Co-firing In Boilers 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.

Enhancement of reaction rate prediction of biomass: A focus on experimental and numerical simulation approaches

While the biomass gasification and cofiring technology is promising for future energy, including green technologies, such as carbon capture and storage and bioresource feedstock, negative carbon emissions are simultaneously possible using these technologies. However, despite these functions, our previous study established that for simulating a biomass reactor, a new model needed to be designed that could improve the accuracy of both real and lab-scale simulations for carbonaceous fuels, such as coal-based applications. Hence, in this study, a biomass experiment utilizing a thermogravimetric analyzer was conducted to obtain varying reaction rate data over carbon conversion, which may then be used to simulate the biomass conversion model and 3D simulation was also conducted for a 500 MWe coal-biomass cofiring boiler. Gasification was obtained at 1000 °C and 1200 °C using CO2 at constant temperature for different biomasses. Compared to the peak exhibited by the random pore model, biomass gasification reaction rates shifted into the later stage of the reaction, thereby yielding irregular reaction rate developments and poor prediction accuracies. With flexibility-enhanced random pore model(FERPM), we observed that correlation factors increased from the previously reported value of 0.7–0.95. In the coal-biomass cofiring boiler, the difference between the Kinetics/Diffusion-limited model and FERPM in biomass combustion aspect was examined, and it was ultimately determined that characteristics of particle reactions through FERPM are valid in 3D analysis. Therefore, this paper proposed a flexibility-enhanced random pore model proven to enhance the prediction accuracy of a simulation.

Analysis of Combustion Characteristics in Boilers Using Comparison of Coal Fuel Mixtures and Bark Biomass To Determine Optimal Combustion Conditions in a Steam Power Plant

Currently, several material production industries have used self-sustaining power generation systems. Where the most common steam power plant system is found as an option to be used as a source of electricity. The use of biomass as an additional material for fuel in power plant has been widely carried out. This method is more commonly known as cofiring. Analysis of the cofiring combustion system of biomass in the boiler needs to be carried out in order to determine the characteristics of the combustion system that occurs. By varying the composition of the fuel, an analysis of the energy produced from the combustion reaction will be calculated. In this study, the comparison of the use of coal and wood bark was varied at conditions 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80. Assuming that the steam rate and temperature conditions to be achieved from the combustion products are constant. From the results of the analysis it was found that an increase in the amount of cofiring bark resulted in a decrease in the heating value of the combustion reaction and an increase in fuel capacity. Thus, it can be concluded that the use of bark cofiring in boilers with a coal design is less effective because it will require additional energy to increase the fuel consumption rate and reduce combustion efficiency due to not achieving optimal combustion energy because the initial design combustion chamber capacity is fixed.

Digital twin of biomass/coal co-firing circulating fluidized bed boiler by using computational fluid dynamics simulation

Combining biomass fuel with coal in circulating fluidized bed (CFB) boilers is attractive as the increasing of energy demand. The characteristics of biomass/coal co-firing in the industrial boiler are then investigated using computational fluid dynamics (CFD). In this study, fuels of interest are coal, wood chips, and bark. The fuel proportions were set for investigating their effects on the combustion using a simplex centroid mixture design. CFD simulations consist of a standard k-epsilon viscosity flow model, Euler multiphase fluid flow model, and a simplified biomass-char combustion reaction model. The predictive responses of the model are bed temperature, heat flux, and carbon dioxide (CO2) and carbon monoxide (CO) mass flows. The simulation results showed that the operation with coal gave the highest temperature and heat flux, followed by wood chips and bark. On the other hand, the operation with biomass releases fewer gas emissions, CO2 and CO, than those of the operation with coal. The type and proportion of boiler fuel can be easily determined using two methods: predictive equation and ternary contour plot graph, which can be likened to the digital twin of biomass/coal co-firing boiler.

Briquettes of acai seeds: characterization of the biomass and influence of the parameters of production temperature and pressure in the physical-mechanical and energy quality.

Agro-industries, leveraged by the high demand of acai products, promote environmental impact through the generation of wastes in several locals in Amazon. The use with bioenergetic purposes has capacity to mitigate these scenario. Thus, the aim of the study was to characterize the biomass of acai seeds and establish the technical parameters of temperature and pressure of work to the production of briquettes of physical, mechanical and thermal quality. Temperatures of 120, 140 and 160°C; and pressures of 15, 20 and 25MPa were studied. We analyzed the briquettes mechanical compressive strength, rate of water absorption, rate of volumetric expansion and energy and apparent density. To the characterization of in natura seeds, the proximate analysis, chemical composition (extractives, holocellulose and lignin contents), higher, lower and useful heating value were determined. The proximate analysis indicated biomass thermal resistance, potential to direct burning and conversion by thermochemical processes. The lignin content may increase briquettes compressive strength produced in high temperatures. It was observed that the temperature had more influence in the evaluated briquettes characteristics than the pressure. The compressive strength was greater in 160°C and 15MPa briquettes, indicating that the lignin works as binder in this temperature, however, with pressure improvement the resistance is not favored due to the limit of resistance to compaction. The rate of water absorption decreased with the pressure increase and the temperature statistically affected in 140°C briquettes. We observed volumetric expansion values in consonance to other found in dense biofuels of the literature. Further, the apparent density and energy density were favored by pressure improvement and the temperature helped in the increase of the apparent density. Moreover, the produced briquettes presented gain in the apparent density regarding the in natura biomass and had energy density comparable to coal and adequate to co-firing in boilers.

Gas Emissions from Mixed Coal-Biomass Derived Fuel Burned in an Industrial Boilers

Textille industry consumes huge amount of coal to operate their boiler. At the same time, the company generated huge amount of bottom ash from the boiler operation and it is considered as hazardous waste. PT. X has been attempting to reuse bottom ash mixed with solid waste compost to generate biofuel named as biomass coal fuel (BCF) briquettes as co-fuel for boiler combustion. This study conducted two boiler combustion experiments: i) co-firing boiler operation with 90% coal and 10% of BCF, and ii) 100% of coal. The SO2 and NO2 emissions were measured from the two experiments. The emission test was carried out using the MRU Optima 7 which is equipped by an electrochemical sensor, combined with an extraction probe to be inserted into the stack. From the emission test results, the SO­2 concentration of 100% of coal burning was 150 mg/Nm3. SO2 concentration of coal fuel with a substitution of 10% BCF was 498.8 mg/Nm3. The NO2 concentration from 100% coal combustion was 174.2 mg/Nm3 while from mixed fuel combustion was 370.3 mg/Nm3. Using BCF as an aggregate for coal combustion did not bring in lower emissions of SO2 and NO2. Emission factor for SO2 from 100% coal combustion is 6.295 g/kg while for coal fuel with a substitution of 10% BCF is 31.09 g/kg. NO2 emission factor from 100%, coal burning is 7.31 g/kg while the emission factor of NO2 in coal fuel with a substitution of 10% BCF is 23.31 g/kg.

Gas Emissions from Mixed Coal-Biomass Derived Fuel Burned in an Industrial Boilers

Textille industry consumes huge amount of coal to operate their boiler. At the same time, the company generated huge amount of bottom ash from the boiler operation and it is considered as hazardous waste. PT. X has been attempting to reuse bottom ash mixed with solid waste compost to generate biofuel named as biomass coal fuel (BCF) briquettes as co-fuel for boiler combustion. This study conducted two boiler combustion experiments: i) co-firing boiler operation with 90% coal and 10% of BCF, and ii) 100% of coal. The SO2 and NO2 emissions were measured from the two experiments. The emission test was carried out using the MRU Optima 7 which is equipped by an electrochemical sensor, combined with an extraction probe to be inserted into the stack. From the emission test results, the SO­2 concentration of 100% of coal burning was 150 mg/Nm3. SO2 concentration of coal fuel with a substitution of 10% BCF was 498.8 mg/Nm3. The NO2 concentration from 100% coal combustion was 174.2 mg/Nm3while from mixed fuel combustion was 370.3 mg/Nm3. Using BCF as an aggregate for coal combustion did not bring in lower emissions of SO2 and NO2. Emission factor for SO2 from 100% coal combustion is 6.295 g/kg while for coal fuel with a substitution of 10% BCF is 31.09 g/kg. NO2 emission factor from 100%, coal burning is 7.31 g/kg while the emission factor of NO2 in coal fuel with a substitution of 10% BCF is 23.31 g/kg.

Alloy degradation in a co-firing biomass CFB vortex finder application at 880 °C

Mechanisms of alloy degradation in a fireside N-S-O-C-H-Cl-Na-K atmosphere at 880 °C were elucidated using SEM-EDS, chemical equilibrium calculations, and XRD. Alloys 310S, 800H/HT, and 600 were studied after 0, 8000, and 16,000 h exposure in a boiler co-firing biomass waste. For 310S and 800H/HT it was shown that nitrogen formed internal Cr nitrides lowering the Cr activity and inhibiting internal alloy Cr permeation, and that NaCl and Na2SO4 reacted with Cr oxide to form chromate and to accelerate the S and the Cl pickup. Alloy 600 showed no nitride or major chromate formation.

Improvement of Performance Calculation Methods for Pulverized Coal and Blast-furnace Gas Co-fired Boilers

In power plants of steel mills, the performance of pulverized coal and blast-furnace gas co-fired boilers was tested according to GB/T10184-2015 “Performance test code of utility boiler”. However, the calculation and analysis models in this code are mainly based on conventional fuels. Besides, the special properties of blast furnace gas were not taken into account. Therefore, the code GB/T10184-2015 is not suitable to be directly used for pulverized coal and blast furnace gas co-fired boilers. According to the differences between co-fired boilers and conventional boilers, the key points for calculating the performance of co-fired boilers were analyzed on the basis of GB/T10184-2015, and the corresponding improved methods were proposed, in view of fuel composition conversion, combustion calculation, coal feed rate, exhaust gas temperature value, and pollutant emission concentration conversion. The results can provide reference for the performance test of such boilers, with certain practical significance.

Thermal Efficiency Calculating Model of Pulverized Coal and Blast Furnace Gas Co-fired Boilers Based on Separate Combustion Calculation

Boiler thermal efficiency is a key index of unit performance assessment. The thermal efficiency of a pulverized coal and blast furnace gas co-firing boiler can be calculated based on either the mixed fuel combustion calculation or the separate combustion calculation. Based on the Chinese Standard Specification GB/T10184-2015 “Performance test code for utility boiler”, this paper proposes a calculating model for the thermal efficiency of the co-firing boilers based on the calculation of the itemized fuel combustion, and takes a 220t/h boiler burning pulverized coal and blast furnace gas in a steel plant as the research object. The comparison between the proposed model and the traditional model based on mixed fuel combustion calculation shows that the boiler thermal efficiency calculated results obtained by the two methods are consistent. The new model proposed in this paper is reasonable and feasible. It can be used to calculate the thermal efficiency of the pulverized coal and blast furnace gas co-fired boilers.

Damper opening optimization and performance of a co-firing boiler in a 300 MWe plant

Effects of secondary air and separated overfire air on boiler performance were experimentally investigated in a 300MWe utility boiler co-firing coal with blast furnace gas and coke oven gas. Moreover, an objective function aiming at simultaneously calculating NOx emissions and boiler efficiency from thirty-seven operating parameters was represented by a back propagation neural network model which was optimized by genetic algorithm, and the nineteen levels damper openings of secondary air and separated overfire air were optimized by adopting genetic algorithm so as to simultaneously achieve low NOx emissions and high boiler efficiency. Damper openings of secondary air located at blast furnace gas nozzles zone (GAA/GA/GBB) and coal combustion zone (AS/BS/CS and AA/AB/BC/CC) were adjusted from 10 to 100% in specially designed burner, and the better damper openings were experimentally obtained. The damper openings of separated overfire air were also changed from 10 to 100%, but it hard to evaluate the better damper openings due to the boiler efficiency and NOx emissions simultaneously decrease with the increase of separated overfire air. Finally, the optimal operation of secondary air and separated overfire air were achieved by using optimization model, which could provide references for the adjustment of secondary air and separated overfire air.

Corrosion Testing of Thermal Spray Coatings in a Biomass Co-Firing Power Plant

Large-scale use of biomass and recycled fuel is increasing in energy production due to climate and energy targets. A 40% cut in greenhouse gas emission compared to 1990 levels and at least a 27% share of renewable energy consumption are set in EU Energy Strategy 2030. Burning fuels with high content of corrosive species such as chlorine and heavy metals causes deterioration of boiler components, shortened lifetime, limited availability of a plant and hence higher maintenance and investment costs and lower thermal and economic efficiency. Coatings can be applied to protect the critical boiler components against high temperature corrosion. In this study, five thermal spray coatings were tested in an actual biomass co-firing boiler for 1300 h with a measurement probe. The coatings were analyzed after the exposure by metallographic means and scanning electron microscope/energy-dispersive X-ray spectroscope (SEM/EDX). The deposits formed on the specimens were analyzed by X-ray fluorescence. At 550 °C, the coatings showed excellent corrosion performance compared to reference material ferritic steel T92. At 750 °C, tube material A263 together with NiCr and NiCrTi had the highest corrosion resistance. To conclude, thermal spray coatings can offer substantial corrosion protection in biomass and recycled fuel burning power plants.

The influence of poisoning on the deactivation of DeNOx catalysts

This paper summarizes the results of a research on the influence of the poisoning of the SCR catalyst on its structure. Samples of commercially available SCR catalysts were exposed to real flue gases inside a pulverized coal boiler co-firing coal and biomass. The catalysts were investigated by SEM-EDS, XRD, AAS, UV–vis and 1-butene isomerization as a test reaction. Additionally, ash collected from the catalysts was characterized. The obtained results showed a decrease in the activity by ash and alkali metals originating from biomass. Neither the structural changes in the support nor the changes in the oxidation state and distribution of vanadium were observed during the entire testing period. The acidity of the catalyst, operated for the shortest period (2270 h), increased due to the formation of sulfate species arising from the presence of SO 2 in the flue gases. The role of sulfate species and alkali cations in poisoning of catalytic sites is discussed. Cet article expose les résultats d’une étude portant sur l’influence de l’empoisonnement du catalyseur de la RCS sur sa structure. Trois échantillons d’un catalyseur commercial de SCR ont été exposés aux gaz en sortie de brûleur dans une chaudière PF pendant la co-combustion de charbon et de biomasse. Les méthodes d’analyse utilisées sont le MEB-EDS, la DRX, la spectroscopie d’absorption atomique, la spectrométrie UV–vis et le test de réaction à l’isomérisation du 1-butène. Les cendres récupérées sur le catalyseur ont été caractérisés. L’activité diminue en présence de cendres et de métaux alcalins dans la biomasse. Ni la structure du support, ni l’état d’oxydation, ni la distribution du vanadium n’ont été modifiés durant toute la durée du test. L’acidité du catalyseur testé le moins longtemps (2270 h) a augmenté du fait de la formation de dérivés du sulfate provenant du SO 2 contenu dans les gaz d’échappement. Le rôle de ces dérivés et des cations alcalins sur l’empoisonnement catalytique des sites est discuté.

High-Temperature Characterization of Inorganic Particles and Vapors in a Circulating Fluidized Bed Boiler Cofiring Wood and Rubber Waste

The effects of varying fuel mixtures and using a lime additive were studied in a 125-MWth circulating fluidized bed boiler. A high-temperature aerosol measurement method using a hot-dilution probe was used to characterize the particles and condensing inorganic vapors upstream from the superheater. The particle size distributions of the extracted samples indicate that when high-sulfur rubber waste, waste wood, and forest fuel were cocombusted, the hot flue gas contained no substantial amount of particulate matter in the fine (<0.3 μm) particle size range, although the SO2 concentration exceeded 70 ppm. Only a nucleation mode was observed, which was presumably formed from inorganic vapors that condensed in the sampling probe. The size-segregated elemental analysis of the extracted samples indicated that when lime was added, the nucleation mode mainly comprised condensed alkali chlorides, while the sulfates dominated the mode when no lime was added. The presumed explanation for the sulfates in the nucleation mode was the sulfation of the alkali chlorides inside the sampling system. When only the wood fuels and no rubber fuel were cocombusted, the SO2 concentration in the gas was approximately 5 ppm. In this case, an alkali sulfate particle mode formed at approximately 70 nm in the hot flue gas. In addition, vapors of alkali chlorides and lead formed particulate matter inside the sampling probe when using low dilution ratios.

バイオマス混焼石炭焚きボイラにおける脱硝触媒の劣化特性

バイオマス混焼石炭焚きボイラにおける脱硝触媒の劣化特性

Thermal Spray Coatings for High-Temperature Corrosion Protection in Biomass Co-Fired Boilers

There are over 1000 biomass boilers and about 500 plants using waste as fuel in Europe, and the numbers are increasing. Many of them encounter serious problems with high-temperature corrosion due to detrimental elements such as chlorides, alkali metals, and heavy metals. By HVOF spraying, it is possible to produce very dense and well-adhered coatings, which can be applied for corrosion protection of heat exchanger surfaces in biomass and waste-to-energy power plant boilers. Four HVOF coatings and one arc sprayed coating were exposed to actual biomass co-fired boiler conditions in superheater area with a probe measurement installation for 5900 h at 550 and 750 °C. The coating materials were Ni-Cr, IN625, Fe-Cr-W-Nb-Mo, and Ni-Cr-Ti. CJS and DJ Hybrid spray guns were used for HVOF spraying to compare the corrosion resistance of Ni-Cr coating structures. Reference materials were ferritic steel T92 and nickel super alloy A263. The circulating fluidized bed boiler burnt a mixture of wood, peat and coal. The coatings showed excellent corrosion resistance at 550 °C compared to the ferritic steel. At higher temperature, NiCr sprayed with CJS had the best corrosion resistance. IN625 was consumed almost completely during the exposure at 750 °C.

Could biomass-fueled boilers be operated at higher steam temperatures? Part 2: Field tests of candidate superheater alloys

Operating superheater tubes of biomass-fired boilers at considerably higher temperatures than can be tolerated by commonly used structural materials could improve boiler efficiency. However, corrosion of the superheater tubes promoted by interaction with the relatively low melting point deposits that accumulate on the tubes becomes a major issue. The objective of this study was to use field exposures to determine if there are materials acceptable for use as superheater tubes that can operate at temperatures at least 100 Celsius degrees above the current maximum superheater temperature. Corrosion probes containing multiple specimens of nine different alloys were exposed for at least 2000 h in the superheater area of three biomass boilers where the deposits were determined to be enriched in potassium or chlorine. Similar specimens were also exposed in a boiler co-firing coal and wood. For the probes, specimen temperatures ranged from a low of less than 400°C to temperatures above 600°C for all but one case. Following exposure, a section was taken from each specimen and examined using light microscopy and scanning electron microscopy. Results of the examination of these specimens showed some alloys performed considerably better than others, but the corrosion resistance could not be related to chromium or molybdenum content of the alloys.

RPF／木質チップ燃焼ボイラー設備概要と運用実績

RPF／木質チップ燃焼ボイラー設備概要と運用実績

Effects on a 50 MWth Circulating Fluidized-Bed Boiler Co-firing Animal Waste, Sludge, Residue Wood, Peat, and Forest Fuels

This work is a part of an effort to maximize the operational safety of a 50 MWth circulating fluidized-bed (CFB) boiler located in Perstorp, Sweden, co-firing animal waste, peat, waste wood, forest residues, and industrial sludge. An increase in the CFB boiler availability reduces the use of expensive fossil fuel (oil) in backup boilers during operational problems of the CFB boiler. The work includes a thorough mapping and analysis of the failure and preventive maintenance statistics, together with elemental analysis of boiler ash and deposits, flue gas, and fuel fractions. Correlations between boiler parameters and boiler availability are sought, and recommendations regarding boiler design and operation are made. An explicit description of the boiler is made to allow for the use of presented material as future reference material. It was observed that the failure frequency is especially high where (1) rapid chloride-rich windward deposit buildup is combined with (2) high construction material temperature and (3) windward soot blowing. In areas where one of these factors was absent, a more moderate material loss could be seen. The flue gas average elemental composition can be regarded as close to constant as it flows through the series of heat exchangers. Thus, the significant differences in deposit buildup of different flue gas cross-sections cannot be a result of changed average flue gas composition. The areas of the steam tubes suffering from rapid material loss are also exposed to high deposit rates. Downstream of a well-defined temperature threshold in the secondary superheater, neither material loss nor substantial deposit buildup could be seen. Tube deposits are dominated by Na, S, Ca, K, and P, but only Na, K, and S are enriched in the windward tube deposits relative to the fly ash bulk composition. The temperature of the flue gas is the major parameter governing the rate of deposit buildup in the boiler heat exchangers. Of the fuel nitrogen, 95 wt % leaves the process as N2(g). Fuel mix ash content analysis via a separate ashing of different fuel fractions by heating to 550°C does not reflect the ash content of the fuel mix correctly. The soot blowing angle of attack on the deposits should be regarded in areas with rapid deposit growth when boilers and soot blowers are designed to allow for efficient tube cleaning. The use of heterogeneous fuel in the boiler creates strong variations in fuel, flue gas, and particle composition and makes it increasingly important to have online measurements to be able to understand and control the furnace chemistry. The filter ash in the flue gas baghouse filter effectively sorbs HCl(g) and NH3(g) from the flue gas already without the addition of sorbents. Online flue gas measurement to control the furnace chemistry must therefore be installed upstream of the filter to enable accurate control. Also, a significantly larger filtration area can be installed in the baghouse filters with a slight increase in cost, to allow for efficient use of the ash as free of cost sorbent and lowered emission levels. Scanning electron microscopy analysis of the flue gas deposits shows that no pieces of ground bone, sand particles, or other relatively large flue gas particles contribute directly to the deposit buildup. White crystals rich in N and Cl, most likely ammonium chloride, precipitate downstream of the flue gas filter. The precipitation interferes with the dust emission measurement and forces a reduced usage of waste-derived fuels because of the exceedance of environmental limits. More expensive forest fuels are used to replace waste-derived fuels, resulting in a higher fuel cost.

A two-tier approach to the data-driven modeling on thermal efficiency of a BFG/coal co-firing boiler

Even though ratio of air to fuel is the major factor in determining the thermal efficiency of a boiler, how to optimize the ratio in the real operation is still more like art than science, especially for a gas/solid multi-fuel combustion system. This study, taking operation data from a real gas/solid fuels co-firing boiler, is aimed to develop the thermal efficiency model. To cope with the complexity of combustion mechanism in a co-firing boiler, this study proposed a two-tier approach to modeling thermal efficiency. The first tier is to transform the plant input variables into the derived variables, which are physically and statistically meaningful to the model-building. In the second tier, this study proposed an adaptive modeling approach by employing nonnegative garrote variable selection and auto-regression integrated moving average correction. Both approaches are first time proposed in building the thermal efficiency model for boilers. The prediction error of boiler thermal efficiency made by the acquired model reaches less than 0.03%. The high accuracy of the proposed modeling approaches makes the implementation of the model-based control of ratio of air to fuel for improving boiler’s efficiency readily practicable.