The Primary gas cooler has three compartments. There is a shell and tube heat exchanger where the service water is exchanged with the CO gas in the two crown zones and with chilling cold water in the bottom zone. IN all zones the tubes are inclined at 15 degree celcius, horizontal. The purpose of this is to provide easy drainage to any naphthalene condensate. However, the main purpose of PGC is to cool the gas from 90°c to 30°c.