Slurry transport

A slurry is a liquid containing solid particles in suspension. Slurries can be divided into two classes settling and non-settling. 

Settling slurries cannot be pumped in laminar flow. Turbulence must exist to prevent the solid particles from settling. Settling slurries should be pumped through pipelines at velocities which just prevent the solid particles from settling. This results in the minimum pressure drop across the pipeline. 

Saltation is also used to transport settling slurries through pipelines [Condolios and Chapus (1963a)]. In this case the solid particles bounce and roll along the bottom of a horizontal pipe. 

Empirical equations are available [Durand and Condolios (1955)], which predict values for the minimum and standard velocities for various slurries. Spells analysed the experimental data of a number of investigators for aqueous slurries of sands, boiler ash and lime flowing in horizontal pipes. He obtained the following empirical equations which give the mean minimum liquid velocity U and the mean standard linear liquid velocity u2 respectively for slurries in horizontal pipes  

Equations 9.38 and 9.39 are based on experimental data for solid particles with diameters in the range 6 x 10-5 to 6 x 10-4 m and pipe diameters of 

Systems for pumping slurries around a process plant are similar to systems for pumping liquids, in regard to the calculation of performance on a basis of head. The slurry can be regarded as a fluid having a density computed from the ratio of solids to liquid (usually water) and the respective densities of the two phases. If the slurry composition is stated on a mass basis, the slurry density is calculated by calculating the volumes of each component of mass, and dividing the sum of the masses by the sum of the volumes. 

When pumping a slurry, the head generated by a centrifugal pump and the head corresponding to system resistance, are substantially unchanged from the values for water or any other low-viscosity liquid. 

There is an increase in the apparent viscosity when there is a significant concentration of very fine solids in suspension, but for many applications the effect is negligible. Usually for in-plant applications, most of the system resistance is required to overcome static, rather than frictional, head. 

System performance and power requirement are therefore normally graphically presented and calculated in the same way as for clear liquids. Subject to some minor corrections, a centrifugal pump will pump the same volumetric flowrate of slurry as for water through a given flow system. The pump discharge pressure and its power draw will be increased in proportion to the slurry specific gravity, as for any clear fluid of increased density. 

In fact, particular slurries tend to have particular characteristics these are not easily predicted theoretically, and only come to be known in practice. Some slurries are relatively easy to handle and, provided that the critical velocity is maintained, are unlikely to settle even with a convoluted flowpath, while other slurries will settle and block the line if only a few long-radius bends are present. 

A slurry is a mixture of a liquid and solid particles. The term sludge typically refers to a highly concentrated slurry containing fine particulate material. Each year, vast tonnages of slurries are pumped. Slurries are often used to transport coal, phosphates and minerals. Dredging of sand and silt in the maintenance of waterways is another example of sohds handled in slurry form. In most slurries, the liquid phase is water. However, coal-oil and coal-methanol fuels are examples of slurries made up with liquids other than water. 

The mixture density of a slurry, p, in terms of the volume fraction of solids Cv is given by  

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. 

Many of the studies of slurry transfer have been made in connection with long distance movement of coal, limestone, ores, and others. A few dozen such installations have been made, in length from several miles to several hundred miles. 

Coal-water slurry transport has been most thoroughly investigated and implemented. One of the earliest lines was 108 miles long, 10 in. dia, 50-60 wt % solids up to 14 mesh, at velocities of 4.5-5.25 ft/sec, with positive displacement pumps at 30-mile intervals. The longest line in the United States is 273 miles, 18 in. dia and handles 4.8-6.0 million tons/yr of coal it is described in detail by Jacques and Montfort (1977). Other slurry pipeline literature is by Wasp, Thompson, and Snoek (1971), Bain and Bonnington (1970), Ewing (1978), and Zandi (1971). 

Principally, investigations have been conducted of suitable linear velocities and power requirements. Slurries of 40-50 vol% solids can be handled satisfactorily, with particle sizes less than 24-48 mesh or so (0.7-0.3 mm). At low line velocities, particles settle out and impede the flow of the slurry, and at high velocities the frictional drag likewise increases. An intermediate condition exists at which the pressure drop per unit distance is a minimum. The velocity at this condition is called a critical velocity of which one correlation is 

D = pipe diameter, d = particle diameter, s = ratio of densities of solid and liquid, g = acceleration of gravity, 32.2 ft/sec2, or consistent units. 

---

Dry soHds, such as as-rnined ore, emshed ore, and dried concentrates, are transported using tmeks, rail cars, ore passes, conveyor belts (see Conveying), or slurry pipelines (qv) as dictated by the logistics, distances involved, and capacity. Within the mill, conveyor belts are more common, but for fine particles, tailings, and coal, slurry transportation is more typical. 

Santhanam. C. J., Liquid C02-Based Slurry Transport Is On the Move, Chemical Engineering, July 11, 1983, p. 50. 

Carbon steels Coal/water. Coal slurry transportation. 

To test the transport rules of slurry particles in the flow field during CMP. An understanding of the slurry transport and particles motion beneath the wafer plays an important role in revealing the interaction process... 

Figure 11-4. Components for additives for slurry transport oleic acid, linoleic acid.

Slurry Transportation Piping, 19 480 Slurry trench excavation... 

J. Coppeta, J. Rogers, L. Racz, A. Philipossian, F. Kaufman, Pad Effects on Slurry Transport Beneath a Wafer During Polishing, Third International CMP for VLSI Multilevel Interconnection Conference, Santa Clara, CA, pp. 36-43, Feb. 19-20, 1998. 

Coppeta et al. [10] made slurry film measurements during using laser-induced fluorescence. By addition of a fluorescent dye to the polishing slurry film thickness was experimentally from the fluorescence intensity of the lubrication film as measured through a transparent substrate. Film thickness measurements were in good agreement with those of Levert et al. [7,8]. This technique can also be used to study slurry transport across the wafer surface, diameter variation in lubrication film thickness, and slurry mixing effects [11]. 

Coppeta, J., Racz, L., Philipossian, A., Kaufman, F., Rogers, C. (1998). Pad effects on slurry transport beneath a wafer during polishing. Proc. 3rd Int. CMP for VLSI Multilevel Interconnect. Conf, Santa Clara. 

J. J. Halloran, No. TIS-S039, Annual Meeting Slurry Transport Association, Houston, Tex., Aug. 24-25,1976. 

Iron and chloride catalysts are basically disposable because they are considered to be rather cheap and difficult to recover from residual products, while Ni-Mo and Co-Mo catalysts are too expensive to be considered disposable (82). Recovery of very fine particles of MoS2 by hydroclone separation has been shown to be promising (83). Disposable catalysts added at levels similar to that of ash mineral contents significantly reduce the potential recovery of oil in both distillation and extraction. This is problematic because equal volumes of oil adhere to solid particles after separation. Slurry transportation of residues suffers from the same problem. Even if the cost of the disposable catalysts is affordable, adding 1 to 5% of the catalyst to the... 

Coal Slurry Pipelines. The first patent covering the pumping of coal and water dates back to 1891. In 1914. the first commercial transport of coal in water was carried out in England, when a short 8-inch (20-centimeler) pipeline was used to cany coal from river barges to a power plant. Thereafter, several proposals were submitted for the long distance transport of coal from mine to market in the eastern United States, but failed to materialize for several reasons, not the least of which were technical problems. Intensive research into slurry transport was continued and, by 1957. technology and engineering had advanced In the point where the... 

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. 

Coal log technology makes possible to transport up to twice more solid fuel in the same diameter of pipe than for slurry transport. Except low carrier liquid and energy consumption, separation and de-watering of coal are much... 

Except traditional slurry transport of coal as coal-water slurry or coal-water fuel, pipeline transport of coal in hydrocarbons seems to bring some advantage especially for arctic areas. 

Metal ore bodies may contain several different minerals that are separated into individual concentrates. These may be slurry-transported in the same pipeline by pumping them in separate batches, each separated by a slug of water to prevent contamination [607]. Such batching also allows pipeline flow to be maintained when the mine or separation site temporarily runs out of ore. 

The cost of transporting wood chips by truck and by pipeline as a water slurry was determined. In a practical application of field delivery by truck of biomass to a pipeline inlet, the pipeline will only be economical at large capacity (>0.5 million dry t/yr for a one-way pipeline, and >1.25 million dry t/yr for a two-way pipeline that returns the carrier fluid to the pipeline inlet), and at medium to long distances (>75 km [one-way] and >470 km [two-way] at a capacity of 2 million dry t/yr). Mixed hardwood and softwood chips in western Canada rise in moisture level from about 50% to 67% when transported in water the loss in lower heating value (LHV) would preclude the use of water slurry pipelines for direct combustion applications. The same chips, when transported in a heavy gas oil, take up as much as 50% oil by weight and result in a fuel that is >30% oil on mass basis and is about two-thirds oil on a thermal basis. Uptake of water by straw during slurry transport is so extreme that it has effectively no LHV. Pipeline-delivered biomass could be used in processes that do not produce contained water as a vapor, such as supercritical water gasification. 

Note that unlike truck transport, there is an economy of scale in slurry transport of materials, since larger throughputs benefit from an economy of scale in construction of the pipeline and associated equipment, and in lower friction losses in larger pipelines. 

Pad-Wafer Contact and Slurry Transport Dual Emission Laser Induced Fluorescence... 

---