ap-3-12.dvi Acta Polytechnica Vol. 52 No. 3/2012 Energy Recovery from Contaminated Biomass Jǐŕı Moskaĺık1, Jan Škvařil1, Otakar Štelcl1, Marek Baláš1, Martin Lisý1 1 Brno University of Technology, Faculty of Mechanical Engineering, Energy Institute, Technická 2896/2, 616 69 Brno, Czech Republic Correspondence to: ymoska03@stud.fme.vutbr.cz Abstract This study focuses on thermal gasification methods of contaminated biomass in an atmospheric fluidized bed, especially biomass contaminated by undesirable substances in its primary use. For the experiments, chipboard waste was chosen as a representative sample of contaminated biomass. In the experiments, samples of gas and tar were taken for a better description of the process of gasifying chipboard waste. Gas and tar samples also provide information about the properties of the gas that is produced. Keywords: gasification in a fluidized bed, contaminated biomass, thermal disposal of waste. 1 Introduction The growth in energy consumption has led to interest in non-conventional fossil fuels. Biomass is an option for reducing the use of primary energy sources. An advantage of biomass is that it can be transformed directly into liquid and gaseous fuels [1]. If these fuels achieve certain quality parameters, e.g. pu- rity or satisfactory heat value, they can be used in a more suitable way. In recent times, there have been considerable advances in recovering energy from biomass, even in large-scale energy production. A well-known example has been the interventions made by the state in support of feed-in tariffs for power coming from renewable sources. A situation devel- oped when, due to the major impact on the market this type of fuel became “scarce goods”, particularly for larger consumers. Then consumers begin to look around for some other type of fuel. These criteria for biomass production are also met by certain non-toxic wastes that can summarily be referred to as contam- inated biomass. Contaminated biomass includes ma- terials such as wastes from agricultural production, and wastes from the furniture industry. Energy re- covery from contaminated biomass can be regarded from two angles, one of which focuses on energy pro- duction, while the other focuses above all on waste disposal. Legislative problems of gasification of con- taminated biomass are beyond the scope of this pa- per, but would form a topic for a separate paper by a different kind of specialist. 2 Basic types of contaminated biomass The main hindrance to recovering energy from con- taminated biomass is its elevated content of unde- sirable substances. Biomass is usually contaminated in its primary, non-energy use. Contaminants may vary significantly, according to the primary use and the origin of the biomass. Basically, contaminated biomass can be classified into a small number of ba- sic groups, as follows: • agricultural production wastes [2] • construction industry wastes • furniture industry wastes • sludge from waste water treatment plants • wastes from paper production and cellulose pro- cessing • wastes from the textile industry — biological components and plant residues used in textile production (flax, cotton, hemp, etc.) Each group has its specific features, according to the type of substances the biomass has been exposed to, or treated with, for its primary use. While wastes from agricultural production tend to have elevated levels of nitrates, construction industry wastes have frequently been treated with protective agents, bond- ing primers, paints, etc. [3]. 3 Experimental fuel Since the material is readily availability, our study fo- cuses on wastes from furniture manufacture. These wastes include materials contaminated by being pro- cessed with chemicals (e.g. bonds and binders, glues and adhesives, lacquers, and also biocidal products). A typical representative of wastes from furniture manufacture is waste chipboard. This waste contains a whole gamut of additives to boost the resistance of the wood. Waste chipboard has a suitable consis- tency and is quite widely available. Chipboard was chosen for experiments using the Biofluid 100 gasi- fier. For operating reasons, the chipboard has to be 77 Acta Polytechnica Vol. 52 No. 3/2012 crushed to be able to be fed way of screw conveyor into the gasifier. An analysis of the elemental composition and the basic properties of the experimental fuel was carried out by an accredited laboratory. The results of the analysis are summarized in the following tables. 4 Analysis of the experimental fuel sample There are only very small quantities of fluorides in crushed chipboard (284 [mg/kg] in dry matter, which corresponds to only 0.000284 %). Fluorides, together with chlorine, are problematic halogen compounds in the fuel sample. Halogens are present here in relatively small quantities; however, what also mat- ters is the compounds in which they are chemically bound. At relatively low gasification temperatures, some compounds may fail to decompose completely. Undesirable compounds may only undergo a trans- formation, giving rise to substances harmful to the living environment [5,6]. Compounds of chlorine are likely to be the most troublesome substances in this respect. In a fluidized bed, however, undesirable pro- duction of harmful substances is expected to be min- imized owing to the large contact area [2]. The wood and chipboard used in furniture pro- duction are very often treated with biocidal prod- ucts. These products are used to prolong the life of the material, to prevent the development of mould and material degradation. Biocidal products often contain chlorine, and their molecular structure often takes after the molecular structure of dioxins or fu- rans. Furans and dioxins rank among the most toxic substances of all [7]. 5 Energy properties of chipboard From the energy point of view, the heat value is probably the most essential property of fuels. Chip- board consists mainly of pieces of wood that have been treated to meet the requirements for furniture- making (e.g. low humidity). All kinds of glues and resins are considerable components of chipboard which also, in most cases, have good heat values. The experimentally verified heat value of chipboard is rel- atively high (see table 2). Table 1: Results of the initial ultimate analysis of the experimental fuel [3,4] Anneal Obtained sample Waterless sample Sample combustible [%] [%] [%] Gross water 4.08 – – Residual water 7.15 – – Water total 11.23 – – Ash content at 550 ◦C 1.02 1.15 – Combustible 87.75 98.85 100 Volatile matter 70.35 79.25 80.17 Fixed carbon 17.40 19.60 19.83 Ultimate analysis Hydrogen H 5.65 6.36 6.43 Carbon C 42.59 47.98 48.54 Nitrogen N 3.64 4.10 4.15 Oxygen O 35.84 40.37 40.84 Sulphur total 0.04 0.05 – Sulphur volatile 0.03 0.04 0.04 Sulphur in ash 0.10 0.01 – Cl total – 0.048 – Fluorides 284 [mg/kg] in dry matter [3, 4] 78 Acta Polytechnica Vol. 52 No. 3/2012 Table 2: Energy parameters of the test specimen of “fuel” [4] Energy parameters Anneal Obtained sample Waterless sample Sample combustible [%] [%] [%] Combustion heat [kJ/kg] 17 601 19 828 20 059 Heat value [kJ/kg] 16 068 18 433 18 647 Table 3: Chemical analysis of ash from crushed fur- niture [3,4] Chipboard ash composition Compound [%] Element [mg/kgash] SiO2 15.30 Pb 223 Fe2O3 3.60 Cd less than 10 MnO – Cu 484 Al2O3 7.28 Hg less than 10 TiO2 25.80 Mn 12 500 CaO 19.00 Cr 170 MgO 4.35 Ni 107 Na2O 1.83 Zn 2 900 K2O 8.90 Cl 0.46 SO3 2.77 P2O5 2.34 6 Chipboard ash The composition of ash has a significant impact on its properties, and consequently also on the ways in which the fuel is utilized in various technologies. This is particularly the case for new untested fuels. Typical problems are with ash sintering, which is dependent on the composition of the ash. Here, the most important elements are silicon, sodium and potassium, because the oxides of these elements have a big influence on the sintering temperature of the ash. Chemical analyses were made of chipboard ash in order to illustrate fully the effect of ash on the equipment. The analyses were performed in an ac- credited laboratory. The ash was obtained by con- trolled annealing of the material at 550 ◦C. The val- ues of the content of individual constituents are given in the table 3. 7 Experimental measurements Test measurements were made on the BIOFLUID 100 experimental unit in 2010 and 2011. A more detailed description of our experimental unit can be found in earlier studies published by our institute. The main purpose of the experimental measurement was to establish the potential for thermal gasifica- tion of crushed furniture chipboard. As this is not a conventional fuel, the initial measurements aimed mainly at finding and verifying a suitable gasifica- tion method for this material. The tests focused on the process of gasification proper of the mate- rial, to see whether there are any process limita- tions. [3] Figure 1: The BIOFLUID 100 experimental gasifica- tion unit [8] In the early stage of the first measurements, dif- ficulties arose with stabilization of gasification tem- perature. These difficulties were successfully resolved in the course of the experiment. The probable cause was the supply of excessive amounts of primary air, and the relatively fine consistency fuel that was prob- ably released from the fluidized bed. In other words, no stable fluidized bed could properly form. Never- theless, the first experiments showed that chipboard can be gasified using Biofluid. However, it is neces- sary to take into account the consistency of the fuel, and changes in the control of the screw conveyor must be made gently. 79 Acta Polytechnica Vol. 52 No. 3/2012 Figure 2: Important temperatures in the gasifier, and an indication of the time course of the gas tar samplings (T101 – temperature on the fire grid, T102 – temperature at the beginning of the fluidized bed, T103 – temperature on top of the fluidized bed, T107 – temperature at the outlet from the gasifier) Figure 3: Measurements of the pressure loss of the fluidized bed are used to describe the stability of the fluidized bed and the gasification process 80 Acta Polytechnica Vol. 52 No. 3/2012 Table 4: Composition of the gas mixture produced during the experiments Sample Temperature CO2 H2 CO CH4 N2 Ethane Misc Sum Total Time [◦C] [%] [%] [%] [%] [%] [%] [%] [%] 11:04 760 16.80 6.38 13.33 5.07 57.81 0.480 0.130 100 11:40 760 17.39 6.54 12.19 4.14 59.28 0.350 0.110 100 12:07 760 17.58 7.25 13.79 4.15 56.83 0.280 0.110 100 12:04 780 17.33 7.63 14.36 3.64 56.76 0.160 0.110 100 12:42 770 17.57 7.09 12.45 2.97 59.69 0.120 0.110 100 13:07 780 18.15 6.54 10.51 2.05 62.04 0.660 0.040 100 13:43 800 16.80 6.19 11.27 1.93 63.07 0.670 0.060 100 14:18 805 17.22 7.44 12.43 2.20 59.90 0.760 0.040 100 14:53 805 15.81 7.09 13.54 2.87 59.74 0.880 0.070 100 Table 5: Summarized results from tar analysis to for comparison Gasification temperature 770 ◦C 800 ◦C Volume of gas [l] 156.0 156.0 Volume of acetone [ml] 156.3 161.8 Benzene [mg/m3] 3 453.7 3 645.5 Toluene [mg/m3] 1 619.0 1 413.3 m+p+o-xylen+ethylbenzene+phenylethyne [mg/m3] 603.4 954.3 Styrene [mg/m3] 725.0 627.1 C3-benzene sum [mg/m3] 1 013.3 847.3 BTX sum [mg/m3] 7 414.4 7 487.6 Oxygenous sum [mg/m3] 2 854.2 1 353.6 other substances (tar) [mg/m3] 398.4 452.0 sum of TAR (wihtout BTX) [mg/m3] 5 779 4 730 tar by TAR protocol [mg/m3] 9 740 8 572 To form an idea, the following graph shows the temperature course of one of the experiments in re- lation to the frequency values of the screw conveyor. It is clear that the initially unstable course of gasifi- cation was successfully stabilized. It was only after an attendant’s intervention in the screw conveyor fre- quency that temperature fluctuations occurred in the gasifier. Another measured variable is the pressure loss of the fluidized bed. A change in this value shows the stability of gasification process during the exper- iment. The next task was to conduct chipboard gasifica- tion at temperatures ranging from 760 ◦C to 830 ◦C, and to assess the impact of the gasification temper- ature on the composition of the resultant gas. Af- ter the unit had been heated to the required op- erating temperature, samples of tar and gas were taken. The following table summarizes the volume concentration values of individual constituents of the produced gas mixture. The samples are indicative of the production of a relatively stable mixture of gases. It was found that the gas composition values and the tar content values in relation to temperature cor- respond with the tar content in the gasification of conventional wood chips. However, deposits of com- pounds that have not yet been closely examined were left on the walls of the sample containers following the sampling. The next table summarizes some of the tar analysis results for the purposes of compar- ison. Only a small part of the total tar analysis is shown, as a single analysis produces a large number of values. 81 Acta Polytechnica Vol. 52 No. 3/2012 8 Conclusions The results of our experiments have shown that it is feasible to gasify crushed chipboard. What is im- portant, however, is stepwise and unhurried control of the screw conveyor operation to avoid clogging. It was also noted that the temperature response of chipboard to the screw conveyor frequency is much slower than in the case of fuel wood chips. The fluctuational pressure loss of the fluidized bed testifies to poorer stability of the proper gasification process. The fluctuations may originate from a lack of homogeneity of the tested fuel. The crushed furni- ture contained a relatively high volume of fine frac- tion, which sank to the bottom of the feedstock con- tainer during handling, and was therefore the first to enter the gasifier. The experiments show that the optimum temper- ature for chipboard gasification is somewhere around 800 ◦C. In gasification at temperatures in excess of 820 ◦C, fuel caking occurs in the fluidized bed, and it also solidifies above the grate. At temperatures be- low 770 ◦C, there is a growing tar content in the gas that is produced. A comparatively high concentration of undesir- able compounds that are harmful to health was as- sumed, due to the high content of additives used in chipboard manufacture. However, the gas that is produced is just an intermediary of this technology. The resultant concentrations of harmful substances should only be quantified after the gas has been com- busted. To carry on with this research, BIOFLUID has been equipped with a special combustion cham- ber, in which the gas will be used as a fuel. In the course of the follow-up research, emission measure- ments will be carried out only with the outlet flue gas. Acknowledgement This research was realized with support from the Faculty of Mechanical Engineering, Brno University of Technology, in project FSI-J-10-40 Thermal Liq- uidation of Contaminated Biomass. References [1] Baláš, M., Lisý, M.: Water-steam influence on biomass gasification process, Acta Metallurgica Slovaca, 11, 1, 2005, 14–21, (in Czech). ISSN 1335-1532. [2] Werthera, J., Saengera, M., Hartgea, E.-U., Ogadab, T.: Combustion of agricultural residues, Progress in Energy and Combustion Science, 26, PERGAMON, 2000,, 1–27. 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