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Pressurized oxy-fuel combustion is recognized as the second generation of oxy-fuel combustion technology that can facilitate carbon capture and reduce energy consumption, while coal and biomass combustion is also an effective way to decrease carbon emissions. This study innovatively integrates these two clean combustion technologies and investigates the effects of pressure and blending ratio on the combustion characteristics (ignition, combustion rate, volatile combustion, semi-coke combustion, burnout) of coal, biomass and their blends using an advanced magnetic levitation HPTGA. The results show that pressurization can improve the combustion rate of coal and biomass, but it will cause ignition delay when system pressure exceeds 0.5 MPa. The effect of pressure on combustion characteristics is both facilitative and inhibitive, in terms of reaction kinetics, pressurization can significantly promote combustion but it also plays a role in inhibiting oxygen diffusion, the competition between the two effect leads to an optimum value of pressure in the combustion performance of the blends, which is about 1 MPa. Biomass is more sensitive to pressure than coal, and pressurization changes the ignition mode of biomass. In addition, a new synergy index is defined to quantify the synergistic effect of the whole co-combustion process. Pressurization could suppress both catalytic and non-catalytic mechanisms in the co-combustion process, and different sensitivities of biomass and coal to pressurization lead to more significant differences in combustion time and temperature interval compared with normal pressure, all these factors contribute to negative synergistic effect under pressurization. • Pressurized oxy-fuel combustion performance of coal and biomass individually and co-firing was explored in 0.1–2.0 MPa. • Pressurization changes the ignition mechanism of biomass, whereas coal consistently exhibits heterogeneous ignition in 0.1–2.0 MPa. • A new synergy index was defined to quantify the synergistic effect of the whole co-combustion process. • The pressurized co-combustion presents a negative synergistic effect, which tends to increase with the rising pressure. [ABSTRACT FROM AUTHOR]

• Pressurized oxy-fuel combustion performance of a typical bituminous coal is investigated. • The thermodynamics parameters and the most probabilistic kinetic model for the pressurized oxy-fuel combustion process are analyzed. • Elevating pressure can significantly improve the combustion performance of coal but the promotion effect gradually alleviates. • The ignition mechanism transforms from heterogeneous to homogeneous when the oxygen concentration reaches 50% at 0.5 MPa. Pressurized oxy-fuel combustion is one of the emerging clean technologies that can efficiently separate and recover CO 2 , and this combustion mechanism differs significantly from atmospheric air combustion. In this paper, the effects of reaction conditions such as total pressure, oxygen concentration and atmosphere gas composition on the combustion characteristics of Xinjiang Bostan coal were investigated using thermogravimetric methods. Furthermore, the thermodynamics parameters and the most probabilistic kinetic model for the pressurized oxy-fuel combustion process were explored. The results showed that the system pressure rising from 0.1 to 1 MPa could enhance the combustion process of coal; however, when the system pressure exceeds 0.5 MPa, the promoting effect is clearly weakened. The ignition mechanism transforms from heterogeneous to homogeneous when the oxygen concentration reaches 50% at 0.5 MPa. The mechanism functions of pressurized oxy-fuel combustion reaction varied as the reaction progressed. In addition, the rise of pressure and oxygen concentration correspond to the higher chemical reaction order of pulverized coal combustion and the pressure has less influence on the reaction mechanism than oxygen concentration. The results obtained may assist with the optimization of pressurized oxy-fuel combustion and guide its industrial applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract To study the characteristics of positive and negative DC discharge under coal pyrolysis gas media at 20 °C–600 °C, the I V characteristics and the current composition are analyzed under different conditions. Due to the difference of ionization mechanism, the corona onset voltage of negative corona is lower than that of positive corona under air gas medium. Under non-electronegative gas media, no corona occurs during negative discharge. However, during positive discharge, with the increase of output voltage, three types of discharge are successively observed, namely corona, glow and arc. Under N 2 gas media and at 400 °C, the maximum collection efficiency of positive electrostatic precipitator is 98%, while that of negative electrostatic precipitator is 82%. When the collection efficiency is 70%, the energy consumption index of negative electrostatic precipitator is about 200 times higher than that of positive electrostatic precipitator. A linear relationship between I/V and V is observed and the ionic mobility can be calculated through the slope. At 350 °C, the ionic mobility under H 2 gas medium is 5.25 cm2/(V*s) while the ionic mobility under N 2 gas medium is 0.1 cm2/(V*s). The ionic mobility is proportional to the absolute temperature according to the discharge experimental data at 350 °C–600 °C. The factor β i , which is only related to gas media, is 0.0001653 cm2/(V*s*T) for N 2 and 0.0087308 cm2/(V*s*T) for H 2. These results assist in understanding the property of ESP at high temperatures. Graphical abstract Unlabelled Image Highlights • Under coal pyrolysis gas medium, corona only occurs in positive discharge. • Under N 2 gas medium, the positive ESP is better than negative ESP. • The ionic mobility under H 2 is about 52 times higher than that of N 2. [ABSTRACT FROM AUTHOR]

Hydrogen production from rice husk was carried out via a two-stage system combining CLG (calcium looping gasification) using Ca(OH) 2 adsorbent in a bubbling fluidized bed and catalytic reforming with Ce–Ni/γAl 2 O 3 catalyst in a connected fixed bed. The results show that the maximum H 2 concentration (69.16 vol%) and H 2 yield (11.86 mmol g−1 rice husk) are achieved at Ca/C (Ca(OH) 2 to carbon molar ratio) = 1.5, H 2 O/C (H 2 O to carbon molar ratio) = 1.5, T g (gasification temperature) = 500 °C, T c (catalytic temperature) = 800 °C. The supplementation of fresh Ca(OH) 2 at Ca/C of 0.5 during calcination helps to activate the regenerated CaO by hydration, maintaining its carbonation activity and CO 2 adsorption. Ce–Ni/γAl 2 O 3 catalyst promotes water gas shift (WGS), steam methane reforming (SMR), and C 2 –C 3 hydrocarbons reforming, also exhibits excellent activity stability to maintain H 2 concentration and H 2 yield above 67.21 vol% and 11.67 mmol g−1 rice husk , respectively, during 5 lifetime tests. • Staged catalytic gasification of rice husk in a fluidized bed for H 2 -rich gas. • Ca(OH) 2 adsorbent promotes WGS and hydrocarbons reforming at a moderate temperature. • Fresh Ca(OH) 2 supplement during calcination activates regenerated CaO by hydration. • Ce–Ni/γAl 2 O 3 catalyst promotes WGS, SMR, and C 2 –C 3 hydrocarbons reforming reactions. • Ce–Ni/γAl 2 O 3 catalyst shows excellent activity stability with low carbon deposition. [Display omitted] [ABSTRACT FROM AUTHOR]

Performing online evolution analysis of tar in actual pyrolysis process is a major challenge. In this work, the effects of heating rate (HR) on evolution curves of in-situ tar for low-rank coals pyrolysis were investigated in a novel laboratory bench. The escape law of volatiles was obtained, the influence of HR on secondary reactions was analyzed, the association between products and molecular structures was constructed, and pyrolysis mechanism was deduced. Aliphatic hydrocarbons (except dienes), phenols, and oxygenated compounds have only one peak, while dienes and aromatics have multiple peaks throughout the pyrolysis process. The first peak is attributed to coal primary pyrolysis. At increased HRs, the second peak for 1∼2ring aromatics is from the cracking of primary volatiles, and that for 3∼4ring aromatics from coal continued cracking. The proportion of phenols and oxygenated compounds decreases, aromatics increases, and aliphatic hydrocarbons varies for different coals. Generally, HR increases the yield of primary volatiles by enhancing coal primary pyrolysis, elevates the proportion of light aromatics by promoting secondary cracking and aromatization of primary volatiles, reduces char yield by inhibiting condensation reactions throughout the pyrolysis process. The similar macromolecular structures of different coals make the evolution curve versus HRs follow a common law. [Display omitted] • Dienes and aromatics have more than one evolution peaks during pyrolysis process. • The first peak of tar components is attributed to the coal primary pyrolysis. • As heating rate rises, the second peak of 1∼2ring aromatics is from the cracking of primary volatiles. • As heating rate rises, the second peak of 3∼4ring aromatics is from the cracking of coal at high temperatures. • The mechanism of heating rate on different low-rank coals remains consistent. [ABSTRACT FROM AUTHOR]

A two-stage system involving alkaline thermal gasification of cellulose with Ca(OH) 2 sorbent and catalytic reforming with Ni/Fe dual-functional CaO based catalysts is proposed and applied to enhance H 2 production and in-situ CO 2 capture. The results show that the H 2 concentration is maximized at a considerably lower temperature (500 °C) than commercialized biomass gasification processes, reducing energy consumption. Sol-gel method is deemed better than impregnation method for its lower cost and higher-concentration H 2 production. Among the prepared catalysts, sol-NiCa catalyst exhibits the best performance in CO 2 absorption, resistance to carbon deposition, and cyclic stability, creating maximum H 2 concentration (79.22 vol%), H 2 yield (27.36 mmol g−1 cellulose), and H 2 conversion (57.61%). Introduction of Ni rather than Fe on the CaO based catalyst promotes steam methane reforming at moderate temperature range of 400–600 °C, generating low contents of CH 4 (5.38 vol%), CO 2 (4.82 vol%), and CO (10.58 vol%). [Display omitted] • A two-stage system involving alkaline thermal gasification and catalytic reforming. • Sol-gel shows higher-concentration H 2 production and lower cost than impregnation. • Introduction of Ni rather than Fe on CaO catalysts promotes SMR at 400–600 °C. • Sol-NiCa catalyst exhibits good carbon deposition resistance and cyclic stability. • Maximum H 2 concentration (79.22 vol%) is achieved at moderate temperature of 500 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • The transformation paths of sulfur during coal steam gasification with CaO addition was identified. • The release characteristics of H 2 S were monitored online. • Factors which might affect the sulfur transformation were analyzed in detail. To investigate the effects of temperature, Ca-based absorbent (CaO) and atmosphere on the sulfur transformation characteristics in coal steam gasification, experiments were conducted in a fixed-bed reactor. As temperature increased from 600 °C to 750 °C, H 2 S-S (sulfur in H 2 S) was elevated by 21.86% and absorbent-S decreased by 7.66%. More gaseous sulfur was captured by organic groups to form organic sulfur in char at higher temperature. CaO promoted the sulfur conversion, and played the role of gaseous sulfur absorbent at the same time, and showed an ability of organic sulfur removal. CaO slowed down the H 2 S release by reacting with it to form CaS, resulting in that the peak concentration of H 2 S without CaO reached 1026.7 ppm, which decreased to 426.3 ppm with CaO. The increase in Ca/C promoted the sulfur conversion slightly and reduced the sulfate content in char. Compared with inert atmosphere, H 2 S-S in the steam atmosphere increased by 35.07%, while absorbent-S decreased by 23.42%. The solid–solid reaction mechanism is more suitable for the sulfate transformation in inert atmosphere, while the gas–solid reaction mechanism is more suitable in steam atmosphere. The sulfur conversion in inert atmosphere was lower, but sulfate had a higher decomposition rate. [ABSTRACT FROM AUTHOR]

In order to investigate the pressurized isothermal pyrolysis characteristics of coal, the effect of pressure on gas release characteristics and the kinetics of pressurized isothermal pyrolysis are explored for the first time in a pressurized micro-fluidized bed reaction analyzer (P-MFBRA). This work finds that the yields of CO 2 , CO, CH 4 , and H 2 increases with temperature and pressure. The difference in the order of gas-releasing reduces as temperature and pressure rises, but that of gas-ending first decreases and then increases with pressure. The most probable mechanism functions of CO 2 , CO and CH 4 change from shrinking core model to homogeneous model at 1 MPa, 0.8 MPa and 0.5 MPa, respectively, showing that reaction is controlled by chemistry under low pressure but affected by diffusion effect with elevating pressure. The rate constant and activation energy (Ea) of each gas appear an increasing-decreasing tendency and the difference between Ea of each gas reduces with pressure. Compared with non-isothermal experiments, the Ea (20.8–475 kJ mol−1) and pre-exponential factor in P-MFBRA are less than those (70–150 kJ mol−1) in the pressurized thermogravimetric analyzer (P-TGA), indicating P-MFBRA can effectively reduce the diffusion inhibition, and the kinetics obtained is close to the reaction in industrial fluidized bed reactor. [Display omitted] • The effect of pressure on gas formation is inconsistent at different temperatures. • It is affected by chemistry but diffusion at low and high pressure respectively. • The activation energy appears an increasing-decreasing trend with pressure. • Pressurized micro-fluidized bed can reduce the diffusion inhibition of reaction. • Pressurized isothermal pyrolysis is first done in pressurized micro-fluidized bed. [ABSTRACT FROM AUTHOR]

Currently, there is no easy-to-use method for determination of catalytic active phase volume (APV). Therefore, the current study designed a calculation method by defining APV (α → β nm) as the difference in pore volume (α → β nm) between the catalyst support and the catalyst (without taking fine structure of the catalyst into account for simplicity). This new method was successfully validated through regression analysis of 15 catalysts (R2 > 0.97). Moreover, the couplings of pore structures and metal loadings on catalytic hydrogenation of reactants were quantitatively assessed based on the calculation of APV. The promotion or inhibition effect of one compound on hydrogenation of other compounds may also vary with the couplings of metal loading and pore structure, but it wasn't taken into account in this study. The key segmented APVs (SAPVs) in various pore sections for hydroconversion of reactants were determined using a stepwise linear regression model at the 95% confidence level. The findings showed that the SAPVs in the pores with a pore size of 5–10 nm and 10–20 nm were responsible for hydroconversion of quinoline and most of the aromatic compounds, respectively. The predicted key SAPVs were consistent with the experimental observations, which demonstrated availability of the proposed APV. [Display omitted] • The QM-based calculation methods for kinetic diameters of molecules were provided. • Coupling effects of metal loading and pore structure were quantitatively assessed. • The catalytic active phase volume (APV) was firstly proposed and validated. • The stepwise linear regression model was used to find the key segmented APVs. • The found segmented APVs accorded well with the experimental observations. [ABSTRACT FROM AUTHOR]