Energy and the New Reality, Volume 1: Energy Efficiency and the Demand for Energy Services Chapter 6: Industrial Energy Use L. D. Danny Harvey harvey@geog.utoronto.ca Publisher: Earthscan, UK Homepage: www.earthscan.co.uk/?tabid=101807 This material is intended for use in lectures, presentations and as handouts to students, and is provided in Powerpoint format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see www.earthscan.co.uk for contact details. Major Industrial Sectors - Iron & Steel - Aluminum - Copper - Cement - Glass - Pulp & Paper - Plastics - Petroleum refining - Chemicals (including fertilizers – Chapter 7) - Food processing (Chapter 7) - General manufacturing Figure 6.1 Industrial Energy use in 2005 as a percent of total energy use in various regions 60 Percent Industrial 50 Global Average: 37.5% 40 30 20 10 0 Africa Europe North America Central America South America Asia Oceania Figure 6.2a Industrial energy use in OECD countries in 2005 Textile and Non-specified 11% leather 2% Iron and Steel 16% Construction 1% Wood and wood products 2% Chemical & Petrochemical 20% Pulp and Paper 13% Food and Tobacco 7% Non-Ferrous metals 6% Mining and Quarrying 2% Machinery 7% Transport equipment 2% Non-metallic minerals 8% Figure 6.2b Industrial energy use in non-OECD countries Non-specified 25% Textile and leather 3% Iron and Steel 25% Construction 1% Wood and wood products 1% Chemical & Petrochemical 13% Pulp and Paper 2% Food and Tobacco 7% Mining and Quarrying 2% Machinery 4% Transport equipment 2% Non-Ferrous metals 5% Non-metallic minerals 11% on C N w at er on ia um in Fe er rt ili an ze d r fla tg St la ai ss nl es s st ee l C op pe C r hr om iu m ta d d le ne in i m m A in at e al es D m lu A hy Et la te re en t em C ra nd pe Pa St ee l Gobal Primary Energy Use (EJ/yr) Figure 6.3 Global primary energy use for production of the 12 commodities (other than the production of fuels) using the most energy 35 30 25 20 15 10 5 0 Definitions: • Primary metals: made from virgin ores (raw materials) • Secondary metals: recycled from scrap • Feedstock energy: The energy content of fossil fuels that become part of the material in a commodity. It is equal to the heating value of the final product. • Process energy: energy (in the form of heat or electricity) used to power a chemical transformation. It is equal to the total energy inputs to the production process minus the embodied energy of the final products • Embodied energy: the total amount of energy (process + feedstock) that went into making something Overview of global production of major commodities of energy interest Commodity Cement Steel Paper & Paper Products Lime Plastics Ammonia Ethylene Non-fibrous glass Aluminum Copper Production (Mt/year) 2600 1320 Primary Energy Intensity (GJ/t) 4-8 20-40 Principle Energy Input Coal, NG, or Oil Coal Ave C Emission (tC/t) 0.3 0.7 365 277 260 132 110 95 38 16 16-42 0.4 50-160 36-44 20-30 20-25 ~160 ~85 Biomass Electricity Oil Natural gas Oil Coal, Oil, or NG Electricity Electricity 0.0 0.03 1-3 0.7 0.6 0.6 4.2 2.2 Figure 6.4: Trends in production of major commodities (solid lines use the left scale, dashed lines the right scale) 3000 2000 Cement Steel Paper Plastics Aluminum Copper x 10 Zinc x 10 250 200 1500 150 1000 100 500 50 0 1960 1970 1980 1990 Year 2000 0 2010 Annual Production (Mt) Annual Production (Mt) 2500 300 Processing of Minerals • Most minerals of interest occur as oxide minerals in ores (rock bodies with various minerals mixed together, besides the ones of interest) • The steps in processing minerals are thus – separation of the minerals of interest from the other minerals in the ores - removal of oxygen (reduction) - purification Reduction of oxide minerals, calcination of CaCO3 (during production of cement), and processing of silica and limestone to make glass all release CO2 • Iron: 2Fe2O3 +3C → 4Fe+3CO2 • Alumina (made first from bauxite): 2Al2O3 + 3C → 4Al+3CO2 • Cuprite (produced by roasting Cu-containing minerals): 2CuO+C→2Cu+CO2 • Calcination of limestone to make cement: CaCO3→CaO+CO2 • Production of glass: nSiO2 + mCaCO3 + xNa2CO3 + .... → Glass + CO2 In the case of iron, aluminum and copper, the C used for reduction comes from fossil fuel inputs, or from materials (such as C anodes) made from fossil fuels, and so is accounted for in the energy use data combined with the emission factors (kgC/kg fuel) for these energy inputs. Thus, fossil fuel energy inputs play two roles in producing Fe, Al, or Cu – as a source of C for the reduction reaction and as a source of heat (through combustion) to drive the reaction. In the case of calcination of limestone or transformation of raw materials into glass, however, the C that is released as CO2 comes from the raw materials themselves and so is not accounted for in the energy use data. Thus, you will find that national CO2 emission data are given separately for coal, oil, natural gas, and production of cement. This latter category refers to the CO2 that is produced through the chemical reactions involved in the formation of cement, and is in addition to the CO2 released from burning the fossil fuels used at the cement plants. Chemical emissions from the production of glass are only about 1% of those from cement (due to about 30 times less global production and a 3 times smaller emission factor), and tend to be ignored in compilations of national emissions. Iron and Steel Figure 6.5a: World production of primary + secondary raw steel 1400 Raw Steel Production (Mt/yr) 1200 1000 Other Ukraine S Korea Russia US Japan China Compounded Growth Rates, 2000-2007: China: 19.1%/yr ROW: 2.8%/yr Overall: 6.4%/yr 800 600 400 200 0 1995 1997 1999 2001 Year 2003 2005 2007 Figure 6.5b: Production of raw steel in 2007 Other 28% China 37% Italy 2% Brazil 2% Germany 3% Ukraine 3% S Korea 4% Russia 5% US 7% Japan 9% Figure 6.5c End uses of steel in the US in 2003 Service Centers and Distributors 27% Other 33% Construction 22% Containers 3% Transportation 15% Figure 6.6 Anthropogenic iron flows in 2000 (Tg Fe/yr) Source: Wang et al (2007, Environmental Science and Technology 41, 5120–5129) Traditional Steps in Making Steel: • • • • Beneficiation of iron ores (removal of impurities) Agglomeration of fine particles Reduction of iron ore to make crude iron Refining of crude iron to make steel (removing impurities, adding trace elements) • Shaping of steel into final products Reduction of iron ore • Commonly done in a blast furnace • C from coke (which is like charcoal, and made from coal by driving off volatile materials) is used as a reducing agent • Theoretical minimum energy requirement is 6.8 GJ/t • Practical lower limit is 10 GJ/t, best blast furnaces use about 12 GJ/y, world average is about 14.4 GJ/t • Coke provides some of the heat energy required (as well as serving as a reducing agent), with the balance supplied by coal Refining of crude iron • 3 options are: Open-hearth furnace, Basic Oxygen Furnace (BOF), Electric air furnace (EAF) • BOF requires pure oxygen (separated from air) • EAF is used for scrap metal and in the new direct-reduction process • Energy by EAFs per tonne of steel fell in half between 1960-1900 Figure 6.7 Refining of reduced iron to produce steel 1200 1000 Other Electric arc furnace Prodcution (Mt/yr) Basic oxygen furnace 800 Open Hearth Furnace 600 400 200 0 1975 1990 Year 2003 Figure 6.8 Energy used by EAFs per tonne of crude steel High power/ long arc operation Oxygen and carbon lance manipulator Computer control Foaming slag practice Water cooled roof/oxy-fuel burner 10 8 Oxygen lancing 6 630 kWh/tcs 4 Water cooled walls Bottom tap hole Pneumatic bath stirring Ladle furnace Secondary metallurgy EBT (slag-free) Scrap preheating Higher electric power supply Electricity consumption 350 kWh/tcs DC technology 2 6.5 kg/tcs Electrode consumption 2.2 kg/tcs 0 1965 1970 1975 1980 1985 1990 year Source: de Beer et al (1998a, Annual Review of Energy and the Environment 23, 123–205) Shaping of Steel, Traditional Method Produce steel in cubical blocks, small bars, or slabs using a continuous caster, then convert into final products using various hot mills (heating and cooling occurs between steps, with an energy loss each time) Shaping of Steel, Alternative approaches: Cast the molten steel closer to the desired final shape, using thin-slab casting, thin-strip casting, or powder metallurgy • Thin-strip casting has the potential to reduce energy use for shaping by 90-95% • In thin-strip casting, the length of the production line has been reduced from 500-800 m to 60 m – about a factor of ten reduction! Alternative Approaches for Reducing Iron Ore: • Blast Furnace with coke through reaction with CO while the ore is still solid (traditional approach) • Direct reduction of the ore using coal or natural gas to produce a H2-rich gas (or direct use of purchased H2) combined with a DC current • Smelting reduction of the ore in the liquid state, directly using coal Figure 6.9a Primary energy use with best current blastfurnace/BOF route for making primary steel 1.9 Coal Iron ore Coke oven 12.4 Blast furnace Ore preparation 2.6 Fluxing agent Pellets Pig iron 0.3 Basic oxygen furnace 0.6 Crude steel Scrap (10%) Refining casting Cast steel 2.1 19.9 GJ/t Rolling Shaping Quality flat and long products Figure 6.9b Primary energy use with advanced blast-furnace/BOF making primary steel 1.2 Coal Iron ore Coke oven 11.9 Blast furnace Ore preparation 2.2 Fluxing agent Pellets Pig iron -1.0 Basic oxygen furnace 0.6 Crude steel Refining casting Cast steel 1.5 16.9 GJ/t Rolling Shaping Scrap (10%) By comparison, the present world average primary energy requirement for primary steel is about 36 GJ/t Quality flat and long products Figure 6.9c Primary energy use with best current direct reduction/EAF steel making 1.4 Iron ore Ore preparation Natural gas or Coal 13.4 3.5 Direct reduction Sponge iron 0.6 Crude steel Oxygen Fossil fuel Refining casting 1.0 Cast steel Rolling Shaping 20.0 GJ/t Flat products/ shapes Figure 6.9d Primary energy use with advanced direct reduction/EAF steel making and advanced refining, casting, and shaping 1.4 Iron ore Ore preparation Natural gas or Coal 11.3 Direct reduction Sponge iron 3.5 Electric arc furnace Crude steel Oxygen Fossil fuel 0.75 Refining casting shaping 16.9 GJ/t Flat products/ shapes Figure 6.9e Primary energy use with advanced smelting-reduction/BOF steel making and advanced refining, casting, and shaping 13.4 -1.0 Smelting reduction Basic oxygen furnace Iron ore Coal Oxygen Pig iron (Scrap) Crude steel 0.75 Refining Casting Shaping 13.2 GJ/t Quality flat and long products This is a reduction by 63% (~two thirds) compared to the present average primary energy use for primary steel of 36 GJ/t. The savings is due in part to an assumed improvement in the efficiency in generating the electricity that is supplied to the steel plant from 40% to 60%. Figure 6.10a Current mill using scrap steel to make secondary steel Scrap 3.4 Electric arc Crude furnace steel 0.6 Refining casting Cast steel 1.0 5 GJ/tcs Rolling Shaping Bar/shapes Flat products Oxygen Fossil fuel Source: de Beer et al (1998a, Annual Review of Energy and the Environment 23, 123–205) Figure 6.10b Advanced mill using scrap steel to make secondary steel Scrap 0.5 2.3 Scrap upgrading Electric arc furnace Crude steel 0.75 Refining casting Shaping 3.5 GJ/tcs Bar/shapes Flat products Fossil fuel Oxygen de Beer et al (1998a, Annual Review of Energy and the Environment 23, 123–205) This is a reduction by 50% from the present world average of 7 GJ/t for secondary steel. The savings is due in part to an assumed improvement in the efficiency in generating the electricity that is supplied to the steel plant from 40% to 60%. Source: de Beer et al (1998a, Annual Review of Energy and the Environment 23, 123–205) Steel Summary: Primary Energy Requirements • Primary Steel: - 36 GJ/t world average today, assuming electricity supplied at 40% efficiency • Secondary Steel: - 7 GJ/t world average today – a reduction by about a factor of 5 compared to primary steel Steel Summary (continued): • Current average with 32% secondary: • Future average with 90% secondary and current best practice as average: This is a reduction by a factor of 3.8 • Future average with 90% secondary, best projected energy intensities for primary and secondary steel: This is a reduction by a factor of 4.5 • All of the above plus 60% electricity supply efficiency instead of 40%: This is a reduction by a factor of 5.8 26.3 GJ/t 6.9 GJ/t 5.9 GJ/t 4.5 GJ/t • Thus, the overall potential reduction in the average primary energy intensity of steel is a factor of 4.5 to 6 Aluminium Figure 6.11a World production of primary aluminium Primary Aluminium Production (kt/yr) 40 35 30 Other US Canada Russia China 25 20 15 10 5 0 1995 1997 1999 2001 Year 2003 2005 2007 Figure 6.11b Production of primary aluminium in 2007 Other 22% China 32% UAE 2% S Africa 2% Norway 3% India 4% Brazil 4% Australia 5% Russia 11% US 7% Canada 8% Figure 6.11c End uses of aluminium in the US in 2003 Other 4% Construction 16% Consumer Durables 7% Transportation 36% Containers & Packaging 23% Machinery & Equipment 7% Electrical 7% Production of Aluminium • Mining of bauxite (mostly Al(OH)3 and AlO(OH)) (most of the mining is through strip mining) • Refining of bauxite into alumina (Al2O3) -grinding, then digestion with caustic soda at high T and P • Smelting of alumina into aluminium, through electrolysis of alumina that has been dissolved into cryolite (Na3AlF6) at 900oC -both the cathode and anode are made of C -the net reaction is 2Al2O3+3C→4Al+3CO2 Figure 6.12 Aluminium Mass Flow in 2005 Bauxite 168.2 MATERIAL FLOW METAL FLOW Alumina 61.3 Total Products Stored in Use Since 1888 560.7 Primary Aluminium used 31.6 Ingots 63.8 Fabricated and Finished Finished Products (input) Products (output) 62.5 37.6 Building 32% Transport 28% o.a.Automotive 16% Net Addition 2005: 22.2 Remelted Aluminium 32.3 Other Applications 1.1 o.a.Recycled Aluminium 15.3 Traded New Scrap 1.3 Bauxite Residues 70.8 and Water 36.1 Fabricator Scrap 17.0 Metal Losses 1.3 Traded New Scrap 7.9 Other 11% Engineering and Cable 28% Packaging 1% Old Scrap 7.4 Not Recycled in Under Investigation: 3.3 2005 3.5 From this diagram it can be seen that a little over 4 t of dry bauxite are mined for every tonne of primary aluminium that is produced Source: IAI (www.world-aluminium.org) Figure 6.13 Secondary energy used in making aluminium metal Materials, Fuels 17.6% Smelting, Electricity 56.4% Mining 0.4% Refining, Electricity 1.7% Refining, Fuels 23.9% Figure 6.14: World average electricity use for the production of aluminium 30 Electricity Use (MWh/t) 25 20 15 10 5 0 1950 1960 1970 1980 Year 1990 2000 2010 Figure 6.15 Efficiencies of individual processes in producing aluminium 80 70 Efficiency (%) 60 50 40 30 20 10 0 Alumina Anode Aluminium Refining Production Smelting Primary Casting Secondary Casting Rolliing Extrusion Shape Casting Source: Thekdi (2003, Aluminum 2003, The Minerals, Metals & Materials Society, 225–237) Figure 6.16: World production of primary and secondary aluminium, and the secondary share of total production Production (Mt/yr) or % Secondary 50 Primary aluminum 40 Secondary aluminum Percent Secondary 30 20 10 0 1971 1976 1981 1986 Year 1991 1996 2001 2006 Aluminium Summary: Primary Energy Requirements • Primary aluminium: - 193 GJ/t world average today, assuming electricity supplied at 40% efficiency • Secondary aluminium: - 17 GJ/t world average today – more than a factor of 10 smaller than for primary aluminium • Average of the above (with 18.7% recycled) is 160.3 GJ/t (more than 5 times that of steel) Aluminium Summary (continued): • Future average with 90% secondary and current average energy use separately for primary and secondary Al: This is a reduction by a factor of 4.6 • Future average with 90% secondary, best projected energy intensities for primary and secondary steel: This is a reduction by a factor of 6.9 • All of the above plus 60% electricity supply efficiency instead of 40%: This is a reduction by a factor of 8.4 34.5 GJ/t 23.3 GJ/t 19.1 GJ/t • Thus, the overall potential reduction in the average primary energy intensity of aluminium is a factor of 5 to 8 Copper Figure 6.17a World copper mining 20 Copper Extraction (Mt/yr) 18 16 14 Other Russia Indonesia Australia US Peru Chile 12 10 8 6 4 2 0 1995 1997 1999 2001 Year 2003 2005 2007 Figure 6.17b Copper mining in 2007 Other 19% Chile 36% Kazakhstan 3% Poland 3% Zambia 3% Canada 4% Russia 5% Indonesia 5% Australia 6% US 8% Peru 8% Figure 6.17c End uses of copper in the US in 2003 Consumer & General Products 11% Transportation Equipment 10% Industrial Machinery & Equipment 10% Electrical & Electronic Products 21% Building Construction 48% Figure 6.18 Anthropogenic copper flows in ca. 1994 in Gg Cu/yr Source: Graedel et al (2004, Environmental Science and Technology 38, 1242–1252) Production of Copper Metal • Copper minerals occur either as oxides (combined with CO3 or SiO2) or as sulfides (combined with S). • A given ore body tends to have oxide minerals in the upper zone (close to air) and sulfide minerals in the lower zone • There are two different produciton routes: Hydrometallurgy (acid related) – tends to be applied to oxide minerals Pyrometallurgy (heat related) – tends to be applied to sulfide minerals • In the transition zone of the ore body, either technique can be applied, but there has been a shift to more use of hydrometallurgy Steps in Pyrometallurgy (1): • Extraction from the mine, crushing, and grinding • Froth flotation – mix with chemical foaming agents, as ore minerals adhere to bubbles and float to surface and can be skimmed off. Produces a concentrate of 25-30% copper, mostly CuFeS2. • Smelting – heating the concentrate in oxygen-enriched air to 1200-1250oC, with addition of silica (SiO2), partially oxidizing the Fe and S, releasing SO2 gas, and producing a molten copper matte (Cu2S*FeS) and molten slag (FeO*SiO2): CuFeS2 + O2 + SiO2 → Cu-Fe-S + FeO*SiO2 + SO2 + heat Steps in Pyrometallurgy (2): • Converting – separating the Cu2S from the FeS in the copper matte and oxidizing the S. Produces blister copper (99% copper) and further iron slag Cu2S + O2 → 2Cu° + 2SO2 + heat 2FeS + 3O2 + SiO2 → 2FeO•SiO2 + 2SO2 + heat The smelting and converting reactions are exothermic – and the heat released is sufficient to maintain the required temperature once the process has started. This eliminates the need for fuel energy in state-of-the-art smelters & converters, but requires continuous rather than batch processing. Steps in Pyrometallurgy (3): • Fire refining. This is a process for removing most of the remaining O and S and, like previous steps, is carried out at a temperature of about 1200oC. The O is removed as CO2 through reaction with a hydrocarbon reducing agent (typically 5-7 kg per tonne of copper), while S is removed as SO2 through reaction with atmospheric oxygen. Fire refining is carried out in special rotating furnaces that are heated by combusting hydrocarbon fuels. The liquid product is directly cast into thin anodes that are interleaved with cathodes in electrorefining cells. The copper anodes still contain about 0.15% O and 0.002% S. Steps in Pyrometallurgy (4): • Electro-refining. This is an electrolysis process that involves electrochemically dissolving copper from impure copper anodes into a CuSO2-H2SO4-H2O electrolyte and electroplating pure copper from the electrolyte onto a cathode without the impurities. After 7-14 days the cathodes are removed from the cell and the pure metal is scrapped off. The reactions are: Cuºanode → Cu 2+ + 2e- at the anode, and Cu 2+ + 2e- → Cuº at the cathode. Steps in Hydrometallurgy: • Leaching – excavate ores, pile in a heap, and add acid to dissolve the ore, or drill holes into the ore body and pump in acid, and weeks to months later, pump out the leachate • Concentration – add organic solvents to the acid solution, to selectively absorb copper from the solution • Refining – an electrolysis process called electrowinning, similar to electro-refining except that the anode consists of an inert Pb-Sn-Ca mixture. The copper is electroplated onto the cathode from the Cu solution supplied from the concentration step rather than supplied by dissolution of a copper anode. The combination of acid leaching and electro-winning is called the solvent-extraction electro-winning process, or SX-EW. As previously noted, SX-EW (hydrometallurgy) is being used more and more. There are three disadvantages with this process: • Any gold, silver, or molybdenum in the ore is lost • The fraction of the Cu present in the ore that can be extracted is much less than using pyrometallurgy • Electro-winning requires much more electricity (18002800 kWh/t) than the electro-refining process (300-400 kWh/t) used in pyrometallurgy On the other hand, hydrometallurgy only requires crushing the mined ore to a 10-13 cm size, rather than grinding it down to the size of individual mineral grains (100-200 μm) (as in pyrometallurgy). The grinding stage is very energy intensive. If 20 kWh of electricity are required per tonne of ore, the amount require per tonne of copper is 20 kWh/(copper fraction in the ore). Thus, for ore with 1% copper (a grade of 1%), the grinding energy requirement is 2000 kWh/tonne – comparable to the energy used for electro-winning (1800-2800 kWh/t) in the hydrometallurgy route. Thus, the amount of energy used in producing copper increases rapidly with decreasing grade of ore. This is because mining and concentrating the Cu account for 1/3 to 1/2 half of the total energy used in producing the pure metal for 1% ores, in contrast to iron and aluminum, where the metal concentrations in the ores are high (4050% for Al, 60-70% for Fe) and mining and concentrating are a very small fraction of the total energy use Figure 6.19 Estimated primary energy requirement to produce rolled copper tubes 300 Primary Energy (GJ/t of copper) Pyrometallurgy, High Pyrometallurgy, Low 250 Hydrometallurgy, High Hydrometallurgy, Low 200 150 100 50 0 0.0 0.5 1.0 1.5 2.0 Grade of Ore (% copper) 2.5 3.0 Table 6.12: Average grade of the remaining Cu ores in different parts of the world R e g io n N o r th A m e r ic a L a tin A m e r ic a E urope O c e a n ia E a s t A s ia C e n tr a l A s ia A fr ic a G rade (% c o p p e r ) 0 .4 7 1 .0 0 1 .5 0 1 .5 6 1 .1 3 1 .5 1 3 .0 0 Source: Giurco (2005, Towards sustainable metal cycles: The case of copper’, PhD Thesis, Department of Chemical Engineering, University of Sydney) Energy Use in Producing Secondary Copper • Depends strongly on the extent to which the scrap copper is contaminated with other materials • Purest copper can be simply melted and recast • Less pure copper is re-melted and cast as anodes, followed by electro-refining • Impure copper must be smelted and converted Figure 6.20 Flowchart for refining and smelting of contaminated copper Copper bearing scrap and coke Low grade ZnO fume Blast furnace Granulated slag Molten black copper (80+% Cu) Scrap (2-6% Sn) Solidified converter slag Mixed Sn/Pb/Zn oxide dust Converting furnace Molten rough copper (95+% Cu) Scrap (>96% Cu) Solidified anode furnace slag Reduction furnace ZnO fume Sn-Pb alloys Anode furnace Anodes (99.5% Cu) Anodes scrap Electrolytic furnace Cathodes < 20 ppm impurities Nickel sulfate & Cu + precious metals slimes Source: Davenport et al (2002, Extractive Metallurgy of Copper, Elsevier Academic Press, Amsterdam) Figure 6.21a Global production of primary and secondary copper, and scrap flow 18 16 Primary Production Secondary Production Annual Flow (Mt) 14 Old scrap flow 12 10 8 6 4 2 0 1966 1971 1976 1981 1986 Year 1991 1996 2001 2005 Figure 6.21b Recycling rate of scrap copper 8000 0.4 7000 Fraction Recycled 0.3 5000 4000 0.2 3000 2000 0.1 Price 1000 0 1966 0.0 1976 1986 Year 1996 2005 Fraction Recycled Price (2005 US$/t) 6000 Figure 6.22 Distribution of the copper stock in the US of 238 kg per person Transportation 28, 12% Railway, Motor ships,aircraft, 12 Vehicles,16 Equipment 39, 16% Domestic, 13 Industrial, 26 Air conditioning and refrigeration, 16 Building & Construction 76, 32% Wiring, 28 Plumbing, 32 Infrastructure, 95, 40% Energy requirements for recycling Cu: • ~ 4 GJ/t for Grade 1 scrap • ~ 20 GJ/t for Grade 2 scrap (≥ 94% Cu) • ~ 50 GJ/t for Grade 3 scrap (contaminated) By comparison, 80-90 GJ/t are required for 1% ore and 180 GJ/t for 0.3% ore (however, one worker gives the primary energy requirement as only ~ 50 GJ/t for 0.35% ore) So, except possibly for contaminated scrap compared to cases of primary Cu with low energy requirements, recycling saves a lot energy – potentially reducing the energy requirement by more than a factor of 40 This dismal picture will likely change soon, as Cu mining is expected by some analysts to peak in about 20 years, due to supply constraints Figure 6.23 Quantity of metals vs grade of ores, showing two modes – corresponding to mineral crystals and atomic substitution Atomic substitution Mineral crystals Ore Grade Source: Ayres et al (2003, The Life Cycle of Copper, Its Co-Products and Byproducts, Kluwer, Dordrecht) Ways to limit demand for copper: • More compact and smaller housing – less length of wire needed • Smaller growth in electricity demand • Replacement of copper with glass fibre in telecommunications • Replacement of copper with PVC pipes in plumbing (PVC pipes are less energy-intensive) Cement Figure 6.24a World cement production 3000 Cement Production (Mt/yr) 2500 2000 Other Japan US India China Compounded Growth Rates, 2000-2007: China: 11.5%/yr Rest of world: 3.5%/yr Overall: 6.9%/yr 1500 1000 500 0 1995 1997 1999 2001 Year 2003 2005 2007 Figure 6.24b Cement production in 2007 Other 26% China 49% Mexico 2% Italy 2% Turkey 2% Spain 2% S Korea 2% Russia 2% Japan 3% India US 6% 4% Figure 6.24c Disposition of cement produced in the US in 2003 Other 2% Masonry cement 4% Building material dealers 3% Contractors 6% Concrete products 13% Ready-mix concrete 72% Production of Cement • Crushing, grinding, and blending of raw materials into a homogenous powder • Heating the raw materials to over 1400ºC in a kiln to produce clinker • Grinding the clinker to a fine powder and mixing it with additions to form cement Concrete is a mixture of about 10% cement and 90% aggregates (sand and gravel), with cement serving as the binding material. When stronger concrete is required, the proportion of cement is increased, so this increases the embodied energy of the concrete (as cement is the energy-intensive part of concrete). Table 6.17: Composition of Portland cement Portland cement (named after the Peninsula Portland in England) is 95% clinker and 5% gypsum. The elemental composition of clinker is as follows: Chemical formula CaO SiO 2 Al2 O3 Fe 2O3 MgO K2O+Na2O Other (incl. SO3) Shorthand notation C S A F M K+N …(? ) Amount 65.0% 22.0% 6.0% 3.0% 1.0% 0.8% 2.2% Source: van Oss and Padovani (2002, Journal of Industrial Ecology 6, 89–105 ) Reactions occurring inside a cement kiln: • Calcination, CaCO3 → CaO + CO2 • Clinkering, 29C+8S+2A+F→2C2S + 6C3S+C4AF “alite” “belite” Table 6.18: Composition of clinker and roles of the different components Chemical formula Ca3SiO5 Shorthand Description notation C 3S Tricalcium silicate (“alite”) C 2S Dicalcium silicate (“belite”) Amount Comment C 3A Tricalcium aluminate 0-15% Ca4Al2Fe2O10 C4AF Tetracalcium aluminoferrite 0-15% CaSO4 •2H2 O C?H2 Calcium sulfate dihydrate 3-7% (gypsum) Ca2SiO4 Ca3Al2O6 50-70% 10-30% Imparts early strength Imparts long-term strength Acts as a flux and contributes to early strength Acts as a flux; contributes to longterm strength, and imparts gray color Controls early setting Source: van Oss and Padovani (2002, Journal of Industrial Ecology 6, 89–105 ) Figure 6.25 Layout of the zones in various cement kilns Preheater/Procalcinor Tower Rotary Kiln Dry, Preheater Precalcinor Kiln ~ 50m Preheater Tower Dry, Preheater Kiln ~ 90m Long Dry Kiln ~ 130m Wet Kiln ~ 200m Drying Zone Raw Materials o 20-200 C Drive off Water Preheat Zone o 200-750 C Heating Upper, “cool” end Calcining Zone o 750-1000 C CaCO3 CaO+CO2 Sintering or Burning Zone o Cooling Zone 1200-1450 C CaO+SiO2+Al2O3+Fe2O3 C3S+C2S+C3A+C4AF C S A F Clinker o 1450-1300 C Fuel Burner Lower, “hot” end Clinker Cooler Source: Van Oss and Padovani (2002, Background Facts and Issues Concerning Cement and Cement Data, Open File Report 2005-1152, US Geological Survey, Reston, Virginia) The binding properties of cement occur when it is mixed with water, which forms hydrated molecules that cling to each other. The binding requires materials with a high surface area (which must therefore be ground to a very fine powder) and materials that can form hydrates. This is relevant to the possibility of producing lower-energy alternatives to traditional Portland cement. • Hydration of alite (gives early strength): 2C3S+6H(water)→C3S2H3 (CSH gel)+3CH (hydrated lime) • Hydration of belite (gives long term strength): 2C2S + 4H(water)→C3S2H3+CH Current national average energy use for producing cement: • • • • • • • • • Theoretical minimum for clinkering: 1.67 GJ/t Japan, 3.1 GJ/t Germany, 3.8 GJ/t European average, 4.1 GJ/t China, 5.0 GJ/t India, 5.0 GJ/t Canada, 5.1 GJ/t USA, 5.5 GJ/t Columbia, 6.1 GJ/t Options for reducing energy use in making cement: • • • • Shifting from wet to dry kilns Better recovery of waste heat from kilns Improved grinding techniques Reducing the clinker portion (95% in Portland cement) by blending in other materials, such as -blast furnace slag -fly ash from coal-fired powerplants -volcanic materials -natural limestone (easy to grind) -ordinary quartz sand (hard to grind) Figure 6.26 Supply of fly ash and blast furnace slag 200 Cement Demand 180 Slag supply 160 Fly Ash supply Mt in 2020 140 120 100 80 60 40 20 SE Asia Japan Korea India China AU & NZ Africa Middle East FSU E Europe W Europe L America USA Canada 0 Source: Humphreys and Mahasenan (2002, Toward a Sustainable Cement Industry, Substudy 8: Climate Change, World Business Council for Sustainable Development, Cement Sustainability Initiative, www.wbcsdcement.org Other options: • Development of entirely new cements • Integrated production of cement and electricity (using waste heat at 300ºC from the clinker cooler) • Use of concentrated solar energy • Improved durability of cement (or of steel reinforcing) • Reduced use where feasible without compromising safety (i.e., baffled basement walls) Glass Glass • Types: container, flat or “float”, and fibrous (insulation, textile fibreglass) • Raw materials: sand, limestone, maybe soda ash, borate, feldspar and clay • Production process: - preparation of inputs - melting of raw materials and refining (removal of bubbles) - shaping the molten glass into the desired final shapes Table 6.22: Typical inputs to glass Material Sand (SiO2) Limestone (CaCO3 or CaMg(CO3 )2 ) Soda ash (Na2 CO3 ) Borate Feldspar Clay Total Chemical CO2 emission (tCO2/t) Chemical CO2 emission (tC/t glass) Container glass 0.65 0.19 0.22 0.00 0.11 0.00 1.17 0.17 0.046 Type of glass Flat (float) Fiberglass glass Insulation 0.73 0.54 0.24 0.19 0.23 0.22 0.00 0.10 0.00 0.11 0.00 0.00 1.20 1.16 0.20 0.16 0.054 0.044 Source: Ruth and Dell’Anno (1997, Resources Policy 23, 109–124) Textile Fiberglass 0.54 0.12 0.00 0.15 0.00 0.34 1.15 0.15 0.041 Types of furnaces for melting of raw materials: • Regenerative, recuperative - use fuels (natural gas), maximum efficiency now ~50% ((heat added to raw materials) / (fuel energy used)), could be pushed to 75% (giving a 1/3 reduction in fuel use) • Electric – efficiency of 70-90%, but must account for losses in generating and transmitting electricity. - applied to fibrous glass Typical primary energy use today • Flat and container glass: • Fibrous glass at 40% electricity supply efficiency: • Fibrous glass at 60% electricity supply efficiency: • Savings through recycling: ~ 20-30 GJ/t ~ 60 GJ/t ~ 40 GJ/t ~ 20-30% USA UK Greece Italy Spain Ireland Portugal France Finland Denmark Belgium Sweden Germany Netherlands Austria Percent Recycled Figure 6.27 Rates of Recycling of Glass Containers 100 90 80 70 60 50 40 30 20 10 0 Paper and Paper Products Production of Paper and Paper Products • • • • Acquisition of fibres Pulping Bleaching Manufacture of paper from pulp Figure 6.28a Production of different kinds of paper and paper products 400 350 Other Wrapping & Packaging Production (Mt/yr) 300 Household & Sanitary Printing and Writing 250 Newsprint 200 150 100 50 0 1961 1966 1971 1976 1981 1986 Year 1991 1996 2001 2006 Figure 6.28b Production of paper and paper products by region 400 350 Production (Mt/yr) 300 250 Africa Oceania L America & Caribbean North America Europe Asia 200 150 100 50 0 1961 1966 1971 1976 1981 1986 Year 1991 1996 2001 2006 Figure 6.29 Annual per capita paper consumption USA Canada Oceania Europe Central America & Caribbean South America Asia Middle East & North Africa Sub-Saharan Africa 350 kg/person/year 300 250 200 150 100 50 0 1960 1970 1980 1990 Year 2000 2010 Japan Canada US Ireland Norway Switzerland Netherlands Sweden UK Slovenia Austria Spain Denmark Portugal France Finland Hungary Italy Belgium Estonia Slovak Republic Romania Latvia Czech Republic Lithuania Greece Poland Bulgaria Cyprus Malta Paper Recycling Rate (%) Figure 6.30 Rates of paper recycling 100 90 80 70 60 50 40 30 20 10 0 Sources of Fibre for Paper: • Roundwood (wood removed from forests or other areas) • Sawmill residues • Discarded paper Pulping Processes • Mechanical • Chemical • Semi-chemical Mechanical Pulping • Breaks apart the wood by grinding • Both fibre and lignin are turned into pulp, so the pulp yield is high - 85% of the original wood mass. • Lots of heat is generated that can be used elsewhere in the paper mill Chemical Pulping • Soften wood chips with steam • Then cook for several hours at 160-170oC under pressure in a highly alkaline solution (contains NaOH and Na2S) called white liquor • This dissolves the lignin, leaving only the fibres (40-55% of the wood) to form pulp • The spent liquor (now called black liquor) and bark are burned to produce heat and electricity for use by the pulp and paper mill Figure 6.31 Annual trade of different kinds of pulp 250 Recycled Non-wood Pulp Production (Mt/yr) 200 Dissolving Semi-chemical Chemical 150 Mechanical 100 50 0 1961 1966 1971 1976 1981 1986 Year 1991 1996 2001 2006 Bleaching • Process of removing residual lignin from the pulp, which otherwise causes the pulp to be dark • Requires a chemical (Cl2, ClO2, H2O2 or O3) that oxidizes the lignin but not the fibre (cellulose and hemi-cellulose) • Cl2 bleaching causes severe water pollution, so there is a move toward elemental chlorine-free (ECF) bleaching (using ClO2) or totally chlorinefree (TCF) bleaching (using H2O2 or O3) Steps in making paper from pulp • Addition of water sufficient to give a water:fibre ratio of 100:1 (i.e., a consistency of 1%). • Forming – spread stock over a wire screen, then remove sufficient water through gravity and suction to give a consistency of 20% • Pressing – increase consistency to 40-45% by passing the sheet with felt through 3-4 pairs of press cylinders • Drying – pass sheet through 40-50 steam-heated cylinders, to give a consistency of 90-95% Options to reduce energy use per unit of paper made • Integration of pulp and paper mills • Heat recovery from mechanical pulping • Reductions in market demand for bleached paper products (through consumer awareness) • More efficient drying of initial pulp sheets • More efficient cogeneration • Increased recycling Cogeneration in the pulp and paper industry • Currently very inefficient – only 10-15% electrical efficiency, in part to avoid producing excess electricity because it can’t be sent to the grid in many jurisdictions due to monopolistic practices by power utilities • Potential electrical efficiency of 27-30% (and 72% overall efficiency) with gasification of black liquor followed by combined-cycle power generation. Some problems still to be worked out • This could make the pulp and paper mill a net source of energy – this would be renewable, biomass-based energy Other possibilities: • Production of dimethyl ether (a substitute for diesel fuel in the transportation sector) from biomass wastes, integrated with pulp and paper production, is potentially more attractive in terms of energy saving than is cogeneration of heat and electricity • Development of completely closed mills – all liquids flow back through the mill, rather than be ejected with heat (and pollutants) to the environment. At present it would be hard to make use of the saved heat. The energy balance in recycling of paper includes: • The net energy required to make paper from virgin fibres, taking into account the energy that can be produced from black liquor and forestry residues and the energy required to make any fertilizers that are applied to plantation forests • The energy that can be obtained from incineration of waste paper to cogenerate heat and electricity if it is not recycled (landfilling is totally out of the question) • The energy required during recycling of waste paper, including the energy required to collect waste paper and transport it to the recycling plant • The energy that could be supplied from the biomass that is saved when waste paper is recycled Rough energy balance: • Paper from wood: gross energy requirement: Potential energy production: Net energy requirement: • Paper from waste paper: ~ 29 GJ/t ~ 31 GJ/t -2 GJ/t ~ 20 GJ/t So, in terms of gross energy requirements, recycling gives a 30% savings. However, in terms of net energy use, recycling increases the energy requirement. There is, of course, more to it • Incineration of waste paper with cogeneration saves ~26 GJ/t of primary energy, so the overall energy gain with production of paper from virgin fibres and later incineration is ~ 28 GJ/t • BUT – for each tonne of waste paper that is recycled, 2.2 tonnes of biomass are saved. • For the set of assumptions in Table 6.29, this saves 52 GJ of primary energy, for a net energy gain of ~ 32 GJ/t • Thus, recycling is slightly better from an energy point of view, but for slightly different assumptions, it could be slightly worse. Plastics • Produced by reacting steam with hydrocarbons at high T and P, thereby breaking the C-C bonds in the hydrocarbons (so this process is called steam cracking) • Most are made from naptha, an intermediate product in the refining of petroleum • Cracking produces methane, olefins, and aromatics, which are the precursors to various kinds of plastic Figure 6.32a: Plastics production in 2007 Middle East & Africa 8% FSU 3% Latin America 4% Europe 24% Rest of Asia 17% Japan 6% NAFTA 23% China 15% Figure 6.32b: Uses of plastics in Europe Other 28% Packaging 37% Electrical and Electronic 6% Automotive 8% Building & Construction 21% Figure 6.33 Plastics and other petrochemicals made from petroleum Source: Geiser (2001, Materials Matter: Towards a Sustainable Materials Policy, MIT Press, Cambridge) Most plastics are long chains of molecules (monomers), hence the prefix “poly” in the names of most plastics. The major plastics are: • • • • Polyethylene Polypropylene Polyvinyl chloride Polystyrene Figure 6.34 Production of plastics in Europe Low density polyethylene 17% Other 19% Polyurethane 7% High density polyethylene 12% PET (polyethylene teraphthalate) 7% Polystyrene 8% Polyvinyl chloride 12% Polypropylene 18% Energy Use in Making Plastics • Feedstock Energy: 20-40 GJ/t • Process energy: 20-120 GJ/t • Total energy: 50-160 GJ/t Energy is used for heating to up to 1000oC (to “crack” naphtha or other raw materials), for chilling (sudden cooling to as low as -150oC is needed for some of the reaction and separation steps), and for pumps and motors Urea resin Feedstock Energy Polyvinyl chloride 140 Polyvinyl acetate Process energy PET 160 Phenol formaldehyde resins Synthetic rubber Polyethylene Polyacrylonitrile Polystyrene Polyurethane Melamine resin Polycarbonate Polyacrylate Epoxy resin Nylon-6 Nylon-6,6 Energy Input (GJ/tonne) Figure 6.35 Primary energy inputs to make plastic 180 120 100 80 60 40 20 0 Energy Savings Potential • For the cracking step – 25% or more savings should be typically possible in the medium term (with modest further improvement of existing state-of-theart crackers) • Improved cogeneration (if present) or implementation of cogeneration (if not already used) (both steam and electricity are required) • Adjustment of piping systems, use of variable speed drives (mentioned in the Buildings chapter), better chiller controls and increasing the temperature of chilled water produced by the chillers reduced electricity use by 50% in one case Energy Savings Through Recycling • The feedstock energy is saved (except possibly for small material losses during the recycling process) • Some (often large) portion of the process energy is also saved (no need to crack hydrocarbons again) • Energy savings is typically 85-90% according to the one source • Obstacle: the need to separate different kinds of plastic from one another Figure 6.36 Disposition of plastics waste in Europe 30 Energy recovery 25 Mechanical recycling Feedstock recycling Sent to landfill 28% Mt per Year 20 20% 15 10 5 0 1995 1997 1999 2001 2003 2005 2007 Year Source: Plastics Europe (2008, The Compelling Facts about Plastics 2007: An Analysis of Plastics Production, Demand and Recovery for 2007 in Europe, www.plasticseurope.org) Where was this photo was taken? Answer: in the middle of the Pacific Ocean, 1400 km north of Hawaii! Eastern and Western Pacific Garbage Patches – about 3-5 Mt each? Floating debris occasionally washes ashore on Hawaii Urban runoff Contents of the gut of an albatross, killed by ingesting floating plastic garbage For more information, go to www.greatgarbagepatch.org Petroleum refining • Potential for 20% savings in the US if no other changes occur. However: • 10% increase in energy use if S concentration is decreased from 30 ppm to 1 ppm to meet more stringent pollution emission requirements (current most-stringent regulations are around a 15 ppm limit) • Increasing energy use with a shift to heavier grades of oil as the lighter grades are depleted. • Big jump in processing energy use for oil shales and tar sands Table 6.31: Energy Use for Petroleum Refining US conventional onshore oil Canadian conventional onshore oil Conventional offshore oil Heavy oils Canadian tar sands Energy Use (GJ/tonne oil) Extraction Refining Total 1.3 2.9 4.2 2.4 3.0 5.4 3.9 3.0 6.9 2.9 3.0 5.9 12.9 3.0 15.9 Energy Use as a % of Energy in Products 10.0 12.8 16.4 14.1 37.8 Source: (S&T)2 Consultants (2005, Documentation for Natural Resources Canada’s GHGenius Model 3.0, www.ghgenius.ca ) Chemicals, General Considerations • Importance of improved catalysts • Importance of advanced membranes (for separating materials) in reducing general energy use in the chemical industry • Importance in capturing exothermic heat (most reactions in the chemical industry are exothermic, and the total exothermic release equals 60% of the overall process energy used in the manufacture of products produced by exothermic reactions) Figure 6.37 Membranes MICROFILTRATION ELECTRODIALYSIS retains suspended matter passes dissolved substances and water retains nonionic matter passes ionic matter GAS SEPARATION ULTRAFILTRATION retains membrane impermeable gases passes membrane permeable gases retains dissolved matter passes some macromolecules, microsolutes, ions, and water REVERSE OSMOSIS H H H retains all ions passes water M M M COUPLED TRANSPORT passes carrier complex ions M+denotes monovalent metal ion H +denotes hydrogen DIALYSIS retains dissolved matter passes microsolutes and water Source: Goldemberg et al (1998, Energy for a Sustainable World, Wiley Eastern, New Dehli) Cogeneration and heat management • It is estimated that the amount of waste heat in exhaust flows and pressurized gases in US industry that could be used in practice to generate electricity is sufficient to supply about 13% of US electricity demand, with no extra fuel use • Efficiencies of electricity generation, and overall efficiencies in industrial cogeneration are quite low, but leave room for substantial improvement (although there are often logistical difficulties in upgrading existing facilities) Figure 6.38a Industrial cogeneration using an internal combustion engine or simple-cycle gas turbine Waste Hea t e1 h3 ICE or Gas Turbine, F1 Heat Recovery 1 h1 h2 2 e1 = h2 = (1- F1 1) 2F Useful Heat 1 1 Typical electrical efficiencies: 22-35% Typical overall efficiencies: 39-54% overall = +(1- 1 )1 2 Figure 6.38b Industrial cogeneration using a steam turbine Waste Heat e2 h7 Steam Turbine h5 4 Heat Recovery h6 Useful Heat 5 h4 h3 Boiler, 3 h3 = 3F2 e2 = 3 4F2 h4 = (1- 3)F2 h5 = 3(1- 4)F2 h6 = 5(h4+h5) overall F2 Typical electrical efficiency: 9-13% Typical overall efficiency: 61-68% = (e2+h6)/F2 Figure 6.38c Combined-cycle industrial cogeneration Waste Heat e4 e3 h13 Gas Turbine 6=0.29 Steam Turbine 8=0.12 h11 Heat Recovery h12 9=0.51 h10 h9 F3 h8 Boiler, F4 ha = 7(h8+F4) e4 = 8h9 h11 = (1- 8)h9 e3 = 5F3 h8 = (1- 6)F3 overall Useful Heat 7 =0.8 h10 = (1- 7)(h8+F 4) h12 = 9(h10+h11) = (e3+e4+h12)/F3+F4) Typical electrical and overall efficiencies: 30-36% and 60-70% Pinch Analysis • Many industrial processes have simultaneous heating and cooling requirements • Pinch analysis is a powerful technique integrating the two (when cold and hot fluid streams are brought together, the hot stream will be cooled and the cold stream warmed) • Heating and cooling energy savings of 50% or more can sometimes be achieved. Figure 6.39 Pinch Analysis o Temperature C 150 497 Units 100 • Heating only above the pinch point • Cooling only below the pinch point • No heat flow from above to below the pinch point should be allowed 50 Pinch Point 417 Units 1000 Units Heat load