Logan City Landfill Gas Collection System and Power Generation

Team: Mariah Brothersen, Megan Lambright, Brady Miller, Jaxon Owens, Megan Pope, Forrest Van Iwaarden

Sponsor: Partner Engineering & Science, Inc

Introduction

Cache Valley continually suffers from damaging levels of air pollution. Landfills are a source of harmful emissions including methane and carbon dioxide. The purpose of this project is to create a collection system to capture emitted natural gas from the Logan City Landfill. This project will reduce the landfill’s greenhouse gas emissions and convert these emissions into a potential power source.

Figure 1. Project site (Logan City Landfill).

Figure 1. Project site (Logan City Landfill).

Project Alternatives

  • Do Nothing: The landfill continues to emit gas without collection. Logan City would not need to spend time or resources constructing a collection system.
  • Flare the Gas: The landfill gas would be sent to a flare. The flare would burn off the methane and emit carbon dioxide into the atmosphere.
  • Collect and Sell: The gas would be collected and sold to a willing buyer for profit.
  • Onsite Generation: The gas would be burned on-site and converted into electricity. The electricity would be added to the Logan City power grid. 

    • Alternative Evaluation and Selection

    The alternatives were compared and analyzed. Onsite Generation was selected due to its high economic feasibility and local environmental impact.

    Score Criteria Do Nothing Onsite Generation Collect & Sell Flare Collect Gas
    Global Environmental Impact 1 35 35 10
    Cache Valley Air Quality Impact 1 100 100 35
    Present Value Cost 100 35 35 10
    Public Opinion 100 10 10 1
    Economic Feasibility 10 35 10 10
    Total Score 212 215 190 66

    Scale

    1 10 35 100
    Low Positive Impact Medium Positive Impact High Positive Impact Very High Positive Impact

    Table 1. Alternatives evaluation decision matrix with impact scale.

    Cost Estimate

    The total cost to implement the collection and energy generation system is $4.9 million. The average annual profit from power generation is projected to be about $1.4 million with a starting year profit of $4.8 million. The average yearly revenue results in a 3.4-year payback period, but with the opening year’s revenue, the payback period would be closer to 1 year

    Equipment and Installation Costs
    Mobilization (10%) $343,300
    Concrete Housing Foundations $73,000
    Generator (3 + Shipping & Installation) $1,365,000
    Boring Hole Fill $36,000
    Electrical Interconnect Equipment (generation to Logan City Power) $344,000
    Wellheads and Pipe Gathering System $1,052,000
    Extraction Wells $290,000
    Flare, Knockout, and Blower System $273,000
    Construction Subtotal $3,776,300
    Engineering Costs
    Design Fee (5%) $189,000
    Construction Observation Fee (1.5%) $57,000
    Environmental Permit (2%) $76,000
    Engineering Subtotal $322,000
    Contingency Costs
    Contingency Costs (20%) $820,000
    Grand Total Cost (2023) $4,918,300

    Table 2. Costs for the collection system and power generation equipment.

    Emissions Over Time

    The total landfill gas emissions peak in 2021 and then decrease as a result of the landfill’s closure. The methane peaks at 9,336 Mg/yr, which has the potential to produce (with a 35% efficiency of the generators) 12 MW of energy. If a collection system was implemented in 2022 and methane was collected until 2071, an average of 2.1 MW could be generated.

    Figure 2. Various gaseous compound in Mg/yr for the Logan Landfill.

    Figure 2. Various gaseous compound in Mg/yr for the Logan Landfill.

    Energy Generation

    Figure 3. Methane Generator

    Figure 3. Methane Generator.

    There will be two CAT G3520C generators with a combined output of 12 MW. These will be installed along with the blower, condenser, and flare.

    Well Installation and Layout

    The well layout was designed to maximize the amount of gas collected from the landfill while minimizing the cost of well installation. This was done by mapping the topography against the landfill boundaries. The wells were then connected in the most efficient and practical format. In total, there are 45 wells. 

    Figure 4. Pipeline Network

    Figure 4. Pipeline Network.

    Well Design

    The wells were designed according to EPA regulations. 

    • Each well has a varying depth ranging from 20 ft to 45 ft. The well depths are related to the well locations in the landfill. 
    • The pipes between each well are 6-inch diameter HDPE pipes.
    • Each well is 3 ft in diameter and composed of nine sections with perforations for gas extraction in the lowest section. Five of these are included in the closing of the landfill and cover the entire landfill. The other four are installed with each well
    Figure 7. Well Section View.
    Figure 7. Landfill Section View.

    Figure 7. Landfill Section View and Well Section View

    Acknowledgements

    This project would not have been possible without the generous help and support of the following individuals:

    • Rex Guyer Mentor and External PE
    • Dr. Ryan Dupont Academic Advisor 
    • Professor Austin Ball Course Instructor
    • Tyler Richards Logan Landfill Operator