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Propagation characteristics of reverse combustion significantly impact the conversion of solid fuels in packed beds, especially under variable reaction atmosphere conditions. In this study, the propagation of reverse combustion was experimentally studied in an oxygen-limited and -enriched O 2 /N 2 flow with an oxygen concentration range of 21–100 % for a bed packed with rice husk. The temperature profile measured by thermocouples along the bed height was processed to appreciate the driving mechanism of combustion front, as well as the reaction structure inside the bed. Besides, the contribution of volatiles gas-phase oxidation and char surface oxidation to reverse combustion was also evaluated. Results show that compared to the air case, an oxygen-enriched condition broadens the operating range of oxygen flow rate for the oxygen-limited reverse combustion. Under high oxygen concentration conditions, the low-temperature oxidation of rice husk inside the reaction front becomes enhanced. Such chemical reaction effect widens the whole reaction front thickness and thereby reduces the oxidation intensity in local regions, resulting in a faster ignition rate and a lower temperature for combustion front. It is found that this process is dominated by the gas-phase oxidation of volatiles, of which oxygen consumed is above 60 % of the supplied. As oxygen concentration increases, the gas-phase oxidation of volatiles becomes further enhanced. Correspondingly, the oxidation ratio of char is gradually approaching a limit, about 12 %, especially at the oxygen concentration above 50 %. These findings will facilitate a better fundamental understanding of driving mechanism of this special combustion process and thereby provide an important theoretical basis for efficient thermal conversion of solid fuels. [ABSTRACT FROM AUTHOR]

Gradation and quality utilization of low-rank coal is promising. In this study, a special counter-current combustion process, characterized by a combustion front traversing the bed against the air supply direction, was innovatively proposed to achieve the carbonization and activation of low-rank coal. This combustion process was first analysed experimentally in a fixed bed test rig. At an air equivalence ratio as low as 0.25, this combustion process was of a front temperature of 889 °C and self-sustainedly traversed the fuel bed at a propagating rate of 0.33 m/h. Accompanied by its propagation, about 82.5% of volatile matter inside the coal was removed. Due to different reaction phases inside the bed, the solids were in-situ activated by self-produced active components. Based on this, intensification experiments of carbonization and activation were carried out in a moving bed test rig. By moving the bed, the heat transfer near the combustion front tended to a quasi-equilibrium state and the residence time of the solids in the high temperature zone was greatly prolonged. The carbonization and activation effects on the solids were promoted. The carbonization effect almost approached the limit because the removal ratio of volatile matter inside the coal was as high as 98.4%. When external heating and active substances intervened, activation reactions of the solids (namely, C–H 2 O and C–CO 2) were intensified in the char reaction phase. The specific surface area and pore volume of the activated char increased up to 594 m2/g and 0.371 cm3/g. Correspondingly, its adsorption values of iodine and methylene blue were 732 and 76 mg/g. This work provides a technical solution for the in-situ high-quality utilization of low-rank coal. • A method to carbonize and activate coal by a combustion process is proposed. • Dynamically propagating combustion front removes 98.4% of volatile matter. • Activation of solids is related to bed structure with different conversion zones. • Intervention of auxiliary heating and active substances promotes the activation. [ABSTRACT FROM AUTHOR]

Ethnopharmacological relevance Orthosiphon stamineus (OS), a traditional Chinese herb, is often used for promoting urination and treating nephrolithiasis. Aim of the study Urolithiasis is a major worldwide public health burden due to its high incidence of recurrence and damage to renal function. However, the etiology for urolithiasis is not well understood. Metabonomics, the systematic study of small molecule metabolites present in biological samples, has become a valid and powerful tool for understanding disease phenotypes. In this study, a urinary metabolic profiling analysis was performed in a mouse model of renal calcium oxalate crystal deposition to identify potential biomarkers for crystal-induced renal damage and the anti-crystal mechanism of OS. Materials and methods Thirty six mice were randomly divided into six groups including Saline, Crystal, Cystone and OS at dosages of 0.5 g/kg, 1 g/kg, and 2 g/kg. A metabonomics approach using ultra-performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) was developed to perform the urinary metabolic profiling analysis. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were utilized to identify differences between the metabolic profiles of mice in the saline control group and crystal group. Results Using partial least squares-discriminant analysis, 30 metabolites were identified as potential biomarkers of crystal-induced renal damage. Most of them were primarily involved in amino acid metabolism, taurine and hypotaurine metabolism, purine metabolism, and the citrate cycle (TCA). After the treatment with OS, the levels of 20 biomarkers had returned to the levels of the control samples. Conclusions Our results suggest that OS has a protective effect for mice with crystal-induced kidney injury via the regulation of multiple metabolic pathways primarily involving amino acid, energy and choline metabolism. [ABSTRACT FROM AUTHOR]