AMERICAN INSTITUTE OF CROP ECOLOGY
A RESEARCH ORGANIZATION DEVOTED TO PRO&
PLANT ADAPTATION AND INTRODUCE
AICE* SURVEY OF USSR AIR POLLUTION LITERATURE
Volume XV\
SOME BASIC PROPERTIES OF ASH AND INDUSTRIAL DUST
IN RELATION TO THE PROBLEM OF PURIFICATION OF STACK GASES
Edited By
M. Y.
The material presented !•
USSR literature on air polli
conducted by the Air Poll:
AMERICAN INSTITUTE OF CROP ECOLOGY
This survey is being conducted under CRA
IRONMENTALPROT
•AMERICAN INSTITUTE OF CROi
SILVER SPRING. MARYLAND 20910
-------
PUBLICATIONS of the AMERICAN INSTITUTE OF CROP ECOLOGY
Rrf,
No
UKRAINE-Ecologicol Crop Geography of the Ukraine or.d the
Ukrainian Agro- Cfimo'tc Analogues in North America
2 POLAND-Agricvllurol Climatology of fblond ond In Agra-
Climatic Anolcgue: In North America
3 CZECHOSLOVAKIA-Agricultural dimalo logy of Czechoslo-
vakia and In Agro-Climatic Analogue! in North America
4 YUGOSLAVIA-Agriculturol Qimatclogyof Yugoslavia and In
Agra-Climatic Analogues in North America
5 GREECE-Ecological Crop Geography of Greece and In Agro-
Climotic Analogues in North Americo
6 ALBANIA-Ecological Plant Geography of Albania, Its Agri-
cuf tural Crops and Some North American Climatic Analogue!
7 CHINA-Ecological Crap Geography of China and In Agro-
Climatic Analogues in North America
8 GERMANY-Eeotogical Crop Geography of Germany and Ih
Agro-Climatic Analogue* in North America
*9 JAPAN (I)-Agriculrural Climatology of Japan and In Agio-
Climatic Analogues in North America
10 FINLAND-Ecologicol Crop Geography of Finland and In Aoro-
Climaric Analogues in North America
1) SWEDEN-Agriculluraf Climatology of Sweden and In Agjo-
Climotlc Analagvei in North Americo
12 NOR WAY-Ecological Crop Geography of Norway ond In Agio-
Oimaric Analogues in North America
13 SIBERIA-Agricul tural Climatology of Siberia, Ib Natural Beln,
ond Agra-CI imatic Anologum in North America
14 JAPAN (2)-Eeolo0ical Crap Geography and Field Precticet of
Japan, Japan's Natural Vegetation, ond Agio-Climatic
Analogue! in North America
IS RYUKYU ISLANDS-Ecologicol Crap Geography and Field
Practices of the Ryukyu Islands, Natural Vegetation of the
Ryukyut, and Agio-Cf inalic Anatoguet in the Northern
Hemisphere
16 PHENOLOGY AND THERMAL ENVIRONMENT AS A MEANS
OF A PHYSIOLOGICAL CLASSIFICATION OF WHEAT
VARIETIES AND FOR PREDICTING MATURITY DATES OF
WHEAT
(Based on Data of Czechoslovakia and of Some Thermally
Analogous Areas of Czechoslovakia in the United States
Pacific Northwest)
17 WHEAT-CLIMATE RELATIONSHIPS AND THE USE OF PHE-
NOLOGY IN ASCERTAINING THE THERMAL AND PHO-
TOTHERMAL REQUIREMENTS OF WHEAT
(Based ooDoro of North America and Some Thermally Anal-
ogous Areas of North America in the Soviet Union and in
Finland)
18 A COMPARATIVE STUDY OF LOWER AND UPPER LIMITS OF
TEMPERATURE IN MEASURING THE VARIABILITY OF DAY-
DEGREE SUMMATIONS OF WHEAT, BARLEY, AND RYE
19 BARLEY-CLIMATE RELATIONSHIPS AND THE USE OF PHE-
NOLOGY IN ASCERTAINING THE THERMA1/AND PHO-
TOTHERMAL REQUIREMENTS OF BARLEY
20 RYE-CLIMATE RELATIONSHIPS AND THE USE OF PHENOL-
OGY IN ASCERTAINING THE THERMAL AND PHOTO-
THERMAL REQUIREMENTS OF RYE
2' AGRICULTURAL ECOLOGY IN SUBTROPICAL REGIONS
22 MOROCCO, ALGERIA, TUNISlA-Phyi'eol Environment and
Agriculture . ...
23 LIBYA and EG YPT-Physical Environment and Agriculture. ..
24 UNION OF SOUTH AFRICA-rViyiicoJ Environment and Agri-
culture, With Special Reference to Winter-Rainfall R««k>nj
25 AUSTRALIA-Phytical Environment and Agriculture, With Spe-
cial Reference to Winter-Rainfall Regions
26 S. E, CALIFORNIA ond S. W. ARIZONA-Physicol Environment
ond Aariculrure of the Desert Regloni
27 THAILAND-Physical Environment ond Agricul lure
28 BURMA-Phyjieol Environment and Agriculture
2BA BURMA-Diieases and Pests of Economic Plants
26B BURMA-Qimore, Sails ond Rice Culture (Supplementary In-
formation and a Bib) iogrophy to Report 28)
29A VIETNAM, CAMBODIA, LAQS-rhystcol Environment and
Agriculture
298 VIETNAM, CAMBODIA, LAOS-Diseases andPestsof Economic
Plants
29C VIETNAM, CAMBODIA, LAOS-Climatological Data (Supple-
ment to Report 29A)
30A CENTRAL and SOUTH CHINA, HONG KONG, TAIWAN-
Phyiicol Environment and Agricul lure $20.00*
XB CENTRAL and SOUTH CHINA, HONG KONG, TAIWAN-
Major Plant Pests and Diseases
31 SOUTH CHINA-lts Agro-Climatic Analogues in Southeast Asia
32 SACRAMENTO-SAN JOAQUIN DELTA OF CALIFORNIA-
Phyitcel Environment and Agricul lure .....
33 GLOBAL AGROCLIMATIC ANALOGUES FOR THE RICE RE-
GIONS OF THE CONTINENTAL UNITED STATE
34 AGRO-CLIMATOLOGY AND GLOBAL AGROCLIMATIC
ANALOGUES OF THE CITRUS REGIONS OF THE CON-
TINENTAL UNITED STATES
35 GLOBAL AGROCLIMATIC ANALOGUES FOR THE SOUTH-
EASTERN ATLANTIC REGION OF THE CONTINENTAL
UNITED STATES
36 GLOBAL AGROCLIMATIC ANALOGUES FOR THE INTER-
MOUNTAIN REGION OF THE CONTINENTAL UNITED
STATES
37 GLOBAL AGROaiMATIC ANALOGUES FOR THE NORTHERN
GREAT PLAINS REGION OF THE CONTINENTAL UNITED
STATES
38 GLOBAL AGROCLIMATIC ANALOGUES FOR THE MAYA-
GUEZ DISTRICT OF PUERTO RICO
39 RICE CULTURE and RICE-CLIMATE RELATIONSHIPS With Spe-
cial Reference to the United Stoles Rice Areas and Their
Latitudinal ond Thermal Analogues In Other Countries
40 E. WASHINGTON, IDAHO, and UTAH-Physical Environment
and Agriculture
41 WASHINGTON, IDAHO, and UTAH-The Use of Phenology
in Ascertaining the Temperature Requirements of Wheat
Grown in Washington, Idaho, and Utah and in Some of
Their Agra-Climafieolry Analogous Areas in the Eastern
Hemisphere
42
43
44
NORTHERN GREAT PLAINS REGION-Preliminery Study of
Phenologicol Temperature Requirements ef a Few Varieties
of Wheat Grown in the Northern Great Plains Region and in
Some Agro-Climatically Analogous! Areas In the Eastern
Hemisphere
SOUTHEASTERN ATLANTIC REGION-Phenoloaieal Temper-
ature Requirements of Some Winter Wheat Varieties Grown
in the Southeastern Atlantic Region of the United States ond
in Several of Its Latirodinally Analogous Areas of the Eastern
and Southern Hemispheres of Seasonally Similar Thermol
Conditions
ATMOSPHERIC AND METEOROLOGICAL ASPECTS OF AIR
POLLUTION-A Survey of USSR >ir Pollution Literature
EFFECTS AND SYMPTOMS OF AIR POLLUTES ON VEGETA-
TION; RESISTANCE AND SUSCEPTIBILITY OF DIFFERENT
PLANT SPECIES IN VARIOUS HABITATS, IN RELATION TO
PLANT UTILIZATION FOR SHELTER IELTS AND AS BIO-
LOGICAL INDICATORS-A Survey of USSR Air fcllutlwi
Literature
(Continued an Imide of bock ew**)
-------
AICE-AIR-72-16
A1CE* SURVEY OF USSR AIR POLLUTION LITERATURE
Volume XVI
SOME BASIC PROPERTIES OF ASH AND INDUSTRIAL DUST
IN RELATION TO THE PROBLEM OF PURIFICATION OF STACK GASES
Edited By
M. Y. Nuttonson
The material presented here is part of a survey of
USSR literature on air pollution
conducted by the Air Pollution Section
AMERICAN INSTITUTE OF CROP ECOLOGY
This survey is being conducted under GRANT R 800878
(Formerly R01 AP 00786)
OFFICE OF AIR PROGRAMS
of the
U.S. ENVIRONMENTAL PROTECTION AGENCY
*AMERICAN INSTITUTE OF CROP ECOLOGY
809 DALE DRIVE
SILVER SPRING, MARYLAND 20910
1972
-------
TABLE OF CONTENTS
Page
PREFACE iv
THE GENERAL ASPECTS OF THE DESIGN AND OPERATION
OF GAS PURIFICATION SYSTEMS
A. A. Rus anov 1
1. Basic Properties of Ash and Industrial Dust 1
2. Parameters of Gases Undergoing Purification 12
3. Discharge of Flue Gases, Their Density, and
Their Ash or Dust Concentration 20
4. Chemical Processes Occurring in Dust Collectors 26
5. Coefficients of Purification of Gases in Dust
and Ash Collectors 30
PRINCIPLES OF DESIGN OF GAS PURIFICATION SYSTEMS
A. P. Anastasiadi 32
1. General Background 32
2. Relationship Between the Height of Smokestacks and
the Required Efficiency of Gas Purification 37
DETERMINATION OF THE BASIC PROPERTIES OF DUSTS AND GASES
A. A. Rus anov 46
1. Determination of the Dispersity of Ash or Dust 46
2. Measurement of the Electrical Resistivity of Dust
Under Industrial Conditions 68
3. Determination of the Moisture Content and Dew Point
of Gases 71
LITERATURE CITED ,' 76
iii
-------
PREFACE
The objective of the authors of the source book* of the translated
papers presented in this volume was to consolidate much of the basic
information relevant to problems encountered in the field of purification
of stack gases. This information, which is intended mainly for engineers
and technicians concerned with problems of removal of ash and dust from
gas-air discharges, may also be useful to certain scientific investigations.
The book deals with the basic properties of industrial dusts and ash
from various types of fuel. It describes the most common designs of units
for trapping ash and industrial dusts and methods of designing them and
of calculating the technical and economic indices. It provides recommenda-
tions for a rational selection of dust removal systems as a function of
the parameters of the dust-charged medium, the requirements for the degree
of purification, and a number of other considerations, it also presents
necessary information on the construction and calculation of gas conduits,
heat insulation coatings, selection of drafting and blowing machines, and
other auxiliary equipment. The main aspects of the operation of gas puri-
fication units are discussed. A separate chapter is devoted to the opera-
tional control and testing of gas purification units.
From this book we have translated the chapters dealing with:
(a) general problems related to the planning and operation of gas
purification systems,
(b) principles of planning gas purification systems,
(c) determination of the basic properties of dusts and gases.
Chapters dealing with the description, illustration, and schematic
presentation of the different Russian mechanical devices with Russian speci-
fications of the models have not been included in these translations.
It is hoped that the papers selected for presentation in this volume
will be conducive to a better appreciation of some of the air pollution
investigations conducted in the USSR. As the editor of this volume I wish
to thank my co-workers in the Air Pollution Section of the Institute for
their valuable assistance.
M. Y. Nuttonson
August 1972
*0chistka Dymovykh Gazov v Promyshlennoy Energetike. (Purification of Stack Gases in the Power Industry.)
A. A. Rusanov, I. I. Urbakh, and A. P. Anastasiadi. Energiya, Moskva, 454 pages, (19&9).
iv
-------
THE GENERAL ASPECTS OF THE DESIGN AND OPERATION
OF GAS PURIFICATION SYSTEMS
A. A. Rusanov
From "Ochistka dymovykh gazov v promyshlennoy energetike". A. A. Rusanov,
I. I. Urbakh, and A. P. Anastasiadi. "Energiya", Moskva, p. 5-38, (1969).
1*-1. Basic Properties of Ash and Industrial Dust
The reliability and efficiency of gas purification systems depends con-
siderably on the physicochemical properties of the ash or dust being trapped.
These properties should be thoroughly studied and taken into account in de-
signing gas purification systems as well as organizing their operation.
The most important characteristics of ash or dust are the adhesiveness,
density, abrasiveness, dispersity, chemical composition, and electrical
resistivity.
1. Agglomerating Capacity
The influence of the physicochemical properties is manifested primarily
in the diverse capacity of ash or dust to agglomerate and adhere to the walls
of gas purification equipment and gas conduits. This property of ash or dust
greatly affects the reliability of gas-purifying units; one of the most common
troubles with gas-purifying equipment is their partial or total obstruction
with ash or dust.
An arbitrary classification of certain types of industrial dusts into
four groups according to their agglomerating capacity is given in Table 1-1.
As is evident from this table, the adhesiveness of the dust depends not only
on the properties of the material constituting it but also on some other fac-
tors such as moisture content, temperature, presence of nonagglomerating
inclusions (particles of unburned fuel), and particle size.
t
The agglomerating effect is closely related to another characteristic of
dust, its friability. The latter is estimated from the angle of rest, which
assumes the dust to be in a freshly poured state. This quantity largely deter-
mines the behavior of dust in the hoppers and chutes of ash- and dust-catching
units, the wall steepness of which is selected as a function of the friability
of the particles being trapped.
Like the agglomerating capacity, the friability depends on the natural
properties of dust, the size and shape of the particles, the moisture content,
etc.
*Editor's note: The first digit represents chapter numbers.
- 1 -
-------
The angles of rest and coefficients of friction for dust are given in
Table 1-2.
Table 1-1
Agglomerating Capacity of Various Dusts.
Group I Group II
Nonagglomerating Dusts
Slightly Agglomerating Dusts
1. Clay dust
2. Slag dust
Group III
1. Fly ash with 3$ of incom-
pletely burned material in
powdered-coal combustion
2. Fly ash from fuel-bed
" firing of any coals
3. Coke dust
4. Hagnesite dust (which has
not adsorbed moisture)
5. Shale ash
6. Blast furnace dust Rafter
primary dust precipitators)
7. Dry apatite dust
Group IV
Medium-Agglomerating Dusts
Strongly Agglomerating Dusts
1. Fly ash without incompletely
burned material (ash from
Moscow coal)
2. Peat ash
3. Manganese dust (which has
adsorbed moisture)
4. Dust of nonferrous metal-
lurgical concentrates and
iron pyrite
5. Oxides of zinc, lead, tin
(precoagulated)
1. Cement dust deposited from
air with a high moisture
content
2. Gypsum and alabaster dust
3- Dust of clay, kaolin and
marls (fine)
4. Cinder dust at SOOfC
5. Flour dust
6. Fiber dusts (asbestos,
cotton, wool, etc.)
7. Dust containingicoarse
admixtures (after sifting
.grain, etc.;
8. Ash of anthracite culm with
less than 25^ of incompletely
burned component
- 2 -
-------
Table 1-2
Angles of Rest and Coefficients of Friction for Ash (Averaged Data).
Angle of Rest, deg
In Motion
40
At Rest
50
Coefficient of Fric-
tion Against Steel
In Motion
0,47
At Rest
0,84
Coefficient of
Friction Against
Concrete
In
Motion
0,84
At Rest
1,00
In regard to the properties of ash friability, it may be noted that ash
trapped after slag-tap furnaces is the most friable (owing to the fused,
rounded shape of its particles) and in the dry form does not usually remain
suspended in the chutes and hoppers. An exception is ASh ash, which has a
tendency to agglomerate.
When moist, ash loses its property of friability, and in some cases,
when its content of binders is high, it acquires a setting tendency.
It should be noted that such properties of dusts as agglomeration and
adhesiveness have been inadequately studied and applied to the solution of
practical problems. An analysis, treatment and classification of disconnected
and sometimes contradictory data on these properties are given in a monograph
by A. D. Zimon [84]. This work also gives some practical recommendations for
controlling the agglomeration and adhesiveness of industrial dusts.
At the time the book went to press, the NIIOGAZ (State Scientific Research
Institute of Gas Purification for Industry and Sanitation) developed a pro-
cedure for determining the agglomerating capacity from the tensile strength of
a layer formed as a result of filtration by placing the instrument inside the
gas conduit, and began a classification of industrial dusts and ash from various
types of fuel on the basis of this characteristic.
2. Density
The most important characteristic of ash and dust is their density,
measured in kilograms per cubic meter or grams per cubic centimeter. The true
density (characterizing the material from which the dust is obtained), bulk
density and apparent density are distinguished.
The bulk density of dust, in contrast to its true density, takes into
account the presence of air gaps between the particles of freshly poured dust.
The bulk density is used for the determination of the volume occupied by the
dust in hoppers. As the particle size uniformity increases, the bulk density
— 3 —
-------
of dust decreases, since there is an increase in the relative volume of the
air spaces.
Of major importance from the standpoint of dust collection is the con-
cept of apparent density, which refers to the ratio of the mass of the
particle to the volume it occupies, including pores, empty spaces, irregu-
larities, etc. A smooth monolithic particle has an apparent density which
practically coincides with the true density. In dry inertial units such par-
ticles are collected better than porous ones, since, for the same mass, they
are subjected to a smaller entraining action of the purified gases leaving
the gas-purifying apparatus. Conversely, particles of lower apparent density
but of the same mass are more efficiently collected in such gas-cleaning
equipment as foam units and bag filters, owing to the higher probability of
trapping of the particles by water or by the filter cloth.
The apparent density of ash depends on its composition and may range
from fractions of a gram for ash particles containing gas bubbles and inflated,
porous particles of incompletely burned material, to several grams per cm^ for
ash containing particles of iron produced by reduction of the oxides entering
into the composition of the mineral component of the fuel.
For comparison, Table 1-3 lists the apparent and bulk densities of ash
from some types of fuel.
Table 1-5
Apparent and Bslk Densities of Ash From Some Types of Fuel
Fuel
Leninskiy, Tkvarcheli coals . •> • •
Apparent
Density,
g/cnP
2 0—2 2
2 2—2 4
1,8—2,0
1 9—2,5
2,3—2,5
2,3—2,4
2,4—2,9
1.8—2.1
Bulk Density,
g/cm3
0 5_0 7
0*8— l'l
0,6—0,7
0 4—0 7
-
1.0—1.1
3. Abrasiveness
In designing and operating gas purification systems it is necessary to
consider the abrasiveness of ash and dust, which ranges over fairly wide
limits. The rate of metal wear at the same velocities and concentrations of
ash or dust particles depends on their hardness, shape, size, and weight. .The,
wearing effect of ash or dust is usually considered in selecting the velocities
of dust-laden gas streams, the thickness of the metal from which the gas conduits
and gas purifying units are made, or in selecting the lining materials for them.
- 4 -
-------
4. Dispersity
The behavior of particles of different sizes in dust collecting units
is different, and therefore it is important to study the quantitative size
distribution of the particles, or in other words, the particle size compo-
sition of ash or dust.
The particles of most industrial dusts have an irregular shape, frequently
that of fragments, or irregular polyhedra. Only in some isolated cases are
the dust particles spherical, particularly when produced by vapor condensation
(sublimation) or when fused at high temperatures.
Particles formed as a result of a technological process (which are
usually called primary) coagulate as they move along the gas conduits, forming
larger (so-called secondary) particles. The latter have a very loose structure,
since the primary particles are packed in such a way that the empty spaces
between them occupy a much larger volume than the particles themselves.
For particles of irregular shape and particularly aggregated particles,
the relationship between the sizes and the various properties (in particular,
inertial properties) determining their behavior in dust-collecting units is
very complex.
The inertial properties of particles are customarily evaluated from their
behavior in a gravity field, namely, their sedimentation rate. To this end,
the concept of the Stokes particle diameter has been introduced. The Stokes
diameter of any particle, including an aggregated particle, is the diameter
of a spherical particle having the same sedimentation rate as a given non-
spherical particle or aggregate.
The particle size composition of ash or dust is determined experimentally.
Some methods and instruments for the experimental determination of the dis-
persity of dusts permit the determination of the actual dimensions of the par-
ticles, while others measure their Stokes diameters.
The gravimetric portion of dust in a certain range of sizes is called a
fraction. By studying the particle sizes one can compile a table of the
fractional composition of a dust.
One can also compile a table which will show what fraction of the dust
is made up of particles larger than a certain size. Examples of such tables
are Tables 1-4 and 1-5, which list the characteristics of fly ash formed under
different conditions of combustion of some types of fuel.
Graphically, the distribution of particles according to size may be
represented in several ways.
- 5 -
-------
Table 1-4
Characteristics of Fly Ash (According to the Data of NIIOGAZ).
Method of
Combustion and
Hilling
Bed type (mechanical
grate)
Powdered coal
Bed-type (hand-
fumace)
In suspension
In eddy-type furnace
of Makar'yev's
systen
Pondered coal (shaft-
mill furnace)
Bed-type (hand
furnace)
Fuel
Moscow coal
Lean coal (3096 in-
completely burned
material)
Lean coal (.7k incom-
pletely burned
material)
Anthracite (commer-
cial culm)
Anthracite (slab,
lump, onippings,
culm)
Peat
Shale '
Moscow coal
Idem
Fractional Composition of Ash, %
Particle Size, um
0-5
1,3
13,2
4,5
1,4
6,5
6.2
4.0
5,0
'
19,4
5-10 | 10—15
3.7
10,8
9.5
1,6
9.0
19.8
6,0
15,0
14.0
1,5
7,0
33,0
2,5
0.5
10.0
6.0
12,0
6,1
15—20
3.5
6.0
19,0
»'
3,5
6.0
7,0
6,0
11,0
7,6
20-30
9,0
10,5
13,0
7,0
8,0
10.0
10,0
16,5
10.5
30—40
22,0
10,0
7.0
8,0
6.0
7,0
9,0
10,0
7.9
40-60
37.0
20.5
6,0
n.o
9.5
11.0
10.0
12.5
10,1
60-90
22.0
22,0
8,0
14,0
11.5
12,0
14,0
5,0
10,8
90
— ^
__
51.0
37,5
17.0
35,0
12,0
13,5
Ash
Density,
g/cV
2,3
2,2
2,2-2,:
—
1.9—2,:
—
2.0-2.J
«
2.0—2.1
-------
Table 1-5
Characteristics of Fly Ash (According to the.Data of TsKTl (Central Scientific Research Institute for Boilers and
Turbines) and VTI (All-Onion Heat Engineering Institute).
Method of Combustion •
and Hilling
PowderebVeoal (tumbling
ball mill;
Same-
n
• ».
Pondered coal (medium-
speed mill)
Same
Powdered coal (hammer mill!
Same
n
» •
» H
• •
• M
Powdered coal (hammer mill
Powdered coal (pneumatic
hammer mill)
Powdered coal (tumbling
ball mill;
Pondered coal (tumbling
ball mill)
Chamber (hammer crusher)
Fuel
Donets lean coal
Kuznetsk lean coal
Kemerovo coal
Chelyabinsk coal
Moscow coal
Intinsk coal
Vorkuta coal
Tkvarcheli coal
Leninskiy coal
Intinsk coal
Vorkuta coal
Kansk coal
. Aleksandriyskiy coal
Kashpir shale'
Gdov shale
Shredded peat
Moscow coal (dried)
n n n
ASh
Volga shale
Total Residue, %
Particle Size, Urn
>o
100
100
100
100
100
100
100
100
100
ICO
100
100
100
100
100
100
100
100
100
100
>G
88
88
92
93
90
93
92
97
96
94
92
95
94
95
93
_
__
—
>10
68
69
79
82
71
80
75
91
91
79
75
88
84
86
90
97,6
54
54
73
88
>20
37
38
57
62
48
53
40
79
75
47
41
66
55
65
34
90,5
35
39
51
75
>so
26
29
40
46
34
39
26
57
53
25
25
47
35
47
19
74,3
26
32
38
64
>40
19
23
30
37
26
30
19
41
38
16
13
34
23
34
12
19
25
30
55
>50
15
18
22
30
19
24
15
32
32
10
8
24
15
25
9
29,3
14
19
24
50
>60
11
13
16
24
14
19
12
27
26
8
5
18
11
16
7
—
11
14
15
47
>80
6
8
8
13
5
11
6
15
16
4
3
9
7
7
4
—
7
6
__
—
>:oo
3
5
5
9
2
8
4
9
12
2
2
6
5
5
2
17
4
1
—
Ash
Density,
g/CDK
2,3-2,5
2,3—2,5
2.2-2,4
2,3-2,4
2,2—2,4
2,2—2,5
2.2—2,5
2,4—2,5
2,4—2,9
2,2-2,5
2,2—2,5
2.2—2,4
2,3—2,4
2.5-2,7,
2,4—2,5
—
_
—
—
-------
'faction of particles with Fraction of particles with
dimensions greater than d, °f> dimensions greater than d, % -.
W**fc*^!$*!*$ ***£****** S§ *"*$ x^*^
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9>
,
,
£
.
S JO 20 30 40 SO ff0 70 ym
b) - ;
^
£
N
\
\
\
1
S
x
•^^
1
—
S 70 20 30 40 SO ff-0 • 70
c)
f
*'} t
t t
v
. .
,
«
\.
^
.« • i i
s
\
•
'
,
\^
s
i
i
^V
1 1 1
V
, <«
d-
\
r 7 234S 70 20 JO SO 100200
- _
-
ym
ym
•• e
ffd,?.
9i
97
9f
n
9f
90
fS
80
?S
70
ff0
SS
30
2S
20
JS
70
3
2
T
0,2
0
Fig. 1-1, Graphical representation of the particle
size composition of ash from lean Donets coal (see
Table 1-5).
a - differential distribution curve; b - fractional
distribution; c - integral distribution on a linear
scale of coordinates; d - integral distribution in
a logarithmic probability coordinate system;
e - probability scale.
- 8 -
-------
A dispersity curve can be plotted by laying off the particles size
along the abscissa axis on a linear scale and the fraction of particles of
corresponding size along the ordinate axis. The curve obtained is called a
differential curve of particle size distribution. An example of such a
curve is given in Fig. 1-1 a.
If we consider that within a certain range the weight fraction of the
particles is constant, a stepwise dispersity curve, i.e., a histogram, is
obtained (Fig. 1-1 b).
The distribution of particles according to size is usually given in the
form of integral dispersity curves. In this case, the particle size d is
laid off along the abscissa axis, and the weight fraction of particles whose
size is either smaller or greater than d along the ordinate axis. One can
use a linear scale with coordinate axes (Fig. 1-1 c) or plot the curve in
the so-called probability coordinate system (Fig. 1-1 d). The advantage of
using such a coordinate system is that certain particle size distribution
functions can be expressed in the form of elementary geometric curves [74].
For example, the Gauss lognormal distribution [75], which according to
many studies governs many types of dust, is transformed into a straight line
in the logarithmic probability coordinate system. This in turn opens up
great possibilities for the interpolation and extrapolation of particle sizes.
According to the lognormal distribution (LND), the distribution of the
log of particle diameters can be expressed by a probability curve (Gauss
curve) whose equation in the integral form is [75]:
where d is the particle diameter;
H is the mean geometric particle diameter;
a is the geometric standard deviation;
In^cr is the standard deviation (dispersion) of the logarithm of the
diameters from their mean value;) tf\nd—\ne^\ is the total weight of the
particles in the range d = 0-d in fractions of unity (or %) , i.e., the weight
content .of particles less than d in diameter.
In the representation of the results of dispersity analysis in the log-
arithmic probability coordinates, the log of the particle diameter is laid
off along the abscissa axis, and the quantity * /hid— In 3^ \ is laid off along
•• * (- m. ;
- 9 -
-------
the ordinate axis on a special functional scale (quantiles).
The lognormal distribution is customarily characterized by two quanti-
ties: the geometric mean diameter and the standard deviation. When the IND
is represented in logarithmic probability coordinates, i.e., in the form of
a straight line, the value of "?g corresponds to the point of intersection of
this line with the abscissa axis. The standard deviation is determined as
the difference of the abscissas for points of the straight line with ordinates
of 84.1 and 50% (or respectively 50 and 15.9%).
Knowing the parameters of a. given IND, i.e., dg and O, one can readily
trace a straight line corresponding to this distribution, which makes it pos-
sible to find the content of particles in any diameter range. Thus, the use
of the logarithmic probability coordinate system affords a means of extremely
brief notation of information on the dispersity of dust obeying the lognormal
distribution.
As a rule, the plotting of the straight line from parameters o and dg
involves no difficulties, but it does become quite inconvenient in the case
of distributions with high values of 0, since the abscissa axis is constructed
for limited values of the diameter and the points of the straight line with
ordinates of 84.1 and 15.9% may fall outside the limits of the graph. It has
therefore been proposed [73] that instead of the variant cr, representing the
difference of abscissas of points with fixed ordinates, another parameter
should be used, namely, the value of the ordinate at an abscissa corresponding
to log 2d , and that this paramete_r be denoted by £(2dg). it should be noted
that instead of the abscissa log 2dg, one can take the abscissa log ~Sg (just as
2~
above, the ordinate 15.9% could have been taken instead of the ordinate 84.1%).
_ The method of plotting the straight line from the parameters log clg and
£(2dg) amounts to the following. First, a point corresponding to log dg is
marked on the abscissa_axis. To the right of this point, a point is then found
corresponding to_log 2dg,_and at this point a perpendicular is erected on which
the quantity £(2dg) or £(dg/2) is laid off. The straight line'is traced through
the end of this perpendicular and through the point on the abscissa axis corres-
ponding to log dg.
The advantage of using £(2dg) or £(dg/2) in place of a consists, in addi-
tion to facilitating the graphical plotting of straight lines with large a
(there is no need to extend the abscissa axis), in the fact that it is no longer
necessary to calculate the difference of the logs of the diameters, and there
is no need for any kind of computations at all.
When these parameters are used, each LND may be briefly denoted by two
numbers, the first of which (in microns) corresponds to dg, and the second
- 10 -
-------
(in percent) to C(2cTg) or
Thus, for example, the distribution characteristic of ash of Donets
lean coal (see Fig. 1-4 d) may be written as follows:
^ = 16 y;
Considering a certain complexity in the construction of a probability
scale which can hold the wide spread of the logarithmic probability coordinate
system, Fig. 1-1 e gives an enlarged probability scale. The abscissa axis can
be constructed by means of an ordinary slide rule.
5. Electrical Resistivity
Experience in the electrical purification of gases shows that a high
electrical resistivity of a layer of ash or dust particles substantially affects
the efficiency of electrostatic precipitators. The critical value of the resis-
tivity above which the characteristics of an electrostatic precipitator decline
rapidly if the layer cannot be readily shaken off the electrodes amounts to
approximately 2 x lO^O ohm cm. The decrease in the efficiency of the electro-
static precipitators is associated with the appearance of a secondary brush dis-
charge on the collecting electrodes, the neutralization of the charge on the
particles in the working compartment of the apparatus, a decrease of the break-
down voltage, and also a redistribution of the working voltage between the dis-
charge gap and the dust layer.
The electrical resistivities of a layer of particles of many types of ash
and dust have values close to critical and depend on the properties of the
individual particles (surface and internal conductance, size and shape of the
particles) and also on the structure of the layer and parameters of the gas
being purified.
The dependence of the electrical resistivity of a layer of ash or dust
particles (or their conductance) on the temperature and humidity of the gas
and some other factors are used in practical electrical purification of gases
for a suitable pretreatment (conditioning) of the gases before they reach the
electrostatic precipitators in order to improve the efficiency of the latter.
The electrical resistivity of certain types of ash is shown in Fig. 1-2.
If the electrical resistivity of the layer is under 103-10^ ohm cm, the
particles quickly lose their charge acquired from the discharge electrodes,
then acquire the charge of the collecting electrodes. If the electrical forces
arising from the newly acquired charge are sufficient to overcome the forces of
adhesion, the deposited particles return to the stream of gases, thus increas-
ing the secondary entrainment of the collected dust.
- 11 -
-------
ohm
10
ohm cm
10°
5
I0n
5
-»*
10"
5
-10*
5
10s
S
*5
V.
Ov
^
•^
\J
\
\
*w
X
XI
\
\
^
N
X
\
\
fltO'C
^
,125'C
X
'100'C
t
,60'C.
5 10 b) IS 20 %
Fig. 1-2. Electrical resistivity of certain types of industrial
dust and ash Cdata of G. M. A. Aliyev and A. Xe. Gonik;.
a - dependence on temperature: b - dependence on moixture content
as illustrated with ash from Moscow coals 1 - ash from Moscow coal:
2 - lead mist; 3 - synthetic catalysts; 4 - cement dust; 5 - ash of
brand ASh from Donets anthracite.
1-2. Parameters of Gases Undergoing Purification
1. Composition of Gases
Usually, the total composition of waste gases is of interest only in
a study of the technological processes taking place in the fuel-burning units,
and is determined by means of chemical gas analyzers based on the principle of
absorption by chemical reagents or afterburning of the individual components of
the gas mixture, by means of gas analyzers TsKTI, VTI-2, etc.
In dust collection processes, the only important factors are the moisture
content and the content in the gases to be purified of sulfur oxides which
cause an appreciable rise of the dew point tj as compared with the condensation
temperature of pure water vapor. The analysis of gases in dust-collecting
practice is used mainly for the purpose of determining the magnitude of suction
of external air into the dust collector. To this end, it sufficies to determine,
at the entrance to the collector and at its exit, the content of any one of
readily determinable components whose absolute quantity remains unchanged during
passage through the dust collector, for example, C02 or C^.
- 12 -
-------
From the difference in the concentrations of one of the components in
the gases at the entrance and exit of the dust-collecting device, one can
determine the infiltration coefficient.
A calculation of the content of sulfur oxides present in the gases to
be purified and formed by the combustion of various types of fuel is given
in § 1-4.
2. Moisture Content
The presence of moisture in gases to be purified may cause the dust to
stick and result in the corrosion of the walls of the dust collector, particu-
larly in operation with gases at temperatures close to the temperature of pre-
cipitation of the condensate, called the dew point or t,, °C.
The moisture content of a gas may be characterized by the following
quantities:
1) Concentration of water vapor d, kg/kg of dry gas (absolute moisture
content of the gas);
2) Concentration of water vapor f', g/m-3 of moist gas under standard
conditions or f", g/m^ of moist gas under actual conditions;
3) Partial pressure of water vapor pjj, n/m2 or mm Hg;
4) Ordinary percentage, equal to "W x 100, where p. is the total
*tot
pressure of the given gas equal to the barometric pressure B— the pressure
(rarefaction) p in the device;
5) The degree to which the saturated state is approached under the given
conditions, i.e., the relative humidity , %.
The relative humidity is the ratio of the weight of water vapor present
in 1 m^ of moist gas to the amount of water vapor which can be contained in
1 TO? of gas in the saturated state under the same conditions, i.e.,
m ?
I
In calculations involving dust collection, the absolute moisture content
and the relative humidity are the quantities most frequently employed.
In the solution of problems connected with the design or operation of
dust collection systems, it is most important to know the dew point of the
purified gases.
The dew point of flue gases formed by the combustion of low-sulfur fuels
can be determined with sufficient accuracy from an I-d diagram (Fig. 1-3),
- 13 -
-------
plotted for moist air if the pressure of the flue gases is close to baro-
metric.
An I-d diagram was plotted for air at a barometric pressure of 100 kn/m^.
The enthalpy of moist air I, in kJ/kg of dry air, was laid off along the
ordinate axis of the diagram.
In order to make the best use of the area of the diagram, the abscissa
axis was drawn at a 135° angle to the ordinate axis. Values of the absolute
humidity d, in kg/kg of dry air, were laid off along the abscissa axis. The
corresponding points were projected on a horizontal (arbitrary) axis d.
The diagram shows the lines of: constant values of d running vertically;
constant values I running at an angle of 135° to the ordinate axis; constant
temperatures of air (gas) 0 and constant relative humidities <|>, equal to the
ratio of the partial pressure of water vapor in air to the partial pressure of
vapor saturating the air at the same temperature. The temperature 0 is also
called the "dry thermometer1' temperature, although actually it is the temper-
ature of the moist unsaturated gas.
The curve for = 100% is the boundary curve. The points of this curve
correspond to the state of saturated air. The area under the curve <(> = 100%
is the area of wet vapor (the "fog" area).
The line of partial pressures of water vapor p = f(d) was plotted under
the curve $ = 100%. The values of pwv can be read off on the right ordinate
of the diagram.
In addition, the dashed lines on the diagram represent the constant
temperatures of the so-called "wet thermometer" t^, running at a small angle
to the lines I = const. In the case of saturation of the air with vapor
(<|> = 100%), a "wet thermometer" (i.e., a thermometer whose measuring end is
wet) will show the same temperature as a "dry thermometer". For this reason,
the isotherms on 0 and t for the same temperatures of the curve <|> = 100%
intersect.
The curves = const show an abrupt change at an air (gas) temperature
0 = 99.4CC, i.e., the boiling point of water corresponding to a barome.tric
pressure of 100 kn/m - In the area above this temperature, the lines of ©
almost coincide with the lines of d.
The diagram relates four basic parameters: the enthalpy of moist air I,
kJ/kg of dry air, its moisture content d, kg/kg of dry air, the temperature t,
°C, and the relative humidity 0, %. Knowing two of these parameters, one can
determine the other two for any state of air. I
I
In order to determine the dew point, it is necessary to trace the line
d = const from the point characterizing the state of the moist gas to the
- 14 -
-------
t. t-
• f-4 -*H
OJ CC
>> 4-
•O .rt
£ -o
§ 2
£ J
3
to tL
• H >^l
O U.
- 15 -
-------
intersection with the curve $ = 100%. The isotherm passing through this
point will give the condensation temperature of water vapor.
The absolute moisture content of flue gases entering a gas purification
system from boiler units may be calculated from the formula
.0 ./ en
, PH,OMI,O
^ 1-0.01 (/!»+ V + 9H«) + (£
kg/kg of dry gases (1-2)
where Vfetno is the volume of water vapor at standard conditions at the entrance
to the dust collector, m^/kg of fuel;
pJ,aOaidpa are, respectively, the densities of water vapor and of dry air at
standard conditions; P?i,o = °'804 Kgfa'.Pa** 1,3 /s;
A , w ; I* are the ^h content, moisture content and hydrogen content of the
working mass of fuel, °/o;
a*n is the coefficient of excess air at the entrance to the dust collecting
etc
system.
The volume of water vapor at the entrance to the dust collector, deter-
mined after the boiler unit, is approximately equal to the theoretical volume
of water vapor formed by the combustion of fuel, i/°
r
V^0j= 0,1
!f 0,0161" 4- 1 ,24 0.05% per MJ/kg, sulfurie
anhydride SO^, which in small amounts is present in the gases together with
sulfurous anhydride SO-, has a substantial influence on the dew point. With
water vapor, sulfurie anhydride forms a certain amount of sulfurie acid H~SO/ ,
- 16 -
-------
the solution of which condenses at a higher temperature than water vapor.
According to the data of the VTI, the dew point at Sred > 0.05% per MJ/kg
may be determined with sufficient accuracy from the formula
,-fH.o ,
— Jcon19ac
' ^
where £ = 195 for excess amounts of air at the end of the furnace,
af = 1.2-1.25 and 0 = 208 for af > 1.25;
a is the fraction of ash in the carryover;
Are" and Srec* are the reduced contents of ash and sulfur in the working mass,
% per MJ/kg.
The condensation temperatures of water vapor and dew points of flue gases
for certain fuels are given in Table 1-6.
At the dew point, the sulfuric acid corrosion occurs most vigorously,
and when the temperature deviates from t, in one or the other direction, the
corrosion rate falls off rapidly (see for example Fig. 1-4).
However, as the temperature of the gases decreases further, condensation
of water vapor on the walls of the gas conduits begins, and the corrosion rate
increases somewhat, reaching a maximum at ^"£nd Thus, two corrosion rate maxima
occur (Fig. 1-4) : at t (higher peak) and at
(lower peak) .
Let us note that a partial trapping of SO
tors; this may lower the dew point and bring i
temperature of water vapor (see § 1-4).
takes place in wet ash collec-
closer to the condensation
a
-
8
120
ISO
metal temperature, °C.
Fig. 1-4. Corrosion rate
versus metal temperature for
flue gases of Moscow coal
(corrosion-prone areas are
crosshatched).
In designing scrubbers it is necessary to
determine /Ha° and t , in order to evaluate the
cond ' d
possibility of corrosion of the gas conduits.
Obviously, for wet ash collectors, the maximum of
sulfuric acid corrosion can take place in the gas
conduits before the ash collector. After the latter,
because of the trapping of SO, and cooling of the
gases,1 steps must be taken against water corrosion.
The minimum permissible temperature of the gases is
established by taking into account the hygroscopic
properties of the collected dust. For coal and
shale dust, ash and other nonhygroscopic dusts,
°C[2]. For hygroscopic dusts
tpg = td + (15-20)
(cement, clay, etc.), t.
Pg
(40-50) °C.
- 17 -
-------
Table 1-6
Condensation Temperature of Water Vapor and Dew Point of Flue Gases
for Certain Types of Fuel (Based on VT1 Data).
H
oo
Fuel
toscow coal
ame
m m
mm ,
Dried Moscow coal •"
Sane
Lean Donets coal
fanie
SK Donets fuel
Kizel coal
Same
Intermediate product of--
JCizel coal
Same
Mixture of Kizel coal •
.with intermediate produo
Intermediate product of'
Donees coking coals
Estonian shale
Shredded peat
Sane
Sulfur containing fuel oi
Coke-oven gas
Sane
Reduced Content, $/MJ/kg of
Sulfur Sw
0,28
0.25
0,25
0,27
0,27
0,30
0,28
0,25
0,29
0,09
0.1!
0,03
0,25
0,26
0,53
0.49
0.41
' 0,14-0.24
0.13
0.017
0,005
0,065
0,005
0,13
0.13
AW
1,67
GO
70
'.03
73
.63
,52
2,11
2,05
0,435
0,81
0.61
1,25
.17
2.27
1,90
1,96
2,65-1,5
3,45
0,61
0,47
0
0
0
0
Mois-
ture "W*
2.90
2,95
2,95
2,95
2.95
1^07
1,18.
0,15
0,20
0,28
0,19
0,19
0,34
0,24
0,34
0,17-0.81
1,13
7.00
0^05
0.05
0.02
0,02
-
0,0035
0,0125
__
^.
0,0100
0,0124
0.0124
0,0087
0,0105
0,0046
0,0055
0,0050
0,0068
0,0038
0,0073
0,0068
0,0038.
0,0075
0.0100
0,0244
0,0153
0.0088
0.0095
0,0103
0,0103
si;
|j!l
T3 OA>
8££
44,7
51,5
49,5
503
43,9
50,0
39,5
43,0
46,0
31,0
34,0
32,0
38,0
38,0
39,5
38,0
38,0
40,0
46,0
64,0
54,0
'.3.0
44.0
4S.O
46,0
J» >
•H O
8 o
0.
a
142,5
142,5
142,5
142,5
141.0
145,0
MO.O
HO.O
138,0
125
125
107
138
132
153
150
147
117—127
78—81
64
63
120
126-142
148
152,5
'd~'
97,8
01,0
93.0
92,2
95.1
95.0
100.0
97,0
92,0
94,0
91,0
75,0
100,0
94,0
113,5
112,0
100,0
77-87
3^,0
0
77
77—93
102
lO'j.S
-------
3. Density
The flue gases formed by the combustion of fuel consist of several
components. In carrying out measurements of dust and calculations of gases,
it is necessary to know the density of the gases p, kg/m3. The density of
the combustion products of energy-producing types of fuel at standard con-
ditions (temperature t = °C and barometric pressure B = 760 mm Hg) can be
assumed with sufficient accuracy for the calculation to be approximately equal
to the air density at the same conditions, i.e., pQ = 1.3 kg/m3.
The actual density of the combustion products (or of their mixture with
air) may be obtained from the formula
k*/*5 (1-5)
where B is the barometric pressure, n/m.2 or mm Hg;
p is the pressure or rarefaction in the gas conduit, n/m2 or mm Hg;
t is the gas temperature, °C;
B = 760 mm HgwlOl 325 n/m2.
In the presence of a high moisture content (for example, when the com-
bustion products are used as the drying agent) , the density of the flue gases
may change to a value which is essential for the accuracy of the calculations
being performed.
A formula is given below which permits one to determine the density of
the gases if their absolute moisture content d, kg/kg of dry gas, is known:
f. kg/** d-6)
0,804
4. Dust Contents
The dust content or concentration of dust in gases designates the weight
of solid particles per m3 of gases' reduced to standard conditions.
^
The dust content is measured in milligrams or grams per m . *
Calculations for the determination of the dust content of gases are given
in § 1-3. The methods of experimental determination of the gas content in gas
* In evaluating the biological harmfulness of discharges into the atmosphere, use is also made of the
concept of countable concentration, which designates the number of particles per unit volume, but this quan-
tity usually is not employed in dust collection practice.
- 19 -
-------
conduits of operating boiler units and industrial heat engineering equipment
are described in Chapter 10.
1-3. Discharge of Flue Gases, Their Density,
and Their Ash or Dust Concentration
The amount of flue gases leaving a boiler unit or industrial heat-engineer-
ing installation is usually indicated when a technical project of a gas purifi-
cation system is issued. This is because the discharge of flue gases must be
calculated ahead of time, in the course of planning of the basic processing
equipment after which the gas purification system must be installed.
If for one reason or another the discharge of flue gases must be specially
computed in the course of planning of the gas purification system, this can be
done by using the formulas given in the present section.
1. Excess air coefficient in flue gases at the entrance to the dust
collector.
(1-7)
where a___ is the excess air coefficient in the escaping gases; after large-
&s o
capacity boiler units, it may be assumed equal to 1.25-1.35, and
after small and middle sized boilers, 1.5;
Aag are the air infiltrations in the gas conduits before the dust
collector; they are assumed equal to 0.001 for every running meter
of length of steel gas conduits and to 0.005 for every meter of
length of brick horizontal flues.
2- Average air excess coefficient in the dust collector.
d-8)
where a^c are the air infiltrations in the dust collector; they are assumed
equal to 0.05 for cyclone ash collectors; 0.1 for electrostatic
precipitators; 0.08 for centrifugal scrubbers, and 0.05 for wet-rod
ash collectors.
3. Volume of combustion products at the entrance to dust collectors
reduced to standard conditions per kg of fuel.
Vgen= 1^ + 1,016 (088-
- 20 -
-------
*j
where V° is the volume of combustion products for a = 1, m /kg;
O
V° is the theoretical volume of air necessary for the combustion of
fuel, m3/kg (for a gas, m^/m^.
The values of V° and V° for different types of fuel are given in
Tables 1-7 and 1-8.
4. Volume of combustion products in the dust collector at standard
conditions per kg of fuel;
(1-10)
V °x =
5. Actual flow rate of gases. In calculations of the actual flow rates
of gases, it is approximately assumed that the volumes of the combustion pro-
ducts and air change in proportion to the absolute temperature:
where B is the calculated discharge of fuel per boiler unit or other fuel-
consuming installation, kg/sec;
6esc and 6" are respectively the temperature of the gases escaping from the
boiler unit or some other processing installation and dust collector,
°C.
For dry dust collectors, 6" = 6 - (5-10) °C; for wet ones, see formula
(3-13).
Formulas (1-10), (1-101) and (l-ll1) are completely valid for dry dust
collectors only. For scrubbers, where vaporization of water takes place and
the gas temperature falls, the formulas can be used conditionally for a pre-
liminary selection of the type and size of dust collector.
The formulas given above apply to the case of complete fuel combustion.
In fuel-consuming industrial heat-engineering units (for example, in furnaces
for oxidation-free metal heating) , the excess air is sometimes reduced relative
to the theoretical amount required to provide a reducing atmosphere in the
working compartment of the unit.
When there is a marked decrease of the excess air required for complete
combustion, the calculation of the amounts of gas to be purified should be
- 21 -
-------
Table 1-7
Average Characteristics of Principal Solid and Liquid Fuels [77 ]
Fuel
Rank
.p
§o>
tss
UUR
-.'I
Si"*
o 3
||
(0 O tD
j3 JjP
§ Jj K?"
o g a
^ | J
g a. n
3 d 3
r-l O
O -H 43
> 41 «
A. Coals
Donets Basin
Long-flame gas foel
Gas fuel
Rich boiler fuel
Lean
Semianthracite
Fine and flaxseed
anthracite
Raw anthracite
Anthracite culm
Intermediate product
of wet dressing
Hud
D
G
PZh
T
PA
AH and AS
Arsh
Ash
PPH
—
13,0
7,0
6,0
5,0
5,5
5,0
6,0
7,0
11,0
20,0
19,6
15,8
18,8
15,2
15,1
13,3
16,9
16,7
40,1
16,0
20200
24700
25000
27300
26800
27100
25500
25100
15300
21200
5.35
6,53
6,53
7,21
7,20
7,21
6.76
6,63
4,15
5,66
5.86
7,01
6,96
7,6
7,55
7,48
7,04
6,93
4,52
6,21
Kuznetsk Basin
Anzhero-Sudzhensk'
Kemerovo
Same
Leninskiy
Sane
Aralichevskiy
Intermediate product
of dry dressing
PS
K-PS-SS
PS-T
D
G
T
PPS
6,5
9,0
8,0
10,0
9,0
7,0
4,0
12,2
15,5
14,7
5,0
10,9
16,7
25,0
28 100
25000
26600
26400
26100
25700
23700
7,47
6,64
7,05
6,88
6,90
6,82
6,19
7,89
7,11
7,47
7,47
7,44
7,22
6,58
Ural
Kizel
Bogoslovka
Chelyabinsk
G
Ba
B
5.5
28,0
17,0
29,3
21,6
249
20800
11900
15750
5,52
3,27
4,18
5,9
3,90
4.71
Other Deposits
Karaganda bituminous coa
Karaganda brown coal
Ekibastuz
Moscow
Pecherskiy
Same
Cheremkhovo
Raychikhiask
L PZh-PS
B
SS
B
PZh
D
D
B
7,5
26,0
8,0
33,0
7,0
11,0
14,0
37,0
25,0
17,0
36,8
23,5
18,6
24,9
21 .5
9,5
22250
15 150
16950
10500
24800
18 150
19500
12850
5,82
4.09
4,51
2,98
6,44
4,82
5,17
3,56
6,23
4,71
4.90
3,62
6,79
5,29
5,70
4,29
- 22 -
-------
Continued 1-7
Fuel
Sane
Artemorskiy ....
Estonian shale - • •
Shredded peat • • •
Lump peat . . .
Wood . . .
Coke fines • • •
Low-sulfur fuel oil •
Sulfur-bearing . . .
fuel oil
Rank
PZh
t
B
B. Othe
_
—
_
— _^
—
_
—
•8-
0) U)
•g *
o
0 MWl
%'xSf
3 f<*
-P O
15
6,0
6*0
28^0
r Fuels
15.0
50,0
40,0
40,0
20,0
3,0
3.0
Vl
o *•
43 W
C M***
0-S""*
ll
21,6
23,5
21 16
5,5
6,6
0.6
12,0
0.3
0,3
VlSto?
oo
-P V
«j g bO
"^"-PHT
t) a1*
11
-JO
24000
24000
13100
11400
9500
10700
10200
21850
39000
38400
o '
^
t-t
r-t'2
a bD
'.p 1^"
Q) Q) S
£4 D
II
6 29
w , *.*/
6,30
2,99
2,51
3,01
2,81
5,91
10,28
10,15
AD bo
f^ M
CO £4
Cj "c> KN*"
vi-l s
t-* «-T
i& .
If 0
6,72
666
4^22
3,50
3,43
3,87
3,75
6,36
11,06
10,92
Table 1-8
Average Characteristics of Principal Gaseous Fuels
Name of Fuel
Blast-furnace gas (from coke)
Coke gas (clean)
Gas from petroleum refining
(pyrolysis)
•Sc»c<
^''fi m B
|||,3
O O E<
JOQ
4000
16500
47250
t-,
.HOK^
9 S
°lc
S'o
0,78
3,93
12.05
*A* ^s
t!3!* -f
o uo to *.
If Si s
>tJ O..+J
1,64
4.67
13,31
Natural gas:
Ukhta
Boguruslan
Kurdyumskiy
Xelshanka (Saratov)
Melitopol'
Dashava (Wesl
Stavropol*
Shebelinskiy
ov) .!
33300
34000
33600
35800
35100
35600
35500
35400
8,83
9,01
8,94
9,51
9,34
9,48
9.45
9,40
9,99
10,22
10,09
10,68
10,49
10,64
10,53
10.48
- 23 -
-------
carried out by using formulas or nomograms given in ref. 76 or in other
literature sources.
6. Density of flue gases at the entrance to the dust collector at
standard conditions
0- 1 — 0,0 IA w + 1.306<4cF°
Pg'= v ' ks/n (1-12)
where Aw is the ash content of the working mass of fuel, %.
7. Actual density of flue gases at the entrance to the dustcollector.
o 273 , 2
%-=Pg'273+ is the heat loss with the mechanical incompletely burned material
(see Table 1-9), %;
Qw is the available fuel heat, MJ/kg;
32.7 is the heat of combustion of the incompletely burned material
(carbon), MJ/kg;
acar is the fraction of ash (and incompletely burned material) in the
carryover assumed equal to:
for pulverized-fuel-fired dry-bottom furnaces 0.9
for shaft-mill furnaces during combustion of coal 0.85
for shaft-mill furnaces during combustion of shales 0.7
for furnaces with heated slag hoppers 0.8-0.85
for wet-bottom furnaces:
single-chamber furnaces 0.9-0.7
twin-chambered furnaces 0.4-0.5
with preliminary chambers 0.1-0.15
for furnaces with chain grates during combustion
of brown and bituminous coals 0.2
for furnaces with chain grates during combustion
of anthracites 0.05-0.3
- 24 -
-------
9. Concentration of carryover in gases at the entrance to the dust
collector. ~~"
For boiler units
>en
Qf '
For fired driers and other industrial heat-engineering units
(1-15)
en_
MiusT"
(1-16)
where
6^ is the amount of material processed in the fuel-operated unit and
entrained by the fuel gases, kg/sec.
For drying units
rcol'
where
m
(1-17)
is the amount of material being dried referred to the moisture con-
tent of the dry material, kg/sec, determined by weighing the material
Gmoist supplied for drying and finding its moisture content wmoist,
% and the moisture content of the dry material W^r, %,
100 - W
moist
100 -
kg/sec;
G , is the amount of dried material discharged from the drier and col-
lected by the preliminary purification stages, kg/sec.
Table 1-9
Heat Loss Due to Mechanical Incompleteness of Combustion q^, %•
Fuel !
Gdov and Estonian shales ....
•A-o
t§S W
•ftri CD
ff-t Q
0) 1 id
>rH C
i— 1 cd w
30 a
CUUGL,
4
2
2
3
1,7
—
,_,
*H Ul
f 8
lg
4
1
5
1.5
1,5
l.b
$
S 0)
C3g
c
-------
1-4. Chemical Processes Occurring in Dust Collectors
In wet dust collectors (scrubbers) , in addition to the process of col-
lection of ash carryover and material processed in heat-consuming units,
there also occur chemical processes of absorption of CO, C02» S02 and SO-
from the flue gases.
This absorption takes place as a result of the solubility of the oxides
in water with the formation of acids, and the reaction of the oxides (acids)
with the hardness salts of the water and with the ash alkalis.
It should be noted that calcium sulfate (CaSO^) formed by the reactions
may cause obstruction of dust collector parts. A moderate water hardness and
ash alkalinity are therefore preferred. A large amount of sulfur oxides in
gases promotes corrosion of the equipment.
The concentration of alkalis in the ash can be found if one knows the
total content of the alkali-forming oxides CaO, MgO and ^0 from the analysis
of the fuel ash. The concentration of free alkali in the ash is then
Alk = C-^KxlO«, mg-eq/kg, (1-18)
where C is the content of oxides based on the ash analysis, %;
V is the valence of oxygen, equal to 2;
M is the molecular weight;
K is a coefficient indicating the ratio of free alkalis to the total
amount of oxides given by the analysis; it is approximately equal
to 0.375.
For CaO, which is the main oxide of the alkali elements, Alk ^134 GC Q.
For different types of fuel, Table 1-10 gives the concentrations of alkalis
in ash and the concentration of sulfur (organic and pyrite) in the working mass
of fuel.
1. Efficiency of collection of sulfur oxides from flue gases. The efficiency
of collection of sulfuric anhydride depends on the hardness of the spray water,
alkalinity of the ash, and also solubility of SO- in pure water. The volume con-
centration of sulf urous anhydride in the flue gases , expressed in percent , is
calculated from the formula
where Sw is the content of organic and pyrite sulfur in the working mass of fuel,
%.
>
V®n is the volume of gases at the entrance to the ash collector at standard
conditions, m
- 26 -
-------
Table 1-10
Alkalinity and Sulfur Content of Fuels [ 1]
Fuel
Estonian shale ....
Gdov shale ....
Angren coal ....
Kansk coal ....
Savel'yevskiy shale ....
Chernovskiy coal ....
Kashpir shale .....
Kyzyl-Kiya coal ....
Sulyukta coal ....
Bogoslovka coal ....
• Aleksandriyskiy coal ....
Hukachevo coal ....
Karaganda coal B ....
Karaganda bituminous coal • ...
Donets lean coal ....
Chelyabinsk coal . . .
Novovolynsk coal . . .
Prokopyevsk coal . . . •
Artema coal ....
Minusinsk coal • • •
Anthracite culm ....
Aralichevskiy -coal ....
Peeherskiy coal D ....
Moscow coal B ....
tegorshino coal A ....
Donets coal PHI ....
Cheremkhovo cdal ....
Sakhalin coal p ....
Lipovets coal D ....
Ikvarcheli coal ....
Kizel coal ' ....
/Ekibastuz coal . ....
-------
The concentration of sulfurous anhydride in the gases, expressed in
milligram-equivalents and referred to 1 kg of spray water, is
(1-20)
where p0,- = 2.858 kg/m3 is the density of SO at standard conditions;
g is the specific consumption of spray water per m3
of gases at standard conditions, kg/m3;
V=2 is the valence of SO.;
M=64 is the molecular weight of SO .
The amount of sulfurous anhydride absorbed (Abs) from the flue gases may
be approximately determined from the relation
Abs=5ol+ H+«Alk', ng-eq/kg, (1-21)
where Sol is the solubility of S0£ in pure water, mg-eq/kg (Table 1-11);
H is the hardness of spray water, mg-eq/kg;
Alk* is the free alkalinity of ash reduced to 1 kg of water, mg-eq/kg;
n is the leaching coefficient; for lack of other data, it may be
assumed equal to unity.
The carbonate hardness of the water spraying the scrubber depends on the
sources of water supply and may vary during the course of the year. Average
data on the carbonate hardness of water of several sources are (in mg-eq/kg):
Volga - 2; Moscow River - 1.5-5.7; Ural River - 2.2-5.7; Don River - 2;
Severnyy Donets River - 8.37; Neva River - 0.56; Black, Caspian and Aral
Seas-67.
Table 1-11
Solubility of Sulfurous Anhydride in Water (ng-eq/kg).
SOg Content of
Flue Gases, %
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
0,50
Water Temperature, "C.
40
2,13
4,19
6,13
8,12
9,81
11,40
13,00
14,60
16,10
17,60
45
1,87
3,59
5,25
6,81
8,31
9,69
11,10
12,40
13,80
15,10
50
1.50
2,94
4,37
5,75
7,06
8,31
9,53
10,70
11,90
13,00
55
1,25
2,45
3,65
4,85
6,00
7,15
8,20
9,30
10,30
11,30
60
1.00
2,00
3,00
4,00
5,00
5,00
6,94
7,91
8,78
6,69
- 28 -
-------
The quantity Alk1 may be determined from the formula
(1-22)
where Alk is the free alkalinity per kg of ash, mg-eq/kg (see Table 1-10);
Aw is the ash content of the working mass of fuel, %;
g' is the specific consumption of spray water per m^ of gases at stan-
dard conditions, kg/m^.
The coefficient of removal of sulfurous anhydride from the gas may be
represented as the ratio of the absorbed S02 to the amount of S0_ present in
the flue gases
/D. (1-23)
Sulfuric anhydride SO, is absorbed by water in greater quantities than is
SO-. For practical purposes, it may be assumed that rion •mbOJi.
A certain amount of sulfurous anhydride may be trapped in dry ash collec-
tors as a result of partial absorption of SO- by ash, in which part of the
S0? (and also SO-) is converted into sulfates. Thus, when shales are burned
to nonvolatile compounds, almost 40% of the sulfur may be bound.
According to VTI data, the coefficient of absorption of sulfur by ash
(or the coefficient of SO removal) may be determined from the following
formula:
•jjcn = 12,5vlO~MdAlk°/n (1-24)
*O\Jj * A * v * » **^£\. f Q j \ .*. *. -T /
where A is the ash content of the fuel in the dry mass, %;
Alk is the alkalinity of the ash, mg-eq/kg (see Table 1-10).
2. Amount of sulfurous- anhydride at the entrance and exit from the ash
collector:
(1-25)
d-25')
(1-25M)
- 29 -
-------
1-5. Coefficients of Purification of Gases
in Dust and Ash Collectors
The coefficient of purification (otherwise referred to as the degree
of purification or dust collector efficiency) gives the ratio of the weight
of the dust collected in the dust collector to the weight of entering dust.
Gen
The determination of the purification coefficient is the final step in
the design of dust collectors. By using it one can evaluate the efficiency of
removal of dust of a certain particle size composition from a gas in a dust
collector of a given design. The value of n obtained (total purification
coefficient) may change with the coarseness of the dust.
The efficiency of a dust collector of a given design is characterized
by the fractional and partial purification coefficients attainable through
its use. The fractional coefficient gives the ratio of the amount of dust of
a given fraction collected in the device to the amount of entering dust of
the same fraction. The partial coefficient involves dust of certain particle
dimensions (diameters):
pcolGcol FcaL
^«r=^ c1-27)
The fractional (partial) purification coefficients for different particle
sizes are determined experimentally or theoretically for dust collectors of
different types and sizes, and their values must be known.
The total purification coefficient may be calculated from the fractional
(partial) composition of ash or dust entering the dust collector and from the
fractional (partial) purification coefficients:
In calculations with the formula it is necessary that the size integrals
for the dust composition and for the fractional purification coefficients be
the same. Instead of ri^ one can use n for the average value of x for the
- 30 -
-------
interval. The stuns Fgn [In formula (L-29) ] and NenAx [in formula (1-30)] should
each amount to 100%.
Frequently, the fractional or partial purification coefficients character-
istic of a device are known for particles with a density differing from that
of the ash or dust susceptible of collection. In this case the conversion from
particle size dkn with density pfcn, for which the partial or fractional purifi-
cation coefficients are known, to the actual size of the particles d . with
density Pact> for which these coefficients will be valid, is accomplished by
using the following relation:
Formula (1-30) may be written more accurately as
/7 V 0 / ^ T Q1 A
3 100 •*' '0< (1~32)
In designing a composite dust collector consisting of two (or more) units
of different types mounted in sequence, it is necessary to determine the frac-
tional composition of the dust leaving the preceding stage and entering the
next stage. In this case, each fraction is recalculated by using the formula
(1-33)
or
where r) and TI are respectively the fractional and partial coefficients of
P P T
gas purification in the first stage, %; n is the total coefficient of gas
purification in the first stage, %.
The total gas purification qoefficient in the second stage is calculated
by taking into account the fractional composition of the dust entering the
second stage.
The total (overall) coefficient of gas purification in a two-stage dust
collector is given by the formula
'!* (1-35)
- 31 -
-------
PRINCIPLES OF DESIGN OF GAS PURIFICATION SYSTEMS
A. P. Anastasiadi
From "Ochistka dymovykh gazov v promyshlennoy energetike". A. A. Rxisanov,
I. I. Urbakh, and A. P. Anastasiadi. "Energiya", Moskva, p. 189-206, (1969).
6*-l. General Backgroimd
The presence in flue gases of certain concentrations of solid particles
depends on the type of fuel and methods of its combustion, the design charac-
teristics of the furnace systems, the efficiency with which the furnace
process is carried out, and the type of fuel-consuming unit and its operating
conditions. The struggle against atmospheric pollution should be waged along
three major lines: first, improvement of the design of fuel-consuming instal-
lations and optimization of their operating conditions; second, by installing
suitably chosen ash and dust collectors, and third, by installing sufficiently
high smokestacks in order to disperse the fly ash and dust over considerable
distances and areas and thus to decrease their harmful effects.
The choice of dust and ash collectors to be included in a system of puri-
fication of flue gases depends on a number of factors. The main factors are
the type and capacity of the boiler or other industrial heat-engineering unit,
the type of fuel and method of its combustion, the presence in the flue gases
of carryover of the material being treated in the technological unit, the
physicochemical properties of the carryover, the most efficient method of dust
and ash removal, the possibility of a convenient combination of gas purifica-
tion equipment, and the required degree of gas purification.
The limited number of designs of steam or furnace boilers commonly used
in the power industry has led to the formulation of certain recommendations
for selecting ash collection systems for them as a function of the type of
fuel burned.
In this section we shall indicate only that boiler houses burning solid
fuel should be equipped with devices for the removal of ash from the flue
gases when the value N of the conventional characteristic of the boiler exceeds
5000,
N = AWB
where Aw is the ash content of the working mass of fuel, %;
B is the maximum hourly estimated fuel consumption, kg/hr.
*Editor's note: The first digit represents chapter numbers.
- 32 -
-------
If N is less than 5000, the installation of ash collectors is required
only if the boiler house is located in a residential area. When solid fuel
is used only for emergency purposes, ash collectors usually are not installed.
Owing to the relatively small absolute quantity of ash discharged,
boiler units usually make it possible to make use of gas purification devices
of moderate efficiency, but on the other hand of low hydraulic resistance,
capable of operating on the natural draft generated by the smokestack.
In industrial heat-engineering units, in addition to the necessity of
ensuring the purification of waste gases for sanitary purposes, the selection
of the system of dust-collecting equipment is frequently determined by the
conditions of recycling of the trapped product. The use of trapped dust in
industry increases the motivation of personnel in trying to achieve a good
performance of the gas purification system.
The concentration of noxious substances in the air of the breathing zone
may be reduced by increasing the height of the stack discharging the flue
gases into the atmosphere. • The higher the stack, the lower the concentration
of noxious substances near the earth. A high smokestack not only decreases
the concentration, but also pushes back the start of the pollution zone. How-
ever, by building high stacks for discharging the waste gases into the atmos-
phere, one can lower the concentration of noxious substances to the maximum
permissible values only for a small part of the installations; in the great
majority of cases, a combination of efficient dust collectors and a smokestack
of suitable height determined by calculation is required.
Before starting the design of a gas purification system, one must make a
thorough study of the design and operating characteristics of the dust and ash
collectors developed thus far. Those most commonly employed are discussed in
the preceding chapters. A whole series of other devices that may be more
suitable in specific cases can be found in the book by V. N. Uzhov [18] and
elsewhere.
The selection of dust collectors must be made in each individual case on
the basis of the technical and economic indices of the dust-collecting system.
Each dust-collecting device is built and designed for a given set of operating
conditions. Therefore, in comparing a given dust-collecting device, it is
necessary to think in terms of devices designed for operation under the same
technological conditions.
Thus, for the purification of flue gases from boiler houses, the compari-
son is made between cyclones, multicyclones, and TsS-VIT scrubbers of approxi-
mately the same efficiency that is adequate for the case under consideration.
When it is necessary to achieve fine cleaning of large volumes of gases from
boilers of medium and large steam capacity, one can compare PGD and PGDS type
electrostatic precipitators MP-VTI type ash collectors, and in some cases bag
- 33 -
-------
filters. When it is necessary to purify gases from industrial heat-engineer-
ing units, which are characterized by the widest range of gas discharge and
required efficiency of dust collection, in addition to the units enumerated
above one can compare type Ts electrostatic precipitators, foam devices,
high-speed gas washers, etc.
When the designing is started, a whole series of initial data must be
collected. Then, it is necessary to draft the possible layouts of the gas
purification system and carry out alternative calculations to permit the
selection of the optimum version from the standpoint of expected efficiency,
hydraulic resistance, capital and operating costs, composition of the equip-
ment, etc. To facilitate the preliminary selection of devices in the drafting
of possible layouts of a system of purification of flue gases, Table 6-1 gives
some average technical economic indices for some of these layouts.
Table 6-1
Average Technical-Economic Indices of Dust Collectors.
Dust Collector
VTI louver-type ash
collector
NIIOQAZ cyclone
Multicyclone
TsS-VIT centrifugal
scrubber
MP-VT 1 wet-rod ash
collector
Foam scrubber
High-speed gas washer
Bagfilter
DVPH vertical-type .elec-
trostatic prepipitator-
DVPH-BTs composite. elec-
trostatic . precipitator
with multicyclone
PGD-type three-pole hor-
izontal elect, precip.
Ts two-pole horizontal
electrostatic precipi-
tator.
i
I-*
o>.ri
gj 4}
ft a
boo
«>-H
no
81
80
90
92
95
93
99
90
98
96—98
97—98
Hydraulic
Resistance,
n/m*
4SO
4EO
500
esc— soo
800
400
icdo
150
600
150
150
Consumption
Expended on
1000 m^to°nof
ff1
• H -
+>W
^IC
0,93
0,93
1.0
1.1
1.3
I.I
14—21
1.5
0,57
1,3
0.93
2.5
^
0»
S
-p
-------
Table 6-2
Partial Purification Coefficients for Various Devices
(Average Values)
Dust Collectors
Multicyclones ....
High-speed gas washer with a large
Dry electrostatic precipitator • • •
Particle sizes, un
50
90
100
99
100
100
99
too
10
85
96
96
94
>99
98
>99
5
67
89
94
88
>99
92
>99
I
10
20
35
60
97
82
99
The color intensity of the discharge and its biological noxiousness are
chiefly determined by the area of the particles contained therein. Hence the
importance of trapping the largest possible amount of fine particles becomes
evident, but this also happends to be the range where the efficiency of the
dust collectors is lowest. Table 6-2 shows that the cyclones most frequently
used for dust and ash trapping have an efficiency of the order of 10% for
particles of 1 p (this being characteristic of dust from sublimation), and
only high-speed gas washers, cloth filters and electrostatic precipitators
have a high efficiency for particles of this diameter.
In combining dust-collecting equipment, the following guidelines should
be used.
The dust collectors are usually installed on the suction side of flue gas
pumps. The installation of dust collectors on the delivery side of the pumps
is possible, but is not recommended, since in this case the pumps are subjected
to abrasive wear.
For convenience of servicing and repair of dust-collecting equipment,
individual dust collectors should be mounted, as a rule, on every processing
unit. '
When a boiler house operates on solid fuel only, the individual ash col-
lectors should not have any gas conduits or horizontal flues surrounding them.
When a boiler house operates on gas fuel, with the utilization of fuel as a
reserve, the ash collectors are placed on horizontal flues surrounding them or
on gas conduits. The main flues or gas conduits should be equipped with
reliable devices for disconnecting them during operation on solid fuel.
- 35 -
-------
Dust- and ash-collecting devices may be installed both inside buildings
and outdoors. One must then consider the climatic conditions of the area,
the periodicity of operation, type of apparatus used, and the volume of the
gas being purified. In practice, however, the majority of dust and ash-
collecting devices may operate outside buildings. For example, most electro-
static precipitators that are the most complex from the standpoint of design
and operating characteristics are installed outside the boiler house. How-
ever, to protect the insulating housings from deposits and to facilitate
their servicing, the top of the electrostatic precipitator is covered by a
tent. The space under the hopper is also covered with light materials. As
a rule, cloth filters and foam devices are mounted inside buildings.
Characteristics of Two-Stage Purification of Gases
Using Electrostatic Precipitators
Experiences with the operation of electrostatic precipitators in differ-
ent branches of industry shows that in the presence of a high initial ash or
dust concentration in the flue gases (over 40-50 g/m^), the efficiency of the
purification decreases. This may be due to a rapid build-up of precipitated
material on the discharge and collecting electrodes, making it necessary to
increase the frequency with which they are shaken off, and thus resulting in
an increase of secondary carry-over.
In order to decrease the concentration of carryover in the gas fed to
the electrostatic precipitators and hence to ensure a more reliable and
stable operation of the precipitators, the use of preliminary (rough) purifi-
cation of flue gases in mechanical ash collectors with a low hydraulic resis-
tance, for example, cyclones or direct-flow cyclones, is recommended. Doubts
are sometimes expressed concerning the usefulness of installing a preliminary
gas purification stage, since in this case mainly fine carryover particles
will reach the electrostatic precipitators. And, since the adhesive properties
of fine carryover particles are much less obvious than those of coarse particles,
serious difficulties will arise in attempts to remove them from the electrodes
of the devices, and the degree of purification of the flue gases will be de-
creased. In any case, in the German Federal Republic, the installation of a
multicyclone as the first stage of purification before the electrostatic pre-
cipitators is recommended only in cases where the content of combustibles in
the carryover exceeds 20%. However, even then the following conditions must be
met: the efficiency of ash collection of the first purification stage should
not be too high, so that the conductance of the carryover is sufficient to
ensure a stable operation of the successive electrostatic precipitators and to
prevent the electrodes of the latter from being grown over with the fine
particles of the carryover.
Results of the operation of electrostatic precipitators at a number of
Soviet power plants where preliminary purification of gases in mechanical
- 36 -
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devices is employed have demonstrated that such doubts and apprehensions
are not always well-founded.
First, when multi-ash fuels are burned, the mere installation of an
electrostatic precipitator, even when a relatively high efficiency is attained,
does not always ensure the sanitary standards of purification of the flue
gases, whereas the installation of a preliminary purification stage, even
though the overall degree of purification is increased by only a few percent,
makes it possible to reach the permissible standards of residual concentration
of the carryover in the purified gas.
Second, the presence of a first purification stage makes it possible to
cut down considerably on the discharge of fly ash into the atmosphere when-
ever the electrostatic precipitators must be disconnected for whatever reason,
since the preliminary stage usually ensures a 60-80% efficiency of ash collec-
tion.
As far as any serious risks to the stable and efficient operation of
electrostatic precipitators should fine carryover particles penetrate into
them, the following example may be mentioned: in the combustion of high-energy
coals in furnaces with a slag removal coefficient of about 80-90%, the gases
leaving the boiler unit contain a comparatively large amount of fine carry-
over particles, but the degree of purification of the flue gases by the electro-
static filters remains quite high [47, 50].
It should be noted that statements are frequently made to the effect that
the installation of a two-stage purification system is undesirable because it
raises the cost of construction and assembly and the operating cost. However,
in several countries and particularly in the U.S.A., a two-stage purification
system of 99% efficiency is a relatively common method of ash collection [55].
In solving the problem of selection of a given gas purification system,
in addition to the economic considerations , one should take into account the
sanitary conditions. In general, according to the recommendations of the
State Institute for the Design and Planning of Structures for Gas Purifica-
tion, the preliminary purification of flue gases in mechanical devices should
be carried out when the initial dust content of the gases is above 40 g/m3.
6-2. Relationship Between the Height of Smokestacks and the
Required Efficiency of Gas Purification
The height of smokestacks of electric power plants and other fuel-consum-
ing enterprises should ensure a dispersal of ash, dust, sulfur dioxide or other
noxious impurities such that their concentrations at ground level drop below
the maximum permissible values (Fig. 6-1).
- 37 -
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For the same amount of polluting solid impurities in the flue gases
at the exit from the boiler or other industrial heat-engineering unit, the
smokestack chosen may be lower the higher the efficiency of the dust-collecting
system, and vice versa.
Therefore, in planning industrial power stations, boilers, etc., one of
two problems must be solved:
1) the minimum stack height is found from known impurity concentrations
in the gases after the gas purification system, and from the maximum permis-
sible concentrations at ground level;
2) the concentrations of noxious impurities which can be permitted at
the exits from the gas purification system are found from the accepted stack
height and from the maximum permissible concentrations at ground level.
In calculating the dispersal of noxious impurities by smokestacks, use
should be made of the "SN-369-67 Recommendations for the Atmospheric Dispersal
of Noxious Impurities (Dust or Sulfur Dioxide) Present in the Discharges of
Industrial Enterprises", worked out by the A. I. Voyeykov Institute and per-
taining to the following enterprises and facilities:
1) boiler houses;
2) sintering ferrous and nonferrous metallurgical plants;
3) pelletizing ferrous metallurgical plants;
4) converter, open-hearth, and electrosmelting plants;
5) blast-furnace production;
6) production of sulfuric acid by the contact process;
7) production of elemental sulfur;
8) petroleum refineries (combustion of fuel oil).
In accord with the Main Sanitary Epidemiological Administration of the
Public Health Ministry of the USSR, these recommendations may be used in calcu-
lating the dispersal of other noxious substances in the atmosphere and may also
be applied to other facilities.
When the atmosphere is polluted by sources whose parameters (see below)
are not covered by the calculations indicated by SN-369-67, use may be made
of P. I. Andreyev's formula [102].
The methods for calculating the dispersal of noxious substances in the
atmosphere are. based on the determination of the concentration of these sub-
stances in the ground layer of air.
- 38 -
-------
. • •I*--.**-*"**' *- •v
-------
For sulfur dioxide and for nontoxic dust, the single MFC's are taken
as 0.5 mg/m3.
Calculation of Atmospheric Concentration of Dust and SO^ Discharges
from Smokestacks According to SN-369-67 Recommendations
Under favorable weather conditions and for a level or slightly dissected
topography, the maximum single concentration from N stacks of the same height
at a distance of 20 stack heights is given by the formula
AFmMs
where A is a coefficient dependent on the temperature stratification of the
atmosphere and defining the conditions of vertical and horizontal
dispersal of the impurity in air, sec2/3 degl'3;
F is a dimensionless coefficient of the physical state of the noxious
substance;
m is a dimensionless coefficient taking into account the influence of
the exit velocity of the gas at the orifice of the discharge source
(stack) ;
Mt is the maximum total discharge of the noxious impurity from all the
stacks, g/sec;
H is the geometric stack height, m;
N is the number of stacks of the same height;
Q is the total volume of the flue gases discharged from all the stacks,
m3/sec;
At is the difference between the temperature of the gases leaving the
stack tg and the temperature of the surrounding air ta, °C.
A method of selection and calculation of these quantities is given below.
Coefficient A is taken for unfavorable weather conditions, when the wind
velocity reaches the unsafe value V and an intense vertical turbulent exchange
takes place. At the same time, the ground concentration of the noxious sub-
stances in air reaches its maximum value.
The following values of A should be taken in the calculations:
For the Caucasus, Central Asia, Siberia, Lower Volga
and Far East .......................................... 200
For the North and Northwest of the European Territory
of the USSR, Ural, Ukraine and Middle Volga ........... 160
For the Central part of the European Territory of the
USSR and regions with similar climatic conditions ..... 120
- 40 -
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In other areas of the territory of the USSR, the values of coefficient A
should be taken on the basis of the similarity between the climatic conditions
of turbulent exchange in these areas and those mentioned above.
If according to the data of the hydrometeorological service unfavorable
local weather characteristics are present, the values of ground concentrations
of noxious substances should be increased by 25% in the calculations in accor-
dance with the existing scientific and industrial experience.
The value of coefficient F as a function of the efficiency of the dust-
collecting system TI and for S02 is given below.
Impurities SOZ
F 1.0
Ash for iJ^OOl
2,0
/o Ash for i)<90/o
2,5
Coefficient m should be determined from parameter f by means of the graph
given in Fig. 6-2.
The applicability of formula (6-1) is restricted by a condition according
to which the parameter
where WQ is the exit velocity of the gas from the mouth of the stack, m/sec,
and D is the diameter of the orifice of the stack, m, should satisfy the
inequality f<6.
In determining the difference At between the temperature of the discharged
gas mixture tg and that of the surrounding air t& it is necessary to assume
the temperature of the surrounding air to be the average temperature of the
hottest month at 1 P.M.
For boiler houses operating in accordance with the thermal graph, the
average temperature of the heating period may be taken in the calculations.
\
The concentrations of noxious substances calculated on the basis of the
present official recommendations pertain to steady conditions of propagation
of the impurity retained in the atmosphere above a level or slightly dissected
topography (with" slopes of not more than 2-3°). In planning enterprises to
be located on rugged terrain, it is necessary to resort to special recommenda-
tions for the calculation of the dispersal of noxious substances in the atmos-
phere compiled by the Main Geophysical Observatory im. A. I. Voyeykov of the
Main Administration of the Hydrometeorological Service, Council of Ministers
- 41 -
-------
of the USSR, and the Main Sanitary Epidemiological Administration of the
Ministry of Public Health of the USSR.
The maximum concentration of noxious sub-
stances at ground level under unsafe meteorological
conditions is reached at a distance JC from the
source, this distance being determined in terms of
the stack height H from the formula
Jfm=20//, .. (6-31
Concentrations of noxious substances differing
from the maximum value by not more than 30% are
observed at distances of (10-40) H.
J if
n/sec/deg
Tig. 672. Graph for deter-
mining coefficient f .
The unsafe wind velocity Vm at a height of 10 m
above ground level, at which the highest ground concentration of noxious sub-
stances in air is reached, is approximately given by the formula
m/sec.
(6-4)
Usually, the wind velocity at the height of 10 m is 0.5-10 m/sec. For
V = 2 m/sec, the flue gases rise vertically upward, and for Vm = 9-10 m/sec,
the flue gases are sheared off the stack orifice and move parallel to the
ground at the level of this orifice. More accurate calculations show that the
estimated unsafe velocity Vm is slightly higher than that calculated from the
formula and is dependent on parameter f . When f
-------
The above-described approximate method for calculating the change of
the concentration of noxious substances in atmospheric air can be used only
when the smokestack orifices are located much higher than the rooftops of
the surrounding buildings. When the stack orifice is located relatively low
above the roof of the boiler house (Fig. 6-la) , the smokestack is in the
zone of eddy formation, located on the leeward side of the buildings, and
the general pattern of propagation of the jet is disturbed; the concentration
of noxious impurities in this case may be much higher than in the case of
propagation of the smoke jet assumed in the derivation of formula (6-1) and
illustrated in Fig. 6-lb.
The general laws of propagation of a smoke jet are also inapplicable
to a mountainous topography, especially when the boiler house is located
at the foot of a mountain or hill. In this
case, the direction of motion of the smoke jet
(its axis) may be parallel to the slope of the
mountain (when the wind blows from the mountain
toward the stack), and the stack gases may reach
the ground much faster than in the case of a
level topography.
. r When expanding a boiler house or planning
'i IT a new enterprise with the discharge of noxious
impurities taking place in an area where atmos-
pheric air has already been polluted with the
Fig. 6-3. Grap^for determining sgme impurities from other industrial plants,
it is necessary to consider the background con-
centration c^. In this case, the sum c^ + c^ must not exceed the MFC
(maximum permissible concentration).
The value of the background concentration is established by agencies of
the Sanitation Inspection.
If several enterprises are located on a single straight line (with a
deviation of not more than 1-1.5 H), then at the point of the assumed concen-
tration maximum the values of % are obtained as the total concentration from
these enterprises.
When the enterprises are not located on the same straight line, the deter-
mination of CL. is made at the point of the assumed maximum on each curve con-
necting the given enterprise with the facility under construction. The value
which is then taken for c^ is the highest value found for each of the straight
lines separately.
The calculation of the maximum concentration for power plants and enter-
prises with stacks of different heights and different discharge parameters is
performed as follows. For each of the stacks, (^ and X^ are first determined
- 43 -
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by means of the graph given in Fig. 6-4, and curves of the change of concen-
tration c with distance X are plotted. The curves for each of the stacks are
then superimposed on a single graph with a common origin of coordinates.
Values of c from all the stacks are then summed up for the values of X, and
the total value is found as a function of distance X. The highest value
represents c^ for the entire system of stacks, and the corresponding value of
^ represents the distance at which the maximum of the total concentration
is reached.
1,0
0,6
Ofi
0,2
•o
x-~—
1 2 3 4- 5 673 9
Fig. 6-4. Distribution of the concentration of discharges from
a smokestack at ground level.
1 - sulfur dioxide; 2 - ash
In cases where individual gas purification units are planned without a
determination of the total single concentrations of the substances from all
the sources producing the background pollution, the degree of purification
of the discharges containing dust is established as a function of the maximum
permissible dust concentration in the air of the work zone of the plant
buildings.
Maximum permissible concentration
of dust in the. air of the work zone
in plant buildings, mg/m3
2 and less
More than 2 to 4
ii ii 4 " g
Permissible content of dust
in the air discharged into
the atmosphere. mg/m3
30
60
80
100
When the concentrations of noxious substances in the atmospheric air
of populated areas remains within limits not exceeding the maximum single
permissible values, the residual amount of noxious substances in the gases
discharged into the atmosphere is not standardized.
- 44 -
-------
It has been decided that discharges containing dust with an average
size of less than 80 y in an amount not exceeding the above-indicated per-
missible dust content in the discharges released into the atmosphere do
not have to be purified.
Example. Determination of the required efficiency of an ash collector for an existing
smokestack.
Initial data.
The boiler house discharges into the atmosphere stack gases at a
rate of 100 m3/sec
Gas temperature at exit from stack orifice 130°C.
Initial ash content of flue gas 14.0 g/m?
Geometric height of existing smokestack 80 m
Diameter of smokestack orifice 2.5 m
Allowing for the existing atmospheric background dust content, the
permissible ash concentration in the breathing zone should not ,
exceed 0.25 kg/m5
Location of boiler house - Ukraine, city of Kherson.
Average air temperature at 1 P.M. during the warmest month
(according to clinatological data) +29°C.
Calculation
Since the temperature of_the gas (l30°C.) is considerably higher than that of the surrounding
air, we check the applicability of the calculation by using parameter f of Recommendations SN-369-6?
l
f ~
The exit velocity of the gas from the orifice of the smokestack is
100-4
**• = 3 14-2.5*" = 20'3 m/sec«
The temperature difference between the gas and the surrounding air is
A/=130—29-101° C.
Substituting the values into the formula for the determination of the parameter
10J-20,31!-2,5
80'- 101
dee
The value of parameter f satisfies the inequality f < 6, and therefore the calculation of the
dispersal is done by using the method of Recommendations SN-369-6?.
The permissible discharge M^ is determined by the formula
g/sec
where A 160 sec2'3 deg1/5 for the Ukraine region;
F = 2 f or an ash collector efficiency of over 90J&5 ,
m = 0.9 according to the graph given in Fig. 6-2 for f = 1.6 m/sec^ deg.
Substituting the above-indicated value into the formula,
100- 101~
=119
= - 160.2-0.9
The maximum permissible residual dust content of the flue gases at the exit from the ash collector is
The minimum required efficiency of the ash collector is
(14 — 1.19)100
- - ^ -
91 ,5
- 45 -
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DETERMINATION OF THE BASIC PROPERTIES OF DUSTS AND GASES
A. A. Rusanov
From "Ochistka dymovykh gazov v promyshlennoy energetike". A. A. Rusanov,
7T~I. Urbakh, and A. P. Anastasiadi. "Energiya", Moskva, p. 405-440, (1969).
11*-1. Determination of the Dispersity of Ash or Dust
In determining the particle size of ash and dust, the following factors
must be distinguished:
a) primary particle size, i. e., the size that characterized the par-
ticles at the time of their formation;
b) particle size after a certain coagulation of the particles during
the motion of dust-laden gases along the gas conduit;
c) size of particles in the form of floes and small clumps after their
separation from the gas phase.
The efficiency of dust-collecting devices depends on the particle size
characteristic of the ash or dust after a certain coagulation of the parti-
cles in the gas conduits. The degree of particle coagulation in the gas
conduits depends considerably on the initial particle size. The coarser the'
particles, the less they tend to coagulate; particles'over 100 U in diameter,
for example, practically do not coagulate. Therefore, if the content of fine
fractions is small, in carrying out calculations of the efficiency of planned
dust-collecting devices, one can use data on the particle distribution over
the sizes in the gas conduits as well as over the original sizes. When the
content of fine particles is considerable, the estimated efficiency of the
dust-collecting devices may turn out to be somewhat low if the calculations
are made by using data on the distribution of the particles over the origi-
nal sizes.
There are a number of methods for determining the particle size. Those
most commonly used are sieve analysis, air separation, liquid sedimentation,
and microscopic analysis. The last few years have seen the development of a
relatively approximate determination of dispersity by the method of three cy-
clones, and a more accurate determination, but with a narrower scope of ap-
plication to the maximum permissible temperature and dust content of gases,
by means of multistage jet settlers. Work aimed at increasing the accuracy
of the three-cyclone method and expanding the range of applicability of the
multistage jet settlers is continuing.
'In the methods of sieve analysis, air separation and liquid sedimenta- j
tion, the'material subjected to analysis consists of dusts separated from tne
gas phase, i. e., in the form of a deposit. The dust taken in this form is
'Editor's note: The first digit represents chapter numbers.
- 46 -
-------
dispersed by some means so as to obtain particles of the original size, and
the size distribution for these particles is then obtained.
The three-cyclone method and multistage jet settlers make it possible
to obtain the particle size distribution without their preliminary separa-
tion from the gas phase, i. e., the distribution over the sizes that they
acquire after a certain coagulation in the dust-laden stream.
The method of microscopic analysis as a function of the method of sam-
pling makes it possible to obtain the particle distribution both over the
original sizes and over the sizes of the particles after a certain coagula-
tion in the gas conduits.
Each of the enumerated methods has a certain scope of application'that
does not always coincide with those of other methods. Therefore, each, de-
spite certain disadvantages, retains its importance.
Sieve Analysis
Sieve analysis is based on sifting the ash or dust sample through sieves
with different meshes. The particle size composition of the dust is estimated
from the weight of the residue on the different sieves. The metal screens '
for the sieves are manufactured in the USSR in accordance with COST 3584-53,
the finest screen having a mesh size of 44 U .
The sieves are in the form of cylindrical shells whose bottom is closed
off by the screens, and they are stacked in a column so that the mesh size
decreases from the top down. A solid bottom on which the finest fraction is
collected is placed under the finest sieve.
The sifting is done either mechanically or by hand.
Mechanical shifting employs a special "Rotap" instrument which shakes
the set of sieves fastened inside it. Other machines are also manufactured.
A predried dust sample weighing 25-100 g is placed in the top, coarsest
sieve. After the machine has operated for 20 minutes, the residue on each
sieve is weighed. The fractions obtained are called incomplete, since the
upper sieves retain a part of the dust which would collect completely on
each of the lower ones. By plotting the values of incomplete residues in a
suitable coordinate system or collecting them in a table (see Fig. 1-lb),
one can obtain the fractional distribution of the dust.
The complete residue on each sieve can be obtained as the sum of in-
complete residues on the same and upper sieves.
By plotting the values of complete residues in suitable coordinate
- 47 -
-------
systems (see Fig. 1-1 c and d), one can obtain curves characterizing the par-
ticle composition of the dust, which in sieve analysis are termed curves of
complete residues on sieves.
Manual sifting is done on each sieve successively, beginning with the
finest, or on & small assortment of sieves. The'sieves are closed off with a
bottom plate and with a lid. During the sifting, two or three brief back-
and-forth movements should be made in the horizontal plane, then the sieve
should be shaken by lightly tapping the bottom plate against'the table and
tilting the sieve at an angle. The sifting is complete when, after checking
by shaking the sieve over a sheet of paper, not more than 0.1% of the weight
of the dust for a given sieve falls on the paper.
Since the finest sieve has a mesh size of 44 y, sieve analysis is appli-
cable only to dusts whose bulk is made up of particles coarser than 45 y.
When sieve analysis is performed, it should be assumed that dust particles
less than 10-20 y in size may coalesce into coarser solid agglomerates during
the sifting, causing substantial errors bedause of the resulting high results
for the coarse fractions. For this reason,'in cases where the dust contains
less than 17o of particles coarser than 60 y, sieve analysis should not be
employed.
Air Separation
This method of determination of the size distribution of dust is based
on the fact that particles of different sizes have different hovering- veloc-
ities and hence are carried out of a vertical tube by a laminar air stream
at different velocities of the latter. The hovering velocity is the free-fall
velocity of particles in stationary air. A nomogram for determining the par-
ticle diameter from their hovering velocity is illustrated in Fig. 3-10*.
The instrument for determining the sizes of particles from their hover-
ing velocity usually consists of three or four vertically mounted tubes of
different diameters about 1 m high.
On the top and bottom, the tubes have conical parts ending in nozzles.
The lower nozzle can be connected by means of a rubber tubing to an attach-
ment for stirring up the dust studied, and the upper nozzle is connected to
a paper filter holder analogous to those used in the determination of the
dust content of gases.
Clean air is blown through the tubes with connected attachments for
stirring up the dust and with filters. By varying the velocity of the air
supplied for stirring up the dust and the tube diameter, one can achieve a
state in which only particles with sizes for which the hovering rates are '
less than or equal to the velocity of the air in the tubes are carried out
of the dust stirred up in the attachment and into the paper filter.
Editor's note: this figure is not available in the section translated.
- 48 -
-------
Air
The most frequently used instrument
consists of three tubes with inner dia-
meters of 140, 70 and 35 mm and the stir-
ring attachment illustrated in Fig. 11-1.
The maximum quantities of air that
can be supplied to each tube are determin-
ed from the condition of laminar flow
Re=2300 = J
(11-1)
where w is the maximum mean velocity
Fig. 11-1. Attachment for
stirring up dust.
of the gas in the tube at which the lami-
narity of the flow is retained, m/sec;
D is the tube diameter, m;
v is the kinematic viscosity of air,
m^/sec.
Along the tube axis, the velocity will
be twice as large as the mean value
w
max
2w
In determining the size composition of the dust by the air separation
method, the following procedure is used:
1. The fractions into which it is desirable to divide the dust under
study are specified.
2. A nomogram is used to determine the hovering velocity for the maxi-
mum size particles entering into the composition of each fraction.
3. Air flow rates are calculated which must be supplied to any of the
tubes in order to obtain along the tube axis the velocities corresponding to
the hovering velocities of the maximum-size particles entering into each of
the specified fractions. It is necessary that these discharge rates be in-
cluded in the above-indicated range, as determined by the conditions of lami-
narity of the flow and stirring up of the dust. This can be done by using
tubes of different diameters.
4. A weighed amount of thoroughly dried dust from 2 to 10 g is loaded
into the attachment.
5. The paper filter is weighed.
- 49 -
-------
6. The attachment and filter are mounted on the tube, for which the ve-
locity permitting the entrainment of the finest of the specified fractions is
calculated.
7. Air for the entrainment of the finest fraction is passed through the
tube with the attachment and filter. During the entrainment, the tube and
attachment should be periodically tapped with a wooden hammer having a rubber
tip. Instead of tapping the attachment, it is preferable to connect it to a
vibrator. The entrainment of the fraction is considered complete when the
weight increase of the filter during the course of an hour ceases to increase
by more than 1% of the original weight of the dust loaded into the attachment.
The entrainment of a single fraction lasts up to several hours.
8. The weight fraction of the entrained fraction is determined in per-
cent. The entrainment of the next fraction is then carried out. The weight
fraction of all the dust fractions is thus obtained. The weight of the dust
remaining in the attachment and on the tube walls corresponds to the weight
fraction of particles with sizes greater than the maximum particle size enter-
ing into the last of the entrained fractions.
In order to reduce the settling of the dust particles on the walls, the
metal tubes should be grounded.
Each type of dust corresponds to an experimentally determined optimum
moisture content of air at which there is a minimum adhesion of fine parti-
cles to the tube walls. The moisture content of the air supplied for the
entrainment of the dust may be controlled by passing part of it through water
or a concentrated solution of sulfuric acid.
The flow rate of air is controlled by means of a rheometer or rota-
meter.
The pretreatment of the air entering the separator, the velocity of the
flow in the latter (mean or maximum), the method of tapping, etc., have not
been standardized. Each institute or organization which carries out the
analysis employs its own procedure. Studies made by Yu. I. Chicherin at the
State Scientific Research Institute of Gas Purification for Industry and
Sanitation (NIIOGAZ) have shown that this causes appreciable differences in
the results of the particle size analysis of one and the same dust carried
out in different institutes.
Liquid Sedimentation
The settling rate of solid particles in a liquid undet the influence of I
the force'of gravity depends on their geometric dimensions, density of the •
particles, density of the liquid in which the particles settle, and its vis-
cosity. The method of determination of the fractional composition of dusts,
- 50 -
-------
based on the observation of the settling rate of particles in a liquid, is
called the sedimentation method. It can be used only when the following
condition is fulfilled:
(11-2)
where Re is the Reynolds number;
d is the particle diameter, m;
w is the fall velocity of the particle, m/sec;
h is the height from which the particle falls, m;
P£ is the density of the liquid, kg/m ;
T is the settling time, sec;
o
y is the dynamic viscosity of the liquid, g sec/m .
To determine the dispersity of dust containing a substantial amount of
other fine particles, in order to satisfy the condition expressed by "equation
(11-2), it is necessary to use liquids of low viscosity (for example, acetone).
The liquids should be chemically neutral toward the dust studied. The concen-
tration of particles in the liquid should not exceed 2%. The size of an in-
dividual particle may be determined from its settling rate by means of the
formula [69]
'* (11-3)
where p, is the density of the dust particle;
d o
g = 9.81 m/sec is the acceleration due to gravity.
The remaining symbols are the same as in equation (11-2).
The values of y, P, and P- are usually known, and therefore, by deter-
mining the velocity w = h/T, one can find the size of the solid particle.
However, a direct determination of the settling rate of an individual par-
ticle is difficult. In a polydisperse'dust, particles of all sizes settle
simultaneously, but at different rates, and thus indirect methods are re-
quired to determine the unknown quantities.
In sedimentation analysis, the particle size distribution may be found
by one of the following methods:
1) weighing of the settling particles at certain time intervals (method
of N. A. Figurovskiy);
- 51 -
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2) use of a sedimentation pipet;
3) study of the change of the density of the liquid during sedimentation.
The methods most commonly adopted involve weighing of the settling parti-
cles and use of the sedimentation pipet.
In studying the particle size distribution by the first method, it is
convenient to use an instrument consisting of a glass cylinder containing a
small glass dish which is attached to a sensitive balance by means of a fine
rod. A torsion balance or a fine glass pointer may be used. The degree of
deflection of the pointer under the load should be directly proportional to
the weight of the load. The pointer should hold the weight of the dish sub-
merged in the liquid plus^l g. The deflections of the pointer under the
weight of the particles'settling on the dish should be recorded by means of
a. horizontal microscope, for example type MG. It is desirable to have a
pointer with a sensitivity of 5 mg per division of the microscope ocular ret-
icle. By weighing the settled particles at certain time intervals one can
find the dispersity of the dust studied.
The second method of studying the particle size distribution involves
the use of the Andreasen sedimentation pipet, illustrated in Fig. 11-2. It
consists of a calibrated cylinder 6 cm in diameter filled with the sedimenta-
tion liquid (volume, 550 cm'). On the stopper closing the cylinder is mount-
ed a 10 cm^ pipet, which makes it possible to collect the sample at the same
depth at certain given time intervals.
The weight of the dust introduced into the sedimenta-
tion liquid is usually 5-10g. By taking the samples from
the same depth at equal time intervals and measuring the
concentration of the suspension, one can find the disper-
sity of the dust studied.
The preparation of the sample for sedimentation anal-
ysis consists in the following. A weighed amount of dust
is crushed with a rubber stopper in a porcelain cup with a
few millimeters of liquid until the lumps disappear. The
suspension obtained is placed in a cylinder in which the
settling will take place, and liquid is added to the de-
sired level. If floes are formed in the suspension, a
stabilizer should be added or a different liquid used.
For water, soda can be used as the stabilizing additive.
The suspension is thoroughly stirred up. If the sedimen-
tation is carried out by using the first method, a dish
attached to a balance is quickly placed in the stirred-up
suspension, the balance lock is released, a stopwatch is
turned on, and the recording of readings at exact inter-
vals is started.
Fig. 11-2. The
Andreasen sedimenta-
tion pipet.
- 52 -
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The balance with the suspended dish should be set at zero before the sus-
pension is introduced into the cylinder.
If the sedimentation study is done by the second method, a pipet is used
to withdraw the same volumes of liquid from the cylinder with the stirred-up
suspension at a given depth and at precise time intervals in order to determine
the concentration of the suspension.*
The results obtained should be processed in the following manner. A set-
tling curve is plotted on graph paper. The readings of the balance or concen-
trations of solid particles in the suspension are laid off along the ordinate
axis, and time in minutes is laid'off along the abscissa axis. After the
settling curves have been plotted, the settling time of the particles of a
given size, for example, 5, 10, 20, 30, 40, and 50 y, is calculated. Tangents
are then drawn through the corresponding points of the curve, and the points
of intersection of these tangents with the ordinate axis are marked. The
intercepts defined by the tangents are converted to percentages of the maximum
value laid off along the ordinate axis, giving the percent content of the frac-
tions.
An automatic liquid sedimentograph using an electromagnetic analytical
balance automatically recording the weight of the sediment in the form of a
continuous settling curve was developed in 1957 at the NIIOGAZ under the di-
rection of Yu. I. Chicherin. This device permits one to perform the analysis
with a very slight concentration of the dispersed phase, and as a result, the
coagulation processes are minimized to such an extent that in many cases it is
possible to do without stabilizing additives, which are quite difficult to se-
lect correctly. In addition, the analyses are simpler to perform, and the
accuracy of the results obtained increases as a result of elimination of the
subjectiveness of the readings and some other factors. The automatic sedi-
mentograph affords a high reproducibility of the results obtained and differs
conveniently in the simplicity of its actuating mechanisms from instruments
proposed earlier. It consists (Fig. 11-3) of a type ADV-200 analytical bal-
ance a photorecording attachment, a recording instrument, a power supply and
a cabinet for carrying out the analyses.
A round mirror 1, 6-8 mm in diameter, one half of which is blackened, is
mounted on the beam of the ADV-200 balance. A solenoid 5 with a permanent
magnet 6 suspended inside it is attached to the balance column by a bracket.
From the bottom of the balance pan on a fine wire is suspended a dish 12,
immersed in cylinder 11 containing the suspension. The finer the wire, the
smaller are the errors resulting from the evaporation of the liquid.
On the upper glass plate of the analytical balance is placed a photo-
electric recording attachment consisting of an illuminator 2, photocell 3 and
electron tube 4. A millivoltmeter or electronic potentiometer 7 can be in-
stalled for automatic recording of the weight change. The apparatus is
*A sedimentation instrument with a rising pipet has been developed at the Leningrad Scientific
Research Institute for the Organization and Protection of Labor (LIOT) [111].
- 53 -
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powered by both line current (through a voltage stabilizer) and BAS-80 dry
batteries (8 and 10).
Fig. 11-3. Diagram of liquid sedimentograph with
automatic weighing.
When the balance is at equilibrium, the beam from the illuminator strikes
the mirror and, upon reflection, enters the photocell. The photoelectric cur-
rent thus generated blanks the electron tube, so that there is no current in
the anode circuit of the tube, and the recording instrument indicates zero.
If the weight on the balance pan increases as a result of the settling of dust,
the balance will go out of equilibrium, the"beam from the illuminator will
strike the blackened surface of'the mirror, and the photoelectric cell will
not be illuminated. As a result, the electron tube will be triggered, a cur-
rent will be generated in the anode circuit, the solenoid interacting with the
permanent magnet will not allow any observable deflection of the pan, and the
balance needle will remain stationary. The magnitude of the anode current
balancing the given weight will be shown by the recording instrument: this
current will be proportional to the weight being measured on the balance pan.
Elements of the circuit which have not been mentioned are: 9 - anode
resistance; 13 - cabinet; 14 - resistance controlling the scale range of the
recorder.
The order in which the results from the settling curve are processed is
no different from the one described above. The instrument is being success-
fully used at the NIIOGAZ and its branches.
Microscopic Analysis
The optical microscope may be used for determining the particle size in
- 54 -
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the range from 1 to 30V . The operating rules for microscopes have been
thoroughly treated in special handbooks and are briefly described in the
instruction manuals supplied with the instruments. We shall therefore con-
sider chiefly the methods of preparation of specimens and particle size de-
termination.
Preparation of specimens. At a dust concentration up to 1 g/m^ and
gas temperature up to 80°C, the sample for microscopic analysis may be with-
drawn directly from the gas conduit by means of a sampling tube (Fig. 11-4),
which contains a nitrocellulose membrane filter (COST 8985-59) or an AFA-V-
18-type filter. After the sample is withdrawn, these filters are transformed
by clarifying in acetone vapors into a thin, texture-free transparent film
on which the deposited particles are counted according to size under a micro-
scope in transmitted light. The temperature restriction is due to the thermal
stability of the filters, and the weight concentration restriction, to the
difficulties involved in the isokinetic withdrawal of a sample containing a
number of particles which are convenient for counting. A convenient amount
of withdrawn dust is one in which there are about 500 particles in the field
of view of the microscope. The volume of collected gas required to satisfy
this condition is determined experimentally.
The rate of withdrawal of the sample by means of a tube of illustrated
design should not exceed 10-15 1/min for reasons of the mechanical strength
of the filters and moderate hydraulic resistance. At a dust concentration
approaching 1 g/m^, it is desirable to have a slow rate of sample withdrawal
so that a number of particles convenient for counting can settle on the
filters within a time interval that can be controlled. In order to observe
the isokinetic conditions at different gas and sample withdrawal velocities,
the tube is provided with interchangeable tips of different diameters.
The membrane filters consist of circular plates 35 mm in diameter and
0.1 i 0.02 mm thick, made of porous nitrocellulose film. Depending on the
pore size, the membrane filters are subdivided into six numbers: 1, 2, 3,
4, 5 and 6. The maximum size for the first five numbers is 0.6, 0.7, 0.9,
1.2, and 1.8 y respectively. For filters No. 6, the maximum pore size is
not regulated by COST 8985-59. The membrane filters are produced by the
Experimental Ultrafilter Plant at Mytishchi, Moscow Province.
The dependence of the hydraulic resistance of the membrane filters on
the air flow rate is illustrated in Fig. 11-5. In order to obtain an
acceptable hydraulic resistance during the withdrawal of the sample, filters
No. 4 and 5 are usually employed. Filters No. 6 may yield a film of in-
homogeneous thickness on clearing, thus complicating the counting of particles.
The AFA-V-18 filters consist of filters as such and protective paper rings
(Fig. 11-6). The filtering material used is FPP-15 cloth. Each filter is
placed in a separate envelope of tracing paper. The sets of filters are
wrapped in a paper ring, ten filters per ring.
- 55 -
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,OJ v 3.6
Knurl
Fig. 11-4. NI10GAZ tube for collection of samples
on membrane filters.
s v v ^s
Flow rate of air, 1/min.
Fig. 11-5. Hydraulic resistance
of membrane filters versus air
flow rate.
Measurements made at NIIOGAZ by
V. S. Morozov and I. F. Ryabinkin
with a 26 mm diameter of working
area of the filter.
Protective
rings
Pig. 11-6. AFA-V-18 type filters.
- 56 -
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,,•4
V
V V
-127V/220V
Fig. 11-7. Arrangement for clarifying membrane filters and
AFA-V-18 filters.
1 - stand; 2 - beaker; 3 - beaker; k - microscope slide;
5 - acetone; 6 - water; 7 - electric hot plate.
When the sampling tube illustrated in Fig. 11-4 is used, a circle 35 mm
in diameter is cut out of the AFA-V-18 filter. Protective rings of correspond-
ing size are cut out of the tracing paper.
The AFA-V-18 filters have a much lower hydraulic resistance than membrane
filters, but owing to the greater thickness and fine fibrous structure of these
filters, the dust particles may penetrate to a certain depth relative to the
surface and come to rest in more than one plane. At considerable magnifications,
this complicates the focusing of the microscope to some extent.
Membrane filters and AFA-V-18 type filters are practically absolute filters.
Analysis of the filtration mechanism has demonstrated, for example, that a mem-
brane filter can hold particles about 10-15 times smaller than the average pore
size [72].
The clarification of the filters in acetone pores may be carried out as
follows.
Filters with samples for the determination of the size composition are
sent to a laboratory and placed on microscope slides. The hanging edges are
cut off. AFA-V-18 filters are placed on the slides so that the dust parti-
cles are located between the filter and the slide, and the membrane filters
are placed in such a way that the dust particles are located on the top. The
slides are marked in India ink with the number of the sample and date of its
collection.
- 57 -
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Water is then poured into a metal, porcelain or glass beaker 2 (Fig.
11-7), and a second beaker 3 of smaller size containing a small amount of
acetone is placed inside the first beaker. The water in the beaker is
heated on a hot plate to approximately 60°C. While the water is heated,
the beaker containing acetone should be covered to prevent the acetone va-
por from escaping. It is best to work under a hood.
Slides 4 with the filters are then laid on metal support 1, and the
latter is placed in the beaker with acetone. Acted upon by the acetone va-
pors, the filters change into a transparent film. The time necessary for
clarification of the filters depends on the water temperature. When the
latter is 60°C, the filters clarify within a few minutes.
Very good specimens for microscopic analysis with membrane filters
may be obtained by means of the attachment designed at the NIIOGAZ, shown
in Fig. 11-8.
When this apparatus is used, the clar-
ification is done as follows:
1. The lower grip ring 6 is placed on
the table. Ebonite ring 7 is inserted into
the cavity of this ring. A membrane filter
is placed on the ebonite ring with its dust-
covered side up, and is covered by the second
ebonite ring and the upper grip ring. The
grip rings are tightened with pins 5.
2. Cotton wad 10 is placed on the bot-
tom of the beaker and soaked with 4-5 ml
of acetone. Cotton wad 11 is placed on a
special shelf inside the body of the beaker
and soaked with'*- 1 ml of ethyl ether.
3. The clamp with the filter is placed
in the beaker, which is covered with glass
3 and lid 1. A seal is made by means of
rubber gaskets 4.
Fig. 11-8. Airtight beaker for clar-
ifying membrane filters, designed by
V. S. ttorozov and I. F. Ryabinkin.
1 - lid; 2 - gasket; 3 - glass;
i - gasket; 5 - clamping bolt with
nut; 6 - upper and lower grip rings;
7 - ebonite rings; 8 - membrane fil-
ter; 9 - body of beaker; 10 - cotton
wad wetted with acetone; 11 - cotton
wad wetted with ether.
The clarification of the filter takes place in 20-30 min. The filter
is considered clarified if one can easily read through it.
4. After the filter has been completely clarified, the lid is opened,
and the ring clamp is taken out. The filter in the clamp must be held over
the beaker for a while so as to allow the filter to dry gradually. Rapid
drying might cause the filter to cloud.
- 58 -
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5. The filter in the clamp is placed under a crystallizer for another
10-15 min of final drying.
6. If after drying the filters are pulled out of the rings, the ebon-
ite rings should be lightly coated with glue 88 or BF-2 before starting the
clarification.
7. After drying, the filter together with the ebonite rings is taken
out of the clamp and placed on the microscope slide.
At a dust concentration in the gases of 1 g/m^ or a high gas tempera-
ture, the method of microscopy is usually employed for the determination of
the original particle size only. To this end, the dust sample collected by
means of a paper or cloth filter is introduced into a beaker with distilled
water and thoroughly stirred with a glass rod. To peptize the fine particles,
one or two drops of a suitable peptizer (frequently ammonia) is added, the
sample is stirred again, a few drops are transferred by a pipette to a mi-
croscope slide, and the drops are spread over the slide with the pipette.
The water is allowed to evaporate. When the specimen obtained is examined
under the miscroscope, one should make sure that the dust particles do not
overlap or adhere to one another; otherwise, a new sample of greater dilu-
tion or with a different peptizer must be prepared.
Determination of particle sizes. The sizes of the particles magnified
by the microscope are measured with objective and ocular micrometers, the
usual assumption being that the particles are spherical in shape. The method
of "constant directions," 1. e., the determination of the size of all parti-
cles along a certain axis (Fig. 11-9), is the most convenient for finding
the particle size distribution.
With dusts whose particles do not differ appreciably in size, it is
sufficient to measure approximately 500 particles; if the polydispersity
is substantial, several thousand particles should be measured.
The counting of dust particles in the microscope is a laborious and
painstaking process. The work is considerably facilitated and more accu-
rate results are obtained if the image of the particles is photographed with
a photographic microscope attachment, and the counting is done on magnified
photographic prints or projections of the negatives on sheets of white paper
placed under the photographic enlarger. The object micrometer is photograph-
ed together with the specimen of dust studied. This makes it easier to deter-
mine the scale of the dust image obtained by means of the enlarger.
In determining the distribution of the dust particles according to the
sizes of their images on the photographic print or screen of the enlarger,
it is convenient to use templates. In this case, the area of dust parti-
cles of irregular shape is compared to the area of circles drawn on the tem-
plate on the corresponding scale.
- 59 -
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Fig. 11-9. Measurement of
dust particle size by the
constant direction method.
Counting the number of particles with sizes in
a certain interval (fractions), gives the so-called
calculated distribution. In order to convert the
distribution of particles according to fractions
into units of weight, it is necessary to know the
average size (diameters) for each fraction. They
can be determined by designating as da and d^ the
extreme sizes of the particles of a fraction, us-
ing the following relation:
rfav =
(11-4)
By using the equality between the weight ratios
of the dust particles in each of the fractions and the volume that they occupy,
one can find the weight percentage of each fraction
(11-5)
Here dav is the average particle size of the fraction;
n is the percent content of particles comprising the fraction;
k is the number of the fraction;
i is the number of fractions into which the analyzed dust is subdivided.
Method of Three Cyclones*
This method of determination of dust dispersity is based on the assump-
tion that the distribution studied obeys the lognormal law. With this condi-
tion, the determination of the size composition of dust can be made if the
following two parameters are known: the average gravimetric geometric dia-
meter clgeom an<^ t*16 dispersion of the distribution, in place of which it is
more convenient to use the quantity £, i. e
particles with a diameter of less than 2d
, the gravimetric content of
Keom (see § 1-1).
The instrument for the determination of dust dispersity by this method
consists of three successively mounted cyclones and a glass wool filter (Fig.'
11-10). Teflon or aluminum beakers are placed inside each cyclone. Befofe ;
the sample is taken, the beaker and the filter are weighed.
*The theory underlying the method has been treated in detail by S. S. Yankovskiy and H. A. Fukst 741
- 60 -
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When a sample of dust-laden gas is taken, the Instrument is introduced
into the gas conduit through a port with a useful cross section of 220 x 80
mm, so that the tip of the inlet tube of the first cyclone is parallel to the
axis of the gas conduit. The port cover should have a connecting pipe for
the introduction of the suction tube from the outside.
When the gas temperature is high, prior to the collection of the sample,
the instrument is kept in the gas conduit for a while in order to warm it up
and thus exclude the condensation of moisture inside it. The suction tube
should be kept open during that time. Because of the rarefaction in the gas
conduit, a slight air current through the tip of the instrument is thus es-
tablished, which prevents dust from entering the instrument during the warm-
up. The tip of the instrument during the heating is turned to coincide with
the direction of gas flow.
•SsSdb^EEEEr--
•Sa^.saeaissa.gTr,^.,.,.., ..,,,,,,,,.....-„. ,...,,,•..,..--. -
":s|MtoJ|1ip' ^gCE
Fig. 11-10. Instrument for determining the dispersity composition
of dust by the method of three cyclones.
1,2, 3 - cyclones; 4, 5, 6 - beakers; 7 7 interchangeable tip;
8 - tube for sucking the gas through the instrument; 9 - glass
wool filter.
The diameter of the tip is chosen so that the isokinetic condition is
fulfilled at a sample collection rate of 10 1/min.
After heating, the instrument is turned with its tip against the flow,
and a certain amount of gas containing from one to several grams of dust is
sucked in through the instrument at the rate of 10 1/min. The instrument is
then removed from the gas conduit, the dust clinging to it on the outside is
wiped off, and the beakers containing the settled dust and the glass wool
filter are taken out. By weighing the beakers and filter for the second time,
one finds the weight of dust settled therin, gp g2> g^i and 8f The avera8e
- 61 -
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gravimetric geometric diameter d and £, the gravimetric content of parti-
cles with diameters less than 2d , which characterize the unknown distri-
geonr
bution, may be determined by means of the nomograms illustrated in Fig. 11-11.
In order to use the nomograms it is necessary to calculate the breakthroughs
of the dust through each of the cyclones, e,, e~ and e«:
e =
..=—^J»
(11-6)
The nomograms show curves of equal breakthroughs through each of the cy-
clones for dusts with different values of d and £.
geom
To find the unknown distribution on the basis of the experimentally ob-
tained values of the breakthrough for the three cyclones, the following pro-
cedure should be used. A tracing paper with coordinate axes is placed on each
of the three nomograms successively, and the three curves corresponding to the
calculated values of e,, e« and e_ are traced on it. If the particle size
distribution of the dust studied is strictly lognonnal and there are no experi-
mental errors, these curves should intersect at a single point whose abscissa
corresponds to the unknown value d and the ordinate to the value of E.
e geom *
Actually, because of measurement inaccuracies and deviations from the log-
normal distribution, the curves_Jform a triangle whose center gives the best
approximation to the values of d and £ of the size composition being sought.
geom
The nomograms were constructed for particles of unit density. If it is
desired to express the distribution__over sizes of particles with density p
-------
a)
micrc«is
b) c)
Fig. 11-11. Nomogram for determining d2 and £ .
a - for first cyclone; b - for second cyclone; c - for third cyclone.
- 63 -
-------
The first point is obtained by marking the value of d on the abscissa
geom
axis. To the right of this point on the same axis, a point corresponding to
2(1 is marked on the same axis, then a perpendicular at this point is raised
geom '
on which the value of £ is marked in percent; the second point is thus deter-
mined .
An accuracy of the results obtained with the instrument, acceptable for
the solution of practical problems, is obtained in this case if the average
geometric size of the particles of the dust under analysis falls within an in-
terval of approximately 25 to 2y . This is because particles larger than 25p
are equally trapped in the first cyclone regardless of the size, whereas those
measuring approximately 1.5 microns practically are not trapped by the cyclones
and fly directly into the filter. If after the sample has been collected it
is found that almost all of the dust has settled in the first cyclone, the
dust in this cyclone should be subjected to a supplementary analysis in an air
separator. The accuracy of the analysis made by the air separation method will
be very high because of the absence of fine fractions. Then, knowing the size
composition and weight fraction of the additionally analyzed dust, one can
readily plot a general distribution curve with much greater accuracy than if
all of the dust had been directly analyzed in the gas separator.
, The instrument is manufactured by interested organizations according to
the NIIOGAZ design.
Multistage Jet Settler
In a multistage jet settler, known abroad under the name of "cascade im-
pactor," use is made of inertial settling of the dust particles caused by the
flow around a flat obstacle by a jet of dust-laden gas. The gas jet passes
through several successive nozzles at a progressively increasing velocity, and
the dust particles settle and are held on surfaces coated with a layer of ad-
hesive lubricant. The presence of a correlation between the size of the set-
tling particles and the gas.velocity allows one to evaluate the dispersity of
the dust by estimating the proportion of particles settled on the surface
opposite each of the nozzles. The principle of inertial settling employed
pertains to the.number of dust particles ensuring the best separation into
fractions. Earlier, jet settlers have been used chiefly for the hygienic eva-
luation of the contamination of atmospheric air and were unsuitable for prac-
tical size analysis of industrial dusts because adhesive lubricants proved
capable of holding reliably only monolayers of the settling particles. Such
small dust samples, first, are impossible to withdraw from the gas conduits
while observing the isokinetic condition (for dust contents of gases typical
of industrial discharges) and second, were impossible to analyze by the most
convenient method of weighing of deposits obtained at different stages of the
apparatus.
- 64 -
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At the same time, the simplicity of design, speed of analysis and fun-
damental possibility of achieving accurate results made the use of jet set-
tlers highly promising for the analysis of industrial dusts when the instru-
ment was placed inside gas conduits. In this connection, the NIIOGAZ selected
a lubricant composition* ensuring the accumulation at each stage of the in-
strument of up to 30-40 mg of analyzed particles, and a suitable design of
the instrument was developed.
The instrument (Fig. 11-12) consists of eight stages, seven of which
are designed for the inertial settling of analyzed dust particles and the
eight for settling by the filtration method. Each of the stages of inertial
settling consists of a beaker which includes a nozzle opposite which is
mounted a tray filled with a special lubricant. Each tray edge has one notch
which makes it possible to mount the trays between suitable pins, as shown in
the figure. The filter of the eighth stage is filled with glass wool. The
first stage of the instrument is equipped with a removable tip, which permits
an isokinetic collection of the sample at different velocities of the gas
stream while the rate of gas flow through the instrument chosen during the
calibration is retained. All the stages of the jet settler are combined in
a cylindrical housing. Packing between the stages consists of teflon gaskets
tightened by the lid of the housing. An additional tightening of the gaskets
is achieved by means of three expansion stay bolts attached to the lid.
W MiTMM
Fig. 11-12. Multistage jet settler (model V).
Outside dimensions of the in^t rurn-nt: lengtr: 2.:5 rim; dianvter 54 irjr,.
The lubricant for holding the particles on the surface of the trays is
a mixture consisting of a solid and a liquid phase. The solid phase gives it
the thickness required to prevent it from splashing when acted upon by the gas
jet, whose velocity at the exit from the last nozzle may be as high as 100 m/sec
The liquid phase holds on to the particles which settle on the surface by wet-
ting them, owing to the diffusion from the lubricant layer into the growing
dust layer. Since the diffusion rate must be slightly higher than the growth
rate of the layer, the applicability of the instrument is limited by a weight
concentration of the dust in the gases of up to 1-7 g/m^, depending on the
bulk density of the dust being analyzed.
*S. S. Yankovskiy and A. A. Rusanov, USSR Authorship Certificate No. 197844.
- 65 -
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Composition of Lubricant at Gas Temperatures up to 80°C
Vaseline oil 2 parts
Gas black 1 part
At gas temperatures from 80 to 150°C
MS-20 oil 1 part
M-14 corundum 3.5 parts
Several modifications of the instrument have been developed which differ
mainly in the number of stages, configuration, and nozzle diameter. The char-
acteristics of the individual stages were determined by the method of micro-
scopic analysis of the particles settling in them, at a flow rate of the gases
through the instruments of 10 1/min. This gas flow rate, specified during the
construction, was chosen for the following reasons: at high flow rates, the
outside dimensions of the instrument increase; at lower ones, the entrance
diameter of the tip required for an isokinetic collection of the sample will
be too small and will start to plug up with the dust. The limiting sizes of
particles of unit density for each fraction settling on the stages of the in-
strument shown in Fig. 11-12 are listed in Table 11-1 (the values are rounded
off slightly).
The determination of the dust dispersity by means of a jet settler amounts
to the following. The instrument with the weighed trays full of lubricant and
with the filter is placed in the gas conduit in such a way that the direction
of the nozzle coincides with the direction of motion of the gases. After it
is heated up to the temperature of the gases, the jet settler is turned by '
180° so that the nozzle faces in the direction opposite to that of the flow,
and a certain amount of the gases is drawn off through the nozzle by means
of a gas blower or other source of suction at a velocity chosen during the
calibration.
Table 11-1.
Number of Stage
I
11
HI
IV
V
VI
VII
VIII
Diameter of
Nozzle, mm
20
14
10
7
5
3,5
2,0
Filter.
Limiting Particle Size,
Microns, at Pd= 1 'g/cm-'j
^42.5
24,5
15,0
8,5
5,2
3,2
1,4
-------
The instrument is then removed from the gas conduit, and the filter and
trays are weighed on an analytical balance.
The plotting of the size composition curve from the experimentally ob-
tained weight increases of the dust in the cups of the various stages and on
the filter is carried out as follows.
The relative fraction f± of particles settled on the first stage is found
as the ratio
(11-7)
where g^, g^, .g^, g^t.g^, gg, and g^ are the weight increases of the first,
second, third, fourth, fifth, sixth, and seventh stages, and g is the weight
increase of the filter. The fraction of particles settled on the first and
second stages is. found as the ratio f = ( g+g) /(g+Sg+g+g+g )•
The fractions f,, f,, . .., £„ of particles settled on the following stages are
found in similar fashion.
Values of the relative amounts of settled particles f - , f«, f_, f,, f,.,
f, and f., are laid off as the ordinates of points with abscissas corresponding
o /
to the separation limits d,, d^, d_, d,, d_, d, and d_ (for which the values
given in Table 11-1 can be taken) in the logarithmic probability coordinate
system (Fig. 1-ld).
At high gas temperatures, the initial weight of lubricant begins to de-
crease owing to the evaporation of the oil and to desorption processes. The
weight lost by desorption is restored partly or fully after a certain time,
but the weight lost through the evaporation of oil is not. The character of
the weight loss of the lubricant for trays filled to the brim and weighed a
day after the heating is shown in Fig. 11-13. This loss should be taken into
account during weighing. The weight loss of the lubricant can be taken into
account most 'accurately as follows. After the dust sample has been collected
for 'analysis, trays with fresh lubricant should be placed in the jet settler,
and, after protecting the dust-collecting tip with a filter of conventional
design, suction of the gases should be carried out "during the same interval
of time during which the dust sample was collected. The averaged weight
losses of the three trays 30 mm in diameter and four trays 23 mm in diameter
will give close- to- true corrections, which should be introduced into the cal-
culations .
- 67 -
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W JO 60 KO
lime, rain.
Fig. 11-13. Weight loss of the lubricant (l g of
MS-20 oil plus 3.2 parts of Ml 4 corundum).
The instrument is manufactured by interested organizations according to
NIIOGAZ blueprints.
11-2.. Measurement of the Electrical Resistivity of
Dust Under Industrial Conditions
At the present time, it is not possible to determine the electrical re-
sistivity (BE) of dust directly on the collecting electrodes of electrostatic
precipitators. Therefore, it is usually necessary to resort to the measure-
ment of the ER of dust (under both laboratory and industrial conditions) be-
tween special measuring electrodes. Host frequently,'a layer of dust is
formed on one of the electrodes in one way or another, and the second mea-
suring electrode is applied on the already-formed dust layer.
The absolute values of the measured quantities are of course strongly
dependent on the method of formation of the dust layer and the method of
measurement.
In selecting the optimum type, size and operating parameters of elec-
trostatic precipitators, it is necessary to have information on the ER
values of different dusts for the parameters of dust-laden gas streams which
the latter have at the entrance to the apparatus.
In order to adopt a single method permitting a comparison of the results '
obtained, the NIIOGAZ has designed an instrument called the "Tsiklonom-1" [85],
which meets the following requirements: simplicity of design and handling;
good reproducibility of the results; ability to measure the ER of dust in f
streams of process gases.
The instrument permits the measurement of the ER of dusts in the 20-
250°C temperature range.
68 -
-------
The instrument consists of a small-sized high-efficiency cyclone and a
dust resistivity gauge located in its hopper. The measuring system of the
gauge consists of cylindrical coaxial electrodes (Fig. 11-14).
The dust-laden gas stream enters through
the intake tube into the cyclone, in which
the dust is separated from the gas. The gas
is then expelled through the exhaust part of
the cyclone, while the dust is poured into
the hopper and fills the interelectrode gap
of the gauge.
' The housing of the gauge is made of"tef-
lon, which has a high volume resistivity,
10 ohm cm at 20°C, and a high surface re-
sistivity.
10 ohm.
The measuring system is connected to a
secondary indicator, a teraohmmeter, by a
wire with a heat-resistant organosilicon in-
sulation of brand PTL-250.
To prevent the contamination of the mea-
suring wires with dust and their vibration
during the flow of the gas around the instru-
ment, the latter is provided with a protective
metallic jacket.
"Tsiklonom-1" is fastened by three hol-
low metal bolts to the flange on which the
instrument is mounted in the gas conduit.
The connecting wires extend out of the gas
conduit through two of the bolts, and a ther-
mometer or thermocouple can be inserted
through the third to check the temperature of
the medium in the immediate vicinity of the
gauge.
In a possible variant of the arrangement, the thermocouple is placed
directly in the measuring system of the gauge.
The design of the instrument makes it possible to: form in the inter-
electrode gap a dust layer by a method excluding subjective errors due to the
distortion of the layer during measurement of the ER by the method of appli-
cation of the electrode on the layer; measure the electrical resistivity of
Fig. 11-14. Instrument for mea-
suring the electrical resistiTv
ity of a dust layer by means of
"Isikionom-1".
1 - handle; 2 - not; 3 - flange;
4 - bolt; 5 - cyclone; 6 - gauge;
7 - protective jacket; 8 - mea-
suring wires; 9 - intake tube.
- 69 -
-------
the dust layer formed directly in the gas conduit over a wide temperature
range and in chemically corrosive media; check the temperature of the gas
stream and hence of the dust layer directly in the zone of the gauge; auto-
matically record the ER of dust on a recording instrument, and read off the
ER directly on the secondary instrument thanks to a suitable choice of the
geometry of the measuring electrodes.
The operational sequence with the "Tsiklonom-1" instrument is as fol-
lows.
Before the instrument is introduced into the gas conduit; the insula-
tion level of the measuring system of the gauge is determined, then the in-
strument is inserted into the gas conduit and warmed up for 10-15 min. After
the warm-up, the insulation level of the measuring system is checked again.
The instrument is connected to a vacuum line, and the gas flow rate is set at
15-25 1/min. The optimum efficiency and hydraulic resistance of the instru-
ment are thus established.
It was found experimentally that a slight distortion of the size com-
position of the sample collected in the instrument, caused by a deviation
from isokinetic withdrawal, did not cuase an appreciable change in the ER of
dust.
To prevent stoppage of the vacuum source with dust that has not been
trapped by the cyclone, it is recommended that a paper filter be installed in
the suction line.
The time required for filling the measuring system with dust is deter-
mined experimentally. Tests of the instrument under industrial conditions
showed that at a gas flow rate of the'order of 20 1/min and a dust content of
the dust-laden gas stream of 5-7 g/m^, the time necessary for filling the
hopper ranged from 15 to 20 min.
When the withdrawal of the gas is complete, the connecting wires are at-
tached to the secondary instrument and the electrical resistivity of the dust
layer between the electrodes of the gauge is determined. To determine the ER
of the layer on measuring electrodes in the form of coaxial cylinders, the
following expression is used:
ln-£- (11-8)
where p is the electrical'resistivity of the dust, ohm cm;
R is the resistance, measured with a teraohmmeter, ohm;
H is the height of the measuring electrode, cm;
r, and r« are the radii of the inner and the outer electrode, cm.
- 70 -
-------
Thanks to a specially chosen electrode geometry, p = 10 R (ohm cm),
i. e., the need for any computations is eliminated.
f
The secondary instrument for measuring the resistance of the dust layer,
the teraohmmeter, measures the total resistance (R ) . of the gauge insulation
(Rin) and the resistance of the dust layer proper (R ), connected in parallel.
If the resistance measured by the teraohmmeter R < 0.01 R, . it may be as-
tot in
sumed with an error of not more than 107., that R = R .In other cases, the
x tot *
resistance of the dust layer must be calculated from the formula
Therefore, in working with the "Tsiklonom-1" instrument, prior to each
experiment it is necessary to check the insulation resistance level of this
gauge. The instrument is manufactured by interested organizations from blue-
prints of the NIIOGAZ institute.
11-3. Determination of the Moisture Content and Dew Point of Gases
A large number of methods have been developed for the determination of the
moisture content of gases. In Chapter 1 it was pointed out that data on the
moisture content of gases are necessary chiefly in order to avoid the cooling
of gases in the lines of dust-collecting systems below the dew point, which
depends on the moisture content.
The moisture content of gases that. do not contain impurities that raise
the dew point is most frequently determined by means of psychrometers ' or by
the condensation method. If the gas contains impurities (for example, 863),
susceptible of substantially raising the temperature of the start of conden-
sation, i. e., the dew point, the latter is determined . by using instruments
based on the principle of measuring the temperature of the cooled surface at
the instant of formation of the dew on it.
1. Determination of the moisture content of gases by means of a psychro-
meter. The psychrometric method of determining the moisture content of gases
is based on the difference between the temperature readings of a dry and a wet
thermometer. The dry thermometer indicates the temperature of the surrounding
unsaturated gas, whereas the wet thermometer placed in the same medium shows
a lower temperature, since water evaporates from its surface and thus consumes
heat. The equilibrium temperature assumed by the surface of the water evap-
orating under adiabatie conditions (when the amount of heat transferred from
the gas to the liquid is equal to the latent heat of vaporization) is referred
to as the wet thermometer temperature. The lower the partial pressure of the
- 71 -
-------
water vapor in the gas bathing the termometers , the larger the difference be-
tween the readings of the dry and wet thermometers.
The pressure of water vapor under the conditions of a psychrometer is
given by the formula
where P^20 is the pressure of saturated water vapor at the wet thermometer
S3.L
temperature, mm Hg (taken from saturated water vapor tables);
t(j is the dry thermometer temperature, °C;
tffi is the wet thermometer temperature, °C;
PpS is the pressure in the psychrometer, mm Hg;
c is a coefficient which depends on the velocity of the air (gas) around
the bulb of the wet thermometer. At «t gas velocity of over 5 m/sec,
c may be taken as 0.00066.
The pressure of water vapor in the gas conduit is calculated from the
formula
pH,Op
— , PS ^g ,,, ,,.
* -- / ' (11-11)
p. — , PS
p
where Pe is the pressure in the gas conduit, mm Hg
O
Knowing the water vapor tension in the gas conduit, one can determine the
dew point and absolute humidity of the gas from tables [ 71] .
A large number of different versions of psychrometers have been proposed
whose main differences lie only in the details and material of which they are
made. We shall discuss an NIIOGAZ-designed psychrometer, which because of its
simplicity of design may be made in any glassblowing shop [70],
The psychroraeter under consideration is in the form of a U-shaped vessel
into which two T-joints are inserted (Fig. 11-15). One of the T-joints (for
the dry thermometer) is bent in the shape of the vessel, and the other (for
the wet thermometer) has the usual straight shape. Two thermometers with a
scale from 0 to 50° (Assman psychrometric thermometers) or from 30 to 100°
(thermometers for Zhukov's instrument) are placed in the T-joints in rubber
stoppers. A scale division of such thermometers is equivalent to 0.2°C. >
Before the installation in the instrument, the thermometer readings
should be thoroughly compared with one another.
- 72 -
-------
Fig. 11-15- Psychroneter
The dry thermometer is lowered down to the elbow
of the T-joint and the "bulb" forming its bottom comes
to rest against the wall of the elbow. The wet ther-
mometer is inserted in the second (straight) T-joint
exactly in its center, so that the end of the mercury
bulb is located at the same level as the end of the
T-joint.
The bulb of the wet thermometer is wrapped in
gauze so that its lower end reaches the bottom of the
vessel, and the upper end protrudes 5 mm beyond the
limit of the upper part of the mercury bulb of the
thermometer. The water supply to the psychrometer is
regulated by means of an equalizing flask.
The assembled instrument is placed in a wooden
case lined with a heat-insulating material.
The gas from which dust has been filtered off and whose temperature is
above the dew point is drawn through the psychrometer, bathing the thermometer
bulbs, first the dry one and then the wet one. In calculating the necessary
amount of gas drawn through (in order to maintain the necessary velocity of
the gas flow around the bulb of the wet thermometer), the inner diameter of
the T-joint and the diameter of the bulb of the thermometer wrapped in gauze
are measured. From the cross-sectional area of the T-joint one calculates
the area occupied by the thermometer, and the volume velocity for this area
is then calculated
Q = v(F—f)60-l(P Jt/min, (11-12)
where w is, the linear velocity (>5 m/sec) of the gas, in/sec;
o
F is the cross-sectional area of the T-joint, m ;
n
f is the area occupied by the thermometer wrapped in gauze, m .
After the readings of the dry and wet thermometers have been established,
these readings are recorded every 2-3 min for 20-30 min, and the results ob-
tained are averaged out.
Determination of moisture content by the condensation method. In this
method of moisture content determination, the gas, which is not saturated with
water vapor, is cooled below the dew point, and the amount of collected, con-
densed moisture and the temperature of the cooled gas are measured.
The moisture content is defined as the sum, referred to a unit volume of
the gas, of the condensed moisture and absolute moisture contents of the satu-
rated gas.
- 73 -
-------
One of the types of instruments for determining the moisture content by
the condensation method is shown in Fig. 11-16. During the determination, no
spray carry-over from the instrument and no condensation in the supply tubes
must be allowed. The amount of gas (from which the dust was first separated
by filtration) passed through the instrument is measured by means of a rhe-
ometer or other flow meter.
Water
Fig. 11-16. Instrument
for determining the hu-
midity of gases by the
condensation method.
1 - reflux condenser;
2 - moisture separator;
5 - burette for meas-
uring the amount of col-
lected condensate; 4 -
thermometer; 5 - manom-
eter.
For a more accurate determination of the moisture
content of gases by this method, one can measure the
amount of condensed water by a gravimetric instead of
a volumetric method. In addition, a wool filter may
be installed to block the spray and mist.
Determination of the moisture content of gases
from observation of dew formation on a cooled surface.
In a direct determination of the dew point, an instru-
ment developed by the VTI and shown in Fig. 11-17 may
be employed. The main element of this instrument is
a measuring cap of molybdenum glass into the surface of
which are fused two platinum electrodes separated by a
distance of 7 mm. A voltage of 12 V is applied to these
electrodes. A platinum/platinum-rhodium thermocouple is
fused into the glass between them.
The instrument is mounted in the gas conduit at
right angles to the motion of the gases or at a slight
angle towards the stream, so that the cap is fully
bathed by the gases and is not located in the aerody-
namic shadow. After the warm-up of the instrument, the
cooling air is supplied into the cap.
When the temperature of the cap falls below the
dew point, a film of moisture that abruptly decreases
the resistance of the segment between the electrodes
appears on the surface of the cap. The changes of tem-
perature and resistance are recorded. The graphical
relations plotted on the basis of the measurements per-
mit one to make an accurate evaluation of the dew point.
- 74 -
-------
A-A
platinum
electrodes d=0.39 mm platinum
tnerm
platinum-rhodium /
' 'num
wcouple, d = 0.3 .
exit of cooling water
i entrance of cooling
water
Fig. 11-17. VT1 instrument for determining the dew point.
- 75 -
-------
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79. V >K o D B. H., O'UiCTKa npoMbiuuieimux rasou aJicKipo^Hflb-
rpauii, MA-BO «Xn.MHn», 1967.
80. \V. Simm, Chem. Ind. Techn., 31, J959.
81. Kponn JI. JL, iFIoTauoB 0. n., TapiiaBCKHfl H. /I.,
<3jieKrpiiibTpe, anTopecpcpar, ypa.nbCKiifi no-in-
Texini'iecKiiil iiiicrHTyT IIM. C. M. KitpoB.n, Cncp.vioBCK, 1964.
1.00. >Ke6p OBCKHH C. II., AnyxTiina E. F., BCCTMHK tex-
H aKOiio-Mii'iecKou HH4>opMamiu, HHHT3XHM, 1962, K° 2.
101 A^iieu F. M. A. it ,ip., AsTopcKoe cBiueiejibCTBo; A's 162113,
CCCP, 1964.
102. nMJieyjiaB.iiiuaiiuc B uneruofi iMeTaji-iyprinr, C6opiiiiK iiayraux
FHI1HBETMBT We 7, HSA-BO «MeTa.i.iypnin», (967.
'- 79 -
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103. S t a i r m opMau>iii, HHHT3XHM, 1932, JSfs 11.
111. EAMiiasi MeroAHKa cpaBiniTCJibiiux iicnbiTauin*i
Jiefi A.in OHIICTKH •BciiTiiJism.iioiiHoro BosAyxa, BHHHOT, 19G7.
- 80 -
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46 THE SUSCEPTIBILITY OR RESISTANCE TO GAS
AND SMOKE OF VARIOUS ARBOREAL SPECIES
GROWN UNDER DIVERSE ENVIRONMENTAL
CONDITIONS IN A NUMBER OF INDUSTRIAL RE-
GIONS OF THE SOVIET UNION-A Survey of USSR
Air Pollution Literature
47 METEOROLOGICAL AND CHEMICAL ASPECTS
OF AIR POLLUTION, PROPAGATION AND DIS
PERSAL OF AIR POLLUTANTS IN A NUMBER OF
AREAS IN THE SOVIET UNION-A Survey of USSR
Air Pollution Literature
48 THE AGRICULTURAL REGIONS OF CHINA
49 EFFECTS OF METEOROLOGICAL CONDITIONS
AND RELIEF ON AIR POLLUTION; AIR CON-
TAMINANTS - THEIR CONCENTRATION
TRANSPORT. AND DISPERSAL-A Survey of USSR
Air Pollution Literature
50. AIR POLLUTIPN IN RELATION TO CERTAIN
ATMOSPHERIC AND METOROLOGICAL
CONDITIONS' AND SOME OF THE METHODS
EMPLOYED IN THE SURVEY AND ANALYSIS
OF AIR POLLUTANTS-A Survey of USSR Air
Pollution Literature
61. MEASUREMENTS OF DISPERSAL AND
CONCENTRATION, IDENTIFICATION, AND
SANITARY EVALUATION OF VARIOUS AIR
POLLUTANTS, WITH SPECIAL REFERENCE TO
THE ENVIRONS OF ELECTRIC POWER PLANTS
AND FERROUS METALLURGICAL PLANTS
-A Survey of USSR Air Pollution Literature
62 A COMPILATION OF TECHNICAL REPORTS ON
THE BIOLOGICAL EFFECTS AND THE PUBLIC
HEALTH ASPECTS OF ATMOSPHERIC
POLLUTANTS - A Survey of USSR Air Pollution
Literature
53 GAS RESISTANCE OF PLANTS WITH S.PECIAL
REFERENCE TO PLANT BIOCHEMISTRY AND TO
THE EFFECTS OF MINERAL NUTRITION - A
Survey of USSR Air Polution Literature
54 THE TOXIC COMPONENTS OF AUTOMOBiLE
EXHAUST GASES: THEIR COMPOSITION UNDER
DIFFERENT OPERATING CONDITIONS, AMD
METHODS OF REDUCING THEIR EMISSION - A
Survey ot USSR Air Pollution Literature
55 A SECOND COMPILATION OF TECHNICAL
REPORTS ON THE BIOLOGICAL EFFECTS AND
THE PUBLIC HEALTH ASPECTS Or
ATMOSPHERIC POLLUTANTS - A Survey of USSR
Air Pollution Literature
56 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL SYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART I) - A Survey of USSR A'T
Pollution Litereture
67 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL SYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART II) - A Survey of USSR Air
Pollution Litereture
58 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL AYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART III) - A Survey of USSR Air
Pollution Literature
59 A THIRD COMPILATION OF TECHNICAL
REPORTS ON THE BIOLOGICAL EFFECTS AND
THE PUBLIC HEALTH ASPECTS OF ATMOSPHER-
IC POLLUTANTS - A Survey of USSR Air Pollution
Literature
Reprint] from varioui pcriodicolt
A INTERNATIONAL COOPERATION IN CROP IMPROVEMENT
THROUGH THE UTILIZATION OF THE CONCEPT OF
AGXOCI.IMATIC ANALOGUES
(The UM of Phenology, Meteorology and Geographical
Latitude for the Purpose! of Plant Introduction and the Ex-
change of Improved Plant Varieliei Between Vetiein
Counfriei.)
8 SOME PRELIMINARY OBSERVATIONS OF PHENOLOGICAL
DATA AS A TOOL IN THE STUDY OF PHOTOPERIODIC
AND THERMAL REQUIREMENTS OF VARIOUS PLANT
MATERIAL
*C AGRO-CllMATOlOGY AND CROP ECOLOGY OF THE
UKRAINE AND CLIMATIC ANALOGUES IN NORTH
AMERICA
0 AGRO-CLIMATOLOGY AND CROP ECOLOGY OF PALES-
TINE AND TRANSJORDAN AND CLIMATIC ANA-
LOGUES IN THE UNITED STATES
USSR— Some Phytical and Agricultural Choracterit'ict of the
Draught Area ondltiClimatic Analogue! in theUnit«dStat«t
THE ROLE OF BIOCLIMATOLOGY IN AGRICULTURE WITH
SPECIAL REFERENCE TO THE USE OF THERMAL AND
PHOTO-THERMAL REQUIREMENTS OF PURE-LINE VAR>
ETIES OF PLANTS AS A BIOLOGICAL INDICATOR fN
ASCERTAINING CLIMATIC ANALOGUES (HOMO-
CLIMES)
•OvtoF Print.
Requntt for tlvdiet ttauld be oddreued to the
American Inititute of Crap Ecology, 809 Dale
Drive, Silver Spring, Maryland 20910.
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