Environmental impacts of future bioenergy pathways: the case of electricity from wheat straw bales and pellets

Abstract

This study presents the life cycle assessment of electricity generation from straw bales and pellets. Straw is the most abundant biomass residue in Europe and its use for energy purposes is promoted on the premise of high greenhouse gas savings. This assumption has delayed the study of sustainability of straw-fired systems on a broader sense and the literature on the topic is almost absent. This study uses data from specific literature and emissions inventories to model a number of straw pathways. The plant modeled is a medium-scale straw-fired power plant of 50 MWth capacity. The results show that electricity from straw-fired power plants can indeed realize high greenhouse gas savings compared both with existing coal plants and with the European electricity mix. The savings are in the range 70-94%. The influence of the geographical origin of straw is analyzed by using datasets for the cultivation of wheat in five different European countries. The highest emissions are recorded for the case of straw from Spain due to the small yields, whereas cultivation processes in United Kingdom and the Netherlands show high environmental impacts due to the high level of fertilization. Other environmental impacts are evaluated, such as acidification potential, eutrophication, particulate matter emissions, and photochemical ozone formation. The bioenergy system scores worse than the current European electricity mix for all the categories. However, it is important to notice that in Spain and United Kingdom the straw system shows lower impacts compared with the local average coal electricity. Finally, the study investigates the 'break-even' distance at which the higher emissions from the pellets production are paid off by the saved emissions in their transport compared with the bales. The results show that no reasonable break-even distance exists for road transport, whereas advantages for pellets are evident in any configuration for transoceanic transport.

Global warming and energy yield evaluation of Spanish wheat straw electricity generation – A LCA that takes into account parameter uncertainty and variability

“…Several studies suggest that lignocellulosic biomass sources for heat and electricity production may perform better in GHG assessments when compared with crops used as feedstock for first generation liquid biofuels [10][11][12][13]. Crop residues [14][15][16][17] and dedicated crops [3,4] can be used as source of lignocellulosic biomass for bioenergy whereas the first ones usually offer higher resource efficiency [2]. Furthermore, the use of dedicated energy plantations for bioenergy in Europe could produce indirect land use changes rising food prices in other countries.…”

“…When data were scarce for a parameter we adjusted triangular or uniform distributions taking into account the data available and our knowledge of the phenomenon being studied. There are several LCAs that evaluate use of wheat straw for combined heat and power (CHP) [14][15][16][17] but we are not aware of any published LCA including parameter uncertainty and variability systematically for all the aspects described previously.…”

Biomass Resources: Agriculture

“…Denmark, the frontrunner in Europe, uses approximately 1.8 million tons of straw each year for energy purposes [18]. In recent years, multiple biofuel plants converting straw to ethanol have come online.…”

The Comparative Life Cycle Assessment of Power Generation from Lignocellulosic Biomass

“…Burning biomass results in various emissions and most emissions are CO2, H2O with 0.3% NOx and some CO and CH4 using poorly-maintained equipment. In addition, the total emissions include some pollutants of 0.1% sulphur, 0.1% chlorine, and trace quantities of inorganic minerals, such as calcium, potassium, silicon, phosphorus, and sodium [26]. The compositions of emissions depend on many factors, including the growing environment of plants, the plant species, any contaminants in the soil, water, or air, etc.…”