5.1 Emission characteristics of combustion appliances
5.2.5 Water balance, condensed water chemical composition and overall system
To evaluate the effect of the scrubbing unit (scrubbing water) on the thermal efficiency of the system, and water balance calculations were conducted. The measured water vapor con-tent downstream of the condensing heat exchanger (underfloor heating at 25-30 °C) was 4.8% on average based on FTIR measurements.
Upstream of the condensing heat exchanger, the measured water vapor content was 8.4%.
The calculated relative humidities downstream of the condensing heat exchanger in both the underfloor heating and high-temperature heating cases (~ 55 °C) were 50% and 57%, re-spectively; hence, there is no risk of water condensation after the condensing heat ex-changer.
In the cases with the water scrubbing unit, the water vapor content downstream of the heat exchanger increased to 7%. The scrubber water was supplied with a flow rate of 95 g/min.
The total amount of scrubbing and condensed water that was collected after the heat ex-changer was 108 g/min, which demonstrates the strong performance of heat exex-changer in recovering a large amount of the water flux. The relative humidity in the heat exchanger outlet increased by 79%; hence, the scrubbing unit does not have a crucial effect on the thermal efficiency of the system.
In the high-temperature heating mode (~ 55 °C), there was no condensed water production downstream of the heat exchanger. With the use of a scrubbing unit, only 41% of the scrub-bing water was recovered downstream of the heat exchanger, which demonstrates a radical increase of the downstream water vapor content and, therefore, a decrease in the thermal efficiency of the whole system. Thus, the use of the scrubber is practicable only for short cleaning periods.
52
In addition, condensed water that was collected downstream of the heat exchanger was an-alysed in terms of the inorganic element content. The results demonstrated a similar chem-ical composition to that of the PM1, with the main elements of K, Na, Cl, SO4 and Zn (Figure 22). Moreover, larger amounts of Ca were found in both the PM1 and the condensed water samples. Elevated amounts of Ca were measured in the condensed water samples, which were due to the use of fresh water that contained 33 g/L Ca in the scrubbing unit.
Figure 22: Chemical composition of the condensed water. From Paper I.
53
6 Review of papers and the authors’ contributions
The experimental research that is presented in the thesis was conducted at the Fine Particle and Aerosol Technology Laboratory at the University of Eastern Finland between 2012 and 2015.
Paper Ianalysed fine particle emissions in a pellet boiler and a technique for their minimi-zation. Two experimental setups and operational settings were used. The experiments were conducted in the laboratory. The experiments were primarily designed by Associate Prof.
O. Sippula and Doc. J. Tissari. The author was mainly responsible for conducting the ex-periments and writing the manuscript. The data analysis and interpretation of the results were conducted with the assistance of Associate Prof. O. Sippula and under the supervision of Prof. J. Jokiniemi.
Paper II presents two fine particle removal techniques using the same experimental setup as in Paper I. Preliminary measurements and data calculations were conducted by the author.
The second measurement campaign was conducted by co-authors. The data were analysed and the manuscript was written by the author with support from the co-authors and under the supervision of Associate Prof. O. Sippula and Prof. J. Jokiniemi. The transmission elec-tron microscopy (TEM) analysis was conducted by Doc. A. Lähde.
Paper III describes the effective densities of the particles that were emitted during the batch and continuous combustion processes. The data that are presented in Paper III were obtained during the HICE campaign (October 2013, UEF). The author participated in the construction of the experimental laboratory setup and in the measurements with the help of the research group. Moreover, the author analysed data from the gas analysers and calculated emission factors with a support of Associate Prof. O. Sippula.
Paper IV characterized the time-resolved particulate and gaseous emissions from batch wood combustion. The data for the research topic in Paper IV, as in Paper III, were obtained during the HICE campaign. The author participated in the construction of the experimental setup and in conducting measurements. In addition, the data from gas analysers and the emission factors were calculated by the author.
54
7 Conclusions and motivation
Small-scale wood combustion generates a substantial amount of fine particle (PM1) emis-sions globally. The worldwide promotion of the use of biomass as a fuel might have unfa-vourable effects on climate and human health that are caused by the residential biomass combustion sector due to a scarcity of regulations on emissions for private sector applica-tions. The directive (2009/125/EC) regarding ecodesign requirements for solid fuel boilers was implemented beginning the 1st of January 2020. Until this day, Finland did not impose any limit values on small-scale biomass appliances; however, there are regulations that are related to fuel usage, programmes and guidelines on the chimney usage, and initiatives for changing old boilers to modern boilers.
In this thesis, residential wood combustion appliances and their contributions to the emis-sions were investigated. Multiple measurements with continuous and batch combustion sys-tems were conducted. The particulate and gaseous emissions, emission factors and their physicochemical properties were investigated to determine how to minimize their impacts on the environment and on human health and to contribute to the upcoming regulations.
This study focuses on secondary emission abatement measures. The novel condensing heat exchanger, shielded corona charger and their combination were investigated for fine particle (PM1) reduction efficiency. In addition, thermal efficiency measurements of the condensing heat exchanger were considered in this study. The fine particle emissions of both these tech-nologies were compared to the commercial boiler emissions, and their implementation in practice was also discussed.
Typically, the average emissions from the automatically controlled modern boiler were 14.9 mg/MJ with wood pellets and 22.6 mg/MJ with wood chips. Due to the efficient combustion conditions, the particulate matter emissions were composed mostly of alkali metals. The emissions from the batch-wise combustion of the softwood spruce were 48,8 mg/MJ on average. Spruce combustion generated the lowest PM1 emissions in comparison to hard-wood species. As an example, beech and birch combustion emitted 65 mg/MJ and 90 mg/MJ PM1, respectively. The spruce batch combustion PM emissions were dominated mainly by soot, organics and inorganics (Na, Zn, Fe and K).
Although the releases of solid particles from modern boilers are moderate in comparison to batch-wise combustion, the main objective of this thesis was to investigate the modern boiler in connection with emission abatement technologies to minimize particulate matter emis-sions . Two types of reduction technologies were examined, namely, the condensing heat exchanger and the shielded corona charger. These technologies and their combination were examined in terms of their PM1 emission reduction efficiencies in comparison with a con-ventional boiler.
Overall, the PM1 emission reduction efficiency for the condensing heat exchanger was 40%
in comparison to a conventional boiler. The PM1emission reduction efficiency of the com-bined condensing heat exchanger and shielded corona charger system was 82% in compar-ison to a conventional boiler. Last, comparing to a conventional boiler, the shielded corona
55
charger reduced the PM1 emissions by 88%. Consequently, although our studies generated useful information, various questions remain to be answered. Therefore, further detailed investigations should be conducted in this field. The condensing heat exchanger offers a cost-efficient solution for small-scale biomass boilers as it replaces the conventional tube exchanger. To maintain the cleanliness of the heat exchanger inlet from deposits, the scrub-bing unit must be installed, which flushes out the accumulated deposits from the heat ex-changer. However, we observed that with the use of the scrubber, the particulate matter emissions increase in comparison to a conventional boiler. Therefore, the scrubber could be used only for the known periods of time to provide pulses of water. To adapt this technology to commercial boilers, additional long-term operation measurements should be conducted.
The electrostatic precipitator is one of the most frequently used high-precipitation-effi-ciency technologies in large-scale power plants. However, the operating principle of the ESPs is also modified for small-scale appliances and can be found on the market or ready to be on the market (for example, Carola Clean Air (CCA), Germany; OEKOtube, Switzer-land; IntEleKt & Hoval, Germany). The tested shielded corona charger is an alternative to the electrostatic precipitators. However, the adjustments for the highest PM collection effi-ciency should be made. In further studies, the relationship between the wood and its quality with the respect to the particle capture by SCC should be investigated. Studies on particle sizes and particle chemical composition would provide a better understanding of the prob-lem under investigation. In our studies, SCC performed well with fine particles; however, the biomass combustion also generates ultrafine particles, and for those, the collection effi-ciency was decreased. In addition, in the future, measurements with a shielded corona charger should be conducted for a longer period of time and with various biomass fuels to demonstrate its technical feasibility in small biomass-fired boilers. The measurements should also be used to identify a cleaning solution during long usage periods. Last, in the future, it would be useful to evaluate the performance of the SCC in batch-wise combustion, where emissions are higher and not controlled as well as in continuous combustion.
56
References
Alakangas, E., Hurskainen, M., Laatikainen-Luntama, J., Korhonen, J. (2016). Suomessa käytettävien polttoaineiden ominaisuuksia. VTT Technology 258.
Antunes, A.A., Lopes de Oliveira, M.C. (2013). Corrosion in biomass combustion: A ma-terials selection analysis and its interaction with corrosion mechanisms and mitigation strat-egies. Corrosion Science, 76, 6-26.
Aragon, G., Sanz, D., Mugica, I., Rojas, E., Larrion, M., Rodriguez Maroto, J., Ramos, R., Escalada, R., Borjabad, E., and Gutierrez-Canas, Ch. (2015). Enhanced Control of Fine Par-ticle Emissions from Waste Biomass Combustion Using a Hybrid Filter. Energy & Fuels, 29, 2358-2371.
Arif, A.T., Maschowski, C., Garra, P., Käufer, M. G., Petithory, T., Trouve, G., Dieterlen, A., Sundermann, V.M., Khanaqa, P., Nazarenko, I., Gminski, R., Giere, R. (2017). Cyto-toxic and genoCyto-toxic responses of human lung cells to combustion smoke particles of Mis-canthus straw, softwood and beech wood chips. Atmospheric Environment, 163, 138-154.
Bäfver, L. S., Leckner, B., Tullin, C., Berntsen, M. (2011). Particle emissions from pellets stoves and modern and old-type wood stoves. Biomass and Bioenergy, 35, 8, 3648-3655.
Bäfer, L., Yngvesson, J., Niklasson, F. (2012). Residential Electrostatic Precipitator – Per-formance at efficient and poor combustion conditions. Energiteknik. SP Rapport:2012:42.
Bianchini, A., Cento, F., Golfera, L., Pellegrini, M., Saccani, C. (2016). Performance anal-ysis of different scrubber systems for removal of particulate emissions from a small size biomass boiler. Biomass and Bioenergy, 92, 31-39.
Blue Angel, The German Ecolabel. Stoves for Wood, DE-UZ212. Edition January 2020, Version 1.
Bologa, A., Paur, H.R., Seifert, H., and Woletz, K. (2012). Fine particle generation, evolu-tion and control by small biomass combusevolu-tion. Management of Environmental Quality An International Journal, 23,1,36-55.
Bolling, A.K., Pagels, J., Yttri, K.E., Barregard, L., Sallsten, G., Schwarze, P.E., Boman, C.
(2009). Health effects of residential wood smoke particles: the importance of combustion conditions and physicochemical particle properties. Particle and Fibre Toxicology, 6:29.
Boman, Ch., Nordin, A., Boström, D., and Öhman, M. (2004). Characterization of Inorganic Particulate Matter from Residential Combustion of Pelletized Biomass Fuels. Energy and Fuels,18, 338-348.
Brogan, R.J. Heat Exchangers. Thermopedia, A-to-Z Guide to Thermodynamics, Heat and Mass Transfer, and Fluids Engineering, 2011. DOI: 10.1615/AtoZ.h.heat_exchangers Brunner, T., Wuercher, G., Obernberger, I. (2018). 2-Year field operation monitoring of electrostatic precipitators for residential wood heating systems. Biomass and Bioenergy, 111, 278-287.
57
Camredon, M., Aumont, B., Lee-Taylor, J., and Madronich, S. (2007). The SAO/VOC/NOx
system: and explicit model of secondary organic aerosol formation. Atmospheric Chemistry and Physics, 7, 5599-5610.
Carlsson, K. Gas cleaning in flue gas from combustion of biomass. Thermal Net (2008).
Availablefrom:https://ec.europa.eu/energy/intelligent/projects/sites/iee-projects/files/projects/documents/thermalnet_gas_cleaning_in_flue_gas_from_combustion _of_biomass.pdf
Carroll, J.P., Finnan, J.M., Biedermann, F., Brunner, T., Obernberger, I. (2015). Air staging to reduce emissions from energy crop combustion in small scale applications. Fuel, 155, 37-43.
Carroll, J., Finnan, J. (2017). Use of electrostatic precipitators in small-scale biomass fur-naces to reduce particulate emissions from a range of feedstocks. Biosystems Engineering, 163, 94-102.
Chang, D.Y., Lelieveld, J., Tost, H., Steil, B., Pozzer, A., Yoon, J. (2017). Aerosol physi-cochemical effects on CCN activation simulated with the chemistry –climate model EMAC.
Atmospheric Environment, 162, 127-140.
Chang, Y.P., Tsai, R., and Sui, F.M. (1999). The effect on the thermophoresis on particle deposition from a mixed convection flow onto a vertical flat plate. Journal of Aerosol Sci-ence, 30,10, 1363-1378.
Cormier, S.A., Lomnicki, S., Backes, W., Dellinger, B. (2006). Origin and Health Impacts of Emissions of Toxic By-Products and Fine Particles from Combustion and Thermal Treat-ment of Hazardous Wastes and Materials. EnvironTreat-mental Health Perspectives, 114, 6, 810-817.
Czech, H., Miersch, T., Orasche, J., Abbaszade, G., Sippula, O., Tissari, J., Michalke, B., Schnelle-Kreis, J., Streibel, T., Jokiniemi, J., Zimmermann, R. (2018). Chemical composi-tion and speciacomposi-tion of particulate organic matter from modern residential small-scale wood combustion appliances. Science of the Total Environment,612, 636-648.
Dastoori, K., Kolhe, M., Mallard, C., Makin, B. (2011). Electrostatic precipitation in small scale wood combustion furnace. Journal of Electrostatics 69, 466-472.
Dastoori, K., Makin, B., Kolhe, M., Des-Roseaux, M., Conneely, M. (2013). CFD modelling of flue gas particulates in a biomass fired stove with electrostatic precipitator. Journal of Electrostatics, 71, 351-356.
de Best, C.J.J.M., van Kemenade, H.P., Brunner, T., Obernberger, I. (2008). Particulate Emission Reduction in Small-Scale Biomass Combustion Plants by a Condensing Heat Ex-changer. Energy & Fuels, 22,1, 587-597.
Directive 2009/28/EC. Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009 on the promotion of the use of energy from renewable source and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC. Official Journal of the European Union. L 140/16.
58
Directive 2009/125/EC on the Ecodesign of Energy-related products: TREN Lot 15-Solid fuel small combustion installations.
Ehrlich, C., Noll, G., Kalkoff, W.D., Baumbach, G., Dreiselder, A. (2007). PM10, PM2.5 and PM1.0 Emissions from industrial plants – Results from measurement programmes in Ger-many.Atmospheric Environment, 41, 29, 6236-6254.
Enestam, S., Bankiewicz, D., Tuiremo, J., Mäkelä, K., Hupa, M. (2013). Are NaCl and KCl equally corrosive on superheater materials of steam boilers?Fuel,104, 294-306.
EN ISO 17294 – 2:2003, Water quality – Application of inductively coupled plasma mass spectrometry (ICP – MS) – Part 2: Determination of 62 elements.
EN ISO 10304-1/2, Water quality – Determination of dissolved fluoride, chloride, nitrite, orthophosphate, bromide, nitrate and sulphate ions, using liquid chromatography of ions – Part 1: Method for water with low contamination (ISO 10304-1:1992); Part 2: Determina-tion of bromide, chloride, nitrate, nitrite, orthophosphate and sulphate in waste water (ISO 10304-2:1995).
Fachinger, F., Drewnick, F., Giere, R., Borrmann, S. (2017). How the user can influence particulate emissions from residential wood and pellet stoves: Emission factors for different fuels and burning conditions. Atmospheric Environment, 158, 216-226.
Febrero, L., Granada, E., Regueiro, A., and Miguez, J.L. (2015). Influence of Combustion Parameters on Fouling Composition after Wood Pellet Burning in a Lab-Scale Low-Power Boiler. Energies, 8, 9794-9816.
Flagan, R.C., Seinfeld, J.H. (1988). Fundamentals of air pollution engineering. Prentice Hall.
Fuzzi, S., Baltensperger, U., Carslaw, K., Decesari, S., Denier van der Gon, H., Facchini, M.C., Fowler, D., Koren, I., Langford, B., Lohmann, U., Nemitz, E., Pandis, S., Riipinen, I., Rudich, Y., Schaap, M., Slowik, J.G., Spracklen, D.V., Vignati, E., Wild, M., Williams, M., Gilardoni, S. (2015). Particulate matter, air quality and climate: lessons learned and future needs. Atmospheric Chemistry and Physics, 15, 8217-8299.
Gröhn, A., Suonmaa, V., Auvinen, A., Lehtinen, E.J.K., and Jokiniemi, J. (2009). Reduction of fine particle emissions with optimized condensing heat exchangers. Environmental Sci-ence and Technology43, 16, 6269-6274.
Guidelines for the design and application of particle precipitators for residential biomass combustion. Report within the scope of the ERA -NET Bioenergy Project ‘FutureBioTec’, October 2012.
Hays, M.D., Smith, N.D., Kinsey, J., Dongb, Y., Kariherb, P. (2003). Polycyclic aromatic hydrocarbon size distribution in aerosols from appliances of residential wood combustion as determined by direct thermal desorption – GC/MS. Aerosol Science, 34, 1061-1084.
59
Hartmann, H., Thuneke, K., Höldrich, A. & Rossmann, P. (2003). Handbuch Bioener-gieKleinanlagen (Manual of Small Bioenergy Plants). Tangram documents, Bentwisch, Fachagentur Nachwachsende Rohstoffe (FNR), Gülzow, 96 pp. (in German).
Hasekamp, O.P., Gryspeerdt, E. & Quaas, J. (2019). Analysis of polarimetric satellite measurements suggests stronger cooling due to aerosol-cloud interactions. Nat Commun 10, 5405.
Hellen, H., Hakola, H., Haaparanta, S., Pietarila, H., Kauhaniemi, M. (2008). Influence of residential wood combustion on local air quality. Science of the Total Environment, 393,283-290.
Heringa, M.F., DeCarlo, P.F., Chirico, R., Tritscher, T., Dommen, J., Weingartner, E., Rich-ter, R., Wehrle, G., Prevot, A.S.H., Baltensperger, U. (2011). Investigations of primary and secondary particulate matter of different wood combustion appliances with a high-resolu-tion time-of-flight aerosol mass spectrometer. Atmospheric Chemistry and Physics, 11, 5945-5957.
Hinds, W.C. (1999). Aerosol Technology: Properties, Behavior, and Measurement of Air-borne Particles. Second edition, John Wiley & Sons.
Houshfar, E., Skreiberg, O., Lovas, T., Todorovic, D., Lars, S. (2013). Effect of excess air ratio and temperature on NOx emission from grate combustion of biomass in the staged air combustion scenario. Energy Fuels, 25, 10, 4643-4654.
Hukkanen, A., Kaivosaja, T., Sippula, O., Nuutinen, K., Jokiniemi, J., Tissari, J. (2012).
Reduction of gaseous and particulate emissions from small-scale wood combustion with a catalytic combustor. Atmospheric Environment, 50, 16-23.
IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 93. Car-bon Black, Titanium Dioxide, and Talc. 2010.
Ibarra, I., Aragon, G., Gomez, I., Mugica, I., Gonzalez, J., Rodriguez Maroto, J., Rojas, E., Sanz, D., Ramos, R., Escalada, R., Borjabad, E., Gutierrez-Canas, C. (2018). Blend design tools for Medium Combustion Plants (MCP) firing biomass wastes. Waste Management, 71, 200-214.
Jalalabadi, K.H., Guzzomi, G. F., Patino, D. et al., (2017). Air staging strategies in biomass combustion - gaseous and particulate emission reduction potentials. Fuel Processing Tech-nology,157,29-41.
Jaworek, A., Krupa, A., Czech, T. (2007). Modern electrostatic devices and methods for exhaust gas cleaning: A brief review. Journal of Electrostatics65, 133-155.
Jaworek, A., Czech, T., Sobczyk, A.T., Krupa, A. (2013). Properties of biomass vs. coal fly ashes deposited in electrostatic precipitator. Journal of Electrostatics, 71, 165-175.
Jenkins, B. M., Baxter, L. L., Miles, Jr. T. R., and Miles, T.R. Combustion properties of biomass. (1998). Fuel Processing Technology, 54 pp. 17-46.
60
Johansson, L.S., Tullin, C., Leckner, B., Sjövall, P. (2003). Particle emissions from biomass combustion in small combustors. Biomass and Bioenergy,25, 435-446.
Johansson, L.S., Leckner, B., Gustavsson, L., Cooper, D., Tullin, C., Potter, A. (2004).
Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets. Atmospheric Environment, 38, 4183-4195.
Kaivosaja, T., Viren, A., Tissari, J., Ruuskanen, J., Tarhanen, J., Sippula, O., Jokiniemi, J.
(2012). Effects of a catalytic converter on PCDD/F, chlorphenol and PAH emissions in res-idential wood combustion. Chemosphere, 88, 3, 278-285.
Kelz, J., Brunner, T., Obernberger, I., Jalava, P., Hirvonen, M.R. (2010). PM emissions from old and modern biomass combustion systems and their health effects. Published in:
Proc. of the 18th European Biomass Conference and Exhibition, May 2010, Lyon, France, ISBN 978-88-89407-56-5, pp. 1231-1243, ETA-Florence Renewable Energies (Ed.), Lyon, France.
Kortelainen, M., Jokiniemi, J., Nuutinen, K. et al., (2015). Ash behavior and emission for-mation in a small-scale reciprocating–grate combustion reactor, operated with wood chips, reed canary grass and barley straw. Fuel, 143, 80-88.
Kortelainen, M. (2019). Fine particles and gas emissions from small-scale biomass combus-tion: temporal variation and influence of fuel type. Academic dissertation. Report Series in Aerosol Science, 217, University of Eastern Finland.
Kubica, K., Paradiz, B., Dilara, P. (2004). Small combustion installations – Techniques, emissions and measurements. Ispra, EUR report.
Laitinen, A., Keskinen, J. (2016). Performance of a sonic jet-type charger in high dust load.
Journal of Electrostatics, 83, 1-6.
Lamberg, H., Sippula, O., Tissari, J., Jokiniemi, J. (2011). Effects of Air Staging and Load on Fine-Particle and Gaseous Emissions from Small-Scale Pellet Boiler. Energy & Fuels, 25, 4952-4960.
Lamberg, H., Nuutinen, K., Tissari, J., Ruusunen, J., Yli-Pirilä, P., Sippula, O., Tapanainen, M., Jalava, P., Makkonen, U., Teinilä, K., Saarnio, K., Hillamo, R., Hirvonen, M.R., Jokiniemi, J. (2011). Physicochemical characterization of fine particles from small-scale wood combustion. Atmospheric Environment, 45, 7635-7643.
Lamberg, H., Tissari, J., Jokiniemi, J., Sippula, O. (2013). Fine Particle and Gaseous Emis-sions from Small-Scale Boiler Fueled by Pellets of Various Raw Materials. Energy & Fuels, 27, 7044-7053
Lanzerstorfer, Ch. (2015). Cyclone fly ash from a grate-fired biomass combustion plant:
Dependence of the concentration of various components on the particle size. Fuel Pro-cessing Technology, 131, 382-388.
Leskinen, J. (2015). Physical characterization of source specific nanoparticles. Academic dissertation. Report Series in Aerosol Science, 177, University of Eastern Finland.
61
Liu, H., Chaney, J., Li, J., Sun, Ch. (2013). Control of NOx emissions of a domestic/small-scale biomass pellet boiler by air staging. Fuel,103, 792-798.
Meiller, M., Zach, J., Jakuttis, M., Hornung, A. (2015). Development of electrostatic precipitator for small scale biomass furnaces. Conference paper.
Melissari, B. (2014). Ash related problems with with high alkali biomass and its mitigation
Melissari, B. (2014). Ash related problems with with high alkali biomass and its mitigation