-------
vtp = tangetial velocity of particle
Vg = linear gas velocity
z^ = ion mobility
P = coagulation constant
e - rate of dissipation of turbulent energy
ep = dielectric constant of particle
G£ = dielectric constant of gas
eQ = permittivity of free space
X = mean free path of gas
X0 = internal scale of turbulence
$ = particle mobility
T| = collection efficiency
v = kinematic viscosity
Pp = particle density
p = density of gas
u = gas viscosity
\|i = coagulation rate
ou = angular velocity
-------
• 1
SUMMARY
The objective of this task was to critically review and evaluate avail-
able literature on methods of removing particulate matter from high
temperature and/or high pressure gas streams. The study was subdivided
into three major areas of work: (a) literature search; (b) theoretical
assessment of the effect of temperature and pressure on particulate col-
lection and agglomeration mechanisms; and (c) identification of promis-
ing technology for this application.
The literature survey revealed very little theoretical or experimental
work conducted in the past on effects of high temperature and/or high
pressure on gas cleaning. Some recent application experiments have been
conducted on pilot-scale hardware or components for elevated temperature/
pressure systems, but considerable development is required before any
system is commercially available.
Since the literature contained such limited information, a review of
theoretical models of aerosol collection and agglomeration mechanisms
was conducted in order to determine the influence on these mechanisms
due to elevated temperature and pressure. Table 1 presents a synopsis
of the results of the theoretical assessment. In many instances the
effectiveness of collection and agglomeration mechanisms decreases with
increases in temperature and pressure. The influence of temperature and
pressure is closaly related to aerosol particle size for many mechanisms
because of the term C/u ,* which is a fundamental part of many of the
equations describing aerosol collection and agglomeration. In general,
increases in temperature and pressure will decrease the effectiveness of
the operative mechanisms for particles greater than 0.5 um in diameter.
C = Cunningham slip correction factor.
u = gas viscosity.
-------
Table 1. SUMMARY OF INFLUENCE OF TEMPERATURE AND PRESSURE ON
AEROSOL COLLECTION AND AGGLOMERATION MECHANISMS
Aerosol collection or
agglomeration mechanism
A. Aerodynamic capture
1. Inertial iippaction
2. Interception
3. Diffusion
Characteristic parameter
STK
C P D v
P P o
9 u D
= Dp/Dc
Pe
3rruD D v
p C O
KTC
Temperature and pressure dependence
of characteristic parameter
See Figures 1 and 2
None
Dependence is dictated by term u/TC
and is somewhat complex.
Trend with elevated temperature and/or
pressure
Inertial impaction efficiency is reduced.
Decrease can be quite significant for
£ 1 urn particles.
Generally unaffected by any variation not
a function of particle size.
Principal effect is for small particles with
net result being a decrease in efficiency.
4. Electrostatic attraction
^-*£vcDpV
5. Gravitational settling
B. Centrifugal forces
C. Flux forces
1. Electrophoresis
2. Thennophoresis
KE =
c qp if
3nu e D v
K o p p-c
G = vs/vo
VFv
CqE
3,7 u D.
VT = f[\, P, p]
Dependence is dictated by ratio C/u
Dependence is dictated by ratio C/u
See Figures 4 and 5
C/u and q are either temperature
and/or pressure dependent. Dependence
of migration velocity, t . on tem-
perature and pressure is complex.
Temperature and pressure dependence as-
sociated with gas mean free path, gas
viscosity and gas density which influence
thennophoretic velocity v^, .
Collection efficiency at high temperature
and pressure is reduced for particles
larger than 0.05 um diameter.
Collection efficiency will decrease with in-
crease in temperature and pressure.
Collection efficiency at high temperatures
and pressures is reduced for particles
larger than 0.1 um diameter.
Particle size has a strong influence on the
impact of increases in temperature and
pressure—especially in the 0.1 to 1.0 urn
diameter.
Influence of temperature and pressure is as-
sociated with Knudsen number, K,, = X/rp .
For KJJ s 0.1 , v is inversely propor-
tional to pressure and directly propor-
tional to T°-6 .
-------
Table 1. (concluded)
Aerosol collection or
agglomeration mechanism
3. Diffusiophoresis
4. Magnetic force
D. Particle agglomeration
1. Thermal agglomeration
2. Turbulent agglomeration
Characteristic parameter
v = f[D, n]
3rr u Dp
K = 4TTDr .
o p
None
3. Charged particle agglomeration k-
4. Sonic agglomeration
(
pCg
Temperature and pressure dependence
of characteristic parameter
Temperature and pressure dependence is
associated with diffusion coefficients
which in turn vary directly with tem-
perature and the ratio C/u .
Temperature and pressure dependence
associated with ratio of C/u .
Temperature and pressure dependence are
associated with diffusion coefficient
which varies directly with temperature
and the ratio C/u .
Temperature and pressure effects are as-
sociated with impact on kinematic vis-
cosity and the turbulent microscale.
Temperature and pressure dependence of
correction factor kem is complex.
Under simplified conditions, kem is
roughly proportional to T^'2 .
Temperature and pressure dependence is
associated with gas density.
Trend with elevated temperature and/or
pressure
Influence of temperature and pressure is as-
sociated with Knudsen number, KJJ = \/r .
For KQ £ 0.1 , VD is directly propor-
tional to temperature and the ratio C/u .
Collection efficiency at high temperature
and pressure is reduced for particles
larger than 0.1 urn diameter.
Net influence of temperature and pressure
dependent upon particle size and relative
increases in temperature and pressure.
Net influences of temperature and pressure
dependent upon relationship of particle
size to interal scale of turbulence.
Agglomeration coefficient will increase
with temperature and decrease with pres-
sure.
-------
The most promising approaches which should be explored for particle col-
lection under high temperature and pressure conditions, based on the
theoretical review, included: (a) centrifugal forces; (b) aerodynamic
capture; and (c) electrostatic forces. Control equipment and systems
for particulate collection were identified which utilize the promising
mechanisms as a primary capture technique. Cyclones, special types of
filter systems (e.g., gravel beds, metallic fibers), scrubbers which
do not cool the gas stream (i.e., molten salt), and electrostatic pre-
cipitators are included in this category.
A review of the status of the above control devices for high tempera-
ture and/or pressure applications was conducted. Table 2 is a summary
of these potential particulate removal systems under the conditions of
interest. Also included in Table 2 is a relative ranking of the potential
for sulfur removal, energy requirements, and potential operating problems.
Cyclones are proven devices for collection of large particles. The tech-
nology is well developed and application to high temperatures and pres-
sures, while needing investigation, should pose a relatively simple task.
The primary problem will be, as with all devices considered, utilization
of materials that maintain structural integrity under elevated tempera-
tures and pressures.
Gravel bed filters such as those under development by Squires and his
co-workers as well as the metal fabric filter being developed by the
Brunswick Corporation have the best potential for high temperature/
pressure applications. Both offer high collection efficiency possi-
bilities with the Squires and similar devices providing additional po-
tential for sulfur removal.
Molten salt scrubbers, while offering potential for desulfurization as
well, may have difficulties due to particle reentrainment. Structural
problems with this device will probably be minimal, since special mate-
rials will be necessary in any event to contain the molten bath.
Electrostatic precipitators require considerable development, although
probable low pressure drop is attractive. Materials of construction for
precipitators poses the most severe potential problem of all the devices,
since alignment of corona wires and plates or pipes, as well as their spa-
tial relationships is unaffected by elevated pressures and high temperatures
for uniform high performance.
All of the systems reviewed require considerable development before they
can be reliably used. Confirmation by both bench-scale and pilot-scale
experiments will be necessary to determine if the collection mechanisms
identified actually function in the manner predicted. Proper materials
of construction and energy tradeoffs will also need better definition.
8
-------
Table 2. SUMMARY OF POTENTIAL PARTICULATE REMOVAL SYSTEMS
Sy stem/Deve loper
I. Cyclones
Aerodyne Torando cyclone/
Aerodyne Development Corporation
Tan-Jet Cyclone/
Donaldson Company
II. Gravel bed filters
Combustion Power
Due an
• Lurgi-MB-Filter
Rexnord
• Squires, CCNY
III. Electrostatic precipitators
IV. Molten salt scrubbers
• Battelle Memorial Institute
Rockwell International Corporation
V. Fabric filters
Silica Fibers, J. P. Stevens Company
Silica Fibers, 3M Company
Metal Fabrics, Brunswick Corporation
Operating conditions
Operated Projected
(°C/atm) (°C/atm)
Particulate Potential
removal ef- for Potential
ficiency for sulfur Energy penalty/ operating
< 1 urn __ removal operating costs problems
900/high > 1100/high Low
None
Low/moderate
Low
500/30 900/30 Moderate None Moderate/high Low/moderate
300/1
> 500/high > 1100/20+ High
150/1
250/1
350/1
500/1
550/1
400/1 950/5+ High
High Moderate
Moderate
None Low
High
900/1
400/1
800/-
1000/-
800/-
1100/5+
High
800/high High
High
None
Moderate
Moderate
Moderate
Comments
Relatively insensitive to variations in tem-
perature and pressure. The cyclone tech-
nology is well developed.
Secondary air requirements and performance at
high temperature and pressure should be
investigated.
Relatively insensitive to fluctuations in tea-
perature, pressure, particle size and gas
composition. Theoretical and experimental
studies are limited. Needs further study in
bed material selection and cleanup.
Sensitive to changes in temperature, pressure,
and gas composition. Needs considerable
developmental work before reliable unit can
be developed. Materials of construction,
alignment, and thermal creep of corona wires
may cause problems.
Particulate entrainment poses additional
cleanup problems. The potential for par-
ticulate removal and desulfurization may be
attractive in some applications.
Needs considerable developmental work. Casing
material, fabric life, removal of collected
material and other fabric filtration prob-
lems have to be investigated.
-------
INTRODUCTION
Concern about the world energy situation has fostered increased interest
in the utilization of coal and coal-derived fuels. Research and de-
velopment activities are underway on a variety of coal gasification and
advanced power systems. Gasification systems in early stages of com-
mercialization utilize raw fuel gas cooling followed by purification of
the gases at moderate temperatures. Many of the proposed processes now
under consideration which produce and/or utilize coal-derived fuels be-
come economically nonviable if conventional low temperature techniques
for gas cleaning have to be employed. Rather, the fuel gases must be
cleaned at high temperatures and/or high pressures. Typical examples of
these systems are:
Coal gasification processes requiring sulfur and particulate removal
at temperatures from 250 to 1250°C and pressures from 1 to 15 atm.
Gas turbine systems utilizing fuels derived from coal, residual oil-
firing, or municipal waste which may require particulate removal at
temperatures of 1000 to 1250°C and pressure of 1 atm.
Magnetohydrodynamic power systems requiring recovery of seeding mate-
rial and/or removal of ash at temperatures from 500 to 1250°C at
pressures around 1 atm.
Advantages which result from gas cleaning under high temperature and
pressure include:
The thermal efficiency of systems is higher.
* Capital costs are reduced by the elimination of gas cooling and reheat-
ing steps.
Removal of primary particulate to meet specifications for gas turbine
inlet conditions could minimize need for additional exhaust gas control
equipment.*
* Possible need for exhaust gas control measures to collect secondary par-
ticles or remove condensed gases or vapors downstream from the turbine
may obviate this potential advantage.
11
-------
The present study was undertaken for IERL-RTP to: (a) define the state
of knowledge regarding the effect of high temperature and pressure on
particulate collection and agglomeration mechanisms; (b) identify promis-
ing technology for this application; and (c) identify research and de-
velopment needs.
The following sections of this report present the results of a litera-
ture search conducted as part of the study, a discussion of the effects
of high temperature and pressure on particle collection and agglomera-
tion mechanisms, a discussion of promising particulate control systems
and a delineation of research and development needs.
12
-------
LITERATURE SEARCH
An extensive literature search was conducted as the initial stage of
this task. Various scientific abstracts, e.g., Chemical Abstracts and
selected technical journals were surveyed for publications on methods of
gas cleaning under high temperature and/or high pressures. Table 3 pre-
sents a list of abstracts and journals that were included in the survey.
The literature search revealed very little theoretical or experimental
information on high temperature and/or high pressure gas cleaning, indi-
cating a general lack of interest in this field in previous years. With
the recent interest in coal gasification and advanced power cycles, there
has been a surge of interest in this area and reports and papers are be-
ginning to appear addressing the problem. Two recent reports prepared by
Aerotherm Corporation::' and Stone and Webster Engineering Corporation!'
present brief reviews of the state of the art of gas cleaning under high
temperatures and pressures.
Since the literature contained limited information on the subject of
interest, we next elected to conduct a review of the theoretical aspects
of aerosol collection in order to determine the influence of high tem-
perature and pressure on collection and agglomeration mechanisms. The
results of the review might then be used to predict possible direction
for development of technology for particulate collection under conditions
of interest. The next section of the report discusses the review of col-
lection mechanisms.
13
-------
Table 3. MAJOR LITERATURE SOURCES REVIEWED IN TASK
Abstracts
Chemical Abstracts
Applied Science and Technology Index
Nuclear Science Abstracts
Journals
Environmental Science and Technology
Staub-Reinhalting der Luft (in English)
Aerosol Science
APCA Journal
Atmospheric Environment
Power
Filtration and Separation
Other
Mining Research Contract Reviews
Office of Coal Research Annual Reports
14
-------
THEORETICAL ANALYSIS OF EFFECT OF TEMPERATURE AND PRESSURE ON
PARTICLE COLLECTION AND AGGLOMERATION MECHANISMS
Particulate collection is effected by passing a gas stream through a
system where particles are acted on by forces which remove them from
the gas stream. To be effective, these forces must be sufficiently
large to take the particles out of gas stream during its residence time
in the system. If the particulates in the gas stream are submicrometer
in size, their removal may be facilitated by agglomerating very small
particles and then collecting the agglomerates.
The basic mechanisms or forces that can be used to collect or agglomer-
ate particles are shown in Table 4. A considerable amount of informa-
tion exists in the technical literature on each of these mechanisms and
3 4 41 42/
how they depend upon various parameters.—2—>—*— The effectiveness of
individual mechanisms is dependent upon various properties of the par-
ticles, gas properties, and temperature and flow fields in the system.
High temperatures and pressures primarily influence gas properties such
as density and viscosity. Since these gas properties in turn influence
particulate collection mechanisms, high temperatures and pressures will
exert some impact on particulate collection. In the following subsec-
tions, the changes in gas properties caused by high temperature and pres-
sure are highlighted and the influence in changes in gas properties on
particle collection mechanisms are delineated.
INFLUENCE OF HIGH TEMPERATURE AND PRESSURE ON GAS PROPERTIES
The main gas properties which are important in particulate collection
and which are also influenced by temperature and pressure are density,
viscosity, and mean free path of the gas molecules. Each of these
properties and their dependence on temperature and pressure are dis-
cussed next.
15
-------
Table 4. PARTICLE COLLECTION OR AGGLOMERATION
FORCES (MECHANISMS)
I. Particle collection
A. Aerodynamic capture
1. Inertial impaction
2. Interception
3. Diffusion
4. Electrostatic attraction
5. Gravitational settling
B. Centrifugal forces
C. Flux forces
1. Electrostatic forces
2. Thermal forces
3. Diffusion forces
4. Magnetic forces
II. Agglomeration and/or particle growth
A. Thermal or Brownian agglomeration
B. Turbulent agglomeration
C. Electrostatic agglomeration
D. Sonic agglomeration
E. Condensation
16
-------
Gas Density
The density of a gas at normal temperatures and pressures can be cal-
culated using the ideal gas law,
- = RT (1)
P
where P = absolute pressure
p = gas density
R = gas constant
T = absolute temperature
Under very high temperatures and pressures, real gases deviate from this
law. Accurate calculation of gas properties can be made using the charts
provided in Appendix A. For air at pressures below 40 atm and 1800°K,
only a very small error is incurred in calculating the gas density by
using Eq. (1).
Equation (1) can be written as:
where p , P and T represent base conditions (i.e., 300°K and
1 atm).
Table 5 shows how the quantity P/PO for air varies with the tempera-
ture and pressure. For example, the density of air at 1300°K tempera-
ture and 10 atm pressure is 2.3 times that at room temperature and
pressure (base condition).
Gas Viscosity
The viscosity of gases increases as the 0.6 power of the absolute tem-
perature but is very weakly dependent on pressure. For air at pressures
less than 20 atm and at temperatures greater than 300°K, dependence of
viscosity on pressure can be safely neglected. The charts in Appendix
A provide a means of calculating the gas viscosity at various pressures
and temperatures. Table 6 gives the values of u/u0 for different tem-
peratures. We see from the charts and Table 6 that the viscosity of air
at 1300°K and 10 atm is 2.6 times that at 300°K temperature and 1 atm
pressure.
17
-------
Table 5. VARIATION OF GAS DENSITY WITH TEMPERATURE AND PRESSURE
(density of air/density of air at 300°K and 1 atm)
Temperature
(°K) 1 atm 4 atm 7 atm 10 atm 40 atm
300 1.0000 4.0035 7.0127 10.025 40.343
500 0.5996 2.3961 4.1892 5.978 23.650
700 0.4283 1.7112 2.9912 4.268 16.875
1000 0.2998 1.1981 2.0946 2.990 11.840
1300 0.2306 0.9218 1.6118 2.30 9.128
2000 0.1666 0.6659 1.1646 1.662 6.610
Table 6. VARIATION OF GAS VISCOSITY WITH TEMPERATURE AND PRESSURE
(absolute viscosity of air/absolute viscosity of air at 300°K
and 1-10 atm pressure)
Temperature
300 1.83 x 10"4 1
500 2.646 x 10-4 1.4461
700 3.303 x 10'4 1.8048
1000 4.116 x 10"4 2.2491
1300 4.803 x 10~4 2.6245
2000 5.777 x 10"4 3.1571
18
-------
Mean Free Path
The mean free path of gas molecules is related to the viscosity and the
density of gas as shown in Eq. (3).
X = u/0.499 p c (3)
where \ = mean free path of the gas molecules
u = viscosity of the gas
p = density of gas
c~ = mean thermal speed of gas molecules
The mean thermal speed of gas molecules is given by
' \
8K/M 1/2
where K = the Boltzman constant
M = molecular weight of the gas
Examination of Eqs. (3) and (4) indicates that the mean free path of
air molecules is almost inversely proportional to the gas density. At
10 atm pressure and 1300°K temperature, mean free path of air molecules
is 0.53 (about half) that at 1 atm pressure and 300°K temperature.
PARTICLE COLLECTION
The gas properties discussed in the preceding paragraphs form a part of
several parameters which characterize the effectiveness of various par-
ticulate collection and agglomeration mechanisms (e.g., impaction param-
eter, interception parameter, Reynolds number). The impact of changes
in gas properties on these parameters, and thus on particulate collec-
tion, is discussed in the next sections.
Aerodynamic Capture
Aerodynamic capture of particles involves the collection of particles
by collecting bodies (e.g., fibers, packing, droplets, etc.). In order
to utilize aerodynamic capture, the gas stream is brought near the col-
lecting bodies and then a number of short-range mechanisms accomplish
the actual collection. The most effective mechanisms are: inertial
19
-------
impaction, interception, diffusion, and electrostatic attraction. The
relative importance of each mechanism varies with the size and velocity
of the particles and the size of the collecting body.
Inertial impaction - The effectiveness of inertial impaction is a func-
tion of Stokes number which arises out of the force balance equation of
fluid resistance opposing the motion of particles. The Stokes number
is defined as:
STK -
9 u Dc
where C = Cunningham slip correction factor
pp = particle density
u = fluid viscosity
Dp = particle diameter
Dc = diameter of the collecting body
VQ = particle velocity upstream
The fluid viscosity, u , and the Cunningham correction factor both are
temperature and pressure dependent.
The Cunningham correction factor, C , is given by:
c = l + IX j-1%246 + 0.42 exp(-0.87 Dp/2\)] (6)
where the mean free path of gas molecules, \ , is calculated using
Bq. (3). The variation of the Cunningham slip correction factor with
temperature and pressure is shown in Figure 1. The slip correction
factor increases with temperature and decreases with pressure, and this
factor becomes increasingly significant for very fine particles at low
pressures. For coarser particles and/or for higher pressures the
Cunningham factor approaches unity and its variation with temperature
and pressure is insignificant.
20
-------
1000
u
z
o
o;
O
0.001
0.01
C=
Kn (A+Q
Kn =2X/D
A = 1.246
Q = 0.42
b = 0.87
X = X0(/i/M0)(TAo)1/2(P
-------
Examination of Tables 5 and 6 and Figure 1 shows that high temperature
and pressure reduce the impaction efficiency by decreasing the ratio
C/u in Eq. (5). The variation of impaction efficiency with temperature
and pressure for 5 and 1 um particles of density 2 in air is shown in
Figure 2 for a typical case of particles moving past a 10 um diameter
fiber at 25 cm/sec. Figure 2 was developed using the experimental cor-
relation of Wong and Johnstone for the relation between Stokes number
and impaction efficiency.^' Figure 2 shows that the influence of pres-
sure on impaction efficiency is much less for 5 um particles than for
1 um particles and that impaction efficiency generally decreases with
increasing temperatures. Compensation for this reduction in efficiency
can be accomplished by increasing the gas velocity or decreasing the
collector body diameter.
Interception - Whenever the streamline, along which a particle approaches
a collecting body, passes within a distance of one-half the particle diam-
eter from the body, interception of the particle by the collecting body
will occur. This mechanism never occurs alone except as a limiting case
for particles of low density. However, it should be taken into account
as a boundary condition to be met along with other aerodynamic capture
mechanisms.
The dimensionless parameter that describes this mechanism is the ratio:
Ri = VDC (7)
where D = particle diameter
Dc = collector body diameter
This parameter is not influenced by changes in external conditions and
thus will not vary with temperature and pressure. RanaZ' has shown that
if the particles follow the gas streamlines, the efficiency of intercep-
tion of a cylindrical target is given by:
7| = A
2(1 + Ri) ln(l + Ri) (8)
where A =
2(2.002 - In Re)
The temperature and pressure dependent term in this efficiency equation
is Re , the Reynolds number, pv D /u . With increasing pressure, the
Reynolds number increases due to increase in gas density whereas with
increasing temperature, it decreases due to the increase in gas viscosity
and a decrease in gas density.
22
-------
100.Or-
10.0
U
z
UJ
U
z
o
U
a.
5
1.0
0.1
Particle Diameter
1 ATM
10 ATM
\
^ \— ] fj.m Particle Diameter
\
300
500
700
1300
1500
1700
900 1100
TEMPERATURE, "K
Figure 2. The Effect of Temperature and Pressure on the Calculated Efficiency
of Inertial Impaction (particles moving past a 10 urn diameter
cylindrical fiber with stream velocity of 25 cm/sec).
23
-------
Thus, particle collection by interception may increase or decrease de-
pending on the gas temperature and pressure, but this variation is inde-
pendent of particle size.
Diffusion collection - Very small particles, because of their Brownian
motion, do not follow streamlines, but have zig-zag movement around
their mean path. This motion can lead to deposition of particles from
gas streams close to the collecting body, but it is only of significance
for particles smaller than 0.5 urn in diameter. Since Browian motion be-
comes more pronounced with decreasing particle size, diffusion collection
also becomes more significant.
The characteristic parameter for the diffusion process is the Peclet
number, which is defined as:
where VQ = freestream particle velocity
D* = particle diffusion coefficient
Dc = collector body diameter
The diffusivity can be calculated from Eq. (10)
D* = KTC (10)
3fTuDp
where K = Boltzmann constant
T - absolute temperature
C = Cunningham slip correction factor
Dp = particle diameter
Combining Eqs. (9) and (10) one obtains:
- 3rniDPDcvo
Pe KTC (11>
24
-------
Based on an analogy between heat and mass transfer, Ranz-t' gives the fol-
lowing expression for the efficiency of particle collection by diffusion:
i D !/6
•n = — + 1.727 —o/o (12)
xe *^
The temperature and pressure dependent terms in Eq. (12) are the Peclet
number (Pe) and the Reynolds number (Re) which involve the parameters
C , u , and p .
The collection efficiencies of a single fiber based on Eq. (12) have
been calculated for particles moving past a 10 urn fiber at 25 cm/sec and
are plotted in Figure 3. These calculations show that for small parti-
cles which are primarily collected by diffusion, collection efficiency
increases with increasing temperature but decreases with increasing
pressure. As the particle size increases, the collection efficiency
by diffusion and its dependence on temperature and pressure decreases.
Since in most cases the relative changes in efficiency with pressure
are much greater than those with temperature, collection by diffusion
will also tend to decrease at high temperatures and pressures.
Electrostatic attraction - When an aerosol particle, or a stationary
object in a flow stream is electrically charged, or when both the parti-
cle and the object carry electric charges, the trajectories of the
aerosol particle past the object are affected. This usually results
in an increase in the number of particles colliding with the object.
Ranz and Wong£' and Kraemer and Johnstone^-' defined the dimensionless
force ratios given by Eqs. (13) and (14) to characterize the forces be-
tween an aerosol particle in the absence of a field across a filter.
- (13)
2 /eD-ef
v — _ I " •*• 1 J- -•
1 " 3 \eP+2V «o^vp-cDC
where gp and e.£ are dielectric constants of the particle and the gas,
respectively, qp is the electrostatic charge on the particle, and qf
is the electrostatic charge on the particle per unit area. The term eo
is the permittivity of free space and u is viscosity of the air. Equa-
tion (13) describes the interaction of a charged particle and collector,
and Eq. (14) describes the interaction between a charged collector and a
dielectric particle on which the collector induces a charge.
25
-------
100.0
• 1 ATM
10 ATM
z
o
CO
UJ
ij
-O.Ol^im Particle Diameter
10.0
Z
O
(—
u
O
u
1.0
-O.l^tm Particle Diameter
0.1 -
0.05
300
Figure 3.
1.0/im Particle Diameter
I
I
I
500 700 900 1100
TEMPERATURE, "K
1300
1500
1700
Effect of Temperature and Pressure Changes on
Collection Efficiency by Diffusion.
26
-------
Parameters KE and Kj may be considered ratios of the electric force
at the surface of the collector to the fluid resistance caused by a rela-
tive particle velocity of v with respect to the collector. It is
noted that when qp and qf are of the same sign, KE is positive and
collection efficiency decreases. Target efficiency by these mechanisms
is negligible when the corresponding parameter is much less than 10~2
and is of the order of unity when the parameter is of the order of unity.
Kramer and JohnstoneZ' suggest that target efficiencies can be calculated
for induced electrostatic attraction by:
and for charge particles and collector electrostatic attraction by:
11 « - n KE (16)
based upon experimental data for a cylindrical collector.
The temperature and pressure dependency of the target efficiences in Eqs.
(15) and (16) can be seen from Eqs. (13) and (14) to be the parameter
C/u . Since the Cunningham correction factor, C , depends also upon the
particle size, the factor C/u depends upon temperature, pressure and
particle size. Using Figure 1 and Table 6, ratios of C/u/(C/u)o were
calculated and plotted in Figures 4 and 5. The subscript zero refers to
the ambient condition (i.e., 300°K temperature and 1 atm pressure). Cal-
culated target efficiences for particles with diameters of 1.0 to 0.01
urn at elevated temperatures and pressures are shown in Figures 6A and 6B.
Values of 0.1 were assumed for both KE and Kj .U Examination of Fig-
ures 4, 5, 6A and 6B and Eqs. (13), (14), (15) and (16) shows that under
conditions of both high temperature and pressure the effectiveness of
electrostatic attraction is reduced for particles above 0.01 urn diameter.
Gravitational settling - Individual particles have a certain sedimentation
velocity due to gravity* As a consequence of this, the trajectory of the
particles deviates from the streamlines of the gas and particles may touch
the collection surfaces and be removed.
The intensity of gravitational deposition is described by the gravitational
parameter, G , which is:
G = Is (17)
vo
where vs is the settling velocity of the particle in the fluid. The set-
tling velocity is determined from:
27
-------
300
500
900 1100 1300 1500 1700
TEMPERATURE,°K
Figure 4. Variation of Ratio C/u with Temperature, Pressure
and Particle Diameter.
28
-------
2.6
T = 1800°K
2.4
2.2
2.0
1.8
1.6
J? 1.4
1.0
0.8
0.6
0.4
0.2
1 ATM
10 ATM
-1800
-1300,
-1000-
--500-^ Z---'
300
l i i i i l I 11 l i
0.001
0.01
0.1 1.0
PARTICLE DIAMETER, ^m
10.0
100.0
Figure 5. Variation of Ratio C/ji with Particle Diameter,
Pressure, and Temperature.
29
-------
100
u
c
0)
U-l
4-1
w
10
O.Olitm Particle Diameter-
Pressure
lOAtm ~*~"-
Coulombic Attraction Parameter, Kg = 0.1
l I I I I I I
1.0 ftm Particle Diameter
A. Effect of Temperature and Pressure on Target Efficiency Due to
Coulombic Attraction.
100
O
c
W
I I I I
0.01 p.m Particle Diameter-
1.0 /xm Particle Diameter _
Pressure
10
300
1 Atm
10 Atm
Image Force Parameter, K| = 0.1
I I I | I I I
I I
500 700 900 1100
TEMPERATURE, K
1300
1500
1700
E. Effect of Temperature and Pressure on Target Efficiency Due to
Image Forces.
Figure 6. Effect of Temperature and Pressure on Target Efficiencies Due to
Electrical Forces for 0.01 and 1.0 um Particle Diameters.
30
-------
vs = — ^ - I- g Dp (18)
18 u
For gases, since P is negligible compared to p , and since only
large particles are removed with this mechanism for which C is close
to unity, gravitational settling is primarily influenced by temperature.
The ratio of settling velocity, vs at a given temperature and pressure
to the settling velocity, VQ at ambient conditions is very nearly equal
to the ratio (C/u)/(C/u) so, Figures 4 and 5 can be used to estimate
impact of temperature and pressure on settling velocity. The settling
velocity of large particles is little effected by pressure and decreases
with increasing temperature.
Centrifugal Forces
Particulate matter is separated from gas in a cyclone by centrifugal
force, or radial force, tending to drive the particles (against the
resistance of motion by the gas) to the cyclone wall. The radial force
imparted to the particle is:
6 • g • r
where Fs - radial separating force
Pp - particle density
p = gas density
Dp = particle diameter
g = gravitational constant
r - radius of rotation
vtp = tangential velocity of particle
The force resisting the particle is given by Stokes1 Law:
(20)
31
-------
where Fr = frictional resistance to flow
p = gas viscosity
v = particle velocity with respect to gas
* O
C = Cunningham correction factor
The ratio of the separating force to the resisting force:
(Pp - P) DpvtpC
Fs/Fr = —= (21)
18 u gr vp_g
provides an indication of the relative ability to remove various size
particles in a cyclone.
Since p is negligible compared to p even at very high pressures,
the temperature and pressure dependent factor in this force ratio is
C/u . The variation of C/u with temperature and pressure for various
particle sizes is shown in Figures 4 and 5 and all the comments made in
connection with inertial impaction or gravitational settling apply.
Flux Forces
Particles can be collected by forces which result from electrical, tem-
perature and concentration gradients, from a magnetic field and from
flux of matter or energy. This group of forces are especially attrac-
tive for the collection of fine particles because the magnitude of the
flux forces does not approach zero as the size of the particles to be
collected approaches the submicrometer range. Individual flux forces
are discussed in the following sections.
Electrical forces (electrophoresis) - If charged particles are subjected
to an unidirectional electric field, they move towards the electrodes
and are deposited. The motion or migration of the particles in the field
is termed electrophoresis. In the absence of turbulence or other aero-
dynamic effects, the migration velocity, ve resulting from the electro-
static force can be obtained from Stokes1 Law and is given by:
32
-------
<22>
where qp = charge on the particle
E = strength of electric field
This expression neglects second order electrostatic effects such as polar-
izability of the particle, and assumes a spherical particle is moving in
laminar flow (Re < 1). Both of these assumptions are normally adequate.—
It is clear from Eq. (22) that temperature and pressure influences migra-
tion velocity through the variables C , u , and qp . For a given parti-
cle size, electric field strength and electric charge on the particles,
the factor ve/ve is a function only of (C/u)/(C/u) I
The charge on the particle qp can be predicted using the equations de-
veloped for two idealized charging conditions, viz, the diffusion charg-
ing and the field charging. In diffusion charging, a suspended aerosol
particle in an ionized gas acquires a charge by virtue of the random
thermal motion of the ions and their consequent collision with and at-
tachment to the particle.
According to White,—' the charge on the particle is given by:
In
n 2e
where K = Boltzmann constant
T = absolute temperature
c" = mean thermal speed of air molecules
e - elementary unit of charge
N = ion concentration
t = exposure time
In field charging, the particles are charged by the bombardment of ions
moving under the influence of the applied electric field. Assuming the
motion of the ions to be confined along the electric line of force,
White has derived the following field charging equation:^/
33
-------
2
EDr
q= (1 + 2 T^ -* I^^TTTl (24)
I" rrNezjt "I
LrrNezJTTT J
where ep = dielectric constant
z^ = ion mobility
E = field strength
Equations (23) and (24) suggest that the charging of particles by dif-
fusion charging and field charging is favored by high temperature. The
effect of pressure is negligible in both the mechanisms.
Analysis of Figures 4 and 5 in conjunction with Eqs. (22), (23), and
(24) indicates that the dependence of migration velocity on temperature
and pressure is quite complex. The particle size of the aerosol has a
strong influence on the impact by increase in temperature and pressure —
especially in the 0.1 to 1.0 urn diameter range. Figure 7 presents an
illustration of the effect of temperature on the calculated migration
velocity.
Thermal forces (thermophoresis) - Particles can be removed from a gas
stream by the use of a temperature gradient. The force which causes
particle motion results from momentum differences imparted to the parti-
cle on opposite sides. The hotter (and thus faster) molecules colliding
with the particle will impart a higher momentum to the particle than the
cooler (slower) molecules. Aerosol particles will then drift in the
thermal gradient toward the cold surface. The motion of aerosol parti-
cles associated with a temperature gradient is called thermophoresis.
The theory of thermophoresis of aerosol particles was recently reviewed
by Derjaguin and Yalamovi2' who showed that thermal forces, like other
interactions between gas molecules, and particles, depend on the Knudsen
number, K , where
where \ = mean free path of gas molecules
rp = particle radius
For very small particles (i.e., large Knudsen numbers) the authors have
developed Eq. (25) for calculating the drift velocity due to thermo-
phoretic force:
34
-------
E
u
U
O
> 4 -
400
800
TEMPERATURE, °C
1200
1600
Figure 7. The Effect of Temperature on the Relative Migration Velocity
of 1 Micron Diameter, 0.1 Micron Diameter, and 0.01 Micron Diameter
Particles in Air for an Electrostatic Precipitator Where the
Migration Velocity of a 1 Micron Diameter Particle at
Ambient Conditions is 10 cm/sec.
35
-------
VT« - 0.37 \/T c (grad T) (25)
where grad T = dT/dx
<: = mean thermal speed of gas molecules
For large Knudsen numbers, the drift velocity is independent of the
particle size and inversely proportional to the square root of tempera-
ture and to the first power of the pressure. Thus, the thermophoretic
velocity would be expected to decrease with increases in either tempera-
ture or pressure.
For moderately large particles (0.01 £ ^ £ 0.1), Brock has developed
the following express ion :JLi'
3u [k /k + c • K! grad T
VT - - - p-2 +— ^ (26)
pT [l + 2kg/kp + Ct Kn| [l + CmKn|
where kg/kp is the ratio of thermal conductivity of the gas to that
of the particle, C^ and C^ are constants and are associated with the
temperature jump and the velocity slip at the particle surface. Brock
suggests that Ct ranges from 1.875 to 2.48 and Cm from 1.0 to 1.27.
Thus, this equation shows that the thermophoretic velocity of moderately
large particles is slightly dependent on particle size and is inversely
proportional to the pressure and directly proportional to iP-6 .
For large particles (K^ > o) Eq. (26) reduces to:
grad T (27)
The temperature and pressure dependence for this case is the same as that
for Eq. (26). Figure 8 illustrates predicted effect of temperature on
thermophoretic velocity of carbon particles in a unit thermal gradient.
Diffusion forces (diffusiophoresis) - In a concentration gradient, which
is accompanied by diffusion but not necessarily by net motion of the gas
phase, the heavier molecules will impart a higher momentum than the
lighter molecules. If there is a net motion of the gas phase (Stefan
flow), additional force is applied to the particles. The combination
of forces due to Stefan flow and the concentration gradient is referred
to as the diffusiophoretic force. Particle movement by this force is
called diffusiophoresis.
36
-------
o
X
I
•8
E
o
10
6
4
1
0.6
0.4
0.2
0.10
0.06
0.04
0.02
400 800 1200
TEMPERATURE, °C
O.l/i
0.01/A
1600
Figure 8. The Effect of Temperature on the Thermophoretic Velocity
of Carbon Particles with Unit Thermal Gradient.
37
-------
Several theoretical models of diffusiophoresis have been developed.
Derjaguin and YalamovJ^' provide a theory for diffusiophoretic force
acting on spheres in the range from free molecule (large 1C ) to con-
tinum ( Kn ^ o ) behavior. The analysis of these investigators
substantially differs from the analysis of Hidy and Brock.—' For
binary gas mixtures, in the case of equimolar counter diffusion and
small particles:
n
rr/8)d0[n1
(28)
grad
where
and
m2
masses of the molecules of the first and second
components of the mixture
n, and n« = concentration of gas molecules
d , d-, and d2 = coefficients in the expansion of the Boltzmann
kinetic equation
D^2 = mutual diffusion coefficients for two components
For large particles, Eq. (29) is applicable.
grad
(29)
where
n
Po = Pi + P2
Cl = nl/n
Equations (28) and (29) show that the diffusiophoretic velocity is a
function of density and the diffusion coefficient. Therefore, the exact
dependence of the diffusiophoretic velocity on increases in temperature
and pressure will depend upon particle size and the relative changes in
temperature, pressure, and the ratio C/u .
38
-------
Magnetic forces - A force (Lorentz force) is generated when an electri-
cal charge or an electrically charged particle moves in a magnetic field
transverse to the field lines. If a dust particle carrying "n" ele-
mentary charges "e" moves with a speed v , the direction of the force
will be at right angles to both the direction of the field and the direc-
tion of motion of the particles so that the particles will be diverted
from its original path. As a result of the change in direction of the
particle, the possibility of particle precipitation exists.
The potential for particle precipitation using the Lorentz force can be
assessed by determining the terminal drift velocity of a particle in a
magnetic field. The terminal velocity can be obtained by equating the
Lorentz force to the resistance of the gas, calculated from the Stokes-
Cunningham Law:
nevB (30)
LI
where n = number of charges on particle
e = elementary charge
v = velocity of particle in field
B = magnetic field strength
u - gas viscosity
Dp - particle diameter
vm «= terminal drift velocity of particle
C = Cunningham factor
The left-hand term in Eq. (30) represents the Lorentz force and the
right-hand term is the gas resistance. Equation (30) can be rearranged
to yield the following expression for the terminal drift velocity:
CnqvB
Equation (31) indicates that terminal drift velocity due to Lorentz
forces is effected by temperature and pressure primarily through the
factor C/u .
39
-------
PARTICLE AGGLOMERATION AND/OR PARTICLE GROWTH
Submicrometer particles can grow to larger, i.e., micrometer-sized par-
ticles by agglomeration and condensation. Therefore, it may be possible
to utilize devices which cause particle agglomeration or growth in con-
junction with conventional control systems to collect fine particles.
Thermal Agglomeration
A variety of forces may cause particles to come in contact with each
other and agglomerate. If agglomeration is strictly as a result of
Brownian motion (diffusion) it is termed thermal agglomeration.
The basic equation of change with time of the size distribution of an
aerosol due to thermal coagulation is given by:—'
/v
K(v-v, v) n(v-v,t) n(v\t) dn
° (32)
/• °°
/ K(v,v) n(v,t) n(v",t) rfv
0
where n(v,t)dv is the number concentration of aerosol at time t whose
volume lies between v and dv and K(v,v) is the coagulation coef-
ficient between the particles of volume v and particles of volume v .
Equation (32) is a partial intergo-differential equation for which there
does not exist an analytical solution.
For the simple case of a narrow size distribution aerosol in which the
coagulation coefficient K can be considered constant, Smoluchowski
gives the rate of particle agglomeration as:^'
~ = - KoN2 (33)
where N = total number of particles per cubic centimeter
K0 = 4TTDrp
D = diffusion coefficient
rp = particle mean radius
40
-------
The diffusion coefficient D* can be calculated using Eq. (10)
Thus, the rate of agglomeration, as a function of diffusivity D* , is
affected by both temperature and pressure. The variation can be seen
to depend upon the factor C/u whose variation with temperature and
pressure was discussed earlier.
Turbulent Agglomeration
Turbulence increases the relative velocities among particultes which in
turn increases the chance of particulate collision. Theoretical studies
on the coagulation of aerosols in turbulent flow have been conducted by
Levich,!3./ East and Marshall,M/ Tunitskii ,il/ Obukhov and
and '
Levich discusses agglomeration effected by fluctuations having a scale
of the same order as the particle size, which is appreciably less than
the internal scale of turbulence, \Q . Levich derived the following
equation for the coagulation rate:
* = 32TrrpV0 « 25 (-) 1/2 rp*n0 (34)
where p - coagulation constant
Y = kinematic viscosity
s = rate of dissipation of turbulent energy per gram of medium
Beal has studied the case where the sink particle is larger than the
turbulent microscale (rp > \o) and has derived the following
equation for the collision rate per unit area of sink particle :.I2/
where
(35)
-3 V Y /
1/4
For the case described by Eq. (34), the temperature and pressure in-
fluence on the coagulation rate results from their influence on the
kinematic viscosity, u/p . Thus
41
-------
1/2
and since p „_ £ and u ~ T°-6
(36)
TO. 8
«
As a result, increasing the pressure will increase the coagulation rate
while increasing the temperature will decrease the rate.
In the situation where Eq. (35) is applicable, temperature and pressure
influence X0 and y • ^e dependence of the coagulation rate on tem-
perature and pressure is given by:
1/4
p0.25
In this case, the coagulation rate increases with increasing temperature
and decreasing pressure.
Agglomeration of Charged Particles
One method of increasing the rate of agglomeration of fine particulates
is to add a bipolar charge, either with or without an externally imposed
field. With proper conditions large electrostatic forces between par-
ticulates can produce a large increase in the rate of agglomeration of
submicron particulates.
Fuchsx/ and Zebeli^' have derived the following equation for the rate
of agglomeration for charged particles:
un __ * ... o /oo\
~ dt kemKon V*>
where K = agglomeration coefficient in the absence of charge
kem = correction factor to allow for both particle charge and
particle mean free path
42
-------
The correction factor, kem is given by:
Nq
6m eNq-l
ipi
-------
Tl/2
Thus, Ka ~ Y/o and the rate of acoustic agglomeration will increase
with temperature and decrease with pressure.
44
-------
POTENTIAL PARTICULATE REMOVAL SYSTEMS FOR HIGH
TEMPERATURE AND PRESSURE APPLICATIONS
The preceding theoretical analysis indicated that centrifugal forces,
aerodynamic capture, and electrostatic forces are promising avenues for
collection of particles under high temperature and pressure conditions.
Since cooling of the gas stream is not considered a viable approach in
this study, scrubbing systems using water are not suitable. Cyclones,
electrostatic precipitators, and special types of filter systems (e.g.,
gravel beds, metallic fibers) and scrubbers which do not cool the gas
stream (i.e., molten salt) are likely systems for use in these applica-
tions. Available information on the performance of these systems is
presented next.
CYCLONES
Cyclones are generally good for removing large particles (> 5 urn), al-
though some of the multiple-tube parallel units attain up to 90% ef-
ficiencies on particles of 3 urn diameter. Cyclones are commonly used
as precleaners for a more efficient collector such as an electrostatic
precipitator, wet scrubber or a fabric filter. In high temperature and
pressure applications, cyclones are being used to remove large particu-
lates in gases from a variety of gas streams and as precleaners for
gravel bed filters.
Cyclones vary widely in physical size, flow capacity, and pressure drop.
To permit comparison between different cyclones, the dimensions of the
cyclone are specified by diameter, D , and seven dimensions ratios
a/D , b/D , De/D , S/D , h/D , and B/D (see Figure 9). A number
of cyclone "standard designs" or sets of dimension ratios have been
suggested in the literature. Several are listed in Table 7. No single
cyclone design will perform best for all dust collection problems.
The theoretical prediction of cyclone pressure drop and collection ef-
ficiency is still not possible because of complexities of flow fields.
Based on simplifying assumptions of the flow fields and on experimental
correlations, a number of equations have been developed for pressure
45
-------
Figure 9. Cyclone with Typical Design Parameters.
46
-------
Table 7. CYCLONE STANDARD DESIGNS
Recommended duty
High efficiency
High efficiency
General purpose
General purpose
High throughput^'
High throughput
D a/D
1 0.5
1 0.44
1 0.5
1 0.5
1 0.75
1 0.8
b/D
0.2
0.21
0.25
0.25
0.375
0.35
De/D
0.5
0.4
0.5
0.5
0.75
0.75
S/D
0.5
0.5
0.625
0.6
0.875
0.85
h/D
1.5
1.4
2.0
1.75
1.5
1.7
H/D
4.0
3.9
4.0
3.75
4.0
3.7
B/D
0.375
0.4
0.25
0.4
0.375
0.4
a/ Scroll type gas entry used.
-------
drop and collection efficiency. However, current design practice empha-
sizes past experience rather than an analytical design procedure. Re-
cently Leith and Mahtaft3/ have evaluated five pressure drop theories and
four efficiency theories against experimental data taken from the litera-
ture. The following equations are considered to be simple and to best
fit the experimental data.
20 21/
(a) Shepherd and Lapple pressure drop equation: ? . '
(42)
where AP = pressure drop in length units of liquid with density PJ
p = gas density
o
a, b, D = are defined in Figure 9
K = 16 for a cyclone with standard tangetial inlet and 7.5 for
a cyclone with an inlet vane, i.e., where the inner wall
of the tangential entry extends past the cyclone inner
wall to a point halfway to the opposite wall
(b) Leith and Licht efficiency equation: —
n = 1 - exp [-2[G(stk/2)]1/(2n + 2>] (43)
where G is a function of the cyclone's dimension ratios only:
ab
h/D - [ J£_ ) * - s/D
= 2.3 ^ KD2/ab)J
where 4/D = 2.3 — (Wab)r/J (45)
D - (D-B) [(S + H - h)/(H - h)l
d/D = =• (46)
D
Here, & is the farthest distance the vortex extends below the gas exit
?*?/
duct as given by Alexander,—' and d is the diameter of the conical
section at that point. The parameter stk is a modified Stokes number,
reflecting the nature of the gas/particle system to be treated:
48
-------
C p D2 v
P P S
- (n + !)
9 p Dc
where C = Cunningham slip correction factor
Pp = particle density
Dp = particle diameter
u - gas viscosity
Vg = gas velocity
The value of the vortex exponent, n , can be calculated from Eq. (48)
where D = cyclone diameter in centimeters
T = absolute temperature in degree Kelvin
The equations given above for pressure drop and collection efficiency
predict numbers close to the experimental data. However, the equations
do not take into account all the factors known to influence cyclone per-
formance. Furthermore, since the experimental data with which these
equations (in fact, all the cyclone theories) are correlated are taken
at ambient conditions, it is not known whether these equations apply
satisfactorily under high temperatures and high pressures.
Experimental data on the performance of cyclones at high temperatures
and pressures are meager. Yellott and Broadley, working with the Loco-
motive Development Committee Program, have experimentally evaluated
several different cyclones.—' Data on the pressure drop and effici-
ency as a function of temperature and gas throughput at ambient pres-
sure are shown in Figure 10. No fractional efficiency data were obtained.
As expected, the mass efficiency of cyclones decreases with temperature.
Current Cyclone Research and Development
Babcock and Wilcox is in the process of developing a proprietary par-
ticulate collection system which may be regarded as an extension of
cyclone collector art. The system has been tested on a paraffin
49
-------
100
Z 90
LU
(3
80
3"AP
I
I
200 400 600 800
TEMPERATURE, °F
1000
1200
1400
100 r-
100 r-
A. Effect of Temperature on Efficiency
•vO
&•*
U
5 90
y
u_ .
u_
LU
80
(
„ ° 0 ._,.. 75 Or 0" AD
o
_L ° e ir\r>AOr O " A p
1 1 | 1 I 1 1 1 1 I I
) 1 2345
|
6
DUST LOADING, GRAINS PER CU. FT.
B. Effect of Loading on Efficiency
02 — ^o
?-
u
5 90
y
u_
u_
LLJ
80
C
0 0.— — — "~° 1000°F
*~
i i i i i i i i i i
) 2 4 6 8 10
I
12
PRESSURE DROP, INCHES OF WATER
C. Effect of Pressure Drop on Efficiency
Figure 10. Efficiency Test Results of Aerotec Separators.
50
247
-------
hydrocarbon mist at ambient temperature with encouraging initial results
on a large laboratory model. Babcock and Wilcox has proposed that this
concept be utilized as an option in a hot fuel gas clean-up system ex-
perimental evaluation. Further tests on fly ash are required to demon-
strate the principle.
Westinghouse has tested an Aerodyne Tornado Cyclone (Figure 11) which
employs the interaction of two counter current high velocities to in-
crease the collection efficiency for the fine particles. Laboratory
data suggests that the design is capable of removing 1 urn particles with
80 to 90% efficiency, which is a significant improvement over the con-
ventional cyclones. Reliable field test data on this system are not
available.
Energy requirements of the secondary flow are also not known. Combus-
tion Power Company studied the use of Aerodyne Cyclones for the CPU-400
system and concluded that secondary air flow requirements would result
in higher power cycle loss penalties than the pressure drops from con-
ventional cyclones with similar cleaning efficiencies.
Donaldson Company, Inc., has recently developed a Tan-Jet cyclone system
(Figure 12) for high temperature and pressure work. The company claims
that the system is significantly more efficient than conventional cyclones
in collecting the particles in the < 5 urn diameter range. However, it
should be noted that in this case too, secondary air power requirements
were not thoroughly investigated.
GRANULAR BED FILTERS
Granular bed filters are a promising technique for high temperature and
pressure gas cleaning. Its attractiveness is enhanced by the possibility
of a single device being capable of removing both particulate matter and
sulfur. In the past, granular beds have found practical application in
atomic energy facilities and the filtering of small volume gas streams.
Their application to industrial sources of particulate pollution has been
limited--especially in the United States. Most recently, granular beds
hav- received increased attention and a number of research projects are
underway to develop these systems.
State of the Art
The gravel bed filter often uses sand, gravel, coke or sintered mate-
rial as the filtering media. Several designs are reported in the techni-
cal literature and they fall into one of three categories depending upon
the movement of the bed material. In the crossflow shaft-falling solid
51
-------
EXHAUST (CLEAN GAS)
SECONDARY
GAS INLET
PRIMARY GAS
DUST INLET
SECONDARY AIR PRESSURE
MAINTAINS HIGH
CENTRIFUGAL ACTION
SECONDARY AIR FLOW
CREATES DOWNWARD SPIRAL
OF DUST AND PROTECTS
OUTER WALLS FROM ABRASION
DUST IS SEPARATED FROM
GAS BY CENTRIFUGAL FORCE,
IS THROWN TOWARD OUTER WALL
AND INTO DOWNWARD SPIRAL
STATIONARY SPINNER
SEPARATED DUST IS DEPOSITED
IN HOPPER
CLEAN GAS
SECONDARY GAS
DUST
Figure 11. Aerodyne Tornado Cyclone.
52
-------
PRIMARY
BLOWER
SECONDARY T 7"
BLOWER [_\°..
DUST
LADEN
GAS
CLEANED
GAS
DISCHARGE
Figure 12. Donaldson Company Tan-Jet System.
53
-------
design, the collecting particles continuously fall through a shaft while
the gas flows across the shaft. This group includes the Dorfan Impingo
filter, the Consolidation Coal Company filter, the Carnegie-Mellon cross-
flow filter, and the Combustion Power Company dry scrubber.
In the intermittent moving-bed type of design, a fixed bed held between
vertical panels moves intermittently. The original Squires panel bed
filter is representative of this type.—
In the fixed-bed granular filter, the bed material is not moved or re-
placed. Rejuvenation of the bed material is achieved by a back flow of
clean gas or mechanical shaking. The Ducon filter,—' the Lurgi-MB-
/ 7 /
filter—' and the Rexnord filter—' are examples of this type. Figures
13 through 16 illustrate some of the available granular bed systems.
Currently available theoretical and experimental information on granular
bed filters was recently reviewed by Shannon.—' At present, there are
no useful models for describing aerosol filtration in granular beds. Our
knowledge of the performance of granular beds has been obtained essen-
tially from experimental studies at both the laboratory and pilot-scale
level. Most experimental work has been at room temperature and pressures
with the exception of a few high temperature studies. Although the gen-
eral conclusions reached from these studies are expected to be valid
under conditions of high temperature and pressure, tests are needed to
confirm these conclusions.
Current Granular Bed Research and Development
Work on granular bed filters is underway at several laboratories. Tests
were recently conducted at Morgantown Energy Research Center on a panel
bed filter developed by Squires. Collection efficiencies of 99% were
reported when the filter was handling coal combustion flue gas at
1000 °C. U
Tests on the Ducon filter have been conducted by Westinghouse, Bureau
of Mines, and IGT with efficiencies of 99% reported. Combustion Power
Company is currently testing their pebble bed filter on a bark boiler
at a pulp mill. Laboratory tests have indicated collection efficiencies
of the order of 80%.
54
-------
Clean
Media
Conveyor
To Dust Storage
Figure 13. Combustion Power Company Dry Scrubber.
55
-------
DIRTY GAS
[
)IRTY IGAS
i
•f,
/i
ri
•T.
)t
X
X
<
<
• ; ,-j.' i*«l^'.*,''*IXXX
j'.vri: If* v* i*
i
X
1
i
!r
\f
—
CROSS-SECTION
OF COLUMN
CLEAN
OUT
BLOWBACK
VALVE
BED
DIRTY
GAS
CLEAN
GAS
CROSS-SECTION
OF FILTER BED
SAND REMOVAL CHUTE
Figure 14. Possible Design for Squires Panel Bed Filter.
56
-------
CLEAN
GAS
DUSTY
GAS
CLOSED
COMPRESSED
FLUIDIZING AIR
NORMAL OPERATION
FLUIDIZED CLEANING
Figure 15. Ducon Fixed Bed Fluidizable Filter.
57
-------
RAKE DRIVE
RAKE MECHANISM
CI
BACKFLUbH __p 1 1 r^
DUCT H ^
CI FAW Ci£ie\ tf
CLEAN AIR
niir.T — «*.
RAW RA^
DUSTY GAS
DUCT /
, —
~~>
X
>^
^
\
II
X
n_
III
/
II
1 — •'
-n
rt
linn
1-ikk
Jllllll
— -^
>•
\
\
If
tin
— _
11
n
v_
^-
/
GRAVEL BED
-.\ynpTFVTiiRr
VVJn 1 C. A 1 UDC.
Fll TFR THAMRFR
CLEAN AIR
CHAMBER
\//*\OTITV T" 1 1 D C
VORTtX 1 UDt
PRIMARY
COLLECTOR
CYCLONE
fir SEPARATOR
COUNTERWEIGHTED
VALVE
Figure 16. Rexnord Gravel Bed Filter.
58
-------
ELECTROSTATIC PRECIPITATORS
State of the Art
In recent years, electrostatic precipitators have been used in chemical
processing, power generation, and mass-transport application involving
temperatures and pressures well in excess of conventionally accepted
limits. Walker,22.' Robinson^/ and more recently Hallli' have reviewed
the application of electrostatic precipitation to extreme conditions of
pressure and temperature. It is reported that successful pilot or full
scale trials have been run at pressures up to 55 atm and temperatures
(not simultaneous) to 800°C.
The understanding of corona discharge phenomenon at elevated tempera-
tures and pressures is essential to the design of a high temperature/
high pressure precipitator. Over the past decade or so, considerable
research work has been done in this area. Important contributions were
made by Robinson,**/ Brown and Walker,,327 and by Shale et al.33»34/
Q /
Robinson^' reported that both the corona starting and spark-over volt-
ages increased with gas density. However, at a critical density the two
voltages coincide. This critical density value depends on the precipi-
tator electrode configuration. Positive polarity has a lower value of
the critical density than negative, all other conditions being equal.
Shale reported that at moderate pressure (pa 6 atm), negative polarity
spark-over potential decreased with increasing temperature and became
unstable above about 700°C while positive polarity corona remained
stable up to the investigation limit of 800°C.35_/ in addition, Shale
has reported that negative corona is more effective than positive in
removing entrained solids at 800°C and 6.4 atm, even though the nega-
tive voltage was limited by sparking and was less than that attainable
by positive corona.
Brown and Walker have concluded that the use of the electrostatic pre-
cipitation process up to temperatures of 900°C+ is entirely feasible
and practical.£=.' Both positive and negative corona were electrically
stable provided a minimum gas pressure of at least 6.4 atm existed.
Their data also indicated that the migration velocity of particles de-
creases with temperature, which is in agreement with the theoretical
predictions.
59
-------
Current Electrostatic Precipitator Research and Development
Currently development of electrostatic precipitators for use under con-
ditions of high temperature and pressure is not being pursued. Develop-
ment work of an electrostatic precipitator at the Bureau of Mines for
operation with a coal fired gas turbine has been discontinued and the
experimental study performed in the course of the CPU-400 program by
Combustion Power Company has given way to the development of alterna-
tive techniques.
MOLTEN SALT SCRUBBERS
Over the past few years scrubbers have found considerable application
in gas cleaning processes. These are efficient for particle collection
and have the capability of removing particulate and gaseous pollutants
simultaneously. The main disadvantage of conventional scrubbers for use
in high temperature and high pressure gas cleaning applications is that
the particle collection media is liquid (water) which evaporates at high
temperatures and cools the gas. More recently, molten salts are being
used as scrubbing liquids—playing the role, in effect, of high tempera-
ture analogs of aqueous solutions.
The main application of the molten salt scrubbers has been scrubbing S02
from stack gases. Atomics International has used a molten eutectic mix-
ture of lithium, sodium and potassium carbonate to scrub a power plant
gas stream.~!£' The sulfur is recovered from the molten salt through ad-
ditional processing.
Battelle Memorial Institute's molten carbonate scrubber is being de-
veloped under contract to the Office of Coal Research.£i' The device
is essentially a horizontal venturi scrubber, which utilizes a molten
salt mixture of sodium, potassium and lithium carbonates as a solvent
for the calcium carbonate which acts as the reactant for sulfur removal.
The Battelle scrubber has achieved both sulfur compound and particulate
removal to below the turbine inlet specifications given Battelle by
Westinghouse.
A major potential limitation of the molten salt scrubber for use in
advanced power systems is entrainment of a salt mist into the turbine.
Current Molten Salt Scrubber Research and Development
Battelle Memorial Institute is developing a molten alkali carbonate
scrubber system under contract to the Office of Coal Research. A pilot
plant scrubber capable of treating 100 cu ft/min of gas is being
60
-------
installed on a Battelle fixed bed pilot plant gasifier. Provision for
particulate removal upstream of the scrubbers will be provided. Down-
stream salt deentrainment is to be accomplished by a demlster constructed
of sapphire fibers and manufactured by Alcoa.
FABRIC FILTER SYSTEMS
State of the Art
Currently one of the most widely used techniques for gas cleaning is the
use of fabric filters. However, conventional fabric filters are not
recommended for use above about 250°C.
A number of particle collection mechanisms cause dust collection in a
fabric filter system. These mechanisms include interception, impinge-
ment, diffusion and to some extent electrostatic forces. These forces
and their effect on particle collection have been the subject of consid-
erable study. Theoretical equations have been developed to predict pres-
sure drop across the filter and the filter cake, but they are not adequate
for design purposes. Thus, the design of fabric filters depends largely
upon the experience gained from previous installations and observations
of existing systems.
Only limited investigation of the performance of fabric filter systems
at elevated temperatures or pressures has been conducted. The use of
fabric filters in high temperature applications and innovations in fil-
ter fabrics for high temperature usage have been recently reviewed by
BergamannPJL' and First.32' It is reported that high temperature (350
to 400°C) needled fabrics woven from yarns prepared by twisting fiber
frax fibers around fine stainless steel monofilaments were prepared by
the Carborundum Corporation 20 years ago. Kane, Chidester, and Shale
have tested the efficiency of fly ash collection to 980°C with an alumi-
num silicate fiber ("fiber frax") which melts at 1750°C.^P-/ They re-
ported that the temperature limit was not imposed by the fiber, but by
the fiber support.
Figure 17 depicts the calculated effect of temperature on the efficiency
of collection of the major mechanisms operating in fabric filters. At
higher temperatures, with rapidly decreasing values of inertial impac-
tion efficiencies and moderately increasing diffusion collection effic-
iences, overall collection efficiency would probably decrease.
61
-------
u
LLJ
U
100
50
20
10
2
1
0.5
0.2
0.1
0.05
0.02
Inertial Impaction
Interception
Diffusion
0
400 800
TEMPERATURE, °C
1200
1600
Figure 17. The Effect of Temperature on the Calculated Efficiency of
Collection in Fiber Filtration (particles moving past a 10 micron
diameter cylindrical fiber with a stream velocity of 25 cm/sec).
62
-------
Current Fabric Filter Research and Development
Presently, the J. P. Stevens Company has a silica fiber filter material
under development which is reportedly capable of operating at tempera-
tures of 800°C. Similarly, Owens Corning has developed an inorganic
bonding material for fiberglass fabrics which they suggest is adaptable
to 500°C gas streams.
The 3M Company has developed filter material of alumina-boria-silica
and zirconia-silica which have maximum operating temperatures of 1200
and 1000°C, respectively.
One of the most promising fabric filter materials for high temperature
applications is under development by the Brunswick Corporation. The
Brunsmet filter uses metal fibers fabricated from materials used by
Pratt and Whitney for turbine seals at temperatures above 1200°C. In-
itial laboratory tests on the Brunswick material have shown a 99% ef-
ficiency for 0.5 urn diameter particles with an air-to-cloth ratio of 120.
Brunswick has constructed a 220 cu m pilot plant for general tests to
establish the filter's operating characteristics.
63
-------
RESEARCH AND DEVELOPMENT NEEDS
Technology for particulate removal from gases under high temperatures
and/or high pressures is at a very early stage of development. Well-
conceived research and development programs are needed to improve and
develop equipment for systems and processes which require high tempera-
ture and pressure gas cleaning. The analysis of particulate collection
and agglomeration mechanisms has shown that the effectiveness of most
mechanisms decreases with increasing temperature and pressure. However,
experimental tests are needed to confirm these predictions and to estab-
lish the prominence of those parameters identified as the governing
factors under the conditions of interest.
FUNDAMENTAL STUDIES
One of the reasons for the lack of experimental data has been the lack
of suitable aerosol generation and sampling techniques for high tempera-
ture and pressure conditions. Therefore, considerable effort should be
invested in developing sampling systems and sampling methodology. Impac-
tors should be valuable sampling systems in high temperature work, so
development of in situ impactors and their collection surfaces is highly
recommended.
Specific experiments on the effect of elevated temperature and pressure
on particle collection should include the study of the factor C/u which
enters in many equations describing the key parameters. The factor C/u
is influenced by temperature, pressure, particle size, and gas proper-
ties. The variation of C/u with temperature and pressure can be ob-
tained directly from mobility experiments or indirectly using a simple
impaction system such as a jet impacting on a plate.
CONTROL EQUIPMENT STUDIES
Two of the most important parameters of any particulate removal system
are the fractional efficiency and the pressure drop. Theoretical models
and experimental correlations developed using laboratory or pilot-scale
65
-------
test units are useful in predicting these two parameters. It is recom-
mended that research be conducted on all the promising particulate re-
moval systems using carefully designed test units. The correlations
developed from these experimental investigations can then be used as a
guide for design of pilot-scale and full-scale models.
The existing pressure drop and fractional efficiency equations for cy-
clones are based on experimental data obtained at ambient conditions.
It is not known whether these relations are valid at elevated tempera-
ture and pressure. It is recommended that the validity of existing
equations be investigated.
The study of corona and particle charging at high temperatures and pres-
sures is necessary for understanding the operation of electrostatic
precipitators under these conditions. Investigations of charging phe-
nomena at high temperature and pressure along with the selection of
materials of construction are recommended.
At present there are no useful models for aerosol filtration in either
granular beds or fabric filters. The potentially high collection ef-
ficiency offered by these devices, especially for fine particles, sug-
gests that substantial efforts should be made to develop these systems
for high temperature and pressure applications. The effect of param-
eters such as the particle size of the bed material or fiber diameter,
face velocity, bed or filter thickness, etc., on total mass efficiency,
fractional efficiency, and pressure drop should be thoroughly investi-
gated. Efforts should also be focused on the selection of bed or filter
material, expected life of bed of fiber material, and materials of con-
struction for housings and associated equipment. Methods of cleaning
or bed regeneration need to be developed and, for granular beds, bed
material attrition and entrainment should be studied. Finally, studies
of combined desulfurization and particulate removal efficiency and the
associated problems are recommended.
66
-------
REFERENCES
1. Fulton, R. W., and S. Youngblood, "Survey of High Temperature
Clean-up Technology for Low Btu Fuel Processes," Aerotherm Divi-
sion, Acurex Corporation, Aerotherm Report 75-134, EPA Contract
68-02-1318, January 1975.
2. Stone and Webster Engineering Corporation, "Purification of Hot
Fuel Gases from Coal or Heavy Oil," EPRI Report 243-1, November
1974.
3. Fuchs, N. A., The Mechanics of Aerosols, Pergamon Press, New York
(1964).
4. Davies, C. N., Aerosol Science, Academic Press, New York (1966).
5. Whitby, K. T., "Calculation of the Clean Fractional Efficiency of
Low Madia Density Filters," ASHRAE J., 7^9):56 (1965).
6. Ranz, W. E., and J. B. Wong, Ind. Eng. Chem.. 44:1371-1381 (1952).
7. Kraemer, H. F., and H. F. Johnstone, Ind. Eng. Chem., 47:2426-2436
(1955).
8. Robinson, M., "Electrostatic Precipitation," Air Pollution Control,
Part I, Werner Strauss, Ed., Wiley--Interscience, New York (1971).
9. White, H. J., Industrial Electrostatic Precipitation, Addison-Wesley
(1963).
10. Derjaguin and Yalamov, The Dynamics of Aerocolloidal Systems, Vol.
Ill, Ed. by Hidy and Brock, Pergamon Press, New York (1972).
11. Brock, J. R. , J. Phys. Chem., 6j3:2857 (1962).
12. Hidy and Brock, The Dynamics of Aerocolloidal Systems, Vol. I,
Pergamon Press, New York (1970).
67
-------
13. Levich, W. , Dokl. Akad. Nauk., SSSR, 9J3:809 (1954a).
14. East, T. W. R., and J. S. Marshall, Q. J. R. Met. Soc., 80:26 (1954).
15. Tunitsky, N. N., Zh. Fiz. Khim., ^0:1136 (1946).
16. Obukhow, A., and A. Yaglom, Prikl. Mat. Makh., L5:l (1951).
17. Beal, S. K., "Turbulent Agglomeration of Suspensions," Aerosol
Science. .3:113-125 (1972).
18. Zebel, G., "Coagulation of Aerosols," in Aerosol Science, C. N.
Davies, Ed., Academic Press, New York (1966).
19. Mednikov, E. P., Acoustic Coagulation and Precipitation of Aerosols,
Consultant Bureau, New York (1965).
20. Shepherd, C. B., and C. E. Lapple, "Flow Pattern and Pressure Drop
in Cyclone Dust Collectors," Ind. Eng. Chem.. .31:972-984 (1939).
21. Shepherd, C. B., and C. E. Lapple, "Flow Pattern and Pressure Drop
in Cyclone Dust Collectors," Ind. Eng. Chem., 12:1246-1248 (1940).
22. Leith, D., and W. Light, "Collection Efficiency of Cyclone Type
Particle Collectors: A New Theoretical Approach," AIChE Sym-
posium Series; Air - 1971 (1972).
23. Alexander, R., McK, "Fundamentals of Cyclone Design and Operation,"
Proc. Australas Inst. Min. Met, (new series), 152-153:203-228
(1949).
24. Yellott, J. L. , and P. R. Broadley, "Fly Ash Separator for High
Pressure and Temperature," Ind. Eng. Chem.. 47:944 (1955).
25. Squires, A. M., and R. Pfeffler, "Panel Bed Filters for Simultane-
ous Removal of Fly Ash and S02: I. Introduction," J. of APCA,
20:523 (1970).
26. Kalen, B., and F. A. Zeng, "Filtering Effluent from a Cat Cracker,"
Chem. Eng. Progress. £9(6):67 (1973).
27. Englebrecht, H. L., "The Gravel Bed Filter—A New Approach to Gas
Cleaning," J. of APCA, 15(2):43 (1965).
68
-------
28. Arras, K. et al., "Thirteen Years Experience in the Dedusting of
Clinker Coolers with Gravel Bed Filters," IEEE Cement Industry
Technical Conference May 1972, Also in Pat Reports, Environ-
mental Science Technology, £(7):601 (1974).
29. Shannon, L. J., "Control Technology for Fine Farticulate Emis-
sions," Midwest Research Institute, EPA Report EPA-650/2-74-027,
May 1974.
30. Walker, A. B., "Application of Electrostatic Precipitation to New
Limits of Pressure and Temperature," APCA Meeting, San Francisco,
Paper No. 66-122, June 1966.
31. Hall, H. J., "Application of Electrostatic Precipitation to Process
Gas Cleaning in High Temperature, High Pressure Coal Gasification
Systems," EPRI Report prepared by Stone and Webster Corporation,
Boston, Massachusetts, November 1974.
32. Brown, R. F., and A. B. Walker, "Feasibility Demonstration of Electro-
static Precipitation at 1700°F," APCA J., 21 (10);617 (1971).
33. Shale, C. C., "The Physical Phenomena Underlying the Negative and
Positive Coronas in Air at High Temperatures and Pressures,"
IEEE International Convention Record (1965).
34. Shale, C. C., and G. E. Fasching, "Operating Characteristics of a
High Temperature Electrostatic Precipitator," U.S. Bureau of
Mines, Report of Investigation 7276, July 1969.
35. Shale, C. C., "Progress in High Temperature Electrostatic Precipi-
tation," Paper No. 66-125, APCA Annual Meeting, San Francisco,
California, 20-24 June 1966.
36. Botts, W. V., and R. D. Oldenkamp, "The Atomics International
Molten Carbonate Process for S02 Removal from Stack Gases," EPA
Report 650/2-73-038, May 1969.
37. Office of Coal Research, "Shaping Coal's Future Through Tech-
nology," Annual Report (1974).
38. Bergmann, L., "High Temperature Fabric Filtration: American Ex-
perience and Innovations," Filtration and Separation, March/
April 1974.
69
-------
39. First, M. W., "New Kinds of Fabric Filteration Devices," Proceed-
ings of Symposium on the Use of Fabric Filters for the Control of
Submicron Participates, Boston, Massachusetts, 8-10 April 1974.
40. Kane, L. J., G. E. Chidester, and C. C. Shale, U.S. Bureau of Mines
Report of Investigations 5672 (1960).
41. Thring, M. W., and W. Strauss, "The Effect of High Temperature on
Particle Collection Mechanisms," Trans. Inst. Chem. Engrs., 41:
248 (1963).
42. Strauss, W., and B. W. Lancaster, "Prediction of Effectiveness of
Gas Cleaning Methods at High Temperatures and Pressures," Atmps.
Environ., 2:135 (1968).
43. Leith, D., and D. Mehta, "Cyclone Performance and Design," Atmos.
.. Environ., 7:527 (1973).
70
-------
APPENDIX A
DATA ON GAS PROPERTIES
71
-------
I.OO
Note 71=2.5, Z»I.OO
R '~ 7?
Deviation >l.0%
Reduced pressure,
Reduced temperature, TR=-=-
Pseudo reduced volume, va' =
0.30
0.0
O.I
0.2
O.3
Reduced pressure, p
Figure A-l- Generalized compressibility chart. SOURCE: L. C.
Nelson and E. F. Obert, "Generalized p-v-T Properties of
Gases." trans. A.S.M.F... 76, 1057 (1954).
-------
to
Reduced pressure, p = —
R
Reduced temperature, Ta=—
Pseudo reduced volume,
0.20
QO 0.5 1.0 1.5 2.O 2.5 3.0
3.5 4.0 4.5 5.O 5.5 6.0 6.5
Reduced pressure, p.
9.5 KD.O
Figure A-2. Generalized compressibility chart. SOURCE: L. C.
Nelson and E. F. Obert, "Generalized p-v-T Properties of
Gases," trans. A.S.M.E., 76, 1057 (1954).
-------
0.4 0.5 0.6 0.8 1.0 234
Reduced temperature Tr = T/TC
5678 10
Figure A-3. Reduced Viscosity ur = u/uc as a Function of Temperature for
Several Values of the Reduced Pressure pr = p/pc . SOURCE:
Bird, Stewart, and Lightfoot, "Transport Phenomena," John
Wiley and Sons, Inc. (1960).
74
-------
TABLE A-l
INTERMOLECULAR FORCE PARAMETERS AND CRITICAL PROPERTIES
Substance
Light elements:
H,
He
Noble gases:
Nc
Ar
Kr
Xc
Simple polyatomic
substances:
Air
N3
O,
o;
CO
coa
NO
N..O
SO,
F2
Cl,
Br,
Is
Hydrocarbons:
CH4
C2H2
C,H4
C2H6
C3H0
C3H8
/i-CjHu,
i-C4H10
;;-C5H12
«-C«H14
«-C7H,,
«-C»H18
H-C»Hj<>
Cyclohexane
C0HC
Other organic
compounds:
CH4
CH.C1
CM..C1,
CHC13
CC1,
C,N,
COS
csa
Molecular
Weight
M
2.016
4.003
20.183
39.944
83.80
131.3
28.97=
28.02
32.00
48.00
28.01
44.01
30.01
44.02
64.07
38.00
70.91
159.83
253.82
16.04
26.04
28.05
30.07
42.08
44.09
58.12
58.12
72.15
86.17
100.20
114.22
128.25
84.16
78.11
16.04
50.49 .
84.94
119.39
153.84
52.04
60.08
76.14
Lcnnard-Jones
Parameters*
a
(A)
2.915
2.576
2.789
3.418
3.498
4.055
3.617
3.681
3.433
—
3.590
3.996
3.470
3.879
4.290
3.653
4.115
4.268
4.982
3.822
4.221
4.232
4.418
—
5.061
—
5.341
5.769
5.909
—
7.451
—
6.093
5.270
3.822
3.375
4.759
5.430
5.881
4.38
4.13
4.438
'
(aim)
12.80
2.26
26.9
48.0
54.3
58.0
36.4e
33.5
49.7
67.
34.5
72.9
64.
71.7
77.8
—
76.1
102.
—
45.8
61.6
50.0
48.2
45.5
42.0
37.5
36.0
33.3
29.9
27.0
24.6
22.5
40.0
48.6
45.8
65.9
60.
54.
45.0
59.
61.
78.
P.
(cm1 g-molc"1)
65.0
57.8
41.7
75.2
92.2
118.8
86.6«
90.1
74.4
89.4
93.1
94.0
57.
96.3
122.
—
124.
144.
—
99.3
113.
124.
148.
181.
200.
255.
263.
311.
368.
426.
485.
543.
308.
260.
99.3
143.
—
240.
276.
—
—
170.
/'«
(g cm"1 scc~')
x 10«
34.7
25.4
156.
264.
396.
490.
193.
180.
250.
—
190.
343.
258.
332.
411.
—
420.
—
—
159.
237.
215.
210.
233.
228.
239.
239.
238.
248.
254.
259.
265.
284.
312.
159.
338.
—
410.
413.
—
—
404.
*.
(cal sec-' cm-' ° K-')
x 10"
—
—
79.2
71.0
49.4 '
40.2
90.8
86.8
105.3
—
86.5
122.
118.2
131.
98.6
—
97.0
—
—
158.0
—
—
203.0
—
—
—
—
—
—
—
—
—
—
—
158.0
—
—
—
—
—
—
75
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-75-020
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Particulate Removal from Gas Streams at
High Temperature/High Pressure
5. REPORT DATE
August 1975
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
A.K. Rao, M.P. Schrag, and L. J. Shannon
8. PERFORMING ORGANIZATION REPORT NO
MRI Project 3821-0(30)
9. PERFORMING OR6ANIZATION NAME AND ADDRESS
Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110
10. PROGRAM ELEMENT NO.
1AB012; ROAP 21ADL-004
11. CONTRACT/GRANT NO.
68-02-1324, Task 30
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research.and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final: 3-5/75
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The report gives results of an evaluation of methods of removing particulate matter
from high temperature and/or high pressure gas streams. Theoretical and experi-
mental information indicates that in many instances the effectiveness of collection
and agglomeration mechanisms decreases with increases in temperature and
pressure. Control equipment and systems which offer promise for application to
particulate cleanup under high temperature and/or high pressure conditions are
discussed. All potential systems reviewed require considerable development before
they can be used reliably under the conditions of interest.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Evaluation
Dust Control
Exhaust Gases
High Temperature
Tests
High Pressure Tests
Agglomeration
Air Pollution Control
Stationary Sources
Particulate
13 B
14B
21B
8. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
83
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2320-1 (9-73)
76
-------