Effects of particle type on the particle fluidization and distribution in a liquid–solid circulating fluidized bed boiler

A liquid-solid circulating fluidized bed boiler is designed and built for visualization research by applying the fluidized bed heat transfer and fouling prevention technology to the water side of the boiler. Four types of engineering plastic particles with different physical properties are selected as the solid working media. The effect of particle types on the fluidization and distribution of particles in the boiler is investigated under different feedwater flow rates and amount of added particles by using the charge couple device image measurement and acquisition system. The results show that all kinds of particles can't be normally fluidized and accumulate in the drum at low amount of added particles and feedwater flow rate. The particles with great density and low sphericity are more likely to accumulate. The average solid holdup in the riser tubes increases with the increase in feedwater flow rate and the amount of added particles. The non-uniform degree of particle distribution in the riser tubes generally decreases with the increase in feedwater flow rate and the amount of added particles. The particles with small density and settling velocity have high average solid holdup in the riser tubes under close sphericity. In generally,the smaller the density and settling velocity, the more uniform the particle distribution in the riser tubes.Three-dimensional diagrams of the non-uniform degree of particle distribution in the riser tubes of the boiler are established.

Compatibility of Fly Ash and Slag from Circulating Fluidized Bed Boiler for Concrete Beam

The applications of fly ash and slag from circulating fluidized bed boiler were studied as mineral admixture and aggregate for steel reinforced concrete beam.The results show that the concrete beam with fly ash and slag from circulating fluidized bed boilers has a similar ultimate cracking load coefficient as the ordinary cement concrete and a higher bending moment limit.Under the same load,it has a smaller deformation than the ordinary concrete.

Hardening Properties of Foamed Concrete with Circulating Fluidized Bed Boiler Ash, Blast Furnace Slag, and Desulfurization Gypsum as the Binder

Recently, a large amount of circulating fluidized bed boiler ash (CFBA) and desulfurization gypsum (DSG) has been produced, and it is essential to develop technology to utilize them. These materials have CaO and SO3, which are considered to be a stimulant for blast furnace slag (BFS). This study presents an experimental investigation of the compressive strength and heavy metal ions immobilization properties of cement-free materials comprising CFBA, BFS, and DSG. The feasibility of manufacturing foamed concrete using these materials was examined, and field test of foamed concrete was conducted. Experimentally, the flow, compressive strength, and heavy metal ions concentration were evaluated via inductively coupled plasma atomic emission spectroscopy (ICP-AES) of the paste and foamed concrete. The experimental investigation revealed the self-healing hardening ability of fluidized bed boiler ash. In addition, the compressive strength was increased with the increasing replacement rates of BFS and DSG in the CFBA paste, and the compressive strength of 14.6 - 17.2 MPa was recorded over 28 days of curing. From the result obtained, the feasibility of manufacturing foamed concrete with a foam volume of 120 L, incorporating the aforementioned materials, is confirmed. It was also found that after 28 days of age, a 7.9-MPa compressive strength of the foamed concrete was attained, and heavy metal ions elution in this foamed concrete was also significantly reduced. Therefore, CFBA, BFS, and DSG could be used as a binder for the foamed concrete.

Combustion and Self-Desulfurization Characterization of Blended Low-Rank Coals for Improved Resource Utilization in Fluidized Bed Boilers

The co-combustion of low-rank coals through fluidized bed boiler(CFB)is an effective approach to enhance the level of resource utilization.To date,there has been a lack of investigation concerning the co-combustion kinetics and self-desulfurization characteristics of coal slime,coal gangue,and raw coal.In this study,we adopted multiple model-free and model-fitting methods to comparatively analyze co-combustion kinetics of blended coals on the basis of thermogravimetric data.Then,the sulfur balance and self-desulfurization of blended coals in the co-combustion were intensively investigated using a tube furnace set-up.The results reveal that in the presence of coal gangue in blended coals,the average activation energy(E_(a))falls within the range of 65.7 kJ/mol to 100.4 kJ/mol,as determined by four model-free methods.Conversely,in the absence of coal gangue,only the Flynn-Wall-Ozawa(FWO)and Friedman(FM)methods are deemed appropriate for calculating the average E_(a),yielding a value of 77.3 kJ/mol.The first order reaction model is confirmed to be reliable for analyzing the co-combustion kinetics of low-rank blended coals.Irrespective of the specific composition of the blended coal,a significant linear correlation exists between the Ea and the natural logarithm of the pre-exponential factor(lnA)within an extensive range of parameters.Moreover,the addition of coal gangue to the blended coal substantially enhances the self-desulfurization level,resulting in an increase from 25.7%to60.7%at 1073 K.The self-desulfurization efficiency exhibits a good linear relationship with both the mass ratio of coal gangue to coal slime and the molar ratio of calcium to sulfur.In a practical implementation,the optimal addition ratio of coal gangue is a trade-off between the self-desulfurization efficiency and the ignition capacity.

Extending EMMS-based models to CFB boiler applications

Recently, EMMS-based models are being widely applied in simulations of high-throughput circulating fluidized beds （CFBs） with fine particles. Its use for low flux systems, such as CFB boiler （CFBB）, still remains unexplored. In this work, it has been found that the original definition of cluster diameter in EMMS model is unsuitable for simulations of the CFB boiler with low solids flux. To remedy this, we propose a new model of cluster diameter. The EMMS-based drag model （EMMS/matrix model） with this revised cluster definition is validated through the computational fluid dynamics （CFD） simulation of a CFB boiler.