142
Water for Energy and Fuel Production
The studies described earlier clearly indicate that water plays an active role as a
reactant for the coal liquefaction under high-temperature and high-pressure conditions. The reactive role of water is further increased near and above the supercritical
conditions. Thus, water should be evaluated as a possible solvent for the coal liquefaction process.
5.5.3 CoAl–WATer mixTure AS Fuel
A slurry of finely powdered coal and water (coal–water mixture as fuel [CWF])
has been found to be an effective fuel for combustion purposes. Presence of water
in CWF reduces harmful emissions into the atmosphere, makes the coal explosion
proof, and also makes the coal equivalent to liquid fuel [125–129] (Penn State’s coalwater slurry fuel program, 2012, pers. comm.). CWF can be used in place of oil and
gas in any size of heating and power station. It can be used in oil and coal boilers.
It can also be used in the diesel engine power plants and the combined cycle gas
turbines. While the energy efficiency of CWF may be somewhat lower (by about
3%) compared to natural gas and oil, depending on the geographical area, the price
per unit energy of CWF can be 30%–70% lower than the equivalent oil or gas. Low
emissions and low BTU cost make CWF a very cost-effective and environmentfriendly fuel for heat and power generation. Another advantage of CWF production
process is the separation of noncarbon material that reduces the ash content by about
2% in CWF, making it a viable alternative to diesel fuel #2 for use in large stationary
engines or diesel electric locomotives [125–129] (Penn State’s coal-water slurry fuel
program, 2012, pers. comm.).
While the first patent on coal–water fuels was granted in 1891 [125], the real
development of coal–water fuels from high-quality coal commenced in earnest in
the United States, Germany, and the former Soviet Union in the 1960s. In the United
States, the research was accelerated in 1970 and early 1980 following oil embargo
and subsequent increase in oil price. While the original objectives of the research
were to produce a cheap substitute for heavy oils in boilers, in the subsequent years
fuels that met environmental regulations and that can also be used for diesel engines
and turbines became important. The use of CWF in boilers, diesel engines, and
turbines required different level of chemical and physical properties and specialized
equipment for handling and transporting slurries [125–129] (Penn State’s coal-water
slurry fuel program, 2012, pers. comm.).
While the thermal efficiency of CWF in boilers is around 2%–3% lower than
that of coal, the intense environmental regulations in 1990 for clean coal technology forced more research for cleaner and the one with better physical and chemical
properties of CWF. The R&D leads to processes that can produce ultralow-ash feed
coals, especially for high-value metallurgical applications, such as the production
of electrode carbons [125–129]. Processes include advanced physical processing to
produce “super coal” that has a very low residual ash and very fine particle size so
60%–70% coal in CWF can be burned cleanly and possess the physical and chemical properties that are acceptable to boilers, diesel engines, and turbines. The use
of CWF in diesel engines and turbines particularly required very fine coal particles in the slurry. The research led to the development of chemical processes that
Water for Energy and Fuel Production
The studies described earlier clearly indicate that water plays an active role as a
reactant for the coal liquefaction under high-temperature and high-pressure conditions. The reactive role of water is further increased near and above the supercritical
conditions. Thus, water should be evaluated as a possible solvent for the coal liquefaction process.
5.5.3 CoAl–WATer mixTure AS Fuel
A slurry of finely powdered coal and water (coal–water mixture as fuel [CWF])
has been found to be an effective fuel for combustion purposes. Presence of water
in CWF reduces harmful emissions into the atmosphere, makes the coal explosion
proof, and also makes the coal equivalent to liquid fuel [125–129] (Penn State’s coalwater slurry fuel program, 2012, pers. comm.). CWF can be used in place of oil and
gas in any size of heating and power station. It can be used in oil and coal boilers.
It can also be used in the diesel engine power plants and the combined cycle gas
turbines. While the energy efficiency of CWF may be somewhat lower (by about
3%) compared to natural gas and oil, depending on the geographical area, the price
per unit energy of CWF can be 30%–70% lower than the equivalent oil or gas. Low
emissions and low BTU cost make CWF a very cost-effective and environmentfriendly fuel for heat and power generation. Another advantage of CWF production
process is the separation of noncarbon material that reduces the ash content by about
2% in CWF, making it a viable alternative to diesel fuel #2 for use in large stationary
engines or diesel electric locomotives [125–129] (Penn State’s coal-water slurry fuel
program, 2012, pers. comm.).
While the first patent on coal–water fuels was granted in 1891 [125], the real
development of coal–water fuels from high-quality coal commenced in earnest in
the United States, Germany, and the former Soviet Union in the 1960s. In the United
States, the research was accelerated in 1970 and early 1980 following oil embargo
and subsequent increase in oil price. While the original objectives of the research
were to produce a cheap substitute for heavy oils in boilers, in the subsequent years
fuels that met environmental regulations and that can also be used for diesel engines
and turbines became important. The use of CWF in boilers, diesel engines, and
turbines required different level of chemical and physical properties and specialized
equipment for handling and transporting slurries [125–129] (Penn State’s coal-water
slurry fuel program, 2012, pers. comm.).
While the thermal efficiency of CWF in boilers is around 2%–3% lower than
that of coal, the intense environmental regulations in 1990 for clean coal technology forced more research for cleaner and the one with better physical and chemical
properties of CWF. The R&D leads to processes that can produce ultralow-ash feed
coals, especially for high-value metallurgical applications, such as the production
of electrode carbons [125–129]. Processes include advanced physical processing to
produce “super coal” that has a very low residual ash and very fine particle size so
60%–70% coal in CWF can be burned cleanly and possess the physical and chemical properties that are acceptable to boilers, diesel engines, and turbines. The use
of CWF in diesel engines and turbines particularly required very fine coal particles in the slurry. The research led to the development of chemical processes that