Fuel for thought – Replacing high temperature grade refractory ceramic fibre (RCF) linings in the petrochemical industry
When it comes to lining fired heaters in the petrochemical industry, RCF has been the go-to material, but it has its drawbacks. Steve Chernack, Global Engineering Manager at Morgan Advanced Materials’ Thermal Ceramics business, looks at how these can be mitigated, and a new option for petrochemical operators.
In the petrochemical world, RCF, also known as aluminosilicate wool (ASW), has long ruled as the material for lining fired heaters. It’s not hard to understand why - the material possesses several attributes that ensure it performs well in the harsh environment. This includes having a low thermal conductivity and heat capacity, superior thermal shock resistance and the ability to withstand extreme temperatures. On the operation side, it is renowned for its excellent handleability and longevity in service, while it has a good resistance to pollutants.
These characteristics mean RCF can extend the life of fired heaters, increase their energy efficiency and ultimately the furnace’s reliability.
However, despite its benefits, RCF does come with its drawbacks. Notably, the material produces crystalline silica as a by-product when fired, which can have an adverse effect on health when overexposure occurs. European Union (EU) regulations are now in place to address the health concerns of RCF and crystalline silica, requiring materials manufacturers to search for innovative solutions to protect workers and introduce furnace linings fit for the future.
Under the EU Carcinogen Directive, businesses are required to use substitutes to RCF where it is technically and economically feasible to do so. However, these requirements are open to interpretation and until recently, no material has been able to match the superior insulating performance and high melting point of RCF for use in units such as reformers and cracking heaters.
The economical vs. ethical vs. regulation argument
For many oil refinery operators, replacing RCF with other alternatives will negatively affect furnace uptime, so is an unpopular and costly option. A typical large furnace can generate product revenues of £100,000 or more per day. Clearly, many operators are having to weigh up the pros and cons between putting furnaces into extended periods of downtime that affects their bottom line and complying with EU regulations designed to further protect worker’s safety.
On the opposite face of the coin, operators do value their ethical approach. In a number of cases, RCF linings have been maintained beyond their expected lifespan, rather than replacing them. This is both for monetary reasons and in the hope that a viable alternative will be made available, as once replaced, the lining will typically be in use for another 15-20 years. However, this conscious decision may be taken at the expense of an efficient and high-performing furnace.
Additionally, from 2020 onwards, producers and users of RCF in Europe will have to keep the amount of fibres in the workplace <0.3 fibres/ml. Many other countries around the world have also imposed similar stringent controls. Such controls make using RCF difficult and expensive. Disposal of RCF is also costly, requiring special landfill sites due to its classification as hazardous waste.
All of this is compounded by the increasing commitment of major industrial companies and trade associations to improve ‘green’ standards and places the onus on the fibre industry to find viable alternatives that match or possibly exceed the performance of RCF. For example, the fibre has been more resistant to attack by alkali-based pollutants than the existing low biopersistence fibre compositions. This has prevented the replacement of RCF in many applications.
A silver lining – The case for operational improvement
Clearly, replacing RCF is easier said than done, and as stated earlier, there is a fine balancing act between economics, ethics and compliance. However, switching out RCF does have benefits that can be easily overlooked.
The first benefit that operators could realise is minimised downtime. When furnaces are scheduled for downtime, it usually takes at least 24 hours before the furnace is cool enough for engineers to even go in to inspect the furnace.
Then, due to the crystalline silica in RCF, before any work in or around a fired heater with an RCF lining can happen, workers must ensure that they wear a full set of appropriate personal protective equipment (PPE). This is to meet guidelines on occupational exposure limits (OELs), but also to protect against other hazards.
Just putting on and taking off the PPE alone can take quite some time, but then when undertaking bigger jobs like repairing linings or metal tubes in the furnace, there can be additional complications. Due to OEL restrictions and the need for extra PPE, engineers cannot work extended periods of time in the furnace. Especially in warmer climates, engineers must stop and vacate the furnace at set intervals.
Finally, if any emergency repairs are needed, then operators need to call in specialists and order materials to repair the lining. Quite quickly, what looked like one day for planned downtime can spiral into days or even weeks of unplanned extended downtime where the furnace and revenue generating abilities are out of action.
Arguably, low biopersistence linings would, to an extent, prevent these scenarios from happening for operators.
The Issue of Hazardous Waste
RCF linings don’t just pose operational problems during their working life. When decommissioned, they also require specialist disposal that adds extra costs.
For example, in Europe, disposal of waste materials in EU Member States is controlled by the implementation of a number of Directives. Wastes containing more than 0.1wt% of RCF are classified hazardous under Directive 91/689/EC. RCF wastes from manufacture and use are required to be handled and disposed of by a licensed waste contractor in an appropriately licensed hazardous waste landfill.
In practice, many RCF users have experienced significantly increased costs because local waste disposal sites are not licensed to or prepared to accept hazardous wastes.
A unique alternative to RCF is born
So, there is plenty of reason to switch from RCF linings to a low biopersistence alternative. However, as alluded to earlier, existing low biopersistence fibre compositions do not perform as well from a thermal perspective, nor do they resist pollutants as well in comparison.
To solve this challenge, Morgan Advanced Materials has been using its Fibre Centre of Excellence in Bromborough, UK to conduct research into RCF alternatives. Instead of attempting to make marginal gains in low biopersistence performance, Morgan has taken a different approach and revisited RCF itself.
The purpose has been to produce a new fibre with all the performance attributes of RCF but has low biopersistence and does not form crystalline silica during use.
The result of this research and development is Superwool® XTRA™, a fibre that uniquely does not form crystalline silica. Crucially, in terms of its effect on environmental, health and safety (EHS) risks, Morgan’s breakthrough material is exonerated from any carcinogenic classification under Nota Q of Directive 97/69EC.
The new insulating fibre was the culmination of almost a decade of research and development, plus almost four years of stringent testing in specified critical applications with customers.
For petrochemical operators, they can be rest assured that Superwool® XTRA™ meets the American Petroleum Institute’s (API) standards, which guides the industry. The API’s classification temperature which is to be used for insulation outlines an obligatory 150°C (302°F) overtemperature capability on the fibre within furnaces.
Critical furnaces within the oil refinery and petrochemicals industry run between 1200°C and 1250°C (2192°F and 2282°F) and therefore require materials with a 1400°C (2552°F) minimum classification rating. With a classification rating of 1450°C (2642°F), Superwool® XTRA™ offers a performance equal, and in many cases superior to RCF.
Making the switch
For operators looking to switch away from RCF, it is important that due consideration is given.
Identifying the need for a new furnace lining is not an easy task as testing and trialling new materials can be costly per trial, not to mention furnace downtime. Ensuring lining quality is essential for protecting personnel, minimising heat loss and maintaining operational reliability
Furnace linings which may have developed breeches over time are prone to increased thermal loss; some of which may not be visible from the outside. To minimise costs, it is recommended that testing coincides with the scheduled downtime, so fabricators can swap-out and install the new lining.
One technique for identifying thermal losses lies in the use of infrared (IR) thermography scans. By using these IR scans, engineers can keep the furnace in operation while conducting an analysis. If a hot-spot is found, if possible, it is always faster and more cost-effective for the repair to be done on-line to reduce business revenue impact.
Consider engineering design carefully
To achieve maximum efficiency and longevity for the materials specified during the furnace relining process, it is critical to ensure the engineering design is appropriate.
Not only must the materials have enough studs to hold them in place, they also require sufficient joints for expansion or shrinkage. If a brick lining is installed without adequate expansion joints, the brick can grow so large that it pushes the entire lining off the furnace wall. This will lead to further inefficiency, requiring the entire process to be repeated.
Over long periods of time at temperature, fibre modules degrade resulting in shrinkage gaps between the modules. These normally need filling with more fibre during scheduled maintenance shut-down periods. With Morgan’s Superwool® XTRA™, the fibre is innovative in that it expands when heated to high temperatures, which has several benefits.
First, potential shrinkage gaps possibly visible at cool-down will close-up during operation. Second, expansion properties allow Superwool® XTRA™ to be used in critical applications when mating dissimilar lining materials. These unique properties and design considerations can result in reduced down-time, minimising labour costs and maximising operational revenues.
Trust the professionals
A new furnace lining which uses the right materials, is designed to requirement and installed correctly, can last for as long as 20 years. With a vast range of furnace lining products available on the market, each requires unique installation methods, so it is important that the personnel employed to carry out the work are highly skilled and experienced. Failing to do so can lead to complications, and ultimately result in large sums of money being lost.
Additionally, degradation of furnace insulation can result in development of hot spots on the casing that can damage equipment and cause an unsafe condition for personnel. It can also disrupt the process as operators compensate for the higher heat loss. In turn, if these hot spots are located near the tubes within the furnace, they can be extremely dangerous, as the typical hydrocarbon process materials in these tubes are highly flammable. If the tubes break, there is a significantly heightened risk of an explosion.
A brighter future
The industry’s search for an RCF alternative is now over and a low biopersistence future for refineries and petrochemical plants has arrived in selected applications.
Superwool® XTRA™ has proven itself through considerable testing and real-world applications to be a viable alternative to RCF. In addition to its efficiency credentials, the product’s improved EHS performance and lack of crystalline silica as a by-product have alleviated worries from operators and installers at petrochemical sites. It is available in various forms and able to provide low-biopersistence thermal insulation not just to the oil refining and petrochemical industries, but also to the iron and steel, and incineration industries.
For more about Morgan Advanced Materials and how Superwool® XTRA™ can answer your concerns about furnace and refractory performance, please visit: http://www.morganthermalceramics.com/SuperwoolXTRA