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Performance of catalysts in Ammonia plant- IFFCO Kalol experience

Development of new catalysts have totally revolutionized the chemicalprocessing industries -particularly the ammonia in fertiliser sector.Catalyst plays an important role in ammonia production. A critical factorin ammonia production is its very significant energy consumption. Theperformance of different catalysts is directly effecting the production ofammonia plant. Reliability of ammonia plant is dependent on goodperformance of various catalyst in use and the conditions under whichthey operate. This has become apparent as capacities of existingammonia units have been increased, and more demands has beenimposed on the role of catalyst. Attempts have been made to highlightsthe experience and various measures taken by IFFCO Kalol for catalysthandling and operation as a part of energy conservation over the periodof two decades.

INTRODUCTION :

IFFCO Kalol unit operates 1100 tpd capacity ammonia plant. The original 910 tpd M.W. Kelloggammonia plant was commissioned in the year 1974 and is based on steam reforming of natural gas. InSept.97, 250 tpd naphtha based pre-reformer system is installed as an add-on unit at upstream of primaryreformer. IFFCO Kalol's ammonia and urea plants are being considered as one of the best run plants inIndia even though technology adopted is of seventies. Ammonia production may be broadly divided intofour sections:

• Feed purification - Desulphurisation (Natural Gas Feed) - Hydrogenation and. Sulphur absorption(Naphtha Feed)

• Synthesis gas production - Pre-reformer/Primary Reformer - Secondary Reformer• Synthesis gas purification - Shift Converters - CO2 removal - Methanation

• Ammonia synthesis - Ammonia converter

Each of above section contains catalysts and performance of each plays significant role for the nextsection. With passage of time, catalyst performance in one section is directly responsible for theperformance of next section. A closely monitoring system is essential to evaluate the performance ofcatalyst for each section since from the catalyst loading to end of run condition for each catalyst. Catalystshould have following characteristic :

• Good mechanical strength• High activity• low pressure drop• high tolerance for contaminants• long life time

B.R. Patel BPS MehtaSr. Manager (Pro.) Sr.Process EngineerIFFCO Kalol Unit IFFCO Kalol Unit

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Feed Purification:

Naphtha as Feed to Pre-Reformer:

Feed purification usually involve a hydrogenation step to convert organic sulphur compound to hydrogensulphide and subsequent removal of hydrogen sulphide by chemisorption on zinc catalyst in sulphurabsorber. Sulphur compounds like hydrogen sulphide, COS, RSH, CS2, R2S2, R2S and thiophenes areabsorbed on sulphur absorber catalyst -ZnO . H2S reacts by following reaction :-

ZnO + H2S ------- ZnS + H2OIFFCO Kalol had commissioned the system recently and it is working satisfactorily.

Natural Gas:

In desulphurisation system usually use the activated carbon as catalyst to remove the sulphur compoundfrom natural gas from 2-3 ppm to less than 0.1 ppm.

Reforming Catalyst:

Steam reforming technology is a persistent challenge to the catalyst manufacturers . The dominant factin the trend is energy efficiency. Main demand of catalyst is its operation at lower steam to carbon ratio.

In the pre-reformer, the endothermic reaction is followed by the exothermic methanation and shiftreactions, adjusting the chemical equilibrium between the carbon oxides, methane, hydrogen and water .The performance of Pre-reformer is directly reflected by the temperature rise/drop across the reactordepending on the type of feed. For heavier feed stocks, such as naphtha, the overall process isexothermic, resulting in an overall temperature rise of about 15 to 20 deg C across the pre-reformer. Thespecially precipitated, high-nickel catalyst is in the form of cylindrical pellets, has the high activityrequired for hydrocarbon steam-reforming reactions at low temperature.

For new catalyst, the outlet concentration of higher hydrocarbon should be negligible and constant.Deactivation of the pre-reforming catalyst is caused by impurities/ poison in the feed stream i.e. sulphur,alkali, silica and arsenic etc.

Primary reforming catalyst has under gone significant development since its early application. Thesimple tablets shape was superseded by the rashing rings shape, with an increased surface area for higheractivity and higher voidage for reduced pressure drop. Since reforming reaction is strongly film diffusioncontrolled and most of reaction occurs at the surface of the catalyst. Activity of catalyst can be improvedby increasing the surface area without effecting the strength .

In secondary reformer, nitrogen is introduced with help of air and oxygen in air is combusted with aportion of methane from primary reformer. Active catalyst help in lowering the charged volume ofcatalyst and increasing the volume of mixing zone. Optimum level of methane slip from primaryreformer is required to maintain the air flow in secondary reformer.

Performance of reforming catalysts is periodically evaluated by considering following parameters andoperating conditions are duly adjusted :

Approach to equilibriumMethane slipPressure dropTube skin temperature

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Reformer Catalysts Performance-IFFCO Kalol

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Deactivation of reforming catalysts is caused by impurities in feed stream. Number of poisons reduce theeffectiveness of the reforming catalyst. Sulphur, which is the most common of these poisons, maydeactivate some catalyst by a process of chemisorption onto the active surface.

EVALUATION OF REFORMING CATALYSTS:

Pre-Reformer:

Pre-Reformer catalyst is in operation for last seven months and is working satisfactory.

Primary Reformer:

Figure 1 show the performance of Pri-reforming catalysts at IFFCO Kalol. Dotted lines shows theexisting catalyst charge in operation. Charge No 5 and 6 were not utilised properly due to two longannual plant turn around and due to first Reformer revamp & frequent tube failure before revamp. Theperformance of existing charge of primary reformer catalyst is the highest and it is at end of runcondition. It is evident from above graph that ammonia production per unit volume of catalyst had goneup from 27,145 MT to 80,270 MT in existing catalyst charge.

Secondary Reformer:

For gas based plant, the decision of catalyst charge replacement is generally taken based on pressuredrop across catalyst bed. It is evident from above figure that secondary reformer catalyst performancewas increasing continuously up to charge no 4 from 5377 to 59,013 MT. The last catalyst charge washaving lower performance.

Shift Converter Catalysts

High temperature catalyst (HTS) is used to convert carbon mon-oxides (CO) in reformer effluent gasesto hydrogen and carbon di-oxide (CO2). The catalyst promotes the exothermic reaction as follow :-

CO + H2) ---- CO 2 + H2 h = - 41.1 kJ/mol

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HTS catalyst operates in the temperature range of 370 to 440 deg C and is consists of iron/ chrome.Active magnetite (Fe3O4) crystals in working catalyst are stabilized by the presence of chromia. Undersevere condition magnetite can be reduced to FeO or even metallic iron. Such change of phases and overreduction causes crystallite changes in the catalyst that lead to physical degradation, weakening andfracture of pellets, and increase in pressure drop. Metallic iron promotes side reaction such as FisherTropsh reaction. Such reactions can affect adversely the performance of down stream catalysts.

Low temperature catalyst (LTS) promote the same reaction as the HTS system. The reaction is carriedout at a lower temperature of 190 to 240 deg C to maximize the conversion. Shift reaction kinetics areslow over an iron based catalyst at above temperature and so a more active copper-zinc catalyst is usedin LTS. Cu-Zn are more susceptible to poison present in the reformed gases. The most common poisonsare sulphur and chloride, few hundreds ppb may cause rapid deactivation of the catalyst. Table-I givessome of the common LTS catalyst poisons

Shift Catalyst Performance at IFFCO Kalol

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EVALUATION OF SHIFT CATALYSTS:

HT Shift Converter:

Figure-2 show the performance of shift catalyst at IFFCO Kalol. Performance of existing HTS catalystcharge has achieved the highest ammonia production per unit volumes as compare to others catalystcharges. From trends diagram, there is always improvement in performance of HTS catalysts. Ammoniaproduced per unit volume of catalyst had increased from 6696 MT to 28,403 MT.

LT Shift Converter:

Performance of existing LTS catalyst charge is satisfactory. From trends diagram, there is alwaysimprovement in performance of LTS catalysts. Ammonia produced per unit volume of catalyst hadincreased from 3445MT to 23133 MT. The performance LTS catalyst is directly effected by poisonspresent in feed.

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Table-I : LTS Shift Catalyst Poisons

Poison Possible Effects on sources catalyst

Sulphur Hydrocarbon feed stock Covers the active copper surfaceSteamQuench waterLubricating oilNew HTS catalyst

Air to secondary reformerChloride Hydrocarbon feed stock Promote growth of

Steam copper crystalsQuenchLubricating oilAir to secondary reformer

Silica Steam Physical blocking of theQuench catalyst surface and pores Lubricating oilUpstream catalyst, brikling,catalyst bed support materials etc.

Methanator catalyst

The residual amounts of CO, CO2 at exit of CO2 removal section are removed by methanation reactionover nickel based catalyst. Carbon oxides are poisons to ammonia synthesis catalyst. For majority ofammonia plant, methanation catalyst lasts more than five years, however it life depends on the efficientoperation of up stream catalyst in shift section and CO2 removal section. Methanator inlet temperatureis maintained at around 290 to 320 deg C. Inlet temperature of Methanator is maintained at around 290to 320 deg C, which required high level energy to re-heat the process gases from CO2 removal section.

P e rform a nce o f M e tha na tor & Am m onia S ynthe sis Ca ta lysts a t IFFCO Ka lo l

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Ammonia Synthesis Catalyst :

Ammonia synthesis catalyst is based on metallic iron promoted with alkali (potash) and various metaloxides such as those of aluminum, calcium or magnesium. The main component of the catalyst ismagnetite (Fe3O4). Various promoters in catalyst plays main role in catalyst activity. Such promoters areclassified as structural or electronic depending on their accepted mode of action. Production andpreservation of porous structure during reduction of ammonia synthesis catalyst is main role ofstructural promoters such as alumina, magnesia and chromium. Alkali metal such as calcium, potassiumrubidium etc. are essential components of catalyst to attain high activity, are called electronic promoter.

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Ammonia synthesis catalyst has longer life than other catalyst in ammonia plant. Deactivation of catalystis slow going process and loss of activity occur by various mechanism, which are common to all thecatalyst. Deactivation may occur by thermal sintering, which lead to loss of iron surface area and henceactivity. Main poisons to synthesis catalyst are oxygenated compounds such as water, CO, CO2.However, loss of activity resulting from exposure to these compounds is reversible, provided that partialpressure of the oxygenated compound is low and that the period of exposure is short. Other poisonssuch as chloride and sulphur affect the catalyst irreversibly. During the reduction period, the over allsurface area of the catalyst increases steadily. Poisoning of ammonia catalyst is normally considered interms of permanent and temporary deactivation. The dotted lines in figure-3 show the performance ofexisting catalyst charge.

EVALUATION OF METAHATOR AND AMMONIA SYNTHESIS CATALYSTS

Methanator:

Figure -3 show the performance of methanator and ammonia synthesis catalysts. It can be seen from thefigure that ammonia produced per unit volume of catalyst had increased from 82178 MT in first chargeto 142243 MT in second charge .Performance of existing charge is satisfactory.

Ammonia Synthesis Converter Catalyst:

It can be seen from the figure that ammonia produced per unit volume of catalyst had increased from17399 MT in first charge to 60706 MT in second charge. Second charge is still in operation andperformance is satisfactory.

Measures to improvement the performance of catalysts at IFFCO Kalol:

From 1967 to this day, IFFCO vision has grown with the need of farmers. IFFCO Kalol was also the firstfertiliser plant in expanding its capacity by adding new equipment in its 22 years plant. This bearstestimony for its maintenance and up-keep of its equipments- quest for existing in quality. ISO-9002certification in August 96 is only a rededication of its pursuit for quality. With passage of time differenttechnical audits are conducted to improve the productivity of plant. Some of the operational andtechnological measures taken in the area of catalyst performance are as under :

(A)OPERATIONAL MEASURES:

Following measures are taken to improve the performance of catalyst at IFFCO Kalol:-

1. Planned Annual Turnaround.

• Annual turnaround of the plant is planned in such a way that maximum utilisation of catalyst isachieved.

• The Start Of Run (SOR) condition parameters like temperature profile of catalyst bed, pressuresdrop, steam to carbon ratio, slip of key components etc. for new charge of catalyst are recorded andmaintained to analyse the performance.

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• Performance of all existing catalysts is checked and the catalysts which are likely to be dischargedwithin next one year are identified and planning is made for expected replacement of the identifiedcatalyst .

• While discarding the catalyst , analysis of end of run (EOR) operating conditions are also recordedand also ammonia produced by per unit volume of that catalyst charge is analyzed. The discardingcatalyst performance is also measured based on number of plant shut downs experienced by thecatalyst.

• Evaluate the SOR condition of new catalyst being put in service and check SOR conditions withearlier charge and find out the deficiency, if any.

2. Unloading of Catalyst:

• Vessel is blinded in all respect from vessel purging to activation of the catalyst .• Vessel is being kept under nitrogen atmosphere till catalyst is oxidised.• Vessel is being inspected for any damage before unloading is being started so that remedial measures

on operation as well as maintenance side can be planned.

3. Loading of catalyst:

Cleaning of the Vessels:

• The entire vessel is thoroughly clean for debris with demineralised water.

• Removal of dust and broken particles from catalyst is carried out . Personnel exposed to catalystdust shall be protected by using dust filtering respiration masks.

• The catalyst is charged either by using buckets or by means of loading chute. Crushing of thecatalyst must be avoided by using of walking planks. Each layer of catalyst should be slightlycompacted along the side wall in order to prevent channeling. Prior to the filling, dust and crushedparticles must be removed by screening.

Inspection:

Vessel is thoroughly inspected for cleanliness before loading is started . All internals are verified as pervessel drawings. In addition , over all inspection is made of all internals for conformance with drawings.Deficiency in inspection, if any, is noted and paid maximum important to rectify during next catalystchange over.

Marking Bed Height :

Established the lower tangent line and mark each bed level and support level etc. in accordance withvessel drawing.

Storing ,Screening and sorting of catalyst:

• Prior to loading, catalyst is pass over suitable screen to remove the dust. In case of primary andsecondary reformers, the broken pieces of catalyst are being sorted out.

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• All the areas where catalyst is handled are covered up and drum are kept clear from damp walls.

• Catalyst sceening or sorting of broken pieces is planned in such a way that handling of the drum isminimised.

• Stacking of drums is avoided. It is not stored in the vicinity of combustible materials.

Loading of catalyst :

• During catalyst loading, care is being taken to ensure that catalyst free fall is not more than specifiedby catalyst supplier.

• A complete record of quantity of catalyst being loaded and bed height achieved at each stage ofleveling is being noted.

• Catalyst loading procedures for each type catalysts are readily available to all operating staff.

• Time taken for each step during loading of vessel is noted and this time is compared with earlier besttime and reasons for increased time are analysed.

(4)Activation of catalyst

• All operating staffs are well informed about the catalyst activation procedures, catalyst poisons,effect of change in operating parameters before activation of new catalyst is being started.

• During activation, all the process parameters are maintained and observed as per catalyst supplierrecommendation.

• Extra care is being taken to meet the unforeseen emergencies to protect the catalyst .

• After completion of activation, catalyst is taken in operation and close monitoring of catalystperformance is made to optimize the plant performance.

(5) Operation of Catalyst:

• Lower and upper limit of operating temperatures for each type of catalyst over a period of time withaging of catalyst are known to the operating staff .

• Operating staff is always well informed with catalyst poisons for each type of catalyst.

• Extreme care is being taken during any shutdown so that catalyst remains in secured and safecondition. Following parameters are monitored on regular basis :-

- bed temperatures profiles of each reactors on hourly basis. - pressures of the each reactors containing catalyst on hourly basis. - reactors are drains for condensate once in each shift.

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(B)Technological Measures adopted by IFFCO-Kalol:

(1)Primary reformer Catalyst:

Primary reformer catalyst tubes along with harp assembly was replaced with improved material . Bettertubes material allowed to increase the internal diameter of the tubes for loading more catalyst. Catalystvolume was increased from 13.6 m3 to 14.4 m3 in first Reformer Revamp and it was further increasedto 17.7 m3 in Second Reformer Revamping in Sept. 1993. Following observations are made :

• Pressure drop across the reformer has reduced .• Tube skin temperature has reduced .• This helps higher through put and longer catalyst tube life.

(2) Secondary Reformer Catalyst :

With the first charge of the catalyst, it was found that the top and center portion of the catalyst wasfound fused and formed lumps. It was observed that removal of this lump was very difficult and ifsufficient care is not taken , this can be detrimental to the refractory of secondary reformer.

Top catalyst layer was fused due to poor mixing of process air and process gas at top of the catalystbed. The catalyst volume was reduced by 14 % from 38.74 m3 to 33.29 m3 to provide more area formixing zone at top of the catalyst bed.

Performance of catalyst charge, after reduction in volume, was checked in subsequent annual plantturnaround. Such catalyst fusion was never experienced after above measure.

(3)LT Shift Converter Reduction Procedure:

In original plant, IFFCO Kalol was using natural gas for LTS catalyst heating and for catalyst reduction. In this procedure , LTS reduction took about five days during start-up .

Nitrogen circulator system was installed with required flow and pressure . Crack gas (mixture of H2 andN2 ) compressor was installed. With this facility, LTS catalyst can be reduce independent of natural gas.Ammonia production is being lined up without any loss of natural gas venting. The same facility is nowbeing utilised for cooling and heating of other catalysts beds as well.

(4)Ammonia Converter Retrofit:

IFFCO Kalol ammonia synthesis converter is having four catalyst beds. In original reactor ,gas flowacross catalyst beds was axial. Ammonia converter retrofit was done by M/S Ammonia Casale inSeptember 1993. Gas flow through the converter is changed from axial to axial -radial type .

With above changes, catalyst volume had increased from 64.81 m3 to 75.0 m3 and smaller size catalystis used in the reactor. Smaller size catalyst have improve the ammonia conversion per pass and hencereduction in circulator power requirement. The pressure drop across synthesis converter has alsoreduced. Energy saving of the tune of 0.27 Gcal /ton of ammonia was achieved with converter retrofit.

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(C) Technological Measures for adaptation of New Catalysts:

Catalysts are procured from different catalyst suppliers. Within the frame work of IFFCO' s purchaseprocedure, following technological measures are taken for adaptation of new catalyst and followingmeasures are taken :-

(1)HT Shift Catalyst:

Changing the catalyst from conventional to low sulfur and copper promoted catalyst. IFFCO hadexperienced the following advantage :-

• Reduction in Start-up time.• Lower operating Steam to Carbon Ratio.

With this catalyst charge, it is expected that the ammonia production per unit volume of Catalyst willimproved.

(2) LT Shift Catalyst:

Changing the Catalyst from low Copper to High Copper had resulted in significant increased inAmmonia Production per m3 of Catalyst.

(3) Ammonia Converter:

IFFCO Kalol is using conventional un-reduced catalyst in Ammonia Converter. During catalyst loading,first bed is loaded with pre-reduced catalyst . By adopting this technological measure, the start-up timeof ammonia converter was reduced considerably from 5 days to 3 days. By using this method,ammonia water generation due to reduction process was also reduced considerably.

Conclusion:

It may be concluded that catalysts plays an important role in overall productivity of plant. Developmentand commercialization of new catalysts with higher activity at lower temperature is main challenge tocatalyst manufacturers. Improvement in performance may be achieved with high activity catalyst withhigh stability and high poison resistance. Significant advantages can be gained by proper selection ofcatalyst with planning and proper operation. A well planned catalyst loading/unloading method followedby precise monitored catalyst activation process will not only improve the catalyst life, but theeconomics of ammonia production also. This offers an unlimited scope of improving the application ofcatalyst by users.

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Table-IV : Performance of Catalyst at Ammonia Plant-IFFCO KALOL

Sr. Area of Life of Catalyst Catalyst Ammonia Ammoniaproduced

No. Service Ch-arge

From To Months Volume,m3 Produced, t per unit volume

No of catalyst, t/ m3

1 Hydrogenator 1 Sept.97 Till date 7 3.2 138714 43348.13

2 Sulphurabsorber

1 Sept.97 Till date 7 19.4 138714 7150.21

3 Pre-reformer 1 Sept.97 Till date 7 6.6 138714 21017.27

4 Primary 1 Nov.74 Dec.76 24.95 13.6 369179 27145.51Reformer 2 Jan.77 May.79 27.91 13.6 665628 48943.24

3 June 79 April 81 21.43 13.6 495292 36418.534 May-81 Dec.83 30.70 13.6 809852 59547.945 Jan.84 March 86 25.80 13.6 572104 42066.476 May-86 April-88 23.50 14.4 587378 40790.147 May-88 Feb.-91 33.47 14.4 849788 59013.068 March-91 Sept.-93 30.07 14.4 726701 50465.009 Oct.-93 Till date 53.00 17.4 1396704 78466.00

5 Secondary 1 Nov.74 March 76 16.66 38.74 208339 5377.88Reformer 2 April 76 May-79 37.79 33.29 827416 24854.79

3 June 79 March-86 80.63 33.29 1867104 56086.034 May-86 Nov.-92 78 33.29 1943105 58369.035 Nov.92 May-97 54 33.29 1347466 40476.606 June-97 Till date 7 33.29 267479 8064

6 HTS 1 Nov.-74 Dec.-76 24.86 55.13 369179 6696.522 Jan.-77 April 81 52.67 55.13 1160920 21057.863 May-81 March-86 58.3 55.13 1371812 24883.224 June 86 June 91 57.67 55.13 1433581 26003.655 March-91 May-97 74 55.13 5904475 107100.946 June 97 Till date 7 55.13 267479 4851.79

7 LTS 1 Nov.-74 March-76 16.7 58.76 208339 3545.592 April 76 Feb.-78 22.33 58.76 483512 8228.593 March-78 April 81 36.93 58.76 853680 14528.254 May-81 April 85 47.1 58.76 1150279 19575.885 May-85 April 88 33.5 58.76 803623 13676.366 May-88 Nov.-92 53.9 58.76 1359311 23133.277 Nov.-92 May-97 54 58.76 1347466 22931.698 June -97 Till date 7 58.76 267479 4552.06

8 Methanator 1 Nov.-74 Dec.-80 73.5 18 1479215 82178.612 Feb.-81 Feb.-90 108 18 2560376 142243.113 March-92 Till date 70 18 1616990 89832.00

9 Synthesis 1 Nov.-74 Nov.-79 60 64.81 1127684 17399.85Converter 2 Dec.-79 Sept.-93 165.2 64.81 3934382 60706.40

3 Oct.-93 Till date 50 75 1396704 18622.0

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Table-I : Existing Charge of different catalysts at Ammonia PlantSr Area Nomenclature Catalyst Name ofNo of catalyst volume, m3 supplier

1. Desulphurisation C-8-6 28.3 UCIL2. Hydrogenator TK 550 3.2 H&T3. Sulphur absorber HTZ-3 19.4 H &T4. Pre-reformer RKNGR 6.6 H&T5. Primary reformer ICI-46-8 17.8 ICI6. Secondary reformer C-14-2/C-15-1 33.29 UCIL7. Shift reactor-HTS SK-12-LS/ SK-201/ C-12-4 55.13 UCIL8. Shift reactor-LTS C-18-HC 58.76 UCIL9. Methantor C-13-4 18.0 UCIL10. Ammonia converter AS-4/ AS-4F 75.0 H &T