| OCR Text |
Show elements placed in a radiation cavity 20 cm long. Coal particles were entrained in a stream of nitrogen at rates of 2 g/hr using the syringe pump feeder arrangement described by (5] and were injected into the alumina tube through a wide bore (1 cm) water cooled injector. Furnace wall temperatures were measured by thermocouples attached to the outside of the alumina tube. Gas temperatures were measured using a suction pyrometer. The furnace wall temperature was kept at 1650K. The gas temperature was about 1600K. The carrier gas flow rate was adjusted to achieve residence times of 2 seconds. The devolatilization loss for the coals ranged between 30-35%. The chars were collected on a filter. To eliminate any tars that might have condensed, the chars were washed repeatedly with tetrahydrofuran and then dried at room temperature for 1 hour. Finally the tar-free chars were sieve-classified into the following size fractions: less than 45J,Lm, 45-53J,Lm, 53-90J,Lm, 90-104J,Lm, 104- 125J,Lm, 125-147 J,Lm and greater than 147 J,Lm. The narrow size fractions 45-53J,Lm and 104-125J.Lm were used in the combustion experiments. A few chemical and physical characteristics of the coal and char are given in Tables 1 and 2. 2.2 Pyrometry The char particles were injected into the furnace via a side injector port in a very dilute stream. After falling about 30 cm, they entered the hot zone and burned quite rapidly while traversing a few millimeters. The burning particles were in the view of the pyrometer detector during the entire duration of combustion. The pyrometer was aligned along the direction of flow of the particles, i. e. axially, looking downward, and thus, was able to 'see' each particle for its entire burning history. The radiation from the burning particles was actually focussed onto a bifurcated optical fiber which transmitted the signal to two silicon photodetectors. Two medium band (70 nm) filters centered at 800 and 1000 nm were used to pass only the desired spectral signals to the detectors. The resulting voltage signals from each detector channel were then read by a high speed, computerized data 4 |
