Investigation of flow behaviour of coal particles in a pilot-scale fluidized bed gasifier (FBG) using radiotracer technique.

Knowledge of residence time distribution (RTD), mean residence time (MRT) and degree of axial mixing of solid phase is required for efficient operation of coal gasification process. Radiotracer technique was used to measure the RTD of coal particles in a pilot-scale fluidized bed gasifier (FBG). Two different radiotracers i.e. lanthanum-140 and gold-198 labeled coal particles (100 gm) were independently used as radiotracers. The radiotracer was instantaneously injected into the coal feed line and monitored at the ash extraction line at the bottom and gas outlet at the top of the gasifier using collimated scintillation detectors. The measured RTD data were treated and MRTs of coal/ash particles were determined. The treated data were simulated using tanks-in-series model. The simulation of RTD data indicated good degree of mixing with small fraction of the feed material bypassing/short-circuiting from the bottom of the gasifier. The results of the investigation were found useful for optimizing the design and operation of the FBG, and scale-up of the gasification process.

Management of traction wire fracture complicating mechanical basket lithotripsy.

BACKGROUND AND STUDY AIMS: The application of basket catheters has become the main method of removing calculi from the biliary and pancreatic duct. However, larger or impacted stones have to be crushed and fragmented by mechanical lithotriptors before removal is possible. Sometimes, fracture of the traction wire occurs as a severe and fraught complication. We describe a precautionary measure which helps to manage this complication. PATIENTS AND METHODS: In a series of 569 consecutive patients suffering from bile or pancreatic duct stones we found 60 (10.5%) who required mechanical lithotripsy for oversized or impacted calculi. Mechanical lithotripsy was always performed initially with a long metal sheath (80 cm) in combination with a standard traction wire. If the traction wire fractured we replaced the long metal sheath stepwise by shorter ones (70cm, 60cm and 50 cm, respectively), allowing immediate continuation of the lithotriptic procedure using the same traction wire. RESULTS: During the lithotriptic procedure three of our patients (5%) were afflicted by traction wire fracture. Two patients could be relieved directly by changing the initial metal sheath to shorter ones. Because of the exceptional hardness of a pancreatic duct stone the third patient needed stone fragmentation by extracorporeal shock wave lithrotripsy (ESWL) before complete mechanical clearance of the duct could be accomplished. CONCLUSION: We advocate the initial use of a long metal sheath (80cm) to perform mechanical lithotripsy. In case of traction wire fracture the use of a shorter metal sheath allows immediate successful continuation of the procedure, thereby frequently avoiding procedures such as ESWL or surgery.