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.
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
- Thermal oxidation
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.
- Waste Treatment
- Front end engineering design (FEED)
- Biological sludge pretreatment system design
- Sludge dewatering
- Sludge drying technologies evaluation
- Cost estimating