The transition of heterogeneous–homogeneous ignitions of dispersed coal particle streams

This work is assessing a study of the collective ignition behaviors of dispersed coal particle streams, with ambience temperature from 1200 K to 1800 K and oxygen mole fractions in the range of 10–30%. The dispersed coal particles of 65–74 μm are injected into an optical Hencken flat-flame burner by a novel de-agglomeration feeder. Three kinds of pulverized coals from different ranks, Hulunbel lignite, high-ash-fusion bituminous and low-ash-fusion bituminous, are considered. The normalized visible light signal intensity, deleting the background noise, is established to characterize the ignition delay of coal particle streams. Firstly, the prevalent transition from heterogeneous ignition to hetero–homogeneous ignition due to ambience temperature is observed. The pure homogeneous ignition rarely occurs, with an exception under high temperature and low oxygen for high-volatile coal. By comparing time scales between pyrolysis and heating processes, the competition of the volatile evolution and heterogeneous surface reaction are discussed. Then, the effects of ambience temperature, oxygen mole fraction and coal rank on the characteristic ignition delay are examined. Finally, the transient mode is developed, which not only well interprets the observed ignition transition phenomena, but also approximately predicts a variation of heterogeneous ignition time as a function of oxygen fraction.     

Thermal–mechanical modelling around the cavities of underground coal gasification

Underground coal gasification (UCG) is an efficient method for the conversion of the deep coal resources into energy. This paper is concerned with a feasibility study of the potential of deeply lying coal seams (>1200 m) for the application of UCG combined with subsequent storage of CO₂ for a site located in Bulgaria. A thermal–mechanical coupled model was developed using the ABAQUS software package to predict the heat transfer, the stress distributions around the UCG and the consequent surface subsidence. Material properties of rocks and coal were obtained from existing literature and geomechanical tests which were carried out on samples derived from the demonstration site in Bulgaria. Three days of gasification has been simulated by assigning a moving heat flux on a cell of 2 m × 2 m × 2 m at a velocity of 2 m/day. Results of temperature and stress distribution showed that the developed numerical model was able to simulate the heat propagation and the stress distribution around cavities under a thermal–mechanical coupled loading during the UCG process. Also, the surface subsidence was found to be 0.08 mm after three days of gasification for the case studied. It is anticipated that the results of this paper can be used for the prediction and optimization of the UCG process in deep coal seams.     

Pyrolysis characteristics and kinetics of upgraded Yi’an gas coal

This article studied pyrolysis characteristics and kinetics of upgraded Yi’an gas coal by low temperature pyrolysis in N₂ atmosphere. The quality of coal before and after modification was examined by thermogravimetric analysis. The pyrolysis of the coal becomes violent in the middle temperature range and is calculated to be a third-order reaction. After upgrading, total weight losses and coal caking properties of different temperatures increase and 250°C is the best upgrading temperature.     

Steam co-gasification of coal and biomass – Synergy in reactivity of fuel blends chars

Development of clean coal technologies is the answer to increasing energy demand and environmental concerns related to conventional coal processing technologies. The technologies of fossil fuel gasification are technically proven and commercially available. Attempts of utilization of waste materials and renewable energy resources in gasification-based energy generation systems has been made, but wide application of such systems is still hindered by issues inherently combined with the characteristics of the materials. These include discontinuous supplies of a fuel of limited resources and varying composition resulting in poor economy of small-scale systems and operating problems related to tars formation and corrosion, especially when biomass utilization is considered. In the light of the above co-gasification seems to offer several advantages through mitigation of undesired effects of both carbon-intensive utilization of coal and low efficient and troublesome operation of biomass/waste-fed gasification systems. The experimental results presented in the paper address the issues of determination of potential synergy effects resulting from the utilization of fuel blends composed of materials of various physical and chemical characteristics, which are still insufficiently discussed in the literature, especially when hydrogen-rich gas production in co-gasification is concerned. The results of reactivity tests of fuel blends of coal and energy crops biomass in the process of steam co-gasification in a laboratory scale fixed bed reactor at 700, 800 and 900 °C are given proving the synergy effect in co-gasification reflected in increased reactivity of fuel blends when compared to coal and biomass chars reactivity under similar process conditions.     

Economic analysis of a typical solar–coal hybrid power plant

Since the 1990s, solar energy has been hybridized with fossil power plants to improve reliability and efficiency. This study proposed an economical model for the solar–coal hybrid system. A conventional 200 MW coal-fired power plant was hybridized with solar heat at approximately 300°C and compared with a typical solar-only thermal power plant. The annual thermal performances of the proposed system were estimated and they were economically assessed using the economic model. The appropriate replacement configurations for the system can be determined for lower solar electricity cost. Therefore, this system may utilize solar energy on the utility scale cost-effectively.     

Study of interaction of entrained coal dust particles in lean methane–air premixed flames

This study investigates the interaction of micron-sized coal particles entrained into lean methane–air premixed flames. In a typical axisymmetric burner, coal particles are made to naturally entrain into a stream of the premixed reactants using an orifice plate and a conical feeder setup. Pittsburgh seam coal dust, with particle sizes in the ranges of 0–25 μm, 53–63 μm, and 75–90 μm, is used. The effects of different coal dust concentrations (10–300 g/m³) entrained into the mixture of methane–air at three lean equivalence ratios, ?, of 0.75, 0.80 and 0.85, on the laminar burning velocity are studied experimentally. The laminar burning velocity of the coal dust–methane–air mixture is determined by taking high quality shadowgraph images of the resulting flames and processing them using the cone-angle method. The results show that the laminar burning velocity reduces with the addition of coal dust having particle sizes in the ranges of 53–63 μm and 75–90 μm, irrespective of the equivalence ratio values. However, burning velocity promotion is observed for one case with particle size in the range of 0–25 μm at an equivalence ratio of 0.75. Two competing effects are considered to explain these trends. The first effect is due to volatile release, which increases the overall equivalence ratio and thus, the flame temperature and burning velocity. The second is the heat sink effect that the coal particles take up to release the volatiles. This process reduces the flame temperature and accordingly the burning velocity also. A mathematical model is developed considering these effects and it is seen to successfully predict the change of laminar burning velocity for various cases with different dust concentrations and equivalence ratios of the gas mixture. Furthermore, the implication of this study to coal mine safety is discussed.     

The transnationalisation of the Indian coal economy and the Australian political economy: The fusion of regimes of accumulation?

The Indian government's economic development program is predicated on increasing electricity generating capacity. Coal fired power and removal of obstacles to private corporations investing in generating capacity are core elements in this program. With difficulties in boosting national coal production, the state-owned Coal India Limited and energy corporations have spearheaded a range of global coal sourcing endeavours, including investing in offshore deposits. Energy security has become reflected in engineering global supply chains, securing control of coal, with two of the largest projects involving Adani and GVK proposing to develop mines in the Galilee Basin in Queensland, Australia. These investments become the institutional and organisational architecture that locks in demand, a global demand which helps to explain successive Australian governments support for and approval of the projects. Notwithstanding considerable environmental opposition, and questions about the economic merits and commercial viability of the projects, Australian governments are wedded to the conviction that expanded development of the economy is tied to extracting and exporting fossil fuels, to consolidating Australia as an ‘energy superpower’.     

Effectiveness analysis of solar replacement scenarios in a typical solar–coal hybrid system

Since the 1990s, solar energy has been hybridized with fossil power plants to improve reliability and efficiency. Hence, this study proposed a methodology to thermodynamically model the solar–coal hybrid system. A conventional 200 MW coal-fired power plant was hybridized with solar heat at approximately 300°C and compared with the Solar Energy Generating Systems VI type. The annual thermal performances of the proposed system were assessed using the established thermodynamic methodology. The appropriate replacement configurations for the system can be determined to enhance solar-to-electricity efficiency. Therefore, this system may utilize solar energy on the utility scale effectively.     

Switching towards coal or renewable energy? The effects of financial capital on energy transitions

Does a country's stock of financial capital affect its ability to achieve energy transitions? This paper uses data for up to 137 countries for the period 1998–2013 to investigate the importance of financial capital for changes in the use of each energy type. I find that financial capital supports transition to more capital-intensive energy types. For high-income countries, financial capital facilitates transitions from fossil fuels to modern renewable energy sources, especially wind. Both private credit from banks and domestic private debt securities support greater shares of wind energy. For lower-income countries, financial capital supports progression from biomass towards fossil fuel energy sources such as coal. I also find that countries with larger stocks of financial capital are more likely to move to more capital-intensive electricity generation systems.     

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm³/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm³/kg) and H₂ content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).     

Economic analysis of coal price–electricity price adjustment in China based on the CGE model

In recent years, coal price has risen rapidly, which has also brought a sharp increase in the expenditures of thermal power plants in China. Meantime, the power production price and power retail price have not been adjusted accordingly and a large number of thermal power plants have incurred losses. The power industry is a key industry in the national economy. As such, a thorough analysis and evaluation of the economic influence of the electricity price should be conducted before electricity price adjustment is carried out. This paper analyses the influence of coal price adjustment on the electric power industry, and the influence of electricity price adjustment on the macroeconomy in China based on computable general equilibrium models. The conclusions are as follows: (1) a coal price increase causes a rise in the cost of the electric power industry, but the influence gradually descends with increase in coal price; and (2) an electricity price increase has an adverse influence on the total output, Gross Domestic Product (GDP), and the Consumer Price Index (CPI). Electricity price increases have a contractionary effect on economic development and, consequently, electricity price policy making must consequently consider all factors to minimize their adverse influence.     

Slagging behavior and mechanism of high-sodium–chlorine coal combustion in a full-scale circulating fluidized bed boiler

The contents of chlorine and sodium in Xinjiang Shaerhu (SEH) coal are extremely high, leading to severe slagging. In this paper, the slag was sampled from a circulating fluidized bed (CFB) boiler purely burning SEH coal, to analyze the slagging mechanism based on the characterization of morphology and composition. The results show a three-layer structure for the slag sampled from the buried heat-exchanger in the dense-phase zone of the CFB boiler. The inner layer close to the heat-exchanger is NaCl, which enhances the adhesion of ash particles, while the middle layer and the outer layer are mainly composed of Ca₂Al₂SiO₇ and other Si–Al materials. In comparison, the slag sampled from the refractory wall shows a molten state without a layered structure and mainly composed of NaCl, NaAlSiO₄, Ca₂Al₂SiO₇, and CaSiO₃. The effect of mixing bed material, on the ash melting and release of chlorine and sodium was further conducted, which indicates that the mixing of bed material has no significant effect on the release of chlorine(Cl) and sodium(Na) but highly affects the melting temperature and compositions. The ash fusion temperature reaches the lowest with a 50% mixing ratio of bed material, which is 120 °C lower than that of SEH coal ash. This study can provide better guidance for controlling severe slagging, from the combustion of high Na and Cl coal in industrial furnaces.     

The role of coal in energy policy and sustainable development of Turkey: Is it compatible to the EU energy policy?

This paper aims to assess the current and future role of coal in energy strategy of Turkey, and evaluates the compatibility of policies to the EU energy policy and strategy. Coal is regarded as the most important indigenous energy source in Turkey together with hydropower to strengthen the supply security of the country. Turkish government set targets to fully utilize coal reserves of the country in next decades. However, the country is also in the process of becoming an EU Member State, hence, it is expected that the energy policies have to comply with the EU. Moreover, Turkey ratified Kyoto Protocol in 2009, thus the country should limit CO₂ emission together with other greenhouse gases. The probable obstacles that Turkey may face due to the utilization of coal were determined as CO₂ emissions, lack of technology and application in Carbon Capture and Storage (CCS) and health and safety issues. It is concluded that coal is a very important domestic energy source for Turkey but new policies have to be developed and adopted immediately, and more realistic targets for the country should be set accordingly.     

Gas permeation field tests of composite Pd and Pd–Au membranes in actual coal derived syngas atmosphere

Three large scale (with each a permeable area of 200 cm²) highly structured composite Pd and Pd–Au membranes were prepared and tested in an actual stream of coal derived, but desulfurized, syngas at the National Carbon Capture Center (NCCC) in Wilsonville, Al. The objective of the study was to investigate the long term membrane stability and to establish the long term effects of syngas contaminants in the coal derived syngas other than sulfur compounds on H₂ permeance and selectivity. The large scale membranes had thicknesses ranging from 7 to 14 μm, H₂ permeances ranging from 20 to 28 Nm³ m⁻² h⁻¹ bar^−0.5, and an undetectable He leak before the actual syngas test. In the syngas atmosphere, composite Pd and Pd–Au membranes showed an outstanding H₂ permeance stability at 450 °C and 12.6 bar for approximately 200 h albeit a fast initial decline upon syngas introduction. The fast permeance decline observed at the introduction of the actual syngas was attributed to possible surface and/or bulk poisoning. An exceptionally high H₂ purity level of 99.89% was achieved at 450 °C and 12.6 bar during the entire period of the measurement of over 200 h in syngas atmosphere representing a breakthrough result in the field never reported before with actual syngas from a coal gasification unit.     

Study of chemical looping co-gasification (CLCG) of coal and rice husk with an iron-based oxygen carrier via solid–solid reactions

The chemical looping gasification (CLG) is a promising gasification technology for syngas production. It reduces the demand for pure oxygen and heat from outside by the cycle of oxygen carriers. The lattice oxygen is transferred by oxygen carrier like Fe₂O₃ in CLG. Considering the synergy between lignite and rice husk, the chemical looping co-gasification (CLCG) of lignite and rice husk with Fe₂O₃ as oxygen carrier was studied in this work. The mass loss of lignite increased by about 3% with the help of rice husk. Due to the synergetic effect, rice husk developed the pyrolysis of coal in the co-gasification. It is found that the most contributing reaction at around 800 °C–1000 °C in CLG is the gasification of char with Fe₂O₃via solid-solid reactions. The kinetic fitting was used to explore the reaction mechanism of CLCG. The modified random pore model (MRPM) fitted the experimental data well, which confirmed the solid-solid reactions between char and Fe₂O₃, and the synergy between lignite and rice husk in CLCG. Finally, the gas analysis was conducted in a fixed bed system with gas analyzers. It is found that Fe₂O₃ enhanced the concentration of CO and CO₂ in CLG process.     

Modification with formaldehyde on the thermal reactivity of >300°C distillation fraction from low-temperature coal tar

A >300°C distillation fraction (300F) from low-temperature coal tar was reacted with formaldehyde. Residual oil (RO) and residual solid (RS) were collected. RO was detected by gas chromatography-mass spectroscopy (GC-MS) and shows that it mainly contains alkanes and polycyclic aromatic hydrocarbons. The degradations under a nitrogen atmosphere of 300F and RO were investigated by Fourier transform infrared spectrometer. The result shows that 300F and RO consist of two degradation stages and five stages, respectively. CO has significant absorbency in the pyrolysis process of RO, not in 300DF. Modification of formaldehyde and compounds with carboxyl, short-chain fatty, and ester group in 300F generates polymers and fixes these compounds.     

The roles of inter-fuel substitution and inter-market contagion in driving energy prices: Evidences from China’s coal market

Coal has been dominating energy supply and consumption in China, with the country becoming the largest energy supplier and consumer worldwide. Due to inter-fuel substitution of crude oil and inter-market contagion of international coal market, China's coal price might be interrelated with crude oil price and international coal price. However, the precise roles of these two effects in determining China's coal price are unknown. This paper contributes to previous literature by investigating this issue. We find that co-movements between China's coal price and crude oil price largely hinge on the shares of oil and coal in China’s energy mix, while its co-movements with international coal price depend on scales of coal trade. Inter-fuel substitution dominated the interaction of China's coal market with other energy types, but the importance of inter-market contagion has been increasing. We also find that China might have become an originator for driving the returns of crude oil and international coal, in particular after 2008. Furthermore, China's coal market is still a net volatility recipient for shocks from both crude oil market and international coal market. Given the increased integration of global energy markets, we anticipate this paper to provide a better understanding on the dynamic changes in China's coal prices.     

An incremental model for coal evaluation—II. Gasification

Values of a coal can vary greatly depending on its use. A model has been devised specifically to evaluate coals as feedstocks for gasification. In this method, incremental values are assigned to all quality parameters relevant to process economics. The incremental values are premium and discount of coal for variation in quality from which coal value as gasification feedstock can be calculated. The method is particularly useful in times of technical uncertainty.     

Kinetics and mechanism of CO2 gasification of coal catalyzed by Na2CO3, FeCO3 and Na2CO3–FeCO3

The purpose is to develop a mild catalytic CO₂-gasification technology that can promote CO₂ utilization and reduce cost in air separation systems with improving system efficiency and obtaining desirable gaseous products. In this study, the influence of Na, Fe and their composite catalysts on the structure and gasification reactivity of chars derived from pyrolysis of Powder River Basin (PRB) coal was investigated. The results showed that a strong positive synergistic effect between Na and Fe catalyst in the gasification process was observed, the catalytic activity of the added catalysts was in order of: 4% Na > 3% Na–1%Fe > 2% Na-2% Fe > 1% Na-3% Fe > 1% Na-2% Fe > 4% Fe > raw coal. The catalysts inhibited the growth of the aromatic ring structure and enriched the generation of O-containing functional groups. Compared to Fe, the Na-based catalyst could easily diffuse into inner pores of coal char, forming C–O–Na structure and thus increasing the gasification reactivity of chars. In addition, due to the formation of inert material between SiO₂ and Na, the catalytic activity of Na catalysts was significantly decrease at the late stage of char conversion. Comparatively, the Fe-based catalysts showed better stability life. Moreover, it was found that the activation energy for CO₂-gasification of PRB coal can be decreased by 50% due to the addition of Na catalyst.     

Small–medium sized nuclear coal and gas power plant: A probabilistic analysis of their financial performances and influence of CO2 cost

Nations or regions with limited electrical grid and restricted financial resources are a suitable market for small medium power plants with a size of 300–400 MWe. The literature presents several comparisons about the economics of large power plants (of about 1000 MWe); however there are not probabilistic analysis regarding the economics of small medium power plants. This paper fills this gap comparing, with a Monte Carlo evaluation, the economical and financial performances of a nuclear reactor, a coal fired power plant and a combined cycle gas turbine (CCGT) of 335 MWe. The paper aims also to investigate the effect of the carbon tax and electrical energy price on the economics of these plants. The analysis show as, without any carbon tax, the coal plant has the lowest levelised unit electricity cost (LUEC) and the highest net present value (NPV). Introducing the carbon tax the rank changes: depending on its amount the first and the nuclear after becomes the plant with lower LUEC and highest NPV. Therefore, the uncertainty in the carbon tax cost increases the risk of investing in a coal plant above the level of the new small medium reactor.