I think your Coker is licensed by M/S CBI & Lummus. They have provided the refractory lining on the collector tray below the shed-deck or packing for safeguard of tray in view the condensation of coke drum vapors. This is the old design concept and having following major demerits :
1- Curing of the refractory inside the column is major concern
2- There may be chances of refractory get damaged & dropped in bottom, it can be affect the Heater charge pump.
In Foster Wheeler and other licensed Coker ,the trays are reliable with metallurgy SS410 and there is no provision for refractory lining.