Batch Calculations

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Batch Calculations
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Batch Calculations

• Uses
• Making the Calculations

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Uses
Batch calculations are used to determine the
amount of each raw material needed to obtain a
specific composition. For example, in many glass
forming systems the raw materials give off gasses
as they are melted. The weight of these gasses
must be taken into account when preparing the
batch. In industrial processes, different
shipments of raw materials may not be exactly the
same. This has to be remedied by doing new batch
calculations to determine the new proportions.

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To CaO
50
Example Composition
Glass Forming Region
Tridymite
SiO2
50
To Na2O
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Making the Calculations

• As an example we will work through the batch
  calculations necessary to produce a glass that
  contains
• 70wt SiO2
• 20wt Na20
• 10wt CaO
• This is the composition of the point on the
  Diagram

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We first have to determine what raw materials are
needed to form a glass of that compositions. To
get SiO2 we will add SiO2, to get Na2O we will
add soda ash(Na2CO3), and to get CaO we will add
limestone (CaCO3). When the soda ash and
limestone are heated they both decompose. Na2CO3
? Na2O CO2 CaCO3 ? CaO CO2 It is
helpful to assume some weight of glass. For our
calculations I will assume that we are going to
end up with 100.00g of glass.
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Using that assumption we know that our glass is
going to contain 70.00g SiO2, 20.00g Na2O, and
10.00g of CaO. The silica does not decompose, so
we just add 70.00g of SiO2 to our batch. The
other two components of the glass do decompose,
so we must calculate the weights of raw material
needed. Na2CO3 ? Na2O CO2 Na2CO3
105.99g Na2O 61.98g Dividing the
mass of Na2CO3 by the mass of Na2O gives
1.71. This means that for every 1.71g of Na2CO3
that goes into the batch we will get 1.00g of
Na2O. Taking 1.71 and multiplying by 20.00g it
gives that we need to add 34.20g of Na2CO3 to our
batch.
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Performing the same calculation for the limestone
CaCO3? CaO CO2 CaCO3 100.09g
CaO 56.08g Dividing the two we get
1.78 1.78x10g 17.85g We need to add 17.85g of
CaCO3. These calculations tell us that the batch
should consist of 70.00g SiO2 34.20g
Na2CO3 17.58g CaCO3 to give us the desired final
composition.