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CN108036585B - 一种lng冷能利用的热泵空气分离系统 - Google Patents

一种lng冷能利用的热泵空气分离系统 Download PDF

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CN108036585B
CN108036585B CN201810013002.2A CN201810013002A CN108036585B CN 108036585 B CN108036585 B CN 108036585B CN 201810013002 A CN201810013002 A CN 201810013002A CN 108036585 B CN108036585 B CN 108036585B
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董学智
许剑
赵洪雷
陈仕卿
高庆
张华良
谭春青
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Abstract

本发明公开了一种LNG冷能利用的热泵空气分离系统，采用LNG冷能冷却原料低压空气，并利用热泵精馏方式进行空气分离，相较于传统空分系统，本发明采用热泵精馏系统只是对原料空气中的部分氮气加压到0.56MPa左右，降低了空分系统中压缩部件总耗功；采用LNG在主换热器中冷却原料空气，部分冷能可转变为氧氮的分离功，液氧产品无需经过主换热器吸热释冷，制液装置可省去；发明采用LNG冷却原料空气，还可以大幅度降低空分系统启动时间；由于压力降低，精馏塔设备费用相较于传统的空分系统大幅度降低，采用氮增压器设备投资也低于原有的空压机系统，提馏塔与传统空分系统并无差异，因此系统总投资会降低。

Description

一种LNG冷能利用的热泵空气分离系统
技术领域
本发明属于空气分离领域，涉及一种热泵空气分离系统，尤其涉及一种LNG冷能利用的热泵空气分离系统。
背景技术
空气分离系统在钢铁、化工、半导体、食品加工以及医疗领域都具有很重要的作用。低温精馏空分系统是实现大规模制取高纯度氮气、氧气以及氩气的主要方案。低温精馏空分系统需要消耗大量能量，尤其是制取液氧与液氮的产品过程中。液化天然气(LNG)是采用深冷工艺将天然气液化得到的低温(约111K)混合液体，其主要成分为甲烷(CH4)，具有燃烧热值高、排放物污染小、储运成本低等优点。LNG冷能不仅数量巨大，而且能量品阶高，常见的运用主要包括直接发电、空气液化分离、制取液化干冰、深冷粉碎以及低温冷库等。考虑到空分系统的工艺温度约为78～100K，比LNG的温度更低，可避免“低温冷能高温用”的情况，符合“温度对口、梯级利用”能的高效利用原理，因此这种冷能利用方案也被认为是目前技术上最为合理的利用方式。
现有的LNG冷能利用空气分离系统的节能效果主要可归为以下两种因素：(1)LNG冷能冷却空压机或氮压机进口工质温度，可使得空分系统对电力能耗的需求降低；(2)LNG冷能可代替进入主换热器高纯度的液氧/液氮的释冷量实现原料空气温度的降低，减少额外的制取低温液体产品冷量所需的电力能耗。经过相关文献与专利计算，与常规空分系统相比，采用LNG冷能的空分系统制取单位液体产品的能耗可降低50％左右。
然而，现有LNG冷能利用的空分系统方案其精馏塔运行压力都接近于0.6MPa，冷能的加入只是减少生产液体产品能耗而对空分系统分离功无任何有益影响。产生这一现象的主要有2个原因：(1)传统空分系统其精馏单元都采用双级精馏塔，通过低压液氧与高压氮气换热实现上塔与下塔回流气液，由于同一压力下氮气的沸点远低于氧气沸点，因此，下精馏塔需要在高压运行；(2)双级精馏塔的工作温度为78～100K，LNG的储存温度为112K，如若LNG冷能作用于精馏过程，仍需要对原料空气进行增压，通过膨胀或节流产生更低工作温度。调节上述两个原因的方法只有通过改变传统的双级精馏冷热耦合方式，降低精馏塔压力，将部分LNG冷能转为分离功，实现LNG冷能利用的空分系统能耗进一步降低。
发明内容
针对现有技术的缺点和不足，本发明旨在提供一种LNG冷能利用的热泵空气分离系统，采用LNG冷能冷却原料低压空气，并利用热泵精馏方式进行空气分离，从而降低空分系统中压缩部件总耗功，降低空分系统启动时间，降低系统总投资成本。
本发明为解决其技术问题所采用的技术方案为：
一种LNG冷能利用的热泵空气分离系统，包括空压机、水冷塔、分子筛、主换热器、过冷器Ⅰ、精馏塔、过冷器Ⅱ、提馏塔、增压器、冷凝蒸发器、LNG存储装置、低温泵、液氧存储装置，其特征在于，
所述主换热器包括空气通路、LNG通路、氮气通路和污氮通路；所述过冷器Ⅰ包括空气通路、氮气通路Ⅰ、污氮通路和氮气通路Ⅱ；所述精馏塔在高度方向上交错布置有塔板，底部设有空气进口和液态空气出口，顶部设有液氮进口和氮气出口；所述过冷器Ⅱ包括液态空气通路、氮气通路、污氮通路和液氮通路；所述提馏塔在高度方向上交错布置有塔板，底部设有液氧出口Ⅰ、液氧出口Ⅱ和液氧进口，上部设有液态空气进口、液氮进口、纯氮气出口和污氮出口，其中，
所述LNG存储装置的出口通过管路经所述低温泵与所述主换热器的LNG通路连通；所述空压机的进气口与外界空气连通，所述空压机的出气口通过管路依次经所述水冷塔、分子筛、主换热器的空气通路、过冷器Ⅰ的空气通路与所述精馏塔底部的空气进口连通；所述精馏塔底部的液态空气出口通过管路经所述过冷器Ⅱ的液态空气通路与所述提馏塔上部的液态空气进口连通，所述精馏塔顶部的氮气出口通过管路依次经所述增压器、过冷器Ⅰ的氮气通路Ⅱ与所述冷凝蒸发器的液氮侧入口连通；所述冷凝蒸发器的液氮侧出口分为两路，一路与所述精馏塔顶部的液氮进口连通，另一路经所述过冷器Ⅱ的液氮通路与所述提馏塔上部的液氮进口连通；所述冷凝蒸发器的液氧侧入口与所述提馏塔底部的液氧出口Ⅰ连通，所述冷凝蒸发器的液氧侧出口与所述提馏塔底部的液氧进口连通；所述提馏塔底部的液氧出口Ⅱ通过管路与所述液氧存储装置的入口连通；所述提馏塔上部的纯氮气出口通过管路依次经所述过冷器Ⅱ的氮气通路、过冷器Ⅰ的氮气通路Ⅰ、主换热器的氮气通路的入口连通，所述提馏塔上部的污氮出口通过管路依次经所述过冷器Ⅱ的污氮通路、过冷器Ⅰ的污氮通路、主换热器的污氮通路的入口连通。
优选地，所述主换热器的氮气通路的出口与氮气存储或利用装置的入口连通。
优选地，所述主换热器的污氮通路的出口与所述分子筛的空气冷却系统连通。
优选地，所述精馏塔顶部的液氮进口处设置有控制阀门。
优选地，所述提馏塔上部的液态空气进口处、液氮进口处均设置有控制阀门。
优选地，所述空压机的出口压力为0.2MPa左右。
优选地，所述精馏塔顶部引出的高纯氮气经所述增压器增压到0.56MPa左右。
优选地，经所述主换热器和过冷器Ⅰ后的空气被冷却至接近泡点温度送入所述精馏塔的底部。
本发明的LNG冷能利用的热泵空气分离系统，主要采用LNG冷能冷却原料低压空气，并利用热泵精馏方式进行空气分离，其具体工作过程为：
空气首先由空压机升压至0.2MPa并经过水冷塔降温，所提升压力用于弥补分子筛、主换热器、过冷器Ⅰ以及精馏塔与提馏塔中的压力损失，经水冷塔降温后的空气进入分子筛中以除去其中的水分和二氧化碳等杂质；经分子筛净化后的带压常温空气进入主换热器中被LNG与返流氮气与污氮冷却至接近泡点温度送入精馏塔的底部，上升的空气与从顶部注入的回流液氮在精馏塔内在高度方向上交错布置的塔板反复冷凝蒸发，使得含氧浓度较高的富氧液态空气在精馏塔的底部集中，高纯氮气在精馏塔的顶部集中；精馏塔底部抽出的富氧液态空气经过冷器Ⅱ后，进入提馏塔的上部进行氧的提馏过程；由精馏塔上部引出的高纯氮气经增压器增压到0.56MPa左右，之后经过冷器Ⅰ冷却，后进入冷凝蒸发器冷凝，返回精馏塔与提馏塔的顶部作为回流液，提馏塔底部生成的液氧在冷凝蒸发器中吸热蒸发并返回提馏塔；提馏塔底部部分液氧直接作为产品输出，提馏塔顶部的纯氮气经过冷器Ⅱ、主换热器复温后作为氮气产品输出，污氮经过冷器Ⅱ、主换热器复温后送至分子筛纯化系统与空气冷却系统。
同现有技术相比，本发明的LNG冷能利用的热泵空气分离系统具有显著的技术效果：(1)相较于传统空分系统，本发明采用热泵精馏系统只是对原料空气中的部分氮气加压到0.56MPa左右，降低了空分系统中压缩部件总耗功；(2)采用LNG在主换热器中冷却原料空气，部分冷能可转变为氧氮的分离功，液氧产品无需经过主换热器吸热释冷，制液装置可省去；(3)本发明采用LNG冷却原料空气，可以大幅度降低空分系统启动时间；(4)本发明中，由于压力降低，精馏塔设备费用相较于传统的空分系统大幅度降低，采用氮增压器设备投资也低于原有的空压机系统，提馏塔与传统空分系统并无差异，因此系统总投资会降低。
附图说明
图1为本发明的LNG冷能利用的热泵空气分离系统示意图。
具体实施方式
为使本发明的目的、技术方案及优点更加清楚明白，以下参照附图并举实施例，对本发明进一步详细说明。需要说明的是，以下所述仅为本发明的较佳实施例，并不因此而限定本发明的保护范围。
如图1所示，本发明的LNG冷能利用的热泵空气分离系统，包括空压机1、水冷塔2、分子筛3、主换热器4、过冷器Ⅰ5、精馏塔6、过冷器Ⅱ7、提馏塔8、增压器9、冷凝蒸发器10、LNG存储装置11、低温泵12、液氧存储装置13。其中，主换热器4包括空气通路、LNG通路、氮气通路和污氮通路；过冷器Ⅰ5包括空气通路、氮气通路Ⅰ、污氮通路和氮气通路Ⅱ；精馏塔6在高度方向上交错布置有塔板，底部设有空气进口和液态空气出口，顶部设有液氮进口和氮气出口；过冷器Ⅱ7包括液态空气通路、氮气通路、污氮通路和液氮通路；提馏塔8在高度方向上交错布置有塔板，底部设有液氧出口Ⅰ、液氧出口Ⅱ和液氧进口，上部设有液态空气进口、液氮进口、纯氮气出口和污氮出口。
LNG存储装置11的出口通过管路经低温泵12与主换热器4的LNG通路连通。空压机1的进气口与空气连通，空压机1的出气口通过管路依次经水冷塔2、分子筛3、主换热器4的空气通路、过冷器Ⅰ5的空气通路与精馏塔6底部的空气进口连通；精馏塔6底部的液态空气出口通过管路经过冷器Ⅱ7的液态空气通路与提馏塔8上部设置的液态空气进口连通，精馏塔6顶部的氮气出口通过管路依次经增压器9、过冷器Ⅰ5的氮气通路Ⅱ与冷凝蒸发器10的液氮侧入口连通，冷凝蒸发器10的液氮侧出口分为两路，一路与精馏塔6顶部的液氮进口连通，另一路经过冷器Ⅱ7的液氮通路与提馏塔8上部的液氮进口连通；冷凝蒸发器10的液氧侧入口与提馏塔8底部的液氧出口Ⅰ连通，冷凝蒸发器10的液氧侧出口与提馏塔8底部的液氧进口连通；提馏塔8底部的液氧出口Ⅱ通过管路与液氧存储装置13的入口连通；提馏塔8上部的纯氮气出口通过管路依次经过冷器Ⅱ7的氮气通路、过冷器Ⅰ5的氮气通路Ⅰ、主换热器4的氮气通路与氮气存储装置(图中未示出)的入口连通，提馏塔8上部的污氮出口通过管路依次经过冷器Ⅱ7的污氮通路、过冷器Ⅰ5的污氮通路、主换热器4的污氮通路与分子筛3的空气冷却系统连通。
本发明的LNG冷能利用的热泵空气分离系统，主要采用LNG冷能冷却原料低压空气，并利用热泵精馏方式进行空气分离，其具体工作过程为：
空气首先由空压机1升压至0.2MPa并经过水冷塔2降温，所提升压力用于弥补分子筛3、主换热器4、过冷器Ⅰ5以及精馏塔6与提馏塔7中的压力损失，经水冷塔2降温后的空气进入分子筛3中以除去其中的水分和二氧化碳等杂质；经分子筛3净化后的带压常温空气进入主换热器4中被LNG与返流氮气与污氮冷却至接近泡点温度送入精馏塔5的底部，上升的空气与从顶部注入的回流液氮在精馏塔6内在高度方向上交错布置的塔板反复冷凝蒸发，使得含氧浓度较高的富氧液态空气在精馏塔6的底部集中，高纯氮气在精馏塔6的顶部集中；精馏塔6底部抽出的富氧液态空气经过冷器Ⅱ7后，进入提馏塔8的上部进行氧的提馏过程；由精馏塔6上部引出的高纯氮气经增压器9增压到0.56MPa左右，之后经过冷器Ⅰ5冷却，后进入冷凝蒸发器10冷凝，返回精馏塔5与提馏塔8的顶部作为回流液，提馏塔8底部生成的液氧在冷凝蒸发器10中吸热蒸发并返回提馏塔8；提馏塔8底部部分液氧直接作为产品输出，提馏塔8顶部的纯氮气经过冷器Ⅱ7、主换热器4复温后作为氮气产品输出，污氮经过冷器Ⅱ7、主换热器4复温后送至分子筛3纯化系统与空气冷却系统。
进一步地，精馏塔6顶部的液氮进口处设置有控制阀门，提馏塔8上部的液态空气进口、液氮进口处均设置有控制阀门。
相较于传统空分系统，本发明采用热泵精馏系统只是对原料空气中的部分氮气加压到0.56MPa左右，降低了空分系统中压缩部件总耗功；采用空压机1对原料空气预先增压，后进入分子筛3进行除杂，可解决主换热器4中原料空气与LNG、氮气以及污氮换热所产生的结冰问题；采用LNG在主换热器4中冷却原料空气，部分冷能可转变为氧氮的分离功，液氧产品无需经过主换热器吸热释冷，制液装置可省去，同时本发明采用LNG冷却原料空气，可以大幅度降低空分系统启动时间，由于压力降低，精馏塔设备费用相较于传统的空分系统大幅度降低，采用氮增压器设备投资也低于原有的空压机系统，提馏塔与传统空分系统并无差异，因此系统总投资会降低。
以上显示和描述了本发明的基本原理、主要特征和优点。本行业的技术人员应该了解，本发明不受上述实施例的限制，上述实施例和说明书中描述的只是说明本发明的原理，在不脱离本发明精神和范围的前提下，本发明还会有各种变化和改进，这些变化和改进都落入要求保护的本发明范围内。本发明要求保护范围由所附的权利要求书及其等效物界定。

Claims (4)

1.一种LNG冷能利用的热泵空气分离系统，包括空压机、水冷塔、分子筛、主换热器、过冷器Ⅰ、精馏塔、过冷器Ⅱ、提馏塔、增压器、冷凝蒸发器、LNG存储装置、低温泵、液氧存储装置，其特征在于，
所述主换热器包括空气通路、LNG通路、氮气通路和污氮通路；
所述过冷器Ⅰ包括空气通路、氮气通路Ⅰ、污氮通路和氮气通路Ⅱ；
所述精馏塔在高度方向上交错布置有塔板，底部设有空气进口和液态空气出口，顶部设有液氮进口和氮气出口；
所述过冷器Ⅱ包括液态空气通路、氮气通路、污氮通路和液氮通路；
所述提馏塔在高度方向上交错布置有塔板，底部设有液氧出口Ⅰ、液氧出口Ⅱ和液氧进口，上部设有液态空气进口、液氮进口、纯氮气出口和污氮出口，
其中，
所述LNG存储装置的出口通过管路经所述低温泵与所述主换热器的LNG通路连通；
所述空压机的进气口与外界空气连通，所述空压机的出气口通过管路依次经所述水冷塔、分子筛、主换热器的空气通路、过冷器Ⅰ的空气通路与所述精馏塔底部的空气进口连通，且经所述主换热器和过冷器Ⅰ换热后的空气被冷却至接近泡点温度送入所述精馏塔的底部，且所述空压机的出口压力为0.2MPa左右；
所述精馏塔底部的液态空气出口通过管路经所述过冷器Ⅱ的液态空气通路与所述提馏塔上部的液态空气进口连通，所述精馏塔顶部的氮气出口通过管路依次经所述增压器、过冷器Ⅰ的氮气通路Ⅱ与所述冷凝蒸发器的液氮侧入口连通，且所述精馏塔顶部引出的氮气经所述增压器后增压到0.56MPa左右；
所述冷凝蒸发器的液氮侧出口分为两路，一路与所述精馏塔顶部的液氮进口连通，另一路经所述过冷器Ⅱ的液氮通路与所述提馏塔上部的液氮进口连通；所述冷凝蒸发器的液氧侧入口与所述提馏塔底部的液氧出口Ⅰ连通，所述冷凝蒸发器的液氧侧出口与所述提馏塔底部的液氧进口连通；所述提馏塔底部的液氧出口Ⅱ通过管路与所述液氧存储装置的入口连通；
所述提馏塔上部的纯氮气出口通过管路依次经所述过冷器Ⅱ的氮气通路、过冷器Ⅰ的氮气通路Ⅰ、主换热器的氮气通路的入口连通，所述提馏塔上部的污氮出口通过管路依次经所述过冷器Ⅱ的污氮通路、过冷器Ⅰ的污氮通路、主换热器的污氮通路的入口连通；
所述主换热器的污氮通路的出口与所述分子筛的空气冷却系统连通。
2.根据权利要求1所述的LNG冷能利用的热泵空气分离系统，其特征在于，所述主换热器的氮气通路的出口与氮气存储或利用装置的入口连通。
3.根据权利要求1所述的LNG冷能利用的热泵空气分离系统，其特征在于，所述精馏塔顶部的液氮进口处设置有控制阀门。
4.根据权利要求1所述的LNG冷能利用的热泵空气分离系统，其特征在于，所述提馏塔上部的液态空气进口处、液氮进口处均设置有控制阀门。
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