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Thermodynamic Equilibrium Model Applied to Predict Fouling Tendency in a Commercial Fluidized-Bed Boiler, Combusting Solid Waste
University of Borås, Faculty of Textiles, Engineering and Business. (Combustion and thermal processes)
University of Borås, Faculty of Textiles, Engineering and Business. (Combustion and thermal processes)
University of Borås, Faculty of Textiles, Engineering and Business. (Combustion and thermal processes)
2015 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 5, 3483-3494 p.Article in journal (Refereed) Published
Abstract [en]

A thermodynamic equilibrium model, combined with an advanced fuel analysis, was applied to predict the fouling tendency in a commercial bubbling fluidized-bed (BFB) boiler, combusting a mixture of solid waste. In order to enhance the performance of the model, further modifications were made, considering the combustion pattern in the fluidized-bed system and also the temperature profile in the combustion zone. The modeling was performed using Factsage, and experimental data obtained during the full-scale measurements were used as input for the model, simulating the deposit formation in the real boiler. The simulation results were then compared with the results obtained during the full-scale combustion tests to estimate the accuracy and validity of the applied model. The thermodynamic equilibrium modeling proved to be a reliable tool for predicting the fouling in the BFB boiler, thus determining the fraction of the melt in the deposited salts formed on the heat transfer surfaces during the flue gas condensation. The calculations showed that the ratio of the SO2 to alkali chloride concentration in the flue gas was the decisive factor that affected the rate of the deposit formation in the boiler. Both the simulation and the experimental results indicated that lower bed temperatures and cocombustion of P-rich fuels decrease the deposition buildup in the boiler. © 2015 American Chemical Society.

Place, publisher, year, edition, pages
2015. Vol. 29, no 5, 3483-3494 p.
Keyword [en]
fluidized-bed combustion, fouling, waste-derived fuels, thermodynamic equilibrium modeling
National Category
Energy Engineering
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-8526DOI: 10.1021/acs.energyfuels.5b00346ISI: 000355158200084Scopus ID: 2-s2.0-84930227296OAI: oai:DiVA.org:hb-8526DiVA: diva2:894317
Available from: 2016-01-14 Created: 2016-01-14 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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