- Email: [email protected]
Research on biomass fast pyrolysis for liquid fuel
Available online at www.sciencedirect.com
Biomass and Bioenergy 26 (2004) 455 – 462
Research on biomass fast pyrolysis for liquid fuel Zhongyang Luo∗ , Shurong Wang, Yanfen Liao, Jinsong Zhou, Yueling Gu, Kefa Cen Clean Energy and Environment Engineering Key Lab of Ministry of Education, Zhejiang University, Hangzhou 310027, China Received 7 December 2001; received in revised form 1 April 2003; accepted 26 April 2003
Abstract A 0uidized bed reactor with 3 kg h−1 throughput operating at an atmospheric pressure with an inert atmosphere at 773 K has been used to produce bio-oils from the wood feedstocks such as Pterocarpus indicus, Cunninghamia lanceolata, and Fraxinus mandshurica, as well as from rice straw. The best oil-producing characteristics were for P. indicus and the worst were with rice straw. These data were used to design a larger scale unit of 20 kg h−1 throughput, and to estimate the production costs at an industrial scale. The quality of the bio-oil produced remains poor, and a combination of high value products and energy applications are needed for pro7tability. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Biomass; Bio-oil; Fast pyrolysis; Fluidized bed
1. Introduction China has a huge energy potential in its coal reserves; however, their use could lead to a carbon dioxide emission potential of 225 Gt [1]. However, biomass is abundant and underutilized in China. On a coal equivalent basis the annual supply is of the order of 700 million tonnes coal equivalent (mtce) [2]. During the last two decades, China has encouraged the development of modern biomass utilization technologies. The present program, “new or renewable energy development program 1996 –2010”, is promoting eBciency in biomass utilization. As a key laboratory of the Ministry of Education, the Clean Energy and Environment Supported by the National Natural Scienti7c Foundation (50176046, 50025618). Supported by the China NKBRSF Project, No. 2001CB409600. ∗ Corresponding author. Tel.: +86-571-87952440; fax: +86571-87951616. E-mail address: [email protected] (Z. Luo).
0961-9534/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2003.04.001
Laboratory of the University of Zhejiang is developing biomass pyrolysis technologies for application in Zhejiang Province. 2. Current situation of energy supply in Zhejiang Province Zhejiang Province is located in the southern part of the Yangtze River Delta on the southeast coast of China, which had a population of 43,430,000 in 1996. It borders Shanghai, the country’s largest city, on the northeast. Hangzhou is the provincial capital. The province covers a total continental area of 101; 800 km2 . Zhejiang Province lies in a subtropical zone of monsoon climate, which is blessed with abundant sunshine, ample rainfall in four distinct seasons. The annual temperature averages 288–291 K with the lowest in January and the highest in July. Zhejiang is de7cient in traditional fossil fuel, such as coal and petroleum. As listed in Table 1, primary
456
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
Table 1 Energy balance of Zhejiang in 1996 (physical quantity) Coal total (104 t) Total primary energy supply Indigenous production Recovery of energy Moving in from other provinces Import Sending out to other provinces (−) Export (−) Stock change Input (−) & output (+) of transformation Loss (−) Total nal consumption (−) Statistical di"erence
4593.81 122.65
Petroleum products total (104 t) 731.20
−38.48
0.16 689.73 360.66 −209.84 −140.78 31.27
−2252.18 −16.85 −2321.87
−90.46 −1.75 −641.19
2.91
−2.20
4679.06 0.58 −170.00
energy supply came mostly from other provinces or imported from foreign countries. And petroleum was hardly supplied by Zhejiang itself. Therefore, it is very urgent to seek eQective ways to solve resource shortage of fossil fuels. Fortunately, biomass is abundant in Zhejiang. Forestry covers 59.4% of the province’s total area with rich resources of economic forests and bamboo groves. Zhejiang has varied vegetation, acquiring the reputation “a treasure house of plants in southeast China”. For example, the rice output of Zhejiang achieved up to 11; 325; 000 t in 1999. However, with the gradual commercialization of rural energy, more and more farmers in rural areas would like to use LPG, electricity and even diesel rather than biomass for their daily energy consumption. Biomass energy consumption for rural residential areas decreased sharply in Zhejiang. For example, straw used for non-commercial energy consumption was about 9; 379; 800 t in 1991, while this value was only 5,885,700 in 1996. As a result, more and more biomass was abandoned at random or just burned ineBciently. So, it is necessary to develop new ways to transform raw biomass to high-quality energy products in Zhejiang. 3. Research on biomass pyrolysis for bio-oil at Zhejiang University At present, thermochemical conversion of biomass by pyrolysis and gasi7cation is becoming increasingly
Electricity (108 kW h)
Heat (1010 kJ)
Coke (104 t)
105.55 74.57
60.74
41.80
75.73
−10.82
−16.80
Other energy (104 tce) 11.29 11.29
1.81 373.79 −39.29 −440.08
3998.30 −162.80 −3835.50
66.77
−11.29
−127.58 −0.07
important for the eBcient production of fuels in commercial and industrial applications for power generation in diesels or boilers. In particular, liquid fuel from biomass pyrolysis, called as bio-oil, is expected to play a major role in the future energy supply. It oQers many advantages over raw biomass as an energy product. For instance, the liquid hydrocarbon product is compatible with the hydrocarbon fuels produced from petroleum. Optimization and upgrading of bio-oil will result in true hydrocarbons capable of substituting for the existing liquid fuels, such as gasoline or diesel, as will remit the petroleum pressure since 1973. Bio-oil also has higher density than raw biomass, which makes transportation and storage more convenient. Generally, fast pyrolysis was used to maximize high-grade bio-oil production [3]. And 0uidized bed technology appears to be the most potential in fast pyrolysis of biomass for bio-oil, as it oQers a high heating rate, rapid devolatilization, easy control, convenient char collection, low cost and so on. Therefore, a 0uidized bed fast pyrolysis reactor operating at atmospheric and nitrogen atmosphere was set up at Zhejiang University in 1999. By altering the value of reaction temperature, particle size, feed rate, reactor height and so on, the heating and pyrolysis rate of biomass were adjusted; also the residence time of particle and volatile were changed. After that, a large-scale 0uidized bed pyrolysis system was set up in 2002 for following feasibility study of industrialization, which had more advantages over the old reactor.
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
457
Fig. 1. Fluidized bed reactor system for fast pyrolysis of biomass.
3.1. Features of pyrolysis system As depicted in Fig. 1, the principal unit of the experimental system was a 0uidized bed reactor. The reactor had a diameter of 80 mm and a height at a varied value between 700 and 1200 mm. Three electric coils of 2 kW each provided the heat required during biomass pyrolysis. Biomass was fed continuously at a maximum rate of about 3 kg h−1 directly into the reactor by way of a unique feeder, which overcame the poor 0uidity and easy carbonization of the biomass material. Measuring points and gas samplers were placed along the reactor vertically to monitor the operation condition. The reaction temperature varied from 723 to 973 K, while nitrogen 0ow for 0uidizing sand in reactor was in the range of 3–6 Nm3 h−1 . Furthermore, in order to avoid low bio-oil collection and pipeline blockage caused from volatile pre-cooling before entering the quencher, the temperature in the connection pipe between cyclone and following the quencher was located always at some temperature higher than 573 K. The duration time of every experiment was de-
termined in the range of 1–2 h, according to the feed rate of biomass material. For gaseous phase path, nitrogen from the bottle was shunted to four routes. Afterwards, the major nitrogen, which may pass the preheating device 7rst according to work condition, entered the reactor bottom directly for 0uidizing bed sand in reactor. At the same time, other three 0ows of nitrogen assisted biomass solids entering the reactor successfully. Then the overall nitrogen together with the volatile released during pyrolysis passed the cyclone separator. After that, the puri7ed hot gas was cooled in the following pipe bundle quencher. And the bio-oil components could be determined by GC–MS analysis. And incondensable volatile with nitrogen was vented after passing the 7lter and gas sampler, whose component would be analyzed by GC method. For solid phase path, biomass solids were fed into the reactor and then heated to some reaction temperature. After thermal decomposition, the residue was carried into the cyclone and then was collected by gas–solid separation.
458
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
Table 2 Biomass analyses
F. mandshurica C. lanceolata P. indicus Rice Straw
Water (%)
Ash (%)
Volatile (%)
Fixed carbon (%)
Heating value (kJ/kg)
C (%)
H (%)
N (%)
S (%)
O (%)
1.85 3.27 1.96 3.61
3.58 0.74 0.44 12.2
76.9 81.2 79.3 67.8
17.9 14.8 18.4 16.4
20,200 19,200 20,500 16,400
48.3 46.5 49.1 40.3
5.95 6.04 5.98 5.55
0.18 0.17 0.22 1.02
0.19 0.12 0.12 0.15
40.1 43.1 42.3 37.3
70 60
50
Composition (%)
Products distribution (%)
60
40
30
20
10
0 700
50 40 30 20 10
740
780
820
860
900
Char
740
780
820
860
900
Temperature (K)
Temperature (K) Bio-oil
0 700
Gas
Fig. 2. Products distribution with temperature (P. indicus, 250 –355 m).
3.2. Experimental results and discussions Some experimental researches have already been carried out on biomass pyrolysis in a 0uidized bed reactor, and mostly focused on the temperature eQect. There is no doubt that temperature plays a major role in pyrolysis; however, biomass pyrolysis behavior is in0uenced crosswise by many parameters, such as particle size, feed rate, volatile residence time. Therefore, extensive experiments had been performed to study the fast pyrolysis behavior on the atmospheric 0uidized bed reactor in this paper. Table 2 show the character of raw biomass material used in the experimental research. As shown in Fig. 2, there existed an optimum temperature of about 773 K to produce more high-quality bio-oil. The result was well consonant with previous works on biomass rapid pyrolysis. For example, Conti et al. [4] arrived at a conclusion that the temperature
CO
CH4
CO2
Fig. 3. Incondensable gas composition with temperature (P. indicus, 250 –355 m).
of 793 K was optimum for bio-oil yield of 45% from bagasse. As temperature was greater than this value, secondary reaction of volatile would become violent, leading to a lower bio-oil yield. On the contrary, rather lower temperature also caused biomass incomplete decomposition. Besides this, the composition of incondensable gas was also in0uenced by temperature. Fig. 3 shows that high temperature would lead to a high proportion of CO and CH4 , while a low proportion of CO2 . This was largely because mostly CO2 was produced by carboxyl release at a relatively low temperature. Furthermore, the secondary cracking of volatile produced CO and CH4 rather than CO2 [5]. So at a higher reaction temperature, a higher heating-value gas could be obtained in pyrolysis of biomass for gas. Meanwhile, particle size had no obvious eQect on products distribution when less than 1 mm. Adjusting the reactor height and feed rate could alter the residence time of particle and volatile.
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
459
Table 3 EQect of biomass species on bio-oil production Biomass species
Temperature (K)
Particle size (m)
Yield (%)
Heating value (kJ/Kg)
Water a (%)
F. mandshurica C. lanceolata P. indicus Rice Straw
823 773 773 773
74 –154 74 –154 250 –355 154 –250
40.2 53.9 55.7 33.7
22,000 19,000 19,000 19,000
39.6 31.4 24.6 53.5
a Analyzed
by Karl Fischer method. Water in bio-oil could not separated from organic compounds easily.
Compared with reactor height, it was more eQective to increase the feed rate to shorten volatile residence so as to restrain secondary cracking. This was because shortening reactor height only acted on the dilute phase area at low temperature. However, with feed rate increase, the volatile residence time in the dense phase area at higher temperature would be cut signi7cantly. Moreover, heat transfer would be more intense as solid concentration rose, caused by feed rate increase. Biomass species played a signi7cant role in its fast pyrolysis. As shown in Table 3, with high yield, heating value and low water content as evaluation criteria, Pterocarpus indicus had the best characteristic in producing bio-oil, followed by Cunninghamia lanceolata and Fraximus mandshurica, and Rice Straw the worst. Correlating with the result in Table 2, this was somewhat related with ash content in biomass, which was not advantageous to obtain a high-quality bio-oil. In fact, ash had a larger eQect on biomass pyrolysis behavior than degree of crystallinity and polymerization [6]. Some elements in ash could catalyze pyrolysis behavior and change products distribution [7]. Besides this, biomass with ash removal could produce more bio-oil and less gas [8]. At the same time, ash had no eQect on biomass apparent weight loss because ash neither volatilized nor decomposed when the temperature was lower than 923 K.
Table 4 Relative content of main compounds in organic composition of bio-oil produced from P. indicus Compound
Relative content (%)
Furfural Acetoxyacetone, 1-hydroxyl Furfural, 5-methyl Phenol
9.06 1.21 1.82 2.55
2-Cyclopentane-1-one, 3-methyl Benzaldehyde, 2-hydroxyl Phenol, 2-methyl Phenol, 4-methyl Phenol, 2-methoxyl
1.58 2.70 5.04 0.51 0.27
Phenol, 2,4-dimethyl Phenol, 4-ethyl
9.62 2.18
Phenol, 2-methoxy-5-methyl Phenol, 2-methoxy-4-methyl Benzene, 1,2,4-trimethoxyl Phenol, 2,6-dimethyl-4-(1-propenyl) 1,2-Benzenedicarboxylic acid, diisooctyl ester 2-Furanone Levoglucosan Phenol, 2,6-dimethoxy-4-propenyl Furanone, 5-methyl Acetophenone, 1-(4-hydroxy-3-methoxy) Vanillin Benzaldehyde, 3,5-dimethyl-4-hydroxyl Cinnamic aldehyde, 3,5-demethoxy-4-hydroxyl
4.15 0.55 3.80 4.25 1.80 5.70 6.75 3.14 0.49 2.94 6.35 4.54 2.19
3.3. Bio-oil analysis Bio-oil had a higher density than raw material, which was not obviously aQected by work conditions. The value of density was located in the range of 1130 –1200 kg m−3 . The kinetic viscosity of bio-oil varied largely with biomass species. The value was mea-
sured with NDJ-1 kinetic viscosity meter in the case of constant temperature bath. For example, bio-oil produced from P. indicus and F. mandshurica had a kinetic viscosity of 70 –350 mPa s and 10 –70 mPa s
460
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
Fig. 4. New fast pyrolysis system at the feed rate up to 20 kg=h.
separately, and bio-oil produced from Rice Straw had a minimum kinetic viscosity about 5 –10 mPa s. This was mainly because the high water content in bio-oil would lead to a lower kinetic viscosity value. Bio-oil should be stored carefully for its corrosion caused by the acid constituents. Bio-oil had a lower pH value in the range of 2– 4, which was largely determined by raw material and water content in bio-oil. Furthermore, bio-oil had more than one hundred compounds, which implied the complexity of following re7ning or usage. According to the GC–MS analysis, bio-oil was mainly composed of levoglucosan, furfural, phenol and aldehyde. Table 4 shows the distribution of some detected compounds in the organic composition of bio-oil, which was produced from P. indicus. Above all, bio-oil was polar, tarry and highly unstable, therefore, upgrading of bio-oil should be processed to remove oxygen and improve bio-oil composition [9]. 3.4. New Pyrolysis system developed at Zhejiang University On the basis of previous experimental work on small-scale 0uidized bed pyrolysis reactor, a new fast pyrolysis system with a feed rate up to 20 kg h−1 constructed in 2002 for feasibility study of industrialization. As shown in Fig. 4, this new system has more special convenient features for application. Flu-
idized bed was also chosen for the reactor, which was designed in variable section to reduce the volatile residence time for restraining secondary cracking. Re-utilization of char and gas would reduce the cost in heat required in pyrolysis and 0uidizing gas. Besides this, multi-stage condensation was adopted for the disposal of heavy oil and high water-content liquid separately, so as to reduce the subsequent processing cost and maximize high-quality fuel oil production. 4. Techno-economic evaluations The object for evaluation is a biomass pyrolysis plant to produce bio-oil, using 0uidized bed technology. The feed rate of sawdust is assumed at the value of 2 t=day, which matches the capacity of a medium-scale wood machinery factory in Hangzhou, Zhejiang. The construction period of the project is half a year and the service life is 15 years. Therefore, the total calculation period is 15.5 years. And the reference data used in evaluation are listed in Table 5. Here, the selling price of bio-oil is pre-determined according to its heating value, which is compared with gasoline or diesel oil. As shown in Table 6, biomass pyrolysis technology has its potential in the future application under the 7nancial support and duty free. However, it is not
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462 Table 5 Basic data for techno-economic evaluation
Table 7 Sensitivity analysis
No.
Item
Unit
Value
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Construction period Service life Calculation period Bio-oil output Char output Sawdust consumption Power consumption Water consumption Depreciation rate Maintain rate Worker number Annual wages per person Sawdust cost Power cost Water cost Bio-oil price
year year year t/year t/year t/year kWh/year m3 % %
0.5 15 15.5 430 70 730 403000 880 6 2 2 10000 150 0.58 1 1200
Yuan Yuan/t Yuan/kWh Yuan=m3 Yuan/t
Table 6 Pro7t and loss statement (Yuan) No. Item
Pro7t and loss per t bio-oil
Annual pro7t and loss
1 2 3 4 5 6 7 8 9
−254.7 −2.0 −543.6 −46.5 −61.2 −183.5 = = +1200
−109500 −880 −233740 −20000 −26300 −78900 = = +516000
Feed stock Water Power Manpower Maintain Depreciation Financial charge Tax Income
Sum
+108.5
461
+46680
feasible to put this technology into application widely until the quality of bio-oil is largely improved. And Table 7 shows that bio-oil price has more eQect on project pro7t than sawdust price. However, if we promote the technology in energy-comprehensive utilization, the cost on bio-oil production will be reduced largely according to the high proportion of heating supply in bio-oil cost.
Vibration range (%)
IRR (%)
Fluctuation range of IRR (%)
Bio-oil price
−20 −10 0 +10 +20
−90.30 −1.10 5.00 10.20 14.90
−286 −122 0 104 198
Sawdust price
−20 −10 0 +10 +20
7.30 6.20 5.00 3.80 2.60
46 24 0 −24 −48
solve the shortage of fossil fuel and exploit abundant biomass resource. Especially liquid produced from biomass fast pyrolysis could be substituted for traditional liquid fuel, such as diesel oil. And detailed experimental research was carried out on a small-scale pyrolysis 0uidized bed reactor with a maximum feed rate of 3 kg h−1 . Experimental result showed that the temperature of 773 K was more suitable for high-quality bio-oil production. Besides this, the composition of incondensable gas was also in0uenced by temperature. Higher heating-value gas could be obtained at a higher reaction temperature in pyrolysis. P. indicus had the best characteristic for producing bio-oil, followed by C. lanceolata. and F. mandshurica, but Rice Straw was the worst. This was mainly because that higher ash content in biomass was disadvantageous to obtain high quality bio-oil production. However, upgrading of re7ning of bio-oil is necessary for its inferior property and complex composition. A larger-scale fast pyrolysis system was set up for research on industrialization, which had its advantage in energy-comprehensive utilization. And a simple techno-economic evaluation was proposed to assess the practicability of fast pyrolysis technology, which has potential in future application.
5. Conclusions
References
Biomass utilization is important for sustainable development of Zhejiang Province, for being able to
[1] Bach W, Fiebig S. China’s key role in climate protection. Energy 1998;23(4):253–70.
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Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
[2] Gu S, Duan M. A survey on biomass resource and energy utilization in China, In: Symposia on Power Generation Using Biomass, Jilin, China, 1998. 1–5 [in Chinese]. [3] Maschio G, Koufopanos C, Lucchesi A. Pyrolysis, a promising route for biomass utilization. Bioresource Technology 1992;42:219–31. [4] Conti L, Scano G, Boufala J. Bio-oils from arid land plants: 0ash pyrolysis of EUPHORBIA CHARACIAS bagasse. Biomass and Energy 1994;7(1– 6):291–6. [5] Boroson ML, Howard JB, Longwell JP, Peters WA. Product yields and kinetics from the vapor phase cracking of wood pyrolysis tars. AIChE Journal 1989;35(1): 120–8.
[6] Antal MJJ, Varhegyi G. Cellulose pyrolysis kinetics: the current state of knowledge. Industrial and Engineering Chemistry Research 1995;34(3):703–17. [7] Richards GN, Zheng G. In0uence of metal ions and of salts on products from pyrolysis of wood: applications to thermochemical processing of newsprint and biomass. Journal of Analytical and Applied Pyrolysis 1991;21:133–46. [8] Raveendran K, Ganesh A, Khilar KC. In0uence of mineral matter on biomass pyrolysis characteristics. Fuel 1995;74(12):1812–22. [9] Sharma RK, Bakhshi NN. Catalytic upgrading of fast pyrolysis oil over HZSM-5. Canadian Journal of Chemical Engineering 1993;71:383–91.
Biomass and Bioenergy 26 (2004) 455 – 462
Research on biomass fast pyrolysis for liquid fuel Zhongyang Luo∗ , Shurong Wang, Yanfen Liao, Jinsong Zhou, Yueling Gu, Kefa Cen Clean Energy and Environment Engineering Key Lab of Ministry of Education, Zhejiang University, Hangzhou 310027, China Received 7 December 2001; received in revised form 1 April 2003; accepted 26 April 2003
Abstract A 0uidized bed reactor with 3 kg h−1 throughput operating at an atmospheric pressure with an inert atmosphere at 773 K has been used to produce bio-oils from the wood feedstocks such as Pterocarpus indicus, Cunninghamia lanceolata, and Fraxinus mandshurica, as well as from rice straw. The best oil-producing characteristics were for P. indicus and the worst were with rice straw. These data were used to design a larger scale unit of 20 kg h−1 throughput, and to estimate the production costs at an industrial scale. The quality of the bio-oil produced remains poor, and a combination of high value products and energy applications are needed for pro7tability. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Biomass; Bio-oil; Fast pyrolysis; Fluidized bed
1. Introduction China has a huge energy potential in its coal reserves; however, their use could lead to a carbon dioxide emission potential of 225 Gt [1]. However, biomass is abundant and underutilized in China. On a coal equivalent basis the annual supply is of the order of 700 million tonnes coal equivalent (mtce) [2]. During the last two decades, China has encouraged the development of modern biomass utilization technologies. The present program, “new or renewable energy development program 1996 –2010”, is promoting eBciency in biomass utilization. As a key laboratory of the Ministry of Education, the Clean Energy and Environment Supported by the National Natural Scienti7c Foundation (50176046, 50025618). Supported by the China NKBRSF Project, No. 2001CB409600. ∗ Corresponding author. Tel.: +86-571-87952440; fax: +86571-87951616. E-mail address: [email protected] (Z. Luo).
0961-9534/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2003.04.001
Laboratory of the University of Zhejiang is developing biomass pyrolysis technologies for application in Zhejiang Province. 2. Current situation of energy supply in Zhejiang Province Zhejiang Province is located in the southern part of the Yangtze River Delta on the southeast coast of China, which had a population of 43,430,000 in 1996. It borders Shanghai, the country’s largest city, on the northeast. Hangzhou is the provincial capital. The province covers a total continental area of 101; 800 km2 . Zhejiang Province lies in a subtropical zone of monsoon climate, which is blessed with abundant sunshine, ample rainfall in four distinct seasons. The annual temperature averages 288–291 K with the lowest in January and the highest in July. Zhejiang is de7cient in traditional fossil fuel, such as coal and petroleum. As listed in Table 1, primary
456
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
Table 1 Energy balance of Zhejiang in 1996 (physical quantity) Coal total (104 t) Total primary energy supply Indigenous production Recovery of energy Moving in from other provinces Import Sending out to other provinces (−) Export (−) Stock change Input (−) & output (+) of transformation Loss (−) Total nal consumption (−) Statistical di"erence
4593.81 122.65
Petroleum products total (104 t) 731.20
−38.48
0.16 689.73 360.66 −209.84 −140.78 31.27
−2252.18 −16.85 −2321.87
−90.46 −1.75 −641.19
2.91
−2.20
4679.06 0.58 −170.00
energy supply came mostly from other provinces or imported from foreign countries. And petroleum was hardly supplied by Zhejiang itself. Therefore, it is very urgent to seek eQective ways to solve resource shortage of fossil fuels. Fortunately, biomass is abundant in Zhejiang. Forestry covers 59.4% of the province’s total area with rich resources of economic forests and bamboo groves. Zhejiang has varied vegetation, acquiring the reputation “a treasure house of plants in southeast China”. For example, the rice output of Zhejiang achieved up to 11; 325; 000 t in 1999. However, with the gradual commercialization of rural energy, more and more farmers in rural areas would like to use LPG, electricity and even diesel rather than biomass for their daily energy consumption. Biomass energy consumption for rural residential areas decreased sharply in Zhejiang. For example, straw used for non-commercial energy consumption was about 9; 379; 800 t in 1991, while this value was only 5,885,700 in 1996. As a result, more and more biomass was abandoned at random or just burned ineBciently. So, it is necessary to develop new ways to transform raw biomass to high-quality energy products in Zhejiang. 3. Research on biomass pyrolysis for bio-oil at Zhejiang University At present, thermochemical conversion of biomass by pyrolysis and gasi7cation is becoming increasingly
Electricity (108 kW h)
Heat (1010 kJ)
Coke (104 t)
105.55 74.57
60.74
41.80
75.73
−10.82
−16.80
Other energy (104 tce) 11.29 11.29
1.81 373.79 −39.29 −440.08
3998.30 −162.80 −3835.50
66.77
−11.29
−127.58 −0.07
important for the eBcient production of fuels in commercial and industrial applications for power generation in diesels or boilers. In particular, liquid fuel from biomass pyrolysis, called as bio-oil, is expected to play a major role in the future energy supply. It oQers many advantages over raw biomass as an energy product. For instance, the liquid hydrocarbon product is compatible with the hydrocarbon fuels produced from petroleum. Optimization and upgrading of bio-oil will result in true hydrocarbons capable of substituting for the existing liquid fuels, such as gasoline or diesel, as will remit the petroleum pressure since 1973. Bio-oil also has higher density than raw biomass, which makes transportation and storage more convenient. Generally, fast pyrolysis was used to maximize high-grade bio-oil production [3]. And 0uidized bed technology appears to be the most potential in fast pyrolysis of biomass for bio-oil, as it oQers a high heating rate, rapid devolatilization, easy control, convenient char collection, low cost and so on. Therefore, a 0uidized bed fast pyrolysis reactor operating at atmospheric and nitrogen atmosphere was set up at Zhejiang University in 1999. By altering the value of reaction temperature, particle size, feed rate, reactor height and so on, the heating and pyrolysis rate of biomass were adjusted; also the residence time of particle and volatile were changed. After that, a large-scale 0uidized bed pyrolysis system was set up in 2002 for following feasibility study of industrialization, which had more advantages over the old reactor.
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
457
Fig. 1. Fluidized bed reactor system for fast pyrolysis of biomass.
3.1. Features of pyrolysis system As depicted in Fig. 1, the principal unit of the experimental system was a 0uidized bed reactor. The reactor had a diameter of 80 mm and a height at a varied value between 700 and 1200 mm. Three electric coils of 2 kW each provided the heat required during biomass pyrolysis. Biomass was fed continuously at a maximum rate of about 3 kg h−1 directly into the reactor by way of a unique feeder, which overcame the poor 0uidity and easy carbonization of the biomass material. Measuring points and gas samplers were placed along the reactor vertically to monitor the operation condition. The reaction temperature varied from 723 to 973 K, while nitrogen 0ow for 0uidizing sand in reactor was in the range of 3–6 Nm3 h−1 . Furthermore, in order to avoid low bio-oil collection and pipeline blockage caused from volatile pre-cooling before entering the quencher, the temperature in the connection pipe between cyclone and following the quencher was located always at some temperature higher than 573 K. The duration time of every experiment was de-
termined in the range of 1–2 h, according to the feed rate of biomass material. For gaseous phase path, nitrogen from the bottle was shunted to four routes. Afterwards, the major nitrogen, which may pass the preheating device 7rst according to work condition, entered the reactor bottom directly for 0uidizing bed sand in reactor. At the same time, other three 0ows of nitrogen assisted biomass solids entering the reactor successfully. Then the overall nitrogen together with the volatile released during pyrolysis passed the cyclone separator. After that, the puri7ed hot gas was cooled in the following pipe bundle quencher. And the bio-oil components could be determined by GC–MS analysis. And incondensable volatile with nitrogen was vented after passing the 7lter and gas sampler, whose component would be analyzed by GC method. For solid phase path, biomass solids were fed into the reactor and then heated to some reaction temperature. After thermal decomposition, the residue was carried into the cyclone and then was collected by gas–solid separation.
458
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
Table 2 Biomass analyses
F. mandshurica C. lanceolata P. indicus Rice Straw
Water (%)
Ash (%)
Volatile (%)
Fixed carbon (%)
Heating value (kJ/kg)
C (%)
H (%)
N (%)
S (%)
O (%)
1.85 3.27 1.96 3.61
3.58 0.74 0.44 12.2
76.9 81.2 79.3 67.8
17.9 14.8 18.4 16.4
20,200 19,200 20,500 16,400
48.3 46.5 49.1 40.3
5.95 6.04 5.98 5.55
0.18 0.17 0.22 1.02
0.19 0.12 0.12 0.15
40.1 43.1 42.3 37.3
70 60
50
Composition (%)
Products distribution (%)
60
40
30
20
10
0 700
50 40 30 20 10
740
780
820
860
900
Char
740
780
820
860
900
Temperature (K)
Temperature (K) Bio-oil
0 700
Gas
Fig. 2. Products distribution with temperature (P. indicus, 250 –355 m).
3.2. Experimental results and discussions Some experimental researches have already been carried out on biomass pyrolysis in a 0uidized bed reactor, and mostly focused on the temperature eQect. There is no doubt that temperature plays a major role in pyrolysis; however, biomass pyrolysis behavior is in0uenced crosswise by many parameters, such as particle size, feed rate, volatile residence time. Therefore, extensive experiments had been performed to study the fast pyrolysis behavior on the atmospheric 0uidized bed reactor in this paper. Table 2 show the character of raw biomass material used in the experimental research. As shown in Fig. 2, there existed an optimum temperature of about 773 K to produce more high-quality bio-oil. The result was well consonant with previous works on biomass rapid pyrolysis. For example, Conti et al. [4] arrived at a conclusion that the temperature
CO
CH4
CO2
Fig. 3. Incondensable gas composition with temperature (P. indicus, 250 –355 m).
of 793 K was optimum for bio-oil yield of 45% from bagasse. As temperature was greater than this value, secondary reaction of volatile would become violent, leading to a lower bio-oil yield. On the contrary, rather lower temperature also caused biomass incomplete decomposition. Besides this, the composition of incondensable gas was also in0uenced by temperature. Fig. 3 shows that high temperature would lead to a high proportion of CO and CH4 , while a low proportion of CO2 . This was largely because mostly CO2 was produced by carboxyl release at a relatively low temperature. Furthermore, the secondary cracking of volatile produced CO and CH4 rather than CO2 [5]. So at a higher reaction temperature, a higher heating-value gas could be obtained in pyrolysis of biomass for gas. Meanwhile, particle size had no obvious eQect on products distribution when less than 1 mm. Adjusting the reactor height and feed rate could alter the residence time of particle and volatile.
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
459
Table 3 EQect of biomass species on bio-oil production Biomass species
Temperature (K)
Particle size (m)
Yield (%)
Heating value (kJ/Kg)
Water a (%)
F. mandshurica C. lanceolata P. indicus Rice Straw
823 773 773 773
74 –154 74 –154 250 –355 154 –250
40.2 53.9 55.7 33.7
22,000 19,000 19,000 19,000
39.6 31.4 24.6 53.5
a Analyzed
by Karl Fischer method. Water in bio-oil could not separated from organic compounds easily.
Compared with reactor height, it was more eQective to increase the feed rate to shorten volatile residence so as to restrain secondary cracking. This was because shortening reactor height only acted on the dilute phase area at low temperature. However, with feed rate increase, the volatile residence time in the dense phase area at higher temperature would be cut signi7cantly. Moreover, heat transfer would be more intense as solid concentration rose, caused by feed rate increase. Biomass species played a signi7cant role in its fast pyrolysis. As shown in Table 3, with high yield, heating value and low water content as evaluation criteria, Pterocarpus indicus had the best characteristic in producing bio-oil, followed by Cunninghamia lanceolata and Fraximus mandshurica, and Rice Straw the worst. Correlating with the result in Table 2, this was somewhat related with ash content in biomass, which was not advantageous to obtain a high-quality bio-oil. In fact, ash had a larger eQect on biomass pyrolysis behavior than degree of crystallinity and polymerization [6]. Some elements in ash could catalyze pyrolysis behavior and change products distribution [7]. Besides this, biomass with ash removal could produce more bio-oil and less gas [8]. At the same time, ash had no eQect on biomass apparent weight loss because ash neither volatilized nor decomposed when the temperature was lower than 923 K.
Table 4 Relative content of main compounds in organic composition of bio-oil produced from P. indicus Compound
Relative content (%)
Furfural Acetoxyacetone, 1-hydroxyl Furfural, 5-methyl Phenol
9.06 1.21 1.82 2.55
2-Cyclopentane-1-one, 3-methyl Benzaldehyde, 2-hydroxyl Phenol, 2-methyl Phenol, 4-methyl Phenol, 2-methoxyl
1.58 2.70 5.04 0.51 0.27
Phenol, 2,4-dimethyl Phenol, 4-ethyl
9.62 2.18
Phenol, 2-methoxy-5-methyl Phenol, 2-methoxy-4-methyl Benzene, 1,2,4-trimethoxyl Phenol, 2,6-dimethyl-4-(1-propenyl) 1,2-Benzenedicarboxylic acid, diisooctyl ester 2-Furanone Levoglucosan Phenol, 2,6-dimethoxy-4-propenyl Furanone, 5-methyl Acetophenone, 1-(4-hydroxy-3-methoxy) Vanillin Benzaldehyde, 3,5-dimethyl-4-hydroxyl Cinnamic aldehyde, 3,5-demethoxy-4-hydroxyl
4.15 0.55 3.80 4.25 1.80 5.70 6.75 3.14 0.49 2.94 6.35 4.54 2.19
3.3. Bio-oil analysis Bio-oil had a higher density than raw material, which was not obviously aQected by work conditions. The value of density was located in the range of 1130 –1200 kg m−3 . The kinetic viscosity of bio-oil varied largely with biomass species. The value was mea-
sured with NDJ-1 kinetic viscosity meter in the case of constant temperature bath. For example, bio-oil produced from P. indicus and F. mandshurica had a kinetic viscosity of 70 –350 mPa s and 10 –70 mPa s
460
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462
Fig. 4. New fast pyrolysis system at the feed rate up to 20 kg=h.
separately, and bio-oil produced from Rice Straw had a minimum kinetic viscosity about 5 –10 mPa s. This was mainly because the high water content in bio-oil would lead to a lower kinetic viscosity value. Bio-oil should be stored carefully for its corrosion caused by the acid constituents. Bio-oil had a lower pH value in the range of 2– 4, which was largely determined by raw material and water content in bio-oil. Furthermore, bio-oil had more than one hundred compounds, which implied the complexity of following re7ning or usage. According to the GC–MS analysis, bio-oil was mainly composed of levoglucosan, furfural, phenol and aldehyde. Table 4 shows the distribution of some detected compounds in the organic composition of bio-oil, which was produced from P. indicus. Above all, bio-oil was polar, tarry and highly unstable, therefore, upgrading of bio-oil should be processed to remove oxygen and improve bio-oil composition [9]. 3.4. New Pyrolysis system developed at Zhejiang University On the basis of previous experimental work on small-scale 0uidized bed pyrolysis reactor, a new fast pyrolysis system with a feed rate up to 20 kg h−1 constructed in 2002 for feasibility study of industrialization. As shown in Fig. 4, this new system has more special convenient features for application. Flu-
idized bed was also chosen for the reactor, which was designed in variable section to reduce the volatile residence time for restraining secondary cracking. Re-utilization of char and gas would reduce the cost in heat required in pyrolysis and 0uidizing gas. Besides this, multi-stage condensation was adopted for the disposal of heavy oil and high water-content liquid separately, so as to reduce the subsequent processing cost and maximize high-quality fuel oil production. 4. Techno-economic evaluations The object for evaluation is a biomass pyrolysis plant to produce bio-oil, using 0uidized bed technology. The feed rate of sawdust is assumed at the value of 2 t=day, which matches the capacity of a medium-scale wood machinery factory in Hangzhou, Zhejiang. The construction period of the project is half a year and the service life is 15 years. Therefore, the total calculation period is 15.5 years. And the reference data used in evaluation are listed in Table 5. Here, the selling price of bio-oil is pre-determined according to its heating value, which is compared with gasoline or diesel oil. As shown in Table 6, biomass pyrolysis technology has its potential in the future application under the 7nancial support and duty free. However, it is not
Z. Luo et al. / Biomass and Bioenergy 26 (2004) 455 – 462 Table 5 Basic data for techno-economic evaluation
Table 7 Sensitivity analysis
No.
Item
Unit
Value
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Construction period Service life Calculation period Bio-oil output Char output Sawdust consumption Power consumption Water consumption Depreciation rate Maintain rate Worker number Annual wages per person Sawdust cost Power cost Water cost Bio-oil price
year year year t/year t/year t/year kWh/year m3 % %
0.5 15 15.5 430 70 730 403000 880 6 2 2 10000 150 0.58 1 1200
Yuan Yuan/t Yuan/kWh Yuan=m3 Yuan/t
Table 6 Pro7t and loss statement (Yuan) No. Item
Pro7t and loss per t bio-oil
Annual pro7t and loss
1 2 3 4 5 6 7 8 9
−254.7 −2.0 −543.6 −46.5 −61.2 −183.5 = = +1200
−109500 −880 −233740 −20000 −26300 −78900 = = +516000
Feed stock Water Power Manpower Maintain Depreciation Financial charge Tax Income
Sum
+108.5
461
+46680
feasible to put this technology into application widely until the quality of bio-oil is largely improved. And Table 7 shows that bio-oil price has more eQect on project pro7t than sawdust price. However, if we promote the technology in energy-comprehensive utilization, the cost on bio-oil production will be reduced largely according to the high proportion of heating supply in bio-oil cost.
Vibration range (%)
IRR (%)
Fluctuation range of IRR (%)
Bio-oil price
−20 −10 0 +10 +20
−90.30 −1.10 5.00 10.20 14.90
−286 −122 0 104 198
Sawdust price
−20 −10 0 +10 +20
7.30 6.20 5.00 3.80 2.60
46 24 0 −24 −48
solve the shortage of fossil fuel and exploit abundant biomass resource. Especially liquid produced from biomass fast pyrolysis could be substituted for traditional liquid fuel, such as diesel oil. And detailed experimental research was carried out on a small-scale pyrolysis 0uidized bed reactor with a maximum feed rate of 3 kg h−1 . Experimental result showed that the temperature of 773 K was more suitable for high-quality bio-oil production. Besides this, the composition of incondensable gas was also in0uenced by temperature. Higher heating-value gas could be obtained at a higher reaction temperature in pyrolysis. P. indicus had the best characteristic for producing bio-oil, followed by C. lanceolata. and F. mandshurica, but Rice Straw was the worst. This was mainly because that higher ash content in biomass was disadvantageous to obtain high quality bio-oil production. However, upgrading of re7ning of bio-oil is necessary for its inferior property and complex composition. A larger-scale fast pyrolysis system was set up for research on industrialization, which had its advantage in energy-comprehensive utilization. And a simple techno-economic evaluation was proposed to assess the practicability of fast pyrolysis technology, which has potential in future application.
5. Conclusions
References
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