DE69307572T2 - DC gas generator - Google Patents

Abstract

The cocurrent gas generator according to the invention has a helical conveyor screw (7) which conveys the fresh material at the same time as the recycled material - that is to say the material which has already passed once or a number of times through the hearth (18) - from the bottom upwards along a conveying chamber (5). The hearth (18) of annular shape is fed with primary combustion air both from the outside and from the inside, so that all the material to be gasified is obliged to pass through the hearth (18) zone and is therefore subjected to a complete process of conversion into charcoal with the formation of carbon dioxide as a result. The gasifying chamber (20) is arranged above the hearth (18) and is used for converting carbon dioxide to carbon monoxide. This gas is then directed outwards for a specified use (combustion, driving engines). The gas generator forming the subject of the invention has the advantage of guaranteeing perfectly controllable gasification conditions, which is indispensable in particular during the treatment of contaminated timber (demolition timber, manufacture residues and waste and the like). <IMAGE>

Description

The present invention relates to a direct current gas generator according to claim 1.

From the applicant's patent application EP-A-0 531 778 a gas generator is known which has the properties described in the preamble of claim 1 of the present invention, in which a helical screw is mentioned, the axial part of which is formed by a central tube through which the material to be gasified is fed from above to the combustion chamber, where the helical screw rotates during operation of the gas generator in such a way that the material is transported from below, i.e. from the combustion chamber upwards, where the tube has an opening through which the material can enter the interior of the tube, both the fresh material to be gasified and the material which has already passed through the combustion zone and has been conveyed upwards by the helical screw.

In practice, this type of gas generator delivers fairly good results, but also has disadvantages that limit its field of application. The first of these disadvantages is that it works with a ring-shaped combustion chamber that is supplied with primary combustion air via a single ring of air supply openings. This means that a circular ring of burning material forms around the pipe with holes for the primary air, although this ring is not always the same width and, above all, does not necessarily extend over the entire combustion chamber which forms the firebox. It is therefore possible that fresh material coming from inside the tube does not necessarily have to pass through the firebox, but can pass through it without being treated, ie without being converted into carbon dioxide and charcoal.

This of course reduces the efficiency of the gas generator and is particularly undesirable in cases where waste wood contaminated with harmful foreign substances is recycled, whereby it can only be ensured that no toxic fumes or tars are formed if the material passes through an area in which it is exposed to a minimum temperature of, for example, over 1000 ºC for a minimum period of, for example, 2 seconds. Another disadvantage of the direct current gas generator according to the state of the art is that the combustion chamber is located at the lowest point of the fuel flow. Therefore, the residues of wood combustion that form in the combustion chamber, especially ash, must be removed downwards through a perforated grate. Such a grate is always an inconvenience, since every grate runs the risk of becoming clogged with encrustation.

The aim of the present invention is therefore to eliminate the disadvantages of the direct current gas generator according to the prior art and in particular to propose a design of the gas generator in which the entire material to be gasified necessarily passes through a combustion chamber for a precisely adjustable period of time and is thereby exposed to a certain minimum temperature, and in which no grid arrangement for the separation of the ash has to be provided. These objectives are met with a gas generator with the characteristic properties according to the characterizing part of patent claim 1.

Because the combustion chamber is located in the extension of the annular chamber and because the primary combustion air is supplied to the annular combustion chamber from both the outside and the inside of the combustion chamber, the material must necessarily pass through a ring-shaped combustion chamber that can extend over the entire cross-section of said annular zone, since it is supplied with the oxygen of the primary combustion air from both sides. Thus, no "dead" zones or places or areas can form in which the primary air supply is insufficient to ensure complete combustion of the material passing through, unlike in the case of the gas generator according to the state of the art, where this could occur.

Furthermore, thanks to the fact that in the gas generator according to the invention the parameters can be freely set which determine the time the material stays in the primary combustion zone, i.e. in the combustion chamber of the gas generator - there are two of them, namely the axial expansion speed of the combustion zone and the rotation speed of the helical screw which determines the speed of the material feed - a minimum time of the material stay in the hot part of the combustion chamber can be ensured. In other words, thanks to the appropriately selected length of the part of the gas generator in which holes are provided both on the inside and on the outside of the combustion chamber, which allow access to the primary air, and thanks to the appropriately selected feed speed of the helical screw - i.e. its pitch and rotation speed - it can be achieved that the material to be gasified stays in the combustion chamber for a certain minimum time, namely in the range where the temperature is between 1000 ºC and 1400 ºC. Experts recognize that if this condition is met, there is no risk of dangerous tar substances or toxic gases such as dioxins being formed, gases that can be produced mainly when wood waste contaminated with glue or various paints is burned. Such a risk exists in particular when a gas generator or a boiler for direct combustion is fed with building demolition material or waste from current furniture manufacturing. It is precisely for this type of fuel that the gas generator according to the present invention has the greatest advantages.

Another advantage of the gas generator according to the present invention that should not be neglected is that no separating grid is required for the ash that is produced. Since the combustion chamber is arranged in the upper area of the spiral screw that feeds the material, the fine ash particles that are produced - consisting of non-combustible particles of a predominantly mineral nature - are carried upwards with the material and are finally - thanks to their low weight - carried upwards by the gas flow into the final combustion area. Of course, these fine ash particles must be removed in a suitable manner depending on the further use of the gas and in compliance with the legal regulations for maintaining the maximum dust content in the combustion gases of such systems. This subsequent cleaning process of the exhaust gases of the system, which can be carried out by means of cyclone filters or electrostatic filters, is a common process step in combustion systems of the type of the present invention, in particular those whose purpose, as in the present case, is to burn contaminated material, and the need to install a filter does not cause any particular difficulties or additional costs compared to current systems. On the contrary, the possibility of not installing a separating grid under the combustion chamber represents a significant advantage.

The embodiment according to claim 2, in which a hollow shaft of the helical screw is provided in order to guide part of the primary air to the combustion chamber, has the advantage that the air supply is very simple and also ensures sustainable cooling of the bearings of the helical screw, so that further measures to avoid heat transfer by heat conduction along the shaft of the screw auger up to its bearing are unnecessary.

The preferred embodiment according to claim 3 represents a particularly simple embodiment for the material return, which also allows recycling without the aid of other moving elements, since the material is put back into circulation by gravity, whereby thanks to the arrangement of the return chamber coaxially to the gasification chamber and the transport chamber, a particularly compact design of the gas generator according to the invention is achieved.

The preferred embodiment according to claim 4 shows an optimal solution to the problem of mixing the "recycled" material coming from above and the fresh material coming from the feed buffer. Thanks to a second helical conveyor screw arranged coaxially to the previously mentioned helical conveyor screw, but separated from it by a shaft area without a screw, screw and thanks to the arrangement of a feed device for the fresh material in the zone without a screw, the problem of material feeding has been solved in an optimal way, without the material accumulating and, above all, without the risk, always present with granulate feeding, of such material becoming jammed between the wall and the helical screw, thus blocking the entire system.

Claim 5 relates to a particularly advantageous embodiment of the feed device for the fresh material, which can be used in the embodiment of the gas generator according to the invention according to claim 4. In this variant, a simple arm forms the feed device, which is arranged to rotate about an axis parallel to the axis of the helical screw: this solution is extremely simple and proves to be very effective in practical application.

The embodiment according to claim 6 is particularly advantageous. In this variant according to the invention, the feed buffer is designed essentially coaxially with the shaft of the helical screw or coaxially with the gas generator, so that the gas generator is enclosed on its entire peripheral surface. This arrangement allows optimal insulation of the gas generator, since the fuel, in particular waste wood, which surrounds the gasification chamber from the base, is an optimal insulating material and prevents heat loss to the outside. The material is heated and dried on its way down to the point where it is mixed with the "recycled" material, both of which are welcome in preparing the material for the subsequent gasification process.

The preferred embodiment according to claim 7 represents a further improvement of the embodiment according to claim 6, since it allows the use of a rotating transport arm which is fixedly attached to the shaft of the coaxial helical screws. Thanks to this arrangement, a separate, movable device for the transport arm mentioned can be dispensed with, which represents a not insignificant simplification when it is taken into account that in a gas generator the number of movable elements should advantageously be kept as small as possible.

Patent claim 8 relates to an additional improvement of the mixing chamber thanks to a second rotating arm which covers the bottom of the mixing chamber, so that on the one hand a better mixing of the components of the fresh and the "recycled" material is achieved, and on the other hand the transport of the material upwards by the helical screw is carried out more safely, in that the second rotating arm conveys the material from the outer circumference of the mixing chamber towards the said helical screw.

Patent claim 9 relates to a preferred embodiment of the invention, in which a particularly simple and effective system is provided for blowing the primary air from the outside into the interior of the annular combustion chamber.

Patent claim 10 relates to a further improvement of the solution according to patent claim 9, in which it is provided that the primary air enters the ring channel arranged outside the combustion zone in a tangential direction, so that a turbulent air flow This measure aims to improve the uniformity of the primary air supply along the entire length of the outer circumference of the combustion chamber and thus to avoid the formation of preferential combustion channels which could arise from the injection openings of the primary combustion air where more air flows in. This arrangement corresponds to one of the main aims of the present invention, to achieve combustion which is "as symmetrical as possible", this term expressing the efforts made to avoid the formation of preferential combustion areas as a result of asymmetric distribution of the primary air. Such differences in fire intensity which can arise when the primary air is able to "make its way" through the material to be burned through paths of less resistance, or when the primary air is injected asymmetrically from the outset, are the cause of locally incomplete combustion, the effects of which on the composition of the combustion gases can easily be imagined.

Patent claim 11 relates to a preferred embodiment of the invention and is characterized in that the ignition process is advantageously carried out by blowing hot air under pressure into the combustion chamber of the gas generator.

Finally, patent claim 12 relates to a preferred design of the upper part of the gas generator above the gasification zone.

According to this patent claim, a reduction chamber is provided below the gasification chamber, the upper part of which is closed off by a grid which homogenizes or evens out the gas flow.

This measure also meets the general requirements aimed at achieving an optimal balance of the gas generator operation according to the present invention and an improved composition of the gas produced.

The present invention is described in more detail below with reference to various embodiments shown in the figures. They show:

Fig. 1 is a vertical section along the axis of the helical screw of a first embodiment of the present invention. Also shown in the figure are various construction details that correspond to preferred embodiments of the invention.

Fig. 2 shows another preferred embodiment of the present invention in a schematic representation, also in vertical section along the axis of the two helical screws provided in this case. The gas generator according to this preferred embodiment ensures particularly reliable transport of the material.

Fig. 3 is a simplified representation of the gas generator in a horizontal cross-section along the plane I - I of Fig. 2, which shows a preferred design of the primary air inlet from the outside of the combustion chamber.

Fig. 4 shows another preferred design of the gas generator according to the invention, shown in a similar manner to the embodiments according to Figures 1 and 2.

In the figures, a feed buffer is designated 1, which is filled in its upper part with fresh material 2 and is provided with a slider or a sealing lock flap 3. The lock flap 3 must be absolutely tight, since the feed buffer 1 fills with gas during operation, which must not escape through the said flap.

Now, however, some information about the fuel to be gasified should be given below. The term "fresh material" should be understood to mean suitably chopped wood material that can be fed into a gas generator. As a rule, a material of this type, which can come directly from the forest, like firewood, or from the demolition or dismantling of buildings or as waste wood from furniture manufacturing, etc., has geometric dimensions that determine its granulometry or grain distribution, which ranges from a few centimeters (about 5 cm) to a few millimeters. Such material is symbolically represented in the figures with small circles. The charcoal obtained by converting the lignite in the gasification chamber is shown graphically in the figures with small lines. According to the present invention, this material returns to the material cycle and mixes with the fresh material, which is why this material is referred to as "recycled" material, which means that according to this definition the material is returned to the combustion process in the gas generator. The term "recycled" therefore has no other meaning in this context than the one mentioned above. In particular, it does not refer to any recycling processes that could take place outside the gas generator.

The feed buffer is equipped with sensors (not shown) which control the lock flap 3 in such a way that the material level of the material 3 in the feed buffer 1 is kept constant within selectable deviation limits.

The feed buffer 1 is connected in its lower part to an annular transport chamber 5. The transport chamber 5 is delimited on the outside by an essentially cylindrical wall 6, in the interior of which a helical screw 7 rotates, which consists of a central shaft 8 and a sheet metal strip 7 helically wound on it and protruding from it. The shaft 8 of the worm screw 7 is rotatably mounted in two bearings 10 and 11, which are fastened in receptacles provided in the base 12 of the gas generator. The shaft of the gas generator is slowly rotated by means of a gear motor 13 and a suitable drive device, for example by means of pulleys 14 and 15 and a belt 16, as shown in Fig. 1. Of course, any other suitable rotary drive can also be used to drive the shaft 8.

The transport chamber 5, delimited on the outside by the cylindrical wall 6 and on the inside by the shaft of the helical screw 7, essentially represents an annular chamber in which the material to be treated is pressed from bottom to top, as will be described in more detail below.

The upper part of the cylindrical wall 6 has a series of holes 17 along a region designated I, through which an air flow, which according to the invention represents only a part of the primary combustion air, from the outside of the wall 6 into the interior, as indicated by the arrow f. The air flow indicated by f is therefore an air flow directed essentially radially inwards from the wall 6. The manner in which this air flow is generated does not represent a fundamental aspect of the present invention. However, various examples of such an air feed are described below and form the subject of corresponding subclaims.

Opposite the aforementioned area 1, a second air flow, as is part of the present invention, is blown in the direction of arrow F through holes 19 from the inside against the outer side of the annular transport chamber 5 in such a way that in the area 1, which is designated as the combustion chamber of the gas generator with the reference number 18, an annular zone is formed which is supplied with primary combustion air both from the outside in the direction of arrow f and from the inside in the direction of arrow F. The particular way in which this second part of the primary air is guided from the inside to the combustion chamber 18 is not of decisive importance for the present invention; however, a preferred solution is described here below, which also forms the subject of a subclaim.

On the other hand, the formation of an annular combustion chamber 18 along the area 1 and its supply with primary combustion air both from the outside in the direction of arrow f and from the inside in the direction of arrow F is an essential part of the present invention. Thanks to this cleverly designed system, it is indeed achieved, as will be described in more detail below, that the material to be gasified inevitably forms a combustion chamber 18 with a well-defined cross-sectional area and shape in which, as a result of the simultaneous injection of primary air from both sides, no areas can form in which combustion is only "partial" and in which the temperature would be lower than that in the other areas of the combustion chamber. The annular zone of the combustion chamber 18 can be designed and dimensioned (diameter and axial length) in such a way as to achieve absolutely homogeneous combustion conditions throughout said zone and while respecting the required quantity of primary air supply. This is a very important condition for the proper functioning of a gas generator, particularly when it comes to the treatment of "contaminated" wood material, which requires that all the material must necessarily pass through an area heated to a predetermined minimum temperature (e.g. 1200 ºC) and remain there for a certain minimum time in order to avoid any formation of harmful substances such as dioxins.

Adjoining the combustion chamber 18, also as a part of the present invention, there is also provided a gasification chamber 20 which is also essentially annular and which is delimited on the outside by the cylindrical wall 6, which accordingly continues beyond this area 1 of the combustion chamber 18. On the inside, however, the shaft of the helical screw 7, the preferred embodiment of which according to the invention is provided with holes 19 from which the second partial flow of the primary air flows out, can - but does not necessarily have to - end at the upper part of the combustion chamber 18, so that the designation "essentially annular" for the gasification chamber 20 is justified in the sense that the said gasification chamber 20 is annular in its lower part and simply cylindrical in its upper part. However, this does not constitute an essential part of the present invention.

For the gas generator to function, it is also necessary that the primary air can reach the holes 17 and 19, i.e. that these - the former from the outside of the wall 6 and the latter from the inside of the shaft 8 of the helical screw 7 - must be connected to a compressed air source. This source can be provided for each of the groups of holes 17 and 19 individually or as a common source for both groups of holes.

In the latter case, it may prove useful to regulate the air supply quantities for each of the two groups of holes 17 and 19 individually, so that the formation of the combustion chamber 18 can be better controlled, i.e. that a good symmetry or balance is ensured over the entire annular cross-section. According to a preferred embodiment of the present invention, the blowing of primary combustion air into the interior of the combustion chamber 18 is ensured by the shaft 8 of the helical screw 7 being hollow and designed as a supply channel for the primary air. The shaft 8 thus has the shape of a tube closed at the top by a cover 21. In the vicinity of its upper end, closed by the cover, one or more rows of holes 19 are arranged symmetrically along one or along different circumferential lines of the tube wall.

At the lower end, which forms the shaft of the helical screw and therefore rotates, the pipe is connected to a fan 24 via a coupling element 22 and an air supply line 23. The air from the fan 24 The air flow, which is conveyed and possibly adjusted, flows through the pipe 8 and emerges radially from the holes 19, whereby this primary air flow supplies the combustion chamber from the inside. Thanks to the constant inflow of outside air through the pipe 8, this and, above all, its pivot bearings are constantly cooled, so that all further measures for insulation or impeding the transport of heat by heat conduction through the pipe walls are unnecessary. Other forms of supply of primary air to the holes 19 can of course be considered (for example from above through the cover 21), but the solution described above seems to be the most favorable.

With regard to the supply of primary air from the outside into the combustion chamber 18, Figure 1 shows a preferred solution, which consists in supplying the said air through the holes 17 provided in the substantially cylindrical wall 6 of the transport chamber 5. The holes 17 are provided in one or more rows distributed over the entire outer perimeter of the wall 6. Furthermore, the supply channel 25 is connected to the compressed air source via a connecting pipe 26. In the present example, the connecting pipe 26 is connected to the fan 24, which supplies the primary air for feeding the combustion chamber from the inside of its annular zone. In this case, it may prove useful to install a regulating slide (not shown) in each of the supply lines to the groups of holes 17 and 19 at a suitably selected point in the system of pipes 23 and 26 in order to regulate the air flow rates if necessary.

The gas generator described above works as follows:

The fresh material to be burned for gasification descends through the feed buffer 1 and reaches the lower part of the helical screw 7 after having passed through the lower part 4 of the feed buffer 1.

The helical screw 7, driven by the reduction gear 13 via the pulleys 14 and 15 and the belt 16, rotates slowly to convey the material from below upwards through the transport chamber 5. As soon as the material reaches the height of the combustion chamber 18, combustion begins under the influence of the supply of primary air from outside through the holes 17 and 19, which transforms the material into charcoal while releasing carbon dioxide.

The regulation of the transport quantity conveyed by the helical screw 7, i.e. the rotation speed of the helical screw, allows, taking into account the dimensions of the gas generator and in particular the axial length I of the combustion chamber 18 and the quantity of primary air blown into the combustion chamber, an appropriate adjustment of the degree of conversion of the wood into charcoal. In the area following the combustion chamber 18, more precisely in the actual gasification chamber 20, the carbon dioxide must pass through a layer of charcoal, with which carbon monoxide is formed, which is the gas to be produced, which can be used either in a secondary combustion in a combustion chamber (not shown) to generate heat or as fuel for internal combustion engines (not shown).

For the functioning of the gas generator it is therefore essential that charcoal is always present in the gasification chamber 20. On the way from below upwards across the charcoal, the carbon dioxide, as a result of combining with the carbon of the aforementioned charcoal, reduces its dimensions, i.e. the pieces of charcoal lose the carbon on their surface while they are gradually pushed upwards by new material conveyed by the helical screw 7. Depending on the "original" dimensions of the pieces of charcoal when they leave zone 1 of the combustion chamber, the amount of carbon dioxide produced in the combustion chamber, the dimensions of the gasification chamber 20 and other parameters which do not require any further description in the present case, the pieces of material to be gasified reach the upper end of the gasification chamber 20 ending at the edge 27 in one of the following three states:

- as an exceptionally fine ash as a residue of complete gasification of the entire carbon content in the charcoal;

- as pieces of material converted into charcoal but not completely gasified;

- as pieces of wood material partially converted to charcoal, which still contains unburned lignite.

The extremely fine ash is then carried upwards in the flow of the gas produced: Experience has shown that the ash produced is so light that in this state separation from the gas is out of the question.

For complete separation of the ash, effective filters must be used (cyclone filters or other filters), which, however, have no direct influence within the scope of the present invention and therefore will not be described further. However, it is important to note that the ash from the gasification is discharged together with the gas produced.

In the embodiment of the invention shown in Fig. 1, however, the above-mentioned material portions of the second and third type inevitably rise over the edge 27 and fall back as recycled material into a return chamber 28 which surrounds the cylindrical part of the transport chamber 5. The lower part of the return chamber 28 is connected to the lower part 4 of the feed buffer 1 so that the material - henceforth referred to as recycled material - mixes there when it is brought together with the fresh material 2 that comes from the feed buffer 2.

This mixture of fresh material and recycled material, which is transported by the helical screw 7, is graphically represented in Fig. 1 and in the following figures with small circles representing the fresh material and with small lines symbolizing the charcoal. Of course, this representation is to be understood purely symbolically, without giving any indication of the proportions of the materials in the mixture: As already explained above, the conversion of the wood material into charcoal is an ongoing process, so that material particles are also found in all intermediate states between the aforementioned initial state and the final state.

As has been found during the operation of the gas generator according to the present invention, this feature represents a very important advantage in terms of the power control of the plant. In order to change the thermal output from the gas generator, ie the amount of carbon monoxide produced, a change in the amount of primary air supplied to the combustion chamber 18 is necessary and sufficient, which in the case of the example shown in Fig. 1 corresponds to a change in the speed of the fan 24. As long as the amount of fresh material supplied by the helical screw is always sufficiently large, more precisely as long as it is always larger than the amount of combustible material corresponding to the intended maximum output of the gas generator, the amount of gas produced depends solely and directly on the amount of primary air supplied to the combustion chamber 18. If the output of the blower 24 is reduced, the conversion of lignite to charcoal is automatically reduced, and accordingly the amount of carbon dioxide produced in the combustion chamber 18 decreases and the conversion of this carbon dioxide to carbon monoxide in the gasification zone 20 also decreases. The only difference in comparison with an operating state with higher output is the increase in the quantity of recycled material and the more or less significant change in the composition of the recycled material (grain size distribution and degree of conversion to charcoal).

The previously described advantage of easy adjustment of the output of the gas generator is of particular importance when the gas generator is used to heat a building, especially when the output must be able to be adapted very flexibly to the user's requirements.

In Fig. 2 a variant of the gas generator according to the present invention is shown, which improves the mixing of fresh and recycled material as well as an increased functional reliability of the system by eliminating any risk of congestion in the mixing chamber and blockage of the helical screw.

The elements of the system according to Fig. 2 which are identical to those in the system according to Fig. 1 are also designated with the same reference numerals in Fig. 2.

The solution shown in Fig. 2 differs from that shown in Fig. 1 in that the return chamber 29 has an annular opening in its lower part, under which a mixing chamber 30 for fresh and "recycled" material is arranged, in which a second helical screw 31 rotates, which has essentially the same dimensions as the helical screw 7 for transporting the material to the combustion zone 18. The second helical screw 31 and the helical screw 7 for transport have a common axis 8 and are separated from each other by a region of the axis 8 without a screw, at the level of which region a feed device pushes the fresh material from the lower part 4 of the feed buffer 1 towards the mixing chamber 30. In a preferred embodiment described further below, which is also shown in Fig. 2, an arm arranged to rotate about an axis 33 aligned parallel to the axis 8 of the helical screw 7 forms the feed device 32, the arm 32 sweeping the lower end wall of the feed buffer 1 as it rotates. In this way, the feed device pushes the fresh material towards the mixing chamber 30, where this fresh material mixes with recycled material that has passed over the edge 27 of the gasification chamber 20 and fallen through the return chamber 28.

In the example shown in Fig. 2, the shaft 33 of the rotating feed device 32 is driven by a pulley 36, which in turn is driven by a belt 16, which also drives the shaft 8 of the helical screws 7 and 31. This arrangement represents only one of the many possible solutions for driving the shaft 33. Likewise, the arm 32 forming the feed device mentioned represents only one, albeit preferred, solution among many possible options. Another device with equivalent functionality could be one with a helical screw (not shown) arranged horizontally in the lower part of the feed buffer 1, which extends into the area of the shaft 8 which does not have a helical screw.

In any case, the arrangement of a feed device 32 must, on the one hand, facilitate the supply of fresh material to the mixing chamber 30 and, on the other hand, prevent the material from becoming jammed between the edge of the helical screw 7 and the lower edge of the cylindrical wall 6; a risk that can arise in any application of helical screws.

The feed device 32 must therefore be designed in such a way that it "cleans" the said lower edge from time to time, removing any pieces of wood or charcoal that may have become jammed there.

In Fig. 3, a horizontal section along the line 1-1 in Fig. 2 is shown, on the basis of which another preferred variant of the gas generator according to the present invention can be described. From this Fig. 3 it can be seen that the connection of the channel 25, which Primary air is supplied from the outside through the ring of holes 17 to the combustion chamber 18, with the source of compressed air being connected by means of one or more supply pipes, in this case by means of the three supply pipes 26', 26" and 26"', which open tangentially into the channel 25. Thanks to this arrangement, air turbulence is created in the channel 25, which better ensures that the distribution of primary air is even over the entire circumference of the cylindrical part 6 of the channel 25. Such uniformity in the supply of primary air along the entire circumference of the combustion chamber 18 is of crucial importance, as it ensures absolute homogeneity of the combustion conditions in the combustion chamber 18 and thus avoids the formation of any areas with a lower temperature. From Fig. 3 it is also apparent that in another preferred embodiment of the invention an electrical resistance is installed in at least one of the feed pipes 26', 26" and 26"' (in the illustrated case in the feed pipe 26"') with the purpose of heating the air flowing through in order to ignite the material to be gasified when the gas generator is started up.

The gas generator is therefore automatically ignited as follows: First, the feed buffer 1 is filled with chopped wood or similar material while the helical screw 7 rotates to fill at least the area of the combustion chamber 18. Then the fan 24 is switched on and at the same time voltage is applied to the resistor 36. The primary air passing the resistor 36 heats up so that the fresh material in the area of the combustion chamber 18 ignites quickly. From this moment on, the production of carbon dioxide begins and the conversion of lignite into charcoal, which - as a result of the constant feed ensured by the helical screw 7 - turns into the gasification zone is shifted. The ignition phase is now complete and the resistor 36 can be switched off again.

Fig. 4 shows another preferred embodiment of the present invention, which allows a compact design of the gas generator and, above all, a reduction in heat losses on the walls of the system, thereby improving the overall efficiency. In Fig. 4, too, the same elements of the variants shown in Figures 1 and 2 are designated with the same reference numerals.

According to the variant shown, the feed buffer 1 is arranged essentially coaxially with the axis 8 of the helical screw 7, so that it completely surrounds the circumference of the actual gas generator. The feed buffer 1 consists of a cylindrical casing with an outer wall 37, the upper part of which is closed with a cover 38, in the middle of which the feed lock 3 is arranged. The actual gas generator is housed in the cylindrical casing 12, which in principle corresponds exactly to the design of the previously described with reference to the two embodiments, and is suspended in the cylindrical vessel 37 by means of the connecting pipes 26 as shown in Fig. 3, or by means of specially provided support arms (not shown).

In its lower part 34, the feed buffer 1 shown in Fig. 4 forms a mixing chamber 30, which is analogous to that shown in Fig. 2. The difference between the mixing chambers 30 shown in Figures 2 and 4 is that in the case of Fig. 4, where the feed buffer is absolutely symmetrical, the mixing chamber 30 is also absolutely symmetrical and has essentially the shape of a truncated cone, the circular wall 39 of which is inclined downwards and retracted, which facilitates the descent of the fresh material 2 coming from the feed buffer 1 and the recycled material coming from the material return chamber 28. The advantages of this arrangement, in addition to those already mentioned, are the reduction in space requirements and the thermal insulation achieved thanks to the intermediate layer of raw material - wood is an excellent thermal insulation material - which fills the space between the vessel 37 and the casing 12, as well as the preheating of the fresh material which thus reaches the furnace already preheated for combustion, including the advantage of the "automatic symmetry" of the mixture - since the raw material and the material meet at this point along the entire circumference of the gas generator, and not just at the lateral junction between the feed buffer 1 and the lower edge of the cylindrical wall 6, as was the case in the variants according to Figures 1 and 2 - not to mention the simplification of the structure. This latter advantage follows directly from the purely cylindrical shape of the feed buffer 1 and its coaxial arrangement with the shaft 8 of the helical screw 7. Thanks to this design, in another preferred variant of a detail of the gas generator, it can be achieved that the rotating arm 40, the function of which corresponds to the rotating arm 32 according to Fig. 2, can be fixedly attached to the shaft 8 of the helical screws 7 and 31, so that its outermost part sweeps over the lower end 34 of the feed buffer 1.

In this arrangement, the arm 40 also performs the function of the feeding device, pushing the raw material coming from the feed buffer 1 towards the centre of the buffer, i.e. towards the shaft 8 of the helical screws 7 and 31, where the said material falls into the mixing chamber 30 and mixes there with the recycled material coming from the return chamber 28.

The advantage of the solution described compared to the solution shown in Fig. 2 is that the shaft that rotates the arm 40 and its drive and control devices are eliminated, i.e. that the already mentioned simplification of the system is achieved.

Another preferred solution for a detail of the present invention, advantageously used in combination with a mixing chamber 30 as shown in the variants according to Figures 2 and 4, provides that a second arm 41 (Figures 2 and 4) is fixedly mounted on the shaft 8 of the helical screw 31, opposite the second helical screw 32, which sweeps the bottom 42 of the mixing chamber 30 and pushes the material towards the center, where it is caught by the second helical screw 31 and transported upwards. The function of the arm 41 corresponds to that of the arm 40, namely to set the material in motion towards the center of the rotational movement thanks to the forwardly curved shape of the arm.

According to another preferred embodiment of the present invention, the upper part of the gas generator, i.e. its part located above the edge 27 of the gasification chamber 20, forms a reduction chamber closed at the top by a grid for homogenizing the gas pressure 44 43. The purpose of this reduction chamber 43 is to reduce the nitrogen oxides present in the gas mentioned. In the presence of carbon monoxide, the latter react with the latter to produce carbon dioxide and nitrogen. Thanks to this reaction, the content of nitrogen oxides in the gas can be reduced considerably, which is very beneficial for the protection of the environment.

Above the grid 44, the gas generator ends in a connection area 45, in which the gas produced is collected and passed through a line 46 to a subsequent system for utilizing the carbon monoxide produced in the gas generator. The use of the gas - combustion in a heat exchanger system for heating purposes or operation of an internal combustion engine or a turbine - is outside the scope of the present invention and is therefore not described further here.

The direct current gas generator according to the present invention, whose dimensions are designed depending on the dimensions of the material to be gasified and its consumption per unit of time, is ideally suited to the gasification of contaminated wood, thanks to the previously described possibility of being able to completely control the residence times and temperatures in the gasification chamber 20. Moreover, it is also ideally suited as a gas generator for heating purposes using all types of firewood: the only condition is that the material to be gasified is brought to a grain size distribution that is compatible with the dimensions of the plant.

Claims (12)

1. Direct current gas generator with a feed (intermediate) store for fresh material and a combustion chamber and a helical screw for transporting the material, which rotates about a vertical axis and transports the material to be gasified in such a way that the material which has already passed through the combustion chamber but which has not yet been completely converted into gas, the so-called "recycled" material, can mix with the flow of fresh material coming from the feed intermediate store and pass through the combustion chamber a second time, even several times, until it is completely converted into gas, characterized in that - the transport by the endless screw of fresh material mixed with recycled material takes place from bottom to top through an annular transport chamber (5) inside which the endless screw (7) rotates, the chamber being delimited on the outside by a substantially cylindrical side wall (6) and on the inside by an axis (8) of the endless screw (7), - the combustion chamber (18) is precisely annular in shape and forms the continuation of the annular transport chamber (5) and - the primary combustion air to the combustion chamber (18) with annular shape from both the outer part and the inner part thereof, and - the annular combustion chamber (18) is followed by a gasification chamber (20) of substantially annular shape, inside which the carbon dioxide produced at the time of combustion reacts with the charcoal to gasify it and transform it into carbon monoxide. 2. Carburettor according to claim 1, characterized in that the shaft (8) of the helical screw (7) is hollow and forms an air passage through which the part of the primary combustion air is supplied which is directed to the combustion chamber (18) of annular shape from its inner side. 3. Gasifier according to claim 1, characterized in that the "recycled" material, which is more or less completely converted into charcoal and passes through the gasification chamber (20), overflows in a circular manner from the gasification chamber (20) over the upper edge (27) and falls into a material return chamber (28) which externally surrounds the substantially cylindrical side wall (6) of the transport chamber (5) and which communicates at its base with the lower part (4) of the intermediate storage (1), so that the "recycled" material mixes at this connection point with the fresh material (2) conveyed from the intermediate storage (1). 4. Carburettor according to claim 3, characterized in that the return chamber (28) closes off downwards by an opening of annular shape (29), below which a mixing chamber (30) for fresh material (2) and "recycled" material, also of substantially annular shape, is arranged, in which a second helical screw (31) rotates, which has substantially the same dimensions as the helical screw (7) of the material transport to the combustion chamber (18), and where furthermore the helical transport screw (7) and the second helical screw (31) have the same axis of rotation (8) and are separated between them by a zone (m) of the axis (8) which is free from the helical screw, in which zone a supply means (32, 40) of fresh material moves, which means transports the latter from the lower part (4) of the intermediate storage (1) in the direction of the mixing chamber (30). 5. Carburettor according to claim 4, characterized in that the means (32, 40) for supplying fresh material is an arm (32) rotating about an axis (33) parallel to the axis (8) of the helical screw (7) which, in its rotation, sweeps over the lower horizontal side wall (34) of the intermediate storage (1) and which thus pushes the fresh material towards the mixing chamber (30). 6. Carburettor according to claim 4, characterized in that the intermediate storage (1) is arranged substantially coaxially to the axis (8) of the helical screw (7) to completely close the carburettor around its outer circumference and that the intermediate storage (1) forms thereunder the mixing chamber (30) of substantially circular shape. 7. Carburettor according to claim 4 and 6, characterized in that the rotating arm (40) is fixedly mounted coaxially on the axis (8) of the helical screws (71 31) and at its outermost part sweeps over the lower part (34) of the intermediate reservoir (1). 8. Carburettor according to claims 4 to 7, characterized in that with respect to the lower part of the second helical screw (31), a second arm (41) mounted on the axis (8) of the helical screw (31) sweeps over the bottom (42) of the mixing chamber (30) and pushes the material towards the center, where the material is taken up again by the second helical screw (31). 9. Carburettor according to claim 1, characterized in that the part of the primary air which is supplied to the combustion chamber (18) from the outer side is fed through holes (17) made in the substantially cylindrical side wall (6) of the annular transport chamber (5), and in that the holes are arranged in one or more rows along the entire circumference of the side wall (6), on its outer side, connected to a source of compressed air. 10. Carburettor according to claim 9, characterized in that the connection of the duct (25) to the primary air source under pressure is realized by means of one or more supply tubes (from 26' to 26'") connected tangentially to the annular duct (25) to create air turbulence in the duct (25). 11. Carburettor according to claim 10, characterized in that at least one of the air supply sources (26', 26", 26'") is provided with an electrical resistance (36) adapted to heat the air passing through in order to trigger the ignition of the material to be gasified at the moment of starting up the carburettor. 12. Carburettor according to claim 1, characterized in that a reduction chamber (43) is provided above the gasification chamber (20), which is closed off by a grid for homogenization (44) of gaseous flow.