A repairable queueing model with two-phase service, start-up times and retrial customers

2010 ◽  
Vol 37 (7) ◽  
pp. 1181-1190 ◽  
Author(s):  
Ioannis Dimitriou ◽  
Christos Langaris
Keyword(s):  
Queueing Model ◽  
Two Phase ◽  
Start Up

scholarly journals Productivity Influence Factors of Tight Sandstone Gas Reservoir with Water Produced

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Yongchao Xue ◽  
Qingshuang Jin ◽  
Hua Tian
Keyword(s):  
Pressure Gradient ◽  
Relative Permeability ◽  
Gas Flow ◽  
Influence Factors ◽  
Stress Sensitivity ◽  
Consumption Pattern ◽  
Tight Sandstone ◽  
Gas Reservoir ◽  
Two Phase ◽  
Start Up

Finding ways to accelerate the effective development of tight sandstone gas reservoirs holds great strategic importance in regard to the improvement of consumption pattern of world energy. The pores and throats of the tight sandstone gas reservoir are small with abundant interstitial materials. Moreover, the mechanism of gas flow is highly complex. This paper is based on the research of a typical tight sandstone gas reservoir in Changqing Oilfield. A strong stress sensitivity in tight sandstone gas reservoir is indicated by the results, and it would be strengthened with the water production; at the same time, a rise to start-up pressure gradient would be given by the water producing process. With the increase in driving pressure gradient, the relative permeability of water also increases gradually, while that of gas decreases instead. Following these results, a model of gas-water two-phase flow has been built, keeping stress sensitivity, start-up pressure gradient, and the change of relative permeability in consideration. It is illustrated by the results of calculations that there is a reduction in the duration of plateau production period and the gas recovery factor during this period if the stress sensitivity and start-up pressure gradient are considered. In contrast to the start-up pressure gradient, stress sensitivity holds a greater influence on gas well productivity.

Cycle analysis of a two-phase queueing model with threshold

2003 ◽  
Vol 144 (1) ◽  
pp. 157-165 ◽  
Author(s):  
Tae-Sung Kim ◽  
Hyun-Min Park
Keyword(s):  
Queueing Model ◽  
Two Phase

Research on the Start-Up Effect of Two-Phase Anaerobic Baffled Reactor

2013 ◽  
Vol 448-453 ◽  
pp. 600-603
Author(s):  
Ling Jing ◽  
Xin Xia Wang
Keyword(s):  
Wastewater Treatment ◽  
Ph Value ◽  
Removal Rate ◽  
Limiting Factors ◽  
Small Cities ◽  
Two Phase ◽  
Anaerobic Reactor ◽  
Anaerobic Baffled Reactor ◽  
Low Concentration ◽  
Start Up

Aiming at the fact that the low concentration sewage in small cities, this paper presents Two-phase Anaerobic Baffled Reactor (TAABR) for living wastewater treatment, importantly, it designs and researches Two-phase Anaerobic Baffled Reactor and its advantages, designs a trial project according to the characteristics of the reactor equip. The experiment uses the method that by shortening HRT to raise the load to start and analyses the operating results during startup as follows: 1. 53 days later anaerobic reactor start-up successes.2. When the load is 0.5kgCOD/m3.d, the removal rate of COD is more than 80%. 3. PH value is not the main limiting factors during start up in the reactor and there is basically no danger of excessive acidification.

Analysis of ABWR Critical Control Operation by TRACG Code

2009 ◽  
Author(s):  
Yoshihiko Ishii ◽  
Kazuaki Kitou ◽  
Tomohiko Ikegawa ◽  
Shin Hasegawa ◽  
Hitoshi Ochi
Keyword(s):  
Diffusion Theory ◽  
Three Dimensional ◽  
Source Model ◽  
Control Mode ◽  
Two Phase ◽  
Control Rod ◽  
Start Up ◽  
Neutron Count ◽  
Calculation Results ◽  
Operation Timing

Hitachi utilized three-dimensional transient analysis to design and verify a critical-control mode algorithm of an automatic power regulator (APR). TRACG has a three-dimensional neutron kinetics model based on diffusion theory and a six-equation two-phase flow model. To verify the APR critical-control mode algorithm, an external-neutron-source model that makes possible to simulate a sub-critical initial core, and an APR system model were developed and added on TRACG. The code was verified by comparison of measurements and calculation results of ABWR start-up operation under the critical-control mode. The modified TRACG could simulate neutron count rates of start-up-range neutron monitors (SRNMs), reactor period, control rod operation timing, CR withdrawal length, and time of criticality declaration, well.

Start up of Thermophilic UASB (Upflow Anaerobic Sludge Blanket) Reactors Using Micro-Carrier and Mesophilic Granular Sludge

1992 ◽  
Vol 26 (3-4) ◽  
pp. 877-886 ◽  
Author(s):  
T. Ohtsuki ◽  
M. Watanabe ◽  
Y. Miyaji
Keyword(s):  
High Performance ◽  
Ph Dependence ◽  
Granular Sludge ◽  
Upflow Anaerobic Sludge Blanket ◽  
Uasb Reactor ◽  
Anaerobic Sludge ◽  
Phase System ◽  
Two Phase ◽  
Start Up ◽  
Initial Seed

Two start-up methods of thermophilic UASB reactor were investigated for fast start-ups; one utilized micro-carrier as an initial support material and the other used intact mesophilic UASB granules as an initial seed. With both methods thermophilic granules having high activity were obtained in less than 3 months, even with acidified wastewater. Maximum sludge load for VFA substrate and sugar substrate were 3.2 and 0.9 kgCOD/kgVSS/day, respectively. Pre-acidogenesis was indispensable for high-performance treatment of sugar-containing substrate. It was proven that with a two-phase system sludge load could be raised to 3.0 kgCOD/kgVSS/day for sugar containing wastewaters. Some features of obtained sludge were examined, including maximum substrate utilizing activities, temperature dependence, pH dependence, and activity deterioration under lower loading conditions.

scholarly journals Investigation of Start-Up Characteristics of Thermosyphons Modified with Different Hydrophilic and Hydrophobic Inner Surfaces

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 765 ◽  
Author(s):  
Xiaolong Ma ◽  
Zhongchao Zhao ◽  
Pengpeng Jiang ◽  
Shan Yang ◽  
Shilin Li ◽  
...  
Keyword(s):  
Contact Angle ◽  
Significant Role ◽  
Smooth Surface ◽  
Hydrophobic Properties ◽  
Two Phase ◽  
Condenser Section ◽  
Chemical Coating ◽  
Evaporator Section ◽  
Wall Superheat ◽  
Start Up

In this paper, the influence of wettability properties on the start-up characteristics of two-phase closed thermosyphons (TPCTs) is investigated. Chemical coating and etching techniques are performed to prepare the surfaces with different wettabilities that is quantified in the form of the contact angle (CA). The 12 TPCTs are processed including the same CA and a different CA combination on the inner surfaces inside both the evaporator and the condenser sections. For TPCTs with the same wettability properties, the introduction of hydrophilic properties inside the evaporator section not only significantly reduces the start-up time but also decreases the start-up temperature. For example, the start-up time of a TPCT with CA = 28° at 40 W, 60 W and 80 W is 46%, 50% and 55% shorter than that of a TPCT with a smooth surface and the wall superheat degrees is 55%, 39% and 28% lower, respectively. For TPCTs with combined hydrophilic and hydrophobic properties, the start-up time spent on the evaporator section with hydrophilic properties is shorter than that of the hydrophobic evaporator section and the smaller CA on the condenser section shows better results. The start-up time of a TPCT with CA = 28° on the evaporator section and CA = 105° on the condenser section has the best start-up process at 40 W, 60 W and 80 W which is 14%, 22% and 26% shorter than that of a TPCT with smooth surface. Thus, the hydrophilic and hydrophobic modifications play a significant role in promoting the start-up process of a TPCT.

PERFORMANCE OF THE WALLUMBILLA LPG PLANT

1986 ◽  
Vol 26 (1) ◽  
pp. 458
Author(s):  
R. Frith
Keyword(s):  
Fast Track ◽  
Control Strategies ◽  
Project Schedule ◽  
Project Proposal ◽  
Two Phase ◽  
Start Up ◽  
Wide Range ◽  
Final Design ◽  
Turbo Expander ◽  
Operating Constraints

Bridge Oil Ltd operates a turbo expander LPG recovery plant at Wallumbilla, near Roma, Queensland. Several novel techniques were adopted to ensure optimum performance under severe operating constraints caused by market characteristics and project economics. These were necessary to maximise recovery over a wide range of throughputs and rapidly fluctuating loads, whilst operating at the end of a two phase pipeline. Flexibility was achieved by recycling gas around the plant, and adopting appropriate control strategies to ensure rapid response to load changes.The project schedule was compressed into 15 months by skid-mounting equipment, and eliminating various activities from the project schedule. Final design was based entirely on feasibility concepts without preparation of a formal project proposal. Protection against delays from wet weather during site work was also gained by shipping fully fabricated process skids to site.Minor problems encountered after start-up were rectified for a cost considerably below the incremental revenues generated by the fast track construction philosophy.

Effect of inoculum-substrate ratio on the start-up of solid waste anaerobic digesters

2001 ◽  
Vol 44 (4) ◽  
pp. 103-108 ◽  
Author(s):  
B. Fernández ◽  
P. Porrier ◽  
R. Chamy
Keyword(s):  
Solid Waste ◽  
Methane Production ◽  
Waste Treatment ◽  
Two Phase ◽  
Anaerobic Reactors ◽  
Start Up ◽  
Anaerobic Degradability ◽  
Substrate Ratio ◽  
Two Phases ◽  
Anaerobic System

The anaerobic systems start-up for solid waste treatment is a fundamental step, especially for those with two phases. It is necessary to know both the waste characteristics and the inoculum conditions. The objective of this work was to study the inoculum-substrate ratio (ISR) influence as a previous step of the start-up of an anaerobic system for the solid waste digestion. During this research spent grain was chosen as residue, working at three different concentrations (7; 13 and 20% w/v), studying the ISR effect in terms of anaerobic degradability (AD) and specific methane productivity (SMP). The initial acetoclastic activities (A0) were calculated based on the equation which describes the methane accumulation during each test. The model constants were also calculated and were adjusted to the experimental data. The results showed that in general the ISR variation has less impact on AD than on SMP. While maximum AD were reached in those tests with high ISR, the greatest values of SMP were with the lowest values of ISR ratio. A low ISR caused a slow hydrolysis, although the methane production was fast. So, during the start-up of a two-phase anaerobic system an elevated ISR would not be necessary in order to reach a good AD and a good intermediate products production, because the hydrolysis and the VFA production must be optimised in the first phase of these systems. While in conventional systems, where phases are together, it is much better to optimise the methane production. The ISR and the SMP indicated which inoculum percentage would be interesting based on the objective of the whole system: methane or intermediate compounds (VFA) production. All this information is important during the conventional anaerobic reactors operation because these tests would show which ISRs avoid inhibition.

Pressure Surge During Cryogenic Feedline Chilldown Process

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Gagan Agrawal ◽  
S. Sunil Kumar ◽  
Deepak Kumar Agarwal
Keyword(s):  
Numerical Study ◽  
Rocket Engine ◽  
Inlet Pressure ◽  
Working Fluid ◽  
Flash Evaporation ◽  
Two Phase ◽  
Numerical Studies ◽  
Start Up ◽  
Flow Through ◽  
Pressure Surge

Cryogenic fluid entering a warm feedline absorbs heat and undergoes rapid flash evaporation leading to pressure surges, which can retard the flow inside the feedline. It may have serious repercussion in operation of the rocket engine during start up. Experimental and numerical studies are carried out to examine the effect of inlet pressure and initial feedline temperature on pressure surges. An analytical model using sinda/fluint software is developed to investigate this complex two-phase flow phenomenon including the various boiling regimes that exist during line chilling. The numerical study is carried out considering 1D flow through a cryogenic feedline of 2.47 m long and 0.01 m inner diameter with liquid nitrogen at 77.3 K as working fluid. Predictions are made for the inlet pressure in the range of 0.28–0.76 MPa and initial wall temperature of 200 K and 300 K. Subsequently, an experimental test rig is setup and the model is validated with the experimental data. The studies show that within the range of parameter considered, the magnitude of pressure surge increases exponentially with increase in inlet pressure and decreases with the prechilling of feedline.

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