A method for stable combustion of a boiler at ultra-low load

Abstract

This invention relates to a method in the field of boiler technology, specifically a method for stable combustion during ultra-low load operation of a boiler. To address the problems of low pulverized coal concentration, difficulty in ignition and stabilization of pulverized coal, and easy boiler flameout during ultra-low load operation of pulverized coal boilers, leading to unit outages, this solution arranges n layers of burners (n≥2) sequentially from bottom to top along the boiler height on the front and rear walls, based on the unit's design load. Each layer of burners is equipped with a pulverized coal concentration-lean separation device, with the number of devices being (n-1)×m, where m is the number of burners in the same layer. The rich primary air pulverized coal flow pipe of any pulverized coal concentration-lean separation device is connected to the primary air channel of the lower burner in two adjacent layers. The oxygen-rich primary air pulverized coal flow pipe of any pulverized coal concentration-lean separation device is connected to the central air channel of the upper burner in two adjacent layers. This solution improves the stability of pulverized coal ignition during low load operation of the boiler.

Description

Technical Field

[0001] This invention relates to a method in the field of boiler technology, specifically to a method for stable combustion during ultra-low load operation of a boiler. Background Technology

[0002] With the large-scale integration of fluctuating and intermittent renewable energy generation capacity, and the significant changes in the power grid where ultra-high voltage AC / DC hybrid connections and distributed power sources coexist, higher demands are placed on peak shaving in the power system. For pulverized coal boilers in thermal power generating units to achieve deep peak shaving, the boilers must operate safely and stably for extended periods under low loads. The minimum stable combustion load of the boiler is affected by factors such as the volatile matter, moisture, ash content, fineness and uniformity of pulverized coal, burner type, and air distribution. Currently, the stable combustion load of conventional pulverized coal burners without oil injection is generally maintained within the range of 30%–40% BMCR. When the boiler operating load drops to 20% BMCR or lower, the boiler requires less fuel. For coal-fired units, due to limitations in the output regulation ratio of the pulverizer itself and issues such as pulverized coal input and dust accumulation, the pulverized coal concentration is low, making ignition and stabilization difficult, and the boiler is prone to flameout, causing unscheduled unit shutdowns. Summary of the Invention

[0003] The purpose of this invention is to address the problem that when the pulverized coal concentration in a pulverized coal boiler is too low, it is difficult to ignite and stabilize the pulverized coal, and the boiler is prone to flameout, causing unscheduled unit shutdowns. This invention provides a method for stabilizing combustion during ultra-low load operation of a boiler.

[0004] The objective of this invention is achieved as follows: a method for stable combustion of a boiler under ultra-low load operation, comprising the following steps:

[0005] Step 1: Based on the unit's design load, arrange n layers of burners sequentially from bottom to top along the boiler's height on the front and rear walls, where n ≥ 2 and n is a positive integer;

[0006] Step 2: Arrange the pulverized coal concentration separation device according to the number of burner layers. The number of the pulverized coal concentration separation device is (n-1)×m, where m is the number of burners in the same layer.

[0007] Step 3: Connect the rich primary air pulverized coal flow pipe of any pulverized coal concentration separation device to the primary air channel of the lower burner in the two adjacent burners; connect the oxygen-rich primary air pulverized coal flow pipe of any pulverized coal concentration separation device to the central air channel of the upper burner in the two adjacent burners.

[0008] Step 4: Connect the primary air blower to multiple pulverized coal concentration separation devices through a coal mill. The primary air from the blower is fed into the coal mill to form a primary air-pulverized coal airflow. The pulverized coal concentration separation devices are arranged on the coal feeding pipeline connecting the coal mill and the burner.

[0009] Step 5: Put the products made in Steps 1 to 4 into the pulverized coal boiler for ultra-low load operation.

[0010] Furthermore, n ≤ 5.

[0011] Furthermore, the burner is an axial swirl burner.

[0012] Furthermore, a secondary air passage, a tertiary air passage, and a quaternary air passage are arranged radially and rearward from the primary air passage of the burner.

[0013] Furthermore, the secondary air duct is a direct current air duct.

[0014] Furthermore, the tertiary and quaternary air passages are vortex air passages.

[0015] Furthermore, in the rich primary air pulverized coal gas flow pipe of the pulverized coal concentration separation device, the air content is 45%-55% and the pulverized coal content is 75%-85%.

[0016] Furthermore, the orifice diameter of the primary air pulverized coal gas flow pipe rich in fuel is greater than that of the primary air pulverized coal gas flow pipe rich in oxygen.

[0017] Beneficial effects:

[0018] This invention achieves the concentration and separation of primary air pulverized coal gas flow into fuel-rich primary air pulverized coal gas flow and oxygen-rich primary air pulverized coal gas flow. The staged combustion of the fuel-rich primary air pulverized coal gas flow and the oxygen-rich primary air pulverized coal gas flow in the vertical height of the furnace improves the stability of pulverized coal ignition during the low-load operation of the boiler. This method can improve the burner's stable combustion capability without oil injection, reduce the minimum stable combustion load of the boiler, and ensure the safe and stable operation of the boiler under ultra-low load conditions. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 A schematic diagram of the burner arrangement;

[0022] Figure 2 This is a schematic diagram showing the connection between any row of burners and a pulverized coal concentration-lean separation device.

[0023] Figure 3This is a schematic diagram showing the connection between each row of two adjacent burners and the pulverized coal concentration separation device.

[0024] Figure 4 This is an enlarged view of the burner. Detailed Implementation

[0025] Combined with appendix Figure 1-4 The following describes the specific implementation method:

[0026] Specific Implementation Method 1: A method for stable combustion of a boiler under ultra-low load operation, comprising the following steps:

[0027] Step 1: Based on the unit's design load, arrange n layers of burners 1 sequentially from bottom to top along the boiler's height on the front and rear walls of the boiler, where n ≥ 2 and n is a positive integer;

[0028] Step 2: Arrange the pulverized coal concentration separation device 2 according to the number of burner layers. The number of pulverized coal concentration separation devices 2 is (n-1)×m, where m is the number of burners in the same layer.

[0029] Step 3: Connect the fuel-rich primary air pulverized coal flow pipe 2-1 of any pulverized coal concentration separation device 2 to the primary air channel 1-1 of the lower burner 1 in the two adjacent layers of burners 1; connect the oxygen-rich primary air pulverized coal flow pipe 2-2 of any pulverized coal concentration separation device 2 to the central air channel 1-5 of the upper burner 1 in the two adjacent layers of burners 1.

[0030] Step 4: Connect the primary air blower 3 to multiple pulverized coal concentration separation devices 2 through the coal mill 4. The primary air from the blower 3 is fed into the pulverized coal flow through the coal mill 4. The pulverized coal concentration separation devices 2 are arranged on the pulverized coal feeding pipes that connect the coal mill 4 and each burner 1.

[0031] Step 5: Put the products made in Steps 1 to 4 into the boiler for ultra-low load operation.

[0032] In this embodiment: the primary air carrying pulverized coal is provided by a primary air fan and enters the coal mill to carry pulverized coal, forming a primary air-pulverized coal gas flow. This flow is then separated into a fuel-rich primary air-pulverized coal gas flow and an oxygen-rich primary air-pulverized coal gas flow by a pulverized coal concentration separator located before the burners. The fuel-rich primary air-pulverized coal gas flow enters the furnace through the primary air passage of the n-1 (n=2, 3…5)th burner. The pulverized coal concentration in this gas flow is 1.5-1.7 times that before concentration. After concentration, the required ignition heat of the pulverized coal is significantly reduced, and the ignition temperature of the gas flow is significantly lowered. The oxygen-rich primary air-pulverized coal gas flow, carried into the furnace through the central air passage of the n (n=2, 3…5)th burner, mixes thoroughly with the rising high-temperature flue gas and ignites rapidly. This achieves staged combustion of the primary air-pulverized coal gas flow in the vertical height of the furnace, improving the stability of pulverized coal ignition, enhancing the burner's ability to maintain stable combustion without oil injection, and reducing the boiler's minimum stable combustion load.

[0033] Specific Implementation Method 2: A method for stable combustion of a boiler under ultra-low load, wherein n≤5.

[0034] Other implementation methods are the same as those in Specific Implementation Method 1.

[0035] Specific implementation method 3: A method for stable combustion of a boiler under ultra-low load, wherein the burner 1 is an axial swirl burner.

[0036] Other implementation methods are the same as those in Specific Implementation Method 1.

[0037] Specific Implementation Method 4: A method for stable combustion of a boiler under ultra-low load: A secondary air passage 1-2, a tertiary air passage 1-3 and a quaternary air passage 1-4 are arranged sequentially behind the primary air passage 1-1 of the burner 1.

[0038] In this embodiment: after the pulverized coal gas flows into the furnace through the primary air duct, it is fully mixed with the high-temperature flue gas brought by the secondary / tertiary / quaternary air recirculation in the area near the burner. It is rapidly heated to the ignition temperature and ignites quickly, which improves the stability of pulverized coal ignition and enhances the burner's ability to maintain stable combustion without oil injection.

[0039] Other implementation methods are the same as those in Specific Implementation Method 1.

[0040] Specific Implementation Method 5: A method for stable combustion of a boiler under ultra-low load, wherein the secondary air duct 1-2 is a direct-flow air duct.

[0041] Other implementation methods are the same as those in Specific Implementation Method Four.

[0042] Specific Implementation Method Six: A method for stable combustion of a boiler under ultra-low load, wherein the tertiary air passage 1-3 and the quaternary air passage 1-4 are swirl air passages.

[0043] Other implementation methods are the same as those in Specific Implementation Method Four.

[0044] Specific Implementation Method 7: A method for stable combustion of a boiler under ultra-low load, wherein the air content in the primary air pulverized coal gas flow pipe 2-1 of the pulverized coal concentration separation device 2 is 45%-55% and the pulverized coal content is 75%-85%.

[0045] Other implementation methods are the same as those in Specific Implementation Method 1.

[0046] Specific Implementation Method 8: A method for stable combustion of a boiler under ultra-low load, wherein the orifice diameter of the primary air pulverized coal gas flow pipe 2-1 is greater than the orifice diameter of the oxygen-enriched primary air pulverized coal gas flow pipe 2-2.

[0047] Design principles:

[0048] The boiler adopts a counter-firing combustion method, with burners arranged on the front and rear walls of the furnace. According to the unit's design load, 2 to 5 layers of burners are arranged on each of the front and rear walls of the boiler, arranged sequentially from bottom to top along the boiler height as the 1st layer of burners, the 2nd layer of burners... ... the nth (n = 2, 3... 5)th layer of burners.

[0049] The burner adopts an axial swirl burner, and the burner channels include a central air channel, a primary air channel, a secondary air channel, a tertiary air channel, and a quaternary air channel.

[0050] Air used to assist combustion is supplied by a blower and enters the furnace through the secondary, tertiary, and quaternary air passages of the burner. These passages are named secondary air, tertiary air, and quaternary air, respectively. The secondary air is direct-flow air, while the tertiary and quaternary air are axial swirling air. The secondary, tertiary, and quaternary air enter the furnace at different stages of combustion, forming an annular recirculation in the near-burner zone. This recirculation carries the high-temperature flue gas back to the near-burner zone, heating the pulverized coal airflow, igniting the pulverized coal, and maintaining flame stability. At the same time, the high-temperature flue gas brought back has a low oxygen content, which is beneficial for NOx reduction. In the far-burner zone, the tertiary and quaternary air complete the combustion of unburned carbon.

[0051] The primary air carrying pulverized coal is supplied by the primary air fan and enters the coal mill carrying pulverized coal, forming a primary air-pulverized coal gas flow. This flow is then separated into a fuel-rich primary air-pulverized coal gas flow and an oxygen-rich primary air-pulverized coal gas flow by a pulverized coal concentration separator located before the burner. The fuel-rich primary air-pulverized coal gas flow, carrying approximately 50% air and 75%–85% pulverized coal, enters the furnace through the primary air passage of the n-1 (n=2, 3…5) burner layers. The pulverized coal concentration in the gas flow is 1.5–1.7 times that before concentration. After concentration, the required ignition heat of the pulverized coal is significantly reduced, and the ignition temperature of the gas flow is significantly lowered. After entering the furnace, the gas flow mixes thoroughly with the high-temperature flue gas brought by the secondary / tertiary / quaternary air recirculation in the area near the burner, and is rapidly heated to the ignition temperature, resulting in rapid ignition. This improves the stability of pulverized coal ignition and enhances the burner's ability to maintain stable combustion without oil injection. The oxygen-enriched primary air pulverized coal gas flow, carrying about 50% air and 15% to 25% pulverized coal, enters the furnace through the central air passage of the nth (n=2, 3...5) layer burner. It mixes thoroughly with the rising high-temperature flue gas and ignites rapidly. This achieves staged combustion of the primary air pulverized coal gas flow in the vertical height of the furnace, improves the stability of pulverized coal ignition, enhances the burner's ability to maintain stable combustion without oil injection, and reduces the minimum stable combustion load of the boiler.

[0052] The central air duct of the lowest burner (first burner) is used for air distribution during the ignition and operation phase. No pulverized coal concentration separation device is installed before the uppermost burner; the pulverized coal airflow directly enters the furnace through the primary air duct of the uppermost burner. Other implementation methods are the same as in Specific Implementation Method One.

Claims

1. A method for stable combustion of a boiler under ultra-low load: characterized in that, It includes the following steps: Step 1: Based on the unit's design load, arrange burners in n layers along the boiler's height direction from bottom to top on the front and rear walls of the boiler (1), where n ≥ 2 and n is a positive integer; Step 2: Arrange the pulverized coal concentration separation device (2) according to the number of burner layers. The number of pulverized coal concentration separation devices (2) is (n-1)×m, where m is the number of burners in the same layer. Step 3: Connect the fuel-rich primary air pulverized coal flow pipe (2-1) of any pulverized coal concentration separation device (2) to the primary air channel (1-1) of the lower burner (1) in the two adjacent layers of burners (1); connect the oxygen-rich primary air pulverized coal flow pipe (2-2) of any pulverized coal concentration separation device (2) to the central air channel (1-5) of the upper burner (1) in the two adjacent layers of burners (1); Step 4: Connect the primary air blower (3) to multiple coal powder concentration separation devices (2) through the coal mill (4). The primary air from the primary air blower (3) is converted into primary air coal powder flow through the coal mill (4). The coal powder concentration separation devices (2) are arranged on the coal powder feeding pipe connecting the coal mill (4) and each burner (1). Step 5: Put the products made in Steps 1 to 4 into the boiler for ultra-low load operation.

2. The method for stable combustion of a boiler under ultra-low load operation according to claim 1, characterized in that: The n≤5.

3. The boiler ultra-low load operation stable combustion method according to claim 1, characterized in that: The burner (1) is an axial swirl burner.

4. The boiler ultra-low load operation stable combustion method according to claim 1, characterized in that: The burner (1) has a primary air passage (1-1) with a secondary air passage (1-2), a tertiary air passage (1-3) and a quaternary air passage (1-4) arranged radially and rearward.

5. The boiler ultra-low load operation stable combustion method according to claim 4, characterized in that: The secondary air duct (1-2) is a direct current air duct.

6. The boiler ultra-low load operation stable combustion method according to claim 4, characterized in that: The tertiary air passage (1-3) and the quaternary air passage (1-4) are vortex air passages.

7. The method for stable combustion of a boiler under ultra-low load operation according to claim 1, characterized in that: In the rich fuel primary air pulverized coal gas flow pipe (2-1) of the pulverized coal concentration separation device (2), the air content is 45%-55% and the pulverized coal content is 75%-85%.

8. The boiler ultra-low load operation stable combustion method according to claim 1, characterized in that: The aperture of the primary air pulverized coal gas flow pipe (2-1) rich in fuel is greater than the aperture of the primary air pulverized coal gas flow pipe (2-2) rich in oxygen.

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