Advanced Supervision and Diagnostic System - The Tool for Improvement Reliability and Efficiency of Utility Boilers Burned Different Coals Type

摘要

Due to the past years experience, we have seen an influence on the coal purchase policies. The main reason for using coal other tan the original design coal, apart from economic considerations, is to reduce SO_2 emission by using a low sulfur content coal as well as decreasing coal index (fixed carbon to volatile matter ratio) in order to reduce NO_x emission etc. Hence, the power generation plant was originally designed to operate on a particular coal, and due to high restriction in environmental requirements, emissions regulations, have led to modifications of the coal type and firing mode, while the boilers must burn a different coal type and its blends. It may lead to boiler reliability degradation and as a result reducing the power plant availability and increasing operating and maintenance cost. In order to prevent a different faults in boiler operation and as a result a reliability reduction, special monitoring and diagnostic techniques is required for engineering analysis and utility production management.In this sense an on-line supervision system have developed and implemented for 575, 550, 360 Mw coal fired units. The aim of the system is to achieve more effective and reliable operation with emission reduction. It is a valuable aid for: (1) operation staff and process engineers to survey the equipment and overall plant performance, (2) electricity production management in order to implement maintenance and operation strategies.The developed system provides an on-line information regards furnace performance, including fireball location, increase in furnace exit temperature indicates that it's necessity to activate furnace sootblowers to control steam temperatures and prevent excessive accumulations of slag and heat surfaces tube overheating. The developed system indicates the superheater and reheater surfaces midwall metal temperature which provides timely information to assist engineering personnel to optimize mode of operation, in order to activate the optimal number of sootblowing of the corresponded surfaces, etc. The system includes also an online analysis of the erosion impact on the boiler backpass heat surfaces. By the using the developed system we found a correlation between furnace fouling and Nox emission due to the effect of flame temperature on the rate of Nox formation. As a result an optimal mode of furnace operation and sootblowing practice is used to reduce the high cost of controlling Nox emission. The developed system allows to fond the proper coal blends which provide a high boiler efficiency and reliability while minimizing Nox emissions.