United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S7-81-166 Jan. 1982
Project Summary
Solar Energy for
Pollution Control
P. Overly, C. Franklin, B. L. Blaney, and C. C. Lee
A study was conducted to
determine which existing or emerging
pollution control processes are best
suited to make use of solar power and
to determine the potential benefits of
such applications. Pollution control
processes were matched with
compatible solar energy systems,
resulting in the following four com-
binations:
• Anaerobic digestion /flat-plate
collector
• Anaerobic digestion/parabolic
trough concentrator
• Baghouse heating/parabolic
trough concentrator
• SOx scrubbing/parabolic trough
concentrator
These combinations were analyzed for
potential nationwide fossil fuel dis-
placement and cost effectiveness.
Based on the results of this survey and
the supporting analyses, solar energy
applied to sludge heating for
anaerobic digestion would result in
the greatest fossil fuel displacement at
the lowest specific cost among the
various pollution control applications
investigated.
This Project Summary was develop-
ed by EPA's Industrial Environmental
Research Laboratory. Cincinnati. OH.
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
A number of pollution control
processes require significant input of
energy, which is typically supplied by
fossil fuel. The result is that the overall
effectiveness of each pollution control
process is decreased by an amount
equal to the pollutantsgenerated during
combustion of the fossil fuel. Solar
energy provides a possible means for
delivering clean energy to the process
load and decreasing the a mount of fossil
fuel required. The energy requirements
of many pollution control processes
could be met by solar energy systems
using currently available technology
and off-the-shelf hardware, at costs
similar to those of existing solar heating
and cooling systems.
A study was undertaken to determine
which existing or emerging pollution
control processes are the most
compatible with solar energy systems,
and to determine the potential benefits
of such applications. The study was
conducted in three parts:
1. Survey of pollution control
processes to determine which are
most compatible with the relevant
solar technologies.
2. Priontization of relevant pollution
control technologies in terms of
potential fossil fuel savings.
3. Determination of the most cost-
effectiveness pollution control/
solar energy system combinations.
The solar energy technologies
considered by this study included those
available off-the-shelf for supplying
-------
thermal energy for process heating and
cooling. A general solar system
schematic shown in Figure 1 was
developed to allow substitution of major
system components to meet the
requirements of each pollution control
process. The system includes an
interface with the process streams by
means of a simple heat exchanger. The
two major components which are
specific to the solar energy system are
the collector and the thermal storage
medium. Flat plate and concentrating
collectors were analyzed in this study.
The two methods of thermal storage
which are currently commercially avail-
able were considered: sensible heat and
latent heat.
Once potential combinations of pollu-
tion control processes and solar energy
systems (PCP/SES) had been identified,
they were analyzed individually for
potential nationwide fossil fuel displace-
ment and cost effectiveness. Fossil fuel
displacement was first determined on a
regional basis. Regions were defined by
their isolation rates, and system sizing,
performance and fossil fuel savings
were determined for each region. The
total fuel savings in a region was the
product of the savings at a typical plant
using the pollution control process and
the number of plants in that region. The
nationwide fossil fuel displacement for
the process was determined by
summing the fuel savings for each
region.
The cost effectiveness of these
candidate PCP/SES combinations was
also considered. For the purpose of this
Solar
Collector
study, cost effectiveness is described in
terms of specific cost of a solar energy
system ($/unit energy displaced). The
specific cost was calculated by dividing
the life cycle of the system by the annual
fossil fuel displacement cost by the solar
system. The after tax Life Cycle Costs
(LCC) were calculated based on the
following formula:
LCC = CRF (I- ITC) (C) + (I -1) OC - t (D)
where
CRF = capital recovery factor, i = 10
percent, n = 20 years
ITC = investment tax credit =10 per-
cent
C = capital costs
t = weighted federal and state tax
rate = 50 percent
OC = tax deductible operating costs
D = depreciation, straight line.
Fossil fuel displacement was taken as
equivalent to the energy supplied to the
pollution control process by the solar
energy system minus the energy
required to operate the solar energy
system (e.g., for powering circulation
pumps).
Conclusions
Three pollution control processes
were identified as most compatible with
3-Way
'Mixing Valve
Auxiliary
Energy
Heat U
^Exchanger \ (
(If required/1
-^
i
1
Load
Circulation
Pump
Process
Load (Stream
Main
Circulation
Pump
/Storage
L. Bypass
Line
the relevant solar technologies. They
are:
• Sludge heating to promote anaer-
obic digestion.
• Baghouse heating for prevention
of acid condensation during shut-
down.
• Flue gas reheat for SO, scrubbing.
Figures 2, 3 and 4 show the three pollu-
tion control technologies, the operating
temperatures associated with each, and
the possible interface points for a solar
energy system.
The three processes were matched
with compatible solar energy systems,
resulting in the following four combina-
tions:
• Anaerobic digestion/flat-plate col-
lector
• Anaerobic digestion/parabolic
trough concentrator
• Baghouse heating/parabolic
trough concentrator
• SO, scrubbing/parabolic trough d
concentrator "
In order to keep collector outlet temper-
ature and storage volume at a min-
imum, the stratified thermal storage
concept was chosen. It was found that
unpressured storage vessels were appro-
priate for the anaerobic digestion and
gas reheat PEP/SES combinations. For
the baghouse/parabolic trough combi-
nation, a 655KPa (95 psia) pressure
vessel was required.
The fossil fuel displacement analysis
revealed that parabolic trough line con-
centrators applied to sludge heating to
promote anaerobic digestion in munici-
pal wastewater treatment plants would
have the greatest impact on fossil fuel
savings. Approximately 67.3 PJ (0.064
Quads) could be saved each year in this
pollution control process. Flat-plate col-
lectors applied to the same process
would yield slightly less savings. The
overall prioritization of pollution con-
trol/solar energy system pairs on the
basis of potential fossil fuel displace-
ment was as follows:
Figure 1. Schematic of basic solar energy system.
2
1. Anaerobic digestion/concen-
trator 67.3 PJ (0.064 Quads)
I
-------
Sludge
0.76 x 106
1/Day —)
(0.20 mgd) at
289 K (60° F)
Heat Exchanger
Possible Interface
Point with
Solar System
Digester
10-Day Retention
at 308 K (95° F)
Further
Treatment
Figure 2. Flow diagram for anaerobic digestion for a typical 0.76 x 10s 1 /day
(0.20 mgd) treatment plant.
Dirty
Flue Gas
4.7-470 m3/sec
(10* - 10s scfm)
Scrubber
sec
ml
Scrubbed
Flue Gas
325 K
(125° F)
Reheat
ft
• To the Stack
352 K
(175° F)
Posible Interface
Point with Solar
Figure 3. Flow diagram of the flue gas reheat for SOX scrubbing.
Heat Exchanger
Baghouse
Ambient Air
.05-470 m3/sec
(JO2 - 10* scfm)
ft
Air at
411 K
(280° F)
Possible Interface
Point with Solar
Figure 4. Flow diagram of baghouse heating during shutdown.
2. Anaerobic digestion/flat-plate
66.7 PJ (0.063 Quads)
3. Baghouse heating/concentrator
7.9 PJ (0.0075 Quads)
4. SOX scrubbing/concentrator
0.5 PJ (0.0005 Quads)
Based upon these results, a ranking
of the pollution control processes in
terms of potential fossil fuel displace-
ment is straightforward. It is as follows:
1. Sludge heating for anaerobic di-
gestion
2. Baghouse heating
3. SOX scrubber flue gas reheat
There are several reasons for anaero-
bic digestion having a clear advantage
over other processes. Wastewater
treatment plants are needed all over the
country and will grow with population.
The lower temperature requirements
are also attractive from the point of view
of collector performance, and give the
process a great cost advantage. An
additional benefit of using solar energy
for sludge heating for anaerobic diges-
tion is that it will free the digestor gas
produced by the process for other uses.
Besides the low energy savings, there
are several technological drawbacks to
using solar energy to heat baghouses
for flue gas reheat. First, there are some
significant problems associated with
installing solar energy systems on plants
using baghouses and SOx scrubbers
Both baghouse and SOx scrubbers are
installed in plants producing high levels
of particulates and other contaminants
in the air. Keeping solar collectors clean
for maximum performance would be
difficult and would certainly add to the
life cycle cost of the system. Further-
more, many of these units are installed
at power plants, where adequate collec-
tor siting areas would be difficult, if not
impossible, to obtain.
The cost-effectiveness analysis indi-
cated that the anaerobic digestion/con-
centrator combination would be the most
attractive, on the basis of specific cost.
For a cost would range from $7.59 to
$17/GJ ($8.01 to $1813/106 Btu),
depending on location, with the lowest
specific cost referring to locations of
greatest isolation. Flat-plate collectors
applied to anaerobic digestion also look
promising, having specific costs in the
range $7.91 to $22.2/GJ ($8.34 to
$23.4/106Btu)'.
Based on these analyses, solar energy
applied to sludge heating for anaerobic
digestion results in the greatest fossil
fuel displacement at the lowest specific
cost among the various pollution con-
trol applications investigated. The only
other PCP/SES combination which
looks promising is the anaerobic diges-
tion/flat-plate system. Both the baghouse
heating and SO. scrubber reheat appli-
cations do not look attractive because of
generally higher specific costs and other,
technology-specific, shortcommmgs asso-
ciated with each of them.
Recommendations
Several pollution control technologies
which could potentially utilize solar
-------
energy were not considered in detail in
this study because of a lack of sufficient
technical data. These included carbon
regeneration for activated carbon ad-
sorption, drying of sludge for compost-
ing, heat treatment of sludge, Carver-
Greenfield oil emersion dehydration,
and waste pyrolysis. Further analysis of
the potential of interfacing solar energy
collectors with these systems is recom-
mended.
Of the PCP/SES combinations ana-
lyzed in depth in this study, the most
cost-effective are those in which solar
thermal energy is supplied for anaer-
obic digestion. It is recommended that
an investigation be conducted to assess
in greater depth the practicality of instal-
ling solar energy systems at specific
anaerobic digestion facilities in the
United States. The investigation should
be conducted in two parts:
• Survey existing wastewater treat-
ment plants and assess specific
applicability of solar energy.
• • Prepare design manual for apply-
ing solar energy to wastewater
treatment plants.
Survey and Assessment of
Solar Applicability
Data to be gathered in the survey
include isolation, specific process energy
requirements, duty cycles and interface
requirements. Afte* a. screening pro-
-^ ' ~ ^^HM-tamf**** ^-"ittjB^C—W"° ~
cess, these data should be used to for-
mulate feasible solar energy system
conceptual designs for selected waste-
water treatment plants. The conceptual
designs should serve as the bases for
detailed performance and economic
analyses. If available, installation, main-
tenance and operation cost information
from an operational solar-assisted waste-
water treatment plant should be in-
cluded in the data base for the economic
analyses. Finally, areas in which costs
can be reduced should be identified in
order to obtain cost competitiveness of
solar energy systems with conventional
power systems.
Solar Energy Design
Manual for Wastewater
Treatment Plants
Based upon the results of the above
task, a design manual for applying solar
energy to wastewater treatment plants
should be prepared. The manual should
provide solar application guidelines to
help design, construct, operate and
maintain plants for communities of var-
ious populations. The manual should
include solar energy system design guide-
lines for sludge drying and space and
hot water heating in addition to anaer-
obic digestion.
P. Overly and C. Franklin are with Acurex Corporation, Mountain View. CA
94042; the EPA authors B. L. Blaney and C. C. Lee (also the EPA Project
Officer, see below) are with the Industrial Environmental Research Labora-
tory. Cincinnati. OH 45268.
The complete report, entitled "Solar Energy for Pollution Control." (Order No.
PB 82-116 658; Cost: $12.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4605
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
U S GOVERNMENT PRINTING OFFICE, 1982 — 559-017/7443
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
Third-Class
Bulk Rate
ItRl0120766
REGION V
"•a. trA
130 S DEARBORN ST
CHICAGO IL 60604
------- |