|Operation phase (during the event)||Normal Operation|
|Operating parameters (during the event)||Unknown|
|Hazard type||Contamination / Impurities|
|Failure Cause||Equipment failure|
|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.
|Risk Level||High risk (9)|
|Prevention Safeguards||Maintain the downstream CO2 removal section in good operating condition to prevent carry over and catalyst damage.|
|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.|