• Energy Research

Salt hydrates have promising potential as heat storage materials by use of their hydration/dehydration reaction. These hydration/dehydration reactions are studied in this paper for CuCl2, CuSO4, MgCl2 and MgSO4. During a hydration/dehydration reaction, the salt shrinks and expands as a result of the differences in densities of the phases. As a result, after the first dehydration cycle, the crystal is fractured into a pseudomorphic state that releases the water molecules more easily. The effect of fracturing is larger in case of hydrates with larger volumetric changes. In this study the performance of hydrates during cyclic loading is related to the pore water production and volume variations. On the basis of such data, it is concluded that CuCl2 is the most promising heat storage material.

Salt hydrates have promising potential as heat storage materials by use of their hydration/dehydration reaction. These hydration/dehydration reactions are studied in this paper for CuCl2, CuSO4, MgCl2 and MgSO4. During a hydration/dehydration reaction, the salt shrinks and expands as a result of the differences in densities of the phases. As a result, after the first dehydration cycle, the crystal is fractured into a pseudomorphic state that releases the water molecules more easily. The effect of fracturing is larger in case of hydrates with larger volumetric changes. In this study the performance of hydrates during cyclic loading is related to the pore water production and volume variations. On the basis of such data, it is concluded that CuCl2 is the most promising heat storage material.

The research on moisture transfer characteristics and surface crack development of a single lignite particle (SLP) driven by humidity difference is helpful to achieve a better understanding of the fragmentation characteristics of lignite during the moisture transfer process. This is of great significance to the safe operation of a drying system. The characteristics of moisture transfer within SLP driven by humidity difference were studied in different stages. Six drying equations commonly used in the literature were selected to describe the moisture transfer behavior. The apparent diffusion coefficient (D eff) of moisture in each stage was calculated to compare the driving forces of moisture transfer in different stages. The surface crack rate (CR) was used to quantitatively analyze the fragmentation characteristics of SLP caused by moisture transfer. The results showed that the moisture transfer process of SLP driven by humidity difference can be divided into three stages, and stage I is the main moisture removal stage. The larger the particle size, the longer the stage I, while less moisture is removed in this stage. A logarithmic drying equation best simulates the moisture transfer process of SLP. The larger the particle size, the larger the D eff value in each stage. The driving force of moisture transfer in stage I is the largest, which is the opposite of a thermal drying process. CR for SLP has experienced a rapid increase - stable at the highest value - rapid decrease - stable during the moisture transfer process driven by the humidity difference.

The research on moisture transfer characteristics and surface crack development of a single lignite particle (SLP) driven by humidity difference is helpful to achieve a better understanding of the fragmentation characteristics of lignite during the moisture transfer process. This is of great significance to the safe operation of a drying system. The characteristics of moisture transfer within SLP driven by humidity difference were studied in different stages. Six drying equations commonly used in the literature were selected to describe the moisture transfer behavior. The apparent diffusion coefficient (D eff) of moisture in each stage was calculated to compare the driving forces of moisture transfer in different stages. The surface crack rate (CR) was used to quantitatively analyze the fragmentation characteristics of SLP caused by moisture transfer. The results showed that the moisture transfer process of SLP driven by humidity difference can be divided into three stages, and stage I is the main moisture removal stage. The larger the particle size, the longer the stage I, while less moisture is removed in this stage. A logarithmic drying equation best simulates the moisture transfer process of SLP. The larger the particle size, the larger the D eff value in each stage. The driving force of moisture transfer in stage I is the largest, which is the opposite of a thermal drying process. CR for SLP has experienced a rapid increase - stable at the highest value - rapid decrease - stable during the moisture transfer process driven by the humidity difference.

AbstractStoring carbon dioxide in depleted petroleum reservoirs is a viable strategy for carbon mitigation, but ensuring that the sequestered CO2 remains in the formation is vital to the success of such projects. There is great concern for the development of leakage pathways through annuli between the well cement and the formation or the casing. Predicting the behavior of such potential leakage pathways is critical. Numerical simulations conducted using a reactive transport module match well with experimental studies, but also show the necessity of quantifying the transport and mechanical properties of the leached solid cementitious solids–predominantly silica gel–produced by carbonic acid corrosion of well cement.Bench-top experiments have been performed with the following goals in mind: (1) to investigate the parameter space of relevant corrosion boundary conditions, e.g. pH, CO2 concentration, and calcium ion concentration, (2) to produce samples that can be used to quantify the transport and mechanical properties of acid corroded Class H well cement, and (3) to validate and improve the accuracy of numerical simulations of the reaction of well cement with carbonic acid.Class H cement samples were uniaxially corroded via exposure to a brine of constant composition. Constant composition is ensured by constant renewal of the brine at a rate larger than cement reaction rate. H+, Ca2+ and CO2 total aqueous concentration in the NaCl brine are controlled independently by adding known amounts of NaCl, HCl, CaCl2 and NaHCO3 and by controlling CO2 partial pressure. Microscopic (30X) time-lapse videos were taken of each sample so that corrosion front movements could be accurately measured. These experiments have yielded corrosion front measurements that clearly show that corrosion front advancement is diffusion controlled (i.e., linear as a function of the square root of time). The uniaxial corrosion of these samples has not only allowed for detailed measurements of the corrosion front, but also affords the opportunity to measure the mechanical properties of the corroded samples as a function of depth. The one-dimensional corrosion also allows for measuring the diffusion coefficient of the outer layer of silica gel by low field Nuclear Magnetic Resonance (NMR).Measuring the kinetics under various boundary conditions has validated the modeling results reported by Huet et al.. The measurements of mechanical and transport properties can now be used to improve the predictive power of these simulations by providing much needed information on the exterior layer of corroded Class H well cement. Additionally, these experiments offer experimental validation that the corrosion kinetics are enhanced by the presence of CO2 and open the door to better understanding of the mechanism of, and boundary conditions that might lead to, “pore-plugging” by the corrosion products, which in turn leads to a drastic retardation of the corrosion reaction.

AbstractStoring carbon dioxide in depleted petroleum reservoirs is a viable strategy for carbon mitigation, but ensuring that the sequestered CO2 remains in the formation is vital to the success of such projects. There is great concern for the development of leakage pathways through annuli between the well cement and the formation or the casing. Predicting the behavior of such potential leakage pathways is critical. Numerical simulations conducted using a reactive transport module match well with experimental studies, but also show the necessity of quantifying the transport and mechanical properties of the leached solid cementitious solids–predominantly silica gel–produced by carbonic acid corrosion of well cement.Bench-top experiments have been performed with the following goals in mind: (1) to investigate the parameter space of relevant corrosion boundary conditions, e.g. pH, CO2 concentration, and calcium ion concentration, (2) to produce samples that can be used to quantify the transport and mechanical properties of acid corroded Class H well cement, and (3) to validate and improve the accuracy of numerical simulations of the reaction of well cement with carbonic acid.Class H cement samples were uniaxially corroded via exposure to a brine of constant composition. Constant composition is ensured by constant renewal of the brine at a rate larger than cement reaction rate. H+, Ca2+ and CO2 total aqueous concentration in the NaCl brine are controlled independently by adding known amounts of NaCl, HCl, CaCl2 and NaHCO3 and by controlling CO2 partial pressure. Microscopic (30X) time-lapse videos were taken of each sample so that corrosion front movements could be accurately measured. These experiments have yielded corrosion front measurements that clearly show that corrosion front advancement is diffusion controlled (i.e., linear as a function of the square root of time). The uniaxial corrosion of these samples has not only allowed for detailed measurements of the corrosion front, but also affords the opportunity to measure the mechanical properties of the corroded samples as a function of depth. The one-dimensional corrosion also allows for measuring the diffusion coefficient of the outer layer of silica gel by low field Nuclear Magnetic Resonance (NMR).Measuring the kinetics under various boundary conditions has validated the modeling results reported by Huet et al.. The measurements of mechanical and transport properties can now be used to improve the predictive power of these simulations by providing much needed information on the exterior layer of corroded Class H well cement. Additionally, these experiments offer experimental validation that the corrosion kinetics are enhanced by the presence of CO2 and open the door to better understanding of the mechanism of, and boundary conditions that might lead to, “pore-plugging” by the corrosion products, which in turn leads to a drastic retardation of the corrosion reaction.

For heat/cold storage systems a granular bed of salt hydrates is studied during dehydration/hydration. The water density in these beds are measured with help of NMR. Diffusion based dehydration of a granular bed of Na2SO4·10H2O is shown to be internally limited as larger grains dehydrate faster than smaller grains as result of cooling of the grains. In case of air flow dominated dehydration of Na2SO4·10H2O the supply of dry air was the limiting factor. On the other hand, for rehydration of CuCl2 with air flow through a granular bed, the absorption rate of water of the grains in the grain was the limiting factor and not the airflow. The observed limitations are not general observations for salts during dehydration and hydration, but may be different for other salts.