Packaged Heating Systems Provide Process Heating Benefits

Consider packaged hating systems for your next process heating project.

According to Process Heating:

We are a species whose existence is dependent on the warmth and energy from a distant ball of fire. Yet, many people are unaware of how the application of one of the universe’s most basic properties — heat — influences nearly every facet of their lives. The industrial process heating market is broad and touches almost everything around us. To illustrate, consider just a few of the areas of daily life made possible by process heating:

• The drinking glass in front of you.
• The yogurt you packed for lunch and the Frosted Flakes you ate for breakfast.
• The powder coating or paint finishing on your file cabinets.
• Your desk chair.
• The circuit boards inside your computer and machines.
• The beer you plan to crack open when you get home.

Beyond products for your personal use, consider how daily life would be different without:

• Heat-treated parts for aircraft, cars and other equipment.
• The raw metals that go into your own products.
• Biomedical joint replacements.
• Chemical dipping tanks.
• Forges and castings.
• The making of hot air for drying and curing of all sorts of items in our lives.

Suffice it to say, mastery of the application of process heat (temperature and energy) to the product is both art and science. It requires engineering knowledge, experience and core competence. Working with an experienced thermal system equipment provider — sometimes called a combustion house — can help optimize your system.

The three main types of heat transfer utilized in industrial process heating are:

• Convection, where hot air moves across the product while carrying heat.
• Induction or conduction, where a hot liquid or solid, while in contact with the product, effects heat transfer.
• Radiation, where energy transfer occurs from photons or electromagnetic waves, much like the sun.

It is the application specifics and the desired end results that determine which type of heat is needed, and how best to apply it. It is certainly not the case in process heating that one approach is best for all uses.

Given the breadth of applications, the precise temperature ranges required for specific results and the often proprietary production processes, it may make sense to purchase industrial process heating equipment in turnkey or packaged systems from a company that specializes in the application of process heat. Doing so can help ensure that the combustion equipment, fuel trains and controls are integrated and designed to work together. What form the packaged heating system takes is generally dependent on the specific application.

One of the first choices an end-user must make revolves around the desired fuel source. In regions with access to low cost electricity, an electrically powered oven or heater might be the most economical choice. Other fuel sources for larger production lines include natural gas, fuel oil or propane.

Heating Systems Options

With a fuel source selected, the most important question must be asked: What type of approach is suited for the specific application? Keep in mind, the process may require a custom approach that may not exist as a machine or process already. This situation arises when the end-user has a unique process or wants to approach the process differently. This is where a system designer or “combustion house” can parley their greater experience in designing heating systems for myriad applications to take the best advantage of potential solutions.

Ovens and Furnaces. Although many use the terms “oven” and “furnace” interchangeably, the industry tends to refer to systems designed to run at temperatures below 1000°F (538°C) as ovens and those designed to run at temperatures from 1000 to 3000°F (538 to 1649°C) as furnaces.

An industrial oven is not just for baking products. Ovens are used for curing or setting myriad fabricated parts. For instance, an industrial heat-treat furnace with an operating temperature approaching 2300°F (1260°C) might be used to manufacture heavy equipment for the Department of Defense. Similarly, a lower temperature box-style oven unit can be designed to melt the wax out of investment castings, or a catalytic infrared oven can be used in the finishing industry to cure paint, powder or other coatings applied to the parts. Regardless, each process requires reliable packaged heating systems to ensure quality, efficiency and profitability.

Whether an oven or furnace is used, the goal is always the same: the transfer of heat from its source to the product precisely in the manner to satisfy the application. The mechanism of that actual transfer, and its rate of transfer, vary based on the products, ambient conditions and the desired results.

Heated Dip Tanks. With this approach to process heating, large tanks are fitted with a serpentine tube that is covered with liquid for the process fluid to be heated. The burner fitted to the tube commonly is referred to as an immersion-tube-fired burner. The combustion takes place in the tube immersed in the tank. The hot flue gases travel down the tube, which is designed for maximum surface area, to transfer the heat of combustion in the flue gas to the liquid surrounding the tube.

One common use for such a heated dip tank is a chemical bath for immersing parts. This approach is used in the chroming and plating industries.

Heated dip tanks also are used for molten salt baths, which are used in the nitriding process. This is done for case hardening, where the carbon and nitrogen from the molten salt diffuse into the steel fabrication being hardened. The temperature of molten salt approaches 1500°F (816°C). Because the salt bath achieves heat transfer via conduction, it is much more efficient than the convection heating used in a furnace. Of course, any process with such a big upside can present a similar downside. In this case, environmental and health concerns exist regarding the caustic nature of salt baths and the dangers surrounding such a high temperature molten liquid. Another pitfall is what occurs if heater failure or process upset causes the molten salt bath to cool. When the salt cools, a solid block of salt is often left behind. These solid salts are difficult to remove and take some time to recover.

Heater Boxes. Heater boxes are appropriate for applications where a user needs to raise the temperature of an airstream or gaseous process stream from a relatively low temperature — for instance, from room temperature to 700°F (371°C) — to be used as a source of energy for numerous types of applications. This approach is simply convection heat.

In such applications, the air-heat-style burner acts as a duct burner and combusts the amount of fuel necessary for attaining the temperature setpoint dictated by the process. As the process stream changes in mass flow, so does the fuel needed to attain the desired results. Typically, the combustion controls, which safely control the amount of fuel and air being combusted, will be close looped to track a thermocouple mounted in the ducting downstream of the burner. Hot air produced by such a system could be used to dry products, bake food items or set ink on high speed printing presses, for instance.

Rotary Hearths. This approach of process heat is most utilized in the steel- and metal-forming industries. During the process of making steel, dirty, dusty debris takes over the workspace. Hidden in the dust, dirt and debris can be ore — precious metals that can be recycled. It is often contaminated with zinc, however, which cannot be recycled and is not conducive to the steel-making process.

The rotary hearth is used to remove the zinc from the dust, allowing direct-reduced iron ore to be captured and recycled into steel. The separated zinc then can go through its own processes — recycled from crude zinc oxide at processing plants — to generate refined zinc.

Calibration, Precise Control and Safety

It has been said before but bears repeating: Mastery of the application of process heat is both art and science. This holds especially true when it comes to the design of the packaged heating system. Certain processes may require precise flame shaping or flame treating of parts, where the product must be exposed at a specific temperature — often within a tight temperature window — for a specific period of time.

In addition, prior to commissioning — and periodically thereafter, depending on the industry or part being produced — a packaged heating system must be calibrated to ensure the temperatures being reported by the human-machine interface (HMI) are true and accurate. Various certifying bodies exist within the United States and internationally to oversee these calibration processes, including the National Institute of Standards and Technology (NIST).

Taking a closer look at the typical components of a packaged heating system for the industrial process market, you can generally divide them into two categories: heat and safety. Components utilized to deliver heat to the product include burners, heaters, elements, ductwork, fuel trains feeding the burner, reflective sheet metal for plenums and hoods, and refractory and insulating materials to hold heat and allow the equipment to run in a more efficient manner. On the safety side, components include flame-safeguard systems, emergency shutoff valves, redundant automatic shutoff valving systems and flame-proving systems such as ultraviolet and infrared scanners and flame rods. All of these are used to “prove” a flame continues to exist.

One of the most dangerous conditions in a process heat application is the unknown or unexpected flow of unburnt fuel into a confined space — room or machine — wherein one spark can cause a devastating explosion. In order to avoid this, flame safeguards constantly check to make sure the burner or heater is still producing a flame and that all safety interlocks are in a proper state. This includes things like proper fuel pressure and proof of airflow. Flame safeguards also check the system is operating below the maximum high limit temperature. Ultimately, the most critical aspect of any process heating system is a properly operating and well-maintained flame-safety system.

An advantage of packaged heating systems for industrial process heating is customization. Design engineers can work with end-users to create a system that custom fits the application and needs. The plug-and-play method of a turnkey system’s installation often causes fewer headaches on-site. In addition, it may be cost effective compared to “field creating” a solution. To install a packaged heating system, in most cases, it is necessary only to connect the equipment as designed, power it up, connect its fuel source and commission the system. With a little help from a trained combustion professional, you are up and running, producing products.

When considering whether a custom-built packaged heating system is worth it, ROI calculations should be used to determine payback. The savings may be substantial.

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