Vision-based investigation on the ash/slag particle deposition characteristics in an impinging entrained-flow gasifier

Coal gasification is widely used for chemical production as well as energy generation, and slag tapping process is crucial to entrained-flow coal gasification, before which particle deposition play an important role in slag formation. In order to investigate the slag tapping under special or abnormal operating conditions, the ash/slag particle deposition and ash/slag layer behavior characteristics have been studied based on a bench-scale impinging entrained-flow gasifier. High temperature endoscopy combined with high speed photography is applied to obtain images inside the gasifier and image processing techniques are used to distinguish the object from the high brightness background. The results show that an ash/slag deposition layer is formed under low operating temperature. In the case of particle deposition: High temperature particle (HTP) with medium size would slide on ash/slag layer after impacting, low temperature ash/slag on the deposition layer adheres on the particles and detach from the deposition layer together. HTPs with big size would attract low temperature ashes while travelling in gasifier space and ash/slag surface after impact, then form a low temperature particle (LTP) group with high temperature core and detach from the basic ash/slag layer. LTPs with big size and high space speed would impact and embed into the ash/slag deposition layer, then particle temperature rises while particle volume decreases. The embedded particles hardly detach from the basic layer. The low temperature ash/slag deposition layer would detach from the old slag layer on refractory wall, and the detachment of ash/slag layer is mainly classified into three typical patterns according to the behaviors of the detach process: detach after sliding pattern, detach after tilting and shaking pattern, detach after warping and fracturing pattern. Detachment after warping and fracturing is the commonest pattern of ash/slag deposits behavior that has been observed. Due to the huge volume of detached pieces, it could be the major source of slagging under abnormal operating condition. Under certain extreme conditions, slag tap hole would be blocked by the bridging of huge ash/slag deposits pieces and leads to overpressure of gasification chamber and slagging failure. In industrial applications, the results of this study would be the theoretical support for the suggested minimum load and suggested feeding period of the gasifier during the unique online pressurized continuous coal-water slurry feeding technique of the opposed multi-burner (OMB) gasification.