CN105783424A - 利用液化天然气冷能生产高压富氧气体的空气分离方法 - Google Patents

利用液化天然气冷能生产高压富氧气体的空气分离方法 Download PDF

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CN105783424A
CN105783424A CN201610255634.0A CN201610255634A CN105783424A CN 105783424 A CN105783424 A CN 105783424A CN 201610255634 A CN201610255634 A CN 201610255634A CN 105783424 A CN105783424 A CN 105783424A
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pressure
air
heat exchanger
oxygen
nitrogen
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CN105783424B (zh
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熊永强
罗鹏
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Jinan University
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    • 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
    • F25J3/04012—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
    • F25J3/04024—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 purified feed air, so-called boosted air
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  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
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  • Environmental & Geological Engineering (AREA)
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Abstract

本发明属于液化天然气冷能利用技术领域，特别涉及一种利用液化天然气冷能生产高压富氧气体的空气分离方法。该方法具体包括了以下步骤：(1)空气压缩和净化；(2)空气液化；(3)空气精馏；(4)LNG冷能利用。本发明方法一方面通过在常规双塔空分流程的基础上增设了一个中压塔和一个中压空气冷凝器与低压塔进行热集成，使得有一部分空气原料空气只需压缩至中压即可进行分离，大幅降低了空气压缩机的功耗。而且该方法以循环氮气为中间介质利用液化天然气冷能冷凝高压塔塔顶的氮气，为空气分离过程提供冷能，因此使用该方法不仅有很高的氧气提取率，而且可以避免液化天然气泄漏进入空气精馏单元，***的安全性能高。

Description

利用液化天然气冷能生产高压富氧气体的空气分离方法
技术领域
本发明属于液化天然气冷能利用技术领域，特别涉及一种利用液化天然气冷能生产高压富氧气体的空气分离方法。
背景技术
为了应对气候变化，世界各国近年来都在大力研发CO2捕集和封存(CCS)技术，其中富氧燃烧捕集技术被认为是最有可能大规模推广和商业化的CCS技术之一。大型富氧燃烧捕集装置需要消耗大量摩尔浓度低于97％的富氧气体，如一个富氧燃烧电厂每天需要上万吨高压富氧，制氧能耗巨大，可使电厂的发电效率降低6～8百分点。
随着社会经济的发展和能源结构的调整，我国的天然气产业进入了快速发展时期。为了弥补国内天然气资源的不足，我国每年从国外进口了大量的液化天然气(LNG)，2014年的进口量已达到了1989万吨。LNG在常压下是一种-162℃的低温液体，使用前需要在接收站内将其增压7～10MPa(绝对压力，下文出现的压力均为绝对压力)后加热汽化，汽化过程中会放出约230kWh·t-1的冷能，具有巨大的利用价值。LNG冷能可以用于空气分离，轻烃分离，低温发电，CO2捕集，低温粉碎和低温冷库等产业，节约生产过程的能耗。LNG冷能的利用效率与所利用的温度相关，利用温度越低，则冷能利用效率越高。因此利用LNG冷能进行低温空气分离可以得到最大有节能效益，是最合理的LNG冷能利用方式。在LNG接收站附近建设富氧燃烧装置，利用LNG冷能生产富氧燃烧捕集CO2所需的高压富氧气体，可以大幅降制氧能耗和CO2捕集的成本，有利于富氧燃烧捕集技术的大规模推广和商业化应用。
目前，国内已经公布了多个利用LNG冷能的空气分离专利技术：
(1)在中国发明专利01127133.7和200510124175.4介绍的利用液化天然气冷能生产液氧、液氮和液氩的空气分离装置中，均采用双塔流程进行氮氧分离，而LNG的冷能通过氮气制冷循环为空气分离装置提供生产液体空分产品所需的冷能。但由于氮气压缩液化过程只能利用深冷部分的LNG冷能，离开空气分离装置的天然气(NG)温度仍远低于常温，冷能未能充分利用。
(2)在中国发明专利200910085213.8，200910059100.0，201010262363.4等利用液化天然气冷能的空气分离方法中，为充分利用LNG的冷能，一方面将深冷部分的LNG冷能用于循环氮气的冷却和液化，为空气分离过程提供冷能；另一方面将LNG汽化后剩余的浅冷部分的冷能经冷媒乙二醇水溶液或氟利昂用于空压机级间冷却和末级冷却，使得LNG冷能得到充分利用。
上述现有的利用LNG冷能的空气分离专利方法都是采用双塔流程来生产高纯度的全液体空分产品，在使用过程中存在如下缺点：(1)由于液体产品的运输费用较高，液体空分装置的产品经济输送半径一般在300km以内，市场规模有限；(2)液氧的生产成本远高于气体产品，也无法直接用于富氧燃烧装置；(3)空分装置最大的能耗来自空气压缩机，而目前大多数的低温空分装置都采用高压塔(下塔)和低压塔(上塔)进行热集成的双塔流程来生产氧气，全部的空气原料都需要从常压压缩至高压(约0.6MPa)以便于进入高压塔进行分离，由于制氧能耗很高，不适合在富氧燃烧捕集CO2的装置中使用。
发明内容
为了克服上述现有技术的缺点与不足，本发明的首要目的在于提供一种利用液化天然气冷能生产高压富氧气体的空气分离方法。一方面，空气分离过程采用三塔流程，即增设一个中压塔与低压塔进行热集成，如此只需将一部分原料空气压缩至高压并进入高压塔分离，而其它空气原料则进入中压塔和低压塔进行分离，降低空压机的能耗；第二方面，从低压塔中段取出一部分冷能用于一股中压空气液化，使其可以利用液体泵增压进入高压塔进行分离，进一步降低空压机的能耗；第三个方面，以循环氮气作为中间介质，利用LNG冷能冷凝高压塔塔顶的氮气，为空分装置提供冷能，而且可以防止LNG泄漏到空分装置内部，提高了装置的安全性能。
本发明的目的通过下述方案实现：
一种利用液化天然气冷能生产高压富氧气体的空气分离方法，包括以下操作步骤：
(1)空气压缩和净化
空气首先进入自洁式空气吸入过滤器1，在过滤器中除去空气中所含的灰尘和其它颗粒杂质后，经空气压缩机2压缩至低压(绝对压力0.2MPa左右，下文出现的压力均为绝对压力)，再在换热器3中利用低温乙二醇水溶液将其冷却至2～10℃，并将空气冷却过程产生的冷凝水分离出来。从换热器3流出的低压空气经分流阀4分成两股，一股进入空气净化器11中脱除空气中的水、二氧化碳和一些碳氢化合物，变成低压干燥空气流；另一股低压空气则经空气压缩机5压缩至中压(压力在0.3～0.4MPa间)，再在换热器6中利用循环冷却水冷却至接近环境温度。从换热器6流出的中压空气经分流阀7再分成两股，其中一股中压空气进入空气净化器12中脱除空气中的水、二氧化碳和一些碳氢化合物，变成中压干燥空气流，而另一股中压空气则先在换热器8中利用低温乙二醇水溶液将其进一步冷却至2～10℃并分离出凝结水，然后进入空气压缩机9中压缩至高压(压力在0.5～0.6MPa间)，再在换热器10中利用循环冷却水冷却至接近环境温度后进入空气净化器13中脱除空气中的水、二氧化碳和一些碳氢化合物，变成高压干燥空气流。
(2)空气冷却
步骤(1)中获得的中压干燥空气经分流阀14分成两股，然后与步骤(1)中获得的低压干燥空气及高压干燥空气全部进入主换热器15中，经与从换热器24流出的低温低压废氮、来自液氧泵28的高压液氧和从换热器34流出的低温循环氮气进行换热，四股干燥空气被冷却至接近高压空气的露点温度。从主换热器15流出的低温低压空气经换热器24进一步冷却降温后进入低压塔26中分离，而从主换热器15流出的低温高压空气则进入高压塔中分离。从主换热器15流出的两股低温中压空气中，一股直接进入中压塔16进行分离，而另一股则先经换热器18进一步冷却到露点温度后进入位于低压塔内部的中压空气冷凝器19中冷凝液化。从冷凝器19流出的中压液体空气经液体空气泵20增至高压后进入换热器18中与来自主换热器15的低温中压空气换热，然后再经分流阀21分成两股后分别进入中压塔和高压塔内进行分离。
(3)空气精馏
步骤(2)中获得的一股低温中压空气和一股高压液体空气分别从塔底和塔中部进入中压塔进行氮、氧精馏分离，从中压塔塔顶获得的中压氮气进入位于低压塔内部的中压塔塔顶冷凝器17内与低压塔内的低温液体换热后全部液化。从中压塔塔顶冷凝器17中流出的中压液氮一部分返回中压塔作为塔顶回流液用于维持精馏工况，另一部分则经换热器24过冷后进入低压塔的塔顶，用于氮、氧的精馏分离。
在步骤(2)中获得低温高压空气和一股高压液体空气分别从塔底和塔中部进入高压塔进行氮、氧精馏分离，从高压塔塔顶获得两股高压氮气，一股则在换热器35中与从节流阀34中流出的循环液氮换热后而液化，并送入位于低压塔底部的冷凝/再沸器23，而另一股高压氮气也进入冷凝/再沸器23内与低压塔底的低温液氧换热后全部液化，而低温液氧获得热量后部分汽化成为低压塔内的上升蒸汽，用于维持精馏工况。从冷凝/再沸器23中流出的高压液氮被分成两股，一股返回高压塔作为塔顶回流液用于维持精馏工况，另一股则在换热器24过冷后又经分流阀25分成两部分，一部分进入低压塔的塔顶，用于氮、氧的精馏分离，而余下的则送入低压液氮罐27中作为液氮产品。
从中压塔和高压塔底部获得两股富氧液空均在换热器24中进一步过冷后进入低压塔中部进行分离，从塔顶排出的含氮较高的低温废氮气体在换热器24中回收部分冷量后进入主换热器15，而从塔底抽出的富氧液体则经液氧泵28增压后也进入主换热器15，为步骤(2)中的空气冷却提供冷能。在主换热器15中回收冷能后，高压液氧全部汽化成为高压富氧气体产品；低温废氮在主换热器15中被加热至接近常温后可以用于空气净化器的再生和循环冷却水的冷却。
(4)LNG冷能利用
步骤(3)中所述的从节流阀34中流出的循环液氮在换热器35中换热后全部汽化，再经主换热器15回收部分冷能后进入氮气压缩机29中增压。增压后的循环氮气在换热器30中与来自接收站的高压LNG换热后经氮气压缩机31进一步增压，然后在分流阀32中分成两股，其中一股进入换热器30中与来自接收站的LNG进料换热后液化，然后再经主换热器15进一步过冷，而另一股则直接进入主换热器15中换热后全部液化并过冷，形成了两股过冷循环液氮。这两股循环液氮在混合阀33中混合为一股，再经节流阀34降压后进入换热器35与来自高压塔顶的高压氮气换热，为空气的精馏分离提供冷量。
来自接收站的高压LNG经换热器30利用了一部分冷能后，温度仍低于其泡点温度，再将其送入换热器36中与来自混合阀39的一股热乙二醇水溶液换热。高压LNG换热后全部汽化，温度升高至0℃以上，成为一股高压天然气，可直接进入高压天然气管网。从换热器36中流出的乙二醇水溶液的温度降低至0℃左右，再经水泵37增压后在分流阀38中被分成两股，其中一股进入换热器3中用于低压空气的冷却，另一股送入换热器8中用于空气压缩机9的进气冷却。换热后，从换热器3和8流出的两股乙二醇水溶液经混合阀39混合后返回换热器36中，形成一个冷能利用循环。
其中：步骤(3)中所述的低压塔塔顶的操作压力在0.12～0.15MPa间，中压塔塔顶的操作压力在0.25～0.35MPa间，高压塔塔顶的操作压力在0.5MPa左右。
步骤(3)中所述的来自分流阀25的过冷高压液氮从塔顶进入低压塔，来自换热器24的过冷中压液氮从塔顶下约2～5块理论板的位置处进入低压塔，从换热器24流出的中压富氧液空和高压富氧液空自低压塔中部进入低压塔，其中高压富氧液空的进料口比中压富氧液空的进料口高5～10块理论板，而从换热器24流出的低压空气在高压富氧液空和中压富氧液空的进料口之间进入低压塔。
步骤(3)中所述的中压塔塔顶冷凝器设置在低压塔内，位于中压富氧液空的进料口下2～5块理论板处，中压空气冷凝器也设置在低压塔内，位于中压塔塔顶冷凝器与塔底之间。
步骤(3)中所述的从主换热器排出的高压富氧气体产品，其中氧的摩尔分率低于97％，压力在1.0MPa以上。
步骤(4)中所述的来自接收站的高压液化天然气压力为0.5～15MPa。
步骤(4)中所述的氮气压缩机29和31的进气温度控制在-120～-150℃间，所述的氮气压缩机29和31的压缩比基本相等，氮气压缩机31的出口压力大于5.5MPa。
步骤(4)中所述的节流阀34的出口压力较高压塔塔顶操作压力低0.04～0.10MPa。
本发明的机理为：
本发明的利用液化天然气冷能生产高压富氧气体的空气分离方法具体包括了以下步骤：(1)空气压缩和净化；(2)空气液化；(3)空气精馏；(4)LNG冷能利用。该方法一方面通过在常规双塔空分流程的基础上增设了一个中压塔和一个中压空气冷凝器与低压塔进行热集成，使得有一部分空气原料空气只需压缩至中压即可进行分离，大幅降低了空气压缩机的功耗。而且该方法以循环氮气为中间介质利用液化天然气冷能冷凝高压塔塔顶的氮气，为空气分离过程提供冷能，因此使用该方法不仅有很高的氧气提取率，而且可以避免液化天然气泄漏进入空气精馏单元，***的安全性能高。
本发明相对于现有技术，具有如下的优点及有益效果：
(1)本发明在常规双塔空分流程的基础上增设了一个中压塔，使得一部分空气原料空气只需压缩至中压即可进行分离，大幅降低了空气压缩机的功耗。
(2)本发明中一部分空气原料在压缩至低压后可以利用液化天然气的冷能和从低压塔分离出来的富氧液体产品及污氮的冷能进行冷却降温，然后可直接进入低压塔进行分离，不仅降低了空气压缩机的功耗，而且无需设置常规低温空气分离装置中制冷所必需的空气透平膨胀机，节省了设备投资费用。
(3)本发明中将中压塔塔顶冷凝器、中压空气冷凝器和冷凝/再沸器集成设置于低压塔内，使低压塔内低温液体的冷能得到了梯级利用，大幅减少了低压塔内液体再汽化过程的冷损失，降低了空分装置的生产功耗。
(4)本发明以循环氮气为中间介质利用液化天然气的冷能冷凝液化高压塔塔顶的氮气，为空气分离过程提供冷能。与现有其它发明中利用高压空气来吸收液化天然气的冷能相比，本发明可获得更高的氧气提取率，而且也可以避免液化天然气泄漏进入空气精馏单元，提高***的安全性能。
附图说明
图1为本发明的工作流程图。
其中：
具体设备编号
1－自洁式空气吸入过滤器；2,5,9－空气压缩机；
3,6,8,10,18,24,30,35,36－换热器；4,7,14,21,25,32,38－分流阀；
11,12,13－空气净化器；15－主换热器；
16－中压塔；17－中压塔塔顶冷凝器；
19－中压空气冷凝器；20－液体空气泵；
22－高压塔；23－冷凝/再沸器；
26－低压塔；27－液氮储罐；
28－液氧泵；29,31－氮气压缩机；
33,39－混合阀；34－节流阀；
37－水泵；
物流图示
具体实施方式
下面结合实施例和附图对本发明作进一步详细的描述，但本发明的实施方式不限于此，对于未特别注明的工艺参数，可参照常规技术进行。
实施例1：
如图1所示，一种利用液化天然气冷能生产高压富氧气体的空气分离方法包括以下步骤和工艺条件：
接收站的液化天然气(LNG)摩尔组成为：甲烷88.78％，乙烷7.54％，丙烷2.59％，异丁烷0.45％，丁烷0.56％，氮0.08％；进入空分装置的LNG压力为10MPa，温度约为-150℃。空气原料的摩尔组成为：氮气77.31％，氧气20.73％，氩气0.92％，CO2为0.04％，水1.02％；空气压力0.101MPa，温度15℃。所有压缩机的等熵效率0.82，机械效率为0.97；所有泵(包括水泵、液氧泵和液体空气泵)的等熵效率0.75，机械效率为0.97。
具体步骤如下：
(1)空气压缩和净化
常压、15℃的空气原料进入自洁式空气吸入过滤器1，在过滤器中除去空气中所含的灰尘和其它颗粒杂质，其流量约为896.4t/h。然后经空气压缩机2压缩至低压(压力为0.205MPa)，温度升高至93.5℃，再在换热器3中与一股来自分流阀38中的970t/h、温度为0℃的低温乙二醇水溶液(乙二醇质量分数为30％)换热，低压空气被冷却至10℃，并将低压空气冷却过程产生的冷凝水约3.0t/h从换热器3中排出。从换热器3流出的低压空气经分流阀4分成两股，其中一股流量约为143t/h的低压空气进入空气净化器11中脱除空气中的水、二氧化碳和一些碳氢化合物，变成低压干燥空气流，流量为142.5t/h，温度约为20℃，压力约为0.165MPa；另一股流量约为750.4t/h的低压空气则经空气压缩机5压缩至中压(压力为0.352MPa)，温度升高至67.6℃，再在换热器6中利用循环冷却水冷却至18℃。从换热器6流出的中压空气经分流阀7再分成两股，其中一股流量为304.0t/h的中压空气进入空气净化器12中脱除空气中的水、二氧化碳和一些碳氢化合物，变成中压干燥空气流，其流量约为302.9t/h，温度约为20℃，压力约为0.312MPa；而另一股流量为446.4t/h的中压空气则先在换热器8中利用171t/h、0℃的低温乙二醇水溶液(乙二醇质量分数为30％)将其进一步冷却至10℃并分离出凝结水约0.6t/h，然后进入空气压缩机9中压缩至高压(压力为0.546MPa)，温度升高至56.2℃，再在换热器10中利用循环冷却水冷却至18℃后进入空气净化器13中脱除空气中的水、二氧化碳和一些碳氢化合物，变成高压干燥空气流，流量约为444.8t/h，温度约为20℃，压力约为0.526MPa。
(2)空气冷却
步骤(1)中获得的中压干燥空气经分流阀14分成两股，流量分别为183t/h和119.9t/h；然后与步骤(1)中获得的低压干燥空气及高压干燥空气全部进入主换热器15中，经与从换热器24流出的低温低压废氮(流量为651.6t/h，温度-177.3℃，压力为0.128MPa)、来自液氧泵28的高压液氧(流量为218.5t/h，温度-179.1℃，压力为1.884MPa)和从换热器34流出的低温循环氮气(流量为325t/h，温度-179.9℃，压力为0.465MPa)进行换热，低压和中压燥空气均被冷却至-176℃，而高压空气被冷却至露点温度-174.4℃，四股干燥空气在主换热器中换热冷却的压降约为0.012MPa。从主换热器15流出的低温低压空气(流量为142.5t/h)经换热器24进一步冷却至-182.1℃后进入低压塔26中分离，而从主换热器15流出的低温高压空气(流量为444.8t/h)则进入高压塔中分离。从主换热器15流出的两股低温中压空气中，一股流量为183t/h的直接进入中压塔16底部进行分离，而另一股则流量为119.9t/h的则先经换热器18冷却至露点温度(约-181.1℃)后进入位于低压塔内部的中压空气冷凝器19中冷凝液化。从冷凝器19流出的中压液体空气(温度约为-183.8℃)经液体空气泵20增至0.525MPa后进入换热器18中与来自主换热器15的低温中压空气换热，温度升高至-181.0℃，然后再经分流阀21分成两股，一股流量为26t/h的进入中压塔中部进行分离，而另一股流量为93.9t/h的则进入高压塔中部进行分离。
(3)空气精馏
步骤(2)中获得的一股低温中压空气和一股高压液体空气分别从塔底和塔中部进入中压塔进行氮、氧精馏分离，从中压塔塔顶获得的中压氮气(摩尔分数为99.8％，压力约为0.29MPa，流量为194.2t/h)进入位于低压塔内部的中压塔塔顶冷凝器17内与低压塔内的低温液体换热后全部液化。从中压塔塔顶冷凝器17中流出的中压液氮一部分(流量约为89.2t/h)返回中压塔作为塔顶回流液用于维持精馏工况，另一部分(流量约为105t/h)则经换热器24过冷至-190℃后进入低压塔的塔顶，用于氮、氧的精馏分离。
在步骤(2)中获得低温高压空气(流量约为444.8t/h)和一股高压液体空气(流量约为93.9t/h)分别从塔底和塔中部进入高压塔进行氮、氧精馏分离，从高压塔塔顶获得两股高压氮气(压力为0.504MPa，氮的摩尔分数均大于99.99％)，一股(流量约为278.1t/h)则在换热器35中与从节流阀34中流出的325t/h循环液氮(压力为0.465MPa，汽相分率为0.15)换热后而液化，并送入位于低压塔底部的冷凝/再沸器23，而另一股高压氮气(流量约为176.6t/h)也进入冷凝/再沸器23内与低压塔底的低温液氧换热后全部液化，而低温液氧获得热量后部分汽化成为低压塔内的上升蒸汽，用于维持精馏工况。从冷凝/再沸器23中流出的高压液氮被分成两股，一股(流量约为263.7t/h)返回高压塔作为塔顶回流液用于维持精馏工况，另一股(流量约为191t/h)则在换热器24过冷后又经分流阀25分成两部分，一部分(流量约为171t/h)进入低压塔的塔顶，用于氮、氧的精馏分离，而余下的(流量约为20t/h)则送入压力为0.2MPa的低压液氮罐27中作为液氮产品。
从中压塔和高压塔底部获得两股富氧液空(流量分别为104t/h和347.7t/h)均在换热器24中进一步过冷后进入低压塔中部进行分离，从塔顶排出的651.6t/h含氮较高的低温废氮气体(压力为0.133MPa，氮的摩尔分数约99.8％)在换热器24中回收部分冷量，温度升高至-177.3℃后进入主换热器15，而从塔底抽出的218.5t/h富氧液体(压力为0.148MPa，氧的摩尔分数为95％)则经液氧泵28增压至1.88MPa后也进入主换热器15，为步骤(2)中的空气冷却提供冷能。在主换热器15中回收冷能后，218.5t/h的高压液氧全部汽化成为高压富氧气体产品，温度约为15.5℃；低温废氮在主换热器15中被加热至15.5℃后可以用于空气净化器的再生和循环冷却水的冷却。
(4)LNG冷能利用
步骤(3)中所述的从节流阀34中流出的325t/h、0.465MPa的循环液氮在换热器35中换热后全部汽化，温度为-179.9℃，再经主换热器15回收部分冷能后，温度升高至-140℃，然后进入氮气压缩机29中增压至1.943MPa。增压后的循环氮气温度升高至-55.6℃，然后在换热器30中与来自接收站的一股10MPa、-150℃、流量为248t/h的高压LNG换热，将其冷却至-140℃后经氮气压缩机31进一步增压至8.30MPa，然后在分流阀32中分成两股，其中一股流量为157t/h的压缩循环氮气进入换热器30中与来自接收站的LNG进料换热后液化，温度降低至-148℃，然后再经主换热器15进一步过冷至-168℃，而另一股流量为168t/h的压缩循环氮气则直接进入主换热器15中换热后全部液化并过冷至-168℃，形成了两股过冷循环液氮。这两股循环液氮在混合阀33中混合为一股，再经节流阀34降压至0.465MPa后进入换热器35与来自高压塔顶的高压氮气换热，为空气的精馏分离提供冷量。
来自接收站的高压LNG经换热器30利用了一部分冷能后，温度升高至-74.4℃，仍低于其泡点温度，再将其送入换热器36中与来自混合阀39的一股流量为1141t/h、温度为22.8℃的热乙二醇水溶液(乙二醇质量分数为30％)换热。高压LNG换热后全部汽化，温度升高至2.6℃(考虑低温乙二醇水溶液在利用过程中有5％的跑冷损失)，成为一股高压天然气，可直接进入高压天然气管网。从换热器36中流出的乙二醇水溶液的温度降低至0℃左右，再经水泵37增压至0.3MPa后在分流阀38中被分成两股，其中一股(流量为970t/h)进入换热器3中用于低压空气的冷却，另一股(流量为171t/h)送入换热器8中用于空气压缩机9的进气冷却。换热后，从换热器3流出的乙二醇水溶液温度升高至25.2℃，而从换热器8流出的乙二醇水溶液温度升高至8.7℃，这两股乙二醇溶液经混合阀39混合后返回换热器36中，形成一个冷能利用循环。
整个空气分离过程中，利用248t/h的高压LNG气化释放的冷能可生产20t/h高纯液氮和218.5t/h、1.86MPa的高压富氧气体(氧的摩尔分率为95％)，氧气的提取率超过99.99％，***总功耗为53942kW(包括水泵和循环冷却水散热功耗)。液氮的功耗按照利用常规空分装置生产能耗的50％(约300kWh/t)来进行计算，则平均生产1吨1.86MPa的高压富氧气体(摩尔分数为95％)的功耗约为219.4kWh/t。而常规方法生产相同的状态的高压富氧气体的功耗约为285kWh/t，因此本专利提出的一种利用液化天然气冷能生产高压富氧气体的空气分离方法来生产富氧燃烧所需的氧气时可节约23％的电能消耗，利用1吨LNG释放的冷能可以节约用电82kWh，具有很好的节能效果。
上述实施例为本发明较佳的实施方式，但本发明的实施方式并不受上述实施例的限制，其他的任何未背离本发明的精神实质与原理下所作的改变、修饰、替代、组合、简化，均应为等效的置换方式，都包含在本发明的保护范围之内。

Claims (8)

1.一种利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于包括以下操作步骤：
(1)空气压缩和净化
空气首先进入自洁式空气吸入过滤器1，在过滤器中除去空气中所含的灰尘和其它颗粒杂质后，经空气压缩机2压缩至低压，再在换热器3中利用低温乙二醇水溶液将其冷却至2～10℃，并将空气冷却过程产生的冷凝水分离出来；从换热器3流出的低压空气经分流阀4分成两股，一股进入空气净化器11中脱除空气中的水、二氧化碳和一些碳氢化合物，变成低压干燥空气流；另一股低压空气则经空气压缩机5压缩至中压，再在换热器6中利用循环冷却水冷却至接近环境温度；从换热器6流出的中压空气经分流阀7再分成两股，其中一股中压空气进入空气净化器12中脱除空气中的水、二氧化碳和一些碳氢化合物，变成中压干燥空气流，而另一股中压空气则先在换热器8中利用低温乙二醇水溶液将其进一步冷却至2～10℃并分离出凝结水，然后进入空气压缩机9中压缩至高压，再在换热器10中利用循环冷却水冷却至接近环境温度后进入空气净化器13中脱除空气中的水、二氧化碳和一些碳氢化合物，变成高压干燥空气流；
(2)空气冷却
步骤(1)中获得的中压干燥空气经分流阀14分成两股，然后与步骤(1)中获得的低压干燥空气及高压干燥空气全部进入主换热器15中，经与从换热器24流出的低温低压废氮、来自液氧泵28的高压液氧和从换热器34流出的低温循环氮气进行换热，四股干燥空气被冷却至接近高压空气的露点温度；从主换热器15流出的低温低压空气经换热器24进一步冷却降温后进入低压塔26中分离，而从主换热器15流出的低温高压空气则进入高压塔中分离；从主换热器15流出的两股低温中压空气中，一股直接进入中压塔16进行分离，而另一股则先经换热器18进一步冷却到露点温度后进入位于低压塔内部的中压空气冷凝器19中冷凝液化；从冷凝器19流出的中压液体空气经液体空气泵20增至高压后进入换热器18中与来自主换热器15的低温中压空气换热，然后再经分流阀21分成两股后分别进入中压塔和高压塔内进行分离；
(3)空气精馏
步骤(2)中获得的一股低温中压空气和一股高压液体空气分别从塔底和塔中部进入中压塔进行氮、氧精馏分离，从中压塔塔顶获得的中压氮气进入位于低压塔内部的中压塔塔顶冷凝器17内与低压塔内的低温液体换热后全部液化；从中压塔塔顶冷凝器17中流出的中压液氮一部分返回中压塔作为塔顶回流液用于维持精馏工况，另一部分则经换热器24过冷后进入低压塔的塔顶，用于氮、氧的精馏分离；
在步骤(2)中获得低温高压空气和一股高压液体空气分别从塔底和塔中部进入高压塔进行氮、氧精馏分离，从高压塔塔顶获得两股高压氮气，一股则在换热器35中与从节流阀34中流出的循环液氮换热后而液化，并送入位于低压塔底部的冷凝/再沸器23，而另一股高压氮气也进入冷凝/再沸器23内与低压塔底的低温液氧换热后全部液化，而低温液氧获得热量后部分汽化成为低压塔内的上升蒸汽，用于维持精馏工况；从冷凝/再沸器23中流出的高压液氮被分成两股，一股返回高压塔作为塔顶回流液用于维持精馏工况，另一股则在换热器24过冷后又经分流阀25分成两部分，一部分进入低压塔的塔顶，用于氮、氧的精馏分离，而余下的则送入低压液氮罐27中作为液氮产品；
从中压塔和高压塔底部获得两股富氧液空均在换热器24中进一步过冷后进入低压塔中部进行分离，从塔顶排出的含氮较高的低温废氮气体在换热器24中回收部分冷量后进入主换热器15，而从塔底抽出的富氧液体则经液氧泵28增压后也进入主换热器15，为步骤(2)中的空气冷却提供冷能；在主换热器15中回收冷能后，高压液氧全部汽化成为高压富氧气体产品；低温废氮在主换热器15中被加热至接近常温后可以用于空气净化器的再生和循环冷却水的冷却；
(4)LNG冷能利用
步骤(3)中所述的从节流阀34中流出的循环液氮在换热器35中换热后全部汽化，再经主换热器15回收部分冷能后进入氮气压缩机29中增压；增压后的循环氮气在换热器30中与来自接收站的高压LNG换热后经氮气压缩机31进一步增压，然后在分流阀32中分成两股，其中一股进入换热器30中与来自接收站的LNG进料换热后液化，然后再经主换热器15进一步过冷，而另一股则直接进入主换热器15中换热后全部液化并过冷，形成了两股过冷循环液氮；这两股循环液氮在混合阀33中混合为一股，再经节流阀34降压后进入换热器35与来自高压塔顶的高压氮气换热，为空气的精馏分离提供冷量；
来自接收站的高压LNG经换热器30利用了一部分冷能后，温度仍低于其泡点温度，再将其送入换热器36中与来自混合阀39的一股热乙二醇水溶液换热；高压LNG换热后全部汽化，温度升高至0℃以上，成为一股高压天然气，可直接进入高压天然气管网；从换热器36中流出的乙二醇水溶液的温度降低至0℃左右，再经水泵37增压后在分流阀38中被分成两股，其中一股进入换热器3中用于低压空气的冷却，另一股送入换热器8中用于空气压缩机9的进气冷却；换热后，从换热器3和8流出的两股乙二醇水溶液经混合阀39混合后返回换热器36中，形成一个冷能利用循环。
2.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(3)中所述的低压塔塔顶的操作压力在0.12～0.15MPa，中压塔塔顶的操作压力在0.25～0.35MPa，高压塔塔顶的操作压力在0.5MPa。
3.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(3)中所述的来自分流阀25的过冷高压液氮从塔顶进入低压塔，来自换热器24的过冷中压液氮从塔顶下2～5块理论板的位置处进入低压塔，从换热器24流出的中压富氧液空和高压富氧液空自低压塔中部进入低压塔，其中高压富氧液空的进料口比中压富氧液空的进料口高5～10块理论板，而从换热器24流出的低压空气在高压富氧液空和中压富氧液空的进料口之间进入低压塔。
4.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(3)中所述的中压塔塔顶冷凝器设置在低压塔内，位于中压富氧液空的进料口下2～5块理论板处，中压空气冷凝器也设置在低压塔内，位于中压塔塔顶冷凝器与塔底之间。
5.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(3)中所述的从主换热器排出的高压富氧气体产品，其中氧的摩尔分率低于97％，压力在1.0MPa以上。
6.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(4)中所述的来自接收站的高压液化天然气压力为0.5～15MPa。
7.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(4)中所述的氮气压缩机29和31的进气温度控制在-120～-150℃，所述的氮气压缩机29和31的压缩比相等，氮气压缩机31的出口压力大于5.5MPa。
8.根据权利要求1所述的利用液化天然气冷能生产高压富氧气体的空气分离方法，其特征在于：步骤(4)中所述的节流阀34的出口压力较高压塔塔顶操作压力低0.04～0.10MPa。
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