Control of fuel combustion in boilers, 1st ed , artur o zaporozhets, 2020 3223

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Studies in Systems, Decision and Control 287 Artur O Zaporozhets Control of Fuel Combustion in Boilers Studies in Systems, Decision and Control Volume 287 Series Editor Janusz Kacprzyk, Systems Research Institute, Polish Academy of Sciences, Warsaw, Poland The series “Studies in Systems, Decision and Control” (SSDC) covers both new developments and advances, as well as the state of the art, in the various areas of broadly perceived systems, decision making and control–quickly, up to date and with a high quality The intent is to cover the theory, applications, and perspectives on the state of the art and future developments relevant to systems, decision making, control, complex processes and related areas, as embedded in the fields of engineering, computer science, physics, economics, social and life sciences, as well as the paradigms and methodologies behind them The series contains monographs, textbooks, lecture notes and edited volumes in systems, decision making and control spanning the areas of Cyber-Physical Systems, Autonomous Systems, Sensor Networks, Control Systems, Energy Systems, Automotive Systems, Biological Systems, Vehicular Networking and Connected Vehicles, Aerospace Systems, Automation, Manufacturing, Smart Grids, Nonlinear Systems, Power Systems, Robotics, Social Systems, Economic Systems and other Of particular value to both the contributors and the readership are the short publication timeframe and the world-wide distribution and exposure which enable both a wide and rapid dissemination of research output ** Indexing: The books of this series are submitted to ISI, SCOPUS, DBLP, Ulrichs, MathSciNet, Current Mathematical Publications, Mathematical Reviews, Zentralblatt Math: MetaPress and Springerlink More information about this series at http://www.springer.com/series/13304 Artur O Zaporozhets Control of Fuel Combustion in Boilers 123 Artur O Zaporozhets National Academy of Sciences of Ukraine Institute of Engineering Thermophysics Kyiv, Ukraine ISSN 2198-4182 ISSN 2198-4190 (electronic) Studies in Systems, Decision and Control ISBN 978-3-030-46298-7 ISBN 978-3-030-46299-4 (eBook) https://doi.org/10.1007/978-3-030-46299-4 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 This work is subject to copyright All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed The use of general descriptive names, registered names, trademarks, service marks, etc in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Introduction The problems of increasing the efficiency of fuel combustion and reducing emissions of harmful substances are especially relevant at present and in those industries where the burning of large amounts of fuel occurs with insufficient completeness and with relatively low efficiency This group includes boiler houses for the household sector and industrial enterprises with boiler units with a capacity of up to 3.5 MW The efficiency of the operation of boiler plants depends on the availability of reliable information on the progress of technological processes The absence of control and measurement systems for the composition of the flue gases leads to the low efficiency of the boiler, in particular, due to poor-quality fuel combustion Therefore, in the current operating conditions of boiler plants, the development of technological solutions aimed at finding and minimizing the causes and mechanisms of the formation of harmful substances in flue gases is relevant Due to the fact that replacing worn-out boiler units with new ones requires significant investment, a promising direction is the modernization of existing boiler units This is a low-cost and efficient way of rational use of fuel while reducing the level of harmful substances in the flue gases It remains relevant to ensure the functioning of control systems for the composition of the air-fuel mixture with a given speed and high reliability of maintaining the excess air coefficient at a stoichiometric level Improving the efficiency of fuel combustion is an important task, the solution of which will lead to the saving of fuel materials by reducing heat loss with flue gases The development and implementation of methods and means of monitoring the composition of the flue gases and automatic control of the fuel combustion process will increase the energy efficiency of boiler units and improve the environmental situation by reducing harmful emissions into the atmosphere (CO, NOx, SOx, etc.), which is therefore an urgent scientific applied problem, the solution of which is given in this monograph The monograph consists of four chapters Chapter analyzes the problems of increasing the efficiency of the use of fuel resources and reducing the level of emissions of harmful substances in boilers and v vi Introduction discusses the current state of the boilers of municipal and industrial heat power systems of Ukraine and ways to modernize them The analysis of methods for determining the concentration of gas mixtures in order to control the composition of the flue gases of boiler plants was carried out In Chapter 2, a model for monitoring and controlling the fuel combustion process based on a stepwise change in the composition of the air-fuel mixture and a method for increasing the accuracy of measuring the excess air coefficient taking into account the current concentration of oxygen in the air are developed and investigated To ensure the efficiency of the fuel combustion process by increasing the accuracy of determining the excess air coefficient, the influence of meteorological parameters on the daily/seasonal change in the concentration of oxygen in the air is studied Chapter discusses the hardware and software implementation of a computerized system for monitoring the process of fuel combustion in boiler units of small and medium capacity The structure of the hardware–software complex for monitoring and controlling the fuel combustion process is justified It is a system for collecting, recording and processing the corresponding informative parameters and is intended to obtain arrays of source data and generate control signals Chapter presents the results of experimental studies of the developed methodology and system for monitoring the process of fuel combustion in boiler units An experimental verification of the adequacy of the proposed model of the daily/seasonal change of the oxygen concentration in the air was carried out by comparing the results of direct measurements, by using a gas analyzer, and indirect ones based on the analysis of meteorological parameters Functional tests of the automatic control system for the fuel combustion process at the NIISTU-5 series boiler were carried out The study of the content of harmful substances in the flue gases of the boiler is completed Book is for researchers, engineers, as well as lecturers and postgraduates of higher education institutions dealing with heat engineering equipment 2020 Artur O Zaporozhets Contents Methods and Means for the Control of the Fuel Combustion Process 1.1 Features of the Formation of Heat Balance of the Boiler 1.2 Approaches to the Formation of Air-Fuel Mixture in the Burner Devices 1.3 Methods for Controlling the Composition of Flue Gases of Boilers 1.4 Analysis of Control Systems for the Combustion Process 1.5 Current State of Boiler Units of Municipal and Industrial Power System and Ways of Their Modernization References Research of the Process of Fuel Combustion in Boilers 2.1 Features of Thermophysical Processes in the Working Area of the Boiler 2.2 Modeling of the Air-Fuel Path of the Boiler 2.3 Features of the Formation of Stoichiometric Air-Fuel Mixtures 2.4 Methods for Improving the Accuracy of Determining the EAC 2.5 Method for Determining the VOC in the Air References 1 15 20 25 30 35 35 37 45 49 55 59 Hardware and Software Implementation of Modules of the System of the Fuel Combustion Control Process 3.1 Generalized Structure of the Combustion Control System in Boilers 3.2 Means of Monitoring the Process of Fuel Combustion Based on Oxygen Sensor 61 61 66 vii viii Contents 3.3 Formation of AFM of a Given Composition Based on Frequency Regulators 3.4 Software for Combustion Control System References Experimental Research of a Computer System for the Control of the Fuel Combustion Process 4.1 Results of Experimental Studies of VOC Changes 4.2 Metrological Evaluation of Experimental Studies of VOC Changing 4.3 Forecasting of VOC in the Air 4.4 Results of Experimental Studies of a Computerized System for Controlling the Fuel Combustion Process 4.5 Ecological Analysis of System Operation 4.6 Economic Analysis of System Efficiency References 70 81 86 89 89 93 102 109 115 116 122 List of Abbreviations AFM AFR DCF EAC ECE FRC FUF GQPC HCS IMS KCF PQPC VOC Air-fuel mixture Air-fuel ratio Diffusion combustion front Excess air coefficient Energy conversion efficiency Frequency ratio controller Fuel utilization factor Generalized qualitative performance criterion Housing and communal services Information-measuring systems Kinetic combustion front Partial qualitative performance criteria Volume oxygen concentration ix 4.3 Forecasting of VOC in the Air 109 Table 4.7 The predicted and calculated values of the oxygen volume concentration in the air (days) Date 01.01.18 02.01.18 03.01.18 08.05.18 09.05.18 10.05.18 t (day) 127 128 129 ]V 20.827 20.823 20.808 20.709 20.734 20.829 [O2 ]pre.1 (t) (%) 20.860 20.860 20.858 20.769 20.774 20.778 δ1 (%) 0.16 0.18 0.24 0.29 0.19 0.25 [O2 ]pre.2 (t) (%) 20.848 20.848 20.847 20.782 20.779 20.777 δ2 (%) 0.10 0.12 0.19 0.35 0.22 0.25 [O2 (%) Fig 4.19 Graphical representation of the predicted and calculated values of the oxygen volume concentration in the air in January and May 2018 (the points reflect the calculated values [O2 ]V , the solid line—the approximation function [O2 ]pre.1 (t), the crosses—the predicted values [O2 ]pre.2 ): a three days in January; b three days in May 2018 Taking into account the value of the calculated relative errors given in Tables 4.4, 4.5 and the graphical representation of the calculated predicted values of the oxygen volume concentration in the air in Fig 4.19, the author prefers calculating the predicted value according to the formula (4.5) 4.4 Results of Experimental Studies of a Computerized System for Controlling the Fuel Combustion Process The research of the developed of automatic control system of the fuel combustion was carried out on the basis of the water heating boiler NIISTU-5 It was highlighted the main approach to improve the efficiency of this boiler – modernization of the 110 Experimental Research of a Computer System for the Control … Fig 4.20 Reconstruction of NIISTU-5 boiler: a the view before the reconstruction; b the view after the reconstruction Table 4.8 Technical characteristics of the NIISTU-5 boiler Parameters Value Volume of the heated room (m3 ) 15,000 Nominal heating capacity (MW) 0.63 Gaseous fuel efficiency (%) 75 Outlet water temperature (°C) 115 Dimensions with walling (cm) 316 × 210, × 280 furnace space of the boiler with a complete replacement of the morally and physically obsolete burner and automatics [16–18] The replacement was carried out on the basis of an automated block of burner PBGM-0.85 ND (Fig 4.20), equipped with a developed automatic control system of the fuel combustion for regulation a work of the burner and boiler as a whole Technical characteristics of the NIISTU-5 boiler are shown in Table 4.8 Due to the fact that the developed control system of the fuel combustion does not use CO sensors, the main criterion of optimality has been the [CO] concentration in the flue gases The appearance of chemical underburning (CO) determines the limit of permissible impact on the reduction of air supply This limit is flexible and depends both from the characteristics of the burners and the load of the boiler Its position is also affected by: the composition of the fuel (the heat of its combustion); climatic conditions; fuel and air temperature; technical condition of the equipment and many other current factors [19] Studies of the [CO] concentration changing in the flue gases from the EAC in the nominal operating mode of the boiler were carried out (Fig 4.21) It was established experimentally that this boiler operates with the lowest [CO] concentration in the flue gases in the regime at α = 1.2 In the cases when the developed control system will be operate on the other boilers, it is necessary to conduct preliminary regime tests to determine the current optimality criterion 4.4 Results of Experimental Studies of a Computerized System … 111 Fig 4.21 Dependence of [CO] concentration from EAR in the flue gases Figure 4.22 shows the experimental graphs of the dependence of the boiler power from the oxygen concentration of in the flue gases In the course of the experiment it was found that the control system allows to maintain the concentration of residual oxygen in the flue gases at the level of 3.3– 3.5%, which in the EAC values is 1.19–1.2 Also, the dependence of air consumption from fuel consumption in the boiler power range from 10 to 100% are established (Fig 4.23) Fig 4.22 Experimental results of the dependence of the boiler power from the concentration of residual oxygen in the flue gases at various boiler loads 112 Experimental Research of a Computer System for the Control … Fig 4.23 Value of the air consumption from fuel consumption at various boiler loads Obtained graphs showed that the system provides a linear dependence of the air consumption from fuel consumption with the determination coefficient R2 in the range from 0.9985 to 0.9999 Figures 4.24 and 4.25 show the dependence of the boiler ECE and the heat losses with the flue gases from the boiler power with control system During calculating the boiler ECE, it was taken into account that the heat losses from the boiler walls is no more than 0.25%, and the heat losses with chemical underburning of the fuel is completely absent Thus, during the experiment it was shown that the maximum ECE of the boiler is ~97.4% achieved at the level of 10% of the rated power Its value decreases linearly and assumes a minimum value (92.4%) with the maximum boiler power In this case, there are minor deviations from a linear drop in the range from 0.2 to 0.3 Gcal/h, which may be due to an increase in the rate of temperature growth of the flue gases The total determination coefficient R2 for the dependence of the boiler ECE changing is 0.997 The increasing in heat losses with flue gases is also linear, with a minimum value of 2.4% at 10% boiler ECE, and a maximum of 7.3% at 100% of the boiler efficiency Figure 4.26 shows an indicative comparison of the dependence of the boiler ECE 4.4 Results of Experimental Studies of a Computerized System … 113 Fig 4.24 Dependence of the boiler ECE from the boiler power Fig 4.25 Dependence of the heat losses with the flue gases from the boiler power from its power during the boiler operating on a mode map and using the developed system As can be seen from Fig 4.26, the using of the automatic control system for the fuel combustion can significantly increase the boiler ECE at any boiler load The maximum ECE difference occurs at 20% of the boiler load and its level is 22.1%, the minimum ECE difference occurs at the rated boiler load and its level is 6.5% Table 4.9 shows the results of ecological and heat engineering tests of the NIISTU- 114 Experimental Research of a Computer System for the Control … Fig 4.26 Comparison of the boiler efficiency with a mode map and with automatic control system based on broadband oxygen sensor Table 4.9 Ecological and heat engineering characteristics of the NIISTU-5 hot water boiler based on the automatic combustion process control system Parameters Heat output Symbol Q Dimension Boiler load in % of maximum value 10% 30% 50% 75% 100% Gcal/h 0.054 0.16 0.22 0.32 0.43 MW/h 0.06 0.19 0.32 0.47 0.64 m3 /h 6.57 19.72 32.87 49.3 65.74 Fuel consumption B Air consumption L 75.1 225.3 375.5 563.3 751 Flue gas temperature Tout °C 70 93 114 151 180 Mass concentration of pollutants C(NO) mg/m3 13.4 22.78 38.86 34.84 41.54 C(CO) mg/m3 50 27.5 12.5 25 38.75 EAC α 1.2 1.2 1.2 1.2 1.2 Heat loss with flue gas q2 % 2.38 3.41 4.34 8.25 10.05 Loss of heat from chemical underburning q3 %
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