Biogas Cogeneration System Sizing and Payback Based on Weekly Patterns of Anaerobic Digestion and Biosolids Dryer Operation

Transcription

1 Biogas Cogeneration System Sizing and Payback Based on Weekly Patterns of Anaerobic Digestion and Biosolids Dryer Operation John Kabouris, PhD, PE, CH2M HILL Bob Forbes, PE, CH2M HILL Tim Shea, PhD, PE, BCEE, CH2M HILL Mike Engelmann, PE, Pinellas County Jim Dulaney, Pinellas County

2 Outline Dryer/cogeneration system description Biogas available for cogeneration Cogeneration technology selection Detailed evaluation Number and capacity of cogeneration units Sensitivity to key parameters of payback and lifecycle benefits Conclusions

3 Cogeneration Evaluation Focused on the 33 mgd Pinellas Co. South Cross Bayou WRF

4 FOG Codigestion to Significantly Increase Methane Production Polymer- Dewatered FOG Belt Filter Press Dewatered Lime FOG

5 SCBWRF Future Codigestion Process Flow Diagram PS; TWAS; BFP cake; lime-fog Polymer-FOG Future Acid Reactors (2) Existing Egg Digesters (2) Mesophilic Heating source: o Dryer (weekdays) o Cogeneration or boiler (weekend) Thermophilic Heating source: cogeneration or boiler FOG and BFP cake to be fed during weekdays Acid phase gas to be flared

6 Digestion-Dryer-Cogeneration System Natural Gas (Back-up) Boiler Flares Utilized Waste Heat Wasted Biogas Fuel Digestion Biogas Fuel Biogas Fuel Dryer Unutilized Dryer Waste Heat Utilized Waste Heat Biogas Fuel Utilized Dryer Waste Heat Natural Gas Unutilized Waste Heat Cogeneration Natural Gas Electrical Power Generation Priority use of biogas in dryer (no siloxanes/sulfide removal) Excess biogas to cogeneration (siloxanes/sulfide removal)

7 Baseline 2012 Cost of Electrical Power $0.10 $0.09 $0.08 $0.07 SCBWRF Electrical Energy Cost Per kwh $0.06 $0.05 $0.04 $0.03 $0.02 $0.01 Monthly Linear (Monthly) Baseline: 9.2 /kwh $

8 Baseline 2012 Cost of Natural Gas SCBWRF Natural Gas Cost Per Therm $1.60 $1.50 $1.40 $1.30 $1.20 $1.10 $1.00 $0.90 $0.80 $0.70 $0.60 $0.50 $0.40 $0.30 $0.20 $0.10 $- Monthly Poly. (Monthly) Baseline: $0.9/therm

9 Estimate is Consistent with 2012 Projection from Florida Long-Term Trend SCBWRF Natural Gas Cost Per Therm $1.60 $1.50 $1.40 $1.30 $1.20 $1.10 $1.00 $0.90 $0.80 $0.70 $0.60 $0.50 $0.40 $0.30 $0.20 $0.10 $ Projection ~ $0.9/therm Monthly Poly. (Monthly) Baseline analysis: $

10 Conceptual Modeling of Weekly Biogas Generation FOG and cake to be fed only during weekdays and pelletizer also typically operated only during weekdays Simplified stepwise variation biogas production model (weekdays vs. weekend) Average weekend biogas reduction assumed to be up to about 17% Existing biogas storage will be utilized to reduce variability and match production and demand

11 Eight Biogas Production Cases Analyzed to Consider Uncertainty of Parameters One, two or three lime FOG truckloads per weekday Depending on digestion capacity and long-term FOG availability Average FOG fraction of VS: 16, 21, 26% Biogas percent of the combined natural gas and biogas fuel blend for the dryer: 35% is the biogas percentage originally used by Andritz in the SCBWRF dryer design calculations (baseline scenario) 90% could potentially be utilized according to Andritz SCBWRF TWAS ultimate VS reduction: 45% (target, based on low SRT AS operation) 23% (based on high SRT AS)

12 Digestion-Dryer-Cogeneration Biogas Balance Used to Determine Available Biogas Biogas Available for Cogeneration (scfm) Target Case Low TWAS Digestibility, Low FOG Case Average Dryer in operation (weekdays) Dryer not in operation (weekends) High FOG and TWAS digestibility allows for cogeneration on biogas without natural gas supplementation

13 Selection of Cogeneration Technology Based on LCAMER application as part of WERF project (Surti et al., 2011) ICE compared to alternative technologies (Stirling engine, gas turbine, microturbine, fuel cell) Internal combustion engine based (ICE) cogeneration system selected based on: Lowest payback period Lowest initial capital investment Highest annual benefits

14 Basic Data for the 1,059 kw and 1,426 kw ICE Cogeneration Sets JMS320 JMS420 Gross output rated capacity 1,059 kw 1,426 kw Electrical efficiency at full load (1) 37.9% 39.3% Thermal energy efficiency at capacity 46.4% 43.1% Net power plus thermal efficiency 84.3% 82.4% 1 Based on net power output at capacity to lower heat value (LHV) of input fuel

15 Capital Cost Estimates JMS420 1,426 kw JMS320 Plus JMS 420 2,485 kw Total equipment cost $1,900,000 $3,000,000 Total project cost $5,200,000 $7,950,000 Unit 1 Including project biogas cost ($/kw) treatment system $3,650 (sulfide, siloxane, moisture) $3,200

16 Selection of the Number and Capacity of ICE Units Based on Baseline Gas Production Scenario JMS 420 JMS 320 JMS 420 Power cost, /kwh Natural gas cost, $/therm Generated energy as percentage of the existing consumption at SCBWRF Annual cost of NG to operate at capacity 39% 68% - - $0.6 mil. $0.76 mil. Payback, years yr lifecycle benefit (PV) $5.4 mil. $9.2 mil. $1.9 mil. $6.3 mil. One JMS 420 selected based on lower payback and higher lifecycle benefit

17 The Selected JMS 420 (1,400 kw) ICE Provides Enough Recoverable Heat Digesters heat demand (% of cogenerated heat) Value (1) Average 61% Dryer operating 48% Dryer not in operation 88% 1 Target biogas case The boiler not expected to be used under normal conditions

18 Lifecycle Benefit Dependence on FOG Quantity and Unit Cost of Electrical Power $5,400,000 $5,400,000 $3,210,000 $9,190,000 $9,190,000 $6,430,000 $9,190,000 $9,190,000 $7,680,000 $5,400,000 $5,400,000 $2,610, year Benefit Baseline: $0.092/kWh; $0.9/therm $0.115/kWh; $1.13/therm $0.115/kWh; $0.9/therm A4 (3 lime FOG truckloads per weekday) A3 (2 lime FOG truckloads per weekday) A1 (1 lime FOG truckload per weekday) $0.092/kWh; $1.13/therm

19 Payback Dependence on FOG Quantity and Unit Cost of Electrical Power Payback Period Baseline: $0.092/kWh; $0.9/therm $0.115/kWh; $1.13/therm $0.115/kWh; $0.9/therm $0.092/kWh; $1.13/therm A4 (3 lime FOG truckloads per weekday) A3 (2 lime FOG truckloads per weekday) A1 (1 lime FOG truckload per weekday)

20 Effect of Cogeneration Availability Factor is Relatively Small Baseline Case Target Avaiability (96%) Reduced Availability (93%) $5.4 $5.1 Payback period (years) 20-year lifecycle net benefit ($ million)

21 Conclusions High FOG addition and high TWAS degradability resulted in relatively uniform amount of biogas available for cogeneration throughout the week Low FOG and low TWAS degradability resulted in excess biogas only during dryer down time ICE based cogeneration provided the maximum lifecycle benefit when compared to alternative technologies The selected 1,426 kw ICE allowed for operating on 100% biogas independent of the price of natural gas At 9.2 cents/kwh the target biogas case had 7.3 years payback and 20-year lifecycle benefit PV of $5,400,000

22 Acknowledgements Pinellas Co staff GE Jenbacher staff WERF

23 Biogas Cogeneration System Sizing and Payback Based on Weekly Patterns of Anaerobic Digestion and Biosolids Dryer Operation John Kabouris, PhD, PE, CH2M HILL Bob Forbes, PE, CH2M HILL Tim Shea, PhD, PE, BCEE, CH2M HILL Mike Engelmann, PE, Pinellas County Jim Dulaney, Pinellas County