Carbon Dioxide Supply Chain Issues
Supply chain issues in recent years have forced many companies to reconsider their entire business approach. Greater priority has been placed on maintaining a steady inflow of required resources. A recent shortage of carbon dioxide supplies has been putting additional strain on businesses nationwide, particularly those in the brewing industry. This shortage can be attributed to a combination of several factors, including the continuation of general supply chain issues, high demand for carbon dioxide over the summer months, and elevated hydrocarbon levels in the product carbon dioxide from the Jackson Dome (one of the nation's largest gas production sites) observed around September 2022.
One strategy to remove some uncertainty in a supply chain is to reduce the number of third-party vendors involved in the business. For example, it may be worthwhile for companies purchasing goods from a vendor to produce said goods on-premises, if possible. This article aims to provide a potential solution for breweries facing delayed deliveries and price increases associated with carbon dioxide: Utilize on-premises nitrogen generation to serve as a partial or full replacement for purchasing liquid carbon dioxide for some processes.
A Pressure Swing Adsorption (PSA) On-Premises Nitrogen Generation System.
Carbon Dioxide and Nitrogen Usage in Breweries
Carbon dioxide and nitrogen have various usages in breweries. They are utilized as process gases (primarily for the movement of fluids while maintaining an inert environment) and for giving beverages distinct taste and visual characteristics.
Carbonation gives beer its fizzy appearance and prevents spoilage. Most beer produced in breweries is carbonated by directing a flow of carbon dioxide through the beverage. This lowers the required process time for carbonation from weeks (via natural carbonation) to days. Beer produced at the commercial level in America is typically highly carbonated and light.
During fermentation of the brewing process, carbon dioxide is released as a byproduct when yeast digests sugars. Technology exists to capture and reuse a portion of the released carbon dioxide during brewing, which reduces the volume of gas needed to be purchased. However, cost and production limitations have prevented many smaller breweries from purchasing these technologies, as said technologies are generally more practical in large scale applications.
Opportunities to Replace Carbon Dioxide with Nitrogen
Carbon dioxide and nitrogen serve similar purposes in brewery processes. Replacing carbon dioxide with nitrogen is a viable solution for processes such as blanketing, purging, moving liquids, etc., where a specific gas may not necessarily be required. Both carbon dioxide and nitrogen are considered to be inert gases, as they do not readily react with other substances. Nitrogen can be utilized as a process gas without altering the carbonation characteristics of the beverage, and is usually added to kegs for pressurization.
Billy Chestnutt, an Industrial Sales Manager at South-Tek Systems, says, “South-Tek Systems entered the brewery market 19 years ago with our BeerBlast Nitrogen Generators that provide beer gas to push beer to the tap. Within the last couple of years, brewers have investigated switching some CO2 processes to nitrogen due to the nationwide CO2 shortage. The applications for nitrogen that we see in the brewing process include purging/blanketing of tanks, pushing product from tank to tank, pre-purge on canning lines, running the keg washer, nitrogenating beer, and testing in the quality assurance lab.”
Many breweries have recently started producing “nitrogenized beers”, which only involves nitrogen during brewing rather than a blend of carbon dioxide and nitrogen. For comparison, brewing ales and lagers typically involves a 70% carbon dioxide and 30% nitrogen blend, whereas stouts and porters tend to utilize a 25% carbon dioxide and 75% nitrogen blend. Nitrogenized beers tend to have a smooth taste and a lasting foam head. Beer is usually nitrogenized by forcing nitrogen into the beverage at high pressures, since nitrogen does not naturally combine with it the way carbon dioxide does.
Nitrogen Generation Processes
The three main processes by which nitrogen is separated from oxygen and other substances in air are cryogenic distillation, membrane systems, and pressure swing adsorption (PSA). Cryogenic distillation was the first of these processes to be developed, dating back to 1895 when it was introduced by Carl von Linde. It is the process by which liquid nitrogen is obtained. Membrane and PSA technologies were not widely used for nitrogen separation until the 1980s. Each of these processes have a range of product nitrogen flow rates and purities in which they are better suited to operate than the others. Membrane or PSA systems are recommended for on-premises nitrogen generation for brewery applications.
Cryogenic distillation involves cooling an input flow of air below the boiling points of its constituents. The difference in boiling points of these constituents allows for their separation. The required temperature to liquify the components of air during this process is extreme; at atmospheric pressure, the boiling points of nitrogen and oxygen are approximately -320°F and -297°F, respectively.
Cryogenic distillation provides the greatest purity nitrogen of the three nitrogen generation processes (>99.9995%). However, it is more energy-intensive and costly than membrane or PSA systems, making it economically viable only for large-scale systems.
Membrane systems operate via selective permeation, where differences in gas molecule diffusion rates through a packed container of hollow fibers drives separation. The hollow fibers selectively permeate oxygen, water vapor, and other impurities from an input flow of compressed air, leaving nitrogen as a product.
Membrane systems can typically provide nitrogen at a purity of 99.5% and are recommended for applications where a flow rate of less than 1,000 SCFH is required, though greater flow rates can be achieved depending on membrane sizes. Figure 1 shows an example of a membrane filtration device designed for nitrogen separation from a compressed air input.
Figure 1: Membrane Filtration Device for Nitrogen Separation.
Pressure Swing Adsorption
The typical PSA process involves two pressure vessels (referred to as “sieve beds”) filled with carbon molecular sieve (CMS), a material that selectively adsorbs gas molecules at pores on its surface. These pore sizes are on the scale of Angstroms, a unit of measurement equal to 0.1 nanometers. When pressurized, gas molecules begin to fill the pores. Oxygen and nitrogen have molecular sizes of 2.99 and 3.05 Angstroms, respectively. Due to the fact that molecules of oxygen are smaller than those of nitrogen, more oxygen molecules are adsorbed at the pores of the CMS.
During the PSA process, only one of the sieve beds is actively separating nitrogen from an input of compressed air. While one sieve bed is active, the other is exhausting gases stored in the CMS from the previous cycle. The rate of adsorption in the CMS of the active sieve bed will decrease with time, as the CMS can only hold a finite amount of gas molecules. Eventually, the output nitrogen purity from the active sieve bed will start to drop (a point referred to as “breakthrough”). The input flow of air is then switched to the other sieve bed, and the cycle repeats itself. Some examples of PSA nitrogen generation systems are shown in Figure 2.
PSA systems can supply a wide range of nitrogen purities and flow rates; nitrogen purities can range from 95% to 99.999%, and typical flow rates can range anywhere from 50 to 35,000 SCFH. Factors affecting nitrogen purity and flow rate include input air flow rate, mass of CMS utilized, cycle timing, adsorption pressure, etc.
Figure 3 is a basic schematic of how a nitrogen generation system is generally arranged. Two tanks (one for input air and one for product nitrogen) are recommended for most applications to stabilize system pressures when the PSA cycle switches the input air flow between sieve beds.
Figure 2: PSA Nitrogen Generation Systems.
Figure 3: General Arrangement of a Nitrogen Generation System.
Benefits of On-Premises Nitrogen Generation
PSA systems designed for the separation of carbon dioxide from other gases exist, though these systems are best applied when a large input flow of flue gas is available, making them unfit for a brewery setting. The average cost of liquid carbon dioxide (due to the impact of recent supply and demand) is about $3.50/kg, or approximately $18/CCF (representative of the gas phase at standard conditions).
Costs associated with nitrogen in liquid bulk tanks, liquid dewars, and high-pressure cylinders are approximately $1/CCF, $5.50/CCF, and $25/CCF, respectively. However, nitrogen generated on-premises can cost as little as $0.10/CCF, which is representative of the electrical power required to operate the system.
The initial cost of a nitrogen generation system may be greater than high-pressure cylinders and liquid nitrogen containers, but most companies will reach a return on investment within 12-18 months with proper sizing of the system based on process demands. Breweries typically experience savings associated with gases of 50-75% by switching to on-premises nitrogen generation. If a regular maintenance schedule is followed, PSA nitrogen generation systems can have a life expectancy of 15-20 years.
Approximately 79% of ambient air is nitrogen, so the system will never have a shortage of gas to process. An on-premises nitrogen generation system provides a reliable supply of process gas, one that does not continually depend on third-party vendors.
About the Author
Garrett Rinker is a Senior Project Engineer at South-Tek Systems. He holds a Ph.D. in Mechanical Engineering. Email: firstname.lastname@example.org.
About South-Tek Systems
Founded in 2003, South-Tek Systems is the industry’s leading nitrogen generation manufacturer. Offering both standard product lines and engineered-to-order generation solutions, South-Tek delivers best-in-class nitrogen generators for worldwide distribution. South-Tek Systems is located in Wilmington, North Carolina. For more information, visit https://www.southteksystems.com.
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