EA014862B1 - Cooling system for the dry extraction of heavy ashes from boilers - Google Patents

Abstract

The present invention relates to an additional cooling system (1) for the dry extraction of large flow of heavy ashes produced by boilers (100) with solid fuel apt to decrease the temperature of the ashes. The system comprises an extractor with metallic belt (2) gathering the ash which deposits onto the bottom of the boiler (100), a crushing system (3), having the purpose of increasing the thermal exchange surface of the material, one or more metallic conveyors (4, 6) having the cooling function by introducing countercurrent air - flow running through transported ashes, an in-line cooling device (5) having the function of putting into contact the ash several times with additional countercurrent air in order to increase the possible exchange without necessarily increasing the air - flow entering the combustion chamber. Such additional air can be sent preferably upstream of the air heater or in atmosphere upon fines' captation (figure 1).

Description

The present invention relates to a plant and method for dry removal and cooling of combustion residues coming from a combustion chamber, in particular large quantities of dense ash resulting from the combustion of fossil fuels used in power plants designed to generate energy.

State of the art

The constant increase in demand for solid fossil fuels for generating electricity leads to more frequent burning of coal and lignites with a high ash content. The combustion of the latter in high-power boilers results in a large amount of dense ash collected in the lower part of the boiler itself, the amount of which can reach values close to 100 t / h. Dry cooling of such quantities requires a large volume of cooling air, two or even three times more than for conventional fossil fuels.

As presented in EP 0471055 B1, in some known ash removal and dry cooling systems, cooling air after heating as a result of heat exchange from the latter is fed to the lower part of the boiler. Therefore, firstly, the greater the amount of ash obtained, the greater the potential heat recovery provided in the boiler using cooling air as described above.

However, to prevent a negative effect on the combustion efficiency and / or the efficiency of the boiler, due to the air supplied to the combustion chamber from the bottom, and not from the furnaces or special air inlets, and / or to eliminate a similar undesirable effect with the production of oxides nitrogen (ΝΟ _Χ ), some boiler designers prefer to limit this amount to a maximum value of 1.0-1.5% of all air supplied to the combustion chamber.

Thus, as was presented above, in the known cooling systems there is no successful implementation of an effective and efficient method of dry cooling or mainly dry cooling of dense ash during the removal of the last and corresponding cooling air, especially in the case when such ash is supplied in large quantities and with high temperature. In particular, even when the problem of such cooling has been successfully solved, this solution is achieved as a result of a significant complication of the installation, followed by very significant costs for implementation and operation.

In addition, the technical problem underlying and solved by the present invention is to provide a system and method for dry removal and cooling of combustion residues coming from a solid fuel combustion chamber, which can eliminate the disadvantages described above with reference to the prior art .

SUMMARY OF THE INVENTION

The problem described above is solved using the system according to claim 1 and using the method according to claim 28. Preferred features of the present invention are presented in the paragraphs dependent on them. The present invention provides some important advantages that will be fully understood after the detailed description below. The main advantage is that in the case of coals with a high ash content, adequate and effective dry cooling of the ash itself is possible without exceeding the above-described limit of 1.0-1.5% of the cooling air supplied to the combustion chamber from below. This advantage, in particular, is especially important in the case of the use of coals with a high dense ash content mentioned above. This is mainly achieved by providing a dry gravity-type air / ash heat exchanger and supplying only a controlled amount of cooling air to the combustion chamber from the bottom, while excess air coming from such a gravity heat exchanger can be released into the atmosphere after specialized filtration, performed in a boiler smoke filtration system, or preferably it is supplied in front of the combustion air heater on the side of the smoke, thereby restoring instantly most of the energy transferred by the ash into the air.

To guarantee the efficiency of heat recovery under all conditions for any amount and temperature of the ash, the amount of cooling air supplied to the system can be adjusted based on a combination of the required amount of ash and / or temperature.

After a detailed description of the preferred embodiments presented below, the present invention mainly relates to an additional cooling system for dry removal of heavy ash obtained in solid fuel boilers, which allows to reduce the temperature of the ash. The system basically comprises a sequentially installed extractor with a metal strip collecting ash deposited in the lower part of the boiler of the type described in the already mentioned patent EP 0471055 B1, and known under the trade name MAS;

crushing system designed to increase the area of thermal exchange of ash;

one or more metal conveyors installed in line with the said extractor, performing the function of transportation and cooling by supplying air in countercurrent; and

- 1 014862 a cooling device installed in a line that performs the function of repeatedly placing ash in contact with additional air in countercurrent to increase possible heat transfer without having to increase the amount of air entering the combustion chamber (as mentioned above), such additional air is then preferably supplied before air heater or released into the atmosphere after the confinement of small particles.

Brief Description of the Drawings

Other advantages, properties, and modes of application of the present invention will be apparent from the following detailed description of the invention in certain preferred embodiments, presented by way of example, and not limitation. In this case, a deal will be made for the attached drawings, in which in FIG. 1 is a general arrangement showing an example of a first embodiment or preferred mode of operation of a system in accordance with the invention, for supplying cooling air from a gravity air / ash heat exchanger to a chimney connected to a combustion chamber in front of an air heater;

in FIG. 2 is a general arrangement showing an example of a second embodiment or preferred mode of operation of a system in accordance with the invention, providing for the movement of air coming from a gravity air / ash heat exchanger using an auxiliary fan and discharged into the atmosphere;

in FIG. 3 is a general layout showing an example of a third embodiment or preferred mode of operation of a system according to the invention, supplying cooling air from a gravity air / ash heat exchanger to a chimney connected to a combustion chamber in front of a dust removal system; and in FIG. 4a and 4b - gravity air / ash heat exchanger in accordance with the previous drawings, equipped with an air dosing system, which shows its side view and front view, respectively.

Information confirming the possibility of carrying out the invention

First, consider FIG. 1, which shows a system for the removal and cooling of combustion residues of this type, which is used, for example, in thermal power plants operating on solid fossil fuels, and in accordance with the first preferred embodiment of the invention, which is generally indicated by the reference numeral 1. As will be better understood from of the following description, system 1 is particularly suitable for treating a large dense ash stream obtained, for example, from the combustion of coal or lignites with a high ash content.

For better clarity of illustration, the various components of the system 1 will be described below with reference to the path that remains of the combustion from the place of their removal from the lower part of the combustion chamber (or boiler), which is indicated by the reference numeral 100, to the place of their disposal.

Directly after the combustion chamber 100 or better after its transition hopper 105, a first removal and / or conveying module is provided in the system 1, in particular a dry extractor 2, mainly made of steel with high resistance to heat. Such an extractor 2 is an extractor of a known type and is described, for example, in EP 0252967, which is incorporated herein by reference. The extractor 2 collects dense ash, which settles down in the combustion chamber 100, through the transition hopper 105 mentioned above.

On the side walls of the own casing of the extractor 2, there are many inlets for supplying external cooling air, distributed essentially regularly along the body of the extractor 2 itself, and each of which is indicated by a reference numeral 13. Such inlets 13 are preferably equipped with means for regulating the flow of cooling air, for example, one or more shut-off valves, which also make it possible to completely close one or more selected inlets.

Cooling air is sucked through the inlet 13 into the extractor 2 and is supplied in countercurrent relative to the transport of ash under the influence of the vacuum present in the combustion chamber 100. In more detail, air is supplied due to the vacuum present in the transition hopper 105, in the lower part of which the vacuum is controlled by the control system of the combustion chamber 100 (usually about 300-500 Pa below atmospheric pressure). Such cooling air entering the extractor 2 then enters the boiler 100 from its lower part.

After the extractor 2, the ash is fed to a grinder or grinder 3, which grinds its largest fractions to increase the heat transfer surface and thereby improve the potential of such heat transfer and improve the cooling process.

After the crusher 3, the ash is transferred to the second removal and / or conveying module, in particular to the cooler conveyor 4 in the form of a steel tape.

On the conveyor 4, the cooling of the ash is continued with the help of air, which is re-sucked externally in countercurrent through the inlets 13 located on the side walls of the conveyor 4 itself, similar to that described above with respect to the first extractor 2. In practice, the air also re-sucked by the above vacuum,

- 2 014862 present in the combustion chamber 100, and also in such inlet openings, flow control means of a type already described can be installed.

In addition, cooling air entering such a second conveyor 4 enters the boiler in its lower part.

A channel for supplying cooling air, indicated by reference numeral 42, may be provided between the conveyor 4 and the extractor 2 to bypass the crusher 3.

It should be understood that the system 1 is equipped with a dry cooling system embodied, inter alia, in the form of air inlets 13.

After the second conveyor 4, such a cooling system comprises a dry gravity air / ash heat exchanger, preferably of the plate type 19, indicated generally by the reference numeral 5, as shown in more detail in FIG. 4a and 4b. The plates 19 are preferably made of wear resistant metal.

Directly in front of the heat exchanger 5, an additional crusher 10 can be provided in the system 1, which can be selectively activated if necessary.

Immediately after the gravitational heat exchanger 5, an additional inlet 17 for cooling air is also provided with a means for regulating the flow of cooling air of the type described above installed therein.

After the heat exchanger 5, a third extraction and / or transportation module is additionally provided in the system 1, in particular a third conveyor 6, ending with a hopper 11 for unloading the ash, for its removal and / or possible reuse.

At the inlet section of the hopper 11, an additional air inlet 14 is provided, in which a means for regulating the flow of cooling air of the type already described above is also equipped.

The additional air entering through the inlet openings 17 and 14 crosses in countercurrent a gravitational heat exchanger 5 and, given the air supplied through the inlet 14, also flows through the third conveyor 6.

In such a gravitational heat exchanger 5, the ash, crushed by the crusher 3 and, if necessary, the crusher 10, mixes well with the air supplied in countercurrent through the inlets 14 and 17, as it falls from plate to plate, thereby increasing heat exchange and thereby increasing the amount of heat transferred from the ash to the air. The greater the number of drops and the weight ratio of air / ash and the smaller the granulometry of the ash, the better the heat transfer and, therefore, the better the degree of cooling is achieved.

The system 1 then contains means for determining the temperature and / or volumetric and / or weight flow of ash, which in this example is placed on the final section or on the discharge section of the conveyor 4 and / or the main extractor 2, or more preferably when the ash is unloaded from the conveyor 6.

System 1 further comprises control means in communication with said sensor means and adapted to control the cooling system mentioned above, as well as removal and / or transport modules 2, 4 and 6.

The system 1 then includes a supply means configured to supply part of the cooling air (and, in particular, additional air supplied through the inlet openings 17 and 14 and which crosses the heat exchanger 5) after the ash cooling process, into the atmosphere or into the chimney 101 connected to combustion chamber 100.

In particular, the additional air mentioned necessary for cooling the ash in the air / ash gravity heat exchanger 5 and supplied through the additional inlet openings 14 and 17 can follow three different paths depending on the specific embodiment or structural configuration under consideration.

In the case considered here, with reference to FIG. 1, the cooling air supplied through the additional inlet openings 14 and 17 is re-sucked after it crosses the counter-heat exchanger 5 in countercurrent using a vacuum in the chimney 101 in front of the heat exchanger 102 connected to the boiler 100. Such a heat exchanger 102, usually present in known systems, is used for preliminary heating air used for combustion. Mentioned cooling air heated by the chamber is then fed into such a heat exchanger 102 (on the smoke side) and used to preheat the air to burn the boiler.

In the present example, said supply means further comprises a channel 20 connecting the inlet of the heat exchanger 5 to the chimney 101. Such a channel 20 must be selectively adjusted and, however, be able to be closed / opened by an automatic valve 15 (or equivalent means) installed along its body.

Channel 20 then connects or is configured to connect the heat exchanger 5 with the economizer region of the combustion system, also operating under negative pressure, relative to one of the heat exchangers 5.

Preferably, to avoid transporting excessive amounts of fine particles,

- 3 014862 directly after the gravitational heat exchanger 5, air / ash, air is passed through a cyclone dust collector 7, mounted in line with the channel 20 and configured to release the said excessive amount of fine dust to the third conveyor 6.

This configuration then makes it possible to efficiently recover the heat contained in the ash using air during the contact time in the air / ash gravitational heat exchanger 5.

To ensure that there is no effect on the ash cooling process on the extractor 2 and on conveyors 4 and 6 and to prevent uncontrolled air supply from the lower part of the boiler, a valve can be installed before entering the air / ash gravity heat exchanger 5 (that is, before the latter relative to the ash flow) with a double damper (not shown) or an equivalent pressure control, such as a differential pressure sensor, installed to measure before and after entering the gravity 5 air / ash heat exchanger, which th after actuating the valve 15 in the channel 20 brings the pressure difference back to zero.

The air flow entering the air / ash gravity heat exchanger 5, which in the present example is the air supplied to the system through the inlets 14 and 17, can be controlled using the aforementioned controls based on the temperature and / or amount of ash detected by the above sensors, also based on threshold values that can be set selectively by the operator controlling the system 1.

In the second configuration configuration shown in FIG. 2, additional cooling air entering the gravitational heat exchanger 5, after it, and possibly after the dust collector 7, follows a path different from that described with reference to the first embodiment. In this case, in fact, in the terminal channel, instead of being sucked in by the vacuum present in the chimney line 101 of the thermoelectric power station, it is sucked in using a specialized fan 16 or equivalent means along the channel 200, in which the regulating means 150, similar to that described above, are installed, and then air is released into the atmosphere after passing through a specialized filter 9 installed in front of the fan 16. In this case, the operation of the fan provides the necessary assistance for crossover eniya air first and second conveyor belts 6 and the heat exchanger 5 then gravitational air / ash.

In the third structural configuration shown in FIG. 3, additional cooling air entering the heat exchanger 5, after possibly passing through the aforementioned cyclone 7 to separate fine particles, is fed to a combustion system 104 of combustion smoke connected to the boiler 100 by feeding into the chimney 101 after the air heat exchanger ( heater) 102 mentioned above. In this case, the channel of the above-mentioned supply means is indicated by the number 201 of the reference position, and the corresponding control means is indicated by the number 151 of the reference position.

It should be understood that even if the configurations shown in FIG. 1-3, were described separately, they can be simultaneously present in one system in different operating modes, which can be activated depending on the specific need.

It should be understood that system 1 has significant operational flexibility and therefore the ability to handle even a very large ash flow without the problems associated with supplying an excessive flow of cooling air from the lower part of the boiler 100. As mentioned above, such operational flexibility is achieved by providing the possibility of controlled feeding even very large quantities of cooling air and the supply of an additional stream of cooling air (in particular, in a ratio exceeding 1.0-1.5% of the total of air used for combustion) into the chimney or outward, since it is impractical to supply such a stream of air to the boiler in its lower part.

The aim of the invention is also to develop a method for removing and dry cooling combustion residues, as described above, with reference to system 1.

The present invention has been described above with reference to preferred embodiments. It should be understood that there may be other variants of embodiment belonging to the same inventive concept, while all of them are within the scope of protection of the following claims.

Claims (35)

CLAIM 1. System (1) for removal and dry cooling of combustion residues, made with the possibility of its use in conjunction with a combustion chamber, in particular for significant flows of dense ash obtained, for example, from fossil fuels in an energy production plant, removal system (1) and cooling, comprising means (2, 4, 6) for removing and transporting combustion residues from the combustion chamber (100, 105); a system (5, 13, 14, 17) for cooling the combustion residues, providing the possibility of supplying cooling air to said removal and transportation means (2, 4, 6) so that the first part of the said cooling air enters the combustion chamber (100) through her bottom - 4 014862 part; and means (20, 15; 200, 150; 201, 151) for supplying another part of the cooling air from the process of cooling the combustion residues directly with air into the atmosphere or into a chimney (101) connected to the combustion chamber (100). 2. System (1) according to claim 1, in which said cooling system (5, 13, 14, 17) comprises a special air / ash heat exchanger (5) installed in line with said removal (2, 4, 6) means and transportation. 3. The system (1) according to claim 2, in which the said means (20, 15; 200, 150; 201, 151) of the supply is configured to supply cooling air crossing the said heat exchanger (5) into the chimney (101) or into the atmosphere. . 4. System (1) according to claim 2 or 3, containing one or more specialized air inlets (14, 17) configured to supply cooling air to the system (1) that crosses said heat exchanger (5). 5. System (1) according to claim 4, in which said specialized inlet or inlets (14, 17) of cooling air are equipped with means for controlling the flow of incoming air. 6. System (1) according to claim 4 or 5, wherein said or at least one (17) of said specialized cooling air inlets is located immediately after said heat exchanger (5). 7. System (1) according to any one of claims 4 to 6, wherein said or at least one (14) of said specialized cooling air inlets is located in an area for discharging ash (11) from system (1). 8. System (1) according to any one of claims 2 to 7, in which the whole arrangement is made in such a way that the intersection of the said specialized heat exchanger (5) with cooling air is performed in countercurrent. 9. The system (1) according to any one of claims 2 to 8, comprising control means configured to control the air flow crossing said specialized heat exchanger (5). 10. System (1) according to any one of claims 2 to 9, wherein said specialized heat exchanger (5) is a gravitational type heat exchanger. 11. The system (1) according to claim 10, in which said gravitational heat exchanger (5) is a heat exchanger with many differences. 12. The system (1) according to claim 10 or 11, in which said gravitational heat exchanger (5) is a heat exchanger with many plates (19). 13. System (1) according to any one of claims 1-12, wherein said supply means (20, 15) is configured to supply part of the cooling air in front of the air / smoke heat exchanger (102) in the chimney (101) for preheating the air for combustion. 14. System (1) according to any one of claims 1 to 13, in which said supply means (20, 15) is configured to supply part of the cooling air to the economizer area connected to the combustion chamber (100). 15. The system (1) according to any one of claims 1 to 14, comprising means (7) for removing dust from a portion of the cooling air, connected to said supply means (20, 15; 200, 150; 201, 151). 16. System (1) according to claim 15, wherein said dust removal means (7) is a cyclone type means. 17. The system (1) according to any one of claims 1 to 16, comprising means for crushing the residues (3, 10) of combustion, installed in line with the said means (2, 4, 6) for removal and transportation. 18. System (1) according to any one of claims 2-12, 17, wherein said crushing means (3, 10) is installed in front of said specialized heat exchanger (5). 19. System (1) according to claim 17 or 18, wherein said crushing means (3, 10) comprises a pair of crushers located across the gap and in line with said removal and transportation means (2, 4, 6). 20. The system (1) according to any one of claims 1 to 19, comprising control means configured to control the flow of cooling air entering the combustion chamber (100) from the bottom and / or carried by said means (20, 15; 200, 150; 201, 151) filing. 21. The system (1) according to claim 20, in which said control means is arranged to perform said regulation in such a way that the cooling air stream entering the combustion chamber (100) from the lower part does not exceed a predetermined amount of total combustion air . 22. System (1) according to claim 21, wherein said predetermined amount is approximately 1.0-1.5%. 23. System (1) according to any one of claims 9, 20-22, wherein said control means performs said adjustment depending on the temperature and / or amount of combustion residues. 24. The system (1) according to any one of claims 1 to 23, containing pressure control means installed in line with said means (2, 4, 6) of removal and transportation, and after said means (20, 15; 200, 150; 201 , 151) supplying a cooling air stream configured to pre - 5 014862 rotation of uncontrolled air supply in the direction of the lower part of the combustion chamber (100). 25. System (1) according to claim 24, wherein said pressure control means comprises one or more elements selected from the group consisting of a double flasher valve and a differential pressure transmitter. 26. System (1) according to any one of claims 1 to 25, wherein said means of (2, 4, 6) removal and transportation comprises a plurality of removal and / or transportation modules installed in series. 27. System (1) according to any one of claims 1 to 26, comprising a removal / cooler tape (2) connected to the lower part of the combustion chamber (100) directly or using a transition hopper means (105), one or more crushers (3 , 10), one or more conveyors / coolers (4, 6), one mounted in line gravitational heat exchanger (5) air / ash, designed to cool the ash using countercurrent air flow using drops formed by special plates (19) , to increase the heat transfer surface between ash and air, a cyclone (7) for collecting dust in the cooling air stream, a piping system (20) for connecting the air / ash heat exchanger (5) air / ash and a chimney (101), a conveyor belt (6) located after operating under the influence of gravity of the air / ash heat exchanger for transporting ash to the final assembly hopper (11), a specialized fan (16) and a filter (9) for supplying air coming from the cyclone (7) to the atmosphere. 28. A method of removing and dry cooling the combustion residues coming from the combustion chamber, in particular for significant flows of dense ash obtained, for example, from fossil fuels in an energy production plant, comprising the following steps, in which: (a) removing combustion residues from the combustion chamber (100, 105); (b) cooling these combustion residues along the removal and transportation path (2, 4, 6) by supplying cooling air along the latter, after which a portion of said air is supplied to the combustion chamber (100, 105) through its lower part; and (c) supplying another part of the cooling air involved in the cooling of the combustion residues using it to the atmosphere or to a chimney (101) connected to the combustion chamber (100). 29. The method according to claim 28, wherein at said cooling step (b), a specialized air / ash heat exchanger (5) is used installed along said removal and transport path (2, 4, 6). 30. The method according to clause 29, in which, at the aforementioned step (c) of the supply, supply is made to the chimney (101) or to the atmosphere of cooling air crossing said heat exchanger (5). 31. The method according to clause 29 or 30, in which the regulation of the flow of air crossing the above-mentioned specialized heat exchanger (5). 32. The method according to any one of paragraphs 28-31, in which the flow of cooling air entering the combustion chamber (100) through its lower part is controlled and / or which is used in the aforementioned feeding step. 33. The method according to p, in which the aforementioned regulation is performed so that the flow of cooling air entering the combustion chamber (100) through the lower part does not exceed a predetermined amount of total combustion air. 34. The method of claim 33, wherein said predetermined amount is about 1.0-1.5%. 35. The method according to any one of paragraphs.31-34, wherein said regulation is performed depending on the temperature and / or flow of combustion residues.