|UPDATE FROM BCIA|
|POSTGRADUATE RESEARCH SCHOLARS|
|Direct Carbon Fuel Cells combine carbon and oxygen to produce energy, and provide the promise of producing highly efficient electricity generation together with a high purity CO2 stream suitable for geological sequestration. It turns out that Victorian brown coal is a highly suitable fuel for such fuel cells – as Adam Rady explains below.|
|Why direct carbon fuel cells love Victorian brown coal|
|By Adam Rady, PhD Candidate at Monash University and CSIRO (Supervisors: Professor Sankar Bhattacharya, Assoc. Prof. Bradley Ladewig, Dr Giddey and Dr Badwal)|
|My PhD project started in 2011 as a collaboration between CSIRO and Monash University, to investigate Victorian brown coal as a viable fuel for DCFC. I started working at Monash University on coal preparation and characterisation.|
|This work was supervised by Prof Bhattacharya, and used Monash’s extensive coal processing and characterisation facilities. I then performed most of the fuel cell testing work at CSIRO, where extensive infrastructure and facilities already existed. |
CSIRO has been developing the direct carbon fuel cell (DCFC) technology since 2008 because of the advantages that direct carbon fuel cells offer over other power generation technologies. In general, fuel cells can efficiently convert the chemical potential in a fuel directly into electrical energy.
DCFC is the only fuel cell capable of operation on a solid fuel, and does so at the highest efficiency of any fuel cell type (>60 per cent total system efficiency), ie. roughly twice that of current coal-fired power stations. In addition, the resulting concentrated CO2 product stream would dramatically reduce the energy penalties associated with CO2 capture and storage (CCS).
|Graphical Abstract from Rady AC, Giddey S, Kulkarni A, Badwal SPS, Bhattacharya S, Ladewig BP. Direct carbon fuel cell operation on brown coal. Appl Energy. 2014;120:56-64.|
|Much of the initial DCFC research by many groups had concentrated on using carbon black as the fuel to establish benchmark and technology feasibility. While carbon black provides a reliable and clean fuel for laboratory-based research and materials development studies, it is not a viable future fuel for the large-scale operation of a stationary power generation system. |
It is therefore necessary to trial readily available ‘real-world’ fuels and understand how their properties affect important parameters of fuel cell operation. Filling this knowledge gap is a primary goal of my project.
Victorian brown coal is a particularly promising fuel for use in DCFCs due to the low ash content and the reactive nature of the coal. Laboratory scale testing of partially charred coals from the Morwell mine has produced exceptional results, out-performing the benchmark carbon black fuel.
|What is it about Victorian brown coal then that DCFCs love so much?|
- Low ash content (but what’s there is the right stuff)
- High Boudouard gasification reactivity
- A surprisingly acceptable electrical conductivity
|The contribution of inorganic matter in Morwell coal, namely Ca, Fe, and Mg, to Boudouard gasification catalysis is well documented. Since CO2 is the primary product of carbon consumption in the cell and is produced at the anode in the presence of the carbon fuel, a reactive char will convert the CO2 to CO in a timely manner. |
This CO can then also be used by the cell as a fuel, generating additional current and CO2, and setting up a cyclic mechanism in the gas phase. The parallel reactions of solid carbon consumption and gaseous CO consumption extend the fuel cell’s performance to higher currents and power output.
Less reactive fuels such as carbon black aren’t able to capitalise on the gas phase reactions of the fuel cell, instead relying on the reaction of solid carbon particles in direct contact with the anode.
A demineralised (acid washed) Morwell char was also produced and tested in the DCFC and performed similarly to the carbon black. The results of this study have been published in Applied Energy (http://dx.doi.org/10.1016/j.apenergy.2014.01.046).
CSIRO has developed the concept of using mixed ion electron conducting (MIEC) fuel electrode (anode) to shift the reaction zone from anode/electrolyte interface to anode/fuel interface specifically to cater for direct solid fuel reactions.
Thus a family of new electrode materials has been developed by CSIRO to produce practical power densities. One of the anode materials that performed well with clean carbon fuels, was found to be unstable with Morwell char, and as a result, new anode materials are now under development.
Work has also been performed at the Australian Synchrotron to investigate the stability of a range of anode materials in the presence of Morwell char, and a new family of materials has been identified for the improved stability of the anode in DCFC environment.
This project is in the write-up phase and experimental work is being finalised. This includes the testing of carbon black doped with common inorganic impurities found in Morwell char to further understand the contribution of these components to cell performance. This study exploring the use of brown coal in a DCFC has resulted in three journal papers, with more to follow.