Heat Transfer Assessment of the Back-Pass Channel in an Industrial Fluidized Bed Reactor

The evaluation of heat transfer in a back-pass channel for an industrial circulating fluidized bed (CFB) reactor was studied. The authors proposed a heat transfer model taking into account (i) convective heat transfer on the tube side, (ii) convective heat transfer on the shell side, and (iii) radiative heat transfer on the shell side. The analysis of heat transfer is based on measured data from tubular heat exchangers (superheater SH Ia, reheaters RH Ia and RH Ib, and economizer ECO). Performance tests were conducted over a wide range of CFB reactor loads (from 40% MCR to 100% MCR) and also at a secondary air-to-primary air ratio of 0.11. The experimental data as a function of flue gas temperature, maximum flue gas velocity, CO2 partial pressure, fly ash concentration, and particle size are discussed. During performance tests, the temperature and velocity of flue gas are no more than 1206 K and 16.3 m/s, respectively. As the CFB reactor load decreases from 100% MCR to 40% MCR, the overall heat transfer coefficient of tubular heat exchangers decreases from 60.61 W/(m2 × K) to 30.1 W/(m2 × K). The overall heat transfer coefficient was higher when the fly ash concentration was higher (from 0.0412 kg/m3 to 0.0612 kg/m3) in the back-pass channel of the CFB reactor. Mean particle size of fly ash corresponds to the maximum overall heat transfer coefficient at bigger (d50 = 0.038 mm) and smaller (d50 = 0.015 mm) particle diameters. Achieved heat transfer findings were calculated at carbon dioxide partial pressure varied between 8.48 kPa and 11.53 kPa. Research studies conducted on an industrial CFB reactor showed that the thermodynamic parameters of steam also influenced heat transfer. The geometry of the heat exchange surfaces affected heat transfer augmentation in the back-pass channel of the CFB reactor. For practicality, the relationships between the heat transfer data and other operational parameters are proposed using regression analysis. Comparing the operational data and the model results, the average absolute error is 19.23%. The heat transfer findings may be used in data-driven design, scale-up, commissioning, and operation of commercial CFB reactors.