The common way of displacement of hydrocarbon of the furnaces, is the steam, where the pressure level is around 150 psig and 200 psig over of the normal operation pressure in the entrance of the furnaces, also take a look the discharge pressure of the pump,since sometime the delta P acroos the heater is assumed from 350 to 550 psi (clean and dirty) and during their operation is smaller, having it the control valve to absorb this difference (that can generate vibration problems in the valve or its bypass at the time of using it)
