Pre-Dryer Heat Recovery Evaporator

Pre-Dryer Application Example

A typical 55 mmgpy ethanol plant with a dryer evaporating 72,000 lbs of water per hour from 66% moisture raw material normally requires about 1,300 Btu per pound of water evaporated, consuming 93.6 million Btu/hr of natural gas energy, costing $936/hr.

By adding a four-pass Pre-Dryer to this same system (with production remaining the same), the natural gas consumption would only be 62.4 million Btu/hr, costing $624/hr for fuel bill reduction of $2.6M per year.

In this example, approximately 24,000 lb/hr of condensate can be reused in the ethanol process after waste water treatment if necessary.

Pre-Dryer Heat Recovery Evaporator

The Rotary Waste Heat Evaporator pre-dries the product using dryer heat that is normally wasted in today’s grain processing systems. Plants that integrate this single piece of equipment with an indirect-fired dryer can save over 30% of their grain drying energy costs and increase their system evaporation rate up to 33%. The Pre-Dryer System reduces particulate matter and the load on other thermal oxidizer components, generates condensate for reuse in the front-end process, and provides flexibility because the recovered heat can be distributed to thin stillage at the required or optimum ratio. (See Process Flow Diagram)

In existing systems, more than 70% of the usable original heat required to dry the product is discharged to atmosphere. Passing these stack gases through an indirect heat exchange rotary kiln will heat and pre-dry the air and wet product flowing through the secondary chambers of the drum.

For further cost and environmental benefit, heat recovery could be maximized by adding a multi-effect thin stillage waste heat evaporator in series with the Pre-Dryer.