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Industrial Visit Report

Sevanagala Sugar Factory

19th December, 2017

Mechanical Engineering Sectional Committee

Institute of Engineers Sri Lanka

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TABLE OF CONTENTS

1. Executive Summery …………………………………………………………………… 01

2. Brief description to the sugar factory …………………………………………………... 02

3. Visit insights …………………………………………………………………………… 09

4. Appreciation …………………………………………………………………………… 11

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1. EXECUTIVE SUMMERY

Mechanical Engineering Sectional Committee (MESC) of The Institution of Engineers Sri Lanka

(IESL) arranged an industrial visit to Sevanagala Sugar Factory in Embilipitiya and 10 MW solar PV

power plant in Hambanthota area on 19th December 2017. A group of 22 members participated in

this event. This visit was organized during the annual maintenance period of the sugar factory and

thus the members participated got a great opportunity to get an exposure to the details of the sugar

manufacturing technology and bagasse based power generation technology which are not usually

visible, by witnessing the dismantled machineries and equipment. This report is a brief description on

the visit to Sewanagala Sugar factory.

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2. BRIEF DESCRIPTION TO THE SUGAR FACTORY

Sevanagala Sugar factory is the 2nd largest sugar manufacturer in Sri Lanka in operation at present and

it has a capacity of 1250 MT per day. Earlier it was a private owned company and from 2010 onwards

it is fully owned by government operated under the name “Lanka Sugar Company”.

Lanka Sugar Company is one of the three sugar manufacturers in Sri Lanka. Sugarcane is the major

sucrose extracting crop used for sugar production. Due to high temperature and dry condition

available in Eastern part of the country, Sugarcane is an ideal crop to cultivate for sugar production.

Monaragala District and Ampara District are largely contributing to sugarcane crop cultivation for

uplifting the country's economy, which helps to reduce annual foreign exchange expenditure spent for

sugar imports. Four sugarcane plantations have largely involved to sugar production in Sri Lanka.

They are Pellwatte, Hingurana, Sevanagala and Kanthale. At present only the first three are in

operation.

2.1. Cane Yard

After weighing, the cane tractors come to the cane yard and there are two cranes for unloading. They

lift the cane to the feeder table. These cranes can lift maximum 10 MT. Once cane is put on the feeder

table, it goes through the leveler first. Then the sugarcane is chopped by two sets of rotating cutters.

After that chopped cane come to the shredder where it is shredded. Those are the cane preparation

steps undergoing in the cane yard section.

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Figure 01 - Cane yard

Figure 02 - Rotating cutters

2.2. Mill House

There are four mills in the factory. Each mill is powered by a steam turbine. Duty of this section is

juice extraction from the cell opened canes effectively. Cane is shredded by the shredder. Shredder is

powered by a steam turbine and it consists of 18 hammers in one line and 8 such lines around the

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axis. After that cane falls on to a belt conveyor and comes to the 1st mill. Cane enters to the mill from

the top roller and feeder roller and comes out through the top roller and discharge roller. 180 kg/cm2

pressure is applied to the top roller. Extracted juice falls to a sump at the bottom. 1st mill bagasse is

sent to the 2nd mill via inter carrier. Likewise, 2nd mill bagasse is sent to the 3rd mill. Extracted juice

from 1st and 2nd mill is sent to the production section directly. But, 3rd mill juice is added back to the

1st mill bagasse at the inter carrier while 4th mill juice is added to the 2nd mill bagasse. Hot imbibition

water at 60 0c is added to the bagasse coming out from the 3rd mill. Final bagasse which comes out

from the 4th mill is sent to the boiler house. Moisture content of the final bagasse should be between

48% and 52% and the POL value (Polarization angle which describes the sugar level of bagasse) is

lower than 2%.

Figure 03 - The shredder

2.3. Boiler house and the steam flow of the factory

This is the place where all the steam required for the factory is produced. Boiler house consists of two

water tube boilers and the capacity of each boiler is 25 MT per hour. Superheated steam at 3600C and

21.1 kg/cm2 is produced by these boilers. Final bagasse of the mill section is used as the fuel for these

boilers. There are two furnaces in this section. Before the bagasse is fed into the furnaces, chemical

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are added to reduce its moisture content. Flue gas of the furnaces are used to preheat ambient air and

that air is blown to the combustion chamber by a blower. This mechanism helps to burn bagasse

effectively.

Firstly, steam produced by the boilers are used to power two turbines in the power house, four turbines

in the mill house and the turbine coupled to the shredder. Then the turbine exhausts are used to

provide the thermal energy for the juice pre-heaters, evaporators and vacuum pan boilers in the

process house. Condensate of each equipment is collected to a tank near the boiler house and is reused

to produce steam.

Figure 04 – Boiler House

2.4. Process House

2.4.1. Juice Clarification

Extracted raw juice comes to the raw juice tanks after screening. Lime is added at a rate of 2 kg per

ton of cane to maintain its pH value. This method is called cold liming. Then juice goes through two

heaters called juice primary heaters. Mixed juice is heated up to 550C to 650C by these two heaters.

Again, lime is added and the pH value of the mixed juice is raised to 6.9 to 7.1. Maintaining pH value

at this level helps sediment mud properly in the clarifier. This liming method is called hot liming.

Limed juice then goes through another two heaters and heated up to 1050C. This is the temperature

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at which the juice solution has the lowest viscosity and it helps a proper sedimentation of mud. This

is called juice secondary heating.

Secondary heated juice is then pumped to a flash tank. Gases are removed from this tank and is called

flashing. Then the juice enters to the juice clarifier. It is also called as subsider. Just before entering to

the subsider, 1g per ton of cane flocculent solution is added to the juice. This helps to settle floating

impurities.

The clarifier consists of five compartments. Each compartment is sloped towards the center of the

clarifier and settled impurities collected from the bottom center of the vessel. Overflow of each

compartment is collected as clarified juice. Retention time of the clarifier is 6 hours.

2.4.2. Rotary Vacuum Filter

Separated mud in the subsider is mixed with baggacillo (fine bagasse separated from final bagasse of

the mill section by a cyclone separator) in a mixing tank. Then the mixture is brought to the mud filter.

Mud filter consist of rotating drum with screened stainless steel surface. Suction pipes are there inside

the drum and connected to the screen to create the vacuum necessary. Drum is rotating approximately

at a rate of 1/3 RPM. The drum is divided to three specific sections; no vacuum, low vacuum (200

mm Hg) and high vacuum (250 mm Hg). Hot water is sprayed from the top of the filter to get the

maximum sucrose from the mud. Filter cake is carried out to the outside by a conveyer and the filtrate

is returned to the juice liming tank. In this way, 99% of the sucrose is recovered.

2.4.3. Evaporators

Clarified juice contains about 85% of water and 15% of dissolved solids. This water is removed by an

evaporation process. This process removes about 75% of water and the end product is called syrup.

There are 4 evaporators in series and the process is called multiple effect evaporation. First three

evaporators work under normal pressure conditions while the 4th one works under a vacuum pressure.

Purpose of applying a vacuum is to boil juice at a lower temperature. This method avoids

caramelization of sucrose. The syrup formed in evaporators is pumped to the storage tanks.

2.4.4. Pan Boiling

Vacuum pans form sugar seeds from the syrups. This is called pan boiling. There are four vacuum

pans, each one with a capacity of 42 MT. Three types of sugar is formed in this process; Type A, B

and C. They are categorized by the grain size.

• C massecuite grain size - 0.3 mm

• B sugar grain size - 0.5 to 0.8 mm

• A sugar grain size - 0.8 to 1.1 mm

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There are two pans for C boiling and C graining. Other two are for A boiling and B boiling. Operating

temperature of each pan is 600C. This temperature should be properly maintained. Otherwise, sucrose

can be caramelized.

In the pan boiling process sugar crystals are developed by adding sugar powder (slurry), which is

prepared at the laboratory. In this method, no crystals are formed. Only executing growth of small

crystal in massaecuite. It is done by adsorbing sucrose in mother liquor onto the crystals. But to

develop crystal in sugar liquid, there should be a considerable super saturation, with the crystal growth,

the super saturation of mother liquid drops. It is maintained using vacuum in pan. There are three

zones of super saturation in sugar process.

• The labile zone: in this zone, existing crystal growth and new crystals form even in the

absence of existing crystals.

• The Intermediate zone: new crystals can form in this zone, but only in the presence of

existing crystals

• The Meta stable zone: being the nearest to saturation, existing crystals increase in size, but

new crystals cannot form. Pan boilers should be kept in this zone at boiling process. Below this zone

sugar crystal will dissolve and above this zone false grain will immediately appear.

2.4.5. Slurry preparation

Crystal size is larger than 185µm, 1000 g raw sugar is mixed 500 ml Butanol in mixing chamber for

about 6 hours. Then 950 ml prepared slurry and 1050 ml Butanol is again mixed. This mixture is used

to prepare C-seed.

Figure 05 - Inside a pan boiler

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2.4.6. Centrifuging

There are five continuous centrifuges (2000 rpm) to separate C sugar from molasses. They are

automated and have 0.2 MT per hour capacity. Similarly, there are 4 number of fully manually operated

centrifuges (1000 rpm) for separate A and B sugar.

Figure 06 - Centrifugal separators

2.4.7. Drying

The commercial sugar (Type A) leaving the centrifugal machine contains 1-1.5 % moisture. Because

of that, it cannot be filled in bags for sale. This moisture content may be reduced to about 0.2%.

Therefore, drying of sugar is done in a rotary dryer with a rate of 12 MT per hour where the excess

moisture is removed from the sugar crystals. Hot air at 60-650C is introduced to the drum of this dryer.

Finally, dried sugar crystals are sent to two bins of capacity 60 MT for storage. Stored sugar is bagged

and sent to the stores.

Figure 07 - Rotary dryer

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3. VISIT INSIGHTS

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4. APPRICIATION

On behalf of the Mechanical Engineering Sectional Committee of The Institution of Engineers Sri

Lanka (IESL), we wish to thank the Chairman of Lanka Sugar Company and Mr. Walter the General

Manager of Sevenagala Sugar for granting special permission for this visit during the factory

maintenance period. Special thanks goes to Mr. Hettiarachchi the senior manager of Sevenagala Sugar

who coordinated and made all necessary arrangement from the company side. Our appreciation goes

to Eng. Vimukthi Maduranga on his support throughout this event and to Eng. O.V.J. Kumara for

providing the information for this report. Finally, our gratitude to all the members who participated

to make this event a success.

Prepared By,

Eng. Asela Janaka Abeywardana

Coordinator – Industrial Visits (MESC – IESL)