Experimental Study on Application of Paddle Dryers for Sludge Cake Drying
Drying tests were conducted on sludge cake using two types of paddle dryers. It was observed that polymer conditioned sludge cake was easier to dry than sludge cake conditioned with inorganic chemicals. Sludge in the dryer was separated into two zones, a
- PDF / 1,055,278 Bytes
- 6 Pages / 595.276 x 790.866 pts Page_size
- 20 Downloads / 204 Views
ABSTRACT Drying tests were conducted on sludge cake using two types of paddle dryers. It was observed that polymer conditioned sludge cake was easier to dry than sludge cake conditioned with inorganic chemicals. Sludge in the dryer was separated into two zones, a paste zone upstream and a lump zone downstream. The heat transfer coefficient of each zone was strongly influenced by moisture content in the sludge and varied from 20 to 600 w/(m 2 ·K).
Cake
Drain Product
Steam
l. INTRODUCTION The widespread application of sewage sludge treatment in recent years has rapidly increased the generation of sludge cake (dewatered sludge). Most of this cake is finally disposed of by such measures as ocean dumping, incineration and landfill. The advantages gained by effective drying of the sludge cake are a reduction in volume, lower fuel costs for incineration and recycling. as fertilizer. The authors conducted experimental studies on the drying characteristics, heat transfer coefficient and other properties of sludge to develop an efficient sludge dryer.
Expected capacity F kg/h (from 80 to 40\ wet base moisture)
2. EXPERIMENT
Heating surface location total area Ao per unit volume
2.1. Apparatus
Paddle rotation
Bench-scale dryer Pilot-scale dryer Fig. 1
r
[m] 0.13 0.32
Specification of test paddle dryers
m2 m2;m3
Number of shafts
479
a
[m] 0.65 1.15
Schematic view of test paddle dryers
Table 1
Sludge cake is usually highly viscous and gives off a strong odor during the drying process. In the author's prior experience, a steam tube rotary dryer and a single shaft dryer proved ineffective for proper drying of sludge cake because they were not equipped with a crushing device. Therefore, a configuration of indirect dryers agitated by twin shafts was chosen, and two paddle dryers of different capacities were fabricated by the authors for the tests. A schematic and specifications of the paddle dryers are shown in Fig.l and Table 1, respectively. The dryers were constructed with hollow shafts and paddles. The heat transfer media passes through each of these shafts and paddles as well as the jacket of the shell walls. The heating area of the pilot-scale dryer was increased four times over that of the bench-scale dryer, anticipating a propOrtional improvement in drying efficiency. Dried sludge is discharged from the overflow weir installed at
R. Toei et al. (eds.), Drying ’85 © Springer-Verlag Berlin Heidelberg 1985
io [m] 1.22 2.10
Product
rpm
Bench-scale
Pilot-scale
100
400
Shell, Paddle, Shaft 19.4 4.9 16.0 19.9 Twin 40
2.2 Procedure Figure 2 shows a flow diagram of the test dryer facility. Sludge cake is supplied to one end of the dryer by a snake pump and is dried while being transfer~ed to the other end. Water evaporated during the drying process leaves the dryer in a carrier gas (hot air) and is introduced to a condenser to be discharged outside the system in the form of condensed water. After moisture is removed from the carrier gas it is passed through a gas heater and heated to approximate 360 K,
Data Loading...
