02-PCRA-NitendraDewangan

ENERGY EFFFICIENCY OPPORTUNITIES

IN

STEEL RE-ROLLING INDUSTRY

AN INTEGRATED ENERGY SOLUTION PROVIDER

www.pcra.org

By : Nitendra Dewangan

Mail : [email protected]

Mobile : 9406122508

Thermal Energy Saving Opportunities

In

Steel Rerolling Industries


www.pcra.org

COST BREAK UP FOR REROLLING

INDUSTRIES – OIL UNIT

SALARY

5%

OIL

43% LABOUR

10%

BURNING LOSS

19%

ELECT

18%

CONSUMABLES

5%

COST BREAK UP FOR REROLLING

INDUSTRIES – COAL UNIT

SALARY

5%

COAL

38% LABOUR

11%

BURNING

LOSS

21%

ELECT

20%CONSUMABLES

5%

What is a Furnace?

A furnace is an equipment to melt

metals for casting or heat materials for

change of shape ( rolling, forging etc)

or change of properties (heat

treatment).

FURNACES

Types and classification of furnaces

Furnace

classification

Recuperative

Regenerative

According

to mode of

heat transfer

According

to mode of

charging

Mode of heat

recovery

Open fire place furnace

Heated through liquid medium

Periodical

Forging

Re-rolling

(Batch / continuous

pusher)

PotContinuous

Glass tank

melting

(regenerative /

recuperative)

Based on the method of generating heat: combustion type

(using fuels) and electric type

Characteristics of an Efficient Furnace

Furnace should be designed so that in a

given time, as much of material as

possible can be heated to an uniform

temperature as possible with the least

possible fuel and labour.

Furnace Energy Supply

• The products of flue gases directly contact the stock,so type of fuel chosen is of importance.

For example, some materials will not tolerate sulphurin the fuel. Also use of solid fuels will generateparticulate matter, which will interfere the stock placeinside the furnace.

Hence, majority of the furnaces use liquid fuel,gaseous fuel or electricity as energy input.

• Melting furnaces for steel, cast iron use electricity in induction and arc furnaces. Non-ferrous melting utilizes oil as fuel.

Reheating Furnace

• Furnace oil and Coal is the major fuel used inreheating Furnace .

• LDO is used in furnaces where presence of sulphur isundesirable

• Furnaces operate with efficiencies as low as 7% asagainst up to 90% achievable in other combustionequipment such as boiler.

• This is because of the high temperature at which thefurnaces have to operate to meet the required demand.For example, a furnace heating the stock to 1200oCwill have its exhaust gases leaving at least at 1200oCresulting in a huge heat loss through the stack.

Rerolling Mill Furnace

Batch type furnace:

•Used for heating up scrap, small

ingots and billets weighing 2 to

20 kg. for batch type rerolling.

•Charging and discharging of the

‘material’ is done manually and

the final product is in the form of

rods, strips etc.

•Operating temperature is1200oC.

•Total cycle time can be

categorized into heat-up time and

rerolling time.

Continuous Pusher Type:

•The process flow and operatingcycles of a continuous pushertype is the same as that of thebatch furnace.

•Operating temperatureis1250oC.

•The material or stock recovers apart of the heat in flue gases as itmoves down the length of thefurnace.

•Heat absorption by the materialin the furnace is slow, steady anduniform throughout the cross-section compared with batchtype.

Continuous Steel Reheating Furnace feature

MAJOR AREAS OF CONCERN

1. FUEL STORAGE, HANDLING AND PREPARATION

2. COMBUSTION OF FUEL AT OPTIMUM LEVEL AND CONTROL OF EXCESS AIR

3. TEMPERATURE CONTROL AND MAINTAINING UNIFORM TEMPERATURE.

4. EFFICIENCT WASTE HEAT RECOVERY

5. AUTOMATION OF MILL TO SPEED UP ROLLING

6. PROPER INSTRUMENTATION FOR EFFICIENT MONITORING

7. BURNING LOSS ESTIMATION AND CONTROL

8. CONTROL ON OPENING

9. TRAINING AND EDUCATION OF PERSONNEL ON BASIC ASPECT OF ENERGY CONSERVATION.

10. ELECTRICAL ENERGY CONSERVATION

11. MORE MONITORING IN DESIGN AND INSTALLATION STAGE

12. QUALITY AND TYPE OF RAW MATERIAL AND FINISHED PRODUCT.

13. NOS OF AVOIDABLE BREAK DURING THE DAY’S WORK

FUEL STROAGE AND HANDLING -OIL

1. Checks on receiving for water, sludge, and

density use water finding paste and regular

sample check.

2. Water drainage facility in MST and DST

3. Arrangement of stand by tank.

4. Filtration at different stage

5. Heating in DST and Heating Pumping Unit with

temp. control system .

6. Insulation of DST and Piping after DST to

burner and return line.

7. Desired temp at burner for FO is 100 to 105 C.

GENERAL LAYOUT

STORAGE

Viscosity of furnace

oil in Redwood no. 1

@ 37.8oC

(100oF)

Temp. below

which oil is not

pumpable

Temp. at which easy

pumpability can be

achieved

Temp. for proper

atomization

600 SEC 4.5°C 11°C-22°C 71°C-87°C

1500 SEC 15.5°C 25°C-37°C 88°C-87°C

3000 SEC 26°C 34°C-46°C 99°C-115°C

LSHS/RFO/HPS 60°C 70°C-80°C 120°C-130°C

Outflow Heating

Viscosity Temperature Relationship of

Fuels

Service Tank

SAVING POTENTIAL BY INSULATION OF FURNACE OIL LINES

SIZE OF THE FO LINE AND RETRUN LINE = 2.5 CM OR 1 INCH

TOTAL LENGTH OF THE BARE FO PIPELINE = 35 M

AVERAGE SURFACE TEMP. OF THE PIPELINE = 85 C

RUNNING HRS OF THE FURNACE PER ANNUM = 4620 HRS

TOTAL SURFACE AREA AT 85 C = 2.8 SQ M

HEAT LOSS FROM THE SURFACE AT 85 C = 550 KACL/SQ M/HR

HEAT LOSS FROM THE SURFACE AT 45 C = 200 KACL/SQ M/HR

SAVING POTENTIAL BY INSULATION = 350 KACL/SQ M/HR

TOTAL HEAT SAVING POTENTIAL = 977 KCAL/HR

EQUIVALENT ELECTRICITY SAVING POTENTIAL = 1.1 KW/HR

TOTAL KWH SAVING POTENTIAL PER ANNUM = 5,249 KWH PER ANNUM

COST OF PUCHASED POWER CONSIDERED = 5 RS/KWH

OVERALL SAVING POTENTIAL = 0.26 LACS/ANNUM

SAVING POTENTIAL BY INSULATION OF FO LINES AND DAY TANK

Description Checks

Oil temperature at the burner Daily

Oil/steam leakages Daily

Cleaning of all filters Weekly

Draining of water from all tanks Weekly

Cleaning of all tanks Yearly

Check List

FUEL STROAGE AND HANDLING –COAL

1. Proper Shed for coal storage to reduce carpet loss and to avoid unnecessary moisture .

2. Sizing of coal - desired is 1.5” to 2”.

3. Addition of moisture only for powdered coal that to the limited amount.1% for each 10 % of fines of below 4mm size

4. About 5% unburned coal observed in the ash removed from furnace due to bigger size coal and improper bed height.

5. Firing of coal at desired frequency and quantity to utilize the combustion air all the time

6. Avoid the stoppage of mill for ash removal by proper bed maintenance and by additional manpower and by better design of fire pit.

COAL SIZES FOR DIFFERENT

FIRING

S. No. Types of Firing System Size (in mm)

1. Hand Firing

(a) Natural draft

(b) Forced draft

25-75

25-40

2. Stoker Firing

(a) Chain grate

i) Natural draft

ii) Forced draft

(b) Spreader Stoker

25-40

15-25

15-25

3. Pulverized Fuel Fired 75% below 75

micron*

4 Fluidized bed boiler < 10 mm

FLOW OF HEAT IN FURNACE

• 1. STOCK

• 2. CRACKS AND OPENING

• 3. GROUND AND SURROUNDINGS

• 4. HEARTH

• 5. DOORS

• 6.PORTION OF STOCK PROTRUDING OUTSIDE

• 7. STACK

• 8. TO COOLING MEDIUM

Heat Transfer in Furnaces

Figure 4.3 : Heat Transfer in furnace

•Radiation from the

flame,hot combustion

products and the

furnace walls and

roof;

•Convection due to

the movement of hot

gases over the stock

surface.

(Flame radiation is function of :

• Composition of fuel

• Fuel to air ratio

• Temp. of fuel and air

• Rate of mixing of fuel & air

• Thickness of flame

• Distance from burner

Variation of Heat Transfer by Radiation &

Convection

% Heat Transfer 1250 C 900 C 400 C

By radiation 70 24.7 3.6

By Convection 30 75.3 96.4

ENERGY CONSERVATION IN FURNACES

Radiation

HEAT FLOW IN REHEATING FURNACEACHIEVABLE – 40 %

IN PRACTICE – 20 TO 25%

HEAT INPUT HEAT OUT PUT

100% 20 TO 25 %

DR

Y

FL

UE

GA

S

42

TO

45

%

MO

IST

UR

E

IN F

LU

E G

AS

9.2

8 %

OP

OE

NIN

G

LO

SS

ES

9 %

RA

DIA

TIO

N

LO

SS

ES

2.7

%

UN

AC

CO

UN

TA

BL

E

10

%

Performance Evaluation of a

Typical Furnace

Figure 4.10 Heat losses in industrial heating Furnaces

What are the furnace losses ?

Figure 4.11 wall losses

Wall losses:

Figure 4.12. Radiation loss

Figure 4.13. Air infiltration from furnace opening.

Stack loss (Waste-gas loss)

Air infiltration

Material handling loss

Cooling media losses

Radiation (opening) loss

Stored Heat Loss:

Wall Loss:

Furnace Efficiency (Direct Method)

Furnace Efficiency (Direct Method)

Fuel input = 400 litres / hr

= 368 kg/hr

Heat Input =368x10,000=3680000 kCal

Heat output = m x Cp x Δ T

= 6000 kg x 0.12 x (1340 – 40)

= 936000 kCal

Efficiency = Output x 100

Input

Efficiency = 936000 x 100

3680000

= 25.43 % = 25% (app)

Losses = 75% (app)

Furnace Efficiency (Indirect Method)

1. Sensible heat loss in flue gas = 57.29%

2. Loss due to evaporation of moisture in fuel = 1.36 %

3. Loss due to evaporation of water

formed from H2 in fuel = 9.13 %

4. Heat loss due to openings = 5.56 %

5. Heat loss through skin = 2.64%

Total losses = 75.98 %

Furnace Efficiency = 100 - 75.98

= 24.02 %

Specific Energy Consumption = 400 litre /hour (fuel consumption)

6Tonnes/hour (Wt of stock)

= 66.6 Litre of fuel /tonne of Material (stock)

General Fuel Economy Measures in

Furnaces

1) Complete combustion with minimum excess air

2) Correct heat distribution

3) Operating at the desired temperature

4) Reducing heat losses from furnace openings

5) Maintaining correct amount of furnace draught

6) Optimum capacity utilization

7) Waste heat recovery from the flue gases

8) Minimum refractory losses

9) Use of Ceramic Coatings

1) Complete Combustion with Minimum Excess Air

The amount of heat lost in the flue gases depends upon

amount of excess air. In the case of a furnace carrying

away flue gases at 900oC, % heat lost is shown in table :

Table Heat Loss in Flue Gas Based on Excess Air Level

Excess Air % of total heat in the fuel carried away

by waste gases (flue gas temp. 900oC)

25 48

50 55

75 63

100 71

EXCESS AIR – AFFECTS AND CONTROL

1. Air – O2 – 23 % Useful , N2 – 77 % Not useful

2. All gases and extra Air ( O2 + N2 ) leaving athigh

temp .

3. 10 % extra air – 1 % fuel loss – Observed values –300 % in coal and 110 % in Oil .

4 Other effect-

a. Reduction in flame temp.

b. Increase the burning losses.

c. Cost due to extra mass handling .

d. Increase in initial heating time .

e. Reducing the overall furnace temperature .

f. Results in non uniform heating of material .

AIR FUEL RATIO FUEL O2 % IN FLUE GAS

• GASEOUS FUELS 2.0

• FUEL OIL 3.5

• PULVERISED COAL 5.0

• SOLID FUEL IN BED 5.0 – 8.0

USE OF SECONDARY AIR

CLINKER FORMATION AND AFFECTS

• Clinker is a mass of rough, hard, slag-like material formed

during combustion of coal due to low fusion temperature

of ash present in coal.

• Presence of silica, calcium oxide, magnesium oxides etc.

in ash lead to a low fusion temperature.

• Typically Indian coals contain ash fusion temperature as

low as 1100oC.

• Once clinker is formed, it has a tendency to grow. Clinker

will stick to a hot surface rather than a cold one and to a

rough surface rather than a smooth one.

ANNUAL FUEL OIL CONSUMPTION = 2500 KL

% OF TOTAL FURNACE RUNNING AT LOW FIRING =

WHEN EXCESS AIR IS HIGH 25 %

AV. % OF TOTAL FUEL OIL CON. AT LOW FIRING

WHEN EXCESS AIR IS HIGH = 625 KL

* PERCENTAGE OF EXCESS AIR % DURING LOW FIRING = 50 %

* TEMP OF EXIT FLUE GAS = 450 DEG C

* AMBIENT AIR TEMP. = 40 DEG C

* AVG FUEL CONSUMPTION/HR = 411 LIT/HR

THEROTICAL AIR REQT.KG/KG OF OIL = 14.1 KG

ACTUAL AIR SUPPLIED KG/KG OF OIL = 21.15 KG

DESIRED LEVEL OF THE EXCESS AIR FOR

OPTIMUM COMBUSTION 20 %

DESIRED LEVEL OF OPTIMUM AIR = 16.92 KG/KG OF OIL

REDUCTION IN AIR SUPPLIED = 4.23 KG/KG OF OIL

SPECIFIC HEAT OF AIR = 0.24 KCAL-KG-C

REDUCTION IN HEAT LOSS DUE TO REDUCTION

IN EXCESS AIR = 416.23 KCAL / KG OF OIL

% SAVING POTENTIAL = 4.4 %

AVERAGE FUEL OIL CONSUMPTION DURING

LOW FIRING WHEN EXCESS AIR IS HIGH = 625 KL

ANNUAL FUEL OIL SAVING POTENTIAL = 27 KL

ANNUAL SAVINGS 5.13 LACS

SAVING POTENTIAL BY CONTROLLING THE EXCESS AIR

IN THE FURNACE DURING LOW FIRING

BURNING LOSS AND CONTROL & MONITORING

1. Contribute about 20 % of total cost.

2. Factors for more burning loss

A. Extra Air than desired in side furnace

B. Over heating of material

C. Extra halt of material in furnace and in oxidizing medium.

D. Non uniform heating of material .

E. Furnace running at negative pressure .

F. Unnecessary openings of doors .

G. Improper damper setting.

3. Control by regular estimation at site and controlling all the factor responsible as mentioned above .

MAT. AND OIL SAVING POTENTIAL BY REDUCTION OF BURNING LOSSES

Details of Mass Balance of 8 Sample Billets

S. No. Item

1 Weight of 8 Billets before charging 481.5

4 Weigh of Finished +losses 469.8

5 Burning Losses 11.7

6 % of raw material heated 2.43

1 Average Production of the plant = 14850 Ton/year

2 Average Raw Material Charged in the furnace = 16335 Ton/year

3 Average Burning Loss = 2.43 %

4 Desired Lvel of Burning Loss = 1.8 %

5 Reduction in Burning Losses = 0.63 %

6 Saving of steel by reduction of burning losses = 102.90 Ton/year

7 Cost of the steel ( Billets) = 19000 Rs/ton

8 Total Saving in Material = 19.55 Lacs

9 Fuel oil consumption per ton = 50 Liter/ton

10 Saving in fuel oil Consumption = 5 KL/year

11 Cost of FO = 14000 Rs/KL

12 Saving in oil = 1 Lacs

13 Total Saving Potential 20 Lacs

2)Correct Heat Distribution

Heat distribution in furnace

Alignment of burners in furnace

Prevent flame

impingement.

To avoid high flame

temperature,damage of

refractory and for

better atomization

Align burner

properly to avoid

touching the

material

To reduce scale

loss

3)Operating at Desired Temperature

Slab Reheating furnaces 1200oC

Rolling Mill furnaces 1200oC

Bar furnace for Sheet Mill 800oC

Bogey type annealing furnaces- 650oC -750oC

CORRECT

TEMPERATURE

ENSURES GOOD

QUALITY

PRODUCTS.

TEMPERATURE

HIGHER THAN

REQUIRED

WOULD ONLY

USE UP MORE

FUEL

Temperature for Different Furnaces

LOSSES DUE TO EXTRA HEATING OF THE MATERIAL

1 Average Raw Material Charged in the furnace = 16335 Ton/year

2 Average Nos of Days Running 300 Days/Year

3 Average Raw Material Heating per Day = 54.45 Ton per Day

4 Desired temperature for the rolling = 1200 C

5 Actual temperature Maintained = 1250 C

6 Additional Heating of Material = 50 C

7 Specific heat of Steel = 0.12 Kcal/Kg/C

8 Extra Heat for extra heating per day = 326700.00 Kcal /day

9 Furnace Efficiency = 25 %

10 Additional heat supplied = 1306800 Kcal/day

11 Calorific Value of FO = 10200 Kcal/kg

12 Saving in oil = 128 kg/day

13 Saving in Oil = 119 liters/day

15 Cost of Oil 19 Rs/lit

16 Saving per day 2264 Rs per Day

17 Annual Saving 36 KL/year

7 lacs /year

LOW TEMPERATURE OF MATERIAL

1. It’s most of the time is non uniform temp. instead low temp.( Extreme Range observed in the same mat. From 1180 C to 1300 C )

2. Major Factors for this problem

A. Furnace Design and mismatch between capacity and actual production.

B. Changing in production speed during the day’s operation.

C. Slow movement of hot material between stands.

D. Improper material feeding in the furnace .

E. Improper combustion

F. Use of unnecessary measures like putting extra material layer, coating of lime solution etc

G. Improper burner alignment and operation .

H. Changing the fuel setting very frequently.

I. No temperature measuring device .

4) Reducing Heat Loss from Furnace

Openings

The heat loss from an opening can be calculated using the formula:

Q=4.88 x T 4 x a x A x H … k.Cal/hr

100

T: absolute temperature (K),

a: factor for total radiation

A: area of opening,

H: time (Hr)

Heat loss through openings consists of direct radiation and

combustion gas that leaks through openings.

Keeping the doors unnecessarily open leads to wastage of fuel

Inspection doors should not kept open during operation

Broken and damaged doors should be repaired

5)Maintaining correct amount of

furnace draught

Negative pressures : air infiltration- affecting air-fuel ratio control,

problems of cold metal and non-uniform metal temperatures,

Positive Pressure: Ex-filtration -Problems of leaping out of flames,

overheating of refractories,burning out of ducts etc.

6) Optimum capacity utilization

There is a particular loading at which the furnace will operate at

maximum thermal efficiency.

Best method of loading is generally obtained by trial-noting the weight

of material put in at each charge, the time it takes to reach temperature

and the amount of fuel used.

Mismatching of furnace dimension with respect to charge and production

schedule.

Coordination between the furnace operator, production and planning

personnel is needed.

10

8

6

4

2

250

FU

EL G

AL

LO

N/H

R.

750

12

STEEL THROUGHPUT (PONDS/HR.)

14

16

500 1000

10

20

30

40

50

60

S.F.C.

Consumption

GA

LLO

N P

ER

TO

N

The ‘No Load’ consumption to maintain a simple

batch type furnace at 1300°C when empty is about

70% of that required to operate at optimum

loading rate.

ENERGY CONSERVATIONIN FURNACES

Loading in Furnaces

WASTE HEAT RECOVERY AND MONITORING

1. Install sufficient temp. indicator to asses

the working of WHR system.

2. Insulation of recuperator and hot air line

to burner ( more than 100 C temp. drop

observed)

3. Installed well designed recuperator instead

of locally made.

4. Regular cleaning and inspection for the

puncture of tubings to be done.

7) Waste heat recovery from the flue gases

• Charge (stock) preheating,

•Preheating of combustion air,

•Utilizing waste heat for other process

WHR POTENTIAL AVAILABLE IN DIFFERENT

FURNACE OPERATION

FURNACE TYPE TEMPERATURE IN eg.C

FORGE AND BILLET HEATING 800 – 1100

ANNEALING 600 – 1100

OPEN HEARTH STEEL FURNACE 550 – 700

GLASS MELTING FURNCAE 1000 – 1300

CEREMIC KILN 700 – 1100

SOLID WASTE INCINERATORS 650-1000

ROTARY KILNS 650 -700

WASTE HEAT RECOVERY EQUIPMENT PLAYS IMPORTANT ROLE

IN WASTE HEAT RECOVERY BUT ALSO THE OPERATING

PARAMETRS OF THE FURNACE

THE HIGHER THE QUANTEM OF EXCESS AIR AND FLUE GAS

TEMPERATUR THE HIGHER WOULD BE THE WASTE HEAT

AVAILABILTY

Sankey diagram for a furnace with recuperator

Air pre-

heating

ENERGY CONSERVATION IN FURNACES

Waste Heat Recovery

Flue

Gas temp

Comb. Air

temp

ADVANTAGE OF HOT AIR

1.SAVING IN FUEL CONSUMPTION

2. INCREASE IN FLAME TEMPERATURE

3. IMPROVEMENT IN COMBUSTION

4. REDUCTION IN INITIAL HEATING TIME.

5. REDUCTION IN SCALE LOSSES

HOT FLUE

GASES

COLD

FLUE

GASES

COLD

COMB.

AIR

HOT

COMB.

AIR

CONVECTIVE TYPE

DOUBLE STAGE CROSS FLOW TYPE

TEMP. OF FLUE GASES AFTER FURNACE = 650 DEG C

*TEMP OF FLUE GAS AFTER RECUPERATOR = 450 DEG C

COMBUSTION AIR TEMP.AFTER RECUPERATOR = 340 DEG C

COMBUSTION AIR TEMP.BEFORE RECUPERATOR 40 DEG C

OVERALL O2 LEVEL FOR THE FURNACE = 4.4 %

*AVG FUEL CONSUMPTION/HR = 411 LIT/HR

ATMOSPHERIC AIR TEMP. 40 C

THEROTICAL AIR REQT.KG/KG OF OIL = 14.1 KG

*PERCENTAGE OF EXCESS AIR % = 26.5 %

ACTUAL AIR SUPPLIED KG/KG OF OIL = 17.8 KG PER KG OF OIL

SPECIFIC HEAT OF FLUE GASAIR = 0.25 KCAL-KG-C

TOTAL HEAT OF FLUE GAS AT ENTRY = 3061 KCAL / KG

HEAT TAKEN BY THE COMBUSTION AIR = 1284 KCAL / KG

EFFICIENCY OF THE RECUPERATOR = 42.0 %

SAVING BY INSULATION OF HOT AIR LINE

AVERAGE TEMPERATURE OF HOT AIR AT BURNER = 210 C

TEMP. DROP BETWEENRECU. AND BURNER = 130 C

ALLOWABLE DROP . MAXIMUM) 30 C

TEMP. OF COMBUSTION AIR CAN BE RAISED BY 100 C

HEAT SAVED BY RISING THE AIR TEMP 428 KCAL / KG OF OIL

% HEAT FUEL OIL SAVING 4.5 %

ANNUAL FUEL OIL CONSUMPTION 2500 KL

ANNUAL SAVING OF FURNACE OIL 113 KL

ANNUAL SAVING OF FURNACE OIL 21.47 lacs

RECUPERATOR EFFICIENCY

RECUPERATOR EFFICIENCY AND

SAVING POTENTIAL BY INSULATION OF HOT COMBUSTION AIR LINE

INSULATION AND OPENINGS

1. Use of ceramic coating on hot face except hearth for better heat transfer and life of refractories .

2. Use of Ceramic lining or Castable before MS plate.

3. Use appropriate cold insulation for burner block

4. Keep all the doors except operating always relined and closed . Have sufficient spare doors for operating door.

5. Keep damper in good operating condition and desired opening to be set as per the operation.

6. Monitoring the surface temperature of furnace regularly.

SALIENT POINTS

• As wall thickness increases, heat loss reduces

• As thickness of insulation increase, heat loss

reduces

• Effect of insulation is better :- (Roughly 1 cm of

insulation brick is equivalent to 5 to 8 cm of

refractory)

• In intermittent furnaces – (Thin wall of

insulations are preferred than thick wall of

refractory to reduces heat stored

5. Ceramic fiber to be used in intermittent

furnaces

ENERGY CONSERVATION

IN FURNACES

Refractory Insulation

Simple fire brick wall

Heat lost to

atmosphere is high

Compound refractory

wall

Heat lost to

atmosphere is

minimum

ENERGY CONSERVATION

IN FURNACES

Refractory/Insulation Thickness

8. Minimizing Wall Losses

About 30% of the fuel input to the furnace generally goes to

make up for heat losses in intermittent or continuous furnaces.

The appropriate choice of refractory and insulation materials is

needed for high fuel savings in industrial furnaces.

The extent of wall losses depend on:

Emissivity of wall

Thermal conductivity of refractories

Wall thickness

Whether furnace is operated continuously or

intermittently

Radiation Heat Loss from Surface of Furnace

The quantity (Q) of heat release from a reheating furnace is

calculated with the following formula:

where

a : factor regarding direction of the surface of natural convection

ceiling = 2.8, side walls = 2.2, hearth = 1.5

tl : temperature of external wall surface of the furnace ( C)

t2 : temperature of air around the furnace ( C)

E: emissivity of external wall surface of the furnace

4

2

4

14/5

21100

273

100

27388.4)(

ttxEttxaQ

Ceramic

Fibre

• Ceramic fibre is a low thermal mass insulation

material

• A recent addition is Zr O2 added alumino silicate

fibre, which helps to reduce shrinkage levels thereby

rating the fibre for higher temperatures

Important Properties of

Ceramic Fibre• Lower Thermal Conductivity

• Light Weight

• Lower Heat Storage

• Thermal Shock Resistant

• Chemical Resistance

• Mechanical Resilience

• Low Installation Cost

• Simple Maintenance

• Ease of Handling

• Thermal Efficiency

9.Use of Ceramic Coatings

The benefits of applying a high-emissivity ceramic

coating:-

Rapid heat-up

Increased heat transfer at steady state

Improved temperature uniformity

Increased refractory life

Elimination of refractory dust.

High Emissivity Coatings

1. DIFFERENT SIZE OF FURNACES FOR

SAME OUTPUT

2. MISMATCH OF COMBUSTION

EQUIPMENTS

3. IMPROPER BURNERS

4. NO CARE FOR BLOWER

5. NO PROPER SELECTION OF MATERIAL

FOR RECUPERATOR

6. NO PROPER DESIGN OF

RECUPERATOR

ENERGY CONSERVATION

IN FURNACES

General Observations of Furnace

7. NO CONTROL ON EXCESS AIR

8. NO INSULATION ON HOT AIR LINE

FROM RECUPERATOR TO BURNER

9. NO PROPER HEATING OF FURNACE

OIL

10. INDUSTRIES ARE DEPENDENT ON

SUPERVISOR

11. NO TRAINED MANPOWER

ENERGY CONSERVATION

IN FURNACES

General Observations of Furnace

Electrical Energy Saving Opportunities

In

Steel Rerolling Industries


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By: PCRA, SRO Raipur (C.G.)

Need to Conserve Electrical Energy


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Electrical Energy Scene of a typical

Rerolling Mill


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Energy Scene of Rolling Mill - Connected Load wise

69%4%

26%1%

Main Motor 1500 HP

Fans & Blowers 78 HP

Motors other than Fans

& Blowers 567.5 HP

Lighting & Air

Conditioning 20 HP

(Rounded Off)

• Main Motor – 65-70 % Load

• Motors other than Fans &

Blowers – 20-25% Load

• Fans & Blowers – 4-10%

Load

• Lighting & Airconditioning –

1-2% Load

Saving Opportunities

• Electricity Tariff

• Reactive Power Compensation

• Proper Maintenance of Motors

• Optimize Transmission Efficiency (belts & gears)

• FRP blades for Cooling Fans

• Lighting System


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Reactive Power Compensation

Agenda

•Reactive Energy & Power factor

•Why to improve the Power factor

•How to improve the Power Factor

•Where to install P.F.Correction capacitors


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To the engineer……..


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Power factor is the ratio between the KW and the KVA drawn by an

electrical load where the KW is the actual load power and the KVA is the

apparent load power.

KW

KVAKVAR

A

B

ø1ø2

As can be clearly seen KVA requirement has been reduced for the same

KW requirement in case A.

To the rest of us……. an analogy helps

You can’t move the

wheelbarrow

(active power delivery)

unless you lift the arms!

(reactive power)


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To the engineer……..

A poor power factor can be the result of either a significant

phase difference between the voltage and current at the load

terminals, or it can be due to a high harmonic content or

distorted/discontinuous current waveform.

Poor load current phase angle is generally the result of an

inductive load such as an induction motor, power

transformer, lighting ballasts, welder or induction furnace.


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Why to improve the P.F


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•Reduction in the cost of electricity

-Through reduced MD & Rebate from SEB

•Technical / Economic optimization

-Reduction in distribution losses

-Smaller Transformers, Switchgear & Cables

-Exact voltage at the motor terminals adding to the

life of the same.

How to improve the P.F


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Improving the power factor of an installation

requires a bank of capacitors which acts as a

source of reactive energy .

The compensation is provided by:

•Fixed value capacitors

•Equipment providing automatic regulation or

banks which allow continuous adjustment as the

loading of the installation changes.

Where to install P.F. correction capacitors


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•Global Compensation – The capacitor bank is

connected to the busbars of the main LT distribution

board of the installation.

•Compensation by sector – The capacitor banks

are connected to busbars of each local distribution

boards.

•Individual Compensation – The capacitors are

connected directly to the terminals of the inductive

circuit.

How to decide the optimum level of

compensation


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KVAR required = KW (tan (cos-1 (p.f.1)) - tan (cos-1 (p.f.2))

Where

KW = Average KW required

p.f.1 = Existing power factor

p.f.2 = Desired power factor

Compensation at the terminals of the

transformers


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•To compensate for the reactive energy absorbed

by the transformer which can amount to about 5%

of the rating of the transformer rating when

supplying its full load.

•In transformers reactive power is being absorbed

by both shunt (Magnatizing) and series(Leakage

flux) reactances.

•Complete compensation can be provided by a

shunt connected LT capacitors.

Reactive Power consumption of

distribution Transformers


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Rated

Power

(KVA)

Reactive Power to be compensated

(KVAR)

No Load Full Load

100 3.5 7.1

160 4.7 10.6

250 6.3 15.7

315 7.3 19.4

400 8.6 23.9

500 10.5 29.7

630 12.3 36.7

Reactive Power consumption of

distribution Transformers


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Rated

Power

(KVA)

Reactive Power to be compensated

(KVAR)

No Load Full Load

800 21 55.5

1000 24.9 73.4

1250 28.4 95.5

1600 32.9 127

2000 38.8 177

The effects of harmonics


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Harmonics are caused by the nonlinear magnetizing impedances of

transformers, reactors, fluorescent lamp ballasts & all the equipments

which uses power electronic components (VSD,Thyrystor controllrd

rectifiers, etc.)

Harmonics on a symmetrical 3-phase power sysytems are generally odd

numbered & the magnitude decreases as the order increases.

Capacitors are especially sensitive to the harmonic components of the

power supply due to the fact that capacitive reactance decreases as the

frequency increases.In practice this means, that a relatively small

percentage of harmonic voltage can cause a significant current to flow

in a capacitor circuit.

These can be reduced to a minimum by harmonic filters.

3 phase Induction Motors

Agenda

• Motor Lifetime

• Size Motors for Efficiency

• Proper Maintenance

• Energy Efficient Motors

• Reactive Power Compensation

• Issue of Motor Rewinding


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Motor Lifetime

•The typical lifetime of small motors in the field is not well

determined. Studies at one manufacturer show that small

motors have an “L10” life (defined as the point where 10

percent of test population has failed) under typical operating

conditions of around 25,000 hours .

•("typical“ assumes no start/stop or excessive vibration, 75 C

bearing temperatures, normal, mineral-oil-based,bearing

lubricants, and regular-sized lubricant reservoirs).

•For an average utilization of 2500 hours per year, that would

yield a ten-year L10 life.


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Motor Lifetime

•The life of a motor depends on a variety of factors in the

service conditions of the application.These include

environment (largely temperature), loading of the motor,

and speed of rotation.

•The studies cited above have shown that bearing failure

is by far the most critical factor in motor failure. In turn,

the main reason for bearing failure is failure of the

lubricant, mainly due to heat generation.


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Energy Efficient Motors

Why ?Energy-efficient

motors, are 2 to 8%

more efficient than

standard motors.


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Design Improvement

•Lengthening the core

•using lower-electrical-

loss steel, thinner stator

laminations.

•more copper in the

windings reduce electrical

losses.

•Improved bearings and a

smaller, more

aerodynamic cooling fan


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• Energy-efficient motors, also called premium or

high- efficiency motors, are 2 to 8% more efficient

than standard motors.

• Motors qualify as" energy-efficient " if they meet or

exceed the efficiency levels listed in the National

Electric Manufacturers Association's (NEMA's)

MG1-1993 publication.


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Reactive Compensation in motors

• Individual motor compensation is recommended where the

motor power (KVA) is significant with respect to the declared

power of the installation.

• The Reactive Compensation at any individual motor shall

not be in any case more than the No-load magnetizing KVAR

of the motor, above which self excitation can occur.

• In order to avoid self excitation ,the kVAR rating of the

capacitor bank must be limited to the following maximum

value:

• Qc ≤ 0.9 Io Un 1.732

Where Io = no load Current

Un = Phase to phase voltage in KV


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Maximum KVAR applicable to 3 phase motor

terminals without the risk of self excitation


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Rating KVAR to be installed

For Speed of rotation (RPM)

KW HP 3000 1500 1000 750

22 30 6 8 9 10

30 40 7.5 10 11 12.5

37 50 9 11 12.5 16

45 60 11 13 14 17

55 75 13 17 18 21

75 100 17 22 25 28

90 125 20 25 27 30

Maximum KVAR applicable to 3 phase motor

terminals without the risk of self excitation


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Rating KVAR to be installed

For Speed of rotation (RPM)

KW HP 3000 1500 1000 750

110 150 24 29 33 37

132 180 31 36 38 43

160 218 35 41 44 52

200 274 43 47 53 61

250 340 52 57 63 71

280 380 57 63 70 79

355 482 67 76 86 96

400 544 78 82 97 106

450 610 87 93 107 117

Proper Sizing & Loading of Motors

Why ?


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• The Efficiency

& Power factor

depends on the

loading of the

motor.

Proper Sizing & Loading of Motors

Why ?

• The fixed Losses remain the

same at lower loads therefore

Size motors to run primarily in the

65% to 100% load range.

• Consider replacing motors

running at less than 40% load with

properly sized motors


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Use Suitable Starters


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• Direct On Line Starter

• Primary resistance or reactance

starter

• Auto transformer starter

• Star Delta Starter

• Soft Starter: A soft starter is

another form of reduced voltage

starter for A.C. induction motors.

Motor Rewinding

• Rewinding can reduce motor efficiency and

reliability.

• Rewind-versus-replace decision is quite

complicated and depends on such variables as the

rewind cost, expected rewind loss, energy-efficient

motor purchase price, motor size and original

efficiency, load factor, annual operating hours,

electricity price, etc.

• Majority of the users would wish to rewind the

motor.


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Motor Rewinding

• During a motor failure or in the stripping of the windingfrom the stator core prior to rewinding, high temperaturescan occur. These temperatures can, in many cases, affectthe electrical characteristics of the stator core steel andresult in increased iron losses and lower motor efficiency.

• Check the no load current before & after rewinding.Maintain a history card of motor rewinding.


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Life Cycle cost of a motor


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Optimizing Transmission Efficiency

•Transmission equipment

including shafts, belts,

chains, and gears should

be properly installed and

maintained.

• When possible, use flat

belts in place of V-belts

• It is better to have a direct

drive for avoiding losses in

transmission system.


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Slip-ring motor

The advantages of a slip-ring motor

• Its susceptibility to speed control by

regulating rotor resistance.

• High starting torque of 200 - 250% of full

load torque.

• Relatively low starting current (250 to

350% of the full load current) compared to

a squirrel-cage motor, which may have a

starting current in the order of 600% of its

full load current.


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Energy savings points

• Maintain High Power Factor

• Use Variable Speed Drives (VSDs) Where Appropriate

• Minimize Phase Unbalance

• Use controls to turn off idling motors

• Match Motor Operating Speeds

• Size Motors for Efficiency

• Follow proper maintenance schedule


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FRP blades for Cooling Fans

Why ?

• The consumption in the fans supplying cooling

air to the workers vary in a wide range from 1.5

KW to 5.5 KW.

• This may be attributed to the material of the fan

blade which of MS & Aluminum and to the motor

rating which varies from 3 HP to 15 HP for the

same type of fans.


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FRP blades for Cooling Fans


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•With the technological improvements

in material processing technologies,

FRP (Fiber Reinforced Plastic) has

come as an alternative to the

conventional Aluminum .

•We recommend replacing the metal

alloy blades of all the fans with FRP

blades. It has been estimated that

energy savings of minimum 20 % can

be achieved by above conversion.

Energy savings in lighting System


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• Make maximum use of natural light (North roof/translucent

sheets/more windows and openings)

• Switch off when not required

• Provide timer switches / PV controls for yard lighting

• Provide lighting Transformer to operate at reduced voltage

• Install energy efficient lamps, luminaries and controls

• Metal halide in place of Mercury and SVL lamps

• CFL in place of incandescent lamps

Instruments Required


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Electrical Measuring Instruments:

These are instruments for measuring

major electrical parameters such as

kVA, kW, PF, Hertz, kvar, Amps and

Volts. In addition some of these

instruments also measure harmonics.

• Demand Analyzer

• Digital power recorder

• Lux Meter

• Anemo meter

• Digital Manometer

• Techometer

Maintenance of Electric Motors

• Under normal operation, motors should be checked on a

regular basis. If the environment is hostile (e.g. wet, dirty

and hot), the checks should be at least on a daily basis.

• Cleanliness of the surroundings, ensuring that cooling

vanes are clear of extraneous matter.

• Signs of grease or oil leakage from the bearings.

• The motor frame and bearing plates (if accessible) are not

unduly hot;


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• The motor is not showing signs of abnormal vibration or noise.

• There is no evident damage to incoming cables and or

terminal boxes.

• Air intakes and filters (if applicable) are not clogged.

• Apply blower to the sealing, especially in motors situated in

dusty areas.

• Check the motors & driven equipment for proper alignment &

Inspect the condition of the belts.


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• Contactors, Relays, Selector switches and push buttons to

be checked for proper working.

• Inspect the foundation of motors for excessive vibration.

Tighten the foundation bolts, if required.

• Physical checkup of the motors to be carried out.

- Take No load & Full load current.

-Check the starters and relay settings.

- Tighten all the connections.

- Apply blower to PCC & MCC panels, Normal checkup to be

done.


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UNDP/GEF PROJECT (STEEL)

“REMOVAL OF BARRIERS TO ENERFY

EFFICIENCY IMPROVEMENT IN STEEL

REROLLING MILL SECTOR”

DETAILED CLUSTER MAPPING PROJECT

REPORT

(RAIPUR CLUSTER)

Overview of SRRM Sector in the Cluster

Chhattisgarh Rerolling mill industry is going through different phase of global competition. It is being increasingly released that technology is tool for competitiveness in the market place. At present 148 rolling mills are running in the region producing:-

1. CTD/TMT Bar / Round (6mm to 100mm) ,

2. Angle (25x3 to 200x10) ,

3. Beam (100x50 to 600 to 210),

4. Channel (75x40) to 400x100) ,

5. Flats (18x3 to 200x12) ,

6. Strip (upto 200mm) ,

7. window section ,

8. wire rod of all sizes.

Distribution

Location wise

• Raipur-122 Nos

• Bhilai –Durg –Rajnandgaon -23 Nos

• Bilaspur-03 Nos

Fuel Used

• Coal Fired - 97 nos

• Oil Fired- 43 Nos

• Producer Gas fired- 8 Nos **

** Producer Gas plus Oil fired units

Location wise Distriution of SRRM in Chhattisgarh

82%

16% 2%

Raipur

Bhilai –Durg -Rajnandgaon

Bilaspur

Product wise distribution

Product Nos of SRRM

• Tor (TMT/CTD Bar/Rounds) 56

• Structure (Angle/Channel/Beam/Joist) 79

• Flat/ Strip 13

Fuel wise distribution of selected 20 % Industries

42%

44%

14%

Coal

FO

Producer Gas

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Specific Energy Consumption of Rolling Mill using FO as Fuel (Lit of FO/Ton of

Production)

Specific Energy Consumption (Lit of FO/Ton of Production)

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Specific Energy consumption of Rolling Mill Using Coal as Fuel

(Kg of Coal/Ton of Product)

Specific Energy consumption of Rolling Mill Using Coal as

Fuel (Kg of Coal/Ton of Product)

0

1

2

3

4

5

6

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Variation in % Scale Loss in the Cluster

% Scale loss

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5

Specific Energy Consumption of Rolling Mill using Producer gas (Kg

of Coal/Ton of production) and FO (Lit /Ton of production) as Fuel

FO consumption in Lit/Ton

Coal consumption in Kg/Ton

100

105

110

115

120

125

130

KWH/Ton

1 4 7 10 13 16 19 22 25 28 31 34 37

Units

Specific Power Consumption

Specific Power Consumption

0,8

0,85

0,9

0,95

1

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35

Variation in Power Factor in the Cluster

Power Factor

Note: - AUXILIARIES INCLUDES Drives for Roller Tables, Fans, Pumps and Shears etc. Operational and Maintenance spares reclaiming facilities etc. Cranes Lighting

TYPICAL ENERGY CONSUMPTION PATTERN IN ROLLING MILLS

Mill Proper 20%

Auxiliaries 10%

Reheating

Furnace 70%

Mill Proper 20%

Auxiliaries 10%

Reheating

Furnace 70%

TECHNOLOGY PACKAGES• Installation of high efficiency recuperator in

conventional pusher hearth continuous oil firedfurnaces.

• Conversion of oil fired pusher hearth furnace to oilfired walking beam furnaces.

• Conversion of oil fired pusher hearth furnaces to gasfired walking beam furnaces with regenerativeburner.

• Conversion of lump coal fired to pulverized coalfiring with recuperator.

• Conversion of lump coal fired to producer gas firedfurnace with high efficiency recuperator.

• Adoption of hot charging in the composite mills.

CUSTOMIZED PACKAGES

(Combustion furnace )

• Installation of improved refractory

lining.

• Adoption of ceramic fiber veneering.

• Adoption of high emissivity coating.

• Installation of high velocity / oil film

burners.

CUSTOMIZED PACKAGES

(Rolling Mill)

• Introduction of crop-length optimizationtechniques.

• Adoption of roller entry and delivery guides.

• Installation of roller bearings for roll necks in themill stands.

• Replacement of cotton and pin type spindles &couplings to universal type spindles.

• Installation of tilting tables on 3-Hi stands.

• Installation of repeaters.

FUEL SAVINGS IN REHEATING FURNACE AT A

GLANCE

ECOTECH

ENERGY

SAVING

(GJ/T OF

PRODUCT)

APPROX.

INVESTMENT

(RS. LAKHS)

EST. COST

OF

ENERGY

SAVING

(RS/MT)

ANNUAL

ENERGY

SAVING

(RS. LACS)

SIMPLE

PAYBACK

PERIOD

(MONTHS)

Solid pusher hearth, single row long

furnace-combustion air heated to 350C

0.18

(50 kwh)120 129 95 15

Solid pusher hearth, double row, high

performance furnace-combustion air

heated to 550C

0.28

(77.84 kwh)145 200 144 12

Walking hearth furnace/e-combustion

air heated to 650C

0.41

(114 kwh)190 293 214 10.6

Walking hearth furnace designed to

work on coal producer gas with

regenerative burners-combustion air

heated to 10000C

0.59

(164 kwh)500 423 510 12

As above plus hot charging - 75%

billets are hot charged at 650C

1.12

(311 kwh)550 802 613 11

(Base Case: Solid pusher hearth, oil fired and 15tph continuous reheating furnace with conventional features with 20 hours/day operation, 250 days working in a year)

PROJECT BENEFITS

Consumption of energy & other

important performance

parameters of re-rolling mills

(Model Units)

Unit Status in the

beginning of

the Project

Target / Expected

Outcome after

project

completion

Oil consumption in the reheating

furnace

Lit/T 42-45 <32

Coal consumption Kg/T 70-80 45-55

Gas consumption Nm3/T 48 30

Productivity of furnace Kg/m2/h 120-220 300-350

Scale Loss % 2.5-3.5 <1

Power consumption kWh/T 90-120 85-100

Yield % 89-93 94-95

Utilization of mill % 65-70 80-85

I. Direct Benefits

PROJECT BENEFITS…Contd.

Sl.

No.

Support Current

Status

During / After Project

Completion

1 Institutional / expert support NIL TIRFAC

2 Design support NIL Software Centre (TIRFAC)

3 Software support NIL -Do-

4 HRD NIL -Do-

5 Data/Information/Knowledge support NIL -Do-

6 Consultancy support Local level -Do-

7 Standardization / Benchmarking NIL -Do-

8 Standard operating & maintenance practice (SOP & SMP),

ISO 9002, 14002 accreditation, etc

NIL -Do-

9 Capacity building to other stakeholders like consultants,

equipment manufacturer, Banks/FIs, etc.

NIL -Do-

10 Market analysis / research (data on sales / price, etc.) NIL -Do-

11 Technology development, R&D Demonstration, etc NIL Hardware Center

(TIRFAC)

II. Indirect Benefits

BENEFITS TO INDUSTRY

• Reduced energy bills.

• Reduction in scale loss.

• Improvement in yield.

• Improvement in product quality.

• Improvement in productivity.

• Technology up gradation of the unit.

• Reduction in manpower Overall increase in

bottom line.


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Documents

02-PCRA-NitendraDewangan