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 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	Coldry Process	RWE-WTA	HTFG	WEC-BCB	UBC	Exergen CHTD	MTE	Kfuel	LCP
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

See also

• Bituminous coal
• Bergius process
• Coal assay
• Coldry Process
• Densified coal
• Energy value of coal
• Orders of magnitude (specific energy density)
• Fischer-Tropsch process
• Karrick process
• Leonardite
• Maddingley Mine
• List of CO₂ emitted per million Joule of energy from various fuels
• Nano Drying Technologies, LLC