Using waste heat to produce electricity

By Anna Austin | January 11, 2011

Capturing waste heat to produce electricity can be made simple by the Green Machine, an organic rankine cycle technology by Reno, Nev.-based ElectraTherm Inc. Co. CEO John Fox described the process and its benefits to a crowd of about 70 at the Pacific West Biomass Conference & Trade Show Jan. 11 at the Sheraton Seattle Hotel. “ElectraTherm targets existing sources of waste heat to convert to electricity,” he explained.

Fox was one of four speakers on the breakout panel Case Studies and Research in the Utilization of Wood Waste Streams for Heat and Power. Organic rankine cycle works similarly to a conventional steam engine, using low-grade heat to boil a working fluid into gas, he explained. The company touts the system’s ability to make electricity with no fuel requirement.

“We put heat into this cycle and take kilowatts out,” he said. The company has 10 systems in the field. “So it’s going very well.” One of those systems has more than 1,000 hours of operating time, using heat from a boiler burning logs and logging slash in South Carolina that would normally be landfilled or openly burned. ElectraTherm is looking at more projects in South Carolina, as well as one at a dairy farm in Wisconsin.

The company’s primary market has been large reciprocating engines, but the enormous amount of waste heat in many global industries has created a market pull from other industries including biomass, Fox explained. The Green Machine has a competitive edge because of its simplified design, its wet operation capability, and the fact that it enables a robust packaged solution to dealing with waste heat, Fox said. The system also has a combined-heat-and-power capability for floor heating, domestic hot water and other uses.

Fellow panelist Jerry Whitfield, director of product development for BioEnergy Systems LLC, also discussed a cogeneration system, but his produces heat and char. In his presentation titled Development of a Combined Heat and Char Reactor to Convert Low Grade Biomass Residues into Renewable Energy, Whitfield explained that the CHC system is still in development but demonstrates meaningful feedstock flexibility. “I want to leave a message with you today about what I consider to be the future of biomass,” he said. “One of the things I see is that the pellet industry has somewhat plateaued.”   

The future of biomass is much more than simply generating energy from combustion, which gets a bad reputation because of sustainability and emissions questions, he continued. The CHC process produces char through slow pyrolysis and thermal energy through the combustion of the producer gas, which is the syngas mixed with vapors from the process, Whitfield explained. The char is solid, carbonaceous, porous and maintains the shape of the raw biomass material. “Char came out looking much the same as the material that went in,” he said.

BioEnergy Systems has experimented with grass pellets, litter pellets, raw litter, paper pellets and other green pellets. About 30 to 45 percent of the energy is contained in the char, which also represents agricultural benefits such as restoration of soil organic carbon; improvement of soil fertility and crop yields; and nutrient management, among others.

“There is a bigger and, I hope better opportunity of doing business,” Whitfield said of the CHC process. “I encourage those of you interested to take a hard look at this and help make this industry a success.”