Common Industrial and Commercial Process Heating Methods

Many industrial processes utilize heat as an energy input

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, soley 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. Alliance Technical Sales specializes 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.

Automatic pH Sensor Cleaning and Calibration Saves Time and Cost

Automated pH sensor cleaning and calibration
with EasyClean 400
Courtesy Mettler Toledo

Measurement of pH is a common analytical operation in liquid processing. Whether chemical or wastewater operations, pH measurement provides useful information about process condition.

The sensors used for measuring pH can require care and maintenance, in the form of cleaning and calibration, to maintain peak performance. Traditionally, these operations have been performed manually by trained technicians. The task, though, is a good candidate for automation to provide cost savings and uniformity for sensor cleaning and calibration.

Mettler Toledo manufacturers four different automated cleaning and calibration systems for their analytical sensors. The offering ranges from simple water rinsing or compressed air cleaning to prevent build up to fully automated cleaning and calibration systems requiring little in the way of human intervention.

The technical data sheet below provides details about the fully automated system. Share your analytical measurement challenges and requirements with application specialists, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Automated pH Sensor Cleaning and Calibration from Alliance Technical Sales, Inc.

Mounting Adaptions Expand Applications for Tunable Diode Laser Gas Analyzers

Tunable diode laser gas analyzer with retroflector
requires no special aiming and puts the source
and detector on the same side of the pipe.
Courtesy Mettler Toledo

Gas analysis is an important part of production, quality control, safety, efficiency, or legal compliance in many industrial operations. Reliable and accurate information about the concentration of certain gas components enables operators to properly control processes and regulate output.

A tunable diode laser gas analyzer (TDL) is essentially an application of absorption spectroscopy. The laser light source can be adjusted to the absorption wavelength of the target gas molecule. The light passes through the gas and is collected and measured by a detector. Based upon known properties of the target gas molecule, its concentration can be determined. The technology provides suitable accuracy, delivers real time measurement data, and in many cases requires little maintenance. Of course, applying technology in the field can present unique site specific challenges.

Dust, other particulates, distance related to pipe diameter, pressure, and temperature can impact the instruments ability to deliver reliable measurements. Additionally, installations using opposing emitters and detectors in a "cross pipe" configuration can have difficulty in achieving and maintaining proper alignment. Solutions are at hand for many of these previously intractable applications. Integrating the light source and detector into a single unit with lighter weight and smaller size enables a less complicated installation scenario. There are other adaptions made to the instrument that overcome many of the commonly encountered difficulties when installing a TDL into an existing or new system.

Mettler Toledo, innovator in the TDL field, authored a white paper illustrating some of the installation challenges and how they can be successfully and easily overcome using a properly adapted tunable diode laser gas analyzer. The paper is included below, taking only a few minutes to read. It's well worth the time spent.

Share your process analytical requirements and challenges with specialists in process analytical solutions, combining your own process knowledge and experience with their product application expertise to reach a successful outcome.

Folded Path Tunable Diode Laser Gas Analyzers from Alliance Technical Sales, Inc.

Retractable Sensor Housing for Analytical Sensors

The retractable sensor housings are available in several configurations

Process analytical sensors generally require some "care and feeding" to maintain specified performance levels. This maintenance can require removal of the sensor from the process in which it is inserted. Clearly, it is seldom advantageous to shut down a process for maintenance when it could otherwise remain in operation. The challenge - how to service the pH, redox, conductivity, or dissolved oxygen sensors without process interruption.

Mettler Toledo, under their Ingold brand of process analytic products, provides a solution in the form of a retractable sensor housing. Models accommodate sensors for pH, redox, conductivity, and dissolved oxygen. The housings are designed to enable safe retraction of the sensor from the process, with in place sensor cleaning or further maintenance operations made simple with the process remaining in operation.

The document below provides additional detail. Share your process analytical challenges with an application expert, combining your own process experience and knowledge with their product application expertise to develop effective solutions.

Retractable Sensor Housings for Analytical Sensors from Alliance Technical Sales, Inc.

Activated Carbon Adsorber as Backup for Thermal Oxidizer

Activated carbon backup for thermal oxidizer
Courtesy Process Combustion Corporation

Volatile organic compounds (VOC) are one class of air pollutants with emission limits described in law. Industrial plants that produce VOC as part of their processing must take steps for the removal or destruction of the pollutant prior to discharge in the atmosphere.

Thermal oxidization systems are routinely employed to remove volatile organic compounds from industrial emission air streams. The systems deliver some operational advantages.

• Ease of operation
• Flexibility to match process changes
• Continuous operation without need to change disposables
• No byproducts requiring further handling or disposal
• Simple process with small number of components
• Broad application range for VOC

Operation of the thermal oxidation system is essential to maintaining continuance of plant operations, since the oxidizer continually processes plant output. The potential costs associated with a work stoppage due to malfunction or maintenance of the thermal oxidation system may make the installation of a backup VOC processor a prudent business decision.

Activated carbon is a well recognized material for the capture of VOC. Along with the addition of other sorbents, the scavenging profile of the fixed adsorbent bed can be tailored to specific process demands. The activated carbon processor is essentially a filtration unit that traps the target compounds as discharged process air flows through the unit. It is a simple effective system with known performance parameters

An activated carbon adsorber will serve as an effective backup unit for a thermal oxidizer. The limitations of the activated carbon unit are its rated flow rate for which VOC removal is defined, as well as the fixed holding capacity of the adsorbent itself. Once spent, the adsorbent must be regenerated or replaced. In selecting a properly sized backup VOC adsorber, these factors should be taken into account.

Share your VOC pollution control challenges with specialists in the field. The combination of your own process knowledge and experience with their product application expertise will produce effective solutions.

Magnetostrictive Level Transmitter

Magnetostrictive level transmitter, showing electronics (head)
mounting plate, sensing tube, and float.
Courtesy Jogler

The numerous level control technologies, methods, and instruments all have an application range or niche where they provide a feature set and performance advantageous to other measurement means. The particular set of attributes that can push one instrument over the top in the selection process is specific to each user and application.

Magnetostrictive level transmitters provide a continuous signal indicating liquid level in a vessel. They should not be confused with what are called magnetic level gauges, an instrument that locally provides a visual indication of liquid level.

Magnetostrictive level measurement employs a precise measuring of the transit time for an electric pulse travelling on a wire extending down an enclosed tube oriented vertically in the subject media. A magnetized float on the exterior of the tube moves with the liquid surface. The float’s magnetic field interacts with a magnetic field produced along the wire to generate a return signal to the transmitter head. Processing the time from emission to return provides a measure of distance to the liquid surface.

These level transmitters offer good accuracy and ease of installation and maintenance. They are best applied with relatively clean fluids. Media that will impede the free movement of the float along the sensing tube should be avoided. Magnetostrictive level instruments are often employed alongside, or integrated with, a magnetic level gauge. The magnetic gauge provides a local indication of tank level, while the magnetostrictive transmitter delivers a level signal to monitoring and control equipment.

Share your level measurement requirements and challenges with a process measurement specialist, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Magnetostrictive Level Transmitter for Industrial Process Measurement from Alliance Technical Sales, Inc.

Keep Condensation at Bay in Your Facility

Condensation accumulates water on
the exterior of this cold glass

Condensation, the accumulation of liquid water on a surface through contact with humid air, can be harmless in some settings, an undesirable or even damaging occurrence in others. In situations where condensation is undesirable, taking steps to prevent the conditions that preclude its formation are relatively simple and deliver a good payback.

What is condensation? In general usage, the term refers to the formation of liquid water droplets that occurs when humid air contacts a cooler surface. It is the liquid moisture that accumulates on the exterior of a glass containing a cold drink. Properly, the term condensation names the process of a vapor changing to a liquid. It is the opposite of evaporation. Condensate (note the different word form) is the liquid accumulated through the condensation process. This article is limited to condensate that forms when atmospheric air contacts a cold surface, so the general usage term condensation will be used.

Where can it happen? Water vapor is contained in air when it has sufficient energy to remain in the vaporous state. Remove some of that heat energy and a calculable quantity of the water vapor will no longer be supported, condensing into liquid water. The temperature at which any given quantity of air will start to shed some of its water vapor content is primarily determined by the concentration of water vapor in the air. A higher water vapor content will result in a higher temperature at which the water vapor will begin to condense. In everyday terms, higher relative humidity leads to a higher temperature at which condensation takes place.

What is the range of impact? Condensation appears to us as water that almost magically manifests on a surface. It seems to come right out of thin air.....because that is where it came from. It can form locally or broadly throughout an area. The potential impact of condensation arises from the fact that it is liquid water. Anything that will be damaged by water will be adversely impacted by condensate formation on its surface. This includes rust and corrosion of metals, spotting on material or object surfaces, the promotion of mold and mildew, and a wide range of other undesirable effects. Accumulated condensate on overhead objects or surfaces can eventually drip onto equipment, materials, and work areas situated below. Puddles of water on a floor can also create a hazard.

Prevention is the best, maybe the only cure.

How to prevent condensate formation?

• Ventilation - If there is a source of moisture in a space that is elevating the humidity, continually diluting the space moisture content by introducing fresh air with a lower moisture content may be an effective prevention method. Ventilation relies on the fresh air conditions always being sufficient for moisture reduction without creating some other adverse impact on the space. For example, ventilating with outdoor air may be effective throughout only part of the year. Without a reliable source of ventilation air with known conditions, this method may not always deliver the desired results. Ventilation is an active method that requires energy to move the ventilation air. Additional energy may be required to adjust the temperature or moisture conditions of the ventilation air, as well.
• Insulation - The surfaces where condensation occurs can be isolated from the moist air by insulating materials. This is common with HVAC ductwork and process piping. If done properly, this method is effective. The goal is to create a new surface that does not exhibit the cooler temperatures of the isolated surface. The thickness and reduced thermal conductivity of the insulation material will achieve this. There is also a vapor barrier on the exterior of the insulation that prevents entry of moisture laden air into the insulation material.  It is important the the vapor barrier installed as part of the insulating process remain intact and undamaged. Otherwise, water vapor will enter the insulating material and condense, with the potential for a localized failure of the insulating scheme. Insulation is a passive measure that requires no added energy to remain effective.
• Dehumidification - Outright reduction of moisture contained in the air of an enclosed space will reduce the temperature at which water vapor condenses. Dehumidification machinery is available in a wide range of sizes and performance levels to suit almost any scenario. Though it requires energy to operate, the machinery is generally simple and operates automatically to maintain a space condition that will not support condensation.
• Heating - Some cases can be most effectively treated using the application of a small amount of heat to the surface where condensation forms. This active method can be very effective when the need is localized. Also, surface heaters can be fabricated that will fit where insulation will not, and the heating assemblies may be more resistant to impact and damage than insulating materials. Proper control of heating equipment will minimize energy consumption.

Implementing an effective plan to combat condensation involves the identification of the conditions that promote its formation in your own facility. Selecting the best prevention plan calls for consideration of costs and reliability of various schemes. Active methods, such as heating or dehumidification, have some capacity for adjustment if conditions change over time. Insulation plans should have sufficient headroom or safety factor in their design to accommodate unforeseen conditions.