Industrial furnaces are commonly used to heat materials during production. In these direct heating devices, heat is generated through the combustion of fuels or gases in the air or by converting electrical energy.
Industrial furnace designs vary according to the method of generating heat, mode of heat transfer, charging materials, function, and other elements. These furnaces benefit temperature control and uniformity during heat treatments at temperatures typically exceeding 400° C (752° F) 1.
The products of combustion in furnaces are discharged as flue gas. Flue gas emissions are a significant concern regulated by standards such as ISO 13577 2. Furnace gas detection provides continuous monitoring of gas concentration levels. Thus, furnace gas detection is an essential consideration in the construction of industrial furnaces.
Industrial furnaces provide heat during annealing, tempering, melting, carburizing, and other processes. Their construction includes burners, heat exchangers, ignition devices, flue blowers, control circuitry, etc. Differences in manufacturing requirements govern variations in furnace design.
Fuel-fired furnaces are more commonly used even though electric furnaces — which heat by dissipating electrical energy — provide better temperature control while avoiding the release of flue gases. Fuel-fired furnaces are more common because of the higher cost of operating electric furnaces.
Fuel is supplied to burners mounted in various locations across the furnace in fuel-fired furnaces. These burners are fitted with oxidizers that convert chemical energy into heat. The type of fuel supplied depends on the type of burner used. Heat transfer is performed through convection (gas flows), radiation (through the burners), or convection (through a solid surface).
A vertical pipe or chimney (flue) discharges heat and gases generated by the heating process. These gases include carbon dioxide, nitrogen, oxygen, and water vapor. It is important to ensure that these gases do not exceed critical safety limits set by environmental and health regulations. Therefore, furnace gas detection is an essential consideration in industrial furnace design.
In the drive towards decarbonization, regulations such as the New Source Performance Standards and ISO 13577 make provisions for the construction, size and function of industrial furnaces 2, 3. Aside from environmental concerns, these regulations also make provisions for dangerous or toxic gases distributed within industrial installations through ventilation systems.
Furnace gas detection systems are installed in industrial facilities to provide continuous monitoring of gas levels. These furnace gas detection systems provide early detection of leaks that prevent the risks associated with toxic or explosive gases or depleted oxygen levels.
Furnace gas detection monitors three forms of hazards: explosive gases, toxic gases, and oxygen depletion.
Explosive gases: Many gases are flammable within a concentration range defined by the lower explosive limit (LEL) and upper explosive limit (UEL). Outside of this range, combustion reactions are not sustainable. Furnace gas detection systems monitor these levels to ensure safety.
Furnace gas detection systems are equipped with catalytic or infrared sensors to monitor concentrations of explosive gases. These sensors are calibrated to the gases with the lowest LEL (typically methane) as part of a risk assessment. Sensors fitted to furnace gas detection systems are set to alarm at 50% of the LEL. Since methane has an LEL at 5% concentration in air, alarms are set at a 2.5% concentration 4.
Toxic gases: Carbon monoxide is an odorless, poisonous gas produced by the incomplete combustion of fossil fuels. Because it is odorless, colorless, and tasteless, it poses particular risks to workers and often proves fatal. Furnace gas detection systems make provisions for detecting carbon monoxide in high-risk areas. They are set to alarm before dangerous concentration levels are reached.
Oxygen depletion: There is an elevated risk of oxygen depletion for workers in areas with high concentrations of gases in the ambient air. Even non-explosive or non-toxic gases can significantly affect oxygen levels in concentrations high enough. Oxygen sensors in furnace gas detection systems typically alarm at 0.1% oxygen concentrations in air.
In addition to installing furnace gas detection systems, it is recommended that industrial facilities perform a risk assessment survey under the guidance of a qualified engineer.
Deltech rotary tube furnaces are resistance heated with silicon carbide or molydisilicide for sustained operations at up to 1,700oC. Treatments can be performed in air, oxygen, or inert atmospheres with customised rotation speeds. Rotary tube furnaces are ideal for procedures requiring continuous loose material throughput. Furnace gas detection systems ensure round-the-clock monitoring of gas concentrations for safe operation.