ISSN 0104-6632 Printed in Brazil

www.abeq.org.br/bjche

Vol. 33, No. 04, pp. 885 - 896, October - December, 2016 dx.doi.org/10.1590/0104-6632.20160334s20150348

*To whom correspondence should be addressed

Brazilian Journal of Chemical Engineering

INFLUENCE OF THE MODEL SCALE ON HYDRODYNAMIC SCALING IN CFB BOILERS

P. Mirek

Institute of Advanced Energy Technologies, Czestochowa University of Technology

Dąbrowskiego 69, 42-201 Częstochowa, Poland. Phone: + 48 34 3250 933; Fax: + 48 34 3250 933

E-mail: pmirek@neo.pl

(Submitted: January 24, 2015 ; Revised: October 17, 2015 ; Accepted: November 4, 2015)

Abstract - The paper presents the results of experimental verification of the simplified set of scaling parameters for which the particle density as well as the cold model length scale may be chosen independently. The tests were carried out on two large scale 1/10 and 1/20 geometrically similar cold models of the Lagisza 966 MWth supercritical CFB boiler. The proposed set of dimensionless quantities allowed the Lagisza 966 MWth CFB boiler to be closely modeled by cold models. However, the agreement between the hot bed and cold model's suspension density distributions is better for the 1/10 scale cold model. That suggests that the choice of the scale of a cold model is not without effect on the macroscopic movements of solids in the riser. Moreover, the study shows that a simplification of the scaling laws which excludes the very important solid-to-gas density ratio can give acceptable results over a wide range of boiler loadings. Keywords: Fluidization; Similitude; Modeling; Dimensionless numbers.

INTRODUCTION

The main environmental advantage of Circulated Fluidized Bed (CFB) technology is its ability to burn a diverse range of difficult low grade fuels of varying quality with low emissions of NOx, low-cost sulfur capture during combustion in the furnace itself, as well as low CO and CxHy emissions due to turbulent conditions and good mixing (Nowak and Mirek, 2013). Although CFB boilers have been investigated extensively for a long time because of their undenia-ble advantages, it is still impractical to design and operate them based on theoretical models (Qi et al., 2008). Due to the complex flow behavior that charac-terizes gas-solid systems, a complete description of circulating fluidized bed hydrodynamics remains a challenging task (Detamore et al., 2001). In the ab-sence of alternative methods, scaling rules developed over the last two decades proved to be a reasonable tool for the scale-up and scale-down of fluidization processes (Sierra et al., 2009). As has been noted by

Horio (1996), there have been three different ap-proaches to the scaling law of fluidized beds: classical dimensional analysis (e.g., Buckingham π-theorem), differential equations (or, more specifically, non-di-mensionalization of the continuum equations that describe multiphase flows) and theoretical solutions and experimental correlations.

Taking into consideration the second approach and differential equations derived by Anderson and Jack-son (1967), Glicksman and coworkers (1994) formu-lated the following set of dimensionless quantities describing the state of the full hydrodynamic similar-ity between two unlike CFB systems:

20 00

0, , , , ,

, ,geometry

p p p f s

f p

ρ U d ρ U HρU GgH ρ μ μ ρ U

φ PSD (1)

All these groups, respectively, refer to the Froude

886 P. Mirek

Brazilian Journal of Chemical Engineering

number FrH based on the gas superficial velocity U0, the solid to gas density ratio, the particle Reynolds number Rep, the Reynolds number ReH based on the riser height, the dimensionless solids flux, the particle sphericity φ , the particle size distribution and finally the geometrical characteristics. In formulation of the dimensionless quantities in Eq. (1) a general assump-tion has been made that particle to particle and parti-cle to wall coefficients of restitution and friction, electrostatic forces and cohesion can be neglected (van der Meer et al., 1999). As follows from the set of scaling relationships, Eq. (1), apart from the re-quirement for geometric similarity, particle sphericity and particle size distribution, there are eight parame-ters 0( , , , , ), , ,p f p sU H g ρ ρ μ d G of importance to flow in the combustion chamber of a CFB boiler. Five of the above eight parameters called dependent ones

0( , , , , ),p p sH ρ d G U cannot be chosen independently. Their values are the result of the scaling calculations. The remaining three parameters ( , , )f gρ μ called in-dependent ones, can be chosen independently. The full set of scaling parameters requires that the small-scale unit needs to be roughly 0.25 the size of a CFB boiler and operated with particles of a density of 3.82 ρp (where ρp denotes here the particle density in a boiler) (Glicksman, 2003). Therefore, in scaling ex-periments where the only aim is to reflect the macroscopic flow pattern and the conditions in the

boiler’s combustion chamber satisfy the relationship Rep ≤ 15 (van der Meer et al., 1999), the set of scaling groups can be reduced to the following form

20 0

0, , ,geometry, ,s

mf p

U U G φ PSDgD u ρ U

(2)

The use of the set of scaling relationships in Eq.

(2) allows the reduction of the number of dependent parameters from five to three and the increase of the flexibility in the scaling process. Thanks to this, it is possible to choose independently the cold model size as well as of the density of the particles in the scale model. In practice, the existence of two independent parameters leads to a question about the influence of the scale of a cold model as well as the density of an inert material, on the macroscopic movements of solids and the riser solids hold-up by volume inside the combustion chamber of a CFB boiler.

The use of a particulate material of a density lower than that resulting from the set of scaling groups in Eq. (1) in scaling experiments has been the subject of studies by many authors (Horio, 1996; Leckner et al., 2011; Kolar and Leckner, 2006; Mirek, 2011; Glicks-man et al., 1987; Glicksman et al., 1993). Those stud-ies have shown that a wide range of particulate mate-rials of densities ranging from 1410 to 8800 kg/m3 can be used in scaling experiments (see Table 1).

Table1: Particulate materials and scale factors used in scaling experiments.

Scaled model References

ρp, kg/m3 dp, μm Scale factor

Plastic 1410 144.5; 99.5 0.25; 0.0625 Glicksman et al. (1993) 1440 136 - Bricout and Louge (2004)

FCC 1500 67 - Qi et al. (2008) FCC Catalyst 1780 46.4 0.25 Horio (1996)

Sand 2368 125 0.17 Kolar and Leckner (2006) 2710 461 - Qi et al. (2008)

Glass beads 2500 71.4 0.05 Mirek (2011) 2530 97 - Bricout and Louge (2004) 2558 81.6; 88.3; 112.3; 78.7 0.25; 0.0625 Glicksman et al. (1993)

Iron 7860 56 0.11 Leckner et al. (2011)

Steel 8027 46 0.11 Leckner et al. (2011) 8097 200 0.25 Glicksman et al. (1987) 7300 58; 49.5 0.25; 0.0625 Glicksman et al. (1993)

Bronze 8563 73.4; 69.5 0.17 Kolar and Leckner (2006) 8800 60 0.11 Sterneus et al. (2002)

Influence of the Model Scale on Hydrodynamic Scaling in CFB Boilers 887

Brazilian Journal of Chemical Engineering Vol. 33, No. 04, pp. 885 - 896, October - December, 2016

As has been reported by Kolar and Leckner (2006), the use of a particulate material of an arbi-trary density is not without an effect on the quality of the scaling process. Measurements taken on a trans-parent 12 MWth boiler model (of scale of 1/6) operat-ing at Chalmers University have clearly shown that the use of bronze particles (ρp = 8563 kg/m3, dp = 73.4 μm, 69.5 μm) allows a better matching of the static pressure curves to be achieved, compared with sand particles (ρp = 2368 kg/m3, dp = 125 μm). A similar conclusion has been reported by Glicksman et al. (1993). Based on the results of the viscous limit scaling using different particle densities (glass parti-cles: ρp = 2558 kg/m3, dp = 112.3 μm; plastic parti-cles: ρp = 1410 kg/m3, dp = 144.5 μm; steel parti-cles: ρp = 7300 kg/m3, dp = 57.7 μm), they found that the solid density profiles of the two hot and cold (the length ratio - 1/4 of the combustor) beds matched fairly well, especially for steel powder used as the inert material.

The second parameter, whose value can be theo-retically assumed at an arbitrary level, is the cold model scale. It has been noted that when the full set of scaling parameters is used, a cold model of an atmospheric combustor has linear dimensions approx-imately one-quarter those of the combustor (Glicks-man, 2003). Nevertheless, as follows from Table 1, a wide range of scale factors ranging from 0.05 to 0.17 have been used by many researchers in scaling ex-periments. Kolar and Leckner (2006) carried out the scaling experiments on a 1/6 scaled-down version of a 12 MWth CFB boiler operating at Chalmers Uni-versity. The authors did not comment on the choice of the cold model length scale but claim that it is not possible to match all the nine scaling parameters simultaneously between the boiler and the cold model. From their point of view, particle size distri-bution as well as fluidizing velocity play a signifi-cant role in matching all scaling requirements. The operational characteristics of a 1/9 scaled-down plas-tic model used by Sterneus et al. (2002) have been calculated based on the following set of dimension-less numbers:

20 0 1

2 0, , , , , ,p s

f mf p

ρU U L G φ PSDgL ρ u L ρ U

(3)

As with work carried out by Kolar and Leckner

(2006), the authors did not comment on the choice of the cold model length scale, but treat it as an input parameter for calculation of all small-scale equiva-lents. As a consequence, the gas velocity in the scale model is lower and is equal to 1/3 of the boiler ve-

locity (Sterneus et al., 2002). In the scaling experi-ments carried out by Glicksman et al. (1993), the operating conditions for a 1/16 cold model were calculated based on a simplified set of scaling rela-tionships of the following form:

20 0 1

2, , , ,f

mf p

ρU U H LgH u ρ D L

(4)

As follows from experimental studies, the simpli-

fied set of dimensionless parameters in Eq. (4) al-lowed the atmospheric CFB boiler Studsvik 2.5 MWth (cross-section: 0.7×0.6 m) to be closely modeled by the 1/16 cold model. Moreover, as has been noted by Glicksman et al. (1993), the average solid fraction profiles between the 1/4 scale cold model and the 1/16 scale cold model are in excellent agreement. This means that the simplified set of parameters in Eq. (4), which includes the gas to solid density ratio, can give acceptable results over a wide range of par-ticle densities and bed sizes, even when the cross-section of a cold model is as small as 0.044×0.037 m. In summary, there are two things that most of the above-mentioned works have in common:

in modeling of circulating fluidized bed hy-drodynamics using the simplified set of dimension-less parameters, the choice of a cold model's length scale smaller than 1/4 is made without giving any reason,

in modeling of large scale hot combustors with relatively small cold models, the solid to gas density ratio, particle size distribution and the fluidizing velocity play a significant role.

However, this brings up two questions: are there any other simplified sets of scaling

parameters, especially excluding the solid to gas density ratio, that allow a cold model to model the macroscopic flow pattern occurring in the atmos-pheric CFB boiler?

how does the scale of the cold model influence the vertical distribution of the inert material flowing inside the combustion chamber?

The purpose of the present paper is experimental verification of the simplified set of scaling parame-ters for which the particle density as well as the cold model length scale may be chosen independently. The unique feature of the current effort is that the experimental investigation has been conducted on two large scale 1/10 and 1/20 geometrically similar cold models of the Lagisza 966 MWth supercritical CFB boiler operating at the company TAURON Wytwarzanie SA - The Lagisza Power Plant, Poland. Of particular interest is the influence of the cold model length scale on the average solid fraction pro-

888 P. Mirek

Brazilian Journal of Chemical Engineering

files between the Lagisza 966 MWth CFB boiler and the 1/10 and the 1/20 scale cold models.

DESCRIPTION OF THE SIMPLIFIED SCALING LAWS

The use of three dimensionless groups for simi-

larity between circulating fluidized beds is justified only for small Reynolds numbers (Red< 4) (Glicks-man et al., 1993). In this case, the simplified set of scaling relationships can be written as follows:

20 0

0, , s

mf p

U U GgD u ρ U

(5)

As can be noted from the comparison of dimen-

sionless groups in Eqs. (1) and (5), in the simplified set of Eq. (5) the density ratio ρp/ρf has been ex-cluded. The exclusion of this group is only justified when the similarity between macroscopic flow fields is more important than the sizes of clusters. Given that for CFBs the terminal velocity is a more appro-priate parameter than minimum fluidization velocity, the set Eq. (5) can be re-expressed in the form pro-posed by van der Meer et al. (1999):

20 0

0, , s

t p

U U GgD u ρ U

(6)

As the measurement of the external solids circula-

tion flux sG in the Lagisza 966 MWth CFB boiler is very difficult to accomplish, it is alternatively as-sumed that the set of Equations (6) can be substituted with the set of the following form:

30 32 320

2( )

, , , geometry, ,−f f p f

t

U d ρ d ρ ρ ρ gU φ PSDμ u μ

(7)

As can be easily noticed, the Froude number and

the ratio 0/ ( )s pG ρ U in the set Eq. (6) have been substituted with the particle Reynolds number and the Archimedes number, respectively. Introducing the Archimedes number allows the direct determina-tion of particle size on the scaling model and, as a consequence, the determination of the superficial velocity U0 from the condition of equality of particle Reynolds numbers. Due to the fact that the Lagisza 966 MWth CFB boiler operates within the viscous flow range (Rep<15), in the set of criterial numbers in Eq. (7) the density ratio ρp/ρf was omitted. When determining the dimensionless terminal velocity of

particles in the boiler, U*, and the terminal velocity, ut, the drag coefficient Cd was calculated using the relationship given by Cheng, (2009):

( ) ( )0.45*

0.54 0.153*3

*

432 1 0.022 0.47 1 −= + + − ddC d e

d (8)

where ∗ refers to the dimensionless particle diame-ter, defined as follows:

1/3

* 32 2( )f p f g

d dρ ρ ρ

μ−⎡ ⎤

= ⎢ ⎥⎣ ⎦

(9)

EXPERIMENTAL STUDY Operational Tests - Lagisza 966 MWth Supercriti-cal CFB Boiler

A reference facility for the cold model studies was the Lagisza 966 MWth supercritical CFB boiler operating at the company TAURON Wytwarzanie SA - The Lagisza Power Plant, Poland (Figure 1).

The size of the combustion chamber at the grid level is 27.6 m long and 5.3 m wide.The depth of the combustion chamber grows with increasing distance from the grid. At the height of 8.95 m, the combus-tion chamber widthis 10.6 m and does not change with a further increase of the distance from the grid. The total height of the combustion chamber is 48 m. During the tests, the boiler was fired with bituminous coal (Ziemowit coal mine, Poland) with properties given in Table 2.

The proximate analysis of the bituminous coal was carried out with the help of the LECO TruSpec CHNS analyzer in accordance with PN-G-04584 and PN-G-04571 Standards. The low heating value (LHV) of the bituminous coal was determined with the help of the C 2000 basic IKA calorimeter in accordance with Standard PN-81/G-04513. The moisture, vola-tile matter and the ash contents of the coal have been determined in accordance with PN-80/G-04511, PN-G-04516:1998 and PN-80/G-04512/Az1:2002 Stand-ards. The inert material samples were taken from the dense combustion chamber region at the hight of 8.3 m from the grid. These samples contained the broad-est particle diameters spectrum and have been used for further cold model studies.A detailed description of the sampling method can be found in (Mirek, Ziaja, 2011). The operational tests were carried out for steady boiler operation conditions under the loads and with the primary (PA) to secondary air (SA) ratios as shown in Table 3.

To

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m; 1/16 c

USIONS

ated by the la

mensionless dossible to scza 966 MWtodels with sc

n the distribmodels dem

e hot bed ane cold modelmodel influenrt material f

d model allodistribution

rily reflectedble in the 1/

very small taps located

ssure measu

erficial velohe test-stand

results, espodels. This traller 1/20 colion betweennsion densitymodels decreair distributoof the test-staspension denperating con

ratio, can givof boiler loaHowever, th

s for the 1/1rates that suhe bigger cowith respect r. This implinces the vertflowing in thion to the e

cksman et air experimens-sections (1cold model

aboratory tes

dynamic simcale down hth supercriticcale factors

butions for thmonstrates thd cold model. This implinces the vertflowing in th

ows the whon registered d in a scalin/20 scale codistances b

d in the clourements we

city and, as s, results in a

pecially in thrend is particld model.

the refereny and the vaeases with ior. and, the highsity. This staditions, whe

ve ad-he 10 us-old to

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Influence of the Model Scale on Hydrodynamic Scaling in CFB Boilers 895

Brazilian Journal of Chemical Engineering Vol. 33, No. 04, pp. 885 - 896, October - December, 2016

the higher values of superficial velocity cause higher values of solids suspension density along the height of the boiler’s combustion chamber.

The use of the simplified set of scaling relation-ships in Eq. (7) allows an increase in flexibility in the scaling process. The number of dependent parameters can be reduced from five to three while maintaining the fluidization regime, macroscopic movements of solids and the distribution of solids suspension den-sity along the height of the combustion chamber. Thanks to this, a large number of experiments can be performed for designing new CFB boilers and for modifying those whose performance can be im-proved. This requires, however, that the tests be car-ried out for small Reynolds numbers.

NOMENCLATURE A cross-sectional area (m2) Ar Archimedes number

3 2( /)p f p fd gρ ρ ρ μ− (-) Cd drag coefficient (-)

pd particle diameter (m)

*d dimensionless particle diameter (-)

32d Sauter mean particle diameter (m)

50d mass mean particle diameter (m) D riser hydraulic mean diameter 4 /A P

(m) g acceleration of gravity (m/s2) h height (m) H combustion chamber height (m) Hb boiler's combustion chamber height (m) Hm cold model's combustion chamber height

(m) FrH Froude number based on H

20 / ) U gH (-)

sG external solids circulation flux (kg/m2s) kx, ky, kz scale factor in x, y and z directions (-) L width of the core region along the line of

measurements (m) 1 2,L L cross-sectional bed dimensions (m)

MCR Maximum Continuous Rating (%) bm mass flow of solids in the boiler (kg/s)

mm mass flow of solids in the cold model (kg/s)

0U superficial gas velocity (m/s)

0bU superficial gas velocity in the boiler (m/s)

0mU superficial gas velocity in the cold model (m/s)

U* dimensionless velocity, ( )1/34 / (3 ) d dRe C (-)

mfu minimum fluidization velocity (m/s)

tu terminal velocity of particle (m/s) p pressure (Pa) P wetted perimeter of the cross-section (m) PSD particle size distribution PA/SA primary/secondary air ratio (-)

HRe Reynolds number based on the riser height H (-)

pRe particle Reynolds number (-)

T temperature (K) x coordinate of the combustion chamber

height (m) Greek Letters

bρ solids suspension density (kg/m3) fρ gas density (kg/m3) pρ particle density (kg/m3)

ϕ particle sphericity (-) μ gas viscosity (Pa s) ε static porosity (-)

ACKNOWLEDGEMENTS

This investigation was financially supported by the fund of statutory research of Czestochowa Uni-versity of Technology. Project No:BSPB-406-301/11.

REFERENCES Anderson, T. B., Jackson, R., A fluid mechanical

description of fluidized beds. I&EC Fundam., 6, 527-539 (1967).

Bricout, V., Louge, M. Y., A verification of Glicks-man's reduced scaling under conditions analogous to pressurized circulating fluidization. Chemical Engineering Science, 59, 2633-2638 (2004).

Cheng, N, -S., Comparison of formulas for drag co-efficient and settling velocity of spherical parti-cles. Powder Technology, 189(3), 395-398 (2009).

Detamore, M. S., Swanson, M. A., Frender, K. R., Hrenya, C. M., A kinetic-theory analysis of the scale-up of circulating fluidized beds. Powder Technology, 116, 190-203 (2001).

Glicksman, L. R., Fluidized bed scaleup. Chapter 13, In: Handbook of Fluidization and Fluid-Particle Systems Edited by Yang, W.-C. Marcel Dekker, New York (2003).

896 P. Mirek

Brazilian Journal of Chemical Engineering

Glicksman, L. R., Hyre, M. R., Farrell, P. A., Dy-namic similarity in fluidization. Int. J. Multiphase Flow, 20(1), 331-386 (1994).

Glicksman, L. R., Hyre, M., Woloshum, K., Simpli-fied scaling relationships for fluidized beds. Pow-der Technology, 77, 177-199 (1993).

Glicksman, L. R., Hyre, M. R., Westphalen, D., Veri-fication of scaling relations for circulating fluid-ized beds. Proc. of 12th Int. Conf. on Fluidized Bed Combustion, 69-80 (1993).

Glicksman, L. R., Yule, T., Dyrness, A., Carson, R., Scaling the hydrodynamics of fluidized bed com-bustors with cold models: Experimental confir-mation. Proc. of 9th Int. Conf. on Fluidized Bed Combustors, 511-514 (1987).

Horio, M., Hydrodynamics. Chapter 2, In: Circulat-ing Fluidized Beds, Edited by Grace, J. R., Knowl-ton, T. M., Avidan, A. A, Blackie Academic and Professional (1996).

Kolar, A. K., Leckner, B., Scaling of CFB boiler hydrodynamics. Proc. of the 1st National Con-ference on Advances in Energy Research (AER 2006), Mumbai, 34-40 (2006).

Kunii, D., Levenspiel, O., Fluidization Engineering. 2nd Ed., Butterworth-Heinemann, USA, Chapter 5 (1991).

Leckner, B., Szentannai, P., Winter, F., Scale-up of fluidized-bed combustion-A review. Fuel, 90, 2951-2964 (2011).

Mirek, P., A simplified methodology for scaling hy-drodynamic data from Lagisza 460 MWe super-critical CFB boiler. Chemical and Process Engi-neering, 32(4/1), 245-253 (2011).

Mirek, P., Ziaja, J., The influence of sampling point on solids suspension density applied in scaling of the hydrodynamics of a supercritical CFB boiler. Chemical and Process Engineering, 32(4), 391-399 (2011).

Nowak, W., Mirek, P., Circulating fluidized bed combustion (CFBC). Chapter 16, In: Fluidized Bed Technologies for Near-Zero Emission Com-bustion and Gasification, Edited by F. Scala, Wood-head Publishing (2013).

Sierra, C., Bonniol, F., Occelli, R., Tadrist, L., Prac-tical scaling considerations for dense gas fluid-ized beds interacting with the air-supply system. Chemical Engineering Science, 64, 3717-3720 (2009).

Sterneus, J., Johnsson, F., Leckner, B., Characteris-tics of gas mixing in a circulating fluidised bed. Powder Technology, 126, 28-41 (2002).

van der Meer, E. H., Thorpe, R. B., Davidson, J. F., Dimensionless groups for practicable similarity of circulating fluidized beds. Chemical Engineering Science, 54, 5369-5376 (1999).

Qi, X., Zhu, J., Huang, W., Hydrodynamic similarity in circulating fluidized bed risers. Chemical En-gineering and Science, 63, 5613-5625 (2008).