CN118320548A - Flue gas scrubbing process and catalytic cracking process - Google Patents

Abstract

The present disclosure relates to a flue gas scrubbing process and a catalytic cracking process. The flue gas washing method comprises the following steps: and introducing the flue gas into a flue gas washing tower to contact with an absorption liquid containing an absorbent, and contacting the flue gas contacted with the absorption liquid with clean water before exiting the tower. The flue gas washing method is simple and easy to operate, can effectively eliminate the tailing phenomenon of the flue gas of the wet method washing tower, and solves the problem of blue smoke and smoke plume sinking.

Description

Flue gas scrubbing method and catalytic cracking method

This application is a divisional application of the Chinese invention patent application with the application date of May 21, 2018, application number 201810491397.7, and invention name “Flue gas washing method and catalytic cracking method”.

Technical Field

The present disclosure relates to a flue gas scrubbing method and a catalytic cracking method.

Background technique

During industrial production, especially in some production processes involving heat treatment steps (drying, roasting, combustion, etc.), exhaust gases such as tail gas or flue gas containing pollutants are generated. For example, in the catalytic cracking (FCC) process, some sulfur and nitrogen compounds in the raw materials enter the coke during the reaction in the riser and are deposited on the spent catalyst. When the spent catalyst enters the regenerator for coking and regeneration, the sulfur and nitrogen compounds in the coke are oxidized to generate flue gas pollutants such as SO _x and NO _x . For another example, in inorganic chemical processes such as catalyst production, when sulfates, nitrates, chlorides, etc. contained in the raw materials are heated and decomposed, tail gas containing pollutants and harmful gases such as SO _x , NO _x , Cl ₂ , HCl, etc. is generated. These flue gases and tail gases containing pollutants and harmful gases need to be purified before they can meet the emission standards.

Wet scrubbing technology with wet scrubber as the core equipment has been widely used in the purification of flue gas and tail gas in industrial processes such as power generation, petrochemical, inorganic chemical, etc. Although there are certain differences in the process flow and structure, the basic principle is to absorb pollutants in the gas phase into the liquid phase through gas-liquid contact to achieve the purpose of purifying flue gas or tail gas. U.S. Patent US20070189949A1 discloses a wet scrubbing system for catalytic cracking regeneration flue gas treatment. By spraying alkaline scrubbing liquid with flue gas, it can achieve the effect of efficiently removing _SO2 and capturing dust at the same time.

However, during industrial operation, it has been gradually discovered that the wet scrubbing process has some problems; for example, it is easy to produce smoke tailing and blue smoke plume sinking, which has a serious impact on the production and living environment in the factory and surrounding areas.

Summary of the invention

The purpose of the present disclosure is to provide a flue gas scrubbing method and a catalytic cracking method to solve the flue gas tailing and sinking problems of existing and newly built wet scrubbing systems and reduce the adverse effects on the plant and surrounding production and living environment.

In order to achieve the above objectives, the first aspect of the present disclosure provides a flue gas scrubbing method, which comprises: introducing flue gas into a flue gas scrubbing tower to contact it with an absorption liquid containing an absorbent, and contacting the flue gas after contact with the absorption liquid with clean water before exiting the tower.

Optionally, the ratio of the clean water to the flue gas is: 0.001-0.5 kg water/Nm ³ flue gas.

Optionally, the clean water is at least one selected from fresh water, reclaimed water and desalinated wastewater;

Preferably, the dissolved solid content of the clean water is not higher than the dissolved solid content of the flue gas condensate collected from the flue gas outlet of the scrubbing tower, preferably, the dissolved solid content of the clean water is not higher than 0.01 wt%.

Optionally, the flue gas is at least one selected from FCC regeneration flue gas, thermal power plant tail gas, waste gas generated by a boiler, waste gas generated by a combustion furnace, and waste gas generated by a calcining furnace;

The temperature of the flue gas is 50-500°C, preferably 100-300°C.

Optionally, the flue gas contains pollutants, and the pollutants include at least one of SOx, NOx, NH ₃ , CO, CO ₂ , Cl ₂ , HCl and solid dust;

Preferably, the flue gas contains: SOx with a concentration of 20-10000 mg/ ^m3 , NOx with a concentration of 20-2000 mg/ ^m3 , and solid dust with a concentration of 10-1000 mg/ ^m3 ; wherein the concentrations are concentrations under standard conditions.

Optionally, an absorption liquid spraying device and a clean water spraying device are sequentially arranged in the scrubbing tower along the flue gas flow direction, and the clean water spraying device includes a clean water nozzle for spraying clean water, so that the flue gas after contact with the absorption liquid contacts with the clean water before leaving the tower;

The pump outlet pressure of the clean water is 0.1-10 MPa, preferably 0.1-1.0 MPa.

Optionally, the flue gas scrubbing tower comprises a scrubbing tower body and a chimney in fluid communication with the scrubbing tower body, and the cleaning water nozzle is located in the chimney.

Optionally, a clean water storage tank is further provided between the clean water spraying device and the absorption liquid spraying device, for collecting the clean water after contacting with the flue gas;

The collected washing water may be sent to the clean water spraying device to be circulated for contact with the flue gas, and/or, the washing water may be sent to the absorption liquid spraying device as supplementary water for the absorption liquid.

Optionally, the number of the absorption liquid spraying device and the clean water spraying device is one or more stages respectively, and along the flow direction of the flue gas, the clean water storage tank is located between the clean water nozzle of the first stage and the absorption liquid spraying device of the last stage.

Optionally, the number of the cleaning water nozzles is 1 to 12; when the number of the cleaning water nozzles is more than 1, the cleaning water nozzles are arranged at equal intervals along the circumferential direction and/or radial direction;

The cleaning water nozzle is at least one selected from a spiral nozzle, a fan-shaped nozzle and an annular nozzle.

Optionally, the method further comprises: allowing the flue gas after contact with the absorption liquid to first pass through a gas-liquid contact enhancement component (14) and then contact with the clean water, wherein the gas-liquid contact enhancement component is a filler and/or a tower plate.

Optionally, the pH value of the absorption liquid is 5-10, preferably 6-8;

The absorbent is at least one of a soluble hydroxide of an alkali metal and a soluble salt of an alkali metal; preferably, the absorbent is at least one selected from sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate and potassium hydroxide.

The second aspect of the present disclosure provides a catalytic cracking method, which comprises: contacting hydrocarbon oil with a catalyst to perform a catalytic cracking reaction, regenerating the catalyst after the reaction, and then washing the flue gas generated by the regeneration according to the method described in the first aspect of the present disclosure;

The catalyst contains 0.1-10 wt % of a sulfur transfer agent, preferably 1-5 wt % of a sulfur transfer agent, and the sulfur transfer agent is used to reduce the SOx concentration in the flue gas under the regeneration condition.

Optionally, the method further comprises: first recovering waste heat from the flue gas and then performing the washing step.

Through the above technical scheme, the flue gas scrubbing method provided by the present disclosure is simple and easy to implement. By making the flue gas contact with clean water before leaving the tower, the length of the flue gas tail is reduced or eliminated, the blue smoke is eliminated, and there is no plume sinking phenomenon. The method disclosed in the present disclosure can be implemented with simple or almost no modification to the existing scrubbing tower, without affecting the operational flexibility of the scrubbing tower and upstream devices, and at the same time helping to slow down equipment corrosion. The method disclosed in the present disclosure is low in cost and can be used for the treatment of flue gas or tail gas in various industrial processes, including power generation, petrochemicals, inorganic chemicals, etc.

In addition, the catalytic cracking method provided by the present invention can pre-remove SOx in the flue gas by adding a sulfur transfer agent to the catalyst, thereby reducing the operating load and absorption liquid consumption of the flue gas scrubber. Combined with the flue gas scrubbing method provided by the present invention, it is more conducive to solving the problems of flue gas tailing and plume sinking.

Other features and advantages of the present disclosure will be described in detail in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

FIG1 is a schematic structural diagram of a flue gas scrubber used in Example 1;

FIG2 is a schematic diagram of the arrangement of the cleaning water nozzles in the flue gas scrubber used in Example 1;

The direction of the arrow in the figure refers to the direction of fluid movement.

Description of Reference Numerals

1 Absorbent solution and water make-up lines

2 Flue gas inlet

3. Washing tower body

4 Absorbent solution and water make-up lines

5. Chimney

6 Smoke outlet

7 Clean water supply pump

8 Clean the water nozzle

9 Absorption liquid circulation pump

10 Absorption liquid nozzle

11 Absorption liquid circulation pump

12 External wastewater pipeline

13 Clean water storage tank

14 Gas-liquid contact strengthening components

Detailed ways

The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

In the present disclosure, unless otherwise specified, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the system when it is actually working, and "inside" and "outside" refer to the outline of the structure itself.

The first aspect of the present disclosure provides a flue gas washing method, which comprises: introducing flue gas into a flue gas washing tower to contact with an absorption liquid containing an absorbent, and contacting the flue gas after contact with the absorption liquid with clean water before exiting the tower.

The flue gas scrubbing method provided by the present invention is simple and easy to implement. By allowing the flue gas to contact with clean water before leaving the tower, the flue gas tailing phenomenon in the wet scrubbing tower can be effectively eliminated, and the problem of blue smoke and plume sinking can be solved.

According to the present disclosure, the ratio of the replenishment amount of fresh clean water (referring to clean water that has not been in contact with the flue gas) to the flue gas is generally not more than 0.15kg/Nm ³ , preferably 0.001-0.05kg/Nm ^3. In a preferred embodiment of the present disclosure, the clean water can be collected and recycled to reuse and increase the spraying amount, and the ratio of the clean water (total spraying amount, i.e., the amount of clean water in contact with the flue gas) to the flue gas can be: 0.001-0.5kg water/Nm ³ flue gas, preferably 0.01-0.2kg water/Nm ³ flue gas, wherein Nm ³ refers to the gas volume under standard conditions.

According to the present disclosure, the clean water can be at least one selected from fresh water, reclaimed water and desalted wastewater. The clean water can also be recycled, that is, the clean water after contacting with the flue gas is collected and recycled for contact with the flue gas. Further, the soluble solid content of the clean water (also called the total soluble solid content or the total salt content) is not higher than the soluble solid content of the flue gas condensate collected by the flue gas outlet of the scrubber, and preferably, the soluble solid content of the clean water is not higher than 0.01% by weight. In addition, according to actual needs, the clean water can also contain additives, as long as the additives do not increase the total soluble solid content of the absorption liquid, and the types of the additives are not particularly limited, for example, they can include but are not limited to defoaming agents, etc. The present disclosure has no special requirements for the temperature of the clean water, and the usual room temperature water temperature is sufficient. Generally, the water temperature does not exceed 90°C, such as 0-90 or 1-80°C or 10-60°C or 5-50°C, preferably 5-35°C.

According to the present disclosure, the flue gas may be flue gas (or tail gas) generated from a power plant, a petrochemical plant, an inorganic chemical plant, such as FCC regeneration flue gas, thermal power plant tail gas, waste gas generated by a boiler, waste gas generated by a combustion furnace, and waste gas generated by a calcining furnace, etc. The temperature of the flue gas may generally be 50-500°C, preferably 100-300°C.

According to the present disclosure, the flue gas contains pollutants, and the pollutants may be at least one selected from SOx, NOx, NH ₃ , CO, CO ₂ , Cl ₂ , HCl and solid dust. For example, the flue gas may contain SOx, CO ₂ , CO, NOx and/or solid dust. Further, the flue gas may contain: SOx with a concentration of 20-10000 mg/m ³ , such as 100-5000 mg/m ³ , NOx with a concentration of 20-2000 mg/m ³ , and solid dust with a concentration of 10-1000 mg/m ³ , such as 30-500 mg/m ³ ; wherein the concentrations are concentrations under standard conditions.

In the flue gas scrubbing method disclosed in the present invention, the flue gas is first introduced into a flue gas scrubbing tower to contact with an absorption liquid containing an absorbent to absorb and remove pollutants in the flue gas. The absorption operation method can be carried out with reference to the prior art, and there is no special requirement in the present disclosure. The absorption liquid is a mixture of an absorbent and water. The absorbent can be at least one of a soluble hydroxide and a soluble salt of an alkali metal or an alkaline earth metal such as sodium, potassium, magnesium, calcium, or an alkaline cation such as ammonium; preferably, the absorbent can be at least one selected from sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate and potassium hydroxide. The absorbent can be dissolved in water to prepare an absorbent solution with a certain concentration (e.g., 10-40% by weight), and then the absorbent solution is sent to the absorbent spraying device through a pipeline alone. At the same time, water is sent to the absorbent spraying device through a pipeline, that is, the absorbent solution and water are sent to the flue gas scrubber through pipelines to enter the absorbent circulation system (e.g., into the absorbent storage tank), and then fully mixed to make the absorbent reach the required pH value, and then sent to the absorbent nozzle through the absorbent circulation pump to spray and contact with the flue gas. The pH value of the absorbent can be 5-10, for example, the pH of the absorbent is 6-8 or 6.5-9. The absorbent is recycled, and the absorbent solution and water are continuously replenished according to its pH value, and the wastewater is discharged to keep the liquid level of the absorbent basically stable. Ozone can also be introduced into the flue gas as needed to oxidize low-valent nitrogen oxides into high-valent nitrogen oxides to facilitate reaction with alkaline substances. The discharge amount of the absorption liquid (or called discharged wastewater) after contact with the flue gas can be adjusted according to the liquid level in the absorption liquid storage tank or the total amount of dissolved solids in the absorption liquid. Usually, the total solid content of dissolved solids in the discharged wastewater is 0.1-10% by weight, preferably 2-8% by weight.

The method disclosed herein can be implemented with simple or almost no modification to the existing scrubber, without affecting the operational flexibility of the scrubber and upstream devices, while also helping to mitigate equipment corrosion.

The method disclosed herein can be implemented by adding one or more clean water spraying devices above the last stage of the absorption liquid spraying devices at each stage of the flue gas scrubber to spray clean water, or directly changing the last stage absorption liquid spraying device to a clean water spraying device, for example, it can be carried out in the flue gas scrubber as shown in Figure 1. In one embodiment of the present disclosure, the scrubber can be provided with absorption liquid spraying devices and clean water spraying devices in sequence along the flue gas flow direction, and the clean water spraying device includes a clean water nozzle 8 for spraying clean water, so that the flue gas after the absorption liquid contacts the clean water before leaving the tower. The nozzle can be any nozzle in the prior art, such as a spiral nozzle, a fan nozzle, an annular nozzle, and a nozzle that can realize the atomization of clean water, such as a pressure atomizing nozzle of various opening shapes, preferably a spiral nozzle. There is no special requirement for the outlet pressure of the clean water pump, as long as the water can be atomized at the nozzle, for example, it can be 0.1-10MPa, preferably 0.1-1.0MPa.

In an optional embodiment of the present disclosure, referring to FIG1 , the flue gas scrubber may include a scrubber body 3 and a chimney 5 in fluid communication with the scrubber body 3, a flue gas inlet 2 is arranged at the lower part of the scrubber body 3, and a flue gas outlet 6 is arranged at the top of the chimney 2. Generally, the structure in the chimney 5 is simpler than that in the scrubber body 3, so in order to facilitate the implementation of the engineering modification, it is preferred to arrange a clean water spraying device in the chimney 5, that is, the clean water nozzle 8 is located in the chimney 5. In addition, locating the clean water nozzle 8 in the chimney 5 allows the flue gas to be sprayed with clean water before it is about to leave the tower, thereby eliminating the flue gas tailing phenomenon to the greatest extent, solving the problem of blue smoke and plume sinking, and not affecting the operational flexibility of the scrubber and upstream devices, while also helping to slow down equipment corrosion.

According to the present disclosure, the amount of pollutants absorbed by clean water after a spray contact with flue gas is limited, and it can be collected and recycled. Therefore, in one embodiment of the present disclosure, a clean water storage tank 13 can also be provided between the clean water spray device and the absorption liquid spray device to collect the clean water (also called washing water) after contact with the flue gas. The collected washing water can be sent to the clean water spray device to be circulated for contact with the flue gas, and/or, the clean water can be sent to the absorption liquid spray device as supplementary water for the absorption liquid. The clean water nozzle 8 and the clean water storage tank 13 can be connected to the clean water supply pump 7 through pipelines, respectively, so that the clean water collected and sprayed by the clean water storage tank 13 can be pressurized by the clean water supply pump 7 and then circulated to the clean water nozzle 8 for spraying, effectively improving the utilization rate of the clean water and increasing the spraying amount of the clean water. In addition, the clean water storage tank 13 may also have a clean water storage tank overflow port, which is connected to a clean water overflow pipeline 19 extending to the washing liquid spraying device. The role of the overflow port is well known to those skilled in the art. When the liquid level in the clean water storage tank 13 is too high and reaches the overflow port of the clean water storage tank, the collected washing water can enter the washing liquid spraying device below through the clean water overflow pipeline 19, so that the excess washing water can be used as supplementary water for the washing liquid spraying device, thereby reducing the amount of washing liquid replenished by the washing liquid spraying device. The clean water storage tank 13, for example, can be provided with a smoke channel on the tank wall and/or the tank bottom for allowing smoke to pass through. In the present disclosure, there is no special restriction on the amount of water sprayed by the clean water nozzle. In the case of recycling clean water, the amount of clean water sprayed can be much higher than the amount of clean water replenished, and the actual amount of spraying depends on the efficiency of the delivery pump and the number of nozzles and the size of the opening.

According to the present disclosure, fresh clean water (referring to clean water that has not been in contact with flue gas) can be continuously or intermittently added to the clean water spray device. In terms of flue gas flow rate, the amount of fresh clean water added relative to the flue gas flow rate is preferably no more than 0.15kg/m ³ , and more preferably 0.001-0.05kg/m ^3. The amount of fresh clean water added is included in the total amount of water added to the scrubber, and the amount of water added to other water replenishment ports is converted according to the evaporation amount and the amount of water discharged. Usually, when the soluble solid content in the clean water storage tank 13 is higher than the soluble solid content in the flue gas condensate collected by the flue gas outlet, or higher than 0.5% by weight, it is necessary to discharge the washing water from the clean water storage tank 13, and reduce the circulation amount or increase the amount of fresh clean water added. It is preferred that the amount of fresh clean water added to the clean water spray device does not exceed the total amount of water added to the flue gas scrubber (the sum of the evaporation amount and the amount of wastewater discharged). In extreme cases, the entire tower can be replenished with water through the clean water spray device to solve the flue gas tailing and sinking problems without significantly increasing the total water consumption.

According to the present disclosure, the number of the absorption liquid spraying device and the clean water spraying device can be one or more stages. Wherein the multiple stages refer to a plurality of absorption liquid spraying devices or clean water spraying devices arranged at different positions (e.g., different height positions of the scrubbing tower) along the flow direction of the flue gas. The first stage of the clean water spraying device is the one closest to the upstream of the flue gas flow direction among all the clean water spraying devices, and the second stage, the third stage, ... and so on along the direction of the flue gas flow are arranged in sequence, and the clean water nozzles 8 arranged at the same position (e.g., the same height) are the same stage. Each level of the clean water spraying device can be provided with its matching clean water storage tank; or a set of clean water storage tanks can be shared by multiple levels of clean water spraying devices. In this case, along the flow direction of the flue gas, the clean water storage tank 13 can be located between the clean water nozzle 8 of the first stage and the absorption liquid spraying device of the last stage. The clean water storage tanks of each level can be partially or completely interconnected, or they can be isolated from each other and each become an independent clean water storage tank.

The method disclosed in the present invention preferably adds one or more clean water spray devices above the last stage of the absorption liquid spray devices at each stage of the washing tower, and more preferably adds one or more clean water spray devices in the chimney above the last stage absorption liquid spray device of the washing tower to spray clean water, or at least one clean water spray device is respectively arranged in the tower body and the chimney. The number of the clean water nozzles can be multiple, for example, 1 to 12, preferably 4 to 8, and can be symmetrically arranged along the cross-section of the tower body or chimney, for example, arranged at equal intervals along the circumferential direction and/or radial direction to improve the spraying effect. Wherein, the circumferential direction and radial direction described here and below are defined based on the circumferential surface of the washing tower and/or chimney. For example, Figure 2 is a schematic diagram of an embodiment in which the number of clean water nozzles is 4 and arranged circumferentially. When the number of the cleaning water spray devices is more than one and the number of cleaning water nozzles of each cleaning water spray device is more than one, the cleaning water nozzles of two adjacent cleaning water spray devices can be arranged crosswise in the circumferential and/or radial directions to further improve the spraying effect. For example, the multiple cleaning water nozzles of each cleaning water unit can be evenly arranged along the radial direction, that is, formed into a row, and the two rows of cleaning water nozzles of two adjacent cleaning water spray units can be arranged at 90° or other angles.

According to the present disclosure, the method may also include: allowing the flue gas after contact with the absorption liquid to first pass through the gas-liquid contact strengthening component 14, and then contact with the clean water. The gas-liquid contact strengthening component 14 is a component that can increase the contact surface between the flue gas and the clean water so that they are strongly mixed with each other, for example, it can be a filler and/or a tower plate. The type of the filler may include but is not limited to various commonly used fillers such as ball ring fillers, step ring fillers, regular fillers, etc., and there are no special requirements for its height and porosity, and the filler type with low pressure drop is preferred. The material of the filler includes but is not limited to various commonly used corrosion-resistant materials such as polytetrafluoroethylene and stainless steel. Allowing the flue gas after contact with the absorption liquid to pass through the gas-liquid contact strengthening component 14 can strengthen the gas-liquid contact and reduce water consumption.

According to the present disclosure, the structure of the absorption liquid spraying device and the process, parameters and other conditions of the absorption liquid spraying can be conventional in the existing wet flue gas scrubbing system. The present disclosure has no special limitations. It should be understood by those skilled in the art that the specific structure of the absorption liquid spraying device does not affect the implementation of the present disclosure.

The second aspect of the present disclosure provides a catalytic cracking method, which comprises: contacting hydrocarbon oil with a catalyst to perform a catalytic cracking reaction, regenerating the catalyst after the reaction, and then washing the flue gas generated by the regeneration according to the method described in the first aspect of the present disclosure. The catalyst contains 0.1-10% by weight of a sulfur transfer agent, preferably 1-5% by weight of a sulfur transfer agent, and the sulfur transfer agent is used to reduce the SOx concentration in the flue gas under the regeneration conditions.

According to the present disclosure, the sulfur transfer agent can be a sulfur transfer agent in the prior art, such as the sulfur transfer agent disclosed in patents CN1102433C, CN1142254C, CN1142015C, CN1148256C, CN100478424C, CN100425339C or CN1323132C. The sulfur transfer agent can at least reduce _SO2 in the flue gas at the inlet of the scrubber by more than 50%, and further reduce _SO2 in the flue gas at the inlet of the scrubber by more than 70%, and reduce _SO3 concentration by more than 90%. The use of the sulfur transfer agent can pre-remove SOx in the flue gas, reduce the operating load and absorption liquid consumption of the flue gas scrubber, for example, the sulfur transfer agent can remove 50% of _SO2 in the flue gas, then the absorption liquid consumption of the scrubber will also be reduced by about 50%, and accordingly, the salt content of the system circulating liquid and the external wastewater collected by the drainage pipeline 18 is also reduced, so that the salt content of the water vapor brought out of the chimney by the flue gas is reduced. In addition, the sulfur transfer agent can efficiently capture SO ₃ that is difficult to handle in the wet scrubbing system and reduce the blue smoke generated by SO ₃ aerosol. When the sulfur transfer agent is used, the operational flexibility of the scrubber is also greatly improved. For example, the last stage of absorption liquid spraying can be directly converted to clean water spraying, that is, clean water instead of absorption liquid is supplied to the original last stage of absorption liquid spraying device, thereby implementing the technical solution of the present disclosure without any engineering modification of the scrubber.

In the catalytic cracking method provided by the present disclosure, there are no special restrictions on the process type, processing scale, catalyst, etc. of the catalytic cracking. The regeneration operation mode can be complete regeneration or incomplete regeneration. The flue gas at the outlet of the regenerator generally needs to be subjected to waste heat recovery, for example, heat exchange through a waste heat boiler and/or a heat exchange device, and then introduced into the flue gas scrubber for scrubbing treatment, that is, the catalytic cracking method of the present disclosure can also include: first recovering the waste heat of the flue gas, and then performing the scrubbing step.

The following briefly introduces the method of the present disclosure described in the specific implementation manner and the flue gas scrubbing tower used to implement the method of the present disclosure in conjunction with Figures 1-2 to further illustrate the present disclosure, but does not constitute a limitation to the present disclosure.

Take the flue gas scrubber as shown in FIG1 as an example. The flue gas enters the tower body 3 of the flue gas scrubber from the flue gas inlet 2 and flows upward, contacts the absorbent sprayed by the absorbent nozzle 10 of the first-stage absorbent spraying device, and the absorbent after contact enters the absorbent storage tank at the bottom of the scrubber, and the flue gas continues to rise, through the ventilation holes in the absorbent storage tank provided below the second-stage absorbent spraying device, contacts the absorbent sprayed by the absorbent nozzle 10 of the second-stage absorbent spraying device, and the absorbent after contact is collected by the absorbent storage tank, and then the flue gas enters the chimney 5, passes through the flue gas through-holes opened in the tank body and/or tank wall (for the conical tank, it is the conical tank wall) of the clean water storage tank, passes through the clean water storage tank 13 provided in the chimney, passes through the gas-liquid contact strengthening component 14, contacts the clean water sprayed by the clean water nozzle 8 of the clean water spraying device, and then is discharged from the flue gas outlet 6. There are 4 clean water nozzles 8, which are arranged at an angle of 90° along the circumferential direction, as shown in FIG2. The washing water collected in the clean water storage tank 13 is circulated and transported to the clean water nozzle 8 for spraying through the clean water supply pump 7, and can also enter the absorption liquid storage tank through the pipeline. The absorption liquid is transported to the absorption liquid storage tank through the absorbent solution and water replenishment pipelines 1 and 4, and the absorption liquid can be circulated and used under the action of the absorption liquid circulation pumps 9 and 11. The external wastewater is collected by the external wastewater pipeline 12, and the flue gas condensate is collected by the flue gas outlet 6.

The present disclosure is further described below through examples, but the present disclosure is not limited thereby.

Example 1

1.5 wt% of sulfur transfer agent prepared according to Example 5 of patent CN1323132C was added to the catalyst system of the catalytic cracking unit, and the regenerated flue gas entered the flue gas inlet of the scrubber after heat exchange through the waste heat boiler. The average composition of the main pollutants in the inlet flue gas was: SO ₂ : 95mg/m ³ , SO ₃ : 10mg/m ³ , NOx: 85mg/m ³ , solid dust: 115mg/m ³ . The flue gas flow rate was 5100Nm ³ /min, and the inlet temperature was 170℃.

The structure of the washing tower is shown in Figure 1, and a first-level clean water spray device is set in the chimney 5. The clean water nozzle 8 adopts a polytetrafluoroethylene spiral nozzle, the number is 4, and it is arranged at an angle of 90° along the circumference, as shown in Figure 2. A honeycomb structured filler with a bed height of 0.3m is filled between the clean water nozzle 8 and the clean water storage tank 13. The temperature of the fresh clean water provided to the clean water spray device is 20°C, the dissolved solid content is 0.002% by weight, the replenishment amount is 1t/h (0.0033kg/ ^Nm3 flue gas), the outlet pressure of the clean water nozzle pump is 0.4MPa, and the total amount of spraying is 0.02kg water/ ^Nm3 flue gas. The clean water is directly sent to the clean water spray device (clean water nozzle) by the clean water supply pump 7, and the clean water collected by the clean water storage tank 13 after contacting the flue gas is also sent to the clean water supply pump 7 for recycling. The total amount of water replenishment for the whole tower (the sum of the evaporation amount and the amount of wastewater discharged) is 20t/h. The absorbent is supplemented with a 30 wt% NaOH aqueous solution (absorbent solution), and the average supplement amount of the solution is 105 L/h. The pH of the absorption liquid is 6.8-7.2. The absorbent solution and water (fresh clean water) enter the washing tower through the replenishment pipeline respectively, and the two are combined and injected into the absorption liquid storage tank at the bottom of the tower. After being fully mixed, they are transported to the absorption liquid nozzle through the absorption liquid circulation pump for spraying. The soluble solid content of the discharged wastewater is 1.1 wt%, and the soluble solid content of the flue gas condensate collected from the flue gas outlet 6 is 0.02 wt%.

The pollutants at the chimney outlet are composed of: SO ₂ : 15mg/m ³ , SO ₃ (containing sulfuric acid mist and/or aerosol): 10mg/m ³ (including all sulfate-containing substances), NOx: 70mg/m ³ , solid dust: 19mg/m ³ . The smoke at the chimney outlet is discharged nearly vertically, the tailing phenomenon is eliminated, and there is no blue smoke plume settling or spreading in the factory area.

Example 2

1.8 wt% of sulfur transfer agent prepared according to Example 5 of patent CN1323132C was added to the catalyst system of the catalytic cracking unit, and the regenerated flue gas entered the flue gas inlet of the scrubber after heat exchange through the waste heat boiler. The average composition of the main pollutants in the inlet flue gas was: SO ₂ : 65mg/m ³ , SO ₃ : 10mg/m ³ , NOx: 82mg/m ³ , solid dust: 124mg/m ³ . The flue gas flow rate was 5100Nm ³ /min, and the inlet temperature was 170℃.

The difference between the washing tower structure and the embodiment 1 is that the clean water spraying device is not set in the chimney, but the absorption liquid feed valve of the second-stage absorption liquid spraying device in the washing tower body is closed, and it is directly converted to clean water spraying, that is, clean water is supplied to it instead of absorption liquid. The temperature of the fresh clean water provided to the clean water spraying device is 20°C, the dissolved solid content is 0.002% by weight, the replenishment amount is 2t/h (0.0065kg/ ^Nm3 flue gas), the outlet pressure of the clean water nozzle pump is 0.4MPa, and the total amount of spraying is 0.03kg water/ ^{Nm3 flue} gas. The clean water is directly sent to the clean water spraying device (clean water nozzle) by the clean water supply pump 7, and the clean water collected by the clean water storage tank 13 after contacting with the flue gas is also sent to the clean water supply pump 7 for recycling. The total amount of water replenishment for the whole tower (the sum of the evaporation amount and the amount of wastewater discharged) is 20t/h, and the absorbent is supplemented by a 30% by weight NaOH aqueous solution (absorbent solution), and the replenishment amount of the solution is an average of 70L/h. The pH of the absorption liquid is 6.8-7.2. The absorbent solution and water (fresh clean water) enter the scrubbing tower through the supplementary pipeline respectively. After the two are merged together, they are injected into the absorption liquid storage tank at the bottom of the tower. After being fully mixed, they are transported to the absorption liquid nozzle through the absorption liquid circulation pump for spraying. The dissolved solid content of the discharged wastewater is 0.9%, and the dissolved solid content of the flue gas condensate collected from the flue gas outlet 6 is 0.012%.

The pollutants at the chimney outlet are composed of: SO ₂ : 17mg/m ³ , SO ₃ (containing sulfuric acid mist and/or aerosol): 6mg/m ³ (including all sulfate-containing substances), NOx: 72mg/m ³ , solid dust: 14mg/m ³ . The smoke at the chimney outlet is discharged nearly vertically, the tailing phenomenon is eliminated, and there is no blue smoke plume settling or spreading in the factory area.

Example 3

The catalyst system of the catalytic cracking unit does not contain sulfur transfer agent. The regenerated flue gas enters the inlet of the scrubber after heat exchange in the waste heat boiler. The average composition of the main pollutants in the inlet flue gas is SO ₂ : 850mg/m ³ , SO ₃ : 590mg/m ³ , NOx: 90mg/m ³ , solid dust: 120mg/m ³ . The flue gas flow rate is 5100Nm ³ /min, and the inlet temperature is 170℃.

The structure of the washing tower is the same as that of Example 1. The temperature of the fresh clean water provided to the clean water spraying device is 20°C, the dissolved solid content is 0.002% by weight, the replenishment amount is 5t/h (0.016kg/ ^Nm3 flue gas), the outlet pressure of the clean water nozzle pump is 0.4MPa, the total amount of spraying is 0.12kg water/ ^Nm3 flue gas, the clean water is directly sent to the clean water spraying device (clean water nozzle) by the clean water supply pump 7, and the clean water collected by the clean water storage tank 13 after contact with the flue gas is also sent to the clean water supply pump 7 for recycling. The total amount of water replenishment for the whole tower (the sum of the evaporation amount and the amount of wastewater discharged) is 23t/h. The absorbent is supplemented with a 30% by weight NaOH aqueous solution (absorbent solution), and the replenishment amount of the solution is an average of 680L/h. The pH of the absorption liquid is 6.7-7.0. The absorbent and the absorption liquid water (fresh clean water) enter the washing tower through the supplementary pipeline respectively. After the two are merged together, they are injected into the absorption liquid storage tank at the bottom of the tower. After being fully mixed, they are transported to the absorption liquid nozzle through the absorption liquid circulation pump for spraying. The soluble solid content of the discharged wastewater is 4.3% by weight, and the soluble solid content of the flue gas condensate collected from the flue gas outlet 6 is 0.025% by weight.

The pollutants at the chimney outlet are: SO ₂ : 16mg/m ³ , SO ₃ (including sulfuric acid mist and/or aerosol): 20mg/m ³ (including all sulfate-containing substances), NOx: 70mg/m ³ , solid dust: 10mg/m ³ . The smoke at the chimney outlet is almost discharged vertically, the tail length is shortened, and there is no blue smoke plume settling or spreading in the factory area.

Comparative Example 1

The catalyst system of the catalytic cracking unit does not contain sulfur transfer agent. The regenerated flue gas enters the inlet of the scrubber after heat exchange in the waste heat boiler. The average composition of the main pollutants in the inlet flue gas is SO ₂ : 850mg/m ³ , SO ₃ : 590mg/m ³ , NOx: 90mg/m ³ , solid dust: 120mg/m ³ . The flue gas flow rate is 5100Nm ³ /min, and the inlet temperature is 170℃.

The structure of the washing tower is different from that of Example 1 in that no clean water spraying device is provided. The total water replenishment of the whole tower is 22 t/h, and a 30 wt% NaOH aqueous solution (absorbent solution) is used to replenish the absorbent, and the replenishment amount of the solution is 620 L/h on average. The pH of the absorption liquid is 6.8-7.2, the soluble solid content of the discharged wastewater is 3.5%, and the soluble solid content of the flue gas condensate collected from the flue gas outlet 6 is 0.26%.

The pollutants at the chimney outlet are: SO ₂ : 20mg/m ³ , SO ₃ (including sulfuric acid mist and/or aerosol): 420mg/m ³ , NOx: 78mg/m ³ , solid dust: 15mg/m ³ . The smoke tailing phenomenon is serious, spreading horizontally for about 100 meters, and the blue smoke plume settles and diffuses around the factory area.

The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims (14)

1. A flue gas scrubbing method, the method comprising: and introducing the flue gas into a flue gas washing tower to contact with an absorption liquid containing an absorbent, and contacting the flue gas contacted with the absorption liquid with clean water before exiting the tower.

2. The method of claim 1, wherein the ratio of clean water to flue gas is: 0.001-0.5kg water/Nm ³ smoke.

3. The method according to claim 1, wherein the clean water is at least one selected from fresh water, reclaimed water, and desalted wastewater;

Preferably, the cleaning water has a soluble solids content not higher than the soluble solids content of the flue gas condensate collected by the flue gas outlet of the scrubber, preferably not higher than 0.01 wt%.

4. The method of claim 1, wherein the flue gas is at least one selected from the group consisting of FCC regeneration flue gas, thermal power plant tail gas, boiler generated exhaust gas, burner generated exhaust gas, and calciner generated exhaust gas;

the temperature of the flue gas is 50-500 ℃, preferably 100-300 ℃.

5. The method of claim 1, wherein the flue gas contains contaminants comprising at least one of SOx, NOx, NH ₃、CO、CO₂、Cl₂, HCl, and solid dust;

Preferably, the flue gas contains: SOx at a concentration of 20-10000mg/m ³, NOx at a concentration of 20-2000mg/m ³, and solid dust at a concentration of 10-1000mg/m ³; wherein the concentration is a concentration in a standard state.

6. The method according to claim 1, wherein an absorption liquid spraying device and a cleaning water spraying device are sequentially arranged in the washing tower along the flow direction of the flue gas, and the cleaning water spraying device comprises a cleaning water nozzle (8) for spraying cleaning water so that the flue gas contacted by the absorption liquid is contacted with the cleaning water before exiting the tower;

The pump outlet pressure of the cleaning water is 0.1-10MPa, preferably 0.1-1.0MPa.

7. The method according to claim 1 or 6, wherein the flue gas scrubber comprises a scrubber tower body (3) and a chimney (5) in fluid communication with the scrubber tower body (3), the clean water nozzle (8) being located within the chimney (5).

8. The method according to claim 6, wherein a clean water storage tank (13) is arranged between the clean water spraying device and the absorption liquid spraying device and is used for collecting clean water after the clean water is contacted with the flue gas;

the collected wash water may be sent to the clean water spray device for circulation for contact with the flue gas and/or the wash water may be sent to the absorption liquid spray device as make-up water for the absorption liquid.

9. The method according to claim 8, wherein the number of absorption liquid spraying devices and cleaning water spraying devices is one or more, respectively, and the cleaning water reservoir (13) is located between the cleaning water nozzle (8) of the first stage and the absorption liquid spraying device of the last stage in the flow direction of the flue gas.

10. The method according to claim 6, wherein the number of cleaning water nozzles (8) is 1-12; when the number of the cleaning water nozzles (8) is more than 1, the cleaning water nozzles (8) are arranged at equal intervals in the circumferential direction and/or the radial direction;

the cleaning water nozzle (8) is at least one selected from a spiral nozzle, a fan nozzle and a ring nozzle.

11. The method of claim 1, wherein the method further comprises: and enabling the flue gas contacted with the absorption liquid to pass through a gas-liquid contact strengthening component (14) and then contact with the cleaning water, wherein the gas-liquid contact strengthening component (14) is a filler and/or a tower plate.

12. The method according to claim 1, wherein the pH of the absorption liquid is 5-10, preferably 6-8;

The absorbent is at least one of soluble hydroxide of alkali metal and soluble salt of alkali metal; preferably, the absorbent is at least one selected from sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate and potassium hydroxide.

13. A catalytic cracking process, comprising: contacting hydrocarbon oil with a catalyst to perform catalytic cracking reaction, regenerating the reacted catalyst, and then washing the regenerated flue gas according to the method of any one of claims 1-12;

The catalyst contains 0.1 to 10 wt.% of a sulfur transfer agent, preferably 1 to 5 wt.% of a sulfur transfer agent, which is used to reduce the SOx concentration in flue gas under the regeneration conditions.

14. The method of claim 13, wherein the method further comprises: and firstly, recovering waste heat of the flue gas, and then, washing.