APPENDIX III
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Calculation of a two-stage extraction system at 30^{o}Bx
and comparison with measured results in a pilot plant
1. Date juice extraction in two stages at 30^{o}Bx (calculated).
Data given are:
- Composition of dates (flesh)
moisture (M): 20%
soluble solids (SS):
70%
non-soluble solids
(NSS): 10%
- Moisture content for presscakes (P)
P_{1} = 62%)
) empirical data
P_{2} = 72%)
- Date juice recovered 30^{o}Bx
- Equilibrium in each extraction stage is reached
- Non-soluble solids do not enter in juice, but remain in presscakes
- No water or solid material is spilled in the process
In the extraction schedule below the underlined figures are known data. To facilitate calculation initially the following letter symbols are used (all on weight basis).
water in S_{2} = a
soluble solids in S_{2} = b
water S_{3} = c
water in P_{1} = w
soluble solids in P_{2} = x
The figures in brackets are the result of the calculations.
Material Balance
OPERATION |
MATERIAL |
COMPOSITION (PERCENTAGE) M SS NSS |
WEIGHTS TOTAL H_{2}0 SS NSS |
|||||
Extraction | Dates Date Juice (S_{2}) |
20 (90.6) |
70 (9.4) |
10 0 |
_{100}^{a + b
} (208.8) |
_{20}^{a
} (189.1) |
_{70}^{b
} (19.7) |
_{10}^{} 0 |
Slurry 1 | ^{100+a+b} (308.8) |
^{20+a} (209.1) |
^{70+c} (89.7) |
_{10} | ||||
Separation | Date Juice (S_{1}) Presscake (P_{1}) |
70 62 |
30 (26.6) |
0 (11.4) |
_{12.4+a+b(221.2)
} ^{} (87.6) |
_{a-34.3(154.8)
}^{w
} (54.3) |
_{46.7+b(66.4)
}^{x
} (23.3) |
_{ }^{} _{0} ^{ } ^{10} |
Extraction | Presscake (P_{1}) Water (S_{3}) |
62 100 |
(26.6) 0 |
(11.4) 0 |
_{(87.6)}^{c
} (169.9) |
_{(54.3)}^{c
} (169.9) |
_{(23.3)}^{} 0 |
_{10}^{ }
^{0} |
Slurry 2 | ^{87.6+c} (257.5) |
^{54.3+c} (224.2) |
^{(23.3)} | ^{10} | ||||
Separation |
Date Juice (S_{2}) Presscake (P_{2}) |
(90.6) 72 |
(9.4) (7.4) |
0 (20.6) |
_{a + b(208.8)
}^{87.6+c-a-b
} (48.7) |
_{a(189.1)
}^{54.3+c-a
} (35.1) |
_{b(19.7)
}^{23.3-b
} (3.6) |
^{0}_{ }
_{ } _{10} |
Calculation
Equilibrium is reached, hence Brix of the juice in the presscake P_{1} is the same as in recovered juice S_{1} (30^{o}). It follows:
out of which x and w can be solved (x = 23.3; w = 54.3).
All other unknown components in weights can now be expressed in a, b and c.
- Since S_{1} is 30^{o}Bx and contains no soluble solids, it follows:
(equation
1)
- Juice in presscake P_{2} and Date Juice S_{2} are in equilibrium hence have the same Brix level, expressed as follows:
and
(equation 2) b
- Moisture content P_{2} is 72%, hence
(equation 3)
Three equations, three unknowns, a, b and c can now be solved:
a = 189.12 rounded 189.1
b = 19.655 rounded 19.7
c = 169.89 rounded 169.9
After having inserted these results in the schedule, all other unknowns can now be calculated and the material balance is completed.
2. Date juice extraction in two stages at 30^{o}Bx in date syrup pilot plant (Libya)
The extraction part of the pilot plant (about 50 kgs/hr date input) consists of two horizontal continuous extraction vessels in which dates and extraction liquid are in contact at 85^{o}C for about ½ hour whilst being sitrred. Separation between the stages consists of a combination of a vibratory screen followed by a twin expeller press. The performance data for the extraction were compiled by determining
a) weight and composition of
dates
b) weight and composition of presscake P_{2}
c) weight and composition of recovered juice, S_{1}
d) composition of juice S_{2} by sampling during operation.
Material Balance
Operational | Material |
Composition |
Weights |
|||||
Extraction | Dates Date Juice (S_{2}) |
20 89.6 |
70 9.3 |
10 1.1 |
100 198.2 |
20 177.8 |
70 18.4 |
10 2.0 |
Slurry | 298.2 | 197.8 | 88.4 | 12.0 | ||||
Separation | Date Juice
(S_{1}) Presscake (P_{1}) |
67.3 63.2 |
30.0 28.5 |
2.6 8.3 |
221.0 77.2 |
148.9 48.9 |
66.4 22.0 |
5.7 6.3 |
Extraction | Presscake (P_{1}) Water (S_{3}) |
63.2 100 |
28.5 0 |
8.3 0 |
77.2 149.4 |
48.9 149.4 |
22.0 0 |
6.3 0 |
Slurry | 226.6 | 198.3 | 22 | 6.3 | ||||
Separation | Date Juice (S_{2}) Presscake (P_{2}) |
89.6 72.0 |
9.3 12.8 |
1.1 15.2 |
198.2 28.4 |
177.8 20.5 |
18.4 3.6 |
2.0 4.3 |