| 1. |
- Hannl, Thomas Karl, M.Sc. 1993-
(författare)
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Fluidized bed combustion and gasification for phosphorus recovery by co-conversion of sewage sludge with biomass
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, the thermal conversion of sewage sludge has proven its applicability for managing this inevitably generated waste. The viability arises from the concomitant features of recovering energy or valuable compounds, the breakdown of potentially harmful organic compounds, the separation or immobilization of heavy metals, and the formation of volume-reduced, sanitized residues. The inorganic residue after thermal conversion of municipal sewage sludge, i.e., the ash, is generally rich in phosphorus (P). However, P in sewage sludge ash is mostly present in a chemical association that is poorly plant-available, e.g., apatite and whitlockite. Since sewage sludge ashes represent a P-rich resource, a number of different post-processing methods have been fathomed to extract P or alter its association in the ash. While extraction methods often focus on eluting P with acids, methods to alter the P-association in the ash rely mostly on thermochemical post-processing with additives. A way of enhancing the plant-availability of P in the ash is the thermochemical treatment with alkali additives, e.g., (Na,K)2SO4 and (Na,K)2CO3, leading to the formation of alkali-bearing phosphates of improved plant-availability. Providing the necessary physiochemical conditions for this phosphate alteration process, there is a potential to achieve the formation of alkali-bearing phosphates already during the thermal conversion of sewage sludge.This work investigates the potential of forming K-bearing phosphates in fluidized bed co-combustion and co-gasification processes of P-rich sewage sludge and K-rich agricultural residues. The focus was set on the fate and role of P in the interaction of the main ash-forming elements based on thermodynamic equilibrium studies, lab-scale investigations, and bench-scale fluidized bed experiments. Additionally, the benefits, e.g., fuel flexibility and high conversion rate, and ash-related risks due to interaction of ash and bed material when using fluidized bed systems are elaborated with a focus on bed material selection and investigating the operational modes of combustion and gasification.The applicability of K- and Na-feldspar bed material in a pilot-scale indirect gasification system was investigated to provide a potential substitute for commonly used bed materials such as olivine and quartz. Olivine often contains heavy metals that could contaminate recovered ashes. Quartz may react with fuel-derived K, which could hamper the targeted formation of K-bearing phosphates and lead to bed material fragmentation and bed agglomeration. The bed material analysis of feldspar used in indirect wood gasification showed significant differences in the interaction phenomena between K- and Na-feldspar with the fuel ash. While both feldspar types displayed Ca-reaction and ash deposition layers on the particle surface, the interaction of Na-feldspar with K additionally led to the formation of K-reaction layers, possibly decreasing the bed particle integrity. The results suggest that K-feldspar is the preferred bed material option in terms of process stability and limiting the potential for side reactions of K when aiming for phosphate alteration toward K-bearing phosphates.Thermodynamic equilibrium calculations (TEC) were conducted with a focus on the fate of P and melting tendencies for a wide range of chemical compositions in biomass ashes and fuel mixtures between sewage sludge and the agricultural residues wheat straw (rich in Si and K) and sunflower husks (rich in K and Ca). The results for the K-Ca-Mg-P-Si-O system were validated with literature references, and an outline of practical implications was given. The results for sewage sludge and mixtures with agricultural residues functioned as a seminal tool for fuel design in experimental investigations. The thermodynamic preference for forming alkali-bearing phosphates in competition with pure Ca-phosphates and incorporating K in silicates could be shown. The analysis of the K-Ca-Mg-P-Si-O system highlighted the influence of elemental ratios between and within the Lewis acid formers (Mg, K, Ca) and the Lewis base formers (Si, P) on the fate of P and the ash melting tendency. The TEC for sewage sludge and mixtures with agricultural residues predicted that these elemental ratios are also the determining factors in the presence of large quantities of Al and Fe.Experimental research regarding the underlying ash chemistry with a focus on the fate of P was conducted in a single-pellet reactor and bench-scale fluidized bed combustion and gasification processes. The approach used sewage sludge pellets and co-pelletized mixtures of sewage sludge with wheat straw and sunflower husks to determine the P-recovery potentials and ash-related operational risks. The parameters were chosen with relevance to practical applications of fluidized bed technologies. The experimental findings supported the TEC results in several aspects, such as the preference for Ca-phosphate formation in sewage sludge ash and the exclusion of Fe from the bulk ash matrix. However, the results also showed practical limitations for the formation of K-bearing phosphates in fuel mixture ashes. The identified limitations were the reaction of K with Si, the high stability of Ca-rich orthophosphates, and the limited interaction of ash-forming elements in char residues from gasification processes. Furthermore, the results from the fluidized bed experiments highlighted the necessity for amendments in terms of fuel selection and fuel mixing to avoid operational risks such as bed agglomeration. The results of the conducted experimental investigations suggest that using K-feldspar as bed material in sewage sludge co-conversion setups with agricultural residues might benefit the incorporation of K in the P-rich ash fractions.The results and discussions presented in this work allowed for the assessment of crucial process and fuel parameters for fluidized bed conversion systems using sewage sludge fuels and biomass fuel mixtures focusing on the formation of K-bearing phosphates. The importance of the ash transformation chemistry and its impact on selecting a suitable bed material could be outlined based on experimental and modeling data. The outcome shall assist the design of future large-scale applications in terms of a viable process and fuel design for energy and resource recovery from sewage sludge and agricultural residues.
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| 2. |
- Hannl, Thomas Karl, M.Sc. 1993-
(författare)
-
Phosphorus recovery from sewage sludge fluidized bed gasification processes
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the most sustainable pathways of sewage sludge treatment in recent years has been thermal conversion. The benefits of thermal treatment of sewage sludge are the recovery of energy or valuable chemical products, the destruction of harmful organic compounds, the separation of heavy metals from the P-rich coarse ash fraction, and the decreased and sanitized ash volume. The ashes created by these thermal conversion processes of sewage sludge are often rich in P that is mostly present in minerals with low plant-availability such as apatite. Due to the enrichment of P in the created ashes, a variety of post-processing steps have been developed to recover P from sewage sludge ashes. One proven way for the sus-tainable recovery of P from such ashes is thermal post-processing with alkaline salts, e.g., Na2SO4 or K2CO3, which was able to transform less plant-available phosphates in the sewage sludge into more plant-available alkali-bearing phos-phates. Based on these results, one could facilitate creating these phosphates with enhanced plant-availability by providing the chemical potential to form them already during the thermal conversion process of sewage sludge. This thesis aims to increase the current knowledge about the ash transformation processes of P and to suggest suitable process parameters for the alteration of the phosphate speciation in sewage sludge ashes by co-conversion with alkaline-rich agricultural residues. More specifically, the possibility of incorporating K derived from agricultural residues in phosphate structures derived from sewage sludge was evaluated with respect to the influence of the process temperature, the conver-sion atmosphere, and the fuel mixture. The studied parameters were chosen to generate knowledge relevant for fluidized bed gasification processes, with a spe-cial focus on dual fluidized bed (DFB) gasification systems.The applicability of feldspar bed materials in fluidized bed gasification systems was investigated to enable the substitution of the commonly used olivine, which often contains heavy metals (potentially contaminating recovered ashes), and quartz, which is very reactive towards fuel-derived K and potentially leads to bed material fragmentation and bed agglomeration (Paper I & II). Subsequently, the thermodynamic potential for the alteration of the P-species in sewage sludge ash during co-combustion and co-gasification processes with agricultural residues was investigated (Paper III). Thereafter, an experimental evaluation of the ash transformation chemistry in thermal conversion processes of sewage sludge with different types of alkali-rich agricultural residues in temperatures relevant for flu-idized bed technology was conducted (Paper IV & V).The methodology employed was chosen with respect to the state of technology of the specific investigated process. Paper I & II applied SEM, EDS, XRD, and thermodynamic equilibrium modeling for bed material samples derived from an industrial indirect gasifier. Paper III applied thermodynamic equilibrium calcula-tions to theoretically evaluate ash compositions resulting from co-conversion of sewage sludge and agricultural residues. Paper IV & V employed SEM, EDS, ICP-AES/MS, XRD, and thermochemical modeling on ash samples derived from single pellet lab-scale experiments.The results obtained by analysis of bed material from indirect wood gasification showed the difference in interaction mechanism for K-feldspar and Na-feldspar, most notably the enhanced disintegration of Na-feldspar by K originating from the fuel (Paper I & II). Thermodynamic models employed for fuel mixtures of sewage sludge and agricultural residues showed the thermodynamic preference for the formation of the desired alkali-bearing phosphates (Paper III). Experi-ments conducted with these fuel mixtures (Paper IV & V) supported the theo-retical findings, and the influence of temperature and process conditions could be obtained. However, practical investigations also showed that attainment of the desired ash composition is subject to significant restrictions.Derived from the elaborated results and discussions, it was possible to assess the critical process and fuel parameters for the development of up-scaled gasification processes focusing on the conversion of sewage sludge with the aim of creating improved phosphate formation in the ash. The selection of a suitable bed material in fluidized bed conversion and the transformation mechanisms defining the ash chemistry were found to be of vital importance for future applications. The pur-suit of the predefined aims in reference to P-recovery from sewage sludge has led to a multitude of suggestions for suitable process parameters that must be ad-dressed in future bench- and pilot-scale experimental runs.
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| 3. |
- Hedayati, Ali, 1984-
(författare)
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Ash transformation in thermochemical conversion of different biomass resources with special focus on phosphorus
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A great potential exists for increasing the use of bioenergy in thermochemical processes by utilizing agricultural biomass, forest residues, and sewage sludge that have high availability. Many of these biomass assortments have high ash contents with relatively high concentrations of ash-forming elements such as potassium (K), calcium (Ca), silicon (Si), and phosphorus (P). These elements can, during thermal conversion, cause several ash-related problems, such as deposit formation, slagging, and particle emissions. In particular, P has been found to play a vital role in such ash-related problems even at relatively low concentrations. In addition, ashes obtained from these biomass assortments could be an important source of valuable elements such as P and K. Therefore, detailed knowledge about the ash transformation and fate of P during thermal conversion of these opportunity biomass resources is of immense importance to mitigate ash-related problems and to recover valuable nutrient elements from the ash. The overall objective of this work was to determine the ash transformation and fate of P during single-pellet and fixed-bed combustion/gasification of different opportunity biomass fuels in the process temperature range of 600-1250°C. Different agricultural biomasses (poplar, wheat straw, grass, and wheat grain residues), forest residues (bark and twigs), and sewage sludge (pure and in mixtures with agricultural residues) were used. These fuels cover a wide range of overall ash compositions and different chemical associations of P in the fuel. The bark and poplar represent fuels rich in K and Ca with minor P content. The wheat straw, grass, and twigs represent typical Si- and K-rich fuels with minor to moderate P contents. The wheat grain residues (WGR) represent typical K- and P-rich fuels with a significant amount of Mg. The produced residual materials, i.e., char, different ash fractions and fine flue gas particles, were morphologically and chemically characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, inductively coupled plasma, and ion chromatography. The interpretation of the results was supported by thermodynamic equilibrium calculations. For all fuels, a major part of the P (> 80%) was found in coarse ash fractions because the studied process conditions favored the formation of stable condensed phosphates. The thermal conversion atmosphere (i.e., gasification/combustion) only caused small effects on the P release and the speciation of the P-compounds formed. Ash transformation pathways generally lead to the formation of orthophosphates (PO43-) such as Ca5(PO₄)3(OH), CaKPO4, and Ca3(PO4)2 with the partial substitution of Ca by some cation forming elements (Fe, Mg, and/or K), as the main P containing crystalline phases. Crystalline pyrophosphate (P2O74-) compounds were also found in the residual ashes from the seed-based fuel (WGR), where P originates from phytate in the biomass. For the fuels containing a certain (sufficient) amount of Si, orthophosphates interact with silicate phases to form both amorphous and crystalline phosphosilicates. For the sewage sludge mixtures, a surplus of available K was needed to form K-bearing phosphates due to side reactions of K with Si and Al. The chemical form of P in the formed ash residues is thus strongly dependent on both the type of P association in the fuel and the relative concentrations of other major ash-forming elements, such as K, Ca, Si, and Al. For the fuels with a high (Ca+Mg)/P molar ratio (AER), i.e., for the typical wood-derived fuels bark and poplar, hydroxyapatite was the main P-containing crystalline phase found in the ash. For the studied fuels/fuel mixtures with moderate AER and a high (K+Na)/(Si+Al) molar ratio (AR), e.g., twigs, grass, wheat straw, and sewage sludge with high mixtures of agricultural residues, there was also a possibility to form alkali-bearing phosphates such CaKPO4 and K-Mg whitlockite, besides hydroxyapatite. Since these fuels contain a high amount of Si, the P can be found in both amorphous phases, i.e. phosphosilicate, and Si substituted crystalline phases, i.e. Ca10(SiO4)x(PO4)6-XOH2-x and Ca15(PO4)2(SiO4)6. For fuels with moderate AER and low AR, e.g., pure sewage sludge and sewage sludge with low mixtures of agricultural residues, K-bearing phosphates were not formed. Instead, P was found in phases such as whitlockite and phosphosilicates. For the WGR fuel with relatively low AER and high AR, K-bearing phosphates were formed in the ashes, where the P was found in crystalline K-Mg/Ca pyrophosphates and K-Mg orthophosphate, as well as amorphous K-Mg-Ca phosphates. The produced knowledge can potentially be used to, e.g., i) suggest efficient measures to mitigate ash-related problems associated with P during thermochemical conversion of opportunity biomass fuels, ii) suggest potential pathways to form plant-available phosphates directly in the thermal conversion process to enable recovery of P and K from the obtained ashes, and iii) find optimal thermal conversion process conditions to obtain bio charcoals that are suitable as alternative fuels and reducing agents in the metallurgical industry.
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| 4. |
- Falk, Joel, 1988-
(författare)
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The fate and ash transformations of phosphorus in combustion of biomass and sewage sludge
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The combustion of phosphorus (P)-rich biomass has a significant potential to increase the stock of biomass resources available for renewable heat and power production. In addition, the P-rich ashes have the potential as a fertilizer and could reduce the need for non-renewable P resources in agriculture. However, several technical challenges must be resolved to realize this potential.During combustion, the ash-forming matter in the fuel undergoes numerous chemical transformations, which can result in the formation of ash melts. Excessive melt formation can lead to durable ash deposits in and around the combustion zone and on heat exchangers, which can lower combustion performance and, in severe cases, lead to a complete shutdown of the process. Further, mono-combustion of P-rich residues such as sewage sludge results in the formation of phosphates with poor plant availability, which can significantly limit the value of the ash as a fertilizer. By co-combustion the sludge with K-rich biomass, it may be possible to alter the chemical speciation of P towards more plant-available phases while simultaneously managing the risk of ash-related operational issues. This work investigates the effect of combustion technology, fuel ash composition, and chemical association of P in the fuel on the fate, i.e., distribution and speciation, and ash transformations of P in combustion and co-combustion of biomass and sewage sludge.The basis of the study was experiments performed in three different combustion technologies, including a fluidized bed (5 kW, 730-800 °C), a fixed bed (20 kW, 950-1250 °C), and a powder burner (150 kW, ~1100°C). The fuels and fuel mixtures included P-rich and P-poor woody biomass, agricultural residues, and sewage sludge, which constitute a wide range of ash compositions in terms of K, Ca, Mg, Fe, Al, Si, and P. The residual ashes from the experiments were collected and chemically characterized with the original fuels and fuel mixtures to determine the ash transformation reactions of P. The experiments were complemented by thermodynamic equilibrium calculations (TECs), which aided the interpretation of experimental data and predicted the risk for operational issues related to the melting of coarse ash fractions.The major share of fuel P was found in coarse ash fractions such as bed ash particles, bottom ash, slag, cyclone ash, wind side deposits, and coarse fly ash. A low share of fuel P was found in fine ash fractions such as leeside deposits and PM1. This generally matched the predictions by TEC, which indicated that P was stable in condensed phases at the relevant compositions and conditions during the combustion experiments. The powder burner experiments produced the highest share of fuel P in PM1 (4-14 wt.%), followed by fixed bed combustion (<4 wt.%), with fluidized bed combustion having the lowest share (<0.6 wt.%). In addition, the experiments with sewage sludge indicated a significantly lower P share in PM1 for a given combustion technology than the other biomass fuels, ranging from <0.2 wt.% in the fluidized bed and <1.2 wt.% in the fixed bed.Combustion and co-combustion of woody biomass and agricultural residues resulted in the formation of a wide range of ortho-, pyro-, and metaphosphates associated with K, Ca, and Mg. Combustion of woody biomass generally resulted in a high share of Ca-orthophosphates, whereas agricultural residues had a higher share of K-rich ortho- and pyrophosphates. Irrespective of biomass assortment, the speciation of P in the ash from combustion and co-combustion followed general trends with respect to the fuel ash composition of the biomass mixture. The frequency and share of pyro- and metaphosphates identified in the coarse ash fractions tended to increase with the relative concentration of P to K, Ca, and Mg in the fuel mixture. A similar correlation was found between the share of K-rich phosphates and the relative concentration of K to Ca and Mg.The crystalline phosphate phases identified in the coarse ash fractions from sewage sludge and K-rich biomass experiments were mainly Fe-rich and Ca-rich orthophosphate. The frequency and share of Fe-rich orthophosphates decreased with the relative P to K, Ca, and Mg concentration in the fuel mixture. However, the sewage sludge mixtures were less prone to form K-rich orthophosphates than the biomass mixtures for a given composition in terms of P to K, Ca, and Mg.Based on TECs, it was possible to qualitatively predict ash-related issues related to the melting behavior of coarse ash fractions, such as slag formation, for woody biomass and agricultural residues by considering the K, Ca, Mg, Si, and P content in the fuel. The share of network formers (SiO2, PO2.5) to total ash oxides had the largest overall influence on the melting tendency of the ash mixture, followed by the ratio of K2O to total network modifiers (K2O, CaO, MgO), which had a high impact on ash mixtures with high relative shares of SiO2. The slagging tendency of fuel mixtures with a high share of sewage sludge could not be predicted based on the melting behavior of the K-Ca-Mg-Si-P-O system due to the high relative share of Fe and Al. The experimental results indicated that the slagging tendency of the sewage sludge was significantly improved by co-combustion with moderate amounts of wheat straw or sunflower husk.Based on the combined results, it was possible to establish four fuel ash molar ratios correlated with the speciation of P in the produced coarse ash fractions and the risk of slag formation in fixed-bed combustion. These ratios were used to recommend practical fuel mixing strategies that could enable the production of combustion ashes with high P-plant availability while simultaneously managing the risk of severe slag formation.
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| 5. |
- Li, Jiajia, 1995-
(författare)
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Constructing Poly(Ionic Liquid)s-Based Composite Solid State Electrolytes and Application in Lithium Metal Batteries
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The pursuit of reliable and high-performance batteries has fueled extensive research into new battery chemistries and materials, aiming to enhance the current lithium-ion battery technologies in terms of energy density and safety. Among the potential advancements, solid-state batteries (SSBs) have captured significant attention as the next-generation energy storage technology. One key factor contributing to their appeal is the utilization of solid-state electrolytes (SSEs) with a wide electrochemical stability window (ESW), making SSBs compatible with high-voltage cathodes. The energy density of SSBs can be further improved by employing the “holy-grail” anode, Li-metal, which boasts the lowest working voltage (-3.04 V vs. Li+/Li) and an ultrahigh theoretical capacity (3860 mAh g−1). Consequently, these batteries are referred to as lithium metal batteries (LMBs). However, realizing the full potential of LMBs presents formidable challenge, including the low ionic conductivity of current SSEs, large interfacial resistance between SSE and electrodes, uncontrollable interfacial reactions, and the growth of Li dendrites. Typically, SSEs can be categorized into three types. Among these, solid composite electrolytes (SCEs) are considered the most promising choice for solid-state LMBs due to their combination of high ionic conductivity and excellent mechanical strength from inorganic solid electrolytes (ISEs) and the flexibility and good interface compatibility provided by solid polymer electrolytes (SPEs). Polymeric ionic liquids (PolyILs), which contain both ionic liquid-like moieties and polymer frameworks, have emerged as highly attractive alternatives to traditional polymers in SCEs. The overall objective of this thesis was to develop PolyIL-based SCEs with enhanced ionic conductivity, wide ESW, high Li+ transference number, and reduced electrodes/electrolyte interface resistance. The main progress achieved in this thesis is as follows:1. We selected three F-based Li-salts to prepare SPEs using poly(ethylene oxide) and polyimide. The investigation focused on assessing the impact of molecular size, F content, and chemical structures (F-connecting bonds) of these Li-salts. Additionally, we aimed to uncover the formation process of LiF in the solid electrolyte interphase (SEI). The result revealed that the F-connecting bond plays a more significant role than the molecular size and F element content, resulting in slightly better cell performance using LiPFSI compared to LiTFSI and substantially better performance compared to LiFSI. The preferential breakage of bonds in LiPFSI was found to be related to its position to Li anode. Consequently, we proposed the LiPFSI reduction mechanism based on these findings.2. Using the template method, we synthesized a monolayer SCE with enhanced Li+ transference number and high ionic conductivity. In this study, boron nitride (BN) nanosheets with a high specific surface area and richly porous structure were employed as inert inorganic filler. These BN nanosheets played a crucial role in homogenizing the Li+ flux and facilitating the Li+ transmission to suppress Li dendrite growth. When integrated into a LiFePO4//Li cell with the optimized SCE, the assembled battery demonstrated remarkable cycling performance. 3. A monolayer GSCE with multifunctionality was synthesized via a natural sedimentation and subsequent UV-curing polymerization technique. This innovative method capitalizes on intrinsic gravity, allowing for the integration of multiple functions within a single layer, thereby eliminating the additional interlayer resistance. The developed GSCE provides an optimum Li+ transportation path and enhanced Li+ transference number, leading to an enhanced ionic conductivity and a long cycle life of Li//Li cells and SSLMBs. Compared with the monolayer uniform SCEs, the gradient structure also alleviates the uncoordinated thermal expansion between fillers and PolyIL, avoiding increased stress during the cycle and battery capacity fade.
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| 6. |
- Bagheri, Marzieh
(författare)
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Integrated sewage sludge treatment scenarios – techno-economic analysis on energy and phosphorus recovery
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sewage sludge is a by-product of wastewater treatment that simultaneously gathers contaminants, valuable organic matter, and nutrients. The treatment of the increasing amount of sewage sludge is important from both pollution prevention and resource recovery perspectives as i) large shares of mineral phosphorus, listed as a critical raw material, terminate in the sewage sludge, and ii) energy recovery from sewage sludge can cover the energy-intensive demand of the treatment process. Previous research has identified sewage sludge combustion as a suitable treatment approach as it both addresses contaminant destruction and paves the way for efficient phosphorus recovery from the sewage sludge ash. The commercial development of this practice has, however, been slow. Therefore, this thesis aims to investigate the challenges in sustainable sewage sludge management, and to, in more detail, identify the economic viability of energy and phosphorus recovery from sewage sludge through combustion.The thesis’ aim is divided into two objectives addressed in three papers. First, to investigate how different aspects of sewage sludge management, such as contaminants, economic efficiency, technical aspects, and legislation, evolve and interact. This has been done by a review of sewage sludge management research over fifty years (Paper I). Second, to investigate the economic viability of simultaneous energy and phosphorus recovery from sewage sludge by comparing different technology and market scenarios. This has been done for i) new sewage sludge mono-/co-combustion plants (Paper II), and ii) the integration of treatment technologies, mainly anaerobic digestion, hydrothermal carbonization, and combustion, in an existing wastewater treatment plant (Paper III). Results from the analysis of sewage sludge management research (Paper I) show a narrow-focused perspective that often excludes inseparable aspects such as combination of economic consideration and advanced extraction technology. The investment viability of a new mono-/co-combustion of sewage sludge (Paper II) is highly conditional on heat, electricity, and fertilizer price, and external financial support is often a crucial requirement. Sewage sludge co-combustion with potassium-rich biomasses improves sewage sludge quality and forms usable ash as fertilizer without further need for phosphorus recovery technology. In this case, the economic feasibility of the process is independent of usable ash revenue, which stimulates a competitive selling price for the ash, thereby improving the marketing of sludge-based fertilizer. Avoided disposal costs of sewage sludge for a retrofitted wastewater treatment plant by introducing hydrothermal carbonization (Paper III) shows good economic feasibility while recovering phosphorus. Integrating anaerobic digestion, hydrothermal carbonization, and combustion may also improve investment incentives by improving energy outputs and phosphorus recovery. The economic feasibility is contingent on product (hydrochar, heat, electricity) prices and sensitive to added equipment costs, and costs for sludge transportation and disposal.
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| 7. |
- Bagheri, Marzieh
(författare)
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Sewage Sludge Treatment Scenarios: Techno-Economic Analyses of Energy and Phosphorus Recovery Focusing on Implementation Challenges
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Managing sewage sludge, an inevitable by-product of wastewater treatment processes rich in both contaminants and valuable resources, presents a dual challenge: ensuring pollution prevention by immobilizing or destroying contaminants, and facilitating resource recovery. Balancing these objectives is critical given the growing volumes of sewage sludge and the imperative to both protect the environment and recover valuable resources. The unknown risks of land application of sludge, the currently most common disposal method, make thermal conversion a promising alternative, as it enables energy recovery, the breakdown of potentially harmful organic compounds, and the formation of volume-reduced, sanitized products. Despite the technical feasibility, the commercial development of advanced recovery technologies has been slow. This thesis aims to expand knowledge on different sewage sludge treatment and disposal scenarios under varying conditions; thereby shedding light on implementation challenges, local opportunities, and the financial dynamics critical for phosphorus and energy recovery from the perspectives of wastewater treatment plants, investors, and policymakers. The aim is primarily addressed by performing techno-economic analysis of sewage sludge treatment scenarios, covering the entire sludge treatment process from sludge treatment to end products and disposal (Paper II-V). The techno-economic analysis is supplemented by a review of academic research on sewage sludge management from 1971 to 2019 (Paper I). Results from the analysis of sewage sludge management research (Paper I) show a narrow-focused perspective that often misses the broader, interconnected aspects of sewage sludge management, leading to research that, while detailed, fails to capture the complexity of the field. The investment viability of a new mono-/co-combustion plant for sewage sludge (Paper II) is highly conditional on heat, electricity, and fertilizer prices, and external financial support is often a crucial requirement. Cocombustion of sludge (in low ratios) with K-rich agricultural biomass requirement in and energy demand of a thermal dryer, and by yielding ash that contains phosphorus in a plant-available form. Utilizing existing heat facility (Paper III) and co-combustion to mitigate investment costs and energy demand in sludge management showed the potential to offer a cost-effective alternative to land application. However, the viability of co-combustion hinges on both a high heat market price (Paper II) and the proximity of affordable biomass resources (Paper III). Without these conditions, co-combustion may increase the financial burden of sludge management on wastewater treatment plants and policymakers. Retrofitting a wastewater treatment plant by integrating hydrothermal carbonization in sludge treatment (Paper IV), demonstrated good economic feasibility, primarily due to the avoided disposal costs, while also recovering phosphorus. However, integrating hydrothermal carbonization in a system designed for a thermal dryer may cause a significant reduction in electricity production.Given the high moisture content of sludge and the low market prices for fertilizer, the potential revenue from energy and phosphorus recovery is inadequate to solely drive investment in advanced sewage sludge treatment technologies (Papers II-V). This issue is exacerbated by the fact that most wastewater treatment plants are small in scale. Collaborative sludge management across neighboring wastewater treatment plants (Paper V) increases phosphorus recovery capacity and leverages economies of scale, fostering investment in advanced technology. This strategy presents a significant opportunity to lower the treatment costs and offers a competitive alternative to land application, while encompassing energy and phosphorus recovery into the sludge treatment.In conclusion, resource recovery and pollution prevention in sludge management is a complex task that necessitates simultaneous consideration of technical aspects, product quality, site-specific conditions, and profitability to ensure a comprehensive and viable approach. Leveraging local infrastructure and resources in sewage sludge management is crucial, highlighting the ecessity for strategies to be tailored to the local opportunities and limitations. Such an approach outperforms mono-combustion by eliminating the investment ensures that solutions are not only environmentally sustainable but also economically viable and socially acceptable.
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| 8. |
- Hedayati, Ali, 1984-
(författare)
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Ash transformation in single-pellet combustion and gasification of biomass with special focus on phosphorus
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The utilization of different biomass feedstocks in thermal conversion systems can contribute towards mitigation of global warming. However, the formation of different ash fractions (i.e., bottom ash, and fly ash) during thermal conversionof biomass can cause several ash-related problems such as deposit formation, slagging, and particle emissions, all of which may limit its usage as an energy source. It has been found that phosphorus (P), even in relatively low concentrations, can play a vitalrole in the abovementioned ash-related problems. However, the ash transformation reactions occurring in the thermal conversion of P-bearing biomass assortments are not fully understood and rarely described in the literature. Therefore, an understanding ofthe phenomena associated with ash transformations with a special focus on P is crucial.The overall objective was to determine the ash transformation and release of P duringsingle-pelletthermochemical conversion ofdifferent types of agricultural and forest fuelsin the low to medium temperature range (600-950 °C). Different agricultural biomasses (poplar, wheat straw, grass, and wheat grain residues), as well as forest residues (bark, twigs, and a mixture of bark and twigs) were used. Thebark and poplar fuels represent a fuel rich in K and Ca with minor P contents. The wheat straw, grass, and twigs represent a typical Si- and K-rich fuel with minor and moderate P contents. The wheat grain residues represent a typical K- and P-rich fuel witha considerable amount of Mg. The produced residual materials, i.e. chars and ashes, were characterized by SEM-EDS, XRD, and ICP-OES. The experimental results were interpreted with support from thermodynamic equilibrium calculations (TECs).The overall findings are that the majority of P (>80%) in all the studied fuels remained in the final condensed residues, and that the main fraction of P release occurred during the devolatilization stage. The chemical form of P in the residuesis strongly dependent on the relative concentrations of other major ash-forming elements such as K, Ca, and Si, as well as the type of association of P in the pure fuel. For woody-based fuels rich in Ca and K (poplar, bark, and twigs in this study), P in theash is generally found in the form of crystalline hydroxyapatite. For herbaceous fuels rich in Si and K (wheat straw and grass), P in the ash is generally found in Ca5(PO4)3OH, Ca15(PO4)2(SiO4),KCaPO4, and K-Ca/Mg phosphosilicate melts. For wheat grain residues rich in P, K, and Mg, P in the ash is found in crystalline forms K4Mg4(P2O7)3, K2MgP2O7,K2CaP2O7, and KMgPO4, as well as amorphous K-Mg/Ca phosphates.The obtained new knowledge can be used to find practical measures to mitigate ash-related problems during thermochemical conversion of P-bearing biomass fuels. It can also be used to find optimal pyrolysis process conditions to obtain biocharsuitable as alternative fuels and reducing agents in the metallurgical industry.
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| 9. |
- Häggström, Gustav
(författare)
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Experimental studies of ash transformation processes in thermochemical conversion of P-rich biomass and sludge
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The efficient use of resources and sustainable recovery of various materials are important to minimize the anthropogenic impact on the climate and environment. One such resource is the phosphorus present in manure and sewage sludge. Various technologies are currently being developed to recover the phosphorus for the use of fertilizers in agricultural applications. Thermochemical conversion presents an opportunity to recover energy from these materials. At the same time, elements can be recovered in ash fractions, potentially harmful organic substances can be destroyed and heavy metals fractionated from the P. Mono-combustion of sewage sludge mainly produce apatite, which is not plant available and useful for fertilization. Co-combustion/-gasification with other fuels enables modification of ash transformation pathways and also remedy potential problems, such as bed agglomeration, associated with e.g. agricultural residues used as fuels. This thesis aims to increase the current knowledge in ash transformation of phosphorus-rich materials in cocombustion/-gasification with woody and agricultural fuels in process temperatures relevant for fluidized bed systems. The work focuses on i) possibility for formation of plant-available K-bearing phosphates ii) the effect of fuel ash composition and chemical association of P in the fuel on the distribution and speciation of P and iii) interaction of P-rich ash with bed material in fluidized beds. Experiments were carried out in bench-scale bubbling fluidized bed (BFB), macro-TGA (thermogravimetric analysis) combustion reactors and a dual fluidized bed (DFB) gasification reactor. Fuels studied were mixtures of chicken litter together with wheat straw and bark, and mixtures of digested sewage sludge combined with wheat straw and sunflower husk. Ash fraction and bed materials were collected and analyzed using ICP-OES/MS, SEM-EDS and XRD techniques. For the mixture of chicken litter and K- and Si-rich wheat straw, combusted in BFB, P and Si together with K and Ca formed homogeneous ash particles with large amounts of potentially amorphous iv content. A similar behavior was observed in sewage sludge and wheat straw mixtures where P and Si were likely present in a melt that is amorphous after extraction. In addition to these particles, P was also found in crystalline compounds such as hydroxyapatite, whitlockite and CaKPO4. For mixtures with Ca-rich bark, most of the phosphate formed was in the form of hydroxyapatite. In the interaction of ash with bed material, P captures Ca and K in phosphates, decreasing the interactions of these elements with the bed material, and thus can decrease the risk for bed agglomeration. The findings show that it is possible to modify the ash transformation of P towards K-bearing phosphates by co-combustion. Furthermore, they suggest that it is possible to recover most of the phosphorus in coarse ash fractions through co-combustion of P-rich materials with agricultural fuels. This means that P and volatile heavy metals can be separated into different ash fractions. This also increases the possibility of utilizing existing boilers for recovery of P as well as increased their flexibility to different fuels. To further validate the agricultural value of the produced ashes, plant growth studies have to be performed.
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- Häggström, Gustav
(författare)
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Studies of ash transformation processes in thermochemical co-conversion of phosphorus-rich manure and sludge with biomass residues
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficient use of resources and sustainable recovery of various materials are important to minimize the anthropogenic impact on the climate and environment. One such resource is the phosphorus (P) present in manure and sewage sludge. Various technologies are currently being developed to recover the element for application as fertilizer in agricultural applications. Thermochemical conversion presents the opportunity to recover energy from these materials. In a single process, elements can be recovered in ash fractions, potentially harmful organic substances can be destroyed and heavy metals fractionated from the P. Mono-combustion of sewage sludge mainly produce apatite, a phosphate mineral with low plant availability and therefore less useful for fertilization. Co-combustion/-gasification with other fuels enables modification of the ash transformation reaction pathways and remedies potential problems, such as bed agglomeration, associated with forestry and agricultural residues when used as fuels.The overall objective of this work was to increase the current knowledge in ash transformation of P-rich materials in co-conversion with forestry and agricultural residues in order to facilitate the P-recovery by formation of suitable phosphates in the ash. The work focuses on i) the influence of co-conversion on ash transformation of P with a focus on altering speciation of P towards the potentially more plant-available K-bearing phosphates ii) the influence of fuel ash composition and chemical association of P in the fuel, temperature and particle interaction on the fate, i.e. speciation and distribution, of P and iii) practical implications of co-conversion in fluidized bed and pulverized fuel systems for P-recovery, specifically interaction of P-rich ash with bed material in fluidized beds and strategies for extracting P-rich ashes.Experiments were carried out in a bench-scale bubbling fluidized bed reactor (BFB), macro-thermogravimetric analysis (TGA) conversion reactor, a dual fluidized bed (DFB) gasification reactor, and an entrained flow reactor (EFR) for pulverized fuel combustion. The fuels studied were mixtures of chicken litter together with wheat straw and bark, and mixtures of digested sewage sludge combined with wheat straw and sunflower husk. The process temperature ranges studied were 800-950 °C for BFB and single-pellet macro-TGA studies, whereas 1000 °Cand 1400 °C were investigated in pulverized fuel combustion studies using the EFR. Ash fractions and bed materials were collected and analyzed using scanning electron microscopy with energy-dispersive Xray spectroscopy (SEM-EDS), powder X-ray diffraction (XRD), inductively coupled plasma with atomic emission spectroscopy (ICPAES) and ion chromatography (IC). The results were interpreted with the support of thermodynamic equilibrium calculations (TECs) using FactSage software with the GTOX & SGPS databases.For all investigated conditions and fuel mixtures, the major part of P (> 90 %) was found in coarse ash fractions, suggesting that the recovery potential is highest in these fractions. This also means that P and volatile heavy metals can be separated in different ash fractions. Crystalline P was to a higher degree observed in the form of K-bearing whitlockite structures and CaKPO4 in mixtures containing low amounts of sewage sludge and high amounts of agricultural residues rich in K. K-bearing whitlockites were also found in ash of chicken litter and its mixture with wheat straw, as well as in ash deposits formed in pulverized combustion with a sewage sludge and wheat straw mixture combusted at 1000 °C. In mixtures with higher shares of sewage sludge, crystalline P was mainly found as Fe- and Mg-substituted whitlockites and hydroxyapatite. The reaction pathway of P appears to mainly occur through substitution and addition reactions in the condensed phase. The findings show that it is possible to modify the ash transformation of P towards K-bearing phosphates by co-conversion and that the difference between combustion and gasification is small.For the mixture of chicken litter and K- and Si-rich wheat straw combusted in BFB, P and Si together with K and Ca formed homogeneous ash particles with large amounts of potentially amorphous content. A similar behavior was observed in sewage sludge and wheat straw mixtures, where P and Si were likely present in a melt that was amorphous after extraction. In addition to these particles, P was also observed in crystalline orthophosphate compounds such as hydroxyapatite, aluminium phosphate, whitlockites and CaKPO4. In the mixture of chicken litter with Ca-rich bark, crystalline P was found in the form of hydroxyapatite. In fuel mixtures with higher amounts of Al with Si, the capture of K in aluminosilicates was higher, making it unavailable to form K-bearing phosphates. Small differences in the fate of P, between organically and inorganically associated P found in the fuels were seen in this work. Lower temperatures (800 °C compared to 950 °C) favored the formation of crystalline K-bearing phosphates in single-pellet combustion of sewage sludge and agricultural residues. In pulverized fuel combustion experiments, more crystalline K-bearing phosphates were found at 1000°C compared to 1400 °C. Fuel ash interaction mainly occurred in condensed phases in ash deposits compared to interactions between particles entrained in the flow.In fluidized bed experiments, P captured Ca and K in relatively high temperature melting phosphates in the fuel ash, decreasing the interactions of these elements with the bed material and thus decreased the risk for bed agglomeration. Possible extraction strategies involve the separation of coarse ash particles from bed material particles or in heated cyclones, avoiding fine ash fractions known to be rich in volatile heavy metals. Mixtures of coarse ash and bed material can potentially also be used for P-recovery. Co-conversion increases the possibility of utilizing existing boilers for recovery of P and increasing their flexibility to different fuels. The results indicate that a powder combustor operating in slagging mode could be a feasible strategy for P recovery because the interaction potential between the formed individual coarse ash particles increases at the hot wall. Plant growth studies have to be performed to further validate the agricultural value of the produced ashes for direct soil application.
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