Process Safety

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Process Safety and Operation Integrity

-- FCCU High Reactor Catalyst Loss Problem --

One important thing in the safety and management system is process hazard identification and risk assessment.

The main hazard in a process operating with problem in the catalyst circulation; (unstable circulation, due to the catalyst losses because of the erosion in the cyclone) is pressure variation in the reactor and the cyclone. This may cause excessive temperature (explosion), due to air enters reactor or hydrocarbons enter regeneration.

The equipments of the FCCU unit will might get affected by this unexpected high pressure and temperature than design. This might cause flow reversal (hot catalyst will enter the air blowers) and/or insufficient feed to the reactor. The unstable flow will cause changes in the temperature which will lead to pressure swing in the regenerator. The pressure variation might affect other parts in the FCCU unit such as the main fractionators and/or the wet gas compressor.

The catalyst losses in the reactor will cause high catalyst content in HFO (heavy fuel oil); leading to HFO being off grade on aluminium specification and the need to downgrade gas oil as a diluent.

Also, reducing the conversion will reduce the profitability of the company, which we need to avoid.

The current feed of FCCU process is 200 t/hr VGO plus 5 t/hr CGO recycle at 75 wt% conversion.

The current FCCU profit is $50/t feed.

The catalyst loss in the reactor side has increased from 1 to 2 t/day, therefore; it will require extra catalyst of 1 t/day at $2000/t.

The cost of an unplanned shutdown for repair before the maintenance turnaround: • 3 weeks lost production
• Maintenance cost $1 M
• Debits is $ 2 M

Reducing catalyst circulation rate by 10% to reduce conversion 5 wt %, this might effect: • Loss of margin (5/75 reduction in profitability)
• Reduction in catalyst losses of 10%

The financial consequences of an unplanned FCCU shutdown in the next 12 months (loss in profitability) will be:

$50/t * 21days * 200t/hr * 24hr = $ 5.04 M (3 weeks of production loss) = $ 240000 loss in production profit/day

The total loss in profit for emergency shutdown in FCCU unit = 3 weeks lost production cost + maintenance cost + logistic debits = $ 8.04 M

Risk Assessment

Scenario 1: High reactor catalyst losses cause loss of fines from the circulating catalyst inventory resulting in unstable catalyst circulation and frequent trips of the emergency shutdown system being ultimately responsible for a shutdown before the planned turnaround.

Probability: The unstable catalyst circulation and frequent trip of the emergency shutdown system means the probability of the risk is high (A).

Consequence: To check what the consequence of this problem is, we need to calculate the loss in the profitability if we wait until the next planned turnaround. Loss in margin (5/75) * $50/t * 200t/hr * 24hr = $16000 per day (10/100) * 1t/day * $2000/t = $ 200 per day

$ 16000/day * 365 days = $ 5.84 M
Increase the catalyst losses to 2t/day * $2000/t * (10/100) *365days= $1.314M The maintenance needs $1 M
Now, the total profit loss is $5.84M + $1.31M + $1M = $ 8.154 M (betwwn $1M - $10 M) which means the consequence category is (II).

The risk = consequence * probability → the risk = IIA (Black box) it is not acceptable, therefore; we need to deal with it immediately, we need the revised risk??

Risk Reduction: Since its frequent trip, therefore we can not reduce the risk but we might be able to mitigate it.

Risk Mitigation: Mitigate the risk by safe operating envelops and reliability operation envelops. Reducing catalyst circulation rate will help to reduce the erosion...
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