A control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler

Abstract

The present invention belongs to the technical field of burners, and specifically relates to a control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler, which is as follows: First, supply primary air, maintain the negative pressure at the furnace outlet, ignite the oil gun, raise the temperature of the boiler bed, feed coal into the furnace, control the heating rate. When the combustion color in the furnace is normal red and the bed temperature is 760°C - 780°C, adjust the ignition oil pressure and the coal feeding amount. When the bed temperature is stably burning and NOx ≤ 45mg / Nm 3 , the ignition is successful; during the heating process, the first denitration spray gun is put into use; after the ignition is successful, the oil gun is withdrawn, secondary air is supplied. When the furnace outlet temperature reaches above 670°C, the second denitration spray gun is put into use, the NOx content in the flue gas decreases, the first spray gun is withdrawn, and the NOx emission amount in the flue gas ≤ 46mg / Nm 3 . By adopting this method, the ultra-low NOx emissions of the flue gas can be effectively controlled during the ignition process of the furnace, and the problem of environmental pollution is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of burners, and particularly relates to a control method for ultra-low emission of NOx during the ignition and start-up process of a circulating fluidized bed boiler. Background Art

[0002] Ultra-low emission means that during the operation and end treatment of a coal-fired boiler, an efficient cooperative removal integrated system technology is adopted to make the flue gas emission concentration of the boiler reach the emission limit of coal-fired units, that is, the emission concentrations of soot, sulfur dioxide, and nitrogen oxides (benchmark oxygen content 6%) do not exceed 5 mg / Nm 3 、35 mg / Nm 3 、50 mg / Nm 3 , respectively. Ultra-low emission of boiler flue gas is a new benchmark for the clean production level of coal-fired power generation units.

[0003] The NOx generated during the coal combustion process of a boiler is mainly nitric oxide (NO) and nitrogen dioxide (NO2), which are collectively referred to as NOx. In addition, a small amount of nitrous oxide (N2O) is also generated. The generation amount of NOx during the coal combustion process is closely related to the coal combustion method, especially combustion conditions such as combustion temperature and excess air coefficient. In a circulating fluidized bed boiler, on the one hand, nitrogen is continuously oxidized to generate NOx during the combustion process, and on the other hand, NOx is also continuously reduced to generate N2 in a reducing atmosphere. Therefore, all factors affecting the oxidation and reduction reactions will affect the concentration of NOx.

[0004] With the increasingly strict national environmental protection requirements, achieving ultra-low emission of flue gas from coal-fired units is a basic requirement. However, the ignition and start-up of a CFB boiler is different from that of other boilers. Ignition and start-up has always been a difficult problem in the operation of this type of boiler. More NOx is generated during ignition and start-up, which has a certain impact on the surrounding environment. Controlling ultra-low emission of NOx in the flue gas during ignition and start-up is an even more important issue. Currently, there is no mature control method for stably achieving ultra-low emission of NOx in the flue gas during the start-up process of a CFB boiler. Summary of the Invention

[0005] In view of the existing problems, the present invention provides a control method for ultra-low emission of NOx during the ignition and start-up of a circulating fluidized bed boiler. By using this method, the ultra-low emission of NOx in the flue gas can be effectively controlled during the ignition furnace process, and the problem of environmental pollution is effectively reduced.

[0006] The technical solution of the present invention is as follows:

[0007] A control method for ultra-low emission of NOx during the ignition and start-up process of a circulating fluidized bed boiler, the specific method is as follows in sequence:

[0008] (1) Conduct one ventilation. The furnace outlet is in a negative pressure state. Ignite with an oil gun. The ignition oil pressure is 0.5 - 1.6 MPa. When the boiler bed temperature rises to 490 - 500 °C, feed coal into the furnace. By adjusting the ignition oil pressure, the coal feed rate ≤ 1.1 t / h, control the temperature rise at 1 - 3 °C / min, the spreader air pressure < 1.5 kPa, and the flue gas oxygen content is less than 13%; by adjusting the ignition oil pressure and the coal feed rate, control the temperature rise rate at 1 - 3 °C / min to make the combustion color in the furnace normal red. Then, by adjusting the ignition oil pressure and the coal feed rate, when the bed temperature is at 760 °C - 780 °C, reduce the ignition oil pressure to 0.5 - 0.7 MPa, and adjust the coal feed rate to 1.1 t / h - 4.2 t / h. Wait for the bed temperature to stabilize at 760 °C - 780 °C for combustion, and the NOx in the flue gas ≤ 45 mg / Nm 3 , and the ignition is successful; during the temperature rise process, when the upper part of the bed material temperature reaches 690 - 715 °C, put the first spray gun into the secondary air outlet of the furnace and spray the denitration agent into the furnace at 60 - 80 kg / h;

[0009] (2) After the ignition is successful, withdraw the oil gun and continue combustion. When the furnace outlet temperature reaches above 670 °C, close the air damper of the lower secondary air nozzle and use the upper secondary air nozzle to supply secondary air; at the same time, when the furnace outlet temperature reaches above 670 °C, put the second spray gun into the furnace outlet and spray the denitration agent into the furnace at 60 - 80 kg / h, and gradually increase the amount of the sprayed denitration agent. During the process of the NOx content in the flue gas decreasing, stop spraying the denitration agent from the first spray gun put into the secondary air outlet and withdraw it, and increase the amount of the denitration agent sprayed by the second spray gun at the furnace outlet to 210 kg / h - 270 kg / h, and the NOx emission amount in the flue gas ≤ 46 mg / Nm 3 .

[0010] Preferably, select suitable ignition coal and the critical fluidization air volume before ignition, and the primary air volume is the critical air volume.

[0011] Preferably, the ignition coal is a low nitrogen content coal type with a calorific value of 4950 - 5050 kcal / kg and a volatile content of 24 - 26%, passing through a 14 mm sieve hole. For low calorific value coal, the ash content is relatively high. After the coal burns in the furnace, there is more circulating material in the circulating material system, which can reduce the generation of NOx.

[0012] Preferably, the critical fluidization air volume is 32500 - 33500 m 3 / h. If the air volume is less than the critical fluidization air volume, the bed material fluidization is not good, and coking accidents occur during ignition. If the air volume is greater than the critical fluidization air volume, the flue gas oxygen content is high, and the NOx emission value in the flue gas is high.

[0013] Preferably, when determining the critical air volume: when the boiler is fed with bed material, the selected slag should have particles sized 0.1 - 8 mm, with a combustible content of ≤ 5%, and the thickness of the bed material laid should be 400 - 450 mm. One reason is to ensure that the bed material contains a relatively large amount of circulating material during fluidization to reduce the generation of NOx; the other reason is that the sieved bed material has smaller particles, which can ensure that the critical fluidization air volume is as small as possible, the primary air volume used during the ignition conversion is small, the excess air coefficient of the flue gas in the furnace is low, and the lower part of the combustion chamber is a CO reducing atmosphere (NOx → N2 + O2), resulting in less NOx generation.

[0014] Preferably, the denitration agent is a urea solution with a mass concentration of 7.5 - 8.5% (urea aqueous solution).

[0015] Preferably, when the furnace outlet is in a negative pressure state, the pressure is -50 to -100 Pa.

[0016] Preferably, the secondary air volume is 10000 - 12000 Nm 3 / h.

[0017] Preferably, when the NOx content in the flue gas drops to 32 mg / m 3 or less, the first spray gun at the secondary air inlet stops spraying the denitration agent and is withdrawn.

[0018] By controlling the primary air volume, the bed temperature, spraying the denitration agent with the first spray gun at the secondary air inlet, and controlling the secondary air volume as well as the alternating increase and decrease of the second spray gun and the first spray gun, the present invention effectively realizes the ultra-low emission of NOx in the flue gas during the ignition furnace process, effectively reduces the problem of environmental pollution; at the same time, it also solves the problem of difficult ignition of the furnace; in particular, the inventor first proposed that during the ignition and temperature increase process, the first spray gun is put into the secondary air inlet to spray the denitration agent to achieve effective denitration; during the conventional ignition process, the bed temperature is controlled at 880 - 920 °C, resulting in more nitrogen oxides generated. The present invention controls the bed temperature at 760 °C - 780 °C, which is significantly lower than the bed temperature setting of the prior art, resulting in less nitrogen oxide generation and achieving the ultra-low emission of NOx.

[0019] The beneficial effects of the present invention: During the ignition process of small and medium-sized circulating fluidized beds, NOx can achieve ultra-low emission; it ensures energy security and realizes the clean and efficient utilization of coal; it greatly reduces the pollution of NOx in the flue gas during the boiler ignition process to the surrounding atmosphere; through the technology of the present invention, it can not only ensure the safe and smooth ignition process of small and medium-sized circulating fluidized beds, but also ensure that the flue gas NOx can achieve ultra-low emission (NOx ≤ 46 mg / Nm 3 ), reducing the impact on the surrounding atmospheric environment. Detailed implementation methods

[0020] The following is a detailed description of the above content of the present invention in the form of specific embodiments, but it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention fall within the scope of the present invention. Unless otherwise specified, conventional prior arts are used in the following embodiments.

[0021] A control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler is as follows:

[0022] (1) Select appropriate ignition coal

[0023] The ignition coal is a coal type with a low nitrogen content, having a calorific value of 5036 kcal / kg and a volatile matter of 26%.

[0024] The specific particle size of the ignition coal is as follows:

[0025]

[0026]

[0027] (2) Determine the critical fluidization air volume

[0028] When the boiler is filled with bed material, the selected slag has particle requirements of 0.1 - 8 mm, a combustible content of ≤5%, and the bed material laying thickness is 437 mm (measured from the top of the air cap). Through a fluidization test (the critical fluidization air volume is determined through a conventional fluidization test in the prior art), the critical fluidization air volume is determined to be 33000 m 3 / h;

[0029] (3) Supply primary air, and the controlled primary air volume is the critical air volume of 33000 m 3 / h, the primary air fan current is 20.5 A, the primary air damper opening is 19.5%, the air chamber pressure is 6.9 KPa, the material layer differential pressure is 7.1 KPa, the average negative pressure at the furnace outlet is -83 Pa. The oil gun is ignited, and the ignition oil pressure is 0.6 MPa. When the boiler bed temperature rises to 500 °C, the ignition oil pressure is adjusted to 1.5 MPa, the coal feeding rate is 1.1 t / h, the temperature rise is controlled at 1 - 3 °C / min, the spreader air pressure < 1.5 kpa, and the oxygen content in the flue gas is less than 13%; the ignition oil pressure is maintained at 1.5 Mpa, the coal feeding rate is 1.8 t / h, the temperature rise rate is 1 - 3 °C / min, so that the combustion color in the furnace is normal red. Then the ignition oil pressure is maintained at 1.5 MPa, the coal feeding rate is 2.3 t / h, the bed temperature is 600 °C, and the oxygen content in the flue gas is 12.5%; the ignition oil pressure remains unchanged at 1.5 MPa, the coal feeding rate is 2.9 t / h, the bed temperature is 720 °C, and the oxygen content in the flue gas is 10.7%. The ignition oil pressure remains unchanged at 1.5 MPa, the coal feeding rate is 3.6 t / h, the bed temperature is 770 °C, and the oxygen content in the flue gas is 9.6%. The ignition oil pressure is reduced to 0.6 MPa, the coal feeding rate is 4.2 t / h. When the bed temperature is stable at 770 °C (±5 °C), the oxygen content in the flue gas is 8.3%, and NOx ≤ 45 mg / Nm 3 , ignition is successful; when the temperature above the material layer reaches over 690 °C during ignition, the first spray gun is put into the secondary air inlet of the furnace, and the denitration agent is sprayed into the furnace at a rate of 70 kg / h;

[0030] (8) After ignition is successful, the oil gun is withdrawn and combustion continues. When the furnace outlet temperature reaches over 670 °C, the lower secondary air nozzle damper is closed, and secondary air is supplied through the upper secondary air nozzle. The secondary air volume is 11000 Nm 3 / h; at the same time, when the furnace outlet temperature reaches over 670 °C, the second spray gun is put into the furnace outlet, and the denitration agent is sprayed into the furnace at a rate of 70 kg / h, and the amount of the sprayed denitration agent is gradually increased. The NOx content in the flue gas drops to below 32 mg / m 3 ; the first spray gun put into the secondary air inlet stops spraying the denitration agent and is withdrawn, and the spraying amount of the second spray gun at the furnace outlet is increased to 260 kg / h. The emission amount of NOx in the flue gas ≤ 46 mg / Nm 3 ;

[0031] The above denitration agent is an 8% urea aqueous solution by mass concentration.

[0032] The present invention effectively realizes the ultra-low emission of NOx in flue gas during the ignition furnace process by controlling the primary air volume, controlling the bed temperature, injecting a denitration agent through the first spray gun at the secondary air inlet, and controlling the alternating increase and decrease of the secondary air volume and the second spray gun and the first spray gun, effectively reducing the problem of environmental pollution; at the same time, it also solves the problem of difficult ignition of the furnace; in particular, the inventor first proposes that during the ignition and temperature increase process, the first spray gun is injected at the secondary air inlet to spray the denitration agent to achieve effective denitration; during the conventional ignition process, the bed temperature is controlled at 880-920°C, and more nitrogen oxides are generated. The bed temperature of the present invention is controlled at 760°C to 780°C, which is significantly lower than the bed temperature setting of the prior art, resulting in less nitrogen oxide generation and realizing the ultra-low emission of NOx.

[0033] A control method for ultra-low emission of NOx during the ignition and starting process of a circulating fluidized bed boiler provided by the present invention can enable ultra-low emission of NOx during the ignition and starting process of the circulating fluidized bed; ensure energy security and realize the clean and efficient utilization of coal; greatly reduce the pollution of NOx in the flue gas during the ignition and starting process of the boiler to the surrounding atmosphere; through the technology of the present invention, it can not only ensure the safe and smooth ignition and starting process of the circulating fluidized bed, but also ensure that the flue gas NOx can achieve ultra-low emission (NOx ≤ 46 mg / Nm 3 ), reducing the impact on the surrounding atmospheric environment.

Claims

1. A control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler, characterized in that, The specific method is as follows: (1) Vent once, the furnace outlet is in a negative pressure state, ignite the oil gun, the ignition oil pressure is 0.5 - 1.6 MPa. When the boiler bed temperature rises to 490 - 500 °C, feed coal into the furnace, the coal feeding amount ≤ 1.1 t / h. By adjusting the ignition oil pressure, control the temperature rise at 1 - 3 °C / min, the spreader air pressure < 1.5 kPa, and the oxygen content in the flue gas is less than 13%. By adjusting the ignition oil pressure and the coal feeding amount, control the temperature rise rate at 1 - 3 °C / min to make the combustion color in the furnace normal red. Then, by adjusting the ignition oil pressure and the coal feeding amount, when the bed temperature is controlled at 760 °C - 780 °C, reduce the ignition oil pressure to 0.5 - 0.7 MPa, and adjust the coal feeding amount to 1.1 t / h - 4.2 t / h. Wait for the bed temperature to stabilize at 760 °C - 780 °C for combustion, and the NOx in the flue gas ≤ 45 mg / Nm³, and the ignition is successful. During the temperature rise process, when the temperature at the upper part of the material layer reaches 690 - 715 °C, put the first spray gun into the secondary air outlet of the furnace and spray the denitration agent into the furnace at 60 - 80 kg / h; After ignition is successful, withdraw the oil injection gun and continue combustion. When the furnace outlet temperature reaches above 670°C, close the air damper of the lower secondary air nozzle and supply secondary air through the upper secondary air nozzle. At the same time, when the furnace outlet temperature reaches above 670°C, put the second spray gun at the furnace outlet and inject denitration agent into the furnace at a rate of 60 - 80 kg / h, and gradually increase the amount of denitration agent injection. During the process of the NOx content in the flue gas decreasing, stop injecting the denitration agent from the first spray gun put at the secondary air port and withdraw it, and increase the amount of denitration agent injected by the second spray gun at the furnace outlet to 210 kg / h - 270 kg / h. The NOx emission in the flue gas ≤ 46 mg / Nm 3 ; The primary air volume is 32,500 to 33,500 m 3 / h; the secondary air volume is 10,000 to 12,000 Nm 3 / h.

2. The control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler according to claim 1, characterized in that, Select appropriate ignition coal and primary air volume before ignition.

3. The control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler according to claim 2, characterized in that, The ignition coal is a low nitrogen content coal type with a calorific value of 4950 - 5050 kcal / kg and a volatile content of 24 - 26%, passing through a 14 mm sieve hole.

4. The control method for ultra-low NOx emission during the ignition and start-up process of a circulating fluidized bed boiler according to claim 2, characterized in that When determining the primary air volume: when loading the upper bed material of the boiler, select furnace slag with particle requirements of 0.1 - 8 mm and a combustible content ≤ 5%, and the bed material laying thickness is 400 - 450 mm.

5. The control method for ultra-low NOx emission during the ignition and start-up process of a circulating fluidized bed boiler according to claim 1, characterized in that The denitration agent is a urea solution with a mass concentration of 7.5 - 8.5%.

6. The control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler according to claim 1, characterized in that When the furnace outlet is in a negative pressure state, the pressure is -50 - -100 Pa.

7. A control method for ultra-low NOx emissions during the ignition and start-up process of a circulating fluidized bed boiler according to claim 1, characterized in that, The NOx content in the flue gas drops to 32 mg / m 3 Below, the first spray gun inserted at the secondary air inlet stops spraying the denitration agent and is withdrawn.

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