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Utilisation of Low Rank Coals

David J Allardice and Brian C Young*

Allardice Consulting 10 Arcady Grove, Vermont, Vic 3133, Australia

david.allardice@allardice.com.au

* Envirosafe International Pty Ltd

1a Yarrbat Avenue Balwyn, Vic 3103, Australia

Abstract

This paper addresses the major uses of low rank coals and the fuel specific technologies developed to cope with their unique properties. The emphasis is on the vast Latrobe Valley brown coals from Victoria, Australia, with their high moisture contents. Reference is also be made to the importance of low rank coals in the international scene.

The combination of the high moisture content and high reactivity of low rank coals necessitates their use close to the mine, unless they can be upgraded to value-added products with improved transport safety and economics. Their primary use is therefore power generation or to provide domestic and industrial fuels for local use, although a number of novel alternative fuel and non-fuel applications provide value-added potential.

Due to the generally low mining cost of these coals, emphasis was previously placed on developing technologies to minimise the capital expenditure rather than maximise thermal efficiency in their use. However, the current concerns over global warming have focussed attention on developing utilisation technologies to reduce the comparatively high CO2 emissions from burning these coals.

1. Introduction

The objective of this paper is to provide an outline of the major uses of low rank coals and the fuel specific technologies developed to cope with the high as-mined moisture content of these coals. While the particular emphasis will be on the vast Latrobe Valley brown coals from Victoria, Australia, reference will also be made to the growing importance of low rank coals in the international scene and some of the current and prospective future technologies developed for these fuels.

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Throughout the paper the terms low rank coals, brown coals and lignites are used interchangeably. They are essentially synonymous, with overlapping definitions in different coal classification systems. ‘Lignite’ is the US ASTM rank terminology, while Australian, ISO and most European systems use ‘brown coal’, although Germans often translate ‘braunkohle’ as ‘lignite’. Subbituminous coal is briefly noted but not addressed.

Low rank coals are characterised by their high bed moisture content, typically 60-70% in the case of Latrobe Valley brown coals. Many other low rank coals have lower moisture contents, in the 30-50% range, but this advantage is often off-set by higher ash levels.

Figure 1 demonstrates the quality variation of some well-known low rank coals, showing the interrelationship between moisture, ash and net wet specific energy. The figure demonstrates the contrast between the two Latrobe Valley coals shown (Yallourn and Loy Yang) with their low ash (2-3%) and for example North Dakota lignite with 35-40% moisture and 7-10% ash.

The other common feature of low rank coals is their high reactivity in combustion, gasification, liquefaction and other processes. The combination of the high moisture and high reactivity necessitates the use of these coals close to the mine, unless they can be upgraded to value-added products with better transport safety and economics.

Figure 1: Comparison of Quality of Low Rank Coals

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2. Patterns of Use of Low Rank Coals

According to Rheinbraun (2000), 950 Mt (million tonnes) of brown coal was mined worldwide in 1998, and this rate of consumption can be maintained for over 500 years from current reserves. This compares with reserves to consumption ratios for hard coal 162 years, oil 45 years and gas 66 years.

Over, 90% of the brown coal mined worldwide is consumed in power stations close to the mine, 4% is consumed by industry, 3% by households and the rest in other applications. The brown coal used by industry and households is largely in processed form as briquettes or dried brown coal. Brown coal provided about 4% of world power generation in 1998 (13% of Europe’s generation) but some countries are extremely dependent on brown coal for their electricity, such as Greece 76%, Yugoslavia 67% and Czech Republic 51%.

The largest brown coal consumer is Germany, where 166 Mt of brown coal was consumed in 1998 and 28% of its electricity was generated from brown coal. This represents a major decrease from the combined German production of about 400 Mt in the late 1980s. This decrease is largely due to the economic downturn in Eastern Germany following unification and the closure of older plants due to environmental concerns, arising from the burning of Central German brown coals of high sulfur content.

In Australia, low rank coal production was reported to be 68 Mt in 2000, dominated by Victoria with over 65 Mtpa from the Latrobe Valley. Smaller amounts are consumed from Leigh Creek in South Australia (3 Mt) and Collie in Western Australia (0.04 Mt). Over 97% of the Victorian production is consumed by power stations, which produced 97% of the State’s electricity supply, or 25% of the national supply. The remainder of the Victorian brown coal is used for briquetting, carbonisation and a range of small volume, value-added applications.

Lignite mining in the USA occurs primarily in Texas and North Dakota, which according to DOE produced 61% and 36% respectively of the total lignite production of 78 Mt in 1999. The bulk of this lignite was used for power generation, although the only commercial coal gasification plant in North America has operated on lignite since 1984 at Great Plains ND. The USA lignite industry has developed rapidly since 1950, but has levelled off in recent years.

The much larger production of higher rank sub bituminous coals for power generation in the USA, 366 Mt in 1999, is beyond the scope of this paper. However, production is dominated by Wyoming, 301 Mt, and Montana, 36 Mt, with smaller contributions from New Mexico, Colorado, Washington and Alaska.

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3. Brown Coal Power Generation

3.1 Pulverised Fuel Combustion

Conventional technology for thermal power generation from high moisture brown coals involves pulverised fuel combustion, where the coal is dried on-line in an integrated mill/drying system (Clark, 1984). In this technology, which was introduced to Victoria from Germany at Yallourn C and D stations in the 1950s, a large proportion (about 50%) of the hot exit flue gas is recycled via large off-take ducts to dry the as-mined coal in the integrated mill/drying/burner system.

The high moisture content of Yallourn coal (66% or 2 tonnes of water for each tonne of dry coal) required a further development, termed separation firing. By use of a centrifugal swirl device, a fuel rich stream (up to 80% of the feed coal) is separated and fed to the main burners to achieve a stable flame. The remaining 20% of the finer coal is carried in the bulk of the recycled flue gas and evaporated coal moisture vapour (70%) and over-fired through the “inerts” or “vapour” burners higher in the furnace.

This basic technology, shown in Figure 2, has been applied to subsequent stations at Yallourn and Loy Yang. Morwell coal, with its lower moisture content (60% or 1.5 t water / t dry coal) and greater ease of ignition, does not require separation firing in the integrated mill/drying system used at Hazelwood Power Station.

Figure 2: Typical Separation Firing System Developed for Victorian Brown Coal

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Because of the high inert gas loading, furnace gas temperatures (~1200ºC) and flame temperatures are several hundred degrees lower than comparable black coal units, and hence they require a larger radiant heat transfer surface to cool the furnace exit gases and minimise superheater fouling. The lower flame temperature has a beneficial effect in reducing nitrogen oxide emissions, but results in a very large and capital intensive plant compared with black coal units of similar capacity as see in Figure 3 (St Baker and Juniper, 1982). For example, a 500 MW Loy Yang boiler is over 100 meters high.

Figure 3: Effect of Coal Rank on Furnace Size

Currently, 6220 MW of brown coal fired generating capacity is installed in the Latrobe Valley, Victoria using this technology. Since the 1950s, unit sizes have increased from 20 MW to 500 MW with little change to the basic technology.

However, significant efficiency improvements have been achieved within the constraints of this technology, and further improvements have been targeted by the operators to meet their Greenhouse Challenge commitments. In addition, the system output has increased by over 20%, through improved plant management and workforce performance, which have raised plant availability factors from around 75% to over 90% following the corporatisation and subsequent privatisation of the State Electricity Commission of Victoria (Price, 1999).

The same basic integrated mill drying principle is used in German power stations burning their high moisture brown coals.

In contrast, the drier US lignites generally do not require pre-drying for combustion, although Texas Utilities use Parry entrained flow evaporative dryers to prepare dry lignite feed to Alcoa’s generating plant in Rockdale, Texas (Willson et al, 1992).

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3.2 Advanced Systems for Brown Coal Power Generation

The high capital cost of conventional thermal brown coal power stations relative to black coal, coupled with their higher CO2 emissions per MWhr due to the need to burn more brown coal to evaporate the moisture, militates against further units of this design being built in Victoria. The future for brown coal power will depend on a new generation of more efficient conversion technologies and/or pre-drying processes.

In Germany, 800 MW brown coal fired units are operating and a 1000 MW unit is under construction at Niederaussem K (Heitmuller et al., 1999). This will burn brown coal with a moisture content of 53%, somewhat lower than Victorian brown coals. Using the advanced ‘BoA’ technology, will raise the net HHV efficiency, from 35% in the existing 600 MW Niederaussem units to 43%. This improvement will be achieved through economies of scale, the use of advanced supercritical steam cycles and more efficient turbines, and other incremental improvements. A further 3-5% improvement has been projected for the BoA+ systems through pre-drying the coal with ‘waste’ heat.

Plans to develop the KOBRA Integrated Gasification Combined Cycle system in Germany have been discontinued, with attention focussing on the BoA+ system. KOBRA was intended to achieve improved efficiency through pre-drying and gasifying brown coal, coupled with combined gas turbine and steam generation cycles (Schippers et al., 1993).

In Victoria, HRL has demonstrated at a 10 MW scale the Integrated Drying Gasification Combined Cycle (IDGCC) process (Figure 4), which offers substantial efficiency improvements and cost savings over conventional brown coal systems (Johnson and Young, 1999). The process uses the hot gas from an air blown fluid bed gasifier to pre-dry the coal under pressure and hence cool the gas, before filtering out entrained particles and burning the gas in the gas turbine cycle. Increased generation is achieved in the gas turbine by the additional mass flow of the evaporated moisture passing through the turbine. Substantial capital cost savings result from the integrated high pressure drying.

For Latrobe Valley coals, IDGCC raises the thermal efficiency to 38-41%, on a Higher Heating Value sent out basis, depending on the moisture content of the coal. This is a substantial improvement over the 29% efficiency achieved in the latest conventional units burning these coals and results in a 20-30% reduction in Greenhouse gases.

The IDGCC technology is now being adapted for retrofitting in the Latrobe Valley (Johnson, 2001). 125 MW units are expected to generate power for 1/3 less than 1000 MW PF brown coal grid stations built less than a decade ago. The technology has potential for application at other lignite and power generation sites around the world.

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Figure 4: The IDGCC Process

The Cooperative Research Centre for Clean Power from Lignite has evaluated a range of advanced cycle generation systems for high moisture coals (McIntosh, 1999). However, it is now concentrating on improving the efficiency of gasification combined cycle systems using dried coal feed (McIntosh, 2001) and retrofit systems with pre-dried coal. The Centre is now focussing its practical investigations on a novel non evaporative drying process, MTE (see Section 6), and fluid bed gasification (see Section 7).

The Lignite Energy Council of North Dakota, through its Lignite Vision 21 Project, is also funding studies to select advanced technology for clean and efficient power generation for a designated new 500 MW generation plant (Porter et al., 2001).

Clearly, major efficiency improvements can be achieved with radically different technologies for the next generation of brown coal-fired power stations. With low rank coals globally being the most under utilised fossil fuel resource and many countries with few economic alternatives to supply large scale grid demand, there is considerable incentive to accelerate these developments.

4. Briquetting

Binderless briquetting is the second largest use for brown coal around the world. However, briquette production as been substantially reduced with the decimation of the industry in Germany where production fell from over 50 Mtpa in 1990 to less than 4 Mtpa in 1998. This resulted from the restructuring of the German economy following unification and the environmentally unacceptable quality of much of the coal available for

NITROGEN

LOCKHOPPERPRESSURISATION

COAL

BUFFER / WEIGHINGHOPPER

COOLED GAS

CLEANEDGAS

DUST

FILTER

COMBUSTOR

COMP

RESS

ORAIR

TURBINE

EXHAUST GASES

WATER PUMP

CONDENSER

ALTERNATOR

TURBINE

BOILE

R

STEAM

STEAMTURBINE

HEATRECOVERY

GASTURBINE

CLEANINGGASIFIERDRYER

COAL

DRIED

COAL DRYINGAND GAS COOLING

CYCLONE

AIR

AIR

HOT GASASH/ CHARCO2

TO STACK STEAM

ASH/ CHAR

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briquetting in eastern Germany. Trials with additives such as lime to retain sulfur do not appear to have reversed this trend.

Large-scale briquetting of Victorian brown coal commenced at Yallourn in 1924 using the German technology. This followed abortive attempts at Yallourn North in the 1890s. The original Yallourn plant closed in 1970 but the Morwell plant, which commenced in 1959, is still operating, with a nominal production capacity of 1.2 Mtpa of briquettes and 170 MW of electricity. The Morwell briquette and power complex is one of the largest cogeneration plants in the Southern Hemisphere. A sister briquetting plant to that in Morwell is operating on Indian lignite at Neyveli, south of Madras.

Briquette production in Victoria peaked at 1.9 Mtpa in 1966 prior to the introduction of natural gas. Production has now stabilised around 400-500 ktpa, primarily for industrial and commercial heat applications, char production and occasional niche market export opportunities because of the high quality of the product.

In the briquetting process (Perry et al., 1994), the brown coal is crushed to – 8 mm, dried in rotary steam tube driers from 66% to about 15% moisture. The dry coal is then cooled and briquetted without a binder, using an Exter extrusion press at 1200 kg/cm2 to form hard compacts with an energy content (21 MJ/kg Net Wet basis) comparable to many higher rank coals. Figure 5 illustrates the briquetting process.

Figure 5: Brown Coal Briquetting

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However, as a result of changes in the quality of Yallourn coal with the development of Eastfield, and competition between the privatised mines, Loy Yang coal now provides 75% of the briquetting coal, with Yallourn Eastfield providing the balance (Davey, 2001).

Several alternative agglomeration technologies for brown coal have also been evaluated. These could supplement or eventually replace the current technology. Processes such as double roll pressing, pellet milling and drum pelletising can offer improved economics for a new installation although questions still remain on product quality and self heating characteristics.

5. Carbonisation

Since 1970, Australian Char Pty Ltd has been manufacturing industrial carbon by carbonising (devolatilising) brown coal briquettes with circulating hot gases in vertical retorts (Kennedy, 1971). The process operates with a carefully controlled temperature profile through the retort to a peak temperature of 800ºC. The controlled thermal history is required to minimise breakage and loss of lump strength due to excessive shrinkage in the drying region around 100ºC and at the onset of volatile release at around 400ºC. The product is a hard lump char (25 mm nominal diameter), with high purity (95% fixed carbon and 3% ash), high reactivity and good absorbent characteristics.

Australian Char can produce up to 80,000 tpa of char, with 2.3 tonnes of briquettes required per tonne of char, (equivalent to over 6 tonnes of raw coal). A substantial proportion of the char is exported, and markets include its use as a metallurgical re-carburiser, in alloy manufacture, as a pyro-metallurgical reductant and chemical feedstock for activated carbons. A valuable market for the char fines is the production of barbecue fuel (Heat Beads and Hot Shots). The fines are re-briquetted in a double roll press with a binder and other additives.

The briquette carbonisation industry in eastern Germany has also collapsed, but Rheinbraun still produces 200 ktpa of char from carbonisation of pre-dried granular brown coal in a rotating “pan cake” oven near Cologne. The char product is sometimes termed lignite coke, although it does not fuse in processing, a normal characteristic of coke. The char is a low cost moderately active carbon used in a variety of environmental applications (Schieb, 1994) including waste gas clean up from incinerators to remove SOx, halides, heavy metals, dioxins and furans. It is also used for waste water clean up, particularly as a control in biological water treatment.

In India, brown coal briquettes are also carbonised in vertical retorts to provide a smokeless cooking fuel. Other carbonisation technologies, such as rotary kilns, fluid beds and entrained flow reactors, can have advantages in specific applications but have not been applied commercially to brown coals.

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6. Drying of Brown Coal

Because of the high moisture content of brown coal, drying is an essential element of any upgrading or utilisation process. Often overlooked or underestimated, the cost of evaporating 60–70% of the mass of feed coal is frequently the major barrier to the economic commercial development of new brown coal technologies. This has led to a plethora of drying processes being investigated, but a major breakthrough on drying cost is still awaited.

Reference has already been made to the integrated mill/drying system in conventional thermal power stations, the high pressure entrained flow direct contact drier in the IDGCC process, and the rotary steam tube driers in the briquette factory.

Potter (1985) invented the Steam Fluidised Bed Drying concept at Monash University, and Lurgi has developed it to a commercial scale. The technology (Figure 6) involves drying the coal in a superheated steam fluidised bed with the product water vapour recompressed to provide the fluidising steam, with the bulk of the steam condensing in a heat exchanger immersed in the bed. As the evaporated moisture is recovered in liquid form, the process offers major efficiency advantages over conventional evaporative drying systems, while the steam fluidising medium provides major safety benefits.

A 150,000 tpa (dry coal) steam fluidised bed drying plant operated for several years at Loy Yang, supplying pneumatically conveyed dry coal dust over 3 km to Edison Mission’s Loy Yang B power plant for use as a start up and auxiliary fuel.

Figure 6: Steam Fluidised Bed Drying

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Despite the technical advantages of the process, the product has proved too expensive to attract other markets for the Loy Yang plant’s surplus capacity. The plant has now ceased operation and Loy Yang B is now using pulverised briquettes as auxiliary fuel, and may switch to natural gas. Rheinbraun operates a similar plant at Wachtberg, and the process is being considered for pre-drying brown coal in the BoA+ power generation technology.

Hydrothermal Dewatering (HTD) (Figure 7) is another drying technology, which was demonstrated in Victoria by the SECV at a 1 m3/h pilot plant scale (Woskoboenko and Allardice, 1996), following tests in a smaller scale plant at the University of North Dakota’s Energy and Environmental Research Centre (Willson, Young and Irwin, 1992).

In the HTD process, a slurry of brown coal is heated to around 300ºC under sufficient pressure to prevent evaporation. After cooling and depressurising, excess liquid water can be separated from the product slurry. The decomposition of the coal structure which occurs under these conditions, is analogous to accelerated coalification.

The product is an upgraded pumpable coal slurry, with an energy content greater than the as-mined coal. It can be fired in conventional boilers and has potential with more development for use in a coal slurry fired gas turbine combined cycle system (Anderson and Johnson, 1993). The CRC for Clean Power from Lignite has conducted further studies on the HTD process but the process is no longer being pursued as an option for mine-side power generation in Victoria because of the high cost of the plant and the waste water treatment requirements.

Figure 7: Hydrothermal Dewatering Process

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HTD has also been piloted in Japan (Hashimoto and Tokuda, 1997) to investigate its longer term potential to convert brown coals into a clean, safe, transportable form. This could provide a means of exporting Australian and/or Indonesian low rank coals. The recent increases in the price of international oil may reactivate interest in coal water slurry processes in the region.

In the 1980s, the SECV operated a 2200 tpa Solar Dried Brown Coal pilot plant in the Latrobe Valley. The process involves wet milling of coal to a pumpable slurry which is dried in open-air ponds to provide a dense lump product. The process requires large land areas and the production is seasonally variable depending on climatic conditions. It does not benefit from economies of scale to the same extent as other drying technologies but could be well suited to low rank coal deposits in arid areas with low labour costs, such as Pakistan or Mongolia.

The most recent option to emerge for brown coal drying is the MTE (Mechanical Thermal Expression) process, initiated by the University of Dortmund, Germany (Berger et al., 1999). In the process (Figure 8) water is expressed from brown coal in a particle board type hydraulic press for a few minutes at up to 60 bar pressure, after steam-heating the coal to 150-200ºC. Some energy can be recovered from the expressed water.

Figure 8: Mechanical Thermal Expression of Water from Brown Coal

Earlier studies in Victoria on ambient temperature press dewatering of brown coal (Banks and Burton, 1989) were abandoned as impractical because of the high pressures required for residence times of 20 minutes or more. The higher temperature used in MTE decreases the pressure and residence time required to manageable levels.

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The MTE process can reduce the moisture content of the brown coal to below 25%, with very little energy consumption and a substantial reduction in Greenhouse gas emissions from even conventional brown coal power generation. The process has been demonstrated at 10 tph scale at Rheinbraun and is now the preferred drying process of the CRC for Clean Power from Lignite and the focus of a significant proportion of the CRC’s current research program.

The CRC for Clean Power from Lignite is developing MTE as a practical concept for retrofitting to existing boilers or to pre-dry the feed coal for an IGCC plant (McIntosh, 2001). The CRC has concluded that MTE is less expensive and provides greater efficiency improvements in these applications than HTD or Steam Fluid Bed Drying. On this basis, the CRC is planning a Latrobe Valley demonstration plant for the technology using additional funds from the State Government.

It should be pointed out that the concept of pre-drying brown coal for commercial scale power generation by whatever means does introduce new operating and safety concerns which need to be managed. However, a growing market has developed in Germany in recent years for granular dried brown coal and dry coal dust, as industrial fuel for small boilers, rotary kilns and fluid bed combustion systems.

It is important to note that any dewatering or drying process which can remove the water from brown coal in liquid form, i.e. without the need to supply the evaporative energy to dry the coal, has the potential to reduce, by up to 25%, the Greenhouse gas emissions arising from the combustion of these coals.

7. Gasification of Brown Coal

Low rank coals, because of their high reactivity, are particularly suited to gasification, as was demonstrated in the Morwell Lurgi Gasification Plant from 1956 to 1970 (Bennett, 1961). The plant gasified brown coal briquettes in a moving bed reactor to supply Melbourne with town gas. Briquettes were required because of the friability of the soft brown coal in the reactor. Unfortunately the economics of the project could not survive the advent of natural gas although remnants of the plant can still be seen at Morwell.

The Great Plains lignite gasification plant near Beulah, North Dakota has operated since 1984. It is the only commercial coal gasification plant operating in North America and involves the Lurgi moving bed pressure gasification of screened lump lignite, with an additional methanation step to produce 3.5 million m3/d of substitute natural gas.

The US$2 billion project has been a technical success but economics have been affected by the reduction in US gas prices where an increasing trend had been expected. The economics have been improved by the sale of by-products including phenol, anhydrous ammonia and cresylic acid.

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Rheinbraun have developed a fluid bed gasification process for brown coal, the High Temperature Winkler process, in which dried granular brown coal is gasified with steam and oxygen (or air) in a fluid bed at high pressure (up to 10 bar). A demonstration plant operated near Cologne until recently, processing 55 tph of dried brown coal to produce 900,000 m3/d of synthesis gas used to manufacture methanol. We understand that further development of this technology has ceased in Germany.

The 10 MW scale IDGCC plant at Morwell also incorporates a 25 bar fluid bed gasifier. A smaller scale (300 kg/hr dry coal) fluid bed gasification pilot plant used in HRL’s IDGCC development program has been leased to the CRC for Clean Power from Lignite and recommissioned for brown coal gasification studies.

8. Brown Coal to Oil

The potential to produce oil from Victorian brown coal by hydrogenation in a recycle oil slurry was demonstrated experimentally in the 1930s (Sinnatt and Baragwanath, 1938). Large-scale production of oil by hydrogenation of German brown coal occurred in World War 2.

Brown coal hydrogenation technology has been developed further and operated on a 50 t/d dry coal pilot plant scale at Morwell by BCLV, a consortium of Japanese companies. The project was funded by the Japanese Government agency NEDO to the extent of $1 billion over 10 years to 1991. This was a long term strategic investment by the Japanese Government to have technology available for alternative oil supplies if the price of oil escalated internationally. The international oil price is currently reaching levels where the wisdom of this strategy is apparent and oil from coal could again be on the international agenda.

The Morwell BCLV plant closed when it had achieved all its technical targets and collected the necessary information to scale up the design to a commercial plant. Further improvements to the BCL technology have since been made at a smaller scale in Japan, increasing the oil yield on a dry brown coal basis to over 60% (Shimasaki et al., 1995).

Testing of Indonesian brown coals in the BCL process confirmed their suitability for conversion to oil with higher yields than from Victorian brown coal. The Indonesian coals have comparable reactivity to Victorian brown coals, but lower moisture and oxygen contents. In 1997, this led to the Japanese and Indonesian Governments and the BCLV companies, initiating feasibility studies on a possible demonstration plant in Sumatra.

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9. Other Value Added Uses

There are many current and potential value-added uses for brown coals, particularly in Victoria. These are generally small scale, requiring only small tonnages of coal. Their viability often depends on the availability of low cost coal from the large-scale coal mines established for the power generation industry.

Although the applications are currently small, they provide valuable additional employment and diversification of the brown coal industry. Some of the products also have significant environmental benefits and growth potential.

9.1 Agricultural Products

Brown coal is essentially 10-50 million year old compost, making it an ideal feedstock for a range of agricultural products. HRL produces and distributes a number of such products from brown coal , although the total tonnage of coal consumed would be less than 1000 tpa. These products include:

• sized brown coal for direct use as a soil conditioner or in potting mixes etc;

• liquid humates chemically extracted from brown coal. This product development has led to a steadily growing commercial market with significant export potential, as well as potential to expand into blended or powdered versions;

• slow release NPK fertiliser in a brown coal matrix. Field trials have been very encouraging and the product has significant potential due to the environmental benefits of the slow release characteristics. An opportunity to commercialise the technology is still being sought;

• treated coal ash from selected sources to capitalise on the calcium, magnesium, sulfur and trace metals present. The product is an agricultural lime/dolomite substitute marketed as Calsulmag. This material would otherwise be a waste residue with a significant disposal cost.

9.2 Activated carbons and absorbents

The high moisture contained in Victorian brown coals makes them extremely porous. Much of this porosity and the associated internal surface area is retained after drying and carbonisation of the coal and can be further tailored to desired pore size distributions by physical and chemical treatments. Coupled with their low ash, this makes them ideal feedstocks for the preparation of products such as activated carbons, filter aids and other absorbents.

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Technology is available (Heng, 1991) to produce activated carbons from brown coal, ranging from ultra hard gold recovery (CIP) carbons to soft water treatment carbons. The small size of the local market, and the wide range of product specifications required, has slowed the commercialisation of these products. However, joint developments with international companies in the industry are being pursued

In the past, small commercial activated carbon production from briquettes was undertaken by Gas and Fuel Corporation and others (Packer and Garner, 1981). As mentioned earlier, Rheinbraun currently supplies water and gas purification systems using its brown coal char as the absorbent.

10. Conclusions

For the foreseeable future, the dominant use of brown coal, globally and in Victoria, will continue to be for power generation. The only risk is that Greenhouse gas emissions penalties are introduced which selectively target existing brown coal plants. New power generation technologies, such as IDGCC or MTE/IGCC offer major improvements in efficiency and reductions of Greenhouse gas emissions. These systems will be ready for the next generation of power stations and have substantial prospects for implementation in other countries with low rank coals.

Interest in the longer term is being shown in briquettes, HTD slurries and other upgraded fuels from brown coal by coal importing countries such as Japan. They anticipate a trend of higher prices, lower quality and reduced availability of internationally traded black coals and see low rank coals as relatively under utilised. An extension of this approach is the encouragement and assistance being given to indigenous use of low rank coal resources, particularly by Indonesia and China, to reduce pressure on international energy markets.

Although the volume of coal currently consumed in value-added products is small, there is significant potential for further growth to provide economic benefits and broaden the industrial base of the brown coal industry.

However, before any new commercial brown coal development proceeds, extensive pilot scale tests should be conducted on a selection of samples representing the range of coal quality in the deposit. This work should involve consultants and organisations familiar with low rank coals and the unique technical challenges associated with their processing, storage and transport.

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11. References

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Banks, P. J. and Burton, D. R., 1989. Press Dewatering of Brown Coal: Part 1 – Exploratory Studies. Drying Technology 7 (1989) 3 pp. 443-475.

Bennett, B. B., 1961. Aspects of the Operation and Development of the Lurgi High Pressure Gasification Plant at Morwell, Australia, 8th Int. Gas Conf., Int. Gas Union, Stockholm, 1961.

Clark, D., 1984. Combustion of Brown Coal for Electricity Generation. Aus IMM Monograph Series 11 Victoria’s brown coal, pp. 127-154.

Davey, B., 2001. Private Communication.

Hashimoto, N. and Tokuda, S., 1997. CWM Production from Upgraded Low Rank Coals. APEC Coal Trade and Investment Liberalisation and Facilitation Workshop, Jakarta, Aug 1997.

Heitműller, R. J., Fisher, H., Sigg, J., and Hartlieb, N., 1999. Lignite-fired Niederaussem K aims for Efficiency of 45% and More. Modern Power Systems, May 1999, pp.53-66.

Heng, S., Perry, G. J. and Allardice, D. J., 1991. Upgrading of Low Rank Coal to Carbon Products. 16th Biennial Lignite Symposium. Billings Montana, May 1991.

Johnson, T. R. and Young, B. C., 1999. Integrated Drying and Gasification: Technology for Power Generation from Brown Coal and Biomass. Proc. Australian Inst. Energy National Conference, p. 239, Melbourne, Dec 1999.

Johnson, T. R., 2001. A Competitive Gasification Technology for Brown Coal. VGB/EPRI Conference - Lignite and Low Rank Coals: “Operational and Environmental Issues in a Competitive Climate”, Wiesbaden, Germany, 17-18 May 2001.

Kennedy, G.L., 1971. Production of Hard Char from Brown Coal Briquettes by Australian Char Pty Ltd. Proc. Inst. Briquetting and Agglomeration Vol. 12 Vancouver, 205, Aug 1971.

McIntosh, M., 1999. Has Brown Coal a Future for Fuelling Power Generation? Proc. Australian Inst. Energy National Conference, p. 277, Melbourne, Dec 1999.

McIntosh, M., 2001. Advanced Power Generation Technologies for Lignite including Repowering of Boiler Plant. Australia-China Workshop on Clean Power from Coal with Maximised Efficiency, Taiyuan, China, 27-30 August 2001.

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Packer, L.J., and Garner, L.J., 1980. High Grade Granular Activated Carbons from Victorian Brown Coal, 5th Int. Conf. on Coal Research, Dusseldorf, p. 255, Sept. 1980.

Perry, G. J., Allardice, D. J., Bates, A. J. and Hutchinson, J. C., 1994. The Briquetting of Victorian Brown Coals. Clean Coal Technology Seminar, Jakarta Oct 1994.

Porter, C. R., Rude, T,. Voss, R. and Weeda, J., 2001. Lignite Vision 21: A Public/Private Partnership with a Vision for the Future – The North Dakota Lignite Partnership. VGB/EPRI Conference - Lignite and Low Rank Coals: “Operational and Environmental Issues in a Competitive Climate”, Wiesbaden, Germany, 17-18 May 2001.

Potter, O.E., Beeby, C.J., Fernando, W.J.N. and Ho, P., 1983-84. Drying Brown Coal in Steam-heated Steam-fluidised Beds. Drying Technology 2(2) 219.

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