thermal hydrolysis: the ins and outs, ups and downs · waste to energy projects ... new digester...
TRANSCRIPT
Thermal Hydrolysis:
The Ins and Outs, Ups and DownsDecember 3, 2015
Agenda
• What is THP?
• What are some types of THP?
• What situations is THP beneficial?
• Where is THP installed?
• Where in the US is using THP?
• Benefits
• Drawbacks
• Operational considerations
• Example analysis
• Wrap up
What Should You Learn From This?
• What is THP?
• How can it be incorporated?
• When might it be considered?
• What should be thought through?
• What an example analysis might look like?
What is THP?
Before We Talk THP…Lets Talk Digestion
Volatile Solids Soluble Organics, Gases
Volatile Solids Reduction (VSR)
THP = Thermal Hydrolysis Process
• Heat
• ~330oF
• Pressure
• 90 to 130 psi
• Time
• 20 to 30 minutes
• Cell lysis
• COD solubilization
• Class A via time/
temperature
• Preheated material
for digestion
Pressure Cooking the Sludge
What Are Some
Types of THP?
Batch Treatment - CAMBI
Batch Treatment - BioThelys
Continuous Treatment - Exelys
Continuous Treatment - TurboTec
Continuous Treatment - Haarslev
Location in Overall Process
• Full pretreatment
• WAS-only pretreatment
• Intra-digestion treatment
• Post-digestion treatment
Full Pretreatment
CAKE SILO
PS
SLUDGE SCREENS
SLUDGE STORAGE
PRE DEWATERING THERMAL
HYDROLYSIS
COOLERS
DIGESTERSDIGESTED SLUDGE
STORAGE & DEGASSING
DEWATERING
CAKE SILO
WAS THICKENING
ELECTRICITY
GAS CLEAN UP
BIOGAS
BIOGASBOILERS
STEAM
GASSTORAGE
WAS
BLENDEDSLUDGE WASTE
HEAT
CHPENGINES
WAS Only Pretreatment
CAKE SILO
PS
SLUDGE SCREENS
SLUDGE STORAGE
PRE DEWATERING THERMAL
HYDROLYSIS
COOLERS
DIGESTERSDIGESTED SLUDGE
STORAGE & DEGASSING
DEWATERING
CAKE SILO
WAS THICKENING
ELECTRICITY
GAS CLEAN UP
BIOGAS
BIOGASBOILERS
STEAM
GASSTORAGE
WAS
WASTEHEAT
CHPENGINES
Intra-Digestion TreatmentVeolia DLD Approach
Post Digestion TreatmentCAMBI SolidStream
How Do the Various Configurations Compare
Conventional
Digestion
Full
Pretreatment
WAS Only
Pretreatment
Intra
Digestion
Treatment
Post
Digestion
Treatment
Relative
THP Size
(approx.)
0% 100% 40% 60% 60%
Relative
Digester
Volume
Required
(approx.)
100% 33% 60% 60% 100%
VSR
(approx.)45% 60% 55% 65% 55%
Relative
Gas
Yield
(approx.)
100% 133% 125% 150% 130%
What Situations is
THP Beneficial?
When to Consider THP?
• Capacity expansion
• Waste-to-energy project
• Hauling limitations
• Storage limitations
Capacity Expansions
• Reduced viscosity allows for thicker (9-12% TS)
feed to digestion process
Digestion Process Impacts
Conventional Digestion
• 10,000 lb/day
• 4.5% TS feed
• 26,650 gpd
• 0.38 lb/gal
THP Digestion
• 10,000 lb/day
• 9.0% TS feed
• 13,325 gpd
• 0.75 lb/gal
Waste To Energy Projects
• Increase VSR
• Mostly of WAS
• More VSR = more digester gas
Hauling Limitations
• Increased VSR = less dry mass
• Increased dewaterability = less water in cake
• Results in fewer truck loads to be hauled away
Storage Limitations
• THP cake is:
• Stackable
• Stable
• Dry
• And has minimal odor
Where is THP
Installed?
THP Facilities Worldwide
Vendor Operating
Facilities
Facilities Under
Construction
Cambi 35 17
Veolia - Exelys 1 2
Veolia - Biothelys 5 2
Sustec - TurboTec 1 1
Haarslev 2 0
Where Are These Facilities
• Europe
• Japan
• China
• Germany
• France
• South America
Where in the US is
Using THP?
Planned US THP Facilities
DC Water Blue Plains AWTP
370 mgd
HRSD Atlantic WWTP
54 mgd
City of Raleigh
75 mgd
Franklin, TN
16 mgd
San Francisco
57 mgd
Trinity River
162 mgd
Benefits
Optimize Digestion Capacity
• Maximize use of existing infrastructure
• Reduce expansion requirements
• Co-digestion
Dry Mass Reduction
DewaterabilityFor a 50,000 lb total weight truck load…
1% point increase in solids
concentration enables 500 lbs of water
to be replaced with solids in each truck
Digester Gas Production
Digester Gas Production
• But more gas may only be desirable if there is a
beneficial use
Drawbacks
Additional Facilities
• Pretreatment – screening and dewatering
Multiple Solids Pumping Steps Possible
• Screen feed
• Pre-dewatering feed
• THP feed
• Intra-THP pumping (if applicable)
• Digester feed
• Digester mixing (if applicable)
• Digested sludge blending
• Final dewatering feed
Operational
Considerations
Operational Considerations
• Redundancy requirements
• Sidestream strength
• Sludge cooling
• Dilution water
• High pressure steam
• “Foaming” and RVE potential
• Polymer dispersion
Redundancy Requirements
• What is likely to need redundancy?
• Pumps – routine maintenance
• Vessels – annual inspections
• Steam system – no steam means no THP
• Possible approaches
• Pumps – duty/standby
• Vessels – storage or short term alternative processing
• Steam system – duty/standby
Sidestream Strength
• Better digestion = increased release of N and P
into soluble forms
• High temperature can produce refractory (non-
biodegradable) N and P compounds
• Can impact the color of the sidestream =
impacts to UV disinfection
Sludge Cooling
Dilution Water
THPCooling
Digestion
12-15%TS,
Pathogen Free
Material
Dilution/Initial
Cooling Water
Target ~9%TS,
Pathogen Free
Material
NEED PATHOGEN
FREE DILUTION
WATER SOURCE
High Pressure Steam
Rapid Volume Expansion
• Rapid drop in specific gravity of digester contents
• Same solids mass + lower S.G. = larger volume
• Potential causes:
• Sudden pressure drop in headspace
• Sudden change in mixing intensity
• Sudden change in temperature
• Sudden change in available “food”
• Anything to result in more gas production without a means to allow the gas to escape
• Can be exacerbated by biological foaming
Polymer Dispersion
Floc tank for
polymer/sludge
mixing before
dewatering
Example Analysis
Sample Facility
• Currently a 10 mgd (AA) facility – looking at
expansion to 20 mgd (AA)
• Strict N and P liquid stream discharge
requirements
• Existing anaerobic digestion for current capacity
• Existing digester gas utilization = hot water
boilers
• 4.5% blended solids feed to digesters
What Was Considered for Capital Costs
Without THP With THP
New digestion capacity (2x) PS/TWAS blend tank
New digester heating system Sludge screening
Gas handling system Screened sludge tank
New digester control building Pre-dewatering
Dewatering feed pumps Cake hopper(s)
CHP system (1.0 MW) THP system
Gas treatment Steam boiler system
Screening/dewatering building
CHP system (1.2 MW)
Gas treatment
Capital Cost Comparison
• Many site-specific considerations
• Rock blasting
• Piping lengths
• Roadways
• Hydraulic grade in digesters in relation to site topography
• Approximately $700,000 difference in estimated
capital costs
Without THP With THP
$36.3 million $37.0 million
So Why Look at THP?Annual Costs…
Without THP With THP
Electricity Consumed (kWh/yr) 2,200,000 2,200,000
Electricity Produced (kWh/yr)
(assume engine generator)8,800,000 10,300,000
Pre-Dewatering Polymer (active
lbs/yr)0 91,000
Cake Wet Mass (wet tons/year) 32,500 17,400
Additional O&M Labor (FTE) 2 2
CHP System O&M ($/year) $220,000 $260,000
Dewatering Polymer (active lbs/yr) 171,000 137,000
So Why Look at THP?Annual Costs…
Without THP With THP
Total Annual Costs $2,130,000 $1,740,000
Less than 5 year payback on capital cost
Wrap Up
What Should You Know Now?
• What is THP?
• How can it be incorporated?
• When might it be considered?
• What should be thought through?
• What an example analysis might look like?
