Korean 3~ Chem. Eng., 16(3), 292-297 (1999) 

Effect of Initial Droplet Size Distribution on Sulfur Removal Efficiency in FGD/SDA 

Eui-Kyung Oh, Gi-Hune Jung, Sun-Geon Kim*, Hyung-Keun Lee* and In-Won Kim** 

Department of Chemical Engineering, Chung Ang University, 221, Huksuk-Dong, Dongjak-Ku, Seoul 156-756, Korea 

*Energy and Environmental Research Department, Korea Institute of Energy Research, 

71-2, Jang-Doug, Yusong-Ku, Taejon 305-343, Korea 

**Department of Chemical Engineering, Kon Kuk Umvel-sity, 93-1, Mojin-Dong, Kwangjin-Ku, Seoul 143-701, Korea 

(Received 5 August 1998 9 accepted 22 February 1999) 

Abstract Dry scrubbing with lime slurry in a spray dryer [spray dryer absorber (SDA)] has been an important 

technology for flue gas desulfi~ization (FGD). Mathematical models based on the heat and mass balances are used 

to predict SO2 removal in the SDA as a function of ilfitial size distribution of slurry di-oplets. Since the existence 

of mois~re in the droplets appreciably enhances the SO~ removal, its removal efficiency depends on the rate of drying as well as that of SO~ removal itself, both depending on droplet diameter. With the increase in the geometric 

standard deviation (GSD) of the initial droplet size distribution, the efficiency of SO 2 removal first increases and 

then decreases, showing a maximum at a certain value of GSD. Tiffs trend is altered by tile sorbent content of the 

droplets, expressed as stoichiometric ratio (SR). The decrease in SR makes the maximum move to higher GSD and reduces the variation in the efficiency with respect to GSD. For SR<0.73, a minimum efficiency also appears, ahead of 

the maximum. Tile results are well ~,r by the spedfic rates of both drying and SO2 removal of the droplets. 

Key words : Flue Gas Destflfmization, Spray Dryer Absorber, Modeling, Droplet Size Distribution, Drying, SO2 Removal 

INTRODUCTION 

In semi-@ FGD processes, the slurry droplets containing 

sorbent particles are sprayed to reactively absorb SO2 in flue 

gas while drying by sensible heat of the gas. Dry and spent 

sorbent particles are either disposed of or recovered. Without a doubt, tile initial size distribution of tile droplets plays 

a very important role in the series of processes described above 

and consequently in SO2 removal [Kliugspor et al., 1983]. 

Although many types of spray have been developed, producing quite different size distribution of droplets, there have 

been very few studies on their size effect. Jozewicz and Rochelle [1984] calculated the time needed to evaporate 99 % of 

the polydisperse spray. They showed the time does not differ 

significantly from that needed for evaporating monodispel-se 

sprays for low values of standard deviation, but the time rises 

dramatically for a standard deviation (expressed in In o-a) larger 

than 1.0 (or o'a> 2.72). They also calculated SO2 removal as 

a fimction of the approach temperature to saturation for different lime stoictfiomeby, wtfich is defined as tile ratio of tile total 

moles of Ca(OH)2 to the moles of SO2 in the flue gas. All the 

results were obtained for the spray of a standard deviation (in 

o'a) of 1.56 (which can be converted to ~ 4.76, an uncommonly large value) assuming an infinite rate of Ca(OH)2 dissolution. At stoichiometry >1.5 the removal of SQ was the same 

as predicted by a simple concurrent model without size distribution. At low stoichiometry and close approach to the satoration tenlperature, all of tile Ca(OH)2 was utilized. Their results 

Wo whom conespoMence should be addiessed. 

E-raail : sgkfln@catt ac.ta 

are, however, too qualitative and unrealistic to generalize and 

apply practically. 

In order to get a clear idea of the droplet size effect on the 

SDA performance, we quantitatively investigated the effect of 

polydispersity on the evaporation of water, removal efficiency 

of SO2, and thus sorbent utilization in SDA, modifying the previous model [Jang et al., 1996]. 

FUNDAMENTAL EQUATIONS AND 

NUMERICAL APPROACH 

292 

In our model, tile sluily droplets containing Ca(OH)2 as sotbent particles are sprayed in the top of the SDA and the flue 

gas consisting of nitrogen, water vapor and SO2 is introduced 

above tile spray. Since tile sprayed droplets injected radially 

lose their velocities in an extremely short period of time, the 

flow of both the gas and droplets is assumed concurrent and 

plug flow. We also assume there is neither circulation nor tempem~re distribution in a droplet and neglect heat loss across the 

SDA wall. Tile size disliibution funcgon of tile sprayed droplets, 

fide) is assumed lognormal, whose applicability has been proven: 

f (ln_ d~-ln_d~ l__!__exp (1) 

2(ln ff~): 

f(d~) 2J~-a (~ 

where fie is tile geometric standard deviation, ctd tile droplet 

diameter and cle tile geometric mean diameter of droplets. All 

tile assumptions above are tile same as those of Partridge, 

1987; Shih, 1989; Kolluri, 1991 and Yuan, 1990. 

1. Rate of SO: Removal 

The rate of SO: removal by di-oplets can be expressed as 
Effect of Initial Droplet Size Disbibulion on Sulfur Removal Efficiency in FGD/SDA 293 

[Kolluri, 1991]: 

m~- 1 1 t~d~Sa~ (2) 

--+ q-- 

where Qc and Ca, are the concentrations of sorbent and SQ in 

liquid and gas phases, respectively, DI,, and Dz~ are the diffusion 

coefficients of SO2 and sorbent in the liquid phase, respectively ; H is the HerLry's law constant ; k ~, and k~, are the mass 

transfer coefficients of SO2 in liquid and gas phases, respectively ; S the hypothetical thickness of the liquid film sur-rounding 

the sorbent particle ; RL is the fraction of the sorbent ura-eacted in the sorbent particle and Np is the number of sorbent particles in a droplet. Eq. (2) can be used only it" the moisture content (X) of the droplet exceeds a certain value, X~, while for 

X < X~, the rate of SQ removal is calculated by gas-solid reaction, m, k,C~, where k~ is the constant of the gas-solid reaction. The threshold moisture content, X; is estimated by X~ = 

6.1*RH*X~ [Shih, 1989], where RH is the relative humidity of 

outlet flue gas and X~ is the equilibrium moisture content of the 

sorbent particle. 

2. Governing Equations 

The structure of the governing equations is almost unchanged compared with those appearing in our previous publication [Jang et al., 1996]. The droplet-phase variables in the gasphase balance equations are, however, expressed in the forms 

integrated with respect to the diameter of the droplets. 

The balance for the mass of the sorbent Ca(OH)2 (m~) in 

a droplet with a diameter of de is : 

dr~(d~) .m0(d~) (3) 

dt i~ 

where i~ is the stoichiometric ratio of SO2 to Ca(OH)2 based 

on mass. 

The balance for the mass of water (m~) in a droplet with 

a diameter of d e is : 

dm~(c!~) .m~(ctd) row(d9 (4) dt i~ 

where i~ is the stoichiometric ratio of SO2 to water based on 

mass, and nb is the &ying rate of water. The rate is expressed 

according to the types of drying-rate period~ respectively, as 

[Partridge, 1987] : 

m~(d~)=2~rC, d~D~ hll Y~w for constant drying-rate period(5) 

1-y,,~ 

m~(d~)=2~rC, d~D~ hl y~X X~ 

1-y,,~ X~.- X. 

for falling chying-rate period (6) 

where Ct is the total molar concentration of the gas phase, 

y~ and y,,~ are the mole fractions of water vapor in bulk gas 

and at the surface of the droplet, respectively, and De~ is the 

diffi~sion coefficient of water vapor in the gas phase. The Wansition from the constant drying-rate period to the falling drying-rate period occurs at the critical moisture content, Xc. 

The energy balance for a slurry droplet with a diameter of 

d~ consisting of sensible heat supply from the gas phase, latent 

and sensible heat consumption by water evaporation, and heat 

effect from dissolution of gaseous SQ into the droplet, is : 

d[m~(d~) %'~(dDT~(d~)] m~.(d~)Ib +m~(d~)h= 

dt 

+~d~h,(G) [T~-TZG)] (7) 

where md, %d and Te are the mass, specific heat and teraperature of the droplet with a diameter of de, respectively, 1% and 

t~ are the specific enthalpies of water vapor and gas-phase 

SO2, respectively, ht the heat transfer coefficient in the gas 

phase, and T~ the gas temperature. 

The SO2 mass balance in the gas phase is: 

dxn~,~ dt NicTic~ f(dd)ddd (8) 

where m~, is the mass flow rate of SQ in the flue gas, N the 

total number flow rate of droplets (number of droplets/see) and 

the integral term represents the mean rate of SQ removal over 

the whole spectrum of droplet size. 

On the other hand, the humidity (Y~) balance in the flue 

gas gives: 

dH 

m~ = Ni~nb(de)f(dd)dd d (9) 

where ma is the mass flow rate of dry flue gas. The integral 

term again represents the mean rate of drying over the whole 

spec~ama of droplet size. 

The energy balance equation in the gas phase, cansistiig of 

sensible heat supply out of the flue gas, and latent and sensible 

heat effects arising from water evaporation, is: 

d(m % T ) 

~-~t '~ ~ =NI= [m~(d~)H~ /rddl~(dd)[T~ Td(dD] 

m~(dDH=]f(dD ddd (10) 

where rn~ and %~ are the flow rate and constant-pressure specific heat of total gas, respectively. The right-hand side term 

also contains an integral form over the whole size spectrum. 

3. Numerical Scheme 

The whole spectlxnn of droplet size approximately in the 

range of in d~+3 in G is divided equally in logarithmic scale 

into 11 classes. For Eqs. (3), (4) and (7), each class of size has 

corresponding expressions to yield a total of 3• ordinary dig 

ferential equations. For Eqs. (8), (9) and (10) for the flue gas, 

the integral tenns in the right-trand side are calculated numerically. All the equations are rewritten in terms of vertical distance instead of time by the following relationship : 

dz 

dt=-- (11) Ud(dd) 

where Ue is the &oplet velocity. As proved in ora- previous 

study [Jang et al., 1996], the droplet velocity is assumed equal 

to the gas velocity U~, which is recalculated at each iteration. 

Korean J. Chem. Eng~0fol. 16, No. 3) 
E.-K. Oh et al. 

145 ~ 

5% 

913 ppm 

11 ~ 

1 

15.2 sec 

82 pm 

37.8 ~ 

1.25 pm 

29.2 % 

6% 

Parameters Base-line value 

0 

E p} 

g 

"6 

g 

LL 

Inlet gas temperature 

% water vapor in inlet gas 

In let SO2 concentration in the gas 

Approach temperature to saturation 

Stoichiometric ratio 

Residence time 

Inlet droplet diameter 

Inlet droplet temperature 

Inlet sorbent particle diameter 

Critical moisture content 

Equilibrium moisture content 

1.0 

(18 

O 

= ' , 

"6 (1'* 

g . ~ . . . , & - - ' ~ ~l'-----~'&---'-- SR=I.0 

* ~--~g=l.0 

ii --&-- ~g=20 

I I I I O~Qon Q2 Q4 Q6 Q8 1.0 

Z 

Fig. 2. Variation in droplet size distribution with respect to dimensionless axial length, Z (SR=I.0, o'F2.0 ). 

The axial distance is then normalized by the total SDA length. 

The thirty-six ordinary differential equations are then solved 

by LSODE package, one of the initial-value ODE solvers. The 

sorbent particles in our study are monodisperse and their size 

is fixed, as shown in Table 1. Their number in each droplet 

is proportional to its volume (d~) for the given SR. 

The SDA data used in this study are Partridge's baseline conditions, which have been quoted by many authors [Partridge, 

1987; Shih, 1989; Yuan, 1990]. Partridge's apparatus has a diameter of 2.13 m, a length of 2.5 m. Table 1 shows the baseline condition set up by Partridge. 

The initial droplet diameter shown in Table 1 is used as the 

geometric mean diameter dg. The geometric standard deviations range from 1.00001 (close to monodispersity) to 2.0. The 

variables in Table 1 are all set to their baseline values except 

the stoichiometric ratio (SR) which is the most significant variable for the SO2 removal [Jang et al., 1996]. SR varies from 

0.6 to 2.0. 

RESULTS AND DISCUSSION 

Fig. 1 shows the initial size distributions of droplets for three 

different values of GSD (a~). The geometric mean diameter of 

the droplets fixed at 82• 6m is the same as the diameter of 

monodisperse droplets (a~-l.0). For a~-l.2, the droplet size 

25 

294 

Table 1. Baseline condition 

~%:1.2 

1.0 

g 

as 4= 

(10 = *, . . 

105 104 103 

dd, m 

Fig. l. Variation in droplet size distribution with respect to dimensionless axial length, Z (SR=I.0, o'g=1.35). 

May, 1999 

1.0 

Q8 

06 

Q4 

02 

no QO Q2 Q4 Q6 Q8 1.0 

Z 

Fig. 3. Effect of initial geometric standard deviation of droplet 

size distribution, ag on exit flue-gas humidity. 

ranges from 50• 6 m to 140• 6m, for az-l.4, from 30• 6 

m to 250• 6m, and for az-2.0, from 10• 6 m to 650• 6 

m. Figs. 2 and 3 show the axial distributions of the fraction of 

sulfur removal in the flue gas, as a parameter of GSD, for SR1.0 and SR-0.6, respectively. For monodisperse droplets, the variations in both cease very close to the inlet, but the increase in 

GSD spreads out their variations further towards the SDA outlet. The figures also show that the fraction for SR-1.0 and az1.35 exceeds that for monodisperse droplets around the middle 

of the SDA while the fraction for SR-0.6 and az-l.80 does 

near the outlet of the SDA. The reasons why will be explained 

later. 

1. The Effect of Size Distribution of Slurry Droplets on 

Their Drying 

Fig. 4 shows the variation in droplet size distribution along 

the SDA axis for the initial a~-1.35. Since, as shown in Eqs. 

(5) and (6), the rate of drying per unit droplet is proportional 

to d~, the corresponding specific rate (rate per mass of droplet) is inversely proportional to d~. Therefore, the smaller the droplets, the earlier they dry up. As a result, along the axis, the size 

distribution of the droplets becomes, in turn, skewed with long 

head (Z-0.01), symmetrical (lognormal) but broader than the 

initial one (Z-0.05), and skewed with long tail (Z-0.1, 0.5). 

Finally the lognormal distribution with the initial broadness is 

recovered (Z-1.0), as all the droplets dry up. In Fig. 5 for the 
Effect of Initial Droplet Size Distribution on Sulfur Removal Efficiency in FGD/SDA 295 

1.4 

"O~'1= 1.2 

~" 1.o 

-% 

"o (18 _c 

-o (16 

~ 

,1= a2 "o 

(10 106 1135 164 103 

d a, m 

Fig. 4. Effect of initial geometric standard deviation of droplet 

size distribution, % on exit flue-gas temperature. 

70 oE 

4~ 

1.0 20 

% 

Fig. 7. Variation in sorbent conversion of droplets with different sizes along SDA axis (SR=I.0, o'g=2.0). 

Q7 

"xD 

__c 

v 

,?, 

,4= 

v 

"10 

[ ~z=0 

i .--o..-z=0.0. 

05 [ ~ z=0.0~ 

I "A -- z=Q1 

I -'- z=o5 

Q4 I ""-V"" z=l.0 

a2 

Ol 

(10 . 10-6 105 10"4 10 -3 

dd, m 

Fig. 5. Effect of initial geometric standard deviation of droplet 

size distribution on sulfur removal efficiency as a parameter of SR. 

distribution of a~-2.0, similar trends are observed. However, the 

large droplets in the broadened distribution do not dry completely even at the outlet and the distribution ends up with a 

long tail. 

Fig. 6 shows the effect of droplet size distribution on the 

flue gas humidity at the SDA outlet, as a parameter of SR. 

The distribution effect is hardly observed for the systems with 

~<1.4, where most droplets dry up within SDA. However, 

for ~>1.4, the humidity decreases appreciably with ~ due to 

the incomplete drying, as described above. For the systems 

with narrower distribution (a~<l.4), the increase in the sorbent 

mass (SR) slightly decreases the humidity since the sorbent 

needs more equilibrium moisture which cannot eventually evaporate from the droplets. It is suggested that the effect is obscured for the systems with broader distribution, due to the 

incomplete drying. The effect of size distribution on the flue 

gas temperature, shown in Fig. 7, is reversed, since the gas 

humidity increases at the expense of the sensible heat of the 

gas. 

2. The Effect of Size Distribution on SO2 Removal Efficiency 

Fig. 8 shows the conversion of sorbent particles in each class 

of droplets along the SDA axis for the system with SR-1 

and the initial ~-1.35. As shown in Eq. (2), the rate of SO2 

removal per unit droplet is proportional to d~r when the third 

term in the denominator in right-hand side (sorbent dissolution 

term) is neglected. If the term is dominant, the SO2 removal 

is proportional to d,~, since Nj, is proportional to d~;. The corresponding specific rates (rates per mass of droplet) are, therefore, inversely proportional to d,~ (n_< 1). Due to higher size-dependence of drying (inversely proportional to d,2~) than SO2 removal, the drying of smaller droplets occurs much faster than 

their SO2 removal (thus, their sorbent conversion) does. As 

described in a previous paper [Jang et al., 1996], the SO2 removal is appreciable only for the droplets having free toolsQ074 

Q072 

Q070 

I 

% 

Fig. 6. Variation in sorbent conversion of droplets with different sizes along SDA axis (SR=I.0, GF1.35 ). 

1.0 

--n-- z=0,01 I /~ 08 --o-- z=0.~ I 

O~ --V-- z=-Q5 I 

~O 06 --,11~ z= 1.0 I 

r 

"6 

'-O 02 

QO i i ~1= 9 9 = = i , , , , 

105 104 103 

dd, m 

Fig. 8. Variation in sorbent conversion of droplets with different sizes along SDA axis (SR=I.0, o'71.35 ). 

Korean J. Chem. Eng.(Vol. 16, No. 3) 
296 E.-K. Oh et al. 

1.0 

SR=l.0,cg=21 

--9 08 --e--z=O.05 

--&-- z'=O I 

--V-- z=-O5 

--4,~ z=l.0 

9 ~114 

O a2 

00 ~ 

10 `5 10 4 10 `3 

rid, rn 

Fig. 9. Variation in sorbent conversion of droplets with different sizes along SDA axis (SR=I.0, O'g=2.0). 

0.75 

0.70 ' --~==~1~-4~~ I ~&-- SR=0.9 

~oE ~ .~--~---.~= I -~ sR-~.0 

o,66,- _ _ ~ I+SR=!5 

0.60 

60 

'~ 0.55 r'- 

o , 

o 0.50 9 

LL 

0.45 

1.0 1.2 1.4 1.6 1.8 2.0 

Og 

Fig. lO. Effect of initial geometric standard deviation of droplet size distribution on sulfur removal efficiency as a 

parameter of SR. 

ture. Therefore, the smaller droplets have higher conversion 

as far as the moisture is retained in them, but their conversion is almost frozen as soon as their drying ends up. On the 

other hand, larger droplets retain moisture much longer than 

smaller ones and have more opportunity to enhance their conversion by the reaction with SO> As shown in the figure, the 

droplet size showing maximum conversion, therefore, moves 

to the larger one along the SDA axis and, at the outlet, the 

largest droplet has the highest conversion, since it has almost 

dried up (Fig. 4). Fig. 9 shows the results for %-2.0. Compared to Fig. 8, the conversions for the droplets in the lower 

part of the broadened distribution are frozen at lower values due to their increased drying rates. On the other hand, 

since the droplets in the upper part of the distribution are not 

completely dried (Fig. 5), their conversions decrease with the diameter of the droplets, as described above. Therefore, the largest droplets do not have the highest conversion even at the exit 

of the SDA. 

The broadening effect of the droplet size distribution on the 

overall SO2 removal efficiency, therefore, appears somewhat 

complicated. It depends on whether the loss of SO2 removal 

capacity in the smaller droplets can be recovered by its gain 

in the larger droplets or not. Fig. 10 shows the effect of size 

distribution on SO2 removal efficiency as a parameter of SR. 

For SR>0.73, the efficiency increases with GSD (%) up to a 

maximum and then greatly decreases to a much lower value 

than the monodisperse (c~z-1) efficiency. For SR>I.0, the SO2 

removal efficiency ranges from 50 to 70 %. It is suggested 

that the slight broadening of the size distribution increases the 

time of water retention in larger droplets, which leads to a 

greater chance for SO2 removal as a whole, and makes the 

gain in larger-sized droplets exceed the loss in lower-sized 

ones more and more. However, with further increase in %, 

the overall removal efficiency declines since the gain is substantially reduced and cannot recover the loss due to the reduction in the rate of SO2 removal, as described before (inversely proportional to d,~, where n<l). 

With the reduction of sorbent content (SR), the GSD showing the maximum efficiency (c~ ma,) moves to a higher value. 

It is suggested that the decrease in SR reduces the rate of SO2 

removal, due to the decrease in both the number (Nj,) and liquid-phase concentrations (Qc) of sorbent particles [Eq. (2)], 

and makes the removal rate more controlled by sorbent dissolution. Therefore, SO2 removal depends less on the droplet 

diameter, since n decreases from unity in the size dependence 

of its specific rate, d,r As a result, for lower SR the decline 

of the efficiency begins at higher GSD. Further reduction in 

SR below 0.73 shows a minimum efficiency at a certain value 

of %<% ...... This implies that such a small increase in broadness is not sumcient for the positive effect on the SO2 removal 

in the upper part of the distribution to exceed the negative 

effect in the lower part, due to much lowered rate of SO2 removal. This and the lowered dependence on the diameter make 

the efficiency variation with respect to GSD appreciably reduced. For example, for SR-0.6, the SO2 removal efficiency decreases up to o-~-1.2, then increases to a maximum at %-1.8 and 

finally decreases afterwards, and the efficiency varies only between 46 and 53 %. 

CONCLUSION 

We have numerically investigated the effect of the droplet 

size distribution on the SO2 removal efficiency of the spray 

dryer absorber (SDA). In general, the size distribution affects 

the efficiency through the variation in both the moisture-retention ability and SO2 removal rate of the droplets. 

1. The size distribution of droplets becomes distorted and 

broader until their drying is completed. 

2. High polydispersity makes the exit gas humidity fall and 

the exit gas temperature rise. 

3. The droplets, which are about to dry up, have the highest 

conversion. The size of the droplets with maximum conversion becomes larger along the SDA axis. 

4. The effect of size distribution on SO2 removal efficiency 

becomes significant with the stoichiometric ratio of sorbent to 

SO> For SR>0.73, the slight broadening in the distribution enhances the SO2 removal efficiency, while a further increase in 

% significantly lowers the efficiency. The maximum efficiency 

moves to higher % with the reduction in SR. 

5. For SR<0.73, the droplet size distribution affects the reMay, 1999 
Effect of Initial I~@ct Size Distribution on Sulfur Removal Efficiency in FGD/SDA 297 

moval efficiency less, though showing both the minimum and 

maximum efficiencies with respect to the standard geometric 

deviation of droplet size distribution. 

ACKNOWLEDGEMENT 

This work was supported by Electrical Engineering mid Science Research Institute in Seoul National University (96-050). 

REFERENCES 

Jang, S. H., Oh, E. K., Lee, H. K. and Kim, S. G., ~Model Development of Spray Dryer Absorber FGD Process" Clean Technology (Korean), 2, 80 (1996). 

Joze~vicz, W. and Rochelle, G. T., ~Modeling of SO~ Removed 

by Spray Dryers~' Proc. First Annual Pittsbmgh Coal Conf., Sept. 

17-21, 663 (1984). 

Klingspor, J., Karlsson, H. T. and Bjerle, I., ~A Kinetic Study of 

the Dry SO2-Limestone Reaction at Low Temperature," Chem. 

Eng. Commun., 22, 81 (1983). 

Kolluri, R., Hatcher, Jr., W. J. and Jefcoat, L. A., ~Simulation of 

Spray Drying with Reaction : Absoiption of Hydi~gm Sulfide 

in Ammoniacal Solution of Zinc Chlofide~' Drying Technology, 

9, 367 (1991). 

Partridge, G.P., Jr., '% Mechanistic Spray Dryer Mathematical 

Model Based on Film Theory to Predict Sulfur-Dioxide Ab-sorpfion and Reaction by a Calcium Hydroxide Slurry in the Constilt Rate Peliod," PhD. Dissertation, Tennessee Univ., Kiloxville, 

U.S.A. (1987). 

Shill, H. 8., "Silllulation of Sulfur-Dioxide Removal via Hydrated 

Lime Slurries in a Spray Dryer Absorber Flue-Gas Desulfurizafion Systen~' Ph.D. Dissertation, Alabama Univ., Tuscaloosa, 

U.S.A. (1989). 

Yuan, C. S., "Simultaneous Collection of SO2 and NO~ via Spray 

Drying:Using Sodium Based and Calcium Based Sorbents 

with Select Additives" Ph.D. Dissertation, Univ. of Illinois at 

Urbana-Champalgn, U.S.A. (1990). 

Korean J. Chem. Eng~(Vol. 16, No. 3)