Wastewater treatment plant (WWTP) utilization of combined heat and power (CHP) systems allows for the efficient use of on-site biogas production, as well as increased annual savings in utility costs. In this paper, a review of biogas energy recovery options, CHP prime mover technologies, and the costs associated with biogas cleaning give a broad summary of the current state of CHP technology in WWTPs. Even though there are six different prime mover technologies, the main ones currently being implemented in WWTPs are micro turbines, fuel cells and reciprocating engines. Different prime movers offer varying efficiencies, installation costs, and biogas impurity (H2S, siloxanes, HCl) tolerances. To evaluate the long-term savings capabilities, a techno-economic assessment of a CHP installation at a case study WWTP shows the payback, annual savings, and initial costs associated with the installation of a CHP system. In this case, a study a payback of 5.7 years and a net present value of USD 709,000 can be achieved when the WWTP generates over 2,000,000 m3 of biogas per year and utilizes over 36,000 GJ of natural gas per year.

In this study, the flame-assisted fuel cell (FFC 1) was investigated by using methane/ air flames. The confrontation between FFC temperature and fuel concentration at various conditions was investigated which uncovered the complex behavior of FFCs performance. Variations in fuel/ air equivalence ratio, fuel flow rate and distance between FFC and burner outlet were studied. A critical distance for FFC placement above the burner outlet was uncovered, which has a significant impact on FFC performance. A high power density of 791mW.cm-2 was achieved which is comparable to the dual chamber solid oxide fuel cell (SOFC) and single chamber SOFC. The short-term test exhibited good stability of the FFCs under operation despite the presence of carbon formation on the anode surface.

Currently the role of fuel cells in future power generation is being examined, tested and 7 discussed. However, implementing systems is more difficult because of sealing challenges, slow 8 start-up and complex thermal management and fuel processing. A novel furnace system with a 9 flame-assisted fuel cell is proposed that combines the thermal management and fuel processing 10 systems by utilizing fuel-rich combustion. In addition, the flame-assisted fuel cell furnace is a 11 micro-combined heat and power system, which can produce electricity for homes or businesses, 12 providing resilience during power disruption while still providing heat. A micro-tubular solid 13 oxide fuel cell achieves a significant performance of 430 mW cm-2 operating in a model fuel-rich 14 exhaust stream.

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Direct flame fuel cells (DFFCs) have been investigated as an alternative means of combustion based power generation devices, but current challenges for this technology have included low fuel utilization and efficiency. In order to overcome these obstacles a new micro-tubular flame-assisted fuel cell (mT-FFC) concept is developed in this work and its performance is assessed at different equivalence ratios and temperatures. The concept is based on fuel-rich combustion exhaust, with the combustion equivalence ratio controlled and the exhaust flowing through the fuel cell for complete electrochemical energy conversion. The results were compared to a hydrogen baseline with the same electron potential as the fuel-rich exhaust. The mT-FFC concept offers significant advantages including high fuel utilization and greater performance stability compared to DFFCs.

The performance of yttria-stabilized zirconia (YSZ)–samaria-doped ceria (SDC) dual layer electrolyte anode-supported solid oxide fuel cell (AS-SOFC) was investigated. Tape-casting, lamination, and co-sintering of the NiO–YSZ anode followed by wet powder spraying of the SDC buffer layer and BSCF cathode was proposed for fabrication of these cells as an effective means of reducing the number of sintering stages required. The AS-SOFC showed a significant fuel cell performance of ∼1.9 W cm−2 at 800 °C. The fuel cell performance varies significantly with the sintering temperature of the SDC buffer layer. An optimal buffer layer sintering temperature of 1350 °C occurs due to a balance between the YSZ–SDC contact and densification at low sintering temperature and reactions between YSZ and SDC at high sintering temperatures. At high sintering temperatures, the reactions between YSZ and SDC have a detrimental effect on the fuel cell performance resulting in no power at a sintering temperature of 1500 °C.

Intermediate temperature solid oxide fuel cell Buffer layer Interlayer Anode-supported solid oxide fuel cell a b s t r a c tThe performance of anode-supported solid oxide fuel cells was investigated as the SDC buffer layer thickness was varied between~0.4 mm and~2.3 mm. The thickness of the buffer layer has a significant effect with the peak performance varying in magnitude by a factor of almost three. A peak power density of 1106 mW cm À2 was achieved at 800 C and an optimal SDC buffer layer thickness of~1.5 mm. The performance variation was complex due to a balance between ohmic and polarization losses, triple phase boundary area, pin holes and interfacial reactions between the BSCF þ SDC cathode, SDC buffer layer, and YSZ electrolyte. Understanding this variation is essential in order to compare two fuel cells having a different porous buffer layer thickness.