US20140044623A1 - High performance mercury capture - Google Patents
High performance mercury capture Download PDFInfo
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- US20140044623A1 US20140044623A1 US13/875,818 US201313875818A US2014044623A1 US 20140044623 A1 US20140044623 A1 US 20140044623A1 US 201313875818 A US201313875818 A US 201313875818A US 2014044623 A1 US2014044623 A1 US 2014044623A1
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- United States
- Prior art keywords
- flue gas
- fabric filter
- mercury
- activated carbon
- capture
- Prior art date
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- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 title claims abstract description 77
- 229910052753 mercury Inorganic materials 0.000 title claims abstract description 72
- 239000003546 flue gas Substances 0.000 claims abstract description 84
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 81
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 68
- 239000004744 fabric Substances 0.000 claims abstract description 67
- 238000000034 method Methods 0.000 claims abstract description 23
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 12
- 239000007789 gas Substances 0.000 claims abstract description 6
- 238000006477 desulfuration reaction Methods 0.000 claims description 24
- 230000023556 desulfurization Effects 0.000 claims description 24
- 239000006096 absorbing agent Substances 0.000 claims description 16
- 239000007921 spray Substances 0.000 claims description 16
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- 239000000356 contaminant Substances 0.000 claims description 5
- 239000002245 particle Substances 0.000 claims description 5
- 239000000428 dust Substances 0.000 claims description 4
- 239000012530 fluid Substances 0.000 claims description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 3
- 238000004064 recycling Methods 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 239000011593 sulfur Substances 0.000 claims description 3
- 238000002485 combustion reaction Methods 0.000 abstract description 16
- 239000004449 solid propellant Substances 0.000 abstract description 9
- 239000003245 coal Substances 0.000 description 13
- 238000010521 absorption reaction Methods 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 150000002731 mercury compounds Chemical class 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 230000003292 diminished effect Effects 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000003344 environmental pollutant Substances 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 231100000719 pollutant Toxicity 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 239000000809 air pollutant Substances 0.000 description 1
- 231100001243 air pollutant Toxicity 0.000 description 1
- 150000001649 bromium compounds Chemical class 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 230000035425 carbon utilization Effects 0.000 description 1
- RCTYPNKXASFOBE-UHFFFAOYSA-M chloromercury Chemical compound [Hg]Cl RCTYPNKXASFOBE-UHFFFAOYSA-M 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000010881 fly ash Substances 0.000 description 1
- 230000002140 halogenating effect Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000003476 subbituminous coal Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000004056 waste incineration Methods 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/64—Heavy metals or compounds thereof, e.g. mercury
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/06—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds
- B01D53/10—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds with dispersed adsorbents
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J15/00—Arrangements of devices for treating smoke or fumes
- F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
- B01D2253/10—Inorganic adsorbents
- B01D2253/102—Carbon
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/60—Heavy metals or heavy metal compounds
- B01D2257/602—Mercury or mercury compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
- B01D2258/0283—Flue gases
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
- B01D53/505—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound in a spray drying process
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2215/00—Preventing emissions
- F23J2215/20—Sulfur; Compounds thereof
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2215/00—Preventing emissions
- F23J2215/60—Heavy metals; Compounds thereof
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2217/00—Intercepting solids
- F23J2217/10—Intercepting solids by filters
- F23J2217/101—Baghouse type
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2219/00—Treatment devices
- F23J2219/30—Sorption devices using carbon, e.g. coke
Definitions
- the present invention relates to a system and a method for removing mercury from the products of solid fuel combustion including flue gases, and more particularly, to a system and a method for removing elemental mercury or mercury compounds from flue gases produced by coal combustion.
- the utilization factor for activated carbon is important as it is costly. Efforts in the industry to reduce carbon costs include halogenating the carbon—usually with bromides. Also, the carbon can be ground to reduce the surface area of the carbon particles and/or injected into the system at higher temperatures, each measure taken for purposes of increasing the carbon's utilization factor. However, even with these industry efforts, compliance with more stringent emission regulations requires increased carbon injection rates.
- An object of the present invention is to provide a method for high performance mercury capture for coal-fired power plants using pulverized activated carbon in a system equipped with two or more fabric filters for purposes of achieving regulatory compliance.
- the method comprises injecting pulverized activated carbon into the system ductwork at a point upstream of the second fabric filter for mercury capture, collecting the pulverized activated carbon from the last fabric filter, and conveying the collected pulverized activated carbon countercurrent to the flow of flue gas through the system for injection at a point upstream of the first fabric filter for system reuse in mercury capture.
- Another object of the present invention is to provide a system for high performance mercury capture for coal-fired power plants using pulverized activated carbon in the system.
- the system comprises a desulfurization spray dryer absorber, at least a first fabric filter, a second fabric filter, and ductwork arranged for recycling pulverized activated carbon collected from the second fabric filter for reinjection into the system countercurrent to the gas flow upstream of the first fabric filter.
- the method and system for high performance mercury capture described above allows for high performance mercury capture with 99.8 percent or greater mercury capture from coal-fired power plant flue gas, as required to meet new U.S. EPA regulations.
- over 90 percent of flue gas mercury is captured in the first fabric filter, and most of the remaining flue gas mercury is captured in the second or last fabric filter. Since the amount of mercury remaining in the flue gas after the first fabric filter is relatively low, the remaining amount of mercury absorbed on the activated carbon and captured in the second or last fabric filter is relatively little. With only very low levels of mercury available for capture, much of the pulverized activated carbon from the second or last fabric filter remains active and capable of removing additional mercury. Hence, the still active pulverized activated carbon removed from the second or last fabric filter is ideal for re-use in the system's first fabric filter.
- FIG. 1 is a schematic diagram of a prior art mercury capture system
- FIG. 2 is a schematic diagram of a high performance mercury capture system of the present invention.
- the present invention relates to a system and a method for removing elemental mercury and/or mercury compounds from the products of solid fuel combustion including flue gas, and more particularly, to a system and a method for removing elemental mercury and/or mercury compounds from flue or process gas produced by coal combustion, such as from a coal-fired power plant.
- PRB coal One common coal in the United States is subbituminous coal, typically from the Powder River Basin, commonly referred to as PRB coal.
- PRB coal can have mercury contents of about 10 pounds per trillion British thermal units (lb/TBtu).
- U.S. EPA United States Environmental Protection Agency
- Current mercury emission regulations are less stringent requiring about 1.2 lb/TBtu, or a little less than 90 percent removal of the mercury present in the flue gas.
- System 10 includes a boiler 22 powered by combustion of a solid fuel such as coal.
- a solid fuel such as coal.
- a combustion product, flue gas flows from boiler 22 through fluidly connected exit duct 38 to a fluidly connected air preheater 14 .
- pulverized activated carbon (PAC) from a PAC supply 12 is introduced via fluidly connected duct 24 into the flow of flue gas through fluidly connected duct 26 .
- PAC pulverized activated carbon
- duct 26 is likewise fluidly connected to and between air preheater 14 and desulfurization spray dryer absorber 16 .
- PAC supply 12 is arranged between air preheater 14 and desulfurization spray dryer absorber 16 so as to be downstream of air preheater 14 and upstream of desulfurization spray dryer absorber 16 with respect to the flow of flue gas through system 10 .
- PAC is conveyed through system 10 along with the flow of flue gas to a desulfurization unit 28 comprising desulfurization spray dryer absorber 16 and fabric filter 18 .
- Desulfurization spray dryer absorber 16 and fabric filter 18 are fluidly connected by means of duct 32 .
- System 110 for high performance mercury capture from flue gas produced by a coal-fired power plant useful to capture greater than 90 percent of flue gas mercury, and more particularly, to capture approximately 99.8 percent flue gas mercury or greater.
- System 110 comprises a boiler 122 for combustion of a solid fuel, such as PRB coal or the like.
- air enters inlet 134 of air preheater 114 and flows through duct 136 fluidly connected thereto and to boiler 122 .
- Flue gas produced by the solid fuel combustion of boiler 122 flows from boiler 122 through fluidly connected exit duct 138 to fluidly connected air preheater 114 .
- the air preheater 114 is operative both for heating air entering inlet 134 prior to the air reaching boiler 122 , and for cooling the flue gas flowing from boiler 122 prior to flow through fluidly connected duct 126 .
- fresh PAC from a fresh PAC supply 112 and recycled PAC from a recycled PAC supply 124 are conveyed to exit duct 138 prior to air preheater 114 .
- fresh PAC flows from fresh PAC supply 112 through fluidly connected duct 142 to fluidly connected duct 140 , which is fluidly connected to exit duct 138 .
- recycled PAC flows from recycled PAC supply 124 through fluidly connected duct 144 to fluidly connected duct 140 , where both the fresh PAC and the recycled PAC are introduced at contact point 138 a into the flow of flue gas through exit duct 138 prior to the flue gas reaching air preheater 114 .
- the temperature of the flue gas at contact point 138 a prior to reaching air preheater 114 is from 400° F. to 1100° F.
- the fresh PAC and the recycled PAC may be introduced in duct 126 upon modifications in the ductwork to fluidly connect ducts 142 and 144 with duct 126 (not shown).
- PAC absorption efficiency may be diminished due to temperature differences between that in exit duct 138 and that in duct 126 . If PAC absorption efficiency is so diminished, costs associated therewith increase. Accordingly, although PAC introduction in duct 126 is an option, PAC introduction in exit duct 138 prior to air preheater 114 is preferred to increase mercury removal efficiency and reduce costs.
- both the fresh PAC and the recycled PAC are introduced at contact point 138 a into the flow of flue gas through exit duct 138 prior to the flue gas reaching air preheater 114 .
- the flue gas and entrained fresh and recycled PAC flow through fluidly connected duct 126 to a fluidly connected desulfurization unit 128 .
- Desulfurization unit 128 comprises desulfurization spray dryer absorber 116 and first fabric filter 118 .
- Desulfurization spray dryer absorber 116 and first fabric filter 118 are fluidly connected by means of duct 132 .
- the flue gas entrained PAC flows through desulfurization unit 128 to complete the first stage reaction.
- both the fresh PAC and the recycled PAC have a median particle size (d50) less than approximately 15 microns, where d50 represents 50 percent of the particles by mass in the batch.
- WO 96/16722 discloses a method, in which lime-containing dust is mixed with water in a mixer and then introduced into a contact reactor to react with gaseous pollutants in flue gas flowing therethrough. The resultant dust including the chemically or physically converted gaseous pollutants is then separated in a filter, circulated to the mixer, and mixed again with water to be reintroduced into the contact reactor to repeat the process.
- This type of desulfurization spray dryer absorber is part of a moist dust fluid bed desulfurization unit.
- the flue gas flows through duct 132 to a fluidly connected first fabric filter 118 .
- Fabric filter 118 captures the dried particulates entrained in the flue gas as the flue gas flows therethrough. Approximately 90 percent of mercury present in flue gas is captured in fabric filter 118 .
- fresh PAC is introduced into the flue gas via fluidly connected duct 146 from a fresh PAC supply 126 for a second stage reaction.
- fabric filter 118 has removed a majority of the mercury, via capture of the PAC on which the mercury is absorbed, a small amount remains in the flue gas.
- the present system provides for contact of the remaining mercury with a substantial amount of fresh carbon or PAC and then re-uses the same in the first fabric filter 118 .
- the fresh PAC from fresh PAC supply 126 adsorbs any mercury remaining in the flue gas.
- the flue gas with the PAC having mercury adsorbed thereon then flows through a second or last fabric filter 128 .
- the second or last fabric filter 128 is so named since system 110 has at least two, but may have more than two fabric filters depending on the composition of the flue gas and the emission control requirements. In the second or last fabric filter 128 , almost all of the mercury remaining in the flue gas after the first fabric filter 118 is captured through the capture of the PAC. Since the PAC added to the second stage is an amount sufficient for both the first stage and the second stage reactions, the PAC available to adsorb mercury in the second stage reaction is far in excess of what is needed for purposes of mercury capture.
- fly ash present in the flue gas from fuel combustion and like byproduct solids from the desulfurization unit 128 are captured in the first fabric filter 118 allowing the PAC captured in the second or last fabric filter 128 to be collected relatively free of contaminants.
- the resultant cleaned flue gas flows out from the second or last fabric filter 128 via fluidly connected duct 148 to a fluidly connected stack 120 .
- the cleaned flue gas flows through stack 120 for release into the atmosphere.
- PAC from second or last fabric filter 128 having only absorbed a relatively small amount of mercury, has additional absorptive capacity and is collected and conveyed through fluidly connected duct 150 to recycled PAC supply 124 . Since most mercury is captured in the first fabric filter 118 , the fresh PAC from fresh PAC supply 126 remains largely unreacted when captured in second or last fabric filter 128 . As such, the PAC from the second or last fabric filter 128 is ideal for purposes of recycling within system 110 for cost reduction.
- a method of high performance mercury capture comprises introducing in a first stage reactor pulverized activated carbon and recycled pulverized activated carbon into a flue gas stream of a combustion system upstream of a desulfurization spray dryer absorber or a first fabric filter, capturing the pulverized activated carbon with flue gas mercury absorbed thereon from the flue gas stream in a first fabric filter downstream of the desulfurization spray dryer absorber, introducing in a second stage reactor pulverized activated carbon into the flue gas stream upstream of a second fabric filter, and capturing the pulverized activated carbon with remaining flue gas mercury adsorbed thereon from the flue gas stream in a second fabric filter to obtain cleaned flue gas acceptable for atmospheric release.
- PAC absorption efficiency may be affected by the presence of SO 3 contamination in the flue gas.
- SO 3 is present in some coals. As such, upon combustion of the coal, SO 3 present therein becomes another contaminant present in the flue gas produced as a result of the coal combustion. If SO 3 is present in the solid fuel or coal, rather than introducing the fresh PAC and the recycled PAC at contact point 138 a into the flow of flue gas through exit duct 138 , in order to achieve regulatory compliance, it may be necessary to introduce the fresh PAC and the recycled PAC at contact point 132 a into the flow of flue gas through duct 132 .
- an additional duct may be arranged to fluidly connect ducts 142 and 144 to duct 132 thus allowing for system flexibility.
- the PAC is either introduced in exit duct 138 via duct 140 or in duct 132 via the additional duct.
- SO 3 is not present in the fuel source, the system is controlled for PAC flow through ducts 142 and 144 to duct 140 for introduction into exit duct 138 .
- the system is controlled for PAC flow through ducts 142 and 144 to the additional duct (not shown) fluidly connected to duct 132 for PAC introduction into flue gas flowing through duct 132 .
- System control as noted above may be through manually controlled or remote computer controlled valves or dampers (not shown) arranged in duct 140 and the additional duct, to control PAC flow therethrough.
- H 2 SO 4 containing flue gas may affect PAC absorption efficiency.
- PAC introduction following at least a portion of H 2 SO 4 removal from the flue gas is desirable. The same may be accomplished in the same manner as that described above for SO 3 containing flue gas.
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Abstract
Description
- This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/680,490; filed on Aug. 7, 2012, entitled “HIGH PERFORMANCE MERCURY CAPTURE” which is incorporated herein by reference in its entirety.
- The present invention relates to a system and a method for removing mercury from the products of solid fuel combustion including flue gases, and more particularly, to a system and a method for removing elemental mercury or mercury compounds from flue gases produced by coal combustion.
- The use of activated carbon for the adsorption of mercury vapor has been successfully demonstrated in various applications such as municipal waste incineration. However, there are significant differences in the concentration of mercury from waste incinerator flue gas as compared to coal-fired power plant flue gas, with the concentration of mercury from the coal-fired power plants being anywhere from 10 to 100 times lower. Also, the flue gas mercury from waste incinerators is usually in the form of mercury chloride whereas the flue gas mercury from coal-fired power plants is usually in the form of elemental mercury. Both of these differences make it more difficult to remove mercury from flue gas produced by a coal-fired power plant.
- The utilization factor for activated carbon is important as it is costly. Efforts in the industry to reduce carbon costs include halogenating the carbon—usually with bromides. Also, the carbon can be ground to reduce the surface area of the carbon particles and/or injected into the system at higher temperatures, each measure taken for purposes of increasing the carbon's utilization factor. However, even with these industry efforts, compliance with more stringent emission regulations requires increased carbon injection rates.
- On Dec. 16, 2011, the United States Environmental Protection Agency (U.S. EPA) issued new more stringent emission regulations for mercury and other air pollutants for both existing and new power plants. The new emission regulation for mercury produced by new power plants not firing low-rank coal is 2.0×10−4 pounds of mercury per gigawatt hour (lb mercury/GWh). Accordingly, a need exists for high performance mercury capture for purposes of achieving regulatory compliance, while minimizing additional costs associated therewith.
- An object of the present invention is to provide a method for high performance mercury capture for coal-fired power plants using pulverized activated carbon in a system equipped with two or more fabric filters for purposes of achieving regulatory compliance. As such, the method comprises injecting pulverized activated carbon into the system ductwork at a point upstream of the second fabric filter for mercury capture, collecting the pulverized activated carbon from the last fabric filter, and conveying the collected pulverized activated carbon countercurrent to the flow of flue gas through the system for injection at a point upstream of the first fabric filter for system reuse in mercury capture.
- Another object of the present invention is to provide a system for high performance mercury capture for coal-fired power plants using pulverized activated carbon in the system. The system comprises a desulfurization spray dryer absorber, at least a first fabric filter, a second fabric filter, and ductwork arranged for recycling pulverized activated carbon collected from the second fabric filter for reinjection into the system countercurrent to the gas flow upstream of the first fabric filter.
- The method and system for high performance mercury capture described above, allows for high performance mercury capture with 99.8 percent or greater mercury capture from coal-fired power plant flue gas, as required to meet new U.S. EPA regulations. As such, in the presently described system, over 90 percent of flue gas mercury is captured in the first fabric filter, and most of the remaining flue gas mercury is captured in the second or last fabric filter. Since the amount of mercury remaining in the flue gas after the first fabric filter is relatively low, the remaining amount of mercury absorbed on the activated carbon and captured in the second or last fabric filter is relatively little. With only very low levels of mercury available for capture, much of the pulverized activated carbon from the second or last fabric filter remains active and capable of removing additional mercury. Hence, the still active pulverized activated carbon removed from the second or last fabric filter is ideal for re-use in the system's first fabric filter.
- Other objects and advantages of the present invention will become apparent from the drawings and detailed description thereof provided below.
- The present invention may be better understood and its numerous objects and advantages apparent to those skilled in the art by reference to the accompanying drawings in which:
-
FIG. 1 is a schematic diagram of a prior art mercury capture system; and -
FIG. 2 is a schematic diagram of a high performance mercury capture system of the present invention. - The present invention relates to a system and a method for removing elemental mercury and/or mercury compounds from the products of solid fuel combustion including flue gas, and more particularly, to a system and a method for removing elemental mercury and/or mercury compounds from flue or process gas produced by coal combustion, such as from a coal-fired power plant.
- One common coal in the United States is subbituminous coal, typically from the Powder River Basin, commonly referred to as PRB coal. PRB coal can have mercury contents of about 10 pounds per trillion British thermal units (lb/TBtu). To meet the United States Environmental Protection Agency (U.S. EPA) regulations for new power plants, the mercury capture equipment or system needs to capture or remove over 99.8 percent of the mercury present in the flue gas. Current mercury emission regulations are less stringent requiring about 1.2 lb/TBtu, or a little less than 90 percent removal of the mercury present in the flue gas.
- A prior art system useful to achieve approximately 90 percent mercury capture is illustrated as
system 10 inFIG. 1 .System 10 includes aboiler 22 powered by combustion of a solid fuel such as coal. For purposes of such combustion, air enters inlet 34 ofair preheater 14 and flows throughduct 36 fluidly connected thereto and toboiler 22. As a result of such combustion, a combustion product, flue gas, flows fromboiler 22 through fluidly connectedexit duct 38 to a fluidly connectedair preheater 14. After the flue gas flows throughair preheater 14, pulverized activated carbon (PAC) from aPAC supply 12 is introduced via fluidly connectedduct 24 into the flow of flue gas through fluidly connectedduct 26. In addition to being fluidly connected toduct 24,duct 26 is likewise fluidly connected to and betweenair preheater 14 and desulfurization spray dryer absorber 16.PAC supply 12 is arranged betweenair preheater 14 and desulfurization spray dryer absorber 16 so as to be downstream ofair preheater 14 and upstream of desulfurization spray dryer absorber 16 with respect to the flow of flue gas throughsystem 10. From its introduction intoduct 26, PAC is conveyed throughsystem 10 along with the flow of flue gas to adesulfurization unit 28 comprising desulfurization spray dryer absorber 16 andfabric filter 18. Desulfurization spray dryer absorber 16 andfabric filter 18 are fluidly connected by means ofduct 32. Mercury present in the flue gas is absorbed by the PAC prior to PAC capture infabric filter 18. After the PAC is captured infabric filter 18, the resultant cleaned gas with approximately 90 percent mercury removal therefrom flows out offabric filter 18 through a fluidly connectedduct 30 to astack 20. As such, the cleaned gas flows throughstack 20 for release to the atmosphere. Whilesystem 10 is effective for removing approximately 90 percent of the mercury present in flue gases from a coal-fired power plant as stated, it is ineffective for purposes of meeting new U.S. EPA mercury emission regulations. - Illustrated in
FIG. 2 is asystem 110 for high performance mercury capture from flue gas produced by a coal-fired power plant useful to capture greater than 90 percent of flue gas mercury, and more particularly, to capture approximately 99.8 percent flue gas mercury or greater.System 110 comprises aboiler 122 for combustion of a solid fuel, such as PRB coal or the like. For purposes of such combustion, air entersinlet 134 ofair preheater 114 and flows throughduct 136 fluidly connected thereto and toboiler 122. Flue gas produced by the solid fuel combustion ofboiler 122 flows fromboiler 122 through fluidly connectedexit duct 138 to fluidly connectedair preheater 114. Theair preheater 114 is operative both for heatingair entering inlet 134 prior to theair reaching boiler 122, and for cooling the flue gas flowing fromboiler 122 prior to flow through fluidly connectedduct 126. - When
system 110 is in use, fresh PAC from afresh PAC supply 112 and recycled PAC from a recycledPAC supply 124 are conveyed toexit duct 138 prior toair preheater 114. As such, fresh PAC flows from fresh PAC supply 112 through fluidly connectedduct 142 to fluidly connectedduct 140, which is fluidly connected toexit duct 138. Likewise, recycled PAC flows from recycledPAC supply 124 through fluidly connectedduct 144 to fluidly connectedduct 140, where both the fresh PAC and the recycled PAC are introduced atcontact point 138 a into the flow of flue gas throughexit duct 138 prior to the flue gas reachingair preheater 114. The temperature of the flue gas atcontact point 138 a prior to reachingair preheater 114 is from 400° F. to 1100° F. - Introducing the PAC at a temperature within the 400° F. to 1100° F. range increases the PAC absorption efficiency. As an alternative to PAC introduction in
exit duct 138, the fresh PAC and the recycled PAC may be introduced induct 126 upon modifications in the ductwork to fluidly connectducts exit duct 138 toduct 126, PAC absorption efficiency may be diminished due to temperature differences between that inexit duct 138 and that induct 126. If PAC absorption efficiency is so diminished, costs associated therewith increase. Accordingly, although PAC introduction induct 126 is an option, PAC introduction inexit duct 138 prior toair preheater 114 is preferred to increase mercury removal efficiency and reduce costs. - As illustrated in
FIG. 2 , both the fresh PAC and the recycled PAC are introduced atcontact point 138 a into the flow of flue gas throughexit duct 138 prior to the flue gas reachingair preheater 114. Fromair preheater 114, the flue gas and entrained fresh and recycled PAC flow through fluidly connectedduct 126 to a fluidly connecteddesulfurization unit 128.Desulfurization unit 128 comprises desulfurizationspray dryer absorber 116 andfirst fabric filter 118. Desulfurizationspray dryer absorber 116 andfirst fabric filter 118 are fluidly connected by means ofduct 132. The flue gas entrained PAC flows throughdesulfurization unit 128 to complete the first stage reaction. For purposes of the first stage reaction whereby PAC absorbs flue gas mercury, both the fresh PAC and the recycled PAC have a median particle size (d50) less than approximately 15 microns, where d50 represents 50 percent of the particles by mass in the batch. - From desulfurization
spray dryer absorber 116, flue gas flows through fluidly connectedduct 132 to a fluidly connectedfabric filter 118. An example of such a desulfurization unit is described in WO 96/16722, incorporated herein in its entirety by reference. WO 96/16722 discloses a method, in which lime-containing dust is mixed with water in a mixer and then introduced into a contact reactor to react with gaseous pollutants in flue gas flowing therethrough. The resultant dust including the chemically or physically converted gaseous pollutants is then separated in a filter, circulated to the mixer, and mixed again with water to be reintroduced into the contact reactor to repeat the process. This type of desulfurization spray dryer absorber is part of a moist dust fluid bed desulfurization unit. - After desulfurization
spray dryer absorber 116, the flue gas flows throughduct 132 to a fluidly connectedfirst fabric filter 118.Fabric filter 118 captures the dried particulates entrained in the flue gas as the flue gas flows therethrough. Approximately 90 percent of mercury present in flue gas is captured infabric filter 118. - As flue gas flows from
fabric filter 118 through fluidly connectedduct 130, fresh PAC is introduced into the flue gas via fluidly connectedduct 146 from afresh PAC supply 126 for a second stage reaction. Althoughfabric filter 118 has removed a majority of the mercury, via capture of the PAC on which the mercury is absorbed, a small amount remains in the flue gas. The present system provides for contact of the remaining mercury with a substantial amount of fresh carbon or PAC and then re-uses the same in thefirst fabric filter 118. As such, the fresh PAC fromfresh PAC supply 126 adsorbs any mercury remaining in the flue gas. The flue gas with the PAC having mercury adsorbed thereon then flows through a second orlast fabric filter 128. - The second or
last fabric filter 128 is so named sincesystem 110 has at least two, but may have more than two fabric filters depending on the composition of the flue gas and the emission control requirements. In the second orlast fabric filter 128, almost all of the mercury remaining in the flue gas after thefirst fabric filter 118 is captured through the capture of the PAC. Since the PAC added to the second stage is an amount sufficient for both the first stage and the second stage reactions, the PAC available to adsorb mercury in the second stage reaction is far in excess of what is needed for purposes of mercury capture. Additionally, fly ash present in the flue gas from fuel combustion and like byproduct solids from thedesulfurization unit 128 are captured in thefirst fabric filter 118 allowing the PAC captured in the second orlast fabric filter 128 to be collected relatively free of contaminants. Following such mercury capture in the second orlast fabric filter 128, the resultant cleaned flue gas flows out from the second orlast fabric filter 128 via fluidly connectedduct 148 to a fluidly connectedstack 120. The cleaned flue gas flows throughstack 120 for release into the atmosphere. - PAC from second or
last fabric filter 128, having only absorbed a relatively small amount of mercury, has additional absorptive capacity and is collected and conveyed through fluidly connectedduct 150 torecycled PAC supply 124. Since most mercury is captured in thefirst fabric filter 118, the fresh PAC fromfresh PAC supply 126 remains largely unreacted when captured in second orlast fabric filter 128. As such, the PAC from the second orlast fabric filter 128 is ideal for purposes of recycling withinsystem 110 for cost reduction. - A method of high performance mercury capture comprises introducing in a first stage reactor pulverized activated carbon and recycled pulverized activated carbon into a flue gas stream of a combustion system upstream of a desulfurization spray dryer absorber or a first fabric filter, capturing the pulverized activated carbon with flue gas mercury absorbed thereon from the flue gas stream in a first fabric filter downstream of the desulfurization spray dryer absorber, introducing in a second stage reactor pulverized activated carbon into the flue gas stream upstream of a second fabric filter, and capturing the pulverized activated carbon with remaining flue gas mercury adsorbed thereon from the flue gas stream in a second fabric filter to obtain cleaned flue gas acceptable for atmospheric release.
- As an important note, PAC absorption efficiency may be affected by the presence of SO3 contamination in the flue gas. SO3 is present in some coals. As such, upon combustion of the coal, SO3 present therein becomes another contaminant present in the flue gas produced as a result of the coal combustion. If SO3 is present in the solid fuel or coal, rather than introducing the fresh PAC and the recycled PAC at
contact point 138 a into the flow of flue gas throughexit duct 138, in order to achieve regulatory compliance, it may be necessary to introduce the fresh PAC and the recycled PAC atcontact point 132 a into the flow of flue gas throughduct 132. By introducing the PAC induct 132 after desulfurizationspray dryer absorber 116, but beforefabric filter 118, at least a portion of the SO3 present in the flue gas is removed therefrom prior to PAC introduction therein. Removing at least a portion of any SO3 present in the flue gas prior to PAC introduction into the flue gas, preserves the absorption efficiency of the PAC for mercury. By preserving the absorption efficiency of the PAC for mercury absorption, costs associated therewith are reduced. Accordingly, if a SO3 containing solid fuel or coal is to be used forboiler 122,duct 140 may be rearranged (not shown) for fluid connection toduct 132 rather than to exitduct 138. As an alternative to rearranging the fluid connections ofduct 140, an additional duct (not shown) may be arranged to fluidly connectducts duct 132 thus allowing for system flexibility. With such flexibility, depending on the type of solid fuel or coal combusted, the PAC is either introduced inexit duct 138 viaduct 140 or induct 132 via the additional duct. As such, if SO3 is not present in the fuel source, the system is controlled for PAC flow throughducts duct 140 for introduction intoexit duct 138. If SO3 is present in the fuel source, the system is controlled for PAC flow throughducts duct 132 for PAC introduction into flue gas flowing throughduct 132. System control as noted above may be through manually controlled or remote computer controlled valves or dampers (not shown) arranged induct 140 and the additional duct, to control PAC flow therethrough. - System operation should likewise be controlled in the presence of H2SO4 containing flue gas, or flue gas with like sulfur contaminants. Like SO3 containing flue gas, H2SO4 containing flue gas may affect PAC absorption efficiency. As such, to preserve PAC absorption efficiency, PAC introduction following at least a portion of H2SO4 removal from the flue gas, is desirable. The same may be accomplished in the same manner as that described above for SO3 containing flue gas.
- While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.
Claims (15)
Priority Applications (5)
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US13/875,818 US8663586B1 (en) | 2012-08-07 | 2013-05-02 | High performance mercury capture |
CA2820516A CA2820516C (en) | 2012-08-07 | 2013-06-20 | High performance mercury capture |
CN201310292507.4A CN103566703B (en) | 2012-08-07 | 2013-07-12 | high performance mercury capture |
EP13178273.2A EP2695659B1 (en) | 2012-08-07 | 2013-07-26 | High performance mercury capture |
PL13178273T PL2695659T3 (en) | 2012-08-07 | 2013-07-26 | High performance mercury capture |
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US201261680490P | 2012-08-07 | 2012-08-07 | |
US13/875,818 US8663586B1 (en) | 2012-08-07 | 2013-05-02 | High performance mercury capture |
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EP (1) | EP2695659B1 (en) |
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Cited By (3)
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US20150265967A1 (en) * | 2012-10-16 | 2015-09-24 | Novinda Corporation | Gaseous Mercury Oxidation and Capture |
CN107965775A (en) * | 2017-11-30 | 2018-04-27 | 成都易态科技有限公司 | The method and apparatus for reducing dioxin in the flue gas of waste incineration discharge |
US10369518B2 (en) | 2017-03-17 | 2019-08-06 | Graymont (Pa) Inc. | Calcium hydroxide-containing compositions and associated systems and methods |
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DE102016124042A1 (en) | 2016-12-12 | 2018-06-14 | Mitsubishi Hitachi Power Systems Europe Gmbh | Process and apparatus for flue gas treatment of flue gases fossil-fired steam power plants by means of an adsorbent |
US11124718B2 (en) * | 2018-02-28 | 2021-09-21 | The Babcock & Wilcox Company | Sorbent utilization improvement by selective ash recirculation from a particulate collector |
CN112426850B (en) * | 2020-10-21 | 2022-07-22 | 苏州麟琪程科技有限公司 | Adsorbent injection device based on adsorbent injection demercuration |
CN113521985A (en) * | 2021-08-17 | 2021-10-22 | 安徽金禾实业股份有限公司 | Device and method for purifying and recycling vent gas in purification section |
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- 2013-05-02 US US13/875,818 patent/US8663586B1/en active Active
- 2013-06-20 CA CA2820516A patent/CA2820516C/en not_active Expired - Fee Related
- 2013-07-12 CN CN201310292507.4A patent/CN103566703B/en not_active Expired - Fee Related
- 2013-07-26 PL PL13178273T patent/PL2695659T3/en unknown
- 2013-07-26 EP EP13178273.2A patent/EP2695659B1/en active Active
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US20150265967A1 (en) * | 2012-10-16 | 2015-09-24 | Novinda Corporation | Gaseous Mercury Oxidation and Capture |
US10369518B2 (en) | 2017-03-17 | 2019-08-06 | Graymont (Pa) Inc. | Calcium hydroxide-containing compositions and associated systems and methods |
US10610825B2 (en) | 2017-03-17 | 2020-04-07 | Graymont (Pa) Inc. | Calcium hydroxide-containing compositions and associated systems and methods |
US10874982B2 (en) | 2017-03-17 | 2020-12-29 | Graymont (Pa) Inc. | Calcium hydroxide-containing compositions and associated systems and methods |
US11344844B2 (en) | 2017-03-17 | 2022-05-31 | Graymont (Pa) Inc. | Calcium hydroxide-containing compositions and associated systems and methods |
CN107965775A (en) * | 2017-11-30 | 2018-04-27 | 成都易态科技有限公司 | The method and apparatus for reducing dioxin in the flue gas of waste incineration discharge |
Also Published As
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CA2820516A1 (en) | 2014-02-07 |
CN103566703B (en) | 2016-06-01 |
EP2695659B1 (en) | 2016-02-03 |
EP2695659A1 (en) | 2014-02-12 |
CN103566703A (en) | 2014-02-12 |
CA2820516C (en) | 2016-06-07 |
PL2695659T3 (en) | 2016-06-30 |
US8663586B1 (en) | 2014-03-04 |
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