co-generation: today’s reality

Co-Generation: Today’s Reality

Larry McFall

Plant Operations Manager

Rock River Water Reclamation District

Rockford, IL

lmcfall@rrwrd.dst.il.us

Introduction

• 1,100 Miles of Sewer

• 33.9 MGD Influent

• 7 Communities

• 75,000 Accounts

• 240,000 Connected Population

Water Treatment

• Primary– Screening, Grit, & Primary Clarification

• Aerobic Activated Sludge– Final Clarification

• Disinfection

Energy Introduction

• Raw Materials

– Waste Organic Material in Wastewater (Feedstock)

• Treatment & Utilization Process

– Anaerobic Digester

– Electrical Generators

• Products

– Electricity

– Heat

– Biosolids (Fertilizer)

Waste Organic Feedstock

• Waste Organic Material in Wastewater– Raw Sludge

• Primary Clarifiers• Gravity Thickener (5.4% Solids)

– Waste Activated Sludge• Gravity Belt Thickener (6.6% Solids)

– Skimmed Fats, Oils & Grease (FOG)

Treatment & Utilization Process

• Anaerobic Digestion– Controlled Conditions– Utilize Waste Heat from Electrical Generators

• Condition Biogas– Remove Moisture– Remove Contaminants

• Electrical Generators– Produce Electricity– Recover Waste Heat

Anaerobic Digestion

• Controlled Conditions– Mesophilic Digestion (100º F or 38º C)– Complete Mix

• Biological Process– Acid Formers– Methanogenic Bacteria

Anaerobic Digestion

• Biogas– Methane, Carbon Dioxide, Nitrogen– Water Vapor– Hydrogen Sulfide, Siloxanes, Hydrogen

• Biosolids– Fixed & Stabilized Organic Solids– Nutrients & Micro Nutrients

Anaerobic Digestion

Biogas

• Biogas Conditioning– 1st Stage Hydrogen Sulfide Removal

• Ferric Chloride Addition to Digesters

– 1st Stage Moisture Removal• Refrigeration to 45º F Dewpoint

– 2nd Stage Moisture Removal• Refrigeration to 34º F Dewpoint• Coalescing Filter

Biogas

• Biogas Conditioning Continued– Pressure Boost– Mixed Carbon Bed

• Siloxane Removal• 2nd Stage Hydrogen Sulfide Removal

– Reheat Gas

Biogas

Siloxane + Oxygen Silicone Dioxide

(Sand)

Biogas

• Siloxanes as Si, mg/M3

– Maximum 46.6– Minimum 2.7– Average 13.4– Major Constituent

• D5 (Decamethylcyclopentasiloxane)

Biogas

0

10

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90

1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

East

West

North

Generators

• 3 Generators @ 1 MW each

• Fuel– Biogas– Natural Gas

• Heat Recovery– Jacket Water– Exhaust Gases

Generators

• Operation and Maintenance– Laboratory

• Gas Analysis• Engine Oil Analysis

– Routine Maintenance• Change Oil and Filters• Gap or Change Spark Plugs• Rectifiers

• Add Generator Picture

Investment

• Capital– $2,000 per kW of Electricity

• Operation & Maintenance– $0.01 per kWhr

Bio-Products

• Electricity– 410 MWhr/Month– $33,000/Month

• Heat– 4.5 Million BTU/hr each Engine– Process Heat for Digesters– Building Heat

Bio-Products

• Biosolids (Fertilizer)– Apply 17,000 wet Tons Annually– 1,700 Acres of Farmland Annually

• Corn• Wheat• Soybeans

– Fertilizer Value of $85/acre

Future Improvements

• Co-Digestion of High Strength Wastes– Fats, Grease and Oils Direct from Source– Bio-diesel Byproducts– Algae– High Strength Food Production Wastes

• Utilization of Waste Heat– Cooling

Co-Generation: Today’s Reality

Questions?

Co-Generation: Today’s Reality

Larry McFall

Plant Operations Manager

Rock River Water Reclamation District

Rockford, IL

lmcfall@rrwrd.dst.il.us