United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-86/016 Apr. 1987
Project Summary
Lime Spray Dryer Flue Gas
Desulfurization Computer Model
Users Manual
R. L. Dotson, F. A. Sudhoff, and T. A. Burnett
The time spray dryer flue gas desul-
furization (FGD) computer model was
developed by the Tennessee Valley
Authority (TVA) to model a lime spray
dryer/baghouse FGD system. The
model is capable of projecting a material
balance, an equipment list, and capital
investment and revenue requirements
for a spray dryer/baghouse FGD system
based on the user-specified input data.
The purpose of this computer model is
to permit the rapid estimation of the
relative economic impacts of variations
in: process design parameters (e.g.,
absorber residence time, baghouse air-
to-cloth ratio), coal composition, SO2
removal efficiency, and spray dryer
operating conditions (e.g., approach-
to-saturation temperature, lime stoic-
hiometry). The model is not intended to
compute the economics of an individual
system to a high degree of accuracy.
Instead, it is designed to allow prospec-
tive users to evaluate several potential
design and operating conditions and
quickly project comparative costs for
these case variations on a common
basis.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
Model Basis
The lime spray dryer FGD computer
model is based on previous generic con-
ceptual designs of the lime spray dryer/
baghouse FGD technology prepared by
TVA and existing information available
on commercially operating spray dryer/
baghouse FGD systems. Although the
numerous spray dryer FGD vendors have
slightly different process designs, most of
the differences are in the spray dryer
vessel itself. The spray dryer vessel in
this model is based on the Niro Atomizer,
Inc., design with a single rotary atomizer,
a side gas exit, and a single recirculating
slurry feed loop with a head tank to feed
the atomizer. Other designs have been
used by vendors, but most of the utility
installations currently being designed,
built, or operated are using the Niro
technology. For this reason, the Niro spray
dryer design was selected as the basis
for this computer model. The remaining
components of the system reflect a gen-
eric process design including a utility-
type, reverse-air baghouse; a lime pre-
paration system (currently limited to a
ball-mill-type slaker); an FGD waste re-
cycle system; and an onsite landfill for
waste disposal. The current model cannot
simulate either once-through operation
(i.e., no recycle) or pond disposal of the
waste.
Process Description
The spray dryer/baghouse FGD system
is a relatively simple process with few
major equipment items as shown in the
process flow diagram (Figure 1). The flue
gas from the boiler air heater enters the
spray dryer vessel at about 150°C through
an inlet scroll around the atomizer and is
intimately mixed with the atomized ab-
sorbent slurry. The paniculate-laden flue
gas swirls downward through the spray
dryer, makes a 180-degree turn, and
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Pulverized
Coal
Boiler
cb
Conomizer ,,,-.,,
Hot Gas Bypass
~JrVarm_$JsjByf>assJJ
Water ~'
, -n_i Headn
\Air Heater
Combustion
Air
y Sprayj±
Dryer
Particulate
Surge
Bin
'tack
Plenum
«,-—., Baghouse
Paniculate
Surge
Bins
Q
a
9
o
_ Intermittent or option flow
Blow pots |
Flap valve or double gate valve
Vaporation gas
Hopper heater
Fan
Pump
Agitator
Atomizer
Compressor
Dryer
Particulate
Recycle
Silo
Water
~\ Baghouse
• Paniculate
Recycle
Crane
Lime
Feed
Bin
Water \y
Water
fi-
Combined
Feed
Tank
Classifier
/g,j rl Is/a
Paniculate^
Disposal
Slurry
Y
To
Landfill
Slaker
Figure 1. Lime spray dryer process.
Slaker
Product
Tank
Inerts
to Disposal
exists through a side gas exit duct inserted
into the centerline of the spray dryer. As
the flue gas passes through the spray
dryer, the SO2 in the flue gas is absorbed
into the alkaline feed slurry and reacts
with the available lime to form a mixture
of calcium-sulfur salts. Simultaneously,
the water in the atomized slurry is
evaporated by the energy absorbed from
the flue gas, thus cooling and humidifying
the flue gas. The spray dryer is sized such
that the water in the feed slurry is evap-
orated before the flue gas leaves the
spray dryer. The combination of the swirl
imparted to the flue gas and the conical
bottom of the spray dryer results in some
of the FGD solids falling to the conical
bottom of the spray dryer. The paniculate-
laden flue gas from the spray dryer passes
to the baghouse. The S02 in the flue gas
continues to react with the absorbent
particles until it passes through the filter
cake in the baghouse. The clean flue gas
from the baghouse passes through the
induced-draft (ID) fan to the stack. The
entrained particulate matter (both fly ash
and FGD solids) which is collected on the
fabric filters as a cake is periodically
dislodged by reverse airflow and falls into
hoppers from which it is removed and
conveyed to either a particulate surge bin
(if baghouse recycle is necessary for the
process) or a particulate disposal silo.
The waste from the particulate disposal
silo is trucked to the landfill site.
The solids from the spray dryer cone
are discharged through a double-flap
tipping valve to a mechanical conveyor,
are moved to a bucket elevator, and are
then transported to the spray dryer par-
ticulate recycle silo. The recycle solids
from the silo are reslurned with water
and pumped to the combined feed tank
where they are mixed with fresh lime
slurry in a.predetermined, ratio.. The re-
sulting combined feed slurry is fed to the
spray dryer using a flooded-loop design.
This flooded-loop design allows a constant
flow of feed slurry to be pumped to the
head tank located above the spray dryer
The slurry required in the process is ble<
off from the head tank to the atomize
while the remaining slurry returns to th
combined feed tank to be recirculatec
The slurry flow to the atomizer is con
trolled by a pinch valve between the hea
tank and the atomizer.
High-calcium pebble lime is receive
by either rail or truck and conveyed to
lime storage silo. As required in the prc
cess, the lime is transported to a day bi
and then to the ball mill slakers. Th
resulting lime slurry overflows to a slake
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product tank and then is pumped to the
combined feed tank where it is mixed
with the recycle slurry for use in the
process.
Model Capability
The lime spray dryer FGD computer
model generates a complete conceptual
design package for a lime spray dryer/
baghouse FGD system including the
landfill for disposal of the wastes. The
model is divided into four major sections:
(1) material balance, (2) equipment sizing,
(3) capital investment, and (4) annual
revenue requirements. The material bal-
ance section projects the flue gas com-
position and flow rate from the boiler and
all process stream compositions and flow
rates based on the input data. The key
design equations which relate the overall
SO2 removal efficiency to the major pro-
cess design variables (lime stoichiometry
and approach-to-saturation temperature)
are based on published data. TVA was
responsible for selecting the best available
equations and constructing the material
balance section of the model. The equip-
ment sizing section is based on TVA's
previous experience with the Shawnee
lime/limestone computer model. The
equipment sizing is determined by the
stream flow rates from the material
balance, any size limitations of the par-
ticular equipment item, and the number
of parallel operating equipment trains.
These equipment sizes are then used in
the capital investment section to estimate
the costs for both the equipment and the
field materials and labor required for the
installation of the equipment. The sum-
mation of the equipment and installation
costs results in an overall direct invest-
ment cost for each of the seven processing
areas in the spray dryer/baghouse sys-
tem. The direct investment for these areas
is summed to obtain a total process capital
cost. After adding services and miscel-
laneous costs and the costs for the landfill
to obtain the total direct investment, the
various indirect investments and other
capital costs are calculated. The sum of
all of these costs is the total capital
investment. In the annual revenue re-
quirements section, first-year and lev-
elized annual revenue requirements and
lifetime revenue requirements are es-
timated based on the results from the
material balance (raw material require-
ments, etc.), the equipment sizing (elec-
trical energy costs), and the capital
investment sections (levelized capital
charges).
The model output includes a detailed
material balance, equipment list, landfill
design, and capital investment and annual
revenue requirement summary tables. It
also includes a list of the major process
design conditions including lime stoichio-
metry and SO2 removal efficiency.
Although the model is designed for
flexibility, it is most accurate for the vari-
able ranges which were anticipated
during its development. These anticipated
ranges for basic design parameters are:
Variable
Power plant
Fuel sulfur content
Fuel SC>2 content
S02 concentration
Approach-to-saturation
temperature
Spray dryer residence
time
Number of operating
spray dryers
Number of spare spray
dryers
Number of spare lime
preparation units
SO^ removal efficiency
Fly ash removal
efficiency
Baghouse pressure drop
Air-to-cloth ratio
Range
New. SQ-1.300MW
0 5-5%
1 0-90/bS02/10 Btu
(430-3870 ng S02/J)
400-4,000 ppm
15-50°FI-9 - +10°CI
5-12 sec
1-10
0-10
0-10
49-97%
1-99.9%
4-8 in. (10-20 cm) water
} 5-3 0 aft /min/ft
cloth area
/7B-J5.2LW*
m3/s • IvT
a The variable ranges were established for model
development purposes Values beyond these ranges
are not necessarily invalid, but the potential for
error is greater when these ranges are exceeded.
''For coal sulfur levels above 2%. the model tends to
underestimate the required lime stoichiometry,
hence the user should operate the model in the
"force-through" mode (i e, specifying both the lime
stoichiometry and the overall S02 removal ef-
ficiency).
Model Usage
While the lime spray dryer FGD com-
puter model is designed to be used by
utility companies or architectural and
engineering firms involved in the selection
of SO2 removal facilities, it has the
potential for use by others interested in
SO2 removal technologies. Although it is
not intended to be used for projecting a
final design, the model can be used to
assist in the evaluation of system alter-
natives prior to a detailed design. The
model should also be useful for evaluating
the impact of changing various design or
operation variables on the process eco-
nomics. While the model is not meant to
be used for comparing the process eco-
nomics of a lime spray dryer/baghouse
FGD system with those of alternative
FGD processes, these comparisons can
be made if the user is careful to maintain
comparability between the design condi-
tions used in the lime spray dryer FGD
computer model and those for the alter-
native FGD processes.
The body of this report discusses the
information necessary and the input data
required to run the overall computer
model. This discussion includes a more
detailed description of the lime spray
dryer/baghouse system, the input data
set, and the options available to the user.
Also discussed is the procedure for either
acquiring a tape copy of the model or
having example runs prepared.
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R. Dotson. F. Sudhoff, and T. Burnett are with TVA's Office of Power, Muscle
Shoals. AL 35661.
Theodore G. Brna is the EPA Project Officer (see below).
The complete report, entitled "Lime Spray Dryer Flue Gas Desulfunzation
Computer Model Users Manual," (Order No. PB87-140 968/AS; Cost: $18.95,
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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 452G8
Official Business
Penalty for Private Use $300
EPA/600/S8-86/016
0000329 PS
'GENCr
230 S DEARBORN STREET
CHICAGO It, 60604
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