A conversion-class model for describing fuel conversion in large-scale fluidized bed units

Lundberg, Louise; Johansson, Robert; Pallarès, David; Thunman, Henrik

doi:10.1016/j.fuel.2017.01.090

Cited by 3 publications

(5 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thermochemical Conversion. The generation and consumption rates of the fuel class (phase components of the fuel phase) n are computed according to eqs 17 and 18, with X n−1,rel being the mass fraction of the foregoing class converted to the gas phase (for details, see ref 35). Each class has a characteristic time related to its thermochemical process, i.e., drying, devolatilization, and char combustion.…”

Section: ∑ ∑mentioning

confidence: 99%

“…Finally, the third class represents the fuel after all moisture and volatiles have been released (the density is calculated consequently), i.e., the char particles. An accurate description would demand representation of the char through several conversion classes (see ref ). However, this would in turn require a description of the fuel fragmentation, which is a complex phenomenon that is highly fuel-dependent and typically not straightforward to characterize.…”

Section: Description Of the Modelmentioning

confidence: 99%

See 1 more Smart Citation

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

Castilla

Montañés

Pallarès

et al. 2021

Ind. Eng. Chem. Res.

Self Cite

View full text Add to dashboard Cite

This work presents a dynamic model of the reactive side of large-scale fluidized bed (FB) boilers that describes the infurnace transient operation of both bubbling and circulating FB boilers (BFB and CFB, respectively). The model solves the dynamic mass and energy balances accounting for the bulk solids, several gas species, and the fuel phase. The model uses semiempirical expressions to describe the fluid dynamics, fuel conversion, and heat transfer to the furnace walls, as derived from units other than the studied ones. The model is validated against operational data from two different industrial units: an 80 MW CFB and a 130 MW BFB, both at steady-state and transient conditions. The validated model is used to analyze: (i) the performance of the reactive side of two FB boilers under offdesign, steady-state conditions of operation; and (ii) the open-loop transient response when varying load or fuel moisture. The results underline the key role of heat capacity on the stabilization time. Within a given unit, the differences in heat capacity between the top and bottom of the furnace affect also the stabilization times, with the furnace top (lower heat capacity) being 1−3 times faster in the CFB unit and up to 10 times faster in the BFB unit. Due to the differences in gas velocity, the investigated boilers are found to stabilize more rapidly to input changes when running at full load than at partial load. Lastly, a variable ramping rate analysis shows that the inherent transient responses of the reactive side disappear when disturbances are introduced at (slower) rates, typical of industrial operation. Thus, the reactive side could be modeled as pseudo-static.

show abstract

Section: ∑ ∑mentioning

confidence: 99%

Section: Description Of the Modelmentioning

confidence: 99%

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

Castilla

Montañés

Pallarès

et al. 2021

Ind. Eng. Chem. Res.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Mass Balances for Fuel Species. The reactive fuel components (moisture, volatiles and char), k, are each divided into a number of classes, j, based on the degree of conversion (see Lundberg et al), 33 all for which a mass balance [eq 7] is solved. Equation 7 is also used to calculate the concentration field of ash along the gasifier, using a single nonreactive class.…”

Section: Energy and Fuelsmentioning

confidence: 99%

“…As seen in Figure 4a, a submodel based on a particle model (described in Lunderg et al), 33 is run for a given fuel prior to the model simulations to generate an interpolation table with values of the apparent conversion rate of conversion class j in fuel component k (R k,j ) for a range of steam concentrations and/or temperatures.…”

Section: Energy and Fuelsmentioning

confidence: 99%

Upscaling Effects on Char Conversion in Dual Fluidized Bed Gasification

2018

Self Cite

View full text Add to dashboard Cite

Dual fluidized bed gasification (DFBG) is an emerging technology that can be employed as a first step in the transformation of lignocellulosic materials into transportation fuels such as substitute natural gas, dimethyl ether, methanol, and Fischer−Tropsch diesel. The present work aims at (i) identifying challenges that arise in the upscaling of DFBG plants, (ii) determining whether the increased fuel residence time that results from the upscaling is sufficient for process optimization, and (iii) evaluating the impact of measures to mechanically control the fuel residence time. The investigations use a semiempirical 1dimensional model, which is validated with industrial-scale measurements. The scope includes both DFBG units delivering gas as the main product and those in which the product gas is a byproduct in a heat and power plant. Moreover, both new designs and retrofit cases of existing CFB combustion plants (i.e., adding a gasifier to the return leg) are considered. Modeling results show that although there is an initial increase in the fuel residence time as the size of the gasifier increases, further upscaling eventually leads to a decrease in the degree of char gasification due to (i) a decrease in the fuel residence time, as there is a transition in lateral fuel mixing from the dispersion-dominant regime to the convection-dominant regime; and (ii) a decrease in the char gasification rate due to an increased bed material velocity, which increases the probability that pyrolysis occurs on the bed surface (leading to a less reactive char as the heat transfer is lower there compared to inside the dense bed). For DFBG units of around 100 MW, proper combinations of operational conditions (e.g., the solids circulation, the steam-fuel ratio, and the temperature of the circulating solids) result in an optimized process when heat and power is the main product, with gas as a byproduct. However, when gas is the sole targeted product, it is likely that baffles are also necessary to achieve sufficient fuel conversion for process optimization.

show abstract

“…Among the possibilities for burning coal, fluidized bed combustors are a promising technology [1][2][3][4][5][6] because the desulphurization process (up to 95 %) can be carried out by injecting calcium-based sorbent into the furnace.…”

Section: Introductionmentioning

confidence: 99%

Effect of sorbent reactivity on flue gas desulphurization in fluidized‐bed boilers under air firing mode

Loscertales

Pajdak

2017

Can J Chem Eng

View full text Add to dashboard Cite

The article presents research into the reactivity and SO 2 sorption abilities of calcareous sorbents, which vary in quality. Two sorbents were used: limestone and travertine, with grain sizes between 0.125 and 0.250 mm. The sorbent reactivity tests were performed on a laboratory test stand. The reactivity index and the conversion degree were also determined. SO 2 sorption studies were conducted in an industrial boiler. The desulphurization efficiency was determined taking into the account the content of calcium and sulphur put into and taken out of the boiler. The relation of the desulphurization process parameters such as fuel sulphur content, stream sorbent, sorbent utilization degree, desulphurization efficiency, depending on the molar ratio Ca/S and the duration of the process was specified. The SO 2 sorption results were compared with the reactivity index of the sorbents. The investigation in dry combustion-gas desulphurization methods showed the high quality of the sorbents whose reactivity index is above 3.5.

show abstract

A conversion-class model for describing fuel conversion in large-scale fluidized bed units

Cited by 3 publications

References 14 publications

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

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

Upscaling Effects on Char Conversion in Dual Fluidized Bed Gasification

Effect of sorbent reactivity on flue gas desulphurization in fluidized‐bed boilers under air firing mode

Contact Info

Product

Resources

About