Rethinking reboilers

2nd May, 2008

External reboilers can provide potential savings of up to $1 million (€631 million), compared with a direct seal heated mash column

The subject of bioethanol divides the world into believers and sceptics. The latter often claim that producing the biofuel requires more energy than it saves.

Whether that is true or not, it is certainly possible to save energy in the distillation process, which, together with the evaporator and dryer, is the biggest consumer of energy in an ethanol plant.

Improving energy efficiency by achieving a lower steam-toethanol rate will increase profits for producers of bioethanol – and provide believers with the benefits of bioethanol through better arguments.

Direct steam injection versus external reboilers There are many different setups of distillation systems.

However, in all types, the ethanol is separated first from the fermented mash and later from water in different distillation columns. All these columns must be heated by a process vapour or steam.

One way to heat them is with direct steam injection, which is the oldest and simplest principle. The steam is directly injected into the column and mixes with the product.

In an external reboiler, the product is heated and partly evaporated without being mixed with the heating media. The two streams flow in independent closed loops.

Typical types of external reboilers are plate, shell and tube and kettle reboilers.

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