Coal upgrading technology

Coal upgrading technology refers to a class of technologies developed to remove moisture and certain pollutants from low rank coals such as sub-Bituminous coal and lignite (brown coal) and raise their calorific values. Companies located in Australia, Germany and the United States are the principal drivers of the research, development and commercialisation of these technologies.

Environmental rationale

Around 30 nations collectively operate more than 1,400 brown coal-fired power stations around the world. Brown coal power stations that cannot economically dewater brown coal are inefficient and cause of high levels of carbon emissions. High emitting power stations, notably the Hazelwood power station in Australia, attract environmental criticism. Many modern economies including Greece and Victoria (Australia) are highly dependent on brown coal for electricity. Improved environmental performance and the need for stable economic environment provide incentive for investment to substantially reduce the negative environmental impact of burning raw ('as mined') brown coal.

Economic rationale

Coal upgrading technologies remove moisture from 'as mined' brown coal and transform the calorific performance of brown coal to a 'cleaner' burning status relatively equivalent to high calorific value black coal. Some coal upgrading processes result in a densified coal product that is considered to be a Black coal equivalent product suitable for burning in black coal boilers.

Victorian brown coal with a characteristic moisture content of 60% by weight is regarded as the 'wettest' brown coal in the world. The high moisture content is the key reason why the state's three major power stations are collectively regarded as the dirtiest carbon emitters in the world. Studies undertaken by the University of Melbourne [1] and Monash University confirm that when moisture is removed from Victorian brown coal, naturally low levels of ash, sulfur and other elements rank it as being one of the cleanest coals in the world. When dewatered upgraded brown coal can compete in the export market at comparable prices to black coal.

With significant levels of brown coal mining occurring around the world, and mining levels increasing, the need for coal upgrading technologies has become more apparent. the technologies will help to address global environmental concern of rising emissions from the burning of brown coal and provide alternative fuel options to rapidly emerging economies such as Vietnam that face difficulty competing for black coal with China, India, Japan and other nations.

Lignite mined in millions of metric tons
Country 1970 1980 1990 2000 2001
 Germany 369.3 388.0 356.5 167.7 175.4
 Russia 127.0 141.0 137.3 86.4 83.2
 United States 5.4 42.3 82.6 83.5 80.5
 Australia 24.2 32.9 46.0 65.0 67.8
 Greece 8.1 23.2 51.7 63.3 67.0
 Poland 32.8 36.9 67.6 61.3 59.5
 Turkey 4.4 15.0 43.8 63.0 57.2
 Czech Republic 67.0 87.0 71.0 50.1 50.7
 People's Republic of China 13.0 22.0 38.0 40.0 47.0
 SFR Yugoslavia 26.0 43.0 60.0 - -
 Serbia and Montenegro - - - 35.5 35.5
 Romania 14.1 27.1 33.5 17.9 29.8
 North Korea 5.7 10.0 10.0 26.0 26.5
Total 804.0 1,028.0 1,214.0 877.4 894.8

Technology comparison

Because of inherent high moisture content, all lignites need to be dried prior to combustion. Depending on the technology type drying is achieved either via a discrete operation or part of a process. The comparison chart identifies different technology drying methods that are in development in different countries and provides a qualitative comparison.

Option Drycol ZEMAG[note 1] Coldry Process[note 2] RWE-WTA[note 3] HTFG[note 4] WEC-BCB[note 5] UBC[note 6]Exergen CHTD[note 7] MTE[note 8] Kfuel[note 9] LCP[note 10][2]
Country of origin United States Germany Australia Germany China Australia Indonesia/Japan Australia Australia United States China
Process Description Drycol Microwave Drying indirect contact drying in tubular dryers exothermic reaction. natural evaporation. accelerated drying at 25-30°C fluidised bed stream drying High temp flue gas fluidised bed drying flash dry coal fines. use pressure to form briquettes mixing crushed coal with oil, heating the mixture to 130-160°C under 19-19.5 Bar pressure, separating the slurry cake from the oil by a centrifuge and then drying and briquetting it Continuous Hydrothermal Dewatering decarboxylation reaction in slurry form at 300 degC and 100 Bar, followed by gas/liquid/solid separation and press drying heat and squeeze at 250°C and 125 Bar, express water from coal heat and squeeze at 200°C and 100 Bar pyrolytic process that employs heat and pressure in an oxygen free environment to continue the coalification process that occurs naturally in the earth
Drying Description Microwave Drying while keeping coal below 90 deg C drying achieved using low pressure steam of max. 180°C, 4 bar drying achieved using low temperature waste heat to provide evaporative drying drying achieved using >100°C low pressure steam drying achieved using >900°C flue gas to dry 0-50 mm raw coal with 2-4% system O2 concentration under slight positive pressure drying achieved via exposure to high pressure combustion stream (flash drying) drying achieved by exposure to 130-160°C under 19-19.5 Bar pressure in oil slurry drying achieved by exposure to high pressure and temperature in a vertical autoclave, followed by a flashing step drying achieved via high pressure and temperature compression drying achieved via high pressure and temperature compression The process employs no additives and extracts both surface and inherent moisture.
Grade of heat used for drying Very Low Low Low Medium Low High Medium Medium High High Medium
Alternative uses for energy consumed in drying None power generation none power generation coal sales (fines used for combustion coal sales (fines used for combustion n/a electrical energy electrical energy electrical energy power generation
Pretreatment requirement Sizing for material handling crushing/screening (normal) (normal) plus mechanical mastication and extrusion (normal) crushing/screening to 50 mm (normal) crushing and mixing wit
CO2 exposures n/a n/a Up to 40% reduction in CO2. Net beneficial CO2 position due to low heat and low pressure Up to 30-40% CO2 reduction from the boiler. (Lost steam energy utilised in fluid bed dryer not accounted for) Up to 25-35% CO2 reduction from the boiler zero net improvement due to energy source for drying is coal combustion n/a Up to 40% reduction in CO2 ~15% CO2 reduction in combustion (detailed analysis not available). Zero net improvement, due to energy used for heating and compression ~15% CO2 reduction in combustion (detailed analysis not available). Utilises energy for heating and compression n/a
Waste streams generated from drying clean water none none none none none waste water stream none waste water stream waste water stream none
Byproduct streams possible none none demineralised water none none none n/a demineralised water none none tar product
Coal output stream description Direct use for briquetting/exporting or power generation coal pellets for use and export input coal for power generation only coal for sale or power generation coal briquettes for use and export coal briquettes for use and export coal for use and export input coal for power generation only input coal for power generation only exportable coal for power generation
Coal output moisture level 10 - 30% 5-20% 12-14% 12-14% 6-30% 10-15% n/a 5-10% ~18% ~20% 1-15%
Coal output - transportable or exportable long-distance transport long-distance transport non-pyrophoric direct to boiler only short-distance transport non-pyrophoric non-pyrophoric non-pyrophoric pyrophoric pyrophoric hydrophobic, transportable & exportable
Industrial maturity Technology in food industry 35 years well established and proven technology, industrial plants of up to 3 MTPA capacity running in Germany and Czech Republic pilot plant operational for 7 years; extensive database of global testing; commencing feasibility for full scale commercial operation by 2014 commercial operations in several locations It was used for coking drying since 1955 for over 200 wash plants one commercial scale plant, operations have not exceeded 30% of nameplate capacity pilot plant operational, demonstration plant 2008-2011 Pilot Plant 2002 - 2008, ready for commercialisation. Tested on Victorian and Indonesian coals pilot plant abandoned pilot plant operational 1MTPA plant in Inner Mongolia fully operational since 2012
  1. ↑ ZEMAG Clean Energy Technology, Germany
  2. ↑ Coldry Process, ECT Limited, Australia
  3. ↑ RWE-WTE = RWE (Rhenish-Westphalian Electric) WTE technology
  4. ↑ HTFG = Delta Drying Technology Ltd
  5. ↑ WEC-BCB = White Energy Company, Binderless Coal Briquetting
  6. ↑ UBC = Upgraded Brown Coal Process, Japan Coal Energy Center & Kobe Steel Ltd.
  7. ↑ Exergen company, Continuous Hydrothermal Dewatering technology
  8. ↑ MTE = Mechanical Thermal Expression, develop|ed by the CRC for Clean Power
  9. ↑ KFuel = Koppelman Fuel, Evergreen Energy, Denver, Colorado, USA
  10. ↑ LCP = LiMaxTM Coal Process Technology, developed by GB Clean Energy

See also

References

  1. ↑ Reactivity and Reactions of Australian brown coals. R.B. Johns and A.G. Pandolfo Dept Organic Chemistry, University of Melbourne. 1980
  2. ↑ http://www.gbce.com/en/technology_process.php
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