A hybrid, knowledge-based system as a process control ‘tool’ for improved energy efficiency in alumina calcining furnaces

Abstract This paper describes the development and implementation of a hybrid SCADA (Supervisory Control and Data Acquisition) system for the air suspension ‘flash’ alumina calciner at Aluminium de Grece St. Nicholas plant. The system includes two additional modules, an ‘expert system’ based on 10 years of commissioning and operating experience and a dynamic model continuously predicting the quality of the product. It is implemented on an industrial PC under an industrial control software environment and interfaces to the furnace through a programmable logic controller (PLC) system. The system guides the furnace operator to reduce sensible heat losses by operating with a marginal excess air flow rate, to take advantage of the higher energy efficiency at higher production rates and, at the same time, to avoid potentially dangerous operating conditions leading to loss of production and consequential energy losses. It also performs the traditional SCADA functions (data acquisition, maintaining history files for important parameters and display of important operating parameters in both a mimic process diagram and a series of graphs.) In addition to these tasks a simplified dynamic model gives the operator a prediction of the current value of the main product quality parameter, which can only be measured with laboratory equipment. Preliminary results have shown that reduction of secondary air flow rate and reduced downtime achieved by the operator under the guidance of the system can reduce energy consumption by as much as 10%. A similar, or even greater, improvement in energy efficiency can be expected by implementing a similar system to cement calcination kilns based on the same technology.