摘要:

The biased subdivision of slurry feed to a number of unit operations (e.g., cyclones) in parallel results in each unit to operate under different separation density, volumetric flowrate, feed pressure, and feed concentration. Consequently, some of the units may operate under sub-optimal conditions, leading to reduced operating efficiencies of sizing and cleaning units. The objective of this work is to identify factors causing biased slurry subdivision in multi-port distributors and to improve the understanding of the complex two-phase flows involved. A number of experimental investigations were carried out on a pilot-plant scale experimental system. The bias with regard to solids concentrations and particle size distributions of substreams was found to decrease with increasing the feed flowrate to the distributor. This bias also results in significant variations in the feed distribution and the performance of the hydrocyclones. Increasing the solids concentration in the slurry feed decreases the bias. There is also a strong dependence of the degree of bias on the density of particles in the slurry. The biased slurry subdivision is mainly caused by non-unifrom solids segregation induced by low line velocity, which reduces the suspension forces on the particles and increases the residence time of particles in the distributor. It has been demonstrated from the experiments that the low line velocity is due to the large diameter of the distributor. Experimental results show that unbiased slurry subdivision can be achieved using a ‘slim’ distributor.

ISSN:0734-9343    

DOI:10.1080/07349349908945596

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper describes investigations carried out as part of a project to determine the potential for sulphur reduction in UK coals and is concerned, in particular, with the effect of particle size reduction on the liberation of sulphur. This work required the development of a modified float/sink procedure to enable the density characterisation of coals down to ultrafine sizes. The liberation data produced were used to determine the theoretical reductions in sulphur emissions that could be achieved for these coals using density based separation methods. Finally, process simulation models were applied to the data in order to predict the results that could be achieved using conventional techniques applied in commercial practice.

ISSN:0734-9343    

DOI:10.1080/07349349908945597

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Chemical and physical properties of typical low-rank coal (LRC) ash are significantly different than bituminous coal ash. With the exception of extraneous ash, which is incorporated during mining or is due to ash partings within or between coal seams, LRC ash consists primarily of inherent ash that is bonded into the coal's organic matrix or finely disseminated mineral matter. This paper reviews the nature of ash from two Alaskan LRCs, both inherent and extraneous, and how this impacts the prospects of producing a low ash coal for formulation into low-rank coal-water fuel for utilization in heat engines. This study is particularly relevant in light of the recently funded Alaskan Low-Rank Coal-Water Fuel - Diesel Project, which is designed to demonstrate the economic feasibility of commercial production and utilization of low-rank coal-water fuel (LRCWF) in an oil-designed, 3MWe boiler and a medium speed (400rpm) diesel engine (9.6MWe). Washability data, proximate and ultimate analyses and ash composition analyses of two Alaskan LRC seams are used as a basis for this discussion. Recent research into the nature and distribution of phosphorous in an Alaskan LRC is also discussed.

ISSN:0734-9343    

DOI:10.1080/07349349908945598

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A combination of semicoking followed by a permanent roll magnetic separator (PERMROLL) has been used for the upgrading of a Turkish low-rank lignitic coal. The lignite samples were subjected to a low temperature carbonization process at 600°C and then upgraded by the PERMROLL. Under optimum conditions, carbonization of lignite particles in −9 + 0.5 mm size range which contained 12.18 wt.% ash and 3.38 wt.% total sulfur produced a product containing 25.90 wt.% ash and 3.19 wt.% total sulfur all reported on a dry basis. Dry magnetic separation employing the PERMROLL upgraded this product to 11.20 wt.% ash and 1.40 wt.% total sulfur with a recovery of 31.52 wt.% based on feed to the carbonization process. The mechanism of desulfurization is discussed on the basis of the presence of iron in the coal that complexes with sulfur to form a magnetic product upon semicoking and its subsequent removal by magnetic separation.

ISSN:0734-9343    

DOI:10.1080/07349349908945599

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Work initiated in 1980 at the University of Alberta and the Alberta Research Council led to the development of the Agflotherm® process for low rank coals (LRC) beneficiation. This process can be considered as low-severity co-processing; upgrading two low grade fossil fuels, namely low rank coals and heavy oils, in a single process.

ISSN:0734-9343    

DOI:10.1080/07349349908945600

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Surface modification approaches have been investigated in vacuum filtration of column flotation froth products of high and low sulfur coal slurries. It was shown that vacuum dewatering of fine coal can be enhanced significantly in terms of both filtration rate and cake moisture by modifying surface properties of fine coal particles with polymeric flocculants and metal ions. As expected, use of cationic or anionic flocculants significantly increased filtration rate. Addition of 5 g/t cationic flocculant to the high sulfur clean coal slurry lowered cake moisture from 26% to 22.3% and increased cake thickness from 5 to 10 mm, however, use of 25 g/t cationic flocculant increased cake moisture to 26.3% at increased cake thickness of 24mm. When cake thickness was maintained constant, use of anionic flocculant significantly reduced cake moisture. Cake moisture was reduced from 27.3% to 18.8% with the low sulfur coal using 25g/t anionic flocculant at cake thickness of 7 mm. Use of metal ions showed less significant effects on fine coal filtration. Mechanisms responsible for observed improvement in fine coal dewatering behavior have been discussed from the perspectives of filtration fundamentals.

ISSN:0734-9343    

DOI:10.1080/07349349908945601

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Coal samples from the Mexican coal mines which supply coal to the power plants situated in the U.S.-Mexico border area, were collected and analyzed for chemical composition and separation characteristics. The analytical data indicate that the Mexican coals usually have a low or moderate sulfur content, l.3–2.5wt%. The pyritic sulfur accounts for 38 to 77% of the total sulfur content, depending on the sample source. Rejection of the pyritic sulfur (as well as ash) using sink-float techniques was evaluated in this study. Washability analyses for selected coal samples (2.00 × 0.841 mm and 0.841 × 0.595mm) from Micare, Palau and Pocito Tec mines, using heavy organic liquids with a density from 1.3 to 2.0g/cm3, were carried out. Also, the coal washability curves were constructed for Micare coal for 25.4 × 12.7 mm and 12.7 × 6.3 ram particle sizes using the X-ray computed tomography (CT) technique. The results indicate that coal samples from Micare, Palau and Pocito Tec regions can be classified as easy to clean.

ISSN:0734-9343    

DOI:10.1080/07349349908945602

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In the present study, the technique of oil agglomeration has been explored with the aim of employing the process for recovery of coal fines from washery/coal industry effluents as well as deashing of coal. Both edible and non-edible vegetable oils have been tested for agglomeration of five different types of Indian coals widely used in power and metallurgical sectors. The yield of agglomerates ranged from 40.0 to 87.5% and ash rejections from 13.5 to 62.0% using different coal-oil combinations. Bacterial pretreatment of coal with mixed culture prior to oil agglomeration improved the selectivity of vegetable oils resulting in higher ash rejections (59.0−76.0%). Also, pretreatment of high sulphur coal withThiobacillus ferrooxidansculture resulted in significant enhancement in pyritic sulphur rejection from 69.0 to 98.5%. Various process parameters have been optimized for vegetable oil agglomeration. Higher rates of biodegradation observed with vegetable oils as compared to that with petroleum fractions further supported their use as environmentally safe agglomerants.

ISSN:0734-9343    

DOI:10.1080/07349349908945603

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor