Refractory Selection and Environmental Footprint
In today’s economic climate, reducing the environmental footprint of a manufacturing facility makes good business sense on a couple of fronts. Improved energy efficiency results in lower net operating costs and either higher profitability or better ability to compete in the marketplace.
|Fig. 3. A hot-face veneer is a fast approach to realize energy savings for an existing refractory lining system.|
A more recent trend is that customers want to do business with companies that have an energy conservation program and can document the steps taken to implement green initiatives. Government legislation, in this regard, is still in a state of uncertainty (carbon credits, etc.). However, it may be wise to be proactive to reduce the environmental footprint of your company.
A carbon credit is the equivalent of 1 metric ton of carbon monoxide (CO) released into the environment. In general terms, it takes 18-million BTUs to generate 1 metric ton of CO. Reducing the BTU requirement to operate your process not only saves money, but it can be documented in terms of carbon credits earned. Pending the results of government legislation, there is the potential that these credits may be shared amongst facilities within the same corporation or actually sold on the open market to firms that require carbon credits in excess of their allocation.
Improved furnace efficiency can be accomplished many ways, some of which require significant capital investment and resultant furnace downtime. A state-of-the-art burner system and controls with the use of preheated combustion air is a good example. As furnace refractories wear and require replacement during the normal course of business, however, there is an opportunity to improve furnace efficiency simply by evaluating the choice for the replacement refractories. Many techniques and products are available to support this concept. Three techniques to improve furnace efficiency will be detailed: complete refractory replacement, backup insulation and a refractory hot-face veneer.
|Fig. 1. Full-thickness linings using ceramic-fiber modules are easily installed and provide superior insulating value.|
Complete Refractory Replacement
Traditional hard refractories (bricks, castables, etc.) are required in many applications due to the nature of the process. These products are often chosen to provide effective protection from physical abuse, molten metal and chemical attack but tend to offer very little insulating value. For these reasons, traditional refractory materials are still used in many applications. Replacing these products without at least evaluating more energy-efficient alternatives, however, may be a missed opportunity to reduce the environmental footprint of your facility.
Over time, ceramic and soluble-fiber product forms have evolved significantly and can now be successfully substituted for traditional refractories in many applications. These products are basically available for use at the same temperatures as traditional refractories but provide the benefits of reduced heat storage and reduced heat loss. For batch operations, the low density of fiber-based refractories allows for faster heat-up and cool-down, resulting in improved productivity and less energy consumption per unit of product output.
Current installation techniques and product offerings provide quick installation of fiber products with minimal customer downtime (Fig. 1).
|Fig. 2. Monolithic backup insulation provides lower furnace shell temperatures and resultant energy savings.|
Refractory Backup Options
Using a low-density product as backup behind traditional refractory will decrease the net density of the lining, thus lowering the heat storage and heat loss of the refractory system. There are a variety of products suitable for refractory backup. Considerations for choosing the best-suited backup material are:
- Interface temperature at the backup lining
- Space or lining thickness considerations
- Compatibility with the hot-face refractory installation method
- Hot-face refractory anchoring system
Taking into account these considerations, in most instances a low-density fiber/refractory cement-based, gunned backup insulation works very well. This technology allows the backup insulation to be gunned around the required refractory anchors and results in a monolithic backup system. More traditional backup materials, such as insulating-grade boards, can result in isolated heat paths due to cracks/openings between the board sections and around anchors. This gunning method also reduces material-handling requirements and is up to three times faster to install than cutting and fitting insulating board (Fig. 2).
Refractory Hot-Face Veneer
As a maintenance tool, energy savings can also be realized by applying a relatively thin veneer (1-3 inches) of low-density ceramic or soluble-fiber insulation onto the hot face of an existing refractory lining. This will also result in lowering the net density of the lining system to achieve energy savings. A veneered lining will also make the furnace temperature more uniform, which may result in faster throughput or improved product quality. Installation of standard fiber-based products, such as bonded modules or blankets, as a veneer can sometimes be difficult because the refractory surface is often irregular or anchors may be required to support the veneer.
A gunned low-density insulation system is very well suited for intricate geometries or irregular refractory conditions common for many veneer applications. This gunned-on system will serve to protect the existing refractory lining and fill any cracks/openings in the refractory. Installation using a gunned system is very fast and in most cases can typically be completed during a short shutdown. Because of the low density of the gunned insulation, there is no critical heat-up requirement to bring the furnace back into service (Fig. 3). Information for the energy savings that can be realized with the options discussed here is provided in Figure 4.
Energy conservation and green initiatives are currently part of today’s industrial practices and will continue in the foreseeable future. Many times, tremendous progress can be made in this regard just by re-evaluating the refractory practices/requirements of your company and by staying current with new refractory technologies available. In most cases, the payback period for the concepts presented is less than 12 months. As standard practice, energy savings and product recommendations are typically made by suppliers of these technologies in order to help your organization reduce its environmental footprint. IH
For more information: Contact Brian Bradley, engineering manager, Unifrax I LLC, 2351 Whirlpool Street, Niagara Falls, NY 14305; tel: 716-278-3806; fax: 716-278-3902; e-mail: firstname.lastname@example.org; web: www.unifrax.com
Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at www.industrialheating.com: environmental footprint, furnace efficiency, refractories, castables, fiber-based refractories, insulating-grade boards, ceramic-fiber modules