TABLE OF CONTENTS

The system has now been in operation for a couple of years and the customer said at a
presentation in Norway that the company was a little bit sceptic in the beginning but
now that it has proven to work he would not hesitate to take the journey again.
Some facts about cascade vs. 2-stage ammonia
The cascade system is designed for Te/Tc = -47,5/42˚C. Tc CO 2
-7˚C and -12˚C for the high
stage compressors
difference of 5 K between the room temperature and the evaporating CO 2
.
The required swept volume is only about 10% of the comparable two-stage ammonia
system on the low stage.
The return lines are remarkably smaller. The liquid lines are bigger but it makes only a
negligible difference.
The customer Nordlaks AS are very happy with the performance of the system.
We have simulated a two-stage ammonia system for the same conditions with an open
intercooler with a temperature at -12˚C
The results are as follows:
• 11 times larger swept volume on the low stage ammonia system
• 8% higher energy consumption
If we then assume the -47˚C in the IQF freezers and 100 meter return line, 10 bends and
a circulation ratio of 2 and a pressure loss of 0,5 K we get:
• Two stage ammonia DN 300
• Cascade system DN 150
Since the heat capacity of ammonia is higher than CO 2
we get following liquid lines:
• Two stage ammonia DN 40
• Cascade system DN 65
65
Another advantage of the cascade system is that the ammonia high stage now only
operates at pressures well above the ambient pressure and therefore there is no need
for air purger and no water enters the system.
Results
The experience with the plant shows that this concept is very reliable and high
performing. When the IQF freezers are in operation there is only a temperature