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To reveal the effect mechanism of CO atmosphere on coal pyrolysis, a study on raw and demineralized lignite was carried out in a horizontal tube furnace under N2 and CO/N2 atmosphere. CO had a negligible effect on the char yield at low temperatures, whereas it enhances the char yield at temperatures higher than 550 °C. The release of tar was higher in the presence of CO above 450 °C because of more free radicals, which reduced low‐temperature crosslinking, and higher selectivity of hydroxyl groups to phenols in the CO‐containing atmosphere. The yields of CO2 and H2 increased, water and CO yields decreased under CO/N2 atmosphere. Light hydrocarbon gases were not affected by changing the reaction atmosphere. The difference between product yields from raw and demineralized coal confirmed that the catalysis of inherent minerals had a great catalytic effect on the water‐gas shift reaction and Boudouard reaction. [ABSTRACT FROM AUTHOR]

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]

Alkali metal pretreatment in pyrolysis is proposed to address alkali-induced issues in high-alkali coal utilization, on the basis of staged fuel combustion. However, the newfound carbon engulfment remains an intractable problem. This work investigated the effect of pyrolysis conditions on enhancing alkali metal pretreatment during Zhundong coal pyrolysis over 500–1000 °C in a laboratory fixed-bed apparatus, which focused on heating rate, volatile-char interaction, and CH 4 atmosphere. Multiple analytical methods were integrated to relate the facilitation effect of pyrolysis conditions on sodium pretreatment with the suppression of carbon engulfment. The results indicated carbon engulfment primarily blocked mesopores with a size <5 nm to retain large quantities of water-soluble sodium species. It resulted from coal swelling induced by the fusibility of semi-fusinites. Fortunately, volatile-char interaction and CH 4 atmosphere eliminated carbon engulfment through the intra-particle reaction between gasification agents/active radicals and char matrix. They fully eliminated carbon engulfment at 800 °C, which mainly reopened mesopores with a diameter of 4–5 nm. They also promoted the formation of sodium silicates/aluminosilicates. A slow heating rate weakened carbon engulfment by limiting the fusibility of semi-fusinites, but to a lower extent. Volatile-char interaction and CH 4 atmosphere were proposed as universal enhancements for alkali metal pretreatment. [Display omitted] • Pyrolysis pretreatment was proposed to address alkali-induced issues in combustion. • It aimed at promoting alkali release and the formation of stable alkali species. • Carbon coating blocked mesopores with width < 5 nm to impede the pretreatment. • Volatile-char interaction and CH 4 removed carbon coating to promote sodium release. • Volatile-char interaction and CH 4 benefited the formation of sodium minerals. [ABSTRACT FROM AUTHOR]

Staged coal combustion is a promising solution to the alkali-induced slagging issue. It innovatively separates coal pyrolysis and char combustion into different reactors. This study investigated migration and transformation of sodium during staged coal combustion of two Zhundong coals in a fixed-bed apparatus. Behavior of sodium during coal pyrolysis and char combustion are integrated. Carbon coating on sodium species was experimentally confirmed for the first time by low-temperature oxygen-plasma ashing and ultrafine grinding. Up to 62 wt% of initial water-soluble Na in ZJ coal and 51 wt% in WCW coal were coated with the carbon matrix during coal pyrolysis. Coated water-soluble Na appeared from 500 °C and its amount reached a peak value at around 700 °C, followed by decrease over 700–1000 °C. Thermoplastic behavior of coal during pyrolysis is expected to play an important role in the formation of coating which hinders pretreatment of sodium. During char combustion, all coated water-soluble sodium species were exposed and participated in the subsequent release. Part of them can also react with minerals to generate insoluble and HCl-soluble sodium species. Char combustion is the main period of the sodium release while coal pyrolysis is the principal period of the generation of HCl-soluble Na. • Carbon coating on sodium species during pyrolysis was experimentally confirmed for the first time. • Sodium behaviors in coal pyrolysis and char combustion are integrated. • Carbon coating is the key point of staged coal combustion in solving the slagging issue. [ABSTRACT FROM AUTHOR]

Circulating fluidized bed (CFB) technology has been continuously developing with an increasing number of large-capacity and supercritical CFB boilers being put into operation. This article reviews the current developments in large capacity CFB boilers in China and presents a note on the most recent development trends. It includes discussions on (1) gas-solid hydrodynamics in large-size CFB furnaces, (2) heat transfer on suspended surfaces, (3) combustion atmosphere and emissions, (4) 3-D CFD numerical simulation for large-scale supercritical CFB boilers, (5) integrated energy saving technologies, (6) optimal operation of an integrated desulfurization system, (7) erosion and protection of heat transfer surfaces, (8) problems in operation and their solutions, (9) combustion of coal with high alkali content. Unlabelled Image • Large-capacity and supercritical CFB boilers operated in China increased. • Current development trends of large capacity CFB boilers are discussed and noted. • Key aspects and issues during CFB development are discussed and noted. [ABSTRACT FROM AUTHOR]

Traditional electrostatic precipitation has a relatively low collection efficiency of fine particles emitted from coal combustion due to insufficient particle charging. This paper establishes an experimental system combining travelling sound waves with wire-duct electrostatic precipitation in order to measure the separated and simultaneous effects of an electric and acoustic field on fine particle penetration efficiency. The ranges of the main physical parameters are as follows: discharge voltage, V = 8–12 kV; acoustic frequency, ƒ = 800–2400 Hz; sound pressure level (SPL), SPL = 130–148 dB; residence time, t = 2–6 s; initial fine particle concentration, N 0 = 6.5 × 10 5 –4.99 × 10 6 /cm 3 . The application of acoustic waves in an electric field is proven as an advisable method to remove fine particles with the lowest total penetration efficiency of 4.4%. Although the sound does not change the current–voltage curves of negative corona, it can distort the motion trajectory of the particles leading to a positive result for fine particle removal. The effectiveness of sound on the improvement of fine particle removal diminishes as the voltage increases. For a given discharge voltage, there exists an optimal frequency and SPL. The optimal frequency slightly increases, while the optimal SPL decreases as the applied voltage increases. The influence of residence time and initial fine particle concentration in combined fields are also studied. [ABSTRACT FROM AUTHOR]

Pyrolysis polygeneration technology is a good way to realize clean and efficient utilization of low-rank coal and heat carrier is a key factor. Aspen Plus is used to establish low-rank coal pyrolysis staged conversion polygeneration technology with semi-coke heat carrier based on dual-fluidized bed (CPSCPC-DFB), which couples with ultra-supercritical semi-coke powder furnace for power generation. Three processes are simulated to co-produce methanol (CPSCPC-DFB-M), synthetic natural gas (CPSCPC-DFB-S) and hydrogen (CPSCPC-DFB-H). Mass and carbon balance are established, techno-economic, environmental and sensitivity analysis are carried out, and the comparison with ultra-supercritical coal-fired power plant (SCFP) is made. The results show that the comprehensive performances of CPSCPC-DFB-M, CPSCPC-DFB-S and CPSCPC-DFB-H are significantly better than those of SCFP in energy loss (49.37%, 47.33%, 45% and 55.6%), CO 2 emissions (2.07, 2.12, 2.22 and 2.52 kg/kg coal), internal rate of return (23.24%, 21.83%, 29.52% and 17.56%). Although the total investment of CPSCPC-DFB is much higher than SCFP, the net present value is better than SCFP. Comparing the three polygeneration systems, the total investment and CO 2 emissions of CPSCPC-DFB-H are slightly higher than those of other two systems, but CPSCPC-DFB-H has absolute advantages in economy. Sensitivity analysis shows that the anti-risk ability of the polygeneration systems are significantly improved. [Display omitted] • A dual-fluidized bed pyrolysis polygeneration system with semi-coke heat (CPSCPC-DFB) carrier is established. • The CPSCPC-DFB can co-produce electricity, oil and chemical products. • The CPSCPC-DFB produced H 2 has high efficiency (53.99%) than traditional plants (42.8%). • The IRR of CPSCPC-DFB produced H 2 (29.52%) is better than traditional plants (17.56%). • The anti-risk ability of the polygeneration systems are significantly improved. [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]