Foamfrax insulation is used to insulate metal, refractory and ceramic fiber surface at operating temperatures to 2450 F (1345 C). The monolithic insulation system is used to repair and/or upgrade existing furnace linings and to install new linings in a shorter time than that required for conventional blanket or module linings. The system offers fast, easy installation and good lining performance and overall cost savings for existing fiber linings, furnace lining patches and refits, and linings over hard refractory. Applying the new system over a partially deteriorated furnace lining can extend furnace lining life and improve furnace efficiency. Foam-frax insulation significantly decreases the overall heat loss and heat storage of the refractory system when applied as a veneer over an existing hard refractory lining, resulting in significant energy savings. While furnaces vary by refractory type and firing cycle, the payback period in terms of energy savings typically is less than six months.
The insulation system has been used in a wide variety of furnaces in chemical processing, ceramics manufacturing and metals processing industries, including ammonia reformers, ethylene furnaces, rotary calciners, batch car-bottom furnaces, ladle preheat stands, batch forge furnaces, roller hearth furnaces, slab reheat furnaces and bell annealers.
The monolithic insulation is a three-component system consisting of bulk ceramic or soluble fibers, an inorganic binder (colloidal silica) and an organic foaming binder. The bulk fiber material and binders are combined in the installation process creating a homogeneous foam/fiber mixture. The organic portion of the binder burns out during the firing process. Fibers are completely coated with the foaming binder solution in the mixing chamber, encapsulating the fibers within the foam matrix, and the homogeneous foam/fiber mixture is gunned onto the target surface. The insulation system is specially designed to control air-borne fiber levels. Unlike sprayable fiber methods that feed dry fiber and binder in separate streams that are partially combined after the product leaves the installation nozzle, the fiber in this system is completely coated within the foaming binder solution while in the mixing chamber. This significantly reduces the potential for airborne fiber to be released into the surrounding environment.
The system features include:
Insulation can be installed at rates in excess of 1,000 board feet per hour, which can be two to six times faster than rates for traditional installation techniques. Trained contractors using patented installation machinery install the insulation quickly and easily. The end user can realize energy savings immediately after the product is installed and the furnace is put back into service. The system can be used to upgrade deteriorating furnace linings and also can be installed as a full-thickness system by using stainless steel anchors that are embedded within the insulation to retain the furnace lining. The following case studies illustrate the latter application technique.
Slab reheat furnace
Foamfrax insulation was used in a complete rebuild of a slab-reheat furnace at a major steel company. The furnace, with an operating temperature of 2150 F (1180 C), was rebuilt using a full thickness system consisting of 9 in. (230 mm) thick Foamfrax Grade II Fiber, 8 PCF (128 kg/m3).
The installation process started with a complete tear-out of the existing ceramic fiber module lining, and pouring a new castable hearth/bench and installing new burner blocks (Fig. 1). In full thickness applications, adhesive-backed plastic spider netting is placed against the furnace shell and "V" anchors are welded in place through the netting. In addition, "X" anchors are installed in the roof to hold the gunning mix.
Foamfrax Grade II Fiber was gunned into the spider netting and around the anchors on the sidewalls. The high impact of the gunning mix allows it to flow and work around the "V" anchors without leaving pockets and/or voids in the lining system. The insulation was installed to a thickness of 9 in. on the sidewalls (Fig. 2).
The transition from sidewall to arch incorporates a 1-in. (25 mm) thick Fiberfrax blanket 3 in. (75 mm) from the lining hot face. The blanket reinforces the foam insulation at the arch/sidewall juncture, preventing cracks or gaps.
The hot face surface is troweled in full-thickness applications using low-density (foamy) surface coating of Foamfrax Grade II Fiber (Fig. 3). The surface is scored using a scoring tool in a grid pattern approximately two feet square to control surface cracking due to thermal shrinkage. The furnace was available for use after scoring (Fig. 4).
The insulation was completed in less than two days, and the furnace was available for immediate service. After anchors were welded in place, actual installation of 1,300 board feet required less than four hours to complete, compared with about 3 days for module installation. The lining met all customer expectations, providing a monolithic ceramic lining with no hotface openings and with all the inherent ceramic fiber thermal properties such as low heat loss and low heat storage.
Cylindrical coil annealer
Coil annealing furnaces require an efficient, lightweight refractory lining because they are subjected to thermal cycling and are lifted and moved on a regular basis. Refractory ceramic fiber is used as furnace insulation because it has the required light weight, as well as resistance to thermal shock and good performance in reducing atmospheres. While standard practice for ceramic fiber installation is module or stackboard construction, a major steel company agreed to try a Foamfrax installation because of its speed of installation and monolithic ceramic fiber construction.
The annealer was 11 ft in diameter and 25 ft high (3.3 and 7.6 m) with an operating temperature of 2000 F (1095 C). The installed lining consisted of 6 in. (152 mm) thick Foamfrax Grade I full thickness lining for the upper walls and roof.
Using "V" anchors and spider netting to anchor the insulation on the sidewall of the annealer, the material was easily gunned around the anchors and against the bench at the base of the wall. Spider netting and "X" anchors (Fig. 5) were used to anchor the Foamfrax insulation on the roof. An initial 4 in. (100 mm) thick layer of insulation was installed before installing the "X" anchors, followed by gunning an additional 2 inches of insulation over the anchors for a total lining thickness of 6 in. (150 mm). A low-density skim coat was applied over the gunned material and the surface was troweled smooth and scored to control thermal shrinkage.
The entire installation was completed in two eight-hour shifts, which is less than half the time required to install a comparable module or stackbond lining. This results in reduced unit downtime and increased productivity.