239 posts
TimePosted 24/11/2010 08:42:31
xxxx says

### Re: coal savings

I do not have a recirculation air provision. it is a simple ball mill with dynamic seoparator for coal grinding. please send me the sheet for calculating the same at rajmadhuri1972@yahoo.co.in

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138 posts
TimePosted 24/11/2010 09:13:11
lalbatros says

### Re: coal savings

xxxx,

You will only be able to use this hot air in the burner.

Hot air at 250°C contains about  0.28  GJ/(1000Nm³).
You need about 8500 Nm³ to burn 1 ton of coal, on a stoechiometric basis.
Therefore, when burning 1 ton of coal, hot air will bring 0.28*8.5 = 2.38 GJ.
If your coal has 27 GJ/t, then hot air will spare you about 9% of the amount of coal needed for drying.
If you admit more than 10% oxygen in the mill/dryer, then you will need 16000Nm³ of hot air, and the saving will be about 17% (less than that since the consumption will increase due to the amount of exhaust gases)

Assuming drying requires about 4 GJ/tH2O, you will need about 0.4 GJ / tCoalDried for drying. This means 15 kgCoalBurned / tCoalDried. For 9 tCoalDried/h this leads to 133 kgCoalBurned / h . Therefore, your hot air requirement will be between 1000 Nm³/h and 2000 Nm³/h . This is very small compared to the availability of hot air.

Lal