Producing Greener Ethanol

Delta-T unveils a new dryer technology that company leaders expect will cut emissions, and reduce energy and water use.
By Roger Moore | August 27, 2007
Bibb Swain keeps his aim high, priorities straight and design green. These virtues have kept Delta-T's chairman and technology director at the leading edge of change in the ethanol industry. They are also readily apparent in his company's newest technology, which is being debuted to the U.S. industry. "Minimizing the biorefinery's environmental footprint while maximizing its economic output is our driving principle," Swain says.

Delta-T's latest biorefinery design "integrates two major changes—High-Efficiency Drying (HED) and high-pressure rectification—in a way that dramatically cuts energy use, water consumption and air emissions, and consequently cuts operating costs by more than $6 million a year for a 108 MMgy plant," Swain says.

Unlike the computer industry, the biofuels industry has no Moore's Law promising to cut energy and water use in half every two years. "Key ethanol production efficiencies have in recent years been grudgingly resistant to improvement" Swain says.

Pursuing Transformational Change
Technological tweaks have lowered the ethanol industry's energy and water use. From 1996 to 2006, ethanol plant energy consumption gradually decreased from approximately 42,000 Btus to 34,000 Btus per gallon of undenatured ethanol with 100 percent distillers dried grains. Water consumption decreased from six to eight gallons to three to five gallons of water per gallon of ethanol produced. Emissions control has improved, and greater economies of scale have helped trim operating costs for the mega-plants springing up across the United States and beginning to dot the globe. However, the industry's "design changes in the past decade have been a series of modest, incremental improvements rather than transformational," Swain says.

The result is a comforting illusion that ethanol processing is humming along in a happy groove, with producers seemingly content to wait for the golden reward of a cellulosic future. Are improvements in grain-fed plant processing efficiency grinding to a standstill, causing the groove to become a rut?

According to Swain, Delta-T doesn't think so. "For corn ethanol plants, this new Delta-T technology reduces energy consumption more than all the advances in the industry combined over the past decade," Swain says.

Three Technological Leaps
"On the heels of our HED system, we have three new major technologies we're developing for grain-fed plants," says Delta-T President and CEO Rob Swain. "Each one will further reduce energy consumption significantly. In addition, we will chop makeup water requirements for corn plants by more than half—to less than 1.5 gallons per gallon of ethanol produced. This is an exciting achievement in today's world where water conservation is a critical factor in most ethanol plant communities and most of the globe."

Rob Swain says the advancements are "three more giant steps--giant steps that will enable our green industry to become even more of an asset for the environment around us."

Cutting Energy, Water and Emissions
At the 23rd annual International Fuel Ethanol Workshop & Expo held in St. Louis in June, Delta-T Director of Engineering Carolyn Kotsol introduced the design concept behind the company's HED. She explained how advances in DDGS dryer waste heat integration reduce energy and water consumption without reducing product quality or process efficiency.

First, Kotsol discussed a 25 percent reduction in energy use—from 34,000 Btus to 26,000 Btus to produce a gallon of ethanol with the drying of distillers dried grains to 10 percent moisture content.

Kotsol also said there is more than a 50 percent reduction in fresh make-up water to less than 1.5 gallons of water required to produce a gallon of ethanol.

Kotsol says the new system dries the distiller grains like traditional dryers, but it captures waste heat from the dryer exhaust and reuses the energy within the plant, giving the facility a huge boost in thermal efficiency. The HED system, coupled with the integration of Delta-T's new high-pressure rectification system, adds about $12 million in capital costs versus the traditional Delta-T plant design. The system will "typically pay for itself in just two years, assuming an energy cost of $8 per MMBtus, and it cuts VOCs (volatile organic compounds) by more than 40 percent. We believe that most environmental authorities will approve our concept where the dryer burner oxidizes the greatly reduced amount of non-condensables from the dryer emissions, allowing for elimination of the thermal oxidizer. The resulting capital savings of eliminating the (thermal oxidizer) would further improve on the already lucrative return on investment for the HED system."

China First to Embrace Innovation
The new HED system springs from Delta-T's close partnership with GEA Barr-Rosin. The system is based on a Barr-Rosin superheated steam ring (flash) dryer, integrated into the Delta-T plant design.

The first commercial installation of the new HED technology was in Zhaodong, China. Delta-T designed a 50 MMgy corn-fed processing plant to produce ultra-high-purity beverage alcohol. Chemtex International of Wilmington, N.C., provided the project's sales, project management, procurement and engineering support. Delta-T provided the technology, process design and start-up training. Plant construction was provided through the owner, China Resources. Barr-Rosin provided the dryer equipment at the core of Delta-T's HED system.

Since its start-up in April 2007, the Zhaodong plant has confirmed Delta-T's expected energy savings, according to Bibb Swain. A second biorefinery using Delta-T's HED design is slated for Renew Energy, a 130 MMgy fuel ethanol plant in Jefferson, Wis., which will be in operation by October 2007.

Capturing and Recycling Waste Heat
Kotsol says the idea behind Delta-T's High-Efficiency Dryer technology was sparked several years ago. "Delta-T followed its instincts that there were still untapped opportunities to reduce energy in the back end of the biorefinery," Kotsol says. "We didn't start off with the sole intent of designing a new drying system. We began by identifying all sources of waste heat in the overall plant design. Then we identified potential integration techniques and energy receptors and what the capital cost would be. Of course, we studied the expected financial return of each approach through a series of iterative studies."

Conventional DDGS-drying accounts for 38 percent to 40 percent of a plant's overall energy consumption. If the quality of dryer exhaust could be improved to nearly pure low-pressure steam, most of the energy input to the dryer could be used a second time by using the dryer exhaust to power another sub-process within the plant.

Delta-T chose an indirect-fired ring dryer using superheated steam as the heating medium as the most appropriate configuration because it could be sealed to prevent entry of unwanted air, something that can't be done effectively with a rotary drum dryer. Although similar HED concepts with a rotary drum dryer are being explored by the ethanol industry, the unavoidable leakage of air through the seals in the rotary dryer will cause it to fall considerably short of the energy recovery available from a sealed dryer. By designing the HED system around the Barr Rosin ring dryer, Delta-T obtained superior thermal energy performance, and its customers benefit from the most proven ring flash dryer in commercial ethanol plants today.

The HED system includes several design elements. It provides the ability to dry distillers grains without scorching, resulting in a bright gold, high-quality livestock feed. It redirects waste heat (atmospheric pressure steam) from the dryer exhaust to drive stillage evaporation instead of sending it up a stack. The system eliminates combustion gases within the dryer, allowing the producer the flexibility of heating with coal, biomass or natural gas. It closes the loop cycle to reduce non-condensables from 60 percent to less than 5 percent, greatly improving exhaust quality and enabling 95 percent heat recovery.

Delta-T's HED system also eliminates the need for a thermal oxidizer by having the dryer burner oxidize the residual non-condensables. Finally, it condenses the dryer exhaust vapor in the evaporator and transfers it to a treatment center, where it is cleaned and reused as cooling tower make-up water.

Kotsol cites safety as another benefit of the HED. Reducing the amount of oxygen in the dryer to less than 1 percent means that there is a greatly reduced chance of a dryer fire because of an insufficient oxygen supply to support ignition. Kotsol says she believes that the incidence of dryer fires, long a problem in the ethanol industry, will be eliminated or greatly reduced with the HED technology.

Rolling Out New Technology
The new dryer is being installed only on new Delta-T biorefineries. In the future, the system will be available for retrofitting existing plants to increase their competitiveness.

Luciano Cantafio, head of Delta-T Europe, confidently predicts that the biofuels industry in Europe and the Commonwealth of Independent States (CIS) will soon be embracing the HED concept. "It makes absolutely no sense to produce a greener fuel by burning so much fossil fuel," he says. "The HED will be a big hit in the environmentally focused EU and CIS."

Bibb Swain agrees. "We'll have a healthier planet and a wealthier investor," he says.

Roger Moore is a freelance writer located in Lancaster, Pa. Reach him at [email protected].