译文：
乙烯装置回收单元低压凝液泵原采用双端面机械密封,密封使用寿命短,封液泄漏严重。改造为干气密封后彻底改变了该泵的运行状况,解决了泄漏问题,减少了检修费用。立式高速泵干气密封的成功改造,为同类立式高速泵轴封改造提供了参考。
高速泵在化工行业中应用广泛,由于其转速高、压力高、密封腔尺寸小等特性,制造比较困难,目前国内只有少数几个厂家可以生产成熟的高速泵用机械密封,而一旦遇到疑难泄漏问题,可供用户选择余地很小。
中石化股份公司天津分公司聚乙烯装置排放气回收单元有2台低压凝液泵G-5213X/5218X,为立式高速泵,轴封形式采用双端面机械密封。这2台泵自2002年10月投用以来,机械密封频繁发生泄漏,经常进行检修,严重影响了生产的稳定运行。本文作者将聚乙烯装置的2台立式高速泵成功地改造为干气密封,为同类立式高速泵轴封改造提供了参考。
1、原双端面机械密封存在的问题
原双端面机械密封的工作流程为:封液罐底部经冷却后的封液沿动环旋转切线方向进入密封腔,对密封副进行冲洗,然后返回封液罐上部。封液的循环靠热虹吸作用实现,罐内有盘管冷却器。封液罐上部接有低压氮气管线,罐内压力略高于泵内密封腔的压力,使封液只能向泵内泄漏,而泵内的危险介质不能向外泄漏。同时,封液也可能向泵大气侧泄漏。
该密封存在以下问题:
(1)外侧密封泄漏严重,需经常停泵补充封液。密封寿命短,平均每两个星期就需更换一次机械密封。曾先后使用过几种机械密封产品,也曾尝试调整弹簧压缩量、改为波纹管式密封、将楔型环改为O形环等手段,均未能解决问题。
(2)设计上存在隐患。
①因封液压力高于泵内压力,一旦内侧密封失效,封液会漏入泵内,液位下降,而设计上封液罐无液位低报开关,若操作人员巡检不及时,会导致封液漏光,导致密封面干摩擦,造成事故。
②封液罐的氮气注入管线上无单向阀,在泵入口阀关闭,而出口单向阀关闭不严的情况下,系统背压会反串入泵内,在密封腔内形成高压,工艺介质通过内侧密封串入封液罐,进而通过低压氮气管线串入其它系统,非常危险。实际运行中曾发生过这种情况。
2、干气密封改造
经与有关密封生产厂家探讨后,决定尝试将原来的接触式机械密封改造为非接触式的干气密封。经计算,此泵的密封面的线速度和密封压力等参数完全可以满足干气密封的要求。
2.1、干气密封工作原理
干气密封是20世纪60年代末期从气体动压轴承的基础上发展起来的一种新型非接触式密封。该密封利用流体动力学原理,通过在密封端面上开设动压槽而实现密封端面的非接触运行。干气密封最初是为解决高速离心压缩机轴封问题而出现的,由于密封非接触运行,因此密封摩擦副材料基本不受pv值的限制,特别适合作为高速、高压设备的轴封。随着干气密封技术的日益成熟,其应用范围也越来越宽广,目前,干气密封正逐渐在离心泵及搅拌器上得到应用。总之,凡使用机械密封的场合均可采用干气密封。干气密封结构与机械密封近似,也由旋转环、静环、弹簧、密封圈以及弹簧座和轴套组成,不同之处在于旋转环密封面上加工出有特殊作用的流体动压槽。
干气密封旋转环旋转时,密封气体被吸入动压槽内,由外径朝向中心,径分量朝着密封堰流动。由于密封堰的节流作用,进入密封面的气体被压缩,气体压力升高。在该压力作用下,密封面被推开,流动的气体在两个密封面间形成一层很薄的气膜,并向内侧泄漏。气膜的厚度约为3μm,且具有良好的刚性,可以保证在发生工艺条件波动或机械干扰时,仍能保持稳定的气膜,保证密封面间的非接触相对运动和稳定的泄漏量。
与机械密封相比,干气密封具有如下优点:
(1)密封使用寿命长、运行稳定可靠;
(2)密封功率消耗小,仅为接触式机械密封的5%左右;
(3)与其它非接触式密封相比,干气密封气体泄漏量小;
(4)可实现介质的零逸出,是一种环保型密封;
(5)密封辅助系统简单、可靠,使用中不需要维护。
干气密封的不足之处是:
(1)就近处需要有一定压力的气源,气源压力要高于介质压力,使现场应用受到限制;
(2)微量密封气体(通常是氮气)会进入工艺流程,所选气体应对生产工艺无不利影响,也使现场应用受到限制;
(3)在启停瞬间未形成有效气膜时密封面会发生干摩擦,在需频繁启动的设备上应用时使用寿命可能会缩短。
2.2、改造方案
将原双端面机械密封改造为双端面干气密封,干气密封结构与原双端面机械密封近似,不需改动原密封腔。主密封气利用原来的封液罐上的精制氮气,原封液罐作为缓冲罐(也可不设)。在现场新安装由过滤器、流量计等组成的控制盘,连接管线作少量改动。
干气密封系统其工作流程为:压力为0.7MPa的密封气(精制氮气)经过缓冲罐,再经过滤减压阀减压至0.6MPa,再通过流量计和单向阀进入密封腔,一小部分密封气通过内侧密封泄漏入泵内,另有一部分密封气通过外侧密封泄漏入大气中。
3、改造效果分析
2004年12月对G-5213X实施了改造,改造后一次试车成功,密封气泄漏量为0.4m3/h左右。随对另一台高速泵G-5218X也进行了改造,同样一次试车成功。2台泵至今已连续运转8个月未发生过轴封泄漏问题,消除了隐患。
低压凝液泵干气密封改造的成功,解决了长期困扰该泵的轴封泄漏问题,不但稳定了生产,也为企业带来了很大的经济效益。改造前,按每2个星期更换一次机械密封、每套机封3000元计算,每年的检修备件费为3000×27=81000元,干气密封每套约1万元,寿命一般为3年,折合每年3300元,此次改造成功每年可节约备件费用7万多元,经济效益明显。据了解,此次改造为全国首例应用于立式高速泵的干气密封改造,此次改造的成功,对同类立式高速泵轴封的改造具有一定的参考价值。
“ Dry gas seal in the vertical high-speed pump technology on ”是由中国闸阀网提供的国际阀门新闻，译文仅供参考。另外，中国闸阀网还提供相关产品搜索：闸阀型号、闸阀价格、闸阀技术、闸阀新闻、闸阀生产商等。
原文：
Ethylene plant recovery unit low-pressure condensate pump of the original double-face mechanical seal, seal life is short, a serious leakage of sealing liquid. After the transformation of the dry gas seal completely changed the operation of the pump, and solve the problem of leakage, reducing maintenance costs. Vertical high-speed pumps dry gas seal the success of transformation, vertical high-speed shaft sealBellow Seal Gate Valve for similar transformation as a reference.
High-speed pumps are widely used in chemical industry, because of its high speed, high pressure, sealing cavity size and other characteristics of a small, manufacturing more difficult, at present there were only a few manufacturers that can produce mature, high-speed pumps with mechanical seal, while the event of difficult leakage problems, to choose from is limited.
China Petrochemical Company Limited, Tianjin Branch polyethylene plant vent gas recovery unit has 2 sets of low-pressure condensate pump G-5213X/5218X, for the vertical high-speed pump, seal the form of double-face mechanical seal. This is 2 sets of pumps since October 2002 has been put into use, frequent mechanical seal leakage, regular maintenance, has seriously affected the production of stable operation. The author of the polyethylene unit 2 sets of vertical high-speed pumps has successfully transformed into dry gas seal, for the same transformation of vertical high-speed shaft seal provides a reference.
1, the original double-end mechanical seal problems
Of the original double-end mechanical seal operational procedures: sealing liquid through the cooling tank at the bottom of the sealing liquid moving along the tangent directionAPI Cast Steel Valves of rotation into the ring sealed chamber, to seal the Deputy to rinse, and then return to the upper part of sealing liquid tank. Sealing liquid circulation by thermosiphon effect achieved with the tank coil cooler. Then there is the upper part of sealing liquid tank low-pressure nitrogen gas pipelines, tank pressure slightly higher than the pump seal chamber pressure, so that liquid can only pump seal leakage, while the media can not pump out the danger of leakage. Meanwhile, the sealing liquid may leak to the pump side of the atmosphere.
The sealing of the following problems:
(1) lateral seal leakage serious, need to supplement the regular stop pump seal liquid. Seal life is short, on average every two weeks on the need to replace a mechanical seal. Who has used several mechanical seal products, I tried to adjust the amount of compression spring instead of bellows seal, will be replaced by wedge-shaped ring O-ring and other means have failed to solve the problem.
(2) The design compromised.
① because of sealing liquid pressure is higher than the pressure pump, once the inner seal failure, sealing liquid will leak into the pump, the liquid level drop, while the design of sealing liquid tank under-reporting of non-level switch, if the operator inspection is not timely, will lead to leaky sealing liquid, leading to the sealing surface dry friction, causing the accident.
② sealing liquid nitrogen tank into the pipeline without a one-way valve, the pump valve closed the entrance and the exit of strict one-way valve closed, the system will be playing a back pressure into the pump, a high-pressure in the sealed cavity, craft media through the string into the sealing liquid inside sealed cans, and then through the low-pressure nitrogen gas into the pipeline string of other systems, is very dangerous. The actual operation had occurred in this situation.
2, dry gas seal transformation
With the manufacturer of the seal, has decided to try to contact the original transformation of non-contact type mechanical seal type of dry gas seal. Calculated, this pump sealing surface of the line speed and sealing pressure parameters fully meet the requirements of dry gas seal.
2.1, dry gas seal works
Dry gas seal is the late 20th century, 60 bearings from the gas dynamic pressure developed on the basis of a new type of non-contact seals. The sealed using fluid dynamics theory, through the opening in the sealed end of the surface dynamic pressure groove and the Seals to achieve non-contact operation. Dry gas seal was first to address the high-speed centrifugal compressor shaft seal problems arise, due to non-contact sealing operation, thus sealing Friction Material from pv value of the basic restrictions, especially well suited for high-speed, high-pressure seal equipment. With the dry gas seal technology has become more sophisticated, increasingly broad range of applications, at present, dry gas seal is gradually being applied on the pump and stirrer. In short, theBellows Gate Valves occasion where the use of mechanical seals can be used dry gas seal. Dry gas seal structure and mechanical seal similar to, but also by the rotating ring, static rings, springs, seals and the spring seat and the sleeve composition, the difference is that processing of a rotating ring sealing surface has a special role of the fluid dynamic pressure groove.
Dry gas seal rotating ring rotates, the seal dynamic pressure tank of gas sucked from the outer diameter towards the center, toward the seal weir flow path components. As the throttling effect sealing weir into the sealing surface of the gas is compressed, the gas pressure increased. In the pressure, the sealing surface is open, and the flow of gas between the two sealing surfaces to form a thin film of gas to leak inside. Gas film thickness of about 3μm, and has a good rigidity, can guarantee in the event of fluctuations in process conditions or mechanical interference can still maintain a stable gas film to ensure the sealing surface relative movement between the non-contact and a stable leakage rate.
Compared with the mechanical seal, dry gas seal has the following advantages:
(1) sealed long life, stable and reliable;
(2) sealing power consumption is small, only-contact type mechanical seal about 5%;
(3) compared to other non-contact seals, dry gas seal a small amount of gas leakage;
(4) can achieve the zero emission medium is an environment-friendly seal;
(5) Seal-assisted system is simple, reliable, and use no maintenance.
Dry gas seal shortcomings are:
(1) need to have some pressure near the gas source, gas source pressure is higher than medium pressure, so that on-site application has been limited;
(2) Trace sealing gas (usually nitrogen) will enter the process, the selected gases without adversely affecting the production process should also make on-site application has been limited;
(3) does not start and stop an instant to form an effective gas film will occur when the sealing surface of dry friction, in the frequent need to start applications on the device life may be shortened.
2.2, rehabilitation programs
Transformation of the original double-end mechanical seal for the double-end dry gas seal, dry gas seal structure with the original double-end mechanical seal approximation, without changes to the original sealed chamber. Main seal gas tank using the original closure refined on the nitrogen tank intact as a buffer tank (or not to set up). New installation at the scene by the filter, flow meter composed of the control panel, the connection pipe to make a small change.
Dry gas seal system of its work processes as follows: pressure of 0.7MPa sealing gas (refined nitrogen) through the buffer tank, and then filtered vacuum valve to 0.6MPa, and then through the flow meter and one-way valve into the sealed cavity, a small part of the seal gas leakage through the inner seal into the pump and another part of the seal gas leakage through the outer seal into the atmosphere.
3, transformation effect analysis
In December 2004 on the G-5213X implemented a transformation after transformation, the success of a test, sealing air leakage rate of 0.4m3 / h or so. With another high-speed pump G-5218X also been modified, the same test a success. 2 sets of pumps has been in continuous operation 8 months did not occur, seal leakage and eliminate potential problems.
Low-pressure condensate pump dry gas seal the success of transformation to resolve a long plagued the pump seal leakage problem not only to stabilize the production, but also for the enterprise has led to great economic benefits. Transformation of the former, per 2 weeks to replace a mechanical seal, seal each machine calculation of 3,000 yuan, the annual fee for maintenance spare parts for 3000 × 27 = 81000 yuan, dry gas seals each about 1 million, life expectancy is generally three years, equivalent to 3,300 yuan per year, this annual savings of spare parts for the successful transformation of fee of 7 million yuan of economic benefit. It is understood that the transformation of the country's first vertical high-speed pumps used in the dry gas seal transformation, the transformation of the success of the same type of vertical transformation of high-speed shaft seal has a certain reference value.
原文来源：http://www.1zhafa.com/ |
