High energy syngas production by waste tyres steam gasification in a rotary kiln pilot plant. Experimental and numerical investigations

This paper presents experimental and numerical results on steam gasification of waste tyres in a rotary kiln pilot plant. Both the process performance and the gas features have been evaluated varying the feeding ratio (FR), defined as the steam/tyres mass ratio. First, several experimental tests have been performed. Then, the obtained experimental results have been used to verify the consistency of a numerical model developed with the aid of the commercial code ChemCAD®. Once done, the effect of increasing the FR on the gas energy content has been evaluated.Numerical results showed that the gas energy content increases as the FR increases as well, achieving a maximum value for FR = 0.33 that produced a gas which composition N₂ free is (H₂ = 52.7%_vol, CO = 18.1%_vol, CO₂ = 7.0%_vol, CH₄ = 22.2%_vol) in correspondence of which the lower heating value (LHV) is equal to 29.5 MJ kg_gas⁻¹. Higher FR values do not produce a further increase of the gas energy content, rather require a greater amount of input energy for heating the steam from the atmospheric to the process temperature.     

Flaming pyrolysis model of the fixed bed cross draft long-stick wood gasifier

The future industrial development of biomass energy depends on the application of renewable energy technology in an efficient manner. Of all the competing technologies under biomass, gasifiers are considered to be one of most viable applications. The use of biomass fuel, especially biomass wastes, for distributed power production can be economically viable in many parts of the world through gasification of biomass. Since biomass, is a clean and renewable fuel, gasification gives the opportunity to convert biomass into clean fuel gas or synthesis gas for industrial uses. The preparation of feedstock for a gasifier requires time, energy and labour and this has been a setback for gasifier technology development. The present work is focused on gasification of long-stick wood as a feed material for gasifiers. This application makes reduction not only in the cost but also on the power consumption of feed material preparation. A 50 m³/h capacity gasifier was fabricated in the cross draft mode. The cross draft mode makes it possible to produce low tar content in producer gas. This cross draft mode operates with 180 W of blower supply for air to produce 10 kW of thermal output. The initial bed heights of the long-stick wood and charcoal are 58 cm and 48 cm respectively. Results were obtained for various flow conditions with air flow rates ranging from 20 to 30 m³/h. For modelling, the flaming pyrolysis time for long-stick wood in the gasifier is calculated to be 1.6 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 34 cm and 30 cm respectively. The rate of feed was between 9 and 10 kg/h. Continuous operation for 5 h was used for three runs to study the performance. In this study we measured the temperature and pressure in the different zones as a function of airflow. We measured the gas flow and efficiency of the gasifier in order to determine its commercial potential for process and power industries.     

Catalytic pyrolysis of biomass for biofuels production

Fast pyrolysis bio-oils currently produced in demonstration and semi-commercial plants have potential as a fuel for stationary power production using boilers or turbines but they require significant modification to become an acceptable transportation fuel. Catalytic upgrading of pyrolysis vapors using zeolites is a potentially promising method for removing oxygen from organic compounds and converting them to hydrocarbons. This work evaluated a set of commercial and laboratory-synthesized catalysts for their hydrocarbon production performance via the pyrolysis/catalytic cracking route. Three types of biomass feedstocks; cellulose, lignin, and wood were pyrolyzed (batch experiments) in quartz boats in physical contact with the catalysts at temperature ranging from 400 °C to 600 °C and catalyst-to-biomass ratios of 5-10 by weight. Molecular-beam mass spectrometry (MBMS) was used to analyze the product vapor and gas composition. The highest yield of hydrocarbons (approximately 16 wt.%, including 3.5 wt.% of toluene) was achieved using nickel, cobalt, iron, and gallium-substituted ZSM-5. Tests performed using a semi-continuous flow reactor allowed us to observe the change in the composition of the volatiles produced by the pyrolysis/catalytic vapor cracking reactions as a function of the catalyst time-on-stream. The deoxygenation activity decreased with time because of coke deposits formed on the catalyst.     

Gas evolution kinetics of two coal samples during rapid pyrolysis

Quantitative gas evolution kinetics of coal primary pyrolysis at high heating rates is critical for developing predictive coal pyrolysis models. This study aims to investigate the gaseous species evolution kinetics of a low rank coal and a subbituminous coal during pyrolysis at a heating rate of 1000 °C s^− 1 and pressures up to 50 bar using a wire mesh reactor. The main gaseous species, including H₂, CO, CO₂, and light hydrocarbons CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, were quantified using high sensitivity gas chromatography. It was found that the yields of gaseous species increased with increasing pyrolysis temperature up to 1100 °C. The low rank coal generated more CO and CO₂ than the subbituminous coal under similar pyrolysis conditions. Pyrolysis of the low rank coal at 50 bar produced more gas than at atmospheric pressure, especially CO₂, indicating that the tar precursor had undergone thermal cracking during pyrolysis at the elevated pressure.     

Biomass gasification using capacitively coupled RF plasma technology

A laboratory-scale capacitively coupled radio frequency (RF) plasma pyrolysis reactor working in reduced pressure has been developed. Experiments have been performed to examine the characteristics of this RF plasma reactor and the products of biomass gasification. It was found that the electrode geometry, input power and reactor pressure were the key parameters affecting the plasma characteristics such as plasma length, temperature, and energy transfer efficiency. Biomass gasification using input power 1600-2000 W and reactor pressure 3000-8000 Pa produced a combustible gas consisted of H₂, CO, CH₄, CO₂ and light hydrocarbons as well as a pyrolytic char. On average, the gas yield can reach 66 wt% of the biomass feed. An energy balance analysis on the RF plasma pyrolysis system was also given.     

Continuous thermal degradation of pyrolytic oil in a bench scale CSTR reaction system

Continuous thermal degradation of two pyrolytic oils with low (LPO) and high boiling point distribution (HPO) was conducted in a constant stirrer tank reactor (CSTR) with bench scale. Raw pyrolytic oil as a reactant was obtained from the commercial rotary kiln pyrolysis plant for municipal plastic waste. The degradation experiment was conducted by temperature programming with 10 °C/min of heating rate up to 450 °C and then maintained with long lapse time at 450 °C. Liquid product was sampled at initial reaction time with different degradation temperatures up to 450 °C and then constant interval lapse time at 450 °C. The product characteristics over two pyrolytic oils were compared by using a continuous reaction system. As a reactant, heavy pyrolytic oil (HPO) showed higher boiling point distribution than that of diesel and also light pyrolytic oil (LPO) was mainly consisting of a mixture of gasoline and kerosene range components. In the continuous reaction, LPO showed higher yield of liquid product and lower residue than those of HPO. The characteristics of liquid products were influenced by the type of raw pyrolytic oil. Also, the result obtained under degradation temperature programming was described.     

Is it possible to predict gas yields of any biomass after rapid pyrolysis at high temperature from its composition in cellulose, hemicellulose and lignin?

Ligno-cellulosic biomass from different sources presents very variable compositions. Consequently, there is a wide variation in the nature and quantities of gaseous products obtained after thermal treatment of biomasses.The objective of this work is to establish a link between the composition of a biomass and its pyrolysis gas yields and composition. Experimental flash pyrolysis of several biomasses at a temperature of 950 °C and a gas residence time of about 2 s was carried out. An attempt was then made to predict gas yields of any biomass according to its composition. We show that an additivity law does not allow the gas yields of a biomass to be correlated with its fractions of cellulose, hemicellulose and lignin. Several potential explanations are then offered and quantitatively demonstrated: it is shown that interactions occur between compounds and that mineral matter influences the pyrolysis process.     

Biomass pyrolysis experiments in an analytical entrained flow reactor between 1073 K and 1273 K

Experiments are performed in an entrained flow reactor to better understand the kinetic processes involved in biomass pyrolysis under high temperatures (1073-1273 K) and fast heating condition (>500 K s⁻¹). The influence of the particle size (0.4 and 1.1 mm), of the temperature (1073-1273 K), of the presence of steam in the gas atmosphere (0 and 20 vol%) and of the residence time (between 0.7 and 3.5 s for gas) on conversion and selectivity is studied. Under these conditions, the particle size is the most crucial parameter that influences decomposition. For 1.1 mm particles, pyrolysis requires more than 0.5 s and heat transfer processes are limiting. For 0.4 mm particles, pyrolysis seems to be finished before 0.5 s. More than 70 wt% of gas is produced. Forty percent of the initial carbon is found in CO; less than 5% is found in CO₂. The hydrogen content is almost equally distributed among H₂, H₂O and light hydrocarbons (CH₄, C₂H₂, C₂H₄). Under these conditions, the evolution of the produced gas mixture is not very significant during the first few seconds, even if there seems to be some reactions between H₂, the C₂ and tars.     

Biofuels from waste fish oil pyrolysis: Continuous production in a pilot plant

Fast pyrolysis of waste fish oil was performed in a continuous pyrolysis pilot plant. The experiment was carried out under steady-state conditions in which 10 kg of biomass was added at a feed rate of 3.2 kg h⁻¹. A bio-oil yield of 72-73% was obtained with a controlled reaction temperature of 525 °C. The bio-oil was distilled to obtain purified products with boiling ranges corresponding to light bio-oil and heavy bio-oil. These biofuels were characterized according to their physico-chemical properties, and compared with the Brazilian-fuel specifications for conventional gasoline and diesel fuels. The results show that the fast pyrolysis process represents an alternative technique for the production of biofuels from waste fish oil with characteristics similar to petroleum fuels.     

Use of novel permeable membrane and air cathodes in acetate microbial fuel cells

In the existing microbial fuel cells (MFCs), the use of platinized electrodes and Nafion^® as proton exchange membrane (PEM) leads to high costs leading to a burden for wastewater treatment. In the present study, two different novel electrode materials are reported which can replace conventional platinized electrodes and can be used as very efficient oxygen reducing cathodes. Further, a novel membrane which can be used as an ion permeable membrane (Zirfon^®) can replace Nafion^® as the membrane of choice in MFCs. The above mentioned gas porous electrodes were first tested in an electrochemical half cell configuration for their ability to reduce oxygen and later in a full MFC set up. It was observed that these non-platinized air electrodes perform very well in the presence of acetate under MFC conditions (pH 7, room temperature) for oxygen reduction. Current densities of −0.43 mA cm⁻² for a non-platinized graphite electrode and −0.6 mA cm⁻² for a non-platinized activated charcoal electrode at −200 mV vs. Ag/AgCl of applied potential were obtained. The proposed ion permeable membrane, Zirfon^® was tested for its oxygen mass transfer coefficient, K₀ which was compared with Nafion^®. The K₀ for Zirfon^® was calculated as 1.9 × 10⁻³ cm s⁻¹.     

Mechanisms and kinetics of homogeneous secondary reactions of tar from continuous pyrolysis of wood chips

The change of mass and composition of biomass tar due to homogeneous secondary reactions was experimentally studied by means of a lab reactor system that allows the spatially separated production and conversion of biomass tar. A tarry pyrolysis gas was continuously produced by pyrolysis of wood chips (fir and spruce, 10-40 mm diameter) under fixed-bed biomass gasification conditions. Homogeneous secondary tar reactions without the external supply of oxidising agents were studied in a tubular flow reactor operated at temperatures from 500 to 1000 °C and with space times below 0.2 s. Extensive chemical analysis of wet chemical tar samples provided quantitative data about the mass and composition of biomass tar during homogeneous conversion. These data were used to study the kinetics of the conversion of gravimetric tar and the formation of PAH compounds, like naphthalene.It is shown that, under the reaction conditions chosen for the experiments, homogeneous secondary tar reactions become important at temperatures higher than 650 °C, which is indicated by the increasing concentrations of the gases CO, CH₄, and H₂ in the pyrolysis gas. The gravimetric tar yield decreases with increasing reactor temperatures during homogeneous tar conversion. The highest conversion reached in the experiments was 88% at a reference temperature of 990 °C and isothermal space time of 0.12 s. Hydrogen is a good indicator for reactions that convert the primary tar into aromatics, especially PAH. Soot appears to be a major product from homogeneous secondary tar reactions.     

GASIFICATION OF GREEK LIGNITE IN AN INDIRECT HEAT (ALLOTHERMAL) ROTARY KILN GASIFIER

This work reports the performance results of a pilot-size lignite gasification plant. The feed material was Greek lignite (Megalopolis), currently being employed for electricity generation in pulverized lignite-fired thermoelectric stations. Low energy conversion efficiency, low station availability, and environmental issues call for developing improved processes, e.g., an IGCC (Integrated Gasification Combined Cycle). An indirect heat (allothermal) rotary kiln was selected as the lignite gasification reactor for developing an overall gasification process of improved efficiency. Weeklong gasification runs, at near atmospheric pressure and maximum temperature in the range 900-950°C, validated high DAF lignite conversions, i.e., 90-95%, and the production of a medium heating value synthesis gas (i.e., 11-13 MJ/Nm 3 dry basis), despite the use of air for burning recycled product gas for process heating. Gas composition is equivalent to that of autothermal gasifiers (e.g., Lurgi, Winkler, Koppers-Totzek), which operate on oxygen, under pressure and strict moisture and particle size specifications. Similarly, the kiln gas is comparable to that of an allothermal, high-pressure, fluidized bed gasifier running with a high rank coal feed. The data indicate satisfactory gasification efficiency and a good thermal efficiency that should be improved further through heat integration of a scaled-up process based on an indirect heat rotary kiln gasifier.     

Full-scale measurements of SO2 gas phase concentrations and slurry compositions in a wet flue gas desulphurisation spray absorber

Two measurement campaigns were carried out at ENERGI E2's Asnæs Power plant, unit 5. The unit has a capacity of 620 MW_e and is equipped with a wet flue gas desulphurisation (FGD) plant employing a counter-current spray absorber with five spray levels. In the first campaign, the power plant was firing Orimulsion^® with 2.85 wt% S resulting in a flue gas concentration of SO₂ exceeding 2000 ppmv. In the second campaign, the fuel applied was a low-S blended coal and the SO₂ concentration in the raw gas was around 400 ppmv. A novel probe for in situ sampling of gas phase concentrations in wet FGD spray absorbers was developed and applied for measuring axial profiles of the SO₂ gas phase concentrations in the absorber. The expected decrease in SO₂ concentrations along the height of the absorber was found in the spray section (from height 26.5 to 36.2 m) whereas the SO₂ concentration above the holding tank and below the gas inlet was quite low probably due to long local residence times in the region. Horizontal variations, due to somewhat different flow conditions near the column wall were investigated and the SO₂ concentrations were found to be higher near the wall. Measurements at different gross loads showed that the SO₂ gas phase concentration at a given position inside the absorber was roughly linearly related to the L/G ratio in the measuring interval. Turning off one of the lower spray levels, while burning coal with low S content, did not lower the overall removal efficiency of the absorber. However, the SO₂ gas phase concentration inside the lower part of the absorber was increased by a factor of 2-3. Measurements of slurry pH at different positions showed a decrease of approximately 0.5 units from the upper to the lower part of the absorber. The full-scale measurements provide a detailed set of experimental data for validation of mathematical models of a wet FGD spray absorber.     

生活垃圾主要组分在回转窑内不同热解阶段的传热特性

采用外热式回转窑,对生活垃圾主要组分[纸类、织物、生物质类(含厨余)]及除去惰性成分的垃圾在不同的升温速率和不同转速下热解过程中的传热特性进行研究,获得物料和内壁面之间的表观传热系数.根据相近升温速率下热重分析结果将热解过程分为干燥阶段、热解预备阶段、剧烈热解阶段以及热解完成阶段4个阶段.研究结果表明:在干燥阶段的表观传热系数最大,并随着温度升高而迅速减小,到水分蒸发完、进入热解预备阶段时降至最低.在热解预备阶段的升温过程中,各物料表观传热系数随温度升高基本不变,具备最低稳定传热系数特征;在剧烈热解阶段,表观传热系数随温度升高而逐渐增大;在热解完成阶段,表观传热系数再次减小.回转窑转速和升温速率对表观传热系数的影响复杂,对不同物料的影响也不相同.总体上在较低的加热速率(22±2)℃·min^-1条件下,更高的回转窑转速(3 r·min^-1)对干燥末段和热解预备阶段的传热有抑制效果;当升温速率增加到(32±2)℃·min^-1时,各种物料在对应热解段的表观传热系数均有增大的趋势,且热解总时间缩短;除生物质外,转速越高,在热解的不同阶段表观传热系数越大,在3 r·min^-1条件下热解预备阶段消失.本研究为回转窑热解反应器的针对性设计提供参考.     

Evaluation of utilization of corn stalks for energy and carbon material production by using rapid pyrolysis at high temperature

Pyrolysis of agricultural residues (corn stalks) took place batch wise in a laboratory captive sample reactor (wire mesh) at atmospheric pressure. The process was studied by varying the temperature (470-710 °C) with an average heating rate of 60 °C s⁻¹ and a reaction time of 0.2 s. The carrier gas used for both pyrolysis and GC analysis was He. The nature and quantity of gases produced and the main characteristics of the charcoals formed have been determined. From the GC analysis, CO showed the higher yield, followed by H₂, CH₄ and CO₂. The increase in temperature is especially important to increase the production of gas, mainly hydrogen. From gas composition and proximate analysis, the heating value of gas and solid phases has been determined. A kinetic model of pyrolysis based on first order kinetics and on total devolatilization has been developed. According to this model, kinetic constants, pre-exponential factors and activation energies have also been determined for low and high temperatures.     

Pyrolysis characteristics of Oriental white oak: Kinetic study and fast pyrolysis in a fluidized bed with an improved reaction system

The kinetic parameters for the pyrolysis of Oriental white oak were evaluated by thermogravimetric analysis (TGA). The white oak was pyrolyzed in a fluidized bed reactor with a two-staged char separation system under a variety of operating conditions. The influence of the pyrolysis conditions on the chemical and physical characteristics of the bio-oil was also examined. TGA showed that the Oriental white oak decomposed at temperatures ranging from 250 to 400 °C. The apparent activation energy ranged from 160 to 777 kJ mol^− 1. The optimal pyrolysis temperature for the production of bio-oil in the fluidized bed unit was between 400 and 450 °C. A much smaller and larger feed size adversely affected the production of bio-oil. A higher fluidizing gas flow and higher biomass feeding rate were more effective in the production of bio-oil but the above flow rates did not affect the bio-oil yields significantly. Recycling a part of the product gas as a fluidizing medium resulted the highest bio-oil yield of 60 wt.%. In addition, high-quality bio-oil with a low solid content was produced using a hot filter as well as a cyclone. With exception of the pyrolysis temperature, the other pyrolysis conditions did not significantly affect the chemical and physical characteristics of the resulting bio-oil.     

The influence of calcination parameters on free calcium oxide content in natural hydroxyapatite

Effect of calcining temperature and time on the content of free CaO in hydroxyapatite of natural origin is presented. Hydroxyapatite was obtained from pork bones in the course of a three-stage process: hydrolysis with the application of lactic acid, pre-calcination at 600 °C and main calcination stage within the temperature range of 750-950 °C. Calcination was conducted in an electrically heated stationary chamber oven in air atmosphere and in a laboratory scale rotary kiln equipped with a gas burner. The FT-IR spectra confirmed that all organic substances were removed during the calcination process. An increase in free calcium oxide content in hydroxyapatite from 0.003% to 0.023% was caused by the increase of calcining temperature from 750 °C to 950 °C respectively. Calcining time at 950 °C gave a distinct impact upon free CaO content ranging from 0.014% (2 h) to 0.023% (3 h). Hydroxyapatite calcined in the rotary kiln contained the lowest amount of free calcium oxide: 0.002% (750 °C) and 0.003% (950 °C). A method of neutralizing of free calcium oxide, present in calcined hydroxyapatite powders of natural origin, through CaO transformation into hydroxyapatite by application of diluted thermic phosphoric acid has been developed.     

Enhancement to the rate-dependent mechanical behavior of polycarbonate by incorporation of triptycenes

The tensile and compressive properties of triptycene-polycarbonates were tested over 6 orders of magnitude in strain rate. Initially we studied a low molecular weight, low triptycene content PC blended with Iupilon^® PC and then a series of higher molecular weight, higher triptycene content polymers. The PC blend with only 1.9 wt% triptycene displayed up to 20% increase in modulus and up to 17% increase in yield strength with elongations over 80% as compared to the Iupilon^® PC. The higher molecular weight T-PCs (up to 26 wt% triptycene) exhibited improvements in modulus by over 20% and improvements in compressive strengths by nearly 50% at both low and high strain rates without any apparent sacrifice to ductility, as compared to Iupilon^® PC. All samples containing triptycene units retained transparency and exhibited no signs of crystallinity or phase separation. Moreover, both the blends and triptycene-PC copolymers displayed significantly altered dynamic mechanical spectra, specifically, the emergence of a pronounced, new β′ relaxation approximately 75 °C above the traditionally observed β relaxation in PC (approximately −100 °C). The enhancement of the mechanical properties observed provides valuable insights into the unique packing and interactions during plastic flow induced by the presence of triptycene units.     

Hydrous pyrolysis of two kinds of low-rank coal for relatively long duration

Brown coal samples were treated with hot water in a stainless steel batch reactor at 623 K for 2-72 h. After this hot hydrous treatment, gas, oils, and residues were recovered. The resulting residues were chemically analyzed in detail to understand the reaction chemistry during hydrous pyrolysis. Oxygen functionalities were analyzed chemically with the titration method and carbon types in the residue were examined by solid-state ¹³C NMR measurement. Elemental analyses showed that the oxygen atoms in the residue decreased markedly up to 2 h while treatments longer than 48 h were also very effective in removing oxygen functionalities from brown coal. The detailed chemical analyses revealed that alcoholic hydroxyl and carboxyl groups were decomposed in the earlier stages of the treatment, and that ether bonds may be cleaved during the latter stages of the hot hydrous pyrolysis. Experiments using two kinds of brown coal gave very different results. A comparison of the chemical structure of these two coals revealed the origin of the difference; one of them has a greater amount of hydroaromatic moieties than the other, which act as a hydrogen source even during hydrous pyrolysis occurring at temperatures as low as 623 K.     

Evaluation of structural features of chars from pyrolysis of biomass of different particle sizes

The structural features of chars derived from pyrolysis of mallee wood of different particle sizes in a novel fluidized-bed/fixed-bed reactor have been investigated. Raman spectroscopy was used for structural evaluation of chars. Spectra were curve-fitted with 10 Gaussian bands representing typical structural features of the chars. The temperature had a significant influence on the evolution of char structure and thus the total Raman peak area between 800 and 1800 cm^− 1 is seen to decrease significantly with increasing pyrolysis temperature for all chars. On the other hand, the ratio I_D/I_{(Gr + Vl + Vr)} between the band intensities of condensed aromatic ring systems (> 6 rings) and amorphous char structures with small aromatic ring (3-5 rings) systems is seen to increase with increasing temperature. The particle size of biomass has a great role in char structure at fast heating rate (> 1000 °C/s) pyrolysis although it has no effect on char structure at slow heating rate pyrolysis (0.17 °C/s). However, in the bigger biomass particle, the structure of char prepared under fast heating rate pyrolysis is similar to that of the structure of char prepared under slow heating rate pyrolysis.