Energy efficiency of lime brining
Practical Action
Figure 1: American Society of Testing Materials
ASTM Rapid Sugar Test (using hydrochloric
acid)
Apparatus
300ml Erlenmeyer flask (a conical flask having
contents volume marked on it).
100ml burette with stand.
Balance capable of weighing 0.85g and 0.5g to
an accuracy of 2%.
No.100 mesh sieve (0.15mm). CO2 - free distilled
water if available.
Hydrochloric acid (specific gravity 1.18).
Methyl orange indicator.
Phenolphthalein indicator.
15g of sucrose (granulated sugar is satisfactory).
Method
This procedure enables a semi-direct reading of the
available CaO to be obtained. It is important to ensure
that the sample is exposed as little as possible to the
atmosphere during preparation and storage.
Prepare a standard HCl solution which has
15.7ml of HCl (specific gravity 1.18) per litre of
CO2 - free distilled water. The solution is
standardised against 0.85g of anhydrous Na2CO3
with methyl orange as indicator so that this
amount will neutralise exactly 90ml of standard
HCl solution. In adjusting for this, add more water
if it is too strong or more acid if too weak.
Take 0.5g of lime which has been passed through
a 100 mesh, brush it into the 300ml flask
containing 20ml of CO2 - free distilled water, and
stopper the flask. Swirl and heat to boiling for two
minutes. Add 150ml of water and at least 15g of
sucrose. Stopper the flask and shake at intervals
for 5 minutes. Allow to stand for 30 to 60
minutes. Add two drops of phenolphthalein, wash
down stopper and sides of flask with more
distilled water then titrate in the original flask
with the standard HCl solution. Add about 90% of
the estimated amount of the acid before shaking
the flask and then complete titration with the
final acid being fed slowly until the pink colour
disappears. Note the reading.
Calculation
A 1ml reading on the burette gives an available CaO of
1%.
Mf
The mass of fuel used per
tonne of quicklime produced
must be carefully recorded in
the field over a set period of
time. It is relatively easy to
obtain a figure if limestone is
burned using a batch process.
However, if a continuous or
semi-continuous process is
used, then care must be
taken that the mass of fuel
used and the mass of
quicklime produced
correspond directly. In our
example, we will take a figure
for the coal used as 200
kg/tonne of quicklime
produced.
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