(254m) Water and Emissions Trade-Offs in the Operation of Biogas-Fueled Combined Heat and Power Systems

Authors: 
Fuentes-Cortes, L. F., Instituto Tecnológico de Celaya
Zavala, V. M., University of Wisconsin-Madison
Ponce-Ortega, J. M., Universidad Michoacana de San Nicolas de Hidalgo
Combined Heat and Power systems (CHP) can achieve much higher resource utilization efficiencies than conventional power plants and thus reduce fuel cost and emissions and losses associated to electricity transmission (Mago et al., 2009). CHP systems can also provide different energy products (steam, hot water, cold water, and eletricity) to commercial buildings, hospitals, housing complexes, and manufacturing facilities (El-Khattam and Salama, 2004). Modern systems can also run on multiple fuels such as natural gas, diesel, coal, biomass, and biogas (Dong et al., 2009).

The ability to achieve high energy integration in CHP systems, however, results in significantly more complex operations. In particular, it is necessary to capture strong and highly dynamic interactions between carriers and resources (Geidl and Andersson, 2007; Cho et al., 2009a), it is necessary to trade-off energy market conditions and local demands (Illerhaus and Verstege, 1999), one must consider dynamics and limited storage (Henning, 1998; Malysz et al., 2014), and one must consider inefficiencies associated to partial load operation (Bracco et al., 2014).

Greenhouse gas emissions and water usage are major factors driving the development of new CHP technologies and fuels. A key issue in the design and operation of advanced CHP systems is that environmental impact associated to water consumption and emissions are controlled by monetization (i.e., one associates a price/penalty to them). We argue that such an approach is highly inefficient when local environmental policies and market conditions are not well developed and this results in limited control of environmental impact and blocks adoption of new technologies. For instance, in some cases one might only be able to control environmental impact using extremely high and unrealistic water prices. We show that adaptive scalarization of objectives is necessary to ensure that water and emissions impact match the actual limits of a wide sprectrum of technologies and under a wide range of operating conditions. We demonstrate our developments using a CHP system for a real residential building complex that incorporates biogas produced from food waste and thermal storage. In particular, we demonstrate that existing carbon emission penalties and water prices do not incentivize the use of biogas and have limited impact on water utilization.

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