Energies 2021 , 14 , 1161
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Table9. Cont .
Estimated Energy Saving
Estimated Emission Reduction
Typeof Technology
TRL
Description
Ref.
Process
Supercritical CO 2 is a new process design that can be applied to pulp and paper drying sections. In this technology, the pulp or paper is dried by changing pressure and temperature, which consumes lower energy than the traditional method. Replacing the air needed to remove water from the paper in the drying section with superheated steam can improve heat recovery (full recovery) and increase energy efficiency. The recovered steam can be used in the next steps of paper production. Dryers are heated with hot gases from gas combustion (which may occur in the drum) instead of steam. This dryer technology improves energy efficiency by 75–80% compared to the 65% of the usual system. This technology is mainly used in the packaging and board paper drying sector. Boost drying by utilizing two combined drying technologies (condensation and press) improves drying efficiency by 12%, and reduces energy consumption and drying time. Paper is dried by exposure to microwave radiation. This technology increases the drying rate and reduces the total energy consumption.
Supercritical CO 2
45%
20% 3
[13]
Superheated steam drying
[13]
50%
25% 3–5
Drying
Gas-fired dryers
10–20% 6–7
[15,18,43]
Boost dryer
12% 6–7
[15,18,43]
Microwave Drying
[15,18,43]
12% 3–4
In Austria, in line with other European paper production sites, the P&P sector has started to improve its energy efficiency in recent decades. The implementation of best available technologies as the use of waste heat recovery systems, the switch from fossil fuels to on-site biofuel production in integrated mills (Figures 3 and 4), and the use of recycled paper in paper processing in the Austrian P&P sector have led to a reduction of CO 2 emissions by around 30% in the last twenty years (Figure 5) [9,25]. However, to reach the target of decarbonization of the entire industry by 2050, direct emissions remain a challenge for the sector, and further efforts in the P&P sector are needed. Regarding the state-of-the-art situation of the Austrian P&P sector, mentioned in the previous paragraph, six technologies were selected from those listed in Tables 8 and 9 in this study, and their individual impacts on the Austrian P & P sector were evaluated. The technology selection was based on three criteria: 1. The selected technologies are applied in one of the energy-intensive steps: Chemical pulping and drying, which use approximately 67% of the total energy required for paper making [10,15] of paper production. In this case study, they have a high energy saving potential (electricity/steam) and influence directly or indirectly CO 2 emissions. 2. The technologies have a high TRL (min 6) and have been proven on an industrial scale or are almost commercial in the short and medium-term. 3. Finally, not yet employed in the Austrian P&P sector. The chosen technologies are as following: • Steam cycle washing (SCW): This is a new washing technology that uses steam to wash the pulp after chemical pulping instead of water. As a result, it is possible to produce higher consistency and stronger (10%) pulp, and reduce energy for pumping and heating in the thickening, screening, and evaporation operations. The global effect is a reduction of 30–40% of the energy needed (fuel or steam consumption) for kraft pulping (overall, not just digesting). This process is in demonstration and is close to the commercialization phase with a TRL 7–8 [15,43,46]. • Impulse drying (ID): This technology is not a replacement for the current drying section. It is a modification in the press section, which consists of pressing the paper against a high-temperature element. This way, the dry content in the paper may become as high as 65%, resulting in an energy saving of 0.44–0.9 GJ per ton of paper,
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