PB84-133347
Process Modifications Towards Minimization of
Environmental Pollutants in the
Chemical Processing Industry
Illinois Inst. of Tech., Chicago
Prepared for
Industrial Environmental Research
Lab.-Cincinnati, OR
Nov 83
U.S. Department of Corererw
National Ta&tol fe&mntkn Serin
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EPA-COO/2-83-120
November 1983
PROCESS MODIFICATIONS TOWARDS
MINIMIZATION OF ENVIRONMENTAL POLLUTANTS
IN THE CHEMICAL PROCESSING INDUSTRY
Professor L. L. Tavlarldes
Department of Chemical Engineering
Illinois Institute of Technology
Chicago, Illinois 60616
EPA Cooperative Agreement
CF. 80G819-01
EPA Project Officer
William A. Cawley
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORf
OFFICE OF RESEARCH AJD DEVET-OPHENT
U.S. ENVIRONMENTAL P;«07ECTIOH AGENCY
CINCINNATI, Oil 45268
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TECHNICAL REPORT DATA
IPteast read Initrucnons on tht reverse be'ore completing)
REPORT NO.
EPA-600/2-83-120
3 RECIPIENT'S ACCES'. ION NO.
P88 k 13334?
TITLE AND SUBTITLE
Process Modifications Towards Minimization of
Environmental Pollutants in the Chemical Processing
Industry ^
6. fERFORMINC ORGANIZATION CODE
AUTHOR'S)
Professor L.I. Tavlarides
I. PERFORMING ORGANIZATION REPORT NO.
REPORT DATE
November 1983
10. PROGRAM ELEMENT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
Illinois Institute of Technology
Chicago, Illinois 60616
11. CONTRACT/GRANT NO.
CR80G819-01
2. SPONSORING AGENCY NAME AND ADDRESS
USEPA Industrial Environmental Research Laboratory
26 West St. CJair St.
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CCDE
EPA 600/12
S SUPPLEMENTARY NOTES
6. ABSTRACT
The report covers the development of a matrix of significant pollution problems and
attendant process modifications which would have impact on the reduction or elimination
of pollutants inherent in these processes. Industries covered are: (1) Refining of
Nonferrous Metals; (2) The Electroplating Industry; (3) Coal Conversion Processes;
(4) Specialty Chemicals;(5) The Paper & Pulp Industry; (6) Iron and Steel Industry;
(7) The Primary Aluminum Industry; and (8) Phosphate Fertilizer Industry.
The matrix for each of the industries noted covers the individual process; the
pollutants .ind their sources in the process; the nature of the pollutant and the
control strategy for mitigation or reduction of the pollutant.
17.
KEY WO PI OS AND DOCUMENT ANALYSIS
DESCRIPTORS
D.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
18. DISTRIBUTIONS' VTEMENT
19 SECURITY CLASb ,'77iuReport)
21 NO. OF PAGES
20 SECURITY CLASS (Thu pagel
22 PRI
EPA Pofm 2220-1 (R«y. 4-77) PREVIOUS EDITION is OBSOLETE
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DISCLAIMER
This document has been reviewed by the U.S. Environmental
Protection Agency and approved for publication. It 1s 1n partial
fulfillment of Cooperative Agreement No. CR 806819-01 between the
Illinois Institute of Technology and the U.S. Environmental Protection
Agency and teas developed as part of the first year of the Industrial
Waste Elimination Research Center. Mention of trade names o. commercial
products does not constitute endorsement or recommendation for use.
11
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TABLE OF CONTENTS
LIST OF FIGURES . v
LIST OF TABLES v111
LIST OF ABBREVIATIONS
INTRODUCTION X1
CHAPTER Page
I. REFINING OF NONFERROUS METALS 1.1
Introduction 1*1
Copper Production by Pyrometallurgical Processes 1.1
Comminution and Froth Flotation
Roasting of Copper Concentrate
Smelting
Electroreflnlng
Recommended Areas for Process Modification
Copper Production by Hydrometallurgical
Processes ...... 1.11
Leaching
Cementation
Solvent Extraction
Recommended Areas of Process Modification
Uranium Production by Hydrometallurgy Processes 1.16
LeachlnR
Solution Purification and Concentration
Recommended Areas of Process Modification
Bibliography 1.21
II. ELECTROPLATING 2.1
Electroplating of Common Metals 2.1
Recommendations for Process Modifications
Bibliography .......... 2.5
111
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III. COAL CONVERSION PROCESSES 3.1
Introduction 3.1
Liquefaction 3.1
Solvent Refined Coal Liquefaction
Particulate Emissions
Coal Pile Drainage
Gas Slag and Fly Ash
Residue from Solids/Liquids Separation
Spent Catalyst
Tail Gas From Acid Gas Removal
NOz Removal
Recommended Areas for Pollution Control P< search:
SRC-Coal
Liquefaction Process
Gaslfica:ion 3.11
Lurgi Coal Gasification
Coal Preparation
Coal Gasification
2as Purification
Gas Upgrading
Gasifi'jr and Boiler Ash
'Spent Guard Catalyst
Spent Shlft/Methanation Catalysts
Ash Quench Slurry
Removal of Sulfur Compounds from
'xectlsol Process
Riicora&ended Areas for Pollution Control
Research: Lurgi Coal Gasification Process
Blbllorraphy 3.23
IV. EXPLOSIVES INDUSTRY 4.1
Introduction 4.1
Nitric Acid Production 4.1
Ammonia Oxidation Process
Nitric Acid Concentration
Spent Acid Recovery
TNT Production 4.9
Nitration
Purification
Finishing
Recommendea Areas for Pollution Control Research
in TNT Production
1v
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Nitrocellulose Production .4.14
Nitration
Purification
Recommended Areas for Pollution Control Research in
Nitrocellulose Production
Bibliography • 4.23
V. IRON AND STEEL INDUSTRY 5.1
Introduction 5.1
Coke Making . 5.4
Coke By-Product Recovery 5.9
Iron Making 5.12
Steel Making 5.21
Acid Pickling 5.27
Recommended Areas far Process Modifications Research .... 5.29
Bibliography 5.34
VI. PAPER AND PULP INDUSTRY 6.1
Introduction .6.1
Kraft Pulping 6.1
Digester System
Brown Stock Washer System
Multiple Effect Evaporator System
Recovery Furnace System ^ 6.10
Smelt Dissolving Tank
Lime Kiln 6.17
Recommended Areas for Process Modification
Research 6.19
Bibliography 6.22
VII. THE PRIMARY ALUMINIUM INDUSTRY 7.1
Introduction 7.1
Bauxite Processing .. 7.1
Primary Aluminium Smelting 7.6
Recommended Research Studies For Pollution Control In The
Primary Aluminium Industry .........7.15
Bibliography 7.19
VIII. FROSPHATE FERTILIZER INDUSTRY 8.1
Introduction .........8.1
Wet Process Phosphoric Acid Production 8.2
Reccnaended Areas For Pollution Coatrol Research: Wet
Process Phosphoric Acid Productioa 8.7
Normal Superphosphate Production 8.8
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Recommended Areas For Pollution Control Research: Normal
Superphosphate Production 8.11
Ammonium Phosphate Production . 8. II
Recommended Areas For Pollution Control
Research: Ammonium Phosphate Production 8.17
Bibliography 8.18
IX. CONCLUSIONS AND RECOMMENDATIONS 9.1
Introduction 9.1
Solvent Extraction ...... 9.1
Catalyst Deactlv&cion 9.1
Leaching Process 9.2
Gas Absorption 9.2
Gas-Llquid-Solld Reactions 9.3
vl
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LIST OF FIGURES
Figure Page
1.1 Flow Chart Showing the Principal Process Steps
For Extracting Copper From Sulphide Ores 1.3
1.2 Conalnution and Froth Flotation 1.4
1.3 Flow Chart For Electrorefining Process 1.8
1.4 Flow Chart For Solvent Extraction Process 1.14
1.5 Process Schematic For Uranium Recover; . 1.18
2.1 Flow Chart For Water Flow in Chromium
Plating Zinc Die Castings, Decorative 2,2
3.1 Flow Sheet For An Integrated Liquefectlcn
Process .....3.3
3.2 lurgi SNG Process 3.13
4.1 Processes In The Explosive Industry 4.2
4.2 How Chart For Nitric Acid 1 reduction 4.3
4.3 Flow Chart For TNT Production ........ 4.11
4.4 Flow Chart For Nitrocellulos Production 4.17
5.1 Overview of Iron and Steel Manufacturing Process ...... 5.2
5.2 Coke Maklne 5.5
5.3 Coke By-Products Recovery 5.10
6.1 Flow Chart of Kraft Pulping Process ... 6.2
7.1 Bauxite Processing 7.2
7.2 Primary Aluminium Production ....... 7.8
8.1 Wet Process Phosphoric Acid Production 8.3
8.2 Flow Chart of Normal Superphosphate
Production Process .......... 8.9
8.3 Flow Diagram For TVA Ammonium Phosphate Process 8.13
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LIST OF TABLES
Table Page
1.1 Flow Rates of Metals In Process Streams ........1.6
1.2 Concentration Ranges in Effluent Streams
Froa Electroreflnlng Process 1.9
1.3 Pollutants and Suggested Control Strategy
for Copper Production by Pyrometallurglcal
Processes J.JO
1.* Pollutants and Suggested Control Strategy for
Copper Production by Hydrometallurgical
Processes 1.15
2.1 Composition of Raw Waste Streams Prom
Conncn Metals Plating 2.3
3.1 Approximate Trace Element Analysis of Coal
Pretreatment Dust After Scrubbing 3.5
3.2 Estimated Trace Elements Composition of
the SSC Liquefaction Residue 3.7
3.3 Pollutants and Control Options in SRC
Liquefaction Process 3.10
3.4 Laboratory Leaching Results of Chen-Fixed
Refinory Wastes 3.15
3.5 Spent Harshaw Nickel Catalyst Analysis 3.16
3.6 Distribution Coefficients for Various Phenols
in Butyl Acetate at 300°K 3.19
3.7 Control Options for the Concentration Wastes ..... 3.20
3.8 Pollutants and Control Options in Lurgi SNG
Process 3.22
4.1 Pollutants and Control Options in Nitric
Acid Production Process 4.8
4.2 Pollutants and Control Options in TNT
Production 4.15
4.3 Pollutants and Control Options in NC
Production 4.21
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Table Page
5.1 Average Analysis Of Quench Water Samples 5.7
5.2 Coke Oven Gasea 5.11
5.3 Analysis Of Blast Furnace Scrubber Wastewaters
Flow Rate . 5.13
5.4 Vastevater Thickener Under Flow 5.14
5.5 Raw Uastewaters From Steel Making
Operations 5.24
5.6 Pollutants and Suggested Control Strategy, Iron
and Steel Industry 5.30
6.1 Typical Emissions Bates From Batch Digester 6.4
6.2 Emission Rates From Vacuum Washer 6.6
.6.3 Emission Rates From HEE 6.8
6.4 Emission Rates >rom Recovery Furnace 6.10
6.5 Participate Emission Rates From the
Recovery Furnace 6*11
6.6 Emission Rates From Smelt Dissolve Tank 6.16
6.7 Lime Kiln Emission Rates .......... 6.18
6.8 Pollutants and Control Options in Kr^ft
Pulping Process 6.20
7.1 Chemical Analysis of Red Muds ............. 7.3
7.2 Emissions From Solderberg Cell 7.1C
7.3 Effect of Cell Operating Parameters as
Flourlde Effluent ... 7.13
7.4 Suggested Process Modifications for Pollution
Control in the Primary Aluminium Industry 7.16
8.1 Pollutants and Suggested Strategy for Selected
Phosphate Rock Fertilizer 8.16
1x
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LISI OF ABBREVIATIONS
Abbreviation Terms
cfn cubic feet per minute
ft3 cubic feot
g/1 grams per liter
K.W.H. kilowatt hours
m3 cubic meters
am millmeters
MG million gallons
N-K-P nitrogen, potassium, phosphorous ratio
ppn parts per million
scf standard cubic feet
SNG synthesized natural gas
n microns
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INTRODUCTION
The objective of this planning project on Process Modifi-
cation Towards Minimization of Environmental Pollutants in the
chemical process industry is to suggest fundamental research
studies which will have significant Impact in the minimization of
industrial pollutants. Towards this end, eight industries are
surveyed to develop a matrix of significant pollution problems
and attendant process modifications which would have impact on
the reduction or elimination of pollutants inherent in these
processes. The industries surveyed are as folJows:
1. Refining of Nonferrous Metals
2. The Electroplating Industry
3. Coal Conversion Processes
4. Specialty Chemicals
5. The Iron and Steel Industry
6. The Paper and Pulp Industry
7. The Primary Aluminum Industry
S. Phosphate Fertilizer Industry
Although these industries are diverse, it is apparent that
generic pollution problems cut across most of these and other
industries not covered in the survey. Accordingly, various
process modification strategies and attendant research programs
which would minimize these pollution problems and are generic
in nature, are indentified.
XI
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CHAPTER 1 1.1
REFINING OF 1,ONFERROUS METALS
1.1 INTRODUCTION
This chapter will concentrate on the refining of non-
ferrous metals from mineral oze. The sections of this chapter
are divided as follows:
1. Copper Production by Pyrometallurgical Processes
2. Copper Production by Hydronetallurgical Processes
3. Uranium Production by Hydrometallurglcal Processes.
1.2 COPPER PRODUCTION BY PYROMETALLURGICAL PROCESSES
Ninety percent of the world's primary copper originates
in the sulphide form. A vast majority of this copper is
extracted by pyrometallurgical techniques because sulphide
ores are not easily leached. Typical copper deposits con-
tain only 1 to 21 copper, therefore, the ore must undergo
several process steps to concentrate the copper before smelting.
This method of copper extraction includes the following steps
(Biswas and Davenport, 1980):
1. Concentration by Froth Flotation
2. Roasting
3. Matte Smelting
4. Converting to blister copper
5. Electroreflnlng
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The pollutants of primary concern include SO-, partlcu-
lates, slag, and dissolved metal salts in various effluent
streams (Barbour, 1980). Figure 1.1 is a flow chart of this
process, indicating the numerous ways in which copper concen-
trate can be smelted to produce blister copper.
Other sources of waste water Include acid plant blow-
down, slag granulation, and cooling of the hoc metal anodes.
Electroreflning also generates waste through spent electrolyte,
washing cathodes, and the recovery of slime (U.S. EPA, Feb. 1975).
1.2.1 Comminution and Froth Flotation
A copper concentrate is produced by a series of flota-
tion cells which selectively float copper sulphide to the
surface of the bath so the concentrate can be skimmed off
the top. Thlt process is depicted In Figure 1.2. The tail-
Ings taken from the tank are piped to evaporation ponds where
the water is clarified and recycled (Biswas and Davenport, 1980).
The tailings require pH adjustments and extraction of
arsenic, cyanide, and some metals. The amount of water con-
sumed for this process step can be reduced if Improvements
are made to the grinding efficiency of the dry ore.
1.2.2 Roasting of Copper Concentrate
The copper concentrate can be refined by several different
methods of roasting and/or smelting as shown in Figure 1.1.
Roasting of sulphide concentrates produce calcines for leach-
Ing or for reverbatory (or electric) furnace smelting. The
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ou
1.3
1
COtMIHUTIOH
i
FUJTAnOS
CELLS
i
1 \»> 1
DRYING
I
ROASTING
DRYING
|S02 ) I90! \ fM2
ELECTRIC
FURNACE
REVERBATORY
FURNACE
FLASH
FURNACE
1
SINTERING
1 I"2
BLAST
FURNACE
SLAG
SLAG
SLIME
SPEHT ELECTROLYTE
Figuri 1.1. Flow Chmrt Showing th« ?rlnclp«l Proeisa Sc«pi
For Extracting Copper from Sulphide OTM.
(Bim* ad Dwtnport. 1980).
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GRINDING
SCREENING
1
HILLING
HYDROCYCLONE
H
FLOTATION
CELLS
H
TAILINGS
POND
Cu Concentrate (24Z Cu)
Figure 1.2. Comminution and Froth Flotation
(Biswas and Davenport, 1980).
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fluid-bed roaster la the best device Cor uulphide roasting
since it has a high production rate ant produces 5-152 by
volume SO. in the flue gases which can be easily converted
into usable forma of sulfur (Gill, 1980).
1.2.3 Smelting
The process of sicelting and converting vary widely in
equipment design •but the pollutants are essentially the same:
SO., parclculates, and slag. There are several reasons for
cleaning gases from metallurgical processing, the most Import-
tant of these are (6111, 1980):
1. To recover value-bearing participate material
which can be returned to the plant for
reprocessing.
2. Environmental pollution, from the viewpoint of
employees exposed to harmful gases and, SO, com-
bining with atmospheric water vapor to form acid
rain, damaging plants and injuring animals.
3 To remove value-bearing gaseous by-products such
as S02, which can be used as the feed material
for the production of marketable sulfurlc acid
or elemental sulfur.
4. To recover fuel value of gaseous by-products
like combustible CO.
5. To reclaim the sensible heat to the flae gases
In waste heat boilers.
-------
Optimization of the smelter design can reduce the amount of
environmental pollution or alter the effluent streams so that
the pollutants can be easily removed. If the S02 concentration
is greater than 4Z by volume, it cen bfc converted into sulphuric
acid without much difficulty. Typically S02 is converted into
sulphuric acid, sulfur, or ammonium sulfate.
A survey of metals in various process streams was tak^n
at a smelting plant owned by the Radian Corporation in Austin,
Texas. Table 1.1 is a compilation cf the flow rates
(Sclwltzebel, e£ al. 1978). Some of the streams were not
measured or recorded but the chart does Illustrate the number
of different elements present in the effluent streams.
TABLE 1.1. FLOW RATES OF METALS IN PROCESS STREAMS
1.6
Flow Rat- Ib/hr
Element
Al
As
Ba
Be
Ca
Cd
Cr
Cu
F
Fe
Hg
Mo
Ni
Pb
Sb
Se
Si
V
Zn
Feed
400
190
3i
0.072
770
59
0.076
16000
3.4
10000
0.018
79
0.70
49
6.0
10
1100
0.92
42
Matte
17
48
33 .
4.1x10
12
37
0.64
18000
0.012
Flue
Slag Outlet
700
48
43
0.032
1900
0.33
3.8
220
2.2
11000 12000
0.020
8.5
2.0
84
4.6
0.17
42
0.33
31
0.0091
89
0.76
13
3.4
5.5
4800
0.86
30
0.10
76
0.64
0.0034
0.011
0.076
0.044
1.8
9.4
0.55
0.033
0.17
0.011
0.38
0.030
0.65
1.7
0.027
0.22
ESP
Catch
1.1
30
0.023
0.0004
2.1
0.74
0.018
62
0.032
42.6
0.00015
6.6
0.059
«.3
1.3
0.16
1.7
0.011
4.6
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To recover the metals from the captured participates, 1*7
it may be possible to use acid leaching and solvent extraction
to selectively remove metals from low concentration leach
solutions.
1.2.4 Sleetrorefining
Electrorefinlro is the final step rf purifying blister
copper to 99.99Z Cu which can be used for most Industrial
applications. The spent electrolyte is recycled, but some of
the acid must be treated to remove excess nickel and unclaim-
ed copper as well as other trace metals. Slime develops from
the participates and precipitates and must be treated to re-
cover cupper and/or precious metals. Figure 1.3 is a flow
chart illustrating the representative steps of the electro-
refining process (U.S. EPA, Feb. 1975).
Table 1.2 lists the concentration ranges of oeveral prio-
rity pollutants contained in the designated process streams.
Slime is either discarded or undergoes further treatment for
recovery of trace metals. A bleed from the electrolyte,
water used to wash the anodes during preparation, and stllae ara
the primary sources of water contamination from the electro-
refining process.
Table 1.3 surmarlzes the pollutants and suggested control
strategy for copper production by pyrometallurgical processes.
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BLISTER
COFFER
ANODE
PREPARATION
•HASH WATER
ELECTROLTTIC
CELLS
ACID
STORAGE
SI DIE
99.991
COFPFR
Cu
LIBERATOR
•ISO..
•te.
COFFER
rigur* 1.3. Flow Chart (or El«etror«flnlng PTOCMS
(U.S. EFA. F«h. 1975).
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Table 1.2. Concentration Ranges in Effluent Screams
POLLUTANT
Astinony
Arsenic
Copper
Lead
Nickel
Selenium
Silver
ELECTROLYTE (g/L)
0.2 to 0.7
0.5 to 12.0
45.0 to 50.0
2.0 to 20.0
SLIME (Z)
0.5 to 5.0
0.5 to 4.0
20.0 to 40.0
2.0 to 15.0
0.1 to 2.0
J..O to 20.0
3.4 to 27.4
Table 1.3 sunmarizes tht pollutants and suggested control
strategy for copper production by pyrometallurgical processes.
1.2.5 Recommended Areas for Process Modifications Research
After evaluating the available lit*, -ature, the following
areas are recommended for further research by the study:
Optimization of the communition of dry mineral
ore to reduce the amount of water used in froth
flotation.
Recover value-bearing products by dissolving the
metals from participates collected in the electro-
static preclpltators and use solvent extraction
procedures to extract the desired products.
Use solvent extraction to recover copper or other
metals from effluent streams before the water is
sent to the tailing ponds.
Improve smelter design to contain and eliminate
the release of SO. and other hazardous flue gases
into the atmosphere.
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Table 1.9. Pollutant* and Suggested Control Strategy for Copper Production
by Pyro»aiallurglcal Proceaaaa
Ptoceae
Ore grinding
froth
flotation
Suiting
(•) Reverb
(b) Electric
(c) rieeb
(41 Blaat
Convert lot
•node
preparat loo
electro-
refining
Pollutant
hrtlnletee
Metele. Dleaolved
•ludya. cyanide,
pH etc.
»-. .l«g
and partleulaica
SO. alag and
pafdculatfla
Dlaaolwd
•etala. HjSO4
Dlaaolved
netal. BjSO^
Source la
Procesi
CniBbere
grlndera.
ball Mill etc.
Tall Inge
Plue geeea.
•lag diap
PliH gaaaa,
•lag diaip
Anode waah
Electrolyte.
cathode cool-
Ing etc.
Mature of
Pollutant
Inorganic
Inorganic and
organic addlclvea
Inorganic and
Caeeoua SO.
Inorganic and
gaacoua SOj
Inorganic
Inorganic
Pollutant Coetrol Strategy
Elactroatatlc preclpltator
Solvent eatrectlon, evaporation,
tailing* pond
Acid plant for SO.. ESP.
oolvent eatractlon
acid plant, ESP, solvent
extraction
Solvent Imtractlon
Solvent extraction
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1.3 COPPER PRODUCTION BY HYDROMETALLURGICAL PROCESSES 1.11
Hydrometallurgy has three advantages over the smelting
and converting processes that are traditionally used for the
manufacture of copper. First* leachiug is a more economical
method of extraction when the ore has a low concentration of
copper. Second, increasing energy costs of the furnaces is
making pyrometallurgy less economical. Third, it Is becoming
increasingly difficult for smelters to meet stringent environ*
mental regulations (Harbour, 1980).
The hydrometallurg-lcal process entails three major steps;
leaching, cementation (or solvent extraction), and electro-
vixmlng. This method of extracting copper from mineral ore
has not been extensively applied to sulflde ores which are
not readily leached. Due to the environmental problems
associated with SO,, hydrometallurgy is becoming a more
acceptable method of producing copper (Biswas and Davenport,
1980).
1.3.1 Leaching
There are numerous methods of leaching and several types
of leaching solutions. Sulfurlc acid is commonly used as a
leaching medium, but new technology has introduced other forms
of leaching solutions such as ammonlacal and ferric chloride
solutions. Leaching of sulflde ores can be Improved by
bacterial enhancement as well. The pregnant leach solution
can undergo either solvent extraction, ion exchange or cemen-
tation to recover the copper while leaving the remaining
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trace metals in the leach solution (Wadsvorth, 1980). 1.12
There are four methods of leaching (Wadsvorth, 1979):
1. In altu leaching
2. Dump and heap leaching
3. Vat leaching
4. Agitated leaching
In situ and dump leaching are long term processes which
can leach the ore with acid solution for several years. Due
to this long period of exposure, significant quantities of
the sulfide minerals will dissolve into the leach solution.
Contamination of ground water may occur and could produce
serious detrimental effects to the surrounding environment.
Vat leaching and agitated leaching are lone with such
smaller volumes of crushed ore at much shorter periods of
exposure. These short term processes are useful for ores
containing copper in the oxide form which dissolve easily
in acid solutions. The pregnant leach solution is taken to
refining process, while the remaining sludge is either dumped
or recycled for additional processing to recover other metals
that were not extracted.
If the leach solution has a high concentration of coppar
(40 r.o 60 g/lj, it can be sent directly to the electrowiming
circuit (Flett, 1974). When the solution has a low concen-
tration, making direct electrowinning uneconomical, then a
process step must be taken to separate the copper from the
rest of the leach solution and redlssolve the copper at a
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higher concentration into an electrolyte. Three commercially 1.13
available processes chat accomplish this cask are cementation
solvent extraction, and ion exchange.
1.3.1.1 Cementation
Cementation is a reaction where copper precipitates
directly onto the surface of the scrap iron. The effluents
contain very large quantities of iron salts and are generally
sent to the tailings pond for vaste treatment.
1.3.1.2 Solvent Extraction
Solvent extraction is a process having several circula-
tion loops where copper lens are selectively extracted from
a leach solution by a specific solvent. The extracted copper
is stripped from the solvent which is then recirculated int
the extraction circuit. The flow chart shown in Figure 1.4
illustrates the multiple circuits of the solvent extraction
process.
Some of the pollution problems that exist in this process
are the build up of trace metals in the leach solution and
entrained solvent in the extraction and stripping sections.
Problems associated with entrainment are complicated by the
unavoidable degradation of the solvent. This reduces the
extraction activity of the organic material and some make up
must be added to che recycle.
Table 1.4 summarizes the pollutants and suggested control
strategy for copper production by hydrometallurglcal processes.
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1.14
Loaded
Solvent
Regenerated
Organ ie
LZACHISG
I
SOLVENT
OCTRACriON
1 1
*
STHimNS
I C«1u»«
ELECTKOVUHtNC
1
RAPntUTE
SPOT
ELECTROLYTE
JO.
rigur* 1.4. now dart of Solvent Extraction Procesa.
(6111. 1980).
-------
Table 1.4 Pollutants and SuggMted Control Strategy for
Copper Production by Hydrome^allurglcal Processea
Process
Leaching In
situ, ho*n,
vat,
ajltated
Cementation
Solvent
extraction
Electro-
winning
Pollutant
Dissolved
metal salts,
aulfurle jetd
organic additives
(wetting agenta)
Dissolved
metal salts
Dissolved
iwtala, entrained
solvents
Dissolved
metals,
acid,
cyanide
Source in
Process
Leech
solution
Iron ion fro*
screp Iron
Excess from
process at reams
solvent degra-
dation
Bxcesu from
process
at reams,
cathode wash
and cooling
Nature of
Pollutant
Inorganic,
metals and acid
Inorganic
Inarganlc metals
and organic
solvents
Inorganic metals
and acid
Pollutant Control Strategy
Recycle Leach solution
after solvent extraction
of excess metals, watch
for seepage of natal* Into
the ground water
Solvent extraction of
effluents
Improve mixer-settlers,
study methods for regeneration
of aolventa
Solvent extraction
of effluenta
-------
1.3.2 Recommended Areas of Process Modification Research 1.16
After evaluating the available literature, the following
areas are recommended for further research by the study:
. Recover trace metals in the effluent streams by
using solvent extraction. Conduct research in
the area of simultaneous extraction of several
metals that are considered hazardous pollutants.
Recover entrained solvents by filtration, flota-
tion, centrifugal separation, etc. Study the various
methods of separating liquid-liquid mixtures and
determine the best process to use.
. Solvents tend to degrade due to temperature, pH,
or radiation extremes. Analyze the by-products
of this degradation and determine the best way to
eliminate these by-products either in the recycle
stream or the exit stream.
Evaluate new techniques for leaching sulphide ores
ot develop new techniques to improve selectivity
in leaching mineral ores.
1.4 URANIUM PRODUCTION BY HYDROMETALLURCY PROCESSES
Uranium is becoming an important energy source since pro-
jected energy demands will greatly increase in the near fu*nre.
Uranium content of a typical ore is in the order of 0.2 to
0.3 percent U.Og. For this reason, large quantities of
material must be handled to mine and extract uranium. The
-------
conventional recovery processes include acid or alkaline 1.17
leaching, solution purification, and product precipitatioa
into yellow cake (U.O.). Solvent extraction and ion exchange
have become the primary methods for solution purification
and concentration of uranium values (Reed, et al. 1979).
Figure l.S is a representation of a process flow chart for
the refining of uranium ore.
1.4.1 Leaching
As mentioned in Section 1.3, there are numerous methods
of leaching with varying degrees of ore preparation. Interest
has increased in the use of in-sltu leaching of underground
deposits for uranium mining. The advantages of in-situ
leaching are the significant reduction of processing costs and
the minimal disturbance to the surface conditions. The
subsurface deposit is flooded with leach solution and then
pumped to the surface ready for uranium recovery. With in-situ
leaching, the ore body remains intact and only the metal is
removed, therefore a relatively small volume of waste requires
disposal.
This method of leaching can only be done when the ore
body is contained within a rock formation which is relatively
impermeable, otherwise the ground water may become contaminated.
The possibility of polluting fresh-water aquifers is present,
particularly when a deposit is contained within an aquifer.
Regulatory authorities require a "cleanup" of the deposit
subsequent to the leaching operations. With proper design,
-------
1.18
>
>
>
REACENT >
\
1
\
POR
0
•
h
I
\ Jt,
.
\
t
nJEED
WPURITY
9KTRUL
f
UACB HELD
sourrios •— LIZIYIART
PRETBEATHERT RECERERATIOH
EVAPORATION
t
108 EZCBANCE \ B LESD\ TAttlHCS
T\ 'T
»au«- / l
1 X\^->»»-, , m BISWSAL
JLVEHT ^ ; ^ISSfT
ucrimi > ' COHTROL
PRECIPITATION ^^|^_____ STEAM AND/OR REACEHTS
»
UEWATEKINC
1 .'
DRTIRC AND
PACICTNC
\
TEUOU CAKE
PRODDCT
CIRCUIT
Flgur* 1.5. Proe**s SctMoatle (or Urntua Racovery
-------
Dp-.ration, monitoring, and cleanup, in-situ leaching can be 1.19
Che most environmentally acceptable method of extracting
metals from subsurface deposits.
Other methods of leaching can be used, but the damage
to the surface, the amount of waste produced, and the costs
for processing the ore will Increase.
Uranium can also be recovered from leach solutions used
for the extraction of other non-ferrous metals like copper,
zinc, nickel, etc. Once the uranium is reclaimed from the
leach solution it can be recycled Into the leaching process
after some "make-up" is added. A tailings pond is used
to store the spent solution so that suspended particals
are allowed to settle and the effluents can be contained
without affecting the surrounding environment.
1.4.2. Solution Purification and Concentration
Leach solutions generally contain a large amount of im-
purities such as molybdenum, vanadium, selenium, iron, copper,
etc. The concentration of pregnant solutions may range between
.6 and 2.0 g/1 U.O-. Solvent extraction techniques, and in
soroe cases ion exchange are used to purify and concentrate
the U,0Q in the solution. The final solution, after solvent
J O
extraction can be made to be 30 to SO g/1. Ion exchange of
clarified leach solution usually results in an elluant con-
taining 10 to 12 g/1 U30g (Reed, et al. 1979).
-------
By using an ion exchange unit first and then a solvent 1.20
extraction process, the amount of solvent required to recover
the uraniua nay be greatly reduced. This modification has a .
tremendous economic advantage by reducing solvent inventory
but may also lessen the pollution effects due to solvent
entrainment and degradation.
1.4.3 Recommended Areas of Process Modification Research
After evaluating the available literature, the following
areas are recommended for further research by the study:
. Evaluate new leaching solutions that may offer
improvement in leaching selectivity and/or efficiency.
. Determine the best solvent for solvent extraction
of uranium salts with minimal degradation.
Divert recycle streams into additional process
circuits to remove trace metals.
-------
BIBLIOGRAPHY 1.21
Barbour, A.K. "The Environmental Pressures on Nonferrous
Metal Production", Metals and Materials. Vol. Mo. 1980,
pp. 42-46.
Biswas, A.K. and Davenport, W.G. Extractive Metallurgy of
Copper. 2nd edition, Pergamon Press 1980.
"Cyprus Bagdad: 'State of the Art1 Copper-Molybdenum
Production", Engineering and Mining- Journal. Vol. 181,
No. 8, 1980, pp. 56-63.
Flett, D.S. "Solvent Extraction in Copper HydroBetallurgy"
Traau. Inatn. Mia. Me tall., Section C, Vol. 83, March,
1974, pp. 30-3.
Gill, C.I. Nonferrous Extractive Metallurgy. John Wiley &
Sonn, Inc., 19807
Reed, A.K., Meeks, B.C., Pomeroy, S.E., and Hale, V.}.
Assessment of Environmental Aspects of Uranium Mining
and Milling. EPA-600/7-76/036, Dec. 1979.
Schvltzebel, K., £t al. Trace Elements Study at a_ Primary
Copper Smelter. Volume I.. EPA/600/2-78/065a7 March,
1978.
U.S. ZPA. Development Document for Interim Final Effluent
Limitations Guidelines and Proposed New Source Performance
Standards for the Primary Copper Smelting Subcatbgory and
the Primary Copper Refining Subcategory of the Copper
Segment of the Nor*errous Metals Manufacturing Point
Source Category. EPA 440/1-75/032-b, February, 19/5.
Wadsworth, M.E. "Review of Developments in Hydrometallurgy
in 1978", Journal of Metals. Vol. 31, no.5, 1979,
pp. 12.
Wadsworth, M.E. "Review of Developments in Hydrometallurgy
in 1979", Journal of Metals. Vol. 32, no. 4, 1980,
pp. 27-31.
-------
SUPPLEMENTAL REFERENCES
Agera, D.W. and DeMent, E.R. "The Evaluation of New LIZ
Reagents for the Extraction of Copper and Suggestions
for the Design of Commercial Mixer-Settler Plants."
Ingenleursblad, 41, 1972, pp. 433-4.
.aderson, S.O.S. and Reinhardt, B. "MAR-Bydronetallurgical
Recovery Processes.", Paper given for the ISEC 77,
Sept. 1977, pp 798-804 oC the CIM Special Vol. 21, 1979.
Ansden, M., Swietin, R., and Treilhard, 0. "Selection and
Design of Texas Gulf Canadian Copper Smelters and
Refinery", Journal of Metala. Vol. 30, Mo. 7, 1978,
pp. 16-26.
"Arizona's Copper Producers Rally to Fight the E.P.A. Smelters
Regulations", Engineering and Mining Journal. Vol. 179,
No. 4, 1978, pg. 33.
Ashbrook, A.W. , Itykovich, I.J.. and Sova, V. "Losaes of
Organic Compounds in Solvent Extraction Procesuas"
Paper given for the ISEC 77, Sept. 1979, pp 781-790 of
CZM Special Vol. 21, 1979.
Baxner, B.E., Hulbred, G.L. , and Kilumpar, Z.V. "Sensitivity
of LIZ Plant Costs to Variations of Process Parameters",
Paper given for the ISEC 77, Sept. 1977, pp 552-560 of
CIM Special Vol. 21, 1979.
Barthel, G. "Solvent Extraction Recovery of Copper frou
Mine and Smelter Waters", Journal of Metala. Vol. 30,
Bo. 7, 1978, pp. 7-12.
"Clarksville Zinc Plant First in the D.S. for 37 Years",
Mining Magazine. Vol. 140, No. 12, 1979. pg. 551.
Cogut, B. "Morenci Clear-Air Prediction System Bas Unique
Potential for Controlling Air Quality", Engineering
and Mining Journal. Vol. 179, No. 4, 1978, pp. 65-70.
Collins, G., Cooper, J.B., and Brandy, M.R. "Designing
Solvent Extraction Plants to Cut the Risk of Fires",
Engineering and Mining Journal. Vol. 179, No. 12,
1978, pp 56-62.
-------
Costle, G.M. "Environmental Regulation of the Metals 1.22
Industry", Journal of Metals. Vol. 30, No. 1, 19^3,
pp 30-32.
Davidson, D.H. "In-Situ Leaching of Nonferrous Metals"
Mining Congress Journal. Vol. 66, No. 7, 1980, pp 52-57.
Finney, S.A. "A Review of Progress in the Application of
Solvent Extraction for the Recovery of Uranium from
Ores Treated by the South African Gold Mining Znd."
Paper given to the ISEC 77, Sept 77, pp 567 to 576 of
the Canadian Institute of Mining and Metallurgy,
Special Volume 21, 1979.
Henrle, F. "Gearing up to Control Trace Elements During
Mineral Processing", Mictog Congress Journal. Vol. 66,
No. 4, I960, pp. 18-20.
Huff, R.V., Davidson, D.A., Boughoan, D., and Axen. S.
"Technology for In-Situ Uranium Leaching", Mining
Engineering. Vol. 32, No. 2, 1980, pp. 163-164.
"Bydrometallurgy Review, 1978", Mining Engineering. Vol. 31,
No. 5, 1979, pp. 527-529.
"Hydroaetallurgy Review, 1979", Mining. Engineering. Vol. 32,
No. 5, 1980, pp. 540-542.
Isenberg, E. "Alternatives for Hazardous Waste Management
in the Metals Smelting and Refitting Industries. EPA/
5307sW-153c.
"Jersey Mines Zinc: Plant Design and Startup", Engineering
and Mining Journal. Vol. 181, No. 7, 1980, pp 65-88.
Jones, H.R. Pollution Control in the Nonferrous Metals
Industry. 1972, Noyes Data Corp., 1972.
Kordoalty, G.A., MacKay, R.D., and Vlrnlg, M.J. "A New
Generation of Copper Extractant". Paper presented
for Metallurgy Society of AIKE, 1976.
MacDonald, B.J. and Weiss, M. "Impact of Environmental
Control Expenditures of U.S. Cu, Pb, and Zn Mining
and Smelting", Journal of Metals. Vol. 30, No. 1,
1978, pp 24-29.
-------
Mackay. D., and Medir, M. "The Applicability of Solvent 1.24
Extraction to Waste Water Treatment", Paper given to
Che ISEC 77, Sept. 1977. pp. 791 to 797 of the CIM
Special Vol. 21, 1979.
Macklv, V.V. "Current Trends in Chemical Met.-lurgy",
The Canadian Journal of Chemical Engineering. Vol. 46,
Ho. 2, 1968, pp. 3-15.
IfcGarr, H.J. "Solvent Extraction Stars in Making Ultra-
pure Copper", Chemical Engineering. Vol. 77, No. 17,
Aug. 10, 1970, pp. 82-84,
Mlzrahl, J., Barnes, E., and Meyer, D. "The Development
of Efficient Industrial Mixer-Settlers", Paper
Presented to the International Solvent Extraction
Conference W4 (ISEC 74), Sept. 1974.
Renzoni, L.S. "Extractive Metallurgy at International Nickel —
A Half Century of Progress", The Canadian Journal of
Ct.eai.eal Engineering. Vol. 47,~No. 2, 1969, pp. 3-11.
Schultz, D.A. "Pollution Control and Energy Consumption at
U.S. Copper Smelters". Journal of Metals. Vol. 30, No. 1,
1978, pp. 14-20.
Stelllng III, J.H.E. "Source Category Survey; Uranium Refining
Industry". EPA-450/3-80/010, May 80.
U.S. EPA. Solution Mining of Uranium; Administrator'a Guide.
PB-301 173. May 79.
U.S. EPA. Heavy Metal Pollution From Spillage at Ore Smelters
and Mills. EPA/600/2-77/171, Aug. 1971.
U.S. EPA. Economic Impact of Environmental Regulation on the
U.S. Copper Industry. EPA/230/3-78/002, Jan. 1978.
Virnig, M.J. "Synthetic Structure, and Bydrometallurgical
Properties of LIX 34", Paper given for the International
Solvent Extraction Conference in 1977 (ISEC 77), Sept.
1977, pp. J35-541.
Veisenberg, I. "Design and Operating Parameters fot Emission
Control Studies; Kennecoct, Hurley", EPA/600/2-76/036d,
Feb. 1976.
Veisenberg, I. "Design and Operating Parameters for Emission
Control Studies; Phelps Dodge, Morenel", EPA/600/2-76/036g.
Feb. 1976.
-------
CHAPTER 2 2<1
ELECTROPLATING
2.1 ELECTROPLATING OF COMMON METALS
Electroplating is a series of process steps that involves
the preparation of the part in addition to the plating opera-
tion. Figure 2.1 is a flow chart of a chromium plating opera-
tion of zinc die castings. The sequence and/or the process
steps may vary from plant to plant because of the many
variables involved with electroplating. Table 2.1 is * list
of pollutants that typically exist In the waste streams and
their respective concentration ranges.
There are numerous methods of treatment for dissolved
materials that exist in effluent streams. They are (U.S. EPA,
April 1975):
. Ion Exchange
Reverse Osmosis
Electrodlalysld
. Chemical Precipitation
. Ion Flotation
. Carbon Absorbtion
. liquid-Liquid Extraction
Each method has advantages and lisadvantages that must be
considered with respect to the specific electroplating industry.
-------
2.2
woa*
run
CLEAN I
MAJUI |
•
H
_
^M
•m
CLEAN
1
RIHSZ
I
AC ID
DIP
I
RINSE
CYANIDE
(.urrui
STRIKE
t
»«„
RINSE
1
ACID
I
ACID
COFFER
PT*Tr
*
RINSE
I
I RIOEL
| PLATE
L I
\ RIRSE
1 caxcniun
L ft «T»
[RINSE ARD
-1
I
1
h
]
h
J
I-
I
L
r
••M
^•M
i^—
ramuaizi AND
PRECIPITATE
OXIDIZE
CTANIDE
I
PRECIPITATE
COPPER
J
1
SLUDGE
1 PRECIPITATE
Niaax AND
1 ^flDWV
1EOBCE
CHltOHlim
»
PRECIPITATE
nramTiTM
n
1
ETTL
^^
^^H
E
^"1
H
.— n
i
rREATED )IATER
KIT
Plfurt 2.1. Flow Chart (or W«t«r ?' M In Oiraolua Plating
Zinc 01* CMtloM, »«eor«tiv« (U.S. EPA, April 1973).
-------
Since these recovery methods are readily available, similar 2.3
methods caa be adopted as additional process steps to remove
trace metals before the water la recycled back Into the process.
TABLE 2.1. COMPOSITION OF RAW WASTE STREAMS FROM COMMON
METALS PLATING (U.S. EPA. August 1979)
(ng/D
Copper 0.032 - 272.5
Mickel 0.019 - 2954
Chromium. Total 0.088 - 525.9
Chromium, Hexavalent 0.005 - 334.5
Zinc 0.112 - 252.0
Cyanide, Total 0.005 - 150.0
Cyanide, Amenable to Chlorination 0.003 - 130.0
Fluoride 0.022 - 141.7
Cadmium 0.007 - 21.60
Lead 0.663 - 25.39
Iron 0.410 - 1482
Tin 0.060 - 103.4
Phosphorus 0.020 - 144.0
Total Suspended Solids 0.100 - 9970
2.1.1 Recommendations for Process Modifications
The best way to reduce the amount of water needed in an
electroplating process is to maintain good "housekeeping"
practices to avoid spillage or "dragout" of treating solutions
into rinse waters. Other recommendations include:
-------
Substitute low concentration solutions in place 2.4
of high concentration baths.
Use non-cyanide solutions in place of the cyanide
treatments.
. Use counter-flow rinses.
Add a wetting agent to rinse wateis.
Install air or ultransonic agitation.
Recover und reuse metals that are in effluent
streams by solvent extraction.
Recycle used rinse waters into the make-up
solutions of their respective treating baths.
-------
BIBLIOGRAPHY 2.5
O.S. EPA. Development Document for Interim Final Effluent
Limitations Guidelines and Proposed New Source Per-
formance Standards for the Common and Precious Metals
Segment of the Electroplating Point Source Category.
EPA/440/1-75/040, April 1975.
U.S. EPA. Development Docunent For Existing Source Pretreat-
ment Standards for the Electroplating Point Source
Category. EPA/4407l-79/003, Aug. 1979.
SUPPLEMENTAL REFERENCES
Belnont, T.V. and Cuxmiff, J.G. "Plating Waste Treatment",
Industrial Wastes. Vol. 26, No. 6, 1980, pp. 14 & 27.
Elicker, L.N. Evaporative Recovery of Chromium Plating
Rinse Water. EVA/600/2-78/127, June 1975.
Hallovell, J.B. Aasesmcent of Industrial Hazardous Waste
Practices. Electroplating and Metal Finishing. Job
Shops. ZPA/530/SW-136C, Sept. 1976.
Landrigan, R.B. end Hollnwell, J.B. HemovtJ. of Chromium
from Plating Rinse Water Using Activated Carbon.
EPA/670/2-75/055, June 1975.
McDonald, C.W. Renoval ot. Toxic Metals from Finishing
Waatewater by. Solvent Extraction. EPA/600/2-78/011,
February, 1J»78.
Petersen, R.J. and Cobian, K.E. New Membranes for Treating
Metal Finishing Effluents by Reverse Osmosis. EPA/600/2-76/
197.
Poon, C. "Electrochemical Treatment of Plating Rinse Water",
Effluent and Water Treatment Journal. July 1979, pp. 351-
355.
Pozlelle, L.T., Kopp Jr., C.V., and Gobian, K.E. New Membranes
for Reverse Osmosis Treatment of Metal Finishing Effluents,
EPA/660/2-73/033.
U.S. EPA. Control of Volatile Organic Emissions from Solvent
Metal Cleaning. EPA/450/2-77/022.
-------
U.S. EPA. Copper, Nickel. Chromium and Zinc Segment of Electro- 2.6
plating Development Document for Effluent Limitations
Guidelines ma New Source Performance Standards. EPA/440/
1-74/— 3a.
U.S. EPA. Innovative Rlnse-and-Recovery System for Metal
Finishing Process. EPA/600/2-77-099.
O.S. EPA. Second Conference on Advanced Pollution Control for
Metal Finishing Industry. EPA/8-79/014.
U.S. EPA. Source Assessment; Solvent Evaporation-Degreaaing
Operations. EPA/600/2-79/019f.
O.S. EPA. Haste Water Treatment acd Reuse in a Metal Finishing
Job Shop. EPA/ 670/2-74/042.
Tost. K.J. and Scarf i, A. "Factors Affecting Zinc Solubility In
Electroplating Waste", Journal £f the Water Pollution
Control Federation. Vol. 51, No. 7, 1979, pp. 1878-1887.
-------
CHAPTER 3 3.1
COAL CONVERSION PROCESSES
3.1 INTRODUCTION
The unpredictability of the international energy market
and the very danger of global oil shortages in the next few
decades.have necessitated a rapid expansion in the dooestlc
energy base in the U.S. Consequently, the commercial produc-
tion of synthetic fuels from the abundant reserves of coal is
a major objective of the nation's energy research and develop-
ment programs. Coal liquefaction and coal gasification
technologies have received renewed interest in this regard.
Economic viability and environmental Impact will be the limit-
ing factors in the commercialization of such processes.
3.2 LIQUEFACTION
All coal liquefaction processes produce liquids from coal
by yitiding a material having a higher hydrogen content than
coal. Fuel oils contain about 9Z hydrogen and 14Z gasoline as
compared to roughly 5Z hydrogen In raw coal. Currently, some
twenty-odd liquefaction processes are in various stages of
development by industry and federal agencies. Coal liquefaction
technologies can be categorized under hydrogenatlon, pyrolysis
-------
and hydrocarbonlzation, and catalytic synthesis. Of these, 3.2
Bydrogenation is the most advanced (Koradek and Fatel, 1976).
In this chapter, the environmental problems associated vith
the following four coal liquefaction technologies vill be dis-
cussed:
1. Solvent Refined Coal, CSRC)
2. Synthoil
3. B-Coal
. 4. Bacon Donor Solvent
The following section will discuss the pollutant streams
from and suggested control methods foi the SRC process.
3.2.1 Solvent Refined Coal Liquefaction
A fully integrated SRC liquefaction system flow scheme
(Shield, .££ al. 1979) is shown in Figure 3.1. Raw coal from
the coal storage facilities is sent to the coal pretreatment
operation where it is sized, dried and mixed with reactor
product slurry recycled from the gas separation processes.
The resulting feed slurry is combined with recycled hydrogen
from the hydrogen/hydrocarbon recovery process and makeup
hydrogen. This hydrogen-rich slurry is pumped through a
preheater to the liquefaction reactor, or dlssolver. Exothermic
hydrogenation reactions initiated in the preheater continue la
the dissolver which typically operates between 435°C - 470°C.
The reactor product slurry is sent to the gas separation pro-
cesses where the gaseous products are removed. Auadlary pro-
cesses separate these gases including recyled hydrogen, SNG,
-------
MAJOR INPUTS
RAW GOAL RAH WATER
\ I
AUXILIARY
PROCESS
FACILITIES:
COAL RECEIVING/STORAGE
STEAM/POWER GENERATION
HTDROCEH GENERATION
OXYGEN GENERATION
ACID GAS REMOVAL
HYDROGEN/HYDROCARBON
RECOVER?
SULFUR RECOVERY
AMMONIA RECOVERY
PHENOL RECOVERY
COAL FROM STORAGE
COAL
PRETREATHENT
FEED
SLURRY
MAKED? AND RECYCLE
HTDROCEH
.iqUEFACTWN
REACTOR
PRODUCT
SLURRY
UKTFUATnt
FLASHED CASES
. WASTEWATER
CAS
SEPARATION
FLASHED CASES
fYDr.oTREAT7.NG
Oil.
J
RECYCLE
SOLVENT
FILTER CAKE
SOLIDS/LIOjl
WASH
SOLVENT
SOLID SHC
SEPA1
FILTERED
PRODUCT
LIQUIDS
1ATIOH
iFRACTIONAtlOB
AMIONIA
SULFUR
SOLID SRC
FUEL OIL
NAPHTHAS
LIGHT OILS
MAJOR PRODUCTS
AND BY-PRODUCTS
Flgur* 3.1. Flov Shan for An Integrated
Uqutfaction Precasi
-------
LNG and sulfur species. The sulfur specijs are further coc- 3.4
verted to by-product elemental sulfur. Part of the separated
slurry from gas separation is recycled to the coal pretreaonent
operation. The remainder of the slurry is sent to the frac-
tlonator. The fractionator generates three streams: a light
distillate which is hydrotreated to form naphtha and fuel oil
products; liquid SRC, the primary product; and a bottom stream
which is sent to solids/liquids separation processes. The
vacuum distillation unit in the solids/liquids separation recovers
additional SRC liquid from the fractionator bottoms, yielding
a residue of high mineral matter content. Part of this
residue is gasified to produce makeup hydrogen.
3.2.1.1 Participate Emissions
Fugitive emissions (i.e., partlculates) will be emitted
from the following sources: coal storage piles, coal reclaim-
ing and crushing, coal receiving, dryer stack gas, and ash
from stream generation. Trace elements of fugitive emissions
from coal preparation have a potential health hazard consist-
ing .predominantly of aluminum, chromium and nickel (Hupkins,
et al. 1978). Trace element concentrations In partlculates
escaping from treated stack gas are enriched in zinc, copper,
zicronlum, molybdenum and selenium. The trace element concen-
tration of coal dust is expected to be similar to that of
the parent coal, although certain trace elements may concentrate
in the smaller size range. Dust (typically 1 to 100 p in size)
generated from coal receiving, storage, reclaiming and crushing
-------
is estimated to be about 24 tons/day fox a 20,000 ton/day SRC i.3
II plant (Rogoahewskl, £t al. 1978). Table 3.1 lists analysis
of some trace elements in dust from coal preparation after
treatment with a vet scrubber (Hopkins, et al. 1978).
Suggested control alternatives for coal dust include
polymer spraying, enclosed storage and water spraying. Of
these, enclosed storage involves $6-8 million capital Invest-
ment for a 10,000 tou csal pile (Rogoahewski, et al. 1978).
Cyclone and baghouse filters are probably the most effective
methods for controlling coal dust. Due to the small particle
range, magnetic and electrostatic filters will be needed.
Table 3.1 Approximate Trace Element Analysis of Coal
Pretreatment Puat after Wet Scrubbing
Element
Aluminum
Arsenic
Chromium
Nickel
g/day
8,910
3.9
13.0
15.0
Degree of Bealt!
Hazard*
2.21
2. SO
17.0
1.3
*De*ree of health hazard • Concentration
-------
3.2.1.2 Coal Pile Drainage 3.6
Coal pile runoff resulting f. on rainfall and such, nay
contain oxidation products of metallic sulfldea. This run-
off nay also be acidic with relatively high concentrations of
suspended and dissolved solids (Rogoshewski, et al. 1978). The
elements in this runoff Include calcium, iron, «T»«m
-------
in dilute acid did not produce any leacheate. Table 3.2 - -
given the composition of some of the elements in this
mineral residue (Hopkins, _e£ al. 1978) which totals about
3(700 Kg/day for a SRC-XI liquefaction plant producing
10,000 ton/day liquids.
Table 3.2 Estimated Trace Elements Composition of the SRC
Liquefaction Residue
Element
Arsenic
Barium
Calcium
Iron
Luterlum
Nickel
Sodium
Zinc
Concentration ppa
24.9
579
33,323
116,760
2,050
126
1.155
1,938
The extraction of metals from this residue is another area
that requires further research.
3.2.1.5 Spent Catalyst
Catalyst used in the shift reaction in hydrogen genera-
tion has been estimated at about 135 m (Hopkins, _et_ al. 1978).
Trace elements, sulfur compounds and heavy hydrocarbons may
be adsorbed on the catalyst. The estimated life time ot a
-------
cobalt molybdate catalyst is three years. Regeneration of 3.8
spent catalyst may not be possible due to the presence of
trace metals and sulfur as well as possible sintering of
the catalyst. It is suggested that valuable metals be
extracted from the spent catalyst at an off-site facility.
Similar facilities may be needed for spent sulfur guard and
methanatlon catalysts.
3.2.1.6 Tail Gas From Acid Gas Removal
Acid gas from the gas purification module and ga_ from
hydrogen production axe routed to a Stratford Unit where
H2S (472 Mg/iay) (Hopkins, et al. 1978) is recovered as
elemental sulfur. The Stretford process has an efficiency
greater than 99.SZ in sulfur recovery and can reduce H_S
concentrations to less than lOppm. However tall gas treat-
ment may be needed before the spent gas can be vented. The
Stretford solution consists of mainly sodium metavanadate,
sodium anthraqulnone dlsulfonate (ADA), sodium carbonate and
sodium bicarbonate In water. The Stretford solution purge
stream has a total salt concentration of 10-25Z. Using a
high temperature hydrolysis technique, vanadium (as solid)
and sodium carbonate, sulfate and sulfite can be recovered
as solidJ. HCN Is completely converted to CO., H.O and N.
(Rogoshevskl, e± a^. 1978). The Stretford tall ga« contains
about 42.7Z CO. and 5,500 ppm hydrocarbons (as C,Hfi).
Direct flame incineration and carbon adsorption with incln-
-------
eration (Ad Sox) is recommended as call gas treatment for 3.9
hydrocarbons. Further scrubbing might be needed to reaove
CO. in the tail gas. It is suggested that the Stretford
solution be modified to reduce CO. emissions In the tail
gas. This is one area which necessitates further research
on adsorption phenomena of SOL and CO. in various solvents.
3.2.1.7 NO Removal
The reported sources of N0_ emissions within the SRC
plant include (Hopkins, et al . 1978):
Steam generation 8.4 Mg/day
Stretford effluent gas 0.003 Mg/day
The
-------
Process
Coal
Pretreatment
Coal
Pretreatment
Caalfler
Solids/
Liquids
Separation
Hydrogen
Gene ratios
Acid gas
Removal
Stean
Generation
Pollutants
Coal Dust
Thickener
Underflow
Slag. Fly
ash
Mineral
Residue
Spent
Catalyst
Tail gaa
NO,
Emissions
Sources in Procesi
Storage, handling
SUing
Coal Pile Run Off
—
Pract lonator
Bottoms
Reactor
Stretford Process
—
Nature of
Pollutants
Similar Original
Coal
Minerals and
Suspended Solids
Inorganics,
Uetals and
Organ ica
Inorganics.
Metals and
Organ ica
—
Hydrocarbons
and COa {'43%)
MO^ gases
Pollutant Control Strategy
Cyclone, vet scrubbing, polymer
Coating, Electrostatic and
Magnetic Filters
Extraction and Disposal of
Tailings.
Leaching of Metals and Strip
Mining.
Extraction of (Toxic) Metals
Extraction of Co, Mo. Hi
Direct Flame Incineration. Modifi-
cation of Stretford process to
remove CO.
Substolchlometrlc supply of air,
Reclrculatlon of Flue Gas
III
•
t"
o
-------
The applicability of electrostatic and magnetic 3.11
filters to control emissions of coal dust particles
in the submJcron range.
teachability of gasifier slag and fly ash to
determine treatment and/or disposal methods.
Extraction of possibly toxic and/or valuable
metals from solids/liquids separation residue.
Extraction of valuable metals (Ni, Co, Ho, etc.)
from spent shift and hydrogen generation
catalysts.
. Studies on the absorption of SOL and.CO, In
Stretford process leading to process modifica-
tion Co reduce CO, emissions in tail gas.
. Modification of steam generation operation to
reduce N0_ emissions.
3.3 GASIFICATION
In this section, the pollution problems and control alter-
natives for the following four High-Btu coal gasification
technologies will be discussed.
1. Lurgi
2. Hy Gas
3. Bl Gas
4. Koppers-Totzek
In the following section, the Lurgi coal gasification process
is discussed.
-------
3.3.1 Lurgi Coal Gasification 3'12
The conversion of coal to SNG involves the reaction of
coal with steam and oxygen in a gaslfier with subsequent
gas processing to (a) adjust the H.:CO ratio by vater-gas
shift reaction, (b) remove acidic components, and (c) cata-
lytic methanation. The corresponding chemical reactions
are:
6(C4fl) + 4 0, + 3H-0 •» 4H, + 2CO + 3CO. + CH.
coal * * L
Lurgi gasification (3.1)
CO + BjO •»• C02 + B2 Water-gas shift (3.2)
•
SHj + CO * CH4 +• HjO Methanation (3.3)
The four major processes in the Lurgi gasification are
discussed below. A flow sheet of the process is given in
Figure 3.2.
3.3.1.1 Coal Preparation
Coal pretreatment in the Lurgi System generally consists
of only crushing and screening the coal to produce 3-35 mn
particles. This larger size range, compared to certain other
gasification processes, decreases fugitive emissions.
3.3.1.2 Coal Gasification
The coal gasifier is operated at a pressure of about
25 to 35 atm and receives coal through a feed hopper at the
top and discharges ash through the bottom. Oxygsn and steau
enter at the bottom of the gasifier and the product gas exits
near the top. On a dry basis the product gas contains about
4Z Hj, 32 C02, 18Z CO and 10Z CB^ as well as higher molecular
-------
COAL
ML PREPARATION
OPERATION
CRUSHING
AND
SCRESHIHG
COAL PINES
(TO BOILER)
COM
C
. GASIFICATION |
VERATIOH
GASIFICATION
1
ASH
(TO DISPOSAL)
GAS PURIFICATION
OPERATION
RAW CAS
IDQUOR
(TO
TAR/OIL
SEPARA-
TION)
CONCENT!
TED ACID
^»
-•
IA-
CASES
(TO SULFUR
PRIHARY
COOLIHT.
SECONDARY
COOLING
RECTISOL
ACID
CAS
REMOVAL
RECOVERY)
TRACE
SULFUR AND
ORCANICS
REMOVAL
CA1
«
'
1 UPGRADING
IPERATION
SHIFT
CCNVERSION
METHAHATIOM.
DRV INC AND
COMPRESSION
\
NCI
(TO BOILER)
Figure 1.2. Lurgt SNC Process.
o
•
t-
-------
weight hydrocarbons, reduced sulfur and nitrogen compounds. 3.J4
3.3.1.3 Gas Purification
Gas purification consists of the removal of ccmdensables
by cooling, Rectisol treatment for the removal of bulk CO^
and reduced sulfur compounds, and removal of trace sulfur
using "methanatlon guards". The condensates produced are
sent to tar/oil separation units and by-product recovery.
The Rectisol process uses cold methanol to absorb acid gases
under pressure. The used solvent is regenerated by stepvlse
depressurlzatlon and heating. Methanation guards are beds
of solid adsorbent (e.g. ZnO). The exhausted beds are
usually discarded rather than regenerated.
3.3.1.4 Gas Upgrading
Cobalt molybdate is used as shift catalyst to obtain a 3:1
E.:CO ratio. Nickel based materials are usually used as
methanation catalysts. Both the spent shift and methanatlon
catalysts are solid wastes requiring treatment for metal
recovery and/or disposal.
3.3.1.5 Gaslfler and Boiler Ash
Wet ash from the gasifler and boiler ash quench systems
is the largest volume solid waste stream in an 5NG plant
(Ghasseml, et al. 1979). A 250 x 106 Scf/day Lurgi SNG
plant using a coal containing 152 ash is expected to generate
about 5400 ton/day wet ash having «« 2Z moisture content. This
ash contains leachable inorganic and organic materials. These
constituents can be possible sources of groundwater contamlna-
-------
tion. An alternative disposal scheme would Involve stabilize- 3.15
cicn to convert the wastes into a chemical form that is more
resistant to leaching in the ultimate disposal site. Table 3.4
presents typical leaching study results for wastes stabilized
by the Chemflx process (Connor, 1974).
Table 3.4 Laboratory Leaching Results of Chem-Flzed
Refinery Wastes
Element Concentration in Concentration in approx.
Raw Sludgpvn 200 ml Leachate water
after Chem Fix ppm
Total Chromium
Iron
Zinc
Nickel
43.5
1310
88.0
8.9
< 0.1
< 0.1
< 0.1
< 0.1
The leachability of the ash produced in Lurgi SNG is an area
which requires further investigation.
3.3.1.6 Spent Guard Catalyst
Zinc oxide beds are used for removing the last traces
of sulfur after gas removal has removed all but a few parts
per million. Water vapor content is critical in that liquid
water can possibly degrade the ZnO bed completely (Ghassemi,
et al. 1979). The sulfur loading capacity of the ZnO
catalyst increases from 35 wtZ at 273°K to = 20 wtZ at 673°K.
-------
However, Che maximum recommended loading la only 3 vtZ when 3.16
the desired exit gae specification is 0.02 ppm HjS (Drano
Corp., 1978). Spent metharation guard material will consist
primarily of zinc sulfide and unreacted sine oxide. Operating
data on the quantity and composition of spent methanation
guard catalyst are needed to evaluate the disposal and/or
reclamation of the spent catalyst (Ghassemi, «. al. 1979).
3.3.1.7 Spent Shlft/Methanatlon Catalysts
Catalysts used for shift and methanation require
periodic replacement; the spent catalysts constitute a
solid waste. Gross composition of spent catalyst is not
expected to be dramatically different from that of fresh
catalyst, although accumulation of carbon, sulfur, and
metallic elements is to be expected. Data is needed on the
characteristics of spent Lurgi SNG catalysts. Cobalt-
Molybdate la used as a shift catalyst. Table 3.5 presents
pilot plant data on spent Barshaw N1-0104-T-1/4 catalyst
(Leppln, 1977).
Table 3.5 Spent Harshaw Nickel Catalyst Analysis
Typical Fresh
Catalyst
Sulfur, Z wt. 0.15
Carbon, Z 3.4
Nickel, Z 60.0
Bottom of First
Stage Methanator
3.7
3.4
52.0
Top of Second
Stage Hethaaator
0.16
4.5
61.0
-------
Spent nickel methanation catalyst is as active as zinc for 3.17
trace sulfur removal and can be used as sulfur guard catalyst
(Ghassemi, et. al. 1978). Sequential interchange of the first
and second stage methanators is also recommended, as it is
apparent from Table 3.5 that the catalyst at the top of
second stage methanator is almost fresh. In the end,
however, spent methanation catalyst constitutes a solid
waste. The large weight percent of Ni on the catalyst would be
an economic incentive for reclaiming metal from the spent
catalyst. Data on the properties of spen.. nickel
methanation catalysts and the applicability of metal
extraction for reclamation are two areas that need
further investigation. Further, the spent catalysts, al-
though of small quantity, are of special concern due to
their content of potentially toxic metals (Ni, Co, Mb)
and coal-derived organlcs (metal carbonyls for example)
and trace elements. Fixed-bed methanation/shlft reactor
system Is reported to have '.he advantages of (1) operation
at conditions removed from carbon formation, thereby
increasing catalyst life, (2) reduction in catalyst
sensitivity to sulfur, and (3) need C02 removal from a
reduced volume of gas. However, this has not been
commercially demonstrated yet (Gassaeml, e_t_ jl. 1978).
-------
3.3.1.8 Ash Quench Slurry 3.18
An ash quench slurry results when process waters are
used to cool and transport gasifler ash to a settling unit
or disposal site. No operating data are available for ash
qunch slurry characteristics (Ghasseml, et al. 1979).
Laboratory data indicates that this slurry can contain
up to 20 g/L of dissolved solids with the dominant ions
being Ca+2, S0~? K* and Ha* (Griffin, et al. 1977). An
increase in the solubility of Fe, Mn, Cd and A£ is also
expected with decreasing pH. In addition, the concen-
tration of certain hatardous elements (e.g. As, Hi, Cr
and Cu) can reach levels which warrant control of the
aah slur.-y discharge. Characterization of ash slurry tracer
la needed to evaluate pollution control alternative.* such
as coagulation and flocculation of solubles.
3.3.1.9 Phenol Recov..*y
Gas liquor from tar-oil recovery contains a high
concentration of phenol:., up to 4200 mg/L (Ghasseml, e£
al. 1979). The Fhenosolvan process using butyl acetate
as solvent is used to extract these phenola. Most of the
available data on the performance of this solvent extrac-
tion process are for the unit in Salsbury, South Africa.
Solvents suggested for the Phenosolvan process Include butyl
acetate, Isopropyl ether and light aromatic oil (Wurm,
•
1969; Earhart, et, al. 1977). For butyl acetate the
following distribution coefiicients for various phenolic
-------
compounds have been reported (Earhart. et al. 1977). 3.19
Table 3.6 Distribution Coefficients for Various Phenols in
Butyl Acetate at 300°K
Compound Kg
Phenol 65
3,5 Xylenol 540
Pyrocatechol 13
Resorcinol 10
**» •
The solverts can remove only limited amounts of non-phenolic
organlcs. A better characterization of the available
solvents for phenol extraction and their removal efficiencies
for various phenols are needed. Further development of
solvent extraction systems to remove non-phenolic organlcs is
also suggested.
3.3.1.10 Removal of Sulfur Compounds from Rectlsol Process
In terms of total volume acd content of B.S and other
reduced sulfur compounds, concentrated acid gas from the
Rectisol process Is the most important gaseous vaate stream
in a Lurgi SNJ facility. Some of the control options for
concentrated acid gas stream (Ghassemi, et_ al. 2979) are
shown in Table 3.7.
-------
Table 3.7 Control Options for the Concentrated Acid Gas
Stream
3.20
Control Opeions
1. Claus Plant Sulfur Recovery
2. Claus Plant Stucur Racovery
and tall gas treatment
3. Claus Plant Sulfur recovery
and SO. control/recovery
4. Stretford Sulfur Recovery
High Concentration of H.S
In tall gaa; feed gas H.S
enrichment sod Hydrocarbon
removal are needed
Net highly effective at high
levels of CO. In feed, appli-
cable only for streams con-
taining 5-15Z B2S
Reasonable option when feed
gases contain more than
5-15J
Inapplicable to waste gases
containing greater than 152
B.S; not economical at high
CO. levels; discharge may
contain high COS and HC
levels
The determination of the best option for the management of
a specific sulfur bearing gas stream must be made on a case
by case basis due to the restrictions on feed compositions
and economics for different processes. Some of the above
options have not appeared in commerical design (Ghassemi,
et al. 1979) due to the lack of engineering data. It is
suggested that research be organized to provide operational
data for various sulfur recovery, SO. and tall gas treatment
processes.
-------
Table 3.8 auauarlzes some of the pollution problems 3.21
associated with the Luzgi SSG process and suggested control
alternatives.
3.3.2 Recommended Arena for Pollution Control Research:
Lurgi Coal Gasification Process
After Evaluating .he available literature, the following
areas are reconmended for further research by the study:
Stabilization of gasif ier and boiler ash to
decrease or prevent leachability.
Opurating data and compos! .ion on spent
methanation guard, shift and nethination catalyst
to determine possible extraction of valuable ar.d
toxic metals.
. Studies on the use of spent methanation catalyst
as sulfur guard.
Development of solvent extraction systems to
remove non-phenolic organics and determination of
distribution coefficients for existing solvents.
Engineering data on various sulfur recovery,
and tail gas yratreatment processes.
,
-------
TafcU J-8. Follutaata and Control Option* In Lurgl SHB Proeaae
Pvfecaee
Coal Kaelfl-
citlon
Rae Upgrading
bKft/Metha-
•atijB
Coal
CMirfccciM
Tar/oil
•*M rat too
A*ld gae
T novel
rallutat*
Mh
Sp«ac Mtto-
nation guard
caMlyat
Spmt
catklysti
aan quench
•lurry
Vtiaaola In
M* llquni
Sulfur
cenDouad*
Soor<-c« in
pr6k.:a«
~
Hathanatlon
guard r*acc«r
Rtactor*
Ttitck*n»r
ovcrflov
—
Rncttael
fall pa*
Nature of
Tollutant
laaehabla lo-
orpanlc.
oritanle
•aurlala
ZaO with
craca orian-
lca( aulfur
and Batalfl
Co, Ho, HI.
with ttaca
ornanlca.
aulfur
Dlcanlvad !o-
organlca,
hacardoua
•acala (a*. Nl)
NonnlMiuillc
organlca
S*»ji H j*. W*2
Pollutant control StrattRv
atabllltatloa of aih to da-
eroana or pravant leach
ability
laelautloa by axtractloo
Spent •ethanatlon catalvet ee
•ethaaatton guard, eitractlon
of toxic aatala (COB apant
cacalyat
Coagulation and rioceulatlon
to ranova dlaaolvad aalta
Batter eharaetarlaattoa of
aol(r«ta Ce •odtfr/davalop
eicractlon eyateaa
Clana oulfur reeevarv and SO
tall aaa treatnent, StretfoiB
•ulfur vacovarr
-------
BIBLIOGRAPHY 3.23
Connor, J.R. Disposal of Liquid Wastes by Chemical Fixation.
Waste Age, Sept. 1974, pp. 26-45.
Dram) Corp. Handbook of_ Gasiflers and Caa Treatment Systems,
EFDA No. FE-1772-11. Pittsburgh, PA, 1976.
Earbart, J.P»,£tal. Recovery of Organic Pollutant a Via
Solvent Extraction. Chen. Eng. Frogr., Kay 1977, p. 67.
Ghaaaeai, M., _« al. Environmental Assessment Data Base for
Hlgh-Btu Gasification Technology; Volume II. Appendices
A, j», and C, EPA-600/7-7&-186b, Prepared for U.S. EPA
• by TRW Environmental Eng. Olv., Redondo, Beach, CA, Sept.
1978.
Chaaseml, H., «£ aJ.. Environmental Assessment Report; Lurgl
Coal Gasification Systems for SNG. EPA-600/7-79-120,
Prepared for U.S. EPA by TRW Environmental Eng. Olv.,
Redondo Beach, CA, Hay 1979.
Griffin, R.A., £t al. Solubility and Torlelty ojf Potential
Pollutants in Solid Coal Waste. Presented at EPA
Symposium on the Environmental Aspects of Fuel Conversion
Technology, Sept. 1977.
Hopkins, H.T., £t ^1. SRC-Sit-Specific Pollutant Evaluation!
Vol. I, Discussion. EPA~600/7-78-223a, Prepared for U.S.
EPA. by Hittmann Associates, Inc., Columbia, Md., Nov.
1978.
Koradek, C.S. and Patel, b.s. Environmental Assessment Data
Base for Coal Liquefaction Technology; Vol. _!. Systems
for 1A Liquefaction Processes. EPA-600/7-7«M.84a,
Prepared for U.S. EPA. by Hittmann Associates, Inc.,
Columbia, Md., Sept. 1978.
Leppln, 9. Slnth Synthetic Pipeline Caa Symposium. Chicago,
IT,, Oct. 31 - Nov. 2, 1977.
Rogoshewskl, P. J., et al. Standards of Practice Manual for
the Solvent Refined Coal Processes. EPA-600/7-78-091,
Prepared for U.S. EPA. by Hittmann Associates, Inc.,
Columbia, Md., June, 1978.
-------
Shields, K.J., .etal. Environmental Assessment Report; Solvent 3.24
Refined Coal (SRC) Systems. EPA-600/7-79-146, Prepared
for U.S. EPA. by Hlttaann Associates, Inc., Columbia, Md.,
June 1979.
Wuzm, H.J. Treatment £f Phenolic Wastes. Eng. Bull. Purdue
Univ.. Eng. Ext. Serv., 132'(II), 1054-73. 1969.
SUPPLEMENTAL REFERENCES
U.S. EPA. Saaol; South Africa's Oil to Coal Story—Back-
ground for Environmental Assessment. EPA-600/8-80-002,
Jan. 1980.
U.S. EPA. Air Emissions from Combustion of Solvent Refined
Coal. EPA-600/7-79-004, Jan. 1979.
U.S. EPA. Coal Processing Technology: Environmental Impact
of Synthetic Fuels Development. Chem. Eng. Progr., 1975,
6.
U.S. EPA. Control Technologies for Particulate and Tar
Emissions from Coal Converters. EPA-600/7-79-170, July
1979.
U.S. EPA. Effects of Combustion Modifications for NO
""^^^^™™^^™™ 3fc
Control on Utility Boiler Efficiency and Combustion
Stability. EPA-600/2-79-190, Sept. 1977.
U.S. EPA. Engineering Evaluation of Control Technology for
the H-Coal and Exxon Donor Solvent Procesaea. EPA-600/7-
79-168, July 1979.
U.S. EPA. Environmental Assessment of Coal Liquefaction!
Annual Report. EPA-600/7-78-019, Feb. 1978.
U.S. EPA. Environmental Assessment of High-Btu Gasification!
Annual Report. EPA-600/7-78-025, Feb. 1978.
U.S. EPA. Environmental Assessment Data Base Ccal Liquefac-
tion Technology! Vol. _!_!. Syntholl. H-Coal. and Eaccon
Donor Solvent Processes. EPA-600/7-78-184B, Sept. 1978.
-------
U.S. EPA. Environmental Assessment Data Base for High-Btu 3.25
Gasification Technology: Volume I. Technical Discussion.
EPA-600/7-78-186A, Sept.. 1978.
U.S. EPA. Evaluation of Background Data Relating to Nev
Source Performance Standards for LURGI Gasification.
EPA-600/7-77-057, June 1977.
U.S. EPA. Evaluation of Pollution Control in Fossil Fuel
Conversion Processes — Liquefaction; SectiOw 2 - SRC
Process. EPA-650/2-74-009P.
U.S. EPA. Evaluation of Pollution Control in Fossil Fuel
Conversion Processes — Gasification.
Section 1 - Koppers-Totzek Process-EPA-650/2-74-009A
Section 3 - Lurgi Process - EPA-650/2-74-009C
Section 5 - Bl gas Process - EPA-650/2-74-009G
Section 6 - Hygas Process - EPA-650/2-74-009H
U.S. EPA. Mechanism and Kinetics of the Formation of NO
and other Combustion Products — Pfr.sae J[I Modified
Combustion. EPA-600/7-76-009B, Aug. 1976.
U.S. EPA. Pollutants from Synthetic Fuels Production;
Sampling and Analysis Method
EPA-600/7-79-201, Aug. 1979.
Sampling and Analysis Methods for Coal Gasification.
/7-7
U.S. EPA. Sulfur and Nitrogen Balances in The Solvent
Refined Coal Processes (Task I). EPA-650/2-75-011. Jan.
1975.
U.S. EPA. Sulfur Retention in Coal Ash. EPA-600/7-78-1538,
Nov. 1978.
U.S. EPA. Symposium Proceedings; Environmental Aspects of
Fuel Conversion Technology. II, Dec. 1975, EPA-600/2-76-
149, June 1976.
U.S. EPA- Symposium Proceedings; Environmental Aspects of
Fuel Conversion Technology. III. Sept. 1977, EPA-600/7-
78-043, April 1978.
U.S. EPA. Symposium Proceedings; environmental Aspects of
Fuel Conversion Technology. VI. April 1979, EPA-600/7-
79-217, Sept. 1979.
U.S. EPA. The Solubility of Acid Cases. In Methanol. EPA-
600/7-79-097, April 1979.
-------
CHAPTER 4 4.1
EXPLOSIVES INDUSTRY
4.1 INTRODUCTION
The processes involved in manufacturing of high explosives
are discussed In this chapter. The purpose of this chapter
Is to provide an Insight In reducing the pollutants arising
from these processes by means of process modification. This
chapter Includes the two most produced high explosives;
trinitrotoluene and nitrocellulose. Both explosives are
generated by nitration processes to yield nltrocompounds.
The explosive Industry as a whole has been grouped Into
four categories:
1. Manufacturing of explosives
2. Manufacturing of propellents
3. Formulation [load, assemble and pack (LAP)l
4. Manufacturing of Initiating compounds
Since both of the compo"ads discussed in this chapter
require large amounts of nitric acid for production, the
process for producing nitric add is also presented. Process
descriptions given here do not include actual formulation
(load, assemble, and pack). Figure 4.1 is an overview flow
chart of the explosive industry.
4.2 NITRIC ACID PRODUCTION
Figure 4.2 demonstrates the role of nitric acid in the
explosive industry. The process given here is not the only
-------
CHEMICAL
MATERIAL
NITRATION
PROCESSING
INDUSTRY
PRODUCTS
EXPLOSIVE
ORGANIC
NITKATION
PRODUCTS
rOUULATlOM
OTHER PORMIUTIOH
INGREDIENTS
rigur* 4.1. ProceiM> In Iha bploelv* In'ustry (Koradak and Pitcl. 1976).
K)
-------
4.3
ri_W
st
SKBT ACID
ttCOTERT
T
L
^^^ TO RECTCLE
AID/OR
rijur. 4.2. Flow Chart for nitric Acid Production
(Hudok nd ParMBC. 1977).
-------
process available for nlcrie acid production. Aa it ia sug- 4.4
gested ia this section, other systems for this process must be
closely ex2Blned«
4.2.1 Ammonia Oxidation Process
Za this process anhydrous ammonia is vaporized and mlsed
with preheated air and combusted under pressure in the pre-
sence of a catalyst tt: produce nitric oxide. Nitric oxide
is further oxidized by excess air to nitrogen dioxide and Its
dioer (NjO^). Typically the catalyst is platlnum-rhubidlum
or platinura-palladiura-mercury. The bed operates at 800-919°C
and 120 psla. The equilibrium mixture of NO. and its dlmer
are adsorbed in a water cooled absorption tower to fora weak
nitric acid (60-65Z HNOj) (Hudak and Parsons, 1977; Patterson,
et al. 1976).
The main source of pollution from the ammonia oxidation
process (AOP) is the tail gas from the absorption tower which
produces approximately 2.5 g NO^/kg ENO^ for the high pressure
process. The conversion is at least 95Z of theoretical with an
ammonia consumption of 0.4 kg/kg HN03 (Hudak and Parsons, 1977).
In addition, the tall gas contains NZ (Patterson, et al. 1976).
Quantitative reduction in pollutants can be achieved as
a direct result of as. increase in HMO. production. The first
strategy in increasing HNO^ output is a more efficient design
for the catalytic bed. Ma^mum yield of nitrogen oxides can
be attained by mixing the gases via a filter near the inlet
-------
before contactIng the guaze and by selection of an optimal 4.5
operating temperature (Smith and Lockyer, 1979; Dorfman,
,££.81. 1978). On the other hand, the mechanism of the
surface catalysis plays an Important role In NO generation.
For small concentrations of NH_ on the catalyst surface,
the conversion of MH^ Into NO Is almost complete. The yield
of NO tends to decrease, since NO Is decomposed to N. .
(Atroschenko, et, al. 1979). This decrease Is a result of
poor exchange between catalyst surface and the gas bulk, and
subsequent accumulation of NO on the catalyst surface.
Based en this argument, the yield of NO In the bed can be
optimized by increasing the rate of mass transfer from the
bulk gas to the catalyst surface. Furthermore, the degree of
dissociation of NO increases linearly with time {Zhidkov,
e£ al. 1979). Thus knowledge of the NO dissociation reaction
and NO production rate will be needed In maximizing NO output.
It is also of value to examine the operating parameters
for the absorption tower. The rate of nitric acid production
can be Improved by controlling the temperature of the absorber.
Dorfman, et al. (1978) accomplished a 4Z increase In BNO. out-
put by adjusting the EjO consumption, thus controlling the
temperature.
4.2.2 Nitric Acid Concentration
The nitric acid concentration process Is a continuous
operation in which nitric acid from the AOP is mixed with
-------
concentrated H.SO, and fed to the distillation tower with 4.6
steam. The sulfuric acid combines with free water while HKO.
vapors (98-99Z) (Hudak and Parson, 1977) form an overhead
stream. The nitric acid vapors, contaminated with small
amounts of NO and 0. Iron HNO, dissociation, pass to a
bleacher and condensor. The HNO.. vapors condense as 95-99Z
HNO_, while NO and 0. pass to the absorber column 'for conversion
to and recovery of additional weak nitric acid. This weak
nitric acid is recycled to the dehydrating unit. The bottom
product, consisting of approximately 68Z H.SO, (Hudak and
Parsons, 1977), Is recovered and sent to a concentration unit
fox reprocessing.
The principle source of emissions, 0.1 - 2.5 5 SO /Kg
HN03 produced (Hudak and Parsons, 1977), is from the absorber
tall gas. The NO^ content of the tail gas is affected by
several variables: insufficient air supply to the absorber,
high temperatures In the absorber, and Internal leakage
which permits gases from the AOP to enter the absorber (Hudak
and Parseme, 1977).
In search of process modifications which may lead to
abatement of pollutants, it is advantageous to consider
other processes for producticn of nitric acid. One such newly
developed process is concentrating nitric acid by surpassing
the azeotrope. In this process k-he gases leaving the oxida-
tion step of AOP are enriched in NO- and then absorbed
-------
in azeotropic acid to produce a super azeotrope mixture C60Z
HNO-). This mixture is then easily distilled. The exiting
gases from this particular process contain 300 ppa o£ HO
(Harzo and Harzo, 1980). The advantage of this process as
opposed to the conventional, oxidation absorption operation,
should be considered.
4.2.3 Spent Acid Recovery
Spent acid from the various nitration processes flow into
the top of a denitrating tower. The HNO, and NO are stripped
from the spent acid by steam. The bottom product contains
H.SO, which is sent to a H.SO. concentrator. Sulfurlc acid
(93Z) from the concentrator is a by-product of most nitration
processes (Patterson, et al. 1976).
i
Waste waters from the spent acid recovery unit are
characterized by high concentrations of suspended solids and
small quantities of nitrogen salts. The solids from these
processes, called nltrobodies, must be removed from the
spent acid for pollution control.
Table 4.1 summarizes some of the pollution problems
associated with nitric acid production and suggests the
control alternatives.
4.2.4 Recommended Areas for Pollution Control Research in
Nitric Acid Production
After evaluating the available literature, the following
areas are recommended for further research by the study:
-------
Table IV-1 Pollutants and Control Options in Nitric Acid Production Process
Process
Ammonia
Oxydation
Procass
Nitric
acid
concentra-
tion
ttpent
acid
recovery
Pollutants
«V N2
N0x
Nitrogen
salts
nitrobodies
Source in
Process
Tail gas
from
absorption
tower
Absorption
tail gas
From nitra-
tion
processes.
Nature of
Pollutants
Inorganic gases
Inorganic gases
Organic and
inorganic
Pollutant Control Strategy
Adjustment of operating
temperature for maximum
HNO, output.
Mixing of gases at the
inlet cf catalytic bed.
Improvement of mass trans-
fer rate between the cata-
lyst and the bulk gas.
Provide sufficient air
supply .
Prevention of leakage
from AGP.
Removal of suspended solid
-------
Studies on kinetics and mass transfer process 4.9
for heterogeneous catalysis to improve the
catalytic bed design which wUi reduce NO dis-
sociation and Increase NH. consumption.
Studies on heat and mass transfer with reaction in
absorption towers to optimize HNO- production by
finding the optimal parameters for adsorption
tower operation.
. Consideration of nitric acid production by means
of a super azeotropic mixture which ma? be use -
ful In modification of the present process.
4.3 TNT PRODUCTION
Trinitrotoluene is the most extensively produced military
high explosive. Production of TNT during 1969-71 exceeded
22,000 tons/month, more than any other high explosive compound
(Patterson, et a.l. 1976). Trinitrotoluene production Involves
three distinct processes, nitration, purification and finishing.
Schematically, TNT production is shown in Figure 4.3.
4.3.1 Nitration
Nitration cf toluene is performed in a series of reactors
with a mixed acid stream flowing countercurrently to the flow
of the organic stream. The oleum fad to the last reactor
emerges as the spent acid from the first reactor. The acid
stream to second and third reactors are fortified with 60Z
-------
SELLITE
Na,CO,
TO HIHD ACID
PREPAMTU
NITRIC ACID
CONCENTBATIOH
TO STORACB
FflkMJLATUM
OR UP
Ptgur* 4.J. Mov Chart for TNT Production (Budak and Parson. 1977).
-------
HNO-. "Yellow water" is added to the second reactor. Approxl-
mately SZ (Hudak and Parsons, 1977; Patterson, et al. 1976)
of the TNT from the third reactor is 6 or 2,3,4 and Y or 3,4,6
isomers (the favorable product is a or the 2,4,6 isoner).
The gases from the nltrator-separator step contain CO, C02>
NO, NO., N20 and trlnitromethane (TNM). These gases are passed
through a fume recovery system, for recovery of NO^ as nitric
acid, and are then vented through a scrubber to the atmosphere.
Final emissions contain unabsorbed NO^ as well as TNM.
Rated capacity for a typical fume recovery system operation
for the continuous process is indicated to be 272 Kg HNO^/houv
(Hudak and Parsons, 1977). Approximately 245 Kg NO^/Mg TNT are
generated by the nitratovs of which 9.6 Kg NO^/Mg TNT are vented
to the atmosphere (Hudak and Parsons, 1977). In addition un-
syonetrlcal "meta" isomers as well as oxidation products are
generated. "Red Wat«sr", the main source of pollution, is the
by-product of the creaunenc of "meta" isomers in the purification
step.
The pollutants from TNT production can c« alleviated by
improving the chemical reaction that would decrease the decom-
position of nitric acid, the oxldative side reactions, and
the formation of unsymmetrlcal Isomers. For this purpose a
low temperature (-10°C) nitration, dlnitrate toluene,
followed by a high temperature (90°C) trlnltratlon is recom-
mended (Hill, et al. 1976; Haas, ,et al. ). The major
-------
changes from the existing process occur in Che dlnlcration 4.12
step. It was shown that lowering the temperature from 33°C
to -8°C In the dlnltrator step results In reduction of "mata"
Isomers concentration In the product from 2.4Z to 1.8Z (Baas,
et, al. ).
The fume recovery system for gaseous emissions in the
nitration separation step trust be designed to operate
efficiently at the nu"Hm.mi production level of TNT.
4.3.2 Purification
The crude TNT from the nitration step is washed with
water to remove free ncids. This step is accomplished by
using a countercurrent flow of water. The TNT is then
neutralized with soda ash and treated with a 16Z aqueous
sodium sulfite (sellite) solution to remove the nltro group
in the meta position is a and Y - TNT by a sodium sulfonate
group, forming highly soluble sodium salts of the corres-
ponding dinitrotoluene sulfonlc acid. The TNT is then
treated in a series of countercurrent extractors with H.O
and is then transferred to the finishing process as a slurry.
The waste stream from the purifications are "yellow
water", "red water" and "pink water". "Yellyw water" is
generated as a result of the first water w*.sh. Some of this
acidic effluent is returned to the dln-i.tration step and the
rest is combined with other process waste waters for treat-
ment. "Red water", the effluent of sellite treatment and
-------
subsequent washing of TNT, is composed of 27.6Z vacer, 17.3% 4.13
organics, 5.2% NaNO^, and 2.9Z NajSO^ (Hudak and Parsons,
1977). The generation of "red water" amounts to 0.34 kg/kg
TNT produced and consists of 0.26 kg process water, 0.06 kg
organics (nltrotoluenes and nitrotoluene - sulfonlc acid
salt), and .02 kg dissolved organics (NaNO^ and NaSO^)
(Hudak and Parsons, 1977). "Pink water" is the waste
stream generated from TNT manufacturing as well as LAP opera-
tion. "Pink water" arises from the nitration fume scrubber
discharge, "red water" concentration distillate, finishing
operation hood scrubber and wash down effluent, and possibly
spent acid recovery waates.
Control strategy for reduction of "red water" has been
discussed in the nitration section.
The traces of TNT in "pink water" and "yellow water"
should be recovered. It is possible to purify these streams
by treating the waste waterr with surfactant, thus forming a
precipitate with TNT which can easily be removed by filtration
(Okamota, _et al. 1979). The "pink water" resulting from TNT
spent acid recovery contains 15-118 kg/day of TNT for a
typical plant (Hudak and Parsons, 1977). In addition "pink
water" contains DNT which, by imporving the nitration process,
should be reduced to a tolerable level.
4.3.3 Finishing
In this process TNT is solidified on a water-cooled
flaker drum or belt and is then scrapped with a blade.
-------
The vaace streaa from che finishing process la mainly
waste from spillage, floor drainage, and washings from Che
finishing area.
The recovery of TNT from these vaste streams should be
considered If TNT appears In any large quantities in these
streams.
Table 4.2 is che summary of the pollution problems
associated with TKT production and suggested control alterna-
tives.
4.3.4 Recommended Areas for Pollution Control Research In
TNT Production
After evaluating the available literature, the following
areaa are recommended for further research by the study:
. Research on kinetics of the nitration reactions
which will permit alleviation of pollutants by
adoption of a low temperature danltration stage.
. Material balances to find the optimal design for the
fume recovery system in the nitration-separation
procesj.
. Recovery at TUT in the "pink water" by application
of f&sn seoarptlcn to an aqueous solution.
4.4 HirBOCEU.OT.OSE PRODUCTION
nitrocellulose (ST.) is the second largest product from
the military sector of the C.S. explosive industry, with a
1969-71 production level ox pearly .2,400 tens/month (Patterson,
-------
Table 4-1 Pollutanta and Control Ope Ion* In TNT Production
Procaia
Nitration
Purification
rtnlahlng
Pollutanta
CO, CO ,NO,KO
y A lin TMM
HjO, mjm
unaynnetrlcal
"hata" laoura
of TNT
"Yellow water"
acidic efflu-
ent trecea of
TUT
•Red «ater"
NaHO , Na.SO
nltrotoluenea
and nltrotolu-
•noa aulfurlc
acid
"Pink water"
DNT. TOT, all
pollutanta pre-
•ent In red
water
Spillage,
Sourcee in
proceaa
Nltratnr-
Beparator
Pune recovery
ayaten
PI ret water
waah
Selllte vaeh
Nitration fuaw
acrubber
dtecharge "led
water" concen-
tration
diatlUatea.
Plnleblng
operation
hard acrubber
UgHh down
effluent
Nature of
pollutant*
InorRanlc and
organic, gaaea
Inorganic and
organic g*aea
-
Inornanlc and
organic liquid
-
tnornanlc and
Organic liquids
Inorganic and
organic liquid
Pollutant control strategy
Low temperature dinltratloa
atage to reduce "r:ta'' Isoneri
and oildea of nitrogen and
carbon.
Change the dealfu- aa to
operate at eiastBii* TNT
prnttuetlon capaclt*
Removal of TNT from all
waate watare by application
of foa« aaparatloe. "Red water"
generation will be conaldarably
lower when "neta" laonera
forvatloa ie decreaeed.
-------
ec al. 1976). MC is Che fundamental ingredient used in the
production of all gun propellants and many rocket propellents.
Cellulose nononitrate, dlnitratc and trlnltrate have nitrogen
contents of 6.75, 11.11, and 14.4Z respectively, representing
progreosive replacements of the -OB groups in the cellulose
unit by ON02 groups. Typically there are three grades of NC;
proxylln, pyrocellulose, and guncotton with 8-12Z, 12.SZ, and
13Z minimum nitrogen content respectively. The preparation
of all grades of NC require the sane procedure with the excep-
tion of the acid nix used In thb nitration process (Mark, 1966).
Manufacturing of NC consist of two processes, nltratioa and
purification. An overall flow chart of NC production is
depicted in Figure 4.4.
4.4.1 Nitration
In this process, pre-purlfied pulp is added to a mixture of
nitric acid and sulfurlc acid In "dipping pots". Since the
nitration reaction is exothermic the vessel is cooled, the
operating temperatures vary from 30 to 34 C as veil as 37 to
40 C. In a continuous process approximately 68 to 70 kg/nln
of crude NC is produced.
The nitration is followed by centrlfuglng the crude NC
to remove spent nitrating acids. The wrung NC is then dumped
into "drowning tubs" filled with water to stop the reaction.
The nitrogen content of NC is held between 10. SZ to 13.8Z
nitrogen (Hudak and Parsons, 1977).
-------
4.17
H,S04OI
"_i
TO MIXED
ACID
'ARATIOT
("" ](°
1. t J l
CELLULOSE
nnic ACID
CIMLUirUTlOB
-£_
Y
PCHOTCATIOH
TO BECTCLE
OR
DISPOSAL
TO
PIOPELLAIIT
POWDUTIOB
Fipin 4.4. Plow Chart for MtreealluloM Production.
(Bud«k nd Panoiw. 1977).
-------
The pollutants emitted from the nitration process are 4.18
0.65g SO and l.OSg NO per kg NC from the reactor pots and J2.5g
SO and 14.Sg NO per kg NC from the acid concentrators. The NO
from the reactors and centrifuge are vented to an absorber where
N0x is oxidized and absorbed in the water generated weak nitric
acid. Most of the waste water from nitration process is due to
clean ups. Thus, waste waters may be expected to have a low pH,
relatively high levels of NO., and suspended solids.
Nitration of cellulose in the "dipping pots" can be formed
at 17 to 45°C (Miles, 1955), depending on the nature of the
desired product. Julian Linares (1966) carried out this
nitration at 29°C producing cellulose nitrate of 13.35Z N
content. Thus, it is evident that the nitration temperatures
are flexible and can result in an end-product of comparable
quality. The optimal operating temperature must be considered
for reduction of SO^ and NO^ emissions. Furthermore, the
possibility of converting the waste acid from the nitration
process to aulfuric acid must be considered. Such a process
involves the reaction of roasting gases containing SO. at
temperatures exceeding 250°C with the acid waste (mostly H.SO,
and HN03) and water spray to form sulfurlc acid
(Rensh and Jenthe, 1967). Absorption of NO from the acid
concentrator also may prove beneficial.
4.4.2 Purification
The purification of NC invloves five processes: boiling
tub house, beater house, poacher house, blender house, and
-------
final wringer house. In the boiling tub house, unstable
sul£ate esters and nitrates of partially oxidized cellulose
are destroyed by acid hydrolysis. In the beater house, the
HC is reduced to a physical state more amenable to purifica-
tion by Jordan beaters. In the poacher house the NC is
treated with soda ash and unpulped fibers are removed. The
function of the bleacher house is to sample and regulate the
quality of the final product. In the final wringer house,
the KC slurry is centrifuged to approximately 30Z moisture
content.
Due to large quantities of process water used during the
manufacturing of HC, the treatment and disposal of waste
water is a formidable problem. Presently, overflow from the
settling pits flows to the waste add neutralization facilities
where CaCO. is added to neutralize the acid. After neutralization,
the material is either discharged directly or transferred to
settling lagoons. Approximately 13.6 x 10 kg CaSO^ sludge
is generated yearly, as a result of waste acid neutralization,
at one NC production plant (Eudak and Parsons, 1977).
Vaste waters from the beater, poacher and blender houses
flew to another pit area where NC fines settle out. Effluent
from the pit is either recycled to the wash lines or is
discharged. The major portion of total suspended solids in
the waste water discharged, is NC fines. One source lists
-------
the following losses during NC purification (Jludak and 4-20
Parsons, 1977):
Boiling tub house 68.2 kg/day
Jordan beater house 295 kg/day
Poacher house 295 kg/day
Nitrocellulose fines lost during the boiling tub, Jordan
beater, and poacher house operations constitute inefficiencies
in NC Purification. NC fines can be recovered from waste
waters by simple filtration, thus reducing the suspended solid
content as well as improving the efficiency of the process.
It is perhaps, not possible to recycle all the water used
in the purification of NC, but it nay be possible to reduce
the volume of the waste water. For this purpose an In-de^th
study of NC purification is necessary. Such studies must
concentrate on methods of purification with minimum water
usage. Thus, an overall material balance of the purification
step will be useful.
Table 4.3 is a summary of the pollution problems
associated with NC production and suggested control
alternatives.
4.4.3 Recommended Areas for Pollution Control Research in
Nitrocellulose Production
After evaluating the available literature, the following
areas are recommended for further research by the study:
Better understanding of the kinetics of the
cellulose nitration will indicate methods of
-------
Table 4-1. Pollutant* and Control Option* In HC Production
Proceaa
Nitration
Purification
Pollutant*
SO., »,. HO,
suspended eolld
Waste acid
HMO,. «,»,
NC rtna*
Froceee uater,
acidic.
Source In
process
Raactore.
nitration
vessel.
Centrifuge
tolling Tub
houee
Jordan better
houae
poacher houaa
Mature of
pollutant
Inorganic gaaea
Mid solid.
IP. irganlc aclda
Organic, •uipended
•olida
Inorganic aclda
Pollutant Control Strategy
Improve reaction by te«peratura
adjuatncnt to reduce
generation of oildea.
Conversion to aulfurlc acid bjr
apraylng acid Haste by mter
In preaence of rotating gaaea
containing SO..
Reaoval by filtration from
waste atreaaa.
•eduction of process water.
-------
operation Co minimize NO and SO formation. 4.22
Better understanding of absorption of SO and
addition of an absorption Cower to the acid
concentrator to recover HO .
Research on filtration operations and filtration
units for effective recovery of NC fines from
boiling tub, Jordan beater and poacher houses.
Reexamlne and modify flow streams to optimize
water usage by recycle and other techniques la the
purification process.
-------
BIBLIOGRAPHY 4.23
Atroshchenko, V., Q al. Simulation of Process and Ammonia
Oxidation Reactor. E. A. Int. Congr. Chen. Eng. Chen.
Equip. Des.. Autom. 1979.
Dorf man, A.D., et al., Methods of Anmania OBcidation Control.
Artom. Khia. Proizvod. (Moscow), 1973.
Baas, R., _et al. Lov Temperature Proceas for TOT Manufacture
Part ji Pilot Plant Development. Industrial and Laboratory
NitraTion. ACS-Symposium Series 22, American Chemlcrl
Society pp. 272.
Hill, M., et al., Lov Temperature Process for TOT Manufacture
Part_! Laboratory Development. Industrial and Labora-
tory Nitration. ACS-Symposium Series 22, American
Chemical Society, 1976, pp. 253.
Hudak, C. and Parsons, T. Industrial Process :*rofiles for
Environmental Use; Chapter 12. The Explosive Industry.
EPA 600/277/023L, Feb. 1977.
Julien Linares, French Patent 87097 <19€5).
Klrk-Othner Encyclopedia of Chemical Technology. Vol. 8,
H.F. Hark, N.T., Wiley 1966.
Karzo, L. and Marzo, J. 'incentratlng Nitric Acid by
Surpassing an Azeotr^pe. Chemical Engineering.
Nov. 3, 1980.
Miles, F., Cellulose Sitrate. Mew York: Interscience
Publishers Inc. 1955.
Okamota, e£ al. Application of Foam Separation t£ Aqueous
Solutions of TNT. Part jl Removal of Organic Explosives
With Surfactant. Order no. AD-A066118, Avail. NTIS.
froaGcv. Rep. Annoce. Index (U.S.) 1979, 79 (15), 239.
Patterson, J.V., et al. St«te of the Art: Military Btploatves
end Propellanta Production Industry Vol. Ill Waste
Water Treatment. EPA/600/2-76/213C, Feb. 1976.
Rensh, Werner, Jenthe, Borst, Ger (East) Patent 58293
(1967).
-------
Smith, Norman, and Loclcyer, John, British Patent 1538198 4.24
(1979).
Zhidkov, B.(
-------
CHAPTER 5 5<1
IRON AMD STEEL INDUSTRY
5.1 INTRODUCTION
The manufacture of steel involves many processes Which
require large quantities of raw materials and other resources.
Due to the vide variety of products and processes, operations
vary from plant to plant. However, the steel industry can
be segregated into two major components; raw steel making, and,
forming and finishing operations. An overview of the iron and
steel process Is given in Figure 5.1 (U.S. EPA, Dec. 1980a).
la the first major process, coal is converted to coke.
dearly all active coke plants are by-product plants which
produce, in addition to coke, usable by-products such as
coke oven gas, coal tar, crude or refined light oils,
ammonium sulfate or anhydrous ammonia, and uapthalene.
Less than 1Z of domestic coke is produced in behive coke
making.
The coke from coke making operations is then supplied
to the blast furnace process where molten iron is produced.
In the blast furnaces, iron ore, limestone and coke are placed
into the top of the furnace and air is blown countercurrently
from the bottom. The combustion of coke provides heat which
produces metallurgical reactions. The limestone forms a
fluid slag which combines with unwanted Impurities in the ore.
Molten iron from <-.he bottom of the furnace and molten slag,
which floats on top of the irou, are periodically withdrawn.
-------
AIR
BEEHIVE | COAL F1KPS
OVEN
COKE
CMS
SINTER
VLANT
COKE
coo
OXYCEN
PUNT
SINTER
HOT
ICETAL
CAS
4
LinuiD
SLAG
COAt
CHEMICAL
SCRAf
STONj
IHO
iLECTHOpf S
COAL DISTILLATION
PRODUCTS
ELECTRIC i.
.. FURNACE LiqUID
TOSIP1 I STEEL
Sllfl
figure S.I. Overview of Iron aiut Steel Hanufactiirlag Proceaa
OXYGEN
BOP
SIAC
OPEN
DEARTH
I
LIQUID
STEEL
IHCOT2
Liquu
*STEE1.
CAST STEEL
INTERMEDIATES
riHlSHED
CAST STEEL
PRODUCTS
M
-------
The blast furnace flue gas. which has considerable heating 3*3
value, is cleaned and then burned in stoves to preheat the
incoming air blast to tbe furnace.
Steel is an alloy of iron containing less than 1Z
carbon. Steel making consists essentially of oxidizing
constituents (particularly carbon) at specified low levels,
and Chen adding various alloying elements according to the
grade of steel to be produced. The basic raw materials for
steel making are hot metal SV pig iron, steel scrap, lime-
stone, burned lime, dolomite, fluorspar, iron ores, and
iron-bearing materials such as pellets or mill scale. The
principle steel making processes in use today are the Basic
Oxygen Furnace (BOP), the Open Hearth (OH) Furnace, and,
the Electric Arc Furnace (EAF).
The hot forming (including continuous casting) and cold
finishing operations follow the steel making procesj. These
operations are so varied that simple classification and
description is difficult. In general, hut forming primary
mills reduce ingots to slabs or blooms and secondary hoc
forming mills reduce slabs or blooms to billets, plates,
etc. Steel finishing operations Involve a number of operations
that basically icpart desirable surface or mechanical
properties r.o the steel. Correct surface preparation is the
most Important requirement for satisfactory application of
protective coatings to the steel surface. The steeJ surface
must be cleaned at various production stages to Insure that
-------
the oxides which form on the surface are not worked into the 5.4
finished product. The pickling process, chemically removes
oxides and scale from the surface of the steel by the action
of Inorganic acids. This method ia the. most widely used due
to comparatively low operating costs and ease of operation.
Pickling win be the only finishing operation considered in
thi* report.
5.2 COKE MAKING
Figure 5.2 provides a flow diagram of a coke plant, the
processes required include:
1. Coal Mining and Transportation
2. Coal Preparation
3. Charging of Coal
A. Coking
5. Pushing and Quenching
6. Coke Handling and Tar Condensation
Coal dust is emitted during size reduction and trans-
portation of the coal. Emissions are estimated to be 5 kg/yr/tor
of coal. Particles are generally less than 0.1 ma In size with
suspended fractlone in the range of 1 to 10 u (Barnes, et al.
1970). The wastewaters produced from coal preparation may
contain up to 200 g/1 of suspended particles (28 mesh to
colloidal dimensions) and most can be eliminated by thickener/,
cyclones and filters (Keystone Coal Industry Manual, 1974).
Some trace elements contained in the wastovater include arsenic,
cadmium and lead.
-------
3.3
111
MINING
AMD
TMRSFORTATIOM
11
HATH
COM.
nCPAAATIO*
AIR
FUEL
HATER
BEMI7ACTED
COAL.
COAL CHARGING
TO OVEN
COXINC
con
PUSHING ARD
WET QUEHCHING
con
HAHDLIHG
COU OVER CAS POR
^BT-PRODUCT RECOVERY
AND COMBUSTION
11 I
T
t
CASEOUS HASTES
LIQUID HASTES
SOLID UASTSS
COKE TO BLAST FUMUCE
Figure S.2. Cok« (taking
-------
Coke is the residue Croa Che deacruccive disCillaclon of 5.6
cool. Coal is heaced in the coke ovens (with no air in the
oven) by adjacent chambers or flues using; 1) some of the
gas recovered from coking operations, 2) cleaned blast
furnace gas, or, 3) a mixture of coke oven and blast furnace
gases. During carbonization about 2QZ to 3SZ by weight of
the initial coal charge is evolved as mixed gases and vapors
which are collected through an opening at the cop of the oven.
Froa one ton of coke about 544-636 kg blast furnace coke,
45-91 kg coke breeze, 270-325 m coke oven gas, 30-45 kg tar,
9-13 kg (NBA)^S04, 54-312 kg ammonia liquor and 9-15 kg light oil
are produced (Keystone Coal Industry Manual, 1974).
Potentially hazardous emissions trom a coke plant Include
CO, amines, organometallies, tar and soot, carbonyls, hydrogen
cyanide, sulfur compounds, etc. (Cavanaugh, et al. 1974).
The use of refined or cleaned coal as a raw material and
better knowledge of coking reactions can eliminate or reduce
some of these pollutants.
Most of the participates generated in hot coke quenching
operations are collected and reused within the plant and do
not constitute a significant pollution problem. However,
wastevaters from wet coke quenching operations contain high
concentrations of ammonia, oil and grease, and phenol (all
of the three exert a biochemical oxygen demand), plus cyanide,
sulfide and suspended solids. Table 5.1 gives an analysis
of quench wastewater samples (U.S. EPA, Feb. 1977).
-------
TABLE 5.1 AVERAGE ANALYSIS OF QUENCH WATER SAMPLES 5'7
Contaminants
Phenols
Sulfates
Chlorides
Total Ammonia
Cyanides
Total Solida
Concentration
(pen)
776
1,066
1,954
2,517
98
5,214
Some of the treatment technologies used for control of
nnllutlon from the quench waters are (U.S. EPA, Jan. 1974):
1. Distillation With Ammonia Recovery of Waste
Ammonia Liquor
2. Alkaline Ammonia Stripping
3. Neutralization
4. Settling
5. Air Flotation
6. Clarification With Vacuum Filtration of Sludge
7. Filtration
8. Carbon Adsorption
Conversion of hot coke quenching from the vet to the dry
process would: 1} eliminate air and wastewater emissions from
the wet quenching process, 2) provide additional potential
for participate emission since control of these emissions
-------
are pare of the the dry quenching design (U.S. EPA, July 1976). 5.8
Pollution control costs are not significant for the dry
process. The hoc quench gases can be cooled recovering
useful energy. Capital and operating costs are significantly
higher than vet quenching operations by up to 10.7 dollars
per ton of coke. Dry coke quenching is claimed to produce
a higher-grade coke by Russian authors, thus reducing the
coke rate in the blast furnace. However, this claim needs
to be demonstrated for U.S. coals.
A detailed description of the dry coke quenching process
is given in "Environmental Considerations of Selected Energy
Conserving Manufacturing Process Options." In dry quenching
of coke, the hot coke pushed from the ovens is cooled in a
closed system. Dry quenching uses "inert" gases to extract
heat from the incandescent coke by direct contact. The heat
is then recovered in waste heat boilers or by other techniques.
The "inert" gases can be generated from an initial intake of
air which reacts with the hot coke to form a quenching gas
containing 14.SZ C02> 0.4Z 02> 10.6Z CO, 2Z Hj and 72.5Z Nj.
After cooling, the gases pass through two dust recovery
cyclones (where participates are collected at -400-600 Ib/hr.)
before being recycled. The partlculates consist mainly of
carbon dust and is bunt as solid fuel. Part of the gases
after participate removal may be sent for removal of evaporated
cyanides and SO , to prevent accumulation. Additional
research is needed to study the applicability of dry quenching
-------
of U.S. cools and the cleaning of recycle gases using systems 5.9
similar to those used in by-product coke recovery operations,
as discussed below.
5.3 COKE BY-PRODUCT RECOVERY
Figure 5.3 shows the various coke by-product recovery
operations (U.S. EPA, Feb. 1977).
The condensace from the cooled coke oven gases contains
tar and ammonia liquor which are decanted. The uncondensed
gases are reheated and passed on to the ammonia scrubber.
Some of the tar derivatives recovered Include creosote oil,
cresols, naphthalene, phenol and medium and hard pitch.
Phenol is recovered from the weak ammonia liquor by scrubbing
with benzene or light oil. The phenollzed benzene or light
oil is contacted with caustic soda to extract sodium pheno-
late. The sodium phenolate is neutralized with CO. to
liberate crude phenols.
The weak ammonia liquor is heated to remove "free"
ammonia and is then contacted with Ca(OH). solution to
remove and strip HH_ as vapor. These vapor* are sent to the
ammonia absorption process. The waste liquor generated In
the ammonia still contains 0.75 of sulfide as 3.3. The
total amount of waste produced ranges between 80-340 tons of
coal carbonized. These wastes may contain up to 20Z by
volume of Ca(OB)2 (U.S. EPA, Feb. 2977). It is suggested
that Ca(OH)2 be recovered from the waste liquids and
recycled to the ammonia still.
-------
COKE
f
ABSORPTION
SULFUR1C
SODIUM PHESOLATE
I3 RECOVLRED
FROM STILL
CRYSTALLIZA-
TION AND
DRYING
WATER IN
0 a
LIGHT OIL
RECOVERY
H
'HATER OUT
H OIL —
EC1RCULATED
it
FRACT10NATIOI
AND
RECOVERY
0 CASEOUS
1 HASTES
I
SOLID
HASTES
FIGURE 5.3. Coke By-ProductB Recovery (U.S. EPA. Feb. 1977).
-------
Ammonia vapors from the primary cooling and heating opera- 5.11
tions and the ammonia still are absorbed in a dll. HjSO^
solution, the (NH^SO^ product is crystallized from the
resulting slurry. Gases leaving the ammonia absorber are
scrubbed with recycled wash oil to remove light oil. The
light oil is refined to produce benzene, toluene and xylene.
The uncondensed "coke oven gases" are sent to a gas holder
and contain mainly CO., CO, N.,^, 0. and H.S. The composi-
tions are given in Table 5.2.
TABLE 5.2. COKE OVEN GASES (AFTER BY-PRODUCT RECOVERY)
(Ess, 1948; Wilson, et al. 1980)
Component
co2
CO
H2
N2
0,
2
H,S
2
It is suggested that H.
Kg/ton of Coal
10.42
31.54
13.66
3.85
7.17
3.25
,S be removed prior to ammonia
absorption using the Glaus or Stretford process (Dunlap, et
al. 1973).
One of the major pollutants from light oil recovery Is
cyanide (Alien, 1979). HCN contained in the gas leaving the
cooling tower at one site amounted to 0.56 Ib/ton of coke.
-------
It is suggested that cyanide be removed by adsorption or other
suitable methods. About the same amount of cyanide is expected
to be in the cooler wastewaters. Biological systems followed by
nutrient addition In the form of phosphoric acid have been
reported to produce a reduction of cyanide of up to 95Z
(Hofstein and Kohlmann, 1980).
5.4 IRON MAKING
Blast furnaces are large cylindrical structures in
which molten iron is produced by the reduction of the iron
bearing ores with coke and limes rone. Reduction is promoted
by blowing heaeed air Into the lower part of the furnace.
As the raw materials melt and decrease in volume, the entire
mass of the furnace charge descends. Additional raw materials
are added (charged) at the top of the lurnace to keep the
amount of raw materials within the furnace at a constant
level.
Iron oxides react with the hot CO from the burning coke,
and the limestone reacts with Impurities in the Iron ore and
coke to form molten slag. These reactions start at the top
of the furnace and proceed to completion as the charge passes
to the bottom of the furnace. The molten slag, which floats
on top of the molten iron, is drawn off (tapped) by way of
a "tapping hole." Blast furnace operations within the U.S.
produce greater than 99% of the basic iron. The total rated
capacity of all U.S. plants is 321,8.'»7 tons/day.
-------
Ti-e ^ases which are produced In the furnace are exhausted 5.13
through the top of the furnace. These gases are cleaned,
cooled, and then burned to preheat the incoming air to the
furnace. Generally, gas cleaning involves the removal of
the larger participates by a dry dust collector, followed by
a variety of wet scrubbers for finer particle removal. Many
of the same pollutants found in coke plant wastewaters are
also found in iron making wastewaters. The phenolic pollu-
tants found In iron making wastewaters are attributable to' the
coke used in the iron making process. Cyanide and ammonia
(reaction products formed within the furnace or transferred
from the coke charge to the furnace gases) are carried over
with the gas stream and transferred to scrubbing waters.
Table 5.3 lists some of the pollutants in these scrubbing
waters (U.S. EPA, Dec. 1980b).
TABLE 5.3. ANALYSIS OF BLAST FURNACE SCRUBBER WASTEWATERS
FLOW RATE. GALLON/TON IRON 2057
Pollutant Concentration
mg/1
63.2
Cyanide 16.9
Phenols 2.77
Flouride 23
Suspended Solids 693
pB 7.1 - 8.3
-------
The cleaned gases are then cooled with direct contact sprays 5.14
In large gas cooling vessels before being burned.
About 901 of the present blast furnace wastewater
treatment systems include recycle (after thickening) and
discharge only about 52 to 10Z of the process flow. The
dewatered solids from thickener are either sent to the sintering
operations or to off-site disposal. These solids contain
Zn, Ag, Ni, Cu, Pb, etc. The effluent concentrations are
listed in Table 5.4.
TABLE 5.4. WAGTEWATER THICKENER UNDERFLOW (U.S. EPA. DEC. 1980b)
FLOW RATE 87 GALLONS/TON IRON
Pollutant
Cu
Pb
Nl
Ag
Zn
Concentration
mg/1
0.19
2.11
0.10
0.023
27.5
It is suggested that the gas cleaning system be modified to
use few and if possible no wet scrubbers. For fine particle
collection the possibility of using electrostatic filters or
magnetic filters should be studied. The cleaned gases are
generally cooled in spray towers (before being burnt) thus
-------
producing more vascevaters. Inscead It is suggested that 1) 5.15
cleaned gases be burnt directly, or 2) be cooled by heat ex-
change with air fesd to the blast furnace and then burnt.
It was suggested for the coke by-product recovery process
that organic compounds be removed by adsorption on activated
carbon. Similar systems are proposed for removal of organlcs
from the blast furnace wastewaters. The use of biological
oxidation and alkaline chlorinatlon systems for treatment of
these wastewaters to remove HCN is also suggested.
Hofstein and Kohlman (1979) report that one of the non-
11. S. plants they visited uses Caros Acid (per-monosulfurlc
acid - H.SOe) to reduce cyanide and phenol levels in the
blast furnace wastewaters to 0.2 mg/1 HCN and 0.5 mg/1
phenol. The normal influent level of phenol at that plant
was 2 mg/1. The addition of polyphosphate in the cooling
towers had been reported to aid in CM removal but at CN
levels above 10 mg/1 it was not effective. Another plant
theorized, based on operating experience, that the formation
oS metallo-cyanlde complexes adsorbed in the sludge reduced
cyanide levels from 0.2 mg/1 to 0.1 mg/1. Another plant in
West Germany uses aeration prior to discharge to the clari-
fiers as an Integral part of the gas cleaning water recircu-
lation system. The purpose of aeration is to strip CO and C02
from the water and to precipitate CaCO.. A portion of the
clarifler sludge is recycled to act as a seed and enhance
precipitation and sedimentation.
-------
Osantowski and Gienopolos (1979) obtained pilot plan1: 5.16
data on the applicability of advanced waste treatment methods
for upgrading blase furnace wastewaters. The treatment
methods investigated included: alkaline chlcrination, clarifi-
cation, filtration (dual media and magnetic), ozonation,
activated carbon and reverse osmosis. Alkaline chlorination
consisted of elevating the pB of the oncoming vastevaters to
11.0-11.5 with addition of sodium hypocblorlte for oxidation
of cyanide; followed by neutralization for ammonia removal.
The settled effluent was dechlorlnated by activated carbon.
These studies showed that above a C12:UH3 ratio of 7.3:1,
NH. levels dropped sharply to as low as 0.48 mg/L, NB3 removal
was high and all other ozidizable contaminants were also rencved.
Further research is needed to optiolze the CljtN^ ratio to
obtain the best ammonia removal. Ozonation was determined to
be effective in meeting discharge levels. Prefiltered waste-
water was elevated to a pH of 10.5 prior to ozonation. The ozone
dosage varied from 0-1, 500 mg/1 of wastewater treated and
contact times from 60-240 minutes. NH, and cyanide levels of
3.1 and 0.001 mg/1 were achieved. Research is required to
find the optimal pB and contact time.
Metals in the raw wastewaters may be better removed by
sulfide precipitation. The use of excess sulfide in a treated
effluent may cause an objectionable odor problem. A decrease
in pH might affect personnel If the wasteweter becomes acidic.
In view of these objections, a ferrous sulfide slurry may be
-------
• good choice since it does not dissociate readily, thus,
controlling the pressence of excess sulfide. To this date,
there are no furnace vastevater systems currently using
sulfide precipitation (U.S. EPA, Dec.l980b), even though this
technology has been demonstrated in the metal finishing
industry. Zt is suggested that applicability of sulfide
precipitation to remove metals from blast furnace vastevaters
be investigated.
There are two types of dust materials collected from the
blast furnace operations; 1) dry-collected dusts are ob-
tained from cyclone dust collectors, and , 2) vet-collected
dusts are obtained from vet scrubbers after reducing the
vater content by thickners and filters. The bulk of this
material Is used as landfill even though some is utilised
In the sintering operations. Coke, pellet, and BOP slag
fragments are the predominant components of the dry dust
materials and include significant quantities of hematite,
magnetite, graphite, calcium carbonate, vusite and silica.
The size distribution of these dusts ranges from 2.3 mm
to 0.014 mm. Vet-collected dusts are similar to dry-
collected dusts and average 24Z by velght Fe and 451 by
weight C, with about 68Z of the material less than 60.5 pn
in size. The high and variable carbon content of this
material makes it difficult to use in the sintering operations.
Furthermore, the high amounts of zinc in the vet-collected
-------
dusts can impede Che blast furnace operations if recycled. 5.18
A briquetting method for dezlncing these dusts has been de-
veloped (Allen, 1979). Typical analysis of salable cine
oxide dust is 63.31 Zn, 6.9Z Pb, and 1.2Z Fe. Another possible
alternative dezincing process may be extracting the zinc from
collected dusts.
The Waelz process is a direct reduction technique that
has been used for 20 years to refine low grade zinc ores.
The Berzelium and Lurgi companies conducted a large scale
experiment in Dinsburg, Germany that used iron and steel
material dusts (Rausch and Serbert, 1948). They observed
that dezlncificatlon vaa possible with a continuous process,
9SZ of the zinc and SOZ of the alkalis were removed and 95Z
of iron was metallized. This process was found to operate
more economically on a lover throughput (10 tons/year) than
other direct reduction processes (U.S. EPA, April 1979) and it
Is less sophisticated since it does not require peUetizing
before reduction.
Advances in technologies such as auxiliary fuel injection,
higher hot blast temperatures, moisture injection, and oxygen
enrichment have been major factors in increasing the effi-
ciency of the blast furnace process. Based on a statistical
analysis technique of certain operating parameters, Quigley
and Sayles (1974) concluded that as the coke stability is
improved by increasing bulk density and coking time, and
Improving coal grinding. They also found that an Increase
-------
of l.SZ in ash content of the coke resulted in over 50Z off- 5.19
quality iron over a two day period. Thus, a study aimed at
improving blast furnace performance by improving the coking
process is suggested.
Slags from the blast furnace usually come into contact
with water immediately after their removal from the blast
furnace. The reaction between slag and water produces E^S
and SO. among other gases, which even though small in quantity
can cause odor problems. Knowledge on the mechanism of HjS
and SO, formation is limiting. It Is believed that SOj result?
primarily from the oxidation of HjS. It is desirable to
suppress the formation of sulfurous gases, primarily HjS. In
laboratory experiments Kaplan and Rengstroff (1973) showed
that treatment of the slag with the oxidizing materials Fe2°3*
CO., CaCO., open-hearth slag or steam decreased the emission
of H.S. In-plant trials where commercial batches of blast
furnace slag was treated with steam prior to water quenching
the hot solid slag and molten slag, the steam treatment resulted
in an Increase in the emission of E^S.
One important process modification then, would be, to
optimize slag quenching methods to decrease H-S emissions.
This would require a better understanding of H^S and S02
formation during slag quenching and the effect of various
additives.
-------
Another option is to produce elemental sulfur from B.S 5.2''
by Che Claus or Stretford Process. If BCN is found to cause
fouling of the Claus catalyst beds or decrease the life of
Stretford absorption solution, ECU may have to be removed
from the feed gases by the polysulflde process which is
known to have removal effJciences of up to 90% of HCN (Hill,
1945).
Cyanides are thought to form in the blast furnace
according to the following reaction:
K20 + 3C + H2 * 2KCN •«• CO (5.1)
This reaction is favored at high temperatures and in the
absence of CO. The oxidation of cyanides takes place accord-
Ing to the following reaction:
2KCN + 4C02 ? K2C03 + NZ + 5CO (5.2)
It would appear that conditions favorable for the formation
of cyanides, i.e., Che coexistence of coke, alkali oxides,
and N. at high temperatures and in a reducing atmosphere are
Inherent in the operation of the iron blast furnace. In
contrast. It may be possible, at least in principle, to
modify the conditions In the stack region, so that oxidation
of cyanides is promoted. Very little work has jeen done,
however, on the kinetics of the reactions in the formation
and oxidation of cyanides In the blast furnace. Sohn and
Szekely (1943) assumed mass transfer to the KCN particle to
-------
be race controlling and concluded Chat there may be a real 5.21
possibility of reducing the net emission of cyanides from the blast
furnace by the appropriate manipulation of the temperature
and CO/CO, profiles within the stack. It is suggested that
research efforts be directed at obtaining kinetic information
on the formation and oxidation of cyanides In the blast furnace
and at optimizing stack design and operation to reduce the total
cYanJue in the effluent gases.
5.5 STEEL MAKING
Steel is an alloy of iron containing less than l.OZ carbon.
Steel making is basically a process in which carbon, silicon,
phosphorous, manganese, and other impurities present in the
raw hot metal or steel scrap, are oxidized to specific mini-
mum levels. The hot steel is then either teemed into ingots
or transferred to a continuous casting or pressure casting
operation for direct conversion into a semi-finished product.
The basic raw materials for the stee?. making processes
are hot metal or pig iron, steel scrap, limestone, burned
lime, dolomite, fluorspar, iron ores and iron bearing minerals
such as nellets, mill scale and waste solids from the lurnaces.
Various types of steel are manufactured by adding alloying
agents either to the hot charge in the furnace or to the
ladle of steel after the hot steel is "tapped" from the
furnace. The three types of steel making processes are:
1. Basic Oxygen Furnace (BOF)
-------
2. Open Hearth Furnace (OH)
3. Electric Arc Furnace (EAF),
A comprehensive discussion of the various operations that
constitute each of these processes is given by McGannon (1964).
The large quantities of airborne gases, dusts, smoke,
and iron oxide fumes generated in the steel making processes
are collected and contained by various gas cleaning systems.
Depending on the type of gas cleaning system used, waste-
waters discharges or sludge generation can result. The
basic gas treatment systems used are:
BOF Semi-wet
Wet-Suppressed Combustion
Wet-Open Combustion
Semi-vet
OH Wet
EAF Semi-wet
Wet
The semi-wet air pollution control systems use water to part-
ially cool and condition the waste gases and fumes prior to
final particulate removal in dry collectors such as precipi-
tators or baghouses. Wet air pollution control systems use
water not only to cool the waste gases but also to scrub the
fume particles from the waste gases. BOF uses combustion
systems, suppressed or open, to control CO emissions.
-------
The two variations of the BOF process are the Ka\do pro- 5.23
cess and the Q-BOP furnace. At present, there is only one
Kaldo installation and only three Q-BOF installations in the
United States. The waste products from the BOF steel making
process include airborne fluxes, slag, carbon monoxide and
dioxide, and oxides of iron (FeO, ^2°3' Fe3°4^ «**-tted as
submicron dust. Also, when hot metal (iron) is poured into
ladles or the furnace, submicron iron oxide fumes are released
and some of the carbon in the iron is precipitated as
graphite, commonly called "kish". Approximately 1Z to 2Z
of the ingot steel is ejected as dust. The primary gas
constituent emitted from the BOF during the oxygen blowing
cycle is CO. CO will burn outside of the BOF, if allowed to
come in contact with outside air (open combustion). If
outside air is prevented from coming in contact with the CO
gas, combustion Is retarded (suppressed combustion).
In the Open Hearth (OH) process, steel is produced in
a shallow rectangular refractory basin, or hearth, enclosed
by refractory lined walls and roof. OH furnaces can use
all scrap steel charge; however, a SOZ scrap/SOZ hot metal
charge is typical. Fuel oil, coke oven gas, natural gas etc.
are burned as fuel and the hot gases are circulated above
the raw material charge. The waste gases are water cooled,
scrubbed with recycled water and sent through a electrostatic
precipltatir before being vented. The waste products resulting
from the OH process are slag, iron oxides as submicroa dust,
-------
waste gases (consisting of air, C02 and water vapor), SO^ and 5.24
NO (due to the nature of certain fuels being burned) and
oxides of zinc.
The Electric Arc Furnace (EA?) steel making process pro-
duces high quality alloy steels in refractory lined cylindri-
cal furn&ces using a cold steel scrap charge and fluxes. The
waste products from EAF process are smoke, slag, CO. CO., metal
oxides (mainly iron) emitted as submicron particles and zinc
oxides.
Raw wastewater characteristics are given in Table 5.5
(U.S. EPA, Dec. 1980b).
TABLE 5.5. RAW WASTEWATERS FROM STEEL MAKING OPERATIONS
CONCENTRATION (mg/1)
I. Basic Oxygen Furnace
a. Semi-wet (Flrvrate - 429 gal/ton)
Suspended Solids 345.0
Cu 0.004
Pb 1.5
Zn 1.0
b. Wet-Suppressed Combustion (Flowrate •
982 gal/ton
Suspended Solids 1500.0
Cr 0.5
Cu 0.25
Pb 15.0
Ni 0.5
Zn 5.0
-------
TA2LE 5.5. Continued 5.25
c. Wet-Open Combustion (Flowrate -
446 gal/ton)
Suspended Solids 4200.0
Cd 0.5
Cr 5.0
Pb 1.0
Zn 5.0
XI. Open Hearth Furnace
a. Semi-Wet (Flowrate - 1163 gal/ton)
Suspended Solids 500.0
Cr 0.8
Cu 0.8
Cyanide 0.04
Zn 0.5
b. Wet (Flowrate - 554 gal/ton)
Suspended Solids 1100.0
Cu 2.0
Pb 0.6
Zn 200.0
III. Electric Arc Furnace
a. Semi-Wet (Flowrate - 60.4 gal/ton)
Suspended Solids 2200.0
Cu 2.0
Pb 30.0
Zn 125.0
-------
TABLE 5.5. Continued 5.26
III. Electric Arc Furnace ".ont'd
b. Wet (Flcwrate - 3060 gal/ton
Suspended Solids 3400.0
Arsenic 2.0
Cd 4.0
Cr 5.0
Cu 2.0
Pb 30.0
Zn 125.0
The zreatmenc methods presently used do not attempt to
remove these toxic metals exclusively (U.S. EPA, Dec. 1980b).
Sulfide precipitation to enhance the precipitation of metals from
wastevaters before recycle is a suggested pollution control
approach. There is a need to develop extraction and ion
exchange systems to remove toxic metals formed in the steel
furnace wastevaters.
Suspended solids in steel making wastevaters are very
fine, red in color, and are principally iron oxide. Magnetic
separation can decrease the level of suspended solids to
25-30 mg/1 (Centl, 1973).
-------
5.6 ACID PICKLING 5'2?
Acid pickling is the sceel finishing process In which
steel products are immersed in heated acid solutions to re-
move surface scale. Based on the type of pickling acid used,
this process can be subdivided into:
1. Selfuric Acid Pickling
2. Hydrochloric Acid Pickling
3. Combination Acid Pickling
Wastewaters are generated by three sources in the pick-
ling process. The largest source is the rlnsewatcr used to
clean the acid solution from the product after it has been
immersed in the pickling solution. The second source is the
spent pickling acid liquor which is used to treat the steel
product. The spent pickle liquor is a small volume waste,
containing high concentrations of iron and toxic metal
pollutants. Vastewater from the wet acid fume scrubbers is
the third source.
Rinse water discharge flows can be minimized with a
cascade of countercurrent rinse systems. These systems
reduce water flow, concentrate the pollutants In the last
rinsing chamber, and achieve more thorough rinsing (D.S. EPA,
Dec. 1980c).
The most common method of recovering spent sulfuric acid
is acid recovery by removing ferrous sulfate through crystal-
lization and rinsing the concentrated acid (U.S. EPA, Dec. 1980c).
-------
The spent liquor from hydrochloric acid pickling contains free 5.28
hydrochloric acid, ferrous chloride, and water. This liquor
is heated to 1,050°C, at this temperature the water is complete-
ly evaporated and Fed. decomposes completely into Fe.O. and
HC1 gas. The iron oxide is separated and removed and HC1
gas is.reabscrbed in the water.
Recycle systems, with recycle rates as high as 90Z-95Z
of the total wastewater flow are used to control pollutants
ger.srated during the scrubbing of acid fumes. Recycle rates
are limited by the build-up of solids. Lime and sulfide
precipitation are suggested to Improve precipitation of
metals in the wastewaters.
Temperature and agitation are Important operating factors
in the pickling process. The temperature of pickling drama-
tically effects the reaction rate. Agitation is probably
the most ignored aid to good pickling. The speed of pickling
can be increased significantly by properly agitating the acid
bath cr using the steel product during the pickling opera-
tion. One method of agitation is an air-operated, mechanical
agitation system. An added benefit of this system is that
the evaporation caused by air agitation concentrates, rather
than dilutes, the acid bath. It is suggested that process
improvements be aimed at decreasing pickling time and main-
taining good agitation and high enough acid concentration
levels during pickling.
-------
Table 5.6 lists the various process modifications 3ug- 5.29
gested for control of pollution from the iron and steel industry.
5.7 RECOMMENDED AREAS FOR PROCESS MODIFICATIONS RESEARCH
After careful evaluation of the available literature, the
following areas are recommended for further research:
Use of refined or cleaned coal in coke making
Study of the formation of cyanides and carbonyls
during coking in order to prevent or reduce
pollutant formation.
. Dry coke quenching of U.S. Coals to eliminate
quench water contamination.
The effect of process variables such as coal
grinding and coking time on coke produced. This
would be used to improve the quality of coke
stability in order to enhance blast furnace
performance.
Development of biological oxidation systems to
remove HCN from by-product coke making vastewaters.
. Absorption of H.S from coke oven gases by Glaus
or Stretford process.
. Development of better CN removal systems from
blast furnace vastewaters by using additives
such as Caros acid (HjSO.) and polyphosphate,
and by aeration.
-------
Table 5-6. Pollutants and Suggested Control Strategy Iron and Steel Industry
Pri-cesa
Coke
Making
Coke
By-Prnduct
Reciwery
Iron
Making
Pollutant
OrganoBatalllcs,
Carbonyls,
HCM. SO^. H2S
Phenols, Sulfatee,
Chlorides, Aononla,
Cyanides
H,S
HCH
Metals
(Zn. Pb. etc.)
Source In Process
Enlaslons froa
coke ovens
Uastewatera froa
coke quenching
Coke oven gases
having by-product
recovery
Cooler Uastewsters
Blast Furnece
wastewsters
Nature of Pollutant
Toxic gases
Dissolved and
suspended solids
Suspended
solids
Pollutant Control
Strstegy
Use of refined
coal, better control
of coking operations.
C -version to dry
coke quenching with
psrtlcalste removal
Removal of H.S by
Claus or StrCtford
Process
Removal of KCH
by biological
oxidation syateos
Conversion irom
wet to dry gas
cleaning aystcBs -
electrostatic.
•agnetic filter*
-------
Table 1-6. Pollutant* aad SuMeeled Control Siraief, for Iron and Steal laduatry (Conl'd)
Proceaa
Iron
Naktnf
Pollutant
C]TMld*
Hoc
"2S- W*
CyMldm
Sourca la Froc**«
•!••( Pur»*c«
lta*t«Mt«r*
•IMI rar«*t«
Oust*
Blast PurMc*
•!•• O"*"11!"*
BUit Vunac*
•aiur* of Pollniut
Inorganic (••••
laoriaatc
patilculatta
rollutanl Control
Strategy
OptlaJtatlon al pa
lad contact lla» to
laprova alkalloo
chlorlnalloo. ua«
of addltlraa aucn M
HjSO. aod B«t])pho«phalae
3ol*mt ••traction
ol.In or t«oa«al by
Ualai proeaaa. racket*
treated dual a to
alnterlna, plant
uao of addillvaa to
••prove oaldalloa of
V
Improved atack de»l|»
and opera! loo to
opllBlia oildalloo of
cyenloae
-------
Table V6. Pollutant* and Suggeeted Control Stratopy for Iron and Staal laduatry (Coat'd)
Procaaa
Staal
Acid
Pickling
Pollutant
Zn. Cr. Pb. Co.
Iron oilda
Spant Plckl*
Liquor (S?L)
•Inaa Hatara
Source In Procaaa
Waatavatara froa cooling
and conditioning of
gaaaa from •(••! auklng
.__-._
product aftar pickling
Nature of Pollutant
Suapended. diaaolvad
aollda
Inorganic aclda.
auepended toalc
etetele. Iron
Inorganic acid*.
•ucpendad toilc
Belale. Iron
Pollutant Control
Stracagy
Sulflda precipitation
of loilc oalala 4
recycle of treated
uaatavatara m*gn«ilc
eeperecloa ef H'lneadet
Iron aildaa.
•olvaut aa tract Ion of
Improved plckllne
procaaa by temperature
control and good
agitation to dacraaaa
SPL. recovery of acid
Hlnlnlilng rlnaauater
dlachargea by uilng
caacada or counter-
currant rlnee eyetaaa
10
-------
Optimization of pH acd contact tine to improve 5.33
Alkaline chlorination and ozonation to upgrade
blast furnace vasteuaters.
Solvent extraction of Zinc or derinciflcatlon by
ttalez process to remove zinc from blast furnace
duata. Such zinc removal can facilitate the use
of treated duats in the sintering process.
Study of kinetics of B.S and SO^ formation during
blast furnace slag quenching to develop methods by
which ELS formation can be decreased.
Study the kinetics of formation and oxidation of
cyanides in the blast furnace to optimize the
design and operation of the stack in order to
oxidize the cyanide.
Development of solvent extraction and sulfide
precipitation methods to remove toxic metals from
the recycled steel plant vastevaters.
Study the effect of temperature and agitation
in order to optimize pickling operations.
-------
BIBLIOGRAPHY 5.34
Allen, E.J. International Mineral Recovery T.td. Dezinclng
Process. Proc. of Che First Symp. on Iron and Steel
Pollution Abatement Technology, Chicago (1979),
EPA-600/9-80-12, PB80-146258.
Allen, G.C., Jr. Environmental Assessment of Coke By
Product Recovery Plant. Proc. of the First Symp.
on Iron and Steel Pollution Abatement Technology,
Chicago. (1979), EPA-600/9-80-012, PB 80-176258.
Barnes, T.M., j£jil. Evaluation of Process Alternatives
to Improve Control of Air Pollutioi from Production
of Coke. Battelle Memorial Institute, Columbus, OH,
Jan. 1970.
Cavanaugh, et al. Potentially Hazardous Emissions from
the Extraction and Processing of Coal and Oil, EPA-
650/2-75-038. April. 1974.
Centi, T.J. A Survey of Wastevater Treatment Techniques
for Steel Mill Effluents, in "The Steel Industry and
The Environment", ed. by, Szekely, J., Marcel Delcker,
Inc., New York, (1973).
Dunlap, R.W., e£ al. Desulfurization of Coke Oven Gas;
Technology, Economics and Regulation Activity, in "The
Steel Industry and The Environment", Szekely, J., (ed.);
Marcel Delcker, Inc., New Tork, (1973).
Ess, T.J. The Modern Coke Plant. Iron and Steel Engineer,
C3-C36, Jan. 1948.
Hill, W. Recovery of Ammonia. Cyanogen. Pyridine. and
other Nitrogenous Compounds from Industrial Gases.
in "Chemistry of Coal Utilization, Vol. II", ed. by,
Lowry, H.H.; Wiley, New York, (1945).
Hofstein, R. and Kohlmann, H.J. Study of Non-U.S. Waste-
water Treatment Technology at Blast Furnace and
Coke Plants. Proc. of the First Symp. on Iron and
Steel Pollution Abatement Technology, Chicago, (1979),
EP4-600/9-80-012, PB 80-176258.
-------
Kaplan, R.S. and Rcngstroff, G.U.P. Emission of Sulfuroua 5.35
Gases from Blast Furnace Slags. In "The Steel Industry
and Che Environment, ed. by Szekely, J.; Marcel Dekker,
Inc., New York, (1973).
Keystone Coal Industry Manual. Mining Information Services
of the McGraw Hill Publishing, 1974.
McGannon, E.H., The Making. Shaping, and Treating of Steel.
United States Steel Corporation, Eighth ed., 1964),
Pittsburgh, Pa.
Osantowski, R. and Geinopolos, A. Physical-Chemical Treat-
ment of_ Steel Plant Wastewaters Using Mobile Plant
UnitTs. Proc. of the First Symp. on Iron and Steel
Pollution Abatement Technology, Chicago, (1979),
ET-A-60079-80-012, PB80-176258.
Qulgley, J.J. and Sayles, N. An Analysis of the Effect
of Coke Characteristics and Other Operating Variables
Upon Blast Furnace Performance. 33rd Iron Making
Conference Proc., Vol. 33, Atlantic City Meeting,
April 28 - May 1, (1974).
Rausch, H. and Serbert, H. Benefaction of_ Steel Plant
Waste Oxides by_ Rotary Kiln Processes. Paper
Presented at Sixth Mineral Waste Utilization Symp.,
Chicago, May 2-3 (1948).
Sohn, H.Y. and Szekely, J. On the Oxidation of Cyanides
in the Stack Region £f_ the Blast Furnace, ed. by,
Szekely, J., Marcel DeJtker, Inc., New York, (1943).
U.S. EPA. Development Document for Effluent Limitations
Guidelines and Standards for the Iron and Steel
Manufacturing Proposed. Point Source Category. Vol. ,1,
EPA-440/l-8C/024-b, December 1980a.
U.S. EPA. Development Document for Effluent Limitations
Guidelines and Standards for the Iron and Steel
Manufacturing — Proposed. Point Scarce Category
Vol. II, Coke Making. Sintering. Iron Making Sub-
categories. EPA-400/l-"0/024-b, December 1980b.
U.S. EPA. Development Document for p*fluent Limitations
Guidelines and Standards for the Iron and Steel
Manufacturing — Point Sourr.e Category. Vol. III.
Proposed, Steel Making Subcatat.ory. Vacuum Degassing
Subcategory. Continuous Casting Subcategory.
EPA—»40/l-80/024-b, December, 1980c.
-------
U.S. EPA. Development Dov-ument for Effluent Limitations 5.36
Guidelines and Standards for the Iron and Steel
Manufacturing — Point Source Category Proposed.
Vol. J7, Scale Removal Subcategoi-y Acid Pickling
Subcategory. EPA-440/l-80/024-b, December, 1980d.
U.S. EPA. Environmental and Resource Conservation Considera-
tions of Steel Industry Solid Waste. EPA-600/2-79/074,
PB-299919, April, 1979.
U.S. EPA. Industrial Process Profiles for Environmental
Use; Chapter 24. The Iron and Steel Industry.
EPA-600/2-77-023X, PB266226.
U.S. EPA. Environmental Considerations of Selected Energy
Conserving Manufacturing Process Options - Vol. Ill -
Iron and Steel Industry Report. EPA-600/7-76-034C,
PB-264269.
U.S. EPA. Development Document for Proposed Effluent
Guidelines and New Source Performance Standards for
Steel Making Segment of the Iron and Steel Point
Source Manufacturing Category. EPA, January, 1974.
Wilson, Jr., P.J. and Wells, J.H. (ed.) Coal. Coke Chemicals
Chap. II. Chen. Eng. Series. McGrav Hill Book Co.,
(1950).
-------
CHAPTER 6
PAPER AND PULP INDUSTRY
6.1 INTRODUCTION
The pulping process, kraft (or sulfate) pulping in
particular, la discussed in this chapter. Pulping wood is
Che initial process in the manufacture of paper and paper
products. The pulping process is the conversion of fibrous
raw material, wood, into a material suitable for use in
paper, paperboard, and building materials. Pulp is the
fibrous material ready to be made into paper.
There are four major chemical pulping techniques:
(1) kraft or sulfate, (2) sulfite, (3) semichemieal, and (4)
soda. Of the major pulping techniques, the kraft or sulfate
process produces over SOX of the chemical pulp produced
annually in the United States. In 1970, there wt-e 116
mills producing 29.6 million tons of pulp by the kraft
process. During the same year the pitlp and paper board
consumption was 56.8 million tons (U.S. EPA, Sept. 1973).
6.2 KRAFT PULPING
The two basic components of the pulp wood are cellulose
and llgnln. The cellulose fibers, which constitute the pulp,
are bound together by lignin, thus, any process manufacturing
pulp must remove the lignin. The Kraft process employs
chemical dissolution of the lignin. The flow chart of the
kraft process is depicted in Figure 6.1.
-------
Evaporator
Gaaaa
Strong
Black
Liquor
Piilp
CM
Condtnsatea
I
»
Cuuatlcizi
Tank
{ . Sattllng
\^ Tank
(CaO) (
Llaa Kiln
Flltar
Mud
(CaCO,)
Kiln
Caaeti
Figure 6.1. Flow Chart of Kraft Pulping Procaaa
(U.S. EPA. Sept. 1973).
-------
The typical pollutants from the kraft pulping process 6.3,
are hydrogen sulfate, methyl mercaptant, dimethyl sulfate,
and dimethyl disulfide. The pollutants containing sulfur are
collectively called total reduced sulfur (TRS). Hydrogen
sulfite emissions are a direct result of sodium sulflde
breakdown in the kraft cooking liquor. Methyl mercaptant
and dimethyl sulflde are formed in the reactions with llgnln.
Dimethyl sulflde is formed thorugh the oxidation of mercaptant
groups derived from the thiollgnin.
The kraft process as a whole can be subcategorized into
two parts; actual pulping, and recovery. The pulping occurs
in the digester system followed by the pulp wash. The
recovery refers to multiple effect evaporators (MEE), recovery
furnace, smelt dissolver, and lime kiln, all of which serve
to recover the white liquor and heat.
6.2.1 Digester System
There are two types of digesters, continuous and batch
digesters. The composition and quality ox digester gases
will differ between the two digester types. Baech digesters
often present air pollution problems because of gas surges
produced during blowing. Continuous digesters, however,
present much smaller pollution problems than batch digesters
because contaminated condensates and odorous gases flow at a
regular rate. Most of the kraft pulping is currently done in
batch digesters (Goodwin, 1978). The following discussion
entails only the batch digester system.
-------
The digestion process is a delignlfication process in 6.4
which white liquor and wood chips are heated to 170-1?5°C.
White liquor is composed of sodium sulfide (Na.S) end
sodium hydroxide (NaOH).
Emissions from the digester are caused by two streams;
the relief gases and blow gases. The relief gases are the
ventilation gases which maintain the digester at the proper
pressures (100-135 psig). The blow gases, steam and other
gases, are from the blow tank where the cooking liquor is
drained from the pulp. Both the relief and blow gases are
condensed for heat recovery. Table 6.1 gives the pollutant
emission rates for the digester system.
TABLE 6.1. TYPICAL EMISSION RATES FROM BATCH DIGESTER
IN kg SULFUR/TON OF ADP* (U.S. EPA. JAN. 1978)
Pollutant
H2S
CH3SH
C3-SCH-
CH-SSCH.
Blow Gases
0-0.1
0-1.0
0-0.25
0-0.1
Relief Gases
0-0.5
0-0.3
0.05-0.8
0.05-1.0
* ADP - Air Dried Pulp
-------
Mercaptants and methyl sulflde are unavoidable by- 6'-5
products of kraft pulping, however, there are few measures
which can limit their production. Generally, h' -h tempera-
tures, high sulfidity and long reaction tines favor »-he
production of the sulfur compounds (Douglas, 1966). Thus,
if the sulfidity of the white liquor is kept at a minimum,
the formation of gaseous sulfur compounds will be reduced.
Sarkanen, .§£ al. (1970), suggests a 20Z sulfidity for most
paper mills.
Final emissions of the digester system is determined by
the effective operation of the condenser (heat exchanger)
units. Experience shows that the surface area of the heat
exchanger, thought originally to be sufficient may later
prove to be too small (U.S. EPA, Oct. 1976). This is due to
fiber carryover by the blow gases and :onsequent fouling of
the heat transfer surfaces. The fiber carryover is caused
by excessive gas velocities at the entrance of the flow
exhaust pipe. The minimum velocity to suspend solid particles
is 18 fps, and the actual velocity in the blow tank
reached 46 fps (Martin, 1969). The recommendations to
reduce fiber carryover are: decrease the digester wood to
liquor ratio, relieve the digester to a lower pressure
before blowing and/or blowing for a longer time period,
installation of a cyclone separator, and initially providing
more heat exchange surface.
-------
6.2.2 Brown Stock Washer System 6.6
The washing process is a minor source of air pollution
as compared to digestion, evaporation, and combustion. The
emission of air contaminated with organic sulfur compounds
is due primarily to the contact of air with black liquor.
The amount of air and sulfur compounds ventilation depends
mainly on the type of washing process and equipment. The
two main washing processes are displacement and diffusion
washing (U.S. EPA, Oct. 1976).
Categorically, displacement washers include vacuum
washers and pressure washers. Of the two, the pressure
washers' hood vent and foaa tank vent will have smaller flow
rates and total reduced sulfur (TRS) emissions.
Typical emission rates from the vacuum washers' hood
vent and the foam tank are shown in Trble 6.2.
TABLE 6.2. EMISSION RATES FROM VACUUM WASHER IN kg
SULFUR/Ton ADP (U.S. EPA. October 1976)
Pollutant
H2S
CHjSH
CH^CILj
CH.SSCH.
Washer Hood Vent
0-0.1
0.05-1.0
0.05-0.5
0.05-0.4
Washer Foam Tank
0-0.01
0-0.01
0-0.05
0-0.03
-------
Diffusion washing Is superior to displacement washing, since
the washing takes place in a closed reactor. In diffusion
washing, ideally, there Is no air Involved, thus, black
liquor oxidation and odor release are very small compared to
displacement washing.
Some mills employ contaminated condensates for washing.
A study of 17 washing systems irdicated an emission rate of
0.014 Ib/ton ADP as HjS using H20, ami 0.35 Ib/ton ADP
treating with eondeneate (U.S. EPA, Sept. 1973). In view of
pollution abatement, water is a better washing medium than
the condenaates. Another possibility is to reduce sulfur
contents of tlie condensate by stripping.
6.2.3 Multiple Effect Evaporator System
Multiple effect evaporators (MZE) are utilized to concen-
trate weak black liquor from 12-18Z solids to 40-55Z solids
(Goodwin, 1978). The weak black liquor is a mixture of
digester spent cooking liquor and stock washer discharge.
Basically each effect consists of a heating element and a
vapor head. The hot vapors from the vapor heat of a previous
effect pass to the heating element of 'lie following effect.
The vacuum Is maintained by means of rapid condensation of
the vapor from the final effect.
This section includes only the most important indirect
steam evaporation system from the view point of pollution.
Thus, the following discussion is for Vacuum MEE. However,
-------
Che pollution control strr-.egies can be readily applied to 6<8
other evaporation techniques. Typical emission rates for
MEE are shown in Table 5.3.
TABLE 6.3. EMISSION RATES FROM MEE IN kg SULFUR/TON
ADP (U.S. EPA, OCT. 1973).
Pollutant Emission Rate
kg Sulfur/ton ADP
*2S
CBjSB
CB_SCH3
CB-jSSCBj
0.05-1.5
0.05-0.8
0.05-1.0
0.05-1.0
The most effective method of reduction of pollution in
MEE is to steam atrip the condensate and to Incinerate the so
called noncondensable gases (H.,S, CH^B, CE^CB^, and CH3SSCB3).
Matteson, e_£ al. (1967) successfully stripped the condensate
generating overhead vapor of more than 95Z hydrogen sulfide,
mercaptants, and dimethyl disulflde. Steam stripping vas
performed in a conventional bubble cap tray stripper result-
ing in a bottom product of nearly pure and reusable water.
The stripped gases and other gases from the MEE can be
incinerated in the lime kiln (Walther and Amberg, 1970).
The liberation of B,S and to a lesser extent CH.SH
depends on the pH of the black liquor. This is due to the
acidic nature of both gases. Furthermore, these gases
-------
« Q
dissociate more readily in an aqueous solution of higher pH. "•'.
Addition of caustic soda to the weak black liquor can be
beneficial in alleviating BjS and CB^SB.
The emissions of H.S and CH^SH arc dependent on the
sulfide concentration of the weak black liquor. Oxidation
of this weak black liquor can convert sulfide to thlosulfate
and CH.SB to CB.SSCB-. These conversions will facilitate
the reduction of R,S and CB^SB emission from MEZ. The
condensata from the HEE processing of oxidize weak black
liquor will require little, if any. treatment for odor
abatement (ZPA, 1976).
Furthermore, Caleno and Amsolen (1970) observed several
benefits of weak black liquor oxidation with 02 a« compared
to lack of oxidation. The oxidation uitllzing 02 resulted
in lower emlsisons of H.S from the MZE, and improved the
evaporator condensate water quality.
There are two major factors which should be considered
in the effectiveness of weak black liquor oxidation to
prevent TRS emission. First, a high degree of oxidation is
required. Second, oxidized sulfur compounds havf tendencies
to revert to sulfide during MEE as well as during extended
ctcrage. Long storage periods after black liquor oxidation
should be avoided.
-------
6.3 RECOVERY FURNACE SYSTEM
The recover? furnace functions include: (1) recovery
of Kodlua and sulfur. (2) production of steaa and, (3)
disposition of unwanted components of the dissolved wood.
The recovery furnace system generally includes the following
units: recovery furnace, flue gas direct contact evapora-
tor, primery particulate control device, and secondary
participate control device. In some cases the direct
contact evaporators have been used to contain the partlculate
emissions er eliminated all together (U.S. EPA, March 1970).
Table 6.4 is a listing of emission rates from the recovery
furnace.
TABLE 6.4. EMISSION RATES FROM RECOVERY FURNACE (U.S. EPA,
OCT. 1976).
Pollutants
V
CH-jSH
CHjSCH^
CH-SSCH-
^2
S°3
NO,
Emission Rate kg/ton ADP
0-25
0-2
0-1
0-0.3
0-40
0-4
0.7-5
The partlculate emission rates are listed In Table 6.5.
-------
TABLE 6.5. PARTICULATE EMISSION RATES FROM THE RECOVERY 6.11
FURNACE (U.S. EPA. OCT. 1976)
Emission Source Emission Rage kg/ton
ADP
Recovery System after
Electrostatic Precipitator 0.5-12
After Venturi Evaporator 14-50
Flue Gas Dust Load 40-75
The three direct evaporators used in the kraft pulping
mills are cascade evaporators, cyclone evaporators, and the
venturi recovery unit. The difference between a venturi and
the other two evaporators is its efficiency in removing
particulatea. While cyclone and cascade evaporators remove
only 40-50Z of the partlculate matter, the venturi recovery
units can be designed to capture better than 90Z of the
participates (U.S. EPA, Sept. 1973). The direct contact
evaporator serves as an adsorption unit for SO. and nearly
all SO-. Furthermore, it absorbes HjS emitted from the
recovery furnace under conditions of high black liquor pH
and low sodium sulfide concentrations in the strong black
liquor.
The direct evaporation unit is also a potential source
of TRS. However, the emission of TRS depends heavily on the
residual sulfide in the black liquor from MEE. For this
-------
purpose, some mills employ strong black liquor oxidation. A 6.11
survey of 32 recovery furnace systems where black liquor
oxidation is not used showed sulfur emission ranging team
0.75-31g/Kg ADP, with an average of 7.7g/Kg ADF. Conversely,
a survey of 17 units that utilized black liquor oxidation
indicated emission ranges of 0.113g/Kg ADF. with an average
of 3.7g/Kg ADP (Goodwin, 1978).
It is possible to eliminate the direct contact evapora-
tor in favor of a non-contact design. This change will
cause an increase in particulate emissions which would then
require installation of a more efficient particulate control
device.
The emission of sulfur compounds from the recovery
furnace is also dependent on the design of the furnace. The
recovery furnace has two functions; recovery of the chemicals
in their reduced state (i.e. sulfur should be present as
sulfide and not sulfate), and recovery of heat to generate
steam for the processes.
Combustion within the recovery furnace la separated
into two zones. The first zone must be maintained under
reducing conditions* less than the required stolchlometric
amounts of air. The products of this zone discharge chemicals
in the molten state with the sulfur present mainly as sulfide
and organic matter as a gas having considerable heat value.
The second zone of combustion starts with the addition of
-------
secondary air. The secondary air should be supplied in 10- 6.13
20Z excess of the amount required for complete combustion.
The release of sodium from the burning char of black
liquor depends on the temperature and the gas conditions in
the border zone between the bed and the flue gas. The TRS
release to the flue gas is affected by the total sulfur
concentration and the sodium to sulfur ratio. Since the
sodium/sulfur ratio in the smelt bed depends on temperature,
the release of sulfur to the flue gas is also a function of
temperature. Hydrogen sulfide may be present in the flue
gas in the pr. -nary air combustion zone at 50-100ppm if the
zone between the bed and the flue gas are kept at the optimal
temperature. Hydrogen sulfide concentrations of 15,000 ppm
have been observed in this region when black out conditions
are present (black out conditions refers to insufficient
rate of combustion in the hearth). Typically, a low tempera-
ture favors the presence of S and H2S (U.S. EPA, Oct. 1976).
There are several advantages In raising the primary air
temperature. The velocity for the same flow of air will
increase and Improve the sodium evaporation from the bed.
Also, the release of sulfur from the bed decreases.
Immediately after introduction of secondary air, the
final combustion starts. The amount of primary air for most
furnaces must be more than 1102 and less than 125Z of the
theoretical air to avoid formation of stick dust. Stick
dust has a tendency to foul the heating svrfaces. The
-------
secondary air should be supplied to the furnace such that it 6.14
mixes with the gas cooing from the primary air combustion
zone. Therefore, efficient regulation and method of intro-
duction of secondary air Is important in the generation of
scick dust.
The variable tffeeting the TRS emissions from the
recovery furnace are as follows: quantity and method of
introduction of combusted air, the rate of black liquor
feed, the degree of turbulance in the oxidation zone,
the 0. content of flow gas, the spray pattern and droplet
size of the liquor fed to the furnace, and the degree of
disturbance In the smelt bed. These variables are Inde-
pendent of the presence or absence of a direct contact
evaporator 'Theon, et al. 1968).
Teller and Amberg (1975) have developed a control
technique for use in the recovery furnace which utilizes
alkaline adsorption with carbon activated cxidatlon of the
scrubbing solution. Pilot plant studies shoved this technique
Is capable of reducing TRS emissions from 20-1500 ppm to
1 to 10 ppm. This method would alno alleviate particulate and
SO. emissions (Teller and Amberg, 1975). Another effective
adsorption method is the TRS system potential by the
Weyerhaeuser Company. The TRS scrubber adsorbs up to 99%
of H-S and collects about 85Z of the particulate matter.
-------
Nitrogen oxides are generated in the recovery furnace 6.15
at a rate of 0.7-5 kg/ton ADP (U.S. EPA, Oct. 1976). The
reduction of NO production lies in provisions for facillta-
3*
tion of a heat sink in the recovery furnace. The endothemic
reaction of Sa_SO, to Na-S in the smelt bed also acts as a
heat sink to inhibit excessive flame temperatures. A reducing
atmosphere above the smelt bed will also reduce NO formation.
The supply of air can be arranged to spread out the flame
front, and in that way, inhibit the increase in gas tempera-
ture.
6.3.1 Smelt Dissolving Tank
The molten smelt accumulated in the recovery furnace,
as a result of combustion, is dissolved in water in the
smelt dissolving tank. Dissolution of the molten smelt
(sodium carbonate and sodivan sulfide) in water forms a green
liquor. The dissolution is aided by agitators and steam,
or a liquid shatterjet system, to break up the smelt stream
before it enters the solution. The large volume of steam
generated by the contact of smelt with water is vented.
Table 6.6 depicts the emission rates from the smelt dissolving
tank.
-------
TABLE 6.6. EMISSION RATES FROM SMELT DISSOLVE TANK 6.16
(U.S. EPA. OCT. 1976)
Pollutants Kg Sulfur/ton ADP
0-1.0
0-0.8
0-0.5
CB3SSCH3 0-0.3
Kg/ton ADP
Particulate Emission
(After Control Device) 0.01-0.5
S02 0-0.2
Particulate matter contains dissolved and undlssolved
NaOE, Na.CO., and Na.S. The particulate emissions are cap-
tured from escaping vent gases by mist eliminator pads.
Typical efficiency of the pads for particulate removal is
70-90Z, however* higher efficiencies can be achieved by
facilitating the smelt tank with a spray or packed scrubber
in addition to mist eliminator pads. Combinations of this
type can be 98Z efficient in removing particulate matter
(U.S. EPA, Oct. 1976). Another alternative is to combine
vent gases from the smelt tank with flue gases from the recovery
furnace prior to entering the particulate collection de-rice.
However, the effectiveness of a electrostatic preclpitator
is reduced due to the water vapor content of the smelt
-------
tank vent gases. Furthermore, the Na.S entrained in the 6.17
smelt tank vent gases coming Into contact with CO, from the
recovery furnace may promote formation of H.S. It is evident
that the best particulate control device for the smelt tank is
a combination of mist eliminator pads and a scrubber.
The TRS emissions depend on the aulfide content of p*srtl-
culate matter, the turbulence in the dissolving tank, the
type of solution used In a scrubber, if present, and pH of the
scrubber liquor. Fresh water is the best solution for scrub-
bing and is capable of producing 0.001 Ib sulfur/ton ADP
(Martin, 1969).
6.4 LIME KILN
The green liquor is converted to white liquor in the
lime kiln. This unit is an essential element of the closed-
loop system. The kiln calcines the calcium carbonate which
precipitate from the causticlzer to produce quicklime (CaO).
The calcined calcium carbonate precipitate is also called
lime mud. The quicklime is wetted (slacked) by the water
in the green liquor solution to form calcium hydroxide for the
causticlzlng reaction.
The mud is contacted by the hot gases produced by the
combustion of natural gas or fuel oil and proceeds through the
kiln in the opposite direction of the gas flow. The lime mud
is a 55-60Z solid-water slurry and is fed at elevation to
the kiln. In the upper part of the kiln the mud dries while
-------
at Che lover end, Che high temperature zone (1800-2000°F), 6.18
1C agglomerates Into snail pellets and is calcined to CaO.
Typical emission races from lime, kiln are given in Table 6.7.
TABLE 6.7. LIME KILN EMISSION RATES (U.S. EPA. OCT. 1976)
Pollutants
V
CH3SH
CH3SCH
CH3SSCH3
S°2
N°x
Lime Kiln Exhaust &
kg Sulfur/ton AOP
0-0.5
0-0.2
0-0.1
0-0.05
kg/ ton ADP
0-1.4
10-25
Line Slaker Vent
kg Sulfur/ ton ADP
0-0.01
0-0.01
0-0.01
0-0.01
kg/ton ADP
—
^•^
Variables affecting the TRS emission of Che lime kiln
are the temperature at Che cold end of Che kiln, Che 0.
content of Che gases leaving Che kiln, the sulflde concent of
the lime mud, and the pH and sulflde content of Che water
used in the participate scrubber (NCASI, 1971). If contami-
nated condensate is used as Che scrubbing solution, Che
exhaust gases could strip out the dissolved TRS and increase
the TRS emission from the lime kiln.
The two most important preventive measures in view of
TRS emission are; maintenance of the proper process conditions,
and scrubbing the exhaust gases with caustic solution. For
-------
example, TRS emission can be reduced by a sufficient supply of 6.19
0. and a reduction in sulfide content of the mud.
The lime kiln is operated with excess air and high tem-
perature, both conditions favor the production of NO^, there-
fore, any measure to reduce TRS may promote generation of
NO . Thus, oxides of nitrogen are unavoidable by-products
of the lime kiln and any measure to control their release
should occur after the kiln.
Table 6.8 summarizes some of the pollution problems
associated with the kraft pulping process and suggests con-
trol alternatives.
6.5 RECOMMENDED AREAS FOR PROCESS MODIFICATION RESEARCH
After evaluating the available literature, the following
areas are reconmendsd for further research by the study:
Research on digestion of wood chips to determine
optimal sulfidity, pH, and temperature to reduce
pollution.
Studies on control of fiber carryover from the blow
tank by cyclone and/or by reduction of relief
pressure and selection of wood to liquor ratio to
prevent TRS emission.
. Comparative studies on design and application of
diffusion and displacement washers to minimize TRS.
Effect of black liquor oxidation and pH control
on weak and strong black liquor to reduce TRS
emission.
-------
Table 6-8. Pollutant* end Control Optima In Kraft Pulping Proccaa
Process
Digester
Broun Stock
Kosher
Multiple
Effect
Evaporators
Recovery
Furnace
Systes)
Snlt Otss'lve
Tank
Lin Kiln
Pollutants
TRS. relief i
blow gases
TRS. noncondena-
ablea
TRS. noncendens-
ables
TRS. SOj SOj,
HO^ Partlculatao
TRS. S02.
Partlculatea
TRS. S02.
HO
Sources In
Process
Digester Tank
blow tank
Vacuusi vainer
Evaporators
Recovery furnace
direct contact
evaporator
Soelt Tank
Kiln
Nature of
Pollutants
Organic, gases
Organic, gaaea
Organic, gaaee
Organic and
Inorganic gases
and solids
Orfanic and
Inorganic gases
=r~i solids
Organic and
Inorganic gases
Pollutant Control Strategy
Lower aulfldlty. lower blow
pressure, reduce fiber
carryover by cyclone or
other aw thuds.
Use water aa washing
fluid, employ diffusion
washers.
Treatment of week black
liquor by oxidation Mt
vUh caustic sods. Effective
stripping of condensate frooi the
condenser unit.
Strong blsck liquor oxidation.
Use direct contact evaporator,
venturl type. Improve design.
Alkaline sdsorptlon with
carbon-activated oxidation of
the scrubbing solution.
Combination cf alst ellatlnstor
pad and scrubber unit. Use fresh
water for scrubbing.
Bslntsln proper process
conditions. Sufficient
supply of O and reduction
In sulfur content of the mud.
-------
Studies on the direct and non-contact evaporation 6.21
in the recovery furnace system to determine capabi-
lity and merits of each unit in reducing the TRS
emission.
Research on combustion of strong black liquor to
prevent black out conditions and stick dust forma-
tion by optimizing the design and operating condi-
tions In the recovery furnace.
Research and application of scrubbing techniques to
reduce TRS emission.
-------
BIBLIOGRAPHY 6.22
Douglas, I.B., "The Chemistry of Pollutant Formation in
Kraft Pulping." In proceedings of International confer-
ence on Atmospheric Emissions from Sulfate Pulping,
April 28, 1966. E.O. Painter Printing Co., 1966.
Galeano, S.F. and Amsden, C.D. "Oxidation of Weak Black
Liquor with Molecular Oxygen". TAPPI. Vol. 53, November
1970, pp. 2142-2146.
Goodwin, D.R. "Draft Guideline Document: Control of TRS
Emissions from Existing Kraft Pulp Mills", EPA 450/2-
78/003A. January 1978.
Martin, G.C. "Fiber Carryover With Blow Tank Exhaust",
TAPPI. Vol. 52, No. 12, December 1969.
Matl,.son, M.J., et al. "Sekor II: Steam Stripping of
Volatile Substances from Kraft Pulping Mill
Affluent Stream". TAPPI. Vol. 50, No. 2,
February 1967.
Sarlr.Jien, K.V., et al., "Kraft Odor", TAPPI. Vol. 53,
No. 5. May 1970.
Suggested Procedure for the Conduct of Lime Kiln
Studies to Define Emissions of Reduced Sulfur
Through Control of Kiln and Scrubber Operating
Variable." NCASI Special Report No. 70-71,
January 1971.
Teller, A.J. and Amberg, H.R. "Considerations in the
Design for TRS and Particulate Recovery from
Effluents of Kraft Recovery Furnaces." TAPPI
Environmental Conference. May 1975.
Theon, G.N., e_t al. "The Affect of Combustion
Variable on the Release of Odorous Sulfur
Compounds from a Kraft Recovery Furnace, TAPPI.
Vol. 51, No. 8, August 1968, pp. 324-333.
-------
"Factors Affecting Emission of Odoroua Reduced Sulfur 6.23
Compound* from Miscellaneous Kraft Proceaa Sourcea",
HCASI Technical Bulletin. So. 60, March 1972.
Bansen. S.P. and Burgesa. P.I. "Carbon Treataent of Kraft
Condeoaatei Vaatea." TA?P1. Vol. SI. June 1966.
pp. 241-245.
Prakaah, C.B. and Hurry, 7.E. "Studies oo H-S Emiaaiooa
during Calcining1*. Pulp and Paper Maaaalne of Canada.
Vol. 74, Hay 1973, pp. 99-102.
Teller, A.J. and Aaberg, H.ft. "Considerations in the Design
for TRS and Partieulate Recovery froa the Effluents of
Kraft Recovery Furnace." Preprint TAPPI Environmental
Conference. May *975.
Ualther, J.E. and Aaberg, B.R. "The Role of Che Direct
Contact Evaporator in Controlling Kraft Recovery.
Furnace Eaisaiona". Pulp and Paper Magatine of Canada.
Vol. 72, October 1471. pp. 65-67.
-------
D.S. EPA. "Control of Atmospheric Emissions la the Wood
Pulping Industry", Environmental Engineering Inc., and
J.E. Sirrlne Company. Final Keport, EPA Contract So.
CPA-22-49-18, March IS, 1970.
O.S. EJA. "Atmospheric Emissions Proa the Pulp and Paper
Manufacture Industry." Environmental Protection Agency.
•Research Park H.C. Office of Air Quality Planning and
Standards. EPA 459/1-73/002, September 1973.
O.S. EPA. "Environmental Pollution Contrcl Pulp and Paper
Industry: Part 1 Air", EPA 625/7-76-001. October 1976.
Ualther. J.E. and Amberg, B.R. "A Positive Air Quality
Program at a New Kraft Mill", Journal of Air Pollution
Control Aasoe.. Vol. 20, No. 2, January 1970.
SUPPLEMENTAL REFERENCES
Anderson. H.K. and Ryan, J. "Improved Air Pollution Control
for a Kraft Recovery Boiler: Modified Recovery Border
No. 3", EPA 650/2-74-071-a. August, 1974.
Bhati*. S.P., £t al., "Removal of Sulfur Compounds from
Kraft Rucuvery Stack with Alkaline Suspension of
Activated Carbon", TAPTI. Vol. 56, Deceabei 1973, pp.
164-167.
Clement, J.L. and Eliot. J.S. "Kraft Recovery Boiler
Design for Odor Control". Pulp and Paper Magazine
of Canada. Vol. 78, NO. 8, February 7, 1969, pp. 47-52.
Cooper. H.B.E. and Roasano. A.T., Jr. "Black Liquor
Oxidation with Koleculor Oxygen in Plug Flov Reactor ,
TAPPI. Vol. 56, June 1973, pp. 100-103.
Douglas. I.B. "Sources of Odor in the Kraft Process:
Odor formation in Black Liquor Multiple Effect
Evaporators." TAPPI. Vol. 52, September 1969.
pp. 1738-1741.
-------
CHAPTER 7 7.1
THE PRIMARY ALUMINIUM INDUSTRY
7.1 INTRODUCTION
The primary alunlnlun Industry consists of processing
bauxite ore to produce alumina (and occasionally aluminium
hydroxide) and processing the alumina » produce aluminium.
Approximately, 7.6 x 106 tons of alumina were oroduced in U.S.
from processing about 15.4 x 106 tons of bauxite in 1972,
942 of the alumina was utilized to make aluminium (Saxton and
Kramer, 1975).
7.2 BAUXITE PROCESSING
Bauxite is composed mainly of met . —c oxides with
aluminium oxide comprising from 20Z to 60Z of the ore as
mined. Approximately 87Z of th* bauxite ore la Imported,
mainly from Jamaica and Surinam. The many environmental
problems associated with bauxite mining and shipping are
caused by fugitive dust and water runoff. Bauxite ore may
contain up to 301 moisture and should be dried at 110°C before
shipping.
An overview of the Bauxite processing Is shown In
Figure 7.1.
The raw bauxite ore la benefacted by grinding to about
100 mesh, digested in caustic at elevated temperatures and
pressures (145CC and 60 psig), and then filtered or thickened
in the presence of flocculants. These operations yield a
-------
7.2
MIHZD BMJXRE ORE
NAKED?
IUOH ^^
—
GRINDING
9IGEST10K AND
THICKHISC
c*o.
HoOB
AUKINATE
LJOOOB
• "•- FLOCCUURT
RED MUD
C«CO f 0 '
1 * ^ffl o—
1 Dlg«*tlon. "
^^ Sintering 7
md
Washing ™| Vi
T
BROWN HUD
PRICIPITATI01I.
TO.TRATIOB.
CALCIHIHG
_, 1 23 9
Handling
•nd
Shipping
1
Lltrrlng
•nd
uhlng
\
ut««
ICM
1 Solid HMCM
Flgun 7.1. Btuxltt ProecMlng
-------
sodium aluminate liquor and a waste stream of "red mud" which 7.3
contains the impurities found In the bauxite ore.
The aluminate liquor is diluted and cooled to hydrolyze
the sodium aluminate, forming a precipitate of aluminium
hydroxide which is filtered and calcined to alumina. The
alumina is then shipped to aluminium smelting if so desired.
Depending on the type of Bauxite processed, 1/3 to 2 kg of
red mud is produced per each kilogram of alumina product.
Table 7.1 gives the chemical analysis of red mud slurries
from different bauxite ores (U.S. EPA, Oct. 1974). The pH
of this slurry is approximately 12.5.
TABLE 7.1. CHEMICAL ANALYSIS OF RED MUDS
Weight Z
Component
Fe203
Ai2°3
sio2
T102
CaO
Ha20
Arkansas
55-60
12-15
4- 5
4- 5
5-10
2
Surinam
30-40
16-20
11-14
10-11
5- 6
6- 8
Jamaica
50.54
11-13
2.5-6
—
6.5-8.5
1.5-5.0
In the combination process, bauxite ores with high
silica content, such as those from Arkansas, the red mud
residue is treated to extract additional amounts of almlna
-------
and to recover sodium values. This additional extraction 7.4
step is accomplished by mixing red mud with limestone and
(Na)2CO., and then sintering this mixture at 1100 to 1200°C.
The important reactions are the conversion of silica to cal-
cium silicate and residual alumina to sodium aluminate. The
sintered products are leached to produce additional sodium
alumlnate solution, which is either filtered and added to the
main stream for precipitation or is precipitated separately.
By the addition of seed material and by careful control of com-
position and agitation, alumina trihydrate is precipitated in
a controlled form.
The ideal solution to the red mud problem would be to
develop a. use for it. A possible application utilizes the
high iron content of the red mud (Table 7.1). Fursman,
£t al. (1970) described a process based on sintering the
red mud with carbon and limestone and melting the sinter in
an electric ore furnace to produce a low priority iron
which could be further processed into steel. This process
was further developed (Guccione, 1971) but has not yet
found commercial application. Other investigators have
examined the applicability of red mud to manufacture port-
land cement, bricks, and road construction (Fursman, et
al. 1970; Solyman and Briudnso, 1973).
There is a need to develop an economically viable
leaching and extraction process for the recovery of mineral
values from red mud wastes.
-------
During Che handling and shipping of alumina, dust is 7.5
formed. The tendency of aluminas to form dust during handling
depends on the degres of calcination and on the particle size
distribution. The size distribution and adsorption capability
of calcined alumina are important in the reduction and dry
gas cleaning stages of aluminium manufacture, as will be
discussed later.
With highly calcined, flowing aluminas, the formation
of dust is prevented by the surface roughness, which increases
as the a-alumlna content rises. If fine grained hydroxide is
calcined to a lower degree, it will start developing dust.
The tendency of weakly calcined aluminas to cause dusting
is counteracted by minimizing the amount of fines. This is
normally done in the precipitation area of the Bayer process,
where the particle size distribution of the hydroxide is
controlled.
Decisive for the mechanical strength acquired by the
individual hydroxide particles are (Schmidt, 1980):
The basic principle applied for crystallization,
i.e., nucleation, crystal growth, or agglomera-
tion conditions
Influence of liquor impurities such as CaCo.
oxalates etc.
The mechanical stresses to which the hydroxides
are exposed during precipitation.
-------
Schmidt, £t al. (1980) reported that the gas/solid 7.6
velocities and thermal stresses in the fluid bed calciner
and in the rotary kiln have a strong Influence on the
particle size distribution of the calcined alumina.
Thus a detailed research program to improve the mechani-
cal strength, adsorption capability and particle size distri-
bution of calcined alumina by modifying the precipitation
and calcining of alumina IB suggested.
Studies conducted in the USSR and elsewhere indicate
the possibility of using nitric acid stripping for the
extraction of alumina from ores containing high amounts of
silica. Sutyrln and Zverev (1976) reported that stripping
at 160°C lowered acid usage and produced solutions less
contaminated by Iron. Acid stripping of domestic D.S. ores
which contain high amounts of silica should be optimized by
proper control of the stripping temperature.
The enrichment of high silica bauxite ores using
heterotrophlc bacteria is reported by Andreev, et^ al. (1976).
It was possible to produce a concentrate with 48.4* A&2°3
content at a recovery of 74Z. Thus, additional research is
needed to develop acid stripping and bacterial enrichment of
domestic bauxite ores.
7.3 PRIMARY ALUMINIUM SMELTING
The large scale, economic production of primary alumi-
nium became possible when, in 1886, C.M. Ball and P. Heroult
independently developed the electrolytic process which has
-------
remained essentially unchanged, except for improvements in 7.7
equipment design and operating practices, it is used in all
the commercial processes in U.S. producing primary aluminium.
There are 31 aluminium reduction plants In the U.S. with
a totax annual capacity of about 4.5 x 10 tons. The energy
consumed annually at full production is estimated to be in
the range of 80 to 100 billion K.W.H.
The basic process for reducing alumina to aluminium is
shown schematically In Figure 7.2.
The raw materials used In the aluminium production
include alumina, cryolite (a double flourlde of Na and A£),
pitch, petroleum coke, and aluminium flourlde. For every kg
of aluminium produced, about 2 kg alumina, 0.25 kg pitch,
0.05 kg cryolite, 0.5 kg petroleum coke, 0.04 kg aluminium
flourlde, 0.6 kg baked carbon and 22 K.W.H. of electrical
energy are needed.
The heart of the aluminium plant is the electrolytic
cell, which consists of a steel container lined with re-
fractory brick with an inner lining of carbon. The cells
are arranged in rows, in an operating unit (potline) as
many as 100 to 250 cells are electrically connected in series.
The electrical supply is direct current and is on the order
of several hundred volts and 60,000 - 100,000 amperes. The
carbon lining at the bottom of the cell acts as a cathode
when covered with molten gl"m-»n
-------
7.8
PETROLEUM COKE
CRUSHING
AND
CLASSIFYING
PITCH
ANODE PASTE
HOT - BLENDING
I COOLING
PRESSING
SOUERBCRG
ANODE
BRIQUETTES
BAKING
ELECTRICAL POWER
SUPPLT ~""
(D.C.)
ANODES
CATHODES
•ALUMINA
CRYOLITE
-CALCIUM rLOURlDE
ALUMINUM PLODRIDE
FUSED SALT
ELECTROLYTIC
CELL
CASES,
DUST
FUMES
CAS
SCRUBBING
BLEHDINC
MOLTEN Al.
TO DEGASSING
AND CASTING
Anthracite
Pitch
AlunloluB
(pig. billet. Ingot.
rod)
DRY PROCESS
SOLIDS TO
CELL
BET
SCRUBBER
LIQUOR
TO
TREATMENT
Spent Potllnere
Figure 7.2. Primer? Aluminium Production.
-------
cryolite (80-85Z by wt.), calcium flourida (5-72), and 7-9
alumina (2-8Z). Alumina la added to the bath intermittently
to maintain the concentration of dissolved elumina within the
desired range. The fused salt bath is usually at a tempera-
ture of 900°C.
The reaction In the aluminium reduction cell is not
completely understood (Kirk-Othmer, 1963). Apparently alumi-
nium is reduced from the trlvalent state assuming ionlzation
in the molten salt, to the liquid metal state at the cathode.
Oxygen, assumed present in the bath in the divalent state
appears at the carbon anode and Limediately reacts with the
anode and forms a mixture of C02 (=75Z) and CO (=252).
Thus, the operation of the elsctrolytic aluminium re-
duction cell results in the continuous consumption of alumina
and the carbon cnode, and the evolui.'on of gaseous reaction
products. The aluminium is withdrawn intermittently from
the bottom of the molten bath and is collected in ladles and
cast into Ingots.
The various anode making operations are conducted in
the anode paste plant. The anode paste consists mainly of
high grade coke (petroleum and pitch coke) and pitch, with
a mjfg-tmmn of 0.7Z ash, 0.72 sulfur, 82 volatiles, 0.5Z alkali
and 22 moisture. The two types of pitch handling systems
are, solid pitch handling and liquid pitch handling (using
organic liquids as a heat transfer medium). Dust and
toxic emissions are the main pollutants from these systems.
-------
The two different anode systems ur-.d differ in the
replacement of the anode.
1. Prebaked system - the anode is replaced inter-
mittently,
2. Solderberg system - the anode is replaced continu-
ously by the anode paste descending from the anode
shell suspended above the electrolytic cell.
The carbon cathode has an average life of between 2-3
years. The spent cathode lining is removed by drilling and/or
soaking In water. About 1200 m of shell vasts is generated
each year in the U.S.
The major pollutants generated during the smelting of
alumina Include particulate emissions, inorganic flourides,
oxides of sulfur, H,S, carbon disulfide, carbonyl sulphide,
CO and CO,, and spent carbon cathode.
Emissions from the horizontal-stud Solderberg cell
and vertical-stud Solderberg cell (Rotari, jet al. 1974)
are shown in Table 7.2.
TABLE 7.2 EMISSIONS FROM SOLDERBERG CELL
Cell Type Emissions Ib. per ton of
Vertical-stud Participates 98.4
Solderberg Gaseous Flourldes (HP) 26.6
Particulate Flouride 15.6
Horizontal-stud Partlculates 78.6
Sblderberg Gaseous Flourides(HF) 30.4
Particulate Flouride 10.6
-------
The partlculatea contain A£.0.f Na.CO. and carbon duac. 7.11
Approximately 60Z of the particulates are leas than 5 ym
In size. Increasing the mechanical strength of AA.O.
by modifying precipitation and calcination operatlona (aa
discussed earlier in this section) may lead to a reduction
of particulace A£_0. emi38ions*
The emissions of both particulate and flourine compounds
from the bath increase with increasing temperature, decreasing
alumina content, and decreasing bath ratio of NaF/A&F. (Kotarl,
et_ al. 1974). The hydrogen flouride emissions are generated
primarily as a result of moisture treating with AW. containing
materials. The HF emissions Increase directly with the water
(Bell and Dawson, 1971). The sources of moisture are from the
atmosphere, the moisture content ?f A£.0_.
The flourid- particulates range in size froa about 0.05 -
0.75 urn with the majority of the particles smaller than 0.25 ym
(McCabe, 1975). The flourine content of the total gases,
withdrawn from the pots or pot rooms may vary from 2 to 40 mg/ft ,
or between 18.97 - 25.63 kg/ton of the raw material (Kotari,
et al. 1974). Cooling the process by 5°C will reduce flourine
consumption by 0.2 kg/ton of raw material (Kotari, £t, al. 1974).
An optimization of the operative temperature of the electrolytic
cell is needed to minimize the generation of hydrogen flouride.
Fifteen percent of the flouride present in the emissions from
prebaked pots occurs as HF, while 90Z of the flouride in Solder-
berg pot emissions occurs as HF (Less and Waddingtern, 1971).
-------
found that the maximum adsorption capacity determined in the 7.12
laboratory is roughly twice that determined under production
conditions. Research efforts are needed to explain this
discrepancy between laboratory and production tests and there-
by improve the adsorption of HF on A&.0. in industrial pollu-
tion control devices. Any increase In the surface area of
M 2°3 per unit weight would Increase its HF adsorption capacity.
Sulfur oxides in the fumes from electrolytic cells are
generally removed by wet scrubbing (in lime scrubbers) and/or
by dry scrubbing (by adsorption on A&20.). It is reported
(U.S. EPA, Dec. 1973) that a venturi type line scrubbing system
at the Mitsui Aluminium Company, Ltd. has operated at SO. removal
efficiencies of 86Z-93Z for more Chan a year. It may be necessary
to improve on the venturi contacting device to improve SO.
removal efficiencies or to use additional dry scrubbing units
to further remove SO..
The low equilibrium value of SO- adsorption. Jn smelter
grade A£203 is a limiting factor in the removal of SOj from
cell gases in a dry scrubber. It was shown by Lamb (1979)
that the presence of adsorbed flourlde from cell gas would
reduce equilibrium adsorption of SO. even further. This
effect will be most important with vertical stud Solderberg
cells where HF loading and concentration is higher than the
horizontal stud Solderberg or prebaked electrolytic cells.
It is necessary to understand the interaction of SO, and
HF on A&.0. to develop dry scrubber systems to remove SO..
-------
Benry (1963) reported on experiaental work vhlch established 7.13
correlations between three cell operating paranetara and effluent
production. The reaulta of theae ezperiaenta are aunnarlsed in
Table 7.3.
TABLE 7.:. EFFECT Of CELL OPERATING PARAMETERS AS FLOURIDB
EFFLUENT
Range of Variables
Cryolite Bath
Ratio (SaF/AiF3)
1.44 to 1.S4
1.30
l.SO
Alumina
Content
4Z
32 to 3Z
4Z
Jeop.
9.73°C
973°C
982°C
Effect on
Flourlde
Effluent
31Z decrease
20Z decrease
24Z decrease
It waa thus shown that by increasing tha bath ratio
the alualna content of tha bath, and decreasing the call tanpera-
tun, a decreaaa waa seen in tha flouride content of tha call
effluent. Rettarch efforta should be directed to aodlfy these
call operational variablea in ordar to minlalza f ourlde production.
There haa been several research afforta directed at tha
reduction of fune troataant by adsorbing B7 on alumina. Xavesti-
gationa carried under production conditions CColpitta, 1972;
Chavinaan and Muhlrad. 1973; Cochran, 1974) show that tha effi-
ciency of the adsorption process falla off once a certain
quantity of gaseous fxourine has been adsorbed, and that this
quantity la directly proportional to tha specific surface area
of Ai-0.. In a recent study, Baverrx and Deltarco (1950) shoved
that BF is adsorbed oc A*2°J ** tvc blaolecular 1«7«". They
-------
The possibility of the uce of chemical additives to
remove sulfur in the coal aa slag ia another research area
Chat la being investigated by Alcoa (West. 1980) under a con-
tract with the DOE. Alkali additives and K^CO^ are known to
achieve high efficiencies in removing S02<
Tschopp. Franke and Bernhauser (1979) report that additions
of Lithiun reduced the operating temperature of the electrolytic
cell by 14°C and reduced flourine evolution by 251. based on
their studies at a Sviaa aluminium plant at Essen.
The used cell linings consist largely of carbon (the cathode),
but also contain cryolite, aluminium carbide, and aluminium nitride.
RaOH and sodium cyanide also appear In waters resulting from
leaching of cell linings. The carbides react with water vapor
in the air to produce methane (CH^), hydrogen, C2H2 and other
hydrocarbons. The nitride yields ammonia. This cathode
material. In the past, has been dumped or used aa landfill.
However, environmental concerns now consider the flouride
content to pose a possible pollution hazard. Over 30Z of the
flouride in scrapped cell linings is water soluble. Lu and
Shelley (1970) describe eleven treatment methods to treat cell
linings. They concluded that apart from the two methods,
sodium hydroxide leaching and steam hydrolysis, already in
commercial use, the most promising approach seems to be the
use of hot water hydrolysis and recycle of treated cathode
material. However, it is unlikely that all the cathode carbon
con be recycled, the problem of flourldes and cyanides in
-------
unused cathode still remains. It is necessary to develop 7-15
leaching methods to reaove flourides oad cyanides to
facilitate dlsp. .al of cathode linings.
Table 7.4 gives the major pollution problems associated
with the Primary Aluminium Industry.
7.4 RECOMMENDED RESEARCH STUDIES FOR POLLUTION CONTROL Hi THE
PRIMARY ALUMINIUM INDUSTRY
After evaluating the available literature, the following
areas are recommended for further research by the study:
. Leaching and extraction of red mud to recover
mineral values.
. Improving the mechanical strength, adsorption
capacity and particle size distribution of cal-
cined alumina by optimizing precipitation and
calcination of alumina.
. Optimizing the temperature for and stripping of
high silica U.S. Bauxite ores.
Enrichment of high silica U.S. Bauxite using
bacterial action.
Improving calcination of f^2°3 to reduce lta
moisture content thereby reducing formation of
HF from electrolytic cells.
Optimization of the cryolite bath QiaF/AiF^)
ratio, alumina content and temperature of cell
•;o reduce flourlde emissions.
Increanlng the adsorption capacity of AJO- to
-------
Table 1-1. Surfeited Process Modification for Pollution Control In the Primary Alumlnluc Industry.
Proceas
Bauilte
Processing.
Handling and
Shipping
Primary*
Aluminium
Smelting
Prlvary
Alu-Mnlum
Sncltlng
Pollutants
Red Mud
Alumina
Alumina
Plourlde*
Source In
Prn*»0aa
Ore DlpesUnn
_w_v_ *_..—*
Electrolytic
Cell
Electrolytic
Cell
Nature of
FollutantB
Pe 0 . AtjO..
• J * J "
etc. oildei
Fartlculatea
Parttculatea
HP
SuMeated Proceaa
Hodiricatloni
Recovery of mineral valuea,
Developing alternative
Ueea for red mud.
Opt tailing precipitation
and calcination to improve
ccchanlcal strength and
particle aiie distribution
of alumina.
Optimising precipitation
and calcination to improve
mechanical strength and
particle else distribution
of alumina.
Improvlnf calcination of At.O.
to decrease rolsture content;
optlmlslne cryolite bath
ratio, alumina content and
temperature of cell; use of
lithium as additive; and.
increasing adsorption capacity
of Al20j.
-------
Table 7-4. Surgeated Proceee Modification for Pollution Control in the Primary Alualnlus Induetry. (Cont'd)
Procete
Prlnary
AluMlnluai
SnelLtng
Prlaiary
AliwInluB
Sneltlng
Pollutant!
*>*
Spent Cathode
Lining*
Source In
Electrolytic
Cell
electrolytic
Cell
Nature of
— — -------
Carbon, cryolite.
aluainlua carbide
aluailnliui nitride.
cyanidca and
flour Ides
Suggested Procaaa
[•proving adsorption of SO
an Al ,Oj In the preaence
IF; Use of additives to reanve
aulfur In coal as alag.
Leaching to reaove cyanldea
and flourldea; and hot-water/
steaa hydrolyala and aodluai
hydroxide leaching to recycle
apcnt cathode.
-------
remove HF in Che fumes from electrolysis. 7.18
Understanding the interaction of HF and SO on
A£2°3 to Improve dry scrubbing of SO gases from
the electrolytic cell.
The effect of various additives in removing
sulfur In coal as slag.
Effect of adding Lithium on cell operating tempera-
ture and HF emissions.
Leaching of cathode linings to remove flourides
and cyanides.
-------
BIBLIOGRAPHY 7.19
Andreev, P.I., .et al. Light Metal Age, 34 (3-4), 5-6, April,
(1976).
Ball. D.F. and Dawson, P.R. Air Pollution from Aluminium
Smeltera. £hem. Proc. Eng., 52, (1971).
Saverez, M. aad Demarco, R. J. of Metala. 32(1), p. 10-14,
Jan. (1980).
Chavinean. A. end Muhlrad, W. Dry Proc
-------
Lamb., W.D. J. of Metals. 31(9), pp. 32-37, Sept., 7.20
(1979). ~
Less, L.N. and Waddington, J. The Characterization of
Aluminium Reduction Cell Fume. AIME, New York,
(1971).
McCabe, L.C. Atmospheric Pollution. I&EC, 47(8),
August, (1955).
Saxtoa, J. and Kramer, M. EPA Finding on Solid Wastes
from Industrial Chemicals. April 28, (1975).
Schmidt, H.W., et al. J. £f Metals, Vol. 32(2). 31-39,
Feb., (1980). ~~
Solyman, K., and Brijdoso, E. Properties of Red Mud in
the Bayer Process and Its Utilization. Paper No. A73-
56, Metallurgical Society of AIME, Feb. 28 - Mar. 1,
(1973), Chicago, Illinois.
Sutyrin, Yu. E. and Zerev, L.V. Light Metal Age. 34 (1-2),
9-10. Feb., (1976).
Tschopp, Th., Franke, A. and Bemhauser, E. J.- of Metals.
,31 (6), pp. 133-135, June, (1979).
U.S. EPA. Operation and Performance of the Lime Scrubbing
System a£ Mitsui Aluminium Co., Ltd. U.S. ETA 450/2-
73-007, Dec., (1973).
U.S. EPA. Trace Pollutant Emission from the Processing
of Metallic Ores. EPA 650/2-74-115. Oct., (1974).
West, C.E. Light Metal Age. 38 (9-10), pp. 16-18, October
(1980).
-------
CHAPTER 8
PHOSPHATE FERTILIZER INDUSTRY
8.1 INTRODUCTION
Fertilizers in general can be categorized by their composi-
tion of plant nutrients. The fertilizers differ in their composi-
tion of plant nutrients of nitrogen, phosphorous, and potassium.
Normal superphosphate contains only one nutrient, phosphorous.
Ammonium phosphate contains phosphorous and nitrogen. Generally,
the aolid and liquid mix fertilizers contain all three nutrients
in varying amounts.
Over 44 million metric tons of phosphate rock were mined
in the United States during 1975. Approximately 22.7j million
metric tons were consumed by the fertilizer industry during
the same period (Nyers, et al. 1979).
The phosphate based fertilizers are produced by conver-
sion of insoluble phosphate ore into the soluble form necessary
for plant consumption. The phosphoric acid, backbone of
phosphate fertilizer, is formed by mixing phosphate rock with
sulfuric acid.
This chapter concentrates on the production of phosphoric
acid, normal superphosphate, and ammonium phosphate. The
preparation of phosphate rock is not discussed in this chapter.
-------
8.2 VET PROCESS PHOSPHORIC ACID PRODUCTION 8>2
Most of the phosphoric acid in the fertilizer industry is
prepared by the wet process. In this process phosphate rock
reacts with sulfuric acid to fora phosphoric acid and gypsum.
The overall chemistry of this reaction is shown In equation 8.1
(Corbridge, 1978):
Ca10(PW2 * 10 H2S04 * 20H2 *
(Flourapatite)
6H3P04 + 2HF + 10CaS04 + 2H2 (8.1)
(gypsum)
Phosphoric acid is the most important intermediate in the
production of phosphate fertilizer. In addition to its use
in the production of ammonium phosphates and concentrated
superphosphate, It is an intermediate for mixed fertilizer,
both liquid and solid (Nyers, et al. 2979).
A simplified flow diagram of the wet process for phosphoric
acid production is given in Figure 8.1. The process consists
of three steps: (1) reaction of phosphate rock, (2) separation
o£ acid from the sulfate, and (3) concentration of the acid.
Important variables for a successful operation are type of
phosphate rock used, the temperature of the reaction, and
the slurry density controlled by recycling weak acid to tLe
digester step.
-------
8.3
PHOSPHATE
ROCK
SUUORIC
ACID
SUUVRIC
ACID
DILUTION WATER
ATTACK
VESSEL
SCRUBBER
FILTRATION
CYTSUH
POHD
CVAFOKAriQfF
CTPSim
BT-PROOUCT
nomicr ACID
Figure R.I. Vet Proccat
(Hyvra, «£..«£
id Production Ptoe««s
-------
Most vet process plants employ the crystallzatior of 8><*
calcium sulfate in the dehydrated state as opposed to heml-
hydrate or anhydrate. This is due to the fact that the de-
hydrate process dees not impose as many operating problems
as the hemi-hydrate or anhydrate process. Acid produced by
the dehydrate process contains about 13% Phosphorus (P) (30Z
P20.) and is generally concentrated to 17 to 24S P (43 to
54Z P2°s) before use. The concentration of phosphoric acid
is facilitated by continuous heated vacuum evaporators
(Olson, et al. 1971).
There is a substantial amount of pollutants evolved by
the wet process. A large portion of reactants become by-
products contributing to the pollution. The main by-product
of the dehydrate process is the impure gypsum of little
practical use. Phosphate roc'.-: is compoied of 2/3 gypsum,
thus making the disposal of the by-products a formidable
problem. The other by-product is flourlde, which evolves
during digestion of phosphate rock and can be recovered
with water by a relatively simple scrubbing procedure.
The evolution of gaseous flouride is caused by any
flourlde containing liquid due to tne vapor przsaure of
flrurlde. The emission rate varies with temp mature, concen-
tration, absolute pressure, and exposed area of the liquid
surface on the digester. Gaseous flouride emissions contain
silicon tetraflourlde, which is formed by the reaction of
-------
hydrogen flourlde in the reactor. Tetraflouride formation 8.5
is favored at temperatures below 100°C (Nyers, £t, al. 1979).
Poorly controlled wet process phosphoric acid (WPPA)
plants may have emissions as high as .07 pound of flouride/ton
of P.O. fuel. On the other hand, well controlled plants using
packed scrubbers or other equally effective control devices
can achieve flourlde emissions below .02 pound/ton of P.O.
input (U.S. EPA, Oct. 1974). The data indicates that the
emission factors for plants that use flouride recovery is p- •
significantly different from those plants that employ the
recovery. The recovery refers to flourlne recovered as
fluosilicic acid, flourides, flousillcates, or other by-
products (Nyers, _e£ jd. 1979).
The final flourlne emission Is strongly dependent on the
type of scrubber used, scrubber operation, and use of fresh
water tail gas scrubbers. Plant? that use flourine recovery
may dispose less volatile flourlne to their pond system, thus
having fewer emissions from the ponds.
The most Important emission source in the typical WPPA
process is the ventilating air from the digester. The
digester vent gases contain water vapor, participate dust,
and S1F.. The removal of flourine can be accomplished by
the wet process or adsorption (solid reagent or adsorption
system) of the ventilating air. The wet process has been
used exclusively, however, the advantages and capabilities
-------
of Che adsorption process should be studied (U.S. IP A, Hatch 1973). 8.6
The design of the scrubbing equipment is Limited by the
cheoistry of the reactions between the gypsum pond water and
tae flourine containing gases discharged from the WPPA plant
reactor. The folloving reactions occur In the reactor:
CaF2 •»• HjSO^ * CaS04 + 2HF (6.2)
or
2HF + S1F, * H.SiPt (8.3)
Furthermore, hydrolysis of SiF^ can occur at high concentra-
tions (i.e. higher than equilibrium concentration) as follows:
3S1F4 + WjO * Si
-------
flow scrubber la v compromise between the counter and co- 8.7
current scrubbers, ic employs the efficiency of the former
with the nechanicel advantages of the latter. The crosa-
f)->- sci-ibbar has been used in combination with spray towers,
venter!. or wet cyclones in pl-.osphorlc acid plants (U.S. EPA,
March 1973).
The efficiency of the scrubber is dependent on the
temperature and rtnooc'tlon of the scrubber nudlum. The
gypaun pond water >iaeo In the ^crvl^er contains 30C9 ppm
to 10,000 ppa of flourine (Nyezs, .ct ;-l. !<)". O. Efficient
renoval of flourine C.-cn the gaa stream is reduced, ^ue to
the high partial pressure of hydrogen flourid In the pond
water. The tnaaa transfer rate alao decreases as temperature
increases, thus, fresh water should be used as the scrubolng
medium in the last stage of scrubbing.
Oxides of sulfur are alao emitted in the WPPA procc*-.
Their production ranges from 0.0077 to O.OS8g/kg P2°s'
However, the origin of SO formation la not clear in tlc
WPPA proceas (Nyera. £££!.• 1979). The cause of its
emlaaion must firat be determined before any measure
regarding Its reduction wit Lin the process la taken.
8.3 RECOMMENDED AREAS FOR FOU.UTIOS CONTROL RESEARCH:
VET PROCESS PHOSPHORIC ACID PRODUCTION
After evaluating the avallab.'c literature, tha following
areaa are recooBended for further research by the study:
-------
. Studies on purification of phosphate feed to
reactor to reduce impurities which cause
by-produce formation.
. Cooper a Live studies on adsorption and absorption
of flourine to determine the most efficient
technique to alleviate flourine emission.
. Research on the design and operating parameters of
the scrubber to reduce plugging and Increase the
rate of flourine transfer from the vent gases to
scrubbing medium.
8.4 UORMAX. SUPERPHOSPHATE PRODUCTION
Normal superphojpoate (RS) Is produced by the reaction of
phosphate rock with aulfuric acid. The phosphate, rock and
ILSO. are nixed In a cone mixer (reactor vessel), the acidulate
la then transfered to an enclosed area (den) to solidify.
The solidified product is then stored for curing. The schematic
diagram of this- process la shown In Figure 8.2.
The HS production csa be accomplished by both continuous
and batch processes. ?or th* batch process, a pan miser
(Instead of cone mixer for the continuous process is used. However,
both processes convert fluorapatlte in the rock to soluble
monecalciuE phosphate. The major reaction la this process is:
3CCaH4 (P04)2 By)! + 7CaS06 * 2HP (8.5)
-------
StrutiHC
ACID
nissiOM
IKTCUD
TO CtmiMC
1.1. flew Chan of HDIM! SupcrphoiphaU Product la*
-------
The source of pollution emissions for a NS plane are the 8.i«x
mixers, den, and curing building. Between 1.5 kg and 9.0 kg
of flouridea/metrle ton of NS are released during production
and the curing process (Myers, et. al. 1979). The flouride emis-
sions occur in form of flouride vapor evolving as hydrogen
flouride and silicon tetraflouride. The flouride emissions
range from 0.07 g F/kg PjOj to 0,45 g F/kg PjO^. Individual
emission rates from each unit is hard to find since all gases
are vented to the same stack.
As previously discussed, tha scrubbing is inhibited by
the formation of a gelatinous mass, generated by the reaction
of tetraflouride and water. Thus, the use of conventional
scrubbing, for pollution abato-neat, is greatly influenced
by this reaction. The effectiveness of the flouride reduc-
tion by a scrubber is determined by Inlet flourine concentra-
tion, outlet saturation temperature, composition and tempera-
ture of the scrubbing liquid, scrubber type and transfer
units, and effectiveness of entrainmenc separation (Heller,
et al. 1968).
The best strategy for pollution control is to use a cross-
flow scrubber. Furthermore, flcurine removal is enhanced by
use of fresh water in the last stage and increasing the number
of stages in the scrubber (Myers, j£ al. 1979).
-------
8.3 RECOMMENDED AREAS FOR POLLUTION CONTROL RESEARCH: NORMAL 8.11
SUPERPHOSPHATE PRODUCTION
After evaluating the available literature, the following
areas are reconnended for further research by the study:
Studies on the scrubber design and optical operating
paraaeters to reduce flourlne emissions.
8.6 AMMONIUM PHOSPHATE PRODUCTION
The production of ammonium phosphate (AP), mostly
dlanmonlum phosphate (DA?), has increased rapidly in the past
3 decades. The total of ammonium phosphate produced in the
U.S. reached nearly 3.7 million tons ^S* vhicn ls 63.4Z
of all phosphate fertilizers produced in the U.S. (Kirk-
Othmer, 1980). Approximately 99Z of AP are used as fertilizer
(Nyers, et al. 1979).
The discussion to follow includes the granulation of
phosphoric acid with anhydrous ammoniation-granulation to
produce granular fertilizer. Ammonium phasphate is produced
by the reaction of phosphoric acid with anhydrous ammonia.
In 1975, 84Z of AP produced in the U.S. was of DAP grade
(i.e. percentage of available N-K-P is 16-0-48 (Myers, et.
al. 1979).
Ammonium phosphate C(NH.j.HPO.3 is produced by the
reaction of 1 mole of phosphoric acid with 2 moles of ammonia
forming a product with 21.1Z nitrogen and 5AZ available
phosphorous. Monoammoaium phosphate (MAP) can also react
-------
with amnonla to yield DAP. The DAP production eaa be 8.12
performed in either a pugmill or rotary drum ammonia tor.
Approximately 95Z of aononiatlon granulation plants in the
U.S. use rotary drum-mixer developed by TVA (Ravlirgs and
Reznik, 1976).
The pollution sources arise from four operations in
tht ammonium production process: (1) reactor, (2) ammonlator,
(3) dryer, and (4) cooliug. Typical emissions include,
ammonia, flouride, particulates, and negligible amount of
combustion gases. The following discussion is for the TVA
process depicted in Figure 8.3.
The reactor or preneutralizer is a vessel into which
70S of ammonia and all of the phosphoric acid is introduced.
The reactor operates at atmospheric pressure and 100-120°C.
The NH.:H.POA ratio Is maintained at 1.3:1 to 1.5:1 for
ma-rim,,m soliblllty of MAP, which is the main product of the
reactor (Nyers, e£ _•!. 1979).
The emissions from the reactor contain ammonia and
flourldes In form of gaseous emissions. The emissions are
caused by volatilization due to incomplete chemical reactions
and excess free ammonia. Collective emissions for reactor
tad ammonlator-granulator are as follows:
Flourldes (as F) 0.023g/kg P^
Particulars 0.076g/kg P20j
Ammonia emission data is available for the AP production
as a whole (Nyers, et al. 1979/.
-------
CypaiM
fond Water
Cypaua
Pond Water
Product to
Storage
Bagging.
or Bulk
ShlpMni
rtgure 8.1. Plow Dlagraa for TVA AMonltw Phosphate Proceaa.
(Nyera. tl rl. 1979).
-------
The reactor emissions can be controlled with a taore 8.14
efficient design of the reactor. Zn theory, the reactor
can be designed without any ventilation, but in practice
they are operated at a 57 - 76 cfa ventilation rate (U.S. EPA,
March 1973).
The reactor design can be modified to reduce the venti-
lation rate and thus the atmospheric emissions. Furthermore,
the excess ammonia should be avoided in the reactor vessel.
The rate of reaction should be increased catalytical.V/ by
changing the process conditions, and/or the residence time
should be Increased in order to achieve complete reaction.
The granulation by agglomeration and by coating particles
with slurry from the reactor takes place in the rotating
drum. Ammonia is supplied by a sparging action underneath
the bed to bring the NH^H^C^ ratio to 1.8:1.0 to 2.0:2.0
(U.S. EPA, March 1973). The granulation can, theoretically, be
performed with no ventilation. The ventilation is mainly
a function of design of the granuletor, thus design considera-
tions play an Imprrtabt role in the final emissions of
ammonia.
The emission from the reactor and granulator are scrubbed
for pollution reductions. Anyone of the various scrubbing
techniques can be applied to these off gases. However, packed
scrubbers should be avoided due to the formation of gelatinous
silicon or DAP, which tend to plug the scrubber. The best
-------
scrubbing technique for pru^ry scrubbing is a venturi cyclone 8-15
scrubber which has good capabilities for absorption of
ammonia and particulate matter.
Moist granules of DAP are dried to 2Z moisture in a
counter-current gas or oil fired dryer unit. The controlled
emissions from the dryer and cooler are 0.015g/kg PjO^
flouride and 0.75g/kg PjOj particulate emissions (Nyers, et
al. 1979).
The flouride emissions are due to ch« dissociation of the
fertilizer -product and particulate emissions are caused by
entrainment of DAP and MAP dusts in the ventilation air
streams. The particulate emissions may contain both
ammonium flouride and ammonium phosllicates (U.S. EPA, March 1973).
Typically, the primary scrubbers are designed to capture the
participates. Thus the design of the primary scrubbers must
account for the particulate as veil as removal of off gases from
the ventilation streams. Furthermore, the scrubbing medium,
in the primary scrubber, should be acidic enough to absorb the
ammonium discharge. For this pruoose 30Z phosphoric acid
solution is used for the primary scrubbing medium to recover
ammonia (U.S. EPA, March 1973).
Whenever the use of only one scrubber is not sufficient
to remove particulares and gases, combination of scrubbers
must be considered.
Table 8.1 contains the summary of pollution problems
associated with the phosphate rock industry and the suggested
-------
Table 8-1. Pollutant* and Suggested Strategy for Selected Phosphite Rock Fertiliser
Industry
Wet process
phosphoric
acid
Normal
Super-
phosphate
Product Ion
Anon 1 urn
Phoephste
Production
Process
Phosphate
Roc* Processing
Phosphste
Rock
Processing
DlammonluB
Phosphate
Production
Pollutanta
Flourldes
Partlculatea,
SOg, k Gypsum.
Flourldes.
Participates
Aanonla. -
Flourldea,
and
Partleul.cea
Source* In
Process
Reactor vessel.
rilteratlon.
vapors t Ion. &
gypsum pond
Nliera. den,
end curing.
Reactor, ~
at.monlator.
fryer, and
cooler.
Nature of
Pollutanta
Inorganic
gases, and
solids
Inorganic
gases, and
solids
Inorganic
gsses, and
solids
Pollutant Control
Cross flow scrubbing with
'fresh water In the Isst
stage, a-.id/or use combi-
nation of scrubbers.
Scrubbing the offgases.
cross flow scrubbing,
and/or use combination
scrubbing
Use combination primary
and secondary acrubblng
Improve the design on
the reactor end smaonlator
to reduce ventilation rate.
CO
•
fr»
o>
-------
strategy. 8.17
8.7 RECOMMENDED AREAS FOR POLLUTION CONTROL RESEARCH:
AMMONIUM PHOSPHATE PRODUCTION
After evaluating the available literature, the following
areas are recommended for further research by the study:
. Research on kinetics of reaction of ammonia
with phosphoric acid to enhance this reaction,
either catalytically or by increasing the resi-
dence time in the reactor vessel, which would
reduce the emission.
Studies on design of the reactor vessel and
granulators to minimize the ventilation rate
which would lead to smaller volumes of gaseous
emission.
Research on the design and selection of optimal
operating parameters for the scrubbing unit to
reduce the ammonia, flourlde, and particulate
emissions.
-------
BIBLIOGRAPHY 8.18
Chemistry and Technology of Fertilizer. V. Sauchelli, ed.
Rlenhold Publishing Corp., New York, New York 1960.
Corbridge, D. Phosphorous. Elsevlor Scientific Publishing
Company, New York, 1978.
Heller, A.N., Cuffi, S.T. and Goodwin, D.R. Inorganic
Chemical Industry. Air Pollution. Vol. Ill: Source
of Air Pollution and Their Control. A.C. Stern, ed.,
Academic Press, New York, New York, 1968.
Lutz, W.A. and Pratt, C.J. Principles of Design and Ope-ation
in: Phosphoric Acid. No. 1, A.V. Slack, ed. Marcel
Dekker, Inc., New York, New York, 1968..
Nyers, J., ££aJL. Source Assessment; Phosphate Fertilizer
Industry. EPA-600/2-79-019C, May 1979.
Olson, R.j.ejtal^ Fertilizer Technology & Use. Soil
Science Society of America, Inc., Wisconsin, 1971.
Rawlings, G T. and Reznik, R.B. Source Assessment! Fertilizer
MixinK Plants. EPA-600/2-76-032C. March 1976.
Slack, A.V. Chemistry and Technology of Fertilizers. John
Wiley and Sons, Inc., New York, New York 196/.
U.S. EPA. Air Pollution Control Technology and Costs in
Seven Selected Areas. Industrial Gas Cleaning Inst.,
Inc.. Stanford, CT, EPA-450/3-73-010, March, 1973.
U.S. EPA. Background Information for Standards of Performance;
Phosphate Fertilizer Industry. Environmental Protection
Agency, Research TriavgjL* Park, N.S. Office of Air
Quality Planning and Standards. EPA-450/2-74-019A, Oct.
1974.
-------
8.19
SUPPLEMENTAL REFERENCES
Gartrell, F.E. and Barber, J.C. Pollution Control Inter-
relationships, Chemical Engineering Progress. 62(10):
44-77, 1966.
Huffstufler, K.K. Pollution Problems in Phosphoric Acid
Production in; Phosphoric Acid. Vol. I, A.V. Slack,
ed., Marcel Dekker, Inc., New York, New York, 1968.
Illarionov, N.V., et al. Zh. Prikl-Khin. Vol. 36, 1963.
Kirk-Othmer Encyclopedia of Chemical Technology, Third
Edition, Volume 101, John Wiley and Sons, New York,
1980.
Lehr, J.R. Purification of_ Wet Process Acid In: Phosphoric
Acid. Volume I, A.V. Slack, ed. Marcel Dekker, Inc.,
New York, 196?.
Muehberg, P.E., Reding, J.T. and Shepherd, B.P. Draft
Report: The Phosphate Rock and Basic Fertilizer
Materials Industry. Contract 68-02-1324, Task 8, EPA,
Research Triangle Park, North Carolina, May 1976.
Shreve, R.N. Chemical Process Industries. Third Edition.
McGraw-Hill Book Company, New York, 1967.
U.S. EPA. Atmospheric Emissions from Wf.t Process Phosphoric
Acid Manufacture. U.S. Department of Health, Education
and Welfare, NAPLA. No. AP-S7, April 1970.
U.S. EPA. Final Guideline Documei.t; Control of Flouride
Emissions from Existing Phosphate Fertilizer Plants.
EPA 450/2-77-0051 March 1977.
-------
CHAPTER 9
CONCLUSIONS AND RECOMMENDATIONS
9.1 INTRODUCTION
Based on Che preparation of the reports submitted for the
eight industries, it is concluded that research programs in the
following areas should yield results encompassed in the objectives
of this program.
9.2 SOLVENT EXTRACTION
Modification of solvent extractor design and operation would
minimize metal ions or non phenolic organlcs in process streams
leaving extractor batteries in hydromet&llurgical and coal lique-
faction processes respectively. Studies could include modelling
of selective ion extraction in multiple metal systems, characteri-
zation of liquid dispersion properties such &3 surface area and
droplet mixing as a function of power consumption, extraction
kinetics, and separation of liquid-liquid dispersions.
9.3 CATALYST DEACTIVATION
Modification of catalyst reactor bed operation and studies
on catalyst deactivation will increase catalyst, life and reduce
the volume of spent catalyst from coal gasification operations.
Studies could Include modelling catalyst deactivation phenomena
as affected by temperature, pressure, feed gas composition,
catalyst structure, and catalyst type. Optimal reactor
operation studies for sulfur guard catalysts (ZnO), shift
-------
9.2
catalysts (cobalc-molybdate), and oethanation catalysts (nickel)
can be conducted.
9.4 LEACHING PROCESSES
Modification and improvement of leaching processes for
aulfide or oxide ores will reduce ground vater contamination
and dissolved metal salts In process streams in' hydrometallur-
gical processes. These results also apply to recovery of metals
from particulates (smelting dust), coal liquefaction ash, spent
catalysts in coal gasification, and coal liquefaction residues.
Studies could Include vat leaching using ammonlal or in organic
acid solutions. Characterization of kinetics of leaching as
affected by particle size, temperature, concentrations and
particle structure can be explored. Minimum power requirements
to suspend particles and maximize particle-liquid mass transfer
ran be studied.
9.5 GAS ABSORPTION
Modification and Improvement of gas absorption processes
such as the Stretford absorption process will reduce emissions
of H2, HCN, and COj in tail gases from coal liquefaction pro-
cesses and H2S and S02 for smelter off gas recovery operations.
Studies could Include gas-liquid mass transfer and gas-liquid
reactions in absorption liquids (sodium metavanedate, sodium
carbonate, sodium bicarbonate, and ADA) as affected by tempera-
ture, pressure, and gas-liquid contacting.
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9.3
9.~6 GAS-LIQUID-SOLID REACTIONS
Modification and improvement cf reactors for contacting
•ad reacting gas-liquid-solid dispersions vould minimize
partlculate emissions in coal liquefaction reactions as well
as vat leaching processes. Studies could include coal dissolu-
tion rates, gas dispersion, participate agglomeration, dissol-
ved gat-particle reactions, and determination of the rate
limiting steps as affected by mechanical imitation, temperature,
pressure and compositions.
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