Coal-water fuels

A coal-water fuel (CWF coal-water slurry fuel) is a slurry of coal in water than is typically fed to a combustor for the generation of heat or power. The CWF represents a new type of clean fuel technology that emerged as a way of using coal as a substitute for fuel oil in the petroleum crises of the last century. The basic composition of the fuel is 70% w/w coal, 30% w/w water, and 1% w/w additive to stabilize the slurry. 

The CWF can be used in place of oil and gas in small, medium, and large power stations. The CWF is suitable for existing gas, oil, and coal-fired boilers. 

The presence of water in the fuel reduces harmful emissions into the atmosphere and makes the coal explosion-proof. By converting the coal into a liquid form, delivery and dispensing of the fuel can be simplified. One side effect of the CWF production process is the separation of non-carbon material mixed in with the coal before treatment. This results in a reduction of ash yield or the treated fuel, making it a viable alternative to diesel fuel 2 for use in large stationary engines or diesel-electric locomotives. 

The advantages of CWF include (1) a complete burning fuel with a burn of 96%-99% and (2) a noticeable effect in protecting the environment. 

Combustion of the CWF results in hydro-agglomerates of the fly ash constituents, with a concomitant reduction in emissions of particulate matter 80%-90%. In addition, transportation (pipe, tank) of CWF reduces unjustified losses during transportation of coal and improves the ecological environment in areas of its use. 

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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. 

Coal-water slurry fuels. High-percent-solid slurries that are stable against settling, so they can be pumped, stored, handled, and burned much like heavy fuel oil. Coal-water fuels have about half the heating value of fuel oil, and because of their water content they burn cooler than pulverized coal, leading to lower production of nitrogen oxides. 

Fig. 7 Simplified schematic of the Beijing Coal Water Fuel Plant, China. Clean coal is first ground in multiple stages to produce a graded size distribution that will fluidize with the minimum amount of water. Drum filters are used to remove excess water from the slurry, and surfactant reagents are combined with the slurry using pug mills. This plant processes 35 metric tons of coal per hour and produces a slurry that is 65% coal by weight. (From Ref.. )...

The requirements for coal slurry intended to be used in IGCC are similar to those for pipeline transport, with the added requirement that, as for coal-water fuels, the slurry needs to atomize easily in the reactor. Atomization has been found to be easier (producing smaller-diameter droplets at lower jet pressures) as the size of the coal particles in the slurry increases, because of weaker capillary forces holding the slurry together and decreased interparticle friction. As the capillary forces and interparticle friction are also responsible for increasing the viscosity in coal slurries, it is clear that low-viscosity slurries will atomize more readily than high-viscosity slurries. 

Metso Minerals. Coal water fuel (CWF) plants raw coal transformed into liquid fuel. http //www.metsominerals.com/inetMinerals/ mmcontent2.nsf/WebWID/WTB-030508-2256B-5B A7F/ File/FLUID C ARBON.pdf. 

Richter, W. and Pohl, J. H., "Scale-Up of coal Water fuels Experiments In Pilot Furnaces For Evaluation of Utility Boiler Performance, 7th Int. Symp. on Coal Slurry Fuels Preparation and Utilization, New Orleans Louisiana, May, 1985. 

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... 

Figure 6. Dynamic uniaxial extensional viscosities of coal-water fuels formulated with different stabilizers.

Ercolani, D. and U. Tiberio. 1994. Start-up and Initial Operating Experience of Porto Torres Integrated Plant for Production and Utilization of Beneficiated Coal-Water Fuels. Proc. 19 International Technical Conference on Coal Utilization and Fuel Systems. Coal Slurry Technology Association. Clearwater, FL. pp. 9-20. 

Zaidenvarg VE, Troubetskoi KN, Murko VI, Nekhoroshii I Kh. Production and use of coal-water fuel. Moscow Academy of Mining Sciences 2001 [in Russian]. 

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