Fuel Processing Technology (v.87, #9)
Editorial Board (CO2).
Diesel upgrading into a low emissions fuel by Roberto Galiasso Tailleur (759-767).
The revamp of existing diesel hydrotreating units using SHP technology was studied to improve the emission of the diesel engine. Gas and liquid-phase reactors were sequentially added to the actual trickle bed reactor. A special catalyst was employed. Micro-plant kinetic studies were performed and the results compared with those obtained with conventional trickle bed reactor operation. It was shown that using the gas and liquid-phase reactor, the hydrogenation, hydrogenolysis, and ring-opening reactions can be enhanced, so can be the sulfur and cetane number properties. The new scheme decreased the mono-aromatic content in the lighter part of the diesel that improve the NO x and particulate emissions in exhaust gases of a diesel engine. A simplified kinetic model for gas and liquid-phase reactors was developed to optimize SHP reactors and to minimize investment.
Keywords: Hydrotreating; Gas and liquid-phase reactors; WNiPd/TiO2Al2O3 catalyst; NO x and PM Diesel emissions;
Kinetics of CO2/char gasification at elevated temperatures. Part II: Clarification of mechanism through modelling and char characterization by Hao Liu; Chunhua Luo; Masaomi Toyota; Shigeyuki Uemiya; Toshinori Kojima (769-774).
Char gasification experiments in a batch fluidized bed reactor at high temperatures revealed that for chars with low ash fusion temperatures, the reaction rate levelled off or even decreased a little as temperature increased. The mechanism was studied through modelling and char characterization. Investigation through modelling revealed that the increase in external mass transfer resistance with temperature was not the main factor accounting for the leveling off or decrease of gasification rate of a char at elevated temperatures. At high temperatures, the porosity and specific surface area increased with pyrolysis temperature for a char with a high ash fusion temperature, but decreased for a char with a low ash fusion temperature. For a char with a low ash fusion temperature, the surface became smooth and ash accumulation near the char surface was apparent after pyrolysis at an elevated temperature. However, for a char with a high ash fusion temperature, its surface became porous and no ash accumulation occurred after pyrolysis at an elevated temperature. According to the results of this work, ash fusion and ash accumulation near the char surface were very likely the main factors accounting for the leveling off, or decrease, of gasification rate at elevated temperatures.
Keywords: Coal char; Gasification; Char characterization; Elevated temperature;
Kinetics of CO2/Char gasification at elevated temperatures by Hao Liu; Chunhua Luo; Shigeru Kato; Shigeyuki Uemiya; Masahiro Kaneko; Toshinori Kojima (775-781).
The gasification kinetics of char has so far been mainly studied based on data measured at low temperatures and low heating rates with a thermo-gravimetric analyzer. The results cannot be directly applied to high temperature gasifiers such as entrained flow gasifiers. In this work, gasification of seven types of chars in CO2 at elevated temperatures and high heating rates was investigated with a uniquely made fluidized bed. It was found that the reaction rates for various chars were very different in low and high temperature ranges, and two orders of magnitude more pronounced in the lower temperature range. From 1273 K to 1673 K, all chars demonstrated a strong tendency to increase reaction rate with temperature. However, at a high temperature range (1773 to 1873 K), different chars demonstrated different temperature dependences. The seven types of chars studied can be roughly separated into three groups based on ash fusion temperature. Each group demonstrated a different temperature dependence at a high temperature range. For chars with low ash fusion temperatures, the reaction rate leveled off, or even decreased a little as temperature increased, which was presumed to be because of the ash fusion at elevated temperatures. These results suggest that a high temperature does not necessarily raise the gasification rate.
Keywords: Coal char; Gasification; Fluidized bed reactor; Elevated temperature;
Evaluation of a Turkish low quality oil shale by flotation as a clean energy source: Material characterization and determination of flotation behavior by N. Emre Altun; Cahit Hicyilmaz; Jiann-Yang Hwang; A. Suat Bagci (783-791).
Evaluation possibility of a low quality Turkish oil shale from Beypazarı, Ankara as an alternative clean solid fuel by froth flotation technique was investigated. Oil shale sample was characterized with mineralogical analysis, XRD and FTIR spectrum studies for its mineral content and surface characteristics. The flotation behavior of the sample and extent of cleaning were determined with respect to non-ionizing and ionizing collectors of anionic and cationic types. The effects of collector dosages and pulp pH on the cleaning performance were investigated. XRD analysis showed that the majority of the inorganic matter was constituted by carbonates, montmorillonite, quartz and feldspar while the sample was poor in organic content. In the FTIR spectrum, strong adsorption bands due to oxygen rich carboxyl groups were observed while the characteristic bands of organic groups were in weak forms. The sample was characterized as a fulvic material with low organic content. Ash content and combustible recovery results showed that cleaning of Beypazarı oil shale was a difficult process on accounts of the high inorganic content and fulvic character of the sample. The most effective cleaning was obtained with amine type collectors. With amines, ash could be reduced from 69.88% to 53.10% with 58.64% combustible recovery using 800 g/ton Armoflote 17 at natural pulp pH.
Keywords: Oil shale; Flotation; Collector; pH; FTIR; XRD;
A comparison of circulating fluidised bed combustion and gasification power plant technologies for processing mixtures of coal, biomass and plastic waste by D.R. McIlveen-Wright; F. Pinto; L. Armesto; M.A. Caballero; M.P. Aznar; A. Cabanillas; Y. Huang; C. Franco; I. Gulyurtlu; J.T. McMullan (793-801).
Environmental regulations concerning emission limitations from the use of fossil fuels in large combustion plants have stimulated interest in biomass for electricity generation.The main objective of the present study was to examine the technical and economic viability of using combustion and gasification of coal mixed with biomass and plastic wastes, with the aim of developing an environmentally acceptable process to decrease their amounts in the waste stream through energy recovery. Mixtures of a high ash coal with biomass and/or plastic using fluidised bed technologies (combustion and gasification) were considered. Experiments were carried out in laboratory and pilot plant fluidised bed systems on the combustion and air/catalyst and air/steam gasification of these feedstocks and the data obtained were used in the techno-economic analyses.The experimental results were used in simulations of medium to large-scale circulating fluidised bed (CFB) power generation plants. Techno-economic analysis of the modelled CFB combustion systems showed efficiencies of around 40.5% (and around 46.5% for the modelled CFB gasification systems) when fuelled solely by coal, which were only minimally affected by co-firing with up to 20% biomass and/or wastes. Specific investments were found to be around $2150/kWe to $2400/kWe ($1350/kWe to $1450/kWe) and break-even electricity selling prices to be around $68/MWh to $78/MWh ($49/MWh to $54/MWh). Their emissions were found to be within the emission limit values of the large combustion plant directive.Fluidised bed technologies were found to be very suitable for co-firing coal and biomass and/or plastic waste and to offer good options for the replacement of obsolete or polluting power plants.
Keywords: Biomass; Co-firing; Circulating fluidised bed; Techno-economic analysis; Co-gasification; Co-combustion;
Experimental study of the reduction mechanisms of NO emission in decoupling combustion of coal by Jingdong He; Wenli Song; Shiqiu Gao; Li Dong; Mirko Barz; Jinghai Li; Weigang Lin (803-810).
Decoupling combustion realized by dividing the coal combustion process into coal pyrolysis and the combustion of volatiles and char can reduce NO emission from coal fired stoves. In this study, decoupling combustion process in coal fired stoves was simulated experimentally with a specially designed dual-bed model reactor. The reactor can simulate various combustion sub-steps occurring in a real stove. The experimental results suggest that NO reduction by burning char may be the major contribution for NO reduction in decoupling combustion process. Compared with normal combustion, up to 40% NO emission can be reduced in decoupling combustion process.
Keywords: Decoupling combustion; Coal; NO;
Sodium borohydride as the hydrogen supplier for proton exchange membrane fuel cell systems by Jung-Ho Wee; Kwan-Young Lee; Sung Hyun Kim (811-819).
This paper introduces and discusses the latest research on the use of H2 generated via the NaBH4 hydrolysis reaction for proton exchange membrane fuel cells (PEMFCs). To realize the NaBH4–PEMFC system, many hydrolysis catalysts such as Ru/anion-exchange resins, Pt/LiCoO2, Co powder/Ni foam, PtRu/LiCoO2 and Ru/carbon have been proposed. Through these efforts, the hydrolysis reaction conversion approached 100%. In addition, the average H2 generation rate based on most of the reports generally ranged from 0.1 to 2.8 H2 l min− 1 g− 1 (catalyst), which produced a level of PEMFC performance equivalent to 0.1–0.3 kW g− 1 (catalyst). However, it was also reported that the H2 generation rate was 28 H2 l min− 1 g− 1 (catalyst) with the catalyst of Pt/carbon (acetylene black).Considering these reports and the advantageous features of NaBH4 hydrolysis, the NaBH4–PEMFC system seems to be technologically feasible and would constitute an alternative system of supplying H2 in fuel cells.However, some challenges remain, such as the deactivation of the catalyst, the treatment of the by-products, and the proper control of the reaction rate. In addition, if the price of NaBH4 were to be further reduced, this system could become the most powerful competitor in portable application fields of PEMFC.
Keywords: Sodium borohydride; Hydrolysis reaction; Proton exchange membrane fuel cell; Hydrogen; Catalyst;
An investigation on effects of various parameters on viscosities of coal–water mixture prepared with Erzurum–Aşkale lignite coal by Ahmet Gürses; Metin Açıkyıldız; Çetin Doğar; Semra Karaca; Ramis Bayrak (821-827).
In this study the effects of parameters such as coal loading (wt.%), the initial pH of mixture, the addition of various electrolytes, surfactants and temperature on the viscosity and rheologic parameters of coal–water mixture (CWM) have been investigated. The apparent viscosity was measured with a RV8-Brookfield rotating type viscosimeter. The additives used were AlCl3 and K2HPO4 as the electrolytes and Cetyltrimethyl Ammonium Bromide (CTAB), Sodium Dodecyl Sulphate (SDS) and Borrosperse NA-3A as the surfactants. It was found that the most effective additives, in terms of the viscosity reduction, were CTAB and K2HPO4, and that the CWM which had coal concentrations up to 50% (based on the weight of dry coal) could be prepared by using each additives. In addition, the viscosities of CWM with increasing temperature were found to increase at low speed, and decrease at high speed.
Keywords: Coal–water mixture; Surfactants; Electrolyte; Rheology; Apparent viscosity;
Aspects of structural features in lignite and lignite humic acids by J. Peuravuori; P. Žbánková; K. Pihlaja (829-839).
Structural features of a South Moravian lignite and its humic acid (HA) fraction were studied by means of UV–vis, 1H and solid-state 13C NMR, and FT-IR spectroscopy in addition to basic elemental analyses. The structural differences between the original lignite and its HA-type fraction were relatively minor, and their unambiguous differentiation into distinct categories was possible only by statistical methods. The tested model functions speak strongly for the importance of choosing enough sensitive and meaningful structural parameters which most likely reflect the character or type-rank of the coal-like carbon in question. The results verified that certain aliphatic compounds have their special tasks in the complicated structural network of lignite HA material, and powerful aprotic solvents are needed to obtain a fully dissolved HA solution. Despite some organic material was lost during different effective washing purification operations, the purified lignite HA was typified without significant loss of structural information on the original HA fraction. FT-IR experiments correlated well with those obtained by 13C NMR. From environmental points' of view, some water soluble organic trace components released from the original lignite material may be potential troublemakers within the area surrounding the deposit.
Keywords: Lignite; Humic acids; Purification; Macromolecular network; FT-IR; 13C NMR;
Calculation of the conditions to get less than 2 g tar/mn 3 in a fluidized bed biomass gasifier by José Corella; José M. Toledo; Gregorio Molina (841-846).
The experimental conditions under which a fluidized bed biomass gasifier can generate a gas with a tar content below 2 g/mn 3 are analyzed by using and developing the model recently published for those gasifiers by Corella and Sanz [Fuel Process. Techn. 2005, 86, 1021–1053]. The analyzed experimental conditions were: the equivalence ratio, the partitioning of the air, between the primary and secondary flows, the location (height) of the inlet of the secondary air flow, the biomass moisture and the biomass flow rate. Results from the modelling work are presented for a given CFB biomass gasifier of commercial size. Some of these results are also being checked in a CFB biomass gasifier at small pilot plant scale. To obtain a gasification gas with a very low tar content the two most important experimental conditions are a high value for the equivalence ratio and a good in-gasifier material which determines the values of the kinetic constants of the reactions involved in the network at the gasifier.
Keywords: Gasification; Tar; Circulating fluidized bed (CFB); Biomass; Gas cleaning; Renewable energies;