Heat-to-Power Technologies

Generating power from waste heat typically involves using the waste heat from boilers to create mechanical energy that then drives an electric generator. While these power cycles are well developed, new technologies are being developed that can generate electricity directly from heat, such as thermoelectric and piezoelectric generation. When considering power generation options for waste heat recovery, an important factor to keep in mind is the thermodynamic limitations on power generation at different temperatures. The efficiency of power generation is heavily dependent on the temperature of the waste heat source. In general, power generation from waste heat has been limited to only medium to high temperature waste heat sources. However, advances in alternate power cycles may increase the feasibility of generation at low temperatures. While maximum efficiency at these temperatures is lower, these systems can still be economical in recovering large quantities of energy from waste heat. The table below summarizes different power generation technologies.

Options for Heat Recovery via Power Generation

Thermal Conversion Technology Temperature Range Typical Sources of Waste Heat Capital Cost ($/kW)
Traditional Steam Cycle Medium High Exhaust from gas turbines, reciprocating engines, incinerators, and furnaces. 1,100 -1,400
Kalina Cycle Low Medium Gas turbine exhaust, boiler exhaust, cement kilns 1,100 - 1,500
Organic Rankine Cycle Low Medium Gas turbine exhaust, boiler exhaust, heated water, cement kilns 1,500 - 3,500
Thermoelectric Generation Medium High Not yet demonstrated in industrial applications 20,000 - 30,000
Piezoelectric Generation Low Not yet demonstrated in industrial applications 10,000,000
Thermal Photovoltaic Medium High Not yet demonstrated in industrial applications N/A

Source: Waste Heat Recovery: Technology and Opportunities in U.S. Industry (DOE, 2008)

Steam Rankine Cycle

Organic Rankine Cycle

Kalina Cycle

Next: Factors Affecting Feasibility
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