natural gas recovery from hydrate compounds using co2 replacement strategies experimental study on thermal stimulation

Abstract CH4 hydrates could represent a sustainable energy source by coupling their extraction to a CO2 replacement process. This permits a permanent CO2 storage in a solid phase and the reduction of the seabed modification due to the CH4 extraction. Promising methodologies for CO2 replacement are depressurization, thermal stimulation (or a combination of both), or the use of chemical inhibitors. We have taken into account thermal stimulation. The CH4 hydrates were formed with a pore saturation of 10%, whereas different concentration of gaseous CO2 were fluxed inside the reactor. In a first set of experiments, the CO2 concentration was fixed at values never higher than 15%, while in a second set the gaseous CO2/CH4 ratio was inverted. Two tests for each condition were performed. In all tests, the temperature was increased at the end, to improve the replacement process. Results demonstrated that the CO2 fluxed leads to hydrates formation and, at the same time, hinder the CH4 hydrates dissociation. Two parameters were evaluated: i) the ratio between the stored CO2 and the amount of CO2 injected (ηcapture), ii) the ratio between both CO2 and CH4 hydrates moles after the replacement process, and the CH4 hydrates moles before the replacement (ηentrapped). The assumed ηcapture value are 0.42 and 0.44 in the first conditions, and 0.27 and 0.28 in the second one. By contrast, the second parameter shows an opposite behavior, being the two values 0.13 for the first conditions and 0.27 and 0.74 respectively for the second ones. This could be explained by the fact that injection of higher quantity of CO2 produces a greater thickness of CO2 hydrates in the external parts of pores, which prevent the CH4 to flowin

The use of sodium chloride as strategy for improving CO2/CH4 replacement in natural gas hydrates promoted with depressurization methods

AbstractNatural gas hydrates represent a valid opportunity in terms of energy supplying, carbon dioxide permanent storage and climate change contrast. Research is more and more involved in performing CO2 replacement competitive strategies. In this context, the inhibitor effect of sodium chloride on hydrate formation and stability needs to be investigated in depth. The present work analyses how NaCl intervenes on CO2 hydrate formation, comparing results with the same typology of tests carried out with methane, in order to highlight the influence that salt produced on hydrate equilibrium conditions and possibilities which arise from here for improving the replacement process efficiency. Sodium chloride influence was then tested on five CO2/CH4 replacement tests, carried out via depressurization. In relation with the same typology of tests, realised in pure demineralised water and available elsewhere in literature, three main differences were found. Before the replacement phase, CH4 hydrate formation was particularly contained; moles of methane involved were in the range 0.059–0.103 mol. On the contrary, carbon dioxide moles entrapped into water cages were 0.085–0.206 mol or a significantly higher quantity. That may be justified by the greater presence of space and free water due to the lower CH4 hydrate formation, which led to a more massive new hydrate structure formation. Moreover, only a small part of methane moles remained entrapped into hydrates after the replacement phase (in the range of 0.023–0.042 mol), proving that, in presence of sodium chloride, CO2/CH4 exchange interested the greater part of hydrates. Thus, the possibility to conclude that sodium chloride presence during the CO2 replacement process provided positive and encouraging results in terms of methane recovery, carbon dioxide permanent storage and, consequently, replacement process efficiency

Hydrate formation as a method for natural gas separation into single compounds: a brief analysis of the process potential

AbstractIn both natural gas and petroleum reservoirs, the extracted gas is not only composed of methane: a variable and significant quantity of other compounds, such as different hydrocarbons (ethane, butane, pentane, propane, etc.), inert gas (nitrogen), and toxic and corrosive molecules (i.e., carbon dioxide and hydrogen sulfide), are present. In order to reach commercial specifications, natural gas has to be treated, in particular for reaching the minimum gross calorific value required and decreasing CO2 and H2S presence under the respective tolerance values. To do this, several different treatments are commonly applied, like inlet separation, sweetening, mercury removal, dehydration, liquid recovery, and, finally, compression for its transportation. Considering the growing demand and the necessity of exploiting also lower quality natural gas reservoirs, in the present paper, an original solution, for performing a gas treatment, is proposed and analyzed. It consists of promoting hydrates formation for both different compounds separation and gas storage. The greatest part of chemicals commonly present in natural gas is capable to form hydrates, but at different thermodynamic conditions than others. Parameters such as the typology of stored compound and the formation process efficiency are mainly related to partial pressure of each element. Here, the present strategy has been explored and the results achievable were shown. In particular, different possible natural gas compositions were taken into account and specifications required for gas commercialization were considered target of the process. Results led to different possibilities of raw gas treatment: in some cases, gas separation led to contemporary CH4 storage into hydrate structures, while, in the presence of different mixture compositions, contaminants were trapped into water cages and methane (and, eventually, other hydrocarbon compounds) remained in the gas phase

Experimental investigation on CO2methanation process for solar energy storage compared to CO2-based methanol synthesis

The utilization of the captured CO2 as a carbon source for the production of energy storage media offers a technological solution for overcoming crucial issues in current energy systems. Solar energy production generally does not match with energy demand because of its intermittent and non-programmable nature, entailing the adoption of storage technologies. Hydrogen constitutes a chemical storage for renewable electricity if it is produced by water electrolysis and is also the key reactant for CO2 methanation (Sabatier reaction). The utilization of CO2 as a feedstock for producing methane contributes to alleviate global climate changes and sequestration related problems. The produced methane is a carbon neutral gas that fits into existing infrastructure and allows issues related to the aforementioned intermittency and non-programmability of solar energy to be overcome. In this paper, an experimental apparatus, composed of an electrolyzer and a tubular fixed bed reactor, is built and used to produce methane via Sabatier reaction. The objective of the experimental campaign is the evaluation of the process performance and a comparison with other CO2 valorization paths such as methanol production. The investigated pressure range was 2–20 bar, obtaining a methane volume fraction in outlet gaseous mixture of 64.75% at 8 bar and 97.24% at 20 bar, with conversion efficiencies of, respectively, 84.64% and 99.06%. The methanol and methane processes were compared on the basis of an energy parameter defined as the spent energy/stored energy. It is higher for the methanol process (0.45), with respect to the methane production process (0.41–0.43), which has a higher energy storage capability

Gas Hydrates Formation for High – Efficiency Waste Water Treatment: Experimental Removal of NH4+ from Water via CO2 Hydrates Formation

Waste water treatment is an essential and mandatory step for most of the industrial processes involving water. It has been widely proved that the overconsumption of this source, together with the exponential growth of anthropogenic damaging processed, lowered the quality of groundwater and, more in general, water resources, at an alarming pace. The removal of salts, ions dissolved in water and other effluents, can be carried out through several methods. Membrane separation, evaporation and crystallization are the most applied for water recovery, while membrane, chemical precipitation, adsorption, ion exchange and freezing/thawing are the most effective techniques for heavy metal ion solutions. When applying these procedures, some critical aspects must be considered, mainly associated to removal efficiency, costs, availability and non-toxicity of the raw materials, environmental concerning and other. In this context, gas hydrates can be considered an alternative solution for water treatment, capable to overcome all the critical issues related to the traditional strategies. In particular, the formation of gas hydrates for ion removal from waste water, was proved to reach extremely high efficiencies; moreover, the removal efficiency was found to be proportional to the size of ions and to decrease with their charge. Based on these experimental considerations, this study deals with preliminary research on the removal of NH4+ from water. This species consists of one of the most affecting pollutants in bio – refineries and its removal is often energy intensive, with consequent high costs. Experiments were carried out in a lab – scale apparatus, where water was initially threated with ammonium chloride at specific concentration. Carbon dioxide was finally chosen for the formation of hydrates

Definition of Probability That Energy Production Differs from Demand, a Statistical Approach

Starting from the average trend of energy demand and energy production related to a specific user, the goal is to produce an immediate estimate, as close as possible to the true value (clearly achievable only through a precise and punctual measurement), of the difference existing between these two values, in order to "a priori" understand whether an energy production surplus should be expected, or the opposite trend will occur. If energy produced exceeds the request, two solutions will be possible. An accumulation system can be provided, that allows to avoid taking energy from the grid whenever the trend reserves and the demand exceeds the production. The second solution consists in directly introduce the whole surplus of energy produced in the electricity grid. Similarly, even if the energy required exceeds the amount of energy produced, two different solutions can be envisaged. In both cases, it will be necessary to take energy from the electricity grid. An accumulation system could be created, sized on the maximum difference between production and energy demand, evaluated when the production exceeds the request (if the production never exceeds the request, it would not make sense to talk about accumulation) or, even in this case, a direct exchange might be promoted, both incoming and outgoing, with the electricity grid. Topic of the present paper is to not reasoning any more in terms of energy performances as a function of time but, on the contrary, determine the probability that the difference existing between production and demand assumes a certain value and, based on this, estimate the amount of energy to be stored and/or exchange with the grid

Thermodynamic assessment and microscale Raman spectroscopy of binary CO2/CH4 hydrates produced during replacement applications in natural reservoirs

The present research deals with the micro – scale characterization of sI hydrates containing a binary mixture of methane and carbon dioxide. The application of replacement strategies in natural hydrate reservoirs, always leads to the formation of “mixed” hydrates, whose mechanical and chemical properties are different from those of pure CH4 and CO2 hydrates. As a function of the technique used for the process and due to the variability of the systems, a wide range of different compositions and morphologies can be obtained and the current literature must be expanded, in order to achieve a wide and accurate experimental database of CO2/CH4 hydrate properties. In this work, binary CO2/CH4 hydrates binary CO2/CH4 hydrates were produced in a small – scale reactor and then supercooled, in order to favour their extraction from the reactor and their stability at environmental conditions for a certain period of time. The gas hydrates, prepared with CO2 hydrates of pure water and with CH4 and CO2 mixtures, also in the presence of specific sands, were ex situ analysed by the use Raman-spectroscopy that confirmed the gas uptake in the hydrate structures by identification of the fingerprint of CH4 and CO2 occupancy in the hydrates. The characteristic of water inside the gas hydrates and the interaction between the host molecules and the lattice of water molecules was clarified. The different gas hydrates, analysed by Field Emission Scanning Electron Microscopy instrument equipped with “Coolstage head” under high vacuum condition, differed in morphology and surface features. The analysis of water Raman spectra of the different GHs permitted to describe the relation between symmetric and asymmetric OHs bands, but also provided information about the characteristics of water inside the different GHs, showing that the least ordered water structure was that of GHs containing sand, while the most ordered one was present on binary CO2/CH4 hydrates

May sediments affect the inhibiting properties of NaCl on CH4 and CO2 hydrates formation? an experimental report.

The equilibria of methane and carbon dioxide clathrate hydrates were measured in presence of a pure-quartz porous sand, with and without NaCl. Two different salt concentrations were tested: 0.030 and 0.037 wt%. Results were compared with phase equilibrium data already present in literature for these species. Despite salt, the porous medium was found to promote the process, mainly for the increased surface/volume ratio and for the improved heat transfer. In presence of salt, sand affected the process differently as a function of temperature: at values higher than 3 – 5 °C, it promoted the process, while for values lower than this range, but still greater than the ice-point, it acted as an inhibitor. However, these results can be considered true only for temperatures above the ice point. Due to similarity of ice water with clathrate hydrates, Raman microscale measurements were performed to gather information about the influence of sediments, salt, and temperature on OH-stretching vibrations of water. The obtained results allowed to clarify how the addition of NaCl, and or sediments to liquid water, under different temperature conditions (15 °C and −15 °C), influenced the water hydrogen bonds. Specifically, the changes of OH-stretching vibrations, when correlated with the NaCl concentrations, demonstrated that the presence of sediments partially inhibited the salt effects in the ice water probably due to hydrophilic interactions with the silanol groups of sediments. SEM measurements showed morphological information on sediments and on ice in different experimental conditions

CIRCULAR ECONOMY APPLIED TO METHANE PRODUCTION FROM NATURAL GAS HYDRATE RESERVOIRS: POTENTIALITIES OF RESIDUAL DUST COMING FROM STEEL PLANTS

Natural gas hydrate represents one of the most promising solutions to answer to the constantly increasing energy demand; in addition, the possibility of recover methane via carbon dioxide injection, with a theoretical exchange ratio equal to 1, makes it a potential carbon neutral energy source. Among them, energetical costs associated to practical operations in marine deposits. The use of chemical inhibitors and or promoters to improve the exchange process is gaining increasing interest and researchers are mainly focused on finding less environmental unfriendly additives and on reducing their costs. In that direction, the present work deals with the possible use of waste dust, produced during steel mill processes, as promoter of the CO2/CH4 replacement process. That sand commonly contains a great variety of compounds, such as metal oxides, alumina, salts, and so on. Some of them have a chemical composition close to well-known hydrate inhibitors/promoters. Moreover, that application could be a further energetic cycle for a waste product. In this work, both methane and carbon dioxide hydrate formation were tested in absence and in presence of cupper oxides, with different concentrations. Hydrate formation and dissociation results where then compared among each other and with hydrate equilibrium values for those compounds

Experimental Characterization of Memory Effect, Anomalous Self-Preservation and Ice-Hydrate Competition, during Methane-Hydrates Formation and Dissociation in a Lab-Scale Apparatus

This study explores the process of methane hydrate formation and dissociation in a small-scale confined environment and in the presence of a porous sediment. The research is focused on answering the shortage of information about the intrinsic properties of the hydrate formation and dissociation processes, such as memory effect and anomalous self-preservation, in a lab-scale apparatus. Experiments were carried out consecutively and with the same gas–water mixture. The temperature reached during dissociation was high enough to ensure the complete dissolution of water cages. At the same time, it was sufficiently low to keep the system able to retain the memory of the previous formation of hydrates. Different well-known phenomena were observed and described; memory effect, anomalous self-preservation and competition between ice and hydrates were shown in detail. Experiments confirmed that the memory effect improves the process mainly during the initial nucleation phase, while it does not provide significant changes in the following massive growth phase. Finally, experiments proved that the formation process can be divided in two different steps: the initial intense growth, due to the small difference in local equilibrium conditions, and the subsequent asymptotic growth, which continues until the process is completed