YSCN0037 Feeding the World - Energy-Topic-7-Oct-21st-2009

YSCN0037 Feeding the World - Energy-Topic-7-Oct-21st-2009 -...

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Unformatted text preview: YSCN0037 Feeding the World Energy consumption in food production Lecturer: Professor David Lee Phillips Department of Chemistry How much is a Joule? The joule (symbol J) is the unit of energy in the International System (SI) of Units . It is named for James Prescott Joule (1818- 1889) It is the energy exerted by a force of one Newton (SI unit of force) acting to move an object through a distance of one metre. Energy scale Examples of energy flow: 1 calorie (4.184 J) of heat is required to raise the temperature of 1 g water by 1 o C 1 Calorie (1000 calorie = 4184 J) is often used in nutritional science. 1 kilowatt-hour (1 kWh=3.6MJ) is a common unit used in electrical bills. A 100W light-bulb consumes ~3 GJ of energy if is light up continuously throughout the year. The energy released by the largest hydrogen bomb tested (in 1961) is around 240 PJ SI unit prefix Meaning Kilo (k) 1000 (10 3 ) Mega (M) 1000000 (10 6 ) Giga (G) 1000000000 (10 9 ) Tera (T) 1000000000000 (10 12 ) Peta (P) 1000000000000000 (10 15 ) Exa (E) 1000000000000000000 (10 18 ) How much energy is needed for producing the chemicals? Fertilizers Production of nitrogen fertilizers are mostly based on the Haber process 2N 2 +3H 2 2NH 3 The minimum energy needed to produce 1 ton of ammonia from nitrogen and hydrogen is 20.9 GJ However, the actual energy requirement is higher than that as the reactants (nitrogen and hydrogen) have to be generated by other materials. Energy inputs in fertilizer productions When the process first became commercialized (~1930), the amount of energy input is ~100 GJ/t (which used coke as a raw material). As the technology improves, the energy needed to produce ammonia have lowered to about 40 GJ/t (around 48 GJ/t N). Currently, some of the best plants can produce ammonia at around 30 GJ/t. Energy inputs in fertilizer productions The extra energy needed to produce urea from ammonia is 9-10 GJ/t N . When other energy inputs (like prilling [making the solid into small granules] and packaging) are taken into account, it takes about 55-58 GJ/t N to produce urea. Summary: Fertilizers derived from ammonia would need ~50-100 MJ/kg to produce Energy inputs in fertilizer productions Phosphorus fertilizers: Mining phosphates cost about 4-5 GJ/t, while the subsequent treatment with acids requires more energy. Single phosphates need a total of 18-20 GJ/t P to produce Concentrated phosphates need 25 GJ/t diammonium phosphate requires 28-33 GJ/t P for production. Summary: Around 20-30 MJ for each kg of phosphorus Energy inputs in fertilizer productions Potassium fertilizers: The energy needed to produce K fertilizers is much smaller than that of the N ones....
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This note was uploaded on 12/08/2010 for the course SCIENCE 0037 taught by Professor Dr. during the Spring '10 term at HKU.

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YSCN0037 Feeding the World - Energy-Topic-7-Oct-21st-2009 -...

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