Computer system for monitoring power boiler operation

Abstract

The computer-based boiler performance monitoring system was developed to perform thermal-hydraulic computations of the boiler working parameters in an on-line mode. Measurements of temperatures, heat flux, pressures, mass flowrates, and gas analysis data were used to perform the heat transfer analysis in the evaporator, furnace, and convection pass. A new construction technique of heat flux tubes for determining heat flux absorbed by membrane water-walls is also presented. Flux tubes mounted at different levels in the boiler work at similar conditions as water-walls tubes. The current paper presents the results of heat flux measurement in coal-fired steam boilers. During changes of the boiler load, the necessary natural water circulation cannot be exceeded. A rapid increase of pressure may cause fading of the boiling process in water-wall tubes, whereas a rapid decrease of pressure leads to water boiling in all elements of the boiler's evaporator — water-wall tubes and downcomers. Both cases can cause flow stagnation in the water circulation leading to pipe cracking. Two flowmeters were assembled on central downcomers, and an investigation of natural water circulation in an OP-210 boiler (with steam capacity of 210 × 103 kg/h) was carried out. On the basis of these measurements, the maximum rates of pressure change in the boiler evaporator were determined. The on-line computation of the conditions in the combustion chamber allows for real-time determination of the heat flowrate transferred to the power boiler evaporator. Furthermore, with a quantitative indication of surface cleanliness, selective sootblowing can be directed at specific problem areas. A boiler monitoring system is also incorporated to provide details of changes in boiler efficiency and operating conditions following sootblowing, so that the effects of a particular sootblowing sequence can be analysed and optimized at a later stage. The current paper also presents an analysis of stresses occurring in the boiler drum and the downcomer junction during-start up and shut-down of the boiler.