Plant Expansion Through Membrane Integration

By Christian Roy | July 08, 2008
While market factors determine the cost of raw materials and selling prices, processing innovations can reduce the cost of producing fuel ethanol. Aside from hedging and smart marketing practices, producers have little control over the costs of corn, distillers grains and ethanol. However, producers do have control over savings associated with reducing energy consumption. A large portion of the energy consumption in ethanol production comes from extracting water from the fermentation liquor product stream. Here is where advanced membrane separation technology for dewatering a water-rich ethanol stream can be used to produce energy savings of as much as 50 percent compared to the conventional distillation and molecular sieve dewatering solution.

Although molecular sieves combined with distillation have proven effective to separate water and ethanol, their use can be energy intensive. Molecular sieve units produce a purge stream which contains between 60 percent and 80 percent ethanol that is recirculated and reboiled in the distillation column.

Molecular sieve units are comprised of a water adsorption cycle during which an ethanol/water vapor mixture circulates across the molecular sieve bed. During this regeneration cycle, fresh ethanol is injected into the molecular sieve bed in a counter current flow with respect to the water adsorption cycle. The binary mixture is sent to the rectifier for reprocessing. The molecular sieve accounts for approximately one-third of the rectifying column total load. Also, molecular sieves may adsorb fuel oil over time.

Vaperma, a Canadian-based company has developed a trademarked Siftek membrane system, which has been designed to increase throughput capacity and save energy. With the Vaperma process configuration, the molecular sieve unit liquid phase purge stream is vaporized and dehydrated in the two-stage Siftek membrane cartridge configuration. The membrane dehydration system consumes less energy than the conventional molecular sieve regeneration method, and it enables significant unloading of the distillation column. The system can increase plant's overall fuel ethanol production by approximately 20 percent to 30 percent.

The membrane dehydrates the molecular sieve purge stream at a reduced cost. The water-rich stream can be directed toward the front end of the plant or is eliminated through the beer column. The membrane retentate end-product is fuel ethanol at 99 percent or higher. The skid-mounted Siftek system can be easily integrated to the facility during plant maintenance shutdown.

How the Technology Works
Through the application of membrane technology the ethanol producer to achieve increased throughput capacities and reduced energy consumption. Siftek's polymeric membrane technology combines solvent and high temperature resistance with a strong proprietary hollow fiber that can be used in a variety of new industrial applications. The membranes are vapor phase separation units that allow the preferred permeation of water over other vapor components in a gas mixture. These membranes are made of a special blend of polymers selected for their specific morphological and chemical properties. The driving force for the separation phenomena is the ratio of the water partial pressure on the lumen and shell sides of the membrane. The high permeability of water across the membrane is due to its relatively high combined adsorption and diffusion rates.

The water/ethanol mixture is slightly pressurized into the bundle of hollow fibers. Dehydration of the water/ethanol vapor mixture occurs by selective permeation of water vapor across the active thin layer of each polymeric hollow fiber. Thousands of hollow fibers form a membrane cartridge bundle which is housed inside a stainless steel vessel.

Cellulosic materials as feedstocks that will not compete with food supplies are considered to be the future of fuel ethanol. Conversion of cellulosic biomass to ethanol is challenging because the sugar concentration is far below that of corn or sugarcane. Processing cellulosic materials to ethanol also requires the removal of huge volumes of water from the fermentation liquor. The membrane solution is an attractive option for dewatering cellulosic ethanol as it is even more effective with an increase in the amount of water present in the feed.

Successful Pilot Testing
Recently, Vaperma and Greenfield Ethanol Inc. of Toronto, Ontario, successfully reported the operation of a Siftek pilot plant over a period exceeding 4,000 hours. The test involved the "all-in-one step" reprocessing of a 60 percent to 90 percent ethanol/water blend into a 99 percent fuel-grade anhydrous ethanol at Greenfield's 25 MMly (6.6 MMgy) plant in Tiverton, Ontario. The first actual industrial field trial enabled the production of approximately 200,000 liters (5,300 gallons) of fuel-grade ethanol. As a result of that field trial, energy savings of 40 percent of actual energy consumption were obtained. The savings represent 3 cents per liter (11.4 cents per gallon).

Commenting on the impact of this new membrane separation technology, Greenfield CEO Robert Gallant said "The unit in Tiverton used substantially less energy and therefore fewer greenhouse gases were created in the process, reducing the plant's carbon dioxide footprint."

Still under field testing, the Siftek membrane at Tiverton processes 1.5 cubic meters per day of feed originating from the beer column. That was enough to encourage Vaperma and Greenfield to move on to a large-scale test of a 7.5 MMly (2 MMgy) membrane.

In mid-June at the International Fuel Ethanol Workshop and Expo, Vaperma announced that it had installed its Siftek field demonstration system at GreenField's plant in Chatham, Ontario. The unit is expected to reach full production capacity by the fall of 2008. "We are confident that the full-scale unit will give conclusive results in reducing our energy costs and consumption compared with conventional technologies," Gallant said.

The Chatham project is also equipped with auditable greenhouse gas protocol and software for measuring the emission reduction benefits generated with the membrane system, thereby creating tradable carbon credits.

At this point, Vaperma's technology has been shown to be low in maintenance with membrane cartridge replacement predicted not to be needed on average until after three years of continuous operation.

Christian Roy is co-founder of Vaperma Inc. and co-inventor of Siftek polymer membrane technology. Reach him at (418) 839-6989.