WO2024052646A1 - NOx REDUCTION - Google Patents
NOx REDUCTION Download PDFInfo
- Publication number
- WO2024052646A1 WO2024052646A1 PCT/GB2023/052254 GB2023052254W WO2024052646A1 WO 2024052646 A1 WO2024052646 A1 WO 2024052646A1 GB 2023052254 W GB2023052254 W GB 2023052254W WO 2024052646 A1 WO2024052646 A1 WO 2024052646A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- nox
- reactor
- adsorber
- treatment system
- exhaust stream
- Prior art date
Links
- 230000009467 reduction Effects 0.000 title description 7
- 239000003054 catalyst Substances 0.000 claims description 100
- 238000000034 method Methods 0.000 claims description 41
- 239000011261 inert gas Substances 0.000 claims description 35
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 31
- 238000010438 heat treatment Methods 0.000 claims description 27
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 25
- 230000008569 process Effects 0.000 claims description 23
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 21
- 239000007789 gas Substances 0.000 claims description 17
- 238000006243 chemical reaction Methods 0.000 claims description 16
- 239000000395 magnesium oxide Substances 0.000 claims description 16
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 16
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 14
- 238000012546 transfer Methods 0.000 claims description 12
- 239000010457 zeolite Substances 0.000 claims description 12
- 229910052763 palladium Inorganic materials 0.000 claims description 11
- 229910052757 nitrogen Inorganic materials 0.000 claims description 10
- 229910052697 platinum Inorganic materials 0.000 claims description 10
- 229910021536 Zeolite Inorganic materials 0.000 claims description 9
- 229910017052 cobalt Inorganic materials 0.000 claims description 9
- 239000010941 cobalt Substances 0.000 claims description 9
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 9
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 claims description 9
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 239000010949 copper Substances 0.000 claims description 7
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 6
- 229910052783 alkali metal Inorganic materials 0.000 claims description 6
- 150000001340 alkali metals Chemical class 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 5
- 230000004044 response Effects 0.000 claims description 5
- 229910000510 noble metal Inorganic materials 0.000 claims description 4
- 239000010970 precious metal Substances 0.000 claims description 4
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 3
- 239000001569 carbon dioxide Substances 0.000 claims description 3
- 230000003197 catalytic effect Effects 0.000 claims description 3
- 229910052684 Cerium Inorganic materials 0.000 claims description 2
- 229910002282 La2CuO4 Inorganic materials 0.000 claims description 2
- 230000004888 barrier function Effects 0.000 claims description 2
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims description 2
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 1015
- 239000003638 chemical reducing agent Substances 0.000 description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 20
- 238000000354 decomposition reaction Methods 0.000 description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 17
- 239000001301 oxygen Substances 0.000 description 17
- 229910052760 oxygen Inorganic materials 0.000 description 17
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 14
- 229910002091 carbon monoxide Inorganic materials 0.000 description 14
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 12
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 11
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 11
- 239000012530 fluid Substances 0.000 description 11
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 10
- 230000009849 deactivation Effects 0.000 description 10
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 10
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 8
- 230000009286 beneficial effect Effects 0.000 description 8
- 238000011144 upstream manufacturing Methods 0.000 description 8
- 239000002253 acid Substances 0.000 description 7
- 239000004065 semiconductor Substances 0.000 description 7
- 238000004891 communication Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 5
- 229910021529 ammonia Inorganic materials 0.000 description 5
- 230000006698 induction Effects 0.000 description 5
- 239000000377 silicon dioxide Substances 0.000 description 5
- 238000001179 sorption measurement Methods 0.000 description 5
- QQONPFPTGQHPMA-UHFFFAOYSA-N Propene Chemical compound CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 238000003795 desorption Methods 0.000 description 4
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 4
- 239000001294 propane Substances 0.000 description 4
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- QKCGXXHCELUCKW-UHFFFAOYSA-N n-[4-[4-(dinaphthalen-2-ylamino)phenyl]phenyl]-n-naphthalen-2-ylnaphthalen-2-amine Chemical compound C1=CC=CC2=CC(N(C=3C=CC(=CC=3)C=3C=CC(=CC=3)N(C=3C=C4C=CC=CC4=CC=3)C=3C=C4C=CC=CC4=CC=3)C3=CC4=CC=CC=C4C=C3)=CC=C21 QKCGXXHCELUCKW-UHFFFAOYSA-N 0.000 description 3
- 229910052709 silver Inorganic materials 0.000 description 3
- 239000004332 silver Substances 0.000 description 3
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- GQPLMRYTRLFLPF-UHFFFAOYSA-N Nitrous Oxide Chemical class [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 2
- 150000001342 alkaline earth metals Chemical class 0.000 description 2
- QVQLCTNNEUAWMS-UHFFFAOYSA-N barium oxide Chemical compound [Ba]=O QVQLCTNNEUAWMS-UHFFFAOYSA-N 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 238000005137 deposition process Methods 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 239000008187 granular material Substances 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000013618 particulate matter Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000004094 preconcentration Methods 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 229910001930 tungsten oxide Inorganic materials 0.000 description 2
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 1
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 229910052777 Praseodymium Inorganic materials 0.000 description 1
- 229910052772 Samarium Inorganic materials 0.000 description 1
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 1
- 238000003916 acid precipitation Methods 0.000 description 1
- 239000000809 air pollutant Substances 0.000 description 1
- 231100001243 air pollutant Toxicity 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000013270 controlled release Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 229910001657 ferrierite group Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000002803 fossil fuel Substances 0.000 description 1
- 239000008246 gaseous mixture Substances 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910000476 molybdenum oxide Inorganic materials 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 229910052680 mordenite Inorganic materials 0.000 description 1
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 description 1
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 description 1
- VVRQVWSVLMGPRN-UHFFFAOYSA-N oxotungsten Chemical class [W]=O VVRQVWSVLMGPRN-UHFFFAOYSA-N 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- PUDIUYLPXJFUGB-UHFFFAOYSA-N praseodymium atom Chemical compound [Pr] PUDIUYLPXJFUGB-UHFFFAOYSA-N 0.000 description 1
- KZUNJOHGWZRPMI-UHFFFAOYSA-N samarium atom Chemical compound [Sm] KZUNJOHGWZRPMI-UHFFFAOYSA-N 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910000077 silane Inorganic materials 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/4412—Details relating to the exhausts, e.g. pumps, filters, scrubbers, particle traps
-
- 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
- B01D53/54—Nitrogen compounds
- B01D53/56—Nitrogen oxides
-
- 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
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8621—Removing nitrogen compounds
- B01D53/8625—Nitrogen oxides
- B01D53/8631—Processes characterised by a specific device
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/04—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium
- B01J20/041—Oxides or hydroxides
-
- 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
- B01D2253/112—Metals or metal compounds not provided for in B01D2253/104 or B01D2253/106
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/40—Nitrogen compounds
- B01D2257/404—Nitrogen oxides other than dinitrogen oxide
-
- 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
- B01D2258/0216—Other waste gases from CVD treatment or semi-conductor manufacturing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2259/00—Type of treatment
- B01D2259/80—Employing electric, magnetic, electromagnetic or wave energy, or particle radiation
- B01D2259/818—Employing electrical discharges or the generation of a plasma
Definitions
- the present invention relates to exhaust treatment systems for NOx abatement from an exhaust stream of a process tool, and to methods of abating NOx from an exhaust stream.
- Nitrogen oxides are air pollutants, produced as a by-product of many processes, including burning of fossil fuels, and the production of semiconductors. NOx can be responsible for photochemical smog and acid rain, therefore, the release of NOx into the atmosphere must be limited and preferably avoided altogether. This is complicated by several challenges associated with the abatement of exhaust streams containing NOx, particularly in the presence of oxygen and/or water vapour.
- NOx reactors such as catalysts
- High NOx abatement rates via a NOx reactor typically requires reductant-rich conditions, so the presence of oxygen in the exhaust stream may reduce the efficiency of abatement reactions.
- the presence of oxygen and/or water in the exhaust stream is largely unavoidable.
- Addition of reducing agents, such as ammonia is often used to facilitate the reaction of NOx - providing a reaction which is feasible in the presence of oxygen or water.
- ammonia is undesirable, since it is an additional consumable reagent which must be dosed.
- a more preferable NOx abatement route would be to make use of reducing agents already present in the exhaust stream.
- reducing agents unoxidised/partially oxidised hydrocarbons and/or carbon monoxide (CO).
- CO carbon monoxide
- the presence of oxygen in the exhaust stream when such reducing agents are used can be detrimental, as the reaction of O2 with CO consumes much of the CO required for the reaction between CO and NO.
- the presence of oxygen and/or water in the exhaust stream may also be undesirable, as it may result in pore blocking.
- the presence of 02 may enable nitric oxide to be converted to nitrogen dioxide, which should be avoided due to the associated health concerns if inhaled.
- a further challenge to achieving efficient NOx abatement is presented by the deficiency of suitable direct NOx catalysts, so-called because they can directly decompose NOx without the need for a reducing agent.
- direct NOx catalysts are available, few provide high enough activity to allow use of a suitably small volume of the catalyst to be appropriate for many industries.
- the footprint of the exhaust treatment system is often limited.
- the overall size of the exhaust treatment system thereby restricts the overall volume of catalyst that can be used.
- many direct NOx catalysts operate more efficiently at elevated temperatures, for example temperatures greater than 200°C.
- the operating cost required to maintain a large volume of catalyst at such high temperatures renders them unfeasible for practical application in many industries.
- the pressure drop associated with using large volumes of catalyst may be too great for many applications, particularly if the catalyst is placed directly into the exhaust of the chemical process.
- Certain applications may provide particularly challenging conditions for NOx abatement.
- Water vapour may be present in the exhaust stream due to the burning of hydrocarbons, and/or water scrubbing processes upstream of the NOx reactor. This water vapour may deactivate the NOx reactor (e.g. catalyst).
- NOx reactor e.g. catalyst
- Certain catalysts such as Cu-ZSM5 catalysts, may be permanently degraded by water vapour present in the exhaust stream.
- the exhaust streams from semiconductor manufacture often contain a net oxidising amount of oxygen in relation to the total concentration of reductants available, thereby lessening the efficiency of the NOx decomposition.
- particulate matter such as silica
- the pressure drop across the NOx reactor may be required to be low, imposing further constraints on such abatement systems.
- a further challenge is posed by variation in the concentration of NOx within the exhaust stream according to the step of the semiconductor manufacture process that is occurring. For example, the NOx concentration in the exhaust stream may be relatively low during deposition processes. Then, the NOx concentration in the exhaust stream may be relatively high during a “clean-step” using NF3. The “cleanstep” typically occurs for a shorter time than the deposition processes.
- the NOx reactor may be required to abate high concentrations of NOx for a relatively short amount of time, then be substantially inactive or slightly active for long periods of time. Therefore, a NOx reactor must be selected that can meet the abatement requirements during the peak concentration of NOx, in spite of it’s relatively short duration. This problem may be exacerbated by the relatively high overall gas flow through the exhaust treatment system.
- the present invention aims to solve, at least in part, these and other problems associated with exhaust treatment systems of the prior art.
- the present invention provides an exhaust treatment system for NOx abatement of an exhaust stream.
- the exhaust treatment system comprises at least one NOx adsorber configured to adsorb NOx from the exhaust stream.
- the exhaust treatment system further comprises a NOx reactor having an offline configuration and an online configuration. When the NOx reactor is in an offline configuration, the NOx reactor is fluidly disconnected from the exhaust stream and the NOx adsorber. Also, the NOx adsorber is fluidly connected to the exhaust stream such that NOx contained in the exhaust stream may be adsorbed by the NOx adsorber. When the NOx reactor is in an online configuration, the NOx reactor is fluidly connected to the NOx adsorber such that NOx adsorbed by the NOx adsorber may be treated by the NOx reactor.
- the exhaust treatment system is preferably for NOx abatement of an exhaust stream from a process tool.
- the process tool may be a tool used in the manufacturing of semiconductors.
- the exhaust treatment system may be an AtlasTM abatement system, as provided by Edwards Limited.
- the exhaust stream may comprise one or more of NOx, nitrous oxides (N2O), nitrogen trifluoride (NF3), fluorine (F2), and/or silane (SiF ).
- N2O nitrous oxides
- NF3 nitrogen trifluoride
- F2 fluorine
- SiF silane
- the (or each) NOx adsorber may reversibly adsorb NOx, such that the NOx may be desorbed when the NOx reactor is online with respect to said NOx adsorber.
- the NOx adsorber may comprise a transitional metal, a precious metal, a noble metal, an alkaline earth metal or alkali metal.
- the NOx adsorber may comprise magnesium oxide (MgO), and/or hopcalite (CuMnOx), and/or palladium, and/or platinum, and/or copper, and/or cobalt, and/or any of the alkali metals or alkaline earth metals, such as magnesium or sodium.
- the NOx adsorber may optionally be dispersed on various supports, such as ceria, silica, alumina, or zeolite supports. In some embodiments, combinations of the above listed metals on a silicate, alumina, ceria or zeolitic supports containing alkali metals or alkaline metals may be used.
- the NOx adsorber may be palladium, platinum, copper, cobalt, potassium, sodium, silver, or combinations thereof supported on ceria.
- the NOx adsorber may comprise magnesium oxide (MgO).
- the or each NOx adsorber may be selected from the list containing magnesium oxide (MgO), barium oxide (BaO), platinum on alumina (Pt/A ⁇ Os), alumina (AI2O3), cerium dioxide (Ce02), platinum on cerium dioxide (Pt/CeO2), palladium on cerium dioxide (Pd/CeO2), palladium on tungsten oxide and zirconia (Pd/WOsZrO2).
- the NOx adsorber may alternatively be palladium (Pd), platinum (Pt), barium oxide (BaO) or lanthanum oxide (LaO), on ceria, alumina, silica, or zeolites.
- the NOx adsorber may alternatively be alumina, silica, zeolites, or ceria, containing platinum (Pt), palladium (Pa), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), and/or yttrium (Y).
- the system of the present invention enables selection from a broad range of materials for the NOx adsorber.
- the NOx adsorber may be cheaper to produce and to replace than the NOx reactor.
- the NOx adsorber may be selected according to the specific composition of the exhaust stream. In embodiments comprising a plurality of NOx adsorbers, the NOx adsorbers may be the same or may differ in composition. Preferably, the NOx adsorbers may have the same composition.
- the at least one NOx adsorber may be arranged in fluid communication with the exhaust stream.
- the exhaust stream may pass across and/or through the NOx adsorber.
- the exhaust treatment system preferably comprises at least one NOx reactor, and may comprise a plurality of NOx reactors.
- at least one NOx adsorber may be arranged fluidly upstream of at least one NOx reactor.
- the NOx reactor When the NOx reactor is in an offline configuration, it is fluidly disconnected from exhaust stream and the NOx adsorber. Fluidly disconnected means that substantially none of the exhaust stream passes across and/or through the NOx reactor. This fluid disconnection may be achieved using a valve or other suitable means.
- the NOx reactor may be simultaneously fluidly disconnected with a first NOx adsorber with which it is in an offline configuration, and fluidly connected with a second NOx adsorber with which it is in an online configuration.
- the NOx reactor When the NOx reactor is in an online configuration with respect to the NOx adsorber, the NOx reactor is fluidly connected to NOx adsorber. NOx may be desorbed from the NOx adsorber, and may transfer to the NOx reactor for treatment. Treatment of the NOx by the NOx reactor may involve reduction of the NOx (i.e. decomposition). Said treatment may preferably comprise direct decomposition, or it may comprise reduction in the presence of a reducing agent.
- the NOx reactor may remain fluidly disconnected from exhaust stream, even when in an online configuration. Most preferably, the NOx reactor may remain fluidly disconnected from the exhaust stream at all times to avoid degradation and/or deactivation of the NOx reactor.
- the outputs of the NOx decomposition may preferably be nitrogen and water.
- exhaust treatment systems according to the present invention may address a number of problems associated with exhaust treatment systems of the prior art.
- the arrangement of the present exhaust treatment system may ensure that substantially no oxygen, water vapour, and/or particulates present in the exhaust stream may pass across or through the NOx reactor. This may be as a result of the NOx reactor being fluidly disconnected from the exhaust stream, and because the oxygen, water vapour and/or particulates are not adsorbed to the NOx adsorber. Accordingly, the likelihood of fouling or deactivation of the NOx reactor may be significantly reduced, and the lifespan of the NOx reactor may be increased.
- the fluid disconnection of the NOx reactor and exhaust stream may allow for direct NOx decomposition, as the NOx reactor is not in an oxygen-rich environment. Beneficially, this may allow for the selection from a wider range of NOx reactors. This may also avoid the requirement of a reducing agent. By having greater control over the conditions of NOx decomposition, the operational lifetime of the NOx reactor may be increased, and the time between servicing may also be increased.
- a further benefit of the fluid disconnection of the NOx reactor and the exhaust stream may be a reduction in the pressure drop within the system, enabling smaller particulates of NOx reactor (e.g. catalyst) to be used. This may also allow use of NOx reactor materials that would otherwise be unfeasible.
- NOx reactor e.g. catalyst
- the NOx reactor may be a catalyst.
- the NOx reactor may be a catalyst unit comprising a catalyst and heating means operable to heat the catalyst.
- the catalyst may be, for example, a Cu-ZSM-5 zeolite catalyst, a cerium doped Cu-ZSM-5 zeolite catalyst, a platinum on alumina catalyst (Pt/AI_2O3), a cobalt(ll, III) oxide catalyst (CO3O4), a Ba(MgO) catalyst, a Na-CosO4 catalyst, a La2CuO4 catalyst, a Fe-ZSM5, Fe-BEA, or Vanadium catalyst doped with molybdenum or Tungsten oxides.
- Pt/AI_2O3 platinum on alumina catalyst
- CO3O4 cobalt(ll, III) oxide catalyst
- Ba(MgO) catalyst a Na-CosO4 catalyst
- La2CuO4 catalyst La2CuO4 catalyst
- Fe-ZSM5, Fe-BEA Vanadium catalyst do
- the catalyst may enable direct decomposition of the NOx.
- the catalyst may be in particulate/granular form.
- the present invention may also facilitate the use of smaller granule sizes of catalyst. As the NOx reactor is fluidly disconnected from the exhaust stream, the greater pressure drop associated with the smaller granule size of the catalyst may not affect the overall pressure drop of the system. In systems of the present invention, the pressure drop of the exhaust stream may be primarily affected by the NOx adsorber, rather than the NOx reactor.
- the NOx reactor may be a catalyst, and the catalyst chamber may be supplied with a reducing agent when the NOx adsorber is in an offline configuration.
- the reducing agent may comprise carbon monoxide (CO), hydrogen (H2), methane (CH4), propane (CsHs), or ammonia (NH 3 ).
- the reducing agent selected may depend on the NOx reactor that is present.
- a methane (CPU) reducing agent may be used with Pt/CeZrO2 catalysts, Co-ZSM-5 catalysts, Co-BEA zeolite catalysts, or Co-Mordenite catalysts.
- a propane (CsHs) reducing agent may be used with Fe-ZSM-5 catalysts, or Fe-BEA zeolite catalysts.
- a carbon monoxide (CO) reducing agent may be used with Pt/AI- 2O3 catalysts, or Pt/CeO2 catalysts.
- the NOx reactor may comprise a plasma reactor.
- Plasma reactor may generate plasma typically using electrical discharge or by electron-beam. In either case, the result is to split the constituents of air into smaller energetic gaseous mixtures of ions and electrons.
- the plasma reactor may comprise a di-electric barrier discharge (DBD) plasma reactor, a radio frequency plasma generator, and/or a microwave frequency plasma generator.
- the plasma may be generated by an electron-beam or electrical discharge method.
- the plasma reactor may be heated.
- this may improve NOx reaction in the plasma reactor.
- the NOx reactor may comprise a plasma-assisted catalyst.
- the NOx reactor may comprise both a catalyst and a plasma reactor.
- the catalyst may be as described hereinbefore.
- the plasma chamber may be as defined hereinbefore.
- the plasma chamber may be fluidly upstream of the catalyst.
- the combination of a catalyst and a plasma reactor may enhance the reaction of NOx.
- a NOx reactor is a catalyst, a reducing agent assisted catalyst, a plasma chamber, and/or a plasma-assisted catalyst.
- the exhaust treatment system may comprise a plurality of NOx adsorbers.
- the NOx reactor may be in an online configuration with respect to at least one NOx adsorber, and in an offline configuration with respect to at least one NOx adsorber.
- the NOx reactor may simultaneously be in an online configuration with respect to at least one NOx adsorber, and in an offline configuration with respect to at least one NOx adsorber.
- the exhaust treatment system may comprise from about 2 to about 4 NOx adsorbers, preferably 2 NOx adsorbers.
- the exhaust treatment system may comprise a NOx reactor and two NOx adsorbers, wherein during operation of the exhaust treatment system, the NOx reactor may be in an online configuration with respect to one NOx adsorber and in an offline configuration the other NOx adsorber.
- the NOx reactor may be switchable between an online configuration and an offline configuration with respect to each NOx adsorber.
- the exhaust treatment system may comprise a plurality of NOx reactors and a plurality of NOx adsorbers.
- at least one NOx reactor may be in an online configuration with respect to at least one NOx adsorber, and at least one NOx reactor may be in an offline configuration with at least one NOx adsorber.
- the plurality of NOx reactors may be the same, or the NOx reactors may be of different types.
- Ensuring that during operation of the exhaust treatment system the (or a) NOx reactor is in an offline configuration with respect to at least one NOx adsorber may advantageously allow for substantially continuous adsorption of NOx from the exhaust stream via said at least one NOx adsorber. Furthermore, NOx adsorbed to the NOx adsorber with which the NOx reactor is in an online configuration can be treated simultaneously.
- the arrangement of the present invention is also beneficial as it may accommodate fluctuations in the NOx concentration of the exhaust stream.
- NOx adsorbers can be highly effective at removing NOx from exhaust streams, even when the flow rate of the exhaust stream across/through the NOx adsorber is relatively high.
- the present invention allows for the NOx adsorber with which the NOx reactor is in an offline configuration to adsorb NOx from the exhaust stream, whilst NOx released from the NOx adsorber with which the NOx reactor is in an online configuration is being treated.
- the present invention may be particularly advantageous for applications wherein the NOx concentration of the exhaust stream is relatively high for a short duration, followed by a longer duration when the NOx concentration is relatively low.
- At least one NOx adsorber can be fluidly connected to the exhaust stream during the short duration wherein the NOx concentration is relatively high, then the NOx reactor can be switched to be online with respect to this NOx adsorber during the period wherein the NOx concentration is relatively low.
- the present invention may thereby allow more time for the NOx reactor to decompose the NOx present during the elevated NOx concentration of the exhaust stream, compared with if the NOx reactor were in continuous fluid connection with the exhaust stream.
- the present invention increases the time allotted for NOx decomposition, such that it is more proportional to the amount of NOx that must be treated. This may advantageously improve NOx reduction.
- the separation of the NOx reactor from the exhaust stream in the present invention may allow for the controlled release of NOx from the NOx adsorber with which the NOx reactor is in an online configuration. This may enable the effects of fluctuations in the NOx concentration of the exhaust stream on the NOx reaction rate to be reduced, as NOx can be released from the NOx adsorber at a substantially continuous rate. Having greater control over the release rate of NOx for treatment by the NOx reactor is beneficial, as this enables greater control over the reaction conditions at the NOx reactor, such that it is not required to be as versatile. Additionally, this may be beneficial when the NOx reactor comprises a catalyst, because controlling the release rate of NOx may enable the volume of catalyst to be reduced.
- Catalysts particularly direct NOx catalysts, are often expensive to produce so a reduction in the amount of catalyst required is beneficial. Furthermore, catalysts may require elevated temperatures to decompose NOx effectively. Reducing the volume of catalyst may decrease the overall energy requirements of the system, whilst still allowing substantially continuous abatement of NOx.
- the present invention may also provide the ability to preconcentrate NOx prior to decomposition by the NOx reactor, by controlling the release rate of NOx from the NOx adsorber.
- the preconcentration of NOx may be beneficial as the rate of NOx conversion (i.e. NOx decomposition) may be concentration dependant.
- NOx decomposition i.e. NOx decomposition
- preconcentration of NOx at the NOx adsorber prior to release may provide improved NOx decomposition.
- the or a NOx reactor may be switchable between an online configuration and an offline configuration with respect to at least two NOx adsorbers.
- this may aid in allowing the substantially continuous abatement of NOx from an exhaust stream.
- at least one NOx reactor - NOx adsorber pair may switch to an online configuration when another NOx reactor - NOx adsorber pair switches to an offline configuration.
- the exhaust treatment system may further comprise a controller.
- the controller may be configured to switch the or a NOx reactor between an offline configuration and an online configuration with respect to the or each NOx adsorber in response to an input signal.
- the input signal may be from a process tool to which the exhaust treatment system is connected. Additionally, or alternatively, the input signal may be from a sensor measuring the exhaust stream. The sensor may measure the NOx concentration of the exhaust stream. Additionally, or alternatively, the sensor may measure other parameters indicative of NOx release.
- the exhaust treatment system may further comprise at least one temperature sensor configured to measure the temperature of the NOx reactor.
- the input signal may be from the temperature sensor connected to the NOx reactor. Additionally, or alternatively, the input signal may be from a timer.
- the controller may be configured to automatically switch the NOx reactor between an offline configuration and an online configuration with respect to at least a pair of NOx adsorbers in response to an input signal passing a threshold value.
- the input signals may be as set out hereinbefore.
- this may allow substantially automatic operation of the exhaust treatment system and enable substantially continuous NOx abatement of the exhaust stream.
- the monitoring of the NOx reactor and/or NOx adsorber(s) may provide information on the activity of the NOx reactor and/or NOx adsorber(s). This may aid in ensuring that the system is adequately abating NOx from the exhaust stream, and may notify the user as to when the catalyst and/or NOx adsorber(s) require maintenance and/or replacement.
- the NOx reactor may be located within a reactor chamber.
- the catalyst when the NOx reactor is a catalyst, the catalyst may be located within a catalyst chamber.
- the catalyst chamber can withstand pressures of up to about 50 bar. The catalyst chamber may therefore be pressurised during operation.
- the exhaust treatment system may further comprise heating means operable to heat the NOx adsorber when the NOx reactor is in an online configuration therewith.
- the heating means may comprise a heating element, a flame (i.e. hot gas), an electrical induction heater, and/or a microwave induction heater.
- the heating means may be operable via the controller, and this operation may be automated. Heating the NOx adsorber with which the NOx reactor is in an online configuration may increase the rate of desorption (i.e. release) of NOx from the NOx adsorber.
- the temperature to which the NOx adsorber is heated may provide control over the release rate of NOx from the NOx adsorber.
- the NOx adsorber when in fluid communication with the exhaust stream (i.e. when the NOx reactor is offline with respect to the NOx adsorber), the NOx adsorber may be heated by the heating means to a temperature of at least 100°C. This may reduce the likelihood of water vapour within the exhaust stream forming hydroxides. Water may also cause physical pore blocking of the NOx adsorber, thereby reducing or preventing NOx adsorption.
- the adsorber when the NOx reactor is online with respect to the NOx adsorber, the adsorber may be heated by the heating means to temperatures greater than about 100°C, preferably greater than about 200°C, for example greater than about 600°C.
- this may aid in the decomposition of NOx.
- the temperature of the NOx reactor may remain substantially constant and NOx left to evolve naturally at the temperature at which it adsorbed.
- the exhaust treatment system may further comprise a substantially inert gas flow operable to transfer NOx released by the NOx adsorber to the NOx reactor.
- the substantially inert gas flow may comprise nitrogen, ‘dry’ air with controlled oxygen concentration, argon, and/or carbon dioxide.
- the substantially inert gas flow comprises nitrogen.
- the substantially inert gas flow may aid in the transfer of NOx from the NOx adsorber to the NOx reactor when the NOx reactor is in an online configuration with respect to the NOx adsorber.
- the flow rate of the substantially inert gas flow may determine the amount of NOx treated at the NOx reactor.
- the flow rate of the substantially inert gas flow may be controlled, preferably via the controller.
- the flow rate of the substantially inert gas flow and the temperature control provided by the heating means may operate in concert to control the release of NOx from the NOx adsorber and the flow rate of NOx across the NOx reactor.
- the substantially inert gas flow may comprise further additives.
- a reducing agent may be added to the substantially inert gas flow.
- the reducing agent may comprise carbon monoxide, hydrogen, ammonia, methane, propane, and/or propene.
- Such additives may be appropriate when the NOx reactor is a catalyst that is particularly susceptible to deactivation by water vapour.
- Co-ZSM-5 catalysts or Co-Ferrierite catalysts are highly sensitive to water vapour within the exhaust gas flow, which can lead to deactivation of the catalyst. Accordingly, in such instances, the inclusion of such additives in the substantially inert gas flow may be beneficial.
- the reducing agent may assist desorption of NOx from the NOx adsorber. Providing net reducing conditions at the NOx adsorber may enable the NOx adsorber to desorb NOx at a lower temperature. This may reduce the running costs of the system.
- the exhaust treatment system may comprise a foraminous burner, electrical induction heater, or plasma reactor.
- the foraminous burner, electrical induction heater, or plasma reactor may be arranged upstream of the NOx adsorber(s). This may enable pre-heating of the exhaust gas stream.
- the exhaust treatment system may further comprise an acid gas scrubber.
- the acid gas scrubber may be arranged upstream of the NOx adsorber(s).
- this may enable removal of acid gases from the exhaust gas stream prior to passing over/through the NOx adsorber(s) and NOx reactor(s).
- the present invention provides a method for abating NOx from an exhaust stream.
- the method comprises the steps of: i) Providing an exhaust treatment system according to any preceding aspect or embodiment. ii) Directing the exhaust stream from the process tool across an NOx adsorber with which the NOx reactor is in an offline configuration. iii) Adsorbing NOx from the exhaust stream onto the NOx adsorber. iv) Switching the NOx reactor from an offline configuration to an online configuration with respect to the NOx adsorber. v) Releasing NOx from the NOx adsorber and directing said released NOx to the NOx reactor for treatment.
- the NOx adsorber and NOx reactor may be as described in relation to the preceding aspect.
- the NOx released during step (v) is substantially free from O2, and/or H2O, and/or particulates present in the exhaust stream. “Substantially free” may be defined as less than about 1 vol. %, preferably less than about 0.1 vol. %.
- this method may significantly reduce the risk of fouling or deactivation of the NOx reactor, as the NOx reactor is not in fluid communication with the exhaust stream. Accordingly, direct NOx decomposition may be possible, allowing selection from a wider range of NOx reactors and the avoidance of the requirement of a reducing agent. The operational lifetime of the NOx reactor may be increased, and the time between servicing may be reduced.
- step (iii) following adsorption of NOx onto the NOx adsorber, the exhaust stream may be directed towards an outlet of the exhaust treatment apparatus, and may be conveyed to the outlet via further abatement apparatus.
- step (iv) further comprises directing the exhaust stream from the process tool across a further NOx adsorber with which the NOx reactor is in an offline configuration.
- this may allow for substantially continuous adsorption and treatment of NOx from the exhaust stream. This may also accommodate fluctuations in the NOx concentration of the exhaust stream.
- the present method may allow the NOx adsorber with which the NOx reactor is in an offline configuration to adsorb NOx from the exhaust stream, whilst NOx released from the NOx adsorber with which the NOx reactor is in an online configuration is being treated. This may provide more time for the NOx reactor to decompose the NOx present during a peak in NOx concentration of the exhaust stream than if the NOx reactor were in permanent fluid communication with the exhaust stream.
- step (v) involves heating the NOx adsorber to a temperature greater than about 100°C, preferably greater than about 200°C, for example greater than about 600°C.
- this may aid in desorption of NOx from the NOx adsorber, allowing transfer of desorbed NOx to the NOx reactor for treatment.
- step (v) further comprises introducing a substantially inert gas flow to transfer the released NOx to the NOx reactor.
- the substantially inert gas flow may comprise nitrogen, argon, ‘dry’ air with a controlled oxygen concentration, and/or carbon dioxide.
- the substantially inert gas flow comprises nitrogen.
- the substantially inert gas flow may comprise further additives. For example, carbon monoxide, ammonia, hydrogen, methane, propane, and/or propene may be added to the substantially inert gas flow as reducing agents.
- the substantially inert gas flow may aid in the control of the transfer of NOx from the NOx adsorber to the NOx reactor, as described hereinbefore.
- the flow rate of the substantially inert gas flow may be selectively modulated to control the delivery rate of NOx to the NOx reactor.
- Having control over the release rate of NOx for treatment by the NOx reactor may be beneficial as the effects of fluctuations in the NOx concentration of the exhaust stream on the NOx reaction rate may be reduced.
- This may be particularly advantageous when the NOx reactor comprises a catalyst, as volume of catalyst required can be reduced.
- the catalyst is often expensive to produce, and may require elevated temperatures to decompose NOx effectively. Reducing the volume of catalyst that must be maintained at elevated temperatures may make the operation of the exhaust treatment system more cost-effective, whilst still allowing for substantially continuous abatement of NOx.
- the method may further comprise the step of modulating the pressure within the NOx reactor chamber during step (v) to increase and/or decrease the rate of decomposition of the released NOx by the NOx reactor.
- Increasing the pressure may increase the rate of decomposition of the released NOx by the NOx reactor, and decreasing the pressure may decrease the rate of decomposition of the released NOx by the NOx reactor.
- the method may be substantially automated by a controller.
- step (iv) may be initiated by a signal output by the process tool to which the exhaust treatment system is connected, and/or by a sensor measuring the NOx concentration of the exhaust stream, and/or by a sensor measuring the temperature of the NOx reactor, and/or by a timer.
- the modulation of the temperature of the NOx adsorber and/or the flow rate of the substantially inert gas flow of step (v) may be automated and controlled by the controller.
- the modulation of the pressure of the NOx reactor may be automated and controlled by the controller.
- the present invention provides the use of magnesium oxide, an alkaline earth material, an alkali metal, a transitional metal, a precious metal, a noble metal, palladium, platinum, copper, cobalt, and/or Hopcalite, to adsorb NOx from an abatement gas stream and subsequently desorb said NOx for catalytic treatment.
- supports such as zeolites may be used also containing such metals copper, cobalt, silver, platinum or palladium.
- the magnesium oxide and/or Hopcalite, or palladium/platinum on silicate supports, or silver, copper and cobalt-based transition metal oxides, or combinations thereof is fluidly disconnected from the means for catalytic treatment when adsorbing NOx from the abatement gas stream.
- the advantages of this aspect are as described in the preceding aspects and embodiments.
- Figure 1 shows a schematic of an exhaust treatment system (1 ) in accordance with the prior art
- FIGS. 2A-B show schematic views of an embodiment of an exhaust treatment system in accordance with the present invention
- FIGS. 3A-B show a schematic views of an alternative embodiment of an exhaust treatment system in accordance with the present invention.
- Figure 4 shows a flow chart of a method in accordance with the present invention.
- FIG. 1 illustrates a schematic of an exhaust treatment system (1 ) in accordance with the prior art.
- the system (1 ) comprises a conduit (2) through which the exhaust stream travels.
- the direction of flow of the exhaust stream through the exhaust treatment system (1 ) is shown by arrows Ai and A2.
- Arrow A1 shows the direction of flow of the exhaust stream from the process tool into the exhaust treatment system (1 )
- arrow A2 shows the direction of flow of the exhaust stream following abatement.
- the exhaust treatment system (1 ) comprises a NOx adsorber (3) attached to a catalyst (4).
- the NOx adsorber (3) and catalyst (4) are arranged in series within the conduit (2), and are both in fluid communication with the exhaust stream throughout operation of the exhaust treatment system (1 ).
- the catalyst (4) contains a heating element (5) embedded within, to maintain the catalyst (4) at elevated temperatures during operation. In use, the temperature of the heating element (5) may be adjusted to improve NOx adsorption and desorption conditions.
- a reducing agent (not shown) may be required to aid in the decomposition of NOx by the catalyst (4).
- the presence of oxygen in the exhaust stream when such reducing agents are used is undesirable, as the reaction of O2 with CO consumes much of the CO required to facilitate the reaction between CO and NO. This may reduce the efficiency of NOx decomposition.
- Water vapour present within the exhaust stream can cause deactivation of the catalyst (4).
- Particulate matter, such as silica, present in the exhaust stream may foul the catalyst (4) and thereby reduce its activity.
- the concentration of NOx within the exhaust stream may vary. As the catalyst (4) is in fluid communication with the exhaust stream, the catalyst (4) must be able to meet the abatement requirements during the peak NOx concentration.
- FIGS 2A-B illustrate schematic views of an embodiment of an exhaust treatment system (6) in accordance with the present invention.
- the exhaust treatment system (6) comprises an NOx adsorber (7) configured to adsorb NOx from an incoming exhaust stream (8).
- the NOx adsorber (7) is a passive NOx adsorber, comprising, for example, magnesium oxide (MgO).
- a heating element (9) is embedded within the NOx adsorber (7).
- the exhaust treatment system (6) further comprises a NOx reactor (10).
- the NOx reactor (10) comprises a catalyst, a reducing agent-assisted catalyst, a plasma reactor, or a plasma-assisted catalyst, as described hereinbefore.
- the NOx reactor (10) may be a Cu-ZSM-5 zeolite catalyst.
- a first valve (11 ) is arranged upstream of the NOx adsorber (7).
- a second valve (12) is arranged downstream of the NOx adsorber (7).
- FIG. 2A shows the arrangement of the exhaust treatment system (6) when the NOx reactor (10) is in an offline configuration.
- the NOx reactor (10) is fluidly disconnected from the exhaust stream (8) and from the NOx adsorber (7).
- this fluid disconnection of the NOx reactor (10) from the exhaust stream (8) and from the NOx adsorber (7) is provided by the downstream valve (11 ).
- the exhaust stream (8) enters the exhaust treatment system (6) from a process tool (not shown) via the first valve (11 ), and is conveyed across the NOx adsorber (7). NOx is adsorbed onto the NOx adsorber (7), and thereby is removed from the exhaust stream (8).
- the treated exhaust stream (13) then travels through the downstream valve (12) and exits the exhaust treatment system (6).
- the temperature of the NOx adsorber (7) is typically at least about 100°C when the NOx reactor (10) is in an offline configuration. This is because NOx is readily adsorbed by the NOx adsorber (7) from the exhaust stream (8) at these temperatures.
- the NOx reactor (10) is not exposed to the exhaust stream (8) at all when in the offline configuration, as the NOx reactor (10) is fluidly disconnected from the exhaust stream (8). Accordingly, no oxygen, water vapour, and/or particulates that might be present in the exhaust stream (8) pass across or through the NOx reactor (10). Beneficially, this may avoid deactivation and/or fouling of the NOx reactor (10), particularly wherein the NOx reactor is a catalyst.
- Figure 2B shows the arrangement of the exhaust treatment system (6) when the NOx reactor (10) is in an online configuration.
- the NOx reactor (10) is fluidly connected to the NOx adsorber (7), via the second valve (12).
- the exhaust stream (8) is no longer entering the exhaust treatment system (6), via the first valve (11 ). Therefore, the NOx reactor (10) is fluidly disconnected from the exhaust stream (8), even when in an online configuration with the NOx adsorber (7).
- the heating element (9) is operated to increase the temperature of the NOx adsorber (7) to a temperature greater than about 200°C, preferably greater than about 300°C, for example greater than about 600°C. This increase in temperature of the NOx adsorber (7) facilitates the release of NOx adsorbed thereto.
- a substantially inert gas flow (14) is activated.
- the substantially inert gas flow (14) comprises nitrogen.
- the substantially inert gas flow (14) is directed across/through the NOx adsorber (7) via the first valve (11 ).
- the substantially inert gas flow (14) transfers the NOx released by the NOx adsorber (7) to the NOx reactor (10) via the second valve (12).
- the NOx reactor (10) treats the NOx carried by the nitrogen gas flow (14).
- FIGS 3A-B illustrate schematic views of an alternative embodiment of an exhaust treatment system (15) in accordance with the present invention.
- the exhaust treatment system (15) comprises a first NOx adsorber (16) and a second NOx adsorber (17), each configured to adsorb NOx from an incoming exhaust stream (18).
- the first and second NOx adsorbers (16,17) are passive NOx adsorbers comprising magnesium oxide (MgO).
- a heating element (19,20) is present within each NOx adsorber (16,17), and configured to regulate the temperature thereof.
- the exhaust treatment system (15) further comprises a NOx reactor (21 ).
- the NOx reactor (21 ) comprises a catalyst, a reducing agent-assisted catalyst, a plasma reactor, or a plasma-assisted catalyst, as described hereinbefore.
- the NOx reactor (21 ) may be a Cu-ZSM-5 zeolite catalyst.
- a series of valves are present and configured to fluidly connect and disconnect portions of the exhaust treatment system (15).
- Figure 3A illustrates when the NOx reactor (21 ) is in an offline configuration with respect to the first NOx adsorber (16), and in an online configuration with respect to the second NOx adsorber (17). Accordingly, the NOx reactor (21 ) is fluidly disconnected from the exhaust stream (18) and from the first NOx adsorber (16).
- the exhaust stream (18) enters the exhaust treatment system (15) from a process tool (not shown) and is conveyed across the first NOx adsorber (16).
- the temperature of the first NOx adsorber (16) is typically at least about 100°C in this configuration. NOx is adsorbed onto the first NOx adsorber (16), and thereby is removed from the exhaust stream (18).
- the treated exhaust stream (22) then exits the exhaust treatment system (15) without passing across/through the NOx reactor (21 ).
- the NOx reactor (21 ) is not exposed to the exhaust stream (18) at all, when in an offline or online configuration with respect to either NOx adsorber (16,17). Accordingly, no oxygen, water vapour, and/or particulates that might be present in the exhaust stream (18) pass across/through the NOx reactor (21 ). Beneficially, this may avoid deactivation or fouling of the NOx reactor (21 ).
- the NOx reactor (21 ) is in an online configuration with respect to the second NOx adsorber (17).
- the NOx reactor (21 ) is fluidly connected to the second NOx adsorber (17), via a valve.
- the second heating element (20) is operated to increase the temperature of the second NOx adsorber (17).
- the temperature of the second NOx adsorber (17) may be increased to greater than about 200°C, preferably greater than about 300°C, for example about 600°C. This increase in temperature of the NOx adsorber (17) releases NOx adsorbed thereto from a previous cycle when the NOx reactor (21 ) was in an offline configuration with respect to the second NOx adsorber (17).
- a substantially inert gas flow (23), preferably comprising nitrogen, is directed across/through the second NOx adsorber (17) to transfer the NOx released by the second NOx adsorber (17) to the NOx reactor (21 ).
- the NOx reactor (21 ) treats the NOx carried by the substantially inert gas flow (23), which then exits the exhaust treatment system (15) via an outlet (25).
- Figure 3B illustrates when the NOx reactor (21 ) is in an online configuration with respect to the first NOx adsorber (16), and in an offline configuration with respect to the second NOx adsorber (17). Accordingly, the NOx reactor (21 ) is fluidly disconnected from the exhaust stream (18) and from the second NOx adsorber (17).
- the exhaust stream (18) enters the exhaust treatment system (15) from a process tool (not shown) and is conveyed across the second NOx adsorber (17).
- the temperature of the second NOx adsorber (17) is typically at least about 100°C in this configuration. NOx is adsorbed onto the second NOx adsorber (17), and thereby is removed from the exhaust stream (18).
- the treated exhaust stream (22) then exits the exhaust treatment system (15) without passing through the NOx reactor (21 ).
- the NOx reactor (21 ) is in an online configuration with respect to the first NOx adsorber (16).
- the NOx reactor (21 ) is fluidly connected to the first NOx adsorber (16), via a valve.
- the first heating element (19) is operated to increase the temperature of the first NOx adsorber (16) to a temperature greater than about 200°C, preferably greater than about 300°C, for example about 600°C. This increase in temperature of the first NOx adsorber (16) releases NOx adsorbed thereto when in the configuration illustrated in Figure 3A.
- a substantially inert gas flow (24), preferably comprising nitrogen, is directed across/through the first NOx adsorber (16) to transfer the NOx released by the first NOx adsorber (16) to the NOx reactor (21 ).
- the NOx reactor (21 ) treats the NOx carried by the substantially inert gas flow (24), which then exits the exhaust treatment system (15) via an outlet (25).
- the system (15) switches between the configuration of Figure 3A and that of Figure 3B. Accordingly, the NOx reactor (21 ) is always in an online configuration with respect to one NOx adsorber
- this may allow substantially continuous NOx removal from the exhaust stream (18), without deactivation and/or fouling of the NOx reactor (21 ) due to exposure to oxygen, water vapour, and/or particulates present in the exhaust stream (18).
- the exhaust treatment system (15) further comprises a controller (26), configured to switch the catalyst (21 ) between an online configuration and an offline configuration with respect to the two NOx adsorbers (16,17). This switching may be automatic and triggered in response to an input.
- the exhaust treatment system (15) may further comprise a sensor (not shown) configured to measure the NOx concentration of the incoming exhaust stream (18). The sensor may output a signal to the controller (26), which can trigger the switch of the configuration of the NOx reactor (21 ), for example when the NOx concentration of the exhaust stream (18) passes a threshold value.
- the exhaust treatment system may further comprise a temperature sensor (27) configured to measure the temperature of the NOx reactor (21 ).
- the temperature sensor (27) may output a signal to the controller (26), which can trigger the switch of the configuration of the NOx reactor (21 ), for example when the temperature of the NOx reactor (21 ) passes a threshold value.
- the NOx reactor (21 ) is located within a chamber (not shown), which may be pressurised to increase and decrease the reaction rate of the NOx at the NOx reactor (21 ).
- the pressure of the chamber may be controller by the controller (26), and is preferably automated.
- the flow rate of the substantially inert gas flow (23,24) may be varied via the controller, preferably this may be automated.
- the pressure of the chamber and/or flow rate of the substantially inert gas flow (23,24) may be selected according to the concentration of NOx of the incoming exhaust stream (18).
- the exhaust treatment system (15) may further comprise heating means (not shown) arranged upstream of the NOx adsorbers (16,17).
- the heating means may be configured to heat the exhaust gas stream (18).
- the heating means may comprise, for example, a foraminous burner, an electrical induction heater, or a plasma reactor.
- the exhaust treatment system (15) may further comprise an acid gas scrubber (not shown).
- the acid gas scrubber may be arranged upstream of the NOx adsorbers (16,17).
- the acid gas scrubber may be configured to remove acid gases from the exhaust gas stream (18).
- the exhaust treatment system (15) is preferably connected to a process tool from a semiconductor manufacturing process during operation.
- Figure 4 illustrates a flow chart of a method in accordance with the present invention.
- An exhaust treatment system according to Figures 2A-B or 3A-B is provided.
- An exhaust stream is directed from the process tool across and/or through an NOx adsorber with which the NOx reactor is in an offline configuration (28).
- NOx present in the exhaust stream is adsorbed onto the NOx adsorber with which the NOx reactor is in an offline configuration (29).
- the NOx concentration of the exhaust stream may be measured by a sensor, and this measurement may be output to the controller (30).
- the sensor may measure the NOx concentration of the exhaust stream at predetermined time intervals, or the sensor may measure the NOx concentration of the exhaust stream substantially continuously.
- the temperature of the NOx reactor may be measured via a temperature sensor, and this measurement may be output to the controller (31 ).
- the temperature sensor may measure the temperature of the NOx reactor at predetermined time intervals, or the temperature sensor may measure the temperature of the NOx reactor substantially continuously.
- the process tool to which the exhaust treatment system is connected may output a signal indicating the NOx concentration of the exhaust stream (32). This signal may be output at predetermined time intervals, or the signal may be output substantially continuously.
- the controller may switch the NOx reactor from an offline configuration to an online configuration with respect to the/a NOx adsorber (33).
- The/a NOx adsorber is heated to a temperature greater than about 100°C, preferably greater than about 200°C, for example to about 600°C (34).
- a substantially inert gas flow preferably comprising nitrogen, may be introduced to the NOx adsorber to transfer the released NOx to the NOx reactor for treatment (35).
- the released NO is substantially free from oxygen, and/or water vapour, and/or particulates that were present in the exhaust stream.
- the pressure within the NOx reactor chamber may be modulated to increase and/or decrease the rate of reaction of the released NOx at the NOx reactor (36).
- the controller may switch a NOx reactor from an online configuration to an offline configuration with respect to another NOx adsorber, which will then proceed through steps (28-32).
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Abstract
The present invention relates to an exhaust treatment system for NOx abatement of an exhaust stream. The exhaust treatment system comprises at least one NOx adsorber configured to adsorb NOx from the exhaust stream, and a NOx reactor operable in an offline configuration and an online configuration. When the NOx reactor is in an offline configuration, the NOx reactor is fluidly disconnected from the exhaust stream and the NOx adsorber, and the NOx adsorber is fluidly connected to the exhaust stream such that NOx contained in the exhaust stream may be adsorbed by the NOx adsorber. When the NOx reactor is in an online configuration, the NOx reactor is fluidly connected to the NOx adsorber such that NOx adsorbed by the NOx adsorber may be treated by the NOx reactor.
Description
NOx Reduction
Field
The present invention relates to exhaust treatment systems for NOx abatement from an exhaust stream of a process tool, and to methods of abating NOx from an exhaust stream.
Background
Nitrogen oxides (NOx) are air pollutants, produced as a by-product of many processes, including burning of fossil fuels, and the production of semiconductors. NOx can be responsible for photochemical smog and acid rain, therefore, the release of NOx into the atmosphere must be limited and preferably avoided altogether. This is complicated by several challenges associated with the abatement of exhaust streams containing NOx, particularly in the presence of oxygen and/or water vapour.
NOx reactors, such as catalysts, are typically used in NOx abatement processes. High NOx abatement rates via a NOx reactor typically requires reductant-rich conditions, so the presence of oxygen in the exhaust stream may reduce the efficiency of abatement reactions. However, for many applications, the presence of oxygen and/or water in the exhaust stream is largely unavoidable. Addition of reducing agents, such as ammonia, is often used to facilitate the reaction of NOx - providing a reaction which is feasible in the presence of oxygen or water. However, for many applications the use of ammonia is undesirable, since it is an additional consumable reagent which must be dosed.
A more preferable NOx abatement route would be to make use of reducing agents already present in the exhaust stream. For example, unoxidised/partially oxidised hydrocarbons and/or carbon monoxide (CO). However, the presence of oxygen in the exhaust stream when such reducing agents are used can be detrimental, as the reaction of O2 with CO consumes much of the CO required for the reaction between CO and NO. In plasma NOx reactors, the presence of oxygen and/or water in the exhaust stream may also be undesirable, as it may result in pore
blocking. Furthermore, the presence of 02 may enable nitric oxide to be converted to nitrogen dioxide, which should be avoided due to the associated health concerns if inhaled.
A further challenge to achieving efficient NOx abatement is presented by the deficiency of suitable direct NOx catalysts, so-called because they can directly decompose NOx without the need for a reducing agent. Although some direct NOx catalysts are available, few provide high enough activity to allow use of a suitably small volume of the catalyst to be appropriate for many industries. For example, in the semiconductor industry, the footprint of the exhaust treatment system is often limited. The overall size of the exhaust treatment system thereby restricts the overall volume of catalyst that can be used. Additionally, many direct NOx catalysts operate more efficiently at elevated temperatures, for example temperatures greater than 200°C. The operating cost required to maintain a large volume of catalyst at such high temperatures renders them unfeasible for practical application in many industries. Furthermore, the pressure drop associated with using large volumes of catalyst may be too great for many applications, particularly if the catalyst is placed directly into the exhaust of the chemical process.
Certain applications, such as the abatement of exhaust streams from process tools used in semiconductor manufacture, may provide particularly challenging conditions for NOx abatement. Water vapour may be present in the exhaust stream due to the burning of hydrocarbons, and/or water scrubbing processes upstream of the NOx reactor. This water vapour may deactivate the NOx reactor (e.g. catalyst). Certain catalysts, such as Cu-ZSM5 catalysts, may be permanently degraded by water vapour present in the exhaust stream. Additionally, the exhaust streams from semiconductor manufacture often contain a net oxidising amount of oxygen in relation to the total concentration of reductants available, thereby lessening the efficiency of the NOx decomposition. Also, particulate matter, such as silica, may be present in the exhaust stream and can foul the NOx reactor and/or reduce its activity. The pressure drop across the NOx reactor may be required to be low, imposing further constraints on such abatement systems.
A further challenge is posed by variation in the concentration of NOx within the exhaust stream according to the step of the semiconductor manufacture process that is occurring. For example, the NOx concentration in the exhaust stream may be relatively low during deposition processes. Then, the NOx concentration in the exhaust stream may be relatively high during a “clean-step” using NF3. The “cleanstep” typically occurs for a shorter time than the deposition processes. Accordingly, the NOx reactor may be required to abate high concentrations of NOx for a relatively short amount of time, then be substantially inactive or slightly active for long periods of time. Therefore, a NOx reactor must be selected that can meet the abatement requirements during the peak concentration of NOx, in spite of it’s relatively short duration. This problem may be exacerbated by the relatively high overall gas flow through the exhaust treatment system.
It would therefore be beneficial to have an exhaust treatment system capable of operating under such conditions with reduced deactivation of the NOx reactor. The present invention aims to solve, at least in part, these and other problems associated with exhaust treatment systems of the prior art.
Summary
In an aspect, the present invention provides an exhaust treatment system for NOx abatement of an exhaust stream. The exhaust treatment system comprises at least one NOx adsorber configured to adsorb NOx from the exhaust stream. The exhaust treatment system further comprises a NOx reactor having an offline configuration and an online configuration. When the NOx reactor is in an offline configuration, the NOx reactor is fluidly disconnected from the exhaust stream and the NOx adsorber. Also, the NOx adsorber is fluidly connected to the exhaust stream such that NOx contained in the exhaust stream may be adsorbed by the NOx adsorber. When the NOx reactor is in an online configuration, the NOx reactor is fluidly connected to the NOx adsorber such that NOx adsorbed by the NOx adsorber may be treated by the NOx reactor.
The exhaust treatment system is preferably for NOx abatement of an exhaust stream from a process tool. The process tool may be a tool used in the
manufacturing of semiconductors. For example, the exhaust treatment system may be an Atlas™ abatement system, as provided by Edwards Limited.
The exhaust stream may comprise one or more of NOx, nitrous oxides (N2O), nitrogen trifluoride (NF3), fluorine (F2), and/or silane (SiF ). The skilled person will understand that the exhaust stream may comprise further constituent components, dependent at least in part on the process from which the exhaust stream is produced.
The (or each) NOx adsorber may reversibly adsorb NOx, such that the NOx may be desorbed when the NOx reactor is online with respect to said NOx adsorber. The NOx adsorber may comprise a transitional metal, a precious metal, a noble metal, an alkaline earth metal or alkali metal. The NOx adsorber may comprise magnesium oxide (MgO), and/or hopcalite (CuMnOx), and/or palladium, and/or platinum, and/or copper, and/or cobalt, and/or any of the alkali metals or alkaline earth metals, such as magnesium or sodium. The NOx adsorber may optionally be dispersed on various supports, such as ceria, silica, alumina, or zeolite supports. In some embodiments, combinations of the above listed metals on a silicate, alumina, ceria or zeolitic supports containing alkali metals or alkaline metals may be used. For example, the NOx adsorber may be palladium, platinum, copper, cobalt, potassium, sodium, silver, or combinations thereof supported on ceria. In a preferred embodiment, the NOx adsorber may comprise magnesium oxide (MgO).
In embodiments, the or each NOx adsorber may be selected from the list containing magnesium oxide (MgO), barium oxide (BaO), platinum on alumina (Pt/A^Os), alumina (AI2O3), cerium dioxide (Ce02), platinum on cerium dioxide (Pt/CeO2), palladium on cerium dioxide (Pd/CeO2), palladium on tungsten oxide and zirconia (Pd/WOsZrO2). The NOx adsorber may alternatively be palladium (Pd), platinum (Pt), barium oxide (BaO) or lanthanum oxide (LaO), on ceria, alumina, silica, or zeolites. The NOx adsorber may alternatively be alumina, silica, zeolites, or ceria, containing platinum (Pt), palladium (Pa), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), and/or yttrium (Y).
The skilled person will appreciate that the system of the present invention enables
selection from a broad range of materials for the NOx adsorber. Advantageously, the NOx adsorber may be cheaper to produce and to replace than the NOx reactor. The NOx adsorber may be selected according to the specific composition of the exhaust stream. In embodiments comprising a plurality of NOx adsorbers, the NOx adsorbers may be the same or may differ in composition. Preferably, the NOx adsorbers may have the same composition.
The at least one NOx adsorber may be arranged in fluid communication with the exhaust stream. Preferably, the exhaust stream may pass across and/or through the NOx adsorber.
The exhaust treatment system preferably comprises at least one NOx reactor, and may comprise a plurality of NOx reactors. Preferably, at least one NOx adsorber may be arranged fluidly upstream of at least one NOx reactor.
When the NOx reactor is in an offline configuration, it is fluidly disconnected from exhaust stream and the NOx adsorber. Fluidly disconnected means that substantially none of the exhaust stream passes across and/or through the NOx reactor. This fluid disconnection may be achieved using a valve or other suitable means. In some embodiments, the NOx reactor may be simultaneously fluidly disconnected with a first NOx adsorber with which it is in an offline configuration, and fluidly connected with a second NOx adsorber with which it is in an online configuration.
When the NOx reactor is in an online configuration with respect to the NOx adsorber, the NOx reactor is fluidly connected to NOx adsorber. NOx may be desorbed from the NOx adsorber, and may transfer to the NOx reactor for treatment. Treatment of the NOx by the NOx reactor may involve reduction of the NOx (i.e. decomposition). Said treatment may preferably comprise direct decomposition, or it may comprise reduction in the presence of a reducing agent. Preferably, the NOx reactor may remain fluidly disconnected from exhaust stream, even when in an online configuration. Most preferably, the NOx reactor may remain fluidly disconnected from the exhaust stream at all times to avoid degradation
and/or deactivation of the NOx reactor. The outputs of the NOx decomposition may preferably be nitrogen and water.
Advantageously, exhaust treatment systems according to the present invention may address a number of problems associated with exhaust treatment systems of the prior art. The arrangement of the present exhaust treatment system may ensure that substantially no oxygen, water vapour, and/or particulates present in the exhaust stream may pass across or through the NOx reactor. This may be as a result of the NOx reactor being fluidly disconnected from the exhaust stream, and because the oxygen, water vapour and/or particulates are not adsorbed to the NOx adsorber. Accordingly, the likelihood of fouling or deactivation of the NOx reactor may be significantly reduced, and the lifespan of the NOx reactor may be increased.
Furthermore, the fluid disconnection of the NOx reactor and exhaust stream may allow for direct NOx decomposition, as the NOx reactor is not in an oxygen-rich environment. Beneficially, this may allow for the selection from a wider range of NOx reactors. This may also avoid the requirement of a reducing agent. By having greater control over the conditions of NOx decomposition, the operational lifetime of the NOx reactor may be increased, and the time between servicing may also be increased.
A further benefit of the fluid disconnection of the NOx reactor and the exhaust stream may be a reduction in the pressure drop within the system, enabling smaller particulates of NOx reactor (e.g. catalyst) to be used. This may also allow use of NOx reactor materials that would otherwise be unfeasible.
In some embodiments, the NOx reactor may be a catalyst. Preferably, the NOx reactor may be a catalyst unit comprising a catalyst and heating means operable to heat the catalyst. The catalyst may be, for example, a Cu-ZSM-5 zeolite catalyst, a cerium doped Cu-ZSM-5 zeolite catalyst, a platinum on alumina catalyst (Pt/AI_2O3), a cobalt(ll, III) oxide catalyst (CO3O4), a Ba(MgO) catalyst, a Na-CosO4 catalyst, a La2CuO4 catalyst, a Fe-ZSM5, Fe-BEA, or Vanadium catalyst doped
with molybdenum or Tungsten oxides. The skilled person will appreciate that the catalyst is not explicitly limited to the above examples.
Preferably, the catalyst may enable direct decomposition of the NOx.
Typically, the catalyst may be in particulate/granular form. The present invention may also facilitate the use of smaller granule sizes of catalyst. As the NOx reactor is fluidly disconnected from the exhaust stream, the greater pressure drop associated with the smaller granule size of the catalyst may not affect the overall pressure drop of the system. In systems of the present invention, the pressure drop of the exhaust stream may be primarily affected by the NOx adsorber, rather than the NOx reactor.
In an alternative embodiment, the NOx reactor may be a catalyst, and the catalyst chamber may be supplied with a reducing agent when the NOx adsorber is in an offline configuration. By way of example, the reducing agent may comprise carbon monoxide (CO), hydrogen (H2), methane (CH4), propane (CsHs), or ammonia (NH3).
The reducing agent selected may depend on the NOx reactor that is present. For example, a methane (CPU) reducing agent may be used with Pt/CeZrO2 catalysts, Co-ZSM-5 catalysts, Co-BEA zeolite catalysts, or Co-Mordenite catalysts. A propane (CsHs) reducing agent may be used with Fe-ZSM-5 catalysts, or Fe-BEA zeolite catalysts. A carbon monoxide (CO) reducing agent may be used with Pt/AI- 2O3 catalysts, or Pt/CeO2 catalysts.
In alternative embodiments, the NOx reactor may comprise a plasma reactor. Plasma reactor may generate plasma typically using electrical discharge or by electron-beam. In either case, the result is to split the constituents of air into smaller energetic gaseous mixtures of ions and electrons. By way of example, the plasma reactor may comprise a di-electric barrier discharge (DBD) plasma reactor, a radio frequency plasma generator, and/or a microwave frequency plasma generator. The plasma may be generated by an electron-beam or electrical discharge method.
Optionally, during operation the plasma reactor may be heated. Advantageously, this may improve NOx reaction in the plasma reactor.
In alternative embodiments, the NOx reactor may comprise a plasma-assisted catalyst. The NOx reactor may comprise both a catalyst and a plasma reactor. The catalyst may be as described hereinbefore. The plasma chamber may be as defined hereinbefore. Preferably, the plasma chamber may be fluidly upstream of the catalyst. Advantageously, the combination of a catalyst and a plasma reactor may enhance the reaction of NOx.
The skilled person will appreciate that further features described in relation to the exhaust treatment system may be used with any embodiment of the NOx reactor. For example, embodiments may include those wherein a NOx reactor is a catalyst, a reducing agent assisted catalyst, a plasma chamber, and/or a plasma-assisted catalyst.
Typically, the exhaust treatment system may comprise a plurality of NOx adsorbers. During operation of the exhaust treatment system, the NOx reactor may be in an online configuration with respect to at least one NOx adsorber, and in an offline configuration with respect to at least one NOx adsorber. Preferably, during operation of the exhaust treatment system, the NOx reactor may simultaneously be in an online configuration with respect to at least one NOx adsorber, and in an offline configuration with respect to at least one NOx adsorber. The exhaust treatment system may comprise from about 2 to about 4 NOx adsorbers, preferably 2 NOx adsorbers.
In a particularly preferred embodiment, the exhaust treatment system may comprise a NOx reactor and two NOx adsorbers, wherein during operation of the exhaust treatment system, the NOx reactor may be in an online configuration with respect to one NOx adsorber and in an offline configuration the other NOx adsorber. The NOx reactor may be switchable between an online configuration and an offline configuration with respect to each NOx adsorber.
The exhaust treatment system may comprise a plurality of NOx reactors and a plurality of NOx adsorbers. In such embodiments, during operation of the exhaust treatment system, at least one NOx reactor may be in an online configuration with respect to at least one NOx adsorber, and at least one NOx reactor may be in an offline configuration with at least one NOx adsorber. The plurality of NOx reactors may be the same, or the NOx reactors may be of different types.
Ensuring that during operation of the exhaust treatment system the (or a) NOx reactor is in an offline configuration with respect to at least one NOx adsorber, may advantageously allow for substantially continuous adsorption of NOx from the exhaust stream via said at least one NOx adsorber. Furthermore, NOx adsorbed to the NOx adsorber with which the NOx reactor is in an online configuration can be treated simultaneously.
The arrangement of the present invention is also beneficial as it may accommodate fluctuations in the NOx concentration of the exhaust stream. NOx adsorbers can be highly effective at removing NOx from exhaust streams, even when the flow rate of the exhaust stream across/through the NOx adsorber is relatively high. The present invention allows for the NOx adsorber with which the NOx reactor is in an offline configuration to adsorb NOx from the exhaust stream, whilst NOx released from the NOx adsorber with which the NOx reactor is in an online configuration is being treated.
The present invention may be particularly advantageous for applications wherein the NOx concentration of the exhaust stream is relatively high for a short duration, followed by a longer duration when the NOx concentration is relatively low. At least one NOx adsorber can be fluidly connected to the exhaust stream during the short duration wherein the NOx concentration is relatively high, then the NOx reactor can be switched to be online with respect to this NOx adsorber during the period wherein the NOx concentration is relatively low. The present invention may thereby allow more time for the NOx reactor to decompose the NOx present during the elevated NOx concentration of the exhaust stream, compared with if the NOx reactor were in continuous fluid connection with the exhaust stream. The present invention increases the time allotted for NOx decomposition, such that it is more
proportional to the amount of NOx that must be treated. This may advantageously improve NOx reduction.
The separation of the NOx reactor from the exhaust stream in the present invention may allow for the controlled release of NOx from the NOx adsorber with which the NOx reactor is in an online configuration. This may enable the effects of fluctuations in the NOx concentration of the exhaust stream on the NOx reaction rate to be reduced, as NOx can be released from the NOx adsorber at a substantially continuous rate. Having greater control over the release rate of NOx for treatment by the NOx reactor is beneficial, as this enables greater control over the reaction conditions at the NOx reactor, such that it is not required to be as versatile. Additionally, this may be beneficial when the NOx reactor comprises a catalyst, because controlling the release rate of NOx may enable the volume of catalyst to be reduced. Catalysts, particularly direct NOx catalysts, are often expensive to produce so a reduction in the amount of catalyst required is beneficial. Furthermore, catalysts may require elevated temperatures to decompose NOx effectively. Reducing the volume of catalyst may decrease the overall energy requirements of the system, whilst still allowing substantially continuous abatement of NOx.
The present invention may also provide the ability to preconcentrate NOx prior to decomposition by the NOx reactor, by controlling the release rate of NOx from the NOx adsorber. For certain NOx reactors, the preconcentration of NOx may be beneficial as the rate of NOx conversion (i.e. NOx decomposition) may be concentration dependant. For example, in embodiments wherein the NOx reactor is a Cu-ZSM5 direct NOx catalyst, preconcentration of NOx at the NOx adsorber prior to release may provide improved NOx decomposition.
Typically, during operation of the exhaust treatment system, the or a NOx reactor may be switchable between an online configuration and an offline configuration with respect to at least two NOx adsorbers. Advantageously, this may aid in allowing the substantially continuous abatement of NOx from an exhaust stream.
In embodiments comprising more than one NOx reactor and more than one NOx adsorber, at least one NOx reactor - NOx adsorber pair may switch to an online configuration when another NOx reactor - NOx adsorber pair switches to an offline configuration.
Preferably, the exhaust treatment system may further comprise a controller. The controller may be configured to switch the or a NOx reactor between an offline configuration and an online configuration with respect to the or each NOx adsorber in response to an input signal. Preferably, the input signal may be from a process tool to which the exhaust treatment system is connected. Additionally, or alternatively, the input signal may be from a sensor measuring the exhaust stream. The sensor may measure the NOx concentration of the exhaust stream. Additionally, or alternatively, the sensor may measure other parameters indicative of NOx release.
Additionally, or alternatively, the exhaust treatment system may further comprise at least one temperature sensor configured to measure the temperature of the NOx reactor. In such embodiments, the input signal may be from the temperature sensor connected to the NOx reactor. Additionally, or alternatively, the input signal may be from a timer.
Preferably, the controller may be configured to automatically switch the NOx reactor between an offline configuration and an online configuration with respect to at least a pair of NOx adsorbers in response to an input signal passing a threshold value. For the avoidance of doubt, the input signals may be as set out hereinbefore. Advantageously, this may allow substantially automatic operation of the exhaust treatment system and enable substantially continuous NOx abatement of the exhaust stream.
The monitoring of the NOx reactor and/or NOx adsorber(s) may provide information on the activity of the NOx reactor and/or NOx adsorber(s). This may aid in ensuring that the system is adequately abating NOx from the exhaust stream, and may notify the user as to when the catalyst and/or NOx adsorber(s) require maintenance and/or replacement.
Typically, the NOx reactor may be located within a reactor chamber. For example, when the NOx reactor is a catalyst, the catalyst may be located within a catalyst chamber. Preferably, the catalyst chamber can withstand pressures of up to about 50 bar. The catalyst chamber may therefore be pressurised during operation.
Typically, the exhaust treatment system may further comprise heating means operable to heat the NOx adsorber when the NOx reactor is in an online configuration therewith. Preferably, the heating means may comprise a heating element, a flame (i.e. hot gas), an electrical induction heater, and/or a microwave induction heater. The heating means may be operable via the controller, and this operation may be automated. Heating the NOx adsorber with which the NOx reactor is in an online configuration may increase the rate of desorption (i.e. release) of NOx from the NOx adsorber. The temperature to which the NOx adsorber is heated may provide control over the release rate of NOx from the NOx adsorber.
Typically, when in fluid communication with the exhaust stream (i.e. when the NOx reactor is offline with respect to the NOx adsorber), the NOx adsorber may be heated by the heating means to a temperature of at least 100°C. This may reduce the likelihood of water vapour within the exhaust stream forming hydroxides. Water may also cause physical pore blocking of the NOx adsorber, thereby reducing or preventing NOx adsorption.
Typically, when the NOx reactor is online with respect to the NOx adsorber, the adsorber may be heated by the heating means to temperatures greater than about 100°C, preferably greater than about 200°C, for example greater than about 600°C. Advantageously, this may aid in the decomposition of NOx. Alternatively, the temperature of the NOx reactor may remain substantially constant and NOx left to evolve naturally at the temperature at which it adsorbed.
Typically, the exhaust treatment system may further comprise a substantially inert gas flow operable to transfer NOx released by the NOx adsorber to the NOx reactor. The substantially inert gas flow may comprise nitrogen, ‘dry’ air with
controlled oxygen concentration, argon, and/or carbon dioxide. Preferably, the substantially inert gas flow comprises nitrogen. The substantially inert gas flow may aid in the transfer of NOx from the NOx adsorber to the NOx reactor when the NOx reactor is in an online configuration with respect to the NOx adsorber. The flow rate of the substantially inert gas flow may determine the amount of NOx treated at the NOx reactor. The flow rate of the substantially inert gas flow may be controlled, preferably via the controller.
Preferably, the flow rate of the substantially inert gas flow and the temperature control provided by the heating means may operate in concert to control the release of NOx from the NOx adsorber and the flow rate of NOx across the NOx reactor.
The substantially inert gas flow may comprise further additives. For example, a reducing agent may be added to the substantially inert gas flow. The reducing agent may comprise carbon monoxide, hydrogen, ammonia, methane, propane, and/or propene. Such additives may be appropriate when the NOx reactor is a catalyst that is particularly susceptible to deactivation by water vapour. For example, Co-ZSM-5 catalysts or Co-Ferrierite catalysts are highly sensitive to water vapour within the exhaust gas flow, which can lead to deactivation of the catalyst. Accordingly, in such instances, the inclusion of such additives in the substantially inert gas flow may be beneficial. Beneficially, the reducing agent may assist desorption of NOx from the NOx adsorber. Providing net reducing conditions at the NOx adsorber may enable the NOx adsorber to desorb NOx at a lower temperature. This may reduce the running costs of the system.
Typically, the exhaust treatment system may comprise a foraminous burner, electrical induction heater, or plasma reactor. The foraminous burner, electrical induction heater, or plasma reactor may be arranged upstream of the NOx adsorber(s). This may enable pre-heating of the exhaust gas stream.
Typically, the exhaust treatment system may further comprise an acid gas scrubber. The acid gas scrubber may be arranged upstream of the NOx adsorber(s). Advantageously, this may enable removal of acid gases from the
exhaust gas stream prior to passing over/through the NOx adsorber(s) and NOx reactor(s).
In another aspect, the present invention provides a method for abating NOx from an exhaust stream. The method comprises the steps of: i) Providing an exhaust treatment system according to any preceding aspect or embodiment. ii) Directing the exhaust stream from the process tool across an NOx adsorber with which the NOx reactor is in an offline configuration. iii) Adsorbing NOx from the exhaust stream onto the NOx adsorber. iv) Switching the NOx reactor from an offline configuration to an online configuration with respect to the NOx adsorber. v) Releasing NOx from the NOx adsorber and directing said released NOx to the NOx reactor for treatment.
For the avoidance of doubt, the NOx adsorber and NOx reactor may be as described in relation to the preceding aspect.
Preferably, the NOx released during step (v) is substantially free from O2, and/or H2O, and/or particulates present in the exhaust stream. “Substantially free” may be defined as less than about 1 vol. %, preferably less than about 0.1 vol. %.
Advantageously, this method may significantly reduce the risk of fouling or deactivation of the NOx reactor, as the NOx reactor is not in fluid communication with the exhaust stream. Accordingly, direct NOx decomposition may be possible, allowing selection from a wider range of NOx reactors and the avoidance of the requirement of a reducing agent. The operational lifetime of the NOx reactor may be increased, and the time between servicing may be reduced.
Preferably, in step (iii), following adsorption of NOx onto the NOx adsorber, the exhaust stream may be directed towards an outlet of the exhaust treatment apparatus, and may be conveyed to the outlet via further abatement apparatus.
Preferably, step (iv) further comprises directing the exhaust stream from the process tool across a further NOx adsorber with which the NOx reactor is in an offline configuration. Advantageously, this may allow for substantially continuous adsorption and treatment of NOx from the exhaust stream. This may also accommodate fluctuations in the NOx concentration of the exhaust stream. The present method may allow the NOx adsorber with which the NOx reactor is in an offline configuration to adsorb NOx from the exhaust stream, whilst NOx released from the NOx adsorber with which the NOx reactor is in an online configuration is being treated. This may provide more time for the NOx reactor to decompose the NOx present during a peak in NOx concentration of the exhaust stream than if the NOx reactor were in permanent fluid communication with the exhaust stream.
Preferably, step (v) involves heating the NOx adsorber to a temperature greater than about 100°C, preferably greater than about 200°C, for example greater than about 600°C. Advantageously, this may aid in desorption of NOx from the NOx adsorber, allowing transfer of desorbed NOx to the NOx reactor for treatment.
Preferably, step (v) further comprises introducing a substantially inert gas flow to transfer the released NOx to the NOx reactor. Preferably, the substantially inert gas flow may comprise nitrogen, argon, ‘dry’ air with a controlled oxygen concentration, and/or carbon dioxide. Preferably, the substantially inert gas flow comprises nitrogen. The substantially inert gas flow may comprise further additives. For example, carbon monoxide, ammonia, hydrogen, methane, propane, and/or propene may be added to the substantially inert gas flow as reducing agents. Advantageously, the substantially inert gas flow may aid in the control of the transfer of NOx from the NOx adsorber to the NOx reactor, as described hereinbefore.
Preferably, the flow rate of the substantially inert gas flow may be selectively modulated to control the delivery rate of NOx to the NOx reactor. Having control over the release rate of NOx for treatment by the NOx reactor may be beneficial as the effects of fluctuations in the NOx concentration of the exhaust stream on the NOx reaction rate may be reduced. This may be particularly advantageous when the NOx reactor comprises a catalyst, as volume of catalyst required can be
reduced. The catalyst is often expensive to produce, and may require elevated temperatures to decompose NOx effectively. Reducing the volume of catalyst that must be maintained at elevated temperatures may make the operation of the exhaust treatment system more cost-effective, whilst still allowing for substantially continuous abatement of NOx.
Preferably, the method may further comprise the step of modulating the pressure within the NOx reactor chamber during step (v) to increase and/or decrease the rate of decomposition of the released NOx by the NOx reactor. Increasing the pressure may increase the rate of decomposition of the released NOx by the NOx reactor, and decreasing the pressure may decrease the rate of decomposition of the released NOx by the NOx reactor.
Preferably, the method may be substantially automated by a controller. Particularly, step (iv) may be initiated by a signal output by the process tool to which the exhaust treatment system is connected, and/or by a sensor measuring the NOx concentration of the exhaust stream, and/or by a sensor measuring the temperature of the NOx reactor, and/or by a timer.
Preferably, the modulation of the temperature of the NOx adsorber and/or the flow rate of the substantially inert gas flow of step (v) may be automated and controlled by the controller.
Preferably, the modulation of the pressure of the NOx reactor may be automated and controlled by the controller.
In another aspect, the present invention provides the use of magnesium oxide, an alkaline earth material, an alkali metal, a transitional metal, a precious metal, a noble metal, palladium, platinum, copper, cobalt, and/or Hopcalite, to adsorb NOx from an abatement gas stream and subsequently desorb said NOx for catalytic treatment. Optionally, supports such as zeolites may be used also containing such metals copper, cobalt, silver, platinum or palladium. Preferably, the magnesium oxide and/or Hopcalite, or palladium/platinum on silicate supports, or silver, copper and cobalt-based transition metal oxides, or combinations thereof, is fluidly
disconnected from the means for catalytic treatment when adsorbing NOx from the abatement gas stream. The advantages of this aspect are as described in the preceding aspects and embodiments.
For the avoidance of doubt, all aspects and embodiments described hereinbefore may be combined mutatis mutandis.
Brief Description
Preferred features of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 shows a schematic of an exhaust treatment system (1 ) in accordance with the prior art;
Figures 2A-B show schematic views of an embodiment of an exhaust treatment system in accordance with the present invention;
Figures 3A-B show a schematic views of an alternative embodiment of an exhaust treatment system in accordance with the present invention;
Figure 4 shows a flow chart of a method in accordance with the present invention.
Detailed Description
Figure 1 illustrates a schematic of an exhaust treatment system (1 ) in accordance with the prior art. The system (1 ) comprises a conduit (2) through which the exhaust stream travels. The direction of flow of the exhaust stream through the exhaust treatment system (1 ) is shown by arrows Ai and A2. Arrow A1 shows the direction of flow of the exhaust stream from the process tool into the exhaust treatment system (1 ), and arrow A2 shows the direction of flow of the exhaust stream following abatement.
The exhaust treatment system (1 ) comprises a NOx adsorber (3) attached to a catalyst (4). The NOx adsorber (3) and catalyst (4) are arranged in series within the conduit (2), and are both in fluid communication with the exhaust stream throughout operation of the exhaust treatment system (1 ). The catalyst (4) contains a heating element (5) embedded within, to maintain the catalyst (4) at elevated temperatures during operation. In use, the temperature of the heating element (5) may be adjusted to improve NOx adsorption and desorption conditions.
The arrangement of the exhaust treatment system (1 ) of the prior art presents a number of issues. A reducing agent (not shown) may be required to aid in the decomposition of NOx by the catalyst (4). The presence of oxygen in the exhaust stream when such reducing agents are used is undesirable, as the reaction of O2 with CO consumes much of the CO required to facilitate the reaction between CO and NO. This may reduce the efficiency of NOx decomposition. Water vapour present within the exhaust stream can cause deactivation of the catalyst (4). Particulate matter, such as silica, present in the exhaust stream may foul the catalyst (4) and thereby reduce its activity.
Additionally, the concentration of NOx within the exhaust stream may vary. As the catalyst (4) is in fluid communication with the exhaust stream, the catalyst (4) must be able to meet the abatement requirements during the peak NOx concentration.
Figures 2A-B illustrate schematic views of an embodiment of an exhaust treatment system (6) in accordance with the present invention. The exhaust treatment system (6) comprises an NOx adsorber (7) configured to adsorb NOx from an incoming exhaust stream (8). The NOx adsorber (7) is a passive NOx adsorber, comprising, for example, magnesium oxide (MgO). A heating element (9) is embedded within the NOx adsorber (7).
The exhaust treatment system (6) further comprises a NOx reactor (10). The NOx reactor (10) comprises a catalyst, a reducing agent-assisted catalyst, a plasma reactor, or a plasma-assisted catalyst, as described hereinbefore. For example, the NOx reactor (10) may be a Cu-ZSM-5 zeolite catalyst. A first valve (11 ) is
arranged upstream of the NOx adsorber (7). A second valve (12) is arranged downstream of the NOx adsorber (7).
Figure 2A shows the arrangement of the exhaust treatment system (6) when the NOx reactor (10) is in an offline configuration. In such a configuration, the NOx reactor (10) is fluidly disconnected from the exhaust stream (8) and from the NOx adsorber (7). In the embodiment shown, this fluid disconnection of the NOx reactor (10) from the exhaust stream (8) and from the NOx adsorber (7) is provided by the downstream valve (11 ). The exhaust stream (8) enters the exhaust treatment system (6) from a process tool (not shown) via the first valve (11 ), and is conveyed across the NOx adsorber (7). NOx is adsorbed onto the NOx adsorber (7), and thereby is removed from the exhaust stream (8). The treated exhaust stream (13) then travels through the downstream valve (12) and exits the exhaust treatment system (6).
The temperature of the NOx adsorber (7) is typically at least about 100°C when the NOx reactor (10) is in an offline configuration. This is because NOx is readily adsorbed by the NOx adsorber (7) from the exhaust stream (8) at these temperatures.
The NOx reactor (10) is not exposed to the exhaust stream (8) at all when in the offline configuration, as the NOx reactor (10) is fluidly disconnected from the exhaust stream (8). Accordingly, no oxygen, water vapour, and/or particulates that might be present in the exhaust stream (8) pass across or through the NOx reactor (10). Beneficially, this may avoid deactivation and/or fouling of the NOx reactor (10), particularly wherein the NOx reactor is a catalyst.
Figure 2B shows the arrangement of the exhaust treatment system (6) when the NOx reactor (10) is in an online configuration. In such a configuration, the NOx reactor (10) is fluidly connected to the NOx adsorber (7), via the second valve (12). The exhaust stream (8) is no longer entering the exhaust treatment system (6), via the first valve (11 ). Therefore, the NOx reactor (10) is fluidly disconnected from the exhaust stream (8), even when in an online configuration with the NOx adsorber (7).
The heating element (9) is operated to increase the temperature of the NOx adsorber (7) to a temperature greater than about 200°C, preferably greater than about 300°C, for example greater than about 600°C. This increase in temperature of the NOx adsorber (7) facilitates the release of NOx adsorbed thereto. A substantially inert gas flow (14) is activated. Preferably, the substantially inert gas flow (14) comprises nitrogen. The substantially inert gas flow (14) is directed across/through the NOx adsorber (7) via the first valve (11 ). The substantially inert gas flow (14) transfers the NOx released by the NOx adsorber (7) to the NOx reactor (10) via the second valve (12). The NOx reactor (10) treats the NOx carried by the nitrogen gas flow (14).
Figures 3A-B illustrate schematic views of an alternative embodiment of an exhaust treatment system (15) in accordance with the present invention. The exhaust treatment system (15) comprises a first NOx adsorber (16) and a second NOx adsorber (17), each configured to adsorb NOx from an incoming exhaust stream (18). The first and second NOx adsorbers (16,17) are passive NOx adsorbers comprising magnesium oxide (MgO). A heating element (19,20) is present within each NOx adsorber (16,17), and configured to regulate the temperature thereof.
The exhaust treatment system (15) further comprises a NOx reactor (21 ). The NOx reactor (21 ) comprises a catalyst, a reducing agent-assisted catalyst, a plasma reactor, or a plasma-assisted catalyst, as described hereinbefore. For example, the NOx reactor (21 ) may be a Cu-ZSM-5 zeolite catalyst. A series of valves are present and configured to fluidly connect and disconnect portions of the exhaust treatment system (15).
Figure 3A illustrates when the NOx reactor (21 ) is in an offline configuration with respect to the first NOx adsorber (16), and in an online configuration with respect to the second NOx adsorber (17). Accordingly, the NOx reactor (21 ) is fluidly disconnected from the exhaust stream (18) and from the first NOx adsorber (16). The exhaust stream (18) enters the exhaust treatment system (15) from a process tool (not shown) and is conveyed across the first NOx adsorber (16).
The temperature of the first NOx adsorber (16) is typically at least about 100°C in this configuration. NOx is adsorbed onto the first NOx adsorber (16), and thereby is removed from the exhaust stream (18). The treated exhaust stream (22) then exits the exhaust treatment system (15) without passing across/through the NOx reactor (21 ).
The NOx reactor (21 ) is not exposed to the exhaust stream (18) at all, when in an offline or online configuration with respect to either NOx adsorber (16,17). Accordingly, no oxygen, water vapour, and/or particulates that might be present in the exhaust stream (18) pass across/through the NOx reactor (21 ). Beneficially, this may avoid deactivation or fouling of the NOx reactor (21 ).
Simultaneously, the NOx reactor (21 ) is in an online configuration with respect to the second NOx adsorber (17). The NOx reactor (21 ) is fluidly connected to the second NOx adsorber (17), via a valve. The second heating element (20) is operated to increase the temperature of the second NOx adsorber (17). Preferably the temperature of the second NOx adsorber (17) may be increased to greater than about 200°C, preferably greater than about 300°C, for example about 600°C. This increase in temperature of the NOx adsorber (17) releases NOx adsorbed thereto from a previous cycle when the NOx reactor (21 ) was in an offline configuration with respect to the second NOx adsorber (17).
A substantially inert gas flow (23), preferably comprising nitrogen, is directed across/through the second NOx adsorber (17) to transfer the NOx released by the second NOx adsorber (17) to the NOx reactor (21 ). The NOx reactor (21 ) treats the NOx carried by the substantially inert gas flow (23), which then exits the exhaust treatment system (15) via an outlet (25).
Figure 3B illustrates when the NOx reactor (21 ) is in an online configuration with respect to the first NOx adsorber (16), and in an offline configuration with respect to the second NOx adsorber (17). Accordingly, the NOx reactor (21 ) is fluidly disconnected from the exhaust stream (18) and from the second NOx adsorber (17). The exhaust stream (18) enters the exhaust treatment system (15) from a process tool (not shown) and is conveyed across the second NOx adsorber (17).
The temperature of the second NOx adsorber (17) is typically at least about 100°C in this configuration. NOx is adsorbed onto the second NOx adsorber (17), and thereby is removed from the exhaust stream (18). The treated exhaust stream (22) then exits the exhaust treatment system (15) without passing through the NOx reactor (21 ).
Simultaneously, the NOx reactor (21 ) is in an online configuration with respect to the first NOx adsorber (16). The NOx reactor (21 ) is fluidly connected to the first NOx adsorber (16), via a valve. The first heating element (19) is operated to increase the temperature of the first NOx adsorber (16) to a temperature greater than about 200°C, preferably greater than about 300°C, for example about 600°C. This increase in temperature of the first NOx adsorber (16) releases NOx adsorbed thereto when in the configuration illustrated in Figure 3A.
A substantially inert gas flow (24), preferably comprising nitrogen, is directed across/through the first NOx adsorber (16) to transfer the NOx released by the first NOx adsorber (16) to the NOx reactor (21 ). The NOx reactor (21 ) treats the NOx carried by the substantially inert gas flow (24), which then exits the exhaust treatment system (15) via an outlet (25).
During operation of the exhaust treatment system (15), the system (15) switches between the configuration of Figure 3A and that of Figure 3B. Accordingly, the NOx reactor (21 ) is always in an online configuration with respect to one NOx adsorber
(16.17), and in an offline configuration with respect to the other NOx adsorber
(16.17). Advantageously, this may allow substantially continuous NOx removal from the exhaust stream (18), without deactivation and/or fouling of the NOx reactor (21 ) due to exposure to oxygen, water vapour, and/or particulates present in the exhaust stream (18).
The exhaust treatment system (15) further comprises a controller (26), configured to switch the catalyst (21 ) between an online configuration and an offline configuration with respect to the two NOx adsorbers (16,17). This switching may be automatic and triggered in response to an input.
The exhaust treatment system (15) may further comprise a sensor (not shown) configured to measure the NOx concentration of the incoming exhaust stream (18). The sensor may output a signal to the controller (26), which can trigger the switch of the configuration of the NOx reactor (21 ), for example when the NOx concentration of the exhaust stream (18) passes a threshold value.
The exhaust treatment system may further comprise a temperature sensor (27) configured to measure the temperature of the NOx reactor (21 ). The temperature sensor (27) may output a signal to the controller (26), which can trigger the switch of the configuration of the NOx reactor (21 ), for example when the temperature of the NOx reactor (21 ) passes a threshold value.
The NOx reactor (21 ) is located within a chamber (not shown), which may be pressurised to increase and decrease the reaction rate of the NOx at the NOx reactor (21 ). The pressure of the chamber may be controller by the controller (26), and is preferably automated. The flow rate of the substantially inert gas flow (23,24) may be varied via the controller, preferably this may be automated. The pressure of the chamber and/or flow rate of the substantially inert gas flow (23,24) may be selected according to the concentration of NOx of the incoming exhaust stream (18).
The exhaust treatment system (15) may further comprise heating means (not shown) arranged upstream of the NOx adsorbers (16,17). The heating means may be configured to heat the exhaust gas stream (18). The heating means may comprise, for example, a foraminous burner, an electrical induction heater, or a plasma reactor.
The exhaust treatment system (15) may further comprise an acid gas scrubber (not shown). The acid gas scrubber may be arranged upstream of the NOx adsorbers (16,17). The acid gas scrubber may be configured to remove acid gases from the exhaust gas stream (18).
The exhaust treatment system (15) is preferably connected to a process tool from a semiconductor manufacturing process during operation.
Figure 4 illustrates a flow chart of a method in accordance with the present invention.
An exhaust treatment system according to Figures 2A-B or 3A-B is provided. An exhaust stream is directed from the process tool across and/or through an NOx adsorber with which the NOx reactor is in an offline configuration (28). NOx present in the exhaust stream is adsorbed onto the NOx adsorber with which the NOx reactor is in an offline configuration (29).
The NOx concentration of the exhaust stream may be measured by a sensor, and this measurement may be output to the controller (30). The sensor may measure the NOx concentration of the exhaust stream at predetermined time intervals, or the sensor may measure the NOx concentration of the exhaust stream substantially continuously.
Additionally, or alternatively, the temperature of the NOx reactor may be measured via a temperature sensor, and this measurement may be output to the controller (31 ). The temperature sensor may measure the temperature of the NOx reactor at predetermined time intervals, or the temperature sensor may measure the temperature of the NOx reactor substantially continuously.
Additionally, or alternatively, the process tool to which the exhaust treatment system is connected may output a signal indicating the NOx concentration of the exhaust stream (32). This signal may be output at predetermined time intervals, or the signal may be output substantially continuously.
In response to a signal (30,31 ,32), the controller may switch the NOx reactor from an offline configuration to an online configuration with respect to the/a NOx adsorber (33).
The/a NOx adsorber is heated to a temperature greater than about 100°C, preferably greater than about 200°C, for example to about 600°C (34). A substantially inert gas flow, preferably comprising nitrogen, may be introduced to the NOx adsorber to transfer the released NOx to the NOx reactor for treatment (35). The released NO is substantially free from oxygen, and/or water vapour, and/or particulates that were present in the exhaust stream.
The pressure within the NOx reactor chamber may be modulated to increase and/or decrease the rate of reaction of the released NOx at the NOx reactor (36).
At step (33), the controller may switch a NOx reactor from an online configuration to an offline configuration with respect to another NOx adsorber, which will then proceed through steps (28-32).
For the avoidance of doubt, features of any aspects or embodiments recited herein may be combined mutatis mutandis. It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.
Reference Key
1. Exhaust treatment system (prior art)
2. Conduit (prior art)
3. NOx adsorber (prior art)
4. Catalyst (prior art)
5. Heating element (prior art)
6. Exhaust treatment system
7. NOx adsorber
8. Exhaust stream
9. Heating element
10. NOx reactor
11. First valve
12. Second valve
13. Exhaust stream (treated)
14. Substantially inert gas flow
15. Exhaust treatment system
16. First NOx adsorber
17. Second NOx adsorber
18. Exhaust stream
19. First heating element
20. Second heating element
21. NOx reactor
22. Exhaust stream (treated)
23. Substantially inert gas flow
24. Substantially inert gas flow
25. Outlet
26. Controller
27. Temperature sensor
28. Step I
29. Step II
30. Step III
31. Step IV
32. Step V
33. Step VI
34. Step VII
35. Step VIII
36. Step IX
37. Step X
Claims
1. An exhaust treatment system for NOx abatement of an exhaust stream, the exhaust treatment system comprising: at least one NOx adsorber configured to adsorb NOx from the exhaust stream, and a NOx reactor operable in an offline configuration and an online configuration; wherein when the NOx reactor is in an offline configuration, the NOx reactor is fluidly disconnected from the exhaust stream and the NOx adsorber, and the NOx adsorber is fluidly connected to the exhaust stream such that NOx contained in the exhaust stream may be adsorbed by the NOx adsorber; and when the NOx reactor is in an online configuration, the NOx reactor is fluidly connected to the NOx adsorber such that NOx adsorbed by the NOx adsorber may be treated by the NOx reactor.
2. The exhaust treatment system according to claim 1 , comprising a plurality of NOx adsorbers, wherein during operation of the exhaust treatment system the NOx reactor is in an online configuration with respect to at least one NOx adsorber and is in an offline configuration with respect to at least one NOx adsorber.
3. The exhaust treatment system according to claim 2, wherein during operation of the exhaust treatment system, the NOx reactor is switchable between an online configuration and an offline configuration with respect to at least two NOx adsorbers.
4. The exhaust treatment system according to claim 3, further comprising a controller configured to switch the NOx reactor between an offline configuration and an online configuration with respect to at least two NOx adsorbers in response to an input signal, preferably wherein the input signal is from a process tool to which the exhaust treatment system is connected, and/or a sensor measuring the exhaust stream, and/or a temperature sensor connected to the NOx reactor, and/or a timer.
5. The exhaust treatment system according to any preceding claim, wherein the NOx reactor is located in a NOx reactor chamber, preferably wherein the NOx reactor chamber can withstand pressures of up to about 50 bar.
6. The exhaust treatment system according to any preceding claim, further comprising heating means operable to heat the NOx adsorber when the NOx reactor is in an online configuration therewith, and/or an inert gas flow operable to transfer NOx released by the NOx adsorber to the NOx reactor.
7. The exhaust treatment system according to any preceding claim, wherein the NOx reactor comprises a catalyst; preferably wherein the catalyst comprises a Cu-ZSM-5 zeolite catalyst, a cerium doped Cu-ZSM-5 zeolite catalyst, a platinum on alumina catalyst, a cobalt (11,111) oxide catalyst, a Ba(MgO) catalyst, a Na-CosO4 catalyst, or a La2CuO4 catalyst.
8. The exhaust treatment system according to any preceding claim, wherein the NOx reactor comprises a plasma reactor; preferably wherein the plasma reactor comprises a di-electric barrier discharge plasma reactor, a radio frequency plasma generator, or a microwave frequency plasma generator.
9. The exhaust treatment system according to any preceding claim, wherein at least one NOx adsorber comprises an alkaline earth material, an alkali metal, a transitional metal, a precious metal, a noble metal, palladium, platinum, copper, cobalt and/or Hopcalite, preferably wherein at least one NOx adsorber comprises MgO.
10. A method for abating NOx from an exhaust stream, comprising the steps of: i) providing an exhaust treatment system according to any preceding claim; ii) directing the exhaust stream from the process tool across an NOx adsorber with which the NOx reactor is in an offline configuration; iii) adsorbing NOx from the exhaust stream onto the NOx adsorber ; iv) switching the NOx reactor from an offline configuration to an online configuration with respect to the NOx adsorber;
v) releasing NOx from the NOx adsorber and transferring said released NOx to the NOx reactor for treatment. The method according to claim 10, wherein the NOx released during step (v) is substantially free from O2, and/or H2O, and/or particulates present in the exhaust stream. The method according to claim 10 or claim 11 , wherein step (iv) further comprises directing the exhaust stream from the process tool across a further NOx adsorber with which the NOx reactor is in an offline configuration. The method according to any of claims 10 to 12, wherein step (v) involves heating the NOx adsorber to a temperature greater than about 100°C, preferably greater than about 200°C, for example greater than about 600°C. The method according to any of claims 10 to 13, wherein step (v) further comprises introducing a substantially inert gas flow to transfer the released NOx to the NOx reactor, preferably wherein the substantially inert gas flow comprises nitrogen, argon, and/or carbon dioxide. The method according to any of claims 10 to 14, further comprising the step of modulating the pressure within the NOx reactor chamber during step (v) to increase and/or decrease the rate of reaction of the released NOx with the NOx reactor. The method according to any of claims 10 to 15, wherein the method is substantially automated, and wherein step (iv) is initiated by a signal output by the process tool to which the exhaust treatment system is connected, and/or by a sensor measuring the NOx concentration of the exhaust stream, and/or by a sensor measuring the temperature of the NOx reactor, and/or by a timer. Use of magnesium oxide, an alkaline earth material, an alkali metal, a transitional metal, a precious metal, a noble metal, palladium, platinum, copper,
cobalt and/or Hopcalite to adsorb NOx from an abatement gas stream and subsequently desorb said NOx for catalytic treatment.
Applications Claiming Priority (2)
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GB2213193.2 | 2022-09-09 | ||
GB2213193.2A GB2622259A (en) | 2022-09-09 | 2022-09-09 | NOx reduction |
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WO2024052646A1 true WO2024052646A1 (en) | 2024-03-14 |
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PCT/GB2023/052254 WO2024052646A1 (en) | 2022-09-09 | 2023-08-31 | NOx REDUCTION |
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Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1994004258A1 (en) * | 1992-08-26 | 1994-03-03 | University Of Delaware | A process for removing nox from combustion zone gases by adsorption |
US20050247049A1 (en) * | 2004-05-05 | 2005-11-10 | Eaton Corporation | Temperature swing adsorption and selective catalytic reduction NOx removal system |
KR102154019B1 (en) * | 2019-10-23 | 2020-09-09 | 주식회사 퓨어스피어 | Apparatus for treating N2O gas without using reducing agent and method for treating N2O gas using the same |
US20210410264A1 (en) * | 2017-01-23 | 2021-12-30 | Edwards Korea Ltd. | Nitrogen oxide reduction apparatus and gas treating apparatus |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20200055035A1 (en) * | 2017-02-22 | 2020-02-20 | Basf Corporation | Exhaust gas treatment catalyst for abatement of nitrogen oxides |
CN109621627B (en) * | 2018-12-27 | 2021-06-01 | 天津大学 | Method for eliminating and recycling nitrogen oxides in combustion tail gas |
WO2020188519A1 (en) * | 2019-03-20 | 2020-09-24 | Basf Corporation | Tunable nox adsorber |
EP4072709A1 (en) * | 2019-12-13 | 2022-10-19 | BASF Corporation | Zeolite with cu and pd co-exchanged in a composite |
-
2022
- 2022-09-09 GB GB2213193.2A patent/GB2622259A/en active Pending
-
2023
- 2023-08-31 WO PCT/GB2023/052254 patent/WO2024052646A1/en unknown
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1994004258A1 (en) * | 1992-08-26 | 1994-03-03 | University Of Delaware | A process for removing nox from combustion zone gases by adsorption |
US20050247049A1 (en) * | 2004-05-05 | 2005-11-10 | Eaton Corporation | Temperature swing adsorption and selective catalytic reduction NOx removal system |
US20210410264A1 (en) * | 2017-01-23 | 2021-12-30 | Edwards Korea Ltd. | Nitrogen oxide reduction apparatus and gas treating apparatus |
KR102154019B1 (en) * | 2019-10-23 | 2020-09-09 | 주식회사 퓨어스피어 | Apparatus for treating N2O gas without using reducing agent and method for treating N2O gas using the same |
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GB202213193D0 (en) | 2022-10-26 |
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