Circulating Fluidized Bed Boiler Research Articles

Application of Fluidization Reconstruction Energy-Saving Combustion Technology on 300MW CFB Boiler

Aiming at high power consumption by auxiliaries of circulating fluidized bed (CFB) boiler, combustion tests were carried out on a 300MW inferior anthracite fired CFB boiler to decrease the bed material inventory via energy saving combustion technologies for CFB boiler based on fluidization reconstruction. The effects of fluidization reconstruction on boiler performance improvement were analyzed. Application practices show that after fluidization reconstruction, the power consumed by auxiliaries of the CFB boiler decreases obviously. Auxiliary power ratio of the 300MW boiler unit has been reduced from 6.1% to 4.3%. The erosion of boiler heating surface has been alleviated obviously.

Application of the Wind-Water Combined Slag Coolers in CFB Boilers

At present, there have been a lot of accidents happened in the wind-water combined slag coolers of the Circulating Fluidized Bed (CFB) boiler power plants, which usually caused the low-load or even stop of the units along with great financial losses. Comprehensively considering the actual conditions of the domestic CFB boiler power plants, the theoretical analysis and thermodynamic calculation were conducted aiming to solve the specific problems found in the operation. There were new designs and retrofitting measures in the integral structure and some key components, such as the slag inlet-tube. The operation effect of the slag coolers, i.e. the stability and heat-recovery efficiency etc., were significantly improved by retrofitting the devices.

Status and Prospect of Large-Scale Circulating Fluidized Bed Boiler

The paper is focused on the present situation and the development of large-scale circulating fluidized bed (CFB) boilers. Several developed technology of CFB such as supercritical and ultra supercritical pressure CFB boilers for power plants, oxy-fuel CFB boiler for CO2 capture and high-density circulating fluidized bed gasifier for advanced IGCC/IGFC are introduced in this paper.

Modeling of heat transfer coefficient in the furnace of CFB boilers by artificial neural network approach

The present work introduces a way of predicting the local heat transfer coefficient in the combustion chamber of the circulating fluidized bed boiler (CFB) by the artificial neural network (ANN) approach.Neural networks have been successfully applied to calculate the local overall heat transfer coefficient for membrane walls, Superheater I (SH I, Omega Superheater) and Superheater II (SH II, Wing-Walls) in the combustion chamber of the 260MWe CFB boiler. The previously verified numerical model has been used to obtain the overall heat transfer coefficients, necessary for training and testing the ANN. It has been shown, that the neural networks give quick and accurate results as an answer to the input pattern. The local heat transfer coefficients evaluated using the developed ANN model have been in a good agreement with numerical and experimental results.

Research on the heat transfer model of platen heating surface of 300 MW circulating fluidized bed boilers

The heat transfer of the platen heating surface of circulating fluidized bed (CFB) boilers is a complex process. Because of technical protection and difficult measurement, at present there is no public calculation method which can be applied to engineering. Three 300MW CFB boilers in actual operation in different field sites were conducted, the parameters of temperature and pressure at the side of steam and flue gas were measured respectively. Based on the tests at different loads, the effects of solids suspension concentration and average temperature parameters etc. on the heat transfer were investigated, and then the heat transfer coefficient calculation model of platen heating surface at the flue gas side was established, which takes the effects of structure and dimension of platen heating surface, furnace temperature, steam temperature, heat transfer coefficient at the steam side, emissivity of tube wall and fluidization velocity etc. into consideration. The field test data obtained from another 300MW CFB boiler were used to verify the model. After comparing the calculated results and the values from the actual field test, it is found that the error is lower than 5%, which is within the precision permission range of engineering application. It is indicated that the calculation results using this model agree well with the experimental results on the site, confirming the reliability of this heat transfer model, which means that it can be used to calculate the heat transfer of platen heating surface of 300MW CFB boiler and can provide reference for design, commissioning, operation of 300MW CFB boilers.

A Study on the acoustical properties of road surfaces of recycled CFB materials

Traffic noise and noise control are major concerns of transportation, as noise and vibration will cause both psychological and physiological consequences. Great efforts have been made to use more sound absorbent road surfaces in order to reduce traffic noise. The raw materials under study are recycled byproducts from circulating fluidized bed boiler (CFB). The recycled CFB materials have been approved for use by the Environmental and Transportation Departments in various regions throughout the United States for road stabilization and base/surface installations. These (CFB) materials have shown good ecological, civil and mechanical properties, and are more environmentally friendly than asphalt and concrete. However, the acoustical properties of the pavements are not known. Two types of measurements have been conducted. First, the traffic noise was measured using the statistical pass-by method on various road surfaces and a comprehensive comparison was conducted. Second, the sound absorption coefficients of the CFB materials were measured using impedance tubes.

Fly ash recirculation by bottom feeding on a circulating fluidized bed boiler co-burning coal sludge and coal

Coal sludge is a by-product of coal washing, whose production is huge. Burning it in Circulating Fluidized Bed (CFB) boiler can both recover the heat and reduce the pollution. However, the combustion performances of CFB boilers burning coal sludge are generally not high because the particle size of fuel is small and its resident time in the furnace is short. With the purpose of improving combustion efficiency and reducing pollutions, fly ash recirculation by bottom-feeding (FARBF) technology was applied to a 75t/h CFB boiler burning mixture of coal sludge and coal. Industrial experiments were carried out to investigate the influence of fly ash recirculation rate on combustion performance and pollutant emission characteristics of the boiler. Results show that with FARBF, the dense bed temperature drops while the furnace exit temperature increases, the temperature distribution in the furnace becomes uniform. Under the condition of 100% maximum continuous rate (MCR), the combustion efficiency increases from 92% to 95% and the desulfurization efficiency increases from 83% to 90% as the fly ash recirculation rate increases from 0t/h to 8t/h. As the recirculation rate increases, the emissions of NO and CO decrease, but the particulate matter emission increases. The present study indicates that FARBF technology can improve the combustion performance and reduce pollution emissions (except for particulate matter emission) for CFB boilers burning coal sludge, and it can bring significant economical and environmental benefits.

Based on Multi-Sensor Information Fusion Circulating Fluidized Bed Boiler Combustion Process Clustering Control Research

Abstract Over the decade, due to the fact that the global energy resources are in deadly shortage, much emphasis is put on the energy consumption in thermal power throughout the world. Following developed is Circulating Fluidized Bed Boiler (CFBB) in recent years, a kind of combustion boiler that can clean and desulfurize the coal efficiently in the combustion process.Circulating Fluidized Bed Boiler (CFBB) is a control object with features of time varying parameters, large delay, and multivariable control tightly coupled. Noticeably, many factors influence the combustion process. This paper designs a three level ART2-BP-BP of data fusion--fusion cluster control system based on methods of multi-sensor information fusion and cluster analysis. It completes data fusion from the data level, the feature level to the decision level. Especially, the concept of Situation Threat Space aiming at the potential threats in CFBB is presented. Results of simulation show that the control system in this paper is feasible and effective, in particular, the control system still has more satisfactory control effect in the case of a variety of sensor failures.

Heat transfer characteristics of fluidized bed heat exchanger in a 300 MW CFB boiler

In order to investigate the heat transfer characteristics of fluidized bed heat exchanger (FBHE), a series of experiments was carried out in a commercial 300MW circulating fluidized bed (CFB) boiler with FBHE. The parameters of steam, solids and air in FBHE were measured at different boiler loads, based on which the absorbed heat and heat transfer coefficient were calculated. Further study indicates that when the calculated results are applied to the design of large-scale CFB boilers, the bed side heat transfer coefficient in FBHE can be simplified as the function of solids temperature and flow. Therefore, the empirical model of heat transfer coefficient at bed side is put forward. The deviation between calculated results and measured values is acceptable in engineering application. This model provides strong support for the FBHE design in 600MW supercritical CFB boilers.

Development of Methane and Nitrous Oxide Emission Factors for the Biomass Fired Circulating Fluidized Bed Combustion Power Plant

This study makes use of this distinction to analyze the exhaust gas concentration and fuel of the circulating fluidized bed (CFB) boiler that mainly uses wood biomass, and to develop the emission factors of Methane (CH4), Nitrous oxide (N2O). The fuels used as energy sources in the subject working sites are Wood Chip Fuel (WCF), RDF and Refused Plastic Fuel (RPF) of which heating values are 11.9 TJ/Gg, 17.1 TJ/Gg, and 31.2 TJ/Gg, respectively. The average concentrations of CH4 and N2O were measured to be 2.78 ppm and 7.68 ppm, respectively. The analyzed values and data collected from the field survey were used to calculate the emission factor of CH4 and N2O exhausted from the CFB boiler. As a result, the emission factors of CH4 and N2O are 1.4 kg/TJ (0.9–1.9 kg/TJ) and 4.0 kg/TJ (2.9–5.3 kg/TJ) within a 95% confidence interval. Biomass combined with the combustion technology for the CFB boiler proved to be more effective in reducing the N2O emission, compared to the emission factor of the CFB boiler using fossil fuel.

Comparative study on air and oxy combustion in a pilot CFB boiler

In the present work, measurement experience of oxy combustion in a pilot scale circulating fluidized bed (CFB) combustor is summarized. The aim was to study combustion dynamics under air-and oxygen-firing conditions in order to develop and validated combustion controls for Flexi-Burn™ CFB combustion technology. Dynamic CFB-pilot combustion tests were carried out including various step and ramp tests in both air and oxy combustion and different operation strategies for oxy combustion.

Experimental research of CFB ash deposition on helical finned tubes

Abstract In order to evaluate the influence of ash deposition on heat transfer, experiments focusing on the influence of ash deposition on heat transfer are carried out in a 75t/h CFB(circulating fluidized bed) boiler unit. The test bundles are made of helical finned tubes in staggered or in-line arrangement. The fouling factor ɛ and the overall heat transfer coefficient ratio ψ are employed to evaluate the influence of ash deposition. The fitting correlations of ɛ and ψ under different flue gas velocities are obtained respectively. The experiment reveals that the fouling factor decreases and the overall heat transfer coefficient ratio increases with the rising flue gas velocity. Compared with the in-line arrangement, the staggered arrangement helps to lighten ash deposition. The fouling factors obtained from the present experiments are one-order smaller in the magnitude than the recommended values that are widely used in China at present. And the present results are of the same order as those gained from cold test with sands instead of fly ash. Compared with the existing research, the present results are more suitable for application in practice.

Unburned carbon fraction with operation variables in a commercial circulating fluidized bed boiler during co-combustion of various anthracites

Reduction of unburned carbon fraction in exhaust during co-combustion of various coals in a circulating fluidized bed boiler (CFB) is required to save energy loss and to optimize coal utilization as well as to improve the boiler efficiency. In this study, the effects of operation variables such as coal, air and heat flow rates, co-combustion ratio of each coal, primary to secondary air ratio on unburned carbon fraction were analyzed and evaluated in two units of 200 MWe circulating fluidized bed boiler in the Tonghae thermal power plant. From the results, the comprehensive correlation among unburned carbon fraction and operation variables in #1 and #2 units of the CFB boiler could be derived with a good agreement. This would be expected to give a good guideline to reduce the unburned carbon content in exhaust in the CFB boiler.

The Study on the Fuzzy Control Algorithm for Main Steam Pressure Control of Circulated Fluidized Bed Boiler

The main steam Pressure is one of the most important guidelines on Circulating Fluidized Bed Boiler (CFBB) operation quality and an important part in control system of CFBB. However, It is very difficult to establish the exact mathematical models of controlled objects because the combustion system of circulating fluidized bed boiler is an object that has many features: distributed parameters, nonlinear, time-varying and long time-delaying. it is unfavorable to control it with traditional controller. Therefore , In this paper fuzzy controller is used in controlling main vapor pressure systems of CFBB, and the fuzzy cascade control system is designed. In computer simulation, the fuzzy cascade control system exert stably, and has perfect control effect to main vapor pressure systems of CFBB.

Heat transfer in the rotary ash cooler with residual char combustion considered

In circulating fluidized-bed (CFB) boilers, some residual char is left in the ash when the ash is drained into the rotary ash cooler (RAC). The residue char will combust in the RAC given oxygen is present. It is important to understand and predict the influence of residual char combustion on the heat transfer process in the RAC in order to avoid slagging and fouling inside the RAC. In this paper, an improved heat transfer model of the RAC was developed in which the residual char combustion process was considered. Based on the analysis, the shrinking sphere model was selected to describe the residual char combustion. The improved model was validated by the final ash temperature and cooling water temperature data measured from a few RACs equipped with the coal fired CFB boilers with different steam output. The predictions of the improved model agree well with the field measurement data, within an error range of ± 10%. The simulation results also show that the heat released from residual char combustion counts for about 60–80% of the total heat released by ash in the inlet section of the RAC, and the influence of residual char combustion decreases rapidly along the ash flow. The final ash temperature increases accordingly with the increase of inlet carbon content, and decreases with the increases of residual char size. As particle size is larger than 3 mm, the final ash temperature changes little at a given carbon content due to a low mass burning rate. It is suggested that combustion of residual char should be considered when the inlet carbon content is over 2.5%; otherwise, the combustion of residual char in the RAC could be neglected.

Development of standardized boilers with a circulating fluidized bed for repowering of TPPs

The current status of circulating fluidized bed (CFB) technology employed at foreign TPPs is briefly analyzed.. It is demonstrated that CFB technology is entirely suitable for the building of 225- and 330-MW units with enhanced steam parameters, and also for replacement of boilers at TPP with cross links. Placement of prospective standards into effect for harmful effluents, and diversification of fuel supply are important advantages of this technology. It is shown that CFB boilers based on unified subassemblies could be built at least for groupings of fuels. Results of mathematical modeling of processes in furnaces of CFB boilers, which are in satisfactory agreement with data obtained from simplified engineering methods, are presented. Further improvement of the mathematical model, and a series of analyses of the furnace circuit in the nonsteady statement with a supercomputer are being traced.

Experimental Study on Microstructure of Fly-Ash from Circulating Fluidized Bed Boilers

Circulating fluidized bed (CFB) combustion techniques have been widely used in China. In order to improve CFB boiler performance it is necessary to study on microstructures of fly-ash. With the help of nitrogen adsorption instrument and scanning electron microscopy, the pore structure of fly-ash in circulating fluidized bed boilers are studied by nitrogen adsorption/desorption isotherms of fly-ash, hysteresis loop and pore distribution. The results indicated that different particle sizes of fly-ash in CFB boilers are of similar nitrogen adsorption isotherms, pore types and the pore size distribution, and the most probable pore radius of fly-ash is about 2nm. Adsorption isotherms of fly-ash is the second type, and the macro-porous and meso-porous types are tapered hole, parallel plate slit hole and the ink bottle shape hole. And meso-pore in proportion is the largest. Micro-pores are not discovered in fly-ash from CFB boilers.

Thermal-hydraulic analysis of a 600 MW supercritical CFB boiler with low mass flux

Supercritical Circulating Fluidized Bed (CFB) boiler becomes an important development trend for coal-fired power plant and thermal-hydraulic analysis is a key factor for the design and operation of water wall. According to the boiler structure and furnace-sided heat flux, the water wall system of a 600 MW supercritical CFB boiler is treated in this paper as a flow network consisting of series-parallel loops, pressure grids and connecting tubes. A mathematical model for predicting the thermal-hydraulic characteristics in boiler heating surface is based on the mass, momentum and energy conservation equations of these components, which introduces numerous empirical correlations available for heat transfer and hydraulic resistance calculation. Mass flux distribution and pressure drop data in the water wall at 30%, 75% and 100% of the boiler maximum continuous rating (BMCR) are obtained by iteratively solving the model. Simultaneity, outlet vapor temperatures and metal temperatures in water wall tubes are estimated. The results show good heat transfer performance and low flow resistance, which implies that the water wall design of supercritical CFB boiler is applicable.

Combustion Characteristics of the External Circulation Loop on Baima’s 300 MWe Circulating Fluidized Bed Boiler

Local measurements of concentrations of O2, CO, SO2, and NOx were carried out inside Baima’s 300 MWe circulating fluidized bed (CFB) boiler. Custom-made probes with a length of 4.8 m were used to take samples from the boiler’s external circulation loop, especially from the cyclones and fluidized bed heat exchangers (FBHEs). Eighteen points were used to introduce the probes, and the penetration depth inside the boiler was up to 3.7 m. Solid particles at the entrance and exit regions of both the cyclones and FBHEs were also sampled for analyzing the particle size distribution and carbon content. Results implied that there was significant combustion in the boiler’s external circulation loop, and most of the combustion was from the cyclones. The flue gas temperature at the cyclone outlet could be 135 °C higher than that at the cyclone inlet. The ratio of the oxygen consumption in the cyclone to that of the entire combustion process of the boiler was nearly 12%. The O2 consumption rate might mainly come from the burn-out of char particles rather than the combustible gas. With regard to the FBHEs, the inside combustion phenomenon was not as severe as that in the cyclones. Obvious differences of gas concentrations were observed at the outlet between those FBHEs with different functions. The experimental results can provide information for adjusting and designing the heat-surface arrangement and lay a foundation for modeling the flow structure, combustion, and heat transfer in similar large-scale CFB boilers.

Adaptive soft sensor for fluidized bed quality: Applications to combustion of biomass

The use of challenging, heterogeneous fuels and multi-fuel combustion is characteristic for modern-day circulating fluidized bed (CFB) combustion. This increases the need for monitoring the performance of the process. However, long-term online measurement of different phenomena in CFB boilers is a challenging task, and the lack of measurements complicates direct monitoring of the process. For this reason there is a need for new methods like soft sensors, which could be used to support or compensate the direct measurements of bed diagnostics. This paper demonstrates an adaptive soft sensor that utilizes process data to estimate the quality of the bed by predicting the grain size distribution in the bottom ash of circulating fluidized bed boilers. The grain size fractions from the sieving of bottom ash are used as reference values for bed quality. Either linear or nonlinear regression can be used to train the model. Adaptive variable selection is performed before constructing the dynamic model, which utilizes the selected variables to estimate the different grain size fractions online. The new approach has been tested using process data and grain size distributions measured from three individual CFB boilers fired by biomass, and the results show that the adaptive approach provides a useful tool for bed diagnostics.