杨木快速裂解过程机理研究

将现代化学分析领域中重要的分析手段－裂解气相色谱法应用于对杨木 快速裂解过程机理的研究。通过系统考察裂解温度400－800℃、裂解挥发性产物停留时间0．6－4s。升温速率改变对杨木快速裂解气、液、固产物以及气相组分产率分布的影响,研究杨木快速裂解过程的反应机理,分析获得最大产油率的工艺操作条件。结果表明,杨木裂解过程中主要存在着生成焦油和生成焦炭两个反应的竞争和一个焦油二次裂化的连串反应,裂解温度、挥发性产物停留时间、升温速率决定着哪一种反应占据主要,从而得到安全不同的产物分布。     

Evaporation of pyrolysis oil: Product distribution and residue char analysis

The evaporation of pyrolysis oil was studied at varying heating rates (～1–10⁶°C/min) with surrounding temperatures up to 850°C. A total product distribution (gas, vapor, and char) was measured using two atomizers with different droplet sizes. It was shown that with very high heating rates (～10⁶°C/min) the amount of char was significantly lowered (～8%, carbon basis) compared to the maximum amount, which was produced at low heating rates using a TGA (～30%, carbon basis; heating rate 1°C/min). The char formation takes place in the 100–350°C liquid temperature range due to polymerization reactions of compounds in the pyrolysis oil. All pyrolysis oil fractions (whole oil, pyrolytic lignin, glucose and aqueous rich/lean phase) showed charring behavior. The pyrolysis oil chars age when subjected to elevated temperatures (≥700°C), show similar reactivity toward combustion and steam gasification compared with chars produced during fast pyrolysis of solid biomass. However, the structure is totally different where the pyrolysis oil char is very light and fluffy. To use the produced char in conversion processes (energy or syngas production), it will have to be anchored to a carrier. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Production of H2 and medium Btu gas via pyrolysis of lignins in a fixed-bed reactor

Lignins are generally used as a low-grade fuel in the pulp and paper industry. In this work, pyrolysis of Alcell and Kraft lignins obtained from Alcell process and Westvaco, respectively, was carried out in a fixed-bed reactor to produce hydrogen and gas with medium heating value. The effects of carrier gas (helium) flow rate (13.4–33 ml/min/g of lignin), heating rate (5–15°C/min) and temperature (350–800°C) on the lignin conversion, product composition, and gas yield have been studied. The gaseous products mainly consisted of H₂, CO, CO₂, CH₄ and C₂₊. The carrier gas flow rate did not have any significant effect on the conversion. However, at 800°C and at a constant heating rate of 15°C/min with increase in carrier gas flow rate from 13.4 to 33 ml/min/g of lignin, the volume of product gas decreased from 820 to 736 ml/g for Kraft and from 820 to 762 ml/g for Alcell lignin and the production of hydrogen increased from 43 to 66 mol% for Kraft lignin and from 31 to 46 mol% for Alcell lignin. At a lower carrier gas flow rate of 13.4 ml/min/g of lignin, the gas had a maximum heating value of 437 Btu/scf. At this flow rate and at 800°C, with increase in heating rate from 5 to 15°C/min both lignin conversion and hydrogen production increased from 56 to 65 wt.% and 24 to 31 mol%, respectively, for Alcell lignin. With decrease in temperature from 800°C to 350°C, the conversion of Alcell and Kraft lignins were decreased from 65 to 28 wt.% and from 57 to 25 wt.%, respectively. Also, with decrease in temperature, production of hydrogen was decreased. Maximum heating value of gas (491 Btu/scf) was obtained at 450°C for Alcell lignin.     

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.     

Mathematical modelling of slow pyrolysis of segregated solid wastes in a packed-bed pyrolyser

Waste segregation is being explored as one of the potential effective ways for waste management, where wastes are separated for either recycling or energy recovery. In this paper, three segregated wastes, contaminated waste wood, cardboard and waste textile are pyrolysed in a slow-heating packed-bed reactor for the purpose of solid, liquid and gas recovery. The effect of final temperature was investigated and product yields and compositions were measured. Mathematical modelling was employed to simulate the heat, mass transfer and kinetic processes inside the reactor. Both a parallel reaction model and a function group model were used to predict the product yields as well as their compositions. Char yield of 21–34%, tar 34–46% and gas 23–43% were obtained. It is found that packed-bed pyrolysis produces 30–100% more char compared to standard TGA tests and the local heating rate across the packed-bed reactor differs remarkably from the programmed wall-heating rate and varies greatly in both time and space. Mathematical modelling suggests that wood has higher tar cracking ability than cardboard and textile wastes during pyrolysis, and the effects of mineral contents in the fuel need to be explored. CO₂, CO, tar and water are the main released species during the major stage of the pyrolysis processes which occurs between 250 and 450 °C, whereas noticeable quantity of hydrogen and light hydrocarbons is observed only at higher temperature levels and at the final stage.     

温度梯度与产物流动对先锋褐煤热解产物分布的影响

通过两段固定床反应器分离了煤热解和二次反应过程,模拟了传统外热式固定床反应器和外热式内构件固定床反应器内挥发性热解产物流动与固相反应颗粒间的相互作用,研究了不同温度的半焦对先锋褐煤热解产物分布和品质的影响。结果表明：当半焦的温度在500～900℃时,焦油发生剧烈的二次反应,热解气收率增加,焦油收率大幅下降,H/C同时大量降低且均低于空白样,油品质下降;在100～400℃半焦作用下,焦油发生轻微的二次反应,热解气收率略微增加,焦油收率缓慢下降,但H/C均高于空白样,油品质提升。该结果验证内构件外热式固定床反应器热解产生的焦油具有更高的收率及品质。     

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.     

间热径向流反应器料层厚度对煤热解特性的影响

考察了方形径向流固定床煤热解反应器中变化煤层厚度对料层升温速度及煤热解产物分布特性的影响。随着料层厚度增加,导致煤热解反应要求的时间增长,热解水和气的产率相应增加,焦油和半焦收率逐渐降低,但焦油中轻质组分(沸点低于360℃组分)含量呈升高趋势,半焦和煤气热值稍许降低。如,加热壁温度900℃、从45 mm至105 mm增加煤料层厚度时,焦油产率从7.17%(质量,下同)下降到6.26% (相对干基煤),但焦油中的轻焦油组分含量则从67%升至72.7%,半焦产率由80.0%降至77.0%,热解水和煤气产率分别由6.96%和5.91%增至8.85%和7.90%,煤气热值则由24348.5 kJ·m^-3下降至20649.2 kJ·m^-3。所得半焦的热值径向上由高温侧向低温侧逐渐降低,煤料层越厚、热值降幅越大,而相同煤料层厚度处与加热壁平行的同一轴向平面上的半焦热值基本相同。针对研究的反应器,气相热解产物在反应器内沿径向(横向)由高温料层区向低温料层区流动。在该过程中伴随着热解产物对远离加热壁的低温煤料的传热、热解生成重质组分的冷凝和在煤/半焦颗粒表面的吸附截留,进而在低温料层进一步升高温度时发生二次裂解等物理化学过程。反应器内煤层厚度越大,上述各种伴随的物化作用越显著,从而明显影响煤料层的升温及热解特性。     

Flash pyrolysis of peat in a fluidized bed

It is shown that high yields of oil can be obtained from a good quality peat by fast pyrolysis in an atmospheric pressure fluidized bed reactor. Maximum oil yields were obtained at about 500°C with an apparent vapor residence time of 0.5 seconds or less. At these conditions, on a m.a.f. basis, yields of tar were about 47–50%, gas about 13%, char 28–32% and product water about 12%. The atomic H/C ratios of both char and tar tended to decrease as temperature increased. Oxygen content of the oil decreased also with temperature and was about 24% at optimum conditions.The pyrolysis oil from peat can probably be used successfully as a substitute fuel oil, or possibly converted to higher quality fuels.     

Product distribution and kinetic scheme for the fixed bed thermal decomposition of sewage sludge

In this paper, a new kinetic model for the thermal decomposition of dry sewage sludge was determined. In order to achieve this main objective, various experiments were carried out to collect enough information for the estimation of the different numerical parameters of the model. These experiments include both results from a fixed bed pyrolysis installation and a thermogravimetric analysis device. The experiments allowed for the detailed monitoring of the dynamical evolution of the mass of the sample under investigation, together with the cumulative amounts of tars and permanent gases produced during thermal decomposition of sewage sludge at low heating rates (5–20 °C/min). Solid mass loss during the pyrolysis shows two regions, between 150 °C and 600 °C, where most of the tar is depleted from the solid and non-condensible gases are formed, and a second one between 600 °C and 900 °C where mainly only non-condensible gases are produced. The solid fraction accounted for about 50% of the initial weight, tar around 30% and gases the remaining 20%.Regarding the formation of non-condensible gases from low temperature, a new kinetic scheme was proposed involving an initial decomposition step of the sludge yielding tar and gases as gas phase products and a solid intermediate compound which decomposes at higher temperatures, giving the char fraction and more non-condensible gases. The comparison between the numerical prediction and the experimental results was excellent.     

Pyrolysis of peat: Product yield and characterization

Pyrolysis of peat obtained from Yeniça?a, Bolu, Turkey was conducted in a fixed-bed tube furnace under various conditions, and variations in the structure of the char, tar and gas products were examined. The chars produced were studied by proximate and ultimate analyses. The maximum tar yield of 20.41% was obtained at a heating rate of 20 °C/min, a temperature of 450 °C, a sweeping gas flow rate of 100 ml/min and a 0.5–2.0 mm size range. The chemical composition of the tar was examined by elemental analysis, FTIR spectroscopy, ¹H-NMR spectroscopy and column chromatography. The chemical composition of the tar with dense aliphatic structure was established to be CH_1.22O_0.25N_0.02. The composition of the gases obtained at a heating rate of 20 °C/min for the 0.5–2.0 mm size range was examined by gas chromatography.     

Pyrolysis of subbituminous coal in relation to in-situ coal gasification

Pyrolysis of Roland Seam (Wyodak) subbituminous coal has been investigated from 383 to 1273 K in an inert gas at 0.1 MPa (1 bar). The gas, liquid (condensibles at 0 °C) and solid products were analysed and characterized. Evolution of the major noncondensible gas products was measured quantitatively. By measuring the rate of gas evolution under linear heating conditions the effective activation energy and kinetic frequency factor for release of each gas were determined. These activation energies range from about 80 to 150 kJ/mol. Most of the liquid product was released between 570 and 770 K and was approximately 75% water and 25% organic tar phase. The composition of the organic tar phase was characterized by its elemental composition, boiling-point range, and chromatographic ‘finger-print’. The effect of temperature on the structure of char was determined by analysing changes in elemental composition, surface area, and electrical conductivity.     

Ambient-pressure thermogravimetric characterization of four different coals and their chars

Ambient-pressure thermogravimetric characterization of four different coals and their chars was performed to obtain fundamental information on pyrolysis and coal and char reactivity for these materials. Using a Perkin-Elmer TGS-1 thermobalance, weight loss as a function of temperature was systematically determined for each coal heated in helium at 40 and 160 °C/min under various experimental conditions, and for its derived char heated in air over a temperature range of 20 to 1000 °C. The results indicate that the temperature of maximum rate of devolatilization increases with increasing heating rate for all four coals. However, heating rate does not have a significant effect on the ultimate yield of total volatiles upon heating in helium to 1000 °C; furthermore, coupled with previous data⁹ for identical coal samples, this conclusion extends over a wide range of heating rate from 0.7 to 1.5 × 10⁴ °C/s. Using the temperature of maximum rate of devolatilization as an indication of relative reactivity, the devolatilization reactivity differences among the four coals tested that were suggested by this criterion are not large. For combustion in air, the overall coal/char reactivity sequence as determined by comparison of sample ignition temperature is: N. Dakota lignite coal ≈ Montana lignite coal > North Dakota lignite char > III. No. 6 bituminous coal ≈ Pittsburgh Seam bituminous coal > Montana lignite char > III. No. 6 bituminous char > Pittsburgh Seam bituminous char. The reactivity differences are significantly larger than those for devolatilization. The reactivity results obtained suggest that coal type appears to be the most important determinant of coal and char reactivity in air. The weight loss data were fitted to a distributed-activation-energy model for coal pyrolysis; the kinetic parameters so computed are consistent with the view that coal pyrolysis involves numerous parallel first-order organic decomposition reactions.     

山楂核热解特性及其产物研究

为研究山楂核热解特性及其产物分布规律,在不同升温速率及不同热解终温条件下对山楂核粉末进行热重分析,并用自制小型固定床热解炉对山楂核粉末进行了热解实验,考察了热解终温和升温速率对山楂核热解的三相产物产率的影响,结果表明：热解终温对焦油产率影响不大,对热解气和焦炭产率有显著影响,随着热解终温的提高,焦炭产率降低,而热解气产量增加。同一热解终温条件下,随着升温速率由5℃/min增加到10℃/min,焦油产率增加（热解终温600℃时,增加量约6个百分点）,焦炭和热解气产率降低,并且热解终温越大,升温速率对焦油产率影响越大;同时,提高热解终温和升温速率会使反应速率增大。     

Thermogravimetric characteristics and pyrolysis kinetics of Giheung Respia sewage sludge

Sewage sludge acquired from Giheung Respia treatment facility was characterized and converted into gas, bio-oil and char by pyrolysis. The rate of conversion as a function of temperature was obtained from differential thermogravimetric analysis (DTG) for different heating rates. The activation energy calculated from data selected conversions shows that the activation energy decreased with increasing conversion up to 10%, steadily increased from 10 to 70%, and substantially increased from 70 to 90%. Depending on the level of conversion, the values of activation energies varied between 181 and 659 kJ/mol. The gas product obtained in the experiment at 450 °C, 20 min mainly included CO₂ (30%), CO (23%) and CH₄ (17%). The product yields of gas, oil and char were systematically studied by changing the pyrolysis temperature and residence time.     

MICROWAVE AND CONVENTIONAL PYROLYSIS OF A BITUMINOUS COAL

A high volatile bituminous coal was pyrolyzed by use of microwave energy and by traditional convective heating. In both cases the pyrolysis was conducted under vacuum to facilitate product recovery. The gas and liquid fractions produced on pyrolysis were analyzed by means of gas chromatography.

Processing by microwave energy was not usually successful unless a plasma initiation procedure was employed. This study found the addition of copper wires within the coal mass to be satisfactory for the purpose. Processing by microwave heating resulted in a higher yield of coal tar liquids compared to convective coal heating. The solid char product produced by the microwave process was highly porous and friable, an indication of a suitable feedstock for gasification.     

Fixed-bed pyrolysis of coal under hydrogen pressure at low heating rates

Fixed-bed hydropyrolysis has been investigated by treating 100 g coal up to 900°C and 10 MPa. The devolatilization rate of Beringen coal (32.8 wt% volatile matter) treated on a fixed bed approximates to that obtained by flash hydropyrolysis. However, the oil yield is smaller because of the slower heating of the coal and the rather longer residence time of the primary volatile matter in the reaction space. The product gas is mainly methane. The oil composition depends on the temperature of pyrolysis. The benzene content of the oil rises with temperature. At constant temperature, the influence of hydrogen partial pressure is important between 0–1 MPa. At higher pressure, the yields and compositions vary only slightly with pressure. It has also been shown that from 580°C pyrolysis under hydrogen yields an additional quantity of water, when compared with pyrolysis under inert atmospheres or under atmospheric pressure. This additional water comes from the hydrogenation reactions of the hydroxyl functions of heavy phenols and xylenols. This implies a hydrogen consumption (from 0.2–0.3 wt% of the coal), varying with the pyrolysis temperature.     

A KINETIC MODEL FOR THE PRODUCTION OF LIQUIDS FROM THE FLASH PYROLYSIS OF BIOMASS

A kinetically based prediction model for the production of organic liquids from the flash pyrolysis of biomass is proposed. Wood or other biomass is assumed to be decomposed according to two parallel reactions yielding liquid tar and ( gas + char) The tar is then assumed to further react by secondary homogeneous reactions to form mainly gas as a product

The model provides a very good agreement with the experimental results obtained using a pilot plant fluidized bed pyrolysis reactor

The proposed model is shown to be able to predict the organic liquid yield as a function of the operating parameters of the process, within the optimal conditions for maximizing the tar yields, and the reaction rate constants compare reasonably well with those reported in the literature     

The chemical nature of a supercritical gas extract including comparison with other coal liquids

A supercritical gas extract of an Australian bituminous coal was separated into oil, asphaltene and pre-asphaltene. The oil was further separated by chromatography into three fractions. Average structure data for each fraction are reported based on NMR spectroscopy combined with elemental, molecular weight and functional group analyses. Unsubstituted alkyl chains (> C₈) were found in every fraction of the extract. The presence of n-alkanes, 1-alkenes and phenyl-n-alkanes were shown. The supercritical gas extract was compared with a flash pyrolysis tar and with hydrogenation liquids from the same coal. The supercritical gas extract and the flash pyrolysis tar had a similar distribution between oil, asphaltene and pre-asphaltene, but the oil, asphaltene and pre-asphaltene from the supercritical gas extract were less aromatic and contained fewer heteroatoms than these fractions from the flash pyrolysis tar. The supercritical gas extract has a higher H/C atomic ratio, higher heteroatom content and a higher percentage of carbon in long unsubstituted alkyl chains than hydrogenation liquids produced at 400°C and 450 °C. The oil/asphaltene ratio and the aromaticity of the oil and asphaltene from the supercritical gas extract were intermediate between those obtained for the two hydrogenation liquids.