Paper360 - July/August 2014 - (Page 26)

millwise | EMISSIONS u.s. Pulp and Paper Industry emissions Improve A study that began in the 1980s shows how successful the U.S. pulp and paper industry has been in reducing atmospheric emissions JOHN E. PINKERTON During the last 30 years, the U.S. pulp and paper industry has devoted significant resources to reducing atmospheric emissions, specifically as relates to two key air pollutants: sulfur dioxide (SO2) and nitrous oxide (NOx). Beginning in 1980, the National Council [of the Paper Industry] for Air and Stream Improvement, Inc. (NCASI), began an industry-wide survey of pulp and paper mills to obtain information on SO2 and NOx emissions. New data are collected every five years.4-10 Here are some of the most recent results: total MIll eMISSIoNS Since 1980, the downward trend in SO2 emissions has been quite remarkable (Figure 1). SO2 emissions in 2010 were more than 70  percent lower than the 1980 emissions, while production is 35 percent greater. Contributing factors include greatly reduced use of fuel oil, reduction in the sulfur content of coal and oil being burned, installation of add-on SO2 control systems on boilers and improvements in energy efficiency. Figure 1. Emissions and paper production trends. Source: NCASI. 26 NOx emissions peaked in 1995 and dropped nearly 40 percent over the next 15 years, while paper and paperboard production declined only 7 percent over the same period. These reductions resulted from less use of oil and coal, declining oil and coal sulfur content, increased use of add-on NOx control systems on boilers and gas turbines, growing use of combustion modification techniques that minimize NOx emissions, improvements in energy efficiency and declining pulp, paper and paperboard production. Table 1 compares EPA nationwide emissions estimates for SO2 and NOx to NCASI estimates for pulp and paper mills from 1980 through 2010.12 As a percentage of national emissions, pulp and paper mill SO2 emissions dropped from 3.4 percent in 1980 to 2.3 percent in 2005. If the 2010 EPA projection of 7.6 million tons of SO2 is accurate, then pulp and paper mill SO2 emissions would increase to 3.1 percent of this total, a reversal of the long-term trend. Pulp and paper mill NOx emissions have ranged between 1 and 1.4 percent of the national total. eMISSIoNS FRoM boIleRS aNd GaS tuRbINeS Figure 2 illustrates the 30-year trend in boiler and gas turbine SO2 and NOx emissions versus total heat input. Boilers have been the dominant source of SO2 and NOx emissions over the entire period. SO2 emissions have dropped steadily over the period, despite rises in total heat input from 1980 to 1995. Since 1995, SO2 emissions have declined almost 50 percent, and NOx by 45 percent. These reductions can be partially attributed to a 7 percent decline in paper production over the 15-year period; however, the decline in total heat input was nearly 30 percent, suggesting a significant industry-wide improvement in energy efficiency. Paper360º JULY/AUGUST 2014 The mix of fuels burned in boilers has changed over the 30-year period. Coal, residual oil, natural gas and wood residues are the primary fuels burned in pulp and paper mill boilers. Natural gas accounts for essentially all of the fuel used in gas turbines. Table 2 shows the amounts of these fuels burned. The percentages in the table are based on average Btu values for each fuel type. Table 2 and Figure 2 show that residual fuel oil use plummeted both in amount burned and percentage of total heat input. Heat input from coal in 2010 was at the lowest level in 30 years after peaking in 1990, but coal continues to provide nearly 30 percent of the heat inputs. Natural gas usage has fluctuated, although there has been a downward trend over the past 15 years. Heat inputs from wood residues have remained fairly steady since 1985, but their contribution to total heat input has grown in the last 10 years and now accounts for the largest percentage of heat input by a considerable amount. Boiler SO2 emissions are not only a function of the amount of coal and oil burned, but also the average sulfur content of those fuels and SO2 removal by add-on control systems. The average sulfur content of coal burned in pulp and paper mill boilers declined from 2 percent in 1980 to 1.3 percent in 2010, while the average for residual oil dropped from 2 to 1.4 percent. Although coal and residual oil are the main sulfur-containing boiler fuels, distillate oil, used oil, petroleum coke, tire-derived fuel (TDF) and other fuels also contain sulfur. The use of petroleum coke and TDF has grown in recent years, while distillate oil use has declined. In 2010, these other fuels accounted for about 5 percent of total boiler heat input. Additional SO2 is formed in boilers at Kraft mills that burn sulfur-containing NCGs to reduce odorous emissions. SO2 reductions over the 30-year period can be partially attributed to increased use

Table of Contents for the Digital Edition of Paper360 - July/August 2014

Over the Wire
Pulp and Paper Innovations
Strategic Importance of Water
Making Workers Heroes
Industry Emissions Improve
TAPPI Journal Summaries
Measuring Color Online
Consolidation Watch
Knowledge Builder
Association News
What’s New on
Advertisers Index

Paper360 - July/August 2014