The scientists from the China University of Petroleum (East China) and the PipeChina Institute of Science and Technology have offered to use the available oil and gas pipelines to transport carbon dioxide. This approach would accelerate the development of the CO₂ capture and storage projects and significantly reduce their cost.
Transporting carbon dioxide is one of the main challenges facing modern technologies of carbon emission reduction. Gas captured at power plants and industrial facilities must be transported to the storage site or for its further use, most often to the depleted reservoirs. Pipelines are the most efficient and economical method, but their construction requires enormous investment and considerable time. At the same time, a lot of countries, especially China, already have an extensive network of oil and gas pipelines that can be converted for CO₂ transport.
However, it is impossible to just switch old pipes to a new task. There is a serious difference between physical and chemical properties of carbon dioxide and oil and natural gas. Even in the presence of small amounts of water, it causes intense corrosion. In case of leakage, CO₂, being heavier than the air, accumulates in low-lying areas and poses a suffocation hazard to humans and animals. When the pressure drops sharply, the gas instantly cools to –78 °C, turning into dry ice and posing a risk of pipe and equipment destruction.
To assess a pipeline suitability for conversion, the Chinese researchers offer a step-by-step algorithm. First, an operating history and current condition of the pipe are analyzed, including its defects and corrosion centers. Then, CO₂ behavior in this particular system is modeled: the pressure and the temperature differences are calculated, and possibility of the undesirable phase transitions is checked. Special attention is paid to the impact strength and crack propagation resistance of the material as carbon dioxide increases the risk of brittle fracture.
Risk analysis is a separate block. The scientists note that the areas affected by CO₂ leaks are fundamentally different from the ones typical for oil or gas. Non-flammable but suffocating gas requires a revision of a “high-risk area” concept as well as the new rules for installation of shut-off valves and leak control systems.
Economic calculations show that despite higher costs of monitoring and corrosion protection, retrofitting of the available pipelines is on average a quarter cheaper over their entire life cycle than building the new ones.
There are no operational CO₂ pipelines in China yet, but experience has been gained in converting pipelines for other fuel types: oil pipelines were converted to gas usage, coal gas pipelines to natural gas usage, and the pipelines for petroleum products were used for transporting other chemicals.
In addition, there is a wealth of international experience in conversion. In particular, the United States operates the largest network of CO₂ pipelines, some of which are built on the basis of the old gas pipelines. In the UK, the Feeder 10 gas pipeline, almost 280 km long, was converted to transporting CO₂ to an underground storage site. In the Netherlands, the OCAP project converted an old gas pipeline into a carbon dioxide supply channel for greenhouse farming.
