Flue gas denitration system with sticky dust pretreatment for alkali recovery furnace

Abstract

The utility model discloses a kind of alkali recovery furnace flue gas denitration systems with sticky dust pretreatment, including adsorption tower and the porous medium adsorption unit of being sequentially arranged in adsorption tower along flue gas flow direction, the porous medium adsorption unit includes porous medium fixed bed and medium module filled and fixed on porous medium fixed bed, the dust particle that is adsorbed to porous medium adsorption unit is cleaned in the flue gas inlet side of every porous medium adsorption unit using ash-removal mechanism;The utility model integrates the adsorption interception and capture process of sticky dust in single fixed bed adsorption tower, system is compact, dust removal efficiency is high;And using the structural characteristics of three-dimensional porous medium, the "easy capture, easy fall off" of dust is realized, fundamentally solve the equipment jam problem caused by sticky dust, the ash-removal mechanism of cooperation setting can guarantee the long-term stable operation of system, reduce the maintenance intensity and cost to adsorption tower.

Description

Technical Field

[0001] This utility model relates to the field of flue gas treatment technology, specifically to a flue gas denitrification system for an alkali recovery furnace with pretreatment of sticky dust. Background Technology

[0002] Paper mills primarily produce pulp in two ways based on raw materials: pulping from plant fibers (wood pulp, non-wood pulp) and pulping from waste paper. The plant fiber pulping process generates a large amount of dilute black liquor as a byproduct. This liquid contains lignin, hemicellulose, and total alkali, with lignin possessing a high calorific value. The dilute black liquor (approximately 15% solids) is concentrated into concentrated black liquor (60%-85% solids) through multi-effect evaporation. The concentrated black liquor is then burned in a recovery boiler, and the chemicals fall into a semi-liquid molten residue at the bottom of the boiler. The molten residue flows out of the boiler and is dissolved in water or detergent to form green liquor. Next, the green liquor is clarified by adding quicklime (CaO). The quicklime converts most of the sodium carbonate (Na₂CO₃) into sodium hydroxide (NaOH), clarifying the green liquor into white liquor (causticization). The white liquor contains sodium hydroxide, which can be used as a pulping chemical, thus returning to the starting point.

[0003] Most alkali recovery boilers use black liquor discharged after concentrated sulfate or alkaline pulping as fuel. The black liquor is burned in the furnace, forming a liquid molten material that is discharged from the bottom of the furnace. After causticization, it is reduced to caustic soda; the resulting hot flue gas exchanges heat with water to produce steam, becoming a secondary energy source. Alkali recovery boilers are not only equipment for recovering alkali used in pulping, but also energy-saving and environmentally friendly equipment for reducing pollutant emissions.

[0004] Currently, the flue gas from the alkali recovery furnace is discharged into the atmosphere through the chimney after electrostatic precipitator and denitrification treatment. Selective catalytic reduction (SCR) is a process that, under the action of a metal catalyst and with the help of a reducing agent (such as NH3) at an appropriate temperature and in the presence of a catalyst, converts NOx into N2 and H2O, which are non-polluting to the atmosphere. The flue gas temperature after electrostatic precipitator treatment in the alkali recovery furnace is around 190-200℃, with NOx as the main pollutant, high water vapor and dust content, and relatively low SO2 content. Chemical analysis of the dust reveals that its main components are sodium sulfate and potassium sulfate, which are easily soluble in water. Sodium sulfate readily hydrates in humid air to form heptahydrate or decahydrate, and loses its water of crystallization above 100℃. The solubility of soluble alkali metal sulfates has a significant impact on the subsequent denitrification efficiency. The application of SCR denitrification catalysts for alkali furnace flue gas is mainly limited by this point. The adhesion of sodium salt after cooling crystallization has a significant impact on the catalyst. The catalyst has sufficient resistance to alkali poisoning and low-temperature activity. The main problem to be solved is the adhesion of alkali crystals. Utility Model Content

[0005] Technical objective: To address the shortcomings of existing alkali recovery flue gas treatment methods, this utility model discloses an alkali recovery furnace flue gas denitrification system with pretreatment of sticky dust.

[0006] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution: A denitrification system for alkali recovery furnace flue gas with pretreatment of sticky dust includes an adsorption tower and a plurality of porous media adsorption units arranged sequentially along the flue gas flow direction in the adsorption tower. Each porous media adsorption unit includes a porous media fixed bed and media modules filled and fixed on the porous media fixed bed. The media modules contain a plurality of porous media layers stacked on top of each other, forming a three-dimensional tortuous gas flow channel through the stacking of porous media layers, causing the dust particles in the flue gas to collide and agglomerate. A dust removal mechanism is provided on the flue gas inlet side of each porous media adsorption unit for cleaning the dust particles adsorbed by the porous media adsorption unit.

[0007] Preferably, the adsorption tower of this utility model is arranged vertically, with a flue gas inlet at the top and a flue gas outlet at the bottom. A dust hopper for receiving adsorbed dust particles is provided at the bottom of the adsorption tower, and the flue gas outlet is located above the dust hopper. An airflow equalization plate for equalizing the flow of flue gas entering the adsorption tower is provided at the flue gas inlet.

[0008] Preferably, the airflow equalization plate of this utility model is a disc shape that matches the cross-section of the adsorption tower, with uniform holes opened on the disc surface to equalize the flow of the incoming flue gas.

[0009] Preferably, the dust removal mechanism of this utility model includes nozzles correspondingly arranged above the porous media adsorption unit. The nozzles are connected to a conveying fan arranged outside the adsorption tower through a dust removal pipe. The dust removal pipe includes branch pipes connected to the nozzles and a main pipe that collects the branch pipes and is connected to the conveying fan. Valves for controlling the airflow are provided on the branch pipes. The airflow ejected from the nozzles cleans the dust accumulated in the porous media adsorption unit.

[0010] Preferably, this invention includes a gas pressure sensor installed inside the adsorption tower to detect the pressure drop across the porous media adsorption unit, and controls the operation of the dust removal mechanism based on the pressure information detected by the gas pressure sensor.

[0011] Preferably, the porous media layer of this invention uses a material with high porosity, high specific surface area, high temperature resistance, and surface inertness.

[0012] Preferably, the porous media layer of this invention is made of one of porous ceramic spheres, sintered metal fiber felt, or modified alumina corrugated plate.

[0013] Beneficial effects: The alkali recovery furnace flue gas denitrification system with pretreatment of sticky dust disclosed in this utility model integrates the adsorption, interception and collection processes in a single fixed-bed adsorption tower. The system is compact and has high dust removal efficiency. Furthermore, by utilizing the structural characteristics of three-dimensional porous media, the dust is "easy to collect and easy to detach", which fundamentally solves the problem of equipment blockage caused by sticky dust. The dust removal mechanism can ensure the long-term stable operation of the system and reduce the maintenance intensity and cost of the adsorption tower. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0015] Figure 1 This is a structural diagram of the adsorption tower of this utility model; Among them, 1-adsorption tower, 2-porous media adsorption unit, 3-porous media fixed bed, 4-media module, 5-flue gas inlet, 6-flue gas outlet, 7-ash hopper, 8-airflow equalization plate, 9-nozzle, 10-conveyor fan, 11-branch pipe, 12-main pipe, 13-valve. Detailed Implementation

[0016] Reference will now be made in detail to embodiments of the present disclosure, one or more of which are set forth herein. Each embodiment and example is provided by way of explanation of the apparatus, composition, and materials of the present disclosure, and not by way of limitation. Rather, the following description provides convenient illustrations for implementing exemplary embodiments of the present disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the teachings of the present disclosure without departing from the scope or spirit of the present disclosure.

[0017] like Figure 1 As shown, this utility model discloses a flue gas denitrification system for an alkali recovery furnace with pretreatment of sticky dust. It includes an adsorption tower 1 and a plurality of porous media adsorption units 2 arranged sequentially along the flue gas flow direction in the adsorption tower 1. The porous media adsorption unit 2 includes a porous media fixed bed 3 and a media module 4 filled and fixed on the porous media fixed bed 3. The media module 4 includes a plurality of porous media layers stacked on each other. The stacking of porous media layers forms a three-dimensional tortuous gas flow channel, causing the dust particles in the flue gas to collide and agglomerate with each other. A dust removal mechanism is provided on the flue gas inlet side of each porous media adsorption unit 2 for cleaning the dust particles adsorbed by the porous media adsorption unit.

[0018] This invention removes sticky dust from flue gas using a porous media adsorption unit 2. The porous structure forms a three-dimensional flow path, which promotes the collision of sticky dust particles, thereby effectively removing them from the flue gas. To facilitate dust particle collection, the adsorption tower 1 is vertically oriented, with a flue gas inlet 5 at the top and a flue gas outlet 6 at the bottom. A dust hopper 7 is located at the bottom of the adsorption tower 1 to receive the adsorbed dust particles, and the flue gas outlet 6 is positioned above the dust hopper 7. An airflow equalization plate 8 is installed at the flue gas inlet 5 to evenly distribute the flue gas entering the adsorption tower 1.

[0019] The airflow equalization plate 8 of this utility model is a disc shape that matches the cross-section of the adsorption tower. Uniform holes are opened on the disc surface to equalize the flow of flue gas, ensuring that the flue gas presents a uniform and relatively stable flow field when it enters the medium layer, so as to ensure the treatment effect of the flue gas.

[0020] The dust removal mechanism of this utility model includes nozzles 9 correspondingly arranged above the porous media adsorption unit 2. The nozzles 9 are connected to the conveying fan 10 arranged outside the adsorption tower 1 through the dust removal pipe. The dust removal pipe includes branch pipes 11 connected to the nozzles 9 and main pipe 12 that collects the branch pipes 11 and is connected to the conveying fan 10. The branch pipes 11 are equipped with valves 13 for controlling the opening and closing of the air passage. The airflow sprayed from the nozzles 9 cleans the dust accumulated in the porous media adsorption unit 1.

[0021] This invention incorporates a gas pressure sensor within the adsorption tower 1 to detect the pressure drop across the porous media adsorption unit. Based on the pressure information detected by the gas pressure sensor, the operation of the dust removal mechanism is controlled. When excessive accumulation of sticky dust in the porous media fixed bed causes the system pressure drop to rise to a specific value, the dust removal device is activated, and the valves open. Compressed air is ejected from nozzles on the dust removal pipe, forming a high-speed airflow. This enables automatic operation of the adsorption tower dust removal process, timely monitoring of the dust particle accumulation status in the porous media adsorption unit. Under the influence of gravity and flue gas scouring, dust particles detach from the surface of the media layer and fall into the ash hopper below for centralized discharge, effectively removing sticky dust from the flue gas and simultaneously completing the self-cleaning process of the porous media adsorption unit.

[0022] The porous media layer of this invention uses materials with high porosity, high specific surface area, high temperature resistance, and surface inertness, such as porous ceramic balls, sintered metal fiber felt, or modified alumina corrugated plates, or a combination thereof. These materials not only provide a huge adsorption surface area, but their surface properties also effectively prevent deep adhesion of dust. The media layers are stacked to form three-dimensional tortuous channels. This structure greatly increases the contact area and contact time between flue gas and the media, while providing space for the collision and aggregation of dust particles.

[0023] By using the adsorption tower structure of this invention, sticky particulate dust in flue gas can be effectively collected and treated, providing qualified flue gas conditions for the subsequent denitrification system and ensuring the long-term stable operation of the SCR catalyst.

[0024] The above description is only a preferred embodiment of the present invention. 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 invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flue gas denitrification system for an alkali recovery furnace with pretreatment of sticky dust, characterized in that, The system includes an adsorption tower (1) and several porous media adsorption units (2) arranged sequentially along the flue gas flow direction in the adsorption tower (1). The porous media adsorption unit (2) includes a porous media fixed bed (3) and a media module (4) filled and fixed on the porous media fixed bed (3). The media module (4) includes several porous media layers stacked on each other. The stacking of porous media layers forms a three-dimensional tortuous gas flow channel, causing the dust particles in the flue gas to collide and aggregate with each other. A dust removal mechanism is provided on the flue gas inlet side of each porous media adsorption unit (2) to clean the dust particles adsorbed by the porous media adsorption unit.

2. The alkali recovery furnace flue gas denitrification system with sticky dust pretreatment according to claim 1, characterized in that, The adsorption tower (1) is set vertically, with a flue gas inlet (5) at the top and a flue gas outlet (6) at the bottom. A dust hopper (7) for receiving adsorbed dust particles is set at the bottom of the adsorption tower (1), and the flue gas outlet (6) is set at a height above the dust hopper (7). An airflow equalization plate (8) for equalizing the flow of flue gas entering the adsorption tower (1) is set at the flue gas inlet (5).

3. The alkali recovery furnace flue gas denitrification system with sticky dust pretreatment according to claim 2, characterized in that, The airflow equalization plate (8) is a disc shape that matches the cross-section of the adsorption tower, with uniform holes on the disc surface to equalize the flow of the incoming flue gas.

4. The alkali recovery furnace flue gas denitrification system with sticky dust pretreatment according to claim 2, characterized in that, The dust removal mechanism includes a nozzle (9) correspondingly arranged above the porous media adsorption unit (2). The nozzle (9) is connected to a conveying fan (10) arranged outside the adsorption tower (1) through a dust removal pipe. The dust removal pipe includes a branch pipe (11) connected to the nozzle (9) and a main pipe (12) that collects the branch pipes (11) and connects to the conveying fan (10). A valve (13) for controlling the opening and closing of the air passage is provided on the branch pipe (11). The airflow sprayed by the nozzle (9) cleans the dust accumulated in the porous media adsorption unit (2).

5. The alkali recovery furnace flue gas denitrification system with sticky dust pretreatment according to claim 4, characterized in that, A gas pressure sensor is installed in the adsorption tower (1) to detect the pressure drop on both sides of the porous medium adsorption unit. The operation of the dust removal mechanism is controlled based on the pressure information detected by the gas pressure sensor.

6. The alkali recovery furnace flue gas denitrification system with sticky dust pretreatment according to claim 1, characterized in that, The porous medium layer is made of a material with high porosity, high specific surface area, high temperature resistance, and surface inertness.

7. The alkali recovery furnace flue gas denitrification system with sticky dust pretreatment according to claim 6, characterized in that, The porous media layer is made of one of the following materials: porous ceramic spheres, sintered metal fiber felt, or modified alumina corrugated plate.

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