PUMPS AND PIPELINES
Controlling your flotation process
Flotation is an important part of mineral processing in most mining operations , requiring an accurate , durable and repeatable level control valve to manage level control in the column , cell , staged reactor or direct reactor , according to Valmet .
The head pressure to the control valve from each type of flotation process makes sizing a critical function to ensure proper operation of the valve and performance of the solution .
For instance , flotation cells have very low driving head pressure to the valve . Since the head pressure is so low , inlet velocities , outlet velocities and any bends or elbows in the piping can affect this low head pressure . If all factors are not considered carefully in this case , the danger is mis-sizing the level control valve on the low side .
Flotation cells have typically been controlled by dart valves , yet , in recent years some customers , OEMs and consultants have begun to recommend pinch valves for flotation control valves .
In certain cell designs , the dart is housed within a metal box on the outside of the flotation cell . This structure adds to the cost of the cell , whereas a pinch valve can be connected directly to the cell with a simple flange . The pinch valve is equally as productive as the dart valve and increases the flow capacity in one valve rather than , in certain cases , two dart valves .
With flotation columns , conversely , there is ample driving head to the inlet of the control valve . However , this type of flotation has risk for control valve cavitation if downstream piping does not supply sufficient back pressure .
Valmet said : “ One common way to create head pressure is to use a barometric leg or J piping arrangement after the control valve to create this back pressure . Without this consideration , many types of valves may cavitate and cause short valve lifetime . In flotation the goal is to have an accurate control valve with a long mean time between failure to keep the flotation at peak operational performance .”
Pinch valves are also ideal for column flotation control , according to Valmet .
In this application , a pinch valve uses a rubber sleeve inside the valve to protect against the abrasive flow stream . The rubber sleeve typically lasts longer than metallic valves due to its superior abrasion resistance , the company says . The valve can be controlled via 4-20 mA signal to a “ smart positioner ” with pneumatic actuation or also via electric actuator equipped with 4-20 mA capability . At the same time , pinch valves very accurately control the column or cell level with no performance issues .
“ The pinch valve provides a long mean time between failure and typical repair is simply replacement of a rubber sleeve ,” Valmet says .
Flotation cells have typically been controlled by dart valves , yet , in recent years some customers and OEMs such as Valmet have begun to recommend pinch valves for flotation control valves
“ The rubber sleeve replacement is cost effective and can be performed by plant maintenance personnel quite rapidly .”
Flotation also requires delivery of reagents to perform the process , with typically these chemicals delivered via some type of pump . These chemicals often have long polymer chains that cannot be agitated . If a high shear pump is selected , it may break these polymer chains and make the chemicals less effective , resulting in overdosing of expensive chemicals to perform the same amount of work . A pump that is low shear should be used in this process , according to Valmet , with peristaltic pumps typically chosen . These pumps come with very low shear , and certain designs can provide very accurate control of the pumping process .
IM