Ni catalysts supported on activated carbon from petcoke and their activity for toluene hydrogenation

Petroleum coke (petcoke) is an abundant resource that can potentially be converted to catalyst support materials through activation to increase the surface area and reduce the sulphur content. In this work, potassium hydroxide (KOH) catalysed activation was employed with petcoke to produce activated carbons, which were characterised with nitrogen physisorption, X‐ray diffraction, scanning electron microscopy and temperature‐programmed reduction. With activation temperatures between 500 and 800°C, the surface area increased from 4 m²/g to between 200 and 2400 m²/g while the sulphur content was reduced from 6.6 wt% to between 1 and 0.2 wt%. Nickel catalysts (nominally 5 wt%) were prepared on the activated carbon supports using wet impregnation. The activities of these catalysts were measured for toluene hydrogenation in a plug‐flow reactor with a toluene liquid hourly space velocity of 2.4/h, a pressure of 1.38 MPa, and a H₂/toluene mole ratio of 90. The catalytic activity varied between zero for nickel supported on petcoke to 98% conversion, with essentially 100% to methylcyclohexane for nickel supported on carbon activated at 750°C. Thus, activated carbon from petcoke was a suitable support for Ni‐based catalysts when used for toluene hydrogenation as a model reaction. © 2011 Canadian Society for Chemical Engineering     

Effects of NTO Oxidizer Temperature and Pressure on Hypergolic Ignition Delay and Life Time of UDMH Organic Gel Droplet

Organic gel propellants are promising candidates for a variety of rocket motor and scramjet applications, since they are intrinsically safe and provide high performance. It is well known that organic gel fuel droplets exhibit distinct combustion characteristics compared with conventional liquid fuel droplets, and furthermore an understanding of the ignition delay and lifetime of these droplets is critical to the improvement of combustor design. In this work, investigations of the combustion of unsymmetrical dimethylhydrazine (UDMH) organic gel droplets in different nitrogen tetroxide (NTO) oxidizing atmospheres were conducted using two sets of experimental apparatus. The combustion characteristics under different conditions of temperature and pressure were compared and analyzed based on the flame shapes observed during experimentation. From these trials, an unsteady combustion model was developed and used for the numerical simulation of spray‐sized UDMH organic gel droplet combustion in an NTO atmosphere. The hypergolic ignition and burning characteristics of the organic gel droplets under conditions simulating either engine startup or steady state combustion were compared, and changes in ignition delay and droplet lifetime with ambient temperature and pressure were analyzed. The experimental and numerical results show that the UDMH organic gel droplets exhibit periodic swell‐burst behavior following the formation of an elastic film at the droplet surface. Each droplet burst results in fuel vapor ejection and flame distortion, the intensity of which declines with increasing ambient pressure. However, the swell‐burst period is extended with increasing ambient pressure, which results in potential flameout. Under conditions of low temperature and pressure similar to those at engine startup, the ignition delay and lifetime of spray‐sized gel droplets decrease with increasing temperature or pressure, although there is a sharp increase in droplet lifetime when the ambient pressure reaches a critical value associated with flameout. The ignition delay was found to be a rate‐limited phenomenon linked to the droplet heating rate. The proportion of ignition delay and droplet lifetime due to droplet heating‐up decreased with increasing temperature or decreasing pressure. Conversely, at high temperatures and pressures simulating the engine’s steady state operating conditions, the droplets were observed to flameout after several swell‐burst periods and both ignition delay and lifetime decreased monotonically with increasing temperature or pressure. The ignition delay time was determined to be rate‐limited by gas phase chemical reactions and contributed very little to the overall droplet lifetime compared with the engine startup condition.     

Distribution of potassium during chemical activation of petroleum coke: Electron microscopy evidence and links to phase behaviour

In this study, direct evidence for chemical penetration into petroleum coke particles during activation is presented. In addition, the porosity development was directly related to the sulphur loss and phase behaviour of the species present. Petroleum coke (petcoke, 6 wt.% sulphur) was activated with KOH and NaOH at temperatures between 400 and 800°C. The C S bonds were broken before 400°C in the presence of KOH and before 500°C in the presence of NaOH. Electron microscopy analysis of cross-sectioned and ultramicrotomed samples revealed that sulphur was still present within the particles and that the hydroxide activation agents had penetrated to the centre of the particles (90–150 μm). After heating to 800°C and washing with a weak acid aqueous solution, essentially all the sulphur was removed, as was any remaining chemical agent. The characterization results, phase diagrams, and complementary experiments with carbonate chemical agents or steam suggest that, during heating, a molten phase formed around the petcoke particles. The composition of this molten phase changed as activation proceeded and both sulphur and ash components were liberated from the petcoke. This better understanding of the activation process will improve the efficiency of preparing activated carbon.     

Evaluation of the oxidation stability of diesel/biodiesel blends

Biodiesel is an alternative fuel derived from vegetable oils, animal fats and used frying oils. Due to its chemical structure, it is more susceptible to oxidation or autoxidation during long-term storage compared to petroleum diesel fuel. One of the major technical issues regarding the biodiesel blends with diesel fuel is the oxidation stability of the final blend, which is, nowadays, of particularly high concern due to the introduction of ultra low sulphur diesel, in most parts of the EU. This study examined the factors influencing the stability of several biodiesel blends with low and ultra low sulphur automotive diesel fuels. The aim of this paper was to evaluate the impact of biodiesel source material and biodiesel concentration in diesel fuel, on the stability of the final blend. Moreover, the effects of certain characteristics of the base diesels, such as sulphur content and the presence of cracked stocks, on the oxidation stability are discussed.     

Fuel characteristics of wheat-based Dried Distillers Grains and Solubles (DDGS) for thermal conversion in power plants

For many years, the sole use of Dried Distillers Grains and Solubles (DDGS) has been as a feed for livestock, due to its high protein and fiber content. Recently there has been interest in DDGS as a power station fuel. In this study, DDGS produced from wheat has been studied for its fuel properties. Pyrolysis studies were conducted via Thermogravimetric Analysis (TGA) and pyrolysis gas chromatography-mass spectrometry (py GC-MS): the former was used to calculate the apparent first order kinetics while the latter helped to characterise pyrolysis products such as methoxyphenols and long chain fatty acids and esters. Fast heating rate chars were made, and nitrogen and sulphur partitioning between volatiles and chars are reported. In addition the chars were studied for their combustion behavior via Simultaneous Thermogravimetric Analysis with Mass Spectrometry detection (STA-MS) to study the conversion of char nitrogen and sulphur to different nitrogen and sulphur-containing species. In addition DDGS was combusted in a 50 kW fluid bed furnace, and the nitrogen species also monitored. DDGS is predicted to have a high alkali index that predicts high fouling tendency due to the high potassium and sodium contents in the ash. The phosphorus content in DDGS ash is also very high. Pyrolysis studies showed some oil evaporation/decomposition occurring at lower temperatures compared to decomposition of the lignocellulosic material. Nitrogen and sulphur partitioning showed that approximately 91% N and 94% S were given off as volatiles. The char was enriched with nitrogen but depleted in sulphur. Char combustion took place in two distinct stages indicating the presence of two types of chars, which yield selective evolution of S and N species during their combustion. Fluid bed combustion studies showed release of both HCN and ammonia during initial stages, when the bed is heating and the fuel undergoes devolatilisation. Steady-state combustion gave NO and N₂O emissions of 290 and 30 ppm respectively, with HCN and NH₃ emissions dropping to below 1 ppm. Agglomeration of the bed was avoided by keeping the combustion temperature below 900 °C     

Biodiesel combustion in an optical HSDI diesel engine under low load premixed combustion conditions

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the spray and combustion processes for biodiesel blends under different injection strategies. The experimental results indicated that the heat release rate was dominated by a premixed combustion pattern and the heat release rate peak became smaller with injection timing retardation. The ignition and heat release rate peak occurred later with increasing biodiesel content. Fuel impingement on the wall was observed for all test conditions. The liquid penetration became longer and the fuel impingement was stronger with the increase of biodiesel content. Early and late injection timings result in lower flame luminosity due to improved mixing with longer ignition delay. For all the injection timings, lower soot luminosity was seen for biodiesel blends than pure diesel fuel. Furthermore, NO_x emissions were dramatically reduced for premixed combustion mode with retarded post-TDC injection strategies.     

Optical Coal Particle Temperature Measurement under Oxy‐Fuel Conditions: Measurement Methodology and Initial Results

Coal combustion under oxy‐fuel conditions shows significant differences to combustion in air. Examinations on the single‐grain level give detailed insight into the combustion phenomena of ignition, volatile combustion, and char burnout and, therefore, provide the fundamentals for the development of large‐scale oxy‐fuel facilities. The combustion of a hard coal in a size fraction of d_p = 90–125 μm was investigated in a laminar flow reactor at a temperature of 1500 K. The gaseous fuel oxidizer contained 3 % O₂ by volume and CO₂ or N₂ as diluents. A third measurement in a CO₂‐rich atmosphere containing 9 % O₂ is also presented to show the influence of O₂ concentration. Particle temperatures were measured for three residence times with an imaging two‐color pyrometer.     

A comprehensive experimental investigation of combustion and heat release characteristics of a biodiesel (hazelnut kernel oil methyl ester) fueled direct injection compression ignition engine

In the present study, hazelnut (Corylus avellana L.) kernel oil was transesterified with methanol using potassium hydroxide as catalyst to obtain biodiesel and a comprehensive experimental investigation of combustion (cylinder gas pressure, rate of pressure rise, ignition delay) and heat release (rate of heat release, cumulative heat release, combustion duration and center of heat release) parameters of a direct injection compression ignition engine running with biodiesel and its blends with diesel fuel was carried out. Experiment parameters included the percentage of biodiesel in the blend, engine load, injection timing, injection pressure, and compression ratio. Results showed that hazelnut kernel oil methyl ester and its blends with diesel fuel can be used in the engine without any modification and undesirable combustion and heat release characteristics were not observed. The modifications such as increasing of injection timing, compression ratio, and injection pressure provided significant improvement in combustion and heat release characteristics.     

Application of the distributed activation energy model to blends devolatilisation

In this study, an investigation was carried out into the thermal behaviour of coal, petcoke and their blend as a generic feedstock in combustion and IGCC plants for energy production. The samples were pyrolysed in a TG analyzer in nitrogen atmosphere (constant flow of 0.0335 m/s) at several heating rates with temperatures ranging from 300 to 1223 K. The distributed activation energy model was applied to study the effects of heating rates on the reactions of single solids. The results obtained were used in the calculation of curves mass loss vs. temperature at more realistic heating rates. The algorithm used to obtain the distribution of reactivities for single solids was successfully implemented to allow the prediction of blends performance.     

Combustion possibility of low rank Russian peat as a blended fuel of pulverized coal fired power plant

Combustion possibility of Russian peat as a blended fuel of commercial thermal power plant was investigated by thermogravimetric analysis (TGA), drop tube furnace (DTF) and ignition temperature (IT) tester. TGA results showed that the linear regression for the Arrhenius plot to the experimental data is very good, and activation energies for overall combustion of bituminous C & A (Coal & Allied, Australia coal name) and peat are 66.83 and 25.05 kJ/mol, respectively. It was derived that activation energies of 30%, and 50% blends produced through mixing of peat of 30%, and 50% to Design C & A (design criteria coal of 500 M coal fired power plant) are 27.76 and 24.22 kJ/mol in reciprocal proportion to blending ratio. The conversion behavior of the samples observed in DTF was similar to that reflected in TGA. DTF studies showed that the combustion of all blends was also completed at residence time of around 1 s, set temperature range of 1200 °C similar to commercial coal fired plant. Although the peat has the highest conversion than the blends, it was not appropriate as the single pulverized fuel of coal fired plant because its initial deformation (IDT) and ignition temperatures of about 1160 and 240 °C, respectively, were too low to cause the slagging in boiler, and the firing at pulverizer. The IDT and FT of the blends ashes of peat of less than 30% was about 1260 and 1410 °C, respectively, and was not expected to be associated with slagging and fouling in pulverized coal fired systems. The liability of spontaneous combustion of coal samples was increased with increasing the moisture and volatile contents whereas the same of peat was the lowest due to the high volatile content and specific heat (Cp). It was therefore proposed that the combustion of blends of peat with less than 30% was the most appropriate for the prevention of slagging and spontaneous combustion at the pulverized coal fired boilers, and has the excellent combustion efficiency.     

垃圾衍生燃料燃烧历程的试验研究*

采用热重、质谱和红外测试等热分析技术,对垃圾衍生燃料(RDF)在不同气氛、不同升温速率、不同氧化钙和无烟煤掺量条件下燃烧过程的失重特性进行了研究。结果表明:(1)垃圾衍生燃料的燃烧过程包含四个阶段,第一阶段为自由水的蒸发过程;第二和第三失重段在空气气氛下表现为纤维类和橡胶等物质的裂解与燃烧,在氮气条件下体现为裂解;第四阶段为固定碳的燃烧及燃烧中间产物的分解过程。(2)空气气氛下的失重速率高于氮气气氛。(3)氧化钙和无烟煤的掺入可以提高RDF的着火温度、延缓燃尽时间。     

甲醇对汽油燃料均质压燃燃烧和排放机理的影响

为了探讨甲醇对汽油均质压燃(HCCI)燃烧和排放机理的影响,利用CHEMKIN软件从理论上研究了甲醇对汽油HCCI燃烧反应动力学机理的影响。结果表明∶甲醇抑制了汽油(甲苯参比燃料)各组分的二次加氧过程,异辛烷基和正庚烷基继续脱氢,再氧化分解产生甲醛;甲苯基则直接氧化分解产生甲醛。随着甲醇体积分数增大,放热开始时刻提前,高温反应阶段的放热率峰值呈先增大后减小趋势。因此,可以通过调整反应中燃料的比例来控制着火时刻和放热峰值。CO和HC摩尔分数随甲醇比例增大逐步减小。随着燃空当量比升高,主燃烧峰值升高,主燃烧持续期延长,OH基生成速率和摩尔分数峰值增大,但放热开始时刻和OH开始生成时刻几乎不变。所以改变当量比可以改变燃烧反应中自由基摩尔分数和反应持续时间,但不能控制着火时刻。CO和HC摩尔分数峰值随当量比增大逐步增大,当量比过小时,大量CO和HC未被氧化。     

Theoretical Evaluation and Experimental Validation of Performance Parameters of New Hypergolic Liquid Fuel Blends with Red Fuming Nitric Acid as Oxidizer

A number of fuel blends based on 3‐carene, norbornadiene, furfuryl alcohol, ethylidene norbornene, and kerosene in different weight proportions have been developed as rocket fuels which exhibit synergistic hypergolic ignition with red fuming nitric acid (RFNA) as oxidizer with low ignition delays (IDs<40 ms). The optimum compositions of fuel blends were determined by measuring ID values of different blends at optimum O/F ratios. Eight selected fuel blends and one neat fuel (ethylidene norbornene) were theoretically evaluated for their performance parameters using NASA‐CEC‐71 software with RFNA as oxidizer at different O/F ratios and at chamber pressure of P_c, 2451.66 and 4903.33 (or 5197.52) kPa, keeping the exit pressure constant at 98.07 kPa. For experimental validation of performance parameters, static firing trials of these fuel blends with RFNA were carried out using 735.5 N thruster at 2451.66 kPa chamber pressure using doublet or triplet impinging stream type of injector. The experimental C* values were compared with theoretically determined C* values to predict combustion efficiencies which were found to be more than 95% in all the cases.     

Performance,emission and combustion studies of a DI diesel engine using Distilled Tyre pyrolysis oil-diesel blends

Increase in energy demand, stringent emission norms and depletion of oil resources led the researchers to find alternative fuels for internal combustion engines. Many alternate fuels like Alcohols, Biodiesel, LPG, CNG etc have been already commercialized in the transport sector. In this context, pyrolysis of solid waste is currently receiving renewed interest. The disposal of waste tyres can be simplified to some extent by pyrolysis. The properties of the Tyre pyrolysis oil (TPO) derived from waste automobile tyres were analyzed and compared with the petroleum products and found that it can also be used as a fuel for compression ignition engine. However, the crude TPO has a higher viscosity and sulphur content. The crude TPO was desulphurised and then distilled through vacuum distillation. In the present work, DTPO-diesel blends were used as an alternate fuel in a diesel engine without any engine modification. This paper presents the studies on the performance, emission and combustion characteristics of a single cylinder four stroke air cooled DI diesel engine running with the Distilled Tyre pyrolysis oil (DTPO).     

Rapid and simple determination by combustion of total sulphur in coal

A simple and rapid procedure for determining total sulphur in coal is described. A stoichiometric recovery from a wide variety of coal types containing 0.1–8 wt% sulphur is obtained by ignition at 1160–1180 °C in the commonly available resistance-type tube furnaces such as those used for carbon determinations. The procedure is accurate and uses readily available materials. It is particularly rapid as it consists of only two steps: sample weighing and mixing with a solid oxidant and combustion in a furnace for 7.5–9 min in an alternating nitrogen-oxygen stream with an accompanying titration. The sample and oxidant (vanadium pentoxide and chromic oxide) are heated to ≈1170 °C, any sulphur trioxide produced is reduced to sulphur dioxide by copper heated to near its melting point and chlorine is removed by a hot aluminium gauze plug. To ensure complete recovery of sulphur, oxygen is introduced in brief cycles into the nitrogen carrier flow system. The resulting sulphur dioxide is absorbed in perchloric acid solution and titrated with potassium iodate.     

Some implications of co-combustion of biomass and coal in a fluidized bed boiler

Laboratory combustion experiments were conducted to clarify some implications of co-firing coal with hog fuel and sludge in a power boiler. Combustion tests in a fixed bed stainless steel reactor at four temperatures (675, 725, 775, and 825 °C) under conditions simulating different moisture contents of hog-sludge blends indicated no problems with ignition. Burn-out of the coal reached 88–99%. However, the burn-out was very sensitive to the excess air, especially when co-firing wet hog fuel. Co-firing with coal will lead to higher sulfur dioxide emissions. Sulfation experiments were conducted in a fixed bed quartz reactor for five limestone particle size ranges (90–150 μm, 212–300 μm, 425–595 μm, 850–1000 μm, 2.0–3.4 mm) at the same temperatures as the combustion tests, with steam added to simulate the variation in the moisture content of the fuel mixture. The tests showed that the capacity of limestone to capture sulfur depends on temperature and particle size. The highest Ca utilization of the limestone was 51% (for the smallest particle size, at 825 °C). At 825 and 775 °C, the sulfur capture capacity of the limestone decreased significantly with increasing particle size, whereas at lower temperatures (725 and 675 °C), the Ca utilization was much less dependent on particle size. The sulfur capture capacity of the limestone was unaffected by the moisture content of the hog-sludge fuel. Calcium contained in the sand used as an inert in the power boiler may be capable of capturing small amounts of sulfur.     

Effects of biodiesel on a DI diesel engine performance, emission and combustion characteristics

Experimental tests were investigated to evaluate the performance, emission and combustion of a diesel engine using neat rapeseed oil and its blends of 5%, 20% and 70%, and standard diesel fuel separately. The results indicate that the use of biodiesel produces lower smoke opacity (up to 60%), and higher brake specific fuel consumption (BSFC) (up to 11%) compared to diesel fuel. The measured CO emissions of B5 and B100 fuels were found to be 9% and 32% lower than that of the diesel fuel, respectively. The BSFC of biodiesel at the maximum torque and rated power conditions were found to be 8.5% and 8% higher than that of the diesel fuel, respectively. From the combustion analysis, it was found that ignition delay was shorter for neat rapeseed oil and its blends tested compared to that of standard diesel. The combustion characteristics of rapeseed oil and its diesel blends closely followed those of standard diesel.     

Ignition characteristics of chars made in the G R & D coal-gasification and coal-to-liquids processes

Chars are obtained as by-products in the coal-gasification and coal-to-liquids processes currently in the pilot-plant stage at Garrett Research & Development Company, Inc. Ignition tests have been carried out on these chars using an ignitability test, i.e. dispersing the chars in oxygen and igniting the mixture in a hot tube. DTA—TGA determinations have also been used to study the static reactions of the chars in air. Both types of char, under roughly simulated pulverized-fuel-firing conditions probably with a significantly lower heating rate, ignited readily at temperatures equal to or lower than those required to ignite the parent coals. Partial oxidation of the char raised the ignition temperature. The heats of combustion of the chars are slightly higher than those of the parent coals and approach that of petroleum coke; the sulphur content per unit of heating value is slightly lower. They are porous materials with a particle-size distribution suitable for use as pulverized fuel. Enough volatile matter remains to give a bright flame after ignition.     

Use of multivariate analysis to determine the influence of some liquid-fuel properties on fuel-bound nitrogen-to-NOx conversion

The interactive relation between five primary liquid-fuel properties (nitrogen content, aromaticity, oxygen content, sulphur content, and volatility) and the capacity to convert fuel-bound nitrogen (FBN) to NO_x during combustion in utility gas turbines was studied using a multivariate analysis technique, in order to obtain optimum fuel composition for minimum FBN-to-NO_x, conversion. Conversion efficiency was computed from fuel NO_x emission data in the literature. An empirical model was developed for these data, using multivariate analysis, and was found to predict the conversion efficiency with reasonable accuracy. Synergistic effects of the fuel components on conversion were found to be highly significant. Variation in conversion efficiency with fuel composition was studied using response-surface methodology. Response surfaces are presented in three-dimensional form. Minimum conversion efficiency of about 14% was obtained for high-nitrogen fuels at high oxygen content and aromaticity, and low sulphur content and boiling point. Minimum conversion efficiency of about 26% was obtained for low-nitrogen fuel at high aromaticity, boiling point and sulphur content, and low oxygen content.     

Lack of correlation between the properties of a petroleum coke and its behaviour during combustion

This work is an attempt to establish links between the properties of the petcoke that can be measured through standard analysis in the laboratory and the behaviour of the petcoke both in terms of its combustion velocity and the emission of gas pollutants.A large number of petcokes, 22, taken from different sources, were burnt in an Entrained Flow Reactor (EFR) in conditions close to those of a fluidised bed of a cement plant precalciner. The burnout for the 22 petcokes ranged from 68% to 81%. The gas emissions resulting from their combustion were analysed. Prior to this, each type of petcoke was characterised in terms of its chemical composition, volatile matter and ash content, structural properties and LCV. The correlation between all these characteristics and the combustion velocity, SO₂ emissions and NO emissions in the EFR were systematically investigated.The combustion velocity does not appear to be correlated to any of the properties. The emissions of SO₂ can be accurately predicted from the content in S of the petcoke. The emissions in NO are not directly linked to the N content of the petcoke. No simple correlation could be established to predict NO emissions.