Pulverized-coal Boiler Research Articles

Carbon-free power generation strategy in South Korea: CFD simulation for ammonia injection strategies through boiler burner configurations in tangentially fired boiler

To achieve carbon neutrality in power generation, incorporating ammonia-coal co-firing into coal-fired boilers effectively reduces CO2 emissions. Here, we aimed to optimize ammonia injection methods by investigating the feasibility of 20 % ammonia co-firing in a pulverized coal (PC) boiler through numerical simulations. These simulations aim to analyze the effects of different ammonia injection strategies and burner configurations on the combustion performance and NOx emission characteristics of a 500 MW tangentially fired PC boiler. Results showed that compared to using five burners, single-burner injection reduced outlet NO concentration by 22.72 ppm and unburned carbon content to 0.30 %, which is 0.80 % lower than multi-burner injection and even below the 0.45 % in coal-only combustion. The optimal case (burner A for ammonia injection) achieved a furnace outlet flue gas temperature of 1247.35 K, close to 1241.98 K in coal-only combustion, with the lowest NO emissions (193.89 ppm) among all ammonia co-firing cases. Positioning the single burner for ammonia injection revealed that utilizing the blending method with the ammonia injection burner, such as in the case of upper burner injection, increases both furnace temperature and high-temperature zone areas. However, employing in-boiler blending methods with lower-positioned burner ammonia injection distributes high-temperature zones more extensively. Comparing ammonia injection through coal and auxiliary oil burners, using only the lowest-level burner can significantly reduce NOx emissions while maintaining combustion and thermal efficiencies. This study is the first to simultaneously consider the number, position, method, and type of ammonia injection burners in large-scale commercial coal-fired boilers, providing a valuable reference for future research and practical boiler operations. This comprehensive analysis underscores how ammonia injection strategy and position can optimize ammonia-coal co-firing boiler performance.

Process system simulation of coupled pyrolysis disposal of domestic waste in coal-fired boiler and pilot study on dioxin emission

The disposal of domestic waste has become a critical and costly problem. Incineration for power generation is currently the primary domestic waste treatment method. Due to its small capacity and low parameters, domestic waste incineration is generally uneconomical and associated with significant risks to public health and environmental safety. The coal-fired power plants are generally characterized with huge capacity and high parameters, consequently resulting in much higher power generation efficiency with lower cost emission control. This indicates that co-disposal of domestic waste using existing coal-fired units may significantly reduce its treatment costs associated with the improvement of utilization efficiency and environmental risks. Base on this, a highly-flexible coupling of pyrolysis-pretreated solid waste in pulverized coal furnace is proposed in this paper, and field tests and numerical simulations have been carried out separately according to the process route. The results show that after coupling with pulverized coal boiler, domestic waste pyrolysis pretreatment unit can operate self-sustainably without external energy supply and the process route is feasible. Furthermore, the coupled co-combustion of domestic waste pyrolysis products and pulverized coal was simulated by fluent software. Compared with pure pulverized coal combustion, mixing domestic waste pyrolysis products can promote pulverized coal combustion in the furnace and help the pulverized coal boiler to burn stably at low load. The emission concentrations of NOx at the outlet of the furnace are 530 ppm, 545 ppm and 478 ppm respectively when pulverized coal is burned purely and mixed with 100 t/d and 200 t/d domestic waste. the NOx emissions could be reduced to a certain extent by mixing domestic waste. On the basis of previous research, the field test of coupling disposal of domestic waste by pulverized coal boiler was carried out, and the dioxin concentration in flue gas and fly ash was tested emphatically. The results show that when the amount of waste is less than 4 %, the concentration of dioxin in flue gas is 0.0107 ng TEQ/m3, which meets the latest emission standard of air pollutants in Shanghai coal-fired sludge power plant of 0.02 ng TEQ/m3. Low proportion of domestic waste will not increase the production and emission of dioxins. These studies show that it is feasible and promising to treat municipal solid waste with low coupling ratio by using existing coal-fired units.

Numerical investigation of stable combustion at ultra-low load for a 350 MW wall tangentially fired pulverized-coal boiler: Effect of burner adjustments and methane co-firing

In the context of deep peak regulation, utility boilers are often required to operate at ultra-low loads, significantly deviating from their designed conditions, which can lead to unstable combustion or even furnace flameout. However, their operating characteristics at 20 % or even lower loads remain unclear. This study focuses on a 350 MW wall tangentially fired pulverized-coal boiler, exploring its combustion characteristics and pollutant emission patterns at 20 % ultra-low load. Through numerical simulation analysis of 14 different combustion scenarios, this research investigates the impacts of burner arrangements, burner horizontal swing angles (ranging from 5° to 20°), and methane (CH4) co-firing ratios (ranging from 0 % to 20 %, calculated by heat value) on flue gas temperature and main flue gas components (O2, CO, NOx, etc.). The results indicate that as the boiler load decreases to 20 %, the average flue gas temperature inside the furnace drops by about 200 K, accompanied by widespread flame impingement on the water-cooled walls, leading to decreased combustion stability of the pulverized coal. Operating only the lower two layers of burners can achieve a higher average flue gas temperature (1540 K) and lower NO emissions (294 mg/m3). Furthermore, setting the horizontal swing angle of the burners to 15° can mitigate the impact of flames on the water-cooled walls and elevate the flame center, with the average flue gas temperature reaching 1559 K, making it the recommended burner swing angle setting. As the CH4 co-firing ratio increases from 0 % to 20 %, the average flue gas temperature rises by 50 K, and the emissions of NO and CO2 decrease by 15.3 % and 6.2 %, respectively, while H2O concentration increases by 21.3 %, potentially leading to low-temperature corrosion issues. The recommended CH4 co-firing ratio is 15 %.

Modernization Potential of Pulverized Coal Boilers in Response to Contemporary Ecological Challenges

The paper presents an analysis of the possibility of modernization of pulverized coal (PC) boilers fired with hard coal or lignite in order to meet contemporary ecological challenges. The increase in the price of CO2 emission allowances causes a decrease in the profitability of coal combustion. Therefore, the construction of large new coal-fired units is becoming more and more risky. The need to keep existing power plants in operation gives a strong impetus to retrofitting PC boilers to reduce their carbon footprint. The paper assesses the following modernizations in terms of improving the environmental impact of the power plant: increasing the efficiency of the boiler, maintaining high efficiency in a wide range of loads, enabling continuous operation with the lowest load, and increasing the unit load change (ramp rate).

TEs enrichment characteristic in different size particulate from coal-fired flue gas: Part 1. Enrichment and leachability

The trace elements (TEs) and particulate matter (PM) emissions from coal-fired power plants have received much concern in recent years due to their harm to human health and the environment, however, the TEs enrichment characteristic in PM and their migration and transformation mechanisms with PM are not clear yet, especially in fine particles. In this work, the enrichment contents of seven TEs Cd, Pb, Mo, As, Ni, Mn, Cr in coal combustion byproducts collected from circulating fluidized bed (CFB) and pulverized coal (PC) boiler were studied to investigate the influence of boiler type on TEs enrichment behavior. The aerodynamic cutting method was used to separate the fine particles PM10 and PM2.5 from bulk fly ash to study the impact of particle size on TEs enrichment behavior. In addition, the modified BCR sequent extraction method was applied to study TEs occurrence forms in different size particles to evaluate their environment contamination risk. The results show that except low volatility Mn, all the TEs are mainly enriched in fly ash rather than bottom slag and gypsum. The coal combustion in PC boiler is more complete so bottom slag in PC boiler commonly has less TEs enrichment content than that in CFB boiler. The volatile TEs including Cr, Ni, As, Cd, Pb are most enriched in PM2.5, while the enrichment contents based on fly ash volume fraction of seven TEs are most in PM50 (for CFB boiler) and PM10 (for PC boiler), since PC boiler has more PM10 volume fraction. Even though the TEs occurrence forms in different size particles are various due to the complexity of TEs combination mechanism with fly ash, the soluble F1 fraction overall exhibits size-dependence and is highest in PM2.5. RAC result indicates that As, Cd, Mn, Ni, Cr have medium environment risks, especially when they occur in PM2.5.

Simulation and Experimental Study of Water Soot Blower for Pulverized-Coal Boiler Based on Discrete Phase Model

A pulverized-coal boiler is a type of boiler that is commonly seen in power plants. During an operation, a portion of the coal is converted to ash. The consequence is a cause of slagging on the furnace wall and a considerable loss in heat transfer performance. In coal-fired power plants, slagging is one of the most common causes of maintenance issues. This problem can be resolved by using a water soot blower cleaning system. It shoots a high-pressure jet of water through a hole in the side of the furnace’s wall to clean the opposite wall surfaces. This study presents a Computational Fluid Dynamics (CFD) investigation of the water soot blower trajectory with a flow field in full-scale boiler. Multiphase-flow simulation is utilized. The turbulence model couple and Discrete Phase Model are used to analyze flow field in boiler and water soot blower trajectory, respectively. The aim is to accurately determine an injection angle degree for the water soot blower. The CFD results are compared with the experiment of water soot blower shooting in Cold Air Velocity Test (CAVT) conditions. The results of the study show that the simulation results agree with the experimental data. Moreover, the velocity profile of numerical study shows that the effect of flow field in boiler has little effect on the water soot blower trajectory.

Variations in the physicochemical properties of spent honeycomb V2O5-WO3/TiO2 catalysts from PC and CFB boilers SCR denitration systems

The massive production of spent honeycomb V2O5-WO3/TiO2 catalysts has caused serious environmental hazards. Revealing the physicochemical property variations of the spent catalysts is of great significance to clarify the deactivation mechanism of catalysts and the recovery of the spent catalysts. This study focused on the changes of typically spent catalysts, selected from pulverized coal (PC) and circulating fluidized bed (CFB) boiler deNOx systems, morphologies, pore structure, chemical composition, carrier, and active components properties, etc. The activities of most spent catalysts could be to more than 95% at 300–400 °C after vibration cleaning. The pore blockage caused by fly ash and sulfur deposition is the major deactivation factor of the catalysts from the two furnace systems. The catalysts from CFB furnaces are more easily deactivated, which is owing to they are more prone to occur severe pore structure loss. The transformation of anatase to rutile TiO2 as one of the major factors causing the pore structure loss would form the irreversible deactivation of the catalysts. The valence state of the active component V has shifted. The spent catalysts from PC systems typically exhibit higher V4+/Vn+ ratios. However, those from CFB systems display a noticeable decrease, which may be attributed to the formation of CaWO4, resulting in the destruction of dispersed active sites on the surface. Finally, the deactivation mechanism of the spent catalysts from different furnaces of coal-fired power plants was summarized. This research is beneficial for further modification of SCR catalysts under different application conditions and provides valuable insights into the classification and recycling of the spent catalysts.

Pilot experimental study on pollutant emission characteristics from co-combustion of coal and spent cathode carbon block

Spent cathode carbon block (SCCB) is a hazardous waste produced by the electrolytic aluminum industry. Collaborative treatment of the SCCB in pulverized coal boilers is a potentially valuable technology. Pilot experiments were carried out on a 240 t/h pulverized coal boiler and its supporting flue gas treatment measures as a function of the mixing ratio of SCCB to verify the feasibility of coal collaborative disposal of SCCB. The thermal conversion characteristics of fluoride after mixing SCCB with coal were studied. A continuous emission monitoring system was used to monitor the impact on SO2, NOx and particulate matter in real time. The effectiveness of existing flue gas control measures was evaluated, and optimization suggestions of the flue gas control measures were postulated. The content of heavy metals (Hg, Cd, Ni, Pb, As, Se) in solid waste from co-combustion and the physical phase of solid waste were investigated. In addition, the transformation of heavy metals such as Hg, Cd, Ni, Pb, Cr, As and fluoride in defluorination wastewater during flue gas treatment were analyzed. The results show that it is feasible to use a pulverized coal boiler to dispose SCCB. The existing flue gas treatment measures proved to be appropriate, and desulfurization wastewater can achieve the discharge standards. Defluorination gypsum, fly ash and slag are not hazardous waste. When the mixing ratio of SCCB is increased, the existing neutralization and flocculation precipitation processes of the desulfurization wastewater are affected. It is suggested to add Al2O3 for the defluorination process before the desulfurization tower.

Plasma ignition of solid fuels at thermal power plants. Part 2. 3D modeling of the furnace of a pulverized coal boiler

Plasma ignition of solid fuels at thermal power plants. Part 2. 3D modeling of the furnace of a pulverized coal boiler

Techno-Economic Analysis of Co-firing for Pulverized Coal Boilers Power Plant in Indonesia

The utilization of co-firing (coal-biomass) in existing coal-fired power plants (CFPPs) is the fastest and most effective way to increase the renewable energy mix, which has been dominated by pulverized coal (PC) boilers, particularly in the Indonesian context. This study aims to investigate the technical and economic aspects of co-firing by conducting a pilot project of three PC boiler plants and capturing several preliminary figures before being implemented for the entire plants in Indonesia. Various measured variables, such as plant efficiency, furnace exit gas temperature (FEGT), fuel characteristic, generating cost (GC), and flue gas emissions, were identified and compared between coal-firing and 5%-biomass co-firing. The result from three different capacities of CFPP shows that co-firing impacts the efficiency of the plant corresponding to biomass heating value linearly and has an insignificant impact on FEGT. Regarding environmental impact, co-firing has a high potential to reduce SO2 and NOx emissions depending on the sulfur and nitrogen content of biomass. SO2 emission decreases by a maximum of 34% and a minimum of 1.88%. While according to economic evaluation, the average electricity GC increases by about 0.25 USD cent/kWh due to biomass price per unit of energy is higher than coal by 0.64×10-3 USD cent/kcal. The accumulation in the one-year operation of 5%-biomass co-firing with a 70% capacity factor produced 285,676 MWh of green energy, equal to 323,749 tCO2e and 143,474 USD of carbon credit. The biomass prices sensitivity analysis found that the fuel price per unit of energy between biomass and coal was the significant parameter to the GC changes.

Evaluation of effects of ammonia co-firing on the thermal performances of supercritical pulverized coal and circulating fluidized bed boilers

Ammonia is an effective fuel in reducing carbon dioxide due to a carbon-free fuel. Accordingly, the use of ammonia co-firing technology for carbon neutrality has emerged in the power generation industry. It is necessary to determine the optimal operating conditions by analyzing boiler performance during ammonia co-firing for optimal power plant operations. In this study, a process simulation was performed to determine the effect of ammonia co-firing on the thermal performances of supercritical pulverized coal (PC) and circulating fluidized bed (CFB) boilers. The target boilers were 870 and 550 MWe supercritical PC and CFB boilers, respectively. The process simulations were conducted using co-firing ratios of 5, 10, 15, 20, and 30%, as well as various coal grades and load conditions at an ammonia co-firing ratio of 20%. Although the amount of CO2 reduction during ammonia co-firing was confirmed, the radiation and convective heat transfer rates decreased due to changes in the flue gas composition and due to increased moisture loss. Accordingly, the plant efficiency decreased due to lower main and reheat steam temperatures. These findings can be used to establish optimal operating conditions for CO2 reduction and improve plant efficiency, which are operational trade-offs during ammonia co-firing.

Conversion of a pulverized coal boiler into a torrefied biomass boiler

The aim of the work is to analyze the possibility of converting a pulverized coal (PC) type OP650 boiler to combustion of 100% biomass in the form of torrefied PKS (Palm Kernel Shell). The replacement of hard coal with torrefied biomass in a PC boiler practically eliminates CO2 emissions. It also reduces the problem of coal shortages in the current political situation in Europe. However, it is necessary to solve the problems of changing the fouling of the boiler, grinding new fuel in coal mills, changing NOx emissions, and changing the exhaust gas dew point. We do not deal with torrefaction, assuming that this problem is technically solved and that such fuel can be purchased. The assessment of the boiler conversion to new fuel was based on the measurements of the boiler in its current state during combustion of coal dust. The HVT (temperature measurement by means of high-velocity thermocouple) measurement of temperature was carried out at points in the area of superheaters, on the rear wall and on one of the sidewalls using a water-cooled aspiration probe. The measurements of the growth rate of high-temperature deposits in the area of platen superheater tubes were also performed. On their basis, a 0-dimensional model of the boiler was created and the risk of slagging after replacing coal with torrefied biomass was assessed. Slagging and fouling tendency of heating surfaces during coal and PKS combustion were compared. The final evaluation of the possibility of converting the OP 650 boiler to combustion of 100% biomass in the form of torrefied PKS was performed. With the same ash fouling of the boiler as for coal, replacing coal with a fuel with a slightly lower calorific value and much lower humidity and ash content, such as torrefied PKS, causes a slight increase in the temperature of live and reheat steam, which in the conditions of the given calculation example gives practically nominal values of these temperatures. In the variant simulating increased fouling of the boiler during biomass combustion, the flue gas temperatures increase even more, which may lead to a strong increase in slagging and fouling. Calculations for wet PKS with significant fouling of the furnace still show high flue gas temperatures in the high temperature area of the boiler. In addition, for a fuel with such characteristics, the risk of slagging is very high. To mitigate the possible operating problems, a doping the PKS with Dunino halloysite from the Polish mine Dunino (DH) was considered. This aluminosilicate is recommended to protect against slagging and fouling. Important advantage of DH is the reduction of chlorine corrosion of the boiler surfaces. The results of the calculations show that during the combustion of PKS, the temperature of the flue gas outlet is higher than during the combustion of coal.

Plasma Ignition System to Start Up Pulverized Coal Boilers: Experimental Simulation and Full-Scale Test

Plasma Ignition System to Start Up Pulverized Coal Boilers: Experimental Simulation and Full-Scale Test

Decoupling Investigation of Furnace Side and Evaporation System in a Pulverized-Coal Oxy-Fuel Combustion Boiler

A distributed parameter model was developed for an evaporation system in a 35 MW natural circulation pulverized-coal oxy-fuel combustion boiler, which was based on a computational fluid dynamic simulation and in situ operation monitoring. A mathematical model was used to consider the uneven distribution of working fluid properties and the heat load in a furnace to predict the heat flux of a water wall and the wall surface temperature corresponding to various working conditions. The results showed that the average heat flux near the burner area in the air-firing condition, the oxy-fuel combustion with dry flue gas recycling (FGR) condition, and the oxy-fuel combustion with wet flue-gas recycle condition were 168.18, 154.65, and 170.68 kW/m2 at a load of 80%. The temperature and the heat flux distributions in the air-firing and the oxy-fuel combustion with wet FGR were similar, but both were higher than those in the oxygen-enriched combustion conditions with the dry FGR under the same load. This study demonstrated that the average metal surface temperature in the front wall during the oxy-fuel combustion condition was 3.23 °C lower than that under the air-firing condition. The heat release rate from the furnace and the vaporization system should be coordinated at a low and middle load level. The superheating surfaces should be adjusted to match the rising temperature of the flue gas while shifting the operation from air to oxy-fuel combustion, where the distributed parameter analytical approach could then be applied to reveal the tendencies for these various combustion conditions. The research provided a type of guidance for the design and operation of the oxy-fuel combustion boiler.

Numerical investigations on the aerodynamics and flue gas recirculation of cyclone-fired coal boiler

Cyclone-fired boilers have gained wide applications due to their ability to burn low ash fusion temperature coals that are unsuitable for pulverized coal (PC) firing. In comparison to PC boilers, cyclone-fired boilers exhibit significantly different aerodynamics and the molten slag layer plays a critical role in the operation of boilers. However, by far there are still lack of CFD models that are able to provide effective guidance to the design and operation of cyclone-fired boilers. In this paper a CFD model that was designed to solve the practical problems of cyclone-fired boilers was developed in which the capture of coal particles by the molten slag layer was considered through a slag layer capture model to remove the captured particles from calculation and release the combustion heat of the remaining combustibles. This model was then employed to investigate the aerodynamics and flue gas recirculation (FGR) optimization design of a 550 MW cyclone-fired boiler. The results demonstrated the highly nonuniform characteristics of furnace aerodynamics of cyclone-fired boilers due to the strong swirling flows created by the cyclones that frequently leads to the formation of localized high temperature zones and severe boiler fouling problems. Thus, it is critical to adapt the FGR design with the nonuniform furnace flow and temperature distributions. The simulation results showed that with the adapted FGR design the high temperature zones in the furnace could be effectively eliminated. This study is instrumental for the design of FGR system of cyclone boilers to avoid the potential severe boiler fouling problems.

Numerical Study of Heat Transfer and Nox Formation in a Pulverized Coal Boiler with a Three-Stage Combustion Arrangement Using Ordinary Fuel and Coal-Water Slurry

Numerical Study of Heat Transfer and Nox Formation in a Pulverized Coal Boiler with a Three-Stage Combustion Arrangement Using Ordinary Fuel and Coal-Water Slurry

Analysis of Combustion Characteristic in Tangentially Fired Pulverized-Coal Boiler with Tilting Burner Angle Variation using CFD

One type of boiler is a boiler with tangential combustion. Tangential combustion is combusted with a burner arrangement located at each corner (corner) of the boiler, where each burner forms a certain angle to the boiler wall. Most of the tangential boilers are equipped with a tilting burner facility. An inclined burner is a facility to direct the burner to face up or down a certain angle to a horizontal line. Changes in the direction of the burner tilt angle will move to the fireball position in the furnace so that there can be changes in temperature, velocity, also species. This study was conducted to determine setting the burner tilt angle by varying the angle simulated using CFD. The data to be obtained are qualitative data in the form of contours and vectors from the distribution of temperature and velocity and quantitative data in graphs and tables. In this study, it is hoped that the ideal angle for the boiler will be obtained so that combustion in the boiler occurs efficiently.

Numerical Optimization of Combustion and Nox Emission in a Retrofitted 600mwe Tangentially-Fired Pulverized-Coal Boiler with Deep-Air-Staging

Numerical Optimization of Combustion and Nox Emission in a Retrofitted 600mwe Tangentially-Fired Pulverized-Coal Boiler with Deep-Air-Staging

Methane Gas Cofiring Effects on Combustion and NO x Emission in 550 MW Tangentially Fired Pulverized-Coal Boiler.

A shift from coal to liquefied natural gas for electricity generation can mitigate CO2 emissions and respond to the intermittent and variable characteristics of renewable energy. With this objective, numerical simulation was performed in this study to determine the optimal position of the methane injector and evaluate the achievable reduction in NOx emissions before applying methane cofiring to an existing 550 MW tangentially fired pulverized-coal boiler (Boryeong Unit 3). The combustion and NOx reduction in the furnace were intensively analyzed based on the methane cofiring rate (up to 40%). The optimal position of the methane injector was found to be inside the oil port based on the spatial distribution of NOx and the stoichiometric ratio along the furnace height. The NOx reduction rate was logarithmically proportional to the methane cofiring rate, and compared to the base case, a 69.8% reduction was achieved at the 40% cofiring rate. In addition, the fraction of unburned char at the boiler outlet was equivalent to that of the existing boiler as the increase in the flow rates of the close-coupled and separated overfire air improved fuel and air mixing. Simultaneously, methane cofiring led to a reduction in the total fuel loss and CO emissions. Finally, this study showed that the recommended optimum cofiring rate was 20% based on the furnace exit gas temperature. Under the 20% methane cofiring condition, the boiler achieved a 57.3% reduction in NOx emissions and a 7.4% improvement in fuel loss.

Pilot-Scale Experimental Study on Impacts of Biomass Cofiring Methods to NOx Emission from Pulverized Coal Boilers—Part 2: NOx Reduction Capability through Reburning versus Cofiring

In this study the NOx reduction capability of reburning three biomasses (i.e., wood pellet, torrefied biomass, and empty fruit bunch) via 12 cases (i.e., four reburning ratios for every biomass) is investigated in a 1 MWth-scale pilot-scale furnace. These reburning cases are compared with 12 cofiring cases presented in the Part 1 paper on a consistent basis. It is found that, for every cost to purchase and prepare biomass, reburning technology provides significantly better NOx abatement performance than cofiring (up to 3.4 times). NOx reduction effectiveness as high as 4.9 could be achieved by reburning, which means the percent of NOx abatement could be 4.9 times higher than the percent of reburning ratio. It is found that the highest NOx reduction per thermal unit of biomass happens at the lowest reburning ratio, and increasing the reburning ratio leads to a reduction in NOx abatement effectiveness in an exponential decay manner. Unlike cofiring technology, reburning was found to have little dependence on the fuel characteristics, such as fuel ratio or fuel-N, when it comes to NOx abatement potential.