Anton Friedl

Analysis of methane potentials of steam-exploded wheat straw and estimation of energy yields of combined ethanol and methane production

Agrarian biomass as a renewable energy source can contribute to a considerable CO(2) reduction. The overriding goal of the European Union is to cut energy consumption related greenhouse gas emission in the EU by 20% until the year 2020. This publication aims at optimising the methane production from steam-exploded wheat straw and presents a theoretical estimation of the ethanol and methane potential of straw. For this purpose, wheat straw was pretreated by steam explosion using different time/temperature combinations. Specific methane yields were analyzed according to VDI 4630. Pretreatment of wheat straw by steam explosion significantly increased the methane yield from anaerobic digestion by up to 20% or a maximum of 331 l(N)kg(-1) VS compared to untreated wheat straw. Furthermore, the residual anaerobic digestion potential of methane after ethanol fermentation was determined by enzymatic hydrolysis of pretreated wheat straw using cellulase. Based on the resulting glucose concentration the ethanol yield and the residual sugar available for methane production were calculated. The theoretical maximum ethanol yield of wheat straw was estimated to be 0.249 kg kg(-1) dry matter. The achievable maximum ethanol yield per kg wheat straw dry matter pretreated by steam explosion and enzymatic hydrolysis was estimated to be 0.200 kg under pretreatment conditions of 200 degrees C and 10 min corresponding to 80% of the theoretical maximum. The residual methane yield from straw stillage was estimated to be 183 l(N)kg(-1) wheat straw dry matter. Based on the presented experimental data, a concept is proposed that processes wheat straw for ethanol and methane production. The concept of an energy supply system that provides more than two forms of energy is met by (1) upgrading obtained ethanol to fuel-grade quality and providing methane to CHP plants for the production of (2) electric energy and (3) utility steam that in turn can be used to operate distillation columns in the ethanol production process.

Determination of glucose and ethanol in bioethanol production by near infrared spectroscopy and chemometrics.

The concentrations of glucose and ethanol in substrates from bioethanol processes have been modeled by near infrared (NIR) spectroscopy data. NIR spectra were acquired in the wavelength range of 1100-2300 nm by means of a transflectance probe for measurements in liquid samples. For building of regression models a genetic algorithm has been applied for variable selection, and partial least-squares (PLS) regression for creation of linear models. A realistic estimation of the prediction performance of the models was obtained by a repeated double cross-validation (rdCV). Reduced data sets with only 15 variables showed improved prediction qualities, in comparison with models containing 235 variables, particularly for the determination of the ethanol concentration in distillation residues (stillages). The squared correlation coefficient, R(2), between the concentrations obtained by HPLC analysis and the concentrations derived from NIR data (using 15 selected wavelengths, test set samples) was 0.999 for ethanol in stillage, and 0.977 for glucose in mash. The standard deviation of prediction errors, SEP, obtained from test set samples was 0.6 g L(-1) for ethanol (2% of the mean ethanol concentration), and 2.0 g L(-1) for glucose (9.6% of the mean glucose concentration).

Modelling selective H2S absorption and desorption in an aqueous MDEA-solution using a rate-based non-equilibrium approach

Abstract A rate-based algorithm was used to yield a predictive tool for MDEA gas scrubbing processes. The model adopts the two-film theory, assuming that thermodynamic equilibrium exists only at the gas–liquid interphase, but not in the boundary layers, where temperature and concentration gradients are present. Correspondingly chemical equilibrium among the reacting species in the liquid phase is assumed for the bulk phase, but not for the liquid boundary layer. Mass transfer is modelled using calculated mass transfer coefficients in combination with an enhancement model to account for the chemical reactions. Correlations for geometric data, like hold-up and interfacial area, and for reaction rates are provided to give reliable results. The latter correlations are also used to describe the desorption process, which is calculated with an equilibrium approach, considering the kinetics of CO 2 desorption. The so obtained tool is tested against measurements done recently by Lurgi GmbH at a commercially operated selective MDEA plant in Germany. A closed absorption and desorption loop was build up using Aspen RATEFRAC™, capable of modelling the whole process with all necessary equipment.

Modeling and simulation of high pressure water scrubbing technology applied for biogas upgrading

Depending on the end of use, the quality of biogas must be upgraded in order to utilize the maximum amount of energy necessary for proper applications. Upgrading biogas refers to the increase of methane concentration in product gas by removal of CO2, which increases its heating power. Several treatment technologies are available for biogas upgrading: high pressure water scrubbing (HPWS), pressure swing adsorption, membrane separation, chemical absorption, and gas permeation. Water absorption based on the physical effect of dissolving gases in liquids (HPWS) is a well-known technology and the most effective upgrading process, since provides a simultaneous removal of CO2 and H2S. This could ensure an increasing methane concentration and energy content per unit volume of biogas. In spite of this, few studies are published on biogas upgrading using pressurized water technology. In order to elucidate the performance of HPWS technology at industrial scale with the possibility of water regeneration and recirculation, effects of different operating parameters on the removal of undesired components from biogas were examined, based on modeling and simulation tools. For simulation, the commercial software tool Aspen Plus was applied. Equilibrium model was applied for simulating the absorption process. The simulation results were validated with experimental data from the literature. The results are summarized in terms of system efficiency, expressed as CH4 enrichment, methane loss, and CO2 removal. Finally, new data which can be further applied for scale-up calculations and techno-economic analysis of the HPWS process are provided.

Modeling a dry-scrubbing flue gas cleaning process

Abstract In the field of flue gas cleaning several proven techniques are well established. According to the forces of free enterprise economy and environmental requirements, the development of an economically reasonable procedure, based on well-known processes, which can also guarantee the fulfillment of legal emissions, was carried out. For the evaluation and scale-up criteria a pilot plant has been built, on which also the relations in the presented model have been verified. At the time, scrubbing of SO 2 , HCl and HF with Ca(OH) 2 below their emission limits according to legal limits for cleaned flue gas (Siebzehnte Verordnung zur Durchfuhrung des Bundes-Immissionsschutzgesetzes Verordnung uber Verbrennungsanlagen fur Abfalle und ahnliche brennbare Stoffe-17. BImSchV vom 23. November, 1990 (BGBl. I 2545, 2832), BRD) is realized. The process, and in consequence the model, which is basis of the discussion of this paper, is built in an open structure to permit rearrangements of and extensions to the process. This paper gives an introduction to the model, which is based on pilot plant data and theoretical reflections under consideration of scale-up criteria. This model has been developed to calculate demands of operating materials and basic dimensions of plants as well as to evaluate theoretical considerations on measurement data.

Lignin from Micro- to Nanosize: Production Methods

Lignin is the second most abundant biopolymer after cellulose. It has long been obtained as a by-product of cellulose production in pulp and paper production, but had rather low added-value applications. A changing paper market and the emergence of biorefinery projects should generate vast amounts of lignin with the potential of value addition. Nanomaterials offer unique properties and the preparation of lignin nanoparticles and other nanostructures has therefore gained interest as a promising technique to obtain value-added lignin products. Due to lignin’s high structural and chemical heterogeneity, methods must be adapted to these different types. This review focuses on the ability of different formation methods to cope with the huge variety of lignin types and points out which particle characteristics can be achieved by which method. The current research’s main focus is on pH and solvent-shifting methods where the latter can yield solid and hollow particles. Solvent shifting also showed the capability to cope with different lignin types and solvents and antisolvents, respectively. However, process conditions have to be adapted to every type of lignin and reduction of solvent demand or the integration in a biorefinery process chain must be focused.

Downstream process options for the ABE fermentation.

Butanol is a very interesting substance both for the chemical industry and as a biofuel. The classical distillation process for the removal of butanol is far too energy demanding, at a factor of 220% of the energy content of butanol. Alternative separation processes studied are hybrid processes of gas-stripping, liquid-liquid extraction and pervaporation with distillation and a novel adsorption/drying/desorption hybrid process. Compared with the energy content of butanol, the resulting energy demand for butanol separation and concentration of optimized hybrid processes is 11%-22% for pervaporation/distillation and 11%-17% for liquid-liquid extraction/distillation. For a novel adsorption/drying/desorption process, the energy demand is 9.4%. But all downstream process options need further proof of industrial applicability.

POMS Membrane for Selective Separation of Ethanol from Dilute Alcohol-Aqueous Solutions by Pervaporation

Lignocellulosic biomass has potential as an alternative to corn as starting material for the production of ethanol for the development of non-fossil fuel energy sources. In this case, low concentration bioethanol is gained by yeast fermentation and it has to be efficiently recovered and concentrated. For this purpose pervaporation separation of dilute alcohol-aqueous solutions was carried out using a poly(octhylmethyl siloxane) [POMS] membrane. The effect of different process parameters (feed composition, feed temperature, feed flow rate, permeate pressure) on pervaporation performance were investigated and discussed in terms of the separation factor and the total flux. The membrane studied was ethanol to water selective at ethanol feed concentrations lower than 2.5% w/w, while the highest permeability was achieved at feed temperature of 95°C.

CFD-simulation of mass transfer effects in gas and vapour permeation modules

Two main factors are important for the design of membrane modules used for gas and vapour permeation: concentration polarisation and flow distribution. The former causes a reduced driving force, significantly affecting membrane performance. A uniform flow distribution will ensure that the complete membrane area is utilised. In order to reduce the influence of concentration polarisation and to ensure an even flow distribution spacers located between two membrane surfaces or plates containing flow channels are employed. A comparison between these geometries using computational fluid dynamics (CFD) is presented. For CFD calculations, the commercial solver FLUENT™ has been used and the mass transfer through the membrane has been modelled by user defined functions.

Integrated Sono-Fenton ultrafiltration process for 4-chlorophenol removal from aqueous effluents: assessment of operational parameters (Part 1)

AbstractAdvanced oxidation processes (AOPs) and membrane separation processes are successfully used in the final stages of wastewater treatment for recycling and reuse purposes. This research proposes a new two stage process including in the first step a homogeneous Sono-Fenton process (as an AOP), coupled with ultrafiltration (UF), as a cleaner and safer alternative for advanced wastewater treatment, designed specially to enhance the removal of priority organic pollutants which are difficult to eliminate by means of conventional treatments. The aim of this study is to analyze experimentally the performances of an integrated ultrasonication-UF process for the removal of 4-chlorophenol (4CP) (as a model-pollutant for priority organic compounds from wastewaters), both from the removal efficiency (expressed as phenolic concentration and chemical oxygen demand reduction) and the energy consumption point of view. The most important factors with influence on both stages of the proposed process, such as acoustic amplitude, power density, and operating mode for the Sono-Fenton process and pressure, time, operating mode, and cleaning operations for the UF stage, were assessed in this paper (Part 1). The experimental results indicate that the process can be applied for such aqueous effluents, in laboratory scale equipments and represent the basis for modeling the process steps and scale-up of different process arrangements (Cailean et al. (2014): “Integrated Sono-Fenton UF Process for 4CP Removal from Aqueous Effluents: Process Modeling and Simulation (Part 2)”), with the purpose to analyze and control such a process, under various conditions and to understand better its advantages and disadvantages.