Lesson 6 - End of Unit SAQ

1.   ***

a)    Describe the uses and sources of nitrogen in a brewery.

b)    A cylinder of compressed nitrogen (N₂) has a volume of 60 L. If the cylinder gas pressure and temperature are 100 bar g and 20°C respectively, what mass of nitrogen is present in the cylinder? (Atmospheric pressure can be assumed to be 100 kPa.)

c)    If nitrogen is to be used to nitrogenate ales and stouts, determine a conversion factor to convert volumes of nitrogen per volume of beer (at STP) to g/L.

2.   ***

A mixed gas stream (70% by volume of nitrogen and 30% by volume of carbon dioxide) is used to pressurise and dispense a keg of beer. If the beer temperature was 5°C, what gas pressure would you choose to yield an equilibrium dissolved CO₂ concentration of 1.5 v/v (at STP)?

The Henry’s law constant for N₂ and CO₂ in beer is 54,000 bar a/mol fr and 900 bar a/ mol fr respectively, both at 5°C. Assume that the molecular mass for beer is the same as for water and the beer density is 1,000 kg/m³.

3.   ***

a)    You want to carbonate a tank of water open to the atmosphere using either a lance or sintered stone at the base of the tank to dissolve CO₂. With reference to the equation below, which describes the rate of dissolution of CO₂, compare and contrast the performance of both technology options.

b)    If the tank could be operated with a back-pressure, what would be the impact on the performance of either technology?