Ultra-Lightweight Gunnites: Increases Refractory Installation Efficiency and Downtime Savings

Furnace design revolves around efficient heat control for optimal energy usage, with the choice of energy source dictating the heating process. The furnace’s inner lining contains the heat generated from sources like gas, coal, wood, or electricity, while various factors such as internal environment, wear, and chemical reactions are considered. Whether the furnace maintains a constant temperature or experiences cycles, a refractory insulation package is crucial to curbing fuel consumption and regulating cold face temperatures.

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Insulation materials like boards, fibers, bricks, and castables offer diverse options, each with distinct considerations like insulation effectiveness, installation, and expense.

When considering the insulation package for the vertical wall of a furnace, stability is essential, necessitating support systems to prevent material settling. This support is facilitated through an anchoring system that links the hot face working lining to the furnace structure, aiding overall stability.

The Complexities of Anchoring Systems and Insulation Installations

Anchoring systems play a crucial role in refractory installations, serving to secure the refractory material to walls, prevent wall buckling from thermal stresses, and offer some support to the refractory weight. However, these systems can pose significant challenges during insulation installation and maintenance. Typically, anchors are welded to the furnace shell before adding insulation and the working lining, but the protruding anchors can complicate insulation placement.

Fiber Insulation, commonly available in blanket form, can be inserted between the anchors to fill gaps and provide insulation. Vibrations are inherent in industrial furnaces, stemming from combustion, exhaust blowers, and other machinery. This perpetual vibration tendency can cause the fiber insulation to slump, potentially resulting in inadequate insulation and subsequent hot spots across the furnace wall.

Insulation Boards, possess enough rigidity to stand on their own and are available in various densities and thicknesses to achieve the required insulation level. However, these boards typically come in sheets that need to be cut and customized to fit around the anchors. This process can demand a substantial amount of labor and time during installation. Considering the potentially high expenses associated with industrial furnace downtime—often translating to substantial profit loss per hour—companies strive to minimize installation time.

Ultra-Lightweight Refractory Gunnites, offer a means of installing a large amount of insulation in a relatively short period of time. A gunnite is a monolithic refractory castable that is pumped dry through a hose under pressure and is mixed with water at the nozzle. Once the wet castable impacts the surface, it stiffens quickly to avoid slumping and hardens as it dries. This means that the gunnite could be installed over the anchors in minimal time. The installer only needs to wrap the ends of the anchors with masking tape to keep them clean for the working lining.

Refractory Gunnite Distinctions

Ultra-Lightweight castables, a subset of Lightweight castables, stand out due to their density contrast. While a typical Lightweight castable at a maximum 2400°F service limit offers densities of around 80 to 90 pounds per cubic foot (pcf), Ultra-Lightweight castables at the same limit possess densities of 25-30 pcf. This disparity becomes significant when evaluating insulation thickness and cold face temperature calculation. Achieving the same cold face temperature in a 2000°F furnace would demand nearly three times more Lightweight castable than Ultra-Lightweight castable.

Notably, Ultra-Lightweight castables like Plicast Airlite 25 C/G (Liquid Board™) from Plibrico offer final densities of 25-30 pcf with service temperatures above 2400°F.

Facilitating rapid installation via casting or gunnite, this product boasts durability, low thermal conductivity, and strong thermal shock resistance. It surpasses labor-intensive insulation board and addresses the hot spot issue of fiber insulation. With Ultra-Lightweight, Liquid Board-type castables, requisite insulation values and extended lining life can be achieved at the speed of refractory gunnite.

Efficient Installation Impact

Considering a real 2000°F production furnace with a 9-inch lining (6 inches dense refractory, 3 inches insulation) and comparing different insulation materials.

• Using 3 inches of 6 pcf Ceramic Fiber Blanket yields a 252°F cold face temperature
• 3 inches of 26 pcf Insulation Board results in a 247°F cold face temperature
• Applying 3 inches of Ultra-Lightweight gunnite like Plicast Airlite 25 C/G (25 pcf density, 2500°F service temp) produces a 262°F cold face temperature

While the cold face temperature difference between Insulation Board and Ultra-Lightweight gunnite is 15°F, the installation time saved can span multiple shifts. This time savings becomes important when you consider that downtime costs, estimated at $250,000 – $1,000,000 per hour for thermal processing companies, can lead to millions in savings.

For instance, in a 750 sq ft round duct application with pre-installed anchors, the estimated labor hours for installing 4″ of various insulation types are as follows:

• Fiber Insulation: 137 hours, ~5.5 sqft/hr
• Insulation Board: 288 hours, ~2.6 sqft/hr
• Ultra-Light Gunnite – Liquid Board: 80 hours, ~9.4 sqft/hr

Rapid installation of Ultra-Light Gunnite – Liquid Board translates to an average estimated downtime savings between $35 – $130 million, directly benefiting a company’s finances.

By including ultra-lightweight gunnites into the total solution for a furnace refractory lining, refractory installers can streamline installation processes. The time efficiency of these materials directly correlates to decreased downtime, translating to enhanced profitability. In the scenario involving a 750 sq ft, round duct application, ultra-lightweight gunnite exhibited significant labor hour savings compared to other insulation options, resulting in multimillion-dollar downtime savings.

An Efficient Solution

Incorporating ultra-lightweight gunnites into furnace refractory linings presents a transformative approach to insulation installation. By significantly expediting the installation process, these materials offer not only increased efficiency but also substantial cost savings through reduced downtime.

The distinct advantages of ultra-lightweight castables, exemplified by products like Plicast Airlite 25 C/G, include remarkable durability, low thermal conductivity, and robust thermal shock resistance. In contrast to labor-intensive insulation board and the potential drawbacks of fiber insulation, ultra-lightweight gunnite stands out as a game-changer. With estimated downtime costs ranging from millions to hundreds of millions, the adoption of ultra-lightweight gunnite promises not only enhanced profitability but also an innovative way forward for refractory insulation in industrial furnaces.
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For more information contact the Plibrico Company at contact@plibrico.com, or 312-337-9000.