Thickeners, costs operating

Operating Costs Power cost for a continuous thickener is an almost insignificant item. For example, a unit thickener 60 m (200 ft) in diameter with a torque rating of 1.0 MN-m (8.8 Mlbf in) will normally require 12 kW (16 hp). The low power consumption is due to the very slow rotative speeds. Normally, a mechanism vi l be designed for a peripheral speed of about 9 m/min (0.5 ft/s), which corresponds to only 3 r/h for a 60-m (200-ft) unit. This low speed also means veiy low maintenance costs. Operating labor is low because little attention is normally required after initial operation has balanced the feed and underflow. If chemicals are required for flocculation, the chemical cost frequently dwarfs all other operating costs. 

There are a large number of processes in the chemical industries that handle a variety of suspensions of solid particles in liquids. The application of filtration techniques for the separation of these heterogeneous systems is sometimes very costly. If, however, the discrete phase of the suspension largely contains settleable particles, the separation can be effected by the operation of sedimentation. The process of sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening,... 

Low operating and maintenance costs Thickened sludge concentration limited for WAS... 

The employment of charcoal adsorption in hydrometallurgical processes offers several advantages (i) the process flowsheet is simplified, since thickening, washing, and filtration steps are avoided this implies a reduction in the capital as well as the operating costs, and... 

Selection of Type of Thickener or Clarifier Selection of the type of unit thickener or clarifier depends primarily on the optimization of performance requirements, installation cost and operating cost. For example, the inclined-plate type of clarifier provides for less solids-holding capacity than a circular or rectangular clarifier, but at a lower installation cost. The high-density thickener maximizes underflow solids concentration, requiring a higher torque rating than conventional thickeners. 

Spray-dryers are simpler and more compact than conventional wet scrubbers and have a lower capital and operating cost. Also, they do not produce large quantities of wastewater, and the spent absorbent is dry, thereby eliminating the need for thickening and filtration of the sludge. However, if the same dust precipitator is used for both the fly-ash and fhe spray-dryer product, the mixture of fly-ash and spent absorbent that they produce is unmarketable, and must be disposed of. Also, they require more expensive absorbents than conventional wet scrubbers. They are most suitable for retrofitting small plants that burn medium-sulfur coals, where capital costs and space restrictions are more of a consideration. ... 

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