Control System Improves Reliability and Safety of Recovery Boilers

摘要

Pulp and paper mill recovery boiler owners and operators strive to maximize recovery boiler safety, reliability and availability. Improved control of boiler water chemistry and the ability to reliably detect boiler leaks both serve those goals. This paper discusses a monitoring and control system used in pulp and paper mills to provide both precise boiler chemistry control and mass balance-based recovery boiler leak indication. The system is described and field results are presented. Good control of boiler water chemistry is necessary to avoid boiler corrosion and deposition, either of which can lead to tube leaks or failures. Maintaining boiler chemistry within congruent pH/phosphate guidelines avoids the corrosive conditions that exist when operating outside the guidelines. Improved response to input variability reduces out of control incidents caused by system upsets. Early detection of leaks is a primary objective of recovery boiler operators because of the potentially serious consequences of a water leak into the furnace. A leak detection system has been developed to provide early detection of leaks while avoiding alarms from signal noise and process variability. This is accomplished through proprietary statistical modelling and by employing fuzzy logic and software that learns and adjusts to each unique boiler. The system uses both chemical and /or water mass balances around the waterside of the boiler to provide early detection and an indication of whether the leak may be in a critical area. The ability of the controller to detect leaks, in addition to providing precise control, further improves the reliability and safety of recovery operations.