Fourteen mature technology biomass refi ning scenarios -involving both biological and thermochemical processing with production of fuels, power, and/or animal feed protein -are compared with respect to process effi ciency, environmental impact -including petroleum use, greenhouse gas (GHG) emissions, and water use-and economic profi tability. The emissions analysis does not account for carbon sinks (e.g., soil carbon sequestration) or sources (e.g., forest conversion) resulting from land-use considerations. Sensitivity of the scenarios to fuel and electricity price, feedstock cost, and capital structure is also evaluated. The thermochemical scenario producing only power achieves a process effi ciency of 49% (energy out as power as a percentage of feedstock energy in), 1359 kg CO 2 equivalent avoided GHG emissions per Mg feedstock (current power mix basis) and a cost of $0.0575/kWh ($16/GJ), at a scale of 4535 dry Mg feedstock/day, 12% internal rate of return, 35% debt fraction, and 7% loan rate.Thermochemical scenarios producing fuels and power realize effi ciencies between 55 and 64%, avoided GHG emissions between 1000 and 1179 kg/dry Mg, and costs between $0.36 and $0.57 per liter gasoline equivalent ($1.37 -$2.16 per gallon) at the same scale and fi nancial structure. Scenarios involving biological production of ethanol with thermochemical production of fuels and/or power result in effi ciencies ranging from 61 to 80%, avoided Modeling and Analysis: Comparative analysis of mature biomass refining scenarios $1.24/gallon). Most of the biofuel scenarios offer comparable, if not lower, costs and much reduced GHG emissions (>90%) compared to petroleum-derived fuels. Scenarios producing biofuels result in GHG displacements that are comparable to those dedicated to power production (e.g., >825 kg CO 2 equivalent/dry Mg biomass), especially when a future power mix less dependent upon fossil fuel is assumed. Scenarios integrating biological and thermochemical processing enable waste heat from the thermochemical process to power the biological process, resulting in higher overall process effi ciencies than would otherwise be realized -effi ciencies on par with petroleum-based fuels in several cases.
The question of whether the world needs biofuels is approached by examining the feasibility of doing without them. Even with aggressive reductions in travel growth, shifts to mass transport modes, strong effi ciency improvements, and deep market penetration by vehicles running on electricity and hydrogen, there remains a large demand for dense liquid fuels in 2050 (80% of transportation fuel) and even in 2075 (50%). This demand is due largely to aviation, ocean shipping, and long-haul trucking. Acknowledging the signifi cant uncertainties involved in such projections and the challenges faced by all candidate technologies and fuels, we conclude that it will likely be diffi cult to achieve a low-carbon transport sector without widespread use of biofuels, and that aggressive efforts to develop sustainable, low-carbon biofuels alongside other options are warranted.
The Role of Biomass in America's Energy Future (RBAEF) project, initiated during the fi rst half of 2003, has sought to identify and evaluate paths by which biomass can make a large contribution to energy services and determine means to accelerate biomass energy use. In addressing these issues, the study has focused on future, mature, technologies rather than today's technology. This perspective -the fi rst of eight papers that comprise this issue -introduces the project, providing an operative defi nition of and method for estimating mature technology, a rationale for choosing the model feedstock, a list of the conversion technologies considered, and as a point of reference, a brief overview of the energy fl ows through a typical petroleum refi nery. The subsequent papers are introduced as well.
We report on further developments of a hybrid numerical model to simulate wave-induced sediment transport. A 2D numerical wavetank (NWT) based on fully nonlinear potential flow (FNPF) equations is used to simulate fully nonlinear wave generation and propagation. A 3D Navier-Stokes model with large eddy simulation (LES) is coupled to the NWT to simulate complex turbulent flows near the ocean bottom or around obstacles. Wave kinematics in the 2D-NWT thus forces flow simulations in the 3D-NS-LES model, and resulting sediment transport over the seabed and around a partially buried obstacle. The latter is calculated in a non-cohesive suspended load transport model simulating the (scalar) sediment concentration, using a constant settling velocity. The 2D NWT is based on a higher-order boundary element method (BEM), with explicit 2nd-order time stepping. The computational grid, thus, is the 2D-NWT boundary and the 3D-LES near-field domain. In the present new formulation, the total velocity and pressure fields are expressed as the sum of irrotational (incident/far-field) and near-field viscous perturbations. The LES equations are formulated and solved for the perturbation fields only, which are forced by the incident fields computed in the NWT. The feasibility of coupling the models in an efficient manner is demonstrated.
The global sustainable bioenergy (GSB) project was formed in 2009 with the goal of providing guidance with respect to the feasibility and desirability of sustainable, bioenergy-intensive futures. Stage 1 of this project held conventions with a largely common format on each of the world's continents, was completed in 2010, and is described in this paper. Attended by over 400 persons, the five continental conventions featured presentations, breakout sessions, and drafting of resolutions that were unanimously passed by attendees. The resolutions highlight the potential of bioenergy to make a large energy supply contribution while honouring other priorities, acknowledge the breadth and complexity of bioenergy applications as well as the need to take a systemic approach, and attest to substantial intra- and inter-continental diversity with respect to needs, opportunities, constraints and current practice relevant to bioenergy. The following interim recommendations based on stage 1 GSB activities are offered: — Realize that it may be more productive, and also more correct, to view the seemingly divergent assessments of bioenergy as answers to two different questions rather than the same question. Viewed in this light, there is considerably more scope for reconciliation than might first be apparent, and it is possible to be informed rather than paralysed by divergent assessments.— Develop established and advanced bioenergy technologies such that each contributes to the other's success. That is, support and deploy in the near-term meritorious, established technologies in ways that enhance rather than impede deployment of advanced technologies, and support and deploy advanced technologies in ways that expand rather than contract opportunities for early adopters and investors.— Be clear in formulating policies what mix of objectives are being targeted, measure the results of these policies against these objectives and beware of unintended consequences.— Undertake further exploration of land efficiency levers and visions for multiply-beneficial bioenergy deployment. This should be unconstrained by current practices, since we cannot hope to achieve a sustainable and a secure future by continuing the practices that have led to the unsustainable and insecure present. It should also be approached from a global perspective, based on the best science available, and consider the diverse realities, constraints, needs and opportunities extant in different regions of the world.The future trajectory of the GSB project is also briefly considered.
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