Dewatering Coal Slurry

Lyu, L.H., Dewatering coal slurries by gel extraction, M.S. Thesis, University of Cincinnati, 1990. 

D. Blankmeister and Th. Triebert, Dewatering Fltrafme Coal Slurries by Means of Pressure Filtration, Aufbereitungstechnik Nr. 1/1986, pp. 1—5. 

SH Gehrke, LH Lyu, K Bamthouse. Dewatering fine coal slurries by gel extraction. Sep Sci Tech 33 1467-1485, 1998. 

Fig. 21. Coal slurry dewatering capability by gel extraction using thermally responsive 10x4 PNIPAAm gel [117], The final solids contents rises as the ratio of gel to slurry increases, but plateaus due to reduced sorption capacities of gels in high solids content slurries. The maximum extent of dewatering declines as the particles become finer...

Gehrke SH, Lyu LH (1990) Final project report Dewatering line coal slurries by gel extraction. Ohio Coal Development Office, Columbus, Ohio... 

Water-solid Coal slurry stabilization" Coal dewatering"... 

Coal slurry pipelines. Slurry is used for transporting the coal through pipelines, but the coal is dewatered at the end before utilization. The slurry is unstable, and the particles are kept in suspension by the turbulence of the flow as they travel through the pipeline. The particles rapidly settle out of suspension once the slurry stops moving. 

Unlike coal slurry fuels, which are utilized in a fluid form, coal transported by pipeline is used as a solid after dewatering. As a result, it does not need to be stable when stored in tanks, and it is not so critical that its solid loading be maximized. The following variables are important for a pipeline system ... 

Once the coal slurry has been transported to its destination by pipeline, it is dewatered for utiliza-tion.f Chemical additives are not normally used in slurry pipelines, as they would be an unnecessary added cost and a possible source of water contamination. It is important to monitor the quality of the water removed from the slurry, as it could contaminate waterways if it dissolves harmful materials before being released. 

Blankmeister, D. and Triebert, Th., Dewatering ultrafine coal slurries by means of pressure filtration , Aji ereirungsfcc/inrk, 1, 1-5 (1986)... 

Moody, G.M. et al. (1997) Novel dewatering system for aiding the solid liquid separation of coal slurries and tailings. XIIICPC Proceedings, Vol. II, pp. 579-588. 

As in the case of coal, which can be pumped in very fine sizes—smaller than 100-125 p.m (mesh 140-120) and as coarse as 50 mm (2 in), all kinds of schemes and equipment have been developed. The economics of preparing the slurry at the feed point of the pipeline, and the cost of building and operating the pipeline, the capital cost of dewatering the slurry to recover the minerals in a solid state combine to define the design criteria of the pipeline and the physics of the slurry. 

At the discharge point of a coal slurry pipeline, water must be removed because coal cannot be burned at such high water contents. It is essential to establish certain criteria for the design of a dewatering station ... 

Dewatering/Reconstitution of Fine Clean Coal Slurry. Proc. 23 International Technical Conference on Coal Utilization at Fuel Systems. Coal Technology Association. Clearwater, FL. March 9-13. pp. 745 - 760. 

A 437 km slurry pipeline, 46 cm in diameter, was started in 1970 to move coal from Arizona to southern Nevada. The coal is cmshed and ground to the fineness needed for proper viscosity and settiing. About 18—20% is —325 mesh (<44 //m), 35—45% is —100 mesh (<149 //m), and 0—2% is + 14 (<1070 fim) mesh. The soflds content of the slurries has approached 70% using additives to stabilize the mixture. The slurry is dewatered with centrifuges before combustion of the coal. 

Use of Surfa.cta.nts, Although the use of steam to improve dewatering is consistently beneficial, the effects of surfactants on residual moisture are highly inconsistent. Additions of anionic, nonionic, or sometimes cationic surfactants of a few hundredths weight percent of the slurry, 0.02—0.5 kg/1 of soHds (50), are as effective as viscosity reduction in removing water from a number of filter cakes, including froth-floated coal, metal sulfide concentrates, and fine iron ores (Table 2). A few studies have used both steam and a surfactant on coal and iron ore and found that the effects are additive, giving twice the moisture reduction of either treatment alone (44—46,49). 

Although filtratioa rates can be much faster with flocculants, the final cake moisture is often higher ia a flocculated cake (60—63). Ia coatrast, usiag flocculants optimized for filtration, coal, and other mineral slurries can be dewatered to moisture contents significantly lower than the untreated cake (64—68). The advantages of rapid filtration rates can also be preserved. Flocculants that provide better filtration tend to form floes having the foUowiag characteristics (65) ... 

A successful variation of oil agglomeration was used for removal and dewatering of soot from a 1—3% soflds suspension consisting of <5 — fim particles in refinery process waters (Fig. 8). Heavy oil was added to the dilute slurry and intensely agitated in a multistage mixer. The soot agglomerated with the oil to form 3—5 mm pellets that were easily screened from the water (95). The pellets contained only 5—10% water. The process was modified to recover very fine clean coal, and it produced highly uniform, hard, spherical pellets 1—2 mm in diameter. 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

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