12 FUEL CELL
Closing The Loop: Electricity And Heat Production From Syngas Fuel cells for a self-sustaining system
Simulating the system Before the plasma gasifier can be successfully integrated with a gas cleaning system and fuel cells, the entire system must be thoroughly evaluated.
H2 + CO
H2O, CO2, H2, CO and heat Anode
Heat e-
Electrolyte
Faecal matter
O
2-
Cathode
Dryer
Plasma gasification
Depleted oxygen/air and heat
oxygen/air
Gas cleaning unit
Raw syngas Microwave generator
The use of Microwave-assisted plasma gasification requires electric power input, and Solid Oxide Fuel Cells (SOFCs) are excellent devices for electricity production from syngas. The syngas originates from the gasification process using partially dried faecal matter.
smaller power levels and also produce valuable heat. By employing fuel cells, the system can become self-sustaining:
A fuel cell is an electrochemical device that, when fuelled with syngas, can generate electricity in an extremely efficient manner even at
Heat is used for drying human waste and for the gas cleaning.
Electricity is reverted back to the microwave-assisted plasma gasifier.
Solide Oxide Fuel Cell System
Clean syngas Electricity
Therefore, a thermodynamic model has been developed using Cycle-Tempo, an in-house developed software: Stacked: While a single fuel cell can produce 30W, a stack consists of 180 cells and produce 3.8kW.
1.To develop efficient system concepts and to determine the final design parameters like dimensions of the components and operating conditions such as pressures, temperatures and flows. 2. To predict the system performance in various cases. For example, when employing different biomass feedstock, with and without drying, varying oxidant-to-fuel ratio etc. Results demonstrate that a self-sustaining system is feasible.
Contaminant experiments
Proof of the pudding
Fuel cells are sensitive to contaminants in the fuel gas such as H2S, HCl, tars, heavy metals, and other compounds. Exposure to such substances, even in very minimal amounts (ppm-level), can detrimentally affect the performance and significantly decrease the lifespan of the cells.
After designing the system, the final step is to actually construct it! The plasma gasifier is integrated with the gas cleaning unit and the fuel cell stack to provide proof-of-principle for the concept.
To design an effective gas cleaning unit, it is necessary to investigate the exact tolerance limits of SOFCs for the contaminants from faecal matter.
Experiments Tests are being carried out on single cells and anode-symmetric cells: Current-Voltage characteristics for various fuel mixes can be obtained which can be used to analyze the effect of fuel composition on the cell performance.
In order to efficiently control the system and guarantee its safe operation, important variables are monitored: pressures, temperatures, mass flows, and gas composition.
Electrochemical Impedance Spectroscopy provides details about the electrochemical behavior of the anodes or cathodes with different fuels/oxidants and operating conditions. Electrochemical impedance contributions diffusion, reactions etc. are evaluated.
Next steps
from
Extensive contaminant testing in order to define specific SOFC tolerance limits.
Long term testing/demonstration of the integrated system.
Closing the loop; reverting electricity to the gasifier and heat to the dryer and system optimization.
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