What if there was a way to increase profit margins and the energy efficiency of your plant by more than five percent — without disturbing your process? A technology has developed that uses silicon to convert waste heat into electricity. It uses solid-state, thermoelectric units that do not have any moving parts. The thermoelectric units are adaptable for use in most process equipment from small kilns to large steel reheat furnaces.
Although it may sound too good to be true, thermoelectric waste heat recovery exploits a well-known thermoelectric effect. Scientists have known for nearly 200 years that a simple temperature gradient can create voltage across some materials. German physicist Thomas Seebeck first reported this “thermoelectric effect” in 1821. In the 1950s, scientists began to explore the properties and nuances of thermoelectrics, particularly in experiments with compounds like bismuth telluride. Thermoelectric modules designed as semiconductor-based components found some use in some electronics cooling applications. Thermoelectric materials are semiconductors that, when placed in a temperature gradient, generate electricity in the solid state.
More recently, for process applications in industries such as chemicals, plastics, construction materials, glass and metals, waste heat recovery technology initially developed at the Lawrence Berkeley National Laboratory could provide adaptable waste heat-to-power devices that are simple to install.
Traditional waste heat recovery options — Rankine cycle or combined heat and power (CHP), for instance — offer high efficiency but also significant cost. In addition, extended downtime can be required for installation, affecting top-line revenue. These limitations can be especially true when trying to scale down traditional waste heat recovery systems to meet the needs of the majority of exhaust flues found in heat processing industries.
In contrast, solid-state silicon thermoelectrics are suited for modular waste heat recovery and power generation from individual exhaust flues. They can be integrated into most existing waste heat streams without effect on the industrial process and requiring little maintenance. Made up of small silicon chips similar in size to what can be found in a home computer, these units can be customized and scaled. The range of scalability — from the size of a small notebook to larger than a 747 — allows for the design of products that are modular and capable of addressing exhaust flues of varying sizes. Thermoelectric heat recovery devices can be suitable for applications in process heating equipment such as burners, thermal oxidizers and heat treatment processes.
The sweet spot for silicon thermoelectrics is high-temperature waste heat in confined environments over 572°F (300°C), which includes most engines as well as many ovens and most furnaces. With a target payback of 24 months or less and a minimum expected useful life of 10 years, silicon-based waste heat recovery technology provides an accessible technology for those companies whose budgets, payback requirements and process sensitivities have kept them out of the waste heat arena in the past.
After two centuries of development, accessible thermoelectric waste heat recovery solutions are no longer a far-fetched idea; they are available and being implemented today. Both the U.S. Army and Air Force have engaged this technology in applications that will help contain defense-related energy costs, especially in remote geographies. Lego-like thermoelectric waste-heat recovery units with short payback times are headed for the industrial mass-market. What we’ve seen so far is just the beginning.
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