Simulation of gas-solid flow characteristics of the circulating fluidized bed boiler under pure-oxygen combustion conditions

Under the pressure of carbon neutrality,many carbon capture,utilization and storage technologies have witnessed rapid development in the recent years,including oxy-fuel combustion(OFC)technology.However,the conventional OFC technology usually depends on the flue gas recirculation system,which faces significant investment,high energy consumption,and potential low-temperature corrosion problem.Considering these deficiencies,the direct utilization of pure oxygen to achieve particle fluidization and fuel combustion may reduce the overall energy consumption and CO_(2)-capture costs.In this paper,the fundamental structure of a self-designed 130 t·h^(-1) pure-oxygen combustion circulating fluidized bed(CFB)boiler was provided,and the computational particle fluid dynamics method was used to analyze the gas-solid flow characteristics of this new-concept boiler under different working conditions.The results indicate that through the careful selection of design or operational parameters,such as average bed-material size and fluidization velocity,the pure-oxygen combustion CFB system can maintain the ideal fluidization state,namely significant internal and external particle circulation.Besides,the contraction section of the boiler leads to the particle backflow in the lower furnace,resulting in the particle suspension concentration near the wall region being higher than that in the center region.Conversely,the upper furnace still retains the classic core-annulus flow structure.In addition to increasing solid circulation rate by reducing the average bed-material size,altering primary gas ratio and bed inventory can also exert varying degrees of influence on the gas-solid flow characteristics of the pure-oxygen combustion CFB boiler.

Current Circulation and Water Renewal Time in the Enclosed Marine Area of Pagasitikos Basin, Greece

Greece boasts an impressive closed coastline stretching across 13,676 km, making it the largest in the Mediterranean basin and one of the largest in the world. Given the significant human activities that take place in coastal areas, understanding the behavior of the sea environment becomes crucial. In this study, we delve into the generation and movement of marine currents as well as the retention time and water age within the waters of Pagasitikos Sea inlet, Greece, through numerical simulation of hydrodynamic characteristics. The main examined points of the understudy region are the area of the port of Volos, the Trikeri channel where the ingress and egress of water from the Gulf takes place and the exchange of seawater through circulation of the Pagasitikos Gulf with the North Evian Gulf. In order to evaluate the results, they were compared with real field measurements and with simulation on a laboratory dummy of the same area. The computational simulation was performed with the ELCOM 2.2 numerical modeling tool and the AEM3D latest version and the main factors simulated are the tide, the consequence that Coriolis force, boundary conditions, the topography and bottom geometry of the bay and the actual meteorological conditions of a whole year.

Numerical Simulation of the Regional Ocean Circulation in the Coastal Areas of China

The regional ocean circulation in the coastal areas of China (including a part of the western PacificOcean, the South China Sea and the Bay of Bengal et al.) is simulated by using the improved Princeton University ocean circulation model (POM). Compared with the modeling results obtained by the large-scaleocean general circulation model (OGCM), the basic ocean circulation features simulated by the regionalocean circulation model al-e in good agreement with that simulated by OGCM and some detailed characteristics such as the regional ocean circulation, sea temperature, salinity and flee sea surface height have alsobeen obtained which are in good accord with the observations. These results indicate that the regional oceancirculation model has good capability to produce the legional ocean circulation characteristics and it can beused to develop coupled legional ocean-atmospheric model systems.

Numerical simulation of wind-driven circulation and pollutant transport in Taihu Lake based on a quadtree grid

In this study,a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid.This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with irregular natural boundaries when focusing on important smallscale localized flow features.The quadtree grid was created by domain decomposition.The governing equations were solved using the finite volume method,and the normal fluxes of mass,momentum,and pollutants across the interface between cells were computed by means of a Godunov-type Osher scheme.The model was employed to simulate wind-driven flow in a circular basin with non-uniform depth.The computed values were in agreement with analytical data.The results indicate that the quadtree grid has fine local resolution and high efficiency,and is convenient for local refinement.It is clear that the quadtree grid model is effective when applied to complex flow domains.Finally,the model was used to calculate the flow field and concentration field of Taihu Lake,demonstrating its ability to predict the flow and concentration fields in an actual water area with complex geometry.

Strengthening of the Walker Circulation under Global Warming in an Aqua-Planet General Circulation Model Simulation

Most climate models project a weakening of the Walker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rainfall increase compared to that of moisture increase, which leads to a decrease in ascending motion. Through an idealized aqua-planet simulation in which a zonal wavenumber-1 SST distribution is prescribed along the equator, we find that the Walker circulation is strengthened under a uniform 2-K SST warming, even though the global mean rainfall-moisture relationship remains the same. Further diagnosis shows that the ascending branch of the Walker cell is enhanced in the upper troposphere but weakened in the lower troposphere. As a result, a ＂double-cell＂ circulation change pattern with a clockwise （anti-clockwise） circulation anomaly in the upper （lower） troposphere forms, and the upper tropospheric circulation change dominates. The mechanism for the formation of the ＂double cell＂ circulation pattern is attributed to a larger （smaller） rate of increase of diabatic heating than static stability in the upper （lower） troposphere. The result indicates that the future change of the Walker circulation cannot simply be interpreted based on a global mean moisture budget argument.

THREE-DIMENSIONAL BAROCLINIC NUMERICAL SIMULATION OF THE SOUTH CHINA SEA CIRCULATION'S SEASONAL CHARACTERISTICS II. MIDDLE AND DEEP CIRCULATION

A three-dimensional baroclinic shelf sea model’s numerical simulation of the South China Sea (SCS) middle and deep layer circulation structure showed that: 1. In the SCS middle and deep layer, a southward boundary current exists along the east shore of the Indo-China Peninsula all year long. A cyclonic eddy (gyre) is formed by the current in the above sea areas except in the middle layer in spring, when an anticyclonic eddy exists on the eastern side of the current. In the deep layer, a large-scale anticyclonic eddy often exists in the sea areas between the Zhongsha Islands and west shore of southern Luzon Island. 2. In the middle layer in summer and autumn, and in the deep layer in autumn and winter, there is an anticyclonic eddy (gyre) in the northeastern SCS, while in the middle layer in winter and spring, and in the deep layer in spring and summer, there is a cyclonic one. 3. In the middle layer, there is a weak northeastward current in the Nansha Trough in spring and summer, while in autumn and winter it evolves into an anticyclonic eddy (gyre), which then spreads westward to the whole western Nansha Islands sea areas.

Study on numerical simulation and dynamic mechanism of win-ter- time circulation in the eastern China seas

An MOM2 based 3-dimentional prognostic baroclinic Z-ordinate model was established to study the circulation in eastern China seas, considering the topography, inflow and outflow on the open boundary, wind stress, temperature and salinity exchange on the sea surface. The results were consistent with observation and showed that the Kuroshio intrudes in large scale into the East China Sea continental shelf East China, during which its water is exchanged ceaselessly with outer sea water along Ryukyu Island. The Tsushima Warm Current is derived from several sources, a branch of the Kuroshio, part of the Taiwan Warm Current, and Yellow Sea mixed water coming from the west of Cheju Island. The water from the west of Cheju Island contributes ap-proximately 13% of the Isushima Warm Current total transport through the Korea Strait. The circulation in the Bohai Sea and Yellow Sea is basically cyclonic circulation, and is comprised of coastal currents and the Yellow Sea Warm Current. Besides simulation of the real circulation, numerical experiments were conducted to study the dynamic mechanism. The numerical experiments indicated that wind directly drives the East China Sea and Yellow Sea Coastal Currents, and strengthens the Korea Coastal Current and Yellow Sea Warm Current. In the no wind case, the kinetic energy of the coastal current area and main YSWC area is only 1% of that of the wind case. Numerical experiments also showed that the Tsushima Warm Current is of great importance to the formation of the Korea Coastal Current and Yellow Sea Warm Current.

Numerical simulation of influence of the anomalies of theCentral-eastern Equatorial Pacific SST and Arctic seaice cover in summer on the atmospheric circulation

A series of numerical experiments have been conducted with a perpetual July, nine-level general circulation spectral model to determine the effect of variation of the Arctic sea ice cover extent and the joint effect of anomalies of both the Arctic sea ice cover and the Central-eastern Equatorial Pacific sea surface temperature on the summer general circulation. Results show that the two factors,anomalously large extent of the Arctic sea ice cover and anomalously warm sea surface temperature over the Central-eastern Equatorial Pacific Ocean, play substantially the equal role in the effect on the summer general circulation, and either of them can notably induce the atmospheric anomalies. The main dynamical processes determining the effect of the Arctic sea ice and the equatorial SST anomalies are associated with two leading teleconnection patterns, i. e. the Asia North/American and Eurasian patterns observed in atmosphere. The results presented in this paper again prove that the general circulation is fundamentally motivated by the non-uniform heating between the equator and the pole on the rotating earth.

3-D BAROCLINIC NUMERICAL SIMULATION OF THE SOUTH CHINA SEA I. UPPER CIRCULATION

A three dimensional baroclinic shelf sea model was employed to simulate the seasonal characteristics of the South China Sea (SCS) upper circulation. The results showed that: in summer, an anticyclonic eddy, after its formation between the Bashi Channel and Dongsha Islands in the northeastern SCS, moves southwestward until it disperses slowly. There exists a northward western boundary current along the east shore of the Indo China Peninsula in the western SCS and an anticyclonic gyre in the southern SCS. But at the end of summer and beginning of autumn, a weak local cyclonic eddy forms in the Nansha Trough, then grows slowly and moves westward till it becomes a cyclonic gyre in the southern SCS in autumn. At the beginning of winter, there exists a cyclonic gyre in the northern and southern SCS, and there is a southward western boundary current along the east shore of the Indo China Peninsula. But at the end of winter, an anticyclonic eddy grows and moves toward the western boundary after forming in the Nansha Trough. The eddy’s movement induces a new opposite sign eddy on its eastern side, while the strength of the southward western boundary current gets weakened. This phenomenon continues till spring and causes eddies in the southern SCS.

Numerical simulation of the dynamic effects of grounding icebergs on summer circulation in Prydz Bay,Antarctica

The Regional Ocean Modeling System(ROMS)is employed to create a three-dimensional numerical model of the summer circulation in the Prydz Bay region,Antarctica.Consistent with the currents measured using an underway acoustic Doppler current profiler during a Chinese cruise,the simulated current field illustrates the major features of the Prydz Bay circulation,including the Antarctic Slope Current(ASC)along the continental shelf break,the cyclonic Prydz Bay Gyre,and the Prydz Bay Eastern Coastal Current(PBECC).The effects of grounding icebergs D15 and B15 on the circulation in Prydz Bay are investigated via numerical simulations.The results indicate that these giant grounding icebergs substantially affect the flows into and within the bay,which may differ with the different grounding locations.As grounding iceberg D15 is located close to the southwestern part of the West Ice Shelf(WIS),it cuts off the coastal current along the outer edge of the WIS,and the ASC can only enter Prydz Bay from the west side of iceberg D15,whereupon it becomes a main source of the PBECC.Iceberg D15 also weakens the circulation in the bay in general.The relatively small iceberg B15 entered Prydz Bay from 2007 to 2009 and grounded on the southwestern section of the Four Ladies Bank.The numerical experiments indicate that iceberg B15 guides the ASC flowing into the bay around its west side and reduces the width of the inflow on the eastern side of the Prydz Bay Channel.The grounding of iceberg B15 has also led to adjustments of the circulation within the bay,among which the most significant is that the outflow along the western flank of Fram Bank has shifted to the west and become more intensive.

NUMERICAL SIMULATION OF SSTA IMPACTS OVER THE GLOBAL OCEAN ON THE ANOMALOUS CIRCULATION OVER EURASIA IN JANUARY 2008

In this paper, we discussed the features of atmospheric circulations over Eurasia as a response to sea surface temperature anomalies （SSTAs） over the tropical Indian Ocean, the equatorial Pacific, Kuroshio and the North Atlantic. Our results are shown as follows： （1） CAM3.0, driven by the combined SSTAs over the four oceanic regions, can simulate well the features of anomalous atmospheric circulations over Eurasia in January 2008, indicating that the effects of the SSTAs over these four regions were one of the key causes of the anomalous systems over Eurasia. （2） The SSTAs over each key region contributed to the intensification of blocking over the Urals Mountains and a main East Asian trough. However, the influence of the SSTAs over individual oceanic regions differed from one another in other aspects. The SSTAs over the North Atlantic had an impact on the 500-hPa anomalous height （Z500A） over the middle-high latitudes and had a somewhat smaller effect over the low latitudes. For the warm SSTAs over Kuroshio, the subtropical high was much stronger, spread farther north than usual, and had an anomalous easterly that dominated the northwest Pacific Ocean. The warm SSTAs over the tropical Indian Ocean could have caused a negative Z500A from West Asia to Middle Asia, a remarkably anomalous southwesterly from the Indian Ocean to the south of China and an anomalous anticyclone circulation over the South China Sea-Philippine Sea region. Because of the La Nifia event, the winter monsoon was stronger than normal, with an anomalously cooler northerly over the southeastern coastal areas of China. （3） The combined effects of the SSTAs over the four key regions were likely more important to the atmospheric circulation anomalies of January 2008 over Eurasia than the effects of individual or partly combined SSTAS. This unique SSTA distribution possibly led to the circulation anomalies over Eurasia in January 2008, especially the atmospheric circulation anomalies over the subtropics, which were more similar to those of the winter E1 Nifio events than to the circulation anomalies following La Nifia.

A Simulation Study of the Effect of Geomagnetic Activity on the Global Circulation in the Earth’s Middle Atmosphere

To investigate how geomagnetic activity affects the formation of the large-scale global circulation of the middle atmosphere, the non-hydrostatic model of the global wind system of the Earth’s atmosphere, developed earlier in the Polar Geophysical Institute, is utilized. The model produces three-dimensional global distributions of the zonal, meridional, and vertical components of the wind velocity and neutral gas density in the troposphere, stratosphere, mesosphere, and lower thermosphere. Simulations are performed for the winter period in the northern hemisphere (16 January) and for two distinct values of geomagnetic activity (Kp = 1 and Kp = 4). The simulation results indicate that geomagnetic activity ought to influence considerably on the formation of global wind system in the stratosphere, mesosphere, and lower thermosphere. The influence on the middle atmosphere is conditioned by the vertical transport of air from the lower thermosphere to the mesosphere and stratosphere and vice versa. This transport may be rather distinct under different geomagnetic activity conditions.

The numerical simulation of Pacific Ocean circulation with five-level model

A five-level oceanic primitive equation model has been developed. This model is integrated numerically with annual mean wind stress and heat flux at sea surface for 30 a. The ocean circulations tend to quasi-stability. The simulated results show that the computed annual mean currents and sea surface temperature agree well with the observations.

Numerical simulation and experimental research on air reverse circulation bit interior fluid territory

By using fluent fluid engineer emulator software to simulate negative pressure formed inside the injector added in the reverse-circulation sampling drilling bit, at six angles of 15, 30, 45, 60, 75 and 90 degrees. The pressure distributing nephogram and the corresponding numerical value gotten compared with the experiment data received by an injector with 6 angles designed by emulation the conclusion. It has been found that the two values are coincident essentially. The article shows that using emulator technology to design optimizely is credible and simple. The cost is low and the design cycle is short compared with the method through experience and test.

Effect of Simulated Microgravity and its Associated Mechanism on Pulmonary Circulation in Rats

Objective To study the effect of Simulated Microgravity and its Associated Mechanism on Pulmonary Circulation in Rats. Methods Rat tail-suspension model was used to simulate the physiological effects of microgravity and changes in pulmonary blood vessel morphology, pulmonary arterial and venous blood pressure, pulmonary vascular resistance, pulmonary vasomotoricity, as well as the regulation of pulmonary circulation by cytokines produced and released by the lung of rats were measured. Results The walls of pulmonary blood vessels of rats were thickened, and the pulmonary artery was reconstructed with increased pulmonary vascular resistance. The pulmonary blood vessels of rats became more prone to dilation as contractions increased. Rat epithelial Adrenomedulin gene transcription and protein expression were upregulated. The level of basic fibroblast growth Factor of rat was also elevated. Conclusion Findings from the present study on rats revealed that the microgravity can affect pulmonary blood vessel structure, pulmonary arterial pressure, and pulmonary blood vessel self-regulation and cytokine production.

Analysis of the Lost Circulation Problem

The well-known“lost circulation”problem refers to the uncontrolled flow of whole mud into a formation.In order to address the problem related to the paucity of available data,in the present study,a model is introduced for the lost-circulation risk sample profile of a drilled well.The model is built taking into account effective data(the Block L).Then,using a three-dimensional geological modeling software,relying on the variation function and sequential Gaussian simulation method,a three-dimensional block lost-circulation risk model is introduced able to provide relevant information for regional analyses.

Simulated circulations off the Changjiang (Yangtze) River mouth in spring and autumn

The circulations off the Changjiang mouth in May and November were simulated by a three dimension numerical model with monthly averaged parameters of dynamic factors in this paper. The area covers the East China Sea (ECS), Yellow Sea and Bohai Sea. Simulated results show that the circulation off the Changjiang mouth in spring and autumn is mainly the Changjiang runoff and Taiwan Warm Current (TWC). The Changjiang discharge is much larger in May than in November, and the wind is westward in May, and southward in November off the Changjiang mouth. The runoff in May branches in three parts, one eastward flows, the other two flow northward and southward along the Subei and Zhejiang coast respectively. The Changjiang diluted water expands eastward off the mouth, and forms a strong salinity front near the mouth. Surface circulation in autumn is similar to that in winter, the runoff southward flows along the coast, and the northward flowing TWC becomes weaker compared to that in spring and summer. The bottom circulations in May and November are mainly the runoffnear the mouth and the TWC offthe mouth, and the runoff and TWC are greater in May than in November.

Numerical simulations and comparative analysis of two- and three-dimensional circulating fluidized bed reactors for CO2 capture

Carbon dioxide(CO2),the main gas emitted from fossil burning,is the primary contributor to global warming.Circulating fluidized bed reactor(CFBR)is proved as an energy-efficient method for post-combustion CO2 capture.The numerical simulation by computational fluid dynamics(CFD)is believed as a promising tool to study CO2 adsorption process in CFBR.Although three-dimensional(3D)simulations were proved to have better predicting performance with the experimental results,two-dimensional(2D)simulations have been widely reported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational efficiency recently.However,the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study.Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions,it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions.In this work,the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the effects of dimensionality on the hydrodynamics and reaction behaviors,in which the separation rate,species distribution and hydrodynamic characteristics were comparatively studied for both model frames.With both accuracy and computational costs considered,the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions,which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.

Long-term operation optimization of circulating cooling water systems under fouling conditions

Fouling caused by excess metal ions in hard water can negatively impact the performance of the circulating cooling water system(CCWS)by depositing ions on the heat exchanger's surface.Currently,the operation optimization of CCWS often prioritizes short-term flow velocity optimization for minimizing power consumption,without considering fouling.However,low flow velocity promotes fouling.Therefore,it's crucial to balance fouling and energy/water conservation for optimal CCWS long-term operation.This study proposes a mixed-integer nonlinear programming(MINLP)model to achieve this goal.The model considers fouling in the pipeline,dynamic concentration cycle,and variable frequency drive to optimize the synergy between heat transfer,pressure drop,and fouling.By optimizing the concentration cycle of the CCWS,water conservation and fouling control can be achieved.The model can obtain the optimal operating parameters for different operation intervals,including the number of pumps,frequency,and valve local resistance coefficient.Sensitivity experiments on cycle and environmental temperature reveal that as the cycle increases,the marginal benefits of energy/water conservation decrease.In periods with minimal impact on fouling rate,energy/water conservation can be achieved by increasing the cycle while maintaining a low fouling rate.Overall,the proposed model has significant energy/water saving effects and can comprehensively optimize the CCWS through its incorporation of fouling and cycle optimization.

Numerical simulation of typhoon- induced storm surge on the coast of Jiangsu Province,China,based on coupled hydrodynamic and wave models

In order to facilitate engineering design and coastal flooding protection, the potential storm surge induced by a typhoon is studied.Using an unstructured mesh, a coupled model which combines the advanced circulation （ ADCIRC ） hydrodynamic model and simulating waves nearshore （ SWAN ） model is applied to analyze the storm surge and waves on the coast of Jiangsu Province.The verifications of wind velocity, tidal levels and wave height show that this coupling model performs well to reflect the characteristics of the water levels and waves in the studied region.Results show that the effect of radiation stress on storm surge is significant, especially in shallow areas such as the coast of Jiangsu Province and the Yangtze estuary.By running the coupled model, the simulated potential flooding results can be employed in coastal engineering applications in the Jiangsu coastal area, such as storm surge warnings and extreme water level predictions.