CN106185801A - 一种能回收甲烷的液氮洗涤装置及其方法 - Google Patents

一种能回收甲烷的液氮洗涤装置及其方法 Download PDF

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CN106185801A
CN106185801A CN201610517358.0A CN201610517358A CN106185801A CN 106185801 A CN106185801 A CN 106185801A CN 201610517358 A CN201610517358 A CN 201610517358A CN 106185801 A CN106185801 A CN 106185801A
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邬慧雄
赵卓雅
赵秋松
余涛
屈艳莉
曹培忠
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Hualu Engineering and Technology Co Ltd
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Abstract

本发明公开了一种能回收甲烷的液氮洗涤装置及其方法，特别是甲烷回收采用双回流甲烷浓缩塔的液氮洗涤装置，包括气液分离器I、气液分离器II、中压氮气冷却器、原料气冷却器I、原料气冷却器II、甲烷浓缩塔、气体混合器、氮洗塔和氢气分离器。甲烷浓缩塔内部分为第一回流洗涤与第二回流洗涤两段，内装填料。氮洗塔内部为液氮洗涤段，内装填料。本发明在实现精制氨合成气的同时，能把原料气中的甲烷回收作为天然气，可以有效地降低能耗和投资，具有良好的经济效益，且环保和安全系数高。

Description

一种能回收甲烷的液氮洗涤装置及其方法
技术领域
本发明涉及一种能回收甲烷的液氮洗涤工艺，特别是甲烷回收采用双回流甲烷浓缩塔的液氮洗涤装置。
背景技术
液氮洗是一个物理吸收过程。原料气体中含有的杂质一氧化碳、甲烷、氩等在低温下被吸收到溶剂液氮中，净化后的原料气再与氮气配气，以满足下游氨合成装置的氢氮比需求。
液氮洗是以煤为原料生产合成氨的重要工序之一，通过液氮洗装置去除合成气中的一氧化碳，二氧化碳等有害杂质，延长合成氨催化剂的寿命，同时脱除甲烷、氩气等杂质。大部分合成氨的原料气中都含有一定量的甲烷，在传统的液氮洗装置中，这部分甲烷经过粗分离后与一氧化碳、氮气等气体作为低热值燃料气一起送出装置。随着天然气价格升高及能源供应的日趋紧张，回收这部分甲烷能够达到节能减排的环保效果，并且具有显著的经济效益。
现有技术主要存在的问题是：在低温和高压的液氮洗操作条件下，常发生甲烷凝固而冰堵的现象，导致装置的停车事故；同时实现甲烷回收和精制氨合成的工艺，能耗高、投资大，且甲烷回收率低。
发明内容
针对目前存在的问题，本发明的目的是提供一种能回收甲烷的液氮洗涤装置及其方法，通过液氮洗涤装置，将原料气中的甲烷成分，经由深冷过程，克服其冷凝成固体，造成冷箱堵塞的问题，经济性地分离出来，作为天然气使用，以提高项目的整体经济效益。
本发明的技术方案是：一种能够回收甲烷的液氮洗装置，其特征在于：所述的原料气冷却器I和原料气冷却器II将原料气体冷却后，通过管道连接到气液分离器I，进行气液分离，其中气体则重新返回原料气冷却器II，进行进一步的冷却。
按照本发明的一个具体方案，所述的气液分离器I底部的液体通过管道和阀门连接到原料气冷却器II，回收其中的冷量后，部分气化，成为气液混合物，再经由管道连接到甲烷浓缩塔的底部，其中的气体自下而上，与来自甲烷浓缩塔顶部和中部的第一回流液体和第二回流液体逆向接触，进一步将气体中的甲烷液化和洗涤下来，同时第一回流液体和第二回流液体中，含有的氢气和部分一氧化碳也会被解吸出来，进而可以成功保证甲烷浓缩塔底部液体甲烷的纯度。
按照本发明的一个具体方案，所述的原料气冷却器II将源于气液分离器I顶部的气体进一步冷却后，通过管道连接到气液分离器II，进行气液分离，其中液体通过管道和阀门连接到甲烷浓缩塔的中部，作为第二回流液体，气体则通过管道连接到氮洗塔的底部，自下而上与来自氮洗塔顶部的液体氮逆向接触，进一步洗涤掉其含有的甲烷和一氧化碳。
按照本发明的一个具体方案，所述的氮洗塔底部的液体通过管道和阀门连接到氢气分离器，将液体中含有的氢气和大部分一氧化碳气化后，进行气液分离，其中气体通过管道与中压氮气冷却器、原料气冷却器I和原料气冷却器II连接，液体则液体通过管道和阀门连接到甲烷浓缩塔的顶部，作为第一回流液体。
本发明在冷箱中设置了气液分离器I和气液分离器II。利用液氮洗系统中的冷量，在-150～-165℃前，把原料气中75～90％的甲烷，在气液分离器I中分离了出来，使得原料气中的甲烷含量大幅度降低。之后，再在-160～-179℃前，将原料气中剩余甲烷的65～95％，在气液分离器II中分离出来，进而使得原料气在进入氮洗塔前，其甲烷含量被降低至0.10～1.0％，同时，其温度被严格控制在甲烷的冰点-182.5℃以上。所以，本发明有效避免了甲烷在冰点以下，固化冰堵，进而导致冷箱冻堵停车的问题，
本发明在冷箱中设置了甲烷浓缩塔。气液分离器I底部的液体，经过减压和原料气冷却器II复热后，其压力降为0.8～3.5MPa，温度上升到-120～-145℃，成为气液混合物，再经由管道连接到甲烷浓缩塔的底部；气液分离器II底部的液体，经过减压，其压力降为0.8～3.5MPa，成为气液混合物，经由管道连接到甲烷浓缩塔的中部；氢气分离器底部的液体，经过减压和原料气冷却器II复热后，其压力降为0.8～3.5MPa，温度上升到-160～-175℃，成为气液混合物，经由管道连接到甲烷浓缩塔的顶部。在甲烷浓缩塔内，气体自下而上，与来自甲烷浓缩塔顶部和中部的第一回流液体和第二回流液体逆向接触，进一步将气体中的甲烷液化和洗涤下来，同时第一回流液体和第二回流液体中，含有的氢气和部分一氧化碳也会被解吸出来，进而可以成功保证甲烷浓缩塔底部液体甲烷的纯度。
本发明一种能够回收甲烷的液氮洗装置，出氮洗塔的氨合成气中一氧化碳体积含量小于2×10-6，氢气回收率大于99％，回收的甲烷气体中，甲烷体积含量大于98％，甲烷回收率高于99％。在实现精制氨合成气的同时，能把原料气中的甲烷回收作为天然气，进而可以有效地降低能耗和投资，具有良好的经济效益，且环保和安全系数高。
附图说明
图1是本发明的工艺流程图。
附图标号：1-中压氮气冷却器，2-原料气冷却器I，3-原料气冷却器II，4-气体混合器，5-气液分离器I，6-气液分离器II，7-氮洗塔，8-氢气分离器，9-甲烷浓缩塔。
具体实施方式
实施例1
下面参照附图，对本发明作进一步描述：
参见附图1，一种能够回收甲烷的液氮洗装置，主要包括气液分离器I5、气液分离器II6、中压氮气冷却器1、原料气冷却器I2、原料气冷却器II3、甲烷浓缩塔9、气体混合器4、氮洗塔7和氢气分离器8；甲烷浓缩塔内部分为第一回流洗涤与第二回流洗涤两段，内装填料；氮洗塔内部为液氮洗涤段，内装填料。
来自上游系统的原料气送入冷箱中原料气冷却器I2和原料气冷却器II3，在此被返流的合成气、燃料气、富氢气和富甲烷气冷却，冷却到-160℃，然后进入气液分离器I5，分离出的液相中，甲烷成分占原料气中甲烷的82％，再经过减压和原料气冷却器II3复热后，其压力降为2.3MPa，温度上升到-135℃，成为气液混合物，再经由管道连接到甲烷浓缩塔9的底部。气液分离器I5分离出的气相进入原料气冷却器II3，在此被返流的合成气、燃料气、富氢气和富甲烷气冷却至-175℃，然后进入气液分离器II6，分离出的液相中，甲烷成分占原料气中剩余甲烷的94％，再经过减压至2.3MPa后，成为气液混合物，经由管道连接到甲烷浓缩塔9的中部。气液分离器II6分离出的气相温度为-175℃，其甲烷含量被降低至0.32％。
在以上过程中，原料气温度被严格控制在甲烷的冰点-182.5℃以上，以有效避免甲烷在冰点以下，固化冰堵，进而导致出现冷箱冻堵停车的问题。
气液分离器II6分离出的气相，进入氮洗塔7下部，与氮洗塔7上部的-188℃的液氮逆流接触，其中所含一氧化碳、氩等在被洗出，净化后的含有少量氮气的-194℃合成气，自氮洗塔7塔顶离开，经过原料气冷却器II3复热至-138℃，然后将中压氮气管线中来的氮气配入(即气相配氮)，基本达到氢氮气化学配比3:1后，再经过原料气冷却器I2和中压氮气冷却器1复热至环境温度后送出冷箱，再经精配氮实现正确的氢氮气化学配比后作为产品气体送入氨合成工序。
在以上过程中，自氮洗塔7塔顶离开的合成气中一氧化碳体积含量小于2×10-6，氢气回收率大于99％。
氮洗塔7底部的-193℃的液体经减压后，在氢气分离器8中闪蒸，气相作为富氢气，经原料气冷却器II3、原料气冷却器I2和中压氮气冷却器1复热至环境温度后送出冷箱进行回收利用。由氢气分离器8底部排出的-189℃的液体，经原料气冷却器II3复热至-168℃后，成为气液两相，送至甲烷浓缩塔9顶部。
来自气液分离器I5的液体，经原料气冷却器II3回收冷量后，以-135℃的气液混合物形式，送入甲烷浓缩塔9的底部，其中的气体自下而上，与来自甲烷浓缩塔9顶部和中部的第一回流液体和第二回流液体逆向接触，进一步将气体中的甲烷液化并洗涤下来，同时第一回流液体和第二回流液体中，含有的氢气和部分一氧化碳也会被解吸出来；来自气液分离器II6的液体，减压至2.3MPa后，以-175℃的气液混合物形式，送入甲烷浓缩塔9的中部，其中的气体自下而上，与来自甲烷浓缩塔9顶部的第一回流液体逆向接触，进一步将气体中的甲烷液化并洗涤下来，同时第一回流液体中含有的氢气和部分一氧化碳也会被解吸出来，而液体作为第二回流液，在塔内自上而下流动；来自氢气分离器8的液体，经原料气冷却器II3回收冷量后，以-168℃的气液混合物形式，送入甲烷浓缩塔9的顶部，液体作为第一回流液，在塔内自上而下流动。
以上过程中，甲烷浓缩塔9中的所有气体自下而上流动，在甲烷浓缩塔9塔顶汇合，再经原料气冷却器II3、原料气冷却器I2和中压氮气冷却器1复热至环境温度后，作为燃料气送出冷箱；所有液体自上而下流动，在甲烷浓缩塔9塔底汇合，再经原料气冷却器II3和原料气冷却器I2复热至环境温度后，作为甲烷产品气送出冷箱。
中压氮气经中压氮气冷却器1和原料气冷却器I2被返流气体冷却至-67℃后，其中大部分经节流直接与自氮洗塔7顶部来的合成气混合，基本达到氢氮气化学配比3:1；其余部分继续在原料气冷却器II3中冷却并液化，液氮进入氮洗塔7顶部，作为洗涤剂将原料气体中一氧化碳、氩等杂质洗下。
在以上过程中，选用的中压氮气压力为5.2MPa、42℃。原料气的压力为5.4MPa、-64℃。
本发明提出的一种能回收甲烷的液氮洗涤装置已通过良好的实施例进行了描述，相关技术人员明显能在不脱离本发明内容、精神和范围内，对本发明所属的结构和技术方法进行改动或适当变更与组合来实现本发明技术。特别需要指出的是，所有相类似的替换和改动，对本领域技术人员来说是显而易见的，都被视为包括在本发明精神、范围和内容中。

Claims (1)

1.一种能回收甲烷的液氮洗涤方法，其特征在于：所述原料气冷却器I(2)和原料气冷却器II(3)将原料气体冷却后，通过管道连接到气液分离器I(5)，进行气液分离，其中气体则重新返回原料气冷却器II(3)，进行进一步的冷却；
所述气液分离器I(5)底部的液体通过管道和阀门连接到原料气冷却器II(6)，回收其中的冷量后，部分气化，成为气液混合物，再经由管道连接到甲烷浓缩塔(9)的底部，其中的气体自下而上，与来自甲烷浓缩塔(9)顶部和中部的第一回流液体和第二回流液体逆向接触，进一步将气体中的甲烷液化和洗涤下来，同时第一回流液体和第二回流液体中，含有的氢气和部分一氧化碳也会被解吸出来，进而可以成功保证甲烷浓缩塔(9)底部液体甲烷的纯度；
所述原料气冷却器II(3)将源于气液分离器I(2)顶部的气体进一步冷却后，通过管道连接到气液分离器II(6)，进行气液分离，其中液体通过管道和阀门连接到甲烷浓缩塔(9)的中部，作为第二回流液体，气体则通过管道连接到氮洗塔(7)的底部，自下而上与来自氮洗塔顶部的液体氮逆向接触，进一步洗涤掉其含有的甲烷和一氧化碳；
所述氮洗塔(7)底部的液体通过管道和阀门连接到氢气分离器(8)，将液体中含有的氢气和大部分一氧化碳气化后，进行气液分离，其中气体通过管道与中压氮气冷却器(1)、原料气冷却器I(2)和原料气冷却器II(3)连接，液体则液体通过管道和阀门连接到甲烷浓缩塔(9)的顶部，作为第一回流液体。
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