Processes 2021 , 9 , 1707
11of 20
TheCO 2 emissions are calculated following the methodology outlined in the ‘Calcula- tion of emissions and emission factors’ from the ‘GHG Inventory Report for the Implemen- tation of the Trading Directive’ [61]. The calculation is performed as shown in Equation (3), where Activity Data represents the energy consumed in the period under consideration. CO 2 (t) = Activity Data (TJ) · · · Emission Factor (t CO 2 /TJ) · · · Oxidation Factor , (3) The calculation of Activity Data considers the total energy supplied during the period, in terajoules, calculated with the invoiced energy data from the external natural gas supplier. The emission factor and oxidation factor correspond to natural gas [61], the fuel used by the factory to produce the steam required to dry the paper. The calculation of paper manufactured requires an indicator in the periods of reference based on European Commission [54,55] methodological guidelines. TheCO 2 emissions have been checked with annual statements of emissions by the factory; this is public data that can be checked according to the European Climate Registry Rules (the EU ETS registry) approved by the Climate Change Committee as well as other annual statements, such as the European Pollutant Release and Transfer Register (E-PRTR); this Europe-wide register provides information about environmental data from industrial facilities in European Union Member States, replacing and improving on the previous European Pollutant Emission Register (EPER), PRTR. The study is based on historical papermaking data from 10 years, which is a repre- sentative period in which there were neither major changes in machine conditions nor alterations that changed their production capacity. 3. Results and Discussion The most important subindicators are detailed in this section, and the influence of each subindicator on ‘t CO 2 /t Paper’ is analyzed. These subindicators are cold water ( Cw ) added to the boiler circuit and the temperature of blown air in the drying section enclosure hood ( Ebt ), the two elements with most significant thermal losses of this process. 3.1. Cold Water Added to the Boiler Circuit The main sources of loss in the steam and condensate loop (Il) that cause more water (Cw) to be needed by the circuit than that required by Bdr are as follows: excess blowdown in steam generators, steam traps, rotary joints in drying cylinders installed in the dryer section, losses through pump mechanical seals, valve seals, and other components, and steam flash produced in atmospheric tanks. Figure 2 shows the daily average steam production and cold water added to the circuit due to boiler blowdown in each year considered. As expected, the evolution of the consumption of steam, cold water, and blowdown follow the same trend. A similar trend can be seen for the energy losses, which decrease starting in period 4 such as the other variables mentioned, while the paper production increases (see Figure 3). The latter is important because although paper production has increased over the years, in this dryer section and in particular in the boiler circuit, the energy losses are reduced. The amount of cold water added to the boiler circuit could be a good environmental indicator that could also be used to check the efficiency of maintenance routines. In Figure 4, the factory CO 2 emissions and CO 2 losses due to the boiler circuit can be observed; starting in period 4, the CO 2 emissions and CO 2 losses decrease; the latter yields percentages of 15.7, 11.2, 7.5, 6.3, 4.8, 2.6, and 4.0 in periods 4, 5, 6, 7, 8, 9, and 10, respectively. The losses of total emissions indicated in Figure 4 represent the associated emissions regarding energy losses due to the energy contained in the blowdown water stream and the reduction in steam losses from rotary joints. The minimum reached in the last three periods indicates that the point of stability has been reached.
Made with FlippingBook Online document maker