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The permeability rebound and recovery of coal reservoirs is one of the key factors affecting the efficient recovery of coalbed methane (CBM). Most studies focus on the permeability rebound and recovery of intact coal reservoirs. Conversely, the permeability rebound characteristics of tectonic coal have only been rarely investigated. In this paper, an improved fully coupled mathematical model for methane transport of tectonic coal and intact coal seam was established. Then, the phenomenon of permeability rebound and recovery was analyzed theoretically, and the permeability rebound time, rebound value and recovery time were proposed to compare the difference in permeability evolution. In addition, the permeability rebound characteristics of tectonic and intact coal were evaluated for different geological parameters of coal reservoirs. The results indicate that the rebound time and recovery time of both intact and tectonic coal increase with the increase of initial gas pressure. As the initial permeability increases, the permeability rebound time of intact and tectonic coal show a decreasing trend. The permeability rebound time of intact coal decreases with increasing initial diffusion coefficient, while that of tectonic coal shows the opposite trend. Furthermore, the change in permeability recovery time for tectonic coal is 6.59 times larger than for intact coal, indicating that the effect of permeability rebound phenomenon is more significant during gas extraction in tectonic coal reservoirs. Finally, a conceptual model was proposed to explain the differential mechanism of permeability rebound between tectonic and intact coal, and its implications for CBM recovery in tectonic coal reservoirs was discussed. Therefore, the results presented in this paper can provide a theoretical basis for the efficient development of CBM in tectonic coal reservoirs. • Methane transport mathematical models of tectonic and intact coal are developed. • The permeability rebound in tectonic and intact coal is quantitatively analyzed. • The evolutionary mechanism of permeability rebound of tectonic coal is revealed. [ABSTRACT FROM AUTHOR]

The paper object is high-quality Shenmu bituminous coal modified by fatty alcohol polyoxyethylene ether sodium sulfate (AES) surfactant. The changes in functional groups, free radicals, Zeta potential, and contact angle of coal modified in AES anionic surfactant were analyzed. Based on the molecular structure of Shenmu coal, a coal-AES-water three-phase dynamic model was constructed. The wetting mechanism of coal was studied by molecular dynamics. The research has demonstrated that as the mass fraction of AES surfactant increases, the proportion of polar groups (-OH, C– O –C, –COOH, –C O), free radical content and Zeta potential increased significantly. The size of contact angle displayed a major negative linear correlation with the proportion of polar groups and free radicals, but positively linearly correlated with the Zeta potential. In the coal-AES-water three-phase dynamic model, the AES molecules adhere to coal molecules as hydrophobic group, while hydrophilic groups extended into the water. This increased H 2 O diffusion coefficient, enhanced action energy between coal and water interface, decreasing surface tension and achieving effective wetting of the coal. This paper supplies s a new idea for selecting efficient surfactants to change the coal microstructure. It is of major importance for improving coal wettability and offers a theoretical foundation for gas drainage and disaster prevention. • After AES modification, the hydrophilic groups of coal significantly increased. • After AES modification, the coal wettability is significantly improved. • After AES modification, coal molecules are more likely to adsorb water molecules. [ABSTRACT FROM AUTHOR]

Spontaneous combustion often occurs when carbonaceous materials are stored for a long time. Up to now, domestic and foreign scholars have done a lot of research on the spontaneous combustion mechanism of coal and biomass fuel, monitoring methods and prevention measures, and achieved fruitful results. It is worth noting that coal and biomass are not the same type of energy, but the internal mechanism and external performance of spontaneous combustion of the two are very similar, and both involve complex physical and chemical reactions. At present, very fruitful results have been achieved in coal spontaneous combustion monitoring and fire prevention in mine, but the spontaneous combustion research around coal storage silos and biomass silos is insufficient, and the spontaneous combustion monitoring and fire prevention technology for them is relatively backward. Therefore, by summarizing and comparing the relevant work in recent years, this paper aims to sort out the similarities and differences of the occurrence mechanism, monitoring methods and prevention measures of the two, explore the technologies and theories that can learn from each other, promote the progress of the two in the study of spontaneous combustion mechanism, and promote the development of more advanced spontaneous combustion monitoring and fire prevention technology. And the application in the mine-out area, coal storage silo, biomass silo and other scenarios, to provide theoretical and technical references for the future safe storage of coal and biomass. • This paper first draws out the similarities and differences between coal and biomass in terms of spontaneous combustion mechanism, monitoring and prevention through case analysis. In order to promote their integration and reference in theory and technology. • Through the comparison of biomass and coal spontaneous combustion studies, this paper puts forward some feasible new ideas in spontaneous combustion monitoring and fire prevention. • This is of great innovative significance for spontaneous combustion monitoring and prevention of coal and biomass under silo conditions. [ABSTRACT FROM AUTHOR]

This paper establishes the equivalent density and equivalent P-wave velocity models of coal bodies with different water saturation, and investigates the P-wave propagation evolution law of coal bodies with different water saturation from the perspective of numerical simulation. When the experimental coal samples continue to use high-pressure water after reaching the natural saturation state, the water saturation can be further increased, and the increase in water saturation is larger, and the corresponding P-wave velocity also appears to be increased more substantially, and this phenomenon also occurs in numerical simulation results, which indicates that the P-wave velocity will have an obvious increasing trend when the coal body is from nearly saturated to fully saturated. The experimental and numerical simulation results show that the P-wave velocity of coal samples increases with the water saturation degree in a similar exponential function, which further verifies the reasonableness and feasibility of the modelling based on the assumption of gas-liquid homogeneous medium. In addition, the propagation of P-wave in coal samples is affected by the pore and fracture structure, and the pore and fracture with small pore size has less influence on the P-wave, and vice versa. • Reveals the P-wave velocity evolution law from near saturation to full saturation in a coal body. • Equivalent density and equivalent P-wave velocity modelling of different water saturation were developed. • Numerical method for P-wave propagation in coals with different water saturations is realised. [ABSTRACT FROM AUTHOR]

The low-temperature oxidation of coal involves multiple gas production paths including desorption, pyrolysis and oxidation. These paths interfere with each other, resulting in unclear kinetic characteristics of CO and CO 2 production in coal oxidation and incomplete mechanism of gas production. Therefore, this paper proposed a method that can effectively exclude the effects of desorption and pyrolysis on gas production and adopted this method to explore the kinetic characteristics of CO and CO 2 production under different paths. Besides, with the aid of microscopic characterization methods, the kinetic steps controlling gas production and the mechanism of gas production were analyzed. The experimental results demonstrate that the proposed method can effectively eliminate the effects of desorption and pyrolysis, and can obtain the kinetic characteristics of gas production under the oxidation path that can reflect the intrinsic characteristics of low-temperature oxidation of coal. Based on the difference method, the activation energies of CO and CO 2 produced under the oxidation path are 59.49 kJ/mol and 60.09 kJ/mol, which activation energies are almost the same, suggesting that CO and CO 2 are likely to be produced from the same precursor. The gas production in low-temperature oxidation is a process in which methylene groups in coal react with oxygen to generate oxygen-containing intermediates which then decompose to produce CO and CO 2. The reaction of methylene groups with oxygen is the control step of gas production kinetics in coal spontaneous combustion, resulting in the same apparent activation energies of CO and CO 2 production in the stable phase under the oxidation path. • A method was established to exclude the effect of physical desorption and pyrolysis gas production. • The activation energies of CO and CO 2 produced in the oxidation path are equal. • The reaction of methylidene with oxygen to form the same intermediate is a key control step to control oxidation. [ABSTRACT FROM AUTHOR]

Underground coal gasification is an essential means of meeting the growing energy needs of some countries. In this paper, a new numerical simulation method of thermal-force-chemical-displacement multi-field coupling is developed, and in order to better adapt to the actual working conditions, taking Shanjiaoshu Coal Mine as the geological background, the first gasification working face of No. 12 coal seam is simulated based on the controlled retraction injection point technology. This method is used to simulate the heating of coal body by the ignition device at the initial stage of UCG, the chemical-thermal changes triggered by spontaneous combustion of the coal body under the continuous backward movement of the injection point, and the simulation of the formation of the cavity after the coal gasification reaction. Finally, the evolution of temperature and displacement fields in No.12 coal seam after gasification reaction is analyzed. Therefore, this study aims to simulate the actual working conditions more realistically, optimize the UCG technology, and produce more clean energy syngas to improve the energy situation in China. • A coupled thermal-force-chemical-displacement multi-field calculation of coal and surrounding rock strata. • Simulating of continuous movement of the gasification point to fit the actual process of CRIP. • The heat flowing into the model is calculated based on the chemical change. [ABSTRACT FROM AUTHOR]

The US Environmental Protection Agency’s plan for a National set of standards limiting mercury emission from coal power plants has recently hit a setback. A decision by the US Supreme Court rejected this based on the two available methods having a burdensome cost basis. Moreover, even if the activated charcoal or bromine addition methods do become standard in the US, their cost may still inhibit global implementation. As a result it is timely to develop alternate methods. This paper outlines further development of such an approach. It is based on mercury’s own chemistry. Previous published work discovered that elemental mercury, although volatile, has a propensity for heterogeneous chemistry on warm non-catalytic surfaces. This paper now reports results of a second pilot plant test continuing its clarification, extension and further validation of practicality. It extends data to inexpensive base metal surfaces that can be used and indicates the extent of mercury control possible. This non-catalytic heterogeneous chemistry has been overlooked due to this disguising role of surfaces. It is this that now suggests a passive mitigation method, natural to the system. By providing inserted metal surfaces in the downstream flue gas flow, mercury can be chemically modified and controlled. [ABSTRACT FROM AUTHOR]

Catalytic coal combustion is a promising technology to realize efficient utilization of coal, however, the catalysis in the coal combustion process is unclear. This paper focused on the effects of two type catalysts (metal oxides and metal compounds) on the combustion reactivity of lignite, bituminous coal and anthracite using thermogravimetric analyzer, and discussed the catalytic mechanisms combining with catalytic thermal decomposition and catalytic char combustion. All catalysts decreased the ignition temperature and burnout temperature of coals to the extent of 0.25–81.25 °C, 24.75–73.25 °C, and increased the exothermic values. The catalytic effect was influenced by coal rank and had the greatest promoting effect on anthracite. Besides, the pyrolysis conversion rates of coals were increased by catalysts, resulting in ignition advance and made the subsequent reaction easier. The results of catalytic char combustion showed that both catalysts significantly reduced the ignition temperature of char, the Na 2 CO 3 had the best catalytic effect on fixed carbon combustion, while CaO mainly affected the release of volatile matter. Finally, the catalytic mechanism in coal combustion was discussed. This article aims to provide theoretical reference for the practical comprehensive application of coal catalytic combustion. • A comprehensive study was conducted on the catalytic combustion process of coals. • All catalysts improve coal combustion reactivity and advance heat release. • The higher the fixed carbon content in coal, the better the catalytic effect. • The overall catalytic mechanism of coal combustion is proposed. [ABSTRACT FROM AUTHOR]

In this paper, THM model and coal molecular model are established to study the gas adsorption and desorption behavior in coal seam at different injection pressures. The results show that, the total energy decreases during the adsorption process and increases in the desorption process. CO 2 has a stronger adsorption capacity which is in a dominant position in the competition adsorption process, while N 2 is in a weak position. The order of the diffusion coefficient is N 2 >CH 4 (CH 4 –N 2) > CH 4 (CH 4 –CO 2) > CO 2. The diffusion coefficient does not necessarily increase with the increase of injection pressure. At the same injection pressure, the relative concentration of CH 4 in the CH 4 –CO 2 system is greater than that in the CH 4 –N 2 system, and injection of CO 2 to promote CH 4 desorption is significantly better than the injection of N 2. With the increase of injection pressure, the average relative concentration of CH 4 /CO 2 /N 2 in the vacuum layer increased. The optimal injection pressure for N 2 injection to promote CH 4 desorption is 2 MPa, and the reasonable injection pressure for CO 2 injection is 1–3 MPa. • THM model and coal molecular model are established to study the gas adsorption and desorption at different injection pressures. • The total energy of the system decreases during the adsorption process and increases in the desorption process. • The diffusion coefficient does not necessarily increase with the increase of gas injection pressure. • Relative concentration of CO 2 in the vacuum layer is lower than N 2 , the adsorption performance of CO 2 is greater than N 2. [ABSTRACT FROM AUTHOR]

According to the different characteristics of coal spontaneous combustion (CSC), different countermeasures can effectively prevent CSC. In this paper, a new characteristic parameter, the oxygen consumption rate integral (OCRI), was proposed. The characteristics of CSC during the latent period and the effect of low oxygen concentration (0–20.96 %) on the CSC were comprehensively examined. Using a lab-built closed oxidation system, isothermal oxidation experiments were performed on different grades of coals at different temperatures. The OCRI was obtained by integrating the oxygen consumption rate as a function of oxygen concentration. The OCRI expresses the sum of the rates of oxygen consumption at different concentrations of oxygen and can be used as an identification index for the propensity of CSC. The kinetic basis for this approach is the variability of initial oxygen consumption rates and oxygen reaction orders for different coals. Finally, the physicochemical structure of the coal was measured by N 2 adsorption and IR analysis. The results were correlated with the OCRI. On this basis, the main microscopic reaction pathways affecting the CSC were revealed. The results can aid in the future direction for research and development of high-efficiency inhibitors. [Display omitted] [ABSTRACT FROM AUTHOR]

Acid fracturing technology is applied to increase the permeability of coal seams to promote gas extraction, but the effects of acid solutions on coal combustion cannot be ignored. This paper focuses on HF, HCl, and HNO 3. The Bagchi method determines the mechanism function of each nonisothermal TG stage of acidified coal. Combining FTIR, TG-DTA, and KTA, this paper studies the combustion performance of acidified coal from the perspectives of the coal molecular structure evolution, combustion phenomenon, and kinetics. The results show that inorganic acids can destroy C=O in coal, resulting in the carbonyl groups in the HF, HCl, and HNO 3 samples decreasing to 21%, 35%, and 0% of that in the RAW samples, respectively. Inorganic acid significantly enhances the reaction rate and thermal effect of combustion stage and improves the comprehensive combustion performance of coal, and the effect is in the order of HF > HNO 3 >HCl. Inorganic acids change the most likely mechanism function of initial weight loss stage. The oxidation increase of the HNO 3 sample is greater than the corrosion weight loss, resulting in a corrosion ratio of −1.74%. HF and HCl reduce the activation energy of oxidation weight gain stage and increase the spontaneous combustion tendency of coal samples. • The most likely mechanism functions of acidified coals are determined. • The combustion mechanism is revealed from the evolution of functional groups. • Inorganic acids reduce carbonyl groups in coal by more than 65%. • The corrosion ratio of the HNO 3 coal sample due to oxidation is negative. • HF and HCl increase the spontaneous combustion tendency of coal. [ABSTRACT FROM AUTHOR]

Coal-based power generation sector is facing important changes to implement energy efficient carbon capture technologies to comply with emission reduction targets for transition to low carbon economy. This paper assesses CaL (Calcium Looping) as one of the innovative carbon capture options able to deliver low energy and cost penalties. The work evaluates how the integration of post-combustion calcium looping influences the economics of power plants providing up-dated techno-economic indicators. Coal-based combustion plants operated in both sub- and super-critical steam conditions were evaluated, as well as coal gasification plant using an oxygen-blown entrained-flow gasifier. As benchmark options used to quantify the carbon capture energy and cost penalties, the same power generation technologies were evaluated without CCS (Carbon capture and storage). The power plant concepts investigated in the paper generates around 545–560 MW net power with at least 90% carbon capture rate. Introduction of CaL technology for CO 2 capture results in a 24–42% increase of specific capital investment, the O&M costs are increasing with 24–30% and the electricity cost with 39–48% (all compared to non-CCS cases). As the techno-economic results suggest, CaL has good application potential in combustion-based power generation. [ABSTRACT FROM AUTHOR]

The thermal decomposition of oxygen-containing functional groups produces CO, CO 2 and active sites that accelerate coal spontaneous combustion. Study on this process is of great significance for research on the mechanism of coal spontaneous combustion. In this paper, research was made on the dependency relationship between gas production and time under the condition of different coal samples, particle sizes and pyrolysis temperatures. Results reveal that the time-dependent generation rate of active sites follows an exponential compound function P = A + B e - t/ K 1 + C e - t/ K 2 during isothermal pyrolysis of coal. Besides, infrared spectrum experiments were also carried out to study changes in oxygen-containing functional groups of raw coal, pyrolyzed coal and room temperature oxidized coal after pyrolysis. The results prove that when coal reaches a certain temperature, oxygen-containing functional groups will adsorb heat and undergo decomposition to produce active sites and a few gas products. Then, active sites are oxidized, generating oxygen-containing functional groups and releasing both massive heat and gas products. Therefore, the whole reaction is a continuous cyclic process where combined effects of the two reactions cause rapid accumulation of heat, which triggers uncontrollable coal spontaneous combustion. The results from this research will be helpful to inhibit the occurrence of coal spontaneous combustion by reducing the generation and oxidation of active sites. • The isothermal pyrolysis experiments of coal samples were carried out. • Isothermal thermal decomposition of oxygen-containing functional groups was studied. • The law of CO and CO 2 gas generation during isothermal pyrolysis was obtained. • The generation law of active sites during isothermal pyrolysis was revealed. [ABSTRACT FROM AUTHOR]

To investigate the reaction pathways of key reactive groups in coal when coal undergoes oxidation at low temperatures, the start-up stage of the reaction pathways, and the evolution of free radicals and functional groups. Firstly, according to the similarity in the types of groups, this paper classifies many reactive groups in coal and uses GaussView 6.0 to construct molecular models of primary (-CH 3 , –OH, –CHO, –COOH) and secondary (-R∙, –C(O)∙, –COO∙, ∙OOH) groups. Then the reaction channels of primary and secondary groups were built and verified based on the similarity of the reaction forms of the groups. The results show that both primary and secondary groups have "dual channel reactions" when coal undergoes oxidation. Channel A of the primary group reacts with O 2 with a start-up stage of 70∼200 °C, and channel B reacts with ∙OH with a start-up stage of 30∼70 °C; channel C of the secondary group reacts with O 2 at about 30 °C and channel D reacts with self-decomposition with a start-up stage of 70∼200 °C. The results show that oxygen insulation and cooling can be adopted according to channels A and C. Channels B, C, and D eliminate R∙ and ∙OH to efficiently prevent and control coal spontaneous combustion(CSC). • The model of primary and secondary groups in coal was constructed. • The reaction channels of each key group were simulated and validated at the atomic and molecular levels. • A two-channel reaction model exists for both primary and secondary groups. • Delineated the initiation phase of each reaction channel. [ABSTRACT FROM AUTHOR]

Colloidal gas foam concrete (CFC) was successfully prepared by high water retention of colloidal gas aphrons (CGA) and cement slurry. The preparation conditions of colloidal gas foam concrete with optimal performance and the addition ratio between its components were determined based on single-factor experiments and orthogonal tests. Then, the compressive strength, water retention, water content, and ability to inhibit coal spontaneous combustion of colloidal gas foam concrete were systematically studied. CFC's performance test to prevent spontaneous combustion of coal showed that CFC could form a hard protective shell of oxygen barrier on the surface of coal, thus inhibiting spontaneous combustion of coal. In addition, compared with traditional aqueous foam concrete (AFC), the water content of CFC increased from 0.65 to 1.40, and the protective shell formed by CFC could still retain some water after seven days without cracking. The programmed temperature rise experiment showed that CFC inhibited coal spontaneous combustion better than traditional AFC, and the cross-point temperature of coal treated by CFC was higher. This paper provides a high-performance mine fireproof material, which is important for the safe and efficient production of mines. • Analysis of the formation mechanism and characteristics of colloidal gas aphrons. • Successful preparation of colloidal gas foam concrete (CFC). • Study of the properties of CFC to prevent spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

The flexibility of the coal-fired boiler depends on the control system, which is designed according to its dynamic characteristics. In this paper, a detailed dynamic model of a supercritical coal-fired boiler is developed in Dymola, and the necessary control models are built. The model is validated against the design values under various conditions with a maximum error of 2.19%. The model is further validated by comparing dynamic simulation results with operating data. Then, the dynamic behavior of the boiler is analyzed under the single- and two-parameter disturbances. When the feedwater temperature, feedwater flow, and coal quantity are all disturbed by −5%, the maximum deviations of the live steam temperature are −21 °C, +32 °C, and −34 °C, respectively. Compared to the simultaneous change of feedwater and fuel, the maximum value of the live steam temperature is reduced by 21.56 °C when the coal quantity is changed 100 s before the feedwater flow. Besides, a first-order inertia compensation element is developed ahead of the feedwater flow command, which effectively improves the performance of the water-fuel ratio control. As the load-variation rate increases, the deviation in the transient process of the thermodynamic parameters increases, and the time required for stabilization lengthens. • A detailed dynamic model of a supercritical coal-fired boiler is developed. • The model is validated for dynamic performance using measured plant data. • The response time and maximum deviation of main parameters are evaluated. • Adding a first-order inertia element before feedwater improves water-fuel control. [ABSTRACT FROM AUTHOR]

Enhanced coalbed methane (ECBM) is an effective development technology to improve energy utilisation and reduce greenhouse gas emissions by injecting N 2 /CO 2 into coal seams. The process involves the adsorption, desorption, and diffusion of N 2 /CO 2 in multi-scale coal pores. This results in gas storage and transport characteristics limited by the coal's structural distribution of nanoscale pores (≤100 nm). Thus, studying N 2 /CO 2 storage and diffusive transport characteristics in pores at different scales is vital for efficiently implementing N 2 /CO 2 -ECBM. This paper performed low-pressure adsorption with N 2 /CO 2 (LPA-N 2 /CO 2) to evaluate coal samples' isothermal adsorption characteristics and pore structure, revealing the dual filling-adsorption mechanism of N 2 /CO 2 in coal. A new coal pore classification method was proposed. Pores (≤50 nm) in coal-N 2 or coal-CO 2 adsorption systems were classified as inaccessible pores (<0.364 nm or < 0.33 nm), filling pores (0.364–1.65 nm or 0.33–1.36 nm), transition pores (1.65–2 nm or 1.36–1.60 nm), and adsorption pores (>2 nm or > 1.60 nm). Combining the experimental results to construct micropore and mesopore models, molecular dynamics were applied to simulate the loading and migration processes of N 2 /CO 2 in the pore models. Filling, transition, and adsorption pores completed loading gas within 0.1–1 MPa, 1–5 MPa and 5–10 MPa in that order, visualising the gas filling-adsorption process in coal. Then, the adsorption capacity of N 2 was controlled by the pore size and adsorption pressure, while CO 2 was mainly influenced by adsorption pressure. [Display omitted] • The filling-adsorption mechanism of N 2 /CO 2 in different coal pores is revealed. • A new pore classification method for coal-N 2 and coal-CO 2 systems is proposed. • The pressure stage for loading gas in various types of pores is defined. • Visualisation of gas filling-adsorption process in coal by simulation is realised. [ABSTRACT FROM AUTHOR]

The ultra-supercritical once-through boiler (OTB) unit is an advanced power generation technology with high plant efficiency and low emissions. However, it is difficult to realize a coordinate control for the ultra-supercritical OTB unit to achieve the fast and stable dynamic response during the load tracking and grid frequency disturbances and in the presence of unavoidable uncertainties. In this paper, an accurate grey box multivariable coupled nonlinear model of an ultra-supercritical boiler-turbine unit is considered. Steam pressure at throttle valve, specific enthalpy in separator and active power are adjusted at desired values by manipulation of the fuel rate command, feedwater rate command and throttle valve opening. In addition to the mentioned accurate model, limitations of operational parameters and uncertainty sources are considered in the controller design. This makes this research unique from previous works. According to affine nonlinear control theory, a nonlinear robust sliding mode controller is developed. Then using MATLAB μ - DK iteration syntax, a linear H-infinity (H ∞) robust control is synthesized with selecting proper weight functions. This method is suitable for all types of power plants with a similar mathematical modeling approach. Simulations in MATLAB Simulink toolbox reveals that both designed controllers achieve appropriate performance in the presence of uncertainties and parameters' limitations, but nonlinear controller has better performance. Finally, deficiencies of a linear controller with respect to the proposed designed robust controllers are denoted. • Improve performance of an ultra-supercritical coal fired once-through boiler-turbine. • Development of robust H ∞ & sliding mode controllers in the presence of various unavoidable sources of uncertainty. • Comparing the efficiency of control approaches in tracking of desired power outputs. • H ∞ controller guarantees the robust stability & performance of the uncertain systems. • Sliding mode controller guarantee robust stability of the uncertain system. A comparison with a linear controller is done. [ABSTRACT FROM AUTHOR]

Abstract As an advanced power generation system, supercritical CO 2 (S-CO 2) coal fired power plant has advantages of high electric efficient and compact system layout. In this paper, the coal combustion characteristics and NO x formation in coal-fired S-CO 2 boiler has been explored by numerical simulation. The boiler wall temperature distributions were determined according to the 1/8 partial flow strategy for S-CO 2 coal-fired power plant. The effect of SOFA ratio on the gas flow field, the gas temperature, the species concentration including NO x distribution was investigated. The results show that the SOFA ratio has a great influence on the coal combustion process and NO x formation. With the increase of SOFA ratio, the O 2 concentration decreases in the main coal burning zone, a higher CO concentration can be found. A lower gas temperature zone in the main burning zone and a lower NO x emission near the furnace outlet can also be observed with a higher SOFA ratio. The results presented promote a better understanding of the NO x formation characteristics and would be benefit for the NO x control in coal-fired S-CO 2 boiler. [ABSTRACT FROM AUTHOR]

The combustion process in blast furnace (BF) has play a significant role in providing heat resources, reducing agent and primary gas flow distribution. Accordingly, large proportion energy was also consumed and discharging massive amount CO 2 , the most effective way to reduce that is to increase the pulverized coal injection (PCI) rate to substitute the coke and maintaining stability state of BF. But the relationship of PCI rate and raceway temperature is still unknown. In this paper, the temperature detection system based on digital imaging techniques (DIT) has been firstly applied to study the tuyere temperature regularity on various conditions in 2500 m3 BF, such as different PCI rates, PCI cease and none PCI processes. And the colorimetric method was used to calculate the temperature distributions of tuyere images in raceway zone of BF. Moreover, the calibration, denoising and edge detection were firstly used to improve the accuracy of temperature detection. At last the influence regularity of PCI rate on the tuyere temperature was obtained. The studies not only could contribute to qualify the effect of the PCI rate on the temperature distribution in raceway zone, but also could useful to understand the pulverized coal combustion mechanism in BF raceway zone. • Regularity of PCI rate on the Blast Furnace tuyere temperature was obtained. • Tuyere temperature changing regularity with and without PCI was studied. • Noise of Blast Furnace tuyere images was eliminated by the wavelet filter. • Edge of Blast Furnace tuyere images was detected by Morphological method. [ABSTRACT FROM AUTHOR]

Abstract As the initial step in coal combustion and gasification, pyrolysis plays an important role in chemical reactions. The influencing mechanism of superfine particle on gas phase products during rapid pyrolysis remains problematic. In this paper, the formation and dissipation mechanism of the gas phase products especially CO, light hydrocarbons and NO X precursors of superfine pulverized coal pyrolyzed in an entrained flow reactor is focused. Pyrolysis experiments are taken out in Ar and N 2 respectively. The influence of particle size, coal rank, pyrolysis atmosphere and the final pyrolysis temperature on the formation and dissipation are analyzed. In addition, pore structures of raw coal and chars are also characterized by synchrotron radiation facility to better reveal the pyrolysis mechanism. Our results indicate that as the particle size decreases, the content of CO, light hydrocarbons and NO X precursors all show a trend of first increase and then decrease. Lower rank coal has larger release concentration of gas phase products. Additionally, with the increment of the final pyrolysis temperature, there is a decrease trend of light hydrocarbons and NO X precursors but an increase trend of CO. The fractal dimension (D SAXS) increases with the increase of the final pyrolysis temperature. Highlights • The release characteristics of gas phase products are affected by particle size. • Lower rank coal has larger release concentration of gas phase products. • Temperature has different effects on the release of gas phase products. • The fractal dimensions of chars increase with the increase of the temperature. [ABSTRACT FROM AUTHOR]

Abstract The combustion characteristics of coal samples with different particle size were investigated using a thermogravimetric analyzer. Three different heating rates were set in the oxygen-deficient atmosphere of 12 vol % oxygen concentration. Experiments were conducted on four particle sizes with a diameter of 0.6, 1.0, 2.0, and 4.0 mm. It was found that ignition and burnout temperatures of coals rose approximately linearly with the increasing particle size. The ignition temperature of the coal with a diameter of 4.0 mm (482 °C–520 °C) varied greatly at different heating rates compared with that of 0.6 mm (473 °C–481 °C). The effect of particle size on the ignition temperature decreased with the increase in heating rate, while the effect on the burnout temperature was promoted. The calculation of the combustion index and the results of the kinetic analysis indicated that the reactivity decreased as the coal particle size increased. The results of this paper can provide guidelines for the development of a staged fuel-feeding horizontal circulating fluidized bed boiler. Highlights • Effects of particle size on ignition and burnout behavior were gained. • Coupling effect of particle size and heating rate was studied. • Combustion process of large coal particles in HCFB boilers was explained. [ABSTRACT FROM AUTHOR]

The following article conducts a meta-analysis to systematically investigate why Representative Concentration Pathways (RCPs) in the Fifth IPCC Assessment are illustrated with energy system reference cases dominated by coal. These scenarios of 21st-century climate change span many decades, requiring a consideration of potential developments in future society, technology, and energy systems. To understand possibilities for energy resources in this context, the research community draws from Rogner (1997) which proposes a theory of learning-by-extracting (LBE). The LBE hypothesis conceptualizes total geologic occurrences of oil, gas, and coal with a learning model of productivity that has yet to be empirically assessed. This paper finds climate change scenarios anticipate a transition toward coal because of systematic errors in fossil production outlooks based on total geologic assessments like the LBE model. Such blind spots have distorted uncertainty ranges for long-run primary energy since the 1970s and continue to influence the levels of future climate change selected for the SSP-RCP scenario framework. Accounting for this bias indicates RCP8.5 and other ‘business- as -usual scenarios’ consistent with high CO 2 forcing from vast future coal combustion are exceptionally unlikely. Therefore, SSP5-RCP8.5 should not be a priority for future scientific research or a benchmark for policy studies. [ABSTRACT FROM AUTHOR]

The changes of physical and chemical structure of coal were investigated during the spontaneous combustion latency. In order to analyze the effect of low temperature oxidation on physical structure, low temperature oxidation experiments, scanning electron microscopy (SEM) and low-pressure nitrogen gas adsorption (LP-N 2 GA) were performed on coal samples. The low temperature oxidation resulted in ravines and asperities on the smooth surface of the raw coal. The pore structure of coal samples changed slightly before 50 °C, and the specific surface area, pore volume and pore diameter were greatly improved at 70 °C. Data from LP-N 2 GA experiment was applied to assess the heterogeneities of percolation pores (D 1) and the irregularities of adsorption pores (D 2) on the basis of Frenkel–Halsey–Hill (FHH) theory. During low temperature oxidation, the pore structure of the coal tends to be internally evident, the inhomogeneity is reduced and the volumetric fractal dimension decreases. The evolution of active groups in coal was analyzed by in situ constant temperature Fourier Transform infrared spectroscopy (FTIR). The results show that the active groups have different reactive activities and changing trends. This paper reveals the changes in the chemical-physical structure of coal samples during the spontaneous combustion latency. [Display omitted] • The temperature rise characteristics of coal during the latency were studied. • The changes of pore and chemical structure of coal were investigated. • The heat effect of this latent process was estimated quantitatively. [ABSTRACT FROM AUTHOR]

Investigating the behavior of coal spontaneous combustion (CSC) is of great significance to the prevention of coal mine fires. and the dangerous area. In this paper, we firstly analyzed the CO concentration variation at different coal sample particle sizes based on the programmed heating experiments, and initially determined the critical temperature (T C) and xerochasy temperature (T X), the two key characteristic temperatures in the CSC process. Afterwards, the three oxidation stages of the coal spontaneous combustion process were divided as per T C and T X , and the apparent activation energy of the corresponding stages was obtained. Conclusively, the variation patterns of the coal spontaneous combustion limit parameters (minimum float coal thickness h min , upper limit air leakage intensity Q max and lower limit oxygen concentration c min) were analyzed. It was found that the smaller the particle size, the greater the CO concentration, oxygen consumption rate and exothermic intensity of the coal samples. An exponential function was fitted between the exothermic intensity and the coal temperature. The apparent activation energy of the oxidation kinetic parameter increases as the coal spontaneously combusts, and is positively correlated with the particle size. This is mainly due to the fact that the larger the particle size, the smaller the contact area between the coal and oxygen and the corresponding reduction in the active material in the coal, resulting in a greater apparent activation energy required for the coal oxygen reaction. Grain size plays a non-negligible role in the spontaneous combustion limit parameters of coal. The smaller the particle size, the smaller the minimum floating coal thickness and the lower oxygen concentration limit, and the greater the upper air leakage intensity. The relationship between coal spontaneous combustion limit parameters and grain size is not only a quadratic function, but also an exponential function. The smaller the grain size of the relict coal in the mining area, the greater the risk of coal spontaneous combustion. The content of this study can provide some support for predicting and preventing the risk of coal spontaneous combustion. • Oxidation stages of the CSC reaction process were classified as per key temperature points. • Apparent activation energy of each oxidation stage was qualitatively calculated. • The correlation between particle size and apparent activation energy as well as the limit parameters of CSC was investigated. [ABSTRACT FROM AUTHOR]

Systematic understanding of the nature of gas adsorption/desorption in coal matrix is the basis for efficient development of coalbed methane (CBM). In this paper, firstly, the coupling control mechanism of coal rank-pressure on gas occurrence is studied. Secondly, a novel concept of surface control field is proposed, and the influence mechanism of coal rank on methane adsorption capacity is revealed. Thirdly, the difference of energy conversion mechanism between adsorption and desorption processes is clarified. Lastly, a new concept of adsorption potential is proposed on the basis of a novel and useful coal rank-pressure linkage model of energy conversion. It is found that: (a) The surface control field generated by two sidewalls of the pore can overlap, resulting in mutual cancellation of gravitational forces from the two sidewalls. (b) The isosteric heat of adsorption calculated on the basis of desorption curve can reflect the real adsorption performance. (c) Although the density of oxygen-containing functional groups in the microscale pores of the high rank coal matrix is low, the mutual cancellation of gravitational forces leads to a high adsorption saturation but a low adsorption potential. • The coupling control mechanism of coal rank-pressure on gas occurrence is revealed. • A novel concept of surface control field in microscale pores is proposed. • The energy conversion mechanism during gas adsorption/desorption is clarified. [ABSTRACT FROM AUTHOR]

Semi-coke is the solid pyrolysis product of low-rank coal, with high carbon content and difficult to ignite and burn out. The blending of semi-coke with bituminous coal can realize a large amount of utilization of semi-coke. In this paper, the combustion, thermal conversion, and kinetic analyses of semi-coke blending with bituminous coal are investigated under oxygen-enriched conditions (30% O 2 atmosphere). Compared with 20% O 2 atmosphere, the ignition and burnout temperatures are reduced by 10, 7, 8, 12, 7 °C and 129, 76, 85, 115, and 152 °C for the semi-coke blending ratios of 0, 30, 50, 70 and 100% under 30% O 2 atmosphere. Oxygen-enriched combustion can effectively decrease the ignition temperature and improve the combustion performance of the mixture. In 30% O 2 and 20% O 2 atmospheres, the synergy effect of the co-combustion process is different. Under the 30% O 2 atmosphere, semi-coke, and bituminous coal have a strong synergistic effect, which can reduce burnout temperature. However, under 20% O 2 atmosphere, the burnout temperature of the mixture will increase. At a higher blending ratio of semi-coke, the effect of oxygen-enriched conditions on co-combustion is greater, and high oxygen concentration will make the interaction of the mixture combustion process more intense. Compared with bituminous coal, the activation energy of the mixture gradually increases with the increase of the blending ratio of semi-coke, and different combustion stages correspond to different mechanism functions, respectively. The research results can provide ideas for the utilization of semi-coke under oxygen-enriched conditions. [Display omitted] • The activation energy of mixture combustion is reduced in 30% O 2 atmosphere. • The co-combustion synergistic effect of mixture is enhanced in 30% O 2 atmosphere. • The increase of semi-coke blending ratio will result in higher activation energy of mixture. • The influence of oxygen-enriched co-combustion is greater under higher semi-coke blending ratio. [ABSTRACT FROM AUTHOR]

Combustion optimization by fine tuning combustion parameters of boilers can cut down NO x emissions effectively with little cost. Coal qualities, which change from time to time, have great influences on NO x emissions. However, the current NO x reduction optimization model cannot handle with this problem well. What is more, the output load would deviate from the demand load as the boiler efficiency is also affected by the optimized manipulated variables (MVs). In this paper, an on-line method to calculate coal qualities based on reverse balance thermal efficiency model was integrated into the optimization model. Furthermore, a new constraint was added to the optimization model to meet the demand load. NO x emission characteristics of some 600 MW capacity utility boiler were investigated. Fine selected MVs were taken as the inputs of support vector machines (SVM) and NO x emission was taken as the output, respectively. Parameters of SVM were fine tuned by particle swarm optimization algorithm (PSO). Combustion optimization for the studied boiler was undertaken based on the proposed optimization model. Results showed that the new model can provide lower NO x emissions and meet demand loads at the same time. [ABSTRACT FROM AUTHOR]

The use of surfactant to enhance the efficiency of coal biodegradation is a promising technology. In this paper, the effects of nonionic-anionic mixed surfactants TR-LAS and TW-LAS on Wucaiwan coal degradation by Nocardia mangyaensis (N. mangyaensis) were investigated, in which TR (octyl phenoxy poly ethoxy) and TW (polysorbate) were nonionic surfactants, and LAS (sodium dodecyl benzene sulfonate) was anionic surfactant. The results demonstrated the enhancement order of surfactant was TR-LAS > TW-LAS > TR > TW > LAS, and when the total mass of TR-LAS was 1000 mg/L and its ratio was 1200:800 (m/m), and the maximum biodegradation rate of Wucaiwan coal was 74.8% which increased by 23.6% than the control group (without surfactant). It was also found that nonionic surfactant TR was more effective than TW and LAS in promoting the growth of N. mangyaensis , meanwhile anionic surfactant LAS was more effective than TR and TW in increase the zeta potential of oxidized coal. The increase of bacterial growth will secrete more coal-degrading alkaline protease, and the increase of coal zata potential will make bacteria and coal contact easier, both of the above actions are conducive to biodegradation of coal. Thus, the mixed surfactants TR-LAS (1000 mg/L) achieved the strongest synergistic effect of nonionic and anionic surfactants, greatly promoting the biodegradation of coal. This study provides valuable information in designing the mixed surfactant to improve the efficiency of coal biodegradation process. • In the presence of TR-LAS, the maximum biodegradation rate of Wucaiwan coal reached. • TR-LAS promoted the growth of bacteria, resulting in the higher biodegradation rate. • TR-LAS increased zeta potential of coal, making bacterial and coal contact easier. • The degradation products mainly included aliphatic compounds, alcohols and esters. [ABSTRACT FROM AUTHOR]

Hydrotalcite is a new fire-fighting material with a sound effect of preventing the spontaneous combustion of coal. In this paper, hydrotalcite (Zn–Mg–Al-LDHs) and rare earth element Ce-modified hydrotalcite (Zn–Mg–Al–Ce-LDHs) inhibitor samples were prepared by the co-precipitation method, respectively. The surface morphology, dispersibility, and pyrolysis properties of the inhibitor were characterized by thermogravimetric experiments. Based on thermogravimetric experiments, the effects of hydrotalcite and modified hydrotalcite containing rare earth element Ce on the spontaneous combustion characteristics of coal were studied. Combined with thermodynamic parameters, the inhibition mechanism of coal spontaneous combustion was analyzed. The results showed that Zn–Mg–Al-LDHs and Zn–Mg–Al–Ce-LDHs inhibitors were successfully prepared. Adding the two to coal can inhibit both coal samples, and the inhibition effect of Zn–Mg–Al–Ce-LDHs is more significant. The Zn–Mg–Al–Ce-LDHs inhibitor can effectively reduce the weight loss rate of coal, delay the critical temperature, and maximum weight loss rate temperature of coal samples by 6 °C and 31.5 °C, respectively, and increase the residual heat by 2.3%. The calculation of apparent activation energy shows that the average activation energies of Zn–Mg–Al–Ce-LDHs for inhibiting coal samples in the stages of water evaporation and gas desorption and thermal decomposition and combustion are 30935.256 J/mol and 76962.582 J/mol, respectively; 464.878 J/mol and 31914.233 J/mol higher than raw coal, respectively. • Ce promotes the regularity of LDHs crystal structure. • The inhibition effect of modified hydrotalcite is in the first and third stages of CSC. • Modified hydrotalcite can increase activation energy to inhibit CSC. [ABSTRACT FROM AUTHOR]

This paper presents the CFD modeling results of the torrefied maize straw co-firing with sub-bituminous coal in various mass ratios in the industrial scale boiler, to recognize possible application issues of the coal substitution with upgraded biomass. The steam torrefaction of biomass took place in a pilot in a counter-flow torrefaction reactor fed with superheated steam from the OP-230 (Rafako, Poland) boiler. Using a TGA, it was possible to analyze the combustion indexes and synergy effects after burning the torrefied biomass-coal mixtures. Additionally, a kinetic model of pyrolysis devolatilization was established and used in the modeling along with Ansys Fluent kinetics of the coal and gas-phase combustion models. Due to the numerical modeling, it was possible to determine the temperature distribution in the boiler's furnace chamber, the heat flux densities, the simulated distribution of carbon monoxides and carbon dioxide concentration, and the decomposition of nitrogen oxides resulting from co-combustion. Steam torrefied biomass indicates higher combustion activity compared to coal, ignites easier, and burns more intensely with better combustion stability. A synergistic effect between the coal-torrefied blend was observed. According to numerical analysis, it was found that with the increase of the share of torrefaction in the fuel mixture, the share of unburned fuel in fly ash increases. Additionally, an increased share of the torrefied biomass in the fuel blend from 30% to 40% results in a slight increase in the molar NO concentration in the furnace chamber. The authors strongly recommend the continuation of work on further investigation of the co-firing of the coal with torrefied biomass in the pre-mixed blends injected through all burners. • Mazie straw torrefied in superheated steam becomes a coal-like product. • Blends of coal with torrefied mazie straw improves ignition without disturbing combustion stability. • Co-firing at increased TMS share increases temperatures, heat flux densities and CO emissions. • Increased TMS share in fuel blend risies share of unburned fuel in fly ash. • Slight increase of molar NO concentration during co-firing of high TMS share fuel. [ABSTRACT FROM AUTHOR]

The paper describes numerical simulations of processes occurring in the combustion chamber of a stoker boiler. The main topic of CFD analysis presented in this paper is the process of reducing nitrogen oxides emission using the patented Furnace Jet Boiler System (FJBS) in combination with the selective non-catalytic reduction (SNCR) method (FJBS+). The presented method is characterized by introducing a compressed urea-air mixture into the furnace. The reagent is injected through supersonic nozzles, the operating conditions of which are shown on a separate CFD model. The developed model enabled optimization of the existing NO x reduction system, especially in the case of a boiler operating at maximum load. The overall effect of the operation of FJBS + technology is a significant reduction of NO x emissions, by approximately 57%. The results achieved are comparable to those obtained from measurements. It was also confirmed that the operation of FJBS + has a positive effect on the equalization of temperature distribution in the furnace and the concentration of flue gas components. Finally, a sensitivity analysis on the basis of two parameters, specific heat of the fuel and thermal conductivity is presented. • The process of combustion in a grate boiler and the process of nitrogen oxides reduction using the SNCR method is shown. • The operation of the supersonic nozzles that are used in the FJBS system is presented. • The simulation results are in good agreement with on-site measurements. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of a numerical investigation into the combustion process in a boiler furnace chamber with swirl burners using design coal (non-coking coal) and substitute coal (coking coal). The paper describes the development of a three-dimensional combustion model for coal burning in a boiler furnace chamber. The utility boiler operates on high-ash non-coking coal with an ash content of 41.94%. Due to the high ash content in the design coal, most of it is released into the atmosphere, which negatively affects the environment and the surrounding area. We suggest that this coal by a different coal with a lower ash content. It was found that during the combustion of substitute coal at the level of burner, the temperature in the entire cross section increases by 200 K, due to more intense fuel burnout at the outer boundary of the burner torches. It is found that the substitute coal may be burned in the boiler furnace chamber and can provide reliable operation if the swirl burner angle is set at 50° for the secondary air and at 45° for the fuel-air mixture. • Numerical modeling was performed for the combustion of the coal in a furnace with a swirl burner. • Performance of the combustion process for two kinds of coals was investigated. • Predicted temperature complies with the experimental data. • The results show the possibility of using substitute coal in the boiler furnace chamber. [ABSTRACT FROM AUTHOR]

As essential parts of the combined heat supply network with multiple heat sources, the electrical-heating and heat storage technology can simultaneously achieve the goal of clean heating and renewable energy accommodation. The paper introduces the integrated electrical-thermal system with multiple heat sources that consist of combined heat and power (CHP), coal-fired boiler (CB), and electrical boiler (EB) with thermal energy storage (TES). Considering the integration of electrical and thermal networks, we construct a comprehensive model that includes the electrical energy transmission and the overall heat transfer and storage processes based on the heat current method. Based on the comprehensive model, the optimal dispatch of the integrated system is discussed, and an iteration solving method is proposed, which can achieve acceptable convergence and solving efficiency. The simulation results show the combined operation of multiple heat sources has higher system operation efficiency but not necessarily a higher utilization rate of renewable energy. In the test system the combined operation of CHP and coal-fired boiler can reduce the coal consumption of the system by 2%. However, the wind utilization of the system decreases by 4.17%. Moreover, the introduction of an electrical boiler with a TES device can improve the system's flexibility and reduce wind curtailment, wherein the test system is 12.11% more wind consumption. Further, the heat load level can affect the operation efficiency of CHP, the combined operation of multiple heat sources can achieve the balance between reducing coal consumption and increasing renewable energy power generation. • Proposed multiple heating sources for heating in the integrated electric and thermal system. • Introduced the heat current method for the comprehensive modeling of integrated energy system. • Coordinatively analyzed the heat transfer process and power transmission of system modeling. • Provided a new coordination dispatch method for optimal scheduling of power and heat generation. [ABSTRACT FROM AUTHOR]

Oxygen-containing intermediates (OCIs) play an important role in low-temperature oxidation of coal. However, since they are in a dynamic intermediate state, it is difficult to test their thermodynamic properties, and their mechanism of action in coal spontaneous combustion(CSC) are not clear. Therefore, this paper proposed a method to measure the thermodynamics of the OCIs. Furthermore, the reasons for the variation laws of the thermodynamics of the OCIs and their mechanisms of action in CSC were investigated from both macro and micro perspectives. According to the experimental results, thermodynamic parameters of the OCIs can be obtained using the proposed method. And the heating rate of OCIs calculated by the mathematical model based on this method is closer to the total rate of coal oxidation before 70 °C, indicating that OCIs play an important role in the starting process of CSC. Besides, the activation energy of OCIs presents different variation characteristics in different stages. The segmentation can be attributed to the stability of OCIs, which is also critical to the prevention and control of CSC. Hence, the risk of CSC can be reduced by improving the stability of OCIs. • A method to quantitatively calculate the thermodynamic parameters of oxygen-containing intermediates (OCIs) was established. • From the point of view of heat, OCIs play an important role in the starting process of coal spontaneous combustion (CSC). • The activation energy of OCIs has obvious segmentation. • The cumulative production and decomposition threshold of peroxide are the key factors affecting CSC. [ABSTRACT FROM AUTHOR]

The ability of coal to absorb gas is one of the most important factors affecting the prevention and control of mine gas-related disasters and safe exploitation of coal seam gas. In this paper, high gas content coal samples from the Pingdingshan mining area are selected as the research object. The micro molecular structure of coal is altered by pyrolysis, combined with experimental methods such as infrared spectroscopy, isothermal adsorption and liquid nitrogen adsorption. The evolution characteristics of functional groups of coal during high temperature pyrolysis and the variation of gas adsorption capacity of coal after pyrolysis at different temperatures were studied from a micro level. The results show that when the pyrolysis temperature increased from 20 °C to 750 °C, the methane adsorption capacity of coal samples decreased with the increase of pyrolysis temperature. C C, –OH, C O, –CH 2 in coal molecules gradually decreased. In terms of the effect of functional groups and the pore structure on methane adsorption, the methane adsorption capacity in descending order is: C C > –OH > C O > –CH 2. The results of this study provide theoretical guidance for the development of new technologies for the development of coalbed methane thermal injection mining technology. • Discover the evolution of functional groups and pore structure in coal under pyrolysis. • Understand the variation of methane adsorption capacity by modifying the molecular structure of coal under pyrolysis. • Establish the correlation between coal microstructure and methane adsorption capacity via macro and microscopic tests. [ABSTRACT FROM AUTHOR]

This paper describes the results of an experimental investigation on the stages of thermochemical transformation of fuels prepared from waste. We studied the combustion of coal slime and its co-combustion with additives (waste turbine oil, sawdust, and rapeseed oil). The mass fraction of the additive was 5%. Fuels in the forms of a pellet, dry loose layer, and slurry were heated in a tubular muffle furnace. The reactivity of the fuels was evaluated, and the duration of the main process stages was recorded. Experiments have shown that it is more expedient to burn coal slime in combination with other components, which improved the ignition and burnout performance of the blends. The addition of turbine oil accelerated the flame combustion by 3–6 times. Rapeseed oil reduced the duration of the endothermic stage by 50–60%. The slurry droplets had the longest pre-flame stage. Their burnout was more intense than that of pellets or a layer and was less dependent on the temperature in the furnace. The longest burnout was typical of pellets. The data obtained are essential in planning and conducting industrial tests on the energy recovery of coal slime, biomass, and refined products. [Display omitted] • Combustion of coal slime is advisable in combination with other components. • The burnout of slurry droplets is the best in comparison with pellets and layers. • The addition of turbine oil (5 wt%) reduced the endothermic period by 3–6 times. • Minimal ignition temperature of waste-derived blends varied from 450 °C to 500 °C. • Coal slime pellets tend to low reactivity and incomplete burnout. [ABSTRACT FROM AUTHOR]

Since the formation of gaseous pollutants during solid fuel combustion in circulating fluidized bed (CFB) units, especially under oxyfuel combustion and chemical looping combustion conditions, is an extremely complex process, the development of a simple predictive model of gas emissions is of practical significance. This paper introduces a novel approach based on fuzzy logic (FL), one of the main artificial intelligence (AI) methods, for the prediction of CO 2 , CO, NO x (i.e., NO + NO 2), N 2 O, and SO x (i.e., SO 2 + SO 3) concentrations in flue gases from coal and biomass combustion in various operational sceneries. The simulations are carried out for different combustion environments, i.e., air-firing, oxyfuel, iG-CLC (in-situ gasification chemical looping combustion), and CLOU (chemical looping with oxygen uncoupling), under a wide range of operating parameters. A mixture of oxygen with CO 2 was used for oxyfuel combustion. Three different oxygen carriers (OC) were examined in the study for iG-CLC and CLOU, i.e., ilmenite, copper oxide (60% wt.) with the support of carbonate waste from ore flotation, and copper oxide (60% wt.) with the support of ilmenite (20% wt.) and fly ash. The validation of the model was successfully performed on a complex geometry laboratory–scale 5 kW th Dual-Fluidized-Bed Chemical-Looping-Combustion of Solid-Fuels (DFB-CLC-SF) facility. The gaseous pollutant emissions predicted using the developed model were in good agreement with experimental results. The maximum relative error between measured and predicted by the model emissions was lower than 8%. The proposed method constitutes a quick and easy-to-run technique and a complementary tool compared to the experimental procedures and the programmed computing approach. The developed fuzzy logic-based model of gaseous emissions from advanced combustion (GasAdComb) of solid fuels can be easily applied by scientists and engineers to simulate and optimize coal and biomass combustion processes. • A comprehensive model of 5 kW th Dual-Fluidized-Bed CLC facility was developed. • Fuzzy logic approach was applied in the study. • Air-firing, oxyfuel, iG-CLC and CLOU under a wide range of operating parameters are considered. • The model was successfully validated against experimental data of gaseous pollutants emissions. • The model constitutes an easy-to-use optimization tool. [ABSTRACT FROM AUTHOR]

The oxygen-staged combustion is an effective strategy to reduce NO emission, but its effects on ash deposition in oxy-fuel combustion of Zhundong high-alkali coal still remain unclear. This paper simultaneously focused on the NO emission and ash deposition during the oxygen-staged oxy-fuel combustion of Zhundong coal using a vertical two-stage furnace system. The air- and oxygen-staged combustion were compared and the impacts of oxygen content and stoichiometric ratio in primary zone (SR 1) in oxygen-staged combustion were further evaluated. The results show that compared to air-staged combustion, the oxygen-staged case in oxy-fuel combustion leads to smaller conversion ratio of fuel-N to NO (X NO) and smaller mass of ash deposit. Under oxygen-staged conditions, both the X NO and deposit mass have an upward trend as the oxygen content increases (15%–50%). About 20 mg more ash could be collected for every 10% increase in oxygen content. The X NO increases when SR 1 gets elevated from 0.5 to 1.2, however, the deposit mass exhibits a downtrend at SR 1 ≤ 0.9 and becomes nearly independent of oxygen supply when the SR 1 further increases. The SR 1 of 0.9 is a reasonable choice, and some measures should be taken to alleviate the ash-related problems if smaller SR 1 is needed. • NO emission and ash deposition of high-alkali coal were simultaneously emphasized. • Different oxygen-staged conditions of oxy-fuel combustion were investigated. • Oxygen-staged combustion is superior to air-staged combustion in present study. • Higher O 2 content increases both the NO emission and ash deposition. • The deeply oxygen-staged combustion reduces NO but worsens the ash deposition. [ABSTRACT FROM AUTHOR]

The integration of process heat with regenerative steam Rankine cycles by preheating the boiler feedwater increases power generation from the steam turbines. In oxy-combustion coal based power plants, considerable compression heat from the air separation unit is available for such heat integration, however, there are at least two challenges: (1) how to integrate a heat stream with the steam cycle, and (2) how to optimize the compression scheme, accounting for the trade-off between compression work requirement and the turbine power output. This paper investigates the optimal integration of the air compression train in a cryogenic air separation unit with the regenerative steam cycle in an oxy-combustion coal based power plant using MINLP (mixed Integer non-linear programming) Two special cases (adiabatic compression and “isothermal” compression) are also investigated to compare with the optimization results. The study shows that such heat integration increases the thermal efficiency of the reference power plant by a maximum of 0.5–0.6% points. The heat integration is less attractive when the temperature difference of the heat transfer between the compressed gas and the boiler feedwater is larger than 40 °C. [ABSTRACT FROM AUTHOR]

Energy-environmental impacts associated with non-renewable electricity generation have attained critical importance in South Africa. These impacts are quantified in order to obtain a monetary cost relative to local electricity prices. The methodology used to perform the analysis is the Impact Pathway Approach. Numerous energy-environmental external impacts have been evaluated in this study. The primary externality contributors were found to be GHG (green-house gas) emissions and public health effects from coal combustion. Other minor but important contributors to externalities are also identified and mentioned within the paper. Aggregated central externality costs were found to range from 5.86 to 35.36 SA c/kWh (1.31–7.95 US c/kWh), with central externalities estimates at 13.43 SA c/kWh (3.02 US c/kWh). These central estimates were found to be 68.5% of average electricity prices during the year 2008. Conversion of externality costs from South African currency to US currency has been made with purchasing power parity exchange rates for the year 2008. This study provides sufficient methodological parity for countries with similar electricity generation backgrounds in Southern Africa and Africa as well as other developing countries, considering South Africa generates roughly 45% of the electricity on the African continent. [ABSTRACT FROM AUTHOR]

Low concentration methane, emitted from various industries e.g. coal mines and landfills into atmosphere, is not only an important greenhouse gas, but also a wasted energy resource if not utilized. In the past decade, we have been developing a novel VAMCAT (ventilation air methane catalytic combustion gas turbine) technology. This turbine technology can be used to mitigate methane emissions for greenhouse gas reduction, and also to utilize the low concentration methane as an energy source. This paper presents our latest research results on the development and demonstration of a 25 kWe lean burn catalytic combustion gas turbine prototype unit. Recent experimental results show that the unit can be operated with 0.8 vol% of methane in air, producing about 19–21 kWe of electricity output. [ABSTRACT FROM AUTHOR]

The EU's energy sector depends heavily on fossil fuels, which contribute to climate change. This is why climate mitigation targets for energy production have been set, including an increased biomass use requirement. In Finland, biomass is commonly utilised but its capital, Helsinki, is still dependent on fossil fuels. With the ambition of becoming climate neutral by 2050, Helsinki is testing, inter alia, low-share wood pellet and coal co-combustion in a CHP (combined heat and power) plant. The objectives of this paper were to assess the net environmental impacts of the co-combustion and changes in urban air quality connected to pellet transport, and to identify environmental hotspots relevant to possible future higher-share co-combustion. The applied methods were screening LCA (life cycle assessment) and fine particle dispersion modelling. The results prove that low-share wood pellet co-combustion in CHP production leads to net environmental impact reductions and does not deteriorate air quality in the urban environment. If higher-share co-combustion were to be implemented, the environmental hotspots to focus on would be the operational issues of a power plant and the origin and sustainability aspects of wood pellet production. [ABSTRACT FROM AUTHOR]

In this paper, systematic research of the physisorption characteristics of oxygen in low-rank coals had been carried out using the Grand Canonical Monte Carlo (GCMC) and the Density Functional Theory (DFT) methods based on the assumption of no chemisorption. Firstly, the surface molecular structure parameters of five different low-rank coals were determined, the coal molecules and their unit cells structure were constructed; Secondly, Oxygen physisorption behaviour in coal molecular unit cells was simulated based on the GCMC and the Molecular Dynamics (MD) method; Finally, the physisorption parameters for oxygen physisorption at each adsorption site were simulated based on the DFT. The results show that the microporous structure of coal molecules is positively correlated with the total physisorption amount of oxygen and has an effect on the physisorption heat; oxygen is gathered around aliphatic hydrocarbons, the mutual distances of methyl and methylene to oxygen were 3.57 Å and 3.81 Å, respectively; the adsorption capacity of the low-rank coal molecules is effected by aromatic, oxygenated aliphatic hydrocarbons, and the degree of condensation of polycyclic aromatic hydrocarbons, the physisorption energy of the aromatic ring, hydroxyl and ether bonds to oxygen were −3.4790 kcal/mol, −2.9933 kcal/mol and −2.9663 kcal/mol respectively. This research will enable us to better understand the physisorption mechanism of oxygen in low-rank coals. [Display omitted] • The macromolecular model of five low-rank coals were constructed. • The physisorption behavior of oxygen in low-rank coals were simulated. • Oxygen in low-rank coals tends to gather around the aliphatic hydrocarbons. • Aromatic rings, hydroxyl and ether with strong physisorption capacity for oxygen. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the effects of the exhaust tube vortex (ETV) on pollutant emissions and carbon burnout performance. The novelty in this study is to improve understanding of combustion behavior with the ETV structure via detailed in-furnace measurements (temperature, gas-phase species concentration, carbon burnout, emissions, and etc.) in a 16-kW th coal-fired furnace. The experiment considered two different swirling flames (co- and counter-swirl) with four air staging positions. A hollow tubular structure such as the ETV structure has been created under the co-swirl condition. The values of NO x emissions are about 430 ppm, but the CO emission is lower and carbon burnout is approximately 2% higher than that of the counter-swirl unstaging condition at the furnace outlet. For the air staging conditions, the air staging position 3 (SL 3) maintained the generated ETV structure stronger in the primary combustion zone. The SL 3 condition produced the lowest CO emission at about 275 ppm, and a relatively low emission of NO x showed with the highest carbon burnout performance of approximately 94.5% or more. The SL 3 condition is the most favorable condition for the synergistic effect of air staging technology on the ETV structure with a low-NO x swirl-stabilized burner. • Combining the two technologies of swirl burner and air staging produces a synergy. • Combustion behavior with the ETV was evaluated by detailed in-furnace measurements. • The ETV was a hollow tube structure with radius greater than 20 mm. • The ETV with air staging has lower exhaust emissions and highest carbon burnout. [ABSTRACT FROM AUTHOR]

The practice of injecting a coal/biomass blend can alleviate the pressure on carbon emissions and energy of ironmaking blast furnaces (BFs). In this paper, corn stalks treated by hydrothermal carbonization (HTC) are used as raw materials to eliminate the harm of alkali metals in the ash. The overall performance of individual behavior of the hydrochar, coal, and their blends are analyzed over the raceway with special reference to gas flow, temperature, species, and combustion efficiency. The results show that the hydrochar with higher volatile content is faster to devolatilize, showing a higher CO 2 content at the nozzle tip, and reaching a higher burnout in the raceway. The addition of hydrochar to coal can improve the overall flow and combustion performance of the blends. The simulated value is higher than the calculated value, indicating the synergistic effect has existed. When the proportion of the hydrochar is 75% in blends, the synergistic effect is most obvious. The model provides an effective tool for the design of coal/biomass blends. • The co-combustion process of hydrochar and coal in BF is simulated. • The burnout of hydrochar is higher than that of coal. • The synergistic effect of hydrochar/coal blending is examined in co-combustion process. • The simulated burnout is 2.1% higher than the calculated burnout in 25%coal/75%hydrochar case. [ABSTRACT FROM AUTHOR]

As the carrier of material circulation, the uniformity of multi-parallel external loops directly affects the operation of large-scale circulating fluidized bed (CFB) boilers. Some non-uniform phenomena have been found, but the non-uniform characteristics and the absorptive capacity in full process of external loops under changeable operating parameters were seldom considered. To solve this, comprehensive cold/thermal field tests were conducted on the external loops of the first 600 MW supercritical CFB boiler. Operating characteristics of the loops and the fluidization uniformity of fluidized bed heat exchangers (FBHEs) under various cases were fully demonstrated. The influence of air-coal distribution on the operating non-uniformity of the external loops were analyzed, and the absorptive capacity to thermal deviations were quantified. The regulation mechanisms of cyclones and FBHEs were clarified, and the key reason of thermal deviations in FBHEs was also figured out. Eventually, a new coal feeding method to maintain heat balance in dense phase zone was proposed. The results of this paper fully reflected the operating characteristic of the full process in external loops and the response characteristics to air-coal adjustments, which could provide the most direct guidance for academic research as well as optimal design and operation of large-scale CFB boilers. • Thermal deviations of full external loops under various conditions were obtained. • Key reason for thermal deviations in FBHEs was tested and verified. • Absorptive capacity and regulation mechanism of external loops were figured out. • A coal feeding method to maintain heat balance in dense phase zone was proposed. [ABSTRACT FROM AUTHOR]

Oxygen-enriched combustion in fluidized bed is a promising clean coal combustion technology which can efficiently control the emission of coal-fired pollutants, especially CO 2. In this paper, by using several judging methods, the combustion characteristics of five kinds of coal under four different oxygen concentrations (20.9%, 27.8%, 40.7% and 52.7%, CO 2 as equilibrium gas) were measured in the small-scale fluidized bed reactor with electric heating in detail. The oxygen consumption and volatile release characteristics were explored online. The influence of coal types, volatile matter and oxygen concentration on coal combustion characteristics was analysed. It's found that the higher the bed temperature was, the faster the reaction rate was and the more oxygen consumption was. At a certain oxygen concentration and proper bed temperature, the separated combustion of volatile and char were observed. When the oxygen concentration was high, the separation phenomenon was more obvious. High-volatile, a certain bed temperature and oxygen concentration were the basic factors for the formation of separated combustion. The total volatile matter is not comprehensive as the index of reaction combustion characteristics and the effect of combustible components should be specifically considered. It's found that for the coal with high combustible components, the separated combustion is more obvious. Volatile matter plays a dual role in the ignition and combustion of coal. The volatile matter (lower volatile matter) of some coals has a great promoting effect on coal combustion at higher temperature, while that (higher volatile matter) of other coals is not, which is closely related to the properties of char and the diffusion of volatile matter in pores. • The combustion characteristics of five kinds of coal were measured. • Four different oxygen concentrations were studied. • The separated combustion of volatile and char was described. • High-volatile was important for separated combustion. • The effect of volatile components on separated combustion was confirmed. [ABSTRACT FROM AUTHOR]

In order to solve existing problems of large working fluid pressure drop and lower reheated working fluid temperature under part load conditions, a new 300 MW S–CO 2 coal-fired boiler heating surface arrangement is proposed and its off-design performances are studied. The new S–CO 2 boiler adopts the single furnace double-tangential circle arrangement without the center wall and increases the proportion of reheat radiant heat exchange surfaces. The performance analysis model is built. The variations of the reheated working fluid temperature, working fluid pressure drop and the off-design performances of the boiler with the changes of coal type, excess air coefficient and operating load are investigated. The results show under the design load, the total pressure drop of working medium in the furnace is reduced by 0.48 MPa, under 30% of the design load, the reheated working medium temperature is increased by 7.62 °C, and the lower heating value and components of coal greatly influence the boiler efficiency. When the excess air coefficient is 1.2–1.4, the best efficiency zone is reached. The load range with the optimal efficiency zone is about 70%–100% of the design load. Achievement of this paper will provide valuable references for the design of the S–CO 2 coal-fired boiler. • The conventional coal-fired boiler configuration is not fit for the S–CO 2 cycle. • Arrangement of heating surfaces of S–CO 2 boiler influences the overall performance. • A new S–CO 2 coal-fired boiler is proposed and off-design performances are studied. • New boiler has better performances at both the design and off-design conditions. • The new boiler configuration can improve the overall system thermal efficiency. [ABSTRACT FROM AUTHOR]

The weight gain curve of corrosion test on metals is a common way to evaluate the degree of corrosion. In this paper, as opposed to the generally used experimental approach, a detailed calculation model was established to predict the corrosion weight gain curve. The model aims at determining the overall process of high temperature corrosion by combustion of coal characterized with high contents of chlorine and sodium. The calculation model focuses primarily on four steps: destruction of protective oxide layer; chlorination of alloying elements; diffusion and oxidation of metal chlorides; shedding of corrosion products. Sha Erhu coal with high contents of chlorine and sodium can cause severe fouling and slagging in boiler according to the reliable index of fouling factor R F. The mechanism of high temperature Cl-induced corrosion is generally called active oxidation. In the present work, a specific analysis of chemical kinetic calculation is carried out for each step of active oxidation mechanism. Besides, the calculation model involves destruction of protective oxide layer before the occurrence of active oxidation reaction and shedding of corrosion products after the corrosion mechanism. The lab-scale experimental results for the corrosion weight gain agree with the calculation model except for pure Cr at 610 °C, and it can be inferred that a low melting point eutectic involving Na 2 CrO 4 occurs. Furthermore, the protective oxide layer is initially formed on the substrate for TP347H (1Cr19Ni11Nb). But for T91 (10Cr9Mo1VNb), the protective oxide layer is not formed due to low content of Cr. The appearance microstructure and the elemental concentration distribution maps on alloy steel have been examined using scanning electron microscope coupled with an energy dispersive spectrometer (SEM−EDS) to provide an insight into material degradation. • A calculation model for chlorine corrosion during coal combustion is established. • Occurrence of low melting point eutectic on substrate means severe degradation. • Significantly higher corrosion resistance of TP347H than other alloy. • Nickel-rich interface formed on substrate after corrosion due to low affinity. [ABSTRACT FROM AUTHOR]