CCR Platforming Turnarounds
Eric J. Hammel UOP LLC Des Plaines, Illinois, U.S.A.
This paper discusses common problems encoun
tered during the turnaround of a CCR Platforming? process unit, provides solutions to these problems, and reviews UOP’s philosophy as it pertains to some of the questions most commonly asked by refiners. Simplified procedures for the essential tasks are included. This information is general in nature and serves as a good starting point from which a refiner should prepare a detailed procedure for each step of a turnaround. The paper is divided into the following topics: ? Platforming unit inspection ? CCR unit inspection ? Catalyst handling Frequency of Turnaround and Reactor Internals Inspection The reactor internals of the Platforming? process should be thoroughly inspected on a routine basis. The first inspection should come after the initial two years of operation. After that, every three to four years should be considered the minimum frequency. The results of the 1998 CCR Platforming Survey show that refiners conduct a Platforming unit turnaround, on average, every 38 months and a reactor internals inspection, on average, every 41 months. Frequency depends on refinery and local government requirements. Although many factors contribute to long operational runs and unit safety, preventative maintenance is probably the most important. A proper and thorough unit inspection during scheduled turnarounds not only results in extended run lengths and maximum safety but also greatly reduces the probability of unscheduled shutdowns. An unanticipated emergency shutdown can be extremely costly, particularly if it results in prolonged interruption to operations. ___________
?UOP LLC 2001. All rights reserved 2
Planning for the next turnaround should start immediately after a turnaround is finished. The benefits of proper planning include minimization of unit downtime, effective use of manpower, anticipation of problems, avoidance of past mistakes, and confidence that the required material and equipment are available when needed. Depending on turnaround scope, the services of a UOP technical advisor or inspector may be useful for planning and advising during the turnaround. Requests for an advisor or inspector should be made several months in advance so that UOP can schedule a suitable person. Turnaround Time Schedule The results of the 1998 CCR Platforming Survey show that the average Platforming turnaround lasts 23 days: survey responses ranged from 5 to 48 days. The duration of a turnaround on a CCR Platforming unit depends on the quantity and severity of work that must be performed. It also depends on how well organized a particular refiner is and to what degree the turnaround plan anticipated all findings. This section addresses the time frame for a minimum turnaround, including shutdown, catalyst removal, reactor cleaning and inspection, catalyst loading, and start-up. Assuming that minimal repair work is required as a result of the inspection and that the refiner is well organized, the turnaround should take about two weeks to complete, based on an around-the-clock schedule. An approximate breakdown of the steps and time required is shown in Table 1. Table 1 Turnaround Timetable Step Time, days Shutdown and cooldown 2-4 Nitrogen purging and blinding 1 Unloading, including inert entry heel catalyst removal 2 Scaffolding 1 Cleaning and inspection 2 Scaffolding removal 1 Catalyst loading 2
Nitrogen purging and blind removal 1 Startup and line-out 1 Total 13-15
Many of these steps can overlap. For example, scaffolding can be erected in one reactor while another is being cleaned and inspected. Cooldown of the reactor to an acceptable temperature for personnel entry can take days when using the recycle compressor and normal heat loss. If timing is critical, once-through nitrogen purging can be used to speed the cooldown. However, extreme care must be taken to avoid metal embrittlement or cooling the reactor internals too quickly, resulting in differential expansion problems. UOP recommends that refiners use an outside vendor, such as UCISCO, who is familiar with the procedures and equipment needed to monitor and control the nitrogen and process piping temperatures. A safe rule of thumb is to keep the nitrogen gas temperature above 80°F (27°C) and always within 200°F (110°C) of the reactor outlet temperature. Blinding should always be done to ensure safety. For Platforming stacked reactor inspection, this blinding is usually performed at each reactor inlet and outlet nozzle. Although blinding at these locations is more difficult than at, for example, the combined feed exchanger, they are the best locations from a safety point of view.
PLATFORMING UNIT INSPECTION
Unloading, inspecting, and reloading of the Platforming unit reactor stack is typically the central activity during a CCR Platforming unit turnaround. However, other equipment within the Platforming unit, such as vessels, fractionation columns, pumps, compressors, heaters, heat exchangers, and piping, should also be inspected. Inspection guidelines from the American Petroleum Institute (API), such as API-510 (Pressure Vessel Inspection Code) and API-570 (Piping Inspection Code) provide a comprehensive account of the information required for a
proper and timely inspection of common refinery equipment. Piping Inspection 管道检查 In general, little corrosion occurs in Platforming units, but a number of areas should be checked. The hot alloy piping on Platforming units with hydrotreated feedstocks has been almost corrosionfree. 一般而言，重整装置的腐蚀都是较小的，但是一些个别区域也应该检查 重整装置有含氢进料的热合金钢管几乎都有腐蚀 In a few instances, carbon steel has been installed by mistake in place of alloy. In each case,the carbon steel failed from hydrogen attack in about 12 months even though the carbon steel showed no metal loss. The cold piping down stream of the reactor product condensers and at the bottom of the product separator is vulnerable to attack by hydrochloric acid. The drains at the low points should be inspected. 在一些例子中，碳钢被错误的用在合金钢的位置。在一些情况下，碳钢受氢气侵 蚀12个月失效，即使碳钢并没有显示有金属的损失。冷管在冷凝器和分离器的底 部是最容易受盐酸腐蚀的。所以应该注意检查排凝的低点
The reciprocating compressor suction piping should be checked for scale accumulation. In some cases, these suction lines need to be acidized to alleviate compressor problems. In units that operate with a relatively high recycle gas moisture content (above 30 mol-ppm), corrosion from hydrochloric acid attack generally occurs in the stabilizer overhead piping, the top of the column, the condenser, and the overhead receiver. 往复式压缩机的出入口管线应该检查鳞状物的积累。在一些情况下，压缩机的出 入口线需要被酸化来减轻压缩机问题。在装置里，腐蚀主要来自架空管线 ，冷 凝器和架空的接收器的盐酸腐蚀 In drier units, hydrochloric acid corrosion has not been encountered, and stabilizer section piping corrosion has been essentially nil. UOP recommends that a thorough piping inspection be made prior to the turnaround to minimize the number of inspection personnel required. 在干燥单元，盐酸腐蚀是不会有的，管道部分的腐蚀基本为零。UOP建议在检修 之前做一个彻底的管道检查，以把大修期间管道检查员工需求降到最少
When the inspectors and maintenance personnel have only piping to check, the inspection can take on a much larger scope. The proper inspection of all piping during a turnaround can be carried out only if a full inspection crew and sufficient maintenance personnel are available. During a turnaround, normal planning usually does not include sufficient time for preparation and inspection of process piping systems. 当检查和维护人员仅仅检查管道时，检查人员会有较多的时间来检查，维护人员 可以不可能对管道进行彻底检查除非有足够的人员，检修期间，正常的检修计划
一般不包括检修管道系统时间。 Some time prior to a scheduled turnaround, a thorough thickness check should be made of all process piping that can be safely and accurately checked at operating temperature. If this check is scheduled prior to the turnaround, fewer inspectors and maintenance personnel are required than if the inspection is performed during the shutdown. 在计划检修之前的时间，在确保操作温度下安全的情况下，应该进行一次全面的 管道厚度检查，这些检查如果在检修之前进行，将会比在停工时检查节省很多人 员 Making holes in insulation and moving ladders can be done by only two people on a normal working-day basis. Also, ladders are more readily available and can be placed where required, and scaffolding can be erected without interfering with other work that normally takes place during a turnaround. 梯子两个人在一个工作日就可以做完，并且应该被放在需要的地方，脚手架也应 该立在不妨碍工作的地方 During an onstream piping inspection, many other important conditions can be noted, and in many cases, rectified, prior to the turnaround: 在检查管道期间，许多重要的工况应该被标注，许多情况下，要在检修之前修改
? Thin piping can be scheduled for replacement, and most of the fabrication can be completed before the shutdown. 管线预期更换，多数建构物在停产之前完成 ? Leaking flanges and valves can be identified and scheduled for repairs. 发现法兰和阀门的泄漏并列入检修计划 ? Inoperative valves can be scheduled for replacement or reworking. 换掉无用的阀门或安装在需要的地方 ? Repair or replacement of poor insulation can be completed either immediately or can be scheduled for a turnaround. 修理或者替换缺失的保温，或者提前换或者列入检修计划中 Because scaffolding may be required to check some piping, the scaffolding can be used to complete insulation repairs when the piping is being checked. 检查一些管道必需用到脚手架，脚手架在保温修理时用到 Because an on-stream piping inspection has many advantages, it is strongly recommended. Even if only one important line is scheduled for replacement during the turnaround, the time saved can more than pay for the time and expense of the inspectors. 生产中作管道检查有很多好处，因此建议在生产中作检查，即使仅有一条重要的 管线在检修期间更换，节省的时间比支付给检查费用要多
Compressors 压缩机 The turnaround maintenance required on compressors in the CCR Platforming unit will be heavily 重整装置的连续运转周期主要取决于压缩机的操作水水平和进料来源， dependent on the operating experience and feedstock source. If a machine has been closely 如果机组关闭了检测显示器，就会没有了设备危险的信号，（像没有了油、汽泄 露信号， monitored, there have been no signs of distress (such as no high rate of seal oil or gas leakage, no 振动偏大趋势，和效率的下降） increasing trends in vibration, and no decrease in efficiency) and it was serviced during the 压缩机将过早的需要维修， previous turnaround, it may be acceptable to defer opening and overhaul until the subsequent unit 延缓首次大修的运转时间使其尽可能接近装置的周期是可以接受的 turnaround. If a compressor is to be serviced during a turnaround, it is recommended that a 如果压缩机在大修期间被维修，机器售后服务代理也是很愿意接受的， vendor service representative be present or readily available. Maintenance on reciprocating net gas machines should not be a turnaround item if there is normally a spare machine available. 如果有备机的话，气压机的维护将不需要周期 However, a turnaround is a good opportunity for cleaning and inspection of suction piping, if this is an issue. 尽管如此，如果有问题，到运转周期后是清理和检查进出口管道的好时机， Vertical Combined Feed Exchangers 立式换热器 At every turnaround, the shell outlet elbow should be removed for a visual inspection of the 每一个周期， 虾米腰都要被移出来，以方便看到波纹管区域 bellows area. This is mainly to look for signs of ammonium chloride salts, gum formation, and 这主要是为了看氯化铵盐结焦状况和腐蚀产物 corrosion products. If deposits are found, it may be necessary to remove the bottom head for 如果发现有沉淀结焦，或者换热器底座膨胀节由于压力和膨胀热应力开裂 必须移开底座以便清理 cleaning. Also inspect for cracks in the expansion bellows at the bottom of the exchanger due to stress corrosion cracking and corrosion of the heat affected zone of the bellows
attachment weld. At every other turnaround, the bottom and top heads should be removed. The expansion 在每一个间隔周期， 底座和顶盖应该拆卸下来， 膨胀节和管束应该通过染料100% 的渗透检查， bellows and both tube sheets should be 100% inspected by dye penetrant testing. Since the detailed design of each vertical combined feed exchanger may differ, the vendor should be 每一个立式换热器的详细设计之间都存在差别，卖方应该 consulted for detailed procedures for removing the heads. UOP does not recommend removing 提供顶盖的详细拆卸步骤，如果不是特别需要，UOP方面不会提供 the VCFE bundle unless absolutely necessary. Care should be taken when removing or 立式换热器管束拆卸的资料。当拆装管束时应该当心 reinstalling the tube bundles. Damage to the tubes has occurred when the bundle has been laid in 当管束中的管子被水平放置时，可能就会发生损坏 the horizontal. Some refiners have had success leaving the bundle hanging in the vertical for 一些炼油厂已经成功直立着分离管束并清理和检查 cleaning and inspection. Since Platforming "should be," and in general is, a clean service, there "should not" be exchanger fouling. UOP's experience with vertical combined feed exchangers, especially in CCR 据UOP人员对于立式换热器尤其是CCR中的换热器经验了解， 入口一般或者总体 来说是很清洁的，没有垢体 Platforming service, bears that out. When tube-side fouling has been seen it has been due to feed 证实了这些，当发现有管端污垢，一般是使用过度或者使用不当造成的 contamination, typically overuse or misuse of a corrosion inhibitor, or from charging feed from unblanketed intermediate storage to the unit. Although unlikely, shell side fouling could result from 或者污垢是来自原始部件的装料。尽管不太可能发生，壳层的污垢可能来源于 PNA (polynuclear aromatics) and/or ammonium chloride salt deposition. PNA are very 多环芳烃和析出的氯化铵盐。多环芳烃是一种致癌物质， carcinogenic, so proper precautions must be taken and proper personal safety used when inspecting this equipment. 因此当检查设备时，必须有合适的防护和安全措施
During turnarounds, it is possible to wash the VCFE with reformate, if the fouling is due to gums or PNA, or water (buffered, if required), if due to ammonium chloride salts. UOP can 在整个检修周期，如果污垢是胶质或者多环芳烃那就用重整油清洗，如果是氯化 铵盐就用水清洗
provide guidelines for these operations. It should be ascertained that the structural support can UOP能为这些操作提供指导方针。清洗之前，首先要确认换热器结构在 tolerate the weight of the liquid and that the exchanger is capable of withstanding the full weight of liquid on one side of the exchanger without pressurization on the other side. There has been 没有外力支撑的情况下，能够承受流体的重量整个空间充满流体重量 success cleaning the tube side using high-pressure (up to 10,000 psi) water blasting. This 现在，已经成功使用高达10000PSI（磅每平方英寸）（约68.950MPa）水压爆破 清洗 cleaning (hydroblasting) can be done without removing the bundle, as both ends can be made 高压喷水清理可以不用拆卸管束，并且冷凝液也是很容易获得的 accessible. If a UOP High-Flux coating has been applied to the inside surface of the tube, 由于管束管子内部有UOP的高通量涂料，水压清理的压力应该限制， hydroblast water pressure should be limited. Note, the water could be acidic due to salts dissolving and may need to be neutralized. If PNA is present, it should be removed before the 特别指出一点，用来清洗的水由于盐（水解）的存在可能显酸性，需要先中和， 如果存在多环芳烃， exchanger is exposed to air. Oxygen reacts with the PNA and makes it insoluble in most solvents. 在暴露在空气中之前应该将其除去。 因为氧气能跟多环芳烃反应可以生成难溶于 多数溶剂的物质 If NH4Cl is present, do not open the exchanger prior to flushing with a buffered water solution, 如果存在氯化铵，在水溶解之前不要打开换热器， since the salts become corrosive upon exposure to the water vapor present in the air. 因为盐类会析出当暴露在水蒸气中时 Fired Heaters 加热炉 Inspection of the radiant coil is required for maintaining mechanical reliability. Typical inspection
必须要检查加热炉的辐射热管， includes visual examination of the tubes for bulges and thickness measurement by UT. All radiant 包括检查炉管上可见的鼓包和用超声波探伤测管的壁厚 tubes should be checked with the tube gauges. The gauges will detect diametrical growth that is 所有的炉管必须用管子的测径工具检查，因为直径的增大用肉眼观察一般是 not apparent through visual inspection. Areas of concern should be checked by banding to 不明显的。相关的区域应该测定直径的增长 determine exact diametrical growth. Coil sampling at multiple points may be required. Destructive 炉管的多点抽样检查也是必须的， testing (Omega) to access remaining life, rate of deterioration, and future course of action must be planned for in advance of unit shutdown. 入口的破坏性测试、损坏速率和将来的运转状况都必须在设备关闭之前做好 In general, most CCR Platforming heaters will develop oxide scale. The radiant efficiency 一般而言，多数的CCR炉子入口都将产生氧化鳞状物。这样热辐射的效率 will decline as the amount of loose oxide scale increases. Light sandblasting to remove scale is 下降随着氧化鳞状物的增多。 在检修周期用轻微的喷砂处理将表面的氧化鳞状物 清除 generally recommended at turnarounds, however a comparison of the cost of the decline in 尽管如此，减少 radiant section efficiency and the rate of that decline with the cost of scale management (sandblasting or sandblasting followed by Cetek ceramic coating) should be performed. Repair of tube spacers, refractory linings, and sealing of any heater casing air leak points should be included 修补炉管间隔部分，炉衬和炉外壳都应该在检修期内完成 in turnaround activities. Problems with burner operation should be corrected as they develop. Heater tube failures 炉子的操作问题也将要显露出来 are usually caused by flame impingement resulting from improper burner setup. Burner vendors 炉管的损坏通常是由于操作不当引起火焰冲击所致 can assist a refiner in reviewing burner performance and ordering parts for the turnaround.
在检修期间炉子的供应商能帮助检测炉子性能和整顿零部件 Before the turnaround begins spare parts should be on site with clear maintenance instructions for 检修之前应该为炉子修补和重新组装准备好备件和清楚的维修操作指南 every burner repair and/or realignment to be undertaken.
Platforming Reactor Inspection反应器的检查 反应器的检查 Once the unit is shut down and prepared for catalyst unloading, all observations of catalyst and 在一次装置停产检修中，催化剂卸剂后，应该记录所有的有关催化剂和反应器内 部数据。 reactor internals should be recorded. Of prime concern is the reactor cover deck area. Many 主要的担忧是反应器的覆盖区域部分， times the cover decks and reactor internals have already been cleaned by the time the refiner’s 过程工程师和UOP的技术顾问有机会去检查时， 覆盖层和反应器内部应该被清理 干净 process engineers or UOP’s technical advisors have an opportunity to inspect. The condition of the cover deck area and the reactor internals immediately following the shutdown often provides 反应器的内部和覆盖区域的状况可能会直接的反映出操作中出现的疑难问题的 原因 clues to the cause of operating problems that may or may not be suspected. Verbal descriptions may not give a clear picture of the condition of the internals. A picture is worth a thousand words, 口头的描述不会有现场照片描述内部状况清楚，一幅照片胜过一百幅画， and a digital photograph is even more valuable because it can be transmitted electronically to 数码照片会更有价值，因为可以供UOP检查和讨论，UOP建议在清理之前，用照 片或者录像记录下反应器内部的状况 UOP for review and comment. UOP recommends that prior to cleaning, the refiner photograph or videotape the condition of the reactor internals. In addition to aiding the refiner in any problemsolving and troubleshooting efforts, photographing or videotaping reactor inspections provides the 除此之外，专家在将来问题解决和故障处理时，反应器内部的照片或者录像资料 将会给炼油厂一个和过去检查时的比较 refiner with a visual history to compare against future inspections. Typical Damage 典型的损坏 The results of the 1998 CCR Platforming Survey show that the majority of refiners
find no 1998年的CCR重整检查结果显示大多数炼油厂并没有发现反应器内部严重的损 坏， significant damage to the reactor internals during their turnarounds. The most-common damage was to the scallops. This kind of damage was experienced by approximately 20% of those 最常见的就是扇形筒的损坏。这种破坏大约占20% responding. This damage was usually crushed scallop bottoms or risers and broken tack welds between the scallop base and the scallop support ring. Scallop damage appeared to be more 这种破坏常常是损坏扇形筒的底座、 升浮器或者损坏扇形筒底座和支撑圈之间的 焊缝 common in the larger reactors of a stack, as would be expected because of the greater forces at 扇形筒的损坏普遍出现在较大的反应器上， play. Expander ring or expander ring lug damage was reported by approximately 10% of the refiners. Minor damage, such as centerpipe tears requiring patching of the profile wire, broken 涨圈和涨圈把手的损坏大约占10%，较小的损坏，像中心管侧面金属网的损坏. tack welds at the scallop and catalyst transfer pipe seal plates, and loss of cover deck wedges, 扇形筒焊缝的损坏、催化剂输送管的损坏和楔形销子的丢失 chains, and lugs, were also reported as well as centerpipe screen plugging. However, the majority of refiners that indicated damage at the various locations experienced only light damage. 尽管如此，各炼油厂都表明各种定位件的损坏都是轻微损坏 Of course, UOP cannot predict what damage, if any, will be found during a Platforming 当然UOP不能完全预测什么部件会损坏 reactor turnaround. Even if damage is suspected, determining the exact location and severity of any damage that may be present is difficult in most cases. However, based on past experience, 即使猜测到损坏的部件， 部件损坏的精确部位和损坏的程度目前来说是很难预测 的，尽管如此，过去的经验和文章后面的备件部分也是可以拿来借鉴的 the information in the “Recommended Spare Parts” section later in this paper should be considered. UOP strongly recommends that when the turnaround starts, the refiner examines all
the 当检修开始的时候， UOP建议炼油厂尽可能早的仔细检查反应器内部和估计修复 需要。 reactor internals and estimates the repairs required, if any, at the earliest opportunity. Usually this earliest opportunity is during inert entry when the heel catalyst is being removed.
通常早的时机是反应器根部被移动之前 Because any damage is usually not severe, most refiners do not have to remove any of their 因为任何损坏通常不是很严重的，多数的炼油厂没有拆卸任何内部件，一些小的 损坏，像扇形筒根部的损坏在反应器内部就能被修理 internals. Minor damage, to the bottom of scallops, for example, can be repaired inside the reactors. Sections of replacement scallop are commonly cut to sizes that fit through the manway and then are welded together within the reactors. 为了出入人孔，扇形筒的零部件通常被剪切成小尺寸，到反应器内部再焊接 Coke Growth 焦炭的形成 Coke grows inside the Platforming reactor by two mechanisms. The first is by maldistribution of hydrocarbon flow through the catalyst. An example is lack of flow or the low flow of hydrocarbon feed because of a plugged scallop or screen. 重整反应器焦炭的形成有两个原理，第一个是碳氢化合物不均匀的流过催化剂， 其中的一个例子就是由于扇形筒或筛网的阻塞使流量小 The second is by metal-catalyzed coking, which is addressed in “CCR Platforming Reactor Coking Revisited,” by Joseph Zmich. In either case, coke may grow between pills, creating coke balls. These coke balls can restrict or stop catalyst movement. The coke on the catalyst that is a by-product of the reforming reactions does not lead to coke formation between catalyst pills. Areas of coke growth range from the reactor cover deck or catalyst transfer pipe flanges to many sections of the reactor. If coke is found, it must be completely removed, because the coke formation may contribute to a low-flow situation that can accelerate further coke growth. If the coke growth was caused by low flow inside the reactor resulting from a mechanical problem, the problem must be corrected. Maintaining the recommended sulfur level in the Platforming unit feed naphtha helps ensure protection against the onset of coke growth resulting from metal-catalyzed
reactions. The following locations should be checked for coke growth at every turnaround: ? Between catalyst transfer pipe flanges (Figure 1) ? Behind and between scallops (Figure 2) ? Underneath centerpipe support assembly gaskets ? Between centerpipe, expansion joint, and outlet line flanges ? Inside an atmospheric CCR unit’s reduction zone lower pot ? Between the riser assembly and scallop of slip-on type scallop risers (Figure 3) ? Bottom of the scallops or outer basket screen and between the scallop support ring and reactor shell ? Underside of the intermediate heads ? On scallop cover plate and seal plates ? On the outside of an atmospheric CCR unit’s reduction zone exchanger tubes ? On the shell wall in the cover deck area ? In the ventilation screens on the expansion joint shroud or manway cover
Scallop Damage 扇形筒的损坏 Some amount of scallop damage is likely to occur if the unit has experienced emergency shutdowns that resulted in rapid changes in reactor inlet temperature. 如果装置发生紧急停车导致反应入口温度发生变化，一些扇形筒就可能损坏 During these temperature changes, or during heat-up and cooldown periods when the rate of temperature change is not well controlled, differential thermal expansion between the thin, stainless steel internals and the thick, low-alloy shell can cause damage. 在温度变化时，如果温度升高或者降低的速率没有控制好，不锈钢内部和低碳合 金钢框架就会有不同的热膨胀， Scallop length and radius are also factors that determine how significant the thermal expansion differences are. Reactors with long scallops of 30 feet (9 m) or more and large scallop radii of 5 inch (125 mm) or more are the most likely to have expansion problems. 扇形筒长度和半径也是热膨胀不同的要素， 有长扇形筒超过30英尺或者半径大于 5英寸或者更大都极有可能出现膨胀方面问题
Evidence of a vertical thermal expansion problem could be any of the following: 垂直方向上的热膨胀破坏主要表现在以下几个方面 ? Scallop riser seal plates have broken tack welds. 扇形筒升气筒焊缝损坏 ? Scallop risers have visible scrape marks from trying to slide through the seal plates. 扇形筒升气筒穿过密封板处有明显的刮痕 ? Scallop risers or scallops have buckled somewhere along the length of the scallop.
扇形筒升气筒和扇形筒被压弯沿着扇形筒轴向方向 ? Scallops have dropped down and the risers do not extend through the seal plate. 扇形筒掉落，升气筒不延续 ? Scallop base and bottom end plate are severely deformed. 扇形筒基座严重变形 ? Scallop support rings are damaged. 扇形筒支撑圈损坏 ? Scallop support ring lugs are damaged. 扇形筒支撑圈手柄损坏 For trouble-free operation, the scallops must be allowed ample room to grow up and down through the seal plate from their relative positions at ambient conditions. The section on “Scallop Modifications” contains information on improving scallop performance. 为了达到无故障运转，扇形筒在穿过密封板处必须有足够膨胀和缩小的空间， 扇形筒的修改包括扇形筒运转状况的改进
Cleaning Screens and Scallops 扇形筒和上筛网的清理 扇形筒和上筛网的清理 For many years, screens were commonly cleaned using a wire brush. Any fines remaining in the reactor after cleaning were removed with a strong vacuum. This method is certainly still adequate. 多年来，筛网通常都是用金属丝的小刷子清理，清理完后，许多剩余的粉尘用真 空吸尘器吸走，这种方法当然是可行的， However, during the last few years, several refiners have reported to UOP that they have satisfactorily used cold jet blasting of carbon dioxide, more commonly called CO2 blasting, to clean the reactor internals as well as the screens of the CCR unit regeneration tower. 尽管如此，在最近的几年里， 一些炼油厂反馈给UOP报告说他们已经成功用二 氧化碳冷喷来清理反应器内部和再生器内部筛网，这种方法俗称二氧化碳爆破 法， This procedure blasts carbon dioxide in the form of small pellets onto the surface of the screen, causing embrittlement of the contaminants. The thermal shock to the contaminants loosens them from the screen or scallop. Some refiners feel that CO2 blasting does a more-complete job than wire brushing and is less labor intensive. 二氧化碳爆破主要就是二氧化碳一小颗粒的形式被喷到筛网的表面， 是表面的污 染物变脆。热振动使筛网或扇形筒表面的污染物脱落，一些炼油厂二氧化碳爆破 法比用金属刷子刷更完备，并且还能减少劳动强度。
Catalyst Transfer Pipe Gasketing催化剂传输管道垫片
Catalyst containment has been lost at the catalyst transfer pipe flanges, on occasion, because of gasketing or bolting problems. UOP now specifies gaskets that are made of corrugated metal (4 to 6% chromium), are double-jacketed, and are filled with flexible graphite (nonasbestos). Recognizing the limited availability and higher cost of 4 to 6% chromium gasketing, 316 stainless steel is now allowed as an acceptable alternative material. The corrugated metal gasket is specified instead of a spiral wound gasket due to the advantage of lower seating stress. The ID of the gasket must be checked against the ID of the catalyst transfer pipe to be sure that there will be no ledges in the catalyst flow path. Also specified are A193-B8M CL. 1 stud bolts with three A194-GR. 8S nuts per stud bolt. This stud bolting now has one nut tack welded to the bolt and double nutting on the other end (Figure 1). These catalyst transfer pipe gaskets have, in a few cases, been severely damaged as a result of coke formation inside the gasket jacketing. The filling of these damaged gaskets is believed to have been asbestos with some iron contamination, and the result is metal-catalyzed coke formation. Reactor Maintenance and Inspection 反应器的保养和检查 Appendix A contains a list of the minimum work to be performed in the stacked reactors during a routine turnaround of a CCR Platforming unit. 附录包括重整装置反应器在检修期间的最小工作量 Prior experience with the reactor stack is assumed to be good. Also assumed is that the refiner has no special concerns resulting from performance problems while the unit was on-line. 据以往的经验假设反应器没有损坏， Dimensional checks of internals are not listed but may be important if the internals have shown signs of catalyst fluidization or poor flow distribution.
A more-detailed list of inspection items, including many dimensional checks, is found in the CCR Platforming General Operating Manual, under section VI. B., “Inspection and Preparation Activities.” An inspection following this detailed list is also strongly
recommended if any repair work has been done inside the reactors during the turnaround. 更详尽的部件检查包括许多尺寸的检查都包括在CCR装置操作说明书里，
New Specifications for Reactor Internals反应器内部说明书 反应器内部说明书 The clearance tolerance from scallop riser to scallop seal plate (Figure 4) has been increased on new designs. This increase is applicable to older units. The tolerance has been increased from 0.015 +0.005/-0 inch (0.38 +0.13/-0 mm) to 0.027 ± 0.004 inch (0.71 ± 0.10 mm). The increased tolerance decreases the likelihood that the scallop riser and scallop seal plate will bind, but is still sufficient to prevent the loss of catalyst containment. Similarly, the acceptable clearance tolerance of the catalyst transfer pipe sleeve to its seal plate has recently been increased from 0.010 +0.005/-0 inch (0.25 +0.13/-0 mm) to 0.021 +0.005/-0 inch (0.55 +0.13/-0mm).
Scallop Modifications扇形筒的改进 In 1986, scallop and scallop expander-ring modifications were introduced in response to reports of frequent scallop damage. As evidenced by the 1998 CCR Platforming Survey, the incidence and severity of scallop damage have declined; however, some older units could perhaps benefit from these modifications. The set of modifications comes in four parts. First, the scallop riser is extended so that it always extends through the seal plate, even during heat-up and cooldown. Second, a reinforcing ring is added to the base of the scallop to help in distributing the axial load experienced during reactor heat-up. Third, the expander rings are revised to include a two-bolt connection, which resists twisting. Fourth, clips are added to the expander ring lugs to prevent the rings from falling off during cooldown. Details of these modifications can be found in UOP drawings C10794-B, C10970-A, C10793-A, and C10790-A, which can be requested from UOP. Recommended Spare Parts 推荐用的备用部件 In preparation for the turnaround, UOP recommends that the refiner have a few spare scallops,
perhaps two or three, of each length in stock. Because most scallop damage occurs near the bottom or at the riser near the top, perhaps eight to ten extra scallop bottom sections and risers with matched seal plates should be available in each size. The refiner should contact the suppliers of various internals, particularly scallops and expander rings, and make them aware of the turnaround plans. Further, the refiner should investigate what arrangements can be made for emergency fabrication and shipping of additional spare parts, should they be needed. Also worthwhile is contacting local shops that may be capable of making small repairs to scallop bottoms or expander rings, for example, bending deformed internals back into shape. In addition, the following should be gathered: ? Internal catalyst transfer pipe gaskets, enough for the entire stack, and bolting to make up for lost or damaged stud and nuts (110% of required) ? Cover deck bolting (110% of required) or wedge pins, wedge pin chains, and wedge pin lugs ? Ceramic fiber rope and ceramic cement ? Centerpipe support corrugated gaskets ? Split ring assembly gaskets and bolting (if downflow reactor design) ? Reactor internal outlet line (mitered elbow and expansion joint) gaskets and bolting ? Reactor nozzle gaskets and bolting ? Appropriate welding rod and equipment available to make any needed repairs
Profile Wire Scallops UOP has recently developed a significant improvement to reactor scallop technology by combining the advantages offered by profile wire screen with the advantages of the fundamental scallop geometry. The new design, the result of a joint development effort between UOP and Nagaoka International Corporation of Japan, offers improved resistance to bending, twisting and buckling through greater strength in the axial direction without loss of flexibility in the radial direction. There is reduced plugging and catalyst attrition through the use of continuous vertical slots and fewer expander rings. If retrofit into an existing unit, reuse of the existing scallop risers and seal plates is possible.
The new generation profile wire scallop is being exclusively manufactured by Nagaoka International Corporation. Please direct your inquiries for additional information and pricing to: Nagaoka International Corporation No. 2-2-91, Mokuzaidouri, Mihara-cho, Minamikawachi-gun Osaka, Japan 587 Phone: 81 723 62-0121 Fax: 81 723 62-0202 KME Supply of Spare Parts KME的备件供应 UOP established the Key Mechanical Equipment (KME) Group in 1990 to focus UOP’s resources on the supply of technology embodied in performance-critical equipment. Although KME can supply replacement reactor internals, the greatest value to the refiner is when UOP supplies new equipment with UOP’s latest design. There are additional benefits. The familiarity of KME’s project management team with Platforming reactor and regenerator internals allows them to anticipate problems and address situations before they affect quality or schedule, thereby maximizing refiner satisfaction. Based on UOP’s decades of experience with the design of Platforming internals, the KME Group can recommend cost-effective modifications to existing internals and so maximize reliability and profitability. Because UOP is the single source for both the design and fabrication of the internals, questions and issues are resolved quickly. The KME Group can provide the highest-quality product, faster production schedules, and reduced cost of products, all because of close working relationships between UOP and fabricators. UOP is able to prioritize work in progress at fabricator’s shops to accommodate emergency or fast-track projects. The KME Group also includes shop inspection of all new equipment over and above the fabricator’s own quality and inspection programs as well as site installation supervision. For additional information on the UOP supply of Platforming reactor or CCR regenerator internals equipment and services packages, contact the UOP KME Group by fax at 847-391-2747 or by
e-mail at KME@UOP.com.
Other Suppliers of Spare Parts其他的一些备件供应 To assist in obtaining bids from possible fabricators, UOP can, on request, supply a list of fabricators, plate and forging suppliers, and internals fabricators for Platforming reactors and regenerators. The following limitations are associated with the list: ? UOP does not rate or rank fabricators. The list is in random order. ? The list is not comprehensive; some suitable fabricators may not be listed. The list is made up of names that UOP’s Engineering Department has seen on drawings or of fabricators with whom UOP has had experience. ? UOP will relate its experience with a fabricator only after receiving a specific written request for information. Platforming Reactor Nozzle Cracking The 1998 CCR Platforming Survey shows that approximately half of all the refiners responding recently checked their Platforming reactors for cracking. Of those who did check, half found some evidence of cracking. The severity of cracking ranged from severe shell cracking, which necessitated replacement of the entire Platforming reactor stack, to minor cracking at the nozzle attachments that required only grinding and no weld repair. UOP wishes to inform refiners of a significant increase in the incidence of reported nozzle cracks on all types of UOP Platforming unit reactors. To a certain degree, this increase may be the result of the industry’s trend toward more thorough inspections and the use of moresophisticated inspection techniques. The American Petroleum Institute (API) and the Materials Property Council (MPC) have investigated the problem of cracking in Cr-Mo equipment, and a summary was presented at the May 15, 1989, meeting of the API Operating Practices Committee. UOP concurs that the recent evidence is significant and wants to alert all of its UOP Platforming process licensees that they need to closely inspect the more highly stressed areas of the reactor vessels for cracks. The cracking phenomenon is primarily the result of creep embrittlement or less-than-optimal postweld heat treatment (PWHT) of these vessels during original fabrication. Low PWHT
temperatures and short PWHT time have been linked with the origin of crack formation. Nozzle cracks have been found in units that have been in operation for as little as five years. A stacked reactor was found recently to have a crack in the shell at the location of the intermediate head attachment weld. This crack was subsequently determined to have been due to localized excessive stress concentrations. UOP’s recommendations are as follows:
? The original fabrication details and procedures for the reactors should be reviewed and compared to present practice for insight into potential problem areas. ? At the next suitable opportunity and at each turnaround, all Platforming process reactor vessels should be thoroughly inspected. Specifically, all areas of nozzle attachment, internal head attachment, bottom reactor shell to skirt band attachment, and seam welds should be inspected. ? Experience indicates that a thorough visual inspection in conjunction with an ultrasonic shear wave and a wet fluorescent magnetic particle examination has been an effective means of determining cracking in reactor vessel shell walls and nozzles. ? If cracks are found, the refiner should consult a qualified vessel vendor for repair information.
CCR UNIT INSPECTION
CCR Platforming units have either atmospheric, pressurized, or CycleMax? regeneration sections. Inspection checklists specific to each licensee’s type of regeneration section can be requested from UOP. These checklists briefly summarize some of the process-related items to check in each piece of equipment. The checklists complement the API’s inspection guidelines, which are a more-comprehensive account of the basic information related to the proper and timely inspection of refinery equipment. Spare Parts 备件部分 Spare parts requirements for the specialized equipment within the CCR unit are found in the UOP Project Specifications. The type and number of recommended spare parts are specific to each
type of regeneration section technology. The following spare parts are common to all three designs and should be available for installation during a CCR unit turnaround: ? Air dryer pre-filter cartridge. The cartridge life is typically one year or less. Oil mist and excess water can dramatically reduce the desiccant life. ? Air dryer desiccant. The life of activated alumina or silica gel in air dryer desiccant service is typically one year or less. In the typical pressure-swing air dryer regeneration system, the use of molecular sieve is not recommended. ? Booster and recycle gas coalescer elements. Change booster and recycle gas coalescer filter elements as necessary. Typical life is only 1 year. ? UOP Dur-O-Lok? couplings. Dur-O-Lok couplings are now supplied by BETE Fog Nozzle, Inc. The refiner should have replacement elastomer-type red silicone o-rings for
each Dur-O-Lok coupling in the unit. For information about Dur-O-Lok couplings, including the replacement o-rings, please contact BETE directly at 413-772-2166 (phone), 413-772-6729 (fax), or email@example.com (e-mail). In 1997, there was an advance in the Dur-O-Lok technology to improve sealing characteristics. A male nub was added that fit into the groove in the lower coupling. The amount of compression on the o-ring gasket has not changed, however this configuration prevents the gasket from extruding when pressure is applied. Regeneration Tower Inspection 再生器的检查 Damage does not usually occur in the regeneration tower in the absence of a high-temperature excursion during operation. UOP recommends that the inner and outer screens of the regeneration tower be cleaned and inspected during the turnaround. 再生器不太容易发生损坏由于运转期间的高温环境， UOP建议检修期间对再生器 内部和外部的筛网进行清理 Both inner and outer screens can first be blown with air and then inspected for plugging of slots with catalyst chips. An earlier section concerning “Methods of Cleaning Screens and Scallops” describes screen-cleaning methods. Spare parts, except for suitable replacement gaskets, should not be needed in the regeneration tower. 内部和外部筛网都会附着一些赃物，前面已经讲了筛网和扇形筒的清理方法，备 件部分，除了适当的更换垫片外，别的不需要更换什么了。 Gap Measurement of Regeneration Tower Inner and Outer Screen
Over the years, the design slot width of the regenerator inner screen has been reduced.
Table 2 shows UOP’s current manufacturing standards for the inner and outer screen as checked by feeler gauge. These standards are also shown in the UOP Project Specification 305.
Table 2 Standard Specification for Slot Widths Specification Inner Screen Outer Screen Average slot width 0.483 mm ± 0.051 0.635 mm ± 0.051 0.019 inch ± 0.002 0.025 inch ± 0.002 Standard deviation, max. 0.0635 mm 0.076 mm 0.0025 inch 0.0030 inch Max. slot width 0.635 mm 0.89 mm 0.025 inch 0.035 inch Min. slot width 0.33 mm 0.38 mm 0.013 inch 0.015 inch A reduced slot width, in combination with improved elutriation, extends the period between screen cleanings. The catalyst chips that plug the screen are about 0.008 inch (0.2 mm) larger than the slot width and are mostly half spheres. The slot sizes on the inner and outer screen increase as a result of exposure to temperatures above design values. The most-common reason for a high-temperature excursion is coke burning in the transition and chlorination zones. If the slot sizes are larger than UOP specification, whole pills could possibly plug the inner screen, thus increasing the frequency of required screen cleaning. For example, one U.S. refiner was cleaning the inner screen every six to eight weeks because the slot widths were 10 to 20% larger than the maximum widths indicated on the UOP specification. After the installation of a newly fabricated inner screen, no cleaning was required in the first 10 months of operation. While the screen slots are being inspected, the screens themselves should be closely inspected for any signs of cracks in the weld seams. In particular, the connection between the inner screen and the upper blank-off should be inspected. When any suspected areas are found, a dye-penetrant inspection is recommended. Appropriate repairs should be made by qualified highalloy welders, preferably from the screen vendor’s shop. Annulus Measurement of Regeneration Tower Inner and Outer Screens
The most-important dimensional check from the point of view of regeneration tower performance is the requirement that the catalyst annulus be as specified in the Project Specification 305. The annulus should be checked during turnarounds, following screen cleaning. For regeneration towers in atmospheric CCR units with a circulation rate of 700 pph (317 kg/hr) or greater and in pressurized and CycleMax CCR units, the annulus can be directly measured by entering the interior of the inner screen and checking the depth with a long machinist’s rule or feeler gauge inserted through the inner screen slot to the face of the outer screen. To ensure acceptable concentricity and annulus depth, UOP has developed a field
inspection procedure of rigorous tests to measure dimensions and tolerances. The annulus check procedure specific to each unit is provided in the unit’s Project Specification 305. Regeneration tower performance is directly and measurably affected if the annulus depth requirements are violated. Inner and outer screens that are significantly out of round may need to be replaced. KME Supply of Regeneration Tower Screens KME供应的再生器纱网 UOP’s KME Group can also supply inner and outer regeneration tower profile wire screens for replacement during a turnaround (see the “KME Supply of Spare Parts” section of this paper for more information). Regeneration Tower Inspection Checklists 再生器检查清单 再生器检查 检查清单 Inspection checklists specific to the regeneration tower design for each licensee’s type of regeneration technology are available on request from UOP.
Catalyst is handled during the unloading of catalyst from the reactor at the beginning of the turnaround and during the loading of catalyst into the reactor at the end of the turnaround. Information based on UOP’s current experience with heel catalyst handling, transport of pyrophoric spent catalyst, density grading, catalyst containers, platinum recovery, and
makeup catalyst requirements is included in this section. Catalyst Unloading 卸催化剂 UOP recommends using the nozzle at the bottom of the catalyst collector to remove catalyst from the reactor stack during a turnaround. This procedure minimizes the mixing of flowing and nonflowing catalyst and therefore minimizes the amount of heel catalyst that must be sent for metals recovery. UOP does not recommend the use of the catalyst unloading nozzles at the bottom of the last reactor for this purpose. The catalyst unloading nozzles should be used only if no free-flowing spent catalyst is reloaded at the completion of the turnaround or if all the freeflowing catalyst has already been removed.
Catalyst Unloading Procedure 卸催化剂步骤 Catalyst unloading can be divided into three stages: ? Unloading free-flowing catalyst from the reactors ? Unloading heel catalyst from the reactors ? Unloading the regenerator and associated vessels Only the first two stages are in the critical time path. Unloading the regenerator can be done any time, as can catalyst screening if catalyst is to be reloaded. Appendix B contains a general procedure for unloading free-flowing catalyst and heel catalyst from the reactors. Unloading the CCR Unit 卸载CCR单元 If the catalyst will be reloaded, the level of catalyst in the disengaging hopper should be minimized prior to shutdown to reduce the quantity of coked catalyst. The CCR unit should be shut down according to normal procedures. When the regeneration tower has cooled to 350 to 400°F (175 to 205°C), all blowers are stopped. A flexible metal hose is attached below the surge hopper on an atmospheric CCR unit or below the lock hopper on the pressurized and CycleMax CCR units. The catalyst is unloaded from the regeneration tower and disengaging hopper into the surge hopper by opening BV-75 and BV-76 on atmospheric CCR units or using the unload keyswitches on the pressurized and CycleMax CCR units. The catalyst is unloaded into drums or bins at grade. A simple slide valve at the end of the hose is used to control flow.
Heel Catalyst Handling 催化剂的处理 The 1998 CCR Platforming Survey showed that in the downflow reactor design (Figure 6), heel catalyst averaged 9 wt-% of the reactor catalyst unloaded (responses varied from 2 to 27 wt-%). In the upflow reactor design (Figure 7), heel catalyst averaged 7 wt-% (responses varied from 1 to 18 wt-%). The upflow reactor design has reduced the amount of heel catalyst, but has not eliminated the problem of heel catalyst handling. The drums or flow bins containing heel catalyst should not be reloaded. Operation of the regenerator in white-burn mode with heel-contaminated catalyst is detrimental to the life of equipment and catalyst. The regenerator was designed to burn carbon at concentrations of 5 wt% on catalyst at the design circulation rate. Although some extra coke-burning capacity is typically present in the unit, it cannot effectively handle the high carbon concentrations of the heel catalyst and so carbon removal will be incomplete. When catalyst containing carbon is exposed to the high concentration of oxygen in the chlorination zone of the regenerator, phase damage to the catalyst and possibly mechanical damage to the equipment result. Even well-distributed heel catalyst develops sufficiently high temperatures to damage itself and the normal catalyst that
surrounds it when its coke is burned at high oxygen concentrations. Phase-damaged catalyst is inactive for reforming reactions and physically weak. Heel catalyst should be kept segregated from flowing catalyst at all times. The drums or flow bins should be specially marked to avoid mistakes. With the downflow reactor design, a portion of the heel catalyst can be reloaded into the reactors (see the section “Reloading Downflow Reactors”). All other remaining heel catalyst, and all heel catalyst from upflow reactor designs, is normally sent for metals recovery. However, an alternative may make it possible for the refiner to recover most of the lowcarbon catalyst that is mixed within this heel catalyst (see the section “Density Grading”).
The 1998 CCR Platforming Survey showed that approximately 65% of refiners send heel catalyst for metals recovery, 20% reload to the heel area as well as sending for metals recovery, and 15% use density grading. Transport of Pyrophoric Spent Platforming Catalyst 运输催化剂产生火花 Pyrophoricity is defined as the property of spontaneous ignition in the presence of air or oxygen. Spent Platforming catalyst is usually pyrophoric because of the presence of iron sulfide contamination, not because carbonaceous materials or hydrocarbons are present. Typically, under the current rules of transport, spent CCR Platforming catalyst unloaded from the reactors falls into packaging groups that are classified as hazardous and require certified steel drums or flow bins for transport. In the United States, the generator of a material is responsible for determining the hazardous characteristics of that material prior to transport. In addition to pyrophoricity, regulations concerning the benzene content may result in the spent catalyst being classified as hazardous for transport. These determinations can be made by either physical and chemical testing or by knowledge of the material and the process. Too many variables affect the characteristics of spent catalyst for UOP to be able to confidently categorize it. The amount of iron sulfide and benzene contamination varies widely based on the operation of the Platforming unit. Regardless of the amount of purging, reducing the benzene content to a nonhazardous level may not be possible. The only way for the refiner to know, with certainty, about the hazardous characteristics of the spent catalyst is to test it prior to shipment.
Density Grading CRI International Inc., based in Houston, Texas, has developed a density-grading technology that has proved successful in segregating catalyst particles by density to recover low-carbon catalyst from the heel catalyst. Significant cost savings can be realized in this recovery
because the material then does not need to be sent for metals recovery and it does not need to be replaced with fresh catalyst. All of the free-flowing heel catalyst unloaded from the reactor, which is typically 10 to 20 wt-% of the catalyst unloaded, is sent for density grading. Of this material, typically 70 wt-% is recovered with less than 6 wt-% average carbon on catalyst. Density-grading technology separates catalyst particles of similar size based on individual particle density. The separation of high- and low-carbon spent Platforming catalyst is an ideal application because of the large density difference. The catalyst is graded into three density groups: the heaviest cut is the catalyst containing the most carbon, the lightest cut is the catalyst containing low amounts of carbon, and the medium cut, which is a mixture of both. The medium cut can then be reprocessed in the same manner to further define the separation and improve recovery. Each light cut is evaluated to ensure that both the average carbon on catalyst and peak carbon on catalyst are within the 6 wt-% carbon specification that UOP recommends. Medium cuts, which have an average carbon level of less than 6 wt-% but a peak carbon level of greater than 12 wt-%, should not be considered for reload. These cuts can be reprocessed to recover material with a peak carbon of less than 6 wt%. Catalyst containing pills with a peak carbon level between 6 and 12 wt-% can be loaded into the disengaging hopper and last reactor of the upflow reactor designs or under the catalyst outlet scoops of the downflow reactor designs. Density grading removes dust, chips, and fines. If the presence of fines raises specific concerns, additional screening can be done. Catalyst pills that are thermally damaged are commonly referred to as white dwarfs. In the heel catalyst, the white dwarfs that do survive the density-grading processing go into the heavy cut. Following start-up with density-graded catalyst in the inventory, regeneration tower operations should be monitored for at least three problem-free cycles. UOP recommends staying in the black-burn mode of operation for at least two cycles and closely monitoring the
appearance and carbon level of catalyst leaving the regeneration tower. Note: Any vendor providing density-grading service must contact UOP and arrange for a nondisclosure letter agreement (NDLA) before processing UOP catalysts.
Density Grading Case Study Refiners’ experience with density grading has been mixed. The following case study illustrates how differences in procedures affect the outcome of density grading and the operation of the CCR Platforming unit after restart. Refinery A viewed the operation as a success and did not encounter any major operational problems after restart. Refinery B experienced major regeneration problems after restart. Refinery A was actively involved with the density-grading operation: they sampled every 1,000 lb (454 kg) of catalyst for carbon content and cross-checked the results. Refinery B relied solely on the external laboratory’s carbon analyses. Refinery B also took only one sample from every 2,000 lb (907 kg) of catalyst. Refinery A loaded the medium cut underneath the outlet scoops in their downflow centerpipe reactor. Refinery B loaded the medium cut into their upflow centerpipe reactor beds on the understanding that less than 1 wt-% of this cut had a peak carbon content of 15 to 18 wt-%. Refinery A maintained black-burn operations in the regeneration tower for two complete inventory cycles following restart and experienced no problems related to the reloading of the density-graded material. Refinery B experienced high burn zone bed temperatures after restart when the portion of catalyst inventory containing the density-graded medium cut was being regenerated. Black-burn operations were maintained for approximately eight cycles for this fraction, which was 15 wt-% of the total inventory. When continuous white-burn operations were maintained, phase damage to the catalyst in the chlorination zone resulted. Refinery B eventually replaced this portion of the inventory with fresh catalyst and has not encountered any further
regeneration problems. Ex-Situ Carbon Burning of Density Graded Catalyst UOP finds the practice of loading ex-situ carbon burned material from the medium cut of a density grading operation inherently unsound. The only acceptable option for this material is metals recovery. The reasons for this are as follows: Heel catalyst pills not only have a high coke content but the coke becomes very carbonaceous (hydrogen-deficient) as it ages. A post-ex-situ carbon burn analysis showing that the carbon content is at a “normal” level, e.g. 5 wt-% average, should not be interpreted as meaning that the coke itself is “normal”. It will still be hydrogen-deficient and hence burn very slowly in the Burn Zone, risking slippage of coke into the Chlorination Zone, with all the usual consequences.
Our experience is that in some cases, ex-situ carbon burn removes coke preferentially from the outer surface of the pill, thus heel catalyst pills are disguised and the determination of true peak carbon content by visual selection and hence determination of the acceptability of the catalyst for reload is made more difficult. UOP has no knowledge of the procedures used for ex-situ carbon burning, but suspect that oxygen levels are higher than we would normally allow, and therefore flame front temperature in the pill would be unacceptably high. Phase damage (transition to alpha-phase), platinum agglomeration, and low chloride level are consequences that have resulted in significant operational problems in several cases. In reloading this ex-situ carbon burned material, the refiner places the performance and profitability of the unit at great risk as well as risking an extended regeneration section shutdown and additional make-up catalyst requirement. Catalyst Containers UOP is often asked by refiners about alternatives to the use of drums for the shipment and handling of Platforming catalyst. One alternative is to use steel flow bins, each typically capable of
holding 12 drums, or 3,000 lb (1,320 kg), of CCR Platforming catalyst. UOP has experience with the successful use of flow bins provided by Federal Container Inc. of Houston, Texas, and now has no objection to a refiner using flow bins if the following requirements are met: ? The flow bin containers are first cleaned by sandblasting. ? The flow bin containers are tight and can be well sealed, so that the intrusion of liquid water or moist air is not possible. ? The flow bin containers are provided with plastic liners. Federal Container requires that flow bins used for precious metals catalysts be shipped in enclosed vans rather than flat-bed trailers. A refiner who wants to unload these bins in the field instead of at a loading dock would have to make provisions for getting a fork-lift into an enclosed van. Although the use of flow bins has been successful, UOP cautions that the flow bins must be carefully inspected prior to, and during, use and that the general guidelines for catalyst handling must still be rigorously observed. The consequence of failure of a single container is significant: up to 3,000 lb (1,320 kg) of catalyst may be lost. UOP is most concerned with moisture intrusion resulting from a poor seal or holes in the flow bin or improper or incomplete cleaning that results in contaminated catalyst. The refiner must exercise his right to reject individual containers that are leaky or dirty or that raise other concerns.
Details of flow bin supply and prices can be obtained from Federal Container by contacting Clifton Ben in their Houston sales office by phone at 713-926-3330 or fax at 713-926-0879. Federal Container also has an office in the Netherlands: phone +31-1899-28192 or fax +311899-25566. Any refiner using flow bins for shipping an order of fresh catalyst should contact the appropriate UOP Customer Sales representative so that the logistics of flow bin arrival and handling at the UOP catalyst manufacturing plant can be coordinated. UOP Catalyst Recovery Service
Although UOP no longer operates a precious metals catalyst-recovery plant, it continues to offer this service to its customers by managing the process and working with other reclaimers on the actual catalyst-recovery processing. A customer can continue to contract with UOP for the spent catalyst recovery when placing an order for fresh catalyst. In addition to selecting the mostsuitable catalyst-recovery process and location, UOP provides representation during the sampling operation at the reclaimer location and an independent assay of the samples taken. UOP then handles the precious metals assay exchange and settlement and arranges to have the precious metals credited to the customer’s UOP account following the reclamation. For details and pricing, contact Dick Llorens, catalyst services manager, by phone at 847-391-2677 or fax at 847-391-3690. Makeup Catalyst Requirements The volume of heel catalyst that is sent for metals recovery must be replaced with fresh catalyst. In addition, if the catalyst is screened, any losses that occur must be made up. About 10 to 15% makeup catalyst is typically needed when reloading after the turnaround, but less is needed if catalyst is recovered through density grading. Far in advance of the turnaround, the amount of makeup catalyst that is required should be checked against the amount of fresh catalyst available on-site, and an order for fresh catalyst placed if necessary. For information on catalyst pricing and availability, contact your UOP Customer Sales representative. Catalyst Loading UOP no longer recommends the pneumatic catalyst loading procedure. Currently, UOP recommends two different methods for loading catalyst into CCR Platforming reactors: reactorbyreactor loading and entire reactor stack loading. Both methods are acceptable regardless of unit design or reactor size. Differences in the quantity of fines generated are minimal. All fines that are generated from handling and loading are removed from the system during the first two or three
catalyst inventory cycles. If the loading is done correctly, these fines will have no effect on the long-term operation of the unit. In the following sections are some notes on preliminary loading activities and a general description of each loading method. The procedures for each catalyst
loading method are found in the CCR Platforming General Operating Manual, under section XIII. A., “Catalyst Loading.” Catalyst Unloading Nozzles 催化剂卸料喷嘴 Although the unloading nozzles, which have been renamed the catalyst disposal nozzles in recent designs, should not have been used to unload catalyst, they may have been opened during the cleaning of the last reactor. Before loading catalyst, the unloading nozzles should be checked to ensure that they are properly bolted with new gaskets. The nozzle usually has a support plate insert to hold the catalyst in the reactor when the blank-off is removed. Placing a layer of ceramic fiber packing on top of the support plate is a good idea. The unloading nozzle should then be loaded with successive 3-inch (75 mm) layers of ceramic support material, ceramic balls, or alumina balls with diameters of 3/4 inch (19 mm), 1/4 inch (6 mm), and 1/8 inch (3 mm). The unloading nozzle should not be loaded with catalyst (Figure 8). Reloading Downflow Reactors 反应器重新安装 As an added safety measure for the downflow reactors, a catalyst dam may be installed around the base of the centerpipe. Dams provide an extra barrier through which the catalyst must pass to migrate through a gap at the base of the centerpipe, if a gap develops (see UOP drawing No. C10963-A, which can be requested from UOP). Heel catalyst can be reloaded into the bottom of downflow reactors to within 2 inches of the catalyst outlet scoops (Figure 9); however, UOP prefers instead that 1/16 inch (1.6 mm) spherical alumina catalyst base be loaded below the scoops. As catalyst circulation begins, some of the material loaded below the scoops may flow out the reactors and get dispersed within the
catalyst inventory. Allowing a small amount of the spherical alumina catalyst base to dilute the catalyst inventory is preferable to having heel catalyst mixed into the flowing catalyst. Because the 1/16 inch (1.6 mm) spherical alumina catalyst base has no metals, it will not coke and become heel catalyst. The spherical alumina catalyst base costs much less than Platforming catalyst. Using ceramic support material or ceramic balls is not recommended because the smallest diameter typically available is 0.125 inch, which is much larger than the catalyst base at 0.062 inch (1.6 mm). If ceramic balls with diameters larger than 0.062 inch (1.6 mm) are used, considerable vapor would bypass through the bottom of the reactors because of the larger void fraction. The use of concrete, firebricks, or ceramic block tile is not recommended in CCR Platforming reactors because of the difficulty in fitting these materials around the catalyst withdrawal scoops. Additionally, these materials prevent hydrocarbon flow through the bottomhead area into the centerpipe so the reactor’s pinning margin would decrease. Reactor-by-Reactor Loading Procedure 卸反应器步骤
The reactor-by-reactor loading procedure has been the most-common method used in the past. Drums of catalyst are hoisted to the reactor manway area, where a temporary loading hopper is situated. The loading hopper can be bolted to the manway, if access can be maintained, but locating it on a deck above the manway is usually easier. As catalyst is dumped into the hopper, it flows out the bottom through piping or conduit and enters the reactor through the reactor manway. At the end of the pipe or conduit is a loading sock that extends a few feet below the reactor cover deck. The catalyst free falls from the open end of the sock to the bottom of the reactor. During the loading procedure, the sock is shifted to different areas of the catalyst bed annulus so that the catalyst fills the reactor uniformly. Catalyst falling in only one area puts uneven stress on the centerpipe and causes variations in the loaded density. This frequent
movement of the loading sock requires that a person be in the cover deck area of the reactor throughout the loading. The piping and sock must be laid out so that the catalyst flows freely. An angle greater than 35 degrees from horizontal is acceptable. When everything is running smoothly, the loading crew should be capable of moving approximately 20 drums per hour. A small variation to this approach can increase the loading rate significantly to more than 60 drums per hour. This variation calls for loading the catalyst into large transfer hoppers at grade and then lifting the transfer hoppers up to the loading hopper. Typical transfer hoppers used by catalyst-handling contractors hold 8 to 12 drums of catalyst. A separate crew at grade is responsible for loading the catalyst into the transfer hoppers. The crew always has a full hopper ready at grade when the empty hopper returns. Regardless of whether drums or bins are used, loading should always start in the lowest reactor and move up to the next highest. Loading in a reactor is complete when the catalyst level is approximately one foot below the open end of the catalyst transfer pipes. Short loading a reactor does not present a problem because the reactor will fill with catalyst from the reactor above. However, if a reactor is overfilled, it will be difficult to install the few cover-deck segments and catalyst transfer pipes not yet in place. The reduction zone or reactor surge zone can be loaded in a similar manner as the reactors by placing a catalyst loading funnel above the catalyst inlet flange at the top of the stack. The nuclear level instrument can be calibrated or otherwise confirmed to operate properly as the catalyst level at the top of the stack is increased. The stack is considered full when the nuclear level instrument indicates normal level; however, this zone should be filled to slightly more than the normal level to make up for volume loss resulting from the mechanical compaction of the catalyst bed prior to catalyst circulation and thermal expansion of the reactor vessel.
Entire Reactor Stack Loading Procedure The entire reactor stack loading procedure calls for loading all the catalyst through the top of the reactor stack. In many respects, this procedure is identical to the reactor-by-reactor loading procedure, except it has only one loading point. This method is preferred when equipment is available to quickly raise the catalyst to this height. Rates in excess of 80 drums per hour are possible when using large transfer hoppers to lift the catalyst to the top of the stack. Usually, a large loading hopper is centered over the catalyst inlet flange on the top of the reduction zone or reactor surge zone, and a short sock joins the hopper to the catalyst inlet nozzle. As the catalyst falls from the reduction zone or reactor surge zone to Reactor 1, to Reactor 2, and so on, it is distributed among the catalyst transfer pipes and fills the reactors uniformly. No problems are encountered with variations in loaded density or uneven stresses on centerpipes.
SUMMARY AND RECOMMENDATIONS
The major benefit of a highly organized and efficient turnaround is the minimization of unit downtime, which directly improves unit profitability. Planning is the key. Because unexpected equipment damage and other problems may occur, the refiner who has thoroughly planned his turnaround has a great advantage. In the face of a difficult and unanticipated problem, having the appropriate equipment, materials, manpower, and expertise available can make the difference between extending the turnaround schedule two days or two weeks. The information contained in this paper should serve as a starting point from which refiners can prepare a turnaround plan or enhance their current plan. UOP encourages refiners to take advantage of the technical assistance and equipment supply available from UOP to make their turnarounds more successful. Today’s market necessitates the use of any opportunities that exist for a more-efficient turnaround and therefore a more-profitable unit.
Beshears, D. R., “Troubleshooting III,” UOP CCR Platforming Symposium, Chicago, Illinois, 1990. Blashka, S. R., and others, “Catalyst Separation Method Reduces Platformer Turnaround Costs,” Oil & Gas Journal, pp. 62-64, Sept. 18, 1995. Furukawa, S. K., “Normal Operations of the CCR Platforming Unit,” UOP CCR Platforming Symposium, Chicago, Illinois, 1993. Hammel, E. J., “Turnaround Update,” UOP CCR Platforming Symposium, Chicago, Illinois, 1998. Throndson, R. L., “Maintenance Information for Stacked CCR Platforming Reactors and Regenerator,” UOP CCR Platforming Symposium, Chicago, Illinois, 1986. Williamson, R. R., “Turnarounds,” UOP CCR Platforming Symposium, Chicago, Illinois, 1990.
Appendix A Stacked Reactor Inspection During Turnaround
The following list is recommended as the minimum work to be performed in the stacked reactors during a routine turnaround of a CCR Platforming unit. Inspection Checklists are also provided to assist with work in the field. In addition, scallop and centerpipe inspection diagram templates are attached. Charting damage or plugging on these templates will help identify any patterns from reactor to reactor or from turnaround to turnaround. UOP assumes that the refiner’s prior experience with the reactor stack has been good and that the refiner has no special concerns as a result of on-line performance problems. Dimensional checks of internals are not listed but may be important if the refiner sees signs of catalyst fluidization or poor flow distribution. A more-detailed list of inspection items, including many dimensional checks, is in Section VI. B., “Inspection and Preparation Activities” of the CCR Platforming General Operating Manual.
Clean the scallops of all catalyst fines and debris plugging the slots in the front of the scallops. Ensure that the bottoms of the scallops are clean on the inside and outside. The majority of the slots can be cleaned by hand with a wire brush. Sometimes hard material is found in the slots, particularly at the scallop bottoms. Removal of this material can be accomplished with a hacksaw blade that has had its teeth ground off. Vacuum any debris or catalyst from the inside of the scallops. The bottoms of the scallops must be clean so that flow can reach the bottom head of the reactor. After vacuuming, place covers over the top of the scallop risers to prevent catalyst, debris, tools, and so forth, from accidentally being allowed inside the scallops. Check the outside surface of the scallops for signs of catalyst fluidization, particularly near the top of the slot openings. Look for polished areas. Inspect the surface of all scallops for tears or oversized holes. No scallops should have openings larger than a catalyst pill. Check that the scallops sit securely on the scallop support ring and are tack welded at one point to the scallop support ring and that their backs are against the reactor wall. Check for cracked welds around the base reinforcing rings, if present, at the bottom of the scallops. The scallops should be plumb and evenly spaced around the circumference of the reactor. Scallop slots are typically specified to be 0.040 inch by 0.500 inch (1.02 x 12.57 mm). It may be possible to correct small slot distortions by carefully bending the surrounding perforated plate into place. A small amount of scallop crushing, less than 0.5 inch (12 mm) in the axial direction at the base of the scallop where it rests on the scallop support ring and perhaps 1 to 2 inch (25 to 50 mm) of deflection in the radial direction on the face of the scallop at the elevations
of the expander rings, is acceptable. Damage beyond these amounts should be repaired, however it is not possible to give a strict guideline since reactor design and operating conditions will influence the maximum scallop cross-sectional area loss that can be tolerated before performance
is compromised. Severely crushed scallops prevent proper flow distribution through the catalyst bed, and the result is coke formation and additional problems. If repairs are made to scallops, welding of new sections to the existing scallop sections must be with a continuous weld, not a stitch or tack weld. Welding must be done by the shielded inertgas method. Slots adjacent to the welds between sections of scallop material should be no more than 1 inch (25 mm) apart. As a general guideline, the maximum acceptable weld protrusion is 0.062 inch (1.6 mm), provided that such a protrusion is smooth on both sides. Horizontal welds on the back and front of scallops should be ground flush and smooth.
SCALLOP SUPPORT RING AND SCALLOP EXPANDER RINGS
Inspect the scallop expander rings and support lugs for any misalignment or cracks on the attachment welds. Ensure the retainer clips are in good condition. The expander rings that hold the scallops against the reactor wall should not be overly tight. The expander rings should be snug: not so loose that they flop around but not so tight that they can't be moved slightly up and down. The recommended tension is achieved if the rings are adjusted so that a 0.08 to 0.20 inch (2 to 5 mm) clearance exists between the ring and all scallops. Inspect the scallop support ring, support lugs, and the tack weld at the bottom of the scallop to ensure that they are in good condition. Check that the bolted joints in the bottom expander ring are in good condition. A slightly larger gap of 0.20 to 0.40 inch (5 to 10 mm) is the recommended clearance between the bottom scallop expander ring and all scallops.
SCALLOP SEAL PLATES
Check the scallop seal plates for any cracked tack welds. Check the fit-up of scallop risers and riser seal plates for any binding and for correct clearances. If any scallops are removed from the cover deck seal plates, ensure that the scallop and seal plate are match marked so that the correct scallop goes back to the correct seal plate. These scallop riser and seal plates have been
custom fit and cannot be interchanged.
Clean the centerpipe screen of all catalyst fines and debris. This work should be completed by hand with a wire brush. Care should be taken not to hit the centerpipe, as the stainless steel can be brittle after extended exposure to operating conditions. The centerpipe should be plumb: within 0.040 inch per foot up to a 0.75 inch maximum (1 mm per 300 mm up to a 19 mm maximum) tolerance from top to bottom. Look for signs of catalyst fluidization on the face of the centerpipe and near the top. Bulging of the centerpipe screen may indicate separation of the screen from the inside layers of the centerpipe. Inspect all seam and blank-off welds for cracks. Obviously, tears, holes, or gaps in the screen, or loose wires need to be repaired while trying not to blank-off a section any larger than 2 inch by 2 inch (50 mm by 50 mm). Weld repairs to the centerpipe screen must be made by the TIG method using a 347 weld rod.
DOWNFLOW CENTERPIPE DESIGN
For downflow centerpipe reactor designs, remove the centerpipe manway and check the split ring assembly at the bottom of the centerpipe. Ensure that the gaskets and bolting are in good condition. A good rule of thumb for split-ring assembly is that when in doubt, repair. Remove any catalyst, dust, and scale from inside the centerpipe. Check that the centerpipe holes are not blocked. Ensure that the reactor outlet lines are well covered so that debris does not fall into these lines. Any material that falls into the outlet line and is not removed either will settle in an interheater, end up in the scallops of the next reactor, or in the case of the last reactor, enter the combined feed exchanger. Inspect the catalyst transfer line scoops or outlet nozzles to ensure they are in good condition. Ensure that the wire dams at the base of the centerpipes are in good condition, if present.
UPFLOW CENTERPIPE SUPPORT
For upflow centerpipe reactor designs, check the centerpipe support assembly for cracks between the centerpipe support bottom plate and the stiffening bars (wheel spokes), particularly at the outer edges of the stiffening bars. Also inspect the catalyst withdrawal funnel attachment welds. In general, it is not necessary to repair cracks in non-strength welds, such as these. The centerpipe support flange attachment welds should also be checked. Cracks there, primarily due to coke growth between the centerpipe support and the interreactor head, have necessitated replacement of the centerpipe support in certain cases. Check the gasket between the centerpipe support and the interreactor head. The gasket integrity should be good, and the gasket should be properly seated all around. Check the gasket seating with a small feeler gauge from the underside and the topside of the bottom head. Nuts should be torqued to specification, and lock nuts should also be snug. Check that the washer under the nuts is intact and fully covers the bolt hole.
CATALYST TRANSFER PIPES
Check all catalyst transfer lines between the reduction or reactor surge zone and Reactor 1 and between reactors to ensure that they are not plugged. Gaskets should be replaced in all the flanges of these catalyst transfer pipes.
COVER DECK AREA
Check the bolting and gaskets on the reactor internal outlet lines, the mitered elbow and expansion joint, catalyst transfer lines, and cover decks. Check that the wedge pin anchor chains are not broken and are tack-welded to both the wedge pin and the coverplate. Remove catalyst, dust, and scale from inside the expansion joint shroud ventilation holes and screen slots or ventilation basket screen slots. UOP does not recommend the expansion joint be inspected unless a problem is
suspected. In order to inspect the expansion joint, the centerpipe should be secured to prevent tipping when the outlet elbow and expansion joint are removed. The expansion joint shipping tie bolts should then be installed to hold the expansion joint in place. The outlet elbow is then removed and secured in the reactor cone area. Finally, the expansion joint assembly is disconnected from the centerpipe and lifted to allow access to the inside surface of the expansion joint.
REDUCTION ZONE OR REACTOR SURGE ZONE
Check that the catalyst inlet pipe to the reduction or reactor surge zone is in good condition and does not contain sharp edges that could damage incoming catalyst. At the ball valve on the catalyst inlet flange, verify that the gaskets are the correct size, the valve is fully open when the external valve position indicator suggests that the valve is fully open, and no protrusions or ledges that might damage incoming catalyst are around the valve. On atmospheric CCR units, check the top tube sheet on the reduction zone exchanger for cracks. Dye penetrant testing is recommended. Check the reduction zone lower catalyst pot for cracks and coke buildup on the inside. Clean debris from the top and bottom pots. On pressurized CCR units, clean debris from the walls and bottom plate of the reactor surge zone. Inspect the catalyst outlet funnels in the bottom plate for signs of erosion. As in centerpipe support assemblies, check the condition of the gasket between the bottom plate and internal head, bottom plate nut torque, and the condition of the washers under the nuts. On CycleMax CCR units, clean debris from the reduction zone walls, bottom head, and catalyst outlet cones and nozzles. Check the catalyst outlet cones and nozzles for signs of erosion and the annular baffles for signs of catalyst fluidization or fines accumulation. Inspect the condition and position of the annular baffles in the upper and lower reduction zones, the reduction zone thermocouple assembly, and the reduced catalyst sampling device. Inspect and clean
the reduction gas inlet and outlet nozzles.
EXTERNAL CATALYST COLLECTOR AND CATALYST TRANSFER PIPES
催化剂收集器和输送管 On units with an external catalyst collector, remove all catalyst transfer lines between the last reactor and the catalyst collector so that the gaskets can be replaced and to ensure that debris from work performed in the reactors does not fall into the catalyst collector and cause problems during start-up. Match mark each transfer pipe to the appropriate nozzle. Remove the top head of the catalyst collector and inspect the inner baffles and surfaces. Clean any accumulation of dust and remove any debris. The re-assembly of the catalyst collector pipes should be done just prior to catalyst loading to ensure no foreign material will enter these pipes or the catalyst collector.
Appendix B Catalyst Unloading
Once the CCR Platforming stacked reactors have been cooled, purged with nitrogen to remove hydrogen and hydrocarbon, and blinded, they can be unloaded. Most of the catalyst will flow by gravity out of the last reactor. To prevent combustion, the reactors must remain under an inert atmosphere until all the catalyst, including the nonflowing catalyst, has been removed. Maintain a slight positive nitrogen pressure throughout the unloading. A convenient location to add the nitrogen is the hydrogen purge line to the catalyst collector. UOP always recommends that the unloading be accomplished through the catalyst collector and not through the catalyst unloading nozzles. Attach a flexible rubber hose or flexible metal tubing to the downstream side of BV-2 on atmospheric units. On pressurized units, the hose can be connected to the downstream side of the hand-operated ball valve after UV-4. On CycleMax
units, the hose can be connected to the downstream side of the hand-operated ball valve after the hand-operated vee-port valve. The hose should run to grade. The flow of catalyst from the reactor can be manually controlled by operating a simple slide valve at the end of the hose at grade. In any case, do not control catalyst flow by using the existing valves in the catalyst line. These valves are best used in the fully open or closed position and are not intended to partially restrict catalyst flow. Frequent use during unloading may result in damage to the seat of the these valves, thus affecting their performance during normal operation. Either drums or flow bins can be used to hold the spent catalyst. The clean drums or flow bins should be purged with nitrogen immediately before being loaded with catalyst. A count of unloaded catalyst containers should be maintained to ensure that all of the flowing catalyst has been removed from the reactors. If the spent catalyst will be reloaded, be sure to number the drums or flow bins as they are unloaded to allow the catalyst to be reloaded in the same order it was removed from the stack. Unloading the free-flowing catalyst should proceed quickly. For example, if BV-2 is a 4-inch valve, unloading 100,000 lb (45 metric ton) of catalyst takes approximately 9 hours. The bottleneck becomes how quickly full drums or flow bins can be replaced by empty ones. Obviously, flow bins that can hold 3,000 lb (1,320 kg) of catalyst are preferred if time is critical. If catalyst is to be reloaded, UOP recommends that it be screened. If time is critical, screening should be done by a separate crew and not as part of the actual unloading. For CCR Platforming catalyst, fines have an effective diameter of less than 0.047 inch (1.2 mm). Fresh CCR Platforming catalyst has an average diameter of 0.0625 inch (1.6 mm). Most large industrial screeners will hold four or more screens in series. The screening crew should install different-size
screens to minimize the load on a single screen and guarantee separation of fines from reusable
catalyst. Table 1 shows typical screen sizes used. Table 1 Typical Screen Sizes U.S. Standard Mesh Aperture, in. (mm) 10 0.078 (2) 12 0.065 (1.7) 14 0.055 (1.4) 16 0.046 (1.2) UOP has the following suggestions to speed the screening: ? The distribution pattern of catalyst on the screen should be checked and the pattern optimized using the adjusting weights on the machine, if possible. ? Purchase a cleaning kit for the screening machine. Some screens have a tendency to “blind,” and using a cleaning kit can prevent "blinding" of the screens. ? Consider use of a rectangular-opening screen, as opposed to a square-opening screen. A rectangular-opening screen should have a minimum opening according to the aperture required and a maximum opening of twice the minimum. A rectangular-opening screen does a better job of removing cracked or broken spheres that may be trapped in a square-opening screen. Screening the entire catalyst inventory is recommended, but it is not always necessary if a small quantity of fines are present in the circulating catalyst and if care is taken not generate fines during the unloading and reloading. Sometimes, screening of the last 20% of the catalyst dumped from the reactors is sufficient. UOP strongly recommends that at least the last 20% of the catalyst be screened before reloading. In addition, UOP recommends that the catalyst from the surge hopper of the atmospheric CCR section always be screened and the surge hopper cleaned of accumulated fines. As the catalyst is screened, continue to number the drums or flow bins so they can be reloaded in the same order they were unloaded. Drums or flow bins should be sealed under nitrogen atmosphere. During unloading, take a sample from every five to ten drums to check visual appearance and carbon level for presence of heel catalyst. More frequent samples should be taken as the last 10 to 20% of the free-flowing catalyst is unloaded. Typically, the last 10 to 20% of the free-flowing catalyst unloaded from the reactors is
designated as heel catalyst. This catalyst contains a mixture of low-carbon catalyst (less than 5
wt-% carbon) and high-carbon catalyst (up to 50 wt-% carbon). The high-carbon catalyst comes from the low-flow areas of the reactors, such as the bottom head and between and behind the scallops. As the catalyst level drops in each reactor, the high-carbon catalyst mixes with the flowing catalyst. Once the last of the flowing catalyst is unloaded, experienced personnel should enter the reactors under inert conditions and vacuum out the heel catalyst remaining in the bottom of each reactor. Almost no catalyst should remain in the bottom of reactors with the upflow centerpipe design. Vacuuming equipment, although still useful, is not critical for upflow units. The catalyst can be bucketed out or pushed into the catalyst transfer pipes to the next reactor and eventually out of the last reactor. Maintain all the reactors under inert environment until all the heel catalyst has been removed. The removal of this last bit of catalyst under an inert atmosphere avoids any risk of ignition of catalyst and iron pyrites. Once all reactors are free of both flowing and heel catalyst and the reactor section has been completely isolated from the other sections of the unit, air can be admitted to the reactors following the refiner’s standard safety procedures. Scaffolding can be erected at this time.