Pulp-froth interface control in the flotation column

Process Simulation and Control

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PULP-FROTH INTERFACE CONTROL IN THE FLOTATION COLUMN A.C. Maffei*, I.L. de Oliveira Luz ~ *Funda95o Centro Tecnol6gico de Minas Gerais / CETEC, Av. Jos6 C~ndido da Silveira, 2000, Horto, CEP 31170-000, Belo Horizonte, MG, Brasil Tel: +5521 489 2363 - e-mail: [email protected] ~ Representa~6es e Consultoria Industrial Ltda, Rua Bambui, 448, Conj. 302, CEP 30310-320, Belo Horizonte, MG, Brasil e-mail: [email protected]

Abstract

Considering the available alternatives for automation of the operation and control of the pulp-froth interface, and aiming at its stabilization, as well as the accomplishment of scale-up parameters, CETEC (Technological Center of Minas Gerais Foundation), located in Belo Horizonte/Minas Gerais/Brazil, developed a computer-control system to vary the pulp-froth interface by varying the flow of non-floated fraction. The chosen alternative to control the flotation column operation aimed to render available an installation, in pilot plant scale, endowed with a control system with faster response and lower cost, compared to what is currently available on the market. In the system which is already in operation, and whose results will be presented here, FIELDBUS technology was used. Besides allowing further implementation of measurements and flow control at a distance, the system presents the basic characteristics of a "network architecture" and has as its main advantages: low installation cost, simple maintenance procedures, options to upgrade, information for quality control, and compatibility with equipment of various manufacturers.

Keywords: flotation, interface, pilot plant, communication, FIELDBUS

Introduction

This paper presents an instrumentation of a flotation column system for process control using digital FIELDBUS communication. The pressure transmitters work with FIELDBUS converters for an intensity of current of 4 mA to 20 mA, which renders possible the link between the conventional part of the pilot plant, the frequency inverters, and the transmitters. A simple interface connects the field instruments to a Pentium II 300 PC, which contains a software configuration for maintenance and supervision of the system. The more complex system depends on a power intelligent board that executes advanced controls and mathematics functions. This system also includes isolated safety barriers, FIELDBUS feed power, impedance controller and FIELDBUS terminator. The large amount of functional blocks and available mathematical controls in this system provides for engineering processes and a large capacity control. The protocol opened leads entirely to a real open solution that permits the use of the software and hardware of several producers at any time. This project is in accordance with the ISO/OSI model and the connections are executed by a normal industrial cable. The equipments provide an intrinsic security

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Proceedings of the XXI International Mineral Processing Congress

for dangerous atmosphere and variables are identified by expressing tags in the engineering units. Functional blocks with input and output standardized parameters, configuration and known algorithm, indicate the variable conditions. Objectives

The goal is to develop an instrumentation in order to reach complete flotation column process control using digital communication. The flotation column automatization makes for easier control of the pilot plant performance. This automatic system makes it possible to collect all technical parameters in order to make the scale-up of the flotation column. Characterization of the components

The FIELDBUS net of the flotation column pilot plant in CETEC consists of six pressure transmitters bus powered type, two converters of current to FIELDBUS, four frequency inverters, one feed power, one impedance for FIELDBUS feed power, two terminators and one PCI board. The AIMAX supervisor program is used and SYSCON is used to configure the system giving a software tool whose requirements consist in: - hardware: PC Pentium II 300 or similar; Microsoft mouse or similar; 8 MB of RAM; 4 MB of hard disk space; VGA monitor (16 colors) with high resolution or a SVGA monitor is recommended; 389 floppy-disk drive, 1.44 MB; interface FIELDBUS of SMAR: BC1 (converter FIELDBUS-EIA-232-R) or PCI (Interface of the Process Control), - software: AIMAX supervisor and SYSCON configuration system work in Microsoft Windows 3.1 or Windows 95 platform, as an application of 16 bits. - pressure FIELDBUS transmitters: model LD302D21Z-001Z-00-2D/I1; capacitance type (capacitance cell); calibration: 0.0000 to 15.0000 and 0.0000 to 50.0000 kPa; range: 5 inch to 200 inch of H20; material of diaphragm/fluid of filling: inox 316L/silicone; without adaptation body; place of indication: digital; without process connection; electrical connection: 89 NPT; without support; installation: directly to the equipment body; precision: + 0.07, 5% of span. - PCI = Interface Process Control: interface FIELDBUS of high performance; multi-canal; ISA card of 16 bits; CPU RISC de 32 bits c/04 channel master FIELDBUS H1 (31.25 Kbps). - BT302 = FIELDBUS terminator: maximum operation tension: 35Vdc; impedance of the entrance: 100 ~+2%@7, 8 KHz. - PS302 = feed power to FIELDBUS: entrance: AC = 90 a 260 Vac to 47 a 440 Hz; maximum power: 45 Watts; DC:127 to 367 Vdc; exit: tension of 24 Vdc + 1%; electrical current: 0 to 1.5 A. - PSI = impedance to the feed of FIELDBUS: feed tension: 24 to 32 Vdc + 10%; outside electrical current (max.): 340 mA; normal dissipated power: 2.5 Watts @ 24 Vdc (max). The project and its configuration

Table I synthesizes the main parameters of the process control.

Process Simulation and Control

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Table I: Flotation column process control. Item 1 2 3 4 5 6 7 8 9 10 11 Equations

Parameter discrimination Froth layer height in the column Air flow rate Air superficial velocity Pulp volume of tailings Pulp mass of the feed Pulp mass of tailings Mass of ore feed Mass of tailings Water weight in the feed Water weight in the tailings Clean water flow rate of net control

configuration

Symbol L Qg Jg Qt Fm Ft Mf Mt Wf Wt Wc of the flotation

Range 0.0 to 100.0 4.6 to 13.8 1.0 to 3.0 100.0 to 2,500.0 100.0 to 3,750.0 100.0 to 3,750.0 0.0 to 2,250.0 0.0 to 2,250.0 0.0 to 1,500.0 0.0 to 1,500.0 0.0 to 500.0

Unit cm 1/min cm/s ml/min g/min g/min g/min g/min g/min g/min ml/min

column

For each one of the three flotation columns, the mathematical algorithms were used to calculate the operational variables: Equation to control the froth level, i.e., the pulp froth interface of the flotation column, was cited by Yichausti et al. (1988): PI "H ~ - P ~ HI

Lm pl_p2+(H2_H1).g.lO_4pe

-

(1)

The specification of each variable is presented in Table II; Pe means froth density varies from 0,2 g/cm 3 to 0,3 g/cm 3. Equation to monitor air density (Holdup) in the flotation column was cited by Yianatos and Finch (1990): Eg(%)- (1-

P2-Pl ) P, "g" ( H 2 - H,)" 10 -4. "10

-

0t means pulp tailing density. Equation of pulp feed flow rate of the flotation column:

-

O f - 24.0-Q(o/o), range from 100.0 1/h to 2,500.0 1/h. Equation of pulp tailing flow rate of the flotation column: Qt = 24.0.Q(%),

(2)

(3)

(4)

-

range from 100.0 1/h to 2,500.0 1/h. Equation of pulp mass in the feed of the flotation column: (5)

-

Mt-=Qf-pf, range from 100. 0 to 3,750.0 kg/h. Equation of pulp mass tailing of the flotation column:

(6)

-

Mt=Qcpt, in kg/h; pt in g/cm 3, varies from 1.0 to 1.5. Equation of ore mass flow rate in the feed of the flotation column: Mo=Mf-8(%), in kg/h; 6(%) varies from 0% to 60%.

(7)

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Proceedings of the XXI International Mineral Processing Congress

-

Equation of water mass flow rate in the feed of the flotation column: (8)

-

Mw=Mfx(100-6(%)), in I/h; 6(%)varies from 0 to 60%. Equation of pulp mass tailing flow rate in the flotation column:

(9)

-

Mt=Otxpt, range 100 to 3.750 kg/h; lot in g/cm 3 varies from 1.0 to 1.5. Equation of ore mass flow rate in the tailing of the flotation column:

-

-

Mo=Mfxr(%), in kg/h; 6(%)varies from 0 to 60%. Equation of water mass flow rate in the tailing of the flotation column: Wt=Mox(100-8(%))

(10)

(11 )

in l/h; 6(%)varies from 0 to 60%. Bias Bias is a parameter which refers to the relationship between the water flow in the feed and in the tailings of the flotation column, such as: Bias = wr ~' (12) Wt When the bias is greater than 1, this means that the water flow rate inside the flotation column is ascendant, otherwise, descendant.

General

aspects of the CETEC's

pilot plant flotation

column

using FIELDBUS

technology

The researchers of the CETEC's Mineral Technology Sector trying for complete control of the operation of three flotation columns decided to use a FIELDBUS system of industrial instrumentation produced by SMAR. This system is very well adapted to the exigencies of the development technology concentration project. FIELDBUS system consists of data transmission network to communicate with instrumentation equipments and pilot plant control, such as: transmitters, makers and controllers. It's a digital network because it transmits information by messages according to defined communication layers with the protocol FIELDBUS system; serial because its information is transmitted and received bit to bit; half-duplex because the communicational is bi-directional, therefore only in one direction at a time and multidrop because it permits communication among several linked equipment in the network. These can be or not be bus powered type, in other words, they can or cannot be fed by the network communication system. Subsequently, in the FIELDBUS network for bus powered equipment, the communication and feed distribution networks converge to only a unique interlaced pair. In this case, the FIELDBUS network must provide current and continuous tension with the necessary power to feed the equipment and permit the communication signals to overcome the DC feed level. The model LD302 FIELDBUS pressure transmitters, two in each flotation column at different heights, are responsible for reading the pressure values, inside of each

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Process Simulation and Control

column, at the point where they are attached. These translate the pressure value to FIELDBUS signs. This data is used in algorithms for the PCI board (Process Interface Control), that is, a high performance FIELDBUS interface which combines advanced process control with multi-channel communication management. This PCI board is capable of manipulating several complex functional blocks which are responsible for the execution of programmed algorithms. These algorithms receive as data input the pressure values read by the LD302 pressure transmitters, flotation column feed values, and other data, such as pulp density and the data collected by the AIMAX supervisory program. The output values from these algorithms are sent to the two FI302 model FIELDBUS current converters, which transform the exit algorithm signals to the 4 mA to 20 mA current signal. Each FI302 converter is capable of communicating with up to three VF-S7 Toshiba frequency inverters which control the pulp flow rate pumps of the feed flotation columns and air flow rate entrance valves in each column. In this way, these algorithms are capable of controlling the pulp-froth interface, the flotation columns feed, the column holdup monitoring, the bubble diameters, carrier capacity of the bubbles, transportation capacity, bias velocity, etc. SYSCON is the software used for the configuration of this system. It guides all algorithms safely and easily. SYSCON also has the responsibility of all the network instruments used in this system. The interface between the FIELDBUS network and its pilot plant operator is made by the AIMAX supervisory system. Through this system, the operator is capable not only of doing his work, but also of determining the best operational conditions, by using the fight process variables, whereby he can observe graphical analyses of the operational stability conditions of each column individually or in group.

Results of the pilot plant test using this system The results are shown in Table II and in Figures 1 and 2. The Table II shows the operational data of the company MANNESMANN MINERA(~AO, an iron ore pilot plant. Figure 1 shows all the flotation column variables used to obtain the mass and metallurgical balances of Figure 2. Table II: Operationalparametersof the system Operational parameters P 1= Superiorpressure transmitter P2 = Inferior pressure transmitter HI = Height of the superior transmitter H2 = Depth of inferior transmitter ( H 2 - H~)

g = Gravity acceleration De = Froth density Dr = Non floated density Froth layer height in the column Eg = Gas holdup

Unit (kPa) (kPa) (cm) (cm) (cm) (cm/s2) (g/cm3) (g/cm3) (cm) (%)

Rougher 10.34 31.32 139.09 331.27 192.18 980.6 0.3 5.2 60.0 21.2

Cleaner 15.83 25.00 144.92 215.49 70.57 980.6 0.2 5.2 27.2 17.2

Recleaner 6.56 44.39 135.41 335.25 199.84 980.6 0.2 5.1 19.0 16.0

Proceedings of the XXI International Mineral Processing Congress

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IQ ~ e r

92,0 l/h

187,91 121,66 110,77 1,544 77,14

I

I Clean water I

I

56,15

100,00 58,96

39,58 36,97 50,84

4,22

2,63

[ ~

~~

Ol U

60,0

199,37 172.24

I I

0,19 1,13

60,82

I

0,62 8,87 10,67

I

0,97

103

E p

';J

~

'

R E

14,31 0,12 0,90 2,96

19o,37

100

I F

zo

I I

172,24

I

03,82 1,16

l l I I

129,56

I

I I

~ ~lid

k I

DATA SHEET

I E

Sd~denaty- g/crd

1,006

10,05 l 0,88 8,80 2,96

4,6 '

~ ~ I

P~dtl;t uat F~p- V~h Pulp- gh

14,44 14,36 0,13

62

103

I

1,16 129,56

'

o.3 ~

~ ' I E

~

: ~

DATA

F

I 11'0~ 1 1~

I

[~

1,46 I 40,96

v

17,0 I/h I ',

i

80,53 I ~ I.-.i

I Clean water 1

3o,o,~ t

0,ooi 1,11

~.66

o,eo

o;1

9.73

I Airflow-NI/~u

100

I

1,0 0,01 1,01 0,64 0,03

J Fmfh- cm I Bias-crrCs I Air wk:}c.- crn/~ I cone va. - or~ I cmy=r ~=g.

Diameter-mrr

8,~

l~~e-,

63,03

,

:~i,Q2 4,67

--~

4,67

29,m 4,69

r"

L. r

I

Figure 1: Flotation column operational variables of the FIELDBUS system. Clean water 17 I/h I

- - Rougher • Tailing Clean water 30 IIIh

Feed

I

~_]

Cleaner

Tailing Rougher

r-

Concentrate

Recleaner

Concentrate

Iv

Cleaner Concentrate

Recleaner Tailing

Products

Flow rate Grade (%) (k~/h) (%) Fe SiO2 A1203 P Column rougher-feed 110.77 100.00 47.06 29.66 0.92 0.0404 Rougher concentrate 69.82 63.03 66.10 1.31 0.98 0.0583 Rougher tailing 40.95 36.97 14.60 78.00 0.83 0.0100 Cleaner concentrate 68.85 62.16 66.10 1.30 0.97 0.0485 Cleaner tailing 0.97 0.88 58.60 10.90 2.03 0.0481 Recleanerconcentrate 68.85 62.16 66.10 1.28 0.96 0.0479 Recleanertailing 0.13 0.12 61.80 25.50 1.78 0.0479 Starch: Rougher column - 378.1 g/t. Amine: rougher column - 55.6 g/t; cleaner

P.F. 2.16 3.01 0.70 3.00 2.74 3.00 3.89 column

Figure 2: Mass and metallurgical balance of the Mannesmann project.

Recovery (%) Fe Si02 100.00 100.00 88.53 2.78 11.47 97.22 87.30 2.72 1.09 0.32 87.30 2.68 0.15 0.10 - 12.4 g/t.

Process Simulation and Control

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Conclusions

The use of this system makes possible the automation of the pulp-froth interface control, and holdup monitoring, to obtain the correct and necessary scale-up parameters. Its main advantages are low-cost operation, simple maintenance procedures, options to upgrade information for quality control, and compatibility with equipments of various producers. References

Yianatos, J. B. and Finch, J. A., 1990. Gas holdup versus gas rate in the bubbly regime. Intemational Journal of Mineral Processing, 29, 141-146. Yichausti, R. A., McKay, J. D. and Foot, D.G., 1988. Column flotation parameters; their effects. Column flotation 88, Chapter 17.