Biogas/RNG Project Lifecycle

PROBLEM STATEMENT/PURPOSE: This paper and presentation will detail the typical lifecycle of a municipal RNG project from the facilities planning phase through post startup operation in order to inform those considering such a project. It will delve into the common key decisions that are made along the way as well as specific details about these types of projects. The lifecycle will be broken down into the following major phases: 1.Planning 2.Design 3.Construction 4.Operation Historically municipalities would choose to anaerobically digest their wastewater sludge to reduce the volume produced to lower hauling and landfill costs compared to other stabilization methods. The biogas produced would mostly be flared with some potentially beneficially used to heat the digestion process. Over time methods have evolved to get increasing higher value out of the biogas that would otherwise be flared. These include electrical power production, combined heat and power systems, and heat recovery steam generation to name a few. In recent years a more lucrative biogas use has grown out of the renewable fuel standard (RFS). Under the RFS gasoline and diesel producers and importers (obligated parties) are required to purchase a certain amount of renewable fuel every year to offset transportation related greenhouse gas emissions and limit reliance on foreign energy. This has driven the value of biogas (in the form of renewable natural gas or RNG for short) to higher than the equivalent amount of natural gas and therefore many municipalities considering upgrades to their biosolids processes today are including anaerobic digestion with a method of selling their biogas (Figure 1 - RIN prices by category over time). RNG value lies largely with the renewable identification number (RIN) trading that occurs between producers and obligated parties. Figure 1 - RIN prices by category over time. RNG PROJECT LIFECYCLE Experience from the following municipal biogas RNG projects will inform the project lifecycle insight provided in this presentation. These projects are in varying stages of the 4 main project phases outlined in this presentation. - Thereasa St. WRRF, Lincoln, NE - Columbia Blvd, WTP, Portland, OR - Papillion Creek WWTP, Omaha, NE - Piscataway WWTP, Accokeek, MD - Cedar Rapids WPCF, Cedar Rapids, IA - Des Moines STP, Des Moines, IA - Arlington WPCP, Arlington, VA PLANNING The first step in an RNG project lifecycle is in the facility planning phase. This phase is usually kicked off when a municipality is looking to either implement an overall biosolids process improvement or wants to beneficially use biogas from an existing digestion process. Biogas beneficial use options at this phase will typically include combined heat and power, electricity generation, thermal drying, and pipeline injection. In most cases if there is a natural gas utility or transportation end user located within a reasonable distance of the plant RNG production will win out over the other alternatives. The strongest argument for RNG is financial but it also has environmental and social advantages over the alternatives which will be detailed (Figure 2 - Example of greenhouse gas (GHG) emissions for design alternatives). When producing and selling RNG is identified as a feasible path forward the highest priority becomes reaching out to potential receivers; either a natural gas utility or a vehicle fleet operator. The receiver must both be receptive to accepting RNG and provide details that will guide the design. These details include gas quality requirements, interconnection design, custody transfer, site location, payment and funding split. DESIGN The next major phase of an RNG project is final design. During this phase many key decisions are made. Many RNG projects have very similar key design decision points. The following are some of the design decisions that will be discussed: - Should there be gas utilization options in addition to RNG (Figure 3) - Biogas design flow and peaking factors - Whether or not to upgrade peaks in biogas production - Should there be gas storage? - Levels of redundancy (flare, compression, upgrading, etc.) - CO2 removal technology and tail-gas treatment - Design H2S, VOC, and siloxane concentrations and how to treat. - Gas conveyance (wet vs. dry) to upgrading system. Other important design details that will be discussed are examples of process control description, commissioning plan, and performance testing plan development. Figure 3 - Example of a process with many gas utilization alternatives. CONSTRUCTION After design the next major phase is construction. During construction coordination with the gas receiving entity continues and this presentation will give examples of the ongoing coordination that can be expected (including potential involvement of a RIN broker). Figure 4 shows an example of initial RNG acceptance coordination with the gas utility during startup. The period of commissioning, functional testing and performance testing is the most operationally intensive phase of construction. This presentation will give examples of how to prepare for a successful commissioning phase that involves all stakeholders. Specific detail will focus on team collaboration and process driven decision making. Figure 4 - Example of RNG acceptance coordination with gas utility. OPERATION The last lifecycle phase that will be covered is operation of an RNG production system. It will give details on what to expect in terms of revenue generation, operation and maintenance, uptime, and potential contingency scenarios (down time). Figure 5 shows maintenance of one of the most common H2S removal technologies, iron sponge adsorption. Figure 5 - Photo of iron sponge H2S removal media change - Courtesy of MV Tech