Flue gas dust removal and denitration device with circulating preheating air multi-channel for alkali recovery furnace

Abstract

The invention discloses an alkali recovery furnace flue gas dust removal and denitration device with circulating preheating air multiple channels, and belongs to the technical field of flue gas purification, the alkali recovery furnace flue gas dust removal and denitration device comprises an inlet main flue for flue gas entering, the inlet main flue is communicated with a plurality of inlet branch flues, the inlet branch flues are communicated with dust removers, and the dust removers are communicated with denitration reactor bodies. The denitration reactor body is communicated with an air outlet mechanism, the inlet branch flue is communicated with a circulating preheating mechanism, and the circulating preheating mechanism is respectively communicated with the dust remover, the denitration reactor body and the air outlet mechanism. The flue gas of the alkali recovery furnace is shunted through the flue gas inlet main flue and the plurality of inlet branch flues and respectively enters each channel, the flue gas firstly enters the dust remover, dust in the flue gas is collected, the flue gas is introduced into the denitration reactor body through the flues, nitrogen oxide in the flue gas and ammonia gas are subjected to oxidation-reduction reaction on the surface of a catalyst to generate nitrogen and water, and the nitrogen and the water are recycled. And finally, the flue gas is discharged through the air outlet mechanism. A circulating preheating air system is adopted, and preheating of a large-circulation device and regeneration of a small-circulation catalyst are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of flue gas purification, and particularly relates to a flue gas dust removal and denitration device for an alkali recovery boiler with a multi-channel of circulating preheated air. Background Art

[0002] The main principle of an alkali recovery boiler is to utilize the waste liquid generated in the alkali pulp making process, namely black liquor. After the concentration of the waste liquid, this part of the waste liquid is input into the boiler as fuel for combustion. During the combustion process, the organic matter in the black liquor is effectively utilized and converted into steam, and this part of the steam is a valuable secondary energy source.

[0003] Its functions are mainly reflected in three aspects: First, burning black liquor can effectively treat the waste liquid generated in the pulping process and recover the alkali in it. The recovery rate of the furnace body is as high as 99%, greatly improving the resource utilization rate. Second, the green liquor generated during the combustion process is the raw material for causticization and is further recycled, reducing the demand for new alkali. Finally, by burning the waste liquid, the alkali recovery boiler significantly reduces pollutant emissions, achieves the goal of energy conservation and emission reduction, and makes a positive contribution to environmental protection.

[0004] The use of an alkali recovery boiler in a paper mill not only realizes the efficient recovery of alkali but also can generate steam for in-plant heating or power generation, thus achieving multiple effects of comprehensive resource recovery, energy conservation, and reduction of environmental pollution. The application of this technology plays a key role in promoting the development of the green paper industry.

[0005] The denitration and dust removal treatment of the flue gas of the alkali recovery boiler in the paper industry are essential.

[0006] At present, the dust removal of the alkali recovery boiler in the paper industry mainly uses a dry-type 3-electric field or 4-electric field dust collector, and the outlet dust concentration is above 50mg / Nm3, not meeting the ultra-low emission index.

[0007] Denitration mainly uses the oxidation + alkali washing method for denitration, generating soluble nitrates. And due to the high flue gas temperature after dust removal, the temperature of the clean flue gas is also high and the humidity is high after alkali washing, and the dust content also does not meet the ultra-low emission index.

[0008] A few years ago, there were occasional cases of SCR denitration, but they were not successful. The main problems were the enrichment of dust on the catalyst surface and the coking and failure of the catalyst surface.

[0009] In recent years, there have also been individual cases of SCR denitration, but the electrostatic precipitator device has not been optimized, and the dust removal effect is not obvious.

[0010] During the start-up and shutdown processes of the device and during maintenance, there is a certain risk of catalyst blockage. Summary of the Invention

[0011] The object of the present invention is to provide a flue gas dust removal and denitrification device for an alkali recovery furnace with a multi-channel of circulating preheated air, so as to solve the problems existing in the above-mentioned prior art.

[0012] To achieve the above object, the present invention provides the following solution: The present invention provides a flue gas dust removal and denitrification device for an alkali recovery furnace with a multi-channel of circulating preheated air, including an inlet main flue for the entry of flue gas, the inlet main flue is communicated with a plurality of inlet branch flues, the inlet branch flues are communicated with a dust collector, the dust collector is communicated with a denitrification reactor body, the denitrification reactor body is communicated with an air outlet mechanism, the inlet branch flues are communicated with a circulating preheating mechanism, and the circulating preheating mechanism is respectively communicated with the dust collector, the denitrification reactor body and the air outlet mechanism.

[0013] Preferably, the circulating preheating mechanism includes a circulating preheated air flue communicated with the inlet branch flue, a circulating preheated air electric heater is arranged in the circulating preheated air flue, and the circulating preheated air flue is respectively communicated with the dust collector, the denitrification reactor body and the air outlet mechanism.

[0014] Preferably, a plurality of dust collector filter elements are arranged at equal intervals in the dust collector, one end of the dust collector is communicated with a high-temperature compressed air tank, an electric heat tracing is arranged on one side of the dust collector, and the end of the dust collector far away from the high-temperature compressed air tank discharges ash outwards.

[0015] Preferably, a gas mixing mechanism is communicated with the top of the denitrification reactor body, the air outlet mechanism is communicated with the end of the denitrification reactor body far away from the gas mixing mechanism, a pre-distribution plate is arranged at the top in the denitrification reactor body, a plurality of catalysts are arranged at equal intervals below the pre-distribution plate, soot blowers are respectively arranged above and below the catalysts, a soot blower is arranged above the pre-distribution plate, a plurality of the soot blowers are respectively communicated with another high-temperature compressed air tank, and the bottom of the denitrification reactor body is communicated with an electric heat tracing of the reactor.

[0016] Preferably, the dust collector and the denitrification reactor body are communicated through a first connecting pipe, the gas mixing mechanism includes a high-temperature ammonia-air generator communicated with the first connecting pipe, the first connecting pipe is communicated with the top of the denitrification reactor body, a precise ammonia adjustment component is arranged between the high-temperature ammonia-air generator and the first connecting pipe, and the first connecting pipe is communicated with the circulating preheated air flue through a second connecting pipe.

[0017] Preferably, the air outlet mechanism includes a branch flue induced draft fan communicated with the bottom of the denitrification reactor body, the branch flue induced draft fan is communicated with an outlet main flue through a third connecting pipe, the outlet main flue is communicated with a chimney, and the circulating preheated air flue is communicated with the third connecting pipe.

[0018] Preferably, baffle gates are respectively provided at one end of the inlet branch flue near the inlet main flue, both ends of the circulating preheated air flue, one end of the third connecting pipe near the outlet main flue, and one end of the second connecting pipe near the circulating preheated air flue.

[0019] Preferably, the pre-set uniform distribution plate is an adjustable variable-aperture uniform distribution plate.

[0020] Preferably, the temperature of the flue gas is between 150°C and 450°C.

[0021] Preferably, the temperatures of the electric tracing for the dust collector and the electric tracing for the reactor are not lower than 150°C.

[0022] The present invention discloses the following technical effects: The flue gas from the alkali recovery furnace is shunted through the inlet main flue and multiple inlet branch flues and enters each channel respectively. In the channel, the flue gas first enters the dust collector to collect the dust in the flue gas, and then is introduced into the denitration reactor body through the flue. The nitrogen oxides in the flue gas and ammonia undergo an oxidation-reduction reaction on the surface of the catalyst to generate nitrogen and water. Finally, the flue gas is discharged through the air outlet mechanism. By adopting a circulating preheated air system, the preheating of the large-circulation device and the regeneration of the catalyst in the small circulation are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0024] Figure 1 is a schematic structural diagram of the flue gas dust removal and denitration device of the alkali recovery furnace with a circulating preheated air multi-channel of the present invention.

[0025] In the figure: 1, inlet main flue; 2, inlet branch flue; 3, baffle gate; 4, circulating preheated air flue; 5, high-temperature compressed air tank; 6, dust collector; 7, electric tracing for dust collector; 8, dust collector filter element; 9, denitration reactor body; 10, pre-set uniform distribution plate; 11, catalyst; 12, electric tracing for reactor; 13, soot blower; 14, high-temperature ammonia-air generator; 15, precise ammonia adjustment component; 16, branch flue induced draft fan; 17, circulating preheated air electric heater; 18, outlet main flue; 19, chimney. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Refer to Figure 1 As shown, this embodiment provides a flue gas dust removal and denitrification device for an alkali recovery furnace with a multi-channel of circulating preheated air, including an inlet main flue 1 for the flue gas to enter. The inlet main flue 1 is connected to a plurality of inlet branch flues 2. The inlet branch flues 2 are connected to a dust collector 6. The dust collector 6 is connected to a denitrification reactor body 9. The denitrification reactor body 9 is connected to an air outlet mechanism. The inlet branch flues 2 are connected to a circulating preheating mechanism. The circulating preheating mechanism is respectively connected to the dust collector 6, the denitrification reactor body 9, and the air outlet mechanism.

[0029] The flue gas of the alkali recovery furnace is shunted through the flue gas inlet main flue 1 and a plurality of inlet branch flues 2 and enters each channel respectively. In the channel, the flue gas first enters the dust collector 6 to collect the dust in the flue gas, and then is introduced into the denitrification reactor body 9 through the flue. The nitrogen oxides in the flue gas and ammonia undergo an oxidation-reduction reaction on the surface of the catalyst 11 to generate nitrogen and water. Finally, the flue gas is discharged through the air outlet mechanism. A circulating preheated air system is adopted to realize the preheating of the large-circulation device and the regeneration of the small-circulation catalyst 11.

[0030] In a further optimized solution, the circulating preheating mechanism includes a circulating preheated air flue 4 connected to the inlet branch flue 2. A circulating preheated air electric heater 17 is provided in the circulating preheated air flue 4. The circulating preheated air flue 4 is respectively connected to the dust collector 6, the denitrification reactor body 9, and the air outlet mechanism.

[0031] In a further optimized solution, a plurality of dust collector filter elements 8 are equidistantly arranged in the dust collector 6. One end of the dust collector 6 is connected to a high-temperature compressed air tank 5. A dust collector electric tracing 7 is provided on one side of the dust collector 6. The end of the dust collector 6 far from the high-temperature compressed air tank 5 discharges ash outward.

[0032] The dust collector filter element 8 adopts a surface-filtered alloy / ceramic sintered filter element that can be washed online or offline.

[0033] The entire shells of the dust collector 6 and the denitrification reactor body 9 are heated by high-temperature electric tracers, and the heating temperature is controlled above 150°C.

[0034] For a further optimized solution, a gas mixing mechanism is connected to the top of the denitration reactor body 9, an air outlet mechanism is connected to one end of the denitration reactor body 9 away from the gas mixing mechanism, a pre-uniform distribution plate 10 is provided at the top inside the denitration reactor body 9, a plurality of catalysts 11 are provided at equal intervals below the pre-uniform distribution plate 10, soot blowers 13 are respectively provided above and below the catalyst 11, a soot blower 13 is provided above the pre-uniform distribution plate 10, and the plurality of soot blowers 13 are respectively connected to another high-temperature compressed air tank 5. The bottom of the denitration reactor body 9 is connected to a reactor electric heat tracing 12.

[0035] For the reverse air blowing of the dust collector 6 and the soot blower 13, heated high-temperature compressed air is used, and the temperature is controlled above 200 °C.

[0036] The denitration agent is a high-temperature ammonia-air mixture containing less than 5% ammonia, and the temperature is controlled above 200 °C.

[0037] After the dust collector 6 and the denitration reactor body 9 are welded, the flaw detection is 100% qualified, and the cold air leakage rate is 0%.

[0038] For a further optimized solution, the dust collector 6 and the denitration reactor body 9 are connected through a first connecting pipe. The gas mixing mechanism includes a high-temperature ammonia-air generator 14 connected to the first connecting pipe. The first connecting pipe is connected to the top of the denitration reactor body 9. A precise ammonia adjustment component 15 is provided between the high-temperature ammonia-air generator 14 and the first connecting pipe. The first connecting pipe is connected to the circulating preheated air flue 4 through a second connecting pipe.

[0039] For a further optimized solution, the air outlet mechanism includes a branch flue induced draft fan 16 connected to the bottom of the denitration reactor body 9. The branch flue induced draft fan 16 is connected to an outlet main flue 18 through a third connecting pipe. The outlet main flue 18 is connected to a chimney 19. The circulating preheated air flue 4 is connected to the third connecting pipe.

[0040] For a further optimized solution, baffle doors are respectively provided at one end of the inlet branch flue 2 close to the inlet main flue 1, both ends of the circulating preheated air flue 4, one end of the third connecting pipe close to the outlet main flue 18, and one end of the second connecting pipe close to the circulating preheated air flue 4.

[0041] For a further optimized solution, the pre-uniform distribution plate 10 is an adjustable variable-aperture uniform distribution plate.

[0042] For a further optimized solution, the temperature of the flue gas is between 150 °C and 450 °C.

[0043] For a further optimized solution, the temperatures of the dust collector electric heat tracing 7 and the reactor electric heat tracing 12 are not lower than 150 °C.

[0044] The physical properties of sodium sulfate and sodium carbonate are as follows:

[0045]

[0046] Sodium sulfate and sodium carbonate are both easily hygroscopic in humid air, and sodium sulfate loses water when the temperature rises.

[0047] The physical properties of alkali recovery furnace dust are very different from those of fly ash, and the device for collecting fly ash cannot be completely applied to collect alkali recovery furnace dust.

[0048] Therefore, the alkali recovery furnace flue gas dust removal usually adopts an electrostatic precipitator 6 instead of a bag filter 6, which is prone to become clogged and ineffective.

[0049] SCR denitrification must also fully consider the physical properties of alkali recovery furnace dust.

[0050] Medium / low temperature SCR catalyst 11 selection: The flue gas temperature can be operated in the range of 150℃--450℃. When the flue gas temperature is higher than 320℃, the medium temperature SCR catalyst 11 is used, and when the flue gas temperature is lower than 320℃, the low temperature SCR catalyst 11 is used.

[0051] Selection of dust collector filter element 8: It is preferred to use alloy / ceramic sintered filter elements with dust corrosion resistance and online or offline water washability for surface filtration, which facilitates the cleaning of the filter element, extends the life of the equipment, and enables the dust content of the flue gas at the SCR inlet to reach the ultra-low emission index.

[0052] Methods to prevent "crusting" on the surface of equipment catalyst 11: It is preferred that the dust collector 6 and the entire shell of the denitrification reactor are heated by high-temperature electric heaters, and the heating temperature is controlled at above 150°C. The dust collector 6 back-blowing and the soot blower 13 use heated high-temperature compressed air, and the temperature is controlled at above 200°C. The denitrification agent is a high-temperature ammonia-air mixture containing less than 5% ammonia, which can be manufactured by processes such as liquid ammonia evaporation, ammonia vaporization, urea hydrolysis / pyrolysis, and carbon ammonium pyrolysis. The temperature of the mixed gas is controlled at above 200°C. Ensure that no hygroscopic sulfates and carbonates appear in the high-temperature flue gas.

[0053] The ammonia-air mixture is mixed with the flue gas using a precise ammonia adjustment component 15 to stabilize the denitrification efficiency of each zone.

[0054] A circulating preheating air system is used to achieve preheating of the large circulation device and regeneration of the small circulation catalyst 11.

[0055] Before the device is cold-started, run the large cycle to preheat the dust collector 6, denitration reactor body 9 and other equipment and flue gas flowing through the channel. After the gas reaches 200°C, open the inlet and outlet doors to let the alkali recovery furnace flue gas in for dust removal and denitration. Before the device is shut down, close the inlet door, open the circulating preheating air system, and convert the flue gas in the device until the smoke and dust are exhausted.

[0056] When the low-temperature catalyst 11 is regenerated, a small cycle is run, the gas temperature is raised to about 350° C., and the catalyst 11 is regenerated.

[0057] The number of dust removal and denitrification channels is consistent with the operating design conditions of the alkali recovery furnace. The alkali recovery furnace has few shutdowns. Usually, the post-treatment system is configured as N+1, and there is always one set of post-treatment systems in standby state.

[0058] Example 1

[0059] The flue gas parameters before dust removal and denitrification of a certain alkali recovery furnace are as follows:

[0060]

[0061] The emission standards for particulate matter and nitrogen oxides are required to be: 10mg / Nm 3 、50mg / Nm 3 .

[0062] After calculation, the process equipment configuration is as follows:

[0063] 1 Determination of the number of channels: Designed to operate stably according to 25% of the flue gas volume at low load of the alkali recovery furnace. Each channel processes 1000000 * 25% = 250000 Nm 3 / h, and the number of channels is 4 + 1 = 5.

[0064] 2 Process equipment configuration

[0065]

[0066]

[0067] Implementing according to the above main equipment configuration can achieve:

[0068] (1) With multiple relatively independent dust removal and denitrification devices, the alkali recovery furnace will not be shut down due to the maintenance of a certain dust removal and denitrification device or the catalyst regeneration problem, ensuring that the alkali recovery furnace operates continuously.

[0069] (2) The sulfate crystallization on the surface of the filter element 8 of the dust collector, the surface of the catalyst 11, the whole shell of the dust collector 6, and the denitrification reactor body 9 will not occur due to the start and stop of the dust removal and denitrification device, ensuring the long-life operation of the dust collector 6 and the denitrification device.

[0070] (3) After the flue gas is dust-removed and denitrified, the emissions of particulate matter and nitrogen oxides can reach 10mg / Nm 3 、50mg / Nm 3 , and the ammonia slip is less than 3ppm.

[0071] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0072] The above-described embodiments are only for describing the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An alkali recovery furnace flue gas dust removal and denitrification device with multi-channel circulating preheated air, characterized in that: The invention comprises an inlet main flue (1) for flue gas to enter, the inlet main flue (1) being connected to a plurality of inlet branch flues (2), the inlet branch flues (2) being connected to a dust collector (6), the dust collector (6) being connected to a denitration reactor body (9), the denitration reactor body (9) being connected to an air outlet mechanism, the inlet branch flues (2) being connected to a circulation preheating mechanism, the circulation preheating mechanism being respectively connected to the dust collector (6), the denitration reactor body (9) and the air outlet mechanism.

2. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 1 is characterized in that: The circulating preheating mechanism comprises a circulating preheating air flue (4) connected to the inlet branch flue (2), a circulating preheating air electric heater (17) is provided in the circulating preheating air flue (4), and the circulating preheating air flue (4) is respectively connected to the dust collector (6), the denitration reactor body (9) and the air outlet mechanism.

3. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 2 is characterized in that: A plurality of dust collector filter elements (8) are arranged at equal intervals in the dust collector (6); one end of the dust collector (6) is connected to a high-temperature compressed air tank (5); a dust collector electric heating (7) is arranged on one side of the dust collector (6); and the dust collector (6) discharges dust outwardly at one end away from the high-temperature compressed air tank (5).

4. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 3 is characterized in that: The top of the denitration reactor body (9) is connected to a gas mixing mechanism, and one end of the denitration reactor body (9) away from the gas mixing mechanism is connected to the air outlet mechanism. A front uniform distribution plate (10) is provided at the top of the denitration reactor body (9), and a plurality of catalysts (11) are evenly spaced below the front uniform distribution plate (10). Soot blowers (13) are provided above and below the catalysts (11), respectively. The soot blowers (13) are provided above the front uniform distribution plate (10), and the plurality of soot blowers (13) are respectively connected to another high-temperature compressed air tank (5). The bottom of the denitration reactor body (9) is connected to a reactor electric heating (12).

5. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 4 is characterized in that: The dust collector (6) and the denitration reactor body (9) are connected via a first connecting pipe, the gas mixing mechanism comprises a high-temperature ammonia-air generator (14) connected to the first connecting pipe, the first connecting pipe is connected to the top of the denitration reactor body (9), a precise ammonia adjustment component (15) is provided between the high-temperature ammonia-air generator (14) and the first connecting pipe, and the first connecting pipe is connected to the circulating preheated air flue (4) via a second connecting pipe.

6. The alkali recovery furnace flue gas dust removal and denitration device with circulating preheated air multi-channel according to claim 5 is characterized in that: The air outlet mechanism comprises a branch flue induced draft fan (16) connected to the bottom of the denitration reactor body (9); the branch flue induced draft fan (16) is connected to an outlet main flue (18) via a third connecting pipe; the outlet main flue (18) is connected to a chimney (19); and the circulating preheated air flue (4) is connected to the third connecting pipe.

7. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 6 is characterized in that: Baffle doors are provided at one end of the inlet branch flue (2) close to the inlet main flue (1), at both ends of the circulating preheated air flue (4), at one end of the third connecting pipe close to the outlet main flue (18), and at one end of the second connecting pipe close to the circulating preheated air flue (4).

8. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 4 is characterized in that: The front uniform distribution plate (10) is an adjustable variable aperture uniform distribution plate.

9. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 1 is characterized in that: The temperature of the flue gas is between 150°C and 450°C.

10. The alkali recovery furnace flue gas dust removal and denitrification device with circulating preheated air multi-channel according to claim 4 is characterized in that: The temperature of the dust collector electric heating (7) and the reactor electric heating (12) is not less than 150°C.

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