Laboratory-scale Fluidized Bed Combustor Research Articles

Effect of combustion temperature on the emission of trace elements under O2/CO2 atmosphere during coal combustion

The effect of combustion temperature on the emission of trace elementswas studied under O2/CO2 atmosphere during coal combustion in a laboratory scale fluidized bed combustor. The elemental composition of fine fly ash particles collected with a low pressure impactor(LPI)was quantified by X-Ray F1uorescence Spectrometer (XRF). The elemental composition of coal and bottom ash was quantified byinductively coupled plasma-atomic emission spectroscopy (ICP-AES). The results indicate that the contents of Mn, Zn, Cd and Cr in the fly ash increase with the rise of combustion temperature. It is found that the enrichment of Zn and Cd is greater in the submicrometer particles than the supermicrometer particles, but Mn and Cr do not enrich in the submicrometer particles. Mn, Zn, Cd and Cr display one peak around 0.1 μm. The relative enrichment factor (Rij) of four elements is in the order of Zn, Cd, Mn and Cr. Zn and Cd are mostly retained in fly ashwhileMn and Cr are retained in both the fly ash and bottom ash.

Gaseous emission and ash characteristics from combustion of high ash content antibiotic mycelial residue in fluidized bed and the impact of additional water vapor

The gas (mainly NO and SO2) emission and ash characteristics from combustion of high ash content antibiotic mycelial residue (AMR) rich in N and S were investigated using a laboratory scale fluidized bed combustor, and the effects of addition of water vapor studied at the same time. The tested combustion temperature, excess air ratio (α) and mass ratios of water vapor-to-fuel (WV/F) varied in 750–950°C, 1.3–1.9 and 0.4–1.4, respectively. Without additional water vapor present, both the concentrations of NO and SO2 in flue gas increased with elevating combustion temperature and excess air ratio, corresponding to the increases in conversion ratio of fuel-N to NO and emission ratio of S. The addition of water vapor facilitated excavating organic matters in the ash to result in its lower C and N contents. Additional water vapor formed partial reducing atmospheres, which were characterized by high CO and H2 concentrations in combustion atmosphere and low valence S in the ash, to thus visibly reduce NO. The SO2 concentration became slightly lower at the presence of additional water vapor and further decreased with more water vapor addition. Additional water vapor strengthened capture of SO2 by the ash. Higher WV/F ratios led to more porous structures in ash, accountable for NO reduction by catalytic effect as well as SO2 absorption. Nevertheless, it seems less possible to reduce NO and SO2 concentrations to meet their respective emission criteria, and other measures will thus have to be taken to control their emissions when directly combusting AMR for energy recovery.

ReEngineered Feedstocks for Pulverized Coal Combustion Emissions Control

New coal reaction technology called ReEngineered Feedstock (ReEF), consisting of post-recycled paper and plastics, was evaluated for combustion emissions control when cofiring with pulverized coal. Experiments were conducted with four types of ReEF in a 2 in. diameter laboratory-scale fluidized bed combustor system heated to 1200, 1400, and 1600 °C. Flue gas emission was continuously monitored with an online infrared multigas analyzer and mass spectrometer. The results indicate that co-firing ReEF with coal provides SO2 emission reduction in flue gas up to 85% and moderate decrease in NO emissions, as well as higher carbon conversion than pure coal combustion. ReEF, slag and fly ash solids were were analyzed by X-ray diffraction; identification of sulfates in the product ash conclusively supports the mechanism of in situ sulfur capture.

Investigation on Interaction of Combustion Parameters of Coal-Water Mixtures Used in Fluidized Bed Combustor

Three different Turkish Lignites (İstanbul-Yeniköy, Manisa-Soma, and Muğla-Milas) were prepared in accordance with coal-water mixtures technology to determine the combustion parameters of a laboratory-scale fluidized bed combustor. In this context, the effects of parameters such as Ca/S, mean bed temperature, preheat, air emission, and feed rate were investigated on SO2, NOx, and CO emissions, while the combustion efficiency and the amount of unburned C were also calculated. In the combustion tests, it was observed that the quantity of SO2 in the flue gas is reduced when there is an increase in the Ca/S ratio in the mixtures. A maximum 95% of sulfur can be removed with Ca/S:4. It was observed that when the temperature in the fluidized bed unit increases, NOx emission increases and CO emission decreases. The optimum bed temperature was found to be approximately 900°C. The preheat temperature of the mixture significantly affects combustion and the efficiency is advanced by increasing preheat temperature. It was also determined that the amount of air added to the combustor affects the efficiency of combustion, with larger quantities of air resulting in lower amounts of unburned C in fly ash; however, increases in air quantities result in higher emissions of NOx.

Bed agglomeration characteristics of palm shell and corncob combustion in fluidized bed

Abstract Bed particle agglomeration was studied experimentally in an atmospheric laboratory scale fluidized bed combustor using quartz sand as bed material. Palm shell and corncob were tested. The objectives of the study were (i) to describe the contributions of the biomass ash properties and the operating conditions on the bed agglomeration tendency in term of the bed defluidization time (tdef) and the extent of potassium accumulation in the bed (K/Bed) and (ii) to further elucidate the ash inorganic behaviors and the governing bed agglomeration mechanisms. Defluidization caused by the bed agglomeration was experienced in all experiments during combustion of these biomasses, as a consequence of the presence of potassium in biomass. The experimental results indicated that biomass ash characteristics were the significant influence on the bed agglomeration. The increasing bed temperature, bed particle size and static bed height and the decreasing fluidizing air velocity enhanced the bed agglomeration tendency. The SEM/EDS analyses on the agglomerates confirmed that the agglomeration was attributed to the formation of potassium silicate liquid enriched on the surface of quartz sand particles in conjunction with the high surface temperature of the burning biomass char particles. Thermodynamic examination based on the phase diagram analysis confirmed that the molten phase formation was responsible for the agglomeration. In this study, the high molten ash fraction resulting from the high potassium content in biomass promoted the agglomeration and thus defluidization.

Study on Freeboard Properties to Maintain Low N2O Emissions from Sewage Sludge in a Fluidized Bed Combustor

A new type of incineration plant, which was equipped with a pressurized bubbling fluidized bed combustor coupled with a turbocharger, was proposed. N2O emissions in the proposed combustor of the demonstration plant were less than half of those observed in an atmospheric plant. In this study, the freeboard properties in the combustor were investigated to clarify the detailed reason for the low N2O emissions under pressurized conditions. First, the effect of a wide range of operating pressures on N2O emissions in a laboratory-scale pressurized fluidized bed combustor, which can control the freeboard temperature independently using an electric heater, was examined experimentally. Second, the effect of the operating pressure on the freeboard temperature profiles was estimated theoretically by a computational analysis. As a result, N2O emissions were obviously decreased with an increasing freeboard temperature even when the operating pressure changed substantially. Thus, the freeboard temperature is an importa...

Discontinuous oxidation and erosion-oxidation of a CeO 2-dispersion-strengthened chromium coating

A CeO 2-dispersion-strengthened chromium coating was developed on a carbon steel using a two-step process: prior electrodeposition of a Ni-CeO 2 nanocomposite film and subsequent chromization using a conventional pack cementation method. Compared to the CeO 2-free coatings prepared on the carbon steel without and with pre-electrodeposition of a pure Ni film, the CeO 2 dispersed chromium coating offered profoundly improved discontinuous oxidation resistance at 900 °C in 5% O 2 + N 2 and in 5% O 2 + 1000 ppm SO 2 + N 2, and erosion-oxidation resistance in a laboratory-scale fluidized-bed combustor (FBC), mainly because of the development of a denser, less wrinkled and more adherent chromia scale.

Mercury Emissions during Cofiring of Sub-bituminous Coal and Biomass (Chicken Waste, Wood, Coffee Residue, and Tobacco Stalk) in a Laboratory-Scale Fluidized Bed Combustor

Four types of biomass (chicken waste, wood pellets, coffee residue, and tobacco stalks) were cofired at 30 wt % with a U.S. sub-bituminous coal (Powder River Basin Coal) in a laboratory-scale fluidized bed combustor. A cyclone, followed by a quartz filter, was used for fly ash removal during tests. The temperatures of the cyclone and filter were controlled at 250 and 150 degrees C, respectively. Mercury speciation and emissions during cofiring were investigated using a semicontinuous mercury monitor, which was certified using ASTM standard Ontario Hydra Method. Test results indicated mercury emissions were strongly correlative to the gaseous chlorine concentrations, but not necessarily correlative to the chlorine contents in cofiring fuels. Mercury emissions could be reduced by 35% during firing of sub-bituminous coal using only a quartz filter. Cofiring high-chlorine fuel, such as chicken waste (Cl = 22340 wppm), could largely reduce mercury emissions by over 80%. When low-chlorine biomass, such as wood pellets (Cl = 132 wppm) and coffee residue (Cl = 134 wppm), is cofired, mercury emissions could only be reduced by about 50%. Cofiring tobacco stalks with higher chlorine content (Cl = 4237 wppm) did not significantly reduce mercury emissions. This was also true when limestone was added while cofiring coal and chicken waste because the gaseous chlorine was reduced in the freeboard of the fluidized bed combustor, where the temperature was generally below 650 degrees C without addition of the secondary air. Gaseous speciated mercury in flue gas after a quartz filter indicated the occurrence of about 50% of total gaseous mercury to be the elemental mercury for cofiring chicken waste, but occurrence of above 90% of the elemental mercury for all other cases. Both the higher content of alkali metal oxides or alkali earth metal oxides in tested biomass and the occurrence of temperatures lower than 650 degrees C in the upper part of the fluidized bed combustor seemed to be responsible for the reduction of gaseous chlorine and, consequently, limited mercury emissions reduction during cofiring. This study identified the important impacts of temperature profile and oxides of alkali metal (alkali earth metal) on mercury emissions during cofiring in the fluidized bed combustor.

Fragmentation of wood char in a laboratory scale fluidized bed combustor

Casuarina equisetifolia, a hard wood, and a popular energy crop in many tropical countries, was investigated experimentally for its char fragmentation in a laboratory scale atmospheric bubbling fluidized bed combustor. The effect of fuel shape and size on wood char fragmentation was studied. Wood particles of spherical, cylindrical (aspect ratio of 1), and cubical shapes of different sizes ranging from 10 to 25 mm were used in the experiments. Fragmentation of wood char was quantified in terms of various parameters, such as Number of Fragments (NF), Percentage of Fragmentation Events, Frequency of Fragmentation, Timing interval of Fragmentation, Size distribution of char and Fragmentation Index (FI). Also, qualitative observations on the evolution of char in terms of deformation, cracks and surface texture are discussed. It was observed that Casuarina equisetifolia wood of sizes greater than 15 mm, of all shapes undergoes primary fragmentation during the devolatilization phase. Furthermore, chars fragment at the early stages (1st or 2nd quarter) of the char combustion phase, underscoring the significance of the phenomenon in fluidized bed combustion. For all the shapes of wood considered, there appears to be a cut-off size of the initial wood, below which its char certainly undergoes fragmentation. It was observed that the average char particle size at any instance during its combustion falls in a narrow range of 3.7–6.9 mm, 3–6.6 mm and 3–9.5 mm for spherical, cylindrical and cubical wood particles, respectively. Wood of initially cylindrical shape undergoes extensive fragmentation when compared with spherical and cubical shapes.

Impact of the Addition of Chicken Litter on Mercury Speciation and Emissions from Coal Combustion in a Laboratory-Scale Fluidized Bed Combustor

Co-combustion of chicken litter with coal was performed in a laboratory-scale fluidized bed combustor to investigate the effect of chicken litter addition on the partitioning behavior of mercury. Gaseous total and elemental mercury concentrations in the flue gas were measured online, and ash was analyzed for particle-bound mercury along with other elemental and surface properties. The mercury mass balance was between 85 and 105%. The experimental results show that co-combustion of chicken litter decreases the amount of elemental and total mercury in the gas phase. Mercury content in fly ash increases with an increasing chicken litter share.

Effect of co-combustion of chicken litter and coal on emissions in a laboratory-scale fluidized bed combustor

Co-combustion of chicken litter (CL) with coal was performed in a laboratory-scale fluidized bed combustor to investigate the effect of CL combustion on pollutant emissions. The emissions of major gaseous pollutants including CO, SO2, H2S and NO and temperature distribution along the combustor were measured during the tests. Effects of CL fraction and secondary air on combustion characteristics were studied. The experimental results show that CL introduction increases CO emissions and reduces the levels of SO2. The ratio of H2S/SO2 increases with increasing fraction of CL. NO emissions either increase or decrease depending on the percentage of CL in the mixed fuels. The temperature in the freeboard region increases with increasing the fraction of CL while the reverse is true for the bed temperature.

Emission potential of condensable suspended particulate matter from flue gas of solid waste combustion

Condensable suspended particulate matter, condensable SPM, is generated during the cooling process of flue gas by mixing with the atmosphere. Condensable SPM from stationary sources, such as power plants, waste incinerators and factories, is rather difficult to evaluate since dust sampling from exhaust gas is usually performed downstream of dust collectors, which are maintained at relatively high temperatures. In this study, in order to discuss the emission mechanism of condensable SPM from waste incinerators, model flue gas comprised Cd and Pb was produced by the sublimation of pure CdCl 2 and PbCl 2 in gas stream. Model flue gas was cooled in a diluter after separation of particulates by a bag filter kept at operational temperatures common to commercial plants. Particle size distribution of generated condensable SPM after a diluter was measured by a differential mobility analyzer (DMA). The composition of the model gases was determined based on our experiments carried out on fueled refuse derived fuel (RDF) in a laboratory-scale fluidized bed combustor. The effect of the CdCl 2 and PbCl 2 sublimation temperature, filtration temperature, and bag filter ash layering on the resulting particle size distribution of SPM was examined. The emission possibility of condensable SPM from solid waste incinerators is discussed based on experimental results and thermodynamic calculation.

Emission Behavior of Condensable Suspended Particulate Matter from a Laboratory Scale RDF Fluidized Bed Combustor

Characterization and measurement of condensable suspended particulate matter emitted from stationary sources, such as coal-fired power plants and waste incinerators, are very difficult since dust concentration in exhaust gas is usually measured at the downstream of dust collectors kept at relatively high temperatures compared with atmospheric air. In the cooling process of flue gas, compounds having solidification points between dust collector temperature and atmospheric temperature have the possibility to become condensable suspended particulate matters. In this work exit gas after bag filtering emitted from a laboratory scale fluidized bed combustor burning refuse-derived fuel (RDF) was sampled by two kinds of cooling methods and elemental analysis was performed. In the experimental results the elemental permeability of a bag filter was high for Pb, Cd, and Zn. To discuss the contribution of fuel composing elements as the origin of measured condensable suspended particulate matters, thermodynamic calculation was performed and the possibility of Cd emission was supported.

Carbon conversion of solid fuels in the freeboard of a laboratory-scale fluidized bed combustor—application of in situ laser spectroscopy

The carbon conversion of different solid fuels (i.e. beech wood, fir wood, bituminous coal) was investigated in the freeboard of a laboratory-scale fluidized bed combustor by in situ tunable diode laser absorption spectroscopy. A room temperature continuous wave InGaAsSb/AlGaAsSb quantum well ridge diode laser emitting at 2.3–2.35 μm was wavelength tuned at 300 Hz to determine simultaneously CH 4 and CO during devolatilization and char combustion in situ 10 mm above the fuel particles. The lower detection limit was 0.2 vol% (5000 ppm m) for both species. In addition, CO, CO 2 and O 2 were determined ex situ by conventional methods. The experimental results obtained for the bituminous coal were compared to a detailed chemical kinetic model. The in situ measurements proved to be advantageous compared to conventional ex situ concentration measurements. The calculations confirm the determination of the primary products of solid fuel combustion during devolatilization and char combustion. A rather simple model for the devolatilization products was proven to describe well the release rates of CH 4 and CO for the bituminous coal.

Agglomeration in bio-fuel fired fluidized bed combustors

This paper presents results from systematic agglomeration experiments in a straw-fired laboratory-scale fluidized bed combustor and a theoretical study of the phenomena. Experiments were carried out at different operating conditions. Defluidization resulting from agglomeration occurred in all experiments. The agglomeration tendency is represented by the time before defluidization is detected. The results show that the temperature has a pronounced effect on the defluidization time, which can be significantly extended with decreasing temperature. Examination by various analytical techniques of the agglomerates sampled during combustion suggests that the high potassium content in straw causes the formation of agglomerates and eventually defluidization. In the combustion process, potassium-containing compounds are prone to remain in the bed and form low melting potassium-rich ash. The molten ashes coat the surfaces of the bed material, promoting agglomeration and defluidization in FBC. Thermodynamic equilibrium calculations have been performed to identify the stable silica, potassium, chlorine and sulphur species. The results show that potassium silicates are the main form present in the bed, which agree qualitatively with the experimental results. Based on a competition between the strengthening adhesive force by the ash coating and sintering processes and the breaking force induced by bubbles in the bed, a simple model has been developed to describe the defluidization time as a function of temperature, fluidization velocity and particle size. The results are in good agreement with experimental results.

Enhancement of combustion efficiency with mixing ratio during fluidized bed combustion of anthracite and bituminous blended coal

In order to investigate the effect of mixing ratio of bituminous coal to blended coal on the enhancement of combustion efficiency, combustion experiments of blended coal with anthracite and bituminous are done in a laboratory scale fluidized bed combustor (10.8 cm ID and 170 cm height). The gross heating values of anthracite and bituminous coal used in this study are 2,810 cal/g and 6,572 cal/g, respectively. Experimental parameters are fuel feed rate, superficial gas velocity and mixing ratio of bituminous coal to blended coal. The combustion efficiency increases with the mixing ratio of bituminous coal due to the lower unburned carbon losses and higher burning velocity of bituminous coal. The rate of combustion in the combustor was increased with mixing ratio resulted from a higher burning velocity of bituminous coal. The measured combustion efficiency experimentally is about 3.5-12.4% higher than that of the calculated value based on the individual combustion of anthracite and bituminous coal under the same operating conditions. The optimum mixing ratio (MR) of bituminous coal determined is around 0.75 in this study.

In-situ laser spectroscopy of CO, Ch4, and H2O in a particle laden laboratory-scale fluidized bed combustor

The pyrolysis, devolatilization and char combustion of bituminous coal and biomass (beechwood, firwood) were investigated in a laboratory-scale fluidized bed combustor by tunable diode laser spectroscopy. Individual fuel particles were suspended in the freeboard of the unit. The bed temperature was 800 ?C, the oxygen partial pressure 0 to 20 kPa (0-10 vol.%). Two Fabry Perot type tunable near infrared diode lasers were deployed for quantitative in-situ species concentration measurements. CH4 and CO were measured simultaneously during devolatilization and char combustion in-situ 10 mm above the surface of the fuel particles as well as H2O using laser spectroscopy. Sand particles were passing the probing laser beam path. Besides the resonant absorption of the laser light by CO, CH4 and H2O severe and strongly transient non-resonant attenuation by partial blocking of the beam and beam steering effects occurred. By wavelength tuning the two laser sources, species concentrations could be determined. The measured absorbances had to be corrected for the real temperature measured at the position of the probing laser beam. In addition, CO, CO2 and O2 were determined ex-situ by con ventional methods. A spatial profile inside the FBC of major species (CH4, CO, CO2, O, H, OH) was calculated using a chemical kinetics program for a single fuel particle in a plug flow reactor geometry. The results were compared to the experimental findings. Good agreement was found. Tunable diode laser spectroscopy was found to be an apt method of determining quantitative species concentrations of multiple gases in a high temperature multi phase environment.

Capacitance probe measurement technique for local particle volume concentration in circulating fluidized bed combustors.

This paper describes a capacitance probe measurement technique for the quantitative determination of local particle volume concentrations inside a fluidized bed combustor. The influence of temperature, water content in the fluidization gas, and burning fuel particles in the solids inventory on the measured signal is investigated in a laboratory-scale fluidized bed combustor. Application of the measurement system is demonstrated on a semi-technical scale circulating fluidized bed (CFB) sewage sludge combustor. By applying a data preprocessing step and a suitable calibration routine, the measurement system is able to quantitatively measure local average solids volume concentration as low as 0.1 vol.-%. Radial profiles of local average solid volume concentrations taken at various elevations inside the riser demonstrate the performance of the technique.

Laboratory-scale coal combustor for flue gas emission studies

A laboratory-scale fluidized bed combustor is described, which is used to produce actual flue gas for emission studies. The combustor operates at 800-935°C with continuous coal feed of 0.03-0.12 kg/h, fluidization velocities of 0.2-0.6 m/s, and gas flow rates in the range 5-15 L(STP)/min. The combustion facility is fully automated through a computer for control and data acquisition. Sulfur dioxide, NO, CO, CO 2 , CH 4 , NH 3 , N 2 O and H 2 O, present in the flue gas, are rapidly analyzed and monitored using a computer-controlled Fourier transform infrared spectrometer with a 10 m path gas cell

Bed material cohesion and loss of fluidization during fluidized bed combustion of midwestern coal

Tests were conducted in a laboratory-scale fluidized bed combustor to determine the factors and mineralogical reactions that initiate agglomeration of bed particles and lead to defluidization of fluidized bed combustors. Combustion products from these tests were analysed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and petrographic relationships were determined from polished thin sections using transmitted polarized microscopy and scanning electron microscopy with an energy-dispersive X-ray detector (SEM-EDX). Loss of bed fluidization resulted when a cohesive aluminosilicate material wetted the surface of bed particles. This occurred when the combustion air was below 100% of theoretical values for complete combustion. Reduced iron may have acted as a flux to promote the flow of aluminosilicate particles. Solid-solid reactions involving calcium oxides and silicates (aluminosilicate cohesive material and quartz grains) also contributed to the bonding of bed particles and loss of fluidization. Reaction products produced without limestone included pyroxene and amphibole; with limestone, wollastonite was ubiquitous.