Abstract
The increasing demand for energy is leading to the increasing use of renewable resources, such as biomass, resulting in the significant development of the wood energy sector in recent years. On the one hand, and to a certain extent, the sector has generated many benefits. On the other hand, the challenges related to wood ash (WA) management such as increasing tonnages, landfilling, restrictive regulations for reuse, etc., have been weighing more heavily in the debate related to the wood energy sector. However, all studies have assumed that no environmental impacts can be attributed to WA production. This study aims at discussing this assumption, whether the WA is a waste or a co-product of heat generation. In the first place, WA deposits were estimated using the biomass database and ash content from the literature regarding the collective, industrial and tertiary biomass power plants (BPP) in the French region of Brittany. Then, the impacts of the generated WA were estimated using the attributional life cycle assessment (LCA) method through two different impact allocation procedures (IAP), “from cradle to gate” (excluding the waste treatment). In Brittany, for the year 2017, an estimated amount of 2.8 to 8.9 kilotons of WA was generated, and this production should increase to 5 to 15.7 kilotons by 2050. The LCA conducted through this study gave an emission of 38.6 g CO2eq/kW h, with a major contribution from the production of the wood chips. Considering the environmental aspect, the IAP analysis indicated that energy and economic allocations were not relevant, and that, using the mass allocation, the environmental production of WA could represent 1.3% of the impacts of the combustion process in BPP. Therefore, WA, and especially the fly ash, can be considered as a waste from BPP heat production, without any environmental impact attributed to its generation.
Highlights
The biomass burnt in biomass power plants (BPPs) constitutes an important alternative to fossil energies for the production of heat which, in a very few cases, can be combined with the production of power [1]
Beyond the estimation of wood ash (WA) deposits for the reference year, the analysis studies the development prospects of the wood energy sector in Brittany which are commonly defined by the Regional Air Climate and Energy Schemes (RACES) for the 2050 horizon [21]
2050 (b) horizon are met [21], tonnages could potentially increase by more than 75% with 5000 to 15,700 tons of ash generated. Note that these results reflect optimum tonnages of WA produced in the studied area and can, be subject to uncertainties. They can be lower in reality due to several factors influencing WA production
Summary
The biomass burnt in biomass power plants (BPPs) constitutes an important alternative to fossil energies for the production of heat which, in a very few cases, can be combined with the production of power [1]. Wood biomass is considered a CO2 -neutral source of energy because, while growing, wood nearly absorbs the amount of CO2 released when burnt [2]. Wood biomass is found in different forms, such as forest wood chips, sawmill residues, end-of-life industrial wood or pellets, which can be burnt. Higher amounts of ash are produced when using the raw materials of biomass for the production of energy [3]. The wood ash composition varies greatly according to the biomass composition, the combustion technology used and other parameters, but industrial wood ash usually contains multiple oxides in various proportions: SiO2 , CaO, Al2 O3 , Fe2 O3 , Na2 O, Al2 O3 , Fe2 O3 , MgO, and K2 O [5,6].
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