CN101163934B - 从液化天然气中两段去除氮 - Google Patents

从液化天然气中两段去除氮 Download PDF

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CN101163934B
CN101163934B CN2006800134387A CN200680013438A CN101163934B CN 101163934 B CN101163934 B CN 101163934B CN 2006800134387 A CN2006800134387 A CN 2006800134387A CN 200680013438 A CN200680013438 A CN 200680013438A CN 101163934 B CN101163934 B CN 101163934B
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natural gas
nitrogenous
nitrogen
tower
stream
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CN101163934A (zh
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C·G·斯皮尔斯伯里
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Air Products and Chemicals Inc
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Air Products and Chemicals Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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
    • F25J3/0228—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 characterised by the separated product stream
    • F25J3/028—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 characterised by the separated product stream separation of noble gases
    • F25J3/029—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 characterised by the separated product stream separation of noble gases of helium
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Abstract

通过两段分离从液化天然气进料(41)中除去氮，在两段分离中，液化天然气(41)被第一次分馏，以提供第一富氮的顶部馏出蒸气流(46)和含氮底部液体流(19)，随后分馏至少部分所述底部液体流(19)，以提供比所述第一顶部馏出蒸气流(46)纯度低的第二富氮顶部馏出氮气流(36)和净化的液化天然气流(50)。在蒸馏塔(23)中进行第一次分馏，使用位于闪蒸罐(25)内的冷凝器(24)中冷凝的氮顶部馏出物作为该蒸馏塔的回流，在所述闪蒸罐(25)中进行第二次分馏。不同浓度的两个含氮物流(26，36)的供应允许控制在天然气液化装置中使用的燃料气体的氮浓度。

Description

从液化天然气中两段去除氮
本发明涉及液化天然气(LNG)流中氮的去除。尤其(但不是唯一的)适用于仅仅使用燃料气体中的部分氮含量，同时将剩余的氮含量排到大气中。提供了一种在不同浓度下和相应装置中在两段中去除氮的方法，该方法用于天然气液化以提供不含氮的LNG产物。
燃气涡轮通常用于提供LNG设备的轴功和电力。这些燃气涡轮的燃料通常是LNG工艺的废气产生的。在传统LNG方法中，通常避免在进料气体中存在的氮进入这些燃料气体流中。然而，这些涡轮机的更加环境友好的低氮氧化物(NOX)燃烧装置具有比在先使用的燃烧装置更低的燃料气体中氮的容限。因此，在一些具有高氮含量的进料气体的装置场合中，需要从LNG工艺中除去比可以被燃气涡轮燃料系统接受的更多的氮。
已经有很多现有技术建议了通过分馏法从具有相对高浓度氮的LNG流中除去氮气，其中制冷剂或热泵流被用来冷凝来自分馏塔中的顶部馏出蒸气或提供塔的回流。
US-A-2500118(1950年3月7日授权)公开了一种天然气液化方法，其中含杂质的LNG进料在分离塔中分离，以生成LNG底部液流和顶部馏出的氮。一部分氮顶部馏出物被冷凝以提供分离塔的回流，而其它部分被排出。没有对分离塔生成的底部LNG中的氮进行进一步去除。
US-A-3205669(1965年9月14日授权)公开了从天然气中回收氦和氮的方法。在图3的实施方案中，来自“第一”分离塔的含杂质LNG底部液流在“第二”分离塔中分离成顶部馏出蒸气和底部液体。部分顶部馏出物提供了燃料气体而剩余部分在氮气塔中分离，以提供底部液体和基本纯净的顶部馏出氮气。来自第二分离塔和氮气塔的底部液体结合在一起并被蒸发，以提供进一步处理的“残余气”。来自第一分离塔的塔顶馏出物被冷却并被进料到氦分离塔中以提供顶部馏出的氦产物和循环物流。在参考图4和5描述的修改方案中，氮气塔被去除，来自第二分离塔的顶部馏出物进料到氦分离塔中而氮作为氦分离塔的底部液体获得。在参考图6和11/11a描述的另一改进方案中，保留氮气塔但是从氦分离塔向第二分离塔进料。在参考图7、8和10描述的另一修改方案中，氮气塔被去除并且从氦分离塔向第二分离塔进料，由此氮气并没有从燃料气体中分离。在所有示例性实施方案中，氦分离塔的氮含量小于第二分离塔，而如果存在氮气塔，第二分离塔的氮含量依次小于氮气塔的含量。
US-A-355947(1971年2月2日授权)公开了在精馏塔中分离LNG进料中的氮的方法，参见图1和2，提供了作为底部液体的纯净LNG产物和氮气顶部馏出物。部分底部液体在塔顶部提供了冷凝负荷，但是其组成并没有改变。
US-A-3721099(1973年3月20日授权)公开了对天然气进行分凝的方法，参考图1，在该方法中，预冷却的天然气被进料被分离成“第一”蒸气部分和“第一”LNG部分。蒸气部分被进一步冷却和分离，以提供含有大约25％氮的“第二”蒸气和含有大约5％氮的“第二”LNG部分。第二蒸气在再沸器/冷凝器中冷凝，以在双精馏塔的高压(HP)塔中提供再沸负荷。部分冷凝的混合物进料到HP塔中，而剩余部分与“第一”LNG部分一起循环以提供冷负荷。HP塔提供了含有大约95％氮的顶部馏出蒸气和含有大约5％氮的底部液体。部分顶部馏出物向低压(LP)塔提供了再沸负荷，而产生的冷凝的顶部馏出物提供了塔的回流。HP塔底部液体和第二LNG部分在LP塔中分离，以提供大约95％氮的顶部流馏出蒸气和含有大约0.5％氮气的LNG底部液体，该底部液体被低温冷却并运送储存。HP和LP塔的顶部馏出物结合一起并被用于提供冷负荷。在改进方案中，LP塔没有回流，并且来自该塔的顶部蒸气含有大约20％氮气并提供了燃料气体(图2)和，任选地(i)全部的来自HP塔再沸器/冷凝器的冷凝蒸气进料到HP塔(图3)或(ii)全部预冷却天然气进料流过HP塔再沸器/冷凝器并被进料到HP塔(图4)。
US-A-3874184(1975年4月1日授权)公开了液化天然气的方法，其中将通过天然气部分液化得到的两相物流快速送入分馏塔中以提供富氮的顶部馏出蒸气和含杂质的底部LNG。顶部馏出物用作燃料气体而底部产物被闪蒸并进料到分离塔中以提供顶部馏出蒸气和底部液体。分馏塔使用蒸发的底部液体再沸腾，而使用低温冷却的底部液体作为分离塔的回流。底部液体随后被闪蒸并在两个连续的分离塔中分离，以提供LNG产物。来自这些分离塔的顶部馏出物提供了热交换负荷。
EP-A-0090469(1983年10月5日授权，对应的US-A-4415345，于1983年11月5日授权)公开了一种从气态天然气中除去氮气的方法，该方法通过使用开环氮气热泵冷却和低压分馏，以产生分馏的液体回流。在单一塔的实施方案中，只对来自部分冷凝的天然气进料的蒸气部分进行分馏。通过冷凝开环氮气制冷剂来提供分馏塔的再沸，并且通过冷凝的氮制冷剂提供塔的回流。在示例性双塔实施方案中，高压塔被部分冷凝的天然气进料再沸，并且开环氮气热泵接收来自两个塔的氮气，并向低压塔提供了再沸负荷和双塔的回流。净化的LNG被天然气进料加热并作为蒸气接收。在方法中没有产生LNG最终产物。
EP-A-0131128(1985年1月16日授权，对应的US-A-4504295，于1985年3月12日授权)公开了一种通过分馏部分冷凝的天然气流将天然气流分离成氮气流和甲烷流的方法，该方法使用闭合循环热泵循环来提供再沸和回流热交换负荷。在该方法中没有产生LNG最终产物。
US-A-4701200(1987年10月20日公开)公开了从天然气中分离氦的方法，该方法使用双塔氮去除单元，其中HP塔顶馏出物分离成富含氦气体和富氮液体部分。前者进一步分离以提供产物氦气体，而后者提供了HP和LP塔的回流，而HP塔底部液体在LP塔中分离成LNG底部液体和氮气顶部馏出蒸气。进料到HP塔的天然气为气态。
WO-A-93/08436(1993年4月29日公开，对应的US-A-5421165，于1995年6月6日授权)公开了一种从LNG流中去除氮气的方法，在该方法中LNG在分馏之前被冷却并被动态和静态膨胀。通过与从塔的中间位置排出的再沸物流进行热交换，冷却至少被部分实施，而再沸物流在低于中间位置的高度回流。来自分馏塔的顶部馏出蒸气可以被压缩和用作燃料气体。任选地部分压缩的顶部馏出蒸气被离开塔的顶部馏出蒸气部分冷凝，并且其压力降低并作为回流进料到塔中。部分冷凝的顶部馏出蒸气可以在辅助塔中分馏，以提供高纯度氮气顶部馏出蒸气和底部液体，其中底部液体压力降低并在进料到分馏塔之前与剩余部分结合。辅助塔底部液体可以用来在辅助塔顶部提供冷凝功能。
EP-A-0725256(1996年8月7日公开)公开了一种方法，在该方法中气态天然气进料被冷却和分馏以除去氮气。通过在塔再沸器中冷却开环氮气制冷剂来提供分馏塔的再沸蒸气。通过使得冷却的氮制冷气体膨胀从而提供少量(4-5％)的液体来提供塔顶部的回流，至少一种来自塔的中间蒸气流被顶部馏出蒸气流部分冷凝，并作为中间回流返回到塔中，该中间回流是很大部分的塔回流。天然气在加热之前被泵压到高压，并作为蒸气产物回收。在该方法中没有产生LNG最终产物。
GB-A-2298034(1996年8月21日公开，对应的US-A-5617741，于1997年4月8日授权)公开了一种从天然气进料流中除去氮气的方法，该方法使用双塔低温蒸馏系统，该系统具有第一塔和第二塔，其中第二塔在与第一塔基本相同的压力下进料和操作。至少部分来自第一塔的底部液体与来自该塔的富氮蒸气进行热交换而膨胀并且至少部分蒸发，以提供回流到第一塔的至少部分冷凝的富氮流，从而提供较高的温度回流。来自第二塔的底部液体与来自双塔之一的顶部馏出蒸气进行热交换而至少部分蒸发，从而提供回流到第一或第二塔的至少部分冷凝的物流，以提供较低温度回流。通过与天然气进料进行热交换来提供双塔的再沸。在该方法中没有产生LNG最终产物。
WO-A-0023164(2000年4月27日公开，对应的US-A-6199403，于2001年3月13日授权)公开了一种方法，在该方法中天然气流进行液化、膨胀，随后在相分离塔中分离，所述分离塔可以是除氮塔。该塔的回流可以通过使用制冷系统冷凝部分顶部馏出物来提供。所述制冷系统可以包括闭环制冷系统、开环制冷系统、和/或与产物流进行间接热交换。冷凝顶部馏出蒸气的部分热交换负荷可以通过从塔中排出和回流到该塔的底部液体流提供。分离的LNG产物液体被泵压到更高压力并被加热。
US-A-6070429(2000年6月6日授权，对应的WO-A-0058674，于2000年10月5日公开)公开了一种方法，其中由被加压的LNG物流得到的压缩气体流在压力连续降低的串联的3个解析塔中分离，以从第三解析塔中产生富氮的气体流和富含甲烷的液体流，其中后者适合循环到断开的甲烷循环液化工艺中和/或用作燃料气体。在每个解析塔中，通过部分冷凝第一部分气体流得到的含有液体的物流与每个气流的第二部分并流接触，以提供顶部馏出蒸气和底部液体。第一和第二解析塔的顶部馏出物分别提供了第二和第三解析塔的进料流。第二和第三解析塔进料流的冷负荷通过来自第三解析塔的顶部馏出蒸气和底部液体提供。在示例性实施方案中，来自第二解析塔的底部液体被进料到第三解析塔中而来自第一解析塔的底部液体可以被用来提供热交换负荷，从而向第一解析塔提供部分冷凝进料部分的热交换功能。
US-A-6449984(2002年9月17日授权，对应的WO-A-03004951，于2003年1月16日公开)公开了一种方法，其中天然气气流被液化，随后被分馏以产生富氮的顶部馏出蒸气和LNG底部液体。通过冷凝部分顶部馏出蒸气来分馏塔的回流。在示例性实施方案中，通过制冷剂流提供冷负荷并且与最后的LNG低温冷却热交换器结合一起。还是在这些实施方案中，液体从分馏塔中间区域排出，并被进料到塔的液化气流加热，然后在较低区域回流到塔中。
WO-A-02088612(2002年11月7日公开)公开了一种通过在液化过程中从富含碳氢化合物物流，尤其是天然气中除去氮的方法，在该方法中部分冷凝的物流进料到双塔除氮系统中。高压塔提供了富氮的顶部馏出蒸气，其被来自低压塔的顶部馏出蒸气冷凝并作为回流进料到低压塔中。来自高压塔的底部液体被冷却并进料到低压塔中，液化产物作为底部液体从低压塔中排出。高压塔被高压塔部分冷凝的进料提供的热负荷再沸。
US2003/0136146(2003年7月24日公开，对应的WO-A-03062724，于2003年7月31日公开)公开了一种用于生产LNG和GTL(气变液技术)产物的集成方法，其中LNG进料在连续的闪蒸罐或其它分离塔中分离，以分别提供顶部馏出蒸气和更加纯净的LNG底部产物。分离塔顶部馏出物用作燃料、GTL进料或循环物流。优选每个连续的分离至少比在前的分离小15psig(1barg)。
US2004231359(2004年11月25日公开，对应的WO 2004104143，于2004年12月2日公开)公开了一种方法，在该方法中天然气流被液化，然后在蒸馏塔中分馏以除去作为顶部馏出蒸气产物的氮，和作为底部液体的被净化的LNG。通过冷凝的氮气流提供塔的回流。通过压缩和膨胀含有氮的制冷剂流来获得回流物流的制冷和冷却纯净LNG流和/或液化的天然气进料，其中制冷剂流可以包括全部和部分来自蒸馏塔的顶部馏出蒸气。在示例性实施方案中，通过进料到塔的液化天然气流来提供分馏塔再沸的热交换负荷。
WO-A-2005/061978(2005年7月7日公开)公开了从LNG进料流中除去氮的方法，该方法通过第一次分馏提供富氮的顶部馏出物(“第一蒸气流”)和贫氮的底部液体(“第一液体流”)，并且底部液体进行第二次分馏，以提供比第一蒸气流纯度更低的富氮顶部馏出物(“第二蒸气流”)和净化的LNG(“第二液体流”)。可以在塔和闪蒸罐中进行分馏。第二次分馏在比第一次分馏更低的压力下进行，并且第一液体流可以通过膨胀冷却，优选膨胀到或接近大气压力。第一蒸气流被作为例如燃起涡轮燃料消费，并且产量不会超过可以在相关装置中消耗的量。第二蒸气流的指定的用途仅仅用作家用燃气。优选地，第一蒸气流具有10-30mol％的氮含量而第二蒸气流具有小于5.5mol％的氮含量。
本发明的目的是提供从任何LNG工艺中除去部分氮的方法，该方法具有最小化的附加设备和对装置属性最小的影响。可以通过本发明达到以上效果，并且生产LNG的热传递设备的结构不会发生任何变化，和具有有限的附加装置。具体而言，本发明免去了必需的附加热泵压缩机，并且允许最终产物LNG用来作用于氮分离塔冷凝器。
在第一和最宽的方面，本发明提供了一种从液化天然气进料中除去氮的方法，包括对液化天然气进行第一次分馏，以提供第一富氮顶部馏出蒸气和含氮的底部液体流，并且对至少部分所述底部液体流进行第二次分馏，以提供比所述第一顶部馏出蒸气流纯度低的第二富氮顶部馏出蒸气流和净化的液化天然气流。
第一富氮顶部馏出蒸气流可以具有超过80mol％的氮气浓度，优选超过90mol％，更优选超过95mol％。
通常，至少部分第一富氮顶部馏出蒸气流被排到大气中，而第二富氮顶部馏出蒸气流被用作燃料气体或添加到燃料气体中，尤其是提供与天然气进料液化相关的功的燃气涡轮的燃料气体。
优选地，第一次分馏在蒸馏塔中进行，其中该蒸馏塔由部分冷凝的第一富氮顶部馏出蒸气提供回流。合适地，通过低温冷却的液化天然气流提供冷凝的热交换负荷，其中所述低温冷却的液化天然气流包括或来自至少部分的含氮底部液体流。低温冷却(sub-cooling)的液化天然气流可以是全部或部分低温冷却和降压后的含氮底部液体流。可以通过液化天然气进料提供的热交换负荷来使得蒸馏塔再沸。
还优选第二次分馏在闪蒸罐中进行。当在蒸馏塔中进行第一次分馏时，通常使用全部或部分在位于闪蒸罐中的冷凝器中冷凝的富氮顶部馏出蒸气提供蒸馏塔的回流。当仅需要部分含氮底部液体流提供冷负荷时，剩余部分可以进料到第二闪蒸罐中，以分离出纯度比所述第一顶部馏出蒸气流低的第三富氮顶部馏出蒸气流和第二净化的液化天然气流。通常，所述第三富氮顶部馏出蒸气流与第二富氮顶部馏出蒸气流相结合，而且所述第二净化的液化天然气流与来自第二次分馏的净化的液化天然气流结合。
如果液化天然气进料流中含有氦，可以通过例如部分冷凝和分离来提供富含氦的蒸气和富氮的液体，以从含有或来自第一富氮顶部馏出蒸气中分离出富含氦气流。可以通过被分离的富含氦的蒸气和/或富氮的液体来提供所述部分冷凝的热交换负荷。
在第二方面，本发明提供了一种制备不含氮的液化天然气进料流的方法，该方法包括液化含氮天然气，以提供含氮液化天然气流，和根据在前描述的第一方面脱除所述液化天然气流的氮气。
在该方面的优选实施方案中，制备不含氮液化天然气流的方法包括：
将含氮天然气流进料到具有液化和低温冷却部分的盘管热交换器中，其中热交换器的冷负荷通过循环制冷系统提供，通过燃料气体驱动的燃气涡轮向制冷系统提供涡轮；
在经过所述液化部分后排出液化气体流；
在精馏塔中对所述液化气体流进行第一次分馏，以提供第一富氮顶部馏出蒸气流和含氮的底部液体流；
在所述低温冷却部分低温冷却至少部分所述底部液体流，并对所述部分降压；
将所述降压的部分在闪蒸罐中进行第二次分馏，以提供纯度低于所述第一顶部馏出蒸气流的第二富氮顶部馏出蒸气流和净化的液化天然气流；
在所述闪蒸罐中冷凝部分第一富氮顶部馏出蒸气流，以提供其中的热量并产生冷凝的富氮顶部蒸气；
将至少部分所述冷凝的富氮的顶部馏出物流作为回流液回流到蒸馏塔中；
将所述第二富氮顶部馏出蒸气流用作燃料气体的至少一部分。
本发明还提供了通过所述第二方面的方法制备不含氮的液化天然气流的装置；所述装置包括：
液化含氮天然气进料的制冷系统；
第一分馏塔；
第二分馏塔；
用于将含氮的液化天然气从制冷系统进料到第一分馏塔的导管；
用于从所述第一分馏塔中排出第一富氮的顶部馏出蒸气流的导管；
用于将来自第一分馏塔的含氮底部液体流传送到第二分馏塔的导管；
用于将第二富氮的顶部馏出蒸气流从第二分馏塔中排出的导管；和
用来从第二分馏塔排出净化的液化天然气流的导管。
根据本发明的优选实施方案，在加压下液化但是并没有完全冷却到其储存条件的天然气被降低到某一中间压力，并被进料到第一氮分离塔中。LNG流迅速进入该塔中产生了具有降低的氮含量的底部液体流。根据降低的最终燃料气体氮含量来确定需要降低的量。从该塔底部排出的LNG被进一步冷却到最终闪蒸系统需要的温度，以生产具有最终需要的氮含量的LNG和必须的热量值的燃料气体。该最终冷却的LNG被送到末端的闪蒸罐中。末端闪蒸罐包括用来冷凝氮分离塔顶部馏出蒸气流并提供该塔回流的热交换器。该塔的顶部蒸气是可以直接排向大气的氮气流。
塔的顶部馏出蒸气冷凝器可以结合到该方法的末端闪蒸罐内，在这种情况下所有的产物LNG都流过该室。任选地仅有部分LNG产物可以流过该室。
氮分离塔可以具有再沸器，通过进料到塔的LNG在降压之前提供该再沸器的再沸，任选通过流体膨胀器降压。
来自塔顶部的氮产物可以被膨胀，并从氮产物中回收对在LNG处理中冷却或液化的物流的制冷。
本发明尤其用于使用LNG液化的盘管热交换器设备的LNG装置。仅仅需要在经过液化部分后排出含氮LNG，并将其在更低压力和贫氮下回流到低温冷却部分并进入到用于冷却的最终产物LNG中。对于C3MR方法，可以简单地通过在倒数第二个和最后冷凝阶段之间将LNG排出和回流并使用衰竭的LNG来实现。类似地对于AP-XTM，LNG可以在主低温热交换器和在冷却器之间排出和回流并使用衰竭(rundown)的LNG。
通过本发明，进料气体中含有的几乎任何部分氮气都可以作为纯净的氮气流排出。
以下仅通过实施例的方式并且参考本发明优选实施方案的附图进行描述。在附图中：
图1显示了应用到丙烷预冷却混合制冷剂(C3MR)LNG装置的基本原理，所述装置采用用于液化和低温冷却的单一盘管热交换器。
图2显示了图1实施方案的一种改进，其结合了除氮塔的再沸器、膨胀塔进料的膨胀器、和用于从顶部馏出蒸气中回收制冷的热交换器。
图3显示了图1的实施方案的一种改进，其中仅有部分LNG流被用来提供冷负荷。
图4显示了图1的实施方案的一种改进，其中盘管热交换器的第二部分被单独的热交换器60替代；和
图5显示了用于从LNG中回收氦的图1实施方案的改进。
本发明的示例性实施方案可以应用在任何LNG液化方法中，其中具有液化部分，在该部分后具有低温冷却部分。例如，本发明可以应用于双重混合制冷(DMR)和混合C3MR预冷却和液化中，其具有氮膨胀器循环LNG低温(AP-XTM)工艺以及图示的C3MR工艺。LNG在液化和低温部分之间取出，并被进料到氮分离塔中，在该塔中氮被排除“净化”。在产物LNG中的部分冷负荷被用于运行氮分离塔冷凝器之后，LNG返回到低温部分。
参考图1，进料天然气流1在预处理单元2中预处理，以除去另外在装置低温部分中冷冻的杂质，例如水和二氧化碳。得到的去除杂质的进料气流3在一个和多个热交换器4中预冷却，之后进入分离塔7中。热交换器可以是一系列的热交换器(4、5，参见图2和3)，其中例如丙烷制冷剂在连续压力降低下蒸发成为冷却物流3，或单个热交换器(4-参见图1和4)，混合制冷剂在其中蒸发。塔7将蒸发的物流6分离成轻质的顶部馏出蒸气部分10和重质的底部液体部分9，该液体部分9含有在LNG产物中不需要的重质组分。顶部馏出蒸气10在冷凝器11中被制冷剂部分冷凝。部分冷凝物流13在分离塔40中分离，以提供通过泵12作为回流返回到分离塔7中的液态冷凝物14和进料到盘管热交换器16中的顶部馏出蒸气15。顶部馏出蒸气在热交换器16的第一部分中被进一步冷却到一定温度，其中在该温度下，当冷却物流17通过膨胀阀和膨胀涡轮18降低到中间压力时仍然可以完全保持液态。热交换器16的冷却通过作为物流27排出热交换器16的混合制冷剂物流得到。
混合制冷剂在一个和多个压缩机28、30中压缩。被压缩的混合制冷剂首先在冷却器31中被冷却介质冷却，然后在冷却器32-35中被第一级预冷却制冷剂进一步冷却和部分冷凝。部分冷凝的制冷剂在分离塔37中分离，而蒸气和液体部分都供应到液化热交换器16中。
在降压后，物流41在除氮塔23中分离，以提供底部液体19和顶部馏出蒸气46。底部液体19与进料到塔23的进料流41相比具有降低的氮气含量，并在热交换器16的第二部分中被混合制冷剂进一步冷却到一定温度，在该温度下，当底部液体19被降低到LNG产品需要的压力下仍然保持完全液态。低温LNG流20通过膨胀阀21降压，而低压物流42进入到闪蒸罐25中，在其中低压物流42被部分蒸发，以提供液体产物LNG部分50和蒸气燃料部分36。闪蒸罐25内的热交换负荷通过热交换器24提供，在该热交换器24中来自除氮塔23的顶部馏出蒸气流46的一部分43被冷凝。顶部馏出蒸气流46的剩余部分26，其具有相对高纯度的氮气，被排到大气中。来自热交换器24的冷凝氮44作为回流到返回到除氮塔23中。任选地，液态氮流22可以从离开冷凝器24的冷凝物流44中排出。
图2的实施方案与图1不同之处在于向除氮塔23添加了再沸器47、添加了膨胀器49以膨胀塔23的进料、添加了热交换器57以从来自塔23的顶部馏出蒸气部分26和/或来自闪蒸罐25的顶部蒸气部分中回收制冷。然而，每一个这些特征都可以分别使用或以任何与除氮塔23相关的结合使用。
再沸器47设置在塔23的底部，以增加该塔除去的氮的量。来自热交换器16的第一部分的冷却高压进料气体17被用来提供再沸器47的热负荷，而离开再沸器47的产生的物流48在进入塔23之前，在膨胀涡轮49中膨胀。
可以从来自塔23和闪蒸罐25的顶部馏出蒸气26和36中的其一和两者回收制冷。可以通过将相应物流流向热交换器57，和如果需要在涡轮膨胀机59中膨胀来自除氮塔的被加热的顶部馏出蒸气58，来实现回收制冷。在热交换器57中通过回收的制冷冷却的物流61可以是进料气体的侧流或循环制冷剂。
图3的实施方案与图1的不同之处在于并不是所有的低温LNG流20流过闪蒸罐25。而是分成进入到第二闪蒸罐52的第一物流53和进入闪蒸罐25的第二物流54。离开闪蒸罐25和52的蒸气被收集并合并成物流56，该物流56被送到燃料气系统。离开闪蒸罐25和52的LNG液体流50和51合并在一起，并作为物流65送到LNG储存罐中。
图4的实施方案与图1的实施方案的不同之处在于热交换器16的第二部分被单独的热交换器60替代。每个热交换器16和60都使用不同的冷凝流体。来自除氮塔23的底部液体19流向热交换器60，并在热交换器60中被合适的第三级制冷剂62、63冷却，其中第三级制冷剂可以是混合制冷剂或例如氮的纯净流体。来自热交换器60的低温LNG流20提供了闪蒸罐25的进料。
本发明的另一实施方案涉及从除氮塔23的顶部馏出蒸气46中回收富含粗氦的气流。在例如图1的实施方案中顶部馏出蒸气46的排出部分26通常在220psia(1.5MPa)的压力和-258
Figure 2006800134387_0
(-161℃)的温度下。如果进料气体含有氦，那么进料气体中的氦的主要部分都包含在物流26中，并且可以在图5的处理方案中容易地从物流26中提取出。物流26在热交换器70中被回流氮气流76和氦气流73冷却。物流71离开热交换器70并被部分冷凝，并且在分离釜72中被分离成液体部分75和蒸气蒸气部分73。基本上是氦的物流73在热交换器70中加热，而得到的粗氦气流78排出用来进一步净化。基本上是氮的物流75通过阀74降压，而得到的冷却物流76在热交换器70中加热，得到的物流77可以被进一步加热以在排到大气之前进一步回收制冷。
实施例1
该实施例基于图1的实施方案的基础上。在环境温度和900psia(6.2MPa)压力下向LNG工艺供应88000 1bmol/h(40000kgmol/h)的进料天热气，其中进料天然气中含有4.8mol％氮，剩余的主要为甲烷。进料气体被干燥和预冷却，并在分离塔7中预处理，使得进料气体在-38
Figure 2006800134387_1
(-39℃)的温度和大约850psia(5.8MPa)的压力下进入到热交换器16中。物流17在-178
Figure 2006800134387_2
(-116.5℃)的温度下离开热交换器16并在进料到除氮塔23之前降压到220psia(1.5MPa)，其中除氮塔在220psia(1.5MPa)的压力下操作。物流19从塔23的底部排出并进一步在热交换器16中冷却到-247
Figure 2006800134387_3
(-155℃)。离开热交换器16的物流20随后降低到低压进入闪蒸罐25中。产物LNG流50在-261(-163℃)温度时从闪蒸罐25中排出，并且具有小于1.5mol％的氮含量。燃料流36从闪蒸罐25中排出，流率为7900 1bmol/h(3600kgmol/h)，具有30mol％的氮含量。氮排空气流26从塔23的顶部排出，流率为6001bmol/h(272kgmol/h)，氮含量为98.0mol％和温度为-257
Figure 2006800134387_5
(-160.5℃)。
实施例2
该实施例基于图1的实施方案的基础上，增加了图5的粗氦提取。在环境温度和900psia(6.2MPa)压力下向LNG工艺供应88000 1bmol/h(40000kgmol/h)的进料天热气，其中进料天然气中含有4.8mol％氮和600ppmv的氦，剩余的主要为甲烷。进料气体被干燥和预冷却，并在分离塔7中预处理，使得进料气体在-38
Figure 2006800134387_6
(-39℃)的温度和大约850psia(5.8MPa)的压力下进入到热交换器16中。物流17在-178
Figure 2006800134387_7
(-116.5℃)的温度下离开热交换器16，并在进料到除氮塔23之前降压到220psia(1.5MPa)的压力，其中除氮塔在220psia(1.5MPa)的压力下操作。物流19从塔23的底部排出并进一步在热交换器16中冷却到-247
Figure 2006800134387_8
(-155℃)。离开热交换器16的物流20随后降低到低压进入闪蒸罐25中。产物LNG流50在-261
Figure 2006800134387_9
(-163℃)温度时从闪蒸罐25中排出，并且具有小于1.5mol％的氮含量。燃料流36从闪蒸罐25中排出，流率为7900 1bmol/h(3600kgmol/h)，具有30mol％的氮含量。氮排空气流26从塔23的顶部排出，流率为710 1bmol/h(322kgmol/h)，氮含量为98.0mol％，温度为-259(-161.5℃)，和压力为220psia(1.5MPa)。参考图5，物流26在热交换器70中被回流73和76冷却到-298
Figure 2006800134387_11
(-183.5℃)的温度，并在分离塔72中分离成液体和蒸气流。液体流被释放到低压，提供了物流76的Joule Thomson制冷，其中物流76的温度达到-310
Figure 2006800134387_12
(-190℃)。液体流76和蒸气流73都在热交换器70中加热。物流77为氮排空气流，流率为6561bmol/h(297.5kgmol/h)和氮含量为97.5％。物流78为粗氦产物流，流率为541bmol/h(24.5kgmol/h)和氦含量为74mol％。
应当认识到本发明并没有限制在以上公开的关于示例性实施方案的详细描述中，而在不背离如下权利要求定义的本发明范围的情况下，可以作出多种改进和变化。

Claims (9)

1.一种制备不含氮的液化天然气流(50)的方法，包括：
将含氮天然气(15)液化以提供含氮液化天然气流(41)，其中燃气涡轮提供和所述液化相关使用的功；
将所述含氮液化天然气流(41)在蒸馏塔(23)中进行第一次分馏，以提供第一富氮顶部馏出蒸气流(46)和含氮底部液体流(19)；
使所述含氮底部液体流(19)的至少部分(20)进行低温冷却以及降压，其中所述低温冷却使用由制冷剂流体(39)提供的冷负荷，而不是来自所述含氮液化天然气流的冷负荷；
使用由冷凝部分所述第一富氮顶部馏出蒸气流(46)提供的热交换负荷，在闪蒸罐(25)中对所述含氮底部液体流(19)的所述低温冷却的、降压的部分(42)进行第二次分馏(25)，以提供比所述第一富氮顶部馏出蒸气流(46)纯度低的第二富氮顶部馏出蒸气流(36)和净化的液化天然气流；
以冷凝的第一富氮顶部馏出蒸气流(45)对所述蒸馏塔(23)进行回流；和
仅使用所述第二富氮顶部馏出蒸气流(36)作为所述燃气涡轮的燃料气体或添加到所述燃气涡轮的燃料气体中。
2.如权利要求1的方法，其中将全部的含氮底部液体流(19)在低温冷却和降压后进料到闪蒸罐(25)中。
3.如权利要求1的方法，其中只有部分(54)低温冷却和降压后的含氮底部液体流(20)进料到闪蒸罐(25)中，而剩余部分(53)进料到第二闪蒸罐(52)中，以分离成纯度低于所述第一富氮顶部馏出蒸气流(46)低的第三富氮顶部馏出蒸气流(55)和第二净化的液化天然气流(51)。
4.如权利要求1的方法，其中第一富氮顶部馏出蒸气流(46)具有超过80mol％的氮浓度。
5.如权利要求4的方法，其中第一富氮顶部馏出蒸气流(46)具有超过90mol％的氮浓度。
6.如权利要求5的方法，其中第一富氮顶部馏出蒸气流(46)具有超过95mol％的氮浓度。
7.如前述任一权利要求所述的方法，其中所述含氮天然气(15)在具有液化和低温冷却部分的盘管热交换器(16)中液化，含氮液化天然气流在经过液化部分后作为冷却物流(17)被排出，而来自蒸馏塔(23)的含氮底部液体流在所述低温冷却部分中被低温冷却。
8.一种通过权利要求1的方法制备不含氮的液化天然气流的装置，所述装置包括：
用于液化含氮天然气的制冷系统；
用于提供和所述制冷系统相关使用的功的燃气涡轮，
蒸馏塔；
闪蒸罐；
位于所述闪蒸罐内的冷凝器；
接收来自制冷剂流体的冷负荷的盘管热交换器；
用于将含氮液化天然气流从制冷系统进料到蒸馏塔的导管装置；
用来从蒸馏塔中排出第一富氮顶部馏出蒸气流的导管装置；
用来将部分第一富氮顶部馏出蒸气流传送到冷凝器的导管装置；
用来将冷凝的第一富氮顶部馏出蒸气流作为回流从冷凝器回流到蒸馏塔的导管装置；
用于将来自蒸馏塔的含氮底部液体流传送到盘管热交换器的导管装置；
用于将来自所述盘管热交换器的低温冷却的含氮底部液体流在降压下传送到闪蒸罐中的导管装置；
用于从所述闪蒸罐中排出第二富氮顶部馏出蒸气流并将其作为燃料气体进料进料到燃气涡轮的导管装置；和
用来从所述闪蒸罐中排出净化的液化天然气流的导管装置。
9.如权利要求8的装置，其中制冷系统包括具有液化部分和低温冷却部分的盘管热交换器；用于将含氮液化天然气流进料到蒸馏塔中的导管装置将所述含氮液化天然气流经过液化部分后从所述盘管热交换器中排出；以及，所述低温冷却部分构成了盘管热交换器的一部分，来自蒸馏塔的含氮底部液体流在该低温冷却部分中被低温冷却。
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