Design, modelling and operation of a 100 kW chemical-looping combustor for solid fuels
Doktorsavhandling, 2012

With the increasing threat of global warming, technologies for efficient capture and storage of the greenhouse gas CO2 are sought after. Chemical-looping combustion is a novel CO2 capture technology that can be applied when burning gaseous, liquid or solid fuels. By using two interconnected fluidised beds with a bed material capable of transferring oxygen from air to the fuel, a nitrogen-undiluted stream of CO2 can be obtained with no direct efficiency loss. This thesis is focused on design, modelling and operation of a 100 kW chemical-looping combustor for solid fuels. The goal of the test rig is validation of chemical-looping combustion at a scale giving both high operational flexibility and semi industrial conditions. Two analytical models that can be applied to any chemical-looping combustor for solid fuels are presented. The first model finds the residence-time from batch-experiments. The second model estimates the gas conversion of a general fuel as a function of the oxygen carrier bed inventory. Furthermore, a cold-flow model of the 100 kW unit has been constructed. Details about the cold-flow model design and experimental results regarding fluidisation, slugging, residence-time and circulation are presented. The 100 kW unit has been operated for over 23 hours with an ilmenite oxygen carrier, using three different fuels. During this time, no instabilities in the bed inventories have been detected. Experiments aiming for optimal performance showed that gas conversion above 84% and CO2 capture over 99% are possible. A detailed analysis of the relation between the global solids circulation, the fuel reactor bed inventory and the gas conversion was conducted. The results revealed that the bed inventory in the fuel reactor had a strong impact on gas conversion, whereas little effect of overall circulation could be seen under the present conditions.

CO2 capture

Fluidised beds

Chemical-looping combustion

Modelling

Carbon capture and storage

Oxygen carriers

HC3-salen, Hörsalsvägen 14, Chalmers tekniska högskola
Opponent: Prof. John Dennis, University of Cambridge, Cambridge, UK

Författare

Pontus Markström

Chalmers, Energi och miljö, Energiteknik

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Under de senaste åren har rapporter om klimatförrändringar gjort både allmänheten och forskare medvetna om Jordens globala uppvärmning. Effekter som ökade havsnivåer och smältande isar indikerar en stark koppling till växthuseffekten, då utsläppen av växthusgaser har ökat i samma takt som temperaturen ökat. Detta har lett till en ökad efterfrågan på olika teknologier gällande infångning och lagring av koldioxidutsläpp. För energiproducerande anläggningar finns idag ett flertal tekniker där koldioxiden kan fångas in, fast till priset av en klart försämrad verkningsgrad. Det energikrävande steget är då kvävgas skiljs från koldioxid inför slutlagring. Kemcyklisk förbränning är en koldioxidinfångningsteknik, som utan detta energikrävande steg kan appliceras på t.ex. ett elkraftverk matat med fossila bränslen eller biomassa i en CFB-panna. Teknologin baseras på cirkulationen av en syrebärande metalloxid som man låter reagera med förgasat bränsle, varvid luftens kväve aldrig blandas med koldioxiden. Denna avhandling behandlar design, modellering och drift av en 100 kW kemcyklisk förbränningsanläggning för fasta bränslen. Driften av anläggningen är flexibel, vilket innebär att driftsparametrar kan varieras i ett stort spann för att utvärdera stabilitet och prestanda. Analytiska modeller för uppehållstid och gasomvandling redogörs för i kombination med utvärdering av över 20 timmars driftstid med tre olika bränslen.

In the last years, reports about climate change have made both the public and researchers aware of the Earth’s global warming. Effects like increased sea levels and melting polar caps indicate a strong connection to the greenhouse effect, as the release of greenhouse gases have increased at the same rate as the increase in temperature. This has led to an increased demand on technologies for capture and storage of carbon dioxide emissions. In energy production, there are today multiple techniques from which the carbon dioxide can be captured, albeit to the cost of a large efficiency drop. The energy demanding step is when nitrogen is separated from the carbon dioxide before storage. Chemical-looping combustion is a carbon dioxide capture technology, which without this efficiency drop can be applied to e.g. a power plant fed with fossil fuels or biomass in a CFB-boiler. The technology is based on the circulation of oxygen carrying particles, led to react with gasified fuel, precluding a mixture of the air’s nitrogen with carbon dioxide. This thesis treats the design, modelling and operation of a 100 kW chemical-looping combustor for solid fuels. Operation of the unit is flexible, which means that operational parameters can be varied in a wide range to evaluate stability and performance. Analytical models for residence-time and gas conversion are reported in combination with an evaluation of over 20 h of operation with three different fuels.

Drivkrafter

Hållbar utveckling

Ämneskategorier

Energiteknik

Styrkeområden

Energi

Fundament

Grundläggande vetenskaper

ISBN

978-91-7385-771-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3452

HC3-salen, Hörsalsvägen 14, Chalmers tekniska högskola

Opponent: Prof. John Dennis, University of Cambridge, Cambridge, UK

Mer information

Skapat

2017-10-07