Asslamoalaikum

Brother i need your support. Actually i have been given a task to develop crude furnace outlet temperature control on yokogawa centum vp DCS. The problem is its mathematical model for calculating its heat duty. I have read many books like process control by myke king but havent got convincing solution. Actually i need refrence or mathematical equatio practicall implemented in other refineries.
Please support me.

Regards
Imran