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Combustion of refuse derived fuel in a fluidized bed
WASTE MANAGEMENT Waste Management 18 (1998) 509±512
Combustion of refuse derived fuel in a ¯uidized bed Guilin Piao a,*, Shigeru Aono a, Shigekatsu Mori a, Seiichi Deguchi b, Yukihisa Fujima b, Motohiro Kondoh c, Masataka Yamaguchi c a Department of Chemical Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8063, Japan Center for Integrated Research in Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8063, Japan c Plant Engineering Department, Toyota Motor Corp., Toyota-cho, Toyota, 471-71, Japan
b
Abstract Power generation from Refuse Derived Fuel (RDF) is an attractive utilization technology of municipal solid waste. To explain the behavior of RDF-®red ¯uidized bed incinerator, the commercial size RDF was continuously burnt in a 3030 cm bubbling type ¯uidized-bed combustor. It was found that 12 kg/h of RDF feed rate was too high feed for this test unit and the CO level was higher than 500 ppm. However, 10 kg/h of RDF was a proper feed rate and the CO level was kept under 150 ppm. Secondary air injection and changing air ratio from the pipe grid were eective for the complete combustion of RDE. It was also found that HCl concentration in ¯ue gas was controlled by the calcium component contained in RDF and its level was decreased with decreasing the combustor temperature. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction In Japan, the municipal solid waste (MSW) has been recognized as one of the promising candidates for a new energy resource. However, the eciency of the MSW ®red power generation is less than 15%. Since the steam condition is limited to avoid the high temperature corrosion of the boiler tube caused by hydrochloric acid gas in ¯ue gas. Recently dioxin problem has been social problem and the serious regulation less than 0.1 ng/m3 was determined for newly built incinerator. Therefore small scale incineration plants less than 100 tons/day could not be operated. To overcome these problem of MSW incineration, densi®ed refuse derived fuel (RDF) which is classi®ed RDF-5 by ASTM standard is attracted by Japanese local government attention as one of new technology to utilized MSW as the energy resources. Since RDF has signi®cant advantage in storage, transportation and higher heating value, RDF produced in the small dispersed towns and cities is collected and can be incinerated in a large scale intensive power generation plant.
* Corresponding author. Tel.: +81-52-789-4674; fax: +81-52-7893271; e-mail: [email protected]
Moreover, the calcium components added in RDF has the capacity to control HCl emission level in ¯ue gas and then higher power generation eciency is expected. It was reported previously that RDF was burnt in two stage exothermic reaction [1]. Combustion characteristics of the single RDF pellet were also reported [2]. However, only limited engineering data of RDF incinerator have been presented, since the size of RDF aects on the behavior of the combustor and their size (25 cm in diameter and 210 cm length) is too large to obtain the continuous operating data by using the small scale experimental unit. In this work, to explain the behavior of the ¯uidized bed incinerator of RDF, the commercial size RDF was burnt in a 3030 cm and 4 m high bubbling ¯uidized-bed combustor. CO and HCl emission from the combustor were measured under the various operating conditions. 2. Experimental apparatus and procedure Fig. 1 shows a schematic diagram of an experimental bubbling type ¯uidized-bed combustor. The combustor is 3030 cm and 2.73 m high from the pipe grid air-distributor.
0956-053X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0956 -0 53X(98)00140-8
510
G. Piao et al./Waste Management 18 (1998) 509±512 Table 2 Operating condition of each run Fuel Bed air (kg/h) (Nm3/h) RUN1 RUN2 RUN3 RUN4 RUN5 RUN6 RUN7 RUN8 RUN9 RUN10 RUN11
Fig. 1. Experimental apparatus (1 ¯uidized bed; 2 pipe grid; 3 belt conveyer; 4 ball valve; 5 cyclone; 6 gas cooler; 7 bag ®lter; 8 fan; 9 temperature tap).
Silica sand (dp = 0.3 mm, umf = 0.0746 m/s at room temperature) was ¯uidized and RDF was continuously fed on the surface of the bed. The bed height was about 35 cm from the distributor. RDF feed system consists of a belt conveyer and two ball valves. Four pipes having 18 holes with 3 mm 1 were used as the distributor. Air feed rate from each pipe was controlled independently. The secondary air could be also fed about 70 cm above the bed surface. Coarse dust in the ¯ue gas was collected by a cyclone and ®ne ¯y ash was collected by a bag house after cooling down by a gas cooler. The bed temperature was observed at 30 cm high from the distributor and the free board temperature was observed at 50 cm high from the bed surface. Flue gas was sampled at the entrance of the gas cooler and HCl concentration was measured at the entrance and the exit of the bag ®lter.
Table 1 RDF fuel analyses Proximate analysis (wt%) Moisture Volatile matters Fixed carbon Ash Ultimate analysis (wt%) Carbon Hydrogen Nitrogen Oxygen Sulfur Chlorine Calcium Ca/(S+0.5 Cl) Heating value (MJ/kg)
12 12 12 12 10 10 10 10 10 10 10
Secondary air (Nm3/h)
Air ratio
Air distribution ratio
0 0 0 12 0 0 0 12 6 0 6
1.14 1.385 1.5 1.5 1.27 1.47 1.8 1.27 1.22 1.27 1.7
1.78 1.69 2.13 4.55 1 1.49 2.13 1 1 3.12 3.57
56 68 74 62 52 60 74 40 44 52 64
As shown in Table 1, low heating value of RDF was 18,392 MJ/kg, volatile matter content was 72.5% and ®xed carbon was only 3.9%. Sulfur content was 0.17% and nitrogen content was 0.75%. Chlorine content was 1.0% and calcium content was 2.7%. Then Ca/(S+0.5 Cl) molar ratio was 3.4. Operating condition of each run are shown in Table 2. In some runs, air feed rate was changed between two center pipes and two side pipes. Air distribution ratio is de®ned as the ratio of air ¯ow rate from center pipes to the side pipes. 3. Experimental results Observed temperature in the combustor and CO, HCl, NOx and SOx concentration in ¯ue gas are shown in Table 3. When RDF feed rate was 12 kg/h, CO concentration in ¯ue gas was decreased with increasing air ratio as shown in Fig. 2. However, CO emission level was over 500 ppm and no signi®cant eect of secondary air injection was found. Then it can be concluded that 12 kg/h is too high for the test unit. Table 3 Experimental results data
11.1 72.5 3.9 12.5 41.7 6.0 0.75 36.3 0.17 1.0 2.7 3.4 18,392
Bed Free board CO temperature temperature (ppm) ( C) ( C) RUN1 RUN2 RUN3 RUN4 RUN5 RUN6 RUN7 RUN8 RUN9 RUN10 RUN11
969 933 964 985 904.5 935.3 905.3 927.7 940.3 964.7 882.6
965.6 941 972 1017 943.5 955.2 910.3 964 975 994.3 1099
4030 819 540 680 127.3 83.12 37.29 29 25.1 25.68 6.02
SOx HCl NOx (ppm) (ppm) (ppm) 212 178 281.2 315 144 247 192 234 216 282 264
79 72.3 102.5 118.16 121.05 128.7 139.4 122.0 122 ± 201.6
0.5 0.2 0.175 0.2 0.1 0.15 0.1 0 0 0 ±
G. Piao et al./Waste Management 18 (1998) 509±512
Fig. 2. CO emission level in ¯ue gas under 12 kg/h RDF feed. &: secondary air ratio=0;*: secondary air ratio=0.2.
Fig. 3. CO emission level in ¯ue gas under 10 kg/h RDF feed. &: secondary air ratio=0; *: secondary air ratio=0.12; ~: air distribution ratio=1.49.
511
Fig. 4. Tempreature in the combustor under 10 kg/h RDF feed and eect of air distribution method. &: bed temperature; &: free board temperature; *: bed temperature with secondary air; *: free board temperature with secondary air; ~: bed temperature at air distribution ratio=2.08; ~: bed temperature at air distribution ratio=2.71.
Fig. 5. Eect of bed temperature and RDF feed on HCl emission level.
512
G. Piao et al./Waste Management 18 (1998) 509±512
in ¯ue gas was increased with increasing bed temperature as shown in Fig. 5. The dierence of RDF feed rate aected slightly the HCl emission level. Although the bed temperature was higher than 900 C, more than 63% of chlorine components were captured by Ca components in the combustor. It is found in Table 3 that SOx emission level was very low as less than 1 ppm. As shown in Fig. 6, NOx level was 100200 ppm. More research work is necessary to discuss the behavior of NOx in the combustor.
4. Conclusion To explain the behavior of an RDF±®red ¯uidized bed incinerator, commercial size RDF was continuously burnt in a 3030 cm bubbling type ¯uidized bed combustor. The following result were demonstrated:
Fig. 6. Eect of air ratio and secondary ratio on NOx. &: NOx, secondary air ratio=0; ^: NOx, secondary air ratio=0.03; ~: NOx, secondary air ratio=0.12.
When RDF feed rate was decreased to 10 kg/h, CO level was kept under 150 ppm and it was decreased with increasing air ratios as shown in Fig. 3. Temperatures in the bed and the free board are shown in Fig. 4, and the temperature showed maximum around air ratio being 1.5. It is found from Figs. 3 and 4 that the secondary air injection and the increasing air distribution ratio were eective to keep complete combustion. The secondary air injection increased both the free board and the bed temperature since the volatile matter combustion in the free board was promoted. Increasing air distribution ratio, strong particle circulation in the bed was built up and then RDF fed from side wall was dragged inside the bed with particle down ¯ow. Then RDF combustion in the bed was promoted and the bed temperature was increased. HCl concentration
1. 12 kg/h of RDF feed was over feed for this combustor and then CO emission level was higher than 500 ppm. 2. 10 kg/h of RDF feed was sucient feed rate and the CO level was under 150 ppm. 3. Secondary air injection and air distribute ratio were eective for the complete combustion of RDF, since free board and the bed temperature were increased. 4. HCl concentration in ¯ue gas was controlled by the calcium component in RDF and its level was decreased with decreasing the combustor temperature.
References [1] Narukawa K, Goto H, Chen Y, Mori S. Combustion characteristics of RFD. Kagakukogaku Ronbunshu 1996;22(3):560±5. [2] Liu G, Goto H, Chen Y, Yamazaki R, Mori S, Fujima Y. Fundamental research on combustion of cylindrical refuse-derived fuels. Int. Conf. on Incineration and Thermal Treatment Technologies, 1997. p. 515±9.
Combustion of refuse derived fuel in a ¯uidized bed Guilin Piao a,*, Shigeru Aono a, Shigekatsu Mori a, Seiichi Deguchi b, Yukihisa Fujima b, Motohiro Kondoh c, Masataka Yamaguchi c a Department of Chemical Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8063, Japan Center for Integrated Research in Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8063, Japan c Plant Engineering Department, Toyota Motor Corp., Toyota-cho, Toyota, 471-71, Japan
b
Abstract Power generation from Refuse Derived Fuel (RDF) is an attractive utilization technology of municipal solid waste. To explain the behavior of RDF-®red ¯uidized bed incinerator, the commercial size RDF was continuously burnt in a 3030 cm bubbling type ¯uidized-bed combustor. It was found that 12 kg/h of RDF feed rate was too high feed for this test unit and the CO level was higher than 500 ppm. However, 10 kg/h of RDF was a proper feed rate and the CO level was kept under 150 ppm. Secondary air injection and changing air ratio from the pipe grid were eective for the complete combustion of RDE. It was also found that HCl concentration in ¯ue gas was controlled by the calcium component contained in RDF and its level was decreased with decreasing the combustor temperature. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction In Japan, the municipal solid waste (MSW) has been recognized as one of the promising candidates for a new energy resource. However, the eciency of the MSW ®red power generation is less than 15%. Since the steam condition is limited to avoid the high temperature corrosion of the boiler tube caused by hydrochloric acid gas in ¯ue gas. Recently dioxin problem has been social problem and the serious regulation less than 0.1 ng/m3 was determined for newly built incinerator. Therefore small scale incineration plants less than 100 tons/day could not be operated. To overcome these problem of MSW incineration, densi®ed refuse derived fuel (RDF) which is classi®ed RDF-5 by ASTM standard is attracted by Japanese local government attention as one of new technology to utilized MSW as the energy resources. Since RDF has signi®cant advantage in storage, transportation and higher heating value, RDF produced in the small dispersed towns and cities is collected and can be incinerated in a large scale intensive power generation plant.
* Corresponding author. Tel.: +81-52-789-4674; fax: +81-52-7893271; e-mail: [email protected]
Moreover, the calcium components added in RDF has the capacity to control HCl emission level in ¯ue gas and then higher power generation eciency is expected. It was reported previously that RDF was burnt in two stage exothermic reaction [1]. Combustion characteristics of the single RDF pellet were also reported [2]. However, only limited engineering data of RDF incinerator have been presented, since the size of RDF aects on the behavior of the combustor and their size (25 cm in diameter and 210 cm length) is too large to obtain the continuous operating data by using the small scale experimental unit. In this work, to explain the behavior of the ¯uidized bed incinerator of RDF, the commercial size RDF was burnt in a 3030 cm and 4 m high bubbling ¯uidized-bed combustor. CO and HCl emission from the combustor were measured under the various operating conditions. 2. Experimental apparatus and procedure Fig. 1 shows a schematic diagram of an experimental bubbling type ¯uidized-bed combustor. The combustor is 3030 cm and 2.73 m high from the pipe grid air-distributor.
0956-053X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0956 -0 53X(98)00140-8
510
G. Piao et al./Waste Management 18 (1998) 509±512 Table 2 Operating condition of each run Fuel Bed air (kg/h) (Nm3/h) RUN1 RUN2 RUN3 RUN4 RUN5 RUN6 RUN7 RUN8 RUN9 RUN10 RUN11
Fig. 1. Experimental apparatus (1 ¯uidized bed; 2 pipe grid; 3 belt conveyer; 4 ball valve; 5 cyclone; 6 gas cooler; 7 bag ®lter; 8 fan; 9 temperature tap).
Silica sand (dp = 0.3 mm, umf = 0.0746 m/s at room temperature) was ¯uidized and RDF was continuously fed on the surface of the bed. The bed height was about 35 cm from the distributor. RDF feed system consists of a belt conveyer and two ball valves. Four pipes having 18 holes with 3 mm 1 were used as the distributor. Air feed rate from each pipe was controlled independently. The secondary air could be also fed about 70 cm above the bed surface. Coarse dust in the ¯ue gas was collected by a cyclone and ®ne ¯y ash was collected by a bag house after cooling down by a gas cooler. The bed temperature was observed at 30 cm high from the distributor and the free board temperature was observed at 50 cm high from the bed surface. Flue gas was sampled at the entrance of the gas cooler and HCl concentration was measured at the entrance and the exit of the bag ®lter.
Table 1 RDF fuel analyses Proximate analysis (wt%) Moisture Volatile matters Fixed carbon Ash Ultimate analysis (wt%) Carbon Hydrogen Nitrogen Oxygen Sulfur Chlorine Calcium Ca/(S+0.5 Cl) Heating value (MJ/kg)
12 12 12 12 10 10 10 10 10 10 10
Secondary air (Nm3/h)
Air ratio
Air distribution ratio
0 0 0 12 0 0 0 12 6 0 6
1.14 1.385 1.5 1.5 1.27 1.47 1.8 1.27 1.22 1.27 1.7
1.78 1.69 2.13 4.55 1 1.49 2.13 1 1 3.12 3.57
56 68 74 62 52 60 74 40 44 52 64
As shown in Table 1, low heating value of RDF was 18,392 MJ/kg, volatile matter content was 72.5% and ®xed carbon was only 3.9%. Sulfur content was 0.17% and nitrogen content was 0.75%. Chlorine content was 1.0% and calcium content was 2.7%. Then Ca/(S+0.5 Cl) molar ratio was 3.4. Operating condition of each run are shown in Table 2. In some runs, air feed rate was changed between two center pipes and two side pipes. Air distribution ratio is de®ned as the ratio of air ¯ow rate from center pipes to the side pipes. 3. Experimental results Observed temperature in the combustor and CO, HCl, NOx and SOx concentration in ¯ue gas are shown in Table 3. When RDF feed rate was 12 kg/h, CO concentration in ¯ue gas was decreased with increasing air ratio as shown in Fig. 2. However, CO emission level was over 500 ppm and no signi®cant eect of secondary air injection was found. Then it can be concluded that 12 kg/h is too high for the test unit. Table 3 Experimental results data
11.1 72.5 3.9 12.5 41.7 6.0 0.75 36.3 0.17 1.0 2.7 3.4 18,392
Bed Free board CO temperature temperature (ppm) ( C) ( C) RUN1 RUN2 RUN3 RUN4 RUN5 RUN6 RUN7 RUN8 RUN9 RUN10 RUN11
969 933 964 985 904.5 935.3 905.3 927.7 940.3 964.7 882.6
965.6 941 972 1017 943.5 955.2 910.3 964 975 994.3 1099
4030 819 540 680 127.3 83.12 37.29 29 25.1 25.68 6.02
SOx HCl NOx (ppm) (ppm) (ppm) 212 178 281.2 315 144 247 192 234 216 282 264
79 72.3 102.5 118.16 121.05 128.7 139.4 122.0 122 ± 201.6
0.5 0.2 0.175 0.2 0.1 0.15 0.1 0 0 0 ±
G. Piao et al./Waste Management 18 (1998) 509±512
Fig. 2. CO emission level in ¯ue gas under 12 kg/h RDF feed. &: secondary air ratio=0;*: secondary air ratio=0.2.
Fig. 3. CO emission level in ¯ue gas under 10 kg/h RDF feed. &: secondary air ratio=0; *: secondary air ratio=0.12; ~: air distribution ratio=1.49.
511
Fig. 4. Tempreature in the combustor under 10 kg/h RDF feed and eect of air distribution method. &: bed temperature; &: free board temperature; *: bed temperature with secondary air; *: free board temperature with secondary air; ~: bed temperature at air distribution ratio=2.08; ~: bed temperature at air distribution ratio=2.71.
Fig. 5. Eect of bed temperature and RDF feed on HCl emission level.
512
G. Piao et al./Waste Management 18 (1998) 509±512
in ¯ue gas was increased with increasing bed temperature as shown in Fig. 5. The dierence of RDF feed rate aected slightly the HCl emission level. Although the bed temperature was higher than 900 C, more than 63% of chlorine components were captured by Ca components in the combustor. It is found in Table 3 that SOx emission level was very low as less than 1 ppm. As shown in Fig. 6, NOx level was 100200 ppm. More research work is necessary to discuss the behavior of NOx in the combustor.
4. Conclusion To explain the behavior of an RDF±®red ¯uidized bed incinerator, commercial size RDF was continuously burnt in a 3030 cm bubbling type ¯uidized bed combustor. The following result were demonstrated:
Fig. 6. Eect of air ratio and secondary ratio on NOx. &: NOx, secondary air ratio=0; ^: NOx, secondary air ratio=0.03; ~: NOx, secondary air ratio=0.12.
When RDF feed rate was decreased to 10 kg/h, CO level was kept under 150 ppm and it was decreased with increasing air ratios as shown in Fig. 3. Temperatures in the bed and the free board are shown in Fig. 4, and the temperature showed maximum around air ratio being 1.5. It is found from Figs. 3 and 4 that the secondary air injection and the increasing air distribution ratio were eective to keep complete combustion. The secondary air injection increased both the free board and the bed temperature since the volatile matter combustion in the free board was promoted. Increasing air distribution ratio, strong particle circulation in the bed was built up and then RDF fed from side wall was dragged inside the bed with particle down ¯ow. Then RDF combustion in the bed was promoted and the bed temperature was increased. HCl concentration
1. 12 kg/h of RDF feed was over feed for this combustor and then CO emission level was higher than 500 ppm. 2. 10 kg/h of RDF feed was sucient feed rate and the CO level was under 150 ppm. 3. Secondary air injection and air distribute ratio were eective for the complete combustion of RDF, since free board and the bed temperature were increased. 4. HCl concentration in ¯ue gas was controlled by the calcium component in RDF and its level was decreased with decreasing the combustor temperature.
References [1] Narukawa K, Goto H, Chen Y, Mori S. Combustion characteristics of RFD. Kagakukogaku Ronbunshu 1996;22(3):560±5. [2] Liu G, Goto H, Chen Y, Yamazaki R, Mori S, Fujima Y. Fundamental research on combustion of cylindrical refuse-derived fuels. Int. Conf. on Incineration and Thermal Treatment Technologies, 1997. p. 515±9.