Boiler Unit Research Articles

Organization of vortex smoke gaz movement over the fuel layer to increase the efficiency of the work boiler unit KVm-2,5 in the village of Mishelevka, Usolsky district, Irkutsk region

Comparative experimental studies of the boiler unit KVm-2.5 in the layer combustion and in the organization of vortex motion of flue gases (VMFG) were carried out in this work. Analysis of the boiler showed that the layer combustion is marked by low efficiency of the boiler unit, excessive fuel consumption, a large amount of harmful emissions into the atmosphere. One of the ways to improve the efficiency of fuel combustion and reduce harmful emissions is the organization of VMFG over the fuel layer. The results of heat-engineering calculations, which allow to estimate economic and ecological expediency of introduction of VMFG are presented in this article.

The effect of the distance between wood and coal particles on the characteristics of their joint ignition under conditions of high-temperature radiation-convective heating

The article presents the results of the experimental studies of the ignition processes of mixed fuels “wood + coal” under conditions corresponding to the furnace spaces of the boiler units of TPPs. It has been established that under conditions of relatively low ambient temperatures, the time characteristics of the ignition process of coal and wood particles in the composition of the mixture differ significantly from the analogous characteristics for the ignition of single particles. It is shown that woody biomass significantly accelerates the ignition of coal, compared to the ignition of homogeneous coal (the delay time is reduced by 20–30%). At the same time, it has been found that coal particles significantly slows down the process of wood ignition (on average by 30%).The analysis of the distance between particles (d) has shown that d has a significant effect on the ignition performance. It was found that there is a certain “optimal” value of d, at which the ignition delay times are minimal. It is also shown that with an increase in the ambient temperature, the effect of the distance between particles decreases significantly.Based on the results of the experimental studies, a mathematical model has been developed for the ignition of wood-coal fuel particles, which differs from the known ones by a detailed description of thermophysical and thermochemical processes occurring in the porous structure of fuels and in a small vicinity of these particles. A comparative analysis of theoretical and experimental values of ignition delay times has shown their good agreement. An asymptotic analysis of the ignition time has shown that the entire induction period can be conditionally divided into two stages: fuel heating and direct thermochemical reaction. The fuel heating time takes about 90% of the entire induction period.

Integrated research of slaging intensityof the boilerunit heating surfaceswhen burning non-project fuels

THE PURPOSE. Comprehensive research of the slagging intensity is the heating surfaces of the BKZ-420-140 boiler unit with solid slag removal at the Abakan CHP when burning non-project fuels. The relevance of the work is due to the technical necessity and economic feasibility of conversion boiler units to combustion of non-design coals. METHODS. The problem has been analyzed by methodology for conducting complex tests, measurements and processing of experimental data, as well as the results of experimental and computational studies of a boiler unit when operating on coals of various qualities. RESULTS. Qualitative and quantitative parameters for assessing the properties of off-design coals and their behavior in real operating conditions of radiation, semi-radiation and convective conditions, taking into account their modes and design functions, have been obtained. CONCLUSION: A computational analysis of the operating modes of boiler units when burning non-design fuels showed that a promising technology for involving non-design coals in the fuel and energy balance of a thermal power plant is providing a scientifically based mixture of design and nondesign fuels.Analysis of the slagging and polluting properties of non-design coals makes it possible to predict changes in the characteristics of the thermal efficiency of heating surfaces and to develop many practical recommendations for optimizing the parameters of the cleaning equipment installed on the boiler.Also, mixtures of fuels were determined for which the wall temperatures of the metal of the outlet stack of the superheater increase, which significantly reduces the strength characteristics of the surface.The assessment and prediction of the reliability of the heating surface is carried out by calculating the temperature of the metal wall in the most heat-stressed place.

Mathematical modeling of the thermochemical processes of nitrogen oxides sequestration during combustion of wood-coal mixture particles

The article presents the results of a mathematical modeling of the combustion process of the particles of biomass/coal mixtures under conditions corresponding to the combustion chambers of the boiler units of the thermal power plants. The mathematical model of the ignition process developed by the authors differs from those presented earlier by a detailed description of the complex of the thermochemical and thermophysical processes that occur both in the boundary layer of the fuel particle and in its pores.The authors have formulated a new hypothesis about the sequestration of anthropogenic nitrogen oxides (NOx) at the initial stage of fuel combustion. It is accepted that the decrease in NOx yield during the combustion of biomass/coal fuel is due to the intensification of the formation of nitric (HNO3) acid vapors and their interaction with solid products of thermal decomposition of coal.The results of a numerical modeling of the processes under study show the possibility of a theoretical analysis of the conditions for co-combustion of the coal and wood particles, which provide a significant decrease in the yield of nitrogen oxides in comparison with the combustion of homogeneous coal.

Failure cause analysis of an expansion bellow of integrated turbine unit

The bellow is a flexible component which compensates an expansion allowance imposed by axial strain during high temperature service. The bellow failure during turbine operation of boiler unit has been systematically investigated. The metallurgy of bellow was AISI 316L stainless steel. The comprehensive laboratory investigation includes visual inspection, chemical analysis, mechanical tests, metallographic and fractographic studies. Visual inspection in the field revealed multiple cracks in the bellow and failed debris were collected for laboratory investigation. The mechanical tests of the expansion bellow confirmed to material property specification. The microstructure revealed austenitic structure and fracture surface revealed striation marks. The striation marks attributed to fatigue failure. Finite element analysis revealed that maximum stress induced in the trough region and stress could be higher as compared to ASME VIII Div 1 design equations. It can be concluded that actual operating pressure range could resulted in sufficient stress cycles to initiate fatigue cracks from surface of the bellow. The large number of stress cycles owing to actual varied pressure range attributed to fatigue failure. It is recommended to reduce many intermittent operating conditions by good operational practice and installation of strain gauges at critical locations of the bellow. It is further proposed to increase the existing ply thickness and install reinforced expansion bellow & sandwich/layered plies for prevention of fatigue failure.

Sewage Sludge Utilization for Power Production

It has been experimentally shown that the Metso Hybex steam boiler, installed at CHP-plant No.1 of AO APPM and designed to burn a mixture of bark and wood waste and sewage sludge, ensures their efficient utilization without fuel oil support flaming. The gross efficiency was 85.22–85.24% at boiler unit loads close to the nominal. The environmental performance of the boiler fully complies with the requirements established by directive 2010/75/EU and GOST 50831-95. The operation of the boiler ensured the complete utilization of sewage sludge generated at the water and wastewater treatment facility. The annual savings of fossil fuels amounted to more than 80 thousand tons of reference fuel. The total content of heavy metals emitted into the atmosphere with fly ash by a Hybex boiler with a bubbling fluidized bed when burning high-moisture biofuels is many times lower than when burning coal.

Development of simplified mathematical model of P-88 recovery boiler for operating modes at loads near the nominal

To improve the design of the elements of combined-cycle plants, and their structural and mode optimization, mathematical models are required. These models show energy efficiency indicators of the equipment under changing operating conditions. Modeling of recovery boilers is traditionally carried out with the application of specialized software systems that implement submodels of thermal-hydraulic calculations of the elements of the boiler water-steam and gas paths. This approach makes it difficult to solve practical tasks, since it requires licensed software and appropriate qualifications of an engineer. The current direction of solving this problem is statistical processing of the results of calculation data obtained with the application of specialized software systems, and development of a simplified mathematical model in the form of regression dependencies of boiler performance on variable parameters. In this study, the problem is solved in relation to the P-88 boiler of the combined-cycle plant-325 power unit in the load range near the nominal one. The initial mathematical model is developed with the application of the software package “TRAKT” designed for verification and engineering design of boilers. The simplified mathematical model is based on the methods of regression analysis of statistical data. The accuracy of the model is estimated based on the operational data of the combined-cycle plant -325 power unit. The authors have developed the mathematical model of the P-88 recovery boiler, which allows to determine the main performance indicators of the boiler when the electric power of the gas turbine and the outdoor air temperature are changing at the loads near the nominal value. The performance indicators are determined without application of specialized software for design calculation of the boiler. The accuracy of the initial mathematical model implemented in the software package “TRACT” is characterized by deviation of the calculation results data from the operational data in the corresponding modes of no more than 2 %. The additional uncertainty value introduced into the calculation results data does not exceed 1,5 % when we transfer from the initial mathematical model to the simplified one. The resulting mathematical description will allow solving the problems of mode optimization and evaluating the efficiency of the recovery boiler and the power unit under changing operating conditions.

Improving the CCS performance of coal-fired drum boiler units base on PEB and DEB strategies

This paper proposes a coordinated control system (CCS) for a coal-fired drum boiler unit based on precise energy balance (PEB) and direct energy balance (DEB) strategies. Firstly, considering the boiler energy storage is extremely complex, this paper proposes a drum boiler model with clear physical meaning. Based on the model, the boiler energy storage is further tested and analyzed. Secondly, considering several key parameters, a PEB strategy for feedforward control is proposed. Combined with the DEB strategy and load command (LDC) reconstruction, the CCS of the unit is designed. Simulation results show that the PEB strategy can achieve precise feedforward control, the LDC reconstruction can greatly improve the evaluation indicators of the unit load, and the CCS can adapt well to changes in coal quality and boiler energy storage. Application results show that the unit load can track its set point well under small and large ranges of load swing. The ramp rate is up to 13.2MW/min, the load accuracy is less than 1.2MW/min, the response time is less than 22s, and the comprehensive indicator is up to 4.35. Therefore, the CCS can be highly adapted to the dispatching demand of power grid. In addition, the boiler combustion is stable, the max deviations of steam pressure and temperature are 0.7MPa and 6.4°C, respectively.

Parameters of heat treatment of coal to obtain combustible volatile substances

The article discusses the theoretical and practical foundations of the study of the possibility of obtaining volatile combustible substances released during special heat treatment of coal, with the aim of replacing ignition fuel oil at thermal power plants. The results of an experimental study of the coals of the Saryadyr field of three Kazakhstan deposits with the aim of obtaining volatile combustible substances, as well as the possibility of using these combustible substances as starting fuel, are presented. The results of calculating the heat of combustion of the gas obtained from the presented coal samples at different heating temperatures showed that with an increase in the heating temperature, the heat of combustion of combustible gases obtained from coal samples also increases. For all the coal samples under consideration, the maximum value of the heat of combustion is traced at a heating temperature of 600 °C. The greatest value is observed for the coal of the Shubarkul deposit - 22.1 MJ/m3, and the minimum value for the brown coal of the Saryadyr deposit is 13.5 MJ/m3. According to the results of experimental studies, we can conclude that of the three presented coals for producing combustible gas, the most suitable are the coals of the Shubarkul and Maikuben deposits. For use in the boiler unit as a starting fuel, it is sufficient to heat coal to temperatures of 350–450 °C.

Experimental Study of a Coil Type Steam Boiler Operated on an Oil Field in the Subarctic Continental Climate

Transportable boiler plants are widespread in the northern regions of the Russian Federation and have a large and stable demand in various spheres of life. The equipment used and the schemes of existing boiler plants are outdated—they require replacement and modernization. Our proposed new installation includes a coil type steam boiler and ancillary equipment designed with the identified deficiencies in mind. The steam boiler coils are coaxial cylinders. The scope of the modernized transportable boiler plant is an oil field in the subarctic continental climate. The work is aimed at completing an experimental and theoretical study of the operation of a coil type steam boilers under real operating conditions. Experimental data on the operation of boiler plants are presented. The dependences of the fuel consumption of boiler plants on the temperature and pressure of the coolant are obtained. Statistical analysis is applied to the collected data. Conclusions are formulated and a promising direction is laid out for further research and improvement of coil type steam boilers. Equations are proposed for calculating the convective component of radiant-convective heat transfer in gas ducts, taking into account the design features of boiler units by introducing new correction factors. Comparison of the calculated and experimental data showed their satisfactory agreement.

Комплексная эффективность применения древесных гранул в энергоустановках

In advanced countries, the dramatic impact of greenhouse gases on the global climate is reduced by replacing fossil fuels with biofuels. This method is being actively encouraged. However, by-products of logging, processing and conversion of wood are classified as difficult to burn fuels due to their high moisture content, low energy density and extremely heterogeneous granulometric composition. A promising direction to increase the energy density and transportability of the timber industry by-products is their granulation. Wood pellet fuel burning in heat-generating plants results in significant increase in their energy and environmental performance. The purpose of the paper is an experimental and calculation study of the energy and environmental performance of 4 MW hot water boilers produced by Polytechnik Luft- und Feuerungstechnik GmbH in the process of burning pine and spruce wood pellets obtained from by-products woodworking. When performing studies, the components of the boiler’s heat balance, gas release, and particulate emissions were determined. Numerical modeling of thermochemical and aerodynamic processes taking place in the boiler combustion chamber was carried out by using the Ansys Fluent three-dimensional simulation software. Together with industrial-operational tests it showed the possibility to reduce the total share of flue gas recirculation into combustion chambers of boiler units to values not exceeding 0.45, in providing an acceptable temperature of combustion products at the combustion chamber outlet and maintaining minimum emissions of carbon and nitrogen monoxides. At the same time, the share of gases fed by recirculation smoke exhausters to the over-bed area of the burner should have higher values than under the reciprocating grates of boilers. Guidelines for comprehensive improvement of wood pellet combustion efficiency in combustion chamber of 4 MW hot water boilers have been developed and implemented. The priorities are: using the air passed through the cooling channels of the setting as secondary air; reducing the rarefaction in the combustion chambers to 30–70 Pa; optimizing the ratio of primary and secondary air, herewith, the share of primary air in the total flow should be 0.26–0.35. Implementation of the developed guidelines allowed to increase the boiler gross efficiency by 0.5–1.8 %, to reduce the aerodynamic resistance of the gas path by 15–20 % and to ensure consistently low emissions of carbon and nitrogen monoxides and soot particles. When designing boiler units for burning wood pellet fuel it is advisable to place heating surfaces in the combustion chamber, included in the circulation circuit of the boiler. This will increase the efficiency and life cycle of the boiler unit.

On the question of increasing the purification efficiency of flue gases from the boiler unit of HEPS Volzhsky automobile plant

The paper considers the measures to suppress emissions of nitrogen and carbon oxides emitted during natural gas combustion, used on the VAZ heat electro-power station territory in Togliatti. The analysis of the quantitative distribution of fuel consumption and pollutant emissions for 2015 - 2019 has been carried out. The description of the process flow diagram of the gas-air duct of the TGME-464 boiler unit (KA No.12) is presented. The possibility of using the method of selective catalytic reduction of nitrogen and carbon oxides on the honeycomb ceramic catalyst surface is considered. The graphical dependences of the volumetric-mass air flow rates, flue gas fuel, specific flow and speed energy on the change in the heat load of the boiler unit are determined. The possibility of using a mathematical model for calculating the change in concentrations and along the length of the catalytic layer depending on the flue gas flow temperature is considered.

On the Perspective of Transfer of Omsk Thermal Power Plants to Combustion of Fired Coals

The existing issues during the combustion of Kazakh coal from the Ekibastuz basin in the Omsk energy system are noted. The environmental problems of coal generation in Omsk are outlined. The possibility of transferring the Omsk coal-fired thermal power plants to the combustion of domestic coals is considered. The options for increasing the efficiency of using solid fossil fuel in the production of electric and thermal energy are given. The existing problem of storing ash and slag wastes obtained by burning high-ash Ekibastuz coals is noted. The transfer of the Omsk CHPPs to the combustion of brown coal from the Kansk-Achinsky deposit, provided that highly effective environmentally friendly technologies are used It is noted that the technology of combustion of fuels in a circulating fluidized bed (CFB) has been industrially developed and implemented in power boilers. The results of operation of the first in Russia CFB boiler of unit No. 9 with a capacity of 330 MW at the Novocherkasskaya SDPP are presented

Modeling the Heat Scheme of the Combined Heat and Power Plants Using the Software Product “Boiler Designer”

This article describes the rationale for the development of a mathematical model of the thermal scheme of Vladivostok thermal power plant. Four types of turbines are installed at this plant, boiler units operate on coal and natural gas. This makes it difficult to effective load distribution between the turbine units. Application of simplified dependencies, built on the basis of the reporting data, allows to analyse the correctness of the load distribution between the units. The article provides an example of comparing the actual parameters of the plant and calculating based on the simplified characteristics of turbines. This example showing the loss of fuel equivalent from non-optimal load distribution. However, the use of such simplified characteristics has several shortcomings. These shortcomings do not allow using this as a universal method. There is a need to create a full-fledged mathematical model of thermal power plants. The model is developing on the basis of the Boiler Designer software package. The program has a modular structure and allows you to create mathematical models of each unit of equipment, and then, through the purpose of connections, assemble the thermal scheme of the station. This approach is actual for cross-linked heat and power plants, since it allows us to evaluate the efficiency of thermal scheme connections, and not just the operation of the equipment itself. The article provides a simplified model of the station, its advantages and disadvantages

Development and prospect of lignite burning power generation in circulating fluidized bed boiler

At present, direct-combustion of lignite for generating electricity is a meaningful way to utilize lignite. The development status of lignite power generation and lignite CFB boiler technology is introduced in this paper. From the aspects of combustion stability, boiler efficiency and pollutant discharge, the technical and economic comparative analysis of lignite power generation technology of pulverized coal boiler and CFB boiler is carried out. As a result, CFB boilers burning lignite have more advantages than pulverized coal boilers in combustion stability, boiler efficiency, and pollutant emission reduction. The development of 600-1000MW ultra-supercritical CFB boiler units burning high moisture lignite is feasible and has certain strategic advantages.

CHARACTERISTICS OF ALCOHOL-COAL-WATER SLURRIES SPRAYING

The aim of this work is to substantiate the efficiency of ethyl or isoamyl alcohol application as the third component of coal-water fuels based on the results of experimental study of coaxial spraying. Studies of alcohols influence on spraying characteristics of coal-water fuels can rarely be found in the literature. Instantaneous fields of fuel droplets velocities in several cross-sections of the jet were determined using Particle Image Velocimetry method. Interferometric Particle Imaging method was used to determine droplets distribution by size in the jet of sprayed coal-water fuel. It was experimentally established that substitution of water (no more than 3 % by weight) in the composition of coal-water slurry by fairly typical alcohols leads to decrease in droplet velocities of alcohol-coal-water slurries in comparison with conventional coal-water fuel by 15–18 %. Concentration of sufficiently small fuel droplets (up to 200 microns) increases by 13.4±0.2 % and by 6.6±0.2 % during atomization of alcohol-coal-water slurries with addition of ethyl and isoamyl alcohol, respectively. Introduction of no more than 5 % by weight of the studied alcohols into the coal-water slurry will reduce the cost of fuel by 15–73 % in comparison with fuel oil. Influence of small additives of ethyl and isoamyl alcohol in the composition of coal-water fuel on spraying characteristics proves the possibility of efficient application of such three-component slurries in thermal power engineering. The results obtained are of practical significance, since they illustrate the possibility of reducing the ignition delay time for droplets of alcohol-coal-water slurries after they are sprayed in the furnaces of boiler units.

Экспертная диагностика интенсивности процессов шлакования и надёжности работы поверхностей нагрева пылеугольных паровых котлов

The article is devoted to the development of a system for the technical diagnostics of slagging processes and contamination of the heating surfaces of coal-fired steam boilers, which operates online based on the interpretation of the standard information of ACS TP and scientifically proved algorithms for processing balanced equations to evaluate the thermal efficiency of radiation, semi-radiation and convective heating surfaces. The system is implemented at the level of algorithmic data and software in the programming language C #, which is built into the current system of the automatic control system of the boiler unit. The project aims to increase the reliability, efficiency and economy of steam boilers by quick maintenance of heating surfaces in an operational clean state, ensuring optimal performance characteristics of the main technological equipment. This system is at the trial operation stage at the BKZ-500-140 boiler unit, station No. 6 of JSC Krasnoyarsk CHP-2. The expected effect of the introduction of this boiler due to the reduction of the blowing cycles and the decrease in the slagging intensity will amount up to 2.175 million roubles annually per one boiler unit.

Enhancement of Technical and Economic Indicators of Power-Generating Units of Thermal Power Plants by Eliminating Flue Gas Recirculation

Boiler units at Ukrainian thermal power plants need to be modernized or replaced in the short run, as this is important for the national energy security. The authors determined one of possible ways to improve the efficiency indicators of coal-fired boiler units and power generating units as a whole up to the values exceeding the design ones. This variant of improvement consists in abandoning the technology of using flue gas as drying agent in pulverized coal systems and replacing it with direct discharge of the gas flow into the boiler furnace. Numerous computations were carried out to study the change of efficiency indicators and manoeuvrability of power generating units due to the replacement of the ball mill pulverizing system using flue gases for coal drying with the scheme including ball-and-race mills that use hot air as drying agent.

Designing Transactive Market for Combined Heat and Power Management in Energy Hubs

This paper introduces a transactive market design for a combined heat and power (CHP) based energy hub (hub). The proposed model allows a hub operator to supply the hub’s demands by participating in the day-ahead market and a transactive market with CHPs and also in the real-time market by using a recursive moving window algorithm. The proposed local energy market for a hub operator and CHPs is based on the double auction P2P trading mechanism. The model develops an optimal bidding and offering strategies for CHPs and hub operators, respectively, to achieve optimal transactions. The CHPs may be equipped with boiler unit and heat buffer tank (HBT) beside CHP units. The uncertain nature of the hub’s electrical load, real-time and day-ahead markets prices and wind speed is addressed by using robust optimization. The procedure aimed at minimizing the worst-case CHP-based hub’s demand procurement cost even though flexibly regulating the solution robustness. Further, case studies investigate the economic impact of robustness on the hub’s cost.

Расчетно-теоретический анализ влияния влажности топлива на эффективность работы жаротрубного котлоагрегата при сжигании древесной щепы

The article presents the results of a computational and theoretical analysis of the performance of the solid fuel boiler unit intended for wood chips combustion, the input fuel moisture content being of 10% to 50%. The authors consider the main design features of the solid fuel boiler unit equipped with a shielded furnace and fire-tube two-pass convective heating surfaces without turbulent movement intensifiers of combustion products. The influence of changes in the moisture content and the operating modes of the boiler unit on the main balance and operating values responsible for the thermal efficiency and economy of the boiler is analyzed.