Lesson 9 - Gases SAQ

1.         * Differentiate between the following:

a) Oil-free and lubricated compressors

b) Single-stage and double-stage compressors

c) m³/s At NTP and m³/s at STP

d) Single-acting and double-acting pistons

2.         ** a) What are the relative advantages and disadvantages of screw compressors versus reciprocating compressors?

b) Would you expect to find more reciprocating compressors in a bigger or smaller brewery? Explain your answer.

3.         ** a) What does it mean when an air requirement is specified as class 0.1.0?

b) How important is the compressed air moisture specification for brewing?

c) You have an oil-free compressor in your brewery. Your manager argues that there should be no need to remove oil through filters. What would your reply be?

4.         ** a) How does a Roots blower differ from other positive displacement compressors?

b) What are the advantages of a Roots blower?

c) Where would you use a Roots blower and why?

5.         ** Nitrogen can be supplied as a gas in pressurised containers. If you only need the nitrogen as gas, why do you think most users still use liquid nitrogen? (Hint – Most nitrogen gas canisters are at 150 bar gauge pressure). Assume that both liquid and gas cylinders have a volume of 100 L. Nitrogen has an expansion ratio of 694.

6.         ** a) What are the principal components in a typical bulk nitrogen storage and supply system? Briefly describe their function.

b) What pressure controls would you find on a typical cryogenic tank, and why are these required?

c) Your manager has complained that the vaporiser on your atmospheric nitrogen vaporiser is always iced up. What is your response?