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Unit 8. Eco-selection: environmentally informed material choice

Unit 8. Eco-selection: environmentally informed material choice. Outline. Material consumption and the material life-cycle. LCA, problems and solutions. Analysis of products. Strategy for materials selection. Exercises. More info:

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Unit 8. Eco-selection: environmentally informed material choice

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  1. Unit 8. Eco-selection:environmentally informed material choice

  2. Outline • Material consumption and the material life-cycle • LCA, problems and solutions • Analysis of products • Strategy for materials selection • Exercises More info: • “Materials: engineering, science, processing and design”, Chapter 20 • “Materials Selection in Mechanical Design”, Chapter 16

  3. Material production Natural fibers: cotton, silk, wool, jute Man-made fibers: polyester, nylon, acrylic, cellulosics

  4. The product life-cycle

  5. Typical LCA output: • Resource consumption • Energy consumption over life • Water consumption • Emission of CO2, NOx, SOx etc • Particulates • Toxic residues • Acidification..Ozone depletion.. Roll up into an Eco-indicator ? Life cycle assessment (LCA) Environmental “stressors” • Full LCA time consuming, expensive, and requires great detail – and even then is subject to uncertainty • What is a designer supposed to do with these numbers? • LCA is a product assessment tool, not a design tool

  6. Market need Problem statement Concept The need Embodiment Strategic tools to guide design Detail Product specification Full LCA Manufacture, distribution A product-assessment tool LCA in the context of design

  7. Increasing detail, cost and time Eco- screening Scoping LCA Streamline LCA Complete LCA Minutes Hours Days Months Strategies for guiding design • Step 1: Seek method that combines acceptable cost burden with adequate accuracy to guide decision making – a design tool • Step 2: Seek single measure of stress • – energy or CO2 • Step 3: Separate life-phases

  8. Cars: use-energy and CO2 cited Appliances: use-energy cited Official fuel economy figures: Combined: 6 – 11 litre / 100km CO2 emissions: 158 – 276 g / km Efficiency rating: A Volume 0.3 m3 330 kWhr / year Strategies for guiding design (2) • Why energy or CO2? • Kyoto Protocol (1997):international agreement to reduce greenhouse gasses • EU directives such as the EuP directive (2006) • Practicality:CO2andEnergy are related and understood by the public

  9. Big picture: energy consumption of products Which phase dominates? Approximate breakdown (Bey, 2000., Allwood, 2006):

  10. Glass PE PET Aluminum Steel Eco-scoping • What should strategic tools do? • Example: drink containers • Aims:  to assess energy or CO2 burden quickly and cheaply •  to explore alternatives

  11. PET bottle Eco-scoping • Separate the phases of life 1. Material production: the embodied energy 2. Bottle manufacture: the processing energy 3. Delivery and use: transport and refrigeration 4. Disposal: collection, recycling, energy recovery • To assess, need both local and generic data.

  12. Generic data • Material energy MJ / kg • Database of embodied energies for materials • Process energy MJ / kg • Database of processing energies for materials What is embodied energy? • Transport, MJ / tonne.km • Sea freight 0.11 – 0.15 • Barge (river) 0.75 – 0.85 • Rail freight 0.80 – 0.9 • Truck 0.9 – 1.5 • Air freight 8.3 – 15

  13. Generic data • Transport, MJ / tonne.km • As before Use (delivery and refrigeration) and disposal 1. Material production: the embodied energy 2. Bottle manufacture: the processing energy 3. Delivery and use: transport and refrigeration 4. Disposal: collection, recycling, energy recovery • Refrigeration, MJ/m3.day • Refrigeration (4oC) 10.5 • Freezing (- 5oC) 13.0

  14. Disposal: recycling – the problems

  15. Recycle fractions for commodity materials

  16. RETRIEVE from database INPUTS by user • Material energy MJ / kg • Embodied energy, PET 85 • Energy to blow mould 11 • Manufacture • PET body moulded 38 g • PP cap moulded 5 g • Use • Refrigeration 5 days • Transport 200 km • Disposal • Recycling ? Yes • Transport 15,000 km • Materials • PET body 38 g • PP cap 5 g Drink container: the scoping tool • Transport, MJ / tonne.km • Sea freight 0.11 • Truck 1.3 • Refrigeration, MJ / m3.day • Refrigeration (4oC) 10.5 • Freezing (-5oC) 13.0

  17. Eco-properties: production Production energy 77 - 85 MJ/kg Carbon dioxide 1.9 - 2.2 kg/kg Recycle ?  Eco-properties: manufacture Injection / blow moulding 12 - 15 MJ/kg Polymer extrusion 3 - 5 MJ/kg Environmental notes. PE is FDA compliant - it is so non-toxic that it can be embedded in the human body (heart valves, hip-joint cups, artificial artery). CES Edu record for PET Polyethylene terephthalate (PET) • General Properties • Density 939 - 960 kg/m3 • Price 1.3 - 1.45 US $/kg • Mechanical Properties • Young's Modulus 0.6 - 0.9 GPa • Elastic Limit 17.9 - 29 MPa • Tensile Strength 20 - 45 MPa • Elongation 200 - 800 % • Hardness - Vickers 5.4 - 8.7 HV • Fracture Toughness 1.4 - 1.7 MPa.m1/2 • Thermal Properties • Max Service Temp 100 - 120 C • Thermal Expansion 126 - 198 10-6/K • Specific Heat 1810 - 1880 J/kg.K • Thermal Conductivity 0.4 - 0.44 W/m.K • Electrical Properties • Resistivity 3 x 1022- 3 x 1024.cm • Dielectric constant 2.2 - 2.4 Energy/CO2 efficient design Thermo-mechanical design

  18. Material Energy breakdown for PET bottle

  19. 2. Strategy Material Disposal Manufacture Use • Select: • recyclable • non- toxic materials • Minimize: • process energy • CO2/kg • Minimize: • weight • heat loss • electrical loss • system • Minimize: • embodied energy • CO2/ kg Applying the strategy 1. Analysis Assess energy use over life Production Manufacture Use Disposal Energy

  20. Hybrids Embodied energy of materials per kg CES Edu Level 2 DB

  21. Hybrids Embodied energy of materials per m3 CES Edu Level 2 DB

  22. Glass PE PET Aluminum Steel Embodied energy per unit of function Function: contain 1 litre of fluid Mass 325 38 25 20 45 g Mass/litre 433 38 62 45 102 g/litre Emb. energy14 80 84 200 23 MJ/kg Energy/litre 8.2 3.2 5.4 9.0 2.4MJ/litre • Steelwins on material embodied energy • Processing? • Recycling? • Toxicity?

  23. Mobile barrier Static barrier Energy M Mf U D M Mf U D Bending strength per unit material energy Criterion Material choice depends on function and system Function Absorb impact, transmit load to energy-absorbing units or supports Dominant phase of life Bending strength per unit mass Selected materials CFRP, Ti-alloy, Al-alloy Cast iron, steel

  24. Supercars Diesel Petrol Hybrid Concept, embodiment, detail

  25. The main points • Scoping LCA gives quick, approximate “portrait” of energy / CO2burden of products. A practical tool for assessing eco-burden and guiding (re)-design. • Separate the life-phases • Material • Manufacture • Use • Disposal Base material choice on relative contributions to stress • Consider system dependence • Optimise within one concept • Explore alternative concepts The CES EduPack provides data to help with this

  26. Demo

  27. Exercises: Eco-comparisons (1) • 8.1 Rank the commodity materials • Low carbon steel • Age hardeing aluminum alloys • Polyethylene • by embodied energy/kg and embodied energy/m3. Use the means of the ranges given in the database. • (Energy per unit volume is that per unit weight multiplied by the density) Answer Polyethylene Density 939 – 960 kg/m3 Embodied energy 76.9 – 85 MJ/kg The Al alloy has the highest energy content, by far, by both measures. Per kg, steel has the lowest energy content; by volume, it is polyethylene.

  28. Exercises: Eco-comparisons (2) 8.2.Plot a bar chart for the embodied energies of metals and compare it with one for polymers, on a a “per unit yield strength” basis. Use the “Advanced” facility to make the function Which materials are attractive by this measure? Answer. The most attractive, from an embodied energy per unit strength perspective are carbon steels and cast irons. Among polymers, biopolymers like Polylactide (PLA) and starch based polymers perform well.

  29. Exercise: the nature of embodied energy 8.3Iron is made by the reduction of iron oxide, Fe2O3, with carbon, aluminum by the electro-chemical reduction of Bauxite, basically Al2O3. The enthalpy of oxidation of iron to its oxide is 5.5 MJ/kg, that of aluminum to its oxide is 16.5 MJ/kg. Compare these with the embodied energies of cast iron, of carbon steel, and of aluminum, retrieved from the CES database (use means of the ranges given there). What conclusions do you draw? Cast iron, grey Embodied energy 16.4 – 18.2 MJ/kg The embodied energies are between 3 and 12 times larger than the thermodynamically necessary to reduce the oxide to the metal. There are several reasons. The largest is that industrial processes, at best, achieve an energy-efficiency of around 33% (the blast furnace, used to make iron, is remarkably efficient). Then there is transport, the energy to run, heat, light and maintain the plant in which the metal is made, and many other small contributions to the total energy input per unit of output. Aluminum alloys Embodied energy 184 – 203 MJ/kg

  30. End of Unit 8

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