ОңТҮстік қазақстан медицина академиясы, хабаршы №4 942, 2021 жыл, том 2
жүктеу/скачать 3,39 Mb. Pdf көрінісі
|
№4942021том2
| sugar cane
grown in Brazil shows one of the greatest benefits. This is confirmed by several studies which all have found that emission reductions of sugar cane ethanol in Brazil far exceed those from grain-based ethanol produced in Europe and the United States. KALTNER et al. (2005) estimate that the total life-cycle GHG emissions reductions associated with the ethanol industry in Brazil are equivalent to 46.6 million tons annually. These are approximately 20 % of Brazil’s annual fossil fuel emissions. This is due to high site productivity in Brazil and its favorable climate for sugar cane, which is highly productive and only needs low inputs of fertilizer. Additionally almost all conversion plants use bagasse for process energy which also reduces GHG emissions. Many plants also co- generate heat and electricity. Well-to-wheel CO 2 emissions of sugar cane-ethanol are estimated to be, on average 0.20 kg per liter of fuel used, versus 2.82 kg for gasoline. These figures based on CO 2 also take methane and N 2 O emissions into account (both mainly released from farming, from the use of fertilizers and from N 2 fixed in the soil by sugar cane then released to the atmosphere). Apart from sugarcane, other combinations of biofuel feedstock and conversion processes can reduce well-to-wheels CO 2 -equivalent GHG emissions to near zero, too. An example therefore is enzymatic hydrolysis of cellulose where ethanol is produced and biomass is used as process fuel. In contrast, ethanol from corn shows very small GHG reductions within all potential feedstock options (WWI 2006 p. 153). Using commercial processes, the use of ethanol derived from grains, brings a 20% to 40% reduction in well-to-wheels CO 2 -equivalent GHG emissions, compared to gasoline . For Europe, ethanol production from sugar beets is important, due to its high dominance in several European countries. Some European studies, which are summarized by OECD/IEA (2004 p. 58f), show that this feedstock and conversion process can provide up to a 56% reduction in well-to-wheels GHG emissions, when compared to gasoline. Nevertheless, some results point out that using ethanol to make ETBE results in even greater GHG savings than blending ethanol directly with gasoline. This is because ETBE replaces MTBE, which has relatively high energy demand, whereas ethanol replaces gasoline, which requires less energy for production than does MTBE. The major part of engine exhaust streams during ethanol combustion consists of the components nitrogen, carbon dioxide and water. All three components are non-toxic to human health. However, about 1.4% of petrol engine exhaust emissions are composed of more or less harmful substances to human health. Apart from the above mentioned emissions, fuel combustion emits particulate matter (PM), volatile organic compounds (VOCs), nitrogen oxides (NO x ), carbon monoxide (CO) and a variety of other toxic air pollutants. VOCs and NO x are precursors for tropospheric ozone. Momentary weather conditions and local |