Research Of Boiler Sootblowing Optimization Based On Entropy Generation Analysis And Numerical Simulation

For coal-fired utility boiler, slagging and ash fouling on heating surfaces are usually inevitable. Heavy slagging and ash fouling can be avoided by sootblowing during the operation. Presently, sootblowing systems of domestic utility boilers are mostly operated on fixed sootblowing period. However, insufficient or too much sootblowing frequently occur under this mode. Therefore, during boiler running, the state and developing trend of slagging and ash fouling should be monitored as accurately as possible, and the sootblower should be operated according to the monitoring results and operation demand to make sure the ash and slagging can be removed effectively and in time.In this thesis, systematically theoretic and experimental studies have been carried out on following problems: the influence of furnace slagging on steam parameters, online monitoring of furnace slagging, online monitoring of convective heating surface fouling under different loads, irreversible energy loss of convective heating surfaces, the establishment of sootblowing optimization model, the determination of sootblowing modes, and the development and application of sootblowing optimization system. Finally, the system was put into practice on several large utility boilers. The main contents are as following:1. Study of furnace slagging monitoring based on numerical simulation1)Numerical simulations of slagging on furnace were carried out, the flue gas temperature distributions of furnace outlet under different slagging conditions and slagging distributions on the water wall of different boilers were determined. The outlet steam conditions of platen superheater were got by thermal calculation, the influence of the furnace slagging conditions and slagging distributions on the water wall on the available steam parameters of platen superheater was analyzed.2)Based on simulation results, fuzzy mode diagnose technology was used, and the diagnose model of furnace slagging conditions was established, online slagging conditions monitoring and diagnose of slagging distributions on the water wall were realized.2. Study and realization of convective heating surface fouling monitoring under different loadsIn order to decrease the difference between monitoring result of static model and practical result under high load changing rate conditions, the dynamic model for convective heating surface fouling monitoring was established according to the analysis of the influence of load on fouling monitoring. The accurate online monitoring of convective heating surface fouling under any load condition was realized. 3. Theoretical and experimental study on sootblowing optimization based on entropy generation analysis1)Irreversible energy losses of convective heating surfaces during coal-fired boiler operation in power plants were studied, calculation models for different entropy generations of convective heating surface were obtained. Total entropy generation and entropy generation index were defined, and entropy generations of different heating surfaces before and after sootblowing were analyzed.2)Based on the analysis of heating surface entropy generation, the equations for calculating maximal sootblowing income of different heating surfaces were proposed, the calculation methods of optimal sootblowing frequency, critical entropy generation index, and critical fouling rate were put forward, which leads to the establishment of sootblowing optimization model based on heating surface entropy generation analysis. Furthermore, principles for determining sootblowing modes were put forward, and four sootblowing optimization modes were built to guarantee the safety, stability and maximum sootblowing income of boiler operation.3)Boiler heating surface fouling monitoring and sootblowing optimization system was developed. The system is of the functions including online operation monitoring, sootblowing guiding and et al. The practical operation on a 328.5MW unit proved that: the proper sootblowing mode can be accurately proposed in time, and the sootblowing can be effectively guided by sootblowing system.