Why breweries are moving from CO2 to onsite nitrogen generation

The brewing sector faces a re-examination of its supply chain management due to global disruptions. A notable impact has been the shortage of carbon dioxide, which is causing breweries to seek alternative solutions. This shortage stems from a combination of challenges, including heightened demand during the warmer months, and quality issues related to increased hydrocarbon levels in carbon dioxide supplies.

Carbon dioxide plays a vital role in creating the effervescence and freshness of beer. Traditionally, it is introduced into beer to speed up carbonation, cutting down the process from weeks to days. During fermentation, carbon dioxide is also a natural by-product of yeast consuming sugars. Advancements in technology now allow for the recapture and reuse of this by-product, reducing the need for external carbon dioxide sources.

In brewery operations, nitrogen can be used interchangeably with carbon dioxide for tasks like tank blanketing, purging, and liquid transfer. As inert gases, they do not easily react with other substances. Nitrogen, in particular, can be used without changing the drink’s carbonation levels.

The use of nitrogen in brewing is expanding to include tank purging, transferring products, preparing canning lines, washing kegs, nitrogenating beers, and conducting quality assurance tests. The production of “nitro beers,” which are made exclusively with nitrogen instead of a carbon dioxide-nitrogen mix, is becoming increasingly popular. These beers are known for their smooth flavor and creamy, long-lasting head, created by infusing nitrogen at high pressures due to its lower solubility compared to carbon dioxide.

The three main techniques for extracting nitrogen from air are cryogenic distillation, membrane separation, and Pressure Swing Adsorption (PSA). Cryogenic distillation is the traditional method for obtaining liquid nitrogen. Each technique is best suited for different levels of nitrogen flow rates and purity, with membrane and PSA systems being ideal for onsite nitrogen generation in breweries.

Cryogenic distillation: Cryogenic distillation involves cooling air to extremely low temperatures to separate gases based on their boiling points. At atmospheric pressure, nitrogen and oxygen turn into liquids at around -196°C and -182°C, respectively. This method produces nitrogen with very high purity levels (>99.9995%), but due to its energy-intensive nature and high costs, it is generally reserved for large-scale operations.

Membrane separation: Membrane systems work on the principle of selective permeation, where air is forced through a module containing hollow fibers. These fibers allow oxygen, water vapor, and other impurities to pass through, leaving nitrogen as the product. Membrane systems can provide nitrogen with a purity of up to 99.5% and are suitable for applications requiring a flow rate of less than 1,000 Standard Cubic Feet per Hour (SCFH), although larger systems can accommodate higher flow rates.

Pressure Swing Adsorption: This is a sophisticated technique involving dual vessels, known as “sieve beds,” filled with carbon molecular sieve (CMS). This material is adept at adsorbing gas molecules within its tiny pores, each about 0.1 nm across. Under pressure, these pores capture gas molecules, with oxygen (0.346 nm) being adsorbed more than nitrogen (0.364 nm) due to its smaller size.

The PSA mechanism operates in phases: one bed actively isolates nitrogen from the air, while the other regenerates, releasing previously adsorbed gases. As the CMS’s capacity is reached, its adsorption efficiency wanes, leading to a “breakthrough” where nitrogen purity starts to decline. The process then switches to the second bed, maintaining a continuous cycle. PSA systems are adaptable, providing nitrogen purities from 95% to 99.999% and flow rates between 50 to 35,000 SCFH. Variables such as air input rate, CMS mass, cycle timing, and adsorption pressure determine the final nitrogen quality and quantity.