胜利褐煤快速热解特性

为考察热解温度对热解产物品质及挥发分残留的影响,在10 kg/h自制褐煤快速热解提质试验设备上,以胜利褐煤为试验原料,考察了400~900℃热解提质温度对热解产物产率、气体产物组成、半焦微观结构以及残余挥发分的影响。结果表明,随着热解温度的升高,半焦产率逐渐降低,气体产率升高,焦油的产率先升高后降低,700℃时焦油产率最大;热解气体中的CO_2随着热解温度的升高逐渐降低,H_2和CO含量随着热解温度的升高而增加;随着热解温度的升高,挥发分不断释放导致半焦含氧官能团以及高活性的小的缩合芳环减少;热解温度≥700℃,半焦残留的挥发分较低,固定碳较多,基本满足电石用焦的要求。     

温度和停留时间对煤热解挥发分二次反应的影响

在两段固定床反应器中考察了温度和停留时间对煤热解挥发分二次反应产物分布的影响. 结果表明,温度和停留时间对二次反应的影响相互关联. 温度≤600℃、停留时间小于2 s时,挥发分基本不发生气相二次反应. 随温度升高和停留时间延长,挥发分二次反应加剧,焦油产率下降,气体产率和积碳产率增加. 温度低于700℃时,焦油主要转化为气体产物,气相二次反应由二次裂解反应控制;高于700℃时,焦油转化为气体和积碳,气相二次反应由裂解反应和结焦反应共同控制. 提高二次反应温度和延长停留时间,热解气中的H2, CH4和CO产率增加,CO2产率减少,焦油中杂原子化合物及其中的酚、甲酚和二甲酚产率降低,大于3环的重质多环芳烃(PAHs)产率增加,H/C和O/C原子比降低,特别是在900℃时,随停留时间延长,H2和重质PAHs产率快速增加.     

Flash pyrolysis of coals. 1. Devolatilization of a Victorian brown coal in a small fluidized-bed reactor

The devolatilization behaviour of finely-ground (< 0.2 mm) Loy Yang brown coal was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal being fed at rates of 1–3 g/h directly into a bed of sand fluidized by nitrogen. Particle heating rates probably exceeded 10⁴ °C/s. The yields of tar, C₁-C₃ hydrocarbons and total volatile matter are reported for a pyrolyser-temperature range of 435 to 900 °C. A maximum tar yield of 23% w/w (dry ash-free coal), 60% more than the Fischer assay, was obtained at 580 °C. Yields of C₁-C₃ hydrocarbons increased with increasing temperature, reaching 8% at 900 °C. Elemental analyses showed that the composition of the tar and char products was strongly dependent on pyrolysis temperature. The effects on the devolatilization behaviour of the coal produced by the moisture associated with the coal, by hydrogen, and by the replacement of the sand by a fluidized bed of petroleum coke were investigated.     

神木烟煤热解产物分布及主要元素的迁移规律

在石英管固定床反应器中对神木烟煤进行热解实验,研究了热解温度对煤热解产物分布和C, H, O, N, S元素在热解产物中分配的影响. 结果表明,在500?900℃范围内,随热解温度升高,半焦产率下降,气体产率增大,焦油产率先增大后降低,600℃时达最大值9.2%(ω);半焦中C, H, O和N元素迁入量下降,S元素迁入量先降低后略有增大,在700℃时达最小值67.0%;热解气中C, H, O元素迁入量增大,N元素和S元素迁入量先增大后减小,分别在800和600℃时达最大值28.8%和27.9%;焦油中C, H, O元素迁入量先增大后降低,均在600℃时分别达最大值9.3%, 14.0%和7.2%,N元素和S元素迁入量缓慢增加;热解水中H和O元素迁入量先增大后略有降低,在700℃时分别达最大值14.5%和48.5%.     

Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h^?1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic $\text{H}\text{C}$ ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic $\text{H}\text{C}$ ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.     

Flash pyrolysis of coals: behaviour of three coals in a 20 kg h−1 fluidized-bed pyrolyser

Flash pyrolysis of Loy Yang brown coal, and Liddell and Millmerran bituminous coals has been studied using a fluidized-bed reactor with a nominal throughput of 20 kg h^?1. The apparatus and its performance are described. The yields of tar and hydrocarbon gases are reported for each coal in relation to pyrolysis temperature, as also are analytical data on the pyrolysis products. The peak tar yields for the dry, ash-free Loy Yang and Millmerran coals were respectively 23% wt/wt (at ≈ 580 °C) and 35% wt/wt (at $\text{\$}\text{?}$600 °C). The tar yield from Liddell coal was 31% wt/wt at ≈ 580 °C. Hydro-carbon gases were produced in notable quantities during flash pyrolysis; e.g. Millmerran coal at 810 °C gave 6% wt/wt (daf) methane, 0.9% wt/wt ethane, 6% wt/wt ethylene, and 2.5% wt/wt propylene. The atomic $\text{H}\text{C}$ ratios and the absolute levels of hydrogen in product tars and chars decreased steadily with increasing pyrolysis temperature.     

Growth of nanocrystalline diamond films by biased enhanced microwave plasma chemical vapor deposition

Nanocrystalline diamond (NCD) films were grown using biased enhanced growth (BEG) in microwave plasma chemical vapor deposition on mirror polished silicon substrates at temperatures in the range from 400 to 700°C. The films were characterized by Raman spectroscopy, X-ray diffraction (XRD), Auger electron spectroscopy and atomic force microscopy (AFM). Hardness of the films was measured by nano-indentor. Apart from graphitic D and G bands in the films, the Raman spectra exhibit NCD features near 1140 cm⁻¹. The relative intensity of the NCD to graphitic G band in the Raman spectra of the films is negligible in the films grown at 400°C. It increases with temperature and attains a maximum at 600°C following a sharp decrease in the films grown at higher temperatures. XRD results also indicate a maximum concentration of NCD in the film grown at 600°C. Average hardness of the films increases with temperature from ∼5 GPa to ∼40 GPa up to 600°C followed by a decrease (∼24 GPa) in the film grown at 700°C. Substrate temperature seems to play a crucial role in the growth of NCD in BEG processes. An increase in growth temperature may be responsible for evolving bonded hydrogen and increasing mobility of carbon atoms. Both factors help in developing NCD in the films grown at 500 and 600°C with a combination of subplantation mechanism, due to biasing, and a high concentration of H atoms in the gas-phase, typical of CVD diamond process. At 700°C the implanted carbon atoms may be migrating back to the surface resulting in domination of surface processes in the growth, which in turn should result in increase in graphitic content of the films at such a high methane concentration and continuous biasing used in the present study.     

Pyrolysis of brown coals. 2. Decomposition of acidic groups on heating in the range 100–900 °C

The pyrolysis of a Yallourn brown coal in the acid form and several different cation forms has been studied at temperatures up to 900 °C, in regard to the decomposition of acid groups, the relation between oxygen products evolved and these groups, and the fate of cations. The exchange of carboxyl groups changes the amounts of both carbon dioxide and water evolved on pyrolysis, indicating that oxygen-containing groups other than carboxyl are affected by the exchange. The total acid-group content of the acid-form coal heated at different temperatures can be related to the sum of the acid group content of the residual char, and carbon dioxide and carbon monoxide evolved during pyrolysis. The results, in general, confirm the conclusion reached previously in regard to pyrolysis carried out at temperatures up to 300 °C. Pyrolysis in nitrogen at 900 °C releases all oxygen from the acid-form coal. In cation coals the amount of oxygen retained in the char in combination with the cation depends on the type of cation and the extent of reaction with nitrogen in the pyrolysis atmosphere.     

Thermal transformations of polyvinyl alcohol as a source for the preparation of carbon materials

The main volatile products of the pyrolysis of polyvinyl alcohol (PVA)—water, carbon oxides, acetaldehyde, methane, and hydrogen—were determined by gas chromatography with the use of a pyrolytic attachment to a chromatograph (so-called stepwise pyrolysis gas chromatography). The correlations of product ratios over various temperature ranges were found. It was demonstrated that the preliminary thermal oxidation of PVA in air at 200°C, which was responsible for the partial dehydration of PVA and the formation of thermally labile oxygen-containing groups in it, facilitated the occurrence of the subsequent carbonization phase. This manifested itself in much more intense dehydrogenation and methane release from the coke residue of thermally oxidized PVA in the region 700–900°C, when the elimination of oxygen-containing compounds was mainly complete, and in an increase in the yield of coke residue and the C: H ratio in this residue.     

Modeling char surface area during coal pyrolysis: Validation of relationship between pore structure and polymer network

The relationship between pore structure and polymer network during coal pyrolysis was studied by analyzing the evolution of microcrystal, pore structure, and functional groups of char prepared from Naomaohu subbituminous coal by a drop-tube furnace reactor at 600–1000°C. The char specific surface area changes little with aliphatic bridge cleaving at temperatures lower than 700°C; starts to increase at 800°C with the beginning of side chain cleaving; then reaches the maximum with the methyl and methylene content together at 900°C; finally decreases with the further cleaving of aliphatic structures at higher temperatures. Moreover, the lattice stacking height is minimum at 900°C, indicating aliphatic structure can reduce the lattice order degree. These phenomena support the assumption in the CPD-PS model that the side chain cleaving generates open pores and meanwhile reduces the adsorption sites in them, making the char specific surface area first increase and then decrease.     

The CO-catalyzed conversion of H2S to H2 + sulfur part 2. The thermal decomposition of COS

The pyrolysis of COS has been studied over the temperature range 300 to 750°C using a variety of catalysts. The observed product distribution confirmed that two parallel reaction paths: 2 COS → 2 CO S₂ (2) and 2 COS → CO₂ + CS₂ (4) are involved in the decomposition. The decomposition yield increased with rising temperature, accompanied with a shift in selectivity. At temperatures lower than ～700°C the disproportionation reaction 4 was predominant, whereas at temperatures higher than 700°C, reaction 2 was favoured. In the high-temperature region (700 to 750°C) it was possible to achieve full suppression of reaction 4 with added CS₂. The pyrolysis of COS was also studied in a reactor packed with quartz chips without catalysts at high temperatures. Between 800 and 900°C, up to 99% conversion (with respect to the thermodynamic limit) could be achieved, with the almost complete absence of the disproportionation reaction 4. The results point to the commercial potential in the two-step reaction sequence: for the economic conversion of hydrogen sulfide to hydrogen and sulfur.     

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H₂, CO, CO₂, H₂S and hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈ and C₄H₆ with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm³. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H₂S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.     

Mechanism of coal pyrolysis in relation to industrial practice

The validity of our earlier postulates of the mechanism of primary pyrolysis (at and up to 600 °C) is critically examined and it is indicated that the mechanism is strictly followed only under ideal conditions, e.g. in thin beds at rapid rates of carbonization, as in fluidbed and transport reactors. The departure of the Gray-King assay (600 °C) from the ideal path of pyrolysis, e.g. by yielding 20–30% less tar than the yield corresponding to hydroaromatic carbon content, is shown to be due to interaction between the potential tar-forming constituents and the incipient coke-forming substance. This appears to be a function of the thickness of the coal bed, the rate of heating, etc. The greater the thickness, the greater is the degree of interaction and consequent inhibition of tar formation, resulting in a proportionate increase in coke yield. Coke and tar yields are thus partly interconvertible, and the proportions of such interaction have virtually no effect on the proportion of carbon appearing as gas. In industrial high-temperature carbonization, the higher yields of coke and lower yields of tar are due to the same interaction, which occurs to a greater extent primarily because of the greater thickness and/or depth of the coal bed in coke ovens. The fixation of up to 75% of the ‘tar-forming’ carbon (hydroaromatic carbon according to the theory) does not appear to be due to cracking of tar after its formation, but is shown to be foreshadowed well within the primary stage of pyrolysis (below 600 °C), perhaps through condensation-polymerization reactions within the formative coke mass, the mechanism of which is ill-understood at present. The process appears to be very different from the cracking mechanism hitherto believed to explain it. This conclusion is also supported by a study of the distribution of carbon in the gas. Further, such comparative studies between laboratory and industrial conditions do not indicate any significant cracking of methane, hitherto believed to occur in coke ovens. Correspondingly, the reasons for carbon deposition on the exposed hot walls and other regions of coke ovens are discussed and doubt is thrown on the belief that it derives from the cracking of tar and gas.     

Pyrolysis of brown coals. 1. Decomposition of acid groups in coals containing carboxyl groups in the acid and cation forms

The effect of low-temperature pyrolysis (up to 300 °C) on the acid groups of two low-rank coals (a brown coal from Victoria, Australia, and a lignite from Texas, U.S.A.) has been studied for samples in both the acid and cation forms. A preliminary study at temperatures above 300 °C was made on the brown coal. The carboxyl groups of coals in the acid form decompose to give one mole of carbon dioxide for each equivalent of carboxyl content. Cation-form coals yield more carbon dioxide on pyrolysis than can be accounted for by the carboxyl groups present. Water is evolved in proportion to the carbon dioxide evolved from both acid- and cation-form coals, but the ratios differ. Findings have been interpreted as indicating that some other oxygen-containing group is associated with the carboxyl group. In the case of the acid-form coal this group decomposes to give water. When the carboxyl group is in the cation form, decomposition of the associated groups gives carbon dioxide as well as water. Phenolic groups appear to be stable, at least to 300 °C.     

Mathematical modelling of lignin pyrolysis

Seven lignins from different sources were pyrolysed (i) isothermally in vacuum over the temperature range 300–1300 °C and (ii) at a constant heating rate of 30 °C min^?1 and a pressure of 0.1 MPa over the temperature range 150–900 °C. The mass fraction of each product—char, tar and gas species—and the elemental composition of the char and the tar were determined for the flash pyrolysis experiments. The evolution rates of the gas species and the tar versus the dynamic temperature of pyrolysis were determined for the constant heating rate pyrolysis experiments. Although the amount of each product species varied from lignin to lignin, the evolution rates were insensitive to the lignin source and the extraction process. To model the data, modifications were made to a recently developed model of coal pyrolysis. The model proved to be successful in simulating both the data from vacuum flash pyrolysis and constant heating rate pyrolysis of Iotech lignin.     

Value-added products from waste: Slow pyrolysis of used polyethylene-lined paper coffee cup waste

The objectives of this study were to examine how to recycle cup waste efficiently and effectively and to determine if cup waste can be converted into liquid, solid, and gas value-added products by slow pyrolysis. The characteristics and potential utilizations of the pyrolysis products were investigated. The study included the effects of temperature, heating rate, and different feedstocks. The yield of pyrolysis oil derived from cup waste increased from 42% at 400°C to 47% at 600°C, while the yield of char decreased from 26% at 400°C to approximately 20% at 600°C. Acetic acid and levoglucosan were identified as the main components of the pyrolysis oil. The char obtained at 500°C was physically activated at 900°C for 3 h with CO₂. The adsorption capacity of the activated char was investigated with model compounds, such as methyl orange, methylene blue, ibuprofen, and acetaminophen. The results showed that the adsorption capacity of the activated char was similar to that of commercial activated carbon produced from peat. The higher heating value of the produced gas stream calculated at 400°C was 19.59 MJ/Nm³. Also, conventional slow pyrolysis (CSP) and microwave-assisted pyrolysis (MAP) technologies were compared to determine the differences in terms of products yields, composition and characteristics of the pyrolysis oil, and their potential applications. The CSP yields higher liquid products than MAP. Also, the pyrolysis oil obtained from the CSP had significantly more levoglucosan and acetic acid compared to that of the MAP.     

The thermal decomposition of polyurethanes and polyisocyanurates

The thermal decomposition of a number of TDI- and MDI-based biscarbamates (model compounds for polyurethane foams) between 200°C and 1000°C showed that the urethane linkage undergoes an O-acyl fission at about 300°C to generate the free isocyanate and alcohol. In the case of the flexible foam analogues, the newly generated TDI reacts further to generate volatile polyureas, termed ‘yellow smoke’. The MDI residues generated in the decomposition of a rigid foams react to yield non-volatile polycarbodiimides. Both the yellow smokes and the polycarbodiimides decompose above 600°C to give a mixture of nitriles (including HCN) as well as a number of olefinic and aromatic compounds. The use of ¹³C labeling indicated that HCN and all the other nitriles generated during the high temperature decompositions originate in the thermal fission of the aromatic ring, the nitrile carbon being the 2-, 4- or 6- carbon of MDI.     

Alternating electrical conductivity of polyphenylenes and their pyrolysis residues after doping

o,m,p-Polyphenylenes were prepared by oxidation-cationic polymerization of biphenyl and then pyrolyzed up to 800°C. The o,m,p-polyphenylenes as well as their pyrolysis residues were doped with anhydrous FeCl₃ from their solution in acetonitrile. The real part of the alternating electrical conductivity σ′ of the undoped and doped materials was determined at room temperature. Decreasing σ′-values of pyrolyzed residues at 600°C without doping were observed because of the large weight losses during the pyrolysis leading to chain scission reactions within the polymer. At higher pyrolysis temperatures (i.e. 700°C, 800°C) the σ′-values are increased due to the formation of closed aromatic systems in the polymer. The doped materials have higher σ′-values in relation to the corresponding specimens without doping, with the exception of the pyrolysis residues at 800°C. The dependence of doping effect and time was also determined. The transition of the organic polymer to the pyropolymers can be followed and characterized by the measurement of alternating electrical conductivity.     

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca²⁺ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic $\text{H}\text{C}$ ratios of the coals in a manner similar to that observed previously with bituminous coals.