EP0531778A1 - Co-current gasifier - Google Patents

Abstract

The co-current gasifier according to the invention has a combustion chamber (1) which is closed off at the bottom at most by a grating (9) for ash removal and is equipped inside with a rotating screw (11), in order to feed upwards the material which is to be gasified and has passed through the firing zone (4). Apart from the technical advantages inherent in the basic principle concerning the purity of the gasification gas produced, the advantages of the co-current gasifier represented here are those of reduced dimensions, which allow the gasifier also to be used suitably for installations with restricted outputs. It is suitable for engine use and for heating use. <IMAGE>

Description

The present invention relates to a direct current gasifier as described in the preamble of claim 1.

Similar carburetors are well known in practice because they were used for the production of gas from wood for the operation of explosion engines, particularly in the years when there was a lack of liquid fuel (petrol).

In order to further explain the field of application of the present invention, it is good to briefly summarize the prior art where it is used.

There are two main models of carburettors, i.e. the countercurrent and cocurrent carburetors. The concept of countercurrent or direct current relates to the fact that the flow of the gas produced flows directly in the opposite direction or in the same direction as the flow of the material to be gasified. This means that in a countercurrent gasifier, the gas generated by the gasification, after chemical reaction C + O₂ = CO₂ (+ 97cal), passes through the "fresh" fuel supply (in the specific case wood) which passes through the combustion zone in the area of this invention " Firing zone ", has not yet reached.

On the other hand, in the case of the direct current gasifier, the gas and material produced move in the same direction, with the result that the gas only passes through the fuel (wood) that has already passed through the furnace and has therefore been converted into pure coal , although its combustion is not yet complete.

The essential difference for the purpose of the present invention now lies in the fact that in a countercurrent gasifier, where the gas still passes through fresh fuel material, waste products contained therein are primarily loaded with tar, which it brings in a gaseous state with it.

As soon as the temperature drops below a certain value, the tar can condense and settles on the parts (pipes, rust, etc.) through which the gas has to flow. This strong tar settling is extremely annoying and often prevents such a carburetor from functioning regularly. Another consequence of this problem is that a countercurrent gasifier cannot be considered as a gas generator for fuel engine operation, since the inevitable tar deposits make it impossible for an explosion engine which is supplied with such a gas to function correctly.

The consequence of this is that the counterflow gasifier type can only be used for heat generation and also here only with all suitable precautions that prevent tar condensation. The most effective of these precautions, albeit very delicate, is if the gas is burned as quickly as possible, i.e. immediately after its formation: this operation carried out at high temperature actually causes the tar molecule to crack, which is thus burned.

In contrast, the formation of tar deposits does not exist with the direct current gasifiers, since the gas never goes through fresh fuel (wood), but only those that have already passed through the furnace and were converted into pure coal after the secondary products had been broken up beforehand. This is the main advantage of direct current gasifiers over those with counter current.

The present invention accordingly finds specific application in the field of DC gasifiers, i.e. those that generate a gas free of tar condensation and are therefore generally suitable for use in explosion engines.

The types of carburettors are known for the use they found in World War II, when the vehicles' explosion engines were used instead of petrol.

A similar carburetor is shown for example in FR-A-25 26 036, where a carburetor for agricultural tractors is described which mainly consists of a V-shaped double chamber.

The upper chamber consists of a cylindrical container, the diameter of which continuously decreases in the lower part: it is therefore conical wedging downwards.

After the narrowest point of this chamber, in which there are radial openings through which the primary air is supplied, the second chamber begins in the interior of the chamber, which is delimited by a circular, conically spreading wall. The whole thing thus forms a double funnel through which the material to be gasified passes through from top to bottom through its own weight. The second chamber is closed at the bottom by a grate, which serves the purpose of retaining the coal particles which are not completely burned in the annular combustion zone. This type of direct current gasifier is hereinafter referred to as "descending" since it is characterized in that the fuel gas formed by the gasification in the combustion chamber, corresponding to the narrowest point of the two connecting chambers, moves from top to bottom in the same direction of material transport.

This type of gasifier therefore has a major disadvantage, i.e. it requires a separation grate below the second chamber: this grate allows the smallest unburned particles of ash and coal to be separated - i.e. not yet completely converted to gas - which are piling up. This disadvantage was not important when using DC gasifiers for driving explosion engines during the war, when many vehicles were equipped with such devices for lack of gasoline. In fact, the carburettor was not operated continuously in this application so that it was possible to clean the grate or collecting chamber from the ash accumulated under the grate at the end of the day or after the short operating period and thus to restore the ideal working conditions of the carburetor .

The disadvantage of the material accumulation above the grate thus prevents the descending direct current gasifier from operating continuously, with an operating period of under continuous operation is understood for several days or weeks without maintenance.

It must also be emphasized that the carburetor application for vehicle propulsion is simpler than for a fixed system, since the inevitable vibrations to which it is subjected cause the "bridging" of the material to be burned in the upper chamber (ie zones where the material is located) stuck to the walls), which interrupt the flow of fuel to the combustion chamber.

The purpose of the present invention is to propose a direct current gasifier without the disadvantages of the above mentioned direct current gasifier according to the preamble of claim 1 and in particular a gasifier which does not require a lower grate, in which the problem of material bridging is also eliminated.

This goal is achieved by means of a direct current gasifier which has the characteristics listed in claim 1.

Thanks to the presence of the screw, which feeds the material to be gasified from the furnace to the upper entry point of the tube by conveying it on the outside of the tube, there is an increasing material flow on the outside and a descending flow inside the tube. A constant circulation of the material is achieved, so that no particles, not even the smallest of the materials, remain unburned, since the material passes through the furnace once or several times until it is completely exhausted. What remains of the fuel after the repeated passes through the firing zone can only be unburned material in the form of fine ash. This ash can be removed in two ways, depending on whether or not the combustion chamber has a finely perforated grate at the bottom. If there is such a grate, which makes up the largest opening provided under the combustion chamber according to the present invention, the ashes can be removed through this grate, as will be described in detail. If, on the other hand, there is no rust under the combustion chamber, but rather a tight seal, the very fine ash, which always forms when wood is burned, is aerodynamically entrained by the gases that are generated with direct current with the material fed by the screw, remove from the carburetor. In this case, it is usually necessary to filter the gases, for example using a cyclone filter, so that they are freed from the fine ash, especially where the gasification gas is intended for explosion engines, ie for the purpose for which the DC gasifier, thanks the gas purity to be achieved is provided. According to the characteristic of claim 2, the inside of the pipe is conical towards the bottom and has a larger diameter in accordance with its starting point at the furnace: thanks to this provision, the combustion material inside the pipe flows more easily downwards and thus avoids any risk of clogging of the material feed.

According to a preferred embodiment of the invention according to claim 3, the taper of the tube has been chosen between 30 'and 4 °, which allows better operating conditions combined with acceptable construction use.

According to a preferred embodiment according to claim 4, the combustion chamber is made at least in its conical section from refractory material. This precaution serves the purpose of achieving optimal thermal insulation of the warmest point of the carburetor in order to avoid heat loss to the maximum.

Another preferred embodiment according to claim 5 provides an angle of inclination of the screw forming the screw and, when measured on the outer tube diameter of 120 mm, is between 10 ° and 25 °. Experience has shown that the angle set between these limits guarantees ideal operating conditions for the carburetor - safety during material transport, reduced friction on the screw, moderate speed of rotation of the screw, etc.

The claim 6 relates to a preferred embodiment of the gasifier according to the invention and proposes a design of the firing zone, which guarantees an excellent supply of the main air to the combustion zone.

Claim 7 relates to a preferred embodiment of the gasifier according to the invention and relates specifically to a feed system of the combustion chamber.

The invention will now be described with the aid of a preferred embodiment, which is illustrated in the various illustrations.

Fig. 1

Die Verbrennungskammer eines Gleichstromvergasers nach Erfindung, im Schnitt,

Fig. 2

Eine Durchschnittansicht eines kompletten Vergasers mit Verbrennungskammer der Fig. 1 und einem oberhalb der Kammer angeordneten Einfüllsilo.

These show:

Fig. 1

The combustion chamber of a DC gasifier according to the invention, in section,

Fig. 2

An average view of a complete carburetor with combustion chamber of FIG. 1 and a filling silo arranged above the chamber.

1 shows the part of a DC gasifier forming the combustion chamber.

The combustion chamber of the carburetor is designated by 1. This chamber 1 is in its upper part a mainly cylindrical shape and enclosed by a cylindrical wall 1, which in the example shown consists of sheet metal. The lower part 3 of the chamber 1 wedges conically downwards and forms the combustion 4 of the carburetor there. This zone, where the combustion or oxidation of the carbon takes place according to laws regulating these processes, will be described in detail later.

The truncated cone wall, which laterally delimits the wedge-out portion 3 of the combustion chamber, can be made of sheet iron. In the embodiment of FIG. 1, however, a preferred embodiment is already shown, according to which the wall 5 consists of refractory material. This solution is particularly advantageous because excellent thermal insulation from the outside is achieved, namely in the warmest zone of the chamber, where the heat losses to be avoided would be greatest.

Between the upper cylindrical zone of the combustion chamber 1 enclosed by the wall 2 and the lower conical 3 For the connection of the two parts, a sheet is used through which the combustion gases, but not the combustion particles, flow. This perforated ring zone 6 thus forms the connection between the inner and outer carburetors, as will be better described later when the operating mode of the device is dealt with.

• die Holztrocknungsphase, während der das im Holz vorkommende Wasser bei Temperaturen bis 200 Grad C., verdunstet.
• die Pyrolysenphasen, die bei höheren Temperaturen als 200 Grad C stattfindet und während der sich die in den Holzfasern enthaltene Zellulose in die Komponenten Kohlendioxyd, Methanol, hochflüchtigen Teer und organische Säuren zu zerlegen beginnt. Ueber 375 Grad C versplittert sich der Holzstoff in kleinere chemische Legierungen und erzeugt Teere die schwieriger flüchtig sind und Kohlenwasserstoff. Ueber 700 Grad C sind dann nur noch Kohlenstoff in Form von Holzkohle vorhanden.
• die Oxydationsphase, die in der Feuerung 4 beim Lufteingangspunkt entsteht. Die Oxydation oder Kohlenstoffvergasung erzeugt Energie, die den Energiebedarf der zuvorbeschriebenen Phasen deckt.
• die Reduktionsphase, in der sich das eigentliche Holzgas bildet als Endprodukt des vorliegenden Vergasers.

The furnace 4 mainly consists of a cover 7, which has a plurality of holes 8 at the bottom, along its circumferential line, for the main air supply, ie air coming from outside. This main air is used to achieve oxidation, ie the process of wood burning that reaches the firing zone 4. Without going into the details of the chemical reactions that occur in practice, which on the one hand go beyond the necessity of this description and on the other hand are known to every expert in the field, we would like to mention that there is a gasification process , as practiced in the carburetor of the present invention, is divided into four successive phases, which are as follows:

• the wood drying phase, during which the water in the wood evaporates at temperatures up to 200 degrees C.
• the pyrolysis phases, which take place at temperatures higher than 200 degrees C and during which the cellulose contained in the wood fibers begins to break down into the components carbon dioxide, methanol, volatile tar and organic acids. Above 375 degrees C, the wood pulp splinters into smaller chemical alloys and produces tars that are more difficult to volatile and hydrocarbons. Only carbon in the form of charcoal then remains above 700 degrees C.
• the oxidation phase that occurs in the furnace 4 at the air entry point. The oxidation or carbon gasification generates energy that meets the energy requirements of the previously described phases.
• the reduction phase in which the actual wood gas forms as the end product of the present gasifier.

What is important to achieve a well functioning gasifier is the fact that the gas generated is as free as possible from low volatile pyrolysis products, i.e. which condense below 400 degrees C and can adhere to the carburetor parts, which would cause unacceptable interference. For this reason, it is necessary that the gas generated in the reduction phase no longer passes through the pyrolysis zone, i.e. the four zones mentioned must also follow each other in the direction of formation and shift of the gas in the above-mentioned order. This is precisely the principle of the co-current gasifier in contrast to that with countercurrent, in which the gases generated in the reduction zone have to pass through the pyrolysis zone and possibly also the drying zone and are thus loaded with heavy tar substances on the way.

• a) Die Verbrennungskammer 1 weist unten höchstens einen Rost 9 mit sehr kleinen Löchern 10 im Vergleich zur Grösse der unverbrannten Holzspäne. Dieser Rost 9 dient nur zur Entfernung der restlichen feinen Asche und ist dort, wo die Asche vom Verbrennungsgasluftzug, vom Vergaser abgegeben, angesaugt wird, nicht notwendig. Auf jeden Fall handelt es sich um einen Rost , durch welchen keine Hauptluft der Verbrennungskammer durchziehen darf, d.h. der Rost hat keinerlei Funktion hinsichtlich des eigentlichen Vergasungsprozesses und kann demnach unterlassen werden.
  In anderen Worten ist die erste Charakteristik des Vergasers nach Erfindung jene, dass er eine Verbrennungskammer 1 aufweist, die unten hauptsächlich geschlossen ist, oder höchstens einen mit Löchern 10 versehenen Rost 9 aufweist, welcher nur den einen Zweck hat, dort wo es notwendig ist die fein verbrannte Asche zu entfernen.
• b) im Innern der Verbrennungskammer 1 ist eine Schnecke 11 angebracht deren äussere Abmessungen sich der kegelförmigen Form der Kammer anpassen und die in ihrem inneren Axialteil aus einem Zentralrohr 12 besteht, durch welches das zu vergasende Material von oben gespeist wird, wie dies später, unter Feuerung 4, besser erklärt wird.

The DC gasifier of the present invention is characterized by two essential aspects, namely:

• a) The combustion chamber 1 has at most one grate 9 with very small holes 10 in comparison to the size of the unburned wood chips. This grate 9 is only used to remove the remaining fine ash and is not necessary where the ash is sucked in by the combustion gas draft, emitted by the carburetor. In any case, it is a grate through which no main air from the combustion chamber is allowed to pass, ie the grate has no function with regard to the actual gasification process and can therefore be omitted.
  In other words, the first characteristic of the gasifier according to the invention is that it has a combustion chamber 1, which is mainly closed at the bottom, or at most has a grate 9 provided with holes 10, which has only the one purpose where it is necessary to remove finely burned ashes.
• b) in the interior of the combustion chamber 1, a screw 11 is attached whose outer dimensions adapt to the conical shape of the chamber and which consists in its inner axial part of a central tube 12 through which the material to be gasified is fed from above, as will be described later on Firing 4, is better explained.

The worm 11 or the inner tube 12 is open in the upper part and is rotated during the carburetor operation by a drive shaft 13 (FIG. 2) which is connected to the tube 12 so that a large part of the inner surface of the tube remains open . The shaft 13 is supported in the upper part of the carburetor by a holder 14, which fastens to the cover 14 and closes the filling silo 16 and is rotated by a geared motor 17 at a very low speed. The details of the geared motor 17 and the shaft connection 13 with the tube 12 are clear to any person skilled in the art, which is why no further detailed explanations are necessary.

The direction of rotation of the screw 11 and the direction of the slope are such that the combustion material flowing out of the lower opening 18 of the tube 12, which went through the firing zone 4, was not completely converted into combustion gas and ash, i.e. partially unburned material, is grasped by the foot 19 below the screw 11 and pushed up onto the inclined surface of the screw 11.

Arrived at the upper end of the screw 11, which is located approximately at the same level as the upper opening 20 of the tube 11, the partially burned material is mixed with fresh material which has not yet burned and more or less partially fills the filling silo 16.

The operation of the carburetor is described in more detail below.

The inventive carburetor also has the following construction elements, which are not essential characteristics of the same, but which, as preferred solutions, guarantee automatic functioning of the system.

The perforated sheet 6 is connected by a thin ring-shaped channel 21 to a further channel 22, also ring-shaped, which, as can be seen on the right-hand side of FIG. 1, is connected to a discharge line for the gases. Through these, the gases generated in the gasification are fed to the intended consumption element (burner, explosion engine) (not shown).

The filling silo 16 (FIG. 2), located above the combustion chamber, is preferably closed off at the top by a hermetic lock 24 through which the fresh combustion material is fed as soon as a sensor 25 placed in the filling silo 16 indicates that the material level has dropped below a certain minimum value is.

According to a preferred embodiment of the invention according to claim 2, the tube 12 is tapered on the inside and has the larger diameter in accordance with its starting point 26 in the vicinity of the furnace 4.

This solution has the advantage of facilitating the descent, by gravity, of the material entering the upper opening 20 of the tube 12. It is known that the transport of material in the form of a grain, such as the type constituting the feed to the furnace 4 in our case, entails the risk of "bridges" or "bulges" being formed. As the name suggests, these are formations of "self-supporting" material blockages, i.e. Designs where fresh pieces of wood and coal lie on top of one another and thus form a material dome, which prevent further feeding of the combustion material to the furnace 4.

This danger is combated effectively thanks to the taper of the tube interior 12. Indeed, a taper, in the sense of a very small extension of the pipe section, is enough to prevent the material from forming "bulges".

This taper is preferably between 30 'and 4 °.

For the purpose of good operation of the DC gasifier according to the present invention, the pitch angle is that of the screw forming screw important.

This angle is measured at the inner point of the screw 11, i.e. in accordance with the outer tube diameter of 120 mm, 12, preferably between 10 and 25 °.

The pitch of the screw 11 is important for the selection of an appropriate speed of rotation of the screw 11 itself. This pitch angle is seen in relation to the other dimensions of the carburetor, which is why it is determined in the present description as a function of the tube diameter 12, which was 120 mm in the example shown.

According to another preferred embodiment of the carburetor according to the invention, the firing zone 4 consists of a central zone 27 with circular holes, closed at the top by a cover 7 mentioned above and an annular shape zone 28 which surrounds the central zone 27. In the ring-shaped zone 28 there is at most one grate with very small holes 10.

The advantage of this particular embodiment of the firing zone 4, as described above, is clear: the arrangement of the holes 8 for the supply of the main air determined by the cover 7 around the central zone 27 results in an ideal, regular distribution of the main air around the firing 4 the same situation that can be found in a normal gas distribution burner in a so-called saving oven, where the gas is distributed symmetrically in flame form around a central plate. The only difference here is that the main combustion air is used instead of gas, but here and there it is important that the combustion takes place regularly so that it is distributed over the entire circumference of the combustion zone 4.

With regard to the grate (s) 9, which are provided as an alternative in the invention, it should also be mentioned that the grate (s) are not absolutely necessary for realizing the present invention. As already said, they can prove to be superfluous where the ashes are so fine as a result of the complete combustion of the fuel that they are continuously removed from the gas that forms. If, on the other hand, the ash formed is large-grained (which can depend on many factors and is unnecessary to explain here) and thus tends to be deposited on the bottom of the ring-shaped zone 28 surrounding the furnace 4, it is useful to provide one or more grids 9 in the ring-shaped zone 28. This one or more grids must be provided with very small holes (in the order of 0.5-2mm in diameter) so that only the ash can fall into the lower part of the carburetor and be removed. In its most extreme form, the grate will cover the entire surface of the ring-shaped zone 28, ie the concept of a single grate 9 also includes the case where the grate consists of a perforated ring-shaped zone over the entire surface.

An automatic removal system for the ashes can be attached under the grate 9 and, in FIG. 1 shown only as an example, may consist of one or more fall silos 29, on the bottom or the bottoms of which the ashes are removed by means of an ejection screw 30. The latter is operated by a continuous or alternative motor 31. It is clear that in the case of a grate 9 in a complete ring shape, as explained above, the lower fall silo 29 also has the ring channel shape.

The operation of the DC gasifier according to the present invention is clearly shown in FIG. 2.

The combustion material (wood chips or small pieces of wood) is introduced from above through the hermetically sealed lock 24 controlled by the level sensor 25. It therefore always fills the lower part of the filling silo 16 up to the minimum height of the sensor 25. The lock 24 is in turn always fed by material through a suitable feed hopper 32 and a conveyor belt 33 in a manner not shown here.

The combustion material then passes continuously in the vicinity of the shaft 13 into the zone 20 of the upper tube opening of the screw 11 and is introduced into the tube. However, the fresh material coming from above mixes, before it reaches the opening 20, with the material which has already been partially burned and fed upwards by the screw 11 on the outside of the tube 12, where the mixture of this material, by slow rotation of the Screw 11 transported upwards with the fresh material by the presence of a deviation plate 34 in the upper one Batch of screw 11, which pushes the "rising" material inwards thanks to its suitable shape.

When the mixture of the fresh material with the partially burned material (due to its previous passage in the firing zone 4) descends into the firing zone 4 after the drying phase - which takes place in the upper part of the tube 12 and also in the filling silo 16 , as well as - the pyrolysis phase - which takes place in the last descending pipe part, just before the furnace 4, where the temperature has reached the necessary values - it goes through the oxidation phase, where the main combustion air is fed through the holes 8. This is followed by the actual reduction phase, which takes place where the material that has passed through the firing zone is grasped by the foot 19 of the screw 11 and transported upwards.

It can thus be seen that the gases forming in the reduction phase, which are drawn in and removed upwards by the perforated sheet 6, the drainage channel 22 and the line 23, only and never pass through the ascending material located in the screw 11 come into contact with fresh material. These gases can therefore not be combined with pyrolysis products, i.e. loaded with heavy tar and flow cleanly and functionally out of the carburetor in order to be able to operate an internal combustion engine without problems of deposits.

The amount of combustion material that is transported from the rotating screw 11 upwards with prior conversion to charcoal in the reduction zone, or reduction in the combustion volume due to the combustion operation and conversion to gas after the previously described gasification process, depends on various functional parameters of the gasifier, such as of the main amount of air supplied to the holes 8, the speed of rotation of the screw 11, the dimensions of the elements, etc. These parameters are improved from time to time, also taking into account the material characteristics of the wood to be burned. This regulatory work is accessible to every specialist and is therefore no longer described in detail here.

The advantages of the DC gasifier of the present invention have been described extensively above and therefore need not be repeated. We would just like to emphasize that the carburettor construction described here, thanks to its limited dimensions, is particularly suitable for the implementation of systems with limited outputs, such as Systems for driving stationary motors for agricultural use or heating systems for single-family houses.

Claims (7)

DC gasifier with a combustion chamber which is cylindrical in the upper part and wedges conically downwards towards the furnace (4), where the combustion chamber is completely hermetic with the exception of the outlet for the combustion gases, and which is fed from above through a dense sluice with wood chips becomes,

characterized in that - the combustion chamber (1) at the bottom has at most one grate (9), the holes of which are very small compared to the size of the unburned wood chips and serve to remove the remaining fine ash, - In the interior of the combustion chamber (1) a screw conveyor (11) is attached, the outer dimensions of which adapt to the conical shape of the chamber and which in its internal axial part consists of a central tube (12) through which the material to be gasified is fed from above to the furnace ( 4) is fed where the screw (11) rotating during carburetor operation transports the material from below, ie from the firing point upwards, where the pipe (12) is provided with an opening through which the fresh material to be gasified and the material that has already been traversed at the firing point (4) and is transported upwards by the screw (11). DC gasifier according to claim 1, characterized in that the tube interior is conical towards the bottom and the larger diameter in accordance with his Starting point (26) at the furnace (4). Carburetor according to claim 1, characterized in that the taper of the tube is between 30 'and 4 °. Carburetor according to claim 1, characterized in that the combustion chamber (1) consists at least in its conical part (3) of refractory material. Carburetor according to claim 1, characterized in that the pitch angle of the screw forming the worm (11), measured on the outer tube diameter (12) of 120mm, is between 10 and 25 °. Carburetor according to claim 1, characterized in that the firing zone (4) consists of a circular central zone (27) which has holes on the circular line for the primary air extraction and of an annular part which surrounds the central zone (27) and which at most has one very Has small holes (10) provided grate (9). Carburetor according to claim 1, characterized in that a filling silo (16) is mounted above the combustion chamber (1), which is closed above by a hermetic lock (24), through which the fresh combustion material is fed after an installed in the filling silo (16) Sensor (25) indicates that the material level has dropped below a certain minimum value.

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