Fossil fuel, low CO2 too?

June 26, 2006
Can the world continue using fossil fuels and achieve lower carbon dioxide emissions as well?

Can the world continue using fossil fuels and achieve lower carbon dioxide emissions as well? A report from the Organization of Petroleum Exporting Countries contends it can.

Fossil fuels are projected to remain the main source of supply of primary energy until at least the middle of the century. The current contribution of new renewables-wind, solar, geothermal, modern biomass, and small hydro-is limited to about 2% of global power generation, according to a report by the OPEC secretariat entitled Oil Outlook to 2025.

However, more than half of total emissions, according to the Intergovernmental Panel on Climate Change (IPCC), are attributable to power stations and energy-related and industrial activities.

Therefore, the OPEC report sees promise in carbon capture and storage (CCS).

CCS technology

The OPEC report outlines the steps involved in applying CCS technology.

First, CO2 must be captured, most likely from energy-related and industrial activities producing concentrated streams of CO2 under high pressure. The OPEC report identifies three approaches to capture: postcombustion systems, precombustion systems, and oxyfuel combustion. Operating conditions determine the approach.

Technologies similar to those used in postcombustion capture are already in large-scale use for the separation of CO2 from natural gas. Technologies that would be used for precombustion capture are now employed for the large-scale production of hydrogen. Oxyfuel combustion for CO2 capture is currently in the demonstration phase.

After capture, CO2 must be transported to a suitable storage site. This, OPEC finds, poses no technical challenges. Pipelines or ships can carry CO2, which is liquid above a pressure of around 5 bars and a temperature of 30° C.

As for storing CO2, OPEC’s analysis says four options are available: (1) conversion into solid inorganic carbonates using chemical reactions; (2) industrial use, either directly or as feedstock for production of various carbon-containing chemicals; (3) injection into the ocean at depths of more than 1,000 m; or (4) injection into geological formations.

The fourth option has received the most attention. Injection of CO2 in deep geological formations involves many of the same technologies that have been developed in the oil and gas industry and have been in use since the late 1980s (OGJ, Mar. 20, 2006, p. 18).

Three types of geological formations are suitable for storage: unminable coal seams, depleted oil and gas reservoirs, and deep saline aquifers. The OPEC paper says saline aquifers offer the largest potential storage volumes. But for the near term, depleted or nearly depleted oil and gas reservoirs represent the most attractive option because of the possibility of linking CCS to enhanced oil recovery (EOR) or enhanced gas recovery processes.

CO2-based EOR has been used extensively in the Permian basin; in Weyburn field in Canada; at Sleipner field off Norway; and at In Salah field in central Algeria.

Costs, future

The cost-effectiveness of CCS relative to other greenhouse-gas mitigation options will be critical in determining the extent of its deployment, OPEC says. Cost estimates vary widely because of differences among power plants and industrial facilities; types and costs of fuel used; distances, terrains, and quantities involved in CO2 transport; and types and characteristics of the CO2 storage.

OPEC further asserts that limited experience with integrated CCS systems adds to the uncertainty about the performance and cost of future CCS technology. Nevertheless, the IPCC’s CCS report indicates that for new coal or gas-based power plants, the total costs, based on current technology, range from $14/tonne to $91/tonne of CO2 avoided, with a large potential for considerable reductions. Thus, CCS could represent an affordable means of achieving a large part of future emissions reductions.

OPEC says CCS can allow the world to continue to rely on fossil fuels even as it addresses the need to moderate CO2 emissions. Needed now, it says, are large-scale CCS demonstration projects.