Practical Guidance for Biogas Leak Detection at Wastewater Facilities

Anaerobic digesters and the biogas they produce have allowed wastewater resource recovery facilities (WRRFs) to transform into power plants. Through the refinement and collection of biogas, renewable natural gas (RNG) can be produced, which is able to be injected into local gas distribution grids or used on-site to offset grid natural gas usage. However, these advancements in waste-to-energy infrastructure provide new challenges for WRRFs. Just like any other type of pressurized gas system, these systems can leak. Biogas/RNG leaks are a direct loss of product, present a health and safety hazard for workers and additionally is a potent greenhouse gas. It is therefore important for plant managers to reduce or eliminate these leaks where possible. To assist in this challenge, the wastewater industry has begun to use tools established in the oil and gas industry, such as optical gas imaging cameras (OGI cameras) that use infrared radiation to visualize methane in air, and portable methane analyzers that use lasers to accurately measure across a range of methane concentrations (these tools are shown in Figure 1). Although these and many other types of methane measurement devices are being tested at wastewater facilities, what is missing is an overarching approach to how to appropriately conduct biogas leak surveys. This presentation will discuss a practical framework for conducting biogas leak finding campaigns at WRRFs as well as case studies utilizing this framework in the hopes of contributing towards our sector's eventual development of best practices. A framework was developed to assist WRRFs in creating effective and efficient leak detection programs following a plan-do-check-act structure for continuous improvement (Figure 1). In general, the planning stage should create a leak finding plan that considers the risk of equipment leaking biogas (age of equipment, leak history, pressure of system, etc.) as well as equipment prioritization. Some facilities may have hundreds to thousands of individual locations that could leak, and it is not typically practical to assess them all in detail, which is why prioritizing equipment/areas is vital. The next step is to do the leak finding study using appropriate tools such as OGI cameras and portable methane analyzers. Once the data is collected, a detailed review of the information must be conducted to compare actual leaks/equipment conditions to the original plan. Finally, observed leaks are actioned, which can include issuing work orders for maintenance repair, longer-term capital repair or improvement, or do nothing (i.e. the leak is too impractical to address, or system operates as designed e.g. methane-laden condensate from biogas drip traps). FIGURE 1: FRAMEWORK FOR CONTINUOUS IMPROVEMENT OF LEAK DETECTION City of Toronto Case Study The City of Toronto's Humber Treatment Plant undertook a fugitive methane leak finding survey following the described framework. Key locations determined in the initial risk assessment were a floating roof digester, pressure relief valves on digesters, digester roofs, gas compressor equipment, and biogas-mixing piping. An OGI camera and portable methane analyzer were selected as suitable tools for the evaluation (Figure 2). The OGI camera used in this study was a FLIR Gx320 (shown in use in Figure 3). The camera visualizes methane and other hydrocarbons such as butane and propane, as black/dark smoke on the device's display (Figure 4). The camera was particularly effective in complex environments, such as around biogas piping, where visual confirmation amidst dense equipment was critical. FIGURE 2: DEVICES USED FIGURE 3: OGI CAMERA IN USE FIGURE 4: OGI CAMERA OUTPUT EXAMPLE WITH METHANE INDICATION CIRCLED IN RED The other device used was a SEM5000, which uses Tunable Diode Laser Absorption Spectroscopy to quantify methane concentrations. The device recorded methane concentrations in parts per million (ppm) at one-second intervals, pairing each reading with time and location data via an integrated GPS module. Several types of information were developed from the observation data, including videos, a map of methane concentrations (Figure 5), and a list of leaks that could be resolved through maintenance activities. A key finding was that almost all biogas piping and gas compressor piping were in good condition, and only a few leaks required addressing. The City of Toronto is currently considering future leak detection assessments at a frequency to be informed by this study. FIGURE 5: VISUALIZED PORTABLE METHANE ANALYZER DATA