Hi Geoff, South Africa exports some 65m tons of iron ore per year. All of this ore is >6.3mm as fines block gas flow in blast furnaces. We have millions of tons of fines on dumps as a result. We have developed a biogas from biomass process that can provide methane into the iron ore industry. Initially this gas will be compressed and used to replace diesel in the mine haul trucks. The second use for the gas is to supply a pellet plant that feeds an HBI (hot briquetted iron) plant. Milling and upgrading the fines (upgrading removes clay and other impurities) raises the iron content in the milled ore to about 67% Fe. These fines are made into 10 to 15mm diameter pellets. Carbon is added to the mix when making the pellet. The pellet is then fed to the HBI plant. Methane (CH4) is steam reformed to syngas - CO and H2 and fed to the HBI plant. The H2 and CO react with the iron oxide stripping away the oxygen. Typically pellets leaving the HBI have about 93% metallisation. While still hot, the reduced pellets are fed to compactors that produce a high density briquette. The briquettes are cooled and exported.
When the briquettes are fed to a blast furnace, they have three major benefits: - they require less carbon to strip out the balance of oxygen - they bring their own carbon into the blast furnace - the high strength of the briquettes reduces mechanical breakdown in the blast furnace providing low pressure drop gas flow paths All three benefits result in high blast furnace productivity that uses less coke. Coke is devolatalised coal as volatiles cause operational difficulties in blast furnaces. Coking coal is rare compared to thermal coal and its price is significantly higher. Hence a saving in coke and an increase in production results in a reduction in the cost of hot metal production. This addresses part of the story. The second part is that there is always a solid fraction coming out of anaerobic digestion. These solids will be filtered, dried and pyrolysed with pyrolysis gas used as a thermal energy source while the char is sent to pelletization for mixing in with the iron ore. The main problem with replacing coke in blast furnaces is the amount of char(coal) required. One industry we have smelts silicon. As silicon reports to the "slag" in the furnaces, the purity is affected by all elements that report to the slag fraction. This includes the ash fractions in coal. As a result, coal is not suitable as a reductant. Charcoal has the double benefit of high fixed carbon and low ash making it the only realistic carbon source that can be used. These guys have charcoal retorts spread across the entire country. The cost of charcoal delivered to the furnace consequently has a high transport element. As charcoal has low density, this simply exacerbates the transport problem. Needless to say, charcoal for the metallurgical industry is a major challenge. I simply cannot see how the world can grow enough biomass to be able to supply the requirements adequately as long as there is "cheap" coal available. There - my 2c worth. Rex Zietsman --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _______________________________________________ Gasification mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/gasification_lists.bioenergylists.org for more Gasifiers, News and Information see our web site: http://gasifiers.bioenergylists.org/
