Micro-tubular flame-assisted fuel cells running methane

Abstract

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.

Micro-tubular flame-assisted fuel cells

“…Limiting the sealing requirements to one end of the micro-tubular SOFC maintains the advantage of rapid startup for the SOFC while having the SOFC not operate directly within the flame can reduce the thermal stresses on the SOFC surface. Fuel utilization of the syngas as high as 34% at an operating voltage of 0.5 V has been reported in this setup when using methane fuel (Milcarek et al, 2016c). A peak power density of 430 mW.cm -2 has also been achieved with methane fuel, which is comparable to the power densities achieved with hydrogen fuel in many commercial systems (Milcarek et al, 2016d).…”

“…For example, chemical equilibrium analysis of propane combustion in air predicts over 20% H 2 and over 15% CO at an equivalence ratio of 2.4 compared to only around 10% of each for methane combustion at an equivalence ratio of 1.64 (i.e., the upper flammability limit). As a result, fuels with higher upper flammability limits may have advantages in generating higher syngas concentrations, which results in higher power densities and higher electrical efficiencies as observed in previous work (Milcarek et al, 2016a;Milcarek et al, 2016c). However, methane does have a higher H:C ratio compared to these other fuels which provides advantages in generating more H2 compared to CO. CO has the potential to coke on Ni based anodes used in SOFCs which is a challenge for these higher hydrocarbon fuels (Achenbach 1994;Farhad et al, 2010).…”

“…While methane combustion exhaust has been reported previously (Milcarek et al, 2016c), propane is investigated here as another fuel for the mT-FFC. The results of the propane combustion characterization, as described in Section 3.1, are shown in Fig.…”

“…Combustion characterization of methane fuel was reported previously (Milcarek et al, 2016c). The details of the experimental approach taken in that work were also detailed elsewhere (Milcarek et al, 2016b).…”

“…A recent innovation on the DFFC design is to continue to utilize the flame for reforming of hydrocarbons to syngas and as a thermal energy source for the SOFC, while also utilizing a dual chamber configuration with sealing only on one end of a micro-tubular SOFC (mT-SOFC) (Milcarek et al, 2016a;Milcarek et al, 2016b;Milcarek et al, 2016c;Milcarek et al, 2016d). This DFFC operating in a dual chamber configuration has been termed a Flame-assisted Fuel Cell (FFC).…”