Renewable Natural Gas (RNG)

Air Pollution Control and Tail Gas Abatement

Traditional open-tip flare systems have long been utilized to destroy methane and other volatile organic compounds contained in biogas. During decomposition, the materials within landfills off-gas harmful toxins and greenhouse gases, some of which are high in energy content. When landfills simply flare these gases they are wasting this potentially valuable resource while releasing large amounts of greenhouse emissions, such as Carbon Dioxide (CO2), into the environment.  

Many municipalities, private landfill owners and waste processing companies have resorted to capturing this biogas for beneficial uses rather than simply flaring it off. A variety of technologies are used to purify biogas by removing the contaminants that don’t meet the stringent pipeline specifications. Often these tail gases are comprised of low heating value, approximately 1 to 15% methane, and therefore 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 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, CO2, nitrogen, oxygen, and other unwanted chemicals are removed 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 where organic material is 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 while released biogas is collected and converted into electricity or renewable natural gas. The tail gases and odors from these operations are also treated in Anguil 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 which hold the molecules together are broken. The low heating value methane and VOCs in the process exhaust stream are converted to various combinations of carbon dioxide (CO2), water (H2O), and thermal energy. As is the case with other industrial emission combustion, it is important to minimize the overall supplemental fuel combustion from the destruction device.

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 both before and after going through an upgrading process to make RNG.  

Wastewater Treatment

Wastewater runoff 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 RNG 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. 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. 

In wastewater treatment, anaerobic digesters help to manage waste and produce renewable energy. The anaerobic digestion wastewater treatment process involves a series of processes where wastewater biosolids are broken down by bacteria in the absence of oxygen. Once the bacteria consumes the suspended particles, all solid matter is then removed before the digesters break down the waste and create digester gas (carbon dioxide and methane).

The digester gas can then be converted to renewable energy to fuel onsite boilers, generate heat or electricity, and more. Anguil’s vapor combustors are utilized in these applications to destroy the harmful pollutants and off-gases generated during the anaerobic digestion and RNG production processes.  

Leachate is a type of wastewater generated from landfills that is 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. 

Industrial Wastewater Treatment

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. We consider the specific function and role of each component and deliver an efficient, cohesive, and properly integrated system. 

For each wastewater treatment solution, we integrate numerous technologies into one complete package to effectively treat wastewater. Our technologies can be used to remove the following contaminants:

• Total Dissolved Solids (TDS)
• Dissolved Metals
• VOCs
• Soluble BOD/COD
• Suspended Solids
• Fats, Oils/Grease

The wastewater treatment process plays a key role in RNG production. Treating and repurposing municipal and industrial wastewater can support a variety of industries and processes. For example, sewage sludge and other biosolids are rich in microorganisms, which can be broken down to generate RNG. To aid in the wastewater treatment and RNG production processes, Anguil has proven designs that will deliver optimal performance while helping to maintain compliance, minimize operator error, and reduce operational costs.

Pollution Reduction Technologies from Anguil Environmental 

Anguil’s diverse catalog of product offerings ensures unbiased equipment selection based on efficiency needs, process parameters, and destruction needs. For more information on our solutions, contact us or visit our document library. 

Resources

• The Coalition for Renewable Natural Gas (RNG Coalition) advocates for the utilization of off-gases from renewable sources like organic digestors and landfill waste gas.
• American Coalition for Ethanol (ACE) is a group of producers and suppliers committed to a sustainable industry that feeds and fuels a growing world.
• The Renewable Fuels Association (RFA) is an advocacy forum for ethanol and bio-product producers and industry stakeholders.
• Advanced Biofuels Association is focused on promoting and advancing low carbon fuel utilization.