CN107990630B - 天然气液化系统、降低压缩机功率消耗的方法及于再液化中的应用 - Google Patents

天然气液化系统、降低压缩机功率消耗的方法及于再液化中的应用 Download PDF

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CN107990630B
CN107990630B CN201711143415.4A CN201711143415A CN107990630B CN 107990630 B CN107990630 B CN 107990630B CN 201711143415 A CN201711143415 A CN 201711143415A CN 107990630 B CN107990630 B CN 107990630B
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heat exchanger
ejector
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outlet
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CN107990630A (zh
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刘国满
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赵锐
杨培智
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Guohong Liquefied Gas Machinery Engineering (dalian) Co Ltd
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Abstract

天然气液化系统、降低压缩机功率消耗的方法及于再液化中的应用，属于天然气能源领域，为了能够解决降低天然气系统的能源消耗的问题，技术要点是：包括换热器、压缩机组、喷射器，所述的换热器为多段换热器，换热器连接压缩机组，压缩机组下游的连接管路其上具有两个以上的并行的出口，每一出口连接一出口管路，每一路出口管路连接一喷射器的入口，每一喷射器的出口连接一段换热器的蒸发腔，喷射器中至少有两个喷射器的容量不同，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的那一段换热器的蒸发腔。

Description

天然气液化系统、降低压缩机功率消耗的方法及于再液化中 的应用
技术领域
本发明属于天然气能源领域，涉及一种天然气液化系统。
背景技术
近年来，非发达国家天然气出口越来越多。由于FLNG解决方案具有下列优势，因而得到越来越多的业主的重视。FLNG的优势：1.减少码头建设费用，如果气源是来自于陆地，只需要一个供气管连接到FLNG上。如果气源直接连接到海上气田，FLNG更是独一无二。2.减少当地征地的不确定性。3.所有液化、储存、装卸等全部在FLNG上，而FLNG可在工业发达地区建造，避免了建造成本和建造周期的不可预见性。4.灵活，当某个地区气源枯竭，可以移到其他地区生产。5.规避风险，当某地发生动荡，可以及时移走，减少业主损失。由于海上浮式装置的特点，建造成本较低且设备较少的混合制冷剂系统不适合FLNG使用环境。阶梯或级联液化系统最适合大型FLNG应用场合。由于以前的液化工厂主要考虑投资回报率，并没有把资源消耗成本更多地计算在内，也就是说，只要投资少回报高，资源消耗放在次要位置。但是随着能源输出国对本国资源的重视，液化系统能源消耗成本也逐步上升，业主不得不重视系统的能源消耗。
发明内容
为了能够解决降低天然气系统的能源消耗的问题，本发明提出如下技术方案：一种天然气液化系统，包括换热器、压缩机组、喷射器，所述的换热器为多段换热器，换热器连接压缩机组，压缩机组下游的连接管路其上具有两个以上的并行的出口，每一出口连接一出口管路，每一路出口管路连接一喷射器的入口，每一喷射器的出口连接一段换热器的蒸发腔，喷射器中至少有两个喷射器的容量不同，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的那一段换热器的蒸发腔。
所述的各段换热器连接的喷射器，其容量为由上至下依次降低。
所述的各段换热器具有上、下两段蒸发腔，喷射器的出口连接在各段换热器的下段蒸发腔，各段换热器的上段蒸发腔的出口连接压缩机组，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的换热器的上段蒸发腔。
所述压缩机组与喷射器入口之间的连接管道安装有凝液收集罐。
在所述压缩机组的下游的连接管道安装海水换热器，所述海水换热器安装在所述凝液收集罐的上游，吸入管路安装截止止回阀，喷射器入口与凝液收集罐之间的管路安装调节阀。
所述出口管路具有一路连接在过冷盘管的一端，过冷盘管的另一端连接在某一喷射器的吸入端，所述喷射器为各喷射器中容量最小的喷射器。
在所述压缩机组的下游的连接管道安装海水换热器，所述海水换热器安装在所述凝液收集罐的上游，吸入管路安装截止止回阀，喷射器入口与凝液收集罐之间的管路安装调节阀，所述容量最小的喷射器的吸入管路安装截止止回阀。
本发明还涉及一种天然气液化系统降低压缩机功率消耗的方法，在多段换热器中，各换热器段对应不同功率压缩机，在换热器能利用膨胀功的节流降压/降温的节点增设喷射器，具有较高容量的喷射器吸入端连接具有较低容量的喷射器对应连接的换热器段，并吸入由该换热器段对应的较低容量的喷射器排出且已经在该换热器段吸热的气体，使较低压力的气体压力提高而使相应的压缩机功率消耗降低。
所述的天然气液化系统在天然气再液化中的应用。
有益效果：本发明主要针对经典阶梯液化系统在降低能源消耗方面的改进，且该改进使系统模块建造成本有限增加的前提下，而且比膨胀机系统制造成本低、可靠性高。尽管喷射器在其它种类的液化系统中均有使用，如高压射流系统采用喷射器等，但均不同于本系统发明所采用的方法，本发明采用喷射器的目的在于利用其喷射能力，形成分级喷射，以减少压缩机做功。
附图说明
图1源料气供给压力等于35bara的液化系统；
图2源料气供给压力低于35bara的液化系统；
图3源料气供给压力高于35bara的液化系统；
图4多个喷射器并联方法的示意图；
图5再液化系统；
图中：101A/B---甲烷/LNG喷射器；102H/L---乙烯喷射器；103H/M/L---丙烷喷射器；201---自动关断阀；301/302/303调节阀；401/402/403---截止止回阀；501---膨胀阀；BOOST COMP---增压压缩机；METHANE COMP---甲烷/天然气压缩机；ETHYLENE COMP---乙烯压缩机；PROPANE COMP---丙烷压缩机；EXC-1---换热器；EXC-2---换热器；EXC-3---换热器；PROPANE CONDENSER---丙烷冷凝器；ETHYLENE COOLER---乙烯冷却器；METHANECOOLER---甲烷冷却器；V/L SEPARATOR---气/液分离罐；LIQUID RECEIVER---凝液收集罐；CONDENSATE TANK---凝结罐。
具体实施方式
实施例1：如图所示1所示，为了在现有技术(经典阶梯系统和优化阶梯系统)中进一步减少能源消耗，本发明包括四种满足不同介质喷射的喷射器，分别满足不同膨胀压力的甲烷、LNG(气源气)、乙烯、丙烷液气区，即湿区膨胀要求。
在阶梯系统中，包括甲烷部分、乙烯部分、丙烷部分，在甲烷部分，甲烷换热器通入冷却介质BOG为通入其中的被冷却介质天然气降温，所述天然气一路是来自气源气，气源气作为被冷却介质直接通入丙烷换热器与冷却介质丙烷换热，后通入乙烯换热器，在其中与冷却介质乙烯换热，后通入甲烷换热器作为被冷却介质；另一路是来自上述BOG，该BOG作为冷却介质在换热后被压缩机吸入加压，并由冷却器冷却再通入丙烷换热器作为被冷却介质换热，后通入乙烯换热器，在其中与冷却介质乙烯换热，后通入甲烷换热器作为被冷却介质。所述甲烷换热器中的被冷却介质天然气与冷却介质BOG换热后被喷射器喷射至气液分离罐，后通入凝结罐。
在乙烯部分，乙烯换热器通入冷却介质乙烯为通入其中的上述的被冷却介质天然气换热，乙烯作为冷却介质在换热后被压缩机吸入加压，并由冷却器冷却再通入丙烷换热器作为被冷却介质换热，后由喷射器喷射至乙烯换热器成为通入的乙烯换热器的冷却介质。
在丙烷部分，丙烷换热器通入冷却介质丙烷为通入其中的上述的被冷却介质天然气换热，丙烷作为冷却介质在换热后被压缩机吸入加压，并由冷却器冷却再通入丙烷换热器成为冷却介质丙烷。
由上述方案：
乙烯部分的喷射器包括高压段喷射器102H和低压段喷射器102L,丙烷部分的喷射器又分高压段喷射器103H、中压段喷射器103M和低压段喷射器103L。喷射器103H吸入端连接到并吸入喷射器103M排出且已经在换热器EXC-3M段吸热的气体，喷射器103M吸入端连接到并吸入喷射器103L排出且已经在换热器EXC-3L段吸热的气体，喷射器103L吸入端连接到乙烯过冷盘管出口。喷射器102H吸入端连接到并吸入喷射器102L排出且已经在换热器EXC-2L段吸热的气体，喷射器102L连接到并吸入天然气/甲烷过冷盘管出口。使以上四种介质湿区膨胀过程的熵增减少而使膨胀过程接近等焓过程，且把部分低压区的气体压缩到较高压力区段，使相应的循环压缩机能耗降低。
尽管喷射器，以及液体膨胀机在其它种类的液化系统中均有使用，如高压射流系统采用喷射器等，但均不同于本系统发明所采用的方法，在现有技术中，喷射器用于喷射增压，而本发明选用喷射器以配合容量不同、吸入管路的连接，其作用为减少压缩机功率。
为了节省能耗，做出下列改进：丙烷压缩机PROPANE COMP.分三段吸入，相应换热器EXC-3分三段膨胀热交换。乙烯压缩机ETHYLENE COMP.分两段吸入，相应换热器EXC-2分两段膨胀热交换。甲烷/天然气压缩机，可分两段、三段或四段吸入，相应换热器也相同段数。主要取决于源料气供给压力，以及是液化系统还是再液化系统。对于再液化系统不存在源料气供给问题，系统均一样；对于液化系统来说，本发明规定三种不同情况：供给压力等于35bara、供给压力低于35bara、供给压力高于35bara。供给压力低于35bara时，增加一个压缩机，把压力提高到35bara；供给压力高于35bara时，采用两个不同压力等级的喷射器
本发明主要针对经典阶梯液化系统在降低能源消耗方面的改进，且该改进使系统模块建造成本有限增加的前提下，而且比膨胀机系统制造成本低、可靠性高。尽管喷射器在其它种类的液化系统中均有使用，如高压射流系统采用喷射器等，但均不同于本系统发明所采用的方法，本发明采用喷射器的目的在于利用其喷射能力，形成分级喷射，以减少压缩机做功。作为进一步的效果，其燃气消耗比经典阶梯系统降低20％以上。
实施例2：图1-4中,丙烷压缩机PROPANE COMP分三段吸入，吸入压力分别为1.4bara、3.45bara、7.3bara,排出压力13.6bara,经过丙烷冷凝器PROPANE CONDENSER后冷凝且收集到收集罐LIQUID RECEIVER PROPANE内，经过三个不同膨胀压力/温度的喷射器103H/103M/103L分别进入换热器EXC-3H/M/L用于冷却乙烯、甲烷、天然气，进入为+40℃,出口-30℃,乙烯在出口冷凝。另外一路乙烯过冷盘管，用于过冷冷凝的乙烯外，其作用是为喷射器103L提供消耗动能的气体。乙烯压缩机ETHYLENE COMP分两段吸入，吸入压力为5.3bara,排出压力20bara,经过乙烯冷却器ETHYLENE COOLER、换热器EXC-3冷凝且收集到收集罐LIQUID RECEIVER ETHYLENE内，在收集罐LIQUID RECEIVER ETHYLENE内过冷。经过换热器EXC-3的乙烯、甲烷和天然气均冷却到-30℃。过冷的乙烯经过两个不同膨胀压力/温度的喷射器102H/102L分别进入换热器EXC-2H/L用于冷却甲烷和天然气，另外一路甲烷/天然气过冷盘管，用于过冷冷凝的乙烯外，其作用是为喷射器102L提供消耗动能的气体。
本系统把压缩机循环的介质定义为“甲烷”，实际上是液化天然气中蒸发的BOG，只是甲烷含量高一些。外部天然气供应定义为“天然气”，即气源气。
换热器EXC-2H/L用于进一步冷却(冷凝)甲烷和天然气，进入为-30℃,出口-95℃,甲烷和天然气在出口冷凝,再经过过冷盘管过冷进入喷射器101A/B，喷射器101A/B吸入从凝结罐CONDENSER TANK分离出的气体，喷射器101A/B出口气/液分离罐V/L SAPARATOR压力为2—2.5bara，气/液分离罐V/L SAPARATOR中的液体通过膨胀阀501进入凝结罐CONDENSERTANK进一步降温/压使之达到全部液化。从气/液分离罐V/L SAPARATOR分离出的气体被压缩机吸入
实施例3：本实施例详细描述整个液化过程，乙烯的换热器与乙烯的压缩机连接，乙烯的压缩机连接海水换热器，通过海水换热器的乙烯通入丙烷的换热器中降温、减压，并在乙烯的凝液收集罐中进一步降温，两路连接喷射器，由喷射器喷射至乙烯的换热器的蒸发腔，第三路连接天然气的凝液回收罐的过冷盘管的一端，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的那一段换热器的蒸发腔，以将较低容量喷射器对应的换热器的中的乙烯转移至较高容量的喷射器对应的换热器中，较低容量的喷射器的吸入端连接在过冷盘管的另一端，气源气及天然气在丙烷的换热器中换热后通入乙烯的换热器换热，并与天然气的凝液收集罐的过冷盘管换热后，通入天然气的换热器中，并由喷射器喷射至气液分离罐，在存储在凝结罐中；
天然气的换热器中通入BOG，并在换热器中与来自乙烯换热器中的天然气与气源气换热，通入天然气压缩机，在通入海水换热器，并由海水换热器通入丙烷的换热器中降温减压；
由上，丙烷的换热器中通入了用于降温的乙烯、天然气、气源气，丙烷的换热器连接丙烷的压缩机组，与丙烷压缩机组出口连接的管路安装海水换热器，海水换热器的下游安装丙烷的凝液收集罐，凝液收集罐的出口连接管路具有并行出口，所述出口通过各出口管路连接在对应的喷射器的入口，各喷射器的出口连接在其对应段换热器的蒸发腔，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的那一段换热器的蒸发腔，丙烷的凝液换热器的出口管路具有一路连接在过冷盘管的一端，过冷盘管的另一端连接在某一喷射器的吸入端，所述喷射器为各喷射器中容量最小的喷射器。
由上述方案，实现了气源气在丙烷、乙烯、天然气的换热器中逐级进行换热以降温减压，而乙烯也在丙烷的换热器中进行换热以降温减压；从而气源气在乙烯换热器中能够更大程度的降温减压，而天然气又在乙烯换热器中进行换热以降温减压，从而气源气与天然气在与BOG换热时，等量的BOG能够与更多的天然气与气源气换热以达到相同的降温减压的目的。而凝液收集罐中的过冷盘管的目的是为了进一步利用更为低温的换热介质再一次对已经换热并即将输出作为的换热介质的介质再一次降温减压，以最大程度利用冷能，这种精细的降温减压的手段，逐级精细执行使得冷能的利用率积累提高，并成为效果可观的一种节能方式。
由该过程，一种改进型天然气液化系统，对经典阶梯液化系统进行了改进，与传统液化系统相比，在能利用膨胀功的三个节流降压/降温的节点增设喷射器，以减少膨胀过程的熵增、通过将较低压力的气体压力提高而使相应的压缩机功率消耗降低。每个喷射器的驱动端通过调节阀与冷剂冷凝收集罐连接，喷射器吸入端与较低一段蒸发段顶部相连，喷射器出口与换热器蒸发腔相连。
所述的三个节流降压/降温节点之一甲烷和液化天然气节点设置喷射器(101A/101B)，且所述喷射器(101A/B)可根据不同场合设置一个或多个不同容量的喷射器。
三个节流降压/降温节点之一的乙烯节点设置喷射器(102H/102M/102L),且所述喷射器可根据不同应用场合设置一个或多个不同容量的喷射器。
所述的乙烯节流降压/降温节点中最低膨胀压力/温度点，喷射器吸入端连接到过冷盘管，用于进一步冷却已经冷凝的甲烷和天然气。
所述的另一个节流降压/降温节点，即丙烷节点设置喷射器(103H/103M/103L)，且所述喷射器可根据不同应用场合设置一个或多个不同容量的喷射器。
所述的丙烷节流降压/降温节点中最低膨胀压力/温度点，喷射器吸入端连接到过冷盘管，用于进一步冷却已经冷凝的乙烯。
本改进型液化系统，将甲烷/天然气压缩机的BOG级吸入端串联在换热器EXC-1中，利用储存舱和/或装卸货返回气的冷能使冷凝的甲烷/天然气过冷，提高液化比例。所述喷射器喉径均为自动调节，保证工况变动时系统效率。
在一个实施例中，该液化系统可以被用于再液化系统中，即本发明不排除改进型LNG阶梯再液化系统。
以上所述，仅为本发明创造较佳的具体实施方式，但本发明创造的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明创造披露的技术范围内，根据本发明创造的技术方案及其发明构思加以等同替换或改变，都应涵盖在本发明创造的保护范围之内。

Claims (7)

1.一种天然气液化系统，包括换热器、压缩机组、喷射器，其特征在于，所述的换热器为多段换热器，换热器连接压缩机组，压缩机组下游的连接管路其上具有两个以上的并行的出口，每一出口连接一出口管路，每一路出口管路连接一喷射器的入口，每一喷射器的出口连接一段换热器的蒸发腔，喷射器中至少有两个喷射器的容量不同，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的那一段换热器的蒸发腔；所述的各段换热器具有上、下两段蒸发腔，喷射器的出口连接在各段换热器的下段蒸发腔，各段换热器的上段蒸发腔的出口连接压缩机组，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的换热器的上段蒸发腔；所述压缩机组与喷射器入口之间的连接管道安装有凝液收集罐。
2.如权利要求1所述的天然气液化系统，其特征在于，所述的各段换热器连接的喷射器，其容量为由上至下依次降低。
3.如权利要求1所述的天然气液化系统，其特征在于，在所述压缩机组的下游的连接管道安装海水换热器，所述海水换热器安装在所述凝液收集罐的上游，吸入管路安装截止止回阀，喷射器入口与凝液收集罐之间的管路安装调节阀。
4.如权利要求1所述的天然气液化系统，其特征在于，所述出口管路具有一路连接在过冷盘管的一端，过冷盘管的另一端连接在某一喷射器的吸入端，所述喷射器为各喷射器中容量最小的喷射器。
5.如权利要求2所述的天然气液化系统，其特征在于，在所述压缩机组的下游的连接管道安装海水换热器，所述海水换热器安装在所述凝液收集罐的上游，吸入管路安装截止止回阀，喷射器入口与凝液收集罐之间的管路安装调节阀，容量最小的喷射器的吸入管路安装截止止回阀。
6.一种天然气液化系统降低压缩机功率消耗的方法，天然气液化系统，包括换热器、压缩机组、喷射器，其特征在于，所述的换热器为多段换热器，换热器连接压缩机组，压缩机组下游的连接管路其上具有两个以上的并行的出口，每一出口连接一出口管路，每一路出口管路连接一喷射器的入口，每一喷射器的出口连接一段换热器的蒸发腔，喷射器中至少有两个喷射器的容量不同，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的那一段换热器的蒸发腔；所述的各段换热器具有上、下两段蒸发腔，喷射器的出口连接在各段换热器的下段蒸发腔，各段换热器的上段蒸发腔的出口连接压缩机组，具有较高容量的喷射器的吸入端由吸入管路连通另一容量低于其的喷射器所相连的换热器的上段蒸发腔；
在多段换热器中，各换热器段对应不同功率压缩机，在换热器能利用膨胀功的节流降压/降温的节点增设喷射器，具有较高容量的喷射器吸入端连接具有较低容量的喷射器对应连接的换热器段，并吸入由该换热器段对应的较低容量的喷射器排出且已经在该换热器段吸热的气体，使较低压力的气体压力提高而使相应的压缩机功率消耗降低。
7.权利要求1-4任一项所述的天然气液化系统在天然气再液化中的应用。
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