CN100424451C - 超低压低温法空气分离氧气制备方法 - Google Patents

超低压低温法空气分离氧气制备方法 Download PDF

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CN100424451C
CN100424451C CNB2006100797828A CN200610079782A CN100424451C CN 100424451 C CN100424451 C CN 100424451C CN B2006100797828 A CNB2006100797828 A CN B2006100797828A CN 200610079782 A CN200610079782 A CN 200610079782A CN 100424451 C CN100424451 C CN 100424451C
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liquid nitrogen
tower
nitrogen
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白杨
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Bai Yang
Cao Pengju
Qiu Jing
Weifang Super Combustion Gas Science And Technology Ltd
Yun Xingsheng
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Abstract

一种超低压低温法空气分离制氧流程，由液氮作冷源的单级精馏制氮流程、液空泵、液空气化器、全低压流程、液氮泵等组合而成，经空气换热器热段预冷的超低压空气与膨胀空气混合，进入液空气化器与液空换热并放出液空气化所需的汽化潜热，再进入空气换热器冷段被过度冷却送入单级精馏塔的底部，初步分离得液空并在冷凝蒸发器低压侧取出纯氮，利用液空泵将液空压缩送入液空气化器后产生的蒸气，替代双级精馏塔原本从另一空气换热器来的低压原料空气，从而实现超低压制氧，双级精馏塔下塔引出的液氮节流后，全部或部分送入单级精馏塔冷凝蒸发器低压侧，再由液氮泵将其压缩送入上塔上部参与精馏，从而防止了低压侧液氮中的高沸点物质特别是氧的浓聚，使液氮作冷源单级精馏塔能正常工作。

Description

超低压低温法空气分离氧气制备方法
技术领域
本发明涉及一种低温法空气分离制氧流程，特别是一种超低压低温法空气分离制氧流程。
背景技术
从1902年德国林德公司制造出第一台10m3/h低温法空气分离制氧机以来至今已有一百多年的历史，在此期间，制氧机由小到大，不断发展。按操作压力分类低温法空气分离氧气制备流程分为高压流程、中压流程、全低压流程，其中全低压流程又包括切换式自清除流程和分子筛纯化带增压透平膨胀机流程。制氧能耗与加工空气的压力有关，加工空气的压力越低制氧能耗越低，目前世界公认能耗最低的流程是全低压流程。我们已经知道，工业上空气液化常用两种方法获得低温，即空气的节流膨胀和等熵膨胀，同时已还知道无论从温降大小及制冷量大小方面比较，等熵膨胀都比节流膨胀效果显著，而且膨胀机还可以回收一部分膨胀功，从而提高其经济性。冷却空气需要冷量，而冷量的产生则要花一定的代价，预先要将空气压缩。按理压缩空气应尽可能多的通过膨胀机制取冷量使其制冷量最大化，从而降低制氧能耗。可是分析目前世界公认能耗最低的全低压流程，可以看出压缩空气中只有小部分(最多约占25％)是通过膨胀机产冷的，大部分(约占75％)则是直接进入装置经节流降压后复热后出装置的，可以认为这部分压缩空气是不产冷的(相对于通过膨胀机产冷时的制冷量而言)。冶金工业出版社1977年8月出版的《制氧机的原理与操作》第31页中说“对于目前的制氧装置，生产的是气氧，要求装置的制冷量不大，只需要装置提供克服跑冷损失与热交换不完全的冷损失的制冷量即可，因此空气不必压缩到很高的压力。由于精馏空气要求精馏塔下塔压力为6大气压，所以只需将空气压缩至下塔压力就可以满足装置所需的制冷量。”单从冷量方面看，这样的理论显然是错误的，因为全低压流程的压缩空气如果全部通过膨胀机产冷的话，其制冷量将大大超过装置所需的制冷量。将通过膨胀机产冷的这部分空气压缩，使装置能够提供克服跑冷损失与热交换不完全的冷损失的制冷量，是必需(须)的，而将并不产冷的空气也压缩至6大气压显然是很无奈的，因此说全低压流程其实是一种很不经济的流程，它迟早会被能耗更低的超低压流程所取代。冶金工业出版社1997年3月出版的《制氧技术》第244页制氧机的发展中说：现在，中、大型制氧机全部为全低压流程。小型制氧机也向全低压方向发展，而且对超低压流程正进行研究探讨。
发明内容
本发明的目的就是要提供一种超低压低温法空气分离氧气制备方法，从而使超低压制氧得以实现，它只需对通过膨胀机产冷的这部分空气压缩，使装置能够提供克服跑冷损失与热交换不完全的冷损失的制冷量即可，对上述提到的压缩空气中不产冷的这部分空气则不再需要压缩至6大气压，而只需压缩至2大气压即可，制氧能耗为低温法空气分离制氧的最低值。
发明是这样实现的：一种超低压低温法空气分离氧气制备方法，制备流程由液氮作冷源的单级精馏空气液化液空制备流程、液空泵、液空气化器、全低压流程、液氮泵等组合而成，所述液空制备流程包括一第三分馏塔和第二冷凝蒸发器组成的单级精馏塔，所述全低压流程包括一第一分馏塔、第二分馏塔和第一冷凝蒸发器组成的双级精馏塔。经第二空气换热器预冷的超低压空气与经过膨胀机膨胀后的空气混合，进入液空气化器与液空换热并放出液空气化所需的汽化潜热，再进入第三空气换热器被过度冷却后送入第三分馏塔的底部，经过初步分离可在第三分馏塔塔底得到富氧液空，在第二冷凝蒸发器的低压侧取出氮气，利用液空泵将得到的富氧液空压缩至所需压力(6大气压)送入液空气化器后产生的蒸气，替代第一分馏塔原本从第一空气换热器来的低压原料空气，从而实现超低压制氧，将第一分馏塔上部引出的液氮节流后全部或部分送入第二冷凝蒸发器的低压侧，再由液氮泵将其压缩至所需压力送入第二分馏塔上部参与精馏，从而防止了第二冷凝蒸发器低压侧液氮中的高沸点物质特别是氧的浓聚，使液氮作冷源的单级精馏塔能够正常工作，即可在第二冷凝蒸发器的低压侧取出氮气，在第三分馏塔的塔底得到富氧液空。
附图说明
附图是依据本发明提出的超低压低温法空气分离氧气制备流程图，图中E101为第一空气换热器、E201为第二空气换热器、E202为第三空气换热器，C101为第一分馏塔、C102为第二分馏塔、C201为第三分馏塔，K1为第一冷凝蒸发器、K2为第二冷凝蒸发器，Fs为过冷器，AP为液空泵，NP为液氮泵，SL为液空气化器，J1为液空节流阀、J2为第一液氮节流阀、J3为第二液氮节流阀，D为液空调节阀，ET为膨胀机，B为膨胀机ET的增压机，增压机后为冷却器用于冷却增压空气(附图中未画出)。
具体实施方式
下面结合附图及实施例对流程的细节和工作原理进一步描述。
附图中的这些部机E101、C101、K1、C102、FS、J1、J2、ET、B等组成一相当于把膨胀后空气复热后放空的全低压流程，双级精馏塔由第一分馏塔C101、第二分馏塔C102和第一冷凝蒸发器K1组成。显然，第一分馏塔C101上部引出经第一液氮节流阀J2节流降压后的液氮是可以直接送入第二分馏塔C102的上部参与精馏的(附图中未画出)，由于通过膨胀机ET的膨胀空气量大小对双级精馏塔的精馏工况没有任何影响，因此膨胀机ET能够提供足够的冷量，那么只用部分返流气体就可以将出第一空气换热器E101压力为6大气压的空气，冷却至饱和温度并少量含湿，从而使得双级精馏塔能够正常工作，即可在第二分馏塔C102的顶部和下部分别取出氮气和氧气，其原理与目前正在广泛应用中的双级精馏塔的工作原理是完全相同的，在此不再作阐述。
附图中的这些部机E201、E202、C201、K2、FS、J3、ET、B等组成一液氮作冷源的单级精馏空气液化液空制备流程，单级精馏塔由第三分馏塔C201和第二冷凝蒸发器K2组成。同样另部分返流气体能将出第三空气换热器E202的空气冷却至饱和温度并少量含湿，冷却后的空气送入第三分馏塔C201的底部，在塔内空气自下而上与回流液接触至塔的上部便得到氮气，氮气进入第二冷凝蒸发器K2的高压侧被冷凝为液氮，一部分液氮作为第三分馏塔C201的回流液沿塔自上而下流动，回流液体中的氧浓度不断提高，至塔底便得到氧纯度较高的富氧液空；另部分液氮引出经过过冷器FS过冷后经第二液氮节流阀J3节流降压后，送入第二冷凝蒸发器K2的低压侧作冷源，使进入第二冷凝蒸发器K2高压侧的氮气被冷凝为液氮，而低压侧的液氮自身受热后便蒸发生成氮气。由于第二冷凝蒸发器K2的高低压侧均为同一种物质氮，实验表明，在不同的压力下，对应的饱和温度也不同。压力越高，饱和温度也增高，亦即压力越高蒸气越容易液化。假设第二冷凝蒸发器K2低压侧的压力为1.5大气压(低压侧压力应该等于氮气克服所通过各设备的阻力及由装置排出时所必须的压力之和)，K2的温差为3K，那么K2高压侧的压力只需2大气压就可以保证进入高压侧的氮气被冷凝为液氮，而低压侧的液氮自身则受热蒸发为氮气，也就是说经第二空气换热器E201、液空气化器SL、第三空气换热器E202进入第三分馏塔C201底部的原料空气只需压缩至2大气压，就可以保证液氮作冷源的单级精馏塔能够正常工作，即可在第二冷凝蒸发器K2的低压侧取出氮气，在第三分馏塔C201的塔底得到富氧液空。
由于第三分馏塔C201的压力只有2大气压，因此可以将经过膨胀机ET膨胀后的空气送入第三分馏塔C201参与精馏。如果将膨胀空气直接送入第三分馏塔C201的底部，就必须使其温度接近或达到饱和温度，以减少过热度对精馏工况的影响，显然这样的温度要求对膨胀机是不利的。本发明将膨胀空气送入经过第二空气换热器E201预冷的正流空气中，既组织了产冷系统，又使得膨胀后空气同样可以进入到第三分馏塔C201参与精馏。
在第三分馏塔C201塔底得到的富氧液空，被液空泵AP压缩至所需压力(6大气压)送入液空气化器SL，在这里部分压力液空由于吸收了由超低压空气和膨胀后空气组成的混合空气放出的汽化潜热而被气化为饱和蒸气，将饱和蒸气和另部分不要求气化而通过液空调节阀D引出的液空，一起送入第一分馏塔C101的底部继续精馏，由于第一分馏塔C101的加工能力是有限的，这时可以缓慢关闭第一分馏塔C101原本从第一空气换热器E101来的低压原料空气(同时也要缓慢关闭第一空气换热器E101的返流气体)，从而实现了超低压制氧的目的。
超低压空气和膨胀后空气组成的混合空气经过液空气化器SL时，由于放出了液空气化所需的汽化潜热，混合空气进入第三空气换热器E202时被过度冷却，部分混合空气被液化为液体流入第三分馏塔C201的塔底，另部分未被液化的混合空气则作为第三分馏塔C201的原料空气参与精馏。由于第三空气换热器E202液化空气的作用明显，用液化器是否会更好些，由专业的工程技术人员考虑决定。
由于精馏塔存在冷损失，为了补偿冷量，加工空气入塔的状况不仅要达到饱和，而且必须含有少量的液体；又由于膨胀后空气是进入第三分馏塔C201底部参与精馏的，膨胀空气的多少对精馏工况没有任何影响，因而膨胀空气量可以随意增加，这样入塔的混合空气中所含的液体比例势必要增加(由于混合空气液化量大，压力会下降，这时需增加超低压空气的供给量，以保证第三分馏塔C201的压力)，显然，这些为了维持装置的冷量平衡，而要求入塔的混合空气中必须含有的液体，是不要求其在液空气化器SL中气化为饱和蒸气的，因而通过液空调节阀D将其引出，使之随同饱和蒸气一起送入第一分馏塔C101底部参与精馏。
由上可知，第三分馏塔C201塔底的液空由三部分的液体构成：1、第三分馏塔C201的回流液；2、入塔混合空气由于放出汽化潜热而被过度冷却液化产生的液体；3、为了维持装置的冷量平衡，而要求入塔空气中必须含有的液体。其中1和2产生的液空是要求在液空气化器SL中被气化为饱和蒸气的，由于进入液空气化器SL的混合空气的温度可以高于压力液空的温度(具体温差由专业的工程技术人员考虑决定)，混合空气的量也大于被要求气化的液空产生的蒸气量，因而压力液空能够被气化为饱和蒸气。
由于从第三分馏塔C201上部引出的液氮不可能达到百分之百的含氮量，那么随着第二冷凝蒸发器K2低压侧液氮的不断蒸发，一些高沸点物质特别是氧就会逐渐浓聚，从而使得第三分馏塔C201的压力逐渐升高，那么从第二冷凝蒸发器K2低压侧取出的氮气的含氧量也升高。因此，单独的液氮作冷源的单级精馏塔实际上是不能正常工作的。为了防止第二冷凝蒸发器K2低压侧液氮中的高沸点物质特别是氧的浓聚，使液氮作冷源的单级精馏塔能够正常工作，本发明将第一分馏塔C101上部引出，经第一液氮节流阀J2节流降压后的液氮全部或部分送入第二冷凝蒸发器K2的低压侧，再由液氮泵NP将其压缩至所需压力送入第二分馏塔C102的上部参与精馏，这样既不影响第二分馏塔C102的精馏，又防止了第二冷凝蒸发器K2低压侧液氮中的高沸点物质特别是氧的浓聚，使液氮作冷源的单级精馏塔能够正常工作，即可在第二冷凝蒸发器K2的低压侧取出氮气，在第三分馏塔C201的塔底得到富氧液空。在这里所用的原理与目前被广泛采用的从主冷中排放相当于气氧产量1％的液氧就可以防止乙炔等碳氢化合物在主冷中浓聚的原理是一样的。同样，液空气化器SL由于不断有液空经液空调节阀D引出，也可以防止乙炔等碳氢化合物的浓聚。由于经液空调节阀D引出的液空量与膨胀机ET提供的冷量大小有关，而膨胀空气又是参与精馏的，不存在空气复热放空造成氧损失的问题，并且膨胀空气量对精馏工况没有任何影响。因此，膨胀机ET的制冷量调节范围很大，必要时可以生产大量的液态产品，使得第一冷凝蒸发器K1更具安全保障。
所述空气视为经过分子筛纯化后的空气。

Claims (2)

1. 一种超低压低温法空气分离氧气制备方法，其特征在于出第一空气换热器(E101)的低压原料空气被部分返流气体冷却至饱和并少量含湿后，送入第一分馏塔(C101)、第二分馏塔(C102)和第一冷凝蒸发器(K1)组成的双级精馏塔的第一分馏塔(C101)底部，经初步分离在第一分馏塔(C101)塔底得到富氧液空在上部引出液氮，引出的液氮经过过冷器(FS)过冷后，经第一液氮节流阀(J2)节流降压后全部或部分送入第二冷凝蒸发器(K2)的低压侧，再由液氮泵(NP)将其压缩至所需压力送入第二分馏塔(C102)上部参与精馏，在第一分馏塔(C101)塔底得到的富氧液空经过过冷器(FS)过冷后，经液空节流阀(J1)节流降压后送入第二分馏塔(C102)中部参与精馏，在第二分馏塔(C102)的顶部和下部分别取出氮气和氧气；经第二空气换热器(E201)预冷的超低压空气与经过膨胀机(ET)膨胀后的空气混合，进入液空气化器(SL)与液空换热并放出液空气化所需的汽化潜热，再进入第三空气换热器(E202)被过度冷却后，送入第三分馏塔(C201)和第二冷凝蒸发器(K2)组成的单级精馏塔的第三分馏塔(C201)底部，经初步分离在第三分馏塔(C201)塔底得到富氧液空在上部引出液氮，引出的液氮经过过冷器(FS)过冷后，经第二液氮节流阀(J3)节流降压后送入第二冷凝蒸发器(K2)的低压侧，受热蒸发出来的气氮作为产品引出，在第三分馏塔(C201)塔底得到的富氧液空经液空泵(AP)压缩至所需压力送入液空气化器(SL)，部分液空由于吸收了混合空气放出的汽化潜热而被气化为饱和蒸气，将饱和蒸气和另部分不需要气化而经液空调节阀(D)引出的液空，一起送入第一分馏塔(C101)底部继续参与精馏，使之替代第一分馏塔(C101)原本从第一空气换热器(E101)来的低压原料空气。
2. 根据权利要求1所述的氧气制备方法，其特征在于第一分馏塔(C101)上部引出的液氮，经过过冷器(FS)过冷后经第一液氮节流阀(J2)节流降压后，部分液氮送入第二分馏塔(C102)上部参与精馏，另部分液氮送入第二冷凝蒸发器(K2)的低压侧，再由液氮泵(NP)将其压缩至所需压力送入第二分馏塔(C102)上部参与精馏，从而防止第二冷凝蒸发器(K2)低压侧液氮中的高沸点物质特别是氧的浓聚，使液氮作冷源的单级精馏塔能够正常工作，即可在第二冷凝蒸发器(K2)的低压侧取出氮气，在第三分馏塔(C201)的塔底得到富氧液空。
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Address before: 545002 Guangxi Liuzhou Liubei North Bird Road, No. 33 Fu Jiang Xiaoyuan 5 Building 2 unit 401 room

Patentee before: Bai Yang

TR01 Transfer of patent right
TR01 Transfer of patent right

Effective date of registration: 20180403

Address after: 545002 the Guangxi Zhuang Autonomous Region, Liuzhou Liu Liu North District, building No. 33, No. 202

Co-patentee after: Weifang super combustion gas Science and Technology Ltd.

Patentee after: Bai Yang

Co-patentee after: Yun Xingsheng

Co-patentee after: Cao Pengju

Co-patentee after: Qiu Jing

Address before: 545002 the Guangxi Zhuang Autonomous Region, Liuzhou Liu Liu North District, building No. 33, No. 202

Co-patentee before: Weifang super combustion gas Science and Technology Ltd.

Patentee before: Bai Yang

Co-patentee before: Yun Xingsheng

Co-patentee before: Cao Pengju

CF01 Termination of patent right due to non-payment of annual fee
CF01 Termination of patent right due to non-payment of annual fee

Granted publication date: 20081008

Termination date: 20200515