SCREW PRESS

The Alfa Laval Screw Press is the ideal choice for dewatering of municipal and industrial sludge when a solution with minimal supervision, low power, noise and vibration levels is required. The high-performance screw press is a user-friendly, reliable and robust piece of machinery with high uptime.

The moderate rotational speed and low power consumption of the screw press have a direct positive impact on operational costs. Another advantage of the moderate rotational speed is the fact that the screw press has extremely low noise and vibration levels, which in turn is a benefit to the
working environment. Alfa Laval controls ensure that the need for supervision is minimal.

Applications:
• Municipal wastewater plant sludges – primary, secondary, mixed or digested sludge
• Industrial biosolids
• Biogas residue.

Design:
The drum is mounted in a casing where the screw conveyor is fixed at either end in strong bearings. The screw conveyor is powered by an electric motor through a geared transmission
to produce the slow rotational speed needed for optimal performance. The entire drum is totally enclosed and provided with inspection hatches for maximum operability and maintainability..

Working principle:
Separation takes place in an inclined drum with a wedge wire screen forming the cylinder wall, and an internal screw conveyor. Polymer is dosed and mixed in the dedicated Alfa Laval Mixing Valve. The flocculated sludge suspension is then led into the screw press’ inlet chamber and to the first drum section for drainage of free water. Gradually, the sludge suspension increases in dry solids content as it enters into the pressure zone of the drum. By virtue of the counter-pressure created by
a restricted outlet, more free water is released from the sludge cake as it progresses towards the outlet. The released water is drained off to the reject-water (filtrate) outlet underneath the
drum. The wedge wire screen is kept clean by intermittent flushing from the outside of the screen (also during operation). The tips of the conveyor flights are fitted with e.g. brushes that
keep the screens clean from within.

Control system:
Two different control systems are available:
• The Basic control panel is based on relays and a variable frequency drive (VFD). The panel controls      the screw press main motor and cleaning procedure.
• The Advanced control panel can control additional scope such as feed pump, polymer dosing, solids    transport and screw press parameters. Feed rate, inlet pressure, main speed and torque can be            followed in real time.

Benefits:
The Alfa Laval Screw Press provides a number of benefits.
• Reduces sludge volume, lowering   transportation and disposal costs
• Polymer mixing valve as standard for optimum   performance and reduced polymer   consumption.
• No additional flocculator tank and mixer   required
• Continuous operation
• Cleaning of screens with screw press in   operation
• Extremely low energy consumption
• Extremely low noise level
• Totally enclosed to limit effect of odour and   aerosols
• Maintenance friendly
• Low spare parts consumption.