While homeowners can cheer the plummeting costs of natural gas, food processors who hoped to harvest methane from their waste streams have had to rethink renewable energy projects. Such was the buyer's remorse at Pearl Valley Cheese in Coshocton County, Ohio, until the company turned its methane into pricier electricity.
Each year in recent history has brought another precipitous drop in the value of energy recapture. The spot price of natural gas averaged $8.86 per million Btu in 2008, the U.S. Energy Information Administration reports, and was selling for half that in 2010. Last year, the average spot price was $2.75/MMBtu.
Natural gas was trading near its peak in 2009 when Chuck Ellis, president of Pearl Valley Cheese, placed an order for a 400,000-gal. anaerobic digester system from Siemens Water Technology. Whey permeate and wastewater from the plant flows into the digester, with the resulting methane siphoned off for storage in a "white bubble" biogas holder. The fluid portion is channeled to dissolved air flotation (DAF) clarifiers to produce biosolids and treated waste water.
Besides harvesting methane to fire his plant's boiler, Ellis envisioned the project as a good-neighbor gesture to his rural community. The village faced an EPA mandate to treat sewage generated by 40 residences. By adding 40,000 gal. of low-biological oxygen demand wastewater daily to the effluent stream, the cheese plant helped overcome hydraulic issues in moving sanitary waste to a treatment plant 5 miles away in West Lafayette, Ohio, while also helping to rationalize an upgrade to the treatment plant because of the higher volumes. "In a rural area, we almost have to create our own infrastructure," Ellis sighs.
Unfortunately, by the time Pearl Valley's waste-to-gas system was commissioned in 2011, the economics had shifted. "We found that the ROI didn't pan out," he flatly states. On the other hand, the village's eastern Ohio location -- the community is approximately midway between Columbus and Pittsburgh -- translates to high electric rates.
Last year, Ellis commissioned GEM Energy, Walbridge, Ohio, to couple a high-pressure system to a 65 kW microturbine. Approximately twice the size of a Chicago two-flat's boiler, the microturbine should approach the theoretical 569 MWh a year it would yield from 24/7 production, according to Jeremy Damstra, energy solutions engineer at GEM Energy.
Low-pressure gas fed the plant's boilers, but the microturbine requires 75 psi gas to operate. The upside of pressurization is that wrings out moisture in the gas, eliminating a gas-cooling step. Should market prices for gas escalate, reverting back to boiler use is a fairly easy process, says Damstra.
GEM Energy is a subsidiary of GEM Inc., a Chatsworth, Calif., firm that has manufactured turbines since the early 2000s. The parent organization licenses turbine distribution in Pennsylvania to another firm, limiting GEM Energy to sales in Ohio, Michigan, Indiana and New York. More than 50 turbines have been placed into service by GEM Energy, ranging from 30 kW to 200 kW units, though most are comparable in size to Pearl Valley's unit.
Optimizing energy recovery from anaerobic systems is a continuous improvement challenge, and converting the resulting methane to electricity results in additional energy losses. While the turbine only delivers 29 percent of the Btu in the gas as electricity, Damstra points out that equates to the efficiency of an electric power plant.
"Food plants are a great opportunity for this technology, but it's still niche equipment and very site-specific," allows Damstra. Large production facilities typically receive more favorable utility rates than a plant the size of Pearl Valley, making the ROI from electricity generation less attractive.
Founded in 1928, Pearl Valley has a daily output of 25,000 lbs. of branded and copacked cheese. The company burnished its reputation for superior Swiss at this year's biennial U.S. Cheese Championships in Green Bay, Wis. It also produces colby, cheddar and specialty cheese varieties.
Pearl Valley's system came on line in March, less than three months after the order was placed. Since then, it has been meeting about 20 percent of the facility's demand, feeding electricity back to the grid when the plant is not in production. The microturbine is designed to accept a heat exchanger, and while the piping and other infrastructure improvements for combined heat and power could not be cost justified this year, a later upgrade is feasible, says Damstra. Preheating of boiler feed water for steam generation is a likely CHP application.
Ellis calculates a 42-month payback on the biogas-to-electricity project.
This article originally appeared in the August 2013 issue of Food Processing Magazine.