The use of Solar Energy in Steel Industries

Mohammed Tahir, Viktoriya Absalyamova Solar Energy Research Center and Material Science department

Dalarna University, SE-78188, SWEDEN

Abstract-The purpose of this study is to make a design and simulation of the solar photovoltaic system which would attempt to cover the energy demand of the initial part of the pickling line hydraulic system at the SSAB steel plant. Proposed photovoltaic pumping systems in this work are to run the system into the hydraulic pump directly, developing of PV systems which produce energy in DC form. The second proposed photovoltaic technology is a type of PV system which delivers power to an AC load. Hydraulic system studied and evaluated and control components performance evaluated to yield a proper set of guidelines contributing towards future energy savings. The study shows that one PV system can deliver energy to an AC motor-pump set covering 17.6% of total energy and another PV system can supply a DC hydraulic pump substituting 26.7% of the demand.

The study includes that the PV system can supply a

significant part of the energy demand of the industrial system

such as the initial part of the pickling line hydraulic system at

the SSAB steel plant. Hydraulic accumulators can work as solar

energy storage quite effectively. The studied method is to

generate a realistic load sequence for the simulation of the PV

system through precise energy consumption calculations within

the hydraulic line. The energy efficiency analysis could show

that the initial part pickling line hydraulic system works with a

low efficiency of 3.3%.

Keywords- Energy efficiency, Energy storage, Photovoltaic system, Solar energy, Hydraulic system, Electrical motors

1. INTRODUCTION

Two important types of solar energy, light and heat, has

been known for some time. The challenges have been how to

exploit and harness these forms of energy. In addition to its

advantages, solar energy reaches the earth within 8 minutes,

from the solar surface.

In a solar cell which is also known as a photovoltaic or

PV cell, the sun's energy converted into electricity. Silicon is

a common used material to manufacture photovoltaic cells

due to its semiconductor properties. Fig. 1 shows a PV cell

and how the electrons are knocked off. As shown is the

figure, when light (photons) hits a solar cell, the

semiconductor material absorbs a part of its energy enabling

978-1-4577-1169-5/11/$26.00 ©2011 IEEE

it to knock off some of the electrons loose which results in

their free flow [1].

The main challenges of solar energy are how to enable

high efficiency storage. Different storage methods were used

in recent years, among others, batteries, flywheel, ultra

capacitor and other. In this project, to enable high efficiency

storage of solar energy in steel industries, the use of

hydraulic accumulates as solar energy storage was studied.

The study shows that the appropriate storage method in steel

industries are hydraulic accumulates due to the difficulties of

storing energy by other means and Industrial lines are the

tight composition of many components performing necessary

tasks chiefly consisting of hydraulic systems driven by

motors.

According to European Steel Technology Platform

(ESTP), renewable energy is one of the main research

priorities leading to industrial sustainability. The Swedish

steel industry, SSAB, IS aiming to reduce energy

consumptions per tone of the steel by 10% at the end of 20 11

compared with 2006. For that reason, further research is

required to replace certain amount of its electricity

requirements by its production through renewable sources of

energy, solar energy [2].

Fig. 1 PV cell and its make-up [3]

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This project was supported by SSAB (Sweden's leading

producer of high-strength steel sheets and plates), where

SSAB is striving to reduce Carbon dioxide (C02) emissions

in conjunction with steel production. It is supporting the EU

project, ULCOS, for steel manufactures which has a goal of

reducing today's C02 emissions by at least 50 percent.

SSAB also wants to reduce C02 emissions by at least 2 %

per ton of steel in today's steel production.

The objectives of this project is to make a preliminary

design and simulation of the Solar PV system which would

attempt to cover the energy demand of the initial part

pickling line hydraulic system at the SSAB Steel plant. The

energy consumptions of the hydraulic system are studied

based on the measurements and corresponding calculations

of the energy input into the system and energy output by it.

The results estimate effective energy use within the studied

hydraulic system. The general analysis of the hydraulic and

control components performance can yield a proper set of

guidelines contributing towards future energy savings.

II. PHOTOVOLTAIC APPLICATIONS AND

THEIR DEMAND WITHIN INDUSTRIAL SECTOR

The use of PV generated electricity is the same as

electricity produced from conventional sources. PV systems

can potentially supply electricity to any specific appliances

or the electricity grid. PV energy production is remarkable

because it can adjoin to any other energy source traditional

or renewable and is flexible in terms of its implementation.

The PV systems' classification is shown in Fig. 2; a grid

connected system where the installed PV system is

connected to the national electricity grid and an off grid or

stand alone type of PV system where the system cannot be

connected to the grid and batteries [3].

One of the features of the photovoltaic pumping system

which is useful for the present project is that the system runs

the hydraulic pump directly. This is because along with the

development of PV systems which produce energy in DC

form, there is the corresponding development of DC motors

technology and therefore DC brushless hydraulic pumps are

finding their way into the market now. Another proposed

photovoltaic technology which can be helpful in this project

is a type of PV system which delivers power to an AC load.

The typical PV system for these kinds of facilities would

encompass a PV modules array, an inverter, AC connections

boxes, and circuit breakers as shown in figure 3.

Photovoltaic systems

Grid-connected systems

Fig. 2 PV systems classification

Fig. 3 Typical PV system which is used to run AC load [l3]

III. HYDRAULICS AND ENERGY USE IN

THE STEEL INDUSTRY

The two classifications of hydraulic systems, mobile or

movable to the spot and fixed non-movable machines are

shown Fig. 4. Industrial or stationary applications are non­

movable oil hydraulic systems of fixed machines which can

be placed in a specific manufacturing environment. These

systems are based on fluid power when an incompressible

fluid solution transforms and does work through a set of

pipes towards the hydraulic motors and pumps [4].

The studied hydraulic system for the steel plant is shown

in Fig. 5. The mechanical energy of the prime mover, Fig. 5,

is transferred into hydraulic energy, and the two parameters

of torque and shaft speed are converted into pressure and

flow by the hydraulic pump. The hydraulic motor, which is

next in the chain on Fig. 5 converts pressure and flow back

into mechanical energy. When mechanical energy is

converted into hydraulic form, it can be easily transferred

into different locations because the pressurized fluid can

flow freely through pathways reaching remote locations

without significant energy losses.

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Hydraulic systems classification

Non-movable or fixed machines

Mobile or self­propelled machines

Fig. 4 Hydraulic systems classification

Speed Speed

Mechanical ----t Hydraulic ----t Mechanical Energy Energy Energy

Fig. 5 Studied hydraulic system for the steel plant

IV. RESULTS AND DICUSSIONS

Based on energy methods the result of energy analysis;

an experiment design and energy efficiency calculation is

presented. Proposed method to perform the energy efficiency

calculations of the initial part of pickling line hydraulic

system is based on the pressure measurements for each

hydraulic component integrated into the hydraulic system

and the current measurements of the electrical motors. The

amount of energy consumed by and delivered to the

hydraulic system by electrical motors is the data that is used

to do the calculations for the overall system efficiency.

A. Photovoltaic system design and simulation

Photovoltaic system design and simulation is shown in Fig.

6. This is done for five powerful motors that run pumps to

provide necessary power demand of an industrial hydraulic

system. The study shows that, at present only 3.3 % of the

energy is finding its way to become a useful output and run

hydraulic actuators in the pickling line of the SSAB plant.

Due to that reason, a precisely calculated power demand of

the pickling line become an objective to conduct the study

about how well a photovoltaic system can be fitted into the

energy delivery chain of the SSAB steel plant.

The result of this project shows also that the pickling line

system could be modified towards an energy efficient

perspective so that the hydraulic accumulators could reduce

the number of hydraulic pumps from five to one as it was

shown in the simulation. For that kind of a solution, the grid­

connected PV system modified as in Fig. 6.a. The primarily

proposed PV system in this project, when the power demand

of the AC electrical motor (ASEA type, ABB) would be used

as a PV system load. The second proposed PV system would

charge the hydraulic accumulators directly by using a DC

brush less hydraulic pump, Fig. 6.b. In this case, the

electrical load for the PV system coincides with the

hydraulic components' energy demand when a DC hydraulic

pump works periodically.

It is important to note that the design and simulation of

photovoltaic systems for industrial purposes only became

possible due to the integration of hydraulic accumulators into

the pickling line hydraulic system. This is because these

hydraulic accumulators were able to reduce short peaks of

high power demand when the power demand would exceed

32 kW.

A typical grid-connected photovoltaic system should

include the specifying of components as it is shown in Fig. 7.

.. 1: ,

Fig. 6 a: Grid-connected Photovoltaic system running AC

motor and hydraulic pump combination; b: Grid-connected

Photovoltaic system running DC motor and variable

hydraulic pump combination

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Photovoltalc System

Fig. 7 General functional diagram of Grid-connected

Photovoltaic system

B. AC motor based Pickling Line Photovoltaic System.

The AC load based pickling line photovoltaic system

would supply the energy demand of one AC motor which

runs a variable hydraulic pump. This combination charges

the hydraulic accumulators and delivers energy into the

pickling line hydraulic system as shown in Fig. 8. Fig. 8a

shows calculated Power delivered by AC and Fig. 8b shows

calculated total energy demand of the AC motor-pump. As

can be seen in Fig. 8, the maximum power is not exceeding

32 kW because it is assumed that hydraulic accumulators

would be introduced into the Pickling Line. Then the used

energy estimated by taking into consideration the fact that

within one hour the pickling line is used three times and with

a loss factor of 20%.

Total Pow-er vs Time delivered by Electrical Motor, kW 32 - - - _.- ----" ---- - - -1- - - ;�e�. ��I- - --

m __________________ 1 ____ [ _

- ------------- - ---- � ---- � -

1

---- ,----i----r - -I 1

22 - - - - - - - - - - - -4 - - - - + - - - - f- - -I

_ _ ____ ....J ____ -l- ____ I-j _I

.�

Total Energy \15 Time delivered by Electrical Motor, kWh

6 - - -I- ___ -l- ___ -I- ___ 4- ___ -l. ___ -I �::���--1 5 ___ L ___ L ___ -l- ___ J. __ ..l ___ --1 ___ --1

� 4 ___ L ___ L ___ ..L __ -I- ___ J ___ ...J ___ ...J

t 3 ___ L ___ .1.. __ .L ___ .1 ___ .l ___ � ___ --1 I I I I I I I

2 ___ 1- __ _ __ -L ___ ...L ___ ..l ___ ...l ___ ...J I I I I Energy, kWh I I

1 ___ ' ___ 1. ___ 1. ___ .1 _ :r OJ .J 1 1

Fig. 8 a: Power delivered by AC type motor within one

Pickling Line cycle, b: Calculated total energy delivered by

AC type electrical motor

V. CONCLUSIONS

This study showed that the PV system can supply a

significant part of the energy demand of the industrial system

such as the initial part of the Pickling line hydraulic system

at the SSAB steel plant. The hydraulic accumulators can

work as solar energy storage quite effectively. A way was

found to generate a realistic load sequence for the simulation

of the PV system through precise energy consumption

calculations within the hydraulic line. The energy efficiency

analysis could show that the initial part Pickling line

hydraulic system works with a low efficiency of 3.3%. The

reasons that reduced energy efficiency with the SSAB

pickling line were discovered and analyzed. The main reason

is that the system is oversized because it was designed for

the worst case upset conditions and because of this, there

was always an excess flow in the system. Due to this, the

pickling line continuously operated in throttling mode due to

partially closed valves which wasted a lot of energy. It was

concluded that the hydraulic system at SSAB needed

modernization because it works with very low energy

efficiency.

REFERENCES

[1] The NEED Project, NEED, 2010. Solar Available at http://www.need.org/needpdf/infobook _ activities/SecInf o/SolarS.pdf [Accessed 26 September 2011]

[2] V. Absalyamova, "Energy Analysis within Industrial Hydraulics and correspondent Solar PV system design", Master Thesis, Solar Energy Engineering, Dalarna University,2010

[3] SolarGenUK, 2010. SolarGen UK's solar photovoltaic systems Available at http://www.solargenuk.com/3asolarpv.html[ Accessed 26 September 2011]

[4] Hydraulics in Industrial and Mobile applications. Italian association of Manufacturing and Trading Companies in Power Equipment and components, 2007

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