摘要:

Low-rank coal (LRC) drying processes are generally categorized by operating temperature, drying environment, and type of feed or product. Within these broad categories, drying processes differ further according to the type of drying equipment and methods of quenching and stabilizing dried products. This paper focuses on the issue of the quality of products produced from a number of LRC drying processes that are commercial or have been demonstrated at a pilot-scale, including low and high temperature evaporative drying and non-evaporative processes, such as hydrothermal drying. Evaporative processes are usually the lowest cost and are preferred when the dried product is used immediately. This avoids the problems of moisture reabsorption, dust generation and spontaneous combustion associated with LRC transportation and long term storage. Hydrothermal drying followed by. low-rank coal-water fuel production is one of the most promising techniques for eliminating stability problems, while producing a value added fuel that will compete in the heavy oil market, not the steam coal market.

ISSN:0734-9343    

DOI:10.1080/07349349708905135

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Aqueous suspensions of moderately hydrophobic Colchester Seam coa! from Illinois were treated with heptane or hexadecane in a laboratory mixing unit which produced a moderate shear rate. Under these conditions air had to be present to produce compact, nearly spherical agglomerates. The yield of agglomerates increased with both oil dosage and mixing time. Conditions which produced a high yield of agglomerates also achieved the best separation of a mixture of Colchester coal and kaolin particles when the agglomerates were recovered subsequently by screening.

ISSN:0734-9343    

DOI:10.1080/07349349708905136

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In Part 1 of this series of papers, it was shown that a definite amount of air had to be present in a laboratory mixing unit which produced a moderate shear rate in order to form compact, spherical agglomerates in an aqueous suspension of moderately hydro-phobic coal using heptane or hexadecane as an agglomerant. In this paper, the effects of different amounts of air including dissolved air are discussed. The results indicate that a small amount of air will trigger the process of agglomeration, and even the air dissolved in water under equilibrium conditions at room temperature and pressure is sufficient to promote agglomeration provided it is released from solution.

ISSN:0734-9343    

DOI:10.1080/07349349708905137

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Microflotation experiments conducted with pyrite showed that the mineral acquires considerable floatability upon superficial oxidation. The flotation occurs at potentials anodic to the stable potential of the mineral identified by chronoamperometric studies conducted on freshly-fractured pyrite electrodes. It is believed that sulfur-rich species, such as iron polysulfides, formed during the initial stages of oxidation are responsible for the flotation. The collectorless flotation of pyrite is suppressed in strongly oxidizing and moderately reducing environments.

ISSN:0734-9343    

DOI:10.1080/07349349708905138

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A turbidmetric method was used to investigate the kinetics of a gas-promoted process for agglomerating an aqueous suspension of coal particles using either heptane or hexadecane as an agglomerant. Suspensions of either Pittsburgh No. S seam coal or Upper Freeport seam coal were mixed with measured quantities of air and an agglomerant in a closed cylindrical tank fitted with baffles and a controllable speed agitator. Agglomeration was monitored by observing the change in turbidity of the suspension. Initial particle concentration, agglomerant dosage, amount of air, and agitator speed were varied among runs. The experimental data were correlated and analyzed by employing a semiempirical rate equation which gave consistent results. During any given run the agglomeration rate (— dN/dt) was proportional to the particle number concentration (N) raised to a power between l.O and 1.3. The rate increased with increasing amounts of either air or agglomerant and with increasing agitator speed. The rate was also greater for Upper Freeport coal than for Pittsburgh coal, apparently because of the greater hydrophobicity of the former.

ISSN:0734-9343    

DOI:10.1080/07349349708905139

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An investigation on the use or a magnetic fluid-based process for float-sink separations of coal was conducted. The required magnetic field was generated with a Frantz electromagnet using redesigned pole pieces. Finite element analysis was used to analyze the magnetic field distribution between the poles as a function of current intensity. The simulated results compared well with the measured values. Viscosity measurements of the water-based magnetic fluid showed that the viscosity remained relatively low even under high magnetic field strengths. Several size fractions of bituminous coal (0.59x0.50mm and 0.18 x0.15mm) and anthracite (0.50x0.l8mm and 0.18 x 0.15 mm) were separated in a batch separation cell, which was designed to fit between the pole pieces. The yields compared well to those obtained using organic liquids and zinc bromide solutions. However, the ash and sulfur contents of the float material were higher when using the magnetic fluid method, particularly in regions of high near-density material. The differences can be attributed to particle misplacement resulting from slight variations in the magnetic field gradient and the subsequent effect on the apparent density of the fluid.

ISSN:0734-9343    

DOI:10.1080/07349349708905140

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor