Regenerative scr denitration process and system for stainless steel mixed acid pickling waste gas

Abstract

The application provides a heat accumulating type SCR denitration process and system for high-concentration nitrogen oxide waste gas in stainless steel mixed acid pickling, the system comprises N heat accumulating reaction chambers, wherein N is greater than or equal to 3, the heat accumulating reaction chambers are sequentially a lower box body, a heat accumulating body layer, an ammonia spraying grid, a static mixer and a denitration catalyst layer from bottom to top, the upper part of the heat accumulating reaction chamber is communicated with a heating communicating chamber, the lower box body of the heat accumulating reaction chamber is connected with an air inlet switching valve, an exhaust switching valve and a flushing switching valve, and the orderly opening and closing switching of the air inlet switching valve, the exhaust switching valve and the flushing switching valve of each heat accumulating reaction chamber realizes the sequential rotation switching of the heat accumulating-heat releasing-purge cleaning three processes of each heat accumulating reaction chamber. The heat accumulating type heat exchange and the SCR denitration reactor are integrated into the integrated heat accumulating type SCR denitration system, heat energy is allowed to migrate back and forth in each heat accumulating reaction chamber while the SCR denitration is performed, the heat energy is efficiently recycled, the heat exchange efficiency can be higher than 90 %, and the low-power-consumption long-term stable operation of the SCR denitration system and device is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of SCR denitrification, and particularly to a regenerative SCR denitrification process and system for stainless steel mixed acid pickling waste gas. Background Art

[0002] During the process of stainless steel mixed acid pickling, a large amount of high-concentration nitrogen oxide waste gas is discharged. The nitrogen oxide concentration discharged from stainless steel mixed acid pickling is as high as 1000 - 10000 mg / Nm 3 , and the waste gas is yellow or even reddish-brown, belonging to high-concentration nitrogen oxide waste gas. Nitrogen oxides (NOx) are not only one of the main precursors of haze air pollution, but also the main pollutants that form acid rain and photochemical smog.

[0003] Due to the characteristics of high nitrogen oxide concentration in the acid mist waste gas of stainless steel mixed acid pickling, using multi-stage alkali washing or other processes not only fails to meet the discharge standards, but also causes secondary pollution. Currently, the SCR denitrification technology is the most reliable process technology for the达标排放 of nitrogen oxide waste gas from stainless steel mixed acid pickling, and this has formed a consensus in the stainless steel industry. Basically, corresponding SCR denitrification devices have been installed in stainless steel mixed acid pickling production lines for purification treatment.

[0004] Currently, the SCR denitrification devices equipped in stainless steel mixed acid pickling lines basically first use a GGH heat exchanger to heat the normal-temperature (about 40°C) acid mist waste gas after water washing to 180 - 250°C, and then use gas heating to further heat the waste gas to about 260 - 320°C and inject ammonia (or urea solution or ammonia water), and then enter the SCR denitrification reactor for SCR denitrification purification. The purified high-temperature clean gas then enters the GGH to exchange heat with the normal-temperature (about 40°C) acid mist waste gas after water washing to recover heat energy and then meets the discharge standards. The function of the GGH heat exchanger is to preheat the normal-temperature acid mist waste gas after water washing with the high-temperature clean flue gas after SCR denitrification reaction, that is, to recover the heat energy of the high-temperature clean flue gas after SCR denitrification reaction to achieve the purpose of energy conservation. However, since the heat exchange efficiency of the GGH heat exchanger generally does not exceed 70%, once it needs to exceed 70% or more, the heat exchange area needs to increase exponentially, resulting in a large footprint of the equipment and a significant increase in equipment costs.

[0005] Taking the SCR denitrification device equipped with a 1680 mm stainless steel continuous annealing hot rolling pickling line of a certain stainless steel production enterprise as an example, its waste gas treatment volume is 25000 Nm 3 / h, and the NOx concentration is about 5000 mg / Nm 3The exhaust gas first undergoes water washing to remove hydrofluoric acid (HF). Afterward, it passes through a GGH heat exchanger to reach a temperature of 195°C. Then, it is heated to 290°C using natural gas combustion. Ammonia is added before the gas enters the SCR reactor for denitrification. The outlet flue gas temperature of the SCR reactor is 350°C. After heat recovery via the GGH, the temperature is reduced to 157°C to meet emission standards. Natural gas consumption is 89 Nm³. 3 Based on an annual operating time of 8600 hours, the annual gas consumption is approximately 765,400 Nm³ / h. 3 The price of natural gas is 3.5 yuan / Nm³. 3 It is estimated that the annual gas cost is approximately RMB 2.6789 million, and the annual CO2 emissions are approximately 1503.46 tons. Since the heat exchange efficiency of GGH heat exchangers is generally no more than 70%, the energy consumption for heating the exhaust gas after GGH heat exchange with secondary gas (or electric heating) is relatively large, resulting in high energy costs and increased CO2 emissions. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention provides a regenerative SCR denitrification process and system for stainless steel mixed acid pickling waste gas.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention provides a regenerative SCR denitrification system for stainless steel mixed acid pickling flue gas, comprising a waste gas preheater, N regenerative reaction chambers, a heating connection chamber, a bypass SCR reactor, an ammonia dilution mixer, and an exhaust stack, wherein N≥3; each of the regenerative reaction chambers has an open top that communicates with the heating connection chamber, and a heater is installed in the heating connection chamber; each of the regenerative reaction chambers has an inlet and an outlet, the inlet of each of the regenerative reaction chambers is connected to the outlet of the waste gas preheater, the outlet of each of the regenerative reaction chambers is connected to the inlet of the exhaust stack, and each of the regenerative reaction chambers is connected to the inlet of the bypass SCR reactor through the heating connection chamber; the outlet of the bypass SCR reactor is connected to the inlet of the ammonia dilution mixer and the inlet of the exhaust stack, respectively; all connections are made via pipelines.

[0009] Furthermore, each of the heat storage reaction chambers includes, from bottom to top, a lower box, a heat storage layer, an ammonia injection grid, a static mixer, and a denitrification catalyst layer. The ammonia injection grid is connected to the outlet of the ammonia dilution mixer through a pipeline equipped with an ammonia shut-off valve.

[0010] Furthermore, the heat storage layer includes bulk ceramic filler heat storage and honeycomb ceramic heat storage, wherein the bulk ceramic filler heat storage includes one or a combination of inert ceramic balls, ceramic rings, and ceramic columns.

[0011] Furthermore, the denitrification catalyst layer includes a honeycomb catalyst, which includes one or a combination of two of the following: vanadium-titanium honeycomb catalyst and rare earth metal honeycomb catalyst.

[0012] Furthermore, the ammonia dilution mixer is equipped with an ammonia spray gun.

[0013] Furthermore, a heat release regulating valve is provided on the connecting pipe between the outlet of the bypass SCR reactor and the inlet of the exhaust stack, and a preheating regulating valve is provided on the connecting pipe between the outlet of the bypass SCR reactor and the inlet of the waste gas preheater.

[0014] Furthermore, each of the regenerative reaction chambers is also provided with a purge port, and each purge port of the regenerative reaction chamber is connected to a flushing fan via a pipe, and a purge valve is provided on the pipe.

[0015] Furthermore, the heater is a gas burner heater or an electric heater.

[0016] Furthermore, an inlet valve is provided on the pipeline between the air inlet of the regenerative reaction chamber and the air outlet of the waste gas preheater, an exhaust valve is provided on the pipeline between the air outlet of the regenerative reaction chamber and the air inlet of the exhaust stack, and a bypass fan is provided on the pipeline between the air outlet of the heating communication chamber and the air inlet of the bypass SCR reactor.

[0017] The present invention also provides a regenerative SCR denitrification process for stainless steel mixed acid pickling waste gas, comprising the following steps;

[0018] Step 1: Divide the N regenerative reaction chambers into three groups: Group 1, Group 2, and Group 3, where N ≥ 3. First, the stainless steel mixed acid pickling exhaust gas, which has been washed and had HF removed by a water washing tower, enters the exhaust gas preheater and is preheated to 50-80℃.

[0019] Step 2: The preheated exhaust gas enters the first set of regenerative reaction chambers for primary denitrification reaction. The heat energy released by the denitrification reaction raises the temperature of the exhaust gas by 10-70°C. At this time, the first set of regenerative reaction chambers is the intake regenerative reaction chamber.

[0020] Step 3: The exhaust gas after the first-stage denitrification reaction enters the heating and connecting chamber, where the temperature is 250-380℃. The exhaust gas from the heating and connecting chamber enters the second set of regenerative reaction chambers from top to bottom. The flue gas first passes through the denitrification catalyst layer for a second-stage denitrification reaction. The high-temperature clean gas obtained after the second-stage denitrification reaction flows through the static mixer and ammonia injection grid before entering the regenerative body layer. The heat energy of the high-temperature flue gas is transferred to the regenerative body to achieve heat energy recovery before being discharged through the exhaust valve to the exhaust stack. At this time, the second set of regenerative reaction chambers is the exhaust regenerative reaction chamber.

[0021] Step 4: After the bypass fan draws and transports a portion of the high-temperature waste gas from the heating connection chamber into the bypass SCR reactor for deep SCR denitrification and purification, a portion of the high-temperature clean gas enters the waste gas preheater to mix and preheat with the stainless steel mixed acid pickling waste gas, and a portion of the high-temperature clean gas enters the ammonia injection grid in the first set of heat storage reaction chamber through the ammonia dilution mixer as ammonia dilution gas.

[0022] Step 5: The flushing fan delivers fresh air to the first set of regenerative reaction chambers for purging and replacement, replacing the residual exhaust gas in the first set of regenerative reaction chambers with fresh air. At this time, the first set of regenerative reaction chambers changes from an intake regenerative reaction chamber to a purging and cleaning regenerative reaction chamber. Simultaneously, the preheated exhaust gas enters the second set of regenerative reaction chambers for primary denitrification reaction. At this time, the second set of regenerative reaction chambers changes from an exhaust regenerative reaction chamber to an intake regenerative reaction chamber.

[0023] Step Six: After the primary denitrification reaction, the exhaust gas enters the third set of regenerable heat storage reaction chambers from top to bottom through the heating and connecting chamber. The flue gas first passes through the denitrification catalyst layer for secondary denitrification reaction. The high-temperature clean gas obtained after the secondary denitrification reaction flows through the static mixer and ammonia injection grid and then enters the heat storage layer. The heat energy of the high-temperature flue gas is transferred to the heat storage to achieve heat energy recovery. Then, it is discharged through the exhaust valve to the exhaust stack. At this time, the third set of regenerable heat storage reaction chambers is called the exhaust heat storage reaction chamber. This completes one operating cycle.

[0024] Step 7: After a running cycle ends, by switching the valve groups of the corresponding heat storage reaction chambers, the exhaust heat storage reaction chamber of the previous cycle is converted into the intake heat storage reaction chamber, the purging and cleaning heat storage reaction chamber is converted into the exhaust heat storage reaction chamber, and the intake heat storage reaction chamber is converted into the purging and cleaning heat storage reaction chamber.

[0025] The present invention adopts the above technical solution and has the following technical advantages compared with the prior art:

[0026] 1. By setting up N regenerative reaction chambers, where N≥3, the sequential switching of the inlet valve, exhaust valve, and flushing valve of each regenerative reaction chamber enables the alternating switching of the three processes of heat storage, heat release, and purging cleaning in each regenerative reaction chamber. While performing SCR denitrification, heat energy is allowed to migrate back and forth between the regenerative reaction chambers, achieving efficient heat recovery. The heat exchange efficiency can reach over 90%. The system has low power consumption and may not even require external heating energy for reheating, achieving long-term stable low-energy operation. This not only reduces the operating cost of nitrogen oxide treatment but also reduces carbon emissions, which is of positive significance for achieving carbon neutrality.

[0027] 2. By installing an exhaust gas preheater, a portion of high-temperature exhaust gas is drawn from the heating interconnection chamber using a bypass fan and deeply purified by a bypass SCR reactor. A portion of the high-temperature clean flue gas (260℃-360℃) obtained after deep purification by the bypass SCR reactor is mixed with the ambient temperature exhaust gas after water washing after the flow rate is regulated by a flow regulating valve and enters the exhaust gas preheater. This ensures that the exhaust gas temperature at the outlet of the exhaust gas preheater reaches 50-80℃, preferably 55-65℃, thereby increasing the temperature of the flue gas entering the regenerative SCR denitrification device to prevent condensation and thus solve the problem of corrosion caused by condensation inside the equipment.

[0028] 3. By setting up a heat storage layer, the heat storage layer includes bulk ceramic heat storage body and honeycomb ceramic heat storage body from bottom to top. The bulk ceramic heat storage body has very good water resistance and will not gelatinize or pulverize when it comes into contact with water. When the exhaust gas passes through the bulk ceramic heat storage body layer, the exhaust gas temperature rises to above 100°C before entering the honeycomb ceramic heat storage body layer.

[0029] 4. Compared to mixing ammonia with waste gas before the bypass SCR reactor, this invention injects ammonia into the heat storage layer of the heat storage reaction chamber. The temperature range of the ammonia injection grid is above 260°C, and no ammonium salts such as ammonium nitrate will be generated.

[0030] 5. By using a portion of the high-temperature clean exhaust gas from the bypass SCR reactor as dilution air for ammonia, compared to using air as dilution air, the flue gas temperature entering the upper SCR denitrification catalyst layer can be increased by 5-10℃, which is beneficial to improving the SCR denitrification reaction efficiency. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the regenerative SCR denitrification system for stainless steel mixed acid pickling flue gas of the present invention.

[0032] The reference numerals in the attached figures are:

[0033] Regenerative reaction chamber 1; Inlet valve 1-1; Flushing valve 1-2; Exhaust valve 1-3; Ammonia shut-off valve 1-4; Lower chamber 1-5; Ammonia injection grille 1-6; Regenerator layer 1-7; Static mixer 1-8; Denitrification catalyst layer 1-9; Flushing fan 2; Exhaust stack 3; Waste gas preheater 4; Ammonia dilution mixer 5; Ammonia spray gun 5-1; Bypass SCR reactor 6; Bypass fan 7; Heat release regulating valve 7-1; Preheat regulating valve 7-2; Heating connecting chamber 8; Heater 9. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0035] refer to Figure 1 This embodiment provides a regenerative SCR denitrification system for stainless steel mixed acid pickling flue gas, including a waste gas preheater 4, N regenerative reaction chambers 1, a heating connecting chamber 8, a bypass SCR reactor 6, an ammonia dilution mixer 5, and an exhaust stack 3, wherein N≥3; each of the regenerative reaction chambers 1 has an open top and is connected to the heating connecting chamber 8, and a heater 9 is installed in the heating connecting chamber 8; each of the regenerative reaction chambers 1 has an air inlet and an air outlet, the air inlet of each of the regenerative reaction chambers 1 is connected to the air outlet of the waste gas preheater 4, the air outlet of each of the regenerative reaction chambers 1 is connected to the air inlet of the exhaust stack 3, and each of the regenerative reaction chambers 1 is connected to the air inlet of the bypass SCR reactor 6 through the heating connecting chamber 8, and the air outlet of the bypass SCR reactor 6 is connected to the air inlet of the ammonia dilution mixer 5, the air inlet of the waste gas preheater 4, and the air inlet of the exhaust stack 3, respectively; all connections are made through pipelines.

[0036] In this embodiment, each of the heat storage reaction chambers 1 includes, from bottom to top, a lower box body 1-5, a heat storage layer 1-7, an ammonia injection grid 1-6, a static mixer 1-8, and a denitrification catalyst layer 1-9. The ammonia injection grid 1-6 is connected to the outlet of the ammonia dilution mixer 5 through a pipeline equipped with an ammonia shut-off valve 1-4.

[0037] In this embodiment, the heat storage layer 1-7 includes a bulk ceramic packing heat storage body and a honeycomb ceramic heat storage body. The bulk ceramic packing heat storage body includes one or a combination of at least two of inert ceramic balls, ceramic rings, and ceramic columns, or it can be one or a combination of at least two of other bulk ceramic packing bodies. Specifically, the lower layer of the heat storage layer 1-7 is a bulk ceramic packing heat storage body, and the upper layer is a honeycomb ceramic heat storage body.

[0038] In this embodiment, the denitrification catalyst layers 1-9 include a honeycomb catalyst, which includes one or a combination of vanadium-titanium honeycomb catalyst and rare earth metal honeycomb catalyst.

[0039] In this embodiment, the ammonia dilution mixer 5 is equipped with an ammonia spray gun 5-1.

[0040] In this embodiment, a heat release regulating valve 7-1 is provided on the connecting pipe between the outlet of the bypass SCR reactor 6 and the inlet of the exhaust stack 3, and a preheating regulating valve 7-2 is provided on the connecting pipe between the outlet of the bypass SCR reactor 6 and the inlet of the waste gas preheater 4.

[0041] In this embodiment, each of the heat storage reaction chambers 1 is also provided with a purge port, and each of the heat storage reaction chambers 1 is connected to a flushing fan 2 through a pipe, and a flushing valve 1-2 is provided on the pipe.

[0042] In this embodiment, the heater 9 is a gas burner heater or an electric heater, and the gas can be one of natural gas, liquefied petroleum gas, cold coal gas, coke oven gas, or blast furnace gas.

[0043] In this embodiment, an inlet valve 1-1 is provided on the pipeline between the air inlet of the regenerative reaction chamber 1 and the air outlet of the waste gas preheater 4, an exhaust valve 1-3 is provided on the pipeline between the air outlet of the regenerative reaction chamber 1 and the air inlet of the exhaust stack 3, and a bypass fan 7 is provided on the pipeline between the air outlet of the heating connecting chamber 8 and the air inlet of the bypass SCR reactor 6.

[0044] In this embodiment, the air inlet valve 1-1, air outlet valve 1-3, and flushing valve 1-2 connected to the lower housing 1-5 of each heat storage reaction chamber 1 form an automatic switching valve group. The air inlet valve 1-1, air outlet valve 1-3, and flushing valve 1-2 are pneumatically or electrically driven. The ammonia shut-off valve 1-4 and air inlet valve 1-1 corresponding to each heat storage reaction chamber 1 are interlocked and opened and closed synchronously. Example

[0045] refer to Figure 1 This embodiment provides a process for a regenerative SCR denitrification system using stainless steel mixed acid pickling flue gas as described in Embodiment 1 above, including the following steps;

[0046] Step 1: Divide the N regenerative reaction chambers 1 into three groups: Group 1, Group 2, and Group 3, where N ≥ 3. First, wash the stainless steel mixed acid pickling exhaust gas (main pollutants are hydrofluoric acid (HF) and nitrogen oxides (NOx), with a NOx concentration of 1000 mg / Nm³) in a water washing tower to remove HF. 3 -10000mg / Nm 3 The exhaust gas (at a temperature of 30-40℃) enters the exhaust gas preheater 4, where it is preheated to 50-80℃.

[0047] Step 2: The preheated exhaust gas enters the first set of regenerative reaction chambers 1. It first enters the lower chamber 1-5 of regenerative reaction chamber 1, and then rises from bottom to top through the regenerative layer 1-7 to be heated to the temperature required for the SCR reaction. This process is called the "exothermic process." After the exhaust gas is heated, diluted ammonia is injected into it through the ammonia injection grille 1-6. The temperature range of the ammonia injection grille 1-6 is above 260℃. Then, it passes through the static mixer 1-8, where the ammonia and exhaust gas are fully mixed. The fully mixed ammonia... The exhaust gas then passes through the denitrification catalyst layer 1-9 in the regenerative reaction chamber 1. Under the action of the denitrification catalyst, the nitrogen oxides and ammonia in the exhaust gas undergo a primary denitrification reaction. The heat energy released by the denitrification reaction raises the temperature of the exhaust gas by 15-70°C. At this time, the first set of regenerative reaction chambers is the intake regenerative reaction chamber. In this process, most of the nitrogen oxides and ammonia in the exhaust gas are converted into nitrogen and water under the action of the catalyst. The ammonia injection grille 1-6 is controlled to open and close by the ammonia shut-off valve 1-4. The ammonia shut-off valve 1-4 and the intake valve 1-1 are interlocked and open and close synchronously.

[0048] Step 3: The exhaust gas after the primary denitrification reaction enters the heating chamber 8. The heating chamber 8 is automatically maintained at a set temperature by adjusting the power of the gas burner or electric heater. The temperature of the heating chamber 8 is 260-380℃. When the nitrogen oxide concentration in the exhaust gas reaches 4000 mg / Nm³... 3 When the SCR reaction generates heat, the exhaust gas temperature rises by 25-35°C, eliminating the need for gas or electric heating to assist in heating. The heat energy released by the SCR reaction enables the entire denitrification system to maintain a self-sustaining reaction.

[0049] Step 4: The exhaust gas passing through the heating and connecting chamber 8 enters the second set of regenerative reaction chambers 1. The exhaust gas passes through the denitrification catalyst layer 1-9 from top to bottom for a secondary denitrification catalytic reaction, where nitrogen oxides and ammonia in the exhaust gas react completely. The high-temperature clean gas after the secondary denitrification reaction then passes through the static mixer 1-8 and the ammonia injection grille 1-6 (no ammonia is injected in this regenerative reaction chamber), and then enters the regenerative body layer 1-7. At this time, the heat energy of the high-temperature clean gas is transferred to the regenerative body layer 1-7, causing the regenerative body layer 1-7 to heat up while the clean gas cools down. That is, the heat energy of the high-temperature clean gas after the reaction is recovered. This process is called the "secondary SCR reaction - regenerative body heat storage process". The heat energy in the high-temperature flue gas is transferred to the regenerative body layer 1-7. After the heat energy of the high-temperature clean gas is recovered, it cools down and enters the lower box 1-5 of the regenerative reaction chamber 1, and is discharged through the exhaust pipe 3. At this time, the second set of regenerative reaction chambers is the discharge regenerative reaction chamber.

[0050] Step 5: After the bypass fan 7 draws and transports a portion of the high-temperature waste gas from the heating and connecting chamber 8 into the bypass SCR reactor 6 for deep SCR denitrification and purification, a portion of the high-temperature clean gas enters the waste gas preheater 4 through the preheating regulating valve 7-2 to mix and preheat with the stainless steel mixed acid pickling waste gas. A portion of the high-temperature clean gas is used as ammonia dilution air to dilute the ammonia and enters the ammonia injection grid 1-6 in the first set of regenerable reaction chamber through the ammonia dilution mixer 5.

[0051] Step Six: The flushing fan 2 delivers fresh air from bottom to top to purge and replace the residual exhaust gas in the first set of heat storage reaction chambers, thus replacing it with fresh air. At this time, the first set of heat storage reaction chambers changes from an intake heat storage reaction chamber to a purge and cleaning heat storage reaction chamber. Simultaneously, the preheated exhaust gas enters the second set of heat storage reaction chambers for a primary denitrification reaction. At this time, the second set of heat storage reaction chambers changes from an exhaust heat storage reaction chamber to an intake heat storage reaction chamber.

[0052] Step 7: The exhaust gas after the first-stage denitrification reaction enters the third set of regenerative reaction chambers through the heating and connecting chamber 8 for the second-stage denitrification reaction. The clean gas after the reaction is completed is discharged through the exhaust stack 3. At this time, the third set of regenerative reaction chambers is called the discharge regenerative reaction chamber. This completes one operating cycle.

[0053] Step 8: After one operating cycle is completed, by switching the valve groups of the corresponding heat storage reaction chambers 1, the exhaust heat storage reaction chamber of the previous cycle is converted into the intake heat storage reaction chamber, the purging and cleaning heat storage reaction chamber is converted into the exhaust heat storage reaction chamber, and the intake heat storage reaction chamber is converted into the purging and cleaning heat storage reaction chamber; the heat storage reaction chambers are switched in turn according to the set program; the valve groups are pneumatically or electrically driven.

[0054] In this embodiment, the automatic switching valve group automatically opens and closes according to a set program to switch the exhaust gas into and out of different heat storage reaction chambers 1, thereby realizing the functional switching of each heat storage reaction chamber 1. The relationship between the function of the heat storage reaction chamber 1 and the opening and closing state of the automatic switching valve group is as follows:

[0055] A: Intake valve open / Exhaust valve closed / Purge and cleaning valve closed - This regenerative reaction chamber is in the "exothermic heating - first-stage SCR reaction" stage;

[0056] B: Intake valve closed / exhaust valve open / purge / cleaning valve closed - the regenerative reaction chamber is in the "heat absorption and cooling - secondary SCR reaction" stage;

[0057] C: Inlet valve closed / Exhaust valve closed / Purge and cleaning activated - This regenerative reaction chamber is in the "purge and cleaning" stage;

[0058] The three regenerative reaction chambers sequentially undergo the ACBACB process, with the three states alternating in turn.

[0059] Since the concentration of nitrogen oxides (NOx) in the acid mist exhaust gas from the pickling of stainless steel with mixed acid is 1000 - 10000 mg / Nm 3 , the concentration is very high, and the temperature of the exhaust gas before entering the regenerative bypass SCR reactor is 50 - 80 °C (preferably 55 - 65 °C). If ammonia is injected into the exhaust gas before entering the regenerative bypass SCR reactor, at a temperature of 50 - 80 °C (preferably 55 - 65 °C), ammonia reacts with nitric acid, NOx, etc. in the exhaust gas to form NH4NO3, but above 110 °C, the chemical reaction to form ammonium nitrate will not occur. Once ammonium nitrate is formed, it will block equipment, pipelines, regenerators, etc. in the low-temperature zone (≤110 °C).

[0060] In this embodiment, compared with mixing ammonia with the exhaust gas before the bypass SCR reactor, in this embodiment, ammonia is injected and mixed above the regenerative layer of the regenerative reaction chamber, and the temperature range of the ammonia injection grid is above 260 °C, and ammonium salts such as ammonium nitrate will not be formed.

[0061] Since the SCR denitration device currently supporting the stainless steel mixed acid pickling line basically treats the acid mist exhaust gas at room temperature (about 40 °C) after water washing. Due to the high concentration of NOx in the exhaust gas, a certain amount of NOx in the exhaust gas will dissolve in water to form nitric acid. At the same time, a small amount of HF remaining in the exhaust gas will also partially dissolve in water to form hydrofluoric acid. Dilute hydrofluoric acid and dilute nitric acid have strong corrosiveness, especially the corrosiveness of HF is extremely strong. Nitric acid and hydrofluoric acid have strong corrosiveness to equipment, valves, etc., causing leakage and equipment corrosion, and shortening the service life of the equipment; the fog droplets entrained in the exhaust gas and the water generated by condensation adhere to the regenerative honeycomb ceramics. After the honeycomb ceramics absorb water, they will gelatinize and pulverize, causing damage and blockage of the honeycomb ceramics.

[0062] In this embodiment, by using an exhaust gas preheater to increase the temperature of the flue gas entering the thermal SCR denitration device, the problem of water adhering to the regenerative honeycomb due to condensation is solved, and the problem of pulverization and gelatinization of the regenerative honeycomb ceramics is solved.

[0063] In this embodiment, a part of the high-temperature clean exhaust gas of the bypass SCR reactor is used as the dilution air for ammonia. Compared with using air as the dilution air, using a part of the high-temperature clean exhaust gas of the bypass SCR reactor as the dilution air for ammonia can increase the temperature of the flue gas entering the upper SCR denitration catalyst layer by 5 - 10 °C, which is beneficial to improving the SCR denitration reaction efficiency. Embodiment

[0064] This embodiment provides an application example of purifying the acid mist exhaust gas from the mixed acid pickling of a 1780 mm stainless steel hot rolling continuous annealing line with an annual output of 700,000 tons in a stainless steel factory using the regenerative SCR denitration process of the above-mentioned embodiment 2. The flue gas volume is 25000 Nm 3 / h, flue gas temperature after water washing is 35℃, NOx concentration is 7500 mg / Nm³ 3 Hydrofluoric acid concentration 6 mg / Nm 3 The SCR denitrification unit for stainless steel mixed acid pickling exhaust gas uses electric heating. The electric heater has a power of 300KW and is controlled by a silicon controlled rectifier (SCR). The flue gas temperature after preheating is 60℃. The regenerative SCR denitrification unit, after heating the exhaust gas in the regenerator and passing through the ammonia injection and static mixer, has a flue gas temperature of 268℃ (the temperature of the flue gas entering the catalyst layer of the first-stage SCR reaction). The ammonia consumption is 126.893 kg / h, and the NOx concentration in the exhaust is 55 mg / Nm³. 3 Ammonia escape rate 8 mg / Nm 3 The electric heater consumes zero electricity. Example

[0065] This embodiment provides an application example of using the regenerative SCR denitrification process described in Embodiment 2 above to purify the mixed acid pickling mist exhaust gas from two 400,000-ton-per-year 1550mm stainless steel cold rolling continuous annealing lines of a metal technology company. The flue gas volume is 40,000 Nm³. 3 / h, flue gas temperature after water washing is 40℃, NOx concentration is 3600mg / Nm³ 3 Hydrofluoric acid concentration 6 mg / Nm 3 The SCR denitrification unit for stainless steel mixed acid pickling exhaust gas uses gas burner heating, with a maximum burner power of 420KW. The burner power is controlled by an air-fuel ratio regulating valve. The flue gas temperature after preheating is 60℃. The regenerative SCR denitrification unit, after heating the exhaust gas in the regenerator and passing through an ammonia injection and static mixer, has a flue gas temperature of 262℃ (the temperature of the flue gas entering the catalyst layer of the first-stage SCR reaction). Ammonia consumption is 86.75 kg / h, and the NOx concentration in the exhaust is 50 mg / Nm³. 3 Ammonia slip rate 9 mg / Nm 3 The average natural gas consumption is 18m³. 3 / h. Example

[0066] This embodiment provides an application example of using the regenerative SCR denitrification process described in Embodiment 2 above to purify the mixed acid pickling mist exhaust gas from two 600,000-ton-per-year coil production lines of a stainless steel company. The flue gas volume is 50,000 Nm³. 3 / h, flue gas temperature after water washing is 40℃, NOx concentration is 2000-8000 mg / Nm³ 3 Hydrofluoric acid concentration 6 mg / Nm 3The SCR denitrification unit for stainless steel mixed acid pickling exhaust gas uses gas burner heating, with a maximum burner power of 630KW. The burner power is controlled by an air-fuel ratio regulating valve. The flue gas temperature after preheating is 60℃. The regenerative SCR denitrification unit, after heating the exhaust gas in the regenerator and passing through an ammonia injection and static mixer, has a flue gas temperature of 262℃ (the temperature of the flue gas entering the catalyst layer of the first-stage SCR reaction). The ammonia consumption is 162.40 kg / h, and the NOx concentration in the exhaust is 40 mg / Nm³. 3 Ammonia slip rate 9 mg / Nm 3 The average natural gas consumption is 21.75 m³. 3 / h.

[0067] In summary, the regenerative SCR denitrification system for stainless steel mixed acid pickling flue gas provided by this invention allows heat energy to migrate back and forth between various regenerative reaction chambers during SCR denitrification, achieving heat energy recovery. The heat exchange efficiency can reach over 90%. The system operates with low power consumption or even no energy required for heating and reheating, achieving long-term stable low-energy operation. This not only reduces the operating cost of nitrogen oxide treatment but also reduces carbon emissions, which is of positive significance for achieving carbon neutrality.

[0068] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A regenerative SCR denitrification system for stainless steel mixed acid pickling waste gas, characterized in that, The system includes a waste gas preheater (4), N regenerative reaction chambers (1), a heating communication chamber (8), a bypass SCR reactor (6), an ammonia dilution mixer (5), and an exhaust stack (3), wherein N ≥ 3; each of the regenerative reaction chambers (1) has an open top that communicates with the heating communication chamber (8), and a heater (9) is installed in the heating communication chamber (8); each of the regenerative reaction chambers (1) is provided with an air inlet and an air outlet, and the air inlet of each of the regenerative reaction chambers (1) is connected to the waste gas... The outlet of the preheater (4) is connected, and the outlet of each of the heat storage reaction chambers (1) is connected to the inlet of the exhaust stack (3). Each of the heat storage reaction chambers (1) is connected to the inlet of the bypass SCR reactor (6) through the heating connection chamber (8). The outlet of the bypass SCR reactor (6) is connected to the inlet of the ammonia dilution mixer (5), the inlet of the waste gas preheater (4), and the inlet of the exhaust stack (3), respectively. All connections are made through pipelines. Each of the heat storage reaction chambers (1) includes, from bottom to top, a lower box body (1-5), a heat storage layer (1-7), an ammonia injection grid (1-6), a static mixer (1-8), and a denitrification catalyst layer (1-9). The ammonia injection grid (1-6) is connected to the outlet of the ammonia dilution mixer (5) through a pipeline equipped with an ammonia shut-off valve (1-4).

2. The regenerative SCR denitrification system according to claim 1, characterized in that, The heat storage layer (1-7) includes bulk ceramic filler heat storage and honeycomb ceramic heat storage. The bulk ceramic filler heat storage includes one or a combination of inert ceramic balls, ceramic rings, and ceramic columns.

3. The regenerative SCR denitrification system according to claim 1, characterized in that, The denitrification catalyst layer (1-9) includes a honeycomb catalyst, which includes one or a combination of two of the following: vanadium-titanium honeycomb catalyst and rare earth metal honeycomb catalyst.

4. The regenerative SCR denitrification system according to claim 1, characterized in that, The ammonia dilution mixer (5) is equipped with an ammonia spray gun (5-1).

5. The regenerative SCR denitrification system according to claim 4, characterized in that, A heat release regulating valve (7-1) is provided on the connecting pipe between the outlet of the bypass SCR reactor (6) and the inlet of the exhaust stack (3), and a preheating regulating valve (7-2) is provided on the connecting pipe between the outlet of the bypass SCR reactor (6) and the inlet of the waste gas preheater (4).

6. The regenerative SCR denitrification system according to claim 1, characterized in that, Each of the heat storage reaction chambers (1) is also provided with a purge port, and each of the heat storage reaction chambers (1) is connected to a flushing fan (2) through a pipe, and the pipe is provided with a flushing valve (1-2).

7. The regenerative SCR denitrification system according to claim 6, characterized in that, The heater (9) is a gas burner heater or an electric heater.

8. The regenerative SCR denitrification system according to claim 7, characterized in that, An inlet valve (1-1) is provided on the pipeline between the inlet of the regenerative reaction chamber (1) and the outlet of the waste gas preheater (4). An exhaust valve (1-3) is provided on the pipeline between the outlet of the regenerative reaction chamber (1) and the inlet of the exhaust stack (3). A bypass fan (7) is provided on the pipeline between the outlet of the heating communication chamber (8) and the inlet of the bypass SCR reactor (6).

9. The process of a regenerative SCR denitrification system for stainless steel mixed acid pickling waste gas according to claim 8, characterized in that, Includes the following steps; Step 1: Divide the N regenerative reaction chambers (1) into the first group, the second group and the third group, where N≥3; First, the stainless steel mixed acid pickling waste gas that has been washed and HF removed by the water washing tower enters the waste gas preheater (4) and the waste gas is preheated to 50-80℃. Step 2: The preheated exhaust gas enters the first set of regenerative reaction chambers for primary denitrification reaction. The heat energy released by the denitrification reaction raises the temperature of the exhaust gas by 10-70°C. At this time, the first set of regenerative reaction chambers is the intake regenerative reaction chamber. Step 3: The exhaust gas after the first-stage denitrification reaction enters the heating and connecting chamber (8), where the temperature is 250-380℃. The exhaust gas after passing through the heating and connecting chamber (8) enters the second set of heat storage reaction chambers from top to bottom. The flue gas first passes through the denitrification catalyst layer (1-9) for a second-stage denitrification reaction. The high-temperature clean gas obtained after the second-stage denitrification reaction flows through the static mixer (1-8) and the ammonia injection grid (1-6) and then enters the heat storage layer (1-7). The heat energy of the high-temperature flue gas is transferred to the heat storage body to achieve heat energy recovery, and then it is discharged through the exhaust valve (1-3) to the exhaust stack (3). At this time, the second set of heat storage reaction chambers is the exhaust heat storage reaction chamber. Step 4: The bypass fan (7) draws and transports a portion of the high-temperature waste gas from the heating communication chamber (8) into the bypass SCR reactor (6) for deep SCR denitrification and purification. After that, a portion of the high-temperature clean gas enters the waste gas preheater (4) to mix and preheat with the stainless steel mixed acid pickling waste gas. A portion of the high-temperature clean gas enters the ammonia spray grid (1-6) in the first set of heat storage reaction chambers through the ammonia dilution mixer (5). Step 5: The flushing fan (2) delivers fresh air to the first group of heat storage reaction chambers for purging and replacement, replacing the residual exhaust gas in the first group of heat storage reaction chambers with fresh air. At this time, the first group of heat storage reaction chambers is changed from the intake heat storage reaction chamber to the purging and cleaning heat storage reaction chamber. At the same time, the preheated exhaust gas enters the second group of heat storage reaction chambers for the first-stage denitrification reaction. At this time, the second group of heat storage reaction chambers is changed from the exhaust heat storage reaction chamber to the intake heat storage reaction chamber. Step 6: After the first-stage denitrification reaction, the exhaust gas enters the third set of heat storage reaction chambers from top to bottom through the heating and connecting chamber (8). The flue gas first passes through the denitrification catalyst layer (1-9) for a second-stage denitrification reaction. The high-temperature clean gas obtained after the second-stage denitrification reaction flows through the static mixer (1-8) and the ammonia injection grid (1-6) and then enters the heat storage layer (1-7). The heat energy of the high-temperature flue gas is transferred to the heat storage body to realize heat energy recovery. Then it is discharged through the exhaust valve (1-3) to the exhaust stack (3). At this time, the third set of heat storage reaction chambers is called the exhaust heat storage reaction chamber. This completes one operating cycle. Step 7: When a running cycle ends, by switching the valve groups of the corresponding heat storage reaction chambers (1), the exhaust heat storage reaction chamber of the previous cycle is converted into the intake heat storage reaction chamber, the purging and cleaning heat storage reaction chamber is converted into the exhaust heat storage reaction chamber, and the intake heat storage reaction chamber is converted into the purging and cleaning heat storage reaction chamber.

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