Dehydration Unit Research Articles

An Investigation of Dehydration Inefficiencies and Associated Design Challenges in a Gas Dehydration Unit: A Case Study of X Gas Plant

The value and contribution of natural gas in both domestic and economic terrains are extensive. However, its contaminant limits direct application and hence must be treated. Water vapour existing in equilibrium with dry gas is the principal among contaminants. Most corrosion both with acid gases and carbonate salts are traceable to the presence of water. Also the formation of solid icy structures called hydrates constitutes a threat to flow assurance. Removal of water by TEG dehydration trains is not uncommon. Dehydration inefficiencies such as high water content of the outlet gas and glycol losses could impair operations and considerably reduce profit. Inefficiency in GDU was identified to be due to design factors and operational conditions/scenarios. In the case studied, laboratory analysis of TEG was combined with process simulation results to resolve inconsistencies in design and operational phases. Recommendations for further improvements were also presented.

Simulation and Optimization of the Utilization of Triethylene Glycol in a Natural Gas Dehydration Process

Abstract The dehydration unit of a plant that processes natural gas uses triethylene glycol (TEG) as an absorbent to remove water from the gas to prevent blockages in pipes due to the formation of hydrates. Although TEG is recyclable, it is usually lost in the system due to vaporization and carryover, which results in economic issues. Therefore, it is necessary to optimize the dehydration process to achieve the allowable water concentration in the gas, to minimize the use of energy, and to minimize the loss of TEG. Experimental set was designed using Design Expert software by utilising data from Farashband gas processing plant, Iran and subsequently, fed to ASPEN HYSYS to construct and simulate the dehydration process. The chosen affecting parameters to the process were the (1) lean glycol circulation rate, (2) the temperature of the reboiler, and (3) the number of trays in the contactor column. Whereas, the response parameters included the (1) amount of glycol that was lost, (2) the reboiler duty, (3) the concentration of water in the dry gas, and the (4) temperature at which the hydrate formed. Then, these data were optimized using the response surface methodology (RSM). The results indicated that the optimum conditions within the experimental range conducted in this study of process parameters chosen, of the lean glycol circulation rate, the temperature of the reboiler, and the number of trays in the glycol contactor column for the gas dehydration process for the plant were 3944 kg/hr, 180 °C, and three trays, respectively.

SOME ASPECTS OF PREVENTION OF CRYSTALLINE HYDRATES FORMATION AT GAS DISTRIBUTION STATIONS

The existing methods for natural gas dehydration both in fields and at compressor stations cannot always provide standatdized values of natural gas dehydration. The analysis of operation of gas distribution systems shows that dehydration units are improperly placed and are often installed out of condensation and freezing zones. This is due to the lack of consideration of phase transitions impact in gas throttling on its temperature condition. Due to insufficient natural gas dehydration, crystalline hydrates can be formed on wellbores, distribution lines and main gas pipelines and at its reduction, disturbing the operation of the equipment of compressor stations, gas distribution stations, deranging instrumentation and automation. The issues of reliability of gas pipeline systems considering the formation of crystalline hydrate plugs in pipelines have been studied. The analysis of the methods and devices preventing hydrates formation and eliminating existing crystalline hydrate plugs has shown that to provide normalized parameters of the transported gas it is necessary to perform additional water vapor, condensate drops and crystalline hydrate particles removal from natural gas at gas distribution stations during winter months. Currently applied methods used to deal with crystalline hydrate plugs in main gas pipelines require significant expenses and do not effectively ensure the reliability of pipelines operation. An energy-efficient design of an integrated treatment unit which provides an additional natural gas treatment at GDS, increases the reliability of gas pipelines protection against hydrate blockage and improves the efficiency of gas supply systems as a whole have been proposed at the Department of Heat and Gas Supply and Ventilation of the SWSU.

Natural gas dehydration by molecular sieve in offshore plants: Impact of increasing carbon dioxide content

Dehydration is a critical operation in natural gas conditioning as it reduces the potential for corrosion, hydrate formation and freezing in process equipment and transportation pipelines. Water dew point adjustment is particularly challenging in the remote ultra-deepwater natural gas reserves of the Brazilian Pre-Salt fields due to their very high carbon dioxide contents – from 30% up to 90% in raw natural gas – which is a consequence from the carbonaceous rock of the reservoir structure and long term elevation of carbon dioxide content due to its injection for early enhanced oil recovery. Under this scenario, the study evaluates the impact of the carbon dioxide content of the natural gas on the performance of water dew point via water adsorption on 4Å Zeolite molecular sieve beds. Process simulation with adsorption simulator Adsim (Aspen Technology, Inc), at varying operation pressures and carbon dioxide contents in raw natural gas, indicated that, although adsorption meets water removal specification in a condensation free operation, the high fugacity of carbon dioxide penalizes the dehydration performance due to probably two facts: (i) higher carbon dioxide fugacity in the humid natural gas imply higher saturation water content in the gas phase, which increases the service of dehydration units; and (ii) higher carbon dioxide fugacity in the humid natural gas establishes a discreet adsorption competition with water resulting in 6.5% increase of adsorbent bed volume for operating pressures of 35bar or higher.

Sensitivity Analysis and Simulation of TEG Dehydration Unit in Central Rumaila Compression Station in Basrah-Iraq

In the operating of TEG- dehydration unit in CentralRumaila Compression Station. Two operating parametersdetermine the efficient operating of the unit, the desired dewpoint depression and the losses of TEG. This work presents anattempt to study the effect of all the operating variables on theefficiency of the dehydration unit such as the effect of pressureand temperature of the natural gas has to be treated on thewater content. Contactor pressure, TEG circulating rate andstripping gas flow rate are also considered in this study. Theresults showed that decreasing the temperature of the absorberfrom 130 F to 120 F will reduce the mass fraction of water inthe dry gas stream from 0.000076 to 0.00002. Increasing theabsorber pressure from 549.7 psia (design pressure) to 600 psiawill also reduce the water content in the outlet dry gas from0.000076 to 0.000022 as a mass fraction. The simulation resultshows a linear relationship between the wet gas flow rate from theregeneration column and the lean glycol flow rate.

Assessment of new and improved solvent for pre-elimination of BTEX emissions in glycol dehydration processes

Emission of benzene, toluene, ethylbenzene, and xylene (BTEX) from natural gas dehydration units was highlighted as an acute environmental impact. Furthermore, recent stringent environmental regulations addressed a pressing need of knowledge to eliminate hydrocarbon's emissions from glycol dehydrators. The primary objective of this study is to combine the minimization of BTEX emissions with an efficient dew point control. However, the approach in this research emphasis on the cause of the BTEX emissions rather than the post treatment process. Chemically modified monoethylene glycol (mMEG) is proposed as a new solvent to replace triethylene glycol (TEG) in the dehydration process. The results of this study showed a significant improvement in the dehydration performance together with the elimination of (BTEX) emissions. The results demonstrated that mMEG could produce gas water content of 0.16ppm (7.6×10−3lb/mmscf) and near zero level of BTEX. This investigation suggests that using mMEG can solve the environmental issue of BTEX in the natural gas dehydration process.

Potencial energético e alternativas para o aproveitamento do biogás e lodo de reatores UASB: estudo de caso Estação de tratamento de efluentes Laboreaux (Itabira)

RESUMO: Este trabalho estuda o potencial de aproveitamento energético dos subprodutos biogás e lodo gerados na estação de tratamento de efluentes (ETE) Laboreaux em Itabira (MG), composta de reatores UASB, filtros biológicos percoladores e unidade de desaguamento do lodo por filtro prensa. Os subprodutos biogás e lodo foram caracterizados em termos quantitativos (produção) e qualitativos (composição e poder calorífico) durante 12 meses de monitoramento. Foram estudados dois cenários de aproveitamento energético dos subprodutos: (i) uso prioritário do biogás para a secagem térmica do lodo e o excedente de biogás para geração de eletricidade em motor de combustão interna; e (ii) uso prioritário do biogás visando à geração de eletricidade e ao aproveitamento do calor dos gases de exaustão para a secagem térmica de lodo. Para a análise desses cenários, utilizou-se o software CHEMCAD(r) a fim de determinar as condições de queima do biogás em câmara de combustão e em motor de combustão interna, assim como na determinação dos balanços de massa e energia. O estudo analisou o potencial de aproveitamento dos subprodutos do tratamento como fonte de energia renovável para uso na própria ETE e para fornecimento a terceiros. No cenário 1, a geração de eletricidade é menor (atendendo 22,2% da demanda de energia da ETE), mas a secagem térmica possibilita maior redução no volume final de lodo a ser disposto ou a eliminação completa de disposição final se o lodo seco final (com 10% de umidade) for utilizado como combustível por terceiros. No cenário 2, a geração de eletricidade é capaz de suprir 57,6% da demanda de energia da ETE, todavia o calor contido nos gases de exaustão não é suficiente para a secagem de todo o lodo desaguado, configurando uma menor redução na quantidade de lodo a ser disposto (13,5 ou 24,9% de redução em massa, conforme a alternativa de remoção de umidade selecionada).

Prediction of water removal rate in a natural gas dehydration system using radial basis function neural network

ABSTRACTNatural gas commonly contains water as a contaminant that can condense to water or form gas hydrates, which causes a range of problems during gas production, transportation, and processing. Therefore, the removal of gas moisture is of great importance. A common and popular method for removing water contamination from natural gas is using solid dehydrators. Calcium chloride is a nonregenerative desiccant to dehydrate natural gas. With continual water adsorption, CaCl2 changes to consecutively higher states of hydration, finally producing a CaCl2 brine solution. This method does not require heating or moving parts. In addition, it does not react with H2S or CO2. These features make this method a popular one for drying natural gas. Nevertheless, precise and simple methods are needed to predict the water content of natural gas dried by calcium chloride dehydrator units. In this study, an intelligent method, called the radial basis function neural network, was incorporated to predict the gas moisture dehydrated by calcium chloride in dehydration units. Modeling was performed under different conditions of a fresh recharge and before recharging. The overall correlation factor of 0.9999 for both the fresh charge and before charging conditions showed that the outputs of the proposed models were in agreement with the experimental data. In addition, the developed models were compared with the previously proposed intelligent models and classic correlations. The comparison showed that the developed model is superior to the previously proposed models and correlations regarding the accuracy of prediction.

Carbon dioxide solubility in Triethylene Glycol and aqueous solutions

CO2 transportation has become a hot topic for research due to its implications for Carbon Capture and Storage (CCS) as well as Enhanced Oil Recovery (EOR). Triethylene Glycol (TEG) is one of the most commonly used chemicals in the gas processing industry. It is used in glycol dehydration units as well as occasionally for hydrate inhibition, hence for economic engineering design, it is essential to understand its phase behavior in the presence of CO2 and/or water. The solubility data are essential in adjusting binary interaction parameters used in predicting inhibitor distribution in multi-component systems. A number of measurements were made to determine the solubility of CO2 in TEG and 90, 60 and 40 weight percent (wt %) TEG solutions. These measurements were conducted in the range of 263.15–343.15 K and 0.3–37 MPa. The experimental measurements from this work are compared to open literature data available together with the thermodynamic model calculations. The solubility of CO2 in TEG and aqueous solutions were correlated with CPA-SRK72 model, using a single variable binary interaction parameter. The CPA-SRK72 EoS showed an absolute average deviation of 2.55% for pure TEG.

Prediction of water formation temperature in natural gas dehydrators using radial basis function (RBF) neural networks

Raw natural gases usually contain water. It is very important to remove the water from these gases through dehydration processes due to economic reasons and safety considerations. One of the most important methods for water removal from these gases is using dehydration units which use Triethylene glycol (TEG). The TEG concentration at which all water is removed and dew point characteristics of mixture are two important parameters, which should be taken into account in TEG dehydration system. Hence, developing a reliable and accurate model to predict the performance of such a system seems to be very important in gas engineering operations. This study highlights the use of intelligent modeling techniques such as Multilayer perceptron (MLP) and Radial Basis Function Neural Network (RBF-ANN) to predict the equilibrium water dew point in a stream of natural gas based on the TEG concentration of stream and contractor temperature. Literature data set used in this study covers temperatures from 10 °C to 80 °C and TEG concentrations from 90.000% to 99.999%. Results showed that both models are accurate in prediction of experimental data and the MLP model gives more accurate predictions compared to RBF model.

Water Content of CO2 -rich Mixtures: Measurements and Modeling using the Cubic-Plus-Association Equation of State

Natural gas is well known as the cleanest fossil fuel. However, it is estimated that more than 40% of the remaining conventional natural gas reserves are deemed to be acidic, i.e., containing significant quantities of CO 2 and H 2 S. As the global consumption of natural gas is expected to steadily grow, the demand will be met by sources such as sour/acid gas fields. In some specific applications that require cryogenic processes (LNG, NGL recovery), this issue is commonly addressed upstream of the gas dehydration unit, so that the gas is already sweet when arriving at the drying section. In the other cases, the effect of the acidic species on the gas water content is often not properly accounted for, even though an accurate appraisal of the water content is paramount for the sizing of dehydration units. In this contribution, the water contents of the ternary system CO 2 + CH 4 + H 2 O were determined for various CO 2 to CH 4 ratios. New experimental data were obtained using a Tuneable Diode Laser Spectroscopy (TDLS) setup, with an accuracy of +/-1%. The Soave-Redlich-Kwong and the Peng Robinson equations of state combined with the Cubic-Plus Association were used to estimate water content on CO 2 rich gas mixtures.

Pilot-scale study on dehydration of synthetic and lignocellulosic ethanol by NaA membrane

A pilot scale vapor permeation unit was assembled to study the dehydration of bioethanols with NaA membrane. The operational parameters, such as feed concentration, temperature, and downstream pressure in permeate, were varied. Long-term operation of an ethanol dehydration unit was demonstrated. Additionally, the lingocellulosic ethanol distillate was dehydrated to fuel grade ethanol with less than 1% water content. The changes in impurities, such as methanol, ethylacetate, 2-propanol, 1-propanol, 1-butanol, and Isoamyl alcohol, were dependent on the volatility of the compounds. The ethanol concentrations in the permeate stream were lower than 1%, indicating high separation performance of the membrane system.

Standardized surface engineering design of shale gas reservoirs

Due to the special physical properties of shale gas reservoirs, it is necessary to adopt unconventional and standardized technologies for its surface engineering construction. In addition, the surface engineering design of shale gas reservoirs in China faces many difficulties, such as high uncertainty of the gathering and transportation scale, poor adaptability of pipe network and station layout, difficult matching of the process equipments, and boosting production at the late stage. In view of these problems, the surface engineering construction of shale gas reservoirs should follow the principles of “standardized design, modularized construction and skid mounted equipment”. In this paper, standardized surface engineering design technologies for shale gas reservoirs were developed with the “standardized well station layout, universal process, modular function zoning, skid mounted equipment selection, intensive site design, digitized production management” as the core, after literature analysis and technology exploration were carried out. Then its application background and surface technology route were discussed with a typical shale gas field in Sichuan–Chongqing area as an example. Its surface gathering system was designed in a standardized way, including standardized process, the modularized gathering and transportation station, serialized dehydration unit and intensive layout, and remarkable effects were achieved. A flexible, practical and reliable ground production system was built, and a series of standardized technology and modularized design were completed, including cluster well platform, set station, supporting projects. In this way, a system applicable to domestic shale gas surface engineering construction is developed.

Optimization of Two-Stage Pressure/Vacuum Swing Adsorption with Variable Dehydration Level for Postcombustion Carbon Capture

To investigate postcombustion capture of CO2 in the presence of water, we developed a pressure/vacuum swing adsorption (P/VSA) cycle model consisting of a system of partial differential algebraic equations incorporating mass and energy balances, the Ergun equation for pressure changes, competitive Langmuir isotherms, and the linear driving force model. Four potential adsorbents, zeolites 13X and 5A and the MOFs HKUST-1 and Ni-MOF-74, are investigated, evaluated, and compared. Using this simulation, a two-stage Skarstrom cycle, coupled with an upstream dehydration unit and a downstream compression unit, is optimized using a nondominant sorting genetic algorithm, NSGA-II, to minimize the overall cost of capturing 90% of CO2 from flue gas at a purity of 90% and compressing it for pipeline transportation at 110 bar. The results show that under dry flue gas conditions, zeolite 13X is the best performing adsorbent with an overall cost of $32.1/ton of CO2. Under humid flue gas conditions, zeolites 13X and 5A per...

Maximization of natural gas liquids production from an existing gas plant

It is known that the price of liquefied petroleum gas (LPG) is higher than that of natural gas from which it is derived. So the modification of a natural gas plant to produce LPG instead of lighter hydrocarbon gases is very important in the view point of economics. The aim of the present work is directed to the modification of Salam gas plant (Khalda Petroleum Company-Egypt) to produce LPG from the NGL instead of producing hydrocarbon gases during the NGL stabilization. This can be achieved after adding de-ethanizer and de-butanizer towers. The simulation tool used in this study is HYSYS version 8.4. The produced LPG of 100ton/day can participate to solve the LPG shortage problem in Egypt and provide a national service to the people of Matruh Governorate. The economic study based on the economic analyzer of HYSIS showed that the pay-back period of the added two towers and their additional equipment has a high investment strength which means that all modification costs will be recovered within a short time. Furthermore, there are other benefits from this modification. The simulation results showed that there is a capacity saving of 56tons/day in the export pipeline which transfers the gases to western desert gas complex (WDGC) at Alexandria. In the same manner, the modified plant provides a capacity saving of 88tons/day in the dehydration unit and reduces horse power consumption in recycle and first stage export compressors. This modification can be taken as guidelines for both new and plants in operation to increase their profits.

A three-stage scenario based operational performance test approaches for production capacity enhancement: Case study on the 5th refinery of South Pars Gas Complex in Iran

In this work, the possibility of capacity enhancement in the South Pars Gas Complex of Iran has been studied. Mass balance is studied and data validation and reconciliation have been carried out in 5th refinery of South Pars Gas Complex in order to achieve the reliable data of the plant. Then the possibility of capacity increase has been studied, taking into account the important parameters such as alteration of the plant pressure profile. Calculation of the key parameters for different equipment at higher feed rate, specified the unit of operations which may have trouble during the capacity enhancement. The performance of export gas compressors, dehydration unit and High-Integrity Pressure Protection System (HIPPS) has been anticipated to be the obstacle of this project according to the results of design basis review. In order to increase the feed rate the operation at constant inlet pressure is considered while the final stage pressure decreases as it is safe procedure for the plant. Then performance test has been carried out to monitor the changes in the plant. Three methodologies were designed and evaluated for implementing the performance test, and the stepwise procedure has been carried out successfully. During the performance test, the feed rate has been increased in three consecutive steps by 4.5%, 3% and 2.5% respectively. The operation of key equipment such as turbo expanders, exports and refrigerant compressors, dehydration beds, columns and filters, have been examined by taking samples from inlet–outlet streams such as feed gas, acid gas, lean and rich amine, LPG product. Following the step wised feed rate increase, the performance test was operationally successful and the production capacity of sweet gas in South Pars has been increased about 10%.

Characterization and preliminary root cause identification of black powder content in a gas transmission network – A case study

Black powder is a global issue faced by almost all gas producing countries. Understanding characteristics and nature of black powder is required for successful pipeline operations and to assess root-cause of its formation. This paper is mainly divided into two parts. First part gives a synopsis of the global black powder experience and summarizes associated issues and challenges. Second part of the current study is dedicated to chemical characterization of black powder samples received from a sales gas pipeline and root-cause assessment of its formation in a gas processing plant in the Middle East. Elemental analysis of black powder samples show presence of mainly iron and sulfur with traces of various other elements. Further analysis shows presence of both iron sulfides and iron oxides in the network. Root-cause assessment measurements are made from three gas treating and dehydration units in a gas processing plant. Analysis of about 5 month's data indicated that the H2S levels in one of the trains were 3–4 times higher than the other two trains. Assessment analysis points to the possibility of black powder being generated in some processing units and in the sales gas pipeline.

Cubic Plus Association Equation of State for Flow Assurance Projects

Thermodynamic hydrate inhibitors such as methanol, ethanol, (mono) ethylene glycol (MEG), and triethylene glycol (TEG) are widely used in the oil and gas industry. On modeling these compounds, we show here how the CPA equation of state was implemented in an in-house process simulator as an in-built model. To validate the implementation, we show calculations for binary systems containing hydrate inhibitors and water or hydrocarbons using the Cubic Plus Association (CPA) and Soave–Redlich–Kwong (SRK) equation of states, also comparing against experimental data. For streams containing natural gas and water, CPA was applied to calculate the loss of the inhibitor to the vapor phase as a function of temperature and pressure. Simulations of dehydration units using TEG were conducted, and the CPA results were compared with that of two commercial simulators which used their available thermodynamic packages for glycol applications, proving that the CPA calculations are in good agreement with these models and showin...

Application of relative sensitivity function in parametric optimization of a tri-ethylene glycol dehydration plant

Water removal from natural gas is an inevitable process in natural gas industry. Tri-Ethylene Glycol (TEG) plant is the most common and economical process for the dehydration of natural gas. In this work, a domestic TEG dehydration unit is simulated to determine the effect of various parameters on water content of the outlet dehydrated gas. The key feature of this work is the use of Relative Sensitivity Function (RSF) to optimize the whole plant. RSF led into a reduction in the water content of dehydrated gas, TEG circulation rate, and re-boiler duty. The final results revealed that relative sensitivity analysis is a convincing method to determine the best operating conditions and to evaluate the effect of various parameters on water content of the dried gas leaving the absorber column.

Determination of Triethylene Glycol Concentration in Natural Gas Dehydration Systems Using Support Vector Machine Algorithm

Triethylene glycol (TEG) liquid stream is used in natural gas dehydration units in order to prevent gas hydrate formation, the blockage of transportation pipelines, and liquid water condensation during transmission of natural gases in pipelines. Hence, it is needed to propose a reliable model to estimate the properties of TEG for better understanding of its performance. In this study, the robust least square modification of support vector machine (LSSVM) methodology is implemented to propose a computer program, by which the TEG concentration in natural gas dehydration unit can be determined at various reboiler pressure and temperature. In the final analysis, the Leverage approach (Williams plot) is applied to determine the applicability domain of the model and to detect any probable erroneous data points. It is found that the proposed TEG model is capable in low pressures compared to high ones. Additionally, the developed LSSVM model results indicate 0.08% average absolute relative deviation from the corresponding TEG concentration literature values, and squared correlation coefficient of 0.98.