while processing Vaccum residue from certain Crude blends (With lower CCR and Asphalenes). Lots of powder coke is getting generated in the coke drums; even at higher Heater Coil Outlet temperature of 501 Deg. C. Powder coke in drums is causing problem during Steam / water quenching as feed line pressure increases beyond 10 kg/cm2 (Normal 5.0 Kg/cm2) and resist the water flow. Moreover because of higher COT, rate of rise of skin temperatures for heaters is also on higher side than expected.
Also Severe hammering occurs in the feed line during steam quenching. The feed line also gets plugged with powder coke. Frequently we had to cut feed to accomodate extra time required for hydrojetting of coke drum feed line, to 65 M3/hr (From 85 M3/hr) for 6 – 7 hours.
Because of problems being faced in drum quenching, hot spots are observed in all the drums while carrying out coke cutting. Severe hot spots may damage coke cutting equipments. Twice, it has damaged insulation of top Delta Valve.
Is it only due to crude blend or some other parameters also affect to this phenomena ?