Research on Distribution Regularities of Dust Concentration and Granularity in Large Mining Height Working Face

The key for dust control of coal mine is to clarify the dust concentration distribution and sedimentation in different areas. Both similarity experiment and numerical simulation method have certain restrictions and are quite different from the actual situation on site. In order to study the dust sedimentation regularity of coal mine in large mining height, “filter membrane method” is adopted in this paper, i.e., to dry and weigh the filter membrane before and after sampling, collect the dust of respirable zone on mining face and calculate the dust concentration based on a main airway of 100 m. The result shows that: A large amount of dust will be produced during coal mining, wherein the maximum dust concentration from 6 m upstream to 100 m downstream of coal cutter is 121 mg/m3, while the minimum dust concentration is 61 mg/m3;The dust concentration in return airway is reduced with the distance increases, while the dust concentration at the entrance is 91 mg/m3;A large amount of dust may fall from roof during section advancing and improves the dust concentration of hydraulic support in walking area obviously;The dust granularity of mining face and return airway is 0 - 100 μm, but the amount of respirable dust is higher than 80%, the larger the dust particle size, the higher the dust concentration. Besides, dust in small particle size can be suspended in air flow for longer, but that in large particle size may subside under the action of gravity;To reduce dust exposure, the mining position shall be located in the windward direction of advancing or coal cutter. This research can provide guidance for taking dust prevention measures of working face in large mining height.

In-Situ Measuring the Particle Mean Size and Dust Concentration by Near-Forward Small Angle Light Scattering

This paper presents a method of measuring the particle mean size and dust concentration by small angle near forward light scattering optics and the extinction theory. Its theory is based on Fraunhofer diffraction theory which is the approximation of Mie scattering within the forward Fraunhofer diffraction lobe, and Rosin Rammler function is introduced to describe the particle size distribution in two phase flow in advance. Compared with the values by the sample weight method, the measurement results have a reasonable agreement. The present work has demonstrated that this method will be probably used to monitor the parameters of two phase flow.

Lead Concentration in Hong Kong Roadside Dust after Reduction of Lead Level in Petrol

Samples of roadside dust were collected from 30 sites in Hong Kong.The total concentrations of 10 metals in the samples were analyzed,and the correlation coefficients among the metal contents and the annual average daily traffic(AADT)in 1986 were determined.Pb was found to have a significant correlation(P<0.01)with AADT.No correlation was found between Al, Ba,Cd,Cr,Cu,Fe,Mn,Ni,and Zn with respect to AADT.A general decrease in the level of Pb in roadside dust in the past few years has been observed since the reduction in the level of lead in petrol.1989 Academic Press,Inc.

Studies on the Hazardous Effects and the Maximum Allowable Concentration of Pyrophyllite Dust

Pyrophyllite (H2Al2,Si4 O22, ) dust (P-dust) is a mixture of silica (10-40% ), differentproportions of a luminium oxide (Al2O3 ), and various metal compounds. People with occupa-tions known to be associated with exposure to P-dust include miners, other industrial workersand persons engaged in artistic carving. Currently, little is known about pyrophyllite pneumo-coniosis from P-dust. This study was designed to investigate the hazardous effects of P-dustand to suggest a maximum allowable concentration (MAC) of the dust.This.study included four parts: (i) Occupational epidemiology surveys in 781 workersfrom 1 pyrophyllite mine (PM) and four pyrophyllite carving mills (PCM), with a registra-tion rate of 98 %. (ii) In vitro studies: Six groups of rats were expeed to different levels ofP-dust; the cytotoxicity of P-dust on rat alveolar macrophages (AM) was investigated by de-termining the potassium'content of AM and the activity levels of lactate dehydrogenase (LDH)in AM culture fluid. (iii) Mineralogical analysis of P-dust: The contents of silica (SiO2 ), alu-minium (Al), ferrum (Fe), niikel (Ni), zinc (Zn) and copper (Cu) in hath PM-dust andPCMdust were determined. (iv ) Determination of P-dust MAC: Using the life-talbemethod, an investigation of the hygiene standard of P-dust was carried out in 625 workers ex-POSed to either PM-dust or PCM-dust, uPon whom routine radiographs were Performed.The results suggest that the risk of developing pneumoconiosis from pyrophyllite dust issignificantly higher for PM workers than for PCM workers. The prevalence rate of PCM-dustpneumoconiosis is significantly higher in men than in women. The content of SiO2 and AlO3in the mixture of P-dust is the most important factor in the etiology of pyrophyllitosis. De-pending on the different P-dust MAC values, we suggest that 2 rng/m3 and 4 mg/m' shouldbe considered as the MAC for PM-dust and PCM-dust, respectively, and 3 mg/m' fOr P-dust. We believe that establishing different hygiene standards is more accurate even thoughworkers are exposured to the 'same' dust

Experimental research on flame propagation characteristics of coal dust combustion

The presence of coal dust explosions in coal mining are significant safety hazards.This study mainly explores the flame propagation of coal dust combustion so as to provide a theoretical basis for the prevention and control of coal dust explosions.In the experiment,a dust cloud ignition device was used to experimentally explore the influence of the coal dust concentration on the flame propagation of the coal dust,and high-speed photography was used to record the coal dust flame propagation process.The results show that the flame propagates vertically along the wall of the vertical glass tube,emits a bright yellow light during the propagation process,and forms a mushroom cloud-shaped flame at the upper end of the vertical glass tube.When the concentration of coal dust is 250 g/m^(3),its burning time is much less than those of 500 g/m^(3)and 750 g/m^(3).When the concentrations are 250 g/m^(3),500 g/m^(3)and 750 g/m^(3),respectively,the corresponding maximum propagation velocities of the flame front reach 1.51 m/s,2.00 m/s and 1.61 m/s at 100 ms,353 ms and 310 ms,respectively.The time for the flame front velocity to reach the maximum and the maximum velocity of flame propagation first increase and then decrease with the rising of concentration.

Design and Development of a High Efficiency Carbon- Granular Bed Filter in Industrial Scale

The new dust removal technical route using the carbon-granular bed filter, packed of carbon particles with appropriate grade derive from an online-process vibration sieve, to replace the traditional baggy filter had been developed successfully for capturing the micro-carbon dusts produced from pulverization of petroleum coke, and the green close loop of carbon materials is thus completed in the combined pulverizing and classifying system and pulverized carbon dust removal process. The high dust removal efficiency greater than 99%, low outlet dust concentration less than 100mg·m-3, low pressure drop through dust filtration chamber less than 980Pa, simple and easy design, and flexible and stable operation were achieved also with the carbon-granular bed filter in both bench and industrial scale operations.

Dust Diffusion Simulation in the Third Layer Construction of Underground Powerhouse

Under forced ventilation,the dust diffusion of underground powerhouse construction is investigated using a 3D high Reynolds number k-ε model.The interfacial momentum transfers and the wall roughness in the wall function are considered.Ventilation in the third layer of underground powerhouse of Xiangjiaba hydropower station is used as a case.The geometric structure has a decisive effect on the airflow distribution.It is concluded that the dust concentration decreases gradually with the increase of the ventilation time.However,iso-concentration curves have the same tendency after 1 800 s.The dust concentration meets the ventilation and dust-prevention health standard after 2 300 s.The prediction by the present model is confirmed by the experimental measurement by Nakayama.

Preliminary Characterization of Respirable Rock Dust Generated from Cutting Potash in Laboratory Full-Scale Tests with Radial Picks at Different Stages of Wear

Airborne rock dust poses serious long-term health effects to workers in mining and tunneling underground rock environments.When inhaled,respirable crystalline silica particles commonly found in quartz and other minerals will scar sensitive lung tissue and cause irreversible lung diseases.Characteristics such as concentration,type of mineral,particle size,and particle shape can harm workers to various extents.Therefore,this study characterizes airborne rock dust particles that are released from mechanically cutting rock.Laboratory full scale linear cutting tests on samples of potash rock were performed with radial picks to generate dust and were collected with various instruments,including Dorr-Oliver cyclones.Three stages of pick wear were tested:new,moderately worn,and severely worn.Comparisons between different stages of pick wear to dust concentration,size distribution,and particle shape characteristics are drawn from this preliminary study using analytical methods,field-emission scanning electron microscope image capture techniques,and laser diffraction.Although further testing needs to be conducted to make viable and concrete conclusions,a review of the test results reveals a strong tendency in generated airborne and deposited dust to be linked to the bit tip wear,which was influenced by tip surface area geometry,such as a sharp tip,blunt tip,or undulating sharp tips.The moderately worn pick,or the pick with the bluntest tip,in these experiments released the highest concentration of dust.The moderately worn(bluntest)pick also generated particle shapes with the highest aspect ratio compared to the other two picks.Additionally,in terms of the particle size distributions,all the picks generated airborne particle size mean values between 0.7 and 1.2µm in aerodynamic diameter.As for deposited particle size distributions,all the picks generated particles with the mode of particle aerodynamic diameter sizes at 13µm.In the end,the results of this preliminary study paired with future testing can confirm and eventually provide the basis for optimum bit management and maintenance systems to control airborne dust exposures.

A Case Study on Parameters Influencing Dust Accumulation on CSP Reflectors

The effect of dust accumulation on CST （concentrated solar thermal） reflectors is to deflect, or scatter, incident light rays missing the receiver with a subsequent power produced loss. Dust fouling is site specific, and the understanding of interactions between different weather and or environmental parameters is crucial for plant profitability. This research intends to provide useful insights on the interaction between the most relevant weather parameters affecting soil accumulation. Results show a significant dependency of dust concentration versus humidity and ambient temperature, as well as a nexus between wind speed and ambient temperature seems to exist. As long as the temperature decreases an increase of humidity and dust concentration occurs. This phenomenon takes place mostly overnight till the first hours of the morning. Therefore, mirror＇s reflectance looks extremely affected by dust accumulation because of high humidity rate during the night and dews of early morning. Further investigations are required to validate the hypothesis that, a more effective cleaning activitie to restore plants＇ reflectivity are to be carried out during the early morning.

Modeling the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer

In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the condition of gentle breeze and normal forced ventilation in heading face using the particle tracking technology of computational fluid dynamics(CFD).The results show that air-flowing tendency in the same section presents great comparability in the period of gentle breeze and forced ventilation,and the difference mainly embodies in the different wind velocity.The influence of ventilation on the dispersion of droplets is faint under the gentle breeze condition.The droplet can be evenly distributed around the cutting head.However,under the normal forced ventilation,a large number of droplets will drift to the return air side.At the same time,droplet clusters are predominantly presented in the lower part of windward side and the middle of the leeward side around the cutting head.In contrast,the droplet concentration in other parts around cutting head decreases a lot and the droplets are unable to form close-grained mist curtain.So the dust escape channel is formed.In addition,the simulation results also reveal that the disturbance of air flow on the droplet distribution can be effectively relieved when using ventilation duct with Coanda effect(VDCE).Field experiment results show that the dust suppression efficiency of total dust and respirable dust increases respectively by 10.5%and 9.3%when using VDCE,which proves that it can weaken the influence of airflow on droplet dispersion.

Initial results for urban metal distributions in house dusts of Syracuse,New York,USA

A program of house dust sample collection and analysis has begun in Syracuse,New York,USA,in order to determine the feasibility of a geography-based exposure assessment for urban metals.The sampling program,and the protocols it employs,is described for two different types of wipe media,Ghost Wipes and Whatman Filters.Preliminary results show that strong spatial patterns of floor dust loading(mg dust per square foot)can be observed for data aggregated at a spatial scale of about 1600 m(~2.5 km^(2)).Floor dust metal concentrations were similar to those found in other urban environments,with some regional variation.The median floor dust Pb concentration was~108 mg·kg^(-1)for this initial data set of~264 sampled residential locations,and varied from 50 to 1100 mg Pb·kg^(-1).