A study of hydrate plug formation in a subsea natural gas pipeline using a novel high-pressure flow loop

The natural gas pipeline from Platform QKI8-1 in the southwest of Bohai Bay to the onshore processing facility is a subsea wet gas pipeline exposed to high pressure and low temperature for a long distance. Blockages in the pipeline occur occasionally. To maintain the natural gas flow in the pipeline, we proposed a method for analyzing blockages and ascribed them to the hydrate formation and agglomeration. A new high-pressure flow loop was developed to investigate hydrate plug formation and hydrate particle size, using a mixture of diesel oil, water, and natural gas as experimental fluids. The influences of pressure and initial flow rate were also studied. Experimental results indicated that when the flow rate was below 850 kg/h, gas hydrates would form and then plug the pipeline, even at a low water content （10%） of a water/oil emulsion. Furthermore, some practical suggestions were made for daily management of the subsea pipeline.

Gas Film Disturbance Characteristics Analysis of High-Speed and High-Pressure Dry Gas Seal

The dry gas seal（DGS） has been widely used in high parameters centrifugal compressor, but the intense vibrations of shafting, especially in high-speed condition, usually result in DGS＇s failure. So the DGS＇s ability of resisting outside interference has become a determining factor of the further development of centrifugal compressor. However, the systematic researches of which about gas film disturbance characteristics of high parameters DGS are very little. In order to study gas film disturbance characteristics of high-speed and high-pressure spiral groove dry gas seal（S-DGS） with a flexibly mounted stator, rotor axial runout and misalignment are taken into consideration, and the finite difference method and analytical method are used to analyze the influence of gas film thickness disturbance on sealing performance parameters, what＇s more, the effects of many key factors on gas film thickness disturbance are systematically investigated. The results show that, when sealed pressure is 10.1MPa and seal face average linear velocity is 107.3 m/s, gas film thickness disturbance has a significant effect on leakage rate, but has relatively litter effect on open force; Excessively large excitation amplitude or excessively high excitation frequency can lead to severe gas film thickness disturbance; And it is beneficial to assure a smaller gas film thickness disturbance when the stator material density is between 3.1 g/cm3 to 8.4 g/cm3; Ensuring sealing performance while minimizing support axial stiffness and support axial damping can help to improve dynamic tracking property of dry gas seal. The proposed research provides the instruction to optimize dynamic tracking property of the DGS.

Numerical Simulation Analysis of the Transformer Fire Extinguishing Process with a High-Pressure Water Mist System under Different Conditions

To thoroughly study the extinguishing effect of a high-pressure water mist fire extinguishing system when a transformer fire occurs,a 3D experimental model of a transformer is established in this work by employing Fire Dynamics Simulator(FDS)software.More specifically,by setting different parameters,the process of the highpressure water mist fire extinguishing system with the presence of both diverse ambient temperatures and water mist sprinkler laying conditions is simulated.In addition,the fire extinguishing effect of the employed high-pressure water mist system with the implementation of different strategies is systematically analyzed.The extracted results show that a fire source farther away fromthe centerline leads to a lower local temperature distribution.In addition,as the ambient temperature increases,the temperature above the fire source decreases,while the temperature and the concentrationof theupperflue gas layer bothdecrease.Interestingly,after thehigh-pressurewatermist sprinkler begins to operate,both the temperature distribution above the fire source and the concentration of the flue gas decrease,which indicates that the high-pressure water mist system plays the role of cooling and dust removal.By comparing various sprinkler laying methods,it is found that the lower sprinkler height has a better effect on the temperature above the fire source,the temperature of the upper flue gas layer,and the concentration of the flue gas.Moreover,when the sprinkler is spread over thewhole transformer,the cooling effect on both the temperature above the fire source and the temperature of the upper flue gas layer is good,whereas the change in the concentration of the flue gas above the fire source is not obvious compared to the case where the sprinkler is not fully spread.

Flow-Optimization to Enhance Gas Quenching Efficiency for Helical Gears Specimen

Numerical simulations based on a conjugate heat transfer solver have been carried out to analyze various gas quenching configurations involving a helical gear streamed by an air flow at atmospheric pressure in a gas quenching chamber. In order to optimize the heat transfer coefficient distribution at key positions on the specimen, configurations involving layers of gears and flow ducts comprising single to multiple gears have been simulated and compared to standard batch configurations in gas quenching. Measurements have been performed covering the local heat transfer for single gears and batch of gears. The homogeneity of the heat transfer coefficient is improved when setting up a minimal distance between the gears (batch density) and when introducing flow ducts increasing the blocking grade around the gears. An offset between layers of the batch as well as flow channels around the gears plays a significant role in increasing the intensity and the homogeneity of the heat transfer in gas quenching process.

Mold Filling and Prevention of Gas Entrapment in High-pressure Die-casting

This paper presents some results of direct observation of mold filling in a specially designed die-casting by X-ray diffraction, including comparison with numerical simulation. Based on such work the authors discuss how to prevent gas entrapment and propose new methods.

Modelling of high speed gas quenching

Gas quenching has been used in vacuum furnaces for many years and its characteristics for bulk quenching of components are well known. More recently the use of gas quenching applied to single or small groups of components that were heated in either vacuum or conventional atmosphere furnaces has been proposed. Gas quenching may be seen as meeting the needs of modern "batches-of-one" processing for "just-in-time" manufacturing. It is clean, non-toxic and leaves no residues to be removed after processing. If this process is to be possible then heat extraction rates equivalent to those obtained from a medium quench oil must be achieved uniformly at the surface of real components. There are several strategies for meeting this aim: first, conventional high pressure quenching; second, moderate velocity quenching utilising a high heat transfer coefficient gas such as helium, and third, high velocity quenching utilising a gas with lower thermal efficiency. The implementation cost for the first strategy is high as is the miming cost of the second unless high cost gas recycling equipment is considered. In the third, overall costs can be minimised by using a low cost gas such as nitrogen without the need to recycle. It is this third strategy which is the subject of this paper. Computational Fluid Dynamics (CFD) was used to determine if indeed the process could achieve the required results and then to optimise the process parameters off-line. Implementation of a feasible process will then be carried out in the field.

Numerical Analysis of Thermal Distortion and Residual Stresses in H13 Steel Due to Vacuum Gas Quenching

Heat treated steel components often suffer distortion and residual stress effects when cooled to room temperature. A numerical analysis of a vacuum gas quenched die block made of H 13 was carried out utilising a nonlinear thermoelastic-plastic stress model together with the fluid flow and thermal profiles within the furnace. Simulation procedures for stress behaviour of the die were developed for both direct quench and marquench processes. Results of the initial thermal analysis indicated that the temperature difference between the surface and core of the die during direct quenching (gas pressure is 4 bar) was larger than that due to marquenching ( gas pressure is 4 bar at the beginning and 2 bar near isothermal hold). Simulation of the cooling rates at the surface and core of the die during marquenching correlated well with the experimental data. Further stress simulation indicated that the final thermal distortion and residual stresses in the die after direct quenching were larger than those due to marquenching. The findings of the numerical analysis suggested that marquenching is recommended for this die because it could reduce the temperature difference in the die and thus result in less thermal distortion and residual stresses.

Productivity Analysis Method of Abnormal High-Pressure Gas Reservoir in Ying-Qiong Basin

Ying-Qiong Basin in the west of South China Sea contains plenty of abnormal high-pressure gas reservoirs, whose stress sensitivity is crucial for well productivity. To explore the influence of stress sensitivity on production, the variable outlet back pressure stress sensitivity experiments were applied to test core sample permeability under different burden pressure and obtain the relational expression of power function of core stress sensitivity. Afterwards, new productivity equation is deduced in consideration of reservoir stress sensitivity, and the affection of stress sensitivity on production is analyzed. The result demonstrates close link between stress sensitivity and productivity, since single well production decreases dramatically when reservoir stress sensitivity has been taken into account. This research is constructive for well-testing data interpretation in stress sensitive gas reservoirs.

Formation of Large-Volume High-Pressure Plasma in Triode-Configuration Discharge Devices

A ＂plane cathode micro-hollow anode discharge （PCHAD）＂ is studied in comparison with micro-hollow cathode discharge （MHCD）. A new triode-configuration discharge device is also designed for large-volume, high-pressure glow discharges plasma without glow-to-arc transitions, as well as with an anode metal needle, and a cathode of PCHAD. It has a ＂needle-hole＂ sustained glow discharge. Its discharge circuit employs only one power supply circuit with a variable resistor. The discharge experiments have been carried out in the air. The electrical properties and the photoimages in PCHAD, multi-PCHAD and ＂needle-hole＂ sustained discharge have been investigated. The electrical and the optical measurements show that this triode-configuration discharge device can operate stably at high-pressure, in parallel without individual ballasting resistance. And the electron density of the plasma is estimated to be up to 10^12cm^-3. Compared with the twosupply circuit system, this electrode configuration is very simple with lower cost in generating large-volume plasma at high pressures.

Understanding CO_2 decomposition by thermal plasma with supersonic expansion quench

CO2 pyrolysis by thermal plasma was investigated,and a high conversion rate of 33% and energy efficiency of 17% were obtained.The high performance benefited from a novel quenching method,which synergizes the converging nozzle and cooling tube.To understand the synergy effect,a computational fluid dynamics simulation was carried out.A quick quenching rate of 10~7Ks（-1） could be expected when the pyrolysis gas temperature decreased from more than 3000 to 1000 K.According to the simulation results,the quenching mechanism was discussed as follows： first,the compressible fluid was adiabatically expanded in the converging nozzle and accelerated to sonic speed,and parts of the heat energy converted to convective kinetic energy; second,the sonic fluid jet into the cooling tube formed a strong eddy,which greatly enhanced the heat transfer between the inverse-flowing fluid and cooling tube.These two mechanisms ensure a quick quenching to prevent the reverse reaction of CO2 pyrolysis gas when it flows out from the thermal plasma reactor.

Natural gas density under extremely high pressure and high temperature: Comparison of molecular dynamics simulation with corresponding state model

This work applied molecular dynamics(MD)simulation to calculate densities of natural gas mixtures at extremely high pressure(>138 MPa)and high temperature(>200℃)conditions(x HPHT)to bridge the knowledge and technical gaps between experiments and classical theories.The experimental data are scarce at these conditions which are also out of assumptions for classical predictive correlations,such as the Dranchuk&Abou-Kassem(DAK)equation of state(EOS).Force fields of natural gas components were carefully chosen from literatures and the simulation results are validated with experimental data.The largest relative error is 2.67%for pure hydrocarbons,2.99%for C1/C3 mixture,7.85%for C1/C4 mixture,and 8.47%for pure H2S.These satisfactory predictions demonstrate that the MD simulation approach is reliable to predict natural-and acid-gases thermodynamic properties.The validated model is further used to generate data for the study of the EOS with pressure up to 276 MPa and temperature up to 573 K.Our results also reveal that the Dranchuk&Abou-Kassem(DAK)EOS is capable of predicting natural gas compressibility to a satisfactory accuracy at x HPHT conditions,which extends the confidence range of the DAK EOS.

Computer Aided Design for the Recovery of Boil-Off Gas from LNG Plant

Boil-Off Gas creation and usage has been a source of worry in Liquefied Natural Gas value supply chain. BOG is generated when there is temperature gradient between the environment and LNG temperature within the carrier tank, process lines or vessels. In this work, Computer Aided Design for the recovery of BOG from flare in an LNG Plant considered the dynamic nature of the BOG with minimized total energy consumption. A rigorous simulation based optimization model using HYSYS V8.8 was presented. Possible BOG scenarios were formulated in this report and considerations taken from the BOG scenarios to form the basic scope of this work. An Aspen HYSYS Software was used to develop a Process Flow Scheme (PFS) which was simulated using the BOG scenarios formulated. The BOG scenario temperatures considered were -15°C for Warm Ship analogy, -90°C for Cold Ship and -140°C for Normal Design Mode. Assumptions were also made on the feed into the developed PFS before quenching the various BOG temperatures. With HYSYS simulation at assumed constant inlet mass flow rate of 25,000 kg/s for BOG FEED, 6250 kg/s for LNG & LNG1 FEED, quenching at various BOG feed temperature -15°C, -90°C and -140°C, gave a meaningful output. The Mass flow rate recovered from Warm Ship at -15°C for Cold Product was 35,183 Kg/s and for Liquid Product 2317 Kg/s. For Cold ship at -90°C, the Cold Product recovered was 32,174 Kg/s and Liquid Product was 5326 Kg/s. Also, for -140°C, the Cold Product was 28,004 Kg/s and the Liquid Product was 9496 Kg/s. The Energy stream for the Compressor, Cooler and Pump in the Process Flow Stream (PFS) were observed in Table 5. At -15°C, the Compressor energy was 3.22E+07KJ/h, while the Pump energy was 3412KJ/h, and the Cooler gave 1.90E+07KJ/h. The results above showed that excessive BOG from Warm ship can be quenched and recovered for other end users rather than undue flaring of the gases. Extra work needs to be done to ensure minimal energy utilisation, optimal recovery and high efficiency of this developed model.

Development of a simplified n-heptane/methane model for high-pressure direct-injection natural gas marine engines

High-pressure direct-injection (HPDI) of natu- ral gas is one of the most promising solutions for future ship engines, in which the combustion process is mainly controlled by the chemical kinetics. However, the employment of detailed chemical models for the multi-dimensional combustion simulation is significantly expensive due to the large scale of the marine engine. In the present paper, a reduced n-heptane/methane model consisting of 35-step reactions was constructed using multiple reduction approaches. Then this model was further reduced to include only 27 reactions by utilizing the HyChem (Hybrid Chemistry) method. An overall good agreement with the experimentally measured ignition delay data of both n-heptane and methane for these two reduced models was achieved and reasonable predictions for the measured laminar flame speeds were obtained for the 35-step model. But the 27-step model cannot predict the laminar flame speed very well. In addition, these two reduced models were both able to reproduce the experimentally measured in-cylinder pressure and heat release rate profiles for a HPDI natural gas marine engine, the highest error of predicted combustion phase being 6.5%. However, the engine-out CO emission was over-predicted and the highest error of predicted NOx emission was less than 12.9%. The predicted distributions of temperature and equivalence ratio by the 35-step and 27-step models are similar to those of the 334-step model. However, the predicted distributions of OH and CH2O are significantly different from those of the 334-step model. In short, the reduced chemical kinetic models developed provide a high-efficient and dependable method to simulate the characteristics of combustion and emissions in HPDI natural gas marine engines.

Study on the inflammatory cytokines after heterotopic transplantation of isolated mouse heart preserved in a high-pressured mixed gas chamber

Background The maintenance of heart viability is important for heart transplantation. Currently, heart preservation is limited to 6 hours of cold ischemic storage. This study explored a new heart preservation method under a high-pressured mixed gas chamber. Methods C57BL/6 male mice were used to establish the model of mice cervical heterotopic heart transplantation. Adult donor mice were randomly divided into three groups subjected to naive operation （Group A）, standard control （Group B） and experimental control （Group C）. The recipient mice were randomly divided into two groups subjected to standard control and experimental control. Group A： hearts were isolated; Group B： hearts were isolated and preserved in HTK solution at 4 ℃ for 8 h and transplanted; Group C： hearts were isolated and preserved in high pressured gas （PO2：3200 hPa ＋ PCO： 800 hPa = 4000 hPa） at 4 ℃ for 8h and transplanted. After transplantation, the state of re-beating and cardiac function were observed for Group B and C. At 24 h after transplantation, samples were collected for HE staining, cardiac cell apoptosis detection by Tunnel staining and analysis of tumor necrosis factor α （TNF-α）, interleukin-1β （IL-1β）, interleukin-6 （IL-6） and interleukin-10 （IL-10） by reverse transcriotion-polymerase chain reaction （RT-PCR）. Results In group C, 15 transplanted hearts were re-beat, while only 6 in Group B. The re-beating rate in Group C was significantly higher than Group B [75.0%（15/20） vs. 30.0%（6/20） ,P = 0.01]. The time of re-beating was significantly different between Group B, and C [（352.35 ± 61.07）s vs. （207.85 ± 71.24） s, P 〈 0.011. HE staining showed that pathologic changes such as ceil edema and inflammatory cell infiltration were more obvious in Group B and C than in Group A, but less obvious in Group C compared with Group B. Tunnel staining showed that Group B had more obvious apoptosis than Group A and C. RT-PCR results showed significant increase of TNF-α, IL-1β and IL-6 expression in Group B than Group C （P 〈 0.01, the expression of IL-10 was higher in Group C than that in Group B. Conclusion Highpressured mixed gas （PO2：3200 hPa ＋ PCO： 800 hPa = 4000 hPa） preservation can reduce cold ischemia and reperfusion injury of donor heart, therefore to maintain myocardial viability and prolong preservation time of donor heart.

Effect of particle size on high-pressure methane adsorption of coal

Adsorbed gas cannot be neglected in the evaluation of coalbed methane and shale gas since a significant proportion of gas is stored in the form of adsorbed gas.Adsorbed methane of coal and shale has been widely studied by high-pressure methane adsorption experiment.In sample treatment of the experiment,the sample is crushed and sieved to a particular particle size range.However,how particle size influence high-pressure methane adsorption is still unclear.In this study,low-pressure nitrogen(N_(2))and high-pressure methane adsorption have been measured on coal samples with different particle size.According to N2 sorption analysis,pore volume and surface area increase with particle size reduction.Pore size distribution of small pores(<10nm)changes among varying particle size.Pore volume proportion of small pores(<10nm)increases and pore volume proportion of big pores(>10nm)decreases with decreasing particle size.Decreasing particle size by crushing sample introduces new connectivity for closed pores to the particle surface.The responses of isotherms of high-pressure methane adsorption are different with different particle size.Methane adsorption at initial pressure(145psi)increases with decreasing particle size.Adsorption increase rate at high pressure(435-870psi)decreases with particle size reduction.This can be explained that fine sample has more pore volume and higher pore volume proportion of small pores(<10nm).Sample with particle size of 150-250μm has the highest Langmuir volume.

Functional Aspects of Silencing and Transient Expression of <i>psb</i>S in <i>Nicotiana benthamiana</i>

MicroRNA-based gene silencing is a functional genomics tool for a wide range of eukaryotes. As a basis for broader application of virus-induced gene silencing (VIGS) to photosynthesis research, we employed a tobacco rattle virus (TRV) vector to silence expression of the nuclear psbS gene in Nicotiana benthamiana. The 22-kiloDalton psbS protein is essential for xanthophyll- and H+-dependent thermal dissipation of excitation in higher plants widely known as nonphotochemical quenching (NPQ). Controls treated with the TRV-VIGS vector containing a bacterial chloramphenicol resistance gene as the silencing target were included to test for non-silencing effects of the viral vector system. PsbS protein was undetectable and both psbS mRNA transcript levels and NPQ capacity were dramatically reduced in new leaf tissue of VIGS-psbS plants only. Photosynthetic performance in TRV-VIGS-treated and uninfiltrated plants was assessed by application of CO2 exchange, chlorophyll fluorescence, and in vivo absorbance changes at 810 nm. TRV-VIGS caused a mild stress based on pigment content and light absorption characteristics in some cases. To assess transient complementation of NPQ, the endogenous psbS gene was silenced using only the transit sequence in the TRV vector followed by Agrobacterium-mediated transient expression of a modified gene consisting of an altered transit sequence fused to the native mature protein sequence. Nevertheless, NPQ in infused fully expanded leaves that expressed this re-introduced form was not fully restored indicating the possible importance of psbS incorporation prior to formation of grana stacks.

Theoretical simulation of high-voltage discharge with runaway electrons in sulfur hexafluoride at atmospheric pressure

The results of theoretical simulation of runaway electron generation in high-pressure pulsed gas discharge with inhomogeneous electric field are presented.Hydrodynamic and kinetic approaches are used simultaneously to describe the dynamics of different components of low-temperature discharge plasma.Breakdown of coaxial diode occurs in the form of a dense plasma region expanding from the cathode.On this background there is a formation of runaway electrons that are initiated by the ensemble of plasma electrons generated in the place locally enhanced electric field in front of dense plasma.It is shown that the power spectrum of fast electrons in the discharge contains electron group with the so-called“anomalous”energy.

Application of difference arithmetic in the continuous annealing process line cooling control at Baosteel

Some of the main cooling processes and equipment that are currently being used in the continuous annealing process line （CAPL） at Baosteel are introduced, as well as their cooling control model techniques, the modeling principium and their application results. With charts indicating the control trends in real processes, the powerful adjusting ability of the control models with process variable differences and their excellent control precision are shown in this study.

Multi-Scale Pore Structure Heterogeneity in Tuff Reservoirs Investigated with Multi-Experimental Method and Fractal Dimensions in Chang 7 Formation,Southern Ordos Basin

The tight tuff reservoir is an unusual type of unconventional reservoir with strong heterogeneity.However,there is a lack of research on the microscopic pore structure that causes the heterogeneity of tuff reservoirs.Using the Chang 7 Formation in Ordos Basin,China as a case study,carbon-dioxide gas adsorption,nitrogen gas adsorption and high-pressure mercury injection are integrated to investigate the multi-scale pore structure characteristics of tuff reservoirs.Meanwhile,the fractal dimension is introduced to characterize the complexity of pore structure in tuff reservoirs.By this multi-experimental method,the quantitative characterizations of the full-range pore size distribution of four tuff types were obtained and compared in the size ranges of micropores,mesopores and macropores.Fractal dimension curves derived from full-range pores are divided into six segments as D1,D2,D3,D4,D5 and D6 corresponding to fractal characteristics of micropores,smaller mesopores,larger mesopores,smaller macropores,medium macropores and larger macropores,respectively.The macropore volume,average macropore radius and fractal dimension D5 significantly control petrophysical properties.The larger macropore volume,average macropore radius and D5 correspond to favorable pore structure and good reservoir quality,which provides new indexes for the tuff reservoir evaluation.This study enriches the understanding of the heterogeneity of pore structures and contributes to unconventional oil and gas exploration and development.

Processing soft ferromagnetic metallic glasses:on novel cooling strategies in gas atomization,hydrogen enhancement,and consolidation

Processing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples.The commercial viability of these materials depends on commercial purity feedstock.However,crystallization in commercial purity feedstock is several orders of magnitude faster than in high purity materials.The production of amorphous powders with commercial purity requires high cooling rates,which can only be achieved by extending the common process window in conventional gas atomization.The development of novel cooling strategies during molten metal gas atomization on two model alloys({(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 and Fe76B10Si9P5)is reported.Hydrogen inducement during liquid quenching significantly improved the glass-forming ability and soft magnetic properties of{(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders.Spark plasma sintering experiments verified that amorphous rings could be produced regardless of the cooling strategies used.While the saturation magnetization was almost unaffected by consolidation,the coercivity increased slightly and permeability decreased significantly.The magnetic properties of the final bulk samples were independent of feedstock quality.The developed cooling strategies provide a great opportunity for the commercialization of soft ferromagnetic glass-forming alloys with commercial purity.