Experimental Investigation Of Ash Discharge Valve Characteristics From CFB Standpipe

Coal gasification plays an important role in high efficient and clean utilization of coal resource, which accords with the present energy status of China. Circulating fluidized bed coal gasification is a promising technology for its good adaptability to coal, high carbon conversion and high desulfurization efficiency. Circulating ratio is important to circulating fluidized bed, and it can be controlled by slagging from stand pipe. How to control the slagging process is the key problem of stand-pipe slagging technology. Non-mechanical valves i.e. loop seal used as ash discharge valve, which may be used to control ash discharge, were investigated in this work.A bench scale CFB set-up was designed and constructed to study the influences of aeration rates in supply and recycle chamber of the loop seal on solids flow behavior, with silica sand used as the bed material and air as the fluidizing agent. Experiment results show that aeration in the supply chamber has a good linear relationship with the solids flow rate. However, when the recycle chamber is fully fluidized, the solids flow rate almost doesn’t change as the aeration in the recycle chamber increases. Experiment about the particle sizes indicates the fact that, as the particle size increases, larger aeration is needed to obtain the same solids mass flow rate. The results also show the height of stand pipe has an important influence on the solids mass flow rate. The pressure drop of loop seal was also discussed in this study. The press drop decreases with the solids circulation rate increases.Based on the research on loop seal, another supply chamber was added in loop seal to obtain higher accuracy and larger applicable scope. The experiments reveal that, different areas of horizontal apertures will influence the ability of controlling solids mass flow rate. Thus, better control performance can be achieved by combining different supply chambers. Results show that, these two supply chambers influence each other. When the two chambers work together, the solids mass flow rate is larger than the sum of the solids mass flow rate when they work respectively. The way to obtain lager control range with smaller aeration rate was also discussed. According to the research, if a supply chamber is used to control as a dominant role and the other used to adjust, more flexible control ability and larger control range will be achieved. The disadvantages of ash discharge valve were also discussed, and improved methods were recommended.