Experimental Investigation On Coal-fired Chemical Looping Combustion Coupled With An Annular Carbon Stripper

Chemical-looping combustion?CLC?is a novel combustion technology,which can achieve CO₂inner separation with capturing CO₂at low energy penalty during combus-tion process.Char gasification rate is normally much slower than oxygen carrier reduction rate in fuel reactor?FR?during the coal-fired CLC,and the unconverted char is easily car-ried by the oxygen carrier into air reactor?AR?and burn directly.Therefore,it is vital to separate the oxygen carrier and char particle.In present work,the binary particle separa-tion rule in the coal-fired CLC was experimentally investigated.An annular carbon stripper?CS?based on the idea of separation in dilute phase was proposed and designed,and a cold model apparatus of the single annular CS was built for studying the binary particle separation rule.Experimental procedure and measurement method of the separation of binary particle contained plastic bead?light?and ilmenite?heavy?were established,which can simulate and quantitatively analyze the char and oxygen carrier separation in the coal-fired CLC.The results indicate that solid feed rate,gas velocity in the annular zone and light particle size are key separation factors.The light particle separation efficiency achieved beyond 95%at the solid feed rate smaller than 40 g/s.The light particle separation efficiency was increased while the heavy par-ticle separation efficiency was decreased when increasing the gas velocity in the annular zone of which the optimized gas velocity is closed to terminal velocity of heavy particle.Further,a reactor design of coal-fired CLC coupled with the annular CS was proposed.A cold model of the coal-fired CLC reactor was built and operated with reasonable pressure balance and stable/controllable solid circulation.The reactor achieved high efficient and continuous binary particle separation,and the light particle separation efficiency was be-yond 85%.It was found that the light particle separation efficiency was decreased about10%due to system effect on the annular CS.For the gas-solid flow structure of the binary particle separation,it was found that solid volume fraction distribution was denser at the bottom region of annular zone and was dilute in the upper region,while the distribution of light particle mass concentration was the opposite.The two distributions both had a dramatic change at the bottom region of annular zone,in which the binary particle separation was vital.Comparing to the single annular CS,fluctuation in the fluidized bed system caused the gas-solid non-uniformity structure in the annular CS more severe,which was main reason of the system effect.A hot model apparatus of the coal-fired CLC coupled with the annular CS was de-signed and built for studying the char and oxygen carrier separation at high temperature.Vietnam ilmenite was used as the oxygen carrier.The system achieved stable and contin-uous solid circulation at high temperature with stable coal?Shenfu bituminous?feed and the system thermal input was 3-10 kW_th.The longest stable and continous operation time was above 15 h and the accumulative operation time was about 100 h.The experimental results indicate that the carbon separation efficiency of annular CS was larger than 90%at860°C.For optimzing carbon capture efficiency,the effects of reactor temperature,oxy-gen carrier circulation rate of system,coal size and gas velocity in the annular zone on the carbon capture efficiency of system were studied.The results showed that increasing temperature greatly promoted the system carbon capture efficiency.At 950°C,the sys-tem carbon capture efficiency reached 95%?It was found that some char was adhered to the ilmenite surface in three forms?cylinder,block mass,reticulum?,which decreased the carbon capture efficiency.Finally,the carbon conversion process in the coal-fired CLC system was summarized and proposed.