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Industrial Energy Systems

Linköping Universitet,

SE-581 85 Linköping, Sweden

24th

May, 2010

Steel Drawing Mill Energy Audit

GROUP MEMBERS:

Mesfin Taye

Wisdom Kanda

S jit V G k j



Table of Contents

1.0

Introduction ................................................................................................................................

1

1.1 Company description .............................................................................................................. 1

1.2 Objective ................................................................................................................................. 1

1.3 Limitation ................................................................................................................................ 2

2.0

Method .......................................................................................................................................

2

3.0 Results ......................................................................................................................................... 2

3.1 Energy Survey .......................................................................................................................... 2

3.2 Energy Savings......................................................................................................................... 5

3.2.1 Energy saving potential in various unit processes. ......................................................... 5

4.0 Discussions and Conclusion ........................................................................................................ 8

5.0 References .................................................................................................................................. 9

6.0 Appendix....................................................................................................................................9



Summary The steel and iron industry is a very important part of the national development and structure.

It has been in existence for aver 2000 years and has evolved to become a high-quality steel

producer through several challenges such as energy intensive consumption.

In addition the consumption of energy does not come lone in the form of direct cost but also

has some added issues relating to the environment such as CO2 emissions. Energy cost make

up for a sizable amount of the running cost of the steel industry. This cost can be controlled

through energy audits to identify and implement possible energy saving measures.

This project presents the energy audit at cold drawn steel mill located in Linköping. It has an

annual steel production of about 50000 ton. The products of this company are delivered

primarily to the Swedish engineering industry whiles other exports go to Nordic countries,

Germany, the UK and the Benelux.

After performing the energy analysis with the help of ENSAM it was clear to identify the

various unit processes and the amount of energy they consumed. This depicted areas of the

processes with high consumption and as targets for energy consumption reduction.

The results show that from an initial annual energy consumption of 3800MWh/y of electricity

with a corresponding cost of 660650€/y it is possible to reduce the consumption and cost.

Energy efficiency measures such as changing of mercury lamps to T5’s and the shutting

down completely on production machines on idle can save several amounts of energy.

The energy savings as can be seen for electricity is 546MWh/y and with the cost of

electricity at 0.063 €/kWh (Europe's Energy portal) there is the potential saving of about

35000 €/year. Looking at other options there in some energy content in the exhaust air which

can be recovered to further reduce the annual oil demand for space heating.With the

employment of a heat excahnger with an efficiency of 75% the oil saving potential is

688MWh/y with an annual cost savings of about 31000€/year with the oil cost of 44€/MWh

provided in the invoice.

The total potential energy savings is 1234MWh/y which represents about 21% reduction. In

terms of cost the total cost savings is about 66000€/year which represent about 9%



1.0 Introduction History has it that steel and iron making in Sweden dates back over two thousand years. Iron

and steel making has been interwoven into the lives of the people to such an extent that it

played a key role in the country’s development. Huge amounts of natural resource reserves

coupled with the forest fuel supply have been very favourable for this Industry in the early

era which played a key role in the development of the country.

Yet the steel manufacturing sector has been faced by challenges in the past which threatened

its existence. In 1976 it was hit hardly by the energy crises. As a consequence of the energy

crises, the ship industry which was a major customer of the steel sector also went down in

production which had a rippling effect on their supply networks. Measures were implemented

to counter these challenges; finally by 1998 the industry was again well known

internationally as a high quality steel producer.

1.1 Company description The company under study is a cold drawn steel mill located in Linköping. It has an annual

steel production of about 50000 ton. The products of this company are delivered primarily to

the Swedish engineering industry whiles other exports go to Nordic countries, Germany, the

UK and the Benelux. The employees are 80 in number. The company production is organised

in campaigns of three weeks with production during 16 days. The production is closed during

midsummer and Christmas as well as during a four week holiday in summer. Office hours for

employees in 9 hours a day while production runs for 16 hours per day from Monday to

Friday1.

Many processes are needed to produce the final product. The raw material is first treated in

the drawing benches where it is pushed and drawn. In then goes into the straightening

machine after which it is ready for profile cutting. In the end it is cut to the specified length

and end machining is done.

As can be understood from the above description the different processes needed to run this

industry are energy intensive. In addition the related energy cost associated with this

processes form a significant part of the company cost. This cost is liable to minimization

through effective energy measures which can only be pointed out through energy audits.



1.3 Limitation The analysis is based on measured data provided as the starting point and further informationis also sourced from the energy manager which is supplemented by some assumptions to

make the process complete.

2.0 Method The method is to adopt a top-down approach in which the unit process concept is also

incorporated. The processes at the steel mill were categorised as either production or support

and then the available data is then apportioned as to the respective process consumption.

The software for energy audit ENSAM was used to determine the possible energy savings

after quantification of unit process consumption.

3.0 Results 3.1 Energy Survey Table 1.0 Steel drawing mill in numbers

Steel drawing mill

Number of employees 80

Production days 255 days/y (3 weeks each of 16 days and closed

for 4 weeks and during Christmas break)

Office hours 9 hours/day from Monday‐Friday* = 2295h/y

Production hours 16 hours/day from Mon‐Fri*=4080h/y

Annual Production(output) 50000ton

Electricity Use 3800 MWh/yr

Oil use 2128 MWh/y

*Energy manager Information

The only sources of energy employed in this company are electricity and oil. The annual cost



The energy distribution among the various unit processes is displayed in Figure 1.0 below.

Make reference to the appendix for a detailed presentation of calculation.

EI

Oil

Micsellaneous

Support

Processes

Production

Processes

LIghting

Ventilation

Compressed air

Space heating

Moulding

3800

2128

521

213

494

20

2128

1720

1248

1720

832



From the Figure 1.0 above it can clearly be seen that lighting consumes the largest portion of electricity in the support processes (521MWh/year). There exists numerous numbers of lamps

in the mill with no specified mode of control or dimming to reduce energy consumption.

According to information provided by the energy manager most of these lamps in the

production and storage area are mercury lamps thus this unit process holds a high potential

for energy savings.

The case for compressed air usage is no different it consumes 40% (Figure 2.0) of theelectricity supplied. This is not so surprising because from the data provided by the energy

audit it is on power throughout the period of measurement.

Ventilation also runs 24 hours and for 7days a week through the year but it consumes quite a

low percentage of electrical energy due to its low power demand.

Though the production processes are few they have higher electricity consumption than thesupport processes. This may be attributed to the higher energy consumption per unit.



3.2 Energy Savings Energy consumption forms a major part of the operating cost of a steel manufacturingprocess. From the view of profits making minimised energy consumptions means savings

cost and also raising annual income. We have identified some salient processes where energy

savings can be done.

3.2.1 Energy saving potential in various unit processes. Lighting

The source of lighting employed in the production and storage rooms consumed so muchpower (400W) . Reasonable measures are to change the lamp types to energy saving lamps

such as T5. Sensors could also be installed to detect the presence of employees and thus deem

or shut off the light source accordingly. With this change the annual electricity use for

lighting reduced from 521MWh/y to 369MWh/y with similar values for light intensity in the

storage, production and office rooms.

Measure Decreaseddemand(kW) Decreased time (h/y) Energysavings(MWh/y)

25 5997 152

Ventilation

In the case of the ventilation system there is no heat exchanger to take advantage of the hot

exhaust air temperature. If the exhaust air temperature is used there could be considerable

savings in oil cost for space heating. Use ventilation system only during production or office

hours and natural ventilation at night instead of running the system all the time. The potential

saving by this time reduction (20%) could save 43MWh/y (EnSAM).

Compressed air

The measures to save energy from compressor are reducing the load and discharge pressure

to reduce the air leakages, performing effective maintenance to the components, using less

compressed air for the unit processes and controlling the operating time as well as running

the equipment under lower pressure conditions. If possible, replace the compressed air driven

tools with electrical ones. The annual electricity demand for the compressor will be decreased

from 494 to MWh/year.



Space heating

Decreasing the heat loss by transmission and ventilation through the building envelope would

be useful. The exhaust air also has some energy content which could be heat exchanged for

space heating. The heat lost through ventilation is 890MWh/y. With the idea to employ to

employ a heat exchanger with 75% efficiency there is a savings potential of 668MWh/y to

save replace some demands for oil.

Production unit processes and others

Improved performance of equipments and energy efficiency can save some amount of energy

in the production processes. Controlling the operating time could be very important herebecause shutting down machines completely instead of leaving them on standby or idle could

save huge amounts of energy. The combined potential of shutting down completely all this

machines is about 87MWh/y of energy (Refer to appendix for detail calculations).

Measure Unit Energy

Savings(MWh/y)

Shut off machine

During non

production hours

Drawing bench 43

Triple straightening

machine

1.2

Levelling machine 10.6

Bulk Throwing

machine

32.4

Total 87



Table 3.0 Energy consumption before and after energy savings improvements

Energy demand

(MWh/y) Energy

demand

(MWh/y)*

Support

processes

Electricity Oil Electricity Oil

Lighting 521 369

Ventilation 213 170

Compressed

air

494 230

Space heating 20 2128 20 1440

sum 1248 2128 789 1440

Production

Processes

Drawing

bench

655 612

Triple

straightening

machine

355 354

Levelling

machine

163 152

Bulk

Throwing

machine

54754

547

515

Sum

1720 1633 1440

Others 832 0 832 0



4.0 Discussions and Conclusion The

steel

industry

is

an

energy

intensive

sector

with

energy

cost

contributing

a high

percentage

of total company cost. In addition to this direct cost, there are also other hidden costs such as

for pollution caused by the intensive use of energy. Therefore energy consumption should be

given particular attention and measures employed to reduce the amount consumed.

In order for a possible reduction in energy consumption to be done there is the need to identify

the various unit processes and their corresponding energy consumption. Then the power

consumption over

time

gives

energy

which

then

can

be

analysed

to

see

possible

means

to

achieve some savings. As a measure to improve accuracy it is advisable that the one doing the

measurements continues to carry on with the energy audit or analysis. When one is presented

with only the data without a direct involvement in how the data was obtained makes it difficult

for the analysis to go on smoothly and leads to several assumptions which could be erroneous.

Obvious conclusions we can draw from this energy audit is that the company does not really

have monitor

on

their

production

equipment

typically

in

instances

of

running

idle

whiles

consuming energy. Having a strict schedule to shut down completely all machines operating on

idle could save amounts of energy as already discussed in the energy saving measures for

production processes. Other simple aids such as the use of sensors and also a consideration of

load management could be useful. The energy source used for space heating could be costly

looking at the current oil prices. This could be changed to bio fuels which are renewable with

reduced environmental impacts.

The energy savings as can be seen for electricity is 546MWh/y and with the cost of electricity at

0.063 €/kWh (Europe's Energy portal) there is the potential saving of about 35000 €/year.

Looking at other options there in some energy content in the exhaust air which can be

recovered to further reduce the annual oil demand for space heating.With the employment of a

heat excahnger with an efficiency of 75% the oil saving potential is 688MWh/y with an annual

cost

savings

of

about

31000€/year

with

the

oil

cost

of

44€/MWh

provided

in

the

invoice.

The total potential energy savings is 1234MWh/y which represents about 21% reduction. In

terms of cost the total cost savings is about 66000€/year which represent about 9% percentage

reduction.



5.0 References 1. Aktiebolaget Svenska Teknologföreningens Förlag. Iron and Steel in Sweden. 2004.

http://runeberg.org/steelswe/. access April 17th, 2010

2. http://www.energy.eu/#industrial access April 29th,2010‐04‐29

3. Table of U‐values. Conservation of fuel and power.

http://www.officecomfort.co.uk/AppendixA_UValues.pdf. access April 26th2009



10

Support processes 6.0 Appendix

Lighting

Facility Number of

lamps

Actual

Power

(W)use/lamp

Operative

hours(h/yr)

Energy

demand(MWh/yr)

Storage 108 425 * 6120*** 281

Production 90 425 6120

24×255**

234

Office 20 140 2295 6

Total 521

*According to extra information provided by the energy manager the storage and production use mercury lamps while the office uses normal fluorescent

lamps. And from factors used in ENSAM the actual power demand for a mercury and fluorescent lamp are 425W and 70W respectively.

** The production is organized in campaigns of three weeks with production during 16 days. The production is closed during Midsummer and Christmas as

well during a four‐week holiday in summer [(52/3×16)‐((4×5) +2)] = 255days.

***Light is

on

throughout

the

day

during

production

days.



11

Ventilation

Production and

Storage

Electrical

power

demand

(kW)

Operating

hours(h/y)

Energy

demand(MWh/y)

Supply fan 6.5 8760*** 57

Exhaust fan 4.5 8760 39

Office fan

5.6*

8760

49

Total Energy =

145

AIR CURTAIN

AIR CURTAIN 1 AIR CURTAIN 2

Electrical

power(kW)

Operative

hours(h/y)

Energy

demand(MWh/y)

Electrical

power(kW)

Operative

hours(h/y)

Energy

demand(MWh/y)

Total Energy

demand(MWh/y)

Production 31.97 624.24 19.95 Production 32.42 1458.80 47.61

Off 0 8135.76 0 Off 0 7301.2 0

19.95 47.61



12

Assumption***: Ventilation

is

on

throughout

the

year.

*Average power consumption for office fan from energy survey data.

Compressed air

*Operative time

is

the

number

of

hours

the

machine

is

on

within

255

production

days

(16h/day×255days/year).

Compressor

is

on

throughout

production

hours.

3 All total energy consumption values have been rounded to the nearest integer.

Total Energy 683

Compressor power use(kW) Operation time(h/y) Energy demand(MWh/y)

Production 56.33477 4080* 230

Non Production

56.33477

4680

264

Total Energy consumption 494



13

SPACE HEATING

Storage

and

Production

Unit U-

value(W/m2K)*

A (m2) UA(W/K)

Wall 0.245 6238.98 1528.55

Floor 2.7 11852.78 32002.53

Window 2.7 750** 2025

Roof 1.067 11852.78 12646.93

∑=48203.01

Tin 18.88**

T*out(oC) TJan = -

2.9

TFeb= -

3.0

TMar= -

0.1

TApril =

5.3

TMay=

11.0

TJune=

15.4

TJuly=

17.7

TAug=

16.4

TSep=

12.2

TOct=

7.1

TNov=

2.7

TDec=

0

Q=UA(Tin-

Tout)

(Watts)

1.049 1.054 0.911 0.654 0.379 0.167 0.057 0.119 0.320 0.568 0.779 0.910

Degree

hours

107459

Energy UA × Degree hours 5180MWh

*From table of U-values

**Energy Manager Information



14

Unit U-

value(W/m2K)

*

A (m2) UA

Wall 0.245 244.96 60.0150

Floor 2.7 1488.21 4018.17

Window 2.7 27.22* 130.656

Roof 1.067 1488.21 1587.920

∑=5796.76

Tin(°C) 22**

T*out(°C) TJan = -2.9 TFeb= -

3.0

TMar= -

0.1

TApril =

5.3

TMay=

11.0

TJune=

15.4

TJuly=

17.7

TAug=

16.4

TSep=

12.2

TOct=

7.1

TNov=

2.7

TDec=

0

Q=UA(Tin-Tout)(Watts)

0.1443 0.1449 0.1280 0.0970 0.064 0.038 0.025 0.032 0.057 0.086 0.112 0.127

Degree

hours

107840

Demand

*Average monthly temperature for Linköping

Office



15

Energy

Demand

UA × Degree hours 625MWh

Aero tempers [Electricity]

Number Power (W) Operative hours (h/y) Energy demand (MWh)

8 200×8 3480* 6

Pump

in

heating

system

[electricity]

*According to the measurement data provided for the year 2005, there is no heating in the months of May till September. So we have taken out the

total number of week days between May till September (which is equal to 110 days) from the total working day over the year (i.e., 255 days) and

multiplied it with 24 hours. [((255‐110)*24) =3480]

Pump power demand(kW) Operation time(h/y) Energy demand(MWh/y)

4 3480 * 14

*Average monthly temperature for Linköping

** Asumption



16

Q ventilation

Q ventilation = air flow rate (m

3

/s) ×density of air (kg/m3) × specific heat capacity of air (kJ/kg.K) × (Troom -Toutside) (K)

Density of air at room temperature (20°C) =1.205 and the specific heat capacity = 1.005 (kJ/kg.K) (The engineering toolbox, 2010)

Toutdoor is the average outdoor temperature for Linkoping

Air flow of supply fans = 5+4.3=9.3(m

3

/s)

Storage and Production

Air flow

rate(m3/s)

9.3

Density of

air(kg/m3)

1.205

Specific heat

capacity of air

(kJ/kg.K)

1.005

Troom 18.88

Toutdoor4 TJan = - TFeb= - TMar= - TApril = TMay= TJune= TJuly= TAug= TSep= TOct= TNov= TDec=

4 Average outdoor temperature for Linkoping was sourced from tutorial material for Building Energy systems



17

2.9 3.0 0.1 5.3 11.0 15.4 17.7 16.4 12.2 7.1 2.7 0

Qventilation(kW) 179.97 178.85 211.51 152.95 88.74 39.19 13.29 27.93 75.23 132.67 182.23 212.64

Hours 744 672 744 720 744 720 744 744 720 744 720 744

Energy Supplied 133.89 120.19 157.36 110.12 0 0 0 0 0 78.71 131.21 158.20

Total Energy 890MWh

Total energy suppled

for space heating Oil

(MWh/y)

Total electricity

supplied for space

heating by electricity

(MWh/y)

2128* 20

*Energy audit information



18

Production processes

Moulding

DRAWING BENCHES

DRAWING BENCH 1 DRAWING BENCH 2

Electrical

power(kW)

Operative

hours(h/y)

Energy

demand(MWh/y)

Electrical

power(kW)

Operative

hours(h/y)

Energy

demand(MWh/y)

Total Energy

demand(MWh/y)

Production 48.1899 5220.36 251.57 Production 156.0695 2313.36 361.04

Idle 5.28 899.64 4.75 Idle 10.70 3531.24 37.78

Off 0 2640 0 Off 0 2915.4 0

256.32 398.82

Total Energy 655



19

TRIPLE STRAIGHTENING MACHINE

Electrical power(kW) Operative hours(h/y) Energy demand(MWh/y)

Production 133.33 2656.08 354.14

Idle 4.59 281.94 1.20

Off 0 5821.98 0

Total Energy 355

LEVELING BENCH

Electrical power (kW) Operating hours(h/y) Energy demand(MWh/y)

Production 75.50 2019.60 152.49

Idle 2.65 3837.24 10.16

Off 0 2903.16 0

Total Energy 163



20

BULK THROWING MACHINE

Electrical power (kW) Operating hours(h/y) Energy demand(MWh/y)

Production 178.04 2888.64 514.30

Idle 13.49 2399.04 32.37

Off 0 3472.32 0

Total Energy 547

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