ARTIKEL DIRECT INDIRECT .

ARTIKEL DIRECT INDIRECT .

Direct or Indirect Cooling. Which Technology is More Efficient for Bulk Solids Cooling?

 

Bulk solids cooling is a common step in many chemical processes. It generally occurs near the end of the processing sequence when powders or bulk solids must be cooled prior to storage or packaging to allow for safe handling and storage.

Most engineers would agree that direct cooling appears to be more efficient than indirect cooling, and from a purely technical standpoint, it is. Cooling a bulk solid by passing cool air through it brings the cooling medium and the product into direct contact. While this would appear to be the most efficient approach, when it comes to bulk solids cooling, a counter-intuitive approach is required to maximize efficiency.

The most common approach to bulk solids cooling is to use air in direct contact with the bulk solid material. With direct cooling, ambient air is taken in using large fans and, in most climates, the air must be chilled before being blown across the product using large horsepower fans. It is then discharged through an emissions stack. Both the chilling process and the circulating fans have high energy requirements.

The alternative is to cool bulk solids indirectly using water. With indirect cooling technology, chilled water is pumped through a vertical bank of hollow stainless steel plates while the bulk solid passes between the plates at a rate sufficient to achieve the required cooling. The water circulates counter-current to the product flow for higher thermal efficiency. Often a plant’s existing cooling towers are sufficient to provide the necessary water and a low horsepower pump is the only source of energy consumption.