Analysis of thermal deviations in L-shape platen superheaters of a supercritical 600 MW circulating fluidized bed boiler

• Published in: Applied thermal engineering 2020-02, Vol.166, p.114752, Article 114752
• Main Authors: Ma, Youfu, Jin, Xin, Lyu, Junfu
• Format: Article
• Language: English
• Subjects: Absorption; Boiler plate; CFB boiler; Fluidized bed reactors; Fluidized beds; Heat conductivity; Heat exchangers; Heat transfer; Heating; Mass flow rate; Mass flow rate distribution; Offsets; Platen superheater; Prediction models; Stress concentration; Superheaters; Temperature; Temperature effects; Thermal deviation
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2019.114752

•Thermal deviations in the L-shape platen superheater of CFB boilers were studied.•Header effect has marked influence on steam flow rate distribution in parallel tubes.•Heat absorption deviation determines the final thermal deviation of the superheater.•Three kinds of heat load models were compared for their effect on thermal deviations.•Utilizing header effect can control thermal deviations of the superheater effectively. In circulating fluidized bed (CFB) boilers, L-shape platen superheaters often suffer from poor working conditions with a high risk of tube wall overtemperature. Thermal deviations of an L-shape platen superheater were studied by using a supercritical 600 MW CFB boiler as reference. Based on the prediction model of thermal deviations and a self-developed software, thermal deviations of the platen superheater were calculated and analyzed under three kinds of heat load distributions. The results show that the heat absorption deviations for steam are related to the heat load and heating area distribution, wherein the heat load is more effective than the heating area. The mass flow rate deviations for steam mainly depend on the header effect and the nonuniform tube length, while the mass flow rate deviations induced by thermal effects are negligible. The mass flow rates of each tube are nearly identical because the header effect offsets the effect of the nonuniform tube length. Therefore, the heat absorption deviations determine the final thermal deviations of the platen superheater. It is suggested to make complete use of the header effect on the mass flow rate distribution; thus, achieving good control of the thermal deviation of platen superheaters.