Coal upgrading technology


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.

Contents

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 environemntal 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[citation needed]
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 Current Use Coldry Process[note 1] RWE-WTA[note 2] WEC-BCB[note 3] UBC[note 4] Exergen CHTD[note 5] MTE[note 6] Kfuel[note 7]
Country of origin n/a Australia Germany Australia Indonesia/Japan Australia Australia United States
Process Description mine lignite 'as is'. Combust untreated. Burn in standard brown coal boiler exothermic reaction. natural evaporation. accelerated drying at 25-30°C fluidised bed stream 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
Drying Description drying achieved in recirculated steam of boiler exhaust gases via high temperature drying achieved using low temperature waste heat to provide evaporative drying drying achieved using >100°C low pressure steam 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
Grade of heat used for drying High Low Medium High Medium Medium High High
Alternative uses for energy consumed in drying steam generation none power generation coal sales (fines used for combustion n/a electrical energy electrical energy electrical energy
Pretreatment requirement crushing/screening (normal) (normal) plus mechanical mastication and extrusion (normal) (normal) crushing and mixing with oils slurrying and high pressure pumping (normal) (normal)
CO2 exposures high end exposure to CO2 - default position 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) 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
Waste streams generated from drying none none none none waste water stream none waste water stream waste water stream
Byproduct streams possible none demineralised water none none n/a demineralised water none none
Coal output stream description input coal for power generation only coal pellets for use and export input coal for power generation only 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
Coal output moisture level n/a 12-14% 12-14% 10-15% n/a 5-10% ~18% ~20%
Coal output - transportable or exportable n/a non-pyrophoric direct to boiler only non-pyrophoric non-pyrophoric non-pyrophoric pyrophoric pyrophoric
Industrial maturity status quo - well established 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 one commercial scale plant, operations have not exceeded 30% of nameplate capacity pilot plant operational Pilot Plant 2002 - 2008, ready for commercialisation. Tested on Victorian and Indonesian coals pilot plant abandoned pilot plant operational
  1. ^ Coldry Process, ECT Limited, Australia
  2. ^ RWE-WTE = RWE (Rhenish-Westphalian Electric) WTE technology
  3. ^ WEC-BCB = White Energy Company, Binderless Coal Briquetting
  4. ^ UBC = Upgraded Brown Coal Process, Japan Coal Energy Center & Kobe Steel Ltd.
  5. ^ Exergen company, Continuous Hydrothermal Dewatering technology
  6. ^ MTE = Mechanical Thermal Expression, developed by the CRC for Clean Power
  7. ^ KFuel = Koppelman Fuel, Evergreen Energy, Denver, Colorado, USA

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

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