United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-81-141a Sept. 1981
Project Summary
Evaluation of the Limestone
Dual Alkali Prototype System at
Plant Scholz: System
Design and Program Plan
J. A. Valencia, R. R. Lunt, and G. J. Ramans
The limestone dual alkali process
developed by Combustion Equipment
Associates, Inc. (ownership of CEA's
Air Pollution Division was sold to
Thyssen-CEA Environmental Systems,
Inc. in late 1980) and Arthur D. Little,
Inc. will be tested at an existing 20
MWe prototype facility at Gulf Power
Company's Scholz Steam Plant. The
intent of this project is not only to
demonstrate the technical feasibility
of the process at a prototype level but
also to supply technical and cost
information related to implementation
of the process at a full commercial
scale.
The project will be carried out in
three phases: Phase 1 - Project
Planning; Phase 2 - Procurement,
Recommissioning, and Construction;
and Phase 3 - Startup, Testing,
Decommissioning, and Data Analysis.
This report covers Phase 1, includ-
ing: the design and description of the
limestone dual alkali system at Scholz;
the test program itself; recommission-
ing and construction costs; and
projected costs for a full-scale 500
MW utility system.
This Project Summary was devel-
oped by EPA's Industrial Environmen-
tal Research Laboratory, Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Background
Combustion Equipment Associates,
Inc. (CEA)1 and Arthur D. Little, Inc.
(ADL) developed, over the past few
years, a dual alkali process for removing
SOa from flue gas generated in coal-
fired utility boilers. The CEA/ADL dual
alkali process is based on the absorption
of SOa in an alkaline sodium solution,
followed by regeneration of the absorb-
ing solution by reaction with a second
alkali, calcium These reactions generate
insoluble calcium-sulfur salts which are
discharged from the system as a moist
cake.
The CEA/ADL process presents two
significant advantages over conven-
tional direct lime or limestone scrubbing.
First, it uses a clear liquor, rather than a
slurry, for scrubbing the flue gas.
Second, the regeneration of the scrub-
bing solution and precipitation of waste
solids take place outside the absorber.
Thus, the potential for scaling and
plugging in the absorber is minimized;
the formation of solids with good
dewatering properties is more easily
controlled; and high SOa removal
efficiencies (>90%) are easily achieved
1 CEA's Air Pollution Division was sold to Thyssen-
CEA Environmental Systems, Inc in late 1980
-------
with alkaline sodium scrubbing solu-
tions by simple manipulation of the
scrubber operating pH.
The CEA/ADL dual alkali process has
been tested extensively at laboratory,
pilot plant, and prototype levels using
lime as the source of calcium for the
regeneration reactions.2 The perform-
ance of the process in these tests
prompted the EPA to select the CEA/ADL
dual alkali process for a demonstration
plant. This lime-based demonstration
plant has been installed on a 300 MW
boiler at Louisville Gas and Electric's
Cane Run Station. The system is
currently undergoing a 1-year test
program.
Although the lime-based system is
technically and economically viable, a
source of calcium cheaper than lime
would increase the economic attractive-
ness of the process. Limestone was
recognized early on as a potential,
cheaper, source of calcium for the dual
alkali process. Extensive testing of
limestone was undertaken by ADL at
laboratory and pilot plant levels under
funding both by EPA3'4 and CEA.
Successful pilot operations using
limestone were achieved in 1977.
The successful performance of the
system during the laboratory and pilot
plant tests revealed the potential of the
limestone-based dual alkali process for
full-scale applications. This project is
aimed at confirming this potential as
well as providing information for its full-
scale application.
Project Objectives
The purpose of this program is to
evaluate the performance, at a prototype
scale, of the CEA/ADL limestone dual
alkali technology for application in flue
gas desulfurization (FGD) of high-
sulfur-coal-fired boilers.
Under this program, the 20 MW. lime
dual alkali system at Gulf Power
Company's (GPC) Scholz Steam Plant
will be modified and converted for the
use of limestone as the regenerating
material. After modification and con-
version to a limestone-based process,
the system will be tested to evaluate its
performance with respect to capabilities
for removal of S02, raw materials and
energy requirements, quality of the
waste material generated, and reliability
and ease of operation of the system.
Furthermore, capital and operating
costs will be estimated for full-scale
utility applications of the limestone dual
alkali FGD technology. The project is
being carried under the sponsorship of
EPA, CEA, GPC, and Southern Company;
the principal cost of the project is being
shared by EPA and CEA. CEA (and later
TESI)6 as the prime contractor to EPA
has the overall responsibility for all
aspects of the project. ADL, as a subcon-
tractor to CEA, will provide process
engineering support to CEA in designing
the modifications to the system, devel-
oping the test plan, and assisting CEA in
the startup of the process and in
coordinating and supervising the test
program.
Parallel to this EPA program, the
Electric Power Research Institute (EPRI)
is sponsoring a program to study and
evaluate the landfill disposal of the
waste cake generated by the limestone
dual alkali system. Prior to its disposal,
the FGD waste cake will be treated with
fly ash and lime. The EPRI test program
will consist of: monitoring the waste
disposal system to characterize its
operation, analyzing the physical and
chemical properties of the treated waste
during and after disposal operations,
and establishing the potential for
revegetation of the waste disp&sal area.
The natural interdependency between
the FGD and the waste disposal system
calls for close coordination between the
EPA and EPRI programs.
Schedule
The work is divided into three phases:
• Phase 1 - program planning.
• Phase 2 - procurement and con-
struction.
• Phase 3 - testing.
This report covers Phase 1, during
which CEA and ADL were to:
• Design the necessary modifica-
tions to the existing prototype
facilities.
2LaMantia, C R., et al., "Final Report Dual Alkali
Test and Evaluation Program," Volumes l-lll,
EPA-600/7-77-050a,b,c (NTIS PB 269904
272770, 272109), 5/77
3lbid
"Oberholtzer, J E , et al, "Laboratory Study of
Limestone Regeneration in Dual Alkali Systems,"
EPA-600/7-77-074 (NTIS PB 272111), 7/77.
5On October 20, 1980, Combustion Equipment
Associates, Inc filed a petition for financial
reorganization pursuant to Chapter 11 of the U S.
Bankruptcy Code Thyssen-CEA Environmental
Systems, Inc (TESI) bought the CEA Air Pollution
Division and began administering this EPA
contract in early December 1980. TESI assumed
financial responsibilities retroactive to October 21,
1980. Although the EPA contract, subject of this
project, was formally assigned to TESI in March
1981, CEA is mentioned in this report in
connection with work or contributions actually
made by CEA
• Develop an overall program
schedule.
• Develop a detailed test plan.
• Estimate capital and operating
costs for a full-scale limestone dual
alkali system.
Work on Phases 1 and 2 commenced
immediately after EPA awarded the
contract to CEA in October 1978. Phase
1 covered a period of 17 months, ending
in February 1980. Phase 2, modification
of the system, was completed in March
1980. The system was started up in
August 1980. In the interim, the system
was operated mechanically in order to
prevent mechanical deterioration of the
equipment. The delay was caused by
equipment delivery problems en-
countered in the installation of the EPRI
waste disposal system. As previously
indicated, EPRI is sponsoring a parallel
test program to study the landfill
disposal of waste generated by the
limestone dual alkali process.
The EPA test program of the FGD
system was originally scheduled to last
6 months, exclusive of start-up pro-
cedures, and was to be conducted in two
periods. During the first period, approxi-
mately 2 months, a baseline for the
operations of the system was to be
established. The second period, approx-
imately 4 months, was to consist of
variational testing of the system.
However, because of budgetary con-
straints, due to actual costs exceeding
those budgeted, delays due to the need
to coordinate with the EPRI program,
and additional delays caused by CEA's
declaration of bankruptcy, the testing
period has been reduced from 6 to 2
months. These 2 months will be devoted,
primarily, to baseline testing, which
began m February 1981. The test
program presented here represents the
original test program issued in draft
form in March 1980.
The Limestone Prototype
System at Scholz
Limestone Dual Alkali
Technology
The CEA/ADL limestone dual alkali
technology incorporates SO2 absorption,
absorbent regeneration, waste solids
dewatering, and raw materials storage
and feed preparation.
SO2 is adsorbed by contacting the flue
gas with a sodium sulfite/bisulfite
solution. The sodium sulfite reacts with
the SO2, producing additional sodium
bisulfite:
-------
Na2S03 + S02 + H20 - 2NaHS03
During absorption, and to a lesser
extent throughout the remainder of the
system, some sulfite is oxidized to
sulfate:
Na2SO3 + 1/2 02 - Na2SO4
The level of oxidation experienced
during absorption is generally a function
of the scrubber configuration, oxygen
content of the flue gas, and scrubber
operating temperature. At excess oxygen
concentrations normally encountered
in utility power plant operations, the
level of oxidation is expected to be on
the order of 5 to 1 0% of the S02 removed
(for medium and high sulfur coal).
The spent scrubbing solution is
reacted with limestone to regenerate
the absorbent. The reaction precipitates
mixed calcium sulfite and sulfate solids,
resulting in a slurry containing up to 5
wt. % insoluble solids. The regeneration
process basically involves:
2NaHSO3 + CaC03 - Na2S03 + CaS03 •
1/2 H2OJ + 1/2 H2O + CO2r
2NaHS03 + Na2S04 + CaC03 - 2Na2S03
+ CaS04 • 1 /2 H2OI + 1 /2 H2O + C02t
Following regeneration, the insoluble
calcium-sulfur salts are separated from
the regenerated liquor. After settling in
a thickener, the insoluble salts are
vacuum-filtered prior to being discharged
as a moist cake. The clarified liquor from
the thickener is returned to the scrubber,
closing the process liquor loop.
The filter cake is washed to recover
most of the soluble sodium salts in the
mother liquor. A portion of the sodium
salts remains occluded in the cake and
is lost. Thus, some Na2C03 is added to
the system to make up for these sodium
losses. Typically, the Na2C03 makeup
amounts to less than 5 mole % of the
SO2 removed.
The amount of limestone added to the
system for absorbent regeneration is
reduced slightly due to the soda ash
makeup. Under normal conditions, the
limestone feed stoichiometry will be
slightly less than 1 .0 mole of CaC03 per
mole of S02 removed.
Description of the Limestone
Dual Alkali System at Scholz
The dual alkali system will take flue
gas from the Scholz Steam Plant Unit
No. 1, a 40 MW nominal capacity (47
MW peak capacity) Babcock and Wilcox
pulverized-coal-fired power boiler. The
flue gas from the boiler passes through
a high efficiency, sectionalized electro-
static precipitator (ESP) designed to
remove up to 99.5% of the particulate
matter. Part of .the gas discharged from
the ESPisdirectedtothelimestonedual
alkali system, which is designed to
ha ndle flue gas flow rate equiva lent to a
20 MW boiler load. The remaining gas is
sent directly to the stack.
The limestone dual alkali system at
Scholz is a modification of a lime dual
alkali system previously installed and
operated at the plant for a test program
sponsored -by Southern Company and
jointly funded with EPA and EPRI. The
modified dual alkali system consists of
four sections as discussed previously:
absorption, regeneration, waste solids
dewatering, and raw materials storage
and feed preparation. A process flow
diagram for the limestone dual alkali
system for S.cholz is given in Figure 1.
The absorption system consists of a
ventun scrubber followed by an absorp-
tion tower. The venturi can be used for
S02 absorption and/or particulate
removal; the absorption tower can be
operated as a tray tower, spray tower, or
a deentrainment separator. For opera-
tion in the limestone dual alkali mode,
the tower will be operated with two
trays. The bottom tray is equipped with a
spray underneath to wet the bottom side
of the tray.
An S02 injection system is provided to
increase the S02 concentration in the
flue gas entering the dual alkali system
by 500 ppm or more. The S02 is injected
upstream of the booster fan before the
gas enters the venturi scrubber.
A booster fan directs the S02-rich f I ue
gas exiting the ESP into the scrubber,
where it contacts the scrubbing liquor.
The liquor is collected at the bottom of
the scrubber in the internal recycle tank.
After being quenched and water-satu-
rated, the partially desulfurized gas
enters the bottom of the absorption
tower. Gas passes upward through the
trays and through a deentrainment
separator. The deentrainment separator
is operated dry, without mist eliminator
wash water. Scrubber flue gas leaving
the tower is finally reheated by the
injection of the hot gas from an oil-fired
reheater before being discharged
through the stack on top of the absorber.
The scrubbing solution, fed to the top
tray of the absorber, flows countercur-
rent to the gas through the tray system.
This counterflow permits high S02
transfer from gas to liquid phase. The
liquor is collected at the bottom of the
absorber in the internal recycle tank,
which serves as the supply for the liquor
sprays beneath the bottom tray.
A bleed from the absorber liquor
recycle line is sent forward to the
venturi recirculation loop where it is
used to quench the gas and provide
additional S02 removal. A bleed stream
of spent liquor is drawn from the venturi
recycle line and is fed to the absorbent
regeneration system.
Slurry from the reactor system is
pumped to the center well of the slurry
thickener. Clear liquor overflow from
the thickener is collected in a thickener
hold tank which acts as surge capacity
for the absorbent liquor feed to the
scrubber system. Process makeup
water is added to this tank to make up
for the total water lost due to evapora-
tion and moisture in the cake.
The regeneration system consists of
five separate reactor tanks in series,
with a total design holdup time of
approximately 100 minutes. The bleed
from the scrubber system can be fed
either to the first or second stage
reactor. Similarly, the modified limestone
silo feed chute can feed dry limestone to
either tank. Thus, the modified reactor
system can be operated as either four or
five reactor tanks in series with dry
limestone feed, or four reactor tanks in
series with slurried limestone feed
prepared in the first stage reactor. The
first four tanks operate on overflow; the
last tank is on level control so that the
effluent can be pumped to the thickener.
The thickened slurry is fed to a rotary
drum vacuum filter. A series of wash
sections are used to wash the filter cake
to recover valuable process liquor.
Solids from the filter cake are discharged
to a weigh belt conveyor for transport to
a waste processing system. The mixed
filtrate and wash liquor from the filter
are returned to the thickener.
Two raw materials are required for
operation of the system—limestone for
absorbent regeneration and soda ash to
make up for losses of sodium salts in the
waste filter cake.
Limestone will be received, stored,
and, under normal conditions, fed to the
system in a dry form: it can be fed to
either the first or second reactor tank.
For operation with limestone slurry,
limestone would be fed to the first
reactor tank along with water, and the
scrubber bleed diverted to the second
reactor tank.
-------
Dense soda ash will be used to make
up for sodium salt losses. Provisions
have been made to prepare soda ash
solutions using either river water or
clarified liquor from the thickener hold
tank. The soda ash solution can be fed to
the thickener, thickener hold tank,
absorber recycle, or venturi scrubber
recycle. Normally, it will be fed to the
thickener hold tank.
The waste processing system will be
installed and operated as part of a
separate test program funded by EPRI. It
is briefly discussed here to indicate the
overall plant operation.
The moist waste cake discharged
from the vacuum filter will be mixed in a
pug mill with fly ash and lime. The
amount of ash added will range from 0.5
to 1.5 parts of ash per part of dry solids
in the cake. Lime will be added at a rate
of 2 to 5 wt.% of the dry solids contained
in the mix of cake and fly ash.
The mix discharged by the pug mill
will be loaded onto trucks and transported
to a sectioned landfill area. Three test
areas will be used for disposing of the
processed limestone dual alkali waste.
Each test area will be filled with a
different waste material mix involving
different combinations of filter cake, fly
ash, and lime.
System Design
The modified limestone dual alkali
process has been designed to operate as
a closed-loop system in accordance
with the following criteria:
• Operation in a "concentrated"
alkali mode (>1.0 M active alkali).
• Operation with minimum sodium
consumption.
• Operation with minimum calcium
consumption (95% limestone utili-
zation).
• Removal of more than 95% of the
incoming SO2.
• Production of a solid waste filter
cake containing a minimum of 55%
insoluble solids (calcium sulfite/
sulfate).
• Reliable system operation with
normal variation of:
- Flue gas composition from the
power plant.
- Boiler load.
- ESP operation.
- Limestone quality.
During the test program, the boilers at
Scholz will be fired with coal containing
2.9 to 3.4 wt. % sulfur. The corresponding
S02 levels in the boiler flue gas have
been estimated to be on the order of
1900 to 2300 ppm. During the test
program, it may be desirable to increase
these levels by injecting SOz into the
flue gas stream before it enters the
scrubber. The modification of the dual
alkali system has been designed to
accommodate operation under normal
conditions without S02 injection, as
well as operation with SOz injection.
The design bases for each operating
mode are given in Table 1.
Normal Operation
Under normal operation without
additional SO2 injection, the flue gas
taken by the dual alkali system (40,000
scfm)* would be equivalent to a load of
approximately 18 MW, with an S02
level of 2200 ppm (dry basis). Removal
of 95% of the S02 present in the inlet
gas would generate about 38 tons/day
of moist waste cake. The solids content
of this filter cake is assumed to be about
55%. Limestone would be added to the
system at a rate of 23 Ib/min (0.986
moles of CaC03/mole of ASO2) and
soda ash at a rate of less than 1 Ib/min
(0.035 moles Na2C03/mole of AS02).
"Metric equivalents are provided later in this
Summary
Table 1. Design Conditions
Internally, the regenerated solutior
would be fed to the absorber/scrubbe
module at a total rate of about 167 gpnr
(corresponding to an L/G = 3.1). The
active sodium concentration in this
solution is 1.7 M, with a [HSOs] to [SOs
ratio of 1.34. The spent solution with t
[HSOal to [SOJ3 ratio of 3.0 would be blec
to the regeneration reactors at aboui
145 gpm. The remaining 22 gpm woulc
be evaporated in bringing the incoming
hot flue gas to saturation.
The reactor effluent would be a slurr\
containing about 2 wt. % insoluble
solids. The solids concentration woulc
be increased to about 25 wt. % in the
thickener and finally to a minimum of 55
wt. % in the filter cake.
Maximum Operation with
SOz Injection
At maximum load and with additiona
S02 injection, the flue gas treated by the
system would amount to 45,000 scfm,
rouqhly equivalent to a 20 MW boilei
load. The SOz loading would be increasec
by about 20% to 2650 ppm by the
injection of SO2. Removal of 95% of the
incoming S02 would produce about 55
tons/day of moist cake (at 55 wt. % dr\
Normal
Operation
SOz Injection
Inlet Gas:
Flow rate, scfm (dry) 40,000 45,000
S02, Ib/min. (ppm dry) 14.9 (2200) 20.2 (2650)
CT. Ib/min. 0.12 0.12
Oz, vol. % 55
Moisture, wt. % 6.O 6.0
Removal Efficiency:
SOz, % 95 95
C1', % 100 100
Absorber Feed Concentration:
Na* associated with
SOI, M 1.02 1.02
HSO~3, M 0.68 0.68
Oxidation and Evaporation:
Oxidation, mole % of AS02 7 10
Evaporation in absorber, gpm 22 24.7
Soda Ash and Limestone Feed:
Soda ash feed rate,
mole Na+/mole ASOz 0.07 0.081
Limestone purity, wt. % 95 90
Limestone feed rate,
mole available CaC03/mole ASO2 0.556 7.070
Waste Solids:
Wash ratio, displacement washes 4 4
Insoluble Solids, wt. % 55 55
-------
solids). Limestone would be added to
the system at a rate of 34 Ib/min (1.010
moles CaCOs/mole of ASOa), and soda
ash at a rate of 1.3 Ib/min (0.040 moles
Na2C03/mole ASOz).
The regenerated scrubbing solution
would be fed forward to the absorber/
scrubber module at a rate of 205 gpm
(equivalent to an L/G = 4.5). The liquor
feed to the absorber has an active
sodium concentration of 1.7 M and an
[HSOs"] to [S03=] ratio of 1.34. The spent
solution, with an [HS03~] to [S03=] ratio of
3.2, would be bled to the regeneration
reactors at a rate of 180 gpm. The
difference in flows, about 25 gpm,
represents the water evaporated to
saturate the incoming flue gas.
The solids concentration in the
resulting slurries are consistent with
those generated in normal operation.
The reactor effluent would contain 2.2
wt. % solids, the thickener underflow
about 25%, and the filter cake a
minimum of 55%.
Test Program
The start-up and break-in testing of
the system will last approximately 2
months; immediately following, the
system will undergo a 6-month period of
testing to characterize its operations.
This test program is aimed at evaluating
the following aspects of the limestone
dual alkali system performance:
• SC>2 capabilities.
• Consumption of raw materials—
soda ash, limestone, and water-
not only as a measure of the
efficiency of the system in utilizing
these materials in the removal of
SOa but also as a measure of the
ability of the system to maintain a
closed-loop operation.
• Consumption of energy—electrical
power, and fuel for the gas reheater.
• Levels of sulfite oxidation experi-
enced by the system as well as the
ability of the system to tolerate
such levels of oxidation.
• Waste cake properties—dewatering,
handling, and washability.
• Particulate matter removal (during
periods of planned ESP turndown)
by the system and the effect of ash
on process chemistry.
• Sulfate emissions in the processed
flue gas.
The test program will be conducted in
two phases. During Phase I, a baseline
for the operation of the system will be
established. Phase 2 will consist of
variational tests of the system.
Start-Up and Break-In Testing
During start-up and break-in testing,
not only will the system be started up,
but it will also undergo preliminary
testing. Information from these tests
will be used to optimize and finalize the
control set points and to verify the
suitability of the testing and analytical
procedures. Furthermore, test results
will be used to make any necessary
adjustments to the system, to the
system operations, and to the test plan.
The preliminary tests will include the
determination of: (a) SO2 removal
efficiency at various gas loadings, inlet
SOa concentrations, and scrubber
operating pH's; (b) regeneration effici-
ency as a function of reactor configura-
tion and type of limestone—if possible,
the effect of limestone particle sizfe will
also be evaluated; and (c) waste solids
properties and conditions for operation
of the thickener, filter, and cake wash
system. A list of the projected operating
conditions during start-up and the test
program is given in Table 2.
Phase 1 — Baseline Testing
In previous pilot plant and laboratory
studies, the general effect of process
parameters and operating conditions on
Table 2. Prototype Test Program Projected Operating Conditions
Period
Nominal
Load
(MW)
Nominal
Inlet S02
(ppm dry)
Limestone
Type*
Reactor
Configuration
Inlet Oz
Vol. %
Particulate
Loading
Comments
2 Months 10-20 J 800-2800
A/B
Variable
4.5-6 None Finalize control set points.
Evaluate testing and analytical
process. Perform preliminary
evaluation of the system re-
sponse to boiler load, SOz load,
reactor configuration, and type
of limestone. Characterize fil-
ter performance. Check gas
flow vs. fan amperage
correlation.
Phase 1
2 Months
Phase 2
4 Months
3 wks
1 -2 wks
1-2 wks
2 wks
2 wks
2-3 wks
2-3 wks
2 wks
18-20
10-20
18
18
18
18
18
18
18
2000-2500
2000-2500
1500-2000
2000-2800
2000-2500
2000-2500
2000-2500
2000-2500
2000-2500
AorB
A or B
A or B
AorB
AorB
AorB
A1 orBI
C
A.B. or C
Standard
Standard
Standard
Standard
Variable
Standard
Standard
Standard
Standard
4.5-6
4.5-6
4.5-6
4.5-6
4.5-6
4.5-10
4.5-6
4.5-6
4.5-6
None
None
None
None
None
None
None
None
Variable
Baseline Testing
Boiler (scrubber) load testing
S02 load testing
S02 load testing
Reactor testing
Scrubber oxidation
Limestone testing
Limestone testing
Particulate load testing
*A, B, C—Different types of limestone. A1, B1—Different particle size.
-------
the performance of limestone-based
dual alkali systems was determined.
The process parameters/operating
conditions and the performance variables
that they affect are listed in Table 3. The
baseline testing for this program will
focus on confirmation and additional
characterization of these relationships.
Most important, baseline testing will
provide a quantitative evaluation of the
overall system performance for an
extended period for at least one (nominal)
set of process parameters/operating
conditions. Subsequent variations in
selected process parameters/operating
conditions and their effect on the
performance of the system will be
studied in Phase 2.
Phase 2 — Variational Jesting
Phase 2 will last approximately 4
months. The results of this variational
test will provide the technical information
needed to determine the range of
application and limitations of the
limestone dual alkali technology. The
various conditions under which the
system will be operated will involve,
primarily, variations in those conditions
which could be expected to be encoun-
tered in full-scale applications:
• Boiler load fluctuations.
• Inlet SOz concentrations.
• Type of limestone used and/or
particle size.
• Reactor configuration and residence
time.
• Boiler excess air (Oz concentration
in inlet flue gas).
• Paniculate loading.
The operation of the system, while
evaluating the effect of each of the
above variables, will constitute a
discrete testing period. Each testing
period will last 2 or 3 weeks unless the
operating conditions or other situations
dictate a more reasonable or convenient
period. A summary of the various
projected operating conditions is given
in Table 2.
Process Parameters and Other Conditions Which Affect the Performance
of the Limestone-Based Dual Alkali System
Parameters/Conditions
Tables.
Performance Variable
Removal Efficiency
Limestone Consumption
Soda Ash Consumption
Energy Consumption
Oxidation
Cake Properties
Paniculate Removal
Process Operability
Inlet SOz concentration/gas flow
Scrubber configuration (venturi + absorber, venturi
alone)
Scrubbing liquor pH (inlet and outlet)
Venturi pressure drop
Active sodium concentration
Inlet SOz and 02 concentration/gas flow
Type of limestone and particle size
Reactor configuration
Reactor holdup time
Inlet SOz and Oz concentration/gas flow
Liquor entrainment in scrubber section
Cake wash efficiency/wash ratio
Gas flow
Inlet SOz concentration
Inlet Oz concentration
Scrubber configuration
Scrubber temperature
Type of limestone
Reactor configuration
Reactor holdup time
Reactor pH
Filter operation
Inlet paniculate concentration/gas flow
Scrubber configuration
Operational upsets in system conditions
(equipment failure, operator error, etc.)
Scaling, pluggage, spills
Economic Considerations
Generalized Cost Estimates foi
A New 500 MW System
In general, a dual alkali flue gas
desulf urization system (FGD) consists o1
several subsystems for the performance
of specialized functions: absorption 01
SOa from the flue gas, regeneration ol
the spent scrubbing solution anc
precipitation of the waste solids,
separation of the regenerated solution
from the solid waste generated, storage
and preparation of raw materials, disposal
of the waste, and provision of utilities.
Basically, the system under considera
tion Is assumed to be designed for 95%
SOz removal efficiency when burning
coal containing 3.5% sulfur. The dual
alkali system is assumed to be installed
in a new 500 MW boiler located in the
Midwest. The base year for cost estimates
is mid-1979.
Although the dual alkali process is
capable of removing particulate matter,
this capability is not incorporated in the
system under consideration. Thus, the
absorbers are assumed to take flue gas,
through booster fans, from high effici-
ency ESPs. The booster fans for the dual
alkali system also serve as induced draft
fans for the boiler. The system is
modular, with four-absorber/two re-
actor trains. Each absorber is sized to
handle 135 MW. Consequently, there is
a 10% spare capacity at full load; the
system can treat at least 80% of the
design flue gas load with one absorber
down. Similarly the reactor system can
handle a full system load with one
reactor train down for short periods. The
vacuum filters are operated and con-
trolled independently and the number of
filters in operation depends on the
system load. Three filters are included—
two operating and one full spare filter
when operating at design conditions.
Cost of Modifying the Scholz
Prototype System
The modification and conversion of
the 20 MW lime-based dual alkali
system for operation with limestone is
being performed under Phases 1 and 2
of the project. The cost of modifying the
system is being shared by EPA and CEA.
The overall projected costforthe modifi-
cation of the system was originally
estimated at $613,500. The fraction of
the total cost to be reimbursed by EPA
would amount to $366,300; CEA's
contribution would be $247,200. (The
actual CEA contribution amounted to
over $400,000.)
4
-------
The estimated total capital invest- The annual operating costamountsto
ment for a generalized 500 MW lime- $15.7 million, equivalent to an annu-
stone dual alkali system is $47.4 million alized cost of 4.5 mills/kWh or $191 /ton
(see Table 4), which is equivalent to S02 removed.
$94.8/kW. This cost does not include
waste cake processing or disposal,
which are considered operating costs.
The process equipment and other
material costs amount to $16 million.
The cost of erecting the system is
estimated at 50% of the process
equipment and additional material
costs. The service, utilities, and miscel-
laneous costs are taken as 6% of all
other direct costs. The indirect costs are
estimated in- direct proportion to the
total direct costs: engineering at 9%
construction field expense at 11%;
contractor's fee at 5%; and contingency
at 20%.
The estimated annual operating costs
of a 500 MW system are given in Table
5. Capital charges, including interest,
depreciation, return on investment,
taxes, and insurance are taken at 14.6%
of the total fixed plant investment.
Table 4. Estimated Capital Investment for a 500 MW Limestone Dual
Alkali System (1979 Dollars)
(OOO's)
Direct Costs
Process Equipment and Materials
Erection Costs
Services, Utilities, and Miscellaneous
• Indirect Costs
• Allowance for Start-up and Interest During
Construction
TOTAL DEPRECIABLE
• Spare Parts, Land, Working Capital
TOTAL INVESTMENT
16,090
8.050
1.450
25.590
11,510
8.150
45.250
2,140
47.390
Table 5. Estimated Annual
Operating Costs for a 50O
MW Limestone Dual Alkali
System (1979 Dollars)
Direct Costs
(OOO's)
Raw Materials
Utilities
Labor and Maintenance
Waste Disposal
Indirect Costs
Capital Charges
Overhead
Total Annual Operating
Cost
Mills/kWh
$/ton SOz Removed
1,930
2.072
1.521
2,780
8,303
6,607
792
7,399
15,702
4.5
191
Applicable Conversion Factors
English to Metric Units
British
Metric
1ft3
1 Ib (avoir.)
1 ton (short)
1 gal.
0.0283 meters2
0.4536 kilogram
0.9072 metric tons
3.7853 liters
J. A. Valencia and R. R. Lunt are with Arthur D. Little, Inc.. Cambridge, MA 02140;
G. J. Ramans is with Thyssen-CEA Environmental Systems, Inc., New York, NY
10022.
Norman Kaplan is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of the Limestone Dual Alkali Prototype
System at Plant Scholz: System Design and Program Plan." (Order No.
PB 81-247 421; Cost: $8.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
. S. GOVERNMENT PRINTING OFFICE.' 1981/559-092/331)
-------
United States Center for Environmental Research p°StaSe %nd
Environmental Protection Information rees raid
Agency Cincinnati OH 45268 P^t'e^Trf"
Agency
EPA 335
Official Business
Penalty for Private Use $300
PS 00003
------- |