Coal-fired Boilers Research Articles

A dynamic modeling method using channel-selection convolutional neural network: A case study of NOx emission

A novel channel-selection convolutional neural network (CS-CNN) is proposed to predict NOx emission from coal-fired boilers under steady-state and transient load conditions. First, a new channel-selection convolutional layer (CS-CL) is presented to replace regular convolutional layer (RCL). The CS-CL evaluates the channel importance of the input variables, selects the Top-C important channels and releases the hyperparameters of the remaining low-importance channels, thus contributing to maximize the utilization of the parameter resources of the model. The advantages of using CS-CLs are the preservation of the great majority of manipulated variables involved in combustion control among the input variables and the prevention of the model overfitting problem due to the redundancy of input variables. Second, a sliding window-based preprocessing method is applied to the historical data of the boiler which is divided into four-dimensional (4D) tensors. Then, comparative tests are performed on long short-term memory (LSTM) model, baseline CNN and CS-CNN using the historical data of a 670 MW boiler. The results of tests showed that CS-CNN has higher prediction performance. Finally, in order to increase the interpretability of the deep learning black box model, this study analyzes the working mechanism of the CS-CNN through ablation analysis and visualization of model parameters.

Methanol-based fuel boiler: Design, process, emission, energy consumption, and techno-economic analysis

Methanol-based alternative energy sources are critical to maintaining energy security, reducing the need for oil imports, and safeguarding the environment in China. However, the use of methanol-based fuels in the field of thermal combustion has not been thoroughly investigated. Therefore, an evaluation of the costs, emissions, and usage of methanol boilers is necessary. The study finds that methanol heaters and air source heat pumps have comparable annual cost values. Methanol heating furnaces emit the least amount of NOx and produce no SO2. After the refurbishment, the boiler's emissions and energy consumption have significantly decreased upon conversion of coal-fired steam boilers to methanol-based fuel hot water boilers. Nevertheless, the economy has also somewhat declined. Additionally, 5499 tce (standard coal) less energy will be used during the heating season, and 1.8 million CNY less will be spent on dust removal and desulfurization. Unfortunately, the economic benefits of methanol are only apparent when the cost of methanol fuel is less than 1900 CNY/t. The research presented in this paper provides an essential technological foundation for the development of methanol-fueled fuel burners and for the renovation of small and medium-sized coal-fired boilers.

Numerical Simulation Study of Hydrogen Blending Combustion in Swirl Pulverized Coal Burner

Hydrogen blending of pulverized coal in boilers is a promising technology. However, there are few studies on hydrogen blending in coal-fired boilers. In order to reduce CO2 emissions from coal-fired boilers, this study investigates the co-combustion of pulverized coal and hydrogen in a swirl pulverized coal burner by numerical simulation. Itis shown that the burnout rate of fuel is 5.08% higher than that of non-hydrogen blended coal when the percentage of hydrogen blended is 5%. The water vapor generated by hydrogen blending not only leads to the formation of a low-temperature zone near the burner outlet; it also results in a prolonged burnout time of moist pulverized coal and a high-temperature zone near the furnace outlet. The greater the amount of hydrogen for blending, the higher the water produced. When 1–3% hydrogen is blended, the water vapor in the furnace reacts with the carbon to produce a large amount of CO. When the amount of hydrogen added to the furnace is more than 3%, the water content in the furnace rises, resulting in a lower temperature at the burner outlet and a decrease in the amount of CO produced. When 1–3% hydrogen is blended, the CO2 emission rises. The CO2 emission decreased by 1.49% for 5% hydrogen blending compared to non-hydrogen blending and by 3.22% compared to 1% hydrogen blending.

Research on laser online monitoring equipment for high-temperature corrosive gas in coal-fired boilers

Research on laser online monitoring equipment for high-temperature corrosive gas in coal-fired boilers

Optimizing Two-Phase Flow Heat Transfer: DCS Hybrid Modeling and Automation in Coal-Fired Power Plant Boilers

Optimizing Two-Phase Flow Heat Transfer: DCS Hybrid Modeling and Automation in Coal-Fired Power Plant Boilers

Direct numerical simulation of the drag, lift, and torque coefficients of high aspect ratio biomass cylindrical particles

Biomass straw fuel has the advantage of low-carbon sustainability, and therefore, it has been widely used in recent years in coupled blending combustion with coal-fired utility boilers for power generation. At present, the drag force FD, the lift force FL, and the torque T evaluation model are very limited. In this study, within a wide range of Reynolds numbers (10 ≤ Re ≤ 2000) and incident angles (0° ≤ θ ≤ 90°), the computational fluid dynamics open source code OpenFOAM-body-fitted mesh method is used to carry out the direct numerical simulation of the flow characteristics of large cylindrical biomass particles with a high aspect ratio of L/D = 9:1. The results show that (1) the projected area of the cylinder begins to decrease after reaching the maximum at θ = 15°, while the change in the incident angle causes the formation of a smaller recirculation zone on the leeward side of the structure, and the effect of the pressure difference on the drag coefficient (CD) is reduced. (2) The lift coefficient (CL) displays a parabolic symmetric distribution when θ = 45°, and then the distribution becomes asymmetrical when Re > 100. The torque coefficient (CT) exhibits a similar trend. (3) Based on the simulation data and the literature data, new models for CD, CL, and CT for cylinders with L/D = 9:1, 10 ≤ Re ≤ 2000 and 0° ≤ θ ≤ 90° are obtained, and the mean square errors are 2.4 × 10−2, 1.4 × 10−2, and 6.4 × 10−2, respectively. This new model can improve the accuracy and adaptability of the universal model of gas–solid dynamics for biomass particles.

Corrosion fatigue property of 2.25Cr-1Mo steels in a high-temperature sulfide corrosion atmosphere simulating the inside of a pulverized coal-fired boiler

Corrosion fatigue property of 2.25Cr-1Mo steels in a high-temperature sulfide corrosion atmosphere simulating the inside of a pulverized coal-fired boiler

Research on combustion visualization of coal-fired boilers based on thermal imaging technology

At present, there?s a lack of combustion visualization in the combustion control of heating boilers. To understand the combustion of coal in the furnace, only experienced workers can observe it through visual inspection. Using infrared thermal imaging technology to monitor the combustion can realize combustion visualization. This paper analyzed and solved two problems: the installation position and number of infrared cameras, and the infeasible of using infrared cameras observing the combustion condition in the furnace through heat-resistant glass. Monitored parameters such as oxygen content, furnace temperature and smoke exhaust temperature, and monitored the concentration of PM, NOx, and SO2 in the main atmospheric pollutants in the flue gas. After calculation, the air leakage coefficient when the inspection doors are opened for observation is 0.04. This value still includes the sum of air leakage from coal hopper, furnace door, grate side seal, peep holes and other parts. The monitored average emission concentration of PM decreased by 16.28%, from which we can concluded that the use of thermal imaging technology to monitor the combustion in the furnace is conducive to emission reduction. The application of thermal imaging technology implementation of coal-fired boiler combustion visualization is feasible.

Numerical investigation of boiler waterwall corrosion by integrated tube temperature prediction and sulfur evolution model

High temperature corrosion has become one of the leading causes of boiler waterwall tube failures because of the wide application of air-staged combustion in coal-fired boilers. High temperature corrosion is strongly affected by the H2S concentration and wall tube temperature distributions in the furnace. Particularly, the corrosion rate increases exponentially with the increase of tube temperature. However, by far most of the numerical studies on high temperature corrosion only considered the effects of H2S concentration while the critical effects of tube temperature were overlooked. Thus, this paper presents a comprehensive corrosion model that incorporates the key effects of both tube temperature and H2S concentration. Specifically, the tube temperature is predicted by a coupled combustion and hydrodynamic model that integrates the critical effects of both the boiler gas flow and steam flow on waterwall tube temperature. The H2S concentration is predicted by a sulfur evolution model describing the devolatilization process of coal sulfur species and their subsequent gaseous reactions. The tube temperature prediction model and H2S evolution model provide all the key parameters for accurate prediction of boiler waterwall corrosion. The corrosion model is applied to a 350 MW supercritical wall-fired boiler. The results show that the tube temperature varies significantly over the boiler waterwall, and hence, has significant impacts on the distribution of wall tube corrosion. Particularly, local high tube temperature zones could form on the waterwall areas of relatively low H2S concentration leading to substantially higher tube corrosion rates than the adjacent wall areas. The results demonstrate the importance of incorporating both the wall tube temperature and H2S concentration in the prediction of boiler waterwall corrosion.

Addressing challenges in high-temperature oxidation of ultra-supercritical boiler tubes via FeCoNiCrMo high-entropy alloy coatings

The engineering realm confronts formidable challenges in combating the persistent issue of high-temperature oxidation in ultra-supercritical coal-fired boiler tubes. This study is dedicated to tackling these challenges by employing high-velocity oxy-fuel spraying (HVOF) and high-frequency induction remelting techniques. Our primary objective is to establish a metallurgical bond between self-fusing FeCoNiCrMo high-entropy alloy (HEA) powder and the conventional 15CrMo boiler steel tube surfaces, all within ambient atmospheric conditions. Our investigation reveals two distinct stages of oxidation for the HEA coating when exposed to a 900 °C air environment. Initially, there is a rapid oxidation stage driven by interfacial reactions, followed by a steady-state slow oxidation stage influenced by ion diffusion. The presence of a dense Cr2O3 layer plays a pivotal role in reducing the oxidation rate significantly, thereby imparting exceptional high-temperature oxidation resistance to the FeCoNiCrMo HEA coating. Notably, during the steady-state stage, the oxidation rate is two orders of magnitude lower than observed in Ni-based superalloys. Minimal phase transformations or transitional layers at the interface underscore superb interface bonding at 900 °C. These findings provide a promising avenue for the cost-effective fabrication of highly oxidation-resistant ultra-supercritical boiler tubes. This advancement contributes significantly to the progress of engineering applications.

Reducing Mercury Emissions from Small-Scale Coal-Fired Boilers Used in Residential Heating

Aim: The aim of the research was to demonstrate that the use of low-emission carbon fuels (obtained using the initial thermal conversion of coal feedstock) in residential heating also makes it possible to reduce mercury emissions from small-scale coal-fired boilers. Project and methods: The publication presents the results of mercury emission tests conducted using five different small-scale coal-fired boilers and five different coal fuels. The research was carried out under laboratory conditions, but also using heating devices of residential users. They covered a wide range of operational parameters, both energy and emission. The flux of coal fuels burned ranged from 2 to 12.2 kg/h, with an equally wide range of boiler efficiencies obtained – 67.6–88.5%. Results: The test results presented in the article show that the amount of emissions of pollutants limited by the criteria of the PN-EN 303-5+A1:2023-05 standard and the ecodesign, namely carbon monoxide, nitrogen oxides, dust and organic substances, depends mainly on the design and operating conditions of the device in which the specific solid fuel is burned. There is a group of pollutants emitted into the atmosphere, for which the amount of emissions depends primarily on the quality of the fuel burned. These pollutants include sulphur oxides and mercury, whose emissions depend primarily on the combustible sulphur and mercury content of the fuel being burned. Conclusions: Experimental studies were carried out to verify what portion of Hg contained in coal during its combustion in domestic boilers with manual and automatic fuel feeding remains bound in bottom ash, and what is emitted into the atmosphere. The content of Hg in bottom ash, regardless of the boiler and fuel used, was at a similar low level, reaching a maximum of about 6% of Hg initially contained in the fuel. As studies have shown, more than 94% of mercury contained in coal fuels burned in small-scale coal-fired boilers is emitted into the atmosphere, contributing significantly to the deterioration of the environment. Replacing traditional coal with low-emission carbon fuels (e.g., such as BC fuel) would significantly reduce mercury emissions from small-scale coalfired boilers, by up to 90% compared to current emissions. Setting a legal requirement for the permissible level of mercury content in coal fuels used in domestic boilers, for example, at a maximum value of 0.05 mg/kg, would reduce mercury emissions from these devices by at least half. Keywords: mercury emission, small-scale coal-fired boilers, low-emission carbon fuel

Four-Stage Multi-Physics Simulations to Assist Temperature Sensor Design for Industrial-Scale Coal-Fired Boiler.

The growth of renewable energy sources presents a pressing challenge to the operation and maintenance of existing fossil fuel power plants, given that fossil fuel remains the predominant fuel source, responsible for over 60% of electricity generation in the United States. One of the main concerns within these fossil fuel power plants is the unpredictable failure of boiler tubes, resulting in emergency maintenance with significant economic and societal consequences. A reliable high-temperature sensor is necessary for in situ monitoring of boiler tubes and the safety of fossil fuel power plants. In this study, a comprehensive four-stage multi-physics computational framework is developed to assist the design, optimization installation, and operation of the high-temperature stainless-steel and quartz coaxial cable sensor (SSQ-CCS) for coal-fired boiler applications. With the consideration of various operation conditions, we predict the distributions of flue gas temperatures within coal-fired boilers, the temperature correlation between the boiler tube and SSQ-CCS, and the safety of SSQ-CCS. With the simulation-guided sensor installation plan, the newly designed SSQ-CCSs have been employed for field testing for more than 430 days. The computational framework developed in this work can guide the future operation of coal-fired plants and other power plants for the safety prediction of boiler operations.

Development of a health monitoring framework: Application to a supercritical pulverized coal-fired boiler

This work details the development of a physics-based equipment health monitoring framework for a supercritical boiler, using first-principles models to estimate the remaining useful life (RUL) of its components. The framework accounts for fatigue and creep life consumption, generating spatio-temporal variations in mechanical and thermal stress. Analysis of the stress profile throughout the boiler highlights the finishing superheater inlet steam header as a vulnerable location susceptible to damage from cycling operation. The framework also yields quantified uncertainty in the RUL projection for specific locations, accounting for uncertainties in material properties and boiler operation. Results indicate that operational uncertainties (e.g., seasonal variation and operational strategy) and material properties (e.g., rupture time coefficients, Young's modulus, yield strength, and coefficient of thermal expansion) significantly impact the RUL of the finishing superheater inlet steam header. Additionally, case studies demonstrate the use of the health monitoring framework as a predictive tool for operational planning under uncertainty, including scenarios with and without updates on the operation of the boiler.

Dynamic characteristics and economic analysis of a coal-fired power plant integrated with molten salt thermal energy storage for improving peaking capacity

Improving the peaking capacity of coal-fired units is imperative to ensure the stability of the power grid, thus facilitating the grid integration and popularization of large-scale renewable energy. To address this issue, this paper introduces a new concept that combines molten salt energy storage with coal-fired power plants. The proposed design consists of extracting a portion of steam from the turbine side and adjusting the extracted steam mass flow rate by adjusting the valve opening to improve the dynamic characteristics of a coal-fired power plant in terms of both increasing the peaking depth and peaking speed. A coal-fired boiler with integrated thermal energy storage was dynamically modeled using Dymola and its accuracy was verified. The results show that the highest equivalent round-trip efficiency is achieved by extracting from the main steam and discharging into the feedwater during charging process and from reheater1 and discharging into the feedwater during discharging process; The peaking potential during charging and discharging is 12.83 % Pe and 6.86 % Pe respectively, with maximum peaking rates of 9.27 % Pe/min and 5.11 % Pe/min respectively, and the optimal peaking method is also proposed according to the different peaking situations. The total cost of equipment and materials to retrofit the conventional coal-fired units was 19,948,193 USD and the levelized cost of delivery was 151.29 USD/MWh.

Dynamic adaptive control of boiler combustion based on improved GNG algorithm

The boiler combustion process contains complex physicochemical changes, which is a nonlinear time-varying industrial process with strong interference and multivariate strong coupling. For this kind of boiler combustion process with typical nonlinear characteristics and complex mechanism, it is difficult to establish an accurate mechanism model by conventional modeling methods, so it is difficult to meet the new requirements for the optimal control of the boiler. The large amount of data accumulated in the operation process contains rich system information, and the data-driven modeling and control method provides an effective way for the operation optimization of the unit. Data dynamic characterization and control technology is an important means of data mining, coal-fired boiler data has obvious temporal and drift characteristics, for the current data tracking and supervision algorithms mostly lack of dynamics, real-time and stability issues, design an adaptive clustering model based on the improved growth of neural gas model (GNG), the establishment of nodes based on the probability, the range of the search, the average distance of node A node generation and deletion mechanism based on probability, range search and average distance of nodes is established to realize real-time monitoring of drift data. Finally, the experiments are carried out by analyzing the dynamic data of coal-fired boiler, and the experimental results show that the model and algorithm have stronger real-time tracking ability for dynamic drift data, and can accurately and effectively monitor and control the dynamic data of coal-fired boiler.

Thermodynamic and thermo-economic analyses of a coupled heat-pump system for low-grade exhaust-air heat exchange in mines

ABSTRACT Combining mine exhaust waste heat with existing heat pump technology is a promising technical route to realise the efficient extraction and scientific use of low-grade waste heat resources in mines and to solve the problem of insufficient heat supply in remote mining areas. This study proposes a new type of mine-exhaust-air heat exchange coupled with heat-pump waste-heat-utilisation system based on deep enthalpy heat extraction. Using a mining area in Northwest China as a representative case, this study establishes a systematic exergy analytical model and a thermo-economic model. Through an in-depth analysis of the different evaporation temperatures and condensing temperatures, the system’s energy efficiency ratio (COP) reaches its optimal performance, with the total exergy efficiency surpassing 90%. The minimum efficiency of the subsystem return air heat exchanger is 35%. The unit thermal costs of the mine exhaust air waste heat utilisation system and a conventional coal-fired boiler system are 0.1291 and 0.1573 million RMB/kW·h, respectively. This is a thermal economics cost saving of 21%. The studied system demonstrates great economic viability and the potential for energy saving throughout its life cycle.

Laser modification of heating surfaces: A new approach to reduce boiler slagging

Slagging and fouling of boilers are typical technological problems in the combustion of solid fuels (especially coal and biomass). This study proposes a novel approach based on laser texturing of the near-surface layer of steel used to make heating surfaces of coal-fired boilers. This approach is aimed at improving the resistance of metal surfaces to slagging. The formation of slag deposits on the surfaces of AISI 310 S steel modified by laser radiation has been experimentally studied. The formation of slag melt was analyzed on the surface of modified and polished steel plates during heating to 1400 °C. High-temperature heating and interaction with slag led to a change in the chemical composition of the steel. A significant increase in the chromium content (up to 47%) of the steel surface and the transformation of its texture with the formation of grains up to 2.5 µm in size were established. Laser surface treatment significantly increased the resistance of the steel to such changes and also reduced the grain size to 1.5 µm. As a result of laser modification of surfaces, the temperature of slag formation shifts to higher values (higher by 60–75 °C compared to the unmodified polished surface). The anisotropic texture (cauliflower type) contributed to a decrease in the size of the slag spreading front, and also had by self-cleaning properties from the mineral melt. The latter allows to increase the reliability and energy efficiency of boiler equipment.

An Effective Strategy for Monitoring Slagging Location and Severity on the Waterwall Surface in Operation Coal-Fired Boilers

It is of great importance to obtain the exact location and severity of slagging deposits on the waterwall surface of an operational boiler to avoid aimless soot-blowing and reduce steam consumption. In this paper, an effective waterwall surface temperature monitoring method is proposed to determine the slagging locations. It has been noted that the temperature difference of the waterwall surface before and after soot-blowing varied with the waterwall location, with more than 80 °C covered with slag and less than 20 °C found clean. According to this, a slagging temperature index was developed to describe the severity of slagging deposits on the waterwall surface. Results indicated that the process of slagging deposit growth included four stages, with the slagging temperature fluctuating in the range of about 90–110 °C in stage III, followed by a rapid drop below 60 °C in stage IV. Furthermore, a digital image monitoring system was used to validate the slag growth process and study the relationship between deposit thickness growth and area expansion. This novel approach provides automated and accurate guidance for each soot blower around the furnace, which reduces soot-blowing steam consumption and avoids serious slagging on the waterwall surface.

Spatiotemporal variation and inter-transport of atmospheric speciated mercury between Kaohsiung Harbor and neighboring urban areas

This study investigated the spatiotemporal variation, gas-particle partition, and source resolution of atmospheric speciation mercury (ASM) in Kaohsiung Harbor and neighboring Metro Kaohsiung. Four sampling sites were selected to determine the pollution characteristics and inter-transport of ASM between the port and urban areas. The yearly average GEM, GOM, and PBM concentrations were 7.13 ± 2.2 ng/m3, 331 ± 190 pg/m3, and 532 ± 301 pg/m3, respectively. Notably, GEM emerged as the predominant ASM species (85–94%), primarily originating from anthropogenic emissions from the harbor area and nearby industrial complex. The study revealed a distinct seasonal variation in ASM concentrations in the Kaohsiung Area in the following order: winter > fall > spring > summer. Concerning spatial distribution, ASM concentrations in the port areas were generally higher than those in the urban areas. This disparity was chiefly attributed to the influence of the prevailing winds, local sources, and atmospheric dispersion. Backward trajectory simulation revealed that polluted air masses blown from the northeast in winter and spring, moving along the western in-land part of Taiwan Island, were likely influenced by local sources and long-range transport (LRT). In summer, air pollutants originating from the south were likely transported from the coastal industrial sources. During fall, air masses blown from the western offshore waters transported air pollutants from Kaohsiung Harbor to neighboring Metro Kaohsiung. The results obtained from principle component analysis (PCA) indicated that primary sources in the port areas included ship emissions, vehicular exhausts, and nearby industrial complex, which align with the primary source factors identified by positive matrix factorization (PMF), which were mobile sources and coal-fired industrial boilers. Meanwhile, mobile sources and sulfur-containing fuel/waste combustion were identified as the primary sources in the urban areas.

Removal of multiple pollutants in air pollution control devices of a coal-fired boiler installed with a flue gas condensation scrubber

This work was conducted through field tests on a coal-fired circulating fluidized bed boiler with a condensation scrubber (CS) for flue gas waste heat recovery installed behind the wet flue gas desulfurization (WFGD) scrubber. Levels of multiple pollutants were investigated along various flue gas devices of the boiler, with the CS being the main focus. The CS demonstrated an excellent effect in removing filterable particulate matter (FPM), reducing it from 10.63–14.00 mg/Nm3 to less than 1 mg/Nm3, providing an alternative solution for ultra-low emission. The CS had the ability to remove SO2, reducing it from 211.8–272.0 mg/Nm3 to 11.1–13.0 mg/Nm3, which could be an aid to the WFGD scrubber. The CS showed an effect on SO3 removal, reducing it from 17.49–17.53 mg/Nm3 to 1.07–1.13 mg/Nm3, which might address the discharge of sulphate aerosols. The CS exhibited an effect in removing condensable particulate matter (CPM), reducing it from 29.68–38.48 mg/Nm3 to 12.18–22.80 mg/Nm3, providing a potential solution for CPM emission control. In addition, the escape of fine desulfurization slurry droplets from the WFGD scrubber could also be mitigated by the CS with the reduction efficiency of 88.30–90.51%. Overall, the synergistic removal of multiple pollutants including FPM, SO2, SO3, and CPM by the CS was verified in this case study. Considering its original function of waste heat recovery, the adoption of the CS is a promising measure for energy conservation and environmental protection.