CN1095496C - 液化天然气的生产方法 - Google Patents
液化天然气的生产方法 Download PDFInfo
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- CN1095496C CN1095496C CN 99120786 CN99120786A CN1095496C CN 1095496 C CN1095496 C CN 1095496C CN 99120786 CN99120786 CN 99120786 CN 99120786 A CN99120786 A CN 99120786A CN 1095496 C CN1095496 C CN 1095496C
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- natural gas
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- JYYOBHFYCIDXHH-UHFFFAOYSA-N carbonic acid;hydrate Chemical compound O.OC(O)=O JYYOBHFYCIDXHH-UHFFFAOYSA-N 0.000 claims description 5
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
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Abstract
一种液化天然气的生产方法，以外循环N2经压缩、膨胀制取冷量在换热器内作为冷源，被预处理的原料天然气，在换热器内不断地被冷却，直至液化，经脱N2塔得纯度为99.5%的液态甲烷，可用作机车燃料，在液化过程中同时还生产出另一种副产品重质烃，可用作化工原料或燃料，其液化率可达100%。而从脱N2塔出来的N2气补充到循环N2气中，从而可保证流程中整套装置长期工作的连续性及安全性。
Description
本发明涉及一种天然气的液化方法，特别是一种含高纯度甲烷天然气(LNG)的生产方法。
天然气的主要成分是甲烷，还含少量乙烷和重质烃。它的液化方法很多。于1997年11月12日的中国专利公报上曾公开了一种“在深冷天然气加工厂中生产液化天然气”的发明创造，其公开号为：CN1164890A。这种生产方法是通过将流出深冷工厂的残余气支流作为一种天然气原料，进行被液化来生产液化天然气(LNG)的。该支流最好先在深冷工厂残余气压缩机中进行压缩。用深冷工厂脱甲烷塔顶气(或工厂的类似冷气流)作冷凝介质将该支流——经残余气压缩机压缩过物流，冷凝成液体。然后，让冷凝液体在一系列逐渐降低的压力下利用一个或多个Doule-Tnomson阀进行膨胀，从而使LNG达到便于贮存和运输的温度和压力。该发明方法虽然能充分利用深冷天然气加工厂的残余气支流冷量，又把残余气支流中所含主要成分甲烷液化成为产品，只需要增加少量设备，且基本投资和能耗成本却减至最低，并且，流程简单，操作方便。但是，由于该方法必须有一个深冷天然气加工厂与之相配合，所说的“深冷的”这一术语是指在华氏-50度以下操作的工厂。并且经残余气冷凝器释放出的物流，必须并入管网，这就使该方法产生了很大的局限性。再则，为保证原深冷天然气加工厂的冷量平衡，需增加一个入口冷却器。又由于残余气冷凝器中利用的冷量是有限的，故此，液化率较低。并且液化天然中含甲烷的纯度不高约为98.5％，而含有甲烷98.81％及98.72％的另两股物流，却被并入管网作燃料使用，是一种浪费。再说由于利用膨胀入口分离器中的气相馏份去膨胀机膨胀，产生气液混合物，这种现象在膨胀过程中是不允许出现的，这是因为液体的产生，会把高速旋转的膨胀机叶轮损坏，造成不应有的损失。
本发明的目的在于提供一种液化天然气的生产方法，它能使气态天然气缩小625倍成液态，含甲烷纯度99.5％，便于贮存、运输，这种高纯度的甲烷液体，可代替汽油，供各类机车的燃料，从而可避免机车尾气污染环境，同时，液态天然气在汽化时，产生的冷量可达121kcal/kg，温度为-162℃，可用于食品速冻保鲜，橡胶轮胎低温粉碎及空调的冷源，在充分利用其冷量之后，再并入燃气管网被使用，经济效益更显著。另外，还同时生产出另一种副产品重质烃，可用作化工原料或燃料。
本发明液化天然气的生产方法是：将天然气物流进行预处理：即在碱液洗涤设备中洗涤、脱硫、脱碳，经冷凝设备冷却，经分离设备分离，除去硫化氢、二氧化碳及水，并干燥，以产生原料天然气物流；其中所说的天然气物流包括来自油田气井喷出的天然气，或煤田在采煤之前排放的瓦斯气，或发现贮有量不大的气井及边远的架设管道不方便、不经济的气井中的天然气。
将所说的原料天然气物流在换热器中被冷却、液化。当冷却到一定温度时，混在原料天然气物流中的高碳烷烃类如乙烷、丙烷、丁烷、乙稀等首先被液化，经分离设备分离出来为副产品，贮存。所说的“一定温度”与压力有关，它可从有关图表中查得。分离出高碳烷烃类后的物流继续冷却被液化，并进入脱N2塔中提纯，脱去物流中的N2气，从塔釜中引出产品99.5％高纯度的液态甲烷(LNG)。
其中所说换热器中的冷量靠外循环N2经压缩、膨胀、制冷来提供。当循环N2在换热器中把冷量传给天然气物流的同时N2本身被复热，又经压缩、膨胀、制冷，如此周而复始循环。其中所说在脱N2塔中的提纯是由来自所说换热器中的液态天然气物流，在脱N2塔釜中被汽化，形成塔中上升气相馏份，与塔顶下流的N2液相馏份，它们二者共同起精馏作用来完成的。
由于本发明采用上述生产方法，所以它具有如下的优点：
(1)原料天然气能全部被液化，其液化率达100％，并且不受原料天然气组份变化的限制。在生产过程中，一些高沸点的组份如乙烷、丙烷、丁烷、乙稀等被先液化，并分离出来为副产品，可作为化工原料或作燃料。而生产的高纯度99.5％的液态甲烷，用作机车的燃料，其燃烧充分，不排放黑碳杂质，可避免对环境的污染，是一种理想的安全、高效而清洁的燃料。
(2)适用于原料天然气的压力范围广，为0.3-20mpa之间。
(3)用N2作为制冷剂。通过N2压缩、膨胀、循环制冷，将天然气液化，在脱N2塔中提取原料天然气中所含少量的N2，补充N2在循环中的消耗，从而可避免空气与天然气混合，保证整个工艺流程的连续性和安全性。
(4)采用本发明方法所需要的整套装置，可因地制宜的拆迁设置；同时，原料天然气来源广泛，它可来自油田气井喷出的天然气；或是来自采煤之前排放的瓦斯气，或者是来自发现贮有量不大的气井以及边远的架设管道既不方便，又不经济的气井中的天然气。
下面结合实施例进一步详细说明本发明的详细内容。
图1表示液化天然气生产方法的流程图。
图2为应用实例1，表示原料天然气压力为0.3mpa时的液化生产方法流程图。
图3为应用实例2，表示原料天然气压力为20mpa时的液化生产方法流程图。
图4为冷冻机组的原理示意图。
实施例：
图1是采用本发明方法液化天然气的流程图。将来自油田的天然气经公知的碱液洗涤预处理，成为含硫化氢小于5ppm、二氧化碳小于10ppm、水小于10ppm的原料天然气，进入冷冻机组([1])降温，使温度从原来的常温降至4～5℃，被降温了的原料天然气中析出水分，在汽液分离器([2])中被去除，再进入分子筛吸附器([3])，进一步去掉硫化氢、二氧化碳，并干燥，又在主换热器([4])内被冷却到-76℃至-100℃之间，最佳温度为-90℃至-95℃之间，使除甲烷和N2外，其它高碳烷烃类如乙烷、丙烷、丁烷、乙稀、硫化氢等均被液化，在重烃分离器([6])内，这些高碳烷烃类的液体被分离出来，作为副产品收集被利用。净化了的原料天然气在液化换热器([5])内被液化，又经节流阀([7])降压，进入脱N2塔([12])，脱N2后，从塔釜引出纯度为99.5％液态甲烷(LNG)作为产品进入低温LNG贮罐([8])，贮存以便利用。
以上所说常温指的是周围环境温度。
所说的冷冻机组([1])如图4所示，由制冷剂压缩机([42])依次与制冷剂冷凝换热器([43])、膨胀节流阀([44])及制冷剂蒸发换热器([45])连接而构成。采用的制冷剂为氨或氟里昂。若被冷却的原料天然气所需要的冷量大，则采用氨为制冷剂，反之选用氟里昂为制冷剂。而原料天然气所需要的冷量是通过原料天然气每小时所冷却的流量以及原料天然气冷却前后的温差计算而得来的。制冷剂压缩机、制冷剂冷凝换热器及膨胀节流阀均由机组随机购置，但制冷剂蒸发换热器，是通过原料天然气流量、温差及压力来设计和选用的，它可因地制宜采用管式或板翅式。
所说的汽液分离器([2])是按原料天然气最高工作压力设计的，但是最低设计压力推荐不得小于0.6mpa，压力容器制作要符合国家颁布的压力容器规程，容器工作性能要达到汽液分离的目的，常用材料为16MNR压力容器用板材，容器直径为原料天然气进口管管径的5-10倍。
所说的压力指的是压力表上的表压。
所说的分子筛吸附器([3])是由两只可互相切换使用的压力容器组成。 当一个压力容器内的分子筛吸附原料天然气中的硫化氢、二氧化碳及水分时，另一个压力容器处于再生阶段，通入高温的干净氮气，带走硫化氢及二氧化碳和水分，放入大气，使分子筛恢复吸附能力，也可用空气作再生气源，但为了安全，必须把容器抽成真空，才可通入高温空气再生，还可采用原料天然气，用毕再生后的原料天然气不必放空，可作为燃料去加温再生气，至于分子筛的工作阶段和再生阶段的时间，取决于原料天然气中所含杂质的多少，以及采用的分子筛性能，后者，也决定了需要再生气的温度。所说的分子筛必须具有吸附硫化氢、二氧化碳及水等且同时能让别的气体通过的特性；所说的压力容器，其设计压力的选定、制造和材料的选择与汽、液分离器([2])相同。
所说的主换热器([4])、液化换热器([5])，可采用管式换热器，也可采用板翅式换热器，其设计压力取决于原料天然气压力和循环N2的压力，二者间的最高工作压力，考虑工况的变换，取3mpa为设计压力。液化天然气流程的关键是冷量问题，膨胀机产生了冷量而换热器却要充分利用，加大液化，所以对换热器的设计要求较高，当二物流逆流换热时，在换热器的进出口处，二物流的温差不得大于5℃。
所说的重烃分离器([6])其设计压力制作要求与汽液分离器([2])相同，但其材料要适合低温下工作，一般选用不锈钢或铝材，此容器工作起来要容易分离出被液化的高碳烷烃类且排出器外。
所说的脱N2塔([12])是氮(N2)和甲烷(CH4)的精馏塔。此塔的工作压力决定于塔顶N2气到压缩机之间的流程阻力和低压缓冲罐([15])工作压力之和。它为由不锈钢、铝、铜材质制成的压力容器，在其中部有50～60块筛板式塔板。塔顶部是-191.5℃的99.9％的液态N2向下喷淋，底部有一股温度为-155.5℃的甲烷(CH4)气态，并含有原料天然气中所带来的N2组合气流上升，上升的气流与下流的液体，在每一块塔板上起精馏作用，从塔顶引出高纯度99.9％N2气，而从塔釜引出高纯度99.5％液态甲烷(CH4)。这里所说的低压缓冲罐([15])是指设计压力为0.06mpa，容积为10立方米的铁制容器。
所说的低温LNG贮罐([8])，在常压下-162℃状态下工作，设计压力为0.06mpa，容积为200升至2000升，材质为不锈钢或铝材。这里所说的常压是指周围环境大气压。
原料天然气从常温到液态温度的整个过程中的冷量靠N2气的循环来完成。将来自所说低压缓冲罐([15])内的N2气在N2压缩机([16])内压缩成2.5mpa的高压N2气，再在主换热器([4])内冷却至所需要的温度，一路经二次绝热膨胀机([14])、([13])膨胀，产生冷量，在换热器内作为冷源，而N2气被复热到所说的常温，再去压缩机参与循环。
其中所说的“液态温度”是指能使甲烷(CH4)液化的温度，液化温度的数值决定于原料天然气的压力，该压力越高，液化温度也越高，反之，液化温度越低，当原料天然气压力确定时，此液化温度可从有关图表中查得。
其中所说的“冷量”的数值必须满足或大于以下三个要求之和，即：①原料天然气从常温到液态温度所需要的冷量；②原料天然气自进入主换热器([4])直至低温LNG贮罐([8])整个流程及设备都处于低温状态，对周围环境温度的冷量损失，俗称冷损；③N2气循环所产生的冷量在换热器内所产生的不完全换热损失。
其中所说的N2循环量取决于机组的容量，即每小时压缩机的排气量或膨胀机的膨胀量，这里，压缩机的排气量要大于膨胀机的膨胀量。
其中所说的“N2气先压缩成为高压N2气”，该高压N2气的压力确定，根据①已计算了所需的总冷量；②绝热膨胀后的低压(脱N2塔的工作压力)；③确定了的N2循环量，就可以计算出该高压N2气的压力。但是这个高压N2气的压力与循环量要反复核实，N2气压力高，N2循环量可减少，N2气压力低，循环量需增加，可因地制宜而确定，在满足总冷量和机组容量的条件下，N2气压力越低越好，这样，造价便宜、电耗也少。
其中所说的N2“经绝热膨胀”是指两台透平膨胀机串联膨胀降压。
其中所说的“所需要的温度”是指进入膨胀机的入口温度，此温度越高，膨胀后的温度也高，因此此温度必须满足膨胀后的温度能达前面所述的原料天然气的液化温度的要求。所以需要冷却到所需的温度后，再绝热膨胀。这里采用在进膨胀机([13])前的温度由阀门调节来控制。
其中所说的“压缩机([16])”最好采用无油润滑压缩机，可保证N2通过压缩机后没有被污染。
从主换热器([4])中引出的另一路N2气继续冷却、降温，通过液化换热器([5])，进入脱N2塔([12])的塔釜中之冷凝蒸发器([9])，在冷凝蒸发器([9])中，高压N2气被液化，而塔釜中的液态甲烷被汽化，甲烷在汽化时带走了溶在液体中的N2，合成一股上升气流，但是液化了的高压N2在液N2过冷换热器([10])中被过冷，又经节流阀([11])降压，从脱N2塔([12])顶部向下喷洒液态N2。汽、液二相在塔内起精馏作用，从塔顶引出高纯度N2气，在液N2过冷换热器([10])中被复热，再与膨胀后的N2合并，一起参与循环，可弥补N2在循环中的损耗。而多余的N2从低压缓冲罐([15])中引出，可作为分子筛的再生气。从塔签底部引出高纯度的液态甲烷。
其中所说的“冷凝蒸发器([9])”，可以是管式的，也可以是板翅式的，其设计压力取N2气的压力，这里定为3mpa。该冷凝蒸发器([9])沉浸在液态甲烷里，高压N2在管内流动液化，管外液态甲烷蒸发。
其中所说的液N2过冷换热器([10])与前面所述的主换热器([4])和液化换热器([5])相同。
前面所说的从主换热器([4])起，直至脱N2塔([12])，低温LNG贮罐([8])，都在低温(比环境温度低)下工作。所以把这些设备都组装在一个铁制的箱体内(俗称冷箱)，阀门的阀杆加长伸出箱外，而膨胀机除工作叶轮在箱内，其余部分均露在箱外，在冷箱内再充填一种保温性能好的珠光砂，这样，使冷损减少到最低，又便于整体搬动。
应用实例1：
图2是采用本发明方法液化压力为0.3mpa的原料天然气的流程图。将来自油田压力为0.3mpa的天然气，以10000m3/天的处理能力送入进料分离器([17])，其规格为Φ1000×3000，在该罐中进行水和重质烃组份分离，并从罐底排出，天然气从罐顶引出，进入规格为Φ600×1000的碱洗脱硫塔([18])下部，在塔下部采用低浓度1-6％的热碱液洗涤，初脱硫脱碳。该热碱液是由规格为Φ800×2000的配碱罐([26])内的碱液经配碱泵([25])，送入规格为Φ800×2000的热碱罐([20])内，经热碱泵([19])送入碱洗脱硫塔([18])下段内的。在塔的中部采用高浓度7-12％冷碱液洗涤，精脱硫脱碳。该冷碱液由上述规格的配碱罐([26])内的碱液，经配碱泵([25])，送入规格为Φ800×2000的冷碱罐([22])内，再经冷碱泵([21])送入碱洗脱硫塔([18])中部。在碱洗脱硫塔([18])的上部采用循环水洗涤，脱除原料天然气中的碱雾。该循环水由规格为Φ800×2000的水罐([24])内的水，经水泵([23])送入碱洗脱硫塔([18])的上部的。从碱洗脱硫塔([18])塔顶出来的原料天然气物流(1)，经氟里昂冷冻机组([1])降温至4～5℃，进入规格为Φ1000×3000的汽液分离器([2])内，在温度为4～5℃，压力为0.3mpa的状况下进行分离，分离出水滴排放。分离后的原料天然气物流(2)，其温度为4～5℃压力为0.3mpa，以18.6kgmol/h的流量进入规格为Φ600×4000的分子筛吸附器([3])中，经过脱硫化氢、脱二氧化碳、干燥后的原料天然气物流(3)，其温度为12～17℃，压力为0.3mpa，该物流以18.6kgmol/h的流量进入主换热器([4])中，冷却到-92℃的物流(4)，再进入规格为Φ800×2000的重烃分离器([6])中，分离出重质烃组份如乙烷、乙稀、丙烷、丁烷、硫化氢等液体，从重烃分离器([6])的底部排出为副产品，贮存，用作化工原料或燃料。而从重烃分离器([6])顶部引出的-92℃的物流(5)，在压力不变的状况下，以18.5983kgmol/h的流量，进入液化换热器([5])内，降温至-141.5℃的液化物流(6)，经节流阀([7])，降压至0.05mpa的物流(7)，进入规格为Φ450×4500+Φ300×4500的脱N2塔([12])内，脱N2，从塔顶出料-191.4℃的99.9％的N2气物流(21)，进入液N2过冷换热器([10])，被加热到-157℃的N2气物流(22)，再与透平膨胀机([13])出口的N2气物流(27)混合成物流(9)，参与N2气压缩、膨胀、循环制冷。而塔釜出料的物流(28)为温度-155.5℃、压力为0.05mpa的液态甲烷99.5％，作为产品装入低温LNG贮罐([8])内，贮存、利用。
将来自低压缓冲罐([15])中温度为常温，压力为0.03mpa的N2气(13)，进入N2压缩机([16])升压至2.5mpa，温度约为40℃的N2气物流(14)，进入主换热器([4])内冷却至-35℃的物流(15)分作两部分，其中一部分N2气物流(24)进入透平膨胀机一段([14])的入口，降压至0.42mpa，降温至-100℃的物流(25)，其中一部分物流(25B)进入液化换热器([5])，被冷却到-141.5℃的N2气物流(26)，再与透平膨胀机([14])出口的另一部分物流(25A)混合为-105℃的N2气物流(26A)，进入透平膨胀机二段([13])中，膨胀至0.05mpa，温度为-147℃的N2气物流(27)，再与脱N2塔([12])顶部出来的N2气物流(22)混合的N2气物流(9)，依次进入液化换热器([5])、主换热器([4])作为冷源提供给原料天然气。而最终被复热到常温的N2气物流(12)，进入低压缓冲罐([15])，再被N2压缩机([16])压缩，再膨胀，循环制冷。而从主换热器([4])中出来的另一部分物流(16)，进入液化换热器([5])中，被冷却到-141.5℃的N2气物流(17)，作为脱N2塔([12])中冷凝蒸发器([9])的热源，使N2气物流(17)进一步被冷却液化至-153℃的液N2气物流(18)，再经液N2过冷器([10])过冷的液N2气物流(19)，经节流阀([11])降压至0.05mpa，降温至-191.8℃的液N2气物流(20)，进入脱N2塔([12])的顶部。塔顶气相N2气物流(21)进入液N2过冷器([10])，与透平膨胀机([13])出口的N2气物流(27)混合参与N2压缩、膨胀、制冷。在低压缓冲罐([15])中，多余的N2气物流(12)排放。也可用作分子筛吸附器([3])的再生气。
所说的N2压缩机([16])选用排N2量等于4000-4300Nm3/h，压力等于2.5mpa～3mpa，所说的透平膨胀机([13])、([14])的流量设计为4000Nm3/h，所说的主换热器([4])、液化换热器([5])、液N2过冷换热器([10])冷凝蒸发器([9])均选用铝制板翅式换热器；所说的冷冻机组中的制冷剂蒸发器选用铝制板翅式换热器，而分子筛吸附器([3])内的分子筛型号选用5A。从主换热器([4])起至低温LNG贮罐([8])均组装在一个铁制大冷箱内，并在箱内填满珠光砂。
应用实例2：
图3是采用本发明方法液化压力为20mpa的原料天然气流程图。将来自油田压力为20mpa，常温的原料天然气，处理量为10000m3/天，依次经节流阀([28])及规格为Φ400×1000的缓冲罐([29])，以及节流阀([30])和规格为500×1250的缓冲罐([31])，二级降压至5mpa。在缓冲罐([29])、([31])内分别把水和重质烃组份分离，并降温至-33℃。进入原料气换热器([35])复热到-17℃。过节流阀([34])降压为2.5mpa，降温至-33℃。进入吸收塔([36])内，被从规格为2m3的10％浓度的碱液贮罐([24])内经碱液泵([42])输入吸收塔([36])内，塔内碱液吸收原料天然气中的二氧化碳、硫化氢等进行预处理。预处理后的原料天然气温度为20℃、压力为2.5mpa，从吸收塔([36])顶部引出。再进入原料气换热器([35])内，降温至4℃。在汽液分离器([41])中去掉液态水。进入分子筛吸附器([3])进一步除去硫化氢、二氧化碳及水。到主换热器([4])冷却至-92℃，进入重烃分离器([40])，除去乙烷、乙稀、丙烷、丁烷、硫化氢等重质烃液态，此重质烃液态为副产品收集，作为化工原料或燃料。从重烃分离器([40])顶部引出的原料天然气，又回到主换热器([4])中复热到-35℃，再经原料气膨胀机([38])进行绝热膨胀，降压至0.3mpa，温度为-90℃。进液化换热器([5])内继续降温，于141.5℃被液化。经节流阀([7])降压至0.05mpa。进脱N2塔([12])脱N2，脱N2后从塔釜引出99.5％的高纯度液态甲烷，进入低温LNG贮罐([8])，贮存。
于前述的吸收塔([36])内，在2.5mpa压力下，原料天然气进口温度-33℃的高压低温下，碱液吸收了原料天然气中的硫化氢、二氧化碳的碱液，经节流阀([33])降至常压(即一个大气压)，进入规格为Φ500×1000的解析器([32])内，在常压(即一个大气压)下释放硫化氢及二氧化碳，被释放的硫化氢和二氧化碳并网，去燃烧炉([39])作燃料燃烧。解析后的-25℃至-30℃的低温碱液，从解析器([32])下部排出，进入解析塔([37])中，在常压下(即一个大气压)被加温，进一步被释放硫化氢及二氧化碳，从塔顶排出，并并网，也去燃烧炉([39])燃烧。而解析后的约18℃的碱液，从解析塔([37])的下部排出，进入碱液贮罐([22])，并经碱液泵([21])再压入吸收塔([36])，周而复始循环使用，适时补充水。但是，解析塔([37])内解析用的热源，来自液态甲烷低温LNG贮罐([8])上部自然蒸发的气相甲烷，依次在液化换热器([5])及主换热器([4])中逐步复热至常温约20℃，在解析塔内去加温-25℃至-30℃的碱液，从解析塔([37])顶部排出的气体，混入从解析器([32])释放出来的气体，一起去燃烧炉([39])，加温来自循环N2过程中吸收了从脱N2塔([12])中放出的多余N2气，使N2气升温到分子筛所需要的温度约220℃，进入分子筛吸收器([3])，带走被分子筛吸附了的硫化氢、二氧化碳及水等杂质，放空。
所说的原料气换热器([35])、原料气膨胀机([38])的选用，是因为原料天然气带压，为充分利用原料气的压力，高压采用节流膨胀制冷，中压采用透平膨胀机膨胀制冷。采用管式原料气换热器([35])代替冷冻机组，同样可保证原料天然气进入分子筛吸附器所要求的4-5℃的温度。在管式原料气换热器([35])的管内流动压力为5mpa的低温原料天然气(所说的低温为-33℃)，管外流动压力为2.5mpa的从吸收塔([36])顶部出来的20℃原料天然气。原料气膨胀机([38])从2.5mpa压力膨胀到0.3mpa压力，它可提供总冷量的22％左右。另外需说明的是公知的绝大多数液化天然气流程中，把膨胀后的天然气称作尾气，返回到城市燃气管网，而本发明流程把此部分低温尾气继续降温液化，所以液化率可达100％，不存在尾气并网的问题。
所说的汽液分离器([41])，重烃分离器([40])的工作压力为2.5mpa，其它均与应用实例1中所说的汽液分离器([2])、重烃分离器([6])相同。
原料天然气从常温(环境温度)到液态温度-156℃的整个过程中冷量靠N2气压缩、膨胀来完成。这个循环制冷的流程同应用实例1。
所说的主换热器([4])比应用实例1中的主换热器多一个通道，其它所选用的设备、机组均与实用实例1相同。
Claims (5)
1、一种液化天然气的生产方法，包括步骤为，
a、将天然气物流进行预处理，即在碱液洗涤设备中洗涤，脱硫脱碳，经冷却设备冷却，分离设备分离，除去硫化氢，二氧化碳及水，并干燥，以产生原料天然气物流，其中所说的天然气物流包括来自油田气井中喷出的天然气，或煤田采煤前排放的瓦斯气，或发现贮有量不大的气井及边远的架设管道不方便又不经济的气井中的天然气，
b、将所说的原料天然气物流在换热器中，于压力为0.3-2.5mPa，温度为0--100℃的条件下进行冷却、液化，此时，混在原料天然气中的高碳烷烃如乙烷、乙稀、丙烷、丁烷首先被液化，经分离设备分离出来，成为一种副产品，贮存，被分离后的甲烷及N2气余物流在压力为0.05-2.5mPa，温度为-101--160℃的条件下继续被冷却、液化，并进入脱N2塔中提纯，脱去物流中的N2气，以生产液化天然气产品，
其中所说换热器中的冷源是靠N2气压缩、膨胀制得冷量来提供的，循环N2气在换热器中把冷量传给原料天然气物流的同时N2气本身被复热，又经压缩、膨胀制冷，如此周而复始循环，所说的N2气经压缩、膨胀制得冷量是指N2气先从低压0.015-0.1mPa，压缩到2-8mPa，再在膨胀机内膨胀作功，使N2气压力下降至0.01-0.1mpa，温度降至-193--140℃来实现的，
其中所说在脱N2塔中提纯是由来自所说换热器中的液态天然气物流，在工作压力0.015-0.1mPa的脱N2塔的底部被汽化，在塔底部被汽化了的天然气物流的温度为-160.5--152℃，生成塔中上升气相馏份，与塔顶部下流的温度为-194--189℃的N2液相馏份，它们二者共同起精馏作用来完成的。
2、如权利要求1的方法，其中步骤b，还包括(i)从脱N2塔顶出来的N2气，收集，参与N2气的压缩、膨胀、制冷循环，补充N2气在循环过程中的损耗，而多余的N2气作为分子筛吸附器的再生气源，(ii)N2气从高压2.5mPa，膨胀到0.05mpa，采用二次串联透平膨胀，在第二次膨胀之前还用阀门调节来控制温度。
3、如权利要求1的方法，在20mPa高压原料天然气液化的流程中，高压采用节流膨胀制冷，中压采用透平膨胀制冷，在节流膨胀中增设一台原料气换热器，把节流膨胀后的冷量，传给原料天然气。
4、如权利要求1的方法，在0.3mPa低压原料天然气液化的流程中，原料天然气被冷却至分离重质烃的温度为-76℃至-100℃之间。
5、如权利要求1的方法，天然气物流的预处理，还可在吸收塔内采用高压低温碱液吸附原料天然气中的硫化氢和二氧化碳，在解析器和解析塔中常压常温从碱液中释放硫化氢和二氧化碳，被释放出来的硫化氢及二氧化碳，又去燃烧炉燃烧，而碱液在吸收塔和解析塔之间通过泵循环使用，所说的高压低温是指2.5mPa，-33℃，所说的常压、常温是指一个大气压及周围环境温度。
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1999
- 1999-10-15 CN CN 99120786 patent/CN1095496C/zh not_active Expired - Fee Related
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101006313B (zh) * | 2004-05-04 | 2012-10-10 | 奥特洛夫工程有限公司 | 天然气液化方法 |
| CN100565058C (zh) * | 2004-10-13 | 2009-12-02 | 普莱克斯技术有限公司 | 生产液化天然气的方法 |
| CN101356412B (zh) * | 2005-12-14 | 2013-06-05 | 雪佛龙美国公司 | 在中等条件下液化伴生气 |
| CN101126041B (zh) * | 2007-03-28 | 2015-05-20 | 林寿贵 | 级联式制备液化天然气的方法 |
| CN101104825B (zh) * | 2007-07-27 | 2011-05-04 | 无锡永大天然气集团有限公司 | 一种矿井瓦斯气的液化天然气生成设备及方法 |
| CN101644527B (zh) * | 2009-08-26 | 2011-12-28 | 四川空分设备(集团)有限责任公司 | 天然气液化工艺的制冷系统和液化系统 |
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