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Raw meal to clinker ratio

In your first example, since you are using kiln feed containing a dust component to calculate your "raw meal" to clinker

ratio, we have to take this dust into account.

Let's say we start with 100t of fresh raw meal. In the kiln feed bin we are adding 8% kiln dust, ie 8t of dust. So, for

every 100t of fresh raw meal passing through the kiln we will actually measure 108t of kiln feed. Therefore, the kiln

feed to clinker ratio will be the raw meal to clinker ratio multiplied by 108/100 = 1.08

ie. if your fresh raw meal to clinker ratio is 1.55, your kiln feed to clinker ratio will be 1.55 * 1.08 = 1.674

However, using the LOI data you have already given, we can calculate your actual fresh raw meal to clinker ratio. eg;-

Given that;-

D = % dust in kiln feed = 8

K = % LOI of kiln feed = 35.4L = % LOI of the dust = 38

If R = % LOI of fresh raw meal

then

R = (1 + D/100) * K - (D/100 * L)

= (1 + 8/100) * 35.4 - (8/100 * 38)

 = 1.08 * 35.4 - 0.08 * 38

 = 35.2

Now that we know that the LOI of your fresh raw meal is 35.2%, we can calculate the actual raw meal to clinker ratio

for fresh raw meal using the formula;- 1 / (1 - R/100) = 1 / (1 - 35.2/100) = 1/(1 - 0.352) = 1/0.648 = 1.54

Therefore your meal to clinker ratio for kiln feed leaving the kiln feed bin is actually;-

1.54 * 1.08 = 1.66

 In your second example, with 4% bypass;-

Assuming the LOI of the bypass dust is close to zero then the kiln feed to clinker ratio would be;- 1.66 * 1/( 1 - 4/100)

= 1.73

If the LOI of the bypass dust is significant (> 10%), then this would have to be taken into account as well, using the

following calculation;-

B = % LOI of bypass dust.

Kiln feed to clinker ratio for 4% bypass = 1.66 * 1/(1 - 4/100 * (1 - B/100))

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The calculations assume that are measuring the feed rate of kiln feed which alreadycontains the recirculation dust. ie

in the situation where you are adding the recirculating dust to the fresh raw meal in the kiln feed bin, with the kiln feed

weigher locatedafter the kiln feed bin.

If you are measuring the kiln feed ratebefore the addition of recirculation dust then there is no need to even consider

the dust at all. You can just use the standard raw meal to clinker ratio calculation. ie.;-

1 / (1 - R/100) ' where R = LOI of fresh raw meal.

In your case this calculates to;- 1 / (1 - 35.2/100) = 1.54

 

To answer your second question regarding the case of 4% bypass dust with an LOI of 4.4%, the ratio will not be 1.65

it will be 1.726. If the ratio when there is no bypass is 1.66, then the ratio with bypass can never be less than 1.66,

because you are losing dust that would potentially have become clinker. So the ratio calculated by (tonnes of kiln feed/

tonnes of clinker) must decrease.

So, for the your case where kiln feed to clinker ratio is 1.66, with 4% bypass at 4.4% LOI the formula becomes;-

1.66 * 1/(1 - 4/100 * (1 - 4.4/100))

= 1.66 * 1/(1 - 0.04 * (1 - 0.044))

= 1.66 * 1/( 1 - 0.04 * 0.956)

= 1.66 * 1/(1 - 0.03824)

= 1.66 * 1/0.96176

= 1.66 * 1.0398

= 1.726

 

To make the formula clearer maybe I should have written it as;-

If A = % bypass dust.  B = %LOI of bypass dust.

then

  1

 Ratio = 1.66 * ---------------------------------

  1- [A/100 * (1 - B/100)]

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