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1.
Comparative studies on the Hailar lignite pyrolysis/gasification characteristics at N2/CO2 atmosphere and the influence of inherent mineral matters, external ash and pyrolysis temperature on its reactivity during gasification at CO2 atmosphere were conducted by non-isothermal thermogravimetric analysis, FTIR, and X-ray diffraction (XRD) analysis. Thermogravimetric test results show that the atmosphere of N2 or CO2 almost has no effects on the pyrolysis behavior, and the gasification reaction under CO2 atmosphere occurs over 943?K at the heating rate of 40?K?min?1. The external ash prepared at 1173 and 1223?K shows a certain catalytic effect on promoting the gasification reaction, although the inherent mineral matters of Hailar lignite are found in stronger catalytic effects on gasification than the external ash. The lignite gasification reactivity decreases with increasing pyrolytic temperature between 1073 and 1273?K.  相似文献   

2.
稻秆焦炭热解和CO2气化过程中碱金属和碱土金属的迁移   总被引:1,自引:0,他引:1  
研究了稻秆焦炭中碱金属与碱土金属(AAEMs)在N2热解和CO2气化气氛下的迁移过程。通过对不同热处理时间的固相样品分析,得到了两种气氛下AAEMs的迁移规律,并讨论了CO2气化气氛对AAEMs迁移的影响机理。在两种气氛下,K的释放比例都随热处理时间延长先快速增加,然后缓慢增加,而Ca和Mg的释放比例都很低。气化前期K的释放比例高于热解,气化后期K的释放比例与热解几乎相同。热解时,焦炭中酸溶K和Ca的比例先降低然后维持稳定,而酸溶Mg的比例几乎不变。气化时,酸溶K的比例先缓慢降低,然后迅速降低;酸溶Ca和Mg的比例则先增加后迅速降低。气化前期,酸溶AAEMs的比例要高于热解相同时间的焦炭样品;气化后期,酸溶AAEMs的比例则明显低于热解焦炭样品。CO2通过与焦炭有机结构反应,促进了char-K的释放,提高了K的释放比例,也促进了难溶的有机结合的AAEMs分解为酸溶AAEMs;在焦炭气化后期,焦炭中的Si会与AAEMs反应生成难溶硅酸盐。  相似文献   

3.
O2/CO2 coal combustion technology is considered as one of the most promising technologies for CO2 sequestration due to its economical advantages and technical feasibility. It is significant to study the sulfur transfer behavior of coal in O2/CO2 atmosphere for organizing combustion properly and controlling SO2 emission effectively. To clarify the effect of atmosphere on the sulfur transfer behavior, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) system was employed to study the formation behavior of sulfur-containing gas species from Xuzhou bituminous coal pyrolysis in CO2 atmosphere compared with that in N2 atmosphere. Also the SO2 formation behaviors during Xuzhou bituminous coal combustion in O2/N2 and O2/CO2 atmospheres were investigated. Results show that COS is preferentially formed during the coal pyrolysis process in CO2 atmosphere rather than in N2 atmosphere. When temperature is above 1000 K, sulfate in the CO2 atmosphere begins to decompose due to the reduction effect of CO, which comes from the CO2 gasification. During coal combustion process, replacing N2 with CO2 enhances the SO2 releasing rate. SO2 emission increases first and then decreases as O2 fraction increases in the O2/CO2 mixture. XPS result of the ash after combustion indicates that higher O2 concentration elevates the sulfur retention ability of the mineral matter in the coal.  相似文献   

4.
The thermal degradation of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) was investigated by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy (TG–FTIR–MS). Thermogravimetric analysis revealed that the thermal degradation process can be subdivided into three stages: sample drying (<200 °C), main decomposition (200–500 °C), and further cracking (>500 °C) of the polymer. The compound reached almost 800 °C during pyrolysis and combustion. The activation energy at the second step during combustion was slightly higher than that of pyrolysis emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, and hydrogen cyanide, and other gases during combustion and pyrolysis were detected by FTIR and MS spectra. It was observed that the intensities of CO2, CO, HCN, and H2O were very high when compared with their intensities during pyrolysis, and this was attributed to the oxidation of the decomposition product.  相似文献   

5.

Oxyfuel combustion represents one way for cleaner energy production using coal as combustible. The comparison between the oxycombustion and the conventional air combustion process starts with the investigation of the pyrolysis step. The aim of this contribution is to evaluate the impact of N2 (for conventional air combustion) and CO2 (for oxy-fuel combustion) atmospheres during pyrolysis of three different coals. The experiments are conducted in a drop tube furnace over a wide temperature range 800–1400 °C and for residence time ranging between 0.2 and 1.2 s. Coal devolatilized in N2 and CO2 atmospheres at low temperatures (?1200 °C) and longer residence times (>?0.5 s), the char-CO2 reaction is clearly observed, whose intensity depends on the nature of the coal. Furthermore, the volatile yields are simulated using Kobayashi’s scheme and kinetic parameters are predicted for each coal. The char gasification under CO2 is also accounted for by the model.

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6.
Thermo-gravimetric technique was used to study the combustion characteristics of pulverized coal in different O2/CO2 environments. The effects of combustion environment, oxygen concentration, particle size and heating rate were considered and the differences of pulverized coal pyrolysis, combustion and gaseous compounds release under two environments were analyzed. Results show that the coal pyrolysis in CO2 environment can be divided into three stages: moisture release, devolatilization and char gasification by CO2 in higher temperature zone. In the lower temperature zone, the mass loss rate of coal pyrolysis in CO2 environment is lower than that in N2 environment. The burning process of pulverized coal in O2/CO2 environment is delayed compared with that in O2/N2 environment for equivalent oxygen concentrations. With the oxygen concentration increase or the coal particle size decrease, the burning rate of coal increases and burnout time is shortened. As the heating rate increases, coal particles are faster heated in a short period of time and burnt in a higher temperature region, but the increase in heating rate has almost no obvious effect on the combustion mechanism of pulverized coal. During the programmed heating process, species in flue gas including H2O, CO2, CO, CH4, SO2 and NO were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O2/N2 environment, much more CO is produced in O2/CO2 coal combustion process, but the releases of SO2 and NO are less than those released in O2/N2 environment. The present results might have important implications for understanding the intrinsic mechanics of pulverized coal combustion in O2/CO2 environment.  相似文献   

7.
The non-isothermal experiments of limestone decomposition at multi-heating rates in O2/N2 and O2/CO2 atmospheres were studied using thermogravimetry. The limestone decomposition kinetic model function, kinetic parameters of apparent activation energy (E), and pre-exponential factor (A) were evaluated by Bagchi and Malek method. The results shown that in 20 % O2/80 % N2 atmosphere, the limestone decomposed slowly following the contracting sphere volume model controlled by boundary reaction (spherical symmetry) in two stages, and the E increased by about 50 kJ mol?1 in the second decomposition stage. But in 20 % O2/80 % CO2 atmosphere, the presence of high-concentration CO2 significantly inhibited the limestone decomposition, and made the decomposition process occur at high temperature with a rapid rate; the decomposition kinetics was divided into three stages, the first stage was an accelerated decomposition process following the Mampel Power law model with the exponential law equation, the second stage followed the nth order chemical reaction model as an αt deceleration process, and the third stage belonged to the random nucleation and nuclei growth model with the Avrami–Erofeev equation. And with the heating rate increasing, the reaction order n showed a slight rise tendency. The E was about 1,245 kJ mol?1 in 20 % O2/80 % CO2 atmosphere, but was only about 175 kJ mol?1 in 20 % O2/80 % N2 atmosphere. The E and A increased markedly in the O2/CO2 atmosphere.  相似文献   

8.
This study is devoted to investigating the continuous coal pyrolysis in a laboratory fluidized bed reactor that fed coal and discharged char continuously at temperatures of 750–980 °C and in N2-base atmospheres containing O2, H2, CO, CH4 and CO2 at varied contents. The results showed that the designed continuous pyrolysis test provided a clear understanding of the coal pyrolysis behavior in various complex atmospheres free of and with O2. The effect of adding H2, CO, CH4 or CO2 into the atmosphere on the tar yield was related to the O2 content in the atmosphere. Without O2 in the atmosphere, adding H2 and CO2 decreased the pyrolysis tar yield, but the tar yield was conversely higher with raising the CO and CH4 contents in the atmosphere. In O2-containing atmospheres, the influence from varying the atmospheric gas composition on the product distribution and pyrolysis gas composition was closely related to the oxidation or gasification reactions occurring to char, tar and the tested gas.  相似文献   

9.
The thermal degradation of epoxy (DGEBA) and phenol formaldehyde (novolac) resins blend was investigated by using thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy and mass spectroscopy. The results of TGA revealed that the thermal degradation process can be subdivided into four stages: drying the sample, fast and second thermal decomposition, and further cracking process of the polymer. The total mass loss of 89.32 mass% at 950 °C is found during pyrolysis, while the polymer during the combustion almost finished at this temperature. The emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, etc., while aromatic products, are emitted at higher temperature during combustion and pyrolysis. It was observed that the intensities of CO2, CO, H2O, etc., were very high when compared with their intensities during pyrolysis, attributed to the oxidation of decomposition product.  相似文献   

10.
The evolution of gases and volatiles during Sulcis coal pyrolysis under different atmospheres (N2 and H2) was investigated to obtaining a clean feedstock of combustion/gasification for electric power generation. Raw coal samples were slowly heated in temperature programmed mode up to 800 °C at ambient pressure using a laboratory-scale quartz furnace coupled to a Fourier transform infrared spectrometer (FTIR) for evolved gas analysis. Under both pyrolysis and hydropyrolysis conditions the evolution of gases started at temperature as low as 100 °C and was mainly composed by CO and CO2 as gaseous products. With increasing temperature SO2, COS, and light aliphatic gases (CH4 and C2H4) were also released. The release of SO2 took place up to 300 °C regardless of the pyrolysis atmosphere, whilst the COS emissions were affected by the surrounding environment. Carbon oxide, CO2, and CH4 continuously evolved up to 800 °C, showing similar release pathways in both N2 and H2 atmospheres. Trace of HCNO was detected at low pyrolysis temperature solely in pure H2 stream. Finally, the solid residues of pyrolysis (chars) were subjected to reaction with H2 to produce CH4 at 800 °C under 5.0 MPa pressure. The chars reactivity was found to be dependent on pyrolysis atmosphere, being the carbon conversions of 36% and 16% for charN2 and charH2, respectively.  相似文献   

11.
The thermal degradation and corresponding decomposition products of fresh and heat-treated soybean oil were investigated by synchronous thermal analyzer combined with Fourier transform infrared spectrometry and quadrupole mass spectrometry (STA–FTIR–QMS). Two longtime heat-treated soybean oil samples were aforehand prepared by consistently heating the fresh soybean oil for 50 and 100 h, respectively. N2 and simulative air (N2/O2 = 4:1, volume) were used as the thermal reaction gas atmosphere. The results showed that one stage of mass loss appeared in analysis of the all oil samples under N2 atmosphere condition and longtime heat pre-treatment had no effect on the thermal behavior of the soybean oil under N2 atmosphere condition. However, four stages occurred in analysis of both untreated and heat-treated oil samples under the simulative air atmosphere condition. Longtime heat pre-treatment influenced the thermal behavior of the soybean oil in certain extent, which was reflected in the different mass loss values of the four stages. According to the infrared absorption profiles and MS spectra of the released compounds in vapor phase, H2O, CO, CO2, hydrocarbons (such as CH4), and hydroxyl, carbonyl, and carboxyl-contained compounds have been confirmed. Therefore, STA–FTIR–QMS can be suggested as a promising technique for investigating of thermal degradation and monitoring the decomposition products of the evolving substances in edible oils.  相似文献   

12.
Thiourea formaldehyde resin (TFR) has been synthesized by condensation of thiourea and formaldehyde in acidic medium and its thermal degradation has been investigated using TG-FTIR-MS technique during pyrolysis and combustion. The results revealed that the thermal decomposition of TFR occurs in three steps assigned to drying of the sample, fast thermal decomposition of polymers, and further cracking. The similar TG and DTG characteristics were found for the first two stages during pyrolysis and combustion. The combustion process was almost finished at 680?°C, while during pyrolysis a total mass loss of 93 wt% is found at 950?°C. The release of volatile products during pyrolysis are NH3, CS2, CO, HCN, HNCS, and NH2CN. The main products in the second stage are NH3 CO2, CS2, SO2, and H2O during combustion. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as HCN, COS etc., are identified. Among the above volatiles, CO2 is the dominant gaseous product in the whole combustion process. It is found that the thermal degradation during pyrolysis of TFR produced more hazardous gases like HCN, NH3, and CO when compared with combustion in similar conditions.  相似文献   

13.
Pyrolysis volatiles and the environmental impact of printing paper in an air atmosphere were investigated using pyrolysis-gas chromatography/mass spectrometry and scanning electron microscopy. CO2 and light-pollution products were found to be the major products from pyrolysis volatiles; furthermore, because oxygen participates in the chemical reaction, many of the pyrolysis volatiles emitted during the paper printing process were different from those formed under an N2 atmosphere. Although a small number of the volatiles were moderately toxic products, the concentrations of these volatiles were low. Heat-induced inkless eco-printing (HIEP) was found to take less time than the pyrolysis experiment in this paper and thus resulted in fewer pyrolysis volatiles. Thus, fewer pyrolysis volatiles will be emitted within the practical temperature range; in particular, no carcinogens were emitted in the pyrolysis temperature range of 250–700 °C. Therefore, HIEP was found to be an ecologically and environmentally preferable technology.  相似文献   

14.
Gasification of char derived from sewage sludge was studied under different oxidizing atmospheres containing CO2, O2 or H2O. The gasification tests were carried out in thermobalance at different temperatures and oxidizing reagent concentrations. The most efficient were the gaseous mixtures containing oxygen. The reaction took place at temperature 400–500 °C, whilst in the case of CO2 and steam much higher temperatures (700–900 °C) were necessary to complete the conversion. Two rate models for gas–solid reaction were applied to describe the effect of char conversion on reaction rate. The shrinking core model for reaction-controlled regime was found to be the best for predicting the rate of char gasification in CO2 and O2 atmosphere. The experimental data for steam gasification of the char were fitted best by the first-order kinetics. The kinetic parameters estimated from the experimental data are in accordance with the literature for lignocellulosic char gasification and are the first published for sewage sludge char gasification.  相似文献   

15.
利用新开发的微型流化床反应分析仪(micro-fluidized bed reaction analysis, MFBRA) 考察了义马烟煤半焦的原位以及两种非原位半焦气化行为并测定了其动力学参数,其中,原位半焦气化是指煤热解温度和气氛与半焦气化过程一致,非原位半焦1气化是指煤在Ar气氛下热解,热态条件下直接在CO2气氛下气化;非原位半焦2气化是指煤在Ar气氛下热解,冷却收集后再在CO2气氛下气化。研究发现,原位半焦具有最大的比表面积和最小的平均孔径,石墨化程度最弱,且对CO2的化学吸附能力最强,表面活性位点最多。在最小化气体扩散的实验条件下,原位半焦气化反应的反应速率明显比非原位半焦气化反应快,且求取的活化能数据较小。实验揭示了原位半焦和非原位半焦结构和反应性的差异,也证明了MFBRA对原位等温气化反应的适用性。  相似文献   

16.
以化学组成相近的燃烧煤灰、气化煤灰和混合氧化物为添加剂,分别通过干混法和湿混法加入石油焦中,并借助热重分析仪在1200-1400 ℃下进行CO2气化实验,研究高温下煤灰掺混方式、含量及物相组成对石油焦CO2气化的影响,并使用混合氧化物替代实际煤灰研究其对石油焦的高温气化催化作用。结果表明,石油焦气化反应速率随煤灰添加量的增加而提升;气化温度为1200、1300 ℃时,使用干混法和气化煤灰对石油焦的气化促进作用较弱;但气化温度为1400 ℃时,改变煤灰和石油焦的掺混方式及其中活性金属存在方式,对石油焦气化反应几乎没有影响。这是高温下煤灰熔融,导致液态熔体与石油焦表面接触良好、活性金属自由度高以及传质阻力增加共同作用的结果。此时混合氧化物的催化指数与混合物中铁钙含量具有线性关系,即添加高铁钙含量的煤灰可以促进石油焦CO2气化反应。  相似文献   

17.
The thermal behavior and gas product distribution during combustion of straw (wheat straw, corn stalks, and cotton stalks), municipal sewage sludge (MSS), and their blends were investigated by thermogravimetry–mass spectroscopy. The experiments were conducted with various blending ratios and temperatures ranging from 323 to 1,173 K. Addition of MSS decreased the combustion performance of the straw. The reactions between wheat straw and corn stalks with MSS proceeded more easily than that of cotton stalks. Significant interactions were observed between the straw and MSS at the char combustion stage. Gaseous species (CO2, SO2, NH3, HCN, and NO) were mainly produced at temperatures of 523–873 K at which most of the mass loss occurred. Higher MSS proportions in the blends resulted in lower emissions peaks for CO2, NH3, HCN, and NO except for SO2. To ensure combustion performance and mitigate problematic gaseous emissions, the proportion of MSS added to the blends should be <30 mass%.  相似文献   

18.
19.
Carbon dioxide was considered as a co-gasifying agent in a coal gasification reactor. The work presented herein describes the simulation results for the process and the experimental data on coal char gasification with CO2 addition as the rate-controlling step for the entire process. To study the potentially beneficial effect of the introduction of CO2 into the gasification system, several simulations were conducted using the commercial process simulation software ChemCAD 6.3®. The results of a Gibbs equilibrium reactor were evaluated. The Boudouard reaction is a critical path for the development of this process, and the kinetics were studied experimentally. Four chars derived from the pyrolysis of Polish coals of different origins were selected for the experiments. The kinetic characteristics of this system were examined using a custom-designed pressurized fixed-bed reactor. To determine the effect of pressure on the gasification rate, several preliminary studies on the gasification of coal chars were performed isothermally at the temperature of 950 °C and pressures of 1, 10, and 20 bars. In contrast to the thermodynamic calculations, the experimental data revealed that increasing the CO2 pressure leads to a higher reaction rate for medium-rank coal chars and low-rank lignite coal char, resulting in higher efficiency for carbon monoxide production. The pressure influences the reactivity more strongly when varied from 1 to 10 bars; a further increase in pressure affects the rate almost insignificantly. The observed behavior representing the changes in carbon conversion degree during gasification is satisfactorily described by the grain model.  相似文献   

20.
Char and tar derived from pyrolysis of Uruguayan Eucalyptus wood has been evaluated as raw materials for the preparation of high mechanical resistance activated carbon pellets. Thermogravimetric analysis was used as the main technique for studying tar and char pyrolysis in N2 and CO2 atmospheres, and to determine the best conditions for CO2 activation of the carbon pellets. Results indicated that activated carbon pellets with high surface area and good mechanical resistance were obtained by CO2 gasification at 1098 K. Pellets properties can be explained as due to the independent contribution of each component.  相似文献   

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