Perspectives of biomass-to-liquid fuels

Biofuels are a feasible tool to achieve EU policy goals, namely securing and diversifying the energy supply for road transport in an environmentally friendly way. Biomass growth for the current vegetable oil-based diesel technologies (FAME and HVO) is not able to keep pace with growth in fuel demand. Indeed, the production potential of conventional biofuels (bioethanol and biodiesel), based on agricultural feedstock, is insufficient to meet the 2010 policy targets. Hence clean alternative biofuel production pathways need to be investigated, which aim at the integral valorisation of biomass.

With a volume of some 700 billion tonnes, cellulose is globally the most widespread organic chemical and therefore highly important as a bio-renewable resource. Only a minor fraction (0.1-0.2 billion tonnes) is used every year as feedstock for further processing. As biomass is highly functionalised, it is preferable to convert biomass into highly valued chemicals rather than under-functionalised and cheap biofuels (essentially alkanes). However, producing biofuels from lignocellulosic material via gas-to-liquid (GTL) technologies — biomass-to-liquid (BTL) fuels — could potentially overcome the aforementioned feedstock limitations. This production pathway is based on a fuel synthesis from gaseous feedstocks (syngas, i. e. CO and H2). Syngas can be obtained from hydrocarbon feedstocks (natural gas, coal) or from biomass (including municipal waste). BTL plants apply the known technology of the

CTL and GTL plants with minor modifications. Many biomass conversion technologies are currently being pushed simultaneously and many of them will probably be used commercially in the long run in order to ensure a reasonable energy mix.

Biomass is expected to contribute 10% of the world’s energy demand in the medium term. The biggest contribution will come from biomass-to- electricity, especially when used in combined heat and power generation plants. Algal power plants are now being commissioned in Europe (e. g. Enalg, Venice). Figure 15.23 shows the alternatives to production of energy (in various forms) from biomass and waste.

Estimates of global potential of biomass resources range from 3250 Mtoe/ yr (2025) to 5650 Mtoe/yr (2050). At an annual global yield of 13 billion tonnes plant material for food/feed purposes, 8 billion tonnes waste material is generated with an energy content equal to the total global energy needs. Consequently, in principle there is no problem in the use of biomass for energy and materials applications. Local problems may arise though, such as food/energy competition, biodiversity, erosion, water use, etc. The estimated EU 25 potential is 600 Mtoe/yr (2050). Reaching the target of a 12% share of renewables in total domestic energy consumption by 2010 requires around 130 Mtoe of biomass (EU15). A renewables share of 20% of total energy in 2020 necessitates about 210-250 Mtoe of primary energy for the EU25.

15.23 Biomass-to-energy.

The recent EU Biomass Action Plan [84] aims at increasing the biomass contribution to primary energy (1486 Mtoe/yr) from 57 Mtoe/yr in 2001 (or about 4%) to 188 Mtoe/yr in 2010 and 227 Mtoe/yr in 2020. There is sufficient biomass potential in the EU25 to support ambitious renewable energy targets in an environmentally responsible way [85]. 6.4 Mt of biomass are used as a raw material option for the production of chemicals in Europe, representing 8-10% of the industry’s total feedstock. Compared to energy generation, material use of biomass still plays only a minor role.

In the United States, a Billion-Ton Vision study [86] identified a potential 1.3 billion tonnes biomass (1 t biomass = 0.43 toe) that could be used as a resource to produce transportation fuels. US expectations are that 90 Bgy of sustainable bioethanol (starch-based and cellulosic) from agricultural residue (corn stover, wheat straw), forestry waste, dedicated energy crops (including switchgrass) and short-rotation woody crops (such as willow and poplar trees) will replace about one-third (or 60 Bgy) of domestic gasoline requirements by 2030 (estimated as 180 Bgy); 15 Bgy would be corn-derived and 75 Bgy from non-food cellulosic feedstocks [87]. It appears that 21 Bgy of cellulosic ethanol could be produced by 2022 without displacing current crops. The Renewable Fuels Standard (see Section 1.2.1) calls for 36 Bgy by 2022. The national goal of 60 Bgy cellulosic biofuels production by 2030 requires a capital investment of US$300 billion.

During processing of biofuels, considerable amounts of by-products are generated and their economic use has to be ensured. The possibility to fully use not only the already naturally highly-refined molecular structure of biogene oils but also the 50-80% remainder of the plant for use as fuel will at least double the yield per hectare to 3-4 t (ester + BTL rapeseed plant) and 8-10 t/ha (ester + BTL from palm FFA). ‘Co-generation of biofuels’ faces an even bigger future than second-generation biofuels.

Waste materials have high water content that reduces their potential for combustion processes because the energy required to dry the materials exceeds the value of the energy recoverable through combustion. Anaerobic digestion reduces both the volume and mass of the waste materials and typically produces a product that is readily dewatered. Superheated steam drying is another biomass drying technology.

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