Energies 2021 , 14 , 1161
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corresponding to 10–25% energy (steam) consumption reduction in papermaking. This technology is in the demonstration phase with TRL 7 [15,43,47]. • Condebelt drying (CD): This is a replacement of the current drying section, in which the paper web is dried in a drying chamber between two steel belts instead of on traditional steam-heated cylinders, achieving higher dryer rates and efficiency. This dryer improves fiber properties such as strength (20–60% increasing), smooth surface, dimensional stability, and moisture resistance. With Condebelt drying, the same strength values can be achieved with recycled fibers as with fresh fibers in conventional drying. The CD reduces energy consumption by 15% (1.6 GJ steam per ton of paper and 20 kWh electricity per ton of paper). This technology is in the demonstration phase with TRL 7–8 [15,43,47]. • Gas-fired dryers (GFD): Gas-fired dryers are an alternative to the current drying drums heating by steam, in which the same method is applied but the drums are heated by combustion inside the drum. This process has a much higher efficiency (energy efficiency increase from 60–65% in steam-operated, compared to 75–80% in gas-operated), and higher temperatures are achieved, resulting in higher drying rates and a faster process. This method reduces the drying energy consumption by 10–20% and increases the production rate by up to 20%. The technology is still in the pilot stage with TRL 6–7, and has low CAPEX since it is an adaptation of the technology used today [15,43,48]. • Dry sheet forming (DSF): A new method of forming which results in large reductions of drying energy. In this method, the paper is formed without the addition of water to the pulp. The sheet is supported by an air jet and a solution of resigns is sprayed on the surface to help to form the paper sheet. This forming method is only suitable for tissue or hygienic paper since the surface smoothness decreases and the thickness has higher variations, but the resulting paper is soft. It is estimated that by using this technology, 50% of the drying energy requirement (fuel used for heat production) can be saved, but the electricity consumption may increase 150 to 250 kWh per ton of paper in an air-layered system to maintain the airflow and motor drive for the equipment. This technology is semi-commercial for the production of special products and will be further developed in the near future for the production of standard paper grades. The TRL of this technology is near 7 [15,43,47]. • Direct electric heating (DEH): DEH can contribute to the electrification of the steam supply of the P&P industry by replacing fossil fuels (especially natural gas) with electric boilers with an efficiency of 90%. Since electric boilers exist and are com- mercially available, this technology can be easily installed in P&P mills. Since the energy demand for paper production by applying this technology is the same with current production processing (and only fossil fuels are replaced by electricity), the feasibility of this option strongly depends on the power grid capacity to achieve such a high load increase without increasing the use of fossil fuels. The generation of a CO 2 -free electricity grid would lead to complete decarbonization of the P&P sector by electrification options [41,45,49]. The abovementioned technologies are applied as single technologies (no technology combination) in the relevant paper grades shown in Table 6. Steam cycle washing, impulse drying, Condebelt drying, and direct electric heating are used in integrated writing paper mills and gas-fired dryer, and dry sheet forming in the non-integrated writing paper and integrated tissue paper mills. The effects of every single technology on the individual paper grade were analyzed using the developed model. The specific energy (heat and electricity) consumption and specific CO 2 emissions of paper grade utilizing the technology were compared with the current situation of the selected paper grade, shown in Figure 7.
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