Low Emission Conversion of Fossil Fuels with Simultaneous or Consecutive Storage of Carbon Dioxide

This thesis evaluates the possibility of using underground coal gasification with a low CO2 footprint. The thesis consists of two parts. In the first part, by using the concept of exergy, a framework was constructed through which the practicality (feasibility) of an energy conversion/extraction method can be systematically evaluated. This framework, based on exergy analysis and cumulative degree of perfection, is described by analyzing a low emission underground coal gasification (UCG) process. For the evaluation of energy conversion processes we introduce a new concept, viz. recovery factor, which is a better indicator of the exergetic viability of a conversion process than the traditionally used efficiency factors. In the second part, various issues related to the aquifer storage of CO2 are studied. Aquifer storage is considered as an option for low emission fossil fuel utilization. Each chapter is summarized as follows: In chapter 2, various options are considered to reduce CO2 emissions when utilizing deep coal by applying UCG, i.e., (1) in combination with carbonation of synthetic minerals (CaO), (2) conventional UCG followed by ex-situ separation of CO2 and (3) upgrading the product gas using naturally occurring minerals (wollastonite). A chemical equilibrium model was used to analyze the effect of the process parameters on product composition and use it for an exergy (useful energy) analysis. The result is presented in terms of theoretical (ideal unit operations), practical (state of the art technology), and zero-emission (applying current CO2 capture and sequestration (CCS) to all sources of CO2 emission) recovery factors. The results show that underground gasification of deep coal can optimally extract 52-68 % of the coal chemical exergy, but zero-emission extraction gives a negative recovery factor, indicating that it is not practical with the current state of the art CCS technology. Using in-situ CaO, which will enhance the H2 production, is theoretically feasible with a recovery factor around 80%, but is not exergetically feasible with the current state of technology, i.e. with a negative practical recovery factor. Ex-situ upgrading of the conventional UCG product gas with wollastonite is exergetically feasible for both practical and zero-emission cases according to the equilibrium model. Slow attainment of chemical equilibrium makes its application questionable. In chapter 3, based on recent successful low-pressure underground coal gasification pilot experiments that use alternating injection of air (oxygen) and steam, a mathematical model is written to evaluate the potential of alternating injection UCG in large scale hydrogen production. This chapter extends an existing steady state model to a transient model that can describe an alternating injection of air and steam for deep thin coal layers. The model includes transient heat conduction, where the produced heat during the air injection stage is stored in the coal and surrounding strata. The stored heat is subsequently used in the endothermic gasification reactions during the steam injection. Comparison of the results with field data show that product composition and temperature oscillation can be predicted with a reasonable accuracy. The stored heat can deliver additional energy that can maintain the gasification during the steam injection period for a limited time. During the steam injection cycle, at low pressure the volumetric flow and the hydrogen content of the product gas are both high, but at higher pressures while the hydrogen composition is still high, the coal conversion rate decreases considerably. The exergy analysis confirms that alternating injection of air/steam describes a practical process for UCG at low pressure. However, injection of a mixture of steam and oxygen results in a practical recovery factor of 50% and produces 0.15 kg CO2 per MJ of exergy, which is higher than the practical recovery factor (40%) of the alternating injection process, which produces 0.12 kg CO2 / MJ of exergy. In the second part of the thesis, two issues related to aquifer storage of CO2 are discussed: injectivity problems due to salt precipitation, and storage capacity and long term storage due to dissolution of CO2 in water. In chapter 4, the negative saturation (NegSat) method, which is a combination of negative flash and multicomponent single/two-phase flow in porous media, is studied. It has been shown to be beneficial in numerical simulations of phase appearance/disappearance for mixtures that consist of volatile components, i.e., components that appear in both liquid and gas phases. The method is extended to a three phase system of CO2 -water-NaCl, in which NaCl appears as a nonvolatile dissolved component (NaCl) and as an immobile precipitated solid phase. The extended method is of practical use to assess carbon dioxide storage options. A detailed thermodynamic analysis of the NegSat method is given and the possibility to extend it to injection in brine aquifers is demonstrated. Precipitation of salt occurs due to evaporation of water into supercritical CO2 . Precipitation decreases the permeability near the injection well forming a dried-out zone. With the ensuing permeability change, the injection pressure needs to be increased to maintain the CO2 injection rate, which requires more compression energy and hence influences the exergetic viability of the carbon dioxide sequestration process.. To address this issue, first a thermodynamic model is optimized to predict the phase behavior of the CO2 -water-NaCl system with reasonable accuracy. Then the NegSat method for two-phase flow is modified to include salt precipitation. The model is solved to analyze the effect of various physical parameters on the injectivity of CO2 . Finally an exergy analysis is performed to quantify the effect of salt precipitation on the compression power requirement for CO2 injection into high pressure-high temperature-high salinity aquifers. Exergetic applicability of carbon capture and sequestration for low emission carbon dioxide fuel consumption, can presently only be achieved if the energy-intensive step of nitrogen-CO2 separation prior to injection can be avoided. In chapter 5, the enhanced mass transfer of CO2 in water for a CO2 saturated layer on top of a water saturated porous medium is studied experimentally and theoretically. Dissolution of carbon dioxide in water has a large effect on the capacity of an aquifer for carbon dioxide storage. Without the dissolution effect the storage capacity of aquifers is low. A high pressure cylinder with a length of 0.5 m and a diameter of 0.15 m is used in pressure decay experiments. The relatively large size of the vessel minimizes the pressure measurement errors that can happen due to temperature fluctuations and small leakages. The experimental results were compared to the theoretical result in terms of onset time of natural convection and rate of mass transfer of CO2 in the convection dominated process. In addition a non-isothermal multicomponent flow model in porous media is solved numerically to study the effect of the heat of dissolution of CO2 in water on the rate of mass transfer of CO2 . The effect of the capillary transition zone on the rate of mass transfer of CO2 is also studied theoretically. The simulation results including the effect of the capillary transition zone show a better agreement with experimental results compared to the simulation result without considering a capillary transition zone. The simulation results also show that the effect of heat of dissolution on the rate of mass transfer is negligible. The overall conclusion is that, for the current state of technology, use of underground coal gasification with a similar carbon foot print as the use of natural gas is not possible. It is to be expected that technological developments will make it possible in the future to use coal with a low carbon footprint.Geoscience & EngineeringCivil Engineering and Geoscience

Effect of Foam on Liquid Phase Mobility in Porous Media

We investigate the validity of the assumption that foam in porous media reduces the mobility of gas phase only and does not impact the liquid-phase mobility. The foam is generated by simultaneous injection of nitrogen gas and a surfactant solution into sandstone cores and its strength is varied by changing surfactant type and concentration. We find, indeed, that the effect of foam on liquid-phase mobility is not pronounced and can be ignored. Our new experimental results and analyses resolve apparent discrepancies in the literature. Previously, some researchers erroneously applied relative permeability relationships measured at small to moderate capillary numbers to foam floods at large capillary number. Our results indicate that the water relative permeability in the absence of surfactant should be measured with the capillary pressure ranging up to values reached during the foam floods. This requires conducting a steady-state gas/water core flood with capillary numbers similar to that of foam floods or measuring the water relative-permeability curve using a centrifuge.Petroleum Engineerin

Experimental And Theoretical Investigation Of Natural Convection In CCS: Onset Time, Mass-Transfer Rate, Capillary Transition Zone, And Heat Of Dissolution

We study the enhanced mass transfer of CO2 in water for a CO2 saturated layer on top of a water saturated porous medium, experimentally and theoretically. A relatively large experimental set-up with a length of 0.5 m and a diameter of 0.15 m is used in pressure decay experiments to minimize the error of pressure measurement due to temperature fluctuations and small leakages. The experimental results were compared to the theoretical result in terms of onset time of natural convection and rate of mass transfer of CO2 in the convection dominated process. In addition, a non-isothermal multicomponent flow model in porous media, is solved numerically to study the effect of the heat of dissolution of CO2 in water on the rate of mass transfer of CO2. The effect of the capillary transition zone on the rate of mass transfer of CO2 is also studied theoretically. The simulation results including the effect of the capillary transition zone show a better agreement with experimental results compared to the simulation result without considering a capillary transition zone. The simulation results also show that the effect of heat of dissolution on the rate of mass transfer is negligibleGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Petroleum Engineerin

Nanoparticle Stabilized Foam in Carbonate and Sandstone Reservoirs

Foam flooding as a mechanism to enhance oil recovery has been intensively studied and is the subject of multiple research groups. However, limited stability of surfactant-generated foam in presence of oil and low chemical stability of surfactants in the high temperature and high salinity of an oil reservoir are among the reasons for foam EOR not being widely applied in the field. Unlike surfactants, nanoparticles, which are shown to be effective in stabilizing bulk foam, are chemically stable in a wide range of physicochemical conditions. Recent studies suggest that synthesized nanoparticles with altered surface properties can aid foam generation and increase foam stability in porous media. In this paper, the focus lies on a silica-based nanoparticle that is available in large quantities and can be processed economically without separate surface treatment, which gives it the potential to become a practical solution in the field. The research is primarily conducted by performing core-flooding experiments under varying conditions to quantitatively assess and compare the potential of the nanoparticle-enhanced foam. Two types of reservoir rocks have been investigated: sandstone and carbonate rocks. It is observed that by adding even low concentrations of nanoparticles to a near-CMC surfactant solution, the foam viscosity considerably increases.Geoscience & EngineeringCivil Engineering and Geoscience

Additively manufactured metallic porous biomaterials based on minimal surfaces: A unique combination of topological, mechanical, and mass transport properties

Porous biomaterials that simultaneously mimic the topological, mechanical, and mass transport properties of bone are in great demand but are rarely found in the literature. In this study, we rationally designed and additively manufactured (AM) porous metallic biomaterials based on four different types of triply periodic minimal surfaces (TPMS) that mimic the properties of bone to an unprecedented level of multi-physics detail. Sixteen different types of porous biomaterials were rationally designed and fabricated using selective laser melting (SLM) from a titanium alloy (Ti-6Al-4V). The topology, quasi-static mechanical properties, fatigue resistance, and permeability of the developed biomaterials were then characterized. In terms of topology, the biomaterials resembled the morphological properties of trabecular bone including mean surface curvatures close to zero. The biomaterials showed a favorable but rare combination of relatively low elastic properties in the range of those observed for trabecular bone and high yield strengths exceeding those reported for cortical bone. This combination allows for simultaneously avoiding stress shielding, while providing ample mechanical support for bone tissue regeneration and osseointegration. Furthermore, as opposed to other AM porous biomaterials developed to date for which the fatigue endurance limit has been found to be ≈20% of their yield (or plateau) stress, some of the biomaterials developed in the current study show extremely high fatigue resistance with endurance limits up to 60% of their yield stress. It was also found that the permeability values measured for the developed biomaterials were in the range of values reported for trabecular bone. In summary, the developed porous metallic biomaterials based on TPMS mimic the topological, mechanical, and physical properties of trabecular bone to a great degree. These properties make them potential candidates to be applied as parts of orthopedic implants and/or as bone-substituting biomaterials.Accepted Author ManuscriptBiomaterials & Tissue Biomechanic

Effect of Permeability on Foam-model Parameters and the Limiting Capillary Pressure

Accurate modelling of foam rheology on the field scale requires detailed understanding of the correlation between the fundamental properties of foam and the scalable parameters of the porous medium. It has been experimentally observed that foam experiences an abrupt coalescence when the capillary pressure in the porous medium approaches a certain value referred to as the “limiting capillary pressure”, Pc*. Current foam models that treat foam texture implicitly mimic this fundamental behaviour with a so-called dry-out function, which contains adjustable parameters like fmdry and epdry (in the STARS foam simulator). Parameter fmdry (called Sw* in other models) represents the water saturation corresponding to the limiting capillary pressure Pc* and epdry determines the abruptness of foam coalescence as a function of water saturation. In this paper, using experimental data, we examine the permeability-dependence of these parameters. We find that the value of fmdry decreases with increasing permeability. We also find that, for the data examined in this paper, the transition from high-quality regime to low-quality regime is more abrupt in lower-permeability rocks. This implies that in high-permeability rocks foam might not collapse abruptly at a single water saturation; instead there is range of water saturation over which foam weakens. In addition, we address the question of whether Pc* is dependent on formation permeability. We estimate Pc* from data for foam mobility in vs. foam quality, and find, as did Khatib et al. (1988), who introduced the limiting capillary pressure concept, that Pc* can vary with permeability. It increases as permeability decreases, but not enough to reverse the trend of increasing foam apparent viscosity as permeability increases.Geoscience & EngineeringCivil Engineering and Geoscience

Effect of salinity and pressure on the rate of mass transfer in aquifer storage of CO2

The growing concern about global warming has increased interest in improving the technology for the geological storage of CO2 in aquifers. One important aspect for aquifer storage is the rate of transfer between the overlying gas layer and the aquifer below. It is generally accepted that density driven natural convection is an important mechanism that enhances the mass Transfer rate.There is a lack of experimental work that study the transfer rate into water saturated porous medium at in-situ conditions, i.e., above critical temperatures and at pressures above 60 bar. Representative natural convection experiments require relatively large volumes (e.g., a diameter 8.5 cm and a length of 23 cm). We studied the transfer rate experimentally for both fresh water and brine (2.5, 5 and 10 w/w %). The experiment uses a high pressure ISCO pump to keep the pressure constant. A log-log plot reveals that the mass transfer rate is proportional to t^0.8, and thus much faster than the predicted by Fick’s law. Moreover, the experiments show that natural convection currents are weakest in highly concentrated brine and strongest in pure water.Geoscience & EngineeringCivil Engineering and Geoscience