Evaluation of the emergy investment needed for bioethanol production in a biorefinery using residual resources and energy
Introduction
The promotion of biofuel has been one of the core elements of the European Union policy in the energy and climate change areas. Since 2003, the European Commission (EC) has emanated several directives and official communications regarding the transport sector (e.g. EC, 2009a, EC, 2009b, EC, 2010, EC, 2011). The interest on the production of fuel alcohol from cellulosic biomass is growing worldwide due to small GHG emission in the overall production process and availability of biomass as agricultural or forestry residue or as byproduct from other processes (Tan et al., 2008, Tolan, 2010). Nevertheless, even though there is high potential for lignocellulosic feedstock, the cost of lignocellulosic biofuels is not competitive with conventional fuels (Huang et al., 2011, Wiloso et al., 2012). In the last years, the idea of a biobased economy emerged: the integration of industrial plants and agricultural ecosystems has been proposed to jointly produce food, energy and chemicals (Dale and Kim, 2010, Ghaley and Porter, 2013, Tiezzi, 2002, Tiezzi et al., 1991). The agricultural and energy components are integrated in a so-called Industrial Symbiosis (Lombardi et al., 2012), a kind of closed loop supply chain. This perspective implies that the output of one plant can be the input for other plants leading to environmental and economic benefits by virtue of a more efficacious use of resources (Gonela and Zhang, 2013, Quariguasi Frota Neto et al., 2010, Veiga and Magrini, 2009). These environmental and economic improvements have been demonstrated, for example, by Jacob (2006) for the Kalandburg Industrial Symbiosis.
For all these reasons, we hypothesized a second generation bioethanol production chain within the Province of Siena (Tuscany, Italy). The performance of the production process has been also evaluated, accounting for resource use and quantifying the environmental investment required. The hypothesized production chain is completely fed by local residual inputs. In particular, the utilization of geothermal heat (residue of the geothermal electricity generation) to supply steam to the industrial plant in order to produce bioethanol from residual straw from crop production has been conjectured. The system production target is designed to accomplish the European requirements for partial substitution of bioethanol for gasoline by 2020 (EC, 2009 a). The efficiency of the production as well as the environmental cost-benefit evaluation of this hypothesized integrated biorefinery has been assessed by means of an emergy based approach.
It is worth to point out that, besides chemical analyses and evaluation of yields in producing bioethanol, systemic accounting methods are useful to understand the level of sustainability of the whole production process in order to account for natural resource exploitation. In fact, as pointed out by Almeida et al. (2013), “it is essential to use proper methodologies to assess the real environmental costs of any cleaner production application to support decision making”. For this purpose, the emergy approach, already used for the evaluation of bioethanol production both for first (e.g. Bastianoni and Marchettini, 1996, Brown and Ulgiati, 2004, Brown and Ulgiati, 1999, Dong et al., 2008, Pereira and Ortega, 2010, Ulgiati, 2001 Dong et al., 2008, Pereira and Ortega, 2010, Ulgiati, 2001) and second generation (e.g. Agostinho and Ortega, 2013, Coppola et al., 2009, Fahd et al., 2012, Ghaley and Porter, 2013, Zhang and Long, 2010), is considered in this paper. Emergy is a holistic and thermodynamics-based metric for the physical evaluation of environmental resources and services supporting a system or a process; it contributes to identify and measure all the inputs (energy and matter) to the system, expressed in a common unit that is the solar emergy joule (semj).
Previous studies present the emergy per unit product (Unit Emergy Value) of bioethanol, calculated in a traditional way; we believe that these values can be compared with the value of the emergy investment per unit product here calculated. The production of bioethanol is feasible in presence of residues; this system considers residues as primary inputs, without taking into account the processes behind their production because these are aimed at producing other goods (food and electricity). Consequently, we have to consider the methodological implications and the results of the analysis that derive from these hypotheses.
Since this process is supposed to be inserted and integrated within a functioning system (e.g. a territorial system), we identify and calculate the emergy investment of bioethanol production to capture the contribution of unexploited flows of resources and obtain usable products (energy in this case). A proper addition of energy, materials, tools or machines in the process is considered and measured in terms of emergy, in order to express the environmental costs of the produced bioethanol from residues; the overall eco-efficiency in the exploitation of resources by the bioethanol production chain, identified with the emergy investment per unit product, is also investigated. Moreover, the supposed project contributes to the substitution of 10% of gasoline consumption in the Province of Siena with bioethanol. Therefore, a portion of gasoline consumed in the Provincial area is saved, and the corresponding emergy is calculated and compared, as a benefit, to the cost of the investment for this substitution.
Section snippets
Bioethanol production system
The hypothesized bioethanol production system is represented in Fig. 1 by using the Energy System Language defined by Odum (Odum, 1991, Odum, 1994, Odum, 1996). Three main assumptions must be considered to take advantage of the peculiarities of the Province of Siena:
- 1)
the production plant treats the residual straw available within the Province of Siena and uses the residual geothermal heat to fuel the process.
- 2)
It must be located in the northwestern part of the Province of Siena, where the majority
Results
From the energy diagram reported in Fig. 1 all the flows of energy and matter involved in the bioethanol production process can be identified and inventoried. Concerning straw collection, the human work and the use of machineries (evaluated as diesel consumption and steel) have been taken into consideration according to Coppola et al. (2009), while the transportation phase has been evaluated according to Pulselli et al. (2008). With regard to the bioethanol production, raw data have been taken
Comparison between the unit emergy investment and the unit emergy value of fuels
The crucial point in this analysis is the fact that residual straw and residual geothermal heat are considered free (if not properly used, they can be classified as wastes), because the energy production system (i.e. the biorefinery) is integrated within a larger framework including cereal and geothermal electricity production. A planned investment enables to exploit residual resources to obtain a very important product for local energy and environmental policy. It consists in the plant, the
Conclusions
Emergy evaluation gives the opportunity to identify and compare the contribution of many inputs to a production process, highlighting the role of environmental resources supporting human activities. In this paper emergy analysis is used to evaluate the consequences of the substitution of bioethanol for 10% of gasoline consumption in the area of the Province of Siena (Italy). The emergy investment, representative of the environmental cost of the project, is more than compensated by the
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