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

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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:

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   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.

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  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

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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.

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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

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  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)

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