ITRM20080662A1 - EXTRACTION AND COOLING SYSTEM FOR LARGE RANGE OF HEAVY ASHES WITH EFFICIENCY INCREASE. - Google Patents

Description

EXTRACTION AND COOLING SYSTEM FOR BIG

CAPACITIES OF HEAVY ASH WITH INCREASE IN EFFICIENCY

DESCRIPTION

Invention sector

The present invention relates to a plant and a method of extracting, cooling and recovering thermal energy for large flow rates of bottom ash produced by solid fuel boilers.

Background of the invention

The continuous growth in demand for solid fossil fuels for the production of electricity makes the combustion of coals or lignites with a high ash content more and more frequent. The combustion of the latter in high-power boilers involves a considerable production of bottom ashes, even up to 100 tons / hour, often containing high percentages of unburnt materials. Dry cooling or mainly dry cooling of these quantities requires considerable cooling air flow rates, even two or three times higher than with fossil fuels with high calorific value.

As illustrated in EP 0471 055 B1, in some known dry ash extraction and cooling systems, the cooling air, once heated by the heat exchange with the latter, is introduced into the boiler from the bottom of the latter. Therefore, in principle, the greater the quantity of ash produced, the greater the recovery of heat that is supplied to the boiler by the cooling air in the aforementioned way, both for the heat exchange with the air and for the combustion of the unburnt.

However, to avoid that the combustion efficiency is negatively influenced by the air introduced into the combustion chamber from the bottom rather than by the burners or other suitable air inlets and / or to avoid similar undesirable effects on the generation of oxides of nitrogen (NOx), boiler designers prefer to limit this quantity to a maximum value of 1.5% of the total combustion air.

As described above, known cooling systems are unable to effectively and efficiently perform dry or mainly dry cooling of the bottom ash and the disposal of the relative cooling air, especially if such ashes are in large flow, at high unburnt content and therefore at high temperature. In particular, even where such cooling, thermal energy recovery and disposal can be obtained, they are achieved with considerable system complications and with consequent very high construction and management costs.

WO2008 / 023393 - the content of which is incorporated herein by this reference - provides that, when the air flow needed to cool the extracted heavy ash exceeds the maximum admissible quantity in the combustion chamber, the excess air can be sent into the smoke duct and this thanks to a pressure separation of the cooling environments operated by the ash itself. Still in WO2008 / 023393, a possible point of introduction of this excess air is located on the aforementioned flue pipe in a position upstream or downstream of the air / flue gas exchanger.

A potential limitation of the WO2008 / 023393 system consists in the loss of the thermal content associated with the cooling air used downstream of the pressure separation system and in the increase in the overall flow rate of the fumes that must be processed by the equipment downstream of the point. of introduction of air.

In fact, in case of introduction of hot air downstream of the air / fumes exchanger, the thermal content of the cooling air is completely lost and results in an overall increase in the temperature of the fumes in the chimney, as well as in an increase of power absorbed by the equipment necessary for the processing of fumes.

In case of introduction of hot air into the flue gas duct upstream of the exchanger, since the cooling air is at a lower temperature than the combustion flue stream, there is an overall increase in the flow of the hot flue air stream entering the exchanger which worsens the heat exchange efficiency of the ambient air / fumes of the device.

In particular, the aforementioned cooling air can reach a temperature of about 200 ° C, and therefore, as just said, its introduction into the fumes whose temperature is about 400 ° C can be uneconomical for the balance on the exchanger. air / fumes, in fact based on the operating principle of the air / fumes exchanger, while increasing the thermal content of the incoming current on the fumes side, this cannot be transferred to the air except for a negligible fraction.

Furthermore, the introduction of hot air into the flue gas duct (whether operated upstream or downstream of the exchanger) ensures that the electrostatic precipitators arranged downstream of the air / flue gas exchanger receive an overall flow rate higher than the design data, in addition to an overall increase in the temperature of the flue gas stream to be processed. This circumstance determines a worsening of the efficiency of the electrostatic separators caused by an increase in the inlet speed and above all by an increase in the resistivity of the ash.

Brief description of the invention

On the basis of what has been stated in the previous section, the technical problem posed and solved by the present invention is that of providing an apparatus and a method which allow to overcome the drawbacks mentioned above with reference to the known art.

This problem is solved by a plant according to claim 1 and by a method according to claim 22.

Preferred features of the present invention are present in the dependent claims thereof.

The present invention provides relevant advantages, which will be fully appreciated in the light of the detailed description set forth below.

The main advantage consists in the fact that the invention allows to maximize the recovery of the sensible heat contained in the excess cooling air used in the second portion of the system downstream of the pressure insulation.

In fact, the configuration proposed in the present invention envisages the introduction of the cooling air into the ambient air stream sent to the air / fumes exchanger before being introduced into the combustion chamber. The ambient air mixed with the hot cooling air before entering the exchanger undergoes an increase in temperature and performs an efficient pre-heating of the same. This configuration leaves the efficiency of the air / fumes heater almost unchanged and allows the recovery of the sensible heat of the cooling air. In fact, the invention allows the total recovery of the sensible heat acquired by the cooling air in the portion of the plant downstream of the pressure separation and at the same time leaves unchanged the flow of fumes and its temperature that pass through the electrostatic precipitators, thus ¬ not to lower their separation efficiency.

The invention also allows to maintain the advantages already present in the system of WO2008 / 023393, that is to obtain an efficient dry or mainly dry cooling of the ashes without exceeding the aforementioned limit of 1.5% for air. of cooling introduced into the combustion chamber from the bottom.

The invention actually allows an optimization of the system described in EP 0 471 055 B1 and in WO2008 / 023393, expanding the potential of heat recovery in the case of applications to large quantities of bottom ash from high-content coals or lignites. of ashes.

Summarizing the detailed description of preferred embodiments reported below, the present invention refers to an air or mixed air / water extraction and cooling system for large flow rates of bottom ash produced by solid fuel boilers, capable of reducing the final temperature of the ash extracted without increasing the flow of air entering the boiler throat, normally set by the boiler designers at a value around 1.5% of the total combustion air. When the air flow needed for cooling exceeds the maximum allowable quantity in the boiler, the system allows the excess air to be sent to the combustion air intake duct and preferably to the secondary air duct, thanks to to a separation of the cooling environments preferably operated by the ash itself.

Depending on the system configurations and therefore on the concentrated and distributed head losses of the cooling air connection line, it may be useful to provide an in-line pressure fan, in order to give the right thrust to the ducted fluid.

The overall temperature increase of the ambient air entering the exchanger results in a negligible reduction in the temperature delta between fumes and ambient air, negatively affecting the overall efficiency of the air / fumes heater.

The separation of the cooling system environments is managed automatically based on a temperature and / or flow rate signal of the ash being discharged from the system.

If the cooling air is not sufficient to cool the ash, the effectiveness of the cooling can be increased by the addition of water spray. The quantity of water added is normally dosed according to the flow rate and temperature of the ash in such a way as to ensure complete evaporation of the injected water to obtain, if necessary, dry ash for discharge, suitable for grinding and transport. pneumatically.

Based on a preferred configuration, the proposed system, in use, is mainly made up of:

1. a transition hopper between boiler and extractor, the latter of the type described in the already mentioned patent EP 0471055 B1;

2. the aforementioned extractor;

3. an ash crusher;

4. a buffer tank for transition between the crusher and a cooler conveyor, said tank-buffer being for example in the form of a hopper;

5. the aforementioned conveyor-cooler, possibly equipped with suitable plowshares which are entrusted with the function of mixing the ash on the conveyor itself and with nozzles for the injection of water;

6. a pipe, or duct, connecting the cooler conveyor (preferably in the area of the latter's exhaust hood) and the most appropriate point of the ambient air inlet system to the air / fumes exchanger for the elimination of the cooling air in excess to the maximum acceptable from the boiler, possibly equipped with a cyclone separator for the abatement of the fine ash contained in the cooling air stream and a regulation valve

7. a possible fan in line with the aforesaid piping in case the concentrated and distributed pressure drops of the line are higher in absolute value than the depression value present at the point of entry of the cooling air;

8. a final unloading equipment, capable of allowing the ash to be discharged while preventing the entry of uncontrolled air into the system (for example a valve or a vibrating extractor or simply a closed connection with other closed equipment for transport or storage);

9. a possible ash-water mixer that will be activated, as an alternative to the final discharge equipment referred to in point 8 above, thanks to the activation of a flow diverter, in case the system, due to the anomalous conditions of the ash ( high flow rate and / or temperature) is no longer able to guarantee adequate cooling of the ash - this mixer will, in turn, be equipped with:

- a connection pipe, or duct, for venting the humid air to the pipe referred to in point 6, and

- a final discharge equipment equivalent to that described in point 8, capable of allowing the ash to be discharged from the system while preventing the return of external air;

10. a regulation and control system, able to ensure the automatic execution of the operations as will be described below in the part of the description of the operation.

Brief description of the figures

Other advantages, characteristics and methods of use of the present invention will become evident from the following detailed description of some preferred embodiments, presented by way of non-limiting example. Reference will be made to the figures of the attached drawings, in which: ∠'Fig. 1 shows an exemplary general scheme of a preferred embodiment of the plant of the invention, in an operating mode that provides for a pressure separation between two environments cooling system and the connection of the second portion of the system to the ambient air inlet line to the air / fumes heater; ∠’Fig. 2 shows a schematic longitudinal section view of a separation area of the two cooling rooms of the plant of Fig.1;

∠’Fig. 3 shows a cross-sectional view taken according to the line A-A of Fig.2;

∠’Fig. 4 shows an exemplary general scheme of the plant of Fig. 1, in a different operating mode that does not provide for said separation into two cooling environments;

∠'Fig. 5 shows a cross-sectional view of a double shaft continuous mixer equipped with nozzles for the cooling water of the plant of Fig. 1, carried out according to the line B-B of this last figure ; And

∠’Fig. 6 shows an exemplary general scheme of the plant of Fig. 1, in an operating mode that involves sending the still hot ash to the mixer of Fig. 5.

Detailed description of preferred embodiments

With reference to the aforementioned figures, a plant for the extraction and cooling of combustion residues, of the type used for example in solid fossil fuel thermoelectric power plants and according to a preferred embodiment of the invention, is generally indicated with 1. As will be better appreciated in the continuation of the description, plant 1 is particularly suitable for managing large flow rates of bottom ash, generated for example by the combustion of coals or lignites with a high ash content.

For greater clarity, the various components of system 1 will be described below with reference to the path followed by the combustion residues from their extraction from the bottom of the combustion chamber (or boiler), denoted with 100, to their disposal.

Immediately downstream of the combustion chamber 100, or rather of a transition hopper 105 thereof, the plant 1 provides a first extraction and transport unit, in particular a dry extractor 9 made mainly of high thermal resistance steel. Said extractor 9 is of a type known per se and described for example in EP 0252967, incorporated herein by this reference. The extractor 9 collects the bottom ash which precipitates downwards into the combustion chamber 100 through the aforementioned transition hopper 105.

The extractor 9 has, in correspondence with the side walls of its casing, a plurality of inlet holes for external cooling air, distributed substantially uniformly along the development of the extractor 9 itself and each denoted by 10. These inlets 10 can be equipped with means for regulating the flow rate or can be made active or deactivated. The extractor 9 can also have a further inlet of external cooling air 19, also preferably regulated by an automatic valve or by equivalent flow control means and arranged substantially in correspondence with an end portion of the extractor 9 same.

The cooling air is recalled through the inlets 10 and 19 into the extractor 9 and in countercurrent with respect to this due to the vacuum present in the combustion chamber 100. More in detail, the air inlet takes place thanks to the vacuum existing in the transition hopper 105, on the bottom of which there is a vacuum regulated by the control system of the combustion chamber 100 (generally around 300-500 Pa under atmospheric pressure).

Downstream of the extractor 9 the ashes are fed to a crusher 3, which crushes the coarser fractions in order to increase the heat exchange surface and thus improve the efficiency of this exchange and therefore the cooling.

Downstream of the crusher 3 there is a further inlet of external cooling air, denoted by 17 and possibly also equipped with flow rate adjustment means such as those already described. Also in this case, the air coming from the inlet 17 is fed in counter-current through the crusher 3 itself and along the first extractor 9 due to the depression present in the combustion chamber 100. This cooling air is useful not only for the cooling of the ash but also for that of the machines.

As illustrated in greater detail in Figures 2 and 3, downstream of the crusher 3 the ashes are conveyed through a hopper / tank 8 to a second steel belt conveyor-cooler 6. As will be illustrated in greater detail below, under certain conditions the system configuration described allows the hopper 8 to operate as a buffer tank, allowing an accumulation of ash such as to guarantee the disconnection of the two atmospheres of the extractor 9 and of the cooler conveyor 6. In particular, in the presence of this accumulation, the conveyor 6 works properly as a second extractor, operating continuously under a head of material which ensures the separation between the extractor environment associated with the pressure regime of the combustion chamber 100 and that of the conveyor / cooler associated with the different pressure regime of the area with which it is connected. The hopper 8 also has associated maximum and minimum level sensors, denoted by 7, and a layer leveler 18, the latter arranged in correspondence with an initial portion of the conveyor mouth 6. The position indication of the layer regulator 18 connected to the speed indication of the belt of the cooler conveyor 6, it provides information on the volumetric flow rate of the ash, useful together with the temperature indication for the regulation of the cooling fluids. On the conveyor 6 the ash continues to be cooled both by means of air drawn from the outside through further inlets 11 arranged on the side walls of the extractor 6 itself in a similar way to what has already been illustrated for the first extractor 9, and similarly it can present a further inlet of external cooling air, equivalent to 19, also preferably regulated by an automatic valve or by equivalent flow rate regulating means and arranged substantially in correspondence with an initial portion of the conveyor 6 itself.

If necessary, cooling on the conveyor 6 can take place by means of finely dosed water by means of further dispensing nozzles 12 positioned inside the cover of the conveyor 6.

It will therefore be understood at this point that system 1 can be equipped with a mixed air-water cooling system, implemented among other things by the air inlets 10, 11, 17 and 19 and by the water dispensing nozzles 12 .

The system 1 also provides means of feeding part of the cooling air, heated following the heat exchange with the combustion residues, into an ambient air delivery duct 50 associated with the air / flue gas exchanger 102. In the present embodiment, these supply means comprise a duct 51, suitably insulated and thermally traced to avoid condensation, able to be selectively regulated and in any case cut off / enabled by means of an automatic valve 150 (or equivalent means) arranged along its length.

More in detail, the duct 51 connects, or rather is suitable for connecting the discharge area of the conveyor 6 (Figure 1) and / or possibly of the mixer 2 (Figure 6) with the secondary room air intake area to the air / fumes exchanger. Therefore, preferably the duct 51 opens upstream of a line associated with a secondary air fan 54 which introduces ambient air to the air / flue gas exchanger 102 (air side), the latter suitable for preheating the combustion air and typically provided in the combustion plants associated with the invention. As is known, this inlet area is at negative pressure provided by the aforementioned air fan 54 or by an equivalent means for controlling the pressure.

The exchanger 102 can be of the type commonly known as Ljungstrom. A separator cyclone 55 or equivalent equipment can be associated with the line of the duct 51, able to collect any fine ash present in the cooling air stream leaving the conveyor 6 and / or the mixer 2 and suitable regulation valves 150 , 59.

Always in line with the duct 51, a fan 56 can be present in case the concentrated and distributed head losses of the cooling air line are greater than the depression foreseen at the point of introduction on the duct upstream of the fan 54 or the available head of the same.

In general terms, the optimal entry point for the cooling air is represented by the intake duct of the combustion air fan which takes the air from the environment and sends it to the air / fumes exchanger. In the case - as in Figure 1 - the exchanger is of the trisector type, that is, it has two inlets, respectively 61 and 62, dedicated to the combustion air (divided into primary and secondary) and an inlet dedicated to the fumes, the preferential point for The intake of the cooling air is identified, as mentioned, by the secondary air intake duct. This point, in fact, is preferred with respect to the suction line of the primary air fan 58, since the pressure level of the primary fan 58 is considerably higher than that of the secondary and therefore the energy lost in pumping à greater.

If the system configuration does not allow connection to the secondary air intake line, the primary air line can be chosen, which in any case offers advantages in terms of heat recovery, albeit to a lesser extent.

The advantage of introducing the cooling air upstream of the fan (primary 58 or secondary 54) also results in ensuring that it always processes the same amount of incoming air and therefore does not undergo variations in exercise.

In an alternative embodiment, the cooling air can be sent directly to the inlet of the air / flue gas exchanger 102 on the air side.

The cooling of the ashes on the conveyor 6 can be made more effective thanks to the presence of suitable mixing means, in particular substantially wedge-shaped elements 14 fixed with respect to the conveyor belt 6 itself and which in the present example have the shape of a share. These ploughshare elements 14 are distributed in a substantially uniform way along the length of the conveyor 6 and arranged in correspondence with the section for transporting the ashes. As mentioned above, the ploughshare elements 14 furrow the ashes operating a continuous mixing during transport on the belt, thus exposing the maximum surface available for heat exchange with the cooling air and / or water.

Downstream of the conveyor 6 there is an automatic diverter valve 16 (or equivalent means for the selective deviation of the ash flow), which selectively allows the cooled ash to be fed to an unloading means 13 directed to the outside or to a continuous mixer 2, also in the present example in communication with the outside and shown in greater detail in Figure 5.

The exhaust conveyor 13 is equipped with an inlet air control device, not shown, to eliminate the uncontrolled entry of air from the outside (or, in variants of construction, to connect the system to other closed transport or storage environments).

The mixer with water 2 allows to complete the cooling of the ash if necessary to reach temperature values compatible with the downstream processes or to humidify the ash to reduce dust emissions in certain transport and disposal conditions. The mixer 2 is equipped with a discharge hood 21, equipped with means capable of allowing the ash to be discharged from the system while preventing the return of uncontrolled external air. This device can be constituted, for example, by a double clapet valve or by rubber flaps which, deforming under the weight of the ash, allow it to be discharged into the minimum necessary passage section.

According to a preferred embodiment variant, a pipe 66 is provided for connecting the mixer 2 with the duct 51 for venting the air and steam in the latter with valve 59 or equivalent means in line.

The plant 1 then comprises sensor means for the temperature and / or volumetric and / or weight flow rate of the ashes, which in the present example are arranged in correspondence with the terminal portion or the discharge of the conveyor 6 and / or on the main extractor 9 or more preferably at the discharge of the ashes at the conveyor 13. Advantageously, sensors of the aforesaid type are also provided at the hopper / tank 8.

Still in correspondence with said hopper 8, load cells or equivalent means can be provided for controlling the level of ash in the hopper / tank.

Furthermore, temperature sensor means may be provided arranged in correspondence with the duct 51.

The plant 1 comprises a control system, in communication with said sensor means, suitable for controlling the operating modes of the plant 1 in relation to the quantity and temperature of the ashes.

The operating modes of the plant 1, and in particular those of its cooling system controlled by the control means described above, will now be illustrated in greater detail.

First of all, the temperature and / or flow rate values of the ashes supplied by the sensor means are compared with predetermined values and stored by the control system, and on the basis of the result of this comparison the most suitable operating mode for the operation of the system is determined. plant 1. As regards the need to perform temperature and / or flow rate measurements, note that the temperature increase of the ash is usually linked to the increase in its flow rate in the system 1 considered here.

The system in the start-up phase is configured in the mode shown in Figure 4, by adjusting all the air inlet valves 10, 11, 17 and 19 and closing the automatic valve 150, so as to obtain that the entire the quantity of air corresponding to 1.5% of the combustion air is recalled through the bottom throat from the hopper 105 of the boiler 100, crossing the ash in counterflow both in the extractor 9 and in the conveyor 6.

This operating mode is followed until the temperature of the ash at the discharge of the conveyor 6 reaches the predetermined value Tminima,

In this operating mode, the control means act on the relative speed of the belt of the extractor 9 and of the belt of the conveyor 6, substantially causing the conveyor 6 to have a potential capacity of ash greater than the extractor 9 in order to avoid the formation of a head of material inside the hopper 8.

When the Tminim value is exceeded, the system acts on the speed of the conveyor 6, in particular by reducing it and adjusting it so as to determine an accumulation of ash in the hopper 8 and therefore the creation of a continuous ash plug and also opens the valve 150 of the duct 51 so as to create two different atmospheres respectively in the extractor 9 and in the conveyor 6, the first connected to the pressure existing in the boiler and the second connected to the pressure existing in the ambient air supply duct 51.

In this operating mode, the air inlet valves 10, 19 and 17 of the extractor 9 and of the hopper 8 are automatically adjusted in order to concentrate the entire 1.5% of the air in the extractor alone. cooling that can be introduced into the boiler and the valves 11 and eventually the nozzles 12 of the conveyor 6 by first adding air up to a percentage calculated so as not to affect the operation of the air / fumes exchanger downstream and then water if necessary to achieve the desired cooling. It should be noted in this regard that for the choice of the point of introduction of the cooling air, the fan 54 always processes the same quantity of air, as the cooling air increases through the duct 51 the air will decrease recalled by the environment.

In this configuration of separation of environments, the cooling air acting on the main extractor 9 introduced through the inlets 10, 17 and 19 crosses this extractor in counter-current and enters the combustion chamber 100 within the limit of 1.5 %. The 1.5% excess cooling air is taken from the outside through the inlets 11 and equivalent to 19 if present of the conveyor 6, and crosses the latter in co-current and is sucked through the duct 51, together with the steam produced by any local water cooling, by the depression generated by the air fan 54 and possibly by the support fan 56 positioned in line with the duct 51.

In this way, the maximum possible combustion of any unburnt products on the belt of the extractor 9 is obtained, returning the relative energy to the boiler and maximum cooling on the belt of the conveyor 6, reducing the intervention of cooling water to a minimum.

These operating modes are exemplified in Figure 1.

In the presence of the aforementioned ash head, the emptying of the loading hopper 8 is avoided by controlling the speed of the conveyor 6 according to the measurements of the maximum and minimum level sensors 7. In particular, if the level reaches the minimum level, the slowdown until the conveyor 6 stops, while when the minimum level is exceeded, the conveyor 6 is restarted and when the maximum level is reached, the speed and therefore the capacity of the conveyor belt 6 are increased.

In the configuration considered here, the control means can take advantage of further information detected by suitable sensor means, relating in particular to the temperature of the ash in the hopper 8 and to the speed of advancement of the conveyor 6. This last, combined with the value (fixed ) of the extraction section precisely defines the volumetric flow rate of ash. It is clarified that the level of extraction, in order to avoid possible hitches in the extraction section itself, must be greater than an appropriate margin of the size of the pieces of ash leaving the crusher 3.

Furthermore, in a further operating mode exemplified in Figure 6, plant 1 can also be managed in the case of very high ash flow rates / temperatures - even higher than the project values - depending for example on the type of fuel or cleaning operations of the combustion chamber 100. In this case, in which the temperature of the ash is supposed to be higher than the very high value, the plant 1 envisages an operating mode as the last described and the discharge of the still hot ash to the mixer 2 instead of to the conveyor 13 through the diverter valve 16. In the mixer 2 an additional quantity of water can be introduced such as to bring the ash to the expected final temperature (typically approximately 80 ° C) with an appropriate moisture content (preferably around 10% ) to guarantee the absence of dust in subsequent handling operations.

To avoid that the steam generated by this cooling in the mixer 2 rises towards the conveyor 6 (with the risk of generating condensate), an inverted `` Y '' connection can be provided directly between the conveyor 6, the mixer 2 and the duct 51 Thanks to this configuration, the air and possibly the steam arriving from the conveyor-cooler 6 goes towards the connection duct with the fumes line, joining the steam generated in the mixer 2. This connection duct (between the mixer 2 and the main duct 51), which can be suitably heated if the design conditions indicate the danger of condensation and related ash deposits.

It will be understood that said predetermined temperature and / or flow rate and predetermined combustion air quota values can be selectively set by an operator managing the plant 1.

It will also be understood that the operating modes described above constitute only one of the management possibilities of the plant 1. A simpler operating mode can, for example, provide that the ash head is created when a predetermined temperature value is reached, and that the management is performed for the rest by suitably modulating the flow of cooling air and water, the latter if necessary.

A series of operating modes such as those considered up to now can be set manually or automatically by means of a management and control system which, based on the temperature / flow rate of the ash, determines the cooling mode of the ash itself by acting on the formation of the ash. separation area, on the flow of air entering the extractor 9 and conveyor 6, on the possible dosage of nebulized water and on the activation of the diverter valve.

In general, it will be appreciated at this point that plant 1 has total operational versatility, and therefore the ability to handle practically any ash flow rate, and this without the problems associated with introducing an excessive amount of cooling air. from the bottom of the boiler 100. As mentioned above, this versatility is obtained by allowing the introduction of very high cooling air flow rates and by adding the additional air flow rate that it is not advisable to introduce from the bottom of the boiler into the ambient air to the air / fumes exchanger and through the possibility of adding cooling water if necessary.

As regards this last aspect, preferably the plant 1, through its control means, can adequately dose the quantity of water used in such a way that it vaporizes completely during the cooling process and that at the exit from the conveyor 6 therefore substantially dry ashes are obtained, suitable for being ground and transported pneumatically. This can be achieved by ensuring that the final ash temperature remains above 100 ° C. The flow rate of water to be nebulized and injected will be controlled by means of a thermal balance which on the one hand equals the heat to be removed from the ash (product of the flow rate for the specific enthalpy variation required between the temperature in the hopper 8 and the final discharge temperature ) and on the other the sum of the evaporation heat of the water and the enthalpy variation undergone by the cooling air.

It will also be appreciated that sending part of the cooling air into the ambient air inlet duct to the air / flue gas exchanger allows maximum recovery of heat associated with the cooling air, allowing to emphasize the efficiency advantages already associated with the dry extractors used here and described in the aforementioned patent EP 0471 055 B1.

It will also be appreciated that the presence of the ploughshare elements or means equivalent thereto, also in conjunction with the possibility of selective activation of the water cooling by means of the nozzles 12, allows the temperature of the ashes to be uniformed.

It will also be appreciated that the temperature sensors arranged in correspondence of the duct 51, in addition to allowing a more complete control of the system parameters, also allow to check the formation of any condensation points in correspondence with the entire duct 51 due to the resulting steam from the cooling water. In fact, knowing both the temperature of the air itself and the quantity of atomized water makes it easy to calculate the relative humidity of the cooling air and to verify that:

â ’on the one hand, the humidity itself is below 100% with an appropriate significant margin; And

â 'on the other hand, even in any cold points present in the path (and that is essentially on the conveyor cover 6 and on the surface of the connection duct 51) the water content in the air is not such as to generate condensation, which could be annoying for the proper functioning of the system.

To avoid any risk of condensation forming in the system, an additional connection duct (or an equivalent means) can be provided between the transition hopper 105 and the conveyor 6 near the hopper 8, selectively moving the inlet of the external air on this duct and providing valves for regulating the flow rate of both the hot air arriving from the transition hopper 105 and the cold ambient air. This allows the temperature of the air in the system to be raised to levels that eliminate the danger of condensation. The aforementioned adjustment of the inlet hot and cold air flow rates can therefore take place on the basis of the readings of the aforementioned temperature sensor positioned on the duct 51.

Finally, it will be understood that the aforementioned separation into two environments can also be obtained by means of devices other than those described above. For example, additional devices such as clapet valves or equivalent devices can be provided between the extractor 9 and the conveyor 6, again the separation of the two environments can be obtained by applying a second flow-rate crushing stage under the hopper / tank 8. variable with respect to the crusher 3, so as to generate in the hopper the necessary ash head suitable for separating the environments.

It will be appreciated that the invention allows an effective recovery of energy deriving from having sent the maximum external air flow on the extractor 9 and having drastically reduced the quantity of air on the second extractor 6 (for the addition of water ) and therefore the energy needed to treat the fumes.

The invention also relates to a method of extracting, cooling and recovering bottom ash energy as described up to now in relation to plant 1.

The present invention has been described heretofore with reference to preferred embodiments. It is to be understood that other embodiments may exist which refer to the same inventive core, all falling within the scope of the protection of the claims set out below.

Claims (41)

CLAIMS 1. Plant (1) for the extraction and cooling of bottom ash with recovery of thermal energy, of the type suitable for being used in association with a combustion chamber and in particular in an energy production plant for large flows of bottom ash deriving from example from solid fossil fuel, which extraction and cooling plant (1) includes: (a) means for extracting and transporting (9, 6) the bottom ash from the combustion chamber (100); (b) a cooling system (10, 11, 19, 17, 12) of the bottom ashes, arranged in correspondence with said extraction and transport means (9, 6) and able to determine a supply of cooling air in correspondence with the latter, the overall arrangement being such that at least part of said cooling air can be introduced into the combustion chamber (100) from the bottom thereof; (c) pressure isolation means (8), suitable for determining a separation of the atmospheres between a first (9) and a second (6) environment of said extraction and transport means (9, 6), said first environment (9) being connected to the atmosphere of the combustion chamber (100) and said second environment (6) being able to be connected with an air intake duct (50; 57) to an air / fumes exchanger (102) or to an inlet of air of the latter; (d) means for supplying (51) part of the cooling air in the air inlet duct (50; 57) to the air / flue gas exchanger (102) or in the inlet of the latter; (e) control means, suitable for determining the activation of said pressure isolation of environments as a function of the temperature and / or flow rate of the ashes. 2. Plant (1) according to claim 1, in which said cooling system (10, 11, 17, 19, 12) is of the mixed air-water type and in which said control means are adapted to determine the activation of water cooling according to the temperature and / or flow rate of the bottom ash. 3. Plant (1) according to any one of the preceding claims, in which the overall arrangement is such that, in said condition of pressure separation of environments (9, 6), said cooling system (10, 11, 17, 19, 12) is adapted to cause a supply of cooling air in counter-current with the flow of bottom ashes in said first environment (9) and in co-current with said flow in said second environment (6). Plant (1) according to any one of the preceding claims, in which said control means comprise temperature and / or flow rate sensors of the bottom ashes, arranged in correspondence with said extraction and transport means (9, 6, 13) and / or in correspondence with the pressure isolation zone (8). Plant (1) according to the preceding claim, wherein said bottom ash temperature and / or flow rate sensors are arranged in correspondence with an end portion of said extraction and transport means (6, 13). Plant (1) according to the preceding claim, in which said temperature and / or flow rate sensors are arranged in correspondence with the bottom ash discharge. System (1) according to any one of the preceding claims, in which said control means comprise load sensors, arranged in correspondence with the pressure isolation zone (8). 8. Plant (1) according to any one of the preceding claims, wherein said control means are adapted to determine said separation of environments (9, 6) in such a way that the quantity of cooling air entering the combustion chamber (100 ) from the bottom does not exceed a predetermined amount of total combustion air, preferably approximately 1.0-1.5%. Plant (1) according to any one of the preceding claims, in which said supply means (51) are adapted to connect the air inlet duct (50; 57) with said second environment (6), substantially downstream of the process cooling. 10. Plant (1) according to any one of the preceding claims, in which said supply means (51) open into the air inlet duct (50; 57) upstream of a fan to increase the air head (54, 58). System (1) according to the preceding claim, wherein said supply means (51) open into the air inlet duct (50) upstream of a secondary air fan (54). Plant (1) according to any one of the preceding claims, comprising means (150) for adjusting the flow rate of air introduced into the air inlet duct (50; 57) by said adduction means (51), arranged in correspondence with these last. 13. Plant (1) according to any one of the preceding claims, in which said pressure isolation means comprise means for disabling / enabling (150) of said supply means (51), controlled by said control means to determine if necessary called separation of environments (9, 6). Plant (1) according to any one of the preceding claims, in which said control means comprise one or more temperature sensors arranged in correspondence with said supply means (51). Plant (1) according to any one of the preceding claims, wherein said extraction and transport means comprise a first extraction unit (9) arranged or adapted to be disposed immediately downstream of the combustion chamber (100) and a second unit transport (6) arranged downstream of said first unit (9), and in which said pressure isolation means (8) are adapted to produce a pressure separation between said first (9) and second (6) extraction and transport units . Plant (1) according to claim 14 or 15, in which said control means are adapted to control the speed of at least one of said extraction and transport units (9, 6). Plant (1) according to any one of the preceding claims, wherein said pressure isolation means (8) comprise means able to create a bottom ash head between said two environments (9, 6), able to determine said pressure separation. Plant (1) according to the preceding claim, wherein said pressure isolation means comprise a tank-buffer means (8) adapted to receive the bottom ashes which create said head. Plant (1) according to the preceding claim, in which said pressure isolation means comprise a hopper (8) adapted to receive the bottom ashes which create said head. System (1) according to any one of claims 17 to 19, wherein said control means comprise one or more level sensors (7) arranged in correspondence of said leaf. 21. Plant (1) according to any one of the preceding claims, comprising means (2) for mixing the bottom ashes, arranged in correspondence with the discharge thereof and suitable for completing the cooling process, and means for sending cooling air and the Possible steam from said mixing means (2) to said adduction means (51). 22. Method of extracting and cooling bottom ash from a combustion chamber, in particular for large flow rates of bottom ash deriving for example from fossil fuel in an energy production plant, which method comprises the steps of: (a) extract the bottom ash from the combustion chamber (100, 105); (b) cooling such bottom ash along an extraction and transport path (9, 6, 13) by supplying cooling air along the latter, introducing, downstream of the cooling process, at least part of said air in the combustion chamber (100, 105) from the bottom of it; (c) depending on the temperature and / or flow rate of the bottom ash, selectively activate a pressure isolation between a first (9) and a second (6) environment arranged along said extraction and transport path, said first environment (9) being arranged immediately downstream of the combustion chamber (100, 105) and said second environment (6) being arranged downstream of said first environment (6) and able to be connected to an air intake duct (50; 57) in an exchanger air / fumes (102) or to an air inlet of the latter; (d) depending on the temperature and / or flow rate of the bottom ash, feed part of the cooling air into the air inlet duct (50; 57) into the air / flue gas exchanger (102) or into the inlet of the latter. 23. Method according to the preceding claim, in which said cooling phase (b) is of the mixed air-water type and provides for the activation of water cooling as a function of the temperature and / or flow rate of the bottom ash. Method according to claim 22 or 23, wherein said step (b) provides for an activation of the water cooling in correspondence with said second environment (6). Method according to any one of claims from 22 to 24, in which said cooling phase (b) provides, in said condition of pressure separation of environments (9, 6), a supply of cooling air in countercurrent with the flow of bottom ash in said first environment (9) and in co-current with said flow in said second environment (6). Method according to any one of claims 22 to 25, which provides for the detection of the temperature and / or flow rate of the bottom ashes performed in correspondence with said extraction and transport path (9, 6, 13) and / or in correspondence with the zone pressure isolation (8). 27. Method according to the preceding claim, wherein said detection of temperature and / or flow rate of the bottom ashes is carried out in correspondence with a terminal section of said extraction and transport path (6, 13). Method according to the preceding claim, wherein said temperature and / or flow rate detection is performed at the bottom ash discharge. 29. Method according to any one of claims 22 to 28, which provides for a load detection, performed in correspondence with the pressure isolation zone (8). Method according to any one of claims 22 to 29, wherein said step (c) provides that said separation of environments (9, 6) is carried out in such a way that the quantity of cooling air entering the combustion chamber ( 100) from the bottom does not exceed a predetermined portion of the total combustion air, preferably equal to approximately 1.0-1.5%. Method according to any one of claims 22 to 30, wherein said adduction into the air inlet duct (50) in the air / fumes exchanger (102) takes place starting from said second environment (6), substantially downstream of the process cooling. 32. Method according to any one of claims 22 to 31, wherein said adduction into the air inlet duct (50; 57) in the air / fumes exchanger (102) provides an outlet in said duct (50; 57) upstream of a fan to increase the air head (54, 58). 33. Method according to the preceding claim, wherein said supply into the air inlet duct (50) in the air / fumes exchanger (102) provides an outlet in said duct (50) upstream of a secondary air fan (54). 34. Method according to any one of claims from 22 to 33, which provides for an adjustment of the flow rate of air fed into the air inlet duct (50; 57) in the air / fumes exchanger (102) or in the air inlet of this € ™ last. Method according to any one of claims from 22 to 34, in which said step (c) provides that said pressure insulation is obtained through the interdiction / enabling of said supply of cooling air in the air inlet duct (50; 57) in the air / fumes exchanger (102) or in the air inlet of the latter. Method according to any one of claims from 22 to 35, which provides for a temperature detection performed at means (51) suitable for carrying out said supply in the air inlet duct (50; 57) in the air / fumes exchanger (102 ) or in the air inlet of the latter. Method according to any one of claims 22 to 36, wherein said extraction and transport path comprises a first extraction portion (9) disposed immediately downstream of the combustion chamber (100) and a second transport portion (6) arranged downstream of said first portion (9) and in which said step (c) provides that said pressure insulation is obtained between said first (9) and second (6) extraction and transport portion. 38. Method according to claim 36 or 37, in which said step (c) provides for the control of the speed of extraction and / or transport of the ashes along said path. 39. Method according to any one of claims 22 to 38, in which said step (c) provides for the creation of a bottom ash head between said two rooms (9, 6), suitable for determining said pressure separation. 40. Method according to the preceding claim, in which said step (c) provides for the detection of the level of said leaf. 41. Method according to any one of claims from 22 to 40, which provides for a mixing of the bottom ashes, carried out in correspondence with the discharge of these and able to complete the cooling process, and an adduction of the cooling air and the any steam used or produced by said mixing in said air inlet duct (50; 57).