CN108731375A - 一种二氧化碳预冷单级氮膨胀的小型天然气液化*** - Google Patents
一种二氧化碳预冷单级氮膨胀的小型天然气液化*** Download PDFInfo
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Abstract
本发明提供了一种二氧化碳预冷单级氮膨胀的小型天然气液化***，包括：二氧化碳膨胀预冷循环、氮气膨胀制冷循环以及天然气液化模块。所述二氧化碳膨胀预冷循环通过二氧化碳两级增压冷却、预冷及膨胀制冷依次为第一级冷却器、二氧化碳换热器提供冷量并实现循环；氮气膨胀制冷循环通过氮气两级压缩冷却、预冷、膨胀降温依次为第二级冷却器、第一级冷却器提供冷量并实现循环；天然气液化模块在第一级冷却器实现预冷，除去重烃后在第二级冷却器得以进一步降温，经过节流阀降压和气液分离得到液化天然气。本发明采用非碳氢化合物作为制冷剂，降低了作业风险，结构简单、流程紧凑，对边际天然气的液化回收有较强的适应性。
Description
技术领域
本发明涉及天然气液化领域，具体而言，涉及一种二氧化碳预冷单级氮膨胀的小型天然气液化***。
背景技术
边际天然气的回收利用可有效降低气体放空量，减少环境污染，增加天然气生产能力。由于远离已建天然气管道或管道建设并不经济，小型天然气液化***是边际天然气的有效回收方式之一。边际气田产量较低、经济收益小、抗风险能力差，小型天然气液化***对流程操作简便性、安全性及经济性的要求更为迫切。
混合冷剂液化流程和氮膨胀液化流程是小型天然气液化***的主要形式。尽管混合冷剂流程能耗较低，混合制冷剂的合理配比是生产管理中的难点，制冷剂组分需与来气条件、工况条件相匹配，流程操作复杂；采用碳氢化合物作为制冷剂，装置布置不利于流程的紧凑设计；此外，混合冷剂通过冷凝、蒸发和节流膨胀产生冷量，其相态在流程中可能处于气相、液相或两相区，海水流动引起的平台晃荡会导致制冷剂在管段或设备中的分配并不均匀，显著影响换热效率，流程对海上使用的适应性差。氮膨胀流程无碳氢制冷剂处理和储存需求，流程紧凑性和生产安全性得到保障；流程循环过程中制冷剂始终处于气相，平台晃荡对换热效率的影响程度较小；流程操作简单、启停方便，满足了小型天然气液化***对生产安全性、流程紧凑性和操作简便性的要求，但该流程的能耗较高。
综上可知，现有技术未考虑小型天然气液化***对陆上撬装和海上使用的综合适应性，在流程紧凑性、生产安全性、操作简便性和能耗上均存在不同程度的不足。
发明内容
本发明的目的在于克服上述现有技术存在的不足，提供一种二氧化碳预冷单级氮膨胀的小型天然气液化***。该发明以非碳氢化合物作为制冷剂，降低了作业风险，结构简单、流程紧凑，对边际天然气的液化回收有较强的适应性。
为实现上述目的，本发明提供一种二氧化碳预冷单级氮膨胀的小型天然气液化***，包括：二氧化碳膨胀预冷循环、氮气膨胀制冷循环以及天然气液化模块，其中：
所述二氧化碳膨胀预冷循环通过二氧化碳两级增压冷却、预冷及膨胀制冷为第一级冷却器、二氧化碳换热器提供冷量并实现循环；
所述氮气膨胀制冷循环通过氮气两级压缩冷却、预冷、膨胀降温依次为第二级冷却器、第一级冷却器提供冷量并实现循环；
所述天然气液化模块在第一级冷却器实现预冷，通过初级分离器脱除重烃，其中液相经过第一级节流阀节流降温后返回第一级冷却器提供冷量，气相进入第二级冷却器进一步降温，经过第二级节流阀过冷后进入二级分离器，其气相依次返回第二级冷却器、第一级冷却器复热，液相即为产品液化天然气。
与现有技术相比，本发明的有益效果在于：
本发明所述的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，结构简单、流程紧凑；与膨胀式流程相比，比功耗大幅度下降；以非碳氢化合物作为制冷剂，具有无毒、无刺激性、无燃烧性及***性的优点，降低了作业风险；采用单一介质作为制冷剂分别实现预冷和制冷功能，无制冷剂配比问题，降低了流程作业复杂度；同时，制冷剂在运行过程始终处于气相，受平台晃动影响较小，可用于海上平台液化使用。
附图说明
图1是本发明提供的一种二氧化碳预冷单级氮膨胀的小型天然气液化***的工艺流程图。
附图标记说明：
101为经过预处理的天然气，102为经过第一级冷却器（HEX-101）预冷的天然气，103为初级分离器（V-101）流出的气相，104为初级分离器（V-101）脱除的重烃，105为经过一级节流阀（VLV-101）节流降温后的重烃，106为复热后的重烃，107为经过第二级冷却器（HEX-102）的天然气，108为第二级节流阀（VLV-102）过冷后的两相混合物，109-LNG为二级分离器（V-102）得到的产品液化天然气，110为二级分离器（V-102）流出的气相，111为返回第二级冷却器（HEX-102）复热的天然气，112为返回第一级冷却器（HEX-101）复热的天然气；201为氮气，202为经过氮气一级压缩机（C-201）增压后的氮气，203为经过氮气一级水冷器（WC-201）冷却后的氮气，204为经过氮气二级压缩机（C-202）增压后的氮气，205为经过氮气二级水冷器（WC-202）冷却后的氮气，206为经过第一级冷却器（HEX-101）预冷的氮气，207为经过氮气膨胀机（EX-201）膨胀降温的氮气，208为第二级冷却器（HEX-102）提供冷量；301为二氧化碳，302为经过二氧化碳一级压缩机（C-301）增压后的二氧化碳，303为经过二氧化碳一级水冷器（WC-301）冷却后的二氧化碳，304为经过二氧化碳二级压缩机（C-302）增压后的二氧化碳，305为经过二氧化碳二级水冷器（WC-302）冷却后的二氧化碳，306为经过二氧化碳换热器（E-301）预冷的二氧化碳，307为经过二氧化碳膨胀机（EX-301）膨胀制冷的二氧化碳，308为第一级冷却器（HEX-101）提供冷量。
具体实施方式
下面结合具体实施例对本发明进行详细说明。以下实施例将有助于本领域的技术人员进一步理解本发明，但不以任何形式限制本发明。应当指出的是，对本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变化和改进。这些都属于本发明的保护范围。
本发明提供的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其工艺流程如图1所示，该***包括二氧化碳膨胀预冷循环、氮气膨胀制冷循环以及天然气液化模块。
所述二氧化碳膨胀预冷循环包括二氧化碳一级压缩机（C-301）和依次相连的二氧化碳一级水冷器（WC-301）、二氧化碳二级压缩机（C-302）、二氧化碳二级水冷器（WC-302）、二氧化碳换热器（E-301）、二氧化碳膨胀机（EX-301）。
所述氮气膨胀制冷循环包括氮气一级压缩机（C-201）和依次相连的氮气一级水冷器（WC-201）、氮气二级压缩机（C-202）、氮气二级水冷器（WC-202）、氮气膨胀机（EX-201）。
所述天然气液化模块包括第一级冷却器（HEX-101）和依次相连的初级分离器（V-101）、第一级节流阀（VLV-101）、第二级冷却器（HEX-102）、第二级节流阀（VLV-102）、二级分离器（V-102）；所述第一级冷却器（HEX-101）、第二级冷却器（HEX-102）为多股流换热器；所述初级分离器（V-101）流出的气相与第二级冷却器（HEX-102）相连，液相与第一级节流阀（VLV-101）相连；所述二级分离器（V-102）流出的气相与第二级冷却器（HEX-102）相连，液相为产品液化天然气。
应用本发明的一种二氧化碳预冷单级氮膨胀的小型天然气液化***的方法具体见以下实施例：
天然气摩尔组分82% CH4 + 11.2% C2H6 + 4% C3H8 + 1.2% i-C4H10 + 0.9% n-C4H10 +0.7% N2、压力4.0MPa、温度35℃、流量440.6kmol/h，一种二氧化碳预冷单级氮膨胀的小型天然气液化***的具体步骤如下：
1.二氧化碳膨胀预冷循环中，二氧化碳（301）初始压力0.96MPa、温度22℃、流量391.7kmol/h，经二氧化碳一级压缩机（W-301）压缩至2.23MPa/93℃，二氧化碳一级水冷器（WC-301）降温至35℃，二氧化碳二级压缩机（W-302）压缩至5.55MPa/116℃，二氧化碳二级水冷器（WC-302）降温至35℃，由二氧化碳换热器（E-301）预冷至20℃后，进入二氧化碳膨胀机（EX-301）膨胀降温至-15℃以完成循环，并依次为第一级冷却器（HEX-101）、二氧化碳换热器（E-301）提供冷量；
2.氮气膨胀制冷循环中，氮气（201）初始压力0.77MPa、温度31℃、流量2391kmol/h，经氮气一级压缩机（W-201）压缩至1.61MPa/116℃，氮气一级水冷器（WC-201）降温至35℃，氮气二级压缩机（W-202）压缩至3.86MPa/139℃，氮气二级水冷器（WC-202）降温至35℃，由第一级冷却器（HEX-101）预冷至-68℃后，进入氮气膨胀机（EX-201）膨胀降温至-133℃，依次为第二级冷却器（HEX-102）、第一级冷却器（HEX-101）提供冷量；
3.天然气液化模块中，天然气经第一级冷却器（HEX-101）冷却到-27℃，流出初级分离器（V-101）的气相部分由第二级冷却器（HEX-102）降温至-132℃，经第二级节流阀（VLV-102）过冷后进入二级分离器（V-102），得到的液相即为产品液化天然气，其压力0.20MPa、温度-151℃。
经模拟计算得出，该发明实施例一种二氧化碳预冷单级氮膨胀的小型天然气液化***的比功耗为30278kJ/kmol，与氮膨胀流程相比能耗下降50%以上。
因此，与混合冷剂流程相比，本发明采用非碳氢化合物作为制冷剂，具有无毒、无刺激性、无燃烧性及***性的优点，降低了作业风险，采用单一介质作为制冷剂分别实现预冷和制冷功能，无制冷剂配比问题，降低了流程作业复杂度；与氮膨胀流程相比，本发明在保留其投资较少、流程紧凑、结构简单、作业风险低等优点的基础上，弥补了能耗较高的缺陷，在流程紧凑性、生产安全性、操作简便性和能耗方面优点显著。
以上对本发明的具体实施例进行了描述。需要理解的是，本发明并不局限于上述特定实施方式，本领域技术人员可以在权利要求的范围内做出各种变形或修改，这并不影响本发明的实质内容。
Claims (6)
1.一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其特征在于，包括：二氧化碳膨胀预冷循环、氮气膨胀制冷循环以及天然气液化模块，其中：
所述二氧化碳膨胀预冷循环通过二氧化碳两级增压（C-301、C-302）冷却（WC-301、WC-302）、预冷（E-301）及膨胀制冷（EX-301）为第一级冷却器（HEX-101）、二氧化碳换热器（E-301）提供冷量并实现循环；
所述氮气膨胀制冷循环通过氮气两级压缩（C-201、C-202）冷却（WC-201、WC-202）、预冷（HEX-101）、膨胀降温（EX-201）依次为第二级冷却器（HEX-102）、第一级冷却器（HEX-101）提供冷量并实现循环；
所述天然气液化模块在第一级冷却器（HEX-101）实现预冷，通过初级分离器（V-101）脱除重烃，其中液相经过第一级节流阀（VLV-101）节流降温后返回第一级冷却器（HEX-101）提供冷量，气相进入第二级冷却器（HEX-102）与氮气换热得以进一步降温，经过第二级节流阀（VLV-102）过冷后进入二级分离器（V-102），其气相依次返回第二级冷却器（HEX-102）、第一级冷却器（HEX-101）复热，液相即为产品液化天然气。
2.根据权利要求1所述的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其特征在于：所述天然气液化模块，天然气进入第一级冷却器（HEX-101）前满足石油天然气行业标准《天然气液化工厂设计建造和运行规范第1部分：设计建造（SY/T 6933.1-2013）》中关于水、二氧化碳及重烃等杂质的净化指标。
3.根据权利要求1所述的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其特征在于：所述天然气液化模块，流入初级分离器（V-101）天然气的温度及压力设置应结合不同小型天然气田气质组分，满足气液两相的要求，以保证初级分离器（V-101）的功能实现。
4.根据权利要求1所述的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其特征在于：所述天然气液化模块，流入二级分离器（V-102）天然气的温度及压力设置应结合不同小型天然气田气质组分，满足气液两相的要求，以保证二级分离器（V-102）的功能实现。
5.根据权利要求1所述的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其特征在于：所述二氧化碳压缩机（C-301、C-302）、氮气压缩机（C-201、C-202）压比在2-3之间，二氧化碳膨胀预冷循环与氮气膨胀制冷循环均采用两级增压。
6.根据权利要求1所述的一种二氧化碳预冷单级氮膨胀的小型天然气液化***，其特征在于：所述第一级冷却器（HEX-101）、第二级冷却器（HEX-102）、二氧化碳换热器（E-301）最小温差不小于2℃。
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