Method for combined removal of chlorine and heavy metals from flue gas of coal and biomass coupled combustion
By preparing tire coke through the pyrolysis of waste rubber and combining it with low-temperature plasma technology, the problem of removing chlorine and heavy metal mercury from biomass co-firing flue gas has been solved, achieving a highly efficient and economical combined removal effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG UNIV
- Filing Date
- 2023-11-10
- Publication Date
- 2026-07-10
AI Technical Summary
Existing technologies are insufficient for efficiently removing chlorine and heavy metal mercury from biomass co-firing flue gas, and traditional methods are costly, require large equipment footprints, and pose a risk of secondary pollution.
Tire coke is prepared by pyrolysis of waste rubber and then injected into the flue gas before an electrostatic precipitator using low-temperature plasma technology. The catalytic and ionization effects of the tire coke are used to synergistically remove chlorine and heavy metal mercury.
It achieves efficient and synergistic removal of chlorine and heavy metal mercury from biomass co-firing flue gas, reduces adsorbent costs, simplifies modification steps, avoids secondary pollution, and reduces equipment footprint and operating costs.
Smart Images
Figure CN117463149B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of flue gas purification technology for coal and biomass coupled combustion, specifically relating to a method for the combined removal of chlorine and heavy metals from flue gas for coal and biomass coupled combustion. Background Technology
[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.
[0003] Coal is my country's primary energy source, but its combustion releases large amounts of CO2, contributing to global warming. The carbon emission intensities of coal, oil, natural gas, and biomass are 1001, 840, 469, and 18 g / kWh (in CO2 terms), respectively, demonstrating that biomass' carbon emission intensity is significantly lower than that of coal, oil, and natural gas. Utilizing existing pulverized coal boilers with biomass co-firing requires only appropriate modifications to effectively reduce CO2 emissions and promote flexible fuel conversion on the boiler side. Agricultural and forestry biomass, in particular, has high volatile matter content; co-firing it with coal can improve fuel combustion performance, enabling stable combustion at low loads and facilitating peak load adjustments. Furthermore, the energy utilization of biomass derived from municipal solid waste, livestock manure, sludge, and waste oils can realize its resource potential.
[0004] Mercury, a heavy metal found in flue gas from biomass co-firing, is highly toxic, bioaccumulative, and persistent, posing a serious threat to human health and the ecological environment. Mercury exists in flue gas in three forms: elemental mercury (Hg)... 0 ), divalent mercury (Hg) 2+ ) and particulate mercury (Hg P Hg 2+ and Hg P Hg can be collected by wet flue gas desulfurization (WFGD) and electrostatic precipitators (or bag filters), respectively; 0 Due to its high volatility and water insolubility, Hg is difficult to remove using existing pollutant removal devices. Currently, activated carbon injection (ACI) technology is considered the best method for removing Hg from flue gas. 0 The most mature and effective method is the use of raw activated carbon, but it suffers from problems such as small adsorption capacity, low adsorption rate, and large spray volume. In view of this, many scholars have used sulfur- or halogen-containing chemical reagents to modify raw activated carbon in order to improve its mercury removal performance and reduce the amount of activated carbon sprayed. The disadvantage is that the use cost of ACI technology is high, which limits its popularization in developing countries. This is mainly because: (1) the cost of raw activated carbon is high (the raw material for the production of raw activated carbon is coal); (2) a large amount of sulfur- or halogen-containing chemical reagents need to be purchased for the modification of raw activated carbon, which leads to increased costs; (3) the chemical modification process is complex, cumbersome and time-consuming, which leads to increased adsorbent production cycle and costs; (4) the modification process is prone to secondary pollution (such as impregnation modification, which produces wastewater containing sulfur or halogens).
[0005] Compared with traditional coal-fired flue gas, biomass co-firing flue gas has its unique properties: (1) Some biomass has a high chlorine content (such as straw), resulting in a high chlorine content in biomass co-firing flue gas, which in turn leads to excessively high chlorine content in desulfurization wastewater and desulfurization gypsum, which is not conducive to subsequent resource utilization. Therefore, it is necessary to achieve efficient removal of chlorine from biomass co-firing flue gas; (2) Some biomass has an excessively high water content (such as kitchen waste), and some biomass has an excessively high sulfur content (such as waste rubber), resulting in excessively high chlorine content in biomass co-firing flue gas. The concentrations of SO2 and H2O in the flue gas are too high, and the traditional modified activated carbon has poor sulfur and water resistance, resulting in poor mercury removal performance; (3) The content of alkali / alkaline earth metals in the biomass co-firing flue gas is high, which affects the mercury removal performance of the adsorbent; (4) For the removal of mercury in the biomass co-firing flue gas, the adsorbent injection technology is usually used, and for the removal of chlorine-containing gas in the biomass co-firing flue gas, the alkaline absorbent is generally used. That is, the two processes are independent, resulting in problems such as large equipment footprint and high cost. Summary of the Invention
[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for the combined removal of chlorine and heavy metals from flue gas of coal and biomass coupled combustion.
[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:
[0008] A method for the combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion includes the following steps:
[0009] Waste rubber is crushed, sieved, and then pyrolyzed to obtain tire coke.
[0010] The tire coke is injected into the flue gas from the coupled combustion of coal and biomass, with the injection point located upstream of the electrostatic precipitator.
[0011] Simultaneously, low-temperature plasma is applied to the flue gas containing tire coke for 1-5 seconds.
[0012] After treatment, the flue gas enters an electrostatic precipitator for dust removal, which removes heavy metals and chlorine-containing gases from the flue gas.
[0013] Tire coke is injected into the flue gas before the electrostatic precipitator. Combined with the ionization effect of low-temperature plasma, chlorine-containing gases are decomposed and transformed, achieving efficient chlorine removal. The tire coke acts as a catalyst, promoting the ionization and decomposition of more chlorine-containing gases. The free radicals generated by ionization can also modify the tire coke, improving its mercury removal performance, ultimately achieving efficient and synergistic removal of chlorine and heavy metal mercury from biomass co-firing flue gas.
[0014] In some embodiments, the particle size of the waste rubber after crushing and screening is less than 500 μm.
[0015] In some embodiments, the waste rubber is one or a mixture of waste tires or waste rubber conveyor belts.
[0016] In some embodiments, the pyrolysis temperature of waste rubber is 400-1000℃, and the pyrolysis time is 10-180min.
[0017] Preferably, the pyrolysis temperature of waste rubber is 500-800℃ and the pyrolysis time is 20-100min.
[0018] Preferably, the pyrolysis atmosphere of waste rubber is an inert atmosphere.
[0019] More preferably, the inert atmosphere is N2, CO2, or Ar.
[0020] In some embodiments, the discharge power of the cryogenic plasma is 100-10000VA.
[0021] Preferably, the discharge power of the low-temperature plasma is 100-10000VA.
[0022] In some embodiments, the amount of tire coke injected into the flue gas is related to the flue gas flow rate by 0.05-10 g / m³. 3 .
[0023] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:
[0024] (1) This invention uses waste tires instead of coal to prepare mercury removal adsorbents, reducing the cost of the adsorbent. Waste tires contain a large amount of ZnO, which is converted into ZnS after pyrolysis. The presence of metal sulfides can improve the sulfur and water resistance of tire coke, avoiding the adverse effects of high concentrations of SO2 and H2O in biomass co-firing flue gas on mercury removal. In addition, the ZnS in the tire coke is generated during the pyrolysis process (i.e., generated in situ), eliminating the need to add metal sulfides to the tire coke to improve its sulfur and water resistance, thus simplifying the preparation process of the mercury removal adsorbent.
[0025] (2) Low-temperature plasma first rapidly ionizes various gases in the biomass co-combustion flue gas (such as chlorine-containing gases, SO2, NO, O2) to generate active free radicals (such as Cl·, Cl·, O·, SO·, NO·). These free radicals can be used to modify tire coke, eliminating the need to purchase large quantities of sulfur- or halogen-containing chemical reagents and reducing adsorbent costs. In addition, tire coke has a catalytic effect, which can promote the ionization and decomposition of more chlorine-containing gases, i.e., low-temperature plasma and tire coke have a synergistic effect.
[0026] (3) Low-temperature plasma modifies tire coke during the flow of flue gas, which means that the chemical modification of tire coke can be completed in a very short time (usually a few seconds). This not only avoids the tedious and lengthy modification steps of the adsorbent in the early stage (realizing the online real-time modification of the adsorbent), but also avoids the secondary pollution that may be generated during the adsorbent modification process. It has strong scalability.
[0027] (4) During the low-temperature plasma modification process, sulfur-containing substances in tire coke interact with chlorine radicals in biomass co-firing flue gas. This results in the mercury removal performance of tire coke modified by both sulfur and halogens being far superior to that of adsorbents modified by sulfur or halogens alone, achieving a 1+1>2 effect. In addition, the presence of SO· radicals in biomass co-firing flue gas can directionally regulate the sulfur form in tire coke, leading to the generation of more organic sulfur, i.e., generating more mercury removal active sites, thus improving the mercury removal performance of tire coke.
[0028] (5) Free radicals such as SO· and NO· generated by low-temperature plasma ionization can react chemically with gaseous alkali / alkaline earth metals in biomass co-firing flue gas to generate stable substances such as sulfates and nitrates, which weakens the adverse effects of alkali / alkaline earth metals on the mercury removal process of adsorbents and also reduces the impact of alkali / alkaline earth metals on the power generation system to a certain extent.
[0029] (6) This invention can effectively remove chlorine and heavy metal mercury from biomass co-firing flue gas, and can also remove other pollutants (such as nitrogen oxides and volatile organic compounds) to a certain extent, avoiding the problems of large equipment footprint and high cost in the removal of single pollutants, and reducing the chlorine content of desulfurization wastewater and desulfurization gypsum. Attached Figure Description
[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0031] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation
[0032] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0033] The present invention will be further described below with reference to the embodiments.
[0034] Example 1
[0035] Step 1. Crush and screen the waste tires to a suitable particle size.
[0036] Step 2. Place the experimental sample obtained in Step 1 into a pyrolysis furnace and introduce a flow of N2 gas at a rate of 200 ml / min as the pyrolysis atmosphere. Raise the pyrolysis furnace to 700°C and maintain it for 30 min. Then cool it to room temperature under the N2 atmosphere to obtain tire coke.
[0037] Step 3. Inject tire coke into the flue and simultaneously turn on the low-temperature plasma discharge device with a discharge power of 100VA and a plasma treatment time of 4s. The treated flue gas is then separated by dust removal to remove particulate matter.
[0038] When Hg in flue gas 0 Concentration of 50 μg / m 3 The HCl concentration was 200 ppm, the reaction temperature was 150℃, and the tire coke injection dosage was 0.8 g / m³. 3 The tire coke particle size is 20μm. Under this condition, 85% of the chlorine-containing gases in the flue gas can be removed, the mercury removal rate is 91%, the NO removal rate is 81%, and the chlorine content in the modified tire coke is 1.32% and the sulfur content is 5.31%.
[0039] Comparative Example 1
[0040] Step 1. Crush and screen the waste tires to a suitable particle size.
[0041] Step 2. Place the experimental sample obtained in Step 1 into a pyrolysis furnace and introduce a flow of N2 gas at a rate of 200 ml / min as the pyrolysis atmosphere. Raise the pyrolysis furnace to 700°C and maintain it for 30 min. Then cool it to room temperature under the N2 atmosphere to obtain tire coke.
[0042] When Hg in flue gas 0 Concentration of 50 μg / m 3 The HCl concentration was 200 ppm, the reaction temperature was 150℃, and the tire coke injection dosage was 0.8 g / m³. 3 The tire coke particle size is 20μm. Under this condition, 17% of the chlorine-containing gas in the flue gas can be removed, the mercury removal rate is 46%, the NO removal rate is 6%, and the chlorine content in the modified tire coke is 0.18% and the sulfur content is 3.21%.
[0043] Comparative Example 2
[0044] Instead of injecting tire coke into the flue, the low-temperature plasma discharge device is activated to treat the flue gas for 4 seconds. When the Hg in the flue gas... 0 Concentration of 50 μg / m 3 With an HCl concentration of 200 ppm and a reaction temperature of 150℃, this operating condition can remove 37% of the chlorine-containing gases in the flue gas, with a mercury removal rate of 59% and a NO removal rate of 28%.
[0045] Example 2
[0046] Step 1. Crush and screen the waste tires to a suitable particle size.
[0047] Step 2. Place the experimental sample obtained in Step 1 into a pyrolysis furnace and introduce a flow of N2 gas at a rate of 200 ml / min as the pyrolysis atmosphere. Raise the pyrolysis furnace to 700°C and maintain it for 30 min. Then cool it to room temperature under the N2 atmosphere to obtain tire coke.
[0048] Step 3. Inject tire coke into the flue and simultaneously turn on the low-temperature plasma discharge device with a discharge power of 200VA and a plasma treatment time of 3s. The treated flue gas is then separated by dust removal to remove particulate matter.
[0049] When Hg in flue gas 0 Concentration of 50 μg / m 3 The HCl concentration was 200 ppm, the reaction temperature was 150℃, and the tire coke injection dosage was 0.8 g / m³. 3 The tire coke particle size is 20μm. Under this condition, 89% of the chlorine-containing gases in the flue gas can be removed, the mercury removal rate is 93%, the NO removal rate is 86%, and the chlorine content in the modified tire coke is 1.67% and the sulfur content is 5.64%.
[0050] Example 3
[0051] Step 1. Crush and screen the waste tires to a suitable particle size.
[0052] Step 2. Place the experimental sample obtained in Step 1 into a pyrolysis furnace and introduce a flow of N2 gas at a rate of 200 ml / min as the pyrolysis atmosphere. Raise the pyrolysis furnace to 700°C and maintain it for 30 min. Then cool it to room temperature under the N2 atmosphere to obtain tire coke.
[0053] Step 3. Inject tire coke into the flue and simultaneously turn on the low-temperature plasma discharge device with a discharge power of 400VA and a plasma treatment time of 5s. The treated flue gas is then separated by dust removal to remove particulate matter.
[0054] When Hg in flue gas 0 Concentration of 50 μg / m 3 The HCl concentration was 200 ppm, the reaction temperature was 150℃, and the tire coke injection dosage was 0.8 g / m³. 3 The tire coke particle size is 20μm. Under this condition, 92% of the chlorine-containing gases in the flue gas can be removed, the mercury removal rate is 96%, the NO removal rate is 90%, and the chlorine content in the modified tire coke is 1.91% and the sulfur content is 6.03%.
[0055] Example 4
[0056] Step 1. Crush and screen the waste tires to a suitable particle size.
[0057] Step 2. Place the experimental sample obtained in Step 1 into a pyrolysis furnace and introduce a flow of N2 gas at a rate of 200 ml / min as the pyrolysis atmosphere. Raise the pyrolysis furnace to 700°C and maintain it for 30 min. Then cool it to room temperature under the N2 atmosphere to obtain tire coke.
[0058] Step 3. Inject tire coke into the flue and simultaneously turn on the low-temperature plasma discharge device with a discharge power of 1000VA and a plasma treatment time of 3s. The treated flue gas is then separated by dust removal to remove particulate matter.
[0059] When Hg in flue gas 0 Concentration of 50 μg / m 3 The HCl concentration was 200 ppm, the reaction temperature was 150℃, and the adsorbent injection rate was 0.8 g / m³. 3 The tire coke particle size is 20μm. Under this condition, 96% of the chlorine-containing gases in the flue gas can be removed, the mercury removal rate is 100%, the NO removal rate is 93%, and the chlorine content in the modified tire coke is 2.56% and the sulfur content is 6.92%.
[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for the combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion, characterized in that: Includes the following steps: Waste rubber is crushed, sieved, and then pyrolyzed to obtain tire coke. The tire coke is injected into the flue gas from the coupled combustion of coal and biomass, with the injection point located upstream of the electrostatic precipitator. Simultaneously, low-temperature plasma is applied to the flue gas containing tire coke for 1-5 seconds. After treatment, the flue gas enters an electrostatic precipitator for dust removal, which removes heavy metals and chlorine-containing gases from the flue gas.
2. The method for combined removal of chlorine and heavy metals from flue gas of coal and biomass coupled combustion according to claim 1, characterized in that: The particle size of waste rubber after crushing and screening is less than 500μm.
3. The method for combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion according to claim 1, characterized in that: The waste rubber is one of waste tires or waste rubber conveyor belts, or a mixture thereof.
4. The method for combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion according to claim 1, characterized in that: The pyrolysis temperature of waste rubber is 400-1000℃, and the pyrolysis time is 10-180min.
5. The method for combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion according to claim 4, characterized in that: The pyrolysis temperature of waste rubber is 500-800℃, and the pyrolysis time is 20-100min.
6. The method for combined removal of chlorine and heavy metals from flue gas of coal and biomass coupled combustion according to claim 1, characterized in that: The pyrolysis atmosphere for waste rubber is an inert atmosphere.
7. The method for combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion according to claim 6, characterized in that: The inert atmosphere is N2, CO2, or Ar.
8. The method for combined removal of chlorine and heavy metals from flue gas from coal and biomass coupled combustion according to claim 1, characterized in that: The discharge power of the low-temperature plasma is 100-10000VA.
9. The method for combined removal of chlorine and heavy metals from flue gas of coal and biomass coupled combustion according to claim 8, characterized in that: The discharge power of the low-temperature plasma is 100-5000VA.
10. The method for combined removal of chlorine and heavy metals from flue gas of coal and biomass coupled combustion according to claim 1, characterized in that: The relationship between the amount of tire coke injected into the flue gas and the flue gas flow rate is 0.05-10 g / m³. 3 .