BRPI0721307A2 - combustion plant, and combustion method suitable for use in a solid fuel thermoelectric power plant - Google Patents

Abstract

Combustion Plant, and Combustion Method Suitable for use in a solid fuel thermoelectric power plant. The present invention relates to a system for dry extraction / cooling of heavy ash and to control the combustion of waste of high unburned residue, allowing: to extract heavy ash from the boiler base (12), promote and adjust the powders. -fueling on the extracting belt (14) by the combined use of oxidising hot air and inert combustion fumes already available inside the boiler, cool the ashes present on the belt and optionally recirculate them - all or partly inside the boiler together with the light ash fraction of the highest unburned residue content.

Description

"COMBUSTION PLANT, Ε, COMBUSTION METHOD SUITABLE FOR USE IN A SOLID FUEL THERMAL ELECTRIC POWER PLANT" FIELD OF THE INVENTION

The present invention relates to a plant and method for drying or, mainly, dry extraction / cooling and reduction of unburnt heavy ash residues produced by boilers of the type used in solid fuel thermoelectric power plants.

Such a plant and method is specifically suitable in the case of boilers burning under co-combustion conventional solid fuel (typically coal dust) and unconventional fuel, especially biomass and / or municipal solid waste derived fuel (RDF). BACKGROUND OF THE INVENTION

The need to reduce CO2 emissions has accelerated the use of alternative fuels instead of coal, such as biomass and the so-called "RDF" (municipal solid waste fuel).

While the use of biomass and unconventional fuels in general, under co-combustion with coal dust, allows a reduction in total CO2 emissions into the atmosphere, on the one hand, it poses a number of problems related to the carbon dioxide system. combustion, including that of fuel spraying. Indeed, while being very reactive to coal, such alternative fuels, and particularly biomass, require remarkable amounts of energy in order to be milled to an appropriate degree / level, thereby ensuring high combustion efficiency. In addition, an excessive level of grinding causes further wear of the grinding members.

Therefore, in common practice, both in order to limit energy consumption and to extend the life of said grinding parts of grinding members, it is preferable to grind biomass to a greater degree, thereby reducing combustion efficiency. . Therefore, a merely partial combustion of the thicker biomass particles causes an increase in the amount of unburned waste in heavy and light ash.

Said heavy ashes are removed from the base of the combustion chamber by a dry extraction / cooling system, typically made as illustrated in European Patent EP 0 471 055 BI, and may be at least partially afterburned in such an extraction system. , in order to reduce the unburnt residue content of the final ashes.

However, in plants of the known art, the modes of control of such post combustion, above all in the most critical applications associated with the use of biomass and RDF illustrated above, are less than optimal and allow a merely limited reduction of unburnt waste. totals. Particularly, in known plants there is, however, the risk of uncontrolled afterburner phenomena in the extractor; This risk also implicitly limits the (complete) usability of measures to trigger or promote such afterburner. SUMMARY OF THE INVENTION

Accordingly, based on what has been described in the preceding section, the technical problem posed and solved by the present invention is to provide a plant and method for the afterburning of unburnt waste in a system for dry - or mainly dry - extraction. heavy ashes, overcoming the disadvantages mentioned above with reference to the known technique.

Such a problem is solved by a mill according to claim 1 and a method according to claim 30.

Preferred features of the present invention lie in its appended claims.

The present invention provides several relevant advantages. The main advantage lies in the fact that it allows, above all in the case of co-combustion of biomass or RDF, an effective and efficient post-combustion of unburned waste from the primary extractor, thereby reducing its content. concomitantly allowing the risk of uncontrolled afterburning to be avoided.

Particularly, to promote the reduction of unburnt residue, the invention preferably acts both on the temperature of the extracted heavy ash and its residence time in an environment of a suitable temperature, typically the belt-equipped extractor part disposed immediately downstream of the ash. combustion chamber and facing it. As the temperature in the afterburner zone increases and the fuel-related residence time there increases, the combustibility rate of the latter increases proportionately. To increase the temperature, the invention provides for hot air to enter the extractor and, in a preferred embodiment, the fuel residence time is adjusted by acting on the speed of the conveyor belt. According to the invention, to control the combustion process and to avoid excessive amount of biomass or RDF resulting in uncontrolled development of heat, combustion exhaust gases (fumes) - preferably collected downstream of the electrofilter (or electrostatic precipitator), typically provided in the plants to which the invention applies - are used to partially or completely replace oxidizing air.

As a result, the invention allows to increase the afterburning capacity of dry or mainly dry extractors, making the extraction environment, where ashes are moved, more favorable to the reduction of unburnt residues present in the ashes themselves.

The combined use of hot air and combustion fumes according to the invention allows full control over the belt after extractor burner. As mentioned above, the afterburning process preferably takes place and is completed in the extractor zone corresponding to the throat at the boiler base and optionally, if necessary and recommended for the plant's needs, also in its subsequent section.

Furthermore, in a preferred embodiment, downstream of a suitable cooling of the extracted heavy ash is provided for their recirculation within the boiler, together with the fraction of light ash of the highest unburned residue content.

Always based on a preferred embodiment, downstream of the post-combustion process begins air cooling of the ash, which in a controlled and adjusted amount is allowed to enter the extractor at the end of transport and / or on a secondary (post-cooler) conveyor / cooler arranged downstream of the primary puller. Preferably, at the exit of the conveyor-cooler, an ash crusher stage (step) is provided and, downstream of it, a sieving station allowing to eliminate any plastic or metal residues present in the ashes. Thus it is possible to obtain suitable ash to be stored or optionally recirculated within a boiler.

Preferably, the residence time of the light ash in said electrofilter (or electrostatic precipitator) is reduced by continuous recirculation in the combustion chamber of the richer fraction of unburned light ash residue. Thus, the invention allows to reduce the risk of fire in the electrofilters when biomass or RDF is used as fuel which, accumulating on the electrofilter hoppers, can cause self-combustion fires, unburnt biomass residues or RDF being too much. reactive to those of coal.

The total reduction of unburned waste, achieved through both post-combustion in the conveyor belt and combustion chamber recirculation, saves on ammonia consumption used for NOx reduction in catalysts. In fact, to achieve the same unburned residue content in total ash, in the absence of recirculation, a higher excess combustion air would be required, with the necessary increase in the exhaust gas NOx rate and the amount of ammonia required. to its reduction.

Summarizing the detailed description of the preferred embodiments listed below, the present invention relates to a system for: extracting heavy ash from the boiler base, promoting and adjusting post-combustion in the extraction belt by the combined use of hot air. Oxidising and inert combustion fumes, already available inside the boiler, cool the ashes in the belt and optionally recirculate them - all or in part - into the boiler, along with the fraction of light ash of the highest unburnt residue. BRIEF DESCRIPTION OF THE FIGURES Other advantages, features and modes of operation of the

The present invention will be apparent from the following detailed description of some preferred embodiments thereof given by way of example and without limiting purpose. Reference will be made to the attached drawing figures, where:

-Figure 1 shows an exemplary general diagram of a

preferred embodiment of the plant of the invention;

Figure 2 shows a cross section of an extractor - afterburner of the power plant of Figure 1 taken along line A-A of the last figure; and

-Figure 3 represents a top plan view of a

detail of a perforated puller belt from the mill of Figure 1. DETAILED DESCRIPTION

Referring to said figures, a combustion plant made in accordance with a preferred embodiment of the invention is generally indicated by 1.

Plant 1 is of the type used in solid fuel thermoelectric power plants burning solid fuel, particularly coal dust, and is suitable for (co) combustion of biomass and / or municipal solid waste derived fuel (RDF).

In the present example, plant 1 will be described with reference to biomass combustion.

For the sake of clarity, the various components of Plant 1 below will be described primarily with reference to the path followed by biomass, starting from collecting storage media to combustion and with reference to the path followed by combustion residues (heavy ash). and light), starting from its collection from the base of a combustion chamber (or boiler) 12 of plant 1 until its post-combustion, optionally recirculating them in the combustion and discharge chamber. First of all, plant 1 provides as a means of

biomass storage the same fuel depots, as they are known, already used for coal. In the present embodiment, the dedicated biomass fuel depots are the two shown on the left in Figure 1 and indicated by 21 and 22 respectively. The other fuel tanks and associated additional components depicted in Figure 1 are intended to be used for coal and will therefore no longer be considered below, their structure and use being of a type known to them. Preferably, the fuel tanks 21 and 22 are those fueling the combustion chamber burners 12 at the highest levels in order to have a longer residence time in the combustion chamber itself during the heavier particles. to the base. From dedicated fuel depots 21 and 22 biomass is extracted by one or more conveyors 3 analogous to those already used for coal or augers. Thus, the biomass is supplied by a stop valve 4 to a dedicated meter 5, in this case with three outputs, respectively indicated by 51, 52 and 53, and from this to one or more dedicated crushers, in this case three, respectively indicated by 61. , 62 and 63. In the present embodiment said crushers 61-63 are implemented by hammer mills known to them.

Accordingly, said conveyors 3 constitute bypass means of the known coal crushers, here indicated by F, associated with fuel deposits 21 and 22. Such deviation, therefore, allows plant 1 not to modify its own default configuration too much with respect to that related to the combustion of coal alone, allowing to leave also installed known crushers F.

The 61-63 shredders are capable of reducing biomass to a desired maximum final grain size (output). As will be better seen at the end of the description, this final grain size need not be particularly thin since the overall structure of the integrated plant 1 allows for complete combustion of the biomass anyway, even at such grain sizes. " rude ".

Downstream of mills 61-63 are respective sieving means 71, 72 and 73 capable of intercepting biomass particles of a grain size greater than a predetermined threshold for resending via dedicated mechanical or pneumatic conveyors 8. , for meter 5 and then into the same hammer mills 61-63 for further milling.

The finest biomass particles intercepting the sieving means 71-73 are conveyed by a common (shared) conveyor 9 to a single IO meter and then, via a two-way valve 91, fed to pneumatic conveyors 93 It is known, the latter already present in existing solid fuel plants in association with F crushers, that is, pneumatic conveyors 93 are those developed from (unused) coal grinding mills associated with fuel tanks 21 and 22.

Then the ground biomasses are introduced into the feed pipes feeding coal dust and from there fed to the boiler burners 12, also of a type already present in existing solid fuel plants.

Once the fuel comprised of said coal and biomass is fed to the combustion chamber 12, the extraction plant and post-combustion process carried out by it develops as described below.

Very fine ash leaves combustion chamber 12 through traditional ducts (conduit pipe) to expel combustion fumes, generally indicated by 13 in Figure 1. Instead, the heavy part of ash and any unburnt residue precipitates for the end and is collected in a conveyor type dry puller 14, of the same type as the subject of EP 0 471 055 and not further described herein.

According to the invention, in said extractor 14 and, in particular, in a post-combustion or a part thereof after burning facing the combustion chamber 12, the post-combustion of the unburnt residue continues. To this end, the top surface of the extraction belt and particularly part 141 receives heat by irradiation from the combustion chamber burners 12.

According to a variant embodiment, the plant of the invention may also comprise a combustion chamber independent biomass meter 18 and a feeder 19, also shown in Figure 1, arranged upstream of extractor 14 (or at least upstream or corresponding to part 141 thereof), to supply biomass of unburnt waste directly to the extractor 14 itself, for a first combustion of the last biomass within the afterburner zone 141. In this case, a first drying of said biomass may be performed by a hot air supply over the feeder 19; advantageously, said hot air may come from an air / smoke changer 29 already present in existing thermoelectric plants and which will be introduced hereinafter.

According to the invention, to enable higher post-combustion efficiency and concomitantly prevent the development of uncontrolled phenomena, it is provided with control means 100 for controlling the post-combustion of unburnt waste occurring in said part of the plant. post-combustion 141.

Said means 100, in turn, comprises hot air supply means 15 and combustion exhaust gas (smoke) means 150, capable of providing a heated air flow and combustion fumes, respectively, in correspondence with said post-combustion part 141 in order to respectively promote and inhibit post-combustion.

In the present embodiment, the feed means 15 and 150 comprise respective ducts for respectively collecting heated air from a chamber 151 associated with the boiler 12 and exhaust fumes downstream of an electrostatic precipitator (electrofilter) 28 from the plant. 1.

Typically, the hot air from the air chamber 151 comes from the aforementioned exchanger 29, which in the present embodiment is a smoke / air exchanger disposed downstream of the combustion chamber 12 and only exploits the residual heat of the combustion fumes to heat up. the air outside. According to a variant embodiment, the hot air fed by the medium 15 may also be exhausted directly from the last exchanger 29.

Said air chamber 151, air preheater 29 and electrostatic precipitator 28, are well known to a person skilled in the art and already present in known plants; therefore, another description of them will be omitted.

Hot air supply means 15 comprises means 143 for controlled (adjusted) external air inlet, for example, inlets made in extractor liner 14 and associated with one or more valves, preferably controlled by control means 100, allowing achieve a desired oxygen content and appropriate air inlet temperature inside the extractor 14.

As a result, the heated air fed through the medium 15 and adequately provided with atmospheric air allows to achieve an optimum post-combustion temperature over the extractor / afterburner belt 14.

Said medium 143 can also exploit negative pressure

present in the combustion chamber 12 for air supply from the outside.

Preferably, the overall arrangement is such that the hot air supply means 15 and the smoke supply means 150 are capable of supplying a countercurrent flow with respect to the belt direction of the extractor 14 itself, at least in part. 141 post-combustion introduced above.

Both air supply means 15 and smoke supply means 150 may be provided with respective means for automatically adjusting the flow, respectively indicated by 102 and 103 in Figure 1, controlled by control means 100.

The control means 100 is capable of adjusting the flow of hot air and / or fumes fed within the afterburner part 141 and for this purpose it comprises automatic means for adjusting said airflow and fumes depending on the temperature. detected by suitable sensors preferably arranged in correspondence with said afterburner parts 141. When the temperature value exceeds a preset threshold, the smoke flow rate is increased and therefore the hot air flow rate is reduced: Thus, the concentration of Oxygen is reduced by reducing the combustion rate. In particular, the fumes produced by the boiler combustion process can integrate or replace oxidizing air to adjust or stop combustion on the belt, thanks to the low concentration (<6%) of O2 in the fumes, allowing its use as an inert gas. Vice versa, when the temperature is below a preset limit, the smoke inlet is inhibited and the hot air flow is increased, optionally also reducing the ambient air flow rate introduced by the medium 143.

To move the fumes an additional fan can be installed when required to provide them with the required height for entry into the extractor / afterburner 14.

In order to avoid acid condensation problems, the supply medium fume pipe 150 should be insulated only to maintain a higher temperature than the condensation temperature.

The fumes used to control combustion, in addition to extinguishing energy, also exhibit appreciable cooling capacity as their temperature is not higher than 150 ° C. In fact, in the present embodiment, said fumes come from the downstream zone of the electrofilter, that is, they are collected when they have already lost their thermal content.

Accordingly, according to a variant embodiment, the post-combustion part 141 is exclusively or almost exclusively concentrated in the irradiated area below the boiler throat 12 and controlled by feeding hot air and / or fumes in the manner described. above. The part of the extraction belt not facing the boiler base is instead dedicated to cooling, which can be accomplished by feeding the combustion fumes (with dedicated media) and cold air (with the medium 143 introduced above), taking the Care is taken to introduce the fluid into the transport zone by exploiting the negative pressure within the boiler and in order to have the fluid tapping the extractor cover 14 and cooling it.

Finally, as another option for combustion control can be provided the use of finely metered water via dispensing nozzles 104, preferably provided in various zones of the extractor / afterburner 14 and particularly (at least) in the primary milling (ie at the end of the extractor 14 with respect to the ash advance direction).

According to a preferred variant embodiment, the hot air fed by the medium 15 is supplied below the extractor belt 14 and particularly below its part 141 as mentioned above against the flow of heavy ash and unburnt debris. In this case, in order to produce more effective and efficient heat exchange and post-combustion, the extractor belt 14 may be provided with perforations (holes) or slots 142 shown in Figure 3. Thus, the hot air, in addition to heating the base of the extractor 14 passes through the ashbed and unburnt debris and partially returns into the combustion chamber 12, thanks to the negative pressure present in the latter, feeding back heat there. Such air passage is promoted by the pressure difference between the base part of the conveyor belt and the boiler base. Hot air through the holes in the conveyor belt 14 enables greater and more effective air contact with the belt ash itself, resulting in increased combustion efficiency of the unburned waste material.

As already mentioned above, in the present embodiment, over the extractor sidewalls 14 - and particularly in correspondence with an end portion of the belt typically not involved in post-combustion - more air inlet means 143 is provided for the extraction. controlled intake of external cooling air.

From the extractor 14, heavy ashes and unburned debris are supplied to a secondary conveyor belt 16 serving as an aftercooler and therethrough a primary crusher 20, preferably water-cooled to withstand high temperatures downstream from which a hopper is positioned. transition 201, simply projected in Figure 1.

In the cooling conveyor 16 an air-assisted cooling of the ash is performed by a countercurrent system, exploiting the negative pressure present in the combustion chamber for air supply outside via controlled inlets 160 present in the side walls of the the conveyor itself 16 as already described in EP 0 471 055.

According to a preferred variant embodiment of the invention, said hopper 201 is part of a pressure isolation system capable of only creating a pressure separation between the environments of the extractor 14 and said cooling conveyor 16. For this purpose, hopper 201 forms a means for accumulating the conveyed material, allowing the formation of a material height between said environments, creating said pressure separation.

Said pressure isolation system allows for more effective control of air-assisted ash cooling as it allows - when necessary and typically based on ash temperature and flow detections performed, for example, on its discharge. on extractor 14 - avoid introducing excessive amount of cooling air into the combustion chamber 12 by only selectively activating such pressure separation as also described in PCT / IT2006 / 000625.

The height of the material forming at hopper level 201 can be adjusted by acting on the relative and absolute feed rates of carriers 14 and 16.

When pressure isolation is activated, the heated air outlet of conveyor 16 is fed into section 26 of the smoke ducts 13 of plant 1 by another suitable duct 25, originating from the end of conveyor 16 itself and provided with means to automatically adjust the flow rate. Such a connection between the aftercooler 16 and the boiler side may occur upstream or downstream of the aforementioned air preheater 29 (smoke side) disposed along the smoke ducts 13. Through said connection the cooling air inlet to the aftercooler 16 is nullified by the negative pressure value existing in said boiler side zone.

Preferably, plant 1 also provides a diversion pipe or duct (for simplicity omitted from the figures) connecting the extractor / afterburner 14 with the transporter-cooler 16 and provided with an automatic open / close valve. Downstream of the cooling conveyor 16 there is provided a

Opposite roller or equivalent type secondary crusher 202 suitable for grinding only ash and in particular capable of reducing the grain size of the latter without changing the grain size of any plastic materials mixed with the ash and deriving from RDF combustion. In this typology of crusher, already known to one skilled in the art, the plastic particles pass through the deforming rollers, yet without breaking.

As a result, a mechanical or pneumatic sieving system 203 located downstream of the second grinding stage (step) associated with the device 202 is provided to separate ash from plastic particulates and any metal parts present in the RDF, which is stored or sent for disposal. through dedicated.

Ground ash is sent to coal pulverising mills via a mechanical or pneumatic conveyor 204 to be recirculated in the combustion chamber through coal pulverising mills and boiler burners as described in International Application PCT / EP2005 / 007536.

With reference to the path of the aforementioned combustion fumes generated in the combustion chamber 12 and the lightly conveyed ashes, said fumes traverse the economizer zone 27 and are then fed through said smoke ducts 13 into the electrostatic ash precipitator. lightweight 28 mentioned herein or equivalent means, optionally by first passing the air / smoke changer 29 mentioned herein.

The light ashes precipitated into said precipitator

28 are collected by suitable means 30 for their recirculation in the combustion chamber.

In summary, therefore, after post-combustion in the extraction belt 14, any unburnt residues still present in the heavy ash, after proper cooling by the conveyor 16, are recirculated in the combustion chamber along with the light ash having a non-residual residue content. burned to achieve a complete conversion of unburned waste.

In addition, plant 1 incorporates a central adjustment and control system capable of automatically performing the steps described herein.

Therefore, at this point, we observe that the described power plant achieves a reduction in the unburned residues present in the heavy ash by a controlled post-combustion process in the extraction belt and by the boiler recirculation of the heavy ash thus produced and the light ash having more high content of unburnt residue, the last ashes from electrofilters.

In addition, we note that the integrated system described above for dry extraction, grinding, biomass and heavy ash post-combustion and recirculation of unburned waste allows the combustion capacity of biomass (and usually unconventional fuel) to be increased as well. increase your combustion efficiency.

The concomitantly described system allows the use of appliances already present in existing thermoelectric power plants, reducing the installation costs of the plant and requiring minimal adjustment of existing ones. In particular, biomass as well (and, in general, unconventional fuel masses) continues to move with the medium used to move coal and heavy ashes. In addition, boiler burners, currently representing the means for accumulating traditional solid fuel material, can be used by biomass as well.

At this point, we also note that, unlike the state of the art, where recirculation in the combustion chamber of heavy ash added to the light ash of higher unburned residue is provided using coal mills for pulverization, The present invention provides the combustion of biomass directly on the extraction belt using part of the preheated air, and it optimizes the combustion of mixed biomass in the coal dust boilers by recirculating heavy ash.

It is noted that the invention also relates to a method of

for the (co-) combustion of biomass in a solid fuel thermoelectric power plant of the type described above, said method providing for the dry extraction of heavy ashes and unburnt waste from the combustion chamber 12 by an extractor 14 of the above type and wherein, in correspondence with part 141 of the latter, an afterburning of the unburned waste occurs controlled by the selective feeding of a hot air stream and a combustion smoke stream in order to respectively promote and inhibit the dust. -combusting, the flow of hot air and / or fumes fed within said post-combustion part being adjusted. Preferred features of said method have already been described

with reference to plant 1.

Finally, we note that even though the integrated system described here optimizes the combustion efficiency of biomass (and unconventional fuel in general) and plant control, separate protection could be required for the different aspects of the invention and in particular, for the system to control air and smoke combustion, for dedicated grinding, for the biomass afterburning system and for the medium for direct combustion of biomass on the extractor by the dedicated meter, each of these aspects allowing, however, , a substantial improvement of said efficiency.

The present invention has been described hereinbefore with reference to its preferred embodiments. It is to be understood that other embodiments could exist, all within the protective scope of the following claims.

Claims (58)

1. Combustion plant (1) suitable for use in a solid fuel thermoelectric power plant in association with a combustion chamber (12) for said fuel, in particular of a type suitable for (co-) combustion of biomass and urban solid waste (RDF) fuel, characterized in that it comprises: a dry ash extractor (14) of heavy ash and unburnt residue from the combustion chamber (12), capable of being disposed downstream of the latter and having a post-combustion part (141) for unburnt waste; and control means (100) for controlling the afterburning of unburnt waste occurring in said afterburning portion (141), in turn comprising means (15) for hot air supply and medium (150) for fuel supply. combustion fumes, capable of providing a flow of heated air and combustion fumes, respectively, corresponding to said post-combustion part (141), in order to respectively promote and inhibit post-combustion, said control means. (100) being able to selectively adjust the flow of hot air and / or fumes fed within said post-combustion portion (141). Plant (1) according to Claim 1, characterized in that the total arrangement is such that said post-combustion part (141) is able to be arranged at least partially towards the base of the chamber. combustion (12), so that the post-combustion exploits the radiating heat from the combustion chamber (12) itself. Plant (1) according to Claim 1 or 2, characterized in that said hot air supply means (15) and / or fumes (150) are configured to supply in correspondence with said part of powders. combustion (141), a countercurrent air flow with respect to the direction of movement of said puller (14). Plant (1) according to any one of the preceding claims, characterized in that said control means (100) comprises automatic means for adjusting said air flow and / or smoke, depending on the temperature detected in correspondence with said part of post-combustion (141). Plant (1) according to any one of the preceding claims, characterized in that the total arrangement is such that said hot air (15) and / or smoke (150) feed means are suitable for exploitation in order to promote the circulation of air and / or fumes, the negative pressure present in the combustion chamber 12. Plant (1) according to any one of the preceding claims, characterized in that said control means (100) comprises means (143) for controlled external air inlet to be mixed with the hot air of said feed medium. (15). Plant (1) according to any one of the preceding claims, characterized in that said hot air supply means (15) collects or is capable of collecting heated air from an air chamber (151) or from a pre-flow. heater (29) capable of supplying heated air to the combustion chamber (12). Plant (1) according to any one of the preceding claims, characterized in that said means (150) for feeding combustion fumes collects or is able to collect said fumes downstream of an electrostatic precipitator (28). Plant (1) according to any one of the preceding claims, characterized in that the total arrangement is such that the temperature of the combustion fumes fed by said medium (150) is equal to or less than approximately 15 ° C. Plant (1) according to any one of the preceding claims, characterized in that said means (150) for feeding combustion fumes comprises a fan for increasing the flow height. Plant (1) according to any one of the preceding claims, characterized in that said dry extractor (14) has side inlets (143) for controlled external air inlet. A plant (1) according to any one of the preceding claims, characterized in that said dry puller (14) comprises a puller belt having, at least in correspondence with said post-combustion part (141), a plurality of perforations 142 capable of promoting air passage through the conveyed material. Plant (1) according to any one of the preceding claims, characterized in that it comprises means (104) for supplying cooling water to said extractor (14), arranged at least in correspondence with an end portion thereof. Plant (1) according to any one of the preceding claims, characterized in that it comprises means for adjusting the residence time of unburnt residues in said post-combustion part (141). Plant (1) according to the preceding claim, characterized in that said adjusting means is based on the speed control of said extractor (14). Plant (1) according to any one of the preceding claims, characterized in that it comprises a cooling conveyor (16) arranged downstream of said dry puller (14). Plant (1) according to the preceding claim, characterized in that it comprises pressure isolating means (201) capable of creating a pressure separation between said extractor (14) and said cooling conveyor (1) environments. 16). Plant (1) according to the preceding claim, characterized in that said pressure isolation means comprises means (201) for accumulating the conveyed material capable of allowing the formation of a material height between said environments, creating said separation. pressure Plant (1) according to any one of the preceding claims, characterized in that it comprises means (30) for the recirculation in the combustion chamber (12) of light ash. Plant (1) according to the preceding claim, characterized in that said recirculating means (30) comprises means for collecting light ash from or immediately downstream of an electrostatic precipitator (28). Plant (1) according to any one of the preceding claims, characterized in that it comprises means (204) for recirculating, in the combustion chamber (12), unburnt residues contained in the heavy ash. Plant (1) according to any one of the preceding claims, characterized in that it comprises means for feeding said fumes into an ash cooling zone disposed downstream of said post-combustion part (141) of said extractor. (14). Plant (1) according to any one of the preceding claims, characterized in that it comprises an unburnt waste biomass feeder (18, 19) arranged upstream or in correspondence with said post-combustion part (141). said extractor (14) and independent of the combustion chamber (12), said feeder (18, 19) being able to place unburnt waste biomass directly into said extractor (14). Plant (1) according to the preceding claim, characterized in that it comprises means for feeding hot air to said feeder (19), capable of first drying the unburnt waste biomass. Plant (1) according to the preceding claim, characterized in that said means for feeding hot air to the biomass is associated with an air / combustion smoke exchanger (29). Plant (1) according to any one of the preceding claims, characterized in that it comprises dedicated grinding means (61-63) arranged or capable of being arranged downstream of the combustion chamber (12) and suitable for grinding the biomass according to a preset maximum output grain size. Plant (1) according to the preceding claim, characterized in that said dedicated crushing means (61-63) comprise one or more hammer mills. Plant (1) according to Claim 26 or 27, characterized in that it comprises bypass device (3) capable of supplying biomass from the storage fuel tanks (21, 22) to said dedicated grinding media (61- 63). Plant (1) according to one of Claims 26 to 28, characterized in that it comprises sieving means (71-73) arranged downstream of said dedicated crushing means (61-63) and capable of intercepting biomass particles. of a grain size greater than a predetermined threshold for resending them to said grinding media (61-63). Combustion method suitable for use in a solid fuel thermoelectric power plant, characterized in that it comprises a combustion chamber (12) for said fuel, in particular of the type suitable for (co-) combustion of biomass and / or municipal solid waste (RDF) fuel, said method providing dry extraction of heavy ashes and unburnt waste from the combustion chamber (12) by an extractor (14) disposed downstream of the latter, said method further comprising a step of post-combustion of unburned waste, occurring in a post-combustion part (141) of said extractor (14), said post-combustion step being controlled by the selective feeding of a hot air stream and a smoke stream combustion in order to respectively promote and inhibit post-combustion, the flow of hot air and / or fumes fed into said post-combustion portion (141) being adjusted. Method according to claim 30, characterized in that said afterburning part (141) is arranged at least partially facing the base of the combustion chamber (12) in order for the afterburning to exploit the heat. of radiation from the combustion chamber itself (12). Method according to claim 30 or 31, characterized in that said hot air and / or smoke supply supplies, in correspondence with said post-combustion part (141), a countercurrent flow with respect to the forward direction. of combustion waste. A method according to any one of claims 30 to 32, characterized in that said air flows and / or fumes are automatically adjusted depending on the temperature detected in correspondence with said post-combustion part (141). A method according to any one of claims 30 to 33, characterized in that said hot air and / or smoke supply exploits, in order to promote air circulation and / or wiring, the negative pressure present in the air chamber. combustion (12). A method according to any one of claims 30 to 34, characterized in that a controlled supply of air from the outside to said post-combustion part (141) is provided. A method according to any one of claims 30 to 35, characterized in that said hot air supply provides for the collection of heated air from a preheater (29) or an air chamber (151), both capable of supply heated air to the combustion chamber (12). A method according to any one of claims 30 to 36, characterized in that said combustion fumes feed provides for the collection of said fumes downstream of an electrostatic precipitator (28). A method according to any one of claims 30 to 37, characterized in that the temperature of the combustion fumes fed into said post-combustion portion (141) is equal to or less than approximately 15 ° C. A method according to any one of claims 30 to 38, characterized in that said combustion smoke feed provides the use of ventilation means to increase the flow height. Method according to any one of claims 30 to 39, characterized in that the controlled external air supply is provided into the dry extractor (14). Method according to any one of Claims 30 to 40, characterized in that it also provides a cooling water supply into said extractor (14), at least in correspondence with a final part thereof. Method according to any one of Claims 30 to 41, characterized in that it provides an adjustment of the residence time of unburnt residues in said post-combustion zone (141). Method according to the preceding claim, characterized in that said adjustment is based on the speed control of said extractor (14). A method according to any one of claims 30 to 43, characterized in that it comprises a downstream cooling step of the extraction performed by said dry puller (14). A method according to the preceding claim, characterized in that it provides the option of activating a pressure isolation between the environments of said extractor (14) and of said cooling step performed downstream thereof. A method according to the preceding claim, characterized in that said pressure isolation is activated by the conveyed material accumulation means (201), capable of allowing the formation of a material height between said environments creating said pressure separation. A method according to any one of claims 30 to 46, characterized in that it provides recirculation in the combustion chamber (12) of light ash. A method according to the preceding claim, characterized in that the light ash to be recirculated is collected from or immediately downstream of an electrostatic precipitator (28). Method according to any one of claims 30 to 48, characterized in that it provides recirculation in the combustion chamber (12) of unburnt waste contained in the heavy ash. Method according to any one of claims 30 to 49, characterized in that it provides an ash cooling step carried out by said combustion fumes. Method according to the preceding claim, characterized in that said cooling step is carried out in said extractor (14). Method according to any one of claims 30 to 51, characterized in that direct biomass feed of unburnt waste is provided in said extractor (14), upstream or in correspondence with said post-combustion part (141). . A method according to the preceding claim, characterized in that a hot air supply is provided to the unburnt waste biomass feeder (18, 19) in order to perform a first drying of the latter. A method according to the preceding claim, characterized in that said biomass-fed hot air is obtained by a combustion air / smoke heat exchanger. Method according to any one of claims 30 to 54, characterized in that it provides the use of dedicated shredding means (61-63) suitable for shredding the biomass to a preset maximum final grain size (output). . A method according to the preceding claim, characterized in that it provides biomass storage within the same type of fuel tanks (21, 22) used for solid fuel and the biomass supply of said fuel deposits (21, 22) for said dedicated crushing means (61-63). A method according to the preceding claim, characterized in that said biomass storage fuel tanks (21, 22) are associated with combustion chamber burners (12) arranged at the highest levels. A method according to any one of claims 55 to 57, characterized in that it provides downstream of said dedicated grinding means (61-63) a sieve for intercepting particles of a grain size greater than a predetermined threshold, and the referral of the latter to said dedicated shredding means (61-63).