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.
Air Compressors
Air compressors are mainly categorised as either positive displacement or dynamic.
The figure below gives an overview of the most common types.
Figure: Classification of air compressors
In brewery applications, we typically encounter mainly screw and reciprocating compressors, so we will focus on them. We will also have a brief look at Roots blowers. They all fall under the category of positive displacement pumps.
Before we go further, let’s quickly look at a few terms used in relation to compressors:
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Duty cycle refers to how long a compressor can run before it needs to rest. It is expressed as a percentage of total time. Thus, a compressor with a 60% duty cycle can only run 60% of the time and needs to be off for 40% of the time to recover or cool down.
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Running a compressor unloaded means the compressor is still running but it is discharging to atmosphere and not the system. This is an alternative to starting/stopping a compressor, which causes wear to the motor. Typically, a compressor will run unloaded for a set time before stopping completely.