Brown coal is the cheapest source of fossil fuel for power generation in Australia, but it produces the highest level of greenhouse gases when burned in conventional boilers in power plants. To ensure its viability in the longer term, where climate change is an accepted fact, we should be looking at ways to make coal burning more efficient and reduce our emissions.
Improved efficiency can be accomplished in many different ways, such as overall energy integration in the power plant and/or adopting new technologies. Coal gasification at high temperature and pressure is one of the best routes to more efficient burning.
Advanced technologies such as Integrated Gasification Combined Cycle (IGCC) will enable higher thermal efficiencies - up to 50 per cent in the future - through a combined cycle which uses a gas turbine followed by a steam turbine to generate electricity.
Pre-combustion CO2 capture is highly suitable in plants with new coal burning technologies such as IGCC as they have a concentrated CO2 stream. In the gasification process, coal is brought into contact with air, making a combustible gas of mostly hydrogen and carbon monoxide (known as syngas). Syngas contains a reasonable amount of CO2 and a significant amount of nitrogen from the air used. This gas mixture is the feed gas that was used for the capture plant in this project.
Pre-combustion capture trials at HRL’s research gasifier, Mulgrave
The key objective of this project was to reduce the technical risk and cost of pre-combustion capture for Victorian coal-fired stations with new coal burning technologies employing gasification.
The trials evaluated pre-combustion CO2 capture technologies to identify the most cost-effective for application to coal gasification power-generation technology. This project also allowed CO2CRC to leverage the existing research base of its capture activities in Victoria. The University of Melbourne developed the solvent and membrane aspects while Monash University undertook R&D on adsorption technology.
In more detail, the program:
- Identified and quantified the impact of realistic pre-combustion gas contaminants (H2S, CH4, CO) and water on the performance of each of the separation technologies;
- Identified and quantified the impact of pre-combustion gas temperature and concentration variations on the performance of the separation media and separation processes;
- Optimised process operating parameters;
- Developed engineering solutions at a scale at which confidence can be established for full scale plant design and assessment;
- Assessed the pre-combustion capture process and energy integration options; and
- Reviewed the technical and economic viability of the commercial use of pre-combustion capture for new Victorian brown-coal power stations using the gasification process route.
The capture technologies under evaluation were:
Solvent absorption – the most mature technology and currently the method of choice for CO2 separation in industry globally. Find out more
Membrane separation – a promising stand-alone technology that can also be integrated with solvent systems. Find out more
Pressure swing adsorption – a new technology that captures CO2 using fixed beds of solid material and releases it by pressure changes. Find out more
While the preliminary trials were conducted without a water gas shift and at a lower operating pressure than in a full scale coal gasification power plant, experimental data from the trials combined with numerical modelling enabled an assessment of the separation performance of each technology against commercial plant conditions.
The technology in this project could be subjected to further trials, including:
- Trials at plants which include extra process steps to maximise the CO2 capture. These steps involve further reacting the syngas with water to produce hydrogen and CO2 (a water gas shift reaction or WGS). The CO2 is captured and the hydrogen can be used in a gas turbine or a fuel cell to produce power.
- Trials in a gasification plant where oxygen has been separated from air before being used in the gasifier.