Combustion of sludge in Fortum s plants with possible phosphorus recycling. Anton Marmsjö Victor Hoffman - PDF

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Combustion of sludge in Fortum s plants with possible phosphorus recycling Anton Marmsjö Victor Hoffman Master of Science Thesis EGI MSC EKV1030 Combustion of sludge in Fortum s plants with possible

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Combustion of sludge in Fortum s plants with possible phosphorus recycling Anton Marmsjö Victor Hoffman Master of Science Thesis EGI MSC EKV1030 Combustion of sludge in Fortum s plants with possible phosphorus recycling Victor Hoffman Anton Marmsjö Approved Examiner Reza Fakhraie Commissioner Fortum Värme Supervisor Reza Fakhraie Contact person Eva-Katrin Lindman Abstract The management of waste is by all means a great challenge to any society. In Sweden, the past decades has seen legislation progressing in congruence with concerns over environmental stress from inefficient waste management. The legislative changes aim primarily to promote waste reduction and better waste utilization. Sludge is a waste-type from different industrial processes and is unfortunately of limited reuse and recycling-value, but sludge combustion for energy recovery appears promising. Also, the oftentimes high phosphorus content in sludge strengthens the potential of extracting phosphorus from combustion ashes. The heat and power industry has shown great interest in sludge combustion. Fortum has a set of different sludge types to choose from as well as many different options available based on where and how the sludge can be incinerated. Yet there are many inherent problems, but also operational benefits, of combusting sludge. These factors combined make the venture multifaceted and therefore not straightforward. Based on this, this thesis is a preliminary study aiming to assess the possibility of combusting sludge in Fortum s existing or future facilities, along with possible phosphorus recovery from the combustion ashes. The study was based on applying either sludge mono- or co-combustion. The scenarios evaluated were; firing tonnes of digested sewage sludge, tonnes of fibrous sludge and tonnes of digestate which all are pertinent sludge amounts in this study. Co-combustion involved firing these together with the base fuels fired in Fortum s grate furnace and fluidized bed boilers in Brista and Högdalen CHP plants. The mixing yielded new characteristics of the combustion input, such as a lower heating value, which were vetted against the boilers capability to handle these. Mono-combustion was compared economically with co-combustion to assess investment profitability. The phosphorus concentration in the ashes from the mixes was determined as well in order to assess the possibility for viable extraction. In addition, proper sludge pretreatment methods were examined. The results showed that co-incineration of tonnes digested sewage sludge was possible in boiler P6 in Högdalen and B2 in Brista. These generated an economic gain with an internal rate of return of 96,3 % and 96,4 % respectively. It was possible to co-incinerate tonnes of fibrous sludge in boilers B1 and B2 in Brista as well as P6 although economic gains were only seen in B1, where the internal rate was 87,5 %. Co-incinerating tonnes of digestate was possible in all boilers except P3 assuming that the similar boilers P1 and P2 in Högdalen can incinerate the sludge in tandem. The incineration of digestate yielded an economic gain for these boilers with an internal rate ranging from 25,7 % for P1 and P2 in tandem to 102,6 % for B1. Although mono-combustion is a practical solution it was found not to be an economically feasible alternative under prevailing economic conditions. The results also indicated that NO x and SO x formation increased in the raw flue gases when co-firing sludge, as also was the case with flue gas volume flow and flue gas water vapor. Fossil CO 2 emissions decreased for all waste fired boilers when co-combusting sludge. Digested sewage sludge and digestate increased combustion ash amounts in all cases, whereas fibrous sludge only did this in B1. All sludge types were found to be beneficial for reducing the risk of corrosion and agglomeration, but digested sewage sludge was remarkably more so than digestate and fibrous sludge. The phosphorus concentration in the co-combustion ashes was deemed insufficient for viable phosphorus extraction, but was promising when firing digested sewage sludge in B1. The concentration was sufficient in a mono-combustion application when firing digested sewage sludge and digestate. Overall environmental impacts are however dubious. There needs to be further investigation in order to properly assess these. Sammanfattning Hanteringen av avfall är en stor utmaning i alla samhällen. I Sverige har lagstiftningen de senaste decennierna utvecklats i takt med ökad oro över miljöbelastningen från ineffektiv avfallshantering. I första hand syftar lagändringarna till att främja avfallsminimering och bättre avfallsutnyttjande. Slam är en typ av avfall från olika industriprocesser och har dessvärre begränsat värde för återanvändning och återvinning, men slamförbränning för energiutvinning verkar lovande. Även den i många fall höga fosforhalten i slam ger en potential att utvinna fosfor ur förbränningsaskorna. Kraft- och värmeindustrin har visat stort intresse för slamförbränning. Fortum har olika slamtyper att tillgå och många olika alternativ gällande var och hur slammet ska förbrännas. Det finns också problem, men även förbränningstekniska fördelar, kopplat till slamförbränning. Tillsammans gör dessa faktorer satsningen mångfacetterad och därför inte helt självklar. Detta examensarbete är en förstudie som syftar till att bedöma möjligheten att förbränna slam i Fortums befintliga eller framtida anläggningar, tillsammans med eventuell återvinning av fosfor från förbränningsaskorna. I studien undersöktes slamförbränning, antingen monoförbränning eller förbränning tillsammans med andra bränslen. Scenarierna som utvärderats innefattar förbränning av ton rötslam, ton fiberslam och ton rötrest vilka är relevanta mängder för denna studie. Samförbränning innebär att dessa blandas och eldas tillsammans med basbränslena i Fortums rosterpannor och fluidiserade bäddar i kraftvärmeverken i Brista och Högdalen. Slamblandningen ger upphov till nya egenskaper hos det inmatade bränslet, till exempel ett lägre värmevärde, vilka jämförs mot pannornas kapacitet att hantera dessa. Monoförbränning jämfördes med samförbränning för att bedöma dess ekonomiska konkurrenskraft. Fosforhalten i askan från blandningarna bestämdes även för att bedöma fosforutvinningspotentialen. Dessutom har lämpliga förbehandlingsmetoder för slam undersökts. Resultaten visar att samförbränning av ton rötslam var möjlig i panna P6 i Högdalen och B2 i Brista. Dessa gav en ekonomisk vinst med en internränta på 96,3 % respektive 96,4 %. Det var möjligt att samförbränna ton fiberslam i panna B1 och B2 i Brista samt panna P6 även om ekonomiska vinster bara visades i B1, där internräntan blev 87,5 %. Samförbränning av ton rötrest var möjligt i alla pannor förutom P3 förutsatt att pannorna P1 och P2 i Högdalen kan förbränna slammet i tandem. Förbränning av rötrest gav en ekonomisk vinst i dessa pannor med internräntor mellan 25,7 % för P1 och P2 tillsammans och 102,6 % för B1. Även om monoförbränning kan vara en praktisk lösning är det inte ett ekonomiskt försvarbart alternativ under rådande ekonomiska förhållanden. I studien gavs det även indikationer på att uppkomsten NO x och SO x i rågaserna ökade vid samförbränning med slam, samt att även rökgasvolymflöde och mängden vattenånga i rökgaserna ökade. Fossila CO 2 utsläpp minskade för de avfallseldade pannorna vid samförbränning. Rötslam och rötrest gav en ökning av mängden aska i alla pannor, medan fiberslam endast ökade denna i B1. Alla slamtyper var fördelaktiga att förbränna för att minska risken för korrosion och agglomerering men rötslam var anmärkningsvärt bättre i det avseendet jämfört med rötrest och fiberslam. Fosforhalten i samförbränningsaskorna bedömdes vara för låg för lönsam fosforutvinning, men var lovande vid rötslamsförbränning i panna B1. Koncentrationen var tillräckligt hög vid monoförbränning av rötslam och rötrest. Det är dock oklart vad den totala miljöpåverkan blir vilket skulle behövas utredas vidare. Acknowledgement We would like to thank Eva-Katrin Lindman for giving us the opportunity to work on this project and for all the help and advice she has provided. To be out in the industry and see Fortum from the inside has truly been a fantastic experience. Additionally we would like to thank Mikael Ljung and Per-Eric Jacobsson for showing us the CHP plants in Högdalen and Brista during our study visits. We would also like to thank our supervisor at KTH, Reza Fakhraie, for being patient with us and giving us advice and help in this thesis. Other employees and consultants have also provided great support and guidance throughout the thesis work. These are, without any internal order; Solvie Herstad Svärd, Johan Alsparr, Ola Axelsson, Harald Svensson, Jan Hedberg, Jacob Held, John Cook, Christer Andersson and Johan Fahlström. Table of Contents 1 Introduction Objectives Method Limitations Background Boilers Fluidized bed Grate furnace Boilers for sludge combustion Operational issues concerning boilers Flue gas cleaning Nitrogen oxides (NO x ) reduction systems Particle removal systems Scrubbers Additional desulfurization for FB Flue gas condensation Fuels Biomass and biomass derived fuels Municipal solid waste MSW PTP Fortum s plants Högdalenverket Bristaverket Sludge Sewage sludge Digestate from biogas production (from food wastes) Fibrous sludge Drying and dewatering of sludge Soil nutrients in sludge Regulations on sludge as an agricultural fertilizer Waste classification Burning sludge separately (mono-firing) Concluding remarks on sludge mono-combustion Mixing sludge with other fuels (co-firing)... 38 4.1 FB combustion Grate furnace combustion Concluding remarks on co-combustion Phosphorus recycling Sludge combustion in Fortum s case Calculation models Sludge mix and LHV determination Distribution of fly ash and bottom ash Combustion table for flue gas flow Drying Combustion related key values for assessing effects on boiler operation Phosphorus Environmental considerations Economic calculations Results Scenario 1 Combust all DSS from Henriksdal Scenario 2 Combust all digestate Scenario 3 Combust all fibrous sludge Scenario 4 Mono-combustion Summary Sensitivity analysis Discussion Conclusions Future work Bibliography Appendices Appendix 1: Combustion table... 77 List of figures Figure 1: The effects of increased air velocity in a fluidized bed (Martin, 2013) Figure 2: A Foster Wheeler BFB boiler (Eija & Flyktman, 2001) Figure 3: Alholmens Kraft s CFB boiler in Pietarsaari, Finland (Laboratory of Energy Engineering and Environmental protection, 2003) Figure 4: A schematic diagram of a sloped grate furnace for biomass combustion (Wellons Fei corp, 2012) Figure 5: A schematic diagram of a multiple hearth furnace (Aselaide Control Engineering, 2013) Figure 6: Layout of a rotary kiln plant from Minpro AB (Minpro AB, 2014) Figure 7: Primary fractions of MSW at Högdalenverket in Stockholm (Avfall Sverige, 2012) Figure 8: Stoker capacity diagram for P1 and P2 at Högdalenverket (Lindman, 2014) Figure 9: Stoker capacity diagram for P3 at Högdalenverket (Lindman, 2014) Figure 10: Stoker capacity diagram for P4 at Högdalenverket (Lindman, 2014) Figure 11: Stoker capacity diagram for P6 at Högdalenverket (Ljung, 2014) Figure 12: Stoker capacity diagram for B2 at Bristaverket (Lindman, 2014) Figure 13: Presence of metals in sludge from Henriksdal sewage treatment plant between (Thuresson & Haapaniemi, 2005) (Haglund & Olofsson, u.d.) Figure 14: Schematic image of different forms of water in sludge (Linder, 2001) Figure 15: Tanner s triangle (Flaga, u.d. b) Figure 16: Sludge water removal process (Flaga, u.d. b) Figure 17: Results on amount of deposits from the projects Agglobelägg 2 and Agglobelägg 3 (Herstad Svärd, et al., 2011) Figure 18: Key values for boiler P6 and B2. P6 Sludge mix: 26 % DSS, 74 % PTP. B2 sludge mix: 28 % DSS, 72 % industrial waste Figure 19: Key values for boiler P1 & P2 and P4. P1 & P2 sludge mix: 16% digestate, 84% MSW. P4 sludge mix: 9% digestate, 91% MSW Figure 20: Key values for boiler P6 and B1. P6 Sludge mix: 12% digestate, 84% PTP. B1 sludge mix: 6% digestate, 94% biomass Figure 21: Key values for boiler B2. Sludge mix: 13% digestate, 87% industrial waste Figure 22: Key values for boiler B1. Sludge mix: 11 % fibrous sludge and 89 % biomass Figure 23: Effect of IRR when unforeseen annual costs are added to economic calculations in Scenario Figure 24: Effect of IRR when unforeseen annual costs are added to economic calculations in Scenario Figure 25: Effect of IRR when unforeseen annual costs are added to economic calculations in Scenario List of tables Table 1: Taxes for different fuels in Sweden 2013 (Energimyndigheten, 2013) Table 2: General energy related tax levels and fees 2013 (Energimyndigheten, 2013) Table 3: Comparison between biomass and other fuels (KTH Department of Energy Technology, 2009) Table 4: Compositional analysis of the biomass fuel used at Bristaverket (Herstad Svärd, 2014) Table 5: Mean compositional analysis of MSW incinerated at Högdalenverket, food waste and a subsequent calculation of MSW without food waste (Avfall Sverige, 2012) (Bohn, et al., 2011) Table 6: Mean compositional analysis of the PTP combusted in P6 (Lindman, 2013a) Table 7: Specifications of the blocks at Högdalenverket (Djurberg, 2011) (Fortum, 2013) Table 8: Specifications of the blocks at Bristaverket (Fortum Värme, 2013) (Djurberg, 2011) (Jacobson, 2014) Table 9: Boiler design specifications based on fuel data (Jacobson, 2014) Table 10: Mean compositional analysis of dewatered digested sewage sludge from Himmerfjärdsverket (Bäfver, et al., 2013) Table 11: Compositional analysis of a digestate from a dry digestion process using food wastes from NSR AB as substrate (Bohn, et al., 2011) and an analysis of a sample taken by the authors from Tekniska Verken s biogas plant in Linköping (BELAB AB, 2014) Table 12: Compositional analysis of fibrous sludge from Holmen paper mill in Hallstavik (Herstad Svärd, 2014) Table 13: Macro- and micronutrients (Hansson & Johansson, u.d.) Table 14: Regulations concerning sewage sludge to be used on farmland (Hansson & Johansson, u.d.) Table 15: Fuel power required for each boiler to maintain 100 % load Table 16: Income per tonne of sludge. Estimated based on alternative prices for other uses (Fortum, 2014b) Table 17: Estimated costs for ash transport and disposal for the different boilers Table 18: General cost of base fuels combusted in P1-P4, P6, B1 and B2 (Fortum, 2014b) Table 19: Technical results Scenario Table 20: Economic results Scenario Table 21: Technical results Scenario Table 22: Economic results Scenario Table 23: Technical results Scenario Table 24: Economic results for Scenario Table 25: Results Scenario Table 26: Economic results from dividing ca tonnes DSS between two or three boilers Nomenclature Abbreviations ar As received BFB Bubbling fluidized bed CFB Circulating fluidized bed CHP Combined heat and power daf Dry, ash-free db Dry basis DS Dry substance DSS Digested sewage sludge Eo1 Light fuel oil (Eldningsolja 1) ESP Electrostatic precipitator WESP Wet electrostatic precipitator FB Fluidized bed FGR Flue gas recirculation GROT Tree branches and tops (from Swedish Grenar och toppar ) IRR Internal rate of return LFO Light fuel oil MSW Municipal solid waste NO x Nitrogen oxide emissions (NO and NO 2 ) O&M Operation and maintenance PTP Paper, wood and plastics (from Swedish Papper, trä och plast ) PVC Poly Vinyl Chloride RDF Refuse derived fuel REACH Registration, Evaluation, Authorization and restrictions of Chemicals RT-chips Chipped recycled waste wood (from Swedish returträflis ) SC Staged Combustion SCR Selective catalytic reduction SNCR Selective non-catalytic reduction SO x Sulfur oxide emissions Tonne Metric ton (1000 kg) wt-% Weight percentage WtE Waste-to-Energy öre 1/100 SEK Symbols and parameters α β bottom,ash β P,bottom,ash ΔAsh ΔAsh disposal ΔBase fuel Ψ η boiler η el η mech Alpha value, produced electricity over total energy Fraction of total ash that becomes bottom ash Fraction of total phosphorus in ash that end up in the bottom ash Relative difference in ash, sludge mix over base fuel Change in amount of ashes that will need to be disposed Change in amount of base fuel needed for the sludge mix Mixing percentage on total weight basis Boiler efficiency Generator efficiency Mechanical efficiency (electricity generation) η HEX Ash bottom Ash fly C C ash disposal C base fuel C drying C inv C op c base fuel c bottom ash c fly ash c inv DR e CO2 Fossil CO2 h water I I DH I el I sludge i DH i el i P i sludge IR LHV m m sludge,ar N NPV P drying P fuel P net P max P max,bottom ash P max,fly ash R R t t op u V P X Y Z Heat exchanger efficiency Massflow of ashes ending up as bottom ash Massflow of ashes ending up as fly ash Total annual costs Total annual costs of disposing ΔAsh disposal in co-combustion cases Annual cost of acquiring ΔBase fuel in co-combustion cases Costs for auxiliary drying of sludge Total cost of investment Annual operational costs for a mono-combustion plant Per tonne cost for base fuel Per tonne cost for disposing bottom ashes Per tonne cost for disposing fly ashes Investment cost per tonne of sludge to handle on a yearly basis Discount rate Fossil carbon emission factor for waste fuels MSW and PTP Annual change in fossil CO 2 emission Heat of vaporization for water Total annual income Income from district heat sales Annual income from electricity sales Annual income/cost from sludge Per MWh income for district heating Per MWh income for electricity sales Per kg value for phosphorus Per tonne income/cost for sludge Internal rate Lower heating value Mass Annual amount of sludge to be received Massflow Economic lifetime of the investment Net present value Power required for drying Fuel power Net power Maximum phosphorus concentration in the total ash amount Maximum phosphorus concentration in bottom ashes Maximum phosphorus concentration in fly ashes Revenue Total revenue year t Yearly operational time of the boiler Moisture content Value of the phosphorus in the ashes Wet mass fraction of a substance Dry mass fraction of a substance Component to be mixed on total or dry basis Subscripts base fuel dry mix sand sludge sludge,dried The base fuel for the investigated boiler Dry basis Mix of sludge and base fuel Bed sand for FB boiler The investigated sludge Sludge after the dryer 1 Introduction Human activities are affecting our natural environment now more than ever before. Growing public concerns over increasing greenhouse gas emissions has seen a significant surge recently, but much of what shapes energy politics today springs from energy security related concerns. The apprehension stems from the consequences of unsustainable energy systems, which disturb natural ecosystems and have led to alarming climate changes. Derived from this, social and socioeconomic systems may decay if solutions are not found and applied in the near future (Stigka, et al., 2014). In April of 2013, an article written by a group of 15 environmental experts was published in Dagens Nyheter, one of Sweden s biggest newspapers. In it, they stressed the importance of a resource effective society as one of the most effective ways to reduce environmental impact, stating inter alia that The waste management sector also has a unique opportunity to not only reduce their own environmental impact, but also help other sectors reduce theirs through increased recycling and reuse. (Finnveden, et al., 2013, English translation by Anton Marmsjö). Waste management and heat and power production are in some aspects joint ventures where many wast
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