Pollution Control 1968

8/11/2019 Pollution Control 1968

1/76

COMMISSION

OF THE EUROPEAN C OM MUNITIES

Technical measures of air pollution control

in the iron and steel industry

Reports and informat ion on research work subsidized by the ECSC

as at June 1968


2/76


3/76

COMMISSION

OF THE EUROPEAN COMMUNITIES

Technical measures of air pollution control

in the iron and steel industry

Reports and informat ion on research work

subsidized by the ECSC

as at June 1968


4/76


5/76

Prepared by

Kurt Guthmann and Gerhard Will


6/76


7/76

CONTENTS

Page

FOREWORD 7

1.

Introduction

1.1 Source s of air po llution in the iron and steel indus try 9

1.2 ECSC activity in the field of air po llutio n con trol 13

1.3 Research and info rm atio n grou ps ' 13

2.

Dust

an d

gas meas uremen t 15

2.0 Scope and problems 15

2.1 Compar ison and improvement of exist ing measur ing instruments and methods and development of

new ones . 16

2.11 Co mp arison of sam pling instrum ents and me thods (Study PS 150) 16

2.12 Development of a por table dust-measur ing instrument wi th a large air sample capaci ty (Study

PS 139) 16

2.13 Mic rop ore mem branes (Study PS 10) 18

2.14 Resea rch on the developm ent of a simple me thod for de term ining free S1O2 con tent (Study

PS 37) 18

2.15 Establ ishment of an internat ional microsco pic coun t ing standard (Study PS 135) 18

2.16 Expe rimental elec tro-aco ustic particle-size mea surem ent (Study PS 141) 20

2.17 Estab lishing the source of dusts (Study PS 35) 22

2.18 Development of dust-measurem ent recording instruments (Studies PS 15 and PS 138) . . . 22

2.2 Mea sureme nts of the dustiness of wo rkin g areas 24

2.21 Dust survey in Germ an steelwo rks (Study PS 20) 25

2.22 Dust survey in Ital ian steelwo rks (Studies PS 11 and 12) 25

2.23 Dust survey in Lux em bou rg steelwo rks (Studies PS 49 and PS 144) 26

2.24 Dust survey in Dutch foun dries (Study PS 17) 27

2.3 Research on dust and gas em issions and their gro un d level con cen tratio n 27

2.31 Research on fluorine

and SO2

co ntaining waste gases discharged by steelworks (Study

PS 129) 27

2.32 Detection and removal of f luor ine in waste gases (Study PS 149) 28

3. Control of brown fum es 30


3.1 Cleaning brow n fumes from Bessemer converters by means of electr ical precipi tator ( Hu cking en

study) 33

3.2 Removal of particles from brown fumes at elevated temperatures in new types of electr ical precipi

tato rs (Stud ies PS 18, 43, 131) 35

3.3 Clean ing of L-D conve rter fume s with bag fi l ters (Study PS 128) 38

3.4 Scrubbing of conver ter gas w i thout subsequent combust ion (Studies PS 130 and PS 132) . . . . 40

3.41 Scru bb ing of L-D conve rter waste gases with ou t subs eque nt com bu stion (Study PS 130) . . 40

3.42 Scru bb ing of L-D AC conve rter waste gases with ou t subs eque nt com bu stion (Study PS 132) . 44

3.5 Exha ustion of dusts and fume s from arc furnac es (Study PS 45) 45

3.6 Uti l ization of the brow n fum e depo sits (Study PS 102) 47


8/76

4. The control of other dusts and waste gase s


4.1 Dust suppression wi th a v iew to protect ing furnace rel ining workers against s i l ica-bear ing dusts

(Stud y PS 101) 53

4.2 R eplacem ent of qua rtz sand by no n-si l ico gen ous mine rals in com press ed air blasting (Study PS 119) 54

4.3 Dust con trol in sinte ring plants and du ring belt-con veyo r cha rging of blast furnac es (Study PS 1) 54

4.4 Control of dust produced in discharging f ine ores and dur ing the preparat ion of the blast furnace

burd en (Study PS 121) 55

4.5 Co ntrol of dust pro duc ed in the dry gra nula tion of blast-fu rnace slag (Study PS 120) 57

5. Summ ary and conclusions 61

6. Figures and tables

Figure

1 Dust pai l overhan ging an industr ial area 9

2 Sou rces of air po llution in the iron and steel industry 10

a) Pig iron pro du ctio n 10

b) Stee lmak ing 11

c) Crude steel proce ssing 12

d) General services 13

3 Dust sphe re at Le Bo uch et (Study PS 150) 17

4 New portable Po rt iko n dust col lector (Study PS 139) 19

5 Gaug e for dust particle co un ting (Study PS 135) 21

6 Kon i test contac t-electr ical dust-mea sur ing instrument (Study PS 15) 23

7 Contac t-electr ical dust-me asur ing instrument (Bonn) (Study PS 138) 24

8 Discharge of brown converter fumes 31

9 Brown fume part ic les (electron microscop e photograph s) 32

10 Cleaning a Bessemer converter by means of an electr ical f i l ter (Huckingen schematic dia

gram) 33

11 Clean ing a Bessemer conve rter by means of an electr ica l f i l ter (Hucking en-asse mb ly) 34

12 Brow n fume s in an electros tatic field (Study PS 18) 36

13 Pilot plant with electr ica l prec ipitato r and l ine con nec ted to the conve rter stack (Study PS 131) . . 36

14 Internal design of expe rimen tal electr ica l prec ipitato r (Study PS 131) 37

15 Clean ing an L-D conv erter with bag fi l ters (schem atic diagram ) (Study PS 128) 39

16 Clean ing an L-D conv erter with bag fi l ters (assembly) (Study PS 128) 39

17 W et-sc rubb ing of un burn ed L-D conve rter gases (schem atic diagram ) (Study PS 130) 41

18 Conv erter with gas colle ctin g hoo d (Study PS 130) 42

19 Stack flares (Study PS 130) 43

20 W et-sc rubb ing of unb urne d LDA C-conve rter gases (schem atic diagram ) (Study PS 132) a) origin al

instal lat ion, b) mod i f ied instal lat ion 45

21 Pilot arc furna ce clea ning plant (schem atic diagram ) (Study PS 45) 48

22 Pilot arc furna ce clean ing plant (assembly) (Study PS 45) 49

23 Fumes discha rged from an arc furna ce (Study PS 45) 50

24 Brique ttes ma nufa ctured from bro wn dust (Study PS 102) 51

25 Sand blasters (Study PS 119) 55

26 Water vap orization above a conve yor belt in a sinterin g plant (Study PS 1) 56

27 Spraying surface -active water on fine-o re bunk ers (Study PS 121) 57

28 Parts of a blast furnac e unit fou led by unclea n dry gra nu lation of slag (Study PS 120) 58

29 Dry gra nu lation of slag.(s che ma tic diagram ) Study PS 120 59

30 Dry gra nula tion of slag (assembly) (Study PS 120) 60

31 Synop tic table showing research organisat ions, subjects of study, resul ts and relevant pu bl icat ions

or ECSC docum ents 64

a) Dust and gas measurement. Compar ison and im proveme nt of dust-mea sur ing devices and methods

and the developm ent of new ones 64

b) Dust and gas measurement. Measurements of the dustiness of working areas. Research on dust

and gas emissions and their groun d level conc entrat ion 66

c) Control of brown fumes 68

d) Co ntro l of othe r polluta nts 70


9/76

FOREWORD

During the past 20 years, ai r pol lut io n has jeopardized m an's heal th to such an extent in many Com mu nity areas

that some member States have been obl iged to introduce new legis lat ion wi th a v iew to l imi t ing the discharge

of dusts, fumes, gases and vapours.

In many work locat ions, ai r pol lut ion is often a very great heal th hazard owing to the concentrat ion of harmful

elements, par t icular ly at the source.

I f any kind of contaminat ion of the atmosphere wi th foreign matter cal ls for prevent ive measures, i t fol lows

that par t icular ly str ingent p recaut ions must be observed at work locat ions so as to afford adequate p rotect ion

to the people working there.

I t must be admitted that in the past much doubt unfor tunately existed regarding the nature and extent of ai r

pol lut ion and the most effect ive steps of prevent ing i t -doubts which have sometimes persisted to the present

day. But, in this sphere, the protection of workers' health is entirely dependent on the answers given to these

quest ions, as does at least a substant ial proport ion of the industry 's prof i tabi l i ty .

In v iew of this, the High Au thor i ty, unt i l m id-1967 the execut ive body of the European Coal and Steel Com mun ity,

headed a campaign for the control of dust and waste-gas pol lut ion in the sectors for which i t was responsible.

The ECSC Treaty par t icular ly charged the High Author i ty wi th promoting product ion and safe working condi-

t ions in the coal and steel industr ies and improving the l iv ing and working condi t ions of labour; accordingly

from 1957 onward, i t set up research programmes for the technological control of dusts in mines and the i ron

and steel industry and has since subsidized many studies in this f ie ld. One of the High Author i ty 's last deci -

sions was to adopt a new draft research programme for the prevent ion and technological control of ai r pol lut ion

caused by the iron and steel industry (14 June 1967).

I t is the Commission of the European Communit ies which is now responsible for the implementat ion of this

research programme, now almost ready for the go-ahead signal . The Commission bel ieves the present moment

to be an opportune one for providing interested part ies wi th a conspectus of work done in this f ield s ince 1958

a decade of research promoted by the ECSC. It also wishes to express its gratitude to al l the members of com-

mittees and study groups appointed to discuss and fol low this work, and also to al l others who helped to ensure

its success.

In addi t ion to merely summariz ing the resul ts achieved by Community-aided research, the present report sets

out to give the reader an idea of the iron and steel industry's diff iculties in control l ing dusts and waste gases

with par t icular reference to the technologica l and econ om ic aspects of ai r pol lut ion c on trol . These are di f f icul t ies

wh ich can only be overcome step by step, by the vigorous and conce rted effor ts of all con cerne d, thereby helping

to solve the urgent and essent ial ly human problem of adequately protect ing the heal th of workers and their

fami l ies.

,^J Mc

C


10/76


11/76

1.

INTRODUCTION

1.1

Source s of air pollution in the iron and steel industry

Whenever reference is made to air pollution caused by the iron and steel industry, this relates often only

to the contaminat ion of the outdoor atmosphere wi th which the general publ ic is fami l iar in the form of dust

and gas em itted by chimneys of converters, open -hearth furnaces, s inter ing plants, power stat ions, etc. (Fig. 1) .

Fig. 1

Dust pall overhanging an industrial area

Despite al l air pollution control measures applied to date, there are residential areas near industr ial centres

where the dai ly deposi t ion of dust exceeds g per square m etre of sur face area and where under ce r tain atm os

pher ic condi t ions the content of SO2 and other gaseous contaminants attains values which cannot be consid

ered as constituting a source of danger to sensitive plants only.

It should not be forgotten that there are many working areas in which air pollutants are to be found in con

centrat ions that often far exceed those measured in the outside atmosphere and cause considerable annoyance

to working personnel whose health is thereby affected. The diagrams in Figures 2a-d give a review of the chief

sources of atmospher ic pol lut ion in i ron and steelworks in regard to both working areas and outside atmos

phere.


12/76

Pig i ron product ion

Coking plant Ore prepara tion

Discharge and storage

of coking coal (dust)

Fi l l ing coke furnaces

(dust, gases)

Emptying

(dust, gases)

Ext inguishing

(dust, gases)


of ores (dust,

sometimes free SiCte)

Mil l ing and screening

(dust)

Plants producing

coal by-products

(gases)

Mil l ing and screening (dust,

sometimes free S1O2)

Ore drying

(dust, vapours)

Sintering plant

(dust, gases)


of raw materials (dust,

sometimes free S1O2)

Discharge, mil l ing

and screening

of sinter (dust)

Sinter cooling (dust)

Blast furnace and auxil iary

blast furnace plants

Preparation of furnace

burden (dust)

Charging blast furnace

(dust, gases)

Pouring and pig

iron casting (dust,

gases, metal vapours)

Desulphurization

(dust, alkali vapours)

Slag granulation

(dust, gases)

Cement works

(dust, gases)

Demolition and l ining

of blast furnaces, air heaters,

etc. (dust, free S1O2)

Flue gas stack

(dust, gases)

Fig . 2

Sources of air pollution in the iron and steel industry

a) Pig iron production

10


13/76

Smelting plants

Mixers (graphite dust,

gases)

Bottom-blown (basic

Bessemer) converters

(dust, brown fumes)

Top-blown oxygen converters

(LD,

LDAC, OLP, Kaldo,

etc.) (dust, brown fumes)

Open hearth furnaces

(dust, sometimes

brown fumes)

Arc furnaces (dust,

sometimes brown fumes)

Induction furnaces

(dust, gases)

Cupolas (dust, gases)

Preparation of iron

alloys (dust)

Steelmaking

Auxil iary plants and work

Lime bunker (dust)

Dolomite plant

(dust, tar vapours)

Converter plant

(dust, tar vapours)

Slag loading (dust)

Basic slag mill (dust)

Demolition and repair of refract

ory l ining of mixers, converters,

open hearth and electric fur

naces and cupolas, ladles,

cen

tral gates, casting plates, etc.

(dust, free S1O2)

Mi l l ing ,

sand blasting

and painting of ingot

moulds (dust, free S1O2,

solvent vapours)

Crushing plant

for refractory bricks

(dust, free S1O2)

Wood-pattern shop

(dust, solvent vapours)

Foundry units

Ingot casting (dust,

gases, metal fumes)

Drawing of ingot moulds

and central gates (dust,

free Si0

2

)

Continuous cast ing

(oi l vapours, fumes)

Mould cast ing

Sand preparat ion

(dust, free S1O2)

Mould and core drying

(dust, free S1O2, gases)

Casting (dust, gases)

Emptying (dust,

free S1O2, gases)

Oxyacetylene cutting

(dust, gases)

Cleaning

(dust, free S1O2)

Welding (fumes, gases)

Annealing (gases)

Fig . 2


b) Steelmaking


14/76

Crude steel processing

Forging and pressing

Heating furnaces

(gases)

Hot rol l ing and drawing

Soaking pits

and heating furnaces

(gases)

Lin- the-surfacing

and mil l ing

(brown fumes, dust)

Cold rol l ing

and drawing

Pickl ing unit (acid

vapours, nitrous gases)

Roll ing stands

(emulsion vapours)

Annealing unit

(gases)

Galvanization

and tinning unit

(metal and acid vapours)

Appl icat ion

of varnishes

and plastics (vapours)

Tarring pipes

(vapours)

Wire patenting

(lead vapours)

Mil l ing and cutting

(dust and sometimes

free SO2 and lead)

Fig . 2


c) Crude steel processing

1 2


15/76

Maintenance

Welding and oxyacetylene

cuttin (fumes, gases)

Mi l l ing ,

sand-blast ing

(dust, free Si0

2

)

Degreasing, painting

(solvent vapours)

General services

Transport

Work locomotives

(fumes, gases)

Motor vehicles

(gases, petrol fumes)

Energy supplies

Boiler house

(dust, gases)

Gas engines

(gases)

Research

and supervision

Laboratories (dust,

gases, vapours)

F i g . 2


d) General services

1.2 ECSC activity in the field of air pollution control

Having rega rd to this s i tuat ion, the ECSC has for ten years been m aking con siderable grants tow ards research

aimed at increasing knowledge on the nature and extent of such air pol lut ion and developing pract ical control

methods. In the i ron and steel industry sector , these grants amount to about 3m. uni ts of account^

1

)

These grants come out of levy revenues and are made in accordance with section 55 of the ECSC Treaty.

They cover both indiv idual studies and ent i re research programmes.

For the examinat ion of requests for grants and the draft ing of research programmes, the ECSC cal ls on

qual i f ied scient ists and technologists of the relevant professional organisat ions and the governments of the

Communi ty count r ies .

For every research subsidized by the ECSC a research contract is conclu ded in which the mutua l ob l igat ions

of the research partners are set out in detail .

The results of these researches, continuously supervized by the special ists, are made available to al l inter

ested part ies in the Community by sui table means such as publ icat ions.

Readers interested in these matters may find further information in previous ECSC publications.(

2

), (

3

)

1.3 Research and information groups

For the implementat ion of the f i rst general research programme on technical methods of dust control in

the i ron and steel industry, the fol lowing three headings were considered to be convenient for the prel iminary

( ') The unit of account = US$1.

(

J

) ECSC Bulletin N o. 41 (1963) The High Authority's Research Policy in the technolo gical sphere .

(

n

) ECSC Bulletin No. 60 (1966) The High Authority's Policy in the field of Prom oting Stud ies and Research on Industrial Health, Medicine and

Safety .

13


16/76

examinat ion of requests for grants, (

4

), (

5

) the pursuance of ECSC-aided research work and the mutual exchange

of exper ience in this subject:

(a) dust and gas measurement,

(b) control of brown fumes,

(c) con trol of other dusts and waste gases.

This is the arrangement fol lowed in the present account of the results of these researches.

C) Official Gazette of the ECSC, Vol. 6, No. 37, p. 610, of 16.12.1957.

(

5

) Official G azette of the ECSC, Vol. 1, No. 16, pp. 379/80 of 20.9.1958.

14


17/76

2.

RESEARCH IN THE FIELD OF DUST AND GAS MEA SUREM ENT

2.0 Scope and problems

The successful control of dusts and waste gases essent ial ly depends on the proper understanding of their

chemical and physical nature and of the amount and concentrat ion wi th which they occur at the working area,

in the outside atmosphere or at the source of emission.

For example, accurate mea sureme nts of the air pollution of a work location are a sine qua non whenever:

(a) the dust n uisance to personnel has to be appraised, or the work locat ion m oni tored to ensure observance

of the maximum acceptable concentrat ions (MAC) or threshold l imi t values (TLV),(

6

)

(b) an exhaust venti latin g system is being plan ned or i ts operating efficiency has to be che cke d after insta l lation ,

(c) the desirabi l i ty of purchasing protect ive apparatus such as dust and gas-masks is under considerat ion,

(d) i t is necessary to study the ambient ai r pol lut ion caused by a change of m ethod of work ing, prod uct ion

swi tch ,

or the use of alternative primary or auxil iary materials.

On the other hand, the emissions from the var ious sources of ai r pol lut ion(

7

) that concern us here, e.g.

a s inter ing plant or boi ler-house, must be measured wi th a v iew to:

(a) apprais ing possible hazard, damage or nuisance caused to ambient environme nt by waste gases,

(b) determ ining the stack height required for adequate atmosph er ic di lut ion of waste gases,

(c) select ing, dimensioning and designing any air -c leaning equipment required,

(d) supervis ing the operat ion of ai r -c leaning equ ipmen t al ready instal led (e.g. for the purpose of ensur ing

compl iance wi th off ic ial regulat ions l imi t ing emission) ,

(e) the ch oice of suitable fuels and raw materials and early de tection of variations in the norm al process .

Measurements of the ground level concentration^)

of dusts and gases are also required when, for exam ple,

(a) i t is necessary to ascertain the causes of damage to vegetation in the neigh bo urh oo d of indu str ial plants,

(b) the eff icacy of dust and stack gas control measures (e.g. chan ging the pro duc t ion process, conversion to

other fuels and raw and auxi l iary mater ials, instal l ing air -c leaning equipment) has to be demonstrated.

All these measurements essential ly consist of two separate procedures, viz.

( i) sampling and

(ii) analysis.

But often they are not differentiated in ordinary speech, or even in the l i terature, so that instruments solely

used for dust sampl ing are frequently designated dust m eters .

() The ma xim um ac ceptable co nce ntra tion of a gaseous, a fume or dusty pollutant is the conc entra tion in the atmos phere of a work space

(measured at the respiratory level) which in general is unlikely to affect the health of persons working in the said space even when they are

exposed to i t for 8 hours a day.

The ma ximu m accepta ble co ncent rations of gases and vapours are usually specified in ppm (cc gas per cm air) for a temp erature of 20C

and a barometric pressure of 760 mm Hg, and that of aerosols (dust, smoke or mist) in mg/m

3

(1 mg material per m

3

air). They are compiled

and published in tables regularly brought up-to-dat by the competent ministries or organisations of the various countries. These values sub

stantial ly correspond in western countries and are known as Valeurs limites de concentration des substances toxiques dans l'air in French-

speaking countr ies,

Maximale Arbeitsplatz-Konzentration

in the Germ an-spea king area,

Valori limite di concentrazione media nell'aria di

sostanze tossiche industriali

in Italian , and as

maximaal aanvaardbare concentratie (MAC )

in the Dutch-speaking area.

(') By em issio n is meant

sol id,

l iquid or gaseous pollutants of any kind or origin which are discharged to the air (e.g. fumes from a chimney

or emissions from motor vehicles).

(*) By gro und level con cen trat ion is meant tha conc entratio n of

sol id,

l iquid and gaseous air pol lutants permanently or temporari ly found near

the ground. Depending on their chemical and physical characteristics and the prevail ing atmospheric conditions, ground level concentrations

may either constitute a nuisance only or else may cause damage to men, animals and plants and also to buildings, steel structures, etc. Such

damage may arise through inhalation, irri tation of the skin, chemical attack of the surface of plants or artefacts. Indirect consequences such

as reduced rad iation from the sun (the smoke pall overhang ing many industrial regions) also deserve men tion. The term , gro und level

conce ntrat ion may be compared wi th F. immission orG . Imm ission .

5


18/76

Both for sampl ing and analysis, there already exist many methods and considerable equipment invar iably

cal l ing for proper ly trained, rel iable and exper ienced personnel and usual ly requir ing a great deal of t ime and

technical effort, but not always yielding satisfactory results.

In this situation it is understandable that despite research workers' efforts to date:

(a) some u nce rtainty ex ists abo ut the rel iabil i ty or com para bil i ty of the results obta ined with various types of

apparatus and methods for determining air pol lut ion,

(b) there are sti l l many gaps in our knowledge of air pollution in various working locations in different iron

and steel plants,

(c) gene rally speaking th ere is sti l l too l i tt le know n about air po llutio n in the vicinity of iron and steel wo rks

(ground level concentrat ion) ,

(d) hithe rto there have only been few prac tical poss ibi l i t ies of mo nito ring the dusts and gases (effluents) dis

charged by the steelmaking industry.

Thus may be defined as the scope of ECSC research on dust and gas measurement:

(a) the compar ison and improvement of exist ing measur ing instruments and methods and the development

of new ones,

(b) research on air pollution in different work localit ies,

(c) research on waste gas emissions and ground level concentrat ion.

2.1 Comparison and improvem ent of existing measuring instruments and methods and development of

new ones

2.11 C omparison of sampling instruments and methods (Study PS 150)

In view of the reasons stated above, a comparative study of sampling instruments and methods should

be given high priority.

Undou btedly some extremely interest ing resul ts and exper ience have been obtained from this study in which

7 inst i tut ions from 5 di f ferent cou ntr ies took pa rt , using al together 10 gravimetr ic dust-sam pl ing instruments

and 12 instruments for the determinat ion of par t ic le s ize.

The tests were conducted both under pract ical and laboratory condi t ions, i .e. once in the sinter ing plant

of a German and in that of a Dutch iron and steel works and twice in the IRCHA's large dust sphere at Le Bou-

chet, which has a capacity of over 2,000 m

3

(Fig. 3).

The first studies carried out in 1961 revealed very few substantial differences in the gravimetric determi

nat ion of dust conc entra t ion, but on the other hand the part ic le count resul ts showed considerable discrepancies

which in par t icular were due to the l imi t of percept ibi l i ty of the var ious measur ing methods.

In later studies in 1963, 194 mean particle concentration values were determined, and one highly important

conclusion was that for any instrument the resul ts obtained in the dust sphere could be compared wi th those

from any other instrument, the standard deviat ion being 15%.

It was found that in general the same compar ison could be appl ied to measurements in the i ron and steel

works. Since dust concentrat ions in the industry are known to be subject to random f luctuat ions, the extra

polat ion can only be appl ied to mean or long-term values, not to short- term ones.

It must be admitted that in this Community study one basic drawback inherent in al l these instruments could

not be overcome, namely that al though they enable dust concentrat ions to be measured at a given point, these

dust concentrat ions do not necessar i ly correspond to the actual dust exposures of workers in their occupational

environment.

2.12 Developm ent of a portable dust-mea suring instrument with a large air samp le capacity (Study PS 139)

Steelworkers are usually not sedentary but move about over areas of varying size in which the dust conditions

f luctuate widely from place to place and from t ime to t ime.

But the instrum ents previously used for determ ining the dus tiness of a work loca lity do not take sufficien t

account of these factors; either their size, weight and power supply reduce their mobil i ty or they operate inter

mittently and usually trap so l i tt le air that their results cannot be considered as generally

val id.

16


19/76


20/76

The following study has to led to a considerable improvement. It related to the developm ent of a small d ust

collector carried on the back

with a suction nozzle in the immediate vicinity of the wearer's mouth and nose

(Fig. 4).

This instrument is about 24 cm

h igh,

of the same width, about 14 cm deep, weighs somewhat more than

8 kg, has an electric fan run off a lead storage battery and operating at 10 m

3

/h against a resistance of 190 mm ,

water gauge, and is provided with a flowmeter and a flexible suction nozzle. In this way it is possible for the dust

iness in the worker's respiratory zone to be determined very accurately even when his work involves constant

movement from place to place.

So great was the demand for this instrument that i t is now being manufactured on a commercial scale.

2.13 Micropore membranes (Stu dy PS 10)

In many cases dusts precipitated on the fi l ters of dust collectors not only have to be weighed and compared

with the amount of the induced air stream, but also subjected to a further chemical, physical and especially

microscopic examination.

In recent years the micropore fi l ter has often been used for this purpose. It consists of cellulose acetate

or cellulose nitrate membranes 1/10 to 2/10 mm in thickness which are rendered transparent or even completely

solub le by certain flu ids. But the use of these very practical fi l ters soon created a number of p roblems , for exam ple

how to fix the particles retained on the membranes.(in order to prevent losses in the transport of dust samples)

or how to assess the errors arising when the particles overl ie each other and cannot be counted separately.

Both these and other problem s were solved by a study re lating to the use of micropore memb ranes for the

determination of dust concen tration in the iron and steel industry.

The object of the study was the development of a definitive method of counting air-borne dusts by means

of membrane fi l ters, the fol lowing factors being investigated:

(i) The effect of air humidity and speed.

It was found that the humidity of the air has no influence and that the air speed is negligible when it does

not exceed 3 m/sec;

(i i) Solubil ization of the membranes.

Since the mem branes c ould be solubil ized, al l the dust was seen in a single micro scop e field instead

of in several layers;

(i i i) Counting by microprojection.

It was fou nd tha t dark dusts, e.g. iron oxide and ca rbon , give the same results as those obtaine d with direct

l ight-field counting, whereas transparent dusts give 10%-15% lower results;

(iv) Fixation of particles settl ing on the membranes.

The method developed prevented losses during the transport of dust samples;

(v) Errors arising when the pa rticles overl ie each other and cannot be counted separately.

It was shown how the errors could be theoretically calculated and how the range of error could be estab

l ished in practice by means of two simultaneous analyses.

2.14 Research on the development of a simple method for determining free SiOz content (Study PS 37)

From an

investigation into the utility of a simple m ethod for determining the free

S/O2

content,

it becam e

apparent that the resuit obtained by counting dust particles retained by fi l ter membranes was always greatly

influenced by the immersion oil used.

It was also demo nstrated that, contrary t o wha t had been assumed fro m prev ious research results, there is no

correlation between the chemically determined free si l ica content of dusts and the ratio between the number

of particles less than 5

(

9

) counted under polarized l ight and then in clear field i l lumination.

2.15 Establishmen t of an international microscopic counting standard (Study PS 135)

The important part played by the dust particle count wil l be apparent from the various studies referred to

above.

The considerable discrepancies in counter results repeatedly found in comparative dust measurement

(differences of a ratio of 1 :10 and over are quite com mon ) are mainly due to the system of m icrosco pic deter

mination employed and also in part to differences in the selective separation factor of the various sampling

instruments.

H 1| im =1/1 000mm.

18


21/76

Fig. 4

New portable Portikon dust collector

(Study PS 139)

In use during the demolition of an open hearth furnace

b. T he interior of the device

9


22/76

The lower particle size which is.sti l l countable primarily depends on the optical system of the sampling

apparatus, although the physiological-optical and psychological effects to which the observer is subject are

also a very importan t fac tor in the proper evaluation of small particles.

To enable such optical system and subjective effects to be allowed for in count results, an ECSC study was

made with a view to discovering a suitable

gauge for the microscopic visibility and counting of dust particles

which:

(a) gives a constant p oint of reference for coun ting and measu ring,

(e) has accurately defined manufac turing sp ecification s,

(c) enables a sufficien t nu mber of secondary strong and handy gauges to be produ ced having a know n deviation

from the pr imary standard.

Apparently the study groups has succeeded in devising a simple and effective method of manufacturing such

a gauge.

Thirty glass tubes with an inside diameter of

to 3 mm and a wall thickness of 0.25 to 0.50 mm are inserted in

a glass tube with an inside diam eter of about 5 to 6 mm. This nest of tubes is drawn in a small electric furnace

into multiple capil lary tubes with an outside diameter from 0.2 to 0.5 mm.

Some 30 such multiple capil lary tubes are again inserted into a glass tube with an inside diameter of about

3 mm , and this nest of tubes, now containing about 30 x 30 capil lary tubes, is again drawn in the furnace into

a capil lary tube with an outside diameter of 0.2 mm.

The drawn glass tube consists of a more or less cylindrical centre-piece and two conical ends. A piece is

cut out of these two ends with a glass cutter and microphotographed. If, as in most cases, the two parts are

foun d to be entirely hom othetic , the cylindrical ce ntre-piece is cut up into 6 to 8 mm sections wh ich when m ount

ed act as a counter gauge.

When used with inc oheren t, oblique i l lumin ation (a conde nsor w ith a large nume rical aperture), the glass acts

as a l ight guide and is brightly i l lumina ted, whereas the tubes c onta ining air are com pletely in the dark. (Fig. 5).

The cross-se ctions of the ends represent a physical (non-op tical) m agnifica tion of the most dra wn-o ut

centre piece. The numerical value of this physical magnification is determined by the microscopic measurement

of the outside diameter of each section. (In the first of these gauges made by IRCHA the ratio of the diameter

of the ends to tha t of the cen tre piec e was 2.25 : 1).

The gauge can be used:

1.

for determin ing the l imit of visibi l i ty of a microsc ope-obse rver system,

2.

for determ ining as a fun ction of the particle diameter the count ing errors of a given observer using a given

microscope.

2.16

Experimental electro-acoustic particle-size measurement

(Stu dy PS 141)

The conventional methods of characterizing dusts by reference to the important particle-size factor are un

fortunately fair ly complex and laborious.

With a view to discovering a simpler technique, aid was given to a research on thedevelopm ent of an e lectro-

acoustic instrum ent for the particle-size mea sureme nt of aerosols.

It was planned to develop a dust collecto r

which would react to a single particle and even record the individual reaction stages depending on the mass of

the separate particle, i .e. which would determine particle number and size.

The experimental design consisted of a large evacuated vessel in which was mounted an electro-dynamic

microphone with a movable diaphragm resting of foamed plastic (for maximum exclusion of extraneous noise).

After suitable amplification with an oscil lograph the instrument was arranged to detect dust particles carried by

the air into the vessel through an approximately 0.5 mm aperture and impinging on the microphone.

The sensitivity of the new instrum ent was such that single particles of 5 diameter co uld be detected but

not more than 100 particles/sec. For counting the separate particles the instrument depends on controlled

d i lu

t ion of the aerosols, which makes it difficult to produce a dust collector for this type of measurement in the work

ing area. But since the technique can be employed at higher temperatures it might, under certain conditions,

become important for the continuous measurement of a relatively high overall dust concentration of about

100 mg/m

3

, for example in stacks.

20


23/76

Fig.

5 - Gauge for dust particle counting Study PS 135)

2


24/76

2.17 Establishing the source of dusts (Study PS 35)

Owing to the great number of different sources of dust and gas emissions in industr ial centres the wrong party

may easily be suspected of causing damage or nuisance by air pollution while the real, unknown of fender cont i

nues unchecked because the source of pol lut ion cannot be detected.

Some ways of improving this unsatisfactory situation are revealed by the results of a study on

dust-source

detection in conne ction with an investigation into dust concen tration in the ore sintering

sector

By improving the analyt ical methods, especial ly by means of microscopic examinat ion under ref lected,

direct or polarised l ight, i t proved possible to establish the source of separate particles in samples of mixed

dusts of the type commonly found in steelworks. Thus i t was possible to dist inguish di f ferent i ron oxides in

dust samples and to say whether they or iginated from Swedish or Lorraine ores or steelmaking processes.

The coke part ic les from a coke oven could also be dist inguished from those emanating from a pulver ised coal-

f i red instal lat ion.

The electron microprobe method proved very useful for ident i fy ing f ine dusts which are often carr ied great

distances. In this new method an electron beam impinges on the dust sample, the x-rays produced at the point

of impact being caught by a detector. Stated briefly, the separate pieces of dust are analysed by the detector into

their const i tuent chemical elements.

In a study of the crude gas com posi t ion of two cyclone separators a 92.5% retent ion was obtained in one case

and 84% in the other. It was pointed out that theoretically the retention by the same separator is not identical

for every particle size but varies according to the type of dust. The research workers concluded from their obser

vations that i t is som etimes better to conside r the qualitative pe rform anc e of a sepa rator rather than its

ef f i

ciency on a purely weight basis.

2.18 Development of dust-measurement recording instruments (Stud ies PS 15 and PS 138)

Provided we know the types of dust occurr ing at cer tain strategic points, a s imple method of determining

their concentrat ion usual ly suff ices for cont inuous control .

But one drawb ack of the conve nt ional methods is that a very great numb er of separate mea surements have

to be taken to o bta in a fair ly accurate idea of the variation in dust conc en tration per unit of t ime .

Not only do these numerous measurements call for considerable staff and facil i t ies, but the results are

only available after a fair ly long delay.

But rapid recogni t ion of the t ime-dependent changes in dust concentrat ion may be very important both

for the control of dust exposures at the work locat ion and, for instance, ensur ing eff ic ient operat ion of sepa

rators and the ear ly detect ion of breakdowns in many product ion processes.

For these reasons two studies relating to the development of continuous dust-measurement recording in

struments were aided by the ECSC.

The first of these studies (PS 15) concerns the testing and development of an instrument for measuring

the dust concentration by electr ic contact (Fig. 6).

In this instrument, a distr ibutor-entrance chamber imparts a rotary movement to the dust- laden stream

of air drawn in. Centrifugal forces bring the dust particles into close contact with the inner surface of an ener

gised tube, thereby causing an electr ic contact interact ion between the dust par t ic les and the wal l of the tube

as a resul t of which both the part ic les and the tube becom e electr ical ly cha rged. Wh i le the part ic le charge plays

no further part, the energized tube charge is earthed as a leakage current via a galvanometer or the input resist

ance of a measur ing ampl i f ier . The ampl i f ied leakage current can then be indicated and recorded by means

of a chart recorder.

Since for a given energized tube the leakage current depends on the type of dust measured (steatite, a mag

nesium hydrosil icate Mg3H2(S40i2) gives the best response of al l energized tube materials studied to date),

the instrum ent,sh ould be cal ibrated wi th the dusts to be measured at the place it is used. To this end, the dust

passing through the konimeter is trapped in a f i l ter at the discharge end, weighed, div ided by the volume of ai r

sampled, and compared wi th the mean leakage current in a character ist ic charge curve.

With an air intake of up to 50 m

3

/h the instrument has a very high col lect ing eff ic iency. Since the count

is recorded pract ical ly instant ly the instrument also detects very rapid f luctuat ions in the dust concentrat ion.

W ithin the mea sur ing range of 0 to about 3 g/m

3

(the only one of practical importance) there is a l inear and repro

ducible relat ionship between the measured value and the gravimetr ical ly determined dust concentrat ion.

22


25/76

General view

Suction fu nnel with roof-shaped cover and annular slot

Cyclone tube embodiment of the Konitest dust detector

D.C. meter amplifier

Continuous-line recorder

Integrator

Differential mano meter for measu ring air flow

Aspirator

Fig. 6

'Konitest'' contact-electrical dust-mea suring recording instrument

(Study PS 15)

b. Cross-sectional view of the dust detector

23


26/76

As the research work progressed, it proved possible to increase the instrument's sensitivity sti l l further

unti l i t even records dust concentrations of only 1 mil l ionth of a gramme per cubic metre and responds to finely

divided iron oxide aerosols of less than 0,3

(primary particles in brown fumes). It can be adjusted by a handle

to different ranges of sensitivity.

The development of a structural variant of a separating cyclone in which 5 fractions are continuously

separated provided a means of simultaneously recording and measuring the concentration of fine dust inhaled

by the lungs and the overall dust concentration; this technique may prove extremely useful for the appraisal

and control of si l icosis hazards in working areas.

Another new embodiment (the use of a Venturi nozzle made of material sensitive to electric contact) led

to a substan tial reduction in the instrum ent's size and weigh t. This embo dime nt can be carried on a wo rkm an's

back and used for measuring the dustiness of working areas and continuously recording the dust concentration

prevail ing in the respiratory zone at any given time.

A grid probe has been developed for recording and measuring heavy dust loadings, e.g. on the crude gas

up-stream side of separators. It consists of several round rods made of material sensitive to electric contact.

It was used in preliminary experiments with pulverized coal burners, and a l inear relationship between dust

loading and measuring current was sti l l found at dust concentrations of 500 g/m

3

. With the usual energized

tube and the Venturi nozzle this l inear relationship is only in the range of 0 to about 8 g/m

3

.

In the second study of this kind

PS 138)

an instrum ent was developed (F ig. 7) with a measuring head th roug h

which an air stream flows at the rate of 6 m

3

N.T.P./h and is passed to a nozzle at a velocity of about 130 m/s.

A 0.5 mm fi lament probe is located at a distance of 2.5 mm from the slotted end of the nozzle. Dust particles im

pinging on this probe generate an electric charge which is continuously led away, its voltage measured with

an oscil lating condenser electrometer and recorded by means of a chart recorder. All dust passing through

the measuring head is captured in a down-stream microsorbant fi l ter for the purpose of calibration curve classi

fication and dust analysis. The instrument provides good detection of concentrations of 0.1 mg/m

3

of dusts

smaller than5 .

The fi lament probe has an advantage over various other materials such as steatite in that there is no risk

of any polarity reversal of the leakage current of certain mixed dust components leading to errors in meas

urements.

2.2

Measurements of the dustiness of working areas

In order to obtain information on the dust conditions prevail ing in different working areas in the iron and

steel industry, the ECSC has promoted suitable research work in four Community countries.

Fig.

7

Contact-electrical dust-measuring

recording instrument Bonn )

Study PS 138)

24


27/76

Owing to their l imited size and set-up they were only primari ly intended as pilot studies, so that the results

obtained, however interesting in detail , must not be regarded as being universally applicable. They are rather

parts of a mosaic which is sti l l far from complete.

2.21 Dusf survey in German steelworks (Study PS 20)

The survey carried out by the Staubforschun gsinstitut des Haup tverbandes der Gew erblichen Berufsgeno s-

senschaften, Bon n, was focussed on workin g areas exposed to dust capable of prod ucing s i l icosis. For instance,

in steelworks, dust measurements were made dur ing the demol i t ion of open-hearth furnaces, the cutt ing, buff-

ing and laying of refractory bricks, and the cleaning of ladles; in foundries, measurements were made of the dust

exposure associated wi th sand processing and the moulding, knocking out, buff ing and fett l ing of cast ings. The

study examines cr i t ical ly the dust condi t ions encountered, some of which were extremely disconcert ing, and

puts forward suggest ions for fur ther research.

For appraisal of the si l icosis hazard the Staubforschungsinstitut makes use of i ts own formu la:

C (SO2 < 5 ) X C

total

< 5 ) =

In this formula, the first factor denotes the concentration of free crystall ine si l ica having a respirable particle

size less than 0.5 , and the second the respirable fine dust concentration less than 0.5 of al l types of dust

in the sample, the concentrat ions being invar iably expressed in m g / m l

If the product Z, i .e. the criterion, does not exceed 0,5 (

10

), no silicosis hazard is assumed to be present.

In order to measure these dust concentrations a given volume of air was drawn through a fi l ter (i .e. a micro-

sorbant fi l ter, and in very hot working areas a paper fi l ter). The respirable dust was determined by elutriation.

Sil icoge nic mineral particles were identified by the x-ray meth od wh ich has a lower dete ction l imit of 1% .

The basic criterion for the entire dust concentration is that

C total

must not exceed 15 m g/m

3

even in the

absence of si licogenic compon ents.

When the dura tion of the work was so short that a particle-size me asurement fai led to give a sufficie nt am ount

of dust for prac tical use (e.g. when refractory bricks are occas ionally cut by hand) particle conce ntratio n measu re

ments were made with a HS (Hasenclever-Sartorius) k onimete r and a projec tion m icrosc ope w ith a total ma gni

fication of 370. An average particle concentration of 200 per cc of si l icogenic dusts (after removal by ignition)

was considered dangerous in continuous work.

It should be added that the resulting criteria vary within the range of from 0.035 (m oulding wo rk in a steel

works fou ndry) to 442 (cleaning the inside of ingot m oulds with a grind ing m achine).

The final reports on the results of this study and the Ital ian study discuss ed be low made it clear to the research

committee that the si l icosis hazard is calculated by different formulas in different countries. It suggested that

this question should be examined in future studies within the framework of the exchange of know-how to see

whether the formulas derived from theoretical considerations and practical experience can be simplified.

2.22 Dust survey in Italian steelworks (Stud y PS 11 + 12)

The report sub mitted by the Clinica del Lavoro, Milan, deals first with the dust measurements made during

the operation of 11 electric furnaces in 5 Ital ian steelworks. Under unfavourable atmospheric conditions a fume

concentration exceeding 5,000 particles of from 0.7 to 5 per cc was found 2 metres above the ground in an

older type of steelw orks using hoodless furnaces . Visibi l i ty was l imited to a few metres. No substan tial air po llu

tion was found in the other steelworks.

Investigation of the refractory bricks used for rel ining furnaces and ladles showed that the high percentage

of free si l icic acid in the respirable dust fraction of less than 5 was only about 20% less than the average for

all dust fraction s. But in most other m aterials the less than 5 dust fraction contains only a half to one -third

the percentage of free si l icic acid.

Investigation of the si l icic acid content of the atmosphere of dust in steelworks showed that generally speak

ing no substantial difference exists between one works and another.

( ') Accord ing to the final rese arch report 1964. The criterion was subsequ ently am ended as fol lows:

(a) below 0.2, no apparent si l icosis hazard,

(b) from 0.2 to 1.0, si l icosis hazard po ssible.

(c) above 1.0, serio us silicosis hazard.

(Cf. Staub-Reinhalt, Luff (26) 1966, pp. 2-8).

25


28/76

With the use of the formula employed by the Clinica del Lavoro for estimating the degree of si l icosis hazard

i t was found that by and large steelworks operat ions are not s i l icogenic, al though in some jobs (par t icular ly

in the demolit ion and rel ining of furnaces) a very considerable si l icosis hazard may occasionally be present.

The above-mentioned formula is as fol lows:

silico sis haza rd R = ' (1 + -5 )

500 1 + q

where

N = total num ber of particles of atm osp heric dust varying from 0.7 to 5

q = num erical percen tage of particles of si l icog enic free si l icic acid in the less than 5 dust

fract ion of atmospher ic dusts

2

= Coefficient of the si l icogenic capacity of inert dusts which is especial ly high with low contents of sili

^ ooge nic free si l icic acid.

No si licosis hazard is assumed to be present wi th values of R = 1 . The hazard increases wi th increasing values

of R exceeding 1.

In this connect ion the

Clinica del Lavoro

also distinguishes between specific hazard and effective hazard.

If, for instance, the actual w ork perfo rme d by a wo rkm an rel ining ladles is l imited to 65% of the shift, then the

actual hazard is only considered to be 65% of the dust hazard peculiar to the job and calculated by means of

the formula. As stated earl ier, i t is necessary to clarify the reasons for the different methods of calculating si l ic-

osis hazard in Community countr ies.

2.23 Dust survey in Luxem bourg steelworks (Studies PS 49 and PS 144)

Two studies on dust concentrat ions in the i ron and steel industry relate to Luxembourg.

The first of these, which was carried out by the Directorate of Public Health of the Grand-Duchy of Luxem-

bourg (PS 49) aimed at obtaining a general survey of the dust concentration found at various work locations

so as to establ ish which were the most highly exposed locat ions to which subsequent more detai led research

work could be devoted.

Both part ic le-size and part ic le-num ber determinat ions were made wi th a v iew to establ ishing the dust con-

centration. The electrostatic sampler was chiefly used for particle-size measurements, and the Hasenclever-

Sartoriu's konimeter for particle-number counts.

It proved diff icult, i f not impossible to compare these instruments with others used (e.g. the Drager dust

trap and the Ernst Haage dust sampling apparatus), so that the report recommends the use of one instrument

for al l comparat ive measurements.

The highest concentrat ions by part ic le number and size of S1O2c ontaining respirable du sts less than

5 were recorded in blast- furnace p lants, fol lowed by basic steelworks, basic s lag m i l ls , rol l ing mi l ls and fou nd -

ries.

Appraisal work was made di f f icul t by the great f luctuat ions in dust concentrat ion from one locat ion to

another, for instance, scatter of from 50 to 3,000 particles per cc in different operations performed by one work-

man at a given locat ion. The report accordingly points out that a cont inuously recording meter would be espec-

ial ly valuable for such cases as this.

The second study made at the Laboratoire de minralogie at the Mus e d histoire naturelle, Luxembourg

(PS 144), was chiefly concerned in determining the crystal lographic properties of the different types of minerals

found in dusts occurr ing in the Luxembourg i ron and steel industry, this determinat ion being important for

identif ication. To this extent i t has certain parallels with the Belgian study PS 35 referred to in section 2.17.

120 dust samples col lected wi th the electrostat ic sampler from di f ferent work locat ions could be classi f ied

according to their mineralogicai com posi t ion , colour and part ic le shape in a card- index system of microp ho-

tographs and radiographs. From these results, the kinds of dust found were classified into 12 different types.

For instance, 3 types of dust could be distinguished in the blast-furnace f ield, v iz. dusts found:

1. dur ing the tapping of pig iron,

2. dur ing the tapping of slag,

3. dur ing the removing of f lue dust.

With a v iew to readier compar ison of unknown dust samples and determinat ion of their main const i tuents,

a series of substances frequently occurring in the iron and steel industry, e.g. magnetite, hematite, siderite,

quartz, cr istobal i te, t r idymite, l ime, calc i te, dolomite, are shown separately.

26


29/76

The di f ferent dust samples were microphotographed:

(a) under natural l ight: in order to dist inguish the opaqu e const i tuents from the transparent ones,

(b) under p olar ized l ight wi th red I wave plates: in order to dist ingu ish the opt ical ly isotropic from the op t ical ly

anisotropic const i tuents,

(c) by nter ferometry: in order to determine the transparent co nst i tuents and to observe the sur face co nd i t ion.

The research report con cludes that i t wou ld be useful to add to the card- index system and that the lat ter co uld

be part icular ly valuable in studies on the contr ibut ion of the var ious dust sources to ai r pol lut ion in the neigh-

bourhood of i ron and steelworks.

2.24 Dust survey in Dutch foundries (Study PS 17)

The most extensive study in the present group of investigations was carried out in the Netherlands by the

Gezondheidsorganisatie

T.N.O.

Delft.

I ts objects was to determine the dust concentrat ion at di f ferent work locat ions in steelworks and to study

the relat ionships between dust concentrat ion and pulmonary lesions. At the t ime of wr i t ing resul ts of research'

work extending over several years had not been completely analysed.

As regards the dust research, in this study it was necessary to:

(a) determine the weigh t, par t ic le num ber, par t ic le-size distr ibut ion and chem ical and physical com pos i t ion

of the dusts at the work location, especial ly the respirable dust particles,

(b) carry out the m easurem ents so as to give a representative pictu re of the volum e of dust inha led d urin g

a fai r ly long per iod (approximately twelve months) wi th an accuracy reveal ing any di f ferences exist ing be-

tween di f ferent groups of workers.

In this study some 7,000 dust measurements were made in nine foundries, so that statistical processing

was necessary.

Since the dust concentrat ion var ied extensively from place to place and from t ime to t ime i t was extremely

di f f icul t to determine the mean dust concentrat ion, and owing to the very large number of samples that had to

be examined i t proved very di f f icul t to determine their composi t ion.

I t was found that a plan based on stat ist ical data is needed for the determinat ion of the mean dust concen-

trat ion relat ing to di f ferent groups of workers. Thus six ser ies of measurements spread over s ix months were

required to dist inguish between the dust exposures of moulders and str ippers.

No correlat ion exists between the di f ferent uni ts of measurement, e.g. weight and part ic le number. I t did

not prove possible to determine the num ber of quartz par t ic les app roximately less than 2 . The num ber of

quartz par t ic les varying from 2 to 5 mm was determined by means of the phase-contrast technique. The determi-

nation of the weight of quartz in dust particles less than 5

presented no difficulty, but there was no co rrelation

with the number.of quartz particles.

A very large number of small dust particles are often encountered in steel foundries, most being soluble

in hydrochlor ic acid. In iron foundries the percentage of dust particles soluble in hydrochloric acid was usually

smaller. Cristobalite was almost entirely confined to steel foundries.

2.3

Resea rch on dust gas emissions and their ground level concentration

Damage to agricultural and forestry areas is often attr ibuted to the effect of fluorine compounds and SO2

discharged by iron and steelworks.

Two studies relating to these areas were therefore carried out with the financial aid of the ECSC.

2.31 Research on fluorine and SO2-containing waste gases discharged by steelworks (Study PS 129)

The first of these studies dealt with the discharge of fluorine and

SO2

containing waste gases discharged

by a single plant centrally situated in a rural locality.

It was particularly concerned with the effect and volume of the various materials involved in the smelting

process, and with the effect of the stacks and atmospheric conditions on the volume and composition of the dusty

waste gases and deposits inside and outside the plant.

27


30/76

The f luor ine and SO2 point sources were the open-hea rth furnaces and a detached electric furnace not con

nected to a chimney. Some very interesting results were obtained on the values of dust emissions and the ground

level concentrat ion.

It was foun d, for exam ple, that the eff luents from an electr ic furnace bath wi thout f luo r i te addi t ive contained

16 % of the sulphur introduced and 4% of the f luor ine; the values for an electr ic furnace bath wi th f luor i te were

15 % and 38% respectively.

An open-hearth furnace containing no fluorite (the plant no longer uses fluorite in this type of furnace) gave

a discharge of 45.6% of the sulphur (S) introduced and 70.6% of the fluorine (F).

The ground level concentrat ions found in the air discharged by the steelworks at a distance of from 2 to

400 metres varied from 2 mil l ionths g F/m

3

to a maxim um of 12 mi l l ionths g F/m

3

, and from 0.05 to 1.0 m g S Os/nr'.

Fluorine mea sureme nts made at a distance of 600 to 3,000 metres from the steelwo rks, i .e. inclu ding the ef

fluents of other plants, gave a blank value of about 2 mil l ionths g F/m

3

, while the waste gases discharged by

the works reached values of 5 to 8 mil l ionths g F/m

3

.

Vegetat ion sam ples taken from points at varying distances and in di f ferent d i rect ions from the works showed

that the sulphur and f luor ine content of crops grown near the works and or iented along the prevai l ing wind

(west) were higher than in the same species grown further away or not oriented along the prevail ing wind.

Of the analyt ical methods employed special mention should be made of the recording SO2 measurement

of stack gases and atmosphere wi th the W sthoff instrument and the recording measurement of gaseous f luor ine

compounds wi th the MINI-ADAK instrument.

Analysis of the stack gases discharged by a 250 ton ope n-hearth furnace w i th these instrume nts sho wed

that the a mo unt of SO2 effluent is invariably increased with a dditio ns of l iquid p ig i ron, bauxite or iron ore, but

not wi th charging. An SO2 peak was found wi th each reversal of the burners. A more intense discharge did not

occu r u nt i l the bath tem perature was increased d ur ing boi l ing . A sudden r ise in the f luor ine c ontent of the stack

gases is attr ibuted to the movement of the bath. When no f luor i te was added, s igni f icant amounts of f luor ine

could f ind their way into the bath from the ore.

2.32 Detection and remova l of fluorine in waste gases (Study PS 149)

The second study carried out some years later by a steelworks in an industr ial centre was concerned with

th e detection and removal of fluorine in waste gases.

The analyt ical methods of determining f luor ine were f i rst checked and, in this connect ion, cer tain important

discover ies we re m ade, most of which have now becom e accepted in the chemistry of f luor ine. I t was con cluded

that f luor ide concentrat ions ci ted in the l i terature should be accepted wi th reservat ion. For instance, i f dust

samples are taken from acid gases for fluorine analysis, the sample should be immediately alkalinised as other

wise the fluorine values found wil l be far too low. The choice of f i l ter is also of paramount importance.

A large number of Bergerhoff and Hibernia instruments were used over a considerable period of years

for measur ing ground level concentrat ions in the neighbourhood of a large steelworks; they showed that under

certain conditions the instrument's position can have a marked effect on the results. If the operator works in

accordance wi th VDI * code 2119 (dust deposi t measurements) and the top of the instruments placed 150 cm

above the ground, they can, for instance, also record i ron ore dust raised near the ground by traff ic or dur ing

charging and which on account of i ts weight is only found wi thin a very narrow compass. After el iminat ion of

this type of error a f luor ide ground level concentrat ion of 2-6 mg/m

2

per diem was measured. Only a small part

of this is soluble and hence physiologically active.

Parallel measurements made in the entire town of Duisburg w i th a v iew to determining the f luor ide con

tent of the atmosphe re gave values varying from 1 to 3 mi l l ionths g /Nm

3

; there are, therefore, no significant

concentrat ions in the neighbourhood of the steelworks.

Free fluorine is such a highly reactive material that i t is hardly met with in waste gases even in steelworks

where the f luor ine compounds that can be measured occur in very var iable concentrat ions. I t was found that

down-stream of al l steelmaking furnaces, especial ly at points where brown fumes occur, the f luor ine compounds

are nearly al l adso rbed by the solid waste gas con stitue nts; this means that sepa ration into ga seo us and

so l

id

f luorides is-no longer possible. If the dust is subsequently caught in any type of air cleaning plant, correspond

ingly few fluorides are discharged. When even very large amounts of f luorite are added, as in the 90 ton L-D

converter (900 kg) and the 80 ton electr ic furnace (500 kg) there are no fluoride emissions down-stream of good

air cleaning plants.

*

Verein Deutscher Ingenieure,

Dsseldorf.

28


31/76

Fortunately, only smal l amounts of f luor ine compounds are discharged in the sinter ing process. But s ince

the waste gases discharged by the sintering plant are acidic, only a part of this fluoride is adsorbed by the dust

and separated again dur ing cleaning. Some improvement was effected by adding alkal ine dusts, e.g. MgO, but

the problem wi l l be automatical ly solved once desulphur isat ion plants are introduced. The problem has been

deferred since f luor ine contents are only of minor s igni f icance owing to the great stack height.

Fluor ide discharges from coal- f i red plants mainly depend on the basic ity of the ash. Groun d level conce ntra

t ions of f luor ide may also be encountered in resident ial distr icts when slag only com bines wi th a minor amo unt

of fluoride. In any case the fluorine discharges of large plants are greatly reduced by air cleaning instal lations.

29


32/76

3. CONTRO L OF BROWN FUMES

3.0 Scope and problems

Undoubtedly the most not iceable of the eff luents discharged by the i ron and steel industry are the brown

fumes produced in vast quant i t ies when oxygen-enr iched air is blown in Bessemer converters, pure oxygen

is blown in L-D and L-D AC converters, oxygen is added in open-hearth and electr ic furnaces, and in the scarfing

of ingots (Fig. 8). Although not constituting a direct health hazard they are capable of intensifying the smoke pall

overhanging industr ial areas and which causes damage to human, animal and plant l i fe by prevent ing solar

radiat ion.

From the physical viewpoint these effluents are waste gases in which are dispersed minute iron oxide parti

cles (Fig. 9), of a size comparable to, say, particles of tobacco smoke. Their f ineness is due to the manner in which

they are produced, viz. as a result of the reaction of oxygen with molten i ron, the melts are locally heated to such

high temperature as to create considerable evaporat ion at these points. The i ron vapour combines wi th oxygen

from the waste gas or present in the air stream and is then condensed to form countless minute iron oxide par

t ic les, which impart the marked brownish-red t inge to the waste gases even when their dust concentrat ion is

scarcely 0.15 g (150 mg) per cubic metre at N.T.P.

There are a number of di f f icul t ies prevent ing technical ly sound and economic c leaning of these fumes.

Of these we may mention:

(a) the extreme fineness of the solid particles,

(b) the high temperature, and

(c) the great volume of waste gas produced per second.

Some figures wil l make this clear.

About 95% of brown fumes consist of par t ic les having diameters of about:

(a) 100 to 800 nm (

n

) in top-b lown oxyg en converters, and

(b) 15 to 80 nm in botto m-b lown co nverters.

At the converter outlet the waste gas temperature is at a temperature of about1,600C and in i ts subsequent

course it may r ise to 2,000C, depending on the conditions with which it is mixed with the air stream. (The theo

ret ical temperature for a combu st ion-air factor n = 1 would be about 2,700C).

The capaci ty of the air c leaning plant should be in accordance wi th the maximum volume of waste gas

passing per second. This volume is in turn dependent on the size of the converter and the charge, the maximum

fuel combust ion rate, and on the amount of ai r and water vapour mixed wi th the converter gases proper dur ing

their subsequent course.

In pig iron refining, 1 kg of carbon burns 0.93 m

3

N.T.P. of oxygen, producing 1.86 m

3

N.T.P. CO. Hence

at a combustion rate of 0.4% C/min, 67,000 m

3

N.T.P. CO/h are discharged from a 150 ton top-blown oxygen

converter . To this amount of gas, which at a temperature of about 1,600C actually occupies about six times

the volume expressed in cubic metres at N.T.P., the entraining air adds an amount of gas whose volume depends

on the given condi t ions; this gas is mixed wi th the converter gas proper or goes into react ion wi th i t (combus

tion), thus considerably increasing the volume of waste gas to be treated.

For instance, a 150 ton oxygen converter operating with a decarbonisation rate of 0.4% per minute and

complete combustion of the converter gases with 50% excess air (air factor n = 1.5), requires an air cleaning

plant having a capacity of about 275,000 m

3

/h N.T.P. of waste gas.

Owing to i ts greater decarbonisat ion rate of about 0.8% C/min and addi t ional ni trogen bal last, a bottom-

blown Bessemer converter discharges practically the same specific amounts of waste gas with a pig iron charge

of only 50 tons.

For cleaning purposes the gases must first be cooled down to temperatures varying from 50 to 300C,

according to the cleaning method selected.

( ) 1 nm = mil l imicron = mill ionth of a mil l imetre.

30


33/76

:si

Fig. 8

Discharge of brown converter fumes

3


34/76

* Brown fume particles

C T

(electron-microscope

32


35/76

The 275,000 m

3

N.T.P. assumed in the example given above would entail treating about 240 to 220 mil l ion

kca l /h . In general, about half is lost by indirect cooling in a waste-heat boiler or cooling vent, the residual heat

being reduced to the required low temperature by water-spraying. When cloth f i l ters are used, water-spraying

is avoided as far as possible and most of the heat drawn off by indirect cool ing. But to ensure good separat ing

eff ic iency, waste gases passing through dry electr ical precipi tators require wett ing or condi t ioning, and those

passing through wet electr ical precipi tators or Ventur i scrubbers need saturat ing, depending on the amount

of water vapour absorbed. The resul t is that the amount of gas actual ly passing through the blower is as much

as three t imes that required under normal operat ing condi t ions ( i .e. about 550,000 to over 800,000 m

3

/h instead

of the above mentioned 275,000 m

3

/h N.T.P.).

The dust content of the waste gases is not constant dur ing the per iod of the charge. In undi luted gas i t is

about 150 to 200 g/gm

3

N.T.P. and depending on ci rcumstances, par t icular ly the amount of inf i l t rat ing air , i t

fal ls to 15 to 40 g/m

3

N.T.P. of con sum ed waste gas. Brow n fumes a ccoun t for about 1-2% by weight of the blast

furnace steel .

Hence converter steelworks prod uce very substant ial am ounts of f ine dusts having a high iron conte nt; these

dusts, ei ther dry or in s lurry form, must be removed from the air c leaning plants, stored, transported and fur

ther problems speci f ic to the air -c leaning method employed.

3.1 Cleaning brown fumes from Bessem er converters by means of electrical precipitator ( Huck inge n s tudy)

The f i rst ECSC-subsidized study on the technical control of ai r pol lut ion related to the cleaning, by means

of an electr ical precipi tator , of the brown fumes discharged by a bottom-blown 40 ton Bessemer converter

(Figs. 10 and 11).

The air cleaning plant consisted of three parts, viz.:

(a) a waste-he at b oiler in which th e waste gases are coo led and the ir heat exp loite d,

(b) a stabil izer in wh ich a water and vapo ur pulve riser coo ls the waste gases sti l l furth er and wets them suf f i

ciently, and

(c) an electr ical precipi tator for dust separat ion.

1 Converter

2 Radiation heating surface

3 Tubular screen

4 Conve ction heating surface

5 Stabilizer

6 Electrical precipitator

7 Fan

8 Pneumatic dust exhaustion

Fig.10

Cleaning a

Bessemer

converter by

means

of a n electrical filter (schem atic diagram) (Huckingen Study)

33


36/76

Flg.

11

Cleaning a Bessemer converter

by means of an electrical filter

assembly

Huckingen

study)

The saturated vapour produced in the waste-heat boi ler was passed to an evaporat ion drum in the form of

a Ruths accumulator and then led to the thermal power stat ion. A superheater fed by blast- furnace gas was in

stal led and special control measures observed to ensure that the steam generated was suppl ied to the plant

network as uni formly as possible.

The steam generated in the waste-heat boiler was an asset which offset the cost of operating the air cleaning

plant.

Since so l i tt le space is usually available in Bessemer steelworks, the space-saving vertical form of precipi

tator was selected for the exp er imental plant. Compared to the hor izontal p recipi tator i t has, however, the draw

back that operation with several voltage fields is diff icult and that during precipitation it cannot be cleaned

of accumulated dust by rapping.

The precipi tated dust was dr ied, removed from the screens by a pneumatic conveyor, and then conveyed

to the steelworks' f i l ter plant in a closed screen waggon. Here it was mixed with dry flue dust and wet slurry

deposi ted on the precipi tator basin to produce recovered mater ial sui table for immediate agglomerat ion. But

it was then found much easier to work up the dust into pellets of adequate consistency by passing in through

a newly developed unit in the immediate vicinity of the hopper, while adding water, the pellets then being used

in the converter or ladle.

34


37/76

This study opened up an ent i rely new f ie ld, and after al l research workers concerned had exerted them

selves to the utmost and count less modi f icat ions and improvements had been made, i t showed that there is

no real reason why a Bessemer converter ca nnot be cleaned wi th the means employe d. It must be said, however,

that the extensive technical faci l i t ies and space required for an air c leaning plant preclude the general introduc

tion of this technique in present-day Bessemer steel works.

3.2 Remov al of particles from brown fumes at eleva ted temp eratures in new types of electrical precipitators

(Studies PS 18,43, 131)

In the convent ional type of electr ical f i l ter operat ing wi th ionis ing electrodes, increasing deposi t ion of

brown fume part ic les on the discharge electrodes may resul t in a corona discharge of reversed polar i ty which

reduces precipi tator eff ic iency, par t icular ly when the dust has such a high resistance that the electr ic charge

conferred on i t is neutral ised too slowly. Depending on the size of this resistance, the construct ion or technical

arrangements employed in convent ional electr ical f i l ters have to be modi f ied to ensure adequate col lect ion

ef f i

ciency, e.g. by humidi fy ing according to the temperature of the waste gases.

No ser ious precipi tat ion di f f icul t ies are to be expected in the 10

4

- 1 0

u

ohm. cm dust resistance range. The

conventional type of electr ical f i l ter also requires certain exposure times, and this may affect the size and cost

of the electrostat ic precipi tator .

Observat ions have shown that i ron oxide aerosols have propert ies enabl ing brown fumes to be precipitated

in electrostatic fields ( i.e. in electr ical f i l ters operat ing w i thou t ionis ing electrodes or the above -men tioned draw

backs of the convent ional method of electr ical f i l t rat ion) .

Three con secut ive studies were subsidised wi th a v iew to test ing the accuracy of these observat ions and

their pract ical possibi l i t ies.

The f i rst study (PS 18)conce rned laboratory tests of an instal lat ion w i th a flow rate of s l ight ly more than

5 m

3

/h N.T.P. of dusty air (brown fumes). The second study (PS 43) was carried out with a 2,000 m

3

/h N.T.P.

unit placed on the roof of a basic Bessemer steelworks.

The fol lowing resul ts were obtained from these two studies:

In the new method operat ing wi th electrodes wi thout corona discharge, i .e. current f low:

(a) the brown converter fumes col lect spontaneously as f loes (Fig. 12) of good precipi tat ion eff ic iency,

(b) increasing depo si t ion of dust par t ic les on the electrodes does not reduce the precipi tat ion eff ic iency,

(c) the fum es can also be precipita ted at tempe ratures of over 200C, wh ich m eans that the waste gases need

not be wetted, a techn ique involv ing the labor ious task of regulat ing the converter gas f low and f indin g room

for the stabil iser,

(d) on ce the precipita ted gas has been dried it f lows rea dily and can be easily remo ved from the fi lter, wh ich

is a great advantage when the dust is returned to the steelmaking process,

(e) dust loads of less than 100 m g /m

3

N.T.P. could be dealt wi th.

The thi rd study (PS 131)was concern ed wi th so lv ing the problems a nt ic ipated when passing from the smal l

pi lot plant to the large-scale unit.

I t related to the development and test ing of exper imental f i l ters capable of handl ing 25,000 m

3

/h N.T.P.

waste gas and equipped wi th electrode systems of the size used in large instal lat ions, and again placed on the

roof of the above-mentioned basic Bessemer steelworks. (Figs. 13 and 14).

The 1.7 x 4.5 metre electrodes were designed to set up a non-uni form electrostat ic f ield whi le remaining

below the dielectr ic strength.

This means that so far as possible the distance between the electrodes must be kept the same. A distance

of 30 mm 3 mm was guaranteed by the suppl iers both for the exper imental f i l ter subsidized by the ECSC

and a second fi l ter of this type of which the entire cost was defrayed by the steelworks.

The sole difference between the two units is in the design of the electrode plates. In one instance these con

sisted of 0.7 mm stamped plate, and in the other of wirenett ing 2.2 mm thick wi th a 8 mm mesh.

The electrostatic systems were so designed that at a nominal volume of 25,000 m

3

/h N.T.P. the gas had

a residence time of 1.25 sees in each f ie ld, or a total t ime of 2.5 sees. With due observance of the tolerances,

the maximum charge possible at normal temperature wi thout spark-over should be at least 27 kV, which would

be equivalent to a f ield intensi ty of E = 9 kV/cm.

35


38/76

Fig. 12

Brown fum es in an electrostatic field

(Study PS 18)

I X

i

l{

ii

f j i 1

SS

Soif

Han

H I J mmm\

Fig.

13

Pilot plant with electrical p recipitator and line connected to the converter stack. (Study PS 131)

36


39/76

Converter flue gas

Side view

1) 1. Ionizing system, about 0.3 m in length

2) 1. Electro-static field, about 1.7 m in length and 4.5 in height

3) 2. Ionizing system, about 0.3 m in len gth

4) 2. Electro-static field as for static field 1.)

Plan view

ing wires / Main electrodes, alternately high tension-earth

Earthed plate

Fig 14

Principle of internal design of experime ntal electrical precipitator

Study PS 131)

37


40/76

In both fi l ters a short corona discharge system was also provided upstream of the electrostatic systems

with a v iew to studying the effect of addi t ional corona discharges on the precipi tat ion in the electr ical f ield.

The residen ce time of the gas in the coro na d ischarge fields was abo ut 0.3 sees. The ionising wires con sisted

of serrated sheet-metal str ips or square wires.

Gas distr ibutors were f i t ted to both f i l ters to ensure uni form gas entry. The suppl iers guaranteed a

uni

form gas distr ibut io n w i th a maximum var iat ion of 10% from the average veloci ty, but after the uni t had been

instal led i t was found that occasional ly both gas distr ibut ion and electrode distances were considerably in ex

cess of the guaranteed tolerances.

Despi te var ious attempts at improvemen t these structural defects cou ld not be subsequently ove rcome.

Al thou gh the p recipi tat ion tests carr ied out wi th these defect ive uni ts essent ial ly co nf i rm the previous resul ts,

the dust concentrat ions in the pur i f ied gas st i l l exceeded the st ipulated maximum values of 150 mg/m

3

N.T.P.

Unfor tunately the off ic ial t ime l imi ts al lowed for c leaning the steelworks precluded fur ther tests wi th basic

al ly d i f ferent electrode arrangeme nts, e.g. cyl indr ical electrodes. As a result the company concerne d was un wi l l

ing to continue its investigations despite the fact that their potential i t ies were by no means exhausted, and

i t was decided to convert the basic Bessemer steelworks to top-blown oxygen converters and to c lean the con

verter fumes with conventional electr ical precipitators. These were put into operation in February 1966, but

even at the time of writ ing (June 1968) they were sti l l not entirely satisfactory.

3.3 Clean ing of L-D converter fume s with bag filters (Study PS 128)

Another study related to the cleaning with bag filters of waste gases discharged by an 18 ton L-D converter

processing phosphorus-rich pig iron.

I t has long been known that c loth f i l ters have a high col lect ing eff ic iency but they soon become clogged

up when the temperature fal ls to below 100C, so that the dust particles are moistened by adsorption of water

vapour. But plastic, cotton and similar cloths are soon destroyed at temperatures exceeding about 100-150C.

Consequently these have hitherto been deterr ing factors to the effective use of such cloth fi l ters for cleaning

brown fumes.

In the present study these hazards were very successfully overcome mainly by providing a Cowper-type heat

exchanger down-stream of the converter stack. In this exchanger the converter gases are precooled in double-

walled suction hood with circulating water, thereby losing most of their residual heat. If sti l l necessary, the

dust- laden gases are then cooled to the required temperature of 85M30C by spraying them with water in a

coo l ing towe r arranged down -stream of the heat exchanger. The gases then enter the bag-f i l ter instal lat ion wh ich

they leave wi th a residual dust volume of just under 6 mg/m

3

N.T.P.

Efficient operation in ensured by a series of measuring, control and safety devices (Figs. 15-16).

The suct ion hood consists of an ordinary boi ler wi th natural water c i rculat ion. Waste steam was vented to

the air, the use of a waste-heat boi ler being con sidered u neco nom ic under the ci rcumstan ces.

The bag fi l ter consisted of 22 cells each containing 24 fi l ter bags, or a total of 528 bags.

The cells were shut down every 7 minutes in a control led sequence and the fi l ter bags cleaned by transverse

shaking and a s imul taneous countercurrent ai r stream.

The dust was collected in hoppers arranged at the bottom of the cells, carried by a screw conveyor to an

automatic bagging device and returned to the converter in 50 kg paper bags.

Pollution Control 1968

Documents

Transcript of Pollution Control 1968