Energy and Fuels, 2022, 36(17), pp. 9588–9615, 2022
Chemical looping combustion (CLC) has unique potential for avoiding the large costs and energy pe... more Chemical looping combustion (CLC) has unique potential for avoiding the large costs and energy penalties of existing CO 2 capture technologies. Oxygen is transferred to the fuel using an oxygen carrier, thus avoiding contact between air and fuel. Consequently, the combustion products, CO 2 and H 2 O, come in a separate stream, and more or less pure CO 2 is obtained after condensation of H 2 O. CLC is normally conceived as a dual fluidized bed process, with high gas velocities in an air reactor driving the circulation, similar to circulating fluidized beds (CFBs), except that the material is led to a fuel reactor before being returned to the air reactor. Crucial for the process is the properties of the oxygen carrier and that circulation is sufficient to transfer needed oxygen and heat to the fuel reactor. Comprehensive literature shows successful use of many oxygen carriers in sustained pilot operation. In contrast, the need for reaching adequate circulation in an industrial-scale system has been given little consideration. Normally, a system similar to CFB boilers is assumed to give sufficient circulation. However, literature data indicate that circulation in CFB boilers is 5−50% of what is needed. Measures to provide sufficient circulation may cause difficulties, such as erosion or bed material loss in the cyclone. Here, a circulation system based on collection of the downflow of particles along the walls is proposed, and a design of a 200 MW th combined CLC−CFB boiler based on this principle is presented. Further, operational strategies and the need for flexibility are discussed. The design is focused on making an industrial-scale demonstration boiler, which can be used in CLC operation with different oxygen carriers and different fuels and that can explore different operational strategies to find optimal conditions. It is recommended that the upscaling of the technology aims directly at the industrial scale.
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Papers by David Pallarès
protocols in order to remain economically competitive while also providing grid-balancing services required to
deal with the inherent fluctuations of variable renewable electricity. This work presents a dynamic model of
fluidized bed combustion plants for combined heat and power production. The novelty of the work lays in that (i)
it provides an analysis of the transient performance of biomass-based fluidized bed combustion plants for
combined heat and power production, (ii) the dynamic model includes a description of both the gas and watersteam
sides and (iii) the model is validated against operational data acquired from a commercial-scale plant. The
validated model is here applied to analyze the inherent dynamics of the investigated plant and to evaluate the
performance of the plant when operated under different control and operational strategies, using a relative gain
analysis and a variable ramping rate test.
The results of the simulations reveal that the inherent dynamics of the process have stabilization times in the
range of 5–25 min for all the step changes investigated, with variables connected to district heating production
being the slowest. In contrast, variables connected to the live steam are the fastest, with stabilization times of
magnitude similar to those of the in-furnace variables (i.e., around 10 min). Thus, it is concluded that the proper
description of the dynamics in fluidized bed combustion plants for combined heat and power production requires
modeling of both the gas and water sides (which is rare in previous literature). Regarding the assessment of
control strategies, the boiler-following and hybrid control (combined fixed live steam and sliding pressure)
strategies are found to be able to provide load changes as fast as 5%-unit/s, albeit while causing operational
issues such as large pressure overshoots. The relative gain analysis outcomes show that these control structures
do not have a steady-state gain on the power produced, and therefore it is the dynamic effect of the steam
throttling that triggers the rapid power response. This study also includes the assessment of a turbine bypass
strategy, the results of which show that it enables fast load-changing capabilities at constant combustion load, as
well as decoupling power and heat production at the expense of thermodynamic losses.
protocols in order to remain economically competitive while also providing grid-balancing services required to
deal with the inherent fluctuations of variable renewable electricity. This work presents a dynamic model of
fluidized bed combustion plants for combined heat and power production. The novelty of the work lays in that (i)
it provides an analysis of the transient performance of biomass-based fluidized bed combustion plants for
combined heat and power production, (ii) the dynamic model includes a description of both the gas and watersteam
sides and (iii) the model is validated against operational data acquired from a commercial-scale plant. The
validated model is here applied to analyze the inherent dynamics of the investigated plant and to evaluate the
performance of the plant when operated under different control and operational strategies, using a relative gain
analysis and a variable ramping rate test.
The results of the simulations reveal that the inherent dynamics of the process have stabilization times in the
range of 5–25 min for all the step changes investigated, with variables connected to district heating production
being the slowest. In contrast, variables connected to the live steam are the fastest, with stabilization times of
magnitude similar to those of the in-furnace variables (i.e., around 10 min). Thus, it is concluded that the proper
description of the dynamics in fluidized bed combustion plants for combined heat and power production requires
modeling of both the gas and water sides (which is rare in previous literature). Regarding the assessment of
control strategies, the boiler-following and hybrid control (combined fixed live steam and sliding pressure)
strategies are found to be able to provide load changes as fast as 5%-unit/s, albeit while causing operational
issues such as large pressure overshoots. The relative gain analysis outcomes show that these control structures
do not have a steady-state gain on the power produced, and therefore it is the dynamic effect of the steam
throttling that triggers the rapid power response. This study also includes the assessment of a turbine bypass
strategy, the results of which show that it enables fast load-changing capabilities at constant combustion load, as
well as decoupling power and heat production at the expense of thermodynamic losses.