The air around us contain moisture which get into the compressor and the pressured air. For large volumes of compressed air, this means a lot of moisture. Without precautions, after approximately 1 hour the abrasive in the blastpot be moist and reduce the result.
To blast a full day without any problems air drying is recommend.
An aftercooler is a good mobile solution. In some (diesel) compressors an aftercooler is build in. Loose aftercoolers are also available electric and air powered. The compressed air passes through a radiator in which a propeller provides cooling for the compressed air. Warm air from the compressor is cooled so drops formed. The separator in the aftercooler removed these drops and the air is about 95% dry. More than enough to blast the whole day without problems.
An air dryer works like a freezer and remove 100% moisture from the compressed air. An air dryer is not suitable for mobile use. The components and the liquid in the airdryer are vulnerable during transport.