Chapter One – What is an Industrial Furnace?
A furnace is a direct fired device used to provide heat for industrial processes that require heat in excess of 400° C (752° F). Any industrial application that relies on heat to create a reaction or heat materials for production uses an Industrial Furnace. Of the many types of equipment and machines used for production and processing, furnaces are the most reliable. Through the combustion of fuels and gases, raw materials and products are heated by direct or indirect contact.
The construction of a furnace includes heat exchangers, air and flue blowers, fuel control, burners, pilot or ignition device, control circuitry, and a thermostat. Though these are typical components, furnace designs vary to meet the need of an application or function. Furnaces differ mainly by the types of fuel and how combustion is initiated. Regardless of the differences of operation, all furnaces serve the primary purpose of providing heat.
Chapter Two – How Industrial Furnaces Work
Different furnaces function differently and burn different types of fuel. For many years, furnaces were powered by wood or coal; this required constant refueling for continuous heat. Modern furnaces have moved on to fuels that are supplied automatically.
How a Furnace Works
The critical element in the operation of an efficient and economical furnace is its fuel. Though coal and wood were used for many years, they polluted the environment, required constant feeding, and made it difficult to keep a steady temperature. Modern furnaces have fuel fed directly into the furnace at a controlled rate or operate using electricity to maintain even temperature.
Fuel fired furnaces are the most widely used. The nature of the fuel determines the design of the furnace but is not relevant to modern furnaces. As with any type of heat operated device, the supply of oxygen is important to the furnace‘s efficient operation.
Electric furnaces use induction or resistance heating. The efficiency of electric furnaces, and the fact that they do not release flue gases makes them environmentally ideal. Unfortunately, the operation of an electric furnace is expensive.
Resistance heating is the most expensive type of electric furnace, and it uses a circulating fan to maintain temperature uniformity. Resistors are made of various types of materials or the load to be heated may serve as a resistor.
With induction heating, electricity passes through a coil that surrounds the load. The frequency of the current is determined by the type of load. The coils are water cooled to prevent them from overheating. Induction heating is used for heating a localized area of a workpiece.
Furnace Burner Types
The fuel is supplied to the burners where, predictably, it is burnt. Most Experimental Furnaces have more than one burner that can be mounted in different sections of the furnace depending on its design. The burner has an oxidizer to change the chemical energy into thermal energy. The type of fuel used in a furnace is determined by the burners. They mix the fuel and air and ignite them. Burners must be stable, cost effective, reliable, and energy efficient, and they must have proper flame dimensions.
The components of the burner include the nozzle, mixing tube, downstream connection, and air fuel ratio control. The fuel and air are mixed to produce the best quality flame; forced air is required for the mixing process.