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Calculating boiler horsepower requirements

Boiler

In some feedmills, steam is required for various cooking processes.  Our high shear dry extrusion generally does not require steam, although some processes do such as fish and pet food manufacturing.  A boiler is critical for operation in those instances, but how do you know what size to purchase?

Determine total steam requirements

The first step is to determine the total amount of steam required for all processes.  This seems simple enough, but it’s easy to omit pieces of equipment.  For example, it’s easy to remember that the extruder preconditioner requires steam, but it’s sometimes easy to forget that a dryer may need some as well.  Steam requirements will be listed in kilograms (or pounds) per hour.  Additionally, a pressure requirement will also be listed, either in bar or PSI.  As an example, our steam preconditioners require 220-250 kg/hr of steam at 125 psi of pressure.

For a dryer, consumption can be rated in BTUs/hour (typically, millions of BTUs/hour).  There are approximately 430.8 BTU/kg of steam (950 BTU/lb), so dividing total BTU requirements by the respective number will calculate the amount of steam required per hour.  This amount can then be added to the other requirements.  As an example, assume a dryer requires 1 million BTUs/hr to operate.  This will equate to 2,321 kg/hr of steam needed (1,000,000 ÷ 430.8).

Determine minimum required power

Once the total amount of steam is known, it is very simple to determine boiler power.  Simply divide the total amount of steam required by either 15.9 kg/boiler hp or 35 lbs/boiler hp (depending on units used).  This will calculate the minimum required power to supply the system.

Considerations

This calculation will only tell you the minimum requirements of power.  If you were to buy the boiler calculated, it would constantly be running to supply your system.  Because of this, you should oversize your boiler by a safety factor of 10-20%.  A boiler supplier will have a better understanding of what to recommend based on your requirements, but this is a good start when trying to size a boiler.