Where Should the Biogas Go?

Transcription

1 Where Should the Biogas Go? Thomas Kunetz, Metropolitan Water Reclamation District of Greater Chicago Steve McGowan, Arcadis-Malcolm Pirnie Eric Auerbach, Arcadis-Malcolm Pirnie IWEA WaterCon Mar 20 th, 2012

2 Digester Gas Utilization Purpose of Project Digester Gas is a valuable energy resource Fully utilizing digester gas can save significant $ and reduce a plant s carbon footprint Purpose: What type of utilization system is best?

3 Stickney WRP (SWRP) Lake Michigan Chicago Stickney WRP Avg influent flow = 750 MGD Receives sludge from another 250 MGD plant (via pipeline) Biosolids drying facility located on site (MBM Facility)

4 Specific Concerns for SWRP Expected increase in gas production Existing plant heating system is steam Plant boiler operators know steam Plant boilers nearing replacement MBM facility can use biogas

5 Outline Digester Gas Production Energy Consumption Selection of Gas Utilization Alternatives Energy Flow Modeling Preliminary Conclusions/Discussion

6 Digester Gas Production Current From operating data Avg Production: 3,400 Mcf/day Projects affecting SWRP Gas Production Replace WS Imhoff tanks with Primary Settling Tanks Upgrades to sludge thickening facilities Future Projected for 2040 with Gas Production Modeling Selected Design Scenario: 6,722 Mcf/day (double of current) 6,722 Mcf/day = 168 mmbtu/hr

7 Energy Types Extensive steam heating piping for buildings Steam to hot water converters for digester heating Plant electrical consumption of 31 MW

8 Energy Consumption Current From operating data Heating Demand: 41 [mmbtu/hr ] (summer) 97 [mmbtu/hr] (winter) 70 [mmbtu/hr] (average) Adjustments for 2040 Energy Consumption Additional flow to digesters Addition of new laboratory facility Future Heating Demand Summer: 31 (Digesters) + 20 (Buildings) = 51 [mmbtu/hr] Winter: 50 (Digesters) + 62 (Buildings) = 112 [mmbtu/hr] Average: 40 (Digesters) + 41 (Buildings) = 81 [mmbtu/hr]

9 Excess Gas Sizing of Systems Summer: 168 Produced 51 Demand = 117 [mmbtu/hr] Excess Winter: 168 Produced 112 Demand = 56 [mmbtu/hr] Excess Average: 168 Produced 81 Demand = 87 [mmbtu/hr] Excess System Sizing: Summer Excess used to size capital equipment (maximum capacity) Average Excess used to determine operating costs and economic performance Cogeneration Sizing: Requires Iterative Loop bigger Cogeneration bigger Digester Gas smaller Plant Heat Demand Plant Heating

10 Long List of Utilization Alternatives Internal Utilizations Utilize Gas in Plant Heating Boilers Gas to MBM Cogeneration Reciprocating Engines Cogeneration Combustion Turbines Cogeneration Steam Turbines Cogeneration Microturbines Cogeneration Fuel Cells Cogeneration Stirling Engines Direct Drive Engines External Utilizations Sell Raw Gas to 3 rd Party Upgrade to Natural Gas and sell to pipeline Upgrade to Natural Gas and make Compressed Natural Gas (CNG) External Utilizations Not in Scope Short List Utilize Gas in Plant Heating Boilers Gas to MBM Cogeneration Reciprocating Engines Cogeneration Combustion Turbines Cogeneration Steam Turbines

11 Summary Economics and Performance Short List Option Capital Cost O&M Cost (Annual) Electrical Efficiency Heat Recovery Efficiency Reciprocating Engines (with siloxane cleaning) $48.4 million $2.8 million 42% 43% Gas Turbines (with siloxane cleaning) $32.1 million $2.9 million 28/33%* 44% Steam Turbines (no gas cleaning) $22.5 million $251,500 17% 65% Send Digester Gas to MBM $900,000 $126,000 NA NA * Due to the compressibility of air, electrical efficiency differs from summer to winter

12 Energy Flow Modeling Different Operational Scenarios Possible Digester Gas? Plant Heating Boilers MBM Facility Cogeneration Natural Gas Plant Heat Demand Plant Electric Demand Power Plant

13 Energy Flow Model Output = Annualized Cost, GHG Reduction, Unused Energy

14 Energy Flow Model - Results

15 Cost Savings Energy Flow Model - Results $2,000,000 GHG Reduction Vs. Cost Savings Steam Turbines $1,500,000 6C 4F 4C 6F Engines $1,000,000 $500,000 $- 5C 5F 3F 4B 4E 6B 6E 4D 4A 6A 6D $(500,000) $(1,000,000) 1A 2A 2B 1B 3C 5B 5E 5D 5A $(1,500,000) $(2,000,000) Baseline2016 3E 3D 3B 3A $(2,500,000) -40,000-20, ,000 40,000 60,000 80,000 GHG Reduction (MT eco2)

16 -$1,752,000 Annualized Cost [$] $597,427 $969,960 $1,588,949 $1,900,268 $1,643,409 GHG Reduction [MT eco2] / Unused Energy [10 mmbtu] Selected Energy Flow Model Results $4,000,000 Annualized Scenario Cost [$] GHG Reduction [MT eco2] Unused Energy [mmbtu] $3,000, $2,000, $1,000, $0 0 -$1,000, $2,000,

17 $(1,752,000) $(559,423) $(1,147,551) Annualized Cost $836,134 $594,236 $630,566 $1,518,767 $1,747,895 $2,201,399 $2,408,683 $2,901,554 $2,884,031 $4,186,800 Sensitivity Analysis Electricity Price $6,000,000 Natural Gas Constant at Baseline Price ($8/mmBtu) $5,000,000 $4,000,000 $3,000,000 $2,000,000 $1,000,000 $- $(1,000,000) $(2,000,000) $(3,000,000) Electricity Low ($0.07/kWh) Baseline Electricity ($0.08/kWh) Electricity High ($0.09/kWh) Electricity High ($0.10/kWh) $(4,000,000) Scenario

18 Triple Bottom Line Analysis Scenario Score Category Weight Sub Category Max Score ENG-NG ST-A ST-B ST-C Cost Savings Economic 50 Sensitivity Total Economic Weighted Score GHG Reduction Environmental 30 Air Pollutants Total Environmental Weighted Score Operability Maintainability Social 20 Implementability Total Social Weighted Score TOTAL OVERALL SCORE

19 Preliminary Conclusions/Discussion Economic returns for Steam Turbines are greater than Engines Engines give more GHG reduction due to greater electrical production Heat Recovery from Steam Turbines more favorable to existing plant steam heating system Engines are more sensitive to electrical prices As electric rates rise, Engines become more cost competitive with Steam Turbines

20 Preliminary Recommendation Steam Turbine Alternate A Uses extraction steam for building and digester heating SWRP Specific Advantages Takes advantage of required boiler replacement Utilizes the existing skills of plant personnel Maintains consistency in plant heating scheme and heating infrastructure