The effective utilization of renewable energy sources is crucial to the global transition away from fossil fuels. In broad terms, Renewable Natural Gas (RNG) refers to the utilization of waste-derived biogases for use as an alternative to fossil fuels. The sources of biomass are numerous: solid waste decomposition at landfills, manure in anaerobic digesters, waste food decay, crop residue from farming, and municipal solid waste treatment are just some of the well-known applications. While RNG offers a wide range of benefits, the industry is moving swiftly to ensure air emissions and water run-off from its operations are not released into the environment where they could contribute to smog, climate change, and soil or water contamination.
Understanding the Challenging Conditions is Key to Compliance
Identifying and designing for the unique operating conditions at an RNG facility is paramount to remaining in compliance with air and water pollution regulations as the resource recovery process can be challenging. For example, RNG facilities face varying concentration levels of a wide range of air and water pollutants from the decomposition process.
Unlike a typical manufacturing facility with consistent byproduct output, renewable energy operations do not always have consistent flows or concentrations. Any pollution control system must be designed with worst-case scenarios in mind and safety always under consideration. Methane, for example, is a common source of renewable fuel because of its abundance and high energy content, but that also makes it a hazard under certain conditions. Pollution technologies in this industry should be designed around process conditions, efficiency requirements, and safety standards.
Preventing Air Pollution
Many municipalities, private landfill owners, and waste processing companies have resorted to capturing biogas from decomposition for beneficial uses, rather than simply flaring it off. A variety of technologies are used to purify biogas by removing contaminants that don’t meet the stringent pipeline specifications. Often these tail gasses are comprised of low heating value – approximately 1 to 15% methane – and therefore are not combustible on their own, but still harmful to the environment when not properly destroyed.
There are several steps involved with cleaning biogas and treating the processing plant’s tail gas. First, hydrogen sulfide (H2S), which is a highly corrosive compound, needs to be removed. This can be accomplished using a dry scrubber or carbon absorber. Filtration using an activated carbon adsorption bed effectively traps and removes H2S particles from waste gas. Next, carbon dioxide (CO2), nitrogen, oxygen, and other unwanted chemicals are removed. This is done using sieves and other technologies to clean the gas until it reaches natural gas specifications, making it suitable for local pipelines. During this cleaning process, waste gas or tail gas is created that must be treated before it can be released into the atmosphere.
Another growing sector of the waste-to-energy industry is the biomass market. Organic material is collected from restaurants, food processors, and municipalities, then broken down by bacteria in the absence of oxygen within large digesters. The solid waste is transformed into safe, reusable material like fertilizer or solid biofuel. Released biogas is collected and converted into electricity or renewable natural gas. The tail gases and odors from these operations are also treated in thermal oxidizers and vapor combustors.
Anguil thermal oxidizers and vapor combustors can eliminate over 99% of the off gases from the various RNG purification processes. The chemical process of thermal oxidation involves raising the exhaust stream temperature to the point that the chemical bonds holding the molecules together are broken. The low heating value methane and VOCs in the process exhaust stream are converted to various combinations of CO2, water (H2O), and thermal energy. Anguil’s designs minimize the overall supplemental fuel combustion from the destruction device as there is a direct correlation between operating costs and greenhouse gas output.
During normal operation, Anguil systems are capable of handling low-flow situations such as excess landfill gas, or high-flow process vapors due to an upset condition. We also offer dual-burner and dual-fan configurations for ultimate control of the process.
Protecting Water Resources
Wastewater runoff at RNG operations can result from numerous upstream sources such as feed lots, wastewater treatment plants, dairy processing, landfills, and green waste collection. It can also come from midstream sources, such as production processes, digesters for biogas production, dewatering of digester sludge, landfill leachate, and other natural gas plants. Byproducts of wastewater like oil, grease, and fat can reach rivers, lakes, and water tables, poisoning the environment and drinking water supply. Onsite wastewater treatment processes aid in the removal of contaminants so that water can be reused or released into the environment. These processes also aid in the production of RNG.
Leachate is a type of wastewater generated from landfills that are formed by the percolation of moisture and rainwater through landfill waste. Many landfills manage leachate by discharging directly to Publicly Owned Treatment Works (POTW) with minimal or no pretreatment. However, due to tightening regulations imposed by the EPA on POTWs, treatment facilities are beginning to limit or are refusing acceptance of landfill leachate, as it is often difficult to treat with the typical technologies currently employed by most POTWs.
Landfills are increasingly taking on more of the management and pretreatment responsibilities of their leachate. One option is to recirculate leachate back to the landfill to increase the production of landfill gas, which requires further purification to RNG standards before it can be sold to the grid. Landfill gas can also be used to fuel leachate evaporators. The evaporator heats up the leachate to drive off water vapor, leaving behind sludge. It is important to note that recirculation of leachate also concentrates the contaminants within the water, making evaporation more problematic in terms of air emissions. Anguil offers a variety of wastewater treatment solutions, including wastewater evaporation systems to aid in the management of landfill leachate.
Wastewater treatment systems used for RNG use various mechanisms and techniques to return contaminated water to its initial state. Anguil’s pollution abatement experts can provide optimized solutions to solve your industrial water purification challenges. For each wastewater treatment solution, we integrate numerous technologies into one complete package to effectively treat wastewater. Our integrated technology solutions can be used to remove contaminants such as total dissolved solids (TDS), dissolved metals, volatile organic compounds (VOCs), suspended solids, fats, oils, and grease. Anguil has proven designs that will deliver optimal performance while helping to maintain compliance, minimize operator error, and reduce operational costs.
At Anguil, we offer quality engineered pollution control solutions that ensure the byproducts of the bioenergy production processes are not offsetting the benefits of these crucial initiatives. Our designs account for process flexibility and ease of maintenance to ensure compliance with strict industry standards while minimizing carbon footprints. Because of this, our holistic solutions are ideal for various applications, including air emissions and odors, as well as zero liquid wastewater discharge projects at renewable fuel operations.