The aluminium foundry industry energy conservation imperatives

The aluminium foundry industry
energy conservation imperatives.
IIR's Light Metals conference
The Hyatt Regency, Rosebank,
Johannesburg

11,12 and 13 May 2009
Dr A E Paterson
– Aluminium Federation of South Africa

Outline:

The energy problem
The energy conservation scheme
The foundry industry
The energy requirement of melting
Furnace efficiencies
The 1973 oil crisis
The USA aluminium foundry industry 1976 energy conservation
workshop
What is the local foundry industry doing at present?
How does the foundry industry pay for it?
Climate change, environmental and trading impacts
Conclusion

Energy sources are not restricted to electricity

They include electricity, natural gas, lpg, heavy and light oils
and, in the case of irons and steel, coke.

Measured against reliability of supply, where possible, multi
source energy could be attractive.

Measured against increasing cost of energy, local pilot studies
have indicated capacity of improvement. RSA foundries
measured in three independent pilot studies showed low
energy efficiencies relative to world leaders.

Energy can be saved at a cost. Embedded capital equipment
requires consideration.

The electrical energy problem – not enough, incorrectly priced

The graphs assume a 4% annual supply growth to underpin a 6% annual
growth in GDP. (This implies a strategic move from supporting primary
industry to supporting down stream value adding industry.)

To maintain surety of supply Eskom require a minimum of a 10% buffer
to allow for foreseen and unforeseen maintenance requirements.

Savings are essential if the country is to avoid a crisis in 2011 to 2013.

Also - Existing power stations come to end of life in the mid 2020’s

Pricing – the electricity price had been kept artificially low and did not
reflect the replacement value of the capital equipment. It was regarded
by the DME as being 76% below the nearest competitor

Electricity is priced differently to industry, commerce and households.

The graphs drawn from external sources relates to households and to
industry respectively. Whilst RSA is not included in the industry
pricing they support the cheaper electricity view.

Demand Supply Country climate Financial SA Probability
reduction options constraints image change sustainability Economy of desired
and outcome
environm
ental
Load Shedding

Rolling Blackouts

Prioritisation of new
load With pcp
Intensified “energy
efficiency” DSM
good but
Severe NMD slow
penalties
Suspend new
applications
Short
Power conservation term
programme
Positive Neutral Negative
impact impact

Four main option types to effect behaviour change were
considered:

Load shedding - unfair and unsustainable.
Substantial price increases - useful in conjunction with rationing
Demand supply management programme – useful
alongside .
rationing
Power conservation programme - Rationing the right to purchase
. (of supply) seen as best
option

PCP is the core underpinning principle linked to pricing penalties


The energy conservation scheme is targeting a 10%
energy saving phased in over three to four years with
a 50% saving in the first year.

Failure to meet the 10% savings targets will result in
punitive energy tariffs in the form of a steeply
inclining power curve block tariff approaching and
exceeding the replacement value cost of electricity.

A phase in period of about two years is anticipated.

The foundry industry is a basic industry.

Castings form the basis of many products

The value chain involves casting, machining, manufacture and
packaging giving added value of the order of 50x at industry level.

Energy is required to melt and cast metals

Energy rationing and sharply increasing price forms a challenge

The 1970’s USA crisis that followed energy rationing and price
increases will be explored to gain insights.

The foundry decision environment

The decision environment includes variables that have a significant
effect on returns.

The four main variables are the market, capital equipment, metal price
and the casting technology and process control.

These are subject to control, subject of influence or not subject to
control of influence.

The main controllable variable is casting technology and process control
Capital equipment is not subject to control or influence once purchased.
(This does not imply that the equipment does not have to be run correctly –
it does imply that the basic structure and character of the furnace exists)
The offerings of furnace and holding oven manufacturers
vary and my differ from market to market. South Africa .
. typically uses batch furnaces.

The foundry decision environment

The main controllable variable is casting technology and process control
Capital equipment is a major decision related to a specific market need
and is cannot be readily changed once purchased.
(This does not imply that the equipment does not have to be run correctly –
it does imply that the basic structure and character of the furnace exists)

The offerings of furnace and holding oven manufacturers vary and differ
from market to market.
The South African foundry sector typically uses batch furnaces to
accommodate a jobbing market with changing alloy specifications.
Some use induction furnaces but these have limited applicatio becaeu of
metal stirring
Some foundries specialising in single alloy volume markets such as the
automotive sector have chosen continuous furnaces such as the Striko.


Crucible furnace – suited to batch
Note energy losses with open crucibles


Crucible furnace – note insulated lid

Closed system design
3 Stage Furnace
Charge preheat shaft
Melting on ramp
adjacent to holding
chamber
Holding in separate
chamber with separate
controls
Continuous process
Doors are the width of
each chamber => easy
cleaning

Modern Striko furnace

Flue

Charge preheating

Striko furnace

Foundries are capital and energy intensive

Equipment lasts a long time

Capital choices reflect specific foreseen circumstances made at
the time of choice

Two issues are the interplay between the costs of capital and
energy

In a cheap energy, expensive capital country, the bias has
been towards lower coat lower energy efficiency.

In expensive energy, cheap capital countries energy saving
equipment is used. The technologies exist.

The question is both what to do and in what order.

The majority of energy (about 70%) is used of melting
Much of the energy use is outside the direct control of the foundry
– it depends on the type of furnace installation

Energy in the from of heat is lost through inefficient conversion,
through furnace walls and through the flue. The majority is lost
through the flue. Modern furnaces use this energy.

Looking to similar energy challenge circumstances the US
response after the 1973 oil crisis was considered.

Energy availability declined rapidly and prices accelerated rapidly.
We face rationing and rapidly increasing prices.

Energy is not only used for melting

It is also used for holding, for casting and for heat treatment
Holding – the structure may lost heat through the foundations,
. the walls of the flue.
- holding practice may hold molten metal for too long.
Casting – too large a runner and riser system requires extra
. metal melted and remelted
- poor practice which results in a high defect ratio
. requires extra energy in remelting.
- impact of poor metal quality or temperature
Heat treatment – temperature, time, insulation aspects

These are the controllable aspects.

• Energy is required for melting, holding and casting

• The vast majority of energy is required for melting.

The theoretical calculation without melt loss, furnace heating,
other losses including rework and volume of runners and risers
is based on:

Specific heat aluminium solid 900J/kgC
Specific heat aluminium liquid 944J/kgC
Latent heat of fusion 3,96 E5J/kg)

• Heat solid from day temperature to melting /kg
900 x (660oC-20oC) = 5,76E5J/kg (54%)*
Melt/kg = 3,96E5J/kg (37%)
Heat liquid to casting temperature of 760oC
944x(750oC - 660oC) = 0.85E5J/kg (8%)
Total = 10,57E5J/kg = 10,57E5Ws/kg
= 10,57E5/1000x3600 = 0,3kWh/kg electrical
(or equivalent electrical energy consumption)

* Aluminium at 660C is not stable. Assume 450C charge pre heat,
so charge heating around 35%
melt plus heat to casting temperature 65%
With pre heated charge a 1/3 saving is possible

Best world practice 0,55 – 0,65 kWh/kg taking the impact of
furnace heating and run round scrap into account.

This is about twice the theoretical minimum requirement for
melting aluminium. But we have to consider the need to heat
the furnace structure and the melt for runners and risers – quite
apart from rework.

Pilot studies by AFSA taking all energy sources into account
and measured against metal purchases (assuming work flow
and quality is a constant) found an energy use of about five
times [and up to ten times] the theoretical minimum, over twice
best practice)

Outline:

The energy problem
The energy requirement of a foundry
The 1973 oil crisis
The USA aluminium foundry industry1976 energy conservation
workshop
Conclusion

Energy loss Energy loss metallurgy
• Where does the (70%) energy go? through flue
• Metal quality
• Too hot
• Returns - process
- quality
Energy loss
All energy
Energy • Process inefficiency
sources - net
Energy • housekeeping
energy in
conversion
into • Furnace walls
at factory gate furnace
eg power factor • through flue
Burn efficiency

Energy opportunity – pre
Coal to energy
heat charge
conversion efficiency
plus electrical Energy
transmission loss conversion
Energy loss Energy needed to (1) heat
Energy loss
Into furnace, (2) raise charge to melt
foundations temperature. (3) melt metal and
The energy conversion of coal (4) raise to casting temperature
to electricity is typically
17%-35% efficient. This is not
very different to the conversion
of petrol to power in cars Energy loss can be divided into: controllable
negotiable
uncontrollable

Management

We know how much energy is required to heat and melt aluminium.
How do we use this to distinguish between furnace efficiency and
management efficiency. Management offers the best returns.
Energy use per unit mass successful casting will increase as:
Volume of runners and risers as a percentage increases
Volume of additional mass later machined off increases
Volume of rejects increases

Management of volume of melt and nature of supply may not
. reflect market (continuous or discontinuous, single or multiple
. alloy) and production realities. This implies identifying and
. measuring what is actually done and optimising the molten metal
. supply and holding parameters to meet actual demand profiles.

Charge pre heating - feed to
Added cooling air melt by adjustable grating

Flue gas heated fresh air directed to
charge to achieve suitable
temperature to avoid upsetting
molten alloy characteristics

Charge pre heating

Crucible furnace – example 1
- note retrofit lid integrated pre-heating unit

Charge pre heating - feed to
Melt by solid transfer
Flue gas heated fresh air
directed to charge to
achieve suitable Added cooling air
temperature to avoid
upsetting molten alloy
characteristics (450oC)

Charge pre heating

Crucible furnace Example 2
- note retrofit lid and charge pre-heating unit

Most 800oC to 1500oC high temperature furnaces are inefficient

Thermal efficiencies can be high but can be as low as 10%
because as the heating or melting of metals requires high waste
gas temperatures leaving the furnace it makes it difficult to design.

Typically over 50% of the heat input may be lost through the flue

If this could be recaptured, it could be used to preheat combustion
air for burners (fossil fuel fired) or to preheat charge metal.

The focus on this paper is on heat recouperation.

Outline:

The energy problem
The 1973 oil crisis
The USA aluminium foundry industry1976 energy conservation
workshop
Conclusion

The USA industry had generally chosen equipment that assumed
cheap plentiful energy.

The increasing price energy crisis that faced the USA at that
stage is not dissimilar to that faced locally today. In addition, the
source of energy, oil, had peaked. Strategic independence was
lost.

The crisis reflected a shortage combined with rapidly rising prices.

The workshop concentrated on metal melting as the most energy
intensive and the one that offered most potential for returns.

The focus was on retrofitted solutions.

US oil production peaked in 1973

In October 1973, as a result of Yom Kippur War tensions, OPEC
members stopped exports to the USA

Oil prices rose from $3/barrel in 1972 to $12 in 1974 (4x)

By the second oil crisis (1979) prices had risen to $35/barrel (12x)

Response:

It was realised that the era of cheap oil had passed.

The US Energy Department became a cabinet office.

The US Government took an active interest in facilitating change

The drive for light weighting of cars grew from the energy crisis.

A USA aluminium foundry industry energy conservation workshop
was held in 1976 to share lessons learned.

Outline:

The energy problem
The 1973 oil crisis
The USA aluminium foundry industry 1976 energy
conservation workshop
Conclusion

The conference focussed on two aspects;

• Increased energy conversion efficiencies
– improved burner efficiency
- furnace preheating

(In South Africa we could add improved power factor
conversion for Electricity, a potential 5% saving)

• Heat recouperation Energy regained is energy saved
This can be used to preheat the
charge, . to preheat the furnace air, etc

The focus is on heat recouperation

A major factor that needed to be taken into account was the
reality of embedded capital equipment.

The 1976 conference focus was on retrofitted solutions.

Two systems were discussed:
Recouperation through radiation
Heat wheels.

Typically the heat captured was cooled to about 400oC by
dilution with ambient air before use and used to preheat charge
metal or to preheat furnace or burner air.

In the recuperator the heat is transferred by different modes:

• Conduction within metals or other bodies,
• Convection between gas or air and solid bodies. The higher the
temperature differential, the better the rate of heat transfer. The
faster the gas or air moves across or along the tubes or other solid
bodies, the higher the heat transfer rates.
• Radiation between solid surfaces – transfer rates increases by the
fourth power of the temperature differential between the two surfaces.
• Gas radiation between certain gases and solid surfaces – transfer
rates increase by about the fourth power of the absolute temperature
difference between the gas and surface. Heat transfer also increases
with higher amounts of C02 and H20 and with large gas volumes.

However, radiation is not very effective at low temperatures of either
the surfaces or the gases.

(Gas) Radiation Recouperators
.
• Consists of two concentric large diameter cylindrical metal shells
welded together at each end by way of air inlet and outlet headers.
• Exhaust flue gases from the furnace at some 1 100oC pass through
the inner shell while combustion air passes through the narrow gap
between the shells.
• Heat from the exhaust flue gas is transmitted to the inner shell
(heating surface) mainly by gas radiation which may be as high as
75% to 95% of the total heat transferred.
• Additional heat is transferred by convection due to the slow flow of
exhaust flue gas through the recuperator as well as by radiation from
the hot inner shell into the recuperator.
• On the other side of the heating surface of the recuperator the
combustion air passes with high velocity to dilute the air and picking up
heat from the inner shell to achieve about 400oC.

Heat Wheels

• Hot exhaust gases are directed through one side of the slowly
rotating heat wheel, absorbing the beat. Cold air flows through the
other side in the opposite direction, stripping the heat put into the
wheel with efficiencies up to 75%.
• Metal wheels have expansion and contraction (causing distortion)
drawbacks for high temperature applications. The seals are difficult to
maintain
• The geometric stability of the ceramic wheel at high temperatures
provides an answer to critical high temperature sealing. This very low
expansion at temperature allows the use of “close gap” ceramic seals.
The seals are also low expansion material.
• Ceramics are generally more resistant to corrosion from chemical
attack than most metals. They have a high efficiency heat exchange
because the low thermal conductivity and high specific heat provide a
greater heat capacity and smaller energy loss between the hot and
cold face than similar metal heat recovery units.

The local foundry industry is undertaking a volunteer forty foundry
by foundry five part fact base energy study:

•Ascertain the quantum of energy input to the factory in joules
•Survey the use of energy in the foundry process up to fettling
•Analyse the top 80% of energy usage for each foundry to
determine efficiency of use
•Propose possible solutions on a cost benefit scale. (Many
housekeeping type solutions are very low cost but need to be
monitored to ensure sustainability)
•Use the data to develop and publicise a country recommendation

The new reality of energy rationing and increasing cost of energy
prices warrants serious attention.
New more energy efficient equipment exists.
Retrofit solutions are well understood and available
The difficulty at present is cash flow.
The combination of the world economic crisis and tight lending
conditions by the banks begs the affordability questions.
Government intervention is a change partnership is desirable
However, if foundries do not invest into energy efficiency for the
future, increased prices (and penalties) come into play.

Foundries contribute to global warming from fossil fuel based
energy sources.

Foundries are also affected by clean air and water legislation.

The application of clean air and water, and waste legislations by
municipalities is an issue of concern as it is unclear how
municipalities will differentiate between manageable and
unmanageable contributors.

In due course this legislation may result in the need to reorganise
foundry layouts as has been found in Germany where heat
sources have been clustered into one area, those producing dust
or other air contaminants into another.


The foundry sources of energy are all fossil fuels.
The CO2e load for energy from coal is 7,18 tons/10 000 kWh
The CO2e load from light fossil fuels is 2,16 tons/cu metre
The CO2e load from natural gas at 1atm is 181kg/kWh
These enable a foundry to calculate the carbon tax effect on its
own operations

The green economy effect on international goods trading

This is related to individual country carbon emissions and reflects
the cost of greenhouse gas reduction on competitiveness.
RSA could face trading penalties.
The so called green trading tax is intended to recognise the cost
of local carbon emission reduction on competition from imported
goods by taxing imports from less carbon efficient countries a levy
based on carbon differences.
This is an important consideration from the point of view countries
that use fossil fuels as the main source of energy – including RSA,
China Australia and the USA.
Green economy taxes have not been applied to date.

Carbon trading
The 1997 Kyoto protocol Clean Development Mechanism (CDM)
is the process through which developed countries can fund
developing countries to implement emission reduction strategies.

The CDM processes are intended to promote sustainable
development, be measurable and additional, and are not intended
to divert funds from government development programmes.
Current value (2009) is ϵ23x0,9/MWh. Minimum criteria is a
verifiable and verified 10 000 tons CO2e per annum.
As individual foundries do not meet the minimum volume criteria.
a foundry group approach may be required.

This is an arena where government
agencies such as Eskom or the dti could offer a service

The South African carbon tax on electricity (2011)

South Africa’s total CO2e emissions are 500million tons per year.
The proposed carbon tax would be applied at producer and at
consumer levels at R165/ton CO2e (Treasury prefers R200/ton).
The only documentation given to date relates to electricity.
The total anticipated 2011/2012 revenue is R82Bn/annum.
This is about half the VAT revenue but drawn from a smaller group.
Fossil fuels appear not to have been addressed but are likely to be.

BUSA has opposed adoption of this tax because of the impact on
country competitveness, growing the economy and job creation.

If the CDM process is adopted and applied by government
. agencies some relief may be achieved.

Outline:

The energy problem
The 1973 oil crisis
The USA aluminium foundry industry 1976 energy conservation
workshop
Conclusion

The energy crisis is real and it is here.
We are faced with both rationing and increased prices for all
forms of energy.
Equipment exists that is more energy efficient
Retrofit low cost/high return solutions are a likely form of
behaviour change
Renewal cost of amortised equipment is likely to be impacted on
by the current trading and borrowing conditions.
A government proactive approach towards a partnership
approach to manage the changed circumstances is desirable

Carbon taxes are likely to have a significant impact. The CDM
mechanism may assist but will need to be bundled.

IIR's Light Metals conference
The Hyatt Regency, Rosebank,
Johannesburg

11,12 and 13 May 2009
Dr A E Paterson
– Aluminium Federation of South Africa

Thank you

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