10 Commercialization of Lime-Limestone Flue
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Gas Scrubbing Technology RICHARD S. ATKINS Research-Cottrell, Inc., Bound Brook, N. J. 08805 Research-Cottrell
has demonstrated the commercial
bility of limestone flue gas desulfurization installation.
Certain chemistry and process
were taken into account in designing
availa-
on a 115
MW
considerations
and operating these
systems. Methods have been developed to minimize
the
occurrence of potential problems.
Q i n c e the first large sulfur dioxide control system was installed at the ^
Battersea plant in London, it has taken almost 50 yrs for calcium-
based scrubbing technology
to become
commercially acceptable.
In
1926, the 125 M W coal-fired Battersea power plant was equipped with a spray packed tower and final alkaline wash section which removed more than 90%
of the sulfur dioxide and particulate ( I ) .
Thames River
water provided most of the alkali for absorption, and about 20% made up from lime addition.
was
The process operated in an open-loop
manner, returning spent reagent to the Thames. Subsequent programs to prevent water and air pollution supported by Imperial Chemicals Industries L t d . , British Power Authority consultants, and Howden Construction Co. led to the development closed-loop, lime-based, sulfur dioxide removal system.
of a
These types of
systems were installed in 1935 at the Swainsea and in 1937 at the Fulham power plants. They operated successfully until World War II when they were shutdown because the vapor plumes provided aerial guidance to the Luftwaffe. For the next 20 yrs no full-scale development work was performed in this area.
In fact, during the mid-sixties, there were several steps
backward when initial U.S. sulfur dioxide control systems started up and failed. For example, in the boiler injection of limestone followed by wet scrubbing, problems resulted from boiler and preheater rather than flue gas scrubbing. 120 Pfeiffer; Sulfur Removal and Recovery Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
pluggage
10.
ATKINS
Current
Lime-Limestone
Industry
Flue Gas
121
Scrubbing
Status
D u r i n g the last 3 yrs m o r e progress has b e e n m a d e i n c a l c i u m s c r u b b i n g t e c h n o l o g y t h a n d u r i n g the p r e c e d i n g q u a r t e r of a c e n t u r y .
Pres-
e n t l y 2500 M W of c a l c i u m - b a s e d scrubbers are o p e r a t i n g w i t h a n o t h e r 7600 M W u n d e r c o n s t r u c t i o n ( 2 ) .
M a n y of the i n i t i a l l y i n s t a l l e d u n i t s
e x p e r i e n c e d difficulties, b u t the n e w e r installations h a v e p e r f o r m e d better
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as the p o l l u t i o n c o n t r o l i n d u s t r y has g a i n e d confidence a n d experience. E P A and pollution industry-supported development programs have c o n f i r m e d m a n y of the process constraints e s t a b l i s h e d d u r i n g the o r i g i n a l H o w d e n - I C I projects ( 3 ) .
T h i s is not to say that w e h a v e m a d e a f u l l
c i r c l e a n d h a v e l e a r n e d no m o r e t h a n w a s a v a i l a b l e 25 yrs ago.
How-
ever, i f our i n i t i a l d e v e l o p m e n t p r o g r a m s h a d b e e n b a s e d o n p r i o r r e search results, w e w o u l d p r o b a b l y b e f u r t h e r a h e a d t o d a y .
T h e major
i m p r o v e m e n t s i n c u r r e n t processes result f r o m the a p p l i c a t i o n of m o d e r n t e c h n o l o g y a n d o p e r a t i n g t e c h n i q u e s to e x t e n d system r e l i a b i l i t y . Research—CottrelP s Status I n t h e mid-1960's R e s e a r c h - C o t t r e l l entered the s u l f u r d i o x i d e c o n t r o l field as a n expert i n p a r t i c u l a t e c o l l e c t i o n b u t as a n o v i c e i n gaseous removal.
I n i t i a l investigations u s e d a
flooded
disc s c r u b b e r
(FDS),
w h i c h is essentially a h i g h e n e r g y v e n t u r i r e q u i r i n g 8 - 1 0 i n . w.c. pressure d r o p for 4 0 - 6 0 % s u l f u r d i o x i d e r e m o v a l . I n s t a l l i n g a series of F D S ' s to i m p r o v e a b s o r p t i o n efficiency r e q u i r e d excessive pressure losses.
There-
fore, R e s e a r c h - C o t t r e l l b e g a n investigations of the F D S i n c o m b i n a t i o n w i t h a p a c k e d t o w e r to increase s u l f u r d i o x i d e r e m o v a l at
moderate
pressure drops. T h e p i l o t p l a n t studies started i n 1966 a n d h a v e c o n t i n u e d ever since. P i l o t units h a v e b e e n i n s t a l l e d at the T i d d S t a t i o n of A m e r i c a n E l e c t r i c P o w e r , the C h o l l a S t a t i o n of A r i z o n a P u b l i c Service, the B i g B r o w n S t a t i o n of Texas U t i l i t i e s , a n d Res ear c h - C o t t r ell's F i n d e r n e R e s e a r c h facility.
D e v e l o p m e n t studies h a v e b e e n s u p p o r t e d b y E P A , b y joint
efforts w i t h utilities, a n d b y this c o m p a n y (4,
5,6).
A s a d i r e c t result of this p i l o t effort, a w e t t e d film p a c k i n g was f o u n d w h i c h exhibits excellent s u l f u r d i o x i d e a b s o r p t i o n w i t h a n e x c e p t i o n a l l y l o w pressure d r o p .
T h i s p a c k i n g has o u t s t a n d i n g mass transfer c h a r a c -
teristics a n d h i g h specific
surface
area.
T h e packing developed
by
M u n t e r s C o r p . is a k e y element i n the limestone-based s u l f u r d i o x i d e r e m o v a l system. L a s t O c t o b e r R e s e a r c h - C o t t r e l l started u p its first gas c l e a n i n g syst e m , a 115 M W
limestone wet
s c r u b b i n g system at A r i z o n a P u b l i c
Service's C h o l l a p l a n t . I n this u n i t p a r t i c u l a t e a n d s u l f u r d i o x i d e are
Pfeiffer; Sulfur Removal and Recovery Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
122
SULFUR
r e m o v e d b y a F D S - p a c k e d t o w e r arrangement.
REMOVAL
AND RECOVERY
B e c a u s e of the results
o b t a i n e d at this c o m m e r c i a l f a c i l i t y a n d f r o m the p i l o t units, the A r i z o n a P u b l i c S e r v i c e a w a r d e d a n a d d i t i o n a l contract for gas c l e a n i n g e q u i p m e n t o n a n e w 250 M W b o i l e r . I n a d d i t i o n , the c o m p a n y is e n g i n e e r i n g 1900 M W of s u l f u r d i o x i d e r e m o v a l e q u i p m e n t for several m a j o r s o u t h w e s t e r n utilities. R e s e a r c h - C o t t r e l l r e a l i z e d that t h e i n d u s t r i a l a n d u t i l i t y m a r k e t s Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 30, 2018 | https://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch010
r e q u i r e d different types of s u l f u r d i o x i d e r e m o v a l e q u i p m e n t .
Therefore,
it c o n t r a c t e d w i t h A b B a h c o V e n t i l a t i o n of S w e d e n to m a r k e t t h e i r s u l f u r d i o x i d e r e m o v a l t e c h n o l o g y i n the U . S . a n d C a n a d a . B a h c o
technology
is p a r t i c u l a r l y a p p l i c a b l e to i n d u s t r i a l b o i l e r a n d process a p p l i c a t i o n s T h e first U . S . B a h c o i n s t a l l a t i o n w i l l h a n d l e seven stoker-type
(7, 8,9).
b o i l e r s at the R i c k e n b a c k e r A i r F o r c e B a s e i n C o l u m b u s , O h i o . Comparison
of Lime—Limestone Wet
Scrubbing
with Other Systems
S i n c e the u t i l i t y i n d u s t r y represents the major m a r k e t for s u l f u r d i o x i d e c o n t r o l systems, it w a s necessary to d e v e l o p
a s i m p l e system
w h i c h w o u l d not r e q u i r e a lot of a t t e n t i o n , be i n e x p e n s i v e to operate, h a v e m o d e r a t e c a p i t a l r e q u i r e m e n t s , a n d not take effort a w a y f r o m t h e i r p o w e r p r o d u c i n g f u n c t i o n . C a l c i u m - b a s e d s c r u b b i n g processes meet a l l of these requirements.
I n a d d i t i o n , the c a l c i u m reagents
are i n e x p e n s i v e a n d
f o r m r e l a t i v e l y i n s o l u b l e r e a c t i o n p r o d u c t s w h i c h c a n be d i s p o s e d of i n s a n i t a r y landfills a n d s l u r r y p o n d s . T h e d i s a d v a n t a g e of c a l c i u m - b a s e d t e c h n o l o g y is the l o w salt s o l u b i l i t y w h i c h necessitates the use of v e r y large a b s o r b i n g surface areas, high liquid
flow
rates, a n d g o o d p H c o n t r o l to p r e v e n t s c a l i n g a n d
p l u g g i n g . M o s t recent t e c h n o l o g i c a l advances are i n the areas of c a l c i u m salt scale p r e v e n t i o n a n d c o n t r o l l e d c r y s t a l l i z a t i o n . S o l u b l e - b a s e d systems h a v e better a b s o r p t i o n c a p a b i l i t i e s a n d l i m i t e d scaling and p l u g g i n g problems.
H o w e v e r they h a v e p r o b l e m s associated
w i t h s o l u b l e salt d i s p o s a l a n d h i g h e r reagent costs.
T h e waste d i s p o s a l
problems have limited their application. B y - p r o d u c t processes h a v e the advantages of s o l u b l e - b a s e d systems b u t h a v e p r o b l e m s associated w i t h m o r e c o m p l e x o p e r a t i o n , i n c r e a s e d c a p i t a l a n d o p e r a t i n g costs, a n d the n e e d to d e v e l o p b y - p r o d u c t m a r k e t s . Therefore,
R e s e a r c h - C o t t r e l l i n i t i a l l y chose to d e v e l o p
calcium-based
s c r u b b i n g t e c h n o l o g y to best m e e t the e x i s t i n g needs of its customers. System
Description
F i g u r e 1 illustrates the c o m p o n e n t s of a t y p i c a l c a l c i u m - b a s e d s u l f u r d i o x i d e s c r u b b i n g system.
F l u e gases enter a q u e n c h i n g section w h e r e
Pfeiffer; Sulfur Removal and Recovery Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
10.
ATKINS
Lime-Limestone
123
Flue Gas Scrubbing
Treated Gas Stack
i
Reheater
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4 Mist Eliminator
Water
i Sulfur Dioxide Absorber
Quencher and Particulate Scrubber
Dirty Stack. Gases
Calcium Reagent
Settling Tank
Scrubber Tank
Absorber Tank
Vacuum Filtration
ΠΓ CaS0
3
CaSOi Fly Ash Waste Disposal Figure 1.
Typical calcium-based
sulfur dioxide scrubbing
system
the gas is c o o l e d a n d p a r t i c u l a t e a n d some s u l f u r d i o x i d e r e m o v a l takes place.
T h e q u e n c h e d gas t h e n enters t h e a b s o r p t i o n section w h e r e the
r e m a i n i n g s u l f u r d i o x i d e is r e m o v e d . w a t e r a n d reagent droplets.
F i n a l l y a m i s t e l i m i n a t o r removes
T h e c l e a n e d gas is r e h e a t e d a n d r e t u r n e d
to the stack.
Pfeiffer; Sulfur Removal and Recovery Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
124
SULFUR
REMOVAL
AND RECOVERY
C a l c i u m reagent is a d d e d to the absorber t a n k a n d p u m p e d to the s u l f u r d i o x i d e absorber. M o s t of the spent reagent is r e t u r n e d to the a b sorber tank, a n d p a r t is p r o v i d e d as reagent m a k e - u p to the q u e n c h e r system. T h e spent q u e n c h e r reagent, c o n t a i n i n g p a r t i c u l a t e a n d r e a c t i o n salts, is r e m o v e d f r o m the process as a s l u d g e b l o w d o w n .
Make-up
w a t e r , to c o m p e n s a t e for e v a p o r a t i o n losses a n d s l u d g e b l o w d o w n , is a d d e d p r i m a r i l y as m i s t e l i m i n a t o r w a s h . Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 30, 2018 | https://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch010
U s i n g this g e n e r a l a p p r o a c h , several sulfur d i o x i d e r e m o v a l systems have been developed.
F i g u r e 2 illustrates t h e C h o l l a sulfur d i o x i d e r e
m o v a l system w h e r e a m o d e r a t e e n e r g y s c r u b b e r is u s e d for p a r t i c u l a t e r e m o v a l , gas q u e n c h i n g , a n d i n c i d e n t a l sulfur d i o x i d e r e m o v a l . p a c k e d t o w e r is the m a j o r sulfur d i o x i d e a b s o r p t i o n d e v i c e .
The
Make-up
reagent is s u p p l i e d to the p a c k e d t o w e r , a n d the F D S receives reagent f r o m the p a c k e d - t o w e r system.
spent
T h u s reagent flow is c o u n t e r -
c u r r e n t to gas flow for m a x i m u m u t i l i z a t i o n .
INLET GAS
REHEATER Ρ*·
FDS
PACKED TOWER
SCRUBBER
Η >
Η
ι ,
TO SLUDGE DISPOSAL
MAKE-UP WATER
MAKE-UP WATER
y FDS SLURRY TANK
Figure 2.
TOWER TANK
Process flow diagram
R e s e a r c h - C o t t r e l l is also s u p p l y i n g a gas c l e a n i n g system u s i n g a n electrostatic p r e c i p i t a t o r for d r y p a r t i c u l a t e c o l l e c t i o n f o l l o w e d b y m u l t i - s t a g e gas l i q u i d contactor for sulfur d i o x i d e r e m o v a l .
The
stage is a c y c l o n i c q u e n c h e r for gas s a t u r a t i o n a n d m o d e r a t e
a
first
sulfur
d i o x i d e a b s o r p t i o n f o l l o w e d b y a spray a n d p a c k e d - t o w e r section w h e r e the m a j o r s u l f u r d i o x i d e a b s o r p t i o n takes p l a c e . a p p l i e d c o u n t e r c u r r e n t to t h e gas
A g a i n the reagent is
flow.
Pfeiffer; Sulfur Removal and Recovery Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
10.
Lime-Limestone
ATKINS
Process
Flue Gas
125
Scrubbing
Chemistry
T h e c h e m i s t r y i n v o l v e d i n l i m e - l i m e s t o n e s c r u b b i n g is v e r y c o m p l e x because of the l i m i t e d s o l u b i l i t y of the n u m e r o u s reagents a n d r e a c t i o n products.
T h e major c o m p o n e n t s a r e :
Reagent:
Ca, Mg, C 0 , O H 3
F l u e gas: S 0 , S 0 , CO >, 0 , N O , N 0 , N 2
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F l y ash:
3
2
L
2
2
N a , C l , K , Fe, C a , M g , Si
T h e m a i n reactions i n c a l c i u m b a s e d s c r u b b i n g are: 1.
D i f f u s i o n of s u l f u r d i o x i d e f r o m the gas phase into the l i q u i d phase, S 0 ( g ) S 0 ( a q ) 2
(1)
2
2. H y d r o l y s i s to f o r m sulfurous a c i d , bisulfite, sulfite, a n d h y d r o g e n ions, S0 (aq) +
H 0 *± H S 0
2
2
2
H S 0 - +± H + + 3
