Chemical fractionation of inorganic constituents in entrained flow gasification of slurry from straw pyrolysis

Pressurized entrained-flow gasification (PEFG) of straw biomass is currently being studied as a potentially sustainable and economically viable process to produce fuels and other vital chemicals. In the process chain the gasification is integrated and straw is converted via pyrolysis into a bioslurry consisting of a liquid, tar-rich phase and char. Afterwards, the slurry is gasified into a tar-free, low-methane syngas which is a basic reactant for the synthesis of biofuels. At the high temperatures over 1200 ◦C the ash constituents of the char in the bioslurry melt and flow down the inner wall as slag. The slag viscosity has to be in a certain range to form a protective layer at the reactor wall and to guarantee a continuous removing. For this reason, the composition of the molten ash at the reactor wall has to be well known. Due to several fractionation processes in the gasifier the composition of the slag at the reactor wall does not correspond directly with the slurry ash. Therefore, experiments were conducted to identify depletion and enrichment processes in the gasifier. Finally, the composition of the slag at the reactor wall is obtained and can be used for the adjustment of the viscosity

CO2 gasification reactivity of char from high-ash biomass

Biomass char produced from pyrolysis processes is of great interest to be utilized as renewable solid fuels or materials. Forest byproducts and agricultural wastes are low-cost and sustainable biomass feedstocks. These biomasses generally contain high amounts of ash-forming elements, generally leading to high char reactivity. This study elaborates in detail how chemical and physical properties affect CO2 gasification rates of high-ash biomass char, and it also targets the interactions between these properties. Char produced from pine bark, forest residue, and corncobs (particle size 4–30 mm) were included, and all contained different relative compositions of ash-forming elements. Acid leaching was applied to further investigate the influence of inorganic elements in these biomasses. The char properties relevant to the gasification rate were analyzed, that is, elemental composition, specific surface area, and carbon structure. Gasification rates were measured at an isothermal condition of 800 °C with 20% (vol.) of CO2 in N2. The results showed that the inorganic content, particularly K, had a stronger effect on gasification reactivity than specific surface area and aromatic cluster size of the char. At the gasification condition utilized in this study, K could volatilize and mobilize through the char surface, resulting in high gasification reactivity. Meanwhile, the mobilization of Ca did not occur at the low temperature applied, thus resulting in its low catalytic effect. This implies that the dispersion of these inorganic elements through char particles is an important reason behind their catalytic activity. Upon leaching by diluted acetic acid, the K content of these biomasses substantially decreased, while most of the Ca remained in the biomasses. With a low K content in leached biomass char, char reactivity was determined by the active carbon surface area.publishedVersio

Inherent Metal Elements in Biomass Pyrolysis: A Review

One of the main drawbacks of using biomass as pyrolysis feedstock consists of the huge variability of the different biomass resources which undermines the viability of downstream processes. Inherent inorganic elements greatly contribute to enhance the compositional variability issues due to their catalytic effect (especially alkali and alkaline earth metals (AAEMs)) and the technical problems arising due to their presence. Due to the different pretreatments adopted in the experimental investigations as well as the different reactor configurations and experimental conditions, some mechanisms involving interactions between these elements and the biomass organic fraction during pyrolysis are still debated. This is the reason why predicting the results of these interactions by adapting the existing kinetic models of pyrolysis is still challenging. In this work, the most prominent experimental works of the last 10 years dealing with the catalytic effects of biomass inherent metals on the pyrolysis process are reviewed. Reaction pathways, products distributions and characteristics, and impacts on the products utilization are discussed with a focus on AAEMs and on potential toxic metallic elements in hyperaccumulator plants. The literature findings are discussed in relation to the applied laboratory procedures controlling the concentration of inherent inorganic elements, their capability of preserving the chemical integrity of the main organic components, and the ability of resembling the inherent inorganic elements in the raw biomass. The goal is to reveal possible experimental inconsistencies and to provide a clear scheme of the reaction pathways altered by the presence of inherent inorganics. This analysis paves the way for the examination of the proposed modifications of the existing models aiming at capturing the effect of inorganics on pyrolysis kinetics. Finally, the most relevant shortcomings and bottlenecks in existing experimental and modeling approaches are analyzed and directions for further studies are suggested

Assessment of Fischer−Tropsch liquid fuels production via solar hybridized dual fluidized bed gasification of solid fuels

To mitigate the emissions from the widely studied and even applied coal to FT liquid (FTL) fuels systems, two kinds of promising renewable energy, biomass and solar energy, have been proposed and assessed as a partial or total substitute for coal feed. The concept of a solar hybridized FTL fuels production system has the potential to obtain higher productivity with lower greenhouse gas emissions, when compared with a conventional system. However, less attention has been paid to the comprehensive system analysis of this topic. Hence, the aim of the present thesis is to achieve the annual performance of the solar hybridized solid fuels to FTL fuels processes with novel configurations. A novel solar hybridized dual fluidized bed (SDFB) gasification process for FTL fuels production is proposed and investigated in the present thesis for cases with high reactivity solid fuels as the feedstock. The concept offers sensible thermal storage of the bed material and a process that delivers a constant production rate and quality of syngas despite solar variability. As a reference scenario for this concept, the proposed solar hybridized coal-to-liquids (SCTL) process is simulated for the case with lignite as the feedstock using a pseudo-dynamic model that assumes steady state operation at each time step for a one-year, hourly integrated solar insolation time series. For a solar multiple of 3 and bed material storage capacity of 16 h, the calculated annual solar share is 21.8%, assuming that the char conversion in the steam gasification process is 100%. However, the solar share is also found to be strongly dependent on the char conversion in the steam gasification process, so that the solar share is calculated to decrease to zero as the conversion is decreased to 57%. New configurations of the solar hybridized solid fuels (biomass and/or coal) to FTL fuels process are proposed and assessed, which are characterized with a novel SDFB gasifier with char separation, the incorporation of carbon capture and sequestration (CCS) and/or the use of FT reactor tail-gas recycle. Montana lignite and spruce wood have been chosen as the studied coal and biomass, respectively. Assessed using the pseudo-dynamic model, the annual solar share of the SCTL system can be increased from 12.2% to 20.3% by the addition of the char separation, for a char gasification conversion of 80%. To achieve well-to-wheel greenhouse gas emissions for FT liquid fuels parity with diesel derived from mineral crude oil, a biomass fraction of 58% is required for the studied non-solar coal and biomass-to-liquids system with a dual fluidized bed (DFB) gasifier. This biomass fraction can be reduced to 30% by the addition of carbon capture and sequestration and further reduced to 17% by the integration of solar energy with a solar multiple of 2.64 and a bed material storage capacity of 16 h. This reduction of the biomass fraction is very important given that biomass is typically more expensive than coal. As the biomass fraction is increased from 0% to 100%, the specific FT liquids output is decreased from 59.6% to 48.3% due to the increasing light hydrocarbons content. These two outputs (for biomass fractions of 0% and 100%, respectively) can both be increased to 71.5% and 70.9%, respectively, by integrating a tail-gas recycling configuration. Co-gasification of biomass with coal has the potential to further reduce the GHG emission from the SCTL systems, as discussed above. The application of biomass is usually limited by some properties (e.g., high moisture, low heating value and so on), which can be improved by torrefaction, as proved by previous work. Previous work also found that torrefaction can impact the bio-char gasification reactivity. In the present thesis, to better understand the influence of torrefaction on the bio-char gasification reactivity, further investigations were carried out on the char physicochemical characteristics that can influence the gasification reactivity, i.e., the char specific surface area, the char carbonaceous structure and the catalytic effect of inorganic matter in the char. The present experimental investigation showed that the influence of the torrefaction on the char gasification reactivity depended strongly on the biomass species and char preparation conditions. For a pyrolysis temperature of 800 ºC, the gasification reactivity of the chars from both the torrefied grape marc and the torrefied macroalgae were found to be lower than that of the chars from their corresponding raw fuels. This is mainly due to a lower specific surface area and a lower content of alkali metals (sodium and/or potassium) in the chars produced from both the torrefied grape marc and the torrefied macroalgae than for those chars produced from their corresponding raw fuels. However, the opposite influence of torrefaction was found for the macroalgae char when the pyrolysis temperature was increased to 1000 ºC. This is mainly due to a higher sodium concentration and a more amorphous carbonaceous structure for the torrefied macroalgae char than for the raw macroalgae char. In the present thesis, the process modelling results can be used for further economic analysis of the proposed novel configurations of solar hybridized coal and/or biomass to FTL fuels system via an SDFB gasifier. In addition, according to the experimental results of this study, the investigation of the influence of torrefaction on the bio-char characteristics can help to better understand the influence of torrefaction on the bio-char gasification reactivity.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 201

Technologies for Coal based Hydrogen and Electricity Co-production Power Plants with CO2 Capture

Integrated Gasification Combined Cycle (IGCC) plants allow the combination of the production of hydrogen and electricity because coal gasification process produces a syngas that can be used for the production of both commodities. A hydrogen and electricity power plant has been denominated as HYPOGEN. This report starts by reviewing the basics of the coal gasification process and continues by trying to map all the technological options currently available in the market as well as possible future trends that can be included in a HYPOGEN system . Besides, it offers an overview of the operating conditions and outputs of each process in order to provide the modeller with a useful information tool enabling an easier analysis of compatibilities and implementation of the model.JRC.F.7-Energy systems evaluatio

Pyrolysis and gasification of lignin and effect of alkali addition

Lignin, a byproduct of the chemical pulping can be gasified to produce fuel gas and value-added products. Two lignins, MeadWestvaco (MWV) lignin and Sigma Aldrich (SA) lignin, were studied using two different reactors. A laminar entrained flow reactor (LEFR) was used initially to determine the effect of lignin type, temperature and residence time on char yield and fixed carbon conversion during pyrolysis and gasification. During both pyrolysis and gasification, the maximum decrease in char yield took place in the initial stage of the reaction and there was little change at longer residence times. There was not much difference between pyrolysis and gasification in the residence times obtained in the LEFR. Furthermore, a thermogravimetric analyzer (TGA) was used to study the effect of lignin type on pyrolysis and gasification. The reaction rates and char yields were affected by the lignin composition. Lignin pyrolysis showed similar behavior until 600°C but only the high-ash SA lignin showed secondary pyrolysis reactions above 600°C. Carbon gasification reactions were delayed in SA lignin. Na2CO3 addition made the primary pyrolysis reaction occur at a lower rate and enhanced the rate for secondary pyrolysis reactions. Fourier Transform Infrared (FTIR) Spectroscopy results showed that the significant loss of spectral detail started at different temperatures for MWV lignin and SA lignin. Kinetic parameters obtained using differential and Coats - Redfern integral method were comparable at lower temperatures but varied at high temperatures. Na2CO3 addition decreased the activation energy of primary pyrolysis.Ph.D.Committee Chair: Sujit Banerjee; Committee Co-Chair: Wm. James Frederick, Jr.; Committee Member: John D. Muzzy; Committee Member: Kristiina Iisa; Committee Member: Preet Sing

Developing biomass-derived carbons for catalytic syngas and methane production from renewable sources

Como resultado de la explotación indiscriminada de los recursos fósiles, el nivel de gases antropogénicos – en particular, el CO2 – ha aumentado drásticamente en los últimos años. Este incremento causaría problemas ambientales como el efecto invernadero y la acidificación de los océanos. En este contexto, diversos esfuerzos se están llevando a cabo para reducir estas emisiones. Por ejemplo, la Unión Europea, a través del Pacto Verde Europeo firmado en 2019, fijó el objetivo de alcanzar la descarbonización completa mediante la promoción y difusión de tecnologías de emisión negativa (NETs). Entre todas las alternativas NETs, la producción de biochar representa una de las estrategias más prometedoras gracias a, entre otros, las características versátiles del material y su relativo bajo coste de producción. Por ello, el interés de la comunidad científica hacia el biochar ha aumentado exponencialmente en los últimos años y, en este sentido, se ha prestado un particular interés a la producción de biochares activados y el uso de materiales derivados de biochar en aplicaciones catalíticas. Esta tesis doctoral se enmarca dentro del European Training Network: The GreenCarbon project (Marie Skłodowska-Curie grant agreement No 721991), cuyo propósito principal fue desarrollar carbonos procedentes de biomasa avanzados para nuevas tecnologías de reciclaje de biomasa/desechos. En este contexto, el objetivo principal de esta tesis doctoral fue estudiar la activación y funcionalización de carbonos producidos por pirolisis de biomasa para producir catalizadores novedosos soportados en biochar como alternativa sostenible a otros más comunes. La primera parte de la investigación se enfocó en la evaluación de la idoneidad del uso de biochars como catalizadores renovables y de bajo coste para la mejora de vapores de pirólisis. A continuación, el trabajo se centró en la identificación de las condiciones más apropiadas de activación del biochar. La última parte de la investigación se dedicó a testar el uso del biochar activado derivado como soporte para la producción de varios catalizadores. Estos catalizadores fueron testados en dos procesos diferentes: el reformado húmedo de los aceites de pirólisis y la metanación del CO2. Los logros más notables obtenidos en esta tesis doctoral son: (i) la determinación del rol que tiene la presión de activación sobre las propiedades del biochar activado resultante y (ii) la producción de un catalizador basado en biochar activado relativamente estable para la mejora de los vapores de pirólisis. El presente documento se divide conceptualmente en cinco bloques principales: I. El primer bloque presenta la introducción y un capítulo relativo al estado del arte sobre los procesos estudiados. II. El segundo bloque presenta una breve descripción del proyecto GreenCarbon y los principales objetivos del proyecto de tesis doctoral. III. El tercer bloque detalla los materiales y métodos empleados en los experimentos realizados. IV. El cuarto bloque presenta los resultados obtenidos. V. El quinto bloque presenta las conclusiones de esta tesis doctoral y los pasos a seguir en el futuro. As result of the indiscriminate exploitation of fossil fuels, the level of anthropogenic gases, in particular CO2, has drastically increased causing several environmental issues such as the greenhouse effect and the oceans acidification. In this context, several efforts are being made to reduce these emissions. The European Union, for example, through the European Green Deal (2019), set the objective to reach complete decarbonization through the promotion and diffusion of negative emission technologies (NETs). Among all the NETs alternatives, biochar production represents one of the most promising strategies due to the versatile features of the material, and its relatively low production cost. Because of this, the interest of the scientific community for biochar has grown exponentially in the last years, and, in this sense, a particular interest has been paid to the production of activated biochars and to the employment of biochar-derived materials in catalytic applications. The present work was conducted within the framework of a European Training Network: The GreenCarbon project (Marie Skłodowska-Curie grant agreement No 721991), which main purpose was to develop advanced biomass-derived carbons to drive new technologies for biomass/biowaste upcycling. In this context, the main objective of this PhD Thesis was to study the activation and functionalization of pyrolysis chars to produce innovative biochar-supported catalysts to be employed as a more sustainable alternative to the commonly used ones. The first part of the research dealt with the assessment of the suitability of biochars to be used as renewable and low-cost catalyst/support for pyrolysis vapors upgrading. After that the research was shifted to the identification of the most appropriate biochar activating conditions. Finally, the resulting activated biochar, produced through an optimized activating procedure, was used as support for the production of several catalysts which were then tested for two different processes: the pyrolysis oil steam reforming and the CO2 methanation. The most remarkable achievements obtained in this PhD project are: (i) the determination of the role that the activating pressure has on the textural properties of the resulting activated biochar and (ii) the production of a relatively stable activated biochar-based catalyst for the upgrading of pyrolysis vapors. This document is conceptually divided in five main blocks: I. The first block is composed of an introductory section and a chapter concerning the state of the art of the studied processes. II. In the second block, a brief overview of the GreenCarbon project and the main objective of the PhD Thesis are reported. III. The third block details the materials and methods employed in this work. IV. The results of this work are resumed in the fourth block. V. Finally, in the last section are drawn the overall conclusions reached in this work accompanied by the indications about the work which needs to be done in the future.<br /

CO2 capture through sorption onto activated carbons derived from biomass

In this study, activated carbons (ACs) were synthesized and tested as CO2 sorbents. In-house ACs were prepared starting both from a traditional biomass (i.e. oak wood) and from an unconventional macroalgal seaweed (i.e. Laminaria hyperborea). In addition to this, a biomass-derived commercial AC was studied as a sorbent on which polyethylenimine (PEI) was impregnated. Biochars were produced both by pyrolysis at 800 °C and by hydrothermal carbonization (HTC) at 250 °C. Pyrolysis chars generally had higher fixed carbon and lower volatile content compared to hydrochars. Moreover, seaweed-derived chars exhibited significantly larger ash content than that measured for oak wood-based chars. Pyrolyzed and HTC-treated biomass were then activated either by physical (CO2) or chemical (KOH) treatment. Limited texture development of the biochars was observed after CO2 activation, yet this treatment proved to be more suitable for the creation of narrower micropores. By contrast, KOH activation, followed by HCl washing, led to a more dramatic texture enhancement (but to lower narrow micropore volumes) and higher purity of the ACs due to a significant demineralization of the chars. The morphology of all materials was examined by Scanning Electron Microscopy (SEM) which revealed the creation of larger pores after KOH activation, whereas chars and CO2-ACs generally showed an undeveloped porous matrix along with particles anchored onto the carbon structure. Furthermore, Energy-Dispersive X-ray spectroscopy (EDX) analyses corresponding to the SEM micrographs proved that these particles were inorganic. In particular, Ca compounds predominated in oak wood-based samples. For macroalgae-derived materials, a significant proportion of alkali (i.e. Na, K), alkaline-earth (i.e. Ca, Mg) metal ions and Cl was detected, along with high levels of Cl. Conversely, reduced or negligible levels of inorganic fractions were detected for all KOH-ACs, which confirmed that demineralization occurred upon HCl washing. The identity of inorganic species was revealed by X-Ray Diffraction (XRD) patterns. In particular, calcium oxalate and Ca(OH)2 were identified in oak wood chars, whereas CO2-activated derivatives had CaCO3 as their main crystalline phase. For macroalgae-based materials, KCl and NaCl were found to be the dominant crystalline phases. In addition, MgO was also identified in pyrolyzed seaweed and in its CO2-activated counterpart. By contrast, a partial or total lack of crystalline phases was found for all KOH-ACs, thus offering further evidence of the loss of inorganic species after HCl rinsing. The intrinsic alkalinity of biomass-derived chars and CO2-ACs was corroborated by the great amount of basic surface groups, whose number was lower for KOH-ACs. CO2 sorptions by chars and ACs were initially measured at T=35 °C, PCO2=1 bar, and Ptot=1 bar by using Thermogravimetric Analysis (TGA). Sorbents showing promising behaviour were then tested for capture of CO2 under simulated post-combustion conditions (T=53 °C, PCO2=0.15 bar, and Ptot=1 bar). Unmodified ACs showed relatively high sorption capacity (up to 70mg CO2∙g-1) at higher partial pressure and lower temperature. Nonetheless, the ACs’ sorption capability dramatically decreased at lower partial pressure and higher temperature. However, the biomass feedstocks included in this work proved to be advantageous precursors for sustainable synthesis of CO2-selective sorbents under post-combustion conditions. In particular, Ca(OH)2 and MgO intrinsically incorporated within the raw materials enabled production of highly basic “CO2-philic” sorbents without applying any chemical modifications. The best virgin ACs also exhibited fast adsorption kinetics, excellent regeneration capacity and good durability over ten Rapid Temperature Swing Adsorption (RTSA) cycles. On the other hand, the CO2 uptake of optimally-PEI modified commercial AC was up to 4 times higher than that achieved by the best performing unmodified AC. PEI impregnation was optimized to maximize post-combustion uptakes. In particular, the influence of various parameters (i.e. PEI loading, stirring time of the PEI/solvent/AC mixture, solvent type and sorption temperature) on the post-combustion capture capacity of the PEI-modified ACs was assessed. Interestingly, longer agitation engendered efficient dispersion of the polymer through the porous network. Additionally, a more environmentally friendly (i.e. aqueous) impregnation enabled uptakes nearly as large as those attained when the impregnation solvent was methanol, despite using lower amounts of polymer and shorter impregnation runs. In addition, when measuring uptakes under simulated post-combustion conditions but at 77 °C, optimization of aqueous PEI impregnation led to a sorption capacity larger than those achieved by the best performing PEI-loaded ACs impregnated using methanol as solvent. The use of an oak wood-derived carbon support or monoethanoloamine (MEA) as impregnating agent did not lead to any significant improvement of the CO2 sorption capacity. On the other hand, tetraethylenepentamine (TEPA)-impregnated AC slightly outperformed the optimally-PEI loaded sorbent, but the use of PEI was preferred because of its thermal stability. The addition of glycerol to the PEI/solvent/AC blend resulted in lower CO2 uptakes but moderately faster adsorption/desorption kinetics along with comparable “amine efficiency”. In addition, PEI-loaded AC showed larger CO2 uptakes and faster kinetics than those attained, for comparison purposes, by Zeolite-13X (Z13X). Furthermore, amine-containing ACs were found to be durable and easy to regenerate by RTSA at 120 °C. This CO2 desorption required ca. one third of the energy needed to regenerate a 30% MEA solution (i.e. the state of the art capture technique), thus potentially implying a lower energy penalty for the PEI-based technology in post-combustion power plant. Overall, at higher partial pressure of carbon dioxide, textural properties were the dominant parameter governing CO2 capture, especially at lower temperatures. This CO2 physisorption appeared to be governed by a combination of narrow microporosity and surface area. In contrast, at increased temperature and lower partial pressure, basic (alkali metal or amine-containing) functionalities were the key factor for promoting selective chemisorption of CO2