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•Study of process parameters effects on the quality and the yield of hydrochar.•Hydrochar more carbonaceous and more thermally stable than untreated biomass.•Dried olive pomace ...demineralized during HTC process.•Increase of 23% reached at 250°C giving hydrochar similar to lignite.•30min, 215°C and 1/6 biomass/water weight ratio maximize the energy yield (83%) of the HTC process.
Hydrothermal carbonization (HTC) of dried olive pomace (DOP) was performed in subcritical water under HTC conditions (180–250°C) to assess the potential of the generated hydrochar to produce energy. The effects of process parameters (holding time, temperature and DOP/water weight ratio) on the yield and the quality of the hydrochar were examined. The mass yield of hydrochar was between 56% and 71% and its HHV increased by more than 23% compared to the HHV of DOP giving a hydrochar similar to a lignite-type coal. The results reveal that a 30min treatment at 215°C with a DOP/water weight ratio of 1/6 maximizes the energy yield (83%) of the HTC process. Both the DOP and the hydrochar were characterized by ultimate, proximate and thermogravimetric analyses. The ultimate and thermogravimetric analyses showed that the hydrochar is more carbonaceous and more thermally stable than untreated DOP. The HTC conversion of raw DOP was carried out by dehydration reactions. The proximate analysis showed that hydrochars contained lower ash and volatile matter compared to the raw DOP.
•Clean coal yield is increased by simultaneous ultrasonic flotation.•Coal surface is physically cleaned by simultaneous ultrasonic flotation.•Ultrasonic treatment creates many micro-bubbles that ...enhance lignite flotation.•Water film on lignite surface may be unstable under ultrasonic treatment.•Water film on lignite surface may be easy to rupture under ultrasonic treatment.
Lignite, as a low rank coal reserve plays an important role in energy supply. However, fine lignite is difficult to upgrade using the conventional flotation because of its high surface hydrophilicity. This investigation was to enhance the flotation recovery of high-ash lignite combined with wet-screening, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and induction time measurer to reveal the mechanism of simultaneous ultrasonic treatment enhancing the lignite flotation. Flotation results indicate the clean coal yield is greatly increased whereas the clean coal ash content is highly reduced by simultaneous ultrasonic flotation compared with the conventional flotation. SEM and XPS results show coal surface is physically cleaned and hence the clay coating is reduced by simultaneous ultrasonic flotation. The removal of high-ash mineral particles from coal surface benefits the coal-bubble attachment. Furthermore, ultrasonic treatment creates many micro-bubbles that enhance the floatability of lignite through micro-bubble-based coating on coal surface. The micro-bubbles play a bridging role in the coal-bubble attachment. The water film on lignite surface may be also unstable and easy to rupture during bubble-coal attachment under the condition of ultrasonic treatment.
The scope of this study is the techno-economic evaluation of the Power to Methanol (PtM) concept, valorising CO2 that comes from high CO2 emitting lignite-fired power plants, in order to investigate ...the prospect of PtM in a future energy market of high RES penetration and advanced lignite-fired power plants. The concept was examined for the case of Greece. Two distinct case studies were selected, regarding the entity that makes the investment in PtM: a) the power plant owner case and b) the private investor case. The study focused on the estimation of the MeOH cost for a marginally feasible investment by fulfilling techno-economic criteria. In the case of the power plant owner the MeOH cost was estimated at 421€/tn MeOH and was about 40% lower than the cost calculated for the private investor case (580€/tn MeOH), due to the higher operating capacity of the H2 and MeOH plants and the lower electricity cost in the first case. The MeOH cost was further decreased in both cases by considering: a) large plant scales, b) low electricity cost, c) high operating time for the H2 and MeOH plants, d) low CO2 costs and/or e) low discount rates. Following the results for Greece, the power plant owner case was also examined for Germany and proved to be even more sustainable, due to the lower electricity cost in Germany.
•A PtM scheme in a lignite fired power plant can be regarded as an energy storage option.•The hydrogen related costs have the highest contribution to the total MeOH production cost.•The MeOH cost is estimated at 421€/tn MeOH for the power plant owner case.•The plant scale, the electricity cost, the operating time for MeOH plant, as well as the CO2 cost influence on the MeOH cost.•The respective results in Germany are proved to be even more sustainable, due to the lower electricity cost.
•The yields of included mineral matter-derived PM1 and PM10 follow a certain rank sequence.•The rank sequence is the HLH lignite>the PDS bituminous coal>the CZ anthracite.•Included siderite in the ...HLH lignite contributes to PM1 emission.
Three density-separated (1.4−1.6g/cm3) and size-fractioned (63−90μm) Chinese coals (HLH lignite, PDS bituminous coal and CZ anthracite), containing dominantly included mineral matter, were prepared and then combusted in a drop-tube furnace in air at 1400°C. Under the experimental conditions, the yields of particulate matter (PM) with aerodynamic diameters of <1μm (PM1), 1−10μm (PM1–10) and <10μm (PM10) as well as some key PM10-forming elements (e.g., Si, Fe and Mg) follow a rank sequence of the HLH lignite>the PDS bituminous coal>the CZ anthracite. Such a rank dependence is attributed to the discrepancies in the properties of included mineral matter in these coals and the coal combustion characteristics. The partition of Fe in the PM1 from the HLH lignite appears to result from the fragmentation and disintegration of included siderite during coal combustion.
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•Modified HY zeolites can significantly upgrade the coal pyrolysis volatiles.•Hydrothermal and acid treatment affect zeolite structure and upgrading performance.•The yields of ...naphthalene and methylnaphthalene increase 8.9 and 6.8 times.•The content of oxygenated PAHs is reduced by 4.3 times.
HY zeolite is modified by hydrothermal and HNO3 treatment and used as the catalyst to upgrade Baiyinghua pyrolysis volatiles on a fixed-bed reactor at 600 °C. The results show that hydrothermal and acid treatment obviously affect zeolite structure and upgrading of pyrolysis volatiles. The dealumination of HY increases with hydrothermal temperature, resulting in the decrease of total surface area and acid amount and the formation of larger pores. However, the content and yield of light tar are enhanced over modified HY, and the cracking of volatiles into gas is retarded. Acid treatment of hydrothermal modified HY at 650 °C removes extra-framework Al, improves surface area and the volatiles cracking. But high acid concentration leads to the destruction of zeolite structure, and is unfavorable to the upgrading. Modified HY by treatment at 650 °C and 0.8 mol/L HNO3 shows the best performance in catalytic volatiles upgrading. About 81.5 wt% light tar content and 61.1% light aromatic hydrocarbons content can be obtained. Especially, the yields of naphthalene and methylnaphthalene are increased by 8.9 and 6.8 times. The content of oxygenated PAHs is reduced by 4.3 times. The improved performance is mainly due to high surface area, large pore diameter and suitable acidity.
•Combustion of single char in a fluidized bed in O2/CO2 and O2/N2 was studied.•Four ranks of coal from lignite to anthracite and one wood were accessed.•Microstructure, combustion rate, burnout time, ...and maximum temperature reached of the char particle were analyzed.•Microstructure of the generated char particle after the devolatilization is independent on the atmosphere.
The effect of an oxy-fuel atmosphere on char conversion in a fluidized bed (FB) was examined by comparing measurements of single fuel particles exposed to O2/N2 and O2/CO2 atmospheres. The experiments were carried out in a transparent and electrically heated FB at 1088K and five O2 inlet concentrations (ranging from 0 up to 40%vol) using four ranks of coal (from anthracite to lignite) and one type of wood, all with 6mm (spherical) diameter. The evolution of temperature with time of the various fuels at different gas atmospheres and the microstructure of the char resulting after devolatilization are presented, from which the effect of the oxy-fuel atmosphere (changing CO2 by N2 at different fixed O2 concentrations) on char combustion characteristics is determined and analyzed. Results show that the apparent average combustion rate of a fuel particle decreases (and consequently the burnout time increases) when changing O2/N2 by O2/CO2. This effect was more significant at high O2 concentrations and most notable for anthracite. Consistently, the time to reach the peak temperature was longer when shifting from O2/N2 to O2/CO2. However, the char specific surface area, pore volume, and average pore diameter of char were not significantly modified by replacing N2 with CO2.
Humic substances readily identifiable in the environment are involved in several biotic and abiotic reactions affecting carbon turnover, soil fertility, plant nutrition and stimulation, xenobiotic ...transformation and microbial respiration. Inspired by natural roles of humic substances, several applications of these substances, including crop stimulants, redox mediators, anti-oxidants, human medicines, environmental remediation and fish feeding, have been developed. The annual market for humic substances has grown rapidly for these reasons and due to eco-conscious features, but there is a limited supply of natural coal-related resources such as lignite and leonardite from which humic substances are extracted in bulk. The structural similarity between humic substances and lignin suggests that lignocellulosic refinery resulting in lignin residues as a by-product could be a potential candidate for a bulk source of humic-like substances, but structural differences between the two polymeric materials indicate that additional transformation procedures allowing lignin architecture to fully mimic commercial humic substances are required. In this review, we introduce the emerging concept of artificial humification of lignin-related materials as a promising strategy for lignin valorization. First, the core structural features of humic substances and the relationship between these features and the physicochemical properties, natural functions and versatile applications of the substances are described. In particular, the mechanism by which humic substances stimulate the growth of plants and hence can improve crop productivity is highlighted. Second, top-down and bottom-up transformation pathways for scalable humification of small lignin-derived phenols, technical lignins and lignin-containing plant residues are described in detail. Finally, future directions are suggested for research and development of artificial lignin humification to achieve alternative ways of producing customized analogues of humic substances.
•Artificial humifications of lignin for versatile applications are discussed.•Top-down ways: alkaline oxidative hydrolysis, composting, vermicomposting, Fenton reaction and Mn-based oxidation.•Bottom-up ways: oxidative polymerization and sodium borohydride reduction.•Potential humification methods to be considered: ozonation, thermal degradation and fermentation with specific microbes.
•Study of co-combustion of sewage sludge with coal and biomass in pellet form, in air.•Analysis of influence of participation of sewage sludge on the total process time.•Correlation between decisive ...parameters about the course of the fuels combustion.
Increased sewage sludge production and disposal, as well as the properties of sewage sludge, are currently affecting the environment, which has resulted in legislation changes in Poland. Based on the Economy Minister Regulation of 16 July 2015 (Regulation of the Economy Minister, 2015) regarding the criteria and procedures for releasing wastes for landfilling, the thermal disposal of sewage sludge is important due to its gross calorific value, which is greater than 6MJ/kg, and the problems that result from its use and application. Consequently, increasingly restrictive legislation that began on 1 January 2016 was introduced for sewage sludge storage in Poland.
Sewage sludge thermal utilisation is an attractive option because it minimizes odours, significantly reduces the volume of starting material and thermally destroys the organic and toxic components of the off pads. Additionally, it is possible that the ash produced could be used in different ways. Currently, as many as 11 plants use sewage sludge as fuel in Poland; thus, this technology must be further developed in Poland while considering the benefits of co-combustion with other fuels.
This paper presents the results of experimental studies of the mechanisms and kinetics of sewage sludge, coal and biomass combustion and their co-combustion in spherical-pellet form. Compared with biomass, a higher temperature is required to ignite sewage sludge by flame. The properties of biomass and sewage sludge result in the intensification of the combustion process (by fast ignition of volatile matter). In contrast to coal, a combustion of sewage sludge is determined not only burning the char, but also the combustion of volatiles. The addition of sewage sludge to hard coal and lignite shortens combustion times compared with coal, and the addition of sewage sludge to willow Salix viminalis produces an increase in combustion time compared with willow alone.
•Effect of addition of four different ionic liquids into NMP on the extraction yield of coal was investigated.•Coal and ILs type affected the extraction yield.•Adding ILs into NMP showed high ...performance for the extraction of lignite, but not effective for bituminous coal.•BmimCl was a more efficient ILs for the extraction of lignite.
In this work, two Turkish coals were extracted with N-methyl-2-pyrrolidone (NMP) and NMP containing a small amount of ionic liquids (ILs) under reflux conditions at atmospheric pressure. The effects of coal type, ionic liquid type, ionic liquid-to-coal ratio, and ultrasonic interactions on extraction yield were investigated. The ILs used were: 1-butyl-3-methylimidazolium chloride (BmimCl), 1-buty-4- methylpyridinium chloride (BmpCl), 1-ethyl-3-methylimidazolium chloride (EmimCl), and 1-butyl-2,3-dimethylimidazolium chloride (BdmimCl). It was found that the extraction yield of coals using NMP/ILs varied with coal type, IL type and amount of IL. ILs were effective on the extraction of Afsin-Elbistan (AE) lignite, but not on the extraction of Üzülmez (UZ) coal. A significant increase in extraction yield for AE lignite was observed when a small amount of IL was added into NMP. It was determined that BmimCl was the most efficient IL used for the extraction of lignite compared to the others ILs used, and the extraction efficiency was found to increase by increasing the amount of ionic liquid added into NMP.
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•The mass balance of the hydrochar was calculated.•The texture characteristics of hydrochar was also calculated.•The combustion performance of hydrochar was improved.•Alkali/alkaline ...earth metal were removed, while heavy metals had accumulation.
This study provided a detailed observation on hydrothermal carbonization (HTC) of Chinese fan palm. The heating value and chemical exergy was calculated. As the reaction severity increased, both heating value (18.84–27.61 MJ/kg) and chemical exergy (21.07–29.06 MJ/kg) had increase trend. The effect of temperature on HTC process was more significant than residence time. Due to the dehydration and decarboxylation, the O/C and H/C atomic ratios decreased gradually. However, the N/C ratio was not linear change. When the temperature was 240 °C, and reaction time was above 60 min, the fuel properties of hydrochar were close to lignite. The water uptake rate (7.22–3.59%) also had very decreased trend. The SEM and XRD analysis showed the surface morphology of hydrochar treated at 240 °C much differed from that of raw sample, the structure is partially destructed. Combustion characteristics of CFP and hydrochar was detected, the 180–60 had optimal combustion characteristics.
