Safe, Efficient, Economic Catalyst Changes

Five factors are the key—trained personnel, proper life support andcommunications, thorough knowledge of system and catalyst, andproper equipment and procedures

C.C. Hager, W.D. Long, and G.T. HempenstallCatalyst Technology, Inc.

Buckner, Ky.

The change-out of catalyst in an ammonia synthesis con-verter can be a relatively calm experience or a very tryingone. As with anything of a complex and unstable nature,knowledge and preparedness are essential for success, buteven more so when dealing with this particular catalyst andthis particular reactor. The margin for error normally presentin most undertakings does not exist here.Less than three years ago. ammonia plants and consultants

to ammonia plants were scheduling 10-14 days on their main-tenance time lines for ammonia converter catalyst change-outs. The economic pressures brought about by high productdemands naturally filtered through to those planning andexecuting the catalyst project per se. As a service organiza-tion, we were torn between two highly desirable goals:1 ) to significantly reduce the time required for the project;and 2) attaining a high degree of safety for both manpowerand equipment, whether it be ours or the clients. Weweren't sure that the two were compatible.

Due to the hazards involved, it was first thought that safetyrisks might present themselves in such magnitudes as tomake any significant efficiency increases impossible. But.after thoroughly examining the hazards present in ourproposed plan and how they would be handled, it becamequite apparent that such risks were no greater, and in somecases significantly less, than in methodes utilized in thepast.

Five key points are involved

The key points considered, for example, were as follows:1) training of personnel; 2) proper life support and com-munications: 3) a thorough knowledge of the reactor systemin question; 4) a thorough knowledge of the catalyst beinghandled; and, 5) proper equipment and procedures.

Training of personnel. This point is of critical import

ance. All the good intentions and equipment possible are oflittle value without the necessary knowledge and experienceessential to successfully accomplish the task. It is a graveerror on the part of all concerned to allow untraned personnelto enter an inert atmosphere, especially in the case of anammonia synthesis converter, where negotiating 60 - 80 ft.of ladder and, 18-20 in. wide manways may be required.

However, there are still those who press to use their ownpersonnel because they feel there is a savings to be realized.They are probably correct, if overall hourly costs are com-pared. The fact is, that an experienced man trained inproper safety and mechanical procedures will be at leasttwice as efficient as his untrained counterpart. In addition,the risk of injury is immeasurably reduced.

Training will not, and cannot, totally eliminate safetyhazards; but it does minimize them and, in addition, enablesmishaps to be handled properly and sensibly, thereby mini-mizing the possibility of serious injury.

Life support and communication. No less than the best isrequired. In our company as much time is spent on this aspectof the business as in mechanical and technical procedure.Aesthetics cannot be allowed to interfere with the incor-poration of the critical elements making up as nearly afail-safe system as is possible. Such a system includes abasic primary air supply and, preferably, multiple back-upsystems. Figures 1,2, and 3 illustrate this subject. CatalystTechnology's approach incorporates five air-supply sources,consisting of two primary supply and three back-up systems,plus wireless communication, safety harness and safetyrope. Figure 4 is a schematic diagram of the system.

Primary concern is always safety

The reasoning behind these multiple systems is not one ofnonconfidence, but one of a simple safety factor. If a man issubjected to conditions wherein his life is totally dependent

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Figure 1. Reactor technician suited up.

Figure 2. Reactor technician entering the manway.

Figure 3. Control panel for breathing air equipment

upon his equipment, then there is no possibility of error thatcan be left unaccounted for. The true realization of thiscomes when a man is in the bottom of a multi-bed reactorin a hostile atmosphere and you and that man know thattotal failure literally means death, because no man can sur-vive for the amount of time it takes to extricate him from amulti-bed ammonia converter.

There has been considerable discussion in our industry oflock-on helmets, of which the air mask is an integral part, vs.a system wherein the helmet and mask are separate pieces ofequipment, and both are removable. Each of these systems

Figure 4. Schematic diagram of the life supportsystem shows two primary air supply sources and asecondary (back-up) source.

have claimed advantages and disadvantages. Cat-Tech hasopted for the removable components for the reason that incase of total failure of the primary and built-in back-upsystems the removable system allows use of an emergencysystem which is completely independent of the primarysystem. This is not available to a man in a sealed or lock-on system.

All the factors incorporated into the entire life supportsystem are basic, simple in design and construction, andsimple to operate. The system is not, however, inexpensive.Each man requires more than $5,000 worth of safety andcommunications equipment. A multi-bed ammonia conver-ter catalyst change-out will require approximately $25,000 -$30,000 worth of investment in safety and communicationequipment alone. It's worth every penny of it. After nearlyfour years and several hundred catalyst change-outs underinert conditions, we have not suffered a single permanentinjury to any of our employees^ much less a fatality.

Knowledge of reactor systems. Changing catalysts inevitably involves reactor internal work, such as removal ofsupport screens, grids, spargers, bubble cap trays, etc. It isonly by having a thorough knowledge of what to expect andhow best to accomplish the impending work that significanttime savings can be effected. It is also the only way thatpre-planned procedures and safety methods can be workedout. It is one thing to cut and weld, use impact wrenchesetc. when out in the open, and entirely another matter in thedepths of a reactor vessel under inert conditions, and whilewearing a life support system.

For these reasons a project should never be attemptedwithout pre-job indoctrination and planning meetings, notonly with the supervision but just as importantly with the re-actor entry specialists actually performing the tasks. Asadditional insurance, a member of supervision normallydons life support equipment himself and oversees the workdirectly

Knowledge of catalyst. Excluding the safety aspect, if anysingle phase of catalyst change-out work could be tagged asthe most important, this would be it. An inadequate knowl-

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edge of the catalyst being handled can be disastrous. Reac-tors and catalyst-handling equipment can be, and have been,criticaly damaged; men have been injured; and days havebeen added to a shutdown, due to ignorance of catalystcharacteristics.

What's it made of? What materials have been, or will be,processed over it? How will it react to various cooling med-iums? What are the peculiarities of the reactor into which itwill be installed? Do those peculiarities require specialmethods of loading? What effect does dust, compaction,pressure drop, particle distribution, density, or even com-position of handling equipment have on resultant processperformance? These questions must all be answered.

Knowledge is an essential

A plant manager should no more consider putting peoplein charge of catalyst projects who are ignorant of such factsthan to put an untrained man off the street on the controlboard. This is true whether the people doing the work arefrom a catalyst service company or from his own organiza-tion. Knowledge of such characteristics as these are essentialto attain smooth job continuity, thereby holding down time toa minimum and resulting in maximum onstream factors, notto mention efficiency of the catalyst change-out itself.

Equipment and procedures. Handling of catalysts, par-ticularly in vacuum removal, involves demands on equip-ment not ordinarily encountered in handling most materials.The pyrophoric nature of these catalysts whose active state isthe reduced form makes the single greatest demand of all.

For these reasons, it is imperative that the equipment hassafeguards and capabilities designed into it to enable smoothjob completion without damage to itself, personnel workingaround it, or the vessel, not to mention resultant time delays.

Assuming the equipment meets required standards, abrief explanation of procedures would be of interest. Thevessel to be considered is a 1,000-ton/day, multi-bed,quench ammonia synthesis converter.

A personal pre-job visit to the proposed job site is alwaysmade to ascertain-the following items:

1. Probable condition of catalyst as determined from pastoperating history, reason for change-out (loss of activity,pressure drop, or both) catalyst age, etc.

2. Vessel and plant equipment layout so as to determineplacement of catalyst handling units and support equip-ment.

3. Location of catalyst change-out on the critical path andtime allowed for completion.

4. Dump site(s) and restrictions, if any:5. Set-up requirements.6. Client briefing on not only what services and

equipment will be provided, but also what is expected fromhim.

Using this sort of basic information, the job is completelypre-planned prior to arrival at the job site. Upon arrival, thejob is commenced immediately.

Vacuum and refrigeration units are placed, vacuum andrecycle lines are set up, lite support systems are assembled,

and personnel placement are all carried out according to thepre-planned lay-out. Proper tools for reactor internals andcatalyst removal are setup to be provided sequentially inorder of expected use to handle the anticipated tasks as de-termined from the pre-job study.

The objective here is to not be surprised by what isencountered, but to expect it. Figure 5 shows the arrange-ment schematically, and Figure 6 is a photograph showingvehicle placement, vacuum and return lines, air-bottlebanks, and supply lines. Figure 7 is a cutaway of the arrange-ment inside the facility, the basic outline of what is happen-ing inside the vessel, communications, life support systemsand back-up systems, vacuum and return lines.

The job is commenced with one man in the vessel and astand-by on the outside. As the work progresses, additionalmen enter the vessel to stand-by in the emptied beds. If thecatalyst becomes agglomerated, appropriate tools arebrought in for its removal. Oxygen levels and catalyst bedtemperatures are continuously monitored, and steps taken toreduce them should they exceed tolerable limits.

Standard procedures are put into effect to handle situationswhen oxygen levels and/or bed temperatures go beyondtolerable limits. It is the lack of understanding of what isactually happening in the case of temperature excursions thatcauses serious and needless problems when such a phe-nomena occurs.

It is not as straightforward as simply concluding that tem-peratures are increasing because oxygen levels are too high.For example, a catalyst bed can overheat with 3-5% oxygenpresent in one case; or it can be kept completely under controlin another case where 5-8% oxygen is present. And, strangeas it may seem, a total lack of oxygen is an undesirable situ-

Figure 5. Schematic diagram of the equipmentset-up.

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Figure 6. Photograph shows equipment arrange-ment in the plant

ation. We have found that an optimum level is 2-3%; how-ever, we have successfully handled levels up to 10%.

Many factors are involved in the handling of varyingoxygen levels. Among them are nitrogen purge placementsand rates, location of oxygen entry, state of catalyst (whichmay vary with bed depths), procedures used by men handlingthe vacuum hose, type of set-up used, and proper use ofrefrigeration. One other important factor is the proper opera-tion of the vacuum unit, which in itself would be a topic for aseparate discussion entirely.

Why catalyst dumping is not mentioned?

It is no doubt noticeable that no mention has been made ofbottom-dumping the catalyst. There's an excellent reason forthis. We have never encountered a single converter whereinthe catalyst was free-flowing. In fact, we have seriously con-sidered changing our name to "Catalyst Technology andMining Company." The usual case in a four-bed reactor isthat the entire fourth bed is tightly agglomerated, and in somecases semi-fused. The third bed is less tightly agglomerated,but still requires power tool removal. The second bed isnormally free-flowing approximately half the way down andthen it is agglomerated. Normally the first bed can be re-moved without the aid of power tools. There have, however,been a couple of cases where the entire charge was hard-top

Figure?. Cutaway showsfor catalyst change-out.

internal arrangement

to bottom. In view of these conditions, the vacuumingmethod is by far the most practical method of removal.

Experience has shown that if the overall points discussedin this article are strictly adhered to, catalyst change-outtimes can be successfully and safely reduced regardless oftheir complexity. Further, it is our opinion that with con-tinued research into methods and equipment, these times canbe improved upon even more, to the point that a 1,000-ton/day ammonia converter will be changed out in up to 10 daysless than was required only two years ago.

The value of such an accomplishment to the ammonia in-dustry is self evident, not to speak of the chemical processindustries in general. Catalyst service companies have a sig-nificant contribution to make if their endeavors are treated asthe science it is instead of a simple materials handling ser-vice, which it is not. #

4ÉHAGER, C.C. HEMPENSTALL, G. LONG, W.D.

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DISCUSSION

ANDERS NIELSEN, Haldor Topsoe: There is onething I would like to bring forward specifically. You arevery careful in stating that the 2-3% oxygen level is inthe space above the catalyst surface and therefore itis the gas that is engaging the catalyst into the hoses.Now may I ask you -1 think it is mentioned in the paper -do you have a bleed from the bottom up through thecatalyst which is still inside the vessel? and is that bleedof pure nitrogen?HAGER: You are exactly right. We have a nitrogenpurge on the bottom of the vessel which is pure nitro-gen. Our system inherently, as hard as we try, will havesome oxygen leaks in it. This is in the recycle system,in the hoses through the truck, through the refrigerationunit, back into the space above the catalyst. The reasonthat I said the 2-3% was optimum, is very simple. Wehave the bag houses, filter bag houses in the vaccum

truck. Dust and fine particles collect on this.When we disconnect our hoses from the bottom of

the reactor, drive the truck to the dump site, we mustexpose it to some degree of air. The 2-3% O2 simply isa controlled oxidation of the catalyst particles on thedust bags themselves. It somewhat stabilizes those, notcompltely, but reduces the possibility of catching a baghouse on fire, which I might say happened rather fre-quently until we learned how to do this.

In addition we do have a nitrogen bottle attached tothe truck and a small purge of nitrogen going into thebag house as we transfer the truck back and forth be-tween the reactor site and the dump site. I do want tomake it perfectly clear - 1 shouldn't use that word - butthere is no oxygen passing through the catalyst bedper se.

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