thermal hydrolysis: the ins and outs, ups and downs · waste to energy projects ... new digester...

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?

QUESTIONS:Matt Van Horne, PE

mvanhorne@hazenandsawyer.com

703-267-2738

December 3, 2015