THE MODEL NEWSPRINT MILL
The model newsprint mill consists of a pulp mill and paper machine along with an effluent treatment facility. The fibre furnish for a modern newsprint mill would consist of thermomechanical pulp (TMP) and/or recycled fibre depending on the fibre availability and market requirements. The energy requirements for pulping and paper making operations are described in the following sections.
TABLE IV Omitted
Thermomechanical Pulp Mill
The energy consumption of a modern TMP mill is shown in Table IV. The mill produces TMP for newsprint manufacture from softwood chips. Jackson and Wild estimated the energy consumption for a 500 BDMT/D single-line TMP mill [5]. The total specific refining energy was 2400 kWh/BDMT, which is typical for TMP from black spruce chips for newsprint production [5]. For comparison, reference may be made to a detailed industrial audit complied by Nygaard [6] for Swedish TMP mills, mostly producing for newsprint. Average external power demand for these mills was similar, about 2420 kWh/ADt.
TMP refining energy is affected by wood species; common Canadian species such as pine require more energy than black spruce [7]. Refining energy is also sensitive to paper grade, with higher-quality mechanical printing paper grades requiring higher energy. Though there are new processes for reducing refining energy somewhat [8], consistent industrial performance has not yet been achieved.
Heat recovery is used in modern TMP newsprint mills to recover some of the refining energy in the form of clean pressurized steam. The clean steam production in Table IV was calculated for heat recovery of the steam from the mainline and rejects refiners by a reboiler [5]. The estimated steam production for the modern TMP mill, 5.5 GJ/ADt, is similar to the possible steam production calculated by Nygaard, 5.2 GJ/ADt, for the same specific refining energy [6]. The average excess steam production for Swedish TMP mills in 1994 was lower, about 4.4 GJ/ADt [6].
Recycled Fibre Mill
The electricity consumption of a modern recycled fibre mill producing de-inked pulp (DIP) for newsprint manufacture is 400 kWh/ADt [3]. The average external power demand for Swedish recycled fibre mills in 1994 was lower, about 330 kWh/ADt [6]. The steam consumption of a modern recycled fibre mill is 0.8 GJ/ADt, taken from the model recycled fibre mill in Nygaard [6]. The average fuel heat demand for Swedish recycled fibre mills in 1994 was lower, about 0.3 GJ/ADt [6].
Paper Machine
The energy consumption for a modern newsprint paper machine is shown in Table V [9]. The average electricity consumption for Swedish newsprint paper mills in 1994 was higher, about 440 kWh/ADt [6]. Talja et al. measured 344 kWh/ADt electricity consumption for a modern paper machine producing SC paper [10].
