Zhu Yan Yan, Zhang Linhua, Cui Yongzhang, Li Kai, Lv Wenchao,
(1. School of Thermal Energy Engineering, Shandong Jianzhu University, Jinan 250101, China; 2. Key Laboratory of Renewable Energy Construction and Utilization Technology, Ministry of Education, Shandong Jianzhu University, Jinan 250101, Shandong, China; 3. Key Points of Shandong Provincial Building Energy Conservation Technology, Shandong University of Technology Laboratory, Jinan 250101, Shandong, China; 4. School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China)
Abstract: Oxygen-enriched combustion is an important method to solve the problem of low direct combustion temperature of biomass energy.According to TG test, the combustion characteristics of corn, cotton stalk and wood chips were tested respectively. The effects of different oxygen concentrations on TG- DTG curves were used to study the effects of oxygen enrichment conditions on the combustion index of three typical biomass pellets.The results showed that the burnout temperature range of the three biomass pellets was nearly 1000 ℃ lower than that of the air under oxygen enrichment conditions and the maximum volatilization The rate of 2 to 2.75 times the air; oxygen-rich conditions, the fuel combustion index rose rapidly, and the largest increase in the corn stalk, indicating that oxygen-strongest promotion of corn stalk.
0 Preface
Biomass accounts for 14% of the world's primary energy consumption, with clean, renewable and CO 2Nearly zero emissions advantages.China's biomass energy sector wide and rich in resources, annual total amount of biomass resources can be converted into 650 million tons of standard coal.Currently the main direct-fired biomass energy to provide living energy for residents, which The combustion method has the advantages of simple operation, convenient material extraction and low cost, but the utilization efficiency is very low, resulting in serious energy waste and environmental pollution.In addition, the biomass fuel combustion flame temperature is generally not higher than 1000% Can solve the problem of low direct combustion temperature of biomass, which can be widely applied in the field of industrial energy.Oxygen-rich combustion can significantly increase the direct combustion temperature of biomass, and is an important method to solve the problem of low direct combustion temperature of biomass energy.
In recent ten years, oxygen enrichment and combustion have greatly developed both at home and abroad.Many developed countries have devoted a great deal of manpower and material resources to studying oxygen enrichment technology, especially Japan, which used to fuel different kinds of fuels such as gas, oil and coal Occasion of oxygen-rich application test, draw the following conclusions: with 23% oxygen-rich combustion can be energy-saving 10% to 25%, with 25% oxygen-rich combustion can save 20% -40%, with 27% The energy saving is as high as 30% -50%, etc. Rousey analyzed the oxy-fuel combustion characteristics of biomass micron fuel and thought that oxygen enrichment could improve the combustion characteristics of biomass micron fuel, and pointed out that when the oxygen enrichment rate is 40%, the furnace temperature Up to 1600 ℃.
Biomass pellet fuel has high pressure, dense texture, and has a small contact area with air when it is burned, so its ignition and combustion characteristics are very different from biomass micronized fuel. The method of judging the combustion performance of biomass fuels is simple and easy, but it can not display the temperature level, maximum precipitation rate and biomass weight loss status of different biomass fuels, therefore, the heat produced by TA Company of USA The three kinds of typical biomass pellet fuel were tested by heavy analyzer. The TG-DTG curve of three kinds of fuel combustion was used to analyze the volatility analysis characteristic index, combustion stability index and combustion index Biomass pellet raw material selection and large-scale biomass combustion furnace design provide a theoretical basis, in addition to improve China's energy structure, environmental protection, and promote rural economic development also has important practical significance.
1 Biomass particle combustion characteristics discrimination index
1.1 volatile analysis of the characteristic index
Volatile analysis of the characteristic index characterizes the volatility of the combustion process of the precipitation performance is to determine the biomass particulate fuel combustion characteristics of an important indicator.
2 experimental device and method
2.1 experimental device
In this experiment, the Q50 thermogravimetric analyzer produced by TA Company of USA was used.The purifier consisted of purge gas system, thermobalance, furnace body, temperature control and measuring system.Purging gas system In the heating furnace, part of the purge gas After the digital mass flow control, the sample flows horizontally and the other part is the protective gas. After passing through the balance chamber, the gas merges with the horizontal purge gas and flows out from the oven side port. The thermobalance is placed in the balance chamber to provide room temperature to 1000 ° C Excellent measurement accuracy and accuracy within the furnace body is a key component of the thermogravimetric analyzer, the most rapid and accurate way to temperature control in the temperature range of room temperature to 1000 ℃; digital mass flow controller with automatic gas Switching device, not only can effectively improve the stability of the data, but also for fast switching inert gas and oxidizing atmosphere.
2.2 Experimental Methods
In order to analyze the combustion characteristics of biomass pellet fuel under oxygen-rich conditions, Q50 thermogravimetric analyzer was used to test three typical biomass pellets of corn stalks, cotton stalks and wood chips under different conditions.Firstly, At 40% O 2, 21% O2, 14% O2And pyrolysis conditions of about 20mg burning test, heating rate of 20 ℃ / min, carrier gas flow rate of 60mL / min, corn stalks, cotton stalks and sawdust TG-DTG curve; followed by the oxygen concentration and Thermogravimetric experiments were performed under conditions of 14% and 60 mL / min, 21% and 60 mL / min, 40% and 60 mL / min, 21% and 50 mL / min and 21% and 70 mL / min, respectively The analysis of volatilization of three kinds of stalks by oxygen enrichment conditions showed the characteristic index Rh, the discrimination index of combustion stability Rw the influence of combustion characteristic index P1.
3 experimental results and analysis
3.1 oxygen enrichment conditions biomass biomass fuel combustion weight loss characteristics
3.1.1 corn stalk TG-DTG curve
As can be seen from Figure 1, 21% O 2Curve as the base TG and DTG curves can be divided into three stages: the first stage is the precipitation of water, the temperature range of 20 ~ 220 ℃ .The four curves are basically the same, indicating the changes of oxygen concentration of corn stover water precipitation process Little effect; the second stage is volatile combustion stage can be seen from the TG curve, 40% O 2Of the oxygen-rich conditions, the combustion range is shorter, the volatile combustion temperature range of 220 ~ 290 ℃, 21% O 2, 14% O2And the pyrolysis curve is not very different, the temperature range of 220 ~ 330 ° C. From the DTG curve can be seen, the four curves showed the peak rate of volatile analysis 40% O 2Of the oxygen-rich conditions, the maximum rate of precipitation was 23% / min, 21% O. 2, 14% O2And the maximum precipitation rate under pyrolysis conditions were 14% / min, 13% / min and 12% / min respectively. The third stage was a fixed carbon combustion stage. From the TG curve, it can be seen that 40% O 2Under the condition of oxygen enrichment, the burning range of corn is obviously shortened, the burning temperature range is 390-440 ℃, 21% O 2And 14% O 2The curve is not very different, the temperature range of 220 ~ 330 ℃.
Compared with the other three pyrolysis curves, there is no obvious transition between volatile combustion stage and fixed carbon combustion stage, and the fixed carbon combustion interval is longer and the temperature range is 330-900 ° C. As can be seen from the DTG curve, Except for the pyrolysis curve, no peak of rate of weight loss appeared, and the other three peaked at the rate of weight loss. 40% O 2Of the oxygen-rich corn stover under the maximum rate of 11% / min, 21% O. 2The maximum deposition rate is 4% / min, 40% O 2The maximum deposition rate in oxygen-rich condition is 2.75 times of that in air, indicating that oxygen enrichment can shorten the volatilization of wood chips and the fixed carbon burning interval, increase the rate of volatile analysis, and make the combustion performance of corn better.
3.1.2 cotton stalk TG-DTG curve
As can be seen from Fig. 2, the curves of TG and DTG of cotton stalks are basically the same as that of corn stalks, and are divided into three stages: the first stage has a temperature range of 20 to 250 ° C. The four curves of this stage are basically the same, The change of concentration had little effect on cotton stalks.The second stage was the combustion stage of volatilization with the temperature range of 250-300 ° C. It can be seen from the TG curve that 40% O 2Of the oxygen-rich cotton stalks volatile combustion temperature range of 250 ~ 290 ℃, 21% O 2, 14% O2And the pyrolysis curve is not very different, the temperature range of 220-350 ° C. It can be seen from the DTG curve, the four curves also showed the peak of the volatile analysis rate, and the peak of the earliest oxygen-rich conditions. 40% O 2The maximum deposition rate of cotton stalks is 19% / min, which is obviously higher than the other three curves. The third stage is the fixed carbon combustion stage. From the TG curve, it can be seen that 40% O 2Under the condition of oxygen enrichment, cotton burning temperature range is 390 ~ 440 ℃, 21% O 2The combustion interval decreased by 100 ° C. It can be seen from the DTG curve that the peak of the rate of weight loss appeared in all three except for the peak of the rate of weight loss in the pyrolysis curve and the earliest appeared in the peak of oxygen enrichment. 2Of the oxygen-rich corn stover under the maximum rate of 12% / min, 21% O. 2The maximum rate of precipitation was 5% / min, 40% O 2The maximum precipitation rate under oxygen-rich condition is 2.4 times of that in air, which shows that oxygen enrichment can shorten the volatile content of cotton stalk and the fixed carbon combustion range, increase the rate of volatile analysis and improve the combustion performance of cotton stalk.
3.1.3 sawdust TG-DTG curve
As can be seen from Figure 3, the TG and DTG curves of sawdust are more similar to those of cotton stalks, but there is no corn stalks and cotton stalks at the boundaries of volatile and fixed carbon combustion.The first phase is the stage of water analysis and the four curves are basically the same, Indicating that the change of oxygen concentration has no significant effect on the process of water analysis of the sawdust; the second stage is the volatile combustion stage.
As can be seen from the TG curve, 40% O 2Of the oxygen-rich cotton stalks volatile combustion temperature range of 250-310 ℃, 21% O 2Reduced by 30 ° C. As can be seen from the DTG curve, 40% O 2Of the oxygen-rich conditions under the maximum precipitation rate of 23% / min 2, 14% 02 and the maximum rate of precipitation under pyrolysis conditions were 17% / min, 16% / min and 15% / min; the third stage for the fixed carbon combustion phase can be seen from the TG curve, 40% O 2Under the oxygen-rich condition, the burning temperature range of sawdust is 320 ~ 440%, which is 100cc less than the burning range under 21% 02. It can be seen from the DTG curve that 14% O 2And the pyrolysis curve did not show a significant peak of the rate of weight loss, indicating that the anaerobic conditions on the fixed carbon burning stage of the larger obstacles.
40% O2Of the oxygen-rich corn stover under the maximum rate of 12% / min, 21% O. 2The maximum rate of precipitation was 6% / min, 40% O 2Oxygen enrichment under the conditions of the maximum rate of 2 times in the air. Oxygen enrichment can shorten the volatilization of wood chips and carbon fixed combustion zone asked to increase the rate of volatile analysis, the combustion of wood chips better performance.
3.2 oxygen enrichment conditions on the characteristics of biomass pellet fuel
3.2.1 The effect of oxygen enrichment on the characteristics of volatile particles in biomass
The Rh values of three typical biomass pellet fuels are shown in Figure 4 under different carrier flows and oxygen concentrations.
Figure 4 shows that with the change of oxygen content, the volatile organic compounds (APIs) of three typical biomass pellets change greatly, and under the condition of lack of oxygen, the volatility analysis indexes of corn, cotton stalk and sawdust are 7.1 , 7.8 and 7.90 mg / (min · K 2), Indicating that the most volatile wood chips and cotton stalk under hypoxic conditions, the most difficult volatile analysis of corn.When 21% O 2Under the conditions, the characteristic indexes of volatile analysis of corn, cotton stalk and sawdust showed an upward trend, indicating that with the increase of oxygen content, the combustion stability of the three straw was enhanced.
40% O2Under the oxygen-rich condition, the volatility of corn, cotton stalk and sawdust were 16.3, 12.2 and 13.7 mg / (min · K 2), Indicating that under the condition of oxygen enrichment, the combustion stability of the three straw significantly improved.Compared with air, the characteristic index of volatilization of corn under oxygen enrichment increased by 7.6mg / (min · K 2), While corn and sawdust increased by 4.1 and 4.8 mg / (min · K, respectively) 2), Indicating that under the oxygen-rich conditions, the promotion of corn volatilization is strongest.
3.2.2 oxygen enrichment conditions on biomass combustion stability
Under different conditions, the Rw values of the three typical biomass pellet fuels are shown in FIG. 5.
Figure 5 shows that the combustion stability of the three typical biomass pellet fuels varies greatly with the change in oxygen content.The combustion stability indices of maize, cotton stalk and sawdust are respectively 800, 740 in the absence of oxygen And 880, indicating that the combustion of wood chips under the best oxygen stability of the best, slightly corn, cotton stalks worst; when reached 21% O 2Combustion stability index of maize, cotton stalk and sawdust were 900, 960 and 930, respectively, which indicated that with the increase of oxygen content, combustion stability of three kinds of straw was enhanced, and stability index of cotton stalk increased 220, corn and sawdust increased by about 100, indicating that increasing oxygen content under hypoxic conditions has the strongest promoting effect on cotton stalks; and 21% O 2Compared to 40% O 2Enriched condition, the stability index of maize increased by 640 and that of maize and sawdust increased by 260 and 430, respectively, which indicated that the oxygen content increased under oxygen enrichment had the strongest promotion effect on maize, followed by sawdust, cotton stalk was the worst. The combustion stability of the three typical biomass pellets changed parabolically downward with the change of carrier gas flow rate.
3.2.3 Effects of oxygen enrichment conditions on biomass combustion index
Under different conditions, P1 values of the three typical biomass pellets are shown in Fig.6.
The changing tendency of P1 value Rh and Rw and the changing trend of the value are basically the same, indicating that the precipitation of biomass particles is conducive to reduce the ignition temperature of the particles to improve its combustion stability and combustion rate.
Under the condition of anaerobic, the burning index of corn, cotton stalk and sawdust is relatively low, which indicates that the ignition and burnout performance of the three kinds of biomass pellets are poor under hypoxic conditions; 21% O 2Under the conditions, the burning stability index of corn, cotton stalk and sawdust showed an upward trend, in which the cotton stalk stability index increased by 2.2mg 2/ (min · K 2), Corn and sawdust increased by 1.5, 0.9mg 2/ (min · K 2), Indicating that with the oxygen content increased, the combustion stability of the three straw has been enhanced, and to increase the oxygen content of stria to promote the strongest; and 21% O 2Compared to 40% O 2Enriched condition, the corn stability index increased 4.0 mg 2/ (min · K 2), Cotton stalks and sawdust increased by 2.4 and 3.6 mg respectively 2/ (min · K 2) Showed that under the condition of oxygen enrichment, the combustion characteristics of the three kinds of straw significantly improved, and the increase of oxygen content had the strongest promotion effect on the ignition, combustion and burnout characteristics of corn, followed by sawdust, The combustion stability of biomass pellets changes parabolically downward with the change of carrier gas flow rate.
4 Conclusion
(1) TG-DTG curve shows that 40% O 2Under the condition of oxygen enrichment, the combustion period of volatile matter of biomass pellet fuel is shortened by 30 ℃ than that of air and the burning period of fixed carbon is shortened by nearly 100 ℃. The peak of volatile analysis under oxygen-rich condition is 2-2.75 times of that of air, Earlier, the biomass combustion performance has been significantly improved.
(2) With the increase of oxygen content, the volatility analysis of corn, cotton stalk and sawdust analysis of the index, the combustion stability of the discrimination index and the combustion characteristics index showed an upward trend in the 14% to 21% The increase of the three indexes is small. 21% ~ 40% O 2Under the condition of oxygen enrichment, the three indices all show a clear upward trend, which proves that 14% ~ 21% O 2Increasing the oxygen content within the concentration range can improve the biomass combustion performance, but the effect is not obvious; 21% ~ 40% O 2Oxygen-enriched conditions can substantially improve the combustion performance of biomass fuels.
(3)21% O2Under the conditions, the three indexes of corn, cotton stalk and sawdust are not big difference, but 40% 0: Three indexes of corn grain are obviously higher than cotton stalk and sawdust under oxygen enrichment condition, Particulate fuel to promote the role of stronger.
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