A π-type boiler with low-temperature heating surface arranged in the furnace and flue gas recirculation

Abstract

The application provides a kind of π type boiler with low temperature heating surface arranged in furnace and flue gas recirculation, and belongs to the field of π type boiler.The outlet of horizontal flue is connected to the tail flue of the boiler, and the tail flue is divided into front tail flue and rear tail flue, low temperature superheater and economizer are arranged in the front tail flue, low temperature reheater and economizer are arranged in the rear tail flue, and flue gas temperature control baffle is installed in the front and rear flue at the outlet of the tail flue;The left and right sides of the boiler bottom hearth are connected to the flue gas recirculation fan through the connecting flue.The application adopts a variety of coupled optimization temperature control mode.Coupled optimization temperature control mode is the comprehensive use of the above several temperature control modes, two or more temperature control modes are used during the operation of the boiler, and the steam temperature is adjusted at the same time.Compared with the use of single temperature control mode, the coupled optimization mode can provide larger temperature control range and more accurate temperature control.

Description

Technical Field

[0001] This invention relates to a π-type boiler that employs a low-temperature heating surface arranged inside the furnace and flue gas recirculation, belonging to the field of π-type boilers. Background Technology

[0002] In recent years, a large number of 620℃-class ultra-supercritical boilers have been successfully put into operation in my country. Their conventional boiler parameters have main steam / reheat steam temperatures of 605 / 623℃. Increasing these parameters to 650℃-class boilers, with main steam / reheat steam temperatures of 655 / 653℃ or 655 / 673℃, can significantly improve unit efficiency. Compared to conventional boilers, however, they present challenges such as higher steam parameters at high-temperature heating surfaces, greater variation in heat absorption ratios, increased difficulty in heating surface arrangement, delayed steam temperature regulation, poor low-load steam temperature regulation characteristics, and limited load regulation range. Summary of the Invention

[0003] The purpose of this invention is to solve the problems existing in the prior art and to provide a π-type boiler that adopts a low-temperature heating surface arranged in the furnace and flue gas recirculation.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A π-type boiler employing an in-furnace arrangement of low-temperature heating surfaces and flue gas recirculation includes water-cooled walls, a low-temperature superheater, a wall-type superheater, a partition screen superheater, a rear screen superheater, a final stage superheater, a low-temperature reheater, a wall-type reheater, a partition screen reheater, a final stage reheater, a flue gas temperature regulating baffle, a connecting flue, a flue gas recirculation fan, and economizers and final stage superheaters. A wall-type superheater is arranged on the front wall near the inner wall of the water-cooled walls in the upper part of the furnace, and wall-type reheaters are arranged on both side walls. The outlet on the upper right side of the furnace connects to the boiler's horizontal flue, within which a partition screen reheater and a final stage superheater are arranged. The reheater is connected to the tail flue of the boiler via a horizontal flue outlet. The tail flue is divided into a front tail flue and a rear tail flue. The low-temperature superheater and economizer are arranged in the front tail flue, and the low-temperature reheater and economizer are arranged in the rear tail flue. Flue gas temperature regulating baffles are installed in both the front and rear flues at the tail flue outlet. The left and right sides of the furnace at the bottom of the boiler are connected to the flue gas recirculation fan via connecting flues. The wall-type superheater, wall-type reheater, screen-type superheater, final stage superheater, final stage reheater, low-temperature superheater, low-temperature reheater and economizer are connected by pipes and headers.

[0006] The present invention discloses a π-type boiler with a low-temperature heating surface arranged inside the furnace and flue gas recirculation. A radiant heating surface is added to the water-cooled wall and is closely attached to the water-cooled wall. The added radiant heating surface is a wall-type radiant heating surface that covers the inner surface of the furnace water-cooled wall and shields the water-cooled wall.

[0007] The present invention discloses a π-type boiler with low-temperature heating surfaces arranged inside the furnace and flue gas recirculation. The positions of the low-temperature superheaters in the front and rear flues can be interchanged.

[0008] This invention discloses a π-type boiler employing a low-temperature heating surface arranged inside the furnace and flue gas recirculation. The π-type boiler uses five methods for temperature regulation, namely:

[0009] 1) Swing burner: The boiler burner is located in the middle area of ​​the boiler furnace, and the boiler uses a swing burner;

[0010] 2) Coal-to-water ratio: Controlling the ratio of boiler coal feed rate to boiler water feed rate;

[0011] 3) Flue gas dampers: By adjusting the opening and closing angle of the flue gas temperature regulating dampers on the front and rear flue ducts, the amount of flue gas in the two flue ducts is changed, thereby changing the heat absorption ratio of the low-temperature superheater and achieving the regulation of reheat steam temperature.

[0012] 4) Excess air volume: Change the excess air coefficient;

[0013] 5) Flue gas recirculation: This includes flue gas recirculation fans, flue gas temperature regulating dampers, and connecting flue ducts. The recirculated flue gas is taken from the low-temperature flue gas of the economizer. The flue gas recirculation fans are used to circulate the flue gas to the bottom of the boiler furnace, thereby increasing the amount of flue gas in the boiler and increasing the convective heat transfer and heat absorption of the boiler's low-temperature heating surfaces.

[0014] This invention discloses a π-type boiler employing an in-furnace arrangement of low-temperature heating surfaces and flue gas recirculation. Five temperature control methods are coupled together for temperature control. The specific steps are as follows: First, the superheater steam temperature is adjusted using the coal-water ratio, the reheater steam temperature is adjusted using the oscillating burner, and the reheat steam temperature is adjusted using the tail-end double flue gas temperature control baffle. The excess air coefficient plays a fine-tuning role in the superheater and reheat steam temperatures. Under low load conditions, when the above methods have been exhausted, flue gas recirculation is used to adjust the reheat steam temperature, which can provide a larger temperature control range and higher sensitivity.

[0015] This invention discloses a π-type boiler employing an in-furnace arrangement of low-temperature heating surfaces and flue gas recirculation. It utilizes multiple coupled and optimized temperature control methods, including a swing burner, coal-to-water ratio, flue gas recirculation system, flue gas dampers, and excess air volume. These coupled and optimized temperature control methods combine several of these approaches. During boiler operation, two or more of these methods are used to simultaneously regulate the steam temperature. Compared to using a single temperature control method, this multi-coupled and optimized approach provides a wider temperature control range and more precise temperature regulation. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the structure of a π-type boiler of the present invention, which adopts a low-temperature heating surface arranged inside the furnace and flue gas recirculation.

[0017] Figure 2 This is a top view of a π-type boiler of the present invention, which employs a low-temperature heating surface arranged inside the furnace and flue gas recirculation. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods are given, but the protection scope of the present invention is not limited to the following embodiments.

[0019] Example 1: As Figure 1-2 As shown, this embodiment involves a π-type boiler with an in-furnace arrangement of low-temperature heating surfaces and flue gas recirculation, including water-cooled walls, low-temperature superheaters, wall-type superheaters, partition screen superheaters, rear screen superheaters, final stage superheaters, low-temperature reheaters, wall-type reheaters, partition screen reheaters, final stage reheaters, flue gas temperature regulating baffles, connecting flues, flue gas recirculation fans, and economizers and final stage superheaters. A wall-type superheater is arranged on the front wall near the inner wall of the water-cooled walls in the upper part of the furnace, and wall-type reheaters are arranged on both side walls. The outlet on the upper right side of the furnace connects to the boiler's horizontal flue, and partition screens are arranged within the horizontal flue. The boiler has a reheater and a final stage reheater. The outlet of the horizontal flue is connected to the tail flue of the boiler. The tail flue is divided into a front tail flue and a rear tail flue. The low-temperature superheater and economizer are arranged in the front tail flue, and the low-temperature reheater and economizer are arranged in the rear tail flue. Flue gas temperature regulating baffles are installed in both the front and rear flues at the outlet of the tail flue. The left and right sides of the furnace at the bottom of the boiler are connected to the flue gas recirculation fan through connecting flues. The wall-type superheater, wall-type reheater, screen-type superheater, final stage superheater, final stage reheater, low-temperature superheater, low-temperature reheater and economizer are connected by pipes and headers.

[0020] The present invention discloses a π-type boiler with a low-temperature heating surface arranged inside the furnace and flue gas recirculation. A radiant heating surface is added to the water-cooled wall and is closely attached to the water-cooled wall. The added radiant heating surface is a wall-type radiant heating surface that covers the inner surface of the furnace water-cooled wall and shields the water-cooled wall.

[0021] The present invention discloses a π-type boiler with low-temperature heating surfaces arranged inside the furnace and flue gas recirculation. The positions of the low-temperature superheaters in the front and rear flues can be interchanged.

[0022] This invention discloses a π-type boiler employing a low-temperature heating surface arranged inside the furnace and flue gas recirculation. The π-type boiler uses five methods for temperature regulation, namely:

[0023] 1) Swing burner: The boiler burner is located in the middle area of ​​the boiler furnace, and the boiler uses a swing burner;

[0024] 2) Coal-to-water ratio: Controlling the ratio of boiler coal feed rate to boiler water feed rate;

[0025] 3) Flue gas dampers: By adjusting the opening and closing angle of the flue gas temperature regulating dampers on the front and rear flue ducts, the amount of flue gas in the two flue ducts is changed, thereby changing the heat absorption ratio of the low-temperature superheater and achieving the regulation of reheat steam temperature.

[0026] 4) Excess air volume: Change the excess air coefficient;

[0027] 5) Flue gas recirculation: This includes flue gas recirculation fans, flue gas temperature regulating dampers, and connecting flue ducts. The recirculated flue gas is taken from the low-temperature flue gas of the economizer. The flue gas recirculation fans are used to circulate the flue gas to the bottom of the boiler furnace, thereby increasing the amount of flue gas in the boiler and increasing the convective heat transfer and heat absorption of the boiler's low-temperature heating surfaces.

[0028] Example 2: Figure 1-2 As shown, the 650℃ tower boiler with low-temperature heating surfaces and flue gas recirculation arranged in the furnace involved in this embodiment has the following specific temperature control method:

[0029] Oscillating burner:

[0030] A swing burner is a type of pulverized coal burner whose nozzle can swing up and down at a certain angle. By swinging the burner up and down, the position of the flame center in the furnace is changed, causing a change in the temperature of the flue gas at the furnace outlet. This, in turn, alters the temperature of the flue gas entering the downstream heating surfaces of the furnace outlet, thereby changing the heat absorption of each heating surface and thus regulating the steam temperature.

[0031] Coal-to-water ratio:

[0032] The coal-water ratio refers to the amount of steam produced per kilogram of coal burned in a boiler, representing the ratio of coal feed to boiler feedwater. Regulating steam temperature through the coal-water ratio essentially means matching the heat input from the fuel with the heat output from the steam, i.e., controlling the coal-water ratio. For supercritical once-through boilers, the fuel and feedwater quantities directly affect the temperature of the working fluid in the steam-water pipelines. Furthermore, changes in the enthalpy of the working fluid at all cross-sections of the boiler outlet and the steam-water pipelines are correlated. When the coal-water ratio changes, it correspondingly causes a shift in the steam-water interface. Therefore, the first effect is a change in steam temperature at the beginning of the superheater section in the evaporation zone, which in turn causes a change in the superheater outlet steam temperature.

[0033] Smoke baffle:

[0034] Flue gas temperature regulation involves placing the heated surface requiring temperature control in one of two parallel flues and installing a regulating damper in that flue. By changing the opening of the damper, the resistance of the flue is increased or decreased, thereby altering the distribution ratio of flue gas in the two flues and thus changing the amount of heat released by the flue gas in the two flues, achieving the purpose of regulating steam temperature.

[0035] Excess air volume:

[0036] The excess air coefficient, also known as the "excess air quantity" or "excess air factor," is the ratio of the actual amount of air supplied for fuel combustion to the theoretical amount of air. It is an important parameter reflecting the fuel-air ratio. In various furnaces or combustion chambers, to ensure complete combustion, the actual amount of air supplied must always exceed the theoretical amount (this excess is called "excess air"), meaning the excess air coefficient must be greater than 1. Changing the excess air coefficient alters the total flue gas volume of the boiler, thereby changing the heat transfer efficiency of the convective heating surfaces and regulating the steam temperature.

[0037] Flue gas recirculation:

[0038] The flue gas recirculation system mainly consists of a flue gas recirculation fan, a flue gas recirculation duct, and corresponding accessories such as dampers. The recirculated flue gas is taken from the low-temperature flue gas at the economizer or preheater outlet and circulated to the bottom of the boiler furnace by the recirculation fan. This increases the amount of flue gas in the boiler, increases the convective heat transfer and heat absorption of the boiler's low-temperature heating surfaces, and plays a role in regulating the steam temperature.

[0039] Various temperature control methods are coupled: Firstly, the coal-to-water ratio is used to regulate the superheater steam temperature, and the oscillating burner is used to regulate the reheater steam temperature. However, in actual operation, the oscillating burner's actuator is prone to jamming, often fixing at a certain angle, thus limiting its adjustment sensitivity. Therefore, the tail-end double flue damper is used to regulate the reheat steam temperature. The excess air coefficient plays a fine-tuning role in the superheater and reheat steam temperatures; however, a large excess air coefficient negatively impacts boiler efficiency, so it is only used as an auxiliary fine-tuning tool.

[0040] Under low load conditions, when all the above methods have been exhausted, using flue gas recirculation to regulate reheat steam temperature can provide a larger temperature regulation range and higher sensitivity.

[0041] The superheater temperature control method uses a combination of coal-to-water ratio and water spray. The coal-to-water ratio adjustment regulates the steam temperature by altering the ratio of input fuel and working fluid. Water spray involves installing desuperheaters on the superheater pipes, injecting lower-temperature water to regulate the temperature of the high-temperature superheated steam. The reheater temperature control method uses a tail-end temperature control baffle combined with an excess air coefficient, assisted by a swing burner. The tail-end temperature control baffle divides the boiler's tail flue into two sections, housing a low-temperature superheater and a low-temperature reheater respectively. Baffles are installed at the outlets of both flues; adjusting the baffle opening changes the flue gas volume in both flues, thus altering the heat absorption ratio of the superheater and reheater, and regulating the reheat steam temperature. The excess air coefficient adjustment involves measuring and changing the oxygen content in the boiler flue gas, thereby altering the total flue gas volume and regulating the heat absorption of the reheater, ultimately regulating the reheat steam temperature.

[0042] This invention discloses a π-type boiler employing an in-furnace arrangement of low-temperature heating surfaces and flue gas recirculation. Five temperature control methods are coupled together for temperature control. The specific steps are as follows: First, the superheater steam temperature is adjusted using the coal-water ratio, the reheater steam temperature is adjusted using the oscillating burner, and the reheat steam temperature is adjusted using the tail-end double flue gas temperature control baffle. The excess air coefficient plays a fine-tuning role in the superheater and reheat steam temperatures. Under low load conditions, when the above methods have been exhausted, flue gas recirculation is used to adjust the reheat steam temperature, which can provide a larger temperature control range and higher sensitivity.

[0043] The superheater temperature control method uses a combination of coal-to-water ratio and water spray. The coal-to-water ratio adjustment regulates the steam temperature by altering the ratio of input fuel and working fluid. Water spray involves installing desuperheaters on the superheater pipes, injecting lower-temperature water to regulate the temperature of the high-temperature superheated steam. The reheater temperature control method uses a tail-end temperature control baffle combined with an excess air coefficient, assisted by a swing burner. The tail-end temperature control baffle divides the boiler's tail flue into two sections, housing a low-temperature superheater and a low-temperature reheater respectively. Baffles are installed at the outlets of both flues; adjusting the baffle opening changes the flue gas volume in both flues, thus altering the heat absorption ratio of the superheater and reheater, and regulating the reheat steam temperature. The excess air coefficient adjustment involves measuring and changing the oxygen content in the boiler flue gas, thereby altering the total flue gas volume and regulating the heat absorption of the reheater, ultimately regulating the reheat steam temperature.

[0044] The added radiant heating surfaces of the superheaters and reheaters are located inside the furnace. These added surfaces are wall-type radiant heating surfaces, covering the inner surface of the furnace water-cooled walls and obstructing them. This reduces the heat absorption of the water-cooled walls while increasing the radiant heat absorption of the superheaters and reheaters, and decreasing the convective heat absorption. This achieves an adjustment of the radiant and convective heat absorption ratio of the water-cooled walls and the superheaters / reheaters.

[0045] The boiler employs a combination of optimized temperature control methods, including oscillating burners, coal-to-water ratio, flue gas recirculation system, flue gas dampers, and excess air volume. This optimized temperature control combines several of these methods, employing two or more of them during boiler operation to simultaneously regulate steam temperature. Compared to using a single method, this multi-method optimization provides a wider temperature control range and more precise temperature regulation.

[0046] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A π-type boiler employing an in-furnace arrangement of low-temperature heating surfaces and flue gas recirculation, characterized in that, The π-type boiler with low-temperature heating surfaces and flue gas recirculation arranged in the furnace includes a water-cooled wall (1), a low-temperature superheater (2), a wall-type superheater (3), a partition screen superheater (4), a rear screen superheater (5), a final stage superheater (6), a low-temperature reheater (7), a wall-type reheater (8), a screen reheater (9), a final stage reheater (10), a flue gas temperature regulating baffle (11), a connecting flue (12), a flue gas recirculation fan (13), and an economizer (14). The boiler furnace is entirely composed of water-cooled walls (1). The upper part of the furnace is equipped with partition screen superheaters (4), rear screen superheaters (5), and final stage superheaters (6). A wall-type superheater (3) is arranged on the front wall near the inner wall of the water-cooled wall (1) in the upper part of the furnace. The wall-type superheater (3) covers the water-cooled wall (1). The inner surface is a wall-type radiant heating surface that shields the water-cooled wall (1); wall-type reheaters (8) are arranged on both side walls. The wall-type reheaters (8) are wall-type radiant heating surfaces that cover the inner surface of the water-cooled wall (1) and shield the water-cooled wall (1). The outlet on the upper right side of the furnace is connected to the horizontal flue of the boiler. A screen-type reheater (9) and a final stage reheater (10) are arranged in the horizontal flue. The outlet of the horizontal flue is connected to the tail flue of the boiler. The tail flue is divided into a front tail flue and a rear tail flue. A low-temperature superheater (2) and an economizer (14) are arranged in the front tail flue. A low-temperature reheater (7) and an economizer (14) are arranged in the rear flue. Flue gas temperature regulating baffles (11) are installed in both the front and rear flues at the outlet of the rear flue. The left and right sides of the furnace at the bottom of the boiler are connected to the flue gas recirculation fan (13) through connecting flues (12). The wall-mounted superheater (3), wall-mounted reheater (8), partition screen superheater (4), rear screen superheater (5), final stage superheater (6), final stage reheater (10), low temperature superheater (2), low temperature reheater (7) and economizer (14) are connected by pipes and headers. The positions of the low-temperature reheater (7) and the low-temperature superheater (2) in the front and rear flues can be interchanged.

2. A π-type boiler according to claim 1, characterized in that, The π-type boiler uses five methods for temperature control, namely: 1) Swing burner: The boiler burner is located in the middle area of ​​the boiler furnace, and the boiler uses a swing burner; 2) Coal-to-water ratio: Controlling the ratio of boiler coal feed rate to boiler water feed rate; 3) Flue gas damper: The opening and closing angle of the flue gas temperature regulating damper (11) on the front and rear flue gas ducts is adjusted to change the amount of flue gas in the two flue gas ducts, thereby changing the heat absorption ratio of the low temperature reheater (7) and the low temperature superheater (2) to achieve the regulation of reheat steam temperature. 4) Excess air volume: Change the excess air coefficient; 5) Flue gas recirculation: including flue gas recirculation fan (13), flue gas temperature regulating baffle (11) and connecting flue (12). The recirculated flue gas is taken from the low-temperature flue gas of the economizer (14). The flue gas is circulated to the bottom of the boiler furnace by the flue gas recirculation fan (13) to increase the amount of flue gas in the boiler and increase the convective heat transfer and heat absorption of the low-temperature heating surface of the boiler.

3. A π-type boiler according to claim 2, characterized in that, Five temperature control methods are coupled to control the temperature. The specific steps are as follows: First, the coal-water ratio is used to adjust the superheater steam temperature, the oscillating burner is used to adjust the reheater steam temperature, and then the tail-end double flue gas temperature control baffle (11) is used to adjust the reheat steam temperature. The excess air coefficient plays a fine-tuning role on the superheater and reheat steam temperatures. Under low load conditions, when all the above methods are exhausted, flue gas recirculation is used to adjust the reheat steam temperature, which can provide a larger temperature control range and higher sensitivity.

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