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Concrete In Australia : March 2012
Concrete in Australia Vol 38 No 1 53 3.0 CO2 EMISSIONS DUE TO MANUFACTURE OF ALKALI ACTIVATORS 3.1 Sodium hydroxide Sodium hydroxide is generally produced concurrently with chlorine through the chlor-alkali process in Australia, and the products NaOH and Cl2 are almost equally produced through the process, by mass ratio of 1.18:1 (this compares similarly with 14 based on production in the US and Europe). Following audits of energy use by the authors, the electricity use by Australian manufacturers in their membrane cell is 2800 kWh per tonne of chlorine. is data was utilised to estimate the CO2-e emission results per kg of NaOH, as summarised in Table 3. e total emission estimate of 1.915 kg CO2-e per kg NaOH is considerably greater than 1.0 reported in 17. 5.2 Sodium silicate e method of sodium silicate production in Australia was confirmed by manufacturers as via melting silica sand and soda ash, although none of the manufacturers were willing to disclose any specific information about energy usage or emissions from the process. Fawer et al 18 completed an extensive LCI for the production of sodium silicate by this process and thus the values from that report are used here. Fawer et al 18 completed an extensive inventory of the energy consumed for the production of five types of sodium silicate, including the type of sodium silicate usually specified in geopolymer concrete; namely, sodium silicate liquor consisting of 44-48% solid and weight ratio SiO2/Na2O of 2.0. Our CO2-e estimates from the energy consumptions outlined in 18 were analysed using NGA 20 and the results are shown in Table 4. Fawer et al 18 also compiled a list of additional air emissions from the process which they attribute to chemical reactions and transport. ese are also shown in Table 4. e total emission estimate of 1.514 kg CO2-e per kg sodium silicate is significantly higher than 1.0 reported in 17. Fawer 18 did not include the energy expended during extraction of raw Emission Unit Electricity used in cell per tonne NaOH 1.285 kWh Emissions from cell 1.581 kgCO2-e Proportion of cell electricity used in process 115.8 % Overall emissions from electricity 1.830 kg CO2-e Percentage of cell electricity used in fuel 25.3 % Energy used on fuel 0.325 kWh Overall emissions from fuel 0.086 kg CO2-e Total Emissions (VIC) 1.915 kg CO2-e Table 3. Emission estimates from NaOH manufacture. Table 4. Estimates of emissions arising due to sodium silicate manufacture 17. Emissions arising from energy expended during manufacturing Energy Flow (MJ/ 1000 kg) Emissions (kg CO2-e/kg) Electricity 3118 1.065 Coal 296 0.027 Oil (heavy) 9 0.001 Oil (average/light) 456 0.033 Diesel oil 144 0.010 Gas 1270 0.076 Others 78 0.009 Total 5371 1.222 Emissions caused by Intermediates and Transport Air Emissions (kg/1000 kg) Emissions (kg CO2-e/kg) Carbon Dioxide (CO2) 288.7 0.289 Methane (CH4) 0.128 0.003 Total 0.292 Grand Total (kg CO2-e/kg) 1.514