeing that the system is continuously monitored, controlled, managed and able to function autonomously.

SECOND, computerized control on site: manages, controls and adjusts all the functions and activities of the plant by intervening and registering all the operations and functional parameters of the same.

THIRD, IT or remote control: it is the faculty of the end user to install a remote control or a data transmission system via Internet to supply the authorities in charge with all the data collected regarding environmental impact.

The authorities in charge of running the gasification plant might take the advantage of having a dedicated line for the control of the parameters of interest, and all the operations and the parameters can be registered and made available to all the interested parties with reference, in particular, to the impact on the environment.

The results of the tests carried out have shown that also with a series of waste materials that represent the materials with the highest resistance to the breakage of the molecular chains, the results were exceptional. The analyses highlighted the levels of the risk agents for the health, not cancerogenic and cancerogenic respectively less than 5.0 per cent and 0.1 per cento as regards to the limits prescribed in USA by EPA (Environmental Protection Agency) and imposed in the UE by the aforementioned Community Directives 76/2000. The concentrations of the contaminants, in fact, resulted to be well below the limits taken as a reference such as qualitative parameters, confirming the performance of the plant and the efficiency of the monitoring within the sphere of the management system of the environmental location.

To be emphasized, for the importance it undertakes compared to the actual thermal treatment systems of the waste to be disposed of or for energy recovery, the complete elimination or to a completely negligible level of permanent volatile compounds, of the furans and of the other chloride compounds such as the dioxins; in fact the high temperatures reached during the gasification process and above all in the secondary cell, enable the age-old problem of the formation of the abovementioned dangerous elements for the environment and for man to be avoided. The technology is calibrated so as to virtually eliminate the production of dioxins and furans. Dioxins and furans form when the chloride unites with complex organic compounds (VOCs - Volatile organic compounds). While the gas passes into the secondary cell, the temperature is increased to over 1200° - 1600° C, destroying said compounds.

While the chloride is still present, the formation of dioxins and furans is avoided thanks to the 100% destruction of the VOCs. The chloride, however, is able to unite with the hydrogen to generate HCI. In the case of organic waste with a high quantity of plastic material, the presence of HCI in the gas could cause problems. In this case however, a semi-dry or dry washing system can be installed to the HCI. These washing systems, made typically with hydrated lime, require a lower temperature compared to the ones present in the cell or secondary chamber, so the process can be provided with an additional heat exchanger. The progress of the process which is basically in a closed circuit with the absence of dispersions from the plant also eliminates every possibility of polluting the water and the soil. Also the ashes become inert and are not dangerous.