Acid Gas Composition Research Articles

Mechanistic analysis of acid gas storage and oil recovery in naturally fractured reservoirs using single matrix block approach

AbstractThe objective of this study is to assess the storage of acid gas, containing CO2 and H2S, in a depleted naturally fractured reservoir (NFR) using single matrix block (SMB) approach. The acid gas dissolution in oil is considered by Peng‐Robinson equation of state and compositional simulation. The PHREEQC package is used to determine acid gas solubility in formation brine. Three types of acid gases with different compositions are used for this study and their swelling behavior and miscibility in relation to the reservoir oil are analyzed. An SMB model, with a matrix block surrounded by fractures, is constructed, and validated for simulation of a real experiment. The simulation is conducted for synthetic and real reservoir fluids when the oil is in its residual saturation. A sensitivity analysis is performed to study the effects of key parameters, such as acid gas composition, reservoir pressure, permeability, porosity and matrix height on the storage capacity and oil recovery factor. The matrix has a volume of 27 m3 and about half of acid gas storage is achieved in the first 5 years while the simulations are run for 30 years. The results show that up to 90% of remained oil is recoverable, and more than 0.67 kmol of acid gas per cubic meter of matrix is stored whether matrix contains a real oil or a synthetic one. Higher storage is achieved for higher matrix porosities and heights and large H2S proportion in acid gas. In all cases about 10% of acid gas is trapped in water and the remaining 90% is dissolved in oil. The mineral trapping was more active in CO2‐rich acid gases. While about 10 kg of the matrix rock was dissolved in the acidic brine when the acid gas contained H2S, the amount of the dissolved minerals in acidic brine resulted from the injection of CO2‐rich acid gas was more than 16 kg. Finally, this study gives a comparative analysis of the storage performance of acid gas mixture and pure CO2. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Acid Gas Re-Injection System Design Using Machine Learning

An “energy evolution” is necessary to manifest an environmentally sustainable world while meeting global energy requirements, with natural gas being the most suitable transition fuel. Covering the ever-increasing demand requires exploiting lower value sour gas accumulations, which involves an acid gas treatment issue due to the greenhouse gas nature and toxicity of its constituents. Successful design of the process requires avoiding the formation of acid gas vapor which, in turn, requires time-consuming and complex phase behavior calculations to be repeated over the whole operating range. In this work, we propose classification models from the Machine Learning field, able to rapidly identify the problematic vapor/liquid encounters, as a tool to accelerate phase behavior calculations. To set up this model, a big number of acid gas instances are generated by perturbing pressure, temperature, and acid gas composition and offline solving the stability problem. The generated data are introduced to various classification models, selected based on their ability to provide rapid answers when trained. Results show that by integrating the resulting trained model into the gas reinjection process simulator, the simulation process is substantially accelerated, indicating that the proposed methodology can be readily utilized in all kinds of acid gas flow simulations.

Multicomponent Spiral Wound Membrane Separation Model for CO2 Removal from Natural Gas.

A spiral wound membrane (SWM) is employed to separate acid gases (mainly CO2) from natural gas due to its robustness, lower manufacturing cost, and moderate packing density compared to hollow fiber membranes. Various mathematical models are available to describe the separation performance of SWMs under different operating conditions. Nevertheless, most of the mathematical models deal with only binary gas mixtures (CO2 and CH4) that may lead to an inaccurate assessment of separation performance of multicomponent natural gas mixtures. This work is aimed to develop an SWM separation model for multicomponent natural gas mixtures. The succession stage method is employed to discretize the separation process within the multicomponent SWM module for evaluating the product purity, hydrocarbon loss, stage cut, and permeate acid gas composition. Our results suggest that multicomponent systems tend to generate higher product purity, lower hydrocarbon loss, and augmented permeate acid gas composition compared to the binary system. Furthermore, different multicomponent systems yield varied separation performances depending on the component of the acid gas. The developed multicomponent SWM separation model has the potential to design and optimize the spiral wound membrane system for industrial application.

Sulfolane and di-iso-propanol lean amine blend operating temperature and pressure effect to natural gas sweetening using process simulation

Blending physical and chemical solvents has shown to be promising for removing hydrogen sulfide, carbon dioxide and mercaptan from natural gas effectively. Studies show that using sulfolane and methyl di-ethylene amine blend yields better performance than traditional methods. However, the Shell process depicts that blending sulfolane with di-iso-propanol amine significantly minimizes the problem associated with amine re-circulation efficiency observed with the application of sulfolane and methyl di-ethylene amine. This study aimed at investigating the effect of temperature and pressure to the acid gas removal performance of sulfolane and di-iso-propanol lean solvent using Aspen HYSYS software. In addition, the determination of optimum blend ratio was considered. The acid gas composition of the natural gas stream was 16.9%. This is a hypothetical data used to mimic a relatively high acid gas content in a typical raw natural gas feed. During the process simulation, the lean solvent temperature and pressure were varied between 5 and 210 °C, and 20 and 250 bar, respectively, while maintaining the reactant flow rate at 819.5 kg/h. Findings informs that the optimum blend formulation obtained was 15% water, 15% sulfolane and 70% di-iso-propanol amine at operating temperature and pressure of 50 °C and 45.5 bar, respectively. At the end of the process, the acid gas composition reduced from 16.9 to 0.26%, with an increase in the methane composition by 16.12%. This was as a result of the reduction in the vapor point of the lean solvent, which significantly contributed to enhancing the contact time and efficiency between the gas feed and lean solvent. Hence, the sales gas specification for natural gas was met at lower operating temperature and pressure below 10 °C and 25 bar, respectively.

An evaluation of kinetic models for the simulation of Claus reaction furnaces in sulfur recovery units under different feed conditions

The modified Claus process is one of the major processes employed to convert hydrogen sulfide to elemental sulfur from acid gas. Kinetic models provide a better estimation of Claus reaction furnace effluents, however, kinetics of the coupled reactions are complex and depend upon the feed composition and conditions. Previous studies focused on fitting the kinetic parameters to better approximate the furnace effluents of the observed plants. In this work, a proposed kinetic model based on key global reactions is examined with different feed conditions and acid gas compositions without parameter fitting. Results of the proposed reduced model are compared with plant data, published data from lab-scale experiments, results of a detailed reaction mechanism and of a reduced kinetic model from the literature. Overall, a good agreement is found with each case for the prediction of the reaction furnace effluent temperature and compositions by the proposed model. The proposed model is computationally efficient for Computational Fluid Dynamics design, and optimization and control studies for Claus reaction furnaces.

Combining soft-SAFT and COSMO-RS modeling tools to assess the CO2–SO2 separation using phosphonium-based ionic liquids

The development of efficient CO2 separation techniques from post-combustion flue gases is a key area of research to green-house gas control. However, CO2 capture is typically affected by the presence of other acid impurities, such as traces of SO2. In that sense, this work assesses CO2 separation from a CO2/SO2 mixture with a set of phosphonium-based ILs. Two different modeling tools, soft-SAFT and COSMO-RS, have been used cooperatively to study the CO2 gas separation on ILs. From one side, the soft-SAFT equation of state, which has been employed for the first time in this family of ILs, has been used to effectively reproduce the absorption properties of these promising CO2 absorbents in a wide range of pressures/temperatures. Additionally, COSMO-RS, employed to evaluate the charge distribution so as to develop representative models for soft-SAFT, has been capable of reproducing the low-pressure absorption region in a purely predictive way. In both cases, the enthalpy and entropy of dissolution and the selectivity of the mixtures are predicted. Also, several ternary diagrams have been built to analyze different acid gas compositions.

Roles of hydrogen sulfide concentration and fuel gas injection on aromatics emission from Claus furnace

Acid gas (H2S and CO2) recovered from sour feedstocks is treated in Sulfur recovery units (SRU) to obtain sulfur. The frequent changes in acid gas composition often result in lean acid gas, containing higher volume of CO2 than H2S. Lean acid gas causes flame instability that result in inefficient destruction of feed impurities in Claus furnace. To mitigate this problem, fuel gas (with >90% CH4) is co-fired with acid gas to increase furnace temperature and prevent flame extinction. The addition of fuel gas in Claus furnace may aggravate the production of polycyclic aromatics hydrocarbons (that cause frequent catalyst deactivation), and CS2 and COS (that reduce sulfur yield). Clearly, the amount of fuel gas injected into Claus furnace needs to be optimized. The previous optimization studies have given less importance to the roles of H2S concentrations in acid gas and the injected fuel gas on the production of aromatics and organosulfur species. This paper explores the fate of undesired aromatics, COS and CS2 in the Claus furnace over a wide range of H2S concentrations in acid gas using a detailed reaction mechanism. Experimental data on species concentration from a SRU is presented, and is used for mechanism validation. The effect of fuel gas co-firing with typical Claus feed containing 30–50% H2S is presented alongside detailed analysis of species compositions in the thermal section. An increase in fuel gas flow rate (from 0 to 200kmol/h) increased aromatics production in the furnace for lean acid gases. For rich acid gas, a decrease in aromatics production occurred as fuel gas flow rates was increased. The divergent trends were found to be occurring due to the reduced reactivity of methane in comparison to H2S at low flame temperatures, the dilution effect of unburnt CH4, CO2, and N2 in the furnace, and the endothermic hydrocarbon pyrolysis reactions leading to aromatics formation and growth. Fuel gas addition also led to COS and CS2 formation to reduce sulfur yield. The results indicate that fuel gas may not be the best solution for aromatics destruction in the Claus process for lean acid gas feeds.

Convective Dissolution Analysis of Long-term Storage of Acid Gas in Saline Aquifers

Geological storage of acid gas in subsurface formations is considered one of viable strategies to reduce emissions of greenhouse gases into the atmosphere. During acid gas such as CO2-H2S injected into saline aquifers, the density difference between the acid gas–rich brine and the brine may induce an unstable hydrodynamic state favorable for natural convection. The dissolution-diffusion-convection (DDC) process of acid gas in brine is numerically simulated. We focus on the effect of acid gas composition on DDC process and find that the dissolved H2S has an inhibitive effect on the convective mixing in the brine phase, the criterion for the diffusive-convective transition and the corresponding critical acid gas composition are illustrated and clarified. The apparent average cumulative amount of dissolved multi-component acid gas in the saline aquifer is also presented. It is decided by the solubility of the acid gas and the density-driven convective mixing, and either of the two affecting factors may become the dominate one due to the variation of acid gas composition with different geological conditions. This implies that for the long-term acid gas storage, the convection effect and the solubility of the acid gas should be paid more attention to reduce the risk of acid gas storage at subsurface formations. The results provide insights into the optimal composition of acid gas for storage at subsurface formations, and facilitate the screening of candidate sites for the geological sequestration.

Numerical Examination of Acid Gas for Syngas and Sulfur Recovery

Increase in energy demand worldwide has caused faster depletion of sweeter feedstock and increased utilization of sulfur-bearing fuels that contain high amounts of acid gases (H2S and CO2) and other associated impurities. The composition of acid gas varies significantly depending on the desulfurization facility. Currently, Claus process is used under near optimum reactor conditions for maximum recovery of sulfur from acid gases. To enhance energy generation and preserve our environment from sulfur-bearing fuels, one must explore alternative means for more efficient treatment of acid gases. Numerical examination of acid gases to produce pure sulfur and syngas is presented and this provides the feasibility of establishing global reactor conditions for such a recovery. Detailed examination of acid gas pyrolysis was conducted with focus on determining optimum conditions for the production of sulfur and syngas that can be used in industry at high conversion efficiency of acid gas. The results revealed that only pyrolysis of specific acid gas composition leads to the production of syngas and that temperature plays an important role in the conversion process. The results provide the role of the acid gas composition on high sulfur yield and production of hydrogen-rich syngas under different operational conditions of the reactor with minimal adverse effect on the environment. The produced hydrogen-rich syngas can be utilized to enhance energy generation or produce value added products. The operational conditions provide means to seek different composition of the syngas. The syngas can then be used to produce biofuels. Detailed results and analysis are presented in the paper.

A process simulation study of hydrogen and sulfur production from hydrogen sulfide using the Fe–Cl hybrid process

Presently, most of the acid gas (H2S) streams from amine gas sweetening and refinery upgrading operations are treated using the modified Claus process. In this process, sulfur and low-quality steam are produced by partial oxidation of H2S. Despite the modified Claus process's success in accomplishing the above tasks, it still has some disadvantages. Additional tail gas treatment unit is needed to improve its efficiency. Also, a valuable commodity, hydrogen, is not recovered.In this work, a process simulation study on the Idemitsu Kosan Co. Fe–Cl hybrid process is carried out. The process is capable of producing sulfur and hydrogen from H2S gas streams. The process was modeled and validated using pilot-scale plant data before been scaled up using the typical acid gas composition profile of one of Abu Dhabi's sulfur recovery plants. The effects the absorber solution flow rate and concentration have on the process’ operability were investigated. Operating at high ferric ions concentration was found to be more beneficial compared to high solution flow rate operations. The ferrous ion constituent of the solution proves to be instrumental in the downstream electrolysis process. Cost estimates of the process indicate the suitability of the process to be implemented in Abu Dhabi gas plants to produce sulfur, and most importantly, hydrogen to be used as fuel or chemical feedstock.

Investigation of sulfur chemistry with acid gas addition in hydrogen/air flames

Investigations on the effect of acid gas (H2S and CO2) addition in hydrogen/air flame are presented. The specific equivalence ratios examined include Claus conditions (Φ=3.0) as well as stoichiometric conditions (Φ=1.0) and fuel-lean conditions (Φ=0.5). Two different acid gas compositions of 100% H2S, and 50% H2S/50% CO2 are reported. Addition of pure hydrogen sulfide acid gas deteriorated the rate of hydrogen oxidation in the hydrogen/air flame. Combustion of hydrogen sulfide alone formed sulfur dioxide rather than more favorable elemental sulfur. In contrast combustion of 50% H2S/50% CO2 acid gas stream produced faster decomposition/production of H2S, SO2, and H2. Presence of carbon monoxide was a distinct mark on the release of oxygen from CO2 into the reaction pool. The presence of carbon monoxide triggered the formation of other sulfurous–carbonaceous compounds, such as COS and CS2.

Interfacial Evolution and Migration Characteristics of Acid Gas Injected into a Saline Aquifer

Acid gas injection into saline aquifers is one of promising ways to reduce greenhouse gas emissions and to dispose hazardous waste simultaneously. On the basis of Level Set method, an improved mathematical model that described interfacial dynamics of acid gas-brine system in a deep confined saline aquifer was proposed for predicting the propagation of the acid gas plume, which was featured by using Peng-Robinson equation and modified Lucas equation to describe variations of the density and viscosity of acid gas in saline aquifers. The evolutional characteristics of acid gas plume were obtained through numerical simulations using COMSOL Multiphysics 3.5a. The results showed that under intrinsic characteristics of aquifers and operational conditions given, the variation of acid gas density was the major factor that influences the patterns and shapes of the plume. The leading edge position of acid gas plume was intensively dependent on the acid gas composition. Under the scheme of fixed mass flow rate injection, as the molar fraction of H2S increased, the position of leading edge advanced gradually towards the injection well. Moreover, the estimation of the storage efficiency of acid gas in saline aquifers was clarified and discussed. The proposed approach and the simulation results will provide insights into the determination of optimal operational strategies and rapid identification of the consequences of acid gas injection into deep confined saline aquifers.

Development of the Strasshof Tief Sour-Gas Field Including Acid-Gas Injection Into Adjacent Producing Sour-Gas Reservoirs

Summary OMV operates two producing sour-gas reservoirs in lower Austria: the Reyersdorfer dolomite (shallow reservoir) and the Schoenkirchen Uebertief dolomite (deep reservoir). A new, separate reservoir called the Perchtoldsdorfer dolomite (Strasshof Tief field) has been discovered, and options for how its acid gas can be handled are being investigated. The two currently producing reservoirs deliver to a gas plant with a 30-tonne/d sulfur plant. The sulfur plant is too small to accommodate the additional production. OMV has evaluated acid-gas injection as an alternative to a new, larger sulfur plant. Acid gas could be injected into either the Reyersdorfer dolomite or the Schoenkirchen Uebertief dolomite. In either case, injection would be occurring concurrently with production. Three injection scenarios are contemplated: 200, 400, and 800×103 std m3/d (6.4, 12.8, and 25.6 MMcf/D). The applied acid-gas composition is carbon dioxide (CO2) (80%), hydrogen sulfide (H2S) (16%), nitrogen (N2) (3%), and methane (CH4 or C1) (1%). The intent of this project was to determine at a scoping level if sufficient injectivity and storativity are available in either the Reyersdorfer dolomite or the Schoenkirchen Uebertief dolomite. Compositional modeling and the prognosis of the breakthrough time at the producing wells were carried out to determine the contamination risk to existing production. The simulation work included generating compositional numerical-simulation forecasts of production-rate/composition forecasts under concurrent injection/production scenarios; modeling in-situ miscibility and gravity-separation effects of acid gas; and evaluating risk scenarios for existing production to determine the optimal solution.

Conversion of Municipal Solid Waste Into Carboxylic Acids by Anaerobic Countercurrent Fermentation: Effect of Using Intermediate Lime Treatment

Municipal solid waste (MSW) and sewage sludge (SS) were combined and anaerobically converted into carboxylate salts by using a mixed culture of acid-forming microorganisms. MSW is an energy source and SS is a source of nutrients. In this study, MSW and SS were combined, so they complemented each other. Four fermentors were arranged in series for a countercurrent fermentation process. In this process, the solids and liquid were transferred in opposite directions, with the addition of fresh biomass to fermentor 1 and fresh liquid media to fermentor 4. An intermediate lime treatment of solids exiting fermentor 3 before entering fermentor 4 was applied to improve the product acid concentration from the untreated MSW/SS fermentations. All fermentations were performed under anaerobic conditions at 40 degrees C. Calcium carbonate was added to neutralize the carboxylic acids and to control the pH. Iodoform was used as a methanogen inhibitor. Carboxylic acid concentration and gas composition were determined by gas chromatography. Substrate conversion was measured by volatile solids loss, and carboxylic acid productivity was calculated as the function of the total carboxylic acids produced, the amount of liquid in all fermentors, and time. The addition of intermediate lime treatment increased product concentration and conversion by approx 30 and 15%, respectively. The highest carboxylic acid concentrations for untreated MSW/SS fermentations with and without intermediate lime treatment were 22.2 and 17.7 g of carboxylic acid/L of liquid, respectively. These results confirm that adding a treatment step between fermentor 3 and fermentor 4 will increase the digestibility and acid productivity of the fermentation.

Conversion of hydrogen sulfide to hydrogen by superadiabatic partial oxidation: thermodynamic consideration

A thermodynamic model for the partial oxidation of hydrogen sulfide (H 2S) was used to study product compositions attainable in the superadiabatic partial oxidation regime. Superadiabatic partial oxidation techniques permit attainment of operating temperatures significantly in excess of the adiabatic temperature of the incoming reactants. The superadiabatic partial oxidation of H 2S is studied numerically by varying acid gas and oxidizer feed compositions with overall goal of optimizing the hydrogen yield. These reactant parameters were varied as follows: (20% H 2 S/80% N 2)/ air , (20% H 2 S/80% N 2)/ O 2 , 100% H 2 S/ air , 100% H 2 S/ O 2 , (75% H 2 S/25% N 2)/ air , and (75% H 2 S/25% N 2)/ O 2 . The performed analysis predicts favorable H 2 and low SO 2 yields in the region of ultra-rich superadiabatic partial oxidation at equivalence ratios above 6 for all studied acid gas and oxidizer compositions. Pure oxygen as an oxidizer shifts the thermodynamic range to equivalence ratios >12. Oxygen operation appears thermodynamically promising. With oxygen, high H 2 and low SO 2 yields are attainable in the superadiabatic systems with lower degrees of heat recuperation.

96/03656 Catalysts for hydrogenation of heavy oils and hydrogenation of heavy oils using them

Presently, most of the acid gas (H2S) streams from amine gas sweetening and refinery upgrading operations are treated using the modified Claus process. In this process, sulfur and low-quality steam are produced by partial oxidation of H2S. Despite the modified Claus process's success in accomplishing the above tasks, it still has some disadvantages. Additional tail gas treatment unit is needed to improve its efficiency. Also, a valuable commodity, hydrogen, is not recovered.In this work, a process simulation study on the Idemitsu Kosan Co. Fe–Cl hybrid process is carried out. The process is capable of producing sulfur and hydrogen from H2S gas streams. The process was modeled and validated using pilot-scale plant data before been scaled up using the typical acid gas composition profile of one of Abu Dhabi's sulfur recovery plants. The effects the absorber solution flow rate and concentration have on the process’ operability were investigated. Operating at high ferric ions concentration was found to be more beneficial compared to high solution flow rate operations. The ferrous ion constituent of the solution proves to be instrumental in the downstream electrolysis process. Cost estimates of the process indicate the suitability of the process to be implemented in Abu Dhabi gas plants to produce sulfur, and most importantly, hydrogen to be used as fuel or chemical feedstock.

On-line fluorescence-monitoring of the methanogenic fermentation

On-line in situ fluorescence measurements of the methanogenic fermentation were conducted with reactors receiving either glucose or a mixture of volatile fatty acids as the substrate. The reactors were perturbed from steady-state conditions in order to assess the response of fluorescence-monitoring probes. Two fluorescence-monitoring probes were evaluated over a period of 8 months; they performed in a consistent manner, and their response was not significantly affected by the changes in pH and redox potential encountered during routine reactor operation. A commercially available probe, designed to measure NAD(P)H, demonstrated particular promise for detecting imbalance caused by the entry of air, inhibitor addition and was capable of distinguishing between different substrates. This fluorescence-monitoring probe detected imbalance more rapidly than other on-line measurements such as pH, Eh, or gas production, or off-line measurements such as volatile fatty acid concentration or gas composition. An experimental fluorescence-monitoring probe, designed to measure coenzyme F(420), also showed some promise in this regard. The response of the fluorescence-monitoring probes also revealed details of the metabolic routes in the reactors and the probes represent a useful research tool. For example, a failure to observe the characteristic response of the NAD(P)H-monitoring probe to formate addition during the metabolism of acetate, propionate, or glucose strongly suggests that any formate liberated during their catabolism is degraded via a different route to exogenously added formate.