CN108731380B - 一种带吸收塔适用于富气的乙烷回收方法 - Google Patents

一种带吸收塔适用于富气的乙烷回收方法 Download PDF

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CN108731380B
CN108731380B CN201810596552.1A CN201810596552A CN108731380B CN 108731380 B CN108731380 B CN 108731380B CN 201810596552 A CN201810596552 A CN 201810596552A CN 108731380 B CN108731380 B CN 108731380B
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蒋洪
张世坚
朱聪
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Southwest Petroleum University
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Abstract

本发明公开一种带吸收塔适用于富气的乙烷回收方法，其原料气经过第一冷箱冷却后进入分离器进行预分离；分离器分离的气相进入第二冷箱中进一步冷却后进入低温分离器；低温分离器分离的气相全部进入透平膨胀机的膨胀端进行膨胀制冷后进入脱甲烷塔中上部，吸收塔塔底部分凝液在第一冷箱中复热后大量气化，之后进入吸收塔底部，另一部分凝液直接接入脱甲烷塔中部；吸收塔塔顶气相出料深冷后再节流降温进入脱甲烷塔上部；脱甲烷塔塔顶气相经过换热升温、增压后，最后经空冷器冷却后外输；脱甲烷塔底的凝液产品进入后续的脱乙烷塔等分馏处理单元进行处理。本发明中富集有更多甲烷的塔顶进料可使脱甲烷塔上部的吸收制冷效果更佳，提高乙烷的回收率。

Description

一种带吸收塔适用于富气的乙烷回收方法
技术领域
本发明涉及天然气的加工工艺技术领域，具体为一种带吸收塔适用于富气的乙烷回收方法。
背景技术
随着国内油气田逐步意识到乙烷产品带来的巨大经济价值，对高效乙烷回收流程的研究与开发变得尤为重要。目前最为典型的乙烷回收流程为部分干气再循环(RSV)工艺，当对较富天然气进行乙烷回收时通常需要制冷剂辅助制冷以提高乙烷回收率。适用于富气乙烷回收的部分干气再循环工艺如图2所示，其流程特征有，脱水后原料气进入冷箱预冷后进入低温分离器。分离液烃节流后进入脱甲烷塔中部，分离气相大部分通过透平膨胀机膨胀端膨胀制冷后进入脱甲烷塔中上部，少部分低温分离器分离气相经过冷箱和节流阀深冷后进入脱甲烷塔上部。脱甲烷塔塔顶外输气为冷箱和提供冷量后进入透平膨胀机增压端和外输压缩机增压再经空冷器冷却后外输。少部分外输干气(5％～15％)经冷箱和冷却后作为脱甲烷塔顶部回流进入脱甲烷塔。脱甲烷塔中下部侧线抽出一股物流对原料气进行预冷，增压后的高温制冷剂作为脱甲烷塔的重沸器为塔底抽出物流加热。脱甲烷塔的塔底凝液产品进入后续的脱乙烷塔等分馏处理单元。
此工艺具有高乙烷回收率的特点，在国外得到广泛运用，目前国内正在筹划的大型乙烷回收装置均采用的部分干气再循环工艺，但主要针对较贫气质。当针对较富气质时，能耗会大幅上升，而回收率会下降。
在针对较富气质进行乙烷回收过程中，部分干气再循环工艺采用一级冷却，原料气在冷箱中预冷后直接进入低温分离器，大量甲烷在低温分离器中冷凝后进入脱甲烷塔中部，造成脱甲烷塔分离负荷增加。一级分离使得制冷剂需要对所有原料气进行冷却，制冷剂循环量大，制冷压缩机能耗高。一级分离也会造成低温分离器中的分离气相减少，同时需要一部分低温分离器分离气相通过冷箱深冷后为脱甲烷塔上部吸收段提供物料，以提高回收率，两种原因都导致透平膨胀的气相量减少，透平膨胀功减小，外输压缩功增大。
为了克服部分干气再循环工艺流程的不足，降低其能耗和提升其回收率，本发明针对较富天然气进行乙烷回收，开发了一种带吸收塔适用于富气的乙烷回收高效流程。
发明内容
本发明所要解决的技术问题是提供一种可以提高乙烷回收率的带吸收塔适用于富气的乙烷回收方法。
本发明解决上述技术问题所提供的技术方案是：一种带吸收塔适用于富气乙烷回收的方法，其特征在于原料气经过第一冷箱冷却后进入分离器进行预分离；分离器分离的气相进入第二冷箱中进一步冷却后进入低温分离器；低温分离器分离的气相全部进入透平膨胀机的膨胀端进行膨胀制冷后进入脱甲烷塔中上部；预分离器分离液相节流后进入脱甲烷塔下部。低温分离器分离液相分为两部分，一部分与吸收塔等气相出料相混合以提高流程的抗CO2冻堵能力，另一部分进入吸收塔顶部，吸收塔塔底部分凝液在第一冷箱中复热后大量气化，之后进入吸收塔底部，吸收塔另一部分凝液直接接入脱甲烷塔中部；吸收塔塔顶气相出料在第三冷箱中深冷后再节流降温进入脱甲烷塔上部；脱甲烷塔塔顶气相依次经过第三冷箱、第二冷箱、第一冷箱换热升温后，再经过透平膨胀机增压端、外输压缩机中增压后，最后经空冷器冷却后外输；脱甲烷塔底的凝液产品进入后续的脱乙烷塔等分馏处理单元进行处理。
进一步的技术方案是，所述部分外输气再经第一冷箱、第二冷箱、第三冷箱冷却并节流后进入脱甲烷塔顶部。
进一步的技术方案是，所述第一冷箱、第二冷箱、第三冷箱均采用多股板翅式换热器，将两股热流与多股冷流、两股热流与两股冷流、两股热流与一股冷流分别集成于第一冷箱、第二冷箱、第三冷箱。
进一步的技术方案是，所述第一冷箱的两股热流分别为原料气、部分外输气，多股冷流分别为经第三冷箱和第二冷箱换热后的脱甲烷塔顶部气相出料、一股脱甲烷塔底侧线抽出的物流、吸收塔塔底的部分凝液。
进一步的技术方案是，所述第二冷箱的两股热流分别为经第一冷箱换热降温后的原料气、经第一冷箱换热降温后的部分外输气，两股冷流分别为经第三冷箱换热后的脱甲烷塔顶气相出料、一股为外部制冷剂提供的冷流。
进一步的技术方案是，所述第三冷箱的两股热流分别为经第一冷箱和第二冷箱换热降温后的部分外输气、吸收塔塔顶的气相，一股冷流为脱甲烷塔顶部出来的气相。
进一步的技术方案是，所述脱甲烷塔底侧设有换热器，脱甲烷塔塔底物流在换热器中对压缩后的高温制冷剂进行降温。
本发明的有益效果是：本发明中富集有更多甲烷的进料可使脱甲烷塔上部的吸收制冷效果更佳，提高流程的乙烷回收率；原料气采用多级分离，有效分离重烃，降低换热器换热负荷，降低制冷剂循环量；相比常规乙烷回收流程，该流程分离器分离气相全部进入透平膨胀机，增大了透平膨胀机透平膨胀功，可有效降低外输压缩机功耗。
附图说明
图1是本发明的工艺流程图；
图2是现有典型外输气回流乙烷回收工艺流程图。
图中所示：E11-第一冷箱、V11-分离器、E12-第二冷箱、V12-低温分离器、K11-透平膨胀机膨胀端、E13-第三冷箱、T11-脱甲烷塔、E14-换热器、T12-吸收塔、A11-空冷器、K12-透平膨胀机增压端、K13-外输压缩机。
具体实施方式
下面结合实施例和附图对本发明做更进一步的说明。
如图1所示，本发明的一种带吸收塔适用于富气的乙烷回收方法，原料气经过第一冷箱E11冷却后进入分离器V11进行预分离；分离器V11分离的气相进入第二冷箱E12中进一步冷却后进入低温分离器V12；低温分离器V12分离的气相全部进入透平膨胀机K11的膨胀端进行膨胀制冷后进入脱甲烷塔T11中上部；分离器V11分离液相节流后进入脱甲烷塔T11下部。低温分离器V12分离液相分为两部分，一部分与吸收塔等气相出料相混合以提高流程的抗CO2冻堵能力，另一部分进入吸收塔T12顶部，吸收塔T12塔底部分凝液在第一冷箱E11中复热后大量气化，之后进入吸收塔T12底部，另一部分凝液直接接入脱甲烷塔T11中部；吸收塔T12塔顶气相出料在第三冷箱E13中深冷后再节流降温进入脱甲烷塔T11上部；脱甲烷塔T11塔顶气相依次经过第三冷箱E13、第二冷箱E12、第一冷箱E11换热升温后，再经过透平膨胀机增压端K12、外输压缩机K13中增压后，最后经空冷器A11冷却后外输；脱甲烷塔T11底的凝液产品进入后续的脱乙烷塔等分馏处理单元进行处理。
本方法中，所述第一冷箱E11、第二冷箱E12、第三冷箱E13均采用多股板翅式换热器，将两股热流与多股冷流、两股热流与两股冷流、两股热流与一股冷流分别集成于第一冷箱E11、第二冷箱E12、第三冷箱E13。
所述第一冷箱E11的两股热流分别为原料气、部分外输气，多股冷流分别为经第三冷箱E13和第二冷箱E12换热后的脱甲烷塔T11顶部气相出料、一股脱甲烷塔T11底侧线抽出的物流、吸收塔T12塔底的部分凝液。所述第二冷箱E12的两股热流分别为经第一冷箱E11换热降温后的原料气、经第一冷箱E11换热降温后的部分外输气，两股冷流分别为经第三冷箱E13换热后的脱甲烷塔T11顶部出来的气相、一股为外部制冷剂提供的冷流。所述第二冷箱E12的两股热流分别为经第一冷箱E11和第二冷箱E12换热降温后的部分外输气、吸收塔T12塔顶气相，一股冷流为脱甲烷塔T11顶部气相出料。所述脱甲烷塔T11底侧设有换热器E14，脱甲烷塔T11塔底物流在换热器E14中对压缩后的高温制冷剂进行降温。
优选的技术方案是，所述原料气采用多级分离，有效分离重烃，降低换热器换热负荷，降低制冷剂循环量；相比常规乙烷回收流程，该流程分离器分离气相全部进入透平膨胀机，增大了透平膨胀机透平膨胀功，可有效降低外输压缩机功耗。在脱甲烷塔T11前增加一座吸收塔T12，对分离器分离的液烃中的甲烷与乙烷等重烃进行强化分离，有效降低脱甲烷塔的分离负荷。脱甲烷塔T11具有两股侧线抽出，热集成度高，特别是脱甲烷塔T11塔底的侧线抽出与压缩后的高温制冷剂换热，可有效降低制冷剂循环的冷却公用工程负荷。
实施例1
如图1所示，4原料气气质组分和工况如下：
原料气处理规模：500×104m3/d
原料气压力：5.5MPa
原料气温度：38℃
干气外输压力：5.5MPa
原料气组成见表1
表1原料气组成
组成 N<sub>2</sub> CO<sub>2</sub> C<sub>1</sub> C<sub>2</sub> C<sub>3</sub> iC<sub>4</sub> nC<sub>4</sub> iC<sub>5</sub> nC<sub>5</sub> C<sub>6</sub>
mol％ 1.24 1.04 72.77 14.29 7.55 0.73 1.84 0.23 0.21 0.1
如图1所示，本发明公开了一种带吸收塔的强化乙烷回收流程，原料气(5.5MPa，38℃)经过第一冷箱E11冷却后进入分离器V11进行预分离，分离出原料气中的部分重烃以减小第二冷箱E12中的换热负荷，分离器V11分离的气相(5.48MPa，-4.73℃)进入第二冷箱E12中进一步冷却后进入低温分离器V12，低温分离器V12分离气相(5.44MPa，-50℃)全部进入透平膨胀机膨胀端K11膨胀制冷后(2.5MPa，-79.65℃)进入脱甲烷塔T11中上部。
分离器V11分离液相节流后(2.6MPa，-18.83℃)进入脱甲烷塔T11下部。低温分离器V12分离液相分为两部分，一部分与吸收塔等气相出料相混合以提高流程的抗CO2冻堵能力，另一部分进入吸收塔T12顶部，吸收塔T12塔底部分凝液在第一冷箱E11中复热后(4.85MPa，-25.83℃)大量气化，之后进入吸收塔T12底部，对塔顶进入的分离液烃进行气提，强化甲烷与乙烷等重烃在吸收塔T12中分离，富集有更多甲烷的吸收塔T12塔顶气相出料(4.8MPa，-53.79℃)在第三冷箱E13中深冷后再节流降温(2.45MPa，-98.09℃)进入脱甲烷塔T11上部，更多甲烷的进料可使脱甲烷塔T11上部的吸收制冷效果更佳，提高流程的乙烷回收率(回收率94％)。而剩余吸收塔T12塔底凝液节流后(2.5MPa，-54.81℃)直接接入脱甲烷塔T11中部。吸收塔T12中的甲烷与乙烷等重烃的预分离减轻了脱甲烷塔T11的分离负荷。脱甲烷塔T11塔顶气相出料分别为第三冷箱E13、第二冷箱E12、第一冷箱E11提供冷量后进入透平膨胀机增压端K12和外输压缩机K13中增压(5.5MPa，117.2℃)，之后经空冷器10冷却后(5.45MPa，50℃)外输，部分外输气(13.26％)经第一冷箱E11、第二冷箱E12、第三冷箱E13冷却并节流至脱甲烷塔7塔压后(2.45MPa，-102.7℃)作为脱甲烷塔T11塔顶回流进入脱甲烷塔T11。脱甲烷塔T11中下部侧线抽出一股物流在第一冷箱E11中复热并为原料气预冷提供冷量，脱甲烷塔T11塔底物流在换热器E14中对压缩后的高温制冷剂进行降温，两股侧线抽出物流有效提高了脱甲烷塔的热集成度。脱甲烷塔T11底的凝液产品(2.5MPa，21.55℃)进入后续的脱乙烷塔等分馏处理单元进行处理。
本发明提出的带吸收塔适用于富气的乙烷回收流程与目前适用于富气较为典型的部分干气再循环工艺相比，外输压缩机功耗可节省360kW，制冷循环压缩机组可节省能耗560.9kW，总压缩功耗节省6.53％。
以上所述，并非对本发明作任何形式上的限制，虽然本发明已通过上述实施例揭示，然而并非用以限定本发明，任何熟悉本专业的技术人员，在不脱离本发明技术方案范围内，当可利用上述揭示的技术内容作出些变动或修饰为等同变化的等效实施例，但凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所作的任何简单修改、等同变化与修饰，均仍属于本发明技术方案的范围内。

Claims (7)

1.一种带吸收塔适用于富气的乙烷回收方法，其特征在于，所述天然气乙烷回收方法包括原料气经过第一冷箱(E11)冷却后进入分离器(V11)进行预分离；分离器(V11)分离的气相进入第二冷箱(E12)中进一步冷却后进入低温分离器(V12)；低温分离器(V12)分离的气相全部进入透平膨胀机(K11)的膨胀端进行膨胀制冷后进入脱甲烷塔(T11)中上部；分离器(V11)分离液相节流后进入脱甲烷塔(T11)下部；低温分离器(V12)分离液相分为两部分，一部分与吸收塔气相出料相混合以提高流程的抗CO2冻堵能力，另一部分进入吸收塔(T12)顶部，吸收塔(T12)塔底部分凝液在第一冷箱(E11)中复热后大量气化，之后进入吸收塔(T12)底部，另一部分凝液直接接入脱甲烷塔(T11)中部；吸收塔(T12)塔顶气相出料在第三冷箱(E13)中深冷后再节流降温进入脱甲烷塔(T11)上部；脱甲烷塔(T11)塔顶气相依次经过第三冷箱(E13)、第二冷箱(E12)、第一冷箱(E11)换热升温后，再经过透平膨胀机增压端(K12)、外输压缩机(K13)中增压后，最后经空冷器(A11)冷却后外输；脱甲烷塔(T11)底的凝液产品进入后续的脱乙烷塔分馏处理单元进行处理。
2.根据权利要求1所述的一种带吸收塔适用于富气的乙烷回收方法，其特征在于，其中部分外输气再经第一冷箱(E11)、第二冷箱(E12)、第三冷箱(E13)冷却并节流后进入脱甲烷塔(T11)顶。
3.根据权利要求1所述的一种带吸收塔适用于富气的乙烷回收方法，其特征在于，所述第一冷箱(E11)、第二冷箱(E12)、第三冷箱(E13)均采用多股板翅式换热器，将两股热流与多股冷流、两股热流与两股冷流、两股热流与一股冷流分别集成于第一冷箱(E11)、第二冷箱(E12)、第三冷箱(E13)。
4.根据权利要求3所述的一种带吸收塔适用于富气的乙烷回收方法，其特征在于，所述第一冷箱(E11)的两股热流分别为原料气、部分外输气，多股冷流分别为经第三冷箱(E13)和第二冷箱(E12)换热后的脱甲烷塔(T11)顶部出来的气相、一股脱甲烷塔(T11)底侧线抽出的物流、吸收塔(T12)塔底的部分凝液。
5.根据权利要求3所述的一种带吸收塔适用于富气的乙烷回收方法，其特征在于，所述第二冷箱(E12)的两股热流分别为经第一冷箱(E11)换热降温后的原料气、经第一冷箱(E11)换热降温后的部分外输气，两股冷流分别为经第三冷箱(E13)换热后的脱甲烷塔(T11)顶部出来的气相、一股为外部制冷剂提供的冷流。
6.根据权利要求3所述的一种带吸收塔适用于富气的乙烷回收方法，其特征在于，所述第二冷箱(E12)的两股热流分别为经第一冷箱(E11)和第二冷箱(E13)换热降温后的部分外输气、吸收塔(T12)塔顶的气相，一股冷流为脱甲烷塔(T11)顶部出来的气相。
7.根据权利要求1所述的一种带吸收塔适用于富气的乙烷回收方法，其特征在于，所述脱甲烷塔(T11)底侧设有换热器(E24)，脱甲烷塔(T11)塔底物流在换热器(E24)中对压缩后的高温制冷剂进行降温。
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