Análise computacional da taxa de produção de vapor gerada em trocador de calor tipo jaqueta acoplado à seção riser de um leito fluidizado circulante de laboratório

Abstract

In last decades, the steam production from circulating fluidized bed (CFB) boilers has deserved importance due to their advantages in terms of energy efficiency and environmental impact. However, the abundant information regarding the operation of evaporators used in commercial CFB boilers contrasts with scarce data detailing the performance of such devices coupled to small fast fluidization units. By recognizing this gap, a procedure to calculate the steam mass flow rate that could be produced from a jacket type heat exchanger externally positioned on the riser column of a labscale circulating fluidized bed unit was proposed. Mathematical models extracted from literature were implemented in the Engineering Equation Solver (EES) software to simulate the heat transfer phenomena related to the water´s phase change through the heat exchanger, as well as to the gas-solid flow in contact with riser walls. Profiles of the steam mass flowrate were predicted as a function of the steam pressure, fluidizing gas velocity in the riser, steam quality, bed mean particle diameter, average bed porosity and temperature of the gas-solid flow. Results showed that the steam mass flowrate generated by the small evaporator can vary from 8.5 kg/h up to 15.7 kg/h, suggesting that both the bed temperature and the bed porosity have the highest impact on the phase change process. Although the predicted results obtained from simulations make sense, experimental tests in the lab scale CFB unit here studied are required to validate the proposed mathematical models.