Boiler refractory plays a critical role inside for proper and efficient operations. Gas and oil-fired burners can produce temperatures upwards of ° F +/-. inside the furnaces or fireside of the boiler. The heating surface of a boiler depends on the water inside for thermal protection and structural retention whereas areas not protected by the water-wall rely on refractory. One exception here is in the throat tile area of certain furnaces. The refractory around the burner head actually protects the flame from being cooled too rapidly (from heat transfer) along with creating the proper flame shape and velocity.
Boiler refractory is heat-resistant material that lines the high-temperature areas of the furnace. Refractory usually consists of castables, bricks, ceramic wools or fibers, and even plastics made from various fireproof compounds. Typical to most industrial and commercial boiler applications is the use of firebricks, castables and, cerewool or fibers.
What is often misrepresented is the important correlation that a boiler’s refractory has to its efficiency and reliability. Bad or deteriorating refractory eventually leads to a whole host of other problems.
If you are looking for more details, kindly visit SINOMETAL.
Over time the refractory will begin to degrade. This is especially true in certain areas like the rear wall that can see some of the highest temperatures. As the refractory begins to fail its effectiveness begins to lessen. Common reasons that cause refractory failure can be due to thermal shock, over-firing of the boiler or excessive temperatures, improperly installed or cured refractory, or wrong material selection.
When castable refractory is not cured correctly, moisture can become entrapped inside and when fired it will flash to steam. As the steam expands it will blow out the refractory and cause voids and recesses inside critical areas that require thermal protection.
The good news is that refractory if installed correctly requires only minimal maintenance. Quarterly to annual inspections based on operational needs are the first step in keeping refractory at its best. Secondly, ALWAYS refer to the boiler manufacturer’s recommendations on refractory inspection frequencies, procedures, and any other specifications.
At a minimum, a fireside open clean and close should be performed annually by a qualified boiler service provider. Trained boiler repair technicians can quickly identify areas of refractory that may be failing. Some operations may require more frequent inspections so plan accordingly.
Certain boilers require an annual wash coat to the rear door or a target wall of the boiler. This is the area that sees the greatest temperatures and a properly applied wash coat with the proper material fills in small cracks that are common to this area. This practice will ensure that the areas subject to common refractory failure are in top shape.
Getting your boiler tuned regularly plays a critical role in keeping refractory intact. Improper combustion only leads to other problems like flame impingements, over-firing or sooting that can begin prematurely degrading the boilers refractory.
The rear door refractory of a dry-back boiler is a common failure point. These areas can fail and leave plants offline with little to no warning. A common practice is to utilize what we refer to as a change-out door. Much like the process of a core part at an auto parts store, an exact match that is cured and ready to install is exchanged versus the extended time of curing on site. Many plants can have a dry back boiler door swapped and installed the same day considering door availability.
All new refractories will still require some installed curring to ensure that the new material is slowly brought up to operating temperature. The improper firing of properly fired new materials will still result in refractory failure. This is again a reason to ensure that only qualified boiler service professionals are performing your facility’s refractory work.
If your facility is in need of refractory inspections, repairs, burner tunes, or an open clean and close, contact Power Mechanical Inc. today. We have been servicing industrial and commercial grade boilers for over 36 years and know what it takes to keep your steam and hot water boilers performing their best. Call today to schedule your boiler service.
Welcome to the first of a five-part blog series on refractory for petrochemical applications.
This first blog is an introduction to refractory that covers the common refractory-lined equipment, future blogs will discuss materials and designs and quality, inspection, and work scope planning.
Refractory is a ceramic material that maintains its strength while resisting damage by heat, pressure, and chemical attack. In the refinery, refractory can come as refractory ceramic fiber (RCF), as a castable or gunned material to be mixed with water, or in brick form. Each of these can be combined to provide equipment with the necessary thermal, erosion and corrosion protection. Each of these is applied in the following key refining applications.
For more information, please visit arc furnace electrodes.
One of the most complex refractory consumers is the Fluid Catalytic Cracking Unit (FCCU), requiring multiple combinations of different refractories. These units require circulating catalyst and high temperatures to make their products, both of which would be a challenge for bare steel vessels. In the FCCU, refractory materials generally fall into three categories: insulating, erosion resistant, and partially insulating, partially erosion resistant. See Figure 1 below for additional details.
Figure 1. A schematic showing how insulating, insulating and erosion resistant, and erosion resistant refractory are used throughout the reactor and regenerator vessels of a typical FCCU.
Fired equipment may employ fiber, castables (monolithics), or brick refractory as well as any combination of the three depending on specifics such as vintage, fuel, or severity of service. Higher temperature furnaces tend to maximize use of refractory ceramic fiber, often in edge-grain or folded modules. On the other hand, firing on heavier fuels employ superduty firebrick to resist the effects of ash and flue gas corrosion. Brick can be employed in a dual-layer lining to protect the backup/insulating layer of castable refractory that is providing the thermal protection to the steel. Refractory in heaters and boilers needs to be especially durable as major repairs require removal of the tubes. For a generic refinery service furnace, an example refractory lining is below (Figure 2).
Figure 2. A schematic showing how medium weight, lightweight, burner block, and corrosion resistant refractory are used throughout a typical refinery service heater.
Sulphur recovery units have the most interesting refractory in the Claus Thermal Reactor containing the main burner. Operating in excess of °F, brick refractory is the best product for the hot face. Brick continues to outperform other refractory types with the increasing use of oxygen enrichment for additional throughput (and associated increase of operating temperature). When manufactured, bricks are high-fired to beyond the process temperature so that high strength bonds can develop in the material. Compared to a castable, which develops its strength during dry out or process start up, bricks are much better in creep resistance. The SRU Thermal reactor refractory lining is critical to reliable process. However, these bricks are poor in insulation, so a backup layer of insulating castable is required to protect the shell.
For many refractory lining applications, reliable performance also depends on metal anchoring. Anchors come in a wide variety of shapes, but in general, secure the refractory lining to a steel component that provides structural support for the lining. Refractory ceramic fiber linings are typically installed onto studs and secured with a mechanically locking cap. Ceramic fiber cut or folded into modules rely on integral anchors that are installed by stud welding. Castable linings are anchored by wire anchors in a V or Y shape. Bricks are often self-supporting in gravity walls or arches but can also be supported with metal anchors. When combined with bricks, metal anchors usually take the form of tiebacks, which hold the bricks in relative position while allowing for thermal expansion. Erosion-resistant linings, when used to protect steel internals from wear in linings, can be installed as thin as ¾” into hexmesh anchoring. The design of the hexmesh accommodates for the differential thermal expansion between the refractory and the underlying steel. Several examples of linings with anchors are shown below (Figure 3).
Figure 3. A schematic showing generic refractory lining details for a castable, and ceramic fiber, and a thin-layer rammable lining with anchors.
Refractory-lined equipment are essential to every refinery. It is the critical detail that enables construction of boilers, furnaces, and large vessels to be fabricated from carbon steel instead of expensive and demanding heat-resistant alloys. Quality lining design requires a combination of lining types and materials installed into a different anchor depending on the exact combination. The next post will discuss the properties that ensure the right refractory for the job as well as more detail about lining designs and combinations.
For questions, comments, and discussion of edge cases, eventualities, or exceptions contact one of Becht’s mechanical experts.
Share This Article: