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A biomass combustion model with a thermally thick approach is presented and applied to the simulation of a commercial biomass domestic boiler. A subgrid scale model is used to divide the particles into several grid points, each representing one of the different combustion stages. These grid points determine the variables of the solid phase located in the packed bed calculated as a porous zone with a volume-averaged approach. The combustion model is coupled with a fuel-feeding model based on Lagrangian trajectories of particles. Those are transformed into solid phase variables as soon as they reach the packed bed, allowing the numerical model to simulate the transient behavior of such a system. This methodology is here applied to a 27-kW boiler operating in stable conditions with two feeding systems: one in which the particle feeding rate is kept constant in time and another in which the feeding rate varies randomly through time. The behavior of such a boiler is better understood thanks to the completeness of the model here presented, whose results are also compared to experimental measurements. The CFD model gives reasonably good predictions of the heat transferred, the flue gas temperature, the excess air coefficient and CO2 emissions, as well as the fluctuations of the boiler when the feeding rate is not constant. However, the model underestimates unburnt species like CO, probably due to the oversimplified gas reaction mechanisms employed in the simulation.

A biomass combustion model with a thermally thick approach is presented and applied to the simulation of a commercial biomass domestic boiler. A subgrid scale model is used to divide the particles into several grid points, each representing one of the different combustion stages. These grid points determine the variables of the solid phase located in the packed bed calculated as a porous zone with a volume-averaged approach. The combustion model is coupled with a fuel-feeding model based on Lagrangian trajectories of particles. Those are transformed into solid phase variables as soon as they reach the packed bed, allowing the numerical model to simulate the transient behavior of such a system. This methodology is here applied to a 27-kW boiler operating in stable conditions with two feeding systems: one in which the particle feeding rate is kept constant in time and another in which the feeding rate varies randomly through time. The behavior of such a boiler is better understood thanks to the completeness of the model here presented, whose results are also compared to experimental measurements. The CFD model gives reasonably good predictions of the heat transferred, the flue gas temperature, the excess air coefficient and CO2 emissions, as well as the fluctuations of the boiler when the feeding rate is not constant. However, the model underestimates unburnt species like CO, probably due to the oversimplified gas reaction mechanisms employed in the simulation.

The commercial solar energy market is dominated by non-concentrating photovoltaics and concentrating solar thermal systems. With the development of high efficiency thermoelectric materials, the solar thermoelectric generator is becoming to be a competitive alternative solar energy technology in certain applications. This paper proposes a simulation model and a design methodology for solar thermoelectric generator. Geometry parameters, namely the height, the fill-ratio, the ratio of the cross-section area of n-type material over p-type material of thermoelectric module, solar concentration ratio, were analyzed under different operating conditions. In order to perform the analysis, an L27 (35) orthogonal array was employed to assess all of the design parameters returning the maximum output power. By the analysis of variance, the effect of each design parameter on the output power performance and the interaction between design parameters are identified. The optimal design parameter set is also obtained and it is found that the optimal design performs can potentially achieve 5.47 W output power compared with the output power of 1.95 W from the original design in most operating conditions.

The commercial solar energy market is dominated by non-concentrating photovoltaics and concentrating solar thermal systems. With the development of high efficiency thermoelectric materials, the solar thermoelectric generator is becoming to be a competitive alternative solar energy technology in certain applications. This paper proposes a simulation model and a design methodology for solar thermoelectric generator. Geometry parameters, namely the height, the fill-ratio, the ratio of the cross-section area of n-type material over p-type material of thermoelectric module, solar concentration ratio, were analyzed under different operating conditions. In order to perform the analysis, an L27 (35) orthogonal array was employed to assess all of the design parameters returning the maximum output power. By the analysis of variance, the effect of each design parameter on the output power performance and the interaction between design parameters are identified. The optimal design parameter set is also obtained and it is found that the optimal design performs can potentially achieve 5.47 W output power compared with the output power of 1.95 W from the original design in most operating conditions.

During operation, solid oxide fuel cell releases quite a great part of hydrogen energy into waste heat, leading to energy waste and even functional component degradation. In this study, solid oxide fuel cell, alkali metal thermal electric converter and organic Rankine cycle are synergistically integrated as a three-stage integration system to gradually and efficiently utilize the waste heat. Accounting a variety of thermodynamic-electrochemical losses within the system, mathematical expressions of power output, energy efficiency, exergy destruction rate, and exergy efficiency for the integration system are deduced. The basic performance features and competitiveness of the integration system are revealed. The maximum power output density of the proposed system allows to be 12407.0 W m−2, which is approximately improved by 103.8 % compared to that of the stand-alone solid oxide fuel cell (6087.4 W m−2). Parametric studies demonstrate that an increase in operation temperature, operation pressure or radiation loss geometric factor enhances the integration system performance, while an increase in β″-alumina solid electrolyte thickness, proportional coefficient or pinch temperature ratio degrades the integration system performance. The results obtained can provide some theoretical support for designing or running such an actual three-stage integration system for efficient power generation.

During operation, solid oxide fuel cell releases quite a great part of hydrogen energy into waste heat, leading to energy waste and even functional component degradation. In this study, solid oxide fuel cell, alkali metal thermal electric converter and organic Rankine cycle are synergistically integrated as a three-stage integration system to gradually and efficiently utilize the waste heat. Accounting a variety of thermodynamic-electrochemical losses within the system, mathematical expressions of power output, energy efficiency, exergy destruction rate, and exergy efficiency for the integration system are deduced. The basic performance features and competitiveness of the integration system are revealed. The maximum power output density of the proposed system allows to be 12407.0 W m−2, which is approximately improved by 103.8 % compared to that of the stand-alone solid oxide fuel cell (6087.4 W m−2). Parametric studies demonstrate that an increase in operation temperature, operation pressure or radiation loss geometric factor enhances the integration system performance, while an increase in β″-alumina solid electrolyte thickness, proportional coefficient or pinch temperature ratio degrades the integration system performance. The results obtained can provide some theoretical support for designing or running such an actual three-stage integration system for efficient power generation.

In this paper the value of the exergetic life cycle assessment (ELCA) has been analysed. The ELCA uses the framework of the life cycle assessment (LCA) and can be seen as the exergy analysis of a complete life cycle. The value of the ELCA besides the LCA has been discussed. It is shown that the ELCA is a more appropriate instrument to quantify the environmental problem of the depletion of natural resources. This has been tested with a case study of different waste wood treatment routes. In the first model waste wood is co-combusted in a coal power plant, while in the second model waste wood has been used to produce chipboard. The ELCA shows that the production of chipboard gives less depletion of natural resources. Furthermore, in model 3 and 4 coal for generating electricity has been replaced by green wood. The ELCA shows that replacing coal by green wood gives less depletion of natural resources than replacing the waste wood with green wood, while the waste wood is used for generating electricity. However, comparing the four models it can be seen that replacing coal by green wood causes more wasting of natural resources, while the depletion of natural resources decreases. It can be concluded that the ELCA can be used in two ways. First, the ELCA can be used to determine the consumption of natural resources and second, the ELCA can be used to calculate the depletion of natural resources. In the latter case, a distinction has been made between renewable and non-renewable exergy resources.

In this paper the value of the exergetic life cycle assessment (ELCA) has been analysed. The ELCA uses the framework of the life cycle assessment (LCA) and can be seen as the exergy analysis of a complete life cycle. The value of the ELCA besides the LCA has been discussed. It is shown that the ELCA is a more appropriate instrument to quantify the environmental problem of the depletion of natural resources. This has been tested with a case study of different waste wood treatment routes. In the first model waste wood is co-combusted in a coal power plant, while in the second model waste wood has been used to produce chipboard. The ELCA shows that the production of chipboard gives less depletion of natural resources. Furthermore, in model 3 and 4 coal for generating electricity has been replaced by green wood. The ELCA shows that replacing coal by green wood gives less depletion of natural resources than replacing the waste wood with green wood, while the waste wood is used for generating electricity. However, comparing the four models it can be seen that replacing coal by green wood causes more wasting of natural resources, while the depletion of natural resources decreases. It can be concluded that the ELCA can be used in two ways. First, the ELCA can be used to determine the consumption of natural resources and second, the ELCA can be used to calculate the depletion of natural resources. In the latter case, a distinction has been made between renewable and non-renewable exergy resources.