CFD design and simulation of ethylene dichloride (EDC) thermal cracking reactor

At high temperature, ethylene dichloride decomposes into vinyl chloride monomer and HCl by a complex reaction mechanism. Due to chemical reaction type and heat transfer mechanism, design and simulation of cracking reactors are complicated. This process is very important from either chemical reaction or transport phenomena’s point of view. In this study, 2D simulation of cracking reactor is performed with FLUENT software. Simulation results were compared with the experimental data. Then, we investigate the simulation results and effect of various parameters on the process. Results show that with process progress and temperature increase during reactor length, conversion and coke formation amount are increased. At the end of the process, conversion is 52.69 that has good agreement with industrial data. Addition of promoter to the process fluid and fluid behavior in different coil outlet temperatures was studied; finally, the effects of these factors are described in detail.     

Semi-quantitative and multivariate analysis of the thermal degradation of carbon-oxygen double bonds in biomass

The aim of this paper was to investigate biomass pyrolysis using diffuse reflectance infrared Fourier transform (DRIFT) studies. The pyrolysis tests were conducted in a nitrogen atmosphere from room temperature (RT) to 600 °C. Infrared techniques provide fast, low-cost and non-destructive analysis. A combination of qualitative and quantitative analysis was applied. Pyrolysis was conducted in an environmental chamber which enabled in-situ spectral measurement. The mass of samples used in DRIFT tests was 3.0 ± 0.1 mg. A semi-quantitative analysis of the oxidation stage was performed for each biomass sample. For a variety of biomass samples, pyrolysis in the temperature range of 250–350° lead to an increase in carbon-carbon double bonds which were formed from cellulose decomposition. The research results showed that the wavenumber assigned to the CO band in carboxylic acids and esters (1742 cm^?1) depends on the temperature and varies with different biomass samples. Also, the intensity of the CO band for ketones and aldehydes (1665 cm^?1) varies with the type of biomass and the pyrolysis temperature. Principal component analysis (PCA) gave information about the similarity of reactions occurring during the pyrolysis of various biomass samples. Efficient conversion of biomass resources to energy requires accurate and detailed knowledge of chemical behaviour during degradation.     

Development of an experimental technique for oil recovery during biomass pyrolysis

A new system to collect and analyse some of the condensable products of biomass pyrolysis is developed and tested. Pyrolysis of olive stone, oak pellet, pine pellet and major components of biomass (cellulose, hemicellulose and lignin) is performed by means of a thermogravimetric analysis (TGA). Some of the pyrolysis oil generated during the pyrolysis process condenses on an aluminium ring located in the gas exhaust of the device. The validity and repeatability of the method were shown when a similar oil mass was collected when the test conditions were repeated with the same material. In the biomass experiments, a larger amount of oil was collected from pellet samples, which have the highest cellulose content. This is consistent with the pure component experiments, as avicel cellulose shows the highest depositions. The depositions of the pure components show greater percentage of oil deposited than those of the biomass samples. The results reveal the important influence that the compositions of the biomass and the interactions among its major components have on the composition and quantity in the final deposit. Finally, the differences between deposits from biomass and deposits from mixed components were revealed by an FTIR analysis of the liquid products.     

Study on solid waste pyrolysis coke catalyst for catalytic cracking of coal tar

Low value solid waste pyrolysis coke was used as a catalyst to catalytically crack gas-phase tar to improve tar yield and gas production. Pyrolysis coke with different pyrolysis final temperature and pyrolysis time were prepared, the effect of tar cracking products was studied, and the optimal pyrolysis coke were screened. The pyrolysis coke catalyst was characterized by BET, FTIR, SEM. The results show that the optimal preparation final temperature of pyrolysis coke is 750 °C, and the optimal preparation pyrolysis time is 2 h. Compared with the pyrolysis of raw coal, the tar cracking rate increased by 9.3%, after added the pyrolysis coke catalyst, the gas increased by 23.2%, and the light component increased to 36.6%. And the OH, C–N and C–O–C functional groups present on coke are the factors that affect the catalytic cracking.     

Reduction of primary tar vapor from biomass by hot char particles in fixed bed gasification

This study investigated the reduction of primary tar vapor from biomass pyrolysis over a bed of hot char particles, focusing on the effect of different operating conditions and char properties. The char samples were prepared from wood, paddy straw, palm kernel shell, and activated carbon. The primary tar was produced from fir wood by pyrolysis at 500 °C and passed through a reactor filled with char particles with different lengths and temperatures.The tar cracking reactions became active above 700 °C, and the presence of hot char particles promoted more tar reduction compared with thermal cracking alone. The mass yield of the primary tar was reduced from 24.8% by pyrolysis to 13.7% by thermal cracking at 800 °C, and further to 7.7% by hot char particles in a reactor volume of 1.48 cm³/g_wood. In terms of carbon yield, these values correspond to 32.1%, 19.9% and 11.8%, respectively. The tar with smaller molecular weights was quickly decomposed to gases, whereas the heavy tar was resistant to cracking, even when the reactor volume was increased to 6.90 cm³/g_wood. The tar cracking behaviors were similar for four char types despite differences in microscopic surface areas, pore-size distributions, and inorganic contents. The results suggest that creating a tar-cracking zone using char particles situated between the pyrolysis and gasification zones could be helpful in converting the primary tar vapor in a downdraft fixed-bed gasifier, but the degree of conversion is not high enough to eliminate tar issues completely.     

Experimental investigation on the cracking of pre-combustion cracking gas with gliding arc discharge plasma

To improve the quality of pre-combustion cracking gas, the gliding arc discharge plasma is adopted in this paper. The influence of incoming flow rate, electrode gap distance and discharge frequency on cracking effect have been experimentally studied. The results show that through plasma cracking, the concentration of H₂ increases while the concentration of CH₄ and C₂H₄ decrease. With different fuel ratio conditions, the variation trend of C/H ratio as well as the mass flow of carbon and hydrogen atoms in the cracking products vary from each other. The cracking effect becomes weaker with the increase of incoming flow rate, while is better when the fuel ratio is larger. Given the flow rate of 18slpm and 24slpm, the best cracking effect can be acquired with the electrode gap of 1.5 mm. Besides, the effect of gliding arc discharge plasma cracking is weakened as the discharge frequency rises.     

基于快速冷却取样方法的正癸烷热裂解研究

根据碳氢燃料热裂解反应的特性,通过将冷却燃料直接与高温裂解产物混合的方法建立了一种碳氢燃料高温裂解的快速冷却取样实验方法。基于该方法,详细研究了正癸烷在超临界压力下的热裂解反应。通过对产物组成和分布的分析,得到了正癸烷热裂解的基本规律。结果表明,对于正癸烷的裂解产物,其选择性随转化率的提高基本保持不变,符合等比例产物分布模型。同时,使用Chemkin Pro软件对实验进行了模拟从而验证了该实验方法的可靠性。     

A new technology for the combined production of charcoal and electricity through cogeneration

This paper presents an historical approach on the development of the existing biomass carbonization technologies in industrial operation in Brazil, the biggest charcoal producing country in the world. The gravimetric yield of charcoal from wood does not usually surpass 25%; the time of each operation cycle is more than seven days; and less than 50% of the energy contained in the feedstock is transformed into charcoal – the rest is discharged into the environment. The electricity generation associated with charcoal production is nowadays inexistent in Brazil. This paper presents the development of an industrial technology of semi-continuous pyrolysis process, characterized by using metallic kilns with forced exhaust system: the Rima Container Kiln (RCK). The results of the test runs are related to 5 m³ and 40 m³ kilns, with a thermal power of 200 kW (pilot scale: 5 m³) and 3000 kW (industrial scale: 40 m³). The low heating value of the pyrolysis gases is 670 and 1470 kJ/m³, respectively.The main results are: a 3 h carbonization time; an average productivity per kiln of 1 ton of charcoal per hour; and a gravimetric yield of 35%. In this paper, four scenarios for the conversion of exhaust gases and tar into electricity were evaluated: the Conventional Rankine Cycle (CRC) and the Organic Rankine Cycle (ORC), each one with and without forest residues utilization. It is shown that the best economic indicators correspond to the scenario where ORC technology is used. The electricity generation cost is around U$30/MWhe for ORC and US$40/MWhe for CRC.     

Experimental analysis of direct thermal methane cracking

The analysis of the viability of Hydrogen production without CO₂ emissions is one of the most challenging activities that have been initiated for a sustainable energy supply. As one of the tracks to fulfil such objective, direct methane cracking has been analysed experimentally to assess the scientific viability and reaction characterization in a broad temperature range, from 875 to 1700 °C. The effect of temperature, sweeping/carrier gas fraction proposed in some concepts, methane flow rate, residence time, and tube material and porosity has been analysed. The aggregation of carbon black particles to the reaction tube is the main technological show-stopper that has been identified.     

Preparation of NiO / PC catalyst with plasma for cracking tar to produce flammable gas

To increase the use of lignite, the tar was pyrolyzed with pyrolysis coke (PC) to produce more combustible gases such as H₂, CH₄, and CO. NiO/PC catalyst with plasma was prepared, and the influence of PC and NiO/PC catalyst on flammable gas was investigated in a two-stage fixed reactor. The catalysts were characterized by SEM, BET, XPS and XRD to analyze the tar cracking mechanism. The results were: (1) PC was prepared at different heating rates, and when the heating rate reached 20 °C/min, the amount of flammable gas was 5.4 L. (2) NiO/PC catalyst was modified with plasma in three background gases withO₂ being the best, mainly because of the increase of the oxygen functional groups. (3) PC was modified and calcined with plasma, and when the power reached 40 W, it produced the most combustible gas, and the volume could grow by 94.4%.     

Fixed-bed pyrolysis of safflower seed: influence of pyrolysis parameters on product yields and compositions

Fixed-bed slow pyrolysis experiments have been conducted on a sample of safflower seed to determine particularly the effects of pyrolysis temperature, heating rate, particle size and sweep gas flow rate on the pyrolysis product yields and their chemical compositions. The maximum oil yield of 44% was obtained at the final pyrolysis temperature of 500°C, particle size range of +0.425–1.25 mm, with heating rate of 5°C min⁻¹ and sweep gas (N₂) flow rate of 100 cm³ min⁻¹ in a fixed-bed lab-scale reactor. Chromatographic and spectroscopic studies on the pyrolytic oil showed that the oil obtained from safflower seed can be used as a renewable fuel and chemical feedstock with a calorific value of 41.0 MJ/kg and empirical formula of CH_1.92O_0.11N_0.02.     

隔热材料导热系数的数值模拟预测

对氧化锆空心球隔热材料进行合理的简化,用数值模拟方法计算氧化锆空心球隔热材料导热系数,并分析空心球半径、温度、发射率等对导热系数的影响。数值模拟结果表明,减小空心球半径,降低空心球表面发射率,抽真空等都有助于降低隔热材料导热系数。数值模拟与实验测量结果良好吻合,用数值模拟计算隔热材料导热系数是一个行之有效的方法。     

煤气化过程中焦油裂解的试验研究

煤在热解和气化过程中产生的焦油，影响系统的正常运行。焦油脱除方法可分为气化炉内(初次脱除)和气化炉外(二次脱除)两类。尽管二次脱除法非常有效，但由于气化炉内初次脱除可以大大减少出口煤气中焦油含量，减轻甚至消除后期处理焦油的压力，故气化炉内脱除法得到重视。采用石灰石为催化剂，在1MW热态试验台上进行了试验，研究焦油和煤气成分在空气气化时添加不同石灰石含量工况下的变化情况，结果表明，石灰石的加入降低了焦油产率，提高了煤气产率，改善了煤气质量。     

秸秆气化炉的研究与探讨

分析了当前的能源现状和形势，阐述了我国发展生物质能的必要性及其重要的现实意义，并对气化特性、热裂解的应用技术进行了总结，发展秸秆气化炉是适应我国可持续发展目标的需要。     

Numerical simulation of a tubular solar reactor for methane cracking

This study addresses the solar thermal cracking of methane for the co-production of hydrogen and carbon black as a medium to avoid CO₂ emissions from natural gas combustion processes. The objective of this work is to numerically simulate the transport processes of momentum heat and mass in an indirect heating solar reactor, which is fed with an argon-methane mixture. The reactor is composed of a cubic cavity receiver, which absorbs concentrated solar irradiation through a quartz window and a graphite reaction tube is settled vertically inside this cavity. A series of numerical experiments were carried out in order to gain a better understanding of the interaction between the several transport phenomena taking place. The simulations showed that, in general, when the temperature of the reaction chamber is higher than 2000 K, the methane conversion is practically 100%. To validate our simulation results we compared them with available experimental data obtaining good agreement. Moreover, our results clearly evidence that most of the reaction takes place at the bottom of the reactor, which is the zone with the highest temperature profiles. Therefore, we propose modifications in the reactor design to increase conversion. The results of this work can thus serve to improve design and control of solar reactors for light hydrocarbons.     

Numerical simulation of emulsified fuel spray combustion with puffing and micro-explosion

The purpose of this study was to develop numerical simulation of spray combustion of emulsified fuel with considering puffing and micro-explosion. First, a mathematical model for puffing was proposed. In the proposed puffing model, the rate of mass change of a droplet during puffing was expressed by the evaporation rate of dispersed water and the mass change rate due to fine droplets spouted from the droplet surface. The mass change rate due to fine droplets was related to the evaporation rate of the dispersed water and each liquid content. This model had only one experimental parameter. The essential feature of this model was that it was simple to apply to numerical simulation of spray combustion. First, the validity of the proposed puffing model was investigated with the experimental results for a single droplet. The calculated results for a single droplet with the experimental parameter varying from 5.0 to 10 were in good agreement with the experimental results. Moreover, numerical simulation of spray combustion of emulsified fuel was carried out. The occurrence of puffing and micro-explosion was determined by the inner droplet temperature. When micro-explosion occurred, a droplet changed to vapor rapidly. When the proposed puffing model was used in numerical simulation of spray combustion, the experimental parameter in the puffing model was determined for each droplet by random numbers within the range 5.0-10. The calculated results of spray combustion of emulsified fuel without considering puffing or micro-explosions were different from the experimental results even where combustion reactions were almost terminated. Meanwhile, the calculated results when considering puffing and micro-explosions were in good agreement with experimental results at the same location.     

Enhanced activity of NiZrBEA catalyst for upgrading of biomass pyrolysis vapors to H2-rich gas

The main objective of these studies was development of competitive catalyst for the upgrading of biomass pyrolysis vapors to H₂-rich gas. The performed experiments were devoted to determination of the effect of incorporation of zirconium into the structure of BEA zeolite on the performance of NiBEA in the mentioned process. Moreover, the most important parameters responsible for the increased activity of NiZrBEA catalyst in comparison to nickel supported on parent zeolite have been identified. The activity of synthesized catalysts was tested in two step fixed bed quartz reactor. Firstly, cellulose or pine were heated to the 500 °C in order to decompose lignocellulosic feedstock. Then, formed pyrolysis vapors were directed through catalyst bed (700 °C) where their upgrading took place. The obtained results revealed that an introduction of zirconium in the structure of BEA zeolite allowed for the increase in the efficiency of Ni catalyst in the formation of H₂-rich gas. It was related to the increase in pore volume of the synthesized materials, formation of smaller nickel oxide crystallites and creation of the catalysts with moderate acidity.     

Characterization of the physicochemical and structural evolution of biomass particles during combined pyrolysis and CO2 gasification

The combination of pyrolysis and CO₂ gasification was studied to synergistically improve the syngas yield and biochar quality. The subsequent 60-min CO₂ gasification at 800 °C after pyrolysis increased the syngas yield from 23.4% to 40.7% while decreasing the yields of biochar and bio-oil from 27.3% to 17.1% and from 49.3% to 42.2%, respectively. The BET area of the biochar obtained by the subsequent 60-min CO₂ gasification at 800 °C was 384.5 m²/g, compared to 6.8 m²/g for the biochar obtained by the 60-min pyrolysis at 800 °C, and 1.4 m²/g for the raw biomass. The biochar obtained above 500 °C was virtually amorphous.     

Effect of cellulose and lignin content on pyrolysis and combustion characteristics for several types of biomass

Fundamental pyrolysis and combustion behaviors for several types of biomass are tested by a thermo-gravimetric analyzer. The main compositions of cellulose and lignin contents for several types of biomass are analyzed chemically. Based on the main composition results obtained, the experimental results for the actual biomass samples are compared with those for the simulated biomass, which is made of the mixture of the cellulose with lignin chemical. The morphological changes before and after the reactions are also observed by a scanning electron microscope. The main compositions in the biomass consisted of cellulose and lignin. The cellulose content was more than lignin for the biomass samples selected in this study. The reaction for the actual biomass samples proceeded with the two stages. The first and second stage corresponded to devolatilization and char combustion during combustion, respectively. The first stage showed rapid mass decrease caused by cellulose decomposition. At the second stage, lignin decomposed for pyrolysis and its char burned for combustion. For the biomass with higher cellulose content, the pyrolysis rate became faster. While, the biomass with higher lignin content gave slower pyrolysis rate. The cellulose and lignin content in the biomasses was one of the important parameters to evaluate the pyrolysis characteristics. The combustion characteristics for the actual biomass depends on the char morphology produced.     

Effect of heating rate on the pyrolysis yields of rapeseed

The pyrolysis yields of rapeseed were investigated applying thermogravimetric analysis technique. The pyrolysis experiments were performed up to 1273 K at heating rates of 5, 10, 20, 30, 40 and 50 K/min in a dynamic nitrogen flow of 40 cc/min. Effects of heating rate on the mass losses from the rapeseed were examined using the derivative thermogravimetric analysis profiles. This study showed that important differences on the pyrolytic behavior of rapeseed are observed when heating rate is changed. At the lower heating rates, the maximum rates of mass losses were relatively low. When the heating rate was increased, maximum rates of mass losses also increased. These variations were interpreted by the heterogeneous structure of biomass. Heating rates also concluded to affect the shape of the peaks. Increase in the heating rate shifted the main peak on the DTG profile to the lower temperatures. At low heating rates, there is probably resistance to mass or heat transfer inside the biomass particles. However, increase in heating rate overcame these restrictions, and led to higher conversion rates. The final pyrolysis temperatures were also affected from the variation of the heating rate. Activation energy values were first increased and then decreased depending on the heating rates.