Loading of in AmmoniaPlants

Improved techniques for loading catalysts make it possible to obtain higher densityand thus more uniform loading of some catalysts in ammonia plants. Reduced time for

loading operations and better safety are additional benefits obtained.

E. Dessen and G. RyntveitNorsk Hydro a.s., N-0240 Oslo, Norway

Y. HaquetPetroval S.A., 76430 Saint-Romain de Colbosc, France

INTRODUCTION

Different methods are normally used when loading thefollowing catalysts types:

- Primary reforming- Other front end catalysts- Ammonia synthesis

The basic principles however, are the same for alltypes of catalyst loading. According to D.R.Goodman (1) the principles are:

- Limited free fall, 0.5-1 m- Even distribution during filling (no heaps and

raking)

In practice the catalyst is charged through tubes in theform of socks or canvas hoses, which are often keptfull of catalyst and moved over the bed. Periodicallythe tubes are shortened.The problem with this technique is bridge formation,especially when the inner diameter of the catalyst tubeis 10 times the particle diameter or less. Bridges mayform when many particles reach the loading surfacesimultanously as described by P.M. Nooy (2). They

will then be locked in less favourable rest positions andform bridges or oversize voids. This is confirmed byexperimental work summarized by D.J. Humberlandand C.S. Crawford (3). Increasing the number ofparticles falling per unit time per unit area above acertain value, causes the packing density to decrease.The packing density increases with the height of dropat low heights but levels out after a certain height isreached.

The importance of high density loading of ammoniasynthesis converters has been confirmed recently byG. Gramatica and N. Pernicone (4) by a theoreticalstudy of the effect of gas maldistribution on theconversion in a radial bed converter.

Vibration may improve the packing density by forcingbridges to collapse, but will generally not solve theproblem completely. This is often the case whenloading ammonia synthesis catalyst since the sharp,heavy, irregular shaped particles do not easily moverelative to each other. A disadvantage with vibrationis break-up of particles.

18

The ideal loading is where each particle is placed in astable, rest position which minimizes the loaded

volume and maintains an acceptable void volume forgas transport.

In practice this is approached by a slow (low ofcatalyst particles over the loading area. To obtain thisthe particles must be allowed to fall in some cases evenfrom the top to the bottom of the catalyst bed.

We have defined this loading as dense loading. Thehigher density obtained increases the catalyst bedpressure drop. The higher free fall also increases thecatalyst particle break-up. However, the disadvantageof these two factors are normally small compared tothe benefits.

In addition to improved performance caused by denseloading, two other benefits are also very important.Dense loading techniques allow higher loading rateswhich reduce the loading time. More important is thesafety aspect since the need for operators inside theconverters during loading is drastically reduced.

In the following sections, the dense loading of the threedifferent catalyst types mentioned above, will bedescribed. The two methods described are NorskHydro method for loading primary reforming catalystand Petroval's Densicat method for loading the othercatalysts.

NORSK HYDRO METHOD FOR LOADINGPRIMARY REFORMER CATALYST

Primary reforming

The primary reformer is one of the most complex andexpensive items in modern ammonia, methanol andhydrogen plants. Reformer tubes are subjected to hightemperatures and pressures, and they are veryexpensive. The quality of the reformer catalystloading will influence on tube wall temperatures andconsequently the life of the tubes as discussed byWJ. Salot (5).

The loading of the primary reformer is normallycarried out by using prefilled plastic or canvas socks.Another method is loading in water. Careful drying ofthe catalyst after the loading is then required.

Sock loading of primary reformer tubes

The sock loading method for primary reformer catalystis explained in detail by D.R. Goodman (1).

Several factors will affect the quality of the loading:

- The ratio particle diameter to tube diameter isimportant. In order to ensure effective packing, J.R.Rostrup-Nielsen (6) has pointed out that themaximum particle size should be less than about 1/5of the tube diameter.

- The particle shape will also influence the packing.According to B.J. Cromarty (7), external surfacewith rectangular edges or ridges may cause "locking"or bridging leading to oversize voids compared to thepacking obtained with particles having smoothsurfaces.

- Vibration by hammering the reformer tube or bymechanical vibrators will normally improve thepacking.

- The quality of the loading depends to a great extenton the operators. We have seen that the fold of thesock has opened too early allowing the catalyst to fallmany meters, the sock has been lost in the tube, etc.The vibration of the tubes varies also from oneoperator to the other.

The quality of the loading is reflected in variation ofthe pressure drop of the reformer tubes. We haveexperienced that more than 20 % of the tubes inreformers have pressure drop outside the interval of ±5 % around the average.

According to B.J. Cromarty (7) a variation in pressuredrop of ± 5 % will result in a variation in tube walltemperature of about 5 °C . He points out thatuniformity of packing between tubes and within eachindividual tube is important. The latter will ensureuniform gas flow and prevent local overheating in eachtube. He expects a variation in pressure drop of 2 - 3% between tubes can be achieved by reasonable careand a systematic approach.

19

Norsk Hydro method

This method meets the expectations stated by B.J.Cromarty (7). The principle of the method is a slowcontinuously controlled loading so that the particlescome to rest in stable positions not influenced by otherparticles loaded at the same time. To avoid thepossibility of the catalyst particles breaking into piecesa rope with a set of brushes is used to reduce the speedof the particles when poured into the tube. Thebrushes are made with flexible springs and the catalystrings are allowed to trickle down from the top to thecatalyst surface by jerking the rope. By using a funnelfor pouring in the catalyst and pulling the rope out ofthe tube as the catalyst layer builds up, the tube isgradually filled. A filling of the tube without oversizevoids and bridges is obtained without any vibration ofthe tubes.

Fig. 1 shows how the method works. A patent ispending. The technique was originally tested out ontubes with 100 mm inner diameter and 17x17x6 mmcatalyst rings (ICI 46-1). By selecting various typesof brushes the technique may be used to load tubeswith internal diameter ranging from 75 to 150 mm.

Fig. 1: Principle of the Norsk Hydro method

Comparison between sock loading and NorskHydro method.

The sock and Norsk Hydro methods were compared byusing a 4 m plexiglas tube. As can be seen from Table

1 the density obtained with the Norsk Hydro method ishigher and has a much smaller range than the sockmethod.

Table 1Loading tests in a 4 m plexiglas tube. Tube i.d.

100 mm using smooth rings.17 x 17 x 6 mm (ICI 46-1). 10 tests were performed

Loading

Density avg. kg/IRange kg/I

Sock method

1.0080.981 - 1.045

Norsk Hydromethod

1.1121.109-1.115

Fig. 2 shows the packing of different catalyst sizes andshapes (G-90B from Süd-Chemie and 890 from Dycat)by using the two methods in the same tube. It isclearly seen that the Norsk Hydro method eliminatesthe tendency to bridging and gives a good packingindependent of catalyst shape and size.

Comparison of the methods has also been made in a 12m long steel tube with 100mm inner diameter. Thecatalyst size was 17x17x6 mm rings with smoothexternal surface (ICI 46-1). When using sock methodthe tube was vibrated after loading of every third sock(7.5 kg in each sock) by one blow and two blows afterthe last sock with a brass hammer. When using NorskHydro method the tube was not vibrated. The tubewas topped up to the same level: 30 cm outage and theloading times were recorded. The loaded density wascalculated and the pressure drop was measured withthe same equipment as used during normal loading.The results of the tests are given in Table 2.

Table 2Loading test in a 12 m steel tube.

Two tests were made for each method.

Density, kg/1Pressure drop, barLoading time (min)Void fraction (calc.)

Sock method

Test 1

1.0150.81

150.544

Test 2

1.0480.9114.5

0.519

Norsk Hydromethod

Test 1

1.1111.0210

0.490

Test 2

1.1121.039.5

0.49

20

Fig. 2: Comparison between sock loading and Norsk Hydro method for different sizes and shapes ofcatalyst particles.

Sock LoadingMethod

Norsk HydroMethod

21

The table shows that an increase in density of about 8% is obtained when using the Norsk Hydro method. Inaddition the reproducibility of the method is better thanthe sock method. The void fraction, e, is calculated onthe basis of an apparent particle density of 2.18 kg/1.The observed pressure drops are nearly proportional tothe factor (1 - e)/£^ commonly used in formulas forfluid flow resistance through packed beds.

The attrition during loading was the same with bothmethods. By filling 10 kg samples of catalyst from thetop to the bottom of 12 m high tubes, we have notobserved breakage of rings. After screening thesamples on a 10 mm screen, about 0.1 % fines anddust was found. However, a major part of the dustwas formed during the unloading of the samples. Afterloading the full length of the tube, with dumping of thecatalyst through the bottom, comparable amounts offines and broken rings are found with the two methods.

The time required to load a tube with the Norsk Hydromethod was 2/3 of the sock loading time.Consequently, the time needed to load a full charge inthe primary reformer can be reduced accordingly.

Plant experience with the Norsk Hydro method

The Tringen II plant at Hydro Agri Trinidad replacedthe primary reformer catalyst in January -92. Theplant is a Braun design with Foster Wheeler reformerwith 1500 STPD design capacity. The previouscharge of catalyst was Dycat 873 (5/8x3/8x1/4) flutedrings and the new charge Dycat 890 with the sameshape and size.

Reformer data:No of tubesInternal tube diameter, mmFill length, m

124, (2X62 tubes)152.410.74

Prior to the unloading of the old catalyst charge theoutage in all tubes were measured and the settling wasfound to vary between 0.33 and 1.22 m. This meansthat the vibration of the tubes (two blows after eachsock) did not remove the oversize voids formed duringthe sock loading. Only start-up and operation havecaused the catalyst settling, probably due to expansionand contraction of the tubes as suggested byB.J. Cromarty (7).

The catalyst was charged in 11 kg plastic socks(prepared for normal sock loading). The loading timeper tube (about 220 kg) was in the range of 18 to 25min. Since this was the first time the method had beenused in a plant, the loading rope became stuck on threeoccasions. This required dumping of the catalyst andsubsequent reloading. All tubes were loaded withoutvibration.

After topping up to design outage the pressure dropwas found to be within ± 5 % of the mean value. Fourtubes were vibrated by 8 blows with a 9 kg hammer onthe top flange and topped up again (abt. 0. l m settling)in order to increase the pressure drop. Two tubes weredumped and reloaded due to high pressure drop. Afterthese adjustments the pressure drop was within ±2.6% of the mean value. The loading and pressure droptesting was completed within three shifts of 12 hours.Table 3 shows the details on the loading in 1989 withthe sock method and in 1992 with the Norsk Hydromethod.

Table 3Loading of Hydro Agri Trinidad Til primary reformer

Loadingmethod

CatalystSize (inch)Vibration

Density, kg/IÄPMeasurement

Sock method-89

Dycat 873 fluted5/8 x 3/8 x 1/4After each sock

and for APadjustment

1.041±5 % of mean

Hydro method-92

Dycat 890 fluted5/8x3/8x1/4

ForAPadjustment onfour tubes only

1.137±2.6% of mean

Compared with the loading in -89 the Norsk Hydromethod had several advantages. The loading wasfaster, higher density was obtained and the pressuredrop variation over the tubes was reduced by about50%.

As can be seen from table 4 the Norsk Hydro loadingmethod has given improved operating conditions.Since start up the reformer operation has been limitedby the firing only, with outlet and tube walltemperatures lower than when sock loading was usedand the pressure drop has been low.

22

Table 4Operating data for

catalyst loaded by the sock and Norsk Hydro method

Time since SOR (months)Load, % of designS/C RatioTinlp.t °CTmitlet °COutlet CH4 (mol %)Pressure Drop, barTWT (avg) East/West, °C

21152.8361968328.93.3

Sock loaded

41102.8461268528.03.0

141142.89613692334.4

834/843

Norsk Hydro loaded

1.51142.8261367128.63.0

41142.8261367128.63.0

760/754

The reformer pressure drop for the present loadingafter 1.5 and 4 months is lower than for the previouscharge at 2 and 14 months and similar load. Thereason for this is most probably carbon deposits fromheavy slugs in the previous loading. The presentpressure drop compares well with the design pressuredrop of 2.4 bar at 100 % load. The lower outlet andtube wall temperatures for the present operationindicates improved performance of the reformer.

DENSICAT LOADING METHOD

Introduction

The general principle of Densicat method has beendeveloped and patented by Total and is nowexclusively marketed by Petroval S.A., France. UntilNorsk Hydro started to utilize the method in loadingone of its ammonia converters in 1989, the method hadmainly been used in refineries. The bulk densityimprovement has been up to 20 % compared toconventional loading methods when loading some ofthe catalysts used in this industry. According toP.M. Nooy (2) the capacity of hydro treating units canbe increased up to 25 % by using dense loadingtechniques.More than 9000 tons of catalyst have been loaded in1991 with Densicat.

Working principle

The apparatus consists of a cylindrical catalyst feederand a rotating particle distributor driven by acompressed air motor as shown in fig 3.

Catjlyst

DtNSUCAT equipment

Strips in rotation

Strips at rest

Catalyst

Inert packing

Figure 3: Densicat Principle

The cylindrical feeder is placed on the converter top orinside the converter in a fixed position. Catalyst is fedto this feeder from a hopper through a hose.

The rotating distributor consist of a number of stripholders in different levels equipped with rubber stripsattached to them. The rotating speed can be variedbetween 30 and 120 r.p.m.

The catalyst will be distributed over the convertercross section in the way indicated in fig. 4.

23

F3 F2

Figure 4: Densicat Flow Distribution

Flow Fl comes from side slits in the feeder, flow F2comes from an opening located at the bottom of thefeeder. Both Fl and F2 are distributed by the strips.Flow F3 comes through openings in the strip holdersbut is distributed by smaller strips. In this way theflows cover the different cross-sections as indicated inthe figure. The catalyst will "rain" over the total crosssection of the converter such that the catalyst bedsurface will remain nearly horizontal. To obtain thisfor different catalyst types and different converters andto minimize the attrition of the catalyst particles thefollowing adjustments are made:

- Shape, size and number of rubber strips.- Strip holder positions and openings.- Rotational speed.

In this way a very homogeneous and dense distributionis obtained. The Densicat equipment is fullymechanized.

The diameter and height of the Densicat machine areonly 0.27 and 0.40 m . This makes it possible to applythe equipment in various converter configurations(radial, axial, multi-bed etc.). The converter diameterscan vary in the range 0.4 to 7.5 m.

DENSICAT LOADING OF FRONT ENDCATALYSTS

The Densicat loading technique has been utilized toload the following front end catalysts:

Plant

Catalysts

Hydro AgriPorsgrunn Nil (4/91)

Secondary reformerHigh temp, shift(bedl)Low temp, shift(guard)

Hydro AgriTrinidad Til(1/92)

Zinc OxideHigh temp, shift

Low temp, shift

Loading of the Hydro Agri Porsgrunn Nil plantcatalysts

The plant is based on steam reforming designed byHumphreys & Glasgow Ltd. and has max. capacity of1250 MTPD.

Table 5 shows a summary of the loading made in theHydro Agri Porsgrunn Nil plant.

Prior to the secondary reformer loading a drop test wasmade. Catalyst attrition formed 0.16 % of dust andpieces less than 10 mm when dropped from a height of4.5 m, similar to the conditions during the loading.

A bottom layer of catalyst, 10 cm, was loadedmanually before the Densicat machine was installed inthe conical part inside the vessel. By using the denseloading of the secondary reformer 33 cm of extraspace was gained between the burner and the catalyst,which will improve the gas mixing and theperformance.

When loading the high temperature shift, theequipment was installed l m below the manhole. The

24

loading time was considerably prolonged due to slowsupply of catalyst. The 2. bed could not be loadedwith the Densicat equipment due to the vessel design.

The guard bed in the low temperature shift section is aradial reactor with 2400 mm inner diameter, centrepipe of 700 mm and loaded height of 6330 mm. Theloading equipment was installed inside the vessel ontop of the centre pipe.

Table 5Loading summary in the Hydro Agri Porsgrunn Nil

plant

Catalyst type

Size mmVesseldiameter, mAmount,1000kgLoadeddensity, kg/1

Sec.reformer

ICI 54-4

17x17x6

3.56

25.2[28.2]1.110

[0.994]

HTS

G-3 & G-3C

9x6 & 6x6

4.76

45.9[40.6]1.297

[1.060]

LTS guard

C18-HCmini

4.8x2.4

2.4 X 0.7

42.3[34.1]1.640*[1.322]

r l numbeis in brackets refer to previous loading.* density of catalyst as filled in drums was 1.409 kgfl.

Loading of the Hydro Agri Trinidad Tu plantcatalysts

The Densicat machine was placed in the manhole ontop of the converters during loading. A summary isgiven in Table 6.

Table 6Loading summary in the Hydro Agri Trinidad

Til plant:

Catalyst typeSize mm

Amount, 1000 kgVessel diameter,mLoaded density,kg/1

Zincoxide

G-72D4.5

extrusions36.7

3.96

1.46

HTS

G-3C6x6 domed

59.0

5.03

1.21

LTS

LK8214.3x3.2

77.1

5.03

1.22

Experience with the dense loading of front endcatalysts

Assessment of the improved loaded densities obtainedis difficult because the converters had differentcatalysts installed previously. The only way thisassessment could be done would be throughcomparison of void fractions for previous catalystcharges. However, the catalyst suppliers do notpublish relevant data on apparent particle densities. Itis therefore difficult to determine the densityimprovements.

Fig. 5 shows a comparison of pressure dropdevelopment (between the present and the previouscharges) in the Hydro Agri Porsgrunn Nil plant. Anincrease is observed in the low temperature shift guardvessel during the first 200 days. The reason is thatmore catalyst is loaded into the same volume with theDensicat technique. This will prevent further settlingand thus mal-distribution of gas in the upper part ofthe radial bed. The low pressure drops after 200 dayson stream is caused by operation at reduced load.

1.2

10.8

0.6

0.4

0.2

0

10.8

0.6

0.4

0.2

01

0.8

0.6

0.4

0.2

0

Delta P, bar

-x-Sec. réf.previous loading

-e-Sec. réf.Densicat loading

-*• HTS 1st bedprevious loading

-e- HTS 1st BedDensicat loading

4f LTS guardprevious loading

-©•LTS guardDensicat loading

200 300 400

Days on stream

500 600

Figure 5: Densicat loading. Comparison of PressureDrop with previous loading in Hydro AgriPorsgrunn Nil plant

25

The loading rates varied from 5 to 22 t/h depending onthe supply of catalyst to the Densicat equipment. Thehighest rates were obtained when the supply of catalystwas not a limiting factor.

DENSICAT LOADING OF AMMONIASYNTHESIS CATALYST

Preparations

Hydro Agri's ammonia synthesis converter inBrunsbüttel, Germany, was the first to be loaded withthe Densicat method. The plant is based onShell gasification of heavy oil and has a max. capacityof 2000 MTPD. Norsk Hydro prereduced catalystAS-4-F was installed. After new internals, based onaxial/radial flow were installed in 1989 by AmmoniaCasale S.A. the bottom bed was loaded by thismethod. The middle and the upper bed werecompacted by vibration due to concern that the quenchgas distributors could lead to uneven loading whenusing the Densicat method due to a "shadow" effect ofthe distributors.

The Casale recommendation to use the method wasbased on the attrition of the particles after free fallfrom the converter top to the bottom of the bottom bed,compared to the attrition caused by vibration. To dothe comparison, the Densicat equipment was installedon the converter top and the bottom of the third bedwas covered with a tarpaulene. After about 50 kg 1.5-3mm pre-reduced catalyst AS-4-F was loaded, thecatalyst was collected and sieved. The attrition duringvibration was checked in a steel cylinder with a centraltube both having the same dimensions as the bottombed cross section. Template and vibration time werethe same as normally used. The results from both testsshowed that less than 1 per cent dust and brokenparticles less than 1 mm were formed. Based on thisfinding the use of Densicat loading was decided.

Loading experience

Table 7 shows the obtained bulk densities and loadingrates. The results of loading Norsk Hydro unreducedand prereduced catalysts AS-4 and AS-4-F in twoidentical Qatar Fertilizer Co. S. A.Q. Casale-revampedcatalyst baskets are also included. The two plants arebased on steam reforming with max. capacity of 1150MTPD. In contrast to the Brunsbuttel-converter, theseconverters have quench distributors in the top bedonly, since they have a heat exchanger between themiddle and the bottom beds. In spite of this Densicatloading was used when loading all the beds in one ofthe converters without any problems caused by the"shadow" effect of the distributor.

Fig. 6 shows the bulk density changes with the free falldistance from the Densicat machine to the catalystsurface.

DENSICAT LOADINGBulk Density vs. Free Fall Distance

V -*-

8 10 12 14 16 18

FREE FALL (M)

Hydro Agri Brunsbüttel, Bed 3 -*-Qafco A2, Bed 3 -*-Qafco A2, Bed 2

-H-QafcoA1,Bsd3 ^Qafco A1, Bed 2

Fig. 6: Densicat loading. Bulk density vs. free falldistance.

After a repair of the Brunsbüttel converter internals in1991 the catalyst had to be replaced. This time it wasdecided to use vibration instead of dense loading. Thereason was a concern that the dense loading in 1989had caused the problems which forced the plant to doan inspection. It turned out that this was not the case,but time did not permit to arrange Densicat loading.The results are shown in table 7.

26

Table 7Experience with loading of Norsk Hydro Ammonia oxidic and pre-reduced synthesis catalysts AS4 and AS-4-F.

Plant

Hydro AgriBrunsbiittel, Germany

ii

Qatar Fertilizer Co. S.A.Q.Umm Said QatarPlant Al

Plant A2

Year

1989

1991

1990

1991

BedNo.

123

123

123

123

Catalystbed

volumem37.5

10.515.9

7.510.515.9

6.010.921.9

6.010.921.9

Catalysttype

AS-4Fit

ti

tt

i t

tt

AS-4-FAS-4

n

AS-4-Fi t

11

Loadingtechnique

Vibrationit

Densicat

Vibrationn

ii

VibrationDensicat

11

Densicatit

n

Bulkdensity

kg/I

2.182.122.32

2.222.172.27

2.172.902.96

2.292.222.35

Loadingratekg/h

Not meas.it

it

120018001200

15001200020000

150035003000

On the basis of our experience the followingconclusions can be drawn:

Densicat loading has improved the bulk density by2-5 % compared to vibration.

The increase in bulk density will reduce the voidfraction and thus increase the pressure drop throughthe catalyst. However, the effect of the higher bulkdensity mentioned above will not have a noticeableeffect on the pressure drop in a radial converter sincethe pressure drop in the gas distributors at the inlet andoutlet of the catalyst beds are normally much higherthan the pressure drop through the catalyst.

The Densicat loading rate is up to 10 times as fast asthe rate which can be used when vibrating the catalyst.The big variation in loading rates given in table 7 iscaused by variations in supply of catalyst to theDensicat machine.

The bulk density seems to be independent of the freefall distance according to figure 6. However, anapparent increase in bulk density with distance forunreduced catalyst AS-4 lower than 5 m may indicate

that the height of drop influences the packing at lowheights.

Safety aspects

The need for operators to be inside the catalyst basketduring loading is reduced when using dense loadingtechniques.

The steady operation of the Densicat machine reducesthe need for frequent checking of the bulk density.When checking is needed the loaded volume can beassessed by catalyst level measurements from theconverter top. When vibration is used the levelmeasurements are often done by the operators insidethe converter, before and after vibration.

Work inside converters during loading involves riskfactors and the operators have to use safety equipment.This often implies limited freedom for the operators tomove around inside the converter. Heavy hosescontaining catalyst represent a risk also. During oneloading using vibration a hose broke and fell down onthe operator doing the vibration. One of his shoulderswas injured. It took more than one hour to get the

27

wounded operator out. After 12 hours safety checkingthe loading could resume.

SUMMARY OF BENEFITS OF USING THEDENSE LOADING IN AMMONIA PLANTS.

One of the most important benefits of the Norsk Hydroloading method for primary reformer catalyst is thepossibility to obtain dense uniform packing even withparticles which do not have smooth external surface.Without using vibration, tubes having diameters assmall as 7.5 cm can be loaded with acceptabledensities and reproducible pressure drop.

The operating benefit of homogeneous loading ofprimary reforming tubes are improved reactionconditions such as:

- Lower tube wall temperatures.- Less tendency to formation of hot spots.- Closer approach to equilibrium

Important aspects of such improvements are prolongedreformer tube life and the positive effect on economics.

The major operational benefit of dense loading of theother catalysts is better utilization of the reactorvolume. This can be done in two ways:

- Increased weight of active catalyst in the maximumvolume available ( as experienced by increased bulkdensity or reduced void fraction).

- Reduced volume occupied by the catalyst to allowmore volume available for gas mixing anddistribution above the catalyst (utilized in the loadingof the secondary reformer catalyst in the Hydro AgriPorsgrunn Nil plant referred to above).

Generally the flow through densely loaded beds is veryhomogeneous which leads to optimal reactionconditions. The penalty is higher pressure drop fromthe start of run (SOR) due to reduced fraction of voids.However, this pressure drop remains constant whereasthe pressure drop in a normal loaded bed increaseswith time and often increases up to SOR level fordensely loaded beds. This may be caused by slowcompaction and breakage of particles due to expansionand contraction of the catalyst basket during shutdowns and operation. In radial reactors this shrinkage

may lead to flow mal-distribution, and in the worstcase partial bypassing of the upper part of the catalystbed.

On the economic side additional benefits are reductionin loading time and man-power. The latter applesespecially to Densicat loading instead of vibration.

On the safety side it is very important that the need foroperators inside the converters during loading isdrastically reduced. This is a major improvementsince this work needs especially trained personnel andadvanced life support equipment. Shorter time for theloading reduces the operators exposure to catalystdust.

LITERATURE CITED

1. D.R. GoodmanCatalyst Handbook, Sec. ed. by M.V. Twigg,Wolfe Publishing Ltd. 1989

2. P.M. NooyOil and Gas Journal, Nov. 12,1984

3. DJ. Humberland, R.S. CrawfordThe packing of particles. Handbook ofpowder technology.Vol. IV, Elsevier 1989

4. G. Gramatica, N. PerniconeCatalytic Ammonia Synthesis Ed. by J.R.Jennings, Plenum Press 1991

5. W.J. SalotAICHE Ammonia Symposium, San Diego1990.

6. J.R. Rostrup - NielsenCATALYSIS - Science and technology.Ed. by J.R. Anderson and M. Boudart, Vol. 5Springer Verlag 1984

7. B.J. CromartyNitrogen '91, Copenhagen 4-6 June 1991

28

DISCUSSION

T. S. Hariharan, Fertil, Abu Dhabi: If any clientchooses to use this method will you supply it?Ryntveit: Yes.K. W. Wright, M. W. Kellogg: What is themaximum free fall for the catalyst using thismethod?

Dessen: For the ammonia synthesis, it was 15meters and in the shift converters 5 meters.Vic Kearns, International Catalyst: We are aDensicat licensee and have successfully loadedhydrocarbon reactors with a 27 m drop on thecatalyst.

G. Ryntveit E. Dessen

Y. Baquet

29

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