A method for converting a solid slag discharge of a once-through boiler to a liquid slag discharge

Abstract

A method for converting a solid slag-discharging once-through boiler into a liquid slag-discharging boiler, the specific steps are as follows: cancel the burners, lower water-cooled walls and cold ash hoppers, lower headers of water-cooled walls and slag conveyors of the original once-through boiler, add a double liquid slag-discharging boiler at the lower part of the original once-through boiler, and set a saddle arch at the bottom of the lower cooling chamber; transform the furnace of the original once-through boiler into the upper cooling chamber of the liquid slag-discharging boiler, the front and rear walls or two side walls of the water-cooled wall both contract inward and are docked with the lower cooling chamber, and the slag-catching tube bundle crosses the combustion chamber outlet flue to catch the liquid slag carried in the flue gas; pulverized coal burns in the combustion chamber through the burner, and the formed ash slag is molten liquid slag, and the liquid slag is discharged through the slag hopper and the slag-discharging port. The invention converts the solid slag-discharging boiler into a double U-shaped liquid slag-discharging boiler, and can burn Zhundong coal with extremely strong caking property or other coal types with low ash fusion point.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid slag removal boilers, and particularly relates to a method for changing a once-through boiler from solid slag removal to liquid slag removal. Background Art

[0002] The alkali metal content of Zhundong coal is high, and there are serious slagging and fouling problems. After the boilers are changed to burn Zhundong coal at present, slagging and fouling have occurred to varying degrees. The water-cooled walls of the cold ash hoppers have been damaged frequently, and there have been operating failures of the slag removal system and blockages in the flue gas ducts. In severe cases, the boilers have to be shut down forcedly. Patent document CN112944331A relates to a method for liquid slag removal transformation of a solid slag removal coal-fired boiler. On the basis of not changing the original boiler main structure, this patent document realizes the liquid slag removal transformation by moving the overall position of the burner downward, reducing the primary air nozzle spacing of the tangentially fired burners at the four corners or the distance between the centers of each tangential burner, and setting a constricted furnace arch above the burner area, still retaining the original combustion mode, and the transformation is not thorough. Summary of the Invention

[0003] The present invention is to overcome the deficiencies of the prior art and provides a method for changing a once-through boiler from solid slag removal to liquid slag removal. This method transforms a solid slag removal boiler into a double-U liquid slag removal boiler, which can burn Zhundong coal with extremely strong coking property or other coal types with low ash melting point, and prevents slagging and fouling of the furnace and other heating surfaces.

[0004] The specific steps of a method for changing a once-through boiler from solid slag removal to liquid slag removal are as follows: cancel the burner, the lower water-cooled wall, the cold ash hopper, the lower water-cooled wall header box and the slag scraper of the original once-through boiler, and add a double-U liquid slag removal boiler at the lower part of the original once-through boiler, including: a lower cooling chamber, a burner, two combustion chambers and two groups of slag-catching tube bundles. The two combustion chambers are symmetrically arranged. Each combustion chamber and half of the lower cooling chamber form a U shape. The burner is inverted and arranged at the top of the combustion chamber. A slag hopper and a slag discharge port are arranged at the lower part of the combustion chamber, and a saddle arch is arranged at the bottom of the lower cooling chamber;

[0005] Transform the furnace of the original once-through boiler into the upper cooling chamber of the liquid slag removal boiler. The front and rear walls or the two side walls of the water-cooled wall both contract inward and are butt-jointed with the lower cooling chamber. The slag-catching tube bundles are formed by pulling out the water-cooled wall tubes on the saddle arch. The slag-catching tube bundles cross the flue of the combustion chamber outlet and serve as the boundary between the combustion chamber and the lower cooling chamber, forming a barrier at the combustion chamber outlet to capture the liquid slag carried in the flue gas;

[0006] The pulverized coal burns in the combustion chamber through the burner, and the formed ash slag is molten liquid slag. The high-temperature flue gas generated by combustion enters the lower cooling chamber and the upper cooling chamber after passing through the slag-catching tube bundles, and the liquid slag is discharged through the slag hopper and the slag discharge port.

[0007] The beneficial effects of the present invention compared with the prior art are:

[0008] The present invention overcomes the deficiencies of the prior art that there are serious coking and fouling problems when burning strongly coking coal types such as Zhundong coal. It transforms a solid slagging boiler into a double-U type liquid slagging boiler. The combustion chamber of the U-type liquid slagging boiler adopts a vertical inverted combustion method, which increases the separation effect of the liquid slag, improves the slag capture rate, reduces the dust content in the flue gas at the furnace outlet, and prevents slagging and fouling of the furnace and other heating surfaces. The obtained double-U type liquid slagging boiler after transformation can burn Zhundong coal with extremely strong coking property or other coals with low ash melting point, which is beneficial to making full use of the rich Zhundong coal resources, reducing the fuel cost, and improving the operation economy.

[0009] The liquid slagging boiler has a high slag capture rate, captures most of the low melting point alkali metal components into the molten slag, reduces the ash content in the flue gas, especially reduces the content of alkali metal substances, and prevents slagging and fouling of the furnace and heating surfaces. The liquid slagging method is an effective way to solve the coking and fouling problems when the boiler burns strongly coking coal types such as Zhundong coal.

[0010] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments: Brief Description of the Drawings

[0011] Figure 1 is a schematic diagram of the original once-through boiler;

[0012] Figure 2 is a schematic diagram of the structure of the liquid slagging boiler obtained after transformation;

[0013] Figure 3 is a schematic diagram of the water wall structure layout of the double-U type liquid slagging boiler after transformation;

[0014] Figure 4 is a developed schematic diagram of the double-U type water wall structure after transformation;

[0015] Figure 5 is a schematic diagram of the water wall feed water flow of the liquid slagging boiler after transformation. Detailed Embodiments

[0016] The embodiments of the technical solution of the present invention will be described in detail below in conjunction with the drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0017] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0018] A method for changing the solid slagging of a once-through boiler to liquid slagging in this embodiment is to transform the original once-through boiler from a solid slagging boiler into a double-U type liquid slagging boiler through transformation;

[0019] The specific steps are as follows: Remove the burner 14, lower water wall and cold ash hopper 16, water wall lower header 11 and slag extractor 17 of the original once-through boiler, and add a double-U type liquid slag removal boiler at the lower part of the original once-through boiler, which includes: a lower cooling chamber 8, a burner 2, two combustion chambers 1 and two groups of slag-catching tube bundles 3. The two combustion chambers 1 are symmetrically arranged. Each combustion chamber 1 forms a U shape with half of the lower cooling chamber 8. The burner 2 is inverted and arranged at the top of the combustion chamber 1. A slag hopper 4 and a slag discharge port 5 are arranged at the lower part of the combustion chamber 1, and a saddle arch 6 is arranged at the bottom of the lower cooling chamber 8;

[0020] Transform the furnace 15 of the original once-through boiler into the upper cooling chamber 7 of the liquid slag removal boiler. The front and rear walls or two side walls of the water wall 10 are both contracted inward and docked with the lower cooling chamber 8. The slag-catching tube bundle 3 is formed by pulling out the water wall tubes on the saddle arch 6. The slag-catching tube bundle 3 crosses the outlet flue of the combustion chamber 1 and serves as the boundary between the combustion chamber 1 and the lower cooling chamber 8, forming a barrier at the outlet of the combustion chamber 1 to capture the liquid slag carried in the flue gas;

[0021] The pulverized coal burns in the combustion chamber 1 through the burner 2, and the formed ash slag is molten liquid slag. The high-temperature flue gas generated by combustion enters the lower cooling chamber 8 and the upper cooling chamber 7 after passing through the slag-catching tube bundle 3. The liquid slag is discharged through the slag hopper 4 and the slag discharge port 5. In this embodiment, the pulverized coal burns in the combustion chamber 1 through the burner 2. The heat load of the combustion chamber 1 is much higher than that of a normal solid slag removal boiler, which increases the temperature in the combustion chamber 1. The ash slag becomes molten liquid slag, and the liquid slag flows into the slag hopper 4 and enters the slag well through the slag discharge port 5. The high-temperature flue gas generated by combustion enters the lower cooling chamber 8 and the upper cooling chamber 7 after passing through the slag-catching tube bundle 3.

[0022] A method for converting a once-through boiler from solid slag removal to liquid slag removal in this embodiment is to remove all the burners of the original boiler, transform the furnace into the upper cooling chamber of the liquid slag removal boiler, and design and add the main structure of a double-U type liquid slag removal boiler under the furnace, including a combustion chamber, a saddle arch, a slag-catching tube bundle and a lower cooling chamber covered with refractory castable, to increase the temperature in the combustion chamber and the lower cooling chamber, melt the ash slag, and achieve liquid slag removal. A tangential burner is used to increase the effect of the liquid slag hitting the wall. The combustion chamber adopts a vertical inverted combustion method, which increases the separation effect of the liquid slag, improves the slag-catching rate, reduces the dust content in the flue gas at the furnace outlet, and prevents slagging and fouling of the furnace and other heating surfaces. The transformed double-U type liquid slag removal boiler can burn Zhundong coal with extremely strong coking property or other coal types with low ash melting point, which is beneficial to making full use of the rich Zhundong coal resources, reducing the fuel cost, and improving the operation economy.

[0023] As a possible implementation, such as Figures 2 - 3As shown in the figure, the flue gas flows downward in the combustion chamber 1. The cross-section of the combustion chamber 1 is rectangular. The combustion chamber 1, the lower cooling chamber 8, the slag hopper 4 and the saddle arch 6 are all surrounded by membrane water walls. The fire-facing side of the membrane water wall is covered with refractory castable. The outer surface of the slag-catching tube bundle 3 is also covered with refractory castable. The fire-facing side of the water wall is welded with studs and covered with refractory castable. The outer surface of the slag-catching tube bundle 3 is also welded with studs and covered with refractory castable. The refractory castable reduces the heat absorption in the combustion chamber 1, reduces the heat absorption of the combustion chamber 1, the slag-catching tube bundle 3 and the lower cooling chamber 8, increases the flue gas temperature in these areas, melts the ash slag, ensures that the ash slag is in a freely flowing liquid state in these areas, and is conducive to the capture of liquid slag and smooth outflow.

[0024] Optionally, the original once-through boiler adopts a Π-shaped layout or a tower layout, and the combustion mode adopts tangential combustion or opposed firing. The original economizer of the boiler is connected from the economizer outlet connecting pipe 18 to the inlet header 11 of the boiler water wall and is changed to be connected by the connecting pipe 12 to the inlet header 19 of the combustion water wall of the combustion chamber 1. The outlet header 20 of the combustion chamber 1 is connected to the inlet header 21 of the upper cooling chamber 7 through the outlet connecting pipe 13. The water wall 10 of the upper cooling chamber 7 is a vertical water wall or a combination of a spiral water wall and a vertical water wall. The upper and lower water walls are connected in series to form a once-through water wall system.

[0025] As a possible implementation, as Figures 3 - 5 shown, taking the arrangement of two combustion chambers 1 as the front wall and the rear wall as an example, the water wall of the double U-shaped liquid slag removal boiler is in a once-through mode. The process is that after the feed water passes through the economizer, it enters the inlet header 19 of the combustion water wall of the combustion chamber 1 through the connecting pipe 12, passes through the water walls of the slag hopper 4 and the saddle arch 6 and the slag-catching tube bundle 3, and enters the front wall and rear wall water walls of the combustion chamber 1. The front wall and rear wall water walls of the combustion chamber 1 are spiral tube screens, and the side wall water walls are horizontal tube screens. The spiral tube screens and the horizontal tube screens are connected end to end and rotate step by step upward. After surrounding the furnace of the double U-shaped liquid slag removal boiler one to two circles, they enter the outlet header 20 of the combustion chamber 1 through the ceiling, and enter the inlet header 21 of the upper cooling chamber 7 through the outlet connecting pipe 13, and enter the start-up separator 9 through the water wall 10. In the above method, the two side walls also refer to the left wall and the right wall (as Figure 4 shown).

[0026] When the combustion chamber 1 is arranged on both sides of the original boiler, that is, arranged on the side walls (left wall and right wall), the spiral tube screen is arranged on the side walls, and the horizontal tube screen is arranged on the front wall and the rear wall. At this time, the arrangement on both side walls can be understood as the arrangement on the front wall and the rear wall, and the corresponding front wall and rear wall are understood as the side walls. The transformation method of this implementation realizes a series-connected double once-through water circulation mode.

[0027] As a possible implementation, the front and rear walls or the side walls at the lower part of the combustion chamber 1 incline inward to form a constriction, and the angle range between the inward-inclined surface of the front and rear walls or the side walls and the vertical direction is 15° - 40°. The constriction is beneficial to the discharge of liquid slag.

[0028] Furthermore, the slag hopper 4 is a conical slag hopper, and there is a slag discharge port 5 at the lowest position of the slag hopper 4. The slag hopper 4 has an inclined bottom, and the angle range between the inclined surface of the bottom and the horizontal direction is 0° - 25°. With such a setting, it is convenient for the discharge of liquid slag.

[0029] As Figure 2 shown, the slag-catching tube bundles 3 are arranged in a staggered or in-line manner. Optionally, the longitudinal number of rows of the slag-catching tube bundles 3 is not less than 2 rows and not more than 6 rows.

[0030] Optionally, the slag hopper 4, the water-cooled walls of the saddle arch 6, and the slag-catching tube bundles 3 are an independent combined process, adopting a once-through or reciprocating flow. The inlet and outlet of the cooling water are both at the upper edge of the slag hopper 4.

[0031] As a possible implementation, the burner 2 is a swirl burner, which further increases the flue gas temperature in the combustion chamber 1 and forms a stable liquid slag film on the inner wall surface of the combustion chamber 1. The burners 2 are arranged in a matrix on the ceiling of the combustion chamber 1, and there are N burners 2 on each combustion chamber 1. Optionally, there are 8 burners 2 on each combustion chamber 1, and the number of burners 2 can be changed according to needs.

[0032] As Figure 2 and Figure 3 shown, the liquid slag flows downward along the saddle arch 6 into the slag hopper 4. The height of the saddle arch 6 is 1 / 5 - 3 / 5 of the height of the combustion chamber 1. The saddle arch 6 is the watershed of two combustion chambers 1, preventing the flue gas from flushing against each other, making the flue gas form a U-shaped turn. At the bottom of the combustion chamber 1, the flue gas makes a nearly 180° turn, and the liquid slag carried in the flue gas is thrown onto the slag hopper 4 and the saddle arch 6 under the action of inertia, improving the liquid slag separation effect.

[0033] All the original burners 14 of the boiler are removed, and the furnace 15 is transformed into the upper cooling chamber 7 of a liquid slag removal boiler. A double-U liquid slag removal boiler structure is designed and added under the furnace. The combustion chamber 1, the saddle arch 6, the slag-catching tube bundles 3, and the lower cooling chamber 8 are covered with refractory castables to increase the temperature in the combustion chamber 1 and the lower cooling chamber 8, melt the ash slag, and achieve liquid slag removal. The swirl burner 2 is used to increase the effect of liquid slag hitting the wall. The combustion chamber 1 adopts a vertical inverted combustion method, increasing the liquid slag separation effect, improving the slag-catching rate, reducing the dust content in the flue gas at the furnace outlet, and preventing slagging and fouling of the furnace and other heating surfaces. The transformed double-U liquid slag removal boiler can burn Zhundong coal with extremely strong coking properties or other coal types with low ash melting points, which is beneficial to making full use of the rich Zhundong coal resources, reducing the fuel cost, and improving the operation economy.

[0034] The upper cooling chamber 7 is not provided with an inlet header 21, and the combustion chamber outlet header 20 is directly connected to the inlet of the water wall 10 of the upper cooling chamber 7.

[0035] The present invention has been disclosed above with preferred embodiments. However, it is not intended to limit the present invention. Any person skilled in the art, without departing from the technical solution of the present invention, can make some changes or modifications to equivalent embodiments of equivalent changes by using the above-disclosed structure and technical content, and all still fall within the scope of the technical solution of the present invention.

Claims

1. A method for converting a dry-bottom slag removal of a once-through boiler to a wet-bottom slag removal, characterized in that, the steps of the method are as follows: Remove the burners, lower water-cooled wall and cold ash hopper (16), water-cooled wall lower header (11) and slag conveyor (17) of the original once-through boiler, and add a double-U wet-bottom slag removal boiler at the lower part of the original once-through boiler, including: a lower cooling chamber (8), burners, two combustion chambers (1) and two groups of slag-catching tube bundles (3). The two combustion chambers (1) are symmetrically arranged. Each combustion chamber (1) forms a U shape with half of the lower cooling chamber (8). The burners are inverted and arranged at the top of the combustion chamber (1). The combustion chamber (1) adopts a vertical inverted combustion mode. The burners are tangential burners. A slag hopper (4) and a slag discharge port (5) are arranged at the lower part of the combustion chamber (1). A saddle arch (6) is arranged at the bottom of the lower cooling chamber (8); the combustion chamber (1), the lower cooling chamber (8), the slag hopper (4) and the saddle arch (6) are all surrounded by membrane water-cooled walls. The fire-facing side of the membrane water-cooled walls is covered with refractory castables. The outer surface of the slag-catching tube bundles (3) is covered with refractory castables; Transform the furnace (15) of the original once-through boiler into the upper cooling chamber (7) of the wet-bottom slag removal boiler. The front and rear walls or the two side walls of the water-cooled wall (10) are both contracted inward and docked with the lower cooling chamber (8). The slag-catching tube bundles (3) are formed by pulling out the water-cooled wall tubes on the saddle arch (6). The slag-catching tube bundles (3) cross the outlet flue of the combustion chamber (1) and serve as the boundary between the combustion chamber (1) and the lower cooling chamber (8), forming a barrier at the outlet of the combustion chamber (1) to capture the molten slag carried in the flue gas; Pulverized coal burns in the combustion chamber (1) through the burners, and the formed ash slag is molten liquid slag. The liquid slag flows downward along the saddle arch (6) into the slag hopper (4). The height of the saddle arch (6) is 1 / 5 - 3 / 5 of the height of the combustion chamber (1). The high-temperature flue gas generated by combustion enters the lower cooling chamber (8) and the upper cooling chamber (7) after passing through the slag-catching tube bundles (3). The liquid slag is discharged through the slag hopper (4) and the slag discharge port (5).

2. A method for converting a dry-bottom slag removal of a once-through boiler to a wet-bottom slag removal according to claim 1, characterized in that: The flue gas flows downward in the combustion chamber (1), and the cross-section of the combustion chamber (1) is rectangular.

3. A method for converting a dry-bottom slag removal of a once-through boiler to a wet-bottom slag removal according to claim 1, characterized in that: The original once-through boiler adopts a Π-type layout or a tower layout, and the combustion mode adopts a tangential combustion or an opposed combustion mode. The economizer of the original boiler is connected from the economizer outlet connecting pipe (18) to the boiler water-cooled wall lower header (11) and is changed to be connected by a connecting pipe (12) to the combustion water-cooled wall inlet header (19) of the combustion chamber (1). The outlet header (20) of the combustion chamber (1) is connected to the inlet header (21) of the upper cooling chamber (7) through an outlet connecting pipe (13). The water-cooled wall (10) of the upper cooling chamber (7) is a vertical water-cooled wall or a combination of a spiral water-cooled wall and a vertical water-cooled wall. The upper and lower water-cooled walls are connected in series to form a once-through water-cooled wall system.

4. A method for converting a dry-bottom slag removal of a once-through boiler to a wet-bottom slag removal according to claim 1 or 3, characterized in that: The water-cooled wall of the double U-shaped liquid slag removal boiler is in a once-through mode. The process is as follows: After the feed water passes through the economizer, it enters the combustion water-cooled wall inlet header (19) of the combustion chamber (1) through the connecting pipe (12), passes through the water-cooled walls of the slag hopper (4) and the saddle arch (6) and the slag-catching tube bundle (3), and enters the front and rear wall water-cooled walls of the combustion chamber (1). The front and rear wall water-cooled walls of the combustion chamber (1) are spiral tube screens, and the side wall water-cooled walls are horizontal tube screens. The spiral tube screens and the horizontal tube screens are connected end to end and rotate step by step upward. After surrounding the furnace of the double U-shaped liquid slag removal boiler for one to two circles, they enter the outlet header (20) of the combustion chamber (1) through the ceiling, and enter the inlet header (21) of the upper cooling chamber (7) through the outlet connecting pipe (13), and enter the start-up separator (9) through the water-cooled wall (10).

5. A method for converting a once-through boiler from solid slag removal to liquid slag removal according to claim 1, characterized in that: The front and rear walls or the side walls at the lower part of the combustion chamber (1) are inclined inward to form a constriction, and the angle range between the inward inclined surface of the front and rear walls or the side walls and the vertical direction is 15°-40°.

6. A method for converting a once-through boiler from solid slag removal to liquid slag removal according to claim 1, characterized in that: The slag hopper (4) is a conical slag hopper, and the slag hopper (4) has an inclined bottom, and the angle range between the bottom inclined surface and the horizontal direction is 0°-25°.

7. A method for converting a once-through boiler from solid slag removal to liquid slag removal according to claim 1, characterized in that: The slag-catching tube bundle (3) is arranged in a staggered or in-line arrangement.

8. A method for converting a once-through boiler from solid slag removal to liquid slag removal according to claim 1, characterized in that: The water-cooled walls of the slag hopper (4) and the saddle arch (6) and the slag-catching tube bundle (3) are an independent process combined together, and a once-through or reciprocating flow is adopted.

9. A method for converting a once-through boiler from solid slag removal to liquid slag removal according to claim 1, characterized in that: The burners are arranged in a matrix on the ceiling of the combustion chamber (1), and there are N burners on each combustion chamber (1).

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