Feeling The Heat

Recent developments could spark renewed interest in CHP technology.
By Holly Jessen | March 29, 2013

In 2008, when the U.S. ethanol industry was in the midst of its build-out phase, the U.S. EPA identified it as one of four strategic markets well-suited for combined heat and power (CHP). “Given the massive construction activity in this sector, the time is right to integrate CHP into new and expanding dry mill ethanol facilities and to ensure that CHP is part of the base design for future cellulosic ethanol biorefineries,” the EPA said. 

The reality today, however, is that only a small percentage of U.S. ethanol plants have implemented the technology, also known as cogeneration. ICM Inc., which designed and built a large percentage of the existing plants, lists 10 ICM facilities with CHP in place, including Adkins Energy LLC and Southwest Iowa Renewable Energy LLC, as two examples. In addition, Poet LLC, the largest dry mill ethanol producer in the U.S., utilizes CHP at four of its 27 facilities. Ethanol facilities utilizing CHP have configured the systems in a variety of ways, including on-site CHP or capturing waste heat from an adjacent industrial facility. 

In December, the spotlight was on CHP again, when the EPA published its final determination on a pathway for grain sorghum-to-ethanol.  Natural gas-fired sorghum ethanol plants earned a renewable fuel designation by meeting the 20 percent greenhouse gas (GHG) emission reduction threshold, compared to petroleum fuels. Of even more interest is that it also includes a pathway to advanced biofuels production for sorghum-ethanol plants utilizing CHP and anaerobic digestion. (See “Sorghum Readies to Advance” in this issue for more information.)

Sorghum ethanol-plants aren’t the only ones interested in CHP. Great River Energy, a not-for-profit electric cooperative, has linked CHP with a proposed ethanol plant project in Spiritwood, N.D. The company first built Spiritwood Station, a CHP power plant that will produce electricity to power homes and businesses as well as steam, intending to provide power to Dakota Spirit AgEnergy as well as an adjacent Cargill malt plant. Although construction is complete on the CHP facility, it’s currently on standby mode, says Lyndon Anderson, North Dakota communications supervisor for Great River Energy. “Once that load would come online, it would help improve the economics for the plant,” he says. 

Plans for Dakota Spirit AgEnergy start with a 65 MMgy corn-ethanol plant with the possibility of adding a 10 MMgy bolt on cellulosic ethanol system to the plant down the road. Great River Energy is currently working to obtain financing so it can begin construction on phase one of the project, which is tentatively planned for this summer. In February, it was announced that the corn-ethanol plant project received certification from the EPA as a renewable fuel producer, meeting the same 20 percent GHG reduction threshold as sorghum ethanol. The fact that the plant would get its electricity and steam from a CHP facility was a primary reason it received the EPA certification, Anderson said.  “Most of the coal-based power plants in western North Dakota are 30 to 35 percent,” he adds. “This is a newer technology CHP plant and if all the steam and all the electricity is fully utilized from the plant, it can reach up to 66 percent energy efficiency.”

Great River Energy isn’t a newcomer to CHP. The company’s Coal Creek Station, a coal-fired power plant located near Underwood, N.D., provides a small amount of waste steam to Blue Flint Ethanol LLC. Although both would be considered CHP power for the ethanol plants, Spiritwood Station was built to provide both electricity and steam as primary products, Anderson says. 

On-site CHP

In Lena, Ill., Adkins Energy has an on-site CHP system that was installed in 2002, when the plant started up. It consists of a natural gas-fired boiler and a turbine large enough to supply all the ethanol plant’s electrical needs, says Jason Townsend, plant manager. The waste heat from the turbine is captured to supply up to 30 percent of the plant’s steam needs. 

CHP has multiple benefits for the facility, says Ray Baker, general manager, including increasing energy efficiency and the opportunity for financial savings. On the electrical side, the company evaluates daily market pricing to determine if it should generate it on-site or purchase it from the local power grid. “Over the course of several years, we have been able to save quite a bit, just based on that point alone,” he says, referring to it as a risk management tool. 

It also means increased power reliability, limiting power outages. “If there is severe weather approaching or if the utility has any repairs that they need to make on their side, we can isolate ourselves from the grid to prevent any shut downs,” Townsend says. Even if an unexpected power outage occurs, the plant can start up its turbine, allowing it to be more self-reliant and avoid potential problems such as freeze ups in the winter. Then there’s the ability to participate in the utility company’s demand curtailment program, Baker points out. On peak electrical demand days the ethanol plant receives payment for generating its own electrical power. 

Currently, because electrical prices are economical, Adkins energy utilizes its turbine for electrical generation only about 25 percent of the time. However, that number rises to 50 to 75 percent usage in warmer weather. “During the summer months, we typically see the higher prices of electricity and we’re on the turbine more frequently,” Townsend says.  

Installing a CHP system at an ethanol plant today would be a challenge due to lower energy costs, Baker and Townsend agree. Still, Adkins Energy has gotten its money’s worth out of its system, which cost $3 million to install. “Our payback was a lot faster early on, because of [high electricity prices],” Baker adds. “Now I think it would give us a payback, but the payback would not be as fast.”

Waste Heat CHP

The CHP system installed at Southwest Iowa Renewable Energy came online in 2009, when the plant started up. The company negotiated with MidAmerican Energy to build a coal-fired power plant next door. At first, it wasn’t an easy sell. The question was, “Why would a power facility want to do this with an ethanol plant,” says Dan Wych, plant manager. “What’s in it for them?” In the end, it worked because SIRE owned a large parcel of land and was able to sell some of it to the power plant. Another factor was the fact that SIRE installed a turbine to generate electricity, which today provides a large portion of the power needed to run the MidAmerican plant. In exchange, SIRE receives its electricity from the power company for a very low rate. It cost $20 million to install the turbine and steam line due to inflated stainless steel prices at the time. 

SIRE has a steam exchange system with MidAmerican’s co-located coal-steam electric plant. High-pressure steam taken from a reheat loop from MidAmerican’s boiler is “desuperheated” to a lower temperature and pressure, Wych explains. The steam then travels through 6,600 feet of pipe to the SIRE steam exchange building, where four shell and tube heat exchangers, or deboilers, use the steam to heat SIRE’s boiler feed water, producing steam for the plant. It’s a closed loop system, meaning SIRE and MidAmerican steam never mix, and steam condensate from MidAmerican steam travels back to the power plant via a second pipe. “This steam exchange system is a very efficient way to produce the steam requirements for our plant,” he says. “We calculate nearly 92 percent energy-to-steam efficiency.” That compares to efficiency in the mid-80 percent range for the company’s natural gas boilers. 

The SIRE CHP system allows it to take 100 percent of its steam needs from the MidAmerican plant. Offering flexibility, the company can also utilize its two traditional natural gas-fired boilers or run the two steam systems simultaneously. “We have the luxury to run either MidAmerican steam line, or natural gas boilers, based on the price of each,” he says, adding that the cost of steam is fixed.  “If the price of natural gas is less than $4 an MCF [1,000 cubic feet] we’ll run on the natural gas boilers,” he says. “Right now, it’s pretty much break even.” (About $4.50 MCF.)

For SIRE, the biggest advantage of its CHP system is increased uptime thanks to having two energy sources. Unlike many plants, which must shut down during repairs or maintenance to its dryers or boilers, SIRE was designed with a standalone boiler package. The facility also has two steam tube dryers, meaning, if needed, it can shut down one dryer, produce wet cake and keep the plant running.  “So I can do a lot of my repairs and maintenance, without shutting the plant down,” he says. “Our downtime is very minimal compared to most plants.”

Another big advantage is the energy savings offered by CHP. Although a typical ethanol plant can use up to 10,000 MCF of natural gas daily, when running on the MidAmerican steam line SIRE only uses about 100 MCF of natural gas to power the regenerative thermal oxidizers. “Our system, we feel is clean,” he says, acknowledging that coal power can have negative connotations while pointing out that SIRE is harnessing waste steam, reducing its natural gas use.

Author: Holly Jessen
Managing Editor, Ethanol Producer Magazine

For additional information about CHP, read about a U.S. DOE training seminar that could help ethanol producers evaluating the technology.