Carbon Capture and Storage
We are seeking solutions to one of the great international challenges – reducing carbon emissions and their impact on climate change. Over the past decade, the prospect of climate change resulting from anthropogenic CO2 has become a matter of deep and growing public concern. Many believe that the precautionary principle is the appropriate response at this time and there is increasing consensus that the action to mitigate this human induced climate change will require not just reducing anthropogenic CO2 emissions, but more importantly stabilizing the overall concentration of CO2 in the earth’s atmosphere. There are many technology options that can help but it appears that almost all will add cost to the price we pay for energy.
Given the scale of the climate challenge and the need to continue to provide affordable energy in many different cultural, social operational settings, a portfolio of approaches will be required. The best solution will not be the same in each case. It seems that the full portfolio of energy technologies will be required. Yet, one option that has broad potential application is the technology of CO2 capture and geological storage. Capture technology is already in use, but only a small scale. While this technology is proven it needs considerable development to enable scale-up for industrial application and to reduce the cost of what is very expensive technology today.
Howe-Baker is determined to find appropriate measures for design and safety assessment of the CO2 pipelines which are transportation.
CO2 that is captured from power plant and other anthropogenic sources is not pure, and the amount and type of impurities are dependent on the nature of the process and the capture technology used. Currently, there is little published work on transport of CO2 with these impurities, the main effect of which is to change physical properties such as the critical pressure, which can have a dramatic impact on the CO2’s hydraulic behaviour. This in turn may change the operating regime of the pipeline, which may have to be operated at a higher pressure than would be required for pure CO2 in order to maintain it as single-phase supercritical or dense-phase.
The presence of impurities in the CO2 stream will not only have a significant effect on the hydraulic parameters such as pressure and temperature, but also on the density and viscosity of the fluid, depending on the impurities present. Some combinations, particularly if hydrogen or nitrogen are present, cause higher pressure and temperature drops for a given pipeline length than others, which has implications for the distance between compressor stations along the pipeline. The pipeline cost increases with the number of compressor stations which, in any event, are not viable for subsea pipelines. Sudden temperature drops can have potential material implications, such as embrittlement, and can also cause hydrate formation, both of which could damage the pipeline.
The solvent properties of supercritical CO2 are known to be detrimental to the elastomers commonly used in valves, gaskets, coatings and O-rings, used for sealing purposes. At high pressures the supercritical CO2 diffuses into the elastomers and, when the pressure is reduced, blistering and even explosions can occur as the material decompresses. Many of the elastomeric materials currently used in oil and gas pipelines are therefore not suitable for CO2 transportation. Similarly, in-line inspection (ILI) of CO2 pipelines is problematic, as the supercritical CO2 dissolves the non-metallic components of the cleaning and ILI tools – although high-durometer elastomers can be used to reduce the problem, they cannot eliminate it totally.
There are other important material issues that will require consideration in CO2 pipeline design. Ductile fracture propagation may be an issue, and the requirement to consider fracture propagation in CO2 pipelines is included in the federal regulations in the US. For some of the US pipelines, it was concluded that the pipe material did not have sufficient toughness to arrest propagating ductile fractures and therefore crack arrestors were required along these pipelines. This experience highlights the need to define the toughness limits for equivalent pipeline networks, particularly considering the effect of impurities on the decompression behaviour of the gas, to avoid the costly requirement to fit crack arrestors. In the US, the CO2 pipelines were designed-for-purpose. If pipeline re-use is to be adopted in the UK and elsewhere, existing pipelines will have to be assessed extremely carefully bearing all of these factors in mind.
Geological storage, on the other hand, builds on the oil and gas industries’ considerable experience of injecting gas for enhanced oil recovery (EOR) gas storage operations and reservoir management, which are all today successfully managed at scale. Capturing and storage CO2 from the combustion of coal, oil and natural gas could deliver material reductions in greenhouse gas emissions and provide a bridge to a lower carbon energy future.