|Louis J Wibberley|
|with Victorian brown coal|
|By Louis J Wibberley, Leader, Advanced Carbon Power, CSIRO Energy Technology|
|The Direct Injection Carbon Engine (DICE) represents a major step towards a dispatchable power generation technology that has low capital cost, high efficiency, low greenhouse gas emissions and provides quick stop / start / ramp times. BCIA is providing funding to continue the development of this exciting technology – Louis Wibberley provides an update.|
|DICE can be used with any carbon-based fuel source, including both renewable and fossil fuels, and can provide back up for intermittent energy sources, such as solar and wind, or provide peaking power to complement fixed-load power stations. DICE also has the potential to provide a synergistic fit with carbon capture technologies.|
Victorian brown coal has proven to be an ideal fuel source for DICE, in the form of low ash coal-water slurry (a micronised refined carbon or MRC). CSIRO modelling suggests that brown coal MRC-DICE should be capable of fuel cycle efficiencies of 48%–50%. This is equivalent to the performance of the proposed next generation ‘advanced ultra supercritical’ steam boilers, which are expected to be much more expensive than DICE.
As part of its 2013 Funding Round, BCIA is providing partial funding for a joint national ‘DICE Development programme’, led by CSIRO Energy Technology. The joint programme is being undertaken collaboratively by the brown and black coal industries and the Commonwealth through ANLEC R&D, in conjunction with MAN Diesel & Turbo, the world’s largest manufacturer of stationary diesel engines. The broad objectives of the national programme are as follows.
- Develop modified fuel handling and injection equipment to allow successful handling of MRC fuel slurry at small demonstration scale.
- Undertake proof-of-concept trials of both brown and black MRC fuels in a large test engine in Japan.
- Create sufficient data to allow an engine manufacturer to implement an engine development programme.
- Define the specification parameters and initial acceptable ranges for both brown and black coal derived MRC fuels.
|The brown coal-specific aspects of the programme will include preparation and characterisation of a brown coal MRC fuel that will remain stable during transport to Japan, small-scale engine testing to investigate possible fouling issues, investigation of the effects of coal ash components on atomiser wear and cylinder abrasive wear, and development of standardised specifications and testing protocols for MRC fuels.|
While the ash content of Victorian brown coal is typically less than 2%, which is very low by world standards, the DICE application requires an ultra-low ash coal containing less than 1.5% mineral ash. The ash in Victorian brown coal typically has four components.
|Figure 1: DICE modified diesel engine at CSIRO Energy Technology, Newcastle NSW. (Murray McKean. Copyright © 2015 by CSIRO. Reprinted by permission.)|
|1. Coarse, abrasive minerals such as quartz (sand) and feldspar.|
2. Finely-dispersed clay minerals.
3. Cations (e.g. Na, Ca, Mg and Fe) associated with the carboxylic acid groups in the coal structure.
4. Salts (mainly NaCl) dissolved in the in-seam water.
|Figure 2: MRC made from Victorian LRC Yallourn. (Copyright © 2014 by Wibberley and Wonhas)|
|CSIRO has shown that the coarse, abrasive minerals can be effectively removed by milling the coal to ultra-fine sizes followed by size-density separation using conventional spirals technology. A large proportion of the ionic species can be removed during hydrothermal treatment (HTD) of the coal, which is essential for producing high quality brown coal MRC. Following such treatment, the main residual ash components are sodium and calcium ions.|
Both sodium and calcium are known to cause problems of slag and ash fouling in existing brown coal pulverised fuel boilers. Since the temperature and pressure cycling in a diesel engine is quite different to the temperature profile in a conventional boiler, it was uncertain whether ash fouling is likely to be a problem for brown coal MRC-DICE. This is potentially a risk for the proposed demonstration-scale engine test in Japan.
In order to address this risk, CSIRO recently completed a test of engine grade brown coal fuel in a small 8 kW laboratory diesel engine. The test was designed to encourage engine fouling, by using brown coal briquettes containing 1.6% ash for the fuel, with a coarse particle size, operating in a small engine running at higher-than-normal combustion temperature.
|Despite these unfavourable conditions, the engine operation was stable over the 12-hour trial, exhibiting good fuel ignition and burnout. There were no carbonaceous deposits in the combustion chamber and no signs of adverse ash fouling.|
This laboratory engine test, while preliminary, is a very encouraging result for brown coal MRC and has served to de-risk the proposed engine trial in Japan. The long- term potential for brown coal ash fouling in DICE remains uncertain, but this can only be properly investigated through much longer duration tests (thousands of hours) in a larger engine.
Successful completion of the DICE Development programme will confirm the technical feasibility and inform our understanding of the commercial viability of DICE, which has great promise as a low-emission power generation technology.