In view of the structural energy supply weaknesses of the European Union and the increase of climatically relevant emissions, political authorities are required to continue to push the expansion of renewable energy carriers. As presented in the Biomass Action Plan of the European Union, great expectations are connected to the energetic use of biomass due to the given amount of potential. In light of guaranteeing sustainable mobility, increased emphasis is being placed upon the necessity to develop innovative procedures through which the bioenergy carriers can be applied for the generation of biogenic fuels along with the supply of electricity and heat.
The biofuels of the second generation appear to be especially promising, in particular the BtL-(biomass to liquid)-fuels. Since the procedural complexity for the production of such synthetic biofuels is very high, the production of these fuels can only take place effectively in large scale plants. However, supplying these large scale plants with a sufficient amount of spatially dispersed biomass involves substantial logistic complexity and can, in most cases, hardly be managed economically under the given conditions.
Therefore, an innovative BtL-concept, which aims to technically and logistically facilitate the use and supply of biomass for fuel generation, is presently being developed at the Karlsruhe Research Center. This so-called bioliq®-concept (in regard to its technical specification also called bioliq®-procedure) is based upon a combination of several regionally dispersed decentral plants for flash pyrolysis in which the biomass is converted into pyrolysis-oil-suspension (slurry) and, in this conditioned form, transported afterwards to a central gasification plant. There the slurry is converted into biofuel within the framework of a gasification and FT-(Fischer-Tropsch)-synthesis. Thereby, a much higher degree of transport efficiency and, subsequently, economicalness of the entire process should be achieved through the supply of a transportable secondary energy carrier (slurry), which possesses up to 10-times the volumetric energy density of the unprocessed biomass.
In connection with the evaluation of the specific supply processes for the bioliq®- concept, knowledge in regard to available biomass potential and its spatial dispersion takes on special significance. Ultimately, it is this knowledge that also decisively determines which spots are potentially suitable as locations for pyrolysis plants and which transport distances must actually be covered in order to deliver biomass and supply slurry to the central gasification/synthesis plant.
In order to produce biofuels according to the bioliq®-concept, the quantitatively significant and, to date, largely unused biomasses, namely forest wood residues and (grain-) remnant straw, which accumulate as energetically usable residues in agriculture and forestry, are of particular interest. Hereby, the bioliq®-procedure primarily opens up further options for the energetic use of straw which, due to its specific consistency, presents difficulties in the case of direct thermal use.
Against this background, it was the aim of this system-analytical dissertation to pursue the question in regard to which potential of (grain-) remnant straw and forest wood residues is available for energetic use in which sites of emergence and to what extent these can be economically supplied through the spatially coupled (decentral-central) bioliq®-concept. Furthermore, in this context, the question should be analysed in regard to which areas are suitable as locations for a pyrolysis plant, thereby taking the existent infra-structure into consideration. For reasons of simplification, all the spatial analyses which were conducted in this dissertation - these took place under implementation of a geographical information system - were limited to the Federal State of Baden- Württemberg. In regard to the spatial analyses, it was the intention to apply all quantities deduced in this dissertation to the municipality as the smallest spatial unit.
The generally available statistical data from agriculture and forestry constitute the inital point for the estimation of remnant straw and forest wood residue emergence. Since these data do normally not show the desired spatial reference, the deduced potentials were attributed to individual municipalities in the same county by a top-down approach which took various parameters and restrictions into account.
The potential estimation of remnant straw, which was deduced from a series of agrarian statistical reports, revealed a gross remnant straw emergence of about 2.9 million Mg FM for Baden-Württemberg in 2003 which is equal to an average yield of 6 Mg FM per ha (area for the cultivation of grain). Calculating the need for livestock keeping (about 0.9 million Mg FM) and the amount to be deducted for the preservation of humus balance (about 0.8 million Mg FM), approximately 1.2 million Mg FM, or rather, 1.0 million Mg DM straw remain in the end, which could be permanently removed from the agricultural production process and supplied for energetic use. The spatial assessment revealed a very favorable remnant straw emergence density, primarily for many municipalities in the regions of Franconia and Danube-Iller. A glance at the development of the past years shows that the amount of straw has constantly grown through yield increases but, in particular, through a continual reduction of livestock along with a simultaneous change in the procedure of animal husbandry. It cannot yet be estimated to which extent this development will continue in the future. However, all things considered, it can be assumed that the high amount of remnant straw will remain almost unchanged within the next few years.
The data of the Forest Administration Planning and the National Forest Inventory from 2002 provided the basis for determining the emergence of forest wood residues. Because data from the wood emergence prognosis model (time horizon 2017), developed by the Forest Research Institute Baden-Württemberg, were reverted to, the estimation of forest wood residue potential is also distinguished by a prognostic aspect. Baden- Württemberg revealed a theoretically available amount of forest wood residue potential of annually 3 million m³, which corresponds to nearly 1.6 million Mg DM. Taking other sortiments of wood (e.g., small dimensional wood and pulp wood) into consideration, this amount could be increased to as much as 2.7 million Mg DM. Deducting an estimated forest wood residue amount of about 0.5 million Mg DM, which could be used as firewood in the future, a theoretically free potential of approximately 2.1 million Mg DM remains. Due to restrictive factors, i.e., developmental situation and property structure, a mere potential of approximately 1.2 million Mg DM may actually be mobilizable, whereby only half can be regarded as easily accessible. Since this amount greatly depends on the development of the (wood chips) market price, an attempt was made within the context of a short excursus to derive a function which reflects the connection between accessible potential and market price. Commensurate to the priceelastic character of this function, based upon present conditions, an increase in the market price of as much as 10 to 30 €/Mg DM could lead to a strong increase in mobilizable potential. Accordingly, at a market price of an estimated 70 to 80 €/Mg DM, the above mentioned 1.2 million Mg DM (free forest road) could be supplied. In view of the positive supply developments, which were documented within the context of both of the previous National Forest Inventories, logging could substantially be increased. Therefore, under favorable conditions, a long-term supply with sufficient amounts of forest wood residues appears to be theoretically possible. In the face of existent forest area distribution, the municipalities with the heaviest emergence are located in the area of the Black Forest, whereby the potential is difficult to access because of unfavorable ground conditions and can, therefore, hardly be economically developed at the present time.
An essential step in the supply process is that of collection, which serves to combine the biomasses to larger amounts on their sites of emergence and prepare them for transport. The costs, which are entailed in the collection of forest wood residues, were not self-estimated, but rather based upon the details of relevant literature. On the other hand, the collection costs for remnant straw were derived from the author's own calculations. Because the collection costs are mainly defined by local conditions (developmental situation, ground conditions, operational structure, etc.), it was attempted to include these as much as possible.
For the collection and supply of straw in bale form - a common procedure -, the conditions in Baden-Württemberg, depending on the size of the removal area and emergence density, revealed estimated collection costs of approximately 40 to 70 €/Mg DM (average value with regard to specific local conditions: 63 €/Mg DM). In light of costoptimization collection, special significance should be attributed to the arrangement of an efficient organization (formation and inclusion of farming collectives and machine syndicates) as this furthers the use of powerful (large bale-) presses in the event of simultaneous optimal utilization capacity.
According to respective local conditions, different mechanized harvesting systems can be used for the collection and supply of forest wood residues in form of wood chips. This resulted in a cost span of 30 to 180 €/Mg DM (free forest road, or rather, forest vincinity chopping location). Taking various local conditions into account, the average collection rate for Baden-Württemberg can be set at about 83 €/Mg DM (free forest road, or rather, forest vicinity chopping location). Therefore, in many cases, the removal of forest wood residues is neither economically nor technically sensible, particularly in several regions of the Black Forest due to the difficult developmental situation there. Such is the case although the logging and subsequent forest wood emergence are the highest in comparison to other regions of Baden-Württemberg.
A comparison between the collection costs for forest wood residues and those for remnant straw reveals a correspondingly wide range for both. However, this range is not nearly as pronounced and the collection costs are altogether lower for remnant straw than for forest wood residues. In view of these high ranges in cost, under the present market conditions (energy price level), a great amount of potential remains unused. To what extent and when it will be possible to mobilize this mostly unused potential for utilization in large scale plants depends primarily on two factors: on the one hand, the development of energy prices and, on the other hand, the extent to which it is possible to create clear national market conditions through organized measures.
Transport represents a further step in the supply process. For the calculation of transport costs, different means and variations of transport were analysed, depending on the goods (straw bales, wood chips, slurry) and the transport distance. Due to lower mass loading and higher transport costs, the transport of straw bales is generally more expensive than that of forest wood chips. However, considering the complexity of the biomass drying process at the plant, the higher costs for the transport of straw are more than compensated. Since the share of dry matter constitutes an important quantity, it is economically advantageous if the forest wood residues can, in the form of predried wood chips, also be supplied at the pyrolysis plant.
Because higher energy density is achieved through the conversion of biomass to slurry, the specific transport costs are much less than those for unprocessed biomass. Considering slurry production costs, the supply of slurry shows cost advantages from a transport distance of approximately 150 km. Correspondingly, the relatively economical long-distance transport, which is decisive for the supply of a large plant, is made possible through the bioliq®-concept. Altogether, several means of transport are available, whereby the selection of which also depends upon the local infra-structure. Due to its cost structure and flexibility, in the majority of cases the truck constitutes the most suitable means of transport for the goods discussed here (straw bales, wood chips, slurry). For the transport of wood chips from distances of 130 km and that of slurry from 100 km, transport by train does, however, prove to be more economical than by truck.
As the transport analyses have shown, the influence of transport distance upon transport costs is less significant than is commonly assumed, since transport also include the expenses for loading, reloading and unloading and this leads to distinctly higher specific transport costs per km than in the case of long transport distances.
The determination of potentially suitable pyrolysis plant locations occurred on the basis of previously estimated potential and estimation costs, thereby taking the existing infra-structure into account. In order to do so, characteristic values of the municipalities were derived within the context of a location analysis, on the basis of which it was possible to compare different locations with one another. By emphasizing specific location characteristics in the form of cartographic presentations, a decision-making aid was created in the search for a location in regard to bioenergy projects. Ultimately, it became apparent that particularly advantageous locations for pyrolysis plants are exclusively to be found in those areas of Baden-Württemberg which have an aboveaverage density of remnant straw emergence. In view of the findings, particularly due to the high supply costs, only a few locations (n<4) in baden-württemberg appear to be currently suitable as locations for a pyrolysis plant (100 mwin, powered by straw and forest wood residues). because the plant capacity of about 56 decentral pyrolysis plants (plant capacity respectively 100 mwin) would be necessary for the slurry supply of a central large scale plant (plant capacity e.g., 4.500 mwin), a sufficient supply can - based upon an assumed location of this central large plant in karlsruhe - only be accomplished by installing several pyrolysis plants in areas outside of baden- württemberg. thereby, in light of competitive utilization options, it remains questionable as to what extent it will be possible to find sufficient suitable pyrolysis plant locations in other regions.
On the basis of the characteristic values attained by means of the locations analysis, three different exemplary locations (Ehingen, Forbach, Schillingstadt; catchment area < 25 km; plant capacity < 100 mwin) were selected and contrasted within the context of this dissertation. according to this, both locations ehingen and schillingstadt, which are characterized by high straw emergence, have an emergence density (remnant straw and forest wood residues; pertaining to ground area) of a total of 0.9 mg dm/ha (average rate for baden-württemberg: 0.6 mg dm/ha). for the supply of biomass on both of these locations, costs arise (free pyrolysis plant ) of an average of about 75 €/mg dm (thereof 16 €/mg for transport). in comparison, forbach, which is located in the northern black forest and is exclusively dominated by the emergence of forest wood residues, achieves a total emergence density (remnant straw and forest wood residues) of merely 0.5 mg dm/ha; the costs for the supply of biomass thereby amounting to slightly over 100 €/mg dm (thereof 12 €/mg dm for transport). in this respect, the assessment once again emphasizes the significance which is attributed to strawdominated locations. moreover, it has been shown that more biofuel would be available through increased expansion of the catchment area and, hence, higher power plant capacity with corresponding cost degression effects could be realized. however, more unfavorable emergence areas, whose biomass is correspondingly more expensive, are often located within the catchment area of the plant. because the average supply price thus rises, the cost reduction potentials, induced by an increase in plant performance, are greatly compensated.
An implementation of the bioliq®-concept, by which the pyrolysis and gasification/ synthesis are combined at one location and the biomass is supplied at the central gasification/synthesis plant without previous conversion to slurry, cannot be recommended. Such is the case, although through the direct spatial coupling of pyrolysis and gasification, a higher net efficiency and, thereby, slightly lower production costs for the BtL-fuel can be achieved. A comparison of both concepts - integrated or decentral - showed, on the basis of a reference plant, that, beside the very high spatial flexibility, a number of further reasons also speak in favor of the decentralized concept.
Under the assumptions made in this dissertation regarding the combined use of wood and straw, the production costs for the BtL-fuels amount to about 1 € per liter (excl. energy tax and VAT), whereby up to 65 % are caused by the costs connected to supplying biomass. Given that increased bioenergy use could lead within the next few years to a tightened market situation regarding economical biomass potential, the defined production costs will hardly be possible to undercut, despite further technical developments, learning and degression effects. However, at present, it is difficult to predict how the market situation and its effects upon bioenergy will actually develop.
As the assessments in this dissertation have shown, there are theoretically sufficient free potentials of both of the most quantitatively significant bioenergy resources, namely remnant straw and forest wood residues, available in Baden-Württemberg for energetic use. However, against the background of the insights gained in this dissertation, an extensive supply of large BtL-plants with sufficient amounts of economical biomass can hardly be achieved under the present conditions. For this reason, a short term realization of the bioliq®-concept in Germany or Baden-Württemberg remains rather doubtful. On a long-term basis, altered framework conditions could indeed change this situation substantially, so that the establishment and operation of one or more pyrolysis plants in Baden-Württemberg could be quite feasible. However, the discussion of the bioliq®-concept in regard to biomass and suitable locations should be much more extensively conducted and not merely limited to that which is feasible in Germany or Europe.
Even if the (industrial) realization of this concept is rather improbable at present, the development of this technology should be further pursued so that, at a given time, if necessary, renewable liquid carbon carriers can be supplied from biogenic remnants and wastes. Thereby, the attention of research and development projects should not only be directed toward the design of plant technical processes, but rather toward supply techniques and the establishment of mobilization and organizational structures connected with supply.
Summa summarum an array of questions of technical, economical and ecological relevance need to be answered on the road to the industrial application of the bioliq®- concept . The dissertation at hand, however, has aimed to disclose potential weaknesses of the Karlsruhe bioliq®-concept and contribute toward objectifying the discussion in regard to the extremely complex issue of the generation of biofuels.