CN117146527A - 液化天然气闪蒸气低温精馏提氦装置及方法 - Google Patents

液化天然气闪蒸气低温精馏提氦装置及方法 Download PDF

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CN117146527A
CN117146527A CN202210562356.9A CN202210562356A CN117146527A CN 117146527 A CN117146527 A CN 117146527A CN 202210562356 A CN202210562356 A CN 202210562356A CN 117146527 A CN117146527 A CN 117146527A
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heat exchanger
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高婷
张菲
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Nisa Shanghai Energy Technology Co ltd
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Abstract

本发明公开了一种液化天然气闪蒸气低温精馏提氦装置，该装置主要包括预冷换热器、液化换热器、深冷换热器、脱甲烷精馏塔和脱氮精馏塔，两精馏塔内部分别设置有再沸器和冷凝器。本发明还公开了应用上述装置从天然气闪蒸气中提取氦气的方法。本发明通过两塔超低温精馏并合理匹配利用冷、热量，实现了以较低的能耗从液化天然气闪蒸气中提取高纯度的氦气，不仅氦气回收率可高达99.9％，而且氦产品气的含氮量可降至1％，大大减少了后续催化脱氢和吸附脱氮制精氦的负荷，为后续氦精制节省了成本和难度。

Description

液化天然气闪蒸气低温精馏提氦装置及方法
技术领域
本发明涉及液化天然气领域，特别是涉及从液化天然气闪蒸气中提取氦气的装置及方法。
背景技术
氦气是一种无色、无味的稀有气体，也是已知沸点最低的气体，具有不易液化、稳定性好、扩散性强、溶解度低等性质。氦气用途广泛，可用于医疗科研、航天军工等领域，是一种不可替代、关系国家安全和高新技术产业发展的重要稀缺战略资源。
含氦天然气主要包括来自天然气田的气层、油气田的气层、油气层中的天然气，以及油层中的天然气等。我国是贫氦国家，天然气中氦的含量很低(约0.04％～0.1％)，直接提取氦的成本极高，大部分的氦气都依赖于进口。因此，从天然气中提取氦气，既可以保障我国的氦资源，也有利于提升天然气的综合利用效率和液化天然气工厂的经济效益。
在液化天然气(LNG)的生产过程中，末级节流阀在节流过程中会产生大量闪蒸气(BOG)。闪蒸气主要包含自LNG冷箱进入LNG储罐、因节流减压而产生的气体，以及LNG储罐热漏而引起气化的部分气体，泛指LNG储罐顶部排出的气相。闪蒸气中含有氦气、氢气、氮气及甲烷。常压下，氦气、氢气、氮气及甲烷的液化温度分别为-269℃、-253℃、-196℃和-162℃；在储罐压力下，氦气、氢气及部分氮气会从LNG中挥发出来，此时相比原料天然气，由于烃类等气体被液化，氦气等不凝性气体可以得到一次富集，因此从BOG中提氦难度和成本相对低。此外，氦气的脱除对于液化天然气工艺也是十分有利的，可以大幅降低LNG大型储罐中LNG因密度差而引起的液体翻滚汽化现象，避免BOG尾气的大量排放和LNG大型储罐的安全事故。
目前，从天然气中提取氦气通常采用冷凝法。冷凝法通常采用深冷分离的工艺或深冷分离加变压吸附的工艺。由于氢气与氦气的常压沸点分别为-252.6℃与-268.9℃，采用深冷分离的办法需要将工艺介质冷却到极低的温度，维持冷箱的冷量平衡需要循环制冷系统，能耗代价十分巨大。尤其是中小型工厂中，液化天然气的氦气属于不凝气，当部分BOG循环至LNG工厂天然气原料入口时，会导致不凝气增加聚集，换热效率受到影响，天然气液化量降低，LNG工厂的产能受到部分影响，LNG回收率降低，BOG气量增大导致BOG压缩机操作波动增大等一系列问题。例如，公开号为CN111692837A的中国发明专利申请披露了“一种利用LNG生产装置联产氦气的系统”，该系统对一部分BOG进行提氦，对另一部分BOG进行氦气富集，来自LNG生产装置的原料气依次经压缩、脱氢、脱水干燥、降温冷凝及低温吸附分离后，得到氦气。这种在低温段通过部分冷凝分离氦中的氮的方法，其分离效果有限，氦气回收率和纯度较低；此外，该系统的低温段制冷由负压液氮提供，设备和运行成本较高。
目前也有采用精馏方法从闪蒸气中提取氦气的。例如，公开号为CN107228526A的中国发明专利申请披露了“一种LNG闪蒸气的提氦、脱氮和再液化装置”，该装置在较高的温度下(-190℃左右)进行精馏分离，先脱氮，再脱甲烷，最后得到的粗氦产品中含有较多的氮(20％以上)和氢，这会增加后续催化脱氢及吸附脱氮的负荷和难度。
发明内容
本发明要解决的技术问题之一是提供一种液化天然气闪蒸气低温精馏提氦装置，它结构简单，能耗低，能获得较高纯度的氦气产品。
为解决上述技术问题，本发明的液化天然气闪蒸气低温精馏提氦装置，主要包括有预冷换热器、液化换热器、深冷换热器、脱甲烷精馏塔和脱氮精馏塔；其中：
所述预冷换热器至少包含A、B、C三条通道，所述液化换热器至少包含F、G、H三条通道，所述深冷换热器至少包含L、M两条通道；
所述预冷换热器的A通道的入口连接原料闪蒸气的进气管线；
所述脱甲烷精馏塔内设置有再沸器和冷凝器；所述脱甲烷精馏塔的再沸器的入口连接所述A通道的出口，出口连接所述液化换热器的F通道的入口；所述F通道的出口连接所述脱甲烷精馏塔的入口；所述脱甲烷精馏塔的底部液相出口连接所述脱甲烷精馏塔的冷凝器的入口；所述脱甲烷精馏塔的冷凝器的出口连接所述液化换热器的G通道的入口，所述G通道的出口连接预冷换热器的B通道的入口，所述B通道的出口连接甲烷成分可达95％的天然气的排气管线；所述脱甲烷精馏塔的顶部气相出口连接所述深冷换热器的L通道的入口，所述L通道的出口连接所述脱氮精馏塔的入口；
所述脱氮精馏塔内设置有再沸器和冷凝器；所述脱氮精馏塔的底部液相出口连接所述深冷换热器的M通道的入口，所述M通道的出口连接所述液化换热器的H通道的入口，所述H通道的出口连接所述预冷换热器的C通道的入口，所述C通道的出口连接尾气的排气管线。
进一步的，可以在所述原料闪蒸气的进气管线设置压缩机。
进一步的，可以在所述脱甲烷精馏塔和脱氮精馏塔的底部液相出口管路上分别设置节流阀。
进一步的，所述预冷换热器还可以包含D通道，所述液化换热器还可以包含I通道，所述深冷换热器还可以包含N通道；所述脱氮精馏塔的再沸器的出口连接所述脱氮精馏塔的冷凝器的入口，所述脱氮精馏塔的再沸器的出口与所述脱氮精馏塔的冷凝器的入口之间的管路上设置有膨胀机；所述脱氮精馏塔的冷凝器的出口连接所述深冷换热器的N通道的入口；所述N通道的出口连接所述液化换热器的I通道的入口；所述I通道的出口连接所述预冷换热器的D通道的入口，所述I通道的出口与所述D通道的入口之间的管路上设置有压缩机；所述D通道的出口连接所述脱氮精馏塔的再沸器的入口。
进一步的，所述预冷换热器还可以包含E通道，所述液化换热器还可以包含J、K两个通道，所述深冷换热器还可以包含O、P两个通道；所述脱氮精馏塔的顶部气相出口连接所述深冷换热器的O通道的入口；所述O通道的出口连接所述液化换热器的J通道的入口；所述J通道的出口连接所述深冷换热器的P通道的入口，所述J通道的出口与所述P通道的入口之间的管路上设置有膨胀机；所述P通道的出口连接所述液化换热器的K通道的入口；所述K通道的出口连接所述预冷换热器的E通道的入口；所述E通道的出口连接氦产品气排出管线。
本发明要解决的技术问题之二是提供一种液化天然气闪蒸气低温精馏提氦方法，该方法流程简单，氦气回收率高。
为解决上述技术问题，本发明的液化天然气闪蒸气低温精馏提氦方法，先通过低温精馏脱除闪蒸气中的甲烷，再通过低温精馏脱除闪蒸气中的氮气，获得仅含氢(如有)和1％左右氮的氦气产品。
精馏脱甲烷的温度优选为-160℃～-150℃；精馏脱氮的温度不低于-210℃，优选为-210℃～-200℃。
优选的，精馏脱甲烷所需的冷量可以由高压(15～30bar)液化甲烷节流制冷后产生的潜热提供。
优选的，精馏获得的氦气可以依次经换热、膨胀制冷后，再次换热至常温常压，在充分利用其冷量后，排出获得氦气产品。
优选的，精馏脱氮所需的冷量可以由气体制冷剂膨胀循环制冷提供。所述气体制冷剂优选为纯氦气。
本发明通过两塔超低温精馏，先脱甲烷，再脱氮气，同时合理匹配利用冷、热量，实现了以较低的能耗从液化天然气闪蒸气中提取高纯度的氦气。与现有提氦技术相比，本发明的液化天然气闪蒸气低温精馏提氦装置和提氦方法，具有以下优点和有益效果：
1.通过外部氦气膨胀制冷提供低温段精馏塔(脱氮精馏塔)冷凝器的冷量，可以在-210℃～-200℃的温度下尽可能地分离出氮和部分氢，从而保证了氦气的高回收率和粗氦产品的低含氮量(氦气回收率可高达99.9％，粗氦的含氮量可降至1％左右)，大大减少了后续催化脱氢和吸附脱氮制精氦的负荷，为后续氦精制节省了成本和难度；
2.本发明在回收氦气的同时，还回收甲烷含量95％的天然气，甲烷回收率可达99％；另外，脱甲烷精馏塔冷凝器的冷量由该塔塔底高压液化甲烷节流制冷后产生的低温度潜热提供，大大节省了外部制冷能耗，降低了总体能耗(本发明的提氦装置的总能耗约为4kWh/Nm3氦)，简化了提氦流程。
附图说明
图1是本发明实施例的液化天然气闪蒸气低温精馏提氦装置和流程示意图。
图中附图标记说明如下：
1、14：压缩机
2：预冷换热器
3：液化换热器
4：脱甲烷精馏塔
5、9：再沸器
6、10：冷凝器
7：深冷换热器
8：脱氮精馏塔
11、12：节流阀
13、15：膨胀机
16～46：管线
A～P：通道
具体实施方式
为对本发明的技术内容、特点与功效有更具体的了解，现结合附图及具体实施例，对本发明的技术方案做进一步详细的说明。
如图1所示，本实施例的液化天然气闪蒸气低温精馏提氦装置，主要包括3个换热器、2个精馏塔、2台压缩机、2台膨胀机以及2个JT节流阀。其中：
预冷换热器2至少包含A～E五个通道。液化换热器3至少包含F～K六个通道。深冷换热器7至少包含L～P五个通道。
预冷换热器2的通道A设置在预冷换热器2的底部，通道A的入口连接管线17。管线17连接压缩机1的出口，压缩机1的入口连接原料气(即天然气闪蒸气)的进气管线16，压缩机1用于压缩原料气。
脱甲烷精馏塔4用于低温精馏脱除闪蒸气中的甲烷。脱甲烷精馏塔4的塔底内部设置有再沸器5，塔顶内部设置有冷凝器6。再沸器5的入口通过管线18连接预冷换热器2的通道A的出口；再沸器5的出口通过管线19连接液化换热器3底部通道F的入口。液化换热器3的通道F的出口通过管线20连接脱甲烷精馏塔4的中部入口。脱甲烷精馏塔4的底部液相出口通过管线21连接节流阀11的入口。节流阀11的出口通过管线22连接冷凝器6的入口。冷凝器6的出口通过管线23连接液化换热器3的通道G的入口，液化换热器3的通道G的出口通过管线24连接预冷换热器2的通道B的入口。预冷换热器2的通道B的出口连接用于排放以甲烷为主要成分的含氮天然气的管线25。脱甲烷精馏塔4顶部的气相出口通过管线26连接深冷换热器7底部通道L的入口。
深冷换热器7的底部通道L的出口通过管线27连接脱氮精馏塔8的中部入口。
脱氮精馏塔8用于低温精馏脱除闪蒸气中的氮气。脱氮精馏塔8的塔底内部设置有再沸器9，塔顶内部设置有冷凝器10。再沸器9的入口通过管线41连接预冷换热器2的通道D的出口。再沸器9的出口通过管线42连接膨胀机15的入口。膨胀机15的出口通过管线43连接冷凝器10的入口。冷凝器10的出口通过管线44连接深冷换热器7的通道N的入口。脱氮精馏塔8的底部液相出口通过管线28连接节流阀12的入口，节流阀12的出口通过管线29连接深冷换热器7的通道M的入口。脱氮精馏塔8的顶部气相出口通过管线33连接深冷换热器7的通道O的入口。
深冷换热器7的通道M、通道N、通道O、通道P的出口分别通过管线30、管线45、管线34、管线37连接液化换热器3的通道H、通道I、通道J、通道K的入口。液化换热器3的通道H、通道K的出口分别通过管线31、管线38连接预冷换热器2的通道C、通道E的入口。预冷换热器2的通道C、通道E分别连接用于排放尾气的管线32、用于排出粗氦产品的管线39。液化换热器3的通道I的出口通过管线46连接压缩机14的入口。压缩机14的出口通过管线40连接预冷换热器2的通道D的入口。液化换热器3的通道J的出口通过管线35连接膨胀机13的入口。膨胀机13的出口通过管线36连接深冷换热器7顶部的通道P的入口。
上述预冷换热器2、液化换热器3、深冷换热器7为绕管式换热器，在其他实施例中，也可以选用其他类型的换热器，例如板翅式换热器。
上述脱甲烷精馏塔4、脱氮精馏塔8可以选用填料塔或板式塔。脱甲烷精馏塔4中的再沸器5和冷凝器6，以及脱氮精馏塔8中的再沸器9和冷凝器10，可以组装在精馏塔上，也可以与精馏塔分开设置。
以下对应用上述闪蒸气低温精馏提氦装置从液化天然气闪蒸气中提取氦气的方法进行详细的说明。
原料气即闪蒸气(BOG)经压缩机1压缩至20～30barg并冷却至常温后，先后经预冷换热器2、脱甲烷精馏塔4塔底的再沸器5和液化换热器3冷却至-110～-130℃，成为气液两相，然后由管线20进入脱甲烷精馏塔4，在脱甲烷精馏塔4内经低温精馏(精馏温度-160℃～-150℃)，在塔底得到甲烷含量95％左右的含氮天然气，由管线21离开脱甲烷精馏塔4，通过节流阀11节流降压到常压后获得接近甲烷沸点-160℃～-155℃的低温，依次为脱甲烷精馏塔4顶部的冷凝器6、液化换热器3和预冷换热器2提供冷量，复温至常温，由管线25排出，后续可返回LNG装置入口进行回收或作为全装置的燃料气进行平衡。
脱甲烷精馏塔4塔顶气体由管线26进入深冷换热器7，进一步降温至-190℃左右，成为气液两相(氦气、液氮和氢气)进入脱氮精馏塔8，在脱氮精馏塔8内经低温精馏(精馏温度为-205℃～-210℃)，液相(含约10％甲烷的液氮)由管线28离开脱氮精馏塔8，经节流阀12节流降压后获得-190℃左右的低温，依次为深冷换热器7、液化换热器3和预冷换热器2提供冷量，复温至常温，由32排出，后续可作为驰放气燃烧排放或是作为天然气液化装置的火炬吹扫气以节约整个装置的燃料气消耗。
脱氮精馏塔8的塔顶气体为粗氦产品，控制脱氮精馏塔8的冷凝器10的温度不低于-210℃(本实施例为-205℃～-210℃)，可以使粗氦中的氮气冷凝为液氮，同时防止氮结冰，如此可将氦气中的氮气脱除到1％左右。脱氮精馏塔8塔顶的大部分粗氦经管线33离开脱氮精馏塔8，依次为深冷换热器7和液化换热器3提供冷量，复温至-90℃～-80℃，然后经膨胀机13膨胀至较低的压力，再次达到-190℃～-180℃的低温，重新返回深冷换热器7、液化换热器3和预冷换热器2充分利用其冷量，最终成为常温常压的粗氦气产品(成分为：氦气79％，氢气20％，氮气1％)从管线39排出，后续可进一步催化脱氢、吸附脱氧氮制取高纯氦。
脱氮精馏塔8的冷凝器10提供的-210℃～-200℃左右的低温(具体冷凝温度由原料气组成及想获得的氦气纯度决定)所需的冷量可由制冷剂——来自于装置外部的闭式氦气膨胀循环制冷提供。来自管线46的氦气经压缩机14压缩至中间压力(15～25公斤)并冷却至常温，再依次经预冷换热器2和脱氮精馏塔8的再沸器9冷却至-150℃～-140℃(氦气制冷剂为脱氮精馏塔8的再沸器9提供热量，使其在膨胀前达到约-150℃～-130℃的较低温度，从而可以提供更低的制冷温度)，由管线42进入膨胀机15膨胀至接近常压，达到-210℃以下的低温，依次为脱氮精馏塔8的冷凝器10、深冷换热器7、液化换热器3提供冷量，最终在-80～-70℃的温度下低温压缩(制冷剂在较低温度下压缩，可节省压缩机能耗)。
上述实施例仅为本发明的可行或较佳实施例而已，是用来说明本发明的，并非用以限制本发明申请专利的范围，因此，凡依本发明申请专利范围所作的均等变化与修饰，均应属于本发明专利涵盖的范围。

Claims (10)

1.液化天然气闪蒸气低温精馏提氦装置，其特征在于，包括有预冷换热器、液化换热器、深冷换热器、脱甲烷精馏塔和脱氮精馏塔；其中：
所述预冷换热器至少包含A、B、C三条通道，所述液化换热器至少包含F、G、H三条通道，所述深冷换热器至少包含L、M两条通道；
所述预冷换热器的A通道的入口连接原料闪蒸气的进气管线；
所述脱甲烷精馏塔内设置有再沸器和冷凝器；所述脱甲烷精馏塔的再沸器的入口连接所述A通道的出口，出口连接所述液化换热器的F通道的入口；所述F通道的出口连接所述脱甲烷精馏塔的入口；所述脱甲烷精馏塔的底部液相出口连接所述脱甲烷精馏塔的冷凝器的入口；所述脱甲烷精馏塔的冷凝器的出口连接所述液化换热器的G通道的入口，所述G通道的出口连接预冷换热器的B通道的入口，所述B通道的出口连接天然气的排气管线；所述脱甲烷精馏塔的顶部气相出口连接所述深冷换热器的L通道的入口，所述L通道的出口连接所述脱氮精馏塔的入口；
所述脱氮精馏塔内设置有再沸器和冷凝器；所述脱氮精馏塔的底部液相出口连接所述深冷换热器的M通道的入口，所述M通道的出口连接所述液化换热器的H通道的入口，所述H通道的出口连接所述预冷换热器的C通道的入口，所述C通道的出口连接尾气的排气管线。
2.根据权利要求1所述的装置，其特征在于，所述原料闪蒸气的进气管线上设置有压缩机。
3.根据权利要求1所述的装置，其特征在于，所述脱甲烷精馏塔和脱氮精馏塔的底部液相出口管路上分别设置有节流阀。
4.根据权利要求1所述的装置，其特征在于，所述预冷换热器还包含有D通道，所述液化换热器还包含有I通道，所述深冷换热器还包含有N通道；所述脱氮精馏塔的再沸器的出口连接所述脱氮精馏塔的冷凝器的入口，所述脱氮精馏塔的再沸器的出口与所述脱氮精馏塔的冷凝器的入口之间的管路上设置有膨胀机；所述脱氮精馏塔的冷凝器的出口连接所述深冷换热器的N通道的入口；所述N通道的出口连接所述液化换热器的I通道的入口；所述I通道的出口连接所述预冷换热器的D通道的入口，所述I通道的出口与所述D通道的入口之间的管路上设置有压缩机；所述D通道的出口连接所述脱氮精馏塔的再沸器的入口。
5.根据权利要求1所述的装置，其特征在于，所述预冷换热器还包含有E通道，所述液化换热器还包含有J、K两个通道，所述深冷换热器还包含有O、P两个通道；所述脱氮精馏塔的顶部气相出口连接所述深冷换热器的O通道的入口；所述O通道的出口连接所述液化换热器的J通道的入口；所述J通道的出口连接所述深冷换热器的P通道的入口，所述J通道的出口与所述P通道的入口之间的管路上设置有膨胀机；所述P通道的出口连接所述液化换热器的K通道的入口；所述K通道的出口连接所述预冷换热器的E通道的入口；所述E通道的出口连接氦产品气排出管线。
6.液化天然气闪蒸气低温精馏提氦方法，其特征在于，先通过低温精馏脱除闪蒸气中的甲烷，再通过低温精馏脱除闪蒸气中的氮气，获得氦气产品。
7.根据权利要求6所述的方法，其特征在于，精馏脱甲烷所需的冷量由15～30bar高压液化甲烷节流制冷后产生的潜热提供。
8.根据权利要求6所述的方法，其特征在于，精馏获得的氦气产品依次经换热、膨胀制冷后，再次换热至常温常压，排出获得氦气产品。
9.根据权利要求6所述的方法，其特征在于，精馏脱氮所需的冷量由气体制冷剂膨胀循环制冷提供。
10.根据权利要求9所述的方法，其特征在于，精馏脱甲烷的温度为-160℃～-150℃，精馏脱氮的温度为-210℃～-200℃。
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