ENERGY CONSUMPTION IN EXISTING AND MODEL NEWSPRINT MILLS

The process steam and electricity consumptions for newsprint mills are shown in Figures 5 and 6. The steam and electricity consumptions were calculated from data in the CPPA Energy Monitoring Report for 1999 [2]. The mills in the CPPA survey used TMP and/or recycled fibre, with an average recycled fibre content of about 20 percent.

In Figure 5, the process steam consumption varied from 2.52 to 12.69 GJ/t, greater than the steam demand of 0.64 GJ/t for the modern newsprint mill. This large variation results from differences in the amount of steam used in the process and differences in heat recovery of refiner steam. Recycled fibre content also affects the steam consumption, since no refiner steam is available for heat recovery in a recycled fibre mill.

The process electricity consumption, shown in Figure 6, ranged from 1220 to 3660 kWh/ADt. The variation in electricity consumption is due in part to variations in recycled fibre content and TMP refining energy. The average electricity consumption was 2850 kWh/ADt. Most mills used more electricity than predicted for the modern TMP/DIP newsprint mill, 2430 kWh/ADt. However, most of the electricity used in a TMP/DIP newsprint mill is used for TMP refining. Thus, much of the higher energy input is likely attributable to the wood species employed and the grade of paper produced. Changes in pumping and agitation throughout the mill may result in a 5 percent overall drop in electricity consumption, or a potential savings of about $5.70/ADt.

The fossil fuel purchases for newsprint mills are shown in Figure 7. The fossil fuel purchases are generally higher than those for the modern mill due to greater steam usage in the process and lower heat recovery. Some mills use large amounts of hog fuel for steam generation, reducing fossil fuel purchases.

The modern mill provides most of its steam requirement by heat recovery under normal operating conditions. Fossil fuel, 0.80 GJ/t, is needed only to provide backup steam during upset conditions. The average newsprint mill purchased 3.56 GJ/t of fossil fuel in 1999, consisting of 1.80 GJ/t of natural gas and 1.73 GJ/t of fuel oil and other fossil fuels. It also purchased 0.90 GJ/t of steam. The modern mill has $16.69/ADt lower thermal energy (fossil fuel and steam) costs than the average Canadian mill, assuming that the purchased steam was produced with natural gas.

Thus, there is also considerable potential for operating cost savings by optimizing energy usage in newsprint mills. Possible savings in fossil fuels for an individual mill can be estimated in the same way as for kraft mills. Possible savings in electricity are more difficult to estimate, since the large electricity use for refining is governed by product quality requirements.