Long-distance trade of raw biomass for liquid fuels feasible - study

Earlier we looked at how bioterminals in the Benelux import raw biomass from all over the world, which is then used either for cogeneration in small CHP biomass plants, in large power plants to be co-fired with coal or as feedstocks for next generation biofuels. The IEA Bioenergy Task 40 group which studies the economics of long logistical chains involved in global trade of bioenergy feedstocks, earlier determined that in many cases biomass can be shipped from continent to continent economically and sustainably. Studies made by Task 40 indicate that the Greenhouse Gas Balances of transporting bioenergy over such long distances remains at sustainable levels for most feedstocks.

Now Dutch researchers say they have determined that with current high oil prices, liquid fuels can be produced economically from biomass, even if all the raw materials have to be imported. They confirm the ongoing Task 40 findings. This is important for the Biopact, because it means that logistics and costs are not a barrier for the developing world to export bioenergy to the wealthy North.

Robin Zwart and colleagues at the Energy Research Center of The Netherlands focused their study on the so-called biomass-to-liquids, or BTL, process - one of the most promising biomass fuel options. BTL involves converting biomass into a gas and then using the Fischer-Tropsch process to convert the gas into liquid fuels that could power motor vehicles. The resulting fuel is known as green 'synfuel' (synthetic fuel).

The study [abstract, full *.pdf] assumes the final liquid fuel production facility is in the European Union, with raw biomass imported after pretreatment at the place of origin. In the base scenario, the importing port is Rotterdam, and the exporting biomass region is the Baltics (Lithuania, Latvia, Estonia), coming down to a distance of 2500km by bulk carrier (1560 miles). The biomass in question comes in a wide variety, either as wood waste, herbaceous biomass (grass, straw), agricultural waste streams, or 'bioslurry'.

The researchers conclude that high-quality liquid fuels could be produced from this imported biomass for 15 €/GJ, or 55 €urocent/liter of diesel equivalent (about US$2.60 per gallon). They write that the process would be economically feasible and capable of competing with conventional fuels, when crude oil prices are about US$60 per barrel or higher:

biomass :: bioenergy :: biofuels :: energy :: sustainability :: trade :: logistics :: biomass-to-liquids :: BTL ::

We reproduce the study below in its entirety, for future reference:

Robin W. R. Zwart, Harold Boerrigter, and Abraham van der Drift: The Impact of Biomass Pretreatment on the Feasibility of Overseas Biomass Conversion to Fischer-Tropsch Products, Energy Fuels; 2006; 20(5) pp 2192 - 2197.

Abstract:

One of the most promising options to produce transportation fuels from biomass is the so-called biomass-to-liquids (BtL) route, in which biomass is converted to syngas from which high-quality Fischer-Tropsch (FT) fuels are synthesized. Pretreatment of biomass is an important part of the BtL route, both to allow feeding of the biomass into the selected entrained-flow gasifier and to reduce transport costs by densification. To determine the technological and economic potential of BtL routes, 10 integrated systems from overseas biomass to the FT product in Rotterdam are assessed on the basis of different pretreatment options, that is, chipping, pelletization, torrefaction, and pyrolysis. The main conclusions of the assessment of 10 BtL production routes are that pretreatment of the biomass at the front end of the BtL route significantly increases the economic feasibility and that overseas torrefaction is the most attractive pretreatment option. Dedicated overseas pretreatment (i.e., torrefaction and pyrolysis) is more attractive than conventional pelletization. A large-scale, central, overseas BtL synthesis plant would be the most attractive route for BtL production. However, local logistic aspects require the construction of several small-scale synthesis plants, causing significant economical disadvantages due to economy of scale. The FT product can be produced from overseas biomass for 15 euro/GJ (or 55 euro ct/L of diesel equivalent). At the crude oil prices of late 2005 (around $60/bbl), large-scale BtL can be considered as an economically feasible technology.
Introduction

Biomass is envisaged to play a major role in the reduction of CO2 emissions and the introduction of renewable energy sources in the European Union. In the long-term vision, 30% or more of the total transportation fuels consumption of the 25 countries of the European Union has to be covered by biofuels in 2040. One of the most promising options to produce biofuels is the so-called biomass-to-liquids (BtL) route, in which biomass is first converted into syngas, and subsequently, a high-quality designer fuel is produced via Fischer-Tropsch (FT) synthesis. Fischer-Tropsch synthesis is a well-established and commercially available process.1

To fulfill the ambitious biofuel targets, large-scale import of biomass is required in the European Union. The main biomass sources globally available for energy purposes are wood and grasslike materials.

Syngas can be produced from biomass by either noncatalytic high-temperature entrained-flow (EF) or catalytic low-temperature gasification technologies. Unlike the already widely demonstrated high-temperature EF gasification technology, the catalytic technologies do not yet exist commercially. Furthermore, they include two conversion steps, making them more expensive. However, most importantly, they are not fuel-flexible, which is considered to be of vital importance in the case of large-scale production facilities.

The EF gasification technology is therefore identified as the optimum process for the production of syngas from a variety of solid biomass streams, for example, woody biomass, and straw and grassy material.

Pretreatment of biomass in BtL systems is required for reasons of feeding the biomass into the gasifier as well as desired for transport costs and improved gasifier operation. Solid biomass "as-harvested" cannot be fed straightforwardly into an entrained-flow gasifier. The gasifier requires small particles or a liquid to establish a stable flame and ensure essentially complete conversion. Furthermore, biomass "as-harvested" has a relatively low bulk density. As storage, transport, and transhipment costs are mainly based on the volume of the material, there is an economic driver to reduce the volume of the biomass prior to transport. Related to the low bulk density of biomass is the low energy density compared to coal. Hence, for a fixed energy throughput, a much larger volume of the gasifier would be required, which influences the hydrodynamics, the amount of slag required, the slag behavior, and the gasifier efficiency. Additionally, much more carrier gas is required to transport the biomass in the feeding system.2

The costs and efficiency losses related to pretreatment are the key issues that determine the technological and economic potential of the BtL route.2,3 In this paper, 10 routes with alternative pretreatment options are compared for the conversion of overseas biomass to FT products in a major port in western Europe.
General System Lineup

Integrated systems from overseas biomass to FT products on an 8 GW syngas scale are assessed. In this study, the biomass production is assumed to take place in the Baltic states, and the Rotterdam harbor is taken as the final location. The general lineup for these systems is presented in Figure 1. The harvested biomass is naturally dried in the forest before being transported by truck to a pretreatment plant. The first step of the pretreatment is size reduction and further active drying, after which the actual pretreatment conversion takes place. The product pretreated biomass is then transported to the BtL plant, where it is compressed to the required pressure for gasification, dosed to the gasifier, and converted into syngas.
Figure 1 General schematic lineup of the complete integrated system for FT crude production from pretreated biomass.

The raw syngas needs to be cleaned and conditioned to make it suitable for the catalytic FT synthesis. After cooling and solids removal, the H2/CO ratio is adjusted to the FT consumption ratio, and CO2 and the bulk impurities are removed (typically in a Rectisol unit). The final step is gas treating to remove any remaining impurities. The syngas is now on specification for FT synthesis, in which hydrocarbons are formed in the whole range of C1 to > C100. The gaseous C1-C4 hydrocarbons are partly recycled to the gasifier, while the remainder is used for electricity production. All liquid C5+ hydrocarbons, after upgrading, are assumed to be products. Water formed in FT synthesis is separated and removed.
Selection of Pretreatment Options

Biomass Feeding Consideration. In the assessment of biomass feeding options, one can choose to apply conventional systems for coal or liquids or to develop new systems dedicated to handling biomass. In the case of applying conventional systems, the biomass needs to be pretreated to give it properties similar to those of coal or the biomass has to be converted into a pumpable liquid or slurry. The possible feeding options are presented in Figure 2 and will be discussed below.
Figure 2 Possible biomass feeding options.

To mill biomass to particles of the same size as those of coal (i.e. ~100 m), the electricity consumption is approximately 7% of the energy value of the biomass. Even then, the milled wood still cannot be fed with conventional systems, as, because of the fibrous nature of the biomass, it does not fluidize and fluffs are formed that plug the piping. Therefore, the milling of biomass to a size of 100 m is not considered to be a feasible option. Alternatively, char might be used, obtained from (slow) pyrolysis. The char, however, contains only approximately 50% of the energy of the biomass.4 The remainder is contained in the (tar-rich) pyrolysis gas, which has to be used on site and is not available for BtL production if the FT process is located elsewhere. Therefore, char is not considered to be a feasible general option because of the low efficiency. Torrefaction is a mild thermal treatment, typically at temperatures in the range of 225-300 C, in which the biomass loses its resilient and fibrous properties.5 It becomes dry and brittle and can easily be milled. At lower temperatures (±250 C) and residence times (±15 min), the energy efficiency (on a lower heating value basis) of the torrefaction step is up to 95%.5 The remainder is torrefaction gas mainly containing H2O, CO2, and small amounts of light (oxygenated) hydrocarbons. This combustible gas is typically used to provide the heat for the torrefaction process.6-8 Torrefaction is considered as a suitable pretreatment option.

Options based on liquid feeding involve pyrolysis. By (fast) pyrolysis, a liquid bio-oil is produced containing up to 70% of the energy of the biomass. The remainder is for 10% in the pyrolysis gas and 20% in the char.9 The gas can be used to generate the electricity for the plant, and about half of the char is required to produce the heat for the pyrolysis process. The other half is surplus. However, in most cases, it is burned inside the process as well. The efficiency of oil production is considered low for large-scale BtL production; therefore, bio-oil is not considered to be a feasible option. Bioslurry is produced in a (fast) pyrolysis process similar to bio-oil production, with the exception that all produced char and oil are isolated as a mixture, that is, the slurry.10 As a result, the energy efficiency of this process is approximately 90%,11 and therefore, bioslurry, unlike bio-oil, is considered to be a feasible candidate option.

Alternatively to converting biomass into liquids or coal-like material, new and dedicated feeding systems for biomass can be developed. In a low-temperature gasifier, the biomass is converted into gas and a small amount of char. The gas with entrained char is fed into the entrained-flow gasifier. Advantages are that no extensive biomass pretreatment is required, as circulating fluidized-bed (CFB) gasifiers can handle relatively large fuel particles. The efficiency is nearly 100%. The easiest solution of feeding biomass to the entrained-flow gasifier is direct piston-screw feeding of 1 mm particles. The electricity consumption for milling is only on the order of 1-2%, and there are no conversion losses. The challenge, however, is to ensure stable feeding and dosing to the gasifier burner to establish a stable flame.

Biomass Transport Considerations. For the transport of biomass over longer distances, biomass should preferentially be converted into a form that is suitable for bulk handling. Biomass forms that are suitable for cost-effective transport over longer distances (considering the biomass feeding issues described before) and allow transhipment with bulk handling processes are chips, pellets, bioslurry, and torrefaction pellets (TOPs). To take advantage of conversion of the biomass in an easily transportable from, evidently, the pretreatment plant should be located preferentially near the production location of the biomass.

Upon the chipping of wood, in most cases, the biomass "as-received" is also dried to 7-15% moisture prior to the process to reduce the electricity consumption. Wood chips are readily transported and transhipped by bulk handling processes; however, because of the relatively low bulk density (~350 kg/m3), costs of transhipment, transport, and storage are relatively high. The production of pellets leads to an increase of the bulk density of the biomass (~450-650 kg/m3). Pellets are suitable for bulk handling as well.

Alternatively, biomass materials can be converted into a bioslurry or into torrefied material. The bioslurry has the advantage of a very high bulk density (~1200 kg/m3), and it can be transported and handled as a liquid (comparable to heavy oil). However, HSE (health, safety, and environmental) aspects of bioslurry are not yet clear. In the case of torrefaction, the biomass can be transported as torrefied wood chips, which are suitable for bulk handling. However, the torrefied branches, leaves, needles, and straw carry too many fines. Torrefaction in combination with pelletization is therefore preferred to produce the so-called "TOP pellets".7 The advantage of additional pelletization is an increase in both energy and material density (the latter one ~850 kg/m3). This also happens in normal pellets; however, because of the resilient nature of fresh biomass, the increase in density is much smaller. Further advantages of torrefied biomass with respect to handling and further processing are the hydrophobic nature of the material and the lower electricity demand during pulverization.

In all cases, the minimum pretreatment prior to transport comprises drying and chipping. The alternatives for biomass transport considered here are chips, pellets, bioslurry, and TOP pellets. The transport of FT crude or FT products, however, should not be forgotten, as after FT synthesis (and upgrading) the bulk mass and energy densities of the product are also significantly higher than that of the original biomass. This, however, implies that synthesis (and upgrading) is performed at either one central port, or hub (with the possible disadvantage of long road transport), or multiple hubs (and not having the economy of scale advantage).
BtL Production Routes

The BtL production routes evaluated in this study are presented in Figure 3, and they comprise the whole chain from biomass to FT liquid products, similar to a previous study on the feasibility of large-scale syngas production from biomass (i.e., virgin wood) imported from the Baltic states.12 The biomass is collected in a number of production forests and chipped after harvesting, and the chips are transported to 80 biomass collection facilities (BCFs). Depending on the route, the biomass is pretreated in the BCFs or directly transported to and stored at eight central ports (hubs). To assess the advantages of pretreatment on transport and storage, the selected pretreatment technologies are considered in the BCF. From the hubs, the (pretreated) biomass is shipped to the location of the one large BtL plant. At this facility with intermediate storage capacity, the biomass is (additionally) pretreated and subsequently gasified.
Figure 3 Overview of the considered BtL production routes.

The gasification and synthesis plant is chosen to be located in Rotterdam (Maasvlakte), on the basis of (i) the port infrastructure being appropriate and (ii) the port being an existing hub in the production and distribution of transportation fuels. Short-term implementation of a BtL route might strongly benefit from a good chemical and petrochemical infrastructure nearby. However, in this study, a reference route (R10) is considered as well, in which gasification and FT synthesis are located in the hub.

The 10 assessed BtL production routes R1 through R10, as presented in Figure 2, can be divided in three groups, that is routes: (1) on the basis of sole chips transport (R1 to R4), (2) in which biomass is pelletized conventionally before transport (R5 to R7), and (3) routes with some kind of thermochemical conversion performed before transport (R8 to R10).

When transporting biomass as chips to the syngas facility in Rotterdam, four concepts are evaluated: (R1) 1 mm powder feeding to the EF gasifier, (R2) bioslurry production, (R3) torrefaction, and (R4) CFB gasification before EF gasification.

When transporting conventional pellets instead of chips, the pellets are (R5) grinded in Rotterdam before being either fed straight to the EF gasifier or (R6) pyrolyzed or (R7) torrefied in order to simplify the feeding into the EF gasifier. The torrefaction process still contains a pelletization step, to take advantage of the densification and because of temporary storage of the torrefied wood at Rotterdam being desired.7 The TOP pellets are pressurized by lock hoppers, followed by intermediate disintegration to 100 m particles, and a pneumatic feeding into the EF gasifier, whereas the bioslurry uses a pump and the 1 mm particles a piston compressor for pressurization and a screw feeding system.

In routes R8 and R9, the pyrolysis and torrefaction are performed in the BCF in order to benefit from logistic advantages. CFB gasification within the BCF as a pretreatment step is not considered, as this would require syngas transport from the BCF to Rotterdam.

The final route R10 is based on EF gasification and FT synthesis in the hub. As the FT synthesis generates more than one product, this requires additional storage facilities at the hub for the transport of all of these products to take place on an economically attractive scale, that is, with large-scale overseas transport. To benefit from the economy of scale, this route would imply that only one hub should be considered instead of eight. However, from the (road) transport of the biomass point of view, one hub is less interesting. This route, therefore, is evaluated on the basis of both one (R10a) and eight (R10b) hubs. The routes R1 and R9 all are based on the existence of eight hubs (and 80 BCFs).
Assumptions

The assessment of the BtL routes is based on the general assumption that, in all routes, biomass, that is, chipped wood logs with a moisture content of 35%, is delivered at the BCF at a fixed price of 4.0 euro/GJ or 45 euro/ton. The economy of the different biomass treatment steps within the production routes, in combination with different efficiencies of these processing steps (Table 1) and logistic costs (Tables 2-4), determines the final production costs of the FT product.

EF gasification is carried out at 40 bar. EF efficiencies, which include efficiencies of syngas cleaning and conditioning, differ for the various feedstocks of the gasifier, as each specific feedstock has its own steam and oxygen demands, as well as a dedicated feeding system with differing amounts of pressurization gases required for the gasification at 40 bar. The efficiencies of chipping, pelletizing, pulverizing, and grinding are set to be equal to 100%, although in reality, some small losses might be expected as result of, for example, dust. The energy consumptions of these processes, however, are included in the assessment.

Biomass logistic costs can be divided into costs of transhipment (Table 2), transport (Table 3), and storage (Table 4). Transhipment costs consist of port charges (i.e., ship taxes for the purposes of the harbors) and transfer costs (i.e., costs for the loading and unloading of cargo). The latter ones depend on the type, form, density, and amount of cargo.13 The actual costs of transport are divided into fixed (mainly labor) and variable costs (labor, fuel, and vehicles). The transport costs from the BCF to the hub are based on large-scale land transport by road, whereas the transport costs from the hub to Rotterdam are based on large-scale sea transport. Transport by rail or pipeline is not taken into consideration.

In the case of land transport, cargo weight is limited to 25 tons, and trucks with a trailer can always transport the associated volume. As a result, there are only small differences in the costs of truck transport, caused by differences in loading and unloading rates and the type of material to be transported.

For sea transport, either dry bulk carriers (with typical capacities of 100 000 m3) or tankers (typically 80 000 m3) can be used. In the case of high bulk densities (e.g., slurries), the ship volume might not be used completely, as ship capacities become limited by weight. As a result, the differences in costs of sea transport are not only caused by differences in loading and unloading rates and the type of material to be transported but by the weight limitation of the ship capacity as well.

Storage costs result from the necessity to create storage possibilities, particularly at points where cargo is transferred between transport modalities of different scales. A different storage facility is needed depending on the form of the biomass. As bulk, pellets can be stored in a silo and chips in a bunker. As a liquid, bioslurry and FT products can be stored in tanks. Although different storage facilities are needed depending on the form of the biomass, all of these different storage facilities in Europe have, taking into consideration different storage times as well as HSE issues, similar costs of approximately 50 euro/m3.13 For storage overseas, it is assumed that the costs are 50% of the costs in Europe. As the FT product is transported straight from the Rotterdam plant, no storage of the FT product is foreseen. In the case of the biomass being pretreated, both storage of the incoming and outgoing biomass is required. Hence, in the case of FT synthesis in the hub (R10), storage of the FT products is accounted for.
Production Costs

In Table 5, the fuel costs along the BtL production route are shown (i.e., those of the as-received biomass, pretreated biomass, biosyngas, and FT products). The resulting total production costs of the FT product at Rotterdam vary between 12.4 and 19.0 euro/GJ, with the costs of the intermediate cleaned and conditioned biosyngas between 9.3 and 13.8 euro/GJ. The calculated fuel costs for chips (in routes R1 to R4) and the FT product costs for pyrolysis (route R8) are in very good agreement with data from other authors; that is, the VTT data gives costs of 4.2 euro/GJ for chips at a sawmill/pulp mill14 (this study: 4.3 euro/GJ), and the FZK data gives ~17.0 euro/GJ costs for FT products12 (this study: 15.6 euro/GJ).
Figure 4 Cost breakdown of the production costs of the FT product.

The lowest production costs for the FT product (12.4 euro/GJ) are achieved by placing the synthesis plant in one hub and not in Rotterdam (R10a); however, from a transportation point of view (i.e., the amount of trucks required to run a day to the centralized plant), one hub is not realistic. Therefore, this case is evaluated on the basis of eight hubs as well (R10b), demonstrating clearly the (dis)advantage of economy of scale as the production costs increase drastically to 17.7 euro/GJ.

The second- to fourth-best routes are based on pretreatment by torrefaction (R9), pyrolysis (R8), or pelletization (R5) in the BCF. When compared to routes with the torrefaction and pyrolysis pretreatment in Rotterdam (R7 and R6, respectively), the advantage of pretreatment at the front end of the BtL production route is clearly demonstrated: the FT product costs are ~3 euro/GJ lower.

This effect can also be observed when comparing the routes based on chips transport with similar routes based on conventional pellets transport (R1 versus R5, R2 versus R6, and R3 versus R7); however, (conventional) pelletizing is less interesting than more advanced pretreatment (i.e., pyrolysis and torrefaction) overseas.

The low-temperature CFB gasification concept was evaluated on the basis of chips transport (R4). This route is the most interesting one of the routes with pretreatment in Rotterdam (R1 to R4). However, CFB gasification as a feeding system for EF gasification, however, will not be able to compete with overseas torrefaction or pyrolysis. The advantages of densification before transport outweigh the advantage of the CFB feeding.

CFB gasification can still be considered as a feeding system in the case of an overseas synthesis plant; however, on the basis of logistic problems overseas (as discussed before), one overseas plant is not realistic, and the advantage of CFB gasification will be compensated by the need for multiple overseas plants and, hence, the disadvantage of economy of scale.
Cost Breakdown

In the cost breakdown, the production costs are divided into biomass costs; transhipment, transportation, and storage costs (i.e., the logistics); capital costs; operation and maintenance costs; and utility, by-, and rest product costs. In the BtL plant, a large amount of heat is produced in both EF gasification and FT synthesis. By heat recovery steam generation in combination with electricity production, in most cases, net power is produced, resulting in additional benefits instead of costs (i.e., cost item utilities).

When looking at the cost breakdown of the FT product (Figure 4), the influence of pretreatment (i.e., densification) of the biomass on the final production costs of the FT product is clearly demonstrated.

The actual biomass costs, that is, initially 4.0 euro/GJ of biomass at the BCF or, taking into account the overall production efficiencies, even up to 7.0 euro/GJ of FT product, account for a significant part of the overall production costs.

The breakdown demonstrates that on an annual basis the actual biomass costs do not differ significantly for the evaluated BtL routes; hence the differences in production efficiency of the different BtL routes, caused by different pretreatment and gasification conditions, have a limited influence on the feasibility of the specific routes.

The breakdown also shows that in the case of chips transport (R1-R4) the logistic costs might run up to approximately one-third of the total production costs, hence providing some financial margin for pretreatment (i.e., densification) steps at the front end of the BtL production route. The additional investments related to these pretreatment steps are less than the associated logistic cost reduction (R5-R9).

Finally, it is noted that storage costs have only a marginal influence on the total production costs. Hence, the disadvantage of overseas FT synthesis with regard to the production of multiple products is limited; the construction of additional storage facilities will have almost no influence on the total production costs.
Conclusions

The main conclusions of the assessment of 10 BtL production routes are as follows: (1) Pretreatment (i.e., densification) of the biomass at the front end of the BtL route significantly increases the economic feasibility of the BtL production route. (2) Advanced overseas pretreatment by means of torrefaction is more attractive than pyrolysis or conventional pelletization. (3) Low-temperature CFB gasification benefits from higher efficiencies, but in order to be competitive with front-end torrefaction, an overseas synthesis plant is required. (4) A large-scale central overseas BtL synthesis plant would be the most attractive route for BtL production. However, local logistic aspects require the construction of several small-scale synthesis plants, causing significant economical disadvantages due to economy of scale, and (5) the FT product can be produced from overseas biomass for 15 euro/GJ (or 55 euro ct/L of diesel equivalent). At the crude oil prices of late 2005 (around $60/bbl), large-scale BtL can be considered as an economically feasible technology.

* Author to whom correspondence should be addressed. E-mail: zwart@ ecn.nl.

1. Steynberg, A.; Dry, M. Fischer-Tropsch Technol. October 2004.

2. van der Drift, A.; Boerrigter, H.; Coda, B.; Cieplik, M. K.; Hemmes, K. Entrained-Flow Gasification of Biomass; Ash Behaviour, Feeding Issues, System Analyses; Report C--04-039; Energy Research Centre of The Netherlands (ECN): Petten, The Netherlands, June 2004; p 58.

3. Boerrigter, H.; van der Drift, A. Syngas: Description of R&D Trajectory Necessary To Reach Large-Scale Implementation of Renewable Syngas From Biomass; Report C--04-112; Energy Research Centre of The Netherlands (ECN): Petten, The Netherlands, December 2004; p 29.

4. Antal, M. J.; Grnli, M. The Art, Science, and Technology of Charcoal Production. Ind. Eng. Chem. Res. 2003, 42, 1619-1640.[Full text - ACS] [ChemPort]

5. Prins, M. J. Thermodynamic analysis of biomass gasification and Torrefaction. Ph.D. Thesis, TU/e, Eindhoven, The Netherlands, 2005.

6. Bergman, P. C. A.; Boersma, A. R.; Kiel, J. H. A.; Prins, M. J.; Ptasinski, K. J.; Janssen, F. J. J. G. Torrefaction for Entrained Flow Gasification of Biomass; Report C--05-067; Energy Research Centre of The Netherlands (ECN): Petten, The Netherlands, July 2005; p 51.

7. Bergman, P. C. A. Combined Torrefaction and Pelletisation: The TOP Process; Report C--05-073; Energy Research Centre of The Netherlands (ECN): Petten, The Netherlands, July 2005; p 29.

8. Bergman, P. C. A. Torrefaction for Biomass Co-Firing in Existing Coal-Fired Power Stations "BIOCOAL"; Report C--05-013; Energy Research Centre of The Netherlands (ECN): Petten, The Netherlands, July 2005; p 72.

9. Weng, X.; Kersten, S. R. A.; Prins, W.; Van Swaaij, W. P. M. Biomass Pyrolysis in a Fluidized Bed Reactor. Part 2: Experimental Validation of Model Results. Ind. Eng. Chem. Res. 2005, 44, 8786-8795.[Full text - ACS]

10. Henrich, E.; Raffelt, K. Two-Stage Rapid Pyrolysis-Entrained Bed Gasification of Coal and Solid Wastes to Synthesis Gas. Patent EP1576621, 2005.

11. Henrich, E. Clean Syngas from Biomass by Pressurised Entrained Flow Gasification of Slurries from Fast Pyrolysis. Presented at Synbios, Stockholm, Sweden, May 18-20, 2005.

12. Calis, H. P.; Haan, J. P.; Peppink, G.; Boerrigter, H.; van der Drift, A.; Venderbosch, R. J.; Faaij, A. P. C.; van den Broek, R. Technical and Economic Feasibility of Large Scale Synthesis Gas Production in The Netherlands from Imported Biomass Feedstock; concept report; SDE: Amsterdam, May 2002.

13. Based on in-house data of the Energy Research Centre of The Netherlands (ECN), Petten, The Netherlands, December 2005.

14. Sipilä, K. Raw Material Availability to Synfuels Production and Remarks on RTD Goals - Results of the BioFuture Project. Presented at Synbios, Stockholm, Sweden, May 18-20, 2005.