Method of regulating a flotation system with a primary and secondary stage

The invention is directed to a method of regulating a flotation system having an inflow quantity of suspension flow dependent on production demands, including a primary flotation stage and a secondary flotation stage where the secondary flotation stage treats the froth of the primary stage, transporting de-aereated froth from the primary flotation stage to a collection vessel which is in fluid communication the secondary flotation stage; recycling suspension flow from the secondary flotation cells of the secondary flotation stage in part to an inlet of the primary flotation stage, and in part to an inlet of the secondary flotation stage, and regulating the level of de-aereated froth in the collection vessel by controlling the amount of suspension flow recycled from said secondary flotation stage to the inlet of the secondary flotation stage.

BACKGROUND OF THE INVENTION 
The present invention concerns the regulation of a flotation system. 
A difficulty with conventional systems consists in the regulation of the 
two flotation stages because of the amount of froth produced and the 
bubbly suspension to be flotated. With known regulation methods it is 
necessary to constantly monitor the amounts of cell overflow at the point 
of origin and to effect a correction of the level set values. 
SUMMARY OF THE INVENTION 
The invention comprises, in one form, a method of regulating a flotation 
system having an inflow quantity of suspension flow dependent on 
production demands, including the steps of determining a back-up level of 
the froth in a froth chute of a primary flotation stage; dependent on the 
back-up level, adjusting an overflow level of suspension flow to the froth 
chute in the primary flotation stage; dependent on the back-up level, 
controlling the suspension flow in the primary flotation stage to provide 
a substantially constant back-up level of the froth in the froth chute of 
the primary flotation stage; transporting de-aereated froth from the 
primary flotation stage to a collection vessel which is in fluid 
communication with the secondary flotation stage; recycling suspension 
flow from the secondary flotation cells of the secondary flotation stage 
in part to an inlet of the primary flotation stage, and in part to an 
inlet of the secondary flotation stage; regulating the level of 
de-aereated froth in the collection vessel by controlling the amount of 
suspension flow recycled from said secondary flotation stage to the inlet 
of the secondary flotation stage; and regulating the ratio of the amount 
of said suspension flow from the secondary flotation cells which is 
transported to the inlet of the primary flotation stage relative to the 
amount of said suspension flow which is transported to the inlet of the 
secondary flotation stage, dependent on the height of froth in the froth 
chute of the secondary flotation stage. 
The following principle of regulation results: 
Regulation of the cell overflow amount by measuring the level of the 
primary froth chute, and indirect level regulation of the primary froth 
chute by variation of the quantity of accepts (primary cell level) while 
the amount of flotation influx is kept constant (flow regulation). 
A constant back-up level also means a constant overflow amount, due to the 
measuring weir in or at the end of the froth chute. 
Measuring the primary cell level serves only as an additional control 
indication. 
Advantages of the present invention include: 
The froth chute level (low volume) reacts sensitively to variations of the 
primary overflow amount, for which reason the primary overflow amount can 
be adjusted very accurately and consistently via the bypass valve. 
The secondary stage, owing to the constant froth chute level, receives 
always a constant amount, so that the secondary overflow amount and the 
amount of reflux suspension are extensively constant. 
While due to the "froth chute regulation" of the primary stage the inflow 
to the secondary stage is constant, the content of air in the secondary 
stage may vary, whereby the amount of overflow, despite unchanged level 
transmitter indication, may vary. 
This effect can be extensively eliminated by the "froth chute regulation" 
at the secondary stage. 
The regulation of the secondary cell overflow amount takes place by 
measuring the secondary froth chute level before an outlet weir (vertical 
slot of about 15 mm width), while an indirect level regulation of the 
secondary froth chute is effected by variations of the amount of reflux 
suspension. 
There is a direct and reproducible correlation (unobstructed outflow behind 
the weir) between the back-up level (froth chute level) before the weir 
and the amount of flow passing through the weir, for which reason the 
secondary overflow amount can be established by adjustment of the froth 
chute level. 
The froth chute level (low volume) reacts so sensitively to variations of 
the overflow amount that the effect of different air contents in the 
overflow suspension is negligibly small, with a reproducible correlation 
resulting between froth chute level and overflow amount.

DETAILED DESCRIPTION OF THE INVENTION 
The primary flotation stage 1, after the mixing chamber, consists 
essentially of the individual, serially arranged flotation cells 20, 20', 
etc., with each of which there is coordinated an injector 22, 22' or other 
feed apparatus for the suspension to be flotated. The feed lines to the 
injectors are referenced 21, 21' etc. Common to all flotation cells is 
here a froth chute 12, to which the purified suspension proceeds over a 
weir of each flotation cell. Moreover, primary stage 1 features in froth 
chute 12 or at the end of froth chute 12 a measuring weir 28. 
Secondary flotation stage 2 is structured similarly to primary flotation 
stage 1, with individual flotation cells 61, 61' injectors 62, 62' the 
transition between the two cells taking place via line 63. Provided here 
as well is a froth chute 13, which is preceded by a weir 29. Here, too, a 
measuring weir 29 is located at the end of, or within, froth chute 13. 
Before measuring weirs 28, 29, the levels are preferably measured each by 
pressure sensors 51, or 53. Regulators 52, or 54, for one, regulate the 
amount of accepts of the primary stage via valve 47, and the amount of 
reflux to primary flotation stage 1, from the secondary flotation stage 2 
via valve 49. The amount of froth, or overflow, of the primary stage is 
via line 36 channeled to a hydrocyclone 10, which assumes the deaeration 
of the bubbly suspension. With its tapered end it dips into a vessel 38 
from which a pump 44 forces the suspension into the line 46. A pressure 
sensor 55, a regulator 56 and a valve 45 in line 42, through which latter 
a circulated amount (in the bypass) is passed to the secondary flotation 
stage 2, serve to keep the level in the vessel 38 constant. 
The adjustment of the weirs in, or on, the individual flotation cells 
remains essentially constant, and the quantities controlled by the 
regulators are changed alone, in keeping with the production quantity 
called for. This makes for simple and clear conditions of regulation.