Exergy Based Assessment of the Production and Conversion of Switchgrass, Equine Waste, and Forest Residue to Bio-Oil Using Fast Pyrolysis

Abstract

The resource efficiency of biofuel production via biomass pyrolysis is evaluated using exergy as an assessment metric. Three feedstocks, important to various sectors of U.S. agriculture, switchgrass, forest residue, and equine waste, are considered for conversion to bio-oil (pyrolysis oil) via fast pyrolysis, a process that has been identified as adaptable to on-or near-farm application. Biomass and biofuel production pathways are defined, material flows are determined, and exergy in-and outflows associated with biomass production and conversion are computed, including the depletion of exergy from its natural state (cumulative exergy demand, CExD). Sources of exergy depletion are quantified and categorized by energy carriers, e.g., electricity and diesel fuel, and materials, e.g., fertilizer, as well as renewable and nonrenewable resources. Yields for biomass to bio-oil conversion by fast pyrolysis are determined experimentally. Breeding factors, a measure of exergy production (the ratio of the chemical exergy of the output product to process exergy inputs), are determined for the production of biomass and bio-oil. The quantification of exergy depletion for process pathways enables the possible identification of more sustainable (resource efficient) pathways for biomass and bio-oil production. It is shown, for example, that feedstocks grown primarily for biomass such as switchgrass may be less sustainable using the exergy measure compared to use of residue (e.g., forest thinnings) or waste biomass (e.g., equine waste). With regard to the pyrolysis process, there is substantial reduction in exergy depletion when the coproducts noncondensable gases and biochar are recycled and utilized as a source of heat. The sustainability of biomass production and conversion, as measured by exergy depletion, is strongly influenced by energy carriers. The study reveals that the method of electricity production, i.e., on-site generation or grid electricity, as well as the choice of grid electricity can have a significant impact on sustainability. The exergy content of the bio-oil produced varies from 24 to 27 MJ/kg bio-oil, which is much lower than traditional fuels. However, the cumulative exergy depletion for the production and conversion to bio-oil varies from approximately 4 to 11 MJ/kg bio-oil, which is also much lower than traditional fuels. Breeding factors for biomass production and conversion to bio-oil based on cumulative exergy depletion vary from approximately 2 to 5, demonstrating the potential exergy benefit of bio-oil production using fast pyrolysis.

Ternary Blends of Renewable Fast Pyrolysis Bio‐Oil, Advanced Bioethanol, and Marine Gasoil as Potential Marine Biofuel

“…Other authors analyzed the sustainability impacts of biofuels by applying the exergy and cumulative exergy demand concepts, based on the maximum theoretical work from a substance if it were to achieve equilibrium with the environment to deeply investigate BOs from different feedstocks . This concept indicates the available work and cumulative exergy measurement of the depletion associated with the conversion of the natural feedstock into products (the whole transformation processes) and is expressed by the functional unity “GWP per energy basis”.…”

Feedstock Recycling of Plastics Waste for Electricity or Fuel: An Exergy Approach

“…The basic principles of the methodology used to assess the impact of industrial processes on the environment and their energy efficiencies have been discussed in numerous scientific articles. Many scientists have analyzed the energy efficiency of thermal processes [12][13][14][15], energy production, fuel gasification and/or combustion [16][17][18][19][20][21][22] and biomass gasification [23][24][25][26][27][28]. Some studies have examined waste utilization methods and waste management systems based on comparative exergetic assessments [29][30][31][32][33][34] and the energetic/exergetic efficiency of selected processes [35,36].…”

“…No cooling system is needed. (3) The amount of sawdust has to be increased from 28 kg/h (that was required in a similar plant converting wastes to liquid product) to 34 kg/h. The stream of flue gases also increased to 1129.8 kg/h.…”

Energy and exergy analyses of sewage sludge thermochemical treatment

“…The energy analysis of the thermochemical treatment of sewage sludge (SS) by means of torrefaction and pyrolysis has barely been investigated, apart from the energetic assessments carried out by Ding and Jiang [28], Caballero et al [29], Kim and Parker [30], Ábrego et al [31], Gil-Lalaguna et al [32], Capodaglio et al [14] and Ruiz-Gómez et al [33]. Exergy analyses of processes such as torrefaction and pyrolysis of biomass are not very common in the literature [12,[34][35][36][37][38] and the information about the exergy analysis of the thermochemical treatment of sewage sludge is even scarcer. Given this little information available and its usefulness when evaluating the feasibility of these processes, the aim of the present work was to assess the energy and exergy analyses of sewage sludge utilization by different thermochemical treatments (specifically, torrefaction and pyrolysis).…”