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