The foundry industry energy conserva4on impera4ves

Transcription

1 The South African Metal Cas4ng. Conference 2017 The foundry industry energy conserva4on impera4ves Tony Paterson, University of the Witwatersrand

2 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

3 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

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5 Energy sources used are not restricted to electricity. However sources of power have tended to follow the Eskom price pattern per kilo joule Sources include electricity, natural gas, lpg, heavy and light oils and coke. Measured against reliability of supply, where possible, multi source energy can be attractive but is not always feasible. Measured against increasing cost of energy, local pilot studies have indicated capacity of improvement. RSA foundries measured in three independent pilot studies showed low efficiency relative to world leaders - as may be expected for what was originally a high capital cost, low energy cost country. Now we have high capital cost and a high energy cost. Energy can be saved at a cost. Embedded capital equipment requires consideration. Not all is amortised. Profitability may be too low to consider renewal.

6 Since 2008, whilst international coal prices for electricity generation have remained flat, local prices have risen by some 18% per annum. RSA electricity prices (and other energy sources), moved from being the lowest or second lowest to the tenth highest by 2015.

7 Highest global electricity prices 2015 # Country Electricity price (USD c/kwh) 9 France South Africa Austria Poland 8.33

8 The cost of energy which used to be very affordable is now a significant part of the cost equation

9 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

10 The foundry industry is a base 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 from metal to product at industry level. Energy is mainly required to melt and cast metals Pilot studies show RSA to be a relatively inefficient energy user (typical uses of five times the theoretical minimum were found.) The pilot study for aluminium conducted by myself assumed constant metal on the factory floor and used cost records of energy sources of any type purchased against sales in tons. Energy rationing and sharply increasing price forms a real challenge The 1970 s USA crisis that followed energy rationing and significant (oil) price increases will be explored to gain insights as to what they did faced with sharply increasing energy costs.

11 The energy use assessment method used by myself was a simple examination of financial records Energy use over a two year period was determined by tabling costs of any fuels used. Fuels were converted into joules i.e. watts/second Sales were determined as kilogrammes of product from purchase records of scrap purchased The tacit assumption made was that the volume of work on the shop floor remained more or less constant.

12 The foundry decision environment The decision environment includes mainly variables that have a significant effect on returns. Six main variables are capital cost, capital equipment choice, energy cost, metal price, market demand, and the casting technology and associated process control. These variables are either subject to control, subject of influence or not subject to control of influence. Control the controllable, influence those that can be influenced and monitor the rest. The main controllable variables are casting technology and process control Capital equipment itself is not subject to control or influence once purchased. Choice of purchase plays capital cost off against energy efficiency (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 oven manufacturers vary and differ from market to market

13 Crucible furnace batch process note energy losses Reverb furnace Note energy losses

14 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 one alloy

15 Note preheating use of flus gasses Striko furnace

16 Foundries are capital and energy intensive The major energy using equipment, furnaces, last a long time. Capital choices reflect specific foreseen circumstances made at the time of choice. The three issues affecting choice are the interplay between the costs of capital and energy and whether to choose for batch or continuous processes In a cheap energy, expensive capital country, the natural bias has been towards less energy efficient equipment (as was the case in the USA before the 1973 oil crisis). In expensive energy, cheap capital countries energy saving equipment is used. The technologies exist.

17 Energy is not only used for melting although this is a dominant use. used for holding and for casting. It is also Conversion is not always efficient. Holding the furnace structure loses heat through the foundations, walls and. particularly the flue. - holding practices may retain molten metal for too long. Casting too large a runner and riser system requires extra metal melted and. remelted - poor casting practices which results in a high defect ratio results in. extra energy in remelting. - impact of poor metal quality or temperature These are the controllable aspects.

18 The question is both what to do and in what order. The majority of energy (about 70%) is used of melting and holding The majority of energy use depends on the type, insulation and installation of the furnace. Some aspects are uncontrollable, some may be modified. Energy in the form of heat is lost through inefficient conversion, through furnace walls and through the flue. Looking to similar energy challenge circumstances the USA response after the 1973 oil crisis was considered. Energy availability declined rapidly and prices accelerated rapidly.

19 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

20 The early 1970 s USA industry had generally chosen equipment that assumed cheap, plentiful energy in the form of oil. The energy crisis that faced the USA at that stage is not dissimilar to that faced locally today. 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 opportunity for returns. The focus was on retrofitted solutions.

21 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 By the second oil crisis in 1979 prices had risen to $35/barrel

22 Response It was realised that the era of cheap oil had passed. The Energy Department became a cabinet office. 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.

23 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

24 Oil was the main source of energy. The conference focussed on two aspects; Increased energy conversion efficiencies improved burner efficiency - furnace preheating (In South Africa with electricity as the main source of energy one could add. improved power factor conversion for Electricity) Heat recouperation Energy regained is energy saved This energy can be used to preheat the charge, to preheat the etc furnace air, The real focus was on heat recouperation

25 A major factor that needed to be taken into account was the reality of embedded capital equipment. The focus was on retrofitted solutions to recover heat. Two systems were discussed: Recouperation through radiation Recouperation through Heat wheels. Typically the heat captured was cooled to about 400 o C by dilution with ambient air before use and used to preheat charge metal or to preheat furnace or burner air.

26 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 C0 2 and H 2 0 and with large gas volumes. However, radiation is not very effective at low temperatures of either the surfaces or the gases.

27 (Gas) Radiation Recouperators (1). 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 o C 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. Efficiency may be as high as 75% to 95% of the total heat transferred.

28 (Gas) Radiation Recouperators (2). 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 400 o C.

29 Heat Wheels (1) Hot exhaust gases are directed through one side of the slowly rotating heat wheel, absorbing the heat. 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 Ceramic wheels are preferred

30 Heat Wheels (2) The South African Metal Cas4ng Conference 2017 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.

31 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies What is the local foundry industry doing at present How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

32 Energy in a foundry is requires for melting Most energy is required for melting how much do we need? Specific (solid) and Latent Heat Values Specific Heat Latent Heat of Fusion Material (cal/g C) (J/kg K) (cal/g) (MJ/kg) Aluminium Copper Iron Lead Magnesium Zinc Source Gieck technical Furmulae

33 Practically the theoretical minimum is not obtainable but forms a base reference case Theoretical minimum calculation without melt loss, without furnace heating: Specific heat aluminium solid 900J/kg o C (as prev slide) Specific heat aluminium liquid 944J/kg o C Latent heat of fusion 3,96 E5J/kg (J/s = W) Heat solid from day temperature to melting /kg 900 x (660 o C-20 o C) = 5,76E5J/kg (54%) Melt/kg = 3,96E5J/kg (37%) Heat liquid to casting temperature of 760 o C 944x(750 o C -660 o C) = 0.85E5J/kg (8%) Total energy required = 10,57E5J/kg = 10,57E5Ws/kg = 10,57E5/1000x3600 = 0,3kWh/kg electrical consumption) Best world aluminium cast component (Nissan Australia) 0,55 kwh/kg 0,65 kwh/kg Industry expectation 5% of primary melting energy requirement, i.e. 0,66 kwh/kg Local aluminium energy investigation found up to 9kWh/kg

34 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

35 Most 800 o C to 1500 o C high temperature furnaces are inefficient Thermal efficiencies can be high but can be as low as 10%. As the heating or melting of metals requires high waste gas temperatures leaving the furnace, design is difficult. 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 the use of waste heat.

36 Where does the (70% of) energy go? All energy sources - net energy in at factory gate Energy conversion e.g. power factor Burn efficiency Energy into furnace Process Energy loss metallurgy Metal quality Too hot Process returns Control Energy loss flue (recovery) Energy loss housekeeping Energy loss - holding Energy loss- Furnace walls Coal energy Conversion and electrical transmission loss 83% loss Energy conversion Energy loss Energy loss Into foundations Energy needed Heat and melt metal Energy needed to heat furnace Energy use can be divided into: required possible improvement unavoidable loss

37 Refurbishment add lid Crucible furnace - note lid

38 Added forced cooling air Charge pre heating - feed to melt by adjustable grating Filtered flue heat directed to charge. Needs added air to pre cool flue air to suitable temperature to avoid upsetting molten alloy characteristics Charge pre heating Crucible furnace example 1 - note retrofit lid integrated pre-heating unit

39 Filtered flue heat directed to charge. Needs added air to pre cool flue air to suitable temperature to avoid upsetting solid alloy characteristics (450C) Charge pre heating - feed to Melt by solid transfer Force added cooling air Charge pre heating Crucible furnace Example 2 - note retrofit lid and charge pre-heating unit

40 Outline: The energy problem post 2008 The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

41 The new reality of steeply rising energy costs 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. On the other hand if foundries do not invest into energy efficiency for the future, increased prices (and possibly penalties) come into play.

42 Outline: The energy problem post 2008 The energy conservation scheme The foundry industry The 1973 oil crisis The US aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

43 The foundry sources of energy are all fossil fuels. These contribute to global warming. Incentives apply. The Kyoto protocol Clean Development Mechanism (CDM) is one mechanism CDM is the process through which developed countries can fund developing countries to implement emission reduction strategies that promote sustainable development, are measurable and additional, and do not divert funds from government development programmers. Current value ϵ23x0,9/mwh. (0,9MwH/CO2e) Minimum criteria tons CO2e per annum. As individual foundries probably do not meet the minimum volume criteria a foundry group approach may be required. The Department of Energy has established a designated National Authority to manage CDM contacts. Of 1135 CDM projects to 2015 only 3 were South African Why?

44 Outline: The South African Metal Cas4ng Conference 2017 The energy problem since 2008 The energy conservation scheme The foundry industry The 1973 oil crisis The aluminium industry 1976 energy conservation workshop The energy requirement of melting Furnace efficiencies What is the local foundry industry doing at present How does the foundry industry pay for improving energy efficiency Climate change, CO2e and the Clean Development Mechanism Conclusion

45 Conclusion The South African Metal Cas4ng Conference 2017 The energy crisis is ongoing, real and here. We are faced with energy limits and increasing prices. An energy use fact base is underway by the foundry sector. Behaviour change will focus on favourable cost/return solutions Equipment exists that is more energy efficient Renewal cost of amortised equipment is likely to be impacted on by the current trading and borrowing conditions. The CDM mechanism may assist but will need to be bundled.

46 The South African Metal Cas4ng. Conference 2017 The foundry industry energy conserva4on impera4ves Tony Paterson, University of the Witwatersrand