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Fly Ash Formation and Characteristics from (Co-)Combustion of an Herbaceous Biomass and a Greek Lignite (Low-Rank Coal) in a Pulverized Fuel Pilot-Scale Test Facility

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Fly Ash Formation and Characteristics from (Co-)Combustion of an Herbaceous Biomass and a Greek Lignite (Low-Rank Coal) in a Pulverized Fuel Pilot-Scale Test Facility energies Article Fly Ash Formation and Characteristics from (co-)Combustion of an Herbaceous Biomass and a Greek Lignite (Low-Rank Coal) in a Pulverized Fuel Pilot-Scale Test Facility Aaron Fuller 1,* ID , Jörg Maier 1, Emmanouil Karampinis 2,3, Jana Kalivodova 4,5, Panagiotis Grammelis 2,3, Emmanuel Kakaras 2,3 and Günter Scheffknecht 1 1 Institute of Combustion and Power Plant Technology, University of Stuttgart, Pfaffenwaldring 23, 70569 Stuttgart, Germany; [email protected] (J.M.); [email protected] (G.S.) 2 Centre for Research & Technology Hellas/Chemical Process and Energy Resources Institute (CERTH/CPERI), Egialias 52, 15125 Marousi, Athens, Greece; [email protected] (E.K.); [email protected] (P.G.); [email protected] (E.K.) 3 National Technical University of Athens/Department of Mechanical Engineering/Laboratory of Steam Boilers and Thermal Plants (NTUA/LSBTP), Heroon Polytechniou 9, 15780 Zografou, Athens, Greece 4 The Energy Research Center of The Netherlands (ECN), Biomass, Coal and Environmental Research, Heat and Power Generation, P.O. Box 1, 1755 ZG Petten, The Netherlands; [email protected] 5 Research Centre Rez, Husinec-_Re_z _c.p. 130, 250 68 Husinec e_Re_z, Czech Republic * Correspondence: [email protected]; Tel.: +49-711-685-63763; Fax: +49-711-685-63491 Received: 1 May 2018; Accepted: 5 June 2018; Published: 15 June 2018 Abstract: The lignite boilers are designed for lower quality fuels, and often the ash is not utilized. This work assessed the impact of combustion of an herbaceous biomass with a low-quality Greek lignite on the quality of the resulting fly ash. Test results were compared with those of fly ash samples from an industrial facility using the same fuel qualities. Inductively coupled plasma-optical (ICP) emission spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscope (SEM) analyses were performed on the collected samples. Despite the significantly higher contents of K, Na and S in the biomass, at a 50% co-firing thermal share, the major and minor oxides in the fly ash were comparable to the lignite fly ash quality. This is attributed to the high ash content of the lignite, the low ash content of the biomass, and the much higher heating value of the biomass. There were improvements in fly ash performance characteristics with the herbaceous biomass in the fuel blend. The initial setting time and volume stability evaluations were improved with the biomass in the fuel blend. The work supports efforts of good practices in ash management, social responsibility, a circular economy, power plant renewable energy operations, and co-firing herbaceous biomass fuels in lignite power plants. Keywords: bioenergy; co-firing; renewable energy; biomass fly ash; herbaceous biomass; by-products; recycled wastes; sustainable energy 1. Introduction Over the last decades there has been increased interest in developing bioenergy technologies worldwide due to declining energy supplies and severe environmental constraints associated with fossil fuel use [1]. The goal of the European Union is to increase the percentage of biomass fuels used in the primary energy consumption, offering a reasonable, acceptable option to reduce greenhouse Energies 2018, 11, 1581; doi:10.3390/en11061581 www.mdpi.com/journal/energies Energies 2018, 11, 1581 2 of 38 emissions [1], mainly CO . However, there are still concerns regarding the acceptability of coal and Energies 2018, 11, x FOR PEER REVIEW2 2 of 37 biomass fuel blends’ ash materials, i.e., by-product quality, current utilization, and disposal routes. ItIt is is not not possible possible to correctlycorrectly predictpredict properties properties of of ash ash material material generated generated from from combustion combustion of a of fuel a fuelmixture mixture from from known known characteristics characteristics of ash of producedash produc fromed from each each fuel fuel [1]. The[1]. The interactions interactions between between fuels fuelsare poorly are poorly understood, understood, and unanticipated and unanticipated ash properties ash properties may arise may when arise combusting when combusting fuel mixtures fuel [1], mixturesso, it is important [1], so, it is to important fully characterize to fully thecharacte ashesrize produced the ashes from produced burning from and co-firingburning and any relativelyco-firing anynew relatively biomass new fuel. biomass fuel. TheThe reaction reaction mechanisms mechanisms of of ash ash formation formation involve involve melting melting of of most most of of the the mineral mineral components components inin the the fuel, fuel, the the formation formation of of small small fused fused drops, drops, and and a a subsequent subsequent sudden sudden cooling cooling that that transforms transforms the the mergedmerged drops drops partly partly or or entirely entirely into into spherical spherical glass glass particles particles [2]. [2]. Smaller Smaller fly fly ash ash particles particles may may cool cool downdown more more rapidly rapidly during during the the cooling cooling process process result resultinging in in a a more more glassy glassy state state and and giving giving rise rise to to a a higherhigher reactivity reactivity [3]. [3]. The The fly fly ash ash yield yield is is the the inor inorganicganic residue residue resulting resulting from from the the complete complete combustion combustion (or(or oxidation) oxidation) of of fuel fuel (e.g., (e.g., coal coal or or biomass), biomass), and and it it consists consists of of original original and and new new inorganic inorganic mineral mineral phasesphases formed formed from from the the inorganic, inorganic, organic, organic, and and flui fluidd components components in the in thefuel fuel [4]. [An4]. overview An overview of the of physicalthe physical transformation transformation involved involved in the in theformation formation of ofash ash during during coal coal combustion combustion is is depicted depicted in in FigureFigure 1.1. FigureFigure 1. 1. PhysicalPhysical transformation transformation in in ash ash formation formation du duringring combustion combustion of of co coal/biomass,al/biomass, Reproduced Reproduced withwith permission permission from from Cieplik, Cieplik, M.K.; M.K.; Fryda, Fryda, L.E.; L.E.; van van de de Kamp, Kamp, W.L.; W.L.; Kiel, Kiel, J.H.A, J.H.A. SolidSolid Biofuels Biofuels for for Energy:Energy: A LowerLower Greenhouse Greenhouse Gas Gas Alternative Alternative; Springer:; Springer: London, London, UK, UK, 2011 2011 (Ref. (Ref. [5], p.[5] 198). p. 198). LigniteLignite flyfly ashash is is subject subject to comparativelyto comparatively larger larg fluctuationser fluctuations compared compared to coal ashesto coal [6 ].ashes Moreover, [6]. Moreover,lignite boilers lignite are boilers designed are fordesigned lower for quality lower fuels, quality and fuels, often and the often ash is the not ash utilized, is not utilized, making co-firingmaking co-firingin lignite in boilers lignite an boilers attractive an solutionattractive to solution improving to theimproving ash quality the [ 7ash]. Co-firing quality ash[7]. generatedCo-firing withash generatedratios within with the ratios interest within of the commercial interest of operation commercial at power operation plants at power has proven plants to has be proven applicable to be in applicableconcrete [ 8in]. concrete Those co-firing [8]. Those experiences co-firing mostlyexperiences employed mostly bituminous employed coals.bituminous Co-firing coals. experiments Co-firing experimentswith herbaceous with orherbaceous agricultural or agricultural biomass in pulverizedbiomass in fuelpulverized power plantsfuel power or test pl facilitiesants or test focusing facilities on focusingfly ash quality on fly ash are limitedquality [are9]. limited [9]. LigniteLignite fly fly ashes ashes have have been been used used for for refilling refilling open open cast cast mines, mines, underground underground mining, mining, surface surface restoration,restoration, soil soil amendment amendment (mechani (mechanicalcal stabilization stabilization and and stabilization stabilization or or strengthening strengthening of of a asoil), soil), immobilizationimmobilization purposes, purposes, hydraulichydraulic roadroad binders, binders, plaster plaster and and mortar, mortar, road road construction, construction, asphalt asphalt filler, filler, blended cement (contributing to CO2 reduction during the production process), concrete blended cement (contributing to CO2 reduction during the production process), concrete addition addition(only after (only receiving after technicalreceiving approval),technical andapproval), various and environmental various environmental uses (retention uses of pollutants(retention andof pollutantssoil rehabilitation) and soil rehabilitation) [6]. Lignite fly [6]. ashes Lignite have fly been ashes successfully have been testedsuccessfully or used tested in self-consolidating or used in self- consolidating concrete [10], an adsorbent for SO2 removal (after separation of enriched carbon fractions) [11], and in combination with a biochar or other organic amendments for improving soil properties [12]. Biochar and fly ash has the potential to improve soil quality, crop yield, and expand the carbon pool for soils [12]. Lignite coal fly ash blended with waste glass was successfully tested in the manufacture of lightweight aggregates [13]. Lignite fly ash with a high calcium content and used Energies 2018, 11, 1581 3 of 38 concrete
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