Dry Scrubbing Research Articles

Cleaning workers’ exposure to volatile organic compounds and particulate matter during floor polish removal and reapplication

The floor polish removal (FPR) and reapplication (FPA) are important cleaning tasks in public buildings that have hard floor surfaces. Usually, the FPR and FPA are conducted once or twice a year, during the periodic cleaning of these buildings. The FPR can be performed either chemically (CFPR) or by using dry scrubber (DFPR), when the polish is ground from the floor. In this study, cleaning workers’ exposure to volatile organic compounds (VOCs) and particulate matter (PM) during the FPR and FPA, and the differences in the exposures between the two FPR methods were investigated. In total, three buildings located in Central Finland were included, and total of six cleaning workers (two per building) participated in the study. In Buildings 1 and 2, the CFPR and FPA were performed and in Building 3, the DFPR was conducted. TVOC (total volatile organic compounds) concentrations in the breathing zone of the workers during the CFPR were 8,740 and 390 µg/m3 (SD 3,290 and 180 µg/m3) for Buildings 1 and 2, respectively. During the DFPR in Building 3, the average TVOC concentration was 400 µg/m3 (SD 180 µg/m3, stationary sampling). The TVOC concentrations during the FPA were high, 1,640 and 2,170 µg/m3 on average (SD 1,570 and 930 µg/m3) for Buildings 1 and 2, respectively. Glycol ethers were the most prominent VOCs during the CFPR and FPA, whereas carboxylic acids were the most common during the DFPR. The inhalable dust concentrations in the workers’ breathing zone were noticeably higher during the DFPR (1.55 mg/m3 on average, SD 0.01 mg/m3) than the CFPR (0.24 mg/m3 on average, SD 0.05 mg/m3). Finnish occupational exposure limit value for organic inhalable dust is 5 mg/m3. As the products used during the CFPR and FPA contain glycol ethers and ethanolamines that are absorbed via the skin as well, the use of skin protection is recommended. Whereas the use of FFP3 respirators and skin protection are recommended during the DFPR to prevent the PM exposure.

Emission Control Technologies for Thermal Power Plants

Coal thermal power plants are one of the primary sources of artificial air emissions, particularly in a country like India. Ministry of Environment and Forests has proposed draft regulation for emission standards in coal-fired power plants. This includes significant reduction in sulphur-dioxide, oxides of nitrogen, particulate matter and mercury emissions. The first step is to evaluate the technologies which represent the best selection for each power plant based on its configuration, fuel properties, performance requirements, and other site-specific factors. This paper will describe various technology options including: Flue Gas Desulfurization System, Spray Dryer Absorber (SDA), Circulating Dry Scrubber (CDS), Limestone-based Wet FGD, Low NOX burners, Selective Non Catalytic Reduction, Electrostatic Precipitator, Bag House Dust Collector, all of which have been evaluated and installed extensively to reduce SO2, NOx, PM and other emissions. Each control technology has its advantages and disadvantages. For each of the technologies considered, major features, potential operating and maintenance cost impacts, as well as key factors that contribute to the selection of one technology over another are discussed here.

Influence of Air Pollution Control (APC) Systems and Furnace Type on the Characteristics of APC Residues from Municipal Solid Waste Incinerators

The characteristics of air pollution control (APC) residues are influenced by the furnace type, APC system, and waste composition. In this study, the characteristics of APC residues from nine municipal solid waste incineration plants (the compositions of incinerated solid waste are similar) with different furnace types and APC systems were compared.APC residues contain a great amount of Ca and Cl, and the contents of Al, Si, and Fe in the APC residues from fluidized bed incinerators are higher. The mineral compositions of APC residues are not influenced by the flue gas treatment process, but their contents vary. The contents of Cd, Pb, and Zn in the APC residues from fluidized bed incinerators are lower, while those of Cr, Ba, Cu, and Ni are greatly influenced by the APC systems, with the "grate+dry scrubber" APC residues having the lowest values. The differences in the heavy metal contents in the APC residues from two incinerators before and after the upgrading of the APC systems are not significant. The leaching toxicity of Pb in the APC residues from grate incinerators is higher than that from fluidized bed incinerators, while some elements with low contents in fluidized bed APC residues can be leached more in acetic acid buffer solution. The acid neutralization capacity of the APC residues is related to Ca content. The leaching concentrations of most heavy metals are significantly increased under strong acidity (Cd, Ni, and Zn:leachate pH < 8; Pb, Cu, and Cr:leachate pH < 4). The maximum leaching concentrations of As, Ba, Cu, Ni, and Pb in the APC residues from grate incinerators are mainly controlled by their total content. The leaching concentrations of As, Ba, Cu, Ni, and Pb in the APC residues from fluidized bed incinerators are lower than those from grate incinerators with similar metal contents, which may be due to their different chemical speciation influenced by furnace types and the complexation with Al and Fe compounds.

C-Energy's Red Hill Plant: Meeting the SO2 Challenge

This case is suitable for graduate-level quantitative analysis, business and government, environment and sustainability, and global economics courses. Students must consider the tradeoffs between continuing to run an old coal-burning plant and purchasing emissions allowances (EAs) versus upgrading to emissions-reducing wet or dry scrubbers. Reducing emissions creates the possibility of selling the plant's surplus EAs (which are likely to increase in price). Choosing a wet or dry scrubber requires considering installation cost and construction time, variable cost, and SO2 removal efficiency. Ideally, the investment should pay back over time, but management believes some net investment could also be justified. For that, however, complete analyses from both economic and environmental perspectives are required. A supplemental spreadsheet is available to accompany the case (UVA-QA-0726X).

Dry Scrubbing of Hydrogen Sulfide Gas Using Nano Zinc Oxide Coated Glass Beads

Abstract. Hydrogen sulfide (H2S) is one of the most toxic and smelly gases emitted from animal production facilities, which also acts as a catalyst poison in many industrial processes. The principal objective of this research was to develop a dry scrubber to adsorb H2S gas efficiently from airstreams mimicking air exhausts of animal and poultry barns at the ambient atmospheric condition. Nano zinc oxide (nZnO) coated 3-mm sized glass beads were investigated to adsorb H2S gas in a vertical dry scrubber setting. Colloids of nZnO were prepared and thin films of nZnO were grown on the surfaces of commercially available glass beads following a sol-gel method. The sizes of nZnO on glass bead surfaces ranged from nm to µm and found to be clustered due to the repeated coatings on the same surfaces. The energy dispersion spectroscopy (EDS) analysis confirms the presence of sulfur (S) compound that indicated a conversion of H2S into zinc sulfide (ZnS) on nZnO coated bead surfaces. The highest H2S breakthrough capacity of 2.54 mg H2S g-1 sorbent was observed. Heating the beads at 550°C regenerated glass beads effectively but experienced a gradual loss of reactivity as a number of regeneration cycles progressed. This research demonstrated that nZnO supported on glass beads are promising adsorbents for capturing H2S gas from airstreams at ambient temperature. Keywords: Airstreams, Breakthrough capacity, Hydrogen sulfide, Nano zinc oxide, Regeneration.

The Pivotal Role of Alumina Pore Structure in HF Capture and Fluoride Return in Aluminum Reduction

Fluoride emissions during primary aluminum production are mitigated by dry scrubbing on alumina which, as the metal feedstock, also returns fluoride to the pots. This ensures stable pot operation and maintains process efficiency but requires careful optimization of alumina for both fluoride capture and solubility. The Brunauer-Emmett-Teller (BET) surface area of 70–80 m2 g−1 is currently accepted. However, this does not account for pore accessibility. We demonstrate using industry-sourced data that pores <3.5 nm are not correlated with fluoride return. Reconstructing alumina pore size distributions (PSDs) following hydrogen fluoride (HF) adsorption shows surface area is not lost by pore diameter shrinkage, but by blocking the internal porosity. However, this alone cannot explain this 3.5 nm threshold. We show this is a consequence of surface diffusion-based inhibition with surface chemistry probably playing an integral role. We advocate new surface area estimates for alumina which account for pore accessibility by explicitly ignoring <3.5 nm pores.

Small Scale Plants for Energy Production: Environmental Impact of Biomasses Pyro-gasification

The production of both thermal and electrical power in pyro-gasification micro co-generative plants sized for small enterprises (sawmills, farms, cattle farms, etc.) is nowadays a growing trend. The electrical power is generated by an engine powered by the syngas produced through a pyro-gasification process; the nominal electric power of the considered plants is in between 30 and 90kW. There are different types of plants currently available on the marketeither able to process only pure wood pellets either high quality virgin wood chips or raw and mixed bio-based materials, such as crops, secondary quality chips and other agricultural residues. In present framework our measurements are related to the third type, fed by secondary quality biomasses. The impact on the environment is due to the combustion of the syngas through the torch, switched on when the engine is off, due to the engineemissions, due to the tar and aromatic compounds intercepted by the filtering systems (according to the types either dry filters or water scrubbers) and finally due to the large amount of biochar resulting from the pyro-gasification process. In the present study the aero-dispersed pollutants measured are both dusts (in diametric classes from 1 to 10μm) and the concentration of few chemical compounds (such as sulfur dioxide, carbon monoxide, nitrogen dioxide and oxides). The concentration of atmospheric pollutants from the engine is related to the engine set-up and to the engine behavior and it is not only strictly related to the biomass quality. The main solid residue is the biochar, that can be a dangerous waste if stocked in unappropriated way but that can provide a beneficial impact in agriculture as well, when distributed and processed with the due techniques and concentrations.

Cost Evaluation of Pollution Control Devices in a Small Scale Foundry

Cost has an important role in setting air pollution control device in small scale foundries in India. The air pollution control devices have different cost estimation based on area, volume, layout of the industry, geographic location of the foundry, electricity, water etc. By providing proper guidance of the economic details of the pollution control devices, the decision making by industrialists relates to installation and operating of air pollution control devices will be made easy. At present many foundries in India wouldn't collect the pollutants from the exhaust gas as per the standards given by pollution control board, because the collection efficiency of the currently installed pollution control device couldn't meet the standards specified by the pollution control board. In this study, alternate system is proposed which encompass wet scrubber and dry scrubber are arranged in serial manner. This paper deals with the methodology to estimate the total capital investment and total annual cost for the wet scrubber, dry scrubber and proposed model. The result of the study is highlighted as the economic analysis based on the annual and capital costs of two such devices when used alone in an industry and when they are used sequentially with its effects on the performance analysis on a longer run.

Examination of a newly developed mobile dry scrubber (DS) for coal mine dust control applications.

The Office of Mine Safety and Health Research of the U.S. National Institute for Occupational Safety and Health (NIOSH OMSHR) conducted laboratory testing of a self-tramming, remotely controlled mobile Dry Scrubber (DS) that J.H. Fletcher and Co. developed under a contract with NIOSH OMSHR to reduce the exposure of miners to airborne dust. The scrubber was found to average greater than 95 percent dust removal efficiency with disposable filters, and 88 and 90 percent, respectively, with optional washable filters in their prewash and post-wash test conditions. Although the washable filters can be reused, washing them generated personal and downstream respirable dust concentrations of 1.2 and 8.3 mg/m3, respectively, for a 10-min washing period. The scrubber's velocity-pressure-regulated variable-frequency-drive fan maintained relatively consistent airflow near the targeted 1.42 and 4.25 m3/s (3,000 and 9,000 ft3/min) airflow rates during most of the laboratory dust testing until reaching its maximum 60-Hz fan motor frequency or horsepower rating at 2,610 Pa (10.5 in. w.g.) of filter differential pressure and 3.97 m3/s (8,420 ft3/min) of scrubber airflow quantity. Laboratory sound level measurements of the scrubber showed that the outlet side of the scrubber was noisier, and the loaded filters increased sound levels compared with clean filters at the same airflow quantities. With loaded filters, the scrubber reached a 90 dB(A) sound level at 2.83 m3/s (6,000 ft3/min) of scrubber airflow, indicating that miners should not be overexposed in relation to MSHA's permissible exposure level - under Title 30 Code of Federal Regulations Part 62.101- of 90 dB(A) at or below this airflow quantity. The scrubber's washable filters were not used during field-testing because of their lower respirable dust removal efficiency and the airborne dust generated by filter washing. Field-testing the scrubber with disposable filters at two underground coal mine sections showed that it could clean a portion of the section return air and provide dust reduction of about 50 percent at the face area downstream of the continuous-miner operation.

Treatment-oriented characterization of dry scrubber residue from municipal solid waste incineration

Dry scrubber residue from municipal solid waste incineration (MSWI) was characterized to identify critical inorganic pollutants and to suggest a conceptual treatment method. The key methods used were thermal analysis, including thermogravimetry (TG) and differential thermal analysis (DTA), pHstat titration, qualitative X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical equilibrium calculations, and statistics such as error propagation, principal component analysis (PCA), and empirical modeling based on factorial designs. Based on EU directives, the major inorganic pollutants Cd, Cr, Pb, and Zn were found. In addition, the pH was too high. With dry scrubber residue stabilization in mind, the impact of carbonation and hydration was assessed and judged to be encouraging. In particular, chemical equilibrium calculations showed that carbonation has considerable potential to lower the pH and the availability of Pb, Zn, and Cr. The impact of carbonation on the mobility of Cd was found to be small. During carbonation, a metal-trapping calcium aluminosilicate hydrate (C–A–S–H) phase is also formed. Both processes together have the potential to lead to a robust, reliable, and reasonable stabilization method for dry scrubber residue. However, to control these processes, the decisive factors need to be identified and their effects need to be quantified. Ca, Cl, Na, and K might be abundant components which would be mobile even after stabilization.

Behavior of Sodium Sulfate in Cryolite-Alumina Melts and Formation of Sulfurous Gases

Sulfurous gases are known for their detrimental effect on local air pollution (particulate matter), acid rain, health and global climate change. Sulfur emissions from an aluminum smelter with an annual production of 200000 tonnes can be as high as 1000 tonnes sulfur per year. The most important reported sulfurous gases from aluminum reduction cells are SO2, COS, H2S and CS2, first two being the predominant. The source of sulfurous gases from aluminum smelters is mainly from the sulfur in carbon anodes. Small amounts of sulfur are also introduced by the feed materials, mostly in the form of sulfates. The study of the behaviour of sulfur compounds has particular interest not only due to the emitted harmful gases, but also its effect on the process of aluminum production. Recent study shows that sulfur has an impact on current efficiency of the aluminum smelting due to several oxidations states available. All experiments were run at 980 °C in a cryolite melt corresponding to a cryolite ratio (NaF/AlF3) equal to 2.5, and with excess amounts of AlF3, Al2O3 and CaF2 of 6.75 wt%, 4 wt% and 5 wt%, respectively. The sodium sulfate reactions and the gaseous products were investigated by adding 0.44 wt% sodium sulfate (1000 ppm sulfur) into the cryolite melt with four different conditions: 1) melt without reducing agents (graphite, aluminum), 2) melt with graphite, 3) melt with graphite and aluminum and 4) melt with graphite, aluminum and plus electrolysis. The bath samples were analysed by using ICP (Inductive coupled plasma) spectroscopy, X-Ray florescence, ion chromatography. The furnace off-gases were passed through a mass spectrometer for qualitative assessment and to support and explain the gas products formed during reactions. The mechanisms are evaluated with respect to the sulfur concentration in the electrolyte as well as the off-gas composition. Thermochemical calculations for the formation of sulfurous gas species as well as equilibrium of the gas composition as a function of temperature have been performed. The results indicate that the presence of reducing agents such as graphite and aluminum have an impact on the sulfur removal rate. Electrolysis has a bigger impact than the presence of graphite and aluminum alone. The sulfurous gases that were observed are: SO2, COS, CS2 and H2S. Emissions of CS2 have not been well understood or explained in the literature. The CS2 gas has been previously observed mostly during anode effects and probably it has been rarely detected due to adsorption to alumina in the dry scrubber. The gas analysis results indicated that CS2 can be formed when there is a source of sulfur and carbon in the melt. This statement also supported by thermodynamic calculations. Measurements show that COS can be formed when there is no electrolysis. The COS was also found to follow the CO2 and cease when the signal decreased. This observed behavior may indicate that the COS formation is a chemical reaction which proceeds after electrochemical reaction.

Review of Design, Operating, and Financial Considerations in Flue Gas Desulfurization Systems

AbstractIn this work, measures available for the reduction of sulfur dioxide stack emissions are discussed. The various flue gas desulfurization (FGD) technologies available in the market, for the reduction of sulfur dioxide emissions, are presented. The process descriptions are discussed and the capital and operating costs of the various methods are presented. Also, possible sources of raw materials required in each process and the viable means of disposal of the end products are discussed. In the FGD market throughout the world, limestone wet scrubbers take the lead, the byproduct of which is a marketable gypsum. Most of the second (other wet scrubbing) covers the similar process but produces a disposal product. This sector also includes the seawater scrubbing process. Other significant sectors include spray dry scrubbers, regenerable processes, and sorbent injection systems. Combined SO2/NOx processes have a small share, and the trend is not expected to change.

Odour Abatement of Waste Gases from Sludge Thickeners in Wastewater Treatment Plant Using Bioscrubber

The research objective was to determine odour abatement efficiency of waste gases from sludge thickeners with the use of bioscrubbers. Olfactometric measurements were performed in the large mechanical-biological wastewater treatment plant in one of the biggest cities in Poland. The installation assessed was the 3-stage British system comprised of two identical bioscrubbers from lava rock media at the beginning, and dry chemical scrubber at the end.A three-day measuring session was conducted in October 2012. Nine observations of the relative difference in odour concentration in the crude and clean gas stream in determined conditions were carried out in each stage. In total, 36 samples were taken - 9 samples for each of the four measuring points. The lung principle method was used for sampling. Parameters necessary to calculate the odour flow rate, such as gas temperature, absolute pressure or volume flow rate were measured using the TESTO 400 meter. The samples were transported to the Olfactometric Mobile Laboratory of the Laboratory for Odour Quality of the Air, located ca. 6 km from the object of study. Odour concentration was measured using the Ecoma TO7 dynamic olfactometer and the experienced panel that met the selection criteria of the EN 13725 standard for the olfactory sensitivity. The quality parameters determined in the Interlaboratory Comparison of Olfactometry 2012 for 1-butanol in nitrogen, were: precision r = 0.453 and accuracy Aod = 0.234.The results confirmed the high odour abatement efficiency of over 90 % for the first bioscrubber, with the odour flow rate order of magnitude of 100,000 ouE/s in the crude stream as well as the second bioscrubber where the odour flow rate order of magnitude was below 9,000 ouE/s. The effectiveness of the use of the two series-connected bioscrubbers exceeded 99% and the overall effectiveness of the three-stage installation equalled 100 %.

PFC Formation in Aluminium Producing Cells during Normal Electrolysis Potentials

Perfluorocarbons (PFCs) are potent greenhouse gases (GHG) with long lifetimes and high global warming potentials, giving them a high capacity to inflict harm on the environment. The aluminium industry is one of the bigger emitters of these gases and consequently a lot of effort has been put into understanding the mechanism behind the emissions. Aluminium is produced electrochemically by consuming alumina (dissolved in molten cryolite) and carbon. In addition to aluminium this also produces CO2 with a fraction of CO. The reversible potential for the reaction is about 1.2 V, but due to overpotentials related to the electrodes and IR drops in different parts of the cell, especially from the electrolyte, a regular industrial cell needs to operate at a much higher voltage (3.8 – 4.5 V). If the alumina concentration in the electrolyte gets too low the polarisation increases which opens the possibility for other anode reactions, like the production of the PFC gases CF4 and C2F6. The phenomenon is termed anode effect (AE) and traditionally when this occurred the voltage could raise to levels of 20 V or higher, and the current distribution over the anodes would become erratic.In recent years, however, these PFC gases have been discovered at several large, high kA, smelters in China [1-3]. It has been proposed that less uniformity in dissolved alumina for larger cells may elevate individual anode overvoltage sufficiently to produce PFC. The large size gives the cell the ability to distribute the current of the PFC producing anode to the remaining anodes without passing the critical current density.Low cell voltage (LCV) PFC formation was monitored after the dry scrubber on a train of 28 cells at a relatively small Norwegian smelter running at approximately 215 kA. For this work a fourier-transform infrared spectrometer was used. Equipped with a mercury cadmium telluride (MCT) detector and retrofitted with a 35 m / 11 l measurement cell it was possible to get the detection limit down in the low ppb range needed for this study.It was discovered that also small cells could emit PFC that was not directly related to the conventional anode effect. Low cell voltage PFC was found to be discrete emissions mostly in the form of CF4; however, the results indicate that C2F6may also form outside the main anode effect. The emissions can be short lived and self-terminate, but they can also endure for a substantial amount of time and end up in a conventional anode effect, as can be seen from Figure 1.

Dispersion Caused by Carbon Dioxide During Secondary Alumina Dissolution: A Lab-Scale Research

Secondary alumina is the byproduct of dry scrubbing in aluminum smelting. Secondary alumina has superior dissolution characteristics to primary alumina. Secondary alumina dissolves in pieces in molten cryolite, which results in larger contact area and better diffusion kinetics. In this work, the dissolution phenomenon of primary alumina, secondary alumina, and primary alumina doped with sodium carbonate or calcium carbonate (mass ratio = 10:1, 20:1) was observed and compared to estimate carbon-induced dispersion in industrial secondary alumina. Temperature fluctuations during sample dissolution were measured to evaluate the benefits of preheating on alumina dissolution. It was found that carbon mixed in secondary alumina significantly influences the dispersion of alumina particles at the moment of feeding, and thermodynamic analysis also shows that the combustion heat from carbon facilitates dispersion.

Comparison of alkaline industrial wastes for aqueous mineral carbon sequestration through a parallel reactivity study

Thirty-one alkaline industrial wastes from a wide range of industrial processes were acquired and screened for application in an aqueous carbon sequestration process. The wastes were evaluated for their potential to leach polyvalent cations and base species. Following mixing with a simple sodium bicarbonate solution, chemistries of the aqueous and solid phases were analyzed. Experimental results indicated that the most reactive materials were capable of sequestering between 77% and 93% of the available carbon under experimental conditions in four hours. These materials – cement kiln dust, spray dryer absorber ash, and circulating dry scrubber ash – are thus good candidates for detailed, process-oriented studies. Chemical equilibrium modeling indicated that amorphous calcium carbonate is likely responsible for the observed sequestration. High variability and low reactive fractions render many other materials less attractive for further pursuit without considering preprocessing or activation techniques.

Mechanism of Dissolution Behavior of the Secondary Alumina

The study on dissolution of alumina in aluminum electrolyte has never been suspended. The raw materials used in aluminum smelter are made up of primary alumina and secondary alumina. The latter is the by-product of a dry scrubbing system. The differences in dissolution behavior of these two kinds of alumina are studied in this article. A see-through cell was used for observing the dissolution behavior of alumina. It was found that the dissolution rate of the secondary alumina was significantly faster than that of the primary alumina. The effect of possible impurities in the secondary alumina on the dissolution behavior, including carbon dust, hydrogen fluoride (HF), and other fluorides (Na5Al3F14, Na3AlF6, AlF3), was investigated. The carbon dust played an important role in improving the dissolution behavior. However, fluorides and chemisorbed HF have little effect on the dissolution behavior of the secondary alumina.

Speciation of mercury in FGD gypsum and mercury emission during the wallboard production in China

During combustion of pulverized coals, most of the mercury (Hg) in coal volatilizes. With the wide use of dry and wet scrubber systems for flue gas desulfurization (FGD), various amounts of Hg are captured by coal combustion byproducts, such as, FGD gypsum. The specification of Hg in FGD gypsum is essential not only to determine the risk when the wastes are recycled or disposed but also to understand the behavior of Hg during coal combustion and the mechanisms of Hg oxidation along the flue gas path. In this study, a temperature-programmed decomposition technique was used in order to acquire an understanding of the Hg species associated with FGD gypsum. A series of Hg reference compounds were used to obtain the characteristic temperature of decomposition for each Hg compound. The decomposition temperature of the Hg species is in an increasing order as Hg2SO4<Hg2Cl2<HgCl2<black HgS<HgO<red HgS<HgSO4. The results also indicate that HgCl2 and HgS are the primary Hg compounds in FGD gypsum samples. Hg stability during the reutilization of FGD gypsum is important due to its health and environmental impact, and its value in improving the Hg emission inventory. The industrial calcining process of wallboard production is simulated in order to determine the Hg emission percentage during the reutilization of FGD gypsum. Results indicate that 12.1–55.1% of total Hg would be emitted from FGD gypsum in this process. A larger percentage of Hg will be emitted when the proportion of Hg2Cl2 and HgCl2 is higher. The Hg re-emissions from FGD gypsum during wallboard production in China were estimated to be 4.7tons in 2008.

CFD modeling of the Dry-Sorbent-Injection process for flue gas desulfurization using hydrated lime

Dry Sorbent Injection (DSI) is a process used to control sulfur dioxide (SO2) by injecting a powdered alkaline sorbent into the flue gas stream. The present paper uses Computational Fluid Dynamics to analyze the dry scrubbing process of an industrial plant made up of a short ductwork followed by a holding vessel. The resulting complex flow field strongly impacts the desulfurization efficiency, evaluated with the adsorption model proposed by Gutierréz Ortiz et al. [1,2]. A modified system’s configuration is also simulated and compared to the previous one in terms of a newly defined mixing efficiency parameter. The latter compares the calculated SO2 removal efficiency with the maximum efficiency achievable under the same operating conditions affecting the adsorption process and is helpful in the design of DSI plants.

1MWe급 순환유동층 열병합 보일러 운전연구

폐기물 고형연료의 순환유동층 연소기술의 시범을 위하여 파일롯트 규모 순환유동층 연소보일러를 설계하고 건설하였다. 보일러의 규모는 출력기준 약 6 MWth에 해당하며 증기질은 <TEX>$400^{\circ}C$</TEX>, 38 ata로 설계하였다. 최대 증기출력은 약 8 ton/h에 해당한다. 연료는 RDF로 휘발분을 주성분으로 하며 점화가 빠르고 연소성이 매우 뛰어났으며 보일러의 연소효율은 99.5%를 능가하였다. 순환유동층 RDF 연소의 안정성은 연료중 회분 이외의 이물질의 존재 여부와 신속한 배출 가능성에 크게 의존하였다. 오염물질의 배출농도는 염소를 제외하고는 법적 기준치 이내에 들었다. 또한 60% 정도의 연료중 염소는 비산재에 흡수되는 것으로 나타났다. HCl을 국내 법 규제에 맞추어 제어하기 위해서는 건식 또는 습식 흡수 장치와 같은 별도의 환경설비가 필요하였다. A pilot scale circulating fluidized boiler (CFB) for refuse derived fuel (RDF) is designed and constructed to demonstrate a performance of CFB technology for waste fuel utilization. The boiler has a design capacity of 6 MWth with <TEX>$400^{\circ}C$</TEX> 38 ata steam generation performance. The maximum steam rate of the boiler was about 8 ton/h. The main component of the fuel was RDF (Refuse Derived Fuel) with high volatile contents and showed fast ignition and easy combustion. The pilot plant showed over 99.5% of combustion efficiency. Stable operation of RDF CFBC depended on the content of non combustion materials other than ash and fast removal of them. Emission level was under legal limit except that of HCl without external flue gas treatment facilities. Also about 60% of fuel chlorine was absorbed to fly ash particles. For HCl emission control flue gas treatment technology is required such as wet and dry scrubber in order to comply with Korean regulation.