Study on the recovery of hydrogen from refinery (hydrogen + methane) gas mixtures using hydrate technology

A novel technique for separating hydrogen from (H2 CH4) gas mixtures through hydrate formation/dissociation was proposed. In this work, a systematic experimental study was performed on the separation of hydrogen from (H2 CH4) feed mixtures with various hydrogen contents (mole fraction x = 40%-90%). The experimental results showed that the hydrogen content could be enriched to as high as ~94% for various feed mixtures using the proposed hydrate technology under a temperature slightly above 0℃ and a pressure below 5.0 MPa. With the addition of a small amount of suitable additives, the rate of hydrate formation could be increased significantly. Anti-agglomeration was used to disperse hydrate particles into the condensate phase. Instead of preventing hydrate growth (as in the kinetic inhibitor tests), hydrates were allowed to form, but only as small dispersed particles. Anti-agglomeration could keep hydrate particles suspended in a range of condensate types at 1℃ and 5 MPa in the water-in-oil emulsion.     

Gas-hydrate formation, agglomeration and inhibition in oil-based drilling fluids for deep-water drilling

One of the main challenges in deep-water drilling is gas-hydrate plugs, which make the drilling unsafe. Some oil-based drilling fluids (OBDF) that would be used for deep-water drilling in the South China Sea were tested to investigate the characteristics of gas-hydrate formation, agglomeration and inhibition by an experimental system under the temperature of 4 ℃ and pressure of 20 MPa, which would be similar to the case of 2000 m water depth. The results validate the hydrate shell formation model and show that the water cut can greatly influence hydrate formation and agglomeration behaviors in the OBDF. The oleophobic effect enhanced by hydrate shell formation which weakens or destroys the interfacial films effect and the hydrophilic effect are the dominant agglomeration mechanism of hydrate particles. The formation of gas hydrates in OBDF is easier and quicker than in water-based drilling fluids in deep-water conditions of low temperature and high pressure because the former is a W/O dispersive emulsion which means much more gas-water interfaces and nucleation sites than the later. Higher ethylene glycol concentrations can inhibit the formation of gas hydrates and to some extent also act as an anti-agglomerant to inhibit hydrates agglomeration in the OBDF.     

An accurate empirical correlation for predicting natural gas viscosity

Natural gas viscosity is an important parameter in many gas and petroleum engineering calculations.This study presents a new empirical model for quickly calculating the natural gas viscosity.The model was derived from 4089 experimental viscosity data with varieties ranging from 0.01 to 21,and 1 to 3 of pseudo reduced pressure and temperature,respectively.The accuracy of this new empirical correlation has been compared with commonly used empirical models,including Lee et al.,Heidaryan et al.,Carr et al.,and Adel Elsharkawy correlations.The comparison indicates that this new empirical model can predict viscosity of natural gas with average absolute relative deviation percentage AARD (%) of 2.173.     

Experimental and Theoretical Study of the Effect of Moisture on Methane Adsorption and Desorption by Activated Carbon at 273.5 K

Adsorption and desorption of methane by activated carbon (AC) at constant temperature and at various pressures were investigated. The effect of moisture was also studied. A volumetric method was used, up to 40 bar, at a temperature of 273.5 K. Results of a dry AC sample were compared with those obtained from a moist sample and two different ACs with different physical and surface properties were used. As expected, the results showed that the existence of moisture, trapped in the AC pores, could lead to a decrease in the amount of methane adsorbed and a decrease in the amount of methane delivered during desorption. To model the experimental results, a large variety of adsorption isotherms were used. The regressed parameters for the adsorption isotherms were obtained using the experimental data generated in the present study. The accuracy of the results obtained from the different adsorption isotherms was favorably compared.     

Oxidative coupling of methane in a fixed bed reactor over perovskite catalyst： A simulation study using experimental kinetic model

The oxidative coupling of methane （OCM） to ethylene over a perovskite titanate catalyst in a fixed bed reactor was studied experimentally and numerically. The two-dimensional steady state model accounted for separate energy equations for the gas and solid phases coupled with an experimental kinetic model. A lumped kinetic model containing four main species CH4, O2, COx （CO2, CO）, and C2 （C2H4 and C2H6） was used with a plug flow reactor model as well. The results from the model agreed with the experimental data. The model was used to analyze the influence of temperature and feed gas composition on the conversion and selectivity of the reactor performance. The analytical results indicate that the conversion decreases, whereas, C2 selectivity increases by increasing gas hourly space velocity （GHSV） and the methane conversion also decreases by increasing the methane to oxygen ratio.     

Effect of temperature fluctuation on hydrate-based CO_2 separation from fuel gas

A new method of temperature fluctuation is proposed to promote the process of hydrate-based CO2 separation from fuel gas in this work according to the dual nature of CO2 solubility in hydrate forming and non-hydrate forming regions [1].The temperature fluctuation operated in the process of hydrate formation improves the formation of gas hydrate observably.The amount of the gas consumed with temperature fluctuation is approximately 35% more than that without temperature fluctuation.It is found that only the temperature fluctuation operated in the period of forming hydrate leads to a good effect on CO2 separation.Meanwhile,with the proceeding of hydrate formation,the effect of temperature fluctuation on the gas hydrate gradually reduces,and little effect is left in the completion term.The CO2 separation efficiencies in the separation processes with the effective temperature fluctuations are improved remarkably.     

Theoretical and Experimental Study on the Adsorption and Desorption of Methane by Granular Activated Carbon at 25 ℃

A theoretical and experimental study was conducted to accurately determine the amount of adsorption and desorption of methane by various Granular Activated Carbon(GAC)under different physical conditions.To carry out the experiments,the volumetric method was used up to 500 psia at constant temperature of 25℃.In these experiments,adsorption as well as desorption capacities of four different GAC in the adsorption of methane,the major constituent of natural gas,at various equilibrium pressures and a constant temperature were studied.Also,various adsorption isotherm models were used to model the experimental data collected from the experiments.The accuracy of the results obtained from the adsorption isotherm models was compared and the values for the regressed parameters were reported.The results shows that the physical characteristics of activated carbons such as BET surface area,micropore volume,packing density,and pore size distribution play an important role in the amount of methane to be adsorbed and desorbed.     

An accurate empirical correlation for predicting natural gas compressibility factors

The compressibility factor of natural gas is an important parameter in many gas and petroleum engineering calculations. This study presents a new empirical model for quick calculation of natural gas compressibility factors. The model was derived from 5844 experimental data of compressibility factors for a range of pseudo reduced pressures from 0.01 to 15 and pseudo reduced temperatures from 1 to 3. The accuracy of the new empirical correlation has been compared with commonly used existing methods. The comparison indicates the superiority of the new empirical model over the other methods used to calculate compressibility factor of natural gas with average absolute relative deviation percent (AARD%) of 0.6535.     

A STUDY ON GEOCHEMICAL CHARACTERISTICS OF CONDENSATE

This paper makes an approach to the characteristics of the compound and carbon iso-topic composition of condensate in the Sichuan, Shaanxi-Gansu-Ningxia, Dongpu and Jiyangbasins in China. The results we have obtained show that the compound properties are re-lated to the maturity. The Paraffin Index Ⅰ and the Saturated-Aromatic Index (SAI) increasegradually from the immature to mature (or over mature) condensate. and the SAI valueincrease from 2 to more than 30. The carbonisotopic composition of condensate is control-led by the type of parent matter. If the oil and condensate come from the same source rock,they will have similar carbon isotopic composition. In the same region there is an obviousdifference in carbon isotopic composition between the condensate generated from coal-bear-ing strata and that from oil-source rocks. The difference can be regarded as a parameter fordistinguishing the coal-type gas from the oil-type gas. In the same basin the carbon isotop-ic composition of the natural gas-oil-co     

Wax phase equilibria: developing a thermodynamic model using a systematic approach

Reservoir hydrocarbon fluids contain heavy paraffins that may form solid phases of wax at low temperatures. Problems associated with wax formation and deposition are a major concern in production and transportation of hydrocarbon fluids. The industry has directed considerable efforts towards generating reliable experimental data and developing thermodynamic models for estimating the wax phase boundary.The cloud point temperature, i.e. the wax appearance temperature (WAT) is commonly measured in laboratories and traditionally used in developing and/or validating wax models. However, the WAT is not necessarily an equilibrium point, and its value can depend on experimental procedures. Furthermore, when determining the wax phase boundary at pipeline conditions, the common practice is to measure the wax phase boundary at atmospheric pressure, then apply the results to real pipeline pressure conditions. However, neglecting the effect of pressure and associated fluid thermophysical/compositional changes can lead to unreliable results.In this paper, a new thermodynamic model for wax is proposed and validated against wax disappearance temperature (WDT) data for a number of binary and multi-component systems. The required thermodynamic properties of pure n-paraffins are first estimated, and then a new approach for describing wax solids, based on the UNIQUAC equation, is described. Finally, the impact of pressure on wax phase equilibria is addressed.The newly developed model demonstrates good reliability for describing solids behaviour in hydrocarbon systems. Furthermore, the model is capable of predicting the amount of wax precipitated and its composition. The predictions compare well with independent experimental data, demonstrating the reliability of the thermodynamic approach.     

Experimental measurement and modeling study for estimation of wax disappearance temperature

Wax deposition is a frequent problem in oil pipelines and down-stream industries. Correct prediction of wax formation conditions is required to prevent this phenomenon. In this study, wax appearance temperature (WAT) of 12 Iranian oil and condensate samples were measured using viscometry data and differential scanning Calorimetry (DSC) analysis. Also, a new empirical correlation and intelligent artificial neural network (ANN) model were developed to estimate wax disappearance temperature (WDT) of crude oils. Specific gravity, pressure, and molecular weight of oil sample were used as input variables for these models. The ANN model was trained using different hidden neurons and training algorithms. Experimental measurements studies were used for validation of the new correlation. Comparing the results indicated that the ANN model has 0.27% error while most thermodynamic models have an average error of 0.35% to 2.19%. Also, the proposed correlation can predict WDT with good accuracy and minimum input data. Results show that this correlation has a maximum error of 1.16% for 310 published experimental data and 1.19% for 9 Iranian samples.     

The wax deposition rate of water-in-crude oil emulsions based on the laboratory flow loop experiment

This paper aims to develop a mathematical model to predict the wax deposition rate of waxy crude emulsions, combining heat and mass transfer mechanisms. According to the flow loop experimental results, the wax deposition rate increases with the decreasing average temperature of oil/wall in a manner of linear regularity, and shows a downtrend with the increase of water cut due to diffusion resistance. An applicable model is developed regarding emulsion properties, radial temperature gradient, shear stress, and wax diffusion coefficient. In model validation, the prediction results are in good agreement with experimental data with the relative errors within 28.87%.     

Prediction of gas condensate properties by Esmaeilzadeh–Roshanfekr equation of state

The Esmaeilzadeh–Roshanfekr (ER) equation of state (EOS) is used to predict the PVT properties of gas condensate reservoir fluids. Three gas condensate fluid samples taken from three wells in a real field in Iran, referred here as SA1, SA4 and SA8, as well as five samples from literature have been used to check the validity of the ER EOS in calculating the PVT properties of gas condensate mixtures. Some experiments such as constant composition expansion (CCE), constant volume depletion (CVD) and dew point pressures are carried out on these samples. In order to have an unbiased comparison between the ER and the Peng–Robinson (PR) equation of state, van der Waals mixing rules are used without using any adjustable parameters (k_ij = 0). Also, no pure component parameters are adjusted. The critical properties and acentric factor for plus-fraction are estimated by the Kesler–Lee, Pedersen et al. and Riazi–Daubert characterization methods. The results of dew point pressure calculations show that the ER EOS has smaller error than the PR EOS. For some mixtures, relative volume, gas compressibility factor and condensate drop-out in CVD and CCE test were also predicted. Comparison results between experimental and calculated data indicate that the ER EOS has smaller error than the PR EOS. The total average absolute deviation was found to be 0.82% and 2.97% for calculating gas compressibility factor and gas specific gravity in CVD test. Also, the total average absolute deviation was found to be 2.06% and 3.42% for calculating gas compressibility factor and relative volume in CCE test.     

Investigation of wax deposition and effective diffusion coefficient in water-in-oil emulsion system

As pipeline transportation is widely used in the petroleum industry, the problem of wax deposition is a severe threat to the safety of oil and gas transportation. In addition, the mechanism of wax deposition is very complicated due to the presence of water phase. This paper tries to clarify the effects of water fraction, temperature difference and experimental period on the wax deposition process in water-in-oil emulsion system by a series of static cold finger experiments. The experimental results reveal that the average diffusion rates decrease with increased water fraction, longer experimental period and reduced temperature difference. Furthermore, on the basis of wax deposition experiments in cold finger apparatus and radial temperature distribution simulations via Fluent, the influence of water phase on heat transfer occurring in the wax molecular diffusion process is revealed, and relationship between mass transfer and heat transfer is investigated. Additionally, the effective diffusion coefficient of wax molecules is calculated on the basis of experimental and simulation results. The calculated effective diffusion coefficients using this approach are significantly lower than the calculated results from conventional methods. This explains the remarkable disparity with previous works due to underestimating the influence of dispersed water.     

Thermal behavior and solid fraction dependent gel strength model of waxy oils

Thermal behavior of waxy oils is investigated using the techniques of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Model waxy oils and real waxy crude oils are utilized. Decomposition temperatures of waxy oils are obtained using TG analysis. The effects of thermal history, wax content, and additive on the gelation process of waxy oils are investigated using DSC. The DSC method provides a measure of wax solubility as well as solid fraction. An integration method and a computation method are utilized to predict solid fraction. In addition, wax crystallization onset points are obtained at the cooling rates ranging from 1 to 20 °C min^?1. Similarly, wax dissolution endset points are obtained at heating rates ranging from 1 to 20 °C min^?1. Extrapolated onset and endset points yield wax precipitation temperature and wax dissolution temperature, respectively. Subsequently, wax solubility curves are obtained using thermodynamic computations. A wax precipitation temperature method and a wax dissolution temperature method combine thermodynamic phase behavior with onset/endset points to predict solid fraction. Both the wax precipitation temperature method and the wax dissolution temperature method can predict solid fraction of waxy oil samples. The wax precipitation temperature method and the wax dissolution temperature method are accurate when the temperature is close to the wax appearance temperature. A heat-integration method provides accurate values of the solid fraction at temperatures significantly below the wax appearance temperature. Therefore, integration method and wax precipitation temperature/wax dissolution temperature method are combined to predict solid fraction. The effect of solid fraction on yield stress is also investigated using differential scanning calorimetry and rheometry. Finally, a new solid fraction dependent gel strength model is obtained for shut in and restart of waxy crude oil pipelines.     

Prediction Model Based on the Grey Theory for Tackling Wax Deposition in Oil Pipelines

1. Introduction Wax deposition from crude oil is an age-long prob- lem in the petroleum industry. This problem includes progressive precipitation and accumulation of waxes at the sand-face and perforations, tubings, surface production lines and storage tanks, thus limiting the production capacity of these facilities. Depending on the severity, wax deposition may lead to loss of production, mechanical failure of tubular equipment, increased production downtime, increased handling costs and mini…     

Predicting the dew point pressure for gas condensate reservoirs: empirical models and equations of state

This paper presents a new empirical model to estimate dew point pressure (DPP) for gas condensate reservoirs as a function of routinely measured gas analysis and reservoir temperature. The proposed model was developed using experimentally measured and collected data of 340 gas condensate samples covering a wide range of gas properties and reservoir temperatures. The new model has an average relative deviation (ARD) of 0.44% and average absolute deviation (AAD) of 7.68% or 346 psia (1 psia=6.894757E−3 mPa). The accuracy of the model has been compared to SRK-EOS, PR-EOS and other correlations. Gas condensate samples from this study as well as from literature have been used to check the validity of the proposed model against EOS simulation. These examples have shown that the model successfully captures the physical trend and that the model is reliable. This model is useful to provide an estimate of the DPP when experimentally measured ones are not available.The current study also shows that predicting the DPP for gas condensates depends on the EOS(s), the number of pseudo-components and the characterization of the plus fraction. For most of the gas condensates used in this study, a 10–12 pseudo-components of the heptane plus (C₇₊) fraction resulted in minimum error in calculation of DPP using PR-EOS with Pedersen et al. characterization of the plus fraction.     

Ultrafiltration of Thin Stillage from Conventional and E-Mill Dry Grind Processes

We used ultrafiltration (UF) to evaluate membrane filtration characteristics of thin stillage and determine solids and nutrient compositions of filtered streams. To obtain thin stillage, corn was fermented using laboratory methods. UF experiments were conducted in batch mode under constant temperature and flow rate conditions. Two regenerated cellulose membranes (10 and 100 kDa molecular weight cutoffs) were evaluated with the objective of retaining solids as well as maximizing permeate flux. Optimum pressures for 10 and 100 kDa membranes were 207 and 69 kPa, respectively. Total solids, ash, and neutral detergent fiber contents of input TS streams of dry grind and E-Mill processes were similar; however, fat and protein contents were different (p < 0.05). Retentate obtained from conventional thin stillage fractionation had higher mean total solids contents (27.6% to 27.8%) compared to E-Mill (22.2% to 23.4%). Total solids in retentate streams were found similar to those from commercial evaporators used in industry (25% to 35% total solids). Fat contents of retentate streams ranged from 16.3% to 17.5% for the conventional process. A 2% increment in fat concentration was observed in the E-Mill retentate stream. Thin stillage ash content was reduced 60% in retentate streams.