United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/053 Apr. 1987
4>EPA Project Summary
Boiler Design Criteria for Dry
Sorbent S02 Control with
Low-NOx Burners: New Unit
Applications
J. P. Clark and A. F. Kwasnik
A study to define the boiler modifica-
tions required to achieve 70% SO2
removal with sorbent injection on a
large tangentially fired utility boiler
without supplemental spray drying was
conducted under EPA sponsorship. This
task was executed as a follow on to a
recently completed broader evaluation
of boiler design criteria for sorbent SO2
control technology. A new 500 MWe
utility boiler burning low-sulfur coal was
considered to be modified to increase
sorbent residence time and decrease
gas quench rate to achieve 70% SO2
removal in the boiler with atmospheric
calcium hydrate prepared on-site. A
second case was considered where no
change was made to gas quench rate or
sorbent residence time. The effects of
adding a pulverizer to the sorbent prep-
aration/injection system to permit
production of a finer sorbent were
determined. Capital costs, cost of
electricity, and cost effectiveness per
ton of SO2 removed were developed
and compared with the results of the
earlier study.
This Project Summary was developed
by EPA's Air and Energy Engineering Re-
search 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).
Introduction
The results of the initial study con-
ducted under this contract, showed that
the combination of limestone sorbent
injection and a spray dryer offered sig-
nificant cost advantages over conventional
flue gas desulfurization in achieving 70%
SO2 removal on new tangentially fired
utility boilers burning low-sulfur coal.
This study was predicated on 50% S02
reduction in the boiler and the remaining
reduction in the spray dryer.
This report gives results of additional
work carried out under the same contract.
The objective of the present study was to
determine the relative costs of designing
for New Source Performance Standards
compliance (70% SO2 removal) using only
furnace sorbent injection on a new 500
MWe tangentially fired utility unit burning
low-sulfur coal.
Results and Discussion
Process Description
A 500 MWe boiler of current design
was selected as the baseline unit for the
study. The low-sulfur coal (0.55% S) used
in the initial study was also used for this
study. The time.temperature characteris-
tic through the critical 1232 to 871 °C
sulfation window was calculated to be
311°C/sec.
Atmospheric hydrated lime [Ca(OH)2]
was selected as the sorbent material for
this study, based on its superior S02
removal performance relative to lime-
stone. On-site hydration was assumed.
The effect on process economics of in-
corporating a pulverizer to provide a finer
sorbent product from the hydrating plant
was determined.
Based on the calculated quench rate
and selected sorbent, a 3.5:1 Ca/S molar
ratio was selected to achieve 70% S02
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removal. To increase residence time and
reduce gas quench rate, open cavities
were created in the convective pass by
relocating the reheat surface to the rear
pass area. Gas quench rate was reduced
to 182°C/sec. Required sorbent stoichio-
metry was reduced to 3.1:1. Low temp-
erature surfaces were rearranged with
wider spaces to minimize erosion poten-
tial. Sootblowing capacity was increased.
As a trade-off study, the cost of achiev-
ing 70% S02 removal with minimal boiler
modifications was determined. No sig-
nificant modifications were made to the
boiler. Gas quench rate remained at
311°C/sec. Sorbent stoichiometry was
3.5:1. Sootblower capacity was increased.
Process Economics
Capital and operating costs were
developed for the cases described above,
including the effect of adding a pulverizer
to the sorbent preparation system. The
costs were developed according to proce-
dures outlined in the EPRI Technical
Assessment Guide and are expressed in
December 1985 dollars for a January
1986 start-up.
Extensive Boiler Modifications
For the extensively modified boiler
design, incorporation of sorbent injection
using Ca(OH)2 to achieve 70% S02 reduc-
tion in the boiler cost $18.45/kW. First-
year cost effectiveness of SO2 removed
was 574.32 $/ton (30-year levelized cost
effectiveness was 1103.26 $/ton). First-
year incremental cost of electricity was
1.66 mills/kW-hr (30-year levelized cost
was3.19mills/kW-hr).
Adding a pulverizer to the sorbent
preparation/injection system to achieve
a finer sorbent product added 2.87 $/kW
to the overall cost for either boiler design.
Minimal Boiler Modifications
Incorporation of sorbent injection to
achieve 70% SO2 removal on a new 500
MWe low-sulfur unit with minimal modi-
fications (no cavities) resulted in a slightly
lower capital cost (17.24 $/kW) than the
unit with cavities, but a higher (poorer)
first-year cost effectiveness of SO2 re-
moved (603.24 $/ton) (30-year levelized
cost effectiveness was 1184.91 $/ton).
First-year incremental cost of electricity
was 1.74 mills/kW-hr (30-year levelized
cost was 3.42 mills/kW-hr).
Initial Study Results
The cost of incorporating sorbent injec-
tion (limestone) plus a spray dryer to
achieve 70% S02 reduction on a new
600 MWe low-sulfur unit was 44.10
$/kW. First-year cost effectiveness of
S02 removed was 788.98 $/ton (30-year
levelized cost effectiveness was 1287.90
$/ton). First-year incremental cost of
electricity was 2.29 mills/kW-hr (30-year
levelized cost was 3.73 mills/kW-hr).
J. P. Clark and A. F. Kwasnik are with Combustion Engineering, Inc., Windsor,
CT06095.
David G. Lachapelle is the EPA Project Officer (see below).
The complete report, entitled "Boiler Design Criteria for Dry Sorbent SOz Control
with Low-NO, Burners: New Unit Applications," (Order No. PB 87-139 952/
AS; Cost: $11.95, 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
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use,$300
EPA/600/S7-86/053
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