Stable combustion and low nitrogen emission cooperative control system of ultra-low load circulating fluidized bed boiler

Abstract

The stable combustion and low-nitrogen emission cooperative control system comprises a hearth, an air distribution device, a primary air system, a cold air chamber, a secondary air system, a cyclone separator, a convection bank, a dynamic combustion balance control system and a graded FGR system. The secondary air system mainly comprises a secondary air duct, a secondary air bellow and a secondary air branch pipe; the dynamic combustion balance control system comprises a control valve, a pressure measuring element, a temperature measuring element and a NOx detecting element. The graded FGR system includes a main FGR flue and a compensation FGR flue. Wherein the main FGR flue is connected with the primary air system and enters the hearth from the bottom of the air distribution device after being mixed with primary air; the compensation FGR flue is connected into a secondary air flue and enters a dilute-phase area of the hearth 100 after being mixed with secondary air. Through the design of the small bed surface air distribution system, the graded FGR system and the dynamic balance combustion control system, ultralow-load stable combustion and low-nitrogen emission of the circulating fluidized bed boiler are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of circulating fluidized bed combustion, and in particular to a coordinated control system for stable combustion and low nitrogen emissions of an ultra-low load circulating fluidized bed boiler. Background Art

[0002] Existing conventional circulating fluidized bed boilers with air distribution plates have the following problems when operating at ultra-low load: The conflict between fluidization and low nitrogen emissions: Low air volume at ultra-low loads leads to an imbalanced fluidization velocity distribution, susceptibly increasing the risk of coking in the dense phase. However, increasing the air volume leads to excessive oxygen levels, making low NOx emissions impossible. The conflict between stable combustion and fluidization: To achieve both normal fluidization and low NOx emissions, flue gas recirculation (FGR) can be used to reduce oxygen concentration. However, this approach makes it impossible to control the optimal oxygen level in the furnace, potentially leading to severe CO emissions exceeding the standard due to extremely incomplete combustion. Summary of the Invention

[0003] To address these technical issues, the present invention designs a coordinated control system for stable combustion and low nitrogen emissions in an ultra-low-load circulating fluidized bed boiler. By designing a small bed-surface air distribution system, a staged FGR, and a dynamic balanced combustion control system, this achieves stable combustion and low nitrogen emissions in a circulating fluidized bed boiler at ultra-low loads.

[0004] The present invention adopts the following technical solutions: A coordinated control system for stable combustion and low nitrogen emissions of an ultra-low-load circulating fluidized bed boiler comprises a furnace, a flue, an air distribution device, a primary air system, a cold air chamber, a secondary air system, a cyclone separator, and a convection tube bundle. The primary air system comprises a primary air duct, the secondary air system comprises a secondary air duct, the cold air chamber is arranged at the bottom of the furnace, an air distribution device is arranged above the cold air chamber, the primary air duct is connected to the cold air chamber, the secondary air duct is connected to the dilute phase zone in the furnace, and the convection tube bundle is installed at the tail end of the flue. The coordinated control system further comprises a dynamic combustion balance control system and a staged FGR system. The graded FGR system includes a main FGR flue and a compensation FGR flue. One end of the main FGR flue is connected to the flue tail and the other end is connected to the primary air duct. After mixing with the primary air, it enters the furnace from the cold air chamber at the bottom of the air distribution device. One end of the compensation FGR flue is connected to the main FGR flue and the other end is connected to the secondary air duct. After mixing with the secondary air, it enters the dilute phase area of the furnace. The dynamic combustion balance control system includes a controller, control valves, temperature sensors, pressure sensors, and NOx detectors. Control valves are installed in the main FGR flue and the compensation FGR flue, respectively. Temperature and pressure sensors are located in the dense phase area of the furnace, and a NOx detector is located at the flue tail outlet. The controller connects and controls the control valves, temperature sensors, pressure sensors, and NOx detectors. The dynamic combustion balance control system comprehensively analyzes the signals from the temperature and pressure sensors in the dense phase area, and the NOx detector at the boiler flue tail outlet, adjusting the control valve opening to control the flow rate.

[0005] Preferably, the air distribution device adopts a small bed surface air distribution device.

[0006] Preferably, an air preheating device is installed on the primary air duct.

[0007] Preferably, an air preheating device is installed on the secondary air duct.

[0008] Preferably, the secondary air system further includes a secondary air blower box and a secondary air branch pipe, and the secondary air duct is connected to the dilute phase zone of the furnace through the secondary air blower box and the secondary air branch pipe in sequence.

[0009] Preferably, the pressure measuring elements in the dense phase zone of the furnace are arranged in at least two layers along the height direction, and the temperature measuring elements are arranged in at least three groups in the horizontal direction.

[0010] Preferably, a circulating fan is installed on the main FGR flue.

[0011] The beneficial effects of the present invention are as follows: (1) The present invention is designed with a small bed surface air distribution device, and the system can ensure the fluidization speed and reduce the primary air volume at ultra-low load conditions. This not only reduces the excess air volume in the dense phase area to cool the bed temperature and maintain the combustion temperature, but also reduces the amount of oxygen entering the dense phase area and reduces NOx emissions; (2) The present invention is designed with a graded FGR system, in which the main FGR flue is connected to the primary air duct, mixed with the primary air and then enters the furnace from the bottom of the air distribution plate, mainly increasing the low-oxygen air volume, ensuring normal fluidization in the ultra-low load dense phase area while avoiding excess oxygen and increasing NOx emissions; the compensation FGR flue is connected to the secondary air duct, mixed with the secondary air and then enters the dilute phase area of the furnace, creating a reducing atmosphere in the dilute phase area and further suppressing the formation of NOx in the suspended section. This not only ensures low-load fluidization and stable combustion, but also reduces NOx emission concentration; (3) The present invention innovatively proposes a dynamic combustion balance control system, which can adjust the control valve to control the main FGR and compensation FGR flue gas volume by adjusting the uniformity of the dense phase layer pressure and the dense phase temperature field, maintain the optimal oxygen content in the furnace, and meet the requirements of complete combustion and low NOx emissions. First, when the layer pressure fluctuates greatly, it indicates local fluidization unevenness. By increasing the flue gas volume of the main FGR flue, the fluidization air volume is increased to ensure fluidization stability (normal pressure fluctuation); secondly, when the pressure fluctuation is normal, according to the dense phase temperature, under the condition of ensuring that the total air volume remains unchanged, the ratio of the primary air volume to the main FGR flue gas volume is dynamically adjusted. At the same time, according to the NOx emission index, the ratio of the secondary air volume to the compensation FGR flue gas volume is dynamically adjusted to control the appropriate oxygen concentration in the furnace, so as to achieve the effects of ultra-low load uniform combustion, low CO emissions, and low NOx emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the present invention; In the figure: 100, furnace, 200, air distribution device, 300, primary air system, 400, cold air chamber, 501, secondary air duct, 502, secondary air bellows, 503, secondary air branch pipe, 600, cyclone separator, 700, convection tube bundle, 800, dynamic combustion balance control system, 801, control valve, 802, pressure measuring element, 803, temperature measuring element, 804, NOx detection element, 901, main FGR flue, 902, compensation FGR flue. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings: Example: Figure 1 As shown, Figure 1As shown, a coordinated control system for stable combustion and low nitrogen emissions for an ultra-low-load circulating fluidized bed boiler includes a furnace 100, an air distribution device 200, a primary air system 300, a cold air chamber 400, a secondary air system 500, a cyclone separator 600, a convection tube bundle 700, a dynamic combustion balance control system 800, and a staged FGR system 900. The primary air system 300 includes a primary air duct, the secondary air system 500 mainly includes a secondary air duct 501, a secondary air box 502, and a secondary air branch pipe 503; the dynamic combustion balance control system 800 includes a control valve 801, a pressure measuring element 802, a temperature measuring element 803, and a NOx detection element 804; and the staged FGR system 900 includes a main FGR flue 901 and a compensation FGR flue 902.

[0014] The main FGR flue 901 is connected to the primary air system 300, with one end of the main FGR flue connected to the tail of the flue and the other end connected to the primary air duct. After mixing with the primary air, it enters the furnace 100 from the bottom of the air distribution device 200; the compensation FGR flue 902 is connected to the main FGR flue at one end and the other end connected to the secondary air duct 501. After mixing with the secondary air, it enters the dilute phase area of the furnace 100.

[0015] Control valves 801 are installed in the main FGR flue and the compensating FGR flue, respectively. Temperature measuring elements 803 and pressure measuring elements 802 are located in the dense phase area of the furnace, and a NOx detector 804 is located at the flue tail outlet. A controller controls these valves, temperature measuring elements 803, pressure measuring elements 802, and NOx detectors 804. The dynamic combustion balance control system analyzes the signals from the dense phase temperature measuring elements 803 and pressure measuring elements 802, as well as the NOx detector 804 at the boiler flue tail outlet, and adjusts the control valve opening to control the flow rate.

[0016] The patent of this invention adopts an air distribution system with a small bed surface design. Through the small bed surface air distribution device, while ensuring the fluidization speed, the primary air volume can be reduced, thereby reducing the amount of oxygen entering the dense phase zone. In order to ensure stable combustion and reasonable NOx emissions, a dynamic combustion balance control system 800 is used. The pressure field and temperature field are comprehensively analyzed through the dense phase area material layer pressure detection element 802, the dense phase area temperature detection element 803 and the tail flue gas NOx detection element 804, and then the opening of the control valve 801 is driven. When the material layer pressure fluctuates greatly, the air volume of the main FGR flue 901 is increased; when the pressure fluctuation is normal, if the dense phase area temperature is low, the air volume of the main FGR flue 901 is reduced, and the primary air volume is increased simultaneously to maintain the total air volume constant. At the same time, the secondary air volume and the compensating FGR flue 902 air volume are appropriately adjusted to ensure that NOx emissions meet the standards; if the dense phase area temperature is high, the air volume of the main FGR flue 901 is increased, and the primary air volume is correspondingly reduced to ensure that the total air volume remains unchanged. Similarly, the secondary air volume and the compensating FGR flue 902 air volume are appropriately adjusted to keep NOx emissions within the standard range.

[0017] After adopting the stable combustion and low nitrogen emission coordinated control system of the ultra-low load circulating fluidized bed boiler of the present invention, the circulating fluidized bed boiler can stably burn under ultra-low load and achieve low NOx emissions at the same time.

[0018] The embodiment described above is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. A coordinated control system for stable combustion and low nitrogen emissions of an ultra-low-load circulating fluidized bed boiler, comprising a furnace, a flue, an air distribution device, a primary air system, a cold air chamber, a secondary air system, a cyclone separator, and a convection tube bundle. The primary air system comprises a primary air duct, the secondary air system comprises a secondary air duct, the cold air chamber is arranged at the bottom of the furnace, an air distribution device is arranged above the cold air chamber, the primary air duct is connected to the cold air chamber, the secondary air duct is connected to the dilute phase zone in the furnace, and the convection tube bundle is installed at the tail end of the flue. The coordinated control system also includes a dynamic combustion balance control system and a staged FGR system; The graded FGR system includes a main FGR flue and a compensation FGR flue. One end of the main FGR flue is connected to the flue tail and the other end is connected to the primary air duct. After mixing with the primary air, it enters the furnace from the cold air chamber at the bottom of the air distribution device. One end of the compensation FGR flue is connected to the main FGR flue and the other end is connected to the secondary air duct. After mixing with the secondary air, it enters the dilute phase area of the furnace. The dynamic combustion balance control system includes a controller, a control valve, a temperature measuring element, a pressure measuring element, and a NOx detection element. Control valves are installed on the main FGR flue and the compensation FGR flue respectively. Temperature measuring elements and pressure measuring elements are set in the dense phase area of the furnace. A NOx detection element is set at the tail outlet of the flue. The controller is connected to control the control valve, temperature measuring element, pressure measuring element, and NOx detection element.

2. The stable combustion and low nitrogen emission coordinated control system for an ultra-low load circulating fluidized bed boiler according to claim 1 is characterized in that: The air distribution device adopts a small bed surface air distribution device.

3. The stable combustion and low nitrogen emission coordinated control system for an ultra-low load circulating fluidized bed boiler according to claim 1 is characterized in that: An air preheating device is installed on the primary air duct.

4. The stable combustion and low nitrogen emission coordinated control system for an ultra-low load circulating fluidized bed boiler according to claim 1 is characterized in that: An air preheating device is installed on the secondary air duct.

5. The stable combustion and low nitrogen emission coordinated control system for an ultra-low load circulating fluidized bed boiler according to claim 1 is characterized in that: The secondary air system further comprises a secondary air blower box and a secondary air branch pipe, and the secondary air duct is connected to the dilute phase zone of the furnace through the secondary air blower box and the secondary air branch pipe in sequence.

6. The stable combustion and low nitrogen emission coordinated control system for an ultra-low load circulating fluidized bed boiler according to claim 1 is characterized in that: In the dense phase area of the furnace, pressure measuring elements are arranged in at least two layers along the height direction, and temperature measuring elements are arranged in at least three groups in the horizontal direction.

7. The stable combustion and low nitrogen emission coordinated control system for an ultra-low load circulating fluidized bed boiler according to claim 1 is characterized in that: A circulating fan is installed on the main FGR flue.

Images