Highest Production Target Achieved from Single Vertical Shaft Kiln (VSK)
Our previous jobs had always been ‘just a job’, but I feel that the role we hold now is more important than that; it has a purpose and gives us a lot of satisfaction in running India’s single largest VSK kiln.
There is only one thing that makes a dream impossible to achieve: the fear of failure and it was with us till we successfully commissioned the VSK kiln — potential to produce 350 Mt/day of clinker.
The kiln is having a diameter of 3700 mm (effective 3400 mm) and a H/D ratio of 3.5 — although, a 3.8 HBD ratio would have been more justified for better cooling of clinker.
Key equipment opted for (i) Screw Feeder with weighing device — 25 tph, (ii) Single-pan nodulizer drum with a movable scrapper, (iii) Dome-type discharge grate at the bottom, (iv) Pneumatic triple discharge gate, and (V) three Air-compressors — each capacity 7500 m3/hr volume at 3500 mmWG pressure, connected in series.
In my previous article, “Vertical shaft kiln” — this was categorically mentioned that an optimum clinker bed descending velocity is required to maintain an ideal residence-time of mix in the high-temp zone (B.Z.). And an ideal stay of material within this high range of temp would be 60–70 minutes to avoid the formation of hard mass and simultaneously it may invite trouble at the discharge grate.
From the above chart, this is quite comprehensible that a suitable material residence time can be maintained at a 300–350 TPD rate. But an optimum condition can be achieved at a 370–380 TPD rate.
Similarly, the kiln has started producing at the rate of 350 TPD in a consistent way and the measured value of kiln-Feed rate, Combustion air, and Exhaust gas volume as determined - shows a close similarity with the pre-calculated data as mentioned.
Composition of black-mix is maintained — keeping heat input around 875 K.Cal/Kg clinker as given below -
Contribution of liquid phase at 30% and keeping less viscous and more fluid (AM=1.34) characteristics to allow smooth bed movements from the top. Avoiding side or center discharge from the top enables the kiln to run in a continuous manner.
One additional booster air arrangement is provided to overcome the inclined fire problem (if it happens) by selecting the respective air inlet(s) to the affected area.
But this is recommended, not to allow more cold air when no such requirement is there.
Generally as discussed, except for some increase in clinker liquid content and an additional booster line — the operation of the kiln almost remains the same as a smaller dia kiln (50–100 TPD).
Earlier (before light-up), this was anticipated that air distribution across the bed would not be uniform because of its bigger cross-sectional area. An estimated 2500 m3 per unit area(m3/m2-effective) combustion air is the normal requirement for a specific heat use of 800–850 K.Cal/Kg clinker. But practically this is found there is no such occurring - like weak centerfire or center discharge.
The advantage of a bigger volume kiln with an optimum volume utilization factor would be favorable for — (i) lesser space requirements, (ii) minimum man-power involvements, (iii) energy savings, (iv) enhance manufacturing capacity (… no longer it can be identified as “Mini Cement Plant”).
And the biggest learning from this achievement is that it can’t become a success without the effort, the pushing back the boundaries, and improving with every fall.
And we think it’s finally settled, also we believe that -
Success is best when it’s shared ……….
