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This paper introduces contact sorption with ceramic sorbents as a method to reduce the moisture content of coal fines produced by coal processing plants. The proposed method was tested on laboratory scale where ceramic spheres with diameters of 3 mm and 5 mm were combined with wet coal fines of size fractions between 0.25 mm and 2 mm. The coal had an initial moisture content of 0.25 g(Water)/g(Coal and water), and was dewatered using contact sorption to an average moisture content of 0.13 g(Water)/g(Coal and water) after 2.5 minutes and 0.05 g(Water)/g(Coal and water) after 10 minutes, respectively. This paper focuses on identifying the solid phase conditions essential to improving the contact sorption drying technology, proving that contact between the coal and sorbent material is the main driving force behind this technology. Increasing the sorbent to coal mass ratio and using smaller sorbents with a larger surface area resulted in improved contact and consequently improved moisture mass transfer. The final coal moisture content that could be achieved was independent of coal particle size. Current studies show a reliance on thermal drying technologies to dry the saturated sorbent material, whereas this paper proves that drying with high airflow at low temperatures is sufficient to regenerate the sorbent material. The loaded sorbent material could easily be separated from the dried coal product by dry screening, and could be dried and regenerated afterwards in an air-blown packed bed within 10 minutes. The re-use of sorbent material showed no decrease in its dewatering efficiency, and it was shown to be possible to re-use the sorbents for a large number of cycles. Contact sorption can prove to be a cost-effective and efficient drying method to dewater coal fines in the industry

This paper introduces contact sorption with ceramic sorbents as a method to reduce the moisture content of coal fines produced by coal processing plants. The proposed method was tested on laboratory scale where ceramic spheres with diameters of 3 mm and 5 mm were combined with wet coal fines of size fractions between 0.25 mm and 2 mm. The coal had an initial moisture content of 0.25 g(Water)/g(Coal and water), and was dewatered using contact sorption to an average moisture content of 0.13 g(Water)/g(Coal and water) after 2.5 minutes and 0.05 g(Water)/g(Coal and water) after 10 minutes, respectively. This paper focuses on identifying the solid phase conditions essential to improving the contact sorption drying technology, proving that contact between the coal and sorbent material is the main driving force behind this technology. Increasing the sorbent to coal mass ratio and using smaller sorbents with a larger surface area resulted in improved contact and consequently improved moisture mass transfer. The final coal moisture content that could be achieved was independent of coal particle size. Current studies show a reliance on thermal drying technologies to dry the saturated sorbent material, whereas this paper proves that drying with high airflow at low temperatures is sufficient to regenerate the sorbent material. The loaded sorbent material could easily be separated from the dried coal product by dry screening, and could be dried and regenerated afterwards in an air-blown packed bed within 10 minutes. The re-use of sorbent material showed no decrease in its dewatering efficiency, and it was shown to be possible to re-use the sorbents for a large number of cycles. Contact sorption can prove to be a cost-effective and efficient drying method to dewater coal fines in the industry

Studies have shown that contact sorption drying is a feasible technique to dewater fine (+0.15mm–0.5mm) and ultra-fine (−0.15 mm) coal. The aim of this article is to further investigate the drying mechanism involved. It could be shown that moisture transfer occurred primarily in the liquid phase, requiring direct contact between the coal and sorbent particles to facilitate the movement of the water. Moisture transfer was enhanced by operating with a higher sorbent to coal mass ratio. When drying smaller coal particle size ranges, the resistance to liquid transport decreased, leading to better desorption results. These improvements were mainly as a result of a greater contact area between the sorbent and coal particles

This paper investigates the air dense medium fluidized bed (ADMFB) as a suitable dry beneficiation technique to upgrade +5.6 mm-13.2 mm South African coal. The separation efficiency of the ADMFB was assessed by determining the effect, if any, of particle size range, medium to coal feed ratios, and the addition of vibration on the separation ability of the bed. The coal was upgraded to varying degrees, depending on the parameters of the applied methods. For example, when considering the bottom bed layer (one quarter of the total bed height) as discard, the cumulative ash yield of the clean coal fraction ranged between 13.0% and 17.6% with a corresponding yield of 82.21%–83.93%, respectively. A variation in feed coal PSD did not significantly influence the response of the bed pertaining to its ability to beneficiate the coal. This was quantified by the similarity in percentage ash yield for the feed, top and bottom layers. In addition, it was established that by feeding a coal and magnetite (+300 µm) mixture, in various mass ratios, did not significantly influence the separation efficiency of the bed, nor did the application of external vibration to the bed aid in the beneficiation of the coal. Although these factors did not influence the performance of the ADMFB, it was found that the minimum fluidization velocity and bed stability were largely improved by the introduction of these variables

Studies have shown that contact sorption drying is a feasible technique to dewater fine (+0.15mm–0.5mm) and ultra-fine (−0.15 mm) coal. The aim of this article is to further investigate the drying mechanism involved. It could be shown that moisture transfer occurred primarily in the liquid phase, requiring direct contact between the coal and sorbent particles to facilitate the movement of the water. Moisture transfer was enhanced by operating with a higher sorbent to coal mass ratio. When drying smaller coal particle size ranges, the resistance to liquid transport decreased, leading to better desorption results. These improvements were mainly as a result of a greater contact area between the sorbent and coal particles

This paper investigates the air dense medium fluidized bed (ADMFB) as a suitable dry beneficiation technique to upgrade +5.6 mm-13.2 mm South African coal. The separation efficiency of the ADMFB was assessed by determining the effect, if any, of particle size range, medium to coal feed ratios, and the addition of vibration on the separation ability of the bed. The coal was upgraded to varying degrees, depending on the parameters of the applied methods. For example, when considering the bottom bed layer (one quarter of the total bed height) as discard, the cumulative ash yield of the clean coal fraction ranged between 13.0% and 17.6% with a corresponding yield of 82.21%–83.93%, respectively. A variation in feed coal PSD did not significantly influence the response of the bed pertaining to its ability to beneficiate the coal. This was quantified by the similarity in percentage ash yield for the feed, top and bottom layers. In addition, it was established that by feeding a coal and magnetite (+300 µm) mixture, in various mass ratios, did not significantly influence the separation efficiency of the bed, nor did the application of external vibration to the bed aid in the beneficiation of the coal. Although these factors did not influence the performance of the ADMFB, it was found that the minimum fluidization velocity and bed stability were largely improved by the introduction of these variables

Spent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterized using FTIR spectroscopy and SEM-EDS analyses, which revealed that the products had the potential for adsorption of heavy metals from solution and confirmed the successful impregnation of biochar with SDS surfactant. The two adsorbents were then used for the removal of cadmium from solution and the adsorption behavior and capacity determined through adsorption isotherm, kinetic, and thermodynamic studies. It was found that the cadmium was adsorbed in several concentric layers on the surface of the adsorbents through a chemisorption mechanism. The PT biochar was identified as a superior adsorbent, with a capacity of qe = 10.67 mg/g compared to the NT biochar with qe = 4.82 mg/g. The adsorption of cadmium onto the PT biochar was further determined to be spontaneous and endothermic. It was therefore concluded that the PT biochar shows potential as an adsorbent and could be considered for implementation in the treatment of metal-polluted effluents

Spent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterized using FTIR spectroscopy and SEM-EDS analyses, which revealed that the products had the potential for adsorption of heavy metals from solution and confirmed the successful impregnation of biochar with SDS surfactant. The two adsorbents were then used for the removal of cadmium from solution and the adsorption behavior and capacity determined through adsorption isotherm, kinetic, and thermodynamic studies. It was found that the cadmium was adsorbed in several concentric layers on the surface of the adsorbents through a chemisorption mechanism. The PT biochar was identified as a superior adsorbent, with a capacity of qe = 10.67 mg/g compared to the NT biochar with qe = 4.82 mg/g. The adsorption of cadmium onto the PT biochar was further determined to be spontaneous and endothermic. It was therefore concluded that the PT biochar shows potential as an adsorbent and could be considered for implementation in the treatment of metal-polluted effluents

Laboratory tests were conducted to investigate the use of ceramic spheres containing about 82-85 wt% alumina as adsorbents for the drying of coal samples from the Highveld coalfield in South Africa. The samples were dried in air and then crushed to a fine coal fraction of +1 mm -2 mm and an ultrafine fraction smaller than 0.5 mm. Drying was carried out in a rotating adsorber and the loaded ceramic and dry coal were then separated by screening and the ceramic dried in a packed bed to be re-used in contact sorption drying. In adsorption experiments carried out at 25 degrees C, fine coal showed an 8 wt% moisture reduction in 14 minutes, while ultrafine coal, which had a higher moisture content, took 87 minutes to reduce the moisture content by about 8%. A coal/ceramic ratio of 1:3 resulted in a faster dewatering rate compared with a ratio of 1:1 as increasing the amount of ceramic resulted in more efficient contact between the coal and ceramic. Increasing the temperature to 55 degrees C reduced the final moisture content by an additional 1 wt%., Laboratory tests were conducted to investigate the use of ceramic spheres containing about 82-85 wt% alumina as adsorbents for the drying of coal samples from the Highveld coalfield in South Africa. The samples were dried in air and then crushed to a fine coal fraction of +1 mm -2 mm and an ultrafine fraction smaller than 0.5 mm. Drying was carried out in a rotating adsorber and the loaded ceramic and dry coal were then separated by screening and the ceramic dried in a packed bed to be re-used in contact sorption drying. In adsorption experiments carried out at 25 degrees C, fine coal showed an 8 wt% moisture reduction in 14 minutes, while ultrafine coal, which had a higher moisture content, took 87 minutes to reduce the moisture content by about 8%. A coal/ceramic ratio of 1:3 resulted in a faster dewatering rate compared with a ratio of 1:1 as increasing the amount of ceramic resulted in more efficient contact between the coal and ceramic. Increasing the temperature to 55 degrees C reduced the final moisture content by an additional 1 wt%.

It is proposed to introduce contact sorption drying as a method to reduce the moisture content in coal fines. The aim of this study was to investigate the possibility of drying fine and ultra-fine coal using porous ceramic as the moisture sorbent. The main focus of this report is to define how the air temperature, particle size variations and mixing ratio would influence the contact between coal and ceramic for effective moisture adsorption. Drying of coal fines assisted by ceramic sorbents proved to be a viable concept as the ceramic was able to not only reduce the moisture content of fine coal, but of ultra-fine coal as well. The larger surface area of smaller ceramics allowed for efficient contact and consequently higher dewatering rates. The addition of more ceramic resulted in better contact with the wet coal and reduced the operating time quite significantly. Improved contact between the coal and ceramic therefore proved to be the main driving force during adsorption drying

A good correlation exists between the amount of moisture adsorbed and the oxygen content of medium-rank B vitrinite-rich and medium-rank C inertinite-rich bituminous coal. Total mass moisture adsorbed per gram of coal determined from the modified BET model provides a better approximation than the BET model. The relationship between the modified BET moisture monolayer coverage and the area of surface oxygen groups suggests that moisture is adsorbed at these sites. Oxygen content is a good indicator of the amount of moisture adsorbed on bituminous coal. Open hysteresis loops indicate that moisture is retained on medium-rank C inertinite-rich bituminous coal

It is proposed to introduce contact sorption drying as a method to reduce the moisture content in coal fines. The aim of this study was to investigate the possibility of drying fine and ultra-fine coal using porous ceramic as the moisture sorbent. The main focus of this report is to define how the air temperature, particle size variations and mixing ratio would influence the contact between coal and ceramic for effective moisture adsorption. Drying of coal fines assisted by ceramic sorbents proved to be a viable concept as the ceramic was able to not only reduce the moisture content of fine coal, but of ultra-fine coal as well. The larger surface area of smaller ceramics allowed for efficient contact and consequently higher dewatering rates. The addition of more ceramic resulted in better contact with the wet coal and reduced the operating time quite significantly. Improved contact between the coal and ceramic therefore proved to be the main driving force during adsorption drying

It is proposed to introduce contact sorption drying as a method to reduce the moisture content in coal fines. The aim of this study was to investigate the possibility of drying fine and ultra-fine coal using porous ceramic as the moisture sorbent. The main focus of this report is to define how the air temperature, particle size variations and mixing ratio would influence the contact between coal and ceramic for effective moisture adsorption. Drying of coal fines assisted by ceramic sorbents proved to be a viable concept as the ceramic was able to not only reduce the moisture content of fine coal, but of ultra-fine coal as well. The larger surface area of smaller ceramics allowed for efficient contact and consequently higher dewatering rates. The addition of more ceramic resulted in better contact with the wet coal and reduced the operating time quite significantly. Improved contact between the coal and ceramic therefore proved to be the main driving force during adsorption drying

Imagine that a sample of coal could be crushed unlimited times to the same or different top size; a different washability would be obtained for each crushing experiment. Depending on the size and distribution of the raw coal components (say vitrinite, inertinite, and mudstone), better yields for a low ash product are obtained as a top size is approached that is the same or smaller than the components that need to be liberated. As the top size approaches the size of the components that need to be liberated (or smaller), near density material will start decreasing and the density differences between the components that need to be separated will become larger, because mostly “clean” single component particles are produced, that have widely different densities. As the virtual particle size decreases, the concentration or yield of the low ash product increases to a maximum, as the macerals are completely liberated from mineral matter In this paper a method is proposed to predict washability characteristics by simulating how coal will behave when crushed to different top sizes and with different virtual particle size distributions, from photographs

A good correlation exists between the amount of moisture adsorbed and the oxygen content of medium-rank B vitrinite-rich and medium-rank C inertinite-rich bituminous coal. Total mass moisture adsorbed per gram of coal determined from the modified BET model provides a better approximation than the BET model. The relationship between the modified BET moisture monolayer coverage and the area of surface oxygen groups suggests that moisture is adsorbed at these sites. Oxygen content is a good indicator of the amount of moisture adsorbed on bituminous coal. Open hysteresis loops indicate that moisture is retained on medium-rank C inertinite-rich bituminous coal

Imagine that a sample of coal could be crushed unlimited times to the same or different top size; a different washability would be obtained for each crushing experiment. Depending on the size and distribution of the raw coal components (say vitrinite, inertinite, and mudstone), better yields for a low ash product are obtained as a top size is approached that is the same or smaller than the components that need to be liberated. As the top size approaches the size of the components that need to be liberated (or smaller), near density material will start decreasing and the density differences between the components that need to be separated will become larger, because mostly “clean” single component particles are produced, that have widely different densities. As the virtual particle size decreases, the concentration or yield of the low ash product increases to a maximum, as the macerals are completely liberated from mineral matter In this paper a method is proposed to predict washability characteristics by simulating how coal will behave when crushed to different top sizes and with different virtual particle size distributions, from photographs

It is proposed to introduce contact sorption drying as a method to reduce the moisture content in coal fines. The aim of this study was to investigate the possibility of drying fine and ultra-fine coal using porous ceramic as the moisture sorbent. The main focus of this report is to define how the air temperature, particle size variations and mixing ratio would influence the contact between coal and ceramic for effective moisture adsorption. Drying of coal fines assisted by ceramic sorbents proved to be a viable concept as the ceramic was able to not only reduce the moisture content of fine coal, but of ultra-fine coal as well. The larger surface area of smaller ceramics allowed for efficient contact and consequently higher dewatering rates. The addition of more ceramic resulted in better contact with the wet coal and reduced the operating time quite significantly. Improved contact between the coal and ceramic therefore proved to be the main driving force during adsorption drying

A good correlation exists between the amount of moisture adsorbed and the oxygen content of medium-rank B vitrinite-rich and medium-rank C inertinite-rich bituminous coal. Total mass moisture adsorbed per gram of coal determined from the modified BET model provides a better approximation than the BET model. The relationship between the modified BET moisture monolayer coverage and the area of surface oxygen groups suggests that moisture is adsorbed at these sites. Oxygen content is a good indicator of the amount of moisture adsorbed on bituminous coal. Open hysteresis loops indicate that moisture is retained on medium-rank C inertinite-rich bituminous coal

Imagine that a sample of coal could be crushed unlimited times to the same or different top size; a different washability would be obtained for each crushing experiment. Depending on the size and distribution of the raw coal components (say vitrinite, inertinite, and mudstone), better yields for a low ash product are obtained as a top size is approached that is the same or smaller than the components that need to be liberated. As the top size approaches the size of the components that need to be liberated (or smaller), near density material will start decreasing and the density differences between the components that need to be separated will become larger, because mostly “clean” single component particles are produced, that have widely different densities. As the virtual particle size decreases, the concentration or yield of the low ash product increases to a maximum, as the macerals are completely liberated from mineral matter In this paper a method is proposed to predict washability characteristics by simulating how coal will behave when crushed to different top sizes and with different virtual particle size distributions, from photographs

Imagine that a sample of coal could be crushed unlimited times to the same or different top size; a different washability would be obtained for each crushing experiment. Depending on the size and distribution of the raw coal components (say vitrinite, inertinite, and mudstone), better yields for a low ash product are obtained as a top size is approached that is the same or smaller than the components that need to be liberated. As the top size approaches the size of the components that need to be liberated (or smaller), near density material will start decreasing and the density differences between the components that need to be separated will become larger, because mostly “clean” single component particles are produced, that have widely different densities. As the virtual particle size decreases, the concentration or yield of the low ash product increases to a maximum, as the macerals are completely liberated from mineral matter In this paper a method is proposed to predict washability characteristics by simulating how coal will behave when crushed to different top sizes and with different virtual particle size distributions, from photographs

Excessive amounts of moisture in product coal can influence the efficiency of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture content of coal by means of gravity drainage and evaporation. This paper is focused on the evaporation of moisture from a coal stockpile surface with the aim of investigating the effect of particle size on the rate of evaporation as well as the depth to which evaporation extends. It was observed that moisture initially evaporates at a higher rate from a stockpile consisting of fine particles (-6.7 mm) than from coarser particles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted to the outer shell of the fine coal stockpile. However, for coarse coal, the porous nature increases the depth at which evaporation occurs. Evaporation of moisture was observed up to the fourth day of each experimental run, after which steady state was obtained. It was shown the water can evaporate from the surface into the body of the stockpile, depending on the coal particle size and void spacing. An experimental reclaim depth of 0.4 m was achieved after 4 days

Excessive amounts of moisture in product coal can influence the efficiency of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture content of coal by means of gravity drainage and evaporation. This paper is focused on the evaporation of moisture from a coal stockpile surface with the aim of investigating the effect of particle size on the rate of evaporation as well as the depth to which evaporation extends. It was observed that moisture initially evaporates at a higher rate from a stockpile consisting of fine particles (-6.7 mm) than from coarser particles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted to the outer shell of the fine coal stockpile. However, for coarse coal, the porous nature increases the depth at which evaporation occurs. Evaporation of moisture was observed up to the fourth day of each experimental run, after which steady state was obtained. It was shown the water can evaporate from the surface into the body of the stockpile, depending on the coal particle size and void spacing. An experimental reclaim depth of 0.4 m was achieved after 4 days

Excessive amounts of moisture in product coal can influence the efficiency of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture content of coal by means of gravity drainage and evaporation. This paper is focused on the evaporation of moisture from a coal stockpile surface with the aim of investigating the effect of particle size on the rate of evaporation as well as the depth to which evaporation extends. It was observed that moisture initially evaporates at a higher rate from a stockpile consisting of fine particles (-6.7 mm) than from coarser particles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted to the outer shell of the fine coal stockpile. However, for coarse coal, the porous nature increases the depth at which evaporation occurs. Evaporation of moisture was observed up to the fourth day of each experimental run, after which steady state was obtained. It was shown the water can evaporate from the surface into the body of the stockpile, depending on the coal particle size and void spacing. An experimental reclaim depth of 0.4 m was achieved after 4 days

Due to health and environmental factors involved with standard float-sink analytical methods, a water-only fractionation procedure was investigated. A laboratory scale 105 × 105 mm reflux classifier was built and used to fractionate fine coal into a number of density classes. The procedure was tested against standard float and sink methods. The reflux classifier was found to be an effective fractionation method, especially if the fractioned samples were to be used in further chemical or reactivity investigations that could be affected by the dense medium adhering to the coal particle surfaces. The procedure was easier, safer and less tedious to perform in the laboratory. Higher density cuts could be achieved, and any number of density intervals could be prepared. It was also confirmed that the separation in the reflux classifier was not totally independent of particle size but it operated well for narrow size distributions above 355 μm. Tracer tests were also done, and it was shown that tracer partition results were a poor predictor of the reflux classifier performance because of hindered settling effects

Due to health and environmental factors involved with standard float-sink analytical methods, a water-only fractionation procedure was investigated. A laboratory scale 105 × 105 mm reflux classifier was built and used to fractionate fine coal into a number of density classes. The procedure was tested against standard float and sink methods. The reflux classifier was found to be an effective fractionation method, especially if the fractioned samples were to be used in further chemical or reactivity investigations that could be affected by the dense medium adhering to the coal particle surfaces. The procedure was easier, safer and less tedious to perform in the laboratory. Higher density cuts could be achieved, and any number of density intervals could be prepared. It was also confirmed that the separation in the reflux classifier was not totally independent of particle size but it operated well for narrow size distributions above 355 μm. Tracer tests were also done, and it was shown that tracer partition results were a poor predictor of the reflux classifier performance because of hindered settling effects

Coal ore isn’t a uniform material. In order to optimize the coal liberation process it is necessary to classify a coal ore sample into its constituent components as quickly and cheaply possible. This paper investigates whether it is feasible to employ image processing and pattern recognition to segment a photographic image of coal ore into its various mineral components prior to the sample being crushed. The key to solving this classification problem is to model the visual texture of the various coal components by means of a low-dimensional texture space consisting of two main dimensions, namely: roughness and regularity. The regularity of each texture is estimated by means of a novel model-based approach. The distribution of the various coal components in the resultant feature space is modelled by means of a mixtures model and a simple nearest-neighbour decision rule is used to classify each pixel in the image. The performance of the classification system is encouraging and shows the feasibility of our idea

Coal ore isn’t a uniform material. In order to optimize the coal liberation process it is necessary to classify a coal ore sample into its constituent components as quickly and cheaply possible. This paper investigates whether it is feasible to employ image processing and pattern recognition to segment a photographic image of coal ore into its various mineral components prior to the sample being crushed. The key to solving this classification problem is to model the visual texture of the various coal components by means of a low-dimensional texture space consisting of two main dimensions, namely: roughness and regularity. The regularity of each texture is estimated by means of a novel model-based approach. The distribution of the various coal components in the resultant feature space is modelled by means of a mixtures model and a simple nearest-neighbour decision rule is used to classify each pixel in the image. The performance of the classification system is encouraging and shows the feasibility of our idea

Coal ore isn’t a uniform material. In order to optimize the coal liberation process it is necessary to classify a coal ore sample into its constituent components as quickly and cheaply possible. This paper investigates whether it is feasible to employ image processing and pattern recognition to segment a photographic image of coal ore into its various mineral components prior to the sample being crushed. The key to solving this classification problem is to model the visual texture of the various coal components by means of a low-dimensional texture space consisting of two main dimensions, namely: roughness and regularity. The regularity of each texture is estimated by means of a novel model-based approach. The distribution of the various coal components in the resultant feature space is modelled by means of a mixtures model and a simple nearest-neighbour decision rule is used to classify each pixel in the image. The performance of the classification system is encouraging and shows the feasibility of our idea

Coal ore isn’t a uniform material. In order to optimize the coal liberation process it is necessary to classify a coal ore sample into its constituent components as quickly and cheaply possible. This paper investigates whether it is feasible to employ image processing and pattern recognition to segment a photographic image of coal ore into its various mineral components prior to the sample being crushed. The key to solving this classification problem is to model the visual texture of the various coal components by means of a low-dimensional texture space consisting of two main dimensions, namely: roughness and regularity. The regularity of each texture is estimated by means of a novel model-based approach. The distribution of the various coal components in the resultant feature space is modelled by means of a mixtures model and a simple nearest-neighbour decision rule is used to classify each pixel in the image. The performance of the classification system is encouraging and shows the feasibility of our idea

The demand for energy has continued to rise worldwide in line with population growth. The majority of South Africa’s electricity is supplied by coal-fired power stations. The amount of fine coal (-2 mm) generated at coal processing plants has increased, due mainly to mechanized mining methods. Fine coal retains more water, which lowers its heating value. Drying the coal is costly and it is difficult to achieve the required moisture content. Consequently, coal fines are often discarded. An estimated 8% of the total energy value of mined coal is lost1. Fluidized bed technology is often used to dry coal thermally, but this method is expensive and has an adverse environmental impact. The objective of this study was to investigate the removal of moisture from fine coal (<2 mm) in a fluidized bed operated with dry fluidizing air at moderate temperatures as the drying agent. The effects of different air temperatures and relative humidity levels were investigated in a controlled environment. The study further investigated the influence of coal particle size on moisture removal. The drying rate was found to increase with increasing temperature. The relative humidity of the drying air had a more pronounced effect on the drying rate, even at temperatures as low as 25°C.. It became more challenging to remove moisture as the particle size decreased. The gain in calorific value was greater than the energy required to dry the coal samples, showing that a fluidized bed using moderately warm dry air is an energy-efficient drying technology. The energy efficiency of the fluidized bed compared favourably with other thermal drying methods

The demand for energy has continued to rise worldwide in line with population growth. The majority of South Africa’s electricity is supplied by coal-fired power stations. The amount of fine coal (-2 mm) generated at coal processing plants has increased, due mainly to mechanized mining methods. Fine coal retains more water, which lowers its heating value. Drying the coal is costly and it is difficult to achieve the required moisture content. Consequently, coal fines are often discarded. An estimated 8% of the total energy value of mined coal is lost1. Fluidized bed technology is often used to dry coal thermally, but this method is expensive and has an adverse environmental impact. The objective of this study was to investigate the removal of moisture from fine coal (<2 mm) in a fluidized bed operated with dry fluidizing air at moderate temperatures as the drying agent. The effects of different air temperatures and relative humidity levels were investigated in a controlled environment. The study further investigated the influence of coal particle size on moisture removal. The drying rate was found to increase with increasing temperature. The relative humidity of the drying air had a more pronounced effect on the drying rate, even at temperatures as low as 25°C.. It became more challenging to remove moisture as the particle size decreased. The gain in calorific value was greater than the energy required to dry the coal samples, showing that a fluidized bed using moderately warm dry air is an energy-efficient drying technology. The energy efficiency of the fluidized bed compared favourably with other thermal drying methods

The demand for energy has continued to rise worldwide in line with population growth. The majority of South Africa’s electricity is supplied by coal-fired power stations. The amount of fine coal (-2 mm) generated at coal processing plants has increased, due mainly to mechanized mining methods. Fine coal retains more water, which lowers its heating value. Drying the coal is costly and it is difficult to achieve the required moisture content. Consequently, coal fines are often discarded. An estimated 8% of the total energy value of mined coal is lost1. Fluidized bed technology is often used to dry coal thermally, but this method is expensive and has an adverse environmental impact. The objective of this study was to investigate the removal of moisture from fine coal (<2 mm) in a fluidized bed operated with dry fluidizing air at moderate temperatures as the drying agent. The effects of different air temperatures and relative humidity levels were investigated in a controlled environment. The study further investigated the influence of coal particle size on moisture removal. The drying rate was found to increase with increasing temperature. The relative humidity of the drying air had a more pronounced effect on the drying rate, even at temperatures as low as 25°C.. It became more challenging to remove moisture as the particle size decreased. The gain in calorific value was greater than the energy required to dry the coal samples, showing that a fluidized bed using moderately warm dry air is an energy-efficient drying technology. The energy efficiency of the fluidized bed compared favourably with other thermal drying methods

Fluidized bed drying is currently receiving much attention as a dewatering option after the beneficiation of fine coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25°C − 40°C) within a controlled environment by lowering the relative humidity of air. It was firstly proven that fluidization has a major advantage over normal static beds when allowed to reach equilibrium. Hereafter, several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. It was, therefore, shown that this is a viable technology for the dewatering of fine coal

Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 × 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2-3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25-55°C) within a controlled environment by lowering of the relative humidity of the air. It was firstly proven that fluidization has a major advantage over non-fluidized beds, with regards to drying rate and final moisture content. Hereafter several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. Parameters tested included relative humidity, temperature and coal composition. Energy balances showed a positive nett energy increase in the dried coal during combustion when related to the energy input during drying. In comparison with thermal drying technologies, fluidized bed drying was proven to be less energy intensive. It was therefore shown that this is a viable technology for the dewatering of fine coal

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25-55°C) within a controlled environment by lowering of the relative humidity of the air. It was firstly proven that fluidization has a major advantage over non-fluidized beds, with regards to drying rate and final moisture content. Hereafter several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. Parameters tested included relative humidity, temperature and coal composition. Energy balances showed a positive nett energy increase in the dried coal during combustion when related to the energy input during drying. In comparison with thermal drying technologies, fluidized bed drying was proven to be less energy intensive. It was therefore shown that this is a viable technology for the dewatering of fine coal

Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 × 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2-3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent

Fluidized bed drying is currently receiving much attention as a dewatering option after the beneficiation of fine coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25°C − 40°C) within a controlled environment by lowering the relative humidity of air. It was firstly proven that fluidization has a major advantage over normal static beds when allowed to reach equilibrium. Hereafter, several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. It was, therefore, shown that this is a viable technology for the dewatering of fine coal

Fluidized bed drying is currently receiving much attention as a dewatering option after the beneficiation of fine coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25°C − 40°C) within a controlled environment by lowering the relative humidity of air. It was firstly proven that fluidization has a major advantage over normal static beds when allowed to reach equilibrium. Hereafter, several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. It was, therefore, shown that this is a viable technology for the dewatering of fine coal

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25-55°C) within a controlled environment by lowering of the relative humidity of the air. It was firstly proven that fluidization has a major advantage over non-fluidized beds, with regards to drying rate and final moisture content. Hereafter several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. Parameters tested included relative humidity, temperature and coal composition. Energy balances showed a positive nett energy increase in the dried coal during combustion when related to the energy input during drying. In comparison with thermal drying technologies, fluidized bed drying was proven to be less energy intensive. It was therefore shown that this is a viable technology for the dewatering of fine coal

Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 × 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2-3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent

Fine coal (-500 μm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was developed at North-West University. It entails deliberately damaging the filter cake during dewatering to allow for an increased flow of air through the cake at the expense of the applied pressure differential. This method resulted in an average improvement in final cake moisture of between 3 per cent and 5 per cent when executed in the laboratory under controlled conditions. A device was designed that could be fitted onto existing belt filters that would damage the filter cake as it passes by. This device was tested on a vacuum belt filter installation at a coal beneficiation operation in the Waterberg coal field in South Africa. The results showed a 3 per cent reduction in final moisture of the cake, proving the validity of the method at full industrial scale.

Fine coal (-500 μm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was developed at North-West University. It entails deliberately damaging the filter cake during dewatering to allow for an increased flow of air through the cake at the expense of the applied pressure differential. This method resulted in an average improvement in final cake moisture of between 3 per cent and 5 per cent when executed in the laboratory under controlled conditions. A device was designed that could be fitted onto existing belt filters that would damage the filter cake as it passes by. This device was tested on a vacuum belt filter installation at a coal beneficiation operation in the Waterberg coal field in South Africa. The results showed a 3 per cent reduction in final moisture of the cake, proving the validity of the method at full industrial scale.

Mycoplasma genitalium, a human mycoplasma species has been established as a cause of nongonococcal urethritis (NGU) in men, particularly in Chlamydia trachomatis-negative patients. It was also shown to play a role in cervicitis and pelvic inflammatory disease (PID) in women. Due to difficulty in culturing, and the lack of routine molecular diagnostic tests, many M. genitalium infections are undetected. The purpose of this study was to evaluate three nucleic acid amplification tests (NAATs) i.e. a recently developed Gen-Probe research only transcription mediated amplification (TMA) assay, a conventional polymerase chain reaction (PCR) assay and a real-time PCR (q-PCR) assay for the detection of M. genitalium in urine specimens of men with symptoms of urethritis. To evaluate the three assays, 300 urine specimens were collected between June 2007 and July 2008 from sexually active male patients presenting with discharge (N=94) and/or burning on micturition (N=206) to a private medical practitioner in Silverton, Pretoria. A specimen was considered positive by extension of the gold standard i.e. if any two of the three assays were positive. This was used to calculate the sensitivity and specificity of each method. TMA detected M. genitalium in 62 (21%), PCR in 43 (14%) and q-PCR in 48 (16%) of the 300 patients. The sensitivities of the assays were 100% (TMA), 92% (q-PCR) and 78% (PCR), with specificities of 90% (TMA), 95% (q-PCR) and 97% (PCR). The sensitivity of the TMA assay was higher than that of the q-PCR and PCR assays. The lower sensitivity obtained by the q-PCR assay might have been due to inhibition and limitations in the amount of the DNA template. However, the q-PCR assay was easy to perform as it combines amplification and detection thus eliminating further handling of PCR products. The PCR, although with a higher specificity, was the least desirable in terms of testing time and problems with subjectivity when reading agarose gels. v We concluded that the Gen

Collection : Mémoires de la Société linnéenne de Normandie. Section zoologique ; 1er vol., 2e fasc., Collection : Mémoires de la Société linnéenne de Normandie ; 1er vol., 2e fasc., Appartient à l’ensemble documentaire : BNormand1, Contient une table des matières, Avec mode texte

Collection : Mémoires de la Société linnéenne de Normandie. Section zoologique ; 1er vol., 2e fasc., Collection : Mémoires de la Société linnéenne de Normandie ; 1er vol., 2e fasc., Appartient à l’ensemble documentaire : BNormand1, Contient une table des matières, Avec mode texte

The degradation of coal and the production of coal fines during handling and transport is a serious problem in processes that depend on closely sized large particles. To minimise the production of fines, a fundamental understanding of coal breakage is required, so, to clarify the complex nature of coal breakage, a series of experiments was conducted to determine the influence of the internal physical coal structures on compression breakage characteristics. The structures investigated are the cleat and layered structure of coal and the mineral inclusions. Samples of uniform size and shape were prepared from a large block of South African Waterberg coal. The samples were analysed nondestructively using microfocus X-ray computed tomography then wrapped in cling film and mechanically compressed while the pressure applied was measured. The virtual three-dimensional volume tomograms of the initial sample and the progeny were compared and the changes qualitatively analysed. Conclusions were drawn as to where the fatal cracks initialised and how the cracks propagated. Particle-size distributions were done to quantify the extent of breakage versus the breakage strength of the sample. It was found that, of all the internal structures, the inherent crack distribution has the biggest influence on breakage and breakage patterns of coal. (Authors.), The degradation of coal and the production of coal fines during handling and transport is a serious problem in processes that depend on closely sized large particles. To minimise the production of fines, a fundamental understanding of coal breakage is required, so, to clarify the complex nature of coal breakage, a series of experiments was conducted to determine the influence of the internal physical coal structures on compression breakage characteristics. The structures investigated are the cleat and layered structure of coal and the mineral inclusions. Samples of uniform size and shape were prepared from a large block of South African Waterberg coal. The samples were analysed nondestructively using microfocus X-ray computed tomography then wrapped in cling film and mechanically compressed while the pressure applied was measured. The virtual three-dimensional volume tomograms of the initial sample and the progeny were compared and the changes qualitatively analysed. Conclusions were drawn as to where the fatal cracks initialised and how the cracks propagated. Particle-size distributions were done to quantify the extent of breakage versus the breakage strength of the sample. It was found that, of all the internal structures, the inherent crack distribution has the biggest influence on breakage and breakage patterns of coal. (Authors.)

Spent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterised using FTIR spectroscopy and SEM-EDS analysis, which revealed that the products had the potential for adsorption of heavy metals from solution and confirmed the successful impregnation of biochar with SDS surfactant. The two adsorbents were then used for the removal of cadmium from solution and the adsorption behaviour and capacity determined through adsorption isotherm, kinetic and thermodynamic studies. It was found that the cadmium was adsorbed in several concentric layers on the surface of the adsorbents through a chemisorption mechanism. The PT biochar was identified as a superior adsorbent, with a capacity of qe = 10.67 mg/g compared to the NT biochar with qe = 4.82 mg/g. The adsorption of cadmium onto the PT biochar was further determined to be spontaneous and endothermic. It was therefore concluded that the PT biochar shows potential as an adsorbent and could be considered for implementation in the treatment of metal-polluted effluents. (Authors.), Spent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterised using FTIR spectroscopy and SEM-EDS analysis, which revealed that the products had the potential for adsorption of heavy metals from solution and confirmed the successful impregnation of biochar with SDS surfactant. The two adsorbents were then used for the removal of cadmium from solution and the adsorption behaviour and capacity determined through adsorption isotherm, kinetic and thermodynamic studies. It was found that the cadmium was adsorbed in several concentric layers on the surface of the adsorbents through a chemisorption mechanism. The PT biochar was identified as a superior adsorbent, with a capacity of qe = 10.67 mg/g compared to the NT biochar with qe = 4.82 mg/g. The adsorption of cadmium onto the PT biochar was further determined to be spontaneous and endothermic. It was therefore concluded that the PT biochar shows potential as an adsorbent and could be considered for implementation in the treatment of metal-polluted effluents. (Authors.)

An investigation of the influence of coal bedding-plane orientation, pre-existing cracks and cleats, micro-lithotype boundaries and mineral boundaries on the breakage of single coal particles due to low-impact energies using X-ray computed tomography is presented. Cubic samples were cut from a block of run-of-mine bituminous coal from Waterberg coalfield, Limpopo province, South Africa, subjected to impact breakage in single-particle drop-shatter tests, the tomograms before and after impact compared and the changes to the internal structure of the coal samples were determined. The results showed that newly formed cracks initiated, terminated or propagated along pre-existing cracks, micro-lithotype boundaries and mineral boundaries. The overall contribution of the physical structures to the breakage characteristics for a population of particles was fitted using a Rosin-Rammier distribution. The values of the size distribution parameters d* and n were 44.2 mm and 2.7, respectively, for the perpendicular-impacted particle populations and 43.2 mm and 3.2, respectively, for the parallel-impacted particle populations. ., An investigation of the influence of coal bedding-plane orientation, pre-existing cracks and cleats, micro-lithotype boundaries and mineral boundaries on the breakage of single coal particles due to low-impact energies using X-ray computed tomography is presented. Cubic samples were cut from a block of run-of-mine bituminous coal from Waterberg coalfield, Limpopo province, South Africa, subjected to impact breakage in single-particle drop-shatter tests, the tomograms before and after impact compared and the changes to the internal structure of the coal samples were determined. The results showed that newly formed cracks initiated, terminated or propagated along pre-existing cracks, micro-lithotype boundaries and mineral boundaries. The overall contribution of the physical structures to the breakage characteristics for a population of particles was fitted using a Rosin-Rammier distribution. The values of the size distribution parameters d* and n were 44.2 mm and 2.7, respectively, for the perpendicular-impacted particle populations and 43.2 mm and 3.2, respectively, for the parallel-impacted particle populations. .

Five coal samples were investigated from three different collieries in the major Witbank-Middelburg, Free State (Sasolburg-Vereeniging) and Limpopo region coalfields. A good correlation was found between the amount of moisture adsorbed and the oxygen content of medium-rank B vitrinite-rich and medium-rank C inertinite-rich bituminous coal. Total mass/g of moisture adsorbed as determined by the modified BET (Brunauer-Emmett-Teller) model provides a better approximation than the BET model, the relationship in the modified model between moisture monolayer coverage and the area of surface oxygen groups suggesting that moisture is adsorbed at these sites. Open hysterisis loops indicate that moisture is retained on the medium-rank C inertinite-rich bituminous coals., Five coal samples were investigated from three different collieries in the major Witbank-Middelburg, Free State (Sasolburg-Vereeniging) and Limpopo region coalfields. A good correlation was found between the amount of moisture adsorbed and the oxygen content of medium-rank B vitrinite-rich and medium-rank C inertinite-rich bituminous coal. Total mass/g of moisture adsorbed as determined by the modified BET (Brunauer-Emmett-Teller) model provides a better approximation than the BET model, the relationship in the modified model between moisture monolayer coverage and the area of surface oxygen groups suggesting that moisture is adsorbed at these sites. Open hysterisis loops indicate that moisture is retained on the medium-rank C inertinite-rich bituminous coals.