Commercial and Industrial Process Heating Methods

Electric heating element of special design

Many industrial processes involve the use of heat as a means of increasing the energy content of a process or material. The means used for producing and delivering process heat can be grouped into four general categories.

• Steam
• Fuel
• Electric
• Hybrid

The technologies rely upon conduction, convection, or radiative heat transfer mechanisms, solely or in combination, to deliver heat to a substance. In practice, lower temperature processes tend to use conduction or convection. Operations employing very high temperature rely primarily on radiative heat transfer. Let's look at each of the four heating methods.

STEAM

Steam based heating systems introduce steam to the process either directly by injection, or indirectly through a heat transfer device. Large quantities of latent heat from steam can be transferred efficiently at a constant temperature, useful for many process heating applications. Steam based systems are predominantly for applications requiring a heat source at or below about 400°F and when low-cost fuel or byproducts for use in generating the steam are accessible. Cogeneration systems (the generation of electric power and useful waste heat in a single process) often use steam as the means to produce electric power and provide heat for additional uses. While steam serves as the medium by which heat energy is moved and delivered to a process or other usage, the actual energy source for the boiler that produces the steam can be one of several fuels, or even electricity.

FUEL

Fuel based process heating systems, through combustion of solid, liquid, or gaseous fuels, produce heat that can be transferred directly or indirectly to a process. Hot combustion gases are either placed in direct contact with the material (direct heating via convection) or routed through tubes or panels that deliver radiant heat and keep combustion gases separate from the material (indirect heating). Examples of fuel-based process heating equipment include furnaces, ovens, red heaters, kilns, melters, and high-temperature generators. The boilers producing steam that was described in the previous section are also an example of a fuel based process heating application.

ELECTRIC

Electric process heating systems also transform materials through direct and indirect means. Electric current can be applied directly to suitable materials, with the electrical resistance of the target material causing it to heat as current flows. Alternatively, high-frequency energy can be inductively coupled to some materials, resulting in indirect heating. Electric based process heating systems are used for heating, drying, curing, melting, and forming. Examples of electrically based process heating technologies include electric arc furnace technology, infrared radiation, induction heating, radio frequency drying, laser heating, and microwave processing.

HYBRID

Hybrid process heating systems utilize a combination of process heating technologies based on different energy sources or heating principles, with a design goal of optimizing energy performance and overall thermal efficiency. For example, a hybrid steam boiler may combine a fuel based boiler with an electric boiler to take advantage of access to low off-peak electricity cost. In an example of a hybrid drying system, electromagnetic energy (e.g., microwave or radio frequency) may be combined with convective hot air to accelerate drying processes; selectively targeting moisture with the penetrating electromagnetic energy can improve the speed, efficiency, and product quality as compared to a drying process based solely on convection, which can be rate limited by the thermal conductivity of the material. Optimizing the heat transfer mechanisms in hybrid systems offers a significant opportunity to reduce energy consumption, increase speed and throughput, and improve product quality.

Many heating applications, depending on scale, available energy source, and other factors may be served using one or more of the means described here. Determining the best heating method and implementation is a key element to a successful project. M.S. Jacobs and Associates specialize in electric heating applications and facets of the industrial production of steam. Share your process and project challenges with them and combine your facilities and process knowledge and experience with their product application expertise to develop effective solutions.

Basics of Infrared Flame Detection

Triple IR flame detector
(courtesy if Sierra Monitor)

A flame detector is a specialized sensor used to detect and respond to the presence of a flame, and accordingly notify an operator, sound an alarm, close a fuel supply valve, shut down a pump, and turn on a fire suppression system. 

Flame detectors are fast acting and accurate, much more so than smoke or heat detectors because of the technology they employ. Some flame detectors can detect fires up to 215 feet away and be accurate enough to detect a 1 sq. foot gasoline pan at 215 feet in less than 5 seconds. 

One popular type of flame detection technology used is measuring infrared (IR) light coming from a source. This type of sensor monitors the infrared light spectrum for very specific patterns given off by hot gases. These hot gases are sensed by a specialized fire-fighting thermal imaging (thermographic) camera. 

One method of determining if a fire exists is by looking for the infrared peak of hot carbon dioxide (approximately 4.4 micrometers). Response times of a typical IR detector is 3–5 seconds. 

There is the possibility, however, of false alarms caused by background thermal radiation and other hot surfaces in the area. Another potential concern is with the formation of condensate on the flame detector's lens, which can greatly reduce its accuracy. Direct exposure to sunlight for these types of detectors can also be problematic. 

An approach to overcome these issues is with dual or triple IR sensors, which compare the threshold signal in two or three infrared ranges. Often one sensor looks at the 4.4 micrometer carbon dioxide (CO2) emission, while the other sensors looks at additional reference frequencies. Modern flame detector design allow users to select different sensitivity levels to ensure no other detectors cross-over detection zones. 

Additional important features to be considered are heated windows to eliminate condensation and icing, HART and Modbus capabilities for digital communications, low excitation power, and compact design. 

When selecting a flame detector for any application, it is important to make sure it is approved and certified for that specific use. Check for third party agency approval including FM, ATEX, IECEx, TUV, and CSA. These approvals and certifications assure the highest quality of products and performance.

Finally, the proper application of flame detectors is critical in many applications for the safety and protection of property and personnel. Therefore, it is always suggested that your application be discussed with a qualified application engineer.