Geomechanical Aspects of CO2/H2 Storage in Salt Caverns
Storing hydrogen and carbon dioxide underground seems an interesting idea. Underground storage capacity is usually much larger than surface storage capacity, permitting one to store more materials, and structures are far more secure and resistant to natural disasters compared to surface storage. Among all methods of storage, salt cavern storage is preferable if a suitable salt formation is available because it is relatively easy to be constructed securely for a long period of time. The challenging aspects, however, are the geomechanical and environmental concerns. In geomechanical design, salt creep and system integrity should be addressed fully, for both short and long term, and for environmental concerns, brine management during cavern construction and operation needs to be pre-planned.
In this study, two case histories were presented: Lotsberg Salt for CO2 storage and Tuz Golou site for hydrogen, after briefly reviewing CO2 and H2 physical properties. In both historical cases, geographical and geological data were presented, and for the Lotsberg salt, drilling and completion programs were described as well. Additionally, in the Lotsberg Salt, the creep model and the compressibility of the internal fluid, as well as appropriate mathematical relationships between geomechanical parameters, were explained. Similarly, for Tuz Golou site, the salt creep model and the integrity of the cavern for three different shapes was addressed.
To compare creep rate, volume change rate, and pressure rate in a cavern with two different fluids (CO2 and H2), the volume and creep change rate equations were linked together. It was found that, having some assumptions, creep rate, and volume loss rate of a cavern is independent of gas type; however, the cavern pressurization rate change is a function of fluid compressibility.
Geomechanical Model of CAES Salt Caverns in Ontario and Alberta
Around the globe, the demand for energy storage is gaining momentum and organizations are looking for methods to store grid scale energy (>100 MW). Energy storage can provide benefits from arbitrage, load levelling, peak shaving, curtailment or reduction of baseload power, CO2 reduction, and renewable energy integration. One of the promising and cutting edge technologies to store grid scale energy is through compressed air energy storage (CAES) in salt caverns. For storing compressed air, salt caverns offer tremendous benefits over on-the-ground storage options in terms of smaller surface footprint, relatively less expensive construction and maintenance, and the fact that salt caverns have proved their ability as underground storage vessels by storing hydrocarbons, waste products, and CO2 in many projects around the world. Involvement of deep underground salt caverns requires designing a comprehensive geomechanical model before starting the project. A geomechanical model includes steps from the pre-approval stage of the project to the commencement of the operations. The four major sections of the geomechanical model for CAES project are: geology, data collection and investigation, detailed geomechanics including geomechanical issues, and monitoring.
In this presentation, Jai Duhan reviewed the geomechanical model of the CAES projects for Ontario and Alberta.
Compressed Air Energy Storage: Creating a Design Framework
Compressed air energy storage (CAES) is a utility scale commercial technology that is used to store energy over medium to long periods of time. Existing CAES projects have demonstrated its applicability to a wide array of grid management applications. Unlike its primary competitor, pumped hydro storage, CAES utilizes mechanical turbomachinery to compress and expand air into and out of an underground cavity in order to generate and store electrical energy for the grid. However, the design and operation of these facilities requires the integration of efforts between multidisciplinary teams of electrical, mechanical, and geotechnical engineers, as well as none engineering professions.
The design of complex, large-scale energy projects requires careful planning and management to carry the project through to successful implementation. While coordination is necessary for project design, engineers involved in large-scale infrastructure projects in today’s society must also consider the impacts to the triple-bottom-line (society, the economy, and the environment). In order to drive a CAES project in Canada to success, the creation and use of a comprehensive design framework is advisable to help manage the complexities. Fraser introduced and discussed the engineering systems in a CAES project, the interdependencies of these systems, and some of the major design decisions to be made within the context of the triple-bottom-line.
Stability of the Cavern Roof
Storage in salt caverns has become an interesting topic in recent years. In order to analyze the possibility of gas/air injection into a salt cavern, the stability of the immediate roof layer is a crucial factor. Thus, the mechanical response of the roof layer should be investigated against different modes of failure, such as snap through, crushing and sliding at the abutments. Due to various joint sets in a rockmass, conventional beam theories cannot model all modes of failures. Researchers have developed "Voussoir Beam" theory to analyze the stability of the excavation's immediate roof layer. One could assess the stability by investigating factors of safety against failures through parametric analysis. Also, a wide range of spans to thickness ratio could be considered for the roof layer. Final results can be applied for a preliminary assessment of the roof stability of a salt cavern.
Thermodynamics of Compressed Air Energy Storage
Today, clean-energy methods and businesses are not just a trend but an entire industry. All around the world companies, governments, and education institutions are investing time, money, and human resources to perfect the production, use, and commercialization of cleaner energy. At the same time, current power generation methods are searching for ways to improve their costs and reduce production difficulties. Compressed Air Energy Storage (CAES) is a potential alternative for improving clean-energy production and ancillary services. In a CAES system, various processes transform the energy, which leads to loses, gains, and different efficiencies. Thermodynamics is the branch of physics that studies energy; this presentation explained what happens with the energy in a CAES system component by component.
Study of Electrical Grid Profile & Behavior and its Impact on Design and Operation of CAES
Decarbonization of the electrical grid is an essential part of the global movement toward mitigating the causes of climate change. In order to achieve this, the grid of future will have to be able to integrate energy generated from multiple renewable sources, with the majority coming from intermittent sources such as wind and solar. This requires a much higher operational flexibility by the grid while maintaining the same service quality and stability. In such an operating environment, Electrical Energy Storage (EES) technologies are essential for stable operation of the electrical grid. Compressed Air Energy Storage (CAES) is a promising EES technology that if designed right, can provide an extensive amount of ancillary and arbitrage services that are required by the grid for stable operation.
The intent of this study was to show how the electrical grid profile impacts the basic operation parameters (criteria) for designing the CAES system. This includes an analysis of hourly and annual supply and demand profile of Ontario grid (based on data obtained from IESO), to determine, capacity requirement, number of charge and discharge cycles, charge and discharge rates and duration and how they can impact the CAES system.
Economic Valuation of Grid-scale Storage Technologies: The Case of Underground Compressed Air Energy Storage
Compressed Air Energy Storage (CAES) is a mature energy storage technology that has already been used for decades. Compared with emerging storage technologies such as Lithium Ion batteries, flow batteries and flywheels, CAES offers unique advantages to support large-scale power applications (100-1000 MW) at relatively low Capital, and Operation and Maintenance (O&M) costs per unit energy. In order to capture techno-economic benefits of CAES for grid support services and renewable integrations, a detailed cost-benefit analysis is required.
The primary objective of this presentation was to provide a critical review of existing economic models that have been developed and applied to Salt Caverns CAES systems and other grid-scale storage systems. The economic value models are mainly driven from production electricity models. A suitable cost-benefit methodology should be able to predict economics of CAES systems for various gird services and under different electricity market structures in form of internal Rate of Return (IRR), cash flow projection, Net Present Value (NPV), and payback time. Balance of System and cost of installation, O&M, and taxes, as well as grid service options are generally included in the economic model as input scenarios.