Sludge Drying

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Sludge Drying

Belt Dryers

  • Evaporation rates from 200kg to 3,000 kg/h
  • Low temperature drying for safe operation
  • Full or partial drying in one step
  • Flexible heating with direct or indirect options
  • High quality granulated final product
  • Uncomplicated operation with rapid start up and shut down
  • Variably adjustable retention time
  • Gentle drying with minimal product attrition
  • Mobile or fixed units

The belt dryer was developed to dry various sludges in a simple, energy efficient and dust free way to d.s contents of 65% to 95%. The mechanically dewatered sludge is extruded on to the perforated belt where it is conveyed slowly through the drying zone and discharged at the end of the conveyor. The retention time can be adjusted very accurately such that homogeneous drying is achieved.

Enhanced Dewatering – Centridry®

The CENTRIDRY® enhanced dewatering process offers a unique single stage process combining mechanical dewatering and thermal drying in a single compact machine with a small footprint.

The CENTRIDRY® system will process municipal and industrial sludges with an incoming d.s. of 2% – 7% and produce, within seconds, fine grained sludge granulate with 60% – 90% d.s.

The main features are:

  • Dewatering and drying in a single machine
  • Water evaporation rates of 300 – 2,000 kg / h
  • Selectable d.s. content of 60% – 90%
  • No back mixing of dried product
  • Simple plant design with minimal
  • Peripheral equipment based upon proven centrifuge technology
  • Short start up and shut down time – suitable for single shift or continuous operation
  • Thermal stage can be fired by natural gas, digester gas or diesel oil
  • Enhanced treatment of sludge, available in bagged or bulk form, pelletised or fine grained
  • Fully automatic safe operation

Process description

Fig.1 shows the main components, which would also include a conventional polymer preparation station to feed the mechanical dewatering stage.

Liquid sludge combined with polymer is pumped into a modified CENTRIPRESS® centrifuge where conventional mechanical dewatering takes place. The dewatered sludge at the dewatering stage needs to reach a minimum d.s. of 25% and is discharged into the thermal stage as a fine-grained spray.

The outer casing of the standard CENTRIPRESS® is replaced in the by CENTRIDRY® by an insulated cyclone jacket which is fed by high speed sweep gas from the hot gas generator. The sludge particles on entering the cyclone chamber are instantly dried such that when making initial contact with the external walls the sludge does not stick to the walls. The particles are instantly entrained and conveyed in the sweep gas and exit the jacket in a matter of seconds during which time the sludge granules are dried and the temperature of the conveying gas is dramatically reduced. The pneumatic conveying and drying process continues during the relatively short transport time to the cyclone where the product particles are separated and discharged via a rotary valve to the stockpile.

The sweep gas, drawn through the system by via the main ventilator fan and is re-heated in the hot gas generator before re-entering the dryer loop.

Excess vapours in the system are drawn off the system by a small blower, and following treatment in a venturi scrubber to remove residual quantities of fine dust and volatile components, are discharged for simple odour treatment.

Enhanced dewatered product

The sludge from the centrifugal dryer has a fine-grained structure. The mean granulate diameter depends on the type of sludge and on the degree of drying and is approx. 1 mm. The mean particle size is therefore comparable to the grain distribution of unscreened sludge from other dryers. The grain shape is not spherical and the individual particles are characterised by a rugged, coarse surface. Due to the way they are generated after the mechanical de-watering in the centrifugal stage, the particles possess a very large specific surface with bulk density ranging between approx. 600 and 750 kg/m³.

The dust free product at 60 -70 % d.s. can realise disposal routes in both agriculture and thermal re-use.

Thermal re-use

The enhanced dewatered sludge product made with the CENTRIDRY® plant can be easily formed into pellets when the dry substance content is between 65% and 85%. Below a d.s. content of 65% the pellet tends to yield and above 85% it has a lower internal coherence and the wear at the pelletiser becomes higher and throughput restricted. For the purposes of a fast and uniform incineration of the dried sludge, pelletising of the sludge is not necessary.

N.B. The information contained in this entry is provided by the above supplier, and does not necessarily reflect the views and opinions of the publisher