ICT2014 Abstracts

Many conventional middle scale Rankine cycle power plants for utility grids use coals as the energy resource. As an example, a state-of-the-art steam Rankine cycle uses superheated steam at a temperature of 813 K and a pressure of 25 MPa to produce 520 MW of power with an efficiency of 41.7%. However, a large amount of exergy is still not used at higher temperature range from the flame to the steam. Even using relatively moderate thermoelectric with ZT~0.7 for the temperature range, e.g. nanostructured SiGe, harvesting such unused exergy is estimated to increase the efficiency of the overall system by 6%.   

We first present the performance analysis based on the electro-thermal co-optimization to find the maximum power generation from the topping thermoelectric module based on a detailed thermo-fluid dynamic modeling of the boiler. Thermoelectric modules are optimized for local available temperatures and heat fluxes. Then, we show the cost analysis minimizing TE material mass usage by reducing the fractional area coverage, i.e. fill factor, of the thermoelectric elements in the module. The trade-offs when parasitic electrical and thermal losses can increase are also discussed. The analysis shows that the optimum design with fill factor of 10-15% provides a competitive cost down to 0.3 $/W even with the use of an expensive thermoelectric material ($2,000 per kilogram). Due to the high temperature, preventing radiation heat leak in a thermoelectric module is a significant concern. Finally, we will also show the extensive analysis of changing basic parameters of the boiler such as fuel burning rate or the boiler diameter to show the potential of simplifying the fin structure on the hot side of the thermoelectric module.