Numerical study of plasmas start-up by electron cyclotron waves in NCST spherical tokamak and CN-H1 stellarator

According to the physics of tokamak start-up,this study constructs a zero-dimensional(0D)model applicable to electron cyclotron(EC)wave assisted start-up in NCST spherical torus(spherical tokamak)and CN-H1 stellarators.Using the constructed 0D model,the results obtained in this study under the same conditions are compared and validated against reference results for pure hydrogen plasma start-up in tokamak.The results are in good agreement,especially regarding electron temperature,ion temperature and plasma current.In the presence of finite Ohmic electric field in the spherical tokamak,a study on the EC wave assisted start-up of the NCST plasma at frequency of 28 GHz is conducted.The impact of the vertical magnetic field B_(v)on EC wave assisted start-up,the relationship between EC wave injection power P_(inj),Ohmic electric field E,and initial hydrogen atom density n_(H0)are explored separately.It is found that under conditions of Ohmic electric field lower than ITER(~0.3 V m^(-1)),EC wave can expand the operational space to achieve better plasma parameters.Simulating the process of28 GHz EC wave start-up in the CN-H1 stellarator plasma,the plasma current in the zerodimensional model is replaced with the current in the poloidal coil of the stellarator.Plasma startup can be successfully achieved at injection powers in the hundreds of kilowatts range,resulting in electron densities on the order of 10^(17)-10^(18)m^(-3).

Numerical Simulation of a Two-Phase Flow with Low Permeability anda Start-Up Pressure Gradient

A new numerical model for low-permeability reservoirs is developed.The model incorporates the nonlinear characteristics of oil-water two-phase flows while taking into account the initiation pressure gradient.Related numerical solutions are obtained using a finite difference method.The correctness of the method is demonstrated using a two-dimensional inhomogeneous low permeability example.Then,the differences in the cumulative oil and water production are investigated for different starting water saturations.It is shown that when the initial water saturation grows,the water content of the block continues to rise and the cumulative oil production gradually decreases.

Dynamic evaluation of a scaled-down heat pipe-cooled system during start-up/shut-down processes using a hardware-in-the-loop test approach

Micro-mobile heat pipe-cooled nuclear power plants are promising candidates for distributed energy resource power genera-tors and can be flexibly deployed in remote places to meet increasing electric power demands.However,previous steady-state simulations and experiments have deviated significantly from actual micronuclear system operations.Hence,a transient analysis is required for performance optimization and safety assessment.In this study,a hardware-in-the-loop(HIL)approach was used to investigate the dynamic behavior of scaled-down heat pipe-cooled systems.The real-time features of the HIL architecture were interpreted and validated,and an optimal time step of 500 ms was selected for the thermal transient.The power transient was modeled using point kinetic equations,and a scaled-down thermal prototype was set up to avoid mod-eling unpredictable heat transfer behaviors and feeding temperature samples into the main program running on a desktop PC.A series of dynamic test results showed significant power and temperature oscillations during the transient process,owing to the inconsistency of the rapid nuclear reaction rate and large thermal inertia.The proposed HIL approach is stable and effective for further studying of the dynamic characteristics and control optimization of solid-state small nuclear-powered systems at an early prototyping stage.

New Start-up Method for a Closed-Cycle Compression System with Gas Bearings and Its Characteristics

Gas bearings,which have the advantages of low frictional resistance and power loss,high rotational speed and high temperature operation,and long life,are more suitable than are traditional liquid lubricated bearings because of their high precision,high rotational speed,and special condition support.However,the problem of starting a closed-cycle compression system with gas bearings still needs to be solved for practical application.Thus,a new start-up method for a closed-cycle compression system with aerostatic gas bearings is proposed in this paper.Further,this paper presents a numerical simulation and experimental investigation of the method’s feasibility and characteristics during the start-up process when the gas tank’s initial pressure is fixed.The results show that the gas tank volume is approximately directly proportional to the start-up time allowable,and a gas tank volume sufficiently small,which not only ensures the feasibility of start-up,but also affects other components only slightly,can be obtained.A perfect combination of radial and axial loads also can be achieved to make the start-up time allowable as long as possible.R134a is a better choice for the working medium than is air,as the start-up time allowable is longer,which leads to a smaller gas tank.This research proposes a new start-up method for a closed-cycle compression system with aerostatic gas bearings which has sufficient load capacity to support system during the start-up method.

Analysis on the Problems in Start-up and Debugging of Two 600 MW Generating Units in Yangzhou No.2 Thermal Power Plant

The problems including excessive flow of attemperating water for boiler, failure of butterfly valve at the outlet of circulating water pump, burnt-out of thyristor for excitation regulator, load variation rate of CCS not complying with the contract target, etc. occurred during start-up and debugging of two 600 MW generating units in Yangzhou No.2 Thermal Power Plant. Through analysis on these problems. the remedial measures were put forward, to which can be referred for similar units.

Start-up of anaerobic ammonia oxidation bioreactor with nitrifying activated sludge

The anaerobic ammonia oxidation(Anammox) bioreactor was successfully started up with the nitrifying activated sludge. After anaerobically operated for 105 d, the bioreactor reached a good performance with removal percentage of both ammonia and nitrite higher than 95% and volumetric total nitrogen removal as high as 149.55 mmol/(L·d). The soft padding made an important contribution to the high efficiency and stability because it held a large amount of biomass in the bioreactor.

基于马尔可夫链嵌入法的两阶段Start-Up验证试验模型

为了给出两阶段start-up验证试验模型相关指标的解析表达式,构造了符合两阶段start-up验证试验模型状态转移规律的马尔可夫链.应用马尔可夫链相关理论给出了试验次数的期望、方差、分布律、分布函数,以及接受和拒绝产品的概率矩阵表达式.数值示例表明,对于各种参数的两阶段start-up验证试验模型相关指标求解问题,有限马尔可夫链嵌入法比概率生成函数法更加有效.

A method to refine the start-up scheme of compression and refrigeration systems in ethylene plants via dynamic simulation

Starting the cracking gas compressor and precooling the refrigeration system are keys to start-up of an ethylene plant and accounts for up to 50% of the total start-up time and plant flare emissions. Premature feeding of cracking furnaces can be avoided if the cracking gas compressor is started and the refrigeration system is precooled in advance using mixed gas as the start-up working medium(SWM). Start-up scenario with mixed gas as SWM could significantly reduce the emission loss and shorten the precooling time. Research shows that making appropriate start-up scheme is important not only to ensure operational safety and feasibility, but also to reduce energy consumption. In this paper, a method is proposed to select suitable start-up operational parameters of compression and refrigeration system with sufficient safe operating ranges and short precooling time. The complex interrelation among key parameters of start-up is analyzed. It is found that higher energy consumption, especially for super high-pressure steam(SS), can promote operational safety and shorten the precooling time during start-up.Based on steady-state and dynamic simulation, appropriate operating parameter ranges are determined with reasonable SS consumption. A real case study demonstrates that an appropriate start-up scheme will optimize the operation.

The exact solution of Stokes' second problem including start-up process with fractional element

The start-up process of Stokes＇ second problem of a viscoelastic material with fractional element is studied. The fluid above an infinite flat plane is set in motion by a sudden acceleration of the plate to steady oscillation. Exact solutions are obtained by using Laplace transform and Fourier transform. It is found that the relationship between the first peak value and the one of equal-amplitude oscillations depends on the distance from the plate. The amplitude decreases for increasing frequency and increasing distance.

The start-up of biohydrogen-producing process by bioaugmentation in the EGSB reactor

Expanded granular sludge bed （EGSB） reactor and bioaugmentation were employed to investigate biohydrogen production with molasses wastewater. The start-up experiments consisted of two stages. In the first stage （0 - 24d） seeded with activated sludge, the butyric acid type-fermentation formed when the initial expanding rate, organic loading rate （OLR）, the initial redox potential （ORP） and hydraulic retention time （HRT） were 10%, 10.0 kg COD/（m^3·d）, -215 mV and 6.7 h, respectively. At the beginning of the second stage on day 25, the novel hydrogen-producing fermentative bacterial strain B49 （AF481148 in EMBL） were inoculated into the reactor under the condition of OLR 16. 0 kg COD/（m^3·d）, ORP and HRT about - 139 mV and 6.7 h, respectively, and then the reaction system transformed to ethanol-type fermentation gradually with the increase in OLR. When OLR, ORP and HRT were about 94.3 kg COD/（m^3·d）, -250 mV and 1.7 h, respectively, the system achieved the maximum hydrogen-producing rate of 282.6 mL H2/L reactor·h and hydrogen percentage of 51% -53% in the biogas.

Experimental research on characteristic of start-up pressure wave propagation in gelled crude oil by large-scale flow loop

In order to research start-up pressure wave propagation mechanism and determine pressure wave speed in gelled crude oil pipelines accurately,experiment of Large-scale flow loop was carried out.In the experiment,start-up pressure wave speeds under various operation conditions were measured,and effects of correlative factors on pressure wave were analyzed.The experimental and theoretical analysis shows that thermal shrinkage and structural properties of gelled crude oils are key factors influencing on start-up pressure wave propagation.The quantitative analysis for these effects can be done by using volume expansion coefficient and structural property parameter of gelled crude oil.A new calculation model of pressure wave speed was developed on the basis of Large-scale flow loop experiment and theoretical analysis.

Start-up and Performance of a Novel Reactor----Jet Biogas Inter-loop Anaerobic Fluidized Bed

A novel anaerobic reactor, jet biogas inter-loop anaerobic fluidized bed （JBILAFB）, was designed and constructed. The start-up and performance of the reactor was investigated in the Process. of .artificial glucose wastewater treatment. With the wastewater recycle ratio of 2.5 ： 1, the recycled wastewater with biogas could mix sludge and wastewater in the JBILAFB reactor completely. The start-up of the JBILAFB reactor could be completed in less than 70 d through maintenance of hydraulic retention time （HR^I＂） and stepwise increase of feed total organic carbon （TOC） concentration. After the start-up, with the volumetric TOC loadings of 14.3 kg·m ^-3·d^-1, the TOC removal ratio, the effluent pH, and the volatile fatty acids （VFA）/alkalinity of the JBILAFB reactor were more than 80%, close to 7.0 and less than 0.4, respectively. Moreover, CH4 was produced at more than 70% of the theoretical value, The reactor exhibited high stability under the condition of high volumetric TOC loading. Sludge granules in the JBILAFB reactor were developed during the start-up and their sizes were enlarged with the stepwise increase of volumetric TOC loadings from 0.8 kg.m^-3.d ^-1 to 14.3 kg.m^-3.d^-1. Granules, an offwhite color and a similar spherical shape, were mainly comprised of global-like bacteria. These had good methanogenic activity and settleability, which were formed probably through adhesion of the bacteria. Some inorganic metal compounds such as Fe, Ca, Mg, Al, etc. were advantageous to the formation of the granules.

Start-up and contaminants removal characteristics of aerobic granules-membrane bioreactor at low temperature

In order to understand the effect of low temperature on the formation process of aerobic granules and contaminants removal characteristics,the aerobic granules-membrane bioreactor (AGS-MBR) has been started up and operated at low temperature using the carbon resource of sodium acetate. Aerobic granules cultivated in AGS-MBR possess smooth surface and compact structure in morphology as well as better settling property and higher biomass after 38 days. The average parameters of aerobic granules are: diameter 3. 1 mm,wet density 1. 041 g/mL,sludge volume index 42. 35 mL/g and settling velocity 20. 6 - 45. 2 cm/min. During the start-up of AGS-MBR,the respectively average contaminants removal efficiencies at low temperature are 91. 9% for chemical oxygen demand (COD) ,89. 2% for NH4 + -N and 86. 3% for PO43- -P,and the overgrowth of filamentous bacteria has been well controlled. In addition,the hollow fiber microfiltration (MF) membrane fouling is light and the regime membrane layer is capable of enhancing membrane filtration as well as the average growth of trans-membrane pressure (TMP) is 1. 07 kPa/d. Compared with the conventional cultivation of aerobic granules,the sludge granulation time significantly decreases from 73 days to 38 days by the application of microfiltration membrane at low temperature.

Study on durability of Pt supported on graphitized carbon under simulated start-up/shut-down conditions for polymer electrolyte membrane fuel cells

The primary issue for the commercialization of proton exchange membrane fuel cell（PEMFC） is the carbon corrosion of support under start-up/shut-down conditions. In this study, we employ the nanostructured graphitized carbon induced by heat-treatment. The degree of graphitization starts to increase between 900 and 1300 ℃ as evidenced by the change of specific surface area, interlayer spacing, and ID/IG value. Pt nanoparticles are deposited on fresh carbon black（Pt/CB） and carbon heat-treated at 1700 ℃（Pt/HCB17） with similar particle size and distribution. Electrochemical characterization demonstrates that the Pt/HCB17 shows higher activity than the Pt/CB due to the inefficient microporous structure of amorphous carbon for the oxygen reduction reaction. An accelerating potential cycle between 1.0 and 1.5 V for the carbon corrosion is applied to examine durability at a single cell under the practical start-up/shutdown conditions. The Pt/HCB17 catalyst shows remarkable durability after 3000 potential cycles. The Pt/HCB17 catalyst exhibits a peak power density gain of 3%, while the Pt/CB catalyst shows 65% loss of the initial peak power density. As well, electrochemical surface area and mass activity of Pt/HCB17 catalyst are even more stable than those of the Pt/CB catalyst. Consequently, the high degree of graphitization is essential for the durability of fuel cells in practical start-up/shut-down conditions due to enhancing the strong interaction of Pt and π-bonds in graphitized carbon.

START-UP AND DYNAMIC PROCESSES SIMULATION OF A DISTILLATION COLUMN

A new dynamic non-equilibrium mixing-pool model for simulating start-up and dynamic re-sponse of a distillation column is reported.The proposed model is established on the basis ofconsidering the two dimensional flow/mixing behavior of actual trays in a distillation column.Com-parison is made among the computed results of the start-up time and the dynamic response time bythe proposed and five other typical models.It is found that the computed time for both dynamicprocesses is longer by the model which considers any flow/mixing pattern than by the model withoutsuch concern.The inertia effect of flow/mixing seems to be important and can not be ignored inmodeling the transient process of distillation.The proposed model,which is believed to be suitableto large column,seems somewhat useful in predicting industrial distillation dynamics.

Start-up phase plasma discharge design of a tokamak via control parameterization method

The tokamak start-up is a very important phase during the process to obtain a suitable equalizing plasma, and its governing model can be described as a set of nonlinear ordinary differential equations（ODEs）. In this paper, we first estimate the parameters in the original model and set up an accurate model to express how the variables change during the start-up phase, especially how the plasma current changes with respect to time and the loop voltage. Then, we apply the control parameterization method to obtain an approximate optimal parameters selection problem for the loop voltage design to achieve a desired plasma current target. Computational optimal control techniques such as the variational method and the costate method are employed to solve the problem, respectively. Finally, numerical simulations are performed and the results obtained via different methods are compared. Our numerical parameterization method and optimization procedure turn out to be effective.

Evaluation of Inocula and Packing Material for Acceleration of Start-Up in Biofilters

Several strategies with different combination of inocula and packing material were investigated to obtain the optimal start-up time and elimination capacity (EC) in toluene biofiltration. The inocula contained the activated sludge and toluene degrading bacteria, and the packing material consisted of different mixing ratios of peat and wood chips. A final toluene load of 21.2 g/(m3·h) was attained step by step in four parallel biofilters. A shortest start-up time of 15 days and a highest EC of 17.0 g/(m3·h) were observed in the biofilter B-4, which was inoculated with a special microbial consortium consisting of three strains of toluene degrading bacteria and was packed with the mixture of peat and wood chips at a ratio of 80:20 (w/w). These results indicated that inoculating pre-acclimatized microbes dramatically shortened the start-up time, and such a composition of packing material could maintain an appropriate environment (with the bed porosity and water content equating to 0.45 and 1.96, respectively) for the growth of dominant toluene degrading bacteria in the biofilter.

Quick start-up of EGSB reactor treating fresh leachate of municipal solid waste

An expanded granular sludge bed （EGSB） reactor inoculated with anaerobic granular sludge was started up with its COD removal performance, self-balancing of pH, biogas production rate and characteristics of the granular sludge during the start-up period being investigated. The results indicated that the EGSB reactor can be started up successfully in 27 d by increasing the organic loading rate rapidly. The removal efficiency of COD was maintained above 93% with influent COD concentration of 25 000 mg/L and OLR of 37.94 kgCOD/（m 3 ·d）. The EGSB reactor with good pH self-balancing could be fed with fresh leachate of low pH value （4 5）. The biogas production rate was closely related with OLR and COD reduction. Every gram of COD fed （consumed） to the reactor produced 0.34 L STP （0.36 L STP ） biogas with 0.21 L STP （0.23 L STP ） methane. Thus, 65% 70% of the produced biogas was methane. Sixty one percentage of COD fed to the reactor was converted to methane, another 33% was converted to biomass by metabolism, and the other 6% was left in the liquid phase. The specific methanogenic activity （SMA） of the granular sludge had increased by 92% after 27 d dynamic incubation. The granular sludge in the reactor had good settlement performance with majority diameter of 1 2 mm.

Tokamak Start-up under Assistance of RF Waves

To improve the start-up behavior of tokamak discharges and realize the low loop voltage start-up is required by performance of large scale, full superconductor tokamaks. In recent years, some kinds of RF wave have been used to assist the start-up and some exciting results have been gained. This paper introduce the investigation on both in physical principle and experimental research of the start-up process, in which high frequency RF waves were used to assist it.

Numerical simulation of the start-up process of a miniature ion thruster

A particle-in-cell Monte Carlo collision model of a discharge chamber is established to investigate the start-up process of a miniature ion thruster.We present the discharge characteristics at different stages(the initial stage,development stage,and stable stage)according to the trend of the discharge current with time.The discharge current is the sum of the sidewall current and the backplate current.During the start-up process,the sidewall current lags behind the backplate current.The variation and distribution characteristics of the discharge current over time are determined by the electron density distribution and electric potential distribution.