Coal Capacity Research Articles

Network Design Mode of In-Seam Gas Extraction Parameters Using Mathematical Modelling—Take Tangan Colliery as an Example

Gas extraction is a practical and effective way to guarantee mining-process safety and deliver greater environmental benefits through reducing greenhouse gas emissions and increase the supply of a valuable clean gas resource. It has been effective in recent years, however it still has a series of problems that need to be solved. Gas extraction design mainly relies on engineering experience rather than quantitative design, resulting in low input-output ratio of gas extraction because of unreasonable design. How to build a bridge of communication between engineers and scientists is the key to realize scientific gas extraction. In this work, taking our previous gas-coal and gas-coal-heat coupling models of gas extraction as the theoretical basis, a new communication and design concept—an engineering design platform for gas extraction—is proposed using the network mode. Through the platform, on- and off-line interactions between service centre (scientific workers) and design objects (enterprises or individuals), such as data transmission, material review, scheme design and reviews, and so on. It greatly improves the efficiency and standardization of gas extraction design. Appling the networked platform, the gas extraction engineering parameters were quantitatively designed in the working face of 3307, Tangan colliery. According to the extraction time, the working face was divided into 6 extraction units. The number of boreholes were 763, the drilling capacity of coal was 0.03 m/t, and the extraction rate of each unit was more than 25%. The networked mode of in-seam gas extraction design would transform the traditional experience to the quantitative mode.

Studies on the influence of moisture on the sorption and structural properties of hard coals

In the conducted research, the effect of moisture on CO2 sorption and transport processes and changes occurring in the coal pore structure were investigated in detail. The measurements were carried out under isothermal (313 K) and isobaric conditions (0.1−0.8 MPa) on the original device - a manometric sorptomat. Coal sorption capacities, Langmuir sorption isotherms, effective diffusion coefficients and structural parameters were analysed. The obtained sorption capacities of the tested samples relative to CO2 for pressures 0.1, 0.3 and 0.8 MPa confirmed that moisture significantly (even up to 6 times) reduces the sorption capacity of coal relative to CO2, and the largest reduction in sorption capacities was noted on coal with the lowest vitrinite reflectance. It was observed that the increase of the sorption equilibrium pressure decreases the effect of the reduction of the sorption capacity of coal under the influence of moisture, and above 1.0 MPa this effect disappears completely. The critical moisture content was estimated, above which there is no further reduction of the coal sorption capacity due to the increase in moisture content. It was observed that the influence of moisture on CO2 diffusion in its pore space is not clear. Structural analysis were carried out by low-pressure CO2 adsorption at 273 K and 0−0.1 MPa. After increasing the coal moisture content, the surface area decreased by 50 % and a decrease in the volume of available pores with diameters in the range of 0.5−0.6 nm was noted.

Clean products from coal gasification waste by flotation using waste engine oil as collector: Synergetic cleaner disposal of wastes

Synergetic cleaner disposal of coal gasification waste and waste engine oil is urgent, as the harmfulness to environment and lacks of clean and efficient technique. In this work, coal gasification fine slag was divided to two clean products without byproducts or wastes by flotation using waste engine oil as flotation collector, achieved the goals of “Carbons Recycle” and “Waste Disposal by Waste”. The waste engine oil improved the flotation property of the −0.5 mm fraction coal gasification fine slag, thereby a flotation concentrate with a loss-on ignition of 88.86 wt% and recovery of 92.13 wt% was produced at the waste engine oil dosage of 3 kg/t. The main components of waste engine oil were hydrocarbons, esters, and heteroatom-containing species, as confirmed by gas chromatography/mass spectrometry. The mechanism of flotation using waste engine oil as a collector for the coal gasification fine slag particles was examined via the measurement of contact angles and wrap angles. The qualified tailings (i.e. flotation tailings and +0.5 mm fraction coal gasification fine slag) with loss-on ignition of less than 5 wt% were also obtained to the standard for direct utilization in building materials. Economic evaluation indicates that the net profit would reach 12309.46 USD/h, with a coal gasification fine slag raw capacity of 400 t/h. This work demonstrates that the application of waste engine oil in coal gasification fine slag flotation is feasible, efficient, economical, and eco-friendly, and it has potential industrial application prospects.

Influence of matrix size and pore damage path on the size dependence of gas adsorption capacity of coal

Gas adsorption laws of coal particles are vital to the natural gas science and engineering. It is commonly believed that coal particle size exerts an important influence on the gas adsorption capacity. However, different trends of adsorption capacities versus particle sizes were reported in literature. The main purpose of this study is to explain the mechanism of gas sorption behaviors occurred in previous experiments and to clarify the relationship between the pore system damage path and the adsorption capacity. First, experiments including proximate analysis, scanning electron micropore test, mercury porosimetry test and low-temperature liquid N2 adsorption test were conducted for obtaining an accurate pore damage path. Then, the matrix size was investigated according to the theory of fractal dimension. Furthermore, based on the experimental results of isothermal adsorption and desorption, critical desorption particle size was obtained to verify the matrix size applied in the theoretical analysis. Finally, an improved Langmuir model was proposed to calibrate the influence of particle size. The results can help improve the accuracy of the evaluation of adsorption capacity for coal.

The Energy Principle of Coal and Gas Outbursts: Experimentally Evaluating the Role of Gas Desorption

Outburst energy is a major factor influencing coal and gas outbursts, albeit its estimation is difficult owing to the lack of amenable means for quantification of gas desorption. In the past decades, determining the mechanism of outbursts is one of the most challenging issues in rock mechanics. In this study, a triaxial coal and gas outburst simulation system was employed to perform simulated experiments using He (to rule out the influence from gas ad-desorption), N2, and CO2. This facilitated understanding of the energy principle underlying the said outbursts and evaluation of the effects of gas desorption on outburst development. Results of this study indicate that outburst energy and energy consumption are influenced by several factors, including outburst pressure, outburst intensity, ejection distance, and particle size of ejected coal. Among these, gas desorption demonstrates the greatest influence when performing controlled tests (using He). Considering the effects of gas desorption, the total outburst energy can be increased by 1.35–2.95 times, thereby causing an enormous increase in the destructive potential of outbursts. Additionally, values of the coal crushing and transport energies can be enhanced by the order of 118.9–206.6% and 157.8–406.6%, respectively, thereby resulting in a stronger conveying capacity of outburst coal–gas flow along with severe coal fragmentation. A further analysis of the energy distribution indicated that in the development stage, gas desorbed from coal acts as the force driving coal transport, whereas free gas energy is mainly consumed during coal crushing. Findings of this study highlight the importance of quantifying contributions of coal gas towards effective interpretation of outburst-causing mechanisms.

Substitution Effect of Natural Gas and the Energy Consumption Structure Transition in China

A crucial problem which China faces is how to improve its energy consumption structure. In this paper, a system dynamic model of energy substitution based on energy capital and putty-clay theory is adopted, in order to explore the substitution effect of natural gas on the energy consumption structure transition in China. The results demonstrate that the huge capital stocks of coal and oil capacities effectively delay the progress of natural gas substitution for optimizing the energy structure, resulting in a limited effect of natural gas substitution in the short term and a large cumulative effect in the long term. Further scenario analyses indicate that natural gas subsidies and carbon price policies have positive effects on the growth of natural gas consumption and the optimization of the energy structure. We also found that a higher pressure of safety supply may emerge to meet the demand for energy consumption in the energy transition. Recommendations are given for improving the energy consumption structure in China from three aspects: allocating capital investment to natural gas, reducing the transition cost between natural gas and other energy sources, and awareness of the systemic risks in energy consumption.

Reducing stranded assets through early action in the Indian power sector

Cost-effective achievement of the Paris Agreement’s long-term goals requires the unanimous phase-out of coal power generation by mid-century. However, continued investments in coal power plants will make this transition difficult. India is one of the major countries with significant under construction and planned increase in coal power capacity. To ascertain the likelihood and consequences of the continued expansion of coal power for India’s future mitigation options, we use harmonised scenario results from national and global models along with projections from various government reports. Both these approaches estimate that coal capacity is expected to increase until 2030, along with rapid developments in wind and solar power. However, coal capacity stranding of the order of 133–237 GW needs to occur after 2030 if India were to pursue an ambitious climate policy in line with a well-below 2 °C target. Earlier policy strengthening starting after 2020 can reduce stranded assets (14–159 GW) but brings with it political economy and renewable expansion challenges. We conclude that a policy limiting coal plants to those under construction combined with higher solar targets could be politically feasible, prevent significant stranded capacity, and allow higher mitigation ambition in the future.

Analysis on the Exploitation and Utilization of Non-oil and Gas Mineral Resources in China from 2015 to 2017

A comprehensive understanding of the exploitation and utilization of non-oil and gas mineral resources, which is of great significance to both the mineral resources management departments and mining investors. This article analyzed the exploitation and utilization of non-oil and gas mineral resources in China from 2015 to 2017, by using the authoritative data which issued by the Ministry of Natural Resources, PPC, and the work achievements of the project “Remote Sensing Monitoring of Mineral Resources Exploitation Environment in China”. It was found that the number of non-oil and gas mines in China was generally decreasing, with a decrease of 20.1% from 2015 to 2017. It showed that the exploitation of non-oil and gas mineral resources in China was changing to large-scale and intensification. China’s coal and iron ore production capacity had been significantly reduced in 2015-2017. It showed that the socio-economic dependence on mineral resources was gradually decreasing. It was suggested that the mineral resources management department should strengthen the crackdown on illegal mining. It was suggested that mining investors should strengthen cooperation, and transform to knowledge intensive industries such as deep processing of mineral products.

Experimental comparison of CO2, CH4, and N2 adsorption capacity on typical Chinese coals at different temperatures

ABSTRACT Competitive adsorption of CO2/N2/CH4 on coals is important to evaluate potential application of CO2- or N2 – ECBM, which is not fully addressed in previous studies. In this paper, CH4, CO2, and N2 adsorption behaviors are experimentally compared at different reservoir temperatures (307 K, 318 K, and 333 K) and pressure up to 9 MPa. It is found that adsorption capacities all decrease with increasing temperature for CH4, CO2, and N2, while the differences in maximum adsorption capacity at different temperatures is not significant. Maximum adsorption capacity of anthracite coal is much larger than those of bituminous coals, while the maximum adsorption capacities of two selected bituminous coal are close to each other. The maximum adsorption capacity of CO2 is 1.93 mmol/g，which is significantly higher than that of CH4 and N2 with exactly 1.80 mmol/g and 1.11 mmol/g respectively. However, for a given coal sample, gas type does not affect the thermal-stimulated desorption capacities significantly.

Evaluating the changes of sorption and diffusion behaviors of Illinois coal with various water-based fracturing fluid treatments

The water-based fracturing stimulation is commonly used for low permeability coalbed methane (CBM) reservoirs. The influence of various fracturing fluids on the gas sorption and diffusion behaviors were experimentally studied in the work. The Illinois basin coal was selected for the experimental measurements. We used slickwater, guar gel and viscoelastic surfactant (VES) fracturing fluids to treat the coal. The sorption and diffusion behaviors were measured and quantified by the volumetric sorption experiments. The microscope was employed for the coal sample surface observation to qualitatively characterize the coating and residue behavior of fracturing fluids. It was found that all types of fracturing fluids can significantly influence the gas sorption capacity of coal. Apart from the low concentration of polyacrylamide (0.1% and 0.3%) slickwater, all other fracking fluids damage the gas sorption capacity. For most fracturing fluids, the sorption capacity can be recovered closely back to its virgin coal condition with extensive water washing. For the coal samples treated by the VES fracturing fluid, both the Langmuir volume and Langmuir pressure were dramatically increased. The adverse effect of fracturing fluids on coal is apparent and all diffusion coefficients decrease with the treatment. Even with extensive washing, the diffusion coefficient cannot recover for slickwater and VES fluids. But guar gel fluid has the best diffusion recovery because of the easy removal of the guar gel. This study provides a preliminary data set for fracturing fluid selection for Illinois coal in terms of sorption and diffusion.

Laboratory investigation of coal characteristics from Tikak Parbat formation of North-East India for coal bed methane study

The increasing demand for cleaner source of energy forces India to explore various energy sources, and in this process, coal bed methane gas attracts lot of attention for its favourable characteristics including abundance of coal, clean gas, mitigation of greenhouse gases, reduction in hazard in mines, etc. However, the challenge faced during exploration and production varies from depth of seam, heterogeneity in coal characteristics, rank, sorption capacity, saturation, etc. So the detail analysis of various properties is important for economical extraction of gas. The present paper investigates coal properties and their influence on coal bed methane potentiality. Samples from core wells have been analysed in laboratory using proximate and ultimate analyser. Linear correlations between coal constituents and vitrinite reflectance as well as sorption capacity of coal have been established statistically. Mutual relations among proximate parameters are developed.

Cost-Benefit Analysis of Coal-Plant Re-purposing: A Case Study for India

Countries retiring old, polluting and uneconomical coal plants are looking to repurpose them for productive end uses. In this paper, we undertake a cost-benefit analysis for a representative coal plant (1000 MW) and examine the value proposition of repurposing over decommissioning for coal plants across three repurposing options- solar, battery energy storage system (BESS) and synchronous condenser (SynCON). Our main findings include the following. First, the benefits of repurposing outweigh corresponding costs of decommissioning – while the direct, indirect and total decommissioning costs are $58.11 million, $59.31 million and $117.42 million, respectively; the corresponding repurposing benefits are up to $122.79 million, $605.94 million and $728.73 million, respectively. Second, the direct and indirect system benefits of repurposing cover at least 60.02% of the capital expenditure of the repurposing option(s). Finally, based on high vintage, high energy charges, and key qualitative factors; we identify a prospective list of Indian coal plants suited for repurposing. Our empirical estimation of costs and benefits provide evidence that repurposing makes an economic case for retiring coal plants over plain decommissioning. The framework developed under this analysis could act as a useful guide for developing countries with sizeable coal capacity nearing retirement such as South Africa, Chile and India.

Quantitative Analysis of Pore Structure and Its Impact on Methane Adsorption Capacity of Coal

Better understanding of the storage and transportation characteristics of methane in coal seams is important to further develop and utilize the methane resources in the coalbed. This study is devoted to investigating the relationship between methane adsorption performance and pore structure by analyzing twelve coal samples derived from the typical methane-rich coalbeds in China. To eliminate the influence of inorganic components such as ash in different coal samples, a specific fixed-bed reactor with internals was employed for the coal treatment. Based on N2/CO2 adsorption analysis at low-pressure condition, the pores in coal were classified into three types in this study: ultra-micropore (pore width ultra-micropore surface area (0.8976) > fractal dimension D1 (0.8862) > N2-BET surface area (0.7915) > micropore volume (0.5035) > micropore surface area (0.5006). This study shows the influence of parameters of pore structure on methane adsorption of coal and clarifies the order importance of these parameters by the GRA method.

Quantum Chemical Study on the Influence of Dodecyl Trimethyl Ammonium Bromide on the CH4 Adsorption of Coal

The adsorption of dodecyl trimethyl ammonium bromide (DTAB) on coal can affect the wettability of coal and change the water absorption of coal. After DTAB treatment, the change in the CH4 adsorption capacity of coal is worth further study. To reveal the microscopic mechanism of the influence of DTAB on the CH4 adsorption capacity of coal, we employed the density functional theory (DFT) with the 6-311 G (d, p) basis set. DFT-based computations interpreted the adsorption process of CH4 and DTAB on coal molecules and determined the stable structure, adsorption distance, Mulliken overlapping populations, and adsorption energies of the two adsorption configurations. The results showed that the adsorption energies of CH4 and DTAB on the molecular model of coal were 2.15 and 42.69 kJ/mol and the adsorption stability distances were 0.261 and 0.238 nm, respectively. The DTAB–coal configuration was more stable than the CH4–coal configuration. When there was competitive adsorption between DTAB and CH4 on coal, the coal molecules preferentially adsorb the DTAB. Infrared spectroscopy and adsorption experiments were also carried out, and the calculation results of quantum chemistry are consistent with the experimental results.

Experimental study of the effects of gas adsorption on the mechanical properties of coal

A coupled gas-solid testing system was developed to quantitatively investigate the effects of gas adsorption on the strength, volumetric strain, and fracture development of coal. Uniaxial loading tests were conducted on coal with samples that had adsorbed helium (He), nitrogen (N2), methane (CH4), and carbon dioxide (CO2) gases. Gas adsorption during the testing process was graphed using MATLAB, and the fractal dimensions of the fractures in coal were obtained. Under the same adsorption pressure, the adsorption capacity and degradation rate of coal were found to decrease in the following order for the four gases: CO2 > CH4 > N2 > He. The adsorption of CO2 had a salient negative affect on coal strength, while the effect of non-adsorptive He was negligible. The peak strength decreased by 48.27% after CO2 adsorption at a pressure of 2.0 MPa, and the deterioration rate of coal strength increased logarithmically under adsorption equilibrium pressure. The fractal dimension and density of coal fractures increased with adsorption capacity. The degree of fracture development in coal with adsorbed CO2 at a gas pressure of 2.0 MPa was 2.28-fold that of coal without adsorbed gas, and fish scale-shaped swelling and shedding were observed. The novel findings of this study provided a scientific basis for the quantitative evaluation of the mechanical properties of coal with adsorbed gases.

Effects of sequence stratigraphy on coal characteristics and CH4 adsorption capacity of the low-rank coal in Santanghu Basin, China

This paper focusses on sequence stratigraphy of coal-bearing strata, coal petrography, coal chemistry, and the CH4 adsorption capacity of the Badaowan Formation in Santanghu Basin, China. The comprehensive coal characteristics of 12 coal samples were determined, coupled with maceral composition, proximate analysis, elemental analysis, reflectance (Ro), and high-pressure CH4 adsorption. The results indicated that maceral composition and chemical properties of coal were controlled by the sequence stratigraphic framework. During the TST, the content of vitrinite, the ratio of vitrinite to inertinite (V/I) and the content of carbon in coal increased gradually from bottom to top. While during HST, an opposite trend was observed. Furthermore, due to the intrusion of the lake water, the ash yield in the TST is higher than that in HST. The CH4 adsorption capacity is positively correlated with the content of vitrinite and V/I. There is a moderate positive correlation between fixed carbon contents and VLad. Ash content was strongly correlated to Langmuir volume under the air-dry basis, with increasing Ad associated with the reduction of the VLad. It was observed that the CH4 adsorption capacity generally gradually increased during the TST, and gradually decreased in the HST. Gas content also shows a similar change rule. CH4 adsorption capacity is functionally dependent on coal characteristics, which again are dependent on sequence stratigraphy and thus the coal-forming environment. The base level and cycles of the sequence establish a theoretical and practical framework for CBM extraction from low-rank coal reservoirs.

Biomass Availability in Europe as an Alternative Fuel for Full Conversion of Lignite Power Plants: A Critical Review

Biomass has been demonstrated as a capable source of energy to fulfill the increasing demand for clean energy sources which could last a long time. Replacing fossil fuels with biomass-based ones can potentially lead to a reduction of carbon emissions, which is the main target of the EU climate strategy. Based on RED II (revised Renewable Energy Directive 2018/2001/EU) and the European Green Deal, biomass is a promising energy source for achieving carbon neutrality in the future. However, the sustainable potential of biomass resources in the forthcoming decades is still a matter of question. This review aims at estimating the availability of biomass for energy reasons in the EU, and to evaluate its potential to meet the coal power plant capacity of the main lignite-producer countries, including Germany, Poland and Greece. Plants in line with the sustainability criteria of RED II have been selected for the preliminary estimations concerning their full conversion to the biomass power concept. Furthermore, the various barriers to biomass utilization are highlighted, such as the stranded asset risk of a future coal phase-out scenario, biomass supply chain challenges, biomass availability in main lignite-producer EU countries, the existing full conversion technologies, and biomass cost. A variety of challenges in the scenario of lignite substitution with biomass in a plant are investigated in a SWOT (strengths, weaknesses, opportunities, and threats) analysis. Technological risks and issues should be tackled in order to achieve the coal phase-out EU goal, mainly with regard to the supply chain of biomass. In this direction, the development of logistics centers for the centralized handling of biomass is strongly recommended.

CH4 and CO2 sorption and diffusion carried out in various temperatures on hard coal samples of various degrees of coalification

The aim of the study was to analyse the effect of temperature on the sorption and diffusion of CO2 and CH4 on hard coal. Four coal samples, characterized by various degrees of coalification, were used in the research. The sorption measurements were carried out in three temperature values: 278 K, 313 K and 353 K and for the consecutive pressure values of 1 bar, 5 bar and 15 bar. Langmuir's sorption capacity in relation to CH4 and CO2 was the highest for the coal with the lowest degree of coalification and was 32.15 cm3/g and 76.4 cm3/g respectively. The lowest Langmuir sorption capacity in relation to CH4 and CO2 were obtained for medium-rank coal (19.23 cm3/g and 29.26 cm3/g) and high-rank coal (20.33 cm3/g and 32.89 cm3/g). The temperature growth resulted in a reduction of the sorption capacity of coal in relation to CH4 and CO2, and that decline was exponential in relation to temperature. The absolute decreases in the total sorption capacity were from 0.03 cm3/g to 0.21 cm3/g in relation to CH4, and from 0.10 cm3/g to 0.51 cm3/g in relation to CO2, per 1 K temperature increase. Within the measurement temperature range of 278–353 K, no „critical temperature point”, above which there is no reduction in CH4 and CO2 sorption, was observed. An increase in the temperature pushed up the values of the effective diffusion coefficients, in relation to CH4 by more than one order of magnitude, and in relation to CO2 by approximately four times. A decrease in the selectivity of CO2/CH4 was also observed along with the coal rank. The ratio of effective diffusion coefficient values DeCO2/DeCH4 for all the investigated coal samples declined strongly along with temperature growth.

Renewable electricity grids, battery storage and missing money

In this study, we investigate the feasibility of using a hybrid renewable energy system with battery storage to power an electricity grid without extra investment in fast-responding, peak-load generation assets. When more renewable energy (RE) sources are integrated into a grid, declining wholesale market prices reduce the incentive to build new thermal capacity – leading to the ‘missing money’ problem; intermittent RE requires more fast-responding (peak-load) generation to maintain system stability. Some regions use capacity payments to incentivize investment in new peak-load capacity. For a fossil-fuel dominated system, we find that battery storage might replace peak gas as a fast-responding generating asset. Specifically, we determine whether Alberta can eliminate coal-fired power and further reduce reliance on natural gas using a hybrid RE system that includes battery storage. We employ 10 years of provincial wind, solar and load data and a mathematical programming model to simulate the choice of optimal generation mixes under various carbon tax scenarios. We find that high carbon taxes incentivize greater wind integration and battery storage, but that solar photovoltaic (PV) remains uneconomical. Coal and gas-fired baseload capacities can be partially substituted by the renewables, but, in the absence of battery storage, fast-responding, open-cycle gas capacity is required to maintain system reliability. A battery can potentially replace some fast-responding gas capacity, thereby mitigating the ‘missing money’ problem, but this is not always the case. Overall, CO2 emissions can be reduced by some 20 percent but at a cost of $200/tCO2 or more.

Modelling for Air Quality Estimation for a Planned Coal Washery to Control Air Pollution

Tasra coal washery has been planned in Tasra block which is located in Jharia coalfield of Jharkhand state in India. In order to predict air pollution impact because of the proposed washery, modelling has been done using fugitive dust model. Dust levels (PM10 and PM2.5) have been assessed both for conditions of controlled and uncontrolled emissions from various sources of the washery. Baseline site specific air quality data (PM10 and PM2.5) of winter season and maximum coal washing capacity of 700 t h−1 have been considered for prediction of air quality in case of worst-case scenario. Based on modelling exercise, it has been predicted that PM10 concentration may increase from 0.058–51.333 and 0.039–17.485 μg m−3 under the conditions of uncontrolled and controlled emissions respectively at the air quality monitoring sites and the selected receptor locations in the nearby vicinity of the proposed washery. Similarly, PM2.5 concentrations may rise from 0.044–16.636 and 0.022–7.219 μg m−3 due to the uncontrolled and controlled emissions respectively. In order to minimize the fugitive dust levels from the washery site, installation of dry fog dust suppression system has been recommended at different dust generating sources in addition to implementation of other dust control measures in and around the coal washery.