IntroductionThe rotary drum vacuum filters are used in various applications and industries including food and chemical industries, and treatment of effluent. Wakeman and Tarleton (2005, p. 244) has noted that there has been slight changes in the basic design of the filters since 1872, when the basic rotary drum filter became a patent. This paper examines a standard rotary drum vacuum filter and makes a discussion of the design and operation of the filter, while pointing out future development of the technology. The designA standard rotary drum vacuum filters consist of seven main parts, but primarily of a drum that rotates in a tub the fluid to be filtered.
These components include a drum, a rotary valve, the piping, the drives, the agitator, a tank or trough, and the discharge mechanism. The drum and pipingThe drum, which is a hollow cylinder, is mounted on the support frame of the trough such that it dips horizontally into the trough and the slurry. It is positioned such that one third of it dips into the slurry or the liquid/solid suspension (Wakeman & Tarleton 2005, p. 244). The face of the drum is divided into several lateral sections that hold the filter medium.
In standard drum set up, internal drain-pipes link the lateral sections to the rotary valve assemblage, while in end- flow set up, the drain-pipes are placed at the ends of the drum such that vacuum is not applied to the inside part of the drum. Drainage grids of either nylon or polypropylene are fitted on to the to the drum face to allow the filtrates across the lateral sections to flow freely to the drain-pipes.
A shaft passes horizontally at both ends of the drum so that its one end links to the drive gearbox, while the other has the drain-pipes bundle linked to the rotary valve assemblage. Figure 1. a diagrammatic representation of the rotary drum vacuum filter with a knife dischargeAs stated earlier, the surface of the drum or the drum deck is compartmentalized, and these compartments or sections further divided by grooved strips that run along the surface of the drum and around its circumference. The strips holds synthetic grids that cover the whole drum face while supporting the filter cloth.
This filter cloth is fixed to the drum with special ropes that are inserted into the grooves. The rotary valveA valve together with a bridge setting is included in the drum vacuum filters to control the cycle sequence such that each of the drum sector goes through the blow, vacuum, and dead-time phases. In some filters, the valve has adjustable blocks, while in others it has a fixed ring. The adjustable block allow the optimization of the drum submergence as well as the form to dry ratio in the filtration cycle.
Many drum filters include a valve that has three bridge brocks and a single-row pipe plate as illustrated below. Figure 2. A diagram showing a drum with a valve and the three bridge blocks One bridge separates the blow and vacuum zones. Another bridge, the dead zone bridge, opens to the vacuum during submergence of a compartment, while the start-up-assist bridge that controls the opening of the opening during start up.