02785 Combustion of agricultural residues

02785 Combustion of agricultural residues

09 Combustion (burners, combustion systems) overall particulate capture, whereas more volatile elements such as selenium and arsenic are captured l...

221KB Sizes 2 Downloads 84 Views

09 Combustion

(burners, combustion

systems)

overall particulate capture, whereas more volatile elements such as selenium and arsenic are captured less efficiently than the ash particulate. Such element-specific behaviour is a consequence of the partitioning of individual trace elements within the combustion and post-combustion environment, resulting in enrichment of the more volatile compounds in the smallest ash particles, coupled to size-dependent particulate penetration through air pollution control devices. In this paper, a model of trace element emissions that incorporates fundamental laboratory results on trace element partitioning as well as recent field emissions data is developed. Model results and comparison to field data indicate that while the emissions of non-volatile elements such as chromium are currently well predicted by existing database-referenced empirical models, predictions of the emitted concentrations of volatile compounds such as arsenic and selenium can be improved by more than 25% through incorporation of element and size-dependent partitioning and penetration. 00102778 A study of the effects of air preheat on the structure of methane/air counterflow diffusion flames Lim, J. Comhusrion and Flame, 2000, 121, (l/2), 262-274. The effects of air preheat on flame structure are studied in counter-flow methane-air diffusion flames, considering air temperatures in the range of 300-560 K. Species concentrations for HZ, 02, Nz, CH4, CO, COz, CzH2, and CzH4 were measured using sampling and gas chromatography. Concentrations of NO were measured using sampling and chemiluminescence analysis. Results of numerical calculations using GRI-Mech 2.11 were compared with the measurements. The results of the numerical calculations and the measurements show excellent agreement for 02, Nz, CHI and good agreement for COZ, HZ and CO. However, they show poor agreement for C2HI and CZH4. Independent of the air temperature in the range 300 to 560 K, measured and predicted concentrations of CHI, CO*, 02, and Nz collapse reasonably well when plotted against the local equivalence ratio. The peak CO and Hz concentrations increase with increasing air preheat. The peak CO concentrations increase because of enhanced dissociation of COZ. The peak HZ concentrations increase because of an increase in H atom concentrations causing enhanced rates of the reaction CH4 + H CH3 + HZ. Both the measured and the predicted NO profiles showed approximately a 70% increase in the peak mole fractions with the increase in air temperature. The predictions of NO mole fractions in the fuel-lean region and near the peak are within 10% of the measurements. However, in the fuel-rich region, the predicted NO mole fractions are lower by up to 70% than the me’asured NO mole fractions. The increase in peak NO mole fractions with air preheat occurs primarily through the enhanced reaction rate of the prompt initiation reaction Nz + CH + HCN + N. The NO production by the thermal mechanism increases significantly with air preheat, but still remains a very small portion of the total. The effects of air preheat on many species and reaction rates manifest through the increased H atom concentrations. 00102779 Application of the EMMS-model to hydro-dynamics of large CFB combustors Ge, W. et rrl. Se/. Rap. Eng. Chem. Merrrll. (China), 1999, 108&116. To the flow structure in large circulating fluidized bed combustors, the energy minimization multi-scale model (EMMS) was applied. It predicts the three-dimensional distribution of the concentrations and velocities of the solids and gas. Analysis of the results demonstrates a typical core annular structure with a downward annular thicker layer, that agrees with the on-site measurements that were available. 00102780 Asymptotic analysis of radiative extinction in counterflow diffusion flames of nonunity Lewis numbers Liu, F. Combtrsrion and Fhme, 2000, 121, (l/2), 275-287. The effects of radiation heat loss and variation in near-unity Lewis numbers on the structure and extinction of counterflow diffusion flame established near the stagnation plane of two opposed free streams of fuel and oxidizer are analysed using the asymptotic method of large activation energy. Radiation heat loss from the reaction zone is accounted for using the optically thin assumption. The main concern of this study is the thermal effects of radiation heat loss and Lewis numbers on diffusion flame extinction, particularly at small stretch rates. The existence of two extinction limits, the radiation extinction limit at a small stretch rate and the conventional quenching limit at a large stretch rate, is theoretically reproduted. This simplified analysis is able to predict the existence of inflammable limits of counterflow diffusion flames in terms of the nearunity Lewis numbers and concentrations of the fuel and oxidizer streams. 00102781 Changes in the quality of coal combustion byproducts produced by Kentucky power plants, 1978 to 1997: consequences of Clean Air Act directives Hower, J. C. er (I/. Fuel, 1999, 78, (6), 701-712. The original US Clean Air Act (CAA), implemented by the Environmental Protection Agency in 1971, and the amendments to the act in 1977 and 1990 have required a considerable evolution in the quality of coal burned by utilities and in the type pollution control equipment needed to reduce SO2 and NO, emissions. Any change in coal quality or emission’s control implies a change in the amount, type, and quality of coal combustion by-products (CCB). CCB is a collective term for fly ash, bottom ash and boiler slag, and flue-gas desulfurization (FGD) or fluidized-bed combustion produced in coal burning. Studies by the University of Kentucky in 1978, 1992, and 1997, the latter two conducted by the Centre for Applied Energy Research, have

308

Fuel and Energy Abstracts

September

2000

focussed on the amount, quality and end use of CCBs from Kentucky power plants, with particular emphasis on fly ash. The evolution of clean air standards has impacted the quality and volume of CCBs in a variety of ways: (1) switching from high sulfur to lower sulfur coal generates lower quantities of spine1 phases and greater amounts of alumina-silicate glasses; (2) switching to Powder River Basin sub-bituminous coals produces Class C fly ash, compared to Class F fly ash from the combustion of the typical eastern bituminous coals; (3) the wider use of beneficiated coals reduces the amount of fly ash and bottom ash produced; (4) use of a wider rank range into the coal blend increases the potential of unburned carbon caused by inefficient combustion of non-design coals; (5) the inclusion of non-coal fuels, such as petroleum coke and with tire-derived fuel, in the coal blend; (6) reduction of NO, emissions has generally meant an initial increase in the amount of carbon in the fly ash; (7) addition of FGD means an added CCB stream, either a calcium sulfite which is generally mixed with fly ash and land-filled, or a calcium sulfate, which is sold for wallboard manufacture. The modification of the petrology and chemistry of the fly ash impacts the potential for utilization. 00102782 Co-processing: co-pyrolysis Of Coal with organic wastes Buchtele, J. e/ al. Acru Man!.. Ser. B, 1998, 8, 29-43. The capability of an appropriate type of coal as a hydrogen donor was positively applied during the co-pyrolysis of a coal mixture/waste plastics. Brown coal (VM 50.3%, C 73.2%) and MMW mixed municipal waste with a high rate of plastics was used. As plastics referential models a copolymer SB and epoxy resin (E) were co-pyrolysed. Tar yield at an additive rate of 3060% was 17-30% (MMW), 28-44% (SB) and 26-39% (E). Tar density was 1.00-1.05 g/cm and the sulfur content below 0.4%. During co-pyrolysis the high oxygen content in brown coals and also in MMW and E additives (1719%) was converted mostly to pyrogenetic water (yield of 12-20%) and to carbon oxides (CO, CO*) in gas. Coke from the pyrolysis had a low sulfur content (S, < 0.8%) and volatile matter (VM 0.9-1.3%) and could be utilized as a smokeless fuel possibly for sorbent production. 00/02783 Co-pyrolysis of waste PVC with coal Straka, P. and Kovarova, J. Acra Monr.. Ser. B, 1998, 8, 45-50. In a stationary reactor, the co-pyrolysis of hard coal with waste PVC was performed. The reason is that the pyrolysis of coal together with waste polymers/organic materials (co-pyrolysis) gives useful solid, liquid and gas products. Therefore, it is one way of treating industrial and municipal waste mixtures. In this case, a waste mixture with PVC was investigated. The mass balance of the process was evaluated and the properties of products characterized. HCI, formed during co-pyrolysis, was partly removed by the preparation of coal with NaOH. The influence of NaOH on the surface parameters of solid carbonaceous rest was investigated. It was found that the solid carbonaceous rest (coke), obtained as the main product, exhibited low ash and sulfur content and satisfactory surface properties. Therefore, the solid rest could be suitable as a smokeless fuel or as an industrial sorbent. The by-products were tar and gas. Because of high aromaticity, low sulfur content, low ash and water content and high calorific value, the tar obtained may be used as a source of chemicals as well as a low-sulfur heating oil. The gas obtained is suitable as the heating gas for energetic purposes as it was highly calorific in nature. 00/02784 Combustion in the research and development program of Ocicarbon Alegria, F. and Montes, M. Ing. Quim. (Madrid), 1999, 31, (355). 143-151. (In Spanish) A description of the research and development programme of ocicarbon is provided. The investigation was carried out for the development of improved processes for energy generation from coal by combustion with decreased environmental impact and increased conversion efficiency, Research projects are described on topics of process control; coal characterization; NO,, SO2 and COZ elimination; gas and smoke filtration, fluidized bed combustion and the utilization of waste products and ashes. 00/02785 Combustion of agricultural residues Werther, J. Progr. Energy and Combusr. Sci., 2000, 26, (I), l-27. In the current overview paper, various issues related to the combustion of agricultural residues are discussed. Attention has been given to the problems associated with the properties of the residues such as low bulk density, low ash melting points, high volatile matter contents and the presence of nitrogen, sulfur, chlorine and sometimes high moisture contents. Consequently the issues discussed include densification, the combustion mechanisms of agricultural residues, problems of low melting point of ash such as agglomeration and fouling, emissions and cocombustion. Further, design considerations of facilities for the combustion of agricultural residues are discussed. 00102788 Copyrolysis of coal and waste plastics under different reactivity gases Liao, H. el rrl. Meiran Zhuanhua, 1998, 21, (4). 62-66. (In Chinese) The contents of sulfur and nitrogen in char and oil were determined through the copyrolysis of Yanzhou coal and polyethylene (PE) under cokeoven gas (COG), hydrogen and nitrogen in a 10-g fixed-bed reactor under the pressure of 3 MPa and heating rate of 10”/min up to 650°C. The results indicated that adding 5% PE in copyrolysis of Yanzhou coal with COG, the oil yield increased 5.7% more than that of non-PE, and the water decreased