november 17 th, 2015 thermal hydrolysis pretreatment (thp) considerations for a 15 dry ton per day...
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November 17th, 2015
Thermal Hydrolysis Pretreatment (THP)
ConsiderationsFor a 15 Dry Ton per Day WRF
Thomas Nangle, PECDM Smith
2015 Annual Conference Raleigh, NC
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Presentation Overview
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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
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Background on THP
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THP and Cake Product Odor (Novak, 2012)
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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”
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THP Regrowth and Sudden Increase vs. Other Class A Processes (Higgins, 2012)
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Other Drivers for THP + AD
½ Digester Capacity Needed Higher % solids loading rates Lower SRTs
Decreased Solids Hauling & Increased Biogas Increased % VSR Increased Dewaterability
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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
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Simplified Process Flow of THP for Franklin, TN
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Advantages & Challenges of Thermal Hydrolysis Pretreatment
AdvantagesMinimal Odor in Digested CakeClass A, minimal regrowthReduce required digester capacityIncreased Solids DestructionIncreased biogas productionImproved DewaterabilityReduce Hauling Costs
ChallengesMore equipment to maintainPressure vessels and high pressure steam
Depending on state may need special licensed operators
Regs typically require annual pressure vessel inspection
High strength side streamsRapid rise riskTwo dewatering steps
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Key Considerations for a 30 DTPD Facility
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THP Ancillary Systems
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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 ProcessNutrient Recovery
CHP System
Electricity to Plant Hot Water to
Treatment Processes
Natural Gas
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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
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Various Methods of Producing Steam
Boiler to produce steam CHP system to reuse biogas
CHP System to Generate all Steam
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Thermal Hydrolysi
s
Thermal Hydrolysi
s
SteamSteam
BiogasBiogasAnaerobic Digester
Anaerobic Digester
BoilerBoiler
Hot Water
Hot Water
Natural GasNatural Gas
CHPCHP
Thermal Hydrolysi
s
Thermal Hydrolysi
s
BiogasBiogas
Anaerobic Digester
Anaerobic Digester
Hot
Wat
erH
ot W
ater
CHPCHP
SteamSteam
Natural GasNatural Gas
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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
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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
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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 (1st 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
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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 3rd 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
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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
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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
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