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With the increasing deployment of renewable energy-based power generation plants, the power system is becoming increasingly vulnerable due to the intermittent nature of renewable energy, and a blackout can be the worst scenario. The current auxiliary generators must be upgraded to energy sources with substantially high power and storage capacity, a short response time, good profitability, and minimal environmental concern. Difficulties in the power restoration of renewable energy generators should also be addressed. The different energy storage methods can store and release electrical/thermal/mechanical energy and provide flexibility and stability to the power system. Herein, a review of the use of energy storage methods for black start services is provided, for which little has been discussed in the literature. First, the challenges that impede a stable, environmentally friendly, and cost-effective energy storage-based black start are identified. The energy storage-based black start service may lack supply resilience. Second, the typical energy storage-based black start service, including explanations on its steps and configurations, is introduced. Black start services with different energy storage technologies, including electrochemical, thermal, and electromechanical resources, are compared. Results suggest that hybridization of energy storage technologies should be developed, which mitigates the disadvantages of individual energy storage methods, considering the deployment of energy storage-based black start services.

Aiming at the problem of gas emissions caused by the high-pressure operation of a large industrial gas (O2, N2, and Ar) pipeline network, this study establishes a mathematical model of the oxygen transmission and distribution system (OTDS) based on TGNET software. In addition, the study conducts transient simulation, comprehensively considering theoretical constraints and actual operation requirements, and adopts a large air separation company for the OTDS as a case study. After comparing two traditional adjustment methods, a compressor short stop adjustment strategy is proposed to reduce the peak pressure of the pipe network system. This study determines the energy-saving benefits and the difference in the scope of application of compressor short-stop adjustment. Compared with the medium-pressure release and inlet guide vane opening adjustment (IGVOA) strategies, the compressor short-stop adjustment strategy reduced oxygen emission by 3850.9 Nm3 and increased by 927.1 Nm3. Furthermore, the compressor operating energy consumption was reduced by 3349 and 2919 kW h. Compared with the IGVOA strategy, the compressor short-stop adjustment strategy has increased the application range of compressor inlet pressure and medium-pressure pipeline pressure by more than 70%. This strategy is effective for reducing the emission of pipeline gases caused by fluctuations in user demand.

Liquid air energy storage (LAES) has been regarded as a large-scale electrical storage technology. In this paper, we first investigate the performance of the current LAES (termed as a baseline LAES) over a far wider range of charging pressure (1 to 21 MPa). Our analyses show that the baseline LAES could achieve an electrical round trip efficiency (eRTE) above 60% at a high charging pressure of 19 MPa. The baseline LAES, however, produces a large amount of excess heat particularly at low charging pressures with the maximum occurred at ∼1 MPa. Hence, the performance of the baseline LAES, especially at low charging pressures, is underestimated by only considering electrical energy in all the previous research. The performance of the baseline LAES with excess heat is then evaluated which gives a high eRTE even at lower charging pressures; the local maximum of 62% is achieved at ∼4 MPa. As a result of the above, a hybrid LAES system is proposed to provide cooling, heating, hot water and power. To evaluate the performance of the hybrid LAES system, three performance indicators are considered: nominal-electrical round trip efficiency (neRTE), primary energy savings and avoided carbon dioxide emissions. Our results show that the hybrid LAES can achieve a high neRTE between 52% and 76%, with the maximum at ∼5 MPa. For a given size of hybrid LAES (1 MW×8 h), the primary energy savings and avoided carbon dioxide emissions are up to 12.1 MWh and 2.3 ton, respectively. These new findings suggest, for the first time, that small-scale LAES systems could be best operated at lower charging pressures and the technologies have a great potential for applications in local decentralized micro energy networks.

The heat-affected zone between the layers of a weld metal is a sensitive and important component of girth welds in X80 pipelines. However, only a few studies have focused on the interlayer heat-affected zone (IHAZ). In this work, thermal simulation was conducted to investigate the relationship between IHAZ microstructure and properties. Results showed that the toughness of the weld metal improved after a single welding thermal cycle but decreased after double welding thermal cycles, particularly when the weld metal was subjected to unaltered coarse grains of IHAZ. The relationship between the microstructure and properties of IHAZ was established to present the correlation of toughness with granular bainite content, grain size, and high-angle grain boundary content. Keywords: Girth weld, Interlayer heat-affected zone, Thermal simulation, Granular bainite, Toughness

Thermochemical energy storage (TCES) has attracted significant attention in recent years due to some unique features of the technology such as very high energy density and negligible heat loss during storage. The TCES, however, is still at its early stage of development currently at a technology readiness level of 1–3. Major technical challenges of the TCES include materials stability, charge/discharge kinetics and limited temperature lift. Here we firstly studied the application of shell-and-tube thermochemical reactor with silica gels as heat storage material in open TCES system by experimental method. And then validated model (the maximum root mean square percentage error of 13.62% between the modeling and experiments) of single tube reactor containing 0.29 kg silica-gel was established to numerically investigate the discharging behavior of the thermochemical reactor under different operating conditions and flow directions of air and water. The numerical simulation results showed inverse heat transfer occurred for a counter-flow of air-water. The problem could be solved by changing the counter-flow of air and water to the parallel-flow. Thus, the water outlet maximum temperature limit was broken through. The total heat uptake increased by at least 24.14% when water flow rate was less than 0.36 kg/h and 11.93% when air flow rate was more than 1.07 kg/h, respectively. By increasing the inlet temperature of air and water from 23 °C to 38 °C, the maximum temperature lift could be significantly increased by 79.94% for air and 80.81% for water, respectively. Meanwhile, the total heat uptake increased by 107.44%. For a completely charging and discharging process, the discharging rate of parallel-flow was faster than that of counter-flow.

Liquid Air Energy Storage (LAES) is one of the most promising large-scale energy storage technologies for intermittent renewable energy. The LAES includes an air liquefaction (charging) process and a power recovery (discharging) process. In the charging process, off-peak electricity is stored in the form of liquid air; meantime, a large amount of compression heat is recovered and stored at over 200 °C for later use in the discharging process to enhance the output power of air turbines. During peak times, liquid air is pumped and heated, and then expands to generate electricity in the discharging process, with cold energy of the liquid air recovered and stored to help liquefying the air in the charging process. It is well known that the recovery and utilization of both the cold and heat energy are crucial to the LAES. However, little attention is paid on the quantity and quality of the cold and heat energy. This paper carries out thermodynamic analyses on the recovered cold and heat energy based on steady-state modelling. It is found that the cold energy has a much more effect on the LAES than the heat energy; the cold energy loss leads to a decrease rate of the round trip efficiency, which is ∼7 times of that caused by the heat energy loss. In addition, the recovered cold energy from the liquid air is insufficient to cool the compressed air to the lowest temperature with the shortage of ∼18% and liquid air yield does not achieve the maximum in the charging process; external free cold sources would be needed to further increase the liquid air yield, and the round trip efficiency could easily break through 60%. Unlike the cold energy, 20–45% of the stored heat energy is in excess and cannot be efficiently used in the discharging process; we propose to use the excess heat to drive an Organic Rankine Cycle (ORC) for power generation. The ORC is considered to work at two different cold sources: the ambient and the sub-ambient. The sub-ambient cold source is generated through an Absorption Refrigeration Cycle (ARC) by consuming part of the excess heat. The combinations of the LAES and ORC with ambient and sub-ambient cold sources are denoted as LAES-ORC and LAES-ORC-ARC, respectively. Comparisons are made among the LAES, LAES-ORC and the LAES-ORC-ARC. The results show that both the LAES-ORC and LAES-ORC-ARC could achieve a much higher round trip efficiency than the LAES, with the maximum improvement of 17.6% and 13.1% under the studied conditions, respectively. It is concluded that the LAES-ORC has a simpler configuration with a better performance than the LAES-ORC-ARC configuration.

Liquid air energy storage (LAES) uses off-peak and/or renewable electricity to liquefy air and stores the electrical energy in the form of liquid air at approximately −196 °C. The liquefaction (charging) process involves multi-stage air compression with the heat of compression harvested by a thermal fluid, which is stored for use in the power recovery (discharging) process. When electricity is needed, the stored liquid air is pumped, heated by environmental heat first and then superheated by the heat of compression stored in the thermal fluid, and other heat sources if available, leading to the expansion of the air by over 700 times to produce power. The current LAES technology, denoted as baseline LAES in this paper, only uses the heat of compression to improve the power output in the discharging process. Our analyses show that the discharging process of the baseline LAES system cannot fully use the stored heat of compression in an efficient manner. The excess heat is in the order of ∼20–40%, mainly because the yield of liquid air lies between 0.6 and 0.78, which is significantly lower than 100%. In this paper, we propose a hybrid LAES configuration, whereby the excess heat of compression is used as a heat source to power an Organic Rankine Cycle (ORC), whereas a Vapor Compression Refrigeration Cycle (VCRC) acts as a heat sink, leading to the production of additional electricity. Thermodynamic analyses show that the newly proposed hybrid LAES system has a round-trip efficiency of 9–12% higher than the baseline LAES system. The exergy efficiency of the discharging process of the hybrid LAES system is 9.6% higher on average than that of the baseline LAES system due to the more effective use of the heat of compression. An economic analysis has also been performed using a project life span of 15 years. The results suggest that the combination of the ORC and VCRC gives a payback period of 2.7 years and a savings to investment ratio of 3.08, which are much better than the use of the single ORC.

Multi-pass welding is used in high-pressure and thick-walled pipes in natural gas and oil pipelines. When a welding layer of a welded joint is subjected to different welding thermal cycles, its microstructure and properties change, thereby affecting the overall welding performance. In this study, the temperature and microstructural variations of the fill pass 2 (FP2) in the entire welding process were investigated by combining the thermal cycle with the cascade welding method. The original FP2 and FP2 after double thermal cycles had the worse deformation ability by tensile test. The toughness of FP2 improved after a single thermal cycle, decreased after double thermal cycles, and improved again after triple thermal cycles. The content of martensite&ndash, austenite (M&ndash, A) constituents and the average grain size of FP2 in the cascade samples were inversely proportional to FP2 toughness. Massive M&ndash, A constituents and their unique distribution at the inter-critical temperature were harmful to weld metal toughness. Controlling the size and fraction of M&ndash, A constituents can improve weld metal toughness.

The energy consumption of urban central heating in northern China is two to four times that in northern Europe and other countries. Beijing has adopted measures, such as &lsquo, coal to gas&rsquo, and &lsquo, coal to electricity&rsquo, to reduce environmental pollution caused by central heating. Given a peak-to-valley difference in the electricity supply of power plant, which is uneven day and night, this study proposes to store the night-time off-peak electricity in the form of heat energy and drive the ammonia absorption system in the form of steam or hot water during peak or flat electricity. Simulation results of ammonia absorption cooling and heating dual-supply system show that heat source temperature increases, evaporation temperature increases, and cooling water temperature decreases are all beneficial to improve the refrigeration coefficient in the summer cooling condition. In the meantime, heat source temperature increases, evaporation temperature increases, and cooling water temperature decreases are beneficial for increasing the heating coefficient in the winter heating condition. The heating and cooling coefficients of the system are 1.38 and 0.65 in the optimal working condition in winter and summer. Benefit analysis shows that, compared with central heating and cold storage air conditioning, the system can save 576,000 tons of standard coal and 1.417 million tons of carbon dioxide if used in 12% of the cooling and heat supply areas in Beijing. The potential for energy saving and emission reduction is large.

Simultaneous multiperiod optimization is conducted for minimizing the oxygen emission of an oxygen-distribution system, based on the generalized MILP-based model, which covers various configurations of the captive oxygen factory in integrated steel mills. By simultaneously optimizing all of the variables, such as the load of air separation units (ASU), the on-off states of compressors, the load of liquefiers, etc., the model can promptly provide mill managers with responsive solutions for adjusting the variables involved on the supply-side to minimize oxygen emission. The case study in this paper shows that the proposed model performs well in minimizing oxygen emission, and provides a global optimization result covering the entire planning horizon. Moreover, based on the proposed model, the emission amounts can be rapidly and readily calculated for various scheduling scenarios of ASU maintenance, which is helpful to the manager seeking to optimally schedule ASU maintenance in time.

Shield metal arc welding (SMAW) has been widely applied in the field of engineering. Phase change performs important functions on weld pool geometry and determines weld quality. Welding torch, which is moved or not, has important effects on the phase change of weld pool and the elements distributions, which affects the weld quality. In this paper, phase change and elements distribution of welding process with torch trace of moving without swing and with e-type swing was simulated. The results show that the geometry of the weld pool under torch trace of moving without swing transfers from initial V-type to final O-type. At the ending of welding, the width of weld pool reaches 12 mm. The distance between center of each symmetrical vortexes and the center of weld pool is 3 mm. The distribution of element C is typical double peak trends and the peak value of its component is 0.0482 % appeared at the center of vortex. Using SMAW with e-type-swing torch moving, the distance of weldment diffusion is changed. The unsteady vortex has a great influence on the phase change in the weld pool. The distribution of elements is single-peaked characteristic. At the center of weld pool, the contents of C, Si, P and S are highest, which contents are 0.050 %, 0.270 %, 0.016 % and 0.010 %, respectively. But the contents of Mn, Mo, Ni and Cr at the same position are lowest, which contents are 1.121 %, 0.063 %, 0.062 % and 0.005 %. The comparison of the simulation and experimental results showed that the error range of their solid–liquid interface geometry is 3.03–4.83 %.

Weld pool geometry performs an important function in improving weld quality during welding. In the present work, the influences of deposited metal material parameters, including surface tension gradient, magnetic permittivity, and thermal expansion coefficient, on weld pool geometry were investigated. Fusion length (FL) and fusion ratio (FR) were proposed to analyze weld pool evolution quantitatively. Results reveal that surface tension gradient exerts the most significant effects on weld pool geometry. The effects of magnetic permittivity are less extensive than those of surface tension gradient, and thermal expansion coefficient exerts only slight influences on weld pool geometry. Considering the effects of surface tension gradient, magnetic permittivity, and thermal expansion coefficient, a classification method for deposited metals was proposed. Based on the characteristics of the weld pool geometry, heat and mass transfer processes in the weld pool, and application conditions, various types of deposited metals were analyzed. Comparison of the simulated and experimental results showed that the error ranges of FR and FL are 3.66–4.53% and 1.03–2.83%, respectively.

Generally in the Chinese iron and steel industry, the electricity consumption of cryogenic air separation unit (ASU) is about 14% of the overall electricity use. To reduce the electricity consumption, the combined variable oxygen (CVO) supply method for ASU is proposed. The exergy calculation program for ASU was developed and the detailed analysis of CVO method was performed. The results show that the general exergy efficiency (GEE) of ASU combined with a liquefaction unit is increased by 11 %–31 %. The consumption of unit oxygen, the total electricity consumption and the overall consumption of unit oxygen (OCUO) was compared. The OCUO is a suitable method to evaluate the energy-saving potential of CVO. Compared with the load regulation method of Automatic Load Control (ALC), the OCUO and the unit consumption of compression of CVO reduced more than 4.47% and 30%, respectively. It means that CO 2 emission of every reduction 1% of gaseous oxygen release in a year in Chinese iron and steel industry will contribute approximately 0.75% to the 2020s CO 2 emission reduction target of China.

Fine silicon particles (mean size of 2.7 μm) are used as entrained materials, and the entrainment characteristics of fine particles are investigated in a cylindrical fluidized-bed (inner diameter of 28 mm and height of 1000 mm) under high speed airflow. The effects of the volume flow of gas (Q , 1 m3 /h to 2.5 m3 /h), the number of holes (N , 1 to 4), the size of holes (D , 1 mm to 3 mm), and the distance between holes and the upper surface of the material layer (H , -100 mm to 200 mm) on the entrainment characteristics (entrainment rate W and entrained powder-gas ratio R ) are experimentally studied through orthogonal experiment. The experimental results show that an increase in Q and H constantly improves the entrainment characteristics; a decrease in D enhances such characteristics, whereas the number of holes N has no significant effect on the entrainment characteristics. An optimal operating condition can result in optimal entrainment characteristics (W , 3.1 g/min and R , 0.058 g/g), which can be achieved with a Q of 2.5 m3 /h, N of 1, D of 2 mm and H of 200 mm.

China's carbon dioxide (CO2) emission ranks the highest in the world. CO2 emission from urban central heating, which has an average annual growth rate of 10.3%, is responsible for 4.4% of China's total CO2 emission. The current policy for improving urban central heating focuses on replacing coal with natural gas. This paper analyzes the existing situation and problems pertaining to urban heating, and evaluates the potential for reducing energy consumption and CO2 emission by heat pump heating. The results show that the current policy of replacing coal with natural gas for urban central heating decreases energy consumption and CO2 emission by 16.6% and 63.5%, respectively. On the other hand, replacing coal-based urban central heating with heat pump heating is capable of decreasing energy consumption and CO2 emission by 57.6% and 81.4%, respectively. Replacing both urban central and decentralized heating with heat pump heating can lead to 67.7% and 85.8% reduction in energy consumption and CO2 emission, respectively. The decreases in CO2 emission will account for 24.5% of China's target to reduce total CO2 emission by 2020.

An experimental study on flow patterns for water boiling in horizontal heated tubes was conducted to observe the evolution and transition of flow patterns while controlling various parameters, such as heat flux, mass velocity, and tube diameter. Six boiling flow patterns are observed in the test tubes, namely, bubble, plug, slug, wave, stratified, and annular flows, which can be further classified into three types based on their various characteristics: intermittent, stratified-wave, and annular flows. The evolution of flow patterns for water boiling in horizontal heated tubes was significantly affected by heat flux, mass velocity, and tube diameter. The increment of heat flux pushed the starting point of each flow pattern toward the inlet of the tube. Intermittent and stratified-wave flows occurred at lower mass velocity, and annular flow occurred with an increase in mass velocity. Moreover, annular flow easily appeared in tubes with smaller diameters. Since the heat per unit of mass for the full tube length increases with either an increase in heat flux or a decrease in mass velocity and tube diameter, the transition always occurs at smaller vapor qualities with the increase of the heat per unit of mass during the transition of the three flow patterns. The experimental data in this study were compared with the adiabatic flow pattern maps proposed by Baker, Mandhane, Taitel, and Weisman. Based on the experimental data, a new flow pattern map for water boiling was proposed for predicting flow patterns in horizontal heated tubes.

China's carbon dioxide (CO 2 ) emission ranks highest in the world. China is committed to reduce its CO 2 emission by 40% to 45% from the 2005 levels by 2020. To fulfill the target, China's CO 2 emission reduction must exceed 6995 million tons. Energy consumption and CO 2 emission of China's urban district heating (UDH) are increasing. The current policy implemented to improve UDH focuses on replacing coal with natural gas to reduce energy consumption and CO 2 emission to some extent. This paper proposes that heat pump heating (HPH) could serve as a replacement for UDH to help realize energy-saving and emission-reduction goals to a greater extent. The paper also analyzes the impact of this replacement on the heating and power generation sectors. The results show that replacing coal-based UDH with HPH decreases energy consumption and CO 2 emission by 43% in the heating sector. In the power generation sector, the efficiency of power generation at the valley electricity time increases by 0.512%, and the ratio of peak–valley difference decreases by 16.5%. The decreases in CO 2 emission from the heating and power generation sectors cumulatively account for 5.55% of China's total CO 2 emission reduction target in 2020.

This paper presents a theoretical model for predicting the radiative heat transfer rate between high-temperature fluidized bed and immersed walls, which can be used upon the base of emulsion packet model of heat transfer in bubbling fluidized bed. The model adopted radiative flux computation method to calculate radiative heat transfer between fluidized disperse phase contacting to the wall and immersed walls, in which the absorption and back-scattering coefficients was obtained from the reflectivity and the absorptivity of a layer of disperse media of a single particle thickness. In such a model, many factors, such as particle size, particle emissivity, bed void fraction, fluidized bed and wall temperatures, and so on, are included theoretically to calculate radiative heat transfer between immersed walls and fluidized beds. As a result, the model results provide a reasonable explanation of the experimental observation of that radiative heat transfer rate in fluidized beds increases with the increases of the superficial fluidizing velocity. In addition, the modeling prediction for the trend of radiative heat transfer rate between the fluidized bed and its immersed surface on the variation of wall temperature conforms to the classical experimental trend.

Field synergy characteristics in condensation heat transfer with non-condensable gas (NCG) over a horizontal tube were numerically simulated. Consequently, synergy angles between velocity and pressure or temperature gradient fields, gas film layer thickness, and induced velocity and shear stress on gas–liquid interface were obtained. Results show that synergy angles between velocity and temperature gradient fields are within 73.2°–88.7° and ascend slightly with the increment in mainstream velocity and that the synergy is poor. However, the synergy angle between velocity and pressure gradient fields decreases intensively with the increase in mainstream velocity at θ ≤ 30°, thereby improving the pressure loss. As NCG mass fraction increases, the gas film layer thickness enlarges and the induced velocity and shear stress on gas–liquid interface decreases. The synergy angles between velocity and temperature gradient fields increase, and the synergy angles between velocity and pressure gradient fields change at θ = 70°, decrease at θ < 70°, and rise at θ > 70°. When the horizontal tube circumference angle increases, the synergy angles between velocity and temperature or pressure gradient fields decrease, the synergy between velocity and pressure fields enhances, and the synergy between velocity and temperature fields degrades.

Granular convection/separation of single and binary component particles are studied in a narrow vibration bed, respectively. With filling the single light particles (molecular sieve beads), the bed exhibits five different states successively by increasing the vibration frequency f from 15Hz to 70 Hz (vibration strength Γ>3), as the global convection, symmetrical heap, unsymmetrical heap, local convection and pseudo solid. Comparatively, the granular bed of the single heavy particles (steel beads) is only in pseudo solid state at the above vibration condition. By filling binary component particles (molecular sieve and same size steel beads) instead of the single component, the bed shows similar convection state with that of the single molecular sieve beads, and the heavy steel beads are aggregated in the centre of convention roll as a core. Varying the initial distribution of binary component particles, the final convection and separation are not influenced, although the aggregation process of steel beads changes.

Granular particles systems under vertical vibration exhibit Brazilian Nut separation (BN), Reversed BN (RBN) separation or transitional phases at different vibrating conditions. In the present work, we investigate the influence of rotation on the BN separation of a binary granular particle system by changing rotational speed. 13X molecular sieve particles with diameter 6.00 mm and 0.60 mm are used. Vibration frequency f is 30 Hz and dimensionless acceleration Γ is 1.52 or 1.75, in which the particle system mainly exhibits BN separation tendency. Rotational speed ω varies from 0 to 150rpm, while the upper surface of the particle system maintains flat. We took the pictures of the particles distribution and measured the particles mass layer by layer to obtain the 3-D distribution of the particles. The results show that rotation enhances the BN separation tendency at slow rotational speed. The BN separation becomes strongest when ω is approximately 50rpm, then the BN separation tendency reduces as ω continues to increase. A butterfly pattern appears in the middle particles layer under the simultaneous stimulations of vibration and rotation.

In the work, the dynamic characteristics of the human skull-dura mater system were studied. For the purpose of our analysis, we adopted a model consisted of a hollow sphere. By using the ‘Patran andAnsys’ finite element processor, a simplified three-dimensional finite element model (FEM) of a human skull was constructed. The model was used to calculate the deformation of human skull with the intracranial pressure changing. This required good representation of the complex anatomy of the skull. Four different entities are distinguished: Tabula externa, Tabula interna, and a porous Diploe sandwiched in between, and dura mater. A thin-walled skull was simulated by composite shell elements. The viscoelasticity of human skull-dura mater system was studied and analyzed by the finite-element Maxwell model. The 1/8 model consisted of 25224 nodes and 24150 three-dimensional 8-nodeisoparametric solid elements. The elastic-viscous mechanical characteristics must be used for the skull. The viscous strains account for about 40% of total strains of human skull and dura mater. And therange of strain errors is from 6.45 to 14.82% after ignoring the viscosity of skull and dura mater.