Crude Charge and Prefractionation Units

The next major unit is the crude furnace or crude heater. This typically a very large fired heater capable of vaporizing significant quantities of crude. It is also 

We specify the overflash specification by using an Adjust block. As a reminder, the oveiflash is the amount of liquid that is vaporized in addition to the all products recovered in the column excluding the residue. The residue is the crude that is not vaporized in the feed of the column. We specify the furnace initially by an estimate of the heat duty. The adjust block will vary a manipulated variable, the furnace heat duty, until we our design specification, vapor fraction (based on mass) of the furnace outlet stream reaches a target value. 

Vaiiatle phase Fiac on a Mass Basis ( aintr Phase) 

User Suppled C Another Obfecl r SpreadSheetC el Qbjeci 

From Table 2.9, we show the sum of the liquid products is 45.84 wt%. We would like to specify an overflash of 3%. Therefore, we expect the vapor fraction (on a mass basis) of the stream leaving the furnace to be 48.84 wt% (sum of liquid products and overflash). We will adjust the heat duty to match the overflash requirement 

---