INCREASED PRODUCTIVITY OF ZINC ROASTERS AND SO2 … · The roaster gas train post the FB furnace consists of a waste heat boiler, ... The formed mercury-selenium double salt is

The Southern African Institute of Mining and Metallurgy Lead and Zinc 2008

Pekka Taskinen, Maija-Leena Metsärinta, Björn Saxen, Sasu Penttinen, Kurt Svens, Bernd Kerstiens

Page 163

INCREASED PRODUCTIVITY OF ZINC ROASTERS AND SO2 -

QUALITY

Pekka Taskinen, Maija-Leena Metsärinta, Björn Saxen

[email protected], [email protected],

[email protected]

Outotec Research Oy, PO Box 69 Pori, FI-28101 Finland

Sasu Penttinen

[email protected]

Boliden Kokkola Oy, PO Box 26 Kokkola, FI-67101 Finland

Kurt Svens

[email protected]

Outotec Oyj, PO Box 86 Espoo, FI-02200 Finland

Bernd Kerstiens

[email protected]

Outotec GmbH, D-61440 Oberursel, Germany

Abstract

Advanced optimizing control of the fluidised bed zinc roaster has been in use for an

extended period at Boliden Kokkola and the implications are seen as extended bed

stability, increased throughput and far better on-line availability. The roaster furnace

control system developed is based on a dynamic and predictive furnace model, with

parameters determined experimentally at the site. The controller maximises the

concentrate feed and keeps the furnace operational parameters inside limits given by

raw material mix and equipment constraints.

The products of a zinc roaster, calcine, sulphur dioxide and the side products, such as

mercury, meet gradually more stringent requirements, in particular as to their assays

and total recoveries in the process chain. The end users of sulphuric acid in northern

Europe, among others in the pulp and paper industry, require mercury levels much less

than the conventional 0.2-0.4 ppm Hg. Therefore, secondary de-mercurising circuits

have been used over the last five years for further cleaning the SO2 stream allowing

production acid grades with less than 0.08 ppm Hg.



Page 164

1 Introduction

Boliden Kokkola Oy is a custom smelter and it uses 10-15 different concentrates each

year and a number of other raw materials as components of the feed mixture. The

today’s zinc production uses two main technologies at the site. The roasting-leaching-

electrowinning route has been in use since late 1960s and the more recent atmospheric

direct leaching [1] as the first treatment step to the sulphidic concentrates, has been in

use since 1998 and comprising today about 40% of total zinc production. Two parallel

technologies give clear advantages and increased flexibility in the use and selection of

raw materials. The produced sulphur dioxide gas is led from the roaster to sulphuric

acid plant by Kemira Oy.

Steam drum

Roaster furnace

Boiler

Cyclones Electric

precipitators

ST LH

Ball mill

Calcine

PT HT

Cooling

Air

Water

Steam

KT

VIT LIT

Stack

Heat exchangers

Contact tower

Air in

Air out

Cooling water

NaHS

Weak acid basins

Funda

Lime

To sea

Buffer

tank

WaterHeat recovery

Water

H2O

H2O

98.8% H2SO4

H2SO4

98.8%

95.6%

95.6%

OUTOKUMPU ZINC ROASTER AND KEMIRA SULPHURIC ACID PLANT

Zn-concentrate

Air

ORC / HVT 2/2000

Weak acid tank

H2O

H2OWater lock

ST = Sulphatating Tower

LH = Weak Acid Tower

SiO2

HCl

PT = Washing tower HT = Halogen tower

Se solution

KT = Drying tower

VIT = Intermediate

absorber

LIT =Final absorber

Figure 1. A schematic flow sheet of the combined zinc roaster-acid plant in Kokkola,

by Boliden Kokkola Oy and Kemira Oy, respectively.

Over the recent years, an extensive development program has been carried out for

increasing the treatment throughput of the two 72 m2 fluidized bed (FB) lines. The



Page 165

production equipment is basically the same as in 1969 when the smelter was started up

[2], Figure 1, but now significant improvements have been gained in the on-line

availability and production rate.

The development program included laboratory-scale and industrial-scale test runs on

the roasting kinetics and the mechanisms of selected sulphidic zinc concentrates, the

factors behind the bed instability phenomena, as well as introduction of a new advanced

control system to the two FB roaster lines. Improvements were also made in the roaster

gas handling, where the emphasis has been in reducing the mercury traces in the

product acid to a new level. This has been accomplished by the primary scrubbing

stages at the roaster were optimized and a secondary scrubbing step was added to meet

the strict requirements of pulp and paper industry.

2 Roaster gas handling

2.1 The gas train

The roaster gas train post the FB furnace consists of a waste heat boiler, cyclones and

two ESPs before the de-mercurising steps. The gas duct from the roaster to the acid

plant is long, about 1.0 km, separating thus the first scrubbing stage within the roaster

area and the second scrubbing stage at the acid plant, see Figure 1.

2.2 De-mercurising steps

The gas train consists of two separate de-mercurising steps, and allows thus production

of high-purity sulphuric acid from all zinc concentrates, sulphidic and oxidic,

independently of their mercury content. The first step is carried out in the immediate

vicinity of the roaster, and the second step is an additional and new feature of the

washing section of the sulphuric acid plant, see Figure 1.

The first de-mercurising step is composed of two physical stages. In the first stage the

de-dusted roaster off-gas post ESP is cooled by direct water quenching to below 200 °C

and then in the second stage it is scrubbed with a carefully controlled sulphuric acid

solution containing chloride and selenium [3] at about 60 °C. The mercury scrubbing

chemistry is based on the reactions:

Hg°(g)+Hg2+

(aq)=2Hg+(aq) (1)

SeO2

2-(aq)+SO2(g)=Se°+SO4

2-(aq) (1’)

Hg°(aq)+Se°=HgSe (1’’)

2HgSe+Hg+(aq)+2Cl

-(aq)=Hg3Se2Cl2 (1’’’)

In a strongly complexed aqueous medium, containing a spectrum of chloride-complexes

of mercury, as shown in Figure 2, the de-mercurising reactions must thus be capable to

remove both elementary and oxidized forms of mercury from the gas. In spite of the

fact that the stable form of mercury in the roaster off-gas is an oxidized substance,



Page 166

elementary mercury is typically determined in such circumstances and it forms a

significant fraction of total mercury [4].

A comprehensive thermodynamic model was built for the scrubber liquid using the

Pitzer model [5], including the complexation of mercury with chloride ions in a strong

sulphuric acid matrix. Description of the acid matrix was taken from a study where

water-sulphuric acid has been modelled to high concentrations and temperatures [6].

The gas phase was assumed to be ideal. The thermodynamic data for the double salt,

equation (1’’’), are not available and thus its saturation limit in the various operational

points could not be optimized.

A typical acid strength of 33-36% H2SO4 is used in the counter-current scrubbing at the

roaster. The other operating parameters of the step have been optimized by extensive

thermodynamic modeling of the gas-liquid –system and by observations at the site on

the mercury content of the off-gas and its speciation between metallic mercury vapour

and nonmetallic gaseous compounds. The formed mercury-selenium double salt is

separated from the scrubber liquid by filtering. The first scrubbing stage is also used for

controlling halogen carry over to the acid making, as the vapor pressured of HCl(g) and

HF(g) are very sensitive to the acid strength and the prevailing outlet temperature of the

scrubber.

1.0E-21

1.0E-19

1.0E-17

1.0E-15

1.0E-13

1.0E-11

1.0E-09

1.0E-07

1.0E-05

1.0E-03

1.0E-01

1.0E+01

100 150 200 250 300

Temperature ( °C )

Mola

lity o

f specie

s (

mol/kg )

Hg(+2a)

HgCl(+a)

HgCl2(a)

HgCl3(-a)

HgCl4(-2a)

Hg(a)

HgOH(+a)

Hg(OH)2(a)

Figure 2. Speciation of aqueous mercury in the scrubber liquid, at the cooling stage in

the first gas purification step at Kokkola zinc roaster, calculated by the thermodynamic

model; the thermodynamic data were taken from [6,9].

The second de-mercurising step is carried out using carefully controlled chemistry and

proper ‘side-reactions’ in the washing section of the acid plant [7]. Instead of pure

water, slightly acidified aqueous solution containing chlorides and selenium is used.

The chemistry is basically the same as shown in equations (1), but the actual process

conditions are different, in particular the scrubber temperatures.



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This solution chemistry has been successfully used at Kokkola since 2001, and the

purity of product acid is typically 0.05 ppm Hg (mg/kg H2SO4), which is much lower

than obtained with the calomel process [8]. In addition to the actual mercury

concentration of each feed mixture, the selenium-to-mercury –ratio is currently actively

controlled at Kokkola, and displayed in the daily roasting reports and instructions.

3 Development work for the operational window of the roaster

In order to improve the stability of the roasting process and to increase the on-line

availability and thus the throughput of the roaster, an extensive series of development

projects was carried out in 1998-2006. It included several limited tests series on the

industrial scale in the roaster area [10-11], dealing with the dynamics of the FB furnace

as well as with the behaviour of various feed mixtures in the roaster line. Various raw

materials were also studied on the laboratory scale [12], in order to get detailed

information about the accretion formation in the roaster vessel and the industrial

roasting kinetics. The overall procedure used is depicted below as the flow chart [13].

3.1 De-mercurising steps

The FB roasters at Kokkola use bed overflow only for the calcine outlet from the

furnace, in addition to WHB and cyclone products. Thus the physical properties of the

furnace calcine produced must meet the requirements of smooth material flow from the

overflow gates and no oversize agglomerates are allowed.

All laboratory scale investigation on the FB roasting of zinc concentrates were carried

out using a small batch-wise operating fluidized bed furnace with an internal diameter

of 40 mm and a typical batch size of 100 g. As the feed mixture in the roaster is

agglomerated by itself or assisted by water additions to conveyer belts or storage bins,

most high-impurity concentrates were additionally roasted as agglomerates in a

horizontal tube furnace [11]. The reason for it was to find out the details of the roasting

mechanisms and origin for the growth of agglomerates during FB roasting.

Mineralogical Analysing Laboratory Plant

evaluations calcine experiments experi-

samples ments

Applications and

operating rules

Thermodynamic Heat balance Active surveillance

evaluations calculations of special situations

in the Roaster



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0

2

4

6

8

1 0

1 2

1 4

1 6

4 9 5 0 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 6 0 6 1 6 2 6 3 6 4 6 5 6 6 6 7 6 8 6 9

Fe w

t%

Zn w t%

S a m p le

A P irs a

Ag u a s T e n id a s

Azn a c o l la r

B ru n s w ic k

C a ye l i

C o lq u ir i

F e i ta is

G a lm o y

G a rp e n b e rg

H -q ty

H e l lye r

L a N e g ra

L is h e e n

M o in h o

N -M iX

N -M ix

P e ru M ix

P ic k L a k e

P o la r is

R e d D o g

S o tie l

T a ra

T rze b io n k a

Figure 3. The analysed iron concentrations in the sphalerite lattice of selected sulphidic

zinc concentrates determined by EPMA.

Figure 4. Copper-rich core (light) formed in a partially roasted zinc concentrate

agglomerate as a result of rapid migration of impurities in a Cu-rich zinc sulphide.

The results obtained gave a lot new information about the behaviour of several

impurities in the oxidizing sphalerite concentrate, as to the bed non-stability phenomena

and furnace build-up formation [2,10-11]. The micrometer-scale phenomena observed

within the primary ZnS grains and on their oxidising surfaces at roasting temperatures

indicate, for example, that some common components of the zinc concentrates cannot

be the origin of bed non-stability, as typically iron dissolved in the sphalerite lattice,

Figure 3, which also indicates a specific type of sulphide mineralogy in the concentrate

where iron sulphides are of pyrrhotite type instead of pyrites. The detailed process

mineralogical structure analyses of partially roasted sulphides indicated the prevailing

oxidation mechanisms that involve copper and lead, if present at high concentrations,



Page 169

migrating in the system. Due to their low melting point compounds they are prone to

forming sinters and thus agglomerating the calcine, Figure 4.

3.2 Impurity control in the feed mixture – heat generation and oxygen

requirement

As various impurities in the concentrates behave in a different manner in the FB

roasting process, their active control is necessary [13]. That typically involves

controlled and limited concentrations for some key elements, as well as for their sum

concentrations and restricted operational temperatures, based on the feed mixture assay.

Therefore, a number of components in the feed mixture have their specific upper

(maximum) limits allowed, as generally used in this industry [14], but also the

mineralogical features of some elements in the concentrates are taken into account

when selecting the feed mixture assay. This typically refers to the distribution of such

elements and their presence in stable, high-melting compounds and less stable phases,

melting around the roasting temperature.

0

200

400

600

800

1000

1200

1400

1600

1 3 5 7 9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

Concentrate source#

Heat value kWh/dmt

O2 requirement Nm3/dmt

SO2 produced Nm3dm/t

Fe*10 wt%

Figure 5. The heat value and oxygen requirement of selected sulphide concentrate raw

materials used in zinc production at Kokkola, organized according to their energy

content [16].

An important and general feature of the FB roaster is its essentially fixed cooling

capacity, which is not a function of the production rate. As the volumetric process air

flow rate is essentially determined by the desired oxygen coefficient of the FB (true

oxygen feed rate to stochiometric oxygen need of the fed mixture) the cooling effect of

the process gas can not be used for controlling the furnace temperature. For this



Page 170

requirement, secondary air introduced above the FB can be used if high bed

temperatures are allowed, but the off-gas should be cooled and possibly after-burned to

lower the residual sulphidic sulphur level of the boiler calcine [15]. This feature is,

however, dependent on the bed calcine outlet, whether it is realized as bed underflow or

overflow. The former design ends up with a higer sulphide sulphur in the calcine, due to

the mixing properties of the fluidized bed.

For stabilising the feed mixture preparation routines, the generation of heat in the

roasting (the oxidation enthalpy of the minerals in the feed mixture to the typical

substances in the calcine) and the amount of oxygen needed (Nm3/dmt) in the roasting

is estimated at Kokkola for all the concentrates and other raw materials used, see Figure

5. The roasting heat generation and oxygen consumption values are determined from

the chemical assay and a mineralogical characterization done from time to time for each

raw material.

4 Furnace control development

Controlling the FB roasting optimally is demanding, since many of the process

variables interact. Thus there is a need for multivariable control strategies, and

development of such requires good knowledge of the dynamic dependencies between

input and output variables. In 2003-2004, a model for the furnace dynamics was

developed [17-18] based on data from plant experiments at Boliden Kokkola. Based on

the dynamic model, a multivariable control application was developed and implemented

in 2005. The controller maximises production within the limits given by process

metallurgy and the equipment.

4.1 Measurements and control variables

Furnace bed temperatures are measured in various locations at the bottom and at the

wall of the lower part of the furnace. The bed temperature has to be kept within certain

ranges to maintain proper conditions for roasting. The temperature at the upper part of

the furnace, which is measured at the boiler inlet, is also important. The concentrate

feed is the primary manipulated variable. Also two water feeds are adjusted: water is

added to the concentrate feed on the load conveyor, but can also be fed directly into the

furnace. Air, which is both the fluidising medium and the source for oxygen, is

normally kept at a fixed value. There is a possibility to feed technical oxygen to the

furnace, although this is option currently not used.

The oxygen coefficient, i.e. the ratio between the actual oxygen feed and the amount of

oxygen needed stoichiometrically to combust the feed mixture, should be kept within

ranges given by the concentrate properties. Current plant practise is to control an

estimate of the oxygen coefficient, based on the oxygen demand of the rated

concentrate mixture. There is a measurement of the oxygen content in the boiler off-

gas, which gives information of the realised oxygen coefficient. However, this

measurement is somewhat uncertain due to air leakages into the furnace and the boiler.



Page 171

4.2 Dynamics

A large number of step-change experiments were carried out to identify the dynamic

behaviour of the FB furnaces. The experiments comprised of changes in six

manipulated variables, see Table 1. During the experiment periods, the existing

automatic controllers for furnace temperature and boiler inlet temperature were

switched off to obtain data from the open loop system. The sampling time was chosen

to ten minutes, since the data collection system at the roaster plant did not store values

more frequently.

The observed effects are qualitatively shown in Table 1. The dependencies are highly

interconnected. For instance, not only the concentrate feed but also the feeds of water

and air affect the furnace temperature. An example of the effect of changes in load

conveyor water feed is shown in Figure 6. The load conveyor water has a rather

complex effect on the furnace bed temperature, the long-term effect is positive, but

there also is an inverse response during the first hour.

Table 1. Dependencies between manipulated and observed variables in the fluidised

bed furnace.

Effect on

Step-change

increase in

Bed

temperatures

Boiler inlet

temperature

Offgas oxygen

content

Windbox

pressure

Concentrate feed increase increases decreases -

Air feed decrease increases increases increases

Oxygen feed diverge - increases increases

Overflow grate area

pressure

- - - decreases

Load conveyor

water feed

temporary

decrease, then

increase

decreases temporary

increases

-

Furnace water feed decrease - - -

Quantitative modelling of the dynamic effects shown in Table 1 was made using

ARMAX type time series models. It was known that this linear model structure could

not describe the furnace behaviour in all situations, e.g. when the oxygen coefficient is

shifted to values below one. However, the primary goal was to develop a model for

normal operation conditions, where a linear description was assumed to be adequate. As

a first step in the identification, partial models (sub-models) were identified for the

single input-output pairs. The aim was to find models as simple as possible describing

the dependencies between input and output observed in the experiments. Zero order and

different first order models were used. Finally, the partial models were combined into

one model for each output, which also included disturbance models.



Page 172

0

100

200

300

400

500

600

L/h

Load conveyor water feed

920

930

940

950

960

06:00 09:00 12:00 15:00 18:00

°C

Furnace temp. 6 Furnace temp. 7

Furnace temp. 12 Furnace temp. 14

Figure 6. The effect of step changes in load conveyor water feed on temperatures in the

furnace bed.

In addition to the step-change experiments, tracer tests were carried out to clarify the

residence time of the solid material in the bed and in the gas line. In the tests, TiO2

material with a density and a particle size distribution close to that of calcine was used

as tracer. The tracer was fed in impulses (batches) to the feed mixture at the slinger belt

feeder. The results indicate that the mean residence time of the solid particles in the bed

is approximately 20 hours, as can be seen in Figure 7. For the gas line, however, very

short residence times were observed. The peak concentration in the cyclone (post

boiler) was obtained around one minute after the impulse in the furnace feed.

0

0.05

0.1

0.15

0.2

0.25

-10 0 10 20 30 40 50 60 70 80 90

Time (h)

Ti (%

)

2.9.2003

22.9.2003

model

Figure 7. Tracer content in the bed overflow in two experiments: the tracer was fed as

an impulse at time 0 h. A first order model with a time constant of 20 h is shown for

comparison.

The results are quite similar to the results by Dimitrov’s [19] in a small FB furnace.

Also Themelis [20] has reported results of retention time tests, using a radioactive

tracer. He showed experimentally that various particle size fractions have different

retention times.



Page 173

5 Control system

A control system was developed to enable real-time production maximisation within the

limits given by process metallurgy and equipment. The input and output signals of the

control application are shown in Figure 8. The optimising control system maintains a

concentrate feed as high as possible so that all variables are within given limits. Water

additions (to the concentrate on the load conveyor and/or directly to the furnace) are

used if they enable a higher concentrate feed.

User specified limits

Concentrate feed

Load conveyor water feedf

Furnace water feed

Bed temperature

Boiler inlet temperature

Temperature of air feed

Oxygen feed

Oxygen requirement of concentrate

Concentrate feed

Load conveyor water feed

Furnace water feed

Air feed

control

model

Oxygen coefficient (min) Concentrate feed (max) Load conveyor water (min, max) Furnace water (min, max) Bed temperature (min, max) Upper temperature (min, max) Offgas O2 (min)

Figure 8. Input and output signals of the optimising control system.

As described in previous chapter, the interactions in the fluidised bed furnace are cross-

coupled. Thus, a MIMO (multiple input – multiple output) control structure was used,

since separate single-input, single-output controllers would not operate optimally. The

control system includes a state estimator based on the dynamic ARMAX models

identified in the step-change experiments, an optimisation routine based on the

SIMPLEX algorithm, and a controller based on state prediction. The algorithms were

developed in MATLAB®

, which is also the environment used for control system

implementation. OPC is used for the communication between the control system on a

PC and the Honeywell TP®

Alcont automation system of the roaster. The operator

interface, where the limits are specified, is in Alcont.



Page 174

M O Q S U NM NO NQ NS

OO

OQ

OS

OUÅçåÅÉåíê~íÉ=ÑÉÉÇI=íLÜ

M O Q S U NM NO NQ NS

PKU

Q

QKO

ñ=NMQ ~áê=ÑÉÉÇI=kãPLÜ

M O Q S U NM NO NQ NSM

RMM

NMMM

Ñìêå~ÅÉ=ï~íÉêI=äLÜ

M O Q S U NM NO NQ NSVMM

VOM

VQM

ÄÉÇ=íÉãéÉê~íìêÉI=…`

M O Q S U NM NO NQ NSMKV

N

NKN

çñóÖÉå=ÅçÉÑÑK

a~óë

éêçÅÉëë

äáãáí

N O

Figure 9. Data from the model-based control of a FB furnace. See text for explanation

of periods 1 and 2.

The calculation interval of the control system is 5 minutes, and the main steps in a

calculation round are:



Page 175

1. Pre-treatment and validity check of process data

2. Updating the state of the dynamic model

3. Searching optimal set of manipulated variables

4. Control actions based on 30 minutes prediction.

Figure 9 shows history trends from 20 days operation of a furnace, and the actions of

the control system. In period 1, the upper limit for bed temperature limits the

production, and the feed of furnace water is at maximum limit. In period 2, the lower

limit for oxygen coefficient limits the production.

6 Conclusions

The complex nature of material flows and the increased requirements as to their quality

and on-line availability, in particular in a large industrial network of several

independent companies, are a major challenge for the metallurgical process industry.

Therefore, an intensive R&D programme has been accomplished at Boliden Kokkola

zinc smelter for securing the quality issues in the zinc production, including also its by

products such as sulphuric acid.

References:

1. Takala H, Leaching of zinc concentrates at Outokumpu Kokkola plant, Erzmetall, 52 (1999) 1, 37-42

2. Metsärinta M-L, Taskinen P, Nyberg J, Ohvo E, Industrial Scale Roasting of Impure Concentrates at Boliden Kokkola, Proceedings of PbZn 2005 – International Symposium of Lead & Zinc Processing (Ed. T Fujisawa, J Dutrizac, A Fuwa, N Piret, A Siegmund), MMIJ, Kyoto (2005) pp. 343-357

3. a. Bryk P, Haani M, Honkasalo J, Kinnunen J, Lindsjö O, Nyholm E, Poijärvi J, Rastas J, Kangas J, Process for removal and recovery of mercury from gases, USP 3 677 696, Outokumpu Oy, appl. July 3, 1970, and b. Kuivala AMF, Leppinen JO, Poijärvi JK, Rastas JK, Process and apparatus for the removal of mercury from sulphur dioxide-bearing hot and moist gases, USP 4 579 726, Appl. Jul. 9, 1984

4. Nishitani T Fukunaga I, Itoh H, Nomura T, The relationship between HCl and mercury speciation in flue gas from municipal solid waste incinerators, Chemosphere, 39 (1999) 1, 1-9

5. Pitzer K, Thermodynamics of Electrolytes. I: Theoretical basis and general equations, The J. Phys. Chem., 77 (1973) 2, 268-277

6. H Sippola, Modelling the solubility of ferrous sulphate in sulphuric acid-water solutions, Helsinki University of Technology, Licentiate thesis, 1992, 109 p.

7. Peltola H, Taskinen P, Takala H, Nyberg J, Natunen H, Panula J, Method for removing mercury from gas, WO 02/45825 A1, Outokumpu Oyj, appl. Dec. 8, 2000

8. Hultbom KG, Industrially proven methods for mercury removal from gases, EPD Congress 2003 (Ed. ME Schlesinger), TMS, Warrendale (PA), 2003, pp. 147-156

9. Roine A, HSC Chemistry for Windows, vers. 5.0, Outokumpu Research Oy, Pori, report 02103-ORC-T, 12.08.2002, 363 p.



Page 176

10. Taskinen P, Jyrkönen S, Metsärinta M-L, Nyberg J, Rytioja A, The behaviour of iron as impurity in zinc roasting, Sulphide Smelting 2002 (Ed. R Stephens & HY Sohn), TMS, Warrendale (PA), 2002, pp. 393-404

11. Metsärinta M-L, Taskinen P, Jyrkönen S, Nyberg J, Rytioja A, Roasting mechanisms of impure zinc concentrates in fluidized bed, Yazawa International Symp., Vol 1. (Ed. F Kongoli, K Itagaki, C Yamauchi & HY Sohn), TMS, Warrendale (PA), 2003, pp. 633-646

12. Metsärinta M-L, Taskinen P, Nyberg J, Ohvo E, Mechanisms of impure zinc concentrates roasting in fluidized beds, Tsvetnye Metally, 6 (2005) 5-6, 92-99

13. Nyberg J, Characterisation and control of the zinc roasting process, PhD Thesis, University of Oulu, 2004, 114 p.

14. Grant RM, Zinc concentrate and processing trends, Int. Symp. – World Zinc ’93, (Ed. IG Matthew) Aust. IMM, Victoria (Aust.), 1993, pp. 391-397

15. Svens K, Kerstiens B, Runkel M, Recent experiences with modern zinc processing technology, Erzmetall, 56 (2003) 2, 94-103

16. Metsärinta M-L, Thesis for Lic. Techn. degree, University of Oulu, 2008 17. Härkönen, J. Identification of a Zinc Roaster Furnace, Master´s thesis. Åbo Akademi

University, Finland, 2003. 18. Saxén, B., J. Nyberg, J. Härkönen, H. Toivonen, Dynamic Behaviour of a Zinc Roaster

Furnace, 11th IFAC Symposium on Automation in Mining, Mineral and Metal processing - MMM 2004, September 8-10, 2004, Nancy, France

19. Dimitrov R, The improvement of zinc concentrates roasting in a fluidized bed, Rudarsko-Metalurški Zbornik, 30 (1983) 4, 397-419

20. Themelis NJ, Freeman GM, Fluid bed behaviour in zinc roasters, JOM, 36 (1984) Aug., 52-57

Documents

INCREASED PRODUCTIVITY OF ZINC ROASTERS AND SO2 … · The roaster gas train post the FB furnace consists of a waste heat boiler, ... The formed mercury-selenium double salt is