1,721,028 research outputs found
Should biomass be used for power generation or hydrogen production?
No full textIn the last several years, gasification has become an interesting option for biomass utilization because the produced gas can be used as a gaseous fuel in different applications or burned in a gas turbine for power generation with a high thermodynamic efficiency.
In this paper, a technoeconomic analysis was carried out in order to evaluate performance and cost of biomass gasification systems integrated with two different types of plant, respectively, for hydrogen production and for power generation. An indirectly heated fluidized bed gasifier has been chosen for gas generation in both cases, and experimental data have been used to simulate the behavior of the gasifier. The hydrogen plant is characterized by the installation of a steam methane reformer and a shift reactor after the gas production and cleanup section; hydrogen is then purified in a pressure swing adsorption system. All these components have been modeled following typical operating conditions found in hydrogen plants. Simulations have been performed to optimize thermal interactions between the biomass gasification section and the gas processing.
The power plant consists of a gas-steam combined cycle, with a three-pressure-levels bottoming cycle. A sensitivity analysis allowed to evaluate the economic convenience of the two plants as a function of the costs of the hydrogen and electrical energy
Analysis of Biomass Integrated Gasification Fuel Cell Plants in Industrial CHP Applications
No full textThe gasification of biomass wastes deriving from certain industrial processes is an interesting option for cogenerating heat and power. The utilization of the syngas in a high temperature fuel cell could lead to the improvement of electrical efficiency in comparison with traditional CHP plants. In this paper the performance of various Biomass Integrated Gasification Fuel Cell (BIGFC) plants are investigated. In particular an atmospheric down-draft gasifier has been considered for syngas production. The fuel cell used for power generation is a 250 kW solid oxide fuel cell, which has been simulated through a zero-dimensional steady-state model and integrated in Aspen Plus® software for evaluating the performance of the entire plant. Various system lay-outs have been investigated to analyze the effect on plant efficiency of the following parameters: (i) gasification air pre-heating; (ii) use of 90% pure oxygen for gasification; (iii) use of enriched air (55% 02) for gasification; (iv) recirculation of anodic gas flow; (v) installation of a SOFC/GT hybrid cycle for power production. BIGFC plants show an electrical efficiency in the range 20-27%, and a thermal efficiency of 39-59%. If a SOFC/GT hybrid cycle is installed electrical efficiency grows up to 39%
Analysis Of Gas-Steam Combined Cycles With Natural Gas Reforming And CO2 Capture
No full textIn the last several years greenhouse gas emissions, and, in particular, carbon dioxide emissions, have become a major concern in the power generation industry and a large amount of research work has been dedicated to this subject. Among the possible technologies to reduce CO2 emissions from power plants, the pretreatment of fossil fuels to
separate carbon from hydrogen before the combustion process is one of the least energy consuming ways to facilitate CO2 capture and removal from the power plant. In this paper several power plant schemes with reduced CO2 emissions were simulated. All the configurations were based on the following characteristics: (i) syngas production via natural gas reforming; (ii) two reactors for CO-shift; (iii) ‘‘precombustion’’ decarbonization of the fuel by CO2 absorption with amine solutions; (iv) combustion of hydrogen-rich fuel in a commercially available gas turbine; and (v) combined cycle with three pressure levels, to achieve a net power output in the range of 400 MW. The base reactor employed for syngas generation is the ATR (auto thermal reformer). The attention was focused on the optimization of the main parameters of this reactor and its interaction with the power section. In particular the simulation evaluated the benefits deriving from the postcombustion of exhaust gas and from the introduction of a gas-gas heat exchanger. All the components
of the plants were simulated using ASPEN PLUS software, and fixing a reduction of CO2 emissions of at least 90%. The best configuration showed a thermal efficiency of approximately 48% and CO2 specific emissions of 0.04 kg/kWh
A Techno-Economic Analysis of Different Options for Cogenerating Power in Hydrogen Plants Based on Natural Gas Reforming
No full textSteam methane reforming is the most common process for producing hydrogen in the world. It currently represents the most efficient and mature technology for this purpose. However, because of the high investment costs, this technology is only convenient for large sizes. Furthermore, the cooling of syngas and flue gas produce a great amount of excess steam, which is usually transferred outside the process, for heating purposes or industrial applications. The opportunity of using this additional steam to generate electric power has been studied in this paper. In particular, different power plant schemes have been analyzed, including (i) a Rankine cycle, (ii) a gas turbine simple cycle, and (iii) a gas-steam combined cycle. These configurations have been investigated with the additional feature of CO2 capture and sequestration. The reference plant has been modeled according to state-of-the-art of commercial hydrogen plants: it includes a prereforming reactor, two shift reactors, and a pressure swing adsorption unit for hydrogen purification. The plant has a conversion efficiency of ∼75% and produces 145,000Sm3/hr of hydrogen (equivalent to 435MW on the lower-heating-volume basis) and 63t∕hr of superheated steam. The proposed power plants generate, respectively, 22MW (i), 36MW (ii), and 87MW (iii) without CO2 capture. A sensitivity analysis was carried out to determine the optimum size for each configuration and to investigate the influence of some parameters, such as electricity, natural gas, and steam costs
A Novel Concept for Combined Heat and Cooling in Humid Gas Turbine Cycles
No full textVarious gas turbine cycles are known where water is introduced as a liquid or as a vapor into the combustor of the gas turbine. Such cycles include the Humid Air Turbine (HAT) cycle, the Steam Injected (STIG) cycle, and the Regenerated Water Injected gas turbine cycle (RWI). The effect of water vapor is the increasing of net power output and the reduction of NOx formation within the combustor. However the net increase in power output is limited in commercial models of gas turbines, because a large addition of water vapor leads to the mismatch between the compressor and the turbine. In this paper a possible method to solve this problem is proposed: it is based on a novel concept for combining refrigeration and power production in humid gas turbine cycles. In the proposed system a fraction of the air at compressor discharge is extracted, cooled to nearly ambient temperature, dried and expanded in a turbine. At turbine outlet the air is at a very low temperature and can be used for providing refrigeration. A thermodynamic analysis has been carried out to investigate the performance of the system in HAT, STIG and RWI cycles for different operating conditions representing the state of art of commercial gas turbines. In particular the pressure ratio and the turbine inlet temperature have been respectively varied in the range 7-45 and 900-1500°C. Sensitivity analyses have been performed to assess how the amounts of extracted air and injected steam affect the net power output, the electrical efficiency and the cooling. The results show that cryogenic temperatures (lower than -100°C) for refrigeration can be achieved in combination with very high electrical efficiency (over 40%, typical of humid gas turbine cycles)
Detailed structural analysis of digital outcrops: a learning example from the kermanshah-qulqula radiolarite basin, zagros belt, iran
Full text linkA digital outcrop example and associated structural analysis of highly deformed sedimentary strata from the Zagros Belt of Iran is presented. By providing this site in open-access, downloadable format, we aim to make this excellent outcrop exposure accessible to a wide range of geoscientists. Digital data extraction techniques are used to constrain structural interpretations and cross section orientation, as well as kinematic restorations of interpreted structures. Structural analysis protocols provided here are well-suited to learning outcomes associated with digital cross section construction, interpretation and restoration. Complex deformation at the study locality and associated uncertainties in horizon and fault mapping yield interpretation and structural restoration results that are likely non-unique. Interpretation uncertainties are discussed in the context of geoscience education, with specific reference to the need for considering and assessing data quality and underlying geological assumptions. Our workflow and results can be used to bridge the gap between field-based training at undergraduate level and the proficiency in 3D digital environments required of professional geoscientists. By using digital outcrops to achieve learning outcomes, knowledge of underlying geological processes and practical skills in digital data handling and treatment can be effectively communicated to future geoscientists within the virtual environment
The Meso-Cenozoic fracture pattern of the Lurestan region, Iran: The role of rifting, convergence, and differential compaction in the development of pre-orogenic oblique fractures in the Zagros Belt
No full textIn this work we present data on fractures and mesoscale folds exposed in the Triassic to Miocene sedimentary
succession of the Lurestan region (Zagros Belt). Data have been collected in tens of field sites, in a 104 km2 area
extending across the High Zagros Zone and the Folded Belt. Fractures and mesoscale folds have been characterised
in terms of orientation, cross-cutting and abutting relationships with the other structures, and relative
timing with respect to sedimentation. Outcrop-scale folds, stylolites, and reverse faults are NW-SE oriented and
developed during NE-SW directed shortening. Extensional fractures, including joints, veins, and normal faults,
are arranged into two assemblages including: (i) NE-SW and NW-SE striking fractures and (ii) NNW-SSE and
WSW-ENE striking fractures. Syn-sedimentary fractures of the two extensional assemblages occur in pre- and
syn-rift Jurassic rocks, but also in post-rift Cretaceous rocks and Cenozoic syn-orogenic rocks. We infer that the
development of these extensional fractures in the Lurestan region was controlled by: (i) NE-SW-directed extension
during both Early Jurassic rifting and early orogenic foreland extension; and (ii) WSW-ENE-directed
stretching caused by differential compaction and related subsidence above NNW-SSE elongated basement
structures, during tectonically quiescent periods
Terrestrial SfM-MVS photogrammetry from smartphone sensors
Full text linkSmartphones can be regarded as cameras, natively equipped with geolocation and orientation sensors, making them powerful, portable, user-friendly and inexpensive tools for terrestrial structure from motion/multiview stereo photogrammetry (SfM-MVS) surveys. Camera extrinsic parameters (i.e. camera position and orientation), required to produce fully georeferenced SfM-MVS 3D models are available for the majority of smartphone images via inbuilt magnetometer, accelerometer/gyroscope, and global navigation satellite system (GNSS) sensors. The precision of these internal sensors is not yet sufficient to directly use them as input to SfM-MVS photogrammetric reconstructions. However, when the reconstructed scene is significantly greater than the positional error, camera extrinsic parameters can be successfully used to register 3D models during post-processing. We present a survey of a 400 m wide vertical cliff to illustrate a workflow that enables the use of smartphone cameras to generate and fully georeference photogrammetric models without employing ground control points. Survey images were acquired at a distance of ~350 m to the mapped scene using a consumer-grade smartphone. This survey image dataset was subsequently used to build an unreferenced 3D model, which was registered during post-processing using orientation and position metadata tagged to each photograph
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