Method for cold start of boiler unit

Abstract

The invention relates to a method for cold-state starting of a boiler unit, which comprises the following steps of: performing a cold-state starting procedure after ignition of the boiler unit, and in the whole cold-state starting procedure, additionally starting a second powder making unit according to the air temperature of hot primary air, and additionally starting a third powder making unit according to the temperature of combustion flue gas at an SCR (Selective Catalytic Reduction) inlet, the starting time of the powder making unit in the prior art can be shortened, the speed of adding the powder making unit is increased, then the temperature rising speed of combustion flue gas at an SCR inlet can be increased, and the time from unit ignition to operation of a denitration system is greatly shortened. And meanwhile, by adjusting the operation parameters of the three powder making units which are started together, the height of the flame center of the hearth and the combustion effect can be improved, and the heating rate of combustion smoke at the SCR inlet is further increased. In addition, before the boiler unit is ignited and started, the existing coal is replaced by the high-calorific-value coal, so that the calorific value of combustion can be increased, the smoke temperature can be increased, and the smoke heating rate can also be increased.

Description

Technical Field

[0001] The present disclosure relates to the technical field of coal-fired power generation, and in particular to a method for cold starting a boiler unit. Background Art

[0002] Boiler units mostly adopt the standard layout of natural circulation coal-fired boilers, generally including boiler pulverizing system, primary main air unit, secondary main air unit, single furnace, single steam drum, solid slag pulverized coal furnace, air preheater, dust removal device, desulfurization device and steam turbine unit, etc. The boiler unit adopts single furnace balanced ventilation, and the tail flue is arranged in an inverted L shape. After passing through the regulating baffle, the flue gas enters the SCR denitrification reactor to remove nitrogen oxides in the flue gas, and then enters two Junkers rotary air preheaters. After heat exchange, the hot flue gas enters two electrostatic precipitators to remove flue gas dust. The dust-removed flue gas enters the wet denitrification tower, and after removing most of the dust, sulfur dioxide and nitrogen oxides in the flue gas, it is finally discharged into the atmosphere through the chimney after reaching the ultra-low emission standard.

[0003] In existing production practices, the environmental protection control assessment during the unit startup phase stipulates that smoke and sulfur dioxide are exempted from assessment within 10 hours after the unit is started, and nitrogen oxides are exempted from assessment within 4 hours after startup and 1 hour before shutdown. During the unit startup process, if any of the environmental parameters of smoke, sulfur dioxide, and nitrogen oxide emissions does not meet the ultra-low emission standards, it will be deemed that the period does not meet the ultra-low emission standards. During the startup process of existing boiler units, the denitrification device is put into use late, the load is low, and the smoke temperature is low, which is not conducive to the operation of the denitrification device. Summary of the invention

[0004] The purpose of the present invention is to provide a method for cold starting of a boiler unit, so as to solve the problem in the prior art that the denitration device of the boiler unit does not meet the emission standards due to late commissioning.

[0005] In order to achieve the above object, the present disclosure provides a method for cold starting of a boiler unit, the method comprising: S1, completing the pre-ignition start-up process of the boiler unit, wherein the pre-ignition start-up process includes adding high calorific value coal to the pulverizing unit; the pulverizing unit includes a first pulverizing unit, a second pulverizing unit and a third pulverizing unit; The main combustion area inside the furnace of the boiler unit includes a first combustion layer, a second combustion layer and a third combustion layer which are connected in sequence from top to bottom; S2, after igniting the boiler unit, perform a cold start process, and monitor the temperature of the combustion flue gas at the SCR inlet in real time; S3. When the temperature of the combustion flue gas at the inlet of the SCR reaches above 285°C, the denitration device is turned on; The cold start process comprises: S21, start the first pulverizing unit, and allow the obtained pulverized coal to enter the first combustion layer for combustion treatment under the action of primary air and sealing air; S22, when the temperature of the hot primary air rises to 140-150°C, continue to open the second pulverizing unit, and allow the obtained pulverized coal to enter the second combustion layer under the action of the primary air and the sealing air to participate in the combustion process; S23, when the temperature of the combustion flue gas at the inlet of the SCR rises to above 265°C, continue to open the third pulverizing unit, and allow the obtained pulverized coal to enter the third combustion layer under the action of primary air and sealing air to participate in the combustion process; S24, adjusting the pulverized coal flow rate and the secondary air flow rate in the first combustion layer, the second combustion layer and the third combustion layer, so that the ratio of the pulverized coal flow rate in the first combustion layer, the second combustion layer and the third combustion layer reaches 1: (1-1.15): (1.2-1.5), and the ratio of the secondary air flow rate in the first combustion layer, the second combustion layer and the third combustion layer is (1.2-1.5): (1.2-1.5): 1; The cold start process also includes, when the main steam entering the high-pressure cylinder of the steam turbine and the reheated steam entering the medium and low-pressure cylinders of the steam turbine meet the start-up parameters, the steam turbine is subjected to a start-up process; the start-up parameters include: the temperature of the main steam is 320~400℃, and the pressure is 5~10MPa; the temperature of the reheated steam is 300~380℃, and the pressure is 0.5~3MPa.

[0006] Optionally, during the process from ignition of the boiler unit to start-up of the steam turbine, the temperature rise rate of the combustion flue gas at the SCR inlet is 70-90° C. / h.

[0007] Optionally, the cold start process also includes: when the total flow rate of pulverized coal in the first combustion layer, the second combustion layer and the third combustion layer reaches 40 t / h, as the total flow rate of pulverized coal in the first combustion layer, the second combustion layer and the third combustion layer increases, reducing the air-coal ratio of the boiler unit.

[0008] Optionally, the furnace negative pressure value of the boiler unit is -100 to -150Pa.

[0009] Optionally, the furnace negative pressure value of the boiler unit is -110 to -140Pa.

[0010] Optionally, step S4 also includes that the ratio of pulverized coal flow rates in the first combustion layer, the second combustion layer and the third combustion layer is 1:1:1.2; and the ratio of secondary air flow rates in the first combustion layer, the second combustion layer and the third combustion layer is 1.2:1.2:1.

[0011] Optionally, after the boiler unit is ignited, at least part of the main steam is mixed with the high-pressure cylinder exhaust steam through the high-pressure bypass until the temperature of the obtained cold reheat steam reaches above 280°C.

[0012] Optionally, when the temperature of the cold reheat steam reaches above 200°C and the pressure reaches above 0.5MPa, the boiler feed water treated by the deaerator is heated by the high-pressure heater and returned to the boiler unit; the inlet and outlet temperature rise of the high-pressure heater is below 45°C.

[0013] Optionally, when the steam turbine is in the start-up process and the temperature of the deaerator inlet water is below 150°C, the deaerator inlet water is first heated by a low-pressure heater before entering the deaerator; the inlet and outlet temperature rise of the low-pressure heater is below 45°C.

[0014] Optionally, the turbine start-up process also includes connecting the steam turbine to the grid after undergoing constant speed processing and parameter adjustment processing in sequence; the conditions for the constant speed processing include: the temperature of the main steam is 320~400℃, and the pressure is 5~10MPa; the temperature of the reheated steam is 300~380℃, and the pressure is 0.5~3MPa; the conditions for the parameter adjustment processing include: the temperature of the main steam is 360℃~370℃, and the pressure is 5~10MPa; the temperature of the reheated steam is 350~360℃, and the pressure is 0.5~3MPa.

[0015] Through the above technical scheme, the boiler unit performs a cold start process after ignition. During the entire cold start process, the second pulverizing unit is opened according to the wind temperature of the hot primary air, and the third pulverizing unit is opened according to the combustion flue gas temperature at the SCR inlet. Compared with the prior art of opening the pulverizing device according to the load of the boiler unit, the opening time of the pulverizing unit can be shortened, the rate of opening the pulverizing unit can be increased, and the temperature rise rate of the combustion flue gas at the SCR inlet can be increased, which greatly shortens the time from the ignition of the unit to the commissioning of the denitrification system. At the same time, by adjusting the operating parameters of the three pulverizing units that are opened together, the height of the center of the furnace flame and the combustion effect can be increased, and the temperature rise rate of the combustion flue gas at the SCR inlet can be further increased. In addition, before the boiler unit is ignited and started, replacing the existing coal with high calorific value coal can increase the calorific value of combustion, which can not only increase the flue gas temperature, but also increase the flue gas temperature rise rate.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings: Figure 1 It is a schematic diagram of a wind and smoke unit of a boiler unit disclosed in the present invention.

[0018] Figure 2 It is a schematic diagram of a water steam unit of a boiler unit disclosed in the present invention.

[0019] Figure 3 It is a schematic diagram of a first pulverizing unit of a boiler unit disclosed in the present invention.

[0020] Description of Reference Numerals 1A primary fan; 1B primary fan; 2 air preheater; 3 boiler unit; 4A blower; 4B blower; 5A heater; 5B heater; 6 electrostatic precipitator; 7 induced draft fan; 8 chimney; 9 steam drum; 10 primary superheater; 11 screen superheater; 12 secondary superheater; 13 high pressure cylinder; 14 reheater; 15 medium and low pressure cylinders; 16 condenser; 17 shaft heater; 18 low pressure heater; 19 deaerator; 20 high pressure heater; 21 economizer; 22 cooling water; 23 flow control valve; 24 flow control valve; 25 raw coal hopper; 26 coal feeder; 27A burner, 27B burner; 27C burner; 27D burner; 28 hot primary air; 29 cold primary air; 30 sealing air; 31 hot secondary air. DETAILED DESCRIPTION

[0021] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0022] The present disclosure provides a method for cold starting a boiler unit, the method comprising: S1, completing the pre-ignition start-up process of the boiler unit 3, wherein the pre-ignition start-up process includes adding high calorific value coal to the pulverizing unit; the pulverizing unit includes a first pulverizing unit, a second pulverizing unit and a third pulverizing unit; The main combustion area inside the furnace of the boiler unit 3 includes a first combustion layer, a second combustion layer and a third combustion layer which are connected in sequence from top to bottom; S2, igniting the boiler unit 3 and performing a cold start process, and monitoring the temperature of the combustion flue gas at the SCR inlet in real time; S3. When the temperature of the combustion flue gas at the inlet of the SCR reaches above 285°C, the denitration device is turned on; The cold start process comprises: S21, start the first pulverizing unit, and allow the obtained pulverized coal to enter the first combustion layer for combustion treatment under the action of primary air and sealing air 30; S22, when the temperature of the hot primary air 28 is raised to 140-150°C, the second pulverizing unit is continued to be opened, and the obtained pulverized coal enters the second combustion layer under the action of the primary air and the sealing air 30 to participate in the combustion process; S23, when the temperature of the combustion flue gas at the inlet of the SCR rises to above 265°C, continue to open the third pulverizing unit, and allow the obtained pulverized coal to enter the third combustion layer under the action of the primary air and the sealing air 30 to participate in the combustion process; S24, adjusting the pulverized coal flow rate and the secondary air flow rate in the first combustion layer, the second combustion layer and the third combustion layer, so that the ratio of the pulverized coal flow rate in the first combustion layer, the second combustion layer and the third combustion layer reaches 1: (1-1.15): (1.2-1.5), and the ratio of the secondary air flow rate in the first combustion layer, the second combustion layer and the third combustion layer is (1.2-1.5): (1.2-1.5): 1; The cold start process also includes, when the main steam entering the high-pressure cylinder of the steam turbine and the reheated steam entering the medium and low-pressure cylinders of the steam turbine meet the start-up parameters, causing the steam turbine to perform a start-up process; the start-up parameters include: the temperature of the main steam is 320~400℃, and the pressure is 5~10MPa; the temperature of the reheated steam is 300~380℃, and the pressure is 0.5~3MPa.

[0023] Through the above technical scheme, the boiler unit 3 performs a cold start process after ignition. During the entire cold start process, the second pulverizing unit is opened according to the wind temperature of the hot primary air 28, and the third pulverizing unit is opened according to the combustion flue gas temperature at the SCR inlet. Compared with the prior art of opening the pulverizing device according to the load of the boiler unit 3, the opening time of the pulverizing unit can be shortened, the rate of opening the pulverizing unit can be increased, and the temperature rise rate of the combustion flue gas at the SCR inlet can be increased, which greatly shortens the time from the ignition of the unit to the commissioning of the denitrification system. At the same time, by adjusting the operating parameters of the three pulverizing units that are opened together, the height of the center of the furnace flame and the combustion effect can be increased, and the temperature rise rate of the combustion flue gas at the SCR inlet can be further increased. In addition, before the ignition and start-up of the boiler unit 3, replacing the existing coal with high calorific value coal can increase the calorific value of combustion, which can not only increase the flue gas temperature, but also increase the flue gas temperature rise rate.

[0024] In one embodiment, the boiler unit 3 and the steam turbine generator set used in the present invention are both conventionally selected in the art. Specifically, the boiler unit 3 used in the present invention is a 330MW unit, wherein the boiler unit 3 is designed and manufactured by Beijing Babcock-Wilcox Co., Ltd., and is matched with a steam turbine generator set of Beijing Heavy Electric Motor Plant.

[0025] In one embodiment, the boiler unit 3 used in the present application includes a unit body, a wind and smoke unit, a powder making unit and a water steam unit.

[0026] In one embodiment, the structure of the unit body includes a furnace, a horizontal flue, a vertical flue and a tail flue; In one embodiment, if Figure 1 As shown, the air-smoke unit includes two sets of air-smoke units, the first set of air-smoke units includes a primary fan 1A, a blower 4A and a heater 5A, and the other set of air-smoke units includes a primary fan 1B, a blower 4B and a heater 5B. The two sets of air-smoke units can share one induced draft fan 7 or use two induced draft fans 7 respectively; the two sets of air-smoke units can share one air preheater 2 or use two air preheaters 2 respectively; the two sets of air-smoke units can share one electrostatic precipitator 6 or use two electrostatic precipitators 6 respectively; the two sets of air-smoke units can share one chimney 8.

[0027] In one embodiment, if Figure 3 As shown, the pulverizing unit includes at least three pulverizing units. Taking the first pulverizing unit as an example, the pulverizing unit includes a raw coal hopper 25, a coal feeder 26 and multiple burners; wherein the number of burners is preferably 4, namely burner 27A, burner 27B, burner 27C and burner 27D; the 4 burners are arranged inside the first combustion layer.

[0028] In one embodiment, multiple burners are provided at the four corners or the front and rear walls of the furnace, and the multiple burners can be respectively arranged at each layer of the main combustion area inside the furnace. Each of the burners is equipped with a large oil gun for spraying oil into the furnace and burning it. The coal feeder is connected to the sealed air duct, the hot primary air duct and the cold primary air duct.

[0029] In this embodiment, during the process of ignition to turbine run-up of the boiler unit 3, the large oil gun of the burner sprays oil into the burner, and the burner ignites the oil. When the temperature of the hot secondary air 31 reaches above 170°C, pulverized coal is required as fuel. When the pulverizing unit is working, the sealed air 30, hot primary air 28 and cold primary air 29 enter the coal feeder and mix, and the primary air volume and outlet temperature of the coal mill are adjusted so that the pulverized coal is carried to the burner by the wind for combustion; the secondary air port is arranged near the burner and sprayed with combustion-supporting air; the direct-blowing boiler blows the pulverized coal directly into the furnace by the pulverizer. After the pulverized coal is burned, fly ash and ash are formed. Fly ash is transported along with the flue gas through horizontal and vertical flues to the dust collector. The dust collector removes more than 98% of the fine ash in the flue gas and drops it into the ash hopper at the bottom of the dust collector. Very little fine ash is sent along with the flue gas into the chimney through the suction fan and discharged into the atmosphere. The ash falls to the bottom of the furnace to form bottom ash, which is removed from the furnace regularly by the ash removal equipment.

[0030] In one embodiment, if Figure 2 As shown, the steam unit includes a steam drum 9, a primary superheater 10, a platen superheater 11, a secondary superheater 12, a high-pressure cylinder 13, a reheater 14, a medium- and low-pressure cylinder 15, a condenser 16, a shaft heater 17, a low-pressure heater 18, a deaerator 19, a high-pressure heater 20 and an economizer 21, which are connected in sequence. A high-pressure bypass is provided between the upstream pipeline and the downstream pipeline of the high-pressure cylinder 13, a low-pressure bypass is provided between the upstream pipeline of the medium- and low-pressure cylinder 15 and the inlet pipeline of the condenser, and a flow regulating valve 23 is provided on the high-pressure bypass, and a flow regulating valve 24 is provided on the low-pressure bypass.

[0031] In one embodiment, the economizer is arranged in layers in the vertical flue, and it uses the flue gas to heat the water sent from the water supply main pipe and then sends it to the steam drum 9. The steam drum 9 is arranged at the top of the boiler unit 3. It plays the role of receiving incoming water, storing water and separating steam and water in the steam-water cycle of the boiler unit 3. The water in the steam drum 9 is sent to the water-cooled wall through the downcomer arranged on the outer wall of the furnace and the lower header of the water-cooled wall. A forced circulation pump is installed in the downcomer of the forced circulation boiler to enhance the water circulation. The water-cooled wall is a row of pipes arranged around the furnace. The heat released by the fuel burned in the furnace heats the water in the water-cooled wall tube into a steam-water mixture. The steam-water mixture enters the steam drum 9 through the upper header and the riser of the water-cooled wall. The steam-water separator in the steam drum 9 separates the steam-water mixture, and the separated steam is sent to the superheater, and the remaining water remains in the steam drum 9 to continue to participate in the water cycle.

[0032] In one embodiment, the reheater of the reheat unit is also arranged in the horizontal flue and the vertical flue. The function of the reheater is to reheat the steam that has done work in the high-pressure cylinder of the turbine to a certain temperature and send it back to the intermediate-pressure cylinder of the turbine to continue doing work.

[0033] In this embodiment, the steam in the steam drum 9 passes through the primary superheater 10, the screen superheater 11, the secondary superheater 12, the high-pressure cylinder 13 of the steam turbine, the reheater 14, and the medium and low-pressure cylinders 15 of the steam turbine and enters the condenser 16 for condensation to obtain condensed water, thereby achieving the goal of using the energy of the steam with higher temperature and pressure to work the steam turbine to generate electrical energy.

[0034] In one embodiment, the present disclosure can divide the main combustion area in the furnace of the boiler unit 3 into multiple combustion layers according to the number of pulverizing units, wherein the number of combustion layers is 3 to 5 layers.

[0035] In one embodiment, a plurality of burners are provided inside each combustion layer. Preferably, the number of burners inside each combustion layer is 2 to 6.

[0036] In a specific embodiment, the boiler unit 3 of the present disclosure is equipped with 5 pulverizing units, wherein each pulverizing unit is composed of a positive pressure direct blowing MPS medium speed coal mill and a pulverizing machine. The main combustion zone in the furnace of the boiler unit 3 is divided into the first combustion layer, the second combustion layer, the third combustion layer, the fourth combustion layer and the fifth combustion layer from top to bottom.

[0037] The burner used in the present disclosure is a conventional choice in the art, and this application does not make any special requirements. For example, the burner can be selected from an AireJet burner and / or a DRB-4Z burner.

[0038] The boiler unit 3 of the present disclosure adopts a front and rear wall counter-combustion method, and two burners are respectively arranged on the front and rear walls of each combustion layer.

[0039] In one embodiment, the high calorific value coal used in the present disclosure is conventionally selected in the art. For example, the high calorific value coal can be selected from one or more of railway coal, Jinzhengtai automobile coal and Funeng automobile coal, preferably railway coal.

[0040] In a preferred embodiment, the parameters of high calorific value coal include: calorific value, sulfur content, ash content, and moisture content. In this embodiment, high calorific value coal with high calorific value and low sulfur content is used to replace the existing coal, which can not only improve the combustion effect of the boiler unit 3, but also reduce the sulfur-containing pollutants in the exhaust gas.

[0041] In one embodiment, the pre-ignition start-up process described in the present disclosure includes a boiler water supply process and a furnace purge process.

[0042] In one embodiment, the boiler can be filled with water after various inspections and tests before starting. When the boiler of the present application is filled with water for the first time, the feed water temperature of the deaerator is maintained at 100°C, and the temperature difference of the lower wall of the drum 9 is not allowed to exceed 50°C; when the boiler is filled with water for the second time, the feed water temperature of the deaerator is maintained at 130°C to increase the furnace temperature. Among them, the boiler filling process described in the present disclosure is a conventional choice in the field, and this application does not make special requirements.

[0043] In one embodiment, when the expansion of boiler water ends and water is continuously added, the water temperature of the deaerator is maintained above 100°C. The electric door of the auxiliary steam header to the deaerator heating steam is gradually fully opened after the steam pipeline is warmed up, and the pneumatic regulating door of the auxiliary steam to the deaerator heating steam is used to control the heating speed. When the deaerator temperature is heated before 100°C, the start steam electric door is used; when it reaches 100°C, the running steam electric door is opened.

[0044] In one embodiment, the pre-ignition start process also includes a secondary air heater pipe heating process and a primary fan pre-start process. The primary fan pre-start process is completed in accordance with the requirements of the Denitration System Operation Ticket.

[0045] In one embodiment, step S21 further includes, before starting the first coal mill, maintaining the opening of the OFA damper of the boiler unit 3 at 50%, and maintaining the opening of the secondary air damper in the first combustion layer at 40%. In this embodiment, maintaining the opening of the OFA damper at a certain opening can maintain an appropriate air-powder ratio and ensure the air outlet velocity and air volume, so that the air-powder is mixed evenly, thereby ensuring good combustion conditions and combustion indicators.

[0046] In one embodiment, the unit ignition and start-up adopts a single-side air and smoke system start-up method, that is, before ignition, the induced draft fan 7, the blower 4A, the primary fan 1A and the primary fan 1B in one air and smoke unit are started first, until the steam turbine starts the blower 4B and the primary fan 1B in the other air and smoke unit. It should be noted that before starting the other air and smoke unit, the communication door of the air and smoke system on both sides needs to be opened until the air and smoke system on both sides is leveled, and then the communication door is closed.

[0047] In one embodiment, before the fan is started, the inlet communication door of the induced draft fan is manually opened to 50%; the outlet communication doors of the supply fan and the primary fan are electrically opened to 100%.

[0048] In a preferred embodiment, when the second coal mill starts normally and the total flow rate of pulverized coal in the first pulverized coal burner and the second pulverized coal burner reaches 50 t / h, another set of air and smoke units is started.

[0049] In one embodiment, after the wind and smoke systems on both sides are leveled, the secondary air is heated to above 45° C. by a secondary air heater and then further heated by an air preheater.

[0050] In this embodiment, by introducing the other side wind and smoke system, the air volume of the secondary air entering the furnace can be further increased, which can not only improve the effect of combustion treatment, but also reduce the pollutant content of the combustion flue gas. In addition, the secondary air is heated by the secondary air heater before passing through the air preheater for heat exchange, which can avoid the deterioration of the heat exchange effect of the air preheater due to the increase of the secondary fan load, and can further increase the temperature of the secondary air entering the furnace, thereby increasing the furnace temperature.

[0051] In a preferred embodiment, step S4 also includes that the ratio of the pulverized coal flow rates in the first combustion layer, the second combustion layer and the third combustion layer is 1:1:1.2; and the flow rate ratio of the secondary air in the first combustion layer, the second combustion layer and the third combustion layer is 1.2:1.2:1.

[0052] In this embodiment, by adjusting the pulverized coal flow rate of the first combustion layer, the second combustion layer, and the third combustion layer so that the pulverized coal flow rate gradually decreases from top to bottom, the height of the flame center during the combustion process can be increased. By adjusting the flow rate of secondary air in the first combustion layer, the second combustion layer, and the third combustion layer so that the flow rate of secondary air gradually increases from top to bottom, the combustion process can be carried out under low oxygen conditions, the combustion is delayed, and the height of the flame center is further increased.

[0053] In one embodiment, the cold start process also includes: when the total flow rate of pulverized coal in the first combustion layer, the second combustion layer and the third combustion layer reaches 40 t / h, as the total flow rate of pulverized coal in the first combustion layer, the second combustion layer and the third combustion layer increases, reducing the air-coal ratio of the boiler unit 3.

[0054] In this embodiment, during the cold start process, the oxygen content in the exhaust flue gas is adjusted according to the total flow rate of pulverized coal in the main combustion area inside the furnace, which is beneficial to improving the combustion effect in the boiler unit 3. The oxygen content in the exhaust flue gas is adjusted by fine-tuning the air supply volume, and the air supply volume is determined by the current load. Generally, we convert the current air volume value by the current unit load. However, there are media such as coal volume between the load and the air volume. Therefore, we indirectly adjust the oxygen content in the exhaust flue gas by adjusting the air-coal ratio. The oxygen content in the exhaust flue gas is adjusted by adjusting the flow rate of secondary air entering the first combustion layer, the second combustion layer and the third combustion layer, that is, adjusting the power of the blower. Among them, the air-coal ratio refers to the ratio between the air flow rate and the coal flow rate. The air-coal ratio can be flexibly adjusted according to actual production needs, and no specific limitation is made here.

[0055] In a specific implementation manner, when the total flow rate of pulverized coal in the first combustion layer, the second combustion layer, and the third combustion layer is 40 t / h, as the total flow rate of pulverized coal in the first combustion layer, the second combustion layer, and the third combustion layer increases, the oxygen content in the exhaust flue gas is reduced. For example, when the total flow rate of pulverized coal is 40 t / h, the oxygen content of the exhaust flue gas is 12 Vol%. When the total flow rate of pulverized coal is 44 t / h, the oxygen content of the exhaust flue gas is 11 Vol%. When the total flow rate of pulverized coal is 53 t / h, the oxygen content of the exhaust flue gas is 9 Vol%. When the total flow rate of pulverized coal is 60 When the total flow rate of pulverized coal is 69t / h, the oxygen content of the exhaust flue gas is 7Vol%, when the total flow rate of pulverized coal is 80t / h, the oxygen content of the exhaust flue gas is 6Vol%, when the total flow rate of pulverized coal is 96t / h, the oxygen content of the exhaust flue gas is 5Vol%, when the total flow rate of pulverized coal is 107t / h, the oxygen content of the exhaust flue gas is 4.5Vol%, when the total flow rate of pulverized coal is 120t / h, the oxygen content of the exhaust flue gas is 4Vol%, when the total flow rate of pulverized coal is 160t / h, the oxygen content of the exhaust flue gas is 3Vol%.

[0056] In one embodiment, the excess air coefficient at the furnace outlet of the boiler unit 3 is 1.5. In this embodiment, the excess air coefficient refers to the ratio of the amount of air actually supplied for fuel combustion to the theoretical amount of air. In order to make the fuel burn as completely as possible, the actual amount of air supplied must always be greater than the theoretical amount of air, that is, the excess air coefficient must be greater than 1. However, combustion theory and operating experience show that too large or too small excess air coefficient is not conducive to combustion. The use of a suitable excess air coefficient can improve boiler efficiency, reduce power consumption of suction fans and blowers, reduce high-temperature corrosion of heating surfaces and prevent the occurrence of high-temperature bonding ash, reduce the generation of sulfur-containing impurities, prevent low-temperature corrosion of heating surfaces, and reduce the generation of nitrogen oxides, which is beneficial to environmental protection.

[0057] In one embodiment, the furnace negative pressure value of the boiler unit 3 is -100 to -150Pa, preferably -110 to -140Pa, and further preferably -120Pa. In this embodiment, during the ignition operation of the boiler unit 3, when the pressure in the furnace becomes positive, the furnace high-temperature flue gas and flames will spray out from some holes and loose places, which will not only affect environmental hygiene and endanger personal safety, but also may cause coking of the furnace and burner, overheating and deformation and damage of the burner, steel beams and furnace walls, etc., and cause unstable and incomplete combustion, reducing thermal efficiency. Therefore, the furnace can be operated under negative pressure conditions. When the negative pressure in the furnace is too large, the air leakage of the furnace and the flue will increase, which will not only reduce the furnace temperature and cause unstable combustion, but also increase the amount of flue gas, aggravate the wear of the tail heating surface and increase the power consumption of the fan, reducing the efficiency of the boiler.

[0058] In one embodiment, when the steam generated in the steam drum 9 meets the water supply standard, the steam in the steam drum 9 of the boiler unit 3 is subjected to heat exchange with the combustion flue gas through the superheater to obtain main steam; the main steam is exhausted through the high-pressure cylinder of the steam turbine to obtain cold reheat steam; the cold reheat steam is subjected to heat exchange with the combustion flue gas through the reheater to obtain reheat steam; the reheat steam is exhausted from the medium and low pressure cylinders of the steam turbine and then enters the condenser for condensation to obtain condensed water; the condensed water is treated in a deaerator and returned to the steam drum 9 as boiler feed water.

[0059] In one embodiment, the method further comprises: mixing at least a portion of the main steam with high-pressure cylinder exhaust steam through a high-pressure bypass to obtain the cold reheat steam; Allow at least part of the reheated steam to be exhausted through the medium and low pressure cylinders of the steam turbine to obtain low pressure steam; allow another part of the reheated steam to be mixed with the low pressure steam through a low pressure bypass and then enter a condenser for condensation; The cooling water obtained by condensation in the condenser is deoxygenated by the deaerator, enters the economizer to recover the waste heat in the flue gas, and then returns to the steam drum 9.

[0060] In this embodiment, the boiler unit 3 disclosed in the present invention is coupled with the steam turbine through the steam drum 9, water-cooled wall, superheater, reheater and economizer, so that the steam generated in the steam drum 9 can do work in the steam turbine to generate electrical energy. The liquid phase in the steam drum 9 is cooled by the water-cooled wall for the main combustion area of ​​the boiler unit 3 to avoid high-temperature corrosion in the furnace.

[0061] In one embodiment, after the boiler unit 3 is ignited, at least part of the main steam is mixed with the high-pressure cylinder exhaust steam through the high-pressure bypass until the temperature of the obtained cold reheat steam reaches above 280°C. In this embodiment, after the boiler is ignited, the opening of the flow control valve on the high-pressure bypass is gradually increased to increase the flushing flow and the water supply, which will increase the heat absorption effect of the reheater and reduce the temperature of the combustion flue gas. At this time, the amount of coal powder added can be increased to ensure the heating rate of the combustion flue gas. In other words, the total flow of pulverized coal in the first combustion layer, the second combustion layer and the third combustion layer is changed by the flow regulation of the high-pressure bypass and the low-pressure bypass.

[0062] In one embodiment, during the process of adjusting the opening of the flow control valve on the high-pressure bypass, the water supply volume increases, and the operating temperature of the deaerator needs to be adjusted immediately to maintain the operating temperature of the deaerator below 180°C.

[0063] In one embodiment, when the temperature of the cold reheat steam reaches above 200°C and the pressure reaches above 0.5MPa, the boiler feed water treated by the deaerator is heated by the high-pressure heater and returned to the boiler unit 3; the inlet and outlet temperature rise of the high-pressure heater is below 45°C.

[0064] In one embodiment, when the turbine is in the start-up process and the temperature of the deaerator inlet water is below 150°C, the deaerator inlet water is first heated by a low-pressure heater before entering the deaerator; the inlet and outlet temperature rise of the low-pressure heater is below 45°C.

[0065] In one embodiment, a primary desuperheater and a secondary desuperheater are provided on the pipelines between the ceiling superheater, the low-temperature superheater, the front screen superheater, the rear screen superheater and the high-temperature superheater, for flexibly controlling the temperature and pressure of the main steam to obtain the main steam of qualified quality. In this embodiment, when the cooling effect of the primary desuperheater and the secondary desuperheater increases, the temperature of the main steam will decrease accordingly. In order to increase the flue gas temperature as soon as possible and start the steam turbine quickly, the total flow rate of pulverized coal can be increased.

[0066] In the above embodiment, after the boiler is ignited, the parameters of the deaerator, high-pressure bypass and low-pressure bypass are adjusted so that the temperature drop of the combustion flue gas after heat exchange with the reheater, water-cooled wall and superheater is smaller, and the temperature can be raised to above 285°C as soon as possible, thereby starting the denitrification device as soon as possible.

[0067] In one embodiment, in order to prevent water plugging in the reheater and the superheater, the steam temperature in the reheater and the superheater is not lower than the saturation temperature.

[0068] In one embodiment, from the time the boiler is ignited to the time the turbine is shut down and connected to the grid, the heating rate of the combustion flue gas and the cold reheat steam at the SCR inlet is 70-90° C. / h.

[0069] In one implementation, in order to further increase the heating rate of the cold reheat steam, the main steam pressure on the furnace side may be maintained at 6-7 MPa to reduce the steam flow rate and the heat exchange between the steam and the flue gas.

[0070] In one embodiment, the steam turbine start-up process further includes connecting the steam turbine to the grid after undergoing speed control and parameter adjustment processing in sequence.

[0071] In one embodiment, the conditions of the constant speed treatment include: the temperature of the main steam is 320-400°C and the pressure is 5-10 MPa; the temperature of the reheated steam is 300-380°C and the pressure is 0.5-3 MPa.

[0072] In one embodiment, the conditions for the parameter adjustment process include: the temperature of the main steam is 360°C~370°C, and the pressure is 5~10MPa; the temperature of the reheated steam is 350~360°C, and the pressure is 0.5~3MPa.

[0073] In one embodiment, the steam turbine is connected to the grid immediately at the top of the hour.

[0074] In one implementation, after the steam turbine is set at a constant speed, parameter adjustment is performed within 1 hour before grid connection.

[0075] In one embodiment, after the steam turbine is connected to the grid, the steam temperature is selectively increased according to the expansion difference. If the expansion difference of the high-pressure cylinder is controllable, the main steam temperature can be increased first. If the expansion difference of the medium and low-pressure cylinders is controllable, the reheat steam temperature can be increased first.

[0076] In one embodiment, the parameter adjustment process further includes: maintaining steam supply from auxiliary steam to the deaerator after grid connection, adjusting the temperature of the deaerator to 165-175°C, and gradually reducing the auxiliary steam to the deaerator heating steam when the load of the boiler unit 3 rises to 165MW. To increase the thermal load of the boiler, the main steam pressure is controlled at 6MPa.

[0077] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0078] Example 1 The boiler unit used in this embodiment is as follows Figure 1 As shown, boiler unit 3 is unit 4 of the 4×330M units of Zhundian Company. The boiler unit 3 is designed and manufactured by Beijing Babcock-Wilcox Co., Ltd. and is matched with a steam turbine generator set of Beijing Heavy Electric Machinery Plant. The method for cold starting the boiler unit 3 includes: S1, completing the pre-ignition start-up process of the boiler unit 3, which includes adding high calorific value coal to the first coal mill, the second coal mill and the third coal mill, completing the pipe warming work before the secondary air is started, manually opening the induced draft fan inlet contact door to 50% before the fan is started, maintaining the OFA damper opening at 50%, and electrically opening the forced draft fan and primary fan outlet contact door to 100%; S2, performing a cold start process on the boiler unit 3, and monitoring the temperature of the combustion flue gas at the SCR inlet in real time; The cold start process comprises: S21, start the first coal mill, and set the opening of the secondary air damper in the first combustion layer to 40%, so that the pulverized coal and primary air obtained by the first coal mill enter the first combustion layer through the first pulverized coal burner, and are burned under the condition of secondary air to obtain combustion flue gas; the combustion flue gas is cooled by an air preheater after heat exchange with a reheater and a superheater to obtain exhaust flue gas; the primary air and secondary air are heat exchanged with the combustion flue gas through the air preheater to obtain hot primary air 28 and hot secondary air 31; S22, when the air temperature of the hot primary air 28 is raised to 147°C, the second coal mill is turned on, so that the pulverized coal obtained by the second coal mill and the hot primary air 28 enter the second combustion layer through the second pulverized coal burner, and are burned under the condition of the hot secondary air 31; S23. When the temperature of the combustion flue gas at the inlet of the SCR is raised to above 265°C, the third coal mill is turned on, so that the pulverized coal obtained by the third coal mill and the hot primary air 28 enter the third combustion layer through the third pulverized coal burner, and are burned under the condition of the hot secondary air 31; the pulverized coal flow rate ratio of the first combustion layer, the second combustion layer and the third combustion layer is 1:1:1.2; the flow rate ratio of the secondary air in the first combustion layer, the second combustion layer and the third combustion layer is 1.2:1.2:1; the heating rate of the combustion flue gas at the inlet of the SCR is 40°C / h; the furnace negative pressure value of the boiler unit 3 is -120Pa; The cold start process also includes, when the main steam entering the high-pressure cylinder of the steam turbine and the reheated steam entering the intermediate-pressure cylinder of the steam turbine meet the start-up parameters, the steam turbine is started up, and then the steam turbine is connected to the grid immediately at the hour after the speed control and parameter adjustment processes are carried out in sequence; the start-up parameters include: the temperature of the main steam is 360°C and the pressure is 6MPa; the temperature of the reheated steam is 340°C and the pressure is 2MPa; When the boiler unit 3 is ignited, at least part of the main steam is mixed with the high-pressure cylinder exhaust steam through the high-pressure bypass until the temperature of the obtained cold reheat steam reaches above 280°C; When the temperature of the cold reheat steam reaches 200°C and the pressure reaches 0.5MPa, the boiler feed water is heated by the high-pressure heater before returning to the steam drum 9; when the turbine is in the start-up process and the temperature of the deaerator inlet water is below 150°C, the deaerator inlet water is first heated by the low-pressure heater before entering the deaerator; the inlet and outlet temperature rises of the high-pressure heater and the low-pressure heater are 45°C respectively; The conditions for the constant speed treatment include: the temperature of the main steam is 360°C and the pressure is 6MPa; the temperature of the reheated steam is 340°C and the pressure is 2MPa; the conditions for the parameter adjustment treatment include: the temperature of the main steam is 370°C and the pressure is 6MPa; the temperature of the reheated steam is 350°C and the pressure is 2MPa.

[0079] S3. When the temperature of the combustion flue gas at the SCR inlet reaches above 285°C, start the denitrification device.

[0080] Through the application of Unit 4 of Example 1, the time from unit ignition to the commissioning of the denitrification system is 4 hours earlier than before on average, and the time from unit grid connection to the commissioning of the denitrification system is about 45 minutes. This can effectively shorten the NOx The time of exceeding emission standards and the time of exceeding NOx standards when the unit is started have been shortened to within 1 hour.

[0081] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0082] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0083] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for cold starting of a boiler unit, characterized in that: The method includes: S1, completing the pre-ignition start-up process of the boiler unit, wherein the pre-ignition start-up process includes adding high calorific value coal to the pulverizing unit; the pulverizing unit includes a first pulverizing unit, a second pulverizing unit and a third pulverizing unit; The main combustion area inside the furnace of the boiler unit includes a first combustion layer, a second combustion layer and a third combustion layer which are connected in sequence from top to bottom; S2, after igniting the boiler unit, perform a cold start process, and monitor the temperature of the combustion flue gas at the SCR inlet in real time; S3. When the temperature of the combustion flue gas at the SCR inlet reaches above 285°C, the denitration device is turned on; The cold start process comprises: S21, start the first pulverizing unit, and allow the obtained pulverized coal to enter the first combustion layer for combustion treatment under the action of primary air and sealing air; S22, when the temperature of the hot primary air rises to 140-150°C, continue to open the second pulverizing unit, and allow the obtained pulverized coal to enter the second combustion layer under the action of the primary air and the sealing air to participate in the combustion process; S23, when the temperature of the combustion flue gas at the inlet of the SCR rises to above 265°C, continue to open the third pulverizing unit, and allow the obtained pulverized coal to enter the third combustion layer under the action of primary air and sealing air to participate in the combustion process; S24, adjusting the pulverized coal flow rate and the secondary air flow rate in the first combustion layer, the second combustion layer and the third combustion layer, so that the ratio of the pulverized coal flow rate in the first combustion layer, the second combustion layer and the third combustion layer reaches 1: (1-1.15): (1.2-1.5), and the ratio of the secondary air flow rate in the first combustion layer, the second combustion layer and the third combustion layer is (1.2-1.5): (1.2-1.5): 1; The cold start process also includes, when the main steam entering the high-pressure cylinder of the steam turbine and the reheated steam entering the medium and low-pressure cylinders of the steam turbine meet the start-up parameters, the steam turbine is subjected to a start-up process; the start-up parameters include: the temperature of the main steam is 320~400℃, and the pressure is 5~10MPa; the temperature of the reheated steam is 300~380℃, and the pressure is 0.5~3MPa.

2. The method according to claim 1, characterized in that During the process from the ignition of the boiler unit to the start-up of the steam turbine, the temperature rise rate of the combustion flue gas at the SCR inlet is 70-90° C. / h.

3. The method according to claim 1, characterized in that: The cold start process further includes: when the total flow rate of pulverized coal in the first combustion layer, the second combustion layer and the third combustion layer reaches 40 t / h, As the total flow rate of pulverized coal in the first combustion layer, the second combustion layer, and the third combustion layer increases, the air-coal ratio of the boiler unit is reduced.

4. The method according to claim 1, characterized in that: The furnace negative pressure value of the boiler unit is -100 to -150Pa.

5. The method according to claim 1, characterized in that The furnace negative pressure value of the boiler unit is -110 to -140Pa.

6. The method according to claim 1, characterized in that Step S4 also includes that the ratio of the pulverized coal flow rates in the first combustion layer, the second combustion layer and the third combustion layer is 1:1:1.2; and the ratio of the secondary air flow rates in the first combustion layer, the second combustion layer and the third combustion layer is 1.2:1.2:

1.

7. The method according to claim 1, characterized in that When the boiler unit is ignited, at least part of the main steam is mixed with the high-pressure cylinder exhaust steam through the high-pressure bypass until the temperature of the obtained cold reheat steam reaches above 280°C.

8. The method according to claim 7, characterized in that When the temperature of the cold reheat steam reaches above 200°C and the pressure reaches above 0.5MPa, the boiler feed water treated by the deaerator is heated by the high-pressure heater and then returned to the boiler unit; The inlet and outlet temperature of the high-pressure heater rises below 45°C.

9. The method according to claim 1, characterized in that: When the steam turbine is in the start-up process and the temperature of the deaerator inlet water is below 150° C., the deaerator inlet water is heated by a low-pressure heater before entering the deaerator; The inlet and outlet temperature rise of the low-pressure heater is below 45°C.

10. The method according to claim 7, characterized in that The steam turbine start-up process also includes connecting the steam turbine to the grid after being subjected to speed control and parameter adjustment in sequence; The conditions of the constant speed treatment include: the temperature of the main steam is 320-400°C and the pressure is 5-10MPa; the temperature of the reheated steam is 300-380°C and the pressure is 0.5-3MPa; The conditions for the parameter adjustment process include: the temperature of the main steam is 360°C~370°C, and the pressure is 5~10MPa; the temperature of the reheated steam is 350~360°C, and the pressure is 0.5~3MPa.

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