Technical Field

The present invention refers to a gasification plant.

Background Art

As known, the gasification consists in a set of thermochemical processes suitable for transforming biomass, of various kinds and origins, into a gaseous fuel, commonly called "syngas" and usable for many purposes, for example as a fuel in internal combustion engines.

The biomass usually used for this type of process consists of wood chips or other organic matter, for example resulting from the treatment of waste. The thermochemical processes occur at high temperatures (above 700-800 °C) and in the presence of a gasifying agent, usually air, oxygen or an air- oxygen, air-steam mixtures under stoichiometric percentage.

The biomass, under these conditions, is subjected to thermal degradation where the long-chain chemical bonds are broken into simpler molecules and the same biomass is transformed into resulting products of various types: gaseous, liquid and solid.

The gaseous products, such as carbon dioxide, methane, carbon monoxide, nitrogen, hydrogen and other gaseous molecules, constitute the fuel gas mixture called syngas.

The solid products, commonly called "char", are materials that they are not reacted during the thermochemical processes and they are at the end of the processes in form of ashes and other solid particles.

The ashes and the solid particles having size greater than about 10 μπι precipitate and are easily removable, while the particles with smaller sizes, commonly called "powder", "particulate" or "dust", are dragged away by the syngas and are contained into it.

The liquid products, excluding water vapor, are commonly called "tar" and are mostly aromatic hydrocarbons of tarry type.

At high temperatures, the tar is found in the gaseous-vapor state in the syngas, and then condenses when the latter is cooled.

Dust and tar are critical considering the use of the syngas in internal combustion engines.

In fact, into the engine the dust collides with the mechanical parts of the engine, depositing and accumulating.

Instead, into the engine the tar condensates and, by its viscous nature, it adheres to the mechanical parts of the engine causing damage and breakage that would compromise the operation of the engine.

For this reason, it is known the need to reduce the fraction of tar and dust content in the syngas obtained from gasification.

In this regard, the common gasification plants, besides including a reactor in which the thermochemical processes described above can occur, require the installation of one or more filtering units placed along the path of the syngas before arriving to the user motor and designed to remove the tar and the dust from the syngas.

More in detail, a gasification plant includes a reactor connected to an internal combustion engine that receives the syngas produced in the reactor itself and uses it as fuel.

The reactor is defined by a substantially cylindrical casing, fillable with combustible biomass, and inside which is established a temperature gradient that allows the development of the thermochemical reactions necessary to chemical degradation of the biomass itself.

Commonly, the insertion of the biomass occurs in the reactor head.

To manage and optimize the loading and unloading processes there is a pre-chamber in which the biomass is stored before being subjected to thermochemical reactions.

The pre-chamber, that can be obtained in the same housing which defines the reactor or it can be external to the reactor itself, is associated to the latter through organs of separation, such as rotary valves or knife gate valves which allow the controlled introduction of biomass into the reactor without that this enters in communication with the pre-chamber.

In standard plants, the syngas is sucked or "pulled" by the suction action of the engine connected to the bottom of the reactor through a specific duct.

There are also different plants that work pressurized, i.e. they are connected to a blower suitable to push gasifying agent in pressure inside the reactor.

Downstream of the reactor and upstream of the engine, the filter units are positioned to purify the syngas from tar, dust and other impurities present in it.

The known filtering units are obtained by assembling one or more types of filters such as multicyclones, sleeve filters, electrostatic filters, wet scrubber etc.

The drawback of these known filters is related to the cost of construction and management.

The various components, in fact, have a high cost and require frequent maintenance that, in addition to involving an additional cost, implies the shout down the syngas production.

To obviate, at least in part, the aforesaid drawbacks, it is known the use of biofilters composed by the same biomass used in the gasification process. These biofilters are made by packing a certain amount of biomass in an appropriate container inside of which passes the syngas produced in the reactor.

Coming in contact with the biomass, the tar content of the syngas condenses and partly adheres to the biomass itself together with particulate matter.

The latter, in turn, can undergo a principle of thermal degradation induced by heat exchange between the biomass and the gas if the temperature of the gas exceed the torref action temperature limit.

The outgoing syngas, devoid of a portion of tar and dust, is send to the engine or to further filtering.

However, even this solution has drawbacks.

The biofilter thus realized, in fact, undergoes saturation losing efficiency. As the biomass particles are crossed by the syngas, the amount of dirt (tar, dust, etc.) retained by the filter increases but the filter reduces its efficiency.

The main drawback is linked to the fact that the saturated biofilter has to be regenerated replacing the biomass with new one.

This necessarily implies turning off the reactor, since the operations of loading and unloading of the biofilter take place discontinuously, according to a type of process "batch" .

This drawback is even stronger if one considers that a biofilter dimensioned according to the rest of the plant tends to become saturated very quickly, requiring cycles of loading-unloading of the biofilter (and thus of the reactor on-off) much more frequent.

Disclosure of the Invention

The main task of the present invention is to provide a gasification plant that optimizes the processes of production and cleaning of the syngas, minimizing the operations of maintenance and the plant switching off time.

One object of the present invention is to provide a gasification plant that allows efficient cleaning of the syngas minimizing the costs of the filters. Another object of the present invention is to provide a gasification plant which allows to overcome the mentioned drawbacks of the known technique within the framework of a simple and rational solution, easy and effective to use and with a low cost.

The above mentioned purposes are achieved by the present gasification plant having the features of claim 1.

Brief Description of the Drawings

Other features and advantages of the present invention become more apparent from the description of a preferred, but not exclusive, embodiment of a gasification plant illustrated by indicative, but not limitative, examples in the accompanying drawings, wherein:

Figure 1 is a schematic view of a first embodiment of the gasification plant according to the invention;

Figure 2 is a schematic view of a second embodiment of the gasification plant according to the invention;

Figure 3 is a schematic view of a third embodiment of the gasification plant according to the invention;

Figure 4 is a schematic view of a fourth embodiment of the gasification plant according to the invention;

Figure 5 is a schematic view of a fifth embodiment of the gasification plant according to the invention;

Figure 6 is a schematic view of a sixth embodiment of the gasification plant according to the invention.

Ways of carrying out the Invention

With particular reference to such figures, it is globally indicated with 1 a gasification plant.

The gasification plant 1 comprises a pre-chamber 3 adapted to store the biomass 4 to be gasified to obtain the syngas.

The pre-chamber 3 has a loading opening 31 and an emptying opening 32. In particular, the pre-chamber 3 has a container body 16 for the storage of the biomass 4 associated with a reaction chamber 2 by interposing the emptying opening 32. The loading opening 31 allows insertion of the biomass 4 in the pre-chamber 3.

The emptying opening 32, however, allows the exit of the biomass 4 from the pre-chamber 3 and its movement to the next reaction chamber 2.

The gasification plant 1 , in fact, presents a reaction chamber 2 associated with the pre-chamber 3, the chamber 2 adapted to accommodate the thermochemical gasification processes useful for transforming biomass 4 into syngas 5.

More in detail, the reaction chamber 2 is a type of reactor, i.e. a housing vessel substantially cylindrical, where main axis is located, in normal operating conditions, in a vertical position.

It is possible to divide the reaction chamber 2 in three different zones according to their functionality.

In particular, the reaction chamber 2 is provided with a loading zone 6 associated with the pre-chamber 3 and adapted to allow the entry of the biomass 4.

The reaction chamber 2 is also provided with a reaction zone 7 in which the biomass 4 is effectively subjected to the thermochemical reactions necessary for its transformation into syngas 5.

The reaction chamber 2 is also provided with an outlet zone 8 suitable for allowing the exit of the produced syngas 5.

In the embodiments illustrated in the figures, the loading zone 6 coincides with the upper portion of the enclosure that defines the reaction chamber 2, the outlet zone 8 coincides with the lower portion and the reaction zone 7 coincides with the central part.

The lower portion of the reaction chamber 2 also includes a storage zone 9 adapted to accumulate, as a function of a subsequent disposal, the ash and the other unburnt products resulting from thermochemical processes.

The gasification plant 1 also comprises a user element 10 adapted to receive the syngas 5 coming from the reaction chamber 2.

Advantageously, the user element 10 is of the type of an internal combustion engine that uses the syngas 5 as fuel for rotating a drive shaft.

The rotary movement within the internal combustion engine 11 allows the engine to suck the produced syngas 5, defining the direction of circulation of the gas within the gasification plant 1.

Are not excluded alternative solutions in which, for example, the user element is a collector for domestic users, or a storage tank in which the syngas 5 is stored in appropriate containers (bottles, tanks, etc.) in order to be transported and/or used later.

In this case, the direction of circulation of the syngas 5 is imposed by additional elements, such as fans, blowers or compressors, with the aim of directing the gas from the reaction chamber 2 toward the user element 10. The gasification plant 1 is provided with a first dividing element 11 associated with the loading opening 31 for controlled closing of the loading opening itself.

In this way, the pre-chamber 3 is separated from the outside environment in an aeraulic manner avoiding, precisely, the entry of air into the pre- chamber itself.

The gasification plant 1 also presents a second partition element 12 associated with the emptying opening 32 for the controlled opening of the emptying opening itself.

In this way it is possible the adjustment of the quantity of biomass 4 to be transferred to the reaction chamber and of the frequency with which it has to be transferred.

The plant 1, in fact, is provided with a conveyor device 13 of the biomass 4 for its movement from the pre-chamber 3 to the reaction chamber 2. According to the invention, the plant 1 comprises a first conveyor element 14 associated with the reaction chamber 2 and the pre-chamber 3, and a second conveyor element 15 associated with the pre-chamber 3 and the user element 10.

The first conveyor element 14 is adapted to convey the syngas 5 from the reaction chamber 2 to the pre-chamber 3.

The second conveyor element 15 is adapted to convey the syngas 5 from the pre-chamber 3 to the user element 10. In this way, under the suction action of the internal combustion engine 11 , the syngas 5 is induced to cross the pre-chamber 3. The crossing of the pre-chamber 3 by the syngas 5 is adapted to filter the syngas 5 for direct contact with the biomass 4. The bed 4 of biomass present in the first chamber 3, in fact, presents the voids between the various elements of biomass 4 adapted to be crossed by the syngas 5. The voids define a tortuous path for the syngas 5 that, losing kinetic energy, is cleaned from the dust. The syngas 5, also, in contact with the biomass 4 cools down giving rise to condensation of tar which adheres to the particles of biomass 4.

In this way, in addition to achieve a purification of the syngas 5, the biomass 4 undergoes a pre-treatment (biomass preheating and tar adhesion to the particles) that promotes the efficiency of thermochemical processes inside the reaction chamber 2. According to a first embodiment, illustrated in Figure 1, the pre-chamber 3 presents the container body 16 for the storage of the biomass 4 associated with the reaction chamber 2 by interposing the emptying opening 32.

In particular, the pre-chamber 3 is placed immediately above the reaction chamber 2 and the emptying opening 32 is associated with the loading area 6 so as to be interposed between the pre-chamber 3 and the reaction chamber 2. In this way the biomass 4 is moved by gravity, from top to bottom. The second dividing element 12 associated with the emptying opening 32 is of the type of a rotary valve and allows to adjust the transfer of biomass 4 in the reaction chamber 2.

The conveyor device 13, in this first embodiment, is the set formed by the second dividing element 12 and a portion of the pre-chamber 3 containing the rotary valve and connected to the reaction chamber 2.

Are not excluded alternative solutions in which, for example, the second dividing element 12 is of the type of a throttle or a double knife valve with two alternatively openable and closable blades that they allow the passage of biomass 4 in the first conveyor device 13 and then into the reaction chamber 2.

Are not excluded solutions that foresee the use of partition elements different from those previously described. In a second embodiment, illustrated in Figure 2, the pre-chamber 3 has the container body 16 for the storage of the biomass 4 that is associated with the reaction chamber 2 by the interposition of a transfer duct 17, with the emptying opening 32 disposed between the container body 16 and the transfer duct 17.

In particular, the transfer duct 17 is connected to the emptying opening 32 by means of a portion of accumulation 16a of the container body 16 in which the biomass 4 is dropped by gravity passing through the rotary valve 12.

The accumulated biomass 4 is moved by an auger 18 contained in the transfer duct 17.

In this case, in fact, the conveyor device 13 includes an auger 18 disposed inside the transfer duct 17 and it is adapted to drag in movement predetermined portions of biomass 4 from the pre-chamber 3 to the reaction chamber 2.

In a third embodiment, illustrated in figure 3, the pre-chamber 3 yet encompasses the container body 16 for the storage of the biomass 4 and, in addition, also the transfer duct 17 interposed between the container body 16 and the reaction chamber 2, the emptying opening 32 being disposed between the transfer duct 17 and the reaction chamber 2.

The second partition element 12 associated with it is located downstream of the auger 18 along the path followed by the biomass 4, so the transfer duct 17 is freely communicating with the pre-chamber 3.

In the third embodiment, the first conveyor element 14 extends between the reaction chamber 2 and the container body 16.

A fourth embodiment, illustrated in figure 4, is substantially equal to the third embodiment, except for the fact that the first conveyor element 14 extends between the reaction chamber 2 and the transfer duct 17.

In this way, thanks to the positioning of the emptying opening downstream of the auger 18, it is possible to enter the syngas in the first chamber 5 by passing it from the transfer duct 17, increasing the time that the syngas 5 remains in contact with the biomass 4.

It is not excluded an embodiment similar to that illustrated in figure 4 in which, however, the pre-chamber 3 is constituted by the transfer duct 17 that extends between the loading opening 31 and the emptying opening 32.

In this case, for simplicity not shown in the figures, the transfer duct 17 also serves as container body 16.

In a fifth embodiment, shown in the figure 5, the first conveyor element 14 is associated with a pump element 20, of the type of a rotor, or a compressor, or a centrifugal fan, or a side channel blower, or similar, adapted to increase the working pressure of the syngas 5 and, therefore, the pressure in the first chamber 3.

By pressurizing the pre-chamber 3, the syngas 5 is moved both in the direction of the second conveyor element 15, both in the direction of the reaction chamber 2.

The portion of syngas that is recirculated to the reaction chamber 2, or recirculated syngas, is indicated with the reference number 5a.

This solution enables a functional separation between the pre-chamber 3 and the reaction chamber 2 without the need to install dividers, such as rotary valves or traps, designed to physically separate the two compartments.

The syngas 5, in fact, is usefully introduced in the first chamber 3 by means of a nozzle system, for simplicity not represented in the figures, so as to form a pressurized gas blade 21 at the gas inlet zone.

The gas blade 21 is adapted to prevent the passage of recirculated syngas 5a from the reaction chamber 2 to the pre-chamber 3 not only and exclusively through the first conveyor element 14, thus avoiding that can be created the typical operating conditions of "counter current" or "updraft" gasifiers. In a sixth embodiment, illustrated in Figure 6, the gasification plant 1 comprises an auxiliary duct 19 adapted to recirculate a part of the syngas 5, also in this case indicated as syngas recirculated 5a. In this way, the recirculated syngas 5a is drawn off from the second conveyor element 15, put under pressure by the pump element 20 and sent to the pre-chamber 3.

The syngas recirculated 5a, therefore, being taken from the syngas 5 exiting the pre-chamber 3 and directed to user element 10, is already filtered gas.

In the sixth embodiment, therefore, is provided a functional separation similar to that of figure 5, with the difference that, in this case, the gas blade 21 is formed by gas already filtered with consequent advantages related to the quality of the produced syngas 5 and related to the efficiency of the plant itself.

The operation of the present invention is as follows.

The biomass 4 is inserted in the first chamber 3 through the first partition element 11.

The latter allows to continuously feed the plant ensuring an aeraulic disconnection between the pre-chamber 3 and the external environment. This disconnection is necessary in order to maintain, in the gas plant 1 , the pressure conditions useful to send syngas 5 to the user element 10.

The biomass 4 accumulated in the first chamber 3 is subsequently sent to the reaction chamber 2 through the emptying opening 32. The second partition element 12 adjusts the amount of biomass 4 to be transferred to the reaction chamber 2 and keeps separate as much as possible the environments of the two chambers.

In the reaction chamber 2, in fact, the environmental conditions must be maintained (especially temperature and pressure) appropriate for the proper development of thermochemical reactions necessary to the transformation of biomass 4 into syngas 5.

Such reactions are developed mainly in the reaction zone 7, even if, already in the loading zone 6, begin the first transformations.

The syngas produced 5, inside the reaction chamber 2, is sucked from the outlet zone 8 and, by means of the first conveyor element 14, sent to the pre-chamber 3.

In the container body 16 contact occurs between the syngas 5 and the biomass 4 allowing the gas purification from impurities such as dust and tar.

Once purified, the syngas 5, through the second conveyor element 15, is dispatched to the user 10.

In the first embodiment (fig.1), the biomass 4 passes into the container body 16, under the effect of the force of gravity, when the second dividing element 12 allows the passage of material.

In the second, the third and fourth embodiment (figure 2, 3 and 4), the biomass 4 outgoing from the container body 16 is loaded by the auger 18 which sends it to the reaction chamber 2 through the transfer duct 17.

In the fifth and in the sixth embodiment, part of the produced syngas 5 is pressurized by the element in pump 20 and sent to the pre-chamber 3 increasing the pressure within the chamber.

The gas blade 21 opposes to a leakage of the syngas 5a from the reaction chamber 2 to the pre-chamber 3 allowing a functional separation of the two chambers without using a physical separation true and proper.

In practice it has been found that the described invention achieves the proposed aims and in particular it is emphasized that the devised gasification plant optimizes the production and cleaning processes of the syngas, minimizing maintenance operations and switching off time.

Use the pre-chamber for filtering the syngas allows, in fact, to eliminate the filter units specially designed in the known plants, or, in any case, to limit their number.

With this solution, in fact, it would be sufficient to add a simple cyclone upstream of the user element to obtain a high quality of the cleaning of the syngas by tar, char dust and other impurities.

In this way considerable savings are possible on the final costs of the plant as well as in terms of ease of use and dimensions.

The fact that the biomass used for filtering the syngas is subsequently subjected itself to reaction processes for the production of syngas, greatly increases the efficiency of the plant.

This is because, when the biomass is in contact with the syngas, undergoes a pretreatment favorable to the gasification process.

Furthermore, the filtering biomass succeeds in retaining tar and carbonaceous components that, being further subjected to thermochemical processes, can be exploited more fully for the production of syngas.