Probable Error Values Research Articles

Theoretical Analysis and Optimization of Fine Lignite Drying and Separation with a Pulsed Fluidized Bed.

We established a pulsed fluidized bed system to dry and concurrently separate fine lignite (−6 + 3 and −3 + 1 mm lignite). The kinetics and evaporation of lignite moisture were investigated in the pulsed air flow. The variation in the evaporation rate was studied theoretically with respect to temperature, velocity of the pulsed air flow, and pulsed frequency. The rubbing effect between the air and lignite particle probably dominates the evaporation of water. The influence of temperature on the evaporation rate is more significant than that of air velocity by merely considering the effect of air entrainment of the evaporated moisture. Four operational parameters, including inlet temperature, air velocity, pulsating frequency, and bed height, were investigated and optimized through a response surface method to study the interactions between factors and determine the optimal separation conditions. Results indicate that the maximum standard deviation of the ash content of 23.74% was recorded under the optimal condition of the inlet temperature (80 °C), pulsating frequency (3.93 Hz), air velocity (1.09 m/s), and bed height (120 mm) for −6 + 3 mm lignite, and the maximum standard deviation of 24.99% was recorded for −3 + 1 mm lignite under the condition of the inlet temperature (100 °C), pulsating frequency (3.49 Hz), air velocity (0.55 m/s), and bed height (80 mm). The probable error values of separations of −6 + 3 mm lignite and −3 + 1 mm lignite with the pulsed fluidized bed were 0.12–0.16 and 0.10–0.16 g/cm3, respectively, which demonstrates that efficient drying and simultaneous separation of lignite can be achieved with the pulsed fluidized bed.

Spatial characteristics of fluidization and separation in a gas-solid dense-phase fluidized bed

To study the fluidization characteristics and separation performance of a gas-solid dense-phase fluidized bed, bed space structure and force analyses of particles in the radial and axial zones are explored. The results indicate that the standard deviation and average bed density increases with increases in the static bed height. As the fluidization number is increased, the average bed density decreases and fluctuates drastically. Under the same fluidization number, the density in the upper layer is low with violent fluctuations, and it is relatively lower in middle layer and higher on the side wall. The ratio of the minimum pressure gradients in the axial and radial zones in the fluidized state was 10, which proved that the main movement mode of particles is settlement motion in the axial direction. The probable error values were 0.095 and 0.097 g/cm3 in optimal test conditions, indicating efficient separation of 13–25 mm coal particles.

Intensification of the density stability in the air dense medium gas–solid fluidized bed based on a binary dense media

Intensification of the density stability in the air dense medium gas−solid fluidized bed is significantly important to the separation efficiency of this density-based separator. A binary dense media composed of the magnetite powder and quartz sand was used to achieve the intensification of the density stability. The fluctuation characteristics of the bed pressure gradients were investigated to seek for the optimum composition of binary dense media. The weight proportion of quartz sand in the binary dense media should not exceed 30%. The stability and uniformity of the bed density along the axial and radial directions of fluidized bed were experimentally investigated. The results indicated that the weight proportion of quartz sand should be controlled within 10%–20%, and the fluidization number should be adjusted from 1.5 to 1.6. A reliable mathematical model was established to predict the bed density. The calculation and measurement results agreed well, which validated the prediction accuracy. With a 10% weight proportion of quartz sand, the ash content of −13+6mm sized coal was decreased from 33.35% to 11.55% with a clean coal yield of 69.48% at a fluidization number of 1.6. A satisfactory probable error value of 0.095g/cm3 indicated notable separation performance.

DRY BENEFICIATION AND CLEANING OF CHINESE HIGH-ASH COARSE COAL UTILIZING A DENSE-MEDIUM GAS-SOLID FLUIDIZED BED SEPARATOR

Dry dense-medium fluidized bed separation provides a new alternative approach for coal beneficiation and cleaning. An indicator of segregation degree Sash was proposed to evaluate the stratified performance of coal samples by bed density. Fluidization stability of the bed was greatly enhanced by mixing a certain amount (21.53%) of fine magnetite powder (< 0.15 mm) into the fluidized media, which indicated a uniform density distribution as well as slight fluctuations in bed. It was found that the favorable density-segregation performance of 3-13 mm coarse coal occurred with a static bed height of 80 mm and a superficial gas velocity of 11.84 cm/s. The optimal segregation degree values of 0.67, 0.74 and 0.76 were obtained for 3-6, 6-10 and 10-13 mm coal samples, respectively. Low-ash clean coal with yields of 50.79, 56.83 and 61.24% were effectively acquired by the dry separation for various coal size fractions, respectively. Probable error values of 0.07, 0.055 and 0.05 g/cm 3 were achieved, indicating

Evaluation of the trade-off between Global Positioning System (GPS) accuracy and power saving from reduction of number of GPS receiver channels

This study is aimed at evaluating the trade-off between Global Positioning System (GPS) accuracy and power saving from reduction of number of channels. The study is conducted for number of GPS receiver channels of 4 to 12 for two scenarios: (1) normal scenario with full range of available GPS satellites and (2) obstruction scenario with GPS satellite elevation cutoff of 20°. It is observed that increase of power saving from reducing the number of channels causes increase of probable error values. This is due to increasing position dilution of precision (PDOP) of the reducing number of GPS satellites tracked. However, reduction of number of channels to match the number of available GPS satellites does not cause degradation of accuracy, as there is no reduction in number of trackable GPS satellites. For the obstruction scenario, with significantly fewer available GPS satellites due to the GPS satellite elevation cutoff, significant power saving can be achieved without degradation of accuracy. An effective power saving system would require the management of minimum number of channels required to achieve the user’s minimum required accuracy.

Separation performance of fine low-rank coal by vibrated gas–solid fluidized bed for dry coal beneficiation

Vibrational energy was introduced to a dense medium gas–solid fluidized bed to improve the separation performance of 1–6mm fine low-rank coal. The setup was termed a vibrated gas–solid fluidized bed and could provide a stable fluidization state and uniform density distribution for dry coal beneficiation by the transfer of vibrational energy and the interaction between vibrations and the gas phase. Favorable segregation of the ash content of the 1–6-mm-sized lignite samples is achieved under suitable operating conditions. Higher yields of cleaning coal were acquired when the ash content was reduced. The probable error values were 0.065 and 0.055 at separating densities of 1.68 and 1.75g/cm3 for the 1–3- and 3–6-mm-sized lignite samples, respectively. Effective beneficiation of 1–6-mm-sized fine lignite could be achieved using the vibrated gas–solid fluidized bed, which provides an alternative technique for the separation of fine low-rank coal in arid areas.

Evaluation of the Effect of Radio Frequency Interference on Global Positioning System (GPS) Accuracy via GPS Simulation

In this study, Global positioning system (GPS) simulation is employed to study the effect of radio frequency interference (RFI) on the accuracy of two handheld GPS receivers; Garmin GPSmap 60CSx (evaluated GPS receiver) and Garmin GPSmap 60CS (reference GPS receiver). Both GPS receivers employ the GPS L1 coarse acquisition (C/A) signal. It was found that with increasing interference signal power level, probable error values of the GPS receivers increase due to decreasing carrier-to-noise density (C/N0) levels for GPS satellites tracked by the receivers. Varying probable error patterns are observed for readings taken at different locations and times. This was due to the GPS satellite constellation being dynamic, causing varying GPS satellite geometry over location and time, resulting in GPS accuracy being location/time dependent. In general, the highest probable error values were observed for readings with the highest position dilution of precision (PDOP) values, and vice versa. Defence Science Journal, 2012, 62(5), pp.338-347 , DOI:http://dx.doi.org/10.14429/dsj.62.1606

Prediction of economic operating conditions for Indian coal preparation plants

The most important optimization concept, which, has long been recognized in coal preparation with multiple cleaning circuits, is the constant incremental quality approach. However, this approach maximizes the overall plant yield for a targeted product quality, without putting any emphasis on coal value/price. So, sometimes confusion arises in the determination of the overall plant yield that would more than offset the price due to lower quality of product. In this paper a method is presented to maximize the coal value by considering the equal incremental quality approach as well. Here the predicted yield of composite coal has been calculated by using a designed probable error value, then the value of a particular coal is maximized. A case study with six different coals of different characteristics is presented to ascertain the merit of this approach. This technique offers the coal preparation engineer an effective and straight forward method for determining the optimum cut points of separation for different coals to achieve maximum economic gain.

Alternative Materials for Dense Medium Separations

In response to concerns regarding cost and future supply of magnetite, a study has been performed to evaluate the potential of alternative materials that can be used to generate a dense medium for coal-cleaning applications. Alternative materials included waste steel slag, fine sand, and high-density material existing in run-of-mine feed. Under certain conditions, each of the materials tested provided separation efficiencies that meet industrial standards including probable error values of around 0.03. Dense medium derived from the non-magnetite sources achieved organic efficiency values exceeding the 95% level over a medium density range from 1.3 RD to 1.6 RD with lower than normal density offsets. Lower cost, coarse magnetite provided excellent separation efficiencies when medium density values above 1.6 RD are sufficient to meet product grade requirements.

Effect of Structured Plates on Fine Coal Gravity Separation in a Liquid Fluidized Bed System

The addition of structured plates in the hindered-settling bed separator (HSBS) is an improved design for the particle classification and gravity separation on the basis of size and density differences. This work presents the experimental test results of coal separation in a lab scale packed column and a series of numerical simulations of the particle classification and gravity separation in the presence of structured plates using an Euler-Lagrange approach from Computational Fluid Dynamics (CFD). In the simulation, the HSBS was used to separate coal particles with a size range of -2+0.25 mm. The changes of liquid phase velocity field and particle separation performance in the packed column are compared with those in the open column to get a better understanding of the possible impact of structured plates on coal separation process. It is concluded that the structured plates can offer a good gravity separation with substantial throughput increase. The throughput is nearly three times higher than that of a HSBS without structured plates. The separation performance in the presence of the structured plates improves with significant decrease in the probable error values.

Analysis of Packed Column Jig for Fine Coal Separation

The multicell packed column jig is a newly developed gravity separator, which uses pulsating upward flow to develop circular movement of particles in each virtual cell surrounded by corrugated plates. This makes for repeated separation in a large number of jigging cells, leading to highly efficient separation with a large throughput capacity. A clean coal of 5-6% ash at 75-90% combustible material recovery can be achieved from a feed of 35-50% ash. These results correspond to 90-98% ash rejection. A low specific gravity of separation, SG50, of 1.45 and a probable error value, Ep, of 0.06 in the particle size range of −1 mm+150 μm are indicative of the high process efficiency achievable by the packed column jig. An integrated fine coal cleaning circuit consisting of a multicell packed column jig and a packed flotation column can be used as an alternative fine coal cleaning circuit to treat −2 mm size fraction. A clean coal product of 6% ash from a feed of 46% ash was obtained, with 87% combustible material recovery.

Altair jig: an in-plant evaluation for fine coal cleaning

Coal preparation plants treat a majority of the run-of-mine coal using various gravity processes, which are known for their low cost and high process efficiency values. Due to the inefficiencies of conventional gravity-based processes in treating −1 mm coal, froth flotation processes are traditionally employed at a relatively high cost. To address cost and separation performance issues, several enhanced gravity separation technologies have been developed and evaluated which may allow effective gravity-based separation to particle sizes as small as 25 μm. The Altair centrifugal jig is an enhanced gravity technology, whose suitability for fine coal cleaning has been demonstrated through an in-plant study as reported in this publication. A relatively low specific gravity cut-point of 1.50 with a probable error value of 0.11 over a wide particle size range 1 mm×45 μm is indicative of the excellent separation performance achievable from the Altair jig. Tests performed with and without ragging material were performed with the goal that the latter would provide enhanced throughput capacities. However, although the performance was close to the theoretical limits over the broad range of product grades generated, the no-ragging experiments resulted in a significant loss in coal recovery under the given conditions. Overall, the centrifugal jig achieved 80% ash rejection and 50% total sulfur rejection while recovering nearly 80% of the combustibles.

Application of dense-medium in an enhanced gravity separator for fine coal cleaning

Dense-medium separators have proven to be the most efficient processes for removing the undesirable gangue material from run-of-mine coal. The application of high-pressure feed injection into dense-medium cyclones to provide an elevated centrifugal force has recently been found to allow efficient separation performances for the treatment of fine coal (i.e., <1000 μm). However, high-pressure injection requires specialized pumps and results in relatively high maintenance requirements. A test prograrn has been conducted to evaluate the potential cleaning of 1000 x 44 μm fine coal using dense-medium in an enhanced gravity separator (EGS), which mechanically generates enhanced gravity field. Test results indicate that the use of dense-medium in an EGS resulted in an 8% weight unit increase in mass yield compared to the use of water-only for the treatment of an easy-to-clean Illinois No. 6 fine coal sample. For a difficult-to-clean coal, the mass yield improvement was significantly greater at nearly 20% by weight. From the treatment offour different coal samples, organic efficiency values greater than 90% were obtained over the entire range of product quality values. These findings are reflective of the highly efficiency, low density separations provided by the dense-medium as indicated by probable error values below 0.05.

Evaluation of the Altair Centrifugal Jig for Fine Coal Separation

A significant effort has been made during the past decade to develop gravity separators for treating fine particles. As a result, several enhanced gravity separators have been developed and commercialized. The Altair Centrifugal Jig is an enhanced gravity separator that provides relatively efficient separations on +25 μm size fractions. An experimental program conducted on −600 μm coal found that the Altair Jig reduced the ash content of the 600×44 urn material from about 30% to 10% with an 86% combustible recovery value. The pulse water pressure, feed volumetric rate and ragging volume were found to be the key operating parameters affecting the separation performance indices obtained from the process. A low density cut point of 1.55 with a probable error value of 0.09 was indicative of the high process efficiency values achievable by the Altair Jig.