Abstract
A soft sensor for oxide scales on the steam side of superheater tubes of utility boiler under uneven circumferential loading is proposed for the first time. First finite volume method is employed to simulate oxide scales growth temperature on the steam side of superheater tube. Then appropriate time and spatial intervals are selected to calculate oxide scales thickness along the circumferential direction. On the basis of the oxide scale thickness, the stress of oxide scales is calculated by the finite element method. At last, the oxide scale thickness and stress sensors are established on support vector machine (SMV) optimized by particle swarm optimization (PSO) with time and circumferential angles as inputs and oxide scale thickness and stress as outputs. Temperature and stress calculation methods are validated by the operation data and experimental data, respectively. The soft sensor is applied to the superheater tubes of some power plant. Results show that the soft sensor can give enough accurate results for oxide scale thickness and stress in reasonable time. The forecasting model provides a convenient way for the research of the oxide scale failure.
Highlights
Oxide scale formed on the steam side of superheaters and reheaters of utility boilers in power plant brings many problems like tube clogging, overheating, and erosion of turbine blade [1,2,3]
In particle swarm optimization (PSO), each feasible solution of the optimization problem is seen as a “particle” of the solution space
Construct thickness soft sensor and stress soft sensor with the data collecting from Steps 5 and 6 and the parameters optimized in Step 7
Summary
Oxide scale formed on the steam side of superheaters and reheaters of utility boilers in power plant brings many problems like tube clogging, overheating, and erosion of turbine blade [1,2,3]. Sabau and Wright [6] studied the effects of creep, growth stress, and thermal stress on the internal stress state of the oxide film. As for the experiment aspect, Galerie et al [8] measured the average thermal stress of oxides on ferritic alloy with flat structure in three ways, namely, Raman spectroscopy, X-ray diffraction, and single-sided bending test. They pointed out that the results measured by Raman spectroscopy were accurate enough without the modifications by the X-ray diffraction and single-sided bending test. During the past few years, its solid theoretical foundation and good behaviors
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