Lesson 8 - Gases
In this lesson we take a closer look at gases, including compressed air. We will look at the quality requirements and specifications for use in the brewery. Different compressed air generation methods will be considered. For nitrogen and oxygen, we will look at the common uses, quality requirements, and options available for supply, storage, usage, and generation.
Oxygen and Nitrogen
Oxygen and nitrogen make up 99% of air. To use them in brewing, they are separated from each other as they fulfil very different roles.
Oxygen (O2) makes up about 21% of the air. Nitrogen (N2) makes up about 78%.
These two molecules are similar in many of their physical attributes. The table below compares the key attributes.
Table: Physical properties of oxygen and nitrogen
|
|
Oxygen |
Nitrogen |
|
Boiling point at 101.3 kPa |
-183.0°C |
-195.8°C |
|
Freezing point at 101.3 kPa |
-218.8°C |
-210°C |
|
Critical temperature |
-118.4°C |
-146.9°C |
|
Critical pressure |
49.6 atm |
33.5 atm |
|
Liquid density at boiling point, 101.3kPa |
1141 kg/m3 |
808.5 kg/m3 |
|
Gas density at 20°C, 101.3 kPa |
1.33 kg/m3 |
1.16 kg/m3 |
|
Latent heat of vaporisation |
213 kJ/kg |
199.1 kJ/kg |
|
Expansion ratio liquid to gas from boiling point to 20°C |
860 |
694 |
As we can see, both oxygen and nitrogen can occur in solid, liquid, and gas states. The solid states are not of any practical value to us. In the brewery, oxygen and nitrogen are nearly always used in the gas state, although they may be delivered and stored as liquids.
Let’s briefly review the uses of nitrogen and oxygen before we delve into the supply side.
Nitrogen and oxygen uses in brewing
You may have heard of nitrogenated beers, but did you know that nitrogen can fulfil numerous other roles? For example:
-
Nitrogen can also be used as a purge gas for vessels and containers, to purge transfer lines, and to chase beer between operations.
-
Nitrogen can be used as a purge gas in deaerated water plants.
-
Oxygen in the brewery is typically used for wort oxygenation and yeast propagation. This is covered in detail in the Diploma in Brewing Modules 1 and 2.
So, as expected, the general quality requirements for nitrogen and oxygen are very similar to those for other gases which come into contact with the product.
Nitrogen and oxygen specifications for brewing
Just as for compressed air, the following are requirements of nitrogen and oxygen for brewing:
-
Free of particulate matter
-
Free of microbiological contaminants
-
Free of oil and grease
-
Dry to prevent microbial growth and corrosion in valve and equipment operations
-
Free of other gaseous contaminants – e.g. carbon monoxide, carbon dioxide, sulphur dioxide, or nitrogen oxide – and any other taints
The purity of the nitrogen depends on the application. If the nitrogen is intended to nitrogenate beer or produce deaerated water, the requirements will be stringent. In this case, purities of 99.999% or higher could be specified. However, if it is used for top pressure, vessel or container purging, or product chasing, the requirement could be less stringent at levels of 99.95%. The important thing to remember is that the impurity is principally oxygen. The reason we use nitrogen is mostly to eliminate oxygen, so nitrogen purity is extremely important.
The oxygen purity requirement can also depend on the application. Oxygen is mainly used for wort aeration. The reason oxygen and not air is used is that in order to dissolve more oxygen in the wort, higher concentrations of oxygen are required. Thus, technically for certain applications where lower wort oxygenation levels are acceptable, the option exists to use ‘oxygen-enriched’ air. For the purpose of this lesson we will, however, concentrate on high-purity oxygen.
Now that we know the requirements of nitrogen and oxygen for brewing, let’s discover how they are supplied to the brewery.