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Weixin Cheng - One of the best experts on this subject based on the ideXlab platform.

  • rhizosphere priming effects on soil carbon and nitrogen dynamics among tree species with and without intraspecific competition
    New Phytologist, 2018
    Co-Authors: Feike A Dijkstra, Weixin Cheng, Peng Wang
    Abstract:

    : Rhizosphere priming effects (RPEs) play a central role in modifying soil organic matter mineralization. However, effects of tree species and intraspecific competition on RPEs are poorly understood. We investigated RPEs of three tree species (larch, ash and Chinese fir) and the impact of intraspecific competition of these species on the RPE by growing them at two Planting densities for 140 d. We determined the RPE on soil organic carbon (C) decomposition, gross and Net nitrogen (N) mineralization and Net Plant N acquisition. Differences in the RPE among species were associated with differences in Plant biomass. Gross N mineralization and Net Plant N acquisition increased, but Net N mineralization decreased, as the RPE on soil organic C decomposition increased. Intraspecific competition reduced the RPE on soil organic C decomposition, gross and Net N mineralization, and Net Plant N acquisition, especially for ash and Chinese fir. Microbial N mining may explain the overall positive RPEs across species, whereas intensified Plant-microbe competition for N may have reduced the RPE with intraspecific competition. Overall, the species-specific effects of tree species play an important role in modulating the magnitude and mechanisms of RPEs and the intraspecific competition on soil C and N dynamics.

  • rhizosphere priming effects on soil carbon and nitrogen dynamics among tree species with and without intraspecific competition
    New Phytologist, 2018
    Co-Authors: Feike A Dijkstra, Weixin Cheng, Peng Wang
    Abstract:

    : Rhizosphere priming effects (RPEs) play a central role in modifying soil organic matter mineralization. However, effects of tree species and intraspecific competition on RPEs are poorly understood. We investigated RPEs of three tree species (larch, ash and Chinese fir) and the impact of intraspecific competition of these species on the RPE by growing them at two Planting densities for 140 d. We determined the RPE on soil organic carbon (C) decomposition, gross and Net nitrogen (N) mineralization and Net Plant N acquisition. Differences in the RPE among species were associated with differences in Plant biomass. Gross N mineralization and Net Plant N acquisition increased, but Net N mineralization decreased, as the RPE on soil organic C decomposition increased. Intraspecific competition reduced the RPE on soil organic C decomposition, gross and Net N mineralization, and Net Plant N acquisition, especially for ash and Chinese fir. Microbial N mining may explain the overall positive RPEs across species, whereas intensified Plant-microbe competition for N may have reduced the RPE with intraspecific competition. Overall, the species-specific effects of tree species play an important role in modulating the magnitude and mechanisms of RPEs and the intraspecific competition on soil C and N dynamics.

  • aridity threshold in controlling ecosystem nitrogen cycling in arid and semi arid grasslands
    Nature Communications, 2014
    Co-Authors: Chao Wang, Weixin Cheng, Xiaobo Wang, Dongwei Liu, Yunting Fang, Wentao Luo, Ping Jiang, Jason Shi, Huaqun Yin, Jizhong Zhou
    Abstract:

    Higher aridity and more extreme rainfall events in drylands are predicted due to climate change. Yet, it is unclear how changing precipitation regimes may affect nitrogen (N) cycling, especially in areas with extremely high aridity. Here we investigate soil N isotopic values (d 15 N) along a 3,200 km aridity gradient and reveal a hump-shaped relationship between soil d 15 N and aridity index (AI) with a threshold at AI ¼ 0.32. Variations of foliar d 15 N, the abundance of nitrification and denitrification genes, and metabolic quotient along the gradient provide further evidence for the existence of this threshold. Data support the hypothesis that the increase of gaseous N loss is higher than the increase of Net Plant N accumulation with increasing AI below AI ¼ 0.32, while the opposite is favoured above this threshold. Our results highlight the importance of N-cycling microbes in extremely dry areas and suggest different controlling factors of N-cycling on either side of the threshold.

Feike A Dijkstra - One of the best experts on this subject based on the ideXlab platform.

  • rhizosphere priming effects on soil carbon and nitrogen dynamics among tree species with and without intraspecific competition
    New Phytologist, 2018
    Co-Authors: Feike A Dijkstra, Weixin Cheng, Peng Wang
    Abstract:

    : Rhizosphere priming effects (RPEs) play a central role in modifying soil organic matter mineralization. However, effects of tree species and intraspecific competition on RPEs are poorly understood. We investigated RPEs of three tree species (larch, ash and Chinese fir) and the impact of intraspecific competition of these species on the RPE by growing them at two Planting densities for 140 d. We determined the RPE on soil organic carbon (C) decomposition, gross and Net nitrogen (N) mineralization and Net Plant N acquisition. Differences in the RPE among species were associated with differences in Plant biomass. Gross N mineralization and Net Plant N acquisition increased, but Net N mineralization decreased, as the RPE on soil organic C decomposition increased. Intraspecific competition reduced the RPE on soil organic C decomposition, gross and Net N mineralization, and Net Plant N acquisition, especially for ash and Chinese fir. Microbial N mining may explain the overall positive RPEs across species, whereas intensified Plant-microbe competition for N may have reduced the RPE with intraspecific competition. Overall, the species-specific effects of tree species play an important role in modulating the magnitude and mechanisms of RPEs and the intraspecific competition on soil C and N dynamics.

  • rhizosphere priming effects on soil carbon and nitrogen dynamics among tree species with and without intraspecific competition
    New Phytologist, 2018
    Co-Authors: Feike A Dijkstra, Weixin Cheng, Peng Wang
    Abstract:

    : Rhizosphere priming effects (RPEs) play a central role in modifying soil organic matter mineralization. However, effects of tree species and intraspecific competition on RPEs are poorly understood. We investigated RPEs of three tree species (larch, ash and Chinese fir) and the impact of intraspecific competition of these species on the RPE by growing them at two Planting densities for 140 d. We determined the RPE on soil organic carbon (C) decomposition, gross and Net nitrogen (N) mineralization and Net Plant N acquisition. Differences in the RPE among species were associated with differences in Plant biomass. Gross N mineralization and Net Plant N acquisition increased, but Net N mineralization decreased, as the RPE on soil organic C decomposition increased. Intraspecific competition reduced the RPE on soil organic C decomposition, gross and Net N mineralization, and Net Plant N acquisition, especially for ash and Chinese fir. Microbial N mining may explain the overall positive RPEs across species, whereas intensified Plant-microbe competition for N may have reduced the RPE with intraspecific competition. Overall, the species-specific effects of tree species play an important role in modulating the magnitude and mechanisms of RPEs and the intraspecific competition on soil C and N dynamics.

Jose Maria Martinez-val - One of the best experts on this subject based on the ideXlab platform.

  • Integration between direct steam generation in linear solar collectors and supercritical carbon dioxide Brayton power cycles
    International Journal of Hydrogen Energy, 2015
    Co-Authors: L. Coco-enríquez, J. Muñoz-antón, Jose Maria Martinez-val
    Abstract:

    Direct Steam Generation in Parabolic Troughs or Linear Fresnel solar collectors is a technology under development since beginning of niNeties (1990's) for replacing thermal oils and molten salts as heat transfer fluids in concentrated solar power Plants, avoiding environmental impacts. In parallel to the direct steam generation technology development, supercritical Carbon Dioxide Brayton power cycles are maturing as an alternative to traditional Rankine cycles for increasing Net Plant efficiency and reducing balance of Plant equipments dimensions and cots. For gaining synergies between these two innovative technologies, in this paper, Direct Steam Generation and Brayton power cycles are integrated in line-focusing solar power Plants. Four configurations are studied: Configuration 1 consists on installing a condenser between solar field and power cycle; condensing the heat transfer fluid (steam water) with the balance of Plant working fluid (carbon dioxide). The condenser would be a shell & tubes type. Along tubes carbon dioxide flows, and steam water condensates at shell-side. Main advantage of the condenser equipment is the high heat transfer coefficient at water condensing-side, reducing condenser dimension and weight. The main disadvantage of this configuration is the high operating pressure required in solar field for condensing steam into liquid water. This pressure should be between 150 bar and 175 bar for obtaining 400 °C at turbine inlet. In the Configuration 2, the superheated steam delivered by solar collectors transfers the heat energy in a primary heat exchanger to the balance of Plant working fluid. In this configuration the steam not condensate into liquid water, and only reduces the temperature from 550 °C-560 °C to 420 °C. The steam pressure drops in solar field along receivers, headers and heat exchangers are compensated by means of steam compressors. This second solution is compatible with higher turbine inlet temperatures, up to 550 °C. The keystones of this second configuration are the steam conditions at compressor inlet, pressure ∼175 bars and temperature ∼420 °C, for minimizing steam compressor electrical consumption. The third design solution (Configuration 3) includes a solar field with direct steam generation in solar collectors with boiling recirculation mode, but the balance of Plant is integrated by two Brayton power cycles in cascade. The first power cycle operating at 550 °C turbine inlet, and the second cycle at 410 °C turbine inlet. Main advantage is the integration between a validated direct steam generation technology (recirculation boiling mode) with the Brayton power cycles avoiding steam compressors, a technology not yet commercially available, and main drawback of this design is the increasing number of balance of Plant equipments. The Configuration 4 is very similar to the Configuration 2, with the same direct steam generation solar field with superheated steam without condensing, and a single reheating stage solar field with molten salt as heat transfer fluid. The Configuration 1 provides similar efficiency and Net power output, for similar solar field effective aperture area, as obtained with molten salt solar collectors with supercritical carbon dioxide power cycle (recompression with main compression intercooling cycle provides 36.6% Net efficiency, for a maximum 400 °C turbine inlet). The second design solution (Configuration 2) Net efficiency is not very much impacted for steam compressor electrical consumption recompression cycle Net efficiency is 43.6% with steam solar field, versus 45.16% with molten salt solar field, in both cases with 550 °C turbine inlet. The Configuration 3 performance is ∼39.7% with two cascade Brayton power cycles with recompression and main compression intercooling. Finally, the Configuration 4 optimum Plant performance is obtained for the recompression cycle with a Net efficiency ∼45.77%, and is constrained by the molten salt drawbacks (material corrosion, material cost, environmental impact, etc).

Peng Wang - One of the best experts on this subject based on the ideXlab platform.

  • rhizosphere priming effects on soil carbon and nitrogen dynamics among tree species with and without intraspecific competition
    New Phytologist, 2018
    Co-Authors: Feike A Dijkstra, Weixin Cheng, Peng Wang
    Abstract:

    : Rhizosphere priming effects (RPEs) play a central role in modifying soil organic matter mineralization. However, effects of tree species and intraspecific competition on RPEs are poorly understood. We investigated RPEs of three tree species (larch, ash and Chinese fir) and the impact of intraspecific competition of these species on the RPE by growing them at two Planting densities for 140 d. We determined the RPE on soil organic carbon (C) decomposition, gross and Net nitrogen (N) mineralization and Net Plant N acquisition. Differences in the RPE among species were associated with differences in Plant biomass. Gross N mineralization and Net Plant N acquisition increased, but Net N mineralization decreased, as the RPE on soil organic C decomposition increased. Intraspecific competition reduced the RPE on soil organic C decomposition, gross and Net N mineralization, and Net Plant N acquisition, especially for ash and Chinese fir. Microbial N mining may explain the overall positive RPEs across species, whereas intensified Plant-microbe competition for N may have reduced the RPE with intraspecific competition. Overall, the species-specific effects of tree species play an important role in modulating the magnitude and mechanisms of RPEs and the intraspecific competition on soil C and N dynamics.

  • rhizosphere priming effects on soil carbon and nitrogen dynamics among tree species with and without intraspecific competition
    New Phytologist, 2018
    Co-Authors: Feike A Dijkstra, Weixin Cheng, Peng Wang
    Abstract:

    : Rhizosphere priming effects (RPEs) play a central role in modifying soil organic matter mineralization. However, effects of tree species and intraspecific competition on RPEs are poorly understood. We investigated RPEs of three tree species (larch, ash and Chinese fir) and the impact of intraspecific competition of these species on the RPE by growing them at two Planting densities for 140 d. We determined the RPE on soil organic carbon (C) decomposition, gross and Net nitrogen (N) mineralization and Net Plant N acquisition. Differences in the RPE among species were associated with differences in Plant biomass. Gross N mineralization and Net Plant N acquisition increased, but Net N mineralization decreased, as the RPE on soil organic C decomposition increased. Intraspecific competition reduced the RPE on soil organic C decomposition, gross and Net N mineralization, and Net Plant N acquisition, especially for ash and Chinese fir. Microbial N mining may explain the overall positive RPEs across species, whereas intensified Plant-microbe competition for N may have reduced the RPE with intraspecific competition. Overall, the species-specific effects of tree species play an important role in modulating the magnitude and mechanisms of RPEs and the intraspecific competition on soil C and N dynamics.

Olav Bolland - One of the best experts on this subject based on the ideXlab platform.

  • Design and off-design simulations of combined cycles for offshore oil and gas installations
    Applied Thermal Engineering, 2013
    Co-Authors: Lars O. Nord, Olav Bolland
    Abstract:

    Abstract Combined cycles applied on offshore oil and gas installations could be an attractive technology on the Norwegian continental shelf to decrease costs related to CO 2 emissions. Current power Plant technology prevailing on offshore oil- and gas installations is based on simple cycle gas turbines for both electrical and mechanical drive applications. Results based on process simulations showed that Net Plant efficiency improvements of 26–33% (10–13%-points) compared to simple cycle gas turbines can be achieved when the steam bottoming cycles are designed for compactness and flexibility. The emitted CO 2 could be decreased by 20–25% by opting for a combined cycle rather than a simple cycle gas turbine. A clear disadvantage for offshore applications is that the weight-to-power ratio was 60–70% higher for a compact combined cycle than for a simple cycle gas turbine based on results in this study. Once-through heat recovery steam generator technology can be an attractive option when designing a steam bottoming cycle for offshore applications. Its flexibility, the avoidance of steam drums, and, with the right material selection, the possibility to avoid the bypass stack while allowing for dry heat recovery steam generator operation are all advantages for offshore applications. All process models, that were developed for offshore installations in the study presented, included once-through technology. A combined cycle Plant layout for an offshore installation with both mechanical drive and generator drive gas turbines was included in the study. This setup allows for flexibility related to changes in demand for both mechanical drive and electricity. With the selected setup, designed for 60 MW shaft power, demand swings of approximately ±10 MW could be handled for either mechanical drive or electrical power while keeping the other drive-mode load constant.

  • integration of low temperature transcritical co2 rankine cycle in natural gas fired combined cycle ngcc with post combustion co2 capture
    International Journal of Greenhouse Gas Control, 2013
    Co-Authors: P Marchioro A Ystad, A A Lakew, Olav Bolland
    Abstract:

    Abstract When integrating a natural gas-fired combined cycle (NGCC) with post-combustion CO 2 capture, an efficiency penalty is induced. In the current work the penalty was a reduction of Net Plant efficiency from 58.5% to 50.6%. The largest part of this penalty is related to the reduction of power output from the power Plant due to steam consumption for CO 2 capture solvent regeneration. The potential of recovering low-temperature un-used thermal energy is limited as this low-grade energy is at a temperature below the low-pressure pinch-point of the steam boiler. In this work, heat sources located in the CO 2 capture process and CO 2 compression process have been identified and integrated with a low-temperature Rankine cycle utilizing CO 2 as working fluid. The approach presented in this paper is novel in the sense that it has not been applied on power Plants operating with post-combustion CO 2 capture. Results show that integration of the low-temperature CO 2 Rankine cycle can increase the Net Plant efficiency of a natural gas-fired Combined Cycle power Plant by 1.6%-points (50.6–52.2%) when using a conventional Monoethanolamine (MEA)-based CO 2 capture process. Capture process modifications (Lean Vapour Recompression) in combination with application of the CO 2 Rankine cycle can increase the efficiency by 1.8%-points (50.6–52.4%). The contribution from the CO 2 Rankine cycle for the latter case is 0.9%-points.

  • a modeling software linking approach for the analysis of an integrated reforming combined cycle with hot potassium carbonate co2 capture
    Energy Procedia, 2009
    Co-Authors: Lars O. Nord, Anusha Kothandaraman, Howard J Herzog, Greg Mcrae, Olav Bolland
    Abstract:

    The focus of this study is the analysis of an integrated reforming combined cycle (IRCC) with natural gas as fuel input. This IRCC consisted of a hydrogen-fired gas turbine (GT) with a single-pressure steam bottoming cycle for power production. The reforming process section consisted of a pre-reformer and an air-blown auto thermal reformer (ATR) followed by water-gas shift reactors. The air to the ATR was discharged from the GT compressor and boosted up to system pressure by an air booster compressor. For the CO2 capture sub-system, a chemical absorption setup was modeled. The design case model was modeled in GT PRO by Thermoflow, and in Aspen Plus. The Aspen Plus simulations consisted of two separate models, one that included the reforming process and the water-gas shift reactors. In this model were also numerous heat exchangers including the whole pre-heating section. Air and CO2 compression was also incorporated into the model. As a separate flow sheet the chemical absorption process was modeled as a hot potassium carbonate process. The models were linked by Microsoft Excel. For the CO2 capture system the model was not directly linked to Excel but instead a simple separator model was included in the reforming flow sheet with inputs such as split ratios, temperatures, and pressures from the absorption model. Outputs from the potassium model also included pump work and reboiler duty. A main focal point of the study was off-design simulations. For these steady-state off-design simulations GT MASTER by Thermoflow in conjunction with Aspen Plus were used. Also, inputs such as heat exchanger areas, compressor design point, etc., were linked in from the Aspen Plus reforming design model. Results indicate a Net Plant efficiency of 43.2% with approximately a 2%-point drop for an 80% part load case. Another off-design simulation, at 60% load, was simulated with a Net Plant efficiency around 39%. The CO2 capture rate for all cases was about 86%, except for the reference case which had no CO2 capture.

  • part load analysis of a chemical looping combustion clc combined cycle with co2 capture
    Energy, 2007
    Co-Authors: Rehan Naqvi, Jens Wolf, Olav Bolland
    Abstract:

    Chemical Looping Combustion (CLC) is a rather novel concept of hydrocarbon fuel energy conversion with inherent CO2 separation. In CLC, a solid oxygen carrier transports oxygen from air to the fuel; hence air and fuel remain in separate environments and the combustion exhaust mainly consists of CO2 and water vapour. CLC can be applied in a circulating fluidised bed reactor system. The main objectives of this work have been the sensitivity study of CLC-reactor system in combination with different oxygen carriers, design of different CLC-combined and CLC-steam cycle configurations, off-design behaviour analysis of CLC-combined cycles and investigation of the possibility to use conventional machinery in CLC-power Plants. The main efforts have been directed towards cycle design including parameter optimisation and cycle performance including off-design operation of combined cycles. The comparison of CLC-cycles with conventional natural gas-fired combined cycles has been presented at all the stages of this work.Energy and mass balance models for CLC based on the oxides of Fe, Cu and Ni in combination with inert supports of Al2O3 and NiAl2O4 have been developed. The results of study on different oxygen carriers in natural gas-based CLC indicate that NiO supported on NiAl2O4 is the most suitable oxygen carrier for achieving a conceivable reactor system. In order to be applicable in CLC-combined cycles, the reactor system and the oxygen carrier must stand a temperature of at least 1000°C and pressure of 10-26 bar.Various configurations of natural gas-fired CLC-combined cycles with NiO/NiAl2O4 oxygen carrier have been studied in this work. The results show that different designs of CLC-combined cycles consisting of single reactor system operating up to 1200°C can achieve 50-52% Net Plant efficiency including CO2 compression to 110 bar. Different CLCcombined cycle configurations employing multi-CLC-reactors and reheat air turbine have also been analysed. CLC-combined cycle with two reactor systems and single reheat air turbine can achieve above 51% Net Plant efficiency at 1000°C oxidation temperature. At the same oxidation temperature, a cycle with three CLC-reactors and double reheat air turbine achieves about 52% Net Plant efficiency. At 1200°C oxidation temperature, single reheat cycle achieves above 53% Net Plant efficiency, while double reheat results in marginal efficiency improvement. All the CLC-combined cycles proposed in this work exhibit higher Net Plant efficiencies with close to 100% CO2 capture compared to a conventional combined cycle with 90% post-combustion CO2 capture. The off-design analysis of CLC-combined cycles shows that a CLC-combined cycle exhibits better relative Net Plant efficiency at partload, compared to conventional combined cycles with and without CO2 capture. However, the CLC-combined cycles need more advanced control strategies, especially if a CO2/H2Oturbine is included. The cycles demand advanced air flow control strategies during the startup, shut-down and at part-load below 60%.Two designs of ultra-supercritical natural gas-fired CLC-steam cycles based on NiO/NiAl2O4 oxygen carrier have also been proposed and analysed in this work. The single reheat CLC-steam cycle can achieve Net Plant efficiency of about 43% while the double reheat CLC-steam cycle achieves 44% Net Plant efficiency with close to 100% CO2 capture. This work suggests that CLC has a high potential for efficient power generation with CO2 capture. However, there are some technological barriers discussed in this thesis, which need to be overcome in order to successfully realise CLC application in power Plants.

  • a quantitative comparison of gas turbine cycles with co2 capture
    Energy, 2007
    Co-Authors: Hanne M Kvamsdal, Kristin Jordal, Olav Bolland
    Abstract:

    Nine different concepts for natural gas fired power Plants with CO2 capture have been investigated, and a comparison is made based on Net Plant efficiency and emission of CO2. The cycles are one post-combustion, six oxy-fuel and two pre-combustion capture concepts. A 400MW combined cycle Plant is applied as a reference case. A common basis for the comparison of all concepts is defined and employed in heat- and mass-balance simulations of the various concepts. As gas turbine cooling impacts the Net Plant efficiency at high turbine inlet temperatures, a simplified turbine cooling model has been applied in the simulations. It is found that the concepts, in which novel technology (the hydrogen membrane separation reformer—-MSR-H2, the advanzed zero emission power Plant—AZEP, the solid oxide fuel cell combined with a gas turbine—SOFC+GT and the chemical looping combustion—CLC concepts) is employed, exhibit the best performance with respect to both efficiency and in most cases also CO2 capture (capture rates close to 100%). Post-combustion capture and pre-combustion capture with auto-thermal reforming, which are based on more mature technology, show a lower efficiency and a capture rate of typically 90%. The SOFC+GT concept exhibits the best cycle performance and even better than a standard CC Plant, however, any realization of a SOFC-GT 400MW Plant has a very distant future perspective. In order to conduct a complete assessment of these diverse concepts, other criteria for comparison such as e.g. technology level and costs should also be considered. This is not, however, included in the present work.