- Email: [email protected]
Experimental study on cyclone air gasification of wood powder
Bioresource Technology 100 (2009) 4047–4049
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Experimental study on cyclone air gasification of wood powder Shaozeng Sun a, Yijun Zhao a,*, Hongming Tian a, Feng Ling b, Fengming Su b a b
Combustion Engineering Research Institute, School of Energy Science and Engineering, Harbin Institute of Technology, 92, West Dazhi Street, Harbin 150001, PR China China Power Complete Equipment Co., Ltd., 15, North Andeli Street, Beijing 100011, PR China
a r t i c l e
i n f o
Article history: Received 25 September 2008 Received in revised form 13 January 2009 Accepted 20 January 2009 Available online 5 April 2009 Keywords: Biomass Gasification Cyclone Air staging
a b s t r a c t In this paper, effects of the equivalence ratio (ER) and the secondary air on the gasification system were studied. The results indicate that as the ER varies in the range of 0.20–0.26, the low heating value (LHV) of the producer gas is in the range of 3.64–5.76 MJ/Nm3, the carbon conversion is 55%–67% and the cold gas efficiency of the gasification system is 33%–47%. In contrast to the gasification without the secondary air, air staged process is a gasification method capable of increasing the LHV of the producer gas from 4.63 to 5.67 MJ/Nm3, the carbon conversion from 65.5% to 81.2%, and the cold gas efficiency of the gasifier from 42.5% to 56.87%, while the tar content of the producer gas decreases from 13.96 to 5.6 g/Nm3. There exists an optimum ratio of the secondary air. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental process
Biomass is a major potential resource for energy production (Zhao et al., 2008). Biomass gasification is an efficient and advanced technology for extracting the energy from biomass. Cyclone gasifier is a type of entrained-flow bed used as both a gas cleaner and a gasifier. This approach was put forward firstly by Fredriksson and Kallner who made experiments at the Royal Institute of Technology (Gabra et al., 2001). An inverted cyclone gasifier was designed by Syred et al. (2004). The gasifier was designed to maximise particle and ash separation from the flow, and remove alkali and other heavy metal traces that agglomerate with the ash particles. Generally technologies controlling tar production can broadly be divided into two categories, treatment inside the gasifier and hot gas cleaning outside the gasifier. The former is gaining much attention due to its economic competitiveness (Abu ElRub et al., 2004). The heat and mass transfer are intense in the cyclone gasifier, which result in smaller volume in the cyclone gasifier than in the fixed bed. It should be noted that the gasifier is not only favourable to decreasing the tar content of the producer gas but also reduce the demand for cleaning equipment after the gasifier, which reduces initial investment significantly.
2.1. Experimental equipment
* Corresponding author. Tel.: +86 451 8641x2618x865; fax: +86 451 8641x2528. E-mail address: [email protected] (Y. Zhao).
The system of experimental equipment is made up of five parts: main body of cyclone gasifier, air supplying system, fuel feeding system, electric heating and temperature control system and sampling system. The chamber of the cyclone gasifier is made of temperature-resistant stainless steel which is 1300 mm in height and 200 mm in diameter. Temperature is monitored by eight thermocouples located along the axial direction of the gasifier, named as T1–T8 in turn. The first temperature point is mounted at the same elevation as the entrance of fuel feeder in the gasifier, and the span between each two adjacent temperature measuring points is 150 mm. Gas analyzer (Gasboard 3020) was used to measure the concentrations of the gas species of interest (CO, CO2, CH4 and H2). The concentrations of CO, CO2 and CH4 in the producer gas were measured continuously with the principle of non-dispersive infrared spectroscopy (NDIR). Hydrogen was measured by using a thermal conductivity detector. The flow rate of sampling gas ranged from 0.7 to 1.2 L/min. 2.2. Experimental procedure The experiments were made with the fuel rate of 15 kg/h at the equivalence ratios in the range of 0.20–0.26. Equivalence ratio (ER) is defined as the ratio of the actual supply air to the stoichiometric air required for complete combustion. Air was used as gasifying
0960-8524/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.01.031
S. Sun et al. / Bioresource Technology 100 (2009) 4047–4049
agent which was supplied by air compressor. To ensure the stability of air flow rate, compressed air was sent to an air tank before entering the gasifier. The first step of gasification experiments was heating the gasifier to approximately 800 °C (monitored at T5) by using the electrical heaters, which stopped working automatically when the target operating temperature was reached. The heat necessary for sustained reactions would then be generated from the reactions themselves. Tests were performed in atmospheric pressure. When the operating temperature variations were kept within ±5 °C, the system was considered to reach stable conditions. The wood powder sample was obtained from a farm in the suburb of Harbin. Wood powder was dried naturally in air. The low heating value (LHV) and moisture content of the sample are 15.09 MJ/kg and 9.20%. The elemental content of C, H and O are 43.01%, 6.42% and 39.64%, respectively. The particle size distribution of the sample is as follows: 0 wt% over 2 mm, 2 wt% 1– 2 mm, 13.80 wt% 0.6–1.0 mm, 52.50 wt% 0.25–0.6 mm, 19.20 wt% 0.16–0.25 mm, 12.50 wt% below 0.16 mm. 3. Results and discussion 3.1. Effect of the ER on the gas temperature
1000
Equivalence Ratio 0.2 0.22 0.24 0.26
Temperature (°C)
900 800 700 600 500 400 300 0
1
2
3
3.2. Effect of the ER on gas composition and parameters of gasification As shown in Fig. 2, the volume fraction of CO, CO2, CH4 and H2 were measured at the exit of the gasifier. Because the N element in the wood powder is 0.17%, it is considered that nitrogen component in the producer gas comes from gasifying agent, which results in the decrease in the LHV of the producer gas. With the increase of the ER, the concentration of CO decreased from 20.4 vol.% to 14.7 vol.% and CH4 decreased from 7.9 vol.% to 3.49 vol.%, whereas the concentration of H2 increased from 3.29 vol.% to 4.9 vol.%. However, the concentration of CO2 increased from 17.46 vol.% to 18.3 vol.%, and then decreased to 17.5 vol.% when the ER was larger than 0.22. It is considered that the increase of the supply air lead to the further combustion of the producer gas, and additional nitrogen dilutes the producer gas, which results in the decrease of the LHV of the producer gas from 5.76 to 3.64 MJ/Nm3. It is not necessary to study the effects of the ER larger than 0.26 because of the low LHV of the producer gas. There are two factors affecting the carbon conversion of entrained-flow bed. The first factor is that with the increase of the ER, more air is available for the exothermic carbon combustion, and the gas temperature increases rapidly, which is considered to promote the pyrolysis of biomass, the secondary pyrolysis of tar and the gasification reactions (Wang et al., 2007). So the carbon conversion increases with the increase of the ER. The second factor is that when the stream velocity accelerated, the amount of carried particle in the stream increases, which results in the decrease of the carbon conversion. Effect of the ER on the carbon conversion is shown in Fig. 2. The carbon conversion was 55%–67% when the ER was 0.20–0.26. When the ER was less than 0.22, the first factor was dominant; when the ER was larger than 0.22, the second factor played a more prevailing role. The cold gas efficiency of the gasification system was 33%–47%. 3.3. Tar content in the producer gas The type of biomass is the main factor that determines the properties of the produced tar, which is also influenced by the gas-
Concentrations of the producer gas (%)
Effect of the ER on the gas temperature is shown in Fig. 1. As soon as the fuel entered the gasifier with air, the temperature of particles increased from the room temperature to approximately 400 °C. Therefore the fuel particle was dried and pyrolysed immediately. As shown in Fig. 1, the temperature between T1 and T2 increased rapidly. The reason may be that the combustible volatiles released in the early stage of the gasification accumulated and homogeneous reactions took place intensively. Then the formed char after pyrolysis reacted with oxygen and as a result, temperature in this zone increased. With the increasing of ER from 0.20 to 0.26, the gas temperature at the first measuring point decreased from 433 °C to 387 °C, due to the cooling effect of the incoming air. Gasification is a thermochemical conversion of biomass under oxygen deficient conditions. At higher ER more air was available for the exothermic carbon combustion. So the peak gas temperature increased with the increase of the ER. When the ER was at 0.20, temperature at T4 reached its highest value, 850 °C. With the increasing of apply air, the flow velocity increased, and the peak gas temperature moved down. When the ER was at 0.26, temperature at T5 reached its highest value, 995 °C. At the late stage of gasification the temperature decreased, which indicated that the endothermic reac-
tions from reduction process played a dominant role after the turning point of temperature. Fig. 1 also shows the peak gas temperature is about 850– 1000 °C which is higher than that in fluidized bed gasifiers. However, in the cyclone gasifier, every fuel particle is dispersed by gas flow, and is pyrolysed and gasified individually. Therefore, there is no slagging in the cyclone gasifier, which is serious in FB gasifier when the temperature is high.
4
5
6
7
8
9
CO2 CO CH4 Gasification efficiency
24
H2 Carbon conversion
70
20 60
16 12
50
8 40 4 0
Caibon conversion (%) Gasification efficiency (%)
4048
30 0.20
0.22
0.24
0.26
Equivalence ratio
Temperature measurement points Fig. 1. Effect of the ER on the gas temperature.
Fig. 2. Effect of the ER on the concentrations of the producer gas, carbon conversion and gasification efficiency.
S. Sun et al. / Bioresource Technology 100 (2009) 4047–4049
4049
Table 1 The gas concentrations and parameters of gasification versus different secondary air ratio.
42.5% to 56.87%, respectively. Furthermore, the tar content of the producer gas decreased from 13.96 to 5.6 g/Nm3.
Secondary air ratio (%)
4. Conclusions
Gas concentrations (%Vol)
Fuel gas production (Nm3/kg) Low heating value (MJ/Nm3) Cold gas efficiency (%) Carbon conversion(%)
CO2 CO H2 CH4
19
23
31
16.01 18.60 5.03 3.84 1.34 4.57 40.40 60.40
18.01 22.00 7.10 3.22 1.51 5.67 56.87 81.20
15.81 20.50 6.00 4.47 1.41 5.22 48.90 68.30
ification process and the operating conditions (Peter, 2002). It is generally agreed that primary tar is formed from pyrolysis of solid fuel in the air gasification. Increasing temperature promotes tar cracking. In the experiments, the tar content significantly decreased from14.99 to 11 g/Nm3 with the increase of the ER. The decrease of tar content could be explained that a part of tar was burnt with the supply air and the other part was further thermally cracked into the secondary tar in local high temperature zone. As shown in Fig. 1, the temperature in the oxidation zone was above 900 °C. Tar could be cracked into lower molecular weight compounds with catalytic reaction above 900 °C (Lai et al., 2004). 3.4. Effect of the secondary air on gasification In this paper, the feeding rate of the wood powder and the total air flow rate were 15 and 13 m3/h, respectively. The secondary air was injected in the reduction zone between T7 and T8. The ratio of secondary air was kept at 19%, 23% and 31%. Table 1 shows the gas concentrations and parameters of gasification at different secondary air ratios. The concentrations of CO2, CO and H2 were the highest when the secondary air ratio was 23%, which reached 18.01 vol.%, 22 vol.% and 7.1 vol.%, respectively. On the contrary, the concentration of CH4 was the lowest. The LHV of the producer gas, the cold gas efficiency and the carbon conversion as function of the secondary air ratio are presented in Table 1. It is necessary to note that their peak value occurs when the secondary air ratio reaches 23%. It is demonstrated that there exists an optimum ratio of the secondary air. In contrast to the gasification without secondary air, air staged process was a gasification method capable to increasing the LHV of the producer gas from 4.63 to 5.67 MJ/Nm3, the carbon conversion from 65.5% to 81.2% and the cold gas efficiency of the gasifier from
In this study investigation into the performance of the cyclone gasifier to generate producer gases from the wood powder has been carried out, and the following conclusions are obtained. (1) The cyclone gasifier system successfully generates the producer gas. The LHV of the producer gas is 3.64–5.76 MJ/ Nm3, the carbon conversion is 55%–67% and the cold gas efficiency of the gasifier is 33%–47%. (2) Gas concentrations in the producer gas are that CO2 ranges from 17.46 to 18.3 vol.%, CO ranges from 14.7 to 20.4 vol.%, CH4 ranges from 3.49 to 7.9 vol.% and H2 ranges from 3.29 to 4.9 vol.%. (3) In contrast to the gasification without the secondary air, air staged gasification increases the LHV of the producer gas from 4.63 to 5.67 MJ/Nm3, the carbon conversion from 65.5% to 81.2%, and the cold gas efficiency of the gasifier from 42.5% to 56.87%. While the tar content of the producer gas decreases from 13.96 to 5.6 g/Nm3. Acknowledgements Financial support from the Heilongjiang Provincial Natural Science Foundation of China (contract no.:1307396) is gratefully acknowledged. References Abu El-Rub, Z., Bramer, E.A., Brem, G., 2004. Review of catalysts for tar climination in biomass gasification process. Industrial and Engineering Chemistry Research 43, 6911–6919. Gabra, M., Pettersson, E., Backman, R., Kjellström, B., 2001. Evaluation of cyclone gasifier performance for gasification of sugar cane residue-part 1: gasification of bagasse. Biomass and Bioenergy 21, 351–369. Lai, Y.H., Lu, M.X., Ma, C.Y., Shi, M.H., 2004. Study on the influence of throat structure on reducing tar content of two-stage biomass gasification reactor. Acta Energiae Solaris Sinica 25, 547–551. Peter, M.K., 2002. Energy production from biomass (part3): gasification technologies. Bioresource Technology 83, 55–63. Syred, C., Fick, W., Griffiths, A.J., Syred, N., 2004. Cyclone gasifier and cyclone combustor for the use of biomass derived gas in the operation of a small gas turbine in cogeneration plants. Fuel 83, 2381–2392. Wang, Y., Yoshikawa, K., Namioka, T., Hashimoto, Y., 2007. Performance optimization of two-staged gasification system for woody biomass. Fuel Processing Technology 88, 243–250. Zhao, W., Li, Z.Q., Wang, D.W., Zhu, Q.Y., Sun, R., Meng, B.H., Zhao, G.B., 2008. Combustion characteristics of different parts of corn straw and NO formation in a fixed bed. Bioresource Technology 99, 2956–2963.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Experimental study on cyclone air gasification of wood powder Shaozeng Sun a, Yijun Zhao a,*, Hongming Tian a, Feng Ling b, Fengming Su b a b
Combustion Engineering Research Institute, School of Energy Science and Engineering, Harbin Institute of Technology, 92, West Dazhi Street, Harbin 150001, PR China China Power Complete Equipment Co., Ltd., 15, North Andeli Street, Beijing 100011, PR China
a r t i c l e
i n f o
Article history: Received 25 September 2008 Received in revised form 13 January 2009 Accepted 20 January 2009 Available online 5 April 2009 Keywords: Biomass Gasification Cyclone Air staging
a b s t r a c t In this paper, effects of the equivalence ratio (ER) and the secondary air on the gasification system were studied. The results indicate that as the ER varies in the range of 0.20–0.26, the low heating value (LHV) of the producer gas is in the range of 3.64–5.76 MJ/Nm3, the carbon conversion is 55%–67% and the cold gas efficiency of the gasification system is 33%–47%. In contrast to the gasification without the secondary air, air staged process is a gasification method capable of increasing the LHV of the producer gas from 4.63 to 5.67 MJ/Nm3, the carbon conversion from 65.5% to 81.2%, and the cold gas efficiency of the gasifier from 42.5% to 56.87%, while the tar content of the producer gas decreases from 13.96 to 5.6 g/Nm3. There exists an optimum ratio of the secondary air. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental process
Biomass is a major potential resource for energy production (Zhao et al., 2008). Biomass gasification is an efficient and advanced technology for extracting the energy from biomass. Cyclone gasifier is a type of entrained-flow bed used as both a gas cleaner and a gasifier. This approach was put forward firstly by Fredriksson and Kallner who made experiments at the Royal Institute of Technology (Gabra et al., 2001). An inverted cyclone gasifier was designed by Syred et al. (2004). The gasifier was designed to maximise particle and ash separation from the flow, and remove alkali and other heavy metal traces that agglomerate with the ash particles. Generally technologies controlling tar production can broadly be divided into two categories, treatment inside the gasifier and hot gas cleaning outside the gasifier. The former is gaining much attention due to its economic competitiveness (Abu ElRub et al., 2004). The heat and mass transfer are intense in the cyclone gasifier, which result in smaller volume in the cyclone gasifier than in the fixed bed. It should be noted that the gasifier is not only favourable to decreasing the tar content of the producer gas but also reduce the demand for cleaning equipment after the gasifier, which reduces initial investment significantly.
2.1. Experimental equipment
* Corresponding author. Tel.: +86 451 8641x2618x865; fax: +86 451 8641x2528. E-mail address: [email protected] (Y. Zhao).
The system of experimental equipment is made up of five parts: main body of cyclone gasifier, air supplying system, fuel feeding system, electric heating and temperature control system and sampling system. The chamber of the cyclone gasifier is made of temperature-resistant stainless steel which is 1300 mm in height and 200 mm in diameter. Temperature is monitored by eight thermocouples located along the axial direction of the gasifier, named as T1–T8 in turn. The first temperature point is mounted at the same elevation as the entrance of fuel feeder in the gasifier, and the span between each two adjacent temperature measuring points is 150 mm. Gas analyzer (Gasboard 3020) was used to measure the concentrations of the gas species of interest (CO, CO2, CH4 and H2). The concentrations of CO, CO2 and CH4 in the producer gas were measured continuously with the principle of non-dispersive infrared spectroscopy (NDIR). Hydrogen was measured by using a thermal conductivity detector. The flow rate of sampling gas ranged from 0.7 to 1.2 L/min. 2.2. Experimental procedure The experiments were made with the fuel rate of 15 kg/h at the equivalence ratios in the range of 0.20–0.26. Equivalence ratio (ER) is defined as the ratio of the actual supply air to the stoichiometric air required for complete combustion. Air was used as gasifying
0960-8524/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.01.031
S. Sun et al. / Bioresource Technology 100 (2009) 4047–4049
agent which was supplied by air compressor. To ensure the stability of air flow rate, compressed air was sent to an air tank before entering the gasifier. The first step of gasification experiments was heating the gasifier to approximately 800 °C (monitored at T5) by using the electrical heaters, which stopped working automatically when the target operating temperature was reached. The heat necessary for sustained reactions would then be generated from the reactions themselves. Tests were performed in atmospheric pressure. When the operating temperature variations were kept within ±5 °C, the system was considered to reach stable conditions. The wood powder sample was obtained from a farm in the suburb of Harbin. Wood powder was dried naturally in air. The low heating value (LHV) and moisture content of the sample are 15.09 MJ/kg and 9.20%. The elemental content of C, H and O are 43.01%, 6.42% and 39.64%, respectively. The particle size distribution of the sample is as follows: 0 wt% over 2 mm, 2 wt% 1– 2 mm, 13.80 wt% 0.6–1.0 mm, 52.50 wt% 0.25–0.6 mm, 19.20 wt% 0.16–0.25 mm, 12.50 wt% below 0.16 mm. 3. Results and discussion 3.1. Effect of the ER on the gas temperature
1000
Equivalence Ratio 0.2 0.22 0.24 0.26
Temperature (°C)
900 800 700 600 500 400 300 0
1
2
3
3.2. Effect of the ER on gas composition and parameters of gasification As shown in Fig. 2, the volume fraction of CO, CO2, CH4 and H2 were measured at the exit of the gasifier. Because the N element in the wood powder is 0.17%, it is considered that nitrogen component in the producer gas comes from gasifying agent, which results in the decrease in the LHV of the producer gas. With the increase of the ER, the concentration of CO decreased from 20.4 vol.% to 14.7 vol.% and CH4 decreased from 7.9 vol.% to 3.49 vol.%, whereas the concentration of H2 increased from 3.29 vol.% to 4.9 vol.%. However, the concentration of CO2 increased from 17.46 vol.% to 18.3 vol.%, and then decreased to 17.5 vol.% when the ER was larger than 0.22. It is considered that the increase of the supply air lead to the further combustion of the producer gas, and additional nitrogen dilutes the producer gas, which results in the decrease of the LHV of the producer gas from 5.76 to 3.64 MJ/Nm3. It is not necessary to study the effects of the ER larger than 0.26 because of the low LHV of the producer gas. There are two factors affecting the carbon conversion of entrained-flow bed. The first factor is that with the increase of the ER, more air is available for the exothermic carbon combustion, and the gas temperature increases rapidly, which is considered to promote the pyrolysis of biomass, the secondary pyrolysis of tar and the gasification reactions (Wang et al., 2007). So the carbon conversion increases with the increase of the ER. The second factor is that when the stream velocity accelerated, the amount of carried particle in the stream increases, which results in the decrease of the carbon conversion. Effect of the ER on the carbon conversion is shown in Fig. 2. The carbon conversion was 55%–67% when the ER was 0.20–0.26. When the ER was less than 0.22, the first factor was dominant; when the ER was larger than 0.22, the second factor played a more prevailing role. The cold gas efficiency of the gasification system was 33%–47%. 3.3. Tar content in the producer gas The type of biomass is the main factor that determines the properties of the produced tar, which is also influenced by the gas-
Concentrations of the producer gas (%)
Effect of the ER on the gas temperature is shown in Fig. 1. As soon as the fuel entered the gasifier with air, the temperature of particles increased from the room temperature to approximately 400 °C. Therefore the fuel particle was dried and pyrolysed immediately. As shown in Fig. 1, the temperature between T1 and T2 increased rapidly. The reason may be that the combustible volatiles released in the early stage of the gasification accumulated and homogeneous reactions took place intensively. Then the formed char after pyrolysis reacted with oxygen and as a result, temperature in this zone increased. With the increasing of ER from 0.20 to 0.26, the gas temperature at the first measuring point decreased from 433 °C to 387 °C, due to the cooling effect of the incoming air. Gasification is a thermochemical conversion of biomass under oxygen deficient conditions. At higher ER more air was available for the exothermic carbon combustion. So the peak gas temperature increased with the increase of the ER. When the ER was at 0.20, temperature at T4 reached its highest value, 850 °C. With the increasing of apply air, the flow velocity increased, and the peak gas temperature moved down. When the ER was at 0.26, temperature at T5 reached its highest value, 995 °C. At the late stage of gasification the temperature decreased, which indicated that the endothermic reac-
tions from reduction process played a dominant role after the turning point of temperature. Fig. 1 also shows the peak gas temperature is about 850– 1000 °C which is higher than that in fluidized bed gasifiers. However, in the cyclone gasifier, every fuel particle is dispersed by gas flow, and is pyrolysed and gasified individually. Therefore, there is no slagging in the cyclone gasifier, which is serious in FB gasifier when the temperature is high.
4
5
6
7
8
9
CO2 CO CH4 Gasification efficiency
24
H2 Carbon conversion
70
20 60
16 12
50
8 40 4 0
Caibon conversion (%) Gasification efficiency (%)
4048
30 0.20
0.22
0.24
0.26
Equivalence ratio
Temperature measurement points Fig. 1. Effect of the ER on the gas temperature.
Fig. 2. Effect of the ER on the concentrations of the producer gas, carbon conversion and gasification efficiency.
S. Sun et al. / Bioresource Technology 100 (2009) 4047–4049
4049
Table 1 The gas concentrations and parameters of gasification versus different secondary air ratio.
42.5% to 56.87%, respectively. Furthermore, the tar content of the producer gas decreased from 13.96 to 5.6 g/Nm3.
Secondary air ratio (%)
4. Conclusions
Gas concentrations (%Vol)
Fuel gas production (Nm3/kg) Low heating value (MJ/Nm3) Cold gas efficiency (%) Carbon conversion(%)
CO2 CO H2 CH4
19
23
31
16.01 18.60 5.03 3.84 1.34 4.57 40.40 60.40
18.01 22.00 7.10 3.22 1.51 5.67 56.87 81.20
15.81 20.50 6.00 4.47 1.41 5.22 48.90 68.30
ification process and the operating conditions (Peter, 2002). It is generally agreed that primary tar is formed from pyrolysis of solid fuel in the air gasification. Increasing temperature promotes tar cracking. In the experiments, the tar content significantly decreased from14.99 to 11 g/Nm3 with the increase of the ER. The decrease of tar content could be explained that a part of tar was burnt with the supply air and the other part was further thermally cracked into the secondary tar in local high temperature zone. As shown in Fig. 1, the temperature in the oxidation zone was above 900 °C. Tar could be cracked into lower molecular weight compounds with catalytic reaction above 900 °C (Lai et al., 2004). 3.4. Effect of the secondary air on gasification In this paper, the feeding rate of the wood powder and the total air flow rate were 15 and 13 m3/h, respectively. The secondary air was injected in the reduction zone between T7 and T8. The ratio of secondary air was kept at 19%, 23% and 31%. Table 1 shows the gas concentrations and parameters of gasification at different secondary air ratios. The concentrations of CO2, CO and H2 were the highest when the secondary air ratio was 23%, which reached 18.01 vol.%, 22 vol.% and 7.1 vol.%, respectively. On the contrary, the concentration of CH4 was the lowest. The LHV of the producer gas, the cold gas efficiency and the carbon conversion as function of the secondary air ratio are presented in Table 1. It is necessary to note that their peak value occurs when the secondary air ratio reaches 23%. It is demonstrated that there exists an optimum ratio of the secondary air. In contrast to the gasification without secondary air, air staged process was a gasification method capable to increasing the LHV of the producer gas from 4.63 to 5.67 MJ/Nm3, the carbon conversion from 65.5% to 81.2% and the cold gas efficiency of the gasifier from
In this study investigation into the performance of the cyclone gasifier to generate producer gases from the wood powder has been carried out, and the following conclusions are obtained. (1) The cyclone gasifier system successfully generates the producer gas. The LHV of the producer gas is 3.64–5.76 MJ/ Nm3, the carbon conversion is 55%–67% and the cold gas efficiency of the gasifier is 33%–47%. (2) Gas concentrations in the producer gas are that CO2 ranges from 17.46 to 18.3 vol.%, CO ranges from 14.7 to 20.4 vol.%, CH4 ranges from 3.49 to 7.9 vol.% and H2 ranges from 3.29 to 4.9 vol.%. (3) In contrast to the gasification without the secondary air, air staged gasification increases the LHV of the producer gas from 4.63 to 5.67 MJ/Nm3, the carbon conversion from 65.5% to 81.2%, and the cold gas efficiency of the gasifier from 42.5% to 56.87%. While the tar content of the producer gas decreases from 13.96 to 5.6 g/Nm3. Acknowledgements Financial support from the Heilongjiang Provincial Natural Science Foundation of China (contract no.:1307396) is gratefully acknowledged. References Abu El-Rub, Z., Bramer, E.A., Brem, G., 2004. Review of catalysts for tar climination in biomass gasification process. Industrial and Engineering Chemistry Research 43, 6911–6919. Gabra, M., Pettersson, E., Backman, R., Kjellström, B., 2001. Evaluation of cyclone gasifier performance for gasification of sugar cane residue-part 1: gasification of bagasse. Biomass and Bioenergy 21, 351–369. Lai, Y.H., Lu, M.X., Ma, C.Y., Shi, M.H., 2004. Study on the influence of throat structure on reducing tar content of two-stage biomass gasification reactor. Acta Energiae Solaris Sinica 25, 547–551. Peter, M.K., 2002. Energy production from biomass (part3): gasification technologies. Bioresource Technology 83, 55–63. Syred, C., Fick, W., Griffiths, A.J., Syred, N., 2004. Cyclone gasifier and cyclone combustor for the use of biomass derived gas in the operation of a small gas turbine in cogeneration plants. Fuel 83, 2381–2392. Wang, Y., Yoshikawa, K., Namioka, T., Hashimoto, Y., 2007. Performance optimization of two-staged gasification system for woody biomass. Fuel Processing Technology 88, 243–250. Zhao, W., Li, Z.Q., Wang, D.W., Zhu, Q.Y., Sun, R., Meng, B.H., Zhao, G.B., 2008. Combustion characteristics of different parts of corn straw and NO formation in a fixed bed. Bioresource Technology 99, 2956–2963.