United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-011 Apr. 1984
SER& Project Summary
Pilot Demonstration of Magnetic
Filtration with Continuous Media
Regeneration
Carroll E. Ball and David W. Coy
A mobile pilot plant with a nominal
flow capacity of 3,060 mVhr (1,800
cf m) was designed and built to evaluate
the use of High Gradient Magnetic
Filtration (HGMF) for participate emis-
sion control on an electric arc furnace
(EAF). A 5-month program was con-
ducted at Georgetown Steel Corpora-
tion's plant in Georgetown, SC. to test
the performance of HGMF. A 500 hour
long-term test was scheduled and later
changed in order to perform additional
characterization studies.
The pilot plant collection efficiency
was less than expected for the stainless
steel wool matrix packed to a density of
1.5 percent by volume. The matrix was
then changed to an expanded metal
packed to a density of 3.5 percent by
volume, which resulted in much lower
pressure drops, but even lower collec-
tion efficiencies. The expanded metal
matrix was then packed to a density of
6.0 percent by volume which gave
higher collection efficiencies than the
steel wool and a slightly lower pressure
drop.
During the field test,, there were no
significant problems with the HGMF
mobile pilot plant equipment.
The report describes the design and
construction of the continuous HGMF
mobile pilot plant, as well as some of
the background work in HGMF at
Research Triangle Institute (RTI). The
field start-up and performance charac-
terization of the mobile pilot plant are
discussed in detail. Experimental data
and data analysis are given, as well as an
economic evaluation and comparison
of HGMF with other particulate control
devices.
This Project Summary was developed
by EPA's Industrial Environmental
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
information at back).
Introduction
Since the commercialization of High
Gradient Magnetic Filtration (HGMF) in
the clay industry 10 years ago, applica-
tions of magnetic separation of process
streams have been steadily increasing.
They include mineral beneficiation, coal
deashing, coal desulfurization, wastewa-
ter treatment, and blood component
separation. The application of HGMF to
air pollution, however, is a recent
development. From 1975 to 1977, RTI
conducted experiments, funded by the
U.S. Environmental Protection Agency
(EPA), in applying HGMF to air pollution
control. Magnetic separation was tested
in the laboratory on several dusts from
the iron and steel industry. There were
promising results from the following iron
and steel industry sources: the basic
oxygen furnace (BOF), electric arc
furnaces (EAF), the blast furnace (BF), the
open hearth furnace, the scarf ing machine,
and the sinter machine.
An earlier pilot plant was designed and
built by RTI and tested on a Pennsylvania
sintering plant. Overall efficiency data
were low for these tests, however, due to
the low specific magnetization of the
sinter plant dust. It was then decided to
design and build a pilot plant with
continuous media regeneration and test
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it on a dust with higher specific magneti-
zation; e.g., BOF or EAF dust.
In June 1981, the pilot plant was
moved to Georgetown, SC, and connected
to a slipstream from the exhaust of three
EAFs, just upstream of a baghouse. After
start-up and debugging, tests were started,
to give results on the effects of filter
density, applied magnetic field, and gas
velocity on overall and fractional collec-
tion efficiency. A 500-hour long-term
test, planned at optimum operating
conditions, was later cancelled due to
lower-than-expected collection efficien-
cies. It was decided to use the remaining
time for additional performance charac-
terization tests with changes in the pilot
plant recycle stream. Total mass and
fractional collection efficiency tests were
conducted, and samples of the dust
entering, exiting, and captured by the
pilot plant were collected for magnetic
and chemical analyses.
Field test results were used for techni-
cal and economic assessments of the
application of HGMF to EAFs, and to
compare HGMF to other types of pollution
control devices.
Background Development
Basic Concept
The fundamental concept of HGMF is
the interaction between paramagnetic or
ferromagnetic particles and ferromag-
netic fibers, in the presence of an applied
background magnetic field. The applied
magnetic field induces a magnetic dipole
in the particle and magnetizes the wire.
This creates a convergence of the field
near the wire resulting in a net force
bei ng applied to the particle. The magnetic
force, competing with the viscous,
inertia), and gravitational forces, causes
the particle to be attracted to the wire and
held there until the applied field is
removed.
The HGMF consists of several cassettes
packed with ferromagnetic fibers (e.g.,
stainless steel wool or expanded metal)
which are moved into a magnetic field as
the particle-laden gas is passed through.
The particle-laden gas is cleansed as the
particles are attracted to and held by the
fibers. When the matrix is loaded, the
cassette is moved out of the magnetic
field and the particles are flushed from
the fibers.
HGMF Development and
Applications
Experiments in HGMF, except for the
EPA-sponsored development begun in
1975, have been most concerned with the
magnetic separation of particles in a
slurry. Several excellent reviews of the
process and its chronological develop-
ment have been published.
The most extensive development of
HGMF has been within the last decade in
the clay industry. Here, HGMF is used to
separate small paramagnetic color bodies
from kaolin clay. The successful demon-
stration of this process in the clay industry
has sparked investigations of HGMF for
many applications.
Detailed Design and
Construction of the HGMF
Mobile Pilot Plant
The mobile pilot plant is a continuous
HGMF system housed in a 12.8 m (42 ft)
freight van. The system is designed for a
nominal flow capacity of 3,060 mVhr
(1,800cfm). Figure 1 is a schematic of the
continuous HGMF system.
The dirty gas enters the pilot plant
through a 0.25 m ID stainless steel pipe
(10 in. schedule 5). The gas passes by test
ports (through which samples can be
drawn to determine inlet dust concentra-
tion, chemical composition, and size dis-
tribution) and then is directed to the
HGMF device. The magnetic filter is a
Sala-HGMS® Carousel Model 120-05-
00(Sala Magnetics, Inc., Cambridge, MA)
incorporating a magnet head and a
cleaning station mounted 180° apart on a
rotating carousel. The magnet coils are
split into a saddle configuration to allow
the carousel to be rotated through the
magnetized zone by a variable speed
drive. The carousel contains 48 removable
cassettes which can be loaded with filter
material to a depth of 0.15 m (5.8 in.). The
magnet head encloses an active face area
of 0.085 m2 (133 in.2) in the direction of
fluid flow. The magnet head is designed
to provide an applied field ofO.Oto5.OkG.
In the range of gas velocities tested, 2 to
10 m/s, the gas residence time in the
filter varied from 0.015 to 0.075 s.
After passing through the magnet, the
gas passes by another set of test ports
and exits the pilot plant. After leaving the
pilot plant, the gas is directed through an
orifice, for velocity (flow rate) determina-
tion, and an induced draft blower and
then is exhausted to the atmosphere
through an 8 m (26 ft) high stack.
After the filter material has passed
through the magnetized zone and collected
the dust particles, it passes through the
cleaning station. The filter is cleaned by
backflushing with compressed air.
The agglomerated dust that is cleaned
from the filter material with the cleaning
air pulse is sent to a cyclone. Exhaust
from the top of the cyclone is recycled into
the dirty gas stream. Dust can be removed
from the cyclone (through a double-
sealed valve) while the power plant is
operating.
The induced draft blower which moves
the gas through the pilot plant is rated at
3,060 mVhr at a suction pressure of
-13.7 kPa (-55 in. HaO) and a temperature
of 250°C. The system is designed to allow
continuous operation at temperatures of
up to 200°C. All interior and exterior pipe
is insulated with jacketed fiberglass.
The utility requirements of the pilot
plant are electricity and water. The main
power panel has 400 A service of 440
VAC input. The total connected load is
300 A. The major equipment operates off
440 VAC, and a transformer is provided to
step down to 240 and 120 VAC. Water
consumption is about 2.3 mVhr (10 gpm)
for magnet cooling, compressor after-
cooler, and occasional use of the laboratory
sink.
Field Operations
Description of the Electric Arc
Furnace at Georgetown, SC
The dust source is an EAF shop utilizing
three arc furnaces operating continuously
in a staggered batch operation. The
Georgetown Steel raw steel production
facilities consist of three 68 Mg (75 ton)
per cycle DeMag electric arc furnaces.
The charge to the furnaces consists of
scrap and prereduced iron pellets: the
scrap is obtained primarily from external
sources (about 5 to 10 percent is
reclaimed scrap), and prereduced pellets
are produced on-site from South American
iron ores. Other materials added to the
furnaces during the production cycle
include limestone, coke, ferromanganese,
and ferrosilicon.
Gas from the furnaces is cleaned by
a positive-pressure baghouse supplied
by American Air Filter. A slipstream of
gas was taken from the duct. Gas
stream conditions at the extraction
point are:
Pressure -1.7kPa (-7 in. H2O)
Temperature 71° C (160° F)
Velocity 17 m/s [55.65 ft/s)
Reynolds No.
4.1 x10°
Performance Characterization
The program was designed to test both
the effects of four variable parameters
(applied field, gas velocity, filter type, and
filter packing density) on collection
efficiency, and the reliability of the
equipment during long-term operation.
Selecting optimum operating conditions
was the goal of this phase of the testing,
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V
Cleaning Air Storage
Flush Station
Figure 1. Continuous HGMF system.
based on statistical analysis of the
performance data obtained under varied
operating conditions. Performance under
each set of conditions was to be measured
by sampling the HGMF inlet and outlet
particulate concentrations. Overall effi-
ciency would be determined on a mass
basis, and fractional efficiency would be
determined by measuring inlet and outlet
particle size distribution. Periodically
during the characterization, bulk samples
of the particulate were to be obtained
from the inlet, outlet, and cyclone catch in
order to determine the chemical composi-
tion and its effect on performance and
vice versa.
The applied magnetic fields were
varied between 0 and 5 kG for each of
three test series. Gas velocities through
the filter were varied between 2 and 10
m/s.
The initial filter medium was American
Iron and Steel Institute Type 430 medium
grade stainless steel wool packed to a
density of 0.015 (1.5 percent by volume)
and came packed in the carousel from
Sala Magnetics. The average fiber
diameter of this material is 120 Aim.
The second and third test series were
run with expanded metal matrices (layers
of wide mesh screen separated by
spacers). The expanded metal matrix can
be packed with all of the fibers perpendi-
cular to the magnetic field and in the
optimum position for particle capture. It
had been hoped that this would create a
higher collection efficiency for the same
pressure drop as was attained with a
stainless steel wool matrix.
The average fiber diameter of the
expanded metal matrix is 300 /urn. In the
second test series, the approximate
packing density of the expanded metal
matrix was calculated to be 0.035. In the
third test series, the packing density was
calculated as O.O6.
Multiple linear (slope-intercept form)
regression techniques were used to
analyze the overall mass efficiency data.
The groups of data for each matrix type
and packing density were obtained in
sequence, rather than randomly, owing
to the difficulty of changing the carousef
cassettes. Also because of this factor,
statistical analyses were performed on
the data grouped by packing type and
packing density. Using statistical tech-
niques, an exponential model was found
to produce the best data fit.
The comparative performance of the
filter system for both matricies and
packing densities is shown in Figure 2.
The performance data are plotted as
penetration (1 -efficiency) versus regres-
sion function. The line through each data
set is the regression curve for that set.
The regression coefficients a, b, and c for
each set of data are given in Table 1.
To compare the performance one must
examine the penetration at low values of
the regression function for each data set.
Looking at the functional relation of each
variable in the regression function, it is
expected that best performance would be
measured for low regression function
values; i.e., low inlet mass, low velocity,
and high field strength. Differing absolute
values of the regression function occur
between sets because of the different
regression coefficients for each data set.
At low values of the regression function,
poorest performance was measured for
expanded metal at 3.5 percent packing
density, with clearly best performance
from expanded metal at 6 percent packing
density.
Table 2 presents the predicted penetra-
tion based on the model and coefficients
in Table 1 for both matrices and packing
densities at fixed system operating
conditions. Predicted penetrations are
lower for expanded metal at 6 percent
packing density and the observed pressure
drop was also lower for this matrix than
for steel wool. Pressure drop was signifi-
cantly lower for expanded metal at 3.5
-------
700
c
.0
g
10
Steel Wool
0.015
Expanded
Metal
0.035
B
Expanded
Metal
0.06
- O
Figure 2.
Table 1.
Model:
10 100
Regression Function _ [Inlet Mass"] [Velocityf
Inlet Mass [field Strength]0 [Inlet Mass]
Georgetown Steel HGMF test--penetration vs. regression function [all matrices and
packing densities].
Regression Coefficients for Each Filter Matrix and Packing Density
= Intercept x
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Table 2. Predicted Filter Performance for Each Filter Matrix and Packing Density
Model: Outlet mass=Intercept x"nlet massf fl^W"
(Field Strength/1
Matrix and packing density
Operating
conditions*
0.1 kG
7 m/s
Steel wool
0.015
Penetration %
26.2
A/*
38.1
Expanded metal
0.035
Penetration %
22.5
A/""
25.4
Expanded metal
0.06
Penetration %
15.2
APb
30.5
2.5 kG
7 m/s
5.0 kG
7 m/s
9.5
7.6
38.1
38.1
14.4
13.1
25.4
25.4
7.3
6.2
30.5
30.5
" Inlet concentration -1.0 g/m3.
" Actual pilot plant AP, cm H-f>.
100
10
|
I
0.1
O i Steel wool matrix 0.015 packing density
D'' Expanded metal matrix 0.035 packing density
A Expanded metal matrix O.O6 packing density
7.0 m/s Velocity
2.5 kG Field strength
0.1
10
100
Particle Diameter, fim
Figure 3. Georgetown Steel HGMF test-penetration vs. particle size.
ces deserve further study toward addi-
tional optimization.
For the given conditions of applied field,
velocity (residence time), and inlet
concentrations, the best overall efficien-
cies achieved were in the range of 94 to
96 percent with outlet concentrations in
the range of 20 to 70 mg/m3. The
efficiency levels are much improved
over those achieved in the previous pilot
plant work on sinter plant emissions. The
performance levels, however, are not
competitive with conventional high
efficiency control devices applied to
electric arc furnaces. The New Source
Performance Standard (NSPS) for electric
arc furnaces limits particulate emissions
to 12 mg/dsm3. The HGMF outlet concen-
trations in these tests were 2 to 6 times
the required level. State standards for
existing sources vary considerably; e.g.,
Pennsylvania equivalent to 18 mg/dsm3,
and Michigan equivalent to 130 mg/dsm3.
On a performance basis, HGMF might
have some limited retrofit potential.
The fractional penetration data shows
that HGMF was not as effective on
particles smaller than 1 fjm in diameter as
on those larger. In terms of fractional
particle size penetration, it is not evident
that any significant qualitative differences
exist between HGMF and conventional
control devices.
The magnetic analyses data reveal that
HGMF did not remove all of the magnetic
material. The magnetic material pene-
trating the collector may do so because of
insufficient residence time or reentrain-
ment. The chemical analyses data reveal
a significant amount of iron penetrated
the filter, especially in the small particle
size (below 1 /urn) fraction. Penetration of
the iron may be due to insufficient
residence time and reentrainment.
However, a recent report, indicating
some iron in electric arc furnace dust to
be present in a "non-magnetic" form
(probably meaning not ferromagnetic),
suggests a third mechanism for penetra-
tion. The HGMF's sensitivity to chemical
composition of particles and their resulting
magnetic susceptability is analagous to
the effects of chemical composition on
particle resistivity and electrostatic pre-
cipitator performance.
An alternative use for HGMF (not
explored in this study) is to separate non-
magnetic components of waste EAF dust
from magnetic components; i.e. ferrous
and non-ferrous. At present, EAF dust is
classified as hazardous waste as a result
of heavy metals contamination. Separa-
tion of the ferrous portion with minor
contamination by zinc might permit its
recycle to steel-making, reducing the
residue for disposal. With sufficient
concentration of zinc, the non-ferrous
portion might be sold to zinc refiners. The
association of iron and zinc in non-
magnetic particles identified in the study
discussed above suggests that this
potential application of HGMF needs
further study to determine the degree of
separation achievable.
Economics
Approximate costs have been developed
for four different options for particulate
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emission control of electric arc furnace
(EAF) dust. The accuracy of these costs,
shown in Table 3, corresponds roughly to
that of a study grade estimate (± 30
percent). Although a best estimate is
presented for both capital and annual
expenses, remember that the absolute
costs of the four options may depend on
special process details, plant location,
and material of construction. Considera-
tion of these details was not within the
scope of the estimate. However, the
estimates were made for the following
common base case:
Volumetric flow rate 8,500 mVmin @ 66°C
Inlet dust loading 1,050mg/sm3
Outlet dust concentration 12 mg/sm3
Annual operation 8,500 hr/yr
For purposes of the economic compari-
sons, it was assumed that HGMF per-
formance could attain the outlet concen-
tration needed to comply with the EAF
NSPS (12 mg/dsm3).
In addition, the following system
parameters specific to each option were
specified based on engineering judgment:
HGMF
Superficial face velocity
7 m/s 5 m/s 2 m/s
Flow velocity
APHGMF-cm H2O
Total fan static AP, design
operating
ESP
Migration velocity
Specific collection area
33.0 178 25
63.5
50.8
50.8
38.1
38.1
25.4
4.6 cm/s
100 mVmVs
APEsp 2.5 cm H20
Total fan static AP, design 5.9 cm H20
operating 3.9 cm H2O
Fabric Filter
Air/cloth 1.0 cm/s
APFF 20.3 cm HZ0
Total fan static AP, design 50.8 cm HZO
operating 38.1 cm HZO
Venturi Scrubber
L/G 93 I/1,000m3
APvs 152 cm H2O
Total fan static AP, design 203 cm H20
operating 191 cm H20
Water recycle ratio 0.9
The scope of the cost estimates includes
flange to flange costs from the confluence
of the paniculate collection hoods (e.g.,
shell and canopy) to the discharge of the
clean air from the control device. For the
venturi scrubber, costs of sludge treatment
equipment are also included. It is
assumed that utilities are available at the
plant site at the following rates:
Electricity $0.05/kWh
Plant water $0.066/kl
Cooling water $0.026/kl
Compressed air $0.706/km3
Capital Costs
The total costs were calculated using
a modified Lang method; i.e., applying
factors to the purchased equipment costs
to account for direct and indirect installa-
tion costs.
Tables.
Costs of Various Control Options for EAF Paniculate Emission
$/m3/s
Total capital costs
Total annual/zed costs
10 yr* 20 yr"
Direct operating costs
HGMFC
2 m/s
5 m/s
7 m/s
ESP
FF
VS
31.31
20.99
14.16
11.94"
11.11
17.58
7.06
5.21
4.07
3.43
3.64
8.11
5.64
4.26
3.43
2.89
3.14
7.31
0.71
0.95
1.20
1.01
1.09
4.55
a Total annual costs are computed for both 10-and 20-year capital recovery periods. The capital
recovery factor for 10 years is 0.16275 and for 20 years is 0.11746.
b Direct operating costs include operation and maintenance labor, supervisory overhead, and
utility costs. They do not include capital recovery charges or taxes, insurance, and administrative
charges (taxes, insurance, and administration are computed at 4 percent or the total capital
costs).
c Values given for three separate face velocities.
" Capital costs for the ESP were calculated in four ways:
(1) Ratio from EPRI research project 834-1, using empirical
factors Cost = $ 11.50/am3/s
(2) Itemized major equipment and cost factors Cost= 10.47/am3/s
(3) Escalate from Environmental Science and Technology, Vol. 12,
No. 13 Cost = 13.11/am3/s
(4) Ratio from EPRI research project 834.1, using "0.6 rule" Cost = 13.13/am3/s
A substantial amount of engineering
judgment is used in formulating these
factors. However, the relative order of
these factors for the ESP, VS, and FF is
consistent with other data. These factors
reflect the expense necessary to install
and put into operation each control
option. The ratio between installation
costs and purchased equipment costs for
HGMF was judged to be lower than for
either the ESP or FF.
Table 3 shows that HGMF is more capital
intensive than either the ESP or FF.
Looking at the annualized costs, the
venturi scrubber is not competitive with
any of the other three options at the given
conditions. Direct operating costs, which
do not include the cost of capital over the
life of the unit, are slightly higher for the
HGMF at 7 m/s than for either the ESP or
FF. However, the difference in both capital
and direct operating costs among the
HGMF, ESP, and FF is well within the
probable error of the estimate (±30
percent).
It is important to note that tax consider-
ations are not part of this estimate.
Investment tax credits and other tax
incentives could offset some of the
initially higher HGMF capital costs by
reducing the total annualized costs of
Table 3.
Conclusions
The following conclusions were drawn
from the field operation of the HGMF
mobile pilot plant:
1. While no long-term continuous 500
-hour test was performed, the
continuous cleaning system for the
filter was capable of maintaining a
stable pressure drop through the
matrix at each of the velocity
conditions during 1- to 2-week
periods of performance characteri-
zation.
2. Test series were performed on two
types of matrices at three levels of
matrix packing density. The best
overall performance of the HGMF
unit was achieved with the expanded
metal matrix at a packing density of
6 percent. The highest efficiency
level achieved was 96.4 percent;
five of nine tests (excluding zero
applied magnetic field tests) were in
the range of 93.9 to 96.4 percent.
3. Pressure drop through the filter
matrices varied directly with the
superficial gas velocity through the
filter, approximately as the square of
the velocity. In the velocity range of
4 to 8 m/s, the expanded metal
matrix at 6 percent had lower
-------
pressure drops (10 to 46 cm H2O)
than the steel wool matrix (16 to 50
cm H2O). Given the better overall
performance (both efficiency and
pressure drop) with the expanded
metal at 6 percent packing density, it
was the preferred filter matrix.
4. Fractional penetration curves show
performance of the HGMF to be
relatively poor (85 percent efficiency
or less) in the particle size range
below 1 /urn.
5. Elemental chemical analyses show
iron removal efficiencies are higher
than overall mass efficiencies as
determined from thimble dust sam-
ples. However, elemental analyses
of cascade impactor samples show
the iron penetration to be as much
as 6 percent when overall mass
penetration is 9 percent. Potential
explanations for inadequate capture
of iron-bearing particles include:
a. Magnetic forces acting on the fine
particles are not sufficient to effect
capture as the gas passes through
the filter due to insufficient resi-
dence time.
b. Some of the iron occurs in complex
compounds with zinc that is not
sufficiently magnetic to be captured;
this is supported by work done at
Lehigh University on waste dusts
from electric arc furnaces.
c. Reentrainment.
6. The overall penetration of electric
arc furnace dust through HGMF
measured in this program must be
reduced by a factor of 2 or 6 to
compete with the performance of
conventional particulate control
devices applied to new sources.
Standards for existing sources in
some states might permit the retrofit
of an HGMF.
7. Assuming HGMF performance can
reach a competitive level in the
configuration and operating mode
tested in this program (e.g., 99
percent efficiency), comparative
annualized costs for HGMF, fabric
filters, ESPs, and venturi scrubbers
show that HGMF can compete
economically with venturi scrubbers,
but is more expensive than fabric
filters and ESPs. Since, to achieve
that level of performance on EAF
dust, it would be necessary to
reduce the gas velocity and/or
increase filter length, it will be
difficult for HGMF to compete as a
control device for EAFs,
Carroll E.Bali and David W. Coy are with the Research Triangle Institute, Research
Triangle Park, NC 27709.
William B. Kuykendal is the EPA Project Officer (see below).
The complete report, entitled "Pilot Demonstration of Magnetic Filtration with
Continuous Media Regeneration," (Order No. PB 84-153 204; Cost: $14.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, MA 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
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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U.S. GOVERNMENT PRINTING OFFICE: 1964-756-102/925
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