Thermics of furnaces

Furnaces and ovens are found in a wide range of industrial sectors, but mainly in the metals, materials and ceramics industries.

These include furnaces for melting and heat-treating metals, ovens and tunnels for cooking food products, dryers for agricultural products, cement rotary kilns and glass melting furnaces.

Furnaces are generally used for the treatment of metals and materials at temperatures in excess of around 300°C; the term oven is reserved for the treatment of organic and inorganic products at temperatures below 300°C and, in particular, for steam treatments. Other terms may be used, such as enclosure, line, tank, bath, reactor, etc., but the thermal study of such equipment is similar to that of furnaces (the term most commonly used in this dossier).

Batch furnaces are also known as intermittent furnaces or batch furnaces, while continuous furnaces are known as tunnel furnaces or continuous furnaces.

The energy used can be electricity, heavy fuel oil (HFO), domestic fuel oil (DFO), natural gas or liquefied petroleum gas (LPG); burners are generally positioned on the side walls for heat treatment and on the roof for melting and maintaining the temperature of the liquid metal. Heating can also be provided by infrared emitters, electromagnetic induction or microwaves.

Simple calculation formulas to determine the efficiency and specific consumption of a furnace are generally sufficient for pre-sizing or to establish an energy operating cost; for greater calculation accuracy, it may be useful to carry out modeling using appropriate software. If the problem posed is difficult (new furnace design, delicate product to be processed, precise temperature requirements, etc.), this modeling is necessary to demonstrate the feasibility of a project and to optimize operating parameters at plant start-up.

When making an investment to install a new furnace or to modify an existing one, it is necessary to calculate heat exchanges and define functional specifications.

Irrespective of the quality of the equipment, the operating conditions of the oven or kiln will influence its performance.