Particle population balance model for a circulating fluidized bed boiler
Introduction
The complex hydrodynamics and char combustion behavior of circulating fluidized bed (CFB) boilers have not been fully understood. The properties and size distribution of particles have significant influence on the hydrodynamics and combustion behavior in the CFB furnace [1], [2], [3]. While a number of models of particle size distribution in fluidized beds have been reported, little is known of the particle size distribution in circulating fluidized bed boilers [4], [5], [6], [7], [8], [9]. Most of the published models for the particle population balance in CFB boilers do not consider some important processes occurring in the furnace, such as char burning and attrition while the particles are traveling in the primary loop, particles with different properties undergo different physical and chemical processes. These previous models still have some limitations in describing the particle properties and population balance in the CFB boilers [7], [8].
The present work is intended to develop a particle population balance model for circulating fluidized beds based on the experiments completed in a 12 MW CFB boiler, taking into account major physical and chemical processes that occur in CFB boilers.
Section snippets
Particle properties in CFB furnace
The solids inventory in a CFB furnace consists of spent and reacting fuel and sorbent particles and inert bed materials. The properties of feed particles have significant influence on the particle population balance in a CFB furnace. Additional bed material, like river sand, may be needed when a fuel with low ash content is fired. Even for a given fuel, properties such as the ultimate analysis may be subject to variations from time to time. In some cases, since the minerals content differs from
Particle population balance model
It has been widely accepted that a CFB furnace may be characterized by two flow regimes: a dense bed at the bottom and a dilute region above the solid entry or secondary air inlet. Because there are great differences in the hydrodynamics between the dense bed and the dilute region, the particle population models for the two respective regimes should be developed separately.
Fragmentation of coal particles
Previous studies suggested that primary fragmentation of coal particles in a fluidized bed occurred within a few seconds after injection of the particles into the bed due to build-up of thermal and devolatilization-induced stresses [7], [9]. It may be assumed that primary fragmentation occurs primarily in the zones close to the feed ports. An empirical correlation was proposed by Bellgardt et al. [9]
Bellgardt et al. [9] suggest that the fragmentation
Model validation
The overall mathematical model of the CFB boiler has been developed by combining the above-discussed models together with sub-models for other physical and chemical processes [26], [27]. The overall model is used to predict the performance of a 12 MW CFB boiler. The bituminous coal-fired boiler is the first of the type operational in China, which employs an external heat exchanger developed by Zhejiang University. The furnace is 21 m high and has a square cross-section measuring m in
Conclusions
A particle population balance model for the CFB boiler furnace has been developed. The core–annulus model is employed to describe the hydrodynamics of the circulating fluidized bed furnace. The particles present in the CFB furnace are characterized and grouped by their size and density. The model considers particle fragmentation, char combustion, attrition and gas–solid separation. The model is integrated into a comprehensive model of a 12 MW CFB boiler developed earlier by the authors for
Acknowledgements
The authors gratefully acknowledge the financial support from the Special Funds for China Major State Basic Research Projects (Grant G1999-022105).
References (27)
- et al.
Particle population model for a fluidized bed with attrition
Powder Technol.
(1987) - et al.
Distribution of trace elements in selected pulverized coals as a function of particle size and density
Fuel Process. Technol.
(2000) - et al.
Particle attrition phenomena in a fluidized bed
Powder Technol.
(1987) - et al.
High-pressure vertical pneumatic transport investigation
Powder Technol.
(1994) - et al.
Particle velocity profiles in a circulating fluidized bed of square cross-section
Chem. Eng. Sci.
(1995) - et al.
Fluid-dynamic boundary layers in CFB boilers
Chem. Eng. Sci.
(1995) - et al.
Comminution of carbon in fluidized bed combustion
Prog. Energy Combust. Sci.
(1991) - et al.
Elutriation from fluidized beds. I. Particle ejection from the dense phase into the freeboard
Chem. Eng. Sci.
(1986) - et al.
A mathematical model for a circulating fluidized bed
Energy
(1999) - et al.
Influence of particle size distribution on the performance of fluidized bed reactors
Can. J. Chem. Eng.
(1991)
The effect of particle size and density on solid distribution along the riser of a circulating fluidized
Chem. Eng. Sci.
Dynamic ash balance in circulating fluidized bed
J. Chin. Combust. Sci. Technol.
Cited by (42)
Hydrodynamics in the transport zone of a large-scale circulating fluidized bed boiler
2023, Powder TechnologyParticle attrition-breakage model for CFD-DEM simulation based on FRM and WPM: Application in blast furnace raceway
2023, Powder TechnologyCitation Excerpt :In previous researches [23,51], the worn material will be directly removed out of the system, which will not satisfy the conservation of solid phase mass, and the fine powders produced by wear also have the impact on the gas-solid flow. Although some studies [25,27] have taken it into account through the population balance model, the model focuses more on the overall balance of the particles and ignores the exact location where the wear material is generated. This work proposes a wear-equivalent particle method (WPM), in which the wear loss is replaced on the wear surface in the form of equivalent particles.
A multiscale analysis approach for the valorization of sludge and MSW via co-incineration
2023, EnergyCitation Excerpt :Different approaches have been used, for example, the use of simulation packages for the entire power island in steady state such as the process simulator W2E [18], as well as integrated systems that include logistics [19]. In addition, some groups have focused on the analysis of the incinerator [20] evaluating circulating beds using population balances [21] as well as different fixed bed reactors [22] using DEM [23] developing surrogate models for the emissions of the combustion [24], as well as studying the dynamics [25], with no details on the removal of dioxins and the co-incineration of sludge and MSW [26]. However, while most of the process studies focus on the thermodynamic yield, a facility that processes MSW requires a flue gas treatment to avoid emitting NOx, SO2 [27] but above all, heavy metals, dioxins, and furans [28].
A bimodal population balance method for the dynamic process of engineered nanoparticles
2022, International Journal of Heat and Mass TransferAnalysis of hematite attrition in a grid jet apparatus
2021, Powder Technology