Sustainable Development of Algal Biofuels in the United States (2012) / Chapter Skim
Currently Skimming:
3 Pathways for Algal Biofuel Production
3 Pathways for Algal Biofuel Production
Pages 77-98
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 77... ...
The pathways described here are used in subsequent chapters to provide a framework for understanding the sustainability impacts of different approaches for producing algal biofuels. The intent is to group pathways that share common processes to help contrast resource requirements and impacts of different approaches and to help clarify the key biological and engineering advances that are needed to improve sustainability.
|
From page 78... ...
A few representative pathways are analyzed to illustrate the current state of the technologies and where advances are needed to reduce the resource requirements. Trends observed in the science and technologies for other biofuel production are likely to occur in algal biofuel production as the latter develops as an industry.
|
From page 79... ...
The reference pathway is drawn from the recent National Renewable Energy Laboratory techno-economic analysis of algal biofuel production (Davis et al., 2011)
|
From page 80... ...
Green process steps represent those associated with algae cultivation, light blue with lipid collection, and FIGURE 3-3 Reference pathway: Open raceway pond producing green diesel, a drop-in hydro carbon fuel. 1Green diesel is a product of hydrotreating of triglycerides.
|
From page 81... ...
The hydrotreating of algal lipids to produce pure hydrocarbon fuels is analogous to second generation biodiesel production, which is based on seed crops to produce green diesel (NREL, 2006)
|
From page 82... ...
Wet processes -- where the cell membranes are disrupted in the aqueous medium to release the lipids which phase separate to enable collection -- are likely to have considerably lower energy use than dry processes (Beal et al., FIGURE 3-5 Carbon and water flow in the reference case scenario: Open raceway pond producing green diesel. SOURCE: Marler (2011)
|
From page 83... ...
FIGURE 3-6 Alternative pathway #1: Open raceway pond producing green diesel, a pure hydrocarbon fuel with coproduct for sale.
|
From page 84... ...
are sold. Others have taken a more measured approach and have claimed that coproducts could contribute to the profitability of algal biofuels while their market develops, and the cost of algal biofuel production would decrease with efficiency improvements and economies of scale.
|
From page 85... ...
Residual biomass is a function of the amount of fuel produced and the fraction of the total dry biomass. Plotting residual biomass as a function of both lipid fraction and annual fuel production indicates the magnitude of the issue (Figure 3-8)
|
From page 86... ...
The use of anaerobic digestion to return nutrients to the algae cultivation and electrical power to the algal biofuel production system is a key component of alternative pathway #1. Removing the residual biomass as a coproduct, therefore, affects the energy balance of fuel production and the required nutrient load.
|
From page 87... ...
. FIGURE 3-11 Inputs and outputs of the alternative pathway #2: Open raceway pond pro ducing a fatty-acid methyl ester (FAME)
|
From page 88... ...
3.5 ALTERNATIVE PATHWAY #3PHOTOBIOREACTORS WITH DIRECT SYNTHESIS OF ETHANOL Previously described processes for algal biofuel production have focused on openpond systems for algae cultivation, and most analyses indicate that photobioreactor systems are cost prohibitive for the production of fuels (Williams and Laurens, 2010)
|
From page 89... ...
. The alternative pathway #3 is effectively the Algenol process, as it was described to the committee (Luo et al., 2010; Chance et al., 2011)
|
From page 90... ...
Comparison of the Algenol results to other studies on algal biofuels is favorable in terms of energy and other resource requirements. Eliminating the need for dewatering reduces energy requirements and is a clear advantage of processes that directly produce fuel.
|
From page 91... ...
are the carbon average molecular weight of the fuel component or residual biomass (Eq.
|
From page 92... ...
In contrast, water was consumed fixing the carbons in both the residual biomass and the fuel component in the case where algal cells are destroyed to collect lipids or to be processed to fuel. carbon average molecular weight of the fuel component and the fuel component mass ratio in the dry biomass.
|
From page 93... ...
The red star is shown for reference and approximates the case for a lipid forming algae at 30-percent lipid. FIGURE 3-18 Overview of the whole-cell processing to make drop-in replacement fuels.
|
From page 94... ...
This process was selected for comparison because of reports suggesting that supplemental energy and hydrogen are not required. As a result, there are no extra feed or effluent streams that would affect the analysis of the overall environmental footprint of fuel production.
|
From page 95... ...
These systems appear to have energy requirements similar to other production techniques in which the cells are killed to harvest product. Clearly, thermochemical pathways can manufacture a range of fuel products.
|
From page 96... ...
The coproduct value depends on the composition of the animal feedstuff and the characteristics of the market in which it would be sold. In general, coproduct volumes swell with the scaling up of algal biofuel production, potentially saturating markets for these products unless a wide variety of coproducts for different markets are produced.
|
From page 97... ...
Presentation to the NRC Committee on the Sustainable Development of Algal Biofuels on August 24. Huber, G.W., and B.E.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.