Boiler Load Research Articles

Impact of boiler unit load changes on furnace processes

Relevance. The need to assess the stability of combustion, thermal stress and nitrogen oxides (NOx) emission during load reduction of a steam boiler. Since renewable energy sources and nuclear power plants will receive great attention in the future, coal-fired thermal power plants are to operate at reduced loads, so it is important to investigate the reliability of operation and environmental parameters of the boiler unit in case of load adjustment. Aim. To investigate pulverized coal fuel burnout, temperature parameters and NOx emission at 50 % reduction of boiler unit load in the base configuration and taking into account installation of tertiary blast nozzles. Objects. Furnace chamber of a natural circulation boiler unit with steam capacity of 220 t/h in the baseline layout and with tertiary air nozzles. Methods. The package of application programs FIRE-3D for numerical study was applied. Combustion of pulverized coal fuel is a complex physical and chemical process, therefore the interaction of gas flow and solid particles was modeled using Eulerian and Lagrangian schemes, respectively. In the gas phase, the combustion of volatiles and CO with further combustion of carbon residue are modeled. NOx emission is modeled using post-treatment models including formation of fast, fuel and thermal nitrogen oxides. Results. Temperature fields, flow characteristics, NOx emissions for different loads of the furnace chamber of the boiler unit with steam capacity of 220 t/hour are obtained on the basics of numerical modeling. The authors have obtained quantitative estimations of furnace environment parameters corresponding to several levels of boiler load reduction up to 50% of the nominal one. Installation of four tertiary blast nozzles allows reducing NOx emissions by 12.75% at theoretically required amount of air in burner devices (α=1.0).

Investigation of heat transfer characteristics and optimization design of platen superheaters in the furnace of a 350 MWe supercritical CFB boiler

With the scale-up of circulating fluidized bed (CFB) boilers, the size of the platen heating surface within the furnace increases. Deformation, crack, and tube explosion of the platen heating surface threaten the safe and stable operation of CFB boiler. Large wall temperature deviation and overtemperature of partial tubes of heating surfaces are two of main reasons resulting in above problems. To identify the causes of large wall temperature deviation and decrease them, the heat transfer characteristics and wall temperature distribution uniformity of platen superheaters in the furnace of a 350 MWe supercritical CFB boiler were studied by experimental tests, and the structure of the high temperature superheater was optimized by numerical simulation to improve the temperature distribution uniformity. The steam parameters and wall temperatures of the platen superheaters were measured at boiler loads of 50 % BMCR, 75 % BMCR, and 100 % BMCR. The heat transfer coefficient, heat flux, and wall temperature uniformity of the platen superheaters were analyzed. At 100 % BMCR boiler load, the average heat transfer coefficient and heat flux of the medium temperature superheater IIs were 165.5 W/(m2·°C) and 56 kW/m2, respectively; while those of the high temperature superheaters were 179.7 W/(m2·°C) and 53.2 kW/m2, respectively. The wall temperature distribution uniformity among six medium temperature superheater IIs or six high temperature superheaters was relative good, while the temperature distribution uniformity of a single platen superheater required improvement. An optimized structure of the high temperature superheater was obtained from eight structures by numerical simulation, achieving a steam temperature deviation of less than 8 °C at the boiler load of 100 % BMCR.

Comprehensive Assessment and Optimization of a Middle-Arch Dual-Channel Municipal Solid Waste Incinerator Using Numerical Simulation Methods.

The present study focuses on a middle-arch dual-channel municipal solid waste (MSW) incinerator facing issues of high NO x emission and overheating. To address these problems and optimize the incinerator, an advanced numerical simulation method was employed to comprehensively assess its bed combustion, freeboard combustion, and NO x emission characteristics. A multiphase fuel bed model considering large-particle characteristics of MSW was developed, coupled with a three-dimensional (3D) model for combustion in freeboard. The analysis revealed that the observed issues stem from multiple factors, including primary-to-secondary air ratio, flame propagation in bed, release of volatiles from bed, and distribution and mixing of components in freeboard. Reducing the proportion of primary air and correspondingly increasing secondary air effectively alleviated the localized overheating in the furnace and reduced NO x emission. Further adjustments to the distribution of primary air in three stages delaying air supply toward the burnout stage, together with the decrease in the grate movement speed, can better control the amount and speciation of N released from the bed. Implementing a counterflow mixing strategy with NH3 in the front channel and NO in the rear channel can greatly reduce the original NO x emission concentration to 95.94 mg/(N·m3), as predicted by a numerical simulation. Subsequent practical adjustments to an actual incinerator led to notable improvements, clearly optimizing the localized high-temperature issues at various locations, especially the front channel suffering severe slagging problems, with the temperature reduced from 1118 to 957 °C. Meanwhile, NO x emission concentration decreased from 200 mg/(N·m3) to around 50 mg/(N·m3), with no negative effect on the boiler load.

Numerical Simulation Study on Rotary Air Preheater Considering the Influences of Steam Soot Blowing

The ash deposition is a general problem that needs to be solved effectively for the rotary air preheater of the coal-fired boiler. Taking the rotary air preheater of a 600 MW power station as the object, the mesh model of the flue gas side of the air preheater, considering the influences of steam soot blowing, is established using the Gambit 2.4.6 software. Based on the SIMPLE algorithm, the velocity field and the temperature field in the air preheater under varied working conditions are simulated using the software of Ansys Fluent 2021R1, and the influences of the boiler load, the operation parameters of the steam soot blower, and the running and outage of the soot blower on the flue gas velocity distribution in the depth direction of the corrugated plates, the soot-blowing coverage area, the inlet flue gas velocity, and the inlet flue gas temperature of the corrugated plates are analyzed. Under the base working condition, the flue gas velocity on the axis of the steam nozzle first decreases rapidly with increasing the corrugated plate depth (Z < 1.0 m), and then it decreases slowly with an almost equal slope. The longitudinal flue gas velocity has a positive correlation with the boiler load. The longitudinal flue gas velocity obviously decreases when the boiler load is decreased, and its reduction increases as the corrugated plate depth increases. It is one reason that the ash deposition is prone to occur on the cold end surface of corrugated plates under the condition of low boiler load. The longitudinal flue gas velocity increases with the soot-blowing steam velocity increasing when the corrugated plate depth is less than 1.5 m, but after that, it is almost not affected by the change in soot-blowing steam velocity. The soot-blowing coverage area has a negative correlation with the boiler load but a slight positive correlation with the steam velocity of the soot blower on the whole. The inlet flue gas velocity of the corrugated plates has a positive correlation with the boiler load and the inlet steam velocity of the soot blower. The average inlet flue gas velocity decreases by 21.7% when the boiler load is reduced by 50%. For every 5 m/s variation in the inlet steam velocity, the inlet flue gas velocity changes by about 10–14% whether the steam soot blower is put into operation or not, which has an obvious effect on the inlet gas velocity of the corrugated plates. The inlet flue gas temperature of the corrugated plates is, respectively, positively correlated with the boiler load and the inlet steam temperature of the soot blower. When the boiler load is reduced from 100% BMCR to 50% BMCR, the average inlet flue gas temperature of the corrugated plates is reduced by 44.2 K; however, when the soot-blowing steam temperature varies by 20 K, the average inlet flue gas temperature of the corrugated plates varies by only about 1.8 K. It means that it is difficult to enhance the cold end flue gas temperature of the corrugated plates only by raising the soot-blowing steam temperature at low boiler load. Adding a soot blower using high-temperature steam or hot air at the outlet of the corrugated plates may be an option to solve the ash deposition of the corrugated plates.

The Effects of Moringa Leaf Extract on the Growth and Microbial Load of Boiler

The adverse effect of microbes in poultry production, especially broiler chicken remains a major concern for poultry breeders. This study determined the effects of Moringa leaf (Moringa Oleifera) extract on the performance and microbial loads of broiler birds. A total of 25 broiler chicks were used and separated into 5 groups in an iron pen with 5 chicks in each group. Group 1 (control, with no treatment), group 2 (received a treatment of 62.5mg/L), group 3 (received a treatment of 125mg/L), group 4 (received a treatment of 250mg/L), group 5 (received a treatment of 500mg/L). After 4 weeks of treatment, the faeces from each group, the control group inclusive were collected for microbial analysis. The result showed that the Moringa Oleifera leaf extract at all doses recorded non-significant difference in the parameters analysed among the groups. It was also noticed that the disparities of the results were great. Some as much as 11.5 and 168. 37 standard error of mean. Moreover, Group 3, receiving 125mg/L, exhibited a substantial reduction in E. coli, salmonella, total bacteria count, and pseudomonas activities compared to other groups. Group 3 had the highest water consumption. Amongst the treatment group, group 3 had the highest increase in weight. In conclusion, Moringa leaf extract effectively lowered the microbial load in broiler chicks at the treatment of 125mg/L without any adverse effects. Keywords: Moringa Oleifera, Moringa leaf, microbial load, broiler birds.

Experimental Study on Temperatures of Water Walls in a 1000 MW Ultra-Supercritical Boiler under the Condition of Flexible Peak Regulation

To meet the Chinese government’s energy-saving and emission-reduction policies, flexible peak regulation is necessary for traditional coal-fired boilers. Flexible peaking leads to large changes in boiler load, which affects the safety of the boiler water wall. In this paper, a 1000 MW ultra-supercritical unit was tracked for three years, and effective data were selected to study the temperature characteristics of the water wall under flexible peak regulation. The results show that the lower the load, the greater the temperature fluctuation of the water wall. The temperature distribution of the spiral water wall is more uniform. The position of the temperature valley value of the rear spiral water wall was found, and the load of more even temperature distribution was also found. The temperature change of the front vertical water wall was the most complex of all the water walls. The 643.9 MW load case showed different behavior to the temperature distribution of the water wall. The side water walls were heated evenly under the different loads. The characteristics of the temperature distribution of the side vertical water wall were found through statistical analysis. The fitting equation for the change rule of the temperature is presented. The higher the load, the better the equations. Finally, this paper gives some advice on how to avoid temperature deviation in the water wall, and the detailed research highlights the safe running of water walls.

Influences of ultra-low load operation strategies on performance of a 300 MW subcritical bituminous coal boiler

To reveal the operational characteristics of subcritical boilers under ultra-low loads, numerical simulations were conducted based on a 300 MW subcritical bituminous coal boiler. The impacts of boiler load and low-load operation strategies on coal combustion behavior, heat transfer process, and NOx emission were thoroughly examined. Results indicate that acceptable aerodynamic and temperature fields can still be formed at 25 % ultra-low load, but the boiler performance is significantly reduced, with the maximum cross-sectional average combustion temperature being reduced by 225.98 K compared with the full-load condition. At 25 % load, the use of only two layers of burners results in a substantial increase in NOx emission from 290.32 mg/m3 to 445.56 mg/m3. The position of in-service burners affects the region where the intense coal combustion and heat release process occurs, and using the middle three layers of burners helps to maintain heat absorption by the suspended heating surfaces and to minimize NOx emissions. Furthermore, increasing primary air velocity at ultra-low loads can promote coal combustion and heat transfer processes in the lower furnace, but increase NOx emission by 14.23 % when primary air velocity is increased from 14.90 m/s to 23.00 m/s at 25 % load. These findings provide valuable insights for optimizing the ultra-low load operation of subcritical boilers engaged in deep peak-shaving processes under the carbon neutrality goal.

Optimization of air distribution and coal blending in pulverized coal boilers for high-temperature corrosion prevention based on POD reduced-order modeling

High-temperature corrosion in coal-fired boilers poses a significant threat to safe operation. However, there is currently a lack of effective online monitoring and optimization methods for high-temperature corrosion. Therefore, this study proposes a novel approach to rapidly predict the distribution of chemical species and evaluate high-temperature corrosion degrees, along with optimizing operating conditions to prevent high-temperature corrosion. Firstly, a total of 564 Computational Fluid Dynamics (CFD) simulations are performed on a 330 MW tangentially fired boiler, covering various operating conditions, including coal blending, air distribution, boiler load, etc., to obtain a database of O2, CO, and H2S distributions within the boiler. Then a method based on Proper Orthogonal Decomposition (POD) and Support Vector Regression (SVR) is used to process the database to realize real-time prediction of boiler chemical species distribution, which is next utilized as inputs of a high-temperature corrosion evaluation to obtain in-situ corrosion degree distribution. Finally, Particle Swarm Optimization (PSO) is used to optimize coal blending and air distribution schemes, effectively reducing severe corrosion ratio from 36.34 % to 10.04 % in a typical case by improving the atmosphere near the water walls. This study thus provides a new perspective for online boiler diagnostics and digital twin construction, particularly by achieving online monitoring of high-temperature corrosion and optimizing operating conditions to prevent corrosion.

Improvements in recovery of rare earth elements (REEs) from coal via fluidized-bed combustion: Thermal alteration of REE mineralogy and its impact on element extractability

The extraction of rare earth elements (REE) from coal ash has attracted significant attention, but satisfactory solutions have not yet been achieved. Indeed, the REE extractability is largely determined by the transformation behavior of REE during coal combustion. This study found that the controlled combustion conditions of circulated fluidized-bed boiler (CFB) can both utilize the heating value and enhance the recovery of REE from coal. Tests were conducted using a bituminous coal with REE concentration of approximately 149 ppm in an industrial 35 t/h CFB boiler with controlled boiler loads and coal sources. Advanced automated image analysis by scanning electron microscopy (AIA-SEM) and sequential leaching procedure were employed to clarify the speciation transformation behavior of REE in boilers and investigate the effects of these transformations on the leachability of REE. Approximately 75 % of REE partitioned into fly ash and enriched in particles < 45 μm (∼710 ppm) after combustion. Acid leaching tests under mild conditions (1 M HCl at 60 ℃ and S/L = 1:25) performed on coal, bulk ashes, and sieved ashes revealed an improvement in REE leaching ratio from coal (21.34 %) to fly ash (71.07 %). Particle size played a crucial role in acid extractability, particularly for middle and heavy REE in cyclone ash but had no influence on those in fly ash. The dominant forms of REE in coal including Ca-REE fluorocarbonates (36.7 %), aluminophosphates (12.0 %), and organic-bound REE (approximately 20 %) significantly decreased, contributing to the formation of leachable rare earth oxides (∼65 %) in ash. Furthermore, the small size of REE mineral grains in coal (over 50 % below 5 μm) and extensive mineral fragmentation occurring in boiler resulted in the enrichment and enhanced REY leachability in fine ash.

Modeling on rapid prediction and cause diagnosis of boiler combustion efficiency

Presently, a method for determining pulverized coal burnout rate (PCBR) was developed on kinetics combustion model. Proposed method can promptly track influence of air coal ratio (ACR), boiler load, uniformity index (UI), coal powder fineness (CPF), particle size, and air powder mixing uniformity (PMUC) on PCBR. Moreover, developed method with fewer computations, time-saving, simplicity and low-cost can be exploited to diagnose decreasing causation of combustion efficiency.Results indicate, for anthracite and lean coal, ACR should be maintained near optimal value with 9.39–11.59 kg/kg to achieve consummate combustion efficiency. Correspondingly, higher and appropriate ACR with 10.87–12.0 kg/kg and 7.18–7.94 kg/kg should be maintained for bituminous coal and lignite. 0.1 UI improving achieves 0.18 % upgrading in PCBR. PCBR is more sensitive to UI variation above 75 % BMCR. More significant effect is presented for lean coal and lignite with changing PMUC especially below 50 % BMCR. Basically 0.1 PMUC improving achieves 0.55 enhancement in PCBR below 50 % BMCR. Concurrently 0.7 increment is delivered for anthracite and lean coal. Coal with high volatile content causes larger particle sizes of coal powder to burn out at furnace outlet. Investigation result can predict potential financial savings from unburnt carbon (UC) reduction.

Experimental combustion characteristics and NOx emissions for a 600‐MWe utility boiler after the retrofitted: Effects of load variation

AbstractTo enhance the rapid switching ability of the boiler load and reduce NOx emissions, a new combustion system was implemented in a 600‐MWe wall‐fired boiler with swirl burners. This system included two levels of overfire air (OFA) and low NOx combustion technology. Industrial tests were conducted at 300‐, 450‐, and 600‐MWe loads before and after the retrofitted. These tests included measuring flue gas and furnace temperatures with thermocouples and analyzing local gas concentrations using a gas analyzer. The research results indicate that under conditions where the OFA ratio exceeds 30%, the burner exhibits good ignition performance at different loads. At the 600‐MWe load, the nitrogen oxides (NOx) emissions were reduced by 55% compared to before the retrofit. After the retrofit, the flame center inside the furnace of different loads was located at the height of 33.36 m, the first and second‐stage cooling water quantities were slightly higher, the reheat cooling water quantity was greatly reduced after the retrofit, and contributes to the boiler's safe operation. Under different load conditions after the retrofit, the gas temperature near the sidewall was below 850°C, and the O2 concentration near the sidewall was above 5%, effectively suppressing sidewall high‐temperature corrosion and slagging.

CO2 Capture Cost Reduction Potential of the Coal-Fired Power Plants under High Penetration of Renewable Power in China

With a significant share of renewable power generation integrated into the power supply, it is crucial to timely adjust the regulating peak load for coal-fired power plants equipped with CO2 capture to ensure the stable operation of the multi-energy supply system. In this paper, the effects of varying boiler loads on the techno-economic performance of the retrofitted power plant were studied. Furthermore, the potential for reducing the cost of CO2 capture was investigated, and early opportunities for demonstration were discussed. Results showed that when the boiler load decreased from 100% turbine heat acceptance condition to 50% turbine heat acceptance condition, the cost of CO2 capture increased from 37.0 $/t CO2 to 57.0 $/t CO2, cost contribution of energy penalty and extra capital investment also increased from 20.6 $/t-CO2 to 25.7 $/t-CO2, and from 16.4 $/t-CO2 to 31.3 $/t-CO2, respectively. Furthermore, by improving separation efficiency from 0.15 to 0.5, a 25% to 30% reduction in CO2 capture cost can be achieved. The cost of CO2 capture could decrease by 42.2–50.5% when the cumulative capacity reaches 250 GW under the high investment learning rate scenario. According to the distribution of coal prices and renewable energy sources in China, the early demonstration projects of multi-energy supply systems should prioritize the northern region. The results of this work can provide informative references for making roadmaps and policies for CO2 emission reduction toward carbon neutrality.

Characteristics of fine particle formation during combustion of high-alkali coal in a new full-scale circulating fluidized bed boiler

High-alkali coal generated an increased number of fine particles during the combustion process. Understanding the transformative characteristics of particulate matter (PM) in a full-scale boiler that burns 100 % Zhundong (ZD) coal is key for controlling pollutant emissions. This paper investigated PM formation in a novel full-scale Circulating Fluidized Bed (CFB) boiler. PM samples were collected from various points along the steam-cooled flue at 50 %, 67 %, and 100 % boiler load. Utilizing Low-pressure impactors and scanning electron microscopy coupled with energy disperse spectroscopy (SEM-EDS) were applied to analyze the mass-based particle size distribution(MPSD), elemental compositions, and morphology of PM. The results show that sub-micron particles produced under low boiler load consist primarily of AAEMs sulfates, whereas under high load, they consist primarily of alkali metal chlorides. Super-micron particles are predominantly sulfates and silicates. The concentrations of Na, K, and Cl in PM0.4 decreased as the flue gas cooled down in the steam-flue of the CFB. At 100 % boiler load, Na, K, Cl and S account for more than 90 % of the total elements in the sub-micron particles. However, these four elements demonstrated a 25 % decrease at a boiler load of 67 % compared to 100 % load. Interestingly, the compositions of super-micron particles seemed to be minimally affected by the boiler load.

Auditing and Analysis of Natural Gas Consumptions in Small- and Medium-Sized Industrial Facilities in the Greater Toronto Area for Energy Conservation Opportunities

This paper presents the findings of fifteen energy audits conducted on industrial sites in Canada’s Greater Toronto Area (GTA). The audits covered a range of industries including food processing, packaged goods, and finishing processes (powder-coating). The primary focus of the audits was to analyze the natural gas consumption and the performance of major-gas-consuming equipment. The audits identified natural-gas-consuming equipment that could be optimized to yield energy and operational cost savings and greenhouse gas (GHG) reduction opportunities. Food production plants’ energy intensity ranges from 5.59 m3/ft2 to 17.73 m3/ft2. Therefore, there is a significant opportunity to improve energy consumption through better technology integration. The results of the audits indicate a trend of an increase in the percentage of non-productive consumption with non-productive time. The proposed energy-saving measures include reducing non-productive natural gas consumption, gas-fired equipment tune-up, optimizing boiler loads, and reducing oven exhaust by using variable frequency drives (VFDs). The findings of this study could be used to develop a demand-side management program specifically for small- and medium-sized industrial facilities in the Greater Toronto Area and other parts of Canada.

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 %.

Method of controlling the volume of combustion products at different boiler loads

Purpose. Development of a method for controlling the volume of combustion products at different load of boiler equipment. Achieving the objective may allow controlling the flue gas temperature and, consequently, the efficiency to increase it. Methodology. Control of the flue gas volume value on the basis of determining the appropriate composition of the fuel gas mixture. Findings. The effect of flue gas temperature increase at use of fuel gases of lower calorific value and increase in ballast gases quantity is revealed. The latter can be the air used as an oxidising agent at its considerable excess. The mechanism of such an effect due to the increase in the quantity and velocity of flue gases is suggested. A parameter determining the volume of flue gases produced per unit calorific value of various fuel gases is proposed. On the basis of this parameter the method for calculating the composition of the mixture of different gases to ensure the constancy of the flue gas volume at variable load is proposed Originality. On the example of the results of verification thermal calculation the change in flue gas temperature and efficiency value is considered. The non-standard character of their change is revealed. In contrast to the case of using fuel gas of constant composition with increasing load, the temperature of flue gases remained close to constant, and the value of efficiency increased. Practical value. The obtained results indicate the possibility of controlling the flue gas temperature and boiler efficiency at a given load. This allows one, unlike the case of using fuel gas of constant composition, to increase the efficiency exactly at maximum load avoiding getting into the condensate mode at minimum load. There is a possibility to save fossil gas and, consequently, to reduce the greenhouse share in CO2 emissions.

Determination of the design features of the device for neutralizing toxic components of flue gases

The influence of the boiler unit load on the area of heterogeneous reactions of the process of catalytic flue gas purification is considered. The optimal geometric characteristics of the neutralizer monolith were determined when the steam capacity of the TGME-464 boiler unit varied from 220 to 500 t/h. The calculations were performed using a mathematical model for the conditions of the operating power equipment. The optimal size of the unit cell of the catalyst block is determined in a wide range of boiler load regulation. The data obtained as a result of the study formed the basis for designing a sample of an industrial neutralizer of toxic flue gas components without the introduction of an external reagent.

Coupled simulation on flue gas and steam deviation of final reheater in a 600 MW tangentially fired boiler with reversed separated overfire air under different loads

Flue gas and steam deviation of the final reheater is an inevitable problem in the tangentially fired boiler due to the remaining gas spinning at the furnace exit. An in-house one-dimensional process simulation code coupled with comprehensive three-dimensional combustion simulation was adopted to accurate investigate the characteristics of the flue gas and steam maldistribution of the final reheater in a 600 MW supercritical tangentially fired boiler. Firstly, the combustion simulation result was validated by the in-house fire-side heat transfer calculation data, then the effect of boiler loads and reversed separated overfire air (SOFA) deflection angles on the gas temperature deviation, velocity deviation and outlet steam temperature of reheater were conducted. The results showed that the deviation of flue gas temperature and velocity increases as the boiler load decreases. The reversed SOFA deflection angle plays a crucial role in improving the gas distribution under low loads, and the deviation of flue gas temperature and velocity is the smallest when the angle is -18? under 100% boiler maximum continuous rating (BMCR), 75% and 50% turbine heat acceptance (THA), but it is the smallest when the angle is -9? under 35% BMCR load. Moreover, the maximum outlet steam temperature difference between parallel heating surfaces of the final reheater increases from 84.68 K to 106.48 K as the boiler load decreases from 100% BMCR to 75% THA, and it is mainly affected by the flue gas temperature deviation rather than the mass flow rate maldistribution when the deflection angle changes from -9? to -18?.

Assessing the impact of wet and dry flue gas recycling on heat transfer in oxygen-fired circulating fluidized bed furnaces

Oxygen-driven circulating fluidized bed combustion (oxy-CFB) has been suggested as a potential technique for facilitating carbon capture in large-scale power generation. Precise modeling of radiative heat transfer is vital for forecasting the thermal performance of such processes. This research examines the impact of wet and dry flue gas recycling on the thermal behavior of a large-scale oxy-CFB furnace, utilizing a combined modeling strategy that merges a three-dimensional furnace process model with a thermal radiation solver. The semi-empirical furnace model operates in steady-state conditions, accounting for fluid dynamics, reactions, and heat transfer phenomena. The radiation solver, based on the zone method, employs novel correlations for radiative heat exchange between optically thick zones. The radiation solver employs a weighted sum of the gray gases model, developed specifically for oxy-combustion, and geometric optics to determine the radiative characteristics of combustion gases and particles, respectively.This research covers various process conditions and boiler loads to evaluate the influence of wet versus dry flue gas recycling on heat transfer and temperature profiles. Model results were successfully compared against small-scale oxygen-fired CFB tests and large-scale measurements in a supercritical air-fired CFB. Utilizing an external radiation solver allows for a more precise representation of radiative heat transfer and the influence of varying process conditions. The insights from this research can aid in the design of large-scale oxy-CFB facilities, and the demonstrated modeling approach can be employed for additional model development, such as integrating the external radiation solver with other modeling tools.

Performance analysis of a novel biomass gasification system coupled to a coal-fired power plant based on heat and water recovery

Biomass gasification co-firing is a technology that can be implemented instantly in almost all coal-fired power plants in a relatively short period to reduce the consumption of fossil fuel. Most studies have focused on improving the system according to variations in the gasification conditions, biomass types, co-firing ratio, and boiler loads. However, the whole system process analysis and structural improvement based on the matter and energy of the co-firing system require further investigation. In this study, a novel biomass air–steam circulating fluidized bed gasification co-firing system based on waste heat and flue gas water recovery with different co-firing ratios (approximately 10 %–40 %) was simulated and compared with the original air gasification co-firing system using Aspen Plus software. The impacts of recovered water participate in gasification process and the optimal steam to biomass ratio (S/B) when it varied from 0.5 to 2, on the syngas quality, thermal characteristics of flue gas, recovered water, coal consumption, exergy loss, and efficiency of the system were analyzed. Compared with the air gasification co-firing system, the results showed that the N2 content in syngas reduced from 41.14 % to 28.92 %, and the heat yield of syngas increased by 7.73 %, along with a 110 t/h recovered water surplus at a 40 % co-firing ratio when steam to biomass ratio was equal to 1. The maximum coal saving amount was 2.26–9.11 t/h and the volume of atmospheric pollutants emissions, such as carbon dioxide (CO2), sulfur oxides (SOx) and nitrogen oxides (NOx), reduced by 0.95 %–6.02 %, 0.91 %–0.95 %, and 11.38 %–36.47 % at a co-firing ratio of approximately 10 %–40 %. Furthermore, the exergy loss can be reduced by 4.35 %–10 % with a 1.72 %–3.96 % increase in exergy efficiency, indicating that the new system mode improves the comprehensive performance of the co-firing system.