Liza Anthonisz, ZeroGen, Australia
While clean coal technologies (CCTs) have been developed over the past 30 years or so to lessen the environmental impact of coal through reducing emissions of particulates, SO2, NOx and mercury, the technology focus has now shifted to the development and deployment of low and near-zero greenhouse gas (GHG) emission CCTs, such as carbon capture and storage (CCS). Endorsed by G8 leaders, the International Energy Agency (IEA), the Intergovernmental Panel on Climate Change (IPCC) and The Stern Review, CCS has been identified as the foundation on which the success of future deployment of contemporary CCTs is contingent.
CCS is a three-step process that involves (1) carbon dioxide (CO2) capture from power plants, industrial sources or natural gas wells with high CO2 content; (2) transportation, often via pipeline or tankers, to the storage site; and (3) geological storage in deep underground saline reservoirs, depleted oil or gas fields, unmineable coal seams, or enhanced oil and gas recovery sites. Capture is possible before combustion (decarbonization of fossil fuels) or after combustion (capture from flue gas) using different processes.
While the potential for CCS to play a key role in global efforts to reduce GHG from coal-based electricity generation is high, there are still barriers to the technology’s deployment that need to be overcome. The technology remains costly, with more investment and substantial increases in global research, design and development budgets necessary.
Demonstration of commercial operation of the technology and the safe and permanent storage of CO2 must be proven. Regulatory frameworks (i.e. liability, licensing, royalties) are required to provide confidence to encourage private investment and public acceptance, and emission mitigation mechanisms such as emission trading schemes must include CCS.
While the individual component technologies for CCS exist, system integration and commercial demonstration are required if the technology is to play a major role in future GHG reduction efforts. It is here that the portfolio of new and ongoing demonstration projects, including the Australian ZeroGen project, come into play.
The ZeroGen project
ZeroGen Pty Ltd (ZeroGen) is charged with delivering a staged programme designed to accelerate the deployment of CCTs, specifically integrated gasification combined-cycle (IGCC) with CCS. While these individual technology components are in use, their integration has not yet been achieved anywhere in the world. As a result, practical demonstration is required to improve availability and reduce costs before the technology can be commercially deployed in electricity markets in Australia and globally.
ZeroGen’s proposed facilities will be near the existing Stanwell power station in Central Queensland
ZeroGen’s objective is to address the integration risks for IGCC with CCS through full demonstration of the technology. The project has adopted a two-stage deployment approach that will see it develop a demonstration-scale IGCC plant with CCS by 2012, and a large-scale plant by 2017. Following the re-structure of the FutureGen project, these timelines have now placed ZeroGen as the leading project worldwide in the development of IGCC with CCS for low-emission baseload power generation.
Stage One of the project will develop an 80 MW net IGCC facility adjacent to the existing conventional coal fired Stanwell power station near Rockhampton in Central Queensland, Australia. Up to 75 per cent of the CO2 will be captured from site and transported approximately 220 km west for injection and storage in deep underground saline reservoirs in the Northern Denison Trough.
Coal will be sourced from local Queensland supply using existing rail infrastructure to supply to the plant, and the facility’s proximity to Stanwell power station will facilitate the use of common infrastructure, including coal handling.
Stage Two of the project will take place concurrently with Stage One and develop a 300 MW net IGCC plant with CCS capable of capturing up to 90 per cent of CO2 for full sequestration. Its location will be determined in a feasibility study that will take into account variables such as coal and water supplies, access to the electricity transmission grid and appropriate CO2 storage sites.
Costs for Stage One of the project are still being finalized as part of the feasibility study but are expected to come in at around A$1.7 billion ($1.6 billion). Funding for the feasibility study is currently being provided by the state government and the Australian coal industry through its low-emissions technology fund. ZeroGen is also in positive negotiations with various equity investors, including Shell Global Solutions.
Artist’s impression of proposed Zerogen power station site
Costs for Stage Two will be investigated in the feasibility study but are expected to come in at around A$2.35 billion (excluding CCS).
The two-stage strategy of the ZeroGen project will allow it to generate contemporary lessons through the design, construction and operation of the technology at demonstration-scale in Stage One, which will guide the concurrent development of the large-scale plant in Stage Two. By integrating the technologies into one low-emission technology package, the project will reduce risks and provide investment confidence in the technology, helping stimulate accelerated deployment of the technology worldwide as mainstream energy infrastructure.
IGCC for carbon capture
The project will further develop IGCC technology utilizing the process of coal gasification with combined-cycle gas turbine (CCGT), a gas turbine with a heat recovery steam generator adapted to use high-hydrogen (h2) syngas as a fuel.
Coal gasification has its origins in the chemical industries, with the technology very different from conventional pulverized coal fired generating plants. Whereas IGCC plants have previously been developed in the interests of controlling oxides of sulphur, they were not aimed at CO2 capture. Consequently, they have not been required to shift carbon monoxide (CO) to CO2 to allow the removal of CO2 prior to combustion.
Schematic of the proposed CCS project
The gasifier being developed for the ZeroGen project will combine coal, limestone, oxygen and steam under pressure. These will undergo a chemical change to produce synthesis gas (syngas), comprised of mainly CO and h2. The syngas will then be cooled and cleaned to remove particulate matter and other pollutants.
The syngas stream produced in the gasifier will undergo a shift conversion in which CO in the presence of steam is catalytically converted to h2 and CO2. The CO2 will be separated from the shifted syngas, producing a clean, low-carbon, high-h2 fuel which is sent to the CCGT to produce power.
The separated CO2 stream will then be dehydrated and compressed to a supercritical state in the CO2 compressor for transportation and partial sequestration. The CO2 separation process also removes sulphur compounds as a separate stream, allowing these compounds to be converted to a valuable high-purity sulphuric acid by-product.
Sulphur removal and recovery will provide a sulphuric acid by-product for sale to meet local demand. Australia is a net importer of sulphuric acid, and in the larger picture of commercial roll-out, this operational by-product has potential to contribute positively to Australia’s balance of trade. Due to demand in the central Queensland region, there is a specific benefit of proximity to market with the proposed location of the demonstration plant.
The incorporation of the CCGT based on demonstrating the use of a 6F turbine running on high-h2 syngas in the demonstration-scale Stage One facility will significantly reduce development risks associated with scaling the technology up to a large-scale facility in Stage Two that will utilize a 9F turbine. The use of high-h2 syngas incorporates the technical challenge of additional diluent nitrogen in the gas turbine, and this calls for the review of material flows when compared with IGCC (without CCS), especially with respect to air separation unit demands.
Water management is also a large topic for design considerations for the facility. To reduce water requirements, the judicious use of air cooling combined with wet surface air cooling technology is proposed for heat rejection instead of conventional cooling towers.
IGCC has the advantage over other developing coal-based low-emission technologies of being relatively advanced in development. Compared with other technologies such as post-combustion capture, IGCC (using pre-combustion capture technology) with CCS provides a pathway to low-cost capture of CO2 due to its highly concentrated and high-pressure pre-combustion stream, and is therefore regarded by ZeroGen as the most promising option for further development. Furthermore, IGCC has significantly lower SOx, NOx, mercury and other emissions compared with conventional coal-based power plants, thus having further beneficial environmental impacts.
IGCC technology also has the added attraction of moving society towards a future h2 economy. h2 can be used as a transport fuel through fuel cells and potentially provide a feed stock for the manufacture of other energy products and chemicals based on coal as the feedstock. The potential to use coal as a large-scale source of h2 would constitute the first step on the path towards an h2 economy, with the possibility of it leading to further reductions in fossil fuel carbon releases beyond the electricity power sector.
CO2 storage programme
The geosequestration component of Stage One of the ZeroGen project is investigating the transportation and injection of CO2 for permanent and safe storage in deep saline reservoirs in the Northern Denison Trough, an on-shore sedimentary basin approximately 220 km west of the IGCC facility.
ZeroGen has been conducting a drilling investigation programme since June 2006 to understand the local geology of the Northern Denison Trough and confirm its ability to safely and securely store CO2. In mid-2007, ZeroGen announced positive results for the first stage of its drilling programme, confirming the suitability of the geology to safely store CO2. The project is now well into the second stage of its drilling programme, aimed at identifying specific reservoirs with sufficient CO2 storage capacity.
Underground storage of carbon dioxide
Five wells have been drilled up to depths of 1.5 km. ZeroGen is also preparing for a test injection of CO2 into the reservoirs to allow it to carry out a series of further studies, which will include CO2 monitoring and verification techniques, and injection optimization.
The CO2 transportation mode being investigated in the feasibility study is a road tanker. While the project was originally investigating a pipeline, tankers are now being investigated due to the flexibility that this method of transport offers for future studies in proving sequestration sites as part of a state-wide programme to prove up sequestration reservoirs.
Timelines for the project’s development currently place it in a leading position globally in its efforts to develop IGCC with CCS technology. The feasibility study for Stage One is due to be completed by late 2009, and assuming a positive outcome, construction of the plant will begin in 2010. Construction is intended to be completed by late 2012, with the plant becoming operational shortly thereafter.
The project’s momentum has further been buoyed following endorsements from key national and international stakeholders, including the Australian coal industry, the World Coal Institute, Electric Research Power Industry, CFMEU (Australia’s largest union for the mining industry) and, recently, the Australian arm of the global environmental organization WWF.
If the project sticks to its development schedule, ZeroGen will develop and deploy the world’s first IGCC with CCS demonstration plant by 2012 and one of the world’s first large-scale plants by 2017, consequently having a significant affect on the technology’s commercialization path in Australia and around the world.