United States
     Environmental Protection
     Agency
 Industrial Environmental Research
 Laboratory
 Research Triangle Park NIC 27711
     Technology Transfer
     Capsule Report
     Adipic Acic
-Enhanced
     Lime/Limestone
     Test Results at the
     EPA Alkali Scrubbing
     Test Facility
                    I'
1'=- — •""- ^



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Technology Transfer
EPA 625/2-82-029
Capsule Report
Adipic Acid-Enhanced
Lime/Limestone
Test Results at the
EPA Alkali Scrubbing
Test Facility
April1982
This report was developed by the
Industrial Environmental Researqh Laboratory
Research Triangle Park NC 27711

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Shawnee Test Facility

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1.  Introduction
and Background
This is the fifth i t a series of capsule
reports describing the results of the
Shawnee Lime and Limestone Wet
Scrubbing Test P|rogram conducted by
EPA's  Industrial   Environmental
Research Laboratory, Research Tri-
angle Park,  North  Carolina  (IERL-
RTP). In this program, flue gas desul-
furization (FGD) tests were conducted
at the EPA 10 WlW prototype Shawnee
Test Facility located at the Tennessee
Valley Authorit|  (TVA)  coal-fired
Shawnee Power Station near Paducah,
Kentucky. Bechtel National, Inc. of
San Francisco was the major contrac-
tor and test director, and TVA was the
constructor and  acility operator.

This  report  describes  the results of
adipic acid-enhanced lime and lime-
stone testing at the Shawnee Test Fa-
cility  from July  1978 through March
1981. It also summarizes earlier adipic
acid  additive test results from the
IERL-RTP 0.1 MW pilot plant, which
led to the testing at Shawnee. Also
reported  are preliminary results from
                                      the 100 MW full
                                      being conducted
                                      Power Plant of
                scale demonstration
                at the Southwest
                Springfield  City
Utilities, Springflield,  Missouri and
                                      from the 27 MW
                                      boiler test at Ricl
                                      Base.

                                      As the emission
                                      dioxide become
                equivalent industrial
                
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2.  Advantages
of Adipic Acid as
Scrubber Additive
A  number of attractive features of
adipic acid as a scrubber additive are
presented below.
                                      Handling
                                      Adipic acid is non-toxic, non-hygro-
                                      scopic, and usually comes in powder
                                      form. It is easy to handle and no
                                      hazards are encountered in the usual
                                      applications other than possible dust
                                      explosions, which  are typical of any
                                      organic dust. At Shawnee, it is rou-
                                      tinely dry-fed directly to the effluent
                                      hold tank, although it has been added
                                      to the fresh limestone slurry makeup
                                      tank in some instances.
                                      Buffer Reaction Mechanism
                                      The mechanism by which adipic acid
                                      buffers the pH is simple. It reacts with
                                      lime or limestone in the effluent hold
                                      tank to form calcium adipate. In the
                                      absorber, calcium adipate reacts with
                                      absorbed S02(H2S03) to form CaS03
                                      and simultaneously  regenerates adipic
                                      acid (the buffer reaction). The regen-
                                      erated adipic acid is returned to  the
                                      effluent hold tank for further reaction
                                      with lime or limestone. With a suffi-
                                      ciently high concentration of calcium
                                      adipate in solution,  usually on the
                                      order of 10 m-moles/liter to react with
                                      the absorbed SO2, the overall reaction
                                      rate is no longer controlled by the
                                      dissolution rate of limestone or cal-
                                      cium sulfite.
the tightness of the liquor loop, the
quantity of adipic acid  required is
quite small in relation to the alkali
feed. At Shawnee, where a filter is
normally used as the final sludge
dewatering device, the adipic  acid
consumption rate is usually less than
10 Ib/ton of limestone fed to the sys-
tem, and sometimes as low as 2 Ib/ton
of limestone. These values correspond
to only 0.6 to 3.0 tons of adipic acid
per day  for a 500 MW plant.
                                      Adipic acid has two pH buffer points.
                                      These are pH  4.5  and 5.5 in the
                                      absence of chloride in the liquor, and
                                      about 4 and 5 with 5,000 to 7,000
                                      ppm chloride. To fully utilize the buf-
                                      fer capacity of adipic acid, therefore,
                                      the slurry pH should be kept above
                                      these values. At  Shawnee, where the
                                      chloride concentration is usually a few
                                      thousand ppm, a slurry pH  above
                                      about 5.2 is sufficient to keep adipic
                                      acid fully active (or ionized). The
                                      optimum  concentration  range  of
                                      adipic acid at a pH above 5.2 is only
                                      700 to  1,500  ppm for 90 percent
                                      removal of approximately 2,500 ppm
                                      inlet SC>2. Higher concentrations
                                      would  be required at a lower pH to
                                      maintain equivalent buffer capacity in
                                      the liquid.  It should  be noted that
                                      most of the degradation products of
                                      adipic acid, such as valeric and glutaric
                                      acid, are also effective buffers.
                                       Retrofit
                                       Use of adipic acid in an existing lime
                                       or limestone system does not require
                                       modification of process flow configu-
                                       ration or absorber design; therefore, it
                                       is particularly suited for retrofit appli-
                                       cations. The fact that it may be added
                                       at any point in the slurry circuit pro-
                                       vides a greater flexibility in the loca-
                                       tion and installation of a simple solids
                                       storage and feed system, a minimal
                                       capital investment.
                                      Quantity and Concentration
                                      Depending on the operating param-
                                      eters, the degree of degradation, and
                                      Limestone Utilization
                                      At a scrubber inlet pH of about 5.2,
                                      the corresponding limestone utiliza-
                                      tion is normally 80 percent or higher
                                      for an adipic acid-enhanced system, as
                                      compared to 65 to 70  percent in unen-
                                      hanced limestone systems at an equiv-
                                      alent SO2 removal. Thus the quantity
                                      of waste solids generated is reduced in
                                      an  adipic  acid-enhanced  system.
                                      Higher limestone utilization also con-
                                      tributes to more  reliable  scrubber
                                      operation by reducing the fouling
                                      tendency. This increased reliability is a
                                      very attractive feature of adipic acid-
                                      enhanced systems, since reliability
                                      problems have  historically  plagued
                                      limestone FGD.

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 Operating pH
 With proper pH control and suffi-
 ciently high adipic acid concentra-
 tion (sufficient buffer capacity), the
 scrubber performance is more stable,
 and steady outlet SO2 concentrations
 can be maintained, even with wide
 fluctuations of inlet SO2 concentra-
 tions.

 With the lower operating pH (about
 4.6 to 5.4) in an adipic acid-enhanced
 limestone system, compared to the
 higher pH  (about 5.5 to 5.8) usually
 needed for  an unenhanced limestone
 system, the system becomes more
 amenable to other process  concepts
 and improvements. Potential advan-
 tages of low pH operation are:
 •  Reduced adipic acid consumption.
    Adipic acid degradation has been
    found to decrease with decreasing
    pH
 •  Easier  forced  oxidation  in  the
    scrubber  slurry  loop or bleed
    stream,  and a smaller air  (and
    compressor energy) requirement
 •  Potential for essentially  complete
    limestone utilization with improved
   scrubber operating reliability
 •  Reduced sensitivity of the system
   to limestone type and grind. Fine
   grinding  of limestone is  probably
   not required
 •  Lower sulfite scaling potential
 •  Better prospects (sensitivity) for
   automatic pH control

•  Greater flexibility for SO2 emission
   control. Higher sensitivity of SO2
   removal at lower pH allows raising
   pH to increase the adipic acid buf-
   fer capacity and SC>2 removal when
   needed
•  Applicability  to  low-sulfur sub-
   bituminous and lignite coals con-
   taining alkaline ashes, which  are
   extractable only at low pH
•  Lower costs due to all of the above
   factors
Economics
Since limestone dissolution is not a
rate-controlling step in SO2 absorption
for an adipic acid-enhanced limestone
system, adipic acid should promote use
of less expensive and less energy-inten-
sive limestone rather than lime.

Adipic acid-enhanced limestone scrub-
bing has lower
operating costs
stone or  MgO-
scrubbing. This
reduced limestc
projected capital and
than unenhanced lime-
enhanced  limestone
is due primarily to the
ne consumption at the
lower operating! pH, the reduced grind-
ing cost, and the reduced quantity of
waste sludge generated.
Forced Oxidation
The mechanism1 by which adipic acid
promotes SO2 removal is not affected
by forced oxidapon. Therefore, it can
be used with both lime and limestone
in systems  with)  or without forced
oxidation.
Since forced ox
dation converts sulfite
to sulfate, it has an adverse effect on
SO2 removal in an unenhanced lime
system in which sulfite is the major
SOa scrubbing species. This is also true
in MgO-enhanced lime and limestone
systems in which the  promotion of
SOa removal relies on an increased
sulfite-bisulfite  buffer. When adipic
acid is used with lime, calcium adipate
becomes a major buffer species; there-
fore, both good SO2 removal and sul-
fite oxidation can be achieved using
within-scrubber-loop forced oxidation.

Chloride Effect
The effectiveness of adipic acid is not
adversely affected by chlorides,  as is
the effectiveness  of MgO in an MgO-
enhanced process. Tests at the 1ERL-
RTP pilot  plant  showed that SO2
removal  efficiency obtained with
17,000 ppm chloride in the scrubbing
liquor  was  not significantly different
from that obtained without chloride
under similar levels of adipic acid con-
centration. Thus, use of adipic acid is
especially attractive for systems with a
very tightly closed liquor loop.
Solids Dewatering
Adipic acid does  not significantly
affect the settling and filtration prop-
erties of oxidized or unoxidized
slurry solids, whereas magnesium does.


Total Dissolved Solids
Addition of adipic acid does not sig-
nificantly increase the total  dissolved
solids in liquid as does magnesium.
High total dissolved solids in liquid
entrainment can increase particulate
emissions and fouling  tendencies of  •
equipment  downstream  of the
scrubber.

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3.  Test Programs
The theoretical basis for the effect of
adipic acid on the performance of lime
and  limestone scrubbers  was  first
developed in detail by G. Rochelle in
1977 ("The Effect of  Additives on
Mass Transfer in CaCOs or  CaO
Slurry Scrubbing of S02 from Waste
Gases,"  Industrial and Engineering
Chemistry  Fundamentals,  16,  pp.
67-75, 1977). In October 1977, EPA
began an investigation of adipic acid
with the 0.1  MW  lERL-RTP  pilot
plant to determine its effectiveness as
an additive to limestone scrubbers for
improving SO2   removal efficiency.
Initial results demonstrated, as pre-
dicted by Rochelle, that adipic acid
was indeed an.attractive and powerful
additive.
                                       Based on the findings at the IERL-
                                       RTP pilot plant, a program was set up
                                       at the 10 MW Shawnee Test Facility to
                                       develop  commercially  usable design
                                       data for adipic acid as a  chemical
                                       additive. Actual testing at Shawnee
                                       began in July 1978, and lasted through
                                       March 1981. The test schedule for this
                                       period is shown in Figure 1. Tests were
                                       conducted  over a period of 33 months,
                                       using both lime and limestone with
                                       and without forced  oxidation. As can
                                       be seen, major emphasis was placed
                                       on limestone  testing with forced
                                       oxidation.
                                      As part of EPA's continuing program
                                      of FGD technology transfer, and to
                                      further demonstrate the effectiveness
                                      of adipic acid and to encourage its use,
                                      EPA contracted with Radian Corpora-
                                      tion in the spring of 1980 to conduct
                                      a  full-scale  demonstration  program
                                      of  adipic acid-enhanced limestone
                                      scrubbing. The program, being con-
                                      ducted  with two 100  MW Turbulent
                                      Contact Absorbers (TCA) located at
                                      the Springfield City Utilities' South-
                                      west Station near  Springfield, Mis-
                                      souri,  continued  through October
                                      1981. Some preliminary test-results
                                      are included in this report, as are data
                                      from the industrial-sized (27  MW)
                                      scrubber test conducted by PEDCo
                                      Environmental, Inc.  on the Bahco
                                      system  at Rickenbacker Air Force
                                      Base.
 During some factorial tests conducted
 at the Shawnee Test Facility in 1979,
 it was noticed that the rate of adipic
 acid addition required to maintain a
 desired concentration in the scrubber
 liquor was substantially reduced when
 the scrubber inlet pH was controlled at
 5.0 or lower. In order to verify the
 Shawnee findings, the EPA initiated
 several programs to study the adipic
 acid degradation  phenomenon.  Con-
 tractors involved included the Univer-
 sity of Texas at Austin, Radian Cor-
 poration,  Acurex Corporation,  and
 Research Triangle Institute. Programs
 were  set up to  investigate the effects
 of pH, oxidation, and catalysts such as
 manganese and iron  on adipic acid
 degradation, to develop analytical pro-
 cedures and to  identify the degrada-
 tion products.  Although the adipic
 acid degradation mechanism is com-
 plex,  the principal variables affecting
degradation  and its major products
 have been identified. The results of
these  studies are beyond the scope of
this report and will  be reported
separately.
                                      Shawnee Test Facility
                                      Tests with adipic acid at Shawnee have
                                      been conducted on two parallel scrub-
                                      ber systems: a venturi/spray tower sys-
                                      tem (Train 100) and a TCA system
                                      (Train  200). Each system has its own
                                      slurry  handling and dewatering facil-
                                      ities, and each is designed to remove
                                      both  SO2  and  particulate  from
                                      approximately 10 MW equivalent of
                                      flue gas (up to 35,000 acfm at 300°F).
                                      The flue gas, which normally contains
                                      1,400  to 3,500 ppm by volume of
                                      SO2, is obtained either upstream (con-
                                      taining high fly ash loading of 2 to 7
                                      grains/dry scf) or downstream (con-
                                      taining low fly  ash loading of 0.2 to
                                      0.6 grain/dry scf) from Boiler No. 10
                                      particulate removal equipment.

                                      In June  1980,  the venturi scrubber
                                      was removed  from Train 100, allowing
                                      operation with  the spray tower only.
                                      Prior to the removal of  the venturi
                                      scrubber, operation with a true spray-
                                      tower-only configuration was not pos-
                                      sible without some interference from
                                      the venturi, even with its adjustable

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plug wide open and minimum slurry
flow for flue gas cooling.


Shawnee Test Blocks
Tests conducted at the Shawnee Test
Facility can be classified into blocks
according to type  of alkali, fly ash
loading in  the flue gas, adipic  acid
addition,  and  forced  oxidation
scheme. Table 1 lists the combinations
of these variables  which have been
tested at Shawnee, including factorial
tests.
Forced oxidation is achieved by air
sparging of the slurry in an oxidation
tank, either on the bleed stream to the
solids dewatering system or on  the
recirculated sluriTy within the scrubber
slurry loop.  For a one-scrubber-loop
forced oxidation system, the slurry
effluent from all scrubbers in the sys-
tem  (e.g., the venturi scrubber and
spray tower at Shawnee constitute a
two-scrubber system, and the spray
tower alone or  TCA, a one-scrubber
system) are sent to a single  effluent
hold tank, whicl-  is the oxidation tank.
For a two-loop forced oxidation sys-
tem, there are two scrubbers in series
(e.g.,  venturi and spray tower at
Shawnee) with effluent from  each
scrubber going to a  separate-tank;
the effluent hold tank  for the up-
stream scrubber (with respect  to gas
flow) is the oxidation tank. For either
one-loop or two-loop forced oxidation
systems, the oxidation tank may be
followed by a second tank, in series, to
provide further limestone dissolution
and gypsum  desupersaturation time
prior to recycle to the scrubber.
Adipic Acid Test Block
Venturi/Spray Tower System (Train 100)
Lime with forced oxidation
Limestone with forced oxidation,
no adipic acid (Widows Creek simulation)
Lime and limestone (Venturi only)
Limestone factorial
Limestone without forced oxidation


Spray Tower System (Train 100)

Limestone factorial, no adipic acid
Limestone factorial
Limestone with forced oxidation


TCA System (Train 200)
Limestone without forced oxidation
Lime without forced oxidation
Lime without forced oxidation.
no adipic acid
Lime with forced oxidation
Limestone with forced oxidation
Limestone factorial
Limestone with forced oxidation,
no adipic acid
Limestone, low fly ash loading
(Springfield simulation)
Limestone without forced oxidation,
no adipic acid (Glitsch Grid packing)
Note: All tests are with adipic acid and high fly
1978
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  Figure 1. Shawnee Adipic Acid Test Schedule

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4.  Test Results
It is beyond the scope of this capsule
report to  present all of the Shawnee
test results from the test blocks listed
in Table 1. Therefore, only the typical
and important test results are  pre-
sented below.  Results of long-term
tests  (longer than one  month) are
included.  Results from factorial  or
partial factorial tests, which normally
lasted a minimum of 12 hours, includ-
ing  5  to 7 hours of steady state opera-
tion,  are also included as figures  to
illustrate the effects of pH and adipic
acid concentration  on  SO2 removal.
A  summary of initial tests  at the
IERL-RTP pilot plant and the prelimi-
nary results from the full-scale TCA
tests at Springfield are also given.

IERL-RTP Pilot Plant Test Results
The  initial testing of adipic  .acid as a
scrubber additive was carried out by
EPA beginning in October 1977 in the
0.1 MW in-house pilot plant  located at
IERL-RTP. A single-loop limestone
scrubber was used for this purpose,
operated with forced oxidation in the
scrubbing loop. In addition to effects
                                        Table 1.
                                        Test Blocks Conducted at Shawnee
Test Fly Ash
Block Alkali Loading
Venturi/Spray Tower
1 Lime
2 Lime
s'a' Limestone
4 Limestone
5 Limestone
6 Limestone
7 Limestone
8 Limestone
9'k) Limestone
Spray Tower System:
10^a' Limestone
1 1 Limestone
12 Limestone
13 Limestone
TCA System:
14 Lime
15 Lime
16'a' Lime
17 Limestone
18 Limestone
ig'a) Limestone
20 Limestone
21 'c' Limestone
22'd' Limestone
23 'd) Limestone
System:
High
High
High
High
High
High
High
High
High

High
High
High
High

High
High
High
High
High
High
High
High
Low
Low
Adipic Acid Oxidation No. of Tanks
Addition Scheme in Oxid. Loop

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No

Yes
Yes
No
No

Yes
Yes
No
Yes
Yes
Yes
No
No
Yes
Yes

2-Loop
No
2-Loop
2-Loop
1-Loop
1-Loop
Bleed Stream
No
2-Loop

1-Loop
No
1-Loop
No

1-Loop
No
No
1-Loop
1-Loop
No
1-Loop
No
1-Loop
No

2
—
2
1
2
1
—
	
2

2
—
2
—

1
—
_
2
1
—
1
	 : . .
1
—
                                          (a) Includes long-term (greater than one month) tests.
                                          (b) Widows Creek forced oxidation simulation tests.
                                          (c) Glitsch Grid packing tests.
                                          (d) Springfield adipic acid simulation tests.

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on SO2 removal and oxidation effi-
ciencies, these tests sought to deter-
mine whether adipic acid caused any
change in  the properties of the oxi-
dized sludge. So that these properties
could be clearly seen, the system was
operated without fly ash. Chloride
was added as HCI and controlled at
the high levels expected for tightly
closed loop systems.

The results of the tests showed adipic
acid to be very effective in improving
SO2  removal efficiency, even when
operating  at chloride levels as high as
17,000 ppm. A TCA scrubber, which
removed 82 percent of the inlet SO2
without the additive, yielded 89 per-
cent SO2  removal with 700 ppm adi-
pic acid,  91  percent removal with
1,000 ppm, and 93 percent removal
with 2,000 ppm adipic acid. The lime-
stone utilization  was concurrently
increased  from 77 percent without the
additive to 91 percent with 1,600 ppm
adipic acid. The observed effects thus
confirmed the theoretical expectations
in all respects.
showed no ser
adipic acid on
oxidizer, opera

The quality of
similar to that
 In addition, the tests
 ous interference by
the performance of the
 :ing  at pH 6.1.

 tie oxidized sludge was
 obtained when opera-
ting without adipic acid, although
small differences were detected. For
example, the fi
80  percent sol
tests) vs 84 pen
 tered sludge averaged
 ds (for  13 one-week
 :ent solids for 11 tests
without the additive, when operating
at 97 to 99 pen
cases. The settl
(fly ash free at
cm/min during
 :ent oxidation in both
 ing rate of the slurry
 50°C) averaged  2.3
 the adipic acid  tests
and 3.4 cm/min without adipic acid;
bulk settled densities averaged 1.0 and
1.2 g  solids/cm3 slurry, respectively.
It was  concluded from these results  _
that the large improvements in sludge
quality that can be achieved by forced
oxidation are nst compromised by the
use of adipic pcid  as a scrubber
additive.

Tests without forced  oxidation  also
demonstrated  the  efficacy of adipic
acid. Operating a TCA scrubber with
2,000 ppm adipic  acid and 6 inches
H2O pressure  drop, 92 percent SO2
removal was obtained at a limestone
utilization  level  of 88 percent. By
comparison, only  75 percent SO2
removal would be expected  in the
pilot plant at these test conditions
without the additive.  At this adipic
acid level, the unoxidized sludge fil-
tered to 49 percent solids; at lower
adipic acid levels (1,500 ppm or less),
the filterability of the slurry was the
same as that obtained without addi-
tives: 55 percent solids.

During the testing with adipic acid, the
scrubbing liquor had a noticeable odor,
even though the additive feed did not.
The odor has been  identified as that of
valeric acid, CH3(CH2)3 COOH, an
intermediate product  formed by side
reactions that  degrade adipic acid at
scrubber operating conditions.  At
Shawnee, this  odor was rarely noticed
and was not a  problem.
                            Flue Gas
                     Reheat.
                                                                                             Makeup Water
                                                                                      Clarified Liquor from
                                                                                    Solids Dewatering System
                                                                                              Bleed to Solids
                                                                                               Dewatering
                                                                                                System
 Figure 2. Flow Diagram for Adipic Acid-Enhanced Scrut bing in the Venturi/Spray Tower System with Two Scrubber
          Loops and Forced Oxidation

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Limestone Long-Term Tests with
Two Scrubber Loops and Forced
Oxidation
The venturi/spray tower system was
modified for two-scrubber-loop opera-
tion with forced oxidation as shown in
Figure 2 (see  previous page). Two
tanks were used in the oxidation loop
(venturi loop); air was injected to the
first of these tanks through a simple
3-inch diameter pipe below the agita-
tor. Adipic acid was dry-fed into the
spray tower effluent hold tank. This
was accomplished by manually adding
one-pound increments hourly to main-
tain specified  concentration, usually
totaling only a few pounds per hour. A
small screw feeder would serve the
purpose in a full-scale plant.

The main advantage  of this two-loop
system, as far  as forced oxidation is
concerned, is that it permits operation
of the first  loop (venturi loop) at
lower pH for  good  oxidation effi-
ciency, while maintaining higher pH in
the second loop (spray tower loop) for
good SO2 removal. This configuration
also maximizes the limestone utiliza-
tion. With adipic acid enhancement,
however, some of these advantages can
also be obtained in a single-loop
scrubber because an adipic acid-
enhanced system can be operated at a
lower pH (4.6 to 5.4). Thus, good
oxidation and SOj removal both can
be achieved  without an independent
first loop.

Table 2 summarizes the results of two
long-term tests  (exceeding one
month),  Runs 907-1A and 907-1B,
with adipic acid addition and with a
variable gas  flow rate. The results
of Run 901-1A, a base case run with-
out additive and with a constant spray
tower gas velocity of 9.4 ft/sec, are
also included for comparison.

Run 907-1A was a month-long adipic
acid-enhanced  limestone  run with
forced oxidation, designed to demon-
strate  operational  reliability  with
respect to scaling and plugging and to
demonstrate the removal enhancement
capability of the adipic acid additive.
This run was controlled at a nominal
limestone stoichiometry of 1.7 (corn-
 Table 2.
 Adipic Acid-Enhanced Limestone Tests on the Two-Loop Venturi/Spray
 Tower System with Forced Oxidation
                   Run No.
        901-1A  907-1A   907-1B
Onstream hours
Fly ash loading
Adipic acid cone, in venturi, ppm
Adipic acid cone, in spray tower, ppm
(controlled)
Spray tower gas velocity, ft/sec
Venturi liquid-to-gas ratio, gal/Mcf
Spray tower liquid-to-gas ratio, gal/Mcf
Venturi slurry solids cone., wt % (controlled)
Spray tower slurry solids cone., wt %
Venturi inlet pH (controlled)
Spray tower inlet pH
Venturi pressure drop, in. h^O
Oxidation tank level, ft
Oxidation tank residence time, min
Desupersaturation tank residence time, min
Spray tower effluent tank residence time, min
Spray tower limestone stoich. ratio (controlled)
Average percent SO2 removal
Average inlet SO2 concentration, ppm
Percent oxidation of sulfite to sulfate
Air stoichiometry, atoms oxygen/mole
SO2 absorbed
Overall percent limestone utilization
Venturi inlet liquor gypsum saturation, %
Spray tower inlet liquor gypsum saturation, %
Filter cake solids content, wt %
187
High
0

0
9.4
21
57
15
5.9
4.50
5.45
9.0
18
11.3
4.7
14.7
1.36
57
2,800
98

2.30
97
95
95
85
719
High
2,360

1,560
4.8-9.4
21-42
57-111
15
6.1
4.65
5.45
3.0-9.6
18
11.3
4.7
14.7
' 1 .77
97.5
2,350
98.5

2.0-3.85
88
110
105
87
1,666
High
2,180

1,510
5.4-9.4
21-37
57-100
15
5.9
4.65
5.35
3.5-9.2
18
11.3
4.7
14.7
1.70
97
2,500
98

1.9-3.3
92
105
110
85
pared to 1.4 for the base case run. Run
901-1 A) and 1,500 ppm adipic acid in
the spray tower. Venturi inlet pH was
controlled at a minimum of 4.5 by the
occasional addition of limestone to the
venturi loop.

Flue gas flow rate was varied from
18,000 acfm to a maximum of 35,000
acfm  (spray  tower  gas  velocity
between 4.8 and 9.4 ft/sec) to follow
the daily boiler load cycle, which nor-
mally fluctuated between 100 and
150 MW. The adjustable venturi plug
was fixed in a position such that the
pressure drop across the venturi was
9 inches H2O at 35,000 acfm maxi-
mum gas rate.  Actual pressure drop
ranged from 3.0 to  9.6 inches H2O.
The slurry recirculation rates to the
venturi and spray tower were fixed at
600 gpm (L/G = 21 to 42 gal/Mcf) and
1,600 gpm (L/G = 57 to 111 gal/Mcf),
respectively.


The oxidation tank level was 18 ft and
the air flow rate was held constant at
260 scfm.
The run began on October 8, 1978 and
terminated November 13, 1978. It ran
for 719 onstream hours (30 days)  with
no unscheduled outages. The scrubber
was down once for a scheduled 3-hour
inspection and again when the boiler
came down for 135 hours to install a
new station power transformer.

-------
Average SO2 removal for Run 907-1A
was 97.5 percent at 2,350 ppm average
inlet SO2 concentration. The  SO2
removal stayed within a narrow range
of 96 to 99 percent throughout almost
the entire run. This was a significant
improvement over the 57 percent SO2
removal for the  base case run, Run
901-1 A, at 9.4 ft/sec spray tower gas
velocity under similar conditions. On
October  19  and  on October 27, SO2
removal dropped briefly to less than
90 percent when the pump which sup-
plied the slurry to the top two spray
headers was brought offstream for
repacking, and the spray tower slurry
flow rate was cut in half to 800 gpm.
At  the reduced  slurry recirculation
rate, S02 removal was 82  to  87
percent.

Venturi and  spray tower inlet pH
averaged  4.65 and 5.45, respectively.
Overall limestone utilization was 88
percent and the spray tower limestone
utilization was 56 percent, demon-
strating the advantage of good lime-
stone utilization in a two-scrubber-
loop operation.

Average  adipic acid concentrations
were 2,360 ppm in the venturi loop
and 1,560 ppm in the  spray tower
loop.

Sulfite oxidation in the system bleed
slurry averaged 98.5 percent, with the
air stoichiometric ratio varied between
2.0 and 3.85 atoms oxygen/mole SO2
absorbed. The filter cake solids con-
tent was 87 percent.

The mist eliminator was clean  during
the entire run. The system  was free
of plugging and scaling and there was
no increase in solids or scale deposits
on the scrubber  internals during  Run
907-1 A.

Following Run 907-1A,  a  second
adipic acid-enhanced limestone long-
term run with forced oxidation was
made during which flue gas monitor-
ing procedures were evaluated by EPA.
This run. Run 907-1B, was made
under the same  conditions  as  Run
907-1A except that the gas flow rate
was varied according to  a  "typical"
utility boiler load cycle rather than the
actual Unit  No.  10 boiler  load.
 Run 907-1B beban on November 13,
 1978 and terrr inated January  29,
1979. It ran for
(69 days) with
scrubber-relatec
was also out of
               1,666 onstream hours
               only 27 hours of
               outages. The scrubber
               iervice 146 hours when
Unit 10 came down for replacement of
a broken turbine thrust bearing.

Excluding boiler outages and sched-
uled inspection;, the combined  Runs
907-1A and 90 7-1B  operated for a
period of over
onstream factor
               3  months with an
               of 98.9 percent. No
deposits whatsoever were observed in
the mist eliminator for the entire 3-
month test period. On only one occa-
sion did solids accumulation cause an
outage; the cross-over line carrying
slurry effluent from the venturi to the
oxidation tank plugged with soft solids
and had to  be cleaned out. Because of
problems associated  with  converting
the Shawnee venturi/spray tower sys-
tem to two-scrubber-loop operation,
this cross-over line followed a tortuous
path (see  Figure 2). A properly
designed systerr
problem.
               would not have this
Results of Run 907-1 B were as good in
every respect as those of Run 907-1 A.
Average SO2 removal remained within
a narrow band of 95 to 99 percent.
SO2 removal dropped  briefly (typi-
cally 30 minutes) below 90 percent
five times when one of the two spray
tower recirculation  pumps was taken
out of service for maintenance, effec-
tively cutting the slurry recirculation
rate in half.

Overall  limestone utilization during
this run was 92 percent. Sulfite oxida-
tion averaged 98 percent and the waste
sludge filter cake quality was excel-
lent, having a solids content of  85
percent.

S02  emissions for Run 907-1A and
907-1B  were calculated based on an
assumed coal heating value of 10,500
Btu/lb,  on 100 percent sulfur overhead
(none in bottom ash), and on an
assumed excess air of 30 percent. This
excess air rate resulted in about 700
ppm inlet SO2 per 1.0 weight percent
sulfur in coal for the above conditions.
The  average SO2 emission for the
entire 3-month operating period was
only 0.20 lb/106 Btu. The highest
24-hour average SO2 emission during
Run 907-1A was 0.37 lb/106 Btu, and
during Run 907-1B  was 0.41 lb/106
Btu.

A material balance calculation for the
adipic acid consumption was made for
Run  907-1 B. Actual adipic acid feed
rate was 8.3 Ib/ton of limestone fed to
the system, of which 1.8 Ib/ton were
discharged with the  filter cake (theo-
retical requirement) and  6.5 Ib/ton
were unaccounted for, giving an actual-
to-theoretical consumption ratio of
4.6.
Limestone Drying, Grinding and Classification System

-------
Limestone Long-Term Test with One
Scrubber Loop and Without Forced
Oxidation
Perhaps the  most straightforward
illustration of the effectiveness of
adipic acid is demonstrated by a long-
term limestone test conducted on the
Shawnee TCA system, in which the
additive was introduced without any
system modifications.

Table 3 lists the results  of the long-
term test, Run 932-2A, with adipic
acid enhancement. The results of  a
base case run. Run 926-2A, without
the additive,  are also included in the
table for comparison.

Figure 3 depicts the simple single-
loop, one-tank configuration of the
TCA system used for these runs. The
TCA contained three beds of 1-7/8
inch diameter, 11.5-gram nitrile foam
spheres retained between bar  grids.
Each bed contained  5 inches  static
height of spheres. Adipic acid was
manually fed by the operator  to the
effluent hold tank.
Table 3.
Adipic Acid-Enhanced Limestone Test on the Single-Loop TCA System without
Forced Oxidation
                   Run No.
926-2A
932-2A
Onstream hours
Fly ash loading
Adipic acid concentration, ppm (controlled)
Scrubber gas velocity, ft/sec
Liguid-to-gas ratio, gal/Mcf
Slurry solids concentration, wt % (controlled)
Limestone stoichiometric ratio (controlled)
Total static bed height, inches of 1 1 .5 gram
nitrile spheres
Effluent hold tank residence time, min
Average percent SO2 removal
Average inlet SO2 concentration, ppm
SO2 make-per-pass, m-moles/liter
Percent oxidation of sulfite to sulfate
Scrubber inlet pH
Percent limestone utilization
Scrubber inlet liquor gypsum saturation, %
Centrifuge cake solids content, wt %
192
High
0
12.5
50
15
1.2

15
4.1
71
2,750
10.1
13
5.65
80
90
37*
833
High
1,620
8.4-12.5
50-75
15
1.2

15
4.1
96
2,450
4-18
21
5.30
82
110
61
  *Clarifier underflow solids content.
 Run 932-2A was made to demonstrate
 both operational  reliability with
 respect to scaling and plugging of the
 TCA and the SO2 removal enhance-
 ment capability of the adipic acid
 additive. The run began on Septem-
 ber  26,  1978  and terminated  on
 November 2,1978, for a total of 833
 onstream hours (35 days). During the
 run, the scrubber was out of service
 for 48 hours due to a boiler outage
 caused by a tube leak, 5 hours for a
 scheduled inspection, and 8 hours for
 unscheduled outages to clean  and
 repair the scrubber induced-draft fan
 damper. Excluding boiler outages and
 scheduled inspections. Run 932-2A
 operated with  an onstream factor of
 99.0 percent. As was typical of all
 long-term runs, the scrubber was more
 reliable than the boiler.

 The run was controlled at a  nominal
 limestone  stoichiometric ratio  of
 1.2  and  1,500 ppm adipic acid con-
 centration in the slurry liquor. Slurry
 solids concentration was controlled
 at 15 percent. The flue gas flow rate
 was  varied between  20,000 and
                        Flue Gas
                 Reheat
 Flue Gas
 Alkali Slurry
 Adipic Acid
                  Effluent Hold Tank
                                                        Makeup Water
       Clarified Liquor
       from Solids
       Dewatering System
                                                         Bleed to Solids
                                                         Dewatering System
 Figure 3.  Flow Diagram for Adipic Acid-Enhanced Scrubbing in the TCA
          System without Forced Oxidation

-------
 30,000 acfm (8.4 to 12.5 ft/sec super-
 ficial gas velocity) as the boiler load
 fluctuated between 100 and 150 MW.
 The slurry recirculation rate was fixed
 at1,200gpm (L/G=50 to 75 gal/Mcf).
 The effluent hold tank residence time
 was only 4.1 minutes.

 SO2  removal  during  Run 932-2A
 averaged 96 percent at an average inlet
 S02  concentration of  2,450  ppm.
 Excluding the first few days of
 unsteady state operation, S02 removal
 stayed within  a narrow range of 94 to
 98 percent as the inlet SO2 concentra-
 tion varied widely between 1,400 and
 3,500 ppm. By contrast, SO2 removal
 during  the  base  case  run  without
 adipic acid, Run 926-2A, averaged
 only 71 percent at 2,750 ppm average
 inlet SO2  concentration, and at con-
 stant 12.5 ft/sec gas velocity and  50
 gal/Mcf liquid-to-gas ratio.

 SO2 emissions were calculated for Run
 932-2A on the same basis as for the
 venturi/spray tower runs,  Runs 907-
 1A and 907-1B. Excluding the first
 few days of unsteady state operation,
 the SO2 emissions  for the 27-day
 period from,October 6 through the
 end of the run on November 2, 1978,
 averaged only  0.26  lb/106 Btu. The
 highest 24-hour average SO2 emission
 during this period  was only 0.44
 lb/106 Btu.

The mist eliminator was completely
clean at the end of  Run 932-2A and
the entire scrubber system was free of
scaling and plugging. Limestone util-
ization during the run averaged 82  per-
cent. Solids discharged from the cen-
trifuge averaged about 61 percent,
which is typical of unoxidized lime-
stone sludge.

An adipic acid material  balance calcu-
lation was made for a 21-day period
during Run 932-2A. The actual adipic
acid feed rate was 9.2 Ib/ton limestone
feed, of which 4.2 Ib/ton were dis-
charged with the centrifuge cake (the-
oretical  requirement) and 5.0 Ib/ton
were unaccounted loss, giving an
actual-to-theoretical consumption ratio
of 2.2. This ratio was less than the
value of 4.6 for venturi/spray tower
Table 4.
Adipic Acid-E
Forced Oxida

Onstream ho
Fly ash load!
Adipic acid c
Scrubber gas
Liguid-to-gas
Slurry solids
Scrubber inlt
Total static t
nhanced Lime Tests on the Single-Loop TCA System without
ion
Run No.
urs
ig
oncentration, ppm (controlled)
velocity, ft/sec
ratio, gal/Mcf
concentration, wt % (controlled)
t pH (controlled)
ed height, inches of 1 1 .5 gram
nitrile spheres
Effluent hold tank residence time, min
Average perc jnt SC>2 removal
Average inlet
SC>2 make-pe
Percent oxid;
Percent lime
SC>2 concentration, ppm
r-pass, m-moles/liter
ition of sulfite to sulfate
utilization
Scrubber inlet liquor gypsum saturation, %
Run 907-1 B v
forced, indicat
tion promotes

978-2A
116
High
0
12.5
50
8
7.0

15
4.1
83
2,350
10.3
21
92
125
fhen oxidation was All three runs

979-2A
177
High
615
12.5
50
8
7.2

15
4.1
93
2,900
14.3
14
92
90

980-2A
247
High
1,305
12.5
50
8
6.95

15
4.1
97.5
2,750
14.3
10
88
75
listed in Table 4 were
ng that forced oxida- operated under the same
idipic acid degradation. except
for the
adipic acic
conditions,
concentra-
However, the zctual feed rate of 9.2
Ib/ton limestore for Run 932-2A was
higher than the 8.3 Ib/ton limestone
for Run 907-1 B, because of the higher
moisture content in the discharge cake
for Run 932-2A without forced oxi-
dation. Thus, the net effect of forced
oxidation was to reduce  the  adipic
acid makeup requirements  by approx-
imately  10 percent.

In summary, tie objectives of this
long-term test were met. High  removal
was consistently achieved at a good
limestone utilisation, and no fouling,
scaling, or plugging occurred.
Lime Tests witi One Scrubber Loop
and Without Forced Oxidation
Tests with adipic acid in lime scrub-
bing also were impressive in enhancing
SO2  removal.
joth  on the venturi/
spray tower and TCA systems. Table 4
shows some ty
acid-enhanced
Shawnee TCA
tion. The flow <
is shown in Fig
sical  results of adipic
lime  tests from  the
without forced oxida-
Jiagram for these tests
jre 3.
                         tion. Run 978-2A was a base case test
                         without adipic acid. For Runs 979-2A
                         and 980-2A, adipic acid concentration
                         was controlled at a nominal 600 ppm
                         and 1,200 ppm, respectively (615 ppm
                         and 1,305 ppm actual).  The scrubber
                         inlet pH was controlled at about 7.0
                         for all runs.

                         Average SO2 removal improved from
                         83 percent at 2,350 ppm average  inlet
                         SO2 concentration for the base case
                         run, to 93 percent SO2 removal at the
                         higher inlet SO2 concentration  of
                         2,900 ppm  with 615  ppm  adipic
                         acid, and to 97.5 percent  removal at
                         2,750 ppm inlet SO2 with  1,305 ppm
                         adipic acid. Thus, with 600 to 1,300
                         ppm  adipic  acid, SO2  removal
                         improved by 10 to 15 percent over the
                         base case removal of 83 percent  at
                         50 gal/Mcf  liquid-to-gas ratio and
                         7.0 scrubber inlet pH.
Lime Test with One Scrubber Loop
and Forced Oxidation
Within-scrubber-loop forced oxidation
in a single-loop scrubbing  system

-------
would not be expected to give good
SOj removal for a  lime scrubber
because of the oxidation of the major
scrubbing species, sulfite ion, into non-
reactive sulfate  ion. With adipic acid
addition,  however, satisfactory S02
removal should be possible because
calcium adipate becomes the major
scrubbing species. In addition, the
lower pH  at which a lime/adipic acid
system operates should facilitate sul-
fite oxidation.

Table 5 lists the test results of such a
lime run.  Run 951-2E, using within-
scrubber-loop forced  oxidation with
1,330 ppm adipic acid. The system
configuration used for this run was the
same as that shown in Figure 3, except
that the oxidizing air was injected into
the  effluent hold tank (oxidation
tank). A single  3-inch diameter pipe
was used for this purpose, with the air
discharging downward at the center
of the oxidation tank 5 inches from
the tank bottom.

Run 951-2E was made with a scrubber
inlet pH of 5.0 (oxidation tank pH).
Higher pH increases the calcium sul-
fite  scaling  tendency  and  also
decreases oxidation efficiency. Lower
pH reduces the calcium adipate buffer
capacity and SO2 removal efficiency.

At 5.0 scrubber inlet pH and 50 gal/
Mcf  liquid-to-gas ratio, sulfite oxida-
tion  averaged 98 percent and the SO2
removal was satisfactory at 82 percent.

It should be noted that under the
operating conditions chosen for Run
951-2E, the major SC>2 scrubbing
species was calcium adipate because
there was little sulfite available. Since
sulfite  is normally the major scrubbing
species in an unenhanced lime system
without  forced  oxidation, 862
removal was reduced.  Higher  562
removal than the 82 percent in Run
951-2E should be achievable by simply
raising the adipic acid concentration
beyond the 1,330 ppm tested.

An SO2 removal of only 65 percent
would be predicted under the same
operating conditions as Run 951-2E,
 Table 5.
 Adipic Acid-Enhanced Lime Test on the Single-Loop TCA System with
 Forced Oxidation
                           Run No.
                                                          951-2E
       Onstream hours                                         103
       Fly ash loading                                        High
       Adipic acid concentration, ppm (controlled)             1,330
       Scrubber gas velocity, ft/sec                             12.5
       Liquid-to-gas ratio, gal/Mcf                               50
       Slurry solids concentration, wt % (controlled)                8
       Scrubber inlet pH (controlled)                            5.0
       Total static bed height, inches of 11.5 gram
         nitrile spheres                                         15
       Oxidation tank level, ft                                   17
       Oxidation tank residence time, min                       4.1
       Average percent S02 removal                             82
       Average inlet SO2 concentration, ppm                  2,400
       SO2 make-per-pass, m-moles/liter                        10.4
       Percent oxidation of sulfite to sulfate                      98
       Air stoichiometry, atoms oxygen/mole S02 absorbed      1.95
       Percent lime utilization                                   97
       Scrubber inlet liquor gypsum saturation, %                105
       Scrubber inlet liquor SO3/HSO§ concentration, ppm       100
       Centrifuge cake solids content, wt %                       72
but without  forced  oxidation and
without adipic acid addition. With  •
forced oxidation and without adipic
acid enhancement, the expected SO2
removal should be significantly lower
than 65 percent.
Limestone Long-Term Test with One
Scrubber Loop and Forced Oxidation
A one-scrubber-loop system has an in-
herent advantage over a two-scrubber-
loop system in its simple design and
lower capital and operating costs. If a
simple one-loop  limestone  (or lime)
system is operated with adipic acid,
which offers the advantage  of lower
operating pH, then both good  SO2
removal and sulfite oxidation can be
achieved with minimum cost.

This was illustrated  in a long-term
adipic acid-enhanced limestone run.
Run  917-1 A, conducted on the
Shawnee spray tower system from
December 26, 1980, to  March  13,
1981. Figure 4 shows the flow diagram
for this long-term run with forced oxi-
dation using two series tanks in the
slurry loop. Oxidation  was forced in
the first tank while fresh limestone
was added to the second. Use of two
tanks in series in a within-scrubber-
loop  forced  oxidation system  has
several advantages  over a single  tank:

•  Lower pH in the first tank (oxida-
   tion tank), which receives the
   scrubber effluent slurry, gives bet-
   ter oxidation efficiency

•  Limestone blinding potential  by
   calcium sulfite is  reduced because
   liquor sulfite is oxidized in the first
   tank before fresh limestone is
   added to the second tank
•  Limestone utilization  is  improved
   with two tanks in series

• The second-tank offers extra time
   for gypsum desupersaturation and
   precipitation

• The second tank provides air-free
   suction  for slurry  recirculation
   pumps

In  any within-scrubber-loop  forced
oxidation  system,  irrespective  of
whether it is additive promoted  or not,

-------
                                                                                       Clarified Liquor from Solids
                                                                                       Dewatering System
                                                                                       Bleed to Solids
                                                                                       Dewatering System
 Figure 4.  Flow Diagram for Adipic Acid-Enhanced Limestone Scrubbing in the Spray Tower System with Forced
           Oxidation and Two Tanks
the possibility exists for calcium sul-
fite blinding of limestone because the
recirculated slurry lacks the  solid
CaSO3 crystal seeds. Under this envi-
ronment, and if the oxidation inten-
sity is not sufficiently high, liquor sul-
fite could build up to a level at which
CaSO3 begins to precipitate on  alka-
line limestone particles, causing  lime-
stone blinding, reduced  dissolution,
and a pH drop. The problem is usually
avoided by increasing  the  air stoi-
chiometry to prevent the buildup of
sulfite in the liquor. The  potential of
limestone blinding is further reduced
by the use of two tanks  in series, as
described above, to permit sulfite
oxidation before limestone addition.
Table 6 summarizes the important test
results of Run 917-1A. As in the pre-
vious runs with forced oxidation, air
was injected into the oxidation tank
through a single 3-inch diameter pipe.
The system was  onstream for  1,688
hours. During the run, the scrubber
Table 6.
Adipic Acid-Enhanced Limestone Test on the Single-Loop Spray Tower
System with Forced Oxidation and Two Tanks
  Onstream ho jrs
  Fly ash load! ig
  Adipic acid CDncentration, ppm (controlled)
 Scrubber gas
 Liquid-to-gas
 Slurry solids
velocity, ft/sec
ratio, gal/Mcf
:oncentration, wt % (controlled)
 Scrubber inlet pH  (controlled)
 Oxidation tat
 Oxidation tar
 Effluent hole
 Average inlet
 SO2 make-pe
 Percent oxide
 Oxidation tar
                      Run No.
                                                                 917-1A
k level, ft
k residence time, min
tank residence time, min
 Average percent SO2 removal
SO2 concentration, ppm
•-pass, m-moles/liter
tion of sulfite to sulfate
 Air stoichiorretry, atoms oxygen/mole SO2 absorbed
kpH
 Percent limestone utilization
 Scrubber inlet liquor gypsum saturation, %
 Filter cake solids content, wt %
      1,688
       High
1,300-1,700
     5.4-9.4
     85-150
         15
     5.0-5.1
         18
        2.8
        8.3
       93.4
      2,660
     4.0-8.9
       99.8
     1.4-2.4
        4.9
       92.6
         93
         86

-------
was out of service for 78 hours due to
equipment problems and 84 hours due
to boiler outages. Excluding  boiler
outages. Run 917-1A operated with an
onstream factor of 95.6 percent.

The run was controlled at a scrubber
inlet pH of 5.0 to 5.1  and an adipic
acid concentration of 1,300 to 1,700
ppm to obtain 90 percent or higher
SO2  removal. The flue gas flow rate
was varied between 20,000 and 35,000
acfm (5.4 to 9.4 ft/sec superficial gas
velocity) according to a "typical daily
boiler load cycle." The slurry  flow rate
was fixed at 2,400 gpm (L/G = 85 to
150 gal/Mcf). Slurry solids concentra-
tion was controlled at 15 percent.

S02  removal during the run averaged
93.4 percent at 2,660 ppm average
inlet S02  concentration. At the  low
L/G of 85 gal/Mcf, SO2 removal varied
from 87 to 92 percent with 1,300 ppm
adipic acid, and from 90 to 93 percent
with 1,700 ppm adipic acid.  At the
high L/G of 150 gal/Mcf, the removal
was 97  to 99 percent.  Daily average
SO2  removal was 92 to 95 percent.

Limestone utilization averaged 92.6
percent. Sulfite oxidation  was excel-
lent at 99.8  percent and the filter cake
solids content  was high,  averaging
86 percent. Gypsum saturation in the
scrubber inlet liquor was  only 93
percent.

The  mist eliminator was completely
clean at the  end of the  run, and there
was no  evidence of plugging or scaling
within the spray tower.

The  actual adipic acid consumption
rate  during  Run  917-1A was only
5.4 Ib/ton of limestone feed, four
times the theoretical  requirement.

Limestone Tests with Bleed Stream
Oxidation
A major advantage of the bleed stream
oxidation is its simple flow configura-
tion. In operation without forced oxi-
dation, the scrubber bleed stream
would be sent directly to  the solids
dewatering system. To oxidize this
bleed stream, it is necessary only to
install an oxidation tank and the asso-
Table 7.
Adipic Acid-Enhanced Limestone Test on the Venturi/Spray Tower System
with Bleed Stream Oxidation
                          Run No.
                                                         915-1C
     Onstream hours                                         127
     Fly ash loading                                        High
     Adipic acid concentration, ppm (controlled)             4,140
     Spray tower gas velocity, ft/sec                           9.4
     Venturi liquid-to-gas ratio, gal/Mcf                        21
     Spray tower liquid-to-gas ratio, gal/Mcf                    57
     Slurry solids concentration, wt % (controlled)              15
     Scrubber inlet pH (controlled)                            4.8
     Venturi pressure drop, in. h^O                             9
     Oxidation tank level, ft                                   17
     Effluent hold tank residence time, min                     9.1
     Average percent SO2 removal                             96
     Average inlet SO2 concentration, ppm                  2,030
     Percent sulfite oxidation in effluent hold tank              54
     Percent sulfite oxidation in oxidation tank                 98
     Air stoichiometry, atoms oxygen/mole SO2 absorbed       1.8
     Oxidation tank pH                                       4.8
     Percent limestone utilization                              88
     Scrubber inlet liquor gypsum saturation, %                 105
     Oxidation tank liquor gypsum saturation, %                100
     Centrifuge cake solids content, wt %                      79
ciated agitator and compressed air sys-
tem  anywhere between the effluent
hold tank and the solids dewatering
area. Thus, the bleed stream oxidation
scheme is particularly well  suited for
retrofit when  modifications of the
existing scrubber system for within-
scrubber-loop forced oxidation are not
possible due to physical constraints.

Bleed stream oxidation of unenhanced
lime or limestone slurry is usually not
feasible because the pH rise caused by
the residual alkali in the oxidation
tank makes it difficult to redissolve
the solid calcium sulfite. With adipic
acid-enhanced  limestone scrubbing,
however, this constraint is removed
because of the low operating pH and
low residual alkali in the bleed slurry.
Thus, the oxidation tank can be main-
tained at a low pH for good sulfite oxi-
dation,  while  achieving high SO2
removal efficiency with a sufficiently
high concentration of adipic acid in
the scrubber liquor.
Table 7 gives the  results of a typical
bleed stream oxidation test, Run 915-
1C, which was conducted with adipic
acid-enhanced limestone on the ven-
turi/spray tower system. The effluent
slurries from the venturi and the spray
tower were discharged into a common
effluent hold tank. The scrubber bleed
stream was pumped from the effluent
hold tank to an oxidation tank into
which  air was injected through a
3-inch diameter pipe. The final system
bleed was withdrawn from the oxida-
tion tank and sent to the solids dewa-
tering system.

Good sulfite oxidation of  98 percent
was achieved in the oxidation tank at
4.8 pH and 1.8 air stoichiometry. SO2
removal was high at 96 percent with
4.8 scrubber inlet pH, 4,140 ppm
adipic acid, and 2,030 ppm inlet SO2
concentration.

Degradation of adipic acid was low, as
expected with the low pH operation.

-------
 The actual-to-theoretical adipic acid
 consumption ratio was only 1.26 for a
 rate of 8.7 Ib/ton of limestone feed.
 The centrifuge cake solids content was
 79 percent.
 Factorial Test Results
 Full or partial factorial tests have been
 conducted at Shawnee, primarily to
 investigate the effects of adipic acid
 concentration and  pH   on  SO2
 removal. These tests usually lasted
 12 hours or longer, including at least
 5 to 7 hours of steady-state operation.
 Scrubber configurations used were:
 venturi alone, spray tower alone, com-
 bined venturi and spray  tower, and
 TCA. Limestone was used in all scrub-
 ber configurations. Lime was  used
 only with the venturi alone. Only the
 typical results from the TCA and spray
 tower tests are  presented below to
 show the degree of effect of pH and
 adipic acid concentration on  SO2
 removal.

 Figures 5 through 7 show the results
 of partial factorial limestone runs con-
 ducted on the TCA system using two
 tanks in series. Operating conditions
 common to all runs were:
   Fly ash loading: High (2  to 7
   grains/dry scf)
   Slurry solids concentration:
   15 percent
   Oxidation tank level (7 ft diameter):
   18ft
   Effluent hold tank  level (20 ft dia-
   meter): 6.2 ft
   Air flow to oxidizer: 220 scfm (for
   runs with forced oxidation)


 Figure 5 shows the SO2 removal as a
 function of adipic acid concentration
 and slurry flow rate for the TCA with-
 out spheres (grid tower). With a con-
 trolled limestone stoichiometry  of 1.2
 (5.6 to 6.1 scrubber inlet pH) and a
 slurry flow rate of 37 gpm/ft2, adipic
 acid concentration greater than 2,000
 ppm would  be required  to achieve
 90 percent S02 removal.

 Figure 6  is similar to Figure 5 except
that the  data used for Figure 6 were
    100
               37 gpm/ft2
               28 gpm/ft2
                                         IN LET SO2 = 1800 - 2800 ppm
                                         GAS VELOCITY = 8.4-1 2.5 ft/sec
                                         SCRUBBER INLET pH = 5.6-6.1
                                         (LIMESTONE STOICH. = 1.2)
                                         HEIGHT OF SPHERES = 0 inch
                                         WITH FORCED OXIDATION
    40
    100
     90
     80
 O
 5
 LLI
 val in the TCA with Four Grids and without Spheres
         o
                                              A 37 gpm/ft2
                                              O 28 gpm/ft2
                                              019 gpm/ft2
                        INLETS02= 1800-2800 ppm
                        GAS VELOCITY = 8.4 - 12.5 ft/sec
                        SCRUBBER IN LET pH = 5.6 - 6.1
                        (LIMESTONE STOICH. =  1.2)
                        HEIGHTOF SPHERES =  15 inches
                        WITH AND WITHOUT FORCED OXIDATION
                             J_
                                                           _L
                  400        800      1200      1600      2000
                       ADIPIC ACID CONCENTRATION, ppm
                                                                2400
Figure 6. Effect of Adipic Acid Concentration and Slurry Flow Rate on SO2
         Removal in the TCA with  Four Grids and 15 Inches of Spheres

-------
obtained using 15 inches (5 inches per
bed) of static height of spheres in the
TCA. With  a  controlled limestone
stoichiometry of 1.2,90 percent SO2
removal could be obtained with 2,000
ppm adipic acid and only 19 gpm/ft2
slurry flow rate, or with only 600 ppm
adipic acid at 28 gpm/ft2  slurry flow
rate. With 37 gpm/ft2, the required
adipic  acid  concentration is only
300 ppm to achieve 90  percent
removal. Both Figures 5 and 6 show
that, at 1.2 limestone stoichiometry
(5.6 to 6.1 scrubber inlet pH), S02
removal  begins to  "taper off" at
about  600  ppm  adipic   acid
concentration.
The effects of scrubber inlet pH and
adipic acid  concentration on  SO2
removal in the TCA are given in Figure
7. In comparing Figure 7 with Figures
5 and 6 (high pH data) at the same
slurry flow rate of 28 gpm/ft2, the low
pH curves of Figure 7  have  a notice-
ably steeper slope for adipic  acid con-
centration above 600 ppm than is the
case for the high pH data. At low pH,
the adipic acid is partially ineffective
because of a significant amount of un-
ionized adipic acid. For  example.
Figure 6 shows that at a scrubber inlet
pH of 5.6 to 6.1  and 28 gpm/ft2,
75 percent S02  removal can  be
achieved  without adipic acid. To
achieve this same 75 percent removal,
Figure 7 indicates that 600 ppm adipic
acid is required at 5.3 scrubber inlet
pH, and 1,700 ppm at 4.6 inlet pH.
Therefore, operation at a very  low pH
with adipic acid-enhanced limestone is
not as attractive as at the higher pH
from the process standpoint, since
adipic acid is only partially utilized for
SO2 scrubbing,' and the S02 removal
is far more sensitive to fluctuations in
both pH and adipic acid concentration.

 Figures 8 and 9 show the results of
 partial factorial limestone runs made
on the spray tower. Common operat-
ing conditions for these runs were:
    Fly  ash loading: High (2 to 7
    grains/dry scf)
    Slurry solids concentration:
    15 percent
    Gas velocity: 9.4 ft/sec
                                          100
    90
    80
>
o
HI
DC
 IN
O
 O
 cc
 111
 Q.
    70
    60
     50
     40
         V PH = 5.6
         <> pH = 5.3
         O pH = 5.0
         A pH = 4.6
                          A
                                       INLET SO2 = 1800 - 2800 ppm
                                       GAS VELOCITY = 10.4 ft/sec
                                       SLURRY FLOW RATE = 28 gpm/ft2
                                       HEIGHT OF SPHERES = 15 inches
                                       WITH  FORCED OXIDATION

                                      J	I	I	
                   400        800       1200       1600

                         ADIPIC ACID CONCENTRATION, ppm
                                                           2000
                                                                    2400
Figure 7.  Effect of Adipic Acid Concentration and Scrubber Inlet pH on SO2
          Removal in the TCA with Four Grids and 15 Inches of Spheres
   Liquid-to-gas  ratio:  85  gal/Mcf
   (2,400 gpm)
   Air flow to oxidizer: 250 scfm (for
   runs with forced oxidation)

For runs without forced oxidation, a
single effluent tank 20 ft in diameter
with 8.5-ft tank level was  used. For
runs with forced oxidation, two tanks
in series were used with an oxidation
tank preceding the effluent hold tank.
The oxidation tank was 8 ft in dia-
meter with an 18-ft tank level.

Figure 8 gives the SO2 removal as a
function of adipic acid concentration
and spray tower inlet  pH for runs
made without forced oxidation and at
a  constant liquid-to-gas ratio  of 85
gal/Mcf. SO2 removal is sensitive to
both pH and adipic acid concentration
within the ranges shown in the figure.
At a liquid-to-gas ratio of 85 gal/Mcf,
90 percent  SO2  removal  could  be
achieved at 5.4 scrubber inlet pH and
1,200 ppm adipic acid, or 5.0 inlet pH
and 2,200  ppm adipic  acid.  At 4.6
                                      inlet pH, the required adipic acid con-
                                      centration is estimated to be in excess
                                      of 3,000 ppm to yield 90 percent SO2
                                      removal.

                                      Figure 9 shows the effects  of scrub-
                                      ber inlet pH and adipic acid concen-
                                      tration on SO2 removal for runs made
                                      with forced oxidation. As in Figure 8,
                                      the liquid-to-gas ratio was held con-
                                      stant at 85 gal/Mcf for the runs shown
                                      in Figure 9. By  comparing  the two
                                      figures, it is seen that forced oxidation
                                      dramatically  improved  the  SO2
                                      removal, especially at  the  scrubber
                                      inlet pH below about 5.0. Forexample,
                                      at 1,200 ppm adipic acid concentra-
                                      tion and without  forced oxidation,
                                      SO2 removals were 59, 77,  and 90 per-
                                      cent at scrubber inlet pH of 4.6, 5.0,
                                      and 5.4, respectively. The correspond-
                                      ing SO2 removals with forced oxida-
                                      tion were 87, 91, and 94 percent.

                                      The reason for improved SO2 removal,
                                      particularly at low pH, is that forced
                                      oxidation eliminates bisulfite species,

-------
thereby reducing the SO2 vapor pres-
sure at the gas-liquid interface and
improving the S02 mass transfer effi-
ciency. This mechanism of improved
SO2 removal holds true when sulfite
is not  a major scrubbing species and
the SO2 removal does not depend  on
the sulfite-bisulfite buffer. In the case
of Figures 8 and 9, calcium adipate is
the major scrubbing reagent.

Therefore,  it would be advantageous
to operate  a low phi, adipic  acid-
enhanced limestone or lime system
with within-scrubber-loop  forced oxi-
dation  which, in addition to improved
SO2 removal, requires low  adipic acid
makeup, minimizes gypsum scaling
potential, and produces a sludge with
good disposal  properties. Based on
Figure  9, 90 percent SO2 removal can
be achieved at 5.0 inlet pH and only
1,100 ppm  adipic acid, or at 4.6 inlet
pH with 1,400 ppm adipic acid.
100
                                         IN LET SO2 = 2380 - 3000 ppm
                                         GAS VELOCITY = 9.4 ft/sec
                                         L/G = 85 gal/Mcf
                                                I	1
                                          40
                                                                    800       1200      1600
                                                                 ADIPIC ACID CONCENTRATION, ppm
                                                                  2400
                                       Figure 8.  Effect of Adipic Acid Concentration and Scrubber Inlet pH on SC>2
                                                 Rerr oval in the Spray Tower without Forced Oxidation
                                         100
                                          90
                                      o
                                      ai
                                      rr
                                      O
                                      to
                                      111
                                      o
                                      OL
                                          80
                                          70
                                          60
                                          50
       O
                                                                                 IN LET SO2 = 2360 to 3090 ppm
                                                                                 GAS VELOCITY = 9.4 ft/sec
                                                                                 L/G = 85 gal/Mcf
                                                                    _L
                                              _L
_L
                                                          400       800       1200       1600
                                                                ADIPIC ACID CONCENTRATION, ppm
                                                                                                  2000
                                                                                                            2400
                                      Figure 9.  Effefct of Adipic Acid Concentration and Scrubber Inlet pH on SO2
                                                Rempval in the Spray Tower with Forced Oxidation

-------
Springfield Full-Scale Demonstration
In August and September 1980, the
EPA, through its contractor. Radian
Corporation, conducted  the first
demonstration  of the  commercial
feasibility of adipic acid addition to a
full-scale limestone scrubber. The host
facility was the Southwest Power Plant
of the City Utilities of Springfield,
Missouri. In that facility, 3.5 percent
sulfur eastern coal is burned in two
boilers with a total generating capac-
ity of 200 MW. The flue gas from the
electrostatic  precipitators  is scrubbed
by two parallel 100 MWTCA's.

During this initial two-month test per-
iod, seven different sets of test condi-
tions were examined. Table 8 presents
the major results of two baseline tests
without  adipic  acid conducted on
Modules S-1  and S-2, and seven tests
with adipic acid conducted on Module
S-1. All tests were without forced
oxidation.

SO2 removal improved from 68 to 72
percent for the  baseline tests to 91,
95, and 96 percent with 840,  1,040,
and  1,650  ppm adipic acid, respec-
tively, at the same scrubber inlet pH of
5.5.  At 5.0 inlet pH, SO2 removal
remained high at 84, 90, and 93 per-
cent with 1,250, 1,300, and 1,800
ppm adipic acid,  respectively.  At  the
lower pH of 5.0, the limestone utili-
zation also increased from 76  to 84
percent for the baseline tests (pH 5.5)
to 84 to 97 percent.

These results are consistent with the
Shawnee findings. Furthermore, the
SO2  removal  obtained at Springfield
lay within 1 to 3 percentage points of
model prediction  based on the  Shaw-
nee  data  under  similar operating
conditions.

It should be noted that the odor asso-
ciated with the adipic acid testing  also
was not a problem at Springfield.

Following these initial tests, the scrub-
ber system was shut down for sched-
uled maintenance.  Subsequently, the
demonstration continued with adipic
acid testing, both with and without
forced oxidation. These results will be
reported separately by others.
Rickenbacker Industrial Boiler
Demonstration

In February, March, and  April 1981,
the EPA, through  its contractor,
PEDCo  Environmental,  Inc.,  con-
ducted adipic acid-enhanced limestone
scrubber tests on an industrial-sized
system. The testing was carried out at
the Rickenbacker Air Force Base on a
Research-Cottrell/Bahco system rated
at 55,000 scfm, or about 27  MW
equivalent. The tests, conducted with
certified instrumentation, indicated an
SO2 removal efficiency increase from
55 percent without  adipic acid, to 90
to 95 percent with  adipic acid. This
improvement was achieved at a scrub-
ber inlet pH of 5.0  and adipic acid
concentrations  of between 2,000 and
2,500 ppm. More complete data will
be reported separately by others.
 Table 8.
 Results of Springfield Full-Scale Adipic Acid Demonstration



Test

Gas
Flow
lO^dscfm

Slurry
Flow*
gpm

Inlet
SO2
ppm dry

Scrubber
Inlet
pH
Adipic
Acid
Cone.
ppm

Av. SO2
Removal
%

Limestone
Util.
%

Test
Period
hrs.
Baseline
S-1
S-2
171
163
13,500
13,500
2,410
2,410
5.5
5.5
0
0
68
72
76
84
497
408
Adipic Acid
(S-1)
1
2
3
4
5
6
7

201
187
190
193
192
196
175

13,500
13,500
13,500
13,500
13,500
13,500
13,500

2,460
2,360
2,420
2,500
2,540
2,500
2,640

5.5
5.5
5.2
5.0
5.0
5.5
5.0

840
1,040
1,000
1,250
1,800
1,650
1,300

91
95
88
84
93
96
90

82
75
94
91
84
73
97

122
50
74
44
33
89
84
   'Slurry contains approximately 10 wt % solids.

-------
5.  Economics
The  economics of limestone scrub-
bing, with or without additive, have
been projected (for forced oxidation
systems designejd to achieve an average
of 90 percent Sp2 removal from high-
sulfur flue gas. the capital investment
and revenue requirements are calcu-
lated using a Dejsign/Economics Com-
puter Program vj/hich was jointly devel-
oped by TVA and Bechtel under EPA
sponsorship.
For the purposes of this report, four
cases were studied,  including a lime-
stone case with MgO additive. The
operating conditions for these cases
are presented in Table 9. The evalua-
tions were based on a 500 MW scrub-
bing facility incorporating  forced
oxidation, and operating on flue gas
from a boiler burning eastern coal
containing 4 percent sulfur by weight.
The cases evaluated were:
                                      Table 9.
                                      Conditions for ^conomic Analysis of Limestone Scrubbing with Forced
                                      Oxidation and vj/ith or without Additive
                                        Capacity:
                                        Coal:
                                        Scrubber:
                                        SO2 removal Efficiency:
                                        Superficial gas velocity:
                                        Number of trains:
                                        Solids dewate'ring:
                                        Onstream factor:
                                        Effluent holdjtank residence
                                           time:     j
                                        Oxidation tanik residence time:
                                        Oxidation tank level:
                                        Air sparger pressure drop:
                                        Oxidation tank agitator Hp:
                                        Solid sulfite oxidation:
                                        Air stoichiomjetry:
                                        Number of tahks:
                                        Alkali:       I
                                 500 MW
                                 4 wt % sulfur
                                 TCA with 3 beds, 4 grids, and 5 inches
                                    of static height of spheres per bed
                                 90%
                                 12.5 ft/sec
                                 5, including one spare train
                                 To 80% solids by thickener and rotary
                                    drum vacuum filter
                                 5,500 hr/yr

                                 5 min
                                 5 min
                                 18ft
                                 5 psi
                                 0.002 brake Hp/gal
                                 99%
                                 1.7 Ib-atoms 0/lb mole SO2 absorbed
                                 2 (effluent hold tank and oxidation tank)
                                 Limestone
                                                   Case No.
                                    1
Additive

Additive cone
Additive rate.


jntration, ppm
Ib/hr
L/G, gal/Mcf
Limestone stoiichiometry, moles
Ca/mole S02 absorbed
TCA inlet pH
Mode of oxidation


	

—
—
58

1.52
5.8
1 loop.
2 tanks
MgO

B^SOo'3)
104
50

1.20
5.4
bleed
stream
Adipic
Acid
800
83.3
50

1.20
5.6
1 loop.
2 tanks
Adipic
Acid
2,000
53.6
50

1.05
4.8
1 loop.
2 tanks
                                        (a) Excess of mip\ar equivalent of chloride.
                                        (b) Five times theoretical consumption.
                                        (c) 1.4 times theoretical consumption.

-------
Case 1 — A limestone base case with-
        out additive operated at rela-
        tively high limestone stoichi-
        ometry and liquid-to-gas ratio
        to achieve 90 percent SO2
        removal. It should be noted
        that long-term reliability with
        this  mode of operation has
        not  been demonstrated  at
        Shawnee.

Case 2 —A limestone case with MgO
        addition. Oxidation of the
        scrubber bleed stream was
        chosen because  in-loop oxi-
        dation is incompatible with
        magnesium-enhanced  scrub-
        bing. As in Case  1, long-term
        reliability  has  not  been
        demonstrated at Shawnee for
        this  mode of operation.

Case 3 —A limestone case with adipic
        acid addition operated at high
        pH.  Although only 800 ppm
        adipic acid is required to
        obtain  90  percent  SO2
        removal,  degradation  of
        adipic acid at  high  pH
        requires about five times the
        theoretical adipic acid addi-
        tion rate.
Case 4 —A limestone case with adipic
        acid addition operated at low
        pH. For this case, 2,000 ppm
        adipic acid is required. How-
        ever, the low pH  operation
        requires only 1.4 times the
        theoretical adipic acid addi-
        tion rate and 1.05 limestone
        stoichiometry.
The results of the economic evalua-
tions are presented in Tables 10 and
11. The capital investment and the
first-year revenue requirement in Table
10 include the dewatering equipment
(thickener and filter) but exclude the
waste sludge (filter cake) disposal area.
Table 11  lists separately the first-year
revenue requirement for the waste
sludge disposal area.

As shown in Table 10, both the total
capital investment and the first-year
revenue requirement are the lowest
for adipic acid-enhanced  limestone
scrubbing at  low pH (Case 4). The
total capital  investment is reduced
by 4.8 percent, and the first year
revenue  requirement  reduced by
5.8 percent for the limestone/adipic
acid/low pH  case  (Case 4), compared
with the conventional limestone case
(Case 1). The revenue requirement
includes 14.7 percent annual capital
charge.

Total capital investment and operating
costs for adipic  acid-enhanced  lime-
stone at high pH  (Case 3) are higher
than those for limestone/adipic acid
at low pH (Case 4), but are still lower
than those for the conventional lime-
stone (Case 1) or the limestone/MgO
case (Case 2). Total capital investment
is lower by  3.9 percent, and the first-
year revenue requirement is lower by
4.0 percent for Case 3, compared with
Case 1.

Table 11 illustrates  the  additional
savings that result from adipic acid
addition. Because of the lower pH
operation, and thus lower limestone
consumption, the amount of waste
solids produced is lower for limestone/
adipic acid cases  (Cases 3 and 4) than
for  a limestone case (Case 1). Assum-
ing  a landfill disposal  cost of $10/dry
ton, including 14.7  percent annual
capital  charge, the first-year revenue
requirements for the sludge disposal
area are 0.97, 0.83, and 0.77 mills/
kWh for Cases 1, 3, and 4, respectively.
 Table 10.
 Results of Economic Analysis Excluding Waste Sludge Disposal Area
                           Total Capital Investment
           Case No.   $ MM (1982)    $/kW    Cost Factor
                           First Year Revenue Requirement

                       $ MM (1984)   Mills/kWh   Cost Factor
1
2
3
4
87.40
85.26
83.97
83.22
174.8
170.5
167.9
166.4
1.000
0.975
0.961
0.952
25.01
24.15
24.01
23.56
9.09
8.78
8.73
8.57
1.000
0.966
0.960
0.942
           Revenue requirement includes 14.7% annual capital charge.
           Raw material costs (1984):       Limestone   — $8.5/ton
                                          MgO        - $460/ton
                                          Adipic Acid  -$1200/ton

-------
Thus, the  total first-year revenue
requirement, including the sludge dis-
posal area,  is 9.34 mills/kWh for Case
4, compared with 10.06 milis/kWh for
Case 1. This is a reduction of 7.2 per-
cent, compared with 5.8 percent when
the  sludge  disposal cost is not
included.

These cost  figures are cited as repre-
sentative of typical scenarios only,
and some variation from them would
be normally expected. Moreover, the
differences in total capital investments
and operating costs between these
cases are small. The principal conclu-
sion from these evaluations is that
adipic acid addition to  a limestone
scrubbing system decreases  cost con-
sistently when compared on the same
basis.         I

It should be noted that adipic acid use
provides a level of flexibility in fuel
and reagent choice and control  level
not available with other systems, and
in site-specific cases, may prove to be
much more economically advanta-
geous than  indicated above.
Table 11.
Revenue Requirement in Waste Sludge Disposal Area
'
Case No.
1
2
3
4

Filter Cake,
dry tons/hr
48.7
41.6
41.6
38.3
First Y
sar Revenue Requirement, Mills/kWh (1984)
Total Excluding Sludge
Sludge Disposal Disposal
9.09
8.78
8.73
8.57
0.97
0.83
0.83
0.77
Total
10.06
9.61
9.56
9.34
Cost Factor
1.000
0.955
0.950
0.928
               Revenue requirement includes 14.7% anijual
               Sludge disposal cost assumes $10/dry tor
                 capital charges.
              , including 14.7% annual capital charge.
                                     CONVERTING UNITS OF MEASURE
Environmental Protection Agency policy is to express all jneasurements in Agency documents in metric units. In this
report, however, to avoid undue cost or lack of clarity, some English units are used. Conversion factors from English to
metric units are given below:
To Convert From
Btu
scfm (60°F)
cfm
°F
ft
ft/hr
ft/sec
ft2
ft2/tons per day
gal/mcf
gpm
To
J
nm3/hr (0°C)
m3/hr
°C
m
m/hr
m/sec
m2
m2/metric tons per day
l/m3
l/min
Multiply By To Convert From
1055
1.61
1.70
(°F-32)f1.8
0.305
0.305
0.306
0.0929
0.10^
0.134
gpm/ft2
gr/scf
in.
in. H2O
Ib
Ib-moles
Ib-moles/hr
Ib-moles/hr ft2
Ib-moles/min
psi
3.79 ton
To
l/min/m2
g/m3
cm
mm Hg
g
g-moles
g-moles/min
g-moles/min/m2
g-moles/sec
kPa
metric ton
Multiply By
40.8
2.29
2.54
1.87
454
454
7.56
81.4
7.56
6.895
0.907

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                                 NOTICE

This report was prepared by D. A. Burbank and S. C. Wang of Bechtel National,
Inc., San Francisco, CA, as an account of work sponsored by the Environmental
Protection Agency (EPA) under Contract No. 68-02-3114. J. E. Williams, R. H.
Borgwardt, and J. D. Mobley were the EPA Project Officers.

Comments or questions regarding this report or requests for information regard-
ing adipic acid as an FGD system additive should be addressed to:

               Industrial Environmental Research Laboratory
                  U.S. Environmental Protection Agency
                    Research Triangle Park, NC  27711

Neither Bechtel National, Inc., nor the EPA nor any person acting on their
behalf makes any warranty or representation, expressed or implied, with respect
to the accuracy, completeness, or usefulness of the information contained in this
report, or that the use of any information, apparatus, method, or process dis-
closed in this report may not infringe upon privately owned rights; or assumes
any liabilities with respect to the use of, or for damages resulting from the use
of, any information, apparatus, method, or process disclosed in  this report.

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