• Energy Research

The replacement of coal-based fuels by renewable fuels such as charcoal is an attractive way to reduce net greenhouse gas emissions from the integrated steelmaking route. Our previous studies have indicated that the potential for savings in net CO2 emissions ranges from 32 to 58 percent, with use as a BF tuyere injectant being the largest application. The current study considered the combustibility of four types of charcoal in comparison with PCI coal under simulated BF raceway conditions. The major findings were that burnouts under standard conditions (air-cooled coaxial lance, O/C = 2.0) were comparable or better than that of the high volatile matter PCI coal studied, and a comparison with the trend line for burnout with injectant volatile matter previously established for coals, indicated that the hardwood charcoals studied had burnouts 40% (abs) higher than those of equivalent coals, and the softwood charcoal studied was higher again. A study of the effects of oxygen enrichment indicated that small increases were effective, and particularly so for the least combustible charcoal. Overall, the burnout results indicated that higherthan- coal injection rates should be possible in industrial practice, and in combination with the previous heat and mass balance results, they indicated the potential for increased BF productivity. The brief study of the combustion of coal-charcoal mixtures indicated good combustibility and predictable burnouts. The microscopic examination of both the charcoal injectants and their combustion chars indicated that there was significant fragmentation of the charcoals during combustion, boosting their already high surface areas and combustibility.

The replacement of coal-based fuels by renewable fuels such as charcoal is an attractive way to reduce net greenhouse gas emissions from the integrated steelmaking route. Our previous studies have indicated that the potential for savings in net CO2 emissions ranges from 32 to 58 percent, with use as a BF tuyere injectant being the largest application. The current study considered the combustibility of four types of charcoal in comparison with PCI coal under simulated BF raceway conditions. The major findings were that burnouts under standard conditions (air-cooled coaxial lance, O/C = 2.0) were comparable or better than that of the high volatile matter PCI coal studied, and a comparison with the trend line for burnout with injectant volatile matter previously established for coals, indicated that the hardwood charcoals studied had burnouts 40% (abs) higher than those of equivalent coals, and the softwood charcoal studied was higher again. A study of the effects of oxygen enrichment indicated that small increases were effective, and particularly so for the least combustible charcoal. Overall, the burnout results indicated that higherthan- coal injection rates should be possible in industrial practice, and in combination with the previous heat and mass balance results, they indicated the potential for increased BF productivity. The brief study of the combustion of coal-charcoal mixtures indicated good combustibility and predictable burnouts. The microscopic examination of both the charcoal injectants and their combustion chars indicated that there was significant fragmentation of the charcoals during combustion, boosting their already high surface areas and combustibility.

Abstract Charcoal produced from sustainably grown biomass can be used to reduce the net CO2 emissions from iron and steel making operations. However careful control of pyrolysis conditions is required to produce charcoal with the necessary properties to optimise substitution for coal and coke in specific applications. The density of charcoal is an important property to control in order to minimise transport and handling costs as well as control of charcoal reactivity and strength. In this work the density of charcoal has been increased through compression of Blackbutt wood chips during pyrolysis. The true density of charcoal prepared under compression of 0.5 MPa and at a heating rate of 2 °C/min was found to increase with pyrolysis temperature, especially at temperatures higher than 450 °C. This increase in true density is likely to be due to restructuring of the graphitic structure at high temperatures. The true density of charcoal was found to be independent of compressive pressure during pyrolysis (0.056–4.0 MPa). The porosity of charcoal increased linearly with pyrolysis temperature and ranged from 0.24 at 300 °C to about 0.46 at 700 °C. The apparent density of charcoal prepared under a compressive pressure of 0.5 MPa was about 1000 kg/m3 and had minimum between 400 and 600 °C. This is similar to the apparent density of metallurgical coke. The results suggest that specially prepared charcoal could be a viable substitute for coal and coke in steelmaking applications which require a dense carbon product.

Abstract Charcoal produced from sustainably grown biomass can be used to reduce the net CO2 emissions from iron and steel making operations. However careful control of pyrolysis conditions is required to produce charcoal with the necessary properties to optimise substitution for coal and coke in specific applications. The density of charcoal is an important property to control in order to minimise transport and handling costs as well as control of charcoal reactivity and strength. In this work the density of charcoal has been increased through compression of Blackbutt wood chips during pyrolysis. The true density of charcoal prepared under compression of 0.5 MPa and at a heating rate of 2 °C/min was found to increase with pyrolysis temperature, especially at temperatures higher than 450 °C. This increase in true density is likely to be due to restructuring of the graphitic structure at high temperatures. The true density of charcoal was found to be independent of compressive pressure during pyrolysis (0.056–4.0 MPa). The porosity of charcoal increased linearly with pyrolysis temperature and ranged from 0.24 at 300 °C to about 0.46 at 700 °C. The apparent density of charcoal prepared under a compressive pressure of 0.5 MPa was about 1000 kg/m3 and had minimum between 400 and 600 °C. This is similar to the apparent density of metallurgical coke. The results suggest that specially prepared charcoal could be a viable substitute for coal and coke in steelmaking applications which require a dense carbon product.

AbstractThe pros and cons of various types of biomass dryers have been documented in this paper. Using dry biomass significantly reduces the cost of handling, transportation and pyrolysis. The main choices for drying biomass are rotary dryers, flash dryers, stationery bed dryers and fluidised bed dryers. The drying medium can be hot air, hot air mixed with steam, and/or superheated steam. A typical example for wood chip drying using a financial model is described, including the environmental performance. The energy requirements and greenhouse gas emissions have been estimated for drying biomass. From this study, it is evident that increasing temperature will decrease drying time and increase throughput but not necessarily decrease the drying cost. This is due to higher energy use and higher cost of capital inputs such as loading/unloading and heat plant. Thus, low drying temperature can be used if throughput is not a key issue for an operation. The global warming potential of the biomass drying process 9.2kg CO2-e/t of oven-dry biomass. This assumes that wood waste is used as fuel and drying is on a moving belt dryer. If this dry biomass is used in a power station as fuel for steam boiler, there is a significant reduction potential of CO2 emission from a typical black coal-fired power plant due to fuel switching. This assumes that trees are planted to produce this biomass sustainably. Environmental impacts of any dryer type should be considered for selection in addition to its traditional techno-economic performance.

AbstractThe pros and cons of various types of biomass dryers have been documented in this paper. Using dry biomass significantly reduces the cost of handling, transportation and pyrolysis. The main choices for drying biomass are rotary dryers, flash dryers, stationery bed dryers and fluidised bed dryers. The drying medium can be hot air, hot air mixed with steam, and/or superheated steam. A typical example for wood chip drying using a financial model is described, including the environmental performance. The energy requirements and greenhouse gas emissions have been estimated for drying biomass. From this study, it is evident that increasing temperature will decrease drying time and increase throughput but not necessarily decrease the drying cost. This is due to higher energy use and higher cost of capital inputs such as loading/unloading and heat plant. Thus, low drying temperature can be used if throughput is not a key issue for an operation. The global warming potential of the biomass drying process 9.2kg CO2-e/t of oven-dry biomass. This assumes that wood waste is used as fuel and drying is on a moving belt dryer. If this dry biomass is used in a power station as fuel for steam boiler, there is a significant reduction potential of CO2 emission from a typical black coal-fired power plant due to fuel switching. This assumes that trees are planted to produce this biomass sustainably. Environmental impacts of any dryer type should be considered for selection in addition to its traditional techno-economic performance.