A petroleum coke calcination rotary kiln tail gas treatment system

Abstract

This application relates to a tail gas treatment system for a petroleum coke calcination rotary kiln, belonging to the technical field of petroleum coke calcination tail gas treatment. The system comprises an SNCR high-temperature denitrification system, a waste heat boiler, a bag filter, a booster fan, a desulfurization tower, and a wet electrostatic precipitator connected to the rotary kiln tail gas pipeline. The SNCR high-temperature denitrification system is connected in parallel with a bypass pipeline. The pipeline between the bag filter and the booster fan is connected in parallel via three-way valves at both ends to a low-temperature denitrification unit consisting of a flue gas heat exchanger and the SNCR denitrification system connected in series. Addressing the low tail gas temperature during the ignition and start-up phase of a petroleum coke calcination rotary kiln, this application adds an SCR catalytic denitrification device after the waste heat boiler. To ensure the flue gas temperature is maintained at the reaction temperature required for SCR catalytic denitrification, an automatic temperature control heat exchange system is added to ensure the SCR denitrification system operates at normal operating temperatures, guaranteeing that NOx emissions meet standards.

Description

Technical Field

[0001] This application belongs to the field of petroleum coke calcination tail gas treatment technology, specifically relating to a petroleum coke calcination rotary furnace tail gas treatment system. Background Technology

[0002] Rotary kilns for calcining petroleum coke are widely used in petroleum coke calcination. After raw petroleum coke enters the rotary kiln, the volatile components of the petroleum coke are fully combusted, and the petroleum coke is subjected to high-temperature calcination treatment. Under anaerobic conditions, residual moisture and small-molecule organic matter are volatilized, thereby forming coke powder that combines a large amount of crystalline elemental carbon with a small amount of high-molecular-weight compounds. The calcination kiln exhaust gas produced during high-temperature calcination has relatively complex characteristics in terms of temperature, composition, etc. The pollutants in the exhaust gas are mainly dust, SOx, and NOx.

[0003] The emission of pollutants from the tail gas of a rotary kiln in petroleum coke calcination generally adopts a technical route of kiln tail + SNCR denitrification + multi-tube dust collector + waste heat boiler + wet desulfurization + electrostatic dust collector. Before the waste heat boiler, urea solution and other ammonia reducing agents are injected into the flue gas using SNCR technology (temperature 800-1000℃). This reacts with harmful NOx in the exhaust gas to produce harmless N2 and H2O, thereby removing nitrogen oxides from the flue gas. Subsequently, the flue gas passes through a ceramic multi-tube dust collector. Dust particles fall under the centrifugal force to the ash discharge port at the bottom of the multi-tube dust collector, where ash is manually discharged to remove larger dust particles from the flue gas. Next, the flue gas is conveyed by a booster fan to the inlet of the desulfurization tower. After passing through stages such as cooling spraying, turbulent mass transfer, slurry circulation, oxidation aeration, and gypsum dehydration, SO2 is removed from the flue gas. Finally, the flue gas enters the wet electrostatic precipitator inlet from the desulfurization tower outlet. The flue gas passes through the high-voltage electric field of the wet electrostatic precipitator, causing the dust and mist droplets in the flue gas to become charged, forming charged ions. These charged ions move towards electrodes with opposite charges, and upon reaching the electrodes, they discharge, forming neutral dust and mist particles. These particles then deposit on the electrodes, condense, and fall, thus being removed. Finally, the treated, compliant flue gas is discharged into the atmosphere through a chimney from the wet electrostatic precipitator outlet.

[0004] In the normal production stage of the rotary kiln, the flue gas temperature at the kiln tail is around 800℃. The SNCR denitrification system at the kiln tail can function normally at this temperature, and the NOx in the calcination kiln tail gas can meet the emission standards after treatment.

[0005] However, the ignition and start-up stage of the rotary kiln for petroleum coke calcination is a slow heating stage, which takes about a week to reach the normal production temperature of 1300℃. During this stage, the temperature of the flue gas at the kiln tail is relatively low and does not reach the 800℃ reaction temperature required for SNCR denitrification, resulting in NOx emissions from the tail gas not meeting the standards during the ignition and start-up heating stage of the calcination kiln. Summary of the Invention

[0006] The technical problem to be solved by this application is to overcome the shortcomings of the existing technology and provide a tail gas treatment system for a petroleum coke calcination rotary kiln. This application addresses the low tail gas temperature during the ignition and start-up stage of the petroleum coke calcination rotary kiln by adding an SCR catalytic denitrification device after the waste heat boiler. In order to ensure that the flue gas temperature is maintained at the reaction temperature required for SCR catalytic denitrification, an automatic temperature control heat exchange system is added to ensure that the SCR denitrification system can operate at normal reverse temperature and ensure that the NOx emissions of the tail gas meet the standards.

[0007] The technical solution adopted in this application to solve the problems existing in the prior art is:

[0008] A petroleum coke calcination rotary kiln tail gas treatment system comprises, in sequence, an SNCR high-temperature denitrification system, a waste heat boiler, a bag filter, a booster fan, a desulfurization tower, and a wet electrostatic precipitator connected to the kiln tail exhaust gas pipeline. The SNCR high-temperature denitrification system is connected in parallel to a bypass pipeline, with both ends of the bypass pipeline connected to the kiln tail exhaust gas pipeline and the waste heat boiler via three-way valves.

[0009] The pipeline between the bag filter and the booster fan is connected in parallel to a low-temperature denitrification unit consisting of a flue gas heat exchanger and an SCR denitrification system, via three-way valves at both ends.

[0010] Preferably, the pipeline between the waste heat boiler and the bag filter is connected in parallel to a sodium-based dry desulfurization device via three-way valves at both ends.

[0011] Preferably, the desulfurization tower consists of a primary desulfurization tower and a secondary desulfurization tower connected in series.

[0012] Preferably, the SCR denitrification system includes a catalyst module, which includes a housing. The housing is divided into a push-pull block placement chamber, a through chamber, and a cleaning chamber that are connected in sequence. The through chamber is provided with connecting flanges at its upper and lower ends, and the connecting flanges at both ends are respectively connected to the intake and exhaust pipes of the SCR denitrification system.

[0013] The cavity contains several horizontally arranged support plates and several strip-shaped catalysts. The catalysts are placed on the support plates. The cavity contains several push-pull blocks, which are fixedly connected to the catalysts.

[0014] Preferably, the length of the push-pull block is greater than the length of the catalyst, and the length of the catalyst is greater than the length of the opening of the through cavity.

[0015] Preferably, the shell is provided with a plurality of partitions arranged for disposal, with adjacent partitions arranged at equal intervals, and a catalyst and a push-pull block forming a single catalyst connection assembly, which is disposed between two adjacent partitions.

[0016] Preferably, the cleaning chamber is open at both the top and bottom, and the cleaning chamber is divided into several independent chambers that are connected to the through chamber by partitions.

[0017] The cleaning chamber is provided with a cleaning cover, which is slidably connected to the cleaning chamber.

[0018] The cleaning enclosure includes an upper enclosure and a lower enclosure, which are respectively located on the upper and lower sides of the cleaning chamber. The upper and lower enclosures are fixedly connected by an external connecting plate. The upper and lower enclosures cover the upper and lower sides of a chamber separated by a partition in the cleaning chamber.

[0019] The upper cover is connected to an air intake pipe, which is connected to the catalyst cleaning gas supply system.

[0020] The lower cover is connected to a waste discharge pipe.

[0021] Preferably, a second linear guide rail is fixed on the housing, and the sliding part of the second linear guide rail is fixedly connected to the outer wall of the upper housing.

[0022] The top surface of the push-pull block placement cavity is provided with a sliding groove, and the top of the push-pull block away from the catalyst is provided with a sliding plate. The sliding plate is slidably disposed inside the sliding groove. Several first linear guides are fixed on the top of the push-pull block placement cavity, and the sliding part of the first linear guide is detachably connected to the sliding plate.

[0023] Both the first and second linear guides are electrically powered linear guides.

[0024] Preferably, the catalyst cleaning gas supply system includes a cleaning gas tank, and the exhaust pipe of the cleaning gas tank is sequentially connected to a gas pump, a heat exchanger, a mixing chamber, and an intake pipe.

[0025] A three-way valve is installed between the air pump and the heat exchanger. One port of the three-way valve is connected to the mixing chamber through a bypass pipe. A temperature sensor is installed on the mixing chamber.

[0026] The heat exchanger's heating inlet is connected to the end pipe of the wet electrostatic precipitator via a pipeline.

[0027] A process for treating tail gas from a petroleum coke calcination rotary kiln, based on the aforementioned petroleum coke calcination rotary kiln tail gas treatment system, includes the following steps:

[0028] During the preheating stage of the rotary kiln:

[0029] The exhaust gas temperature at the kiln tail is low. During this stage, the SNCR high-temperature denitrification system and the sodium-based dry desulfurization system are shut down. The low-temperature exhaust gas is directly transported to the bag filter through pipelines to collect and recover most of the dust in the exhaust gas.

[0030] Subsequently, under negative pressure, the exhaust gas enters the cold end of the flue gas heat exchanger and begins to heat up. Then, the exhaust gas enters the inlet pipe of the SCR desulfurization system, and the combustion furnace inside the SCR desulfurization system reheats the exhaust gas to about 350°C. After that, the SCR desulfurization system reduces nitrogen oxides into nitrogen and water vapor.

[0031] The exhaust gas discharged from the SCR desulfurization system passes through the flue gas heat exchanger again, and the temperature of the exhaust gas drops to dry gas in the temperature range of 100-150℃. The exhaust gas enters the booster fan through the air duct, and then enters the desulfurization tower and wet electrostatic precipitator in sequence before being released.

[0032] When the rotary kiln preheating is complete and the production stage begins:

[0033] The exhaust gas temperature at the kiln tail is high. During this stage, the SNCR high-temperature denitrification and sodium-based dry desulfurization systems are activated, while the flue gas heat exchanger and SCR desulfurization system are deactivated. The exhaust gas passes through the high-temperature denitrification system, waste heat boiler, sodium-based dry desulfurization system, bag filter, booster fan, desulfurization tower, and wet electrostatic precipitator before being released.

[0034] Compared with the prior art, the beneficial effects of this application are as follows:

[0035] (1) In view of the low tail gas temperature during the ignition and start-up stage of the rotary kiln for calcining petroleum coke, this process technology route adds an SCR catalytic denitrification device after the waste heat boiler. In order to ensure that the flue gas temperature is maintained at the reaction temperature required for SCR catalytic denitrification, an automatic temperature control heat exchange system is added to ensure that the SCR denitrification system can operate at normal reverse temperature and ensure that the NOx emissions of the tail gas meet the standards.

[0036] (2) Baking soda (NaHCO3) or highly active calcium hydroxide is injected into the SDS dry desulfurization system. Baking soda decomposes rapidly into sodium carbonate (Na2CO3) upon contact with hot waste gas. The large specific surface area and porosity of sodium carbonate can undergo a vigorous metathesis reaction with acidic gases such as sulfur dioxide (SO2), sulfur trioxide (SO3), and hydrochloric acid (HCl) in the waste gas to produce carbon dioxide (CO2) and sodium sulfate (Na2SO4). This process can remove some of the acidic gases in the waste gas to achieve pre-desulfurization and greatly reduce the possibility of poisoning and deactivation of the subsequent SCR catalyst.

[0037] (3) Considering investment and operation and maintenance costs, this process technology route adopts a sodium-based dry desulfurization technology (SDS) + calcium-based wet lime / gypsum desulfurization process. The dust removal process adopts a low-pressure pulse bag dust removal technology + wet electrostatic dust removal technology. The denitrification process adopts selective non-catalytic reduction (SNCR) denitrification technology + selective catalytic reduction (SCR) denitrification technology. The overall equipment is arranged in series + bypass and independent island form. This process scheme can flexibly switch the operation of the main system and the bypass system according to the characteristics of the tail gas at different stages from ignition and start-up to stable operation of the calcining rotary kiln. It effectively solves the problem of different tail gas compositions at different stages of petroleum coke calcining rotary kiln and the difficulty of treatment, and ensures that the tail gas meets the emission standards. Attached Figure Description

[0038] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0039] Figure 1 This is a diagram of a petroleum coke calcination rotary kiln tail gas treatment system according to this application.

[0040] Figure 2 This is a structural diagram of the catalyst module inside the SCR reactor in a petroleum coke calcination rotary kiln tail gas treatment system according to this application.

[0041] Figure 3 This is a partial cross-sectional view of the catalyst module housing of this application.

[0042] Figure 4 This is the first cross-sectional view of the catalyst module in this application.

[0043] Figure 5 This is a structural diagram of the catalyst connection assembly in the catalyst module of this application.

[0044] Figure 6 This is a cross-sectional view of the shell in the catalyst module of this application.

[0045] Figure 7 This is a structural diagram of the catalyst cleaning casing in the catalyst module of this application.

[0046] Figure 8 This is a second cross-sectional view of the catalyst module of this application.

[0047] Figure 9 This is a structural diagram of the catalyst module in the catalyst clean state of this application.

[0048] Figure 10 for Figure 9 Partial sectional view of the middle shell.

[0049] Figure 11 This application presents a flowchart of a catalyst clean gas supply process in a petroleum coke calcination rotary kiln tail gas treatment system.

[0050] In the diagram: 1-Catalyst, 2-Push-pull block, 201-Slide plate, 3-Shell, 301-Push-pull block placement cavity, 302-Through cavity, 3021-Support plate, 3022-Connecting flange, 303-Cleaning chamber, 304-Baffle plate, 305-Support frame, 4-First linear guide rail, 5-Second linear guide rail, 501-Fixing device, 6-Cleaning cover, 601-Upper cover, 602-Lower cover, 603-Connecting plate, 7-Drain pipe, 8-Third linear guide rail, 9-Inlet pipe, 10-First synchronous belt, 11-First pulley, 12-First gear, 13-Second synchronous belt, 14-Second pulley, 15-Second gear, 16-Wiring pulley, 17-Guide pulley, 18-Cleaning gas tank, 19-Air pump, 20-Three-way valve, 21-Heat exchanger, 22-Bypass pipeline, 23-Mixing chamber. Detailed Implementation

[0051] The accompanying drawings provide a more detailed description of a petroleum coke calcination rotary kiln tail gas treatment system and process, but this is not intended to limit the scope of this application.

[0052] Depend on Figure 1 As shown, a petroleum coke calcination rotary kiln tail gas treatment system includes an SNCR high-temperature denitrification system, a waste heat boiler, a bag filter, a booster fan, a desulfurization tower, and a wet electrostatic precipitator connected sequentially to the rotary kiln tail gas pipeline.

[0053] The aforementioned SNCR high-temperature denitrification system is connected in parallel with a bypass pipeline, the two ends of which are connected to the kiln tail exhaust gas pipeline and the waste heat boiler respectively via three-way valves. The pipeline between the bag filter and the booster fan is connected in parallel with a flue gas heat exchanger and the SCR denitrification system in series to form a low-temperature denitrification unit via three-way valves at both ends.

[0054] The pipeline between the waste heat boiler and the bag filter is connected in parallel to a sodium-based dry desulfurization unit via three-way valves at both ends. The desulfurization tower consists of a primary desulfurization tower and a secondary desulfurization tower connected in series.

[0055] Depend on Figures 2 to 10 As shown, the SCR denitrification system includes a catalyst module, which comprises a housing 3. The housing 3 is divided into a push-pull block placement cavity 301, a through cavity 302, and a cleaning cavity 303, which are connected in sequence. The top surface of the through cavity 302 is higher than the top surfaces of the push-pull block placement cavity 301 and the cleaning cavity 303, while the bottom surface of the through cavity 302 is lower than the bottom surfaces of the push-pull block placement cavity 301 and the cleaning cavity 303. Connecting flanges 3022 are provided at both the upper and lower ends of the through cavity 302, and the connecting flanges 3022 at both ends are connected to the intake and exhaust pipes of the SCR denitrification system, respectively.

[0056] The through cavity 302 has several horizontally arranged support plates 3021 inside, and several strip-shaped catalysts 1 are arranged inside the through cavity 302. The catalysts 1 are placed on the support plates 3021. The push-pull block placement cavity 301 has several push-pull blocks 2 inside, and one push-pull block 2 is fixedly connected to one catalyst 1 to form a catalyst connection assembly.

[0057] The length of push-pull block 2 is greater than the length of catalyst 1, and the length of catalyst 1 is greater than the opening length of through cavity 302.

[0058] The housing 3 has a plurality of partitions 304 arranged inside, with adjacent partitions 304 arranged at equal intervals, and the catalyst connection assembly is disposed between adjacent partitions 304.

[0059] The cleaning chamber 303 is open at both the top and bottom, and is divided into several independent chambers by the partition 304, which are connected to the through chamber 302.

[0060] The cleaning chamber 303 is provided with a cleaning cover 6, which is slidably connected to the cleaning chamber 303.

[0061] The cleaning housing 6 includes an upper housing 601 and a lower housing 602, which are respectively disposed on the upper and lower sides of the cleaning chamber 303. The upper housing 601 and the lower housing 602 are fixedly connected by an external connecting plate 603. The upper housing 601 and the lower housing 602 cover the upper and lower sides of a chamber of the cleaning chamber 303 separated by a partition 304. To prevent the connecting plate 603 from bending under the weight of the lower housing 602 after prolonged use, thus affecting the sealing effect, in this embodiment, the bottom of the cleaning chamber 303 is fixed by a support frame 305, and the lower housing 602 is mounted on the support frame 305, which bears its weight. At the same time, a third linear guide rail 8 is also fixed on the housing 3. The sliding part of the third linear guide rail 8 is fixedly connected to the outside of the lower housing 602 for limiting its movement. The third linear guide rail 8 can be a non-powered guide rail.

[0062] The upper cover 601 is connected to the air inlet pipe 9, which is connected to the catalyst cleaning gas supply system. The lower cover 602 is connected to the impurity discharge pipe 7.

[0063] A second linear guide rail 5 is fixed on the housing 3, and the sliding part of the second linear guide rail 5 is fixedly connected to the outer wall of the upper cover 601.

[0064] The top surface of the push-pull block placement cavity 301 is provided with a sliding groove, and the top end of the push-pull block 2 away from the catalyst 1 is provided with a sliding plate 201. The sliding plate 201 is slidably disposed inside the sliding groove. Several first linear guide rails 4 are fixed on the top of the push-pull block placement cavity 301. The sliding part of the first linear guide rail 4 is detachably connected to the sliding plate 201.

[0065] Both the first linear guide rail 4 and the second linear guide rail 5 are electric linear guide rails.

[0066] Depend on Figure 11 As shown, the catalyst clean gas supply system includes a clean gas tank 18, and the exhaust pipe of the clean gas tank 18 is sequentially connected to a gas pump 19, a heat exchanger 21, a mixing chamber 23, and an intake pipe 9.

[0067] A three-way valve 20 is provided between the air pump 19 and the heat exchanger 21. One port of the three-way valve 20 is connected to the mixing chamber 23 through the bypass pipe 22. A temperature sensor is provided on the mixing chamber 23.

[0068] The heating port of heat exchanger 21 is connected to the end pipe of wet electrostatic precipitator via a pipeline.

[0069] Regardless of whether it is a honeycomb, flat plate, or corrugated plate catalyst 1, during the waste gas treatment process, ammonium bisulfate at low temperatures will adhere to the micropores, and fly ash in the waste gas will block the channels of catalyst 1 through the adhesive deposition of ammonium bisulfate NH4HSO4, resulting in a reduction in the catalytic effect of catalyst 1, and thus affecting the treatment effect of nitrogen oxides in the waste gas.

[0070] In existing technology, when catalyst 1 becomes clogged, the machine needs to be stopped to remove it. Then, the fly ash is blown away with compressed air, it is soaked in deionized water using ultrasonic vibration, and finally, it is rinsed in reverse with a high-pressure water gun. This process is time-consuming, and both the compressed air and the high-pressure water chamber can affect the structure of catalyst 1.

[0071] In this embodiment, since each catalyst assembly is isolated by the partition 304, it is equivalent to being arranged independently. Therefore, each catalyst 1 can be cleaned individually. Cleaning does not require stopping the system and does not affect the normal operation of the SCR denitrification system.

[0072] During cleaning, the first linear module 4 pushes the push-pull block 2 to move, pushing the catalyst 1 into the cleaning chamber 303. After the catalyst 1 is in place, the push-pull block 2 is arranged inside the through chamber 302 to prevent gas leakage. The second linear module 5 moves the cleaning cover 6 to the position of the catalyst 1. The upper cover 601, the catalyst 1, and the lower cover 602 form a sealed chamber.

[0073] The air pump 19 pumps the gas from the clean gas tank 18 into the heat exchanger 21 for heating, and then flows into the mixing chamber 23. By adjusting the opening of the three-way valve 20, a portion of the gas enters the mixing chamber 23 without being heated through the bypass pipe 22, maintaining the gas temperature inside the mixing chamber 23 at 350℃-400℃. Then, it enters the upper chamber 601 through the inlet pipe 9 to heat the catalyst 1.

[0074] Because NH4HSO4 can decompose and vaporize at temperatures above 316℃, breaking down into NH3, SO3 and H2O, it loses its stickiness. Consequently, the fly ash remaining inside catalyst 1 can be easily carried out by the high-pressure gas and discharged through the discharge pipe 7. The discharge pipe 7 can be connected to the subsequent desulfurization tower or booster fan pipeline.

[0075] The gas inside the cleaning gas tank 18 can be an inert gas, such as N2. This provides an oxygen-free environment, preventing NH3 or SO3 from being oxidized to form nitrogen oxides (NOx). x (or sulfate deposition) ensures that the decomposition products exist in gaseous form.

[0076] The gas inside the cleaning gas tank 18 can also be a mixture of inert gas and hydrogen. Hydrogen can act as a reducing agent, which can further suppress side reactions and reduce the possibility of NH3 and SO3 recombine to form NH4HSO4.

[0077] Since the cleaning housing 6 needs to slide along the cleaning cavity 303, a guide rail is provided on the housing 3 to prevent the air intake pipe 9 from bending or getting stuck between the cleaning housing 6 and the outer wall of the through cavity 302. A wiring pulley 16 is slidably installed inside the guide rail.

[0078] A guide pulley 17 is mounted on the top of the upper cover 601. The air intake pipe 9 is guided by the wiring pulley 16 and the guide pulley 17 before being vertically inserted into the upper cover 601. The guide pulley 17 ensures that the air intake pipe 9 enters the upper cover 601 vertically. The wiring pulley 16 adjusts the length of the air intake pipe 9 for wiring, ensuring that the wiring pattern of the air intake pipe 9 remains consistent throughout the cleaning process at the cover 6. Figure 7 The snake shape shown.

[0079] Depend on Figure 9 or Figure 10 As shown, when the cleaning housing 6 moves from right to left, it can pull the wiring pulley 16 to slide and perform wiring. However, when the cleaning housing 6 moves from left to right, it cannot move the wiring pulley 16 to the right without external force. If an elastic band or spring is used to connect the guide rail end to the wiring pulley 16, the elastic mechanism can drive the wiring pulley 16 to move to the right. Because the guide rail is too long, when the wiring pulley 16 moves to the left, it squeezes the elastic mechanism, causing excessive force on the wiring pulley 16 and the air inlet pipe 9 on the guide pulley 17, which can easily be squeezed into a sealed state, affecting the ventilation effect.

[0080] Therefore, in this embodiment, the housing 3 is connected to a first synchronous belt 10 and a second synchronous belt 13. The two ends of the first synchronous belt 10 are supported by a first pulley 11, and the two ends of the second synchronous belt 13 are supported by a second pulley 14. Both the first pulley 11 and the second pulley 14 are rotatably connected to the housing 3 through bearing seats.

[0081] The lower end of the first synchronous belt 10 is fixedly connected to the sliding part of the second linear guide rail 5 through the fixing device 501, and the upper end of the second synchronous belt 13 is fixedly connected to the wiring pulley 16.

[0082] One of the first pulleys 11 is connected to a first gear 12 via an overrunning clutch, and one of the second pulleys 14 is connected to a second gear 15 via an overrunning clutch. The first gear 12 and the second gear 15 are meshed, and the number of teeth of the first gear 12 is less than the number of teeth of the second gear 15.

[0083] Because when the cleaning housing 6 moves to the right, for proper wiring, the guide pulley 17 needs to move at a speed greater than the wiring pulley 16, bringing the two components closer together. Through this structure, the number of teeth on the first gear 12 is less than the number of teeth on the second gear 15, ensuring that when moving to the right, the guide pulley 17 moves at a speed greater than the wiring pulley 16, bringing the two components closer together.

[0084] As the cleaning cover 6 moves to the left, the first pulley 11 cannot drive the first gear 12 to rotate under the action of the overrunning clutch. The guide pulley 17 is pulled by the air intake pipe 9. At this time, the second pulley 14 also cannot drive the second gear 15 to rotate, so there is no interference.

[0085] A process for treating exhaust gas from a rotary kiln used for calcining petroleum coke, based on the aforementioned exhaust gas treatment system for a rotary kiln used for calcining petroleum coke, includes the following steps during the preheating stage of the rotary kiln:

[0086] The exhaust gas temperature at the kiln tail is low. During this stage, the SNCR high-temperature denitrification system and the sodium-based dry desulfurization system are shut down. The low-temperature exhaust gas is directly transported to the bag filter through the pipeline to collect and recover most of the dust in the exhaust gas.

[0087] Subsequently, under the action of negative pressure, the exhaust gas will enter the cold end of the flue gas heat exchanger and begin to heat up. Then, the exhaust gas enters the inlet pipe of the SCR desulfurization system, and the combustion furnace inside the SCR desulfurization system will reheat the exhaust gas temperature to about 350°C. After that, the nitrogen oxides will be reduced to nitrogen and water vapor by the SCR desulfurization system.

[0088] Ammonia injection grids are installed inside the pipes of the SCR reactor. During the flow, the waste gas is uniformly mixed with ammonia. The mixed gas flows vertically downwards through the guide plates and distributor at the top of the SCR reactor, passing over the catalyst. Upon contact with the catalyst, ammonia and nitrogen oxides (NOx) undergo a catalytic reduction reaction, reducing the nitrogen oxides in the hot waste gas to nitrogen (N2) and water vapor (H2O). Subsequently, the nitrogen and water vapor are discharged from the SCR reactor with the waste gas and re-enter the hot end of the flue gas heat exchanger. Through heat exchange, the temperature of the original waste gas is increased, saving fuel for the heating furnace while meeting the SCR denitrification requirements. This also reduces the SCR outlet flue gas temperature, achieving low-temperature and high-efficiency conditions that meet the needs of fan operation and desulfurization.

[0089] The flue gas heat exchanger has a structure similar to that of a plate heat exchanger or a tubular heat exchanger, including a first medium inlet and a second medium inlet and outlet. In this embodiment, the exhaust gas from the bag filter enters through the first medium inlet and exits through the outlet, then enters the SCR reactor. The exhaust gas from the SCR reactor enters through the second medium inlet and exits through the outlet, then enters the booster fan.

[0090] The exhaust gas discharged from the SCR desulfurization system passes through the flue gas heat exchanger again, and the temperature of the exhaust gas drops to dry gas in the temperature range of 100-150℃. The exhaust gas enters the booster fan through the air duct, and then enters the desulfurization tower and wet electrostatic precipitator in sequence before being released.

[0091] When the rotary kiln preheating is complete and the production stage begins:

[0092] The exhaust gas temperature at the kiln tail is high. During this stage, the SNCR high-temperature denitrification and sodium-based dry desulfurization systems are activated, while the flue gas heat exchanger and SCR desulfurization system are deactivated. The exhaust gas passes through the high-temperature denitrification system, waste heat boiler, sodium-based dry desulfurization system, bag filter, booster fan, desulfurization tower, and wet electrostatic precipitator before being released.

[0093] Specifically, denitrification spray guns are arranged at appropriate locations within the SNCR high-temperature denitrification system to perform SNCR high-temperature denitrification and meet nitrogen oxide emission requirements. The high-temperature hot exhaust gas after denitrification enters a waste heat boiler for heat recovery and utilization. The exhaust gas with a flue gas temperature of 150-180℃ exiting the waste heat boiler flows through the pipeline and is injected with sodium bicarbonate (NaHCO3) or highly active calcium hydroxide through a sodium-based dry desulfurization system. The sodium bicarbonate decomposes rapidly into sodium carbonate (Na2CO3) upon contact with the hot exhaust gas. The large specific surface area and porosity of sodium carbonate enable it to undergo vigorous metathesis reactions with acidic gases such as sulfur dioxide (SO2), sulfur trioxide (SO3), and hydrochloric acid (HCl) in the exhaust gas, producing carbon dioxide (CO2) and sodium sulfate (Na2SO4). This process can remove some of the acidic gases from the exhaust gas, achieving pre-desulfurization and greatly reducing the possibility of poisoning and deactivation of the subsequent SCR catalyst. The products of dry desulfurization flow along with the exhaust gas into a pulse bag filter. The filter collects the desulfurization products and dust in the exhaust gas and discharges them into the ash hopper at regular intervals. When the flue gas temperature is low and the content of unreacted sodium bicarbonate in the desulfurization products is high, it can be collected into a ton bag by the screw conveyor at the bottom of the ash hopper and added back into the sodium-based system for recycling.

[0094] Switching the bypass valve to the open state, the exhaust gas after bag filter dust collection is sent into the bypass pipe by the induced draft fan. The exhaust gas no longer passes through the SCR denitrification system but is sent into the first-stage wet desulfurization tower. The exhaust gas temperature before entering the tower is still relatively high. The exhaust gas is rapidly cooled by the cooler at the tower inlet and then enters the first spray layer, where it is cooled again and undergoes initial desulfurization. This is a process measure taken because the flue gas temperature and the efficiency of calcium-based wet desulfurization are negatively correlated. The exhaust gas continues to rise and the airflow pattern is adjusted by the cyclone separator. Then it passes through the three-stage spray layer, where the sulfur dioxide in the exhaust gas comes into contact with the liquid phase of the lime slurry and undergoes a chemical reaction to achieve the purpose of desulfurization. The humid gas after the first-stage desulfurization continues to rise and passes through the demisting zone and the tower top reflux, achieving most of the gas-liquid separation. The gas carrying a small amount of mist droplets enters the second-stage desulfurization tower through the connecting duct. After being sprayed and uniformly circulated again, it enters the third-stage spray layer. The residual sulfur dioxide in the exhaust gas reacts with the lime slurry, effectively ensuring the SO2 emission requirements. The droplets and dust adsorbed in the demisting zone inside the tower are flushed back into the tower by the backwashing system and a large amount of water. Simultaneously, after being washed by a continuous two-stage spray system, the exhaust gas, with its low temperature and only carrying a small amount of droplets, continues to rise and enters the wet electrostatic precipitator through the outlet duct. Under the influence of the internal electric field, a corona zone is formed throughout the entire settling electrode tube. Within the corona zone, high-concentration negative ions (electrons) continuously move directionally from the corona electrodes towards the settling electrode tube, forming a corona current. When water mist carrying dust particles enters the settling electrode tube, the water mist and dust particles become charged due to ion collisions and diffusion. Under the influence of the electric field, they rapidly reach the inner wall of the settling electrode tube and simultaneously release their charge, forming a liquid film on the inner wall. This liquid film flows under gravity into the collection tank at the bottom of the electrostatic precipitator for centralized treatment, thus achieving the purpose of capturing droplets and dust particles in the flue gas. The clean gas, due to positive pressure flow, is finally discharged into the atmosphere through the external chimney.

[0095] Among them, sodium-based dry desulfurization desulfurizer uses sodium bicarbonate (sodium bicarbonate granules) or highly active calcium-based desulfurization, wet desulfurization desulfurizer uses quicklime powder, SNCR / SCR denitrification agent uses urea, and the combustion furnace feedstock uses natural gas.

[0096] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application.

Claims

1. A petroleum coke calcination rotary kiln tail gas treatment system, comprising, in sequence, an SNCR high-temperature denitrification system, a waste heat boiler, a bag filter, a booster fan, a desulfurization tower, and a wet electrostatic precipitator connected to the rotary kiln tail gas pipeline, characterized in that: The SNCR high-temperature denitrification system is connected in parallel with a bypass pipeline, and the two ends of the bypass pipeline are connected to the kiln tail exhaust gas pipeline and the waste heat boiler respectively through a three-way valve. The pipeline between the bag filter and the booster fan is connected in parallel to a low-temperature denitrification unit consisting of a flue gas heat exchanger and an SCR denitrification system, via three-way valves at both ends.

2. The petroleum coke calcination rotary kiln tail gas treatment system according to claim 1, characterized in that: The pipeline between the waste heat boiler and the bag filter is connected in parallel to a sodium-based dry desulfurization device via three-way valves at both ends.

3. A petroleum coke calcination rotary kiln tail gas treatment system according to claim 1 or 2, characterized in that: The desulfurization towers are a primary desulfurization tower and a secondary desulfurization tower connected in series.

4. The petroleum coke calcination rotary kiln tail gas treatment system according to claim 3, characterized in that: The SCR denitrification system includes a catalyst module, which includes a housing (3). The housing (3) is divided into a push-pull block placement cavity (301), a through cavity (302), and a cleaning cavity (303) that are connected in sequence. The through cavity (302) is provided with connecting flanges (3022) at the upper and lower ends respectively. The connecting flanges (3022) at both ends are connected to the air intake and exhaust pipes of the SCR denitrification system respectively. The through cavity (302) is provided with several horizontally arranged support plates (3021), and several strip-shaped catalysts (1) are arranged inside the through cavity (302). The catalysts (1) are placed on the support plates (3021). The push-pull block placement cavity (301) is provided with several push-pull blocks (2), and the push-pull blocks (2) are fixedly connected to the catalysts (1).

5. The petroleum coke calcination rotary kiln tail gas treatment system according to claim 4, characterized in that: The length of the push-pull block (2) is greater than the length of the catalyst (1), and the length of the catalyst (1) is greater than the opening length of the through cavity (302).

6. The petroleum coke calcination rotary kiln tail gas treatment system according to claim 5, characterized in that: The housing (3) is provided with several partitions (304) arranged for disposal. Two adjacent partitions (304) are arranged at equal intervals. A catalyst (1) and a push-pull block (2) form a single catalyst connection assembly. The catalyst connection assembly is located between two adjacent partitions (304).

7. The petroleum coke calcination rotary kiln tail gas treatment system according to claim 6, characterized in that: The cleaning chamber (303) is open at both the top and bottom. The cleaning chamber (303) is divided into several independent chambers by partitions (304) and is connected to the through chamber (302). The cleaning chamber (303) is provided with a cleaning cover (6), and the cleaning cover (6) is slidably connected to the cleaning chamber (303); The cleaning housing (6) includes an upper housing (601) and a lower housing (602). The upper housing (601) and the lower housing (602) are respectively disposed on the upper and lower sides of the cleaning chamber (303). The upper housing (601) and the lower housing (602) are fixedly connected by an external connecting plate (603). The upper housing (601) and the lower housing (602) cover the upper and lower sides of a chamber of the cleaning chamber (303) that is separated by a partition (304). The upper cover (601) is connected to the air inlet pipe (9), which is connected to the catalyst cleaning gas supply system; The lower cover (602) is connected to a waste discharge pipe (7).

8. The petroleum coke calcination rotary kiln tail gas treatment system according to claim 7, characterized in that: A second linear guide rail (5) is fixed on the housing (3), and the sliding part of the second linear guide rail (5) is fixedly connected to the outer wall of the upper cover (601). The top surface of the push-pull block placement cavity (301) is provided with a sliding groove, and the top end of the push-pull block (2) away from the catalyst (1) is provided with a sliding plate (201). The sliding plate (201) is slidably disposed inside the sliding groove. Several first linear guides (4) are fixed on the top of the push-pull block placement cavity (301). The sliding part of the first linear guide (4) is detachably connected to the sliding plate (201). Both the first linear guide (4) and the second linear guide (5) are electric linear guides.

9. A petroleum coke calcination rotary kiln tail gas treatment system according to claim 7 or 8, characterized in that: The catalyst clean gas supply system includes a clean gas tank (18), and the exhaust pipe of the clean gas tank (18) is connected in sequence to a gas pump (19), a heat exchanger (21), a mixing chamber (23) and an air inlet pipe (9). A three-way valve (20) is provided between the air pump (19) and the heat exchanger (21). One valve port of the three-way valve (20) is connected to the mixing chamber (23) through the bypass pipe (22). A temperature sensor is provided on the mixing chamber (23). The heating port of the heat exchanger (21) is connected to the end pipe of the wet electrostatic precipitator through a pipeline.

Images