CN108613478A - 一种极寒地区天然气液化装置及方法 - Google Patents
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- F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
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Abstract
本发明公开了一种极寒地区天然气液化装置及方法,装置包括乙烷液化制冷系统和甲烷过冷制冷系统;所述乙烷液化制冷系统包括依次连接的乙烷压缩机、乙烷空气冷却器、乙烷凝液收集罐、高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器;所述甲烷过冷制冷系统包括依次连接的天然气过冷器、甲烷压缩机和甲烷空气冷却器;来自外部净化天然气管道和来自甲烷空气冷却器的甲烷管道均依次与高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器连接。本发明采用两级阶式制冷,除具有传统阶式制冷工艺特点外,还具有简化流程、减少一组压缩机组,操作更便捷,同时冷剂压缩机、换热器国产化等特点。
Description
技术领域
本发明涉及一种极寒地区天然气液化装置及方法。
背景技术
北极地区拥有待发现天然气技术可采储量超过47万亿立方米,占全球未开采天然气储量的30%。那里的天然气储量大、埋藏深度浅,几乎不含硫化氢,气体纯净度高,但大自然并不会轻易地把这些能源宝藏交到人类手上,极度严寒时时刻刻考验着开采者。迄今为止极寒地区已建天然气液化工厂共3座,分别位于俄罗斯萨哈林、挪威哈默菲斯特岛和美国阿拉斯加基耐,分别采用DMR、MFC、康菲级联三种液化工艺。
受到国外天然气液化技术和关键设备的垄断,我国大型液化厂建设成本和周期无法得到有效地控制。另一方面,当今全球各国都在积极开发北极能源,我国也提出了“冰上丝绸之路”的构想,因此开发一种能适用于极寒地区、大型又能使用我国自主化设备的天然气液化工艺已非常必要。
发明内容
为了克服现有技术的缺点,本发明提供了一种极寒地区天然气液化装置及方法,结合了传统阶式制冷工艺优点,同时从关键设备国产化对传统阶式制冷工艺的技术进行了改进及创新,由传统三级阶式制冷优化为本工艺两级阶式制冷,除具有传统阶式制冷工艺特点外,还具有简化流程、减少一组压缩机组和投资,缩小占地面积、操作更便捷,同时冷剂压缩机、换热器国产化等特点,方便采购、投资更省。
本发明所采用的技术方案是:一种极寒地区天然气液化装置,包括乙烷液化制冷系统和甲烷过冷制冷系统;所述乙烷液化制冷系统包括依次连接的乙烷压缩机、乙烷空气冷却器、乙烷凝液收集罐、高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器;所述甲烷过冷制冷系统包括依次连接的天然气过冷器、甲烷压缩机和甲烷空气冷却器;来自外部净化天然气管道和来自甲烷空气冷却器的甲烷管道均依次与高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器连接。
本发明还提供了一种极寒地区天然气液化方法,包括如下步骤:
1)乙烷液化制冷系统直接将天然气和甲烷冷却至约-85℃:
来自乙烷凝液收集罐的15℃液态乙烷经一级J-T阀节流,压力降至1.626MPa.g后进入高压乙烷蒸发器,对天然气和甲烷进行冷却;高压乙烷蒸发器的液态乙烷经二级J-T阀节流,压力降至0.731MPa.g后进入中压乙烷蒸发器,对天然气和甲烷进行冷却;中压乙烷蒸发器的液态乙烷通过三级J-T阀节流,压力降至0.236MPa.g后进入低压乙烷蒸发器,对天然气和甲烷进行冷却,低压乙烷蒸发器的液态乙烷通过四级J-T阀节流,压力降至0.105MPa.a后进入低低压乙烷蒸发器,对天然气和甲烷进行冷却至-85℃并液化;
2)甲烷过冷制冷系统为天然气和甲烷自身过冷提供冷量:
甲烷将乙烷液化制冷系统已液化的天然气通过天然气过冷器过冷至-156℃,过冷后的天然气节流后温度降至-160℃,进入LNG储罐储存;同时,制冷剂甲烷在天然气过冷器中冷却到-156℃后出天然气过冷器,然后通过节流阀降温降压至-160℃和260kPa.a,然后返回天然气过冷器,为天然气和自身过冷提供冷量。
与现有技术相比,本发明的积极效果是:利用高纬度极寒地区环境温度低的优势,通过空气冷却直接预冷天然气和制冷循环冷剂。经过自然预冷的净化天然气在四个蒸发器和一个天然气过冷器中温度逐渐降低,直至液化过冷;液化过程所需的冷量由乙烷和甲烷两个系统提供,该系统调节手段丰富,能够为天然气液化过程提供相匹配的冷量,从而体现出该方法在操作上的灵活性和对原料的适应性。与现有技术相比,具有以下优点:
一、天然气液化过程能耗低。
对于天然气液化而言,影响能耗的主要因素为制冷温度和制冷换热过程的换热温差。在相同的制冷温度工况下,换热温差越大,制冷系统的能耗越高。
采用本发明的适用于极寒地区天然气液化工艺对天然气进行液化,乙烷在四个不同的压力等级下蒸发,分成四个温度等级冷却天然气,各个压力下的蒸发的乙烷冷剂进入相应级数的乙烷压缩机压缩。最后采用甲烷作为过冷剂为天然气和自身的冷却提供冷量。整个换热过程中每个蒸发器温差分配较为均匀,无传热瓶颈,有效能损失小,节能明显,比国际主流工艺C3/MRC工艺能耗低约12%。
二、冷剂压缩机均为单组分压缩机,设计更容易,采购周期短更方便,压缩机运行更稳定,并可采用国产化设备,有效降低了液化厂建设周期和投资。
冷剂压缩机包括乙烷压缩机和甲烷压缩机,其中乙烷压缩机最低吸气温度为-88℃,对于乙烷压缩机在国内低温行业已经进行广泛的运用,尤其在炼油化工行业,因此该压缩机很容易采购,实现国产化。同时对于极寒地区大型化LNG工厂,乙烷冷剂可以通过分馏塔进行精馏,乙烷制冷剂完全实现自给自足。
采用本发明的天然气液化工艺,甲烷压缩机的最低吸气温度提高到-88℃,采用一级进气,此工况的压缩机在国内低温行业中已有成熟业绩,解决了国内大型LNG工厂国产化的瓶颈,装备国产化得到了有效的保障。
三、液化过程换热器选择范围大,可采用板翅式结构,也可采用管壳式结构,或两者相结合的结构。
国内外LNG工厂的主换热器设备主要是绕管换热器和板翅式换热器,绕管换热器的现有世界生产商只有APCI和LINDE两家,价格较高,而板翅式换热器在国内的生产厂家较多。国外大型LNG工厂中的主换热器都采用的绕管。采用本发明的天然气液化工艺,蒸发器和天然气过冷器均可采用管壳式换热器或板翅式换热器,目前国内已经完全能能够实现热虹吸式蒸发器和过冷器组合在一起的板翅式结构,大型液化工厂国产化不再受主换热器的形式限制。
附图说明
本发明将通过例子并参照附图的方式说明,其中:
图1是本发明的工艺原理流程示意图。
具体实施方式
一种极寒地区天然气液化装置,如图1所示,包括:乙烷压缩机1、乙烷空气冷却器2、乙烷凝液收集罐3、高压乙烷蒸发器4、中压乙烷蒸发器5、低压乙烷蒸发器6、低低压乙烷蒸发器7、天然气过冷器8、甲烷压缩机9、甲烷空气冷却器10。其中:
乙烷压缩机1、乙烷空气冷却器2、乙烷凝液收集罐3、高压乙烷蒸发器4、中压乙烷蒸发器5、低压乙烷蒸发器6和低低压乙烷蒸发器7依次连接,构成乙烷液化制冷系统,用于对天然气和甲烷进行冷却至约-85℃液化。
天然气过冷器8、甲烷压缩机9和甲烷空气冷却器10依次连接,构成甲烷过冷制冷系统,用于为天然气和甲烷自身过冷提供冷量。
本发明还提供了一种适用于极寒地区天然气液化方法,包括如下步骤:
1)乙烷液化制冷系统直接将天然气和甲烷冷却至约-85℃:
乙烷经乙烷压缩机1增压至3.72MPa.g后经过乙烷空气冷却器2空冷至约15℃,进入乙烷凝液收集罐3储存;来自乙烷凝液收集罐3的约15℃液态乙烷经一级J-T阀节流,压力降至1.626MPa.g后进入高压乙烷蒸发器4,对天然气和甲烷进行冷却;高压乙烷蒸发器4蒸发的乙烷回到乙烷压缩机1增压,部分液态乙烷经二级J-T阀节流,压力降至0.731MPa.g后进入中压乙烷蒸发器5,对天然气和甲烷进行冷却;中压乙烷蒸发器5蒸发的乙烷回到乙烷压缩机1增压,部分液态乙烷通过三级J-T阀节流,压力降至0.236MPa.g后进入低压乙烷蒸发器6,对天然气和甲烷进行冷却,低压乙烷蒸发器6蒸发的乙烷回到乙烷压缩机1增压,部分液态乙烷通过四级J-T阀节流,压力降至0.105MPa.a后进入低低压乙烷蒸发器7,对天然气和甲烷进行冷却至约-85℃并液化,低低压乙烷蒸发器7蒸发的乙烷回到乙烷压缩机1增压进行循环。
2)甲烷过冷制冷系统为天然气和甲烷自身过冷提供冷量:
甲烷作为过冷段的制冷剂,将液化段(乙烷液化制冷系统)已液化的天然气通过天然气过冷器8过冷至-156℃,过冷后的天然气节流后温度降至-160℃,进入LNG储罐储存;同时,制冷剂甲烷在这一级中冷却到-156℃左右,然后通过节流阀降温降压,压力降至260kPa.a,温度降至-160℃,再返回天然气过冷器8,为天然气和自身过冷提供冷量。节流后的甲烷出天然气过冷器8的温度为-88℃,该气体直接进入甲烷压缩机9增压,增压完成后通过甲烷空气冷却器10空冷,然后进入乙烷液化制冷循环。
本发明的优势和基本原理是:由于高纬度地区常年环境温度较低,相应环境温度的乙烷冷凝压力也相应降低,可以调整乙烷压缩机转速,降低乙烷压缩机出口压力。完全充分利用环境冷量冷却乙烷和甲烷冷剂。通过只需降低压缩机转速即可实现。同时由于热流热量的减少,乙烷和甲烷冷剂循环量均相应减少,从而大大降低液化过程中的功率,减小能耗。较低温度级的循环将热量转给相邻的较高温度级的循环。通过环境自然预冷,第一级乙烷液化制冷循环为天然气和制冷剂甲烷提供冷量;第二级甲烷过冷制冷循环为天然气及自身提供冷量提供冷量。通过四个换热器(蒸发器4至7)和一个天然气过冷器8冷却,天然气的温度逐渐降低,直至液化并过冷。也可以通过一个板翅式换热器将4至8集成为一个换热器,减小设备占地面积。
Claims (10)
1.一种极寒地区天然气液化装置,其特征在于:包括乙烷液化制冷系统和甲烷过冷制冷系统;所述乙烷液化制冷系统包括依次连接的乙烷压缩机、乙烷空气冷却器、乙烷凝液收集罐、高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器;所述甲烷过冷制冷系统包括依次连接的天然气过冷器、甲烷压缩机和甲烷空气冷却器;来自外部净化天然气管道和来自甲烷空气冷却器的甲烷管道均依次与高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器连接。
2.根据权利要求1所述的一种极寒地区天然气液化装置,其特征在于:所述高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器的蒸发乙烷出口接入乙烷压缩机。
3.根据权利要求2所述的一种极寒地区天然气液化装置,其特征在于:在乙烷凝液收集罐和高压乙烷蒸发器之间设置一级J-T阀。
4.根据权利要求3所述的一种极寒地区天然气液化装置,其特征在于:在高压乙烷蒸发器和中压乙烷蒸发器之间设置二级J-T阀。
5.根据权利要求4所述的一种极寒地区天然气液化装置,其特征在于:在中压乙烷蒸发器和低压乙烷蒸发器之间设置三级J-T阀。
6.根据权利要求5所述的一种极寒地区天然气液化装置,其特征在于:在低压乙烷蒸发器和低低压乙烷蒸发器之间设置四级J-T阀。
7.根据权利要求1所述的一种极寒地区天然气液化装置,其特征在于:所述高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器、低低压乙烷蒸发器和天然气过冷器集成为一个板翅式换热器或管壳式换热器。
8.一种极寒地区天然气液化方法,其特征在于:包括如下步骤:
1)乙烷液化制冷系统直接将天然气和甲烷冷却至约-85℃:
来自乙烷凝液收集罐的15℃液态乙烷经一级J-T阀节流,压力降至1.626MPa.g后进入高压乙烷蒸发器,对天然气和甲烷进行冷却;高压乙烷蒸发器的液态乙烷经二级J-T阀节流,压力降至0.731MPa.g后进入中压乙烷蒸发器,对天然气和甲烷进行冷却;中压乙烷蒸发器的液态乙烷通过三级J-T阀节流,压力降至0.236MPa.g后进入低压乙烷蒸发器,对天然气和甲烷进行冷却,低压乙烷蒸发器的液态乙烷通过四级J-T阀节流,压力降至0.105MPa.a后进入低低压乙烷蒸发器,对天然气和甲烷进行冷却至-85℃并液化;
2)甲烷过冷制冷系统为天然气和甲烷自身过冷提供冷量:
甲烷将乙烷液化制冷系统已液化的天然气通过天然气过冷器过冷至-156℃,过冷后的天然气节流后温度降至-160℃,进入LNG储罐储存;同时,制冷剂甲烷在天然气过冷器中冷却到-156℃后出天然气过冷器,然后通过节流阀降温降压至-160℃和260kPa.a,然后返回天然气过冷器,为天然气和自身过冷提供冷量。
9.根据权利要求8所述的一种极寒地区天然气液化方法,其特征在于:高压乙烷蒸发器、中压乙烷蒸发器、低压乙烷蒸发器和低低压乙烷蒸发器蒸发的乙烷均回到乙烷压缩机增压至3.72MPa.g后经过乙烷空气冷却器空冷至15℃,进入乙烷凝液收集罐储存。
10.根据权利要求8所述的一种极寒地区天然气液化方法,其特征在于:节流后的甲烷出天然气过冷器的温度为-88℃,然后直接进入甲烷压缩机增压,增压完成后通过甲烷空气冷却器空冷,然后进入乙烷液化制冷循环。
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