PLANT ADAPTATION Lakc hlead also offered a substantial supply of fresh water, which is always an asset t o a chemical plant. 4. Conversion of an unused bromide plant to the production of lithium carbonate: In order to avoid writing entirely about work that was done 6 or 8 years ago in the postwar period, the author looked for a more recent example and found that the American Potash and Chemical Co. is using a bromide plant a t Trona, Calif., to produce lithium carbonate ( 2 ) . The conversion (meant to save time and money) was made in less than 3 months. The report of this conversion ( 2 )states that it is a relatively simple trick to engineer a new process into a plant built specificall for the process, particularly if you can draw on extensive pi& plant work and have a wide choice of new equipment. But squrezing into an existing plant, and making old equipment do, all without benefit of a pilot plant, requires a firm grasp of the fundamentals of chemical engineering. Correspondence with an officer of the American Potash and Chemical Co. brings this later reaction. While they are “quite happy with the conversion of this plant,” such a conversion generally results in a crowded plant with less than ideal material flow arrangements. They would far prefer a plant specifically designed for the purpose. It is doubtful if anyone would attempt this type of conversion exccpt where the economic and/or time factors are of considerable importance.
looking A h e a d Finally, we come to the question of opportunities in this field today. Certainly most of the war plants have been disposed of and delivery of equipment is generally not delayed. The opportunities lie in our own backyards. What new chemicals can be made with minor changes to some nonprofitable unit? Can engineering departments be challenged by the chance to try out production of a new chemical that may not justify the cost of a new plant? This type of experience may be just what young engineers need to wean them from lazy thinking habits that may have developed during a period of rapid expansion and easy capital.
Literature Cited (1) Burt, R. B . , IND. ENC.CHEM.,46, 2479 (1954). (2) Chem. Eng., 60, 144 (1953). (3) Waddell, H. L., Factory Managenaant and Maintenance, 108, No. 4, B-59 (1950). RECEIVED for roview April 13, 1954. .4CCEPTED August 30, 1964.
Engineering in Plant Revamp Work J. M. BLACK The M. W. Kellogg Co., 225 Broadway, New York, N. Y.
Available figures covering the cost of a new plant built from the ground up are apt to be fairly accurate. When it appears that an alternate program of plant adaptation or revamp is possible, then a similarly accurate comparative estimate should be prepared. This i s a difficult assignment. The purpose of this paper i s to highlight the engineering and construction factors that greatly influence the correctness of revamp estimated costs.
IN
T H E coinparatively young and rapidly advancing fields of the petroleum and petrochemical industries, new processes are often developed in the laboratory faster than commercial aize plants can be built. In fact companies in these industries sometimcs find that a plant under construction is already outmoded Fortunately, this represent6 extreme rather than averagc rate of obsolescence so that usually amortization is substantially accomplished. However, the outmoding often occurs long before the useful lifc of the physical equipment has been realized. Therefore, probably without parallel in other industries, refiners may be confronted 15 ith acres of installed vessels, pumps, piping, supporting structures, buildings, power generating equipment, and attendant water and waste handling facilities and are faced with the pi essing economic question, should u-e revamp? The first blush reaction of management is apt to be “why not?” This response results from being influenced by assumed iuvestment and calendar time advantages over competitors who will have to build entirely new plants from scratch. There is only one way t o find out, and that is by means of a very careful survey. Obtaining proposals for new plant construction is comparatively simple and routine. With fixed price bids, the figures arc apt t o be quite accurate and can only be affected by inflation and strikes, which are common to all new construction. This is not true of thc so-called revamp project. Here fixed bids are less practical and estimates can be grossly in error unless all the problems peculiar to this type n orlc are carefully studied and taken into consideration. I t is the purpose of this paper to highlight those items which most greatly influence the final dollar figure in revamp ~ o r by k December 1954
citing a few case histories in the oil refining field and to signal engineering and construction pitfalls. The writer is not aware of any conversion job that did not prove to be a successful financial venture finally. However, the tendency is to underestimate the original cost of the reinvestment. It is this point that is emphasized-stressing what might be overlooked, or insufficicntly appreciated.
Exampies The majority of so-called revamp projects in oil refineries basically involve plant capacity increase by enlargement or modernization of equipment to remove bottlenecks. There are also many projects where the feed and/or type product characteristics are altered sometimes by established means and other times by completclp new process approaches. The following are typical: 1. Existing catalytic cracker vapor recovery unit revamped for greater propylene production t o product improved aviation gasoline blending stock and ethylene feed stock for petrochemical processes. 2 . Portion of combination thermal cracking unit revamped to a vacuum distillation unit to supply catalytic cracker feed stock. 3. Portion of combination thermal cracking unit revamped into a n atmospheric distillation unit to supply highly fractionated straight run distillates plus reduced crude feed t o a vacuum unit for catalytic cracker feed stock. 4. Entire hydrofluoric acid alkylation aviation gasoline plant built for Defense Plants Corp. during war converted to lube oil plant. The last mentioned case represents a good cxample of plant adaptation. Right after Korld War 11, demands for aviation
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT alkylate dropped off, but the market for lubes was maintained. Ph&s pet&unl had a large alkylation unit which could llo longer pay for itself so it mas converted into a lube unit. Figure 1 shows the ‘.before” and “after” combination plot pluii-flon arrangement diagrams of the entire plant. I n the deivaving area only about of the original eq;ipment could be reused distillation and deasphalting area 5 t,o 40% of In the the existing equipment was reused. Figure 2 s h o m “before” and “after” photographs of the phenol treating section. This area represents a case of how ideally revamp work can work. Of 5 fract,ionation towers, 11 drums, 27 exchangers, 2 furnaces, and 26 pumps, only one new furnace, 13 exchnngew: and 11 pumps had t o be added or replaced.
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General Summary of Problem I t is assumed that cost data will be available covering a completely new comparative plant of the process under consideration. A general approach for assembling a comparative figure covering a revamp alternate is outlined. Preliminary Process Study. The preliminary step is a plant survey t o determine the availability of an outmoded unit which will provide most of the equipment required by the new process, the elimination of which can be (or has been) accomplished by alterat,ions and/or additions elsewhere in the plant. Further, the preliminary process study must indicate that principal towers, furnaces, and eschangers appear to have sufficient pot’ential duties and capacities and that sufficient space is available for necessary additions. I n making this study, t,he process designer should not overlook the possibility of adapting the new process t o suit t’he existing equipment. An example would be the shifting of the order of towers for successive distillations to suit the size and pressure ratings of available fractionating columns. Roundup of Data on Existing Plant. One of the most important items in determining the authenticity of the evaluation figures is t,he ext,ent and accuracy of mechanical design and operating data concerning the existing unit,. This might appear to be a routine matter; however, it is amazing how plant records concerning equipment 10 years and older are either coinpletely absent or so meager as to be unreliable, because
1. Durable original prints or tracings were either never received or not kept under responsible custody and change records
arc completely absent. Equipment has been added or eliminated; lines rerouted with no engineering record with the exception of miscellaneous instructions to the maintenance department. The original contractor’s drawings hence become quite unreliable. 2. Performance and repair records covering pumps, drivers, piessuie and heat exchanger equipment are apt to cover only those in the most criticd services in the existing operation. Orlly for pipe Corrosion measurements are apt to be and vessels in hot and high pressure, or highly corrosive service. Either it must be assumed that t,he remaining equipmentresembles the original installation or else find out how closely it does. The necessity for checking the original design against the esisting plant cannot be overly stressed. An emergency shutdown will occasionally force material substitution not in the original specifications. These stopgaps often turn out to be perfectly satisfactory for the existing plant-such as using brass exchanger tubes for steel, using a smaller pump impeller or motor driver, and juggling valve trim materials. These may seem like minor points, but unless they are discovered originally, they can incur costly completion delays by not being discovered until the unit is actually being reconstructed. Even major equipment locations should be rechecked. I n one job, two single unit,swere being consolidated. The space betn-cen the two units was to be used as a new pipe alley, utilizing existing columns in each of the t\vo adjoining original units as uprights. After some 20 odd heavy I beams had been delivered t o the site to act as the horizontal members it developed that t,he second unit had been built some 6 inches farther away from the first one than the refinery map indicated. One of the most difficult items to obtain concern8 internals of towers and exchangers. The process engineers must have all data concerning tower trays-Le., depth of seals at bubble caps and seal pots, cross-sectional areas of bubble cap slots, details of downflowe, weirs, and inlet distributors. This information is most often lacking if the towers are in clean and uncorrosive service, where no maintenance has been required. A heat exchanger evaluation for new service is useless unless all details of the tube layout’, baffle spacing, and free area data are a t hand. Pump charact’eristic curves for cent’rifugal pumps should be available-not the vendor’s original quotat,ion curve but the actual plotted test curve. This item is of great importance, because the pump that was purchased for the original service may have been finally designed with an excessively large safety factor to allow for unknown process variables in the original setup. In
w TANK
C A R LOADING
UNdADIhG
r L 4 r
COURTESY PHILLIPS PETROLEUM C O W .
(Before) Alkylation U n i t
Figure 1. 2472
(After) tube Plant
Combination Plot Plan-Flow Arrangement Diagram
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other words, there are apt to be pumping units available with a potential capacity that is 20 to 30% greater than that used under actual service. Furnace tube header arrangements also have a habit of becoming rearranged over the years, and an evaluation of furnace usefulness for a new duty is dependent on accurate information, Detailed Process Study. Once the basic mechanical information has been assembled, the process engineer may proceed with detailed fractionation, heat distribution, pressure drop, pumping, and storage studies. Survey of Equipment Conditions. After basic re-usable equipment has been pinpointed from a process angle, it becomes necessary to restudy the actual physical condition of this equipment. Up-to-date inspection reports may or may not be available. Fairly accurate records are usually kept on pressure shell condition of vessels. Normally the practice is to re-use vessels in the new process in services that present somewhat less severe pressure and corrosion conditions than those for which the vessels were originally designed. .4 more difficult problem is to figure out how good the piping is. This is particularly true with plants built between 1941-44. Korld War I1 restrictions necessitated the use of a great amount of butt-welded and lapwelded pipe and “bedpost” tubing. It is often nearly impossible to determine whether an old piece of pipe is welded or seamless. Hence, it is safest to figure on allowable stresses of welded pipe in plants constructed during World War 11. If new service conditions are to be substantially higher than the existing operation, a careful inspection program of scntrp holes or audio gaging is in order. COURTESY PHILLIPS PETROLEUM CORP. The condition of pump cases should be Figure 2. Revamp of Phenol Treating Unit known. There have been situations where a Foundations, steel work, and vessels were left i n position; internals were redesigned; extract particular esisting pump was selected for a furnace occupies the foundation used b y heater i n “before” photo new service, and when the pump was disassembled for the addition of a new impeller, the that may not seem important a t the time of the original estimate case was found to be pitted beyond the point of safety. By the is whether to bring outmoded equipment up-to-date, such as t h e a new case was secured an entire new pump designed spepumps, dryers, filters, and the more general category of control cifically for the new service (with twice the efficiency) could have and recording instruments. The first mentioned items are too been bought. The new pump would have paid for itself in one specialized to permit gene1a1 discussion. However, serious year, if the cost of the replacement case for the existing pump consideration should be given to modernization of instruments. were taken into consideration. The maintenance and operating departments may have facts The condition of supporting structures is apt to be overlooked. and figures that indicate that obtaining replacement parts for Steel structures generally are kept in fairly good condition by periodic paintjng. Exposed elevated concrete structures for obsolete controllers is an increasingly difficult problem and maybe the proposed alteration program presents an excellent occasupporting towers or exchangers located in corrosive atmospheres sion to re-evaluate the existing instrumentation setup. sometimes tend to deteriorate and spall. These are hard to reOccasionally operators become accustomed to sloppy feed pair, because the extent of t,he deterioration is not known. A control to a fractionation tower caused by a slow reacting level careful study of joints and sheer points should be made on struccontroller in a preceding tower. Such control may have been tures that shorn any signs of deterioration before any new or tolerated under the less stringent fractionation requirements of increased Ioads are planned. A point that can greatly affect a budget is whether to reline the older process but may never meet new even-flow requirements furnace v,dls, ceilings, breechings, or stacks a t the time of renecessary for the new process. Survey of Auxiliary Facilities. The selection of process equipvamp. A study may indicate that i t is cheaper in the long run to repair or completely replace the refractories and insulation ment is only part of the problem. One of the advantages of a revamp program over new construction is that electric power, when the whole plant is down for alteration rather than try to (or have to) do it during a semiannual, one- or two-week turnsteam, water, and waste facilities are already a p t to be available However, unless all factors are considered, the evaluation study around. Obsolescence of Machinery and Instruments. A factor can become quite inaccurate. December 1954
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT The lack of re-examining the less glamorous auxiliaries, such as the sewer collecting and disposal systems, the slop, blowdown, and flare systems, can result in unexpected cost extras, start-up delays, and possible public nuisances. Invariably the new plant will result in different type water contaminating wastes that will require a redistribution of the collecb ing systems. Digging up existing sewers and re-laying new ones around existing foundations can be very costly. This consideration should be emphasized during the spotting of equipment. Settlers will have to be re-examined for the new quantity and quality of the sewerage. The new plant will undoubtedly contain a different proportion of heavy versus light ends-the blowdown stack versus flare stack distribution is apt to change. There are many old crude stills buried in the middle of the refinery v hich are ripe for revamping. Routing of a new flare line from this central location to a remote site beyond the tank farm can beconie expensive and must not be overlooked in the budget. Study of Land and Construction Costs. The revamp job saves the cost of new land, but construction problems are increased because of the lack of working room. By no%-,the existing unit is invariably surrounded by other units. The blank adjacent area that was originally available for construction offices, shops, material and construction tool storage, change houses, and parking area is now gone. The only space available for these facilities may be many blocks away. This can increase construction costs considerably, and ample allon ance must be included in the estimatc if such is this case. The lack of working space can doubIe the cost of what otherwise would be a routine operation-euch as the erection of a tower. On a new clean site, the construction sequences can be worked out in advance in a logical manner to allow C R S ~movement of large equipment to the lifting rigs. The routing of a new tower in a crowded existing unit will require an immense amount of planning and will often necessitate the temporary relocation of existing equipment that otherwise would be undisturbed Labor Consideration. Early in the study it should be established whether the revamp job can incur labor dieputes between the refinery maintenance unions and thoee unions which must be utilized by a construction contractor. On new work, the largeness of the project will generally negate possibilities of union conflicts. However, on smaller alteration jobs, the situation should be clarified and understood from the very outset of the program. Cost of Shutdown Time. The redesigned unit has been conceived to increase the over-all profit made by the refiner. But if it is assumed that the existing unit is still in operation, and on its running depends the operation of a number of other eubsequent units in the chain of refining in the plant, then the length of down time of that unit can become crucial. Two approaches may be taken to cut this time. Obviously, one is to work overtime, and the othey is to shop fabricate as much pipe as possible. This pipe may not seein so expensive but will require many, many more break flanges and unions rrhich in turn require more careful detailing of the pipe. Searly every line R-ill have to be checked in the field for exact dimensions before release to the shop fabricator. The situation can occur where the nature of the original process or the condition of the original equipment is such that the unit’s turnaround schedule demands routine shutdowns for inspection and overhaul that occur long before the long-delivery items of thc new process are received. Certain alteration work can be accomplished during thebe peiiods such as removing existing unused lines and equipment and installing blinded or valved-off stub ends in existing pipe headers for the future lines. Other considerations are how long and where burning and welding can be tolerated a t the site. Again, the unit t o be revamped is apt to be c1,ose to an operating unit handling highly volatile hydrocarbons. The refincrg safety department may not
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permit welding in an area that may encompass the new alteration project. Careful liaison and preplanning can save money and a possible conflagration. These items that affect shutdown time are vastly important Doubling the labor budget combined with careful planning of shutdown time to coincide with other unit routine turnarounds will prove worth while. There are cases where the cost of shutdown time is so impoitant that it is possible to justify the building of a new unit adjacent to the existing unit, which latter unit would then be shut don n permanently and “cannibalized” for other servicei, rather than take the production loss that would ensue if a revamp program was instituted. Detailing Revamp-Home Office Versus Job Site. Whether the engineering is detailed by the parent company or by an outside concern, consideration must be given to the relative economics regarding what portion of the work shall be done in the home office and how much shall be done a t the job eite The chances are slim that the main engineering office is near or evcn in the same toun (or state) as the job site. This again, bringsup the matter of “How accurate are the original drawings, specifications, and data sheets?’ If this inforrnation can be relied on then a great portion can be safely done in the home office. However, coming back to the all-important factor, length of donn time, one must accentuate the seriousness of construction delays caused by inaccurate dimensions, If a small competent engineering group is available for checking all phases of the existing plant a t the job site, its services should definitely be planned on with adequate allowancefor travelingexpenses included in the engineering budget.
Estimafe Summary After all process, engineering, and construction matters have been carefully thought out and all work and purchasing itema turned to dollars, the matter of adding the figures and arriving at a total cost is quite simple. But there remains thc vital item of contingency. The contingency figure must be high in an estimatc covering a revamp. You may think that you have covered evory possible item. But there Till always be hundreds of little unforeseen items that will crop up until the actual work is started. The removal of a tower tray lays bare the fact that its support ring is practically corroded through, or the tray instead of being bolted in place was welded in place. The attempted inetallation of a new shop fabricated and atress relieved alloy line to an existing pump d l reveal the fact that thermal stresses from the original suction line have pushed inch off its original location. the pump and its foundation a/l The digging of a trench unearths a vital sewer line or powei line that v a s not known to have run through that area. The disassembling of a pump indicates that a complete ne15 mechanical seal is required.
CoRcluSion .\s mentioned in the introduction, the author has no knowledge of a revamp job t’hat did not justify itself. But a t the same time, every refiner seemed disappointed a t the discrepancy between what he originally thought the change-over might cost and n-hat it finally cost. Once the refiner is resigned to this built-in characteristic of conversion work, his only problem is to find the engineers who are willing to go through Winston Churchill’s “blood, sn-eat, and tears” that are so inherent in revamp work. Luckily for the sake of conservation of our natural resources, the Bmerican refiner is not so wasteful with his plant facilities as he is with his own private automobile. He will give his oiti process unit an overhaul job and make it better than ever rather than scrap it’and build an entire new unit just to keep in style. RECEIVEDfor review RIarch 26, 1964.
ACCEPTLDSeptember 23, 1954.
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