CN103998733B - 排气系统和选择性催化还原方法 - Google Patents
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Abstract
本发明涉及一种内燃机(16)用排气系统,其包括至少一个涡轮增压器(4)、用于将废气从内燃机(16)的气缸(15)中导出的排气管(19)、布置在涡轮增压器(4)的涡轮机(4a)下游的用于进行选择性催化还原的催化转化器(12)、布置得离开排气管(19)且与加压气体源(3,6)流体连通的混合空间(1,2)、以及用于将还原剂引入混合空间(1,2)的装置(10,13)。混合空间(1,2)与内燃机(16)的排气管(19)流体连通以将还原剂和加压气体的混合物从涡轮增压器(4)的涡轮机(4a)的上游导入排气管(19)内。本发明还涉及用于进行选择性催化还原的方法。
Description
技术领域
本发明涉及以下第一方面所述的内燃机用排气系统。本发明还涉及以下第二方面所述的选择性催化还原方法。
背景技术
船与发电厂的内燃机的氮氧化物(NOx)排放越来越受到关注,并且持续受到由国际海事组织(IMO)和其他立法机构所设定的越来越严格的条例的管制。在某种程度上,由不同条例设定的要求可以利用与内燃机的运行直接关联的手段来达到,例如废气再循环、柴油机中的高燃料注入压力、进气管内注水等。然而,许多用于减少NOx排放的发动机相关措施对燃料效率有负面影响,并且它们不足以满足最严格的排放限制。对于最终的NOx减少,需要选择性催化还原(SCR)。利用SCR,可以实现最高90%甚至更高的NOx减少。
在SCR系统中,使用催化剂材料和还原剂来分解在燃烧期间形成的NOx。在常见的SCR系统中,催化剂被布置在位于反应器内部的形成蜂窝结构体的支撑性陶瓷材料的表面上。在催化剂的表面上,NOx与用作还原剂的氨反应,并形成氮气和水。在实践中,出于安全原因常常用脲代替氨。这尤其适用于其中氨泄漏会形成严重危险的海事应用中。将脲以水溶液形式注入废气流。由于废气的温度高,水会蒸发并且脲分子分解为氨和二氧化碳。
为了有效地减少NOx并使脲的用量最小化,并且为了使透过SCR系统漏出的氨最小化,脲与废气的有效混合非常重要。在许多现有技术的解决方案中,已通过在脲注入点和催化剂单元之间设置相对长的排气管段来确保充分的混合。然而,这为排气系统的构建带来了限制。尤其是在可利用空间有限的船中,理想的是排气系统需要的空间尽可能的少。另一个问题在于,现代中速和低速发动机的热效率的提高导致废气温度较低。如果将催化转化器放置得离发动机较远,废气的低温可能会对催化转化器的功能发挥产生负面影响。
通过将催化转化器布置在具有两级涡轮增压的发动机中的涡轮机级之间,可以实现对于SCR而言足够高的废气温度。然而,为了实现还原剂与废气的充分混合,往往需要从高压涡轮增压器的涡轮机的上游进行注入。从涡轮机上游注入脲存在其难度。废气的高压和高温会造成注射器堵塞和脲结晶的风险。另外,若涡轮机被液滴击中,则其会暴露于腐蚀之下。
发明内容
本发明的一个目的在于提供一种改进的内燃机用排气系统。本发明的排气系统的特征性特点在以下第一方面中给出。本发明的另一目的在于提供一种改进的选择性催化还原方法。本发明的方法的特征由以下第二方面给出。
根据本发明的第一方面,一种内燃机用排气系统包括:至少一个涡轮增压器,用于将废气从发动机的气缸内导出的排气管,以及布置在所述涡轮增压器的涡轮机下游的用于进行选择性催化还原的催化转化器。在离开所述排气管的位置设置有混合空间,所述混合空间与加压气体源流体连通。所述排气系统还包括用来将还原剂导入所述混合空间的装置,并且所述混合空间与发动机的排气管流体连通,以将还原剂和加压气体的混合物从涡轮增压器的涡轮机的上游导入所述排气管内。
根据本发明的一个实施方式,提供一种内燃机16用排气系统,所述排气系统包括:
-至少一个涡轮增压器4,
-排气管19,所述排气管19用于将废气从所述内燃机16的气缸15中导出,和
-催化转化器12,所述催化转化器12被布置在所述涡轮增压器4的涡轮机4a的下游,用于进行选择性催化还原,
-混合空间1,2,所述混合空间1,2被布置在离开所述排气管19的位置,且与加压气体源3,6流体连通,和
-装置10,13,所述装置10,13用于将还原剂引入所述混合空间1,2,
所述混合空间1,2与所述内燃机16的所述排气管19流体连通,以将所述还原剂和所述加压气体的混合物从所述涡轮增压器4的所述涡轮机4a的上游导入所述排气管19内,
其特征在于,所述加压气体源3,6是所述内燃机16的排气歧管3或进气管6。
在本发明的第二方面,提供一种进行选择性催化还原的方法,在该方法中,在将内燃机的废气导入催化转化器之前,将还原剂与所述废气混合。在将还原剂从涡轮增压器的涡轮机的上游导入发动机的排气管之前,将还原剂与加压气体在混合空间中混合。
根据本发明的一个实施方式,提供一种进行选择性催化还原的方法,在所述方法中,在将内燃机16的废气导入催化转化器12之前,将还原剂与所述废气混合,在将所述还原剂从涡轮增压器4的涡轮机4a的上游导入所述内燃机16的排气管19之前,将所述还原剂与所述加压气体在混合空间1,2中混合,其特征在于,所述加压气体是所述内燃机16的废气或进气。
通过将还原剂与加压气体混合,在将还原剂导入排气管之前,还原剂完全蒸发。这有助于避免排气管和涡轮增压器中的腐蚀问题。由于催化转化器被布置在涡轮增压器的涡轮机的下游,在废气进入催化转化器之前,还原剂已与主废气流良好混合。
混合空间可以是混合室或混合管。根据本发明的一个实施方式,加压气体源是发动机的排气歧管。当发动机的废气被用作加压气体时,不必存在用于调节气流的任何控制装置,但是,通过将相关导管设定为合适的尺寸,可以实现合适的进入混合空间的废气流。
根据本发明的另一个实施方式,加压气体源是发动机的进气管。当还原剂与清洁的进气在适中的温度下混合时,可避免还原剂注射器的结晶和堵塞问题。因此,可以使用大量的极小型注射器喷嘴,这确保了即使在载量低和进气温度低时脲也会完全蒸发。
附图说明
图1示意性显示了具有一种SCR布局的内燃机。
图2示意性显示了具有另一种SCR布局的内燃机。
图3示意性显示了具有又一种SCR布局的内燃机。
具体实施方式
现在参考附图对本发明的实施方式进行更详细的说明。
在图1中示意性地显示了具有SCR系统的大内燃机16。内燃机16可以例如为船的主发动机或辅助发动机,或者是用于在发电厂发电的发动机。图1中显示了4个气缸15,但内燃机16可以包括任何合理数目的气缸15,气缸15以例如直线或者V型构造排布。内燃机16的排气系统包括串联连接的高压涡轮增压器4和低压涡轮增压器14。高压涡轮增压器4的涡轮机4a被布置成接收来自内燃机16的废气。废气从高压涡轮增压器4被导引至低压涡轮增压器14的涡轮机14a。排气系统还包括用于将废气从内燃机16的气缸15中导出的排气管19。排气管19包括排气歧管3、中间排气管20和低压排气管21,排气歧管3将内燃机16的气缸15连接至高压涡轮增压器4的涡轮机4a,中间排气管20将高压涡轮增压器4的涡轮机4a连接至低压涡轮增压器14的涡轮机14a,而低压排气管21将废气从低压涡轮增压器14的涡轮机14a导出内燃机室。废气歧管3包括收集管3a和多个支管3b。在内燃机16的每个气缸15与收集管3a之间布置有一个支管3b,以将气缸15与收集管3a连接。
内燃机16的进气首先被低压涡轮增压器14的压缩机14b加压。进气从低压涡轮增压器14被导入高压涡轮增压器4的压缩机4b,以进一步提高进气的压力。在低压涡轮增压器14的压缩机14b和高压涡轮增压器4的压缩机4b之间布置有第一增加气体冷却器17。在高压涡轮增压器4的压缩机4b的下游布置有第二增压气体冷却器18。进气管6中的进气被导入内燃机16的气缸15内。进气管6包括低压进气管24、中间进气管23和进气歧管22,低压进气管24将进气导入低压涡轮增压器14的压缩机14b中,中间进气管23将进气从低压涡轮增压器14的压缩机14b导入高压涡轮增压器4的压缩机4b中,而进气歧管22将高压涡轮增压器4的压缩机4b连接至内燃机16的气缸15。
内燃机16设置有用于进行选择性催化还原(SCR)的催化转化器12。催化转化器12被布置在高压涡轮增压器4的涡轮机4a与低压涡轮增压器14的涡轮机14a之间。在涡轮增压器4、14的涡轮机4a、14a之间,废气温度对于SCR而言足够高。选择性催化还原需要还原剂与废气在废气通过催化转化器12中的催化剂材料之前先混合。在附图的实施方式中,还原剂为水溶液形式的脲。脲储存在还原剂罐9中。在将脲导入排气管19中的主废气流之前,使脲与加压气体在混合空间中混合,所述混合空间布置在离开排气管19的位置。在图1的实施方式中,混合空间是混合室1。加压气体是内燃机16的废气。因此,混合室1与内燃机16的排气歧管3流体连通。为此目的,内燃机16设置有废气输送管5,该废气输送管5包括收集管5a和多个支管5b。废气输送管5的支管5b与废气歧管3的支管3b连接,这充当加压气体源。废气输送管5的直径小于废气歧管3的直径,因此内燃机16的废气仅有一小部分通过废气输送管5。可调泵13和注射器10被用作将脲导入混合室1的装置。在混合室1中,脲与废气混合。混合室1还经由输送管11与排气管19流体连通。通过输送管11,脲与废气的混合物在高压涡轮增压器4的涡轮机4a的上游从混合室1输送至排气管19中。所述混合物被引入主废气流的地点位于废气歧管3的所有支管3b的下游。
通过将脲与废气混合,脲溶液在被导入排气管19之前就完全蒸发。这有助于避免排气管19和高压涡轮增压器4中的腐蚀问题。由于催化转化器12被布置在高压涡轮增压器4的涡轮机4b的下游,因而在废气进入催化转化器12之前,脲已与主废气流很好地混合。
图2显示了本发明的另一个实施方式。在该实施方式中,混合空间是混合管2,而不是混合室1。此外,在该实施方式中,加压气体是内燃机16的废气。混合管2与内燃机16的废气歧管3流体连通,并且平行于废气歧管3。废气从废气歧管3的收集管3a被导入混合管2。混合管2的直径小于废气歧管3的收集管3a的直径,因此内燃机16的废气仅有一小部分通过混合管2。脲由注射器10导入混合管2。可调泵13用于从还原剂罐9输送脲溶液。为了确保有效的混合,混合管2中的脲注入点位于混合管2的在废气流动方向上的前四分之一内。在与高压涡轮增压器4的涡轮机4a接近的位置,混合管2连接于排气管19。连接点位于高压涡轮增压器4的涡轮机4a的上游,但位于废气歧管3的支管3a的下游。
图3显示了本发明的第三实施方式。在该实施方式中,与还原剂混合的加压气体是内燃机的进气。混合空间是混合室1。混合室1以供气管7与内燃机16的进气管6连接。供气管7设置有用于调节进入混合室1的气流的阀8。脲由注射器10引入混合室1。可调泵13用于从还原剂罐9输送脲溶液。在高压涡轮增压器4的涡轮机4a的上游、但在废气歧管3的支管3b的下游的位置,脲与进气的混合物从混合室1被导入内燃机16的排气管19内。
当脲与清洁的进气在适中的温度下混合时,可避免注射器10的结晶和堵塞问题。因此,可以使用大量的极小型注射器喷嘴,这确保了即使在载量低和进气温度低时脲也会完全蒸发。脲的完全蒸发有助于避免对涡轮增压器4的涡轮机4a的腐蚀损害。此外,也能避免排气管19的管壁的润湿问题。
本领域技术人员应该理解,本发明不限于上文所述的实施方式,而是可以在所附权利要求的范围内变化。例如,本发明还可以应用于具有一级涡轮增压的发动机。在V型发动机中,发动机的每排气缸均设置有其自己的涡轮增压器,排气系统可以包括用于发动机的每排气缸的独立的混合空间。
Claims (6)
1.一种内燃机(16)用排气系统,所述排气系统包括:
-至少一个涡轮增压器(4),
-排气管(19),所述排气管(19)用于将废气从所述内燃机(16)的气缸(15)中导出,和
-催化转化器(12),所述催化转化器(12)被布置在所述涡轮增压器(4)的涡轮机(4a)的下游,用于进行选择性催化还原,
-混合空间(1,2),所述混合空间(1,2)被布置在离开所述排气管(19)的位置,且与加压气体源(3,6)流体连通,和
-装置(10,13),所述装置(10,13)用于将还原剂引入所述混合空间(1,2),
所述混合空间(1,2)与所述内燃机(16)的所述排气管(19)流体连通,以将所述还原剂和所述加压气体的混合物从所述涡轮增压器(4)的所述涡轮机(4a)的上游导入所述排气管(19)内,
其特征在于,所述加压气体源(3,6)是所述内燃机(16)的排气歧管(3)或进气管(6)。
2.如权利要求1所述的排气系统,其特征在于,所述混合空间(1,2)是混合室(1)。
3.如权利要求1所述的排气系统,其特征在于,所述混合空间(1,2)是混合管(2)。
4.一种进行选择性催化还原的方法,在所述方法中,在将内燃机(16)的废气导入催化转化器(12)之前,将还原剂与所述废气混合,在将所述还原剂从涡轮增压器(4)的涡轮机(4a)的上游导入所述内燃机(16)的排气管(19)之前,将所述还原剂与所述加压气体在混合空间(1,2)中混合,其特征在于,所述加压气体是所述内燃机(16)的废气或进气。
5.如权利要求4所述的方法,其特征在于,所述还原剂与所述加压气体在混合室(1)中混合。
6.如权利要求4或5所述的方法,其特征在于,所述还原剂与所述加压气体在混合管(2)中混合。
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WO1997000376A1 (en) * | 1995-06-19 | 1997-01-03 | Caterpillar Inc. | A METHOD FOR TREATING AN EXHAUST GAS STREAM FOR THE REMOVAL OF NOx |
EP2280155A2 (de) * | 2009-07-30 | 2011-02-02 | MAN Nutzfahrzeuge AG | Verfahren und Vorrichtung zur Reinigung eines Abgasstroms einer abgasaufgeladenen Brennkraftmaschine |
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