Patent Description:
In particular, the invention concerns a plant and a method for implementing an oxidative or autothermal pyrolysis process, i.e. in the presence of limited amounts of oxygen, by means of a pyrolyser of the auger type.

It is known that the pyrolysis process consists of the thermal decomposition of organic material in the absence of oxygen.

The main products of the process are a carbonaceous solid (char) and vapours with a high content of organic substances derived from the thermal decomposition of the organic material (pyrogas).

These vapours can be condensed to obtain a liquid fraction normally called bio-oil (or pyrolysis oil) from which to obtain a liquid fuel or products with high added value. A fraction of the vapours produced within the reactor is composed of non-condensable gases mainly carbon monoxide (CO), carbon dioxide (CO<NUM>), methane (CH<NUM>) and hydrogen (H<NUM>). The yield of the products varies depending on the reaction conditions, in particular temperature and residence time in the reactor. Pyrolysis is generally classified based on the operating conditions of the process into fast, intermediate and slow.

Table <NUM> compares the main operating parameters and the typical yields of the products of the three types of pyrolysis.

Fast pyrolysis is therefore characterised by high heating rates, even high temperatures and low residence times of the hot vapours, so as to maximise the liquid yield. On the contrary, slow pyrolysis is distinguished by low heating rates, moderate temperatures and high residence times of the hot vapours, so as to promote the production of char. Finally, intermediate pyrolysis combines prolonged residence times of the hot vapours in the reactor and moderate heating rates so as to obtain a combined production of char and bio-oil.

To implement the pyrolysis process there are different types of reactor, or pyrolyser that can be chosen depending on the application, the material treated and the desired characteristics of the products obtained.

In particular, fixed bed or "moving bed" static reactors are known in which the movement of the treated material can take place fluid-dynamically (fluid bed) or mechanically (rotary kiln or auger reactor).

The auger reactors of known type use a helical screw to move the biomass inside the reactor and, unlike the fluid bed reactors, have a simpler design and are also suitable for small-scale applications.

In this type of reactors, typically cylindrical in shape, the biomass is inserted from one end through a volumetric loading system, also called "feeder", and is subsequently transported along the axis of the reactor, thanks to the rotation of the screw or auger by means of a motor. The biomass can be heated upon contact with the walls of the reactor, maintained at high temperatures thanks to the heat provided by electric heaters (indirect heating), or by the combustion of the pyrolysis gases themselves (direct heating) or by another energy carrier specially introduced into the reactor, previously heated externally or internally (through processes such as the electrical induction).

The non-condensable gases and the pyrolysis vapours are extracted from the reactor and the char produced is collected at the opposite end, usually by gravity. The movement of the screw also favours the mixing of the biomass particles and the contact with the walls, increasing the heat transfer.

The auger reactors have significant advantages that make them an industrially attractive choice. Among them, the main advantages lie in the accurate control of the flow rate of the biomass and of the residence time in the reactor, the simplicity of the separation of the solid fraction from the gases produced by the reaction, in the fact that the pyrolysis gases obtained are less diluted than in a fluid bed reactor, in addition to the high flexibility in choosing the dimensions and characteristics of the input material and the design, operation and maintenance simplicity.

However, the current auger reactors also have significant limitations, such as the high residence time of the produced pyrolysis gases inside the reactor compared to fluid bed reactors, the mechanical wear of the moving parts at high temperature, and the difficulties of obtaining an efficient heat transfer to the treated biomass.

It is also known that when the heat necessary for pyrolysis is provided by the partial oxidation of the biomass itself and of the pyrolysis products, the pyrolysis becomes a process called oxidative or autothermal pyrolysis.

Pyrolysis occurs in this case in the presence of a limited oxygen concentration.

By providing heat internally to the reactor, the limitations on heat transfer towards the biomass from the outside through the surfaces of the system are eliminated. In general, it is therefore acknowledged that the autothermal pyrolysis has the considerable advantage of simplifying the configuration of the plant (reducing heat exchangers, combustors) and of increasing the scalability of the heating process. The autothermal configuration also allows to increase the performance of the plant in terms of incoming biomass flow rate, and for this reason it is considered a process intensification system.

Currently, the oxidative pyrolysis is mainly used in fixed bed reactors and in some fluid bed applications in which the fluidization of the bed takes place through the injection of a gas through a porous plate and the addition of a small fraction of oxygen in the gas that allows to increase the coefficient of heat exchange with the biomass by providing the heat necessary to make the pyrolysis process autothermal. At present, the oxidative pyrolysis has not found application in plants using auger reactors, this is due to the technical difficulty of inserting air or oxygen directly into an auger reactor, both due to the established practice of performing the pyrolysis processes in inert environments that are not partially oxidative, and due to the difficulties of ensuring a suitable heat exchange between hot gases and biomass in a reactor of this type, i.e. an auger reactor.

From document <CIT> pyrolytic auger reactor is known inside which the solid component is "packed" in a section of the reaction chamber completely filled, with the volatile matters and the water generated during the pyrolysis that are recirculated. In this example, the oxidizing agent, air, is inserted, air, through radial appendages of the axis of the auger at predefined points close to the solid generating a flow of syngas in countercurrent to that of the biomass.

From document <CIT> further example of reactor is known which is provided with an auger for advancing the solid in the pyrolysis chamber, which is operated to obtain the filling of the chamber and the packing of the solid, inside which the injection of an oxidizing agent takes place along the walls of the reactor at several points located on the surface in the second terminal half of the length of the reactor, generating a gas flow in countercurrent to that of the biomass.

Also these solutions have significant limits, in particular because the feeding of the solid until compaction and the injection of oxidant directly or close to the compacted solid mass results in a high residence time, greater risk of cracking of the liquid products and the onset of heterogeneous reactions, in addition to the fact that the oxidation step of the pyrolysis solid reduces the yield of the plant in terms of char production.

With the present invention it is therefore intended to overcome the drawbacks of the already known solutions and to propose a method and a pyrolizer apparatus that implement a process for the oxidative pyrolysis of organic material, preferably a biomass, by means of a reactor of the hollow auger type, i.e. an auger without a central shaft in order to obtain in the reactor a controlled oxidation process between the introduced air and the pyrolysis vapours and gases and that shows a high char production efficiency.

The realization of a method and a plant for treating organic material by pyrolysis according to the appended claims have allowed to achieve these aims, wherein there is provided a controlled blowing of an oxidizing agent (for example air) in one or more points inside the reactor obtained by means of a perforated lance that is independent and coaxial with respect to the material advancement auger, provided with an axial distribution of holes for the injection of an oxidizing agent inside the reaction chamber in contact with the pyrolysis gases and vapours.

A first advantage consists in the high efficiency of the heat exchange between the treated material particles and the surface of the reactor.

A further advantage consists in the high uniformity of the heating of the treated material obtained along the axis of the reactor.

A still further advantage consists in the high versatility of the process and of the plant in terms of both treatable material and reachable operating conditions, allowing for example to vary the residence time of the solids inside the reactor by adapting the rotation speed of the auger, for example from a few minutes to more than <NUM> hr.

A further advantage of the proposed solution with respect to for example rotary kiln reactors lies in the fact that the cylinder of the reactor does not rotate, but the material is moved by the movement of the auger. This allows to reduce the problems related precisely to the large-sized rotating seals on the drum, which must guarantee a barrier to the unwanted and controlled entry of air/oxygen into the reactor, which is at a high temperature.

A still further advantage consists in stirring the treated material and therefore the high consistency and predictability of the characteristics of the products obtained.

A still further advantage consists in the possibility of adjusting in a precise manner the flow rate and the point of introduction of the oxidizing agent (for example air) introduced into the reactor in order to promote the oxidative pyrolysis process.

A still further advantage consists in the possibility of controlling the degree of oxidation of the treated material and of the pyrolysis vapours.

A still further advantage consists in the possibility of sampling the pyrolysis vapours at several points along the axis of the reactor, instead of exclusively at the end of the reactor, minimising their residence time inside the reactor and thus being able to limit the onset of secondary reactions.

A still further advantage consists in the possibility of controlling the distribution of the thermal energy provided by the partial oxidation of the treated material.

A still further advantage consists in increasing the flow rate of treated material that can be fed in input to the reactor when the system operates in oxidative mode compared to the conventional mode, thanks to said controlled distribution of the oxygen and therefore of the thermal energy provided to the material, as well as to the modes adopted to introduce the oxidizing agent into the reactor.

An even further advantage consists in the increase in the flow rate of the products obtained.

An even further advantage consists in the reduced sizes of the plant with the same flow rate compared to the conventional plants.

Yet, a further advantage consists in limiting the oxidation of the char since the oxidant is inserted in the part of the volume where the pyrolysis gases are usually present, thus favouring the homogeneous oxidation reactions (oxidation of the pyrogas) compared to the heterogeneous ones (oxidation of the char), preserving the char mass yield.

Yet, a further advantage consists in the possibility of modifying the points of insertion of the oxidizing agent.

These and other advantages will be better understood by any person skilled in the art from the following description and the accompanying drawings, given as a nonlimiting example, in which:.

With reference to the attached drawings, a plant for treating organic material by pyrolysis according to the invention is described.

The plant comprising a reactor <NUM> inside which an advancement auger <NUM> can rotate, preferably made of stainless steel, moved in rotation at a speed controlled by a motor <NUM> inside a process chamber <NUM> delimited by a metal casing <NUM> and heated by suitable heating means <NUM>, for example electrical resistors arranged in order to promote a heating of the chamber by zones. By way of example, three resistors may be provided which are configured to ensure either a uniform and equal temperature over the three zones concerned, or three different temperatures for the three zones.

More in detail, as better evident from <FIG>, the auger <NUM> is an auger without a central shaft and has at the ends two supports <NUM>, <NUM> of which the second one is mechanically connected to the motor <NUM> that allows the transmission of the motion. The auger may be provided with specific elements connected to it, capable of favouring the stirring of the material in the reactor. Said elements may also be consistently arranged with similar elements in the inner surface of the cylindrical reactor, always in order to further favour a suitable stirring.

According to the invention, the plant comprises oxidizing agent (for example air) blowing means <NUM> communicating at the inlet with a oxidizing agent (for example air) source <NUM>, for example a compressor controlled by a control unit <NUM> and at the outlet with a distribution of points <NUM> of introduction of a controlled amount of oxidizing agent (for example air) at a sub-stoichiometric value inside said process chamber <NUM> in order to promote a partial and controlled oxidation process between the introduced oxidizing agent and the pyrolysis vapours and gases.

To this end, the feed of the material to be treated, the speed of the auger and the exit of the solid from the reactor are adjusted so as not to cause the complete filling of the chamber and allow the oxidising agent exiting the holes <NUM> to come into contact mainly with the pyrolysis gases and vapours and not with the solid component.

In the example described, the blowing means comprise in particular a pipe or perforated lance <NUM>, better represented in figures <NUM>-<NUM>, arranged coaxially to the auger <NUM> and independent of it being able to rotate inside the supports <NUM>, <NUM> and fixed to a joint <NUM> that allows to keep it stationary even during the rotation of the auger.

The casing <NUM> of the process chamber is also preferably made of stainless steel, is wrapped by a layer of a thermal insulating material, for example rock wool, and extends from an initial end <NUM> to a final end <NUM> of the process chamber where the extraction points of the pyrolysis products are located.

Preferably, for the control of the rotation speed, the auger is connected to the motor <NUM> by means of a gear motor and a sensor <NUM> is also provided to monitor the rotation speed of the auger which allows the modulation of its rotation speed, allowing the residence time of the material inside the reactor to be varied in a time interval that can vary from a few minutes to just over <NUM> hr. The adjustment of the rotation speed of the auger can take place by means of an inverter coupled to the motor <NUM>, or mechanical rev variator.

Advantageously, the adjustability of the rotary movement of the auger allows a stirring of the treated material, for example biomass, favourable to the heat exchange between the particles of the same and the surface of the reactor, ensuring a more uniform heating along the axis of the same and at the same time to study the effects of the speed of rotation, and therefore of advancement of the material, on the yield and composition of the pyrolysis products, both vapours and solids.

To this end, it can also be provided for one or more sampling points <NUM> along the process chamber so as to be able to extract and possibly use and analyse the pyrolysis gas, one or more pressure sensors <NUM> to monitor the internal pressure of the reactor, and a temperature sensor distribution T1, T2 to monitor the temperature of the metal casing and the temperature of the vapours and gases inside the process chamber. The presence of several gas extraction points allows to obtain some advantages, including: limiting the overpressure in the reactor, allowing an easier disposal of the flow rate of vapours and gases; limiting the contact between char and vapours, thus limiting the effects of the secondary reactions; improving the quality of the solid product.

Advantageously, the monitoring of the process can be carried out through a control unit <NUM> connected to the sensors T1, T2, to the sampling analysis instrumentation, to the heating system <NUM> (consisting indifferently of resistors or inductors), and to the motor <NUM> of the auger <NUM>, in order to be able to continuously adjust the heating means and the rotation speed of the auger according to the temperatures detected by the sensors T1-T2 and of the remaining data acquired, for example of the chemical-physical characteristics of the gaseous products extracted at different points of the process chamber or of the pyrolysis solids obtained at the end of the process.

In the illustrated embodiment, the material to be treated is fed by a feed <NUM> and introduced with a controlled flow rate to an inlet point <NUM> in the reactor located in proximity to the first end <NUM> of the chamber.

Preferably, the material to be treated is introduced into the reactor through a doser <NUM>, for example a screw doser connected to the inlet <NUM>, which is also connected to the control unit <NUM>.

A controlled flow of an inert gas, for example nitrogen, is also introduced into the inlet <NUM>, in co-current with the flow of the organic material to be treated, coming from a feed <NUM>, for example a nitrogen cylinder, and passing through a flow regulator <NUM> possibly connected to the control unit <NUM>.

Preferably, the feed of the process with inert gas comprises a distribution of injection points <NUM> arranged along the line <NUM> of the inerting gas, possibly communicating with the perforated lance <NUM> through an inlet point <NUM>'.

In the illustrated example, the injection points <NUM> are arranged between the feed <NUM> and the inlet <NUM> in the reactor of the material between two valves VG1, VG2 which are installed so as to ensure the creation of a watertight chamber that will be inertized before proceeding with the introduction of the material to be treated into the reactor.

At the end <NUM> of the chamber <NUM> there is a first outlet <NUM> for extracting pyrolysis vapours and gases from the reactor which preferably communicates with an extraction pipe <NUM> comprising further heaters <NUM> in order to avoid a possible condensation of the pyrolysis vapours which are extracted by means of an extraction fan <NUM> placed downstream of a condensation unit <NUM>.

Advantageously, the fan <NUM> can also be configured to create a slight depression in the reactor <NUM> and to ensure that the pyrolysis vapours/gases can be continuously extracted from the reactor and in a controlled manner from the different pyrogas extraction points.

In proximity to the terminal end <NUM> of the chamber <NUM> there is also arranged a second outlet <NUM> for extracting the solid char produced by the pyrolysis process, preferably a tank <NUM> for collecting by fall said solid pyrolysis products, by opening an electropneumatic valve VG3.

In a preferred embodiment example, in order to improve the safety of the plant, the char collection is carried out in "batch mode", that is, not continuously but when the appropriate conditions occur. In particular, it is known that the hot char can only be considered safe at limited temperatures, generally below <NUM>° C, for which the finer powders, if at a higher temperature, could catch fire on contact with air. For this reason, in the process described, the char produced by the pyrolysis section and continuously accumulated in the discharge tank, is allowed to cool (according to various technological and process solutions, from simply keeping in the tank for a suitable time, to introducing inert gas at low temperature, to liquid cooling) inside the tank for a period of time such as to make its subsequent transport and storage safe. In the operation of the illustrated plant, the organic material to be treated, for example a biomass, is introduced into the reactor through the screw doser <NUM> which is connected to the reactor <NUM>.

Through the flow of nitrogen, coming from the cylinder <NUM>, it is proceeded, if necessary, with the inertization of the reaction atmosphere.

The biomass then enters the heated reactor <NUM> from the inlet point <NUM> and is moved forward along its axis by the auger <NUM> moved in rotation by the motor <NUM>.

Through a suitable choice of the number, diameter and arrangement of the holes <NUM> on the lance <NUM> and through a flow controller, for example of the mass-thermal type, which interfaces directly with the control system <NUM>, it is possible to adjust the flow rate of oxidizing gas, for example air.

The axial position of the perforations on the injection lance determines the section of reactor involved in the oxidative conditions; therefore, by varying the axial position of the air injection it is possible to realize arbitrary combinations of anoxic/oxidizing treatment durations on the pyrolysed material. For example, a first phase of anoxic treatment can be followed by a second phase of treatment in the presence of oxidant, directly affecting the properties of the material produced as a result of the treatments. The possibility of introducing the oxidizing agent (e.g. air) inside the reactor implies greater flexibility compared to systems in which the oxidizing agent (e.g. air) is introduced by one or more lances that cross the walls of the reactor, as the latter are constrained in position (same axial coordinate of introduction), while the lance system allows the axial coordinate of introduction to be varied without changing the structure of the reactor.

The number and the width of the perforations is determined by the: pressure of introduction of the oxidizing agent and by the desired flow rate of oxidizing agent into the reactor.

The adjustment of the flow rate of the oxidizing agent is finally determined on the basis of the elemental composition of the processed material (carbon, oxygen, hydrogen, nitrogen, sulfur) and of the flow rate of the processed material; equivalence ratio (air flow rate/stoichiometric air) desired.

Advantageously, the plant operates in an autothermal mode thanks to the fact that the amount of oxidizing agent at a sub-stoichiometric value inserted in the reactor allows the partial combustion of the pyrolysis vapours/gases in a limited and controlled manner, with the development of the heat necessary to feed the pyrolysis process without the need for external thermal energy input and at the same time without significantly reducing the flow rates of pyrolysis gases and solids obtained at the end of the process.

The geometry and the mode of operation of the auger pyrolysis plant therefore presents a significant advantage for the development of the oxidative pyrolysis process because the oxidizing agent can be introduced at certain points and in the desired amount into the reactor by exploiting the perforated introduction lance <NUM> ensuring an almost unchanged yield of the char at the end of the process.

The internal atmosphere of the process chamber of the reactor can be maintained inert thanks to the introduction of a certain flow rate of nitrogen from the points <NUM> and/or <NUM> of the lance <NUM> which will also act as a fluidizing gas, directing the pyrolysis vapours and gases towards the extraction points <NUM> which thus allow to locally study the effects of the variation of the flow rate and of the residence times of the vapours in order to guarantee the maintenance of a residence time of the hot vapours corresponding to a slow pyrolysis process and to promote the secondary pyrolysis reactions with further formation of char and pyrolysis gas.

The pyrolysis vapours and gases produced are then conveyed by the nitrogen (or other inert) flow rate, and in the case of oxidative pyrolysis also by the oxidizing agent, towards the condensation unit <NUM> through the heated and insulated piping <NUM> and from here extracted thanks to the pressure difference generated by the fan <NUM>. The solid products i.e., in the case described, the char obtained from the biomass pyrolysis process, are instead conveyed by a specific extraction system, for example a screw system <NUM>, inside the sealing tank <NUM> through the opening of electropneumatic valves VG4, VG3 respectively upstream and downstream of the extraction system <NUM>.

In a preferred embodiment, the plant is configured to implement a process in which, indicatively, the pyrolysis takes place at a temperature between <NUM> and <NUM>, with a heating rate preferably of less than <NUM> / min and with a residence time of the biomass in the reactor of maximum <NUM>.

The system and the process described achieve important advantages.

In particular, the lack of a central shaft of the auger allows inserting a lance or similar system into the reactor with a series of perforations placed at a predetermined distance through the entire length of the reactor that allow nitrogen or oxidizing agent to be inserted into the reactor itself and thus be able to condition the process in progress in the reactor. By varying the perforations of the lance it is further possible to introduce air or oxygen at different points, and by varying the diameter of the same in combination with the characteristics of the feed fan, with different speeds and flow rates.

As described above, the introduction of a small percentage of oxidizing agent into the reactor (under sub-stoichiometric conditions) allows in fact to provide the heat necessary for the pyrolysis process through the oxidation of the organic vapours produced and of a small part of the pyrolysis char. In this way, the pyrolysis process becomes autothermal and the heaters of the reactor only have to provide the energy needed to overcome the thermal losses of the reactor to the outside.

This feature represents a considerable advantage compared to the plants and to the processes of known type, in which the main limitation to the application of the pyrolysis process on an industrial scale is given by the limit imposed by the heat exchange with the biomass inside the reactor. The conventional auger reactors, in fact, are heated externally through electrical resistors or by means of a heat transfer fluid (diathermic oil, combustion fumes, etc.) and the treated material is then heated indirectly. The external heat source must therefore first heat the entire surface of the reactor which then transfers the heat internally to the biomass mainly by conduction. Therefore, the available heat exchange surface is thus the limiting factor for the capacity of the reactor.

On the contrary, through the direct autothermal heating inside the reactor it will therefore be possible, with the same volume of the reactor, to insert a greater amount of material to be treated increasing the flow rate of the feed system and, consequently, of products, thus making the process potentially scalable with a reduction in the operating costs and a better feasibility.

The insertion of the oxidizing agent into the reactor through a specially perforated lance also allows a better adjustment of the oxidation, in fact by varying the position and the size of the holes it is possible to adjust the amount of oxidizing agent to be inserted into the reactor in each zone of the reactor as well as the speed of introduction and therefore the penetration of the jet. This greater flexibility therefore allows, for example, to provide more air or oxygen in the zones with the higher temperature, thus adjusting the oxidation of the treated material and of the vapours inside the reactor and varying the process temperatures in the reactor.

The introduction of the oxidizing agent through a lance passing through the entire length of the reactor also allows the configuration of the holes to be varied according to the operating conditions simply by replacing the lance with one having a different arrangement and diameter and/or number of the holes. Depending on the type of material treated, it will be in fact necessary to vary the reaction temperature and consequently to vary the amount of oxidizing agent to be inserted and the position and size of the supply holes.

The lance passing through the centre of the reactor coaxially to the auger also allows the oxidizing agent to be inserted in proximity to the moving bed of treated material. In this way, the flame will form in proximity to the bed, distributing the thermal energy necessary for the reaction more evenly over the material and avoiding any dispersion in the volume of the reactor.

Claim 1:
. Plant for treating organic material by pyrolysis, comprising a reactor (<NUM>) comprising
a pyrolytic process chamber (<NUM><NUM>) delimited by a casing (<NUM>) and extended from a first end (<NUM>) to a second end (<NUM>),
an inlet point (<NUM>) in the reactor of a controlled flow rate of organic material to be treated coming from a feed (<NUM><NUM>), located in proximity to said first end (<NUM>),
an auger (<NUM>) for advancing the organic material to be treated from said first end to said second end of said chamber (<NUM>), moved in rotation inside the chamber (<NUM>) by a motor (<NUM>),
a feed (<NUM>) of a controlled flow of an inert gas from said first end to said second end of said chamber (<NUM>),
a first outlet (<NUM>) for extracting pyrolysis vapours and gases from the reactor located in proximity to said second end (<NUM>),
a second outlet (<NUM>) for extracting solid pyrolysis products from the chamber (<NUM>) located in proximity to said second end (<NUM>),
a temperature sensor distribution (T1-T2) to monitor the temperature of the vapours inside the process chamber (<NUM><NUM>) and/or the temperature of the metal casing (<NUM>) inside the reactor,
heating means (<NUM>) for said chamber (<NUM>),
a control unit (<NUM>) to adjust said heating means according to the temperatures detected by at least one of said sensors (T1 -T2),
oxidizing agent blowing means (<NUM>, <NUM>) communicating with an oxidizing agent source (<NUM>) external to the chamber (<NUM>) and with blowing points (<NUM>) internal to the reactor to introduce a controlled amount of oxidizing agent into said process chamber (<NUM>,)
wherein said blowing means comprise a hollow-axis auger (<NUM>) inside which a perforated lance (<NUM>) is coaxially arranged extending along the entire length of said chamber (<NUM>) and provided with a distribution of holes (<NUM>) in order to promote a controlled oxidation process between the introduced air and the pyrolysis vapours and gases.