mumias sugar company report

INTRODUCTION Mumias Sugar Company is situated in the western province of Kenya, Butere-Mumias

district. The company was started in 1973, with the aim of making the country self sufficient in

plantation white sugar. The factory has grown, over the years, with a change in management,

design improvements and scale of production.

The location of this factory was enhanced by such factors as:

Ample land for premise construction Presence of sufficient water from river Nzoia Enough manpower from the surrounding community Availability of enough sugar cane (raw materials) Enough capital The company is, so far, the leading white sugar producer in East and Central Africa,

following the introduction of the diffuser, in1997. In Kenya, Mumias Sugar Company competes

with other companies like Nzoia, Sony (South Nyanza), Chemilil, Muhoroni and West Kenya .It

produces about 45% of the sugar sold locally.

Five well-knit departments run this organization namely:

Production Quality control and assurance Engineering Human resource and Finance

The factory crushes about 350 tonnes of cane per hour, with a daily delivery of cane of

about 8,000 tonnes. This appears as sugar at a rate of about 32 tonnes per hour. Three main

products are obtained at the end of the process; Bagasse, plantation white sugar and final

molasses.

Bagasse is the source of fuel for the boilers, while sugar and molasses are sold to the

market. This report covers the work done in the production section and other affiliate parts.

Various unit operations and process procedures are covered in this report with the necessary

recommendations and conclusion made.

Attachment Report 1

CHAPTER ONE WEIGHBRIDGE AND CANEYARD OPERATIONS 1.1 The weighbridge

There are three weighbridges in operation, namely; A, B and C.All these work in the

same way but on different materials. The work of the weighbridge is to account for the weight

of products, goods or materials entering and leaving the factory. Two weighbridges are mostly

in use, B and C.B is for weighing cane only while C is for products and other materials.

Weighbridge A can perform both tasks and so it is standby

1.1.1Cane weighbridge

This is referred as weighbridge B, meant for cane only. It has four passages: B1, B2, B3

and B4.Incoming tractors with cane pass through one side of each office (2 in number) and exit

through other, to enhance weight calculation.

Documents brought to this weighbridge include:

i. The delivery note: This carries the delivery note number, name of the farmer, area of

location of the field, drivers name and number of stacks carried.

ii. The weighbridge ticket: Bears the date and time received, the gross, net and tare weight,

cane growers distribution number and name, and vehicle number.

Both documents mentioned above leave the station (in different copies) together with others,

including:

Copies of the delivery note and the weighbridge ticket Weighbridge reports for both nucleus and out growers cane Daily cane delivery report Cane yard offloading rates report-in tons (an hourly record for a given shift).

1.1.2 Product weighbridge

It is referred to as weighbridge C.It only allows vehicles to enter and leave through

single points on either side of the office. Weighing of fertilizers, sugar, molasses and other

public materials like building stones is done here.

Documents that enter this station are mostly weighbridge tickets for the goods

mentioned, and those that leave include: daily sugar haulage reports for cash and credit

purchases, copies of documents that came in.

Attachment Report 2

1.2 The cane yard

The cane yard constitutes of a large space within the factory where cane is offloaded. Offloading

is done by hydro-unloaders at a steel wall or directly onto the feed tables, four in number, when

processing is on course; otherwise, the cane is stored at the cane yard for night shift use.

Types of offloading equipment

1.2.1Hydro-unloaders

These are hydraulic machines, four in number. Their operation involves hooking at the

grooves on the tractor side and lifting the detachable bar with the cane, and then pouring it onto

the cane feed tables.

1.2.2 Wheel loaders

Are earth moving equipment (heavy vehicles) meant to push and lift cane on the ground

to the feed tables or to the cane yard for storage.

1.2.3 Overhead gantry cranes

These serve to move stored cane on the yard from place to another (for space creation to

incoming cane) or from storage to feed tables, harmonizing delivery breakages, which limits

supply to the tables.

1.2.4 Cane feed tables and the steel wall

There are four cane feed tables that consist of a continuously moving metal base with

open spaces, inclined at some suitable angle to enable movement of cane swiftly to the auxiliary

carrier (a continuously moving horizontal metal carrier that feeds the knives). On the fed tables

are cane-kikers; which align cane moving to the auxiliary carrier.

1.2.5 Stone-watcher cabins

People who watch on any destructive incoming material like stones and metal objects,

likely to spoil knives, occupy these. They stop the system, in cases of any emergency and

corrective measures taken.

Attachment Report 3

1.3 Cane storage and rotation

The cane yard stores cane that becomes useful during night shifts, when no tractors are

moving in to bring sugarcane. Cane stored at the yard is never allowed to stay for a long time

before processing since it deteriorates very fast through inversion.

Any cane brought earlier to the yard is moved forward and piled up such that it is

processed first.

1.4 Tractor movement in the cane yard

Tractors coming in from the weighbridge are systematically controlled by the cane yard

supervisor on duty and instructed on where to offload to avoid congestion and accidents at the

cane yard. The tractors line-up, to the offloading site, one at a time.

1.5 Types of wastes at the cane yard and their remedies

a. Trash falling under and around the cane feed tables/auxiliary carrier. This kind of waste

is cleared manually and disposed together with bagasse, by way of transportation using

Lorries (trucks) to the fields.

b. Stones, fine grit and mud. Large stones and metals can be noticed and removed but fine

grit and mud can not be fully cleared at the yard, they are carried along the process and

cleared at the boiler as sand or appear at the centrifugals as components of molasses.

Attachment Report 4

CHAPTER TWO CANE PREPARATION, THE DIFFUSER AND DEWATERING MILLS 2.1 Cane preparation

2.1.1 Objectives of cane preparation

1. Leveling of the cane mat to avoid chokes

2. To increase the bulk density of cane, thus increasing the capacity of the diffuser and

mills respectively.

3. To break down the hard cell structure (rind) of the cane.

4. To expose cells for easy juice extraction and increase the imbibitions dilution.

2.1.2 Equipment used in cane preparation

2.1.2.1 hydro-unloader/Gantry cranes /Wheel loaders

These equipment are used to load the feed tables, where feeding must be regular to

avoid overfeeding hence choking the knives.

2.1.2.2 Cane carriers; which convey cane to the knives.

2.1.2.3 The leveler knives

They consist of a steam turbine, driving a shaft on which knives are tightly bolted for

cutting cane, reducing the load to heavy-duty knives and leveling up the irregular heaps.

2.1.2.4 The heavy duty knives

These reduce the cane to smaller pieces exposing cells for subsequent extraction at the

diffuser. This system consists of a steam turbine driving the shaft containing knives. The unit

has more knives than the leveler and tends to cover the entire surface of the carrier.

2.1.2.5 The shredder

It completes the work of cane knives. It consists of a steam turbine controlled by a

governor; driving a shaft on which hammers are fitted to fall freely, passing between anvil

plates. The hammers hit the cane and disintegrate it into a fluffy mass. The speed of this

equipment is 1,000-1,500 rpm.

Figure 1.Flow diagram of cane preparation

This is shown on the appendix, Fig.1

Attachment Report 5

2.2 THE DIFFUSER

The diffuser is an enclosed carrier through which a bed of prepared cane is slowly

dragged, while copious quantities of water and thin juice percolate through the bed to wash out

the pol-bearing juice.

True diffusion means diffusion of juice through unbroken cell walls; this is a slow

process, and in this case, juice removal involves washing pol(sucrose ) out of shredded cells, a

process we can call leaching.

2.2.1 Imbibition water

Imbibition water is one used for washing juice from cane. The fibrous residue is called

baggasse and is mainly used as fuel.

Imbibition water temperature is controlled well between the values 80-90c to avoid

growth of leuconostoc bacteria which enhances inversion, an irreversible process.

Sucrose glucose + fructose

Cane juice is acidic in nature, having pH values of 3.5-4.5.Operating at low pH values

can easily corrode the plant components hindering operation at high temperatures. To avoid

these problems, lime (CAOH) is added at the 2nd and 7th stages of the diffuser to increase the pH

(to between 7&8).

2.2.1.1 Types of imbibition

i. Simple imbibition: This is affected by imbibing once at the dewatering mills (as

seen later) to avoid choking and increase capacity of the second mill.

ii. Compound imbibition: This is done at the diffuser (and where multiple mills are

applied). Imbibition is done at the 12th stage of the diffuser, and then continuous

serial imbibition done, with thin juice, backwards to the 1st stage.

Concentrated juice (called draft juice) is drawn from the 1st stage

and pumped to the treatment section.

2.2.1.2 Importance of imbibition: It enables extraction and recovery of sucrose from the cane cells.

2.2.2 Some diffuser design parameters

Tonnes of cane per hour 350

Attachment Report 6

Fibre % cane 16

Preparation index (%) minimum 90

Heating vapour temperature 105

Sucrose % cane 13.2

Extraction % 96.7

Area of diffuser bed-effective (m2) 465

Area of diffuser bed-Total (m2) 474

Effective bed length (m) 51.7

Total bed length (m) 52.7

Width inside diffuser (m) 9

Total extraction stages 12

Draft juice stage 1

Bed depth (m) 1.7

Normal bed speed (m/min) 0.72

Bed speed-max (m/min) 1.08

Average operating temperature (c) 85

Stage juice flow rate-average (ton/hr) 314

Draft juice flow rate-max (ton/hr) 500

2.2.3 Diffuser process control

a) Cane bed depth: Prepared cane admitted at the diffuser is evenly distributed to obtain a

level bed. The design bed height is 1.7m.The height is measured by level sensors. It is

adjusted by adjusting diffuser bed speed at a particular throughput.

b) Imbibition water: a flow control loop and control valve controls its flow. Its temperature

and flow are monitored on the Control panel.

c) Scalding juice heating: temperature transmitters in the outlet juice pipes from each of the

two juice heaters are used to control outlet temperatures through control valves or the

vapour supply to each heater.

d) Bed liquid level control: controlled to obtain optimum performance. The system maintains

constant liquid level near the top of the bed maximizing percolation at all times.

Attachment Report 7

e) Bed temperature control: two sets of three direct injections vapour heating pipes provided

for temperature control to about 85 c.

f) Diffuser monitoring: some devices that monitor conditions at the diffuser are:

a. Temperature indicators in 2nd and 7th tray

b. High level alarm on each juice tray

c. Pressure indicators on: -Juice heater

- Vapour supply

d. Measurement of liquid flows to each scalding juice heater

e. Bed speed indicator

2.2.4 Factors that affect extraction:

1. Preparation (of the cane) where two aspects exists

a) Degree of fineness measured by the preparation index (PI)- the higher the PI

value, the better the extraction.

b) Type of preparation- Size of distribution and particle shape. It is dependent on

cane quality and influenced by relative amount of shredding and knifing. There

should be minimum separation of fines, which lead to a more open cane bed and

higher juice percolation rates.

2. Throughput: increase in throughput reduces residence time of cane in the diffuser and

extraction is affected directly. Better extraction is achieved by running at a steady throughput.

3. Throughput evenness: The cane rate into the diffuser should be as steady and even as

possible leading to steadier and more efficient operation.

4. Flooding: This reduces extraction performance, and should be avoided at all times.

5. Juice flow system: Juice flow rates through each stage should be as high as possible; high flow

rate promotes the rate of extraction

6. Bed height excessively high or low levels should be avoided.

2.3 MILLING (DEWATERING MILLS)

Milling is defined as the passage of prepared cane, which has gone through the diffuser,

through the dewatering mills.

2.3.1 Milling equipment

A) Rollers

Attachment Report 8

i. Feed roller: Is on the front side of each mill feeding the other rollers with cane.

ii. Top roller: Is usually under pressure to squeeze the juice at two points, that is, at

delivery and feed rollers.

iii. Delivery roller: This delivers bagasse from both mills.

B) Trash plate

This is put between the feed roller and delivery roller to keep the fibre passing through

the mills under some pressure and prevent fibre from falling between the bottom rollers.

2.3.2 Factors that influence milling efficiency

1. Operational factors-like milling staff

2. Mill setting

3. Mechanical condition of the plant-grooves/length of rollers

4. Design of the plant (number of rollers)

5. Cane preparation

6. Pressure applied

7. Imbibition

8. Mill speeds in revolutions per min.(rpm)

9. Specific fiber loading

10. Steam pressure

CHAPTER THREE STEAM GENERATION 3.1 Introduction

Steam generation is the process by which soft clean water is pumped through the boiler

water tubes (for a water tube boiler), which transfers heat from fire to the water, which

vapourises into steam. This steam is then superheated and then passed under high pressure to

prime movers (turbines) and other process equipment (to provide energy).

3.2 Source of fuel for the boilers

The chief source of fuel is bagasse. The bagasse has (and indeed should have) a low

moisture content (usually 48-50%) for better combustion

Attachment Report 9

A high moisture fuel requires a slower distribution into the furnace, for complete

combustion (but will reduce amount of heat produced), while that with low moisture require

slightly lower distribution to give maximum turbulence and accelerate combustion of volatiles

released. Combustible constituents include: Carbon, Hydrogen and Sulphur.

3.3 Use of the boilers

They are used to provide steam for use in driving the turbines, which in turn produce

electric power for use within, and without the factory.

Steam produced is also used for heating purposes within the factory, washing and

driving heavy machines like mill rollers, both leveler and cane knives and shredder.

3.4 Boiler types

3.4.1 Fire-tube (low pressure) boilers: In this type of boilers, the heating agent (fire/flames) pass

through the numerous tubes from the furnace and water surrounds the tube bank. They find

use where low-pressure steam is needed.

3.4.2 Water-tube (high pressure) boilers: These are the ones applied in this factory. Here, the water

passes through the tubes and the fire surrounds the tube bank. They are actually high-pressure

boilers suitable for the kind of applications in the factory like evaporation and power

generation.

3.5 Boiler feed water and its quality

3.5.1 Feed water source

Condensed steam from evaporators, heaters and pans calandrias is usually the source of

feed water. This water is clean but still requires some treatment of hardness, total dissolved

oxygen (TDS) and oxygen scavenging.

Usually the same amount of water is not gained; this is because of some losses due to

steam leakages, its use in centrifugals, pan steaming, soot blowing and other areas. Therefore

vapour is always condensed and additional make-up water added from the treatment plant.

3.5.2 Feed water treatment

3.5.2.1 Alkalinity: Due to entrainment in the evaporators, vapour may contain some sugar traces

in the feed water. Sugar traces will decompose at high temperatures to form organic acids in the

boiler, hence destructive; causing corrosion if present in any quantity.

Attachment Report 10

Alkalinity is controlled and maintained above 8.5.Sodium hydroxide (NaoH) is

preferred to maintain a high alkalinity of necessary boiler water.

3.5.2.2 Total dissolved oxygen (TDS): Conductivity indicates the total dissolved solids. These

may include; Ca, Mg, Al, Fe, Zn, Ca (HCO3)2, C12H22O11, oxides and others. Calcium bicarbonate

forms the following products on disintegration:

Ca (HCO3) 2 CaCO3+CO2+H2O

But,

CO2+H2O H2CO3

H2CO3 is corrosive and therefore dangerous. Both intermittent and continuous blow

downs are employed to lower dissolved and suspended solids content, to prevent scaling and

entrainment.

3.5.2.3 Removal of oxygen: Oxygen is feared for its oxidizing power. If present in large

quantities then there is a risk of oxidizing the boiler tubes especially under high temperature

conditions. Its scavenged by adding Sodium Sulphite.

2NaSO3(S) + O2(g) 2NaSO4(S)

3.5.2.4 Removal of calcium and hardness: This is removed by adding sodium phosphate.

2Na2PO4 + 2Ca2+ Ca2(PO4)2 + 2Na+

Hardness should read zero at all times. Antifoams are usually used combined with

sludge conditioners.

3.6 Steam generation trends

It was observed that the temperature of the flue gases, which left the furnace, was in the

region of 350-380c.This reduced to about 110c after passing through the heat recovery

equipment (the economizer and air heater). This is a sign of good heat recovery. Further it was

noted that if exit temperature reduced to less than 100c, condensation is likely to occur,

forming water that might combine with SO2 and SO3 to form H2SO3 and H2SO4, damaging the

chimney and other parts at the exit.


It was observed that, for the purposes of mass and energy balancing, every given

amount of water entering the boiler, the same (should) appear as steam.

CHAPTER FOUR POWER HOUSE OPERATION 4.1 Some theory

Basically, to generate power we need a conductor and a magnetic field. The conductor is

made to rotate in (or cut) a magnetic field by either:

1) Rotating the field and stationing the conductor or

2) Rotating the conductor and stationing the magnetic field.

For the case at hand, several prime movers (turbine blades driven by dry steam) are used to

rotate the conductor as in 2 above.

4.2 Equipment used for electrical power generation

Two kinds of equipment similar in operation exit, namely:

i. Turbine and


ii. Diesel generators. Synonymously referred to as alternators.

Turbine alternators are five in number, namely: TA1, TA2, TA3, TA5 and TA6.Diesel

alternators are3; DA1, DA2 and DA3, which operate.

Several voltages are produced by these generators and later synchronized to form a

larger voltage. Power is generated at 3,300 volts (3.3KV) and later distributed in three phases to

supply a voltage of 415 Volts (after passing through a step down transformer) to motors and

control panels.

There exists a bus on the voltages are merged and inter-pass transformer that steps down

3.3 KV to 415V and vice versa between two control panels.

4.3 Power demand at the factory

The entire factory needs about 7MW.Fortunately, the powerhouse produces about

10MW, which is excess. The remainder is used to serve the residential estates and sometimes

supplied to the KPLC national grid.

The leveler, heavy-duty knives and the shredder are among the highest consumers of

power, taking about 3MW cumulatively.

The consumer equipment determines the voltage and quantity of current to be used. A

voltage of 240V is supplied to the residential estates. The equipment used in these areas

consumes a current varying with the use. Therefore protection is done by use of circuit breakers

and fuses, rated at different respective currents.

For proper utilization, power is tapped from the Main line (overhead) in an alternating

way, a phase at a time.

Some factors that keep the alternators in good condition are:

i. Good quality of steam

ii. Clear lubrication oil and

iii. Enough cooling water for bearings


CHAPTER FIVE JUICE TREATMENT AND EVAPORATION 5.1 JUICE TREATMENT

5.1.1 Role of the juice treatment station a) Receiving and weighing (massing) juice from the diffuser b) Heating the juice c) Clarification, by chemical addition and chemical addition/settling d) Evaporation of treated juice and sulphitation of syrup.

5.1.2 The treatment process 5.1.2.1 Requirements Proper conditions for effective treatment which include:-Temperature,pH and flow rate Necessary clarifying agents which include:-Lime, heat, sulphur dioxide, phosphate and

flocculant. 5.1.2.2 The treatment process The juice treatment process is summarized in figure 2, as shown below.

Milk of lime To Evaporators (Through Pre-heaters)

Weigher Scale

Mixed juice tank

Juice heaters (primary &Secondary)

Clear juice Tank

Mud mixer

Flocculant tank

Clarifiers Distribution box

Flash tank

To diffuser

Fig.5.1 Flow diagram of juice treatment and equipment used.

5.1.2.3 Juice heating


Reasons for heating juice are:

o To sterilize the juice (especially mill juice) o To speed-up lime juice reaction o To coagulate finely suspended matter, like proteins.

Heating juice at its natural pH accelerates inversion. Heating is therefore carried out as

rapidly as possible and the juice limed, adding hydrated lime (Ca (OH)2), to a pH slightly

above 7.

5.1.2.4 Juice clarification

The purpose of clarification is to produce a clear juice that is neutral, light in colour and

free of suspended matter and to do this with minimum pol (sucrose) loss and reducing sugar

degradation.

Clarification depends on formation of a precipitate throughout the bulk of juice. This

precipitate encloses impurities when it forms, and entraps more impurities as it compacts and

settles-the whole process being rather like forming a huge sponge that is then allowed to

collapse.

Some chemicals necessary in clarification are:

9 Phosphoric acid:-Important in raw juice defecation. It is added when there are minimal amounts of phosphates in the cane.

9 Polyelectrolytes: -Synthetic water soluble polymers that induce flocculation of particles of precipitate forming heavier and denser flocs that settle more rapidly to make clear

juice.

9 Sulphur dioxide: -For bleaching purposes. 5.1.2.5 Reactions of lime in cane juice

Lime reacts with phosphates in the cane juice to form, first, a very fine amorphous

calcium phosphate, apart from neutralization of organic acids of juice.

3Ca (OH) 2(aq) + 2H3PO4(aq) Ca3 (PO4)2(s) + 6H2O(l)

During this reaction and under the action of heat and increase in pH, other non-sugars

are precipitated out of solution: amount and type of non-sugars precipitated depend on the

juice characteristics.


The amorphous precipitate crystallizes into more complex compounds and under the

action of the polyelectrolyte or simply with time form large intricate flocs, which entrap finer

particles of precipitate, which are then entrained during settling.

The size, amount and density of floc particles have important bearing on quality of

clarification. It is important therefore that all conditions leading to good clarification be studied

and applied. Some of these are:

a) Optimum phosphate content of juice

b) Enough lime to ensure adequate precipitation

c) Point of addition of lime to ensure good flocculation and avoid floc breakage.

Excess liming cause destruction of reducing sugars, formation and form complex

products likely to increase the viscosity of massecuite and increase scaling of evaporators. It

should therefore be avoided.

5.2 EVAPORATION

5.2.1 Introduction to evaporation

Juice obtained from cane is too dilute for the process of crystallization, by which sugar is

extracted. Consequently, the juice has to be concentrated in evaporators.

Concentration of juice should not go too far or else crystals will come out at>70 brix.

Usually a concentration of 60-65 brix is not exceeded, so that the false grains may be dissolved

when the syrup is fed into the vacuum pans.

5.2.2 The evaporation process description

Clear juice (from preheaters) is taken to evaporators at a temperature of about 103c.The

heating agent is steam (exhaust steam from the power generation turbines at a controlled

temperature). Juice passes in the tube side of the heat exchange equipment (evaporator), while

steam passes at the shell side, where the steam heats the juice externally.

It should be noted that the main aim of evaporation is to boil off water from clear juice;

increasing its brix concentration from about 11 percent to about sixty five percent.

For every effect, vapour is withdrawn and designated as either vapour 1(for the 1st

evaporator), vapour 2 for the 2nd e.t.c., depending on which evaporator is involved in a given

stream.Vapour 1(V1) is used to heat the 2nd evaporator and some withdrawn to heat vacuum

pan boilers (for crystallization), and the secondary heaters when necessary.V2 heats the third


evaporator for a given stream, some taken to heat the primary heaters and those heating

diffuser juice.

Vapour withdrawn from a preceding evaporator is use for the next evaporator

consecutively until finally a vacuum created at the 4th evaporator through a barometric

condenser withdraws it.

Juice from the evaporators is called raw syrup and is held at raw syrup extraction tanks

before getting pumped to the raw syrup boxes. Condensate from the 1st &2nd evaporators of

each stream is termed pure condensate; since it is supposed to be free of sugar traces, and is taken

for steam generation at the boiler.

Condensate from the 3rd & 4th evaporators is called sweet water condensate and is stored in

sweet water tanks from where it is used for various industrial tasks like imbibition in the

difusser, thinning at pans and other cleaning purposes, to the sumps.

5.2.3 Determination of evaporation efficiency

The amount of water evaporated or to be evaporated is obtained by performing a brix

balance.

Let J = Weight of juice

Bj = Brix of juice

Bs = Brix of syrup

E = Weight of water evaporated

S = Weight of syrup

Then,

J.Bj = S.Bs

S = J.Bj/Bs

E = J- S = J (1 - Bj/Bs)

E = (Bs - Bj)/Bs* 100 = Percentage of evaporation obtained

The amount of evaporation necessary is about 80% of the weight of juice and this

represents a great amount of heat. Thus, it is important that it should be done as efficiently as

possible, hence the use of multiple effect evaporators.

5.2.4 Evaporator main controls

a. Amount of steam admitted to the 1st evaporator (effect)


b. Level of liquor in the 1st effect

c. Brix of liquor (syrup) leaving the last effect

d. Proper bleeding of incondensable gases

e. Temperature on each evaporator (effect)

f. Vacuum level on each evaporator

Steam admitted in the 1st effect provides the driving force for the whole apparatus.

Consequently it I adjusted according to the amount of evaporation required. If we have

more juice to evaporate or want more concentrated syrup, we admit more steam.

A typical diagram of the evaporator is shown in appendix

CHAPTER SIX SUGAR (VACUUM PAN) BOILING AND CRYSTALLIZATION 6.1 Pan boiling process description

The vacuum pans are divided into two classes, namely:

-Low-grade pans (1-6), typically cylindrical pans and


-High-grade pans (7-11), which are coil pans.

Low-grade pans, numbered (1-6), boil sugar from B-molasses, a product of B-massecuite,

while high grade pans are numbered 7-9, called A-sugar pans and 10&11 for B-sugar.

Syrup leaves the last the last evaporator set at about 65% brix and at a purity of about

85%. This is the feed to the vacuum pans. The work of the pans is to grow sugar crystals (on

sucrose in syrup) in as many steps as may be required to reduce the purity of that syrup until it

attains the purity of final molasses, and maximize the amount of pol recovered in raw sugar.

Pan boiling is typically done in three boiling steps; each step producing, after

crystal/molasses separation, A-sugar and A-molasses-sugar and B-molasses-sugar and C-

molasses or final molasses.

The kinds of pans used in the factory are of the batch type. Batch pans are similar to

evaporators. However, their tubes are shorter (1m long) and of larger diameter (102mm) and

have a larger downtake. At the bottom cone is a discharge valve through which each batch of

massecuite is discharged.

A pan boiling flow diagram is shown in figure 2 below.

6.2 Terminologies used in pan boiling

6.2.1 Graining: Is the introduction of fine sugar particles (crystals) into a boiling mass.

6.2.2 Footing: Is a crystal content of a given (boiled) mass, enough to give one panful, without

formation of false grains and with the sugar size well developed to the required one. Example:

For A-massecuite; 1mm sugar crystal, B-massecuite; 0.5 mm, C-massecuite; 0.35 mm

6.2.3 A strike: Is the action of releasing an already boiled mass into the receiver tanks

(crystallizers).

6.2.4 Slurry: Is suspension of powdered sugar in alcohol (industrial spirit) 6.2.5 Massecuite: Is a mixture of molasses and sugar crystals from a given pan (A, B, C) or stage. 6.2.6 False grains: Refers to crystals that form spontaneously. They are smaller than main crystals and cause difficulty in separating the molasses from the crystals. They also go through the centrifugal screens, raising purity of molasses. 6.3 Factors/conditions for good granulation

i. Optimum temperature; of 65-70c.Any temperature below this gives weak crystals and if above, caremalization is likely to occur (or sugar is burnt and its colour spoilt)

ii. Steady vacuum-of about 20 in Hg iii. A steam pressure of about 5 psi iv. Proper control of circulation of material in the pans


Treated syrup from evaporators

A-massecuite from pans 7,8&9

C-massecuite

Final/C-molasses C-melt

B-massecuite

B-magma B-molasses

White (market) Sugar A-molasses

Treated syrup from Evaporators

A-massecuite from pans 7,8&9

Molasses storage Tank

Figure 6.1: Flow diagram of the pan boiling process

6.4 Super saturation and zones of pure sucrose super saturation

Saturation is dependent on temperature. If the solution is heated, more sugar is

dissolved. If the hot saturated solution is carefully cooled so as to avoid crystallization of

sucrose, a supersaturated solution results.

6.4.1Supersaturation coefficient (SSC)

This is the sucrose concentration in the sugar solution to its concentration in the same

but saturated solution at the same temperature. SSC is the driving force in all sugar boiling. It

is a state of tension; the solution strives to return to its saturated state by expelling sucrose;


forming new crystals, or by depositing it onto existing ones. At very high SSC spontaneous

formation of crystals occurs.

6.4.2 Zones of super saturation

a) The unsaturated zone: Here there is a low concentration of sucrose in the solution.

Therefore no crystallization takes place.

b) The metastable zone: Here, the SSC lies slightly above 1.Added crystals will grow while

no new crystals will form. Sugar boiling is carried out here.

c) The intermediate zone: The SSC is moderately high. Added crystals will grow and new

crystals form, but only in the presence of existing ones.

d) Labile zone: The SSC is very high. New crystals form spontaneously while crystals

growth is rapid.

6.5 Crystallization

Crystal nuclei are introduced into, and grown in, the vacuum pans. This growth is due

to sucrose molecules from the mother liquor (syrup, A-molasses or B-molasses) depositing onto

the crystals. A high SSC is maintained to make the crystals grow. When the pan has been struck,

the SSC of the mother liquor is still high; now this represents a potential to obtain further crystal

growth, until the SSC drops nearer to 1.If the crystals are separated from the mother liquor

directly after striking, this potential is wasted.

Crystallizers are stirred semi-circular tanks, where massecuites are retained while the

SSC of the mother liquor falls as the crystals grow. What occurs in the crystallizers is a

continuation of crystal growth, but through cooling rather than boiling.

CHAPTER SEVEN CENTRIFUGATION AND DRYING OF SUGAR 7.1 CENTRIFUGATION

Massecuite leaving the crystallizers has to be separated into sugar crystals and molasses.

The more efficient this separation, the more sucrose will be recovered as sugar and the less

sucrose will be lost in molasses

Centrifuges are machines that separate liquor from the crystals in a massecuite. Only

after the mother liquor passes through the screen that it is called molasses.

7.1.1 Batch centrifugals


Basic centrifugation in this type of centrifugals involves spinning massecuite in a

perforated basket; centrifugal force acts on the molasses, forcing it through the perforations

while the sugar remains on the basket wall.

A monitor casing that catches the molasses spun off the machine surrounds the basket.

A typical cycle of operation is as follows:

a) The machine is loaded with massecuite while turning at 50 rpm

b) Massecuite feed is stopped and the machine sped up to 1,500 rpm for about 2 minutes

c) At this speed, most of the molasses is spun off. hot water and steam are sprayed

consecutively, onto the sugar layer for a few seconds

d) The basket is slowed down to 50 rpm and a plough, provided, peels the sugar away

from the screen, letting it to fall through the center of the basket onto a carrier

underneath

e) The screen is washed and the cycle restarted. One cycle takes 3to4 minutes.

Batch centrifugals are exclusively used to produce raw (market) sugar, on A massecuites.

7.1.2 Continuous centrifugals

These centrifugals have a cone shaped basket; belt driven from underneath by a motor;

mounted upside down alongside the machine. The machine rotates at a fixed speed of 1,500

rpm.

Massecuite via the pug mill is continuously fed to the centre of the cone; sugar crystals

ride up the inclined screen while molasses is forced through the perforations, into the molasses

compartment. The crystals fly off the top edge of the cone to strike the wall of the monitor

casing. The high speed of the crystals cause breakage that is not a disadvantage for B and C

sugar, as these are used as seed or remelted

7.1.3 Factors that affect crystal separation

a. Viscosity of the massecuite

b. Grain size: false grain formation

c. Amount of wash water applied at the centrifugals (steam)

Centrifuging is done to obtain market sugar magma and C-melt, with their respective

molasses. Market sugar is withdrawn from the centrifugals to be dried and bagged for sale

sugar (magma) is used as seed for crystallizing A-sugar. C melt is mixed with raw syrup and


taken back to the process as recovered sugar. A molasses is the feed for B- sugar boiling

molasses feed for C-sugar boiling and C-molasses the final one.

7.2 SUGAR DRYING

Sugar leaving the A centrifugals has a moisture content of 0.4 to 1 %. This quantity of

moisture, although apparently small, has an extremely detrimental effect on the keeping quality

of raw sugar. Deterioration takes place mainly in the moisture in the molasses film around the

crystals and dying is therefore indispensable. The moisture content of sugar at a 93.3% pol should be 0.04% water In the drier, the moisture is driven off from the surface of the liquor layer covering the

crystal. The sucrose on the surface crystallizes, forming a skin that traps bound moisture. In

stockpiled sugar, bound moisture causes hardening (caking), but this occurs only in a thin outer

layer of the sugar pile, thus insulating the rest of the pile.

A single type of equipment; the rotary louvre drier is used to bring the sugar into contact

with the hot air. This is a drum set horizontally with a tilt towards its discharge end.

Longitudinal louvers are lined in the inside of the drum. It rotates and the sugar is picked up

from the bottom, and then dropped in curtains through the flow of air.

A fan is used to draw atmospheric air via air filters, which then passes on hot steam coils

to gain heat, before finding use in the drier. Otherwise cold air is also drawn by another route to

cool down the hot one, when theres need, to maintain the temperatures below fifty-five degrees

celcius. Higher temperatures decompose sugar.

7.2.1 The cyclone

Light sugar dust exhausted from the drier is scrubbed clean of its sugar dust by spraying

water into it in a cyclone separator. The resultant sweet water is returned to the process.

7.2.3 The vibrating screen

This serves to separate (classify) sugar crystals, such that only the required size of

CHAPTER EIGHT

BAGGING, PACKAGING OF SUGAR AND WAREHOUSE OPERATIONS Almost all sections of the factory deal directly with this part of the factory. The electrical

and instruments section serves to maintain, install and give instruction on operating the

machines involved. This is done in conjunction with the mechanical engineers. Quality

assurance and production sections liaise to give a high quality sugar for packaging.


8.1 Sugar packaging

Belt conveyors to sugar bins, stationed above the packing station convey dried sugar.

Packaging goes on as long as sugar is in the bins (produced).

The packaging process is automated to pack 2kg (for 2kg machines), 1kg, 1/2kg and

1/4kg packets. The machines are calibrated to give the following sugar packets weight limits:

Max. Min.

1. 2kg bale (12 packets) 24.60 24.16

2. 1kg bale (24 packets) 24.60 24.16

3. 1/2kg bale (30 packets) 15.40 15.20

4. 1/4kg bale (60 packets) 15.40 15.60

8.2 Sugar bagging

Bagging of sugar is done separately in 50kg bags. Sugar for bagging has its own bins and

its storage done on a larger space. There are four functional bagging machines. Also provided

are conveyors that take bagged sugar to the store.

The amount of sugar packed and bagged is accounted for by keeping records of the

number and weight of the outgoing packed/bagged units in bagging and packaging reports

respectively.

Sugar is continuously tested for colour, crystal size and purity, at the laboratory, as often

as possible. Samples are taken from the packing section for this purpose. To maintain a clean

product, the packaging area is cleaned often and the staff dress in proper attire to avoid sugar

contamination.

The warehouse serves to store packed/bagged sugar. It is always kept clean for health

reasons. Bales/Bags are kept here, waiting purchasing. External warehouses also exist, where

sugar is transferred to when in surplus.


Sugar from the drier

(vibrating screens)

Packaging

Adjustable distributor

Bagging

Packed sugar

Warehouse

Sugar bagging section bins

Sugar packaging section bins (hoppers)

Fig. 8.1: Flow Diagram of Sugar Bagging, Packaging and Warehousing


CHAPTER NINE WATER TREATMENT 9.1 The treatment process

River Nzoia serves as the main source of the water used in and around the factory. The river already serves two processing industries upstream; Webuye paper mills and Nzoia Sugar Company. Therefore the water, having substantial hardness has to be treated. The water is pumped from the river via two pumps, located in a river pump house, with a total of 4 pumps. The two pumps that operate at a time have a capacity of 180-200 tons of water/hour. They are 3-phase pumps, operating at 415 volts, 190 amps and with water-cooled bearings. Raw water goes t reatment plant in two pipes. One of them is used to make-up for spray pond water and thPrimco, a flocculant is dowater then moves to a diunderground, wedge shaand is held in clarified wportable/drinking waterof water supply (flow rat Make-up to spray Ch

River House

Domestic/portWater tower

Po

Supply to estates, school

Temporary hardne

following reaction takes o the t

e other feeds the treatment section. Before reaching the break-tanks, sed online and then a coagulant, magnafloc in the break-tanks. The stribution box (tank), which then feeds four clarifier tanks, ped, at different rates. Water leaving the clarifiers is clarified water ater tank. it is from this tank that the water is fed to filters, to get (chlorinated) and that used in various process purposes. The amount e) varies with the demand, ranging from 250-50 liters/second.

Settling Clocculant dosing Break tanks tanks

ponds

lorination

To factory

pump

Rapid Mixing Slow Mixing

Distribution box

Filters

able

rtable water tank

Clarified water tank

s &hospital

Fig. 9.1 Water treatment flow diagram

ss (carbonate hardness) can be eliminated by boiling, where the

place:


2HCO3-(aq) + Mg MgO(s) + 2CO2 (g) + H2O(aq)

After removal of temporary hardness, any Ca and Mg remaining is capable of forming

scum with soap or boiler scale. This is permanent hardness, which is eliminated by addition of

more chemicals or de-ionization.

Boiler water is de-ionized via a resin based filter or taken from the cooling ponds and

treated by application of Na2SO3 and Na2(PO4) whose presence or level is checked by testing for

phosphates and sulphates at the laboratory.

9.2 treatment of portable (domestic) and boiler water

Clarified water is passed through filters; which consist of granular matter (basically

stones and sand) of varying size, in layers-These are referred as immedium&dual filters.

There also exist activated carbon filters and a de-ionizing unit through which boiler water is

passed. Domestic water is only taken through the sand filters and dosed with chlorine in

optimum amounts, as shown in the diagram above.

9.3Cleaning the filters and regenerating the resin

The resin contained in de-ionizing plant is basically a long chain hydrocarbon with a

charged tail, where adsorption of dirt takes place. The resin cannot be active for good otherwise

much dirt will pass through untraped; it needs regeneration. Regeneration is done by passing a

solution of sodium based salt like NaCL, in an operation called backwashing.

In backwashing, the granular matter is partially suspended in a reversed flow stream of

air, water and/or Nacl solution.

9.4 Instruments used at the water treatment station

1. Loviboard comparator: equipment used in chlorine DPD method for testing amount and

presence of chlorine in portable water.

2. Microprocessor turbidity meter: Used to measure water turbidity (a measure of total

dissolved solids). It uses infrared light as the basis for measurement.

3. Streaming current detector (SCD):Its operation is as follows:

A submersible pump samples water from the river Analyzer determines the charge and sends a relay to the controller


The controller directs the pump, at which rate to pump the flocculant The dosing pump transfers the chemical from the storage tank to the raw water

line.


CHAPTER TEN LABORATORY OPERATIONS

The laboratory is the heart of quality control in the factory .The laboratory staff performs

the following tasks:

Sampling Analysis of various products and raw materials Reagent preparation and Generation of lab (advisory) reports

10.1 Sampling and sampling methods

Correct sampling methods of different products at different stages of manufacture was

seen to be a crucial step for effective chemical control

The method of sampling depends on the nature of the particular product. Two sampling

methods are eminent:

a) Continuous sampling: whose examples are-Mixed juice, Neutralized (limed) juice,

clarified juice, prepared cane& mud flow rates, raw(treated)syrup,A,B&C molasses.

b) Intermittent samples: Like-Massecuite, Magma (B-sugar), commercial sugar (can also be

continuous), C-sugar, Boiler water, Mud& milk of lime, Bagasse, Prepared cane& the stage

juices.

Sampling from the diffuser and its environs is done alongside scale reading of important

parameters like: - -prepared cane (tons/hr)

-Imbibition water (tons/hr)

-Mudflow -rate from the process house

10.2Analysis of inter-stage process products

Analyses made include:

i. Determination of brix

ii. Determination of *pol in syrups, massecuites and in final molasses

iii. Measurement of pH

iv. Boiler water and condensate analysis

v. Direct analysis of cane and

vi. Other special tests like; biological oxygen demand and crystal sizes.


*Pol-Of a solution is the concentration (in grams solute per 100 gm solution) of a solution of

pure sucrose in water, having the same optical rotation at the same temperature

10.2.1 Boiler water and condensate tests

The following analyses are carried out:

I. Total hardness test

II. Test for sulphates

III. Alkalinity tests for O, P and M

IV. pH

V. Silica test (SiO2)

VI. Phosphate (PO4) test and

VII. Sugar trace test.

10.2.2 Direct analysis of cane (DAC) tests

These include:

i. Moisture determination for both cane& bagasse

ii. Cane preparation index (PI)

iii. Brix and Pol extract for both bagasse& cane

10.2.3 Other special and routine analyses

They include:

Biological oxygen demand (BOD) Sugar crystals test Bulk density measurement of the sugar Sugar colour test Instrument calibration

10.3 Preparation of reagents

Reagent preparation is a sensitive practice and should be done with a lot of carefulness.

The following standard methods are used to prepare some of these reagents:

a. Preparation of Barium chloride

Use: Determination of sulphates and alkalinity

To prepare it, 100g of barium chloride, Bacl.H2O, are transferred into a 1000 ml

volumetric flask, and half fill with distilled water. Shake until the solution is complete, and

made to mark with distilled water and stored well in amber coloured bottles

b. Preparation of Buffer solutions


Use: Calibration of pH meters

Preparation: Special anhydrous salts and freshly prepared and cooled distilled water used for

accurate buffer solutions. This special salts of given weights are used to make buffers of

different pH.

c. Erichrome Black T indicator solution

Use: Determination of hardness in water.

Preparation: To 30mls of distilled water add 1ml of normal sodium carbonate solution and 10g

of erichrome Black T and mix. Make to 100 ml with isopropyl alcohol and mix. Store in amber

coloured bottle.

Other chemicals prepared through other standard methods include:

i. Cleaning solutions like Chromic-sulphuric acid

ii. Calcium carbonate

iii. Chloroform

iv. Ammonium molybdate solutions

v. Lead acetate solution and other solution

10.4 Generation of laboratory reports

Reports are generated on an hourly, daily, weekly, monthly or yearly basis, depending

on their destination and use. Reports destined for the boiler or processing house are written by

the analysts themselves, and their content only gives the analysis results obtained. The results

are meant to aid processing and maintain product quality.

There are reports generated for every shift and consequently a daily one. Values of

analyses done within the laboratory are recorded in an analysis book that makes it easier to

trace any problem arising in the process.

Reports from the weighbridge(s) showing hourly or daily cane and sugar tonnages

brought in and leaving the factory respectively are brought to the lab, where they are fed into

the computer. In addition there is also a time account, to deal with any stoppages (recorded on

a daily shift report, by the shift manager on duty).

The time account report, the cane delivery report, sugar reports, molasses accounted for,

factory performance reports, and cane diffused are all combined in an integrated factory daily

report. From the factory daily reports, a factory weekly report is kept; where averages for time


account, cane delivered, mixed juice, imbibition, bagasse produced, milling rates, sugar bagged

and others are made to help generate monthly and then yearly reports.


CHAPTER ELEVEN RECOMMENDATIONS AND CONCLUSION 11.1 Recommendations

A number of recommendations are made here, after recognition of a few problems and

setbacks in some operations in sugar manufacturing at Mumias.

11.1.1 Problems encountered at the boiler station and their proposed remedies

a. Control of boiler feed water pH: A low amount of caustic soda (NaOH) will

mean minimal pH reduction; hence it might tamper with the boiler tubes. The

corrective measure can be addition of a suitable amount of NaOH after frequent

pH tests at the laboratory (hourly).

b. Boiler tube failure, rapturing (or bursting):If there is a high degree of scale

formation (pitting), the tube is overheated due to reduction in the heat transfer

coefficient, and in a bid to maintain required temperatures& pressures,

consequently the tube may fail. The solution to such a problem is proper feed

water treatment and firing. If it occurs, the boiler should be shut down and

replacement done to avoid further damage.

c. Presence of (a lot of) sand/silt in the bagasse: During rainy seasons, a lot of mud

is brought along with the cane, which finally end up as sand in baggasse.lots of

sand slow don combustion and lower temperatures. This problem can be solved

by constant blow-down of the boiler and trying to employ a suitable sand

separation process like using a shaker.

d. High temperatures around the boiler (working) area. This makes the personnel

on duty uncomfortable and a lot of heat lost. As a remedy, the most suitable

material should properly lag all the steam pipes and the boiler body.

e. High intensity of noise; especially when the steam pressure is high, leading to

bleeding some steam to the atmosphere from the safety valves. This is usually a

short tem problem that can be solved by generating manageable levels of steam

or venting it to the ground to reduce the noise.

f. Air pollution by bagasse: During windy periods, a lot of bagasse is blown and

suspended on the air, from the conveyor belts and the storage site. This problem

can be solved be enclosing (shielding) the bagasse on the storage yard and the

conveyor belts well from wind.


g. It is proposed that analysis of the flue gases fro the boiler be done after some

time to determine its safety and degree of combustion.

11.1.2 Cane delivery

To reduce the problem of cane delivery delays, it is proposed that an introduction of

own-off-loading vehicles be made. Increased cane delivery will mean less loss of sucrose and

increased sugar production.

11.1.3 Loss of sucrose along the process

To enhance less residence time at the diffuser, the juice held at every stage should be

minimal. To facilitate this process, smaller retention capacities at the stages should be

introduced and continuous vacuum pans be put into place, to accomplish minimum sugar

processing time.

11.1.4 The number of conveyor belts in bagasse distribution and storage

There are a lot of conveyors for this purpose. This leads to a waste of space and electrical

power that drives them and encourages the pollution quoted above.

11.2 Conclusion

It is true that much was leant from this attachment. It was noted that the sugar industry

is an ideal place for a chemical and process engineer. It was enjoyable to know a lot of new

things.

On the side of the company, it would be advisable to give some financial allowance,

since there is some substantial contribution to production.


References 1. Raphael. Kaplinsky, Sugar Processing, the development of the 3rd world technology.

2. Manual for laboratory procedure, Mumias Sugar Company -quality assurance.

3. Alex Higgins & Stephen M. Elonka, Boiler Room Equations and Answers, 2nd edition.

4. Sugar milling research institute handbook, University Of Natal, Durban.

5. Sugar Technology volume 1& 2(cane handling and milling, juice weighing, heating,

clarification, filtration and evaporation), regional sugar cane training centre for Africa

Reduit Mauritius.


Appendix 2


Appendix 3


Appendix 4


Appendix 5


Appendix 6


Appendix 7


Appendix 8


Appendix 9


Appendix 10


Appendix 11



INTRODUCTIONCHAPTER ONEWEIGHBRIDGE AND CANEYARD OPERATIONS1.1 The weighbridge1.2 The cane yard1.3 Cane storage and rotation1.4 Tractor movement in the cane yard1.5 Types of wastes at the cane yard and their remedies

CHAPTER TWOCANE PREPARATION, THE DIFFUSER AND DEWATERING MILLS2.1 Cane preparation2.2 THE DIFFUSER2.3 MILLING (DEWATERING MILLS)

CHAPTER THREESTEAM GENERATION3.1 Introduction3.2 Source of fuel for the boilers3.3 Use of the boilers3.4 Boiler types3.5 Boiler feed water and its quality3.6 Steam generation trends

CHAPTER FOURPOWER HOUSE OPERATION

4.1 Some theory4.2 Equipment used for electrical power generation4.3 Power demand at the factoryCHAPTER FIVEJUICE TREATMENT AND EVAPORATION5.1 JUICE TREATMENT5.2 EVAPORATION

5.2.1 Introduction to evaporation5.2.2 The evaporation process description5.2.3 Determination of evaporation efficiencyCHAPTER SIXSUGAR (VACUUM PAN) BOILING AND CRYSTALLIZATION6.1 Pan boiling process description6.2 Terminologies used in pan boiling6.3 Factors/conditions for good granulation6.4 Super saturation and zones of pure sucrose super saturat6.5 Crystallization

CHAPTER SEVENCENTRIFUGATION AND DRYING OF SUGAR7.1 CENTRIFUGATION7.2 SUGAR DRYING7.2.1 The cyclone

CHAPTER EIGHTBAGGING, PACKAGING OF SUGAR AND WAREHOUSE OPERATIONS8.1 Sugar packaging8.2 Sugar bagging

Fig. 8.1: Flow Diagram of Sugar Bagging, Packaging and WarehWATER TREATMENT9.1 The treatment process9.2 treatment of portable (domestic) and boiler water9.3Cleaning the filters and regenerating the resin9.4 Instruments used at the water treatment station

CHAPTER TENLABORATORY OPERATIONS10.1 Sampling and sampling methods10.2Analysis of inter-stage process products10.3 Preparation of reagents10.4 Generation of laboratory reports

CHAPTER ELEVENRECOMMENDATIONS AND CONCLUSION11.1 Recommendations11.2 Conclusion

References