MANAGING CHALLENGES AT MLNG SATU DISTILLATION COLUMNS

Abstract

To realise the ultimate operating potential of distillation columns via maximising the yield throughput without compromising product quality at lower operating costs has always been an aspiration for Malaysia LNG Sdn Bhd (MLNG Satu). Existing Advanced Process Control (APC) has been helping the plant to deliver better process stability at the Fractionation Unit. Operating high-purity distillation columns in MLNG Satu imposes a challenge to APC control because of its non-linear and intensely interactive dynamics. In addition, frequent changes in feed compositions and feed flow must be dealt in a continuous basis, which failed to do so will results in a significant upset in the product compositions. The distillation process is also known to utilise a large amount of energy, which can significantly influence the overall plant profitability. Realising energy optimisation has a significant contribution towards overall operational costs in distillation columns’ operation. Therefore this has become a prime target when performing APC revamp that recently took place at MLNG Satu (De-ethaniser, De-propaniser, De-butaniser column). This abstract describes the challenges and implementing control strategies to establish a disturbance feedforward model, minimise energy consumption and maintain optimum product impurity. Although distillation processes are inherently non-linear, a process control system based on linear input-output model can be acquired if operated over a sufficiently small region. Hence, a linear multivariable predictive control is developed, provides multiobjective control handling based on objective hierarchy. The applied control strategy has successfully improvised the dynamic control performance, resulting in a reduction in product quality variability, increment in product yield, and minimisation of the unit operating cost. It is expected to bring more value as the APC controller uptime increases over time. Intangibly, the competency of plant operators in dealing with advanced technology, i.e., APC, to optimise plant operation, has been enhanced from control to supervisory role, allowing for overall plant optimisation to be done in minute intervals.
 Keywords: Advanced Process Control (APC), Non-Linear, Distillation Columns