Solid Fuels 6-A
- 2. Liquefaction
The term liquefaction refers to the conversion
of the coal to a product that is primarily a liquid
(CTL)
Several very old processes… since WWII
Same general theme: increase H/C ratio
Can make a wide variety of hydrocarbon
products (e.g. synthetic crude or synfuel)
Two basic methods: direct and indirect
- 3. 3
Advantages of Coal To Liquid
(CTL) Fuels
• CTL Improves national and economic security
• Lessens dependence on foreign oil
• Uses domestic resources
• Provides environmental benefits
- Cleaner fuels that reduce NOx and particulate emissions
- Enables use of higher efficiency engines
• Is capable of capturing CO2 emissions
• Provides geographic diversity as energy source
- 4. 4
Direct Liquefaction of Coal Attractive
Because of
Low transportation cost
Less chemical transformation required
Higher efficiency than high Btu gas production
Easy to store
Less water required for manufacture
However, processing slurries at high temperature
and pressure presents difficulties with equipment
life and solid/liquid separation (still not
commercial)
- 5. 5
Coal Liquefaction
Very expensive
Liquefaction attractive for transportation fuel
Indirect liquefaction commercially proven
(>50 yrs)
Acid gas removal by amines (CO2, H2S)
S removal by Claus Process
H2S + O2 = H2O + SO2
H2S + SO2 = S + H2O
- 6. 6
Two Basic Approaches To Convert Coal
To A Liquid Fuel
1. Direct Liquefaction:
• Dissolves coal in a solvent at elevated
temperature and pressure
• Combine with hydrogen gas and a catalyst
2. Indirect Liquefaction:
• Involves first gasifying coal, followed by reacting
carbon monoxide and hydrogen together
nCO + (2n+1)H2 = CnH2n+2 + nH2O
- 7. 7
Adds hydrogen to break down the
coal
Dissolves in a solvent followed by
hydrocracking
Operates at 450 C and 170 bars
Light products are distilled
Medium and heavy distillates
obtained from vacuum distillation
Liquid yields of 70% of the dry
weight of coal feed
Further upgrade is needed for use
as transportation fuels
Complete breakdown of coal with
steam and oxygen
Sulfur is removed from the
syngas
Syngas reacted over catalyst at
300 C and 20 bars
Produces a lighter suite of
products; high quality gasoline
and petrochemicals
Oxygenated chemicals
Comparison of Processes
DIRECT
LIQUEFACTION
INDIRECT
LIQUEFACTION
- 8. 8
SASOL in South Africa
• South Africa’s SASOL Co. developed a commercial
coal liquids industry (fuel plus chemicals)
• The plant produces about 150,000 barrels daily
Indirect Coal liquefaction is proven technology
- 9. 9
Concerned about increasing dependence on oil imports and its impact on
economic growth and national security, China is making a massive $6
billion investment in new coal liquefaction plants.
Planned $2 billion Shenhua facility will eventually produce 50,000 barrels
daily of diesel fuel and gasoline.
Coal To Liquids in China
- 11. Coal
Raw ICL Products
Raw DCL Products
H2
H2
F-T Tail Gas
Final
Products
Coal
Gasification
Indirect Coal
Liquefaction
(F-T)
Product
Blending and
Refining
Hydrogen
Recovery
Direct Coal
Liquefaction
Hybrid DCL/ICL Plant Concept
- 13. Indirect Coal Liquefaction Overview
Natural Gas
Coal
Pet Coke
Biomass
Wastes
Synthesis Gas
Production
• Gasification
• Reforming
• Steam
• POX
• ATR
Oxygen
Plant
Air
O2
F-T
Liquid
Synthesis
Slurry/Fixed/
Fluid-Bed
Liquid
Fuels
Product
Storage
Naphtha/
Diesel
Tail
Gas Power
Generation
H2
Hydrogen
Recovery
Wax
Hydrocracking
Liquids
Wax
Product
Recovery
- 17. 17
• Coal-based liquid fuel becomes viable when the per-barrel price of
oil is expected to exceed the $70-100 range for 20+ years
• CTL has high front-end capital cost
- A 50,000 barrel-a-day plant would cost over $3 billion to construct
• The product refinement process is three to four times more
expensive than refining an equivalent amount of oil
• The cost of sequestering the captured CO2 would increase the
price of the end product by $10-20 a barrel.
• The imposition of a carbon cap and trade policy would also raise
the cost of fuel produced with CTL technology
CTL Costs
- 18. 18
CTL is Very Water-Intensive
CTL requires ~7:1 water to fuel ratio
~7 gallons of water per gallon of fuel produced
Water scarcity can be a limiting factor for CTL plant
permitting
Conventional gasoline
1-2.5 gallons of water per gallon of fuel produced
Irrigated Biofuels
1000 gallons of water per gallon of fuel
- 19. 19
Liquids Fuels Summary….
Proven technologies
All processes require adding hydrogen
All processes remove sulfur and ash
Product include liquid, gas, and combustible
solid(char)
Several long-standing commercial processes
(e.g., S. Africa - SASOL)
So far no large-scale use without government
support
- 20. 20
Coal to Liquids Summary….
Good promise because of very large coal
deposits in the world
Numerous processes that can generate a wide
variety of products
Environmental issues include some hazardous
wastes and byproducts
Does not yet effectively compete with natural gas
or oil production … requires some form of
subsidy
- 21. Carbonization
Carbonization is the process by which coal is heated
and volatile products—gaseous and liquid—are driven
off, leaving a solid reside called char or coke.
The coke produced by carbonization of coal is used in
the iron and steel industry and as a domestic smokeless
fuel
Only a limited range of coals produces acceptable
metallurgical cokes.
These coals are in the bituminous rank range but not all
bituminous coals are caking coals.
- 22. Carbonization
Coal carbonization processes are classified into
i. high-temperature
ii. low-temperature
High-temperature
Carbonization processes performed at temperatures in
the range of 900 − 1200°C.
The main purpose of high-temperature carbonization is
the production of metallurgical coke for use in blast
furnaces and foundries.
- 23. Carbonization
Low-temperature
In low temperature carbonization heating is carried out at
500-700°C.
Coke produced is not mechanically strong so it is not
used as metallurgical coke.
Low-temperature carbonization was originally developed
to provide town gas for residential and street lighting and
to manufacture a smokeless fuel for domestic and
industrial heating
- 24. Carbonization
Characteristics Low temperature
carbonization
High temperature
carbonization
1 Heating temperature 500-7000C 900-1200°C
2 Yield of coke 75−80% 65−75%
3 Volatile matter content 5−15% 1−3%
4 Mechanical strength Poor Good
5 Calorific value 6500−9500 kcal/m3 5400−6000 kcal/m3
6 Quantity of by-product
gases
130−150 m3/tone 300−390 m3/tone
7 Coke produced Soft Hard
8 In gas, percentage of
(a) Aromatic
hydrocarbons
(b) Aliphatic
hydrocarbons
Lower
Higher
Higher
Lower
9 Uses Domestic Metallurgy
- 25. Coal Properties for Coke Production
The ability of a coal to melt upon heating and to form a
coherent residue on cooling is termed caking;
caking is an essential prerequisite for a coking coal that
it should cake or fuse when heated.
Coals that are low in rank, such as lignites, or high in
rank, such as anthracites, do not cake and therefore are
not capable of forming coke.
Several properties of coals are measured to identify
appropriate coking coals, including swelling, fluidity,
composition etc.