Paliva (Fuels) is a scientific journal issued quarterly by the Faculty of Environmental Technology, ICT Prague. Fuels publishes papers on a broad range of topics covering exploitation, processing, upgrading, and utilization of various types of fuels, and power engineering.
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Current issue

4/2025

Construction and testing of the combined adsorption-methanation unit

Marek Staf, Karel Ciahotný, Anatoli Shestak, Pavel Hron, Ondřej Hlaváček
Possibilities for partial utilization of carbon dioxide, which is produced by burning fossil fuels, biomass, waste, etc., have been recently sought. The Power-to-Gas (P2G) conception, in which the captured CO2 is converted into methane using hydrogen produced from nonfossil
sources, such as water electrolysis using surplus electricity in distribution networks, is one of the ways. However, surplus energy fluctuates strongly during the day and calendar year, which negatively affects the efficiency and financial return of P2G. The article is devoted to the development of a test unit that allows capturing CO2 from flue gases and converting it in-situ to methane (in the same reactor), if an adequate amount of hydrogen is available. Conversely, in the event of H2 shortage, the system produces concentrated CO2 suitable for  compression and, for example, geological storage. The paper contains a detailed description of the self-designed test stand, which both simulates the conditions in the considered real operating facility very well (at the TRL 5 level) and is compact enough to be easily transported as a single module to an industrial source of flue gases. Two adsorbents/catalysts based on nickel-modified substrates gamma−Al2O3 and Envisorb B+ were developed. After preliminary laboratory tests including measurements of adsorption capacities, structural stability, optimization of working media dosing, etc., the system was transported to the Ško-Energo, s.r.o. plant. After the installation and activation of the stand and all peripherals, intensive tests are underway at the time of publication of the paper, which verify the laboratory results and will allow the  level of technological readiness to be increased to the TRL6 value within the framework of subsequent development. However, the first phase of testing has already provided valuable data on the unit and the designed sorbents/catalysts..The stand has proven to be fully functional in terms of combining CO2 adsorption and its subsequent reaction to methane within a single reactor. The gamma−Al2O3-based sorbent/catalyst showed promising conversion at an average of 72%. In contrast, the material prepared from the commercial adsorbent Envisorb B+ proved unsuitable for the given purpose with a conversion of 2.8% only. Further tests will address the improvement of the still low adsorption capacity (approximately 0.5% by weight) by switching to a higher-pressure level than the atmospheric one used so far.
Keywords: adsorption, catalysis, methanation, carbon dioxide, flue gas, fixed bed
4/2025 - pages 71 - 80DOI: 10.35933/paliva.2025.04.01

Effect of mixing on rheological and structural changes in sludge during thermal hydrolysis

Anna Cardova, Pavel Jenicek, Lise Appels

Thermal hydrolysis (THP) is an established pretreatment method to enhance sludge biodegradability and dewaterability, yet the specific impact of mixing during THP on its efficiency remains unclear. This study systematically compared THP of waste activated sludge with and without mechanical mixing under identical thermal conditions (160 °C, 30 min) to evaluate sludge solubilization (dissolved solids and soluble COD release), disintegration degree, extracellular polymeric substance (EPS) degradation, sludge rheology, and dewaterability. The results showed that mixing enhanced thermal disruption, increasing soluble COD by ~60% and disintegration degree from 12.4% to 20.0%. Combined mixing and heating reduced viscosity and particle size, indicating enhanced floc fragmentation and improved fluidity. Surprisingly,  however, this enhanced fragmentation did not translate into improved dewaterability. The centrifuged cake solids content was 12.7% for mixing and heating, which was slightly lower than the 13.7% for the heating-only treatment. These results demonstrate that mechanical shear synergistically enhances sludge disintegration during THP, yet mixing may hinder solid–liquid separation in the downstream treatment. Further evaluation under realistic THP operating conditions (≈16 % solids, including flash phase) is recommended to identify the optimal balance between disintegration and dewaterability. 

Keywords: degree of disintegration, dewaterability, extracellular polymeric substances, mechanical mixing, particle size distribution, thermal hydrolysis pretreatment, viscosity
4/2025 - pages 81 - 88DOI: 10.35933/paliva.2025.04.02

Characterization of biochar derived from demineralized poultry litter in terms of its candidacy towards alternative solid fuel

Kevin Nyoni, Leungo Kelebopile

An increase in global energy demand results in coal dependance which contributes to greenhouse gas emissions. Poultry litter is a potential substitute, but its poor physicochemical and combustion properties reduce its combustion efficiency; hence, demineralization and pyrolysis to biochar value-adds. The study analyzed the characterization of biochar derived from demineralized PL and selected the best-suited combustion technology. The PL was mechanically fractioned (4 mm) and leached in deionized water and pyrolyzed (300 ℃; 15 min). The biochar physicochemical properties improved the higher heating value (22.31 MJ kg-1) and reduced the Ash Content (18.63 %) compared with undemineralized biochar. Increase in TGA/DTG heating rate shifted the reaction region to high temperature (58.57–548.93 ℃) reducing the ease of ignition and combustion. The biochar has high fouling and slag tendency, and the fluidized bed combustion chamber was the preferred chamber technology. Mass of air at 7.83 kg kg-1 fuel is required to combust the biochar and produce 3.26 kg kg-1 fuel of flue gas. Flue gas produced with 25 % excess air produced a higher enthalpy than stoichiometric conditions, attaining a thermal efficiency of 86.20 %. Demineralized PL biochar exhibits excellent physicochemical and combustion properties making it an ideal fuel candidacy.

Keywords: biochar; combustion properties; demineralized poultry litter; fluidized bed combustion; physicochemical characterization; thermal behavior.
4/2025 - pages 89 - 110DOI: 10.35933/paliva.2025.04.03


technical support editor-in-chief