Organics to Energy Program

Transcription

1 Organics to Energy Program From Waste Management to Resource Management City of Tacoma Environmental Services Department James Parvey, PE, LEED AP

2 Program Overview Utilize excess anaerobic digestion capacity to produce energy Assess locally available organic feed stocks for suitability Capture methane (RNG) from digestion CNG Vehicle fuel best economic option Convert Solid Waste Fleet to CNG 2

3 Consulting Team Brown and Caldwell Organic Feedstock Analysis Design of pre-processing equipment for digesters Kennedy Jenks Potential uses of gas from digestion process KPFF/Marathon CNG Fueling Station Design WIH/Fuel Solutions CNG Consultation Carollo Engineers Internal stakeholder engagement 3

4 An Opportunity Excess Digester Capacity With UWT evaluated digestion process impacts associated with co-digestion with the dual-digestion process at CTP. The pilot study focused on the impacts of the feedstock to the process to ensure significant conversion of co-digestion substrate to biogas was feasible while maintaining Class A biosolids status and biosolids aesthetics. 4

5 Current System 5

6 Organic Waste Market Analysis B&C conducted a three-step market survey of the Tacoma region to determine possible digestion feedstocks. The survey consisted of initial research and contact of feedstock (waste) providers in the area, discussions with the City, and a ranking classification of available substrates to identify the best potential sources. The market survey indicated that 6 feedstocks could warrant follow up. 6

7 Commercial Food Waste 7

8 Food Waste Pilot Program The viability of the food waste diversion and digestion program will be evaluated through a Food Waste Preprocessing and Digestion Demonstration Project. How the food waste diversion program can be integrated into existing City operations. Volume and type of contamination (wrappers, wires, fruit labels, etc.). Level of preprocessing. Operating parameters required to size a scaled up facility (i.e. gas production rates, gas energy content). 8

9 Food Waste Pilot Program Approximately 800-1,000 commercial food waste generators in the City 65 currently on pilot program City provided containers 5-7 tons collected per week 1,750 tons since program inception July

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11 Processing at the Landfill 11

12 Brown and Caldwell (B & C) B&C has produced two studies which discuss digestion at the City s Central Treatment Plant (CTP), Investigation of Co-Digestion at the Tacoma Central Treatment Plant (2010) and City of Tacoma Food Waste Preprocessing and Co-Digestion Feasibility Study (2011). Both documents present alternative uses for the digester gas generated by the CTP and by the addition of food waste for co-digestion. 12

13 Investigation of Co-Digestion Report The Plan is comprised of four technical memoranda: Organic Waste Market Analysis and Ranking Digestion System Capacity Assessment Alternative Organic Waste Receiving and processing and Cost Benefit Analysis Evaluation of Acceptance of Pulped Food Waste. 13

14 Alternative Organic Waste Receiving and Processing Two options were investigated: Constructing a new dedicated receiving facility capable of receiving solids 5 days a week and feeding the system 7 days a week, or Retrofitting the existing hauled sludge receiving facility. The investigation showed very little incentive to construct a new receiving facility, due to the high capital costs. Low capital costs of a retrofit appear to be a more favorable option for increasing return on investment. Greatest return on investment may come from increasing the capacity of the system, to allow for an increase in potential substrate received. This would increase gas production and increase revenue from tipping fees due to the large amount of substrate available in the area. 14

15 Evaluation of Acceptance of Pulped Food Waste The scenario evaluated by B&C assumed that the Solid Waste Division would provide pulped and screened waste to the CTP, providing the preprocess required, and the CTP would increase its process capacity. Four digester configurations, as well as the current CTP process scenario were analyzed A range of increased energy production from 5 million to 27 million kilowatt-hours (kwh) per year were obtained. The Study showed that an increase in digester capacity greatly increased the potential power produced. 15

16 Gas Utilization Study Reviewed Brown and Caldwell reports to analyze potential uses of the volumes of gas that could be generated under different CTP configurations Evaluated three alternatives for gas utilization Co-generation of heat and power Put gas into natural gas pipeline Compressed Natural Gas as fuel for City or outside fleet 16

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18 Co-Generation Option Capital and operation and maintenance (O&M) costs for the project created a 20- year return on investment Due to the lack of available digester biogas that could be used to run the cogeneration engines low power costs available from Tacoma Power 18

19 Pipeline gas Digester gas can be upgraded for supply to the natural gas pipeline. requires that all of the CO2 is removed as well as any impurities. currently in use at two local facilities, the South King County Regional WWTP and the Cedar Hills Landfill. Gas supplied to the pipeline must have a gross (higher)heating value greater than 985 British thermal units per cubic foot (Btu/cf). Typical biogas, which consists of 60 percent CH4 and 40 percent CO2, can be upgraded to meet this specification. 19

20 Pipeline Gas Puget Sound Energy (PSE), the local natural gas supplier in the Tacoma area, has different standards for introduction of gas into their systems. requires any supplier feeding into their pipeline to meet the Btu content which occurs at that point in the pipeline. The natural gas in the local PSE pipeline has a gross heating value of 1,031 Btu/cf. Digester gas must be augmented to meet this standard. 20

21 CNG Fueling Station Vehicles can be modified to operate on CNG instead of gasoline or diesel fuel. Current output could be utilized to produce approximately 200 gallons of gasoline equivalent (GGE) per day. This production rate would allow the CTP to fuel plant vehicles with CNG. 21

22 CNG Fueling Station The CTP produces enough digester gas over the year to potentially meet nearly all of the fuel requirements of the City vehicles. The City purchases almost 354,000 gallons of diesel fuel annually. If all of the existing digester gas is upgraded to CNG, the CTP could potentially produce over 430,000 GGE annually, without implementing co-digestion. 22

23 CNG Issues Treatment Plant uses 4,400-7,000 MBH/hour for process and building heat. This reduces gas available for fuel use substantially Adding food waste to the system and a heat pump to recapture energy from heated effluent water will provide process and building heat AND allow for complete fuel use. 23

24 Associated Petroleum Products Have an existing commercial fuel lock station across the street from the CTP Willing to partner with City to provide CNG at their station Reduces transportation costs to the City Will provide City with tax credits that can be sold 24

25 Carollo There were operational concerns at the CTP How would food waste impact existing processes? Impact on Tagro Tacoma s award winning Class A bio-solid Carollo was hired to be a neutral third party to help program planners and CTP operators understand each other s concerns. 25

26 Solid Waste Fleet Conversion Developing plans for CNG fueling station at the transfer station. Approximately 84 trucks by

27 Other collection options Insinkerator (garbage disposal) is being tested in large scale kitchens and in a pilot neighborhood. Reduces ick factor of storing food waste in house and concerns about vectors while food is in container outside Food waste is still getting to the CTP digesters where it can be turned into energy 27

28 Other City Benefits City can sell Also known as Green Tags, Renewable Energy Credits, Renewable Electricity Certificates, or Tradable Renewable Certificates tradable, non-tangible energy commodities in the United States that represent proof that 1 megawatt-hour (MWh) of electricity was generated from an eligible renewable energy source. 28

29 Other City Benefits Tradable Carbon Allowances or Carbon Offset or Carbon Credit An allowance, offset, or credit is granted to an individual, organization, or government entity for reducing greenhouse gases (GHGs). They represent the reduction of 1 metric ton of carbon dioxide equivalent (CO2e). These allowances can be purchased, sold, or voluntary traded. The certificates are valued based on a market condition or level set by a government, other authority, or the marketplace. 29

30 Benefits Reduced expense for diesel and biodiesel fuel purchases Tradable Carbon Allowances or Carbon Offset or Carbon Credit Reduced greenhouse gas emissions Reduced Particulates Renewable Energy Certificates (REC) Augment nutrients to treatment plant 30

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