Project Synopsis

Detailed technical and economic evaluation of critical operations associated with a biological sludge pretreatment system to prepare a sludge stream for continuous processing through a thermal treatment system. 

Project Summary

SLUDGE PRETREATMENT SYSTEM ALTERNATIVES TECHNICAL AND ECONOMIC EVALUATION

The client owns and operates a waste thermal treatment system.  Process Engineering Associates, LLC (PROCESS) was contracted to perform a detailed technical and economic evaluation of the critical operations associated with a sludge pretreatment system design to prepare a biological sludge stream for continuous processing through the thermal treatment system.  Technical and economic evaluations were performed for alternatives associated with the following operations:

  • Sludge dewatering
  • Sludge drying
  • Sludge dryer offgas organic removal

Each technical and economic evaluation included completion of the following work tasks:

  • Process design basis development, including feed stream characterization and unit operation performance requirements.
  • Alternatives technical screening to eliminate alternatives not technically suitable for the application.
  • Alternative mass and energy balance and process flow diagram preparation.
  • Vendor bid request preparation and vendor bids review for the purpose of establishing alternatives purchase costs.
  • Capital, operating, and annual cost estimates preparation.
  • Alternative selection based on technical and economic considerations.

Alternatives for the sludge dewatering application included:

  • Sedimentation centrifuge
  • Filtration centrifuge
  • Filter press
  • Filter/dryer system (nutsche filter)
  • Pressure leaf filter
  • Rotary drum vacuum filter
  • Horizontal vacuum filter.

Alternatives for the sludge drying application included:

  • Rotary kiln dryer
  • Thermal screw
  • Tumble (double-cone) dryer
  • Tray dryer
  • Turbo-tray dryer
  • Filter/dryer (nutsche dryer)
  • Drum dryer
  • Conveying screen dryer
  • Steam-tube rotary dryer
  • Vacuum rotary dryer (ribbon dryer)
  • Multiple-hearth dryer
  • Fluidized-bed dryer
  • Spray dryer
  • Pneumatic conveying dryer

Based on technical and economic considerations, the combination nutsche filter/dryer was selected for the filtering and drying applications (i.e., one unit operation for both applications).

Alternatives developed for the sludge dryer offgas organic removal application included:

  • Carbon adsorption with on-site disposal via the existing thermal treatment unit
  • Carbon adsorption with on-site regeneration
  • Carbon adsorption with off-site regeneration
  • Alternative adsorbent with on-site disposal via the existing thermal treatment unit
  • Alternative adsorbent with on-site regeneration
  • Alternative adsorbent with off-site regeneration
  • Condensation
  • Thermal oxidation
  • Absorption

Based on technical and economic considerations, carbon adsorption with on-site disposal was selected for the sludge dryer offgas organic removal application.

The selected alternatives were carried forward for the preparation of a process design package for the sludge pretreatment system.

Industry Type

  • Waste Treatment

Utilized Skills

  • Front end engineering design (FEED)
  • Biological sludge pretreatment system design
  • Sludge dewatering
  • Sludge drying technologies evaluation
  • Cost estimating

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