operate the rawmill without the hot gas generator

Anyone can tell me how to operate the rawmill without the hot gas generator. Our plan have a rawmill without hot gas generator. The heat sourse is from the kiln, but at initial we just use the heat when heat the kiln. So the heat sourse from heating the kiln is enough for operate the rawmill? and if increase the heat sourse from increasing the fuel firing in Calciner is affect to refractory of the suspension preheater

• It has been observed that normally hot gas generator is used for initial start up of the new kiln when raw mill must be started before the kiln. In such cases, precalciner can be used as hot gas generator even before the kiln light up without any problem. But please remember that this arrangement is only for those plants who intend to maintain at least 50% stock of raw meal in silo during operation. If raw meal silo level is often taken to below 50% level at the time of kiln shut down and raw mill capacity just meets the required kiln feed rate then it is better to have a hot gas generator to ensure regular supply of raw meal at start up of kiln
• my coal ball mill is 2.5 *4m with 10 tph having coal with 7 % input moisture & 1 % output moisture.
• it is connected with a auxiliary furnace.
• i want to calculate the amount of coal fired into the furnace to get grind the coal.
• Mill outlet temp . 80 deg
• velocity through mill 1.5 m/s
• media in mill is 27 t

xxxx, whoever you are,

The picture below shows what a typical answer to your question might be. (never trust any model !)
For this calculation, I made some assumptions that might not be suitable for your application (specially concerning safety):

– coal with Low Heat Value of 25.9 GJ/t (wet basis 1% moisture)
– coal analysis CHONS-Ash = { 66%, 5%, 5% , 1.5%, 1%, 20.5%}
– recirculation of 70% of the hot gases
– mill power consumption of 400 kW, fan power consumption of 40 kW

As you can see, 51 kg/h of coal are needed, in this case.
This is equivalent to an heat consumtion of 2.05GJ/tWaterVapor.
This is rather low and it is explained by the heat generated by the mill itself.
The sensible heat from the hot gases represent a power of 367 kW, which is slightly lower than the power of the mill.
The oxygen content in the exhaust gases is rather high: 16.5% .
This might be very undesirable depending on the volatile content and the fineness.
I maintained the requested gas speed at mill end (1.5 m/s).
Finally, the dew point of the exhaust gases is 54°C which is nearly 30°C between the gas temperature.

Increasing the recirculation will decrease the oxygen level.
Increasing the recirculation will also decrease the heat consumption.
For example, with a recirculation of 90%, the oxygen level drops to 9.7% and the heat consumption to 38 kg(coal)/h  or 1.53 GJ/tWaterVapor.
Note that increasing the recirculation also increases the dew point in the gas circuit. Eventually, the dew point will come too close to the gas temperature, and the risk of condensation on cold points will increase. Here, for 90% recirculation, the dew point rises to 77°C which is only 7°C below the gas temperature.

Overall, I like pictures!

What should be ideal tyre migration values for all three stations for a 6.2×90 , 10000 TPD kiln? Is there any relation between Kiln dia and ideal value?

The normal maximum design ovality for a tyre is .2% relative to the inside diameter of the kiln shell. This would give a difference to 8 mm between the horizontal and vertical outside dimension on a tyre for a 4000 mm kiln. Under ideal conditions, this would result in a shell ovality of 0.23%, but in practice this is rarely achieved. Experience has shown that ovalities become very critical at .5% and this should, therefore, be treated as an absolute maximum, with .4% being the point at which correction should be made.

Under cold conditions, it would be normal to find ovalities approaching .5% or, in some cases, even more. It is, therefore, important to obtain the minimum cold gap, but at the same time giving ample clearance to allow the shell to expand within the tyre without waisting occurring. It is normal to assume a temperature differential of 200°C at the hottest tyres which would fall to 100°C at the coldest tyre. The differential of 200°C would normally assume a maximum shell temperature of about 325°C. Hotter shell temperatures will require larger cold gaps and thus increase ovality and refractory stress when turning the kiln cold or at low shell temperatures for any appreciable length of time. High shell temperatures also reduce the stress and deflection resistance capabilities of the shell which result in reduced shell life.

Best regards