Thermal Dryer Selection and Procurement Approaches in Athens-Clarke County Georgia

Summary This paper will share the progressive evaluation and selection of a thermal drying technology for application at the Athens-Clarke County Public Utilities Department (ACCPUD) North Oconee Water Reclamation Facility (NOWRF). The progressive evaluation and selection process was conducted in multiple phases and included: - Confirmation of Sizing Criteria - Evaluation of the 'World of Options' for Thermal Dryers - Screened Technology Assessment Site Visits - Technology Type Selection and Competitive Pre-Procurement Process - Detailed Design and Bidding This paper and presentation will share the progressive process utilized by ACCPUD for the selection of a dryer technology and a technology provider using a combination of cost and non-cost evaluation factors in a multi-criteria procurement process. Confirmation of Sizing Criteria The current plant is permitted for a 14-MGD capacity and uses an advanced activated sludge process for treatment coupled with high solids centrifuge dewatering to produce a cake for landfill disposal. Future plans are to expand the plant by adding primary treatment and anaerobic digestion. Dryer sizing was confirmed against current and future residuals production rate scenarios and a design evaporation of of 4,500 lb-water per hour was selected. Evaluation of the 'World of Options' for Thermal Dryers The first phase assessment included a preliminary screening of the following thermal dryer technologies for possible application of at NOWRF: - Belt Dryers, - Rotary Drum Dryers, - Indirect Paddle Dryers; and - Fluid Bed Dryers Based on the preliminary screening of technologies the belt dryers and indirect paddle dryer technologies were selected for additional screening assessment. Screened Technology Assessment Site Visits Following the preliminary screening site visits were arranged for plant operating and maintenance staff to visit operating installations of the belt and paddle dryer technologies. Site visits were conducted in Pennsylvania, North Carolina and Tennessee to view operating installations and have discussions with facility operators. Results of these site visits will be summarized in the paper and presentation. Technology Type Selection and Competitive Pre-Procurement Process Following the site visits and discussions with facility operators of belt and paddle dryers ACCPUD operations and maintenance staff selected the indirect paddle dryer technology as the most appropriate technology for application at the NOWRF. Based on the preliminary screening of technology suppliers a competitive procurement process was designed that would consider both cost and non-cost factors in the final selection of a technology vendor. The competitive procurement was conducted between the Komline-Sanderson Paddle Dryer and the Andritz-Gouda Paddle Dryer systems based on development of a detailed technical specification describing the system and the minimum required system elements coupled with a preliminary general arrangement drawing for location of the facility on the plant site and integration with the existing dewatering system. The competitive procurement scoring allocated 25% of the scoring points to cost factors and 75% of the scoring points to non-cost factors. Cost based scoring criteria considered the following: (1) equipment capital costs, (2) estimated building costs to house the equipment, and (3) system operating and maintenance costs based on power consumption and thermal energy efficiency of the dryer system. The non-cost factors were allocated to the following major criteria: (1) manufacturer experience; (2) operability and maintainability; (3) air permitting and air emissions rates; and (4) process safety. The paper and presentation will share the results of the cost and non-cost scoring for the selection of the technology supplier. Detailed Design and Bidding Following selection of the technology supplier detailed design activities were initiated for the project. Preliminary design activities included sending a large sample (~ 15 cubic feet) of dewatered cake to the selected technology supplier to test in their pilot plant to confirm heat transfer coefficients and the minimum ignition temperature (MIT) for the paddle dryer. The sludge-specific heat transfer coefficient was utilized to confirm adequacy of the proposed heat transfer surface area. The minimum ignition temperature was used to confirm the paddle dryer thermal oil operating temperature. Results of the pilot testing will be shared in the paper and presentation. Detailed design has progressed through the 'bid ready' stage and the project has been bid and will begin construction in late 2021 / early 2022.