Impact of Ash on the Properties of Fluidized Bed Materials
Doktorsavhandling, 2022

The utilization of the fluidized bed technology offers the possibility of thermally converting a large variety of biogenic feedstocks. The characteristics of the bed material which is used in the process play a major role regarding the overall process performance. These characteristics are influenced by interactions between the bed material and the fuel ash. The materials investigated within this work were quartz, ilmenite, olivine, and two different feldspars. This work investigates several different properties of the bed material which can be influenced by interactions with the fuel ash. Depending on the combinations of fuel and bed material, as well as the choice of thermal conversion process, these interactions can be beneficial or detrimental.

It was found that quartz and ilmenite have a strong tendency to react with alkali and can thereby mitigate to a certain degree alkali-induced corrosion of metallic components in the reactor. In the case of quartz, this bed material-alkali interaction leads to the formation of alkali-silicates which exhibit a low melting temperature and can therefore cause agglomeration of the bed material.

Olivine and feldspar are more resistant towards agglomeration. Interactions with biomass ash led to the formation of an ash layer which has catalytic properties towards tar removal, which is necessary to avoid problems associated with tar condensation during gasification. After longer residence times, the particles acquire an oxygen carrying ability due to the formation of a surface layer containing Fe and Mn. This decreases the calorific value of the product gas and requires bed material replacement. If fuel containing high amounts of phosphorus is converted, this waste stream can further be utilized for nutrient recovery.

Ilmenite is used in a process which exploits its oxygen carrying ability. Dilution of ilmenite by fuel ash diminishes this property but the necessary replacement of material can be decreased by magnetically separating active ilmenite from inactive ash.

ash interaction

layer formation

agglomeration

fluidized bed

catalytic tar removal

oxygen carrying

bed material

EF-salen, Hörsalsvägen 11, Göteborg
Opponent: Professor Maria Zevenhoven, Åbo Akademi University, Finland

Författare

Robin Faust

Chalmers, Kemi och kemiteknik, Energi och material

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Robin Faust, Ali Valizadeh, Ren Qiu, Alyona Tormachen, Jelena Maric, Teresa Berdugo Vilches, Nils Skoglund, Martin Seemann, Mats Halvarsson, Marcus Öhman, Pavleta Knutsson; Ash Layer Formation in Dual Fluidized Bed Gasification of Wood – Impact of Surface Morphology

Robin Faust, Katharina Fürsatz, Panida Aonsamang, Marcus Sandberg, Matthias Kuba, Nils Skoglund, Pavleta Knutsson; Early Layer Formation on K-Feldspar during Fluidized Bed Combustion with Phosphorus-rich Fuel

Anthropogenic greenhouse gas emissions are a major driver for global warming. Especially the CO2 emissions by burning of fossil fuels for heat and power generation have contributed to an increase in global greenhouse gas concentrations since the industrial revolution. Replacement of fossil fuels with renewable sources is one way of decreasing further CO2 emissions into the atmosphere. Furthermore, the utilization of biomass and waste as fuel for heat and power generation offers the possibility to reduce the dependence on fossil fuel imports.  

A suitable technique to achieve efficient conversion of these complex and inhomogeneous feedstocks, is through the application of a fluidized bed. In a fluidized bed reactor, the fuel is immersed in a sand bed and a gas stream is led from below through the bed material. Thereby, the sand acquires fluid-like characteristics which improve the distribution of heat throughout the reactor, which is beneficial for the thermal conversion of inhomogeneous fuels.

An important factor for the efficiency of fluidized bed reactors are the interactions between the sand bed material and the fuel ash. Depending on the process conditions as well as the compositions of fuel and bed material, these interactions can improve the process and facilitate the generation of a gas which can be used to produce, for example, biofuel. In other cases, the interactions can be detrimental and require replacement and disposal of the ash-enriched bed material. Handling and recycling of parts of this waste stream is important to reduce the waste fraction and increase the overall circularity of the process.

This work provides insight into the different challenges and opportunities that exist for the application of renewable fuels for thermal conversion in fluidized bed reactors.

Ämneskategorier

Oorganisk kemi

Kemiska processer

Materialkemi

Bioenergi

Infrastruktur

Chalmers materialanalyslaboratorium

ISBN

978-91-7905-693-3

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5159

Utgivare

Chalmers

EF-salen, Hörsalsvägen 11, Göteborg

Opponent: Professor Maria Zevenhoven, Åbo Akademi University, Finland

Mer information

Senast uppdaterat

2022-08-05