VGB POWERTECH 7 (2020) - International Journal for Generation and Storage of Electricity and Heat

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The Biofficiency Project | Part 1 VGB PowerTech 7 l 2020 The Biofficiency Project Part 1: Handling ash-related challenges in biomass-fired cogeneration plants Lynn Hansen, Thorben de Riese, Richard Nowak Delgado, Timo Leino, Sebastian Fendt, Pedro Abelha, Hanna Kinnunen, Partik Yrjas, Flemming Frandsen, Bo Sander, Frans van Dijen and Hartmut Spliethoff Kurzfassung Das Biofficiency Projekt | Teil 1: Umgang mit aschebedingten Herausforderungen in biomassebefeuerten Heizkraftwerken Das von der EU geförderte Projekt Biofficiency entwickelte einen Entwurf für die nächste Generation von Biomasse-gefeuerten Kraft-Wärme- Kopplungsanlagen, die mit Brennstoffen niedriger Qualität arbeiten und eine sichere und nahezu kohlenstoffneutrale Stromerzeugung gewährleisten. In diesem ersten Teil einer Reihe von zwei Publikationen wird eine Zusammenfassung der Aktivitäten zur Bewältigung aschebedingter Probleme in biomassegefeuerten Kesseln gegeben. Die drei untersuchten thermochemischen Vorbehandlungsmethoden, Torrefi zierung, hydrothermale Karbonisierung und Dampfexplosion erwiesen sich als geeignet, um Reststoffe durch eine Erhöhung der Energiedichte und Verbesserung der Lager- und Hand- Authors Lynn Hansen, M.Sc. Thorben de Riese, M.Sc. Richard Nowak Delgado, M.Sc. Dr.-Ing. Sebastian Fendt Chair of Energy Systems, Technical University of Munich, Garching, Germany Timo Leino, M.Sc. VTT Technical Research Center, Jyväskylä, Finland Dr. Pedro Abelha Energy Transition, TNO, Petten, Netherlands Dr. Sc. Hanna Kinnunen Valmet Technologies Oy, Tampere, Finland Dr. Partik Yrjas Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Turku, Finland Dr. Tech. Flemming Frandsen Department of Chemical and Biochemical Engineering Technical University of Denmark, Lyngby, Denmark Bo Sander, PhD Ørsted, Markets&Bioenergy, Fredericia, Denmark Dr. Ir. Frans van Dijen ENGIE Laborelec, Linkebeek, Belgium Prof. Dr.-Ing. Hartmut Spliethoff Head of Institute Chair of Energy Systems, Technical University of Munich, Garching, Germany habungseigenschaften zu Veredeln. In Versuchen vom Labor- bis zum Vollmaßstab in Staubfeuerungs- und Wirbelschichtanlagen wurden aschebedingte Probleme bei der Biomasseverbrennung wie Depositionen, Feinstaubbildung und Korrosion untersucht. Depositionsproben in staubgefeuerten Kesseln zeigten, dass Additive einen ausgeprägten Einfluss auf die Bildung von Ablagerungen haben, wobei die Additivmenge von größerer Bedeutung ist als die Art des Additivs. Auch auf die Feinstaubbildung zeigte die Verwendung von Additiven einen positiven Einfluss. Bei Versuchen in Wirbelschichtsystemen wurde eine Optimierung der Additivzusammensetzung durchgeführt, wobei sich elementarer Schwefel als der kostengünstigste Zusatzstoff für diesen Fall herausstellte. Es konnte gezeigt werden, dass die Vorbehandlung von Stroh durch Torrefizierung in Kombination mit einem Waschschritt eine wesentlich geringere Menge an Additiven erfordert, die während der Verbrennung zugegeben werden muss. Biomasseaschen aus verschiedenen Quellen wurden auf der Basis ihrer Zusammensetzung und möglicher Verwertungswege klassifiziert, um künftig eine umweltschädliche Deponierung von Biomasseaschen zu vermeiden. Es wurden innovative Nutzungsoptionen identifiziert, wie z.B. die Verwendung von Biomasseaschen in Baustoffen oder die Rückgewinnung von Nährstoffen. l The EU funded project Biofficiency developed a blueprint for the next generation of biomass-based cogeneration plants using difficult fuels while assuring a secure and nearly carbon-neutral power generation. In this first part of a series of two publications, a summary of the activities handling ash-related challenges in biomass boilers is provided. Three thermochemical pre-treatment technologies, torrefaction, hydrothermal carbonisation and steam explosion proved suitable for upgrading residual biomass feedstock by increasing energy densities and improving storage as well as handling properties. In combustion tests, both in pulverised fuel (PF) and fluidised bed (FB) systems ashrelated problems, namely deposit build-up, fine particle formation and corrosion were examined. Deposit tests in PF boilers showed that the additives have a pronounced effect on deposit propensity, the additive amount being of greater importance than the type of additive. The use of additives also showed positive influence on aerosol formation. In FB firing, an optimisation of the additive composition and insertion was performed, where elemental sulphur was found to be the most cost-effective additive for this case. It was demonstrated that pre-treating straw by torrefaction combined with a washing step requires a substantially lower amount of additive to be added during combustion. Biomass ashes from different sources were classified based on their composition and possible utilisation pathways with the goal to avoid landfilling were developed. Innovative utilisation options were identified such as utilisation in construction materials or recovery of valuable elements. 1. Introduction This article summarises the findings of the H2020 project Biofficiency, that focused on the improvement of biomass utilisation for combined heat and power generation (CHP). The mobilisation of currently unused biofuels like agricultural or other bioindustry residues for high-efficiency power stations is required to meet this goal. The overall objective of the project was the development of next generation biomassbased CHPs using difficult fuels while assuring secure and nearly carbon-neutral power generation. Commonly used biomass types for heat and power generation can reduce CO 2 emissions by 55 to 98 percent when compared to the current fossil fuel mix in Europe, if no land-use change is caused [1]. Especially in the heating sector, biomass can help to reduce the share of coal in the power system by using it in medium- to large-scale CHP stations. Compared to small-scale heating systems, larger power stations have a much higher efficiency due to improved steam parameters during electricity production and highly optimised heat production. Furthermore, the flue gas cleaning systems in power stations are designed 62
VGB PowerTech 7 l 2020 The Biofficiency Project | Part 1 Tab. 1. Classification of different sources of biomass for energy and investigated feedstock in Biofficiency. Adapted from Main sector Sub sector Examples Investigated in Biofficiency Agriculture Forestry Organic waste Dedicated cultivation By-products and residues Crops for biofuels (corn, sugarcane, rapeseed, oil palm, cassava etc.), energy grasses (miscanthus, switchgrass), short rotation forests, others Herbaceous by-products: Straw from cereals, rice, corn, bagasse, empty fruit bunch from oil palm, prunings from stover, empty corn cobs, etc. Woody biomass: regeneration orchards, vineyards, olive and oil palm plantations Other forms: Processing residues such as kernels, sunflower shells, rice husks, animal manure, foliage Miscanthus Wheat straw, empty fruit bunches Sun flower husk, digestate Main product Stems, wood fuel from forests or trees outside forests, woody biomass from landscape cleaning Wood pellets By-products and residues Residues of forest harvest (branches, tops, stumps), residues of wood industry (bark, sawdust, other wood pieces, black liquor, tall oil, recycled wood) Municipal solid waste (MSW), food waste from stores, restaurants and households, used kitchen oil, waste from the food industries (from dairy, sugar, beer, wine, fruit juice industry, olive oil filter cake, from slaughterhouses), sewage sludge Spruce bark, fir brushwood Manure, sewage sludge, olive pomace, urban leave litter, road side grass, tomato foliage to meet strict limits for fine particles, nitrogen oxide and sulphur oxide emissions. The project addressed current bottlenecks in solid biomass combustion, namely increase deposit formation, corrosion and ash utilisation by a variety of new, promising approaches. The goal was to deepen the understanding of biomass combustion, to improve biomass pre-treatment technologies, as well as to contribute to the field of biomass ash utilisation. The following main objectives and goals were defined in order to develop the next generation, biomass-fired CHP plant: –– Increase efficiency of CHP plants by elevated steam temperatures through solving and understanding of ash-related problems – slagging, fouling and corrosion. –– Reduce emissions – i.e. CO 2 , particulates, CO, NO x , and SO 2 – by efficiency gain, reduction of impurities and by tailored plant design. –– Widen the feedstock for pulverised fuel (PF) and fluidised bed (FB) power plants using pre-treatment methods with focus on the reduction of harmful components in the biomass (torrefaction, hydrothermal carbonisation and steam explosion). –– Optimise the use of additives in the combustion of solid biomass. –– Widen ash utilisation and nutrient recirculation, study new concepts and explore possible utilisation options based on in-depth ash characterisation. The main results of the project are presented in a series of two technical papers in VGB Power Tech, whereby in this first part the focus lies on handling ash-related issues in biomass boilers and accessing difficult biomass feedstock for energetic use via pre-treatment. 2. Accessing difficult biomass feedstock via pre-treatment 2.1 Available bioenergy carriers Biomass is organic material that originates from plants and animals and can be used as a source of renewable energy. Traditionally, biomass has always been utilised as fuel for domestic applications such as heating and or cooking. Nowadays modern technologies are available for the energetic utilisation of biomass. For example, when biomass is burnt, it releases heat that can be used in subsequent combined heat and power generation. Biomass accounts for roughly two thirds of renewable energy in the European Union [2]. It plays the most crucial role in the heating sector, where biomass is responsible for over 90 % of all renewable heat generated. Ta b l e 1 provides a classification of the different potential sources of biomass for energetic utilisation. In Biofficiency, biomass feedstock from almost all these sectors have been investigated. The selection was based on availability, cost and potential. All biomass feedstocks selected in the Biofficiency project were characterised thoroughly. The data is available on the open source database Phyllis II of project partner TNO. Due to the transition of the European energy system towards higher shares of renewable resources and energy carriers, there is an increasing demand for biomass to be used for energy. Hence it competes with the existing use for production of e.g. construction materials, pulp and paper, and even for more novel uses such as chemicals. Therefore, an important question is how much sustainable biomass will be available for bioenergy in Europe in the future. F i g u r e 1 gives an overview of the technical and sustainable potentials of the above-mentioned biomass classes in the EU by 2020 [3]. Technical potential is the available biomass for all uses under current framework conditions with the current technological possibilities including existing harvesting techniques, infrastructure and accessibility and processing techniques. Potential for energy use is a proportion of the technical potential after satisfying other existing and projected competing uses of the same biomass feedstock. Sustainable potential constricts energy potential based on the sustainability criteria. As seen in F i g u r e 1 , agricultural and forestry residues represent a large portion of the available biomass feedstock. Consequently, these feedstocks are of increasing interest in the energy sector, due to the lower associated fuel costs as well as higher local availability. Mtoe 500 450 400 350 300 250 200 150 100 50 0 Technical potential Potential for energy use Manure, Sewage, other waste Forest residues, wood residues Forest stemwood Agricultural waste Energy crops Sustainable potential Fig. 1. Technical potential, potential for energy use and sustainable potential (Mtoe) of fuels for bioenergy in the EU 2020. Adapted from [3]. However, most of these biomass feedstock suffer from low bulk density, high moisture content, low calorific value and their high hydrophilic nature [4, 5]. With these properties, multiple problems arise [5]. Firstly, hydrophilic biomass is subjected to biological deterioration, limiting the practical time for storage, a challenge for seasonally available agricultural residues. Further, the fibrous nature of biomass materials brings milling and fuel handling difficulties. Compared to fossil fuels, biomass often contains higher amounts of alkali metals and chlorine, which are responsible for many undesirable reactions leading to operational problems in combustion furnaces and boilers. 63
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