Choosing the Right Furnace
Following are some considerations to keep in mind when choosing a furnace or kiln using an electric heating system:
- Resist the temptation to purchase a system with much more capability than you can realistically expect to use. It is prudent to have margins of safety with respect to processing capacity (furnace volume and maximum thermal input) and maximum process temperature. However, over-specification of these parameters not only wastes capital but can also result in higher operation and maintenance costs. For example, a product processed a periodic kiln that is under-utilized with respect to processing capacity will have a higher specific (per unit mass) energy cost than the same product produced in a kiln with near-optimum capacity because of the greater amount of energy required to heat the refractory of the over-sized kiln. From the standpoint of maintenance costs, operating high-temperature heating elements at certain critical lower temperatures can actually reduce heating element life.
- When comparing the investment cost of furnaces or kilns using different types of electric heating systems, be sure to consider the total cost of the heating system. This cost includes not only the cost of the elements themselves, but also the cost of the installation accessories, the power control equipment, and the electrical wiring required. In many cases, site-specific considerations will determine the lowest-cost choice (all other things being equal).
- With respect to the choice of electric heating element type, it is important to develop realistic estimates of relative life-cycle costs. Heating element vendors can normally provide estimates of the range of element life given accurate information on the firing cycle, element watt loading (watts per unit of radiating surface area) and process atmosphere. This information can be used to estimate the maximum/minimum life-cycle cost of the element itself on a “cost per operating hour” basis. The other major factor is the material and labor cost for element replacement, which depends on the type of element and the specific furnace design. This can also be estimated and reduced to a “cost per operating hour” based on element replacement frequency. The sum of these two costs represents an estimate of the life-cycle cost of the element, which can be used to compare element types and/or heating system designs.