Drop of kiln feed rate
Dear Mr. TED.
Your suggestions in the form are very infermative and problem solving in nature. We have a problem in our process. Details of the problem are as follows.
The Kiln which is running with 350 TPH is falls down to 250/260 TPH only. Even after reducing the kiln feed rate up to 250 TPH, nox is not developing more than 300 ppm (Normally we run the kiln at 500 ppm) also the cooler and kiln is getting dusty and burning zone visibility is poor. But at this operating condition also the fee lime content is <0.50 % and liter weights are 1300 g/l.
To over come the problem we increased the Liquid Content from 28.5 % to 30.5 % to boost up the kiln feed rate. We succeed in increasing the feed rate from 250 to 330 TPH and sustain for three days only.
Again the same problem has repated though the raw mix & coal composition are same when the kiln ran with 330 TPH.
Raw mix compostion in different feedarates are :
Feed rate : 330 260 Clinker at 330 Clinker at 260
SiO2 : 13.32 13.03 22.36 22.40
Al2O3 : 2.91 2.92 5.29 5.11
Fe2O3 : 3.15 3.19 4.89 4.99
CaO : 43.11 43.57 64.76 64.58
MgO : 0.90 0.88 1.46 1.43
Mn2O3 : 0.08 0.08 0.13 0.13
SO3 : 0.05 0.05 0.47 0.45
Na2O : 0.00 0.01 0.06 0.05
K2O : 0.29 0.31 0.49 0.50
TiO2 : 0.22 0.22 0.38 0.38
P2O5 : 0.07 0.08 0.14 0.15
Free silica : 8.64 8.50 - -
LSF : 99.77 102.50 88.5 88.3
AM : 1.03 1.04 1.22 1.16
Technical details: 6 stage pre-heater (PSP) with ILC, Multi channel burner & IKN Pendulum Cooler. Current Miics of kiln and coller are attached for your reference
We eagerly await for your valuable suggestion.
Thannks in advance.
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re Drop of kiln feed rate
Based on chemistry of KF and clinker , it seem lower AM ( 1.16-1.22) resulting lower viscosity of flux and dusty operation of kiln. You can increase AM to 1.4 in clinker by reducing Fe2O3 step by step.
Is there any changes in residue level of KF or coal ash?
re Drop of kiln feed rate
I agree with Tushar that your AM is quite low and would normally contribute to a dusty kiln situation. However, as you pointed out, your kiln production has been acceptable for 3 years with the same AM. So, although your low AM may contribute somewhat to the dustiness, I don't think that it is the major cause in this instance.
The most common cause of dustiness in the kiln is a high sulphur recirculation. And, although the alkalis and sulphur in your clinker appear balanced (Alk/SO3=1.09), lack of oxygen in the back end of the kiln may still cause a significant degree of sulphur (and alkali) recirculation, since excess O2 is required to ensure that alkai sulphates are produced and exit the kiln. A lack of O2 at the back end of the kiln will also result in increased CO, which destroys NOx. This may explain the drop in NOx you experienced. Do you know the O2 and CO levels in your kiln inlet gas stream?
Looking at your raw meal and clinker sulphur content, it seems that a large proportion of the sulphur in the clinker is coming from the fuel. Do you use any petcoke or other high sulphur fuel component? A high sulphur fuel requires a higher oxygen content than normal in the back end to ensure complete alkali sulphatisation. What is the SO3 content of your hotmeal? Do you have data for hotmeal SO3 for both good and bad production rates?
Dusty kiln problems can also be process-related rather than chemisty-related.
I noticed your free lime is very low (<0.5%). Hard burning promotes large alite crystals which can result in excessive dust generation and, as the dust load increases, the clinker nodules become coated with a very porous, brittle layer which abrades away to dust in the cooler. This dust is then blown back into the kiln with the secondary air and this sets up a dust cycle that is hard to escape from. To improve nodulisation and escape this type of cycle you may need to increase the AM, increase liquid phase and/or slow down the kiln rotation.