A flue gas recirculation energy utilization system
By using a flue gas recirculation system and staged combustion control, the problems of nitrogen oxide emissions and energy waste in coal-fired boilers have been solved, achieving ultra-low emissions and energy-saving effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- BEIJING YINGXIANG BORI REFRACTORIES TECH CO LTD
- Filing Date
- 2025-06-18
- Publication Date
- 2026-06-05
AI Technical Summary
Coal-fired boilers generate a large amount of nitrogen oxides and waste heat during combustion, which is difficult to solve effectively with existing technologies. In addition, SCR and SNCR systems have problems such as large consumption of ammonia or urea and ammonia escape.
Design a flue gas recirculation energy utilization system that recirculates the flue gas discharged from the boiler back to the combustion system for combustion support. Combined with SNCR and SCR denitrification technologies, the system utilizes the waste heat of the flue gas to reduce the generation of nitrogen oxides and controls the ratio of flue gas volume to fresh air volume through staged combustion.
It achieves ultra-low nitrogen oxide emissions, reduces the amount of ammonia or urea used, reduces equipment corrosion and heat loss, and improves energy efficiency.
Smart Images
Figure CN224327182U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the fields of energy utilization and environmental protection technology, and in particular to a flue gas recirculation energy utilization system. Background Technology
[0002] Currently, combustion systems generally emit large amounts of harmful substances and generate a large amount of unused heat. Therefore, how to reduce harmful emissions and achieve energy-saving effects has always been a technical problem that various combustion systems have been unable to solve effectively.
[0003] Taking coal-fired boilers as an example, a large amount of nitrogen oxides (NOx) are emitted during combustion. The principle behind this is that most NOx emissions from coal-fired boilers are thermal. During coal combustion with air support, 78% of nitrogen participates in the combustion process, generating a large amount of thermal NOx. Thermal NOx generation is minimal below 800°C and above 1500°C; the highest NOx generation occurs between 900°C and 1400°C. Therefore, to achieve a NOx emission level of 50 mg / m³ in coal-fired boilers... 3 To achieve ultra-low emissions, the best approach is to address the issue at the source of boiler combustion. Current methods for effectively removing nitrogen oxides involve connecting SCR or SNCR denitrification systems downstream of coal-fired boilers. However, these methods suffer from drawbacks such as high ammonia or urea consumption and ammonia escape. Furthermore, the high-temperature flue gas (approximately 300–500°C) exiting the boiler furnace enters the air preheater, carrying a significant amount of waste heat, which is not adequately utilized, leading to energy waste.
[0004] Therefore, this utility model is proposed. Utility Model Content
[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a flue gas recirculation energy utilization system to save combustion resources, save energy, and reduce the large amount of nitrogen oxides used and ammonia escape phenomena in nitrogen oxide treatment systems.
[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:
[0007] According to one aspect of the present invention, a flue gas recirculation energy utilization system is provided, characterized in that it includes a combustion system, a flue gas treatment system, and a flue gas recirculation system; the downstream side of the combustion system is connected to the upstream side of the flue gas treatment system;
[0008] One end of the flue gas recirculation system is connected to any one or more nodes in the flue gas treatment system for removing flue gas, and the other end of the flue gas recirculation system is connected to the air inlet side of the combustion system, thereby sending the removed flue gas back to the combustion system for combustion support.
[0009] Optionally, the combustion system includes a coal-fired boiler, and the flue gas treatment system includes an SCR denitrification device, an economizer, an air preheater, a dust collector, an induced draft fan, a desulfurization device, and a chimney connected in sequence; the flue gas circulation system includes a first circulation path, one end of which is connected to any or more nodes in the flue gas treatment system, and the other end is connected to the air chamber of the coal-fired boiler after passing through the air preheater, the mixing box, and the blower in sequence, or the other end is connected to the air chamber of the coal-fired boiler after passing through the mixing box and the blower in sequence; the mixing box also has a fresh air inlet for introducing fresh air.
[0010] Optionally, the flue gas recirculation system further includes a second recirculation path branching off from the first recirculation path. One end of the second recirculation path is connected to the node between the flue gas inlet of the first recirculation path and the mixing box, and the other end is connected to the air chamber of the coal-fired boiler via a secondary blower. The secondary blower has a fresh air inlet end for introducing fresh air.
[0011] Optionally, the gas circulation system further includes a second circulation path parallel to the first circulation path. One end of the second circulation path is connected to any one or more nodes in the flue gas treatment system, and the other end is connected to the air chamber of the coal-fired boiler via a secondary blower. The secondary blower has a fresh air inlet for introducing fresh air.
[0012] Optionally, the flue gas inlet of the flue gas recirculation system is connected to the outlet of the dust collector or the outlet of the induced draft fan.
[0013] Optionally, the fresh air is outdoor air and / or indoor air; if it is indoor air, the indoor air intake is located at the top of the boiler room.
[0014] The control method for the above-mentioned flue gas recirculation energy utilization system includes:
[0015] Detect the combustion status of the combustion system;
[0016] Adjust the amount of flue gas returned to the combustion system by the flue gas recirculation system according to the combustion conditions.
[0017] Optionally, adjusting the amount of flue gas returned to the combustion system by the flue gas recirculation system according to the combustion conditions specifically includes:
[0018] Adjust the ratio of flue gas volume returned to the combustion system by the flue gas recirculation system to the fresh air volume introduced by the flue gas recirculation system according to the combustion conditions. When a higher combustion temperature is required, increase the flue gas volume; when a lower combustion temperature is required, increase the fresh air volume.
[0019] Optionally, the flue gas recirculation system includes a first recirculation path and a second recirculation path, which respectively guide the flue gas back to the combustion system after mixing with air through a blower system with a fresh air inlet. When the combustion system is a coal-fired boiler, the first recirculation path guides the flue gas back to the main combustion zone of the coal-fired boiler, and the amount of flue gas returned to the combustion system through the first recirculation path is controlled to achieve oxygen-deficient combustion; the second recirculation path guides the flue gas back to the burnout zone of the coal-fired boiler, and the amount of flue gas returned to the combustion system through the second recirculation path is controlled to replenish air.
[0020] Optionally, detecting the combustion conditions of the combustion system includes detecting the grate speed of the coal-fired boiler; the faster the grate speed, the more combustion gas is required.
[0021] The flue gas recirculation energy utilization system provided by this utility model recirculates the flue gas generated by the combustion system back to the combustion system for combustion. Since the waste heat of the flue gas is utilized and most of the nitrogen in the flue gas participates in the combustion, there is basically no nitrogen oxide produced after the flue gas is recirculated back to the combustion system. Therefore, the concentration of nitrogen oxides can be reduced by flue gas recirculation. Furthermore, ultra-low flue gas emission standards can be easily achieved by using SNCR and SCR denitrification technologies. At the same time, it can also reduce the amount of ammonia or urea used, reduce corrosion of boilers, flues and other equipment, reduce ammonia escape, and reduce heat loss. Attached Figure Description
[0022] Figure 1 A schematic diagram of a flue gas recirculation energy utilization system provided in an embodiment of this utility model;
[0023] Figure 2 A schematic diagram of a flue gas recirculation energy utilization system provided for another embodiment of this utility model;
[0024] Figure 3 A schematic diagram of the structure of a flue gas recirculation energy utilization system (dual circulation path) provided for another embodiment of the present invention;
[0025] Figure 4 A schematic diagram of the structure of a flue gas recirculation energy utilization system (dual circulation path) provided for another embodiment of the present invention;
[0026] Figure 5 A schematic diagram of a flue gas recirculation energy utilization system provided for another embodiment of this utility model;
[0027] Figure 6 A schematic diagram of a flue gas recirculation energy utilization system provided for another embodiment of this utility model;
[0028] In the picture:
[0029] 1-Coal-fired boiler; 2-SCR denitrification device; 3-Economizer; 4-Air preheater; 5-Dust collector; 6-Induced draft fan; 7-Desulfurization device; 8-Chimney; 9-First circulation passage; 10-Mixing box; 11-Blower; 12-Air chamber; 13-Second circulation passage; 14-Secondary blower. Detailed Implementation
[0030] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.
[0031] This utility model provides a flue gas recirculation energy utilization system, including a combustion system, a flue gas treatment system, and a flue gas recirculation system; the downstream side of the combustion system is connected to the upstream side of the flue gas treatment system; one end of the flue gas recirculation system is connected to any one or more nodes in the flue gas treatment system for extracting flue gas, and the other end of the flue gas recirculation system is connected to the air inlet side of the combustion system, so as to send the extracted flue gas back to the combustion system for combustion assistance.
[0032] Below, this utility model embodiment uses a coal-fired boiler as an example of the combustion system to introduce the entire flue gas recirculation energy utilization system.
[0033] Combination Figure 1-6As an example, the combustion system includes a coal-fired boiler 1 with multiple air chambers 12 at the bottom, and a combustion chamber above the air chambers, containing a grate covered with a coal bed. The flue gas treatment system includes an SCR denitrification device 2, an economizer 3, an air preheater 4, a dust collector 5, an induced draft fan 6, a desulfurization device 7, and a chimney 8 connected sequentially from the flue gas outlet of the coal-fired boiler 1. These nodes are existing technologies and will not be described in detail here. The flue gas recirculation system includes a first recirculation path 9, one end of which is connected to any one or more nodes in the flue gas treatment system, and the other end, after passing sequentially through the air preheater 4, a mixing box 10, and a blower 11, connects to the air chamber 12 of the coal-fired boiler 1, or the other end, after passing sequentially through the mixing box 10 and the blower 11, connects to the air chamber 12 of the coal-fired boiler 1. The mixing box 10 also has a fresh air inlet for introducing fresh air. For example, the inlet of the first circulation path 9 can be located at the outlet of the dust collector 5. At this point, the flue gas has already undergone most of the purification process, reducing corrosion to equipment such as the air preheater 4, burner, fan, and pipelines. Alternatively, the inlet of the first circulation path 9 can also be located at the outlet of the induced draft fan 6. The first circulation path 9 can enter the mixing box 10 via the air preheater 4, or it can directly enter the mixing box 10 (if the air preheater 4 is not used). After the flue gas is combined with fresh air in the mixing box 10, it is sent back to the air chamber 12 of the coal-fired boiler 1 for combustion via the blower 11. After being fully mixed with fresh air, it is reintroduced into the combustion zone. The amount of flue gas taken out is adjusted according to the boiler load, and the 6% residual oxygen in the recirculated flue gas participates in combustion. Since the recirculated flue gas will not generate nitrogen oxides again, the generation of thermal NOx can be reduced.
[0034] As an example, the flue gas recirculation system also includes a second recirculation path 13, which can be branched off from the first recirculation path 9 or set directly in parallel with the first recirculation path 9. The second recirculation path 13 is returned to the coal-fired boiler 1 via a secondary blower to ensure the flue gas recirculation volume and staged combustion. By controlling the staged combustion and the flue gas recirculation volume, staged low-NOx combustion and energy-saving effects are achieved.
[0035] For example, one end of the second circulation passage 13 is connected to the node between the flue gas inlet of the first circulation passage 9 and the mixing box 10, such as between the air preheater 4 and the mixing box 10, and the other end is connected to the air chamber 12 of the coal-fired boiler 1 via the secondary blower 14, which has a fresh air inlet end for introducing fresh air.
[0036] Alternatively, one end of the second circulation passage 13 is connected to any one or more nodes in the flue gas treatment system. Like the first circulation passage 9, the flue gas intake is located at the rear end of the induced draft fan 6, and the other end is connected to the air chamber 12 of the coal-fired boiler 1 via the secondary blower 14. The secondary blower 14 has a fresh air inlet for introducing fresh air to perform air mixing.
[0037] In the above embodiments, the fresh air is outdoor air and / or indoor air; if it is indoor air, the indoor air intake is located at the top of the boiler room. Changing the intake from outdoor air to indoor air increases the initial temperature of the air intake point, and the indoor air intake is located at the top of the boiler room where the room temperature is relatively high. To meet the indoor air volume requirements, windows can be opened for ventilation as appropriate.
[0038] The technical effects of flue gas recirculation in this embodiment of the invention will be introduced below, based on the principle of nitrogen oxide generation in coal-fired boilers:
[0039] As is well known, air is composed of 21% oxygen, 78% nitrogen, and other inert gases.
[0040] Most of the nitrogen oxides produced by coal-fired boilers are thermal, because 78% of nitrogen participates in the combustion of coal during the air-assisted combustion process, and a large amount of thermal nitrogen oxides (NOx) are generated during the combustion process.
[0041] Thermal nitrogen oxides are generated in very small amounts below 800°C and above 1500°C; the highest amount of nitrogen oxides are generated between 900°C and 1400°C. Therefore, to achieve ultra-low nitrogen oxide emissions (50mg / m3) from coal-fired boilers, the best approach is to address the issue at the source of boiler combustion.
[0042] The applicant discovered in the application that nitrogen oxides could be reduced from an original concentration of 400 mg / m³ through flue gas recirculation. 3 Reduced to 200mg / m 3 With the addition of SNCR and SCR denitrification technologies, ultra-low flue gas emission standards of <50mg / m³ can be easily achieved. 3 This also reduces the amount of ammonia or urea used, reduces corrosion of boilers, flues, and other equipment, reduces ammonia escape, and reduces heat loss. Furthermore, flue gas recirculation allows for the reuse of escaped urea and ammonia.
[0043] This utility model embodiment also provides a control method for the above-mentioned flue gas recirculation energy utilization system, including:
[0044] Step S1: Detect the combustion status of the combustion system;
[0045] Step S2: Adjust the amount of flue gas returned to the combustion system by the flue gas recirculation system according to the combustion conditions.
[0046] Among these, monitoring the combustion system's operating conditions involves detecting the combustion load, so that the amount of flue gas required for reburning can be adjusted accordingly. There are various detection methods, such as monitoring the grate's operating speed; the faster the speed, the greater the combustion load and the larger the required amount of flue gas.
[0047] As an example, step S1 includes: adjusting the ratio of flue gas volume returned to the combustion system by the flue gas recirculation system to the fresh air volume introduced by the flue gas recirculation system according to the combustion conditions. When a higher combustion temperature is required, the flue gas volume is increased, and when a lower combustion temperature is required, the fresh air volume is increased.
[0048] As described in the previous embodiments, the flue gas recirculation system may include a first recirculation path and a second recirculation path, which respectively guide the flue gas back to the combustion system after mixing with air through a blower system with a fresh air inlet. When the combustion system is a coal-fired boiler 1, the first recirculation path guides the flue gas back to the main combustion zone of the coal-fired boiler 1, and the amount of flue gas sent back to the combustion system through the first recirculation path is controlled to achieve oxygen-deficient combustion; the second recirculation path guides the flue gas back to the burnout zone of the coal-fired boiler 1, and the amount of flue gas sent back to the combustion system through the second recirculation path is controlled to replenish air.
[0049] In practical applications, electric valves can be installed on the piping of the flue gas recirculation system (such as at the nodes before the mixing box 10 and the secondary blower 14 in the first recirculation passage 9 and the second recirculation passage 13), and electric valves can also be installed on the fresh air ducts leading to the mixing box 10 and the secondary blower. In this way, the opening degree of the electric valves can be controlled by a PLC or other controller, thus adjusting the ratio of flue gas volume to fresh air volume. Furthermore, control valves can also be installed on the piping leading to the inlet of each air chamber in the flue gas recirculation system. This allows for selective control of the recirculation passages to deliver an appropriate proportion of flue gas to the corresponding air chamber, achieving the staged combustion described above.
[0050] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.
Claims
1. A flue gas recirculation energy utilization system, characterized in that, It includes a combustion system, a flue gas treatment system, and a flue gas recirculation system; the downstream side of the combustion system is connected to the upstream side of the flue gas treatment system; One end of the flue gas recirculation system is connected to any one or more nodes in the flue gas treatment system for removing flue gas, and the other end of the flue gas recirculation system is connected to the air inlet side of the combustion system, thereby sending the removed flue gas back to the combustion system for combustion support.
2. The flue gas recirculation energy utilization system according to claim 1, characterized in that, The combustion system includes a coal-fired boiler, and the flue gas treatment system includes an SCR denitrification device, an economizer, an air preheater, a dust collector, an induced draft fan, a desulfurization device, and a chimney connected in sequence. The flue gas circulation system includes a first circulation path, one end of which is connected to any one or more nodes in the flue gas treatment system, and the other end is connected to the air chamber of the coal-fired boiler after passing through the air preheater, the mixing box, and the blower in sequence, or the other end is connected to the air chamber of the coal-fired boiler after passing through the mixing box and the blower in sequence. The mixing box also has a fresh air inlet for introducing fresh air.
3. The flue gas recirculation energy utilization system according to claim 2, characterized in that, The flue gas recirculation system also includes a second recirculation path branching off from the first recirculation path. One end of the second recirculation path is connected to the node between the flue gas inlet of the first recirculation path and the mixing box, and the other end is connected to the air chamber of the coal-fired boiler via a secondary blower. The secondary blower has a fresh air inlet end for introducing fresh air.
4. The flue gas recirculation energy utilization system according to claim 2, characterized in that, The gas circulation system also includes a second circulation path parallel to the first circulation path. One end of the second circulation path is connected to any one or more nodes in the flue gas treatment system, and the other end is connected to the air chamber of the coal-fired boiler via a secondary blower. The secondary blower has a fresh air inlet for introducing fresh air.
5. The flue gas recirculation energy utilization system according to claim 3 or 4, characterized in that, The flue gas inlet of the flue gas recirculation system is connected to the outlet of the dust collector or the outlet of the induced draft fan.
6. The flue gas recirculation energy utilization system according to any one of claims 2-4, characterized in that, The fresh air is outdoor air and / or indoor air; if it is indoor air, the indoor air intake is located at the top of the boiler room.