CN101532768B - 一种高效利用液化天然气冷能的空分系统 - Google Patents

一种高效利用液化天然气冷能的空分系统 Download PDF

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CN101532768B
CN101532768B CN2009100591000A CN200910059100A CN101532768B CN 101532768 B CN101532768 B CN 101532768B CN 2009100591000 A CN2009100591000 A CN 2009100591000A CN 200910059100 A CN200910059100 A CN 200910059100A CN 101532768 B CN101532768 B CN 101532768B
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nitrogen
heat exchanger
pressure
lng
natural gas
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CN101532768A (zh
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黄震宇
易希朗
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Sichuan Air Separation Plant (group) Co Ltd
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Sichuan Air Separation Plant (group) Co Ltd
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    • 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
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/04218—Parallel arrangement of the main heat exchange line in cores having different functions, e.g. in low pressure and high pressure cores
    • F25J3/04224—Cores associated with a liquefaction or refrigeration cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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
    • F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
    • F25J3/0403—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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
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    • 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
    • F25J3/0406—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 nitrogen
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    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/0423—Subcooling of liquid process streams
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    • F25J3/04254—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using the cold stored in external cryogenic fluids
    • F25J3/0426—The cryogenic component does not participate in the fractionation
    • F25J3/04266—The cryogenic component does not participate in the fractionation and being liquefied hydrocarbons
    • F25J3/04272—The cryogenic component does not participate in the fractionation and being liquefied hydrocarbons and comprising means for reducing the risk of pollution of hydrocarbons into the air fractionation
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    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04333—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/04351—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams of nitrogen
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    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising loop
    • 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
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/904—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by liquid or gaseous cryogen in an open loop

Abstract

本发明公开了一种高效利用LNG冷能的空分系统。包括LNG-氮换热器和氮-氮换热器两组换热器，以压力氮气作为封闭循环介质，液化天然气在LNG-氮换热器中将冷量传递给循环氮；循环氮在氮-氮换热器中将冷量传递给空分精馏塔的压力氮，空分不与循环介质直接接触，避免天然气进入空分装置而带来的危险。循环氮利用LNG冷能冷却，降低压缩功耗，获得超临界压力氮，为弥补LNG高品位冷量的不足，高压液氮一路节流到中压压力，另一路可通过液体膨胀机膨胀回收能量后，部分进入LNG-氮换热器对高压液氮进行深度过冷，其余液氮进入空分系统，换热器通道数目极少、流程组织简洁，安全可靠，操作控制方便，成本低廉、适用范围广。

Description

一种高效利用液化天然气冷能的空分系统
技术领域
本发明涉及一种高效利用液化天然气冷能的空分系统。
背景技术
天然气作为化学能源之一，因其巨大的储藏量和低污染性，被渐渐提升为及煤、石油之后的主要能源支柱，具有广阔的应用前景。天然气的贸易形式主要通过管道输送和液化天然气(LNG)运输，LNG在进入天然气用户管网前，需要从液化状态气化至常温，其气化过程将产生巨大的冷量。空气分离装置通过充分利用LNG的气化冷能，可以大大降低电耗、增加液体的生产量，提高产品在市场销售中的竞争力。利用LNG冷能的空分系统一般比常规的系统要节电50％以上，例如一套日产液氧320T，液氮290T，液氩10T的液体空分，以85bara，-151℃的LNG为冷源，包含氧氮氩的分离功，平均电耗耗仅0.25KW/kg液体。相同装置的常规液体空分平均单耗0.65KW/kg以上。LNG冷能空分装置经济效益十分明显。但由于空分系统是氧气富集区，天然气作为碳氢化合物，大气烃含量偏高，是极为敏感的有害物质，因此，对LNG冷能的利用通常采用中间介质置换冷能，避免LNG与空分系统的直接接触。纵观国内外LNG冷能空分联合装置，普遍存在其流程组织过于复杂，且能耗较高，实施不易，操作控制不方便或安全可靠性欠佳现象。比如采用多台压缩机、多台膨胀机、分离罐等，换热器通道多，尤其是LNG为高压，其换热器通道多，造成成本急剧增加。此外流程组织复杂，阀门、测量点等电气元件较多的区域需防爆，为装置的安全性带来隐患。
如中国发明专利说明书CN101033910公开了一种集成空气分离与液化天然气冷量回收系统，该系统从分馏上塔顶部引出的氮气经过液氮液空过冷器、主换热器的复热后，经压缩增压后进入液化天然气换热器进行预冷换热。冷却后的氮气经汽液分离器分离后，部分液氮节流后在液氧换热器、主换热器中复热完成氮气循环。这套系统中的循环氮气在液化天然气换热器进行预冷换热时，如果一旦高压的液化天然气泄漏，随着管道进入液氧换热器、主换热器，将对这些主冷设备的安全产生威胁，并造成对液氧产品，液氮产品的污染。此外，该套系统采用从上塔顶部引出的低压氮气低压氮(～10KPaG)循环完成氮气循环，为了达到中压透平压缩机的工作压力2.5MPa-5.0MPa，即使是按照2.5MPa，其压缩比也至少需要1.1∶25，压缩级数多，至少需要三段，此外整个过程中，物流数量多，能耗偏高，投资高，为了提高主冷的安全性需另外排放液氧，同时需配置气液分离器等，十分复杂。
中国发明专利说明书CN101392981，公开了一种利用液化天然气冷量获得液氮的方法和装置，同上所述，其液氮产品易受高压天然气换热器泄漏污染的威胁；此外装置中采用了两级增压透平膨胀机，依赖膨胀机转移冷量，而增压透平膨胀机转换效率受到限制，能耗因中间环节转换反而高，装置复杂因动设备多而复杂，投资高，可靠性差，同时需配置气液分离器等，十分复杂。
发明内容
本发明要解决的技术问题是提供一种安全可靠、流程简洁、操作控制方便，成本低廉、适用范围广、高效利用液化天然气冷能的空分系统。
为了解决以上技术问题，本发明包括空分装置和液化天然气冷量回收系统以及循环氮系统；所述空分系统至少包括分馏塔，主换热器；其特征在于：还包括氮-氮换热器；所述液化天然气冷量回收系统至少包括LNG-氮换热器、循环压缩机；所述氮-氮换热器包括循环液氮回热通道和氮气放热通道；所述LNG-氮换热器包括天然气回热通道、循环压力氮气放热通道、循环中压氮气放热通道、循环高压氮气放热通道，循环压力氮气放热通道依次与循环压缩机的低压段、循环中压氮气放热通道、循环压缩机高压段、循环高压氮气放热通道连通；所述主换热器包括循环氮气回热通道；所述氮-氮换热器的循环液氮回热通道、主换热器的循环氮气回热通道、LNG-氮换热器的循环压力氮气放热通道、循环中压氮气放热通道、循环高压氮气放热通道，以及在上述循环通道和压缩机管道内的循环氮构成循环氮系统；液化天然气经LNG-氮换热器的天然气回热通道复热至常温输出；从分馏下塔顶部引出的氮气进入氮-氮换热器的氮气放热通道冷凝成液氮。
以上利用LNG冷能的空分系统，以压力氮气作为封闭循环介质，设有LNG-氮换热器和氮-氮换热器两组换热器，液化天然气在LNG-氮换热器中将冷量传递给循环氮；循环氮在氮-氮换热器中将冷量传递给空分精馏塔的压力氮，空分不与循环介质直接接触，避免天然气进入空分装置而带来的危险。进入循环压力氮气放热通道的压力氮压力(～370KPaG)，无需低压氮到压力氮的压缩过程，采用两个压力等级液氮液氮过冷。不设置低压氮过冷，简化LNG-氮换热器。压缩机仅两段压缩，压缩比小(约10-12)，压缩级数少，物流数量少，能耗低，受外界干扰影响小，操作简单；通过低温循环压缩机两段压缩，利用LNG冷能冷却，降低压缩功耗，获得超临界压力氮，在LNG-氮换热器中吸收LNG的冷量。在LNG-氮换热器对高压氮进行液化过冷，但不深度过冷，采用较高温度的循环系统的液氮在氮-氮换热器中复热。
更进一步的改进是，LNG-氮换热器的循环高压氮气放热通道的输出端分成三路，分别连接氮-氮换热器的循环液氮回热通道的输入端、LNG-氮换热器内的循环压力氮气放热通道、循环中压氮气放热通道。为弥补LNG高品位冷量的不足，高压液氮经两路不同压力节流。循环压力氮气进入LNG-氮换热器冷却，汇合过冷高压液氮而复热的压力氮进入低温循环压缩机压缩，压缩到一定压力进入LNG-氮换热器冷却，并汇合液化过冷高压液氮而复热的中压氮进入低温循环压缩机继续压缩，再次进入LNG-氮换热器冷却液化并过冷，分成三股，其中一股节流到中压氮压力返回换热器，一股节流到压力氮压力返回换热器，其余液氮节流进入空分冷箱系统氮-氮换热器，液氮被汽化，进入主换热器复热作为循环氮气。
更进一步的改进是，所述循环压力氮气放热通道通过压缩机管道输出的高压氮气压力为超临界压力，压力值为50-60bar。常用压力值为36-60bar。
更进一步的改进是，所述循环中压氮气放热通道的输入端与循环高压氮气放热通道的输入端之间设有可开关的连接管路。当液化天然气冷量不足时，可以打开连接管路，循环氮不再进入两级压缩机压缩放热。所述分馏下塔顶部或分馏塔顶部的氮气出口设置有与氮-氮换热器的循环液氮回热通道输出端和主换热器的循环氮气回热通道输入端连接的可开关的管道。可以在设备运行初期或循环系统的氮量不足时，打开连接管路，从空分装置中为氮循环系统提供循环氮。
采用上述装置，其具有以下优势：
安全：由于氮循环系统完全封闭，不参与精馏，盛装液氧液氮产品的大型贮槽不会遭受污染，液体贮存安全。分馏塔冷凝器由于大量排放产品液氧，烃类难以在冷凝器富集，因而更安全。由于LNG-氮换热器冷箱，流程组织简单，防爆测量和控制元件锐减，系统更安全。
简洁：本发明液体产品均来自空分系统，空分系统流程组织自然、简洁；LNG高压液化器无低压过冷，物流通道少，控制简单。
低廉：由于流程组织合理简洁，控制部件少，投资降低，尤其LNG高压液化器成本降低，调节阀、测点、管道等投资大大降低。
可靠：流程简洁，部件越少越可靠，风险小，易于操作，系统稳定性较好。
产品质量好：由于产品来自空分，完全不必担心高压LNG泄露，即使泄露也不影响产品纯度，两者是隔离的。由于主冷液氧大量作为产品排放，液氧产品含烃较少。
节能：本发明换热器温差合理，不可逆损失小，可通过阀门进行调节，避免重复换热带来的不可逆损失，设计紧凑，减少了设备、管路、阀门等系统冷损，因而能耗低。
适用范围广：LNG冷能品质不同，冷量回收程度不同，则压缩机进口温度和流量不同。
附图说明
本发明将通过实施例并参照附图的方式说明，其中：
图1本发明实施例1生产液氧液氮液氩的典型装置。
图2本发明实施例2生产液氧液氮的典型装置。
图3本发明实施例3生产液氮的典型装置。
图4本发明实施例4生产液氧液氮液氩的装置。
图5本发明实施例5生产液氧液氮的装置。
图6本发明实施例6生产液氮的装置。
AF1001：空气过滤器，TC1001：空压机，MS1201/2：吸附器
EH1201：加热器，E1：主换热器，E2：过冷器，C1：下塔，K1：主冷，C2：上塔
E3：氮-氮换热器，K701：粗氩冷凝器，C701：粗氩一塔
C702：粗氩二塔，K702：精氩冷凝器，K703：纯氩蒸发器
C703：纯氩塔，ArP701：工艺氩泵
E-LNG-N2：LNG-氮换热器，NC601：低温循环压缩机
E801：循环冷却剂换热器，501：冷却剂循环泵
E501：冷库冷媒换热器，ET601：液体膨胀机
V1：补气阀，V2：放空阀，V3：启动阀，V4：节流旁通阀
CB-ASU：空分冷箱，CB-LNG-N2：天然气氮换热冷箱
具体实施方式
本说明书中公开的所有特征，或公开的所有方法或过程中的步骤，除了互相排斥的特征和/或步骤以外，均可以以任何方式组合。
本说明书(包括任何附加权利要求、摘要和附图)中公开的任一特征，除非特别叙述，均可被其他等效或具有类似目的的替代特征加以替换。即，除非特别叙述，每个特征只是一系列等效或类似特征中的一个例子而已。
实施例1
如图1所示为本发明生产液氧液氮液氩的典型装置。
1空分系统
1.1压缩冷却及纯化
外界空气100经空气过滤器AF1001过滤，进入空气压缩机TC1001压缩冷却，冷却剂采用低温循环冷却剂冷却。
工艺空气102进入用来吸附除去水份、二氧化碳、部分碳氢化合物的吸附器MS1201/2，一台吸附，另一台则由来自冷箱中的GWN污氮气133通过加热器EH1201加热后进行再生。
1.2空气精馏
出空气纯化系统的洁净工艺空气103(～460KPaG)进入空分冷箱CB-ASU内的主换热器E1，被返流出来的气体冷却，接近露点的空气104进入精馏下塔C1的底部，进行第一次分馏。在精馏下塔中，上升气体与下流液体充分接触，传热传质后，上升气体中氮的浓度逐渐增加。下塔顶部获得纯压力气氮(～460KPaG)，部分压力气氮111进入氮-氮换热器E3冷凝成液氮112，从天然气氮换热冷箱来的液氮610进入氮-氮换热器被汽化成气氮611(～400KPaG)，进入主换热器E1复热作为循环氮气601(～390KPaG)；部分气氮115进入下塔顶部的主冷凝蒸发器K1被冷凝成液氮113，在气氮冷凝的同时，主冷凝蒸发器中的液氧得到汽化，作为上塔C2的上升气体。一部份液氮114作为下塔的回流液下流，另一部分液氮116经过冷器E2过冷后，部分作为产品液氮118抽出外，其余液氮119节流后送入分馏上塔。
在下塔中产生的液空105也经过冷器E2过冷，液空106节流后进入上塔参与精馏，在上塔内，经过再次精馏，得到氮气120、污氮130及液氧201，分别经过冷器E2换热，液氧经过冷作为产品202；氮气121，污氮131再经主换热器复热，获得低压氮气产品122，污氮132。
分馏下塔顶部的氮气出口设置有气氮611的输出端和主换热器的循环氮气回热通道的输入端连接的可开关的管道。在设备运行初期或循环系统的氮量不足时，打开补气阀V1连接管路，从空分装置中为氮循环系统提供循环氮613。也可以不需要该连接管路，而采用外部供氮装置，该装置通过连接管道、启动阀V3连通天然气氮换热冷箱与氮-氮换热器之间的液氮输出通道，为氮循环系统提供循环氮612。低压氮气产品122通过管道、放空阀V2连接主换热器复热输出的循环氮气601至天然气氮换热冷箱的循环压力氮气放热通道输入管道。
1.3氮-氮换热
下塔顶部部分压力气氮111(～460KPaG)进入氮-氮换热器冷凝成液氮112；液化冷箱来的液氮610被汽化成气氮611(～400KPaG)，进入主换热器复热作为循环氮气601。
1.4氩的制取
与常规空分类似。氩的制取采用全精馏制氩技术，为了制取氩，从分馏塔上塔C2下部的适当位置引出一股氩馏份气送入粗氩一塔C701进行粗馏，使氧的含量降低，粗氩塔I的回流液体是由粗氩二塔C702底部引出经液体泵ArP701输送来的液态粗氩。从粗氩一塔C701顶部引出的气体进入粗氩二塔C702并在其中进行深度氩氧分离，经过粗氩二塔C702的粗馏，在其顶部得到含氧量合格的粗氩气，粗氩二塔C702的顶部装有冷凝蒸发器K701，以过冷器后引出的液空108经节流后送入其中作为冷源，绝大部分的粗氩气经冷凝蒸发器K701冷凝后作为粗氩塔的回流液。其余部分由粗氩二塔C702顶部引出并送入精氩塔C703，精氩塔的底部装有一台蒸发器K703，以下塔底部引出的压力氮气123作热源使液氩蒸发，同时氮气被液化。在精氩塔的顶部装有冷凝器K702，以液氮126作为冷源，使绝大部分上升气体冷凝作为精氩塔的回流液，经过精氩塔的精馏，在精氩塔底部得到精液氩，作为产品液氩701引出冷箱。
2天然气氮换热冷箱
来自用户的高压低温LNG 801(4-9.5MPa)作为冷源进入LNG冷量回收冷箱系统的LNG-氮换热器E-LNG-N2，自身被复热汽化，复热至常温天然气803进入用户管网，部分较低温度的天然气802从LNG-氮换热器引出，进入循环冷却剂换热器E801与冷却剂换热，复热至常温天然气804并入用户管网。
循环压力氮气601进入LNG-氮换热器冷却到一定温度，汇合过冷高压液氮而复热的压力氮，压力氮602进入低温循环压缩机NC601低压段压缩，压缩到一定压力获得中压氮603进入LNG-氮换热器，并汇合液化过冷高压液氮而复热的中压氮，中压氮604进入低温循环压缩机NC601高压段继续压缩，高压氮605再次进入LNG板式冷却液化并过冷成液氮606，分成三股，其中一股液氮608节流到中压氮压力返回换热器，一股液氮608节流到压力氮压力返回换热器，大部分液氮609节流进入空分冷箱系统氮-氮换热器。低温循环压缩机的各段入口温度与LNG的压力温度及LNG冷量回收程度相关，在冷量充足的情况下，降低压缩机入口温度，压缩功耗降低，但需注意压缩机入口要高于液化温度并有足够安全温差，确保压缩机进气不带液，因此本发明适用的范围很广，存在衍生系列，例如当一段压缩出口温度与二段压缩入口温度一致时，则开启循环中压氮气放热通道的输入端与循环高压氮气放热通道的输入端之间的连接管路(图中未示出)，氮压缩后不与天然气换热冷却，但这属于本发明的保护范围。中压压力由压缩机压缩比决定，回收越彻底，能耗越高，两段压缩最终高压压力须高于临界压力，氮的临界压力为33.94bara，经模拟计算末级压力36bara以上均能顺利通过，方案均可实施，压力越高，越有利于吸收高温端冷量，但需兼顾压缩机压缩比，综合考虑，一般为50-60bar，一段压缩出口中压氮压力则根据压缩机的情况及总压缩比决定分段压缩比获得最佳压力。
例如一套日产液氧320T，液氮290T，液氩10T的液体空分，以85bara，-151℃的LNG为冷源，LNG要复热到＞1℃，不含冷库系统，其典型参数：压缩机入口温度～-120℃，高压氮压力～60bara，中压段压力～17bara，LNG每天需求量为～1170T，含氧氮氩的分离功耗，平均电耗耗仅0.25KW/kg液体。
例如一套日产液氧320T，液氮290T，液氩10T的液体空分，以85bara，-151℃的LNG为冷源，LNG要复热到＞27℃，无冷库系统，采用循环水冷却系统冷却空压机各类冷却器，采用空分氮水塔回收空分放散的氮气、污氮，其典型参数：压缩机入口温度～-80℃，高压氮压力～60bara，中压段压力～17bara，LNG每天需求量为～673T，平均功耗则要增加很多。
上述例子也可变更压缩机压力，如压缩机末级排压为～42bara，中段排压～14bara。因此本发明根据情况不同参数可灵活变更，不便于一一例举。
3低温循环压缩系统C601
循环压力601氮气进入LNG-氮换热器E-LNG冷却到一定温度，汇合过冷高压液氮而复热的压力氮，压力氮602进入低温循环压缩机C601压缩，中压氮603进入换热器冷却，并汇合液化过冷高压液氮而复热的中压氮，中压氮604进入低温循环压缩机C601继续压缩，高压氮605再次进入换热器冷却液化并过冷，高压液氮606分成三股，其中一股液氮608节流到中压氮压力返回换热器，一股液氮607节流到压力氮压力返回换热器，大部分液氮609节流进入空分冷箱系统氮-氮换热器E3。
4低温冷却剂循环系统
低温冷却剂循环系统利用LNG低品位冷能，并非必需系统，若不考虑能耗，可以采用传统的循环水冷却系统，低温冷却剂循环系统适合于LNG冷能充足的情况。
空压机及各类油冷却器均采用低温冷却剂冷却，冷却剂处于封闭循环，因此补充损耗少，节约了大量水。压缩机吸入温度越低，能耗越低，冷能空分降低能耗的重要措施是降低压缩机入口温度，但由于空气含有水分，需保证在冰点以上。
冷却剂504与低温天然气802或启动初期与LNG801在循环冷却剂换热器E-801换热，获得较低温度的冷却剂501，经冷却剂循环泵P-501获得的冷却剂502与冷库气体在冷库冷媒换热器E501进行热交换，冷却剂503与空压机TC1001，其他压缩机及各类油冷却器、空调系统等换热，冷却剂通过冷却剂循环泵P-501循环。
5冷库冷源系统
冷库冷源系统只是利用LNG低品位冷能，并非必需系统，冷库冷源系统适合于LNG冷能充足的情况。
利用空分产生的氮122和污氮132进行调和满足冷库含氧要求。利用低温循环冷却剂502作为冷源与冷库气体在冷库冷媒换热器E501进行热交换，减少高压LNG换热器投资，且更安全。
实施例2
如图2所示，与实施例1比较，没有制氩系统，其他同实施例1。获得的空分产品为液氧和液氮。
实施例3，
如图3所示，与实施例1比较，分馏塔C1为单塔，空气进入分馏塔后，从分馏塔顶部获得的部分压力气氮111进入氮-氮换热器E3冷凝成液氮112，天然气氮换热冷箱CB-LNG-N2来的液氮610被汽化成气氮611(～180KPaG)，进入主换热器E1复热作为循环氮气601(～170KPaG)；部分纯氮115进入分馏塔顶部的主冷凝蒸发器K1被冷凝成液氮113。一部份液氮114作为下塔的回流液下流，另一部分液氮116经过冷器E2过冷后，部分作为产品液氮118抽出，其余液氮119节流后经过冷器E2、主换热器E1复热后，得到氮气122。
在下塔中产生的液空105经主换热器E1过冷，液空106节流后进入分馏塔上部参与精馏，在分馏塔内，经过再次精馏，得到污氮130，再经主换热器复热，获得污氮132。分馏塔内获得的富氧液空201引出节流后安全排放。
分馏塔顶部的氮气出口设置有氮-氮换热器的气氮611的输出端和主换热器的循环氮气回热通道的输入端连接的可开关的管道。
其他同实施例1。
实施例4
与实施例1比较，液化天然气冷量回收系统还包括液体膨胀机ET601和节流旁通阀V4。循环压力氮气601进入LNG-氮换热器冷却到一定温度，汇合过冷高压液氮而复热的压力氮，压力氮602进入低温循环压缩机NC601低压段压缩，压缩到一定压力获得中压氮603进入LNG-氮换热器，并汇合液化过冷高压液氮而复热的中压氮，中压氮604进入低温循环压缩机NC601高压段继续压缩，高压氮605再次进入换热器冷却液化并过冷成液氮，高压液氮606分成两股，其中一股液氮607节流到中压氮压力返回换热器，另一股高压液氮经液体膨胀机ET601膨胀后(液体膨胀机停用时通过V4节流旁通)，一股压力氮608返回换热器，大部分液氮609进入空分冷箱系统氮-氮换热器E3。
实施例5
其与实施例2不同的是，液化天然气冷量回收系统还包括液体膨胀机和节流旁通阀。所增加的液体膨胀机和节流旁通阀连接关系和工艺同实施例4的液体膨胀机和节流旁通阀的描述。
实施例6
其与实施例3不同的是，液化天然气冷量回收系统还包括液体膨胀机和节流旁通阀。所增加的液体膨胀机和节流旁通阀连接关系和工艺同实施例4的液体膨胀机和节流旁通阀的描述。
LNG冷能的空分系统能耗高低与LNG压力、温度相关，LNG压力、温度越高，高品位冷量(低温端冷量)越少。一般LNG汽化供气压力很高，高品位冷量不足，低品位冷量(高温端冷量)过剩。为了充分利用LNG低品位冷量，通常的方法液化装置是通过膨胀获得低温冷量，膨胀能量由压缩机获得，同时将氮压缩到高于超临界压力吸收冷量，增压膨胀方式涉及动设备，操作复杂投资高，因存在增压膨胀机的增压端膨胀端效率有限，多次转换导致能耗增加。本发明通过压缩获得超临界高压氮，通过高压液氮节流和压力液氮返回补充冷量，并可利用液体膨胀机回收能量。氮的压力越高，吸收效果越好，但要受设备制约。通过利用液化天然气的冷量，压缩和超临界氮吸收足够冷量，可大大降低液体产品的电力消耗，起到节能环保和高效运营的作用，达到变废为宝、提高能源综合利用率的目的。获得液体氧氮氩，运输方便，销售市场很大。
本发明实现了循环氮气与空分精馏介质完全隔离，两段氮压缩循环两级补充冷量实现高压液氮液化过冷，液体膨胀机回收能量，换热器通道数目极少、流程组织简洁，安全可靠，操作控制方便，成本低廉、适用范围广。
本发明不局限于前述的具体实施方式。可扩展到任何在说明书中披露的新特征或新的组合，以及披露的任一新的方法或过程的步骤或任何新的组合。

Claims (5)

1.一种高效利用液化天然气冷能的空分系统，包括空分装置和液化天然气冷量回收系统以及循环氮系统；所述空分装置至少包括分馏塔，主换热器；其特征在于：还包括氮-氮换热器；所述液化天然气冷量回收系统至少包括LNG-氮换热器、循环压缩机；
所述氮-氮换热器包括循环液氮回热通道和氮气放热通道；
所述LNG-氮换热器包括天然气回热通道、循环压力氮气放热通道、循环中压氮气放热通道、循环高压氮气放热通道；循环压力氮气放热通道、循环压缩机的低压段、循环中压氮气放热通道、循环压缩机高压段、循环高压氮气放热通道依次连通；
所述主换热器包括循环氮气回热通道；
所述氮-氮换热器的循环液氮回热通道、主换热器的循环氮气回热通道、LNG-氮换热器的循环压力氮气放热通道、循环中压氮气放热通道、循环高压氮气放热通道，以及在上述循环通道和压缩机管道内的循环氮构成循环氮系统；
液化天然气经LNG-氮换热器的天然气回热通道复热至常温输出。
2.如权利要求1所述的高效利用液化天然气冷能的空分系统，其特征在于：LNG-氮换热器的循环高压氮气放热通道的输出端分成三路，节流后分别连接氮-氮换热器的循环液氮回热通道的输入端、LNG-氮换热器内的循环压力氮气放热通道、LNG-氮换热器内的循环中压氮气放热通道。
3.如权利要求2所述的高效利用液化天然气冷能的空分系统，其特征在于：所述循环压力氮气放热通道通过压缩机管道输出的高压氮气压力为超临界压力，压力值为36-60bar。
4.如权利要求3所述的高效利用液化天然气冷能的空分系统，其特征在于：所述压力值为50-60bar。
5.如权利要求2所述的高效利用液化天然气冷能的空分系统，其特征在于：所述循环中压氮气放热通道的输入端与循环高压氮气放热通道的输入端之间设有可开关的连接管路；所述分馏塔顶部的氮气出口设置有与氮-氮换热器的循环液氮回热通道输出端和主换热器的循环氮气回热通道输入端连接的可开关的管道。
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