The present invention concerns a gasifier with an improved air inlet assembly.

In particular, the invention concerns an air inlet assembly arranged in a median portion of the gasifier, and comprising a double type of air inlet pipe.

A preferred application of the present invention is solid fuel consisting of irregularly sized pieces of wood.

As is known to persons skilled in the art, regularly sized pieces of solid fuel have a direct effect on the uniformity of the passage of the air, of the gases produced and, therefore, of the heat inside the gasifier. This effect occurs in particular in the combustion area with insufficient oxygen, in the oxidisation area and in the fuel drying and pre-heating area.

Irregularly sized pieces of solid fuel, for example waste wood from agriculture, result in the formation of areas with insufficient passage of air and/or gas, in which wood tar forms due to condensation of the components present in the gases produced during the gasification. The presence of said tar has the drawback of necessarily requiring constant plant maintenance.

For some time now, it has been common practice to provide air inlet (usually by suction of the gases) above the oxidization area in order to enlarge said oxidization area. Usually, this air inlet is provided both in a radial direction through openings communicating with an annular pre-heating chamber, and in a vertical direction through openings obtained in a head end of a vertical pipe (lance) arranged in an axial position. The air passing through the lance pre-heats slightly in relation to the speed of passage.

Practice has shown that the horizontal radial openings or, in any case, openings inclined downwards, do not allow penetration and therefore effective action of the air introduced due to the pieces of solid fuel moving slowly down the wall of the gasifier.

Generally, the openings provided at the end of the vertical inlet lance are positioned at a higher level than the radial lateral openings and, therefore, are not sufficient to obtain a wide area for effective passage of the air such as to determine a uniform passage comprising the entire section of the inner layer of the gas generator.

The inventor of the present invention has produced an air inlet assembly such as to prevent the formation of tar inside the gasifier in the peripheral zones of the oxidisation area during the gasification of solid fuels, in particular those having an irregular size and/or containing resins, lymph or phenolic and ethereal substances (creosol, guaiacol and homologues).

The subject of the present invention is a gasifier, the essential characteristics of which are reported in claim 1, and the preferred and/or ancillary characteristics of which are reported in claims 2-7.

An embodiment example is provided below for purely illustrative non-limiting purposes with the aid of the attached figures, in which

• Fig. 1 is a longitudinal section of the gasifier according to the present invention;
• Fig. 2 is a cross section according to the section line II-II of figure 1 with parts removed; and
• Fig. 3 is a lateral view with parts shown transparently of a detail of figure 2.

In figure 1, the number 1 indicates overall the gasifier according to the present invention.

The gasifier 1 comprises a base portion 2, an outer layer 3, which rests on said base portion 2, and an inner layer 4 supported by the outer layer 3. The inner layer 4 has a lower portion 4a housed inside the outer layer 3 and an upper portion 4b which projects outside the outer layer 3 and terminates in a loading inlet 5. On the loading inlet, a hopper and a loading apparatus are provided, known and not illustrated and described for the sake of brevity.

The gasifier 1 comprises internally a fixed grid 6, arranged at an upper end of the base portion 2, and a rotating grid 7.

The gasifier 1 comprises internally a truncated conical collecting structure 8 arranged below a lower end of the inner layer 4 and in which the rotating grid 7 is housed.

The gasifier 1 comprises a first air inlet assembly 9 known and not described in detail and arranged below the fixed grid 6 and the rotating grid 7.

The inner layer 4 is fixed to the outer layer 3 by means of two radial walls 10 and 11 which delimit, together with a portion 4a of wall of the inner layer 4 and a portion 3a of wall of the outer layer 3 between them, an annular pre-heating chamber 12.

The annular pre-heating chamber 12 communicates with the outside of the gasifier by means of an air inlet duct 13.

The gasifier 1 comprises a second air inlet assembly 14 arranged above the oxidization area and substantially in a median zone of the inner layer 4. The second air inlet assembly 14 comprises two types of air inlet ducts 15 and 16 extending radially towards the inside from the wall of the inner layer 14. In particular, the two types of air inlet ducts 15 and 16 are arranged on the same plane and, as illustrated in figure 2, in an alternate sequence.

Both types of air inlet ducts 15 and 16 have a first end 15a and 16a connected to the annular pre-heating chamber 12 by means of respective openings 17 obtained on the wall 4a of the inner layer 4.

In particular, the air inlet ducts 16 have a second closed end 16b, while the air inlet ducts 15 have a second end 15b connected to a lower end 20a of a vertical duct 20, which is arranged coaxially with the inner layer 4 and receives the air from the outside of the gasifier at an upper portion of the inner layer 4.

In other words, the air inlet ducts 15 extend in a radial pattern from the lower end 20a of the vertical duct 20 to the wall 4a of the inner layer 4, and are arranged in an alternate manner to the air inlet ducts 16.

Both types of air inlet ducts 15 and 16 comprise a plurality of mushroom-shaped nozzles 18, each of which comprises an upper cap 19, preferably cone shaped, adapted to favour a lateral outflow of the air. Preferably, the lateral outflow of the air occurs at 360°.

Unlike the above description, the two types of air inlet ducts 15 and 16 can also be arranged on two different planes which, however, must have a maximum distance between them equal to the height of the mushroom-shaped nozzles.

Lastly, in the wall of the outer layer 3 a lateral outlet 21 is obtained for outflow of the combustible gases produced during the combustion with insufficient oxygen due to incomplete oxidization of the carbon.

To summarize, while the nozzles 18 relative to the air inlet ducts 16 introduce exclusively air coming from the annular pre-heating chamber 12 and at the pressure present therein, the nozzles 18 relative to the air inlet ducts 15 are connected both to the annular pre-heating chamber 12 and to the vertical duct 20 which supplies external air that mixes with the air coming from the pre-heating chamber in relation to the pressures.

From the above description, the air inlet duct 13 and the vertical duct 20 can introduce air at different pressures. In this regard, the gasifier 1 preferably comprises a pressure/temperature regulation unit for regulating the air, in terms of pressure and/or temperature, introduced through the vertical duct 20 into the air inlet ducts 15, which allows regulation of the air coming out of the nozzles 18 in relation to the operating regime of the gas generator.

The invention does not exclude the known introduction of water, or water vapour, in order to produce "mixed gas" (air gas + water gas); also in this case the above-mentioned arrangement of the nozzles and any differentiated regulation of the latter allows operation of the gas generator adapted to prevent the condensation of tar and/or the formation of waste due to said condensation.

The gasifier according to the present invention guarantees a uniformly distributed introduction of air for the entire horizontal transverse section in the median zone of the inner layer with the effect that the oxidization due to the combustion with insufficient oxygen occurs mainly in this area, thus resulting in an effective vertical extension and an enlargement of the oxidization area. Said extension of the oxidization area, also in the presence of solid fuels in very irregular sized pieces and containing components (resins, lymph, phenolic substances) tending to form tar, entails a uniform diffusion of the reaction heat and, therefore, prevents formation of the condensation of tar.