There are three biomass feedstocks: carbohydrate (starch, cellulose and hemicellulose) and lignin from lignocellulosic biomass, triglycerides (soybean, palm, rapeseed, sunflower oil) and mixed organic residues. Ligno — cellulosic feedstocks can be obtained through the production of dedicated crops such as miscanthus or short rotation woody crops such as willow or poplar. Agricultural residues such as rice or wheat straw and paper pulp from the paper industry are other examples of sources of lign — ocellulosic material. Figure 1.5 shows the two main types of biomass feedstocks.

Biorefineries can be subdivided via over simplification into biorefineries of phase I, II and III according to the feedstock and process used, as well as product targeted (chemicals or energy) (Cherubini et al, 2009; Kamm and Kamm, 2004). A table listing examples of different technological processes to be used in a biorefinery are listed in Table 1.3.

Phase I biorefineries focus on the conversion of one feedstock, using one process and targeting one product. A biodiesel production plant would be a good example of a phase I biorefinery: rapeseed or sunflower is used for oil extraction, which is subsequently transesterified to produce fatty acid methyl esters or biodiesel using methanol and a catalyst (Shahid and Jamal, 2011).

Phase II biorefineries differ from phase I biorefineries by the number of outputs they can produce. A typical example of a phase II biorefinery is the production of starch, ethanol and lactic acid together with high fructose syrup, corn syrup, corn oil and corn meal from corn wet mil operations (EPA, 2011).

1.5 The two main types of biomass feedstocks available (adapted from Cherubini et al., 2009).

Phase III biorefineries allow for a wider range of technologies, to be combined (e. g., supercritical CO2 extraction followed by biological transformation), in comparison to phase I and II biorefineries. They also allow for a higher number of valorized outputs since several constituents of the feedstock used can be treated separately. Biorefineries falling into that category can also be called ‘product-driven biorefineries’. They generate two or more bio-based products and the residue is used to produce energy (either fuel, power and/or heat). Examples of phase III biorefineries include whole crop biorefineries which make use of several agricultural by-products originating from the same crop. Phase III biorefineries are typically the

ones targeting the production of chemicals and fuels. Sub-categories also exist according to the type of technology used (thermo-chemical or biochemical biorefineries).

Another classification has now been adopted by the IEA Bioenergy Task in 2010 to take into account the complexity of the biorefinery concept and its future developments around new technologies. It is based around the four cornerstones of the biorefinery concept: feedstock used (i. e., dedicated crop, process or agricultural residue, algae), platform products obtained (i. e., C5 sugars, pyrolysis oil or syngas), final products obtained (energy or chemicals) and process used (Cherubini et al, 2009). This classification has the advantage of accounting for the need to apply a given technology to different feedstocks and will therefore include biorefineries developed in the future. Biorefineries should not be designed in a generic way but should be adapted to the best technology and the best feedstock available in the geographical location chosen.

2.3.1 Biomass cost estimates by feedstock type

Lignocellulosic biomass feedstocks employed by biorefineries can broadly be divided into two categories: dedicated energy crops and residues. Dedicated energy crops are crops grown specifically for use as biomass feedstocks in biorefineries. These are divided into two further categories: herbaceous energy crops and short-rotation woody crops. Herbaceous energy crops contain little to no woody material and are exemplified by grasses. Common examples include switchgrass, Miscanthus giganteus, and energy cane. Short-rotation woody crops are softwoods and hardwoods with short harvest rotations. Common examples include hybrid poplar and eucalyptus. Short-rotation woody crops have longer harvest rotations than most herbaceous crops but compensate for this by also producing higher yields by biomass weight.

Biomass residues are waste products from either urban or rural areas. Residues from urban areas include both municipal solid waste (MSW) and processing residues from factories and manufacturing centers utilizing biomass as an input. Residues from urban areas are characterized by high concentration and low costs due to the avoidance of tipping fees otherwise paid to waste haulers. The disadvantages to using urban residues as biorefinery feedstocks are their heterogeneous nature (for example, MSW frequently contains plastics, metals, and glass capable of damaging a biorefinery) and high values for nearby land, thereby increasing biorefinery costs in the form of either capital or transportation costs. Biomass residues from rural areas most commonly take the form of agricultural residues left on the field after a crop harvest, such as corn stover. These are spread out over a large area and require specialized collection equipment, resulting in higher costs as biorefinery feedstocks than urban residues. Agricultural residues have the advantages of being homogeneous and located near inexpensive land, allowing biorefineries employing them as feedstock to minimize both capital and transportation costs.

Two methods are employed for estimating biorefinery feedstock costs. The first is the use of field trials that account for detailed costs of feedstock production, collection, transportation, and mitigation of negative environmental effects (e. g., nutrient replacement necessitated by the removal of corn stover). Several studies employing field studies have calculated the cost of agricultural residues to be lower than the cost of dedicated energy crops; the delivered cost of stover is calculated to be in the range of $47/MT to $75/MT (Brechbill et al., 2011; Perlack and Turhollow, 2003; Petrolia, 2008) while that of switchgrass is calculated to be in the range of $80/MT to $96/MT (Brechbill et al., 2011). The disparity between the costs of agricultural residues and dedicated energy crops is due to the fact that residues do not require an accounting of production costs and opportunity costs, as they are produced during the normal course of crop production and just need to be collected and transported to the biorefinery. Dedicated energy crops must account for these costs in addition to production and opportunity costs.

The second method employed for estimating biorefinery feedstock costs is the use of economic models based on a combination of field trials, supply chain data, and macroeconomic prices. Two recent examples have been developed by researchers at North Carolina State University (Gonzalez et al., 2011) and the National Research Council (Committee on Economic and Environmental Impacts of Increasing Biofuels Production, 2011). In both cases the costs estimated by the economic models have been greater than those from field trials, with the delivered cost of switchgrass ranging from $94/MT to $108/MT and stover ranging from $96/MT to $101/MT.

The higher cost estimates from the economic model methodology relative to the field trial methodology can be attributed to the highly specific and localized nature of the latter. Field trials are commonly performed at the farm — or county-scale, which are then sometimes extrapolated to the state — scale. While this entails a high degree of accuracy on smaller scales, these results are not suitable for analyses at the regional or national scale. Economic models produce results at the regional or national scale and, while they do not have the levels of detail and accuracy found in field trials, they are more suitable for large-scale analyses.

There is a growing desire to optimize TEA models and understand the implications for real systems. Modern process modeling tools include optimization functions or can couple with stand-alone optimization software like IBM ILOG CPLEX Optimizer, GurobiTM, and GAMS among others. These tools allow researchers to systematically identify optimal operating parameters that meet certain constraints.

TEA models include parameters bounded by system constraints. For example, biorefineries include both technical (reactor temperature) and economic (minimum feedstock cost) constraints that need to be considered within the model. Within the bounds of the allowable parameters there are usually one or more function maxima or minima. In this regard, TEA systems are somewhat simpler than other mathematical models — the function space is well defined. The major challenges for optimization of TEA models are large, complex models with hundreds of parameters, and models that express extremely nonlinear behavior. Techniques that address both of these challenges are the subject of much research.

Researchers employ model surrogates or reduced order models (ROMs) to optimize large models that are either too complex or computationally expensive to evaluate. ROMs can significantly reduce the time required to optimize high-fidelity models at the risk of over-simplifying the problem. Therefore, several approaches have been proposed for the identification of ROM parameters and the evaluation of ROM accuracy.

The benefits of process optimization go beyond identifying optimal values. They also identify tradeoffs between differing objectives. These tradeoffs can be illustrated by a Pareto curve. Pareto curves describe the incremental changes of a given objective value due to improving a second objective. For example, biorefineries commonly face a tradeoff between lowering process costs from the use of fossil fuels and increasing their overall environmental footprint.

These emerging trends suggest a bright future for techno-economic analysis study and its impact on the advancement of biorefineries. The study of demonstration-plant data, combination of TEA and LCA, evaluation of risk and uncertainty, and optimization of system models are fertile grounds for future research and development.

1.3.1 Drivers for change

The EU has recognized that, in order to sustain our demands in energy, chemicals and food, while addressing environmental issues, we need to substantially reduce our dependence on oil by establishing a bio-based economy. The European Commission recently issued Mandate M/429 (European Commission, 2011) to develop a standardization programme for

bio-based products, raising the general public’s awareness for bio-based products (since no external, perceptible characteristics differentiate them from oil-derived products). It was developed with the contribution of industry, research organizations, sector associations and standardization bodies and is anticipated to take a life cycle approach to evaluation and be sensitive to eco-system issues which have become so evident in the bio-fuels arena. Critical issues will include moving away from first generation feedstocks, increasing use of wastes, and ensuring the use of sustainable and low environmental impact technologies throughout the supply chain alongside a consequent reduction in wastes in new feedstock industries.

Early research on renewable resources focused heavily on crops such as rapeseed, corn or sugar cane. However, the controversial competition between food and non-food uses of biomass had an negative effect on crop prices as well as on press feedback concerning biofuels (OECD, 2008). Other sources of biomass are now studied and waste is increasingly considered as another renewable feedstock for the production of bio­derived chemicals, materials and fuels.

In times which increasingly value resource efficiency, waste has become a luxury. DEFRA, the Department of Environment, Food and Rural Affairs in the UK, has estimated that businesses could save up to £23 billion by re-using resources more efficiently (DEFRA, 2012). In the EU, Council Directive 99/31/EC, better known as the Landfill Directive, will drastically reduce the amount of landfill space available as the amount of biodegradable waste sent to landfill in member countries by 2016 will have to reach 35% of the 1995 level. As a result, landfill gate fee has increased from £40-£74 to £68—£111 (including landfill tax) in the UK between 2009 and 2011 (WRAP, 2009, 2011). Policy makers support alternatives to landfill (e. g., value recovery from waste), especially in the context of achieving a zero waste economy and the vision of the European Bioeconomy 2030 (European Commission, n. d.). At the same time, our society faces a huge looming crisis of resources. Globally, ‘30% fewer resources [are needed] to produce one Euro or Dollar of GDP than 30 years ago; however, overall resource use is still increasing […] as we consume growing amounts of products and services’ (Giljum et al, 2009). As traditional resources such as oil and minerals become scarcer, their availability will become more politically controlled leaving them vulnerable to highly politicized negotiations and pricing.

Waste valorization represents a promising research topic from both environmental and economic points of view as ‘there is a considerable emphasis on the recovery, recycling and upgrading of wastes’ (Laufenberg et al., 2003). Current management practices of waste should be replaced by strategies which have a lower environmental impact and which allow the recovery of marketable products for existing or new markets, thus offering

added revenues for companies. Valorizing our waste also has the potential to reduce a process’s carbon footprint and dependence on fossil resources, increase its efficiency and cost-effectiveness and moving towards ‘closed loop manufacturing’, one of the EU’s clear future strategies, highlighted in the Europe 2020 strategy document (European Commission, 2010). The use of renewables in consumer products is especially relevant at a time when public awareness of environmental issues and cradle-to-grave concerns is growing, leading to industry’s increasing concern over their ‘green’ credentials and environmental performance.

The United States has employed a number of biofuel subsidy and tariff programs since the 1970s that have influenced the economic feasibility of biorefineries. The majority of these programs expired at the end of 2011 (Pear, 2012) and the US government has switched the focus of biofuels policy from protectionist programs to a low-carbon mandate in the form of the Renewable Fuel Standard. Whereas past biofuels programs have focused primarily on first generation biofuels and ethanol pathways, the current mandate is broader in scope and includes biofuel pathways ranging from ethanol to butanol to biobased gasoline and diesel (so-called drop-in biofuels).

Up until their expiration at the end of 2011, the US maintained a redeemable tax credit (i. e., a credit first applied against a taxpayer’s tax burden with any excess being received as a direct payment) worth $0.45 for every gallon ($0.12/liter) of pure ethanol blended with gasoline for use as transportation fuel in the form of the volumetric ethanol excise tax credit (VEETC). A concurrent tariff on ethanol imports was also employed to prevent foreign ethanol producers (particularly Brazilian, as sugarcane ethanol has historically been cheaper to produce than corn ethanol) from utilizing the subsidy. Ethanol importers were required to pay a 2.5% ad valorem tariff plus a fixed $0.54/gal tariff on all imported ethanol. This had the effect of making Brazilian sugarcane ethanol more expensive in the US than US corn ethanol (see Table 2.5) despite the former’s smaller production costs. A number of smaller subsidy programs affected other biofuel pathways. Biodiesel producers received a $1 non-refundable tax credit (i. e., a credit applied only to a taxpayer’s tax burden) for every gallon ($0.26/liter) blended with diesel or sold as fuel. Cellulosic ethanol producers received (and still receive) a $1.01 non-refundable tax credit for every gallon ($0.27/liter) of cellulosic ethanol blended with gasoline or sold as fuel in the form of the cellulosic biofuel producer tax credit (CBPTC). Non-refundable tax credits were also available for small ethanol producers and liquefied gas producers.

Popular concerns that corn ethanol production was causing starvation in the developing world (Runge and Senauer, 2007) and deforestation in the Amazon (Searchinger et al, 2008) combined with a shift toward government austerity in the US to undermine political support for first generation biofuel protectionism. With the exception of the CBPTC, all of the aforementioned subsidy and tariff programs were allowed to expire by Congress at the end of 2011, leaving the Renewable Fuel Standard as the primary driver of US biofuel policy. The first iteration of the Renewable Fuel Standard (RFS1) was created by the Energy Policy Act of 2005 to serve as a simple biofuel mandate. Rapid growth in US corn ethanol production left it obsolete soon after its creation and the Energy Independence and Security Act of 2007 replaced it with a greatly expanded (both in scope and volume) Renewable Fuel Standard (RFS2). The RFS2 combines an increased biofuel mandate (36 million gallons (136 million liters) per year by 2020) with a low-carbon fuel standard (LCFS). Four separate yet nested biofuel categories exist whereas the RFS1 had only one: (1) total renewable fuels, (2) advanced biofuels, (3) biomass-based diesel, and (4) cellulosic biofuels. Each category has a particular volumetric mandate that changes over time; total renewable fuels comprise the majority of the mandate but are permanently capped in 2015, and by 2022 the cellulosic biofuel category becomes responsible for a plurality of the mandate.

The definitions of each RFS2 category encompass both biofuel type and feedstock source (Energy Independence and Security Act, 2007). To qualify for the total renewable fuels category, a biofuel must be sourced from renewable biomass (i. e., biomass meeting land-use restrictions) and achieve a 20% lifecycle greenhouse gas emission (GHG) threshold relative to gasoline. Advanced biofuels must achieve a 50% GHG reduction and cannot include corn ethanol (regardless of its lifecycle GHG analysis). Biomass-based diesel must also achieve a 50% GHG reduction and includes both biodiesel produced via transesterification and renewable diesel. Finally, cellulosic biofuels must achieve a 60% GHG reduction versus gasoline and be sourced from lignocellulosic feedstocks. Emissions from indirect land — use changes (ILUC) must be accounted for when determining whether a biofuel achieves a category’s GHG reduction threshold.

The RFS2 impacts the economic feasibility of biorefineries by attaching a renewable identification number (RIN) to every gallon of biofuel blended with or sold as transportation fuel in the US. The RFS2 requires blenders to own a certain number of RINs proportionate to their market share at the end of each year to demonstrate compliance with the mandate. A blender that has met its share of the mandate can sell any excess RINs to a blender that has not, or can bank them for future use. RIN values increase when the supply of biofuels within an RFS2 category exceeds demand and can serve as an important source of income for biofuels producers, as RIN values for the biomass-based diesel category reached $1.60/gal in August 2011 (McPhail et al., 2011). When demand exceeds supply (i. e., when the mandate has not been met), the core value of an RIN is the difference between the biofuel’s production cost and the market price of gasoline or diesel (RIN values do not drop below 0 when this market price exceeds the biofuel’s production cost). RINs are allowed to be publicly traded, however, so speculator activity can also affect RIN value.

The effect of the RINs is to ensure that biofuel producers receive the minimum value necessary to cover costs of production. When gasoline and diesel prices are greater than biofuel production costs, then the core RIN value is 0, as biofuel producers do not need additional incentive to produce up to the mandated volume. When gasoline and diesel prices are less than biofuel production costs, then the core RIN value increases to the level necessary to incentivize sufficient production to meet the mandate. As an example, assume that the three lignocellulosic ethanol TEA results presented in Table 2.7 are three different biorefineries and the cellulosic ethanol produced by each qualifies for the cellulosic biofuels category of the RFS2. Initial production will fall short of the mandated volume (the

EPA has waived the cellulosic biofuels mandate in recent years due to a complete lack of production) and, assuming a pre-tax gasoline price of $3/ gal, the RIN value will be sufficiently high to incentivize production at all three biorefineries, or $2.10/gge (the difference between the highest biofuel production cost, $5.10/gge, and the pre-tax gasoline price). The biorefinery capable of achieving the lowest production cost will attain the greatest profit but all three will be profitable. This will change as total cellulosic biofuel production exceeds the mandated volume, however. Assuming the first two biorefineries produce enough to satisfy the mandate and the pre-tax gasoline price remains $3/gal, then the RIN value will decline to the difference between the pre-tax gasoline price and the second highest biofuel production cost ($4.29/gge), or $1.29/gge. In this way, the RFS2 ensures that biofuel producers remain economically feasible when gasoline and diesel prices are low while eliminating the prospect of government — subsidized windfall profits when gasoline and diesel prices are high.

L. SCHEBEK and O. MR AN I, Technische Universitat Darmstadt, Germany

DOI: 10.1533/9780857097385.1.67

Abstract: Given the fact that biorefineries are gaining increasing attention as a technology for mitigation of climate change and sustainable development in general, it is not surprising that sustainability assessment of biorefineries has also become an issue. The interaction of biorefineries with their environment is very complex. In general, it can be stated that biorefineries may have impacts on the natural or physical as well as on the economic and social-cultural environment. Life cycle assessment (LCA) is a systematic approach to analyze and examine the impacts of products or services on the environment. Most LCA studies on biorefineries consider or compare products or raw materials, thus such other classification features of biorefineries as platform and process appear only in the background. Challenges in the future include assessment of the expected competition between material and energetic use on one hand, and land for cultivation of food and feed production on the other hand. As a general prerequisite, the technological processes must be most efficient. In addition to that, social and economic implications of a broad implementation of biorefineries must be better understood, in order to facilitate implementation of solutions.

Key words: sustainability assessment, biorefineries, life cycle assessment (LCA).

3.1 Introduction

The concept of sustainability was introduced by the World Commission on Environment and Development (WCED, 1987) in its famous report ‘Our Common Future’, delivered on behalf of the United Nations in 1987. Since then, it has been broadly discussed in scientific literature as well as in public debates at various levels of society. The WCED report defines sustainable development as ‘Development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs’. The popularity of this concept resides in its comprehensive and inclusive idea of fairness today and in future, with nature conservation as prerequisite to implement this idea of global equity. However, its universal applicability raised the need for further specification of goals and strategies

© 2014 Woodhead Publishing Limited

to make it operational. A widespread idea of sustainability states that sustainable development must be based on three dimensions: environmental, economic and social (Janicke et al., 2001). From this generic view, individual strategies for stakeholders may be derived. As one example, Alles and Jenkins propose that in organizational strategies three objectives must be considered (Alles and Jenkins, 2010):

• people — the social consequences of its actions

• planet — the ecological consequences of its actions

• profits — the economic profitability of companies (being the source of ‘prosperity’).

So far, many international, national and company indicator systems to assess sustainability have been worked out. Assefa and Frostell report that more than 500 projects have been implemented to develop quantitative indicators for sustainable development (Assefa and Frostell, 2007). These may be used to assess progress of sustainability on various levels and for different applications. Research and political interest in sustainability assessment of technologies increased during the last decade. The reason is the far-reaching impact of novel technologies, which may contribute to sustainable development, but may also raise novel problems of sustainability.

Given the fact that biorefineries are gaining increasing attention as a technology for mitigation of climate change and sustainable develop­ment in general, it is not surprising that the sustainability assessment of biorefineries has also become an issue. Biorefineries are supposed to have a considerable potential to replace fossil fuels and to develop a new concept of economic production in the chemical industry. At the same time, this might pose new challenges. The demand for biomass supply and new patterns for production and workplace surroundings are an example for these. Consequently, environmental impacts are the focus of all sustainability assessments, but also other issues have to be taken into account to obtain a comprehensive picture.

There is a growing recognition that the twin problems of waste management and resource depletion can be solved together through the utilization of waste as a resource. Some initiatives looking at the re-use of waste already exist, like in Spain for example, where the environmental complex of Montalban, Spain (Epremasa, Complejo Medioambiantale de Montalban), is a unique example of integrated waste management (EPREMASA, n. d.). It was built to meet the new EU directives regarding waste management; concentrating, recovering and valorizing waste in order to avoid landfilling as much as possible. The company is responsible for waste management operations in the province of Cordoba, Andalusia. It provides home collection of municipal solid waste (household waste, paper, cardboard, glass and electric appliances), transportation, processing and landfill man­agement for 74 municipalities (approximately 475,500 inhabitants). This strategy and the scale of operations allows the facility to be cost-effective with more flexible working procedures and a rationalization of human and material resources involved in the cycle.

The complex is an integrated facility which combines high efficiency waste scanning and segregation, recycling, composting, electricity generation and landfilling activities on the same site. The complex is able to produce high quality recycled plastic by sacrificing 40% of the organic waste through the use of a more rigorous process. Its efficiency is around 90% as only 10% of the plastic arriving at the facility is landfilled (mainly plastic contained in Tetrapack® packaging). As a result, the higher quality plastic meets the specifications for being used in further plastic packaging applications which, up to now, was limited. In addition, compost is commercially produced from organic waste, as well as 1.2 MW of electricity as the composters are connected to a biogas plant.

This process illustrates how the valorization of waste can provide first generation waste-derived feedstocks (recycled plastic, compost, biogas/ energy) as an alternative source of carbon. Such applications reduce the need to use virgin land and finite resources such as oil.