Enhanced properties of stone coal-based composite phase change materials for thermal energy storage

Phase change materials (PCMs) can be incorporated with low-cost minerals to synthesize composites for thermal energy storage in building applications.Stone coal (SC) after vanadium extraction treatment shows potential for secondary utilization in composite preparation.We prepared SC-based composite PCMs with SC as a matrix,stearic acid (SA) as a PCM,and expanded graphite (EG) as an additive.The combined roasting and acid leaching treatment of raw SC was conducted to understand the effect of vanadium extraction on promoting loading capacity.Results showed that the combined treatment of roasting at 900℃ and leaching increased the SC loading of the composite by 6.2%by improving the specific surface area.The loading capacity and thermal conductivity of the composite obviously increased by 127%and 48.19%,respectively,due to the contribution of 3wt% EG.These data were supported by the high load of 66.69%and thermal conductivity of 0.59 W·m^(-1)·K-1of the designed composite.The obtained composite exhibited a phase change temperature of 52.17℃,melting latent heat of 121.5 J·g^(-1),and good chemical compatibility.The SC-based composite has prospects in building applications exploiting the secondary utilization of minerals.

Advancing respirable coal mine dust source apportionment:a preliminary laboratory exploration of optical microscopy as a novel monitoring tool

Exposure to respirable coal mine dust(RCMD)can cause chronic and debilitating lung diseases.Real-time monitoring capabilities are sought which can enable a better understanding of dust components and sources.In many underground mines,RCMD includes three primary components which can be loosely associated with three major dust sources:coal dust from the coal seam itself,silicates from the surrounding rock strata,and carbonates from the inert‘rock dust’products that are applied to mitigate explosion hazards.A monitor which can reliably partition RCMD between these three components could thus allow source apportionment.And tracking silicates,specifically,could be valuable since the most serious health risks are typically associated with this component-particularly if abundant in crystalline silica.Envisioning a monitoring concept based on field microscopy,and following up on prior research using polarized light,the aim of the current study was to build and test a model to classify respirable-sized particles as either coal,silicates,or carbonates.For model development,composite dust samples were generated in the laboratory by successively depositing dust from high-purity materials onto a sticky transparent substrate,and imaging after each deposition event such that the identity of each particle was known a priori.Model testing followed a similar approach,except that real geologic materials were used as the source for each dust component.Results showed that the model had an overall accuracy of 86.5%,indicating that a field-microscopy based moni-tor could support RCMD source apportionment and silicates tracking in some coal mines.

Mechanism of micro-wetting of highly hydrophobic coal dust in underground mining and new wetting agent development

The internal mechanism of the high hydrophobicity of the coal samples from the Pingdingshan mining area was studied through industrial,element,and surface functional group analysis.Laboratory testing and molecular dynamics simulations were employed to study the impact of three types of surfactants on the surface adsorption properties and wettability of highly hydrophobic bituminous coal.The results show that the surface of highly hydrophobic bituminous coal is compact,rich in inorganic minerals,and poorly wettable and that coal molecules are dominated by hydrophobic functional groups of aromatic rings and aliphatic structures.The wetting performance of surfactants as the intermediate carrier to connect coal and water molecules is largely determined by the interaction force between surfactants and coal(Fs-c)and the interaction force between surfactants and water(Fs-w),which effectively improve the wettability of modified coal dust via modifying its surface electrical properties and surface energy.A new type of wetting agent with a dust removal rate of 89%has been developed through discovery of a compound wetting agent solution with optimal wetting and settling performance.This paper provides theoretical and technical support for removing highly hydrophobic bituminous coal dust in underground mining.

Current status and technical challenges of C_(2)storage in coal seams and enhanced coalbed methane recovery:an overview

In the past two decades,research on C_(2)storage in coal seams and simultaneously enhanced coalbed methane recovery(ECBM)has attracted a lot of attention due to its win–win effect between greenhouse gas(C_(2))emission reduction and coalbed methane recovery enhancement.This paper presents an overview on the current status of research on C_(2)-ECBM in the past two decades,which involves C_(2)storage capacity evaluations,laboratory investigations,modelings and pilot tests.The current status shows that we have made great progress in the ECBM technology study,especially in the understanding of the ECBM mechanisms.However,there still have many technical challenges,such as the definition of unmineable coal seams for C_(2)storage capacity evaluation and storage site characterization,methods for C_(2)injectivity enhancement,etc.The low injectivity of coal seams and injectivity loss with C_(2)injection are the major technique challenges of ECBM.We also search several ways to promote the advancement of ECBM technology in the present stage,such as integrating ECBM with hydraulic fracturing,using a gas mixture instead of pure C_(2)for injection into coal seams and the application of ECBM to underground coal mines.

Online coal dust suppression system for opencast coal mines

Coal is the major source of power in India and world over.Coal mining is an essential industry which has a major role in the economic development of the country.Most major mining activities contribute directly or indirectly to air pollution.Coal dust is a major air pollutant which affects the personal working in the mines and also people residing in villages near the mines.Air pollution due to coal particulates can affect human health and cause damages to the environment.Hence effective pollution control mechanisms are needed to keep the pollution levels within permissible levels.The easiest and most common method employed for dust suppression worldwide is sprinkling of water.In majority of mines,water sprinklers are operated manually and can lead to wastage of water due to over sprinkling.It can also prove to be ineffective in dust suppression if sprinkling is not done properly.The paper proposes a system which can be deployed to automate the dust suppressions sprinklers.The system will monitor the concentration of PM_(10) and PM_(2.5) in the air and initiate sprinkling operation when the particulate matter content exceeds preconfigured limits.

A systematic review of occupational exposure to respirable coal mine dust(RCMD)in the U.S.mining industry

Cumulative inhalation of respirable coal mine dust(RCMD)can lead to severe lung diseases,including coal worker's pneu-moconiosis(CWP),silicosis,mixed dust pneumoconiosis,dust-related diffuse fibrosis(DDF),and progressive massive fibrosis(PMF).Statistics from the number of reported cases showed a significant decrease in the progression of respiratory diseases in the 1990s.However,an unexpected increase in the number of CWP cases was reported in the late 1990s.To date,there has been no comprehensive systematic review to assess all contributing factors to the resurgence of CWP cases.This study aims to investigate the effects of various mining parameters on the prevalence of CWP in coal mines.A systematic review using the preferred reporting items for systematic reviews and meta-analysis(PRISMA)method was conducted to investigate the health effects of RCMD exposure and identify the factors that may contribute to the recent resurgence of CWP cases.The systematic review yielded a total of 401 papers,which were added to the database.The total number of 148 and 208 papers were excluded from the database in the process of screening and eligibility,respectively.Then,18 papers were considered for data selection and full-text assessment.The review revealed that factors including geographic location,mine size,mining operation type,coal-seam thickness,coal rank,changes in mining practices,technology advancement,and engi-neering dust control practices are contributing to the recent resurgence of CWP among coal workers.However,the evidence for root causes is limited owing to the methodological constraints of the studies;therefore,further detailed studies are needed.

CO_2 –H_2O–coal interaction of CO_2 storage in coal beds

In order to study the physical and chemical reaction after CO2 injected into coal beds at different condition.The physical and chemistry reaction among CO2,H2O and coal was studied,and the influence on permeability and porosity of coal beds was carried out.The experimental method was used,so did the basic theory of mineralogy,coal petrology,geochemistry,analytical geochemistry and physical chemistry.In this experiment,the changes of mineral and permeability of coal and water quality were observed through CO2 solution reacting with different coal samples.The differences could be found out by comparing the properties and microcrystalline structure before and after the reaction.There are three results were carried out:First,the content of carbonate in coal beds decreases because of the dissolution reaction between carbonate minerals and CO2 solution,and precipitation is formed by reaction of chlorite and orthoclase.Second,the result that permeability and porosity of coal beds are improved after the reaction is proposed.Third,the initial permeability of different coal samples plays a great role on the reaction,and the improvement of permeability is not obvious in the samples which have too low or too high permeability,and the improvement is good in medium permeability(0.2–3 mD).

Insights into carbon dioxide sequestration into coal seams through coupled gas flow-adsorption-deformation modelling

Injecting carbon dioxide(CO_(2))into coal seams may unlock substantial carbon sequestration potential.Since the coal acts like a carbon filter,it can preferentially absorb significant amounts of CO_(2).To explore this further,desorption of the adsorbed gas due to pressure drop is investigated in this paper,to achieve an improved understanding of the long-term fate of injected CO_(2) during post-injection period.This paper presents a dual porosity model coupling gas flow,adsorption and geomechanics for studying coupled processes and effectiveness of CO_(2) sequestration in coals.A new adsorption?desorption model derived based on thermodynamics is incorporated,particularly,the desorption hysteresis is considered.The reliability of the proposed adsorption-desorption isotherm is examined via validation tests.It is indicated that occurrence of desorption hysteresis is attributed to the adsorption-induced pore deformation.After injection ceases,the injected gas continues to propagate further from the injection well,while the pressure in the vicinity of the injection well experiences a significant drop.Although the adsorbed gas near the well also decreases,this decrease is less compared to that in pressure because of desorption hysteresis.The unceasing spread of CO_(2) and drops of pressure and adsorbed gas depend on the degree of desorption hysteresis and heterogeneity of coals,which should be considered when designing CO_(2) sequestration into coal seams.

Experimental Study of Spontaneous Combustion Rule of Ground Coal Storage Pile

By field measurement and laboratory experiment, a yieldable thermometric instrument was studied and manufactured on the basis of the spontaneous combustion rule of ground coal storage pile The instrument has been applied to the ground coal storage pile in Meiyukou Coal Mine of Datong Bureau and the depths of its self-heating and combustion layers and the inherent property of its spontaneous combustion have been obtained.

Development of Sensible Heat Storage Materials Using Sand, Clay and Coal Bottom Ash

In this paper, the mechanical and thermal properties of a sand-clay ceramic with additives coal bottom ash (CBA) waste from incinerator coal power plant are investigated to develop an alternative material for thermal energy storage (TES). Ceramic balls are developed at 1000°C and 1060°C using sintering or firing method. The obtained ceramics were compressed with a compression machine and thermally analyse using Decagon devise KD2 Pro thermal analyser. A muffle furnace was also used for thermal cycling at 610°C. It was found that the CBA increased the porosity, which resulted in the increase of the axial tensile strength reaching 3.5 MPa for sand-clay and ash ceramic. The ceramic balls with the required tensile strength for TES were selected. Their volumetric heat capacity, and thermal conductivity range respectively from 2.4075 MJ·m-3·°C-1 to 3.426 MJ·m-3·°C-1 and their thermal conductivity from 0.331 Wm-1·K-1, to 1.014 Wm-1·K-1 depending on sand origin, size and firing temperature. The selected formulas have good thermal stability because the most fragile specimens after 60 thermal cycles did not present any cracks. These properties allow envisioning the use of the ceramic balls developed as filler material for thermocline thermal energy storage (structured beds) in Concentrating Solar Power plants. And for other applications like solar cooker and solar dryer.

Early Opportunity of CO_2 Storage in Coal Bed of China

A study to identify potential early opportunities for CO2 storage in coal bed has been performed. CO2-ECBM can enhances the recovery of coalbed methane,and also store CO2 in coal for geological time.CO2-ECBM is an effective measure for CO2 mitigation,and also enhance the recovery of coalbed methane that can reduce the cost of CO2 geological storage.The evaluation index system of feasibility

Assessment of the Radiological Impact on the Environment near a Storage Site of Coal Ashes in a Thermal Power Plant

The radiological impact of coal ashes, with enhanced natural radioactivity in the storage site, is due to the presence of naturally occurring radionuclides. Some of these radionuclides have a radioactive period of several million years and will, therefore, have time to migrate to the soil, atmospheric air, surface water, and groundwater. This impact depends mainly on the activity of these coal ashes, the duration of exposure to such waste, transfers to the air, and the leaching phenomenon by rainwater. In this study, and so as to assess the radiological impact of coal ashes of the storage site of the JLEC-Morocco thermal power plant on environment, some analyses are performed by alpha dosimetry and a digital dosimeter on samples of coal ashes, soil, atmospheric air, surface water and groundwater belonging to a perimeter of 10 km around that site. The obtained results show that, within the studied area, the radiological impact on the soil of the coal ashes of the storage site is insignificant even though the concentrations of radon in the near vicinity (1 to 2 km) are moderately important, and remain below 200 Bq/m3. In the atmospheric air, this impact remains medium for the neighborhoods of the storage site (2 to 3 km) with radon activities superior to 10 Bq/m3. These results also show that there may be a water contamination of wells located at the storage site without any transfer of radioactivity into the groundwater of the area studied where the concentrations of radon are less than 11.1 Bq/l.

Assessment of gas and dust explosion in coal mines by means of fuzzy fault tree analysis

During the past decade, coal dust and gas explosions have been the most two serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. In this paper, an evaluation model of coal dust and gas explosions was constructed based on a fuzzy fault tree by taking the Xingli Coal Mine as a research site to identify the risk factors of coal dust and gas explosions.Furthermore, the hazards associated with such explosions were evaluated for this particular coal mine.After completing an on-site investigation, the fuzzy probabilities of basic events were obtained through expert scoring, and these expert opinions were then aggregated as trapezoidal fuzzy numbers to calculate the degrees of importance of all basic events. Finally, these degrees of importance were sorted. According to the resulting order, the basic events with higher probabilities were determined to identify key hazards in the daily safety management of this particular coal mine. Moreover, effective measures for preventing gas and coal dust explosions were derived. The fuzzy fault tree analysis method is of high significance in the analysis of accidental coal mine explosions and provides theoretical guidance for improving the efficiency of coal mine safety management in a scientific and feasible manner.

Surface characteristics and wetting mechanism of respirable coal dust

In this study,FTIR and XPS spectroscopy,specific surface area and pore size analyses,wetting and other experimental means have been applied to investigate respirable coal dust surface properties and wetting mechanism.The research shows that coal dust surface structures,chemical and element compositions are changed in the refining process of coal dust.Compared with large particle coal dust,respirable coal dust is a weak hydrophilic and strong hydrophobic substance.The reason:the smaller the particle size of coal dust,the more unsaturated its surface.The absorption of air is strong and it is easy to form an air film on coal dust surfaces. Coal dust contact with water is actually a compound contact of liquid in contact with a solid and gas in contact with a solid. The smaller the particle size,the larger the pore volume and the higher the degree of surface roughness,the larger the area of gas in contact with a solid and the worse the coal dust wettability.Another reason is that the changes in the composition of atoms on the dust surface and structures affect coal dust wettability.The results of this study establish a theoretical basis for the invention of effective reduced-dust technology.

The geomechanics of Shenhua carbon dioxide capture and storage(CCS) demonstration project in Ordos Basin,China

Carbon dioxide(CO2) capture and storage(CCS) is considered widely as one of promising options for CO2emissions reduction,especially for those countries with coal-dominant energy mix like China.Injecting and storing a huge volume of CO2in deep formations are likely to cause a series of geomechanical issues,including ground surface uplift,damage of caprock integrity,and fault reactivation.The Shenhua CCS demonstration project in Ordos Basin,China,is the first and the largest full-chain saline aquifer storage project of CO2in Asia.The injection started in 2010 and ended in 2015.during which totally 0.3 million tonnes(Mt) CO2was injected.The project is unique in which CO2was injected into 18 sandstone formations simultaneously and the overlying coal seams will be mined after the injection stopped in 2015.Hence,intense geomechanical studies and monitoring works have been conducted in recent years,including possible damage resulting from the temperature difference between injected CO2and formations,injection induced stress and deformation change,potential failure mode and safety factor,interaction between coal mining and CO2geological storage,determination of injection pressure limit,and surface monitoring by the interferometric synthetic aperture radar(InSAR) technology.In this paper,we first described the background and its geological conditions of the Shenhua CCS demonstration project.Then,we gave an introduction to the coupled thermo-hydro-mechano-chemical(THMC) processes in CO2geological storage,and mapped the key geomechanical issues into the THMC processes accordingly.Next,we proposed a generalized geomechanical research flowchart for CO2geological storage projects.After that,we addressed and discussed some typical geomechanical issues,including design of injection pressure limit.CO2injection induced near-field damage,and interaction between CO2geological storage and coal mining,in the Shenhua CCS demonstration project.Finally,we concluded some insights to this CCS project.

Performance of N95 elastomeric respirators in high humidity and high coal dust concentration environment

High humidity and high dust concentration in deep coal mines may severely challenge the performance of respirators worn by coal miners.This paper aims at quantitatively evaluating the respirators used in deep coal mines and providing scientific guidance for the respiratory protection of miners.Based on the self-designed in-situ PM2.5 collector,controllable PM2.5 generator,human breathing simulator,and respirator simulation testing system,under the simulated deep mine working condition,this study investigated the effects of dust loading,wearing time,and dust concentration on the filtration efficiency,breathing resistance,and quality factor of N95 elastomeric respirators.With the increase of dust loading,the respirator filtration efficiency firstly decreased,then increased(minimum value 97.5%).The breathing resistance increased exponentially from 120 to 180 to 1020-1530 Pa,and the quality factor decreased logarithmically from 0.051 to 0.076 to 0.0058-0.0085 Pa^(-1).As the PM2.5 coal dust concentration increased from 5 to 50 mg/m^(3),the wearing time for the respirator breathing resistance to exceed 300 Pa reduced from 7 h to less than 1 h.One N95 elastomeric respirator is not able to perform an 8-h work shift.To avoid the excessive breathing resistance caused by dust loading,more filter cartridges are needed for coal miners.

Design of a water curtain to reduce accumulations of float coal dust in longwall returns

Accumulation of float coal dust(FCD)in underground mines is an explosion hazard that affects all underground coal mine workers.While this hazard is addressed by the application of rock dust,inadequate rock dusting practices can leave miners exposed to an explosion risk.Researchers at the National Institute for Occupational Safety and Health(NIOSH)have focused on developing a water curtain that removes FCD from the airstream,thereby reducing the buildup of FCD in mine airways.In this study,the number and spacing of the active sprays in the water curtain were varied to determine the optimal configuration to obtain peak knockdown efficiency(KE)while minimizing water consumption.

Effects of rock dusting in preventing and reducing intensity of coal mine explosions

As an explosion control measure, rock dusting has been used in underground coal mines in many major coal producing countries with different standards. The effectiveness of the rock dust in reducing explosion intensity has been proven by historic events and laboratory experiments. The main functions of rock dust in controlling mine explosions （i.e., isolator, physical heat sink and chemical energy absorber） have been quantitatively studied and results are presented in this paper.

Floor dust erosion during early stages of coal dust explosion development

An ignition of methane and air can generate enough air flow to raise mixtures of combustible coal and rock dust.The expanding high temperature combustion products ignite the suspended dust mixture and will continue to propagate following the available combustible fuel supply.If the concentration of the dispersed rock dust is sufficient,the flame will stop propagating.Large-scale explosion tests were conducted within the National Institute for Occupational Safety and Health(NIOSH)Lake Lynn Experimental Mine(LLEM)to measure the dynamic pressure history and the post-explosion dust scour depth.The aim of this effort is to provide quantitative data on depth of dust removal during the early stages of explosion development and its relationship to the depth of floor dust collected for assessing the incombustible content most likely to participate in the combustion process.This experimental work on dust removal on is not only important for coal mine safety but also for industrial dust explosions.

Comparative study of the explosion pressure characteristics of micro- and nano-sized coal dust and methane–coal dust mixtures in a pipe

Coal dust explosion accidents often cause substantial property damage and casualties and frequently involve nano-sized coal dust.In order to study the impact of nano-sized coal on coal dust and methane–coal dust explosions,a pipe test apparatus was used to analyze the explosion pressure characteristics of five types of micro-nano particle dusts(800 nm,1200 nm,45μm,60μm,and 75μm)at five concentrations(100 g/m3,250 g/m3,500 g/m3,750 g/m3,and 1000 g/m3).The explosion pressure characteristics were closely related to the coal dust particle size and concentration.The maximum explosion pressure,maximum rate of pressure rise,and deflagration index for nano-sized coal dust were larger than for its micro-sized counterpart,indicating that a nano-sized coal dust explosion is more dangerous.The highest deflagration index Kst for coal dust was 13.97 MPa/(m·s),indicating weak explosibility.When 7%methane was added to the air,the maximum deflagration index Kst for methane–coal dust was 42.62 MPa/(m·s),indicating very strong explosibility.This indicates that adding methane to the coal dust mixture substantially increased the hazard grade.