In the morning, I followed Awang (BO) to the roof of the control room to make air-condition changeover. Air conditioner for control room was changed from 1B to 1A.
From Nooter Eriksen Operating manual, I learnt that recirculation pump on HP and LP economizers are use to increase the inlet feedwater temperature. It is required during the distillate oil as fuel. Condensation of acid can occur and corrodes the tubes of economizer if the temperature is low.