This article presents a lumped-parameter model (LPM) providing a deeper understanding of the compliant backplate in capacitive micro-electromechanical systems (MEMS) microphones. Some previous models ...simplify the backplate as stationary, whereas others treat it as vibrating. This work not only models the backplate as vibrating but also considers the coupling effect between the mechanical and electrical domains. The extended model allows for a more detailed analysis of how the microphone converts sound into an electrical signal. Specifically, the theoretical derivations using Lagrange equations show how backplate motion can impact the microphone's performance. The analysis of the LPM aligns well with the results of finite element analysis (FEA) when the frequency is below the high-order resonance, validating the theoretical concepts. In particular, the model with electrical coupling of the vibrating backplate effectively captures the sensitivity dip resulting from the backplate resonance, unlike models lacking this coupling. The theoretical framework is also extended to the phenomenon of pull-in. A backplate that is overly compliant can narrow the operating frequency range and increase the likelihood of experiencing pull-in. Thus, there is a tradeoff between optimizing the microphone's acoustic performance and ensuring its mechanical robustness. This work provides valuable insights into navigating these tradeoffs.
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•Detailed description of lumped-parameter equivalent circuits for moving-coil microphone.•The influence of sound scattering to the microphone has been considered.•Comprehensive ...predictions for microphone characteristics, such as sensitivity, impedance, directivity and proximity effect.•Good agreement between the simulation and measurement up to frequencies at 13 kHz.
This article presents a lumped-parameter model combined with external sound pressure field simulation, based on the boundary element method (BEM) for utilization in a directional microphone. A study about microphone capsule of a typical handheld moving-coil microphone with hyper-cardioid pattern has been conducted. In the BEM simulation, a simplified 3D model of the capsule that met sound waves which radiated from a point sound source has been taken into account. The blocked average pressure at the openings of the capsule is used to drive the lumped element equivalent circuit model. Through the model, the sensitivity, directivity, and impedance of the microphone were analyzed. Hence, the proximity effect is observed and discussed. To verify our simulation, the microphone characteristics were experimentally measured by B&K devices with SoundCheck software in an anechoic chamber. The simulation data are in good agreement with the measurement data at low and medium frequencies below 13 kHz, and there were larger errors at higher frequencies, which may indicate that the lumped parameters is less applicable at higher frequencies. The proposed method gains more precise and comprehensive prediction for the microphone characteristics, which therefore could be utilized in optimizing the choice of materials and size of the microphone capsule design.
•Low-temperature two-stage fluidized bed incineration was applied for soil remediation.•Co-firing of polyethylene with co-contaminated soil was studied.•Co-firing of polyethylene in soil remediation ...can promote residue quality.•The leachability of heavy metals passed the regulatory threshold values.
This study presents the application of a low-temperature two-stage fluidized bed incinerator to remediate contaminants in the soil. The system was designed to control emissions of both gaseous pollutants and heavy metals during combustion. Soil co-contaminated with lube oil and heavy metals such as cadmium, chromium, copper, and lead was examined. Experiments were conducted by estimating various parameters such as operating temperature in the first-stage reactor (500–700 °C), ratio of sand bed height/diameter in the second-stage reactor (H/D: 3, 4, 6), and gas velocity (0.21–0.29 m/s). Heavy metal and gaseous pollutant emissions were also investigated during contaminated soil co-firing with polyethylene. The experimental results indicated that the destruction and removal efficiency of lube oil in treated soil products ranged from 98.27 to 99.93%. On the other hand, leaching tests of bottom ashes illustrated that heavy metals such as chromium, copper, and lead in leachates were complied with the regulations. For gaseous emissions, carbon monoxide concentrations decreased apparently with increasing ratio of sand bed height/diameter in the second-stage reactor. The increase of gas velocity had significant potential to generate the lowest carbon monoxide and particulate matter emissions. Nevertheless, during co-firing with polyethylene, emissions of organic pollutants such as benzene, toluene, ethylbenzene, and xylene and polycyclic aromatic hydrocarbons decrease by using the low-temperature two-stage fluidized bed incineration system.
This study focused on the effect of particle size distribution (PSD) on agglomeration and defluidization in a fluidized bed. The four PSDs studied were narrow, Gaussian, binary and flat. The ...experimental variables studied included the gas velocity, the operating temperature, the Na concentration and the addition of Ca. The defluidization time decreased with increasing operating temperature and Na concentration, and these effects were independent of the sand bed's PSD. In contrast, the defluidization time increased with increasing gas velocity for all PSDs. Comparing the four PSDs, the narrow and Gaussian distributions had higher defluidization times when using operating temperatures of 700°C and 800°C, gas velocities of 0.163m/s and 0.187m/s, and Na concentrations of 0.5% and 0.7%. However, the flat and binary distributions had lower defluidization times under these conditions because they had poor fluidized quality. Thus, the PSD apparently affects the agglomeration and defluidization properties of a sand bed. However, if the system operates at extreme conditions (e.g., high operating temperature, poor mixing and high Na concentration), the PSD's influence on agglomeration will decrease. According to TGA/DTA results, there were two melting points in the agglomerate: 575°C and 782°C. This result confirmed that the liquid-phase eutectic species were formed at the incineration temperature (700–900°C).
Comparing the four PSDs, the narrow and Gaussian distributions had higher defluidization times when using operating temperatures of 700°C and 800°C, gas velocities of 0.163m/s and 0.187m/s, and Na concentrations of 0.5% and 0.7%. However, the flat and binary distributions had lower defluidization times under these conditions because they had poor fluidized quality. Display omitted
► The defluidization time decreased with increasing temperature and Na concentration. ► Generally, the narrow and Gaussian distributions had higher defluidization times. ► Effect of PSD on agglomeration will decrease at high temperature and Na concentration.
In this study, a pilot-scale low-temperature two-stage fluidized bed incinerator was evaluated for the control of heavy metal emissions using various chlorine (Cl) additives. Artificial waste ...containing heavy metals was selected to simulate municipal solid waste (MSW). Operating parameters considered included the first-stage combustion temperature, gas velocity, and different kinds of Cl additives. Results showed that the low-temperature two-stage fluidized bed reactor can be an effective system for the treatment of MSW because of its low NOx, CO, HCl, and heavy metal emissions. The NOx and HCl emissions could be decreased by 42% and 70%, respectively. Further, the results showed that heavy metal emissions were reduced by bed material adsorption and filtration in the second stage. Regarding the Cl addition, although the Cl addition would reduce the metal capture in the first-stage sand bed, but those emitted metals could be effectively captured by the filtration of second stage. No matter choose what kind of additive, metal emissions in the low-temperature two-stage system are still lower than in a traditional high-temperature one-stage system. The results also showed that metal emissions depend not only on the combustion temperature but also on the physicochemical properties of the different metal species.
To compared with the different fluidized bed systems on metal capture in first and second stage under various chloride additives. Display omitted
•The low-temperature two-stage incinerator can control NOx and HCl emission.•Compared with different Cl additives, inorganic Cl has a lower metal emission.•After adding the Cl additives, this new system also has a lower metal emission.•The metal control depended on sand bed adsorption and the filtration.
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To compared with different metal distribution patterns on the first-stage sand bed in the LTTSFB incineration under the various Cl additives. The results showed that polyvinyl ...chloride addition increased metal mobility in the reacted sand bed. NaCl addition reduced metal mobility due to the formation of eutectic material.
•Metal patterns were determined in low-temperature two-stage bottom ash.•Higher metal mobility phase was discovered in the low-temperature sand bed.•Polyvinyl chloride addition increased metal mobility in bottom ash.•NaCl addition reduced metal mobility due to the formation of eutectic material.•Second-stage sand bed had a lower risk of metal leaching than first-stage.
A novel low-temperature two-stage fluidized bed (LTTSFB) incinerator has been successfully developed to control heavy-metal emissions during municipal solid waste (MSW) treatment. However, the characteristics of the residual metal patterns during this process are still unclear. The aim of this study was to investigate the metal patterns in the different partitions of the LTTSFB bottom ash by chemical sequential extraction. Artificial waste was used to simulate the MSW. Different parameters including the first-stage temperature, chloride additives, and operating gas velocity were also considered. Results indicated that during the low-temperature treatment process, a high metal mobility phase exists in the first-stage sand bed. The main patterns of Cd, Pb, and Cr observed were the water-soluble, exchangeable, and residual forms, respectively. With the different Cl additives, the results showed that polyvinyl chloride addition increased metal mobility in the LTTSFB bottom ash, while, sodium chloride addition may have reduced metal mobility due to the formation of eutectic material. The second-stage sand bed was found to have a lower risk of metal leaching. The results also suggested that, the residual ashes produced by the LTTSFB system must be taken into consideration given their high metal mobility.
In this study, CaO and CaCO3 were used as additives to investigate the inhibition of agglomeration/defluidization and adsorption of Pb and Cd. The results showed that defluidization time may be ...prolonged when CaO or CaCO3 is added to the artificial waste. Before defluidization, Pb and Cd emissions were not intensified significantly in the existence of Na; however, after defluidization, the emission of Pb and Cd increased significantly. The heavy metal emission concentration was lower when CaO or CaCO3 was added to the artificial waste than when only Na was added. CaCO3 showed a stronger defluidization inhibition effect because of the longer defluidization time. For different parameters, the heavy metal emission concentration appeared to decrease with an increase in the operating temperature; however a change in the gas velocity did not affect the heavy metal emission. In addition, an increase in the bed material size considerably reduces the defluidization time. A small bed material size is more favored as the large specific surface area in this case allows for the adsorption of a greater amount of heavy metal and more efficient mixing with waste.
Under different operating parameters the addition of Ca compounds (either CaO or CaCO3) could prolong defluidization time. The emission trends of the different heavy metals were largely similar despite having different volatility properties. After the occurrence of defluidization in the sand bed, the heavy metal emission increased significantly. When CaO or CaCO3 was added, the majority of the results suggested that the heavy metal emission concentration is lower than that in the case when no Na was added. The presence of CaO or CaCO3 shows equal potential in reducing the heavy metal emission. Comparison of the impact of CaO or CaCO3 on the agglomeration/defluidization process and heavy metal emission shows CaCO3 to be more effective in inhibiting defluidization. Display omitted
•Defluidization time is prolonged if CaO or CaCO3 is added to waste.•After defluidization, the emission of Pb and Cd increases significantly.•Defluidization time increases with a decrease in temperature and particle size.•Added CaO or CaCO3 would decrease the heavy metal emission concentration.•CaCO3 shows stronger defluidization inhibition effect than does CaO.
To better understand the mechanism of the second-stage sand bed in controlling the pollutant emissions from a low-temperature two-stage fluidized bed (LTTSFB) incinerator, different parameters of the ...second-stage sand bed, including the particle size, bed height, and particle size distribution (PSD), were determined in this study. Artificial waste that contained heavy-metals (Pb, Cr, and Cd) was used to simulate municipal solid waste (MSW). Particle, heavy-metal, and organic—polyaromatic hydrocarbon (PAH) and benzene, toluene, ethylbenzene, and xylene (BTEX)—pollutant emissions were the main concerns. During the initial test, the removal efficiency of the BTEX and PAH pollutants were between 70% and 76% after the second-stage treatment. The results also showed that the particle emission was correlated with the organic and heavy-metal emissions. Compared with the different particle sizes in the second-stage, the bubble-phase ratio and the sizes of voids in the sand bed were observed to be the major factors that controlled the pollutant emissions. Greater secondary sand-bed height also resulted in a greater likelihood of trapping the particles and heavy metals. But, it had a limitation. With respect to the PSD in second-stage, the results revealed that a flat-type distribution exhibited better efficiency in controlling the particle and metal emissions.
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•Particle emission was correlated with the organic and heavy-metal emissions.•Organic pollutants could be controlled efficiently after second-stage treatment.•Bubble-phase ratio and void size in second sand bed were the major factors.•Flat-type of second sand bed has a better metal and particle control efficiency.
This study develops a low-temperature two-stage fluidized bed system for treating municipal solid waste. This new system can decrease the emission of heavy metals, has low construction costs, and can ...save energy owing to its lower operating temperature. To confirm the treatment efficiency of this system, the combustion efficiency and heavy-metal emission were determined. An artificial waste containing heavy metals (chromium, lead, and cadmium) was used in this study. The tested parameters included first-stage temperature and system gas velocity. Results obtained using a thermogravimetric analyzer with a differential scanning calorimeter indicated that the first-stage temperature should be controlled to at least 400 °C. Although, a large amount of carbon monoxide was emitted after the first stage, it was efficiently consumed in the second. Loss of the ignition values of ash residues were between 0.005% and 0.166%, and they exhibited a negative correlation with temperature and gas velocity. Furthermore, the emission concentration of heavy metals in the two-stage system was lower than that of the traditional one-stage fluidized bed system. The heavy-metal emissions can be decreased by between 16% and 82% using the low-temperature operating process, silica sand adsorption, and the filtration of the secondary stage.
Display omitted Heavy-metal emission concentrations in flue gases under different temperatures and gas velocities (dashed line: average of the heavy-metal emission in flue gases in the one-stage fluidized-bed incinerator).
•Low temperature two-stage system is developed to control heavy metal.•The different first-stage temperatures affect the combustion efficiency.•Surplus CO was destroyed efficiently by the secondary fluidized bed combustor.•Metal emission in two-stage system is lower than in the traditional system.•Temperature, bed adsorption, and filtration are the main control mechanisms.
AbstractThis paper aims to investigate the emission characteristics during the thermal treatment of co-contaminated soils containing lube oil and heavy metals (Cd, Cr, Cu, and Pb). Experiments were ...conducted using a laboratory-scale bubbling fluidized bed combustor under various fluidization parameters including temperature (500–800°C), air velocity (11.5–17.9 cm/s), and sand bed particle size (545–920 μm). The emission products from the system, including flue gas, fly ash, and bottom ash, were sampled, and the concentrations of heavy metals and organic pollutants (such as benzene, toluene, ethylbenzene, xylene, and polycyclic aromatic hydrocarbons) along with the metal leachability were determined. The average emissions were lowest at 800°C, air velocities were in the range of 13.7–17.9 cm/s, and sand bed particle diameters were 770–920 μm. Removal of more than 99% and 48–85% of lube oil and heavy metals, respectively, was observed. Portions of the heavy metals were vaporized and attached to the fly ash, while the residual heavy metal fractions in bottom ash were supposed the effect of particle aggregated during thermal treatment. The experimental results showed that all heavy metals were concentrated in the bottom ash due to particle agglomeration; therefore, the metals leachability was in accordance with the standards.
