Improvements on a gravity-driven low-rate particle feeder.
A gravity-driven particle feeder has been modified to achieve sustained operation at steady rates. Particle reservoirs and rod for controlling the nozzle opening are completely redesigned. Particle attrition and rod wobbling are the two main contributors to the feed instabilities. They, in turn, are affected by the height of the particle bed, particle contact time with the moving rod, strength of the magnetic field, and the weight, shape, and position of the rod in the magnetic field. A secondary reservoir minimizes the residence time of particles in the main reservoir. Its shape, orientation, and connection with the main reservoir have profound influences on the feeding stabilities. Tests have been conducted with particles of different types, sizes, and feed rates; results showed good long-term and short-term stabilities.
A gravity-driven low-rate particle feeder.
A gravity-driven particle feeder has been designed, fabricated, and tested to feed particles at low rates. A solenoid and a digital timer regulate the feed rate. This design avoids moving parts at the system periphery and thus avoids possible air leakages. It does not use pressurized gas to blow the particles into the desired location and thus pressure disturbance is avoided. The feeder can be operated at either a batch or a near continuous mode. Moreover, feeding a single large particle at a desired time is also feasible in such gaseous environments.
Stable Oxides on Chars and Impact of Reactor Materials at High Temperatures
This paper reports our first study on the deactivation of young chars in flame conditions. The quantity and strength of surface oxides on young chars are monitored in situ by temperature-programmed desorption (TPD) up to 1700 °C. Young chars contain more abundant surface oxides than old chars over a wide range of temperature. Lignite chars possess more oxides than chars derived from a bituminous coal. Chars oxidized at 629 °C show desoprtion products at three distinct temperatures:  725, 1430, and 1700 °C. The TPD peaks around 725 °C correspond to activation energies in the range of 107−170 kJ/mol and have been well-documented in the literature. CO desorbed at around 1430 °C corresponds to activation energies over 300 kJ/mol, signifying the possible roles of strongly bound oxides on the basal planes of carbon. Search of the oxygen source for the huge amount of CO production at 1700 °C reveals that commonly adopted alumina tubes and support materials decompose to Al2O(g) and emit a notable amount of O2 at ...