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Water for Energy and Fuel Production
is dried and stored. The spent liquor is dried and sent to the gas absorber where
hydrogen fluoride (HF) and H 2 SiF 6 are recovered and excess H 2 SiF 6 is passed to
a hydrolyzer for conversion to silica and HF is returned to the dissolution circuit [134,135]. More improved process contains two dissolution steps [125–129]
involving hydrofluoric acid and fluosilicic acids (Penn State’s coal-water slurry
fuel program, 2012, pers. comm.).
5.5.3.1.3 Hypercoal
Hypercoal is a low-ash, low-alkali coal product produced by dissolving the coal
matter into an organic solvent, then flashing off the solvent for recycling to the
dissolution step of the process [125–129,136] (Penn State’s coal-water slurry
fuel program, 2012, pers. comm.). The insolubles are retained in the high-ash
byproduct coal. Hypercoal process is very different from UCC process in that this
process aims to separate solvent-soluble coaly matter from the ash and insoluble
coal, thereby producing a high-ash coproduct. The process involves five steps:
slurry preparation, extraction at 360°C temperature, separation of the extracts,
removal of alkali from the liquid component and removal of ultrafine particles
by filtration, and finally drying of the final product. A number of solvents such
as tetralin, 1-methyl-naphthalene, dimethylnaphthalene, and light cycle oil have
been used as solvents for extraction. The key features of the technology are as
follows [125–129]:
1. On a dry coal basis, the yield can be as high as 80%. The process removes
most alkalis from raw coal.
2. The higher ash (coproduct) is suitable for domestic power generation.
3. The process can be applied to all subbituminous and bituminous coals.
Yields are lower for subbituminous coals than for bituminous coals. Yields
for subbituminous coals can be increased by pretreating the coal with HCl
or weaker acids.
5.5.3.2 Fuel Preparation and transportation
The science and technology behind the production of UCC CWF has been well published [125–130] (Penn State’s coal-water slurry fuel program, 2012, pers. comm.).
Most systems involve the preparation of coal–water slurries containing 60%–70%
coal, together with additives to provide slurry stabilization and to lower the viscosity. The energy density of such slurry is about 18 GJ/m 3 . Additives consist of
dispersants and stabilizers. The dispersants such as sodium sulfonate of naphthalene, polystyrene, polymethacrylate, and polyolefin maintain the separation of coal
particles within the slurry [125–130]. Stabilizers include additives such as cellulose
or xanthum gums. For gas turbines and diesel engines, the water penalty for CWF
is much smaller and probably negligible when the overall power cycle is considered, and therefore, CWF slurry transportation is a preferred form. Final preparation
of CWF requires that the coal is either premilled dry before slurry preparation or
milled (micronized) wet as either a part of slurry preparation process or immediately prior to combustion. In general, wet milling has lower cost and lower energy
consumption [125–130].
Water for Energy and Fuel Production
is dried and stored. The spent liquor is dried and sent to the gas absorber where
hydrogen fluoride (HF) and H 2 SiF 6 are recovered and excess H 2 SiF 6 is passed to
a hydrolyzer for conversion to silica and HF is returned to the dissolution circuit [134,135]. More improved process contains two dissolution steps [125–129]
involving hydrofluoric acid and fluosilicic acids (Penn State’s coal-water slurry
fuel program, 2012, pers. comm.).
5.5.3.1.3 Hypercoal
Hypercoal is a low-ash, low-alkali coal product produced by dissolving the coal
matter into an organic solvent, then flashing off the solvent for recycling to the
dissolution step of the process [125–129,136] (Penn State’s coal-water slurry
fuel program, 2012, pers. comm.). The insolubles are retained in the high-ash
byproduct coal. Hypercoal process is very different from UCC process in that this
process aims to separate solvent-soluble coaly matter from the ash and insoluble
coal, thereby producing a high-ash coproduct. The process involves five steps:
slurry preparation, extraction at 360°C temperature, separation of the extracts,
removal of alkali from the liquid component and removal of ultrafine particles
by filtration, and finally drying of the final product. A number of solvents such
as tetralin, 1-methyl-naphthalene, dimethylnaphthalene, and light cycle oil have
been used as solvents for extraction. The key features of the technology are as
follows [125–129]:
1. On a dry coal basis, the yield can be as high as 80%. The process removes
most alkalis from raw coal.
2. The higher ash (coproduct) is suitable for domestic power generation.
3. The process can be applied to all subbituminous and bituminous coals.
Yields are lower for subbituminous coals than for bituminous coals. Yields
for subbituminous coals can be increased by pretreating the coal with HCl
or weaker acids.
5.5.3.2 Fuel Preparation and transportation
The science and technology behind the production of UCC CWF has been well published [125–130] (Penn State’s coal-water slurry fuel program, 2012, pers. comm.).
Most systems involve the preparation of coal–water slurries containing 60%–70%
coal, together with additives to provide slurry stabilization and to lower the viscosity. The energy density of such slurry is about 18 GJ/m 3 . Additives consist of
dispersants and stabilizers. The dispersants such as sodium sulfonate of naphthalene, polystyrene, polymethacrylate, and polyolefin maintain the separation of coal
particles within the slurry [125–130]. Stabilizers include additives such as cellulose
or xanthum gums. For gas turbines and diesel engines, the water penalty for CWF
is much smaller and probably negligible when the overall power cycle is considered, and therefore, CWF slurry transportation is a preferred form. Final preparation
of CWF requires that the coal is either premilled dry before slurry preparation or
milled (micronized) wet as either a part of slurry preparation process or immediately prior to combustion. In general, wet milling has lower cost and lower energy
consumption [125–130].