ES2213327T3 - APPLIANCE TO HELP COMPLETE THE COMBUSTION OR POSCOMBUSTION OF AN INCOMBUSED MATTER. - Google Patents

Abstract

An apparatus and method to promote the completion of the combustion of unburnt matter contained in ash arising from the combustion of solid fuel are described. The apparatus for the postcombustion of ash arising from the combustion of solid fuel comprises a combustion chamber (14) and an extractor (16) arranged so as to receive ash falling from the combustion chamber, the unburnt matter of said ash having to be burnt, said extractor comprising in turn a metallic belt (18) for ash transportation, said apparatus being characterized in that said conveyor belt is provided with parts or openings for the passage of combustion feeding air, said air thus passing through said ash during at least a part of the forward advancing stretch of said belt. <IMAGE>

Description

Apparatus to help complete combustion or Afterburning of an incombustous matter.

Field and background of the invention

The present invention relates to an apparatus and procedure to help complete combustion or post combustion of an incombust matter that is still in heavy ash from the combustion of solid fuel of any kind in combustion chambers for pulverized fuel, when said Ash falls from the combustion chamber. The present invention produces greater advantages the higher the content of incombust matter in the ash

The present invention can be considered as an improvement of the invention described in the EP-0 252 967 B1, and is applicable in those cases in which the content of incombust matter is high and / or the degree of afterburner that can be obtained with the apparatus described in said prior art document it is not satisfactory.

The apparatus described in said document, vindicates the increase in efficiency achieved by reducing the matter incombusta to heavy ash due to the introduction, to through adequate openings, of air moving to countercurrent against the flow of ash and that helps it perform combustion due to the consequent oxidizing environment.

This result was verified experimentally in many applications of said prior invention, for example in traditional boilers that use coal dust often, to replace wet extraction systems such as the so-called submerged hopper, and produced a reduction of the incombust matter of  approximately three quarters of the amount conventional. However, the reduction in other cases was not so significant, such as in an application to extract ash from a boiler that used lignite, where the reduction of the incombustant ash was between 10% and 20% approximately.

The reasons for this different behavior are mainly due to two interrelated factors: the ash reactivity (or afterburning speed) and the temperature drop In fact, in the case of lignite and Normally low quality fuel, calorific value and high ash content make the ash that comes out of the chamber of combustion experience a temperature drop.

EP 0471055 B1 (corresponding to the WO-A-91/13293) describes a system to discharge lower ash from boilers that produce steam, in where the conveyor belt is partially sealed to prevent ashes from falling through the tape and air is introduced countercurrent in the system, only at the upper end of the ash discharge extractor and the aftercooler, which circulates above the ashes.

The document WO-A-96/29546 does not describe a camera afterburner that is part of a combustion chamber. The ash combustion takes place in the chamber where the air is blows over and not through the ashes.

Brief Description of the Invention

In view of the above drawbacks, the main object of the present invention is to provide a apparatus and a procedure that solve these problems to allow:

one.

Keep the ash that conveys the conveyor belt the necessary time to a temperature that allows a significant reduction of matter fire that is still in the ash.

two.

Carry out subsequently cooling said ash to discharge it of the system at a temperature compatible with the systems of Normal transport, in the storage tank.

Brief description of the drawings

The aforementioned objects and others are they get brilliantly with the apparatus described in the independent claim 1 and with the method to be described in independent claim 12. Other advantageous features of the apparatus and the procedure are indicated in the corresponding dependent claims. TO Below is a detailed description of the device and the procedure according to the present invention, given as an example in correspondence with the attached drawings, in which:

Figure 1 is a schematic overview of an embodiment of the apparatus.

Figure 2 is a schematic partial view of a possible embodiment of an ash measuring device.

Figure 3 is a sectional view of the afterburner arranged under the combustion chamber.

Figure 4 is a top plan view part of a known conveyor belt system of plates.

Figure 5 is a schematic detail of the air inlet openings.

Figure 6 shows schematically how the Ash thickness limits lateral penetrations through the areas that are above and below the tape.

Figure 7 shows the area of afterburning

Figure 8 is a partial schematic view of the ash discharge zone.

Figure 9 and last, is a schematic of the air circulation in the final extraction part.

Detailed description of the invention

In the figures, the same reference numbers indicate the same or equivalent elements from the point of view functional.

Figure 1 shows, schematically, a embodiment of the apparatus 10 according to the present invention that understands:

to)

a tight seal 12 between the boiler 14 and the extractor 16, said joint expanding Airtight down due to thermal expansion. Said board Airtight can be mechanical (as shown in Figure 1) or hydraulics. As said seal is known, it is not described. in detail; it is enough to say prevents air from entering inconvenience between the boiler and the belt post combustion;

b)

the extractor 16, comprising a metal tape 18 that travels so continues and allows the afterburning of ash 34. Throughout the trajectory of the extraction belt 18, can be recognized two zones with different functions: a first hot zone of post-combustion A and a second cold cooling zone B;

c)

a system 22 of recovery of fine material that is deposited at the bottom of the container 24 in which the extraction belt 18 is placed. Said system 22 is formed by a chain 26 provided with sheets scrapers 28 to collect the fine material and transport it to the ash discharge point C;

d)

a breaker 30 ready to crush possible pieces of ash formed in the combustion chamber or in said post combustion belt; Y

and)

a refrigerator of final ash 32 that performs the final cooling up to a temperature compatible with current transport systems down.

The post-combustion belt 18 is located directly below the combustion chamber 14 and receives the ash 34 that falls continuously from said combustion chamber. The tape moves at a speed with which you can get the optimal combination of ash layer thickness and time of ash stay on the tape as a function of quantity of ash produced. In fact, although on the one hand an increase in Ashes stay time causes an increase in after combustion, on the other hand it produces an increase in the thickness of the ash layer on the tape, which reduces air diffusion necessary for combustion within the ash layer. The regulation of the optimal combination can only be performed time, when the operating conditions are so stable that they allow it, or more frequently in a continuous way by means of a continuous measurement of the actual thickness of ash 34 that is in the tape 18, for example with a device 36 shown in the Figure 2. Said measuring device 36 comprises a sheet 38 shaped so as not to hinder the advance of ash 34, hinged at the top of the container 24. Of the value of the angle α formed by said sheet located on the bed of ash, the thickness of said bed can be deduced. Said sheet 38 has also another function of great relevance in the procedure of the invention, function described below.

The post-combustion zone A extends exceeding the tape when stretched below the boiler, to also offer a suitable stay time to the ash that has been deposited on the tape near the exit. The extension of the afterburner area outside the boiler is determines for each individual plant as a function of the general configuration of the boiler area and the degree of desired afterburner. As explained before, it is essential keep the temperature at high values although in harmony with the need to safeguard the mechanical characteristics of components involved in the high temperature zone, namely the tape and support rollers. For this purpose, as shown in Figure 3, the side walls 40 of the post-combustion zone A, in addition to the cover of said area at the exit of the chamber of combustion, they are thermally insulated.

This setting allows scattering to be limited. thermal sideways and up, although not enough to achieve the desired thermal performance. With respect to this is of fundamental importance the amount of air that is Enter into the system. That amount must obviously be enough to ensure a good oxidizing environment, far superior to stoichiometric amount, although at the same time limited to do not overcool the important area as it is known that air enters the afterburner at a temperature considerably less than desired in this area. Also I know you must enter the correct amount of post-combustion air into the post-combustion zone so that air diffusion is stimulated from below into the ash layer. This can be achieve by making air inlet openings 42 (figure 5) between the plates 44, without modifying the geometry of the conveyor belt of plates shown in figure 4.

The air inlet openings 42 must have a limited size in the direction of advance of the belt for limit ash fall through such openings. Whether maintains a positive differential pressure between the area that is below the tape and the area above the tape, the  air is forced to pass through the aforementioned openings of entry. To obtain said positive differential pressure, having note that combustion chambers work normally with little empty, it is necessary to seal the area as much as possible located above the tape. Thus, the area above of the tape will be with said vacuum level of the chamber of combustion, while the area below the belt It will be at a pressure close to atmospheric pressure. For this one Finally, the thickness of the ash layer 34 will limit the lateral penetrations through the area below the tape 18 and the area above tape 18 for all the length of said tape.

The afterburner zone A can be divided, during the advance of the belt, as follows (see figure 7):

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starting area A1: In this area, a slope 46 transports ash 34 to belt 18. The purpose of the slope is to restrict as much as possible the position of the tape in which the ash layer is not significant. Between the slope 46 and the tape 18 it is possible placing a fixed pad 48 on said slope 46 to limit the inevitable reentry of air between the motionless slope and the mobile tape plates. In this area, the lateral penetration of air in the afterburner zone (air that does not come into contact intimate with ash) should be limited by fixed pads in the transition duct. The geometry of the slope must be suitable to optimize the distribution of ash through the belt. By example, if ash tends to accumulate in the central part of the tape, the slope can be formed to increase the distribution of ash on the sides of the tape or vice versa. In addition, a 50 dike is located in the area under the tape, to create a loss of load in the air duct and limit the penetration of air through the tape grooves of this area.

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an intermediate area A2: in this area, the ash layer, even if there is no achieved the maximum height, has already obtained a thickness that forces the post-combustion air 52 to pass through the ash to be attracted by the vacuum that exists in the combustion chamber. Therefore, in this area, the differential pressure between the area of external and internal afterburning is greater than in the first area, even if it has not reached its maximum value. If it's necessary, an additional air shield can be inserted.

-

and a final area A3: this area is that located outside the combustion chamber and the Ash layer thickness is constant at maximum value. The differential pressure between the external area that is below the tape and the afterburner area is at the maximum level and is approximately equal to the difference between atmospheric pressure and the vacuum in the combustion chamber. The final area A3 ends on the aforementioned sheet 38, which also has the task of prevent the direct passage of air from the cooling zone to the post-combustion zone to force air to pass from below to through the ash layer and at the same time allows the ash leave the afterburner zone.

Both in the intermediate zone and in the zone final, if the amount of air required for combustion exceeds the limits and crosses the ash pushed by the pressure differential, it is advisable to provide additional input to through some side channels 70 shown in the figure 6.

At the exit of the combustion zone, the air cold that has been introduced into the device through an opening adequate crashes into the ash to begin the process of refrigeration. Said cooling process is completed when unload the tape material in the free atmosphere, in the area in which it falls towards the first crusher 30 as well as in the subsequent contact with heat exchanger 32. In this last device, the hot ash is cooled by the contact with cold air and with metal plates 54 that are at your once hit by rising cold air; these plates can be provided with lower nerves (not shown) to increase the thermal exchange with the air and keep its temperature in minimum values

The air rising from the refrigerator to the afterburner, forming all or part of the air of combustion, is taken to the area where ash is discharged from the tape through a conduit of adequate size to minimize The loss of load. This duct is shown in Figure 8.

Finally, figure 9 shows the scheme of air circulation in the final part of the extractor, and should appreciate that the air is guided to the side channels and below of the ribbon, from where it passes later through the ash layer and above it, as described later, due to the vacuum that exists in the combustion chamber.

In this scheme, you can see the following elements: a cold air inlet 56 through the opening of the end of the afterburner zone; an air inlet 58 from the final refrigerator 32, a drum 60 that drives the belt; bliss tape 18; the ash layer 34 on the tape; the channels or grooves sides 62 in which the air is forced to move and enter again in the combustion chamber attracted by the vacuum; and the lower channel 64 which has the dual function of diverting the possible ash particle fall on the sides of the container extractor, to avoid this fall in the return interval of the tape and the consequent erosion, and form together with the channels  lateral a duct that distributes hot air below the tape for the subsequent passage through the grooves of the plates.

In this air circulation scheme, you can also note that in the cooling zone there will be a pressure positive differential, even if it is minimal, between the area that is above the bed of ash and the one below the tape in the cooling zone. This fact prevents the passage of air through this area from below through the bed of ash, avoiding so continue combustion.

A variant of the situation may occur which has been illustrated, in the case where the air that passes through the Ash layer is insufficient to obtain good combustion. In this case, positive pressure air from an air heater, that is, at a temperature suitable for Good combustion Said air is transported below the layer of ash, where it is forced to pass through the layer of ash being confined in it, between the lower channel (which should be placed as close as possible to the container) and two vertical membranes between the channel and the tape, one at the beginning and the others at the end of the afterburner zone, to limit the air leak.

With such configuration, the air that comes from the final refrigerator is absorbed without hindrance from the vacuum of the combustion chamber, and for this purpose, the sheet of figure 2 must be modified to maintain its function of measuring the level of ash on the tape, but not the function of forming a separation between the two environments of the afterburner zone and the zone of refrigeration.

Although the invention has been described in a very detailed, it is clear to anyone versed in the field, that in the invention many modifications can be made, variations and substitutions of elements for other equivalents from the point of functional view, without moving away, however, from its field of protection as defined in the appended claims.

Claims (21)

1. Combustion chamber (14) with an apparatus (10) for the afterburning of ash (34) from the combustion of solid fuels, comprising a vacuum combustion chamber (14) and an extractor (16) arranged to receive of said combustion chamber (14) the falling ash, whose incombust matter must be burned, said extractor (16) comprising in turn a metallic ash conveyor belt (18), characterized in that said conveyor belt (18) is provided with openings or grooves (42) for the passage of the post-combustion air (52), said post-combustion air passing through the ash (34) for at least a part of the advancing section of the belt (18). 2. Apparatus according to claim 1, characterized in that means are provided in at least a portion of said belt advance section, to realize a negative differential pressure between the area above the belt and that below the belt. headband. 3. Apparatus according to any of the previous embodiments, characterized in that it further comprises an air heater (62, 64) for creating positive pressure air, said air being transported below the belt and forced to pass through the ash. 4. Apparatus according to any of the previous embodiments, characterized in that it also comprises lateral channels (70) to which the complementary post-combustion feed or ash combustion air is guided, in addition to the air under the belt, passing then said additional air above the ash bed due to the vacuum that exists in the combustion chamber
(14). 5. Apparatus according to any of the previous embodiments, characterized in that said extractor (16) comprises a post-combustion zone (A) and an ash cooling zone (B), said zones being preferably divided by means of separation such as movable sheets ( 38). 6. Apparatus according to any of the previous embodiments, characterized in that the angle of rotation or rotation (α) of the sheet (38) that is located on the ash bed is related to the thickness of the ash bed (34) located above the tape (18). 7. Apparatus according to any of the previous embodiments, characterized in that it further comprises cold air inlet means (56) at the end of the afterburner zone (A), or at the beginning of the cooling zone (B) and inlet means of air (58) from a final refrigerator (32), creating the air thus introduced into the cooling zone (B) a positive differential pressure that prevents air from passing through the ash bed (34) that is in the passage double the belt (18), thus stopping the compression
bustion 8. Apparatus according to any of the previous embodiments, characterized in that it further comprises means (22) for recovering fine ash that has fallen from the belt (18), said recovery means comprising a chain (26) provided with scraper blades (28) or the like, said sheets (28) being arranged under the tape (18). 9. Apparatus according to any of the previous embodiments, characterized in that it comprises distribution means (46) adapted to effect a uniform distribution of ash through the belt (18). 10. Apparatus according to any of the previous embodiments, characterized in that the space between said distribution means (46) and said conveyor belt (18) has been sealed with flexible means such as pads. 11. Apparatus according to any of the previous embodiments, characterized in that it further comprises crushing means (30) for grinding any possible piece of ash. 12. Procedure for carrying out post-combustion of heavy ash with a high content of incombustible material, from the combustion chamber (14), which comprises the phases of: depositing said ash on the conveyor belt (18) of an extractor (16 ); providing on the forward path of said belt a post-combustion zone of ash (A) and a cooling zone of ash (B); and take at least a part of the air used to cool the ash, characterized by the phases of causing at least a part of the air taken from the cooling zone (B) to pass said ash that is in the post-combustion zone (A) to through openings or grooves (42) in said belt (18), and drag the post-combustion air (52) to the combustion chamber
(14). 13. Method according to claim 12, characterized in that there is a negative differential pressure between the area above the belt and the area below the tape. 14. Method according to claim 12 or 13, characterized in that it further comprises the phase that consists in limiting the lateral penetrations of the air through the area below the belt and the area above the tape (18) by means of the thickness of the ash bed (34). 15. Method according to any of claims 12 to 14, characterized in that the belt (18) moves at a speed that is related to the thickness of the ash bed (34). 16. Method according to any of claims 12 to 15, characterized in that said post-combustion air comes from a refrigerator
(32) 17. Method according to any of claims 12 to 16, characterized in that said post-combustion air is positive pressure air that comes from a heater. 18. Method according to any of claims 12 to 17, characterized in that the phase of causing the air to pass through said bed of ash (34) is carried out by transporting the air below the belt (18) and through side channels ( 62). 19. Method according to any of claims 12 to 18, characterized in that the phase consists of transporting the ash from the combustion chamber (14) to the belt (18) by means of distribution means (46) to distribute evenly the Ash by the tape. 20. Method according to claim 19, characterized in that it comprises the phase consisting in sealing the area between said distribution means (46) and the plates (44) by means of a pad (48). 21. Method according to any of claims 12 to 19, characterized in that it provides a separation (38) between the afterburner zone (A) and the cooling zone (B).