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K. Reisinger, C. Haslinger, M. Herger, H. Hofbauer
Institute of Chemical Engineering, Fuel and Environmental Technology, University of Technology Vienna, Getreidemarkt 9,
1060 Wien, Austria
The increased utilisation of biofuels for heat and power production has become a political demand in the European Union.
This demand has resulted in a large number of biofuels being proposed for energy supply without sufficient consideration
given to their suitability for thermal conversion. For this reason the database BIOBIB was installed to bring together
the most relevant data for thermal utilisation of biofuels analysed by standard analytical methods. BIOBIB includes data
of the ultimate analysis of the elements, the proximate analysis, the analysis of the minor and trace elements, data about
the melting behaviour of the ashes and much more. BIOBIB does not only cover information about different types of wood,
straw and energy crops but also waste-wood samples and biomass-waste-assortments of different biomass-treating industries
(e.g.: wood processing industry, pulp and paper industry, food industry). Currently the database contains 647 different
samples. An Internet- homepage of BIOBIB has been installed which will make it possible to search for and download specific
data from BIOBIB through Internet. In the near future data about the gaseous emissions of different fuels, the fuels
reactivity under combustion conditions, specific data for the gasification of biofuels and other properties will be added
to the database.
KEYWORDS: Biomass - Database - Internet - BIOBIB
In 1992 a project was started to establish a database for Biofuels [1]. At this time it was possible to find isolated analysis on various biofuels in the literature which were mostly incomplete and sometimes even contradictory. In any case, such data were insufficient for a complete overview of the properties of biofuels in relation to thermal conversion. The above mentioned project financed the analysis of 94 different samples of biomass fuels which were analysed by standard analytical methods in order to obtain comparable results. For each sample the same analytical size was tested and the same testing procedure was used. Particular attention was given to those biofuels which could be considered as energy crops in central Europe. In a second step the database was then extended by the results recorded in various scientific publications and similar analysis [2]. A number of analysis of different biofuels, mainly data from woody biomass, were found in this period, the credibility of the data was checked and the data imported into BIOBIB. In a third step mainly biomass- waste- assortments [3] such as waste wood, particle boards, husks and shells from different plants, industrial residues and others were added to the database in order to cover all areas of biofuels. BIOBIB was also accepted as IEA project during TASK X, Activity one.
Today BIOBIB covers 647 different samples biofuels with a more or less complete set of analysed properties. All fuels were classed with related species into 8 main groups of biofuels as explained in table 1. The number of samples in these main groups are shown in graph 1.
Table 1: Classification of the BIOBIB- fuels into 8 main groups.
Main groups Remark --------------------------------------------------------------------- wood uncontaminated wood from forests, chipped wood straw straw from annual crops biomass-waste waste wood, residues from industries, railroad ties bark bark from different species energy crops miscanthus, other energy crops, whole crops husks and shells sunflower husks, cocoa hulls, pistachio shells grass grass from different species others sewage sludge, coconut fibre, cellulose, rapeseed
Graph 1: Amount of different biofuels in the main groups (GIF 9K)
To make it easier to survey, the fuels of a main group were divided into subgroups however many fuels found in literature were not sufficiently specified to insert them into their matching subgroup of biofuels. These data were integrated within the subgroup "not specified". Therefore it should be even be possible for unskilled users to find the demanded biofuel by using BIOBIB.
Today 47 different properties of the biofuels and the original quotation in literature are given in the database. The properties of the biofuels can be grouped into 7 different main fields as shown in table 2.
Table 2: Classification of the properties represented in BIOBIB.
Main fields Remark --------------------------------------------------------------------------------- ash analysis of the ash content ultimate analysis analysis of C, H, N, S, Cl calorific value analysis of the gross and net calorific value proximate analysis analysis of Si, Fe, Al, Ca, Mg, Na, K, Ti, CO2, SO3 and Cl ash- thermal behaviour analysis using DIN 51 730 in oxygen atmosphere ash- heavy metals analysis of Pb, Cd, Cu, Hg, Mn, Cr other analysis analysis of Mg, Ca, Al, Si, P, Fe, Pb, Cd, Cu, and others
As the data were collected from several different scientific publications the given properties were gappy analysed. Thus many data of interesting biofuels are incomplete. Examples of incomplete data are the missing chloride contents of some straw assortments. Investigations should be done to fill up the missing data by analysing specific data of selected biofuels. The percentage of values of the total possible amount of the main groups are given in graph 2.
Graph 2: Quantity of values of the main groups in percentage of the total possible amount (GIF 10K)
Due to the fact that the different data were analysed by different laboratories using different analytical methods the comparison of the data was checked by a round robin analysis [4]. A sample of straw was analysed by laboratories from Austria, Denmark, Sweden and the United Kingdom measuring the most relevant parameters for thermal utilisation as given in the BIOBIB.
The results of the ash content measurement, the ultimate analysis and the proximate analysis were reasonably comparable. Analysing the minor elements such as lead, copper and cadmium from the plants as well as from the ashes a great variety between the obtained results from the laboratories was found. Concerning lead a factor of 10 between the highest and the lowest reported value was determined.
Comparing the results from the analysis of the fusibility of the ashes analysed by different laboratories differences of 200°C were determined. The authors suggest that the analysis of the fusibility should be done by one operator using the same apparatus. Therefore all data in the BIOBIB concerning the fusibility of the ashes were measured by one operator using the same apparatus at the Institute of Chemical Engineering, Fuel and Environmental Technology at the Technical University of Vienna.
In general many efforts were made to lower the risk of wrong data by using standardised analytical methods and importing only reliable data to BIOBIB.
The properties of some data of BIOBIB differ very much from the average due to specific treatment of some biofuels. Inspecting for instance the copper content of the fuel ashes the values vary from 1.6 (Miscanthus) to 89300 ppm (salt impregnated wood). Such information must be considered concerning ash separation of the flue gases during thermal conversion of some assortments.
The ash content of the biofuels vary from 0.02 of oak wood to 45.8 of a sewage sludge fraction from Austria. These information should influence the technology of the incinerator. Other examples of great deviation to the average are the chloride content which varies from nearly zero (some woods) to 7627 mg/kg (rejects from the waste paper preparation) as well as the nitrogen content which varies from very low values to 5.93 percent of the dry matter (particle boards). As chloride and nitrogen influence the HCl and NOx emissions as described in paragraph 5 the above mentioned assortments require special flue gas cleaning.
Comparing the melting behaviour of straw and energy crops (Miscanthus) with any other biofuels it is obvious that most of the ashes of straw and Miscanthus start melting in a range of 600- 950°C whereas ashes from normal wood do not start melting before 1100°C. Data about the ash melting behaviour should be taken into consideration to avoid slagging problems in furnaces.
The heavy metal contents of untreated biomass are very low and even efforts were made to use biomass ashes for fertilisation in agriculture. Contaminated wood however can cause environmental problems during thermal conversion if there is no efficient fly ash separation from the flue gases. The ash fractions of these assortments should be deposited on save landfills with a leach water treatment facility.
In the last years efforts were made to use biomass by-products such as straw for thermal conversion. Using straw in fluidized bed incinerators with silica sand as bed material slagging problems occur and no constant operating conditions can be achieved. This slagging is not found during thermal conversion of wood or coal in the same facilities. To find out the reason for the slagging of straw ashes, BIOBIB was used to correlate the ash thermal behaviour with the main ash components. Doing this relevant data from BIOBIB were entered into SPSS multiple regression software program. Equations were found which describe the influence of the ash components to the thermal behaviour of the ashes [5]. It came out clearly that high potassium contents lead to low fusibility whereas high calcium or phosphorus contents lead to high fusibility of the ashes and the influence of the silica content was lower than engaged. As the potassium content of straw ashes are higher than from other fuels the reason of the slagging problem during thermal conversion of straw was discovered by BIOBIB.
Practical slagging and melting analysis with ashes and additives corroborate the equations found by the multivariate analysis of the data from BIOBIB. Because of this results some incineration plants in Austria already inject lime to the biofuels to avoid slagging of the ashes.
Several authors (such as [6]) found a correlation of the nitrogen content of the fuels and the NOx- emissions as shown in graph 3. Similar relations are true for sulphur and SO2 as well as chlorid and HCl. Therefore it is possible to predict a range in which the emissions of some pollutants will be, by looking up the ultimate analysis of the demanded biofuels in BIOBIB.
Graph 3: NOx- emissions of some biofuels with different fuel nitrogen contents (GIF 51K)
BIOBIB is a database created with Microsoft Access 2.0(R). With this database, the entering and updating of new data and the search for certain kind of biofuels is better executable than in other software programs like MS Excel(R). MS Access is an SQL-database, which means nothing more than data can be very easily administrated and, what is also important, new relations can be easily implemented.
Up to now, 647 biofuels and 47 analysed components (properties) are available and complemented. The biofuels were separated in groups, shown in Graph 4.
The query for specified BIOBIB-data will be available in the near future using the Internet on the following location:
http://edv1.vt.tuwien.ac.at/AG_HOFBA/BIOBIB/Biobib.htm
At the moment the BIOBIB-home-page and the data in crude tables are available.
Graph 4: Groups and subgroups of biofuels in the database (GIF 7K)
In the near future it is planned to implement more fuel-properties to BIOBIB as mentioned in the next paragraphs. It is no longer necessary to implement more biofuels but investigations should be done to fill up data of some gappy analysed fuels.
Emission data depend on both fuels and furnaces. Investigations will be done to implement emission data such as NOx, SO2 and HCl of specific furnaces and biofuels to BIOBIB.
The aim of implementing data about fuels reactivity is to describe carbon conversion kinetics dependent on fuel and combustion characteristics for each fuel. If these characteristics are specified BIOBIB should reveal the fuels reactivity which is the basis for designing and optimising combustors.
For these reasons, activity is also taken in IEA Task XIII Biomass utilisation, where all laboratory methods to characterise fuels under various conditions are compared and evaluated. The results of this project should be directly used in BIOBIB. Additionally work will be done in including the fuel nitrogen chemistry for prediction of the fuels potential for NO and N2O emissions.
Due to the fact that research and development activities of gasification processes are increasing in many European countries implementation of specific data for gasification such as the thermal behaviour of biomass- ashes in a reductive atmosphere to BIOBIB will occur.
Due to the large scale industry use of biomass for the production of fuel alcohol in particular in both the USA and in Brazil, quantitative data on the amounts of free sugars, cellulose and hemicellulose will be integrated.
Further data concerning the biological gasification of biomass will also be included.
To complete the database agricultural data such as yields or fertilisation needs of different plants will be added to BIOBIB.
As the new media can be used for scientific data exchange efforts are made improve the possibility to find specific data from BIOBIB through Internet and save the dedicated information on any local computer. It will also be possible to send some new data to the homepage of BIOBIB which can be implemented after seriously checking the correctness of the new information.
BIOBIB gives information about useful data for thermal conversion of biofuels. Properties of 647 different samples of many different species form mainly European plants are implemented to BIOBIB. A round robin analysis of 6 European laboratories analysing the same sample concluded that the results are reasonably comparable.
Due to the large amount of data statistical methods can be used to find data correlation.
A homepage of BIOBIB on Internet has been installed which will increase exchange and accessibility of data. Data search as well as data implementation (after seriously checking the credibility) will be possible for specific users on Internet. The possibility of implementing data through Internet will still increase the number of biofuels in the near future.
Investigations will be done to implement more fuel properties such as emission data, fuel reactivity data, gasification data and agricultural data to BIOBIB. These data will not only consider the combustion- process of biofuels which will enlarge the fields of application of BIOBIB.
In general BIOBIB should help to increase biomass utilisation.
