Fuel Processing Technology (v.89, #9)

Selective cracking of natural gasoline over HZSM-5 zeolite by Marcelo J.B. Souza; Fabiano A.N. Fernandes; Anne M.G. Pedrosa; Antonio S. Araujo (819-827).
This work presents a study on the catalytic cracking of natural gasoline (extracted from natural gas) over HZSM-5 zeolite. A factorial planning was carried out to evaluate the effect of temperature and W/F ratio on the cracking of natural gasoline, analyzing their effects on conversion and product distribution using an analysis based on surface response methodology. The process was optimized focusing on the maximization of the mass fractions and the production of specific products such as ethene, propene and butanes. The results have shown that the maximum selectivity and hourly mass production of ethene is obtained at high temperature (450 °C) and low catalyst weight to flow rate ratio (W/F) (7.2 to 8.2 gcat h/mol). Maximum selectivity of propene is obtained at 350 °C and 7.0 gcat h/mol, while the best condition for maximum mass production is found at 421 °C and 5.7 gcat h/mol. The highest mass production of butanes is favored by high temperature (450 °C) and mid range W/F ratios (12.1 gcat h/mol), while the highest selectivity is found at low temperature (350 °C).
Keywords: Natural gasoline; Cracking; Zeolite HZSM-5; Optimization; Neural network;

Gasification and co-gasification of biomass wastes: Effect of the biomass origin and the gasifier operating conditions by Magín Lapuerta; Juan J. Hernández; Amparo Pazo; Julio López (828-837).
Air gasification of different biomass fuels, including forestry (pinus pinaster pruning) and agricultural (grapevine and olive tree pruning) wastes as well as industry wastes (sawdust and marc of grape), has been carried out in a circulating flow gasifier in order to evaluate the potential of using these types of biomass in the same equipment, thus providing higher operation flexibility and minimizing the effect of seasonal fuel supply variations. The potential of using biomass as an additional supporting fuel in coal fuelled power plants has also been evaluated through tests involving mixtures of biomass and coal–coke, the coke being a typical waste of oil companies. The effect of the main gasifier operating conditions, such as the relative biomass/air ratio and the reaction temperature, has been analysed to establish the conditions allowing higher gasification efficiency, carbon conversion and/or fuel constituents (CO, H2 and CH4) concentration and production. Results of the work encourage the combined use of the different biomass fuels without significant modifications in the installation, although agricultural wastes (grapevine and olive pruning) could to lead to more efficient gasification processes. These latter wastes appear as interesting fuels to generate a producer gas to be used in internal combustion engines or gas turbines (high gasification efficiency and gas yield), while sawdust could be a very adequate fuel to produce a H2-rich gas (with interest for fuel cells) due to its highest reactivity. The influence of the reaction temperature on the gasification characteristics was not as significant as that of the biomass/air ratio, although the H2 concentration increased with increasing temperature.
Keywords: Gasification; Co-gasification; Biomass origin; Circulating flow gasifier;

This work proposes a transient heat transfer model to predict the thermal behaviour of wood in a heated bed of sand fluidized with nitrogen. The 2-D model in cylindrical coordinates considers wood anisotropy, variable fuel properties, fuel particle shrinkage, and heat generation due to drying and devolatilization. The influence of initial fuel moisture content, thermal diffusivity, particle geometry, shrinkage, external heat transfer coefficient, chemical reaction kinetics and heats of reaction on temperature rise is presented. The cylindrical wood particles chosen for the study have length (l) = 20 mm, diameter (d) = 4 mm and l  = 50 mm and d  = 10 mm, both having an aspect ratio (l/d) of 5. The bed temperature is 1123 K. The model prediction is validated using measurements obtained from literature. The temperature rise in the wood particle is found to be sensitive to changes in the moisture content and thermal diffusivity and heat of reaction (in larger particles) while it is less sensitive to the external heat transfer coefficient and chemical kinetics. Also shrinkage is found to have a compensating effect and it does not have any significant influence on the temperature rise. Beyond an aspect ratio of three, the wood particle behaves as a 1-D cylinder.
Keywords: Thermal behaviour; Model; Wood; Cylinder; Two-dimensional; Fluidized bed;

Biodiesel production from waste cooking oil via alkali catalyst and its engine test by Xiangmei Meng; Guanyi Chen; Yonghong Wang (851-857).
Waste cooking oils (WCO), which contain large amounts of free fatty acids produced in restaurants, are collected by the environmental protection agency in the main cities of China and should be disposed in a suitable way. Biodiesel production from WCO was studied in this paper through experimental investigation of reaction conditions such as methanol/oil molar ratio, alkaline catalyst amount, reaction time and reaction temperature which are deemed to have main impact on reaction conversion efficiency. Experiments have been performed to determine the optimum conditions for this transesterification process by orthogonal analysis of parameters in a four-factor and three-level test. The optimum experimental conditions, which were obtained from the orthogonal test, were methanol/oil molar ratio 9:1, with 1.0 wt.% sodium hydroxide, temperature of 50 °C and 90 min. Verified experiments showed methanol/oil molar ratio 6:1 was more suitable in the process, and under that condition WCO conversion efficiency led to 89.8% and the physical and chemical properties of biodiesel sample satisfied the requirement of relevant international standards. After the analysis main characteristics of biodiese sample, the impact of biodiesel/diesel blend fuels on an YC6M220G turbo-charge diesel engine exhaust emissions was evaluated compared with 0# diesel. The testing results show without any modification to diesel engine, under all conditions dynamical performance kept normal, and the B20, B50 blend fuels (include 20%, 50% crude biodiesel respectively) led to unsatisfactory emissions whilst the B′20 blend fuel (include 20% refined biodiesel) reduced significantly particles, HC and CO etc. emissions. For example CO, HC and particles were reduced by 18.6%, 26.7% and 20.58%, respectively.
Keywords: Biofuel; Biodiesel; Transesterification; Waste cooking oil; Orthogonal test; Diesel engine test;

Investigation of the carbonization behavior of hybrid poplar by Mustafa Hakan Özyurtkan; Didem Özçimen; Ayşegül Ersoy Meriçboyu (858-863).
Carbonization experiments of hybrid poplar samples were performed in a thermogravimetric (TG) analyzer to investigate the effect of carbonization conditions, such as heating rate, particle size and sweep gas flow rate on the biochar yield. During carbonization, samples were heated from room temperature to the temperature of 723 K in an inert atmosphere. A statistical design technique was applied by using a two-level factorial design matrix to elucidate the experimental results. It was obtained that the biochar yields of samples were changed depending on the carbonization conditions. Empirical relations between the biochar yield and the carbonization conditions were developed. Biochar yields of samples were decreased with the increasing heating rate and sweep gas flow rate and increased with the increasing particle size. Kinetic analysis of the carbonization TG curves was achieved by using three different methods of calculation; also, 19 different model equations of possible solid-state rate controlling mechanisms were considered. A computer program in BASIC which enables regression analysis was used to calculate kinetic parameters from experimental TG data. It was observed that the carbonization conditions and the method of calculation influenced the kinetic results obtained.
Keywords: Biomass; Carbonization kinetics; Hybrid poplar; Biochar; Statistical design;

To satisfy the increasing propylene demand, reprocessing FCC naphtha in a secondary riser of the FCC unit was investigated. To this aim, a full range FCC naphtha was cracked over a mixture of two kinds of commercial equilibrium FCC catalysts, which contained 95 t.% Y zeolite-based catalyst and 5 wt.% ZSM-5 zeolite-based additive. The effects of operating parameters such as reaction temperature (temperature of the riser outlet), catalyst-to-oil ratio and residence time on FCC naphtha cracking were studied in a continuous pilot plant. This work demonstrates that FCC naphtha requires high operating severities to crack, and approximately 12–19 wt.% FCC naphtha can be transformed into propylene. The conversion and yield of propylene showed a rapid increase with increasing reaction temperature, and the increase of catalyst-to-oil ratio also enhanced FCC naphtha cracking, even at high reaction temperature. However, at high catalyst-to-oil reactions, hydrogen-transfer reactions constrain further increases in light olefin yields. At these high operating severities, shortening residence time is an appropriate way to obtain high yields of propylene combined with (i) lower yields of dry gas and (ii) a lower apparent hydrogen-transfer coefficient.
Keywords: Propylene production; Catalytic cracking; Naphtha recycling; Riser;

CFD simulation and experimental validation of co-combustion of chicken litter and MBM with pulverized coal in a flow reactor by J.M. Heikkinen; B.C.H. Venneker; G. di Nola; W. de Jong; H. Spliethoff (874-889).
The influence of co-combustion of solid biomass fuels with pulverized coal on burnout and CO emissions was studied using a flow reactor. The thermal input on a fuel feeding basis of the test rig was approximately 7 kW. Accompanied with the measurements, a reactor model using the CFD code AIOLOS was set up and first applied for two pure coal flames (with and without air staging). Reasonable agreement between measurements and simulations was found. An exception was the prediction of the CO concentration under sub-stoichiometric conditions (primary zone). As model input for the volatile matter release, the HTVM (high temperature volatile matter as defined by IFRF [IFRF, www.handbook.ifrf.net/handbook/glossary.html. ]) was used. Furthermore, a relatively slow CO oxidation rate obtained from the literature and the ERE (Extended Resistance Equation) model for char combustion were selected. Furthermore, the model was used for simulating co-firing of coal with chicken litter (CL) and meat and bone meal (MBM). The conditions applied are relevant for future co-firing practice with high thermal shares of secondary fuels (larger than 20%). The major flue gas concentrations were quite well described, however, CO emission predictions were only qualitatively following the measured trends when O2 is available and severely under-predicted under substoichiometric conditions. However, on an engineering level of accuracy, and concerning burnout, this work shows that co-combustion of the fuels can reasonably well be described with coal combustion sub-models.
Keywords: Co-combustion; Coal; Meat and bone meal; Chicken litter; Burnout; CFD;

Catalytic gasification of char from co-pyrolysis of coal and biomass by Wenkui Zhu; Wenli Song; Weigang Lin (890-896).
The catalytic gasification of char from co-pyrolysis of coal and wheat straw was studied. Alkali metal salts, especially potassium salts, are considered as effective catalysts for carbon gasification by steam and CO2, while too expensive for industry application. The herbaceous type of biomass, which has a high content of potassium, may be used as an inexpensive source of catalyst by co-processing with coal. The reactivity of chars from co-pyrolysis of coal and straw was experimentally examined. The chars were prepared in a spout-entrained reactor with different ratios of coal to straw. The gasification characteristics of chars were measured by thermogravimetric analysis (TGA). The co-pyrolysis chars revealed higher gasification reactivity than that of char from coal, especially at high level of carbon conversion. The influence of the alkali in the char and the pyrolysis temperature on the reactivity of co-pyrolysis char was investigated. The experimental results show that the co-pyrolysis char prepared at 750 °C have the highest alkali concentration and reactivity.
Keywords: Co-pyrolysis; Catalytic gasification; Alkali; Coal; Straw;

Progress in carbon dioxide capture and separation research for gasification-based power generation point sources by Henry W. Pennline; David R. Luebke; Kenneth L. Jones; Christina R. Myers; Badie I. Morsi; Yannick J. Heintz; Jeffery B. Ilconich (897-907).
The purpose of the present work is to investigate novel approaches, materials, and molecules for the abatement of carbon dioxide (CO2) at the pre-combustion stage of gasification-based power generation point sources. The capture/separation step for CO2 from large point sources is a critical one with respect to the technical feasibility and cost of the overall carbon sequestration scenario. For large point sources, such as those found in power generation, the carbon dioxide capture techniques being investigated by the Office of Research and Development of the National Energy Technology Laboratory possess the potential for improved efficiency and reduced costs as compared to more conventional technologies. The investigated techniques can have wide applications, but the present research is focused on the capture/separation of carbon dioxide from fuel gas (pre-combustion gas) from processes such as the Integrated Gasification Combined Cycle (IGCC) process. For such applications, novel concepts are being developed in wet scrubbing with physical sorption, chemical sorption with solid sorbents, and separation by membranes. In one concept, a wet scrubbing technique is being investigated that uses a physical solvent process to remove CO2 from fuel gas of an IGCC system at elevated temperature and pressure. The need to define an “ideal” solvent has led to the study of the solubility and mass transfer properties of various solvents. Pertaining to another separation technology, fabrication techniques and mechanistic studies for membranes separating CO2 from the fuel gas produced by coal gasification are also being performed. Membranes that consist of CO2-philic ionic liquids encapsulated into a polymeric substrate have been investigated for permeability and selectivity. Finally, processes based on dry, regenerable sorbents are additional techniques for CO2 capture from fuel gas. An overview of these novel techniques is presented along with a research progress status of technologies related to membranes and physical solvents.
Keywords: Carbon dioxide; Carbon capture; Carbon separation; Membranes; Fluorinated solvents; Ionic liquids;

Metal oxides, are widely used as sorbents to remove H2S from hot gases produced by gasification processes. These oxides, however, suffer from several problems such as low capacity, sintering, evaporation, low duration and mechanical strength. Pure metal oxides or their admixtures loaded on inert materials have been used to overcome these problems.In this study, Cu/SBA-15 type sorbents were prepared by the wet impregnation method, in which copper and SBA-15 are active and support material, respectively. The prepared sorbent samples contained 21.97% and 40.2% Cu by weight.The H2S removal characteristics of the samples were investigated by using a laboratory scale fixed bed reactor through sulfidation–regeneration cycles in the temperature range of 788–838 K. Characterization results showed that the preparation method does not have a serious destructive effect on the structure of the support material. The average breakthrough point sulfur uptake capacities of the sorbents with 21.97% Cu and 40.22% Cu were determined to be 0.63 and 1.57 g S/100 g adsorbent, respectively, after three cycles. The XRD and nitrogen adsorption analysis indicated that the structures of the sorbents were destructed to some extent during the sulfidation–regeneration cycles. Changes in the sulfur up take, however, were not comparable and remained limited.
Keywords: Sorbent; Desulfurization; Hot gas; SBA-15; CuO;

Techno-economic study of CO2 capture and storage in coal fired oxygen fed entrained flow IGCC power plants by Y. Huang; S. Rezvani; D. McIlveen-Wright; A. Minchener; N. Hewitt (916-925).
The attractiveness of fossil fuel as a feedstock for power generation depends on the development of energy conversion systems that are efficient, clean and economical. Coal fired power plants are generally considered to be “dirty” since they have high CO2 emissions, with the exception of those coal fired power plants that employ CO2 capture technology. Among the coal fired options, Integrated Gasification Combined Cycle (IGCC) systems have the best environmental performance and are potentially suitable candidates. The objective of this work is to provide an assessment and analysis of the potential for reduction of the output of greenhouse gas from the oxygen fed entrained flow gasifier systems, including the cost and cost-effectiveness of each likely conceptual scheme.The ECLIPSE process simulator was used successfully to perform technical, environmental and economic assessment studies for a wide range of IGCC power generation systems. Two IGCC power generation designs were selected, the Shell dry feed and GE (previously called Texaco) wet feed entrained flow gasifiers. As a reference fuel input, the American Federal coal was also used in IGCC systems. The performance of two IGCC systems was optimised within the constraint of being based on one particular advanced gas turbine and using a subcritical steam system.In this work, several IGCC plant attributes such as the fuel consumption, utility usages, plant performance as well as the specific CO2 generation and capture rates were simulated and weighed against each other. Factors affecting the IGCC plant performance, specifically net power output, process efficiency, power consumption coming from the Air Separation Unit (ASU) and CO2 removal and overall emissions were also evaluated and discussed. Finally, an economic evaluation of the system was conducted and the costs of CO2 capture plus transport are illustrated. This case study shows that the option of using IGCC for capturing CO2 could be technically feasible and cost-effective.
Keywords: Integrated Gasification Combined Cycle (IGCC); Greenhouse gas (GHG); Air separation unit (ASU); CO2 capture and storage (CCS); Entrained flow gasifier; Techno-economic analysis;