2015

Foaming of Catacarb™ C02 Removal System leads to

Methanator Runaway Reaction and Expander Fire Incident

Fatima Fertilizer Ammonia Plant / aced massive CO/DeaTh solution /oaming in the C02 Towers followed by solutioll carryover to Methanalor causing runaway reactions and downstream Expander fire incident. This paper describes the sequence of events, how the problem was

analyzed, what tests were performed and how the problem was eventually solved.

M uhammad Hashim, Reh man Hanif Fatima Fertilizer Company

Introduction

Fatima Ferti lizer Ammonia Plant is designed by CF Braun & Co. Alhambra California built in 1967. This Plant was initially operated

Exxon. Then plant was bought by Kemira in 1985 and kept the same operational philosophy with exemplary service factor and production record of 1767 MTPD. Due to some business reason this plant was shut down in 2000. Kemira initial plan was to scrap this plant therefore it was never mothballed. Fatima moved this plant from the Netherlands to Pakistan in 2007 and started successful production on 15th March 2010 with a design capacity 1500 MTPD.

This paper will focus on the following systems:

I. Importance of activated carbon filtration specifically how badly it can burt the

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Catacarb TM solution if not kept in service during normal operation.

2. Importance of color index measurement in Catacarb analysis.

3. Methanator trip Logic modification to avoid Methanator run away reaction

4. Expander trip logic modification to avoid oi l console over pressurization and fire incident

Incident Description :

The Ammonia plant was in restart phase after 10 days planned shutdown while restarting the ammonia plant from 29th August 2012, various problems were encountered including foaming in Catacarb caus ing excessive and repeated carryover of solution to Methanator. Methaoator temperature increased from trip limit 806°F whereas Methanator trip logic was oat actuated automatically due to its built in

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selector switch option on DCS HMI (Refer to Figure#1 page#7) Once it was observed that temperature reached to 960°F Methanator inlet valve HV -025 was immediately closed and that action cut downstream seal gas flow towards Expander. Cold box Expander process gas breakthrough from HP drain to oil console causing console over pressurization and consequently hydrogen fire incident. Issues were resolved one by one by taking appropriate engineering controls and operational measures. Production was resumed on ISth Sept. 2012.

Sequence of Events:

31st August at 1730 hrs; Plant was in start up, Front End was taken into operation with 65% load and Catacarb solution carried over with process gas to downstream exchangers and Methanator (R-104) due to foaming and flooding in CO2 absorber. R-I 04 was immediately isolated, depressurized and drained.

1st September at 1430 hrs; Catacarb solution carryover was again observed due to foaming causing high level of C02 absorber downstream Knock Out Vessel (D-133).

2nd September at 1030 hrs; Due to poor perfonnance of Methanator feed effluent exchanger E- 120A/B, flushing of E-120A/B was carried out with turbine condensate.

3rd September at 1540 hrs; Even with excessive shock dosing of anti foam in Catacarb solution, foaming could not be controlled and Methanator bed temperature increased to maximum value of 960 of on top bed TI-02SB due to high C02 slip from absorber. Methanator trip security 1-6 was manually actuated due to high temperatures of Methanator because trip selector button was selected on bottom of the Reactor bed. (Refer to Figure I)

.... -.. . .... ~­-­._ ..... -D.'"

~=='{',elh .. nator

TTlI .. A

TTlI ...

Tro>ll"

TrO>. O

~-K.ODn."" __ ""', ... __ Goo Gooc_, _ _ --'

I ._ .. I AllBlIU .... __ c ....... _

OM .",c_,., -~

xv_'nB

Figure J.- Methanator Selector Switches & Discontinuation of Seal Gas flow caused cold process gas ingress to sour oil return towards oil console

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4th September at 0915 hrs; As the cold box expander located downstream of the Methanator a huge fire occurred at Cold box Expander C-I03 oil console due to oil splashing on hot steam lines caused by over­pressurization of oil console due to process gas entering at -220 of into sour oil HP drain line because of emergency cut of seal gas towards expander during C02 Absorber Carry over time (Refer to Figure 1.)

12th September at 1850 hr, ; Catacarb foaming still not in control even after taking all control measures maximizing air injection, reducing circulation rates, increasing anti foam doze etc. Vendor Eickmeyer & Associate was also consulted and reached on site but situation was not kept under control and production loss pressure was increasing day by day due to low load operation so it was decided to replace 40% of the total catacarb charge available in warehouse. 15th September at 2330 hrs; Ammonia production was resumed however under low load operation (70%) and with controlled foaming and acceptable flooding.

Root Cause analysis Key Findings:

1. Solution foaming tendency:

Fatima CATACARB system was designed to remove C02 from the Process gas having molar flow 11370 kmollhr contallllDg (H2~52.7%, N2~26.4%, C02~ 1 8.26%,

CO~0.3%, CH4~2%, AF0.26%) and total catacarb volume 550 m3 with Energy effic iency 840 KCallNm' C02. It was equipped with a carbon filter to treat around 30 m3/h of solution continuously to remove suspended solids and keep format level in design limit i.e. Less than I N. The best defense against foaming was extensive

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carbon and mechanical filtration. Fatima had kept the activated carbon filter idle since start up based on the lab results. Without carbon filtration, the solution foaming tendency had bt::t::n rising organic contaminants gradually accumulated in the solution, for example, derivatives of heavier hydrocarbons, amine degradation products, glycols from antifoam, alcohols from shift reactors etc. The contaminants reduced solution surface tension and lllcrease foaming tendency.

2. Passivation

Avai lable Inhibitor remained greater than 70% of the total Vandaium. During foaming instance Iron contents increased the limit from 100 to 155 ppm for shorter time duration but it came down to 6()'--70 ppm

3. Suspended solids:

I-I ere it wi ll be worth mentioning that we didn't have experience of co-relating the solution color change with rise in suspended solids that should be adsorb on activated carbon filter if we take it in service since commissioning (15th March 2010) It took about two years to change this color from straw yellow to dark black. 3.1 Laboratory sample results misguided the whole team. When samples were sent to nearby external laboratories for further testing suspended solids were reported 1560 ppm against our Lab value 166 ppm but iron contents in both in house and external laboratories testing remained less than 100 ppm. See results in Table I

3.2 Color index method was not being used since commissioning as it was not mentioned in Vendor analysis guidelines. During foaming incident when color index analysis was carried out it reached to 23360

AMMONIA TECHNICAL MANUAL

Hz whereas nonnal value should be 3000 Hz 4. Foaming tendency by Shake Test:

Foam shake test help operators to develop close understanding of froth iness of solution Laboratory Results:

Max. but this technique was not being used. Foaming tendency was being checked by spa.rger test only. Shake test usually offers advance warning against pending problems.

Test Catacarb Samples Resutt Semi lean Regenerator (5th September 2012)

Time (Hrs) Unit Normal Value

K2C03 % 14-18

KHC03 % 14-18

Equivalent K2C03 % 26·30 Total V Ippmw 000 V+5 ppmw 2800

V+4 ppmw 1200

Iron Total ppm 100 max

Amine % 1

Chlorides ppm 100 max

Formate % 1 Max

Foaming Height ml 20

Foam break time Sec 5

pH 10-1 1

Color index Hz 3000max

Suspended Solids ppm 100 max

Note:

1) Amine reporting was in %age whereas Licensor changed this practice in form of normality (0.4-0.6 N) after this incident.

2) Color Index was not introduced init ially and after the incident we started measuring Color Index.

Table I : Results from external laboratories

s. Methanator Trip Logic:

Due to Catacarb carry over during flooding from CO2 Absorber CO/C02 slippages increased. Methanator trip logic was built in only to deal with high temperatures but there was no built-in trip logic upon Methanator inlet valve closure so that it can initiate downstream trip logics.

6. Expander Trip Logic:

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Fatima Laboratory External Laboratory Results Results

14.3

18

26.7 26.8 3800 4400 3000 ~OOO 800 ~OO 91 62

0.9 1.1

22 24

1.49 2.5

NI ~O Nil 9.6

10 10. 1

23360 1.313 Abs

166 1560

During Catacarb solution canyover Methanator inlet isolation valve HV-025 was closed but Expander C-103 was not manually tripped and forgot in flooding emergency. Methanator inlet HV -025 closure stopped the seal gas flow towards Expander and caused inadvertent mixing of cooled expander process gas with oil into oi l console caused over pressurization and finally a fire incident.

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Root Cause: (Key Factors and other Contributory Factors)

a) Putting Carbon filtration system out of service since commissioning thinking no need of it till laboratory results are Donnal whereas mechanical filtration system remained in service. (Key Factor)

b) Different methods for analyzing Suspended solids misguided the whole TEAM when samples compared with the results from the external laboratory and came to know the significant difference. (Contributory Factor) Gravimetric method was used earlier whereas external laboratories were using spectrophotometirc method that was adopted after the incident with mutual agreement by Licensor.)

c) Color Index measurement is also a good tool to quantify fonnat salts and suspended solids in Catacarb System but that practice was not adopted (Other Factor)

d) No built in Expander Trip Logic upon closure of Methanator inlet valve HV-25 caused no seal gas availability and process gas ingress into Expander Oil Console caused FIRE incident. (Otber Factor)

Corrective Actions

I. Installation of one more carbon filter and put both carbon fi lters into continuous service with an additional upstream mechanical filter of 5-10 microns for suspended solids and a downstream filter of 1-2 microns for carbon fines. Nonnal Results of Suspended Solids were achieved in late October 2012.

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2. Replacement of activated carbon beds at 5. 6 months time period or if change in color index is not prominent at inlet and outlet whichever comes first.

3. Analyzing avai lable inhibitor according to licensors redox titration method revised in September 2012.

4. Performing shake test on semi-lean sample to get foam time in each shift to get advance warning against foaming issue

5. Monitor suspended solids and keep it below the recommended 100 ppm by keeping both Filtration Systems mechanical and carbon filteration in service once catacarb facility is commissioned.

6. Drain solution back to storage tank if plant outage is more than a week.

7. Rcgcncratc solution after shutdown by keeping reboiler in operation for 2-4 hours so that it strips out dissolved gases and bicarbonate conversion drops below 20%.

8. Clean the open sump from time to time and provide a SS liner during next Turnaround to avoid in-leaks of contaminants.

9. Expander C-103 logic modification to automatically trip C- I 03 on-

9.1) Methanator inlet HV-25 Closure 9.2) DP across seal gas and HP seal oil

(POI-OSO) < 0.2kg/cm2 9.3) DP across seal gas and expander casing

(pOI-OS I) drops below 0.1 kg/cm2.

10. Installation of degasitying tank at sour oil HP drain line to avoid Oil console

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over pressurization and consequent fire due to higher seal gas venting.

Conclusion

The foaming and flooding instance was very costly and inconvenient and we had suffered production loss from 31 st August to ) 5th September partially or completely. We learned that:

.:. CA TACARB needs adequate care in day to day life to sustain safe operation .

• ;. SEAL GAS SYSTEM to rotary machines like Expander needs more attention during start ups and shut downs to avoid seals damage.

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