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Coalmining will take on a whole new future with the prospect of converting our vast lignite reserves into fuel. Mark Rogers talks to Solid Energy on its ‘coal to liquid’ vision through ‘ignite’ technology. Solid Energy, through the technology of Australian company Ignite Energy Resources, is developing its capacity to convert lignite and biomass resources into fuel.
“The Ignite technology is slightly further back in its development path,” says Gamble. However, in comparison to the more developed indirect processing method, the Ignite company system has advantages of increased efficiency and fewer waste products. The indirect process first produces a synthesis gas (an H2 and CO mixture), which then goes through a Fischer-Tropsch reaction. The Ignite process takes lignite, containing carbon, and uses water as a super critical solvent to produce hydrocarbon molecules. The water performs two functions. First, it breaks up structures around the carbon molecule. Second, water provides hydrogen for the hydrocarbon reaction. This hydrocarbon, which is a chain of carbon molecules surrounded by hydrogen, produces an oily coal. A product separation step then occurs, with the output of oil and char. Char is the solid material that remains after light gases such as coal gas and coal tar have been extracted from a carbonaceous material during the first stages of combustion. Further stages of combustion (with or without char deposits) are known as gasification reactions. If biomass is used exclusively as the input, only oil is produced. Due to no char output, there is no need for the separation step at the back end. To upgrade this oil to a transport fuel, refining is required. The expectation is that the oil will be blended into either an existing refinery or will need hydro-processing. Estimates are that one tonne of lignite feedstock will produce one barrel of coal oil (approximately 159 litres) and 300kg of char. For biomass, the conversion yield is significantly higher due to no char output. For each tonne of biomass, two barrels of oil (approximately 318 litres) is expected. As a technology, ‘ignite’ has the potential to deliver a number of benefits. “Firstly, it can be scaled” Gamble explains. “One disadvantage with indirect gasification technologies is that to get economies of scale, you need a significant scale plant at the first step. Ignite can be built at a pilot demonstration level initially, and scaled up incrementally.” For Solid Energy, this avoids significant capital costs associated with international scale plants, while enabling gradual development as knowledge of the technology increases. From the community view, it provides opportunity to understand the plant, and feel comfortable with the effects of it, before further growth occurs. “Secondly, it has a significantly lower energy requirement to convert or upgrade the product. An indirect gasification process requires high energy inputs, around 1500-1600 degrees Celsius, to produce the syngas output. However, the ignite process converts the product at a significantly lower temperature.” Another advantage is the carbon footprint is significantly lower than most alternatives. With excess carbon reporting as char, it is not being emitted during processing. As a saleable product, the CO2 energy in the char can be used for economic benefits, with a value return through its use in home heating. Finally, the ignite technology runs on both lignite and biomass. “Interestingly, if you talk to Ignite Energy Resources, they don’t consider lignite a coal. They consider lignite ancient biomass. You’ve got modern biomass, which is wood, and you’ve got your ancient biomass, which is lignite. “Their process works across both of those products. So, the pilot scale plant we are looking at bringing to New Zealand can potentially run on wood waste, on lignite, or a combination of the two.” This ability to handle both modern and fossil biomass as a feedstock will allow Solid Energy to manage the carbon signature impact. Ignite Energy Resources currently runs a small scale plant in Sydney. The next stage for development in New Zealand is a pilot plant. While still relatively small, it would be a step up from the Sydney plant. This new plant, if run continuously, would produce between half a million and a million litres of oil and around 6,000 tonnes of char per annum. In terms of feedstocks, run solely on coal the input would be around 20,000 tonnes a year. Alternatively, if biomass was the sole input the quantity would be approximately 6000 tonnes per annum. As Gamble explains, there is somewhere between 12 and 15 billion tonnes of lignite deposits nationally. The majority is in Southland, with around a billion tonnes in Otago. “If it is a plant that we want to use multi-feed, or run predominantly on lignite, then we would look to locate it in Southland.” Due to lignite in Southland being shallow, it would be extracted through conventional mining techniques. With little overburden, the operation is completed with a ‘moving mining footprint’. Overburden removed from the area about to be mined is replaced on the area where extraction has just occurred. This is rehabilitated into farmland. Solid Energy also has a number of biomass sites around the country. “There is potentially an opportunity for us to locate a pilot plant run solely on biomass at one of those sites” says Gamble. Biomass in New Zealand is predominantly radiata pine, and sourced from by-products. Waste products from the ignite process are minimal, with CO2 being the main by-product. Minimised through manufacture as char, the remaining carbon is captured for biosequestration. After capture, CO2 is pressurised until it becomes a liquid. This is pumped through high pressure pipelines into cavities at least 900 metres underground. This depth provides sufficient pressure to maintain CO2 in liquid form. Significant research of these ‘carbon reservoirs’ is necessary prior to any injection, ensuring capacity and competency requirements are met. Solid Energy says it is looking at a range of possibilities for sequestration. The focus is on maintaining a reasonable proximity to the coal resource due to this being where CO2 is produced. This will save on transportation, providing both economic and environmental benefits.
Energy NZ Vol.4 No.5 September-October 2010 |
“Ignite as a technology takes a low-rank coal, lignite in New Zealand terms, and produces two products with high energy contents, one a coal oil and the other a char,” explains Brett Gamble (pictured), general manager new energy, of Solid Energy. This is achieved through a system closely related to direct liquefaction. Solid Energy normally looks for technologies that are at commercial scale and proven elsewhere in the world.