A basic refractory lining in the burning zone must have a good protective coating in order to achieve maximum refractory life. The type of coating depends largely on the chemical composition of the kiln feed and is uniformity. Volatile constituents such as alkalis, sulphur, and chlorides can attack and become a cause for refractory failure.
That to say a plant chemist must not only concern himself with the ultimate cement quality a kiln feed will deliver but must also design the mix to possess good burnability and coatability properties in the rotary cement kiln.
Quality of workmanship in refractory lining installations has a profound influence on how well these refractories perform in a rotary kiln. Proper installation according with established procedures, some extra efforts exerted during construction of refractory lining can pay dividends in longer refractory life and kiln uptime.
Apart from the right type of refractories for each zone and location of the rotary kiln, refractory shapes should not deviate by more than 2 mm on each plane. For more detail see:Properties and Type of Refractories required for a Rotary Cement Kiln
The liquid has a critical role in clinker nodulization and clinker mineral development and properties. Solid-solid reaction is very slow process while solid-liquid reaction
Since the costs of refractories are much lower in comparison to the costs for the loss in kiln production, labour expenses, fuel for reheating the rotary kiln, it is advisable to consider the refractory quality and performance ahead of the price of the refractory itself.
kinetics is much faster, so without liquid phase the diffusion of Ca ions towards C2S would be extremely slow, and the conversion of C2S and free lime to C3S would be almost impossible in the kiln. The amount of liquid phase in the burning zone varies between 23% and 29%.
Higher values can be damaging to most refractory bricks in the absence of a stable coating. As the refractory brick is infiltrated and saturated with liquid, its elastic modulus (relation between stress and strain) increases and so does its tendency to spall off. This simple fact explains why hotter than normal temperatures are so beneficial to clinkering and yet so harmful to the refractory lining as low viscosity liquid infiltrates the refractory lining faster, leading to its premature failure.
There are a number of cement plants using Oxygen Enrichment Technology in order to improve production capacity. Oxygen Enrichment Technology is an oxygen injection system that connects to kiln burner or precalciner burner to enhance the combustion of the fuel. In general, the use of oxygen enriched combustion air in the clinker burning process allows an increase of the energy efficiency, production capacity or substitution of fossil fuels by low calorific value.
The process helps to raise the adiabatic flame temperature and the flame becomes shorter and brighter. However, Oxygen Enrichment Technology is limited by increasing damages of the kiln refractory and higher NOX emissions due to increasing thermal NOX formation in the sintering zone.
In continuation of our previous articles regarding life of refractory lining of a cement rotary kiln (First part: How to minimize Refractory Failure and wear of Refractories inside a Rotary Kiln Second Part:Factors Responsible for Refractory Failures and Wear of Refractories of a Cement Rotary Kiln) here (Third and Last Part), we have outlined few more causes of refractory failures, their remedial measures in order to get the maximum life of refractory lining inside a cement rotary kiln :
Each rotary cement kiln with every revolution undergoes shell deformations in the vicinity of the rotary kiln tire that have a detrimental effect on the refractory lining. This deformation is referred to as Shell Ovality. Ovality can be checked with the "HOLDERBANK" shell test unit.
Each cement plant should have a schedule to frequently check the slippage of the kiln tire at least twice a month as there is a direct relationship between this slip and shell ovality. Excessive slippage is a warming signal that shell ovality might be too high. Of equal importance are annual checks of rotary kiln alignment preferably when the cement kiln is in operation because misaligned rotary cement kilns too, is responsible for excessive stress and wear of refractories.
Last but not the least - following proper kiln operating procedures and being consistent in control follow-up are two things, very important for achieving a longer refractory lining life. There are no short-cuts in this respect.