Oxygen carrier aided combustion: Implementation of oxygen carriers to existing industrial settings
Doctoral thesis, 2019

Utilization of biomass and waste to produce heat and power is necessary for a sustainable future energy mix. Thermal conversion of biomass is considered to yield CO2 neutral emissions and the utilization of waste reduces its volumes in a world struggling to dispose of ever-increasing amounts. However, these fuels can be difficult to combust as they are complex in their composition. One technology allowing for conversion of both biomass and waste is fluidized bed conversion. Commonly, fluidized bed boilers are operated with an excess of air which lowers the efficiency of the plant. Replacing the quartz sand used as bed material during biomass and waste conversion with an oxygen carrier is referred to as oxygen carrier aided combustion (OCAC). By this replacement, oxygen availability is increased throughout the combustion chamber with increased boiler efficiency as a consequence.

This thesis presents the implementation of oxygen carriers to existing industrial units. The development has been rapid due to the possibility of conducting research through integration of scales. Experiments on semi- and full industrial scale validated the improved distribution of oxygen. Bed materials extracted from the industrial units were analyzed and tested for their oxygen transferring capacity on laboratory scale. The evaluation of bed materials provided for an understanding of how oxygen carriers can be utilized for the concept. The oxygen carriers included in this work are two types of ilmenite: sand and rock, and a manganese ore.

This work provides a comprehensive understanding of how the bed material develops regarding oxygen transfer, as well as chemical and mechanical resistance. Sand and rock ilmenite show different characteristics when exposed to the process. When following their progression of iron and structural development after being subjected to OCAC, sand ilmenite develops cavities inside the particles to which iron migrates and which further causes mechanical instability and shattering of particles over time. Iron migrates to surfaces on rock ilmenite particles, which are decomposed by splitting. The materials interact similarly with main ash constituents of the fuel. A heterogenic outer layer is formed, consisting mainly of Ca but also traces of other elements from the fuel ash. Ca and K diffuse inward and are incorporated in the ilmenite structure. The ash interactions are not found to directly inhibit the oxygen carrying capacity, however, a decline in capacity is noticed as ash layers build up and become thicker.

This work shows that the oxygen carrier ilmenite can be implemented in existing industrial settings, without reconstruction of the current system. Optimization measures are proposed where magnetic separation allows for reuse of bed material that still contain oxygen transferring capacity and the regeneration of bed material can be decreased in comparison to quartz sand. Thus, the results of this thesis suggest that OCAC is a feasible concept for conversion of complex fuels.

Ilmenite

Oxygen carrier aided combustion

Fluidized-bed

Biomass

Hörsal KC, Kemigården 4
Opponent: Prof. JoAnn Slama Lighty, Dean College of Engineering, Boise State University, USA

Author

Angelica Gyllén

Chalmers, Space, Earth and Environment, Energy Technology, Energy Technology 2

Gyllén, A. Knutsson, P. Lind, F. Thunman, H. Oxygen carrier activity dependence of ash layers on natural ilmenite.

A Scale-Up Project for Operating a 115 MWth Biomass-Fired CFB boiler with Oxygen Carriers as Bed Material

Proceedings of the 5th International Conference on Chemical Looping,; (2018)

Paper in proceedings

Den ökande koncentrationen växthusgaser i atmosfären ger upphov till en ökad temperatur på jorden med klimatförändringar som följd. Samtidigt fortsätter konsumtionen av produkter att öka globalt. Tillverkning av produkter kräver energi och dessutom måste avfallet hanteras när produkten är uttjänt. På global nivå kommer i dagsläget den största delen energi från fossila bränslen och den övervägande mängden avfall läggs på deponi.

För att möta dessa utmaningar står världen inför en stor omställning i dess energisystem. Efterfrågan på energi ökar fortfarande och för att försäkra en hållbar framtid som inte tär på jordens resurser måste vi fokusera på att ställa om till fossilfria och hållbara energikällor. Ett problem med att byta ut förbränning av kol och olja mot mer hållbara alternativ som biomassa och avfall är att dessa bränslen är betydligt mer komplexa och därmed ställer högre krav på själva förbränningsprocessen.  

I detta arbete presenteras en innovativ metod för att utvinna energi ur dessa svåra bränslen. Genom att använda en så kallad syrebärare i förbränningsprocessen kan kontakten mellan syre och bränsle förbättras. Metoden har prövats från laborativ skala till full industriell skala med goda resultat. Detta arbete fokuserar främst på den naturligt förekommande syrebäraren ilmenit, och hur den påverkas under processens gång.

More efficient combustion of heterogeneous biomass mixtures in fluidized beds (B6)

E.ON Sverige, 2018-01-01 -- 2019-12-31.

Subject Categories

Energy Engineering

Chemical Process Engineering

Bioenergy

Areas of Advance

Energy

ISBN

978-91-7905-124-2

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4591

Publisher

Chalmers University of Technology

Hörsal KC, Kemigården 4

Opponent: Prof. JoAnn Slama Lighty, Dean College of Engineering, Boise State University, USA

More information

Latest update

5/9/2019 1