Power, Heating and Cooling using Thermal Exhaust Sources
Why is this technology needed?
Hot engine exhaust and industrial waste heat represent a resource that is often rejected to the environment without further utilization. This resource is most prevalent in the transportation sector, but stationary engine-generator systems also typically do not utilize this resource. In the transportation sector alone, considering long haul trucking and automobile operation, an estimated 12.5 quads of high grade thermal energy is exhausted to the environment without further use nationwide. In the industrial sector, waste heat from materials processing and other operations generate an estimated 10 quads of heat. This resource can potentially be utilized by various approaches to produce electricity or to drive heating and cooling systems.
How does this technology address the need?
MBI researchers are developing thermoelectric modules and Organic Rankine Cycle (ORC) systems for utilizing exhaust heat. Either separately, or in unique dual-cycle configurations that combine the best attributes of each technology, co-functional power/cooling systems are being applied to this waste energy resource. Of the unique configurations being explored, microchannel heat transfer components are being used in the co-functional arrangement to integrate thermoelectric conversion as a topping cycle and the ORC as the bottoming cycle. This approach is being developed to fully utilize the thermal energy contained in hot exhaust streams. The system is composed of a high temperature heat exchanger that extracts thermal energy for driving the thermoelectric conversion elements and a closely integrated bottoming cycle to capture the large amounts of remaining thermal energy in the exhaust stream. Modeling has been carried out to determine optimum operating conditions. Many interacting parameters that define combined system operation are employed in the model to determine overall system performance including output power, efficiency and total energy utilization factors. The model also identifies a maximum power operating point for the combined system. That is, the model can identify the optimal amount of heat to remove from the exhaust flow to drive the thermoelectric elements for maximizing the combined cycle output.
A working system using advanced bismuth/telluride TEC modules and an ORC with R245fa as the working fluid has been designed and built. Testing of the system is on-going to determine how actual system operating performance matches up with model results. Figure 2 shows a completed system that is capable of providing cooling from a waste heat source. A small-scale ORC is coupled to a vapor compression cooling system to form an integrated unit. Scroll technology is used for both compression and expansion in the completed unit.
Figure 3 shows microchannel boilersfor a dual cycle system. The microchannel boilers shown in the figure take hot air representing exhaust heat to boil an ORC working fluid, in this case, R245fa. The microchannel boiler component uses 35 layers of chemically etched stainless steel shim stock to form the final device through diffusion bonding.
How is MBI contributing to the solution?
Both PNNL and OSU have conducted significant work in the area of thermoelectric power modules and small-scale power cycles (including the ORC). Through the MBI, research and development work on integrating systems in practical configurations has been funded by DoD and DoE. Also, partnerships and working relations have been established with commercial groups for microchannel component fabrication and thermoelectric module development.
The MBI has laboratory facilities where heat activated heat pump systems and co-functional systems are developed and tested. The Energy Systems Laboratory has been specifically built and outfitted to conduct research into small-scale energy systems that use microchannel devices for heat transfer components.
- Richard B. Peterson, Director of the Tactical Energy Systems Program
- Terry Hendricks, Director and Lead PI for Co-Functional Systems Development
For additional information
Contact Hailei Wang.