DRAIMAD® sack filter

Operating principles

This system is modular and is designed to optimise the filling and dewatering cycle of the filter sacks. Once this cycle is over the full sacks can be removed, sealed and stored in the open air for a further period of dehydration, reducing the weight and volume of the sludge cake. The special water repellent material of the sacks prevents rainwater from entering but allows dehydration of the contents by evaporation. The sacks are mounted on a special stainless steel frame, designed to distribute the sludge. The system is electronically controlled from a programmable control panel, ensuring correct process operation. Before dewatering the sludge should be conditioned with polyelectrolyte. After a few hours operation, dry solids content of 15 - 20% can be achieved, depending on the nature of the sludge. The volume of dewatered sludge is dependent on the solid content. For 1% dry solids, one machine can treat up to 20 m3 per day.
After the initial dewatering stage on the machine, the sacks are sealed and removed with a special sack trolley and stored in an open area (after 10-24 h). During the second phase, due to the special hydrophobic sack material, sludge weight and volume continue to reduce, regardless of weather conditions. After 2-3 months storage, a cake of 50-70% DS content is produced. As an example, 1500 kg of sludge at 1% solids content would give, after the first phase - weight of sludge 70-80 kg ( 20% dry solids), after two months, a cake of at least 50% dry solids content. This would weigh only 30 kg and represents almost a 50-fold reduction of the original weight.

Structure

Description

Various models are available, with 2, 3, 6 and 12 sacks. Operation may be manual, with filtration taking place under gravity, or automatic with pressurised filtration. Multiple units may be installed, either in series or in parallel, to meet any requirements. The feature of all models:

• compactness and low space requirements,
• an internal sludge distribution system with sack collars and clamps in stainless steel,
• a drainage collection tray beneath the machine and sack positioned for easy handling,
• filtrate collection tank,
• a specially designed sack trolley for handling the full sack.

Automatic operation

Automatic operation consists of: programming to optimise filtration cycles and maximise capacity, the ability to alter the operating cycle to handle sludges with varying characteristics, automatic operation of a sludge feed pump or valve to feed sludge to the unit as required, automatic finishing of the filtration cycle when the unit is full and the option of extending the pressurisation phase.

Pressure operation

Pressurisation using low pressure air (0.2 - 0.3 bar) almost doubles the capacity of the units. The sacks are mounted in stainless steel cages designed to allow rapid sack replacement.

Advantages

• high efficiency, dewater to 50 - 70% D.S.,
• low operating and maintenance costs,
• min. consumption of energy,
• very small area of installation,
• very small area of installation,
• low costs of transport, sludge mass decreased up to 60 times,
• use of normal means of transport for sludge disposal,
• modular units - easy increase of capacity,
• simple to install, without special construction work,
• neatness and comfort in the all process,
• safe for environment,
• highly effective and reliable work throughout the year,
• total costs reduction of sludge disposal.

Technical data