Innovations in Thermal Conversion

Bill Toffey, MABA

Stan Chilson, GHD-CET

Biosolids Session, WaterJAM

September 10, 2012

A Holy Grail for Biosolids

Biosolids to Biofuels

• Enjoys popular public support as “sustainable”

• Addresses risks of land application and disposal for release of pollutants and odors

• Biofuels for transportation the highest value form of energy

• Draws from the innovative-rich biofuels sector

• The wastewater agency itself is customer and avoids retail costs

• High biosolids disposal costs attracts investors

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Like the Grail Search… an Adventure

What we face with conversion of biosolids

• Landscape littered with failures over 30 years

• “Oil from Sludge” (OFS) efforts in Canada , LA City

gasifier, Carver-Greenfield, and the Subiaco Plant in

Australia ended long ago

• A more complicated biomass than woodchips

• A wet material with a high inorganic content

• Complicated material handling

• A “gummy” phase at the 55% to 75% content

• Procurement difficulty: long-term, innovative

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The Energy in Wastewater Solids

Rules of Thumb• Influent Organic Energy per Population

Equivalent = 0.12 pounds per day

• BTU of a pound of organic matter = 10,000

• Proportion of O.M. = 60 to 80%

• Rough conversion of influent organic matter to sludge solids = 1.0 : 0.8, so about 1/10th pound of organic energy per capita or 1,000 BTUs per capita.

• If all converted to biomethane = 1 S.C.F.

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The Variable Value of Energy

Energy Units vary in price• Natural Gas is CHEAP: $8/MMBTU ($.03/kWh)

• Biodiesel is EXPENSIVE: $24/MMBTU ($.10/kWh)

• Electricity is EXPENSIVE: $30/MMBTU ($.12/kWh)

Energy Production Varies in Cost• Natural Gas Fueled Generator: $1,000/kW

• Biogas CHP production: $4,000/kW

• Solar PV: $6,000/kW

• MSW Electric: $8,000/KW

Biosolids Thermal Processing• Biosolids dryer: $ 1000/dryton/yr or $60,000/ MGGY

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Biosolids to Biofuels

Status of Full Scale Operations

EnerTech: thermal

depolymerization and drying to fuel in

Rialto, California, recently declared

bankruptcy

MaxWest: facility in Sanford, CA,

with “second generation” gasifier, now

undergoing commissioning.

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EnerTech Slurry Carb Process

SlurryCarb® technology thermally converts biosolids and other high-moisture feedstocks into a renewable fuel through a molecular rearrangement, processing biosolids as a fluid and creating an eFuel that is an excellent replacement for fossil fuels with zero net greenhouse gas emissions.

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Biosolids to Biofuels

Examples of Demonstration/Proposed Facilities• California demonstration unit: conversion of biosolids to

syngas followed by steam reformation to liquid fuel using Fischer-Tropsch catalysis.

• Greenharvestone: demo unit planned in Lancaster County PA WWTF digester and gasifier.

• Intellergy a thermal process in California to produce hydrogen for fuel cell operation, demo not funded.

• Enginuity Engineers’ “Ecoremedy” gasification of biomass to syngas to steam-powered generator.

• PyroBioMethane create pyrolysis oil from dried pellets, returned to anaerobic digester for methane for CHP.

• Delta Thermo in Allentown PA plans to pressurize biosolids with MSW as fuel for steam-fired generator.

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Pyrolysis/Gasification - the Distinction

Pyrolysis:

Thermal Conversion of solid fuel in the complete absence of oxidizing agent (air / oxygen)

Volatile matter is chemically changed to carbon by heat. ( typically 1,200 to 1,650 F)

Gasification:Carbon is gasified through reaction with air / oxygen / steam / hydrogen at elevated temperatures.

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Indirectly Heated Rotary Kiln for Pyrolysis

The most common pyrolysis furnace has been the indirectly heated rotary

kiln (externally heated, high alloy, stainless steel tube). Only a very limited

number have been used in waste-to-energy applications.

Few of these have been used for biosolids

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Pyrolysis Typical Heat & Material Balance

Pyrolysis

Reactor

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Fast pyrolysis yield of bio-fuels up to 75% of dry feed, typically, 65% liquids

and 10% non-condensable gases; at higher temps, convert more to syngas

Slow pyrolysis maximizes the charcoal yield.

Fast vs. Slow Pyrolysis Yield

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What is Gasification ?

Gasification is a two step or combined step

thermo-chemical reaction.

1. Pyrolysis – Volatile matter is chemically changed to

carbon by heat.

2. Carbon is gasified through reaction with air /

oxygen / steam / hydrogen.

(about 30% of oxygen required for combustion)

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Gasifier Configuration

• Air / Oxygen / Steam Heating Systems

Air - 150 to 250 Btu / cu ft Syngas

Oxygen - 300 to 350 Btu / cu ft Syngas

Steam - 350 to 500 Btu / cu ft Syngas

• Up-Draft - Counter - Current Fixed Bed

• Down-Draft - Co-Current Fixed Bed

• Fluid Bed, Mixed Bed, Entrained Bed

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COUNTER-CURRENT FIXED BED (up-draft) GASIFIER

Fixed bed of carbonaceous fuel through which the "gasification agent" (steam, oxygen and/or air) flows in counter-current configuration.

CO-CURRENT FIXED BED (down-flow) GASIFIER

Similar to the counter-current type, but the gasification agent gas flows in co-current configuration with the fuel.

Gasifiers Deployed for Biomass

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Small Downdraft Gasifier

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Nexterra Up-flow Gasifier Eisenmann

Corporation Pyrobustor

Updraft Gasifiers

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Feedstock is fluidized in air, or oxygen and steam. The ash is removed dry as heavy agglomerates that defluidize.

Fluidized Bed Gasifier

Courtesy:

Energy Products of Idaho

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Thermal Conversion Benefits

• Clean emissions, Carbon Neutral

• Greater biosolids volume reduction than dryers alone.

• Process autogenous, No auxiliary fuel if input is dry.

• No wet scrubber, no recycle streams to WWTP.

• No pathogens, odors,

• Persistent organics destroyed

• Low or no NOx, SOx.

• Immobilization of heavy metals.

• Carbon char may have beneficial uses.

• Even antibiosolids activists, support energy conversion

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ChallengesReduction of moisture in biosolids is the primary

impediment to export energy from thermal biosolids

processes. Separate stage drying is necessary for

process viability.

Biosolids can have low ash fusion temperatures.

Addition of aluminum or lime may be required for the

raising the fusion temperatures.

Gasification of biosolids biomass remains in the

development stage, with rare exceptions, based on its

relatively high cost and the low reliability for long-term

operation compared to direct combustion

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Pyrolysis / Gasification used to produce liquid fuels (oil)

using Integrated Gasification Combined Cycles, with the

possibility of producing methane and hydrogen for fuel

cells.

Challenges

Gasification technologies have been developed that use

plastic-rich waste as a feed. In Germany such a

technology converts plastic waste via syngas into

methanol.

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The efficient removal of tar / slag remains a technical

barrier for the successful commercialization of

biomass gasification technologies.

Financial and regulatory climate averse to risk, energy

prices are soft, and public demand for response to

climate change has softened.