Search Results (70)

In arid and water-stressed regions, groundwater desalination plants are critical for ensuring reliable potable water supplies, making improvements in their operational efficiency and cost effectiveness a priority for utilities. In many such facilities, lime and soda ash softening remain common pretreatment practices, which increase chemical consumption and sludge generation, prompting the need for alternative low-chemical strategies. This study evaluates the technical, operational, and economic implications of transitioning a full-scale brackish groundwater desalination plant, from lime–soda ash softening (old plan) to a low-chemical pretreatment strategy based on antiscalant dosing (new plan) upstream of reverse osmosis (RO). Key parameters, including pH, total hardness, calcium and magnesium hardness, silica, iron, alkalinity, and total dissolved solids (TDS), were measured and compared at multiple locations within the treatment plant under both the old and new plans. Removing lime and soda ash caused higher levels of hardness, alkalinity, and silica in the water before RO treatment, increasing the risk of scaling. Operationally, the feed pressure increased from 11.43 ± 0.16 bar (old plan) to a peak of 25.50 ± 0.10 bar in the new plan, accompanied by a decline in water production. Chemical cleaning effectively restored performance, reducing feed pressure to 13.13 ± 0.05 bar, confirming that fouling and scaling were the primary, reversible causes. Despite these challenges, the plant consistently produced water that complied with Saudi Standards for Unbottled Drinking Water (e.g., pH = 7.18 ± 0.09, TDS = 978.27 ± 9.26 mg/L). Economically, the new strategy reduced operating expenditure by approximately 54% (0.295 → 0.135 $/m³), largely due to substantial reductions in chemical and sludge handling costs, although these savings were partially offset by higher energy consumption and more frequent membrane maintenance. Overall, the findings emphasize the importance of systematic performance evaluation during operational transitions, providing guidance for utilities seeking to optimize pretreatment design while maintaining compliance, long-term membrane protection, and environmental sustainability. Full article

The thermal transformation mechanism of pyrite in coal, which governs sulfur emissions and ash deposition, remains highly controversial. There are significant discrepancies in reported activation energies (E_a) (60–310 kJ/mol) and conflicting reaction pathways. To resolve these long-standing controversies, this study proposes a competition-coupling mechanism: pyrolysis and oxidation compete under local O₂ and temperature gradients, while coupling through microstructural evolution. Specifically, pyrolysis generates a porous Fe_1−XS that facilitates oxidation, which in turn can form a passivating oxide/sulfate layer that promotes further pyrolysis. This mechanism reconciles longstanding kinetic controversies by showing that the apparent activation energy is not a fixed value but instead a dynamic parameter, shifting along a continuous curve that bridges pyrolysis and oxidation-dominated regimes. Furthermore, we construct a unified phase diagram by incorporating the competition-coupling mechanism into classical thermodynamic equilibria. This diagram uses the molar ratio FeS₂/(FeS₂ + O₂) and temperature to categorize the transformation process into four distinct regions—pyrolysis-dominated, competition-coupling, oxidation-dominated, and melt-dominated. The key contribution of this work lies in the diagram which offers a practical framework for optimizing combustion and roasting systems, allowing for improved control over sulfur emissions and ash-related issues such as slagging and fouling. Full article

Advancing circular bioeconomy in thermochemical biorefineries requires species-specific data that link biomass composition and thermochemical performance. Here, we provide the first integrated thermochemical dataset for Quercus pubescens bark combining FT-IR, XRD, XRF, TGA, and measured ash fusion temperatures (AFT). The results reveal that bark is enriched in phenolic extractives (21.2%) and inorganics (15%), with calcium oxalate monohydrate (COM) dominating the inorganic fraction, as confirmed by FT-IR and XRD. Thermal decomposition occurs between 150 °C and 690 °C. Pyrolysis follows diffusion-controlled kinetics, with apparent activation energies for bark and its fractions ranging between 70 and 103 kJ mol⁻¹. Extraction increases the activation energy of bark. The ash exhibits a high AFT (softening: 1421 °C, flow: 1467 °C), placing this feedstock within the low-slagging, moderate-fouling range compared to other lignocellulosics. The observed COM-to-CaCO₃/CaO transformation upon heating contributes to the elevated AFT. Reactivity analyses of bark fractions support thermochemical biorefinery routing of fractions: extracted bark (EB) and desuberinised bark (DB) are highly reactive and well-suited to combustion/gasification, whereas raw bark (B) and Klason lignin (KL) exhibit higher thermal stability and yield more persistent char, favoring slow pyrolysis for biochar production. Such routing strategies optimize energy recovery and also enable co-products with environmental co-benefits. Full article

Blending kaolin is an effective method to alleviate fouling and slagging during the combustion of Zhundong coal. The influence of blending kaolin with varying particle sizes on the adsorption behavior of alkali metal sodium and the ash fusion characteristics was studied using sodium capture experiments and ash fusion temperature tests. The results indicate that kaolin particle size is a critical factor influencing sodium retention. As the particle size decreases, the sodium retention rate increases accordingly. In the absence of kaolin, the sodium retention rate was only 28.03%. However, when 75–100 µm particles of kaolin were added, the retention rate increased to 43.49%. Further reducing the particle size to 20–63 µm resulted in an additional increase of 10.51%. Additionally, decreasing the kaolin particle size contributed to the noticeable increase in ash fusion temperatures. After 75–100 µm kaolin was blended, the DT and FT of the ash were 1137 °C and 1161 °C, respectively. With 20–63 µm kaolin, the DT increased by 42 °C, and the FT increased by 36 °C. This trend is attributed to the enhanced decomposition and transformation of sulfates in the ash, which promotes the formation of high-melting-point feldspar minerals such as anorthite and gehlenite. These findings provide important data support for understanding the influence of kaolin particle size on the ash fusion behavior during the combustion of Zhundong coal. Full article

The demand for clean energy to improve waste valorization and enhance resource utilization efficiency has been increasingly recognized in the last few years. In this context, the co-carbonization of different waste streams, aiming at solid fuel production, appears as a potential strategy to address the challenges of the energy transition and divert waste from landfills. In this work, refuse-derived fuel (RDF) samples were subjected to the co-carbonization process with low-quality animal fat waste in different proportions to assess the synergistic effect of the mixture on producing chars with enhanced fuel properties. Dry (DC) and hydrothermal carbonization (HTC) tests were conducted at 425 °C and 300 °C, respectively, with a residence time of 30 min. The RDF sample and produced chars with different animal fat incorporation were analyzed for their physical, chemical, and fuel properties. The results demonstrated that increasing the fat proportion in the samples leads to an increase in mass yield and apparent density of the produced chars. Furthermore, char samples with higher fat addition presented a proportional increase in high heating value (HHV). The highest values for the HHV corresponded to the char samples produced with 30% fat incorporation for both carbonization techniques (27.9 MJ/kg and 32.9 MJ/kg for dry and hydrothermal carbonization, respectively). Fat addition also reduced ash content, improved hydrophobicity in hydrochars, and lowered ignition temperature, although additional washing was necessary to reduce chlorine to acceptable levels. Furthermore, fat incorporation reduced concentrations of elements linked to slagging and fouling. Overall, the results demonstrate that incorporating 30% fat into RDF during DC or HTC is the most effective condition for producing chars with improved physical, chemical, and fuel properties, enhancing their potential as alternative solid fuels. Full article

Ash deposition on economizer heating surfaces degrades convective heat transfer efficiency and compromises boiler operational stability in coal-fired power plants. Conventional time-scheduled soot blowing strategies partially mitigate this issue but often cause excessive steam/energy consumption, conflicting with enterprise cost-saving and efficiency-enhancement goals. This study introduces an integrated framework combining real-time ash monitoring, dynamic process modeling, and predictive optimization to address these challenges. A modified soot blowing protocol was developed using combustion process parameters to quantify heating surface cleanliness via a cleanliness factor (CF) dataset. A comprehensive model of the attenuation of heat transfer efficiency was constructed by analyzing the full-cycle interaction between ash accumulation, blowing operations, and post-blowing refouling, incorporating steam consumption during blowing phases. An optimized subtraction-based mean value algorithm was applied to minimize the cumulative attenuation of heat transfer efficiency by determining optimal blowing initiation/cessation thresholds. Furthermore, a bidirectional gated recurrent unit network with quantile regression (BiGRU-QR) was implemented for probabilistic blowing time prediction, capturing data distribution characteristics and prediction uncertainties. Validation on a 300 MW supercritical boiler in Guizhou demonstrated a 3.96% energy efficiency improvement, providing a practical solution for sustainable coal-fired power generation operations. Full article

High ash content in algal biomass limits its suitability for biofuel production by reducing combustion efficiency and increasing fouling. This study presents a green deashing strategy using nitrilotriacetic acid (NTA) and deionized (DI) water to purify Scenedesmus algae, which was selected for its high ash removal potential. The optimized sequential treatment (DI, NTA chelation, and DI+NTA treatment at 90–130 °C) achieved up to 83.07% ash removal, reducing ash content from 15.2% to 3.8%. Elevated temperatures enhanced the removal of calcium, magnesium, and potassium, while heavy metals like lead and copper were reduced below detection limits. CHN analysis confirmed minimal loss of organic content, preserving biochemical integrity. Unlike traditional acid leaching, this method is eco-friendly after three cycles. The approach offers a scalable, sustainable solution to improve algal biomass quality for thermochemical conversion and supports circular bioeconomy goals. Full article

With the rapid development of renewable energy, the co-combustion of Zhundong coal and biomass has attracted more and more attention. However, the high content of alkali metals in Zhundong coal and biomass leads to serious slagging and fouling in the co-combustion process. In this study, cotton straw was selected for co-combustion with Zhundong coal. The ash deposition model was established according to the melting ration calculated by Factsage, and the ash deposition characteristics during the co-combustion of Zhundong coal and cotton stalks in the actual boiler were explored by Fluent. The results showed that the K₂O content in ash increased from 0.31% to 9.31% with the increase in the blending ratio, while the contents of other components had no significant changes. In addition, with the increase in the blending ratio, the ash deposition rate increased from 0.00327 kg/(m²·s) to 0.00581 kg/(m²·s), an increase of 77.6%. The reduction in the tangential circle diameter obviously alleviated the ash deposition on the wall. When the tangential circle diameter was reduced to 400 mm, the ash deposition rate was 0.00207 kg/(m²·s), which was 37.6% lower than the original condition. Full article

Combustion of Zhundong coal in utility boilers is frequently challenged by ash-related issues (fouling/slagging) and stringent NO emission control requirements. This study conducted numerical simulations to investigate burner configuration effects, specifically yaw angle adjustments (modulating the imaginary tangential circle diameter, ITCD) and downward tilt angles, on the NO emissions and slagging propensity in a 330 MW subcritical tangentially fired boiler. The results reveal a compromise mechanism between NO emission control and furnace slagging mitigation. ITCD reduction via yaw angle optimization increases furnace exit NO concentrations by 1.5–3% but decreases total deposition rates by 1.3–2%. By altering the burner downward tilt angle to 15° and 25°, NO emissions increase by 8% and 19%, respectively, with about a 7% reduction in total particle deposition rate. An optimal burner yaw and tilt angle is identified to achieve a compromise between NO emission and furnace slagging control. The findings provide some guidance for the combustion optimization of Zhundong coal-fired boilers. Full article

To investigate the effect of NiCrTi coating on the ash condensation characteristics of high-alkali coal in Xinjiang South Mine, we first built an experimental rig for high-alkali-coal flue gas condensation and carried out experimental research on high-alkali-coal flue gas condensation. Physicochemical characterization of the initial layer of the ash deposit (initial deposit) condensation products was also carried out using XRD, SEM, and EDX. Finally, the priority of products generated on the surface of NiCrTi coating and the three-phase diagram of Na₂O-SiO₂-Al₂O₃ were analyzed by using FactSage 8.3 thermodynamic software. The results show that the condensation products in the initial deposits layer of 15CrMo alloy contain other sodium salts, such as sodium feldspar (NaAlSi₃O₈), NaCl, and Na₂SO₄, and that other protective oxides, such as Cr₂O₃, NiCr₂O₄, and TiO₂, are formed on the surface of the NiCrTi coating. At the same time, the condensation experiment allows the fouling phase to be divided into four parts. Secondly, it was found that the densely flaky particles on the surface of NiCrTi coatings not only have excellent anti-fouling properties but also can effectively inhibit the penetration of other elements such as S. Finally, the reaction priority of protective oxides on NiCrTi coatings was calculated by FactSage 8.3 and found to have the following order: NiCr₂O₄ > Cr₂O₃ > TiO₂. The results of this paper provide theoretical support for the development of anti-staining NiCrTi coatings. Full article

Biomass combustion in small-scale boilers in Eastern Europe has recently become a very popular heating option. Biomass boilers are gradually replacing old, coal-fired installations, especially in the domestic sector. In comparison with coal, biomass contains more phosphorus, chlorine, and potassium, which may cause the corrosion, slagging, and fouling of heating surfaces inside the combustion chamber. Such problems may be reduced by properly controlling the combustion process, as well as adding substances like halloysite to the fuel. This paper presents the results of adding halloysite to wood pellets made of coniferous wood, rape straw, and wood/rape blend in the combustion process of a 25 kW retort boiler. The results demonstrate that adding halloysite to biomass increases the ash sintering temperature, which may, in turn, reduce slagging. The addition of halloysite also reduces the KCl concentration in the ash and the total solid compounds, potentially lowering the risk of corrosion in the boiler. A slight reduction in CO, OGC, and SO₂ concentrations was observed for rape straw biomass pellets with the halloysite addition. Moreover, the experimental results indicate that the addition of halloysite to fuel may influence boiler efficiency, especially during the combustion process of agricultural biomass and its blends. Full article

The aim of this study is to predict the ash fusion temperatures of the lignite ash produced in Western Macedonia, Greece, by their composition. The lignite mined in northwest Greece feeds the power plants of Agios Dimitrios, Kardia, Ptolemais, Amyntaio, and Meliti. An extensive number of samples, which were collected by the feeders of power plants during a 10-year period, were investigated. All lignite ashes were mineralogical and chemically quantitatively analyzed by XRD and XRF, respectively. Using a heating microscope, the ash fusion temperatures of the ashes were identified. According to their chemical composition, ashes can be characterized as calcareous. Indices based on the chemical composition showed that, qualitatively, the tendencies of slagging and/or fouling were found to vary mainly between medium to high. For a quantitative estimation, correlations were identified between the quantitative mineralogical composition and the ash fusion temperatures using regression analysis. The whole study focused on creating a model for the prediction of lignite behavior during combustion in power plants. The finest models achieved a mean adjusted regression coefficient of around 0.87, while the accuracy, according to root mean square errors, was less than 40 °C. Full article

The present study aims to resolve the existing research gaps on olive pomace (OP) hydrochars application as a fuel by evaluating its molecular structures (FTIR and solid NMR analysis), identifying influential characteristics (Pearson correlation analysis), process optimization (response surface methodology), slagging–fouling risks (empirical indices), and combustion performance (TG-DSC analysis). The response surfaces plot for hydrothermal carbonization (HTC) of OP slurry performed in a pressure reactor under varied temperatures (180–250 °C) and residence times (2–30 min) revealed 250 °C for 30 min to be optimal conditions for producing hydrochar fuel with a higher heating value (32.20 MJ·Kg⁻¹) and energy densification ratio (1.40). However, in terms of process efficiency and cost-effectiveness, the optimal HTC conditions for producing the hydrochar with the highest energy yield of 87.9% were 202.7 °C and 2.0 min. The molecular structure of hydrochar was mainly comprised of aromatic rings with methyl groups, alpha-C atoms of esters, and ether bond linkages of lignin fractions. The slagging and fouling risks of hydrochars were comparatively lower than those of raw OP, as indicated by low slagging and fouling indices. The Pearson correlation analysis emphasized that the enrichment of acid-insoluble lignin and extractive contents, carbon densification, and reduced ash content were the main pivotal factors for hydrochar to exhibit better biofuel characteristics for energy applications. Full article

Napier grass is a herbaceous biomass that can be used as biofuel; however, its high ash, potassium, sulfur and chlorine content may cause problems when combusted. Napier grass was submitted to vapothermal carbonization (VTC) and hydrothermal carbonization (HTC) processes at 190 and 220 °C to compare their ability to enhance its fuel properties. The different water distribution between phases in the two processes was verified: up to 14.5% of the water vaporized to steam in the VTC ran at 220 °C, while over 99% of the water remained in the liquid state and in contact with the solids during all HTC runs. Both processes improved the calorific value of the Napier grass (up to 20.6% for VTC220 and up to 29.8% for HTC220) due to the higher C content in the chars. Both processes reduced the sulfur content, removing up to 15.3% of it with VTC190 and 28.5% of it with HTC190 compared to that of Napier grass. In contrast, the two processes had different effects on the ash and chlorine content. While HTC removed both ash and Cl from the Napier grass, VTC concentrated it in the chars (ash: 5.6%wt. Napier grass, 3.3%wt. HTC chars, 7.1%wt. VTC; chlorine: 1.08%wt. Napier grass, 0.19%wt. HTC chars, 1.24%wt. VTC). Only the HTC process leached high percentages of Cl (up to 80%), S (up to 70%), sodium (Na, up to 80%) and potassium (K, up to 90%) into the process water. This may prevent fouling and slagging problems when burning HTC char. The biofuel qualities of the raw Napier grass, VTC, and HTC chars were evaluated using two standards: the international standard for solid biofuels, EN ISO 17225, and the Korean regulation for biomass solid recovered fuels (Bio-SRF). Napier grass and VTC chars presented problems regarding Cl content thresholds for both EN ISO 17225 and Bio-SRF. Both VTC and HTC chars along with the Napier grass fulfilled the requirements for heavy metals (Pb, Ni, Cr, and Cd) except for copper. The choice of process in practical applications will depend on the goal; HTC improves fuel quality and VTC has higher high solid, carbon and energy yields. Full article

The use of biomass can be a strategic way to realize a carbon-neutral energy plan, ensuring a fuel feedstock. Residual biomass arising from pruning is demonstrated to be an important energy resource in terms of quantity and quality. In the Salento peninsula, Apulia Region, in the south of Italy, a dramatic outbreak of Xylella fastidiosa has decimated olive trees since 2013, gaining a considerable amount of wood biomass. This paper, starting from the need to find a way to optimize the use of this available stock, reviews the main technologies on the utilization of olive wood for energy purposes. In particular, processes and products are here described, and an energy analysis compares lower heating value (LHV), higher heating value (HHV), mass yield, process operating conditions, and energy generated and spent by the process in order to find the most effective technology in order to optimize the energy use of olive biomass. The conclusions show the advantages and disadvantages of each technology. Pyrolysis performs well, showing the best results for both char HHV and syngas yield under different operating conditions. Gasification seems to be the most appropriate among conversion technologies to optimize olive tree pruning for energy purposes, as it can be used to produce both electrical and thermal energy. In terms of economic valorization, char is the most promising material representing a value-added product, the quality and versatility of which ranges from fuel to soil improvers and additives for the construction of supercapacitors. Conversely, its disadvantages are mainly represented by high ash content, which can slightly decrease the boiler efficiency. Finally, the amount of alkali metals can produce several problems, such as fouling, slagging, corrosion, etc., posing a challenge for combustion control and pollutant minimization. Full article