Ethanol Dehydration Units
Our quality and service has facilitated the growing use of our products in Ethanol Dehydration Units (EDUs). Market feedback, plant size criteria, and production demand has allowed Hengye to design a 3A Molecular Sieve, EthaDry, that is ideal for ethanol dehydration with optimized selectivity for water over ethanol and increased capacity per cycle to provide a high purity end product. Our goal in creating this specialized adsorbent is to help ethanol plants flourish and increase output without needing to expand current operations. This product is built to withstand typical operation conditions when properly maintained and aims to add an overall positive return-on-investment for ethanol producers.
How EDUs Work
Through distillation alone, ethanol can only be dehydrated to around 95% to 97% purity, with the remaining water unable to be removed due to the formation of an azeotrope. This phenomenon leaves the ethanol unsuitable for use as a fuel or additive. To achieve fuel purity ethanol, pressure swing adsorption (PSA) technology, along with the use of molecular sieve, is applied and anhydrous ethanol can be achieved. Molecular sieve is widely used in the biofuel industry for removing water from ethanol in the generation process. EthaDry, a Hengye Inc. product, has been designed specifically for use in ethanol production, and when handled correctly in a system that is properly operated throughout its working life, can improve an ethanol dehydration unit’s dynamic adsorption capacity of water, raise ethanol output, while reducing by-products.
Inside a Cycle
The graphic to the right represents one ethanol dehydration bed at three different stages in the dehydration cycle. At the Start of Cycle, the majority of the bed is an Active Zone, where sieve is dry from regeneration and ready to adsorb water. The Mass Transfer Zone (MTZ), where sieve is actively adsorbing water, is beginning to move down the bed. At the Middle of Cycle, the MTZ has moved about half way down the bed. At the top of the bed, where ethanol and water enter the unit, water has fully saturated the sieve beads, this is known as the Equilibrium Zone. At the End of Cycle, the Mass Transfer Zone has made its way to the bottom of the bed and water will soon break through, so the cycle ends and the bed will be regenerated.
The image above shows three different vessels, each with different Mass Transfer Zone (MTZ) heights. The height of the MTZ plays an important role in overall bed capacity. The Most Desirable bed has the shortest Mass Transfer Zone and the largest Equilibrium Zone, meaning that this bed has adsorbed more water in one cycle than the other two. The Least Desirable bed, on the far right, has the tallest MTZ and smallest Equilibrium Zone, so this unit has adsorbed the least amount of water. It’s important for operators to optimize the conditions within the dehydration unit and select a molecular sieve with an ideal Mass Transfer Rate to minimize the height of the Mass Transfer Zone and increase the overall capacity for water per cycle.
Products for Ethanol Dehydration Units
We considered the conditions that dehydration units need to be able to operate at peak performance and designed a molecular sieve with ideal physical properties and selectivity to optimize productivity.