Furnace distillation reboilers

The reformed gas leaves the furnace at a high temperature where high grade heat is recovered successively to a reformed gas boiler, steam superheater process feedstock heater and boiler, feedwater heater. The reformed gas then passes to the distillation area where low grade heat is efficiently recovered via column reboilers and a demineralized water heater. 

The pyrolysis oil stored in the oil drum is fed into the distillation column with reboiler and separated into three fractions light oil from the top, medinm oil from the middle and heavy oil from the bottom of the column. These three types of oils are stored in separate oil tanks and sent to the furnaces and cogeneration system in the plant as fuel through piping, or loaded onto a tank lorry for shipment. 

On a process flowsheet, distillation towers, furnaces, reactors, and large vertical vessels often are arranged at one level, condenser and accumulator drums on another level, reboilers on... 

The first petroleum fractionator simulated is a simple distillation column that removes some of the light material in the crude. Figure 11.16 gives the Aspen Plus flowsheet of this unit. There are two crude feed streams that are combined and heated in a furnace in which the feed is partially vaporized before entering the bottom of the column. There is no reboiler. Live steam is introduced in the bottom of the column to strip out some of the light components in the bottoms stream, which is fed to a pipestill to be considered in Section 11.4. 

The distillate rate is set at 20,000 B/D. This will be adjusted later to obtain a desired ASTM 95%pointof 375 °F for the liquid distillate product, which is a fight naphtha stream. Note that there is only one degree of freedom in this rectifying column since there is no reboiler. All of the vapor coming up the column comes from the partially vaporized furnace effluent. 

As the heated charge leaves the furnace and enters the distillation column, a fraction of the feed vaporizes and rises up the column, while the heavier components (still in liquid state) drop down the column. This initiates the process of separation by boiling point. Because the energy in the process stream begins to dissipate immediately, a reboiler or heating source is attached to the column. This allows the separation process to continue. Some distillation columns are steam traced to ensure even temperature control. 

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