75 T/h Oil Shale CFB Boiler Design And Numerical Simulation Of Gas-solid Two Phase Flow In Furnace

Energy and environment problem has become more serious in recent years. For all nations, shortage of oil is restricting economic development, which makes oil shale draw more and more attention as an important fossil energy with huge reserves. There is a huge difference between oil shale and conventional coal. Oil shale is an inferior fuel with high volatile and low fixed carbon content and calorific value, and shaped as flaky particles after crushing. The rise of new CFB(Circulating Fluidized Bed) combustion technology, especially suitable for combustion of inferior fuel with low calorific value such as oil shale, because it can make oil shale combustible under low temperature with low emissions of SO2 and NOx.In this paper, three-dimensional simplified model simulation for 75t/h oil shale CFB boiler was developed to study the influence of particle size, fluidization velocity and furnace cone Angle. The results showed that particle density presents a law of low in the center and high close to wall. Small size particles solid content rate is lower. However, the smaller the particle size of the particle is, the more the particle fluidization is more intense and the mixing is more intense. Particles size of 1 mm has the best fluidization effect. With the same furnace height, when the fluidization wind velocity is higher the granular solid content rate is lower, and the particle speed tends to parabolic distribution. When the fluidization wind speed is 5 m/s, particles mix more intense. When furnace cone Angle is smaller, which makes easier to gather in the side wall with higher granular solid content rate. If furnace cone Angle is higher and granular solid containing rate is lower by the side wall, the fluidization wind speed is lower, which leads particels can’t reach the ideal fluidization effect. When the furnace cone Angle is 75 °, solid particles has a higher upward velocity in the central area, and the downward speed in the side wall is lower. Based on comprehensive consideration, it is concluded that when the furnace cone Angle is 75 ° the fluidization effect is best, so the furnace cone Angle 75 ° can be regared as the optimized design parameters.Combined numerical simulation results with design experience of the as-run oil shale circulating fluidized bed boiler, completed the structural design for 75 t/h oil shale circulating fluidized bed boiler. Oil shale has lower calorific value, to ensure full combustion of oil shale it is unfavorable for arrange pipe laying or other convection heating surface inside the chamber. Oil shale shaped by flaky particles after crushing, to improve the fluidization air velocity slightly reduce cross-section of dense-phase zone is required. When the combustion share in dense-phase zone is low, to ensure the combustion efficiency of furnace increase the dilute phase zone section to reduce the gas velocity and prolonged the time of oil shale stay in the furnace is also required. By thermodynamic calculation check shows that designed thermal efficiency is 89.81% with a reasonable furnace design.