avance en el control en celdas de flotacion.pdf

7/30/2019 AVANCE EN EL CONTROL EN CELDAS DE FLOTACION.pdf

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Advanced Process Control of aFroth Flotation Circuit

October 23, 2008

Dr. Sebastian GaulocherDr. Eduardo GallesteyABB Switzerland Ltd.

Henrik Lindvall

2008 ABB Switzerland Ltd, Corporate Research, CH-RD.C1

Boliden Mineral AB, Sweden


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2

What material is this coin made of?

A riddle to make you awake

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copper

zinc


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3Zinc is omnipresent

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4Production and price of zinc

Zinc mines in the world Artists view of mining

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Total annual production:

10 million tons (2006)

Zinc price is skyrocketing(Annaberger Bergaltar)


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5

Flotation: unit operation at the heart of mineral processing

What is flotation?

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6Explanation of the Flotation Process

Objective:separation of valuable minerals and gangue

Ore is

extracted from the mine

ground in a mill, and

mixed with water and chemical rea ents

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(activator, collector, and depressant).

Pulp flow in which

desired mineral particles are

hydrophobic gangue particles are hydrophilic

Reagent addition

Semi-autogenous mill


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7Explanation of the Flotation Process

In a flotation cell,

a feed port provides incoming pulp,

an impeller mixes the pulp,

air is blown into the cell and dispersed,

hydrophobic particles attach to the air

air bubbles float and form froth on the

concentrate

feed

air

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surface

Separation between

hydrophobic (desired mineral) and

hydrophilic (gangue) particles

into concentrate (froth) and tailings (pulp)

airbubble

Hydrophobicparticles

buoyancy

Flotation of mine-

ral particles

Sketch of a flotation cell

tailings


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8

Flotation cell

Several flotation cells form a flotation bank

Several flotation banks form a flotation circuit

Explanation of the Flotation Process

conc.

tail.feed

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Several flotation circuits form a concentrator

Cu-Pbflotation

Cuflotation

Znflotation

Cu conc.

Pb conc.

Zn conc.

gangue

ore


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9Manipulated and measured variables of a circuit

FA301 FA302 FA303 FA304 FA305

tailingsfeed

FT

FT

AT

AT

AT

AT

BL031

Legend:

recirculating flow

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FA101FA104 FA103 FA102

concentrate

hydro-cyclone

regrindingmill

FTATAT

AT

AT

FT

X-ray analyzer

volume flow meter

air addition

froth level change

reagent addition


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10Where are we and where do we want to go?

State of the art Manual control, intricate due to

intricate dynamics (e.g. recirculating flows),

frequent feed variations (quantity and quality), and

operator shift changes

No circuit-wide automatic controlat present

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Objectives Maximizationof plant output

Observanceof minimum concentrate grade

Reductionof chemical reagent use Preventionof costly unplanned plant stops by respecting operating

range of plant


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11Expert Optimizer ABB Standard platform for APC

Features: General Calculations

Arithmetic, Boolean

Fuzzy Logic Human reasoning

Neural Networks

Soft sensors

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Model Predictive Control (Piecewise) Linear

Hybrid systems

Non-linear (Modelica)

Web Based HMIs Highly Configurable

Drag and Drop


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12General set-up of estimation and control

process

Sensors

Signal processing

State estimates

Estimation of process state variables

(MHE, moving horizon estimation)

Measurements

on

tro

lp

latfor

m

Parameter

Requiresolving an

rcommun

icat

ion

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Flotat

io

Actua

tors

Computation of optimal set-points

(MPC, model predictive control)

Postprocessing of set-points

Set-points

ABB800xA

c

es ma on

problem

OPC

pro

toco

lf

Done in Expert Optimizer


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The process model is:

Mechanistic (first principles)

Mass and volume balances

Pulp-to-froth transfer model

Variables: volumes and volumeflows of relevant fractions

Linearised first-principle approach

Component model

MLD Fl. cell

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near ze a out an operat ng po nt Formulated in discrete time

Generic and modular (component-wise):

flotation cell, mixing tank, analyzers, volume flow meters,

Easily understandable, maintainable,adaptable, and reusable

Component library

Circuit assembly inExpert Optimizer


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14Linearised first-principle approach

Model predictive control (MPC):

Optimization variables:

Air rates

Collector addition

Objectives:

Minimize tailings flow

Guarantee minimum concentrate grade

click on picture to enlarge

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Moving horizon estimation (MHE):

Optimization variables:

Dynamic states (cell and tank contents)

External disturbances (feed, water)

Objective:

Find a compromise between pastmeasurements and the process model inorder to obtain the optimal estimates forplant states and disturbances

click on picture to enlarge


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15Pilot Plant and Results

Development of control strategy in a cooperationbetween

ABB (Switzerland and Sweden) and

Boliden Minerals AB, Garpenberg Concentrator (Sweden) Application of control strategy to an industrial plant

(zinc flotation circuit as shown in flow sheet)

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on ro er s curren y e ng ong- erm es ewith encouraging results so far:


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Method for handling disturbances and forecast changes

Main ingredients are

Plant model

Objective functional

Model predicts system

Model Predictive Control

past future

controlled

variable

manipulatedvariable

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into the future

Requires solution of

optimization problem at

every sampling time

t t+ t+m t+p

t+1t+2

t+1+m t+1+p


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Assembly of flotation circuit for model predictive control:

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Assembly of flotation circuit for moving horizon estimation:

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20Mixed Logical Dynamical System (MLD)

Developed at Federal Institute of Technology Zrich(ETH Zrich), Switzerland

Framework for handling both real-valued and boolean-

valued variables (hybrid system) Can describes plant constraints, interconnections and

the objective function

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54132

321

321

)()()()(

)()()()()(

)()()()()1(

EtxEtuEtzEtE

tzDtDtuDtCxty

tzBtBtuBtAxtx

+++

+++=

+++=+

x ens on o c ass ca s a e-space approac re ox


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21Flotation Cell

Mechanistic model of a flotation cell

Three inputs: feed, froth level, and air

Two outputs: concentrate and tailings

Volume balance in the cell:

vol[k+1] = vol[k] + T( feed[k] tail[k] conc[k] )

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22Flow sheet of a froth flotation circuit

FA301 FA302 FA303 FA304 FA305

tailingsfeed

FT

FT

AT

AT

AT

AT

BL031

Legend:

recirculating flow

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FA101FA104 FA103 FA102

concentrate

hydro-cyclone

regrindingmill

FTATAT

AT

AT

FT

X-ray analyzer

volume flow meter

air addition

froth level change

reagent addition


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23Feed grade variation

Zincgrade

Solidfraction

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Day time (Mar 3, 2008) Day time (Feb 27, 2008)

avance en el control en celdas de flotacion.pdf

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