Secondary-juice flow-control strategy at Rocky Point Sugar Mill

An effective juice-flow control system is an essential component of juice clarification. It assists in maintaining other process variables at set point, makes use of the buffering capacity of the installed juice tanks including the incubator for starch reduction, and steadies the flow to the clarifier to enhance its performance. Consideration is given to potential sucrose losses through microbial activity and/or acidic inversion if excessive quantities of juice are held in the tanks. Major disturbance to the flow control system is caused by variations in the incoming juice flow rate due to variations in the instantaneous crushing rate and the juice/fibre ratio of the incoming cane. Rocky Point sugar mill is the smallest sugar factory in Australia. Over the last several years an increase in process automation has been implemented to maintain a low manning operation to keep the factory financially viable. As part of this factory efficiency program, a secondary-juice (SJ) flow-control strategy was implemented to meet the following requirements: maintain a practicable minimum of juice in process; prevent additional added water into the evaporator supply juice (ESJ) tank; smooth juice flow rate to enhance clarifier performance; control starch levels in sugar without the addition of amylase; minimise the required operator intervention to the control system. The adopted strategy is based on a calculated remote set- point for the secondary-juice flow rate using inputs derived from the mixed-juice (MJ) flow rate, the secondary-juice tank level and the ESJ tank level. This paper outlines the mill’s installed equipment, control system and how the control strategy was able to meet the factory’s processing objectives. Key words Secondary juice, flow control, turbidity, added water, starch