Fluidized bed plants for heat and power production in future energy systems
Doctoral thesis, 2023

Fluidized bed (FB) plants are used for heat and power production in several energy systems around the world, with particular importance in systems using large shares of renewable solid fuel, e.g., biomass. These FB plants are traditionally operated for base-load electricity production or for heat production, and thus characterized by relatively small and slow load changes. In parallel, as the transition towards energy systems with net-zero emissions increases the share of variable renewable energy (VRE) sources, the need for implementing variation management strategies at various timescales arises – giving heat and power plants the possibility to adapt their operations to accommodate the inherent variability of VRE sources. Following this, FB technology is envisioned for a wide range of novel applications expected to play significant roles in the decarbonization of energy systems, such as thermochemical energy storage and carbon capture and storage. In this context, research efforts are needed to investigate the technical and economic features of FB plants in energy systems with high levels of VRE.
The aim of this thesis is to elucidate the capabilities of FB plants for heat and power production in net-zero emissions energy systems. For this purpose, two main pathways are explored: i) transient operation as fuel-fed plants, and ii) the potential conversion into decarbonized plants, i.e., into VRE-fed layouts providing dispatchable outputs.
For fuel-fed FB plants, a dynamic model of biomass-fired FB plants has been developed, considering the two types of FB boilers (BFB and CFB) and including validation against steady-state and transient operational data collected from two commercial plants. As a novelty of this work the model describes both the gas (in-furnace) and water-steam sides such that the interactions between the two can be assessed. The results of the simulations show that i) the characteristic times for the gas side are shorter in BFB furnaces than in CFBs, albeit these times are for both furnace types not longer than those for the water-steam side; ii) the computed timescales for the dynamics of FB plants fall well within those required for offering complementing services to the grid; and iii) the use of control and operational strategies for the water-steam side can confer capabilities superior to fuel-feeding control in terms of avoiding undesirable unburnt emissions and providing temporary overload operation. The retrofit of fuel-fed FB plants into poly-generation facilities cogenerating a combustible biogenic gas is also assessed, revealing that partial combustion of this gas can be used to provide faster inherent dynamics than the original configuration.
For VRE-fed FB layouts, techno-economic process modeling has been carried out for large-scale deployment of solar- and electricity-charging processes based on three different chemical systems: i) carbonation/calcination (calcium); ii) thermally reduced redox (cobalt oxides); and iii) chemically reduced redox (iron oxides). One attractive aspect of these layouts is the possibility to build part of them by retrofitting current fuel-fed FB plants. While the technical assessment for solar applications indicates that cobalt-based layouts offer the highest levels of efficiency and dispatchability, calcium-based processes present better economics owing to the use of inexpensive calcium material. The results also show that electricity-charged layouts such as iron looping can play an important role in the system providing variation management strategies to the grid while avoiding costly H2 storage. Further, the economic performances of VRE-fed FB layouts are benefitted by the generation of additional services and products (e.g., carbon capture and on-demand production of H2), and by scenarios with high volatility of the electricity prices.

biomass combustion

combined heat and power

thermal power plant

process control

operational flexibility

KC, Kemigården 4
Opponent: Franz Winter, TU Wien, Austria


Guillermo Martinez Castilla

Chalmers, Space, Earth and Environment, Energy Technology

Comparison of the Transient Behaviors of Bubbling and Circulating Fluidized Bed Combustors

Heat Transfer Engineering,; Vol. 44(2023)p. 303-316

Journal article

Dynamic Modeling of the Reactive Side in Large-Scale Fluidized Bed Boilers

Industrial & Engineering Chemistry Research,; Vol. 60(2021)p. 3936-3956

Journal article

Martinez Castilla G., Guío-Pérez D.C., Papadokonstantakis S., Johnsson F., Pallarés D., "Techno-economics of solids-based thermochemical energy storage systems for high-temperature applications at large scale"

There is a long future ahead of fluidized bed plants for heat and power production!

Energy supply is the single largest contributor to climate change, with up to 40% of the greenhouse emissions linked to the combustion of fossil-fuels corresponding to generation of electricity and heat. Thus, a key element in the transition towards a sustainable energy system is the generation of electricity through variable renewable energy (VRE) technologies, namely wind and solar power, which in the last years have experienced a large reduction in cost and is undergoing a wide deployment worldwide. However, as the share of VRE increases, so do the needs for balancing supply and demand across different timescales.

Fluidized bed (FB) reactors have several characteristics (fuel flexibility, efficient conversion, good mass and heat transfer) providing them the potential to aid the penetration of VRE technologies. Nonetheless, research efforts are needed to clarify the capabilities of FB technology in terms of flexible load operation and of serving new applications such as thermochemical energy storage (TCES) and poly-generation systems.

This thesis explores new operational and process design opportunities for FB plants to contribute towards net-zero emissions energy systems. Specifically, this work first investigates the ability of fuel-fed FB plants to provide rapid load changes. Second, the thesis assesses the potential of FB plants to decarbonize (i.e., become fuel-free) by storing VRE and dispatching heat and power on-demand.

Regarding fuel-fed FB units, this thesis studies the inherent dynamics of FB heat and power plants and evaluates how the use of different control and operational strategies can help attaining rapid load changes. Results show that, contrary to the previous general belief, FB plants can reach similar dynamic features as heat and power plants with other reactor technologies.

VRE-fed FB systems providing energy storage for high-temperature applications show strongly improved economic feasibility for scenarios with high volatility of the electricity prices and when the processes are designed to provide additional products (H2 on-demand or pure O2) or services (capturing CO2 from a nearby emitter).

Cost-effective and flexible polygeneration units for maximised plant use

Swedish Energy Agency (P46459-1), 2018-07-01 -- 2021-12-31.

Subject Categories

Energy Engineering

Chemical Process Engineering

Energy Systems

Areas of Advance




Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5389



KC, Kemigården 4


Opponent: Franz Winter, TU Wien, Austria

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