The Economics of Direct Steam Injection

Sludge heating, to maintain temperature in anaerobic digesters, is typically performed by utilizing indirect heat methods, specifically heat exchangers that utilize hot water as a media source. Increasingly, direct steam heating is being explored as an alternative means of maintaining digester temperature. The costs of installing, operating and maintaining the various heating designs is outlined. In addition, the effect on the heaters relating to fouling and buildup were examined. It is shown that direct steam heating has advantages in the area of size, cleanliness and reduced maintenance requirements. Indirect heaters are the heating method of choice when a treatment plant does not have steam available, or deems the addition of a boiler beyond the needs of the plant.