Post on 17-Apr-2018
transcript
Basics of Using Excess Biogas at Wastewater Treatment Plants
Tom Mossinger, PE – Carollo Engineers
Energy Trust of Oregon Biogas Co-Generation Workshop November 5, 2015
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BioGas Utilization Overview
• 30,000 ft Overview • O&M Issues • Available Technologies
– Cogeneration Technologies – BioFuel
• Pipeline injection • Vehicle BioCNG
• Incentives & Procurement Options • Questions/answers
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Why is BioGas Utilization Important to Your Operation?
• Best use of available resources
• Sustainable • Cost effective • Offers security/
reliability • Supports
regulatory compliance
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O&M Importance Bio-Gas Treatment
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Typical Digester Gas Composition and Characteristics • Approximately 60% CH4
• Water vapor – saturated at 95-100 degrees F • Trace levels of contaminants including H2S and
Siloxanes, greases, dirt, hair, etc. – H2S varies from 50 to >10,000 ppmv – Siloxanes vary by site and are increasing over time
• Typical pressure: 2-12 inches w.c.
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Contaminants of concern
• H2S – Forms by biological breakdown of organics in anaerobic
conditions – Typically present at levels approaching 2000 ppmv if
untreated – Most air districts regulate H2S in some way, typically
gas must have levels reduced to < 200 ppmv
• Siloxanes – Organic Silicon compounds – Derived from several common household products
(shampoos, cleaning products, solvents, foods, etc.) – Generally water soluble
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Consequences of Contaminants
• H2S – Forms with water vapor both in the gas and in the
combustion products to form H2SO4 – Health hazard – Degrades lubricants – Causes corrosion
• Siloxanes – Causes hard abrasive “glass” like buildup on
combustion equipment such as engine valves and pistons
– forms fine powdery “ceramic” like substance upon cooling which plugs boilers, heat exchangers, silencers, etc.
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Siloxane Damage
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Contaminant Detection • Laboratory analysis
– Various sampling and analysis methods • H2S can be sampled with drager tubes, but not reliable to low
levels – Requires upwards of a week for results for Siloxanes – Expensive; Typically $500 to $3,000+ for testing
• H2S can be monitored with electrochemical gas diffusion sensors
– Real time monitoring – typically used for controlling mercaptan level in natural
gas
• Siloxanes can be monitored with on-line gas chromatograph
– Near real time Siloxane and H2S measurement
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Value of Digester Gas Treatment • Gas quality has direct impact on cost of
maintenance – Cummins quotes maintenance as follows:
• $0.008/kWh for units operating on natural gas, or equiv. • $0.020/kWh for units operating on digester gas with
approximately 100 ppmv H2S • Siloxanes are required to be removed for either
• Less frequent maintenance – Oil changes, spark plug life, O2 sensors, overhauls
Gas Treatment
Less Down Time
More kW Produced and
Less Maintenance
$$$
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H2S Treatment Options
• Iron sponge (adsorption) • Ferric Chloride into process
– Odor control in sewers or liquid process – Advanced primary treatment – Struvite control – Digester gas H2S control
• Water stripping • Biological removal • Caustic Scrubbing/Oxidation
• Biological oxidation • Chemical oxidation
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Siloxane Treatment Options
• Adsorption (patented products)
– Carbon – Desiccant
• Remove water from gas (gas drying)
• Typically both are required due to quantity of Siloxane compounds in the gas
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Bio-Gas Utilization
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What Are The Available Technologies?
• New cogeneration technologies
• Biogas supply/wholesaling • Renewable motor vehicle
fueling
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Traditional Digester Gas Power Generation
Technology
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Reciprocating Engines • Proven technology for using
digester gas • Electrical Output Efficiency = 40+% • Proven technology for over 40 years • Strict (and getting stricter) air
permit regulations • Regulations often now require CO
oxidation catalysts and sometimes even SCR and CEMS
• Installations now require extensive fuel conditioning to remove contaminants – no longer optional
1.7-MW Digester Gas Fueled Cogeneration System, Union Sanitary District, CA
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Micro Turbines
• Easy to permit (CARB Certified low emissions) • Only two manufacturer’s with DG experience
(limited) • Low efficiency; approximately 25-27% • Requires >50 psi fuel pressure • Effective fuel conditioning is required
250-kW Landfill Gas Fueled Cogeneration System, Lancaster, CA
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Gas Turbines
• Strict air permit regulations • Limited manufacturer’s with experience on DG • Effective fuel conditioning is required • Competitive only for larger installations;
greater than 3MW • Efficiency typically 25-35% • Requires >200 psi
fuel pressure
8-MW Digester Gas Fueled Cogeneration System, King County DNR, Renton, WA
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Fuel Cells • Efficiency = 45-47% • Advantages
– Ultra low emissions – Significant tax credit/grant
funding available
• Extreme fuel conditioning required
• Emerging technology results in down time often exceeding expectations
• One manufacturer with DG experience
1-MW Fuel Cell Cogeneration System, Riverside, CA WWTP
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BioFuel/BioCNG
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BioFuel
• BioFuel – Conversion of digester gas for pipeline
injection • Typically cost effective only for large sizes due to
interconnection requirements and costs – although this is changing
• Often interconnection issues are significant and costly • Value limited to various credits for being renewable
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BioCNG
• BioCNG – Conversion of digester gas to vehicle fuel
• Traditional digester gas treatment followed by CO2 removal, compression, storage and fueling
• Requires significant fleet available to use gas nearly 24/7
• Value is in offset of expensive transportation fuel as well as various credits
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Sampling of Incentives/Credits/Grants For Cogeneration Projects
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Identifying Funding Opportunities Is Important to the Feasibility of any Project
Funding Opportunities
Incentives
Tax Credits Loans
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Potential Traditional Cogeneration Project Incentives
• Business Energy Investment Tax Credit • Renewable Energy Production Incentive • Renewable Electricity Production Tax Credit • U.S. Department of Energy - Loan Guarantee
Program • Clean Renewable Energy Bonds (CREBs) • Commercial Loan Programs • Energy Trust of Oregon • Renewable Energy Development Grants • State Energy Loan Program (SELP)
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Potential funding sources for “biogas to fuel” projects
• Renewable Fuel Standard RINs
• Biofuel Tax Credits or Deductions
• Biofuel Infrastructure Grants
• Low Carbon Fuel Standard Credits • Alternative Fuel Vehicle & Alternative
Fuel Rebates • Alternative Fuel Grants
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Grants, Funding - Oregon • Oregon Department of Energy – Business Energy
Tax Credit – Up to 50% of Total Project Costs for Renewable Energy
Generation Projects – Can be passed through to Municipal entities
• Energy Trust of Oregon – Open Solicitation Program – Innovative/Renewable Energy Projects
• Oregon Department of Energy – Small Scale Energy Loan Program – Loans up to $20 million for municipal renewable energy
projects
• PACE Loans & Small-Scale Energy Loan Program • Community Renewable Energy Feasibility Fund
Program
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Procurement Methods
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Traditional Design-Bid-Build
• Traditional approach for Municipalities • Maintains control of project • Easy to implement • Downsides:
– Upfront costs • Can be mitigated via performance loans
– Commitment to maintenance • Service contracts can minimize staffing impact
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Design-Build
• Traditionally used with the hope of saving time and $$$
• Control of project outcome depends on amount of upfront engineering
• Often difficult for municipalities to implement • Downsides:
– Contracting often difficult – Often does not save time, nor $$$ – Loss of control of installation quality
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Design-Build-Operate
• Traditionally used to obtain fixed costs for life of project
• Control of project outcome not as important as DBO entity will operate the facility for extended period
• Often difficult for municipalities to implement • Downsides:
– Contracting often difficult – Often does not save time, nor $$$, disputes over
maintenance, upgrades, etc.
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Design-Build-Own-Operate • Traditionally referred to as Power Purchase
Agreement – City would purchase power for fixed term at known cost – Other arrangements are possible; selling gas for example
• Typical for Solar PV installations • No upfront costs • Downsides:
– Contracting often difficult – Actual availability/performance often poor; disputes over
maintenance, upgrades, etc. common
Thank You