In this article, we will discuss the most common causes of refractory failure, how to inspect fired heaters or furnaces for damage, and the methods of repairing refractories online without the need to disrupt normal operation.
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Types of refractory lining include refractory ceramic fiber, brick, and castable or concrete. If refractory failure results in an unplanned shutdown, it can cost plants more than $1m/day in lost production.
Refractory linings are insulating and minimize heat loss, making them essential to retaining the high-temperature environment. However, when subjected to high temperatures, refractory can deteriorate and potentially lead to failure if remedial work is not carried out.
All process heaters operate at high temperatures and are constructed with process tubes inside a refractory-lined enclosure, which is heated by radiant heat from gas-firing or, less commonly, oil-firing.
As refractory linings age, their physical properties change. The high-temperature environment causes microstructural changes to the binders within the materials, leading to a loss of surface or internal strength. If the refractory material carries a compressive load, such as bricks, or castable linings, this can lead to local, or widespread failure.
If the refractory is subject to flame impingement, which is common in many radiant wall applications, the useful life will be shorter.
In oil-fired heaters, refractory deterioration is accelerated by corrosive agents in the combustion products. Fortunately, there are few cases where oil-firing is used now.
A combination of refractory materials is a common feature in fired heaters. Openings such as doors often use fiber and brick material, and peep sights may use IFB, castable, or fiber modules.
A standardized design using different materials can be challenging as each material has varying properties at high temperatures. Therefore, refractory linings can become damaged, leaving the shell exposed to hot flue gases and causing hot spots.
To lower the risk of mismatched refractory materials, it is a good idea to work closely with the refractory supplier to ensure comparable materials are used around openings.
All types of refractory linings are attached to and supported by the external steel shell of the fired heater. The conventional support is provided by an anchoring system, which is welded to the shell.
Frequently, the welded joint between the shell and the anchor is compromised by corrosion and support is lost. The corrosion is caused by hot flue gases penetrating through the refractory lining and condensing upon reaching the cooler shell. The local environment is ideal for rapid oxidation, or corrosion of the weakest point; the weld.
Once support is lost, individual bricks, modules, etc. can fall away, leaving the metal shell exposed, which creates a domino effect and the failure of adjacent refractory lining.
At a plant in Europe, a hot spot was discovered on the transition shell ducting between the radiant and convection sections of a CCR Platformer. In this case, the failure of the ceramic fiber blanket in the roof left the shell exposed to hot flue gas. This caused the external shell temperature to exceed 560°C/ °F.
To prevent overheating the shell until failure, the production rate on the CCR Platformer had to be decreased, resulting in a loss of production of more than $400,000 per day.
The plant used Hot-tek&#;s hot refractory repair service to fix the hot spot issue until the next planned turnaround. This service is discussed in more detail later in this whitepaper.
There are several factors that can cause mechanical stress to lead to refractory failure. This includes:
Vibration or interference from other equipment can cause refractory to become displaced and break down over time.
This occurs when refractory linings expand and contract at different rates due to thermal conditions. This often leads to cracking and spalling which can cause failure if not repaired.
Mechanical impact from falling objects or components can also damage refractory.
Improper installation or maintenance is a common cause of refractory failure. Factors such as installation techniques, curing time, inadequate support, or poor-quality materials can all weaken the refractory and contribute to its failure.
Refractory installation begins at the manufacturing stage. Good communication between the manufacturer and the plant is critical to ensure that the refractory is fit for purpose. It should be resistant to thermal stresses and other processes caused by the operating environment. Parameters such as temperatures, start-ups and shutdowns, flue gas temperature and chemical components, and required heat loss should all be evaluated.
Once manufactured, the refractory should be stored in a dry, well-ventilated space and installed within three months for high-temperature or high-abrasion operating environments. If installed and maintained correctly, refractory linings should last 20 years or more.
However, several characteristics could suggest issues at the installation stage. For example, if you notice fiber modules have fallen from the roof or gaps have appeared, it could be due to an issue such as insufficient stud welding. It could also be a sign of shell corrosion, which is more common if a protective alloy cladding, such as IGS&#; High Velocity Thermal Spray (HVTS) has not been applied to the shell before installation.
Whilst there is a range of potential installation issues that can lead to refractory failure, regular and diligent inspections can help to identify damage early to allow remedial work to be carried out.
Often the first sign of refractory failure is a hot spot on the external steel shell since direct observation of the problem area is not possible. IGS has designed and developed Cetek&#;s Lancescope&#; fired heater inspection tool. It allows the undertaking of a high-temperature furnace inspection to determine the scope of the problem, often avoiding an expensive shutdown of the heater.
The hot inspection system uses a state-of-the-art digital camera system, which provides clear, detailed images of problem areas up to °F (°C). The furnace inspection system can be inserted into openings as small as 2.75&#; (7cm) and reach up to 30ft (10m). In applications below °F (540°C), the heater inspection system provides illumination via a high-temperature light source for optimum clarity.
The benefit of performing a hot inspection includes:
Once the damage has been identified, there are usually options to fix the issue. Production can be interrupted to take the asset offline and carry out conventional repairs, or the furnace can continue to run at reduced performance until the next planned turnaround. However, this could exacerbate any existing damage.
Alternatively, an online refractory repair service is offered by Hot-tek&#;, where there is no need to bring the heater off-line and production will not be interrupted or capacity limited. This is a good option to temporarily fix damage until the next planned turnaround.
A team of refractory technicians can be mobilized at short notice and the repair involves creating minimal access point openings to insert specially designed components and repair material, delivering a semi-permanent repair lasting at least until the next turnaround.
There are numerous causes of refractory failure, but shutting down the furnace should always be a last resort as this has a huge impact on production and revenue. The operating environment is responsible for most refractory failures and a common oversight is to increase the furnace temperature without assessing the impact that this will have on the design parameters of the refractory. Planning for over-capacity can help to mitigate the risk of refractory failure if specifications change after installation.
Understanding and preventing refractory damage is key to the overall furnace performance. IGS recognizes the effects of asset failure and works in partnership with plants worldwide to optimize equipment reliability and performance. Identifying refractory damage early and understanding the reasons behind it will help operators increase furnace up-time and maximize overall performance which could save millions in otherwise lost revenue.
If unexpected performance losses are impacting your operations, IGS can mobilize quickly to help you identify, fix, and prevent future damage.
Manufacturing is an industry that many people assume has a negative impact on the environment and natural resources. The reality, of course, is much more complex. Industrial manufacturing, including the refractory industry, certainly has its challenges, but it also possesses huge potential to be a positive force for good.
The refractory industry can help reduce deforestation and other production impacts while continuing to drive economic growth through innovation and new technology. With the right mindset, manufacturers can embrace sustainability and see net zero as an opportunity.
The first step in embracing sustainability is understanding how your company currently impacts the environment. This requires taking an honest look at everything from water usage to greenhouse gas emissions and waste management practices. Once you know your current impact, you can begin identifying ways to become more sustainable by reducing your environmental footprint.
Why is Net Zero Important?
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Most manufacturing facilities use natural resources, emit greenhouse gases, and produce waste. These are the traditional metrics for measuring a facility&#;s environmental impact. Some companies have reduced their impact by implementing more sustainable practices, but many struggle to go beyond the basics.
There is a significant gap between what is being done and the potential for manufacturers to reduce their overall impact. For the refractory industry to truly achieve sustainability on a large scale, manufacturers need a more comprehensive way of measuring their environmental impact.
This is where net zero comes in. Net zero is a way of measuring environmental impact that goes beyond the traditional metrics. It looks at the interconnections between the systems contributing to a company&#;s overall environmental impact. This includes everything from the facility&#;s energy use and waste management to the products being manufactured and the materials used to produce those products.
Identifying opportunities to become more sustainable
There are a number of areas in which a manufacturer of refractory products can reduce their environmental impact. The first step is to assess which areas of your operation currently have the most significant environmental impact. Once you know where you need to improve, you can begin exploring ways to reduce your impact. This can range from investing in renewable energy sources to changing how you use water or transport your products to reducing overall waste production.
Helping the Environment Through Manufacturing
Manufacturers can help the environment through the production process by using renewable energy and reducing the amount of waste they produce. They can also help the environment by diverting waste from landfills and re purposing refractory materials that would otherwise be discarded.
There are several ways manufacturers can help the environment through the production process. One way is to reduce the energy use of your production process. This can be done by investing in energy-efficient machinery, optimizing the use of energy resources, and improving facilities with the help of sustainable development experts. Another way the production process can help is by using sustainably sourced materials. This is important because many of the materials used in refractory manufacturing come from natural minerals and resources.
Manufacturers embracing net zero and focusing on reducing their overall impact can enjoy the reputational benefits of serving a climate-aware customer or business base. In contrast, shareholders can benefit from the net zero approach in eliminating climate risk without sacrificing near-term returns.
The refractory industry has come a long way in terms of environmental sustainability, but there is still room for improvement. Net zero represents a giant leap forward in measuring and improving sustainability.