Hot Oil Boiler

WHY MUST USE HOT OIL ?
At the current technology we need high temperature on the heat transfer liquids. This high temperature can be obtanied and used whitout pressure.
For obtaining of saturated steam and superheated water 250-350 C temparature with 40bar up to 90 bar pressure is needed. On thr other hand to obtain of 300 C hot oil we need only under the 3 bars fort he pressure of pipeline and boler.
On the otherhand cause of corrosion and calcity that occures erosion and erode we need in