Limestone Dust Research Articles

Particle separation from gases using cross-flow filtration

Most filters used in solid/gas separation are applied in the “dead-end” mode, where the aerosol particles arrive at the filter on trajectories that are approximately perpendicular to it. This study concerns the alternative method of cross-flow filtration, which is in common use for filtering liquids. In this mode, previously studied by Menard et al. [Powder Technol. 71 (1992) 263], Thomas et al. [Powder Technol. 76 (1993) 79] and Ferrer et al. [Powder Technol. 113 (200) 197], some of the flow passes through the filter, depositing particles on the surface, while some sweeps past the surface, causing shear on the deposited cake. Depending on the operating conditions, particle aggregation can occur on the surface and the resulting aggregates can be removed by the through-flow and collected in a downstream device. Laboratory scale equipment has been set up in which a cross-flow filter module is coupled to a cyclone postseparator to separate the aggregates leaving the filter. The filters used were ceramic tubes of 6 cm outside diameter, 4 cm inside diameter and variable lengths. An aerosol of limestone dust particles (mmd=5.0 μm) in ambient air enters the inside of the filter along the axis; due to the aerodynamic conditions within the filter some of the particles are deflected towards the filter and are captured. The results show that the cake is detached in the form of loose agglomerates rather than individual particles, which are easily collected by means of the cyclone. The collection efficiency shown by the cross-flow filter/cyclone combination is over 99% for 5.0 μm (mmd) particles under optimum conditions compared to ≈90% shown by the stand-alone cyclone. This separation efficiency is comparable to that of a surface filter and the pressure loss savings with this system make it an attractive gas cleaning option.

Determination of the Fractional Efficiencies of Fibrous Filter Media By Optical In Situ Measurements

ABSTRACT An experimental setup is introduced to determine the fractional efficiency of fibrous filters. The device includes two optical particle counters for the in situ measurement of the particle flux and size upstream and downstream of a test filter. The simultaneous measurement in the raw and clean gas by a counting method allows a rapid determination of the fractional efficiencies of various filter media within a few minutes. In the first experiments performed with different aerosols (latex spheres, bacterial aerosol, limestone dust) the apparatus proved to be a reliable instrument for the investigation of the collection behaviour of fibrous filters influenced by various parameters. The fractional efficiency yields more information about the filter performance, i.e., respirable fraction, collection minimum, particle bouncing off etc., than the total collection efficiency. Thus it is possible to compare different filter media of the same or different filter class and determine their optimum operationa...

Stabilization of an arid, saline sabkha soil using additives

Abstract This paper describes the results of an investigation on the effect of five stabilizing agents, namely limestone dust, marl, emulsified asphalt, cement and lime, on the properties of an arid, saline sabkha soil from eastern Saudi Arabia. Standard compaction and unconfined compressive strength tests were performed, the latter on wrapped specimens that had been allowed to cure for seven days. The results indicated that the density of sabkha mixtures could not be used as a primary criterion in any stabilization programme and the maximum strength of sabkha mixtures was attained at moisture contents much lower than the optimum. Despite the sabkha's coarsegrained nature, neither addition of marl nor of emulsified asphalt gave any significant improvement in the properties of sabkha and the effect of adding limestone dust was marginal. However, the addition of either lime or cement in the range of 2.5 to 100y weight of soil increased the strength between and 22 times.

CHARACTERISTICS OF AEROSOLS IN BEIJING-TIANJIN AREA OF CHINA BY PIXE AND INAA AND IDENTIFICATION OF THEIR SOURCES BY CEB

Proton Induced X-ray Emission (PIXE) and Instrumental Neutron Activation Analysis (INAA) techniques were used to measure the contents of 45 elements in 150 air-filter samples collected by cascade impactor with 8 stages at 10 sites in Beijing-Tianjin area of China during the periods of the winter of 1983 and the summer of 1984. It was noticed that the toxic elements such as As, Sb, Se, Pb, Hg, Cu and Ni were mainly enriched in fine particles with diameter less than 2 um. The major seven sources of coal burning, soil dust, oi1 burning, sea-salt aerosol, motor vehicle emission, limestone dust and industrial refuse attributing to the pollution in Tianjin area were identified by Chemical Elements Balance method (CEB). Among them the most important sources were the soil dust and the emission from coal-combustion followed by contributions from limestone and industrial refuse.

Outlet Mass Flux from a Pulse-Jet Cleaned Fabric Filter: Testing a Theoretical Model

Mass penetration through a pulse-jet cleaned fabric filter was evaluated as a function of particle size. The fabric bags were conditioned by 150 cleaning cycles before data were collected. Particle penetration data were collected over 24 different operating conditions for a three-bag, pilot-scale filter using polyester felt bags with either a rough, untreated surface or a smooth, polytetrafluoroethylene-laminated surface. Each bag filtered limestone dust or fly-ash for 30, 120, or 480 seconds and was then cleaned either on-line or off-line. The applicability to these data of the Leith and Ellen becker (1980) model for outlet mass flux through a filter was analyzed for a geometric progression of 13 particle diameters from 0.10 to 6.7 μm. Model parameters were found to be strongly dependent on particle size and on fabric surface treatment but were not affected by fabric cleaning mode or cleaning cycle time. Dust type may have affected filter performance but the effect was not significant statistically. After the model had been calibrated using the present data set, it was used to predict results for an independent data set and performed reasonably well. Model parameters may be sensitive to the degree to which bags are conditioned with dust.

Comparison of sewage ash, crushed limestone and cement kiln dust as ameliorants for acid soils

A field experiment and a glasshouse experiment showed that crushed limestone, cement kiln dust and sewage ash were all effective in ameliorating adverse soil factors associated with acid soils. Pasture plant yield could be more than doubled by the addition of up to 6 t of ameliorants/ha. Twenty-six months after incorporating ameliorants in the top 10 cm of soil in the field experiment pH had substantially increased, however, there was a much smaller effect in the 10-20 cm zone. In the glasshouse experiment, clover yield on the strongly acid (pH 4.1 in CaCl2) well-buffered soil from the field experiment site responded to the addition of up to 4 t of ameliorants/ha. On a slightly acid (pH 4.7 in CaCl2) poorly buffered soil from another site, ameliorant rates above 2 t/ha reduced clover yield because of factors associated with an increase in pH (CaCl2) to 6.6 and above. Sewage ash tended to be better than the other ameliorants in improving plant yield. This was attributed to the presence of about 3% of P in the ash, which increased soil extractable P, and P content and yield of the herbage.

Rôle du volcanisme explosif et du vent dans la formation des précipités calcaires quaternaires («tosea») de la Pampa argentine

Calcretes have been a traditional subject of polemics between edafologists considering them as generated by pedogenic processes, and geomorphologists who attributed the transportation of their calcium carbonate to surficial run-off. Recently, some english-speaking Authors have gathered evidence of the role of wind in dust transport and on the contribution of this dust for the formation of soils. J. Tncart, in 1968, demonstrated that the alcalis which turn rural development very difficult in the pampa Deprimida of Argentine, has been transported by westerly winds and has probably a volcanic origin. The present paper treats of the regions which form half a circle from the NW to the SW of the pampa Deprimida They are characterized by limestone deposits, indurated ("tosca", equivalent of the mexican "caliche"), or not The following results have been obtained from field observations, as unfortunately no laboratory investigations have been possible. 1) The calcium carbonate, which predominates in the area, and the alcalis of the "sahtrales" are wind transported. 2) In some places, calcium carbonate is mixed with volcanic ashes and small pyroclastic debris. It is therefore presumed of volcanic origin. 3) Rainfalls, presumably resulting for a part of the volcanic explosions themselves, have partially dissolved the limestone dust and precipitated the carbonate when water evaporated It resulted in a diagenesis of the carbonate into laminated calcrete and, underneath, when water was abundant enough, into veins and concretions along the water paths, amist the unconsohdated silty carbonate Regional differences can be noted according to the amount of precipitations, which is lower westwards, and which have changed during the pleistocene with alternating dry and wet periods, as demonstrated in the Pampa Deprimida. 4) "Tosca" does not result from pedogenic processes : it crops frequently, without any cover, on the highest points of the landscape, so that it cannot be an exhumed BCa horizon. Presently, in the wetter parts of the area investigated, i.e. around Sta Rosa, calcrete suffers a destruction by pedogenesis and rendzina soils are forming In the West of La Pampa Province, alcalis have been deposited on solid basalt, contained in aeohan sandy loams. Their lixiviation by throughflow feeds extensive "sahtrales" which seem to be the equivalent of the closed basins of the western side of the Andes, in the Chilean Pampa del Tamarugal, where nitrate has been mined and still is in decreasing quantities. 5) The volcanic dust, both calcarous and alcaline, has been transported by westerly winds, as formerly established by investigations in the Pampa Deprimida. Sedimentation decreases eastwards. Calcareous dust, probably coarser than alcaline dust, has been deposited first and has not reached the Pampa Deprimida when alcali aerosols did Alcaline dust is found along a kind of beam from Corral de Piedra to the Pampa Deprimida, passing through the extensive "sahtrales" near Puelén (Salitral de la Perra). The distribution of both calcareous and alcaline wind-born products suggests that they come from the South of Neuquén Provinc but from volcanoes, not yet precisely identified. 6) Calcareous dust have been deposited from the North of the Rio Negro Province to the South of Cordoba Province, during at least 3, more probably 4 paroxysmal periods during the Pleistocene.

Effect of operating conditions on pressure drop in a pulse‐jet cleaned fabric filter

AbstractTests were conducted to determine the effect of operating conditions on pressure drop in a pulse‐jet cleaned fabric filter. A three‐bag, pilot‐scale filter was used. Polyester bags with ptfe‐laminated surface and untreated surface collected fly ash and limestone dust at 30, 120, and 480 seconds between cleaning pulses to each bag. Tests were conducted using off‐line and on‐line cleaning. Results were compared to predictions of theoretical models. The models should be used only when sufficient dust is on the fabric to cause model parameters to remain constant.

Using the Kst nomographs to estimate the venting requirements in weak dust-handling equipment

Abstract The K st nomographs have been extended, using Heinrich's equation, to take into account dusts with K st values less than 50 bar m s −1 , and values of reduced explosion pressure less than 1.2 bar a. A series of experiments to validate the extended nomographs is described. An 18.5 m 3 explosion vessel was used, with mixtures of coal dust and limestone dust as the dusts of low K st value. The measured reduced explosion pressures are shown to be in good agreement with predictions from the extended nomographs. Predictions from the extended nomographs for reduced explosion pressures less than 1.2 bar a are compared with extrapolations of data by Donat, to experimental measurements in the 18.5 m 3 vessel and to predictions from an equation suggested in the new draft NFPA. In all three comparisons, the extended nomograph is shown to give acceptable predictions of vent area.

MINIRAM Calibration Differences

Abstract The MINIRAM (Miniature Real-time Aerosol Monitor), manufactured by MIE, Inc. (formerly the GCA Corporation), is a small aerosol monitor using the scattering of electromagnetic radiation to measure particulate aerosol concentrations. The manufacturer calibrates the response of the MINIRAM against a gravimetric reference using Arizona Road Dust (ARD). However, it has been observed that different MINIRAMs may not show the same concentration when simultaneously measuring the same aerosol. This paper presents the results of comparative measurements obtained in the laboratory, under controlled conditions, with 46 actively operated MINIRAM instruments. Comparative measurements were obtained in ARD, silica dust, and limestone dust aerosols. Using one of the MINIRAMs as a reference, comparative measurements were obtained with each of the other instruments by sampling through an inlet manifold which allowed two instruments to be simultaneously exposed to the same aerosol. Aerosol concentrations indicated b...

Performance of Concrete Incorporating Limestone Dust as Partial Replacement for Sand

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Comparison of Mass Concentrations Determined With Personal Respirable Coal Mine Dust Samplers Operating at 1.2 Liters Per Minute and the Casella 113A Gravimetric Sampler (MRE)

Measuring respirable dust concentrations in coal mine environments is currently done using approved personal respirable dust sampling equipment operating at a flow rate of 2.0 liters per minute (Lpm). Measurements made with approved coal mine dust sampling equipment are converted to equivalent concentrations that would be obtained with a Mining Research Establishment (MRE) instrument known as the Casella 113A gravimetric sampler, using a conversion factor of 1.38. NIOSH has recently recommended that coal mine dust samplers (CMDS) used to measure respirable dust levels in mine environments be operated at 1.2 Lpm and measured concentrations be multiplied by 0.91 to obtain an equivalent MRE concentration. The purpose of this recommendation is to reduce systematic error caused by the variation in mine dust distributions. This paper presents and discusses data collected in the laboratory and in underground coal mines to evaluate the recommended 1.2 Lpm flow rate and 0.91 conversion factor. Comparative measurements were obtained in the laboratory with the CMDS operating at 2.0 and 1.2 liters per minute and the MRE, using aerosols of coal and limestone dust of varying particle size distribution. Similar comparative measurements were made in a number of underground coal mines at locations with environments having particle size distributions representative of different underground mining operations. It was concluded from this study that there is no significant change in the variability associated with the constant factor used to convert respirable dust measurements, obtained with approved respirable CMDS, to equivalent MRE measurements when the flow rate of the CMDS is reduced from 2.0 to 1.2 Lpm.

Dust removal characteristics of fabrics used in pulse-jet filters

Dust removal characteristics of three fabrics used in pulse-jet filters were investigated. All fabrics were polyester felt but had different surface characteristics; fabrics with an untreated surface, a singed surface, and a surface with a microporous PTFE laminate were used. Three dusts (fly ash, limestone, and granite dust) were tested on each fabric at each of three filtration velocities (50, 75 and 100 mm/s), so that a total of 27 different operating conditions were examined. Both fabric cleaning efficiency, defined as the fraction of deposited dust that is removed from the fabric by cleaning, and system cleaning efficiency, defined as the fraction of deposited dust that reaches the hopper during a cleaning cycle, were measured for each operating condition. Resultant data fell into three groups. Group 1, consisting of the PTFE-laminated fabric collecting all dusts, had the highest fabric and system cleaning efficiencies. Group 2, consisting of limestone and granite dust deposited on untreated and singed fabrics, had the poorest fabric cleaning efficiency but a system cleaning efficiency intermediate between the other groups. Group 3, consisting of fly ash deposited on untreated and singed fabrics, had fairly high fabric cleaning efficiency but the lowest system cleaning efficiency; much of the fly ash removed from these fabrics probably redeposited on the fabrics instead of falling to the hopper. Fabric cleaning efficiency was independent of the filtration velocities tested here and dependent on the dust deposit areal density.

Dust Emission Characteristics of Pulse-Jet-Cleaned Fabric Filters

Essentially all dust penetration through a pulse-jet filter occurred by seepage of collected dust through the filter fabric rather than by a failure to collect the dust in the first place. The flux of dust through the fabric increased with time as the dust deposit on the fabric increased; this behavior is consistent with seepage theory. The flux of dust through pulse-jet cleaned bags was measured for dusts with three size distributions (granite dust, limestone dust, and fly ash), using polyester felt fabrics with three surface treatments (untreated surface, singed surface, and surface with microporous ptfe laminate), at three superficial filtration velocities (50, 75, and 100 mm/sec). Dust type and fabric type affected the amount of dust carried by the bag at steady state; the amount of dust carried determined the flux of dust through the fabric. Measurements of flux through the bags for all 27 tests correlated well with a single parameter, which was derived assuming seepage accounts for all penetrating dust.

The effect of limestone dust on vegetation in an area with a Mediterranean climate

Possible effects of limestone dust on photosynthesis and transpiration throughout the summer season were assessed. Calculations were based on measurements of the dust accumulating on the leaves during the summer season, photosynthesis light curves of representative species, effect of dust on the optical characteristics of the leaves and stomatal diffusion resistance in the region of the quarry based on meteorological data. On a seasonal basis the dust was calculated to have only a very small effect in reducing photosynthesis and transpiration. A field experiment in which irrigated Xanthium strumarium plants were grown at different distances downwind from the quarry showed no deleterious effect of the dust even when plants close to the quarry were heavily coated. Comparison of aerial photographs taken just before the quarry was opened and 22 years later revealed no changes in the size, number or distribution pattern of the perennial, tree and shrub vegetation. It is concluded that, in an area with a Mediterranean climate, limestone dust, whilst being aesthetically offensive, does not significantly affect the growth of the natural vegetation.

Fine dust collection in a rotary flow cyclone

When collecting fine limestone dust, a rotary flow cyclone performs considerably below manufacturer's expectations. The performance is only slightly worse than predicted from fluid/particle mechanics, up to a particle size of 4 μ. Beyond this, complete collection is predicted, but only 90% collection is achieved.

Waterproofing of stonedust

Stonedust is used in arresting and suppressing explosions in coal mines. Its dispersibility is adversely affected when exposed to underground mine environment. By waterproofing, this deleterious effect can be counteracted. Limestone dust has been waterproofed by Stearic, Palmitic and Oleic acid with different quantities (0·05, 0·1 and 0·2 per cent by weight). The effect of waterproofing on moisture adsorption, dispersibility, loss in inerting property and bulk density of the stonedust has been investigated.

Effects of limestone dust accumulation on lateral growth of forest trees

Four species of trees from two sites in southwestern Virginia were used for annual ring measurements to determine the effects of limestone dust on lateral growth of forest trees. The sites were similar in all respects except dust accumulation. One site, the control, had essentially no dust accumulation, whereas the other had heavy dust accumulation from nearby limestone processing plants. A reduction in lateral growth of at least 18% was shown for Acer rubrum, Quercus prinus and Q. rubra. Lateral growth of Liriodendron tulipifera, however, increased by 76%. Prior to this study, dust accumulation had not been correlated with a significant increase in lateral growth of trees.

Atmospheric Pollution: Limestone Dust on Trees

Atmospheric Pollution: Limestone Dust on Trees

Effects of limestone dust accumulation on composition of a forest community

Two sites in southwestern Virginia were sampled to determine the effects of dust accumulation on structure and composition of a forest community. The sites were similar in all respects except for dust accumulation. One site, the control, had essentially no dust accumulation, whereas the other had heavy accumulation from limestone processing plants. When compared with the control site, significant changes in structure and composition were found to have occurred in the seedling-shrub and sapling strata of the experimental site. Dominance in the tree stratum was also shown to be changing. Leading dominants in the control site were Quercus prinus, Q. rubra, and Acer rubrum, whereas those in the dusty site were Quercus alba, Q. rubra, and Liriodendron tulipifera. Species expected to assume ultimate dominance in the experimental site, if dust accumulation continues, are L. tulipifera, Acer saccharum, and, possibly, Quercus muehlenbergii. This is the first known attempt to assess the long-term effects of dust accumulation on structure and composition of forest communities.