24 research outputs found
System Identification for Limit Cycling Systems: A Case Study for Combustion Instabilities
This paper presents a case study in system identification for limit
cycling systems. The focus of the paper is on (a) the use of model
structure derived from physcal considerations and (b) the use of algorithms
for the identification of component subsystems of this model structure.
The physical process used in this case study is that of a reduced order
model for combustion instabilities for lean premixed systems. The
identification techniques applied in this paper are the use of linear system
identification tools (prediction error methods), time delay estimation (based on
Kalman filter harmonic estimation methods) and qualitative validation of
model properties using harmonic balance and describing function methods.
The novelty of the paper, apart from its practical application, is that
closed loop limit cycle data is used together with a priori process
structural knowledge to identify both linear dynamic forward and nonlinear
feedback paths. Future work will address the refinement of the process
presented in this paper, the use of alternative algorithms and also the use
of control approachs for the validated model structure obtained from
this paper
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Kinetics of coal pyrolysis
This report contains results of a coordinated, multi-laboratory investigation of coal devolatilization. Data is reported pertaining to the devolatilization for bituminous coals over three orders of magnitude in apparent heating rate (100 to 100,000 + {degree}C/sec), over two orders of magnitude in particle size (20 to 700 microns), final particle temperatures from 400 to 1600{degree}C, heat transfer modes ranging from convection to radiative, ambient pressure ranging from near vacuum to one atmosphere pressure. The heat transfer characteristics of the reactors are reported in detail. It is assumed the experimental results are to form the basis of a devolatilization data base. Empirical rate expressions are developed for each phase of devolatilization which, when coupled to an awareness of the heat transfer rate potential of a particular devolatilization reactor, indicate the kinetics emphasized by a particular system reactor plus coal sample. The analysis indicates the particular phase of devolatilization that will be emphasized by a particular reactor type and, thereby, the kinetic expressions appropriate to that devolatilization system. Engineering rate expressions are developed from the empirical rate expressions in the context of a fundamental understanding of coal devolatilization developed in the course of the investigation. 164 refs., 223 figs., 44 tabs
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Thermodynamic properties of pulverized coal during rapid heating devolatilization processes
Knowledge of the thermodynamic and morphological properties of coal associated with rapid heating decomposition pathways is essential to progress in coal utilization technology. Specifically, knowledge of the heat of devolatilization, surface area and density of coal as a function of rank characteristics, temperature and extent of devolatilization in the context of rapid heating conditions is required both, for the fundamental determination of kinetic parameters of coal devolatilization, and to refine existing devolatilization sub-models used in comprehensive coal combustion codes. The objective of this research is to obtain data on the thermodynamic properties and morphology of coal under conditions of rapid heating. Specifically, the total heat of devolatilization, external surface area, BET surface area and true density will be measured for representative coal samples. In addition, for one coal, the contribution of each of the following components to the overall heat of devolatilization will be measured: the specific heat of coal/char during devolatilization, the heat of thermal decomposition of the coal, the specific heat capacity of tars, and the heat of vaporization of tars. Calibration of the heated grid calorimeter (Task 2) was completed this reporting period. Several refinements to the heated grid apparatus have been implemented which allow quantitative determination of sample heat capacity at high heating rates
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Investigation of the rank dependence of tar evolution
Despite its high nitrogen concentration levels relative to the parent coal samples, 7.2% vs. 1.4 - 2.0%, little volatile nitrogen evolution is observed until decomposition temperatures of 600[degree]C or greater are obtained. Due to the lack of decomposition via tar evolution and as contrasted to parent coals, no significant bound nitrogen is evolved with heavy hydrocarbons at particle temperatures less than 600[degree]C. Similar to virgin'' chars and tars formed during rapid devolatilization, the polyimide samples begin to evolve significant fractions of bound nitrogen as IR-active light gases at particle temperatures between 650 and 750[degree]C. Unlike coal samples, however, relatively large fractions of the light gases are observed to be ammonia. The IR-active, nitrogen-containing light gas evolution rapidly declines at polyimide char temperatures greater than 750[degree]C, again in contrast to observed behavior in virgin coal char samples. It is not certain if the nitrogen evolution kinetics changes from selectively forming ammonia and hydrogen cyanide to benzonitriles or free nitrogen at these temperatures. The light gas evolution pattern with decomposition temperature of polymide could contribute to our understanding of the low conversion efficiencies observed for bound nitrogen to NO[sub x] conversion in the char combustion phase of pfc combustion
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Thermodynamic properties of pulverized coal during rapid heating devolatilization processes. Quarterly progress report, October--December 1992
Knowledge of the thermodynamic and morphological properties of coal associated with rapid heating decomposition pathways is essential to progress in coal utilization technology. Specifically, knowledge of the heat of devolatilization, surface area and density of coal as a function of rank characteristics, temperature and extent of devolatilization in the context of rapid heating conditions is required both, for the fundamental determination of kinetic parameters of coal devolatilization, and to refine existing devolatilization sub-models used in comprehensive coal combustion codes. The objective of this research is to obtain data on the thermodynamic properties and morphology of coal under conditions of rapid heating. Specifically, the total heat of devolatilization, external surface area, BET surface area and true density will be measured for representative coal samples. In addition, for one coal, the contribution of each of the following components to the overall heat of devolatilization will be measured: the specific heat of coal/char during devolatilization, the heat of thermal decomposition of the coal, the specific heat capacity of tars, and the heat of vaporization of tars. Calibration of the heated grid calorimeter (Task 2) was completed this reporting period. Several refinements to the heated grid apparatus have been implemented which allow quantitative determination of sample heat capacity at high heating rates
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Investigation of the rank dependence of tar evolution
The objectives of this study are to develop an improved understanding of the process of coal tar evolution, its relationship to the structural characteristics of the parent coal, and the dependence of the chemical and physical properties of the tar products on the conditions of devolatilization. Data from this study are expected to allow hypothesis testing and refinements of coal devolatilization models relevant to the pulverized coal combustion process. The program is divided into seven major technical areas: tar evolution rates in rapid heating conditions; molecular weight and vapor pressure characteristics of tars; chemical structure and calorific values of tars; influence of interphase mass transport phenomena; gas phase secondary reactions of primary'' tars; parent coal nitrogen evolution during devolatilization; and model hypothesis testing. A range of coal ranks, from a Texas lignite to a Pennsylvania anthracite, are employed in the investigation. In addition, a high temperature polymer, a polyimide, is utilized as an additional reference case. The polyimide serves as a truly polymeric reference material for examining the nitrogen evolution behavior of coal. The samples are subjected to elemental composition determination, infrared absorbance characteristics, calorific value, high temperature ash analysis, and maceral composition. Consideration is being given to NMR analysis as well as tetrahydrofuran (THF) solubility. Results are discussed. 4 refs., 27 figs., 4 tabs