CN101839612B - 基于lng卫星站冷能利用的倒灌式空气分离系统及方法 - Google Patents

基于lng卫星站冷能利用的倒灌式空气分离系统及方法 Download PDF

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CN101839612B
CN101839612B CN2010101410715A CN201010141071A CN101839612B CN 101839612 B CN101839612 B CN 101839612B CN 2010101410715 A CN2010101410715 A CN 2010101410715A CN 201010141071 A CN201010141071 A CN 201010141071A CN 101839612 B CN101839612 B CN 101839612B
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nitrogen
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heat exchanger
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CN101839612A (zh
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金滔
沈崴
汤珂
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Zhejiang University ZJU
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Abstract

本发明公开了一种基于LNG卫星站冷能利用的倒灌式空气分离系统及方法。本发明通过调节循环氮气量来适应LNG用量的波动，同时利用倒灌液氮的方法在LNG所供冷量不足时补足系统所需的制冷量要求。在空分流程引进LNG冷量后取消了氮气外循环系统，设备上省去了氮透平膨胀机和氟利昂制冷机组，使流程得到了简化。主换热器出口处的循环氮气温度被从传统的100K左右提升至253～263K，避免了传统系统中循环氮气的低温压缩问题。由于循环氮气的出口温度提高，使得主换热器的其他几股用于冷却进料空气的流体温度降低，而这部分剩余的冷量又通过与压缩机前的进料空气换热，复温至常温后排出，使得进料空气的温度进一步降低至273K～280K，从而又节约了空压机的能耗。

Description

基于LNG卫星站冷能利用的倒灌式空气分离系统及方法
技术领域
本发明涉及深冷空气分离方法及系统，尤其涉及一种基于LNG卫星站冷能利用的倒灌式空气分离系统及方法。
背景技术
液化天然气(LNG)是通过低温液化工艺制成的低温液体混合物，是一种十分洁净的燃料，其主要成分为甲烷(由于产地差异，甲烷含量从80％～90％不等)。近年来，我国沿海多个地区建成或规划建造LNG接收站，站内的LNG在输送到用户前，通常需要利用海水或空气对其加热汽化，在此过程中没有对汽化潜热以及复温显热(0.1MPa下从112K汽化成300K的天然气时所释放的冷能约为950kJ/kg)很好地加以利用，从而造成极大的资源浪费。深冷空分设备为获得77K的液氮温区，需要消耗大量的机械功，是一种能耗较高的流程设备。鉴于LNG冷能温度位与空分所需温度相近，合理利用LNG的冷能以减少空分流程中的压缩能耗是一种可行方案。利用LNG冷能的空分流程有以下3个主要优点：一是在离LNG最接近的温度位对其冷能进行利用，可用能利用程度高；二是可以在较低能耗指标下得到大量液态产品；三是可以缩短空分流程启动时间。大型LNG接收站为广泛类型的用户供气，包括调峰电厂、化工企业、城市用气等，因此供气相对比较平稳，可供利用的冷能量也比较稳定。然而，主要负责个别城市天然气供应的LNG卫星站却有很大的不同，其LNG消费量随季节以及日夜甚至各时段用气量的不同而呈现波动特征，因此所能提供的冷能也会随时间按一定规律波动。若想合理利用LNG卫星站的冷能，需要采取相应的措施解决该不稳定问题，特别是对于基于LNG冷能的空分系统，如何保证其稳定运行是非常关键的。本发明针对上述问题，提出一种小型空分流程，可实现相应工况调节来适应LNG冷能的波动。
发明内容
本发明的目的是克服现有技术的不足，提供一种基于LNG卫星站冷能利用的倒灌式空气分离系统及方法。
基于LNG卫星站冷能利用的倒灌式空气分离系统包括空气过滤器、空气压缩机、水冷机组、空气纯化器、主换热器、过冷器、氮气压缩机、LNG换热器、天然气压缩机、空气预冷器、LNG储罐、液氮储罐、精馏系统，精馏系统包括下塔、冷凝蒸发器、上塔；空气过滤器与空气预冷器、空气压缩机、水冷机组、空气纯化器主换热器的进料空气流道、下塔下部进料空气进口依次相连，上塔顶部的产品氮气出口与过冷器、主换热器的产品氮气流道、空气预冷器依次相连，下塔上端部的循环氮气出口与主换热器的冷循环氮气流道、氮压缩机、水冷机组、LNG换热器的循环氮气流道、主换热器的热循环氮气流道、下塔上端部的循环氮气进口依次相连，冷凝蒸发器液氮出口分为两路，冷凝蒸发器液氮出口一路与液氮储罐、精馏系统的下塔端部的倒灌液氮进口依次相连，冷凝蒸发器液氮出口另一路与过冷器、上塔的液氮进口依次相连，下塔底部的富氧液空出口与过冷器、上塔的富氧液空进口依次相连，LNG储罐与LNG换热器的LNG流道、天然气压缩机依次相连。
基于LNG卫星站冷能利用的倒灌式空气分离方法是：进料空气经空气过滤器过滤，与空气预冷器中的产品氮气和污氮气换热后，进入空压机加压至0.58MPa，水冷至293K后进入空气纯化系统除去其中的水分和二氧化碳，进入主换热器被循环氮气、产品氮气和污氮气冷却，进入下塔底部精馏，下塔内空气与回流液氮在多层塔板上反复冷凝和蒸发，下塔底部积聚富氧液空，富氧液空通过过冷器过冷，经节流阀降压至0.13～0.14MPa，进入上塔提供上塔冷量；下塔上端部富集的氮气通过冷凝蒸发器冷凝成液氮，当LNG用量小于LNG卫星站LNG平均用量时，冷凝成的液氮全部经过冷器进一步降温，再经液氮节流阀降压至0.13～0.14MPa，进入上塔顶部作为上塔的回流液体；当LNG用量大于LNG卫星站LNG平均用量时，冷凝成的液氮一部分经过冷器进一步降温，经液氮节流阀降压至0.13～0.14MPa，进入上塔顶部作为上塔的回流液体，冷凝成的液氮另一部分进入液氮储液罐储存，当LNG用量小于LNG卫星站LNG平均用量时，液氮储液罐储存的液氮倒灌进入下塔，补充冷量，以维持系统稳定运行；上塔顶部的产品氮气以及上塔中上部的污氮气经过过冷器回收部分冷量，进入主换热器，冷却进料空气和过冷经过LNG换热器后的循环氮气，再与压缩前的进料空气换热，充分利用其残余的冷量，使进入空气压缩机的空气温度降低至273K～280K，以减小空气压缩机的能耗；下塔上端部的循环氮气经过主换热器冷却进料空气，温度升至253K～263K的循环氮气进入氮压缩机加压至3.3MPa，经冷水机组降温后，进入LNG换热器吸收LNG的汽化潜热和复温显热，循环氮气液化后进入主换热器继续与产品氮气、污氮气以及循环氮气换热，得到的过冷液氮通过节流阀降压至0.55MPa，回到下塔提供冷量。
本发明是基于LNG卫星站冷能利用的倒灌式空气分离系统，通过调节循环氮气量来适应LNG用量的波动，同时利用倒灌液氮的方法在LNG所供冷量不足时补足系统所需的制冷量要求。在空分流程引进LNG冷量后取消了氮气外循环系统，设备上省去了氮透平膨胀机和氟利昂制冷机组，使流程得到了简化。主换热器出口处的循环氮气温度被从传统的100K左右提升至253～263K，避免了传统系统中循环氮气的低温压缩问题。由于循环氮气的出口温度提高，使得主换热器的其他几股用于冷却进料空气的流体温度降低，而这部分剩余的冷量又通过与压缩机前的进料空气换热，复温至常温后排出，使得进料空气的温度进一步降低至273K～280K，从而又节约了空压机的能耗。
附图说明
图1是倒灌液氮与循环氮气联合调节的LNG预冷循环氮气空分流程；
图中：空气过滤器1、空气压缩机2、水冷机组3、空气纯化器4、主换热器5、下塔6、冷凝蒸发器7、上塔8、过冷器9、氮气压缩机10、LNG换热器11、天然气压缩机12、空气预冷器13、LNG储罐14、液氮储罐15、精馏系统16。
具体实施方式
如图1所示，基于LNG卫星站冷能利用的倒灌式空气分离系统包括空气过滤器1、空气压缩机2、水冷机组3、空气纯化器4、主换热器5、过冷器9、氮气压缩机10、LNG换热器11、天然气压缩机12、空气预冷器13、LNG储罐14、液氮储罐15、精馏系统16，精馏系统16包括下塔6、冷凝蒸发器7、上塔8；空气过滤器1与空气预冷器13、空气压缩机2、水冷机组3、空气纯化器4、主换热器5的进料空气流道、下塔6下部进料空气进口依次相连，上塔8顶部的产品氮气出口与过冷器9、主换热器5的产品氮气流道、空气预冷器13依次相连，下塔6上端部的循环氮气出口与主换热器5的冷循环氮气流道、氮压缩机10、水冷机组3、LNG换热器11的循环氮气流道、主换热器5的热循环氮气流道、下塔6上端部的循环氮气进口依次相连，冷凝蒸发器7液氮出口分为两路，冷凝蒸发器7液氮出口一路与液氮储罐15、精馏系统16的下塔6端部的倒灌液氮进口依次相连，冷凝蒸发器7液氮出口另一路与过冷器9、上塔8的液氮进口依次相连，下塔6底部的富氧液空出口与过冷器9、上塔8的富氧液空进口依次相连，LNG储罐14与LNG换热器11的LNG流道、天然气压缩机12依次相连。
基于LNG卫星站冷能利用的倒灌式空气分离方法是：进料空气经空气过滤器1过滤，与空气预冷器13中的产品氮气和污氮气换热后，进入空压机2加压至0.58MPa，水冷至293K后进入空气纯化系统4除去其中的水分和二氧化碳，进入主换热器5被循环氮气、产品氮气和污氮气冷却，进入下塔6底部精馏，下塔6内空气与回流液氮在多层塔板上反复冷凝和蒸发，下塔底部积聚富氧液空，富氧液空通过过冷器9过冷，经节流阀降压至0.13～0.14MPa，进入上塔8提供上塔冷量；下塔上端部富集的氮气通过冷凝蒸发器7冷凝成液氮，当LNG用量小于LNG卫星站LNG平均用量时，冷凝成的液氮全部经过冷器9进一步降温，再经液氮节流阀降压至0.13～0.14MPa，进入上塔8顶部作为上塔的回流液体；当LNG用量大于LNG卫星站LNG平均用量时，冷凝成的液氮一部分经过冷器9进一步降温，经液氮节流阀降压至0.13～0.14MPa，进入上塔8顶部作为上塔的回流液体，冷凝成的液氮另一部分进入液氮储液罐15储存，当LNG用量小于LNG卫星站LNG平均用量时，液氮储液罐15储存的液氮倒灌进入下塔6，补充冷量，以维持系统稳定运行；上塔8顶部的产品氮气以及上塔中上部的污氮气经过过冷器9回收部分冷量，进入主换热器5，冷却进料空气和过冷经过LNG换热器后的循环氮气，再与压缩前的进料空气换热，充分利用其残余的冷量，使进入空气压缩机2的空气温度降低至273K～280K，以减小空气压缩机2的能耗；下塔6上端部的循环氮气经过主换热器5冷却进料空气，温度升至253K～263K的循环氮气进入氮压缩机10加压至3.3MPa，经冷水机组3降温后，进入LNG换热器11吸收LNG的汽化潜热和复温显热，循环氮气液化后进入主换热器5继续与产品氮气、污氮气以及循环氮气换热，得到的过冷液氮通过节流阀降压至0.55MPa，回到下塔6提供冷量。
空气100经过空气过滤器1过滤掉灰尘等机械杂质后101，先经过与出流的氮气502和污氮气602换热，冷却至263K～273K左右，然后进入空压机2加压至0.58MPa，再经过水冷至293K，随后进入空气纯化系统除去其中的水分和二氧化碳；接着，这部分经过预处理的空气102进入主换热器5进行冷却，在主换热器5中，冷却进料空气的的冷量由3股流体提供，分别是循环氮气401、产品氮气501和污氮601。在主换热器5出口，进料空气102被冷却至99K～102K，然后进入下塔6底部开始精馏。
下塔内空气与回流液氮在多层塔板上反复冷凝和蒸发，在下塔底部积聚了含有较多液氧的富氧液空200，抽出后通过过冷器9过冷，然后经节流阀降压至略高于上塔压力(0.13～0.14MPa)，进入上塔8提供上塔冷量；下塔顶部富集氮气400，通过冷凝蒸发器7冷凝成液氮403后，一部分液氮405被引出下塔，经过过冷器9进一步降温后，再经液氮节流阀降压至略高于上塔压力(0.13～0.14MPa)，进入上塔8顶部作为上塔的回流液体；当LNG用量大于平均用量时，有另一部分液氮404产生，该部分液氮流到液氮储液罐15储存，用于当LNG用量小于平均用量时倒灌通入下塔6，来补足冷量，维持系统稳定运行。
上塔8顶部的产品氮气500以及近塔顶处引出的污氮气600经过过冷器9回收部分冷量后，进入主换热器5，冷却进料空气102和过冷经过LNG换热器后的循环氮气408；之后再与压缩前的进料空气101换热，充分利用其残余的冷量，使空气在进压缩机2前的温度尽量低，以减小压缩机能耗。
下塔6上端部的循环氮气401首先经过主换热器5冷却进料空气102，并以253K～263K的温度出主换热器，随后进入氮压缩机10加压至3.3MPa，经冷水机组3降温后，直接进入LNG换热器11吸收LNG汽化潜热和复温显热，液化后408进入主换热器5的后部继续与出流的产品氮气501、污氮气601以及循环氮气401换热，过冷液体409流出主换热器5后通过节流阀降压至约0.55MPa，回到下塔6提供冷量，完成一个循环。
典型工况算例
基于LNG卫星站冷能利用的倒灌式空气分离系统流程得到的主产品为液氧(纯度：0.999)，附带得到大量的氮气产品(纯度：0.9999)。通过对循环氮气的调节，下面根据LNG卫星站实际LNG使用量波动情况，对LNG用量分别为9000kg/h、7000kg/h、5000kg/h和3000kg/h的四种工况进行模拟。这些算例仅用于说明本发明而不用于限制本发明的范围，从本发明简单延伸而未做创造性改变的流程系统及方法均应落于本发明所附权利要求书所限定的范围。
进料空气的初始状态参数为0.1MPa、293K，摩尔组分为(N2：0.781，O2：0.210％，Ar：0.009％)，加工气量为30000kg/h。在模拟计算值中，物性方程选用SRK方程，压缩机等熵效率取0.85，机械效率为0.9。LNG组分按如下组分比例(CH4：82.3％，C2H6：11.2％，C3H8：4.6％，N2：0.8％，其他：1.1％)计算，LNG换热器进口参数取为0.2MPa、112K，出口参数为0.2MPa、263K。流程模拟计算结果如表1所示，其中液氮产量为负值时表示倒灌液氮，单位液体产品能耗定义为总能耗与液氮和液氧总产量的比值，即
Figure GSA00000072738000051
表1流程模拟结果
Figure GSA00000072738000061
从表1中可以看到，在LNG流量为平均流量时(工况3)，系统全部产液氧，无液氮产出；在LNG流量大于平均流量时(工况1、2)，增大循环氮气流量，系统同时生产液氧、液氮，而这部分液氮则贮存于液氮罐中，在LNG流量小于平均流量时(工况4)，倒灌入系统以补足系统所需冷量。循环氮气压缩机进口温度约在253～263K范围内波动，消除了低温压缩的困难。

Claims (2)

1.一种基于LNG卫星站冷能利用的倒灌式空气分离系统，其特征在于包括空气过滤器(1)、空气压缩机(2)、水冷机组(3)、空气纯化器(4)、主换热器(5)、过冷器(9)、氮气压缩机(10)、LNG换热器(11)、天然气压缩机(12)、空气预冷器(13)、LNG储罐(14)、液氮储罐(15)、精馏系统(16)，精馏系统(16)包括下塔(6)、冷凝蒸发器(7)、上塔(8)；空气过滤器(1)与空气预冷器(13)、空气压缩机(2)、水冷机组(3)、空气纯化器(4)、主换热器(5)的进料空气流道、下塔(6)下部进料空气进口依次相连，上塔(8)顶部的产品氮气出口与过冷器(9)、主换热器(5)的产品氮气流道、空气预冷器(13)依次相连，下塔(6)上端部的循环氮气出口与主换热器(5)的冷循环氮气流道、氮压缩机(10)、水冷机组(3)、LNG换热器(11)的循环氮气流道、主换热器(5)的热循环氮气流道、下塔(6)上端部的循环氮气进口依次相连，冷凝蒸发器(7)液氮出口分为两路，冷凝蒸发器(7)液氮出口一路与液氮储罐(15)、精馏系统(16)的下塔(6)端部的倒灌液氮进口依次相连，冷凝蒸发器(7)液氮出口另一路与过冷器(9)、上塔(8)的液氮进口依次相连，下塔(6)底部的富氧液空出口与过冷器(9)、上塔(8)的富氧液空进口依次相连，LNG储罐(14)与LNG换热器(11)的LNG流道、天然气压缩机(12)依次相连。
2.一种使用如权利要求1所述系统的基于LNG卫星站冷能利用的倒灌式空气分离方法，其特征在于进料空气经空气过滤器(1)过滤，与空气预冷器(13)中的产品氮气和污氮气换热后，进入空压机(2)加压至0.58MPa，水冷至293K后进入空气纯化器(4)除去其中的水分和二氧化碳，进入主换热器(5)被循环氮气、产品氮气和污氮气冷却，进入下塔(6)底部精馏，下塔(6)内空气与回流液氮在多层塔板上反复冷凝和蒸发，下塔底部积聚富氧液空，富氧液空通过过冷器(9)过冷，经节流阀降压至0.13～0.14MPa，进入上塔(8)提供上塔冷量；下塔上端部富集的氮气通过冷凝蒸发器(7)冷凝成液氮，当LNG用量小于LNG卫星站LNG平均用量时，冷凝成的液氮全部经过冷器(9)进一步降温，再经液氮节流阀降压至0.13～0.14MPa，进入上塔(8)顶部作为上塔的回流液体；当LNG用量大于LNG卫星站LNG平均用量时，冷凝成的液氮一部分经过冷器(9)进一步降温，经液氮节流阀降压至0.13～0.14MPa，进入上塔(8)顶部作为上塔的回流液体，冷凝成的液氮另一部分进入液氮储罐(15)储存，当LNG用量小于LNG卫星站LNG平均用量时，液氮储罐(15)储存的液氮倒灌进入下塔(6)，补充冷量，以维持系统稳定运行；上塔(8)顶部的产品氮气以及上塔中上部的污氮气经过过冷器(9)回收部分冷量，进入主换热器(5)，冷却进料空气和过冷经过LNG换热器后的循环氮气，再与压缩前的进料空气换热，充分利用其残余的冷量，使进入空气压缩机(2)的空气温度降低至273K～280K，以减小空气压缩机(2)的能耗；下塔(6)上端部的循环氮气经过主换热器(5)冷却进料空气，温度升至253K～263K的循环氮气进入氮压缩机(10)加压至3.3MPa，经冷水机组(3)降温后，进入LNG换热器(11)吸收LNG的汽化潜热和复温显热，循环氮气液化后进入主换热器(5)继续与产品氮气、污氮气以及循环氮气换热，得到的过冷液氮通过节流阀降压至0.55MPa，回到下塔(6)提供冷量。
CN2010101410715A 2010-04-06 2010-04-06 基于lng卫星站冷能利用的倒灌式空气分离系统及方法 Expired - Fee Related CN101839612B (zh)

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