November 17 th, 2015 Thermal Hydrolysis Pretreatment (THP) Considerations For a 15 Dry Ton per Day WRF Thomas Nangle, PE CDM Smith 2015 Annual Conference Raleigh, NC
Presentation Overview
Background on Thermal Hydrolysis Pretreatment Relevance Definition Advantages & Challenges Key Considerations for 30 DTPD Installation Ancillary System Considerations Pre-dewatering Steam Production Digesters Post Dewatering Enhancing Class A Product Co-Digestion with FOG Redundancy Questions 3
Background on THP
THP and Cake Product Odor (Novak, 2012) 5
Regrowth and Sudden Increase in Digested and Centrifuged Biosolids 6 See Also WERF Report “Examination of Reactivation and Regrowth of Fecal Coliforms in Centrifuge Dewatered, Anaerobically Digested Sludges”
THP Regrowth and Sudden Increase vs. Other Class A Processes (Higgins, 2012) 7
Other Drivers for THP + AD ½ Digester Capacity Needed Higher % solids loading rates Lower SRTs Decreased Solids Hauling & Increased Biogas Increased % VSR Increased Dewaterability 8
Definition of Thermal Hydrolysis Pretreatment Lysis = The disintegration of a cell by rupture of the cell wall or membrane. 503 rules for Class A through Alt 1 – Time and Temperature Pasteurization 70 degrees C for 30 minutes Thermal Hydrolysis 165 degrees C for 20 minutes Sterilize vs Pasteurize Pasteurization reduces the number of viable pathogens so they are unlikely to cause disease. Sterilization is any process that kills or removes all forms of life. Thermal Hydrolysis sterilizes sludge through lysis via heat and flashing Less viscous = easier to pump, mix, and dewater Higher loading rates Higher % solids dewatered cake Already hydrolyzed = Lower SRTs and Higher %VSD 9
Simplified Process Flow of THP for Franklin, TN 10
Advantages & Challenges of Thermal Hydrolysis Pretreatment Advantages Minimal Odor in Digested Cake Class A, minimal regrowth Reduce required digester capacity Increased Solids Destruction Increased biogas production Improved Dewaterability Reduce Hauling Costs Challenges More equipment to maintain Pressure vessels and high pressure steam Depending on state may need special licensed operators Regs typically require annual pressure vessel inspection High strength side streams Rapid rise risk Two dewatering steps 11
Key Considerations for a 30 DTPD Facility
THP Ancillary Systems 13 Pre-Dewatering Thermal Hydrolysis (THP) Steam Mesophilic Anaerobic Digestion Post-Dewatering Sludge Cooling Heat Exchangers Sludge Recirculation Side Stream Treatment Additional Drying or Beneficial Reuse Liquids Process Nutrient Recovery CHP System Electricity to Plant Hot Water to Treatment Processes Natural Gas
Pre-Dewatering Considerations THP heats incoming sludge via steam injection ↑ mass of sludge (biosolids + water), ↑ steam required Each supplier has their own percent solids “sweet spot”: Cambi ~16% Kruger/Veolia’s Exelys is 22% or greater Considerations WAS only limits of Dewaterability Small plant with one THP train. Cake Storage vs Ability to divert cake solids 14
Various Methods of Producing Steam Boiler to produce steam CHP system to reuse biogas CHP System to Generate all Steam 15 Thermal Hydrolysis Steam Biogas Anaerobic Digester Boiler Hot Water Natural Gas CHP Thermal Hydrolysis Biogas Anaerobic Digester Hot Water CHP Steam Natural Gas
Steam Production & Application Considerations Beneficial use of low grade heat. Building heating (digester bldg.) Heating of FOG Preheating steam generator water for more efficiency Preheating dilution water Digester heating during THP downtime CHP system can be optimally designed to provide required steam based on what other resources are most valuable. Electricity Generated Hot Water Produced 16
Anaerobic Digester Considerations Rapid Rise Higher Gas Productions Up to 10-15% volume expansion Mixing System Less viscous sludge Solids will settle faster Provide mixing system vendors with hydrolyzed sludge rheology Heating Sources Normally incoming sludge During startup and THP downtime, alternative heat source is needed 17
Post Dewatering Considerations Compared to MAD ~10% increase in dewatered cake solids Post-Dewatering filtrate Ammonia levels double (2,200-2,800 mg/L) Technology Considerations Centrifuge Belt Filter Press (high ammonia levels, would want to enclose the press for odor control – similar cost to screw presses if you take into account the cost of enclosure). Screw Press (1 st THP application that we know of, when factoring in ) Side Stream Ammonia treatment Equalization High Rate Nitrification Process or Proprietary Processes SHARON ANITA Mox Anammox InNitri Others 18
Market for Class A End Product Begin with the end in mind Additional equipment: Sludge Screens Removes undesirables – cleaner Class A product to market Increases uptime of downstream equipment. Supplemental Drying/Pelletizing Dryer product - higher value Less mass to haul off site You have a great Class A product, now what? Sell/give to 3 rd party distributer (Franklin route) Brand the product and start marketing! “Promoting Your Product: Marketing Tips and Techniques to Stimulate Biosolids Sales and Distribution.” WEF Webcast 19
Co-Digestion with FOG Few existing THP installations treat FOG FOG needs to be treated to Class A Can be accomplished different ways, Separate pasteurization of FOG Lower temps require less energy input Additional equipment needed, economies of scale with redundancy (larger the loads, better bang for the capex) Comingled with sludge and thermally hydrolyzed. Heating to higher temps, Potential issue with heat exchanger fouling (Cambi solved with sludge recirculation, now standard) Limited additional equipment needed. More complicated THP feed logic Screening of FOG Protect equipment and enhance Class A end product 20
Redundancy Considerations Smaller Plants (≤30 DTPD) can be processed by one small THP train. Two trains provide redundancy, but lower utilization of equipment & ROI One train provides better ROI, but increased risk (limited redundancy) Cannot bypass THP to digesters (Why redundancy is important) Contamination of tanks and pipes risk Class A. Tanks don’t have capacity because of longer SRTs associated with MAD Upset of digester (change in feed characteristics and loading). Redundancy by component Vessels don’t need much redundancy, and are a high capital cost item Mechanical equipment require frequent maintenance, must have redundancy to limit unplanned downtime. Annual inspection of pressure vessels Sludge storage Divert of pre-dewatered sludge 21
Questions?