Preparation method for preparing denitration, dioxin and VOCs (volatile organic compounds) removal integrated catalyst by fractional precipitation method and prepared catalyst
阅读说明：本技术 分步沉淀法制备脱硝脱二噁英脱VOCs一体化催化剂的制备方法、制得的催化剂 (Preparation method for preparing denitration, dioxin and VOCs (volatile organic compounds) removal integrated catalyst by fractional precipitation method and prepared catalyst ) 是由 王光应 赵羽 梁燕 于 2021-09-08 设计创作，主要内容包括：本发明公开分步沉淀法制备脱硝脱二噁英脱VOCs一体化催化剂的制备方法,涉及催化剂技术领域,本发明以纳米二氧化钛为催化剂载体,氧化钴氧化锰氧化铜为活性物质,其中活性物质的负载方法为分步沉淀法。本发明还提供采用上述方法制得的催化剂。本发明的有益效果在于：本发明供述的催化剂,可在200℃反应条件下对NO-(x)、二噁英和VOCs的脱除效率分别达到了达80％、90％和90％以上。(The invention discloses a preparation method of an integrated catalyst for denitration, dioxin removal and VOCs removal by a fractional precipitation method, and relates to the technical field of catalysts. The invention also providesFor the catalyst prepared by the method. The invention has the beneficial effects that: the catalyst provided by the invention can be used for NO under the reaction condition of 200 DEG C x The removal efficiency of dioxin and VOCs respectively reaches more than 80%, 90% and 90%.)
1. The preparation method for preparing the denitration, dioxin and VOCs integrated catalyst by a fractional precipitation method is characterized by comprising the following steps of: the method comprises the following steps:
(1) mixing and stirring nano titanium dioxide and water to obtain a carrier suspension;
(2) slowly adding a cobalt precursor salt solution into the carrier suspension in the step (1), simultaneously dripping alkali liquor to adjust the pH value, standing the obtained mixed suspension, performing suction filtration and separation, drying the obtained solid, and then roasting at a low temperature to obtain an intermediate A;
(3) mixing and stirring a manganese precursor salt solution and the intermediate A, slowly adding an alkali liquor to adjust the pH value, standing the obtained mixed suspension, performing suction filtration and separation, drying the obtained solid, and then performing low-temperature roasting to obtain an intermediate B;
(4) stirring and mixing the copper precursor salt solution and the intermediate B, slowly adding alkali liquor to adjust the pH value, standing the obtained mixed suspension, performing suction filtration and separation, drying the obtained solid, and then performing high-temperature roasting to obtain the integrated catalyst for denitration, dioxin removal and VOCs removal.
2. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the specific surface area of the nano titanium dioxide is 50-150m2/g。
3. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the mass ratio of metal oxides in the denitration, dioxin and VOCs removal integrated catalyst is cobalt oxide: manganese oxide: 0.5-1.5% of copper oxide: 5-15: 1-3.
4. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the precursor salts of cobalt, manganese and copper comprise nitrate and chlorate.
5. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the alkali liquor in the steps (2), (3) and (4) is NaOH, KOH or Na2CO3、K2CO3、NaHCO3And KHCO3The concentration of the alkali liquor is 1-10M.
6. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: and (3) adjusting the pH value of the mixed suspension to 9-11 by adopting alkali liquor in the steps (2), (3) and (4), and standing the mixed suspension for 2-12 h.
7. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the drying temperature in the steps (2), (3) and (4) is 80-100 ℃.
8. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the roasting temperature in the steps (2) and (3) is 150 ℃.
9. The preparation method of the denitration and dioxin and VOCs integrated catalyst by the fractional precipitation method according to claim 1 is characterized in that: the roasting temperature in the step (4) is 300-450 ℃, and the roasting atmosphere is air.
10. An integrated catalyst for denitration, dioxin and VOCs removal prepared by the fractional precipitation method of any one of claims 1 to 9.
Technical Field
The invention relates to the technical field of catalysts, in particular to a preparation method for preparing an integrated catalyst for denitration, dioxin removal and VOCs removal by a fractional precipitation method and a prepared catalyst.
Background
The energy structure of China is mainly coal, and NO produced by the coalxThe emission amount of the fuel is increased year by year, and the fuel is the first in the world at present. The fifth five-year planning compendium for the national economy and social development of the people's republic of China (compendium for short) unprecedentedly proposes a green development concept, and the environmental protection work is improved to a new historical height by penetrating the green development concept throughout the planning. The compendium proposes the tasks and objectives of strengthening the atmospheric pollution control and improving the environmental quality, and proposes to treat SO2And NOxAnd continuously implementing total amount control, and increasing fine particles as a constraint index. The annual output of urban garbage in China is about 1 hundred million tons, the urban garbage is increasing at a speed of about 10 percent per year, and at least 2/3 cities in China are surrounded by garbage. In the plan of China, in the coming decade, 3% of the total amount of garbage to be treated adopts an incineration mode, but the tail gas of the incineration of the garbage generally contains nitrogen oxides, dioxins, VOCs and the like. It is expected that the problem of atmospheric pollution will become increasingly serious as the proportion of waste incineration increases.
The multi-pollutant emission reduction technology which is applied to industrial production at the earliest is an activated carbon method which can effectively remove SO in sintering flue gas2、NOxDioxin, VOCs, alkali/heavy metal and other acid gases, and activated carbon can be analyzed and regenerated, but the method has huge investment and high operation cost. Catalysts currently on the market, usually only for dioxins or NOxOr removing single substances of VOCs or removing two substances, such as a denitration and dioxin removal catalyst disclosed in the patent with the publication number of CN 106345454A. The stepwise catalytic removal requires more complex engineering equipment and results in increased costs.
Disclosure of Invention
The technical problem to be solved by the invention is that NO is removed by step-by-step catalysis in the prior artxThe cost is increased due to the fact that more complex engineering equipment is needed for dioxin and VOCs, and the preparation method for preparing the denitration and dioxin and VOCs integrated catalyst by the step-by-step precipitation method and the prepared catalyst are provided.
The invention solves the technical problems through the following technical means:
the preparation method for preparing the denitration, dioxin and VOCs integrated catalyst by the fractional precipitation method comprises the following steps:
(1) mixing and stirring nano titanium dioxide and water to obtain a carrier suspension;
(2) slowly adding a cobalt precursor salt solution into the carrier suspension in the step (1), simultaneously dripping alkali liquor to adjust the pH value, standing the obtained mixed suspension, performing suction filtration and separation, drying the obtained solid, and then roasting at a low temperature to obtain an intermediate A;
(3) mixing and stirring a manganese precursor salt solution and the intermediate A, slowly adding an alkali liquor to adjust the pH value, standing the obtained mixed suspension, performing suction filtration and separation, drying the obtained solid, and then performing low-temperature roasting to obtain an intermediate B;
(4) stirring and mixing the copper precursor salt solution and the intermediate B, slowly adding alkali liquor to adjust the pH value, standing the obtained mixed suspension, performing suction filtration and separation, drying the obtained solid, and then performing high-temperature roasting to obtain the integrated catalyst for denitration, dioxin removal and VOCs removal.
Has the advantages that: the catalyst prepared by the step method can reach NO at the reaction temperature of 200 DEG CxThe removal rate is more than 80%, the removal rate of dioxin is more than 90%, and the removal efficiency of VOCs is more than 90%.
If fractional precipitation is not adopted, the obtained catalyst is used for NOxAnd the removal efficiency of dioxins and VOCs is low.
Cobalt oxide and manganese oxide can provide active sites for SCR denitration reaction to remove NOxConversion to N2And H2O; copper oxide and manganese oxide provide active sites for catalytic oxidative degradation of dioxin and VOCs, and dioxin and VOCs are thoroughly mineralized into CO2、H2O and HCl. Therefore, the ternary composite oxide catalyst can synergistically remove NOxDioxin and VOCs, which are three-way catalysts, can simplify flue gas post-treatment equipment and reduce the dosage and cost of the catalysts.
The addition of cobalt oxide can effectively reduce NO adsorbed on the surface of the catalystxActivation energy and increase of NO in gas phase2Thereby remarkably improving the SCR denitration activity of the catalyst.
The manganese oxide mainly improves the low-temperature SCR activity of the catalyst, and when the smoke temperature is higher than 300 ℃ and hydrocarbon and HCl exist in smoke, the concentration of dioxin substances at the SCR outlet is higher than that at the SCR inlet. Therefore, in order to prevent the regeneration of dioxin and ensure the efficiency of dioxin removal, the optimum temperature for the catalytic oxidation of dioxin is below 300 ℃.
The catalytic degradation of dioxin can be divided into three steps: dioxin is adsorbed on active sites on the surface of the catalyst, the dioxin obtains lattice oxygen of the active sites on the surface of the catalyst, and the dioxin obtaining the lattice oxygen is decomposed until the dioxin is completely mineralized. The copper oxide can provide a large amount of lattice oxygen for the catalytic degradation process of the dioxin, so that the catalyst modified by the copper oxide has higher dioxin removal performance. The degradation process of VOCs is similar to that of dioxins.
Preferably, the specific surface area of the nano titanium dioxide is 50-150m2/g。
Has the advantages that: the nano titanium dioxide carrier has high specific surface area, can effectively disperse active components, and has SCR denitration activity.
Preferably, the specific surface area of the nano titanium dioxide is 100m2/g。
Preferably, the mass ratio of the metal oxides in the denitration, dioxin and VOCs removal integrated catalyst is cobalt oxide: manganese oxide: 0.5-1.5% of copper oxide: 5-15: 1-3.
Preferably, the cobalt, manganese, copper precursor salts include nitrates, chlorates.
Preferably, the alkali liquor in the steps (2), (3) and (4) is NaOH, KOH or Na2CO3、K2CO3、NaHCO3And KHCO3The concentration of the alkali liquor is 1-10M.
Preferably, the pH value of the mixed suspension is adjusted to 9-11 by alkali liquor in the steps (2), (3) and (4), and the standing time of the mixed suspension is 2-12 h.
Preferably, the drying temperature in the steps (2), (3) and (4) is 80-100 ℃.
Preferably, the calcination temperature in the steps (2) and (3) is 150 ℃.
Preferably, the calcination temperature in the step (4) is 300-450 ℃, and the calcination atmosphere is air.
The denitration and dioxin and VOCs removal integrated catalyst prepared by the method is adopted.
The invention has the advantages that: the catalyst prepared by the step method can reach NO at the reaction temperature of 200 DEG CxThe removal rate is more than 80%, the removal rate of dioxin is more than 90%, and the removal efficiency of VOCs is more than 90%.
If fractional precipitation is not adopted, the obtained catalyst is used for NOxAnd the removal efficiency of dioxins and VOCs is low.
Cobalt oxide and manganese oxide can provide active sites for SCR denitration reaction to remove NOxConversion to N2And H2O; copper oxide and manganese oxide provide active sites for catalytic oxidative degradation of dioxin and VOCs, and dioxin and VOCs are thoroughly mineralized into CO2、H2O and HCl. Therefore, the ternary composite oxide catalyst can synergistically remove NOxDioxin and VOCs, which are three-way catalysts, can simplify flue gas post-treatment equipment and reduce the dosage and cost of the catalysts.
The addition of cobalt oxide can effectively reduce NO adsorbed on the surface of the catalystxActivation energy and increase of NO in gas phase2Thereby remarkably improving the SCR denitration activity of the catalyst.
The manganese oxide mainly improves the low-temperature SCR activity of the catalyst, and when the smoke temperature is higher than 300 ℃ and hydrocarbon and HCl exist in smoke, the concentration of dioxin substances at the SCR outlet is higher than that at the SCR inlet. Therefore, in order to prevent the regeneration of dioxin and ensure the efficiency of dioxin removal, the optimum temperature for the catalytic oxidation of dioxin is below 300 ℃.
The catalytic degradation of dioxin can be divided into three steps: dioxin is adsorbed on active sites on the surface of the catalyst, the dioxin obtains lattice oxygen of the active sites on the surface of the catalyst, and the dioxin obtaining the lattice oxygen is decomposed until the dioxin is completely mineralized. The copper oxide can provide a large amount of lattice oxygen for the catalytic degradation process of the dioxin, so that the catalyst modified by the copper oxide has higher dioxin removal performance. The degradation process of VOCs is similar to that of dioxins.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Test materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
The specific techniques or conditions not specified in the examples can be performed according to the techniques or conditions described in the literature in the field or according to the product specification.
Example 1
The preparation method for preparing the denitration, dioxin and VOCs integrated catalyst by the fractional precipitation method comprises the following steps:
1) 10g of nano titanium dioxide (specific surface area 50 m)2/g) and 200mL of water are fully mixed to obtain a carrier suspension and the carrier suspension is continuously stirred;
2) 0.446g of Co (NO)3)2·6H2Dissolving O in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding the mixed metal salt solution into the carrier suspension, and simultaneously dripping NaOH with the total concentration of 1M: na (Na)2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 9, the obtained mixed suspension is kept stand for 2 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at the temperature of 80 ℃ and then is roasted at the low temperature of 150 ℃ for 3 hours, and an intermediate A is obtained;
3) 5.80g of Mn (NO)3)2(50% aqueous solution) and intermediateStirring and mixing the body A in 200mL of water to obtain a mixed metal salt solution with a certain concentration, and slowly dropping NaOH with the total concentration of 1M: na (Na)2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 9, the obtained mixed suspension is kept stand for 2 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at the temperature of 80 ℃ and then is roasted at the low temperature of 150 ℃ for 3 hours, and an intermediate B is obtained;
4) 0.698g of Cu (NO)3)2·3H2Stirring and mixing the O and the intermediate B in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding alkali liquor to adjust the pH value to 9, standing the obtained mixed suspension for 2h to fully precipitate metal salt, performing suction filtration and separation, drying the obtained solid at 80 ℃, and then roasting at 300 ℃ for 3 hours to obtain the integrated catalyst for removing the NOx, the dioxin and the VOCs.
Example 2
The preparation method for preparing the denitration, dioxin and VOCs integrated catalyst by the fractional precipitation method comprises the following steps:
1) 10g of nano titanium dioxide (specific surface area 100 m)2/g) and 200mL of water are fully mixed to obtain a carrier suspension and the carrier suspension is continuously stirred;
2) 0.892g of Co (NO)3)2·6H2Dissolving O in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding the mixed metal salt solution into the carrier suspension, and simultaneously dripping KOH with the total concentration of 5M: k2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 10, the obtained mixed suspension is kept stand for 7 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at 90 ℃ and then is roasted at the low temperature of 150 ℃ for 3 hours, and an intermediate A is obtained;
3) adding 11.6g of Mn (NO)3)2(50% aqueous solution) and the intermediate A are stirred and mixed in 200mL of water to obtain a mixed metal salt solution with a certain concentration, and KOH with the total concentration of 5M is slowly dropped: k2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 10, the obtained mixed suspension is kept stand for 7 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at 90 ℃ and then is burnt at low temperature of 150 ℃ for 3 hours, and an intermediate B is obtained;
4) 1.396g of Cu (NO)3)2·3H2Stirring and mixing the O and the intermediate B in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding alkali liquor to adjust the pH value to 10, standing the obtained mixed suspension for 7h to fully precipitate metal salt, performing suction filtration and separation, drying the obtained solid at 90 ℃, and then roasting at the high temperature of 400 ℃ for 3 hours to obtain the integrated catalyst for removing the NOx, the dioxin and the VOCs.
Example 3
The preparation method for preparing the denitration, dioxin and VOCs integrated catalyst by the fractional precipitation method comprises the following steps:
1) 10g of nano titanium dioxide (specific surface area 150 m)2/g) and 200mL of water are fully mixed to obtain a carrier suspension and the carrier suspension is continuously stirred;
2) 1.0938g CoCl2·6H2Dissolving O in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding the mixed metal salt solution into the carrier suspension, and simultaneously dripping NaOH with the total concentration of 10M: NaHCO 231: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 11, the obtained mixed suspension is kept stand for 12 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at 100 ℃ and then is roasted at the low temperature of 150 ℃ for 3 hours, and an intermediate A is obtained;
3) 6.11g of MnCl2And stirring and mixing the intermediate A and 200mL of water to obtain a mixed metal salt solution with a certain concentration, and slowly dripping NaOH with the total concentration of 10M: NaHCO 231: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 11, the obtained mixed suspension is kept stand for 12 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at 100 ℃ and then is roasted at the low temperature of 150 ℃ for 3 hours, and an intermediate B is obtained;
4) 1.478g of CuCl2·2H2Stirring and mixing the O and the intermediate B in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding alkali liquor to adjust the pH value to 11, standing the obtained mixed suspension for 12h to fully precipitate metal salt, performing suction filtration and separation, drying the obtained solid at 100 ℃, and then roasting at the high temperature of 450 ℃ for 3 hours to obtain the integrated catalyst for removing the NOx, the dioxin and the VOCs.
Comparative example 1
1) 10g of nano titanium dioxide (specific surface area 50 m)2/g) and 200mL of water are fully mixed to obtain a carrier suspension and the carrier suspension is continuously stirred;
2) 5.80g of Mn (NO)3)2(50% aqueous solution) was mixed with 200mL of water to obtain a mixed metal salt solution of a certain concentration, and slowly added to the above carrier suspension while dropping NaOH of a total concentration of 1M: na (Na)2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 9, the obtained mixed suspension is kept stand for 2 hours to ensure that metal salt is fully precipitated, the mixed suspension is filtered and separated, and the obtained solid is dried at the temperature of 80 ℃ and then is roasted at the high temperature of 300 ℃ for 3 hours.
Comparative example 2
1) 10g of nano titanium dioxide (specific surface area 50 m)2/g) and 200mL of water are fully mixed to obtain a carrier suspension and the carrier suspension is continuously stirred;
2) 0.446g of Co (NO)3)2·6H2Dissolving O in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding the mixed metal salt solution into the carrier suspension, and simultaneously dripping NaOH with the total concentration of 1M: na (Na)2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 9, the obtained mixed suspension is kept stand for 2 hours to fully precipitate metal salt, the mixed suspension is subjected to suction filtration and separation, the obtained solid is dried at the temperature of 80 ℃ and then is roasted at the low temperature of 150 ℃ for 3 hours, and an intermediate A is obtained;
3) 0.698g of Cu (NO)3)2·3H2And stirring and mixing the O and the intermediate A in 200mL of water to obtain a mixed metal salt solution with a certain concentration, and slowly dripping NaOH with the total concentration of 1M: na (Na)2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 9, the obtained mixed suspension is kept stand for 2 hours to ensure that metal salt is fully precipitated, the mixed suspension is filtered and separated, and the obtained solid is dried at the temperature of 80 ℃ and then is roasted at the high temperature of 300 ℃ for 3 hours.
Comparative example 3
1) 10g of nano titanium dioxide (specific surface area 50 m)2/g) and 200mL of water are fully mixed to obtain a carrier suspension and the carrier suspension is continuously stirred;
2) 0.446g of Co (NO)3)2·6H2O、5.80g Mn(NO3)2(50% aqueous solution) and 0.698gCu (NO)3)2·3H2Dissolving O in 200mL of water to obtain a mixed metal salt solution with a certain concentration, slowly adding the mixed metal salt solution into the carrier suspension, and simultaneously dripping NaOH with the total concentration of 1M: na (Na)2CO31: 1 (molar ratio) alkali liquor is used for adjusting the pH value to 9, the obtained mixed suspension is kept stand for 2 hours to ensure that metal salt is fully precipitated, the mixed suspension is filtered and separated, and the obtained solid is dried at the temperature of 80 ℃ and then is roasted at the high temperature of 300 ℃ for 3 hours.
Experimental data and analysis:
the performance of the catalysts obtained in example 1, comparative example 1 to comparative example 3 was measured.
Wherein NOxThe method for measuring the removal rate of dioxin and VOCs comprises the following steps:
the performance test was carried out in a fixed bed, and the catalyst was cut into 20mm by 30mm samples in the direction of the channels and placed in the bed along the axis of the reactor. The components of the flue gas are NO (1000ppm) and NH3(1000ppm), chlorobenzene (2ppm), toluene (200ppm), O2(6vol.％)、N2As carrier gas, the airspeed of the mixed gas is 6000h-1(ii) a The reaction temperature was 200 ℃. Before introducing the reaction gas, introducing air into the fixed bed reactor, raising the temperature to 400 ℃, keeping the temperature for 4 hours, reducing the temperature to the reaction temperature, and then introducing the reaction gas for performance test.
The catalyst of the invention can reach NO at the reaction temperature of 200 ℃ through measurementxThe removal rate is more than 80%, the removal rate of dioxin is more than 90%, and the removal efficiency of VOCs is more than 90%. The catalyst has good use performance and can treat NO in smokexAnd dioxin and VOCs are effectively removed.
In the catalyst of comparative example 1, in which only manganese salt was added, NO was achievedxThe removal rate is more than 80%, but the removal activity to dioxin and VOCs is not high; in comparative example 2, only copper salt and cobalt salt are added, so that the removal rates of dioxin and VOCs are over 90 percent, but NO NO is addedxAnd (4) removing the function. So that NO can be realized only by compounding three metals of manganese, cobalt and copperxAnd the three-effect synergistic removal of dioxin and VOCs. In comparative example 3, three metal salts were coprecipitatedTo the catalyst, albeit with NOxThe catalytic activity of the three-effect synergistic removal of dioxin and VOCs is low, and NO is generated at 200 DEG CxThe removal efficiencies of dioxins and VOCs were 50%, 30% and 35%, respectively. Therefore, the fractional precipitation method can form a good catalytic interface between metal oxides, and has higher catalytic removal activity compared with a metal oxide solid solution formed by coprecipitation.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
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