Natural Gas Streams Research Articles

Insights on Cryogenic Distillation Technology for Simultaneous CO2 and H2S Removal for Sour Gas Fields.

Natural gas demand has dramatically increased due to the emerging growth of the world economy and industry. Presently, CO2 and H2S content in gas fields accounts for up to 90% and 15%, respectively. Apart from fulfilling the market demand, CO2 and H2S removal from natural gas is critical due to their corrosive natures, the low heating value of natural gas and the greenhouse gas effect. To date, several gas fields have remained unexplored due to limited technologies to monetize the highly sour natural gas. A variety of conventional technologies have been implemented to purify natural gas such as absorption, adsorption and membrane and cryogenic separation. The application of these technologies in natural gas upgrading are also presented. Among these commercial technologies, cryogenic technology has advanced rapidly in gas separation and proven ideally suitable for bulk CO2 removal due to its independence from absorbents or adsorbents, which require a larger footprint, weight and energy. Present work comprehensively reviews the mechanisms and potential of the advanced nonconventional cryogenic separation technologies for processing of natural gas streams with high CO2 and H2S content. Moreover, the prospects of emerging cryogenic technologies for future commercialization exploitation are highlighted.

DFT calculations for adsorption of H2S and other natural gas compounds on (Fe, Co, Ni, Cu and Zn)–Y zeolite clusters

The acid compounds removal from natural gas by adsorption on zeolites is an environmentally friendly alternative technology for its purification and commercialization. However, despite numerous theoretical studies determining the adsorption energies for gases on zeolites are found, for important natural gas compounds adsorption on Y zeolite they are poorly reported, especially with respect to long range van der Waals interactions, the description of their nature and related thermodynamic properties. Thus, this work aims to pre-select transition metal-exchanged Y zeolite for selective removal of H2S and other acid compounds from natural gas streams by DFT calculations for H2S, COS, CO2 and CH4 adsorption on Fe–Y, Co–Y, Ni–Y, Cu–Y and Zn–Y zeolite clusters. Adsorption energies, thermodynamic properties, chemical hardness, electronegativity, Natural Bond Orbital (NBO) and Energy Decomposition Analysis (EDA) were determined using B3LYP hybrid functional and Grimme's D3 empirical dispersion correction. Comparison between H2S and other compounds adsorption energies indicates that Ni–Y zeolite has potential for selective removal of H2S, despite Co–Y zeolite presents stronger adsorption energy for all compounds. Moreover, the NBO and EDA analyzes reveal that there is a transfer of d electrons from H2S molecule to unoccupied orbitals of the cation. Charge transfer and polarization phenomena contribute mainly to the adsorption energy of H2S, COS and CO2 in transition metal-exchanged Y zeolite clusters, showing the presence of surface chemisorption.

Investigation on the effects of air gap distance on the formation of cellulose triacetate hollow fiber membrane for CO2 and CH4 gases permeation

CO2 removal is essential for the sweetening process of sour natural gas in order to meet the desired specifications for natural gas to be utilized and transported. CO2 separation from natural gas stream can be achieved through the application of membrane technology which will enable natural gas to be suitable for commercial use. Cellulose triacetate (CTA) is a well-known polymer material for CO2 removal due to its high affinity towards CO2. As compared to flat sheet membranes, hollow fiber configuration is preferable due to its large surface to unit volume ratio and self-supporting characteristics, therefore making it a superior choice compared to other configurations. In this work, fabrication of hollow fiber membranes by employing CTA as a polymer for the separation of CO2 and CH4 gases is focused. During fabrication, the air gap distance was varied from 1 cm to 7 cm. Following that, the morphology of the resulting fibers was investigated by using a scanning electron microscope (SEM). Next, the CO2 and CH4 gas permeation, and CO2/CH4 gas pair selectivity of the resultant HFMs were assessed using a custom-built gas permeation test rig. In addition, post-treatment of HFM with polydimethylsiloxane (PDMS) was also carried out. Then, the gas permeation and gas pair selectivity of the resultant hollow fiber membranes before and after the PDMS coating were compared. The optimum gas permeation performance of CTA HFM was obtained at an air gap distance of 3 cm and a feed pressure of 3 bar as it yielded the highest CO2 permeance of 78.77 GPU and CO2/CH4 gas pair selectivity of 2.80. Whereas for PDMS coated CTA HFM, fibers spun at air gap distance of 1 cm demonstrated the highest CO2 permeance of 14.85 GPU and CO2/CH4 selectivity of 2.54 at feed pressure of 9 bar.

Atomically Dispersed Tin-Modified γ-alumina for Selective Propane Dehydrogenation under H2S Co-feed

Developing an earth-abundant catalyst that is sulfur-tolerant, active, and highly selective is of great interest for valorizing natural gas streams containing sour gas. A tin-modified alumina catal...

The effect of ethanol added to the natural gas stream on the top of line corrosion: An approach on vapor phase condensation and carbonic acid generation yield

This study investigates the side effect of ethanol, added to the natural gas stream as hydrate inhibitor, on vapor condensation and top of line corrosion (TLC). The methodology presented allowed the measurements of both condensation and TLC rates under 1 barg and 8 barg CO2 partial pressures. Tests were performed without any hydrate inhibitor and with ethanol or monoethylene glycol (MEG) for comparison. Ethanol greatly reduced TLC rates, providing TLC rate inhibition efficiencies of at least 80% in the absence of acetic acid (HAc) and above 42% when HAc is present. Simulated data indicates ethanol concentration of 70% w/w in the condensates, indirectly reducing the conversion degrees of dissolved CO2 into H2CO3 (for instance, 0.01 instead of 0.12 at 8 barg in the absence of HAc). Also, the presence of ethanol reduces the dissociation of HAc into free H+ and Ac− when compared with other condensates. Therefore, indirectly, ethanol reduces the cathodic reactions’ rates and, hence, the anodic reaction rate. Additionally, ethanol changed the condensation mode from dropwise to Marangoni, which proved to be convenient since it probably provided low water concentration at the solid-liquid interface. These observations bring up the benefit of adding ethanol to the natural gas stream not only as hydrate inhibitor but also as a support for consolidated TLC prevention techniques.

Economic analysis of hydrogen-powered data center

The data center needs more and more electricity due to the explosive growth of IT servers and it could cause electricity power shortage and huge carbon emission. It is an attractive and promising solution to power the data center with hydrogen energy source. The present work aims to conduct an economic analysis on the hydrogen-powered data center. Configurations of hydrogen-powered and traditional data centers are compared and the differences focus on backup power system, converter/inverter, fuel cell subsystem, carbon emission, hydrogen and electricity consumptions. Economic analysis is conducted to evaluate the feasibility to power the data center with hydrogen energy source. Results show that electricity price increasing rate and hydrogen cost are the main factors to influence economic feasibility of hydrogen-powered data center. When the electricity price keeps constant in the coming two decades, the critical hydrogen price is about 2.8 U.S. dollar per kilogram. If the electricity price could increase 5% annually due to explosive growth of electric vehicles and economy, critical hydrogen price will become 6.4 U.S. dollar per kilogram. Hydrogen sources and transportation determine the hydrogen price together. Hydrogen production cost varies greatly with hydrogen sources and production technologies. Hydrogen transport cost is greatly influenced by distances and H2 consumptions to consumers. It could be summarized that the hydrogen-powered data center is economic if hydrogen could be produced from natural gas or H2-rich industrial waste streams in chemical plant and data center could not be built too far away from hydrogen sources. In addition, large-scale hydrogen-powered data center is more likely to be economic. Solar hydrogen powered data center has entered into a critical stage in the economic feasibility. Solar hydrogen production cost has restrained the H2 utilization in data center power systems now, since it could be competitive only when more strict carbon emission regulation is employed, hydrogen production cost reduces greatly and electricity price is increasing greatly in the future. However, it could be expected solar hydrogen-powered system will be adopted as the power source of data centers in the next few years.

Effects of salinity on solid particle settling velocity in non-Newtonian Herschel\u2013Bulkley fluids

Settling velocity or depositional velocity is considered a key parameter to account for in the drilling technology of oil and gas wells as well as hydrocarbon processing since an accurate estimation of this parameter allows the transport of cuttings efficiently, avoids non-productive time, and helps avoid costly problems. Understanding the settling velocity in fluid with high salinity will help for the better separation of oil and natural gas streams in processing facilities. Although a great amount of effort was given to rheology and settling velocity measurements for power-law fluid and Bingham fluids, there are limited studies available in the literature for Herschel–Bulkley (H–B) fluid with salinity. The present study analyzes the fluid rheology of non-Newtonian fluids with, and without, salinity. Moreover, experiments have been conducted to measure the settling velocity of different diameters of solid particles through Herschel–Bulkley fluids with various salinity conditions. For the rheology analysis, it is found that higher weight percentages of NaCl lead to low values of shear stresses. As well, higher weight percentages of CaCl2 concentration result in a slight increase in shear stresses per a given shear rate. On the other hand, higher percentages of salt concentration cause an increase in the terminal velocity.

Comparative analysis of absorption, membrane, and hybrid technologies for CO2 recovery

The implementation of hybrid systems for carbon dioxide (CO2) capture has been studied by several researchers in recent years. Systems based on the combination of membrane and absorption with amines technologies are the ones that have attracted more interest as industrial applications. In this work, a parametric sensitivity analysis was performed on the hybrid system (membrane and absorption with amines), and on each technology separately, in order to evaluate the most relevant operating variables of each system. Then, the energy requirements and greenhouse gases emissions (GHG) were estimated using process simulation tools. A natural gas stream with a concentration higher than 20 mol% of CO2 was used as feed. This stream was considered the feed of the three different treatment systems: two membrane systems, an absorption system with amines, and a hybrid system (membranes and amines). In the case of the membrane systems, a single-stage and two-stage arrangements were considered, using the total area of membrane as the response variable under analysis. The results showed that the single membrane area module requires around 2700 m2, while the two-module system allowed a 28% reduction in the total area. Amine inlet flows on the separation performance in the amine system were studied, determining a minimum value of 322.54 m3/h of diethanolamine (DEA) at 30% w/w. The hybrid process required a membrane area of 400 m2 and an amine flow of 123.25 m3/h to meet gas sale specifications. Considering energy requirements and carbon emissions, the hybrid system showed the best results among the analyzed technologies. The specifications were reached by showing low energy costs and carbon emissions and an acid gas stream with appropriate purity for enhanced oil recovery (EOR) and other applications.

A flat-plate spiral-channeled membrane heat exchanger for methane dehumidification: Comparison of kraft paper and thin-film composite membrane

Membrane heat exchangers were used for moisture and heat recovery from a hot and humid natural gas stream in indirect contact with an air stream. A plate membrane module with spiral channels on each side was designed to configure gas and air streams in co-current and counter-current flow. Two types of membranes, a commercial kraft paper, and a laboratory-made thin-film composite membrane, were used as the module core. The thermal efficiency and the water recovery from the humid gas were calculated and compared under different operating conditions. At a unit flow ratio of air/gas, the greatest effectiveness was achieved at a methane flow of 100 cm3/min, but water recovery increased at higher gas flows. For the counterflow configuration, an air/methane flow ratio of 2 was sufficient to achieve the highest total effectiveness and water recovery; however, larger air/gas ratios were beneficial to improve heat and moisture transfer for the co-current configuration. The highest water recovery by the kraft paper and composite membrane was achieved (approximately 15 mgH2O/cm2.h) for the input gas with the highest humidity. The dehumidification performance of kraft paper as a porous and hydrophilic membrane was slightly better than that of the composite membrane containing a dense hydrophilic polymer thin film in most cases. A relatively low heat transfer coefficient was found for the module, which was increased by using higher gas flow rates at higher humidity conditions.

Developed hydrogen liquefaction process using liquefied natural gas cold energy: Design, energy optimization, and techno‐economic feasibility

This study focuses primarily on improving large-scale hydrogen liquefaction process by integrating liquefied natural gas (LNG) stream to utilize LNG cold energy. For the hydrogen liquefaction process, a large amount of energy is required for the compression and the cryogenic refrigeration system. LNG is one of the main sources for producing hydrogen, and it can be an opportunity to save energy because LNG cold energy is normally discarded into seawater during regasification. The objective of this study is to reduce the specific energy consumption and specific liquefaction cost. The proposed design which produces 300 ton/day of liquid hydrogen is compared with a base case design comprising two-stage mixed refrigerant refrigeration cycles. To minimize the specific energy consumption, multiparameter optimization is conducted by connecting simulation results to a genetic algorithm. Through the optimization, the flow rates of LNG and MR in the precooling cycle decrease by 1.08 and 21.00 kg/s, respectively. The specific energy consumption is reduced from 4.36 to 4.07 kWh/kg-LH2. Particularly, in the precooling cycle where the LNG stream is integrated, it decreases by more than 26.40%. Regarding the specific liquefaction cost of hydrogen liquefaction, the capital expenses are reduced by 15.16%, and annual operating expenses are diminished by 9.05%. Therefore, the total specific cost liquefaction shows a reduction of approximately 7.7%. Overall, an efficient hydrogen liquefaction process will provide a guideline for LNG-dependent countries by reducing the specific energy consumption and the specific liquefaction cost by recovering the waste cold energy.

Dehydration of natural gas and biogas streams using solid desiccants: a review

Natural gas and biogas are two mixtures that consist of methane as their main component. These two gas mixtures are usually saturated with water vapor, which cause many problems, such as damaging the gas processing equipment by increasing the gas’s corrosion potential or clogging the pipelines due to gas hydrate formation. Thus, removing water vapor from these gas streams is mandatory. In this review paper, the main dehydration methods have been overviewed, and scrutiny of the adsorption dehydration has been carried out. Furthermore, the most important solid desiccants and their improvements have been reviewed.

Analysis of a phosphoric acid fuel cell-based multi-energy hub system for heat, power, and hydrogen generation

Natural gas (NG) is delivered to homes and businesses through a complex pipeline network that mainly consists of high-pressure main feed lines and many low-pressure local distribution lines. To date, throttling valves have been employed to reduce the NG pressure between the two types of pipeline, leading to the loss of the work potential generated by the expansion of pressurized NG in the NG supply chain. As a result, research is currently underway to replace throttling valves with turbo expander generators (TEGs) to obtain additional work power. In this study, a multi-energy hub system consisting of phosphoric acid fuel cell (PAFC) and TEG modules is proposed and analyzed using ASPEN-HYSYS® modeling and simulations. The key concept underlying the system configuration is to maximize overall system efficiency through the integration of exothermic PAFC and endothermic TEG operations. When the TEG system is combined with four 460kWe PAFC stacks, the simulation results show that roughly 1.73 MWe of power can be produced in the TEG system via the expansion of a 28,000 kg/h NG stream. However, when the PAFC stack runs under hydrogen production mode (which requires high voltage operation), an additional heating source is required to fully deliver the expansion work generated by the NG flow within the TEG system. This study clearly illustrates the beneficial features of the proposed multi-energy hub system in terms of thermal integration and overall efficiency but also reveals that the system configuration and operation need to be carefully optimized in order to advance the technology.

Fouling propensity of nonstoichiometric pyrrhotite polytypes in glycol gas dehydration units

Fouling formation in gas dehydration units is performed mainly by gradual accumulation of sulfur-containing compounds and its corrosion products in glycol streams. High concentrations of iron-sulfur species in glycol media increase the fouling propensity on the tube surfaces of heat exchangers. Therefore, the factors affecting the fouling formation and their ranks were determined in a pilot plant gas dehydration unit. Then, the morphology and composition of the fouling layers were studied by qualitative and quantitative XRD patterns. The results revealed that among studied parameters, the concentration of dissolved iron in glycolic media is the main factor responsible for the formation of iron-sulfide deposits. Moreover, it was showed that non-stoichiometric pyrrhotite polytypes 4C, 5C and 6C are the base components of fouling scales deposited on the surface of heat exchangers. Distribution of iron-based species was also determined in the cross-section of a typical heat exchanger and the results showed that the deposited layers are consisted of hydrocarbon residues and pyrrhotite polytypes. Over the time, the pyrrhotite polytypes in deposited layers are covered by paraffin residues absorbed by TEG phase from the natural gas stream.

Physical - chemical interaction of injection waters with depleted gas formations

In order that the physical - chemical interaction of the injection water with the porous-permeable or fissured medium of reservoirs do not lead to their degradation, it is necessary that the waters to meet a number of quality conditions. The treatment and conditioning of the injectable waters is imperative to do so due to the fact that their provenance is different, such as reservoir waters, wastewater resulting from various operations – petroleum operations, meteoric waters, etc. and, in particular, due to the very large volumes of injected water. Failure to follow the steps associated with the water treatment process inevitably leads to premature reduction of the injection wells receptivity. This aspect, as well as another, will be analysed in the context of this article. The injection of water in different geological formations, usually highly depleted, is a connected and defining one in the process of extraction of natural gas from reservoirs. The claim is based on the fact that the very large volumes of reservoir water taken from natural gas stream must be stored safely, otherwise their free discharge would create a real ecological catastrophe

Investigating efficiency improvement in sulfur recovery unit using process simulation and numerical modeling

Hydrogen sulfide exists mostly as a detrimental byproduct in the gas processing units as well as refineries, and it must be eliminated from natural gas streams. In a Sulfur Recovery Unit (SRU), hydrogen sulfide is converted into the elemental sulfur during the modified Claus process. Efficiency of sulfur recovery units significantly depends on the reaction furnace temperature. In this work, the effect of oxygen and acid gas enrichment on the reaction furnace temperature and accordingly on sulfur recovery is studied, using both numerical modeling and process simulation. Then, simulation and numerical model are benchmarked against the experimental data of an SRU unit. The validated model provides spotlight on optimizing the upstream sulfur removal unit as well as the oxygen purification process. Two cases of acid gas streams with low and high H2S content, 30% and 50%, are studied to investigate the effect of operating parameters on the overall recovery. Finally, average errors of the models are presented. According to the absolute difference with experimental values, the developed numerical model shows great potential for accurately estimating overall efficiency of the recovery unit.

Techno-economic analysis of power generation by turboexpanders in natural gas pressure reduction stations

The objective of this paper is to perform a techno-economic feasibility study of recovering pressure energy of natural gas stream through installing turboexpanders in a pressure reduction station and selling the generated electrical power to the national grid. As a case study, the operating and real conditions of a major pressure reduction station in Iran is collected throughout the years 2015, 2016 and 2017. To account for the effects of the inherently variable operating conditions, a thermodynamic model based on exergy analysis estimates off-design turboexpander isentropic efficiency, size and cost estimate as well as minimum preheating temperature required to avoid hydrate formation due to the expansion process. The detailed economic analysis shows that for the project to be economically feasible, an electricity purchase price of > $0.08/kWh is required. Furthermore, the results of this study are useful for designing automatic preheating temperature control system.

Techno-economic analysis of power generation by turboexpanders in natural gas pressure reduction stations

The objective of this paper is to perform a techno-economic feasibility study of recovering pressure energy of natural gas stream through installing turboexpanders in a pressure reduction station and selling the generated electrical power to the national grid. As a case study, the operating and real conditions of a major pressure reduction station in Iran is collected throughout the years 2015, 2016 and 2017. To account for the effects of the inherently variable operating conditions, a thermodynamic model based on exergy analysis estimates off-design turboexpander isentropic efficiency, size and cost estimate as well as minimum preheating temperature required to avoid hydrate formation due to the expansion process. The detailed economic analysis shows that for the project to be economically feasible, an electricity purchase price of > $0.08/kWh is required. Furthermore, the results of this study are useful for designing automatic preheating temperature control system.

Energy, exergy and economic analysis of utilizing the supercritical CO2 recompression Brayton cycle integrated with solar energy in natural gas city gate station

The pressure of natural gas stream must be reduced in city gas station. The natural gas has to be preheated before pressure reduction takes place usually through throttling valves. In conventional city gas stations, the natural gas is preheated by indirect water bath heaters, which burn a large amount of the natural gas as fuel. In this study, the rejected heat from a supercritical carbon dioxide recompression cycle using solar energy is recovered for preheating the natural gas. The novel design of this system generates uniform electricity as well as preheats the natural gas in city gate station. The proposed system is simulated for Birjand city gas station as a case study, and a thorough techno-economic analysis is performed in Engineering Equation Solver for evaluating the system performance. The results of this study demonstrate that parabolic trough collectors with 25 rows are the most efficient solar system while the annual average of thermal and exergy efficiency of the system is 0.56 and 0.41, respectively. The exergetic analysis of the system shows that the highest average exergy destruction takes place in the throttling valve and the second highest in the solar collectors. Also, the total amount of fuel saving is estimated at 4.87 million cubic meters annually and the net power output is equal to 2.86 MW. From the economic point of view, the value of the payback period is estimated 4 years and, based on the net present value method, after 8 years, the initial investment could be returned.

Odorant Monitoring in Natural Gas Pipelines Using Ultraviolet-Visible Spectroscopy.

The remote, timely and in-field detection of sulfured additives in natural gas pipelines is a challenge for environmental, commercial and safety reasons. Moreover, the constant control of the level of odorants in a pipeline is required by law to prevent explosions and accidents. Currently, the detection of the most common odorants (THT = tetrahydrothiophane; TBM = tertiary butyl mercaptan) added to natural gas streams in pipelines is made in situ by using portable gas chromatography apparatuses. In this study, we report the analysis of the ultraviolet spectra obtained by a customized ultraviolet spectrophotometer, named Spectra, for the in-field detection of thiophane and tertiary butyl mercaptan. Spectra were conceived to accomplish the remote analysis of odorants in the pipelines of the natural gas stream through the adoption of technical solutions aimed to adapt a basic bench ultraviolet spectrophotometer to the in-field analysis of gases. The remotely controlled system acquires spectra continuously, performing the quantitative determination of odorants and catching systemic or accidental variations of the gaseous mixture in different sites of the pipeline. The analysis of the experimental spectra was carried out also through theoretical quantum mechanical approaches aimed to detect and to correctly assign the nature of the intrinsic electronic transitions of the two odorants, thiophane and tertiary butyl mercaptan, that cause the ultraviolet absorptions. So far, these theoretical aspects have never been studied before. The absorption maxima of thiophane and tertiary butyl mercaptan spectra were computationally simulated through the usage of selected molecular models with satisfactory results. The good matches between the experimental and theoretical datasets corroborate the reliability of the collected data. During the tests, unexpected pollutants and accidental malfunctions have been detected and also identified by Spectra, making this instrument suitable for many purposes.

Novel Porous Organic Polymer for the Concurrent and Selective Removal of Hydrogen Sulfide and Carbon Dioxide from Natural Gas Streams.

Natural gas sweetening currently requires multistep, complex separation processes to remove the acid gas contaminants, carbon dioxide and hydrogen sulfide. In addition to being widely recognized as energy inefficient and cost-intensive, the effectiveness of this conventional process also suffers considerably because of limitations of the sorbent materials it employs. Herein, we report a new porous organic polymer, termed KFUPM-5, that is demonstrated to be effective in the concurrent separation of both hydrogen sulfide and carbon dioxide from a mixed gas stream at ambient conditions. To understand the ability of KFUPM-5 to selectively capture these gas molecules, we performed both pure-component thermodynamic and mixed gas kinetic adsorption studies and correlated these results with theoretical molecular simulations. Our results show that the underlying polar backbone of KFUPM-5 provides favorable adsorption sites for the selective capture of these gas molecules. The outcome of this work lends credence to the prospect that, for the first time, porous organic polymers can serve as sorbents for industrial natural gas sweetening processes.