In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of... more In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert raw moist biomass into dry and pelletized hydrochar. By means of mass and thermal balances and based on common equations specific to the various equipment, thermal energy and power consumption were calculated at variable process conditions: HTC reactor temperature T: 180, 220, 250 • C; reaction time θ: 1, 3, 8 h. When operating the HTC plant with grape marc (65% moisture content) at optimized process conditions (T = 220 • C; θ = 1 h; dry biomass to water ratio = 0.19), thermal energy and power consumption were equal to 1170 kWh and 160 kWh per ton of hydrochar produced, respectively. Correspondingly, plant efficiency was 78%. In addition, the techno-economical aspects of the HTC process were analyzed in detail, considering both investment and production costs. The production cost of pelletized hydrochar and its break-even point were determined to be 157 €/ton and 200 €/ton, respectively. Such values make the use of hydrochar as a CO 2 neutral biofuel attractive.
Greenpeat is a new sustainable material that can be produced from wet biodegradable organic waste... more Greenpeat is a new sustainable material that can be produced from wet biodegradable organic waste, both solid and liquid, through a very efficient process, studied and developed by HBI Srl, an innovative startup founded by a researcher and an entrepreneur, who works in the field of the innovative green technologies. Greenpeat has been produced from agro-industrial organic by-products and optimized according to its potential different uses, namely for energy production or as a highly performing material for agronomic uses. At specific process conditions, it is possible to give to Greenpeat calorific values in the range of 22-28 MJ/kg, which represent interesting values for renewable and clean energy production applications. Furthermore, by using Greenpeat as a substitute of common solid fossil fuels, both the emissions related to fossil resources extraction and those produced during combustion are interestingly lowered. On the other hand, when ligno-cellulosic residues are treated in...
Hydrochar is produced by means of hydrothermal carbonization at relatively low temperatures (180-... more Hydrochar is produced by means of hydrothermal carbonization at relatively low temperatures (180-260°C) in sub-critical water. While, in many respects similar to biochar, its physical and chemical properties differ significantly (Basu, 2018). Of particular interest for this work are the higher energy density and lower ash content, that make hydrochar a possible feedstock for gasification plants with energy generation purposes. A gasification step is used instead of direct combustion to convert solid fuels in energy to achieve cleaner combustion and higher efficiency (Wang and Stiegel, 2016). In this work a 400 kg/h hydrochar gasification plant was modelled to identify optimal conditions and energetic yield of hydrochar obtained from municipal sewage. The fixed bed, updraft, gasification reactor was modeled in detail using a multi-scale, multiphase methodology already widely tested on biomass (Corbetta et al., 2015; Ranzi et al., 2014). The gas solid kinetic model was coupled with a detailed gas-phase kinetic scheme with over 200 species, including reaction intermediates, and 2000 reactions for reliable product yield prediction. Using Visual Basic Application as an interface, the predictions from the detailed simulation package were delivered to a commercial simulation package to model the energy generation section of the plant. Aspen HYSYS V10 was used for this purpose for the simplicity of integration and its widespread use in similar industrial plants. The gasification was carried out with air, air enriched in oxygen to 28%, air enriched in oxygen to 35% and pure oxygen with different amounts of steam to control the temperature in the chamber and at different values of equivalence ratio. The gasification performance was evaluated in terms of lower heating value of the generated fuel gas while the H2S formation was accounted for only in a superficial manner using rules of thumb derived from previous experimental experience.
Improving the agronomic use of recycled nutrients derived from organic waste is one of the priori... more Improving the agronomic use of recycled nutrients derived from organic waste is one of the priorities within the measures adopted by the European community to reduce environmental issues but remains an unexplored area of research. This study focused on investigating the possibility of using innovative fertilizer solutions in hydroponic systems for the growth of agricultural plants. To this purpose, a liquid fraction [aqueous hydrothermal carbonization (HTC) liquid (AHL)] derived from HTC of cow manure digestate was chemically characterized (pH, electrical conductivity, mineral elements, and organic compounds such as phytotoxins), diluted with distilled water (1:30, 1:60, and 1:90, v/v) to reduce its potential phytotoxicity, and used to grow hydroponic maize (Zea mays L.) plants instead of the classical full-strength nutrient solution. The results indicated that the dilution ratio 1:30 of the AHL solution maintained a high level of toxicity for the plants (phytotoxic substances, espe...
WOOD-UP è un progetto di ricerca applicata, che mira a produrre risultati concreti e spendibili c... more WOOD-UP è un progetto di ricerca applicata, che mira a produrre risultati concreti e spendibili con ricadute positive sui settori chiave (quali, agricoltura, energia ed ambiente) dell'economia dell'Alto Adige. I recenti risultati conseguiti nell'ambito del presente lavoro di ricerca hanno suggerito che il char, uno dei sottoprodotti del processo di gassificazione, ottenuto a partire dalla biomassa legnosa, potrebbe rappresentare una risorsa preziosa, qualora fosse utilizzato
La diffusione di impianti di gassificazione di piccola scala ha avuto un importante incremento in... more La diffusione di impianti di gassificazione di piccola scala ha avuto un importante incremento in Alto Adige nell'ultima decade, sia a causa dell'elevata quantità di biomassa legnosa disponibile in questa regione, sia per le condizioni economiche favorevoli generate dagli incentivi nazionali sulle energie rinnovabili. Attualmente gli impianti di gassificazione oltre a produrre energia elettrica e termica, generano uno scarto solido ad alto contenuto di carbonio chiamato char. L'analogia di questo materiale con
In the present investigation grape marc was processed in a HTC batch reactor at different operati... more In the present investigation grape marc was processed in a HTC batch reactor at different operating conditions: 180, 220, and 250 °C and 1, 3, and 8 h residence time. The mass yield of the resulting phases (gaseous, liquid and solid) was measured. The hydrochar and gas compositions were evaluated through elemental analysis and gas-chromatography, respectively. The experimental results allowed to calibrate a kinetics model, based on a two-step reaction mechanism. The activation energy and pre-exponential factor of the various degradation reactions were determined by means of least square optimization versus the experimental data. A simplified dynamic analytic model was also built – based on lumped capacitance method– in order to simulate the thermal behavior of the system, using the actual temperature profile imposed by the reactor external heater. A resistance-capacitance network was used to describe the system, taking into account the thermo-physical properties of the systems (i.e....
In this work, heat flux Differential Scanning Calorimetry (DSC) was used coupled with high-pressu... more In this work, heat flux Differential Scanning Calorimetry (DSC) was used coupled with high-pressure crucibles to evaluate the enthalpy change of Hydrothermal Carbonization (HTC) applied to cellulose, wood, and digestate from an anaerobic digestion plant. The temperature program, constant heating rate of 5 °C/min up to 250 °C, then 3 hours at 250 °C, was run twice on each crucible containing the sample: in the first run the HTC process takes place and completes, in the second run (the blank) the thermal effect is not related to the process. The two curves are then subtracted to obtain the process enthalpy change. 8 mg of dry substrates and 64 mg of distilled water were used for each run. For each substrate, three replicates were performed. Results showed high reproducibility and agreed with the available literature about DSC of wood and cellulose. The results for digestate were in the same range, but lower due to the less energetic nature of the substrate. Interestingly, the enthalpy...
WOOD-UP is an applied-research project that aims to produce expendable results, with an impact on... more WOOD-UP is an applied-research project that aims to produce expendable results, with an impact on key sectors (agriculture, energy, environment) of the economy of South-Tyrol (ST). Recent research findings has suggested that biochar, one of the gasification by-products, may represent a valuable resource, when used in agriculture as soil amendment. However, the characteristics of the biochar produced in ST are only partially known, and its ability to improve soil fertility is still unknown. Moreover, the woody biomass used is rich in secondary compounds, which could be used by the pharmaceutical, cosmetic and food industry. These compounds could be extracted before the use of biomass for energy production, increasing the economic sustainability of the entire value chain. In this framework, the aims of this work were: 1. assess the state of the art of the gasification of woody biomass in ST; 2. physically and chemically characterize the biochar produced in ST; 3. study the effect of biochar application on the soil, through in vasu germination and phytotoxicity tests.
Carbon black is a carbonaceous material (more than 97 wt.% of colloidal carbon) used for tires an... more Carbon black is a carbonaceous material (more than 97 wt.% of colloidal carbon) used for tires and rubber production as well as plastics, conductive packaging and inks. It must possess low ash content and, to improve adhesion, convenient amounts of unsaturated functions and graphitic defects. At present, the processes used for carbon black production exploit non-renewable substrates (mainly aromatic hydrocarbons and natural gas) and produce non-negligible amounts of hazardous air pollutants. On the contrary, hydrochar is recognized to have very low environmental impacts. Indeed, hydrochar is a carbon-based material, produced from organic residues or waste substrates during hydrothermal carbonization (HTC), a wet thermochemical process. During HTC, the feedstock undergoes mainly dehydration and carbonization that enhance the colloidal carbon particles formation. For this purpose, HTC was applied to a specific substrate, i.e. the residue classified by the European Waste Catalogue as E...
ABSTRACT In this paper, a study on the reaction kinetics of the hydrothermal carbonization (HTC) ... more ABSTRACT In this paper, a study on the reaction kinetics of the hydrothermal carbonization (HTC) process is presented. A fundamental piece of information for the design of a HTC process is the knowledge of its kinetics: the process conditions do not allow the establishment of thermodynamic equilibrium and the reaction kinetics approach becomes mandatory for understanding how the process occurs, evolves over time and depends on the operating conditions. Experimental data have been collected applying the HTC process to an organic waste residue coming from the wine-making industry: the grape marc. Starting from the yield and analytical results, a kinetic model based on a two-step kinetic mechanism was calibrated. The activation energy and pre-exponential factors of the various degradation reactions were determined by means of least square optimization versus the experimental data. The calibrated model allowed a characterization of the HTC time scale under different process conditions, showing that a two-step reaction mechanism can be suitably used to describe the evolution in time of the hydrochar yield at different process temperature.
Small-scale-woody-biomass gasification plants installation have seen a rapid growth in the last y... more Small-scale-woody-biomass gasification plants installation have seen a rapid growth in the last years in South Tyrol. More than 40 plants have been installed, producing about 42 GWhel and 84 GWhth, most of them exploited in local district heating grids. Among the energy production, char is produced to an extent of up to 2000 ton per year. At present this material is managed as waste, with an average cost of more than 300 k€ every year. Within this context and under the perspective of poly-generation (i.e., the generation of at least three valuable products), the Free University of Bolzano developed the Novel EXTension of biomass poly-GENERATION to small scale gasification systems in South-Tyrol (or NEXT Generation project), aiming to investigate the quantity, quality and environmental impact of the by-products of small-scale biomass-gasification-based CHP plant in South-Tyrol, and to assess possible route for their valorization. Thus, in this paper the NEXT project is described and the preliminary results are presented. Moreover, some important remarks on possible valorization pathways for char exploitation are provided.
Hydrothermal carbonization (in acronym, HTC) is a thermochemical conversion process through which... more Hydrothermal carbonization (in acronym, HTC) is a thermochemical conversion process through which it is possible to directly transform wet organic substrates into a carbonaceous material, referred as hydrochar. Hydrochar has chemical and physical characteristics that make it similar to fossil peats and lignite. Depending on the process conditions, mostly temperature and residence time, this material can be enriched in its carbon content, modifying its structure and providing it interesting characteristics that make it possible to be used for several applications, such as for energy production, as a soil conditioner and improver, for carbon dioxide sorption and sequestration, and some others reported in literature. HTC is a different process, if compared to other common thermochemical processes, such as pyrolysis, torrefaction, gasification, etc., because it works in wet conditions (humidity content higher than 60%). As a matter of fact, biomass is transformed into hydrochar because ...
ABSTRACT The work presented is a part of a wider project with the target to realize in-deep studi... more ABSTRACT The work presented is a part of a wider project with the target to realize in-deep studies on the applicability of the hydrothermal carbonization process to the treatment of high moisture biomass. To get this challenging objective, a batch reactor has been built to perform preliminary tests to get insights on the thermochemical process. Several substrates have been carbonized, obtaining interesting results, useful for the modelling stage. A numerical model of a batch hydrothermal carbonization reactor have been developed. The model integrates both mass, momentum and heat equations within the reactor domain by means of finite volumes method (f.v.m.) approach. Convective and radiative exchange between the reactor and the fluid within the reactor have been implemented in the f.v.m. model. To calibrate the model, experimental tests have been performed to collect data referred to temperature profiles (outside and inside the reactor) and pressures. Under two strong assumptions (mono-component and mono-phase fluid, which fulfils the reactor), it has been possible to estimate the behaviour of an equivalent fluid (eq_fluid), in terms of thermal properties of the fluid (thermal capacity, thermal conductivity and thermal diffusivity). The foreseen upgrading of the model can help to obtain a better description of the process.
Abstract During the last few years, there has been an increasing interest in small-scale biomass ... more Abstract During the last few years, there has been an increasing interest in small-scale biomass gasification in Central and Northern Europe. Since 2011, almost fifty small-scale biomass gasification plants have been authorized and built in the South Tyrolean region (Italy), and most of them are currently operating. Within this framework, an extensive survey was performed by means of questionnaires to the plant owners for assessing the biomass and char flows in the region. Moreover, a comprehensive monitoring campaign was carried out onsite on representative plants of almost all the available operating technologies. For each of the monitored plants, the feedstock and the gasification products were characterized and their fluxes quantified, leading to energy and mass balances. This allowed collecting an extended set of data and drawing up a unique overview of the reference values for the ranges of operation of small-scale biomass gasification systems currently available in the European market, in terms of equivalence ratio, dry gas composition and heating value, specific electricity production, and conversion efficiencies. Moreover, samples of chars were deeply characterized, providing an insight into possible utilization pathways for the valorization of this by-product that is currently disposed of, representing an economical and environmental burden.
The management of digestate, the main by-product of the anaerobic digestion (AD) process, is one ... more The management of digestate, the main by-product of the anaerobic digestion (AD) process, is one of the most serious environmental issues. Although digestate is used on arable land as a fertilizer, it can have a negative impact on the environment due to nitrate leaching into the groundwater and ammonia volatilization into the atmosphere, with high economic and environmental disposal costs. Therefore, hydrothermal carbonization (HTC), a thermochemical biomass conversion process, could represent a sustainable and efficient alternative for digestate management. Hydrochar, the solid product of the HTC process, has been recently proposed as a plant growing medium in soilless culture systems (SCS). Here, using cow manure digestate as feedstock, we investigated the influence of the HTC process reaction temperature (180, 220 and 250 • C) and residence time (1 and 3 h) on the physical-chemical properties (pH, electrical conductivity, and mineral element concentrations) of the resulting hydrochars. Furthermore, in order to fully valorize hydrochar as a growing medium, their possible phytotoxic effects and those of their water extracts (prepared at two different concentrations and at different pHs) were tested in germination tests with cress seeds (Lepidium sativum L.). Concentrations of nutrients, heavy metals, organic acids, sugars and furan compounds were determined in the water extracts. Characterization analysis of these hydrochars revealed that they can be distinguished from each other by their physical-chemical properties, which were significantly affected by the two process parameters. Specifically, the HTC temperature had a greater effect on the composition of hydrochars than the residence time. Germination tests found hydrochar water extracts to show significantly lower phytotoxicity than the hydrochars themselves. Notably, the phytotoxic effect of the extracts decreased with increasing extraction ratio and decreasing pH. The chromatographic characterization of extracts identified the presence of potential phytotoxins, such as furan compounds (i. e., hydroxymethylfurfural and furfural). However, before using hydrochars as potential and innovative growing media for plants, their phytotoxicity should be limited, for example through their dilution with other substrates. Overall, AD-HTC coupling could represent a valuable eco-sustainable expedient in the field of biomasses, green economy and waste conversion and, therefore, further investigations in this direction are necessary.
International Journal of Environmental Research and Public Health, 2020
Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable... more Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable residues into value-added materials, such as hydrochar. HTC has been studied for decades, however, a lack of detailed information on the production and composition of the process water has been highlighted by several authors. In this paper the state of the art of the knowledge on this by-product is analyzed, with attention to HTC applied to municipal and agro-industrial anaerobic digestion digestate. The chemical and physical characteristics of the process water obtained at different HTC conditions are compared along with pH, color, organic matter, nutrients, heavy metals and toxic compounds. The possibility of recovering nutrients and other valorization pathways is analyzed and technical feasibility constraints are reported. Finally, the paper describes the main companies which are investing actively in proposing HTC technology towards improving an effective process water valorization.
Grape marc is a residue of the wine-making industry, nowadays not always effectively valorized. I... more Grape marc is a residue of the wine-making industry, nowadays not always effectively valorized. It consists of grape seeds (mostly lignocellulosic) and grape skins (mostly holocellulosic). In order to understand possible correlations between seeds and skins in forming hydrochar for it to be used as a solid biofuel, hydrothermal carbonization (HTC) was applied separately to grape marc and its constituents. HTC was performed at several process conditions (temperature: 180, 220 and 250 • C; reaction time: 0.5, 1, 3 and 8 h), in order to collect data on the three phases formed downstream of the process: solid (hydrochar), liquid and gas. An in deep analytical characterization was performed: ultimate analysis and calorific value for hydrochar, Total Organic Carbon (TOC) and Inductively Coupled Plasma (IPC) analyses for liquid phase, composition for gas phase. In previous works, the same experimental apparatus was used to treat residual biomass, obtaining interesting results in terms of possible hydrochar exploitation as a solid biofuel. Thus, the main objectives of this work were both to get results for validating the hypothesis to apply HTC to this feedstock, and to collect data for subsequent theoretical investigations. Moreover, a severity model was developed to allow a predictive description of the hydrochar yield as a function of a unique parameter condensing both temperature and reaction time effects. The results obtained demonstrate that this process can upgrade wet residues into a solid biofuel ad that the process can be satisfactorily described in terms of a severity factor.
A remarkable number of scientific papers are available in the literature about the process of hyd... more A remarkable number of scientific papers are available in the literature about the process of hydrothermal carbonization (HTC), also called wet or hydrous pyrolysis, applied to biomass substrates. However, the biggest share of it focuses on the characterization of HTC products obtained from different feedstocks. Only a few works are available on the process thermodynamics, particularly about the determination of the enthalpy change and the related heat release or absorption during HTC, which is a key parameter to understand the nature of the process and to evaluate the heat requirements for the design of industrial scale HTC plants. The present review summarizes the research carried out with the aim of assessing the process enthalpy for HTC. Two main approaches have been identified and described, and the research works are sorted into two categories: enthalpy calculation based on the direct application of the Hess's law and enthalpy evaluation based on differential heat measurement. The hypotheses and results obtained by the different authors are critically analysed and discussed, and directions for further research are proposed.
In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of... more In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert raw moist biomass into dry and pelletized hydrochar. By means of mass and thermal balances and based on common equations specific to the various equipment, thermal energy and power consumption were calculated at variable process conditions: HTC reactor temperature T: 180, 220, 250 • C; reaction time θ: 1, 3, 8 h. When operating the HTC plant with grape marc (65% moisture content) at optimized process conditions (T = 220 • C; θ = 1 h; dry biomass to water ratio = 0.19), thermal energy and power consumption were equal to 1170 kWh and 160 kWh per ton of hydrochar produced, respectively. Correspondingly, plant efficiency was 78%. In addition, the techno-economical aspects of the HTC process were analyzed in detail, considering both investment and production costs. The production cost of pelletized hydrochar and its break-even point were determined to be 157 €/ton and 200 €/ton, respectively. Such values make the use of hydrochar as a CO 2 neutral biofuel attractive.
Greenpeat is a new sustainable material that can be produced from wet biodegradable organic waste... more Greenpeat is a new sustainable material that can be produced from wet biodegradable organic waste, both solid and liquid, through a very efficient process, studied and developed by HBI Srl, an innovative startup founded by a researcher and an entrepreneur, who works in the field of the innovative green technologies. Greenpeat has been produced from agro-industrial organic by-products and optimized according to its potential different uses, namely for energy production or as a highly performing material for agronomic uses. At specific process conditions, it is possible to give to Greenpeat calorific values in the range of 22-28 MJ/kg, which represent interesting values for renewable and clean energy production applications. Furthermore, by using Greenpeat as a substitute of common solid fossil fuels, both the emissions related to fossil resources extraction and those produced during combustion are interestingly lowered. On the other hand, when ligno-cellulosic residues are treated in...
Hydrochar is produced by means of hydrothermal carbonization at relatively low temperatures (180-... more Hydrochar is produced by means of hydrothermal carbonization at relatively low temperatures (180-260°C) in sub-critical water. While, in many respects similar to biochar, its physical and chemical properties differ significantly (Basu, 2018). Of particular interest for this work are the higher energy density and lower ash content, that make hydrochar a possible feedstock for gasification plants with energy generation purposes. A gasification step is used instead of direct combustion to convert solid fuels in energy to achieve cleaner combustion and higher efficiency (Wang and Stiegel, 2016). In this work a 400 kg/h hydrochar gasification plant was modelled to identify optimal conditions and energetic yield of hydrochar obtained from municipal sewage. The fixed bed, updraft, gasification reactor was modeled in detail using a multi-scale, multiphase methodology already widely tested on biomass (Corbetta et al., 2015; Ranzi et al., 2014). The gas solid kinetic model was coupled with a detailed gas-phase kinetic scheme with over 200 species, including reaction intermediates, and 2000 reactions for reliable product yield prediction. Using Visual Basic Application as an interface, the predictions from the detailed simulation package were delivered to a commercial simulation package to model the energy generation section of the plant. Aspen HYSYS V10 was used for this purpose for the simplicity of integration and its widespread use in similar industrial plants. The gasification was carried out with air, air enriched in oxygen to 28%, air enriched in oxygen to 35% and pure oxygen with different amounts of steam to control the temperature in the chamber and at different values of equivalence ratio. The gasification performance was evaluated in terms of lower heating value of the generated fuel gas while the H2S formation was accounted for only in a superficial manner using rules of thumb derived from previous experimental experience.
Improving the agronomic use of recycled nutrients derived from organic waste is one of the priori... more Improving the agronomic use of recycled nutrients derived from organic waste is one of the priorities within the measures adopted by the European community to reduce environmental issues but remains an unexplored area of research. This study focused on investigating the possibility of using innovative fertilizer solutions in hydroponic systems for the growth of agricultural plants. To this purpose, a liquid fraction [aqueous hydrothermal carbonization (HTC) liquid (AHL)] derived from HTC of cow manure digestate was chemically characterized (pH, electrical conductivity, mineral elements, and organic compounds such as phytotoxins), diluted with distilled water (1:30, 1:60, and 1:90, v/v) to reduce its potential phytotoxicity, and used to grow hydroponic maize (Zea mays L.) plants instead of the classical full-strength nutrient solution. The results indicated that the dilution ratio 1:30 of the AHL solution maintained a high level of toxicity for the plants (phytotoxic substances, espe...
WOOD-UP è un progetto di ricerca applicata, che mira a produrre risultati concreti e spendibili c... more WOOD-UP è un progetto di ricerca applicata, che mira a produrre risultati concreti e spendibili con ricadute positive sui settori chiave (quali, agricoltura, energia ed ambiente) dell'economia dell'Alto Adige. I recenti risultati conseguiti nell'ambito del presente lavoro di ricerca hanno suggerito che il char, uno dei sottoprodotti del processo di gassificazione, ottenuto a partire dalla biomassa legnosa, potrebbe rappresentare una risorsa preziosa, qualora fosse utilizzato
La diffusione di impianti di gassificazione di piccola scala ha avuto un importante incremento in... more La diffusione di impianti di gassificazione di piccola scala ha avuto un importante incremento in Alto Adige nell'ultima decade, sia a causa dell'elevata quantità di biomassa legnosa disponibile in questa regione, sia per le condizioni economiche favorevoli generate dagli incentivi nazionali sulle energie rinnovabili. Attualmente gli impianti di gassificazione oltre a produrre energia elettrica e termica, generano uno scarto solido ad alto contenuto di carbonio chiamato char. L'analogia di questo materiale con
In the present investigation grape marc was processed in a HTC batch reactor at different operati... more In the present investigation grape marc was processed in a HTC batch reactor at different operating conditions: 180, 220, and 250 °C and 1, 3, and 8 h residence time. The mass yield of the resulting phases (gaseous, liquid and solid) was measured. The hydrochar and gas compositions were evaluated through elemental analysis and gas-chromatography, respectively. The experimental results allowed to calibrate a kinetics model, based on a two-step reaction mechanism. The activation energy and pre-exponential factor of the various degradation reactions were determined by means of least square optimization versus the experimental data. A simplified dynamic analytic model was also built – based on lumped capacitance method– in order to simulate the thermal behavior of the system, using the actual temperature profile imposed by the reactor external heater. A resistance-capacitance network was used to describe the system, taking into account the thermo-physical properties of the systems (i.e....
In this work, heat flux Differential Scanning Calorimetry (DSC) was used coupled with high-pressu... more In this work, heat flux Differential Scanning Calorimetry (DSC) was used coupled with high-pressure crucibles to evaluate the enthalpy change of Hydrothermal Carbonization (HTC) applied to cellulose, wood, and digestate from an anaerobic digestion plant. The temperature program, constant heating rate of 5 °C/min up to 250 °C, then 3 hours at 250 °C, was run twice on each crucible containing the sample: in the first run the HTC process takes place and completes, in the second run (the blank) the thermal effect is not related to the process. The two curves are then subtracted to obtain the process enthalpy change. 8 mg of dry substrates and 64 mg of distilled water were used for each run. For each substrate, three replicates were performed. Results showed high reproducibility and agreed with the available literature about DSC of wood and cellulose. The results for digestate were in the same range, but lower due to the less energetic nature of the substrate. Interestingly, the enthalpy...
WOOD-UP is an applied-research project that aims to produce expendable results, with an impact on... more WOOD-UP is an applied-research project that aims to produce expendable results, with an impact on key sectors (agriculture, energy, environment) of the economy of South-Tyrol (ST). Recent research findings has suggested that biochar, one of the gasification by-products, may represent a valuable resource, when used in agriculture as soil amendment. However, the characteristics of the biochar produced in ST are only partially known, and its ability to improve soil fertility is still unknown. Moreover, the woody biomass used is rich in secondary compounds, which could be used by the pharmaceutical, cosmetic and food industry. These compounds could be extracted before the use of biomass for energy production, increasing the economic sustainability of the entire value chain. In this framework, the aims of this work were: 1. assess the state of the art of the gasification of woody biomass in ST; 2. physically and chemically characterize the biochar produced in ST; 3. study the effect of biochar application on the soil, through in vasu germination and phytotoxicity tests.
Carbon black is a carbonaceous material (more than 97 wt.% of colloidal carbon) used for tires an... more Carbon black is a carbonaceous material (more than 97 wt.% of colloidal carbon) used for tires and rubber production as well as plastics, conductive packaging and inks. It must possess low ash content and, to improve adhesion, convenient amounts of unsaturated functions and graphitic defects. At present, the processes used for carbon black production exploit non-renewable substrates (mainly aromatic hydrocarbons and natural gas) and produce non-negligible amounts of hazardous air pollutants. On the contrary, hydrochar is recognized to have very low environmental impacts. Indeed, hydrochar is a carbon-based material, produced from organic residues or waste substrates during hydrothermal carbonization (HTC), a wet thermochemical process. During HTC, the feedstock undergoes mainly dehydration and carbonization that enhance the colloidal carbon particles formation. For this purpose, HTC was applied to a specific substrate, i.e. the residue classified by the European Waste Catalogue as E...
ABSTRACT In this paper, a study on the reaction kinetics of the hydrothermal carbonization (HTC) ... more ABSTRACT In this paper, a study on the reaction kinetics of the hydrothermal carbonization (HTC) process is presented. A fundamental piece of information for the design of a HTC process is the knowledge of its kinetics: the process conditions do not allow the establishment of thermodynamic equilibrium and the reaction kinetics approach becomes mandatory for understanding how the process occurs, evolves over time and depends on the operating conditions. Experimental data have been collected applying the HTC process to an organic waste residue coming from the wine-making industry: the grape marc. Starting from the yield and analytical results, a kinetic model based on a two-step kinetic mechanism was calibrated. The activation energy and pre-exponential factors of the various degradation reactions were determined by means of least square optimization versus the experimental data. The calibrated model allowed a characterization of the HTC time scale under different process conditions, showing that a two-step reaction mechanism can be suitably used to describe the evolution in time of the hydrochar yield at different process temperature.
Small-scale-woody-biomass gasification plants installation have seen a rapid growth in the last y... more Small-scale-woody-biomass gasification plants installation have seen a rapid growth in the last years in South Tyrol. More than 40 plants have been installed, producing about 42 GWhel and 84 GWhth, most of them exploited in local district heating grids. Among the energy production, char is produced to an extent of up to 2000 ton per year. At present this material is managed as waste, with an average cost of more than 300 k€ every year. Within this context and under the perspective of poly-generation (i.e., the generation of at least three valuable products), the Free University of Bolzano developed the Novel EXTension of biomass poly-GENERATION to small scale gasification systems in South-Tyrol (or NEXT Generation project), aiming to investigate the quantity, quality and environmental impact of the by-products of small-scale biomass-gasification-based CHP plant in South-Tyrol, and to assess possible route for their valorization. Thus, in this paper the NEXT project is described and the preliminary results are presented. Moreover, some important remarks on possible valorization pathways for char exploitation are provided.
Hydrothermal carbonization (in acronym, HTC) is a thermochemical conversion process through which... more Hydrothermal carbonization (in acronym, HTC) is a thermochemical conversion process through which it is possible to directly transform wet organic substrates into a carbonaceous material, referred as hydrochar. Hydrochar has chemical and physical characteristics that make it similar to fossil peats and lignite. Depending on the process conditions, mostly temperature and residence time, this material can be enriched in its carbon content, modifying its structure and providing it interesting characteristics that make it possible to be used for several applications, such as for energy production, as a soil conditioner and improver, for carbon dioxide sorption and sequestration, and some others reported in literature. HTC is a different process, if compared to other common thermochemical processes, such as pyrolysis, torrefaction, gasification, etc., because it works in wet conditions (humidity content higher than 60%). As a matter of fact, biomass is transformed into hydrochar because ...
ABSTRACT The work presented is a part of a wider project with the target to realize in-deep studi... more ABSTRACT The work presented is a part of a wider project with the target to realize in-deep studies on the applicability of the hydrothermal carbonization process to the treatment of high moisture biomass. To get this challenging objective, a batch reactor has been built to perform preliminary tests to get insights on the thermochemical process. Several substrates have been carbonized, obtaining interesting results, useful for the modelling stage. A numerical model of a batch hydrothermal carbonization reactor have been developed. The model integrates both mass, momentum and heat equations within the reactor domain by means of finite volumes method (f.v.m.) approach. Convective and radiative exchange between the reactor and the fluid within the reactor have been implemented in the f.v.m. model. To calibrate the model, experimental tests have been performed to collect data referred to temperature profiles (outside and inside the reactor) and pressures. Under two strong assumptions (mono-component and mono-phase fluid, which fulfils the reactor), it has been possible to estimate the behaviour of an equivalent fluid (eq_fluid), in terms of thermal properties of the fluid (thermal capacity, thermal conductivity and thermal diffusivity). The foreseen upgrading of the model can help to obtain a better description of the process.
Abstract During the last few years, there has been an increasing interest in small-scale biomass ... more Abstract During the last few years, there has been an increasing interest in small-scale biomass gasification in Central and Northern Europe. Since 2011, almost fifty small-scale biomass gasification plants have been authorized and built in the South Tyrolean region (Italy), and most of them are currently operating. Within this framework, an extensive survey was performed by means of questionnaires to the plant owners for assessing the biomass and char flows in the region. Moreover, a comprehensive monitoring campaign was carried out onsite on representative plants of almost all the available operating technologies. For each of the monitored plants, the feedstock and the gasification products were characterized and their fluxes quantified, leading to energy and mass balances. This allowed collecting an extended set of data and drawing up a unique overview of the reference values for the ranges of operation of small-scale biomass gasification systems currently available in the European market, in terms of equivalence ratio, dry gas composition and heating value, specific electricity production, and conversion efficiencies. Moreover, samples of chars were deeply characterized, providing an insight into possible utilization pathways for the valorization of this by-product that is currently disposed of, representing an economical and environmental burden.
The management of digestate, the main by-product of the anaerobic digestion (AD) process, is one ... more The management of digestate, the main by-product of the anaerobic digestion (AD) process, is one of the most serious environmental issues. Although digestate is used on arable land as a fertilizer, it can have a negative impact on the environment due to nitrate leaching into the groundwater and ammonia volatilization into the atmosphere, with high economic and environmental disposal costs. Therefore, hydrothermal carbonization (HTC), a thermochemical biomass conversion process, could represent a sustainable and efficient alternative for digestate management. Hydrochar, the solid product of the HTC process, has been recently proposed as a plant growing medium in soilless culture systems (SCS). Here, using cow manure digestate as feedstock, we investigated the influence of the HTC process reaction temperature (180, 220 and 250 • C) and residence time (1 and 3 h) on the physical-chemical properties (pH, electrical conductivity, and mineral element concentrations) of the resulting hydrochars. Furthermore, in order to fully valorize hydrochar as a growing medium, their possible phytotoxic effects and those of their water extracts (prepared at two different concentrations and at different pHs) were tested in germination tests with cress seeds (Lepidium sativum L.). Concentrations of nutrients, heavy metals, organic acids, sugars and furan compounds were determined in the water extracts. Characterization analysis of these hydrochars revealed that they can be distinguished from each other by their physical-chemical properties, which were significantly affected by the two process parameters. Specifically, the HTC temperature had a greater effect on the composition of hydrochars than the residence time. Germination tests found hydrochar water extracts to show significantly lower phytotoxicity than the hydrochars themselves. Notably, the phytotoxic effect of the extracts decreased with increasing extraction ratio and decreasing pH. The chromatographic characterization of extracts identified the presence of potential phytotoxins, such as furan compounds (i. e., hydroxymethylfurfural and furfural). However, before using hydrochars as potential and innovative growing media for plants, their phytotoxicity should be limited, for example through their dilution with other substrates. Overall, AD-HTC coupling could represent a valuable eco-sustainable expedient in the field of biomasses, green economy and waste conversion and, therefore, further investigations in this direction are necessary.
International Journal of Environmental Research and Public Health, 2020
Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable... more Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable residues into value-added materials, such as hydrochar. HTC has been studied for decades, however, a lack of detailed information on the production and composition of the process water has been highlighted by several authors. In this paper the state of the art of the knowledge on this by-product is analyzed, with attention to HTC applied to municipal and agro-industrial anaerobic digestion digestate. The chemical and physical characteristics of the process water obtained at different HTC conditions are compared along with pH, color, organic matter, nutrients, heavy metals and toxic compounds. The possibility of recovering nutrients and other valorization pathways is analyzed and technical feasibility constraints are reported. Finally, the paper describes the main companies which are investing actively in proposing HTC technology towards improving an effective process water valorization.
Grape marc is a residue of the wine-making industry, nowadays not always effectively valorized. I... more Grape marc is a residue of the wine-making industry, nowadays not always effectively valorized. It consists of grape seeds (mostly lignocellulosic) and grape skins (mostly holocellulosic). In order to understand possible correlations between seeds and skins in forming hydrochar for it to be used as a solid biofuel, hydrothermal carbonization (HTC) was applied separately to grape marc and its constituents. HTC was performed at several process conditions (temperature: 180, 220 and 250 • C; reaction time: 0.5, 1, 3 and 8 h), in order to collect data on the three phases formed downstream of the process: solid (hydrochar), liquid and gas. An in deep analytical characterization was performed: ultimate analysis and calorific value for hydrochar, Total Organic Carbon (TOC) and Inductively Coupled Plasma (IPC) analyses for liquid phase, composition for gas phase. In previous works, the same experimental apparatus was used to treat residual biomass, obtaining interesting results in terms of possible hydrochar exploitation as a solid biofuel. Thus, the main objectives of this work were both to get results for validating the hypothesis to apply HTC to this feedstock, and to collect data for subsequent theoretical investigations. Moreover, a severity model was developed to allow a predictive description of the hydrochar yield as a function of a unique parameter condensing both temperature and reaction time effects. The results obtained demonstrate that this process can upgrade wet residues into a solid biofuel ad that the process can be satisfactorily described in terms of a severity factor.
A remarkable number of scientific papers are available in the literature about the process of hyd... more A remarkable number of scientific papers are available in the literature about the process of hydrothermal carbonization (HTC), also called wet or hydrous pyrolysis, applied to biomass substrates. However, the biggest share of it focuses on the characterization of HTC products obtained from different feedstocks. Only a few works are available on the process thermodynamics, particularly about the determination of the enthalpy change and the related heat release or absorption during HTC, which is a key parameter to understand the nature of the process and to evaluate the heat requirements for the design of industrial scale HTC plants. The present review summarizes the research carried out with the aim of assessing the process enthalpy for HTC. Two main approaches have been identified and described, and the research works are sorted into two categories: enthalpy calculation based on the direct application of the Hess's law and enthalpy evaluation based on differential heat measurement. The hypotheses and results obtained by the different authors are critically analysed and discussed, and directions for further research are proposed.
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Papers by Daniele Basso