System and process for recovering methane and carbon dioxide from biogas and reducing greenhouse gas emissions

Abstract

Various illustrative embodiments of a system and process for recovering high-quality biomethane and carbon dioxide product streams from biogas sources and utilizing or sequestering the product streams are provided. The system and process synergistically yield a biomethane product which meets gas pipeline quality specifications and a carbon dioxide product of a quality and form that allows for its transport and sequestration or utilization and reduction in greenhouse gas emissions. The system and process result in improved access to gas pipelines for products, an improvement in the carbon intensity rating of the methane fuel, and improvements in generation of credits related to reductions in emissions of greenhouse gases.

Description

RELATED APPLICATIONS[0001]This application claims the benefit, and priority benefit, of U.S. Provisional Patent Application Ser. No. 62 / 907,348, filed Sep. 27, 2019, the disclosure and contents of which are incorporated by reference herein in their entirety.BACKGROUND1. Field of the Invention[0002]The presently disclosed subject matter relates to recovery of biomethane and carbon dioxide product streams from biogas sources.2. Description of the Related Art[0003]Biogas is gas produced through the decomposition of organic matter in facilities such as solid waste landfills, wastewater treatment plants, or other anaerobic digesters. Biogas is composed primarily of methane and carbon dioxide, but also contains lesser amounts of other compounds. The gas is typically either flared to thermally destruct the combustible compounds or is beneficially utilized for its methane content. Typical beneficial use applications include combustion of the biogas for industrial heating applications, combu...

AI Technical Summary

Benefits of technology

The patent is about a system and process for creating high-quality biofuel (biomethane) and carbon dioxide from biogas. This system and process allow for the efficient recovery of gas pipeline quality biomethane and a carbon dioxide product that can be sequestered or utilized. The process includes low temperature liquefaction of carbon dioxide from a biogas source and simultaneous purification of biomethane from contaminants. The biomethane can be used as fuel for vehicles, process heat, or for production of chemicals, while the carbon dioxide can be sequestered or utilized. The system and process allow for improved access to gas pipelines, improved carbon intensity rating of the biofuel, and reduction of greenhouse gas emissions, and additionally drive improvements in overall methane recovery efficiency for biogas processing facilities. The monitoring of material and energy inputs and outputs from the facility verifies the reductions in greenhouse gas emissions.

Problems solved by technology

For example, the disposal of cosmetics and deodorants within household waste leads to siloxanes in the biogas, the presence of refrigerants leads to halogenated hydrocarbons in the biogas, and the operation of the landfill gas collection system under vacuum in an effort to limit fugitive emissions often incidentally leads to the presence of nitrogen and oxygen in the biogas.

Biogas beneficial use applications which involve processing the gas to generate a biomethane product for injection into natural gas pipelines require that the biomethane product be sufficiently purified from compounds that may jeopardize the integrity of pipeline systems, lead to damage of downstream equipment, or would pose risks to human or environmental health.

These conventional processes have certain limitations including limitations on methane product purity and methane recovery rate.

Despite the processing efforts, conventional methods can leave trace amounts of halogenated hydrocarbons, other volatile organic compounds, siloxanes, oxygen, nitrogen, hydrogen, and heavy metals in the product gas.

Further, the carbon dioxide portion of the biogas is typically separated in a gaseous state along with other contaminants which impairs and prevents subsequent transport, utilization, or storage of the carbon dioxide.

Because the transport, utilization, or storage of the carbon dioxide portion of the biogas is impaired under conventional processing techniques, reductions in overall emissions of greenhouse gases are limited and the carbon intensity of the methane fuel is typically limited to around 30-60 gCO2e / MJ.

While previous patents have attempted to present viable methods for recovering both biomethane and carbon dioxide from biogas, these teachings have failed to present the most efficient methods for processing biogas to maximize recovery of both biomethane and carbon dioxide products of adequate quality and form to enable any subsequent use.

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