CN105423701B - 焦炉气深冷分离制取sng的方法 - Google Patents
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Abstract
一种简单实用的焦炉气深冷分离制取SNG的方法。其设备，包括氮气压缩机或氮－甲烷压缩机、高压脱氢精馏塔、低压脱氮精馏塔、脱氢塔顶冷凝器、脱氢塔回流液分离罐、脱氮塔顶冷凝器、脱氮塔回流液分离罐、主换热器、过冷器、脱氮塔再沸器。所述的主换热器的氮气或氮－甲烷气进料管与氮气压缩机或氮－甲烷压缩机的出料管连接，所述的主换热器的氮气或氮－甲烷气的出料管与氮气压缩机或氮－甲烷压缩机的进料管连接。本发明是只采用氮压机或氮甲烷压机循环制冷的方法制取冷量。本方法流程结构简单，能耗低、成本低。
Description
技术领域
本发明涉及天然气生产领域，具体说是一种焦炉气深冷分离制取SNG的方法。
背景技术
煤制天然气通常指采用已开采原煤，经过气化工艺来制造合成天然气（SyntheticNatural Gas，以下简称SNG）。在实践中，业界往往把煤地下气化（亦称为地下采煤，Underground Coal Gasification，UCG）也作为煤制天然气的一种。
在“十一五”期间，随着中国政府节能减排与资源综合利用政策的实施，焦炉煤气的利用开始转向生产SNG。由于单个项目规模较小，不可能为焦炉煤气制SNG项目建设管网，因此产品一般采取压缩后制压缩天然气(以下简称CNG)和液化后制液化天然气（以下简称LNG）的方案，进入市场销售。
从目前我国能源结构看，甲醇产能过剩，而天然气供需严重不足，开辟新的清洁能源，将焦炉气甲烷化制SNG，是重要的发展方向。焦炉煤气甲烷化生产天然气技术，具有投资小，消耗低，无污染、能量利用率高、产品市场前景好等优势，是焦化企业煤气利用的较佳选择。再进一步生产CNG或LNG，会产生更明显的经济效益与社会效益，对促进焦化行业技术进步与产业可持续发展具有重要的意义。
CNG以燃烧压缩天然气为动力，“喝”的是天然气，“吐”出来的是二氧化碳和水蒸汽，节能环保。目前，市场上已经开发了采用混合制冷剂或膨胀机双级氮膨胀及氮冷剂+混合制冷剂的制冷循环回路来制取SNG，其方法复杂。动力设备为转动机械，易发生故障。
目前的MRC工艺主要采用N2和C1~C5烃类的混合物作为循环制冷剂。混合冷剂的组成比例根据原料气的组成、压力、工艺流程而异，因此对制冷剂的配比和原料气的气质要求更为严格，一旦确定是不易更改的。即使满足该条件，要使整个液化过程（25℃~-162℃）所需冷量与制冷剂所提供的冷量完全匹配是达不到的，而只能趋近与冷却曲线。这使得配比很难控制。实际运行中，配比一直是一大难题困扰着人们。
发明内容
本发明的目的是提供一种焦炉气深冷分离制取SNG的方法。从根本上解决了现有SNG生产设备操作复杂、系统部件多、占地面积大、维护成本高、初期投入多等问题。
本发明的目的是这样实现的：该制备合成天然气的焦炉气深冷分离系统，其技术要点是：所述制备合成天然气的方法在焦炉气深冷分离系统中进行，该系统包括压缩机I、II、主换热器、高压脱氢精馏塔、低压脱氮精馏塔、脱氢塔顶冷凝器、脱氮塔顶冷凝器、过冷器、脱氢塔回流液分离罐、脱氮塔回流液分离罐，低压脱氮精馏塔底部设有脱氮塔再沸器，原料气管线经过主换热器后与脱氮塔再沸器的进料端相连，脱氮塔再沸器的出料端与高压脱氢精馏塔底部的进料端相连，高压脱氢精馏塔底部的出料端通过过冷器后与低压脱氮精馏塔中部的进料端相连，并设置节流阀I，低压脱氮精馏塔底部的出料端经过主换热器后与压缩机II的进料端相连，压缩机II的出料端与CNG管网相连；
低压脱氮精馏塔顶部设有两个出料口分别与脱氮塔顶冷凝器、脱氮塔回流液分离罐的底部进料口相连，脱氮塔顶冷凝器的底部出料口与脱氮塔回流液分离罐中部相连，脱氢塔回流液分离罐的顶部出料口依次与过冷器、主换热器相连；
高压脱氢精馏塔顶部设有两个出料口分别与脱氢塔顶冷凝器、脱氢塔回流液分离罐的底部进料口相连，脱氢塔顶冷凝器的底部出料口与脱氢塔回流液分离罐中部相连，脱氮塔回流液分离罐的顶部出料口与主换热器相连；
脱氢塔顶冷凝器以及脱氮塔顶冷凝器的顶部出料端分别经过主换热器与压缩机I的进料端相连，压缩机I的出料端经过主换热器分别与脱氢塔顶冷凝器以及脱氮塔顶冷凝器的顶部进料端相连，并分别设置节流阀II、节流阀III；
焦炉气深冷分离制取SNG的方法，包括以下步骤：
1) 净化后的原料焦炉气在-40℃，1.55MPa.G进入冷箱内的主换热器，被返流的低温富氢气及低温富氮气冷却至-135℃，1.55MPa.G，以气液混合物的形式进入脱氮塔再沸器；
2) 气液混合物作为低压脱氮精馏塔底部的热源被进一步冷却至-137℃后，进入高压脱氢精馏塔底部精馏后，在高压脱氢精馏塔底部获得富甲烷液体，在高压脱氢精馏塔顶部获得高压富氢气；
3）高压脱氢精馏塔顶部的高压富氢气经过位于脱氢塔顶冷凝器内的脱氢塔回流液分离罐后进入过冷器过冷LNG，经主换热器复热送出；
4）高压脱氢精馏塔底部富甲烷液体经过过冷器过冷减压至-145℃，0.45MPa.G，通入低压脱氮精馏塔中部进行精馏，在低压脱氮精馏塔底部获得LNG，LNG通过主换热器复热后获得37℃，0.38MPa.G的SNG，经压缩机II压缩成40℃，4.1MPa.G的CNG，送入CNG管网；
5）低压脱氮精馏塔顶部的低压富氮气经过位于脱氮塔顶冷凝器内的脱氮塔回流液分离罐冷却至-169℃，0.43MPa.G后，经主换热器复热后送出；
37℃，0.4MPa.G的氮气或氮-甲烷气经过压缩机压缩至40℃，6.4MPa.G后返回主换热器，被冷却至-177℃，0.48MPa.G由节流阀II、节流阀III控制节流进入脱氢塔顶冷凝器和脱氮塔顶冷凝器作为步骤3）和步骤5）的冷源，被气化后进入主换热器复热后送出至压缩机I的进料端，经压缩机I增压后完成一次循环过程。
本发明的深冷分离系统，相比其它常用流程，减少了混合制冷剂压缩机及氮膨胀机两组大型动力设备，焦炉气液化所需冷量仅由一台（氮气或氮－甲烷）压缩机提供。流程非常简单，节省了能耗、降低了投资费用、操作调节方便、易于维护，大大提高了整个系统的可靠性。
采用液氮（或氮-甲烷混合气）作为低压脱氮精馏塔的冷源，能耗低，无需混合制冷剂、膨胀机制冷，杜绝了含氢介质膨胀机密封、制造难度较大、制冷剂通道冻堵或节流不制冷等问题。由于无需混合采用制冷剂制冷，避免了配比不当所引起的诸多问题，冷箱内不但省去了压缩机，而且也省去分离罐及调节阀门。冷箱内的设备更少，冷箱体积更小，投资费用更小。
此外，为了进一步降低制冷循环的功耗，还可采用氮-甲烷双组分混合气体代替纯N2。与混合冷剂循环相比，氮-甲烷制冷循环流程更简单、控制更容易、制冷剂测定和计算更方便等优点。同时由于缩小了冷端换热温差，它比纯氮压机制冷循环节省 10%~20%的动力消耗。对于同样的装置，采用氮气压缩机和采用氮-甲烷压缩机来循环制冷，经模拟分析，相差约30%的能耗。
附图说明
图1是本发明的工艺流程结构示意图；
图2是主换热器中各管路中主要组分换热前后的具体参数。
附图标记说明：1压缩机I、2高压脱氢精馏塔、3低压脱氮精馏塔、4脱氢塔顶冷凝器、5脱氢塔回流液分离罐、6脱氮塔顶冷凝器、7脱氮塔回流液分离罐、8主换热器、9过冷器、10脱氮塔再沸器、11节流阀I、12节流阀II、13节流阀III、14压缩机II。
具体实施方式
以下结合图1~2，通过具体实施例详细说明本发明的内容。
实施例1
该制备合成天然气的焦炉气深冷分离系统包括压缩机I 1、压缩机II 14、主换热器8、高压脱氢精馏塔2、低压脱氮精馏塔3、脱氢塔顶冷凝器4、脱氮塔顶冷凝器6、过冷器9、脱氢塔回流液分离罐5、脱氮塔回流液分离罐7等部分。其中，脱氢塔回流液分离罐5位于脱氢塔顶冷凝器4内，脱氮塔回流液分离罐7位于脱氮塔顶冷凝器6内。低压脱氮精馏塔底部设有脱氮塔再沸器10，原料气管线经过主换热器8后与脱氮塔再沸器10的进料端相连，脱氮塔再沸器10的出料端与高压脱氢精馏塔2底部的进料端相连，高压脱氢精馏塔2底部的出料端通过过冷器9后与低压脱氮精馏塔3中部的进料端相连，并设置节流阀I 11，低压脱氮精馏塔3底部的出料端经过主换热器8后与压缩机II 14的进料端相连，压缩机II 14的出料端与CNG管网相连；
低压脱氮精馏塔顶部设有两个出料口分别与脱氮塔顶冷凝器6、脱氮塔回流液分离罐7的底部进料口相连，脱氮塔顶冷凝器6的底部出料口与脱氮塔回流液分离罐7中部相连，脱氢塔回流液分离罐7的顶部出料口依次与过冷器9、主换热器8相连；
高压脱氢精馏塔顶部设有两个出料口分别与脱氢塔顶冷凝器4、脱氢塔回流液分离罐5的底部进料口相连，脱氢塔顶冷凝器4的底部出料口与脱氢塔回流液分离罐5中部相连，脱氮塔回流液分离罐5的顶部出料口与主换热器8相连；
脱氢塔顶冷凝器4以及脱氮塔顶冷凝器6的顶部出料端分别经过主换热器与压缩机I 1的进料端相连，压缩机I 1的出料端经过主换热器8分别与脱氢塔顶冷凝器4以及脱氮塔顶冷凝器6的顶部进料端相连，并分别设置节流阀II 12、节流阀III 13。
采用上述系统制备合成天然气的方法，具体包括以下步骤：
1) 净化后的原料焦炉气在-40℃，1.55MPa.G进入冷箱内的主换热器，被返流的低温富氢气及低温富氮气冷却至-135℃，1.55MPa.G，以气液混合物的形式进入脱氮塔再沸器；
2) 气液混合物作为低压脱氮精馏塔底部的热源被进一步冷却至-137℃后，进入高压脱氢精馏塔底部精馏后，在高压脱氢精馏塔底部获得富甲烷液体，在高压脱氢精馏塔顶部获得高压富氢气；
3）高压脱氢精馏塔顶部的高压富氢气经过位于脱氢塔顶冷凝器内的脱氢塔回流液分离罐后进入过冷器过冷LNG，经主换热器复热送出；
4）高压脱氢精馏塔底部富甲烷液体经过过冷器过冷减压至-145℃，0.45MPa.G，通入低压脱氮精馏塔中部进行精馏，在低压脱氮精馏塔底部获得LNG，LNG通过主换热器复热后获得37℃，0.38MPa.G的SNG，经压缩机II压缩成40℃，4.1MPa.G的CNG，送入CNG管网；
5）低压脱氮精馏塔顶部的低压富氮气经过位于脱氮塔顶冷凝器内的脱氮塔回流液分离罐冷却至-169℃，0.43MPa.G后，经主换热器复热后送出；
37℃，0.4MPa.G的氮气经过压缩机I压缩至40℃，6.4MPa.G后返回主换热器，被冷却至-177℃，0.48MPa.G由节流阀II、节流阀III控制节流进入脱氢塔顶冷凝器和脱氮塔顶冷凝器作为步骤3）和步骤5）的冷源，被气化后进入主换热器复热后送出至压缩机I的进料端，经压缩机I增压后完成一次循环过程。该制冷循环为脱氢塔顶冷凝器4以及脱氮塔顶冷凝器6提供冷源。
步骤3）~5）以及制冷循环均可为步骤1)中-40℃，1.55MPa.G的原料气提供冷源，使其冷却至-135℃，1.55MPa.G。相对的，步骤1）以及制冷循环也为氢气、氮气、LNG的复热提供了热源，使整个系统得以顺利运转。
图2中，为便于说明省略了氮-甲烷混合气这一实施方式，由于压缩机I的循环过程中，进入主换热器前的氮气作为脱氢塔顶冷凝器中富氢气体和脱氮塔顶冷凝器富氮气体冷凝的冷源，所需冷凝的富氢气体和富氮气体量由于流速、投料量等因素影响，其实际数值对本发明的产品质量并无实际影响，因此未作进一步限定。
实施例2
将氮气冷源替换为摩尔含量40%~90%的氮-甲烷混合气，其他同实施例1。
说明书中所涉及的压力如无特别说明，均是指表压（G）。
说明书中所涉及的脱氮设备（脱氮精馏塔、脱氮塔顶冷凝器、脱氮塔再沸器、脱氮塔回流液分离罐）在脱氮的同时还脱去了少量的一氧化碳，但由于一氧化碳并非主要考虑的杂质，为方便行文的简洁并未详细描述。
说明书中所涉及的原料气可以是甲烷化的焦炉气，也可以是未甲烷化的焦炉气。为节省能耗，未甲烷化的焦炉气最好采用氮-甲烷压缩机。
实施例中，氮-甲烷混合气的主要成分（氮-甲烷）摩尔含量为40%~90%时，在综合考虑成本等因素时，可达到最佳的使用效果。
Claims (2)
1.一种焦炉气深冷分离制取SNG的方法，其特征在于：所述制备合成天然气的方法在焦炉气深冷分离系统中进行，该系统包括压缩机I、II、主换热器、高压脱氢精馏塔、低压脱氮精馏塔、脱氢塔顶冷凝器、脱氮塔顶冷凝器、过冷器、脱氢塔回流液分离罐、脱氮塔回流液分离罐，低压脱氮精馏塔底部设有脱氮塔再沸器，原料气管线经过主换热器后与脱氮塔再沸器的进料端相连，脱氮塔再沸器的出料端与高压脱氢精馏塔底部的进料端相连，高压脱氢精馏塔底部的出料端通过过冷器后与低压脱氮精馏塔中部的进料端相连，并设置节流阀I，低压脱氮精馏塔底部的出料端经过主换热器后与压缩机II的进料端相连，压缩机II的出料端与CNG管网相连；
低压脱氮精馏塔顶部设有两个出料口分别与脱氮塔顶冷凝器、脱氮塔回流液分离罐的底部进料口相连，脱氮塔顶冷凝器的底部出料口与脱氮塔回流液分离罐中部相连，脱氢塔回流液分离罐的顶部出料口依次与过冷器、主换热器相连；
高压脱氢精馏塔顶部设有两个出料口分别与脱氢塔顶冷凝器、脱氢塔回流液分离罐的底部进料口相连，脱氢塔顶冷凝器的底部出料口与脱氢塔回流液分离罐中部相连，脱氮塔回流液分离罐的顶部出料口与主换热器相连；
脱氢塔顶冷凝器以及脱氮塔顶冷凝器的顶部出料端分别经过主换热器与压缩机I的进料端相连，压缩机I的出料端经过主换热器分别与脱氢塔顶冷凝器以及脱氮塔顶冷凝器的顶部进料端相连，并分别设置节流阀II、节流阀III；
焦炉气深冷分离制取SNG的方法，包括以下步骤：
1) 净化后的原料焦炉气在-40℃，1.55MPa.G进入冷箱内的主换热器，被返流的低温富氢气及低温富氮气冷却至-135℃，1.55MPa.G，以气液混合物的形式进入脱氮塔再沸器；
2) 气液混合物作为低压脱氮精馏塔底部的热源被进一步冷却至-137℃后，进入高压脱氢精馏塔底部精馏后，在高压脱氢精馏塔底部获得富甲烷液体，在高压脱氢精馏塔顶部获得高压富氢气；
3）高压脱氢精馏塔顶部的高压富氢气经过位于脱氢塔顶冷凝器内的脱氢塔回流液分离罐后进入过冷器过冷LNG，经主换热器复热送出；
4）高压脱氢精馏塔底部富甲烷液体经过过冷器过冷减压至-145℃，0.45MPa.G，通入低压脱氮精馏塔中部进行精馏，在低压脱氮精馏塔底部获得LNG，LNG通过主换热器复热后获得37℃，0.38MPa.G的SNG，经压缩机II压缩成40℃，4.1MPa.G的CNG，送入CNG管网；
5）低压脱氮精馏塔顶部的低压富氮气经过位于脱氮塔顶冷凝器内的脱氮塔回流液分离罐冷却至-169℃，0.43MPa.G后，经主换热器复热后送出；
37℃，0.4MPa.G的氮气或氮-甲烷气经过压缩机压缩至40℃，6.4MPa.G后返回主换热器，被冷却至-177℃，0.48MPa.G由节流阀II、节流阀III控制节流进入脱氢塔顶冷凝器和脱氮塔顶冷凝器作为步骤3）和步骤5）的冷源，被气化后进入主换热器复热后送出至压缩机I的进料端，经压缩机I增压后完成一次循环过程。
2.一种制备合成天然气的焦炉气深冷分离系统，包括压缩机I、II、主换热器、高压脱氢精馏塔、低压脱氮精馏塔、脱氢塔顶冷凝器、脱氮塔顶冷凝器、过冷器、脱氢塔回流液分离罐、脱氮塔回流液分离罐，其特征在于：所述低压脱氮精馏塔底部设有脱氮塔再沸器，原料气管线经过主换热器后与脱氮塔再沸器的进料端相连，脱氮塔再沸器的出料端与高压脱氢精馏塔底部的进料端相连，高压脱氢精馏塔底部的出料端通过过冷器后与低压脱氮精馏塔中部的进料端相连，并设置节流阀I，低压脱氮精馏塔底部的出料端经过主换热器后与压缩机II的进料端相连，压缩机II的出料端与CNG管网相连；
低压脱氮精馏塔顶部设有两个出料口分别与脱氮塔顶冷凝器、脱氮塔回流液分离罐的底部进料口相连，脱氮塔顶冷凝器的底部出料口与脱氮塔回流液分离罐中部相连，脱氢塔回流液分离罐的顶部出料口依次与过冷器、主换热器相连；
高压脱氢精馏塔顶部设有两个出料口分别与脱氢塔顶冷凝器、脱氢塔回流液分离罐的底部进料口相连，脱氢塔顶冷凝器的底部出料口与脱氢塔回流液分离罐中部相连，脱氮塔回流液分离罐的顶部出料口与主换热器相连；
脱氢塔顶冷凝器以及脱氮塔顶冷凝器的顶部出料端分别经过主换热器与压缩机I的进料端相连，压缩机I的出料端经过主换热器分别与脱氢塔顶冷凝器以及脱氮塔顶冷凝器的顶部进料端相连，并分别设置节流阀II、节流阀III。
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| CN205279605U (zh) * | 2015-11-17 | 2016-06-01 | 辽宁中集哈深冷气体液化设备有限公司 | 制备合成天然气的焦炉气深冷分离系统 |
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