Coal slurries particle distribution

A small sample of a coal slurry containing particles with equivalent spherical diameters from 1 to 500 pm is introduced into the top of a water column 30 cm high. The particles that fall to the bottom are continuously collected and weighed to determine the particle size distribution in the slurry. If the solid SG is 1.4 and the water viscosity is 1 cP, over what time range must the data be obtained in order to collect and weigh all the particles in the sample ... 

Coal slurry pipelines have been constructed in severaJ countries, including a 38-mile (61-kilometer) 12-inch (30.4-centimeter) diameter pipeline m Russia, a 51 -mile (82-kilometer) pipeline in Poland, as well as Olliers in Prance and other locations in Europe. The feasibility of slurry transportation depends upon Ihc resolution of a number of variables, rhe most important of which from a hydraulic standpoint are (I) Size consist (2) velocity and (3) concemrauon. The selection of a proper size eonsisi (gradation) is important in order that homogeneous flow can he achieved at prudent operating velocities. For coal slurry, such a consist is on the order of 8 mesh by 0 (approximately 0.1-inch (2.5-millimeter) particle size to dust) Homogeneous flow (solids evenly distributed across the pipe diameter) is important if excessive wear in the bottom of the pipe is to be avoided and stable operation achieved. 

The first way is pipeline transport of concentrated coal-water slurry. It assumes that utilisation of coal particle distribution preparation and/or using the various additives can substantially increase mass concentration of coal-water slurry till 70-80 %. For example, Black Messa Pipeline realised in USA transports 4.8 million tons of coal per year over the distance 439 km from the colliery in North Arizona to power plant Mohave near the border of Nevada and California with mass ratio of coal to water about 1 1, without using any additives, [5]. Recently, in the USA, Italy, China, Russia and other countries several coal pipelines were already realised. Even Oil and gas should be effectively transported as hydrate slurries, [6],... 

The size distribution of particles will control the amount of liquid needed to fluidize a given quantity of coal. In general, a fine size distribution will produce a more viscous slurry than a coarse size distribution at the same wt% solids, and the fine particles will produce a more non-Newtonian rheological curve. This can be seen in the laboratory results shown in Fig. 3, which compares a coarse coal slurry to a fine coal slurry. It is clearly seen that the fine slurry is much more viscous, its pseudoplastic character is very pronounced, and its yield value is high, while the coarse coal slurry is clearly a Bingham plastic. ... 

A graded size distribution, where fine particles fill the interstices between coarse particles as shown schematically in Fig. 4, will minimize the amount of void space that must be filled by fluid, and so will reduce the quantity of liquid needed to produce a flowable slurry. The best size distributions for this purpose have proven to be multimodal distributions, made up of several fairly narrow size fractions. An example of such a size distribution is shown in Table 1. To achieve such a multimodal size distribution, coal slurry production facilities are designed to generate several coal streams, which are each ground and sized to the desired particle sizes and then combined to give the proper size distribution. 

These are, in turn, controlled by the size distribution and density of the coal particles. To maintain homogenous flow, which is necessary to minimize wear of the pipeline, a coal slurry should have the following properties, assuming a coal specific gravity of 1.4 ... 

As the research on coal/water slurries shows, the suspension viscosity can also be reduced by close control of the particle size distribution bimode particle distributions seem to be the most beneficial. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

In short process lines slurries are readily handled by centrifugal pumps with large clearances. When there is a distribution of sizes, the fine particles effectively form a homogeneous mixture of high density in which the settling velocities of larger particles are less than in clear liquid. Turbulence in the line also helps to keep particles in suspension. It is essential, however, to avoid dead spaces in which solids could accumulate and also to make provisions for periodic cleaning of the line. A coal-oil slurry used as fuel and add waste neutralization with lime slurry are two examples of process applications. 

Pulido, J.E. Rojas, C.P. Acero, G. Duran, M. Orozco, M. Rheology of Columbian coal-water slurry fuels effect of particle-size distribution. Coal Sci. Technol. 1995, 24, 1585-1588. 

When a raw coal is wet ball-milled for a sufficient time to produce a slurry with a particle diameter mode in the range of 4 pm there results two forms of mineral matter That fractured away from the coal and that which is still enveloped in the coal particles. Figure 3 illustrates a typical particle size distribution for the separated product coal as compared to the separated free mineral matter (90 weight percent ash) from one milling test. The separated mineral matter is clearly smaller in diameter than the coal which is probably due to its more brittle properties. Note that in Figures 3 and 4 an integration of the curves will yield 100% of the mineral matter (or ash) under consideration rather than the ash content of the coal as was the case in Figures 1 and 2. 

Stabilizers, dispersants, and particle size distributions can have tremendous impacts on the elongational rheology of coal-water fuels while minimally impacting the shear rheology. In particular, stabilizer structure and aspect ratios of the particles present in the slurry may exert profound influences on the atomization of... 

For the use of coal at power stations and for treatment by some of the newer beneficiation techniques (e.g., for coal/water slurries), grinding is employed to further reduce the top size and produce material with a given particle size distribution. The principal equipment used for coal grinding is the following ... 

Coal, after washing and upgrading, is transported to industrial centers either by rail, trucks, barges, ships or slurry pipelines (Chapter 6). Generally, the manner of coal handling is substantially affected by particle size, particle size distribution, moisture content, and local weather conditions. 

Field showed that a combined anionic flocculant/cationic coagulent system, at constant coagulent dose, performs better on coal-tailings than when flocculant alone is used. In general, it is the type of solid-liquid processes in use which dictate the molecular weight of the chosen electrolyte—see Table 4.5. On the other hand, the chemical type necessary generally depends on the slurry characteristics, i.e. solid chemical surface type, particle size distribution, the dissolved electrolytes and the pH. 

Project Description (25-32). Figure 3-2 is a block flow diagram of the Cool Water CGCC plant. Unit trains deliver coal to the site, where it is stored in two 6,000 ton silos. The coal is crushed to a 100% minus 3/4 inch by cage mills, followed by final crushing in wet rod/ball mills. Close control of the crushing in the wet rod mills and recycle produces the optimal particle size distribution for a maximum slurry concentration of about 60-65 weight percent (wt%) solids. 

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