KILN CARS IN KILNS
FIRED WITH PET COKE
In Spain, starting in the early eighties, pet coke was introduced as a fuel for red clay firing kilns, triggered by the petrol crisis. Pet coke remains an abundant resource in today’s market.
After the fever of the first years, the basic concepts became strengthened by experience.
Combining pet coke with gas or fuel oil in the first burner rows is necessary.
Several firing systems evolved and were replaced by more advanced systems. Only the systems assuring a controlled uniform feed of fine particles survived.
Pet coke should be used only when it will not affect the final color and texture of the product.
There are a few disadvantages; however, there are significant advantages in direct cost.
As a result, the use of pet coke has been closely related to the fluctuation in price of alternative fuel options (gas or fuel oil).
Gas prices remained relatively low for quite some time. This prompted many brick and tile plants to convert from pet coke and heavy fuel oil, which was the “classic” fuel in Spain, to gas. However, due to the recent increase in gas prices, a renewed interest
in pet coke in Spain and abroad has developed.
Pet coke has, in good reason, been blamed as being chemically aggressive to the kiln cars refractory linings. Pessimistic extremists state that pet coke should not be used at all because it destroys all refractories. Optimistic extremists believe that a good coating is enough for full protection.Frequently, we have been asked to supply “a protective paint,” even after the refractory has suffered
In our more than 12 years of experience, we have followed the performance of our refractories working with pet coke. We have discovered that it is possible to limit the damage and operate profitably with this fuel while following a few basic guidelines.
No kiln car refractory, whatever its chemical composition, can be harmed by vanadium or other components of the pet coke without first being damaged. The goal is to drastically reduce the rate of deterioration.
The life of the refractory must be sufficient for a profitable use of the pet coke. Below are a few basic guidelines which should be followed to insure profitable employment of Pet Coke.
1. A GOOD COMBUSTION IS ESSENTIAL
to avoid the development of a layer of unburned particles on the refractory surface. Those layers create a “micro-climate” with a reducing atmosphere;
which produces a high concentration of all the aggressive elements present in the fuel.
It is essential that:
The fuel particles burn fast while they are in the air. This will require very fine grinding, as pet coke is a fuel with a very low volatile content.
The burners should feed the fuel evenly, both in spatial distribution and over time.
No pet coke should be fed to low temperature zones in the kiln, where the combustion velocity would be too low. In most cases the first burner rows should be fed with gas or liquid fuel.
2. ACCUMULATED ASH LAYERS MUST BE AVOIDED
Even when the ash content is very low in pet coke, repeated passes through the kiln can accumulate layers of ash, especially under the setting blocks. The effect of such layers is similar to the effct of the non burnt layers, or even worse (we should not forget that most of the aggressive components of the pet coke get concentrated within the ashes).
A complete vacuum cleaning of the kiln car linings must be performed after every pass through the kiln, including the lifting of the setting supports and cleaning underneath.
3. THE RIGHT REFRACTORY QUALITY SHOULD BE USED
It should be able to withstand the working conditions without degrading prematurely. It must be considered that working conditions are not the same in all
kilns as they vary from case to case. Because the pet coke does not have a stable composition, many times the aggressive components of the clays are also present. An unlimited number of possibilities present different combinations.
For those reasons, only extensive experience in several different kilns and conditions can establish how the refractory will perform when used with pet coke
as a fuel. At this time, no laboratory test allows the evaluation of the life expectancy in every specific working condition, even with a reasonable approach.
Forgestal and Refractarios Campo can provide evidence of more than 12 years of repeated experiences of success in the same conditions where other refractories failed.
Materials have been developed and tested all along in actual processes for the optimal life span under strong chemical attack conditions, especially when the aggressiveness of the fuel and the clays come together.
The life expectancy of those refractories can reach up to 3 or 5 times the life span of other refractories.
4. REFRACTORY PROTECTIVE PAINTS
Only when the three former points have been assured, can we consider an ADDITIONAL positive effect of a protective coating.
After testing different mixes of protective coatings in actual operating conditions, Forgestal optimised its protective coating; which has given the best results when applied to Forgestal refractories.
It should be applied as soon as possible, before a visible attack has developed.
It is important to understand that a protective coating is an additional step you can make to improve the behaviour but ONLY WHEN POINTS 1, 2 and 3 HAVE
BEEN PROPERLY RESOLVED. A protective coating will be of little or no use if applied on a bad foundation or when attacked with non burnt particles or ashes.
Even with all the listed precautions, the need for maintenance will be, normally, higher than would be with a chemically unaggressive fuel.
The replacement of damaged sections for new ones will assure that the lining remains in excellent operating conditions.
A profitable life span of the refracory is completely compatible with the use of pet coke as a fuel, provided that:
A perfect combustion is assured, without accumulated non burnt sediment.
Accumulation of sediment and ash is avoided by conducting an efficient vacuum cleaning.
The right refractory is used, with a proven resistance to chemical attack.
The life span of the refractory can be improved by applying a good protective coating from the beginning, and a good maintenance with a quick replacement
of damaged sections.
Layers of non burnt particles accumulate on the kiln car because of rough grinding, uneven feed or feeding pet coke into a low
Accumulated, non burnt particles and/or ash create a “micro-climate” with an aggressive atmosphere for the refractory.
Standard refractory, strongly attacked by the
Penetration of the attack after 2.5 years working simultaneously in the same kiln with pet coke.
Forgestal / Refractarios Campo kiln cars working with pet coke