Fluidized Bed Combustion Boiler Research Articles

Mechanical Activation of CaSO4 Enriched Petroleum Coke Fly Ash for Development of Green Pellets

Mechanical Activation of calcium sulphate enriched petroleum coke fly ash (PCFA) generated from circulation fluidized bed combustion (CFBC) boiler was investigated to improve the surface reactivity of PCFA. The physico- chemical, mineralogical (XRD), morphological (SEM) characteristics of PCFA, activated PCFA and developed green pellets were studied in detail. It was found that the milling time of 45 minutes is efficient for the activation of PCFA and results in fragmentation of coarse particle into fine porous particles. Mechanical activation results in enhancing physical properties and reactivity of PCFA without any further chemical treatment. The mean particle size of activated PCFA with 45 min milling time was 12.51-12.60µm and the porous morphology were seen through SEM. The hydration phases like ettringite, portlandite and calcium silicate hydrate mainly contribute to the development of mechanical strength in activated PCFA pellets which were also confirmed through morphology of needle-shaped crystallites. The study recommends that mechanically activated PCFA could be used as an adsorbent material for heavy metals removal from waste waters.

Optimization of Circulating Fluidized Bed Boiler Combustion Key Control Parameters Based on Machine Learning

During the coal-fired circulating fluidized bed unit participation in the peak regulation process of the power grid, the thermal automatic control system assists the operator to adjust the mode focusing on pollutant control and ignoring the economy so that the unit’s operating performance maintains a huge potential for deep mining. The high-dimensional and coupling-related data characteristics of circulating fluidized bed boilers put forward more refined and demanding requirements for combustion optimization analysis and open-loop guidance operation. Therefore, this paper proposes a combustion optimization method that incorporates neighborhood rough set machine learning. This method first reduces the control parameters affecting multi-objective combustion optimization with the neighborhood rough set algorithm that fully considers the correlation of each variable combination and then establishes a multi-objective combustion optimization prediction model by combining the online calculation of boiler thermal efficiency. Finally, the NSGAII algorithm realizes the optimization of the control parameter setting value of the boiler combustion system. The results show that this method reduces the number of control commands involved in combustion optimization adjustment from 26 to 11. At the same time, based on the optimization results obtained by using traditional combustion optimization methods under high, medium, and medium-low load conditions, the boiler thermal efficiency increased by 0.07%, decreased by 0.02%, and increased by 0.55%, respectively, and the nitrogen oxide emission concentration decreased by 5.02 mg/Nm3, 7.77 mg/Nm3, and 7.03 mg/Nm3, respectively. The implementation of this method can help better account for the economy and pollutant discharge of the boiler combustion system during the variable working conditions, guide the operators to adjust the combustion more accurately, and effectively reduce the ineffective energy consumption in the adjustment process. The proposal and application of this method laid the foundation for the construction of smart power plants.

Experimental Analysis of CFBC Boiler and AFBC Boiler with Different GCV, Boiler Loads and Excess Air

Abstract: The main motive of this study is to experimental analysis of the Atmospheric fluidized bed combustion boiler and Circulating fluidized bed combustion boiler with different gross calorific value of coal, boiler loads and excess air. For this analysis, use textile waste as a primary fuel and calculate GCV with help of bomb calorimeter. Conduct energy calculation of the overall plant and determine the efficiencies and energy losses of all the major components of the thermal power station. The study was carried out at Thermal power station of Industry Yarns at Mandideep and boiler section of thermal power plant is considered for the purpose of exergy analysis. The boiler of a power plant is the most effective section in eliminating exergy. Calculate the efficiency of CFBC and AFBC Boiler with different GCV of Textile waste and it is clearly shows that efficiency of CFBC boiler is higher than AFBC boiler in same GCV of textile waste. The present investigation show results of 30 mw power plant. Experiments were conducted using 0%, 20 %, 30% and 40% of excess air and 65%,70%,75%,80%,85%,90%,95% ,100% boiler loads. In the present investigation boiler house gives the best results at 0% excess air with maximum boiler load as far as the boiler efficiency (75.2%) are concerned. 65% boiler load With 0% excess air the boiler efficiency is found to be maximum (75.2%), which gives minimum heat loss. Without excess air AFBC boiler is not capable to burn low grade fuels show it is clear that for low grade fuel maximum efficiency of thermal power plant achieved by CFBC boiler because low grade fuel completely burns with 0% excess air.

Investigation of fouling and corrosion of low-temperature reheater in a CFBC boiler

A remarkable feature of circulating fluidized bed combustion technology is the adeptness to handle a wide variety of solid fuels and their mixtures with high availability and low emissions. The fuels mainly used in fluidized bed boilers are various types of coal, peat, refuse-derived fuels, wood and other biomass. Nonetheless, the properties and behavior of some solid fuel ashes present challenges in power production regardless of the combustion technology and may even limit the use of these fuels. Biomass-based fuels typically contain high contents of easily vaporizable alkalis and chlorine, as also oil shale does. Extensive vaporization of alkalis or chlorine from the fuel increases the risk for ash-related problems such as fouling, slagging and corrosion.Co-utilization of biomass and retort gas in oil shale-fired power stations is an additional process option that increases the fuel flexibility but at the same it also increases operational risks, especially fouling and corrosion.Operational experience from Foster Wheeler two circulating fluidized bed combustion units, which were commissioned in 2004 and 2005, have proven that the above-mentioned fouling or slagging issues have been avoided. Even with different fuel mixtures. This was one of the main reasons why 300MWel Auvere power plant was acquired with circulating fluidized bed combustion technology in 2011. The plant was due to be handed over to Eesti Energia by General Electric (former Alstom) in November 2015. It was delayed since emission limits were not achieved. Therefore, additional flue gas cleaning devices were needed to be installed. Meanwhile, the power plant continued operating at loads where emissions standards were met.The 300MWel Auvere power plant was finally commissioned in 2018. Since then, the circulating fluidized bed combustion boiler has been facing severe operational problems such as fouling and corrosion of the low-temperature reheater.The failures of low-temperature reheater tubes have been occurred as a result of operation conditions.Three different reasons for low-temperature reheater malfunctions have been determined: erosion, changes in metal structure and high temperature chlorine corrosion.

Optimization of Atmospheric Fluidized Bed Combustion Boiler by Computational Fluid Dynamics

Optimization of Atmospheric Fluidized Bed Combustion Boiler by Computational Fluid Dynamics

Iron based oxygen-carrier-aided oxy-fuel combustion of coal char: Reactivity and oxygen transfer mechanism

Adding an active oxygen carrier to the inert bed material may favor the oxygen distribution in fluidized bed (FB) combustors. This so-called method “Oxygen-carrier-aided combustion, OCAC” has been applied recently to air combustion in FB boilers, but could also be potentially interesting in oxy-fuel combustion. Here we analyze OCAC in oxy-fuel combustion by experimental determination of the reactivity of char from three coals (lignite, bituminous and anthracite coal) using three oxygen carriers (OC, analytical reagent Fe2O3, hematite, and steel slag). The tests were conducted in a micro thermo-gravimetric analyzer (micro-TGA) and the combustion kinetics was determined for the nine combinations of char and OC. Additional tests were conducted in a macro-TGA i.e., much sample in a big ceramic crucible, to evaluate the phase composition and crystal quality using X-ray diffraction (XRD) to the combustion residues collected at various degrees of carbon conversion (0.2, 0.5, and 0.8). The results show that the burnout temperature decreases with OCs as the combustion rate increases, while the ignition temperature hardly changes. The enhancement of the rate of char combustion by OCs is in the following order: steel slag < hematite < AR-Fe2O3. The lower the fuel rank, the stronger the effect of the oxygen carrier. The combustion kinetics of chars using OC has a higher activation energy and pre-exponential factor than pure char. The enlarged lattice constant of Fe2O3 measured by XRD during the char combustion indicates that the redox reactions of Fe2O3 accelerate the oxidization of char by enhancing the rate of oxygen transport to the carbon surface.

Extending the Life Cycle of Cement Binders by Partially Replacing Portland Cement with Different Types Fluidized Bed Combustion Fly Ash

A significant reduction in the CO2 emission associated with cement production is obtained by partially replacing Portland cement with supplementary cementing materials (SCM’s): e.g., siliceous fly ash or granulated blast furnace slag. In the near future, the limited availability of these materials will do more attractive to use ashes from combustion in fluidized bed boilers, which currently are mainly deposited in various landfills. Paper identifies the effect of Fluidized Bed Combustion (FBC) fly ash from both hard and brown coal combustion on the durability of mortars exposed to sodium and magnesium sulfate solution at different curing temperature: 20 and 5 °C. The evaluation was based on the results of long-term linear changes of mortar samples made with Portland cement and different amounts of FBC fly ash addition stored in a corrosive environment, as well as the evaluation of the type of formed corrosion products using XRD and microstructural studies (SEM/EDS). It has been shown that amount of FBC fly ashes used in binders significantly determines sulfate resistance of prepared cements as well as its chemical composition. By using fluidized ashes, the sulfate resistance of cement binders can be achieved with their content even of 15%.

Enhanced autogenous self-healing of cement-based composites with mechanically activated fluidized-bed combustion fly ash

This study investigates the effect of the modification of cement-based composites with mechanically activated fly ash from lignite combustion in fluidized bed boilers (MAFBC fly ash) on self-healing. The subject of the research was mortar samples in which, after 28 days of maturing, cracks 0 to 750 µm wide were mechanically induced, followed by curing for 152 days. Via computer processing and analysis of high-resolution scanner (HRS) images, the maximum average crack width reduction was determined to be 43%. The analysis of samples via ultrasonic pulse velocity (UPV) measurements estimated the degree of crack filling with newly formed material during self-sealing to be as high as 58%. In terms of mechanical properties, a maximum flexural strength recovery of 54% was observed due to microstructural changes in the contact area between the cement matrix and polypropylene fibers. To examine self-healing at a microstructural level, optical and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) were applied to the surface of cracks and fragments cut out of the samples. The results showed that the use of MAFBC fly ash as a partial substitute for cement led to the modification of the products of self-healing. Hydrated calcium aluminates were observed in the cracks in addition to typical self-healing products. In the interior of the samples, the complete filling of cracks up to a width of 110 µm was observed.

Preparation schemes of crushed coal for combustion in fluidized bed boilers using a gravity separator

The low concentration of nitrogen oxide during coal combustion in fluidized bed furnaces is due to the limited proportion of primary air in the combustion zone. The schemes applied for the preparation of crushed coal are mostly for the use of coal breakage screens with a fixed maximum particle size in the mixture. The primary air flow is limited to the conditions of the fluidization of the bed and can be reduced only by reducing the size of the particles fed into the furnace. With a constant particle size and lower boiler loads, the proportion of primary air and thus the concentration of nitrogen oxides in the flue gas increase. The use of separators to change the particle size has never been considered, since it is a priori assumed that the separators cannot provide the required disperse composition of crushed coal. To assess the possibility of using separators in the schemes of preparing crushed coal for combustion in a fluidized bed and to determine the necessary separation boundaries, variants calculations were carried out in respect to the coal preparation scheme for boiler No. 9 of the Novocherkasskaya hydro-power plant. It is shown that the disperse composition of the fine separation product in the gravity separator with overturning shelves along the 5 mm boundary is identical to the disperse composition of crushed coal obtained in the scheme with a screen and crusher. The dependence of the maximum particle size of crushed coal on the separation boundary of the separator is given. It is shown that in the scheme of preparation of crushed coal for combustion in a fluidized bed, replacement of screens with gravity separators will not lead to violation of the requirements for the dispersed composition of crushed coal. At the same time, the proposed replacement allows you to quickly change the maximum particle size of crushed coal during operational activity and thereby to maintain the optimal fraction of primary air when the boiler load changes.

Repurposing Fly Ash Derived from Biomass Combustion in Fluidized Bed Boilers in Large Energy Power Plants as a Mineral Soil Amendment

This research involved studying the physico-chemical parameters of fly ash derived from the combustion of 100% biomass in bubbling and circulating fluidized bed boilers of two large energy plants in Poland. Chemical composition revealed that ash contains substantial amounts of CaO (12.86–26.5%); K2O (6.2–8.25%); MgO (2.97–4.06%); P2O5 (2–4.63%); S (1.6–1.83%); and micronutrients such as Mn, Zn, Cu, and Co. The ash from the bubbling fluidized bed (BFB) was richer in potassium, phosphorus, CaO, and micronutrients than the ash from the circulating fluidized bed (CFB) and contained cumulatively less contaminants. However, the BFB ash exceeded the threshold values of Cd to be considered as a liming amendment. Additionally, according to our European Community Bureau of Reference (BCR) study Pb and Cd were more mobile in the BFB than in the CFB ash. Except for a low nitrogen content, the ash met the minimum requirements for mineral fertilizers. Acute phytotoxicity revealed no inhibition of the germination and seed growth of Avena sativa L. and Lepidium sativum plants amended with biomass ash. Despite the fact that low nitrogen content excludes the use of biomass fly ash as a sole mineral fertilizer, it still possesses other favorable properties (a high content of CaO and macronutrients), which warrants further investigation into its potential utilization.

Modeling and dynamic characteristics of the dense phase region of a biomass-fired circulating fluidized bed combustion system using Modelica

Using Modelica language, a mathematical model combining static and dynamic contributions of the dense phase region of a 130 t/h biomass circulating fluidized bed boiler combustion system was established on MWorks simulation platform. The mathematical model adopted modular packaging to increase the universality of the model, and it used an implicit, high-order, and multi-step Dassl integration algorithm to conduct the simulation. Under the design condition parameters, the relative error between the bed temperature of the dense phase region obtained by the simulation model and the actual temperature was less than 3.8%, which indicated that the static characteristics of the established simulation model were accurate. The effects of biomass feed and primary air volume step changes on the bed temperature, oxygen content in the flue gas, height of the dense phase region, and the bed pressure difference in the dense phase region were investigated. Both the biomass feeding and the primary wind step of 10% reduced the temperature, and it was obvious that the primary wind had a greater impact on the bed temperature. Meanwhile, the primary wind had a greater impact on the bed pressure difference than the biomass feeding.

Performance assessment of 2×90 tph (afbc) boiler and study of hp heater

TNPL (Tamilnadu Newsprint and papers limited) unit-2 has two boilers; each boiler is 90 Tons per hour capacity. These are single drum, natural circulation water tube, under bed and over bed firing, top supported pressure parts and bed plate design atmospheric fluidized bed combustion (AFBC) boiler. Imported coal is the fuel for these boilers, for better operation, a performance assessment study of these boilers has been made, also HP (high pressure) heater is a special type of heat exchanger designed for recovering of heat from extraction steam to preheat feed water. They provide efficiency gain by increasing the initial water temperature. A study has been made how the HP heater can increase the efficiency of boilers. For HP heater motive steam from turbine extraction is used after generation of power.

Concept design of supercritical CO2 cycle driven by pressurized fluidized bed combustion (PFBC) boiler

Boiler is key to influence supercritical carbon dioxide (S-CO2) cycle performance. Here, S-CO2 cycle driven by pressurized fluidized bed combustion (PFBC) boiler is investigated. The proposed systems A and B include recompression cycle with reheating (RC + RH), air compression-gas turbine (AC-GT), simple Brayton cycle (SRC), and RC + RH, AC-GT, respectively. A simulating code is developed for system analysis. We show that system A has higher efficiencies than system B. Larger flue gas pressure drop in PFBC boiler apparently worsens system performance. Effect of combustion pressures of PFBC boiler (Pfur) is thoroughly analyzed. Energy distributions in the system is affected by Pfur. With Pfur increase from 1.0 MPa to 3.5 MPa, boiler efficiencies are increased due to the decreased flue gas heat discharged to environment. Power generation efficiencies are increased but approach constant value. To overcome the challenge of heating surface arrangement in boiler, bubbling PFBC boiler is recommended. Compact heat exchangers are suggested in the top “pure” flue gas region. To further make it easier for heating surface arrangement, excess air coefficient is suggested to be increased to decrease thermal load fraction in furnace αfurnace. Flue gas recirculation is a better way to decrease αfurnace, which is applicable for system B.

Properties of Matrix using Diatomite Based on Blast Furnace Slag

we have experimented to reduce fine dust which is a problem in the world. Fine dust is known to cause various diseases in the human body. Diatomite with adsorption characteristics was used to reduce fine dust, which is a source of indoor air pollution. As a binder, blast furnace slag and a circulating fluidized bed combustion boiler fly ash were used to replace cement. The assessment items are flexural strength, compressive strength, flow ability, density, water absorption, fine dust concentration. As the replacement ratio of diatomite increases, the density decreases and the water absorption tends to increase. It is considered that this is due to the porous property of diatomite. Flowability decreased with increasing diatomite replacement ratio. As the replacement ratio of diatomite increased, the amount of air content to increase. As the replacement ratio of diatomite increased, the adsorption performance per minute of fine dust increased. This is because the amount of fine dust adsorbed per specific surface area increased as the replacement ratio of diatomite having porous properties increased. If additional experiments are done and used for finishing materials, it will contribute to the improvement of indoor air quality.

Emission and Migration Characteristics of Mercury in a 0.3 MWth CFB Boiler with Ammonium Bromide-Modified Rice Husk Char Injection into Flue

The emission and migration characteristics of flue gas mercury in a pilot-scale 0.3 MWth circulating fluidized bed combustion boiler system by injecting the adsorbent of ammonium bromide (NH4Br)-modified rice husk char (NBr-RHC) into the flue duct before a fabric filter (FF) were investigated in this study. Mercury concentration in the flue gas was sampled by the Ontario Hydro Method. Meanwhile, the feeding coal, lime, process water, fly ashes both in the flue gas and FF hopper, bottom ash, gypsum, and wet flue gas desulfurization (WFGD) effluent were also collected during the flue gas mercury sampling. The temperature-programmed desorption (TPD) method was used to identify the mercury species in the sample of fly ashes. The results show that the combination system of the selective catalytic reduction (SCR) + adsorbent injection (AI) + FF + WFGD obtains a total flue gas mercury removal efficiency of 94.62%, which is 13.42% higher than that without the AI of NBr-RHC. A total of 93.83% of mercury exists in byproducts of the solid and liquid, and the amount of mercury collected by FF accounts for 97.28% due to the physisorption and chemisorption of gaseous mercury by NBr-RHC injection. The TPD analysis for mercury compound in the particulate matters from the AI device indicates that HgBr2 formation is the key reason for NBr-RHC having high mercury removal efficiency. Elemental mercury is found to oxidize across the SCR, with 70.23% converted to oxidized mercury. WFGD exhibits a good oxidized mercury absorption rate of 86.67%, but elemental mercury increases from 0.19 to 0.26 μg/m3 due to the oxidized mercury reduction, and more attention should be given on this increase.

Exergy Analysis of Captive Power Plant

Energy sector is one of the important areas in the economic development of any country. Meeting the growing demands at acceptable costs in various sectors like industries, commercial, transport etc. is challenge to energy planner. The present work is an account of energy and exergy losses and distribution in Heat Exchanger of captive power plant of M/S Vardhaman Acrylics ltd, Jhagadia, Bharuch, Gujarat, India. This plant consists of 5.5 MW turbine-generator set with two extraction points which supply the heat energy to meet process demand. The steam is generated in 1?42 TPH capacity 45 kg/cm2 pressure, atmospheric pressure fluidized bed combustion boiler supplied by M/S Thermax Babcock &amp; Wilcox Ltd,Pune ,India. The complete energy &amp; exergy analysis of Heat Exchanger is carried out based on massive data collection over a period of three months. The energetic and exergetic losses of various components &amp; suggestion for improving energetic &amp; exergetic efficiency of the plant form core of this work.

Fine particle alteration monitoring in flue gas at the convection pass inlet of a commercial circulating fluidized bed combustion boiler during solid recovered fuel combustion

A simple and effective method of fine particle sampling at the convection pass inlet in a boiler that burns solid recovered fuel is developed and demonstrated. The fine particles, which are assumed to be mineral salt in flue gas, easily combine with other fly ashes and then attach to the superheater tubes and form clinkers. This clinker deposits on the tubes cause deterioration of the boiler performance and lead to tube corrosion. Two commercially available chemical agents, ammonium sulfate ((NH4)2SO4) and borax solution, used for clinker control are tested to monitor their activity on clinker formation. When ammonium sulfate is applied, the PM2.5 particles of fly ash collected in the convection pass inlet increased. When borax solution is used, the PM10 particles are almost completely removed. The borax solution seems to absorb molten salt in the flue gas and make fine particles grow, whereas ammonium sulfate increases the 2.5 μm particles by changing the metal chlorides to metal sulfates. The borax solution shows potential to control fine particles, and especially PM10 particles. However, both additives increased sub-70 μm particles of convection pass bottom ash.

Analysis and Optimization of Material Flow inside the System of Rotary Coolers and Intake Pipeline via Discrete Element Method Modelling

There is hardly any industry that does not use transport, storage, and processing of particulate solids in its production process. In the past, all device designs were based on empirical relationships or the designer’s experience. In the field of particulate solids, however, the discrete element method (DEM) has been increasingly used in recent years. This study shows how this simulation tool can be used in practice. More specifically, in dealing with operating problems with a rotary cooler which ensures the transport and cooling of the hot fly ash generated by combustion in fluidized bed boilers. For the given operating conditions, an analysis of the current cooling design was carried out, consisting of a non-standard intake pipeline, which divides and supplies the material to two rotary coolers. The study revealed shortcomings in both the pipeline design and the cooler design. The material was unevenly dispensed between the two coolers, which combined with the limited transport capacity of the coolers, led to overflowing and congestion of the whole system. Therefore, after visualization of the material flow and export of the necessary data using DEM design measures to mitigate these unwanted phenomena were carried out.

Calcium looping performance under extreme oxy-fuel combustion conditions in the calciner

Calcium looping (CaL) for post-combustion CO2 capture is an emerging technology that has developed rapidly due to its similarities with existing circulating fluidized bed combustion boilers. This work presents an alternative calciner configuration as it is applied in La Pereda CaL pilot plant, the aim of which is to minimize or altogether eliminate the need to recycle CO2 during the oxy-fuel combustion of coal in the calciner. The strategy underlying this configuration is to reduce the heat demand in the calciner, and hence the energy penalty of the whole CaL system. After undergoing several modifications, the pilot was able to operate under O2-rich conditions in a series of experiments with a coal thermal input of up to 2.0 MWth in the calciner and 75 O2%v in the oxidant. No hot spots were detected in the calciner reactor in these conditions due to the thermal ballast effect produced by the circulating solids from the carbonator. This new operation mode in the calciner in no way undermined the performance of the carbonator and CO2 capture efficiencies close to the maximum limit permitted by the equilibrium were achieved during the experimental campaigns. In short, the results of this work indicate that it may well be possible to operate the calciner of a CaL system using pure oxygen.

Use of fly ash from fluidized bed boilers in clinker-slag-ash based binders

The study presents the state of knowledge regarding physical and chemical properties, as well as trends for application of fly ashes from combustion in fluidized bed boilers in building materials. Clinker - slag - ash based binders were tested that contained up to 40 mass % of fly ashes from combustion in fluidized bed boilers. It was demonstrated that fluidized bed combustion fly ashes (FBC fly ash), apart from granular blast furnace slag, could be the ingredient of low clinker Portland cements (ca. 20% by mass). These cements, compared to CEM I Portland cement, have higher water demand and durability in the corrosive environment, and a lower compressive strength value. Based on test results of binders with various content of blast furnace slag and fly ash, the clinker - slag - ash based binder was singled out, which demonstrated the higher durability in the corrosive environment. It was found that production of clinker - slag - ash based binders was possible in the strength class 32.5 even with 30% by mass of FBC fly ash content.