Many industrial applications operate at elevated temperatures to ensure that the materials within the pipes are viscous enough to move efficiently throughout the system. These elevated operating temperatures typically range from 150 to 1200°F (65 to 649°C), though there are some applications that can reach even more extreme temperatures. High temperature systems present a host of challenges for system designers that can be difficult to address if not considered during the design phase. The most significant challenge among these is minimizing heat loss.
Minimizing heat loss is critical to high temperature industrial operations for several reasons:
- To optimize process operations.
- To reduce heating cost.
- To protect personnel.
- To protect operations and assets.
The primary reason system designers must limit or minimize heat loss is to maintain process control. Process control allows industrial facilities to run their processes and applications at optimized temperatures. Many industrial applications are fine tuned to operate at specific temperatures intended to ensure that the materials within the pipes are viscous enough to travel freely. Process control accounts for controlling these temperatures to ensure maximum efficiency at the industrial facility. Naturally, heat loss deteriorates process control.
Heat loss can lead to poor efficiency, resulting in costly energy bills. It also can pose a hazard to facility personnel if the recommended safe-to-touch temperatures specified by the Occupational Safety and Health Administration are not maintained throughout the facility. (Surface temperatures maintained at or below 140°F (60°C) throughout the facility.) Heat loss also can result in regulatory fines if the facility cannot adhere to energy-efficiency regulations due to heat loss.
For these reasons, minimizing heat loss is a primary concern for most high temperature industrial system designers. Typically, system designers use insulation to optimize process control and minimize heat loss. While there are many high temperature insulations available to help minimize heat loss, there is no one-size-fits-all insulation that will work for every industrial application. Industrial applications are too diverse with varied requirements for a single insulation to be an optimal solution for every application.
As a result, myriad of insulation solutions are available to achieve process control and minimize heat loss in industrial applications. This article will look at the most common high temperature industrial insulation solutions.
Calcium silicate is a rigid, molded insulation that some manufacturers make with a corrosion inhibitor integrated into the insulation.
Calcium Silicate. A rigid, molded insulation that some manufacturers make with a corrosion inhibitor integrated into the insulation, calcium silicate is used in applications up to 1200°F. It also can be manufactured to be water resistant. Calcium silicate offers good compressive strength (~100 psi) and is suited for applications where the insulation system might be exposed to exterior impact or abuse.
Expanded perlite is hydrophobic, and it can be manufactured with a corrosion inhibitor.
Expanded Perlite. Another rigid, molded insulation, expanded perlite also can be used in applications up to 1200°F. It is slightly more brittle than calcium silicate, and its compressive strength is also slightly less than calcium silicate (~80 psi). That being said, expanded perlite is hydrophobic, and it can be manufactured with a corrosion inhibitor. For these reasons, it is commonly used in the Gulf Coast as a method for controlling both heat loss and corrosion under insulation (CUI).
Mineral wool is lightweight, and it comes in different forms, including mandrel-wound pipe, boards and blankets.
Mineral Wool. A fibrous insulation with good acoustical properties, mineral wool is often one of the least expensive insulations. Typically, mineral wool is made from basalt rock and bonded with an organic binder. When compared to rigid insulations, mineral wool is lightweight, and it comes in many forms such as mandrel-wound pipe, boards and blankets. It can be used in applications up to 1200°F; however, because mineral wool is made with an organic binder, it may experience binder burnout starting at temperatures around 400°F (204°C). Binder burnout can compromise the structural integrity of the insulation in some applications (primarily those with high vibration levels). Mineral wool most often is used in three types of applications: where acoustical control is a high priority, where weight should be minimized and where costs are the primary concern.
Microporous blanket is a thin, highly thermally efficient, hydrophobic blanket that can be used in applications up to 1200ºF.
Microporous Blanket. A thin, highly thermally efficient insulation, the hydrophobic microporous blanket can be used in applications up to 1200°F. It comes in 0.20 and 0.39” (5 and 10 mm) thicknesses, and microporous blankets can achieve the same thermal performance as other insulations at a fraction of the overall thickness. For this reason, microporous blankets are commonly used in applications where there are space constraints. It often requires more layers than thicker insulations, but the total thickness of the microporous system typically is less than the total thickness of a traditional insulation system.
Polyisocyanurate is a rigid, hydrophobic insulation that is manufactured in bun-stock and then fabricated into the appropriate shapes for the application.
Polyisocyanurate (PIR). A rigid, hydrophobic insulation, polyisocyanurate is manufactured in bun-stock and then fabricated into appropriate shapes for the application. On the high temperature end, PIR can be used in applications up to 300°F (149°C); however, it also can be used in cryogenic applications to -297°F (-173°C). For this reason, PIR is a common choice for systems that cycle between hot and cold temperatures. It often is used in liquefied natural gas (LNG) applications where cryogenic temperatures are commonplace.
Silica aerogel blankets are commonly used in applications with space constraints.
Silica Aerogel Blanket. Another thin, hydrophobic blanket, silica aerogel blanket is similar to the microporous blanket in terms of physical properties. The silica aerogel blankets tend to perform slightly better than the microporous blankets at the lower end of the temperature spectrum (below 200°F [93°C]) before undergoing thermal shift.
Designers can mitigate issues that could arise from thermal shift by using “shifted” values in their insulation thickness calculations in the design phase.
Thermal shift is a unique characteristic of silica aerogel blankets. Their thermal performance degrades somewhat after prolonged exposure to high temperatures. It is a function of exposure time and temperature. The degradation is limited, however, leveling off over time. Thus, designers can mitigate issues that could arise due to thermal shift by using “shifted” values in their insulation-thickness calculations in the design phase. Silica aerogel blankets are commonly used in applications with space constraints.
Cellular Glass. A rigid, hydrophobic insulation, cellular glass is suitable for applications that range from cryogenic temperatures to 900°F (482°C). It is inherently hydrophobic, and it has compressive strength comparable to calcium silicate. Cellular glass is fabricated from blocks into the appropriate shapes for the application. Cellular glass is one of the more expensive insulating materials, and it is also one of the more challenging to fabricate and install. It is most commonly used in applications with hot and cold cycling conditions or in cryogenic applications.
Each of these insulations has benefits and drawbacks — ranging from price to performance — that system designers need to consider before making a material selection. Once a material has been selected, system designers will need to specify the appropriate thickness to minimize heat loss.
Insulation-Thickness Calculation Tool
While system designers can reach out to an insulation manufacturer for support in determining how much material they will need for their application, the North American Insulation Manufacturers Association (NAIMA) offers a free calculation tool. The 3E Plus, as the tool is called, can help system designers establish exactly how thick the insulation should be for the specific requirements and goals of the application and design.
The insulation-thickness calculation tool allows system designers to establish their criteria based on one of three considerations:
- Economic: How much insulation is needed to maximize the ROI on the insulation?
- Efficiency: How much insulation is needed to optimize efficiency?
- Environmental: How much insulation is needed to decrease the environmental impact of the facility operations?
This tool allows system designers to input the unique use-case requirements for their application. From there, the software utilizes generalized values based on ASTM standard specification criteria to establish the thermal performance of the insulation and relative thickness based on the application requirements.
Some insulation manufacturers offer custom versions of the NAIMA insulation-thickness calculation tool that incorporate the specific values of their products. This allows system designers to get the exact thickness they need for the specific brand of material they are using.
In addition to examining heat loss requirements in the design phase, system designers should consider two other components that can influence heat loss in an industrial application.
First, the material must be installed correctly per the manufacturer’s guidelines. This includes appropriate application and installation of the weather-protective metal jacketing over the insulation. This jacketing protects the insulation from damage and weather events and also helps prevent water from entering the system. This helps ensure that the thermal integrity of the system is not hindered by the presence of highly thermally conductive water.
Second, system maintenance is key to ensuring that the insulation has not been damaged. An effective insulation system will have a well-outlined maintenance plan. Frequently, insulation can become damaged during operation. If this damage causes the insulation to compress or break away, the thermal integrity of the system will be compromised.
Integrating a well-designed and well-installed insulation system is critical to ensuring optimized process control that minimizes heat loss and ensures that the operations at a facility run as efficiently as possible. The key to this integration is confirming the physical properties of the insulation are able to withstand the rigors of the application in terms of both thermal performance and physical strength. Finally, developing a robust maintenance plan is critical to ensure that any damaged insulation is removed and replaced and that a system performs as designed and heat loss is minimized.