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Dynamic simulation of fouling in a circulating fluidized biomass fired boiler
Mälardalen University, School of Sustainable Development of Society and Technology.ORCID iD: 0000-0003-1962-2232
Mälardalen University, School of Sustainable Development of Society and Technology.ORCID iD: 0000-0001-8849-7661
Mälardalen University, School of Sustainable Development of Society and Technology.ORCID iD: 0000-0002-7233-6916
Mälardalen University, School of Business, Society and Engineering. (MERO)ORCID iD: 0000-0001-8191-4901
2011 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 5, p. 1813-1824Article in journal (Refereed) Published
Abstract [en]

A dynamic model is presented for a biomass-fired circulating fluidized bed boiler. The model is based on energy and mass balances for the components in the boiler and on a combustion model for the fluidized bed. The main purpose of the model is to simulate how deposits affect the boiler efficiency and performance. The model is verified against the municipal circulating fluidized bed boiler in Vasteras, Sweden, which produces 157 MW. The distribution of deposits on the surfaces in the boiler is well known from inspections. These observations are used as inputs to the model to simulate their effects on boiler performance. The heat exchanger most affected by fouling is Superheater 2, which is the first heat exchanger in the flue gas channel. Deposits typically reduce the heat transfer rate by half over a season despite soot blowing. This and other fouling scenarios are simulated and presented in this article. The simulations show that fouling on superheaters redistributes the heat transfer rate from the superheaters to Reheater 1 and partially redistributes turbine power from the high pressure turbine to the intermediate pressure turbine. If the boiler is running at maximum load, water injection to Reheater 1 has to increase to maintain temperatures below the permitted limit. The dynamic effects of fouling are small and the total efficiency of the boiler is only marginally affected. Fouling on evaporating surfaces has major dynamic effects and dramatically decreases the boiler efficiency. A decrease in fuel rate flow is needed to maintain temperatures in the fluidised bed and in the flue gas channel within acceptable limits.

Place, publisher, year, edition, pages
2011. Vol. 88, no 5, p. 1813-1824
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-13209DOI: 10.1016/j.apenergy.2010.12.006ISI: 000288360500038Scopus ID: 2-s2.0-79551537174OAI: oai:DiVA.org:mdh-13209DiVA, id: diva2:452336
Available from: 2011-10-28 Created: 2011-10-28 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Fouling in biomass fired boilers
Open this publication in new window or tab >>Fouling in biomass fired boilers
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes a detailed investigation into fouling in biomass fired boilers according to fuel mixture, combustion conditions, transportation of particles by the flue gas and the probability of particles impinging and sticking onto heat transfer tubes. The effects of fouling on overall boiler performance and the efficacy of soot blowing are also investigated.

Both theoretical simulations and practical experiments on a 157 MW circulating fluidized bed boiler are presented.

The deposit thickness on and around a heat exchanger tube is shown to be mainly dependent on the ash particle size, as particles larger than 10 µm (Stokes number larger than 0.1) mainly impinge on the windward side of tubes. The study also shows that fuel containing small amounts of chlorine and zinc – common elements in recycled wood – may cause both higher deposit growth rates and rapid increases in corrosion rates. These elements (chlorine and zinc), together with alkali metals from the biomass have the potential to form sticky compounds that increase the deposit growth rate.

Reducing deposits by soot blowing is very effective at removing loose deposits but the hard sintered part of the deposits is almost unaffected. The use of recycled wood has a larger impact on the deposit growth rate than the soot blowing interval.

Numerical simulations show that deposits on the superheater tubes redistribute the heat transfer rate from the superheaters to reheater 1 and partially redistribute turbine power from the high pressure turbine to the intermediate pressure turbine

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2011
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 116
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-13204 (URN)978-91-7485-047-5 (ISBN)
Public defence
2011-12-20, Delta, Mälardalens högskola, Västerås, 13:30 (English)
Opponent
Supervisors
Available from: 2011-10-28 Created: 2011-10-28 Last updated: 2013-11-04Bibliographically approved
2. Process Modeling of Combustion and Digesters for On-line Applications
Open this publication in new window or tab >>Process Modeling of Combustion and Digesters for On-line Applications
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of biomass has increased in recent years due to the efforts to reduce the high emissions of greenhouse gases, primarily carbon dioxide from combustion of fossil fuels. At the same time industrial processes have become more complex because of increased production rates and profitability requirements. A higher degree of automation is needed when the processes are too complex to be handled manually. There is a need to find modeling strategies that can automatically handle the challenges that the conversion of biomass in an industrial process entails, such as operational changes, decreasing component and overall system efficiency, drifting sensors, etc. The objective of this thesis is to develop a methodology for on-line applications in industrial processes. Dynamic process models have been developed for continuous digesters and boilers. Process models have been evaluated for their use in continuous industrial process. Applications that have been studied are monitoring and diagnostics, advanced control and decision support. The process models are designed for on-line simulations. The results shows that the use of mathematical simulation models can improve the use of both process data and process understanding, to achieve improved diagnostics, advanced control and process optimization. In the two examples of industrial processes covered in this thesis, we can see that similar types of models can be used for completely different types of processes, such as pulp digesters and boilers. It also demonstrates the ability to combine soft sensors and hard sensors with physical models to take the information to a higher level of utilization.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2015
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 194
National Category
Energy Engineering
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-29462 (URN)978-91-7485-244-8 (ISBN)
Public defence
2015-12-15, R2-025, Mälardalens högskola, Västerås, 08:15 (English)
Opponent
Supervisors
Available from: 2015-11-12 Created: 2015-11-11 Last updated: 2015-11-25Bibliographically approved

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Sandberg, JanFdhila, Rebei BelDahlquist, ErikAvelin, Anders

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