energy conservation in sugar manufacturing

Salient Aspects of Energy Conservation and Latest Trends in Sugar Manufacturing

Submitted by

S. Ramesh

A. Muralee

D. Mohan Rao

APRIL 2011

AVANT-GARDE ENGINEERS AND CONSULTANTS (P) LTD

(AN ISO 9001:2008 ORGANISATION)

No. 68A, Porur Kundrathur High Road, Porur

Chennai - 600 116, India

Tel: + 91 -44 -2482 8717/ 18/ 19/ 20

Fax: + 91 -44 -24828531

[email protected]

www.avantgarde-india.com

i

CONTENTS

Abstract ii

Introduction 1

General 1

Energy Conservation Measures 1

Latest Trends in Sugar Manufacturing 11

Cogeneration 12

Conclusion 12

Acknowledgement 13

References 13

Avant-Garde Profile 14

ii

Abstract

This paper highlights the latest changes in machinery and equipment in the industries

that has led to saving on power and steam required in sugar manufacture station wise.

It also deals with the overall changes in concepts both in juice extraction as well as

sugar extraction that has resulted in energy efficiency and improvement in product

quality acceptable to international standards and Pharma industries. This assumes

grate significant in view of the increasing demand for power and energy in the country

and also up-gradation of power products to effectively compete in the international

markets.

1 AVANT-GARDE Engineers and Consultants (P) Ltd

1.0 Introduction Sugar cane is the oldest crop cultivated in India for more than several thousand years. Evidence is found in the Hindu Vedas about sugar cane. Sugar cane process industries are having the tradition of more than one and half century background. The first cane milling plant was invented in China during middle of the 19th century. It was during the same period that “Parry” started their sugar operation at Nellikuppam in the year 1852 in Tamil Nadu. In the olden days cane milling plants were high energy consuming plants. Even though the plants had their own cogeneration facilities they had to import additional power and fuel for the operations. This trend continued till about 1970, when factories started saving bagasse and sold it to paper plants and other uses. Nowadays due many innovations in the thermal, mechanical and electrical engineering field, the sugar cane process industries have become highly efficient compare to other process industries. Processing of Cane Juice to sugar also have undergone a lot of up gradation to improve processing efficiency and better sugar colour value. 2.0 General As we know sugar cane process industries are broadly divided into two main divisions, namely engineering and process. But of late “Cogeneration” has become a third and equally important division. For sugar cane processing both thermal and electrical energy are required, and that is drawn from the cogeneration plant. Bagasse from the sugar plant is used as the fuel for the cogeneration plant during crushing season. 3.0 Energy Conservation Measures 3.1 Sugar Cane Processing Sugar cane processing is divided into following categories

• Cane handling and preparatory system • Juice Extraction system • Juice clarification system


• Evaporation • Crystallization & Centrifuging

3.1.1 Cane handling and preparatory system As we know, in the olden days harvested cane from the field were weighed and fed to the cane carrier by manual unloading. In later days EOT cranes and feeder tables were invented to ease the cane feeding operation without any shortfalls to milling/diffusion juice extraction system. 3.1.1.1 Cane Un-loaders Grab un-loaders lead to frequent kick loads. Nowadays hydraulic grabs and sling system are introduced to avoid the kick loads and are working satisfactorily. Hydraulic tipplers are introduced in the northern part of our country and are giving trouble free operation. The hydraulic tippler reduces the power requirement and also reduces the kick loads. 3.1.1.2 Feeder Tables As we know that feeder tables are used to store the cane and feed it in to the cane carrier continuously. These feeder tables were driven by constant speed induction motor coupled with Eddy current coupling to vary the feeding surface speed till recently. Nowadays due to development of Variable Frequency Drives, motor speed will be varied as per the requirement and also at the same time power will be saved during slow speed operation. In the past low efficient worm and worm wheel type single stage gearboxes and open spur gears or chains were used for speed reduction. Nowadays highly efficient (95%) shaft mounted planetary gearboxes, are used for speed reduction, which reduces power consumption considerably.


The View of Feeder Table Drive Arrangement with ACVFD Motor and Shaft Mounted Planetary Gearbox

By introducing ACVFD and planetary gearboxes installed power is reduced by two third of earlier requirement. Feeder table of 8M x 7M is installed in a 6000 TCD sugar plant with only 15 kW motor in place of 22 kW motor which was required for old drive arrangements, thus saving one third power. 3.1.1.3 Cane Carrier Like cane feeder table, cane carrier also was driven by squirrel gauge induction motor with eddy current coupling for speed variation and with conventional gearbox and open gears for speed reduction. Nowadays conventional motor with eddy current coupling is replaced by ACVFD motor with planetary gears for speed reduction. By this arrangement one third electrical power gets saved. 3.1.1.4 Cane preparation philosophy Till date we are using kicker, leveler/chopper, cutter and fibrizer/shredder for cane preparation, and the average power consumption will be around 65 kW per ton of fiber. This process required lot of attention in each unit as well as maintenance. This is replaced by latest development of inline shredder with feed drum and carding drum. The power consumption in this area is reduced from 65 kW to 56 kW per ton of fiber and cane preparative index will be around 90+ with long fibers.


3.1.2 Juice Extraction System In general juice extraction plant is broadly divided into two types, one is commonly well known in India, as the milling technology and another one is diffusion technology. 3.1.2.1 Whole Cane Diffuser Diffusion technology is commonly used in Australia and African countries. The diffusion technology is highly energy efficient than milling technology. But in our country the technology did not gain acceptance during its introduction period itself, because diffusion technology mainly depends upon the cane preparation and the automation. In diffusion system cane preparative index should be 90+ for juice leaching in the diffuser. At the time of introduction of diffuser in India (during 1980’s), we were having the cane preparation equipments only to get maximum value of 70-80 PI and hence the system failed to prove the performance. Moreover the performance of the diffuser depends on the automation controls. The juice pH and temperature inside the diffuser have to be controlled properly to get maximum juice extraction in the diffuser. At the time of introduction of diffuser in our country automation was not even thought of. The following are the comparison of diffuser with mills. Comparison of Installed Power in 2500 TCD Sugar Plant

Cane Diffusion (HP) Milling (HP)

CANE PREPARATION

i. Cane Chopper 150 150

ii. Cane Cutter 250 250

iii. Fibrizer 1600 1600

iv. Cane Carrier 60 75

v. Rake Carrier 40 50

vi. Drag conveyor 22 -

Total (A) HP 2122 2125


JUICE EXTRACTION

i. 4 sets of Mills 4 x 600 - 2400

ii. One Set of Diffuser 455 -

iii. De-Watering Mills 1035 -

iv. Mill Juice Pump 22 60

v. Intermediate Carrier 87.5 120

Total (B) HP 1599.5 2580

Total (A + B) HP 3721.5 4705

Note: - A diffuser achieves a RME of 97+. To achieve this RME at a milling plant, six numbers of three roller mills are required, increasing the installed power by another 1260 HP. Advantages of Cane Diffuser over Milling Tandem

1. Increase in extraction (Reduced Milling Extraction by 2.0% ) 2. Reduction in maintenance cost (less moving parts) 3. Increase in plant availability (Downtime low, hence plant time efficiency increases) 4. Reduction in maintenance Man Hours(down by 70% due to less moving parts) 5. Reduction of re-shelling of rollers (down by 75% due to elimination of 3 mills) 6. Mill sanitation improvement (higher temperature maintained in diffuser reduces sugar

loss due to bio chemical inversion) 7. Automation (less man power and efficiency improved) 8. Reduction of sugar loss in filter cake and disposal problem (down by 0.07% cane

(50%): colloids are coagulated during scalding juice heating, filtered by the bagasse blanket back in diffuser. Less dissolved solids are expected to enter the clarification process, so muddy juice % cane is largely reduced, resulting in less filter cake % cane)

9. Increase in available bagasse (up by 0.75%) cane due to less use of bagacillo in vacuum filter since less muddy juice % cane.

10. Steady juice flow rate to boiling house. 11. Decrease scale formation in evaporators. 12. Reduction of oil and grease in effluent (down by 60%) 13. Less sulphur consumption for clarification house (down by 20%) 14. Reduction of electrical power consumption.


Feed

3.1.2.2 Milling Tandem Various type of mills are available in the world as per the manufactures designs, like vertical head stack, inclined head stake, auto setting, self setting mills etc. Normally conventional mills are having three rollers with feed, top and discharge rollers along with under feed rollers. The mills are having trash plate to convey the bagasse from first compression to second compression in the mills. Usually the static trash plate consumes about 15% to 20% of the mill drive power. During the traveling of bagasse a lot of extracted juice in the compressions zone will be reabsorbed by bagasse due to improper drainage in the mills. Top Feed Discharge Juice drainage Latest development in the milling technology is two roller mill. These mills are not like our conventional olden days crusher. The typical arrangement of two roller mill is as shown below.

Reabsorbtion Limiting Device

Juice drainage Every droplet of extracted juice is properly drained in this system. In the past mills were driven by steam engines (14% thermal efficiency) or by steam turbines (35% thermal efficiency) drives, which are very low efficient drives. Nowadays these drives are gradually replaced by energy efficient (90% and above) DC Drives/ACVFD Motors. ACVFD motors are most suitable for mill drives because of their own advantages.

Top

Bottom


For steam turbines power transmission system for mills, three stage gearing systems were used i.e. high speed reduction gearbox, slow speed reduction gearbox and bigger size open gearing arrangements. Total gearing efficiency in this system was around 80.8% only. After introduction of electrical drives the first stage high speed gearbox is completely eliminated and two stage speed reduction efficiency of 82.0% is achieved. At present planetary gearbox eliminates slow speed gearbox and open gearing arrangement and its efficiency is around 95%.

View of ACVFD Motor with Planetary Gearbox for 36” x 78” Two Roller Mill

The above view shows the 3500 TCD milling tandem having four numbers two roller mills with the installed power of 430 kW ACVFD motor with foot mounted planetary (four stage) gearbox. Whereas the same capacity sugar plant having three roller mills of 36” x 78” size required an installed power of 600 kW (considering 150% safety factor). In the two roller mill trash plate is eliminated and there will not be any hydraulic load on mill roller journals. Hence the power consumption in the milling will reduce to one third of total power consumption. Inter Rake Carrier Normally inter rake carrier in the milling tandem are driven by constant speed motor and speed variation is done through eddy current coupling and power transmission is by single stage worm gearbox and open gearing. Nowadays this system is replaced by ACVFD motor and planetary gearbox for power saving. Here also one third power will be saved.


View of Foot Mounted Planetary Gearbox With ACVFD Motor

For Inter Rake Carrier

View of Shaft Mounted Planetary Gearbox with ACVFD Motor for

Short Distance Inter Rake Carrier Pumps Nowadays all the material handling pumps like screened juice, sulphited juice, clear juice, syrup extraction pumps etc., are driven through ACVFD Motors to control the constant flow to process to achieve good boiling house performance and also save energy. 3.1.3 Juice Clarification Mass Flow Meter In the juice clarification area juice weighment is carried out through mass flow meter replacing the conventional mechanical tipper scale. This totally eliminates the mechanical weighing system and weighed raw juice pumps and its operation and maintenance. Juice Heaters Juice heating by the tubular heater is gradually being replaced by Direct Contact Heaters and Wide Gap Plate Type Heat Exchangers. Because of this juice can be heated by later effect evaporator’s vapour to reduce the steam consumption of the process. The approach temperature for the new generation heaters is very low (10C). De-scaling of juice heaters is completely eliminated in the Direct Contact Heaters. In the plate type heat exchanger automated cleaning systems are introduced and de-scaling down time is reduced considerably.


Juice Clarifier The conventional 444 clarifier is slowly getting replaced by Short Retention Time Juice Clarifier. Normally juice retention in this type of clarifier is 45 min as against 180 min in the conventional clarifier. This eliminates the falling of clear juice temperature reduction coming out form the clarifier. Hence additional thermal energy required to raise the clear juice temperature is reduced. Filtrate Juice Clarification Filtrate juice from the Vacuum Filter/ Decanter is treated in the filtrate juice clarification system (either by flotation or sedimentation process), the clarified juice can be directly taken into clear juice for further process. This eliminates around 12% juice re-circulation in the clarification process. 3.1.4 Juice evaporation Old concepts like vapour cell with quad and DEVC with quad is getting replaced by quintuple effect evaporation with common condenser. Because of the high pressure cogeneration the exhaust pressure available for the first effect will be easily maintained around 1.5 Kg/cm2 and 1300 C constantly. This eliminates the thermal shocks in the evaporation system. The first effect Roberts bodies are being slowly replaced by Semi Kestner and Falling Film Evaporators which are providing lower ∆T in the evaporation. Even fourth body vapours can be utilized for pan boiling. Automatic juice flow stabilization control in clarification and auto control in evaporator operation ensures consistency of operation and efficiency of the systems 3.1.5 Crystallization and Centrifuging Pan Boiling In the crystallization process nowadays continuous vacuum pans both horizontal and vertical type are being utilized. These pans can be operated with low temperature vapour. Hence later effect evaporator’s vapour (third and even fourth effect) will be sufficient for the pan boiling. In the batch pans mechanical circulators (either bottom mounted or top mounted) increases the circulation of massecuite and hence vapour consumption reduces. By the above total


steam consumption for sugar boiling is reduced, by more than 2%. Total automation of pan boiling controls results in consistency, uniformity & efficiency. Condensers To create vacuum in evaporation and crystallization system in olden days Barometric condensers were used. Later these were replaced by Double Entry Multi Jet Condensers. Nowadays these double entry multi jet condensers are replaced by single entry multi jet condensers. Single entry multi jet condensers are highly efficient and hence the water requirement for the condensing system is reduced by one third and also it can be easily automated to reduce energy consumption. Latest development in the condensing system is single common condenser for entire process. Such system is already in operation in some new installations. Which are quite successful as well as energy efficient. Crystallizers Massecuite dropped from the pans are stored and cooled in the crystallizer. Open type horizontal air cooled crystallizers are used for high grade massecuite and open type horizontal water cooled crystallizers are used for low grade massecuite in the past. At present for the lower grade massecuite single unit of mono vertical crystallizer is used. This will save lot of energy and maintenance cost. Very low efficient worm and worm wheel type gears for crystallizer drive are gradually replaced by high efficient planetary gearbox. This saves nearly 50% of power consumed in this area. Also in the centrifugal area pug mill and magma mixer drives are replaced by planetary gears. By this replacement 50% electrical power will be saved in this area.


View of Shaft Mounted Planetary Gearboxes in Crystallizers and Magma Mixer Centrifugals

In the batch centrifugal area high efficient regenerative ACVFD motors are used to reduce the power consumption form 3.0 kW per cycle (conventional three speed motor) to 1.08 kW per cycle. The above configuration will be reducing the steam and power consumption in the sugar plant operation. Steam Requirement for sugar process will get reduced to around 32% on cane and power consumption for entire sugar plant operation will be 22 kW per TCH for all electric sugar plant). 4.0 Latest Trends in Sugar Manufacturing 4.1 Sugar Cane Juice Processing Cane Juice Process depends upon the juice clarification process; the following are the world wide process adopted to remove the impurities and colouring maters from the sugar cane juice.

a. Defecation Process b. Double Sulphitation/Carbonation Process and c. Phosphitation Process

The defecation & Phosphitation process are used to make raw sugar with colour value of about 800 ICUMSA.


The double sulphitation/Carbonation Process are used to make direct consumable plantation white sugar with the colour value of around 100 ICUMSA. In our country we are traditionally adopting double sulphitation process to make direct consumable plantation white sugar. As per our Indian Sugar Standard Sulphur content allowed is 70 mg/kg (Max) for double sulphitation process and 15 mg/kg (Max) for refined sugar process. Sulphur content of 70 mg/kg in the sugar is not acceptable by the developed countries. Operation & maintenance of sulphur burners and SO2 gas lines are expansive and also the cost of sulphur is high. To avoid the above, nowadays leading sugar manufacturers are switching over to defecation followed by raw sugar production, and modified refining process with R1 & R2 massecuite boiling, to produce lustrous, sulphurless white sugar of less than 50 ICUMSA units, acceptable to international market and pharma grade. Apart from that they are having the refinery columns for refined sugar production. By this process sugar colour value comes down to 20 to 30 ICUMSA. 4.2 Muddy Juice Filtration: The latest developed decanter system for Muddy Juice filtration is completely eliminated the bagacillo requirement (around 0.8% on cane) and the same is effectively used in the cogeneration plant for additional revenue. Also mud volume and pol loss in the mud is drastically reduced to 0.012 on sugar. 5.0 Cogeneration Olden day’s people were thinking that bagasse is not suitable for high pressure cogeneration cycle boiler, as fuel. Nowadays it is proven that cycle parameters of 125 ata with 5450 C are achievable. This cycle parameter is very high efficient and suitable for even 3500 TCD sugar plant. In this cycle steam fuel ratio is high and specific steam consumption is low. 6.0 Conclusion The above said measures are not just a myth it is being practically achieved by latest installations.


7.0 Acknowledgement The authors would like to express their sincere and grateful thanks to the management of Avant Grade Engineers and Consultants (P) Ltd., for giving kind permission & encouragement for publishing this article. 8.0 References 1. Peter Rein – Cane Sugar Engineering 2. E. Hugot – Hand book of cane sugar engineering


About Avant-Garde

Avant-Garde is one of the leading Engineering and Consulting Company with over two

decades of experience in Co-Generation plant installations in sugar plants. The company has

an excellent track record in providing engineering services for the Preparation of Feasibility

reports, Detailed Project reports, Contract detailed Engineering services and Supervision of

Erection and Commissioning for the Co-Generation plants. Avant-Garde have successfully

executed / are executing nearly 100 co-generation plants in the industry, totaling to about

2000MW of power addition to the Nation.

Engineering Services Provided for Sugar Plants

• Feasibility Report for new sugar plants installation

• Feasibility Report for sugar plant expansion with additional facilities

• Detailed Project Report for new sugar plant installation

• Detailed Project Report for sugar plant expansion

• Detailed Project Report for sugar complex consisting of sugar plant, distillery and

cogeneration plants

• Investigative and Solution services for the Existing Sugar Plant

• Plant layout, project design and equipment layout

• Sugar plant Automation for Diffuser type / Milling type plants, Automation for

plantation white sugar, refinery, and raw sugar manufacturing facilities

• Procurement services for Sugar plant machineries either on package basis or on EPC

basis

• Supervision of the plant installation and commissioning

• Energy efficiency studies in Sugar plants

• Introduction of Automation in Sugar plants for various sections

• Engineering services for distillery installation

• Engineering services for SLOP fired boiler installation to achieve zero discharge from

distilleries

• Engineering services for strategic addition of co-generation plants


Plant Automation

Automation helps an industry to get more out of each stage of the process. Automation of

sugar plant not only saves the energy consumption but also improve plant operation and

product quality. The following are the areas where Avant-Garde has provided services for

plant automation.

• Cane Feed Automation

• Mill Automation

• Imbibitions Automation

• Juice Flow Stabilization

• Auto lime feeding

• Temperature controls

• Regulating Juice level in Evaporator

• Pan Automation

For more information on any of our services, please contact us on +91 -44- 2482 8717 / 18 / 19/ 20 or by email at [email protected]

energy conservation in sugar manufacturing

Documents