Chemical Engineering Report: Sugar Beet Juice Purification Analysis

This report provides a comprehensive analysis of the sugar beet juice purification process, focusing on the preliming stage within a classical purification method. The report outlines the objectives of purification, which include increasing the purity of the juice and removing impurities such as suspended solids, non-sugars, and reducing pH. The design methodology includes detailed calculations for vessel sizing, material balances, and energy balances. The preliming process is examined in detail, including the reactions involved, the role of lime addition, and the design considerations for the reactor. The report includes assumptions, calculations, and the design of the cooling system and process control systems. It also details the chemical reactions and stoichiometry, and the overall material and energy balances for the prelimer, and the results of the design, including the required cooling capacity. The report also provides the design of process control systems and a mechanical design specification sheet.

Report
Purification
Introduction
This section will cover the purification segment of the process. This segment will initially provide
an outline and different phases of purification for the method chosen. The strategy, assumptions
and techniques of the design of each unit operation will be described. The major results from
the design will be evaluated and the design methods will be elaborated. Departure
Purpose of Purification
The primary objective of purification is to prepare the raw juice for evaporation and fermentation
by increasing the purity of the solution. In this case, the diffusion juice is purified from 87.5% to
93% by dry mass. Untreated sugar beets are composed of 2.5% by mass impurities that are
comprised of a variety of minerals, acids colloids and nitrogenous compounds. Because of
pre- treatment and diffusion, these impurities are released into the juice, and their presence can
affect the operation of the evaporators and fermenters. The purification process removes
 suspended solids,
 decreases the non-sugar levels,
 reduces pH
 Reduces the hardness of the solution.1
Theory of Purification
As raw juice consists of certain impurities such as non-sugars, suspended solids and collides.
Milk of lime (MOL) is added to the heated raw diffusion juice in a few steps to precipitate and
destabilize the non sugars. Carbonation gas, CO2 is also added in two steps, which absorbs the
impurities and colors to precipitate the lime as calcium carbonate (CaCO3), a byproduct. It traps
the color bodies and impurities from the liquor by inclusion within the carbonate crystals.
The precipitated calcium carbonate is separated from the juice in the clarifier2.Thin juice is the
product of this section and Calcium Carbonate is the byproduct. Thin recovered thin is
sent to downstream sections for further processing
Following Reaction takes place
Ca (OH )2 +CO2 yields
→
CaCO3 + H2 O
Thin Juice obtained has following characteristics.
 Low color
1 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons, Page 190
Technology, N.I.o.S.a. Carbon Dioxide. Thermochemistry Data for Carbon Dioxide]. Available
from: http://webbook.nist.gov/cgi/cbook.cgi?ID=C124389&Units=SI%2F&Mask=1#ThermoGas
2 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons, Page 213

 High purity
 Minimal hardness
 Free of insoluble solids
 adequate settling and filterability
 adequate thermal stability (resistance against heating without alteration)
Method of Purification
The process of purification involves the addition of lime and carbon dioxide gas in a series of
stages. Two methods are widely used in industry Classical Purification and Defeco Purification.
Defeco purification involves combining two or more of the liming and carbonation stages to
reduce the number of vessels required, however requires a very large recycle of suspended
solids, which causes additional costs.
Appendix consists of detailed study of both methods and comparison sheet. Classical
purification method is selected for this project. Classical Purification steps include:
 Prelimar,
 Mainlimer,
 First Carbonation,
 Clarifier
 second carbonation
 Ultrafiltration
The ancillary operation is a rotary drum filter that dries the underflows solids from the clarifier.
Overall Purification section will be able to produce 59716 Kg/Hr purified thin juice to
downstream evaporation Section.

Process Description
1. Prelimer
This section will provide an overview of the function of the Preliming step. This section will detail
the design process for the preliming reaction starting with the reaction kinetics and vessel
sizing. The energy and mass balances over the prelimer will be demonstrated. The reaction
vessel requires cooling to maintain isothermal operation and cooling jacket and coil design will
be discussed.
Agitation design will then be detailed. Finally, process control arrangements shown on the
schematic below will be discussed. A mechanical design specification sheet will also be
produced
Preliming has these main functions:
 To neutralize the acidity of the diffusion juice
 To precipitate certain nonsugars
 To destabilize the colloids

The lime is added in the form of Ca (OH )2 solution which causes precipitation and neutralization
reactions. In Preliming, small amount of lime (about 0.2 to 0.7% on juice) is added. The
prelimer operates at pH 8.5, atmospheric pressure and 40°C3. The liming time of the juice in
this step is about 10 to 15 minutes.
Six-second order reactions occur in the Prelimar. Three Precipitation reactions and three
neutralization reactions occur, although, the neutralization reactions do also produce
precipitates. The precipitation reactions occur between Ca(OH)2 and oxalate minerals of
sodium, potassium and magnesium with each forming calcium oxalate precipitate and the
corresponding metal hydroxide. The lime causes the neutralization of oxalic, citric and tartaric
acid which each produce a calcium precipitate and water.
In theory there are 4 processes happening in the liming stages and these include precipitation,
neutralization, destabilization and decomposition. The milk of lime in the form of Ca(OH)2
solutions reacts with a variety of impurity components. In Preliming, the two main processes are
precipitation to reduce mineral content and neutralization to reduce acidity in the juice. The
content of diffusive juice is variable and complex. Therefore, the Preliming process is simplified
to six major reactions that are most likely to occur during the Preliming process.4
Design Method
3 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons page 232
4 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons page 122

Size of the Prelimar5
Juice flow= 452181 Kg
Hr =7536.35 Kg
min
Density of Juice= 1.03 Kg
L
Volume= Mass
Density =7536.35 Kg/min
1.03 Kg
L
= 7316.85 L
min
Assumptions
1- Hold time 10 minutes
2- 10% increased between diffusion juice and limed juice
3- 10% extra capacity for foam
Hence the volume calculated is
V =
( 7316.85 L /min
1000 L
m3 ) × ( 10 min× 1.1× 1.1 ) =88.5 m3
General Assumption Height to Width ration 2:1
V = ( π
4 × D2 ×h )= ( π
4 × D2 ×2 D )=( π
2 × D3
)
D= 3
√ 2 v
π =3
√ 2 ×88.5
π =3.9m
Hence dimension of Prelimer
Diameter=3.9m Height=7.7 m
Material Balance
5 Beet-Sugar Handbook, 2007, John Wiley and Sons page 234

Average Raw sugar Beet Composition 6
Component Position
water 75
SBP 5
Sucrose 17.5
Nitrogenous Compounds 1.1
Non-nitrogenous
Compounds 0.9
Minerals 0.3
Unknown/Other 0.2
Raw juice received is 87.5% pure (As stated overall balance sheet). This means that 100 kg of
dry substance of this juice (after all its water has evaporated) contains 87.5 kg of sugar and 12.5
kg of nonsugars or impurities, which need to be removed.
Total Beet Flow= 490672 Kg
Hr
Total Impurities ( 2.5 % ) =.0025× 490672 kg
Hr = 12266.8 Kg
hr
Mineral compositoin= 0.3
2.5 × 12266.8 Kg
Hr =1472 Kg
Hr
Nitrogenous compounds and unknowns are considered as colloids.
Colloids=
( ( 1.1
100 )+( 0.9
100 ))× 490672 kg
hr =9813.44 Kg/ Hr
Assumptions
 The following assumptions were made based on the above table to simplify design:
All mineral composition was represented by Oxalates compounds of Sodium, Potassium
and Magnesium.
 All are present in equal masses.
All non-nitrogenous compounds are represented by oxalic, citric and tartaric acid. All
present in equal quantities
 The nitrogenous compounds and unknown is assumed to contain long chained colloids
and other components that will pass through purification unchanged. The colloids flow
calculated above is 9813.44Kg/Hr.
6

Mineral compositoin each= 490.7 Kg
Hr
Molar flow rate of minerals can be calculated as
Component MW (g/mol) Mass (kg/h) Molar Flow (mol/s)
Sodium Oxalate 134 490.7 1.017
Potassium Oxalate 166 490.7 0.821
Magnesium Oxalate 112 490.7 1.217
Non−Nitrogenous Compunds Compostion= 0.9
2.5 × 12266.8 Kg
Hr = 4416 Kg
Hr
Each compunds=1472 Kg/ Hr
Molar flow rates of these compounds can be computed as
Component MW (g/mol) Mass (kg/h) Molar Flow (mol/s)
Oxalic Acid 90 1472 4.54
Citric Acid 195 1472 2.10
Tartaric Acid 150 1472 2.73
Table 92 - Non-nitrogenous compounds composition
The reaction stoichiometry used to determine relative molar quantities for each reaction. Industry
suggests that the extent of reaction of the precipitation and neutralization reactions are 35% and 65%
by moles respectively.7 Therefore, the Ca(OH)2 requirement can be determined in each case and the
unreacted Ca(OH)2 will also be known: Detail of chemical reactions explained in Appendix A
Reaction Extent of Reaction (%
moles)
Ca(OH)2 in
(mol/s)
Ca(OH) Out
(mol/s)
1 35 1.017 0.661
2 35 0.821 0.534
3 35 1.217 0.791
4 65 4.54 1.589
5 65 2.1 0.735
7 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons page 105

6 65 2.730 0.956
Total 12.425 5.27
Ca(OH)2 Requirement can be determined as
Ca(OH)2 Required 12.425 mol/s 3314.5Kg/Hr
water required 70%8 2320 Kg/Hr
Lime flow rate 5635Kg/Hr
Mass Balance
Component MW (kg/kmol) Molar Flow (mol/s) Mass Flow (kg/Hr)
Water 18 6037.76 391247
Sucrose 342 39.528 49647.00
Sodium Oxalate 134 1.017 491
Potassium Oxalate 166 0.821 491
Magnesium
Oxalate 112
1.217
491
Oxalic Acid 90 4.54 1472
Citric Acid 195 2.10 1472
Tartaric Acid 150 2.73 1472
Colloids 9813
Lime flow - - 5635
Total 462230
Material Out:
Component MW (kg/kmol) Molar Flow (mol/s) Mass Flow (kg/Hr)
Water 18 6037.760 394524.0
Sucrose 342 39.528 49647.00
Lime - 5.27 1662
k2c2o4 166 0.53400 319
Na2C2O4 134 0.66100 319
MgC204 112 0.79100 319
H2C2O4 90 1.590000 513
C6H8O7 195 0.735000 513
C4H6O6 150 0.860000 513
Colloids and
Unknown - - 9813
CaC204 128 2.95000 1360.000
Ca3(C6Hs07)2 498 0.680000 1220.000
CaC4H4O6 188 1.77000 1201.000
KOH 56.1 0.574000 116.0000
NaOH 40 0.712000 102.0000
Mg(OH)2 58.3 0.42600 89.0000
Total
462230
8 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons page 216

Energy Balance
Energy Balance
An Energy Balance conducted over the prelimer. The diffusion juice enters the reactor at 50°C
after being cooled by E-501. The Milk of Lime solution enters the reactor at ambient
temperature of 25°C. The reaction proceeds isothermally at 40°C, so the product stream also
exits at 40°C. With the concentration of reactants being so low and the complicated nature of
the reaction process in this instance, heat of reaction will be assumed to be negligible and will
not be considered. Impurities in the streams will be considered energetically equal and can be
represented by one specific heat capacity of 1.0 kJ/kgK as this is averaged over the known
impurities. The milk of lime heat capacity if determined as a function of pure component heat
capacities and mass fractions:
Cp of Ca(OH )2 Solution= ( 3314.493
5634. .638∗1.18 KJ
KgK )+( 2320.145
5634.638∗4.18 KJ
K )=2.45 KJ /kgK
The sucrose and water can be represented by a heat capacity for a sucrose solution of 3.75
kJ/kgK.9
Also, assuming a reference temperature of 25°C for all enthalpy calculations.
Therefore the enthalpy of the inlets is:
As the outlet temperature is 40°C, the outlet enthalpy can be calculated as
Component Mass Flow (Kg/s) Specific heat
Capacity (kJ/kgK) Inlet Temperature (°c) Enthalpy
(kJ/s)
Sucrose Solution 125.61 3.75 50 11775.9
Impurities 3.130 1 50 78.3
Lime 2.490 2.45 25 152.5
. Enthalpy 12006.70
9 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons page 221

Component Mass Flow (Kg/s)
Specific heat
Capacity (kJ/kgK) Inlet Temperature (°c)
Enthalpy
(kJ/s)
Sucrose Solution 125.18 3.75 40 7041.4
Impurities 2.190 1 40 32.9
Lime 1.050 2.45 40 38.6
. Enthalpy 7137
Q=Hout −Hin=7137−12006.70=−4870 KW
Since the heat of reaction is being neglected and the outlet temperature is 40°C, the outlet
enthalpy can be determined.
This duty indicates that the prelimer requires a cooling system capable of removing 4893KW to ensure
that the reaction is isothermal at 40°C.
Cooling system Design
***
Process Control
As seen from the vessel schematic, R-501 has been designed with a basic control system.
Temperature Control
Control valve CV-501 is controlled by the temperature controller TC-501. TC-501 measures the
temperature inside the vessel and can adjust the flow rate to increase or decrease flow of
cooling water to combat any set point deviations. TC-501 should be a direct acting controller as
in the event of an increase in vessel temperature, CV-501 would need to be opened more to
increase the cooling rate to drive the temperature back to the set point. This valve should be an
air-to-close valve because in the event of air instrument air failure, the valve should fail fully
open to ensure that cooling is maintained. As the alternative is no cooling would be available at
all.
PH Control

Control Valve CV-502 is controlled by pH controller pHC-501. pHC-501 is measuring the pH
inside the reactor vessel. The pH should be maintained at 8.5 and if the pH decreases pHC-501
will open CV- 502 to increase the flow of lime to the vessel to increase pH. pHC-501 should be
a reverse acting controller as an increase in pH would require a decrease in flow of Lime and so
pHC-501 would act by closing CV-502. CV-502 should be an air-to-open valve as a result of air
failure, inventory would need to be controlled and or else it would be unloaded into the reactor.
Level Control
Control Valve CV-503 is controlled by level controller LC-501. LC-501 is measuring the level in
the tank and controlling CV-503 to maintain the desired liquid level. LC-501 should be direct
acting controller as it detects an increase in level in the vessel will send a signal to open CV-
503. CV-503 should be an air-to-open valve due to a failure of air supply, the inventory would
need to be controlled and the vessel would have a capacity to handle an increase in level to
give time for operator intervention.
Stage 2 – Mainlimer R-02 (CG)
Introduction
This section will provide an overview of the function of the mainliming stage. This section will
detail the design process for the preliming reaction starting with vessel sizing. Then energy and
mass balances over the mainlimer will be demonstrated. The reaction vessel requires heating
with steam to maintain isothermal operation with a steam jacket. Agitation design will then be
detailed. Finally, process control arrangements shown on the schematic below will be
discussed. A mechanical design specification sheet will also be produced.
Theory
The main purpose of the Mainlimer to supply lime in excess in preparation for the first
carbonation process. Lime is added to between 1-2.5% by mass of the vessel contents10.
 Mainlining is performed for the following reasons:
 To increase the pH and alkalinity of the juice
 To complete the reactions between nonsugars and lim
To overlime the juice (the excess lime is used as filter aid) This is done so that during
carbonation, when CO2 gas is bubbled through, calcium carbonate precipitates form and this
helps in settling and filterability. The outlet from the prelimer and the milk of lime are both fed in
to the top of the Mainlimer vessel. It also raises the pH to 11 which causes the decomposition of
invert sugars.
This invert decomposition defines the residence to 15 minutes to reduce the level to a negligible
presence. This process takes place at 85°C. Colloid destabilization is also assumed to happen
at this stage. It is estimated that 90% of the colloids are destabilized by 10% of the Ca(OH)2
present. The layout and structure of the Mainlimer vessel is the same as for the prelimer with
the temperature controller controlling steam supply instead of cooling water.
10 Asadi, M., Beet-Sugar Handbook, 2007, John Wiley and Sons page 787

Design Methods
Vessel Sizing
The mainlining process is very empirical and the kinetics are not clear. Therefore, it is very
difficult to estimate the size of the vessel by conventional kinetics based design equations. The
residence time, which is 15 minutes, is used to estimate the size.
The mass flow rate of lime required to comprise 1.5% of the reactor volume can be determined
and then the total volumetric flow rate can be calculated assuming a bulk density of 1100 kg/m3,
which increases the presence of suspended solids.
Lime Requirment =Limer Feed
0.985 −Limer Feed=( 127.17
0.985 −127.17 )= 1.94 Kg
s
Unreacted Lime∈the feed= 0.391 Kg
s
Water required (70 %)= 0.273 Kg
s
Total Lime Feed=0.391+0.273=0.664 Kg/ s
The respective volumetric flow rates can then be determined:
Component Mass Flow rate (kg/s) Density (kg/m3) Volumetric Flow rate (m3/s)
Main Feed 127.17 1100 0.11561
Lime Feed 0.664 1200 0.00055
Total 216.17 0.1161
V =t ×q=900 × 0.1161=105 m3
Hence dimension of Mainlimer
Diameter=4.1 m Height=8.2 m
Material Balance
The material balance carried out over Main Prelimer and is as below
Material In
Component Mol/s Mass Flow (kg/Hr)
Sucrose 0.648 49647
water 6.09 394524
Impurities 2496
Lime Feed 2390.4
Colloids from feed 9813.44
Total 458870.84
Material Out