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.

Decreasing NOx Emissions by Way of the Staged Fuel Combustion

The purpose of this scientific paper was to analyze the mathematical model built for the staged arrangement of the fuel combustion system and calculate the formation of nitrogen oxides throughout the boiler furnace height for the different distributions of thermal loadings along the full vertical extent of the combustion chamber. The obtained results enable the determination of the overall amount of nitrogen oxides formed in the boiler and it allows us to provide appropriate ecological indices for the boiler when regulating the air concentration in the burner rows. In practice, to suppress the formation of nitrogen oxides we often use such basic methods as low-toxic burners, staged fuel combustion, flue gas recirculation, etc. The analysis of the computations done allows us to draw a conclusion that the operation of the boiler with ecological indices that satisfy standard values of the European Directive 2010/75/EU is only possible for the load below 40 %. After reconstruction of the burner system and adjustment of the air supply system with the observation of above ecological norms the boiler power can be increased up to 80 % using the staged fuel burning with the ensurance of environmental performances during its operation. Computational and experimental data errors varied in the range of 8 % to 12 %. With the increase in the overall chemical incomplete combustion by 40 % to 60 % (q3) these losses are compensated by a decrease in absolute losses due to the boiler aggregate load and the losses through external walls (q5) due to an increase in the boiler power.

Simulation of thermal processes in the lining of the ship's boiler

Судовой котлоагрегат подвергается воздействиям высокого давления рабочего тела и температуры дымовых газов. Кроме того работа его осложняется также быстрой и частой сменой нагрузки. Для продолжительной и надёжной работы котлов необходимо обеспечить прочность их конструкций, в частности, футеровки. Судовые котельные агрегаты футеруются огнеупорными материалами, во многом определяющими срок службы котла. При тепловом воздействии на теплоизоляционные материалы футеровки возникают термические напряжения, приводящие к деформации, растрескиванию и разрушению кирпичной кладки. Однако ввиду сложности постановки прямого физического эксперимента пока нет однозначного ответа на вопрос, какие условия способствуют разрушительному тепловому воздействию на футеровку котла. Потому авторы предлагают исследовать тепловые процессы в кирпичной кладке методами математического моделирования. В прикладном пакете ANSYS R17.2 WORKBENCH была создана твердотельная модель элемента футеровки (кирпича), на которой исследовались стационарные и нестационарные процессы теплообмена с граничными условиями первого и третьего рода. В результате экспериментов установлено, что разность деформаций соседних слоев огнеупора пропорциональна градиенту температуры, причём в нестационарных режимах теплообмена величина температурного градиента может значительно превышать его значение в стационарных условиях. Если учесть, что при форсированной нагрузке температура дымовых газов в топочном объёме достигает предельных значений, а интенсивность конвективного теплообмена существенно возрастает, то температурные напряжения, возникающие в футеровке котла, могут превысить предел прочности огнеупора. The ship's boiler unit is exposed to the high pressure of the working fluid and the temperature of the flue gases. The operating conditions are aggravated with rapid and frequent alternations in load. To ensure continuous and reliable operation, boiler and its elements, including lining, design needs to be strong. Ship boilers are lined with fire resistant materials, which lining basically defines lifetime of a boiler. Any heat impact to lining insulation will result in thermal stress that leads to deformation, cracking and destruction of brickwork. However, as direct physical experiment is difficult to conduct, there has been no clear understanding as to what conditions cause destructive thermal impact to the boiler lining. In light of this, the authors propose to investigate thermal processes in brickwork by mathematical modeling methods. Using ANSYS R17.2 WORKBENCH application package, the solid model of the lining element (brick) was created and stationary and non-stationary heat exchange processes with the boundary conditions of the first and third order were investigated. The experiments showed that the difference of deformations of neighboring lining layers was proportional to temperature gradient, yet in non-stationary heat exchange mode the temperature gradient can be significantly higher than that in stationary conditions. Considering that in forced loading mode the temperature of flue gases in boiler furnace can reach its limit and intensity of convective heat exchange increases significantly, the temperature stress that occurs in the boiler lining can exceed the strength of fire resistant brickwork.

Development of a simplified methodology for furnace aerodynamics with vortex combustion of organic fuel modeling

This paper describes the process of developing a simplified methodology for furnace aerodynamics during the development or modernization of combustion schemes with direct-flow burners. This technique is based on the use of numerical modeling of air movement and turbulence phenomena in the furnace volume and allows for a relatively short period of time to analyze a large number of options for the burners and nozzles location. This is its advantage in comparison with the use of experimental modeling or numerical simulation with combustion when analyzing a variety of schemes. The model was developed on the basis of validated results of combustion processes numerical simulation in the K-50 boiler furnace. The paper presents the results of calculations performed for several variants of the simplified methodology. For further use, the option that best corresponds to full-scale studies taking into account the fuel combustion process has been selected. The main states of the methodology are formulated.

Study on Optimization Control of Hydrogen Sulfide Concentration in Coal-fired Boilers

H2S is an important element to high-temperature corrosion for the water-cooled wall of coal-fired boilers, thus, it is an effective means to prevent high-temperature corrosion through reducing the concentration of H2S near the boiler wall. Since the concentration of H2S in the boiler is closely related to the concentration of O2 and CO, the research on the distribution of H2S atmosphere in the boiler furnace was conducted in this paper. With the air distribution regulation as the means, local O2 concentration is increased, to avoid the accumulation of H2S near the wall and reduce high-temperature corrosion.

Numerical simulation of fuel staged swirl combustion in the invert furnace of boiler on advanced ultra-supercritical steam parameters

The paper considers the schemes of Kuznetsky lean coal combustion for the M-shaped boiler. With such a boiler profile, it is possible to significantly reduce the length of main steamlines, which is especially important for the advanced ultra-supercritical parameters of the superheated steam. The furnace in this boiler unit is performed downward (invert). In this work, the aerodynamics of 6 combustion schemes was simulated by means of computational fluid dynamics. All considered schemes were designed on the basis of direct-flow burners and nozzles. For the most aerodynamically reasonable scheme the thermal processes in the boiler furnace firing Kuznetsky lean coal have been simulated by means of computational hydrodynamics. The simulation results showed a high efficiency of fuel burnout: loss due to unburned combustible equaled 0.1%, carbon-in-ash loss equaled 0.8%. Carbon monoxide concentration at the furnace outlet in conversion to excess air equal α = 1.4 amounted 226 mg/m3, the nitrogen oxides concentration in the flue gases (in conversion to normal conditions) equaled 424 mg/m3. It is appropriate to use the results obtained in this research in the development of new solid fuels combustion schemes.

SUGGESTIONS OF NEW TECHNOLOGIES FOR PROCESSING COAL ON THE BASIS OF USING UNIVERSAL MODULES OF INDUSTRIAL DISINTEGRATORS/ACTIVATORS

The UMID/A developed by the authors of the present paper represent the devices, which are fully compliant with the nano energetics of the Sixth Technological Paradigm and possess unique technical characteristics (extremely high density of the magnetic induction, which is close to the hundred percent of the performance factor, low consumption of materials etc.) that provides for the possibility of grinding in those modules of various materials up to nano dimensions with the purpose of using the ground materials in various sectors of industrial manufacturing, chemistry and medicine. Unique characteristics of the UMID/A determined the possibility of using such disintegrators in the principally new, developed by us technologies for obtaining inexpensive alkaline nano-cements/concretes without additional annealing of the waste of mining and metallurgy productions, inexpensive and environmentally friendly pure arbolite made of alkaline cements, boiler furnace fuel, diesel fuel, lubricating preparations made of coal inexpensive carbon nanotubes and binders of brittle and not very demanded by the construction industry inexpensive materials.

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.

Digital Model of Boiler Furnace Processes

The normative method (NM) of thermal boiler calculation, which has been confirmed and refined multiple times, contains the structure of ideas and methods retained and adapted during the transition to digital technologies. As applied to the analysis of thermal processes in the boiler furnace with flare furnaces, this required the transformation of a large array of initial and reference data, which cannot be used unchanged in digital technologies, including computer-assisted. This applies to graphical and tabular data, which occupy up to 80% of the NM volume. The main regulatory elements of the digital model in this case are the temperature of adiabatic combustion of the fuel, the coefficient of attenuation of radiation by the combustion medium, the degree of emissivity of the furnace taking into account the size of the radiating layer, the coefficient of thermal efficiency of the furnace wall pipings, the resulting Boltzmann number and the final calculated value of the gas temperature at the exit from the furnace. The use of specific data for a boiler with D = 400 t/h made it possible to clarify the structure of analytical dependencies, as well as the magnitude of deviations from the standard values in the final temperature values. The paper presents a developed transition to dependencies accounting for the thermal power of the boiler and the type of fuel. The digital model adaptation to the boiler conditions with all types of fuel in use made it possible to determine the average deviations of the final parameters. Quantitatively, the entire material corresponds to the normative data, is presented digitally and corresponds methodically to the Mathcad-15 package. In contrast to acclaimed works in this area, all factors affecting the heat balance are represented by approximations taking into account temperature variability.