Decanter Centrifuge For Waste-Water or Sludge Process

As more and more attention has been paid to environmental protection, Waste-water or sludge treatment has become the most important issue of environmental protection. Waste-water treatment plants for municipal and farm applications are designed to produce a clean, safe water discharge. Complexity of the plant depends on the immediate environmental considerations and consent limits negotiated with authorities. New plants built today are more and more sophisticated, making the decanter centrifuge ideal for precise wastewater treatment. Waste-water or sludge series decanter centrifuges from Crown Machinery provides effective concentration and dehydration during the waste water treatment process. Also, the working water purification and reuse process is applied. For the high pH value material, corrosion-proof materials of wetted parts are adapted.

Waste-Water or Sludge Thickening and Dewatering

In sludge thickening, surplus sludge, which is generated during the biological stages, is concentrated from 1 % or less total solids content to 5 – 8 % before it is pumped into the digester. As a result, the amount of sludge is reduced by 90 to 95 % in volume.

Recent studies which took all relevant fixed costs(capital and labor) as well as variable costs (consumption of power, water, and polymer as well as spare parts) into account, show that a thickening decanter has advantages over other thickening equipment. These advantages become increasingly significant in the case of large capacities and long operation time.

Regardless of whether the sludge is transported after dewatering, reused as fertilizer, disposed of in landfills or incinerated – maximum dryness is the most critical factor.The other key factors are cost efficiency in terms of consumption of polymers, energy, water and spare parts, as well as continuous, automatic operation at minimal costs.

Decanters stand out from the competition with their reliability and cost efficiency.

To a certain extent, the consumption of flocculants during sludge dewatering and concentration depends on the design of the machine. In order to achieve maximum efficiency, the formation of flocculation sludge must be at the appropriate time and position.

Thickening and Dewatering Principle

A decanter centrifuge can be viewed as a settling pond wrapped around an axis. In the settling pond, solid particles, which are heavier than the liquid, settle to the bottom driven by gravity and build up a sediment layer on the bottom of the pond. In the rotating bowl of the centrifuge, solid particles, which are heavier than the liquid, move to the inner diameter of the bowl driven by centrifugal force and build up an annular sediment layer on the inner surface of the centrifuge bowl. Since the centrifugal force in the decanter is approximately 3000 x g instead of 1 x g in the settling pond, separating solid particles from a liquid in a centrifuge becomes much faster and more efficient.

The bowl shell of a decanter centrifuge has a cylindrical – conical shape. It rotates at a high speed creating the centrifugal force needed for the separation. Inside the bowl, there is a scroll conveyor for the continuous discharge of the sediment which is packed on the inner surface of the bowl wall. The scroll conveyor rotates at a speed relative to the bowl speed. This differential speed is created by a rotating gear box at the drive end of the bowl.

The sludge to be separated enters the bowl via a stationary feed pipe. From the feed pipe it enters the separation zone via feed ports in the scroll body. In the separation zone, it separates into a sediment layer and liquid layer. The sediment is scraped off the bowl wall via the scroll conveyor and delivered out of the pond on the conical end of the machine, also called the dry zone, before it leaves via discharge ports on the conical end of the bowl. The separated liquid flows to the cylindrical end of the bowl where it is discharged by gravity via an overflow weir.

Integrated System Design

In order to optimize the separation results, maximize machine reliability and minimize operating costs, the centrifuge should be properly matched with all surrounding plant components. A Crown System can be stationary, mobile, or semi-mobile. It can be skid-mounted on a platform or installed in a closed container. Our engineers have many years of experience in the layout of plant components such as control cabinets, pumps, flocculation units, piping, etc. We know that customer requirements vary and depend on process, location and other circumstances