Ash Deposition Characteristic Prediction And Life Evaluation Of Reheater Based On Heat-Engine Plant DCS Data

Reheater is one of the main high-temperature heating surfaces of the boiler, which has to work under severse conditions. Except high temperature,high pressure effect, it has to undertake erosion,abrasion and fatigue from steam or flue gas. Whether the reheater can operate safely or not influence the boiler's safety directly. In boiler accidents, the pressure-containing member's bursting problems account for a large proportion and the reheater's bursting problem is one of the most common accidents. It is one of the most important problems that influences the power plant's safe operation. Thus,to study the reheater's ash deposit and life is a urgent job.Ash deposition on reheater surfaces is a common phenomenon in fossil fuel fired power plant. To monitor the reheater's ash deposition extent and developing trend can help decrease the loss because of ash deposition and enhance the power plant's safety and economy capability. Based on the on-line monitoring parameters of boiler,this thesis developed a kind of on-line monitoring technique which can monitor the fouling condition of the convection heating-surfaces and built a ash-monitoring model of reheater. Deposition Coefficient is used to assess the fouling condition of reheater. Most of the real-time data that the ash-monitoring model depends on comes from DCS system. Compared with other method, this technique doesn't need to install new measuring points and it's theory is simple. This thesis also presented a calculation flow chat and a design proposal of the monitoring system. Based on the model ,this thesis compiled a ash-monitoring procedure with Matlab .This procedure includes four parts :the calculation of ideal heat-transfer coefficient,the calculation of actual heat-transfer coefficient,the calculation of Deposition Coefficient and the calculation of equivalent ash thickness.Taking a high-temperature reheater of a 300MW unit for example, this paper analyzed it's deposition condition. This thesis selected a period of time when the load is steady and noted data once an hour. Twelve DC and equivalent ash thickness are calculated and the results inosculate with practical situations. This thesis presented the conception of equivalent ash thickness. The calculations indicate that the thickness can help assess the heating surfaces' ash deposition condition and can guide the boiler's optimized soot-blowing to a certain extent.This thesis ,taking a high-temperature reheater for example, analyzed the life-loss rule and reason of the pressure components. Based on the study of the main failure mechanism ,ignoring minor factor ,this thesis presented a simple calculation method of life-loss. Using these simplified calculation models, this thesis presented a calculation flow chat of the reheater's life-loss. The flow chat and core calculation method is the basis for the on-line life loss monitoring system.