A large number of national and international techno-economic studies on industrially integrated gasifiers for production of biofuels have been published during the recent years. These studies comprise different types of gasifiers (fluidized bed, indirect and entrained flow) integrated in different industries for the production of various types of chemicals and transportation fuels (SNG, FT-products, methanol, DME etc.) The results are often used for techno-economic comparisons between different biorefinery concepts. One relatively common observation is that even if the applied technology and the produced biofuel are the same, the results of the techno-economic studies may differ significantly.
The main objective of this project has been to perform a comprehensive review of publications regarding industrially integrated biomass gasifiers for motor fuel production. The purposes have been to identify and highlight the main reasons why similar studies differ considerably and to prepare a basis for “fair” techno-economic comparisons. Another objective has been to identify possible lack of industrial integration studies that may be of interest to carry out in a second phase of the project.
Around 40 national and international reports and articles have been analysed and reviewed. The majority of the studies concern gasifiers installed in chemical pulp and paper mills where black liquor gasification is the dominating technology. District heating systems are also well represented. Only a few studies have been found with mechanical pulp and paper mills, steel industries and the oil refineries as case basis. Other industries have rarely, or not at all, been considered for industrial integration studies. Surprisingly, no studies regarding integration of biomass gasification neither in saw mills nor in wood pellet production industry have been found.
There are several reasons why the results of the reviewed techno-economic studies vary. Some examples are that different system boundaries have been set and that different technical and economic assumptions have been made, product yields and energy efficiencies may be calculated using different methods etc. For obvious reasons, the studies are not made in the same year, which means that different monetary exchange rates and indices have been applied. It is therefore very difficult, and sometimes even impossible, to compare the technical as well as the economic results from the different studies. When technical evaluations are to be carried out, there is no general method for how to set the system boundaries and no right or wrong way to calculate the system efficiencies as long as the boundaries and methods are transparent and clearly described. This also means that it becomes fruitless to compare efficiencies between different concepts unless the comparison is done on an exactly equal basis.
However, even on an equal basis, a comparison is not a straight forward process. For example, calculated efficiencies may be based on the marginal supply, which then become very dependent on how the industries exploit their resources before the integration. The resulting efficiencies are therefore very site-dependent. Increasing the system boundaries to include all in- and outgoing energy carriers from the main industry, as well as the integrated gasification plant (i.e. total plant mass and energy balance), would inflict the same site-dependency problem. The resulting system efficiency is therefore a measure of the potential improvement that a specific industry could achieve by integrating a biomass gasification concept.
When estimating the overall system efficiency of industrial biorefinery concepts that include multiple types of product flows and energy sources, the authors of this report encourage the use of electrical equivalents as a measure of the overall system efficiency. This should be done in order to take the energy quality of different energy carriers into concern.
In the published economic evaluations, it has been found that there is a large number of studies containing both integration and production cost estimates. However, the number of references for the cost data is rather limited. The majority of these have also been published by the same group of people and use the same or similar background information. The information in these references is based on quotes and estimates, which is good, however none of these are publically available and therefore difficult to value with respect to content and accuracy.
It has further been found that the variance in the operational costs is quite significant. Something that is particularly true for biomass costs, which have a high variance. This may be explained by natural variations in the quality of biomass used, but also to the different markets studied and the dates when the studies were performed. It may be seen from the specific investment costs that there is a significant spread in the data. It may also be seen that the differences in capital employed and process yields will result in quite large variations in the production cost of the synthetic fuels. On a general note, the studies performed are considering future plants and in some cases assumes technology development. It is therefore relevant to question the use of today’s prices of utilities and feedstock’s. It is believed that it would be more representative to perform some kind of scenario analysis using different parameters resulting in different cost assumptions to better exemplify possible futures.
Due to the surprising lack of reports and articles regarding integration of biomass gasifiers in sawmills, it would be of great interest to carry out such a study. Also larger scale wood pellet production plants could be of interest as a potential gasification based biorefinery.
Göteborg: Svenskt kunskapscentrum för biodrivmedel, f3 , 2013. , 52 p.