LONG TERM EXPERIENCE OF THE REAL TIME FOUUNG DEPOSITS THICKNESS MEASUREMENTS FOR ONLINE SOOTBLOWING OPTIMIZATION

摘要

Over the past years there has been a dramatic increase in the regulatory requirements for low emissions. Renewable energy targets and CO_2 emissions markets drive the transition to a cleaner and renewable energy production system. In addition to increasing the overall plant cycle efficiency, there two principal means of the reduction of the CO_2 from coal fired power plants: by coal and biomass co-firing and by the capture and long term storage of the CO_2 emitted from power plant. Carbon dioxide capture and storage will involve substantial capital investment, accompanied by a significant power plant cycle efficiency penalty, and is not currently available on a fully commercial basis. Co-firing biomass, in comparison with other renewable sources, is the main contributor to technologies meeting the world's renewable energy target. However, the impact of biomass co-firing on boilers performance and integrity has been modest. Operational problems associated with the deposition and retention of ash materials can and do occur on all the major gas-side components of combustion and boilers. The process occurs over a wide range of flue gas and surface temperatures, and dependent both on the characteristics of the ash and on the design and operation conditions of the furnace and boiler. Development and validation of the predictive models have been hindered significantly by the practical difficulties in the obtaining reliable data from the boilers operated with coal and biomass. Although specialized on -line deposition monitoring and sootblowing control systems are commercially available, but they are based on a very simple estimates of the fouling factors, which results in crude and not reliable approach to optimization of sootblowers operation. In the present paper an alternative approach and a new technique based on electro-optical sensor are demonstrated. The long term experience with the system attached to the furnace wall and capable to move the compact sensor in and out of the furnace, allowing to measure simultaneously deposits thickness and reflectivity, is described in details . Results of our study show that dynamics of both parameters on the operated power unit can be registered simultaneously in real time and then interpreted separately. Experiments have been carried out with different coal types at 575MW unit equipped with CE tangential boiler and 550 Mw equipped with B&W boiler with opposite fired burners. The measurements were performed in different locations of the furnace. It was shown that dynamics of thickness and reflectivity variation just after the wall cleaning activation are quite different. Situations have been registered where changes of reflectivity have a significant impact on heat transfer, comparable and sometimes even greater than that of growing fouling thickness. Technique and device exploited in this study appears to be a very useful tool for sootblowing optimization and, as a result, for improvement of boiler efficiency and reduction of water wall erosion and corrosion in both pulverized coal and co-firing boilers.