CN106247759B - 一种lng接收站回收轻烃的方法 - Google Patents

一种lng接收站回收轻烃的方法 Download PDF

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CN106247759B
CN106247759B CN201610670438.XA CN201610670438A CN106247759B CN 106247759 B CN106247759 B CN 106247759B CN 201610670438 A CN201610670438 A CN 201610670438A CN 106247759 B CN106247759 B CN 106247759B
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gas
lng
ethane
dethanizer
domethanizing column
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CN106247759A (zh
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王秀林
侯建国
穆翔宇
赵思思
隋朝霞
侯海龙
张瑜
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China National Offshore Oil Corp CNOOC
CNOOC Gas and Power Group Co Ltd
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CNOOC Gas and Power 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
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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
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the feed stream
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    • F25J3/0615—Liquefied natural gas
    • 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
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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
    • F25J3/0204—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 feed stream
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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
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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
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    • F25J3/0242—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 CnHm with 3 carbon atoms or more
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    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/04—Processes or apparatus using separation by rectification in a dual pressure main column system
    • 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
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    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/40—Features relating to the provision of boil-up in the bottom of a column
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    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/74—Refluxing the column with at least a part of the partially condensed overhead gas
    • 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
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    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
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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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
    • 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
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    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/60—Methane
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Abstract

本发明公开了一种LNG接收站回收轻烃的方法。该方法中，LNG经低压泵增压后分两股物流，两股物流分别经换热后进入脱乙烷塔，在脱乙烷塔中实现LPG的分离，分离出的LPG储存在LPG储罐中，脱乙烷塔塔顶气体经冷却后，液体回流到脱乙烷塔内，气体经降温后进入脱甲烷塔；脱甲烷塔内气体在脱甲烷塔内实现甲烷和乙烷分离，塔底乙烷储存在乙烷储罐中，塔顶气态组分经冷却后，液体回流到脱甲烷塔内，气体组分经换热、天然气压缩机增压后，一股气体作为脱甲烷塔的气提气，另一股天然气进入外输管网外输。本发明方法可在低压下实现甲烷、乙烷和LPG的分离；回收轻烃后甲烷以气态形式存在，经换热和增压后，可直接输入天然气管网系统。

Description

一种LNG接收站回收轻烃的方法
技术领域
本发明涉及轻烃回收工艺，尤其涉及一种适用于大型液化天然气接收站的轻烃回收方法。
背景技术
天然气主要成分为甲院、热值高，是世界上一次性能源的三大支柱之一。并且和石油、煤相比，天然气的燃烧产物污染更低，可以作为一种优质的清洁能源，因此天然气越来越受到重视，天然气在常压下将被降温到-162℃后变为液态，体积缩小为原来的1/600，这就是液化天然气(LNG)。液化天然气更有利于储存和运输，因此近年来液化天然气也得到了极大发展和运用。
液化天然气除了主要含有甲烷外，还有少量的乙烷、丙烷和丁烷。根据液化天然气中轻烃含量的不同，可分为贫气和富气。目前，国际市场上有相当一部分是富气，其含有质量分数8％以上的C2、C3及少量烃类。富气中的轻烃是一种优质且应用广泛的化工原料，具有很高的附加值，用其代替石脑油作为乙烯的原料能够节省投资30％，乙烯装置能耗降低30％-40％，综合成本降低10％左右。
CN104140349A“一种新型液化天然气的轻烃分离系统和方法”，其提出了：LNG增压到1.0-3.8MPa后进行预热，先进入脱甲烷塔(气提塔)脱除甲烷，再进行脱乙烷塔(精馏塔)脱除乙烷和LPG。
CN204240702“一种利用液化天然气冷能回收轻烃的装置”，其提出了：LNG增加到1.75-2.25MPa后，先进入脱甲烷塔实现甲烷和C2+的分离，脱甲烷塔出口经压缩机增加到2.9-3.3MPa后，进入冷箱冷却成液态，再经LNG泵后外输。
CN105065900A“LNG接收站轻烃回收工艺”，其提出了：LNG经罐内低压泵后，采用LNG高压泵增压并达到外输压力后，进入轻烃回收装置将LNG和乙烷分离，实现LNG中轻烃回收，该专利轻烃回收装置的压力较高(天然气外输压力下)，主要实现LNG和乙烷的分离。
目前，关于LNG中轻烃回收的专利主要存在如下问题：
(1)轻烃分离需在高压下进行操作，造成投资成本过高，运行风险较大，增大了企业投资的风险系数。
(2)分离出来的甲烷全为液态，需要气化后才能输入天然气管网系统，而气化过程需要大量的热源，变向增加了装置的运行成本。
发明内容
本发明的目的是提供一种LNG接收站回收轻烃的方法。
本发明提供的LNG接收站回收轻烃的方法中，LNG经低压泵增压后分两股物流，两股物流分别经换热后进入脱乙烷塔，在脱乙烷塔中实现LPG的分离，分离出的LPG储存在LPG储罐中，脱乙烷塔塔顶气体经冷却后，液体回流到脱乙烷塔内，气体经降温后进入脱甲烷塔；进入脱甲烷塔的气体在脱甲烷塔内实现甲烷和乙烷分离，塔底乙烷流体储存在乙烷储罐中，塔顶气态组分经冷却后，液体回流到脱甲烷塔内，气体组分经换热、天然气压缩机增压后，一股气体作为脱甲烷塔的气提气，另一股天然气进入外输官网外输。
上述的方法中，所述LNG经低压泵增压后，LNG的压力可为0.3MPaG～1.0MPaG。
上述的方法中，所述两股物流分别记为LNGⅠ和LNGⅡ；所述LNGⅠ进入所述脱乙烷塔塔顶的冷凝器中作为所述脱乙烷塔的冷源与所述脱乙烷塔塔顶气体进行换热；所述LNGⅡ进入所述脱甲烷塔塔顶的冷凝器中作为所述脱甲烷塔的冷源与所述脱甲烷塔塔顶气体进行换热。
上述的方法中，所述脱乙烷塔的操作压力可为0.3MPaG～1.0MPaG。
上述的方法中，所述脱甲烷塔的操作压力可为0.3MPaG～1.0MPaG。
上述的方法中，所述脱乙烷塔为精馏塔，实现LPG的分离，其中塔底液相组分主要为LPG，塔顶气体组分为甲烷和乙烷混合物。
上述的方法中，所述脱甲烷塔为气提塔，实现甲烷、乙烷分离，其中塔底液相组分主要为乙烷，塔顶气体组分为甲烷。
上述的方法中，所述脱甲烷塔塔顶流出的气体组分在所述换热后的温度可为-10～40℃，所述增压后，外输压力可为3.0MPaG～8.0MPaG。
本发明具有如下有益效果：
本发明LNG接收站回收轻烃的方法可在低压下实现甲烷、乙烷和LPG的分离；回收轻烃后甲烷以气态形式存在，经换热和增压后，可直接输入天然气管网系统。
附图说明
图1为本发明LNG接收站回收轻烃的工艺流程图。
具体实施方式
下述实施例中所使用的实验方法如无特殊说明，均为常规方法。
下述实施例中所用的材料、试剂等，如无特殊说明，均可从商业途径得到。
下面结合说明书附图对本发明作进一步说明，但发明并不局限于下述实施例。
实施例1、LNG接收站回收轻烃
按照图1所示工艺流程图对LNG中的轻烃进行回收，具体步骤如下：
LNG接收站的LNG(流量为800t/h，摩尔组成为：甲烷86％，乙烷9％，丙烷4％，丁烷0.9％，氮气0.1％)经低压外输泵增压至0.8MPaG后，分成两股物流LNGⅠ和LNGⅡ，LNGⅠ进入脱乙烷塔塔顶的冷凝器中作为脱乙烷塔的冷源，与脱乙烷塔塔顶的气体换热后通入脱乙烷塔中进行分离；LNGⅡ进入脱甲烷塔塔顶的冷凝器中作为脱甲烷塔的冷源，与脱甲烷塔塔顶的气体换热后进入脱乙烷塔中进行分离。
脱乙烷塔为精馏塔，脱乙烷塔入口温度为-70℃，操作压力为0.75MPaG，脱乙烷塔塔底液相组分-40℃的LPG进入LPG储罐中储存，即可回收得到LPG；脱乙烷塔塔顶气体经冷却后，液体回流到脱乙烷塔内，气态组分(甲烷和乙烷的混合气体)经冷却到-115℃后进入脱甲烷塔中。
脱甲烷塔为气提塔，在脱甲烷塔中实现甲烷和乙烷分离，脱甲烷塔的操作压力为0.60MPaG；将脱甲烷塔塔底液相组分送入乙烷储存罐中，即可回收得到乙烷；脱甲烷塔塔顶气体经冷却后，液体回流到脱甲烷塔内，气态组分经换热至常温(3℃)后，经天然气压缩机增压后，一股气体作为脱甲烷塔的气提气，另一股气体进入外输管网外输，外输压力为6MPaG，即可回收得到甲烷。
经模拟可知脱乙烷塔塔顶LPG(物流1)、脱甲烷塔塔顶(物流2)和塔底物流(物流3)摩尔组成如表1所示。
表1、轻烃回收工艺关键产品摩尔组成
物流1 物流2 物流3
温度，℃ -35.00 -117.00 -80.00
压力，MPaG 0.77 0.60 0.72
甲烷(mol％) 0 99.20 0
乙烷(mol％) 6.00 0.60 97.3
丙烷(mol％) 70.00 0 2.10
丁烷(mol％) 23.30 0 0.70
氮气(mol％) 0 0.20 0.00
实施例2、LNG接收站回收轻烃
按照图1所示工艺流程图对LNG中的轻烃进行回收，具体步骤如下：
LNG接收站的LNG(流量为2000t/h，摩尔组成为：甲烷92％，乙烷5％，丙烷2.4％，丁烷0.5％，氮气0.1％)经低压外输泵增压至0.4MPaG后，分成两股物流LNGⅠ和LNGⅡ，LNGⅠ进入脱乙烷塔塔顶的冷凝器中作为脱乙烷塔的冷源，与脱乙烷塔塔顶的气体换热后通入脱乙烷塔中进行分离；LNGⅡ进入脱甲烷塔塔顶的冷凝器中作为脱甲烷塔的冷源，与脱甲烷塔塔顶的气体换热后进入脱乙烷塔中进行分离。
脱乙烷塔为精馏塔，脱乙烷塔入口温度为-75℃，操作压力为0.35MPaG，脱乙烷塔塔底物料-50℃的LPG进入LPG储罐中储存，即可回收得到LPG；脱乙烷塔塔顶气体经冷却后，液体回流到脱乙烷塔内，气态组分(甲烷和乙烷的混合气体)经冷却到-120℃后进入脱甲烷塔中。
脱甲烷塔为气提塔，在脱甲烷塔中实现甲烷和乙烷分离，脱甲烷塔的操作压力为0.30MPaG；将脱甲烷塔塔底液相组分送入乙烷储存罐中，即可回收得到乙烷；脱甲烷塔塔顶气体经冷却后，液体回流到脱甲烷塔内，气态组分经换热至常温(5℃)后，经天然气压缩机增压后，一股气体作为脱甲烷塔的气提气，另一股气体进入外输管网外输，外输压力为7MPaG，即可回收得到甲烷。
经模拟可知脱乙烷塔塔顶LPG(物流1)、脱甲烷塔塔顶(物流2)和塔底物流(物流3)摩尔组成如表2所示：
表2、轻烃回收工艺关键产品摩尔组成
物流1 物流2 物流3
温度，℃ -50.00 -122.00 -90.00
压力，MPaG 0.33 0.28 0.33
甲烷(mol％) 0 99.40 0
乙烷(mol％) 5.70 0.50 96.2
丙烷(mol％) 72.00 0 3.20
丁烷(mol％) 22.30 0 0.60
氮气(mol％) 0 0.10 0.00

Claims (7)

1.一种LNG接收站回收轻烃的方法，其特征在于，LNG经低压泵增压后分两股物流，两股物流分别经换热后进入脱乙烷塔，在脱乙烷塔中实现LPG的分离，分离出的LPG储存在LPG储罐中，脱乙烷塔塔顶气体经冷却后，液体回流到脱乙烷塔内，气体经降温后进入脱甲烷塔；脱甲烷塔内气体在脱甲烷塔内实现甲烷和乙烷分离，塔底乙烷储存在乙烷储罐中，塔顶气态组分经冷却后，液体回流到脱甲烷塔内，气体组分经换热、天然气压缩机增压后，一股气体作为脱甲烷塔的气提气，另一股天然气进入外输管网外输；
所述增压后，LNG的压力为0.3MPaG～1.0MPaG。
2.根据权利要求1所述的方法，其特征在于：所述两股物流分别记为LNGⅠ和LNGⅡ；所述LNGⅠ进入所述脱乙烷塔塔顶的冷凝器中作为所述脱乙烷塔的冷源与所述脱乙烷塔塔顶气体进行换热；所述LNGⅡ进入所述脱甲烷塔塔顶的冷凝器中作为所述脱甲烷塔的冷源与所述脱甲烷塔塔顶气体进行换热。
3.根据权利要求1或2所述的方法，其特征在于：所述脱乙烷塔的操作压力为0.3MPaG～1.0MPaG。
4.根据权利要求1或2所述的方法，其特征在于：所述脱甲烷塔的操作压力为0.3MPaG～1.0MPaG。
5.根据权利要求1或2所述的方法，其特征在于：所述脱乙烷塔为精馏塔，实现LPG的分离，其中塔底液相组分主要为LPG，塔顶气体组分为甲烷和乙烷混合物。
6.根据权利要求1或2所述的方法，其特征在于：所述脱甲烷塔为气提塔，实现甲烷、乙烷分离，其中塔底液相组分主要为乙烷，塔顶气体组分为甲烷。
7.根据权利要求1或2所述的方法，其特征在于：所述脱甲烷塔塔顶流出的气体组分在所述换热后的温度为-10～40℃，所述增压后，外输压力为3.0MPaG～8.0MPaG。
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