Throughout the world, nations are seeking ways to decrease CO2 emissions and to reduce their dependency on fossil fuels, especially oil and gas deriving from so-called politically unstable regions. The efforts comprise the energy sector (heat and electricity) as well as the transport sector. An increasing use of biomass as energy carrier is in both sectors a prioritised way of achieving these aims, and for the transport sector, the conversion of biomass to ethanol is at present the technological pathway most strongly promoted by governments in countries all over the world.
Recent research has, however, shown that by following this path, we will lose more than we gain on both CO2 emission and fossil fuel dependency. Being renewable, CO2 neutral and storable, biomass is a priority resource for fossil fuel substitution in general. Investigations of the magnitude of biomass that is or can be made available for energy purposes - be it from waste, agricultural residues or energy crops - show, however, that biomass is very limited compared to the potential use of it. Even in the most optimistic near term scenarios (30 years ahead), the total physically available biomass can at maximum substitute around 30% of the fossil fuel consumption, and including economic aspects it is much less. Moreover, an economic analysis shows that biomass will not be able compete in a liberal fuel market, i.e. we will need to subsidise it in one way or the other - and money is a limited resource as well. Therefore, there is not enough biomass for 'everyone', not physically and not in terms of money to promote its use. This leads to the conclusion that any use of biomass for energy purposes will have to compare to the lost opportunity of using it for something else.
In this perspective, the choice to use biomass for bio-ethanol production will not lead to reduction but to increase in CO2 emission and fossil fuel dependency. Both first and second generation bio-ethanol suffer from a biomass-to-ethanol energy conversion efficiency as low as 30-40 %, and moreover external fossil fuels are used to run the conversion. There is only a small difference between first and second generation, the difference being that second generation has a slightly lower biomass-to-ethanol energy efficiency due to the energy needed to pre-treat the cellulose and other compounds before fermentation. Co-products are produced along with the ethanol, but they do not improve the energy balance enough for bio-ethanol to compete with alternative uses of the biomass. When using biomass to substitute fossil fuels in heat & power production, a close to 100% substitution efficiency is achieved. The best alternative for CO2 reduction and oil saving is, therefore, that biomass substitutes gas in the heat & power sector and gas substitute oil in the transport sector. By taking this path, we overall achieve almost twice as high a CO2 reduction and save almost twice as much oil, as if we want to substitute the oil via car engines through conversion to ethanol.
We must acknowledge that society will use natural gas and other fossil fuels for heat & power production for the next 40 years ahead. Throughout this period of time, therefore, we can save them more efficiently there, and we will only lose on CO2 and oil dependency, if we use our scarce biomass for ethanol. After this period of time, when we are facing a world without oil and gas, it is, moreover, very dubious if we can accept the very low efficiency of the combustion engine of say 25% energy efficiency and a conversion efficiency in ethanol fermentation of up to say 50% resulting in an overall energy conversion of 10-20% for transportation. At that time, the electric car/fuel cell car has probably had time enough to mature, and it has a much higher energy efficiency. Therefore, bio-ethanol is not the right intermediate (short term) technology, and it is not the right long term technology either
|Titel||ECCE6 Book of Abstracts|
|Redaktører||Rafiqul Gani, Kim Dam-Johansen|
|Forlag||Technical University of Denmark|
|Status||Udgivet - 2007|
|Begivenhed||European Congress of Chemical Engineering - Copenhagen, Danmark|
Varighed: 16. sep. 2007 → 20. sep. 2007
Konferencens nummer: 6
|Konference||European Congress of Chemical Engineering|
|Periode||16/09/2007 → 20/09/2007|