EXPERIMENTAL DESIGN AND TESTING IN A PILOT-SCALE ROTARY KILN FOR THE TORREFACTION OF BEECH WOOD UNDER SYSTEM RESTRICTIONS

摘要

The torrefaction process increases the energy density of the torrefied feedstock through the loss of volatiles and moisture. The anhydrous weight loss (AWL) measures the loss of volatiles and it is easily correlated with the net calorific value (NCV) of the torrefied product. This work has two different parts. The first part consists of the design of the experiments and the second includes the experiments with results. The system used in CENER, where the simulation and experiments were completed, is a rotary kiln with a maximum capacity of 500 kg/h and a range of operating temperatures between 220-310°C. The innovative design feature of this reactor is the extraction of the gases from the middle of the reactor, in such a way that the direction of the gases is co-current in half of the reactor (at the beginning) and countercurrent in the last half. Besides the reactor, there is a flare which combusts the gases from the reactor before releasing them to the atmosphere, and does not allow flows higher than 120 Nm~3/h. The two variables that can be modified to overcome the restrictions and achieve the target AWL are the temperature of the reactor (controlled by the temperature of the thermal fluid used to heat the reactor), and the input capacity to the reactor. The relationship of the gases produced to the temperature is straight, the higher the temperature the more gases are produced due to a higher devolatilisation of the feedstock. On the other hand, when the input capacity was modified, it is more difficult to estimate the gas production yield; with an increased feeding rate, the AWL is lower and the amount of volatiles released reduces but there is a higher release of the total amount of moisture content due to a higher feed rate. Given a lower input of feedstock, the total amount of water evaporated is lower but the AWL and the devolatilisation degree of the feedstock is higher and, consequently, more volatiles are produced.