Acid Gas Mixtures Research Articles

Energy exploitation of acid gas with high H2S content by means of a chemical looping combustion system

In gas and petroleum industry, the waste gas stream from the sweetening process of a sour natural gas stream is commonly referred as acid gas. Chemical Looping Combustion (CLC) technology has the potential to exploit the combustible fraction of acid gas, H2S, to produce energy obtaining a flue gas highly concentrated on CO2 and SO2, which can be cost-effectively separated for subsequent applications, such as sulfuric acid production. At the same time, a concentrated CO2 stream ready for storage is obtained. The resistance of oxygen carriers to sulfur becomes crucial when an acid gas is subjected to a CLC process since the H2S content can be very high. In this work, a total of 41h of continuous operation with acid gas and H2S concentrations up to 20vol.% has been carried out in a 500 Wth CLC unit with two oxygen carriers based on Cu (Cu14γAl) and Fe (Fe20γAl). The formation of copper sulfides and the SO2 emissions in the air reactor made the Cu14γAl material not adequate for the process. In contrast, excellent results were obtained during acid gas combustion with the Fe20γAl oxygen carrier. H2S was fully burnt to SO2 in the fuel reactor at all operating conditions, SO2 was never detected in the gas outlet stream of the air reactor, and iron sulfides were never formed even at H2S concentrations as high as 20vol.%. Furthermore, it was found that a H2S content of 20vol.% in the acid gas was high enough to turn the CLC process into an auto-thermal process. Based on these results, it can be concluded that the Fe-based materials prepared by impregnation are very adequate to exploit the energy potential of acid gas mixtures with CO2 capture.

An Environmental Application in Acid Gas Cracking With a High-Frequency Pulsed Gliding Arc

An environmental application of a high-frequency pulsed gliding arc (HFPGA) is presented in this paper. It consists of the degradation of an acid gas mixture (CO2 and H2S) considered as a residue during its sweetening process and contained in sour gas. Plasma interaction with acid gas, leads to a molecular dissociation, mainly forming CO and H2, also known as syngas. In recent years, the syngas has become one of the alternative energy sources more profitable and investigated. The mixture of carbon monoxide and hydrogen, recovered from the decomposition of organic material, provides energy power with innovative applications in microturbines and fuel cells, in conjunction with others applications. The molecular dissociation is achieved with a HFPGA, which, among other properties, has the possibility of working as cold plasma and thermal plasma. Electric analysis was performed to determine instantaneous current, voltage, and power used in the HFPGA for acid gas treatment. From analysis of power consumption, the SE and ECE were 17.62 kJmol-1 and 59.05%, respectively. The analysis of solid residues obtained during the treatment with HFPGA is also presented.

Experiment and modeling solubility of CO2 in aqueous solutions of Diisopropanolamine + 2-amino-2-methyl-1-propanol + Piperazine at high pressures

Removal of acid gases from natural and flue gases is vital in gas treatment processes. Using a high pressure cell, the (vapor+liquid) equilibrium data for solubility of CO2 in the aqueous mixtures of diisopropanolamine (DIPA)+2-amino-2-methyl-1-propanol (AMP)+piperazine (PZ) are obtained at 313.15, 328.15 and 343.15K and pressure range of 1–40bar. Also the experimental measurements for solubility of CO2 in the aqueous (DIPA+AMP) -(DIPA+PZ) systems and the binary aqueous DIPA system are carried out at the same conditions as above. The compositions of the quaternary aqueous mixtures are: (36wt.% DIPA+7wt.% AMP+2wt.% PZ), (30wt.% DIPA+10wt.% AMP+5 wt% PZ), (24wt.% DIPA+13wt.% AMP+8wt.% PZ), for the ternary mixtures are: (24wt.% DIPA+21 wt% AMP), (24wt.% DIPA+21wt.% PZ) and for the binary mixture is 45wt.% DIPA, keeping the total aqueous amine concentration at 45wt.%. The results are presented as the partial pressure of CO2 against acid gas loading (mol CO2/mol total amine). It’s observed that using the AMP-PZ blend as an activator for the DIPA solution increases the CO2 loading so that the absorption of CO2 enhances in the aqueous DIPA solution. Moreover, the Electrolyte-NRTL model is used to model the experimental data of this work and the other aqueous alkalonamine+acid gas mixtures from the literature data.The percent of the average absolute deviation, AAD%, between the calculated partial pressure of CO2 and experiment is 20.3 for the quaternary aqueous-alkanolamines mixtures.

Reactive Transport Modeling of Interactions between Acid Gas (CO2 + H2S) and Pozzolan-Amended Wellbore Cement under Geologic Carbon Sequestration Conditions

The implementation of acid gas cosequestration requires investigation of the potential for acid gas leakage along existing wellbores at sequestration sites. In this study, the interaction between pozzolan-amended wellbore cement (35 vol % pozzolan/65 vol % cement, hereafter referred to as 35:65 sample) and acid gas (e.g., a mixture of CO2 and H2S) was simulated using the reactive transport code CrunchFlow. The model was applied to describe, interpret, and extrapolate scanning electron microscopy-backscattered electron (SEM-BSE) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) results on pozzolan-amended cement samples exposed to a 1 wt % NaCl solution saturated with an acid gas mixture of 21 mol % H2S and 79 mol % CO2 under the temperature of 50 °C and pressure of 150 bar. Simulation outputs included calcite volume percentage, total Ca and S weight percentages in the solid phase, porosity, and effective permeability from the surface to the interior of pozzolan-amended wellbore cement. The model reproduced the observed calcite zone formed in the brine-cement interface region of the sample after 2.5 days of exposure. The model also predicted that the calcite layer became dense (calcite vol % in the layer reached 55%) after 90 days of exposure, consistent with the experimental observation. C–S–H was the primary Ca2+ source to form the calcite layer, followed by C3S and Ca(OH)2. The main observed products of reaction between the 35:65 sample and H2S were pyrite and ettringite. Pyrite was primarily formed within 0.5 mm from the brine-cement interface; ettringite mainly formed within 1 mm from the interface. The model simulated these reactions that only the interface region (up to 2 mm distance from the surface) of the 35:65 sample became porous after 30 years of exposure. However, this narrow porous region could still serve as a migration pathway for acid gas, which was indicated by the increase in effective parallel permeability values determined from the simulation results. Those results show consistency with results of neat cement samples exposed under similar conditions. An increase in H2S content (in the range of 0 mol % to 40 mol %) results in more dissolution of Ca-bearing minerals in cement and more precipitation of calcite. Overall, this study indicates that an increase of porosity and permeability of pozzolan-amended wellbore cement at the cement interface with brine saturated with CO2 and H2S can cause significant changes in effective permeability of the cement.

Polyaniline/poly(ethylene terephthalate) film as a new optical sensing material

Thin polyaniline (PANI) films are known as good optical gas sensors to ammonia but have weak mechanical properties that limit their industrial applications. To improve these properties we have developed new robust transparent PANI based composite films using the combination of aniline polymerization inside a thin (∼1μm) surface layer of a poly(ethylene terephthalate) (PET) film and specific chemical treatments. We demonstrate that the final PANI/PET composite films have an increased surface area; give strong, fast and reversible optical sensor responses to ammonia or formic acid gas mixtures when in doped or dedoped PANI states respectively. Specifically in case of ammonia–air gas mixtures we demonstrate that the doped (PANI–HCl)/PET films give linear optical responses to ammonia gas in concentration ranges of 5–200ppm and 200–920ppm. The undoped PANI/PET films give linear optical response to formic acid in the concentration ranges of 15–200ppm and 200–1600ppm.

Mineralization of basalts in the CO2–H2O–H2S system

Basalt samples representing five different formations were immersed in water equilibrated with supercritical carbon dioxide containing 1% hydrogen sulfide (H2S) at reservoir conditions (100bar, 90°C) for up to 3.5 years. Surface coatings in the form of pyrite and metal cation substituted carbonates were identified as reaction products associated with all five basalts. In some cases, high pressure tests contained excess H2S, which produced the most corroded basalts and largest amount of secondary products. In comparison, tests containing limited amounts of H2S appeared least reacted with significantly less concentrations of reaction products. In all cases, pyrite appeared to precede carbonation, and in some instances, was observed in the absence of carbonation such as in cracks, fractures, and within the porous glassy mesostasis. Armoring reactions from pyrite surface coatings observed in earlier shorter duration tests were found to be temporary with carbonate mineralization observed with all the basalts tested in these long duration experiments. Geochemical simulations conducted with the geochemical code EQ3/6 accurately predicted early pyrite precipitation followed by formation of carbonates. Reactivity with H2S was correlated with measured Fe(II)/Fe(III) ratios in the basalts with more facile pyrite formation occurring with basalts containing more Fe(III) phases. These experimental and modeling results confirm potential for long term sequestration of acid gas mixtures in continental flood basalt formations.

Thermodynamic modeling of CO 2 and H 2S solubilities in aqueous DIPA solution, aqueous sulfolane–DIPA solution, and aqueous sulfolane–MDEA solution with electrolyte NRTL model

A thermodynamic model developed for CO 2 and H 2S solubilities in aqueous MDEA solution is extended to cover CO 2 and H 2S solubilities in aqueous DIPA solution, aqueous sulfolane–DIPA solution, and aqueous sulfolane–MDEA solution. The model makes use of the 2009 version of the electrolyte NRTL model for liquid phase activity coefficient calculations and the PC-SAFT equation of state for vapor phase fugacity coefficient calculations. The NRTL binary parameters for the molecule–electrolyte pairs required for the H 2O–DIPA–CO 2 ternary and the H 2O–sulfolane–DIPA–CO 2 quaternary are regressed against the solubility data of CO 2 in aqueous DIPA solution and aqueous sulfolane–DIPA solution, respectively. The NRTL binary parameters for the molecule–electrolyte pairs required for the H 2O–DIPA–H 2S ternary and the H 2O–sulfolane–DIPA–H 2S quaternary are regressed against the solubility data of H 2S in aqueous DIPA solution and aqueous sulfolane–DIPA solution simultaneously. The NRTL binary parameters for the electrolyte–electrolyte pairs involved in the H 2O–DIPA–CO 2–H 2S quaternary are regressed against the solubility data of the acid gas mixtures in aqueous DIPA solution. Likewise, the NRTL binary parameters for the sulfolane–electrolyte pairs required for the H 2O–sulfolane–MDEA–CO 2 quaternary and the H 2O–sulfolane–MDEA–H 2S quaternary are regressed against the solubility data of the acid gases in aqueous sulfolane–MDEA solution. The predicted enthalpies of acid gas absorption are compared favorably with the literature data available for the H 2O–DIPA–CO 2 system, the H 2O–DIPA–H 2S system, and the H 2O–sulfolane–MDEA–CO 2 system.

Modeling phase equilibria for acid gas mixtures using the CPA equation of state. Part II: Binary mixtures with CO 2

In Part I of this series of articles, the study of H 2S mixtures has been presented with CPA. In this study the phase behavior of CO 2 containing mixtures is modeled. Binary mixtures with water, alcohols, glycols and hydrocarbons are investigated. Both phase equilibria (vapor–liquid and liquid–liquid) and densities are considered for the mixtures involved. Different approaches for modeling pure CO 2 and mixtures are compared. CO 2 is modeled as non self-associating fluid, or as self-associating component having two, three and four association sites. Moreover, when mixtures of CO 2 with polar compounds (water, alcohols and glycols) are considered, the importance of cross-association is investigated. The cross-association is accounted for either via combining rules or using a cross-solvation energy obtained from experimental spectroscopic or calorimetric data or from ab initio calculations. In both cases two adjustable parameters are used when solvation is explicitly accounted for. The performance of CPA using the various modeling approaches for CO 2 and its interactions is presented and discussed, comparatively to various recent published investigations. It is shown that overall very good correlation is obtained for binary mixtures of CO 2 and water or alcohols when the solvation between CO 2 and the polar compound is explicitly accounted for, whereas the model is less satisfactory when CO 2 is treated as self-associating compound.

Injection of Acid Gas Mixtures in Sour Oil Reservoirs: Analysis of Near-Wellbore Processes with Coupled Modelling of Well and Reservoir Flow

The reinjection of sour or acid gas mixtures is often required for the exploitation of hydrocarbon reservoirs containing remarkable amounts of acid gases (H2S and CO2) to reduce the environmental impact of field exploitation and provide pressure support for enhanced oil recovery (EOR) purposes. Sour and acid gas injection in geological structures can be modelled with TMGAS, a new Equation of State (EOS) module for the TOUGH2 reservoir simulator. TMGAS can simulate the two-phase behaviour of NaCl-dominated brines in equilibrium with a non-aqueous (NA) phase, made up of inorganic gases such as CO2 and H2S and hydrocarbons (pure as well as pseudo-components), up to the high pressures (~100 MPa) and temperatures (~200°C) found in deep sedimentary basins. This study is focused on the near-wellbore processes driven by the injection of an acid gas mixture in a hypothetical high-pressure, under-saturated sour oil reservoir at a well-sector scale and at conditions for which the injected gas is fully miscible with the oil. Relevant-coupled processes are simulated, including the displacement of oil originally in place, the evaporation of connate brine, the salt concentration and consequent halite precipitation, as well as non-isothermal effects generated by the injection of the acid gas mixture at temperatures lower than initial reservoir temperature. Non-isothermal effects are studied by modelling in a coupled way wellbore and reservoir flow with a modified version of the TOUGH2 reservoir simulator. The described approach is limited to single-phase wellbore flow conditions occurring when injecting sour, acid or greenhouse gas mixtures in high-pressure geological structures.

High-Pressure Acid-Gas Viscosity Correlation

Acid gases containing hydrogen sulfide (H2S) are often encountered in the petroleum industry. However, reliable experiments on their thermophysical properties in reservoir conditions, on viscosity in particular, are scarce. From a modeling point of view, H2S and carbon dioxide (CO2) are polar compounds and as such are often considered rather difficult to model accurately. In this work, we propose a correlation with a strong physical background based on a corresponding-states (CS) approach to predict the viscosity from the temperature and the density of a large variety of systems for all stable thermodynamic states (gas, liquid, and supercritical). In particular, this correlation is applicable to predict the viscosity of sour/acid-gas mixtures, whatever the thermodynamic conditions. This approach is based on the Lennard-Jones (LJ) fluid model, which has been studied extensively thanks to molecular-dynamics (MD) simulations over a wide range of thermodynamic conditions. This fluid model can be extended to deal with polar molecules such as CO2 or H2S without a loss of accuracy. First, we demonstrate that the proposed physically based correlation is able to provide an excellent estimation of the viscosity [with average absolute deviations (AADs) below 5%] of pure compounds, including normal-alkanes, CO2, or even H2S, whatever the thermodynamic conditions (gas, liquid, or supercritical). Then, using a one-fluid approximation and a set of combining rules, the correlation is applied to various fluid mixtures in a fully predictive way (i.e., without any additional fitted parameters). Using this scheme, the deviations between predictions and measurements are as low as those on pure fluids using temperature and density as inputs. The viscosity of natural- and acid-gas mixtures at reservoir conditions is shown to be very well predicted by the proposed scheme. In addition, it is shown that this correlation can also be applied to predict reasonably the viscosity of asymmetric high-pressure mixtures, even in the liquid phase. This physically based approach is easy to include in any simulation software as long as, apart from temperature and density, the only inputs--the molecular parameters of each species--can be estimated from the critical temperature and the critical volume when not known.

Modeling phase equilibria for acid gas mixtures using the CPA equation of state. I. Mixtures with H2S

AbstractThe Cubic‐Plus‐Association (CPA) equation of state is applied to a large variety of mixtures containing H2S, which are of interest in the oil and gas industry. Binary H2S mixtures with alkanes, CO2, water, methanol, and glycols are first considered. The interactions of H2S with polar compounds (water, methanol, and glycols) are modeled assuming presence or not of cross‐association interactions. Such interactions are accounted for using either a combining rule or a cross‐solvation energy obtained from spectroscopic data. Using the parameters obtained from the binary systems, one ternary and three quaternary mixtures are considered. It is shown that overall excellent correlation for binary mixtures and satisfactory prediction results for multicomponent systems are obtained. There are significant differences between the various modeling approaches and the best results are obtained when cross association is explicitly accounted for, especially using the cross‐association energy from independent experimental studies rather than from combining rules. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Modeling of phase equilibria with CPA using the homomorph approach

For association models, like CPA and SAFT, a classical approach is often used for estimating pure-compound and mixture parameters. According to this approach, the pure-compound parameters are estimated from vapor pressure and liquid density data. Then, the binary interaction parameters, kij, are estimated from binary systems; one binary interaction parameter per system. No additional mixing rules are needed for cross-associating systems, but combining rules are required, e.g. the Elliott rule or the so-called CR-1 rule. There is a very large class of mixtures, e.g. water or glycols with aromatic hydrocarbons, chloroform–acetone, esters–water, CO2–water, etc., which are classified as “solvating” or “induced associating”. The classical approach cannot be used and the cross-association interactions are difficult to be estimated a priori since usually no appropriate experimental data exist, while the aforementioned combining rules cannot capture the physical meaning of such interactions (as at least one of the compounds is non-self-associating). Consequently, very often one or more of the interaction parameters are optimized to experimental mixture data. For example, in the case of the CPA EoS, two interaction parameters are often used for solvating systems; one for the physical part (kij) and one for the association part (βcross). This limits the predictive capabilities and possibilities of generalization of the model. In this work we present an approach to reduce the number of adjustable parameters in CPA for solvating systems. The so-called homomorph approach will be used, according to which the kij parameter can be obtained from a corresponding system (homomorph) which has similar physical interactions as the solvating system studied. This leaves only one adjustable parameter for solvating mixtures, the cross-association volume (βcross). It is shown that the homomorph approach can be used with success for mixtures of water and glycols with aromatic hydrocarbons as well as for mixtures of acid gases (CO2, H2S) with alcohols and water. The homomorph approach is less satisfactory for mixtures with fluorocarbons as well as for aqueous mixtures with ethers and esters. In these cases, CPA can correlate liquid–liquid equilibria for solvating systems using two adjustable parameters. The capabilities and limitations of the homomorph approach are discussed.

Hydrogen Sulfide Viscosity Modeling

As regulations for emissions of carbon dioxide and hydrogen sulfide into the atmosphere are becoming stricter and the penalty for violation increases, new and economical ways of reducing these emissions are becoming increasingly important to everyday operations. One promising sequestering option is the injection of acid gas mixtures into formations for disposal/storage. During the design of these acid gas injection schemes a comprehensive knowledge of the thermo-physical properties is of utmost importance in determining the feasibility and size of these operations. Recently, the friction theory (f-theory) for viscosity modeling has been shown to accurately determine the viscosity behavior of a wide range of petroleum fluid systems ranging from natural gases to heavy crude oils. This technique has also been shown to accurately model mixtures containing various concentrations of CO2. However, in the development of the f-theory hydrogen sulfide was not explicitly studied and therefore needs to be accounted for to ensure it is accurately modeled. The development/validation of any modeling approach requires a thorough knowledge of the available data. With this in mind, an exhaustive collection of the data available in the literature has been performed revealing a very limited number of experimental points available in the open literature for the viscosity of pure H2S and H2S mixtures. Although limited data for pure H2S exists in the literature, a critical evaluation of the data was performed and a reference viscosity model based on the generalized friction theory (f-theory) was developed. The developed reference viscosity model gives reasonable modeling results over the T-η-P surface for H2S. The one parameter f-theory was also extended to include H2S, and the model was shown to accurately reproduce existing experimental viscosities of hydrogen sulfide and its mixtures in ranges relevant to the natural gas and petroleum industry.

Molecular Dynamics Simulation of Acid Gas Mixtures: A Comparison between Several Approximations

Molecular dynamics simulations of CH4, CO2, H2S, and their mixtures, chosen as representative of acid gas mixtures, have been performed. Static properties (pressure or density) and dynamic properties (shear viscosity) have been computed. A comparison has been performed between results from three different models: a simple Lennard-Jones (LJ) model, an isotropic multipolar (IMP) one, and the usual LJ plus point charge (LJP). For pure fluids, a reasonable agreement is found between all three models and experiments except for CO2, for which the LJ model suffers from its lack of electrostatic contributions. Concerning CH4−H2S mixtures, results obtained using the three molecular models are consistent with each other for static and dynamic properties. In addition, no significant differences between the results obtained using both Lorentz−Berthelot and Kong combining rules were noticed. For the CH4−H2S−CO2 mixture, the situation is different: a strong dependence of the pressure on the molecular models as well a...

The Phase Behaviour of Acid Disposal Gases and the Potential Adverse Impact on Injection or Disposal Operations

Abstract As increased volumes of acid gases (containing carbon dioxide and hydrogen sulphide) are processed, the technique of downhole re-injection of the concentrated acid gas for disposal of these unwanted fluids continues to become more popular. In many cases, bottomhole injection temperature and pressure conditions are such that the injected acid gas phase is a supercritical fluid that is miscible with the existing reservoir fluids and, thus, the potential for adverse relative permeability effects (due to thecreation of in situ immiscible liquid and vapour phases) is avoided. In other cases, however, combinations of lower reservoir temperatures and/or initially depleted disposal zone pressures, or blending of the acid gas with the in situ lean gas, can result in the formation of both liquid and vapour acid gas phases in the formation in the near-wellbore region. This can often cause very significant relative permeability effects, which may result in large reductions in injectivity of the acid gas on either a permanent or transient basis. This paper provides actual examples of such systems, as well as reviewing the design protocol that must be used to evaluate if potential phase behaviour problems can occur downhole during an acid gas disposal operation. This hasproven to be a key parameter in the successful evaluation of anacid gas disposal operation. Introduction In many acid gas injection operations, the bottomhole pressure condition is high enough that, over the entire life of the injection operation and at all possible blended compositions between the acid injection gas and the reservoir fluids, a monophasic condition is present. In some cases, when the initial reservoir pressure is low, initial injection commences in the "gas" phase region, and as pressure gradually increases, the phase condition of the fluids around the injection wells enters the two-phase region where a "liquid" acid gas phase is in thermodynamic equilibrium with an acid gas "vapour" phase. This may also occur when the acid gas blends with reservoir gas which may elevate the dew point pressure line upwards above the current injection pressure level, once again resulting in a condition of two-phase flow. The creation of these two immiscible phases (which have an interface and measurable interfacial tension between them) can, particularly in lower permeability formations, create significant adverse relative permeability effects which may result in large transient or permanent reductions in injectivity, possibly compromising the economics of the acid gas injection operation. Understanding the phase behaviour in such situations and how it interacts with the capillary pressure and relative permeability phenomena present within the matrix of the proposed injection zone is essential. Limited data is available in the literature on the properties of high temperature and pressure acid gas mixtures and their specific phase behaviour(1–8). This is also the case with data regarding the specific interaction of single and multiphase acid gas interactions with reservoir rock(9–11) and the effects of multiphase acid gas induced relative permeability effects(12). The motivation of this work was to obtain a dataset to expand the knowledge base in this area.

Occupational exposures to acid mists and gases and ulcerative lesions of the oral mucosa.

This study examines the hypothesis that acid mist or mixtures of acid mists and acid gases are associated with ulcerative lesions of the oral mucosa. All 665 active male workers of a metal processing factory were the study population. Semi-quantitative measures of exposure were estimated from a job exposure matrix constructed with industrial hygienist scoring and job titles. Ulcerative lesions of the oral mucosa were identified with standardized clinical dental exams. Past exposure to acid mists were positively associated with ulcerative lesions of the oral mucosa but only among workers without lip sealing (age- and alcohol consumption-adjusted prevalence ratio (PR), PR(adjusted) = 3.40; 90% CI: 1.48-7.85). Also in this worker group, the mixture of acid mists and acid gases was associated with ulcerative lesions of the oral mucosa limited to exposure in the past (PR(adjusted) = 2.83; 90% CI: 1.12-7.17). There is a positive association between acid mist or mixtures of acid mists and acid gases and ulcerative lesions of the oral mucosa only in the absence of lip sealing. The evidence of a chronic rather than acute irritative process suggests a possible step on the etiology of oral malignancies, which needs investigation.

Phase Equilibria Relevant to Acid Gas Injection: Part 2-Aqueous Phase Behaviour

Abstract The purpose of this paper is to review the literature for the available experimental data and briefly survey methods for calculations of the aqueous equilibria of acid gas mixtures; notably, the water content of the gas and liquified acid gas. In addition to water, this study will include the following components: hydrogen sulfide, carbon dioxide, methane, ethane, and propane. The design engineer should be fully informed of the capabilities of the model selected to perform the calculations. If uncertain, it is wise to verify the chosen model by comparing it with experimental data. However, as will be demonstrated, the design engineer should be critical when interpreting the available data. Acid Gas Injection As was stated in the first part of this paper, acid gas injection has become an important method for dealing with unwanted acid gas. A common approach in the design of an acid gas injection scheme is to take advantage of the thermodynamics of these systems. The water content of acid gas mixture has a minimum as a function of the pressure. The design of an acid gas injection project should attempt to take advantage of this minimum, in order to eliminate the need for dehydration(1). Water Content An essential aspect of the design of an acid gas injection scheme is the water content of the acid gas mixture. In addition, it is important to know the effect of the state (gas or liquid) of the acid gas on the water content. Table 1 lists experimental investigations into the water content of mixtures containing hydrogen sulfide and/or carbon dioxide. The study of Selleck et al.(2) is considered the benchmark investigation of the system hydrogen sulfide + water. They published tables of smoothed data, which are commonly quoted in the literature. However, these tables are based on relatively few and scattered experimental data points. Carroll and Mather(3) re-evaluated the phase behaviour in this system, presenting a clearer picture of the equilibria and accurately reflecting all of the available experimental data. There have been many investigations of the water content of CO2-rich fluids. In general, there is reasonable agreement amongst the various sets of data in the low and moderate pressure regions. The benchmark investigation of the phase behaviour in the system carbon dioxide + water was that of Wiebe and Gaddy(4–6). Finally, the author of this paper has performed thorough reviews of the literature, and is unaware of any experimental data for the water content for binary mixtures of H2S + CO2 in the public domain. Such data, if available, would be very useful. There have been several experimental investigations into the water content of hydrocarbons. Table 2 lists those of interest in this study. In this paper, we are not strictly interested in the water content of hydrocarbons, but in acid gas mixtures containing hydrocarbons. We require a model that accurately predicts the water content of hydrocarbons in order to have the confidence that it will work for multicomponent mixtures.

Phase Equilibria Relevant to Acid Gas Injection, Part 1-Non-Aqueous Phase Behaviour

Abstract The design of an acid gas injection scheme requires a significant amount of information regarding phase equilibria. The purpose of this paper is to review the literature for the available experimental data, and survey methods for calculations of the non-aqueous equilibria. This study will be limited to the following components: hydrogen sulfide, carbon dioxide, methane, ethane, propane, and, to some extent, water. It is demonstrated that the widely available Peng-Robinson equation of state is adequate for predicting the non-aqueous phase equilibria in these mixtures. However, the design engineer should be cognizant of the capabilities of the model selected to perform the calculations. If uncertain, it is wise to verify the software package, and more importantly the chosen model, by comparing it with experimental data. Available data are compiled as a part of this paper. ACID GAS INJECTION Acid gas injection has become the environmentally friendly way to deal with the unwanted by-product of the sweetening of natural gas. In the future it may become a means of dealing with carbon dioxide from other sources as well. In a basic acid gas injection scheme, the acid gas off the amine regenerator tower is compressed and transported via pipeline to an injection well. From there, it is injected into a suitable formation for disposal. The formation is selected based on geological criteria such as the size of the disposal reservoir, and the containment of the injected acid gas. In an acid gas injection scheme, pressures can range from near atmospheric up to 30 MPa or more; the upper limit is dictated by the selected reservoir. The temperature can range from about 30 °C up to as much as 200 °C; again the upper limit is being the reservoir conditions. The design of the injection scheme requires a thorough knowledge of the phase equilibria encountered in wet acid gas mixtures. This paper reviews the experimental investigations into the relevant systems. This study is limited to the following components: hydrogen sulfide, carbon dioxide, methane, ethane, propane, and water. Even so, an interesting variety of phase equilibria will be presented. The design engineer is advised to be aware of all of the various phenomena encountered in mixtures of these components, as they will have a significant effect on the design. Experimental Investigations In this section, experimental investigations important to acid gas injection will be reviewed. Typically, in acid gas injection schemes, we are not concerned with hydrocarbons heavier than propane. So, for this study, only equilibrium between the acid gas components and methane, ethane, and propane will be considered. Hydrogen Sulfide +Carbon Dioxide The most important non-aqueous system involved in acid gas injection is the binary mixture hydrogen sulfide +carbon dioxide, since acid gas is composed almost exclusively of these components. Two early studies of the phase equilibrium in the system hydrogen sulfide +carbon dioxide were Bierlein and Kay(1) and Sobocinski and Kurata(2).

New applications of equations of state in molecular models of complex fluid mixtures

Two different types of problems are approached by connecting simplified molecular models with equations of state (EOS). For aqueous–organic solutions of gases chemically reacting with solvent, special techniques to handle electrostatic and nonelectrostatic interaction contributions in the calculation of liquid composition and fugacity coefficients are applied for modeling VLE. A modified hole model and the Soave–Redlich–Kwong (SRK) EOS are utilized to describe solubility of gases in water–alkanolamine–acid gas (CO 2, H 2S) mixtures. A polydisperse version of a thermodynamic micellization model proposed earlier is formulated and applied to describe asphaltene phase drop-out from crude oils.

Formation of aerosols in absorption processes forexhaust gas purification

Formation and growth of fog droplets by heterogeneous condensationof mixtures of water and acid gases under the specific conditions of absorption processes are investigated. It is shown that aerosols with very small droplet sizes are formed, especially for high concentrations of foreign nuclei in the gas.