The Experts below are selected from a list of 6240 Experts worldwide ranked by ideXlab platform
Chuguang Zheng - One of the best experts on this subject based on the ideXlab platform.
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mercury emission and speciation in fly ash from a 35 mwth large pilot boiler of oxyfuel combustion with different flue Gas Recycle
Fuel, 2017Co-Authors: Jianping Yang, Yongxin Feng, Yongchun Zhao, Kai Xu, Junying Zhang, Shihong Zhang, Yi Zhang, Jun Xiang, Chuguang ZhengAbstract:Abstract The behaviour of mercury is investigated in a 35 MW th large pilot boiler of oxyfuel combustion with dry and wet flue Gas Recycle (FGR). The mercury species in fly ash particles as well as the involved reaction mechanism are systematically investigated. The results suggest that higher concentration of Gas–phase mercury (Hg g ) is contained in oxyfuel combustion flue Gas. The conversion of Hg g to particulate associated mercury (Hg p ) is enhanced in oxyfuel combustion. Different mercury species are presented in fly ash collected from air and oxyfuel combustion: trigonal red HgS is the main mercury species in air combustion; mercury bound to organic matter (Hg–OM) and trigonal red HgS are both dominant in the samples from oxyfuel combustion. The prominent difference is the significantly increase of Hg–OM in oxyfuel combustion atmosphere. The oxyfuel combustion atmosphere would favor the formation of oxygen–rich functional groups, especially the C O group, which is responsible for the adsorption of mercury and formation of Hg–OM in fly ash.
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A numerical investigation on flame stability of oxy-coal combustion: Effects of blockage ratio, swirl number, Recycle ratio and partial pressure ratio of oxygen
International Journal of Greenhouse Gas Control, 2017Co-Authors: Sheng Chen, Stanley Santos, Chuguang ZhengAbstract:Abstract Keeping the flame stable and having the appropriate flame shape is essential in operating an oxyfuel combustion coal fired power plant with CO 2 capture. This is more critical if the boiler is required to operate in full and partial thermal load with varying volume of flue Gas Recycled. Therefore, in designing the oxyfuel combustion burner, it is important to evaluate the burner stability, shape structure and flame type. This work presents numerical investigation of a burner designed for oxyfuel combustion coal fired boiler. The study evaluated the effects of the blockage ratio, swirl number, flue Gas Recycle ratio, and oxygen partial pressure in the primary RFG stream on the flame stability, type, shape and structure. The model results were validated against experimental data obtained from a novel oxyfuel combustion burner designed and operated in a 2.5MWt test pilot facility. The model developed for this study incorporated a modified chemical reaction mechanism that allows the addition of CO and Boudouard reaction that is considered significant in an oxyfuel combustion flame. The results show that the stability of an oxyfuel combustion flame is greatly improved by having a moderate to strong internal recirculation zone to produce a Type-II flame; and could also be easily destabilized by a high velocity jet of unburned carbon/char as illustrated by a dark central region emanating from the centre of the burner. Additionally, it could also be illustrated that the swirl number and flue Gas Recycle ratio have a strong influence to the formation of the central dark region along the centerline of the burner. It could be concluded that maintaining the flame Type-II over the whole range of thermal load should maintain the necessary flame stability appropriate to an oxyfuel combustion boiler.
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Effect of steam on ignition of pulverized coal particles in oxy-fuel combustion in a drop tube furnace
Fuel, 2016Co-Authors: Lei Cai, Chun Zou, Yanwen Guan, Huiqiao Jia, Liang Zhang, Chuguang ZhengAbstract:Oxy-fuel combustion is recognized as a promising technology to reduce CO2 emissions from coal-fired power plants. Typical oxy-fuel combustion is O2/CO2 Recycled combustion, in which the dilute Gases are the mixture of O2 and CO2. Wet flue Gas Recycle combustion (O2/CO2/H2O atmospheres) should be promoted due to some merits over dry flue Gas Recycle combustion (O2/CO2 atmospheres). In this study the ignition of bituminous coal was studied using experimental and numerical methods under O2/CO2/H2O atmospheres. The experiments were conducted in a drop tube furnace using a high-speed camera with oxygen mole fractions of 21%, 30% and 40%. The substitution of CO2 by 5%, 10%, 20% and 30% steam were implemented to evaluate the effect of the mole fractions of steam on the ignition of coal in O2/CO2/H2O atmospheres. The experimental results reveal that the ignition distances are barely affected when low mole fraction of steam (5%, 10% and 20%) was added to O2/CO2 atmospheres. As the mole fraction of steam is increased to 30%, the ignition distance is significantly decreased. The effect of steam on the ignition of coal in O2/CO2/H2O atmospheres was particularly analyzed using a proposed CFD model. The numerical results indicate that the physical properties of steam lead to the ignition delay of coal when CO2 is replaced by steam in O2/CO2 atmospheres. The lower specific heat and higher diffusivity of steam compared to CO2 lead to the advanced ignition of coal, and the higher thermal radiation of steam leads to the ignition delay of coal. The chemical properties of steam are beneficial to the ignition. The steam shift reaction played a more important role in the advanced ignition of coal than the steam Gasification reaction.
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exergy based control strategy selection for flue Gas Recycle in oxy fuel combustion plant
Fuel, 2015Co-Authors: Wei Luo, Qiao Wang, Junjun Guo, Zhaohui Liu, Chuguang ZhengAbstract:Abstract Control system design is one of the key elements which need to be studied before commercial implementation of oxy-fuel power plants. Among others, the control strategy for flue Gas Recycle process should be firstly considered as it is one of the major differences between oxy-fuel combustion and traditional power plants. In this paper, a dynamic model combined with exergy analysis was firstly proposed to design the control system and evaluate the performance of potential control schemes for flue Gas Recycle process. The dynamic model had been extensively validated using static and dynamic data from a 3 MW th oxy-fuel combustion facility. Based on the dynamic model, the characteristics of the flue Gas Recycle system was investigated and two possible control configurations, RR (Recycle valve coupled with Recycle fan) and SR (stack valve combined with Recycle fan), were proposed. The control performances of the two candidates were tested in three typical types of disturbances usually occurred in the operation and further evaluated from the perspective of exergy efficiency. It was shown that both control loops could maintain the target variables (flue Gas Recycle ratio and Recycled flue Gas pressure) stable in the disturbances, while the total exergy destruction of flue Gas Recycle system in RR is 2.4%, 1.7% and 0.6% higher than that in SR during the disturbance tests, respectively. The exergy-based control strategy selection method proposed in this paper provides good insight to obtain the optimum control method for other subsystems in the power plant.
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numerical investigation on oxy combustion characteristics of a 200 mwe tangentially fired boiler
Fuel, 2015Co-Authors: Junjun Guo, Zhaohui Liu, Peng Wang, Xiaohong Huang, Chuguang ZhengAbstract:Abstract In recent years, oxy-fuel combustion in coal-fired plants has become one of the most promising technologies for carbon capture and storage (CCS). Compared with air-fired combustion, high concentrations of CO2 and H2O in the flue Gas cause a remarkable change in the pulverized coal combustion and heat transfer characteristics in furnace. In this study, improved models for the Gas radiative properties and chemical reaction mechanisms were incorporated into the computational fluid dynamics (CFD) code to simulate a 200 MWe tangentially fired utility boiler, which is expected to operate at full load under both conventional air-fired and oxy-fuel combustion. Different flue Gas Recycle patterns: dry Recycle and wet Recycle, were also investigated. The results indicate that, stable combustion is achieved by a compatible burner design in both air-fired and oxy-fuel combustion. In the oxy-fuel combustion, the flue Gas peak temperature and wall heat flux decrease and high CO concentration appears in the burner region, resulted from higher heat capacity of CO2 and chemical effect of CO2 (Liu et al., 2003, Glarborg and Bentzen, 2008). Based on the comparison of the wet Recycle and dry Recycle, it shows the wet Recycle has more advantages than dry Recycle. This study indicates a slight increase in total heat transfer, when the oxygen concentration in oxidant increases from 23% to 29%, consistent with the results of Vattenfall and Callide pilot scale oxy-combustion plant. Thus, compared with air-fired combustion, the full load of a boiler may decrease by 5–10% under oxy-fuel combustion.
Xiaoping Chen - One of the best experts on this subject based on the ideXlab platform.
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three dimensional cfd simulation of oxy fuel combustion in a circulating fluidized bed with warm flue Gas Recycle
Fuel, 2018Co-Authors: Daoyin Liu, Lunbo Duan, Jie Xiong, Xiaoping ChenAbstract:Abstract Among various CO2 capture methods, the oxy-fuel combustion technology exhibits great potential for CO2 capture in an economical way. Based on a pilot-scale circulating fluidized bed (CFB) combustor, computational fluid dynamics (CFD) is applied to simulate the oxy-fuel CFB combustion with warm flue Gas Recycle (WFGR). In this work, the WFGR in the oxy-fuel CFB combustion is realized by the Eulerian-Eulerian CFD simulation. Detailed profile of the hydrodynamics, temperature, Gas characteristics and pollutant emission is analyzed with good agreement between the simulated result and the experimental data achieved. Special attention is paid to the comparison of Gas distribution under the combustion conditions with and without WFGR, illustrating the unique advantages of the oxy-fuel CFB combustion with WFGR in the CO2 capture and pollutant reduction. Besides, influence of the oxy atmosphere with different O2 concentrations (from 21% to 40%) on the overall performance is conducted, successfully predicting the oxy-fuel combustion with WFGR under a high O2 concentration and enriching the investigation method of the CFB combustion study.
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coal combustion characteristics on an oxy fuel circulating fluidized bed combustor with warm flue Gas Recycle
Fuel, 2014Co-Authors: Lunbo Duan, Haicheng Sun, Changsui Zhao, Wu Zhou, Xiaoping ChenAbstract:Abstract More than 100-h steady warm flue Gas Recycle operation was carried out on a 50 kW th oxy-fuel circulating fluidized bed (CFB) combustor burning three kinds of fuel. The results demonstrate the good safety benefit of oxy-CFB operation, especially in the oxy-transition process. A slightly higher oxygen concentration, ranging from 22.2% to 23.4% for different fuels in oxy-fuel operation, can bring equivalent or higher carbon burnout than air combustion. SO 2 concentration in ppm unit is higher in flue Gas while the SO 2 emission in mg/MJ unit is lower than air combustion. The desulfurization efficiency of limestone can reach 80% in oxy-fuel combustion in this test. The higher Ca utilization rate burning coal in oxy-fuel combustion than that in air combustion may be associated with the high moisture content in the flue Gas. Fuel nitrogen conversion ratio in oxy-fuel is much lower than in air combustion, and it looks like higher volatile content in fuel leads to a bigger reduction of NO in the Recycle flue Gas.
Timothy C Merkel - One of the best experts on this subject based on the ideXlab platform.
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co2 capture from natural Gas power plants using selective exhaust Gas Recycle membrane designs
International Journal of Greenhouse Gas Control, 2017Co-Authors: Richard W Baker, Brice Freeman, Jay Kniep, Xiaotong Wei, Timothy C MerkelAbstract:Abstract This paper describes membrane processes to capture the CO2 produced by combustion Gas turbines in natural Gas combined cycle power plants. Because combustion turbines typically use a large excess of air, the resulting turbine exhaust Gas is relatively dilute (only 3–4% CO2), making subsequent CO2 capture difficult and costly. Previously, we’ve shown that a membrane process can be used to selectively Recycle CO2 to the combustion step, which significantly increases the CO2 content in the exhaust Gas. In this way, selective exhaust Gas Recycle (S-EGR) makes CO2 capture energetically easier. Here, various membrane design concepts incorporating S-EGR are described and compared. A combination of S-EGR with non-selective exhaust Gas Recycle (EGR) is shown to offer advantages in reduced capital, while retaining most of the energy benefits of S-EGR alone. For all of the membrane designs analyzed, the energy and cost of capture vary with the capture rate. Generally, if flue Gas compression is not used, the lowest capture cost ($/tonne CO2) for membranes occurs at partial capture rates of 60–70%. Of the process designs studied, the lowest cost of capture (∼$44/t) is achieved by an integrated turbine/membrane design that would require changes to existing turbines.
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Selective Exhaust Gas Recycle with Membranes for CO2 Capture from Natural Gas Combined Cycle Power Plants
Industrial & Engineering Chemistry Research, 2012Co-Authors: Timothy C Merkel, Zhenjie He, Lloyd S. White, Johannes G Wijmans, Richard W BakerAbstract:Low natural Gas prices are contributing to rapid growth in natural Gas combined cycle (NGCC) power production in the United States. CO2 capture from the exhaust Gas of these plants is complicated by the relatively low CO2 concentration in this flue Gas (3%–4%). A membrane process using incoming combustion air as a sweep stream in a selective exhaust Gas Recycle configuration can be used to preconcentrate CO2 from 4% to 15%–20% with almost no energy input. Depending on the process configuration, the selective Recycle membrane design reduces the minimum energy of a CO2 capture step by up to 40%. An all-membrane design using a capture step in series with a selective Recycle membrane can capture 90% of CO2 from an NGCC power plant using less energy and at a lower cost than the base-case amine process analyzed by the U.S. Department of Energy. The current state-of-the-art membranes for use in this process have a CO2 permeance of 2200 gpu and a CO2/N2 selectivity of 50. Higher CO2 permeance will improve the eco...
Richard W Baker - One of the best experts on this subject based on the ideXlab platform.
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co2 capture from natural Gas power plants using selective exhaust Gas Recycle membrane designs
International Journal of Greenhouse Gas Control, 2017Co-Authors: Richard W Baker, Brice Freeman, Jay Kniep, Xiaotong Wei, Timothy C MerkelAbstract:Abstract This paper describes membrane processes to capture the CO2 produced by combustion Gas turbines in natural Gas combined cycle power plants. Because combustion turbines typically use a large excess of air, the resulting turbine exhaust Gas is relatively dilute (only 3–4% CO2), making subsequent CO2 capture difficult and costly. Previously, we’ve shown that a membrane process can be used to selectively Recycle CO2 to the combustion step, which significantly increases the CO2 content in the exhaust Gas. In this way, selective exhaust Gas Recycle (S-EGR) makes CO2 capture energetically easier. Here, various membrane design concepts incorporating S-EGR are described and compared. A combination of S-EGR with non-selective exhaust Gas Recycle (EGR) is shown to offer advantages in reduced capital, while retaining most of the energy benefits of S-EGR alone. For all of the membrane designs analyzed, the energy and cost of capture vary with the capture rate. Generally, if flue Gas compression is not used, the lowest capture cost ($/tonne CO2) for membranes occurs at partial capture rates of 60–70%. Of the process designs studied, the lowest cost of capture (∼$44/t) is achieved by an integrated turbine/membrane design that would require changes to existing turbines.
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Selective Exhaust Gas Recycle with Membranes for CO2 Capture from Natural Gas Combined Cycle Power Plants
Industrial & Engineering Chemistry Research, 2012Co-Authors: Timothy C Merkel, Zhenjie He, Lloyd S. White, Johannes G Wijmans, Richard W BakerAbstract:Low natural Gas prices are contributing to rapid growth in natural Gas combined cycle (NGCC) power production in the United States. CO2 capture from the exhaust Gas of these plants is complicated by the relatively low CO2 concentration in this flue Gas (3%–4%). A membrane process using incoming combustion air as a sweep stream in a selective exhaust Gas Recycle configuration can be used to preconcentrate CO2 from 4% to 15%–20% with almost no energy input. Depending on the process configuration, the selective Recycle membrane design reduces the minimum energy of a CO2 capture step by up to 40%. An all-membrane design using a capture step in series with a selective Recycle membrane can capture 90% of CO2 from an NGCC power plant using less energy and at a lower cost than the base-case amine process analyzed by the U.S. Department of Energy. The current state-of-the-art membranes for use in this process have a CO2 permeance of 2200 gpu and a CO2/N2 selectivity of 50. Higher CO2 permeance will improve the eco...
Xi Kang - One of the best experts on this subject based on the ideXlab platform.
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galaxy formation with cold Gas accretion and evolving stellar initial mass function
The Astrophysical Journal, 2010Co-Authors: Xi Kang, Weipeng Lin, Ramin A Skibba, Dongni ChenAbstract:The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the.CDM model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models (SAMs) of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0. In addition, there is a strong correlation between star formation rate (SFR) and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using an SAM that includes (1) cold Gas accretion in massive halos at high redshift; (2) tidal stripping of stellar mass from satellite galaxies; and (3) an evolving stellar initial mass function (IMF; bottom-light) with a higher Gas Recycle fraction. Our results show that the combined effects from (1) and (2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, while the combined effects of (1) and (3) can reproduce the correlation between SFR and stellar mass for star-forming galaxies across a wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.
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galaxy formation with cold Gas accretion and evolving stellar initial mass function
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Xi Kang, Weipeng Lin, Ramin A Skibba, Dongni ChenAbstract:The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the $\Lambda {\rm CDM}$ model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0 . In addition, there is a strong correlation between star formation rate and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using a semi-analytical model that includes: 1) cold Gas accretion in massive halos at high redshift; 2) tidal stripping of stellar mass from satellite galaxies; and 3) an evolving stellar initial mass function (bottom-light) with a higher Gas Recycle fraction. Our results show that the combined effects from 1) and 2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, While the combined effects of 1) and 3) can reproduce the correlation between star formation rate and stellar mass for star-forming galaxies across wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.
