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 2
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 SubiacoPlant 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 3
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 1/10 th pound of organic energy per capita or 1,000 BTUs per capita. If all converted to biomethane= 1 S.C.F. 4
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 5
Biosolids to Biofuels Status of Full Scale Operations EnerTech: thermal depolymerizationand drying to fuel in Rialto, California, recently declared bankruptcy MaxWest: facility in Sanford, CA, with second generation gasifier, now undergoing commissioning. 6
EnerTech Slurry Carb Process SlurryCarb technology thermally converts biosolids and other highmoisture feedstocksinto a renewable fuel through a molecular rearrangement, processing biosolids as a fluid and creating anefuelthat is an excellent replacement for fossil fuels with zero net greenhouse gas emissions. 7
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. Intellergya thermal process in California to produce hydrogen for fuel cell operation, demo not funded. EnginuityEngineers Ecoremedy gasification of biomass to syngas to steam-powered generator. PyroBioMethanecreate 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. 8
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. 9
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 10
Pyrolysis Typical Heat & Material Balance Pyrolysis Reactor 11
Fast vs. Slow Pyrolysis Yield 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 12 Slow pyrolysis maximizes the charcoal yield.
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) 13
Gasifier Configuration Air / Oxygen / Steam Heating Systems Air Up-Draft - 150 to 250 Btu / cu ft Syngas Oxygen - 300 to 350 Btu / cu ft Syngas Steam - 350 to 500 Btu / cu ft Syngas - Counter - Current Fixed Bed Down-Draft - Co-Current Fixed Bed Fluid Bed, Mixed Bed, Entrained Bed 14
Gasifiers Deployed for Biomass 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. 15
Small Downdraft Gasifier 16
Updraft Gasifiers Nexterra Up-flow Gasifier Eisenmann Corporation Pyrobustor 17
Fluidized Bed Gasifier Feedstock is fluidized in air, or oxygen and steam. The ash is removed dry as heavy agglomerates that defluidize. Courtesy: Energy Products of Idaho 18
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 19
Challenges Reduction of moisture in biosolids is the primary impediment to export energy from thermal biosolids processes. Separate stage drying is necessary for process viability. 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 Biosolids can have low ash fusion temperatures. Addition of aluminum or lime may be required for the raising the fusion temperatures. 20
Challenges The efficient removal of tar / slag remains a technical barrier for the successful commercialization of biomass gasification technologies. 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. Pyrolysis / Gasification used to produce liquid fuels (oil) using Integrated Gasification Combined Cycles, with the possibility of producing methane and hydrogen for fuel cells. Financial and regulatory climate averse to risk, energy prices are soft, and public demand for response to climate change has softened. 21