Direct thermal drying of sludge using flue gas and its environmental benefits

This paper reported a sludge disposal technology that uses 100–200°C flue gas to dry sludge through a systematic analysis of the relationship between sludge drying rate/temperature and moisture content. Using this direct drying technology, the sludge drying capacity for the dryer tested can reach 86?tons?d^?1 at 160°C. The experimental results show this technology can also preserve 95% calorific value in the sludge, and remove 16–42% PM_2.5, 26–55% PM₁₀, and 7–25% SO₂ from the flue gas. The exhaust gas from the sludge dryer consists mainly of chain alkanes while benzenes only 9.65% when dried at 100°C.     

Cobenefit of SO3 reduction on mercury capture with activated carbon in coal flue gas

Parametric experiments were carried out to study the interactions of mercury, SO₃, and injected activated carbon (AC) in a coal flue gas stream. The levels of SO₃ vapor in flue gas were altered by individually varying flue gas temperature, moisture, or sodium fume injection in the flue gas. Meanwhile, mercury emissions with AC injection (ACI) upstream of an electrostatic precipitator (ESP) were evaluated under varied SO₃ concentrations. SO₃ measurements using a condensation method indicated that low temperature, high moisture content, and sodium fume injection in flue gas shifted SO₃ partitioning from the vapor to particulate phase, subsequently improving mercury capture with ACI. 0.08 g/m³ of DARCO^® Hg-LH injection only provided approximately 20% mercury reduction across the ESP in a bituminous coal flue gas containing 28 ppm SO₃, but mercury capture was increased to 80% when the SO₃ vapor concentration was lowered less than 2 ppm. Experimental data clearly demonstrate that elevated SO₃ vapor is the key factor that impedes mercury adsorption on AC, mainly because SO₃ directly competes against mercury for the same binding sites and overwhelmingly consumes all binding sites.     

Influence of SO3 on mercury removal with activated carbon: Full-scale results

Activated carbon injection is considered one of the most cost-effective options for mercury control at PRB-fired power plants. However, roughly 30% of sites firing PRB coal use SO₃ for flue gas conditioning. The presence of SO₃ in flue gas can decrease mercury capture by activated carbon, sometimes dramatically. Overcoming activated carbon performance limitations caused by SO₃ conditioning for units with this configuration is essential to enable these plants to cost-effectively meet pending mercury emission regulations. Ameren's Labadie Unit 2 fires PRB coal and uses SO₃ to enhance particulate capture in the electrostatic precipitator (ESP). Full-scale sorbent injection tests at Labadie were conducted from 2005–2007. Six sorbents were tested at SO₃ injection concentrations ranging from 0 to 10.7 ppm. Sorbent performance was evaluated at two injection locations (the air preheater (APH) inlet and outlet). Native mercury capture on fly ash was typically less than 15%. When the mercury sorbents were injected downstream of the air preheater, the SO₃ concentration resulted in a decrease in mercury capture from 85% (no SO₃ injection) to 17% (SO₃ injection set at 10.7 ppm). Mercury sorbents were more effective when injected upstream of the air preheater. With the SO₃ system off, mercury removal increased from 75% when injecting 5.1 lb/MMacf of brominated carbon at the APH outlet, compared to 95% when injecting at the inlet. With the SO₃ system on, test results indicated an increase from about 30% injecting at the outlet to 58% injecting at the inlet. Tests evaluating the ADA-ES patented onsite milling process showed that 85% mercury capture was achieved injecting 4 lb/MMacf of milled activated carbon compared to a requirement of 10 lb/MMacf to achieve the same removal using as-received carbon, representing a 60% reduction in activated carbon consumption. No changes in opacity, APH and ESP performance, or other balance-of-plant effects were observed in these tests.     

Reduction of amine mist emissions from a pilot-scale CO2 capture process using charged colloidal gas aphrons

In the CO₂ capture process from coal-derived flue gas where amine solvents are used, the flue gas can entrain small liquid droplets into the gas stream leading to emission of the amine solvent. The entrained drops, or mist, will lead to high solvent losses and cause decreased CO₂ capture performance. In order to reduce the emissions of the fine amine droplets from CO₂ absorber, a novel method using charged colloidal gas aphron (CGA) generated by an anionic surfactant was developed. The CGA absorption process for MEA emission reduction was optimized by investigating the surfactant concentration, stirring speed of the CGA generator, and capture temperature. The results show a significant reduction of MEA emissions of over 50% in the flue gas stream exiting the absorber column of a pilot scale CO₂ capture unit.     

Electrohydrodynamic Flow and Particle Transport Mechanism in Electrostatic Precipitators with Cavity Walls

The electrohydrodynamic (EHD) flow induced by the corona wind was observed in a model electrostatic precipitator (ESP) of the simple geometry composed of the plates with a cavity. And the influence of the EHD flow and the turbulence condition of inlet cross-flow on the particle behavior inside the ESP and its collection efficiency were elucidated through experimental and numerical analysis. The profiles of streamwise gas velocities and turbulence intensities were measured in the ESP with a laser Doppler anemometer.A laser beam sheet visualized particle trajectories. Collection efficiencies were measured with a particle counter. In addition, numerical computations were performed to compare with the experimental results. The numerical results showed good agreement with the experimental data. As the corona voltage increased, the gas velocities of the core flow and the circulating flow inside the cavity increased due to the corona wind and the turbulence intensity increased near the cavity region. As the corona voltage increased for the low bulk gas velocity, corona wind prevented the particle transport into the cavity. And the particle transport into the cavity by turbulent dispersion was observed as the bulk gas velocity increased. When the flow with high turbulence intensity entered the ESP, the turbulent dispersion enhanced the transport of particles into the cavity; hence, the collection efficiency was higher compared with the case of the relatively lower inlet turbulence intensity below a critical corona voltage. However, the collection efficiency was slightly lower for the high inlet turbulence than for the low inlet turbulence above the critical corona voltage due to the turbulent diffusion of particles toward the centerline downstream from the corona wire.     

A Shelter to Protect a Passive Sampler for Coarse Particulate Matter,PM10 − 2.5

This work designed and tested a shelter to protect a passive sampler for measuring coarse particulate matter, PM _{10 ? 2.5} . The shelter protects the sampler from precipitation and reduces the effects of wind on the deposition of particles to its collection surface. Six shelters were tested in a wind tunnel at three wind speeds: 2, 8, and 24 km hr ^?1 . Shelter performance was expressed as the ratio of PM _{10 ? 2.5} measured with the passive samplers to that measured with a filter-based dichotomous sampler. For most shelters, the PM _{10 ? 2.5} ratio averaged across wind speeds was well above one (2.4 to 8.5) and was generally dependent on wind speed. However, the PM _{10 ? 2.5} ratio for one shelter, the Flat Plates shelter, was 1.04 with substantially less effect on particle deposition from wind speed. Eight week-long field tests were conducted to compare PM _{10 ? 2.5} measured with a passive sampler installed in a Flat Plates shelter to that measured with a collocated filter-based dichotomous sampler. In these tests, the mean PM _{10 ? 2.5} ratio was 1.29. The linear relationship between PM _{10 ? 2.5} measured passively to that measured with the filter-based sampler had a Pearson correlation coefficient of 0.97 and was not significantly affected by the addition of weekly mean wind speed (p = 0.35). Although temperature was significant in this regression model (p = 0.02), it only improved the relationship marginally. The passive sampler in a Flat Plates shelter offers an inexpensive means to assess ambient PM _{10 ? 2.5} without on-site measurement of wind speed.     

Modeling of particle interaction dynamics in standing wave acoustic field

Interactions between fine particles (PM_2.5) suspended in flue gas can be promoted via application of acoustic fields. This may lead to particle collision and agglomeration, thereby facilitating possible realization of PM_2.5 abatement. The dynamic behavior of particle interactions in standing wave acoustic fields, however, is not well understood, and this severely restricts the development of practical acoustic agglomeration devices. Availability of limited information concerning PM_2.5 interactions, insufficient consideration of interaction mechanisms, and neglect of spatial variation in acoustic velocity under the standing wave condition are a few limitations of previous studies performed in this regard. To address these concerns, a theoretical model capable of accurately describing the interaction between two neighboring particles in a standing wave acoustic field was developed in this study. Experimentally obtained parameters, such as particle velocity due to acoustic entrainment, interaction pattern, and collision time, were reproduced via numerical simulations performed using the proposed model. Additionally, the influences of model improvements on PM_2.5 interaction dynamics were analyzed. Finally, the proposed model was adopted to investigate the effect of particle size on collision time. Results demonstrate that in cases involving identically sized particles, the collision time significantly reduces with increase in particle size. Maintaining the size of a particle constant whilst increasing that of the other particle causes the collision time to decrease. This is coupled with reduction in initial orientation angle range corresponding to particle collision. Consequently, no collisions occur when a substantial difference exists between particle sizes.

Copyright © 2019 American Association for Aerosol Research     

Effects of Electrohydrodynamic Flow and Turbulent Diffusion on Collection Efficiency of an Electrostatic Precipitator with Cavity Walls

The effects of electrohydrodynamic (EHD) flow and turbulent diffusion on the collection efficiency of particles in a model ESP composed of the plates with a cavity were studied through numerical computation. Electric field and ion space charge density in the ESP were calculated by the Poisson equation of electric potential and the current continuity equation of ion space charge. The EHD flow field was solved by the continuity and momentum equations of gas phase, including the electrical body force induced by the movement of ions under the electric field. RNG k - l model was utilized to analyze turbulent flow. Particle concentration distribution was calculated from the convective diffusion equation of particle phase. As the ion space charge increased, the collection efficiency of charged particles increased because the electric potential increased over the entire domain in the ESP. The collection efficiency decreased as the EHD flow became stronger when the electrical migration velocity of charged particles was high. However, the collection efficiency could increase for the stronger EHD flow when the electrical migration velocity of charged particles was relatively lower. Also, the collection efficiency decreased as the turbulent diffusion of particles increased when the electrical migration velocity of particles was high. However, the collection efficiency could increase with the turbulent diffusion when the electrical migration velocity of particles was relatively lower.     

Capture of submicrometer particles in a pressurized electrostatic precipitator

This study investigated the influence of gas pressure on the submicrometer particle capture performance of an electrostatic precipitator (ESP). Current-voltage characteristics and particle capture performance of the ESP were studied in air and in simulated flue gas (SFG) under 1, 2, and 3 atm. Using negative corona and air as the feed gas, the penetration of most particles of 40–400 nm in diameter decreased from 8 × 10^?4 ? 2 × 10^?2 to 2 × 10^?4 ? 1 × 10^?2 as pressure increased from 1 atm to 3 atm at constant current; and increased from 3 × 10^?5 ? 1 × 10^?3 to 2 × 10^?4 ? 1 × 10^?2 as pressure was elevated when the voltage was held roughly constant. Similar type of disparity under different pressures was also observed for positive corona and for SFG. Experiments set up to capture fly ash in the ESP showed that with constant current, higher pressure resulted in a higher initial charge fraction of the particles from the furnace, which could facilitate the penetration of fly ash particles. A semiempirical model was developed based on the Deutsch–Anderson equation and experimental data under 1, 2, and 3 atm to calculate the particle penetrations under high pressure. The total charge number on a particle (n') is calculated by incorporating the effects of current (I) and pressure (P) on relative weights of the diffusion charging number (n_diff) and field charging number (n_field), that is, n' = B₁(I,P)n_diff + B₂(I,P)n_field, where B₁(I,P) and B₂(I,P) are both empirical coefficients dependent on current and pressure. Experimental penetrations under 1.5 and 2.5 atm validated this model over the particle diameter range in 100–400 nm.

Copyright © 2016 American Association for Aerosol Research     

Evaluation of solid sorbents as a retrofit technology for CO2 capture

Processes based upon solid sorbents are currently under consideration for post-combustion CO₂ capture. Twenty-four different sorbent materials were examined on a laboratory scale in a cyclic temperature swing adsorption/regeneration CO₂ capture process in simulated coal combustion flue gas. Ten of these materials exhibited significantly lower theoretical regeneration energies compared to the benchmark aqueous monoethanolamine, supporting the hypothesis that CO₂ capture processes based upon solids may provide cost benefits over solvent-based processes. The best performing materials were tested on actual coal-fired flue gas. The supported amines exhibited the highest working CO₂ capacities, although they can become poisoned by the presence of SO₂. The carbon-based materials showed excellent stability but were generally categorized as having low CO₂ capacities. The zeolites worked well under dry conditions, but were quickly poisoned by the presence of moisture. Although no one type of material is without concerns, several of the materials tested have theoretical regeneration energies significantly lower than that of the industry benchmark, warranting further development research.     

亲水改性碳钢极板用于PM2.5脱除

火电厂大气污染物排放标准日趋严格,湿式静电除尘器作为终端治理设备逐渐得到广泛应用。以亲水改性刚性极板为研究对象,建立了卧式湿式静电除尘器中试实验台,开展了PM_2.5脱除特性的实验研究,研究了改性极板表面水膜增强颗粒物脱除效率的机制,考察了气体温度、停留时间、工作电压、初始浓度、冲洗水流量等主要运行参数对颗粒物脱除效率的影响规律。结果表明：改性刚性极板表面的纤维层可以减少反冲气流,减少颗粒的电迁移阻力;表面在小水量情况下亦可维持均匀稳定的水膜,水膜的存在抑制了反电晕和二次扬尘的发生,使得电晕电流高且水膜蒸发使烟气湿度提高,颗粒荷电量和电迁移速度提高,这两方面均提高了颗粒脱除效率。停留时间延长、工作电压提高均会引起颗粒脱除效率的增加,但颗粒物入口浓度、冲洗水流量对颗粒脱除效率影响不大。使用改性刚性极板的湿式静电除尘器可减少阳极冲洗水量,对粒径0.04～0.48 μm的颗粒有较高脱除效率,可在低电压下达到较高的颗粒物总脱除效率,具有较好的应用前景。     

A model on an entrained bed-bubbling bed process for CO2 capture from flue gas

A simplified model has been developed to investigate effects of important operating parameters on performance of an entrained-bed absorber and bubbling-bed regenerator system collecting CO₂ from flue gas. The particle population balance was considered together with chemical reaction to determine the extent of conversion in both absorber and regenerator. The calculated CO₂ capture efficiency agreed with the measured value reasonably well. Effects of absorber parameters — temperature, gas velocity, static bed height, moisture content of feed gas on CO₂ capture efficiency — have been investigated in a laboratory scale process. The CO₂ capture efficiency decreased as temperature or gas velocity increased. However, it increased with static bed height or moisture concentration. The CO₂ capture efficiency was exponentially proportional to each parameter. Based on the absolute value of exponent of the parameter, the effect of gas velocity, static bed height, and moisture content was one-half, one-third, and one-fourth as strong as that of temperature, respectively.     

CO2 Absorption Behavior with a Novel Random Packing: Super Mini Ring

Abstract

For the purpose of capturing CO₂ from flue gas the absorption of CO₂ into an aqueous solution of monoethanolamine was measured by using a column packed with a novel packing, Super Mini Ring (SMR). The SMR gave a higher absorption performance relative to pall ring packing due to a larger effective surface area and also reduced the frictional pressure gradient. The absorption mechanism was observed to be mainly gas phase controlling. It was concluded that for the treatment of flue gas the SMR packing could reduce the height of the absorption column by 20% relative to a pall ring packed column.     

A Novel Multifilter PM10–PM2.5 Sampler (MFPPS)

A novel multifilter PM₁₀–PM_2.5 sampler (MFPPS) that enables the collection of four PM₁₀ and four PM_2.5 samples simultaneously has been developed and tested. The MFPPS uses a PM₁₀ impactor as the inlet and operates at 33.4 L/min. After the inlet, the aerosol flow is divided half by a Y-type fitting. Half of the flow is directed into four PM₁₀ filter cassettes, while the other half is directed into four PM_2.5 filter cassettes after the aerosols are further classified by a PM_2.5 impactor. An active flow control system consisting of two mass flow controllers (MFCs), one for PM₁₀ and the other for PM_2.5, is used to fix the total flow rate of 16.7 L/min for four PM₁₀ or four PM_2.5 channels based on the ambient pressure and temperature. To ensure flow rate uniformity through each of the four PM₁₀ or four PM_2.5 filter cassettes, an orifice is assembled behind each of the filter cassettes to increase the pressure drop, such that the flow rates of eight sampling lines are nearly equal using just two MFCs. The MFPPS was calibrated in the laboratory for particle collection efficiency curves first. Then, the ambient PM concentrations were compared with those of other two collocated FRM samplers, the dichotomous PM₁₀ and the EPA WINS PM_2.5 sampler in the field study. Calibration results showed the cutoff aerodynamic diameters of the PM₁₀ and PM_2.5 impactors were 9.8 ± 0.1 and 2.5 ± 0.05 μm, respectively. Field comparison results indicated PM₁₀ and PM_2.5 concentrations agreed well with the other two PM samplers.     

Development and Evaluation of a Continuous Ambient PM2.5 Mass Monitor

A Continuous Ambient Mass Monitor (CAMM) for fine particle mass (PM_2.5) has recently been developed at the Harvard School of Public Health. The principle of this method is based on the measurement of the increase in pressure drop across a membrane filter (Fluoropore^TM) during particle sampling. The monitor consists of a conventional impactor inlet to remove particles larger than 2.5 mu m, a diffusion dryer to remove particle-bound water, a filter tape to collect particles, a filter tape transportation system to allow unassisted sampling, and a data acquisition and control unit. For each sampling period (typically 30- 60 min), a new segment of the filter tape is exposed so that particles remain close to equilibrium with the sample air during their collection. This results in mini mization of volatilization and adsorption artifacts during sampling. Furthermore, since the required flow rate for the fine particle mass monitoring channel is only 0.3 L / min, the relative humidity of the air sample can be easily reduced to 40% or less using a NafionTM diffusion dryer to remove particle-bound water. The CAMM has a detection limit of > 5 mu g / m³ for PM_2.5 concentrations averaged over 1 h. The performance of the newly developed monitor was investigated through laboratory and field studies. Laboratory tests included a calibration of the CAMM using polystyrene latex (PSL) and silica particles. A series of field studies were conducted in 7 cities with presumably different PM_2.5 chemical composition. The 24 1-h CAMM measurements were averaged and compared to Harvard Impactor (HI) 24 h PM_2.5 integrated measurements. Based on 211 valid sampling days, the measurements obtained from the Harvard Impactor and the CAMM were highly correlated (r² = 0.90). The average CAMM-to-HI concentration ratio was 1.07 (+- 0.18).     

A Single Stage Membrane Process for CO2 Capture from Flue Gas by a Facilitated Transport Membrane

Carbon dioxide is the most important anthropogenic greenhouse gas and it accounts for about 80% of all greenhouse gases (GHG). The global atmospheric CO₂ concentrations have been increased significantly and have become the major source responsible for global warming; the greatest environmental challenge the world is facing now. The efforts to control the GHG emissions include the recovery of CO₂ from flue gas. In this work, feasibility analysis, based on a single stage membrane process, has been carried out with an in-house membrane program interfaced within process simulation program (AspenHysys) to investigate the influence of process parameters on the energy demand and flue gas processing cost. A novel CO₂-selective membrane with the facilitated transport mechanism has been employed to capture CO₂ from the flue gas mixtures. The results show that a membrane process using the facilitated transport membrane can also be considered as an alternative CO₂ capture process and it is possible to achieve more than 90% CO₂ recovery and 90% CO₂ purity in the permeate with reasonable energy consumption compared to amine absorption and other capture techniques.     

螺旋板换热器轴向错流通道湿法捕尘拟均相模型

提出了螺旋板换热器轴向错流通道冷却冷凝湿法除尘的方法,指出了PM_2.5在尾气对流传热传质边界层内热泳和伴随水蒸气冷凝的扩散泳运动特征和冷凝液膜吸收除尘机理并建立了拟均相模型,获得了PM_2.5浓度衰减函数和以冷凝通量n_w为参数的捕尘效率模型。通过“三传”类比获得了从尾气流速求取模型参数的方法,并通过恒壁温条件下冷却冷凝实验数据验证了模型参数计算方法的正确性,结果表明水蒸气组分扩散体积通量即PM_2.5扩散泳速度V_w是控制性参数,其值在20～40 mm·s^-1范围。     

Dynamic modelling and analysis of post-combustion CO2 chemical absorption process for coal-fired power plants

Post-combustion capture by chemical absorption using MEA solvent remains the only commercial technology for large scale CO₂ capture for coal-fired power plants. This paper presents a study of the dynamic responses of a post-combustion CO₂ capture plant by modelling and simulation. Such a plant consists mainly of the absorber (where CO₂ is chemically absorbed) and the regenerator (where the chemical solvent is regenerated). Model development and validation are described followed by dynamic analysis of the absorber and regenerator columns linked together with recycle. The gPROMS (Process Systems Enterprise Ltd.) advanced process modelling environment has been used to implement the proposed work. The study gives insights into the operation of the absorber-regenerator combination with possible disturbances arising from integrated operation with a power generation plant. It is shown that the performance of the absorber is more sensitive to the molar L/G ratio than the actual flow rates of the liquid solvent and flue gas. In addition, the importance of appropriate water balance in the absorber column is shown. A step change of the reboiler duty indicates a slow response. A case involving the combination of two fundamental CO₂ capture technologies (the partial oxyfuel mode in the furnace and the post-combustion solvent scrubbing) is studied. The flue gas composition was altered to mimic that observed with the combination. There was an initial sharp decrease in CO₂ absorption level which may not be observed in steady-state simulations.     

Development and Laboratory Performance Evaluation of a Personal Multipollutant Sampler for Simultaneous Measurements of Particulate and Gaseous Pollutants

A personal multipollutant sampler has been developed. This sampler can be used for measuring exposures to particulate matter and criteria gases. The system uses asingle personalsampling pump that operates at a flow rate of 5.2 l/min. The basic unit consists of two impaction-based samplers for PM_2.5 and PM₁₀ attached to a single elutriator. Two mini PM_2.5 samplers are also attached to the elutriator for organic carbon (OC), elemental carbon (EC), sulfate, and nitrate measurements. For the collection of nitrate and sulfate, the minisampler includes a miniaturized honeycomb glass denuder that is placed upstream of the filter to remove nitric acid and sulfur dioxide and to minimize artifacts. Two passive samplers can also be attached to the elutriator for measurements of gaseous copollutants such as O₃, SO₂, and NO₂. The performance of the multipollutant sampler was examined through a series of laboratory chamber tests. The results showed a good agreement between the multipollutant sampler and the reference methods. The overall sampler performance demonstrates its suitability for personal exposure assessment studies.     

Development and application of a simultaneous measurement method for gaseous ammonia and particulate ammonium in ambient air

Ammonia gas is one of the precursors contributing to the formation of secondary particulate ammonium via reactions with atmospheric acids, such as sulfuric and/or nitric acids, which are present in ambient air. In this study, a new instrument that is suitable for measuring ammonia gas and fine particulate ammonium (PM_2.5 NH₄⁺) concentrations simultaneously under ambient conditions was developed. A wetted frit sampler was connected in the back of a counter-current flow tube (CCFT) sampler, and the NH₃ gas and PM_2.5 NH₄⁺ samples were collected by CCFT and wetted frit samplers, respectively. An air sample was drawn through the samplers at a flow rate of 1.0 dm³ min^?1 and an absorption water flow rate of 120 mm³ min^?1. Then, the ammonium that formed in the absorption solution was detected by the indophenol method using a continuous flow analysis system. The estimated detection limits were 43 and 49 ng m^?3 for ammonia gas and PM_2.5 NH₄⁺, respectively. Notably, the ammonia gas was collected on the CCFT sampler with a collection efficiency of 98.5%, but most of the PM_2.5 NH₄⁺ passed through it and was captured on the wetted frit sampler with a collection efficiency of approximately 100%. The present method was applied to measure NH₃ gas and PM_2.5 NH₄⁺ at two urban sites: Osaka, Japan and Ho Chi Minh City, Vietnam. It was found that the simultaneous measurement method performed very well and that the measured concentrations were comparable with those obtained with the annular denuder method.

Copyright © 2016 American Association for Aerosol Research