Furnace for biomass combustion – Comparison of model with experimental data

As one of the most easily accessible renewable energy resources, straw can be burned to provide heat energy. In this paper, results of theoretical and experimental research conducted under the proceedings of mathematical – numerical modeling of turbulent reacting flows has been presented. Two-dimensional turbulent flow model with homogeneous chemical reactions has been developed. The proposed model has been analyzed on the example of adiabatic combustion chamber for combustion of agricultural biomass. Turbulent flow is considered using time averaging Navier–Stokes equations that are closed by k–ε turbulence model. Calculations based on the proposed models were conducted using commercial CFD package FLUENT 6.3.26. For the purposes of experimental research, measurements of fluid flow and thermal parameters, such as continuous measurement of temperature in different points in the workspace furnace, air flow, flue gas flow, continual analysis of combustion products as well as setting heat and material balance, were carried out. Comparative analysis of the results of experiments and calculations indicate satisfactory agreement between the model and experiment.     

A line by line based weighted sum of gray gases model for inhomogeneous CO2–H2O mixture in oxy-fired combustion

The HITEMP 2010 spectral emissivity database has been employed in line by line (LBL) calculation to produce an accurate total emissivity database for H₂O–CO₂ mixtures of the composition characteristics for the oxy-fired combustion. A wide range of temperatures, pressure-path length products and molar fraction ratios have been covered in the database. By using the LBL based emissivity database, an accurate set of coefficients has been obtained for the weighted sum of gray gases model (WSGGM). Compared to the standard WSGGM, the present model includes the molar ratio of H₂O–CO₂ mixtures in its formulation which leads to one set of coefficients required to represent the entire range of molar ratio. This simplifies the implementation of the model in the simulation of radiative heat transfer in high inhomogeneous media providing higher accuracy. The model is validated against the benchmark solutions for oxy-fired conditions. Obtained results have been compared with some of the previously reported WSGGMs.     

A physically consistent FVM interpolation scheme based on the discretized convection–diffusion equation

A physically consistent difference scheme is proposed to discretize the convection–diffusion equation in this paper. The interface variables of control volume are calculated by the interpolation of the discretized convection–diffusion equation rather than the direct interpolation with neighbor nodes in the direction perpendicular to the interface. In the new scheme, all the nodes of parallel and normal to the interface are involved, which means that the influence of cross-stream fluxes is considered. Obviously, the proposed interpolation scheme is full of physical meaning and better than the traditional convective interpolation schemes. Two simulations of typical benchmark problems, lid-driven cavity flow in square cavity and flow over a backward-facing step, are carried out with this scheme and some traditional schemes to prove the advantages of the proposed scheme.     

A Ginzburg–Landau model for material aging depending on temperature

ABSTRACT

We consider a model describing the behavior of a body subject to aging and fatigue. These phenomena are supposed to be affected by both mechanical and thermal effects. The material is assumed to be viscoelastic where the stress–strain relation is based on a new fractional derivative proposed in Caputo and Fabrizio. The order of derivative is regarded as a new variable whose evolution is ruled by a Ginzburg–Landau equation. The model also includes an evolutive equation for the temperature deducing from the first law of thermodynamics. In this article, thermodynamic compatibility is shown and some numerical simulations are performed.     

Hydrogen production from steam gasification of biomass: Influence of process parameters on hydrogen yield – A review

Steam gasification is considered one of the most effective and efficient techniques of generating hydrogen from biomass. Of all the thermochemical processes, steam gasification offers the highest stoichiometric yield of hydrogen. There are several factors which influence the yield of hydrogen in steam gasification. Some of the prominent factors are: biomass type, biomass feed particle size, reaction temperature, steam to biomass ratio, addition of catalyst, sorbent to biomass ratio. This review article focuses on the hydrogen production from biomass via steam gasification and the influence of process parameters on hydrogen yield.     

Auto-ignition model based on tabulated detailed kinetics and presumed temperature PDF – Application to internal combustion engine controlled by thermal stratifications

The prediction of the auto-ignition sensitivity to the temperature in new engine combustors is a challenge in the community of numerical combustion. This paper is devoted to the modeling of temperature fluctuations for the simulation of reactive flows in real internal engine configurations. It aims at validating the temperature fluctuation equation model Truffin and Benkenida and its coupling with the ECFM3Z combustion model of Colin and Benkenida. Especially, this study focuses on the auto-ignition process which is described by the TKI (Tabulated Kinetics for Ignition) model of Knop and Jay. TKI is based on a tabulation method for reaction rates and its coupling with the temperature fluctuation is achieved through a presumed PDF approach. The integral limits for the PDF integration are determined locally through transport equations with appropriate closures on isothermal walls. The resulting model, called TKI–υ_T, is applied on Homogeneous Charge Compression Ignition (HCCI) combustion mode engine for which the only source of thermal stratification is wall heat loss. Comparisons with experiments demonstrate the impact of temperature fluctuations and the ability of the model to improve the prediction of the auto-ignition model.     

CO2 emissions in the global supply chains of services: An analysis based on a multi-regional input–output model

As the service sector dominates the economy in developed countries, its environmental impact has become an important issue. Based on a multi-regional input–output model, this paper estimates consumption-based emissions of service sectors of 41 countries and regions, and discusses the emission abatement policy of service sectors. The results indicate that consumption-based emissions of the service sector in most countries and regions are much greater than direct emissions generated by the service sector. Further decomposition by production sources demonstrates that final demand for services in certain countries causes substantial emissions in the other countries. In most countries, major parts of consumption-based emissions of the service sector come from upstream emissions in non-service sectors due to the intermediate consumption of non-service inputs in the service sector. For the US and China, the consumption-based emissions of their service sectors are traced back to different service consumption bundles and production sectors, which enable us to identify service categories and production sectors that play key roles in the impact of service sectors on CO₂ emissions. Finally, policy implications of the results are discussed for the climate effect of the service-oriented economy, global mitigation of climate change, sustainability, and the decarbonization of the service sector.     

The hydriding kinetics of Mg–Ni based hydrogen storage alloys: A comparative study on Chou model and Jander model

Two kinds of kinetic models, which are Jander model and Chou model, were applied to investigate the hydriding kinetic behavior of Mg–Ni based alloys. By comparing the calculated values with experimental data, it can be seen that both models were successfully used in the diffusion-controlled hydrogen absorption process of Mg–Ni system. However, Chou model was not only convenient for use but also gave a set of physical meaningful explicit analytic expressions. Chou model should be preferentially recommended to deal with the calculation at multi-temperatures and multi-pressures without multistep calculation. The application of Chou model to Mg₂₀Ni₈Cu₂ and Mg₂₀Ni₈Co₂ alloys shows that the calculated results agreed well with the experimental data and it is reasonable to expect that this model will also suitable for other Mg–Ni based alloys if the mechanism is similar.     

A semiempirical efficiency test for solar cells based on AlGaAs–GaAs and Si

A semiempirical method is used to obtain an equation for the solar cell efficiency factor. It is shown that the obtained equation may explain the experimental dependence of the solar cell efficiency factor on temperature.     

A kinetic model for air-steam reforming of bio-oil over Rh–Ni/γ-Al2O3 catalyst: Acetol as a model compound

A new kinetic model is proposed for catalytic reforming of acetol to synthesis gas over a Rh–Ni/γ-Al₂O₃ catalyst. Acetol is one of the most important bio-oil model compounds formed under reactive flash volatilization reaction conditions. The model was implemented in the Aspen Plus simulation package and used to predict the product gas composition at different reaction temperatures and steam and oxygen ratios. The contributions of the reactions both in the reactor freeboard and the catalytic bed were assessed using CSTR and PFR reactor models, respectively. The reaction scheme included decomposition, steam reforming, and water-gas shift reactions. The results from the model predicted the product distribution within an acceptable degree of tolerance. This study confirms that thermal decomposition and partial oxidation of acetol precede the catalytic reactions involving steam. The effects of temperature, oxygen concentration in the feed, the volume of the freeboard, and the catalyst bed height can all be evaluated with this new kinetic model. This work suggests that bio-oil decomposed into different fractions of molecules like acetol can be successfully modelled by a series of decomposition reactions followed by partial oxidation and catalytic steam conversion. The heat transfer within the catalyst bed is found to be critical for achieving a good match with the experimental results.     

A wide range kinetic modeling study of pyrolysis and oxidation of methyl butanoate and methyl decanoate – Note II: Lumped kinetic model of decomposition and combustion of methyl esters up to methyl decanoate

The aim of this work is to develop and discuss a lumped kinetic model to simulate the pyrolysis and combustion behavior of methyl decanoate. Validation of the lumped kinetic model of methyl decanoate in a very wide range of conditions, with temperature ranging from 500 to more than 2000 K, pressures up to 16 bar and equivalent ratios from lean to pyrolysis conditions, proved that, despite the drastic simplifications, the model can properly reproduce the experimental measurements in pyrolysis as well as in an oxidation environment, in both the low temperature regime and in flame conditions. This model is an extension of the lumped model of methyl butanoate developed and discussed in the first part of this work [1]. Thus, the lumped kinetic model of methyl butanoate and methyl decanoate is also quite simply applied to simulating the combustion behavior of intermediate methyl esters, by using the lever rule between the two reference components. The overall agreement with experimental measurements is very encouraging and lays the basis for the extension to the lumped kinetic scheme to soy and rapeseed biodiesel fuels.     

A solid oxide fuel cell operating on liquid organic hydrogen carrier-based hydrogen – A kinetic model of the hydrogen release unit and system performance

In this paper, a kinetic model for the catalytic dehydrogenation of perhydro dibenzyltoluene (H18-DBT), a well-established Liquid Organic Hydrogen Carrier (LOHC) compound, is presented. Kinetic parameters for hydrogen release at a Pt on alumina catalyst in a temperature range between 260 °C and 310 °C are presented. A Solid Oxide Fuel Cell (SOFC) system model was coupled to the hydrogen release from H18-DBT in order to validate the full sequence of LOHC-bound hydrogen-to-electric power. A system layout is described and investigated according to its transient operating behavior and its efficiency. We demonstrate that the maximum efficiency of LOHC-bound hydrogen-to-electricity is 45% at full load, avoiding any critical conditions for the system components.     

Research on optimization and performance of Na2HPO4·12H2O mixture system combining fuzzy optimization model based on analytic hierarchy process

In order to determine optimal salt hydrates matching and adding fraction of Na₂HPO₄ · 12H₂O, crystal characteristics, latent heat of phase change, supercooling degree, and phase change temperature were studied. According to experimental data, optimal salt hydrates matching and adding fraction of Na₂HPO₄ · 12H₂O are determined by adopting multi-objective fuzzy optimization model based on analytic hierarchy process. Aimed at 3% Na₂SiO₃ · 9H₂O-Na₂HPO₄ · 12H₂O optimized by the method, thermal cycling performance test is implemented. Test results show the following: the Na₂SiO₃ · 9H₂O-Na₂HPO₄ · 12H₂O system has lower supercooling degree than Na₂HPO₄ · 12H₂O. It forms stable crystal after multiple thermal cycles, the phase separation is eliminated completely, and supercooling degree is 3.6°C. Latent heat of phase change maintains at 164 J/g after 100 thermal cycles. It is a modified intermediate product of salt hydrates with development potential.     

Macro-economic impact of large-scale deployment of biomass resources for energy and materials on a national level—A combined approach for the Netherlands

Biomass is considered one of the most important options in the transition to a sustainable energy system with reduced greenhouse gas (GHG) emissions and increased security of enegry supply. In order to facilitate this transition with targeted policies and implementation strategies, it is of vital importance to understand the economic benefits, uncertainties and risks of this transition. This article presents a quantification of the economic impacts on value added, employment shares and the trade balance as well as required biomass and avoided primary energy and greenhouse gases related to large scale biomass deployment on a country level (the Netherlands) for different future scenarios to 2030. This is done by using the macro-economic computable general equilibrium (CGE) model LEITAP, capable of quantifying direct and indirect effects of a bio-based economy combined with a spread sheet tool to address underlying technological details. Although the combined approach has limitations, the results of the projections show that substitution of fossil energy carriers by biomass, could have positive economic effects, as well as reducing GHG emissions and fossil energy requirement. Key factors to achieve these targets are enhanced technological development and the import of sustainable biomass resources to the Netherlands.     

V2G or VEG?An investigation into the business model for future electric vehicles based on technological developments

基于目前电动汽车产业发展的困境认识,提出未来电动汽车技术发展与商业实现的VEG模式(Vehicle-Energy station-Grid).在VEG模式中,电动汽车充电方式由用户自己选择,可以在能量站快充,也可以在停车场或家庭车库进行慢充.能量站安装有低成本,长寿命的MW级储能电池,能够从电网充电储存电量后给电动汽车快速充电;同时,能量站能够与电网互动,用于电力调峰或调频.作者认为,开发低成本长寿命的新型储能电池和可以安全快速充电的新型动力电池是实现VEG模式的两大技术关键.只有这两大技术关键突破后,纯电动汽车产业发展的春天才能够真正到来.     

Numerical investigations of catalyst–liquid slurry flow in the photocatalytic reactor for hydrogen production based on algebraic slip model

A new device of photocatalytic reactor with solar concentrator for hydrogen production was introduced in this paper. In order to investigate the effects of the slurry flow and catalyst distributions in the reactor on photocatalysis for hydrogen production, an algebraic slip mixture model (ASM) was used to simulate the dynamics of the catalyst–water slurry flow. A block-structured non-uniform grid was applied to discretize the entire domain and an algebraic multi-grid (AMG) method was used to solve the pressure field. The mean slurry pressure gradients obtained by the model were in agreement with the experimental data in former literature. Based on this verification, catalyst particle distributions, slurry velocity distributions and inter-phase slip velocity distributions in photocatalytic reactor pipe were investigated. The results show that the catalyst tends to distribute near the bottom of the pipe in the reactor, leading to a concentration gradient along the vertical direction of cross section. But due to the effects of turbulence force against the gravity, a heterogeneous suspending state will be achieved in a fully developed flow.     

Energy demand in the fifteen European Union countries by 2010 —: A forecasting model based on the decomposition approach

This paper develops a forecasting model based on the complete decomposition method. The forecasting model allows the trend effect, the rebound effect and dematerialization/materialization to be estimated. To demonstrate the model, a case analysis of the probable energy demand in the 15 European Union (EU) countries up to 2010 has been made. The results show that the aggregate energy demand in the 15 EU countries by the end of 2010 will have increased from 258 to 426 Mtoe compared to the 1997 level, and dematerialisation will have increased from 73 to 225 Mtoe.     

How the removal of energy subsidy affects general price in China: A study based on input–output model

In China, most energy prices are controlled by the government and are under-priced, which means energy subsidies existing. Reforming energy subsidies have important implications for sustainable development through their effects on energy price, energy use and CO₂ emission. This paper applies a price-gap approach to estimate China's fossil-fuel related subsidies with the consideration of the external cost. Results indicate that the magnitude of subsidies amounted to CNY 1214.24 billion in 2008, equivalent to 4.04% of GDP of that year. Subsidies for oil products are the largest, followed by subsidies for the coal and electricity. Furthermore, an input–output model is used to analyze the impacts of energy subsidies reform on different industries and general price indexes. The findings show that removal of energy subsidies will have significant impact on energy-intensive industry, and consequently push up the general price level, yet with a small variation. Removing oil products subsidies will have the largest impact, followed by electricity, coal and natural gas. However, no matter which energy price increases, PPI is always the most affected, then GDP deflator, with CPI being the least. Corresponding compensation measures should be accordingly designed to offset the negative impact caused by energy subsidies reform.