Geoscientist Online

The recent Beijing Olympics highlighted the problem of emissions from China’s industrial powerhouse. Adler DeWind reports on how China is working with BGS scientists to capture the carbon that it currently pumps into the air.

Geoscientist 18.12 December 2008

Before the Olympics began, China started a campaign of "Defending the Blue Sky" – or, improving the dire state of the Chinese capital's air quality. This involved relocating more than 1000 heavy industrial and power-generation plants outside the city. Coal accounted for ~63% of China’s primary energy demand in 2005, and the capital's reliance on this fuel was reduced by gradually introducing natural gas for domestic and industrial use, as well as processed coal with reduced sulphur content.

However, Beijing's progress bucks a larger national trend: China's carbon dioxide emissions from coal-fired power stations will double by 2030, reaching 11.4 Gt . "It should be remembered that per-capita emissions remain below current average OECD levels and are predicted to remain low over the next few decades" says Dr Mike Stephenson Head of Science (Energy) for British Geological Survey (BGS). In 2006 China built 105GW of new power plants1, almost all of which were coal-fired, largely to meet demands for increased industrial output for both internal and export markets and for building materials for the domestic construction industry.

"It is important to minimise emissions when coal is burned to generate electricity, energy demand will continue its dramatic increase with China's growing economy. With carbon capture and storage (CCS) China can fuel economic growth without irreparably harming their environment" agrees Ceri Vincent, also of BGS. "Energy demand is projected to more than double between 2005 and 2030. With carbon capture and storage, China can hopefully have both."

BGS is currently providing additional scientific support to explore the opportunities in selected regions of north-east China. This is part of a three-phase EU funded project to run a full scale demonstration of carbon capture and storage in China by 2020.

BGS scientists, together with others from the UK and EU, are working closely with Chinese colleagues in universities and institutes across China to transfer existing knowledge of CCS - gained in the North Sea - and to develop scientific links that they hope will encourage future Sino-British collaboration in this vital technology.

Says Stephenson: "Carbon dioxide can be either separated from gasified coal to produce hydrogen and CO₂ before combustion (‘pre-combustion capture’) or scrubbed from flue gases (‘post-combustion capture’). It can then be stored in rocks below depths of about 800m (where CO₂ is a dense buoyant fluid), in rocks which have high porosity and permeability and are sealed by overlying impermeable overlying strata. Storage sites include oil and gas fields, deep saline aquifers and unmineable coals."

Currently, three projects - COACH (Cooperation Action within Carbon Capture and Storage China-EU), NZEC (Near Zero Emissions from Coal) and GeoCapacity - are investigating the potential for geological storage of CO₂ in parts of onshore north-east China. Large point sources of CO₂ (over 100 kt/a) are being identified in Hebei, Shandong and Jilin provinces.

Vincent says: "A large number of sources have been catalogued already. The number is increasing year on year. In 2006, the Hebei Province produced 114 Mt of CO₂ per year from 23 large sources. By the end of 2007, 220 Mt of CO₂ was being produced per year from 88 sites!"

A Chinese Government initiative reduce emissions and increase energy efficiency by phasing out small power plants and replacing them with larger, more efficient power stations is underway. Although this increases efficiency, as energy demand grows, so must the emissions.

Potential sites for the geological storage of CO₂ are also being investigated, says Stephenson. "Storage capacity can be categorised as "theoretical" (assuming all the space in a potential storage reservoir can be utilised), "effective" (incorporating site-specific geological constraints), "practical" (accounting for regulatory, economic and legal factors) or "matched" - where a storage site is matched to a single point source." (See figure.)

To date, the theoretical storage for all the suitable oilfields has been calculated as well as effective storage capacity for key large fields in the Huabei oilfield complex (see map). Stephenson says: "Although the Dagang oilfield has a relatively low storage potential in its Tertiary sandstone reservoirs (due to structural and stratigraphical complexity) Tertiary aquifers in the Jiyang Super depression and Jizhong Depression (located centrally in the Bohai Basin) are believed to be more suitable due to thicker sandstone layers."

In some cases a convenient and economically beneficial use of CO₂ is in enhanced oil recovery (EOR). This is being considered in the Huabei, Dagang, Shengli, Jilin and Jiangsu fields, with a number of pilot tests being undertaken. One problem identified early in the projects is that onshore Chinese oilfields have a high density of old wells (there are over 1100 in the Dagang field alone) which may present significant risks to containment is not appropriately abandoned.

An alternative opportunity for CO₂ storage currently being considered is Enhanced Coal Bed Methane recovery (ECBM). When coal seams are formed by compaction of plants, gases like methane form and accumulate in joints and fractures within the seam. If carbon dioxide is pumped into the coal seam it displaces the methane due to its higher relative CO₂ adsorption.

Vincent says: "Injecting CO₂ into coal seams that are too deep and complex to mine enables not only CO₂ storage but also methane recovery – a real win-win". Chinese scientists are currently evaluating coal from the Kailuan coalfield for adsorption of CO₂ and chemical properties, and carrying out basin-wide analyses of the Qinshui basin for CO₂ coal storage and ECBM. Shallow coals are being considered for ECBM, deeper coals for storage

Both Stephenson and Vincent agree that lowering CO₂ emissions in China is vital to the global goal of tackling global climate change. "It is even arguable" says Stephenson "that developing worldwide CO₂ storage initiatives positively requires that China come on board. China is committed to providing a secure energy supply and meeting current and future energy demand. This will require full exploitation of its vast coal resources in electricity generation as cleaner and renewable energy sources are developed worldwide. Thus projects like COACH, NZEC and GeoCapacity, which foster technology transfer, as well as long term scientific links, are very important in the first tentative steps towards achieving lower global emissions."

Further Information

• COACH website http://www.co2-coach.com/
• NZEC website http://www.nzec.info/en/
• GeoCapacity website http://www.geology.cz/geocapacity

References

1. World Energy Outlook 2007 – China and India Insights, International Energy Agency, Paris, 2007.

Acknowledgments

Director of BGS (NERC). IEA Greenhouse Gas R&D Programme (2006) and Tsinghua University for the information on CO2 sources for 2006 and 2007 respectively. China University of Petroleum (Huadong) for photo of conference delegates at Dongying. United States Geological Survey for shapefiles of province and basin information illustrated on map. Oil and gas field information from ‘Energy Map of China 2008’, copyright of The Petroleum Economist Ltd, London. Institut Francais du Petrole (IFP), COACH project lead; IEA Energy and Environment, NZEC project lead; Geological Survey of Denmark and Greenland (GEUS), GeoCapacity project lead.