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Reduced bed temperature in a commercial waste to energy boiler: Impact on ash and deposit formation
University of Borås, School of Engineering.
University of Borås, School of Engineering.
2013 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 105, 28-36 p.Article in journal (Refereed) Published
Sustainable development
The content falls within the scope of Sustainable Development
Abstract [en]

Waste combustion for power production is associated with many problems due to the composition and inhomogeneity of the fuel stream. A reduction of alkaline and chlorine products in the superheater region should ease these problems significantly. Ashes and deposits from different combustion tests in a commercial 20 MWth bubbling fluidised bed (BFB) boiler were characterised by XRD and SEM-EDX. The fuel combusted was a mix of sorted municipal solid waste (MSW) and industrial waste, often referred to as RDF (refuse derived duel). These waste fuels often contain more alkali and chlorine than does biomass and are therefore considered risky fuels prone to causing bed agglomeration, deposit formation, and corrosion. The aim of this study was to investigate whether a lowered bed temperature could change alkali and chlorine distribution in the boiler to reduce corrosion and deposit formation. The boiler used was designed for a bed temperature in the range of 850–900 °C, which in this investigation was decreased by approximately 150 °C. Data were collected through deposit measurements and solid sampling. The lowered bed temperature resulted in reduced demand for fresh sand, decreased agglomeration, and reduced rates of deposit formation.

Place, publisher, year, edition, pages
Elsevier BV , 2013. Vol. 105, 28-36 p.
Keyword [en]
Reduced bed temperature, RDF, Alkali, agglomeration, Deposit formation, BFB, Resursåtervinning
National Category
Energy Engineering
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-1382DOI: 10.1016/j.fuproc.2011.09.001ISI: 000312414400005Local ID: 2320/11633OAI: oai:DiVA.org:hb-1382DiVA: diva2:869406
Available from: 2015-11-13 Created: 2015-11-13 Last updated: 2017-05-02Bibliographically approved
In thesis
1. Ash Behavior in Fluidized-Bed Combustion and Gasification of Biomass and Waste Fuels: Experimental and Modeling Approach
Open this publication in new window or tab >>Ash Behavior in Fluidized-Bed Combustion and Gasification of Biomass and Waste Fuels: Experimental and Modeling Approach
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the past few decades, a growing interest in the thermal conversion of alternative fuels such as biomass and waste-derived fuels has been observed among the energy-producing companies. Apart from meeting the increasing demand for sustainable heat and power production, other advantages such as reducing global warming and ameliorating landfilling issues have been identified. Among the available thermal conversion technologies, combustion in grate-fired furnaces is by far the most common mode of fuel conversion. In recent years, Fluidized-Bed (FB) technologies have grown to become one of the most suitable technologies for combustion and gasification of biomass and waste-derived fuels.In spite of the benefits, however, some difficulties are attributed to the thermal conversion of the alternative fuels. Ash-related issues could be a potential problem, as low-grade fuels may include considerable concentrations of ash-forming elements such as K, Na, S, Ca, Mg, P, Si and Cl. These elements undergo many undesirable chemical and physical transformations during the thermal conversion, and often cause operational problems such as deposition-related issues, slag formation in furnaces, corrosion of the heat transfer surfaces, and bed agglomeration of the fluidized-beds. Ash-related problems in the utility boilers are a major concern that may result in decreased efficiency, unscheduled outages, equipment failures, increased cleaning and high maintenance costs.This thesis investigated the ash behavior and ash-related problems in two different FB conversion systems: a Bubbling Fluidized-Bed (BFB) boiler combusting solid waste, and a Dual Fluidized-Bed (DFB) gasifier using biomass as feedstock. Full-scale measurements, chemical analysis of fuel and ash, as well as thermodynamic equilibrium modeling have been carried out for the BFB boiler (Papers I-IV), to investigate the impact of reduced-bed temperature (RBT) and also co-combustion of animal waste (AW) on the ash transformation behavior and the extent of ash-related issues in the boiler. For the DFB gasifier (Paper V), a thermodynamic equilibrium model was developed to assess the risk of bed agglomeration when forest residues are used as feedstock.The experimental results showed that the RBT and AW co-combustion could decrease or even resolve the ash-related issues in the BFB boiler, resulting in a lower deposit-growth rate in the superheater region, eliminating agglomerates, and a less corrosive deposit (in RBT case). Thermodynamic equilibrium modeling of the BFB boiler gave a better understanding of the ash transformation behavior, and also proved to be a reliable tool for predicting the risk of bed agglomeration and fouling. The modeling of the DFB gasifier indicated a low risk of bed agglomeration using the forest residues as feedstock and olivine as bed material, which was in good agreement following the observations in a full-scale DFB gasifier.

Place, publisher, year, edition, pages
Borås: Högskolan i Borås, 2016
Series
Skrifter från Högskolan i Borås, ISSN 0280-381X ; 78
Keyword
Fluidized-bed, combustion, gasification, waste-derived fuels, biomass, ash-related problems, deposit, fouling, slagging, bed agglomeration, thermodynamic equilibrium modeling
National Category
Environmental Biotechnology
Identifiers
urn:nbn:se:hb:diva-9563 (URN)978-91-88269-14-0 (ISBN)978-91-88269-15-7 (ISBN)
Public defence
2016-06-09, E310, University of Borås, Allégatan 1, Borås, 10:00 (English)
Available from: 2016-05-11 Created: 2016-04-08 Last updated: 2017-05-02Bibliographically approved

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