HK1135754A - Cooling system for dry extraction of heavy bottom ash for furnaces during the storing step at the hopper - Google Patents

Description

Cooling system for dry extraction of heavy ashes of a furnace in a storage step at an ash hopper

Background

In the solid slag extraction system (see european patent EP 0471055B1), cooling of the ash on the extractor conveyor and the subsequent conveyors is achieved by heat exchange with forced convection of return air drawn into the system due to the low air pressure at the bottom of the furnace. The cooling air flows back through suitable inlets placed on the extractor side walls and subsequent conveyors and flows through the ash counter-currently passing through the conveyor line from end to end until it reaches the combustion chamber. The operating mode of the known slagging systems provides the power to close the valves located at the bottom of the furnace and to store the ashes in the hopper. This operation gives the system the best flexibility to perform maintenance operations. During the storage step carried out at the hopper, the ash begins to settle on the bottom valve and initially when the ash level is not yet high, cooling air can flow into the hopper to cool the just-settled ash, then through the bed and cool the free falling ash and flow counter-currently across it. As the ash level increases above the bottom valve, the air encounters greater and greater resistance as it enters the hopper, and the air volume becomes less and less until the air is completely blocked. In this case, there is no external intervention for cooling the stored ash and this is due to the excellent hopper capacity, the amount of ash discharged onto the extractor at high temperatures during the opening of the bottom valve is such that the ash cannot be cooled by the counter-flow air of the system, and accelerated wear problems as well as malfunctions are caused by local deformations, in particular of the grinding members located downstream of the extractor.

Even when the storage duration is short, since the ash storage profile in the hopper for a front combustion furnace (front combustion furnace) or a tangential combustion furnace (tangential combustion furnace) is not uniform, the air distribution in the hopper is not constant, and thus there may be no very cooled region since it is difficult for air to pass through the formed ash layer.

Further, in case the solid slag extractor has a slope higher than the natural inclination angle of the material transferred thereto, there may be ash storage at the curve section. In this case, the section between the conveyor belt and the cover is occupied by material, blocking the passage and restricting the passage of cooling air through the area below the belt. The thin ash stored under the conveyor belt, which causes failure of the thin ash recovery system, is trapped along with the air.

Disclosure of Invention

The above problems are all solved by means of a system according to the present invention, which provides a suitable number of air inlets placed on the side walls of the hopper and on the upper part at the maximum height of the ashes. The air inlets may be interconnected by only one pipe connected to the extractor and dimensioned such that an even distribution of cooling air over the entire hopper wall is achieved. A valve is installed on the pipe connecting the hopper to the extractor, which is opened when cooling of the ash is ensured during the storage step.

During the storage step, with the bottom valve closed, the cooling air entering the system through the inlet on the extractor side wall flows alternately transversely through the path maintained by the air during operation in normal mode.

The cooling effect of the inlet air is enhanced, if desired, by means of water flowing through nozzles placed on the hopper side walls or in the hopper air inlet. The position of the air inlet and the nozzle is such as to ensure free entry of air even when the ash is stored to the desired maximum height. The generated steam, which is sucked in due to the low air pressure inside the furnace, flows back to the furnace and contributes to further cooling by flowing across the counter-current falling ash. The amount of water flowing to the nozzles is finely adjusted based on ash temperature and flow rate values indicated by suitable sensors so that the water amount helps to cool properly without wetting the ash.

Drawings

The novel features, objects, and advantages of the invention will be apparent from the following description and drawings in connection with non-limiting forms of embodiment, of which:

fig. 1 is a side view of an extractor provided with an air inlet on a side wall of an ash hopper connected to the extractor environment by means of a valve;

FIG. 2 is a top view of an air inlet at the ash storage hopper and a connection device to the extractor environment;

FIG. 3 is a sectional view of the slag extractor at the ash storage hopper, which is shown with a cooling water supply nozzle;

fig. 5 is a sectional view of the extractor at the hopper, showing the presence of a cooling water supply nozzle arranged into the side inlet.

With respect to the above figures, like reference numerals in different figures identify the same or similar elements.

Detailed Description

The subject of the invention, the ash cooling system, allows, during the ash storage step at the hopper 1, the cooling of the ash as it falls through the discharge of the furnace 12, by means of a system with lateral inlet 2. Since the air distribution channel 3 is directly connected to the extractor 6, air enters from the extractor environment through the same side of the used inlet 4 during normal operation steps. Thus, the amount of air used for cooling during the continuous operation or storage step is always the same.

The additional air inlet 2 is provided on the side wall of the hopper 1 at a height higher than the maximum height of ash that can be stored on the bottom valve 5, so that clogging and malfunctioning of the air inlet 2 due to large ash heights can be avoided. Such air inlet 2 is connected to the sides of the hopper 1 by a single channel 3 connected to the lid 7 of the extractor 6, by means of manual or automatic valve 8 arrangements. Therefore, when the storage step at the hopper 1 starts with the bottom valve 5 closed, cooling air is sucked from the outside through the side inlet 4 by opening the valve 8 due to the low pressure inside the combustion chamber.

Opening the valve 8 is simply done by closing the bottom valve 5. After closing the bottom valve 5, the air sucked from the outside through the side inlet 4 enters the extractor 6 and cannot enter the furnace because the bottom valve 5 is closed, but is restricted to flow towards the channel 3. The bottom valve 5 is not gas tight and so a certain amount of air will remain through the bottom until the passage is completely closed by the stored ash layer on the bottom valve 55.

The use of an ash cooling system during the storage step is also useful in equipment configurations that provide an extractor ramp that is greater than the natural inclination angle of the transferred material. In this case, during the slag discharge step at the curve, some ash storage may occur together with the material collapse on the inclined section.

When this occurs, the passage zone 9 comprised between the conveyor belt 13 and the cover 7 is completely blocked, and the cooling air is then restricted to pass on the lower conveying section. Because the cooling air is laden with thin layers of ash, the thin layers of ash settle to the bottom of the recovery system 11, thus plugging the recovery system 11. When the valve 8 is opened alternately, air can bypass the upper part, thus avoiding clogging the recovery system 11.

This way of air flow into the furnace has significant advantages in cooling the stored ash, since the air is distributed more evenly over the entire passage surface of the falling ash and there is no need to increase the amount of air entering the furnace.

Another configuration of the cooling system at the hopper provides for the use of cooling water 14 through nozzles suitably placed in the hopper, which helps to cool the ash stored on the bottom valve 5, flowing through the bottom valve 5 after being finely dosed, to cool but not wet the ash. The amount of water supplied to the nozzles is in fact regulated on the basis of the temperature and flow rate values of the stored ash, measured by suitable sensors (not shown) placed inside the hopper. The steam output produced in the water cooling process is sucked in due to the low air pressure at the furnace and mixed with the combustion fumes and thus additionally cools the ash falling from the combustion chamber further. This further advantageous result is an important contribution to the ash cooling process, since it makes use of the latent heat of vaporization of water, which reduces the heat of the ash stored at the hopper, drying the ash recovered from the bottom of the hopper by the known extraction systems.

Claims (5)

1. A cooling system for the heavy ashes formed inside a fossil fuel furnace during the storage step at the ash hopper (1), characterized by the fact that suitable air inlets (2) arranged on the side walls of the ash hopper (1) at the bottom of the furnace, a controlled amount of air sucked in due to the depression in the combustion chamber, enters the combustion chamber through a channel (3) by means of the air inlets (2), the channel (3) being connected to the lid (7) of a metal container comprising an extractor (6).

2. A cooling system according to claim 1, characterized in that the cooling of the stored ash is enhanced by adding water to the hopper (1) which is supplied in an amount which cools the ash but does not wet it.

3. The cooling system according to claim 2, characterized in that the cooling water is supplied into the hopper (1) through suitable nozzles (14) arranged on the side walls of the hopper (1) or in the air inlet (2).

4. Cooling system according to claim 1, characterized by a set of pipes (2) and block valves (8) for even distribution of cooling air, said block valves (8) being manual or automatic and opening after closing a bottom valve (5) connecting said pipes (2) to an extractor environment (6) allowing said cooling air to enter said hopper (1).

5. A cooling system according to claim 3, characterized in that the amount of water supplied to the nozzles (14) is finely dosed and the steam output resulting from the cooling process is carried away together with combustion fumes based on the flow and temperature values of the stored ash measured by suitable sensors installed in the hopper (1).