POLLUTANT ATMOSPHERIC EMISSIONS FROM PORTUGUESE KRAFT PULP MILLS

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1 Chemical Eng. Dept., ISEL From the SelectedWorks of João F Gomes 1997 POLLUTANT ATMOSPHERIC EMISSIONS FROM PORTUGUESE KRAFT PULP MILLS João F Gomes Available at:

2 ELSEVIER The Science of the Total Environment 208 (1997) Pollutant atmospheric emissions from Portuguese Kraft pulp mills Jo50 C.M. Bordadoa**, Jo50 F.P. Gomesb Chemical Engineering Department, Technical University of Lisbon, Institute Superior Tkcnico, Au. Rovisco Pais, 1096 Lisboa Codex, Portugal benvironmental Technologies Center, Institute de Soldadura e Qua&lade, Apartado 119, 2781 Oeiras Codex, Portugal Received 26 June 1997; accepted 29 September 1997 Abstract This paper describe systematic work done in the field of atmospheric emissions from Portuguese Kraft pulp mills. This study led to the determination of emission factors from stationary sources that proved to be an important tool in assessing the need for investment in air pollution abatement equipment Elsevier Science B.V. 1. Introduction At present, bleached Kraft pulp is one of Portugals largest exports due to the availability of pine and eucalyptus forests in the country. The existence of these natural resources led to the development of specific methods of pulp production from eucalyptus that has been applied since pulp mills began to operate in the late 1950s. Since that time production has been gradually increased with the construction of newer plants to face the demands from external markets. The revamping of the mills enabled them to evolve *Corresponding author. with alternative and improved technological processes that resulted in greater productivity, a decrease in raw material consumption and a more environmentally friendly operating process. Eucalyptus forests are not common in Europe, since eucalyptus grows mainly in Australia, Africa and South America. Portugal is the main European producer of eucalyptus pulp. This particular type of wood can be used for the production of pulp and writing paper with very good characteristics in terms of strength and whiteness. It has also been noticed that emissions from pulp production from conifers are higher than from eucalyptus, mainly in terms of volatile organic compounds (USEPA, 1986). Particular attention is focused upon the concern /97/% Elsevier Science B.V. All rights reserved. PZZ SOO (97)

3 140 J.C.M. Bordado, J.F.P. Gomes / The Science of the Total Environment 208 (1997) for the environmental impact of pulp production in Portugal. Mills and Environmental Authorities are taking measures to reduce the negative environmental impacts which require a precise characterisation of pollutant s emission from Kraft pulp plants (Borg et al., 1974). 2. Review of the most significant emissions to the atmosphere occurring from the Krah process The production of pulp by the Kraft process results in atmospheric emissions which are mainly composed of dusts, solid particulate, steam, carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen oxides, hydrogen sulphide and mercaptans, such as methylmercaptan, dimethylmercaptan and dimethyldisulphide. The three main stationary sources of particulate emission are: recovery boiler stacks; limestone kiln stacks; and also the stack from the smelt dissolving tank. These stacks are specific to this production process. Other sources include other existing boilers, not specific to the Kraft process, such as auxiliary boilers and bark fired boilers. The particulate emissions from recovery boilers and smelt tank stacks consist mainly of sodium salts. The limestone kiln stack also produces calcium salts. In both cases the emissions result primarily from the entrainment of ashes and other solids carried by turbulent fumes. The typical odour of these plants is due to the emission of reduced sulphur compounds, such as mercaptans and hydrogen sulphide, substances that have very low detection levels in terms of smell. Of these compounds, the most significant is hydrogen sulphide, which is emitted from various diffuse sources within the process that include leaks and exhausts from evaporators, digestors, scrubbers and retention tanks and also the limestone kiln stack. Sulphur dioxide is emitted as an oxidation product formed in the recovery boiler. Carbon monoxide and carbon dioxide are emitted from stationary sources connected to processing units as a result of the combustion of materials which take place in units, such as recovery boiler, lime kiln, bark and other auxiliary boilers. The American Federal Environmental Protection Agency (USEPA, 1986) gives as typical emission factors for these compounds, 1.0 kg/ton of air dried pulp (tad) for the recovery boiler and 0.5 kg/tad of produced pulp for the lime kiln. This difference is mostly due to the different values of flame temperatures occurring within these units. Pinkerton (1993) calculated the emission factors for stationary sources from the Kraft process in the United States, based on measurements made from 1980 to 1990, as indicated in Table 1, which are only indicative to Portugal, In Europe, the Best Available Technologies for pulp production were defined and the most recent emission factors (Virtanen et al., 1995) are shown in Table 2. Apart from the pollutants already mentioned, which are considered the traditional atmospheric emissions from the Kraft process, others are now being considered, such as volatile organic compounds WOCs), dioxins (PCDDS) and furans (PCDFs). Recent studies have shown these non-traditional pollutants to be noxious to human health and the environment (Cutbirh et al., 1993). The USEPA recently revised the Clean Air Act and classified pollutants, such as VOCs as Hazardous Air Pollutants (HAPS), which include, PCDDs and PCDFs. These compounds are now classified under the Clean Air Act Amendment. When this bill was approved little knowledge existed about the emission of these particular compounds by the Kraft pulping process, thus an extensive inventory study took place in the state of Texas aiming to detect at least 90% of VOCs emitted from the Kraft process (Cutbirh et al., 1993). Table 1 Emission factors for 1990 (kg/tad pulp) in the USA Source SO, NO, Recovery boiler Direct contact Indirect contact Limestone kiln Smelt tank Biomass boiler Wood (conifers) kg/tad wood

4 J.C.M. Bordado, J.F.P. Gomes /The Science of the Total Environment 208 (1997) Table 2 Emission factors reflecting best available technologies applicable for European pulp in both ECF (elemental chlorine free) and TCF (total chlorine free) plants Source Recovery boiler Smelt Limestone kiln Auxiliary boiler Particulate (ECF) o.oi-0.1 (TCF) SO (ECF) (TCF) NO Note: values presented as kg/tad except for auxiliary boiler which is in kg/ton of fuel and Bkg NO,/tad. W Mercaptans Portuguese legislation, as in law Pt. No 286/93, characteristic pollutants from this process at the defines the air emission limits which are de- following stacks: recovery boiler, biomass and scribed in Table 3. It should be noted that the auxiliary boiler, smelt tank and lime kilns (Games, emission limits are defined as concentration and 1994). USEPA methods were followed and Annot as emission factors, the exception being the dersen stack sampling equipment according to limit for the smelt dissolving tank. these methods was used. The ISQ laboratory is the only Portuguese laboratory accredited by the Portuguese authori- 3. Atmospheric emissions from Portuguese Kraft ties to perform this type of test, pulp mills Project Corinne-Air was launched by the European Commission in 1985 (Carneiro et al., 1985). This project aims at listing the atmospheric emissions from stationary sources within heavy industries. Portugal was chosen as a pilot country and the field work was performed from 1987 to This inventory included the stationary sources from the Kraft pulp mills. The experimental work was carried out by the Chemical and Environmental Laboratory of ISQ. In the case of Kraft pulp mills it consisted of an exhaustive campaign of sampling and analysis of The 1987 inventory has been annually updated by request of the pulp mills and also as an inspection task performed for the governmental authorities. Table 4 presents the global Portuguese emissions from the heavy industries referred to in 1987 and also the emissions from the Kraft pulp mills for 1987 and The first year the emission inventory was available for Portugal was 1987 and 1995 is the year when all the investments made by the pulp mills for air pollution control were already put into practice, due to an agreement between the pulp sector and the Ministry of the Environment. Table 3 Air emission limits according to Portuguese legislation Source Particulate SO, NO, H,S Recovery boiler Smelt Limestone kiln Auxiliary boiler Note: values presented as mg/nm3 except for the smelt dissolving tank which is in mg/kg of dry black liquor. 4. Discussion The results obtained show the effect of the important investments made in pollution abatement equipment during the referred period, in the pulp sector. The investment consist of: 1. particulate abatement: optimisation and en-

5 142 J.C.M. Bordado, J.F.P. Gomes /The Science of the Total Environment 208 (1997) Table 4 Two sets of data are considered: the initial Contribution from Kraft pulp mills to global emissions inventory of 1987 and the 1995 update, after the Pollutant National (1987) Kraft (1987) Kraft (1995) completion of phase I of these investments. From this data, it can be seen that, considering Particulate the particulate emissions, the main abatement (ton/year) Not available SO, (ton/year) effort was directed to the specific sources of the NO, (ton/year) Kraft process. On the other hand the auxiliary HrS (ton/year) Not available boiler s emissions have not received as much at- The nitrogen oxides increase results from an incomplete iden- tention, which resulted in an increase of its sigtification of the sources of this pollutant in nificance in the scope of global particulate emissions. largement of electrostatic precipitators (ESP) In terms of sulphur dioxide it is evident that installed before the stacks of boilers; installa- the measures taken were not effective for limetion of ESP in limestone kiln stack lines. stone kilns and auxiliary boilers, two types of 2. Sulphur dioxide: installation and optimisation units that had their significance increased. Meanof scrubbers on limestone kiln stack lines and while, the investments made resulted in major smelt tanks. abatements of hydrogen sulphide emissions in 3. Hydrogen sulphide: collecting and burning of limestone kilns and were not so effective in recovmercaptans in limestone kilns. ery boilers. This fact could be expected as the measures The success of these measures are shown in taken for abatement of oxidised compounds often Table 5, for the distribution of emissions from the result in an increase of reduced compounds. Kraft process by pollutant and by source. The emission data combined with the respec- Table 5 Distribution of emissions from the Kraft process (referred to the total emissions presented in Table 4) Source Particulate so2 NO, HzS Recovery boiler (%I Smelt (o/o) Limestone kiln (%) Auxiliary boiler (%) Incinerator (%) Table 6 Emission factors for two Portuguese Kraft pulp mills (kg/tad) Source Particulate so2 NO, W A B A B A B A B Recovery boiler Smelt Lime kiln Auxiliary boiler Incinerator

6 J. C.M. Bordado, J.F.P. Games / The Science of fhe Total Environment 208 (1997) tive production data allows the calculation of the emission factors for the stationary sources of two of Portugals largest Kraft pulp mills for 1996, as shown in Table 6, where A is the largest plant producing bleached eucalyptus ECF (elemental chlorine free) pulp ( tad/year). B is a somewhat smaller plant producing bleached eucalyptus TCF (total chlorine free) pulp ( tad/year). These data are important in order to assess the compliance of these sources within the accepted values for the best available technologies for this particular process. Table 6 presents the latter values applicable for the units installed in both plants A and B. 5. Conclusions The data presented in Tables 5 and 6 makes it possible to study the need for further investment in air pollution abatement in each plant and on each source. For instance, it can be noted that, as a whole, the situation in both mills A and B is better than average, referring to the typical values for best available technologies as presented in Table 2. The exception occurs for limestone kiln emissions of mill A in terms of nitrogen oxides and hydrogen sulphide emissions. Also, particulate emitted from the smelt dissolving tank of mill A are outside of the interval described as the one for best available technologies. The next step in this study will be the sampling and analysis of mercaptans, as a whole and also as individual compounds, both from stationary sources and diffuse sources, such as retention tanks, evaporators and digestors. This latter study is also important to assess the viability in the collection of gases containing mercaptans and/or hydrogen sulphide and its burning in boilers or lime kilns. References Borg A, Teder A, Warnqvist B. Inside a Kraft recovery furnace - studies on the origins of sulphur and sodium emission. Tappi J 1974;57:126. Cameiro AP, Neves GC, Vasconcelos IB. Invent&i0 das emissbes de poluentes atmosf&cos. Lisboa: DGQA, Cutbirh JW, Ayer CH, Fergunson BB. Texas air emission speciation study. TAPPI Environ Conf Proc 1993;27:1993. Gomes JFP. Indicadores t&nicos de polui@o industrial. Tecno1 Qua1 1994;14:26. Pinkerton JE. Emissions of SO, and NO, from pulp and paper mills. Air Waste 1993;43:1404. USEPA. Compilation of air pollutant emission factors. vol. I. Research Triangle Park, Virtanen Y, Mietlinen P, Juntilla V. Emission factors and development in emission reduction technology. In: UETP/VTT, editor. Energy Issues in life cycle assessment, Comett II, Helsinki, 1995.