Accurate and reliable level control is one of the key operating variables in flotation. Especially in big cells, every minute of lost concentrate mass pull is worth a considerable amount of money. Changing process conditions and low availability may lead to requirements for improving level control arrangements and design.
Performance, availability and low running costs are the main design criteria of the improved dart valve level control arrangement. The Dart Valve Upgrade is suitable for Outotec TankCell, OK-cell, and similar flotation machines.
Accurate and responsive control
Smooth froth flow rate is one of the key factors affecting froth recovery and has a positive influence on overall metallurgical performance. Accurate and responsive level control is vital in order to ensure this. Properly sized steep-angle plugs need to be matched with a long stroke actuator. The length of the stroke is a key element contributing to accurate level control. Furthermore, with correct sizing, the response to the control input is practically linear.
Improved actuator design
The new actuator unit measures the valve position accurately by using intelligent piston positioners. In the old design, the position was measured mechanically from outside, that lead to a situation where construction got easily mechanical damages. The actuator unit reliability has been improved by designing an articulated joint that removes tensions directed to the unit. The improved actuator unit also includes a fail-safe function as an option for scenarios when the loss of air pressure or electricity occurs. The fail-safe function allows the operator to operate dart valves manually twice after an electrical or pneumatic malfunction.
Wear life
The key design criteria is to maximize the wear life of the level control components. The Inside Dart with open design has proven to offer the longest wear life of all known dart valve arrangements. Open tank area around the inlet and a wide intermediate channel after the socket are essential. They guarantee the lowest possible flow rates from cell to cell without risk of sanding. Laminar flow and moderate velocity are the key factors contributing to long wear life. A properly selected range of stroke is another important factor determining wear. If the stroke in typical conditions is too short, i.e. the valve operates near the closed position, the flow rate will be high, thus inducing wear.
Scope of upgrade
Dart Valve Upgrade consists of dart valve socket, plugs, a rod, and an actuator unit. Depending on the requirements only some of the scope can be applied.
