Fuzzy Control Applied to Combustion in Sugarcane Bagasse Boilers

Abstract

Abstract In the sugarcane industry, boilers are widely used for cogeneration. This industry uses mainly sugarcane bagasse as the primary fuel source, followed by other types of biomass. Fuel price has a major impact on the industry results, due to the scenario of the energy market. Therefore, optimizing the combustion is an important lever to reduce this cost. Real-time measurement of oxygen content in the boilers flue gas is one of the requirements for this optimization. Due to the capital cost and the requirements for personnel qualification for maintenance and calibration, sugarcane mills rarely apply such analyzers in closed loop. In this work, a fuzzy control was implemented in the combustion air flowrate of a large boiler in the Tereos group, to maintain the oxygen content in the combustion products within the optimum range. A tool was used to identify the process dynamics and to tune the control loop in real time. After downloading the new strategy in the factory control system and tuning the controller, the oxygen control loop started operation in automatic mode. After twenty-four hours of continuous operation, regulatory and servo controls were able to keep the desired setpoint with low variability (± 1.2% variation in excess air coefficient) and respond to setpoint changes with good response speed (1.5-20 minutes) and overshoot (8-56%). No previous references were found in the literature on the use of fuzzy logic for the combustion control of sugarcane bagasse-fired boilers, especially high pressure and high steam throughput boilers. Results reached so far demonstrate the applicability of fuzzy control for combustion in boilers on sugarcane bagasse, with 40% less variability than a PID controller, and 69% less variability compared to operation in manual mode.