DE69619062D1 - Lufttrennungsverfahren und Vorrichtung zur Herstellung von Stickstoff - Google Patents

Lufttrennungsverfahren und Vorrichtung zur Herstellung von Stickstoff

Info

Publication number
DE69619062D1
DE69619062D1 DE69619062T DE69619062T DE69619062D1 DE 69619062 D1 DE69619062 D1 DE 69619062D1 DE 69619062 T DE69619062 T DE 69619062T DE 69619062 T DE69619062 T DE 69619062T DE 69619062 D1 DE69619062 D1 DE 69619062D1
Authority
DE
Germany
Prior art keywords
bottoms
liquid
stream
column
vaporised
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
DE69619062T
Other languages
English (en)
Other versions
DE69619062T2 (de
Inventor
Joseph P Naumovitz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linde LLC
Original Assignee
BOC Group Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BOC Group Inc filed Critical BOC Group Inc
Publication of DE69619062D1 publication Critical patent/DE69619062D1/de
Application granted granted Critical
Publication of DE69619062T2 publication Critical patent/DE69619062T2/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/044—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a single pressure main column system only
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04048—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04048—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams
    • F25J3/04066—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams of oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/04321—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/72—Refluxing the column with at least a part of the totally condensed overhead gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/52—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being oxygen enriched compared to air, e.g. "crude oxygen"
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/50—Processes or apparatus involving steps for recycling of process streams the recycled stream being oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/20—Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Emergency Medicine (AREA)
  • Analytical Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • General Chemical & Material Sciences (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Treating Waste Gases (AREA)
  • Separation Of Gases By Adsorption (AREA)
DE69619062T 1995-11-07 1996-11-06 Lufttrennungsverfahren und Vorrichtung zur Herstellung von Stickstoff Expired - Lifetime DE69619062T2 (de)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US08/553,173 US5582034A (en) 1995-11-07 1995-11-07 Air separation method and apparatus for producing nitrogen

Publications (2)

Publication Number Publication Date
DE69619062D1 true DE69619062D1 (de) 2002-03-21
DE69619062T2 DE69619062T2 (de) 2002-10-31

Family

ID=24208392

Family Applications (1)

Application Number Title Priority Date Filing Date
DE69619062T Expired - Lifetime DE69619062T2 (de) 1995-11-07 1996-11-06 Lufttrennungsverfahren und Vorrichtung zur Herstellung von Stickstoff

Country Status (17)

Country Link
US (1) US5582034A (de)
EP (1) EP0773417B1 (de)
JP (1) JP4057668B2 (de)
KR (1) KR100198352B1 (de)
CN (1) CN1103438C (de)
AT (1) ATE213060T1 (de)
AU (1) AU704118B2 (de)
CA (1) CA2183511C (de)
DE (1) DE69619062T2 (de)
IL (1) IL119056A (de)
MX (1) MX9603980A (de)
MY (1) MY118753A (de)
PL (1) PL316839A1 (de)
SG (1) SG44970A1 (de)
TR (1) TR199600708A2 (de)
TW (1) TW360618B (de)
ZA (1) ZA967298B (de)

Families Citing this family (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5689973A (en) * 1996-05-14 1997-11-25 The Boc Group, Inc. Air separation method and apparatus
JP2875206B2 (ja) * 1996-05-29 1999-03-31 日本エア・リキード株式会社 高純度窒素製造装置及び方法
US5924307A (en) * 1997-05-19 1999-07-20 Praxair Technology, Inc. Turbine/motor (generator) driven booster compressor
US5836175A (en) * 1997-08-29 1998-11-17 Praxair Technology, Inc. Dual column cryogenic rectification system for producing nitrogen
JP3719832B2 (ja) * 1997-10-14 2005-11-24 日本エア・リキード株式会社 超高純度窒素及び酸素の製造装置
US5868006A (en) * 1997-10-31 1999-02-09 The Boc Group, Inc. Air separation method and apparatus for producing nitrogen
US5934106A (en) * 1998-01-27 1999-08-10 The Boc Group, Inc. Apparatus and method for producing nitrogen
US6279345B1 (en) 2000-05-18 2001-08-28 Praxair Technology, Inc. Cryogenic air separation system with split kettle recycle
US6494060B1 (en) 2001-12-04 2002-12-17 Praxair Technology, Inc. Cryogenic rectification system for producing high purity nitrogen using high pressure turboexpansion
CN100443838C (zh) * 2005-04-20 2008-12-17 苏州市兴鲁空分设备科技发展有限公司 一种返流膨胀空气分离的方法和装置
CN100400995C (zh) * 2006-11-22 2008-07-09 苏州市兴鲁空分设备科技发展有限公司 空气分离的方法和装置
DE102007024168A1 (de) * 2007-05-24 2008-11-27 Linde Ag Verfahren und Vorrichtung zur Tieftemperatur-Luftzerlegung
DE102007051184A1 (de) 2007-10-25 2009-04-30 Linde Aktiengesellschaft Verfahren und Vorrichtung zur Tieftemperatur-Luftzerlegung
DE102007051183A1 (de) 2007-10-25 2009-04-30 Linde Aktiengesellschaft Verfahren zur Tieftemperatur-Luftzerlegung
DE102008064117A1 (de) 2008-12-19 2009-05-28 Linde Ag Verfahren und Vorrichtung zur Tieftemperaturzerlegung von Luft
JP5415192B2 (ja) * 2009-03-16 2014-02-12 Ｊｆｅスチール株式会社 空気の成分分離方法および装置
EP2236964B1 (de) * 2009-03-24 2019-11-20 Linde AG Verfahren und Vorrichtung zur Tieftemperatur-Luftzerlegung
EP2662653A1 (de) 2012-05-08 2013-11-13 Linde Aktiengesellschaft Verfahren und Vorrichtung zur Gewinnung von wasserstofffreiem Stickstoff
EP2789958A1 (de) 2013-04-10 2014-10-15 Linde Aktiengesellschaft Verfahren zur Tieftemperaturzerlegung von Luft und Luftzerlegungsanlage
CN103776240B (zh) * 2014-01-13 2016-07-06 浙江海天气体有限公司 单压缩双增压双膨胀高纯氮制取装置
EP3059536A1 (de) 2015-02-19 2016-08-24 Linde Aktiengesellschaft Verfahren und Vorrichtung zur Gewinnung eines Druckstickstoffprodukts
EP3290843A3 (de) 2016-07-12 2018-06-13 Linde Aktiengesellschaft Verfahren und vorrichtung zur erzeugung von druckstickstoff und flüssigstickstoff durch tieftemperaturzerlegung von luft

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2120374B (en) * 1982-05-11 1985-09-18 Petrocarbon Dev Ltd Improvements in the production of nitrogen from air
JPS61110872A (ja) * 1984-11-02 1986-05-29 日本酸素株式会社 窒素製造方法
JPH05187767A (ja) * 1992-01-14 1993-07-27 Teisan Kk 超高純度窒素製造方法及びその装置
US5363657A (en) * 1993-05-13 1994-11-15 The Boc Group, Inc. Single column process and apparatus for producing oxygen at above-atmospheric pressure
US5396772A (en) * 1994-03-11 1995-03-14 The Boc Group, Inc. Atmospheric gas separation method

Also Published As

Publication number Publication date
KR970025674A (ko) 1997-06-24
ATE213060T1 (de) 2002-02-15
TW360618B (en) 1999-06-11
US5582034A (en) 1996-12-10
EP0773417A2 (de) 1997-05-14
AU704118B2 (en) 1999-04-15
IL119056A (en) 2000-07-16
SG44970A1 (en) 1997-12-19
IL119056A0 (en) 1996-11-14
AU6430596A (en) 1997-05-15
CN1103438C (zh) 2003-03-19
MX9603980A (es) 1997-05-31
CN1152108A (zh) 1997-06-18
ZA967298B (en) 1997-05-22
KR100198352B1 (ko) 1999-06-15
JP4057668B2 (ja) 2008-03-05
EP0773417B1 (de) 2002-02-06
CA2183511C (en) 1999-10-12
EP0773417A3 (de) 1998-02-04
JPH09132404A (ja) 1997-05-20
MY118753A (en) 2005-01-31
CA2183511A1 (en) 1997-05-08
DE69619062T2 (de) 2002-10-31
PL316839A1 (en) 1997-05-12
TR199600708A2 (tr) 1997-05-21

Similar Documents

Publication Publication Date Title
DE69619062T2 (de) Lufttrennungsverfahren und Vorrichtung zur Herstellung von Stickstoff
KR950003776A (ko) 공기의 분리방법
KR960024196A (ko) 저온 공기 분리 방법 및 장치
EP0687876B1 (de) Lufttrennung
KR950031896A (ko) 순수한 아르곤을 회수하기 위한 방법 및 장치
US5485729A (en) Air separation
US5711167A (en) High efficiency nitrogen generator
EP0520738B2 (de) Verfahren zur Herstellung von reinstem Stickstoff
KR20000006031A (ko) 극저온공기분리공정에의한아르곤제조방법
GB2180923A (en) Process and apparatus for the production of pressurized nitrogen
US5440885A (en) Process and installation for the production of ultra-pure nitrogen by distillation of air
US5590543A (en) Production of ultra-high purity oxygen from cryogenic air separation plants
US5049174A (en) Hybrid membrane - cryogenic generation of argon concurrently with nitrogen
EP0752566B1 (de) Lufttrennung
KR970002229A (ko) 초-고순도 산소의 제조 방법 및 장치
KR970010644A (ko) 초-고순도 산소의 제조 방법
CA2108847C (en) Cryogenic air separation process and apparatus
US5123946A (en) Cryogenic nitrogen generator with bottom reboiler and nitrogen expander
EP0807792B1 (de) Verfahren und Vorrichtung zur Lufttrennung
JPH0650658A (ja) 空気分離方法
CA1280360C (en) Air separation process with waste recycle for nitrogen and oxygen production
CA2259063A1 (en) A multiple expander process to produce oxygen
GB2120374A (en) Improvements in the production of nitrogen from air
BR0103987A (pt) Processo e dispositivo para a produção de nitrogênio altamente puro pela decomposição do ar em baixa temperatura
TH26952B (th) วิธีการผลิตไนโตรเจนและเครื่องมือ

Legal Events

Date Code Title Description
8364 No opposition during term of opposition