FIORDA Case Study – High Pressure Drop in Methanator Catalyst Bed due to CO2 Removal Solution Carry Over

 

No: 15
Date 04/02/2019
Plant Code TQC
Incident Code TQC-BSS-A
Technology Ammonia
Plant section Methanation
Main Equipment Methanator
Sub-Main Equipment Catalyst
Operation phase (during the event) Normal Operation
Operating parameters (during the event) Unknown
Medium Methanator Inlet
Risk category Operational
Hazard type Contamination / Impurities
Failure Cause Equipment failure
Failure Mode Contamination
Hours of operation Unknown
No of failures last 6 months Unknown
No of failures last 12 months Unknown
No of failures last 24 months Unknown
Warning signs High Dp
Event description Methanator catalyst performance remained satisfactory with respect to CO & CO2 slippage, however, the pressure drop across the reactor gradually increased to 1.5 kg/cm2g (21.3 psig) compared to the normal value of 0.1 kg/cm2g (1.4 psig).

The most probable reasons for the high-pressure drop were Benfield solution carry-over, due to partial damages in CO2 absorber column, and breakage of catalyst particles with aging.

Immediate response action Planning for skimming of the catalyst
Findings The high-pressure drop was apprehended due to the presence of a hard layer formed by Benfield solution carryover, being observed from the CO2 removal section. New catalyst charge might also have high-pressure drop due to carry-over problem from CO2 removal section which was not expected to resolve soon. Therefore loading the fresh catalyst would not ensure resolving high-pressure drop problem, unless carryover problem from CO2 removal section is fixed, even at the cost of the new catalyst.
Consequence Primary Loss of production
Consequence Primary cost Unknown
Consequence Secondary Catalyst replacement
Consequence Secondary cost Unknown
Consequence Details Catalyst performance remained satisfactory with respect to CO & CO2 slippage, however, the pressure drop across the reactor gradually increased to 1.5 kg/cm2g (21.3 psig) compared to the normal value of 0.1 kg/cm2g (1.4 psig). The most probable
Reasons for high-pressure drop were Benfield solution carry-over, due to partial damages in CO2 absorber column, and breakage of catalyst particles with aging.
Comments A hard thick crust was observed in the centre of the bed on top of the alumina balls. Samples were collected and analyzed for potassium carbonate. Results indicate that it is 44.6% K2O. An annular depression had been created by the flow of gas all along the vessel wall, reducing the cross flow area significantly and causing a high-pressure drop.

The pressure drop across the methanator catalyst bed was reduced from 1.5 to 0.1 kg/cm2g (21.3 psig to 1.4 psig) after catalyst skimming.The removed layer of catalyst primarily contained dust (crushed catalyst particles). Alumina balls were found buried in the catalyst bed up to the depth removed.

Consequence Moderate
Likelihood Moderate
Risk Level High risk (9)
Prevention Safeguards Maintain the downstream CO2 removal section in good operating condition to prevent carry over and catalyst damage.
Mitigation Safeguards None
Corrective Recommendation Catalyst screening

Initiate the shut-down sequence and prepare for reactor cooling. Open manhole and initiate unloading of alumina balls using vacuum blower system. A total of 762 mm (2.5 ft) outage from bottom of manhole was achieved. This corresponds to ~ 10% of the catalyst bed. A total of 80 drums were screened using mesh size of 3 x 3 mm which took around 8 hrs. The skimmed catalyst was made-up with HTAS catalyst PK-5R.

Lesson Learned The methanator catalyst skimming not only resolved an issue of high pressure drop across the catalyst bed but also saved the cost of the most part of new catalyst charge. Catalyst performance has remained satisfactory for more than 2 years after the skimming activity. The reaction front is still in the upper half of the catalyst bed. This experience will surely provide guidance and confidence to all those who seek to rectify a high pressure drop problem due to carryover from CO2 removal section.

 

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