By David Moore, Commercial Director (Thermal) at Calderys.
In today’s world, minimizing operational downtime is key to profits. The more a plant runs and produces, the more it is able to create profits to re-invest back to their facilities and more importantly their employees. Since 2015, aluminum pricing has been on a steady incline as auto producers and aerospace focus on reducing weights for fuel economy. This steady increase in aluminum prices has caused aluminum producers to have to define new ways to increase their run time.
Melting and casting are at the core of an aluminum plant’s operation. Maintenance of these areas are often done multiple times per year as the equipment operates at temperatures close to 1315°C (2400°F). All of the melting equipment is lined with high temperature materials called refractories. Refractories are mined all over the world and proprietarily blended to create unique concrete type materials that can have tremendous strength and metal resistance at high operating temperatures. At Calderys, we have the ability to make monolithic castables, gunnite, shotcrete, plastic, brick and precast refractories.
In aluminum, a melting furnace may be repaired annually with a complete rebuild happening every 5 to 7 years. This annual outage could take between 1 and 3 weeks and multiple pieces of equipment would often be repaired simultaneously around the clock. With lost production cost approaching $.15 per pound of output, facilities that produce 1M pounds per piece of equipment could lose as much as $150,000 per day. Some plants have 10, 20 and up to 30 pieces of melting equipment with multiple pieces of equipment being repaired. In most cases, contractors are evaluated and materials planned 6 to 12 months in advance of these very expensive outages.
Each detail is carefully considered to evaluate the best materials that can be used to balance the price and speed of installation. In many cases, any prefabrication of the refractory lining (also called precast or prefab) helps reduce installation time because you are able to install large sized prefired shapes with minimal skilled labor. Aluminum producers use the above graph where they consider how much time they have for their repair and which method of installation for the refractory they will choose. In most cases, the better materials are available as brick or cast in place but their methods of installation are much slower. Precast shapes allow for critical areas to be prefabricated prior to installation. Because these shapes can be done in controlled reproducible production environments, their physical properties are considerably better than field-installed materials of the same formulations.
The comparison chart above is of the same material: one is cast in place and the other is installed as a large precast shape. As you can tell, there are considerable advantages to lower water being used. Water is necessary for many refractories to be displaced. Shotcretes and chemical bonded materials also use a high ratio of water during their displacement. These types of applications shoot or spray the refractories through a hose for installation. Casting in place is done much like cement is mixed and poured with water. All this water must have time to dry properly prior to operation. The more water that is used determines how long the equipment must be dried out prior to operation. As per the materials solution triangle picture (above), the quickest installation is usually done by spraying this lining and the slowest is pouring castable refractories or conventional bricking.
In many cases the solution is not always just one way or the other. Some customers prefer to create an “à la carte” effect by choosing something in between. These repairs are called hybrid repairs. Hybrid repairs are often done when the customer sees unique advantages of each type of refractory in their operation and they select a balance with their timeline. The picture below is a project that was completed by Calderys USA for one of their aluminum customers.
As you can see, Calderys produced these roof tile shapes (top left) prior to installation, saving days of installation time. This type of time savings is the reason why more and more industries are considering prefabricated refractory components. In this particular case, the roof was installed in 8 hours, where a cast in place roof would have taken 3 days which resulted in a savings of $388,000.
As more and more companies feel the pressure to increase their operational run time, careful planning and considerations must be made with regards to refractories and their installation methods. Focusing on the value of production time prior to selecting the contractor or material supplier is fundamental to see what works best for the customer’s operation.
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