A high-temperature denitrification, fly ash re-combustion, and in-furnace dust removal boiler

Abstract

The present invention provides a high-temperature denitration, fly ash re-combustion, and in-furnace dust removal boiler, which has a combustion chamber, a furnace, and a long throat cavity connecting the combustion chamber and the furnace, the long throat cavity is narrowed relative to the cross-section of the combustion chamber and the furnace and has a height of 1 meter to 4 meters, and the boiler also has a urea nozzle positioned near the junction of the long throat cavity and the furnace. In addition, the furnace is defined by the front wall, left wall, right wall, and a front screen of a specific shape of the boiler, the front screen is substantially perpendicular to the left wall and the right wall and extends from the left wall to the right wall, and the upper end is connected to the drum in the top wall of the boiler, and the lower end is connected to the lower header of the front screen; the portion of the front screen that defines the furnace forms a concave surface facing the inner concave portion of the front wall, thereby extending the travel path of the flue gas. In addition, the boiler includes a horizontal flue connected to the top of the furnace, and the boiler has a trough-type separator located in the horizontal flue. An ash hopper is arranged below the trough-type separator, and the ash hopper can be selectively connected to the furnace to send the collected ash into the furnace for re-combustion.

Description

Technical Field

[0001] The invention relates to a boiler, in particular to a high-temperature denitration, fly ash re-combustion and in-furnace dust removal boiler. Background Art

[0002] Nitrogen oxides (NOx) are one of the harmful substances emitted by boilers along with flue gas. Control of NOx emission is one of the most important measures to protect the atmospheric environment. NOx control is usually carried out in the following ways: first, the combustion temperature is reduced by using a fuel-rich and oxygen-deficient method to reduce the amount of NOx generated by thermal nitrogen; second, non-catalytic reduction treatment is performed on the flue gas containing NOx to generate non-toxic nitrogen and water; third, catalytic treatment is performed on low-temperature flue gas (at 350°C).

[0003] From the perspective of economical application, convenience and practicality, controlling the amount of NOx generated during combustion is the best choice, which will reduce the difficulty, complexity and economic cost of flue gas treatment. Layer-burning furnaces have the inherent advantages of fuel stratification and air stratification in combustion mode. Under the premise of ensuring continuous fire, oxygen-deficient combustion can control NOx at 250-350mg / m 3 Next, by spraying urea aqueous solution into the flue gas for non-catalytic reduction, the national key area NOx emission standard or higher standard can be achieved.

[0004] At present, the commonly used method of spraying urea to reduce NOx is to spray urea liquid into the flue at the top of the furnace or at the rear heating surface, i.e., the front area of ​​the economizer, for denitration. This method has the following problems: the temperature of the reduction reaction is low (far from the optimal temperature of 800-950°C), the time, space, and path of the reaction are limited, and the concentration of escaping NOx and urea is high, so the ideal denitration effect cannot be achieved. In addition, the water generated during the reaction and the water in the urea liquid will wet the smoke particles, causing serious adhesion and ash accumulation on the rear heating surface of the economizer, which will hinder heat exchange in the mild case and clog the economizer in the severe case. In addition, when the combustion temperature is reduced by the method of rich fuel and lack of oxygen to reduce the amount of NOx generated by thermal nitrogen, the unburned carbon in the flue gas increases, resulting in a decrease in combustion efficiency and an increase in energy consumption.

[0005] Therefore, a technical solution that can solve any of the above technical problems is welcome. Summary of the invention

[0006] The present invention is dedicated to solving the deficiencies of the background technology.

[0007] 1. In terms of denitration, the urea nozzle is moved forward to the furnace entrance as far as possible, thereby extending the reaction time of the denitration reaction and making the mixing more complete. In addition, by setting a long throat cavity between the combustion chamber and the furnace, the flue gas temperature at the urea nozzle is controlled within the optimal reduction reaction temperature range of 800-950°C, so that the temperature of the denitration reaction is optimized. In addition, by constructing the contour of the furnace, the flue gas travel path is further extended, the reaction time is increased, and the flue gas and urea are mixed more fully. In addition, the residual urea and NOx are forced to be remixed through the trough separator, which greatly reduces the concentration of escape and makes the denitration more complete and effective.

[0008] Second, in order to reduce the unburned carbon in the fly ash, the fly ash is returned to the furnace for reburning through the trough separator and the flue ash hopper, thus avoiding the loss of unburned carbon with the smoke due to low-temperature combustion, and improving the combustion efficiency.

[0009] 3. In order to reduce the ash sticking and accumulation at the tail of the economizer caused by humidified flue gas, a rear screen with a specific shape is set to guide the flue gas so that the smoke particles are separated and discharged into the slag trough under the action of inertia and centrifugal force. This not only reduces the ash sticking and accumulation that hinders heat exchange, but also greatly reduces the original dust concentration of the boiler.

[0010] 4. To ensure that the urea nozzle is not damaged by high temperature, the nozzle is installed in the header on the front wall so that it is cooled by working fluid water to avoid intermittent denitrification due to damage by burning.

[0011] According to a first aspect of the present invention, there is provided a boiler having a combustion chamber and a furnace, characterized in that the boiler further comprises a long throat cavity connecting the combustion chamber and the furnace, the long throat cavity is narrowed relative to the cross-section of the combustion chamber and the furnace and has a height of 1 to 4 meters, and the boiler further comprises a urea nozzle positioned near the junction of the long throat cavity and the furnace.

[0012] In a feasible implementation manner, the cross-section of the long throat cavity is rectangular.

[0013] In a feasible implementation manner, the cross-section of the long throat cavity is zigzag-shaped.

[0014] In a feasible implementation manner, the urea nozzle is arranged in a header on the front wall of the boiler, so that cooling is achieved by using the working medium water in the header.

[0015] In a feasible embodiment, the urea nozzle slightly rises or horizontally penetrates the pipe wall of the header of the front wall, and its front end extends into the furnace.

[0016] In a feasible embodiment, the boiler has a front screen of a specific shape that is approximately perpendicular to the left wall and the right wall of the boiler and extends from the left wall to the right wall. The upper end of the front screen is connected to the boiler drum in the top wall of the boiler, and the lower end is connected to the header in the front screen. The combustion chamber, the furnace and the long throat cavity are defined by the front wall, the left wall, the right wall and the front screen of the boiler.

[0017] In a possible embodiment, the portion of the front panel defining the furnace forms an inner recess with a concave surface facing the boiler front wall, thereby extending the travel path of the flue gas.

[0018] In a feasible implementation manner, the cross section of the inner recess is arc-shaped or broken line-shaped.

[0019] In a feasible embodiment, the inner recess includes a vertical section, a first inclined section and a second inclined section, the lower end of the first inclined section is continuous with the upper end of the vertical section, and the upper end of the second inclined section is continuous with the lower end of the vertical section.

[0020] In a feasible embodiment, the boiler has a horizontal flue connected to the top of the furnace, so that the flue gas can move horizontally after moving upward along the inner recess of the front screen, thereby forming an S-shaped flue gas travel path, thereby further extending the flue gas travel path.

[0021] In a feasible embodiment, the boiler also has a rear screen of a specific shape that is roughly perpendicular to the left wall and the right wall of the boiler and extends from the left wall to the right wall. The upper end of the rear screen is connected to the boiler drum in the top wall of the boiler, and the lower end is connected to the lower header of the rear wall of the boiler.

[0022] In a feasible embodiment, the boiler has a slot-type separator connected to the drum and arranged in a space defined by the upper ends of the front screen and the rear screen, and the upper ends of the front screen and the rear screen each have their own first light pipe grid segment.

[0023] In a feasible embodiment, the front screen has a first non-light pipe grating segment located below its first light pipe grating segment and continuous with the first light pipe grating segment, and the rear screen also has a first non-light pipe grating segment located below its first light pipe grating segment and continuous with the first light pipe grating segment, and the first non-light pipe grating segment of the front screen and the first non-light pipe grating segment of the rear screen define an ash collecting hopper.

[0024] In a feasible implementation manner, the front screen and the rear screen further define an ash return chamber located below the ash collecting hopper and communicated with the ash collecting hopper.

[0025] In a feasible embodiment, a gravity flap valve is provided on the top of the ash return chamber, and the bottom of the ash return chamber is defined by an inclined ash return guide plate extending from the front screen to the rear screen, and the upper portion of the front screen adjacent to the ash return guide plate has a second light tube grille section to provide an ash return port, so that when the smoke collected in the ash hopper reaches the threshold of the gravity flap valve, the flap valve flips, and the smoke falls onto the ash return guide plate and then enters the furnace defined by the front screen and the front wall of the boiler through the ash return port.

[0026] In a feasible embodiment, the front screen and the rear screen also define an economizer accommodating space located below the ash return chamber for arranging an economizer, the economizer accommodating space and the ash return chamber are spatially separated from each other by the ash return guide plate, and the rear screen is formed with a smoke inlet on the portion defining the economizer accommodating space.

[0027] In a feasible embodiment, a plurality of smoke damping plates are connected to the bottom of the slot-type separator, which are substantially perpendicular to the left and right walls of the boiler and extend from the left wall to the right wall, and whose bottom edges are opposite to the first non-light tube grating segment of the front screen and have a predetermined gap therewith, wherein the gap provides smoke damping to force the smoke to pass through the slot-type separator and move toward the first light tube grating segment of the rear screen after passing through the first light tube grating segment of the front screen, rather than bypassing the slot-type separator.

[0028] In a feasible embodiment, the rear screen has a second light tube grating segment continuous with the first non-light tube grating segment, and the second light tube grating segment defines the smoke inlet. The smoke inlet is farther away from the boiler rear wall than the junction of the first light tube grating segment and the first non-light tube grating segment of the rear screen, so that the smoke moves obliquely downward and enters the smoke inlet after passing through the horizontal flue and impacting the rear wall.

[0029] In a feasible implementation manner, the rear screen is provided with a dust shield on one side of the smoke inlet close to the rear wall of the boiler.

[0030] In a feasible implementation manner, the dust shield is substantially perpendicular to the left wall and the right wall of the boiler and extends from the left wall to the right wall.

[0031] In a feasible embodiment, the space between the rear screen and the rear wall forms a smoke separation chamber, and the smoke separation chamber is used to collect smoke particles separated from the smoke.

[0032] In a feasible embodiment, the rear screen has a third light pipe grille segment located near the lower end thereof, and the third light pipe grille segment provides a dust collecting port for the smoke and dust separation chamber.

[0033] In a feasible embodiment, the bottom of the dust collecting port is connected to a cover that can be opened and closed, or is connected to a comb-shaped dust removal and smoke exhaust box, which is comb-shaped as a whole, with an upper dust collecting hopper and a row of comb-toothed dust exhaust pipes at the bottom. The dust collecting hopper defines a dust collecting chamber, and the dust exhaust pipe defines a dust exhaust passage. The dust collecting chamber and the dust exhaust passage are connected to each other, and the comb-toothed dust exhaust pipes are spaced apart from each other to define the smoke exhaust port. The boiler has a water tank arranged below the comb-shaped dust removal and smoke exhaust box, and the dust exhaust pipe is immersed in the water tank to achieve a water seal, so that when in use, smoke particles fall into the water tank via the dust collecting port, the dust collecting hopper, and the dust exhaust pipe of the comb-shaped dust removal and smoke exhaust box.

[0034] In a feasible implementation manner, the dust removal and smoke exhaust box is a trough box body formed by welding steel plates, and an openable and closable inspection door is provided on the outer wall panel.

[0035] In a feasible implementation manner, the comb-shaped dust removal and smoke exhaust box also serves as the boiler outer wall.

[0036] According to a second aspect of the present invention, a boiler is provided, which has a urea nozzle, wherein the urea nozzle is arranged in a header on a front wall of the boiler, so that cooling is achieved by using working medium water in the header.

[0037] In a feasible embodiment, the urea nozzle slightly rises or horizontally penetrates the pipe wall of the header of the front wall, and its front end extends into the furnace.

[0038] According to a third aspect of the present invention, there is provided a boiler having a furnace, wherein the furnace is defined by a front wall, a left wall, a right wall and a front screen of a specific shape of the boiler, the front screen being substantially perpendicular to the left wall and the right wall and extending from the left wall to the right wall, and having an upper end connected to a boiler drum in a top wall of the boiler and a lower end connected to a front screen lower header; a urea nozzle is provided in a portion of the front wall defining the furnace, and this portion of the front screen defining the furnace forms a concave surface facing an inner recess of the front wall, thereby extending the travel path of the flue gas.

[0039] In a feasible implementation manner, the cross section of the inner recess is arc-shaped or broken line-shaped.

[0040] In a feasible embodiment, the inner recess includes a vertical section, a first inclined section and a second inclined section, the lower end of the first inclined section is continuous with the upper end of the vertical section, and the upper end of the second inclined section is continuous with the lower end of the vertical section.

[0041] In a feasible embodiment, the boiler has a horizontal flue connected to the top of the furnace, so that the flue gas can move horizontally after moving upward along the inner recess of the front screen, thereby forming an S-shaped flue gas travel path, thereby further extending the flue gas travel path.

[0042] According to a fourth aspect of the present invention, there is provided a boiler comprising a furnace and a horizontal flue connected to the top of the furnace, the boiler having a trough-type separator in the horizontal flue, an ash hopper being arranged below the trough-type separator, and the ash hopper being selectively connectable to the furnace so as to deliver the collected ash into the furnace for re-combustion.

[0043] In a feasible embodiment, the boiler has a front screen of a specific shape that is approximately perpendicular to the left and right walls of the boiler and extends from the left wall to the right wall, the upper end of the front screen is connected to the boiler drum in the boiler top wall, and the lower end is connected to the front screen lower header; and the boiler also has a rear screen of a specific shape that is approximately perpendicular to the left and right walls of the boiler and extends from the left wall to the right wall, the upper end of the rear screen is connected to the boiler drum in the boiler top wall, and the lower end is connected to the lower header of the boiler rear wall; the trough separator is connected to the boiler drum and is arranged in the space defined by the upper end of the front screen and the upper end of the rear screen, and the upper ends of the front screen and the rear screen each have their own first light pipe grating segment; the front screen has a first non-light pipe grating segment located below its first light pipe grating segment and continuous with the first light pipe grating segment, and the rear screen also has a first non-light pipe grating segment located below its first light pipe grating segment and continuous with the first light pipe grating segment, and the first non-light pipe grating segment of the front screen and the first non-light pipe grating segment of the rear screen define the ash hopper.

[0044] In a feasible implementation manner, the front screen and the rear screen further define an ash return chamber located below the ash collecting hopper and communicated with the ash collecting hopper.

[0045] In a feasible embodiment, a gravity flap valve is provided on the top of the ash return chamber, and the bottom of the ash return chamber is defined by an inclined ash return guide plate extending from the front screen to the rear screen, and the upper portion of the front screen adjacent to the ash return guide plate has a second light tube grille section to provide an ash return port, so that when the smoke collected in the ash hopper reaches the threshold of the gravity flap valve, the flap valve flips, and the smoke falls onto the ash return guide plate and then enters the furnace defined by the front screen and the front wall of the boiler through the ash return port.

[0046] In a feasible embodiment, the front screen and the rear screen also define an economizer accommodating space located below the ash return chamber for arranging an economizer, and the economizer accommodating space and the ash return chamber are spatially separated from each other by the ash return guide plate.

[0047] In a feasible embodiment, a plurality of smoke damping plates are connected to the bottom of the slot-type separator, which are substantially perpendicular to the left and right walls of the boiler and extend from the left wall to the right wall, and whose bottom edges are opposite to the first non-light tube grating segment of the front screen and have a predetermined gap therewith, wherein the gap provides smoke damping to force the smoke to pass through the slot-type separator and move toward the first light tube grating segment of the rear screen after passing through the first light tube grating segment of the front screen, rather than bypassing the slot-type separator.

[0048] According to a fifth aspect of the present invention, a boiler is provided, which has a horizontal flue, which is directly opposite to the rear wall of the boiler, and the downstream smoke inlet immediately following the horizontal flue is positioned so that the flue gas moves obliquely downward away from the rear wall after impacting the rear wall through the horizontal flue, thereby utilizing inertial force and centrifugal force to separate smoke particles from the flue gas.

[0049] In a feasible embodiment, the boiler has a rear screen of a specific shape that is approximately perpendicular to the left and right walls of the boiler and extends from the left wall to the right wall, the upper end of the rear screen is connected to the boiler drum in the boiler top wall, and the lower end is connected to the lower connecting box of the boiler rear wall; the rear screen has a first light tube grating segment located at the upper end, a first non-light tube grating segment located below the first light tube grating segment and continuous with the first light tube grating segment, and a second light tube grating segment continuous with the first non-light tube grating segment; the horizontal flue passes through the first light tube grating segment; the second light tube grating segment defines the smoke inlet, and the smoke inlet is farther away from the boiler rear wall than the junction of the first light tube grating segment and the first non-light tube grating segment of the rear screen, so that the smoke moves obliquely downward away from the rear wall after passing through the horizontal flue and impacting the rear wall.

[0050] In a feasible embodiment, the space between the rear screen and the rear wall forms a smoke separation chamber, and the smoke separation chamber is used to collect smoke particles separated from the smoke.

[0051] In a feasible embodiment, the rear screen has a third light pipe grille segment located near the lower end thereof, and the third light pipe grille segment provides a dust collection port.

[0052] In a feasible embodiment, the bottom of the dust collecting port is connected to a cover that can be opened and closed, or is connected to a comb-shaped dust removal and smoke exhaust box, which is comb-shaped as a whole, with an upper dust collecting hopper and a row of comb-toothed dust exhaust pipes at the bottom. The dust collecting hopper defines a dust collecting chamber, and the dust exhaust pipe defines a dust exhaust passage. The dust collecting chamber and the dust exhaust passage are connected to each other, and the comb-toothed dust exhaust pipes are spaced apart from each other to define the smoke exhaust port. The boiler has a water tank arranged below the comb-shaped dust removal and smoke exhaust box, and the dust exhaust pipe is immersed in the water tank to achieve a water seal, so that when in use, smoke particles fall into the water tank via the dust collecting port, the dust collecting hopper, and the dust exhaust pipe of the comb-shaped dust removal and smoke exhaust box.

[0053] In a feasible implementation manner, the dust removal and smoke exhaust box is a trough box body formed by welding steel plates, and an openable and closable inspection door is provided on the outer wall panel.

[0054] In a feasible implementation manner, the comb-shaped dust removal and smoke exhaust box also serves as the boiler outer wall.

[0055] In all the aforementioned aspects and embodiments, the front wall, the rear wall, the left wall, the right wall, the top wall, the front screen and the rear screen are all membrane wall structures, and the boiler is a layer-fired boiler.

[0056] In summary, this high-temperature denitrification fly ash re-combustion furnace dust removal boiler has unique comprehensive superior performance in denitrification, energy saving and emission reduction, and also has certain advantages in economic operation and feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a schematic three-dimensional cross-sectional view of a boiler according to an embodiment of the present invention.

[0058] Figure 2 yes Figure 1 Schematic side cross-sectional view of an embodiment.

[0059] Figure 3 is a schematic cross-sectional view of an embodiment of a urea spray nozzle.

[0060] Figure 4 It is a partial cross-sectional diagram of a comb-shaped dust removal and smoke exhaust box. DETAILED DESCRIPTION

[0061] Figure 1 and Figure 2 A schematic cutaway stereogram and a corresponding schematic cross-sectional diagram of a boiler according to an embodiment of the present invention are shown. This embodiment includes several aspects of the present invention, but those skilled in the art should understand from the following description that these aspects can be used in combination or separately. The following is a detailed description.

[0062] See first Figure 1 and Figure 2 The boiler according to this embodiment of the present invention has a front wall 100, a rear wall 200, a left wall 300, a right wall 400 and a boiler top wall 500. These walls define the internal space of the boiler. In the internal space, a front screen 10 and a rear screen 20 are arranged. The front screen 10 is substantially perpendicular to the left and right walls of the boiler and extends from the left wall to the right wall, and has a specific shape. The upper end of the front screen 10 is connected to the drum 50 in the boiler top wall, and the lower end is connected to the lower header 106. Similarly, the rear screen 20 is also substantially perpendicular to the left and right walls of the boiler and also extends from the left wall to the right wall. It also has a specific shape, and the upper end is also connected to the drum 50 in the boiler top wall, and the lower end is connected to the lower header 23 of the rear wall 200.

[0063] Preferably, the front wall, rear wall, left wall, right wall, top wall, front screen, and rear screen are all membrane wall structures. Those skilled in the art should know that the membrane wall is generally a wall structure formed by welding a plurality of roll-formed finned tubes side by side, or by welding flat steel (flat steel plates) between light tubes. The membrane wall may have a light tube grating segment, that is, the segment only has light tubes without welded flat steel (or the tubes in the segment do not have fins), so as to facilitate the passage of flue gas, for example. Therefore, the membrane wall may include light tube grating segments and non-light tube grating segments. The front screen and the rear screen in the present invention both include light tube grating segments and non-light tube grating segments, which will be described in detail later.

[0064] As for the "header", those skilled in the art will know that it is also called "collector", which refers to a slender cylindrical pressure vessel in a boiler that connects many tubes with the same function and arranged in parallel. The header mainly plays the role of collecting, mixing, and redistributing the working medium (usually water) in the system. A large number of headers are used for the water-cooled membrane wall, economizer, superheater, reheater and other heating surfaces of the boiler. The header is mostly made of seamless steel pipes with a larger diameter and the same material as the heating surface. According to the position of the header on the length of the tube bundle, the header can be divided into an upper header (located at the upper end of the tube bundle), a middle header (located in the middle of the tube bundle), and a lower header (located at the lower end of the tube bundle, such as the lower header 23 of the rear wall 200). The above-mentioned "boiler drum 50" is actually also a header.

[0065] exist Figure 1 and Figure 2 In the illustrated embodiment, the front wall 100 and the front screen 10 define a combustion chamber 101, a combustion chamber throat 2, a long throat cavity 4 and a furnace 8 in sequence along the direction of smoke travel (from bottom to top in the illustrated embodiment).

[0066] The upper ends of the front screen 10 and the rear screen 20 are provided with light pipe sections, which define a horizontal flue 14, through which the flue gas from the furnace 8 can travel downstream. A smoke and dust separation chamber 21 can also be formed between the rear screen 20 and the rear wall 200.

[0067] According to a preferred embodiment, the upper parts of the front screen 10 and the rear screen 20 may define a funnel-shaped ash hopper 15, the lower parts of the two may define an economizer accommodation space 61 for accommodating the economizer 60, and the middle parts of the two may define an ash return chamber 11. The bottom of the ash return chamber 11 is defined by an inclined ash return guide plate 9, which isolates the ash hopper 15 from the economizer accommodation space 61.

[0068] It should be noted that the directions “up, down, left, right, front, back” in this article are combined for the purpose of easy understanding. Figure 1 and Figure 2 The invention is described with reference to the illustrated orientation and does not constitute a limitation to the invention.

[0069] Next, several aspects of the present invention are described one by one.

[0070] 1. Denitrification

[0071] The first aspect of the present invention relates to denitration. The main technical concepts include: first, the urea nozzle 5 is moved forward to the entrance of the furnace 8 as far as possible, thereby extending the reaction time of the denitration reaction and making the mixing more complete; second, the flue gas temperature at the urea nozzle is controlled within the optimal reduction reaction temperature range of 800-950°C by setting a long throat cavity 4 between the combustion chamber 101 and the furnace 8; third, by designing the shape of the front screen 10 and providing a specific contour of the furnace, the flue gas travel path is further extended, the reaction time is increased, and the flue gas and urea are mixed more fully; finally, the residual urea and NOx are forced to be remixed by the trough separator 12 to achieve further denitration and significantly reduce the concentration of escape. The above aspects are described in detail below.

[0072] like Figure 1 and Figure 2 As shown, the boiler according to the first aspect of the present invention comprises: a combustion chamber 101, a furnace 8, and a long throat cavity 4 connecting the combustion chamber and the furnace, wherein the long throat cavity is narrowed relative to the combustion chamber 101 and the furnace 8. The height of the long throat cavity 4 depends on the fuel and the combustion temperature, and can generally be between 1 meter and 4 meters.

[0073] In the illustrated embodiment, the combustion chamber 101, the furnace 8 and the long throat cavity 4 are defined by the front wall 100, the left wall 300, the right wall 400 and the front screen 10 of the boiler, but they may also be defined by other structures, which does not exceed the scope of the present invention.

[0074] The front arch 1 and the rear arch 3 defining the combustion chamber 101 are respectively arranged at the lower part of the front wall 100 and the front screen 10. The fuel burns in the combustion chamber 101 to generate flue gas, which flows upward from the combustion chamber 101 through the combustion chamber throat 2 into the long throat cavity 4, and then into the furnace 8. When passing through the long throat cavity 4, the flue gas exchanges heat with the working medium water in the front wall and the front screen, so that the temperature at the top of the long throat cavity, i.e., the junction with the furnace, drops to the optimal non-catalytic denitrification reduction reaction temperature of about 800-950°C. The urea nozzle 5 is arranged at the junction of the furnace 8 and the long throat cavity 4, so that the flue gas with the optimal temperature is mixed with the urea gas-liquid mixture ejected by the urea nozzle and a reduction reaction occurs. Since the flue gas has the optimal reaction temperature, the generation of NOx is reduced and the denitrification effect is improved.

[0075] Unlike the present invention which is provided with a long throat cavity, in the prior art, the boiler is at most provided with a throat 2 without a long throat cavity 4. Compared with the long throat cavity 4, the height of the throat 2 is almost negligible (usually only on the order of one to twenty centimeters). In the prior art, the urea nozzle is either set at the top of the furnace 8 or at the throat 2. The problem faced by setting it at the top of the furnace is that the flue gas reaction temperature is too low, and the mixing and reaction time is short; the problem faced by setting it at the throat is that the flue gas temperature is too high, so that the reduction reaction can hardly be carried out effectively. In the present invention, by setting the long throat cavity 4 and setting the urea nozzle at the junction of the furnace and the long throat cavity, the flue gas is cooled to the optimal reaction temperature after heat exchange with the long throat cavity 4, and can be mixed and reacted from the entrance of the furnace, so that the mixing is more sufficient and the reaction time is longer, thereby maximizing the reduction of NOx generation.

[0076] exist Figure 1 and Figure 2 In the embodiment shown, the cross section of the long throat cavity is rectangular. However, in other feasible embodiments, the cross section of the long throat cavity may also be other shapes, such as a zigzag shape or other tortuous shapes, so that the passage path of the smoke can be increased without increasing the height of the long throat cavity, thereby extending the heat exchange time. The cross-sectional shape of the long throat cavity can be achieved by setting the shapes of the front wall and the front screen.

[0077] In addition to controlling the reaction temperature, the present invention also envisions designing the shape of the front screen to extend the flue gas path and increase the reaction time, thereby further improving the denitration effect. To this end, the portion of the front screen 10 that defines the furnace 8 forms a concave portion facing the boiler front wall 100, thereby extending the flue gas path, such as Figure 1 and Figure 2 As shown. The lower end of the concave portion is substantially flush with the urea nozzle. In this way, the flue gas entering the furnace 8 upward through the long throat cavity 4 is pressed toward the right side of the furnace 8 by the urea gas-liquid mixture sprayed from the urea nozzle 5, that is, pressed toward the concave portion of the front screen 10, and then moves along the concave shape of the front screen, and finally reaches the top of the furnace 8, thus extending the reaction time of the flue gas and the urea gas-liquid mixture.

[0078] exist Figure 1 and Figure 2 In the non-limiting embodiment shown, the cross section of the inner recess is a broken line shape, in particular, a three-section broken line shape, including a vertical section A, a first inclined section B, and a second inclined section C, the lower end of the first inclined section B is continuous with the upper end of the vertical section A, and the upper end of the second inclined section C is continuous with the lower end of the vertical section A. However, it can be understood that the inner recess can also be other broken line shapes, or other concave shapes such as arcs, as long as the smoke travel path can be extended.

[0079] In order to further improve the denitration effect, the present invention also envisions setting a trough separator 12 in the horizontal flue 14 of the flue gas. When passing through the trough separator 12, the flue gas and urea are mixed again, so that the residual urea and nitrogen oxides NOx that have not participated in the reduction reaction are fully reduced again, further improving the denitration effect.

[0080] 2. Urea nozzle

[0081] A second aspect of the present invention relates to the arrangement of urea nozzles. Figures 1 to 3 The urea nozzle 5 is arranged in the header 102 of the front wall 100, so as to be cooled by the working medium water in the header, thereby avoiding the burning of the urea nozzle caused by the high temperature of the furnace, thereby ensuring the safe use of the urea nozzle.

[0082] In a preferred embodiment, the urea nozzle 5 is made of the same metal material as the front wall header 102, for example, to facilitate the welding connection between the two. The urea nozzle 5 can be slightly raised or horizontally penetrate the pipe wall of the front wall header 102 and welded and sealed with the header 102. The rising angle is generally not more than 30°. The advantage of the urea nozzle being slightly raised is that the flue gas slows down and the density decreases when it enters the expanded space of the wider furnace from the narrow long throat cavity. At this time, the urea nozzle is slightly raised so that more urea can be mixed with the flue gas in the area where the flue gas speed slows down and the density decreases, so that the mixing is more sufficient. The rear end of the urea nozzle 5 can be sleeved with a hose 53 for conveying liquid gaseous urea, and the front end 52 of the urea nozzle 5 can extend beyond the header 102 to the furnace 8, and the length of the excess is in the range of 10-20 mm.

[0083] 3. Fly ash re-ignition

[0084] The third aspect of the present invention relates to the re-ignition of fly ash. That is, the collected ash particles (mainly unburned carbon) are sent back into the furnace to be burned again, thereby improving combustion efficiency and reducing energy consumption. To this end, the present invention provides a trough-type separator and an ash hopper thereunder, and the ash hopper can be selectively connected to the furnace, so that the ash in the ash hopper can be sent back to the furnace to achieve re-ignition. As a further improvement scheme, the present invention also designs the rear screen to utilize its light tube grille segment with a horizontal extension component to further collect ash particles in the flue gas coming out of the trough-type separator. Details are given below.

[0085] First, see Figure 1 and Figure 2The upper ends of the front and rear screens are both connected to the drum 50 in the top wall of the boiler. In the space defined by the upper ends of the front and rear screens, a slot separator 12 is arranged, which is also connected to the drum 50. The upper end of the front screen 10 has a first light pipe grating segment D, and the upper end of the rear screen 20 has a first light pipe grating segment E, so as to allow flue gas to enter the slot separator 12 between the two and leave from the slot separator 12.

[0086] The front screen 10 has a first non-light pipe grating segment B located below and continuous with its first light pipe grating segment D, and the rear screen 20 also has a first non-light pipe grating segment F located below and continuous with its first light pipe grating segment E. The first non-light pipe grating segment B of the front screen and the first non-light pipe grating segment F of the rear screen define an ash collecting hopper 15.

[0087] The front screen 10 and the rear screen 20 further define an ash return chamber 11 located below the ash collection hopper 15 and communicating with the ash collection hopper. In the illustrated embodiment, the ash return chamber is defined by the vertical sections of the front and rear screens, but may also be defined by sections of other shapes and orientations.

[0088] like Figure 1 and Figure 2 As shown, a gravity flap valve 16 is provided at the top of the ash return chamber, and the bottom of the ash return chamber is defined by an inclined ash return guide plate 9 extending from the front screen 10 to the rear screen 20, and the upper portion of the front screen 10 adjacent to the ash return guide plate 9 has a second light tube grille segment A1 to provide an ash return port 17, so that when the smoke collected in the ash hopper 15 reaches the threshold of the gravity flap valve 16, the flap valve 16 flips over, and the smoke falls onto the ash return guide plate 9 and then re-enters the furnace 8 through the ash return port 17 and re-burns in the rising high-temperature flue gas flow to achieve re-combustion.

[0089] In order to ensure that the flue gas passes through the slot separator 12 instead of bypassing the slot separator 12 after passing through the first light tube grid section D of the front screen, a plurality of flue gas damping plates 13 are connected to the bottom of the slot separator 12 (for example, welded), and the flue gas damping plates 13 are approximately perpendicular to the left and right walls of the boiler and extend from the left wall to the right wall, and the bottom edge thereof is opposite to the first non-light tube grid section B of the front screen 10 and has a predetermined gap d therewith, and the gap provides flue gas damping. The flue gas damping plates 13 are preferably arranged vertically. By setting up the flue gas damping plates, the flue gas bypass is actually prevented, so that the flue gas can only pass through the slot separator, because the resistance of the flue gas when passing through the aforementioned gap d (especially considering that there will be soot falling from the slot separator at this gap) is significantly greater than the resistance from the inlet side to the outlet side of the slot separator. In other words, by setting up the flue gas damping plates, the flue gas will basically pass through the inside of the slot separator, from the inlet side to the outlet side, and move downstream. When the flue gas passes through the trough separator, the smoke particles contained therein are separated by impacting with the fin tubes of the trough separator and fall into the ash collecting hopper 15. The trough separator is well known to those skilled in the art, and its structure is not described in detail.

[0090] According to an improved solution of the present invention, the ash hopper 15 further collects ash particles in the flue gas passing through the trough separator 12, which is achieved by designing the shape of the upper end of the rear screen to have a horizontal extension component.

[0091] by Figure 1 and Figure 2 As shown in the non-limiting embodiment shown, the first light tube grid segment E of the rear screen includes a substantially vertical segment E1 and a substantially horizontal segment E2. The substantially horizontal segment E2 provides a horizontal extension component of the first light tube grid segment E. When the boiler is in operation, the flue gas undergoes a first separation of smoke particles when passing through the trough separator 12, then passes through the substantially vertical segment E1, and moves horizontally toward the rear wall above the substantially horizontal segment E2. In the process of moving along the substantially horizontal segment E2, the smoke particles in the smoke can fall into the ash hopper 15 through the horizontal segment E2 under the action of gravity to perform a second separation of smoke particles.

[0092] Therefore, in this improved solution, the ash hopper 15 collects the smoke particles from the trough separator (which come from the gap d between the smoke damping plate and the front screen) on the one hand, and collects the smoke particles in the smoke coming out of the trough separator on the other hand.

[0093] In the illustrated embodiment, the first light pipe segment D of the front screen 10 is a straight segment arranged substantially vertically, but it should be understood that the light pipe segment D may also have other shapes, such as an arc or a polygon. According to the above description, those skilled in the art should understand that the first light pipe segment E of the rear screen 20 composed of a substantially vertical segment E1 and a substantially horizontal segment E2 may also be replaced by other forms of light pipe segments, such as a substantially arc-shaped light pipe segment or an inclined linear light pipe segment, as long as it has a horizontal extension component.

[0094] In summary, although the front screen 10 and the rear screen 20 are shown in the figure as a "multi-segment structure" consisting of multiple vertical segments and multiple inclined segments, the present invention is not limited to this. For example, two or more adjacent segments can be replaced by arc segments with smooth transitions, as long as the front and rear screens can define the ash collecting hopper and the ash returning chamber.

[0095] 4. Dust removal in the furnace

[0096] The fourth aspect of the present invention relates to dust removal in the furnace, which mainly includes: providing a horizontal flue, and making the horizontal flue face the rear wall of the boiler, so that the flue gas directly hits the rear wall of the boiler, and by designing the shape of the rear screen, the flue gas in the horizontal flue is guided to turn back at an acute angle, so that the smoke dust particles in the flue gas will hit the rear wall due to inertia and fall along the rear wall, and are further removed under the action of centrifugal force during the acute angle turning process.

[0097] In the illustrated embodiment, the horizontal flue is defined by the first light tube grid segment D on the upper part of the front screen and the first light tube grid segment E on the upper part of the rear screen. The projections of the two light tube grid segments in the horizontal direction from the front wall to the rear wall are roughly aligned, thereby defining the horizontal flue, and the horizontal flue is directly opposite to the rear wall of the boiler.

[0098] The rear screen 20 defines a smoke inlet 18 downstream of the horizontal flue. After passing through the horizontal flue, the smoke will move toward the downstream smoke inlet 18. In order to make the smoke return at an acute angle, the smoke inlet 18 is further away from the boiler rear wall 200 than the joint EF of the first light tube grid segment E and the first non-light tube grid segment F of the rear screen, so that the smoke moves obliquely downward after passing through the rear wall 200 of the horizontal flue. In this process, the smoke particles in the smoke will hit the rear wall due to inertia and fall along the rear wall, and will also be further removed under the action of centrifugal force during the acute angle turning process.

[0099] In the illustrated exemplary embodiment, the smoke inlet 18 is disposed on a portion of the rear panel 20 defining the economizer accommodating space 61 , and is provided by a horizontal second light pipe grid segment H, for example.

[0100] In a further preferred embodiment, the rear screen 20 is provided with a dust shield 19 on one side of the smoke inlet 18 close to the boiler rear wall 200. The dust shield 19 is substantially perpendicular to the left and right walls of the boiler and extends from the left wall to the right wall, and is preferably arranged vertically.

[0101] The space between the rear screen 20 and the rear wall 200 forms a smoke separation chamber 21, and the smoke separation chamber 21 is used to collect the smoke particles separated from the smoke by inertial force and centrifugal force.

[0102] The lower end of the rear screen 20 is connected to the lower header 23 of the rear wall 200. The rear screen 20 has a third light pipe grille segment J located near the lower end thereof, and the third light pipe grille segment J provides a dust collection port 22. In order to facilitate the collection of smoke particles, the lower portion of the rear screen 20 can be inclined or extended in an arc shape so that the smoke particles can slide down and gather in the dust collection port 22.

[0103] The bottom of the dust collecting port 22 can be connected to a cover that can be opened and closed for regular cleaning; or a comb-shaped dust removal and smoke exhaust box 24 according to the present invention can be connected. The comb-shaped dust removal and smoke exhaust box is in the shape of a comb as a whole, and has an upper dust collecting hopper 242 and a row of comb-shaped dust exhaust pipes 244 at the bottom. The dust collecting hopper defines a dust collecting chamber, and the dust exhaust pipes define a dust exhaust passage. The dust collecting chamber and the dust exhaust passage are connected to each other, and the comb-shaped dust exhaust pipes 244 are spaced apart from each other to define a smoke exhaust port 246. The boiler has a water tank 28 arranged below the comb-shaped dust removal and smoke exhaust box, and the dust exhaust pipe 244 is immersed in the water tank 28 to achieve a water seal, so that when in use, smoke particles fall into the water tank 28 via the dust collecting port 22, the dust collecting hopper 242 of the comb-shaped dust removal and smoke exhaust box, and the dust exhaust pipe 244.

[0104] In a feasible embodiment, the dust removal and smoke exhaust box 24 is a trough box body made of welded steel plates, and is connected to the dust collection port 22 via a flange. Preferably, the outer wall plate of the dust removal and smoke exhaust box 24 is provided with an openable and closable inspection door 245.

[0105] The comb-shaped dust removal and smoke exhaust box 24 can also be used as the outer wall of the boiler, that is, as an extension of the rear wall 200.

[0106] The economizer accommodating space 61 and the ash return chamber 11 are spatially separated from each other by the ash return guide plate 9. In the illustrated embodiment, the economizer accommodating space 61 is defined by the lower part of the front screen 10, the lower part of the rear screen 20, and the comb-shaped dust removal and smoke exhaust box 24, and the economizer 60 is arranged in the economizer accommodating space 61. The upstream flue gas enters the economizer accommodating space 61 through the smoke inlet 18, then passes through the economizer 60, and is finally discharged from the smoke exhaust port 246 between the dust exhaust pipes 244 of the comb-shaped dust removal and smoke exhaust box 24.

[0107] Thus, according to the present invention, the smoke particles moistened by the urea solution and the water generated by the reduction reaction are separated and discharged due to the inertial force and the centrifugal force before entering the economizer, so that the smoke in the flue gas entering the economizer is greatly reduced, thereby reducing the adhesion and ash accumulation on the heating surface of the economizer, improving the heat exchange efficiency, and on the other hand, greatly reducing the original dust concentration of the boiler.

[0108] VII. Other aspects

[0109] Those skilled in the art will appreciate that the aforementioned aspects of this specification can be used alone or in any combination. In addition, those skilled in the art will appreciate that the movement of the flue gas in the entire boiler can be achieved by a blower and / or an exhaust fan.

Claims

1. A boiler having a combustion chamber and a furnace, characterized in that: The boiler further comprises a long throat cavity connecting the combustion chamber and the furnace, the long throat cavity is narrowed relative to the cross-section of the combustion chamber and the furnace and has a height of 1 meter to 4 meters, and the boiler further comprises a urea nozzle located near the junction of the long throat cavity and the furnace, The boiler has a front screen of a specific shape which is substantially perpendicular to the left wall and the right wall of the boiler and extends from the left wall to the right wall. The upper end of the front screen is connected to the drum in the top wall of the boiler, and the lower end is connected to the lower header of the front screen. The combustion chamber, the furnace and the long throat cavity are defined by the front wall, the left wall, the right wall and the front screen of the boiler. The boiler also has a rear screen of a specific shape that is substantially perpendicular to the left and right walls of the boiler and extends from the left wall to the right wall, wherein the upper end of the rear screen is connected to the drum in the top wall of the boiler, and the lower end is connected to the lower header of the rear wall of the boiler; The boiler has a slot-type separator connected to the drum and arranged in a space defined by an upper end of the front screen and an upper end of the rear screen, wherein the upper ends of the front screen and the rear screen each have a respective first light pipe grid segment; The front screen has a first non-light tube grating segment located below its first light tube grating segment and continuous with the first light tube grating segment, and the rear screen also has a first non-light tube grating segment located below its first light tube grating segment and continuous with the first light tube grating segment. The first non-light tube grating segment of the front screen and the first non-light tube grating segment of the rear screen define an ash collecting hopper. The front screen and the rear screen also define an ash return chamber located below the ash collecting hopper and connected to the ash collecting hopper. The bottom of the ash return chamber is defined by an inclined ash return guide plate extending from the front screen to the rear screen, and the upper portion of the front screen adjacent to the ash return guide plate has a second light tube grating segment to provide an ash return port, and the ash return chamber is connected to the furnace via the ash return port.

2. The boiler according to claim 1, wherein: The cross section of the long throat cavity is rectangular.

3. The boiler according to claim 1, wherein: The cross section of the long throat cavity is zigzag-shaped.

4. The boiler according to claim 1, wherein: The urea nozzle is arranged in the header of the boiler front wall, so that the working medium water in the header is used for cooling.

5. The boiler according to claim 1, wherein: The urea nozzle slightly rises and penetrates the pipe wall of the header of the front wall, and its front end extends into the furnace.

6. The boiler according to claim 1, wherein: The urea nozzle penetrates the pipe wall of the header of the front wall approximately horizontally, and the front end thereof extends into the furnace.

7. The boiler according to claim 1, wherein: The portion of the front screen defining the furnace forms an inner recess with a concave surface facing the boiler front wall, thereby extending the travel path of the flue gases.

8. The boiler according to claim 7, wherein: The cross section of the inner concave portion is arc-shaped or folded-line-shaped.

9. The boiler according to claim 8, wherein: The inner concave portion includes a vertical section, a first inclined section and a second inclined section, the lower end of the first inclined section is continuous with the upper end of the vertical section, and the upper end of the second inclined section is continuous with the lower end of the vertical section.

10. The boiler according to claim 7, wherein: The boiler has a horizontal flue communicating with the furnace, so that the flue gas can travel horizontally after traveling upward along the inner concave portion of the front panel, thereby forming an S-shaped flue gas travel path, thereby further extending the flue gas travel path.

11. The boiler according to claim 1, wherein: A gravity flap valve is provided on the top of the ash return chamber, so that when the smoke collected in the ash hopper reaches the threshold of the gravity flap valve, the flap valve flips over, and the smoke falls onto the ash return guide plate and then enters the furnace defined by the front screen and the boiler front wall through the ash return port.

12. The boiler according to claim 10, wherein: The front screen and the rear screen also define an economizer accommodating space located below the ash return chamber for arranging an economizer. The economizer accommodating space and the ash return chamber are spatially separated from each other by the ash return guide plate, and the rear screen is formed with a smoke inlet on the portion defining the economizer accommodating space.

13. The boiler according to claim 1, wherein: A plurality of smoke damping plates are connected to the bottom of the slot-type separator, which are substantially perpendicular to the left and right walls of the boiler and extend from the left wall to the right wall, and whose bottom edges are opposite to the first non-light tube grating section of the front screen and have a predetermined gap therewith, wherein the gap provides smoke damping to force the smoke to pass through the slot-type separator and move toward the first light tube grating section of the rear screen after passing through the first light tube grating section of the front screen, rather than bypassing the slot-type separator.

14. The boiler according to claim 12, wherein: The rear screen has a second light tube grating segment continuous with the first non-light tube grating segment, and the second light tube grating segment defines the smoke inlet. The smoke inlet is farther away from the boiler rear wall than the junction of the first light tube grating segment and the first non-light tube grating segment of the rear screen, so that the smoke moves obliquely downward and enters the smoke inlet after passing through the horizontal flue and impacting the rear wall.

15. The boiler according to claim 14, wherein: The rear screen is provided with a dust shield on one side of the smoke inlet close to the rear wall of the boiler.

16. The boiler according to claim 15, wherein: The dust shield is substantially perpendicular to the left wall and the right wall of the boiler and extends from the left wall to the right wall.

17. The boiler according to claim 16, wherein: The space between the rear screen and the rear wall forms a smoke separation chamber, and the smoke separation chamber is used to collect smoke particles separated from the smoke.

18. The boiler according to claim 17, wherein: The rear screen has another light pipe grille section located near its lower end, and the other light pipe grille section provides a dust collecting port for the smoke and dust separation chamber.

19. The boiler according to claim 18, wherein: The bottom of the dust collecting port is connected to a cover that can be opened and closed, or is connected to a comb-shaped dust removal and smoke exhaust box, which is comb-shaped as a whole, with an upper dust collecting hopper and a row of comb-toothed dust exhaust pipes at the bottom. The dust collecting hopper defines a dust collecting chamber, and the dust exhaust pipe defines a dust exhaust passage. The dust collecting chamber and the dust exhaust passage are connected to each other, and the comb-toothed dust exhaust pipes are spaced apart from each other to define the smoke exhaust port. The boiler has a water tank arranged below the comb-shaped dust removal and smoke exhaust box, and the dust exhaust pipe is immersed in the water tank to achieve water seal, so that when in use, smoke particles fall into the water tank through the dust collecting port, the dust collecting hopper of the comb-shaped dust removal and smoke exhaust box, and the dust exhaust pipe.

20. The boiler according to claim 19, wherein The dust removal and smoke exhaust box is a trough box body formed by welding steel plates, and an openable and closable inspection door is arranged on the outer wall plate.

21. The boiler according to claim 19, wherein: The comb-shaped dust removal and smoke exhaust box also serves as the boiler outer wall.

22. A boiler as claimed in any one of claims 1 to 21, wherein: The front wall, rear wall, left wall, right wall, top wall, front screen and rear screen of the boiler are all membrane wall structures, and / or the boiler is a layer-fired boiler.

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