Bypass flue fluidized bed drying system and process

Abstract

The application discloses a bypass flue fluidized bed drying system and process, and belongs to the field of desulfurization wastewater treatment. The system adopts double bypass flue staged heating: high-temperature flue gas is led out before an air preheater and is used for fluidized drying and tower wall anti-sticking; low-temperature flue gas is led out after a dust remover and is partially sent to the tower top after passing through a wastewater preheater for reheating and dehumidification. A fluidized bed and a fixed bed structure are used in the tower, and wastewater is preheated, atomized and then enters the fluidized bed for drying, and the fixed bed realizes interception and material returning. The system is provided with an online flushing device and can be stably operated for a long time. The application does not need external heat source, is energy-saving, has high drying efficiency and reliable operation, can realize zero discharge of desulfurization wastewater and is suitable for large-scale engineering application in coal-fired power plants.

Description

Technical Field

[0001] This invention belongs to the field of desulfurization wastewater treatment technology in coal-fired power plants, specifically relating to a bypass flue fluidized bed drying system and process. Background Technology

[0002] Desulfurization wastewater generated by wet desulfurization systems in coal-fired power plants is characterized by high salt content, high chloride ion content, high suspended solids, and strong corrosivity, posing a core challenge to near-zero discharge treatment of power plant wastewater. Current mainstream desulfurization wastewater treatment technologies, including evaporation concentration and flue gas spray drying, have significant drawbacks: the former, evaporation crystallization, involves high equipment investment and energy consumption, resulting in poor economic efficiency; the latter, by directly spraying wastewater into the main flue gas duct, while utilizing waste heat, is prone to uneven atomization, flue gas corrosion and blockage, and disruption of dust removal equipment operation; conventional independent fluidized bed drying requires additional external heat sources such as steam and electricity, resulting in low thermal energy utilization and susceptibility to wall adhesion, scaling, and blockage during operation, making system stability difficult to guarantee and severely impacting long-term stable operation and drying efficiency. Therefore, developing a desulfurization wastewater drying system and process that efficiently utilizes waste heat from flue gas, has low energy consumption, and enables long-term stable operation has significant engineering application value. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a bypass flue gas fluidized bed drying system and process that can efficiently, stably and economically utilize the waste heat of power plant flue gas; through dual bypass staged heat extraction, it can achieve efficient, energy-saving and stable drying of desulfurization wastewater.

[0004] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0005] A bypass flue fluidized bed drying system includes a main flue, a fluidized bed drying tower, a flue gas supply unit, a wastewater supply unit, and a flushing unit;

[0006] The main flue is equipped with an air preheater and a dust collector along the flue gas flow direction;

[0007] The fluidized bed drying tower includes a tower body, and inside the tower body, from bottom to top, there are an air distribution device, a fluidized bed layer and a fixed bed layer; the bottom of the tower body is provided with a tower bottom air inlet, the middle of the tower body is provided with a tower middle tangential air inlet at a position opposite to the fluidized bed layer, the upper part of the tower body is provided with a tower top air inlet above the fixed bed layer, and the top of the tower body is provided with a tower top flue gas outlet.

[0008] The flue gas supply unit includes a high-temperature bypass flue and a low-temperature bypass flue. The inlet of the high-temperature bypass flue is connected to the main flue before the air preheater, and the outlet of the high-temperature bypass flue is divided into two paths: one path is connected to the bottom air inlet of the tower, and the other path is connected to the tangential air inlet in the middle of the tower. The inlet of the low-temperature bypass flue is connected to the main flue after the dust collector. After passing through the flue gas side of the wastewater preheater and forming a heat exchange with the wastewater, the low-temperature bypass flue is divided into two paths: one path flows back to the main flue after the dust collector, and the other path is connected to the top air inlet of the tower.

[0009] The wastewater supply unit includes a wastewater tank, a wastewater preheater, a transfer pump, and an atomizing device. The outlet of the wastewater tank is connected to the inlet of the atomizing device after heat exchange with the flue gas via the wastewater side of the wastewater preheater and the transfer pump. The outlet of the atomizing device is arranged facing the fluidized bed.

[0010] The flushing unit includes a high-pressure flushing pump and two sets of flushing nozzles, one above the other. The upper nozzle is located above the fixed bed and sprays downwards, while the lower nozzle is located below the fixed bed and sprays upwards. Both sets of nozzles are connected to the outlet of the high-pressure flushing pump.

[0011] II. Process Method

[0012] A bypass flue gas fluidized bed drying process, implemented based on the above system, includes:

[0013] Flue gas is introduced through a high-temperature bypass flue to preheat the drying tower and establish a stable fluidization state.

[0014] Flue gas is introduced through a low-temperature bypass flue and exchanges heat with desulfurization wastewater in the wastewater preheater to achieve wastewater preheating;

[0015] The preheated wastewater is atomized and sprayed into the fluidized bed to dry in contact with the high-temperature flue gas and bed material.

[0016] The particles and unevaporated droplets generated during drying rise to the fixed bed and are trapped there, while some material is returned to the fluidized bed to continue drying.

[0017] The flue gas, after heat exchange in the wastewater preheater, is sent to the top air inlet of the tower to reduce the moisture content of the flue gas at the top of the tower.

[0018] The dried flue gas returns to the main flue through the top outlet of the tower, and the system periodically performs online flushing of the fixed bed.

[0019] Compared with the prior art, the present invention has the following significant advantages:

[0020] (1) This invention employs multi-path bypass flue gas synergistic heating to achieve graded utilization of flue gas waste heat: high-temperature flue gas is drawn from before the air preheater as the main heat source, and low-temperature flue gas is drawn from after the dust collector to preheat wastewater. Preheating not only reduces the energy consumption of the main heat source, but also avoids temperature fluctuations caused by cold droplets directly contacting the hot bed, ensuring a stable and efficient drying process.

[0021] (2) The fluidized bed drying tower is preferably equipped with redundant dual-fluid spray gun groups, which can be flexibly adjusted according to the load, and can achieve non-stop maintenance when some spray guns are repaired or blocked, ensuring continuous and stable operation of the system.

[0022] (3) The tower body is equipped with tangential air inlet to maintain the tower wall temperature by using flue gas and prevent material from sticking to the wall.

[0023] A fixed bed is arranged above the fluidized bed inside the tower to intercept unevaporated droplets and fine ash, serving both as a return material and a separation mechanism, thereby improving drying efficiency and protecting downstream equipment. Furthermore, some of the preheated flue gas is introduced from above the fixed bed to reheat the flue gas at the top of the tower, reducing its moisture content and further improving the overall system efficiency. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0026] This specific embodiment employs a bypass flue fluidized bed drying system, the overall structure and connection relationships of which are as follows:

[0027] The main flue duct 1 is arranged with an air preheater 1-1 and a dust collector 1-2 in sequence along the flue gas flow direction; the fluidized bed drying tower 2 is a vertical cylindrical structure, and the air distribution device 2-1, the fluidized bed layer 2-2, and the fixed bed layer 2-3 are arranged in sequence from bottom to top inside the tower; the tower body is correspondingly provided with a bottom air inlet 2-4, a middle tangential air inlet 2-5, a top air inlet 2-6, and a top flue gas outlet 2-7.

[0028] The inlet of the high-temperature bypass flue 3 is connected to the main flue 1 before the air preheater 1-1, and the outlet is divided into two paths, which are connected to the bottom air inlet 2-4 and the middle tangential air inlet 2-5 respectively. The inlet of the low-temperature bypass flue 4 is connected to the main flue 1 after the dust collector 1-2, and after passing through the wastewater preheater 5, the flue gas is divided into two paths. One path flows back to the main flue 1 after the dust collector 1-2, and the other path is connected to the top air inlet 2-6.

[0029] Wastewater tank 6 is connected to wastewater preheater 5 via transfer pump 7. The outlet of wastewater preheater 5 is connected to atomizing device 8, which is arranged facing the fluidized bed 2-2. The high-pressure flushing pump 9 of the flushing unit is connected to the upper flushing nozzle above the fixed bed 2-3 and the lower flushing nozzle 10 below it.

[0030] 1. System Structure and Parameter Settings

[0031] This embodiment is applied to the desulfurization wastewater treatment of a 600MW coal-fired power unit. The specific system settings are as follows:

[0032] Fluidized bed drying tower 2: Vertical cylindrical structure, with a total tower height of 12m and an inner diameter of 3.2m. The air distribution device 2-1 inside the tower adopts a conical air distribution plate + automatic pneumatic vibration dust removal device, which can automatically remove dust according to the running time or air pressure difference to ensure uniform air distribution and stable fluidization.

[0033] Fluidized bed 2-2: filled with inert quartz sand particles with a particle size of 0.3–0.8 mm (alumina or ceramic inert particles can also be used), with a bed thickness of 0.8 m, which is the main drying area for desulfurization wastewater.

[0034] Fixed bed 2-3: adopts a multi-layer corrugated plate staggered structure with a layer height of 1.2m. It is used to intercept unevaporated droplets and fine particles, and return the material to the fluidized bed 2-2 for further drying. It also has the functions of gas-solid separation and material return.

[0035] Atomizing device 8: It adopts 6 sets of dual-fluid spray guns, arranged around the circumference of the tower body, with redundant configuration and independent control of groups, which can adapt to the fluctuation of wastewater load. The system can operate without stopping when a single set of spray guns is under maintenance; the atomization pressure is 0.6MPa, which can atomize wastewater into 30-80μm droplets.

[0036] Wastewater preheater 5: It adopts a shell-and-tube heat exchanger with a heat exchange area of ​​about 150m², and uses low-temperature flue gas to preheat the desulfurization wastewater to 70–85℃.

[0037] Flushing unit: High-pressure flushing pump 9 with a design pressure of 2.0MPa and a flushing flow rate of 15m³ / h; two sets of flushing nozzles 10 are respectively arranged 0.3m above and 0.5m below the fixed bed layer 2-3, which can realize full-coverage online flushing.

[0038] 2. Flue gas system operation process

[0039] High-temperature flue gas supply

[0040] High-temperature bypass flue 3 draws high-temperature flue gas with a temperature of 280–340℃ from the main flue 1 before the air preheater 1-1. After passing through the high-temperature induced draft fan and regulating valve, it is divided into two paths:

[0041] One route enters through the bottom air inlet 2-4 of the tower, serving as the main heat source for fluidization and drying, thus fully fluidizing the fluidized bed 2-2;

[0042] Another route allows the wastewater to enter the tower body tangentially through tangential inlets 2-5, maintaining the tower wall temperature above 120℃ to prevent wastewater droplets from adhering to the wall and forming scale.

[0043] Low-temperature flue gas supply

[0044] Low-temperature bypass flue 4 draws low-temperature flue gas with a temperature of 100–150℃ from the main flue 1 after the dust collector 1-2, and sends it into the shell side of the wastewater preheater 5 by the low-temperature induced draft fan to exchange heat with the desulfurization wastewater in the tube side.

[0045] After heat exchange, the flue gas is divided into two paths: about 70% flows back to the main flue 1 after the dust collector 1-2, and the remaining 30% enters the tower through the top air inlet 2-6 to reheat the flue gas at the top of the tower, reduce the moisture content of the flue gas, and avoid low-temperature dew point corrosion.

[0046] 3. Wastewater treatment operation process

[0047] The desulfurization wastewater, after pretreatment in the triple-tank, has a solid content of about 15% and a chloride ion concentration of about 20,000 mg / L. It is stored in the wastewater tank 6 and then sent to the tube side of the wastewater preheater 5 by the wastewater transfer pump 7.

[0048] Wastewater exchanges heat with low-temperature flue gas in wastewater preheater 5 and is preheated to 70–85°C before being sent to atomization device 8.

[0049] The atomizing device 8 atomizes the preheated wastewater into tiny droplets, which are then sprayed into the fluidized bed 2-2 to fully contact the high-temperature flue gas and fluidized bed material for rapid evaporation and drying.

[0050] 4. Drying, Separation and Return Process

[0051] The atomized wastewater droplets come into intense contact with high-temperature flue gas and inert particles in the fluidized bed 2-2, causing the water to evaporate rapidly;

[0052] The solid particles formed during drying and the small droplets that have not been completely evaporated move upward with the airflow and are intercepted when they reach the fixed bed layer 2-3.

[0053] The trapped solid particles and droplets return to the fluidized bed 2-2 under the action of gravity and airflow, and continue to dry until dry powder is formed;

[0054] The dried flue gas carries a small amount of fine ash and flows upward. After being reheated at the top of the tower, it returns to the air preheater 1-1 and then to the main flue duct 1 through the flue gas outlet 2-7 at the top of the tower. Finally, the fine ash is collected by the dust collector 1-2.

[0055] 5. Online flushing and maintenance process

[0056] The system performs an online flush once a week after running continuously for 168 hours.

[0057] Start the high-pressure flushing pump 9, with the upper flushing nozzle spraying downwards and the lower flushing nozzle spraying upwards, to flush the fixed bed layer 2-3 in all directions and remove the trapped ash and crystals;

[0058] Each flush lasts 20–30 minutes. During the flushing process, the system continues to operate, with only the flue gas flow rate being appropriately reduced, without interrupting the desulfurization wastewater drying process.

[0059] 6. Performance

[0060] In this embodiment, the system is designed to treat 10 m³ / h of desulfurization wastewater, and the continuous operation results are as follows:

[0061] The evaporation rate of desulfurization wastewater is ≥90.8%;

[0062] The dried product is a dry powder solid with a moisture content of ≤0.5%, which can be directly landfilled or utilized as a resource.

[0063] The system consumes only the power of the induced draft fan and compressed air, saving more than 65% energy compared to the traditional steam drying process;

[0064] The system has a continuous operating availability rate of >98%, with no wall adhesion, scaling, or clogging.

[0065] Zero liquid discharge of desulfurization wastewater and flue gas emissions meet national environmental protection standards.

Claims

1. A bypass flue gas fluidized bed drying system, characterized in that: Includes main flue (1), fluidized bed drying tower (2), flue gas supply unit, wastewater supply unit and flushing unit; The main flue (1) is provided with an air preheater (1-1) and a dust collector (1-2) in sequence along the flue gas flow direction. The fluidized bed drying tower (2) includes a tower body, inside which an air distribution device (2-1), a fluidized bed layer (2-2), and a fixed bed layer (2-3) are arranged sequentially from bottom to top; a bottom air inlet (2-4) is provided at the bottom of the tower body, a tangential air inlet (2-5) is provided in the middle of the tower body corresponding to the fluidized bed layer (2-2), a top air inlet (2-6) is provided at the top of the tower body above the fixed bed layer (2-3), and a top flue gas outlet (2-7) is provided at the top of the tower body. The flue gas supply unit includes a high-temperature bypass flue (3) and a low-temperature bypass flue (4); the inlet of the high-temperature bypass flue (3) is connected to the main flue (1) before the air preheater (1-1), and the outlet of the high-temperature bypass flue (3) is divided into two paths, one of which is connected to the bottom air inlet (2-4) of the tower, and the other is connected to the tangential air inlet (2-5) in the tower; the inlet of the low-temperature bypass flue (4) is connected to the main flue (1) after the dust collector (1-2), and the low-temperature bypass flue (4) is divided into two paths after the flue gas from the wastewater preheater (5), one of which flows back to the main flue (1) after the dust collector (1-2), and the other is connected to the top air inlet (2-6); The wastewater supply unit includes a wastewater tank (6), a wastewater preheater (5), a transfer pump (7), and an atomizing device (8); the outlet of the wastewater tank (6) is connected to the wastewater side of the wastewater preheater (5) via the transfer pump (7), the wastewater side outlet of the wastewater preheater (5) is connected to the inlet of the atomizing device (8), and the outlet of the atomizing device (8) is arranged facing the fluidized bed (2-2). The flushing unit includes a high-pressure flushing pump (9) and two sets of flushing nozzles (10) above and below. The upper flushing nozzle is located above the fixed bed (2-3) and sprays downwards, while the lower flushing nozzle is located below the fixed bed (2-3) and sprays upwards. Both sets of flushing nozzles (10) are connected to the outlet of the high-pressure flushing pump (9).

2. The bypass flue gas fluidized bed drying system according to claim 1, characterized in that, The air distribution device (2-1) includes a conical air distribution plate and a matching automatic pneumatic vibration dust removal device; the fluidized bed (2-2) is filled with quartz sand, alumina or ceramic inert particles.

3. The bypass flue gas fluidized bed drying system according to claim 1, characterized in that, The fixed bed (2-3) has a multi-layer corrugated plate staggered structure, which can intercept unevaporated droplets and fine particles and return the material to the fluidized bed (2-2).

4. The bypass flue gas fluidized bed drying system according to claim 1, characterized in that, The atomizing device (8) consists of multiple redundant dual-fluid spray guns that can be controlled independently in groups.

5. The bypass flue gas fluidized bed drying system according to claim 1, characterized in that, High-temperature flue gas is introduced into the tangential air inlet (2-5) of the tower to maintain the tower wall temperature above 120°C.

6. The bypass flue gas fluidized bed drying system according to claim 1, characterized in that, The wastewater preheater (5) preheats the desulfurization wastewater to 70–85°C; the flue gas introduced into the top air inlet (2-6) is used to reduce the moisture content of the flue gas at the top of the tower.

7. A bypass flue fluidized bed drying process, implemented based on the bypass flue fluidized bed drying system according to any one of claims 1-6, characterized in that, Includes the following steps: A. Flue gas is introduced from the air preheater (1-1) through the high-temperature bypass flue (3) to preheat the fluidized bed drying tower (2) and establish a stable fluidization state; B. Flue gas is introduced from the dust collector (1-2) through the low-temperature bypass flue (4) and exchanged with the desulfurization wastewater in the wastewater preheater (5) to achieve wastewater preheating; C. The preheated wastewater is atomized by the atomizing device (8) and sprayed into the fluidized bed (2-2) to dry in contact with the high-temperature flue gas and bed material; D. The particles and unevaporated droplets generated during drying rise to the fixed bed (2-3) and are trapped, while some of the material is returned to the fluidized bed (2-2) for further drying; E. The flue gas after heat exchange by the wastewater preheater (5) is sent to the top air inlet (2-6) of the tower to reduce the moisture content of the flue gas at the top of the tower. F. The dried flue gas returns to the main flue (1) from the flue gas outlet (2-7) at the top of the tower. The bypass flue fluidized bed drying system regularly flushes the fixed bed (2-3) online through the flushing unit.

8. The bypass flue gas fluidized bed drying process according to claim 7, characterized in that, The temperature of the fluidized bed (2-2) after preheating is not lower than 250℃; the wastewater is atomized to form droplets with a particle size of 30–80μm.

9. The bypass flue gas fluidized bed drying process according to claim 7, characterized in that, The bypass flue fluidized bed drying system is flushed online every 168 hours of operation.

10. The bypass flue gas fluidized bed drying process according to claim 7, characterized in that, The evaporation rate of desulfurization wastewater is ≥90.8%, and the moisture content of the dried product is ≤0.5%.

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