Boiler Design Research Articles

Research on selection optimization technology of air fan for ultra-supercritical circulating fluidized bed boiler

In recent years, with the improvement of the capacity and parameters of domestic CFB boiler units and the potential of technology from design, operation adjustment and equipment transformation, the CFB technology has been relatively mature, and economic indicators are significantly improved. The successful application of new technologies in project provides good conditions for the development of selection optimization technology of air fan. Combined with the application and project practice of the energy-saving technology of air fan for supercritical CFB boiler in service, the energy distribution of air fan after design and energy-saving transformation is quantitatively analyzed through the experiment. Based on this, the energy-saving technology of air fan is researched. From the low bed pressure design, selection optimization of air fan parameter and frequency conversion energy-saving, the selection optimization technology of air fan for ultra-supercritical CFB boiler is proposed, which provides a technical basis for the lower energy consumption technology of ultra-supercritical CFB boiler design in the future.

Modeling of the Coal Particle Behavior in an Ultra-Supercritical Boiler With Large Eddy Simulation

Abstract Large eddy simulation (LES) is becoming a promising tool for the design and retrofit of utility boilers. It explicitly calculates the large-scale eddies which play an important role in the particle behavior inside the boilers. An ultra-supercritical tangentially fired boiler was simulated under the boiler maximum continuous rate (BMCR) condition by LES. The particle phase was tracked by the simplified direct quadrature method of moments in the Eulerian framework. Five particle sizes were adopted to represent the wide particle size distribution. The predicted gas velocities were in good agreement with the thermal calculation. The LES results showed that the particles were more likely to be concentrated in the main burner zone while quickly dispersed in the over fire air (OFA) zone. A theoretical analysis found that the particle Stokes number based on the sub-grid scale was much smaller than one. The particles would behave as tracers for the eddies resolved by LES. However, some differences between the small and large particles were observed in the particle number density distributed along the vertical and horizontal directions. It meant that the inertial effects on the particle motion cannot be neglected.

Chemical study of fly ash deposition in combustion of pelletized residual agricultural biomass

Agricultural residual biomass has great potential as an energy source, but is used only to a limited extent mainly because of the characteristics of its ash (quantity and composition), which can lead to problematic phenomena during combustion, among them fly ash deposition, the focus of this study. A previous work presented the results of laboratory experiments carried out using a fixed-grate reactor and involving four different agropellets under different operating conditions; the variables tested were deposition rate, bottom ash proportion and sintering degree during combustion. Based on these results, the analysis has been taken further and the fly ash deposits collected during these tests have been characterized by SEM-EDS and XRD. A methodology to differentiate between deposits caused by condensation (including thermophoresis and turbulent diffusion) and by inertial impact of coarse fly ash entrained from the bed has been proposed. Deposition by condensation has been found to decrease for higher values of excess air ratio in all cases. Conversely, deposition by inertial impact does not show a common behavior, due to the influence of bottom ash sintering degree and fuel composition. The ultimate aim of this study is to gain a better understanding of fly ash deposition, in order to develop better fuel blends, boiler design and operating parameters, enhancing the market penetration of agricultural residual biomass.

Numerical simulation of combustion in a biomass briquette chain boiler

A bed and furnace integrated model of biomass briquette chain boilers was built on basis of theories of computational fluid mechanics, heat transfer, thermodynamics, and chemical reaction kinetics. The combustion in the biomass briquette chain boilers was characterized under five working parameters (air-preheating temperature, fuel bed thickness, grate advancing speed, particle diameter, air supply mode) through experimental design, numerical simulation, and mathematical programming. Finally, these parameters were optimized with the ant colony algorithm. It was found that the combustion efficiency and economic benefits were both optimized at the air-preheating temperature of 553.22 K, fuel bed thickness of 0.16 m, particle diameter of 0.02 m, and uniform centered air supply. This study offers some theoretical basis and method for the optimized design and operation of biomass briquette chain boilers.

Heat exchanger simulation and recovery device design of waste heat boiler of gas turbine generator set on ocean platform

Heat exchanger simulation and recovery device design of waste heat boiler of gas turbine generator set on ocean platform

Study of circulation ratio for natural circulation in water-tube boiler at different operating conditions.

The basic objective of the paper is to identify the desired circulation ratio for the natural circulation of water tube boilers in different operating conditions. This requires the basic study of heat flux and the mode of the boiling heat transfer, and the phenomenon like departure from nucleate boiling and tube overheating. The parameters, which need to be studied are heat flux, pressure, dryness fraction, void fraction, liquid velocity and their impact on the required circulation ratio. For a natural circulation boiler, the circulation ratio is one of the most important design parameters as the other design parameter like critical heat flux and skin temperature are mainly derived from the circulation ratio. The required circulation ratio can vary with the boiler pressure, liquid velocity and maximum heat flux. This study is intended to provide input for the safe and optimum design of a natural circulation boiler.

Desired Circulation Ratio for Natural Circulation in Water-Tube Boiler

The basic objective of the paper is to identify the desired circulation ratio for the natural circulation of water tube boilers in different operating conditions. This requires the basic study of heat flux and the mode of the boiling heat transfer, and the phenomenon like a departure from nucleate boiling and tube overheating. The parameters, which need to be studied are heat flux, pressure, dryness fraction, void fraction, liquid velocity and their impact on the required circulation ratio. The present work is to develop a circulation analysis model for the natural circulation of the water tube boiler and to check the boiler design for different failure modes. For a natural circulation boiler, the circulation ratio is one of the most important design parameters as the other design parameter like critical heat flux and skin temperature are mainly derived from the circulation ratio. The required circulation ratio can vary with the boiler pressure, liquid velocity and maximum heat flux. This study is intended to provide input for the safe and optimum design of a natural circulation boiler.

Simulation of Mass Flow Rate of Air through Rectangular Split Duct

Adequate supply of oxygen is essential for the complete combustion of fuel in the furnace of a boiler and defective duct design may cause serious loss in the boiler efficiency due to incomplete combustion. In boiler there is a system which controls the air flow rate reaching to the furnace. FD fan helps to build the pressure and force the air to pass through the duct and wind box. In wind box, this air will be sent to the furnace for helping combustion process. The main objective of this work was to simulate the flow of air from blower to the inlet of a wind box through rectangular split duct to see whether it could provide improved flow conditions and to see whether there was equal mass flow rate of air through both the legs of a split duct. The purpose of providing a split duct was to eliminate one blower which would otherwise be required for two separate ducts arrangement. A 3D model using CFD was prepared to capture the changes in the mass flow distribution in the duct at two different outlets. Through this analysis, it was found that the mass flow rates of air through the two legs of the split duct were not equal. The damping needs to be provided for the duct having longer length in order to have equal mass flow rate of air through both the legs of the duct.

English

English

Large eddy simulation of a 660 MW utility boiler under variable load conditions

Large eddy simulation (LES) has become a promising tool for pulverized coal combustion with the development of computational fluid dynamics (CFD) technologies in recent years. LES can better capture the unsteady features and turbulent structures of coal jet flame than Reynolds averaged Navier Stokes (RANS). The coal-fired power plants in China are now required to be operated in a wide load range and quickly respond to the electric grid. The boiler performance of variable loads should be evaluated in terms of flow, heat transfer, and combustion processes. In this paper, LES was applied to simulate a 660 MW ultra-supercritical boiler under BMCR (boiler maximum continue rate), 75%THA-100, and 50%THA-100 conditions. The predicted gas velocities agree well with the thermal calculation and the temperature error is less than 130 K. The simulation results show that the operation load has significant effects on the boiler performance. It is also proved that LES can provide guidance for the design and operation of advanced coal-fired boilers.

Design-Based Thermal Efficiency Correction Method for Hot Water Boiler

In the boiler design process, the thermal efficiency of the boiler operating under specified parameters is given in accordance with the design specifications. However, under the actual operating conditions, the specified parameters in the design book cannot be met at the same time. Especially for the hot water boiler, the coal quality component and the deviation of low calorific power, the feed water temperature and the ambient temperature will directly affect the operating efficiency of the boiler. In the current boiler energy efficiency test standards, the test conditions are very demanding. It is required to be the design coal type and it also gives fluctuation ranges for several parameters that affect the boiler operation efficiency. For non-design conditions, the boiler operation condition test method can only be executed referring to the standard. However, the measured efficiency is highly variable. This paper aims to analyze and study several parameters affecting boiler efficiency based on the perspective of boiler design, and give corresponding efficiency correction method to provide reference for the correction of energy efficiency test results under non-design conditions.

Laboratorijskim istraživanjem do izbora mjesta uvođenja stepenovanog vazduha za sagorijevanje u ložište

In general, the mixing the reactants is very important to the process and the rate of combustion of each fuel, especially low-ranked coals with low reactivity. The appropriate excess air coefficient for combustion and the position and mode of supply of individual portions (air sta- ging) of the total air in the furnace are one of the key influ- encing factors for the mixing, respectively the efficiency of the combustion process, and the level of emissions. Today, the air staging (primary, secondary, tertiary and over fire air-OFA) is an indispensable process in the design of new industrial and energy boilers. Also, this measures are used for the reconstru- ction of existing furnace of large boilers. The implementation of this primary measure in the furnace does not require signi- ficant financial resources - the costs of investing in the intro- duction of air staging supply for combustion in the furnace are very low in relation to the multiple positive effects and bene- fits of such a system, especially a lower NOx emissions. However, the first condition for the correct and reliable design of the air staging system in the furnace is the choice of the optimal position for the supply OFA air. Determination of this position on the furnace depends on several factors, primarily the type and characteristics of the fuel, grinding quality, co- mbustion technology, furnace structure, type, number and arra- ngement of burners. On this topic, the Faculty of Mechanical Engineering of the University of Sarajevo, in the Laboratory for Coal and Biomass Combustion, conducted extensive rese- arch on the pulverized combustion of coal blends of the Ce- ntral Bosnia Mining Basin, including co-firing of these coals with waste wood biomass (beech and spruce sawdust). Here is presented some of the results of those NOx emission studies for different fuels and combustion temperatures, depending on the mode of supply and the positions of the combustion air supply in the boiler furnace.

Numerical simulation of combustion and emission of blast furnace gas boiler

Taking an 110t/h full-fired blast furnace gas boiler as the research object, the numerical simulation method is used to calculate the combustion process in the furnace. The influence of flow field on combustion is analyzed, and the influence of air preheating temperature and oxygen concentration on combustion and NOx emission is discussed, which provides a theoretical basis for optimal design and reasonable operation of blast furnace gas boiler. The results indicate that with the increase of air preheating temperature and oxygen concentration, the CO consumption rate is increased, the in-furnace maximum temperature and average temperature are increased to different extents, the temperature distribution is basically unchanged, and the NOx concentration at the furnace outlet is also increased. The NOx concentration multiplies as the oxygen concentration increases.

Design of a 1 t/h Biomass Chain Boiler and ιts Fuel Adaptability Analysis

The arch is an important component of a biomass boiler. Initial arch design of most boilers is generally gained through manual computation, thus resulting in uncertain reasonability of flue gas flow. Moreover, biomass fuels in the market have instable characteristics, which influence the utilization of biomass energies considerably. To address the problems concerning reasonable flue gas flow caused by the collaborative design of arch and air staging and the combustion adaptability of fuels, a cold modeling experiment of a 1 t/h biomass boiler under different staged air distribution ratios when the rear arch coverage varies was conducted using Fluent software in this study after thermal performance computation and initial structural design of grate and furnace. Furthermore, a boiler performance test based on main fuels and a combustion adaptation test of auxiliary fuels were also performed. The experiments show that the best flue gas flow in the furnace is achieved when the rear arch coverage is 60% and the primary–secondary air distribution ratio is 4:6. The mean boiler efficiency and the mean boiler heat output are 81.26% and 715.76 kW/h by using Pinus koraiensis pellets, wood–straw mixed pellets, and cotton straw briquettes as main fuels; and the tested pollutant emissions are in compliance with the limits of the national standard. The results of the combustion adaptation test reveal that the excessive particle size, the high ash content and the relatively low calorific value of biomass molded fuels are all against the combustion of biomass boilers. Fuel upgrading based on washing process and other methods is suggested. This study can provide references to the performance optimization of traditional small-scale biomass chain heating boilers.

ОБ ОДНОМ РЕШЕНИИ ЗАДАЧИ ВЫБОРА КОЛИЧЕСТВА И МОЩНОСТИ КОТЛОВ ПРИ ПРОЕКТИРОВАНИИ КОТЕЛЬНОЙ УСТАНОВКИ

Introduction. The problem of energy saving in the housing and communal services sector is the most urgent problem of the present time; its solution is possible, including through a rational choice of the technical composition of the boiler plant. Therefore, consideration of the boiler design issues is an important task. Objective. Consider the task of choosing the number and capacity of boilers for the designed heat supply source. Materials and methods. The methods for solving this problem, which are available in the literature, are analyzed. It is indicated that the task is very diffi-cult, primarily because of its multicriteria, and that in the literature on its solution there are recom-mendations mainly of a qualitative nature. Results. A new formalized calculation method is pro-posed, which includes three options for solving this problem. It is established that the number of boilers in the boiler room in all three calculation options does not at all depend on the calculated heat load, but is determined only by the calculated and permissible internal air temperatures, as well as by the calculated and average outdoor temperatures for the heating period. A larger number of boilers is obtained when calculating according to the first option, and a smaller number when calcu-lating according to the third option; therefore, the first option is preferable in the sense that when it is implemented, it is possible to have a nominal or close to nominal mode of operation of the boilers during the entire heating period. This is achieved by changing the number of boilers included in the operation. The second solution to the problem involves the installation of two types of boilers in the boiler room, and in the other two versions the boilers are of the same type. It is noteworthy that the rated power of the boilers calculated according to the first option is equal to the rated power of the boi-lers calculated according to the second option for operating conditions at an average outdoor tempera-ture of the heating period. The rated power of the additional boiler for the second option is equal to the rated power of the boilers for the third calculation option. Conclusion. The developed technique allows to streamline the procedure for selecting possible options for the technical composition of a boiler room, reduces the number of such possible options, what subsequently (during the economic analysis, as well as, in general, when designing) helps to reduce the amount of computational work. The tech-nique has been tested on a specific example and is recommended for use in solving design problems.

Numerical Simulation of Annular Flow boiling in Millimeter-scale Channels and Investigation of Design Parameters Using Taguchi Method

As the technology progresses, the electronic components become smaller and at the same time continue to produce more heat, and therefore development of new high heat-flux cooling technologies have become obligatory. The mini and millimeter-scale phase change cooling systems, which have a reduced size and a large surface area where heat transfer can take place, have become an integral part of advanced cooling systems. When comparing phase-change cooling systems with other cooling systems, a relatively low flow rate of very high evaporation heat, which is associated with the phase change for most fluids, allows large amounts of heat to dissipate with flow boiling and substantially solves the many problems. The two-phase cooling technologies used for critical applications include; heat pipes, loop heat pipes and capillary pumped loops which are all passive hence very reliable solutions relying on only capillary effects. Though this passive device cannot meet future high cooling demands because of the limitations of the capillary pumping in terms of heat flux, transport distance and multiple heat source capabilities. On the other hand, in boiling and condensing flows functionality problems arise since at the micrometer and millimeter-scale, shear/pressure forces dominate over gravitational forces and cause thermally hydro-dynamically ineffective/problematic liquid-vapor configurations – such as plug/slugs flow regimes. For this reason, to overcome the requirement of large amounts of heat transfer from limited spaces and resolving the above problem, novel millimeter-scale phase-change devices should be developed. In this study, for the design of millimeter-scale boilers a 3D Ansys-Fluent© simulation model was developed and numerical simulations were conducted for two different cooling fluids (water and FC-72), different mass flow rates and two different channel heights. Moreover, to examine the simulation results Taguchi method was used. In order to realize thin film annular flow over the boiler surface, employed specific boundary conditions in the 3D simulation model were obtained by means of one dimensional Matlab© simulation code. By means of utilizing the evaluated numerical results, distribution of heat transfer coefficient, vapor quality and pressure drop over the heat transfer surfaces were reported.

The competitive behavior for O2 and CO2 reaction during char oxy-fuel combustion: effects of temperature and inherent minerals

Coal O2/CO2 combustion is a promising carbon capture and storage technology for coal-fired power plant. Char consumption rate prediction is essential for the boiler design, but challenging for O2/CO2 combustion since char reaction behavior within dual reactive gas media is complex. There is also a doubt of whether or not the O2 reaction and CO2 reaction occur independently, whereby the overall rate would be simply additive, or the two reactions compete for the same char actives, in which case the rate prediction could be more complicated. Here, the competitive behavior for O2 and CO2 reactions of char active sites was investigated via thermogravimetric approach, with a focus on the effect of temperature and inherent mineral composition. For char combustion within O2/CO2 environment with molar fractions of 30/70, the contribution of O2 to char consumption is the same as the O2 reaction alone. However, as being out-competed by O2, only 37% CO2 could occupy char active sites and react. Consequently, the overall char reaction rate within O2/CO2 is only 83% of the sum of that for individual gases at 900 °C. With increasing temperature, this ratio becomes even smaller, as the contribution of CO2 that being out-competed (to the sum of individual gases) is larger. With increasing O2 fraction, it occupied more active sites, thus further inhibiting CO2 reaction. The inherent alkali and alkaline earth metal provides the char with more active sites, thus muting the competition and inhibition for CO2 gasification.

Evaluation of a distributed combustion concept using 1-D modeling for pressurized oxy-combustion system with low flue gas recirculation

Although process modeling of the pressurized oxy combustion (POC) with low flue gas recirculation (FGR) approved a great potential for CCUS cost reduction, there is no globally agreed concept for the boiler design that can satisfy the technical requirements of PC (pulverized coal) boiler operation. In this paper, a new concept for the boiler design and firing configuration based on distributing the combustion into multi-burner levels along the boiler height was evaluated using 1-D modeling. The 1-D model is mainly based on Gurvitch method to deal with radiation exchange between hot flue gases and water walls. Distributing combustion is proved to have remarkable potentials to control the peak flame temperature and heat flux. Two boiler sizes based on 30% and 53% FGR were analyzed which satisfied the critical indexes of the PC boiler operation. Finally, it was shown that distributed combustion concept has good potentials to operate under two abnormal conditions: i) with zero slag thermal resistance on the wall and ii) under low boiler operational load.

The design, fabrication, and performance evaluation of a locust bean boiler

African locust bean is a leguminous plant that is rich in nutrients and is used as food condiment. The traditional method of processing this food condiment is mostly unhygienic; consume a lot of fire wood, human energy and time. Using traditional methods for boiling 33.7Kg of locust bean would take about 12 hours. This study attempts to mechanize the existing traditional methods of boiling locust bean by designing, constructing, and evaluating electrically powered locust bean boiler. The boiler consists of three composite drums, each with a cylindrical upper part and conical lower part. The boiling chamber is made of 304 austenitic stainless steel which contains the heating elements. Fibre glass is lodged between the steel materials as an insulator. As power is supplied to the boiler, the elements convert the electrical energy to heat energy attaining the temperature of 200.7°C in 5 minutes. The machine has the capacity of boiling 33.7Kg of locust bean in 1 hour at 90°C. The cost of producing a unit is ₦20,207.5.

Micro-generation technologies and consumption of resources: A complex systems’ exploration

This study is motivated by a research gap in the systemic implications that wider adoption of multiple micro-generation technologies may bring to interdependent infrastructures. It explores how the adoption of battery electric vehicles, solar photovoltaics, solar thermal water heating, rain water harvesting, grey water recycling, and waste heat recovery affect system-level consumption of water, gas, gasoline, electricity, CO2 emissions, and electricity generation cost. The simulations based on a new agent-based model show that grey water recycling and rain water harvesting reduce water and solar thermal water heating and waste heat recovery reduce gas demand respectively. A wider adoption of battery electric vehicle and solar photovoltaics have no effect while a reduction in the number of gasoline cars and gas users leads to higher electricity consumption, CO2 emissions, and electricity generation cost. The following policy implications are identified: grey water recycling and rain water harvesting should be actively promoted; improvements in the design and use of gas boilers may be better options than solar thermal water heating and waste heat recovery; battery electric vehicle should be adopted together with solar photovoltaics; solar photovoltaics should not be supported with feed-in-tariffs. If the last two implications are not addressed, then a more complementary electricity generation mix is necessary otherwise policies that promote replacement of gasoline cars by battery electric vehicles may result in negative systemic impacts.