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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]

An experimental-scale electrostatic precipitator (ESP) was built to investigate the influence of temperature and gas media on collection efficiency and energy consumption. High temperature was harmful to the performance of the ESP and had a considerable influence on large particles. The maximum collection efficiency was lower and energy consumption was higher under coal pyrolysis gas media than under air. Two improvement methods, namely, gas media conditioning and positive polarity power supply, were studied in this work. Both methods can improve the performance of high-temperature ESP under coal pyrolysis gas media. The improvement in collection efficiency under the effect of gas conditioning decreased and that under the effect of a positive power supply increased with the increase in temperature. Gas conditioning and positive power supply increased the maximum collection efficiencies of the ESP at 600 °C under coal pyrolysis gas media by 3.0% and 11.8%, respectively. Unlabelled Image • High temperature was harmful to the performance of the ESP. • The performance of ESP in coal pyrolysis gas is inferior to that in air. • Gas conditioning and positive power supply can improve the performance of ESP. [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]

Steady‐state process simulation and techno‐economic analysis of a pyrolysis‐based coal staged conversion polygeneration (CSCP) plant, integrated with wastewater biochemical treatment after phenol‐ammonia recovery, are studied using Aspen Plus software. Appropriate models for the proposed system are set up in detail. Furthermore, by optimization of a methanation unit, a conventional supercritical circulating fluidized bed (SCCFB) power plant with the same capacity is chosen for comparison. Simulation results reveal that system energy and exergy efficiency of the CSCP system can reach much higher values than those of a conventional SCCFB power plant. In conclusion, a CSCP plant will have practical and economic advantages in the near future. A coal staged conversion polygeneration plant for the coproduction of coal gas, tar, and electricity power, integrated with wastewater biochemical treatment after phenol‐ammonia recovery, is proposed and simulated. Appropriate models for the proposed system are assessed. Such kind of plant exhibits practical and economic advantages, with excellent values of system energy and exergy efficiency. [ABSTRACT FROM AUTHOR]

Char is the solid product of coal pyrolysis and its utilization is closely related to the scale of coal pyrolysis and tar processing. Char gasification is a promising choice for char utilization as it can provide hydrogen, which is needed for tar hydrogenation and chemical synthesis. However, reliable and mature coal char gasification technology has not yet been developed. The fluidized bed has been adopted as a gasifier in many studies, and its gasification temperature is relatively low. In this work, the feasibility of char gasification using a fluidized bed has been studied. A pyrolyzed bituminous coal char was gasified in a mixture of O2 and steam using a circulating fluidized bed. The height of the fluidized bed is 2360 mm and the inner diameter is 66 mm. The reactor is made of Ni-Cd alloy steel, and a loopseal was used for solid circulation. In the experiments, the gasification temperature was varied between 870 and 900 °C, and the effects of O2/char and steam/char mass ratios on the gasification results were analyzed. The volume fraction of combustible gas, dry gas yield, carbon conversion, and lower heating value of the best case were 43.92 %, 1.64 Nm3 kg−1, 0.85, and 5.17 MJ N m−3, respectively. In addition, a simple model and a complex model were established by using Aspen Plus software. The two models were used to simulate char gasification, and the simulation results were validated with the experimental results. The results indicated that the complex model is more accurate than the simple model and is more suitable to simulate char gasification in a circulating fluidized bed. [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]

Highlights: [•] A lignite pyrolysis-based polygeneration plant was proposed and modeled. [•] Polygeneration plant has a 9.04% point higher efficiency than CFB power plant. [•] Polygeneration plant increases ca. 14% point of IRR based on CFB power plant. [•] Electricity price rise makes polygeneration plant less competitive. [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]

The present paper was devoted to investigate the sulfur transformation during pyrolysis of the mixture of coal and CaSO 4 in a fixed bed reactor at a temperature range of 500–800 °C. The results indicated that the presence of CaSO 4 could promote the evolution of H 2 S and COS at high temperature, which should be due to the higher decomposition rate of organic sulfur and the reactions between CaSO 4 and pyrolysis products, e.g., H 2 and CO. Moreover, when the blending ratio(CaSO 4 /coal) exceeded 20%, CaSO 4 could greatly promote the decomposition of organic sulfur at 800 °C. The mechanism of organic sulfur decrease due to CaSO 4 was proposed. In comparison of raw coal, sulfide sulfur was significantly increased with the addition of CaSO 4 above 600 °C, which should be mainly due to CaS formation through CaSO 4 decomposition. [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]