D e s c r i p t i o n

The present invention relates to a plant for molecular dissociation of waste material or a molecular dissociator .

It is known that a molecular dissociator is a plant used for waste disposal. The treatment carried out therein is of the thermo-chemical type and allows the organic substances to be decomposed converting them into a gaseous form. A disintegration of the solid waste and production of synthesis gas (known as "syngas") occurs that can be used as a normal gaseous fuel.

The Italian Patent for Utility Model No. 0000251875 discloses an incinerator, also known as thermo- destructor, for waste fuel materials for thermal feeding of boilers or the like, which comprises a gasification chamber provided with an opening for feeding the material to be thermally destroyed and an oxidation chamber communicating on one side with the gasification chamber and on the opposite side with the boiler to be thermally fed. The material to be burnt is fed by means of an Archimedean screw connected to a hopper, through the feeding opening. In the gasification chamber the material is laid on fixed and movable grates under which a space connected to an electric fan is delimited for forced delivery of controlled comburent air. A second electric fan forcedly feeds air into the gasification chamber and the oxidation chamber, through a throttling air lock and holes formed in the side walls. The forced delivery of air through the grates continuously feeds combustion and ensures gasification. The gases produced by combustion or flue gases are oxidised in the oxidation chamber losing their toxic-noxious content.

The Applicant has noticed that the plants of known type like that described above can be improved under different points of view, mainly in connection with control of the properties (in particular the calorific power) of the synthesis gas produced by combustion.

In particular, the Applicant has perceived the necessity to be able to adjust amount, purity and temperature of the synthesis gas produced, so that it can be used with the greatest efficiency in different users (boilers, explosion engines, gas turbines, for example) and not only in boilers, as described in said Italian Utility Model No. 0000251875.

Within this context, the technical task underlying the present invention is to propose a plant for molecular dissociation of waste materials overcoming the above mentioned drawbacks of the known art.

In particular, it is an aim of the present invention to make available a plant for molecular dissociation of waste material that is able to control the production of synthesis gases starting from organic substances of any nature (solid, liquid, powdered waste materials, municipal and industrial waste, CDR or fuel derived from waste material, biomasses or compounds of organic and vegetable origin such as flours, sludge, saw dust, chips, etc.), by partial combustion with air addition having controlled oxygen flow rate, temperature, humidity and content. It is a further aim of the present invention to propose a plant for molecular dissociation of waste material that is able to reach very high temperatures (up to 1600 ⁰ C) acting on the air distribution in a single chamber and on the air flow conditions.

The technical task mentioned and the aims specified are substantially achieved by a plant for molecular dissociation of waste material comprising the technical features set out in one or more of the appended claims.

Further features and advantages of the present invention will become more apparent from the description given by way of example and not in a limiting sense, of a preferred but not exclusive embodiment of a plant for molecular dissociation of waste material, as shown in the accompanying drawings, in which:

- Fig. 1 is a diagrammatic side elevation view partly in section of a plant for molecular dissociation of waste material according to the present invention; and

- Fig. 2 is a top view of the plant seen in Fig. 1.

With reference to the drawings, a plant for molecular dissociation of waste material and production of synthesis gas (syngas) made in accordance with the present invention has been identified by reference numeral 1.

In the present specification and in the appended claims, the term "waste material" means organic substances of any nature and origin such as: solid, liquid, powdered combustible materials, municipal and industrial waste, CDR (fuel derived from waste material) , biomasses or compounds of organic or vegetable origin such as flours, sludge, saw dust, chips, etc.

Plant 1 comprises a metallic holding body 2 preferably in the form of a parallelepiped.

In the embodiment given by way of example in the accompanying figures, the holding body 2 comprises a base 3 resting on the ground, a first vertical wall 4 in which a first opening 5 is formed for feeding the waste material to be burnt, a second vertical wall 6 facing and opposite to the first wall 5 in which a second opening 7 is formed for escape of the synthesis gases produced by combustion, two vertical side walls 8 and an upper horizontal wall 9. The upper wall 9 is preferably equipped with a lid that can be opened to enable inspections and maintenance.

The holding body 2 is made of ribbed sheet metal internally lined with insulating panels made of mineral fibre containing an inner envelope of special refractory material, not shown, resisting to high temperatures and oxidising agents. The insulating inner layer of refractory material preferably has a thickness included between about 150 mm and about 300 mm. The refractory material preferably is of the thixotropic type, with an alumina content at least as high as 80%, bonded with resin and such produced that it ensures high resistance to corrosion and sufficient thermal inertia for working of plant 1 at temperatures as high as 1600 ⁰ C.

The holding body internally delimits a conversion chamber 10. In the conversion chamber and close to base 3, perforated surfaces 11 or grates are installed. Perforated surfaces 11 moved by suitable actuators with a reciprocating motion are alternated with fixed perforated surfaces 11. The perforated surfaces 11 are disposed so as to partly overlap each other in a decreasing extension from the first wall 4 to the second one 6. The first opening 5 opens just above the perforated surface 11 against the first wall 4. A compartment 12 divided by vertical partitions 13 is delimited under the perforated surfaces 11.

In addition, mouths 14 of a first duct 15 open into the first wall 4 for forced feeding of primary air, which mouths 14 enter the compartment 12 through airspaces formed in the walls of the holding body 2. The first duct 15 has one end connected to the first wall 4 and an opposite end connected to a first electric fan 16.

Installed in the first duct 15 is a primary motor- driven air lock and downstream thereof relative to the flow direction of the primary air, is a flowmeter for air measurement 18.

Further disposed in the first duct 15 is first heating means 19, preferably defined by an electric resistor, and a first and a second nozzle 20, 21 for introduction of pure oxygen and water respectively.

The first nozzle 20 is part of an oxygen circuit comprising a pure-oxygen source 22, defined by a bottle and a first pipeline 23 connecting the bottle 22 to the first nozzle 20. The oxygen circuit further comprises a first flow control valve 24 and a first flowmeter 25 disposed on the first pipeline 23 and adapted to intercept the oxygen along the path of travel thereof.

The second nozzle 21 is part of a water circuit comprising a water source 26, defined by the waterworks for example, and a second pipeline 27 connecting the waterworks 26 to the second nozzle 21. The water circuit further comprises a second flow control valve 28 and a second flowmeter 29 disposed on the second pipeline 27 and adapted to intercept the water along the path of travel thereof.

In addition, the mouths of a second duct 31 for forced feeding of secondary air open into the first wall 4 and side walls 8, which mouths 30 appear above the perforated surfaces 11 and the first opening 5 through airspaces formed in the walls of the holding body 2.

The second duct 31 has one end connected to the first wall 4 and the opposite end connected to a second electric fan 32.

Installed in the second duct 31 is a secondary motor- driven air lock 33 used to throttle the secondary air flow within chamber 10.

Further disposed in the second duct 31 is second heating means 34 preferably defined by an electric resistor .

Chamber 10, while defined by a single volume, is operatively divided into a gasification region located at the compartment 12 where primary air is admitted and at the perforated surfaces 11, and into a turbulence region located above the perforated surfaces 11 where secondary air is admitted.

In base 3, close to the second opening 7 and at the foot of the lowest perforated surface 11, evacuation conveying means 35 is positioned which is adapted to exhaust the ashes and conversion residues to the outside of chamber 10. In particular, this evacuation conveying means 35 comprises an Archimedean screw (shown) or a conveyor belt housed in a hollow of base 3, oriented parallel to the second vertical wall 6 and coming out of a side wall 8.

Plant 1 comprises means 36 for conveying the waste materials to be burnt into chamber 10 through the first opening 5. This means 36 comprises a hopper 37 or a cylindrical loader and a feeding duct 38, preferably defined by an Archimedean screw or a conveyor belt connecting hopper 37 to the first opening 5. In an alternative embodiment not shown, the feeding duct 38 is made of two mechanically uncoupled lengths for ensuring the thermal break. For instance, the Archimedean screw is defined by a first Archimedean screw having a first end disposed in hopper 37 and a second end in side by side relationship with the end of a second Archimedean screw terminating in the first opening 5 of the holding body 2. The material from hopper 37 reaches the end of the first Archimedean screw and is poured into the second Archimedean screw.

Plant 1 further comprises control means capable of detecting at least one operation parameter 1 and regulating the flow rate, composition and temperature of the primary air, the flow rate and temperature of the secondary air and the flow rate of the waste materials to be burnt so as to vary, as described in more detail in the following, the features of the synthesis gas produced.

The control means comprises a control box 39 and at least one temperature sensor 40 placed in chamber 10 and connected to the control box 39.

Also part of the control means is the first flowmeter 25, second flowmeter 29, flowmeter 18 for measurement of the primary air, which are all connected to the control box 39 to send it signals indicative of the monitored parameters.

Also part of the control means is the first flow control valve 24, second flow control valve 28, primary motor-driven air lock 17, secondary motor-driven air lock 33, first heating means 19, second heating means 34 receiving from the control box 39 command signals as a function of the signals indicative of the monitored parameters. The control box 39 is further connected to the motors of the first and second electric fans 16, 32 and the motor of the Archimedean screw 38.

The control box 39 further receives an input signal from the user (oxidation chamber and boiler, engine, turbine, etc., for example) coupled to plant 1. This signal is indicative of the type of user present and also based on this signal the control box 39 controls plant 1.

If the user is a gas turbine or engine, the synthesis gases produced are directly sent to the user itself.

If the user is a boiler, a further chamber 41 referred to as oxidation chamber (partly and diagrammatically shown in Fig. 1) is interposed between the boiler and plant 1 as above described. A duct system, preferably formed in the walls of the holding body 2 and the walls of the oxidation chamber 41, connects the second duct 31 to the oxidation chamber 41 through a plurality of holes opening on the inner faces of said oxidation chamber 41. A third motor-driven air lock 42 (referred to as oxidation air lock) preferably installed in the second duct 31, regulates the air admitted to the oxidation chamber 41.

In use, the waste materials introduced into hopper 37 are picked up by the Archimedean screw 38 and brought to the perforated surfaces 11 or grates that, through their movement, keep the material constantly in a turbulence condition. Once started, combustion in the gasification region is self-fed by forced delivery of primary air into the mass of the material through the perforates surfaces 11.

The slow, constant and gradual movement of the perforated surfaces or moving grates keeps the fuel material always in movement and in constant turbulence, thus enabling a controlled gasification of the material itself. The gasification is continuously fed by introducing material and primary air the amount and frequency of which depends on the request of gas at the user.

In the first duct 15 the primary air is regulated in terms of: flow rate as a function of the amount of treated material and the air needs for conversion of same; oxygen content (20% to 100%) and humidity content (from room conditions to beyond saturation) , for regulating the composition and therefore the calorific value of the synthesis gas. The primary air is metered and divided through the vertical partitions 13 into fixed proportions towards the different treatment steps of the material.

The primary air is enriched with oxygen (it may even be replaced by pure oxygen) in order to: maintain the mass of the solid material to a temperature higher than the adiabatic flame temperature in air, limit the flow rate of the primary air, reduce the amount of nitrogen in the produced gas for preventing the subsequent use from giving rise to an excessive formation of NOx. Each of these variables can act in override on a set value of air composition.

The primary air is humidified by injection of water to provide an additional amount of hydrogen to the conversion reaction, in particular where the H-C ratio in the starting material is particularly- disadvantageous. The proportion of water to be injected in the air flow is established a priori as a function of the chemical composition of the treated material and can vary from 0 to 50% (as absolute humidity) ; it is also possible to modify the set point in operation in order to reduce the residual coal in the ashes when anomalous values are found.

In the turbulence region, the addition of secondary air causes a partial combustion of the synthesis gas and a very turbulent motion for the purpose of maintaining the temperature in chamber 10 constant and uniform.

The secondary-air injection aims at causing a partial combustion of the generated gas so as to keep a turbulence capable of maintaining constant and homogeneous temperature conditions in the whole chamber, and also for helping in maintaining the temperature in the gasification region. The amount of secondary air is regulated as a function of the temperature detected in the turbulence region above the gasification region or possibly of the temperature difference between the two regions or yet for any other combination of the two temperatures.

Said partial combustion can also be controlled in such a manner as to guarantee the temperature of the outgoing gas, should the type of user asks for it, in which case the regulation loop acts based on an outer signal replacing the temperature control in the turbulence region.

The associated regulation of the two components amount of material, through the Archimedean screw 36 (preferably by adjusting the speed of the Archimedean screw 36 through an electronic variator controlled by the control box 39) , and air, through the primary 17 and secondary 33 motor-driven air locks - allows the requirements that are continuously transmitted as an input signal by the user to the central box 39 to be followed and supported. In particular, regulation of the composition and humidity of the air allows the quality (mainly the calorific value) of the synthesis gas to be adapted to the user's requirements.

The plant for molecular dissociation of waste materials according to the invention is able to produce synthesis gases by partial combustion, failing the oxygen of the material. According to the process carried out in said plant, the amount and properties of the synthesis gas are modulated by acting on flow rate, temperature and composition of the primary air and preferably also the secondary air and said synthesis gas is delivered under pre-established conditions as a function of the type of user installed downstream. The properties of the synthesis gas produced are indirectly detected through the operation parameters of the plant and the user installed downstream, which can be of any kind.

If, for instance, the user is a boiler, it is detected: the temperature, pressure and flow rate of the water entering the boiler, the temperature and pressure of the steam coming out of the boiler, the content of 02, NOx, CO of the exhaust gases from the boiler.

If, for instance, the user is a gas turbine or engine, it is detected: the mass and volume flow rate of the gases entering the engine/turbine, the electric power supplied by the alternator of the engine/turbine, the content of 02, NOx, CO of the exhaust gases from the engine/turbine .

If, for instance, the user is a fuel cell, it is detected: the mass flow rate of the incoming gas, the mass flow rate of the outgoing gases, the flow rate of the air entering the cell, the flow rate of the air coming out of the cell, the flow rate of the air to the oxidator, the electric energy delivered to the cell.

These magnitudes, after possible suitable processing, are sent as input signals to the control box 39 that acts in "loop", modifying flow rate, temperature and composition of the primary air and, preferably, also of the secondary air to keep the input signal (or signals) in the neighbourhood of a reference value (or respective reference values) . In case of use in a boiler, the regulation must ensure a constant heat exchange depending on the combination of flow rate and delta T of the flue gas. The control of the material flow rate and primary air is acted upon for regulating the flow rate of the synthesis gases, in this case the secondary air acting as comburent air and being metered so as to ensure full combustion (taking place with the oxygen content in the flue gas) . Should the user be a gas engine or turbine, the gas flow rate would be regulated in the same manner, while it is necessary to regulate the Wobbe index (WI) by balancing the conversion degree through the reaction temperature (as a function of the flow rate of the secondary air) and the content of inert materials (by modifying the composition of the incoming air) . In case of use in a fuel cell, the percentage of hydrogen in the gas would have to be maximised by increasing the water injection, the requirements of maintaining the operating conditions permitting it.

The primary 17 and secondary 33 motor-driven air locks ensure that, on varying of the amount of material introduced, the overall air flow rate increases in proportion, maintaining the pre-established ratio based on the type of treated material.

The primary 17 and secondary 33 motor-driven air locks (and possibly the third motor-driven oxidation air lock) further manage division of the air between the gasification region and the turbulence region (and possibly the oxidation region) in an independent, continuous and automatic manner.

Regulation of the conversion and of the gasification, turbulence and possibly oxidation steps takes place in a separate and independent manner. The slow movement of the perforated surfaces 11 progressively translates the burnt material to the bottom of chamber 10 where, being now inert ashes, is collected and conveyed to the outside by the Archimedean screw 35 housed in the hollow of base 3. The full inactive and inert state of the ashes is ensured by the fact that the operating temperature is always maintained above 1200 ⁰ C.

The plant safety is guaranteed by the presence of the temperature sensor 40 that, in addition to ensuring control and assurance of maximum temperature, allows a continuous monitoring in real time of the thermal conditions within chamber 10 and enables an intervention sufficiently in advance for regulating the operating conditions.