After bleaching earth dosing, the oil flows into the continuous heater. The oil heater 621 and the bleacher 622 are combined so as to form one vessel with the oil heater installed on top of the bleacher 622/21. Agitation is obtained by injecting sparge steam through the crown(s) installed at the bottom of the oil heater. This agitation under vacuum ensures deaeration and perfect dispersion of bleaching earth in the oil. The sparge steam agitation also assures optimal heat exchange.