Fuel Processing Technology (v.86, #7)
Editorial Board (CO2).
Effect of rank, temperatures and inherent minerals on nitrogen emissions during coal pyrolysis in a fixed bed reactor by Xiao Yan; Defu Che; Tongmo Xu (739-756).
Pyrolysis of 11 coals with carbon contents of 77–93 wt.% (daf) and corresponding demineralized samples has been studied in a fixed bed quartz reactor with a heating rate of 20 K/min to examine rank, demineralization, temperature and inherent mineral species dependences of nitrogen distribution. Nitrogen mass balances fall within 92.5–104.6%. The results indicate that the chars derived from the coals with higher rank show larger nitrogen retention. Demineralization suppresses volatile nitrogen emission during coal pyrolysis, especially for low rank coals. Coal-N conversion to tar-N reaches the asymptotic values at 600 °C. HCN yields are lower than NH3 yields during coal pyrolysis. The trends in HCN and NH3 emissions are very similar and the yields reach the asymptotic value at about 1200 °C. N2 starts emitting at 600 °C, and as the temperature increases the conversion increases linearly with a corresponding reverse change of char-N. With the catalysts added, N2 formation is prompted with the sequence of Fe>Ca>K>Ti≫Na≫Si≈Al, meanwhile, char-N decreases correspondingly. Fe, Ca, K, Na, Si and Al increase coal-N conversion to NH3 with the sequence of Fe>Ca>K≈Na≫Si≈Al in the pyrolysis. Na addition prompts HCN formation; however, the presence of Ti and Ca decrease the HCN yields with small value. The other catalysts have no notable influence on HCN emission in the pyrolysis. Demineralization and Ti addition increase coal-N conversion to tar-N slightly whereas K, Ca, Mg, Na, Si and Al additions decrease tar-N yield weakly, other catalysts hardly influence tar nitrogen emission. N2 emits mainly from char-N with slight contribution of volatile nitrogen. The mechanism of different N-containing species formation and catalysts influence in the pyrolysis is also discussed in the paper.
Keywords: Coal pyrolysis; Demineralization; Catalyst addition; Nitrogen distribution;
Characteristics of particulate matter from emissions of four typical coal-fired power plants in China by Chengfeng Zhang; Qiang Yao; Junming Sun (757-768).
The size distribution, microstructure, and chemical composition of particulate matter samples from coal-fired power plants in China were measured using a laser particle analyzer, a scanning electron microscope (SEM), and an inductively coupled plasma-atomic emission spectrometer (ICP-AES). The size distribution showed differences between the electrostatic precipitator capture efficiencies for coarse and fine particles. The microstructure measurements showed three typical particulate microstructures, spherical particles, plerospheres, and irregular particles. The surfaces of most spherical particles had microspheres that were often agglomerated together. The chemical composition of the particulate matter changed as the size decreased, while had differences from different feed coal.
Keywords: Particulate matter; Microstructure; Size distribution; Chemical composition;
Model study of pyrite demineralization by hydrogen peroxide oxidation at 30 °C in the presence of metal ions (Ni2+, Co2+ and Sn2+) by Dipu Borah; Mrinal K. Baruah; Probin C. Gogoi (769-779).
Dissolution of pyrite involving oxidation by hydrogen peroxide (H2O2) in the presence of metal ions (Ni2+, Co2+ and Sn2+) has been investigated. Before oxidation, pure and well crystalline structure of the acid washed pyrite sample, used in the present investigation, was confirmed by X-ray diffraction and chemical analysis. Oxidation of pyrite was examined by the determination of soluble sulfur. The rate of oxidation of pyrite with H2O2 is best represented by determining the rates of total soluble sulfur production. Each experiment was carried out for short (1–4 h) and extended (24 h) time periods. Pyrite is oxidized by H2O2 (1:1) up to the extent of 31.3% at short time period, which however remained the same even at extended time period. Increased amount of soluble sulfur has been observed when pyrite was oxidized by H2O2 (1:1) in the presence of Ni2+ or Co2+ or Sn2+ ion at short time period. The effectiveness of these metal ions in relation to pyrite oxidation at short time period decreases in the order Co2+>Sn2+>Ni2+, while at extended time period the order is Co2+>Ni2+>Sn2+. With Co2+ ion, the highest pyrite oxidation is obtained both at short (34.0%) and extended (35.0%) time period, while it is the lowest 31.3% with Ni2+ ion at short time and 25.3% with Sn2+ ion at extended time period. The effect of chloride ion on the rate of oxidation of pyrite is not pronounced in the metal ion containing systems. Substantial depletion in the concentration of externally added metal ions is in good agreement with the level of oxidation and infers certain adsorption or precipitation of metal ions on pyrite surface. The results of this study throw a new light of the influence of metal ions in the dissolution of pyrite in oxidation systems and has considerable applications in fields of demineralization, desulfurization and environmental science.
Keywords: Pyrite; Oxidation; Hydrogen peroxide; Metal ions; Soluble sulfur;
Proposed novel dynamic equations for direct determination of activation energy in non-isothermal isothermal systems by Dipu Borah; Mrinal K. Baruah (781-794).
A new mathematical approach for the estimation of apparent activation energy is proposed for non-isothermal dynamic process in both weight loss and weight gain conditions and is tested in different organic and inorganic systems. Satisfactory agreement between the new approach and the classical Arrhenius equation is observed. The proposed equations are applicable to a particular change occurring at two specified reaction temperatures at a constant heating rate without recording the intermediate weight changes and the temperatures. The principal advantages of this model are that the knowledge of rate constant and the graphical work are not necessary for the determination of activation energy. Moreover, the order of the reaction course is the one which yields maximum value of activation energy. Direct determination feature further simplifies the new approach and is considered as a pragmatic achievement in academic and technological fields.
Keywords: New mathematical model; Direct determination; Activation energy; Non-isothermal systems; Weight loss and weight gain;
Lack of correlation between the properties of a petroleum coke and its behaviour during combustion by J.-M. Commandré; S. Salvador (795-808).
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.
Keywords: Petcoke; NO emissions; SO2 emissions;
Effect of coal weathering on technological properties of cokes produced at different scales by J.L.G. Cimadevilla; R. Álvarez; J.J. Pis (809-830).
The effect of weathering (natural oxidation) on the technological properties of cokes obtained at three different scales (laboratory, pilot plant and semi-industrial), from two medium volatile bituminous coals stored at INCAR open stockyard for several months, has been studied in this work. The results show that the procedure developed at laboratory scale is useful for studying the evolution of coke quality because the trends of the main quality indexes (mechanical strength and reactivity to CO2) are in agreement with those of the cokes produced at larger scales. Furthermore, it was found that the total porosity and the micropores specific surface area of the cokes vary with the scale of carbonization, and that they increase as follows: semi-industrial<pilot plant<<laboratory. All of which are related to the evolution of the mechanical strength and reactivity to the CO2.
Keywords: Weathering; Bituminous coal; Coke quality; Porous texture; Optical texture;
A comprehensive comparison of fuel options for fuel cell vehicles in China by Congwei Wang; Shuailin Zhou; Xuelun Hong; Tong Qiu; Shudong Wang (831-845).
Fuel cell vehicles (FCVs) offer the potential of ultra-low emissions combined with high efficiency. Proton exchange membrane (PEM) fuel cells being developed for vehicles require hydrogen as a fuel. Due to the various pathways of hydrogen generation, both onboard and off-board, the question about which fuel option is the most competitive for fuel cell vehicles is of great current interest. In this paper, a life-cycle assessment (LCA) model was made to conduct a comprehensive study of the energy, environmental, and economic (3E) impacts of FCVs from well to wheel (WTW). In view of the special energy structure of China and the timeframe, 10 vehicle/fuel systems are chosen as the study projects. The results show that methanol is the most suitable fuel to serve as the ideal hydrogen source for fuel cell vehicles in the timeframe and geographic regions of this study. On the other hand, gasoline and pure hydrogen can also play a role in short-term and regional applications, especially for local demonstrations of FCV fleets.
Keywords: Fuel cell vehicle; Life-cycle assessment; Fuel options; Energy efficiency; Emissions; Economic;