Energy Fuels 2010, 24, 6142–6150 Published on Web 11/01/2010
: DOI:10.1021/ef100875g
Sustainable Valorization of Bamboo via High-Temperature Steam Pyrolysis for Energy Production and Added Value Materials Efthymios Kantarelis,*,† Junli Liu,‡ Weihong Yang,† and Wlodzimierz Blasiak† † Royal Institute of Technology, School of Industrial Engineering and Management, Division of Energy and Furnace Technology, Brinellv€ agen 23, 100 44 Stockholm, Sweden, and ‡Institute of Chemical Industry of Forestry Products, CAF, National Engineering Laboratory for Biomass Chemical Utilization, Key Laboratory on Forest Chemical Engineering, SFA, Nanjing 210042, China
Received July 8, 2010. Revised Manuscript Received October 8, 2010
Bamboo is an abundant plant in many Asian countries and especially in China; it has an extremely rapid growing rate, and it can be considered as a sustainable wood resource. In this paper, a comparative study of pyrolysis of bamboo in the presence of high-temperature steam and an inert atmosphere (N2) as well as characterization of products has been conducted. Evaluation of experimental results showed that faster devolatilization can be achieved in the presence of high-temperature steam. Furthermore, the gas composition indicates interaction of steam with vapors and solid species even at low temperatures. Analysis of the obtained liquid after steam pyrolysis at 797 K revealed that the H/C and O/C ratios in the liquid are 1.54 and 0.16, respectively. The characteristics of the products indicate possible exploitation of derived char as an activated carbon precursor, a reducing agent in metallurgical processes, or a solid fuel for gasification and combustion processes. The composition of the liquid fraction suggests further exploitation as a liquid fuel and/or chemical feedstock.
hydrodeoxygenation, catalytic cracking, etc.6 These upgraded fuels exhibit properties similar to those of diesel and jet fuels.1 From the facts given above, it can be easily understood that biomass exploitation for the production of liquid fuels is promising as well as challenging. Nevertheless, the reckless use of biomass resources and especially of biomass species that are used in the food chain is under severe criticism. Therefore, exploitation of abundant species with a very fast growing rate, which do not compete with foodcrops, shall ensure further sustainability. Bamboo is widely planted and spread in China; however, its utilization has not been fully explored.7 Bamboo belongs to the woody-grass group of biomass and is a member of the Bambusoideae family, encompassing ∼1250 species within 75 genera worldwide.8 Bamboo grows very fast and usually takes 3-6 years to harvest, depending on the species and the plantation.8 The abundance of bamboo species in Asia and the fast rate of replenishment resulted in a growing global interest in bamboo as a structural material.9 Bamboo is widely used in building construction, building facade, wall repairs, decoration and sign erection, the furniture industry, and household wares.10,11 In Hong Kong, 7500 tons of bamboo scaffoldings are generated from the construction industry annually.12 Bamboo
Introduction The growing interest in biomass is a consequence of the increased awareness of the environmental, social, and energy security challenges the world is facing. Biomass is a promising alternative to fossil fuels because of its high rate of replenishment, environmental characteristics, and product versatility. There is widespread interest in developing liquid fuels from nonfossil sources, and biomass pyrolysis is considered the most attractive route.1 Liquid fuels from biomass pyrolysis are attractive because they can easily be transported, stored, and upgraded. They can be used for power generation in furnaces and boilers, replacing fossil fuels as feedstock.2 Raw bio oil can also be used in slow- to medium-speed diesel engines because they can tolerate low-grade fuels, while thermal efficiency has been reported to be approximately equal to that for diesel fuel.3 Bio oil can even be used in high-speed diesel engines if blended with certain beneficial additives.4 However, bio oil has poor fuel properties when considering it as a transportation fuel. Among them, one of the most important is oxygen content.5 To improve those properties, several researchers have investigated several upgrading methods such as *To whom correspondence should be addressed. Telephone: þ46 8790 8459. E-mail:
[email protected]. (1) Demirbas, A. Appl. Energy 2011, 88, 17–28. (2) Fan, J.; Kalnes, T. N.; Alward, M.; Klinger, J.; Sadehvandi, A.; Shonnard, D. R. Renewable Energy 2011, 36, 632–641. (3) Czernik, S.; Bridgwater, A. V. Energy Fuels 2004, 18, 590–598. (4) Suppes, G. J.; Natarajan, V. P.; Chen, Z. Autoignition of Select Oxygenate Fuels in a Simulated Diesel Engine Environment, Paper (74 e), Presented at the AIChE National Meeting, New Orleans, 1996. (5) Qiang, L.; Zhi, L. W.; Feng, Z. X. Energy Convers. Manage. 2009, 50, 1376–1383. (6) Zhang, Q.; Chang, J.; Wang, T.; Xu, Y. Energy Convers. Manage. 2007, 48, 87–92. r 2010 American Chemical Society
(7) Liu, Q.-S.; Zheng, T.; Wang, P.; Guo, L. Ind. Crops Prod. 2010, 31, 233–238. (8) Scurlock, J. M. O.; Dayton, D. C.; Hames, B. Biomass Bioenergy 2000, 19, 229–244. (9) Chung, K. F.; Yu, W. K. Eng. Struct. 2002, 24, 429–442. (10) Mui, E. L. K.; Cheung, W. H.; Valix, M.; McKay, G. J. Hazard. Mater. 2010, 177, 1001–1005. (11) Jung, S.-H.; Kang, B.-S.; Kim, J.-S. J. Anal. Appl. Pyrolysis 2008, 82, 240–247. (12) Mui, E. L. K.; Cheung, W. H.; Lee, V. K. C.; McKay, G. Waste Manage. 2010, 30, 821–830.
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Energy Fuels 2010, 24, 6142–6150
: DOI:10.1021/ef100875g
Kantarelis et al.
Figure 1. Experimental setup.
the char exhibits good adsorption characteristics.17-21 Furthermore, a new concept of biomass and waste treatment in the presence of a high-temperature agent (HTAG) suggests production of medium- to high-calorific value gas.22,23 According to this concept, superheated, high-temperature steam is used not only as a gasifying and pyrolyzing agent but also as a heat carrier, and thus, no or minimum external heating or partial oxidation of the feedstock is needed to maintain the temperature.24 Furthermore, more uniform (“volumetric”) heating occurs.25 Uniform heat transfer to the total volume of the biomass is of great importance for the quality of the products. A combination of the HTAG concept with biomass pyrolysis in the presence of steam will therefore combine the advantages for the production of energy and valuable products from bamboo powder mentioned above. The goals of the paper are to investigate the effects of highly superheated steam present during pyrolysis of bamboo and to characterize the derived products.
has been reported to be extensively cultivated also in Korea, with more than 5000 ha of cultivated area.11 Despite the fact that bamboo waste is abundant in Asia and may have potential as a crop for niche markets, there have been a limited number of studies concerning its valorization in terms of energy.8 Bamboo char has been reported to have a large amount of micropores and a very large surface area approximately 4-10 times greater than that of wood char;13 therefore, bamboo studies were focused on producing activated carbons.7,10,14,15 Recently, a small number of studies concerning the generation of energy from bamboo with respect to cocombustion of bamboo with coal16 and bio oil production11 have been conducted. Jung et al.11 investigated the pyrolysis of bamboo sawdust for bio oil production in a fluidized bed reactor. A liquid yield of 70 wt % at 673-773 K and a low calorific value gas (9 MJ/ kg) were obtained. They concluded that the bio oil obtained can be used as fuel or feedstock for useful chemicals. The limited number of studies concerning bamboo energetic valorization denotes that its potential has not been widely realized. As mentioned above, a suitable process for treating bamboo is pyrolysis. However, for further sustainable exploitation of bamboo, advanced pyrolysis aspects have to be considered. Several researchers have reported that the bio oil yield increases when the raw biomass is pyrolyzed in a steam atmosphere and the liquid obtained is of higher quality, while
Experimental Section The experiments were conducted at the Royal Institute of Technology, Division of Energy and Furnace Technology, in Stockholm, Sweden. Experimental Procedure. The experimental facility used was a batch-type fixed bed reactor 1 m in length with an internal diameter of 0.1 m. The system was coupled with a personal computer for online measurement of temperature and mass. The schematic representation is shown in Figure 1.
(13) Zhao, R.-S.; Yuan, J.-P.; Jiang, T.; Shi, J.-B.; Cheng, C.-G. Talanta 2008, 76, 956–959. (14) Asada, T.; Ishihara, S.; Yamane, T.; Toba, A.; Yamada, A.; Oikawa, K. J. Health Sci. 2002, 48, 473–479. (15) Mizuta, K.; Matsumotoa, T.; Hatate, Y.; Nishihara, K.; Nakanishi, T. Bioresour. Technol. 2004, 95, 255–257. (16) Chao, C. Y. H.; Kwong, P. C. W.; Wang, J. H.; Cheung, C. W.; Kendall, G. Bioresour. Technol. 2008, 99, 83–93. (17) Yardim, M. F.; Ekinci, E.; Minkova, V.; Razvigorova, M.; Budinova, T. Fuel 2003, 82, 459–463. (18) Minkova, V.; Razvigorova, M.; Bj€ ornbom, E.; Zanzi, R.; Budinova, T.; Petrov, N. Fuel Process. Technol. 2001, 70, 53–61. (19) Putun, E.; Ates, F.; Putun, A. E. Fuel 2008, 87, 815–824. (20) Putun, E.; Uzun, B. B.; Putun, A. E. Biomass Bioenergy 2006, 30, 592–598.
(21) Zanzi, R.; Bai, X.; Capdevila, P.; Bj€ ornbom, E. Pyrolysis of Biomass in Presence of Steam for Preparation of Activated Carbon, Liquid and Gaseous Products. Proceedings of the 6th World Congress of Chemical Engineering, Melbourne, September 23-27, 2001. (22) Ponzio, A.; Yang, W.; Lucas, C.; Blasiak, W. Clean Air 2006, 7, 363–379. (23) Gupta, A. K.; Cichonski, W. Environ. Eng. Sci. 2007, 27, 1179– 1189. (24) Umeki, K.; Yamamoto, K.; Namioka, T.; Yoshikawa, K. Appl. Energy 2010, 87, 791–798. (25) Ponzio, A. Thermally Homogeneous gasification of biomass/ coal/waste for medium or high calorific value syngas production. Ph.D. Thesis, Royal Institute of Technology, Stockholm, 2008.
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: DOI:10.1021/ef100875g
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Table 1. Bamboo Powder Analysis moisture (wt %) cellulose (wt %) hemicellulose (wt %) lignin (wt %) extractives (wt %)
1.87 39.61 17.53 22.61 18.38
Ultimate Analysis C (wt %) H (wt %) O (wt %) N (wt %) Al (wt %) Ca (wt %) Fe (wt %) K (wt %) Mg (wt %) Mn (wt %) Na (wt %) P (wt %) Zn (wt %)
47.98 6.59 42.875 1.93 0.004 0.044 0.05 0.417 0.044 0.01 0.042 0.012 0.002
Figure 2. Char yields for N2 and steam pyrolysis.
Dry gas analysis was used for detection of O2, N2, CO, CO2, H2, CH4, C2H2, C2H4, and C2H6 using the gas chromatograph. The gas chromatograph used was a Varian micro-GC CP4900 model equipped with a thermal conductivity detector. Argon and helium were used as carrier gases on MOLSIEVE 5A and PORAPLOT columns, respectively. The temperatures of the columns were kept at 90 and 40 °C, respectively, at a constant pressure of 25 psi. The sampling and analysis time was 90 s. For liquid fraction analysis, gas chromatography and mass spectrometry (GC-MS) were used. The analysis of the bio oil fraction was conducted with a GC-MS system (Agilent 6890N/ 5973N) equipped with a fused silica capillary column (DB1701MS, 60 m 0.25 mm 0.25 μm film). The detector consisted of an Agilent 5973 mass selective detector (EI at 70 ev). The GC-MS temperature profile was set as follows: isothermal conditions at 45 °C for 4 min, temperature increase to 280 °C with a heating rate of 3 °C/min, and isothermal conditions at 280 °C for 15 min under a He atmosphere. The flow rate of the carrier was 1.0 mL/min, and the distribution ratio was 100:1. Pyrolysis products were identified by using the mass spectrum library of NIST02 and MSD Productivity ChemStation. Sample Characterization. Bamboo powder with a particle size of 200-500 μm was used. The elemental analysis was performed using a Vario Micro Elemental Analysis instrument. The alkali content and other metals present in the material were analyzed using a PE5300DV inductively coupled plasma spectrometer. From the analysis presented in Table 1, the empirical chemical formula of bamboo can be written as CH1.65O0.67. Bamboo was treated under an inert atmosphere with a nitrogen flow of 1 N m3 h-1 over a temperature range from ∼750 to ∼1150 K. The time for exposure to highly preheated nitrogen was such that complete devolatilization was achieved. Around 9-12 min was required for complete devolatilization of the samples. Steam pyrolysis experiments were performed with a steam flow of 7.85 ( 0.2 g/min. The steam pyrolysis runs were performed over the same temperature range described above. The total time of treatment was almost the same as in nitrogen pyrolysis runs, and it was determined by gas evolution and mass loss. The experimental run was considered finished when no apparent mass loss was observed (accuracy of 0.01 g) and the CO and CO2 content in the gas was less than 0.1 mol %.
Heat was supplied by the incoming medium (nitrogen or steam) that was flowing through a preheated ceramic honeycomb. This arrangement has been shown to provide highly effective heating with reported temperatures of up to 1473 K.26 The experimental procedure could be distinguished in three different phases: heating phase, stabilization phase, and experimental phase. During the heating phase, methane and air were combusted in the chamber to heat the ceramic honeycomb. The hot flue gases were driven out of the reactor to an exhaust system. During the stabilization phase, the pyrolysis agent (nitrogen or steam) was fed to the reactor and heated by ceramic honeycomb, attaining a nearly constant temperature. During the stabilization phase, a temperature decrease of ∼100 °C was observed. The gas temperature was measured by an S-type thermocouple placed after the ceramic honeycomb. The sample was placed inside the cooling chamber just above the reaction chamber, and it was continuously cooled with nitrogen. It has to be noted that during the stabilization phase the gas composition was continuously monitored to ensure the maintenance of an oxygen-free atmosphere. After temperature stabilization, the cooling nitrogen flow was stopped and the basket with the sample introduced into the reactor. The temperature of the sample was measured with an S-type thermocouple that was placed at the center of the basket. The heating rate of the sample varied with time and the preheated gas temperature from 50-60 to 100-110 K/min. The sampling line was comprised of three gas washing bottles immersed in an ice bath. Inside the washing bottles, glass bearings were introduced to enhance the cooling rate. During the experimental phase, the gas composition was measured every 90 s. When no further mass loss was observed, the basket was placed in the cooling chamber and cooled to
