A combined combustion device suitable for pulverized coal / natural gas dual-fuel boilers

Abstract

This utility model discloses a combined combustion device suitable for pulverized coal / natural gas dual-fuel boilers. The combustion device comprises the following arrangement: from the bottom of the boiler furnace upwards, the burners are arranged in the following order: an independent natural gas burner, an independent pulverized coal burner, two layers of independent natural gas burners, and an independent separate burnout air burner. The pulverized coal burner, natural gas burner, and separate burnout air burner are all arranged tangentially at the four corners. The pulverized coal burner adopts a direct-flow structure and is distributed through a large air box system. The natural gas burner adopts a weak swirling structure, and the air duct drawn from the large air box is connected to the inlet of the burner body. This utility model improves the boiler's fuel adaptability and environmental performance, achieving low emissions, high efficiency, and low-cost operation.

Description

Technical Field

[0001] This utility model relates to a combined combustion device suitable for pulverized coal / natural gas dual-fuel boilers. Background Technology

[0002] The existing boilers in my country are basically pure pulverized coal boilers, and there are also some gas-fired boilers. Boilers that can burn pulverized coal at full load or pure natural gas at full load and can co-fire pulverized coal and natural gas have not yet been widely developed. Therefore, there is no burner arrangement scheme suitable for such pulverized coal / natural gas dual-fuel boilers.

[0003] Based on the background section, this utility model aims to solve key defects in existing boiler technology, the main problems of which include:

[0004] 1. Lack of multi-fuel compatibility:

[0005] Most existing boilers are designed to burn only pulverized coal or only natural gas, and cannot simultaneously achieve full-load operation of pulverized coal, full-load operation of only natural gas, or a mixture of pulverized coal and natural gas. This limits the boiler's flexibility in fuel selection and makes it difficult to adapt to the ever-changing energy market.

[0006] 2. Inefficient spatial arrangement:

[0007] Traditional burner layouts are not optimized for boiler space, which may lead to an excessive increase in boiler height or occupation of the cold ash hopper area when adding a natural gas combustion layer, affecting structural compactness and thermal efficiency.

[0008] 3. Poor fuel adaptability:

[0009] Existing solutions cannot meet the full-load requirements of 400-1000t / h boilers for multiple fuels (pulverized coal, natural gas), hindering the application of boilers in carbon reduction scenarios. Utility Model Content

[0010] This invention provides a burner arrangement scheme that can be fully loaded with coal, fully loaded with gas (natural gas), and can co-fire pulverized coal / natural gas.

[0011] This invention proposes a combined burner arrangement scheme, in which, from bottom to top, there are independent natural gas burners, independent pulverized coal burners, independent natural gas burners, independent natural gas burners, and independent separate burnout air burners. This arrangement scheme is suitable for pulverized coal / natural gas dual-fuel boilers with a capacity of 400-1000 t / h. It allows the boiler to achieve low nitrogen oxide emissions when burning only pulverized coal while maintaining full boiler load, and also achieves low nitrogen oxide emissions when burning only natural gas while maintaining full boiler load, simultaneously satisfying the requirements for co-firing of the two fuels.

[0012] In this utility model, the pulverized coal burner uses a large air box for air distribution, and the natural gas burner and the separate burnout air burner are connected to the inlet of the burner body through the air duct led out of the large air box.

[0013] The resistance difference between the pulverized coal burner and the natural gas burner of this utility model is less than 3 kPa, and the air volume is adjusted only by the damper at the inlet of the burner, without the need for an additional air volume adjustment device.

[0014] This utility model adopts four-corner tangential combustion technology, with the pulverized coal burner, natural gas burner and burnout air burner all arranged at the four corners of the boiler.

[0015] This utility model of pulverized coal burner adopts a direct current type. The pulverized coal burner achieves air grading by setting a separate burnout air burner, thereby controlling the nitrogen oxide index generated by pulverized coal combustion.

[0016] The natural gas burner in this project adopts a weak swirl type, which can meet the requirements of the tangential combustion scheme at the four corners of the boiler. The nitrogen oxide index generated by natural gas combustion is controlled through flue gas recirculation technology.

[0017] This project can employ air staging technology during natural gas combustion, and the separate burnout air burner can meet the air staging requirements for natural gas combustion.

[0018] This project arranges a layer of natural gas burners below the pulverized coal burners, which can make reasonable use of the space at the corner from the bottom layer of pulverized coal to the cold ash hopper.

[0019] Preferably, the burners are arranged sequentially from the bottom of the boiler furnace upwards as follows: Bottom layer: Independent natural gas burners, positioned above the corner of the cold ash hopper at an elevation of 2m ± 0.5m to prevent flame scouring of the cold ash hopper; Middle layer: Independent pulverized coal burners, located 2m ± 0.5m above the bottom layer; Upper layer: Two independent first and second natural gas burners, with the first natural gas burner positioned 2m ± 0.5m above the middle layer; the distance between the two independent natural gas burners is 3m ± 0.5m; Top: Independent separate burnout air burners, located 3.0m ± 0.5m above the second natural gas burner; all burners are arranged tangentially at four corners, with each group of burners corresponding to one corner of the boiler; this arrangement is suitable for boilers of 400-1000t / h capacity, achieving full-load operation in pure pulverized coal, pure natural gas, and mixed-fire modes, with a load capacity ≥ 100%, and controlling nitrogen oxide emissions through air grading and flue gas recirculation, with a natural gas mode emission ≤ 30mg / Nm³. 3 Nitrogen oxide emissions are controlled through a denitrification system, with a maximum emission level of ≤50 mg / Nm³ in pulverized coal mode. 3 .

[0020] Preferably, the pulverized coal burner adopts a direct-flow design and is equipped with a large air box distribution system, connected to the burner body inlet via an air duct; the natural gas burner adopts a weak swirling structure, which is more suitable for four-corner tangential combustion. It is also equipped with a dedicated flue gas recirculation pipeline, with a flue gas recirculation ratio not exceeding 25%; the separate burnout air burner adopts a staged air distribution design, with an air volume accounting for 25%-40% of the total air volume.

[0021] Preferably, the resistance difference between the pulverized coal burner and the natural gas burner is less than 3 kPa (measured range 1-2.5 kPa), and the air volume adjustment is achieved only through the secondary air damper at the burner inlet. The damper opening adjustment range is 10%-100%, with an opening accuracy of ±1%, and no additional air volume adjustment device is provided.

[0022] Preferably, the primary air velocity of the pulverized coal burner is controlled at 24-28 m / s, and the excess air coefficient in the main burner area is 0.72-0.9; the fuel nozzle diameter of the natural gas burner is 1000 mm ± 200 mm, and the material is a special alloy that is resistant to temperatures up to 1400℃.

[0023] Preferably, during operation, the flue gas recirculation rate is dynamically adjusted according to the mode: 15%-25% for pure natural gas mode and 0% for co-firing mode; the oxygen concentration is controlled as follows: 3.5%-4.0% for pulverized coal mode, 1%-2.2% for natural gas mode, and 3.5%-4% for co-firing mode.

[0024] Preferably, the system includes fuel switching control logic: when starting in pure pulverized coal mode, the pulverized coal burner is turned on and the burnout air opening is adjusted to 10%-100%; when starting in pure natural gas mode, the natural gas burner is turned on and the flue gas recirculation system is started.

[0025] When starting the co-firing mode, the pulverized coal burner and one or more layers of natural gas burners are simultaneously activated, while maintaining the pressure difference between the large air box and the furnace at less than 3 kPa; the entire process is controlled in a closed-loop manner through an online NOx monitoring system (threshold 50 mg / Nm³). 3 ).

[0026] Preferably, the separate burnout air burner is equipped with a dynamic adjustment mechanism: when the online NOx value exceeds 50 mg / Nm³, 3 At the same time, adjust the damper opening to form a strong reducing zone (O2 concentration < 3%) to suppress NOx generation.

[0027] Preferred implementation case for a 410t / h boiler, wherein the pulverizing system includes 4 HP743 medium-speed coal mills, each with an output of 22.1t / h, and 3 of them can operate at full load; the natural gas system includes 12 burners in three layers, each with a heat load of 34.3MW and a full-load thermal efficiency of >94%.

[0028] Preferably, alternative implementation schemes are provided to cover boilers of different capacities: for compact boilers ≤300t / h, the first natural gas burner is retained, the second natural gas burner is eliminated and replaced with a single-layer natural gas burner; and the independent burnout air layer is eliminated and its function is integrated into the upper natural gas burner; for the 1000t / h extended scheme, the number of burnout air burner layers is increased to two layers, and the natural gas burner is upgraded to a dual swirl structure.

[0029] This project arranges two layers of natural gas burners between the pulverized coal burner and the separate burnout air burner, which can effectively utilize boiler space and avoid excessively increasing the boiler height.

[0030] This utility model achieves significant technical effects through the aforementioned combined combustion device, as detailed below:

[0031] 1. Multi-fuel full-load capacity:

[0032] When burning pulverized coal, it can operate at full boiler load (e.g., 400-1000 t / h level) and achieve air grading through a separate burnout air burner, keeping nitrogen oxide emissions at a low level.

[0033] When burning only natural gas, it can operate at full load and utilize flue gas recirculation technology combined with air staging technology to reduce NOx emissions to 30 mg / Nm³. 3 .

[0034] When pulverized coal and natural gas are co-fired, stable combustion and full-load output are maintained, which broadens the range of boiler fuels and adapts to different energy supply scenarios.

[0035] 2. Space optimization and compact structure:

[0036] Arrange a layer of natural gas burners below the pulverized coal burners, make reasonable use of the space at the corner of the cold ash hopper, and avoid excessively increasing the furnace height.

[0037] The two-layer natural gas burner is arranged between the pulverized coal burner and the separate burnout air, which effectively utilizes vertical space and reduces the overall size of the boiler (suitable for compact boiler designs).

[0038] 3. Efficient control and simplified operation:

[0039] By controlling the pressure difference between the air box and the furnace through the large air box air distribution system, the air volume can be reasonably distributed without the need for additional air volume adjustment devices, thus reducing equipment complexity and maintenance costs.

[0040] The natural gas combustion process employs a weak swirling design, which is adapted to tangential combustion at four corners and supports flue gas recirculation, thereby improving combustion efficiency while reducing carbon emissions.

[0041] 4. Economic benefits and environmental advantages:

[0042] To meet my country's carbon reduction needs, boilers can flexibly switch fuels (such as prioritizing the use of natural gas in areas with strict carbon quotas) to help users meet carbon emission quotas (such as annual carbon emission reduction of 40%-50%).

[0043] In practical implementation (such as a 410t / h boiler in a power plant), the pulverizing system (4 medium-speed mills) and the natural gas layer (three layers with 12 units) operate in coordination to ensure stable full-load operation and provide technical support for market expansion.

[0044] 5. Multi-capacity coverage capability:

[0045] Compact type (≤300t / h): Maintains full-load capacity even after reducing the natural gas combustion layer. Maintains low-NOx capacity even after eliminating the burnout air burner.

[0046] Extended type (1000t / h): The two-layer burnout air scheme and dual swirl structure are more suitable for combustion in ultra-high parameter furnaces.

[0047] Overall effect: This utility model improves the fuel adaptability and environmental performance of the boiler, and achieves low emission, high efficiency and low cost operation. Attached Figure Description

[0048] Figure 1 A side view of the overall layout structure of the combined combustion equipment;

[0049] Figure 2 This is a top view of the overall layout structure of the combined combustion equipment. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0051] like Figure 1 The diagram shows a side view of the overall layout of the combined combustion equipment. The diagram clearly shows the hierarchical arrangement of the burners: from the bottom of the furnace upwards, there is an independent natural gas burner A (located at the bottom layer), an independent pulverized coal burner B, two independent natural gas burners C and D (located above the pulverized coal burners), and an independent separate burnout air burner E (located at the top layer). Figure 1 The advantages of the burner's spatial distribution are also illustrated. For example, the lower-level natural gas burner makes good use of the space between the pulverized coal burner and the cold ash hopper, avoiding an excessive increase in boiler height.

[0052] like Figure 2The diagram shows a top-view schematic of the overall layout of the combined combustion equipment, highlighting the direct-flow structure of the pulverized coal burner and the weak swirl design of the natural gas burner. The diagram emphasizes the four-corner arrangement of the burners (one set of burners at each corner) and shows the connection points of the air distribution system (such as the air duct from the large air box connecting to the burner inlet).

[0053] I. Combustion Equipment Structure

[0054] 1. Overall layout plan:

[0055] like Figure 1 As shown, burner groups are installed at the four corners of the boiler, and each group consists of the following from the bottom of the furnace upwards:

[0056] Bottom layer (Layer A): Independent natural gas burners (4 units at the corners), with the center elevation 1.5 to 2.5 meters from the angle of the cold ash hopper to prevent the flame from scouring the cold ash hopper.

[0057] Middle layer (B layer): Independent pulverized coal burners (4 sets at the corner), 1.5 to 2.5m away from layer A, adopting a direct-flow design, with a primary air velocity of 24-28m / s.

[0058] Upper layer (C / D layer): Two independent natural gas burners (8 in total, corners), with layer C 1.5-2.5m from layer B, and the distance between the two independent natural gas burners 2.5-3.5m.

[0059] Top (E layer): Separate burnout air burners (4 sets, corners), 2.5-3.5m from D layer, accounting for 25%-40% of air volume. 2. Key component parameters:

[0060] Pulverized coal burner: Inlet damper opening adjustment range 10%-100%, burner resistance not greater than 1.2 kPa.

[0061] Natural gas burner: fuel nozzle diameter 1000±200mm, flue gas recirculation rate 15%-25%, burner resistance not greater than 3kpa.

[0062] II. Implementation Cases

[0063] Example 1: A 410t / h boiler

[0064] Fuel system:

[0065] Pulverizing system: 4 medium-speed coal mills (model HP743), each with an output of 22.1t / h, and 3 of them can operate at full load (redundant design).

[0066] Natural gas system: three layers with a total of 12 burners, each with a heat load of 34.3MW and a full-load thermal efficiency of >94%.

[0067] Performance indicators:

[0068]

[0069]

[0070] III. Key Operations

[0071] 1. Fuel switching procedure:

[0072] Coal to gas switching: First, start the first layer of natural gas burners (30% load), gradually reduce the amount of pulverized coal, and simultaneously start the other layers of natural gas burners, maintaining air volume balance throughout the process (resistance fluctuation <1kPa).

[0073] Co-firing adjustment: The secondary air distribution ratio is adjusted in real time by the secondary air damper to ensure stable combustion.

[0074] 2. Emission control strategy:

[0075] Pulverized coal mode: The combustor damper is opened at 10-100% to form a strong reducing zone (O2 concentration <3%), suppressing NOx formation. Natural gas mode: 90% of the combustor is shut off, reducing the excess air coefficient to 1.05, and combined with recirculated flue gas to lower the flame temperature.

[0076] This invention applies to two 410t / h boilers. This project involves a dual-fuel (pulverized coal / natural gas) boiler. The pulverizing system uses four medium-speed mills, three of which can operate at full load. The natural gas burners are arranged in three layers with twelve burners, capable of handling the full boiler load. Preferably, a partitioned arrangement of the natural gas and pulverized coal burners is adopted. One layer of natural gas burners is placed between the pulverized coal burners and the cold ash hopper, while two layers of natural gas burners are placed between the pulverized coal burners and the burnout air burners. This arrangement balances the air-staged combustion technology requirements of the pulverized coal burners with the requirement for the natural gas burners to operate at full boiler load. Furthermore, the vertical air-staged combustion technology can reduce nitrogen oxides during natural gas combustion.

[0077] The above description is a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model. These improvements and modifications are also considered to be within the protection scope of the present utility model, and the protection scope of the present utility model shall be defined by the claims.

Claims

1. A combined combustion device suitable for pulverized coal / natural gas dual-fuel boilers, characterized in that, The combustion equipment includes the following arrangement: from the bottom of the boiler furnace upwards, the burners are arranged in the following order: an independent natural gas burner, an independent pulverized coal burner, two layers of independent natural gas burners, and an independent separate burnout air burner; wherein, the pulverized coal burner, natural gas burner, and separate burnout air burner are all arranged in a four-corner tangential manner, the pulverized coal burner adopts a direct-flow structure and is distributed by a large air box air distribution system; the natural gas burner adopts a weak swirling flow structure and is connected to the burner body inlet by an air duct led out from the large air box.

2. A combined combustion device suitable for pulverized coal / natural gas dual-fuel boilers, characterized in that: The burners are arranged sequentially from the bottom of the boiler furnace upwards as follows: Bottom layer (A): Independent natural gas burner, located above the corner of the cold ash hopper, at an elevation of 2m ± 0.5m, to avoid flame scouring of the cold ash hopper; Middle layer (B): Independent pulverized coal burners, located 2m ± 0.5m above the bottom layer (A); Upper layer (C, D): Two independent first natural gas burners (C) and second natural gas burners (D), with the first natural gas burner (C) located 2m ± 0.5m above the middle layer (B); the distance between the two independent natural gas burners is 3m ± 0.5m. Top (E): Independent separate burnout air burner, located 3.0m ± 0.5m above the second natural gas burner (D); all burners are arranged tangentially at the four corners, with each group of burners corresponding to one corner of the boiler; The aforementioned configuration is suitable for boilers with a capacity of 400-1000 t / h, enabling full-load operation in pure pulverized coal, pure natural gas, and mixed-fire modes, with a load capacity ≥100%. Nitrogen oxide emissions are controlled through air staging and flue gas recirculation, with a nitrogen oxide emission level ≤30 mg / Nm³ in natural gas mode. 3 Nitrogen oxide emissions are controlled through a denitrification system, with a maximum emission level of ≤50 mg / Nm³ in pulverized coal mode. 3 .

3. The combined combustion device according to claim 1, characterized in that: The pulverized coal burner (B) adopts a direct-flow design and is equipped with a large air box air distribution system, which is connected to the inlet of the burner body through an air duct; The natural gas burners (A, C, D) adopt a weak swirling structure, which is more suitable for the four-corner tangential combustion mode, and are equipped with a dedicated flue gas recirculation pipeline, with the flue gas recirculation ratio not exceeding 25%. The separate burnout air burner (E) adopts a staged air distribution design, with the air volume accounting for 25%-40% of the total air volume.

4. The combined combustion device according to claim 3, characterized in that: The equipment has a resistance difference of less than 3 kPa between the pulverized coal burner and the natural gas burner. The air volume is adjusted only through the secondary damper at the burner inlet. The damper opening range is 10%-100%, with an opening accuracy of ±1%. No additional air volume adjustment device is provided.

5. The combined combustion device according to claim 1, characterized in that: The primary air velocity of the pulverized coal burner (B) is controlled at 24-28 m / s, and the excess air coefficient in the main burner area is 0.72-0.9; the fuel nozzle diameter of the natural gas burner (layers A, C, and D) is 1000 mm ± 200 mm, and the material is a special alloy that is resistant to temperatures up to 1400℃.

6. The combined combustion device according to claim 1, characterized in that: During operation, the flue gas recirculation rate is dynamically adjusted according to the mode: 15%-25% for pure natural gas mode and 0% for co-firing mode; the oxygen concentration is controlled as follows: 3.5%-4.0% for pulverized coal mode, 1%-2.2% for natural gas mode, and 3.5%-4% for co-firing mode.

7. The combined combustion device according to claim 1, characterized in that: Including fuel switching control logic: When starting the pure pulverized coal mode, turn on the pulverized coal burner (B) and adjust the burnout air opening to 10%-100%; When starting in pure natural gas mode, turn on the natural gas burners (A, C, D) and start the flue gas recirculation system; When the co-firing mode is started, the pulverized coal burner (B) and one or more layers of natural gas burners (A / C / D) are turned on simultaneously, and the pressure difference between the large wind box and the furnace is kept less than 3 kPa. The entire process is controlled in a closed-loop manner using an online NOx monitoring system (threshold 50 mg / Nm³). 3 ).

8. The combined combustion device according to claim 1, characterized in that: The separate burnout air burner (E) is equipped with a dynamic adjustment mechanism: when the online NOx value exceeds 50 mg / Nm³, 3 At the same time, adjust the damper opening to form a strong reducing zone (O2 concentration < 3%) to suppress NOx generation.

9. The combined combustion device according to claim 1, characterized in that: This is applicable to a 410t / h boiler implementation case, in which the pulverizing system includes four HP743 medium-speed coal mills, each with an output of 22.1t / h, and three of them can operate at full load; the natural gas system includes three layers with a total of 12 burners, each with a heat load of 34.3MW and a full-load thermal efficiency of >94%.

10. The combined combustion device according to claim 1, characterized in that: Provide alternative implementation schemes to cover boilers of different capacities: For compact boilers with a capacity of ≤300t / h, only the natural gas burner (C) can be retained, while the natural gas burner (D) and the independent burnout air layer (E) can be eliminated, and the separate burnout air function can be integrated into the upper natural gas burner (C). For the 1000t / h expansion scheme, a burnout air burner (F) can be added 3m-5m above the burnout air burner (E), and the natural gas burner can be upgraded to a dual swirl structure.

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