Impact of Torrefaction on Fuel Properties of Aspiration Cleaning Residues

To maximise the use of biomass for energy purposes, there are various options for converting biomass to biofuels through thermochemical conversion processes, one of which is torrefaction. Higher utilisation of waste from the aspiration cleaning of grains, such as wheat or maize, could be one of the means through which the dependence on fossil fuels could be reduced in the spirit of a circular economy. In this study, the effect of torrefaction on fuel properties of agricultural residues was investigated. The tested materials were waste by-products from the aspiration cleaning of maize grains and waste from wheat. The materials were treated by torrefaction under a nitrogen atmosphere (225 °C, 250 °C, and 275 °C), over a residence time of 30 min. During the treatment, weight loss was monitored as a function of time. Proximate and elemental composition, as well as calorific values, were analysed before and after torrefaction. Torrefaction has a positive effect on the properties of the fuels in the samples studied, as shown by the results. The carbon content increased the most between temperatures of 250 °C and 275 °C, i.e., by 11.7% wt. in waste from maize. The oxygen content in the maize waste samples decreased by 38.99% wt. after torrefaction, and in wheat waste, it decreased by 37.20% wt. compared to the original. The net calorific value increased with increasing temperatures of process and reached a value of 23.56 MJ·kg−1 at a peak temperature of 275 °C in by-products from maize. To express the influence of the treatments on combustion behaviour, stoichiometric combustion calculations were performed. Differences of up to 20% in stoichiometric combustion parameters were found between the two types of waste. A similar case was found for fuel consumption, where a difference of 19% was achieved for torrefaction at a temperature of 275 °C, which fundamentally differentiated these fuels

Evaluation of Co and Nox Emissions in Real-Life Operating Conditions of Herbaceous Biomass Briquettes Combustion

The issue of carbon monoxide and nitrogen oxides emissions into the atmosphere is very current. This article thus focuses on the assessment of elemental composition of selected herbal biomass species and emission concentrations during combustion in a commonly available grate combustion device for briquetted fuel. In tests, emission concentrations were evaluated in contrast to the oxygen concentration in flue gas and flue gas temperatures. Samples of camelina (Camelina sativa), giant miscanthus (Miscanthus gigantheus), reed canary grass (Phalaris arundinacea L.) and sorghum (Sorghum bicolor) were used. Elementary and stoichiometric combustion analyses were conducted for these samples (LECO AC-600 semi-automatic calorimeter, CHN628 + S elemental analyser and LECO TGA-701 analyser). Analyses of C, H, N and S concentrations and calorific values showed that samples of briquetted herb biomass had insignificant differences and could be used for energy purposes without limitation. The limiting factor was the high amount of ash, which amounted to 6.59% of dry weight in reed canary grass briquette sample. Furthermore, a high percentage (1.91% wt.) of nitrogen was observed in reed canary grass briquettes. Such a high amount of nitrogen during combustion tests resulted in an increase in NOx emission levels in flue gas of the Phalaris arundinacea L. sample, in which it reached the maximum concentration of 375.20 mg·m−3. The combustion tests showed that even under steady-state conditions, high concentrations of carbon monoxide could not be avoided for tested briquetted biofuels without active regulation of the combustion process

Use of Spent Coffee Ground as an Alternative Fuel and Possible Soil Amendment

Spent coffee ground is a massively produced coffee industry waste product whose reusage is beneficial. Proximate and ultimate and stochiometric analysis of torrefied spent coffee ground were performed and results were analyzed and compared with other research and materials. Spent coffee ground is a material with high content of carbon (above 50%) and therefore high calorific value (above 20 MJ·kg−1). Torrefaction improves the properties of the material, raising its calorific value up to 32 MJ·kg−1. Next, the phytotoxicity of the aqueous extract was tested using the cress test. The non-torrefied sample and the sample treated at 250 °C were the most toxic. The sample treated at 250 °C adversely affected the germination of the cress seeds due to residual caffeine, tannins and sulfur release. The sample treated at 350 °C performed best of all the tested samples. The sample treated at 350 °C can be applied to the soil as the germination index was higher than 50% and can be used as an alternative fuel with net calorific value comparable to fossil fuels

The Effect of Reservoir Cultivation on Conventional Maize in Sandy-Loam Soil

Maize grown on sloped areas is susceptible to surface runoff and soil erosion, especially if traditional technology with tillage is employed. As a result, other solutions are being sought that address this risk and are acceptable to farmers. The combination of inter-row cultivation with the formation of small reservoirs appears to be a suitable alternative solution applicable in traditional corn cultivation. In the years 2020, 2021, and 2022, three plots of land in southern Bohemia, Czech Republic, were selected for testing, on which this approach was tested. During the field experiments, three variants were compared each year: inter-row cultivation with reservoirs, inter-row cultivation only, and a control without any mechanical intervention. All variants were subjected to rain simulation, from which the surface runoff was evaluated. The highest retention of runoff was manifested with reservoir cultivation by 2.4–4.2 min, compared to the cultivated variant, and 2–4.2 min compared to the control. This result would correspond to a difference of 5.7–9.8 mm retained precipitation and 4.6 to 7.3 mm, respectively. The hydraulic conductivity of the soil was evaluated after canopy closure. The lowest values were invariably reached in the reservoirs, up to 88% lower than with the cultivated variant and 79% lower than the control. The fresh matter yield of forage maize was shown to be inconclusively higher by up to 10% in 2020 and 2022 in cultivation with reservoirs. However, the dry matter yield was always lower in the variant with reservoirs compared to inter-row cultivation only. Overall, reservoir cultivation appears to be an effective method for the retention of rainwater on agricultural land with a slope up to 6° without a significant effect on the yield of maize

Properties of Biochar Derived from Tea Waste as an Alternative Fuel and Its Effect on Phytotoxicity of Seed Germination for Soil Applications

Tea waste as a potential biofuel and bio fertilizer was analyzed. Samples were collected from various tea species and torrefied to five different temperatures. All samples were analyzed for their proximal composition and calorific value. From the results, stoichiometric properties were calculated. A phytotoxicity test was performed, and the germination index was measured. Tea waste torrefied at 350 °C may be suitable biofuel reaching the calorific value of 25–27 MJ kg−1, but with quite a high share of ash, up to 10%, which makes its use technically challenging and may lead to operating issues in a combustion chamber. The same biochar may be a suitable fertilizer for increasing the germination index, therefore, applicable to the soil. The non-torrefied sample and the sample treated at 250 °C are not suitable as fertilizers for being toxic. The total phenolic content in waste black tea was reduced from 41.26 to 0.21 mg g−1, depending on the torrefaction temperature. The total flavonoid content was also reduced from 60.49 to 0.5 mg g−1. The total antioxidant activity in the non-torrefied sample was 144 mg g−1, and after torrefaction at 550 °C, it was 0.82 mg g−1. The results showed that black tea waste residues have the potential for further use, for example, in agriculture as a soil amendment or as a potential biofuel

Changes in the Composition and Surface Properties of Torrefied Conifer Cones

The paper investigated the torrefaction of cones from three tree species: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.), and European larch (Larix decidua Mill.). The objective was to determine the effects of torrefaction temperature on the properties of cones with a view to their further use as a renewable energy source. Torrefaction was conducted at 200, 235, 275, and 320 °C for 60 min under an inert gas atmosphere. Elemental composition, ash content, and lower heating value (LHV) were measured for the original and torrefied samples. Torrefaction performance was evaluated using formulas for solid yield, higher heating value (HHV), HHV enhancement factor, as well as energy yield. Scanning electron microscopy (SEM) was used to assess elemental composition and structural changes at the surface of the torrefied material. For all the studied conifer species, the higher the torrefaction temperature, the greater the carbon and ash content and the higher the LHV (a maximum of 27.6 MJ·kg−1 was recorded for spruce and larch cones torrefied at 320 °C). SEM images showed that an increase in process temperature from 200 to 320 °C led to partial decomposition of the scale surface as a result of lignin degradation. Cone scales from all tree species revealed C, O, N, Mg, K, and Si at the surface (except for pine scales, which did not contain Si). Furthermore, the higher the temperature, the higher the enhancement factor and the lower the energy yield of the torrefied biomass. Under the experimental conditions, spruce cones were characterized by the lowest weight loss, the highest HHV, and the highest energy yield, and so they are deemed the best raw material for torrefaction among the studied species

Regional wood chip quality parameters decomposition and price linkage with impact on Polish energy sustainability: Time frequency analysis between 2013 and 2019

The study aims to analyze and decompose the qualitative parameters of wood chips in Poland. The European Green Deal brings the new framework to support sustainability and elimination of emissions. The Wavelet coherence and Wavelet Discrete Decomposition are used for determination of relations among significant qualitative parameters. Thus, the possible uses are discussed. For the obvious relationship between moisture and calorific value there is evidence of strong correlation. The behaviour of these interrelations are different at frequencies in the long and short time. The wood chip price is inter-transmitter from moisture parameter to calorific value in a positive (in-phase) relationship. At both low and high frequencies there is evidence that the variables of moisture and calorific value are highly correlated. The transient effect of linkage is presented at values between 0.1 and 0.3 in coherence map. The empirical findings provide implication for local producers and policymakers

Assessment of the Composition of Forest Waste in Terms of Its Further Use

This paper presents the results of the analysis of the chemical composition and content of heavy metal contamination in forest logging residues, in order to assess the possibility for their further utilisation. The samples were divided into 9 groups, which included coniferous tree cones, wood, and other multi-species logging residues. The elementary composition, ash content, and calorific value were determined as energy use indicators for the samples. Additionally, the content of heavy and alkali metals, which may affect combustion processes and pollutant emissions, was tested. The high content of heavy metals may also disqualify these residues for other uses. The research shows that the test residues are suitable for energy use due to their high calorific value and low content of heavy metals. However, an increased ash content in some samples and the presence of alkali metals, causing high-temperature corrosion of boilers, may disqualify them as a potential fuel in the combustion process. The forest residues may be used in other thermal processes such as pyrolysis or gasification. A low content of heavy metals and a high content of organic matter permit the use of these residues for the production of adsorbents or composite materials

Decolorization and Oxidation of Acid Blue 80 in Homogeneous and Heterogeneous Phases by Selected AOP Processes

This paper is a kinetic study that compares the rate of decolorization and subsequently the mineralization of Acid Blue 80 in model dyeworks wastewater, both in the homogeneous phase using the Fenton and photo-Fenton reactions, UV-C and UVC/H2O2 processes, and in the heterogeneous phase, where the proven commercial photocatalysts P25, P90, and AV01 based on TiO2 were used. The influence of pH of the environment was studied and in the case of the Fenton reaction, the influence of the concentration of catalyzing Fe2+ ions on the rate of decolorization of the model wastewater was also studied. The optimal molar ratio of H2O2/Fe2+ was 10:1. For describing the reaction kinetics, first-order speed constants were best-suited. In all applied processes, the dye chromophore degraded, which was accompanied by a quantitative decolorization of the model wastewater. Subsequently, the mineralization of colorless intermediate products was studied through a decrease in COD or, more precisely, TOC. The mineralization efficiency in the homogeneous phase ranged between 18.6 and 97.1% after 24 h. In the case of heterogeneous photocatalysis, it ranged between 79.6 and 97.3% after 24 h, with efficiency declining in the order P90 > P25 > AV01

Decolorization and Oxidation of Acid Blue 80 in Homogeneous and Heterogeneous Phases by Selected AOP Processes

This paper is a kinetic study that compares the rate of decolorization and subsequently the mineralization of Acid Blue 80 in model dyeworks wastewater, both in the homogeneous phase using the Fenton and photo-Fenton reactions, UV-C and UVC/H2O2 processes, and in the heterogeneous phase, where the proven commercial photocatalysts P25, P90, and AV01 based on TiO2 were used. The influence of pH of the environment was studied and in the case of the Fenton reaction, the influence of the concentration of catalyzing Fe2+ ions on the rate of decolorization of the model wastewater was also studied. The optimal molar ratio of H2O2/Fe2+ was 10:1. For describing the reaction kinetics, first-order speed constants were best-suited. In all applied processes, the dye chromophore degraded, which was accompanied by a quantitative decolorization of the model wastewater. Subsequently, the mineralization of colorless intermediate products was studied through a decrease in COD or, more precisely, TOC. The mineralization efficiency in the homogeneous phase ranged between 18.6 and 97.1% after 24 h. In the case of heterogeneous photocatalysis, it ranged between 79.6 and 97.3% after 24 h, with efficiency declining in the order P90 > P25 > AV01