Active coke modification-based demercuration adsorbent as well as preparation method and application thereof

Abstract

The invention belongs to the field of pollutant control, and particularly discloses a demercuration adsorbent based on active coke modification and a preparation method and application thereof.The preparation method comprises the steps that active coke is heated to 300 DEG C-600 DEG C in the mixed atmosphere of inert gas and SO2 so as to be subjected to pyrolysis modification, cooling is conducted after the reaction is finished, and the demercuration adsorbent based on active coke modification is obtained. According to the present invention, the SO2 active coke modification temperature is reduced to 300-600 DEG C, such that the demercuration principle of the prepared demercuration adsorbent can be changed, the prepared demercuration adsorbent is suitable for the low-temperature demercuration working condition, and the good demercuration effect and the good sulfur resistance can be obtained at the low reaction temperature.

Description

Technical Field

[0001] The present application belongs to the field of pollutant control, and more specifically, relates to a mercury removal adsorbent based on modified activated coke, and a preparation method and application thereof. Background Art

[0002] Mercury is one of the most volatile substances produced by coal-fired boilers. It has attracted widespread attention due to its toxicity, cumulative effects on the biosphere, and potential harm to humans and animals. At present, China's Ministry of Environmental Protection has issued the "Air Pollutant Emission Standards for Powder Coal Plants" (GB13223-2011), which limits mercury emissions to less than 30ppb. At the same time, 87 countries including China signed the "Minamata Convention on Mercury" in 2013, so the task of reducing mercury release in flue gas is imminent. At present, mercury removal adsorbents are mainly used to remove mercury from flue gas.

[0003] Traditional coal-fired power plants remove mercury and other conventional pollutants through means such as SCR, ESP and WFGD, but as emission standards become increasingly stringent, it is necessary to achieve near-zero emissions of pollutants. The prior art proposes a low-temperature deep removal technology for coal-fired pollutants (Cold Oxidation Adsorption Process, COAP technology), which can achieve near-zero emissions of coal-fired flue gas. In power plants using COAP technology, the use of existing demercuration adsorbent modification methods including impregnation with halogens, impregnation with metal compounds, and mechanochemical modification will increase operating costs and generate hazardous waste. CN107737581A discloses a method for preparing a modified petroleum coke-based demercuration adsorbent, which uses delayed coking petroleum coke as a raw material and SO2 gas as an active modifier, and can obtain a demercuration adsorbent with developed pores and a large number of sulfur-containing functional groups on the surface. However, the modification temperature of this method is relatively high and is not suitable for application in COAP technology. At the same time, the current research temperature of COAP technology for demercuration adsorption is mainly concentrated between 30℃ and 160℃. There is no research on the effect of common modification methods on mercury adsorption at low temperatures (0-40℃), which is not conducive to the implementation of COAP technology. Summary of the invention

[0004] In view of the defects of the prior art, the present application provides a mercury removal adsorbent based on activated coke modification and a preparation method and application thereof, aiming to solve the problems that the existing modification methods are high in cost and cannot be adapted to COAP technology.

[0005] According to one aspect of the present application, a method for preparing a mercury removal adsorbent based on modified activated coke is provided. The preparation method specifically comprises: heating the activated coke to 300°C to 600°C in a mixed atmosphere of inert gas and SO2 for pyrolysis modification, and cooling after the reaction is completed to obtain the mercury removal adsorbent based on modified activated coke.

[0006] Through the above technical scheme conceived by the present application, compared with the prior art, the present application reduces the temperature of SO2 activated coke modification to 300°C~600°C, which can change the demercuration principle of the prepared demercuration adsorbent, making it suitable for low-temperature demercuration conditions, thereby adapting to a demercuration environment with a wider temperature range.

[0007] As further preferred, the pyrolysis time is 30 min to 180 min.

[0008] As a further preference, the volume fraction of SO2 in the mixed atmosphere is 5% to 45%.

[0009] As a further preference, the volume fraction of SO2 in the mixed atmosphere is 25% to 35%.

[0010] As further preferred, the flow rate of the mixed atmosphere is 200 ml / min to 2000 ml / min.

[0011] As further preferred, the particle size of the activated coke is 40 mesh to 100 mesh.

[0012] According to another aspect of the present application, a mercury removal adsorbent prepared by the above preparation method is provided.

[0013] According to another aspect of the present application, a method for improving the mercury removal efficiency of a power plant is provided, the power plant comprising a boiler, a dust collector, a cascade cooling tower, a low-temperature adsorption tower and a regeneration tower connected in sequence, the deactivated activated coke in the low-temperature adsorption tower is sent to the regeneration tower, and the tail gas of the regeneration tower is sent back to the regeneration tower to form a mixed atmosphere of inert gas and SO2, while ensuring that the temperature of the regeneration tower is between 300°C and 600°C, thereby achieving SO2 modification of the deactivated activated coke and sending the modified activated coke obtained back to the low-temperature adsorption tower.

[0014] As further preferred, the volume fraction of SO2 in the regeneration tower is 5 to 45%.

[0015] As further preferred, the volume fraction of SO2 in the regeneration tower is 25% to 35%.

[0016] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art:

[0017] 1. The present application reduces the temperature of SO2 activated coke modification to 300°C to 600°C, which can change the demercuration principle of the demercuration adsorbent, making it suitable for low-temperature demercuration conditions, and still achieve good demercuration effect and sulfur resistance at a lower reaction temperature, thereby having a wider temperature range and stronger adaptability;

[0018] 2. At the same time, the present application optimizes the volume fraction of SO2 in the mixed atmosphere, which can further improve the mercury removal efficiency of the mercury removal adsorbent;

[0019] 3. In addition, the present application applies the preparation method to power plants using COAP technology, which can match the temperature of the regeneration tower, thereby further reducing the preparation cost of the modified activated coke, and the modified activated coke obtained can adapt to a wide temperature range of mercury removal environment, and still has a high mercury removal efficiency at 0 to 40°C, which is conducive to the implementation of the COAP technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of a power plant using COAP technology provided in an embodiment of the present application;

[0021] Figure 2 This is a comparison chart of the mercury removal efficiency of the mercury removal adsorbents obtained under the conditions of pyrolysis temperature of 400° C., pyrolysis time of 60 min, and different SO2 concentrations provided in the examples of the present application;

[0022] Figure 3 This is a comparison chart of the mercury removal efficiency of the mercury removal adsorbents obtained at different pyrolysis times in a pyrolysis temperature of 400° C., a mixed atmosphere of 75% N2+25% SO2 and a pure N2 atmosphere provided in the embodiments of the present application;

[0023] Figure 4 It is a comparison chart of the mercury removal efficiency of the mercury removal adsorbents obtained at different pyrolysis temperatures in a pyrolysis time of 60 min, a mixed atmosphere of 75% N2+25% SO2 and a pure N2 atmosphere provided in the embodiments of the present application;

[0024] Figure 5 is a comparison chart of the mercury removal efficiency of the mercury removal adsorbents prepared in Example 1 of the present application and Comparative Example 1 at different mercury removal temperatures;

[0025] Figure 6 This is a comparison chart of the mercury removal efficiency of the mercury removal adsorbent prepared in Example 1 of the present application at mercury removal temperatures of 20° C. and 140° C. in different atmosphere environments;

[0026] Figure 7 The XPS results of the demercuration adsorbent prepared in Example 1 of the present application after demercuration at demercuration temperatures of -20°C and 140°C under different atmospheres;

[0027] Figure 8 This is a diagram of a preparation device for a mercury removal adsorbent based on modified activated coke provided in an embodiment of the present application;

[0028] Fig. 9 It is a schematic diagram of the bench used for the wide temperature mercury removal test in this application.

[0029] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0030] 1- boiler, 2- dust collector, 3- cascade cooling tower, 4- low temperature adsorption tower, 5- regeneration tower, 6- gas mixing bottle, 7- tubular furnace, 8- flue gas cooling tube, 9- low temperature water bath. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] The present application provides a method for preparing a mercury removal adsorbent based on modified activated coke, the preparation method comprising: heating the activated coke to 300°C to 600°C in a mixed atmosphere of inert gas and SO2 for pyrolysis modification, and cooling after the reaction is completed to obtain the mercury removal adsorbent based on modified activated coke.

[0033] The specific steps include:

[0034] S1 crushing and screening, washing, crushing and screening the activated coke to obtain activated coke particles with a particle size distribution of 40 mesh to 100 mesh;

[0035] S2 drying treatment: the activated coke particles screened in the early stage are sent to a 105℃ oven for drying for 12 hours to ensure the evaporation of water;

[0036] S3 thermal insulation modification, such as Figure 8 As shown, the temperature of the tubular furnace 7 is raised to 300° C. to 600° C., the inert gas and SO2 are introduced into the mixing bottle 6 for mixing and then introduced into the tubular furnace 7, the activated coke particles dried in the early stage are purged for a period of time in the mixed atmosphere of the inert gas and SO2 to ensure that there is no oxygen, and then quickly put into the tubular furnace, and kept warm for a period of time in the same mixed atmosphere, and then taken out, and finally cooled in the mixed atmosphere to obtain the demercuration adsorbent based on the modified activated coke.

[0037] The present application utilizes sulfur dioxide thermal reduction to modify activated coke, effectively increasing the active sites on the surface of the activated coke. The blocked active sites weaken the slow reaction rate caused by low temperature and the negative impact of SO2 on mercury control, so that the adsorbent has good anti-sulfur and mercury removal properties under low temperature conditions. More importantly, the present application reduces the temperature of SO2 activated coke modification to 300℃~600℃, which has a higher mercury removal efficiency compared with the high-temperature modification of the prior art, and can still achieve good mercury removal effect and sulfur resistance at a lower reaction temperature.

[0038] Furthermore, the pyrolysis time is 30 min to 180 min, and the mercury removal efficiency first increases and then decreases with the pyrolysis time, reaching a peak at 2 hours. Therefore, the pyrolysis time is further preferably 60 min to 120 min. Within this range, the mercury removal efficiency of the mercury removal adsorbent is the highest.

[0039] Furthermore, the volume fraction of SO2 in the mixed atmosphere is 5-45%, and the mercury removal efficiency first increases and then decreases with the SO2 concentration, reaching the highest peak when the sulfur dioxide concentration is 35%. Therefore, the volume fraction of SO2 in the mixed atmosphere is preferably 25%-35%, and the mercury removal efficiency of the mercury removal adsorbent is the highest within this range. The flow rate of the mixed atmosphere is 200ml / min-2000ml / min.

[0040] According to another aspect of the present application, a mercury removal adsorbent prepared by the above preparation method is provided.

[0041] According to another aspect of the present application, a method for improving the demercuration efficiency of a power plant is provided. The power plant includes a boiler 1, a dust collector 2, a cascade cooling tower 3, a low-temperature adsorption tower 4 and a regeneration tower 5 which are connected in sequence. The cascade cooling tower 3 can achieve enhanced removal of particulate matter, SO3 and heavy metals through cascade cooling. The low-temperature adsorption tower 4 uses modified activated coke to achieve efficient adsorption of gaseous pollutants and deep removal of particulate pollutants. The deactivated activated coke after the reaction is sent to the regeneration tower 5 for thermal regeneration. Considering that most sulfur dioxide will be released from the activated coke at low temperature (as shown in Table 1), the modification of the activated coke in a SO2 atmosphere at low temperature can effectively improve its demercuration performance and is more suitable for low-temperature demercuration reaction conditions.

[0042] Table 1 Main components of flue gas in the regeneration tower

[0043]

[0044] Therefore, the method provided in the present application sends the tail gas of the regeneration tower 5 back to the regeneration tower 5 to form a mixed atmosphere of inert gas and SO2, and ensures that the temperature of the regeneration tower 5 is between 300°C and 600°C, so as to achieve in-situ modification of the deactivated activated coke by sulfur dioxide, and send the obtained modified activated coke back to the low-temperature adsorption tower 4. The modified activated coke obtained under the reaction conditions can have a good mercury adsorption effect at low temperature (0-40°C), which is more suitable for the temperature of the low-temperature adsorption tower 4 in the COAP technology.

[0045] Furthermore, the volume fraction of SO2 in the mixed atmosphere is 5-45%, and more preferably, the volume fraction of SO2 in the mixed atmosphere is 25%-35%. Within this range, the mercury removal efficiency of the mercury removal adsorbent is the highest.

[0046] The technical solution provided in this application is further described below based on specific embodiments.

[0047] Example 1

[0048] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0049] Example 2

[0050] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 95% N2+5% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0051] Example 3

[0052] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 85% N2+15% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0053] Example 4

[0054] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 65% N2+35% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0055] Example 5

[0056] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 55% N2+45% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0057] Example 6

[0058] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 30 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0059] Example 7

[0060] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 120 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0061] Example 8

[0062] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 180 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0063] Example 9

[0064] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 300°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0065] Example 10

[0066] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 600°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0067] Embodiment 11

[0068] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, and placed in a mixed atmosphere of 75% N2+25% SO2 with a total airflow of 200 ml / min, and pyrolyzed at 500°C for 60 minutes. After natural cooling, a demercuration adsorbent based on activated coke modification is obtained.

[0069] Comparative Example 1

[0070] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 60 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0071] Comparative Example 2

[0072] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 600°C for 60 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0073] Comparative Example 3

[0074] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particles are distributed between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 120 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0075] Comparative Example 4

[0076] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 30 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0077] Comparative Example 5

[0078] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 400°C for 180 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0079] Comparative Example 6

[0080] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 300°C for 60 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0081] Comparative Example 7

[0082] First, the activated coke raw material is crushed and sieved to obtain particles that meet the sieving standards, and the particle distribution is between 40 and 100 meshes; the activated coke particles are dried at 105°C for 12 hours, 3 g of activated coke particles are weighed and put into a tubular furnace, placed in a pure N2 atmosphere with a total airflow of 200 ml / min, and pyrolyzed at 500°C for 60 minutes. After natural cooling, a demercuration adsorbent is obtained.

[0083] The obtained mercury removal adsorbent was Fig. 9 A demercuration test is carried out on the wide temperature demercuration test bench shown in the figure. O2, SO2, N2 and NO are mixed to simulate flue gas and sent into a U-shaped tube filled with demercuration adsorbent through a flue gas cooling pipe 8. The flue gas cooling pipe 8 and the U-shaped tube are both placed in a low temperature water bath 9 to adjust the demercuration temperature using the low temperature water bath 9. The low temperature water bath can be adjusted in the temperature range of -40°C to 200°C, thereby realizing a wide temperature demercuration test.

[0084] The mercury removal test was carried out on the mercury removal adsorbents obtained under the conditions of pyrolysis temperature of 400°C, pyrolysis time of 60 min and different SO2 concentrations, including the mercury removal adsorbents prepared in Examples 1 to 5 and Comparative Example 1. The results are as follows: Figure 2As shown, the demercuration efficiency first increases and then decreases with the SO2 concentration, reaching the highest peak when the sulfur dioxide concentration is 35%, with an average adsorption efficiency of 92.3% and a maximum of 100%. By testing the sulfur content of each demercuration adsorbent, it was found that the sulfur content in activated coke modified with different SO2 also showed a trend of first increasing and then decreasing, reaching the highest sulfur content of 5.507% when the modified concentration was 35%. Therefore, the mercury removal efficiency of the demercuration adsorbent is the highest when the volume fraction of SO2 is 25% to 35%.

[0085] Mercury removal tests were conducted on mercury removal adsorbents obtained at different pyrolysis times in a pyrolysis temperature of 400°C, a mixed atmosphere of 75% N2 + 25% SO2 and a pure N2 atmosphere, including the mercury removal adsorbents obtained in Example 1, Examples 6 to 8, Comparative Examples 1, and Comparative Examples 3 to 5. The results are as follows: Figure 3 As shown in the figure, under 400℃, the adsorption efficiency is nearly 50% after 0.5h of heat preservation, indicating that short-term heat preservation can still effectively improve the demercuration efficiency. In addition, the demercuration efficiency first increases and then decreases with the pyrolysis time, reaching the highest peak at 2 hours of heat preservation. By testing the sulfur content of each demercuration adsorbent, it is found that the sulfur content in the activated coke at different pyrolysis times also shows a trend of first increasing and then decreasing. The total sulfur content in the activated coke is 5.205% after 2 hours of heat preservation. However, long-term heat preservation may cause the sulfur-containing surface functional groups to break bonds to form gaseous molecules, thereby causing the sulfur content to decrease, resulting in a decrease in removal efficiency.

[0086] Mercury removal tests were conducted on mercury removal adsorbents obtained at different pyrolysis temperatures in a pyrolysis time of 60 min, a mixed atmosphere of 75% N2 + 25% SO2 and a pure N2 atmosphere, including the mercury removal adsorbents obtained in Example 1, Examples 9 to 11, and Comparative Examples 1, 2, 6, and 7. The results are as follows: Figure 4 As shown in the figure, with the increase of temperature, under the same atmosphere and pyrolysis time conditions, the demercuration efficiency is getting higher and higher. Under the pyrolysis temperature of 400℃, the average demercuration efficiency is greater than 80%, which has met the industrial demercuration needs. On the one hand, with the increase of temperature, the total sulfur content continues to increase, so the relative content of active sulfur-containing functional groups also increases; on the other hand, the increase in temperature is conducive to the carbon thermal reduction of sulfur dioxide, so that more sulfur dioxide molecules are reduced to form small molecular sulfur-containing substances, thereby improving the demercuration efficiency.

[0087] The mercury removal adsorbents prepared in Example 1 and Comparative Example 1 were subjected to mercury removal tests at different mercury removal temperatures. The results are as follows: Figure 5As shown, under different mercury removal temperature conditions, the mercury removal efficiency shows a trend of first increasing and then decreasing, showing an increasing trend in the range of ~30~0℃, with a peak at about ~10℃ or 0℃, and then decreasing. At the same time, the mercury removal adsorbent prepared in Comparative Example 1 is particularly affected by temperature, while the mercury removal adsorbent prepared in Example 1 is relatively less affected by temperature. Since the mercury removal adsorbent prepared in Comparative Example 1 basically does not contain sulfur-related functional groups, physical adsorption cannot be effectively converted into chemical adsorption under low temperature conditions, resulting in poor adsorption capacity; with the increase of temperature at about ~10~0℃, a dynamic balance between physical adsorption and chemical adsorption is reached, and the highest peak of adsorption efficiency appears, with an average adsorption efficiency of about 71.34%; and as the temperature continues to rise, although chemical adsorption is promoted, physical adsorption is inhibited, resulting in ineffective adsorption of elemental mercury. The demercuration adsorbent prepared in Example 1 contains more sulfur-containing functional groups, so that under low temperature conditions, it still shows good performance with an average adsorption efficiency of ≥80%; while in the high temperature section, the demercuration efficiency will also decrease, with the lowest average demercuration efficiency of ≥50%. Therefore, the demercuration adsorbent prepared in this application can be well adapted to the working conditions of low-temperature demercuration in COAP technology.

[0088] The mercury removal adsorbent prepared in Example 1 was used to carry out mercury removal tests at mercury removal temperatures of -20°C and 140°C in different atmospheres. The mercury removal efficiency was as follows: Figure 6 As shown. Under -20℃, 500ppm SO2 can make the mercury removal efficiency reach 100%, and with the continuous increase of SO2 concentration, the removal efficiency first increases and then decreases. Compared with 140℃, although the trend is similar, the highest peak of mercury removal efficiency appears at 1000ppm, which is 90.27%, indicating that SO2 is more easily physically adsorbed than mercury at low temperatures. The modified activated coke shows good sulfur resistance at -20℃, and at 1500ppm, the mercury adsorption efficiency is equivalent to or slightly improved to that of pure nitrogen atmosphere at the original temperature.

[0089] The demercuration adsorbent prepared in Example 1 was subjected to demercuration tests at different demercuration temperatures, and XPS tests were performed on the demercuration adsorbent before demercuration (Fresh) and the demercuration adsorbent after demercuration at different temperatures (Used-demercuration temperature). The results are as follows: Figure 7 As shown, Figure 7 The corresponding valence distribution is shown in Table 2.

[0090] Table 2S morphology distribution

[0091]

[0092] As the temperature increases, the relative content of RSS- increases, and the R-SO X(x＝1，2) The relative content of SO4 2-The increasing content indicates that in the range of -20 to 140 °C, RSS- and R-SO play the main role in mercury removal. X(x＝1，2) However, as the temperature rises, the dominant functional group will gradually change from RSS- to R-SO X(x＝1，2) Comparing the results of Hg-TPD, it can be found that the RSS-bound Hg atoms mainly react to form HgS (black), while R-SO X(x＝1，2) The main reaction of combining with Hg atoms is to generate HgS (red) and HgSO4. In the prior art, when the modification temperature is greater than 600°C, the sulfur dioxide modified activated coke contains a large amount of sulfur atoms or low-valent sulfur-containing functional groups, and the modification results in this application are mainly based on the oxidized sulfur-containing functional groups, resulting in differences in the reaction products of the existing mercury removal adsorbents.

[0093] The overall reaction equation is:

[0094] Hg (g) →Hg (ads) (1)

[0095] Lowering the temperature, the following equation is favored:

[0096] Hg (ads) +RSS-→HgS(black) (ads) +RS-(2)

[0097] Increasing the temperature tends to the following equation:

[0098] 4R-SO X(x＝1，2) +4Hg (ads) →(4-x)HgS(red) (ads) +xHgSO 4(ads) +2R-R(3)

[0099] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a mercury removal adsorbent based on modified activated coke, characterized in that: The activated coke is heated to 300°C to 600°C in a mixed atmosphere of inert gas and SO2 to be pyrolyzed and modified, and after the reaction is completed, it is cooled to obtain a mercury removal adsorbent based on the modified activated coke.

2. The preparation method according to claim 1, characterized in that The pyrolysis time is 30min~180min.

3. The preparation method according to claim 1, characterized in that: The volume fraction of SO2 in the mixed atmosphere is 5% to 45%.

4. The preparation method according to claim 1, characterized in that: The volume fraction of SO2 in the mixed atmosphere is 25% to 35%.

5. The preparation method according to claim 1, characterized in that: The flow rate of the mixed atmosphere is 200ml / min to 2000ml / min.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The particle size of the activated coke is 40-100 meshes.

7. A mercury removal adsorbent prepared by the preparation method according to any one of claims 1 to 6.

8. A method for improving the mercury removal efficiency of a power plant, the power plant comprising a boiler (1), a dust collector (2), a cascade cooling tower (3), a low-temperature adsorption tower (4) and a regeneration tower (5) connected in sequence, characterized in that: The deactivated activated coke in the low-temperature adsorption tower (4) is sent to the regeneration tower (5), and the tail gas of the regeneration tower (5) is sent back to the regeneration tower (5) to form a mixed atmosphere of inert gas and SO2, while ensuring that the temperature of the regeneration tower (5) is between 300°C and 600°C, so as to achieve SO2 modification of the deactivated activated coke and send the modified activated coke back to the low-temperature adsorption tower (4).

9. The method according to claim 8, characterized in that The volume fraction of SO2 in the regeneration tower (5) is 5 to 45%.

10. The method according to claim 8, characterized in that The volume fraction of SO2 in the regeneration tower (5) is 25% to 35%.

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