ISSN:0734-9343    

DOI:10.1080/07349349408905227

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The suction potential method for measuring the three-phase contact angle was modified and used to determine the oil-water-solid contact angle for various samples of coal. The method involves measuring the pressure changes required to draw an oil/water interface and then an oil/air interface into a packed bed of solid particles. Before the latest modification, the method was very time consuming and difficult to control. These problems were overcome by modifying the apparatus and measuring technique. Values of the contact angle determined with the new technique were very similar and as reproducible as those determined with the older method. Also, measurements of the contact angle for a series of oxidized coal samples were consistent with other surface property measurements. In addition, for this series of samples, the recovery of coal from an aqueous suspension by oil agglomeration was found to correlate very well with the contact angle.

ISSN:0734-9343    

DOI:10.1080/07349349408905228

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

While wettability determines the flotation properties of coal, coal moisture content determines the maximum loading of coal water fuels. Both the wettability and moisture content result from the interaction between water molecules and the coal surface; they are also affected by coal porosity.

ISSN:0734-9343    

DOI:10.1080/07349349408905229

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A laboratory and pilot-scale test program was carried out to assess the merits of installing column flotation cells at the Middle Fork coal preparation facility. The test data showed that column cell technology was superior to single- and multi-stage conventional flotation circuits in terms of fine coal recovery and product grade. In light of these promising results, a full-scale column flotation circuit was designed, installed and commissioned at the Middle pork plant. The circuit utilizes five 3-m diameter Microcel™ flotation columns to process approximately 100 tph of minus 150 μm raw coal. The column retrofit reduced the ash content of the plant's flotation circuit by nearly 7 percentage points and increased the combustible recovery by approximately 27 percent. This article provides a summary of the test results and discusses the scale-up procedures used to design the commercial columns.

ISSN:0734-9343    

DOI:10.1080/07349349408905230

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The aims of the study reported here were to investigate whether column notation technology could be used to recover a saleable quality coal from a −0.15 mm fines sample obtained from a Natal colliery producing a coking quality coal; and to determine which column cell operating parameters had a dominant effect on the yield and grade of concentrate produced. Seven parameters were investigated namely, froth height, frother concentration, air flow rate, volumetric slurry feed rate, wash water addition rate, sparger type and column height. Tests runs were performed according to a 2-level 27.3IV fractional factorial design.

ISSN:0734-9343    

DOI:10.1080/07349349408905231

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Dense-medium separations were analyzed using a batch hindered-settling model. This model can predict the size/density distribution of settling particles at any point along a column. The separations were analyzed by treating the particles above a cut height as the product and the particles below this height as the refuse. This allowed fractional recovery curves to be generated for a wide range of simulation conditions. For this study, the variables examined included the size/density distribution of the coal, the solids concentration of the feed stream, the retention time of the particles, the cut height, the magnitude of the g force, and the size distribution of the magnetite. It was found that the separations were affected by the density gradient of the magnetite along the column, and as such, the results were often much different than those predicted by a batch free-settling model. The results from this study are presented in this paper.

ISSN:0734-9343    

DOI:10.1080/07349349408905232

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Magnetite losses are generally significant in commercial coal cleaning plants using high-density medium techniques. It is common practice to monitor the cleaned coal, slurries, and refuse using a Davis Tube method in order to isolate and correct unnecessary losses. To ensure the Davis Tube yields correct results, tests were made by comparison with the magnetization determined with a Faraday balance and a vibrating sample magnetometer. The results showed the Davis Tube gives reasonably correct percentage composition of magnetic and non-magnetic fractions, but was not reliable to determine the magnetite concentration in a sample. Further tests showed that commercial heavy-media magnetite has up to a 20 percent lower magnetization than bulk magnetite. Commercial magnetite often contains significant amounts of α- and γ-Fe2O3, in addition to magnetite. As α-Fe2O3is non-magnetic, it is not removed in the magnetic separator and is discharged in the refuse. It is believed that this is the cause for much of the loss of heavy media experienced in the coal cleaning plants. Reduction of Fe2O3to Fe3O4by controlled heating of the magnetite in hydrogen increases the magnetization and points out a possible method which may be used to reduce plant losses.

ISSN:0734-9343    

DOI:10.1080/07349349408905233

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The flow profile on spiral separators alters with feed rate and this affects the performance of coal spirals in a different way from mineral spirals. The effect of flow rate is examined in terms of mass and volume recovery to coal product and equations are developed for three different spirals, based on the performance recorded in 684 tests covering 198 different coal samples. A generic coal spiral model is also developed based on the total data for the three types of spiral. A set of test data is then reported and examined in detail for each spiral and the anticipated variation in performance, predicted using wash-ability data and the equations developed earlier, is compared with the test results. The importance of selecting and maintaining the correct feed rate to spiral separators is emphasised and distributor performance is discussed. An application of the models to the problem of defining the requirements for an automatic distributor control system is then illustrated.

ISSN:0734-9343    

DOI:10.1080/07349349408905234

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Recent work has suggested that the moisture of a sub-bituminous coal may exist in three forms, namely free moisture, loosely bound moisture and tightly bound moisture (these moistures do not include chemically bound moisture). The complete drying of each type of moisture requires a stepwise changing amount of energy, known as the heat of drying. This stepwise change in the heat of drying in relation to the moisture content of coal was, in the current study, incorporated into a mathematical model that describes the spontaneous heating process. More detail of the influence of moisture transfer on the maximum possible temperature rise in moist coal piles are revealed. Comparison between the predicted temperature levels and the published experimental observations provided greater confidence in using the proposed mathematical model and the physical and chemical parameters to predict quantitatively the spontaneous ignition process.

ISSN:0734-9343    

DOI:10.1080/07349349408905235

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0734-9343    

DOI:10.1080/07349349408905236

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor