Direct Coal Liquefaction: Comprehensive Review Of Current State Of The Art

Drivers for Coal Liquefaction (CTL) 

Routes of coal liquefaction

Indirect coal to liquid (ICL): Reaction of coal with steam/oxygen (primarily CO + H2) which is then converted into liquids via FischerTropsch (F-T) reaction

Direct coal to liquid (DCL): Hydrogenation at relatively high temperature and pressure.

Studies comparing the two routes of CTL 

Comparison of DCL and ICL [4-7]

Advantage DCL

• 5-10 % more thermally efficient
• Lesser water consumption
• Lesser production of CO2
• Lower capital cost (~ 30 %)
• Higher liquid yields
• Can process wide stock of coal 

Relative analysis ([8])

Hybrid DCL/ICL diagram [9]

DCL Technologies

• DCL processes aim to add hydrogen to the organic structure of coal
• DCL technologies
• Single stage processes
• Two stage processes
• Co-processing (petroleum derived oil/ coal) technologies

Hydrogen/carbon ratio [4]

Brief history of DCL technologies [10]

Single/Two stage processes

Schematic diagram: H-Coal process [11]

Single stage DCL process give distillates products via one primary reactors or train of reactor in series

Schematic diagram: Catalytic two stage liquefaction process [11]

Two stage DCL process give distillate products via two reactors or reactor train in series

• Primary reactor: Solubilize coal (with/without low activity disposable catalyst)
• Second reactor: Heavy coal liquids are hydro treated in presence of a high activity catalyst to produce additional distillates

Single Stage Processes 

• Technologies differ on the reaction scheme/ catalyst / hydrogenation solvent
• NEDOL, IGOR+,CTSL, LSE are considered ready for commercialization by developers
• Three phase (slurry/ebullated) bed reactors used in most process

DCL Technologies 

Shenhua DCL Plant

YPC (Yulin) Co-processing Unit

DCL Economics

Detailed feasibility studies of DCL (Indian application) is essential to understand its potential (economic competitiveness) for production of chemical and fuels

Factors affecting the DCL yield 

• Pretreatment of coal
• Preheat treatment
• Hydrothermal treatment
• Drying and oxidation
• Coal swelling in solvents
• Coal rank
• Solvents
• Hydrogen transfer mechanisms
• Catalyst mediated hydrogen transfer
• Catalysts in direct coal liquefaction
• Dissolution catalysts
• (Fe-based catalysts, non Fe-based catalysts, Acid Catalyts)
• Catalyst for coal liquids upgrading
• Catalyst deactivation 

Summary and Conclusion

• Various single and two stage processes have been developed for DCL. IGOR/VCC, NEDOL in single stage and LSE, CTSL in two stage processes are available for licensing.
• Equivalent crude selling price for DCL to be profitable range between $30-$82. Detailed feasibility studies of DCL is essential to understand its potential for production of chemical and fuels.
• Hybrid DCL/ICL plant are more cost competitive, feasibility studies of such plants need to be looked into.
• Shenhua commercial DCL plant in China has shown acceptable liquid yields as per figures in open literature. Plant at YPC, China based on VCC technology has shown excellent conversion for coprocessing residue and coal.
• Shenhua corporations have developed their commercial plants (scaling from lab, bench, pilot to demo scale facilities) and in the process filed ~104 patents (37 granted) between 2004-2010.
• R&D facilities for DCL in India need to be developed for understanding the kinetics and hydrodynamics of DCL technologies specific to coal of our interest.
• Consortium of Public-Private companies, CSIR, Academia labs need to formulated to develop CTX technologies. 

The 10 largest coal producers and exporters in the Indonesia:

1. Bumi Resouces
2. Adaro Energy
3. Indo Tambangraya Megah
4. Berau Coal
5. Bukit Asam
6. Baramulti Sukses Sarana
7. Harum Energy
8. Mitrabara Adiperdana 
9. Samindo Resources
10. United Tractors

Source:

Dr. Ankit A. Jain & Dr. Ajay Gupta
Refining R&D
Jamnagar