Low-power Boilers Research Articles

Influence of Geometrical Features of Solid Biofuels on the Implementation of the Combustion Process

ABSTRACT The article discusses the influence, in a broad spectrum, of geometric features of various solid biofuels (pellets and briquettes in several sizes) of plant origin (wheat straw, rye straw, oat straw, birch, and pine sawdust) on the combustion process, in particular on the ignition time, flame duration and fuel afterburning in a low-power boiler. The research used a test stand, an essential element of which was the standard grate boiler with a cuboidal combustion chamber surrounded by a water jacket. This type of device allowed for the combustion of fuels with various geometrical features – pellets and briquettes – in the same combustion chamber. The particles of the combusted fuel had a surface area (S) from 281 to 13188 mm2, a volume (V) from 345 to 115 787 mm3 and a density (ρ) from 602 to 1127 kg·m−3, which resulted in a total combustion total time from 600 to 1500 s. The duration of individual combustion stages of the tested biofuels was proportional to the product of the square of the volume/area quotient and the fuel density. It was found that the coefficients C0 (start combustion time coefficient), C1 (flame combustion time coefficient), C2 (afterburning combustion time coefficient) of their duration increase with the decrease in the value of the product of the square of the ratio of the volume to the area and the fuel density, which is characteristic for pellets. The distribution of the fuel ignition, flame combustion, and afterburning constants as a function of the product of the square of the volume/area quotient and the fuel density takes the power distribution with the fit values of 0.9017; 0.9779; 0.9322 respectively. The conducted correlation tests showed quite strong dependencies between the geometrical features of the fuel and the time of its combustion. At the same time, the correlations between the ash content in fuels and the duration of individual combustion stages did not show solid, regular relationships. The analysis of the course of their combustion concerning the duration of the various stages of combustion regarding variable geometrical features given to formed biofuels allows predicting the course of their combustion. It is essential at the level of exploitation of heating devices. From the perspective of this research fuels with a higher value of the square of the quotient of the volume to the area and the fuel density would be optimal.

Chlorine Corrosion in a Low-Power Boiler Fired with Agricultural Biomass

The selection of appropriate heat-resistant materials which are at the same time resistant to atmospheres rich in chlorine and its compounds is one of the most important current construction problems in steel boiler elements when using biomass fuels of agricultural origin. In the research presented here, an area was identified in the furnace of a 10 kW boiler where there was a potential risk of chlorine corrosion. This zone was determined based on numerical analysis of the combustion process; it is the zone with the highest temperatures and where the gas atmosphere conducive to the formation of chlorine corrosion centers. Subsequently, tests were carried out in the process environment of the combustion chamber of a 10 kW boiler (the fuel was barley straw) by placing samples of eight construction materials in a numerically-designated zone. These included samples of steel (coal boiler St41K, heat-resistant H25T and H24JS, and heat-resistant valve 50H21G9N4) as well as intermetallic materials based on phases (FeAl, Fe3Al, NiAl, and Ni3Al). The samples remained in the atmosphere of the boiler furnace for 1152 h at a temperature of 750–900 °C. After this time, the surfaces of the samples were subjected to SEM microscopy and scanning analysis. The results showed that the St41K boiler steel was not suitable for operation under the assumed conditions, and that a thick layer of complex corrosion products was visible on its surface. The least amount of corrosion damage was observed for the samples of 50H21G9N4 steel and intermetallic materials.

Совершенствование использования твердого топлива при слоевом способе сжигания

The article presents the results of studies, the purpose of which is to improve the efficiency and quality of using solid fuel in the layered method of combustion in low-power boilers. In order to achieve this, there are considered the tasks of increasing the efficiency of fuel use, reducing atmospheric pollution and improving the properties of slag, simplifying its further processing. The methodology of work is based on the use of active additives applied directly to the burning fuel layer. The action of the additives was determined by the methods of gas analysis and the compilation of the heat balance of the boiler. There have been obtained boiler performance indicators, which prove the effectiveness of the method. Recommendations have been developed for the implementation of the method in the conditions of poorly automated boiler houses with minimal costs for its implementation. Scientific and practical results of the study make it possible to significantly increase the efficiency of boilers, reduce emissions of products of incomplete combustion into the atmosphere, increase the density of slag, and reduce its volume and erosion. An additional positive social effect is an improvement in the working conditions of boiler operators and an increase in the culture of boiler maintenance.

Research of thermotechnical characteristics of domestic boiler with a mechanical pellet burner

An experimental study of technologies for direct combustion of pellets in a domestic boiler was conducted. Experimental studies to determine the thermophysical characteristics of the process of burning pellet fuel in the bulk layer were performed using a pellet burner Pelletron-15.To determine the patterns of the process of burning pellets in the burner and the thermal characteristics of the domestic boiler with a pellet burner, studies of the temperature of the boiler volume at different modes of operation of the burner were performed. Temperature measurement was performed using HA-thermocouples with open junction, located in the furnace space at different heights and different distances from the initial cross section of the burner. The analysis of the chemical composition of flue gases, which was determined using a gas analyzer TESTO 330-2LL, namely determined the temperature of the flue gases at the measurement point, as well as the concentration of oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx) and other parameters.According to the results of experiments, the temperature distribution in the furnace space of the solid fuel boiler Viadrus with a thermal capacity of up to 24 kW with a mechanized burner Pelletron-15 with a pellet feed hopper built into the front panel was determined.In addition, based on the results of some experimental studies, the heat of combustion, humidity and ash content of pellets were determined. The dependences on the time change of the boiler temperature at the stage of quasi-stationary mode of wood pellet combustion are obtained: at the minimum and maximum fuel supply from the hopper, as well as at the maximum fuel supply mode after the supply of additional air from the fan and in the pellet combustion process.The influence of speed and temperature of air introduced into the combustion chamber was determined. According to the research results, measures are proposed to improve the design characteristics of the pellet burner in low-power boilers (10…30 kW).

Trace Elements in Popular Coals Burnt in Low Power Boilers

Trace Elements in Popular Coals Burnt in Low Power Boilers

Analysis of Polycyclic Aromatic Hydrocarbon Content in Ash from Solid Fuel Combustion in Low-Power Boilers

The production of thermal energy is one of the sources of environmental pollution, especially when it uses traditional fossil fuels (in particular hard and brown coal). Burning conventional fuels contributes to air pollution because of emitting gases and producing waste after the process of burning in the form of ash. The work below was aimed at determining the indirect emission of PAHs in the form of fly ash, depending on the type of fuel burned. The conducted research showed which solid fuel combustion content leaves the lowest content of PAH in the fly ash. This work contains the analysis and assessment of the content of 16 PAHs (polycyclic aromatic hydrocarbons) in fly ash from the combustion of five selected solid fuels in low-power boilers. The following fuels were chosen for the research: hard coal with granulation above 60 mm, coal with the grain size of 25–80 mm, coal with the grain size of 8–25 mm, pellets with the grain size of 6 mm, and mixed dry wood. The results of the research showed that the most frequent and most concentrated compounds were naphthalene and acenaphthylene from the PAH group. These hydrocarbons have the smallest number of rings in a molecule. It was also found that the content of the LMW (Low Molecular Weight Polycyclic Aromatic Hydrocarbons) fractions in the fly ash from the analyzed fuels in ∑PAHs exceeds 57% in the case of 6 mm pellets and in the case of the ash from wood and hard coal when the grain size >60 mm. The opposite dependence can be observed in the case of the HMW (High Molecular Weight Polycyclic Aromatic Hydrocarbons) fraction.

Вплив адміністрування екологічного податку на вартість теплової енергії в Україні

The article provides an overview of approaches to greenhouse gas emissions taxation and tax rates in European countries. To compare heated boilers with different characteristics, which run on different fuels the average cost of thermal energy for the life cycle LCOH was used. Environmental tax on environmental pollution (as a component of LCOH) is calculated for the three most common types of boilers in Ukrainian boilers with a capacity of 4.65 to 58 MW, burning natural gas, coal, and fuel oil, as well as for low-power boilers (0.5 and 1 MW ), burning fossil fuels and biofuels. The eco-tax for biofuel boilers is calculated under current taxation and subject to the adoption of a European approach to taxation of carbon dioxide emissions. It is established that at the current rates there are almost no economic incentives for the introduction of technologies to reduce the concentration of pollutants in emissions, but increasing the rates of environmental tax may change this situation. However, provided that rates are evenly increased for all types of boilers, the eco-tax for natural gas boilers will remain the lowest, while for biofuel boilers it will increase significantly, which contradicts the stated goal of decarbonizing the economy. It is shown that not only the change of environmental tax rates can be an effective tool for achieving the goals of sustainable development, as the principles of its administration are also important.

Comparison of Carbonaceous Compounds Emission from the Co-Combustion of Coal and Waste in Boilers Used in Residential Heating in Poland, Central Europe

In this study, the effect of the addition of waste on the emissions from coal co-combustion was investigated. Coal was co-combusted with different additions of medium-density fiberboard and polyethylene terephthalate plastic (10 and 50%), in a low-power boiler (18 W). Polycyclic aromatic hydrocarbons, phenols, alkylphenols, phthalates, and biomass burning markers emissions were determined. Gas chromatography, coupled with a mass spectrometry detector, was used to analyze these compounds in particulate matter and gas phase, after extraction and derivatization. The emissions of polycyclic aromatic hydrocarbons were the highest among all the compounds determined. The total emission of these compounds was 215.1 mg/kg for coal, and 637.7 and 948.3 mg/kg for a 10 and 50% additive of polyethylene terephthalate plastic, respectively. For the 10 and 50% additive of medium-density fiberboard, the total emission was 474.2 and 464.0 mg/kg, respectively. The 50% addition of PET also had the highest emissions of phenols (638.5 mg/kg), alkylphenols (246.5 mg/kg), and phthalates (18.1 mg/kg), except for biomass burning markers, where the emissions were the highest for the 50% addition of medium-density fiberboard (541.3 mg/kg). In our opinion, the obtained results are insufficient for the identification of source apportionment from household heating.

Analysis of Low-Power Boilers Work on Real Heat Loads: A Case of Poland

The paper presents the methods of determination of the actual operation of solid fuel heating boilers in Poland. The analysis was based on an average annual distribution of the actual power outputs of the solid fuel heating boilers operated in four selected locations in Poland. Based on said data, three characteristic percent shares have been estimated of the nominal power outputs, at which the heating boilers in Poland operate throughout the year (divided into four characteristic portions—the seasons of the year). Additionally, for the analysis, the authors took into account the average annual temperature amplitude and the annual air quality information for the discussed locations and analyzed 30 solid fuel heating boilers in terms of their performance in the laboratory certification tests. In the final stage of the investigations, the authors initiated laboratory tests on the application of the combustion quality analyzers and their potential benefits.

Energy efficient modernization of KVG and TGV boilers

At present, the district heating systems of Ukrainian cities are in a critical state. They need significant modernization. This especially applies to very important components of district heating systems – heating water boilers. Unsatisfactory condition of boilers is mainly due to the obsolescence of basic equipment, including boilers. The operating time of them exceeds the passport lifetime. There ia a lack of modern automation, especially in terms of controlling operating modes. Nominal power of them exceeds the real heat loads. The range of hot water boilers used is not large. These are low-power boilers of the series NDIST, "Universal", "Energiia", "Fakel" and others, medium-power boilers of the series TVG and KVG and high-power boilers of series PTVM and KVGM. According to their prevalence, special attention should be paid to boilers of the series TVG and KVG. The series are installed on quarter boiler houses. The boilers of these series have an efficient design of the furnace volume and an optimized design of the convective part. Nevertheless, in terms of automation, gas supply and air supply systems, they no longer meet today's requirements. They are outdated comparing to the achieved level of technical solutions. The article discusses the main shortcomings of the design of boilers: insufficient durability of the gas collector in the hearth burner, small diameter of the pipes of the convective part and the use of fireclay materials in the setting of the burners. The first two shortcomings were overcome by the developers by the increase in the diameter of the pipes of convective packages and the modernization of MPIG-3 hearth burners. The third shortcoming should be overcomed by replacing the setting with a modern one during off-season repairs. Reserves for improving the energy efficiency of boilers of these series are found. To do this, it is necessary to install additional convective heating surfaces (economizers or air-heaters), replace the setting and equip the boilers with a modern automation system with cascading the burners. It allows improving efficiency up to 94...95 % and environmental performance according to the modern requirements.

The influence of environmental tax rates on the Levelized cost of heat on the example of organic and biofuels boilers in Ukraine

In December 2019, the European Commission officially presented The European Green Deal, a new EU economic development program aimed at achieving climate neutrality on the European continent by 2050. Many previous global, European, and national programs also aim to reduce emissions of pollutants into the atmosphere. In this context, one of the ways to reduce emissions is the development of alternative energy sources (in particular the wider use of biofuel boilers) and increasing environmental tax rates. When choosing the optimal heating boilers, the practice of using the levelized cost of heating (LCOH) indicator is common. Environmental pollution tax (as a component of LCOH) is calculated for the three most common types of boilers (for Ukrainian boiler houses) with a capacity of 4.65 to 58 MW, burning natural gas, coal, and fuel oil, as well as low-power boilers burning organic and biofuels, for existing environmental tax rates, for projected increasing in 4 times (according to the bill) and subject to the introduction of minimum and maximum rates in EU countries. It is established that at the current environmental tax rates in Ukraine there are almost no economic incentives for the introduction of technologies to reduce the concentration of pollutants in emissions, but increasing environmental tax rates may change this situation. This, in turn, once again suggests that changing environmental tax rates can be an effective tool for achieving sustainable development goals.

Combined scheme of solid fuel combustion in low power boilers

Different constructive schemes of solid fuel combustion in heating boilers up to 100 kW with the analysis of their efficiency depending on the quality of the burned solid fuel are considered. It is established that low-power solid fuel boilers with various types of combustion devices depending on the characteristics of the burned fuel and the accepted level of service are used in heat supply systems of premises, buildings and structures: from simple furnaces with manual maintenance to automated combustion devices of complex design. Mostly pre-prepared high-quality fuel is used for combustion: fuel pellets, briquettes, high-quality coal, the high cost of which significantly increases operating costs. In order to reduce capital and operating costs, it is advisable to introduce relatively inexpensive models of low-power heating boilers with an acceptable level of mechanization of combustion technology of cheap fuel, including local, with minimal costs for its preparation. The design of a heating water boiler with a semi-mechanical furnace and a technological scheme of combustion is proposed, which combines the processes of drying, gasification and combustion of fuel in a shaft with a clamping grate and combustion of coke in a layer on a moving grate. It is noted that the periodic supply of fuel in the furnace with a moving grate is maintained the stability of the combustion process in the combustion chamber, in the period between cleaning of ash and slag, without significant changes in the composition of above-layer gases. Due to the smooth movement of the next portion of hot coke from the fuel shaft to the combustion chamber on the rotating grate, conditions are created to maintain the uniformity of the boiler with the normative indicators. A reduction in harmful emissions in the exhaust gases was achieved during the combustion of the reaction fuel by passing a secondary blast of air through a collector and directing it to the combustion zone of light substances at the outlet of the clamping grate. Analytical equations for determining the size of the combustion zone according to the regime and design parameters of the combustion process are given. The efficiency of application of the combined (shaft-layer) technological scheme in low-power boilers was tested during testing of combustion of different quality coal in a semi-mechanical furnace with a rotating grate in the electric coal boiler with a heat output of 50 kW for railway carriages.

Features and problems of environmental pollution from decentralized heating systems (on the example of Chita)

This article is devoted to the study of the environmental load of decentralized energy facilities using the example of furnace heating in Chita. Existing residential and non-residential buildings heated with household stoves and low-power boilers increase the environmental burden on the environment. There are tendencies to switch to long-burning boilers. An analytical assessment of the change in the amount of emissions of the main pollutants when changing the operating modes of boilers is presented. Mechanisms for solving problems are proposed.

Modeling an automated management system of technological processes in public energetics

The article presents an algorithm for managing the fluidized bed boiler during solid fuel combustion at the enterprises of the fuel and energy complex. The review of technological features of fuel combustion in low-power boilers of high-temperature fluidized bed is performed. The calculated parameters of the furnace processes in transient operating modes are modeled. A program for managing calculated parameters in dynamic modes from the operator’s graphical panel has been developed, which is used as a training model in the educational process of training thermal-power and sanitary engineers.

Numerical investigation of coal-water fuel combustion in two-chamber furnace of a low-power boiler

In this work, a 1 MW hot water boiler equipped with a two-chamber combustion chamber for droplet-flame combustion of a coal-water fuel (CWF) is studied numerically. The effect of the second chamber with screen tubes on aerodynamics of the exhaust gas flow and temperature redistribution in the furnace volume is shown.

Transient operating regimes modeling in low-power boilers of a high-temperature fluidized bed

The paper proposes a comprehensive solution to the issues of sustainable and high-quality operation of low-power boilers with a fluidized bed at public utilities. The techniques of mathematical modeling of stationary and transient regimes of operation are used, which is necessary for the correct selection and tuning of the controllers of the automated control system. A mathematical model of the change in temperature and concentration of combustible substances over time when burning solid fuel in a fluidized bed is presented. Dependences of changes in the main parameters of the combustion process are shown. Graphs of transient processes of changing the layer temperature over time during the application of disturbing effects during the combustion of coal and peat are given.

Improvement of coal boiler’s efficiency after application of liquid fuel additive

The aim of research is to provide a comprehensive view of the combustion process of coal with a liquid fuel additive. The studies were carried out in laboratory conditions and on low and high power boilers which are usually used in households and local district heating plants. TGA/DSC analysis shows that the additive decreases the ignition temperature of coal as well as increases the maximal heat flow and its temperature. Application of the additive significantly decreases oxygen O2 concentration, while maintaining the same flue gas temperature. This affects the increase of efficiency of low power boiler by 2.49 p.p. (percentage point). Emission of hydrocarbons, formaldehyde, benzene and hydrogen cyanide was lowered, whereas there was no significant impact on SO2 and NOx emission. The studies carried on the industrial boiler with thermal output of 12 MW demonstrate that the flue gas heat loss and unburnt fuel heat loss decreased by ca. 2 p.p. As a result, the efficiency increased from ca. 86 to 88% which, in turn, influences the decrease of CO2 emission per unit of energy by 5%. The originality of the work is comprehensive research on the impact of additive on the coal combustion process, mainly concerning the efficiency.

Impact of Ignition Technique on Pollutants Emission during the Combustion of Selected Solid Biofuels

Nowadays, heating using wood, briquettes, or pellets is a curious replacement to fossil fuels such as coal, oil, or gas. Unfortunately, the combustion of biofuels, especially in low-power boilers with unstable operating conditions, releases a lot of gas pollutants (e.g., carbon monoxide (CO), nitric oxide (NO), and various organic compounds) that are usually generated due to the incomplete product combustion. The combustion of biofuel in grate boilers with top-down ignition is a new approach, popular in society (mainly used for coal fuels), which improves the combustion process and reduces the amount of pollutants emitted. This study evaluated the impact of ignition techniques on the emission level of gas pollutants during the combustion of wood logs, briquettes, and pellets of pine in grate-based charging boilers. The combination of top ignition mode with pinewood logs allowed us to achieve a reduction of 6% in CO and sulfur dioxide (SO2) emission into the atmosphere. However, the combination of top-down ignition mode with pellets and briquettes produced, in fully operational conditions, 1- to 18-fold higher levels of CO and SO2 respectively, than bottom-up ignition, after an initial period of low level CO and SO2 emissions. During the tests (mainly with ignition from top), substantial emissions of NO were observed of up to 400 mg·m−3 at 10% O2. Therefore, further research is required to decrease emission related to the content of nitrogen in biomass. In this respect, research of impact on the combustion temperature of such emissions is needed.

ПОКАЗНИКИ РОБОТИ ПАРОГЕНЕРАТОРА Е - 1- 9 ПРИ ПЕРЕВЕДЕННІ НА СПАЛЮВАННЯ ТВЕРДИХ ВИДІВ ПАЛИВ

In the work it is noted that the use of renewable fuels for the production of heat and electricity under conditions of energy shortages is an urgent task today. The numerical studies of the performance of the steam generator E-1-9 in the combustion of wood, coal, peat, straw wastes were carried out. The analysis of literary information on the experimental studies of boilers using alternative fuels has been carried out. Based on the analysis of the literature, it is shown that for wide use of alternative fuels in low power boilers (up to 3 MW), thorough experimental studies of the combustion processes of such fuels and appropriate adjustments of the Normative method are required. To study the performance of the steam generator, a mathematical model of the boiler was created, which was implemented in the MSExcel. The mathematical model consists of four modules: module of calculations of volumes of combustion products, module of calculations of heat exchange in a furnace, module of calculations of heat exchange in a convective beam, module of calculations of heat exchange in a cast iron economizer. The influence of the coefficient of excess air on the adiabatic temperature and the flue gas temperature at the outlet of the furnace is investigated. It is shown that as the coefficient of excess air increases, the adibat temperature decreases, which is explained by the fact that more cold air enters the furnace. For peat and wood, the values of the adiabatic temperature are close. The adiabatic temperature for coal is almost 350 ° C higher than that of wood. The influence of the coefficient of excess air on the efficiency of the steam generator is analyzed. It is shown that the highest value of the efficiency is the steam generator when burning coal, which is explained by the higher heat of combustion and lower moisture content of the fuel. Comparison of pollutant emissions in the case of solid fuel combustion in a steam generator.

Тoxicity of exhaust gasessolid fuel boiler KE-25-14S

The article deals with the implementation of the new national environmental legislation, which provides for the division of all energy enterprises into 4 categories depending on the degree of negative impact on the environment, the introduction of technological rationing, implemented on the principles of the best available technologies, provided that they are technically possible to use them, and the differentiation of state regulation measures in the field of environmental protection. Within the framework of this approach, the values of the total index of harmfulness (toxicity) of combustion products formed during the burning of Berezovsky coal of the B2 grade (enrichment class P) were determined by numerical experiments in order to assess the impact on the environment of emissions from low-power boilers KE-25-14C. The total emission hazard index is determined by taking into account the contribution of specific hazard indicators of combustion components represented by nitrogen oxides, sulfur dioxide, carbon monoxide, ash particles, vanadium pentaoxide and benz(a)pyrene. The private contribution of the considered pollutants to the total toxicity of emissions in the implementation of combustion regimes with moderate and large chemical underburning of fuel is established. Practical recommendations are given for using the results of the study as input data for setting technological standards for boilers of thermal power plants in the process of approval and obtaining a comprehensive environmental permit, and for developing a program to improve the environmental efficiency of energy enterprises.