A partition control system and a partition control method of a circulating fluidized bed boiler

Abstract

The application discloses a kind of partition regulation and control system and partition regulation and control method of circulating fluidized bed boiler, including circulating fluidized bed boiler, 2-8 cyclone separators and 2-8 return material devices, the inlet of each cyclone separator is respectively connected with the outlet of different positions in the top of circulating fluidized bed boiler, the solid outlet of each cyclone separator is respectively communicated with different areas in the bottom of circulating fluidized bed boiler by a return material device, to form multiple circulating combustion units, each circulating combustion unit is respectively provided with feed pipe, and is respectively provided with sensor assembly;The inlet acceleration section and outlet section of each cyclone separator are provided with denitration agent lance;Sensor assembly, feed pipe, denitration agent lance, cyclone separator and return material device are connected with control system.

Description

Technical Field

[0001] This invention belongs to the field of circulating fluidized bed boiler control and operation optimization technology, specifically relating to a zone control system and zone control method for a circulating fluidized bed boiler. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Circulating fluidized bed (CFB) boilers have advantages such as high combustion efficiency, wide fuel adaptability, and low pollutant emissions, and have been widely used in China. However, with increasingly stringent environmental standards, especially after the implementation of the "Emission Standard of Air Pollutants for Thermal Power Plants" (GB 13223-2011) and the "Action Plan for Upgrading and Retrofitting Coal-fired Power Plants for Energy Conservation and Emission Reduction (2014-2020)," how to fully utilize the environmental characteristics of CFB boilers and meet the requirements of the latest environmental standards while avoiding high equipment investment and operating costs is an important issue affecting the development of CFB boilers.

[0004] On the other hand, with the continuous increase in the capacity of circulating fluidized bed boilers, the furnace size is constantly increasing. The large furnace cross-section also brings about differences in combustion and mass and heat transfer in different areas of the furnace, specifically manifested as: 1) High temperature or low temperature zones appear in local areas of the boiler; 2) High initial emission concentration of pollutants; 3) Large consumption of denitrification reducing agent and in-furnace desulfurization agent; 4) Deterioration of boiler regulation response characteristics.

[0005] Furthermore, because the sampling points of the environmental monitoring system for circulating fluidized bed boilers are generally located in the tail flue or the inlet flue of the chimney, the flue gas measurement results have a significant time lag, making it difficult to effectively guide operational adjustments. To achieve ultra-low emissions, excessive addition of denitrification reducing agents and in-furnace desulfurizing agents is often necessary, and even excessive ammonia injection can lead to large amounts of escaped ammonia clogging the heating surfaces of the tail flue. Load adjustments can also easily cause significant fluctuations in environmental and operational control parameters, affecting the boiler's safety, environmental friendliness, and economic efficiency. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a zone control system and method for circulating fluidized bed boilers, so as to achieve real-time optimization of the environmental protection and economic indicators of circulating fluidized bed boilers under different load conditions, optimize the combustion process of circulating fluidized bed boilers, deeply suppress the original generation of sulfur dioxide and nitrogen oxide pollutants, reduce the escape of ammonia caused by SNCR denitrification, and thus reduce the environmental protection costs to meet ultra-low emissions.

[0007] To address the above technical problems, one or more embodiments of the present invention provide the following technical solutions:

[0008] In a first aspect, the present invention provides a zone control system for a circulating fluidized bed boiler, comprising a circulating fluidized bed boiler, 2-8 cyclone separators and 2-8 return material devices. The inlet of each cyclone separator is connected to an outlet at a different position on the top of the circulating fluidized bed boiler. The solid outlet of each cyclone separator is connected to a different area at the bottom of the circulating fluidized bed boiler through a return material device, forming multiple circulating combustion units. Each circulating combustion unit is provided with a feed pipe and a sensor assembly.

[0009] Each cyclone separator is equipped with a denitrification agent spray gun at the inlet acceleration section and the outlet section;

[0010] The sensor assembly, feed pipe, denitrification agent spray gun, cyclone separator, and return device are all connected to the control system.

[0011] Secondly, the present invention provides a method for zoned control of a circulating fluidized bed boiler, comprising the following steps:

[0012] The oxygen content, temperature, and gas concentration of each zone in the boiler furnace are monitored separately. When the pollutant concentration in the corresponding zone exceeds the standard, the dosage of denitrification reducing agent and desulfurization reducing agent in that zone is increased, the primary air volume in that zone is reduced, the opening of the slag discharge port in that zone is reduced, and the opening of the return valve of the return material device is increased to increase the amount of circulating material until the pollutant gas concentration in that zone reaches the set value.

[0013] Compared with the prior art, one or more technical solutions of the present invention have achieved the following beneficial effects:

[0014] It enables precise control of different areas of circulating fluidized bed (CFB) boilers, and is particularly suitable for the large cross-section structure of large CFB boilers; it can achieve real-time optimization of the environmental protection and economic indicators of CFB boilers under different load conditions; the measurement results have a short response time, which can quickly optimize the combustion process of CFB boilers, deeply suppress the original generation of sulfur dioxide and nitrogen oxide pollutants, and minimize the consumption of denitrification reducing agents and in-furnace desulfurizing agents; it reduces the escape of ammonia caused by excessive ammonia injection during denitrification at the source, and lowers the environmental protection cost of achieving ultra-low emissions; the construction is simple, the investment is low, and the method is applicable to new units and the optimization and retrofitting of existing units. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1This is a schematic diagram of the circulating combustion unit of the zone-controlled circulating fluidized bed boiler system involved in Embodiment 2 of the present invention.

[0017] Figure 2 This is a schematic diagram of the partitioned control circulating fluidized bed boiler system involved in the embodiments of the present invention;

[0018] Figure 3 This is a top view showing the distribution of the slag discharge port and air chamber at the bottom of the furnace according to an embodiment of the present invention;

[0019] Figure 4 This is a front view showing the distribution of the slag discharge port and wind chamber at the bottom of the furnace according to an embodiment of the present invention.

[0020] In the diagram: 1-furnace; 2-cyclone separator; 3-feeding device; 4-returning device; 5-control system; 6-slag discharge port; 7-primary air chamber; 8-air distribution plate; 9-air cap. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] In a first aspect, the present invention provides a zone control system for a circulating fluidized bed boiler, comprising a circulating fluidized bed boiler, 2-8 cyclone separators and 2-8 return material devices. The inlet of each cyclone separator is connected to an outlet at a different position on the top of the circulating fluidized bed boiler. The solid outlet of each cyclone separator is connected to a different area at the bottom of the circulating fluidized bed boiler through a return material device, forming multiple circulating combustion units. Each circulating combustion unit is provided with a feed pipe and a sensor assembly.

[0024] Each cyclone separator is equipped with a denitrification agent spray gun at the inlet acceleration section and the outlet section;

[0025] The sensor assembly, feed pipe, denitrification agent spray gun, cyclone separator, and return device are all connected to the control system.

[0026] In some embodiments, a secondary air distribution port is provided above the middle of the furnace of the circulating fluidized bed boiler, and the secondary air distribution port is provided in correspondence with the circulating combustion unit.

[0027] Furthermore, the desulfurizing agent nozzle is located inside the secondary air cloth outlet or / and downstream of the secondary air cloth outlet or / and on the inclined leg of the return valve of the return material device.

[0028] Furthermore, the desulfurizing agent nozzle is positioned 150-500mm downstream of the secondary air distribution outlet.

[0029] Furthermore, the desulfurizing agent nozzle is connected to a pneumatic conveying pipeline, which is equipped with an air volume regulator, and the air volume regulator is connected to the control system.

[0030] Furthermore, each secondary air distribution duct is equipped with an air volume regulator, which is connected to the control system signal.

[0031] In some embodiments, the feed valve in each feed pipe is signal-connected to the control system.

[0032] This is to enable the control system to control the opening degree of the feed valve.

[0033] In some embodiments, the return valve of each return device is connected to the control system via a signal connection.

[0034] In some embodiments, the slag discharge port at the bottom of the furnace is provided in a one-to-one correspondence with each circulating combustion unit, and the opening degree of the slag discharge valve at each slag discharge port is connected to the control system signal.

[0035] Furthermore, each primary air distribution outlet is correspondingly set to one of each circulating combustion unit, and each primary air distribution duct is equipped with an air volume regulator, which is connected to the control system signal.

[0036] Secondly, the present invention provides a method for zoned control of a circulating fluidized bed boiler, comprising the following steps:

[0037] The oxygen content, temperature, and gas concentration of each zone in the boiler furnace are monitored separately. When the pollutant concentration in the corresponding zone exceeds the standard, the dosage of denitrification reducing agent and desulfurization reducing agent in that zone is increased, the primary air volume in that zone is reduced, the opening of the slag discharge port in that zone is reduced, and the opening of the return valve of the return material device is increased to increase the amount of circulating material until the pollutant gas concentration in that zone reaches the set value.

[0038] In some embodiments, different denitrification reducing agents may be used, such as an aqueous solution of urea, ammonia, or liquid ammonia.

[0039] Furthermore, the concentration of these denitrification reducing agents is 5%-15%, where % is a mass percentage.

[0040] Example

[0041] like Figure 1 As shown, a zone-controlled circulating fluidized bed boiler system includes a furnace 1, a cyclone separator 2, a feeding device 3, a return device 4, and a control system 5. The cyclone separator 2 is connected to the upper part of the furnace 1 through an outlet flue. The return device 4 is used to connect the cyclone separator 2 and the lower part of the furnace 1. The feeding device 3 is located at the front end of the furnace 1 and is connected to the furnace 1 through a feeding pipe. A primary air distribution system and a slag discharge port are provided at the bottom of the furnace 1, and a secondary air system is provided above the middle part of the furnace 1.

[0042] Cyclone separators 2 are arranged side by side on one side of the furnace 1 or symmetrically on both sides of the furnace 1, so that the furnace is divided into two or more combustion zones according to the arrangement of cyclone separators 2; several denitrification reducing agent spray guns are arranged inside the cyclone separator 2, on the outside, inside or mixed on the outside, inside and above the inlet acceleration section of the cyclone separator 2, and the outlet section of the cyclone separator 2.

[0043] The system also includes a desulfurizing agent nozzle, which is located inside the secondary air system or 20 cm below the secondary air outlet, or on the inclined leg of the return valve of the return device 4.

[0044] A schematic diagram of a combustion zone containing three cyclone separators, as shown below. Figure 2 As shown (other cases are similar), two or more cyclone separators 2 are provided, and two or more outlet flues and return devices 4 are provided in a one-to-one correspondence with cyclone separators 2, so that combustion zones corresponding to cyclone separators 2 are formed in the furnace 1, and combustion circulation units are formed between the combustion zones and outlet flues, cyclone separators 2, and return devices 4.

[0045] Each section of the feeding device 3 is equipped with a feeding pipe, and a feeding valve is installed inside the feeding pipe; the return device 4 is equipped with a return valve.

[0046] The primary air system includes a main primary air duct and branch primary air ducts. Each duct is equipped with an airflow regulator. The structural positions of the slag discharge port and the air chamber are shown in the top view. Figure 3 and face it squarely Figure 4 As shown, the slag discharge ports in each zone are evenly distributed according to the air chambers;

[0047] The secondary air system includes a main secondary air duct and secondary air branch ducts, with an air volume regulator installed in front of each duct.

[0048] The desulfurizing agent is injected into the furnace through pneumatic conveying via nozzles, and an airflow regulator is provided to adjust the pneumatic conveying flow. The slag discharge port, feed valve, return valve, airflow regulator, and denitrification reducing agent spray gun can be monitored and controlled by the control system.

[0049] It also includes the use of different denitrification reducing agents, which can be aqueous solutions of urea, ammonia, or liquid ammonia, with a mass concentration of 5%-15%.

[0050] Fuel is added to the furnace 1 through the feeding device 3. The ash and desulfurized limestone produced by combustion accumulate in the furnace 1 and are fluidized by fluidizing air. They flow through the cyclone separator 2 and the return device 4 and then return to the furnace 1 to form a circulating combustion unit.

[0051] The control system 5 measures the oxygen content, temperature, and gas concentration of each zone. When the pollutant gas concentration exceeds the standard, the control system 5 adjusts the injection volume of the denitrification reducing agent and desulfurization reducing agent in that zone, reduces the primary air volume of that zone by adjusting the air volume regulator to reduce the oxygen content in the furnace 1, reduces the opening of the slag discharge port of that zone to reduce the bottom ash discharge, and increases the circulating material volume by changing the opening of the return valve of the return material device 4 in that zone until the control system 5 detects that the pollutant gas concentration in that zone is normal.

[0052] Application 1

[0053] A 300MW-class subcritical circulating fluidized bed boiler, see [reference] Figure 1 and Figure 2 .

[0054] Three cyclone separators are installed. During boiler operation, the flue gas measuring point is located at TL in the tail flue. The measured oxygen content at full load is 2.7~3.5% on the left and 3.5~4.2% on the right. Limestone is used as the in-furnace desulfurizing agent to control the SO2 emission concentration to not exceed 600 mg / Nm³. 3 The corresponding calcium-to-sulfur molar ratio is 1.8~2.2, NO x Original emission concentration 280~320 mg / Nm 3 After SNCR denitrification, NO x Emission concentration reduced to 25~75 mg / Nm 3 However, the actual measured ammonia escape exceeded 30 mg / Nm³. 3 This causes frequent blockage of the heating surface of the tail flue. In addition, SO2 and NO are generated during load increases and decreases. x Emission concentrations can easily exceed control limits.

[0055] To address this, technical modifications were implemented. The furnace was divided into three zones based on the number of cyclone separators. Gas composition monitoring devices were installed at high-temperature gas composition measurement points in the flue gas outlet of each cyclone separator to monitor oxygen and carbon monoxide concentrations in the flue gas. By adjusting airflow, fuel quantity, denitrification reducing agent dosage, and desulfurization dosage, the operating conditions of the three zones were optimized in real time. After comparing long-term operating data, the denitrification reducing agent dosage decreased by 30%, and the desulfurization agent dosage decreased by 15%.

[0056] Application 2

[0057] A 350MW-class supercritical circulating fluidized bed boiler, see [reference] Figure 1 and Figure 2 .

[0058] Three cyclone separators were installed. During the construction phase, gas component monitoring devices were added to the high-temperature gas component measuring points at each outlet flue of the cyclone separators to monitor the oxygen and carbon monoxide concentrations in the flue gas. The furnace was divided into three zones according to the number of cyclone separators. During operation, the oxygen concentration in zones A and C was controlled at approximately 2%, and the oxygen concentration in zone B was controlled at approximately 2.4%. With only limestone in-furnace desulfurization and no SNCR denitrification, the SO2 emission concentration was 15-25 mg / Nm³. 3 NO x Initial emission concentration was 20~40 mg / Nm³ 3 Furthermore, during load adjustments, the boiler's operating and environmental parameters can still stably meet the requirements of ultra-low emission technology, saving a significant amount of equipment investment and operating costs.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A zone control system for a circulating fluidized bed boiler, characterized in that: It includes a circulating fluidized bed boiler, 2-8 cyclone separators, and 2-8 return material devices. The inlet of each cyclone separator is connected to the outlet at a different position on the top of the circulating fluidized bed boiler. The solid outlet of each cyclone separator is connected to a different area at the bottom of the circulating fluidized bed boiler through a return material device, forming multiple circulating combustion units. Each circulating combustion unit is equipped with a feed pipe and a sensor assembly. The sensor assembly, feed pipe, denitrification agent spray gun, cyclone separator, and return material device are all connected to the control system. The denitrification agent spray guns of the circulating fluidized bed boiler zone control system are set in the inlet acceleration section and outlet section of each cyclone separator, and the desulfurization agent nozzles are set in the secondary air distribution port and / or downstream of the secondary air distribution port and / or set in the return valve inclined leg of the return material device. The amount of denitrifying reducing agent fed into each denitrifying agent spray gun and the amount of desulfurizing agent fed into each desulfurizing agent nozzle can be independently adjusted based on the detection data of the control system. The detection data of the circulating fluidized bed boiler zone control system includes the oxygen content, temperature, and gas concentration of each zone in the furnace. When the pollutant concentration in the corresponding zone exceeds the standard, the dosage of denitrification reducing agent and desulfurization reducing agent in that zone is increased, the primary air volume in that zone is reduced, the opening of the slag discharge port in that zone is reduced, and the opening of the return valve of the return material device is increased to increase the amount of circulating material until the pollutant gas concentration in that zone reaches the set value.

2. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: A secondary air distribution port is installed in the middle and above of the furnace of the circulating fluidized bed boiler, and the secondary air distribution port is set in accordance with the circulating combustion unit.

3. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: The desulfurizing agent nozzle is located 150-500mm downstream of the secondary air distribution outlet; The desulfurizing agent nozzle is connected to the pneumatic conveying pipeline, which is equipped with an air volume regulator that is connected to the control system.

4. The zone control system for a circulating fluidized bed boiler according to claim 2, characterized in that: Each secondary air distribution duct is equipped with an air volume regulator, which is connected to the control system signal.

5. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: The feed valve in each feed pipe is connected to the control system via a signal connection.

6. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: The return valve of each return device is connected to the control system via a signal connection.

7. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: The slag discharge ports at the bottom of the furnace are set one-to-one with each circulating combustion unit, and the opening degree of the slag discharge valve at each slag discharge port is connected to the control system signal.

8. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: Each primary air distribution outlet is set up in a one-to-one correspondence with each circulating combustion unit, and each primary air distribution duct is equipped with an air volume regulator, which is connected to the control system signal.

9. The zone control system for a circulating fluidized bed boiler according to claim 1, characterized in that: Different denitrification reducing agents are used, such as aqueous solution of urea, ammonia, or liquid ammonia.

10. The zone control system for a circulating fluidized bed boiler according to claim 9, characterized in that: The mass concentration of the denitrification reducing agent is 5%-15%.

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