Economics of cellulosic ethanol production in a thermochemical pathway for softwood, hardwood, corn stover and switchgrass

The economics of producing cellulosic ethanol using loblolly pine, natural mixed hardwood, Eucalyptus, corn stover, and switchgrass as feedstocks was simulated in Aspen Plus using the thermochemical process via indirect gasification and mixed alcohol synthesis developed by NREL. Outputs from the simulation were linked to an economic analysis spreadsheet to estimate NPV, IRR, payback and to run further sensitivity analysis of the different combinations of feedstocks. Results indicate that forest-based feedstocks including loblolly pine, natural hardwood and eucalyptus may present more attractive financial returns when compared to switchgrass and corn stover, mainly due to their composition (%C, %H, %ash) and alcohol yield. Simulated alcohol yields from forest-based feedstock were significantly higher than from switchgrass and corn stover. Simulations run with switchgrass and corn stover, also demonstrated greater sensitivity to changes in ethanol price, alcohol yield, capital investment and biomass costs. Furthermore, moisture content of receiving feedstocks greatly affected the economics of the biorefinery. A difference of − 10% in the moisture content of the receiving feedstock affected the NPV of the simulated project by + 25% (with respect to central NPV of ~$192 million).     

用于降低卷烟烟气中CO含量的Pd-Cu/活性炭催化剂

用浸渍法制备用于降低卷烟烟气中CO含量的Pd-Cu/活性炭催化剂,考察该催化剂对模拟卷烟烟气[4.4%CO-4.2%H2O-19.2%O2-72.2%N2(体积分数)]中的CO常温催化氧化性能,研究催化剂活性组分及其负载量、催化剂栽体、原料气中CO浓度和气体空速对催化剂的CO常温氧化活性的影响.研究表明,生产成本较低的...     

Combination of thermochemical recuperative coal gasification cycle and fuel cell for power generation

An integrated power generation cycle combining thermochemical recuperation, brown coal gasification and a solid oxide fuel cell (SOFC) was proposed based on the concept of thermochemical recuperative energy. Process simulation combining the coal gasifier, gas turbine cycle, and SOFC module was conducted using the ASPEN Plus process simulation tool. The simulation indicated that the cycle efficiency increases from 39.5% (HHV) without the SOFC to about 45% (HHV) with the SOFC.     

Energetic use of the tomato plant waste

A study of the conventional pyrolysis of the tomato plant waste has been carried out. The objective of this work was to characterize the solid, liquid and gaseous phases obtained in the process for their possible utilization in energy generation. Also, a study of the influence of operation variables has been performed, determining the optimal conditions in which the process can be accomplished. The operation variables studied were temperature (400–800 °C), the initial sample mass (2.5–10 g of tomato plant waste) and the particle size (0.63–2.00 mm). Under the conditions studied here, an increase in reaction temperature leads to a decrease in solid and liquid yields and to an increase in gas phase yield. However the variation in the initial sample mass and the particle size does not seem to exert a defined influence in the yield of the different phases. The higher heating value (HHV) of solids and liquids was determined; also the immediate analysis of the solid phase was carried out. The gas phase, mainly composed of H₂, CO, CH₄, CO₂ and traces of ethane and ethylene, was analyzed chromatographically. The solid phase is constituted for a charcoal with an average higher heating value of 26 MJ kg^− 1, the liquid phase presents a HHV of 7.8 MJ kg^− 1 at 400 °C, this value diminishes when the temperature is increased, and the gas phase has an HHV between 0.5 and 8.0 MJ (kg of raw material)^− 1. According to their characteristics and energy contents, the solid phase can be used as fuel or precursor for the manufacture of activated carbons. The liquid phase could be used as liquid fuel or as organic-compounds source. The gas phase could be used to heat the pyrolysis reactor or to generate heat and electricity in a gas-turbine/vapour-turbine combined cycle. Finally, as previous step to the design of the industrials equipments, a kinetic study of the process, based in the generation of the principal gases, has been carried out. For this study it has been considered that the gases are formed through parallel independent first-order reactions, with different activation energy. From this model, rate constants for the formation of each gas component and their corresponding activation energies were determined.     

Chemical makeup and physical characterization of a synthetic fuel and methods of heat content evaluation for studies on MSW incineration

A well-characterized synthetic fuel is often needed for research related to the efficiency or completeness of combustion and emissions from municipal solid waste incinerators. Knowledge of the chemical makeup, physical characteristics and heat content of such a synthetic fuel is important to establish accurate baseline operating conditions for experiments and to provide a mechanism for verification of data.A synthetic fuel was formulated to be representative of municipal solid waste (MSW) found in the US waste-stream, after some recycling. A majority of the fuel consists of cellulose in the form of paper and wood. Low-density polyethylene is chosen to represent the plastic polymer content, and iron represents the metal content. The waste food organic content is simulated by animal feed. Water and the inert component silica make up the rest of the fuel. The fuel is fabricated in three stages: (i) mixing the components, (ii) size reduction by shredding and (iii) compaction into cylindrical pellets of 2.5 cm diameter and approximate length 5 cm. Chemical analysis of the fuel includes testing its chlorine, nitrogen and sulfur content. The physical characterization includes tests for fixed carbon, ash, volatile matter and moisture content of the fuel. The heat content of the synthetic fuel is determined by three different methods.The first method to determine the heat content is the standard bomb calorimeter method, in which a powdered sample of fuel is burned with excess oxygen in an adiabatic calorimeter. The second method, also experimental in nature, is to apply calorimetry on the individual components of the synthetic fuel. The third method is to investigate literature values for the heat content of the individual fuel components and then multiply them by their mass fractions and sum to find the total heat content. These three values for the heat content are compared, and close agreement is found. The value determined by all three methods is the ‘higher heating value’ (HHV), that is, it includes the latent heat of condensation of water vapor, which is formed during combustion. Thus, in all three methods, among the final combustion products the water content is taken to be condensed (liquid). The data show that any one of the three methods can accurately determine the heat content of a synthetic fuel.     

Performance optimization of two-staged gasification system for woody biomass

The performance of a small-scale two-staged gasification system is reported. In this system wood chips are gasified with a fixed bed gasifier and then tar in the produced gas is reformed in a non-catalytic reformer, finally the production gas is used to generate electricity. In this system, the gasifying agents are high temperature air and steam supplied into the gasifier and the reformer. This paper reports on optimum gasification air ratio (defined as the ratio of the oxygen mole supplied into the gasifier to the oxygen mole required for complete combustion of biomass), reforming air ratio (defined as the ratio of the oxygen mole supplied in the reformer to the oxygen mole required for the complete combustion of biomass) and steam ratio (defined as the ratio of the steam mole supplied into the gasifier to the carbon mole in biomass supplied into the gasifier) for producing required gas supplied into a dual-fueled diesel engine. The results showed that, under optimum conditions, the higher heating value of the reformed gas was 3.9 MJ/m³_N; the cold gas efficiency (defined as the ratio of HHV reformed gas × reformed gas flow rate to HHV biomass × biomass feed rate) of the gasification system was 66%, and the gross thermal efficiency of the overall system was 27%.     

Computational Fluid Dynamics Modeling of Combustion of Synthetic Fuel of Thermochemical Heat Recuperation Systems

CFD modeling of the combustion of synthetic fuel formed in the systems of thermochemical recuperation of waste flue gas heat due to steam methane reforming was performed using the ANSYS Fluent software. Scientific justification and validation of the physicomathematical approaches involved the ANSYS Fluent for the problems of modeling the combustion of multicomponent hydrogen-containing gas mixtures. Numerical results were validated against experimental data. A visual comparison of the flame contours obtained by burning syngas at Reynolds numbers of 600, 800, and 1000 was performed. In all cases there is obvious convergence of the results. Change in the temperature of the fuel–air mixture at the entrance to the combustion chamber was found to have no significant effect on the temperature of the combustion products. The obtained results are of practical importance for the design of burner units of high-temperature plants with thermochemical heat recuperation.     

麦渣与制浆废液共混制备成型颗粒燃料及其燃烧特性分析

为研究麦渣与制浆废液共混制备的成型颗粒燃料的燃烧特性, 通过热重分析法对其燃烧热力学及燃烧动力学进行了研究。结果表明: 制浆废液的添加使颗粒燃料出现固定碳的二次燃烧阶段, 有利于降低成型颗粒燃料的挥发分、固定碳燃烧阶段的点火温度及最大燃烧速率温度, 对颗粒燃料的燃烧有正向协同作用; 制备的颗粒燃料的一阶动力学模型拟合曲线的相关系数在0.95以上, 颗粒燃料在挥发分燃烧和固定碳燃烧阶段的活化能和指前因子均随制浆废液的添加而降低。当废液固形物质量分数为53%时制备的成型颗粒燃料, 其挥发分燃烧阶段和固定碳燃烧阶段的活化能为72.85和83.52kJ/mol, 指前因子为2.82×10⁶和3.73×10⁵min^-1。制浆废液的添加使颗粒燃料更易燃烧, 且燃烧过程稳定不易爆燃。     

O2/H2O气氛下CH4燃烧特性与置换天然气水合物联产方案

对O2/N2, O2/CO2和O2/H2O三种气氛下CH4燃烧特性及主要污染物生成进行了数值模拟,将出口O2浓度作为污染物排放的协同考虑因素,提出了基于O2/H2O气氛燃烧置换天然气水合物的新技术方案,比较了3种燃烧气氛对甲烷燃烧温度、燃烧速率、污染物(NOx和碳黑)生成量及燃烧效率等的影响. 结果表明,相较于O2/N2和O2/CO2气氛,O2/H2O气氛下燃烧温度最低、燃烧速率最高、污染物生成量最少、燃烧效率最高、出口O2浓度最低. 确定了与传统燃烧温度分布特征曲线相匹配的浓度配比为32vol% O2/68vol% H2O. 基于模拟研究结果,提出了一套O2/H2O燃烧技术与开发天然气水合物联产的技术新思路.     

Reaction rates for the oxidation of highly sulphurised petroleum cokes: the influence of thermogravimetric conditions and some coke properties

The reaction with air of a large number (22) of high-sulphur petroleum cokes was studied by temperature-ramped thermogravimetric analysis. The kinetic parameters for each coke were established, based on BET surface areas. The oxidation rates (kg_C m⁻² s⁻¹ atm⁻¹) were found to vary with sample mass. This was a result of limitations on oxygen transfer, despite the small masses and low heating rates used. Limitations were present both externally (from the crucible mouth to the bed surface) and internally (from the sample surface to the bed interior). A method to take these effects into account was adopted, based on an analysis of the relevant diffusion rates. Application of this method reconciled the rate data for four different sample masses, except at high temperatures. The formation of a partially fused ash crust is believed to be the reason for this latter effect.The activation energies of the cokes varied between 195 and 280 kJ mol⁻¹, and the absolute rates varied by a factor of 10. They were between 1000 and 10,000 times higher than the average reactivity of carbon as reported in the literature. The elevated apparent rates are believed to have two causes, one in the combustion process and the other in the interpretation of the results. The first cause is the strong catalytic effect of the inorganic components, although the ash contents ranged only from 0.3 to 1.5%. The most active metal is vanadium, which is present in significant concentrations. The effectiveness of V₂O₅ as a gasifying catalyst is believed to be due to its low melting point. Increasing sulphur content in the cokes produces no perceptible change in the combustion rates. The second cause for poor combustion correlation is the inadequacy of BET surface area for expressing combustion rates.     

A zinc nanoparticles-dispersed multi-scale web of carbon micro-nanofibers for hydrogen production step of ZnO/Zn water splitting thermochemical cycle

Water splitting via the two-step ZnO/Zn thermochemical cycle is a promising and environmentally benign method for producing hydrogen from steam. In this study, we focus on the second step of the cycle, which is the exothermic hydrolysis reaction of Zn nanoparticles with steam. The unique Zn nanoparticle-dispersed carbon micro-nanofibers (Zn-CNFs) were prepared by impregnating carbon microfibers (ACFs) with a sodium dodecyl sulfate (SDS)-mediated mono-dispersed aqueous solution of Zn(II), followed by calcinations and reduction. The surfactant increased the metal (average crystal size ∼ 25 nm) loading by approximately two-fold on the ACFs. The CNFs were grown on Zn-ACF at 700 °C by catalytic chemical vapor deposition (CCVD) using acetylene as the carbon source. Zn has dual roles in this system, one as a catalyst for CNF growth and the other as a reactant in the hydrolysis reaction. The water-splitting reaction was performed at different steam and N₂ flow rates and reaction temperatures. The production rate and yield of H₂ at a reaction temperature of 600 °C were calculated as 1.66 × 10⁻⁶ mol/g s and 80%, respectively, which are comparable to or higher than results reported in the literature. The Zn-CNFs prepared in this study are a potential candidate for the H₂ production step of the ZnO/Zn thermochemical cycle.     

A correlation for calculating HHV from proximate analysis of solid fuels

Higher heating value (HHV) and composition of biomass, coal and other solid fuels, are important properties which define the energy content and determine the clean and efficient use of these fuels. There exists a variety of correlations for predicting HHV from ultimate analysis of fuels. However, the ultimate analysis requires very expensive equipments and highly trained analysts. The proximate analysis on the other hand only requires standard laboratory equipments and can be run by any competent scientist or engineer. A few number of correlations of HHV with proximate analysis have appeared in the solid fuel literature in the past but were focused on one fuel or dependent on the country of origin. This work introduces a general correlation, based on proximate analysis of solid fuels, to calculate HHV, using 450 data points and validated further for additional 100 data points. The entire spectrum of solid carbonaceous materials like coals, lignite, all types of biomass material, and char to residue-derived fuels have been considered in derivation of present correlation which is given as below: HHV=0.3536FC+0.1559VM−0.0078ASH (MJ/kg) (where FC 1.0-91.5% fixed carbon, VM 0.92-90.6% volatile matter and Ash 0.12-77.7% ash content in wt% on a dry basis). The average absolute error of this correlation is 3.74% and bias error is 0.12% with respect to the measured value of HHV, which is much less than that of previous correlations of the similar kind. The major advantage of this correlation is its capability to compute HHV of any fuel simply from its proximate analysis and thereby provides a useful tool for modeling of combustion, gasification and pyrolysis processes. It can also be used in examining old/new data for probable errors when results lie much outside the predicted results.     

Performance and combustion characteristics of a DI diesel engine fueled with waste palm oil and canola oil methyl esters

This study discusses the performance and combustion characteristics of a direct injection (DI) diesel engine fueled with biodiesels such as waste (frying) palm oil methyl ester (WPOME) and canola oil methyl ester (COME). In order to determine the performance and combustion characteristics, the experiments were conducted at the constant engine speed mode (1500 rpm) under the full load condition of the engine. The results indicated that when the test engine was fueled with WPOME or COME, the engine performance slightly weakened; the combustion characteristics slightly changed when compared to petroleum based diesel fuel (PBDF). The biodiesels caused reductions in carbon monoxide (CO), unburned hydrocarbon (HC) emissions and smoke opacity, but they caused to increases in nitrogen oxides (NO_x) emissions.     

Characterization of Chinese, American and Estonian oil shale semicokes and their sorptive potential

The primary byproduct of current oil shale oil extraction processes is semicoke. Its landfill deposition presents a potential threat to the environment and represents a waste of a potentially useable byproduct. Here we examine the sorptive characteristics of oil shale semicoke. Oil shale samples from Estonia, China and the United States were pyrolyzed at 500 and 1000 °C and their products analyzed for organic char content, surface area and porosity. Pyrolysis of the oil shales at temperatures of 500-1000 °C yields semicokes with organic char contents from 1.7% to 17.5% and BET surface areas of 4.4-57 m² g⁻¹, corresponding to 100-550 m² g⁻¹ of organic char. For comparison, the BET surface areas of class F coal fly ashes (combustion byproducts of bituminous coals) typically range from 2 to 5 m² g⁻¹, corresponding to 30-60 m² g⁻¹ of carbon while class C fly ash (from low rank coals) have carbon BET surface areas comparable to oil shale semicoke organic char surface areas.     

Carbon particle type characterization of the carbon behaviour impacting on a commercial-scale Sasol-Lurgi FBDB gasifier

Char-form analysis, whilst not yet an ISO standard, is a relatively common characterization method applied to pulverized coal samples used by power utilities globally. Fixed-bed gasification coal feeds differ from pulverized fuel combustion feeds by nature of the initial particle size (+6 mm, −75 mm). Hence it is unlikely that combustion char morphological characterization schemes can be directly applied to fixed-bed gasifier chars. In this study, a unique carbon particle type analysis was developed to characterize the physical (and inferred chemical) changes occurring in the particles during gasification based on coal petrography and combustion char morphology. A range of samples sequentially sampled from a quenched commercial-scale Sasol-Lurgi fixed-bed dry-bottom (FBDB) Gasifier were thus analysed.It was determined that maceral type (specifically vitrinite and inertinite) plays a pivotal role in the changes experienced by carbon particles when exposed to increasing temperature within the gasifier. Whole vitrinite particles and vitrinite bands within particles devolatilized first, followed at higher temperatures by reactive inertinite types. By the end of the pyrolysis zone, all the coal particles were converted to char, becoming consumed in the oxidation/combustion zone as the charge further descended within the gasifier.The carbon particle type results showed that both the porous and carbominerite char types follow similar burn-out profiles. These char types formed in the slower pyrolysis region within the pyrolysis zone, increasing to around 10% by volume within the reduction zone, where 53% carbon conversion occurred. Both of these char forms were consumed by the time the charge reached the ash-grate at the base of the reactor, and therefore did not contribute to the carbon loss in the ash discharge. It would appear as if the dense char and intermediate char types are responsible for the few percent carbon loss that is consistently obtained at the gasification operations.The carbon particle type analysis developed for coarse coal to the gasification process was shown to provide a significant insight into the behaviour of the carbon particles during gasification, both as a stand alone analysis and in conjunction with the other chemical and physical analyses performed on the fixed-bed gasifier samples.     

The modeling of the combustion of high-ash coal-char particles suitable for pressurised fluidized bed combustion: shrinking reacted core model

An investigation was undertaken involving the combustion of high-ash coal/char particles under conditions suitable for pressurised fluidised bed combustion, in order to evaluate an overall combustion model. The use of very poor quality feedstocks (greater than 40% ash, low calorific value and high sulphur content) in conventional pulverised fuel combustors (PFC) could be technically difficult and un-economical, and has the associated disadvantage of generating gaseous pollutants. Pressurised fluidised bed combustion (PFBC) which is an attractive alternative process and which uses millimetre-sized coal particles is increasing in use on a commercial scale and is the basis for several clean coal technology processes. A Thermogravimetic Analyser (TGA) was used for the experimentation, which was capable of handling relatively large coal/char particles at high pressures and temperatures. Experimentation with prepared coal/chars particles with a diameter of 3 mm at a pressure of 487 kPa and temperatures between 750 and 950 °C was carried out. For the determination of the overall kinetics of combustion it was found necessary to deviate from the established methods (surface-based reaction) and that it was essential to incorporate diffusion in the overall reaction model. Also, the concept of carbon concentration variation in the particle is introduced to account for the effect of high ash content (a mixture of carbon and minerals), instead of assuming pure carbon. This model, which consists essentially of a shrinking reactive core, was found to agree very well with experimental results and all relevant parameters required for an overall rate equation were evaluated. It is also shown that at high temperatures the shrinking reacted core model results approached the results obtained from the conventional shrinking unreacted core model.     

Thermal ignition and self-heating of carbon nanotubes: From thermokinetic study to process safety

A comprehensive investigation on the kinetics of combustion of multiwall carbon nanotubes (MWCNTs) produced by vapour chemical deposition has been undertaken. The kinetics parameters were determined from isothermal and non-isothermal combustion tests i.e. by both thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The activation energy of CNT combustion was found to be about 150 kJ mol⁻¹. The oxidation of carbon nanotubes (CNTs) appears to be a single step reaction well represented by a cylindrical shrinking core model. The consistency of this model was assessed both by comparing the activation energy extracted from TGA and DSC, and by theoretical considerations on the geometrical development of CNT oxidation. The influence of oxygen concentration on CNT combustion was also studied. Finally, these results combined with those obtained by self-ignition tests in baskets lead to recommendations for a safe handling and storage of CNTs.     

Prediction of higher heating values of biomass from proximate and ultimate analyses

Two new empirical correlations based on proximate and ultimate analyses of biomass used for prediction of higher heating value (HHV) are presented in this paper. The correlations have been developed via stepwise linear regression method by using data of biomass samples (from the open literature) of varied origin and obtained from different geographical locations. The correlations have been validated via incorporation of additional biomass data. The correlation based on ultimate analysis (HHV = 0.2949C + 0.8250H) has a mean absolute error (MAE) lower than 5% and marginal mean bias error (MBE) at just 0.57% which indicate that it has good HHV predictive capability. The other correlation which is based on proximate analysis (HHV = 0.1905VM + 0.2521FC) is a useful companion correlation with low absolute MBE (0.67%). The HHV prediction accuracies of 12 other correlations introduced by other researchers are also compared in this study.     

A correlation between stoichiometrical ratio of fuel and its higher heating value

The Stoechiometric Ratio (SR) is a key parameter to determine the equivalence ratio (ER) for combustion of materials, and which will play an important effect in energy conversion processes such as combustion, gasification, pyrolysis and reforming of fossil and renewable fuels. In this paper, an equation is presented that correlates the equivalence ratio (ER) with the higher heating value (HHV). From this, the SR can be calculated. The error in the analysis is calculated for 28 fuels, showing remarkable accuracy of the new.     

Heavy fuel oil combustion in a cylindrical laboratory furnace: measurements and modeling

The finite-volume based commercial CFD-code Fluent was used to simulate the reacting flow in a heavy fuel oil fired laboratory furnace. Both the standard k−ε turbulence model and the Reynolds stress model (RSM) were tested. The combustion model was based on the conserved scalar (mixture fraction) and prescribed probability density function approach. The heavy fuel oil droplet trajectories were predicted by solving the momentum equations for the droplets using the Lagrangian treatment. The soot distribution in the furnace was calculated by solving a transport equation for the soot mass fraction. Simple expressions for the soot formation and oxidation rates were employed. The radiation heat transfer equation was solved using the finite volume method. The formation of thermal NO from molecular nitrogen was modeled according to the extended Zeldovich mechanism. Fuel-based NO was modeled assuming that all the nitrogen in the fuel is released as hydrogen cyanide (HCN), which then further reacts forming nitric oxide NO or molecular nitrogen N₂, depending on the local combustion conditions. The formation of prompt NO was also included in the calculations. The CFD-code was validated against experimental data for a combustor fired by an industry-type swirl burner for which the initial conditions of the spray have been characterized. It was found that the standard k−ε model does not satisfactorily predict the highly swirling flow field in the furnace. The RSM was able to improve the prediction of the flow field. The predicted gas species concentrations were found to be in a reasonable agreement with the measurements, except near the burner and in the vicinity of the furnace axis where discrepancies were found.