Designing and Operating Reliable Gasifiers

Handling of bulk solids takes place in gasifiers either at the feed point or at the section of discharging waste and residues of the combustion and gasification. In large gasifiers, significant amounts of waste are expected to be produced, hence a proper gasifier design that allows an effective discharge of the waste from its bottom is essential for a smooth and reliable gasification. Poor gasifier design may result in unwanted flow patterns of the waste and formation of stagnant zones of ash in the discharge section, which may melt and eventually cause slagging and plugging of the gasifier. An experimental investigation was carried out to study the impact of two retrofitting techniques on the flow pattern and rate of discharging solids from a conical bottom discharge section of a cylindrical column simulating a gasifier. The two retrofits were a double pyramid insert and a throttling vertical tube attached to the outlet orifice. Glass beads were used as the bulk solids. The double pyramid insert was able to effectively change the flow pattern in the conical bottom of the surrogate gasifier from the undesired funnel flow to the most desired mass flow. Furthermore, it also promoted a uniform and homogenous flow preventing undesired delays in the discharge of the solid particles. On the other hand, attaching the vertical throttling tube to the outlet orifice developed severe and sudden constriction, causing transition from packed bed to suspension flow regime, hence increasing the discharge rate of the bulk solids by 7 to 8 folds.