Technical Field

The present invention refers to a reactor for gasification plants.

Background Art

As known, the gasification is composed of a set of thermochemical processes aimed at transforming biomass, of various kinds and origins, in a fuel gas, commonly called "syngas", and usable for many purposes, for example as fuel in internal combustion engines.

The set of thermochemical processes takes place in specific gasification reactors.

In co-current and counter-current fixed-bed reactors, that they are used for small and medium size installations (up to about 1 MW), the set of thermochemical processes can generally be divided into four main stages: drying, pyrolysis, oxidation and reduction.

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 take place at high temperatures (exceeding 700 ° - 800° C) and in the presence of a gasifying agent, usually air under stoichiometric percentage.

In particular, in the oxidation phase temperatures of about 1100 ° C or higher are reached.

The biomass, under these conditions, is subjected to a 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 obtained depend on the type of gasifying agent and form a combustible gas mixture called syngas.

In case air is used as a gasifying agent, the products of the reactions are carbon dioxide, methane, carbon monoxide, nitrogen, hydrogen and other gaseous molecules. The solid products, commonly called "char", are material not reacted during the thermal and chemical processes and they are, at the end of the processes, in the form of ash and other solid particles.

The ash and the solid particles having sizes greater than about 10 μπι precipitate and can easily be removed from the gaseous phase produced, while the particles with smaller sizes, commonly called "powder" or "dust", are dragged away by the syngas and are contained into it.

Thermochemical processes above are normally made in a suitable reactor, that is placed in a container suitable for being filled at least partially with the biomass to be processed into syngas.

Providing a sufficient amount of heat, within the reactor is established a temperature gradient that allows the development of the thermochemical reactions necessary to the degradation of biomass and the creation of favorable conditions for the various stages of the gasification process. The temperature gradient is self sustaining in time and the reactions continue as long as it is supplied biomass and gasification agent.

The biomass present in the reactor progressively undergoes the thermochemical degradation while gradually moves from the upper portion of the reactor to the bottom for effect of the loading and unloading operations.

Ideally, the four phases in which can be split the gasification process can be identified in four different zones within the reactor.

The drying step takes place in the upper portion of the reactor, until temperatures to about 250 °C.

The step of pyrolysis takes place in the immediately underlying portion with temperatures in the range between about 250 ° C and 600 °C.

The oxidation phase occurs in the underlying portion, where usually the reactor becomes narrower forming a constriction, with temperatures that reach maximum values even over 1100 °C.

The last stage of reduction takes place in the lowest portion, starts at temperatures in a range between about 800 °C and 1100 °C and, due to endothermic behavior, ends at temperatures of about 600 °C or less. In literature reactors, i.e. "co-current" type, in the portion where the oxidation phase takes place, nozzles are used for the gasifying agent (air) introduction.

Moreover, the co-current reactors are open in their lower part to allow the passage of the syngas from the portion where the reduction takes place. Other known types of reactors, such as for example the reactors of "countercurrent" type, are similar to the "co-current", while differing from them for the verse of the syngas extraction respect the verse the biomass feeding into the reactor.

In countercurrent reactors, in fact, the gas flows through the bed of biomass in the opposite verse respect to the advancement verse of the same biomass in the reactor.

The patent document WO 2014/097236 describes a pyro-gasification reactor comprising a casing that surrounds part of the reaction chamber where a duct supplies a gasifying agent such as air. The air is then sent to the combustion chamber through holes formed on the outer wall of the chamber itself enclosed in the casing.

In this way, the air to be sent into the combustion chamber is not free to circulate and remains confined in the tube and inside the casing until, by pressure difference, is pushed inside the combustion chamber through the holes.

The patent document WO 2010/095025 describes a gasifier with a modified combustion chamber in which the gasifying agent is entered through feed lines directly connected with the combustion chamber.

The Patent EP 2 653 525 describes a gasifier reactor where the combustion chamber is placed inside a container casing and is linked to an air supply duct designed to provide air flow straight into the combustion chamber. The solutions proposed by the documents WO 2010/095025 and EP 2653525, therefore, consider a direct air supply inside the combustion chamber without countercurrent passages in additional interspaces.

Anyway, it is known the need to cope with the drawbacks related to the high temperatures reached inside the reactor, especially in the portion where the oxidation takes place.

In particular the problem is related to the effect that high temperatures have on the walls that defines the reactor itself.

At such temperatures, in fact, the mechanical and oxidation resistance of some materials with which the reactors are made, such as the commercial steels, is significantly reduced, thus making critical the use of these type of materials for the realization of the casing.

Alternatively to commercial steels is known the use of refractory and ceramic materials, resistant to high temperatures.

Even in this case, however, there are drawbacks related both to the high costs of this type of materials, and to their poor resistance to temperature variations that make the material more brittle.

The latter drawback is particularly evident when the reactor requires frequent switching on and off or simple maintenance cycles.

Disclosure of the Invention

The main task of the present invention is to provide a reactor for gasification plants which allows to lower the temperature of the walls of the reactor without reducing at the same time the thermal efficiency.

One object of the present invention is to provide a reactor for gasification plants that, for equal thermal insulation, allows to reduce heat losses from the reactor to the outside ambient.

A further object of the present invention is to provide a gasification system which allows to overcome the mentioned drawbacks of the known literature within the framework of a simple, rational solution, easy and effective to use and with a low cost The above mentioned purposes are achieved by the present gasification system 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 an indicative, but not limitative, example in the accompanying drawings, wherein:

figure 1 is an axonometric view of the reactor according to the invention;

- figure 2 is a partially exploded view of the reactor according to the invention;

figure 3 is a sectional view of the reactor according to the invention; figure 4 is a sectional axonometric view of the reactor according to the invention.

Ways of carrying out the Invention

With particular reference to such figures, it is generally indicated with 1 a reactor for gasification plants.

The reactor 1 comprises a first container body 2 adapted to be filled at least partially with biomass to be gasified to obtain synthesis gas (syngas). The first container body 2 is provided with an upper portion 3 adapted to receive the incoming biomass.

In the present discussion, the terms "upper", "lower", "upward", "downward" and similar refers to the solution commonly adopted, to place the reactor in such a way that its main axis is in vertical position.

The upper portion 3 is a portion in which such temperatures and conditions are reached to allow the development of the drying phase and part of the pyrolysis phase.

Conveniently, the upper portion 3 is provided with an inlet 4 designed to be connected to biomass transfer systems such as, e.g. hoppers, augers, pistons, etc., adapted to insert the biomass in the reactor itself. In the present embodiment, the inlet 4 is surrounded by coupling means 5 use to provide stable connection between the reactor 1 and the transfer systems mentioned above.

The first container body 2 also includes a central portion 6.

The central portion 6 is the portion of the first container body 2 adapted to host the stage of oxidation of the biomass.

In the central portion 6, in fact, the developed conditions guarantee to continue the pyrolysis started above and to reach the biomass combustion with average temperatures of about 800 °C.

In this portion the gasifying agent 7 is supplied, it is usually air, but it is not excluded the use of other agents such as pure oxygen or steam, in under stoichiometric proportions to perform the oxidation step.

For this purpose, in correspondence of the central portion 6 are pierced the holes 9 for the input of the gasifying agent 7.

In the embodiment illustrated in the figures the holes 9 are made at the same level and equally spaced from each other to ensure an gasifying agent 7 supply as homogeneous as possible.

Advantageously, the central portion 6 comprises an upper section 6a of substantially cylindrical shape, having an upper edge linked with the upper portion 3, and a lower sector 6b substantially shaped as a truncated cone turned upside down and linked with the upper stretch 6a.

In the present discussion, with cone "inverted truncated" is meant the configuration in which the truncated cone larger section is placed above the section having a smaller size.

As illustrated in the figures, the outer surface of the central portion 6 is smooth, but are not excluded alternative solutions in which, i.e. on that surface are created heat exchange fins or other devices designed to increase the heat exchange surface of the central portion itself.

The first container body 2, finally, comprises a lower portion 10 adapted to complete the reduction reactions and to allow the exit of gasified biomass (ash and other inert material) and of the synthesis gas 8.

In particular, in correspondence of the lower portion 10 occurs the main reactions of reduction that contribute to the formation of the fuel part of the syngas (hydrogen, carbon monoxide, etc.).

The lower portion 10 is linked to the central portion 6 and, in the present embodiment, also it has a truncated cone shape, in this case not overturned, so having the section with larger size placed below the section with smaller dimensions.

In particular, the lower stretch 6b has a lower extremity 11 linked to the lower portion 10.

In the present embodiment, therefore, the lower extremity 11 coincides with the coupling section between the central portion 6 and the lower portion 10.

The first container body 2 illustrated in the figures, therefore, presents a narrowing in its lower extremity 11.

The lower extremity 11, due to its placement and its geometry, is subjected to very high temperatures and has less surface area to be used to disperse the excess of heat.

For this reason, it appears to be the part of the first container body 2 more susceptible to wear and thermal stress.

The reactor 1 also includes a second container body 12 that internally includes the first container body 2.

In the present embodiment, the second container body 12 entirely covers the first container body 2, but it is not excluded the solution in which the latter can exit beyond the second body.

In particular, the second container body 12 is associated with the first container body 2 in correspondence of the upper portion 3 and it is provided with at least one port 13 designed to allow the gasifying agent supply in the second body container itself.

In the present embodiment it is present a port 13, but are not excluded alternative solutions in which the second container body 12 comprises a different number of ports 13.

Furthermore, as shown in the figures, it is also present an auxiliary port 13a adapted to allow the agent supply in the gasifying reactor 1.

Are not excluded different solutions in which, for example, the port 13 is closed and the gasifying agent intake is only the port 13a.

The second container body 12 has a substantially cylindrical shape and, in correspondence of the upper base, is provided with a lid 12a shaped as a circular crown with an open center and superimpo sable at the entrance 4. In correspondence of the lower base, on the other hand, the second container body 12 has coupling means 14 to a support structure 15 adapted to support the same container body.

Always in correspondence of the lower base, the second container body 12 comprises a discharge area 16.

The latter is positioned below the first container body 2 and is adapted to accumulate the gasified biomass, i.e. ash and other material resulting from thermochemical processes of gasification, outgoing from the first container body itself.

According to the invention, the reactor 1 comprises a primary cylinder 23 including the first container body 2 and open at the top for the transit of the gasifying agent 7 to the holes 9. In particular, between the primary cylinder 23 and the first container body 2 is defined a cooling interspace 24 that is crossed by the gasifying agent 7 skimming at least in part the upper portion 3 and the central portion 6.

This feature allows the gasifying agent 7 to subtract heat as it goes toward the central portion 6.

In the present embodiment, the primary cylinder 23 is a cylindrical trunk positioned between the second container body 12 and the first container body 2.

At the bottom, the cylindrical trunk is closed by the discharge area 16, while, at the top, is open.

In fact, the cylindrical trunk has a height lower than the height of the second container body 12, therefore, is not in contact with the lid 12a. This characteristic causes the gasifying agent 7 entering from the port 13 or 13a, should pass the primary cylinder 23 passing upwardly to it before going down to the holes 9.

In this way the gasifying agent 7 enters the cooling interspace 24 from above, resulting in a progressive heat exchange that involves more parts of the reactor as it proceeds towards the holes 9.

Always according to the invention, the reactor 1 comprises an auxiliary casing 17 that it is placed inside the cooling interspace 24 and it surrounds at least partially the central portion 6.

In particular, the auxiliary casing 17 is linked to the central portion above the holes 9 and is provided with an opening 18 below the holes 9 so the auxiliary casing 17 conveys the gasifying agent 7 to go upwards around the central portion 6 with an upward motion.

In the present embodiment, the auxiliary casing 17 allows the passage of the gasifying agent 7 from the second container body 12 to the holes 9 so the central portion 6 can be skimmed by the agent gasifying itself.

The auxiliary casing 17, in fact, defines a space between the central portion 6 and the housing, closed at the top by a substantially horizontal lid 17a and accessible through the opening 18.

The gasifying agent 7 then passes from the port 13, or 13a, to the holes 9, before passing above the primary cylinder 23 and entering the cooling interspace 24, then going down towards the opening 18 and going through it lapping central portion 6.

In the present embodiment, the auxiliary casing 17 entirely surrounds the central portion 6 so as to wrap it completely.

In particular, the auxiliary casing 17 comprises a top section 17a of substantially circular ring shape that surrounds the upper stretch 6a. The auxiliary casing 17 also comprises a lower sector 17b substantially shaped as a truncated inverted cone which surrounds the lower sector 6b of the central portion 6. The opening 18 is placed at the base of the lower section 17b so as to convey the passage of the gasifying agent 7 in proximity of the lower extremity 11.

In this way, the gasifying agent 7 can move over the whole central portion 6, performing in fact a heat exchange that allows the cooling of the central portion itself and especially of the lower extremity 11 which, as said, is the one of the components most susceptible to wear and thermal stress. Again with reference to the embodiment illustrated in the figures, in the second container body 12 it is placed a dividing partition 21 associated externally to the first container body 2 in correspondence to the lower extremity 11.

The dividing partition 21 in fact prevents the gasifying agent 7 from skimming over the lower portion 10, facilitating the conveying of the agent itself towards the opening 18.

In addition to the bodies containers described above, the reactor 1 comprises a conveying chamber 19 that it is placed in the second container body 12 and it is associated to the lower portion 10 of the first container body 2.

This chamber is adapted to collect the synthesis gas 8 leaving the first container body 2 conveying it outside of the reactor 1, for example towards the filtering units adapted to purify the gases from impurities and / or towards the user parts, such as internal combustion engines or other utilities.

In the present embodiment, the conveying chamber 19 comprises at least partially the primary cylinder 23.

In particular, the primary cylinder 23 defines the inner wall of the conveying chamber 19.

This conformation allows a heat exchange between the gasifying agent 7, that flows descending interspace 24, and the gases, which flow ascending in the conveying chamber 19.

As illustrated in the figures, the gasifying agent 7 skims over the conveying chamber 19 also externally even before entering the cooling interspace 24 increasing the efficiency of the heat exchange.

Are not excluded alternative solutions in which, for example, the primary cylinder 23 and the conveying chamber 19 are two different elements associated to each other, or two different items separate and arrange to pass the gasifying agent 7 above of the primary cylinder 23 with then convey it towards the holes 9.

The conveying chamber 19, illustrated in the figures, has at least one conveying duct 20 that exits from one of the ports 13, or from another point, and adapted to remove the synthesis gas output 8 from the reactor 1. In particular, the conveying duct 20 is outgoing from the second container body 12 through the aforesaid port 13.

As illustrated in the figures, the conveying duct 20 is a tubular element of smaller diameter than that of the port 13 and such as to cross the port 13 without preventing the gasifying agent 7 to enter in the reactor.

Usefully, the conveying chamber 19 comprises as many conveying ducts 20 as many are the ports 13 are present in the second container body 12. In the present embodiment, the conveying chamber 19 has the shape of an annular cylinder and it is disposed in the reactor 1 interposed between the first container body 2 and the second container body 12.

The base of the conveying chamber 19 is secured to the lower portion 10 of the first body container 2 by preventing the synthesis gas 8 from expanding inside the second container body 12 and conveying it outward. Conveniently, the conveying chamber 19 and the lower portion 10 are coupled together to define a volume 22 surrounding the first container body 2 and closed at the top with a partition 21.

In particular, the base of the conveying chamber 19 is linked to the lower portion 10 so as to define the volume 22 around the first container body 2 which, in the present embodiment, is closed at the top with a dividing partition 21.

Conveniently, this volume 22 can be filled with material, for example, sand or other siliceous material, adapted to increase the thermal inertia of the lower portion 10.

This way is possible to increase the thermal inertia maintaining more constant the temperature of the lower portion of the surface 10 and thus avoiding temperature peaks which can compromise the proper performance of the gasification reactions.

The operation of the present invention is as follows.

The gasifying agent enters through ports 13 and 13a and superiorly crosses the primary cylinder 23.

Subsequently, the gasifying agent enters the cooling interspace of 24 and then descend to the holes 9 leading to a gradual heat transfer that involves several parts of the reactor as it progresses towards the holes 9.

Once entered the cooling interspace 24, the gasifying agent 7 descends towards the opening 18 and, going back through the latter, skim over the lower extremity 11 and the central portion 6.

In this way, the gasifying agent 7 extracts heat at these portions and then cools down and preserve these elements from thermal stress.

Entering through the holes 9, the gasifying agent contributes to the gasification of the biomass present in the first container body 2.

Here the synthesis gas 8 that is formed, sucked or pushed, proceeds through the lower portion 10 and, then, enters into the conveying chamber

19.

Here it is conveyed out of the reactor 1 through the conveying ducts 20. In its exit path, which goes from the first container body 2 to the conveying ducts 20, the gas transfers heat to the gasifying agent 7 that skims over the walls of the conveying chamber 19 and of the primary cylinder 23.

It is, in practice, been found that the described invention achieves the proposed aims and in particular it is emphasized that the devised reactor for the gasification systems allows to lower the temperature of the hot walls of the reactor, without reducing the efficiency of the reactor itself. The path followed by the gasifying agent, in fact, allows its preheating useful for efficiency of the system.

This reduce the amount of heat to be supplied to the reactor to maintain the conditions useful to thermochemical processes for the transformation of the biomass into synthesis gas.

The conformation and the arrangement of the auxiliary casing ensure that the incoming air can subtract heat to parts reactor most exposed to high temperatures.

In this way it is possible to increase the efficiency of the reactor and build it with materials less expensive and more easily available on the market as, for example, the commercial steels.

Furthermore, since the auxiliary casing and the primary cylinder envelop the whole first container body, the surfaces involved in the heat exchange are wide, and this feature has a positive effect on thermal efficiency.

To this it is also added the fact that the auxiliary placing, the primary cylinder and the second container body together involve an increase to the shielding effect that reduces the heat losses towards the outside, increasing efficiency.