Sugar Plant Design Calculation
Short Description
sugar plant design calculations...
Description
Sugar Definition Sucrose is common table sugar obtained from sugar cane and sugar beets. The chemical Formula C12H22O11 which does not reduce Tollens or Feling’s reagents is determined by the stereochemistry of the D-Glucoside and D-Fructroside linkage to form sucrose. The results of XRay studies and the Synthesis of +sucrose lead to the conclusion that (+) Sucrose is a beta DFructoside and an alpha D-Glucoside.
The Chemical Form of the Sucrose
In Simple Form of sucrose
Physical properties of Sucrose 1) Pure Sucrose Crystal are Transparent and colorless 2) Heat Conductivity of crystallized Sucrose Only Crystal of sucrose 00.00139 cal/cm-sec°c 3) The Dipole moment is found to be 3.1x1018 dyne/cm² 4) The Dielectric constants of sucrose Crystal is different directions values and between 3.5 and 3.85 was found. 5) Piezoelectric effect of sucrose was observed, the sucrose is Dia-magnetic, and the specific magnetic susceptibility is being 0.57. 6) The density of crystalline Sucrose at 1.5°c is 1.5879gm/ml, were found powdered crystalline sucrose. 7) Linear thermal expansion 8) Melting point of sucrose is 185-186°c 9)
Specific Volume of Crystallized Sucrose is 0.63ml/gm @ 15°c under Normal pressure.
10) Molecular weight of sucrose is 342.296 11) Normal Entropy of sucrose is 86.1kcal/mole 12)
Enthalpy of formation is 530.8 kcal/mole
13)
Work of formation amount to -317.6kcal/mole at 25°c and 760mm pressure of Hg.
14)
Enthalpy of combustion is -1351.3kcal/mole
Chemical Properties of Sucrose: 1) Sucrose is a carbohydrate of the formula C12H22O11 2) It is a disaccharide, consisting of monosaccharide components. 3) Refined sugar contains about 99.99% of sucrose. 4) Purest sucrose is obtained by redissolving sugar in water precipitating with absolute Ethyl Alcohol. 5) Sucrose is very soluble in water and faintly hygroscopic. 6) Small quantities of salt decrease the solubility of sucrose, while higher quantities of salt increase it. 7) When sucrose solutions are treated with metal hydroxides under suitable conditions, colloidal turbidities, syrup gels or flake precipitates are obtained. 8) In the presence of hydrogen ions a hydrolytic, decomposition of sucrose takes place. 9) When the sucrose solutions are heated in presence of OH-Ions, decomposition takes place. 10) In a solution of sucrose with lime of Ph 12, the sugar loss in one hour boiling under normal pressure was found to be about 0.5%.
Cane Preparation Equipment The following table gives recommendations on cane preparation equipment Installed Specific powers and tip speeds. Cane Preparation Equipment Installed Power
Specific Power Description [kW/tfh] Leveller knives 6 First knives 15 Second knives (heavy duty) 30 Shredder 60 Total 111 Southern African industry average 84
Tip Speed [m/s] 50 60 60 100
Tip Clearance [mm] 1000 150 50
Installed Specific Power for Milling Table of required installed power for a milling tandem
Number of Mills
Specific Power per Mill [kW/tfh]
Four mills
22
Five mills
20
Six mills
18
Diffuser + two mills
25
Mill Capacity Calculations There are a large number of formulae for the calculation of the capacity of a milling tandem
Hugot gives the following formula:
A = 0.8 c·n·√N· (1-0.06·n·D) ·L·D2/f
Where
c is a factor dependent on the cane preparation equipment, c= 1.3 if the tandem is preceded by a shredder
n is the mill speed in rev/min
N is the number of rollers in the tandem
L is the length of the roll in meters
D is the mean diameter of the rollers in meters
f is the fiber percent cane
Example: Capacity of the plant---------------------5000 TCD Cane crushing per hour--------------5000/22 =227.27 TCH Imbibitions percentage of cane-----------35±2% Bagasse percentage on cane--------------29±1% Hugot gives the following formula: A = 0.8 c·n·√N· (1-0.06·n·D) ·L·D2/f (Or)
Mill setting calculation (based on Fiber Index loaded Method) Fiber loaded in various mill the following formula FL=1000x AxF/60x3.14xDxNxl (Kg/m2) Where, A=Total Cane crushing per hour F=Fiber percentage of cane (i.e-14%) D=Pitch Circle Diameter of the Top Roller N=Speed of the Roller (rpm) L=Length of the Roller
A, Fiber % of Bagasse Approximately percentage of fiber in bagasse foe each mill
first mill=34% Second mill=39% Third mill=45% Fourth mill=50%
Formula for fiber Index is given =Fiber % of bagassex1.75x10 kg/m³
Discharge roller setting Dr=Fiber Load/Fiber Index (mm) Feed Roller setting Fr=mill ratio x Discharge work opening Trash plate setting Tp=1.75 x feed roller work opening
Mill Sizing Nomogram The nomogram below from is a quick guide to sizing a milling tandem
Geometry of Mills
Ratio of feed opening to discharge opening in the mill ratio = 2 working position
Top roll mean diameter Discharge roll mean diameter
MDT = 45 in MDD = 45 in
Feed roll mean diameter
MDF = 45 in
Tooth Pitch
TP = 2 in
Tooth Flat
T fl = 6 mm
Tooth Angle
T ang = 45°
Tooth Depth
T depth = (TP - T fl) / (2 · tan(Tang / 2))
Roll Length
l roll = 7 ft
Speed of top roll
n = 3 rpm
Tooth Profile
Mill Operating Parameters
Cane throughput
tch = 250 ton/hr f%c = 15%
fiber % cane
fibre throughput
fibrethput = tch · f%c fibrethput = 567 kg/min
Average peripheral velocity of top/feed rolls
vTF = n / 2 · (MDT + MDF) / 2 vTF = 10.77 m/min
Average peripheral velocity of top/discharge rolls
vTD = n / 2 · (MDT + MDD) / 2 vTD = 10.77 m/min ffD = 850 kg/m3
fibre fill in the discharge opening
fibre fill in the feed opening
ffF = ffD / mill ratio
described volume in the discharge opening
volEscrD = fibrethput / ffD volEscrD = 0.667 m3/min
Feed Work Opening
woF = volEscrF/ (vTF · l roll) woF = 58 mm
Top - Feed roll Centers (Working)
TF = MDT / 2 + MDF / 2 + woF TF = 1201 mm
Top - Discharge roll Centers (Working)
TD = MDT / 2 + MDD / 2 + woD TD = 1172 mm
Vertical distance between top and side roll centers Vrest = 33.25 in at rest
mill lift
l = 15 mm
Horizontal distance between top roll and feed roll HF = √(TF2 - (Vrest + l)2) centers HF = 839 mm
Horizontal distance between top roll and discharge HD = √(TD2 - (Vrest + l)2) roll centers HD = 797 mm
set feed opening (Tip to Bottom)
soF = √(HF 2 + Vrest2) - MDT / 2 + MDF / 2 soF = 47 mm
set discharge opening (Tip to Bottom)
soD = √(HD2 + Vrest2) - MDT / 2 + MDD / 2 soD = 18 mm
Trash Plate Settings Hugot notes that the ideal shape of a trash plate is the logarithmic spiral, and points out that the Simplest approximation to this is an arc whose center is offset from the centre point (in the Working position) of the top roll along a horizontal line towards the discharge roll. The amount Of the offset is given below. The work opening on the vertical plane through the centre of the top roll is 1.75 times the feed work opening.
Offset Distance from center of top roll to center of radius for trash plate surface
Ow = (MDT / 2 + woF) / 25 Ow = 25.2 mm Rw = MDT / 2 +1.75 · woF
Radius of Trash Plate in working position
Length of vertical line from centre point of top roll (in set position) to top surface of Trash Plate
Rw = 673.1 mm Rs = MDT / 2 +1.75 · woF – l Rs = 658.1 mm
Recommended fibre fill [kg/m3] for a milling train Mill No
7 Mill Tandem
6 Mill Tandem
5 Mill Tandem
1
500.0
500.0
500.0
2
583.3
600.0
625.0
3
666.7
700.0
750.0
750.0
800.0
875.0
833.3
900.0
1000.0
4 5
6
916.7
7
1000.0
1000.0
Mill Bearings Bearing Pressures The maximum pressure that a bearing can withstand is mainly a function of the bearing material. The bronzes that are common in sugar mills have a recommended maximum bearing pressures of up to 100 MPa for phosphor bronze and 50 MPa for tin-bronzes. Standard sugar mill practice limits the bearing pressure to about 10 MPa. Materials for Plain Bearings The two essential elements in a plain bearing are the bearing or bearing material itself, and the shaft or moving member. The bearing or bearing material is located in a housing or structure, and may or may not be integral with it. Separating these two elements is the lubricant, introduced, generally in the case of sugar mills, by external pressure feeding. The material of the shaft or journal is established from considerations of strength and rigidity, and will invariably be steel. Because the conditions under which bearings must operate in service may vary over a wide range, it is necessary that bearing materials be used which have certain desirable properties. Amongst these we must include such factors as
mechanical strength;
softness and low melting point;
low modulus of elasticity;
corrosion resistance;
high thermal conductivity; and of course,
Economic considerations.
Since these factors cannot all be obtained to a desirable degree in a single material, it is necessary in practice to make a compromise. The most common bearing materials consist of a. white metals, b. copper base alloys, and c. Aluminum-base alloys.
White Metal White metals is a term used to include the tin and lead-base metals, broadly referred to as Babbitt (after Isaac Babbitt, 1839), and since such metals are highly competitive, they are recommended for most applications where the loading is not severe. Babbitt bearings are manufactured with the white metal lined onto steel, cast iron and copper base alloys. Since white metal suffers a reduction in fatigue strength with increase in temperature, and this reduction is a function of thickness, it is usual to limit the thickness to between about 0.100-0.175 mm and thicknesses of only 0.025-0.050 mm are used with copper lead over the back-up material. White metal is not commonly used as a sugar mill bearing material Copper-base Alloys Copper-base alloys including lead-bronze, gun-metal and phosphor-bronze are widely used as bearing materials. Lead-bronze is the cheapest, and is used for general service bearings. It has a low tendency to seizure, in common with the white metal bearings, and has greater fatigue strength to withstand higher temperatures. Lead bronze bushes are frequently used in the form of single, solid units, i.e. as bushes without the supporting shell surrounding the bearing material, as is required of the Babbitt or white metal bearing materials. Gun-metal provides a relatively cheap and easy to machine material, having well bearing properties and capable of withstanding Somewhat higher loads than the lead-bronze alloys. This alloy also has good resistance to corrosion in sea water. Phosphor-bronze is used for heavily loaded bearings, where high frictional stresses are likely to occur. Because of the high hardness of this material, it demands the use of a hardened steel journal. Typical Sugar Mill Bearings Rein in Cane Sugar Engineering states that typically sugar mill bearings are tin bronzes with the following composition
Cu
84%
Sn
10%
Pb
3%
Zn
3%
Lubrication Sugar mill shafts do not turn sufficiently fast for a hydrodynamic film of lubricant to be formed between the journal and the bearing. Consequently hydrostatic lubrication is required. This is achieved by supplying lubricant to the bearing under pressure. Under these conditions, attention must be given to the adequate supply of lubricant at all times, and in particular to the location of oil Supply holes and grooves. Bitumen based lubricants are often used in sugar mill bearings. Bearing Loads and Sizes Specific roll loads are in the range of 2 to 3 MN per square metre of projected roll area. This together with the allowable bearing pressure mentioned above indicates that the total bearing area should be about 20% to 30% of the projected roll area. It is usual practice to allow the top roll of a sugar mill to float in the vertical direction to:
keep a nearly constant pressure on the mat of bagasse in the mill
allow some throughput variation without sacrificing extraction
protect the mill from damage from tramp iron
Typically hydraulic rams together with a gas accumulator provide the downward force on the bearing caps to resist the upward force of the bagasse on the mill roll. The gas accumulator acts as an air spring. The hydraulic oil in the system is not compressible, but the gas in the accumulator is and it is this gas that has the give that allows the roll to float. The gas in the accumulator is precharged with a particular gas pressure. The higher the precharge pressure the softer the spring rate. A low precharge pressure will make the system very stiff and may not allow sufficient float to let tramp iron through the mill, which may cause damage. A high precharge pressure will make the system very soft and the top roll bearing may continually rise up to its maximum lift. This means the mill headstock may be subjected to very high forces, not anticipated in design. The correct precharge pressure which ensures that the top roll floats about its design position is important to ensure good extraction and to protect the mill from damage.
Sugar Mill Lubricants Castrol SMR Grades Castrol SMR lubricants are especially formulated for sugar mill roll bearings and gearboxes. They are viscous black oils fortified with load bearing additives and incorporate emulsifiers to resist the harmful effects of the inevitable contamination with sugar juices encountered in use. They also find use in other heavily loaded open gears and pinions. These grades are now lead free.
Description
SMR SMR MEDIUM CLEAR
HEAVY
ASMR MEDIUM*
ASMR HEAVY*
Density @
0,949
0,914
0,952
0,995
1205
1925
1 228
11450
Viscosity @ 100°C (mm2/s)
50,5
126,0
50,5
VIE
84
160
83
74
Color
Black
Red/Green
Black
Black
Pour Point (°C)
0
6
0
+12
Flash Point CCC (°C)
250
212
254
256
Bitumen
Yes
Nil
Yes
Yes
Compounding
Yes
Yes
Yes
Yes
Yes
Yes
Yes
20°C Viscosity @ 40°C (mm2/s)
EP Additives
167,0
Bagasse Calorific Value Gross calorific value, also known as the higher calorific value (HCV) of bagasse is calculated from the following formula: HCV= [19 605 - 196, 05(moisture % sample) - 196, 05(ash % sample) - 31, 14(brix % sample)] kJ.kg-1
The net calorific value, also known as the lower calorific value (LCV), assumes that the water formed by combustion and also the water of constitution of the fuel remains in vapor form. In industrial practice it is not practicable to reduce the temperature of the combustion products below dew point to condense the moisture present and recover its latent heat, thus the latent heat of the vapor is not available for heating purposes and must be subtracted from the HCV. By ASTM standards the HCV is calculated at atmospheric pressure and at 20°C. LCV of bagasse is calculated by the formula:
LCV= [18 309 - 207, 6 (moisture % sample) - 196, 05 (ash % sample) - 31, 14 (brix % sample)] kJ.kg-1
Do online calculations of HCV and LCV. Select the parameter to be used as the graphs X-axis by clicking the appropriate radio button. Example: Capacity of the plant---------------------5000 TCD Cane crushing per hour--------------5000/22 =227.27 TCH Imbibitions percentage of cane-----------35±2% Bagasse percentage on cane--------------29±1% Mixed Juice Percentage on cane-------------------105±2% As per our capacity of the mill: Imbibitions percentage of cane-----------79.54 tons (227.27 TCH) Bagasse percentage on cane--------------68.181 tons (227.27 TCH) Mixed Juice Percentage on cane-------------------238.6 Tons (227.27 TCH) Mill Balance calculation: Mill Input=Mill Out put Cane + Imbibitions water=Bagasse + Mixed Juice 227.27+79.54=238.6+68.181 306.81≈306.781 Pipe sizing Use these pages to calculate pipe sizes and pressure drops due to friction in the pipes, for the following products: The pressure drop is calculated from the following formula
hf = 4·f·le / d · v2/ 2·g where
hf = head loss due to friction
f = friction factor calculated from the formula below
le = equivalent pipe length taking into account valves and fittings
d = bore of pipe
v = average flow velocity
g = acceleration due to gravity 9.81m/s2
f = 0.001375 · (1 + (20000· k / d + 106 / Re)1/3) Where
k = relative roughness of the bore of the pipe
Re = Reynolds Number = ρ·v·d / μ
ρ = density
µ = dynamic viscosity
To be select the imbibitions water pump & motor Specific Speed of Pumps Pumps (and fans) can be characterized by various dimensionless parameters.
Specific Speed, Ns
Flow parameter, φ
Pressure parameter, ψ
Power parameter, Π
Diameter parameter Δ
The most important of these is the specific speed Pump Selection These dimensionless parameters can be used calculate how similar pumps operate under differing conditions (the similarity laws). These similarity laws (detailed below) can be used to select a pump given a duty point. Specific Speed The specific speed,Nsis given by; Ns = Q0.5·n/ (g·H)0.75 Specific speed can also be calculated as follows where φ
and ψ are defined below Ns = φ0.5/ψ0.75 The specific speed of a pump is associated with the impeller shape Low Specific Speed Ns=0.05
Medium Specific Speed Ns=0.10
High Specific Speed Ns=0.20
Flow Parameter The flow parameter, φ is given by; φ = Q/n/D3
Pressure Parameter The pressure parameter, ψ is given by;
ψ = g·H/n2/D2 Power Parameter The power parameter, Π is given by; Π = φ·ψ·η Diameter Parameter The diameter parameter, Δ is given by; Δ = ψ0.25/φ0.5 Pipe Specifications Each sugar factory needs a pipe specification so that when a pipe is being repaired or a section of plant is being added those implementing the change know exactly which type of pipe, fittings, flanges, gaskets and valves to use. The following are the main types of pipe that will be needed with recommended
pressure, temperature, corrosion allowance and material parameters
Corrosion Allowance
Material
Full vacuum 100°C to 10 bar g
2 mm
Carbon Steel
Full vacuum 100°C to 10 bar g
0.5 mm
Stainless steel
pressure Full vacuum 200°C to 3 bar g
2 mm
Carbon Steel
Condensates
Full vacuum 130°C to 10 bar g
3 mm
Carbon Steel
05
High steam
31 bar g
400°C
1.6 mm
Carbon Steel
06
Vacuum
Full vacuum
100°C
0.5 mm
Stainless steel
Sl.no
Product
Pressure
01
Non food grade
02
Food grade
03
Low steam
04
pressure
Temperature
Pipe Stress Analysis Why? The reasons one does a pipe stress analysis on a piping system are as follows
to comply with legislation
to ensure the piping is well supported and does not sag or deflect in an unsightly way under its own weight
to ensure that the deflections are well controlled when thermal and other loads are applied
to ensure that the loads and moments imposed on machinery and vessels by the thermal growth of the attached piping are not excessive
to ensure that the stresses in the pipe work in both the cold and hot conditions are below the allowable
How? The model is constructed from piping general arrangement drawings, piping isometric drawings and piping and valve specifications. Once the system is
accurately modeled, taking care to set the boundary conditions, comprehensive stress analysis calculations are done, modifications to the model are made to ensure compliance with the above requirements. The modifications may include one or more of the following tools Restraints A device which prevents, resists or limits the free thermal movement of the pipe. Restraints can be either directional, rotational or a combination of both. Anchors A rigid restraint which provides substantially full fixity, i.e. encastre or built-in, Ideally allowing neither movement nor bending moments to pass through them. True anchors are usually difficult to achieve. A seemingly solid gusseted bracket Welded to a house column does not qualify as an anchor if the column does not Have the strength to resist the loads applied to it. Expansion Loops A purpose designed device which absorbs thermal growth; usually used in Combination with restraints and cold pulls. Neutral Planes of Movement This refers to the planes on the 3 axes of a turbo machine or pump from where expansion of the machine starts eg the fixed end of a turbine casing. This information is normally provided by the equipment manufacturer. If not available from this source, the fixed points of the machine must be determined by inspection and an estimation of the turbine growths calculated. A pipe restraint positioned in line with a neutral plane prevents differential Expansion forces between the pipe and the machine. Cold Pull or Cold Spring This is used to pre-load the piping system in the cold condition in the opposite direction to the expansion, so that the effects of expansion are reduced. Cold pull is usually 50% of the expansion of the pipe run under consideration. Cold pull has no effect on the code stress, but can be used to reduce the nozzle loads on machinery or vessels. Spring Hangers Used to support a piping system that is subjected to vertical thermal movements. Commercially available single coil spring units are suitable for most applications.
Supplier's catalogues adequately cover the selection of these springs. According to Hooke's law, the spring's supporting capacity will vary in direct proportion to the amount of displacement the spring undergoes due to thermal movement. This variation between cold and hot should be between 25 and 50% of the hot loaded condition. Solid Vertical Support In places where vertical thermal movement does not create undesirable effects, or where vertical movement is intentionally prevented or directed, solid supports in the form of rollers, rods or slippers are used. It is important that free horizontal movement of the pipe is not impeded unless horizontal restraint is desired. Slipppers and rollers must be well designed and lubricated.
Fluid Flow Velocities Guidelines for the acceptable ranges of flow velocity for various fluids found in a sugar factory Goodall Description
Velocity[m/s]
Water for space heating
2
4
Water for boiler feed
3
6
Saturated steam
30
50
Superheated steam
50
100
Hugot Description
Velocity[m/s]
Superheated steam
40
76
24
37
31
46
37
49
46
76
1
1.25
Saturated steam Exhaust (wet/oily) Bled vapor Vapor under vacuum Suction Water
Juice Syrup Molasses Massecuites
1
1.2
0.5
1
0.25
0.5
0.1
0.2
1.25
2.5
1.2
2
0.75
1.25
0.5
0.75
0.15
0.3
Delivery Water Juice Syrup Molasses Massecuites
Lyle Description
Velocity[m/s]
Water
1.22
2.44
46
61
31
40
21
31
46
61
61
107
Superheated steam Dry Saturated steam Wet exhaust steam Moderate vacuum water vapor High vacuum water vapor
Babcock & Wilcox Description High pressure steam
Velocity[m/s] 41
61
Low pressure steam Water general
61
76
2.54
3.81
m/s
ft/s
0.5 - 0.7
1.6 -8.2
1.0 - 2.5
3.3 - 8.2
1.5 - 2.5
4.9 - 8.2
0.5 - 1.0
1.6 - 3.3
1.5 - 2.5
4.9 - 8.2
1.0 - 2.0
3.3 - 6.5
1.0 - 3.0
3.3 - 9.8
m/s
ft/s
25 - 40
82 - 131
- 60
- 197
30-40
99 - 131
- 50
- 164
- 25
- 82
m/s
ft/s
- 0.5
-1.6
From a source on the internet Maximal velocity in pipes Water Tap water (low noise) Tap water Cooling water Boiler feed water. Suction Boiler feed water. Discharge Condensate Heating circulation Steam Saturated Steam. high pressure Saturated Steam. in special cases Saturated Steam. medium and low pressure Saturated Steam. at peak load Steam / Water emulsion Oil Suction lines for pumps
Suction lines for pump (low 0.1 - 0.2 pressure) Discharge line for booster pump 1.0 - 2.0 Discharge line for burner pump Air
0.3 - 0.65 3.3 - 6.5 - 3.3
- 1.0
m/s
ft/s
Combustion air ducts Air inlet to boiler room Warm air for house heating Vacuum cleaning pipe Compressed air pipe Ventilation ducts (hospitals)
12 - 20
40 - 66
1-3
3.3 - 9.8
0.8 - 1.0
2.6 - 3.3
8 - 15
26 - 49
20 - 30
66 - 98
1.8 - 4
5.9 - 13
Ventilation ducts (office buildings) 2.0 - 4.5 Exhaust gas m/s Ducts at minimum load Stack at minimum load Boiler with one-step burner (on off) Boiler with two-step burner (high - low) Boiler with modulating burner (3:1) To keep the surface free from soot the velocity should always exceed
6.5 - 15 ft/s
- 4.0
- 13
- 5.0
- 16
5.0 - 8.0
16 - 26
10 - 15
31 - 49
15 - 25
49 - 82
3.0 - 4.0
9.8 - 13
It is recommended that the maximum inlet velocities applied to control valves should be as shown in the tables below Gate Valve Size
mm 15 - 25 40 - 50 65 - 100 150 - 200 250 – 400 Angle
Liquid
Steam or Gas
m/s
ft/s
m/s
ft/s
9
30
120
400
7.5
25
90
300
6
20
75
250
6
20
70
225
4.5
15
55
175
Valves Liquid
Steam or Gas
Size mm 15 - 25 40 - 50 65 - 100 150 - 200 250 - 400
m/s
ft/s
m/s
ft/s
13.5
45
135
450
12
40
105
350
10.5
35
90
300
9
30
85
275
7.5
25
70
225
Cavitations in Centrifugal Pumps There may be, on the low-pressure side of the runner, regions in which the pressure falls to values considerably below atmospheric. In a liquid, however, the pressure cannot fall below the vapor pressure at the temperature concerned. If at any point the vapor pressure is reached, the liquid boils and small bubbles of Vapor form in large numbers. These bubbles are carried along by the flow, and on reaching a point where the pressure is higher they suddenly collapse as the vapor condenses to liquid again. A cavity results and the surrounding liquid rushes in to fill it. The liquid moving from all directions collides at the centre of the cavity, thus giving rise to very high local pressures (up to 1 GPa). Any solid surface in the vicinity is also subjected to these intense pressures, because, even if the cavities are not actually at the solid surface, the pressures are propagated from the cavities by pressure waves similar to those encountered in water hammer. This alternate formation and collapse of vapor bubbles may be repeated with a frequency of many thousand times a second. The intense pressures, even though acting for only a very brief time over a tiny area, can cause severe damage to the surface. The material ultimately fails by fatigue, aided perhaps by corrosion, and so the surface becomes badly scored and pitted. Parts of the surface may even be torn completely away. Associated with cavitating flow there may be considerable vibration and noise; when cavitations occurs in a turbine or pump it may sound as though gravel were passing through the machine. Not only is cavitation destructive: the larger pockets of vapor may so disturb the flow that the efficiency of a machine is impaired. Everything possible should therefore be done to eliminate cavitation in fluid machinery, that is, to ensure that at every point the pressure of the liquid is above the vapour pressure. When the liquid has air in solution this is released as the pressure falls and so air cavitation also occurs. Although air cavitation is less damaging than vapour cavitation to surfaces, it has a similar effect on the efficiency of the machine.Since cavitation begins when the pressure reaches too low a value, it is likely to occur at points where the velocity or the elevation is high, and particularly at those where high velocity and high elevation are combined.Cavitation is likely to occur on the inlet side of a pump particularly if the pump is situated at a level well above the surface of the liquid in the supply reservoir. For the sake of good efficiency and the prevention of damage to the impeller, cavitation should be avoided.
Applying the energy equation between the surface of liquid in the supply reservoir and the entry to the impeller (where the pressure is a minimum) we have, for steady conditions
p0 /ρg + z1 - hf = pmin /ρg + v12 /2g where
v1
is the fluid velocity at the point where the static pressure has its least value
pmin is the minimum static pressure
z1 the elevation of the surface of the liquid in the reservoir above this point where the static pressure has its least value
p0 the absolute pressure at that surface p0 = pgauge + patm
ρis the density of the fluid at its operating temperature
hf is the head loss due to friction in the suction line, care must be taken to include the effect of all devices such as strainers and valves in the suction line. Re-arranging the above equation gives
pmin /ρg = p0 /ρg - hf - v12 /2g + z1 For cavitation not to occur
pmin > pv where
pv is the vapour pressure of the liquid. These equations can be rearranged to give the criterion for no cavitation in the pump suction line.
p0 /ρg - pv /ρg - hf - v12 /2g + z1 > 0 A parameter called Nett Positive Suction Head (NPSH) is defined as
NSPHa = p0 /ρg - pv /ρg - hf + z1 The NPSH available at the inlet flange of the pump can be calculated from the above equation. The pump curves in the pump catalog generally give the NPSH required at each volume flow the pump is required to do. For good pump operation
NPSHavailable > NPSHrequired
Mixed Juice Percentage on cane-------------------238.6 Tons (227.27 TCH) So selection of the pipe materials as per the reference of the table above
Sl.no
Product
Pressure
Temperature
01
Food grade
Full vacuum to 100°C 10 bar g
Corrosion Allowance
Material
0.5 mm
Stainless steel
So, we can select the pipe line material is Stainless steel. We can consider the following points to select the pipe size: Density is a physical characteristic, and is a measure of mass per unit of volume of a Material or substance. It is a measurement of the amount of matter in a given volume of Something. The higher an object's density, the higher its mass per unit of volume. The average density of an object equals its total mass divided by its
total volume. A denser object (such as iron) will have less volume than an equal mass of some less dense substance (such as water). Water is the reference with its highest density at 3.98 °C (ρ = 1 g/cm3) and the correct SI unit of ρ = 1000 kg/m3. 1 m3 = 1,000,000 cm3. Density Examples: Solid - water - noble gas Copper has a density of 8950 kg/m3 = 8.95 kg/dm3 = 8.95 g/cm3. Water has a density of 1000 kg/m3 = 1000 g/L = 1.000 kg/dm3 = 1.000 kg/L = 1.000 g/cm3 = 1.000 g/mL. Helium has a density of 0.1785 kg/m3 = 0.1785 g/L = 0.0001785 kg/dm3 = 0.0001785 kg/L = 0.0001785 g/cm3 = 0.0001785 g/mL. Density of Sugar Factory Products The tables below give the approximate range of densities for selected cane factory products. This data is taken from multiple sources including Hugot and Tromp
lb/ft3
kg/m3
Whole stick cane, tangled and tamped 12.5 down as in a cane transport vehicle
200.2
Whole stick cane, neatly bundled
25
400.5
Billeted cane
22
352.4
Whole stick tangled cane but loosely 10 tipped into cane carrier
160.2
Knifed cane
18
288.3
20
320.4
7.5
120.1
Sugar Cane
Shredded cane Bagasse exiting the final mill
Bagasse stacked to 2 metre height 11 (moisture = 44%)
176.2
Sucrose crystal
99.0
1586.2
Amorphous sucrose
94.1
1507.7
Bulk white sugar
54.9
880
Bagged white sugar
43.7
700
Raw sugar (96° Pol) in a pile
56.2
900
Bagged raw sugar
42.4
680
The International Standard Atmosphere For the design of pans, evaporators, barometric condensers and in NPSH calculations for pumps it is necessary to know the atmospheric pressure. While many cane sugar factories are close to the sea, there are those that are at higher altitudes where atmospheric pressure is below the well known 101325 Pa for sea level there are tables of atmospheric pressure variation with altitude; the table below is the International Standard Atmosphere adapted from Thermodynamic and Transport Properties of Fluids arranged by GFC Rogers and YR Mayhew, 3rd edition International Standard Atmosphere Z [m] -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500
p [Pa] 135210 127780 120700 113930 107480 101325 95460 89880 84560 79500 74690
T [K] 304.4 301.2 297.9 294.7 291.4 288.15 284.9 281.7 278.4 275.2 271.9
ρ [kg/m3] 1.5473 1.4782 1.4114 1.3470 1.2849 1.2250 1.1673 1.1117 1.0582 1.0066 0.9570
3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 10500 11000
70120 65780 61660 57750 54050 50540 47220 44080 41110 38300 35650 33150 30800 28580 26500 24540 22700
268.7 265.4 262.2 258.9 255.7 252.4 249.2 245.9 242.7 239.5 236.2 233.0 229.7 226.5 223.3 220.0 216.8
Tables are not convenient for computer calculations: regression formulae have been prepared from the above data for temperature and density; pressure can then be calculated from the universal gas law. T = 288.15 - 0.006492255 · Z ρ = 1.225 · e(-0.09543718·(Z/1000) - 0.001321598·(Z/1000)2) p = ρ·R0/M·T where
T is temperature in Kelvin
ρ is density in kg/m3
p is pressure in pascals
Z is altitude (above mean sea level) in meters
R0 is the universal gas constant = 8134.4 J/kg/K
M is the molar mass of air = 28.9647 kg/kmol
Water Pipe Sizing Water Properties
Temperature
°C
Pressure
bar abs
0.9093 0.8634 0.8194 0.7770 0.7365 0.6975 0.6602 0.6243 0.5901 0.5573 0.5258 0.4958 0.4671 0.4397 0.4136 0.3886 0.3648
Mass Flow
ton/h
Max Flow Velocity
m/s
Pipe System
Type
Description Short Radius 90º Bends Long Radius 90º Bends Short Radius 45º Bends Tees - Line Flow Tees - Branch Flow 180º Return Bends Gate Valves (Fully Open) Globe Valves (Fully Open) Angle Valves (Fully Open) Butterfly Valves (Fully Open) Ball Valves (Fully Open) Plug Valves (Fully Open) Swing Check Valves Wafer Check Valves
The above are consider to be select the pipe size:
Numbers/Length
Example: Mixed Juice
Temperature
45 °C
Pressure
5 bar abs
Mass Flow
238.6 ton/h
Max Flow Velocity
1.2 m/s
Type
Description
Numbers/Length
Pipe length
60mtrs
Short Radius 90º Bends
5
Long Radius 90º Bends
2
Short Radius 45º Bends
2
Tees - Line Flow
0
Tees - Branch Flow
0
180º Return Bends
0
Gate Valves (Fully Open)
4
Globe Valves (Fully Open)
0
Angle Valves (Fully Open)
0
Butterfly Valves (Fully Open)
0
Ball Valves (Fully Open) Plug Valves (Fully Open)
0 0
Swing Check Valves
0
Wafer Check Valves
0
Water Pipe Sizing – Results Water Temperature Mass Flow Density Viscosity Volume Flow Flow Velocity Frictional Head Loss Pipe Size Short Radius 90° Bends Long Radius 90° Bends Short Radius 45° Bends Tees - Line Flow Tees - Branch Flow 180° Return Bends Gate Valve (Fully Open) Angle Valve (Fully Open) Butterfly Valve (Fully Open) Ball Valve (Fully Open) Plug Valve (Fully Open) Swing Check Wafer Check
45.0°C 238.0 ton/h 990.4 kg/m3 0.6 mPa.s 240.3 m3/h 0.9 m/s 0.4 m DN300 5 2 2 0 0 0 4 0 0 0 0 0 0
Steam Pipe Sizing Steam Properties
Pipe System
Temperature
°C
Pressure
bar abs
Mass Flow
ton/h
Max Flow Velocity
m/s
Type
Description Short Radius 90º Bends Long Radius 90º Bends Short Radius 45º Bends Tees - Line Flow Tees - Branch Flow 180º Return Bends Gate Valves (Fully Open) Globe Valves (Fully Open) Angle Valves (Fully Open) Butterfly Valves (Fully Open) Ball Valves (Fully Open) Plug Valves (Fully Open) Swing Check Valves Wafer Check Valves
Example Evaporator Steam Inlet Pressure—3kg/cm² Temperature----120°c Flow rate---35 t/hr Saturated steam velocity----50
Numbers/Length
Steam Properties
Temperature
120 °C
Pressure
3 bar abs
Mass Flow
35 ton/h
Max Flow Velocity
50 m/s
Pipe System
Type
Description
Numbers/Length
Pipe length
60mtrs
Short Radius 90º Bends Long Radius 90º Bends
5
Short Radius 45º Bends
3
Tees - Line Flow
0
Tees - Branch Flow
0
180º Return Bends
0
Gate Valves (Fully Open)
2
Globe Valves (Fully Open)
0
Angle Valves (Fully Open)
0
Butterfly Valves (Fully Open)
0
Ball Valves (Fully Open) Plug Valves (Fully Open)
0 0
Swing Check Valves
0
Wafer Check Valves
0
Steam Pipe Sizing – Results
Steam Temperature Steam Pressure Mass Flow Specific Volume Viscosity Volume Flow Flow Velocity Frictional Pressure Loss Pipe Size Short Radius 90° Bends Long Radius 90° Bends Short Radius 45° Bends Tees - Line Flow Tees - Branch Flow 180° Return Bends Gate Valve (Fully Open) Angle Valve (Fully Open) Butterfly Valve (Fully Open) Ball Valve (Fully Open) Plug Valve (Fully Open) Swing Check
120.0°C 3.0 bar abs 35.0 ton/h 0.6 m3/kg 12.9 µPa.s 5.7 m3/s 49.6 m/s 12.6 kPa DN400 0 5 3 0 0 0 2 0 0 0 0 0
Pump selection The following data can required the pump selection Pump duty Volume flow= ______________m3/h Head Density
= = kg/m3
Line Frequency=50Hz/60Hz Example:
m
Mixed Juice: 238 tons/hr Volume Flow: 238tons/hr (or) m³/h Head= 30 m (approx) Density=320.4 kg/m³ Line Frequency=50 Hz
Selection Speed [rpm] 2955 1478 985 739
Dia Max [%]
Eff Op [kW]
Power
Installed Power [kW]
Pump Size
Imp [mm]
No Selection
173
75.8
8.2
11
150-315
315
72.0
8.7
11
No Selection
459
65.3
9.5
11
No Selection
604
58.5
10.6
15
Dia Max [%]
Eff Op [kW]
Mixed Juice: 238 tons/hr Volume Flow: 238tons/hr (or) m³/h Head= 30 m (approx) Density=320.4 kg/m³ Line Frequency=60 Hz Selection Speed [rpm] 3546 1773 1182 887
Power
Installed Power [kW]
Pump Size
Imp [mm]
No Selection
150
76.0
8.2
11
125-315
267
73.8
8.4
11
No Selection
387
68.8
9.1
11
No Selection
507
63.0
9.9
15
Liquid - Liquid Heater Rapid Design Usually imbibitions water is hot condensate from the process house, often contaminated with sugar and not suitable for boiler feed water. This hot condensate is too hot for imbibitions duty, for two reasons;
hot imbibitions releases waxes from the canes causing the mills to slip
during the winter months hot imbibitions can cause clouds of mist in the mill house which reduces visibility (a safety hazard)
This hot condensate must be cooled before it can be used as imbibitions. The obvious product to cool it against is the mixed juice from the mills. Hence a liquid liquid heater
Cane throughput
TCH
Fibercon
%
Brix%Cane
%
Imbibition%Fibre in Cane Moisture%Bagasse Brix%Bagasse
% %
Imbibition Temperature (into heater)
°C
Imbibition Temperature (out of heater)
°C
Juice Temperature (into heater) Mixed Juice Purity Tube Length OHTC
Example:
%
°C % m kW/m2K
Cane throughput
227TCH
Fibercon
15%
Brix%Cane
15%
Imbibition%Fibre in Cane
300% 50%
Moisture%Bagasse
2%
Brix%Bagasse
95°C
Imbibition Temperature (into heater)
70°C
Imbibition Temperature (out of heater)
35°C
Juice Temperature (into heater)
85%
Mixed Juice Purity
3.8m
Tube Length
0.4kW/m2K
OHTC
Basic Data
Juice Flow
258.2t/h
Imbibition Flow
102.2t/h
Juice Inlet Temp
35.0°C
Juice Outlet Temp
44.9°C
Imbibition Inlet Temp
95.0°C
Imbibition Outlet Temp
70.0°C
LMTD
42.1°C
Tube Length
3.8m
Heat Flux
2978.5kW
176.9m2
Heating Surface
Design Options The following table gives a number of options that should provide an acceptable design of liquid liquid heater
Tube Dia
Tubes per Pass
Passes
Flow Velocity
35
37
13
2.3
42
31
13
1.9
42
37
11
1.6
54
19
16
1.8
76
7
29
2.5
Vacuum Equipment Purpose of the Vacuum Equipment The vacuum equipment's function is to remove the incondensable gases that find their way into the vapour stream. The incondensable gases come from the following sources:
leakage of air into the vessels;
inherently in the juice;
air in the heating steam
air in the cooling water
Quantity of Air to be Removed A number of authors have expressed an opinion on the the amount of incondensable gas to be removed from the condensers. Sadly, and as is typical there is little agreement among them. the quantities of air to be removed as
follows.
leakage of air [kg/h] = 0.345·V, where V is the volume of the vessel [m3]
air in the juice [kg/h] = 0.1·mj, where mj is the flow of juice [t/h]
air in the cooling water = 0.035·mw, where mw is the flow of cooling water [t/h]
air in the heating steam is not counted
Juice Clarifiers Introduction A clarifier is used to separate out the solids suspended in the cane juice. These solids originate from sand adhering to the cane stalks as well as from material inherent in the cane stalk. The separation takes place by allowing the solid particles to settle out onto a tray. The solids are swept from the tray into a mud compartment, from which it is pumped to filters for desweetening and dewatering. In the past multitray clarifiers, such as the Dorr, Graver, Bach and RapiDorr were popular, but the SRI clarifier is almost standard for all new installations. The SRI clarifier is a single tray clarifier (also known, oddly, as a tray less clarifier), characterized by short juice retention times (usually 40 minutes or less). The benefits of the single tray short retention clarifier are:
Short retention time, hence less sucrose destruction, and color formation
Higher throughput capacity
Lower capital cost
Lower maintenance cost
Easy to liquidate and hence regular cleaning is possible
Flocculent usage and operability appear to be no different from multitray clarifiers Design The main design parameters are up flow velocity and the residence time Up flow Velocity The up flow velocity is calculated as half the initial settling rate of the mud in the juice. The initial settling rate is the slope of the steeply downward sloping part of
the settling curve below. In the case of a Greenfield project where the settling characteristics of the mud are unknown, the up flow velocity can be assumed in the range 65 to 80 mm/min (Most SRI clarifiers in South Africa operate with an Up flow velocity below 72mm/min).
Residence Time The residence time is usually on the range of 40 to 45 minutes. Sizing Given the volumetric juice flow and the above two parameters; the cross sectional area (hence diameter) and the operating depth of the clarifier can be calculated
Specification for Vacuum Pan, Evaporators And Juice Heater Tubes Less Than Three Meters Long Scope This specification covers the material selection, dimensional tolerances, heat treatment, surface condition, inspection and testing, marking, and packing for
tubes that will be installed in vacuum pans, evaporators and juice heaters in which the tubes are less than three meters long. Quantities and Sizes
Number of tubes required:
Length of tube required:
Nominal outside diameter of tubes
Wall thickness of tubes
Material The tubes shall be of TP304L stainless steel, with a longitudinal welded seam Code of Manufacture The tubes shall be manufactured, inspected and tested in accordance with ASTM A269 Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service Dimensional Tolerances The dimensional tolerances shall be in accordance with ASTM A269 Heat Treatment The heat treatment shall be in accordance with ASTM A269 Surface Condition The external and internal weld bead shall be made flush. The tubes shall be supplied free of mill scale. This can be achieved either by pickling or bright annealing. The tube ends shall be cut square and deburred. Inspection and Testing The tubes shall be inspected and tested in accordance with ASTM A269. The inspection and testing will be done using an independent inspection authority, at the client's cost. Marking Each shall be marked in accordance with ASTM A269 and in addition shall bear the
following marks Sugartech Specification Packing The tubes shall be packed in bundles with wooden frames to protect the tube ends. The bundles shall be strapped and shrink-wrapped in plastic. A means of lifting the bundle, in a way that will not damage the tubes, shall be provided. Specification for Vacuum Pan, Evaporators And Juice Heater Tubes More Than Three Meters Long Scope This specification covers the material selection, dimensional tolerances, heat treatment, surface condition, inspection and testing, marking, and packing for tubes that will be installed in vacuum pans, evaporators and juice heaters in which the tubes are more than three meters long. Quantities and Sizes
Number of tubes required: Length of tube required: Nominal outside diameter of tubes Wall thickness of tubes
Material The tubes shall be of TP439 stainless steel, with a longitudinal welded seam Code of Manufacture The tubes shall be manufactured, inspected and tested in accordance with ASTM A268 Standard Specification for Seamless and Welded Ferritic and Martensitic Stainless Steel Tubing for General Service Dimensional Tolerances The dimensional tolerances shall be in accordance with ASTM A268 Heat Treatment The heat treatment shall be in accordance with ASTM A268
Surface Condition The external and internal weld bead shall be made flush. The tubes shall be supplied free of mill scale. This can be achieved either by pickling or bright annealing. The tube ends shall be cut square and deburred. Inspection and Testing The tubes shall be inspected and tested in accordance with ASTM A268. The inspection and testing will be done using an independent inspection authority, at the client's cost. Marking Each shall be marked in accordance with ASTM A268 and in addition shall bear the following marks Sugartech Specification Packing The tubes shall be packed in bundles with wooden frames to protect the tube ends. The bundles shall be strapped and shrink-wrapped in plastic. A means of lifting the bundle, in a way that will not damage the tubes, shall be provided. Sugar Factory Tubes for Heating, Evaporating and Crystallizing Some desirable characteristics of tubes for juice heaters, evaporators and pans are
easy to expand into the tube plate
corrosion resistant
similar co-efficient of thermal expansion to the shell of the vessel
have a good heat conductivity
have a smooth and bright inside surface: a very low surface roughness favors a higher flow of the juices
have a long life
have a good cost : benefit ratio
The choice material is between:
mild steel
copper (or brass)
austenitic stainless steel (types AISI 304 and / or 316)
special alloys (with higher chromium / nickel contents)
ferritic stainless steel
In practice the choice is between mild steel, 304 stainless steel or 439 stainless steel. 304 for shorter tubes and 439 for longer tubes. Carbon steel is not recommended because in the long run (a period of say 20 years) carbon steel tubes work out more expensive. Carbon Steel If it is decided that carbon steel tubes are to be used the recommended specification is BS3605 Gr 320 304 Stainless This grade of stainless steel can be used where the tube length is less than three meters. The coefficient of thermal expansion for 304 is 1.8×10-2 mm/m/°C which is substantial more than that of carbon steel. When the vessel is hot the thermal stresses in the tubes will be high. Tubes of 304 stainless steel should always be annealed after welding. 439 Stainless Steel ASTM TP439 is a titanium stabilized ferritic grade of stainless steel (17-19% Cr) which is recommended for long evaporator or pan tubes (in excess of 5m long) Advantages of grade 439
fully ferritic metallurgical structure (ensured by the titanium stabilization)
very good weld ability and ductility;
inter-crystalline corrosion resistance;
pitting corrosion resistance;
Full immunity to stress corrosion.
Coefficient of thermal expansion (in the range 0°C - 100°C) is 1.02×10-2 mm/m/°C
Stress corrosion cracking This type of corrosion occurs when
A susceptible material is subject to
mechanical stress in a
corrosive environment
In an evaporator, pan or juice heater under the above conditions the result will be cracks leading to breakage in the area near the tube plate. The danger of stress corrosion cracking exists in virtually all evaporators. The risk will be higher if tubes over 7 meters in length (some designs of continuous pans, Falling-film evaporators and Kestner evaporators). Ferritic stainless steels are immune to stress corrosion cracking Heat transfer Thermal conductivity of ferritic stainless material is 40% higher than that of austenitic grades (like 304, 304L, 316 or 316L) i.e.: 26 vs. 15 watt/metre/°C. Recommended Wall Thickness For evaporators and heaters, with tube length less than five meters a wall thickness of 1.2 mm is acceptable, for tubes longer than five meters a wallthickness of 1.50 mm is quite sufficient (even on longer lengths up to 11 m) Tubes with 2.0 mm would be harder to swage into the holes and would require a 600°C Pre-heating of tube ends. Wall-thickness 1.6 or 1.75 mm are recommended for those tubes located near Steam-entrance and subject to some vibration during the process. For vacuum pans with 100 mm diameter tubes the recommended wall thickness is 1.5 or 1.6mm.Allow 0.6 mm clearance between tube and plate. Tube Hole Tolerances and Clearances The following definitions will help explain the calculation of hole clearances Tolerance Is the amount by which the actual size of the hole or tube varies from the nominal size. This variation depends on the manufacturing process and on
random errors. Clearance Is the difference in size between the hole and the tube. Because there is a maximum and a minimum tube outside diameter and a maximum and a minimum hole diameter there will be a range of clearances. Tolerances The tube OD tolerances depend on the tube manufacturer and his equipment and process. In the same way the tube sheet hole tolerances are a function of the hole making process. The best we can do is specify tolerances the manufacturer can achieve at a reasonable cost.
Clearances The designer of a vessel can control the clearance between tube OD and tube sheet hole diameter. But as noted above this will be a range. The minimum clearance should be such that the tube material once expanded into the tube undergoes plastic deformation; that is, the strain has exceeded the yield point. In most stainless steels there is no definite yield point, rather a 0.2% proof strain is regarded as the yield criterion. The criterion set for minimum clearance is thus 0.3% strain for no good reason other than it is greater than 0.2%.The maximum clearance shall be such that the tube material is not strained more than 2.0%. See graph below (from Thum and Micleots)
It must be noted that both the minimum and maximum clearance criteria are Somewhat arbitrary, but they have proved themselves in practice in a number of Different types of vessels. Practical Application Kestner evaporator tube For this example we will consider a 2 in nominal diameter tube. The tube OD Tolerance is given by the manufacturer as +/- 0.23 mm. Tube nominal diameter
Dtnom = 50.8 mm Tube OD tolerance
told = 0.23 mm Minimum tube diameter
Dtmin = Dtnom - told
Dtmin = 50.57 mm Maximum tube diameter
Dtmax = Dtnom + told Dtmax = 51.03 mm In order to get plastic deformation of the tube as it is expanded it must be strained more than 0.2%, say 0.3% Diametral strain
ε = 0.30% Diametral dilation
Δd = ε Dtnom Δd = 0.152 mm Nominal hole diameter
Dhnom = Dtmax + Δd Dhnom = 51.18 mm The hole is going to be drilled and an ISO tolerance of H12 is achievable i.e. the tube hole diameter is 51.18H12. The H12 tolerance is +0.000 +0.300 Tube hole tolerance
tolh = 0.300 mm Minimum hole size
Dhmin = Dhnom + 0.000 mm Dhmin = 51.18 mm Maximum hole size
Dhmax = Dhnom + tolh Dhmax = 51.48 mm
Check We will now check that the calculated clearances meet our criteria set above Minimum clearance
Cl min = Dhmin - Dtmax Cl min = 0.15 mm Minimum diametral strain
εmin = Clmin / Dtnom εmin = 0.3% - Okay Maximum clearance
Cl max = Dhmax - Dtmin Cl max = 0.91 mm Maximum diametral strain
εmax = Cl max / Dtnom εmax = 1.796% - Okay Continuous vacuum pan tube In this example we will consider a 4 in nominal diameter tube. The tube OD Tolerance is given by the manufacturer as +/- 0.38 mm. Tube nominal diameter
Dtnom = 101.6 mm Tube OD tolerance
told = 0.38 mm Minimum tube diameter
Dtmin = Dtnom - told Dtmin = 101.22 mm Maximum tube diameter
Dtmax = Dtnom + told
Dtmax = 101.98 mm In order to get plastic deformation of the tube as it is expanded it must be Strained more than 0.2%, say 0.3%
Diametral strain
ε = 0.30% Diametral dilation
Δd = ε Dtnom Δd = 0.305 mm Nominal hole diameter
Dhnom = Dtmax + Δd Dhnom = 102.28 mm The hole is going to be drilled and an ISO tolerance of H12 is achievable ie the Tube hole diameter is 102.28H12. The H12 tolerance is +0.000 +0.350 Tube hole tolerance
tolh = 0.350 mm Minimum hole size
Dhmin = Dhnom + 0.000 mm Dhmin = 102.28 mm Maximum hole size
Dhmax = Dhnom + tolh Dhmax = 102.63 mm
Check We will now check that the calculated clearances meet our criteria set above Minimum clearance
Cl min = Dhmin - Dtmax Cl min = 0.30 mm Minimum diametral strain
εmin = Clmin / Dtnom εmin = 0.3% - Okay Maximum clearance
Cl max = Dhmax - Dtmin Cl max = 1.41 mm Maximum diametral strain
εmax = Cl max / Dtnom εmax = 1.393% - Okay Tube Installation Points to note when expanding tubes into tube plates 1. Ends of expanded tubes must never be welded to tube plates. 2. When expanding tubes into plates it is essential to start at the top of the vessel surplus of 5 mm (3/16") must be kept. One must ensure that tube ends remain exposed above the tube plates. 3. Five-roller expander with safety clutch should preferably be used instead of usual three-finger expander. 4. Provide a crash stop in order to avoid swelling of the tubes just inside the plate-level. 5. When replacing tubes in plates, make sure that the surface of the bottom plate is quite clean and smooth. If necessary it must be repaired adequately. 6. It is necessary to protect tubes near the steam entrance. Baffles should be built in. This will avoid thermal shock and mechanical stresses which might be especially high at this particular part of the vessel.
Sugar Factory Tubes Sheet Ligaments The ligament on a tube sheet is the material between two tube holes. In a perfect
World the all the ligaments on a tube sheet will be exactly the same size. However Due to the variation in hole size due to tolerance and also due to mistakes in hole Centre positioning there may be ligaments which are smaller than the theoretically Calculated ligament. Now if it is found that on a particular tube sheet one or more Of the ligaments is smaller than the others are we to reject the tube sheet and all The work done on it? If the tube sheet is rejected, the manufacturing Programme Will be delayed, and costs incurred. The Tubular Exchanger Manufacturers Association (TEMA) has guidelines on Minimum allowable ligaments on tube sheets. Unfortunately their Recommendations only go up to 2 inch OD tubes, and so some extrapolation for 4 Inch tubes are required.
tube dia tube pitch [inch] [inch]
maximum hole diameter [inch]
nominal ligament [inch]
minimum permissible ligament [inch]
dt
p
p/d t
p-d t
dh
p-dh
0.250
0.313
1.250
0.063
0.259
0.054
0.025
0.250
0.375
1.500
0.125
0.259
0.116
0.060
0.375
0.500
1.330
0.125
0.384
0.116
0.060
0.375
0.531
1.420
0.156
0.384
0.147
0.075
0.500
0.625
1.250
0.125
0.510
0.115
0.060
0.500
0.656
1.310
0.156
0.510
0.146
0.075
0.500
0.688
1.380
0.188
0.510
0.178
0.090
0.625
0.781
1.250
0.156
0.635
0.146
0.075
0.625
0.813
1.300
0.188
0.635
0.178
0.090
0.625
0.875
1.400
0.250
0.635
0.240
0.120
0.750
0.938
1.250
0.188
0.760
0.178
0.090
0.750
1.000
1.330
0.250
0.760
0.240
0.120
0.750
1.063
1.420
0.313
0.760
0.303
0.150
0.750
1.125
1.500
0.375
0.760
0.365
0.185
0.875
1.094
1.25
0.219
0.885
0.209
0.105
0.875
1.125
1.290
0.250
0.885
0.240
0.120
0.875
1.188
1.360
0.313
0.885
0.303
0.150
0.875
1.250
1.430
0.375
0.885
0.365
0.185
1.000
1.250
1.250
0.250
1.012
0.238
0.120
1.000
1.313
1.310
0.313
1.012
0.301
0.150
1.000
1.375
1.380
0.375
1.012
0.363
0.185
1.250
1.563
1.250
0.313
1.264
0.299
0.150
1.500
1.875
1.250
0.375
1.518
0.357
0.180
2.000
2.500
1.250
0.500
2.022
0.478
0.250
Standard Ligaments
96% of ligaments shall be greater than ligstd = p - dh - (0.0032 t / dt in + 0.030 in) Where t = tube sheet thickness Minimum Permissible Ligament
No ligament shall be less than ligmin = -0.0010465 + 0.510467 · (p-dh) The factors in the above formula come from a linear regression of the data in the
Table above. Example 1 In this example we consider a 2 in kestner evaporator type tube Tube plate thickness
t = 25 mm Tube outside diameter
dt = 2 in dt = 50.8 mm Maximum tube hole dia
dmax = 51.48 mm Tube hole pitch
p = 70 mm Drill drift tolerance
toldd = 0.0016 in · t / dt toldd = 0.02 in Standard ligament
lstd = p - dmax - (2 · toldd + 0.030 in) lstd = 17.72 mm Minimum ligament
lmin = 0.0010465 mm + 0.5067383 · (p - dmax) lmin = 9.38 mm Example 2 In this example we consider a 4 in continuous vacuum pan type tube Tube plate thickness
t = 25 mm Tube outside diameter
dt = 4 in dt = 101.6 mm Maximum tube hole dia
dmax = 102.63 mm Tube hole pitch
p = 120 mm Drill drift tolerance
toldd = 0.0016 in · t / dt toldd = 0.01 in
Standard ligament
lstd = p - dmax - (2 · toldd + 0.030 in) lstd = 16.59 mm Minimum ligament
lmin = 0.0010465 mm + 0.5067383 · (p - dmax) lmin = 8.78 mm
Desuperheating of Steam A desuperheater is a device that cools superheated steam to a temperature close to its saturation temperature, usually by spraying atomized droplets of water into The flow of superheated steam. Superheated steam is steam that is at a Temperature above its saturation temperature. Desuperheating of steam is an almost universal feature of a sugar factory. This is for two reasons
Steam turbines are generally designed to leave some superheat in their exhaust to prevent erosion of turbine blades by water droplets
Juice and syrup should be boiled at less than about 125°C to reduce color formation and sucrose destruction
There are numerous methods of desuperhing steam each with their own advantages and disadvantages: a good discussion on the various approaches to Desuperheating is given by Sprirax Sarco Theory A heat and mass balance over the desupeheater yield two equations ms2hs2 = ms1hs1 + mwhw ms2 = ms1 + mw
Combining these yields mw = ms1 · (hs1 - hs2) / (hs2 - hw) Symbols m --mass flow rates [kg/s] h -- enthalpy [kJ/kg] Subscripts w --cooling water s1 --steam upstream of the desuperheater s2 --steam downstream of the desuperheater
Sucrose Losses in a Cane Sugar Factory The data below are the industry average figures from South African factories as published in SASTA Procedings. The figures given in the table and graph below are as a percentage of the sucrose entering the factory in cane. The losses in 1993 and 1994 were high as a result of the drought at that time. It is quite clear that the losses in bagasse and filter cake are almost constant, while the loss in molasses varies a lot, the undetermined loss is fairly stable from year to year
Sucrose losses as a percentage of sucrose entering the factory Bagasse
Filter Cake
Molasses
Undetermined
Total
1988
2.37
0.27
9.64
1.96
14.24
1989
2.40
0.27
9.26
1.85
13.78
1990
2.33
0.26
8.76
1.98
13.33
1991
2.25
0.29
9.02
1.92
13.48
1992
2.05
0.27
8.86
1.76
12.94
1993
2.19
0.25
11.31
2.23
15.98
1994
2.25
0.25
12.07
2.29
16.86
1995
2.13
0.22
10.97
2.01
15.33
1996
2.31
0.22
11.37
2.15
16.05
1997
2.28
0.25
9.84
1.81
14.18
1998
2.26
0.24
9.40
2.00
13.90
1999
2.27
0.25
9.29
2.10
13.91
2000
2.07
0.19
9.25
1.99
13.50
2001
2.25
0.18
9.45
1.92
13.80
2002
2.04
0.18
8.62
1.87
12.71
2003
2.21
0.15
8.96
1.67
12.99
2.13
0.17
9.48
1.95
13.73
2.02
0.14
9.65
1.96
13.77
2.21
0.23
9.73
1.97
14.14
2004 2005 Average
Sulphitation Part I Sulphitation processes are subject to almost as many modifications as simple Defecation. The variations may include the following: 1. modifications of the sequence of addition of lime and SO2 (liming first, sulphiting first, simultaneous addition of lime and gas, fractional procedures); 2. temperature modifications (sulphiting cold or hot, stepwise heating); and
3. Addition of reagents (batch, continuous, with either manual or automatic control). Obviously these variables permit a large series of combinations, and only the most commonly used are outlined here. Cold Sulphitation The cold raw juice is pumped through a tower or box with a counter-current of SO2 to absorb as much gas as possible (acidity 3.0-4.0 ml 0.1 N alkali for 10 ml of juice; pH 4.0 or below). Liming to slight acidity (pH about 6.5) is followed by heating, settling, and decanting as in the defecation process. Evaporation to a thin syrup follows, and the syrup is settled for 6-24 h before vacuum pan boiling. One boiling, yielding a near-white sugar that is heavily washed in the centrifugal, is frequently followed by a second boiling to a raw sugar. The "boil-back" molasses is allowed to settle for several weeks before it is placed on the market. The success of the process is largely dependent on the quality and price of this molasses. Sulfitation can also be carried out by injecting SO2 (industrial liquid SO2 in cylinders) into the cold raw juice to a level of about 400 ppm SO2. This is for the production of raw sugar and A molasses. The A molasses is inverted to yield a sucrose-invert ratio of about 1:1, giving a total sugar of 65% at 80 Brix, with an SO2 level of 30-40 ppm. Sulphitation after Liming This process is termed alkaline sulphitation as opposed to acid sulphitation previously described. It uses about 8 gal (30 liters) of 26 Brix milk of lime per 100 gal (378 liter) of juice giving a large excess of lime. Sulphitation is then carried out to about pH 7.5 producing a heavy precipitate that may be removed with settling and decantation. Heavier liming (10-12 gal, 38 - 45 liter), will result in a precipitate that permit filter-pressing. After evaporation the syrup is cooled and sulphited to slight acidity (pH 6.5). Treating diffusion juice with lime and then sulphitation decreases the color of syrup, raw sugar, and refined sugar by 25% 46% and 35% respectively the filterability is improved and molasses purity is
lower, giving better sugar recovery Hot Sulphitation Hot sulphitation serves to reduce the solubility of calcium-sulphite, which is more soluble at low temperatures, the minimum solubility is at about 75°C (167 °F). The juice is first heated to this temperature then sulphited and limed boiled, and settled. Harloff's process is a hot treatment procedure in which the juice is heated to 75 °C and the lime and SO2 are added simultaneously in such a way as to maintain the reaction acid to phenolphthalein and alkaline to litmus (pH about 7.47.8), except toward the end, when a quantity of lime is added to attain a strongly alkaline reaction (pH 10+), after which the sulphitation is completed to neutrality to litmus (pH about 7.2). As in all other similar processes, the juice is finally brought to boiling temperatures in juice heaters and settled.
Continuous Sulphitation Continuous sulphitation means the continuous addition of SO2 and lime to the constantly flowing stream of juice. Marches shows many different procedures with diagrams indicating construction details, methods of lime and gas addition, baffles to ensure proper circulation and other details. Many of the continuous liming processes may have different fractional procedures, but are not in general practice. Sulphitation of Syrup Sulphiting the syrup leaving the evaporators gives a sugar of higher and more regular quality than juice sulphitation alone. The syrup density is lower than in ordinary defecation processes, 55 Brix against 65 Brix or higher Sulphited syrup is usually maintained at a distinct acid reaction, pH 6.1 - 6.5. Control of Temperatures and Reactions
Good circulation and thorough mixing both of the lime and of SO2 are very important a bent circulation baffle devised by Thompson gives the best results in cylindrical sulphitators Avoidance of high alkalinities at high temperatures or for extended periods is recommended for the same reasons as in defecation control: such high alkalinities result in decomposition of reducing sugars and in color formation. Poor mixing of lime and juice may produce local over-liming. Temperatures above 75 °C are detrimental and some prefer not to exceed 70 °C until the final pH adjustment is made, to give a clarified juice to the evaporators of pH 6.9-7.0.
Sulphitators Generally the mixed cold juice is sprayed into tall vertical cylindrical tanks, 4ft (1.2 m) or more in diameter and possibly 15 ft (4.5 m) high, fitted for the upper twothirds with a series of hardwood grids made of 2 x 4 ft (0.6 x 1.2 m) timbers set on edge. The juice enters the top of the tower in a spray and falls through the wooden grillwork, where it encounters the rising current of SO2. Either the flow of gas through the system is induced by an air ejector or the SO2 is under pressure. The sulphitated juices are drawn from the conical bottom of the tower at a pH of 3.8-4.0, limed in a separate liming tank to pH 6.5-6.8, then heated to boiling and settled. Continuous sulphitation can be carried out in cylindrical sulphitators holding a fixed volume of juice. Heated juice (75 °C) flows through the tank continuously, while the milk of lime is added constantly to the entering juice and a continuous pressurized flow of SO2 into the liquid near the bottom of the tank supplies the needed circulation. The supply of gas is kept constant, and the lime addition is regulated by a controller. In actual practice, the juice is pre-limed before entering the sulphiting tank, generally to neutrality, then is maintained near the neutral
point by the sulphitation-lime addition. Zozulya et al. describe a new sulphitator which comprises a vertical tank with a feed-line at right angles to the top of the side wall. The juice is fed into the feedline through a perforated disc and comes into contact with SO2 gas metered through a valve at right angles to the liquid stream. An internal cyclone at the top of the tank acts as exhaust gas-liquid separator and as supplementary mixer for the incoming gas and the juice. Performance data of this new design show results superior to the conventional spray type with better gas utilization and Decolourisation. Sulphitation with Bentonite A process employing colloidal bentonite combined with sulphitation was developed in Argentina for the production of direct-consumption white sugars, especially with juices of deteriorated or frozen cane. Bentonite is clay, and the material selected is sold in Argentina under the trade name Clarigel. The advantages claimed are lower sulphur and lime consumption, much greater removal of organic non-sugars, better boiling properties of syrups and molasses because of reduced viscosities, and less scaling of evaporators. Sulphur Stoves or Burners The production of SO2 occurs when sulphur is burned in a current of air. Oldertype stoves operate intermittently; modem burners provide for the addition of sulphur without interruption of the burning. In any type of sulphur burner the air supplied to the furnace should be dry, because moisture in the air will cause the formation of sulphuric acid, obviously detrimental to piping, and soon, and can be especially serious if it reaches the juice. The drying agent is generally quicklime spread on trays, and it should be replaced before it becomes saturated with water, about every 8 h. Rotary sulphur burners use induced draft. Mechanical feed ensures continuous
operation. Best results are obtained with sulphur of high purity (99.6-99.9%). The sulphur melts by its own heat of combustion in the rotating cylinder, presenting a large surface for combustion as the sulphur drips through the air. Air is drawn in at an adjustable neck ring and anti-sublimation sleeve at the connection between the rotating drum and combustion chamber, a cast-iron or brick lined compartment with baffles, where the oxidation of the sulphur and mixing with the diluting air are completed. A uniform gas (5-16% SO2) free of sulphuric acid is delivered to the sulphitators. There are new methods of SO2 generation. The Swedish Celleco SBM-250 sulphur burner
has a burning capacity of 5 t/d but has a turn-down ratio of 20:1, or 250 kg/d. It is normally operated at 2.0-3.0 psig, but can also function effectively at 42 psig. A typical flow scheme for a modern SO2 generation plant is given
Liquid Sulphur Dioxide Where transportation costs will permit, liquid SO2 offers many advantages. MeGinnis diagrams a system for the introduction of liquid SO2. The method is comparatively trouble free and adapts itself readily to automatic pH control. A large reduction in sulphur consumption results; freedom from sulfuric acid, precise control of SO2 addition, and elimination of sulfur-burning equipment are other advantages.
Hydrogen Peroxide Hydrogen peroxide has also been tried in sugar refining. and reduced white sugar
color by 46% and ash by 20%.
Sulphitation Part II Current Technology The carbonated liquor after the first filtration still contains an appreciable amount of calcium in solution which has to be removed. This is done. By treating the filtrate with sulphur dioxide to form calcium sulphite precipitate. The latter is then separated from the liquor during a second filtration to produce a final clear liquor. Sulphitation is not an essential part of a carbonization refinery, another Process such as ion-exchange can also be used to remove excess calcium. Equipment Because sulphitation is only a minor operation in a carbonization refinery, geared mainly to reducing excessive alkalinity to the neutral point, the amount used is relatively small and the apparatus sometimes a bit crude. Especially the sulphur burner. The equipment in use in our refineries to perform liquor sulphitation consists of: 1. the sulphur burner for production of SO2 gas 2. a tower for contacting liquor and SO2 Or a venturi system of contacting, such as the Quarez sulphitator. Design Considerations Sulphur burner, Production of SO2 gas: The combustion of sulphur is required to produce sulphur dioxide, because the reaction takes place in the gaseous state between sulphur vapour and oxygen, according to the formula: S + O2 → SO2 + 293 kJ The reaction is exothermic and the combustion gas has an SO2content of 6 to
16%. A simple type of sulphur burner is normally used being of the stationary type and quite suitable for the light sulphitation of liquor required. Ideally the design and operation of sulphur burners require that some important points be Recognized, in particular: 1. Keep to a minimum the formation of SO3 which will react with moisture in the air to produce sulphuric acid. The cooling of SO2 gas to below 200°C is essential, the production of SO3 then being negligible (5). The, drying of the air of combustion is also required to prevent the formation of H2SO4. 2. Prevent the sublimation of sulphur, which can cause blockages and impair SO2 production by controlling the furnace temperature to less than 300°C. 3. The air flow should be kept constant and controlled. 4. A regulated supply of sulphur should be provided, if possible. The points mentioned above are not easy to control in the type of furnace in use, but then the operation is not critical enough to warrant a more complex approach. The Sulphur Tower As the name implies this is a tower containing splash trays, stacked on top of one another and designed to create a continuous passage for the liquor from the top to the bottom, while the SO2 gas travels up the tower. The liquor is broken into droplets in falling from one splash tray to the next. The gas is drawn up the tower by suction from a fan and the exhaust fumes are dispersed into the atmosphere. Reaction takes place as the SO2 conies into contact with the liquor. The sulphited liquor, with calcium sulphite precipitate in suspension, exits the tower at the base into a small seal tank, since the tower is under slight vacuum. The Quarez The Quarez sulphitation system consists of a holding tank, a circulating pump, a venturi and sulphur furnace to produce SO2 the level in the tank is kept constant by means of an overflow. Liquor in the holding tank is circulated by the pump and a certain amount is forced through an injector creating a vacuum, which causes the SO2 gas to be sucked in and mixed. The rest of the liquor by-passes the
injector by means of an adjustable valve, the setting of which controls the amount of gassing and the final pH of the liquor. This system is in operation in Pongola and the data available on the installation is given here:
22
Tons/hr
25
Tons/hr
Volume of liquor to Sulphitation
20
m³/hr
Number of circulations
15
/hr
300
m³/hr
Refined sugar throughput Tons Brix in Raw Melt
Capacity of circulating pump
PRACTICAL CONSIDERATIONS Operating control Sulphitation is carried out to a pH of 7.0 and even at 6.9 – 6.8; but a lower pH than this will result in inversion of sucrose and must be avoided. It is therefore of paramount importance to reliably control the final pH set point. This is generally done by varying the proportion of SO2 gas to liquor by measuring liquor pH. Filtration Filtration of the sulphited liquor should take place at or near 85°C to take advantage of the decreasing solubility of calcium sulphite at high temperatures as well as lower viscosity. A heat exchanger of the shell and tube type is normally
used for this purpose. The amount of calcium sulphite precipitate is much less than the carbonate precipitate and less filtering surface is required. Disposal of Sweet Water The cake from the primary and secondary filters is sent to sludge filters for sweetening-off. The sweet water should be returned to process that is C and B sugar melting, B and C, pan movement water, etc and preferably not back to the raw sugar refinery melter, on account of color and ash increase in refinery melt.
Distillery Yields Background Just as in a sugar factory there are a number of measures of operational efficiency in a distillery. In the sugar industry ratios like extraction, boiling house recovery, and overall recovery are well defined and universally understood. Sadly in the alcohol industry things are a little more disorderly. To help bring a little order the following is offered Theory There are four commonly used measures of yield
Fermentation yield
Fermentation efficiency
Alcohol recovery
Overall Conversion Efficiency
Fermentation yield Fermentation yield is measured in liters of absolute alcohol in beer per ton of sugars in molasses, and is calculated by the formula below Yf = Vb · ab / (Mm · fsm) where Yf = fermentation yield Vb = volume of beer [liter]
ab = alcohol content of beer (v/v) Mm = mass of molasses [tonne] fsm
= fermentable sugars content of molasses (m/m)
Fermentation efficiency Fermentation efficiency is an expression of how much alcohol was actually produced in beer relative to the amount that could be theoretically produced, and is given by Ef = Yf · 0.794 / 0.5111 × (100/1000) The factor 0.794 corresponds to the specific gravity of absolute alcohol and the factor 0.5111 is best explained as follows: If one kilogram of sugar was completely fermented (using theoretical 100% efficient yeast); 511.1 grams of alcohol and 1000 - 511.1 = 488.9 grams of carbon dioxide would result. Alcohol recovery Alcohol recovery is a measure of how much alcohol was finally produced relative to the amount that was in the beer. It shows the amount of losses in the evaporation and distillation sections combined. Alcohol recovery is calculated as follows Ede = (aaVp + ssVf) / aaVb · 100 where Ede = Alcohol recovery (or distillation and evaporation efficiency) aaV p
= volume of potable alcohol as liters absolute alcohol
ssV f
= volume of feints as liters absolute alcohol
aaV b
= volume of beer as liters absolute alcohol
Overall Conversion Efficiency Overall conversion efficiency is a measure of how much alcohol is finally produced relative to the amount that could be theoretically produced, and is given by
Eo = Ef · Ede · 100
Values of Yield The following table gives values of yield that one would expect in a well run Distillery Parameter
Value
Alcohol Recovery
98.5%
Fermentation Yield
573
Fermentation Efficiency
89%
Overall Conversion Efficiency
87%
Alcohol from Cane Molasses This article sets out a way of calculating how much alcohol you can make from the molasses your sugar factory produces. How much molasses? The fist step is to calculate how much molasses you will produce. In the Southern African Industry it is usual to express the amount of molasses made per tonne of cane crushed at a standard molasses brix of 85° The South African Industry average figures for the past five years are shown Below
Molasses at a standard 85°Bx Year
Molasses% Cane
2000/01
3.70
2001/02
3.93
2002/03
4.03
2003/04
3.73
2004/05
4.16
So the amount of molasses produced is M = C · M85 · 0.85 / Bm where M = tonnes molasses produced C = tonnes cane crushed M85 = Molasses at 85° brix as a percentage on cane crushed Bm = Actual brix of molasses produced Fermentable sugars The next step is to calculate the amount of fermentable sugars (FS) in the molasses. The fermentable sugars in molasses are sucrose, glucose and fructose; there are other sugars present in molasses, they are either unfermentable or are in small enough quantities that they can be ignored. There are a number of ways of measuring fermentable sugars in molasses; the most accurate is High Performance Liquid Chromatography (HPLC). The Lane and Eynon method also described in the SASTA Lab Manual is a two step process, which measures reducing sugars by titration. Reducing sugars are those sugars which reduce Fehlings reagents. Glucose and fructose reduce Fehlings reagents, sucrose does not, so the sucrose is inverted using hydrochloric acid and the reduction titration is repeated and the total reducing sugars can be calculated. The problems with this method are
there are other substances in the molasses which are also reducing agents, but are not fermentable sugars, so this method overestimates the amount of fermentable sugars, and
the titration is complex and requires a degree of skill to ensure repeatability, that may not always be present in a sugar factory laboratory.
South African Industry data on molasses quality are given as a guideline
South African Industry Average Molasses Quality Year
Refractometer brix
Sucrose/refractomete r brix Purity
Fructose%
Glucose%
FS%brix molasses
2000/01
84.26%
37.21%
7.55%
5.41%
52.59%
2001/02
84.44%
37.03%
7.58%
5.47%
52.48%
2002/03
85.09%
37.24%
7.14%
5.13%
51.66%
2003/04
84.79%
37.92%
7.08%
5.22%
52.43%
2004/05
83.97%
36.94%
7.93%
5.20%
52.58%
So, it is clear that about 52.5% of the brix in molasses are fermentable sugars. To calculate the tonnes of fermentable sugars in molasses we use the following Formula FS = M · Bm · FS%B where FS = tonnes fermentable sugars in molasses M = tonnes molasses produced Bm = Actual brix of molasses produced FS%B = fermentable sugars as a percentage on brix in molasses Alcohol Yield
in
The amount of alcohol produced is given by A = FS · Yf · Ede where A = liters of alcohol produced Yf = Fermentation yield Ede = Alcohol recovery (or distillation and evaporation efficiency) Design a limed juice flash tank
Tank Mixed Juice Diameter Flow [tonne/h] [mm]
Flash [DN]
Pipe Juice [DN]
Inlet Juice [DN]
Outlet
Drain [DN]
A
B
C
D
E
50
1457
350
150
200
80
60
1625
400
150
200
80
70
1756
400
150
200
80
80
1878
450
150
250
100
100
2097
500
200
250
100
125
2344
550
200
250
100
150
2569
600
200
300
100
175
2774
650
250
300
100
200
2966
700
250
350
150
225
3146
750
250
350
150
250
3146
800
300
350
150
275
3478
800
300
400
150
300
3633
850
300
400
150
325
3700
900
300
450
150
350
3926
950
300
450
150
375
4063
950
350
450
150
400
4194
1000
350
450
150
Juice Heaters Because high pressure steam is very valuable, exhaust steam is often used for juice heating or, if possible, preferably bled vapour from the evaporators. It is thus necessary to have a heat exchanger between vapour and juice; this is provided by the juice heaters. The juice heater (below) consists of an assembly of tubes; the juice circulates through the tubes, and the vapour outside them. Suitable headers force the juice to pass a certain number of times from bottom to top and from top to bottom of the heater by restricting the juice each time to a few of the tubes.
Vertical Juice Heater (Coil) The basic calculation of the juice heater is to calculate the amount of heat transferred using the overall heat transfer co-efficient (OHTC), the log mean temperature difference (LMTD) and the heating surface area. Q = h· A· ΔTlog
Where
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