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Ignition and Emission Characteristics of Ignition-assisting Agents for Densified Corn Stover Briquette Fuel
PRODUCT ENGINEERING AND CHEMICAL TECHNOLOGY Chinese Journal of Chemical Engineering, 18(4) 687ü694 (2010)
Ignition and Emission Characteristics of Ignition-assisting Agents for Densified Corn Stover Briquette Fuel YUAN Hairong (၏ںఔ)1,2, PANG Yunzhi (ၩᄄ)1,*, WANG Kuisheng (ฆࣩಖ)1, LIU Yanping (ঞཙ)1, ZUO Xiaoyu (ᆰ໋ဳ)1, MA Shuqing (৴ೞࢡ)1 and LI Xiujin (ह༎ࠡ)1,* 1 2
Centre for Resources and Environmental Research, Beijing University of Chemical Technology, Beijing 100029, China Planting Industry Service Centre of Yanqing County of Beijing City, Beijing 102100, China
Abstract Ignition-assisting agents for densified corn stover briquette fuel (DCBF) were developed, and their ignition and emission characteristics were investigated using type LLA-6 household cooking stove. Three waste liquid fuels, waste engine oil (E), diesel oil (D), and industrial alcohol (A), were used as raw materials to make 25 ignitionassisting agents by mixing at different ratios. Their ignition performance was evaluated in terms of ignition time and cost. It was found that ignition-assisting agents ED15 (a mix of E and D at volume ratio of 1Ή5) and DA51 (a mix of D and A at volume ratio of 5Ή1) presented better ignition results with shorter ignition time (4053 s) and lower cost (6.1 and 5.3 cents) at the dosages of 9 ml and 8 ml, respectively. The emission of O2, CO, CO2, NOx, and SO2, the temperature in fume gas, and combustion efficiency were investigated for ED15 and DA51. The results show that the emission of ED15 with the dosage of 9 ml is lower than that of DA51 with the dosage of 8 ml in the ignition process. ED15 at the dosage of 9 ml achieves satisfactory combustion efficiency and emits less pollutant, so it is recommended for practical application. The study will provide a cost-effective and environmentally friendly approach to fast ignite DCBF and break the barrier to the practical application of DCBF. Keywords ignition-assisting agent, densified corn stover briquette fuel, fume gas, emission
1
INTRODUCTION
China is one of the largest agricultural countries in the world. Approximate 700 million tons of various crop stalks are generated annually [1]. There are a few ways to use the crop residues, such as animal feed, direct combustion, gasification, paper-making, fertilizer, and building materials. Densified biomass briquette fuel (DBBF) made from crop stalks is widely used in rural areas in China, due to the advantages such as easier and cheaper transportation and storage as well as convenient utilization. In 2008, the total amount of DBBF in China is about 20 million tons [2]. DBBF is mainly used for centralized gas station or household cooking stove to provide cooking and heating energy for the families living in rural areas. Nowadays, there are about 50 million biomass household cooking stoves using DBBF in China [3]. However, DBBF is facing a bottle-neck problem with ignition. DBBF is a kind of densified biomass with high density (0.81.4 g·cm3), which is very difficult to be ignited [4]. Farmers normally take 20 to 30 minutes for successfully igniting cooking stoves, three times each day, so that most people are unwilling to use DBBF. In addition, long-time ignition causes thick smoke and harmful gas emissions, which is a serious environmental pollution and threat to health. Therefore, it is imperative to develop efficient and cost effective ignition-assisting agents. Ignition-assisting agents are widely studied for improving coal combustion and are very effective. Shi and Xue [5] made a coal combustion agent by using KCl [4%10% (by mass)], industrial salt [60%80%
(by mass)], KNO3, K2Cr2O7 [2%8% (by mass)], and KMnO4 [3.5%7% (by mass)], and the ignition temperature of coal decreased from 350450 qC to 200300 qC. Miao [6] made an agent with oxidizing agent [18%45% (by mass)], sulfur-fixing agent [4%7% (by mass)], catalyst [4%8% (by mass)], dust removal agent [1%3% (by mass)], and appropriate amount of binding agent, which effectively improved the combustion efficiency of coal. Demirbas [7] reported that hazelnut shell pyrolytic oil could increase the durability of briquette fuel. The biological additives (e.g. maize, rye flour) in wood pellet production are commonly used [8]. However, ignitionassisting agents for DBBF used in household cooking stove have not reported in literature. Ignition-assisting agents can be made of various materials. Using wastes as raw materials is one of options. China has become one of the largest car manufacturers and costumers in 2009, and owns 186.58 million vehicles. It is estimated that about 60 million tons of waste engine oil and waste diesel oil are generated in 2010 [9]. Most of waste oils are not appropriately treated and used, leading to serious environmental problems. Waste oils are fossil fuels, which are potentially used as raw materials to make ignition-assisting agents for DBBF. This will bring some other benefits such as reducing the pollution by waste oils. The objectives of this study are: (1) develop efficient and affordable ignition-assisting agents by using waste fuels; (2) evaluate the ignition performance and analyze the emissions of the ignition-assisting agents; (3) determine the best ignition-assisting agent for DBBF in terms of cost, performance and emissions.
Received 2010-04-20, accepted 2010-06-08. * To whom correspondence should be addressed. E-mail: [email protected], [email protected]
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MATERIALS AND METHODS
2.1
zhou Daxu Bio-energy Technology Co., Ltd., widely used in northern part of China, and granted Gold Award by Shell Foundation in the United States in 2007.
Materials
The corn stover used in this study was collected from Yanqing County of Beijing City. Crushed corn stover was pressed by 9SGJ-1000 type biomass briquetting equipment of Shijiazhuang, Hebei, Yan-feng Machinery Manufacturing Co., Ltd. The dimension of DCBF was 32 mm × 32 mm × (3080 mm) with a density of about 0.9 g·cm3. The DCBF composition [10] is shown in Table 1. Table 1
Composition of DCBF
C/%
H/%
O/%
N/%
S/%
Mad/%
Aad/%
Vad/% Fcad/%
45.43
6.24
46.36
0.92
0.17
9.25
11.84
72.19
6.72
Three waste liquid fuels, waste engine oil (E), diesel oil (D), and industrial alcohol (A), were used as raw materials and mixed at different volume ratios to make 25 kinds of ignition-assisting agents, which are named according to the raw materials and volume ratios. For instance, ED15 means that the agent is made by mixing waste engine oil (E) and diesel oil (D) at volume ratio of 1Ή5; EDA151 represents that the agent is made by mixing waste engine oil (E), diesel oil (D), and industrial alcohol (A) at volume ratio of 1Ή5Ή1. 2.2
Stove type
Figure 1 shows type LLA-6 household cooking stove used for all experiments. The stove is 340 mm × 340 mm × 720 mm in size with a cone-shaped chimney in 1.5 m of height. It weighs 52 kg and consists of two parts. The lower part is the combustion chamber with air adjusting damper and the upper part is the gasification chamber. The stove is made by Beijing Shen-
Figure 1 Schematic diagram of type LLA-6 household cooking stove 1üupper stove; 2ülower stove; 3üfeed box damper; 4üchimney; 5ügasification chamber; 6ücombustion chamber; 7ücombustion device
2.3
Ignition experiments
DCBF was first filled in the combustion chamber of the stove. An ignition-assisting agent was sprayed on the surface of the DCBF and then ignited by a match. It was considered as a successful ignition if the fire flame reached the stove mouth (30 cm in height) in 3 min. Each ignition test was repeated six times. 2.4
Emission analyses
After the DCBF was ignited, the emissions of O2, CO, CO2, NOx, and SO2, and the temperature in the fume were recorded at intervals of 3 seconds by the Master 2000 Flue Gas Analyser. The ignition process was completed within 70 seconds. The initial temperature was ambient temperature. When temperature of combustion chamber was reduced to ambient temperature, the stove was refilled for the next experiment. 3 3.1
RESULTS AND DISCUSSION Performance of ignition-assisting agents
Table 2 shows ignition results of 25 ignition-assisting agents. The time needed for the fire flame to reach height 30 cm is represented by “t”. The ignition-assisting agent is marked “Ĝ” if DCBF is ignited successfully all six times, otherwise it is marked “×”. “ż” means that the cost of ignition-assisting agent is too high and not acceptable. The acceptable ignition cost is 6.5 cents. Ignition-assisting agents ED55-ED52 ignite DCBF successfully, with the dosages more than 5 ml. It means that the dosage affects the ignition. Certain amount of dosage is required in order to provide enough heating energy to ignite DCBF. Agent ED51 fails to ignite DCBF at all dosage levels, implying that diesel amount is important, which is easier to ignite than waste engine oil. Agents EA45-EA14 were made by mixing waste engine oil and industrial alcohol at different ratios. Generally, EA agents are not satisfactory, because they fail to ignite DCBF or their costs are higher than acceptable value (6.5 cents). The reason is that alcohol is very easy to be ignited and is quickly combusted, so that the composition of waste engine oil is not ignited before alcohol composition is burnt out. EDA agents consist of waste engine oil, waste diesel, and industrial alcohol. EDA 151 and EDA161 can ignite DCBF at the dosages of 58 ml and 78 ml, respectively. Their costs are also acceptable. Compared to EDA161, EDA151 needs lower dosages and lower cost, so that it is better. DA agents are comprised of waste diesel and
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Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010 Table 2
Ignition results of 25 ignition-assisting agents
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
t /s
Ignition results
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
t /s
Ignition results
1
ED55
3
2.73
151
¥
6
ED45
7
6.09
67
¥
4
3.63
122
¥
8
6.96
ż
5
4.54
147
¥
9
7.83
ż
6
5.45
120
¥
10
8.7
ż
7
6.36
79
3
2.47
372
¥
8
7.27
ż
4
3.3
304
¥
2
3
4
5
6
ED54
ED53
ED52
ED51
ED45
¥
7
ED35
9
8.18
ż
5
4.12
85
¥
10
9.09
ż
6
4.94
80
¥
3
2.84
×
7
5.76
74
4
3.79
×
8
6.58
ż
5
4.74
171
¥
9
7.41
ż
6
5.68
141
10
8.23
ż
7
6.63
ż
3
2.28
×
8
7.58
ż
4
3.04
9
8.53
ż
5
3.8
10
9.47
3
2.99
4 5
¥ 8
ED25
¥
× 135
¥
ż
6
4.56
81
¥
188
¥
7
5.32
66
¥
3.98
111
¥
8
6.08
55
4.98
128
¥
9
6.84
ż
6
5.97
168
10
7.6
ż
7
6.97
ż
3
2.03
×
8
7.96
ż
4
2.71
×
¥ 9
ED15
¥
9
8.96
ż
5
3.39
183
¥
10
9.95
ż
6
4.07
79
¥
3
3.17
×
7
4.75
75
¥
4
4.23
×
8
5.42
68
¥
5
5.29
288
¥
9
6.1
40
6
6.34
195
¥
10
6.78
10
7
7.4
ż
3
3.59
×
8
8.46
ż
4
4.79
×
9
9.51
ż
5
5.99
×
10
10.57
ż
6
7.19
ż
3
3.42
×
7
8.39
ż
4
4.56
×
8
9.58
ż
5
5.7
×
9
10.78
ż
6
6.84
ż
10
11.98
ż
7
7.98
ż
3
3.61
×
8
9.12
ż
4
4.81
×
9
10.26
ż
5
6.01
×
10
11.4
ż
6
7.21
ż
3
2.61
×
7
8.41
ż
4
3.48
90
¥
8
9.62
ż
5
4.35
105
¥
9
10.82
ż
6
5.22
87
¥
10
12.02
ż
11
EA46
¥ ż
EA45
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Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010
Table 2 (Continued) No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
12
EA44
3 4 5
6.04
6
7.25
7
8.46
ż
8
9.66
9
10.87
10 3
13
14
15
16
17
EA43
EA42
EA41
EA34
EA24
t /s
Ignition results
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
3.62
×
17
EA24
7
8.34
ż
4.83
×
8
9.54
ż
¥
9
10.73
ż
ż
10
11.92
ż
3
3.54
×
ż
4
4.72
×
ż
5
5.9
×
12.08
ż
6
7.08
ż
3.64
×
7
8.26
ż
4
4.86
×
8
9.44
ż
5
6.07
×
9
10.62
ż
6
7.28
ż
10
11.8
ż
7
8.5
ż
3
2.24
×
8
9.71
ż
4
2.98
×
151
18
19
EA14
EDA151
t /s
Ignition results
9
10.93
ż
5
3.73
126
¥
10
12.14
ż
6
4.48
124
¥
3
3.67
×
7
5.22
184
¥
4
4.89
×
8
5.97
53
¥
5
6.12
×
9
6.71
ż
6
7.34
ż
10
7.46
ż
7
8.56
ż
3
2.17
×
8
9.78
ż
4
2.89
×
20
EDA161
9
11.01
ż
5
3.62
×
10
12.23
ż
6
4.34
×
3
3.71
×
7
5.06
81 90
¥
4
4.94
×
8
5.78
5
6.18
×
9
6.51
ż
6
7.42
ż
10
7.23
ż
7
8.65
ż
3
1.99
×
8
9.89
ż
4
2.65
148
¥
9
11.12
ż
5
3.31
130
¥
10
12.36
ż
6
3.97
72
¥
3
3.6
×
7
4.63
71
¥
4
4.8
×
8
5.3
56
¥
5
6.01
×
9
5.96
54
6
7.21
ż
10
6.62
7
8.41
ż
3
2.2
×
8
9.61
ż
4
2.93
×
21
22
DA51
DA52
¥
¥ ż
9
10.81
ż
5
3.67
10
12.01
ż
6
4.4
167
×
3
3.58
×
7
5.13
102
¥
4
4.77
×
8
5.86
81
¥
5
5.96
×
9
6.6
ż
6
7.15
ż
10
7.33
ż
¥
691
Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010 Table 2 (Continued) No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
23
DA53
3 4 5 6 7 8 9 10 3 4 5 6
2.36 3.14 3.93 4.72 5.5 6.29 7.07 7.86 1.89 2.52 3.15 3.78
24
DA54
t /s
139 63 65 50
Ignition results × × ¥ ¥ ¥ ¥ ż ż × × × ×
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
24
DA54
25
DA55
7 8 9 10 3 4 5 6 7 8 9 10
4.41 5.04 5.67 6.3 2.4 3.2 4 4.79 5.59 6.39 7.19 7.99
t /s
Ignition results × × × × × × × × × × ż ż
Note: ¥ü6 times successful ignition; ×üone or more unsuccessful ignition; żüunacceptable cost.
industrial alcohol. Ignition results of DA agents, except for DA54 and DA55, are better than those of EA agents, when the dosage is more than 6 ml. DA54 and DA55 can not ignite DCBF successfully because industrial alcohol is quickly burnt out, and the diesel oil composition can not provide enough thermal energy to ignite DCBF. Therefore, DA51-DA53 are satisfactory. Based on the experimental results in Table 2, ED15 with 9 ml dosage and DA51 with 8 ml dosage are considered as the best ignition-assisting agents in terms of their lower costs and shorter ignition time. The two agents were future investigated and compared for their emissions. 3.2
Figure 2 Changes of O2 concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Emission and combustion characteristics
Investigations indicate that the indoor air pollution from biomass fuel combustion in cooking stove threatens the health of women in rural areas, who are usually responsible for family cooking and spend two or even more hours daily in the kitchen [11]. In this study the emissions from fume gas from cooking stove are analyzed in order to evaluate potential pollution when ignition-assisting agents ED15 and DA51 are used.
Figure 3 Average O2 concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
3.2.1 Oxygen contents The amount of consumed O2 is an indication of the amount of fuel combusted [12]. The more fuel is combusted, the lower O2 concentration is in the fume gas. O2 concentrations in fume gas were analyzed during the ignition period for ED15 and DA51 with different dosages. Fig. 2 shows that O2 concentrations decline slowly with time. Fig. 3 shows the average O2 concentrations for ED15 and DA51 at different dosages. The average O2 concentrations for ED15 are higher than those of DA51 at all dosages. This may be due to the lower kindling temperature of alcohol (12 qC) [13], leading to easy ignition and quick burning out. As the dosage increases, the average O2 concentrations decrease slightly for both agents, since more agent consumes more oxygen.
3.2.2 CO2 CO2 emission from stove is one of major concerns for DCBF fuel. The more fuel is combusted, the higher CO2 concentration is in the fume gas. Fig. 4 shows CO2 concentrations in fume gas during the ignition period for ED15 and DA51, which increase very quickly in the beginning of ignition and is from the combustion of agents rather than DCBF fuel in the ignition period. Afterwards, CO2 concentrations maintain at higher levels and fluctuate, indicating that the DCBF fuel is combusted and the air supplied from stove bottom is unstable. Fig. 5 shows the average CO2 concentrations for ED15 and DA51 at different dosages. The average CO2 concentration with ED15 is obviously lower than that with DA51. This may be
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Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010
Figure 4 Changes of CO2 concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Figure 7 Average CO concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
these CO emissions are less than 0.2%, which meet the requirement designated by Beijing local standard “General Technical Requirements of Household Biomass Stoves” [15].
Figure 5 Average CO2 concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
attributed to the higher kindling temperature of engine oil, resulting in slower ignition and less CO2 emission. In addition, as the dosage increases, the average CO2 concentration increases for both agents, because more agent is combusted. 3.2.3 CO Incomplete combustion of biomass releases carbon monoxide. The release of CO from a traditional stove has been identified in such level that is potentially poisonous to human [14]. Fig. 6 presents the changes of CO concentrations in fume gas with time. CO concentrations for both ED15 and DA51 increase slowly after ignition, and CO emission from DA51 is higher than that from ED15. The average CO concentrations of ED15 with 7, 9, and 11 ml dosage and DA51 with 8, 10, and 12 ml dosage are 0.01%, 0.02%, 0.03%, 0.03%, 0.04%, and 0.05% on DCBF dry matter basis, respectively, during the ignition period (Fig. 7). All
Figure 6 Changes of CO concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
3.2.4 NOx NOx are typical pollutants, which are produced from the combustion of nitrogen in the biomass material [16, 17]. Fig. 8 shows the changes of NOx concentrations for ED15 and DA51 at three dosages. All NOx concentrations increase after ignition. The average NOx concentration for ED15 increases from 0 to 38 mg·m3 at the end of ignition, while that for DA51 increases from 0 to 63 mg·m3 (Fig. 9). NOx emission of ED15 at different dosages is generally less than that of DA51. NOx concentrations are higher as dosage increases. NO2 concentrations are only 24 mg·m3 (Fig. 10) and NO accounts for the main part of NOx emission (Fig. 11). This is similar to the result reported
Figure 8 Changes of NOx concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Figure 9 Average NOx concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010
Figure 10 Average NO2 concentrations in fume gas with time 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
Figure 11 Average NO concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
for coal combustion [18, 19]. There are three routes for formation of NO during coal combustion, namely, thermal NO, prompt NO, and fuel NO [20]. Thermal NO is formed in the oxidation of molecular nitrogen with oxygen in the combustion air at temperatures higher than 1300 qC, whereas the fuel NO is formed from the organic nitrogen in the fuel [21]. Prompt NO results from the radical CH formed as an intermediate at the flame front, which reacts with the nitrogen in the air to form HCN and further forms NO at high temperatures. The combustion temperature in the stove in this study is 250357 qC, so that it is expected that NO is mainly from the nitrogen in the fuel rather than from the air [22]. The nitrogen content in the DCBF is 0.92% (by mass) (Table 1), which is low and leads to relatively lower NO emission. 3.2.5 SO2 SO2 is produced from the combustion of sulfur element in the biomass material [16], so its emission in fume gas is mainly determined by the content of S in DCBF. Fig. 12 presents the changes of SO2 concentrations in fume gas with time. SO2 contents with DA51 are generally higher than those with ED15 at three dosages, but overall SO2 concentrations are very low in fume gas (Fig. 13) compared to NOx and CO, since the sulphur content is low, at 0.17% in the DCBF (Table 1). The average concentrations of SO2 are 0, 1, 1, 6, 5, and 11 mg·m3 for ED15 at the dosages of 7, 9, and 11 ml, and for DA51 at the dosages of 8, 10, and 12 ml, respectively. All S emissions with ED15 and DA51 are lower than the requirement of less than 50 mg·m3 by Beijing local standard.
693
Figure 12 Changes of SO2 concentrationsin fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Figure 13 Average SO2 concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
3.2.6 Temperature The temperature of fume gas affects the heat energy efficiency of stove. The fume gas with higher temperature will bring more energy out of stove and decrease the energy efficiency. Fig. 14 shows that the temperatures of fume gas for ED15 and DA51 increase with the combustion of agents. The temperature with DA51 is higher than that with ED15, due to the lower kindling temperature of DA51, in which the alcohol is easier to be ignited and burns rapidly, releasing more heat energy [23]. The highest fume gas temperatures are 62 and 88 qC for ED15 and DA51 at the dosage of 9 ml and DA51 at the dosage of 12 ml, respectively, during the ignition process.
Figure14 Changes of temperature in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
3.2.7 Combustion efficiency Combustion efficiency is defined as the ratio of carbon released as CO2 to total carbon [16]. Complete combustion will extract all the energy available in the fuel. However, 100% of combustion efficiency is not
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achievable practically. Common combustion processes may reach efficiencies of 10%95%. Fig. 15 shows the combustion efficiencies of the stove in this study for ED15 and DA51 at three dosages. During the ignition period, the average combustion efficiencies are 84.5%, 85.6%, and 85.4% for ED15 at the dosages of 7, 9, and 11 ml, while they are 84.5%, 84.8%, and 84.6% for DA51 at the dosages of 8, 10, and 12 ml, respectively. Compared to other agents and dosages, ED15 at the dosage of 9 ml achieves satisfactory combustion efficiency but emits less pollutant, and is recommended for practical application.
2 3
4
5 6 7
8
9 10 11
Figure15 Changes of combustion efficiency in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
4
CONCLUSIONS
12
13 14
Twenty-five ignition-assisting agents were obtained by mixing waste engine, waste diesel oil, and industrial alcohol at different volume ratios. ED15 and DA51 achieved better ignition results. ED15 with 9 ml dosage and DA51 with 8 ml dosage took 40 and 53 seconds to ignite the DCBF successfully, respectively, which were 3040 times shorter than those without using ignition-assisting agent. ED15 and DA51 showed similar combustion characteristics in terms of O2, CO, CO2, NOx, and SO2 emissions, temperature of fume gas, and combustion efficiency. The average concentrations of CO, CO2, NOx, and SO2 for ED15 and DA51 at all dosages met the requirements by Beijing local standard. Compared to other agent and other dosages, ED15 at the dosage of 9 ml achieved satisfactory combustion efficiency but emitted less pollutant. It will provide a cost-effective and environmentally friendly approach to fast ignite DBBF and break the barrier to the practical application of DBBF.
15
16 17 18
19
20
21
22
REFERENCES 1
National Bureau of Statistics of China, China Statistical Yearbookü 2009, China Statistics Press, 1215 (2009). (in Chinese)
23
Qin, W., “Biomass: ecological energy on the road”, China Equip., 10, 4446 (2009). (in Chinese) Hao, F.Z., “China’s densified biomass briquette fuel and stove industry in the development country”, Agric. Eng. Technol., 8, 57 (2009). (in Chinese) Meng, H.B., Zhu, M., Wang, Z.Y., “Status and experience of bio-energy development & application in Sweden, Germany, Italy”, Agric. Eng. Technol., 4, 5356 (2007). (in Chinese) Shi, S.Q., Xue, Z.Z., “Combustion assistant for coal”, Anhui Sci. & Technol., 1, 3435 (1995). (in Chinese) Miao, J., “The combustion-supporting agent of coal and its recipe principles”, J. Jiaozuo Institute Technol., 14, 5357 (1995). (in Chinese) Demirbas, A., “Properties of charcoal derived from hazelnut shell and the production of briquettes using pyrolytic oil”, Energy, 24, 141150 (1999). Obernberger, I., Thek, G., “Physical characterisation and chemical composition of densified biomass fuels with regard to their combustion behaviour”, Biomass Bioenergy, 27, 653669 (2004). Qian, M., “Waste oil recycling: Reengineering a large oil field”, China Chemical Industry News, No.007, Sep. 20 (2007). (in Chinese) Liu, R.H., Yuan, H.R., Xu, L., “Kinetic study of maize straw pyrolysis”, Acta Energy Solaris Sinica, 28, 527531 (2007). (in Chinese) Duflo, E., Greenstone, M., Hanna, R., “Cooking stoves, indoor air pollution and respiratory health in rural Orissa”, Econ. Political Weekly, 9, 7180 (2008). Altun, N.E., Hicyilmaz, C., Bagci, A.S., “Combustion characteristics of coal briquettes (I) Thermal features”, Energy Fuels, 17, 12661276 (2003). Yao, R.H., Alcohol Fermentation Technology, South China University of Techonlogy Press, Guangzhou (1999). (in Chinese) Miah, M.D., Rashid, H.A., Shin, M.Y., “Wood fuel use in the traditional cooking stoves in the rural floodplain areas of Bangladesh: A socio-environmental perspective”, Biomass & Bioenergy, 33, 7078 (2009). Beijing Bureau of Quality and Technical Supervision, DB11/T 540-2008, Beijing local standards “General technical requirements of household biomass stoves”, May 1 (2008). (in Chinese) Demirbas, A., “Hazardous emissions from combustion of biomass”, Energy Sources, Part A, 30, 170178 (2008). Xu, X.C., Zhou, L.X., Combustion Technology Manual, Chemical Industry Press, Beijing, 1270 (2007). (in Chinese) Brown, S.D., Thomas, K.M., “A comparison of NO release from coals and entrained-flow reactor chars during temperature-programmed combustion”, Fuel, 72, 359365 (1993). Wang, W.X., Brown, S.D., Hindmarsh, C.J., “NOx release and reactivity of chars from a wide range of coals during combustion”, Fuel, 73, 13811388 (1994). Molina, A., Eddings, E.G., Pershing, D.W., “Char nitrogen conversion: implications to emissions from coal-fired utility boilers”, Prog. Energy Combust. Sci., 26, 507531 (2000). Duo, W., DamJohansen, K., Ostergaard, K., “Widening the temperature range of the thermal DeNOx process, an experimental investigation”, In: 23rd Symp. Combust., 297303 (1990). Werther, J., Saenger, M., Hartge, E.U., “Combustion of agricultural residues”, Prog. Energy Combust. Sci., 26, 127 (2000). Liu, S.Y., “Development and test study on biomass (straw) briquettes combustion equipment”, Ph. D. Thesis, Henan Agric. Univ., Zhengzhou (2003). (in Chinese)
Ignition and Emission Characteristics of Ignition-assisting Agents for Densified Corn Stover Briquette Fuel YUAN Hairong (၏ںఔ)1,2, PANG Yunzhi (ၩᄄ)1,*, WANG Kuisheng (ฆࣩಖ)1, LIU Yanping (ঞཙ)1, ZUO Xiaoyu (ᆰ໋ဳ)1, MA Shuqing (৴ೞࢡ)1 and LI Xiujin (ह༎ࠡ)1,* 1 2
Centre for Resources and Environmental Research, Beijing University of Chemical Technology, Beijing 100029, China Planting Industry Service Centre of Yanqing County of Beijing City, Beijing 102100, China
Abstract Ignition-assisting agents for densified corn stover briquette fuel (DCBF) were developed, and their ignition and emission characteristics were investigated using type LLA-6 household cooking stove. Three waste liquid fuels, waste engine oil (E), diesel oil (D), and industrial alcohol (A), were used as raw materials to make 25 ignitionassisting agents by mixing at different ratios. Their ignition performance was evaluated in terms of ignition time and cost. It was found that ignition-assisting agents ED15 (a mix of E and D at volume ratio of 1Ή5) and DA51 (a mix of D and A at volume ratio of 5Ή1) presented better ignition results with shorter ignition time (4053 s) and lower cost (6.1 and 5.3 cents) at the dosages of 9 ml and 8 ml, respectively. The emission of O2, CO, CO2, NOx, and SO2, the temperature in fume gas, and combustion efficiency were investigated for ED15 and DA51. The results show that the emission of ED15 with the dosage of 9 ml is lower than that of DA51 with the dosage of 8 ml in the ignition process. ED15 at the dosage of 9 ml achieves satisfactory combustion efficiency and emits less pollutant, so it is recommended for practical application. The study will provide a cost-effective and environmentally friendly approach to fast ignite DCBF and break the barrier to the practical application of DCBF. Keywords ignition-assisting agent, densified corn stover briquette fuel, fume gas, emission
1
INTRODUCTION
China is one of the largest agricultural countries in the world. Approximate 700 million tons of various crop stalks are generated annually [1]. There are a few ways to use the crop residues, such as animal feed, direct combustion, gasification, paper-making, fertilizer, and building materials. Densified biomass briquette fuel (DBBF) made from crop stalks is widely used in rural areas in China, due to the advantages such as easier and cheaper transportation and storage as well as convenient utilization. In 2008, the total amount of DBBF in China is about 20 million tons [2]. DBBF is mainly used for centralized gas station or household cooking stove to provide cooking and heating energy for the families living in rural areas. Nowadays, there are about 50 million biomass household cooking stoves using DBBF in China [3]. However, DBBF is facing a bottle-neck problem with ignition. DBBF is a kind of densified biomass with high density (0.81.4 g·cm3), which is very difficult to be ignited [4]. Farmers normally take 20 to 30 minutes for successfully igniting cooking stoves, three times each day, so that most people are unwilling to use DBBF. In addition, long-time ignition causes thick smoke and harmful gas emissions, which is a serious environmental pollution and threat to health. Therefore, it is imperative to develop efficient and cost effective ignition-assisting agents. Ignition-assisting agents are widely studied for improving coal combustion and are very effective. Shi and Xue [5] made a coal combustion agent by using KCl [4%10% (by mass)], industrial salt [60%80%
(by mass)], KNO3, K2Cr2O7 [2%8% (by mass)], and KMnO4 [3.5%7% (by mass)], and the ignition temperature of coal decreased from 350450 qC to 200300 qC. Miao [6] made an agent with oxidizing agent [18%45% (by mass)], sulfur-fixing agent [4%7% (by mass)], catalyst [4%8% (by mass)], dust removal agent [1%3% (by mass)], and appropriate amount of binding agent, which effectively improved the combustion efficiency of coal. Demirbas [7] reported that hazelnut shell pyrolytic oil could increase the durability of briquette fuel. The biological additives (e.g. maize, rye flour) in wood pellet production are commonly used [8]. However, ignitionassisting agents for DBBF used in household cooking stove have not reported in literature. Ignition-assisting agents can be made of various materials. Using wastes as raw materials is one of options. China has become one of the largest car manufacturers and costumers in 2009, and owns 186.58 million vehicles. It is estimated that about 60 million tons of waste engine oil and waste diesel oil are generated in 2010 [9]. Most of waste oils are not appropriately treated and used, leading to serious environmental problems. Waste oils are fossil fuels, which are potentially used as raw materials to make ignition-assisting agents for DBBF. This will bring some other benefits such as reducing the pollution by waste oils. The objectives of this study are: (1) develop efficient and affordable ignition-assisting agents by using waste fuels; (2) evaluate the ignition performance and analyze the emissions of the ignition-assisting agents; (3) determine the best ignition-assisting agent for DBBF in terms of cost, performance and emissions.
Received 2010-04-20, accepted 2010-06-08. * To whom correspondence should be addressed. E-mail: [email protected], [email protected]
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MATERIALS AND METHODS
2.1
zhou Daxu Bio-energy Technology Co., Ltd., widely used in northern part of China, and granted Gold Award by Shell Foundation in the United States in 2007.
Materials
The corn stover used in this study was collected from Yanqing County of Beijing City. Crushed corn stover was pressed by 9SGJ-1000 type biomass briquetting equipment of Shijiazhuang, Hebei, Yan-feng Machinery Manufacturing Co., Ltd. The dimension of DCBF was 32 mm × 32 mm × (3080 mm) with a density of about 0.9 g·cm3. The DCBF composition [10] is shown in Table 1. Table 1
Composition of DCBF
C/%
H/%
O/%
N/%
S/%
Mad/%
Aad/%
Vad/% Fcad/%
45.43
6.24
46.36
0.92
0.17
9.25
11.84
72.19
6.72
Three waste liquid fuels, waste engine oil (E), diesel oil (D), and industrial alcohol (A), were used as raw materials and mixed at different volume ratios to make 25 kinds of ignition-assisting agents, which are named according to the raw materials and volume ratios. For instance, ED15 means that the agent is made by mixing waste engine oil (E) and diesel oil (D) at volume ratio of 1Ή5; EDA151 represents that the agent is made by mixing waste engine oil (E), diesel oil (D), and industrial alcohol (A) at volume ratio of 1Ή5Ή1. 2.2
Stove type
Figure 1 shows type LLA-6 household cooking stove used for all experiments. The stove is 340 mm × 340 mm × 720 mm in size with a cone-shaped chimney in 1.5 m of height. It weighs 52 kg and consists of two parts. The lower part is the combustion chamber with air adjusting damper and the upper part is the gasification chamber. The stove is made by Beijing Shen-
Figure 1 Schematic diagram of type LLA-6 household cooking stove 1üupper stove; 2ülower stove; 3üfeed box damper; 4üchimney; 5ügasification chamber; 6ücombustion chamber; 7ücombustion device
2.3
Ignition experiments
DCBF was first filled in the combustion chamber of the stove. An ignition-assisting agent was sprayed on the surface of the DCBF and then ignited by a match. It was considered as a successful ignition if the fire flame reached the stove mouth (30 cm in height) in 3 min. Each ignition test was repeated six times. 2.4
Emission analyses
After the DCBF was ignited, the emissions of O2, CO, CO2, NOx, and SO2, and the temperature in the fume were recorded at intervals of 3 seconds by the Master 2000 Flue Gas Analyser. The ignition process was completed within 70 seconds. The initial temperature was ambient temperature. When temperature of combustion chamber was reduced to ambient temperature, the stove was refilled for the next experiment. 3 3.1
RESULTS AND DISCUSSION Performance of ignition-assisting agents
Table 2 shows ignition results of 25 ignition-assisting agents. The time needed for the fire flame to reach height 30 cm is represented by “t”. The ignition-assisting agent is marked “Ĝ” if DCBF is ignited successfully all six times, otherwise it is marked “×”. “ż” means that the cost of ignition-assisting agent is too high and not acceptable. The acceptable ignition cost is 6.5 cents. Ignition-assisting agents ED55-ED52 ignite DCBF successfully, with the dosages more than 5 ml. It means that the dosage affects the ignition. Certain amount of dosage is required in order to provide enough heating energy to ignite DCBF. Agent ED51 fails to ignite DCBF at all dosage levels, implying that diesel amount is important, which is easier to ignite than waste engine oil. Agents EA45-EA14 were made by mixing waste engine oil and industrial alcohol at different ratios. Generally, EA agents are not satisfactory, because they fail to ignite DCBF or their costs are higher than acceptable value (6.5 cents). The reason is that alcohol is very easy to be ignited and is quickly combusted, so that the composition of waste engine oil is not ignited before alcohol composition is burnt out. EDA agents consist of waste engine oil, waste diesel, and industrial alcohol. EDA 151 and EDA161 can ignite DCBF at the dosages of 58 ml and 78 ml, respectively. Their costs are also acceptable. Compared to EDA161, EDA151 needs lower dosages and lower cost, so that it is better. DA agents are comprised of waste diesel and
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Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010 Table 2
Ignition results of 25 ignition-assisting agents
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
t /s
Ignition results
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
t /s
Ignition results
1
ED55
3
2.73
151
¥
6
ED45
7
6.09
67
¥
4
3.63
122
¥
8
6.96
ż
5
4.54
147
¥
9
7.83
ż
6
5.45
120
¥
10
8.7
ż
7
6.36
79
3
2.47
372
¥
8
7.27
ż
4
3.3
304
¥
2
3
4
5
6
ED54
ED53
ED52
ED51
ED45
¥
7
ED35
9
8.18
ż
5
4.12
85
¥
10
9.09
ż
6
4.94
80
¥
3
2.84
×
7
5.76
74
4
3.79
×
8
6.58
ż
5
4.74
171
¥
9
7.41
ż
6
5.68
141
10
8.23
ż
7
6.63
ż
3
2.28
×
8
7.58
ż
4
3.04
9
8.53
ż
5
3.8
10
9.47
3
2.99
4 5
¥ 8
ED25
¥
× 135
¥
ż
6
4.56
81
¥
188
¥
7
5.32
66
¥
3.98
111
¥
8
6.08
55
4.98
128
¥
9
6.84
ż
6
5.97
168
10
7.6
ż
7
6.97
ż
3
2.03
×
8
7.96
ż
4
2.71
×
¥ 9
ED15
¥
9
8.96
ż
5
3.39
183
¥
10
9.95
ż
6
4.07
79
¥
3
3.17
×
7
4.75
75
¥
4
4.23
×
8
5.42
68
¥
5
5.29
288
¥
9
6.1
40
6
6.34
195
¥
10
6.78
10
7
7.4
ż
3
3.59
×
8
8.46
ż
4
4.79
×
9
9.51
ż
5
5.99
×
10
10.57
ż
6
7.19
ż
3
3.42
×
7
8.39
ż
4
4.56
×
8
9.58
ż
5
5.7
×
9
10.78
ż
6
6.84
ż
10
11.98
ż
7
7.98
ż
3
3.61
×
8
9.12
ż
4
4.81
×
9
10.26
ż
5
6.01
×
10
11.4
ż
6
7.21
ż
3
2.61
×
7
8.41
ż
4
3.48
90
¥
8
9.62
ż
5
4.35
105
¥
9
10.82
ż
6
5.22
87
¥
10
12.02
ż
11
EA46
¥ ż
EA45
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Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010
Table 2 (Continued) No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
12
EA44
3 4 5
6.04
6
7.25
7
8.46
ż
8
9.66
9
10.87
10 3
13
14
15
16
17
EA43
EA42
EA41
EA34
EA24
t /s
Ignition results
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
3.62
×
17
EA24
7
8.34
ż
4.83
×
8
9.54
ż
¥
9
10.73
ż
ż
10
11.92
ż
3
3.54
×
ż
4
4.72
×
ż
5
5.9
×
12.08
ż
6
7.08
ż
3.64
×
7
8.26
ż
4
4.86
×
8
9.44
ż
5
6.07
×
9
10.62
ż
6
7.28
ż
10
11.8
ż
7
8.5
ż
3
2.24
×
8
9.71
ż
4
2.98
×
151
18
19
EA14
EDA151
t /s
Ignition results
9
10.93
ż
5
3.73
126
¥
10
12.14
ż
6
4.48
124
¥
3
3.67
×
7
5.22
184
¥
4
4.89
×
8
5.97
53
¥
5
6.12
×
9
6.71
ż
6
7.34
ż
10
7.46
ż
7
8.56
ż
3
2.17
×
8
9.78
ż
4
2.89
×
20
EDA161
9
11.01
ż
5
3.62
×
10
12.23
ż
6
4.34
×
3
3.71
×
7
5.06
81 90
¥
4
4.94
×
8
5.78
5
6.18
×
9
6.51
ż
6
7.42
ż
10
7.23
ż
7
8.65
ż
3
1.99
×
8
9.89
ż
4
2.65
148
¥
9
11.12
ż
5
3.31
130
¥
10
12.36
ż
6
3.97
72
¥
3
3.6
×
7
4.63
71
¥
4
4.8
×
8
5.3
56
¥
5
6.01
×
9
5.96
54
6
7.21
ż
10
6.62
7
8.41
ż
3
2.2
×
8
9.61
ż
4
2.93
×
21
22
DA51
DA52
¥
¥ ż
9
10.81
ż
5
3.67
10
12.01
ż
6
4.4
167
×
3
3.58
×
7
5.13
102
¥
4
4.77
×
8
5.86
81
¥
5
5.96
×
9
6.6
ż
6
7.15
ż
10
7.33
ż
¥
691
Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010 Table 2 (Continued) No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
23
DA53
3 4 5 6 7 8 9 10 3 4 5 6
2.36 3.14 3.93 4.72 5.5 6.29 7.07 7.86 1.89 2.52 3.15 3.78
24
DA54
t /s
139 63 65 50
Ignition results × × ¥ ¥ ¥ ¥ ż ż × × × ×
No.
Name of ignition-assisting agent
Dosages /ml
Cost /cent
24
DA54
25
DA55
7 8 9 10 3 4 5 6 7 8 9 10
4.41 5.04 5.67 6.3 2.4 3.2 4 4.79 5.59 6.39 7.19 7.99
t /s
Ignition results × × × × × × × × × × ż ż
Note: ¥ü6 times successful ignition; ×üone or more unsuccessful ignition; żüunacceptable cost.
industrial alcohol. Ignition results of DA agents, except for DA54 and DA55, are better than those of EA agents, when the dosage is more than 6 ml. DA54 and DA55 can not ignite DCBF successfully because industrial alcohol is quickly burnt out, and the diesel oil composition can not provide enough thermal energy to ignite DCBF. Therefore, DA51-DA53 are satisfactory. Based on the experimental results in Table 2, ED15 with 9 ml dosage and DA51 with 8 ml dosage are considered as the best ignition-assisting agents in terms of their lower costs and shorter ignition time. The two agents were future investigated and compared for their emissions. 3.2
Figure 2 Changes of O2 concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Emission and combustion characteristics
Investigations indicate that the indoor air pollution from biomass fuel combustion in cooking stove threatens the health of women in rural areas, who are usually responsible for family cooking and spend two or even more hours daily in the kitchen [11]. In this study the emissions from fume gas from cooking stove are analyzed in order to evaluate potential pollution when ignition-assisting agents ED15 and DA51 are used.
Figure 3 Average O2 concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
3.2.1 Oxygen contents The amount of consumed O2 is an indication of the amount of fuel combusted [12]. The more fuel is combusted, the lower O2 concentration is in the fume gas. O2 concentrations in fume gas were analyzed during the ignition period for ED15 and DA51 with different dosages. Fig. 2 shows that O2 concentrations decline slowly with time. Fig. 3 shows the average O2 concentrations for ED15 and DA51 at different dosages. The average O2 concentrations for ED15 are higher than those of DA51 at all dosages. This may be due to the lower kindling temperature of alcohol (12 qC) [13], leading to easy ignition and quick burning out. As the dosage increases, the average O2 concentrations decrease slightly for both agents, since more agent consumes more oxygen.
3.2.2 CO2 CO2 emission from stove is one of major concerns for DCBF fuel. The more fuel is combusted, the higher CO2 concentration is in the fume gas. Fig. 4 shows CO2 concentrations in fume gas during the ignition period for ED15 and DA51, which increase very quickly in the beginning of ignition and is from the combustion of agents rather than DCBF fuel in the ignition period. Afterwards, CO2 concentrations maintain at higher levels and fluctuate, indicating that the DCBF fuel is combusted and the air supplied from stove bottom is unstable. Fig. 5 shows the average CO2 concentrations for ED15 and DA51 at different dosages. The average CO2 concentration with ED15 is obviously lower than that with DA51. This may be
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Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010
Figure 4 Changes of CO2 concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Figure 7 Average CO concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
these CO emissions are less than 0.2%, which meet the requirement designated by Beijing local standard “General Technical Requirements of Household Biomass Stoves” [15].
Figure 5 Average CO2 concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
attributed to the higher kindling temperature of engine oil, resulting in slower ignition and less CO2 emission. In addition, as the dosage increases, the average CO2 concentration increases for both agents, because more agent is combusted. 3.2.3 CO Incomplete combustion of biomass releases carbon monoxide. The release of CO from a traditional stove has been identified in such level that is potentially poisonous to human [14]. Fig. 6 presents the changes of CO concentrations in fume gas with time. CO concentrations for both ED15 and DA51 increase slowly after ignition, and CO emission from DA51 is higher than that from ED15. The average CO concentrations of ED15 with 7, 9, and 11 ml dosage and DA51 with 8, 10, and 12 ml dosage are 0.01%, 0.02%, 0.03%, 0.03%, 0.04%, and 0.05% on DCBF dry matter basis, respectively, during the ignition period (Fig. 7). All
Figure 6 Changes of CO concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
3.2.4 NOx NOx are typical pollutants, which are produced from the combustion of nitrogen in the biomass material [16, 17]. Fig. 8 shows the changes of NOx concentrations for ED15 and DA51 at three dosages. All NOx concentrations increase after ignition. The average NOx concentration for ED15 increases from 0 to 38 mg·m3 at the end of ignition, while that for DA51 increases from 0 to 63 mg·m3 (Fig. 9). NOx emission of ED15 at different dosages is generally less than that of DA51. NOx concentrations are higher as dosage increases. NO2 concentrations are only 24 mg·m3 (Fig. 10) and NO accounts for the main part of NOx emission (Fig. 11). This is similar to the result reported
Figure 8 Changes of NOx concentrations in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Figure 9 Average NOx concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
Chin. J. Chem. Eng., Vol. 18, No. 4, August 2010
Figure 10 Average NO2 concentrations in fume gas with time 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
Figure 11 Average NO concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
for coal combustion [18, 19]. There are three routes for formation of NO during coal combustion, namely, thermal NO, prompt NO, and fuel NO [20]. Thermal NO is formed in the oxidation of molecular nitrogen with oxygen in the combustion air at temperatures higher than 1300 qC, whereas the fuel NO is formed from the organic nitrogen in the fuel [21]. Prompt NO results from the radical CH formed as an intermediate at the flame front, which reacts with the nitrogen in the air to form HCN and further forms NO at high temperatures. The combustion temperature in the stove in this study is 250357 qC, so that it is expected that NO is mainly from the nitrogen in the fuel rather than from the air [22]. The nitrogen content in the DCBF is 0.92% (by mass) (Table 1), which is low and leads to relatively lower NO emission. 3.2.5 SO2 SO2 is produced from the combustion of sulfur element in the biomass material [16], so its emission in fume gas is mainly determined by the content of S in DCBF. Fig. 12 presents the changes of SO2 concentrations in fume gas with time. SO2 contents with DA51 are generally higher than those with ED15 at three dosages, but overall SO2 concentrations are very low in fume gas (Fig. 13) compared to NOx and CO, since the sulphur content is low, at 0.17% in the DCBF (Table 1). The average concentrations of SO2 are 0, 1, 1, 6, 5, and 11 mg·m3 for ED15 at the dosages of 7, 9, and 11 ml, and for DA51 at the dosages of 8, 10, and 12 ml, respectively. All S emissions with ED15 and DA51 are lower than the requirement of less than 50 mg·m3 by Beijing local standard.
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Figure 12 Changes of SO2 concentrationsin fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
Figure 13 Average SO2 concentrations in fume gas 1üED15, 7 ml; 2üED15, 9 ml; 3üED15, 11 ml; 4üDA51, 8 ml; 5üDA51, 10 ml; 6üDA51, 12 ml
3.2.6 Temperature The temperature of fume gas affects the heat energy efficiency of stove. The fume gas with higher temperature will bring more energy out of stove and decrease the energy efficiency. Fig. 14 shows that the temperatures of fume gas for ED15 and DA51 increase with the combustion of agents. The temperature with DA51 is higher than that with ED15, due to the lower kindling temperature of DA51, in which the alcohol is easier to be ignited and burns rapidly, releasing more heat energy [23]. The highest fume gas temperatures are 62 and 88 qC for ED15 and DA51 at the dosage of 9 ml and DA51 at the dosage of 12 ml, respectively, during the ignition process.
Figure14 Changes of temperature in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
3.2.7 Combustion efficiency Combustion efficiency is defined as the ratio of carbon released as CO2 to total carbon [16]. Complete combustion will extract all the energy available in the fuel. However, 100% of combustion efficiency is not
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achievable practically. Common combustion processes may reach efficiencies of 10%95%. Fig. 15 shows the combustion efficiencies of the stove in this study for ED15 and DA51 at three dosages. During the ignition period, the average combustion efficiencies are 84.5%, 85.6%, and 85.4% for ED15 at the dosages of 7, 9, and 11 ml, while they are 84.5%, 84.8%, and 84.6% for DA51 at the dosages of 8, 10, and 12 ml, respectively. Compared to other agents and dosages, ED15 at the dosage of 9 ml achieves satisfactory combustion efficiency but emits less pollutant, and is recommended for practical application.
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Figure15 Changes of combustion efficiency in fume gas with time ƹ ED15, 7 ml;ƵED15, 9 ml; ƷED15, 11 ml; ƺDA51, 8 ml; ƶDA51, 10 ml; ƸDA51, 12 ml
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CONCLUSIONS
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Twenty-five ignition-assisting agents were obtained by mixing waste engine, waste diesel oil, and industrial alcohol at different volume ratios. ED15 and DA51 achieved better ignition results. ED15 with 9 ml dosage and DA51 with 8 ml dosage took 40 and 53 seconds to ignite the DCBF successfully, respectively, which were 3040 times shorter than those without using ignition-assisting agent. ED15 and DA51 showed similar combustion characteristics in terms of O2, CO, CO2, NOx, and SO2 emissions, temperature of fume gas, and combustion efficiency. The average concentrations of CO, CO2, NOx, and SO2 for ED15 and DA51 at all dosages met the requirements by Beijing local standard. Compared to other agent and other dosages, ED15 at the dosage of 9 ml achieved satisfactory combustion efficiency but emitted less pollutant. It will provide a cost-effective and environmentally friendly approach to fast ignite DBBF and break the barrier to the practical application of DBBF.
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