Annex 47 Complementary information to source category 7a Pulp and Paper Production
Overview of recent revisions
No revision to emission factors was made.
Derivation of emission factors
Release to Air
The major emissions to air from pulp and paper mills originate from steam generation and not from the manufacturing process itself.
Pulp and paper mills burn lignin (from the pulping process) for generation of energy utilized in the mills. In addition, residual wood chips bark chips, etc., can be burned in the boilers. For both, sulfite and Kraft mills, average volumes are 6,000-9,000 m³/t of pulp and concentrations around 0.41 ng I-TEQ/m³ (range: 0.036-1.4 ng I-TEQ/m³) (CEPA-FPAC 1999). The higher emissions are based on measurements from coastal areas in British Colombia where salt-loaded wood enters the pulp mills. For black liquor boilers from non-wood fiber processing pulp mills, no information on PCDD/PCDF concentrations has been found. Thus, presently it has to be assumed that the same emission factors as for wood-processing plants apply. However, it should be noted that non-wood fiber plants do not have recovery boilers.
Kraft liquor boilers are used by the pulp and paper industry to burn the concentrated black liquor. Most are equipped with some simple flue gas cleaning devices, e.g., cyclones, wet scrubbers or electrostatic precipitators (ESP). Average stack concentrations are between 0.004 and 0.008 ng I-TEQ/m³ (CEPA-FPAC 1999). For the Toolkit, the emission factor as determined by NCASI and used in the US-EPA Reassessment of 0.07 μg TEQ/t of black liquor will be used (US-EPA 2000, Volume 2, 5-26).
US-EPA (1998) reported emissions from pulp mills burning sludge and wood residues in wood boilers (stoker with ESP) between 0.0004 and 0.118 μg I-TEQ/t of sludge or wood, respectively. The default emission factor for pulp mills burning sludge or wood residue is 0.06 μg TEQ/t of feed (i.e., sludge or wood residue). There will be no differentiation between different technologies, e.g., flue gas cleaning devices.
In Canada, salt-laden hog fuel (waste wood) boilers are operating at coastal pulp mills. A typical boiler consists of a combustion furnace, steam superheaters, a generating bank, an economizer, an air heater, multicyclones, electrostatic precipitators or wet scrubbers, and a stack. Hog fuel has 0.06%-2.2% NaCl and 49%-66% moisture. Stack emissions ranged from 0.01 ng TEQ/m³ to 2.8 ng TEQ/m³ (at 11% O2) (Duo and Leclerc 2004). Tests performed at a fluidized bed hog-fuel boiler gave an average PCDD/PCDF emission of 0.295 ng TEQ/Nm³ (at 11% O2). Upon co-firing of 5% tire-derived fuel (containing 1.6% sulfur), the emissions were reduced to an average of 0.119 ng TEQ/Nm³ (at 11% O2). The hog fuel tested had 0.072-0.585% chlorine (Duo et al. 2002, Duo et al. 2003).
Kraft pulp mills have lime kilns to reburn the calcium carbonate formed during the recausticizing process. The rotary kiln operates at temperatures from 800°C at the start of the calcination reaction and 1,000-1,100°C to complete the reaction. The gas flow in the lime kiln is around 1,000 Nm³/t of pulp. Here, the emission factors for lime kilns should be used see source category 6b.
The default emission factor for wood burning at pulp mills has been derived from those determined for wood burning, see Source group 3. CORMA (2004) reported emission factors between 0.16 and 0.4 μg TEQ/t of feed for bark boilers (Class 2); thus, an default emission factor of 0.2 μg TEQ/t of feed is suggested for this Toolkit.
Release to Water
The pulp and paper industry is one of the largest water users. Sulfite mills discharge more water than Kraft mills. A modern bleach plant discharges between 15 and 20 cubic meters of water per ton of Air-dried pulp (15-20 m³/t ADt).
In 1988, in the USA, a typical pulp and paper mill used 16,000 to 17,000 gallons of water per ton of pulp produced (60-64 m³ of water/t pulp); in the EU water consumption varied between 15 and 100 m³/t. Water consumption can be reduced by increasing internal water recirculation. Typical figures for wastewater discharge are 20-40 m³ per ton of pulp. For the Toolkit, 30 m³ of water per ton of pulp produced will be used.
Concentrations in effluents ranged from 3 pg TEQ/L to 210 pg TEQ/L with a median of 73 pg TEQ/L (US-EPA 1998a). The default emission factor for Kraft bleached pulp using old bleaching sequences is 4.5 μg TEQ/t of pulp. Alternatively, the concentration in the effluent can be used and multiplied with the total mass of water discharged per year to calculate the annual release.
Replacement of Cl2 in the first bleaching stage by ClO2 will dramatically reduce the formation of 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF (below detection limits of 0.3-0.9 pg/L).
Data generated and published by NCASI (National Council (of the Paper Industry) for Air and Steam Improvement, Inc.) (1998) in the USA from 20 bleach lines at 14 U.S. Kraft mills that use complete chlorine dioxide substitution for chlorine gave 119 data pairs for 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF in pulp mill effluents. The results showed that 2,3,7,8-Cl4DD was not detected in any sample above the proposed guideline concentration of 10 pg/L. 2,3,7,8-Cl4DF was detected in two samples from the acid stage at concentrations in the range of 15-18 pg/L and in the alkaline stage at concentrations in the range 11-18 pg/L.
The default emission factor for releases from modern pulp mills utilizing chlorine dioxide will be set to 60 ng TEQ/t of bleached pulp using a conservative approach. The emission factor will be applied only if there is direct discharge into the environment. If sludge is generated, the dioxin freight will be collected in the sludge and the effluents leaving from the effluent treatment plant will have non-accountable concentrations of PCDD/PCDF.
A special case of higher concentrations has been detected in effluents from pulp mills located in coastal areas of British Columbia in Canada. Here, special operating conditions occur where salty hog is burned and where ashes are disposed in the effluent treatment plant. Any similar occurrence should be notified; at present no default emission factor for these pulp mills can be given.
Pulping of pentachlorophenol treated wood may increase the concentrations in the effluent although no data have been published. Any use of PCP or of PCP-treated wood in the pulp and paper industry should be notified.
Much higher concentrations than from wood pulping in European or American pulp mills were reported from Chinese pulp and paper mills that bleach non-wood fibers (Zheng et al. 2000). The PCDD/PCDF concentration in the wastewaters from a pulp mill in China using a bleaching sequence C-E-H was 316 pg I-TEQ/L of which 2,3,7,8-Cl4DD was 230 pg/L and 2,3,7,8-Cl4DF was 122 pg/L.
In mechanical pulp and paper mills (integrated mills, TMP), the water systems are usually quite closed in order to maintain high process temperatures. Consequently, wastewater volumes are small – 5-10 m³/ADt. No emission factors were found.
Release in Products
Products from the pulp and paper industry can be contaminated with PCDD and PCDF. The degree of the contamination depends on the technology used in the bleaching. High concentrations of PCDD/PCDF have been reported when elemental chlorine bleaching sequences have been applied. Modern technologies result in lower concentrations in the products. Replacing Cl2 with ClO2 results in a reduction of 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF concentrations to non-detectable levels. However, complete elimination of PCDD/PCDF in ECF bleached effluents and products is a question of kappa-number and purity of ClO2. With high kappa numbers and impure ClO2 (i.e. high impurities of Cl2) the probability of forming PCDD/PCDF increases.
Concentrations in pulp can be in the range from 0.6 ng TEQ/kg pulp to 200 ng TEQ/kg bleached pulp (US-EPA 1998a, Table 8-1). The median concentration applying “old technology” has been calculated to be 9 ng TEQ/kg Kraft bleached pulp. The default emission factor is 10 μg TEQ/t of Kraft bleached pulp.
Chinese bleached pulps exhibited high concentrations of PCDD/PCDF (Zheng et al. 1997, Zheng et al. 2000). Zheng et al. (2000) report 24.7 ng I-TEQ/kg of pulp for a C-E-H bleach sequence with a relatively “typical” chlorine bleach pattern (2,3,7,8-Cl4DF = 13.6 ng/kg and 2,3,7,8-Cl4DD = 2.0 ng/kg but high concentrations of 1,2,3,7,8-Cl5DD = 29.8 ng/kg and Cl6DD = 35.8 ng/kg). Zheng et al. (1997) also found high concentrations in five bleached pulp from non-wood fibers that ranged from 33.5 ng I-TEQ/kg to 43.9 ng I-TEQ/kg. These samples were characterized by very high concentrations of 2,3,7,8-Cl4DD, 1,2,3,7,8-Cl5DD, and 1,2,3,4,7,8-Cl6DD but had no quantifiable 2,3,7,8-substituted Cl4DF and Cl5DF.
Thermo-mechanical pulp (TMP) pulp in Sweden had concentrations of around 1 μg TEQ/t pulp (de Wit 1989) and between 0.17 ng I-TEQ/kg and 1.65 ng I-TEQ/kg in Germany (Santl et al. 1994a). The emission factor for TMP is 1 μg TEQ/t pulp.
Unbleached sulfite pulps have low concentrations of PCDD/PCDF. The emission factor for sulfite pulp is 0.1 μg TEQ/t pulp.
Recycled papers from waste papers with low PCDD/PCDF content has an emission factor of 3 μg TEQ/t based on information provided by CORMA (2004) and recycled pulp/paper from impacted sources, e.g., waste papers with high PCDD/PCDF content has an emission factor of 10 μg TEQ/t based on data by Santl et al. (1994a, 1994b).
Replacement of Cl2 in the first bleaching stage by ClO2 will dramatically reduce the formation of 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF and to 0.1-0.3 pg/g bleached pulp corresponding to 0.1-0.3 μg/t of bleached pulp.
Concentrations of PCDD/PCDF in Kraft bleached papers using free chlorine (Cl2 gas) and the respective default emission factors are 5 μg TEQ/t for cosmetic tissues, shopping bags and other consumer papers and 2 μg TEQ/t for filter papers and newspapers from primary fibers. If chlorine dioxide or total chlorine-free bleaching is utilized, the emission factor will be 0.5 μg TEQ/t.
Sulfite papers using old technologies have an emission factor of 1 μg TEQ/t paper. Applying new technology will lower the emission factor to 0.1 μg TEQ/t.
Unbleached papers have an emission factor of 0.5 μg TEQ/t.
Recycling papers will have an emission factor of either 10 μg TEQ/t for recycling papers originating from pulp made by the old Kraft process or 3 μg TEQ/t for recycling papers made of primary papers made with modern bleaching technology.
Release in Residues
The major and dioxin-relevant residues from pulp and paper mills are the pulp sludges from the wastewater treatment. Sludge production is between 14 and 140 kg of sludge produced per ton of pulp (US-EPA 1998a). The EU reports 30-60 kg of organic wastes per ton of Kraft bleached pulp and an additional 40-70 kg of inorganic wastes per ton of pulp. Unbleached pulp produces 20-60 kg dry solids per to of pulp. For the calculation of the emission factor, it is assumed that production of one ton of pulp generates 50 kg of sludge (dry matter).
Release vectors into the environment will be determined by the way the sludge is handled. Common disposal practices include landfill and surface impoundment, land application, recycling (compost, animal bedding) or incineration.
The concentrations in pulp sludge using old bleaching sequences is in the range from 2 ng TEQ/kg d.m. to 370 ng TEQ/kg d.m. with a median of 93 ng TEQ/kg sludge. The emission factor for bleached Kraft sludge is 4.5 μg TEQ/t of bleached Kraft pulp. Alternatively, the concentration in the sludge of 100 ng I-TEQ/kg sludge can be used and multiplied with the total mass of sludge disposed of per year to calculate the annual release.
Almost no difference in the concentrations of the sludge from wastewater treatment systems was found between mills using conventional delignification and those mills using oxygen delignification. The sludges have been analyzed for 2,3,7,8-substituted Cl4DD and Cl4DF as well as for all 17 2,3,7,8-substituted PCDD and PCDF congeners. The concentrations ranged from 3.8 ng TEQ/kg d.m. to 5.2 ng TEQ/kg d.m. for conventional delignification and from 1.8 ng TEQ/kg d.m. to 4.5 ng TEQ/kg d.m. for ED or ED/OD delignification (see also category 9c Open Water Dumping).
With an estimated average of 4 ng TEQ/kg d.m., the default emission factor for pulp sludge using modern technology will be 0.2 μg TEQ/t of pulp.
At a recovered paper mill, Santl et al. (1994b) found between 24.9 and 44.37 ng TEQ/kg in”the deinking sludge. Upon treatment of the effluents, the contamination in the sludge was reduced to 11.01 ng I-TEQ/kg. In this Toolkit, an emission factor of 30 μg TEQ/t sludge will be applied for the combined deinking and fiber sludges.
Especially the recovered pulp and papermaking generates a number of wastes with high organic carbon content (e.g., paper rejects, de-inking sludge, bio-solids). This waste can be landfilled or incinerated. In Europe, there is an increasing number of large plants on-site for generating steam or co-fire the sludge in power plants. The emissions from a stand-alone incinerator equipped with active carbon or zeolite injection are low in PCDD/PCDF in the range of 0.1 ng I-TEQ/m³; also co-firing of pulp sludge in large, well-operated fossil fuel power plants gave results below 0.1 ng I-TEQ/m³ (BREF 2000a). As there is no effect of the alternative fuel observed, the emission factors for sludge burning (1e Sewage sludge incineration) or for fossil fuel power plants co-firing sludge (3a Fossil fuel power plants) should be applied.
In the Canadian study on salt-loaden hog fuel boilers, concentrations in ashes were 3.80 μg TEQ/kg ash for the normal operations and 2.63 μg TEQ/kg for the tire-cofiring condition (Duo et al. 2003, Duo et al. 2002).
In this Toolkit the same emission factor as the one for wood burning in source group 3 is applied for wood/bark boilers. Data from CORMA (2004) gave an emission factor of 48 μg TEQ/t of ash for bark boilers.
The disposal of the ash should be monitored and potential releases into the environment included (uncontrolled, land spreading) or excluded (landfill).