Suneerat Pipatmanomai

COMPREHENSIVE STUDY OF PRESSURE-DROP BALANCE AND PERFORMANCE OF AN L-VALVE IN A CIRCULATING FLUIDIZED BED

Pressure-drop balance and L-valve performance in a circulating fluidized bed (CFB) were investigated for variation in gas superficial velocity (Ug), secondary air fraction (SA), total solids inventory (Is), and external aeration flow rate (QA), at ambient temperature. The study shows that the solids discharge rate of an L-valve (Gs) changes with the system control variables. Apparently, a wider range of Gs is achieved at increasing Ug, decreasing SA, increasing Is, and increasing QA. The pressure-drop analysis indicates that these characteristics are directly governed by the loop pressure balance. Standpipe bottom pressure is found to be an important indicator of the operating status of the riser, standpipe, and L-valve. The experimental results confirm that an L-valve can be operated effectively by regulating the standpipe bottom pressure. The knowledge obtained from this study is essential for maintaining the performance of a CFB system for combustion operation, as well as for operating circulating fluidized beds on a practical scale.

Characteristics of Products from Rubber Woodchip Gasification in a Fluidised-Bed Reactor:Effect of Equivalent Ratio

In this study, rubber woodchip was gasified in an atmospheric bubbling fluidised-bed gasifier to investigate the effect of equivalent ratio (ER) on gasification behaviour and its product characteristics. The suitable range of ER for gasification was found to range from 0.2–0.4. The temperature inside the reactor was affected by ER; the bed temperature increased from 720°C by about 100°C as ER was increased from 0.2 to 0.4. The concentration of CO2 continuously increased with ER, while CO and H2 found their maxima at ER=0.26. The concentration of CH4 was about 4 % and unaffected by ER, while C2 hydrocarbon gases were also detected with < 1 % in total. At ER=0.26, the LHV of product gas was the highest at 4.6 MJ/Nm3. Carbon-in-ash was found to be related with ER, the higher the ER the less unburned carbon in ash. Different chemical compositions of tars obtained from various ER were thought to be the influence of temperature as a consequence of changing ER; higher temperature appeared to yield tar with relatively higher proportion of large to small molecular weight fractions.