Upgrading biogas transforms it from a raw, low-value fuel into a high-quality energy source, unlocking its full potential. For agricultural actors, this process offers key benefits: increased revenue through biomethane sales, reduced environmental impact, and the opportunity to meet the growing demand for renewable energy. The primary goals of biogas upgrading are to increase methane purity, remove unwanted compounds, and adapt the gas for specific applications like grid injection, vehicle fuel, or local energy use.
The first objective is to maximize methane content, as raw biogas typically contains only 50–70% methane, the remainder being carbon dioxide and trace contaminants. Removing CO₂ not only increases energy density but also ensures compliance with gas grid or fuel specifications. Impurities such as hydrogen sulphide must also be eliminated to prevent corrosion, protect equipment, and improve safety. Additionally, water vapor must be extracted to produce dry gas suitable for transport or storage.
Achieving these outcomes requires employing advanced technologies tailored to biogas upgrading. Water scrubbing is a straightforward and cost-effective method widely used on farms. By dissolving CO₂ in water under high pressure, this process separates it from methane, delivering biomethane with improved purity. For operations needing compact and scalable solutions, membrane separation systems use selective membranes to isolate methane from other gases, ensuring high efficiency and flexibility. Pressure swing adsorption (PSA) is another reliable option, utilizing material that selectively binds CO₂ under controlled pressure conditions to achieve high methane concentrations.
For larger-scale applications, amine scrubbing offers superior performance, especially when precise gas quality is essential. In this method, CO₂ chemically bonds with amine solutions and is later separated, resulting in nearly pure methane. Additionally, some systems integrate cryogenic separation, which cools biogas to very low temperatures, freezing out impurities and CO₂ while allowing methane to remain in gaseous form.
Once upgraded, biomethane becomes a versatile energy source. It can be injected directly into the natural gas grid, substituting fossil natural gas for heating, cooking, and industrial processes. Alternatively, biomethane can be compressed or liquefied for use as a clean transportation fuel, particularly for heavy-duty vehicles, which benefit from its high energy density and reduced emissions compared to diesel. For farms and rural communities, local use of biomethane in microgrids or combined heat and power (CHP) systems can help energy independence and reduce reliance on external suppliers. Its compatibility with existing infrastructure and diverse applications ensures biomethane remains a key player in the transition to renewable energy.
Meanwhile, the carbon dioxide extracted during biogas upgrading need not go to waste either. Instead, it presents valuable opportunities for reuse. In agriculture, purified CO₂ can be used in greenhouses, boosting plant growth and productivity. Food and beverage industries often use CO₂ for carbonation, packaging, or refrigeration but they need it to be pure. Beyond these applications, captured CO₂ can be sequestered underground to permanently remove it from the atmosphere, contributing to climate mitigation efforts. Emerging technologies are also exploring the conversion of CO₂ into chemicals, building materials, fuels, and even more biomethane, creating additional revenue streams and expanding the potential of biogas upgrading to contribute to a circular and sustainable economy.
Each technology comes with distinct advantages and operational requirements, and the choice often depends on factors like feedstock composition, plant size, and intended biogas use. Regardless of the approach, upgrading biogas represents a strategic investment for agricultural stakeholders, paving the way for sustainable energy generation and enhanced economic resilience. The next step is making it more accessible for smaller production units, as the process of upgrading biogas still is quite energy intensive.
Upgrading Biogas: From an energy source to a marketable product