Throughout the United States, an abundant source of emission-free power is being overlooked. This source is waste heat, a byproduct of industrial processes that could reinvigorate American manufacturing, create jobs, lower the cost of energy and reduce overall emissions from electric generation. If not captured and used to generate emission-free renewable-equivalent power, waste heat is released to the atmosphere through stacks, vents, flares and mechanical equipment.
Waste Heat to Power (WHP) works by capturing waste heat with a recovery unit and converting it to electricity through a process called heat exchange. This process produces no emissions because no fuel is burned. By using the waste heat to generate emission-free power, industrial users can route the power back to the facility or sell it to the grid to support clean energy production, distribution and use.
WHP systems use the same technologies deployed in a number of industries including the geothermal industry. The main technologies used by WHP developers are Steam Turbine Technology, Organic Rankine Cycle, Supercritical CO2, Kalina Cycle, Stirling Engine, and emerging technologies such as Thermoelectrics. Through the application of these technologies, industrial waste heat is no longer just a byproduct – it is a valuable resource for emission-free electricity.
Steam Turbine Technology
Steam Turbine Technology is more than 100 years old and has been utilized for WHP systems since the 1970’s. Steam turbines extract the thermal energy from waste heat (steam) and use that energy to drive an electric generator. Steam turbines are generally deployed in larger scale industrial facilities which produce high temperature waste heat.
Organic Rankine Cycle
Organic Rankine Cycle (ORC) technology is a heat exchanging process that utilizes a refrigerant for its working fluid and captures waste heat at lower temperatures and from smaller scale projects than the steam turbine. Since the majority of industrial waste heat in the United States is below 600 degrees Fahrenheit, the ORC’s ability to capture low temperature resources opens up many new applications for waste heat to power (WHP) projects.
Supercritical CO2, Thermoelectrics, Kalina Cycle®, Stirling Engine
Additional technologies make up a smaller but growing portion of the waste heat to power industry. Supercritical CO2, or scCO2, uses supercritical carbon dioxide as the working fluid. Thermoelectrics are solid-state semiconductors that capitalize on a difference in temperature to turn heat into electricity with few or no moving parts. The Kalina Cycle®, which uses a solution of water and ammonia for its working fluid, takes advantage of the different boiling points of the two liquids to extract heat over a wider range of temperatures. And the Stirling Engine uses cyclic compression with gases as the working fluid to capitalize on very low temperature waste heat.