plant start up

7
W ork on a chemical project in- volves basic engineering, detail engineering, procure- ment, erection, precommis- sioning and startup. While each of these activities has its own impor- tance, construction and precommis- sioning are the two crucial activities that determine a smooth startup. Commissioning of a plant involves all activities from mechanical comple- tion up to the certification of guaran- tees embodied in the contract between the EPC (engineering procurement and construction) contractor and the owner. In general, the commissioning costs, as a percentage of total plant in- vestment, are: • 5–10% for established processes • 10–15% for relatively new processes • 15–20% for novel processes In order to ensure that a plant under- goes a smooth startup, it is important that the last phase of mechanical com- pletion and the preparatory activities for commissioning are thoroughly per- formed. These include such activities as: cleaning, and leak-testing pipelines and vessels; loading lubri- cants, chemicals and catalysts; in- stalling mechanical seals, and column and vessel internals; removing tempo- rary bracings; aligning rotating equip- ment; and inerting the system. Other activities include closing (box-up) of columns and vessels, test runs of rotat- ing equipment, drying of fired heaters, calibrating of instrumentation, and performing loop and functional checks. Once these activities are completed, the plant is ready for startup. These and other procedures for preparing a typical process unit for startup are described below in greater detail. The term “process unit” can have wide range of definitions, depending on the industry; whether it is related to, for instance, petroleum refining, petro- chemicals, fertilizers, plastics, pharma- ceuticals, oleochemicals, detergents, pulp and paper, paints, metal refining, or beer brewing. While it is not possible to write instructions covering every type of process unit, the guidelines pre- sented here cover typical activities that are required for a broad range of process industries. Proper planning is essential The precommissioning and operations personnel should be in touch with the construction staff at an early stage of piping erection in order to establish priorities for mechanical completion. Ideally, when construction activities have achieved about 75% completion, the construction team should be refo- cused according to the needs of the precommissioning team. At the outset, the plant should be di- vided into various sections in the order in which mechanical completion is de- sired. For example, process gas com- pressor(s), if any, may have to be test run at a fairly early stage in order to rectify possible problems. Therefore, all process lines and equipment falling in the compressor loop will have to be precommissioned on a priority basis. Similarly, reactors, which ordinarily have to be filled with catalyst, must normally undergo a drying cycle in- volving fired heaters. Therefore, equip- ment and piping included in the cata- lyst and fired-heater loop also need to be precommissioned at an early stage. Refrigeration systems, which are used to chill a process stream or prod- uct, also fall under this priority cate- gory and need to be test-run at an early stage. It is therefore essential that a schedule be prepared, well be- fore the commencement of startup ac- tivities. The schedule should take into account those activities that fall on the time-critical path. An example of such a precommissioning schedule is shown in Figure 1. Personnel needs Making sure the right personnel are in place is also critical. A typical struc- ture for the organization of the pre- commissioning team is shown in Fig- ure 2. The team, headed by the precommissioning manager, consists of process engineers who are, in turn, supported by instrumentation, electri- cal, machinery and piping engineers. The number of engineers required from each discipline is determined by the scale and complexity of the plant. Vendor representatives for packaged items, such as refrigeration and com- pressors, also form part of the team and are called upon at appropriate times during test runs of respective packaged units. In addition, the avail- ability of a dedicated skilled-labor force, with necessary tools and proper equipment, is very important to take care of temporary installations, such as replacing control valves by spool pieces, preparing and installing tem- porary lines, fabricating adaptable fit- tings for connecting temporary hoses, and similar activities. Typically, such a labor force should consist of welders, gas cutters, grinders, fitters and rig- gers. Some EPC companies prefer the erection sub-contractor to provide this labor force. However, precommission- ing activities require such fabrication work only for temporary purposes. Some companies, therefore, hire such a team from the local market, usually at lower rates than they pay for per- manent employees. Cover Story 36 CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005 Preparations for Initial Startup of a Process Unit Here is what to do just after a new plant is built, to make sure it will have a smooth startup Siddhartha Mukherjee Lurgi India Company Ltd.

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Plant Start Up

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Page 1: Plant Start Up

Work on a chemical project in-volves basic engineering,detail engineering, procure-ment, erection, precommis-

sioning and startup. While each ofthese activities has its own impor-tance, construction and precommis-sioning are the two crucial activitiesthat determine a smooth startup.

Commissioning of a plant involvesall activities from mechanical comple-tion up to the certification of guaran-tees embodied in the contract betweenthe EPC (engineering procurementand construction) contractor and theowner. In general, the commissioningcosts, as a percentage of total plant in-vestment, are:• 5–10% for established processes• 10–15% for relatively new processes• 15–20% for novel processesIn order to ensure that a plant under-goes a smooth startup, it is importantthat the last phase of mechanical com-pletion and the preparatory activitiesfor commissioning are thoroughly per-formed. These include such activitiesas: cleaning, and leak-testingpipelines and vessels; loading lubri-cants, chemicals and catalysts; in-stalling mechanical seals, and columnand vessel internals; removing tempo-rary bracings; aligning rotating equip-ment; and inerting the system. Otheractivities include closing (box-up) ofcolumns and vessels, test runs of rotat-ing equipment, drying of fired heaters,calibrating of instrumentation, and

performing loop and functional checks.Once these activities are completed,the plant is ready for startup.

These and other procedures forpreparing a typical process unit forstartup are described below in greaterdetail. The term “process unit” can havewide range of definitions, depending onthe industry; whether it is related to,for instance, petroleum refining, petro-chemicals, fertilizers, plastics, pharma-ceuticals, oleochemicals, detergents,pulp and paper, paints, metal refining,or beer brewing. While it is not possibleto write instructions covering everytype of process unit, the guidelines pre-sented here cover typical activities thatare required for a broad range ofprocess industries.

Proper planning is essentialThe precommissioning and operationspersonnel should be in touch with theconstruction staff at an early stage ofpiping erection in order to establishpriorities for mechanical completion.Ideally, when construction activitieshave achieved about 75% completion,the construction team should be refo-cused according to the needs of theprecommissioning team.

At the outset, the plant should be di-vided into various sections in the orderin which mechanical completion is de-sired. For example, process gas com-pressor(s), if any, may have to be testrun at a fairly early stage in order torectify possible problems. Therefore,all process lines and equipment fallingin the compressor loop will have to beprecommissioned on a priority basis.

Similarly, reactors, which ordinarilyhave to be filled with catalyst, mustnormally undergo a drying cycle in-volving fired heaters. Therefore, equip-ment and piping included in the cata-lyst and fired-heater loop also need tobe precommissioned at an early stage.

Refrigeration systems, which areused to chill a process stream or prod-

uct, also fall under this priority cate-gory and need to be test-run at anearly stage. It is therefore essentialthat a schedule be prepared, well be-fore the commencement of startup ac-tivities. The schedule should take intoaccount those activities that fall onthe time-critical path. An example ofsuch a precommissioning schedule isshown in Figure 1.

Personnel needsMaking sure the right personnel arein place is also critical. A typical struc-ture for the organization of the pre-commissioning team is shown in Fig-ure 2. The team, headed by theprecommissioning manager, consistsof process engineers who are, in turn,supported by instrumentation, electri-cal, machinery and piping engineers.

The number of engineers requiredfrom each discipline is determined bythe scale and complexity of the plant.Vendor representatives for packageditems, such as refrigeration and com-pressors, also form part of the teamand are called upon at appropriatetimes during test runs of respectivepackaged units. In addition, the avail-ability of a dedicated skilled-laborforce, with necessary tools and properequipment, is very important to takecare of temporary installations, suchas replacing control valves by spoolpieces, preparing and installing tem-porary lines, fabricating adaptable fit-tings for connecting temporary hoses,and similar activities. Typically, sucha labor force should consist of welders,gas cutters, grinders, fitters and rig-gers. Some EPC companies prefer theerection sub-contractor to provide thislabor force. However, precommission-ing activities require such fabricationwork only for temporary purposes.Some companies, therefore, hire sucha team from the local market, usuallyat lower rates than they pay for per-manent employees.

Cover Story

36 CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005

Preparations for InitialStartup of a Process Unit

Here is what to do justafter a new plant is built,to make sure it will have

a smooth startupSiddhartha MukherjeeLurgi India Company Ltd.

36-42 CE 1-05 12/29/04 2:42 PM Page 36

Page 2: Plant Start Up

Plant inspectionBefore precommissioning operationsbegin, it is important that all equip-ment and pipes be thoroughly checkedto ensure that they confirm to the de-tailed P&IDs and the project specifica-tions. In this manner, mistakes com-mitted during construction can befound and rectified. Inspection of theplant can be basically divided into thefollowing areas:• Personnel and safety• Vessels and heat exchangers• Reactors and columns• Machinery• Piping• Electrical and instrumentationFor each of these areas, a checklist ofthe essentials is provided in the tableon pp. 40 and 41. This checklist can beused as a “to do” list before commenc-ing preparations for startup.

Commissioning of utilitiesSoon after the plant is constructed,the utilities, such as steam, coolingwater, and air, must be put in service.Once steam is available at the batterylimits, the steam system can bewarmed up and blown free of all de-bris. Three different categories ofsteam blowing are used, depending onthe lines involved:• For steam-tracing lines and hose

stations, blowing steam throughonce (the “once-steaming” method)is usually sufficient

• For process-steam lines, the warm-ing up operation is performed gradu-ally, with the steam-supply valveopened by a few turns before everyblowing cycle. In each cycle, steam

blowing is generally performed forabout 10 minutes. Thereafter, thevalve is closed and the system al-lowed to cool for at least an hour.This cycle of warming up, blowing,and cooling down of the pipe, is car-ried out a number of times, and therepeated expansion and contractionof the pipe causes rust, weld slag orspatter to peel off the pipe surface.This leads to a more effective blowing

• For superheated steam lines thatsupply steam turbines, the “target-plate” method is applied. In thismethod, in addition to the heating-blowing-cooling cycle describedabove, a target plate is installed atthe blow-off end, usually after thethird cycle. A final blowing cycle isdone for 10 minutes after thewarming step, and the target plateis removed and inspected. If thenumber of minute particles de-posited per unit area is not below apre-specified value, the steamblowing must be repeated

Before putting steam into the system,all steam traps, control valves, tur-bines, heaters, instruments, vacuumejectors and strainers should be re-moved or blanked off from the system.Condensate must be drained manu-ally, as it forms, to prevent steamhammering. When blowdown of thesteam system is complete, the trapsand other equipment that were re-moved prior to the blow-off may be re-connected. The system is then re-heated and placed in service.

Cooling-water lines should beflushed with cooling water, as is dis-cussed in detail below. All condensers,

sample coolers, lube oil cool-ers at pumps, and coolingwater to case jackets of rota-tional equipment should bedisconnected from the sys-tem. The inlet lines should beflushed one at a time, usingflow from the cooling-waterpumps. Flushing is next donethrough the users (the equip-ment) themselves. There-after, flushing is donethrough the users andthrough the outlet line fromthe users. Finally, the returnline is flushed.

The plant air lines shouldbe blown thoroughly with plant air.The instrument air lines should beblown with instrument air. Subse-quent service testing should be carriedout on these lines before putting theminto service.

Potable-water lines to eyewashand safety showers and drinkingwater fountains should be flusheduntil debris and harmful substancesare removed. The drinking watermust be analyzed at each point ofhuman consumption to ascertainwhether the water is suitable forhuman consumption.

Regarding the fire-water system,each fire hydrant and turret should beflushed after removing all nozzles. Be-fore flushing the sprinkler systems,all sprinkler heads should be re-moved. Before reinstallation, theheads should be inspected to ensurethat they are clean.

Condensate lines should be cleanedwith a strong flow of water from bat-tery limits.

Cleaning lines and equipmentPipelines must be cleaned to removeany foreign material that may havebeen left behind during the construc-tion period or formed during pipingwork. Naturally, generated rust alsoneeds to be removed. Otherwise, de-bris from uncleaned pipelines canlead to contamination, clogging ofpipe or control valves, malfunction-ing of equipment, or damage of rotat-ing equipment.

Various types of cleaning methodsexist. The common ones are hydraulic-pressure and power flushing, pigging,

CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005 37

ActivityWeek

Precommissioning Schedule

%1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Target progress Actual progress Duration of activity % = Percent of precommissioning completion

Functional testsInerting

Mechanical cleaning and inspection of equipment

Loading of chemicalsLoading of catalystTightness test of process systems

Hydraulic flushing of process linesRun in of rotating equipment

Pickling or chemical cleaning operations

Blowing of plant air linesBlowing of instrument air lines

Test run of compressorDrying out of fired heaters and reactors

Power flushing of process lines

Blowing of nitrogen linesFlushing of plant water linesFlushing of DM water linesBlowing of steam lines

Final box-up of equipment

90

100

70

80

50

60

Mobilization and preparatory work

10

20

30

40

FIGURE 1. Proper planning is essential to make sure the different tasks are performed at thecorrect time. A schedule, such as the one shown here, should be drawn up in advance

36-42 CE 1-05 12/29/04 2:43 PM Page 37

Page 3: Plant Start Up

38 CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005

air blowing or blasting, steam blow-ing, oil flushing, acid cleaning, alka-line boiling and manual (mechanical)cleaning. One, or a combination, ofthese methods is applied, dependingupon how critical the process is, andother site requirements.Mechanical cleaning: Initially,equipment that is very dirty may needa round of mechanical cleaning with awire brush or cloth to ensure that it isfree from weld spatters, constructiondebris, welding rods and so on.Water flushing and air blowing:After the initial round of mechanicalcleaning, piping and equipment shouldbe subjected to flushing or blowing op-erations, similar to those outlinedabove for the utility systems. Thesemethods utilize the kinetic energy of afluid to dislodge foreign materials,such as sand, rust and weld slag. Ingeneral, water flushing may be appliedat the intake of pumps (usually con-nected to columns and vessels) as wellas the discharge piping, which can beflushed with the pump in operation. Itcan also be applied to piping andequipment that can be convenientlycleaned by water flowing under grav-ity, using a water or fire hose. Airblowing can be used where the pres-ence of water is not permitted. Reac-tors, for example, are items of equip-ment where air blowing should takepreference over water flushing.

For water flushing, any of the fol-lowing methods may be adopted:• By injection of huge volumes of

water (using any temporary device,such as a hose connection andpump), pipes are water-flushed

• By discharge of water filled in thecolumn, drum, or vessel concerned,pipes connected downstream arewater-flushed

• By flushing (with the pump operat-ing with water), pipes connecteddownstream of the pumps arewater-flushed. The pump used forpower flushing is a permanently in-stalled piece of equipment

Air blowing, using air from a utility airsupply or a temporary compressor, canbe carried out in the following ways:• In the air-accumulation method, a

column, drum, or vessel associatedwith the pipe is filled with com-pressed air. Then, the pipe at the

downstream end is blown out byopening the valve. This procedure iscommonly used for instrument-air,plant-air, nitrogen, fuel-gas, hydro-carbon, and cold-service lines

• In the direct-blowing method, thepipe to be air-blown is connected tothe air supply source using a tempo-rary pipe or hose. The method oftenis applied in chemical lines and in-strument and plant-air lines

• In large-diameter pipes (8 in. ormore), where it is difficult to get suffi-cient velocities for air blowing, the“cardboard-blasting” method is ap-plied. First, one end of the pipe is cov-ered by a thin polymer film. The pres-sure is slowly raised by connecting airthrough a hose or temporary connec-tion. When the film bursts, the shockwave carries the dirt along with it.The blowing or blasting procedure isrepeated until foreign particles are nolonger visible in the discharge. If nec-essary, the thickness of the film canbe gradually increased so that higherpressures can be used.

Chemical cleaning: For process rea-sons, certain units demand furthercleaning beyond just flushing or blow-ing. A good example is a butadiene ex-traction unit. The cleaning operationis usually carried out by circulation ofappropriate solutions (describedbelow) through the piping and equip-ment. Such cleaning is usually sub-contracted to specialists. As anotherexample, suction lines of compressorsneed to be pickled. Pickling of pipes iscarried out to remove piping scale,rust, weld slag, spatter and other for-eign matter, which might, if dis-lodged, damage the compressors.

The cleaning procedure begins witha wash of cold water during which, thesystem is filled with water and circu-lated. This is followed by a degreasingcycle using measured quantities ofcaustic soda and detergent solution.In this cycle, oil, grease and lubricantsthat are insoluble in acid are removed.

An intermediate wash with dem-ineralized (DM) water is then carriedout. Then, citric acid and corrosion in-hibitor are added to the circulatingwater. The temperature is raised to60°C, and the pH is maintained at3–3.5 by adding ammonia, as re-quired. The circulation is continued

and the iron concentration measuredevery half hour. When the iron con-centration stabilizes, the circulation isstopped. The system is then drainedunder a blanket of nitrogen.

When this cycle has been com-pleted, the system is filled with DMwater and circulated. Draining andrefilling is continued until the pH isneutral and the iron concentration isless than 100 ppm.

This is followed by a rinse with 0.2%citric acid at 60°C. After stabilization ofiron concentration, ammonia is addedto the system till the pH is raised to 9.5.Thereafter, sodium nitrite (0.5–1.0%)is added to the circulating solution, andcirculation continued for 4–6 hours.The system is then drained under ablanket of N2 and dried.

Finally, the chemically cleaned sur-face should be visually inspected. Theinternal surfaces of pipes and equip-ment should be uniform and free of de-posits. If a steel-gray magnetite coatingis observed on the surface, the chemicalcleaning is deemed to be complete. Thecleaned system should then be pressur-ized with N2 and maintained under N2until startup.

During chemical cleaning or pick-ling, care should be taken to ensurethat all control valves, orifice plates,venturi meters and other instrumen-tation are removed and replaced byspool pieces.

Calibration of tanks and silosLevel indicators must be calibratedagainst the tanks and silos onto whichthey are mounted, in order to deter-mine the relationship between thelevel indication and the actual content.For tanks, a measured quantity ofwater is added stepwise, and the levelreadings recorded at each step. Fromthe recorded values, a calibration curveis prepared. This calibration procedurealso serves the additional function offlushing the vessel with water.

For levels in silos, three differentmeasuring principles can be used:weighing, or capacitive or ultrasonicmeasurement. When one is using ca-pacitive measurement, the chips usedfor calibration must correspond tothose used later in production. If dif-ferent material is used, differences indisplay can be expected later.

Cover Story

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Page 4: Plant Start Up

Inspection and boxupProcess licensors normally like tocarry out a check of the column inter-nals, vessels, and heat exchangers be-fore final boxup since these internalsare directly linked to their processguarantees. The best time to involvethe licensor is immediately after theplant inspection has been carried outby precommissioning personnel, andcleaning of lines and equipment is inprogress. The EPC contractor shouldeffectively coordinate with the ownerto have licensor’s personnel at the siteon time, since several activities arelinked to each other at this stage.After each piece of equipment is me-chanically cleaned, the licensor’s per-sonnel are invited to carry out a checkof the internals to ensure compliancewith specifications. Any errors can berectified at this stage. Thereafter, theequipment are boxed up and flushingor blowing continued.

Run-in of rotating equipmentBefore motors are coupled to their re-spective drives, they are usually runfor three to four hours under the su-pervision of an electrical specialist tocheck and verify the machines forsmooth operation. The followingchecks are carried out during mechan-ical run-in:• Rotational direction• Bearing temperature• Vibration• Other necessary gage readingsPrior to a unit startup, all centrifugalpumps should be thoroughly checkedand, if possible, properly run-in. Testruns of agitators are also carried out at

this stage. Often, pumps are used forwater flushing of the discharge linesafter flushing of the suction line. Dur-ing that flushing procedure, the pumpruns for several minutes, which isoften sufficient to serve as the test ofthe pump. However, one must beaware that many high-head pumps arenot designed to pump water. To do socan result in damage to the pump orthe motor, or both. Vendor’s specifica-tions should be checked before at-tempting to run-in pumps with water.

Calibration is carried out for meter-ing pumps. At various pump speeds,the pumping rates are measured bythe amount of liquid collected in ameasuring vessel in a given time,using a stop watch. Calibration curvesare generated for pumping rateagainst the pumping speed.

In plants where handling of solidmaterials is involved, the conveyingequipment, such as belt conveyors,should be given trial runs. If possible,these runs should be made with mate-rial, to detect bottlenecks in chutes orother critical points. This work shouldbe started early to avoid unnecessarydelays in plant startup.

Other material handling equip-ment, such as vibrating screens, isalso tested at this stage. The usualmethod begins with starting up thescreen, following the manufacturer’sinstructions. While the material ispoured, the product distribution andvibrating behavior are observed, typi-cally over eight hours of operation.Checks are performed to determinewhether the product has flowed, viathe screen, evenly in the proper direc-

tion and that the product conforms tospecifications.

Process systems dryingEquipment and piping of the plantmay still hold residual water fromhydro testing, or moisture if blowingwas carried out with air that was notdry. In either case, the moisture needsto be removed, especially from systemswhere its presence could cause prob-lems during normal operation. Typicalexamples include refrigeration sys-tems, and carbon steel pipes that han-dle dry chlorine; beyond a certain hu-midity, Cl2 is aggressive to carbonsteel, and corrosion becomes rapid.

The plant should be divided into sec-tions and dried sectionwise using in-strument air or N2. Dead corners andline ends should be dried with particu-lar care. In cases where a fired heater ispart of the loop, the drying out becomesvery effective if a mild firing is main-tained so that the hot air is available.

Furnace dryingFurnaces need to be dried in order to re-move water or moisture trapped insidethe refractories. This excess moisturecan be slowly expelled from the insulat-ing concrete or refractory by graduallyraising its temperature before any ap-preciable load is put on the heater. Thiswork must be done with extreme care tobe assured of a long heater life withminimum maintenance.

Before commissioning the fuel-gaslines, the furnace firebox must bethoroughly purged with steam until asteady plume of steam can be seen ris-ing out of the stack. Thereafter, a gas-

CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005 39

Precommissioningmanager

Project secretary Document controller

Safety engineer

F&G systemvendor

representative

Turbine vendor representative

Insulation vendor representative

Turbine vendorrepresentative

PLC vendorrepresentative

Safety engineer

Lead electrical engineer

Vendorrepresentative

Leadinstrumentation

engineer

Piping erectionvendor

representative

Compressorvendor

representative

DCS vendorrepresentative

Lead pipingengineer

Lead machineries engineer

Precommissioningfield supervisor

(process)

Precommissioningfield supervisor

(technical)

Field supervisor (functional checks)

Field supervisor (package units)

Field supervisor(heater drying)

Field supervisor(catalyt and

chemical loading)

Field supervisor(pickling andpassivation)

Field supervisor(package units)

Leadprecommissioningengineer (unit 01)

Leadprecommissioningengineer (unit 02)

Leadprecommissioningengineer (unit 03)

Precommissioning Organization

FIGURE 2. The precommissioning team is made up of engineers fromthe different areas, including instrumentation, electrical, mechanical andpiping, as well as representatives from the equipment vendors

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Page 5: Plant Start Up

free test is carried out before lightingthe pilot burners.

After the pilot burners are lit, thearch temperature is raised to 120°C atthe rate of 25°C per hour by lighting afew main burners. The temperature isheld at 120°C for about 24 hours. Thetemperature is next increased to200°C at the rate of 25°C per hour andheld for about 12 hours. At this tem-perature, steam, air or N2 is circu-lated through all process tubes inorder to prevent overheating. There-after, the temperature is increased to400°C and held for 24 hours. Finally,the temperature is increased to 500°Cand held for 12 hours.

During the dry-out period, the oper-ation of the burners is rotated fre-quently in order to distribute the heatevenly. Further, during the final dry-out period, it is advisable to try out allinstruments and controllers on auto-matic control and see that all alarms,warnings, and other safety featuresare functioning properly.

At the end of the dry-out period,the temperature is reduced at a rateof 50°C per hour. Flow through thetubes is also reduced. At tempera-tures of about 200°C, the firing maybe cut off and the fuel-gas lines areblinded. When the firebox is cool

enough, the refractory is inspectedfor any signs of failure.

Loading of catalysts Some process licensors prefer to bepresent to supervise the loading of thecatalyst. Generally two types of cata-lyst loading are followed, namely, low-density and high-density.Low-density catalyst loading: Astationary hopper fitted with a slidevalve is mounted on top of the reac-tor manhole. Fitted to the hopper isa canvas sleeve that extends down tothe reactor bottom. A mobile hopperthat can contain three or four drumsof the catalyst is kept at groundlevel and is lifted by a crane to thetop of the stationary hopper and itscontents emptied. First, inert ballsare added to the bottom of the reac-tor through a canvas sleeve. There-after, the catalyst is introduced intothe reactor. For large reactors, aperson is stationed inside the reac-tor who ensures that the correct lev-els are maintained and that the lev-els of the bed are uniform. As thecatalyst height builds up inside thereactor, the length of the canvassleeve is progressively reduced bychopping off the extra portion. Oncethe lower bed is complete, distribu-

tors and other internals are in-stalled and the procedure is re-peated for successive beds.High-density loading: The loadingmethod described above is the techniquemost industries follow. However, cata-lysts can be loaded using a high-densityloading technique, which enables oper-ators to load, in a given volume, a higherquantity of catalyst. A transportable kitis used, which consists of a rotating dis-tributor that is introduced into the reac-tor from the top flange. The function ofthe distributor is to sprinkle catalystevenly over the bed, allowing it to be dis-tributed uniformly on the surface. Thismore uniform distribution reduces therisk of channeling.

Technical audit, plant handoverThe concept of a technical audit hasbecome popular nowadays when largeprojects are handled on the basis oflump-sum-turnkey contracts. Beforehanding over a plant to the owner, thecontractor is required to offer varioussections of the plant (normally in theorder of their completion) to the ownerfor an audit. In the course of this audit,the owner’s personnel carry out a thor-ough check of the unit before takingover. The check is mainly carried outwith respect to the P&IDs. In addition,

40 CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005

TABLE. CHECK LIST FOR PLANT INSPECTIONPersonnel Safety Vessels/Heat Exchangers Columns/Reactors

1.0 Medical checkup of all site General cleanliness General cleanlinesspersonnel prior to commencement of work

2.0 Copies of accident prevention Internal baffles: type, Column trays levelregulations are available orientation, levelness

3.0 First aid kits are available Dip pipes correctly installed All internals proper fit

4.0 Emergency telephone numbers for accidents, Vortex breakers as Trays liquid tightfire, etc. are displayed at important places per specifications

5.0 Fire extinguishers available Demisters correctly installed Type and height of packings correct

6.0 Necessary safety clothing used Location and orientation of All boltings and clips tightby all personnel at site instrument nozzles verified

7.0 All necessary safety equipment available Insides of tubes inspected to Catalyst bed correct heightcheck possible fouling

8.0 Guidelines for handling of dangerous Motor switches located near Feed pipe or distributor materials are available exchangers for air coolers direction/orientation correct

9.0 Procedure for issue of work permits Proper motor rotation Type and size of agreed with owner vortex breakers correct

10.0 Make spark-free tools available at site Tube fin surfaces in good condi- Distributor trays tion with no construction debris leak tested

11.0 Gas and fire alarm systems For water-cooled exchangers, checked Support plates securely functioning properly for location of thermal-relief valve, vent fastened

and drain inside the outlet block valve12.0 Area demarcated for precommissioning Instrumentation easily accessible Valve caps and other contact

and commissioning cordoned off from grade devices move freely13.0 Safety and eye wash showers Drains connected to safe location Instrumentation easily

functioning properly accessible from grade14.0 All gratings firmly anchored Relief valves bench tested and Drains connected to

correctly installed safe location15.0 All construction debris removed from site Insulation provided as specified Relief valves bench tested and

installed correctly

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Page 6: Plant Start Up

they also check compliance with allrelevant specifications with respect topiping, instrumentation, electrical,and structural requirements. Follow-ing an audit, the owner generates a listof whatever defects, or areas of non-compliance with respect to specifica-tions, were discovered during theaudit. At this stage, defects (if any) arenormally minor. For example, under-sized studs or bolts may have beenused occasionally in some equipment,or the painting may not be correct, or acheck valve may have been mounted inthe reverse direction. The contractorshould rectify any errors, after which,the owner performs a final check. Oncethe owner is satisfied, the audit is con-sidered complete.

Tightness testMany process units handle com-bustibles or toxic substances (or both),the leakage of which could result indisaster, damage, or economic loss. Toprevent the occurrence of such inci-dents, it is necessary to confirm thatthe plant complies with the requiredtightness before startup. Tightnesstest can be carried out by one of thefollowing methods:Air or nitrogen bubble test: In thismethod, the system is isolated and

pressurized with air or N2 to the testpressure, typically the operating pres-sure of the component. Possible leaksthrough flanges, screw connections andvalves are checked with a soap solu-tion. Any leaking connections, whichshow up as tiny bubbles, are retight-ened until the foam disappears. Nor-mally, such test results are deemed ac-ceptable when the leakage rates fallbelow the agreed specified value.Service test: Such tests are performedfor all N2, water, compressed air, andsteam piping and equipment with nor-mal operating fluids. The system is firstpressurized with operating fluids andthen checked for leakage. For air andN2 lines, leaks can be found using soapsolution. For water and condensatelines, the leakage can be observed visu-ally. Leakage points found during thetest are retightened. The test is deemedsuccessful if no foam is observed fromsoap solution, or if no water or conden-sate is observed visually.Vacuum hold test: All vacuum sys-tems must be leak tested. Air inside thesystem is first evacuated to attain therequired vacuum. Then, the valve tothe vacuum pump is closed and the sys-tem’s pressure is monitored to deter-mine the leak rate (in millimeters ofmercury per hour). If the vacuum loss

falls below the agreed specified value,the test is normally deemed accepted.

Tightness testing is usually per-formed on one section of the unit at atime rather than the whole plant atonce. Otherwise it is difficult to pin-point the source of a leak.

During the leak check, it is impor-tant that personnel be organized andready to document any leaks found.The best way is to start at one end ofthe section and work through to theother end, checking flanges, valves, fit-tings, instruments, and other equip-ment. Each leak is tagged, making iteasy for the maintenance team andpersonnel of the next shift to continuewith the work. The maintenance crewshould work together with the leak-check team as far as possible.

It is preferable to do the leak checkshortly before startup. This minimizesthe chances of new leaks developing.for example, after additional mainte-nance has been performed.

InertingThis is an activity that is especially re-quired when hazardous process materi-als, such as hydrocarbons, are involved,to prevent the formation of explosivemixtures. Once a system is mechani-cally complete and all preliminary

CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005 41

Piping Machinery Electrical/InstrumentationCorrect gasket types installed NPSH requirements met Control system configuration correct

Insulation provided as Discharge-pressure guage readable Instruments correctly locatedspecified from discharge-block valveSteam/electrical tracing Suction strainer easily removable Flow instruments and control provided as specified for cleaning control valves correctly installed Check valves installed in Minimum flow bypass provided Measuring ranges and correct flow direction if required scales correctSlopes provided as per Check valves installed in correct Temperature sensors have requirements direction correct lengthRequirement of no pockets Venting and draining the pump Orifice plates have correct bore diam-adhered to as specified casing adequate eter and installed in correct directionInsulation provided as per All drains and vents routed to Interlock sysyems checkedspecification safe locationField instruments visible Pulsation dampeners provided Emergency shutdown systems checkedfrom grade for reciprocating pumpsValves to be operated Relief valves provided for Functional checks accessible from grade reciprocating pumps carried outPressure relief valves bench Warm-up lines provided across discharge Analysers calibratedteated and correctly mounted check valve when pumping hot liquidsVents and drains Suction/discharge valves and auxilliary piping Emergency and redundant properly located and controls easily accessible and operable power supplies checked

Insulation provided Pumps and drivers correctly aligned Insulation, screening, wherever required earthing of power lines checkedPiping requirement for special Cooling water to mechanical seal (centrifugal Switching devices, motor controls,procedures correctly done pumps) provided with sight flow indicators setting of protection relays checkedSpectacle blinds installed Reciprocating pumps Direction of rotation of in the correct position calibrated all electrical drives checkedLocked open/closed valves Alignment properly performed Lightening protection and locked in proper position grounding systems checked

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Page 7: Plant Start Up

checks have been carried out, purgingis done to remove air (oxygen) from thesystem before the introduction ofprocess materials. The following meth-ods are normally used for inerting:Evacuation and N2 filling: In thismethod, air from the system is firstevacuated by means of a steam ejectorand then N2 is introduced up toslightly positive pressure. This evacu-ation-filling cycle is repeated until thesystem’s O2 content in the system isreduced to acceptable limits.

A simple way to assess this is toplace the O2 monitor inside a clearplastic bag, and attach the bag toone of the vents in the system. Asmall hole at the end of the bag(which acts like a bellows) lets thepurge gas flow through while the O2concentration within is monitored.Steam out: In this method, steam isintroduced into the system, with thevent-valves opened, to displace theair. Steam out is continued for four to

six hours, depending on the systemvolume. After this, the steam flow isreduced, the inlet and outlet valvesare closed, and N2 is introduced intothe system until the desired pressureis reached. Periodically, any conden-sate that accumulates is drained.Pressurization and depressuriza-tion: In this method, N2 is introducedinto the system up to a pressure of 1 to2 barg. The system is allowed to standfor about 30 minutes to allow thegases to homogenize. Then the systemis vented (rapidly depressurized)down to a pressure of 0.1–0.2 barg.The cycle is repeated until the O2 con-tent meets the specifications.Nitrogen sweeping: In this method,N2 is continuously introduced from oneend of the system or equipment and itdisplaces the air as it sweeps throughthe system to the other end. The ventgas is composed of a N2-air mixturewith gradually decreasing O2 content.The process is stopped when O2 con-

centration in the system meets thespecifications. This method consumes alarge volume of N2, so it should be usedas the last option, especially when theN2 availability is limited.

Commitment & communicationAside from the technical issues just dis-cussed, the successful completion andtimely handover of a plant to its ownerdepends upon the following factors:• Proper selection of team personnel

based on qualification and experience• Preparing written procedures be-

fore commencing any precommis-sioning activity

• Proper emphasis on personnelsafety, to minimize accidents andmaintain a high team morale

• Proper overlap between the con-struction and the precommissioningteam to avoid repetition of work

• Active interest of members of themanagement, without overridingthe responsibilities of the lead engi-neers, and providing advisory helpwherever necessary

• Holding regular meetings betweenthe EPC contractor’s and theowner’s personnel regarding the ac-tivities planned on a day-to-daybasis. This ensures a smooth func-tioning and unhindered progress

• Effective coordination with licensorpersonnel, since activities may getdelayed if they are not at the site atthe right time

• Finally, maintaining a good relationwith owner’s personnel, to fostergood cooperation and a healthyteam spirit ■

Edited by Gerald Ondrey

Cover Story

42 CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2005

AuthorSiddhartha Mukherjee is asenior process manager atLurgi India Company Ltd. (A-30 Mohan Cooperative Indus-trial Estate, Mathura Road,New Delhi 110 044, India.Phone: +91-11-2695-0035;Fax: +91-11-2695-0042; Email: [email protected]). For the past five years,he has been involved as a leadengineer in the design, pre-

commissioning and commissioning of chemicaland petrochemical plants in India and elsewhere.He has also been involved in inorganic and oleo-chemistry while at Lurgi. Prior to this, Mukher-jee worked as an environmental engineer withthe Development Consultants Ltd. (Calcutta),doing various environmental assessment projectsinvolving thermal power plants. Mukherjeeearned his B.Tech. and Ph.D. chemical engineer-ing degrees from the Indian Institute of Technol-ogy, Kharagpur. He holds lifetime membershipsin India’s Institution of Engineers and the IndianInstitute of Chemical Engineers.

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References1. Mosberger, E., others, “Ullmann’s Encyclo-

pedia of Industrial Chemistry, Volume B4,”VCH Publishers, Weinheim, Germany, 1992.

2. Bush, K., Gilmar, D., Andre, P., and Ademir,D. Z., Hydrocarbon Proc., June 2000.

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