Owner/operator: Archer Daniels Midland Co.

In the heart of corn country, Archer Daniels Midland is using seed corn that is no longer suitable for planting, along with coal, to power its 180-MW Clinton cogeneration plant. The cogeneration plant, which began operations in 2008, supports ADM’s Clinton corn processing plant, one of the largest corn wet mills in the world. It also supports ADM’s facility that produces renewable plastic from corn sugar. Firing up to 20% biomass along with coal, the new cogeneration plant is capable of providing 100% of the steam and electrical power needs of both facilities.

Designed to accommodate a wide variety of fuels, including materials that would otherwise be discarded, Archer Daniels Midland’s (ADM’s) cogeneration plant in Clinton, Iowa, has lessened the economic impact of changing energy costs and reduced the need for fossil energy.

In addition to supporting ADM’s large corn processing operations, the Clinton cogeneration plant also provides process steam and electricity to a facility at ADM’s Clinton complex that produces renewable plastic. Named “Mirel,” these plastic resins are made by using corn sugar and can biodegrade in natural environments. The Mirel facility also produces a biomass co-product that the cogeneration plant will use as a fuel to help minimize the facility’s overall carbon footprint.

With its experience at two other major cogeneration sites (Cedar Rapids, Iowa, and Decatur, Ill.), ADM recognized the importance of having the flexibility to burn alternatives fuels, because they potentially create both economic and environmental benefits. ADM’s Clinton cogeneration plant also burns a biomass by-product from the company’s wastewater treatment facility.

“The new cogeneration plant has reduced ADM’s vulnerability to fluctuating energy costs,” said Kevin Duffy, plant manager of the Clinton cogeneration plant. “We continue to seek ways to improve efficiency and reduce costs. Burning alternative fuels, including biomass, is part of this initiative. Our plant began burning biofuels in January 2010.”

Constructing the New Cogeneration Plant

“The old powerhouse (50% natural gas–fired boilers, 50% coal-fired) did meet our steam production needs but only provided up to 30% of our electrical power requirements,” Duffy said. “We decided to invest in a new cogeneration plant rather than upgrade the existing plant. The new cogeneration plant is capable of providing 100% of our steam and electrical power needs.”

In August 2004, ADM began purchasing property for the site, which today is more than 44 acres. On June 8, 2005, the company broke ground at the site. In September of 2008, the cogeneration plant started the first boiler. By July 2009, construction was completed and the facility was in full operation.

Facility Operations

Although the plant has a 180-MW total nameplate capacity for its two generators, the normal generation capacity is 130 MW to meet the requirements of the processing site.

“In the last 12 months, the facility generated 938,000 MWh, inclusive of some downtime related to commissioning issues,” Duffy said. “The plant normally generates more than 1,000,000 MWh on a yearly basis.”

Duffy provided the following information about equipment currently used at the cogeneration plant:

â–  Two steam turbine generators manufactured by GE Energy (GE Model 7A6): Unit 1 has a 75-MW generator, nine-stage, noncondensing turbine and generator, and Unit 2 has a 105-MW generator, 14-stage, extraction-condensing turbine and generator.

â–  Three circulating fluidized bed (CFB) boilers manufactured by Metso Power: 1,200,000 lb/hr steam at 1,310 psig and 900F.

â–  One fuel storage dome manufactured by Dome Technology: 298 feet in diameter by 164 feet high and concrete-reinforced.

â–  The stacker/reclaimer located inside the dome was manufactured by MVT Materials Handling GmbH: type CSST-2420-1375/90 with a 1,650-tph stackout rate and a 950-tph reclaim rate.

“A complete standalone water-makeup facility draws water from three wells to generate high-purity boiler feedwater and cooling tower makeup,” Duffy said. “The water is purified using reverse osmosis and mixed bed polishers. The water system cleans returned condensate from the processing plants with mixed bed resin polishers to increase overall efficiency of the operations.”

Air Pollution Control Technologies

“We designed, built, and permitted with intentions of burning up to 20% of alternative fuels,” Duffy said. “We monitor these fuels and make sure they will allow compliance with our existing air permits.”

Because a large percentage of the fuel mix used by the facility is coal, the plant uses crushed limestone for sulfur dioxide (SO2) control, anhydrous ammonia for controlling nitrogen oxides (NOx), and fabric filter baghouses for particulate control. Both fly ash and bottom ash are conveyed from the boilers to ash storage silos via pneumatic conveying.

Limestone is received by truck, conveyed into storage silos, and conveyed from there to individual day bunkers at each boiler. Coal is received by rail and truck; conveyed to covered dome storage; and then reclaimed, crushed, and conveyed to individual day bunkers at each boiler, as well. A multiple-lined flue accommodates the three boilers with a 412-foot-tall chimney.

The three CFB boilers started up with a selective noncatalytic reduction system, which was designed and supplied by DNX Engineers for NOx control, sorbent addition for SO2 control, and reverse-air baghouses for particulate control. The technology helped the processing facility and cogeneration facility reduce overall SO2 emissions by 79% and its NOx emissions by 60% in 2009 compared to 2008 emissions.

Using Biomass for Fuel

“The plant uses Powder River Basin coal and Illinois coal at an 80% and 20% blend,” Duffy said. “We can burn up to 20% of alternative fuels based on input Btu heat value. The biomass waste stream from ADM’s new biodegradable plastics processing plant could eventually make up 20% of the alternative fuel once fully operational.”

There are many biomass fuels that have potential, such as corn stover, switch grass, wood products, and dried distillers’ grains. “Discarded seed is a very easy biofuel to handle, and it is blended daily with the coal in our boiler bunkers,” Duffy said (Figure 1).

1. Corn belt. Discarded seed is blended daily with coal in the boiler house at the ADM Clinton cogeneration plant. The facility has experienced some seed spillage around the conveyor belt, but overall, the seed conveyance operation has performed better than expected. Courtesy: ADM

Duffy described a number of unique issues that the cogeneration plant faces related to using biomass as a fuel source:

  • ADM must continue to monitor its operations to see if additional maintenance on the boilers is required due to the use of alternative fuels.
  • Plant personnel have the daily challenge of making appropriate adjustments to accommodate an appropriate blend of fuels, to mix the biomass fuel uniformly, and to monitor the combustion process accordingly.
  • The staff have the additional logistical challenges of having to coordinate biomass material delivery on a time-of-day basis so as to not interfere with coal, lime, and ash traffic at the plant.

Dedicated Operations Team

“We have a superb operations team in regards to safety, housekeeping, and training, and the team has great pride in the plant,” Duffy said.

The average night and weekend operation includes six operations personnel on each of four shifts. In addition, there are four material handlers on the Monday through Friday day shift schedule who handle the unloading of coal, lime, and biofuel, as well as the loading out of ash. The plant has a maintenance staff and instrumentation and electrical staff of 13 employees. All together, the total facility staff includes 53 ADM employees.

The ADM operations staff commissioned the plant to make safety its top priority. They have worked over three and a half years without a recordable incident related to a violation of the Occupational Safety and Health Act. Plant employees, along with all contracted staff, have adopted a values-based safety observation program to help them realize the ADM belief that “Zero is Possible” when it comes to workplace injuries.

Angela Neville, JD, is POWER’s senior editor.