CN110108090B - 一种降低空分装置上塔压力和系统能耗的方法 - Google Patents

一种降低空分装置上塔压力和系统能耗的方法 Download PDF

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CN110108090B
CN110108090B CN201910347093.8A CN201910347093A CN110108090B CN 110108090 B CN110108090 B CN 110108090B CN 201910347093 A CN201910347093 A CN 201910347093A CN 110108090 B CN110108090 B CN 110108090B
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nitrogen
energy consumption
air separation
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CN110108090A (zh
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王立
张培昆
童莉葛
杨亚翔
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University of Science and Technology Beijing USTB
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Abstract

本发明提供一种降低空分装置上塔压力和系统能耗的方法，属于空分技术领域。该方法在常规空分装置上增设污氮引风机、氮气引风机和冷冻机，污氮引风机设置在上塔抽出污氮管路，氮气引风机设置在出上塔塔顶氮气管路，在污氮管路和冷冻水管路上设置冷冻机。该方法进一步降低空气压缩机出口压力，减少空气压缩机的能耗，实现空分系统的节能。通过引风设备协助出上塔压力损失最高气体(主要是污氮)的后续管路中压力损失，实现上塔、下塔以及空气压缩机出口压力的降低，并改善空分装置的精馏条件，降低空分系统能耗。

Description

一种降低空分装置上塔压力和系统能耗的方法
技术领域
本发明涉及空分技术领域，特别是指一种降低空分装置上塔压力和系统能耗的方法。
背景技术
中国是工业大国，尤其是在化工和钢铁产业方面，其产能遥遥领先于世界上其他任何国家，但中国的工业单位生产能耗与世界上发达国家还有一定的差距。在钢铁和化工等行业中，都需要大量氧气和氮气的供应，例如在钢铁企业中，空气分离设备所消耗电量占到整个钢铁企业耗电量的约14％，而空气压缩机又是空分系统中的主要耗电设备，如果降低空气压缩机能耗，对于整个空分装置、整个钢铁企业、甚至全国的节能减排工作都有重大意义。如果按照中国每年钢产量为8亿吨、吨钢氧耗约为120Nm3、0.45kWh/Nm3氧电耗来计算，如电耗量节约1％，每年能够节约电耗量为4.32*10^8kWh，普通燃煤电厂按普通燃煤电厂35％发电效率，能够节约1.516*10^5吨标准煤，CO2每年的减排量约为3.784*10^5吨。
空气压缩机能耗主要与空气压缩机出口压力、压缩机压缩气体量以及压缩机性能相关，由于压缩机性能已经日臻完善，以及生产一定量氧气或氮气的空气压缩量已经固定，所以减少空气压缩机能耗主要从降低空气压缩机出口压力入手。空压机出口压力取决于精馏塔下塔压力，下塔压力取决于维持主冷凝蒸发器的温差，主冷凝蒸发器的温差取决于上下塔的压力差。只有上塔压力降低了，下塔压力才有可能降低。上塔压力取决于各种出塔气体出塔后到离开空分设备前管路系统的压力损失，也即管路压力损失最大的出塔气体压力决定了上塔总体压力的大小。出上塔气体中管路压力损失最大的是污氮气体，污氮气体除了像其他出塔气体一样克服管道和主换热器阻力损失外，还需要克服分子筛纯化器的阻力损失。如果在污氮管道上增设引风机用于克服分子筛纯化器阻力，那么上塔压力可整体降低。或再进一步降低上塔压力时可增设氮气引风机，氮气经引风后温度有所升高，水冷塔内水温有所提高，需加大冷冻机功率，例如当某35000Nm3/h空分装置中的氮气引风压差为0.01bar时，氮气温度可升高0.81K左右，冷冻水温度升高值大约为0.29K，冷冻机制冷能耗大约为6.91kw；与此同时空气压缩机能耗降低量为39.76kw，约是冷冻机制冷能耗的6倍。
发明内容
本发明要解决的技术问题是提供一种降低空分装置上塔压力和系统能耗的方法，通过降低空气压缩机出口压力降低压缩机能耗。
该方法通过降低上塔压力降低冷凝蒸发器中液氧的饱和温度，进而在冷凝蒸发器换热温差固定不变的情况下实现下塔塔顶氮气压力的降低，于是下塔压力和空气压缩机出口压力也随之而降低，并且其压降约三倍于上塔的压降。在降低上塔压力后，为保证出上塔气体有足够压力克服出塔后设备和管路阻力，需在出主换热器污氮、氮气管路上增设引风装置；在污氮进分子筛吸附器之前引风导致分子筛吸附器再生冷吹污氮温度升高，需在污氮管路上增设冷冻机；在氮气进氮水预冷器前引风导致氮水预冷器冷冻水温度升高，需在氮水预冷器和空气冷却塔之间增设冷冻机或增加冷冻机功率；当氮气压力充足或是通过调整氮气通过的管路和设备(主要为主换热器)参数降低其阻力时可不增设氮气引风机。简言之，通过在出上塔的污氮和氮气在主换热器中换热后到分子筛吸附器出口或是氮水预冷器出口的管路上增设引风装置，降低上塔、下塔和空压机出口压力，进而降低空压机以及整个空分装置的能耗。
即本发明方法在常规空分装置上增设污氮引风机、氮气引风机和冷冻机，其中，污氮引风机设置在上塔抽出污氮管路上，氮气引风机设置在出上塔塔顶氮气管路上，冷冻机增设在污氮管路和冷冻水管路上。
其中，污氮引风机可设置在污氮出主换热器到分子筛吸附器入口之间，污氮引风机的能耗转化为污氮内能，在分子筛吸附器再生加热阶段可抵消部分加热能耗，在分子筛吸附器再生冷吹阶段增设冷冻机降低污氮温度。
污氮引风机还可设置在分子筛吸附器的污氮出口处，污氮引风机对分子筛吸附器再生过程无不利影响。
氮气引风机可设置在氮气出主换热器到氮水预冷器入口之间，氮气引风机能耗转化为氮气内能，氮气和出氮水预冷器的冷冻水温度升高，用冷冻机降低冷冻水温度。
氮气引风机还可设置在氮水预冷器的氮气出口处，所述氮气引风机对氮水预冷器中冷冻水无不利影响。
冷冻机用于进一步冷却氮水预冷器中的冷冻水温度和降低分子筛吸附器再生冷吹污氮温度。
本发明的上述技术方案的有益效果如下：
上述方案中，通过引风装置解决气体出上塔到出空分装置之间的阻力不平衡问题。通过在最大阻力气体管道上增设引风装置，能够有效降低上塔、下塔和空气压缩机出口压力，从而在很大程度上降低空压机能耗，其能耗减少量大于增设引风系统和增加冷冻机的能耗总和。同时，上塔和下塔压力降低有利于塔内气体的精馏，可进一步降低上塔、下塔和空气压缩机出口压力，从而降低整个空分装置的能耗。本方案增加引风设备改造成本低，节能效益明显。
附图说明
图1为本发明实施例中国内某钢铁企业引进APCI35000Nm3/h的外压缩空分装置在污氮和氮气管路上增加引风设备和冷冻设备后的示意图。
其中：1-空气过滤器；2-主空压机；3-空气冷却塔；4-氮水预冷器；5-空冷塔冷却水泵；6-冷冻水泵；7-氟利昂制冷系统；8-分子筛吸附器；9-分子筛后过滤器；10-分子筛再生气加热器；11-分子筛再生电加热器；12-主换热器；13-增压透平膨胀机；14-气液分离器；15-液氧吸附器；16-热泵；17-下精馏塔；18-冷凝蒸发器；19-上精馏塔；20-粗氩塔；21-污氮过冷器；22-纯氮过冷器；23-粗氩塔冷凝器；24-污氮引风机；25-氮气引风机；26-污氮冷冻机。
具体实施方式
为使本发明要解决的技术问题、技术方案和优点更加清楚，下面将结合附图及具体实施例进行详细描述。
本发明提供一种降低空分装置上塔压力和系统能耗的方法，以解决空分当中压缩机出口压力高，而造成的空分装置能耗大的问题。
该方法在常规空分装置上增设污氮引风机、氮气引风机和冷冻机，其中，污氮引风机设置在上塔抽出污氮管路上，氮气引风机设置在出上塔塔顶氮气管路上，冷冻机增设在污氮管路和冷冻水管路上。
其中污氮引风机在引风加压时使污氮温度升高，在分子筛吸附器再生加热阶段，可代替电加热设备，效果等同或高于电加热设备，冷吹时温度升高，增设冷冻机降低污氮温度；其中氮气在出主换热器后无需保证同污氮一样较高的压力，所以出上塔氮气管路引风设备在上塔压力降低到一定值后再进行加设，当氮气进行引风加压后温度升高，出氮水预冷器冷冻水温度升高，即需要在冷冻水管路上加设冷冻机或提高冷冻机功率；其中氧气是出主换热器三股气流中压力最高的一股，一般情况下无需在氧气管路上增设引风设备，并且在内压缩空分流程中氧气以高压液氧形式进入换热器换热，对液氧加压能耗可以忽略不计。
下面结合实例具体实例予以说明：
如图1所示，为国内某钢铁企业引进APCI35000Nm3/h的外压缩空分装置增加引风设备的工艺流程示意图，在该空分装置中，空气经过空气过滤器1进入主空压机2，然后进入空气冷却塔3进行降温和除湿，空气冷却塔3的水来自于氮水预冷器4并经过氟利昂制冷系统7进行降温。空气冷却塔3连接空冷塔冷却水泵5，冷冻水泵6设置在氮水预冷器4和氟利昂制冷系统7之间。出空气冷却塔3的空气进入分子筛吸附器8进行吸附和纯化。在空气出分子筛吸附器8后的管路上设置分子筛后过滤器9。分子筛吸附器8中的再生气是来自管网的污氮气并经分子筛再生气加热器10和分子筛再生电加热器11加热。经过吸附和纯化的空气一部分经主换热器12换热后进入下精馏塔17(即下塔)，一部分经增压透平膨胀机13增压后进入主换热器12，并从主换热器12中部抽出一部分进入增压透平膨胀机13膨胀制冷，另一部分出主换热器12经气液分离器14分离气液，气体部分与从主换热器12中抽出的空气混合进入增压透平膨胀机13膨胀制冷后经热泵16换热进入上精馏塔19(即上塔)，液体部分直接进入下精馏塔17。上精馏塔19底部部分液氧需要抽出进入液氧吸附器15消除液氧中碳氢化合物，防止发生爆炸，然后经过热泵16换热后进入上精馏塔19。上精馏塔19和下精馏塔17之间通过冷凝蒸发器18进行热交换，实现下精馏塔17顶部氮气的冷凝和上精馏塔19底部液氧的蒸发气化。空气在下精馏塔17和上精馏塔19中经过精馏实现氧氮的分离。氧气从上精馏塔19下部抽出经主换热器12复热后送入氧气管网。氮气从上精馏塔19顶部抽出，依次经纯氮过冷器22和主换热器12复温后送入氮气管网。氩馏分从上精馏塔19中部抽出进入粗氩塔20中精馏，粗氩塔20上部设置粗氩塔冷凝器23，粗氩塔20顶部的部分气体被富氧液空冷凝回流，产品氩气从粗氩塔顶部抽出进入主换热器12中换热。污氮从上精馏塔19上部抽出，经污氮过冷器21进入主换热器12复热成为分子筛吸附器的再生气。
本方法在上述装置出主换热器的污氮气和氮气管路上分别增设污氮引风机24和氮气引风机25，保证在上塔压力降低时能够使这些气体克服管路和空分设备当中的阻力；同时在污氮管路上增设污氮冷冻机26，降低分子筛吸附器再生冷吹阶段污氮温度。上塔压力降低，使得下塔和空压机出口压力降低，空气压缩机能耗也将会降低。
以上述空分流程为例，以0.01bar为单位量降低上塔压力，当上塔压力降低量为0.1bar时，空分装置中的空气压缩机、污氮引风机、氮气引风机和冷冻机能耗如表1所示，在上塔压力降低时空气压缩机能耗明显降低，其他引风设备和冷冻设备能耗增加，其中污氮引风能耗为分子筛吸附器冷吹时能耗，即在分子筛吸附器再生加热阶段的污氮引风能耗抵消掉氮气加热器的能耗，冷冻机能耗为污氮冷冻机和冷却冷冻水的冷冻机能耗之和。具体最终能耗的变化关系如表2所示，在表2中列出了上塔压力的降低量同空压机出口压力和能耗降低量之间的关系，该表中的能耗降低量为空压机能耗降低量减去引风机和冷冻机能耗的增加量，能耗降低比为能耗降低量同空压机能耗的比值，空压机能耗为14914kw。
表1上塔压力降低量同各个空分设备的能耗关系表
Figure GDA0002396104720000061
表2上塔压力降低量同空压机出口压力以及能耗降低量关系
Figure GDA0002396104720000062
从上表中可以看出，当上塔压力降低量为0.04bar时，空分流程能耗降低量为116.34kw，如果压力继续降低能耗变化量不再明显，在降低0.1bar时，能耗降低量达到136.71kw，约占整个空压机能耗的0.92％，接近1％。如果按照每年开车时间为365天，每天24小时，工业用电电价0.8元/千瓦时，能耗降低量为136.71kw，每年节省成本约为95.80万元。
通过能耗分析得出最优节能方案，污氮引风装置和污氮冷冻机设置不变，将氮气引风装置设置在氮气出氮水预冷器的出口处，氮气的压力降低，体积流量增加，引风装置能耗增加，但是氮气温度不变，冷冻水的冷冻机能耗也将不会增加。其具体上塔压力降低量同能耗量关系如表3所示。
表3上塔压力降低量同能耗降低量关系表
Figure GDA0002396104720000071
从上表中可以看出，当上塔压力降低0.1bar时，总能耗降低量为147.83kw，能耗降低量占整个空压机能耗的0.99％，每年电力成本可节约103.60万元。如果通过调整氮气通过的管路和设备参数降低其阻力，可不增设氮气引风装置，既不增加增设氮气引风机的固定投入成本，也没有增加氮气引风机和冷冻机的能耗，当上塔压力降低0.1bar时，整个空分装置的能耗降低量约为335.74kw，约占空气压缩机能耗的2.25％。如果按照上述成本计算方式，当能耗降低量为335.74kw，每年能耗节省成本约为235.29万元。本发明使得上塔压力降低，上塔内部的精馏环境改善，提高精馏了效果，当上塔压力降低0.1bar时，出上塔的氮气和污氮浓度几乎不变，氧气产品浓度提高0.067％。
以上所述是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明所述原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (6)

1.一种降低空分装置上塔压力和系统能耗的方法，其特征在于：在常规空分装置上增设污氮引风机、氮气引风机和冷冻机，其中，污氮引风机设置在上塔污氮管路上，氮气引风机设置在氮气管路上，冷冻机增设在污氮管路和冷冻水管路上。
2.根据权利要求1所述的降低空分装置上塔压力和系统能耗的方法，其特征在于：所述污氮引风机设置在污氮出主换热器到分子筛吸附器入口之间，污氮引风机的能耗转化为污氮内能，在分子筛吸附器再生加热阶段能够抵消部分加热能耗，在分子筛吸附器再生冷吹阶段通过增设冷冻机降低污氮温度。
3.根据权利要求1所述的降低空分装置上塔压力和系统能耗的方法，其特征在于：所述污氮引风机设置在分子筛吸附器的污氮出口处。
4.根据权利要求1所述的降低空分装置上塔压力和系统能耗的方法，其特征在于：所述氮气引风机设置在氮气出主换热器到氮水预冷器入口之间，通过冷冻机降低出氮水预冷器冷冻水温度。
5.根据权利要求1所述的降低空分装置上塔压力和系统能耗的方法，其特征在于：所述氮气引风机设置在氮水预冷器的氮气出口处。
6.根据权利要求1所述的降低空分装置上塔压力和系统能耗的方法，其特征在于：所述冷冻机降低出氮水预冷器的冷冻水温度和降低分子筛吸附器再生冷吹污氮温度。
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