09 Combustion (burners, combustion systems)

the TGA under air, and then switching the gas flow to nitrogen and allowing the sample to further devolatilize until 1000°C. Also, partly burnt and/or pyrolysed samples were obtained from the TGA and characterized by optical microscopy techniques. It was observed that the volatile yields of all the coals were substantially reduced as a consequence of their initial heating under air. Besides, evidences of melting and thermal annealing in the inner core of burning coal particles were noticed to occur at lower temperatures than in pyrolysing particles. This was attributed to a sealing effect of the oxidation rim formed in the early stages of combustion, which might give rise to higher pressure build-up in the inner part of burning particles, thus enhancing the likelihood for condensation reactions to take place in the newly formed metaplast. As combustion profiles are commonly used to infer about combustion behaviour of coals, much care should be exercised in interpreting them, since even in a pure vitrain, two rather than one single material will be involved in the measured weight losses, and, more, these materials will often display fairly different reactivities.

02/02157 Pilot-scale air toxics results for PCPlcreosote- treated wood cofiring for pulverized coal combustion applications Freeman, M. et al. Proceedings - Annual Inrernational Pitrshurgh Coal Cmference, 2000, (17). 1873-1890. This paper presents combustion and emissions tests results for cofiring pentachlorophenol- (PCP) and creosote-treated wood with a baseline Upper Freeport bituminous coal using the pilot-scale Combustion and Environmental Research Facility (CERF) at the National Energy Technology Laboratory (NETL). Cofiring tests were conducted with 10% energy-basis treated wood to provide a comprehensive assessment of air toxics, including dioxins, furans, polycyclic aromatic hydrocar- bons (PAHs), heavy metals (Hg, Sb, As, Cd, Cr, Co, Pb, Mn, Ni, and Se), formaldehyde and other aldehydes, ketones, other volatile organic compounds, total hydrocarbons, HCI, and particulates. CERF test data included the measurement of ‘uncontrolled’ emissions (upstream of flue gas cleanup devices) to directly evaluate differences between the baseline coal and treated wood cofiring cases. These test results clearly showed that PCP/creosote-treated wood could be successfully co-fired with pulverized coal without increases in trace organic emissions that were typically very low, and often near or below detection limits, as a result of the high temperatures and good mixing associated with pulverized coal combustion. Although cofiring treated woods did increase uncontrolled HCI emissions, HCI emissions were still within the range of other US coals. This paper is presented to discuss the potential environmental and permit barriers for cofiring PCP/creosote- treated woods in pulverized coal utility boilers. Treated woods, such as telephone poles, transmission poles, railroad ties, etc. are a potentially attractive opportunity fuel for cofiring given their very low sulphur, nitrogen, and ash contents as well as high heating value. Treated woods are readily available across the US and often have very high disposal/ landfill costs. The completed pilot-scale CERF tests provide encoura- ging results and comprehensive air toxics data that may help utilities deal with permitting issues related to the cofiring of PCP/creosote- treated woods.

02lO2158 Prediction of the combustion behavior of blended coals in coal blending for power Dai, C. et al. Proc. - Annu. Int. Pittsburgh Coal Cotzf., 2000, (17), l83- 187. The quality parameters of the blended coals, such as ash content, calorific value, sulfur content, moisture content, volatile matter, and so on, are identical with that of the single coal, but the combustion behaviour of the blended coals may be different from that of the single cqal. In order to nicely forecast the combustion behaviour of blended coals, it is necessary for us to find the method to predict combustion behaviour of blended coals in coal blending for power in China. This paper studies the relations between ‘burning profile curve’ DTG of coals of different types or ranks and their quality parameters by thermal gravimetric analysis. The results show that DTG of single coal displays a peak and the relation between the peak temperature (T,,) of DTG of single coal and the logarithm of its fuel ratio index F (the ratio of fixed carbon to volatile matter) is linear namely: T,,,=68.86Ln F +512.2”. Therefore, DTG of the blended coals can be derived according to F of its component coals in coal blending. Then, the combustion behaviour of the blended coals can be predicted according to the rule that if DTG of coals are the same, their combustion behaviours are alike. The practical combustion of blended coals in the small test boiler is performed, which prove that the method to predict the combustion behaviour of blended coals is correct.

OH02159 Pyrolysis products from different biomasses: application to the thermal cracking of tar Fagbemi, L. et al. Applied Energy, 2001, 69, (4), 293-306.

The purpose of this study was to evaluate the amounts of various pyrolysis products (gases, water, tar and charcoal) from three biomasses (wood, coconut shell and straw) and to suggest a kinetic equation for the thermal cracking of tar at temperatures varying from 400 to 900°C. From the results, a comparative analysis is done for the biomasses, and a kinetic model of thermal cracking of tar is proposed for a residence time ranging from zero to 4 s. This can be applied to the purification of gasification gases used as a feed gas to a combustion engine, and so contributes to the design of gasifiers.

02lO2160 Research on key parameters in coal self-ignition Guo, X. el al. Xi’an Jiaorong Da.me Xuebao, 2001, 35, (7), 682-686. (In Chinese) According to the analysis of the process of coal self-ignition, it is put forward that the process of spontaneous combustion is a variety process of thermo-balance relation between heat producing from oxidizing coal and heat radiating to surroundings. The prerequisite for temperature rising of coal is presented by analysing the thermal balance relation in the process of coal self-ignition. Some key limit parameters of spontaneous combustion, include superior intensi!y limit of air leakage, superior particle size limit of coal, inferior limit of oxygen concen- tration and inferior thickness limit of the limit of coal, are obtained. The study shows that the spontaneous combustion will be possible for every kind of coal only when the following conditions are simul- taneously met: the intensity of air leakage in coal is smaller in coal is smaller than the upper limit of intensity of air leakage, the granularity of coal is smaller than its upper limit granularity, the concentration of oxygen in coal is larger than its lower limit concentration of oxygen and the thickness of coal is larger than its lower limit of thickness. The study provides essential theoretical basis for advanced improvement of spontaneous combustion theory and study of the prevention and cure of spontaneous combustion.

02lO2161 Spontaneous combustion mechanism of gangue in Jingang Coal Mine Huang, W. e, ul. Chongqing Dovue Xtrebuo. Zirun Ke.webun. 2001, 24, (4), 67-70. (In Chinese) The temperature rise rate in the oxidation process of gangue and coal specimen from Jingang Coal Mine was investigated and the sulphur

‘configuration in various kinds of gangue was analysed to explore their deal of heat is released with the oxidation of Fe& in pyrites, the accumulation of heat results in gangue spontaneous combustion when the temperature reaches a certain degree.

02lO2162 Strengths of pressurized fluidized bed combustion filter cakes: their chemical causes at 750°C and 950°C Smith, D. H. and Seshadri, K. S. Proc. - Annu. Inr. Pittsburgh Cocrl Cm/., 2000, (l7), 2252-2258. Excessively hard filter cakes have occurred during filtration of fine particles from hot gases in pressurized fluidizea bed combustion (PFBC) power plants. To better understand the mechanisms of filter cake hardening, shear strengths were measured (at 22°C) for cakes formed from powders taken from the hot-gas filtration vessel of a PFBC demonstration power plant. The measurements were made both before and after heating at 750°C (1 h) or at 950°C (1 h ot 3 h). Sample strengths were significantly increased by the heat treatment at 95O”C, but not at 750°C. In filter vessels operating at 750°C. formation of MgzCa(SOa)j from MgO, SOx, and CaS04 is the main cause of the development of excessive cake strengths. However, these reactions and the concomitant strength increases cannot occur in the laboratory, if filter cake powder is heated in the absence of one or more of the reactants (MgO and/or SO,). At 950°C and in the absence of coal ash, the formation of MgzCa(SOa)? occurs even more rapidly. However, at 95o”C, FezOz and other components of coal ash promote the decomposition of MgzCa(SOa)3. Hence, depending on the tempeta- ture, sorbent, amount of coal ash, and its composition, formation of Mg2Ca(S04)3 and/or sintering of CaS04 may be the important cause(s) of cake hardening.

02/02163 Study of coal pyrolysis characteristics in N2 and Ar atmosphere Chang, L. el crl. Proc. - Annu. In/. Pirrsburgh Coul Cmf., 2000, (17), 78- 80. - In this paper, a series of experiments were designed for investigating the pvrolysis characteristics of coal in Nz. and Ar atmosphere respeciively and the effect of coal rank on its pyrolysis rate. Three coals were selected for these experiments TGDTA system was used for detecting the rate of coal pyrolysis. X-ray diffraction technology analyses the microcrystalline structure of coal. Element Analyser confirms the element composition of coal. From the experimental results, It can be seen that the rate of three coals during pyrolysis is different and coal types and pyrolysis atmosphere affect the rate.

Fuel and Energy Abstracts July 2002 279