The Experimental Investigation On Particles Flow Character In The Circulating Fluidized Bed Boiler

According to the characteristics of water-coal-slurry Fluidization-suspension combustion technology, the effects of operation parameters on the particle velocity and concentration and pressure distribution in circulating fluidized bed boiler. The results show that when the flow speed was 2.57m/s,the quality of circulation flow rate was 0.58kg/(m2·s), the first air flow was 480m3/h and the secondary air flow was 313m3/h, the distribution of particle velocity and pressure drop, fluidization state and circulating system presented a more stable level. There is bubbling fluidized bed in the bottom zone and fast fluidized zone along the bed height, and a core–annular flow frame where the movement of particle in the core area is upward and downward at the wall area.Using the PV6A type particle velocity measuring instrument, U-tube and Pitot tube, the particle velocity and concentration and pressure distribution in circulating fluidized bed boiler were thoroughly and closely measured and the effects of operation parameters on these variables were qualitatively analyzed. The results show that pressure distribution depends on the fluidized air velocity and is slightly affected by the ratio of first and secondary air. The standpipe is the equilibrium point of pressure distribution in the circulation system, which can automatically control the height of stockpiling so that the system can reach the new equilibrium. Secondary air affects greatly the particle velocity in the bottom area of riser section zone and the influence decrease gradually with the increase of height. The higher ratio of first and secondary air, the less non-uniform of particle velocity distribution is. Also, the injecting direction and the location of secondary air can affect the velocity in the CFBB. The higher mass circulation rate, the more uniform particle velocity distribution is, but is affected greatly by the particle mean velocity. The particle concentration distribution in riser section zone shows a core–annular flow frame where the solid is denser in the annular region than core region. The particle concentration in the wall area is 1.2-1.7 times as much as in the core zone,reaches the highest value in the corner of the furnace , slightly increase with the increase of height and is affected by the particle mean velocity. When particle mean velocity increase, particle concentration also grows, but the velocity continues increasing, particle concentration will slightly decrease.