Research On The Drying Characteristics Of Sewage Sludge In A Fluidized Bed

Being a decreasing contain, innocuity and resource disposal mode, try wet sludge by combustion is recognized widely. However, it was the studied emphasis on how to reduce the accessorial fuel in the wet sludge combustion. Research on drying of wet municipal sewage sludge in a fluidized bed was made and is described in detail in the thesis.The experimental study was carried out in a fluidized bed to determine mixing characteristics. The results show that the more the sludge pellets in the bed, the larger the minimum fluidization velocity is. Mixing is the better when the mass fraction of sludge pellets in the mixture is close to 1:1. The more the moisture in the sludge pellets, the larger the minimum fluidization velocity of mixture is. Based on the experimental data, a correlation of the minimum fluidization velocity of the mixture of sludge pellets and sand is proposed.Drying and breaking characteristics of a single municipal sewage sludge pellet in a bubbling fluidized bed of sand were studied. The results show that the bed temperatures and sizes of sludge pellets affect the drying rates exponentially. The drying rate and the breaking index are larger with higher sludge moisture. When the bed is fluidized at larger velocities, which are more than 2 times of minimum fluidization velocities, increasing of fluidization velocities (from 2 to 5 times minimum fluidization velocities) can not affect the drying rate. First breaking is the main in the sludge pellets breaking process. After breaking, sizes of sludge pellets are decrease and the drying rate is increase. Moisture borderline of breaking is proposed and the curves of moisture borderline are gained by experiment. Based on the experimental data, a semi-theoretical model of sludge drying in a bubbling fluidized bed is proposed.The integrative technology of drying and combustion of wet municipal sewage sludge was investigated in a 0.15MWth circulating fluidized bed. The result shows that adjusting the hot ash flux and the sludge feeding rate can keep the dryer and combustor steady. After drying and breaking, the moisture of sludge pellets decrease to 20 percent and the average diameter is 2 mm.